Energy Management in Plastics Processin: Strategies, Targets, Techniques, and Tools [3 ed.] 9780081025079

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Energy Management in Plastics Processing

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Energy Management in Plastics Processing Strategies, targets, techniques and tools Third edition 2018

Robin Kent Tangram Technology Ltd

Elsevier Radarweg 29, PO Box 211, 1000 AE Amsterdam, Netherlands The Boulevard, Langford Lane, Kidlington, Oxford OX5 1GB, United Kingdom 50 Hampshire Street, 5th Floor, Cambridge, MA 02139, United States Copyright © 2018 Elsevier Ltd. All rights reserved. No part of this publication may be reproduced or transmitted in any form or by any means, electronic or mechanical, including photocopying, recording, or any information storage and retrieval system, without permission in writing from the publisher. Details on how to seek permission, further information about the Publisher’s permissions policies and our arrangements with organizations such as the Copyright Clearance Center and the Copyright Licensing Agency, can be found at our website: www.elsevier.com/permissions. This book and the individual contributions contained in it are protected under copyright by the Publisher (other than as may be noted herein). Notices Knowledge and best practice in this field are constantly changing. As new research and experience broaden our understanding, changes in research methods, professional practices, or medical treatment may become necessary. Practitioners and researchers must always rely on their own experience and knowledge in evaluating and using any information, methods, compounds, or experiments described herein. In using such information or methods they should be mindful of their own safety and the safety of others, including parties for whom they have a professional responsibility. To the fullest extent of the law, neither the Publisher nor the authors, contributors, or editors, assume any liability for any injury and/or damage to persons or property as a matter of products liability, negligence or otherwise, or from any use or operation of any methods, products, instructions, or ideas contained in the material herein. British Library Cataloguing in Publication Data A catalogue record for this book is available from the British Library Library of Congress Cataloging-in-Publication Data A catalog record for this book is available from the Library of Congress

ISBN: 978-0-08-102507-9

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Contents Preface ...................................................................................... 1 1

Introduction to energy management ............................................ 3 1.1 Where we are going........................................................................................................... 4 1.2 The drivers for energy management................................................................................... 6 1.3 The importance of energy costs ......................................................................................... 8 1.4 The efforts, opportunities and obstacles ........................................................................... 10 1.5 Energy management systems – the basics....................................................................... 12 1.6 Energy management systems – the standard................................................................... 14 1.7 Energy management systems – the changing standard.................................................... 16 1.8 Energy management – where are you now?..................................................................... 18 1.9 Financial management – where are you now?.................................................................. 20 1.10 Technical management – where are you now?................................................................. 22 1.11 Awareness and information – where are you now?........................................................... 24 1.12 Purchasing – where are you now? ................................................................................... 26 1.13 Project assessment and selection .................................................................................... 28 1.14 Energy management projects – where are you now? ....................................................... 30 Key tips .................................................................................................................................... 32

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Energy benchmarking ............................................................. 33 2.1 The framework and energy use drivers............................................................................. 34 2.2 The basic internal site data .............................................................................................. 36 2.3 The effect of management ............................................................................................... 38 2.4 The effect of the process.................................................................................................. 40 2.5 Variations on the site base and process loads.................................................................. 42 2.6 What do we want to do?................................................................................................... 44 2.7 Assessing site performance – internal benchmarking ....................................................... 46 2.8 Assessing site performance – past performance .............................................................. 48 2.9 Budgeting for future site energy use ................................................................................. 50 2.10 Complex sites – multi-variate analysis.............................................................................. 52 2.11 Site SEC and production volume...................................................................................... 54 2.12 External site benchmarking – general............................................................................... 56 2.13 External site benchmarking – injection moulding .............................................................. 58 2.14 External site benchmarking – extrusion ............................................................................ 60 2.15 External site benchmarking – extrusion blow moulding ..................................................... 62 2.16 External site benchmarking – rotational moulding............................................................. 64 2.17 External machine benchmarking – general ....................................................................... 66 2.18 External machine benchmarking – injection moulding....................................................... 68 2.19 External machine benchmarking – injection blow moulding............................................... 70 2.20 External machine benchmarking – extrusion .................................................................... 72 2.21 External machine benchmarking – extrusion blow moulding ............................................. 74 2.22 External machine benchmarking – thermoforming ............................................................ 76 Key tips .................................................................................................................................... 78

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Targeting and controlling energy costs ........................................ 79 3.1 Understanding energy use – the basics............................................................................ 80 3.2 Understanding energy use – the site energy map............................................................. 82 3.3 Integrating energy into the accounts – monitoring and targeting ....................................... 84 3.4 Data collection and analysis............................................................................................. 86 3.5 Setting targets.................................................................................................................. 88 3.6 Reporting energy costs .................................................................................................... 90 3.7 The energy dashboard report ........................................................................................... 92 3.8 Capital expenditure and equipment selection ................................................................... 94 3.9 Verifying energy savings – the theory............................................................................... 96 3.10 Verifying energy savings – the practice ............................................................................ 98 3.11 The energy manager’s job.............................................................................................. 100 3.12 Targeting and controlling – where are you now?............................................................. 102 Key tips .................................................................................................................................. 104

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Services ............................................................................ 105 4.1 Power supply – electricity terms ..................................................................................... 106 4.2 Power supply – reducing electricity costs........................................................................ 108 4.3 Power supply – transformers.......................................................................................... 110 4.4 Power supply – voltage management ............................................................................. 112 4.5 Power supply – electricity supplier data .......................................................................... 114 4.6 Power supply – analysing interval data........................................................................... 116 4.7 Power supply – sub-metering ......................................................................................... 118 4.8 Power supply – gas........................................................................................................ 120 4.9 Power supply – solar and wind ....................................................................................... 122 4.10 Power supply – combined heat and power and tri-generation (CCHP) ............................ 124 4.11 Power supply – what to do when it fails (power outages) ................................................ 126 4.12 Power supply – where are you now? .............................................................................. 128 4.13 Motors – understanding motor use and costs ................................................................. 130 4.14 Motors – the programme ................................................................................................ 132 4.15 Motors – minimise the demand: turn it off ....................................................................... 134 4.16 Motors – minimise the demand: reduce transmission losses .......................................... 136 4.17 Motors – minimise the demand: reduce the load at source ............................................. 138 4.18 Motors – optimise the supply: get the right size motor..................................................... 140 4.19 Motors – optimise the supply: improve the motor efficiency ............................................ 142 4.20 Motors – optimise the supply: slow the motor down ........................................................ 144 4.21 Motors – optimise the supply: the savings from slowing motors down ............................. 146 4.22 Motors – motor maintenance and management.............................................................. 148 4.23 Motors – where are you now? ........................................................................................ 150 4.24 Compressed air – the system......................................................................................... 152 4.25 Compressed air – the programme .................................................................................. 154 4.26 Compressed air – minimise the demand: reduce leakage ............................................... 156 4.27 Compressed air – minimise the demand: reduce use...................................................... 158 4.28 Compressed air – optimise the supply: improve generation ............................................ 160 4.29 Compressed air – optimise the supply: optimise treatment ............................................. 162 4.30 Compressed air – optimise the supply: improve distribution............................................ 164 4.31 Compressed air – heat recovery..................................................................................... 166 4.32 Compressed air – where are you now? .......................................................................... 168 4.33 Cooling water – the programme ..................................................................................... 170 4.34 Cooling water – minimise the demand: reduce heat gains .............................................. 172 4.35 Cooling water – minimise the demand: increase temperatures ....................................... 174 4.36 Cooling water – optimise the supply: reduce cooling costs with chillers........................... 176 4.37 Cooling water – optimise the supply: reduce cooling costs with cooling towers ............... 178 4.38 Cooling water – optimise the supply: reduce cooling costs with free cooling.................... 180 4.39 Cooling water – optimise the supply: reduce cooling costs with ground water ................. 182 4.40 Cooling water – optimise the supply: reduce distribution costs........................................ 184 4.41 Cooling water – where are you now?.............................................................................. 186 4.42 Drying – the programme................................................................................................. 188 4.43 Drying – minimise the demand: dry the right materials.................................................... 190 4.44 Drying – minimise the demand: store materials correctly ................................................ 192 4.45 Drying – optimise the supply: improve control systems and insulation............................. 194 4.46 Drying – optimise the supply: reduce drying costs with desiccant drying ......................... 196 4.47 Drying – optimise the supply: reduce drying costs with other methods ............................ 198 4.48 Drying – where are you now? ......................................................................................... 200 4.49 Vacuum generation........................................................................................................ 202 4.50 Hydraulics systems ........................................................................................................ 204 4.51 Robots ........................................................................................................................... 206 4.52 Fans .............................................................................................................................. 208 Key tips .................................................................................................................................. 210

5

Processing ......................................................................... 211 5.1 5.2 5.3 5.4 5.5 5.6

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Processing – where are we going?................................................................................. 212 Injection moulding – where does all the energy go?........................................................ 214 Injection moulding – the basics....................................................................................... 216 Injection moulding – machine selection .......................................................................... 218 Injection moulding – machine monitoring........................................................................ 220 Injection moulding – process setting............................................................................... 222

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5.7 Injection moulding – motors............................................................................................ 224 5.8 Injection moulding – new and retrofitted VSDs................................................................ 226 5.9 Injection moulding – all-electric machines....................................................................... 228 5.10 Injection moulding – heating........................................................................................... 230 5.11 Injection moulding – mould temperature controllers........................................................ 232 5.12 Injection moulding – mould design ................................................................................. 234 5.13 Injection moulding – hydraulic fluid................................................................................. 236 5.14 Injection moulding – IMM energy rating .......................................................................... 238 5.15 Injection moulding – where are you now? ....................................................................... 240 5.16 Extrusion – general ........................................................................................................ 242 5.17 Extrusion – motors ......................................................................................................... 244 5.18 Extrusion – heating ........................................................................................................ 246 5.19 Extrusion – profiles ........................................................................................................ 248 5.20 Extrusion – profiles: calibration and cooling.................................................................... 250 5.21 Extrusion – sheet ........................................................................................................... 252 5.22 Extrusion – blown film .................................................................................................... 254 5.23 Extrusion – oriented film................................................................................................. 256 5.24 Extrusion – other processes ........................................................................................... 258 5.25 Extrusion – where are you now? .................................................................................... 260 5.26 Extrusion blow moulding – general................................................................................. 262 5.27 Extrusion blow moulding – extrusion and blowing........................................................... 264 5.28 Extrusion blow moulding – heating and cooling .............................................................. 266 5.29 Extrusion blow moulding – tops and tails management................................................... 268 5.30 Extrusion blow moulding – where are you now? ............................................................. 270 5.31 Injection blow moulding.................................................................................................. 272 5.32 Injection blow moulding – where are you now?............................................................... 274 5.33 Injection stretch blow moulding – general and moulding ................................................. 276 5.34 Injection stretch blow moulding – blowing....................................................................... 278 5.35 Injection stretch blow moulding – where are you now? ................................................... 280 5.36 Thermoforming – general and pre-heating...................................................................... 282 5.37 Thermoforming – heat losses ......................................................................................... 284 5.38 Thermoforming – heating and cooling ............................................................................ 286 5.39 Thermoforming – where are you now? ........................................................................... 288 5.40 Rotational moulding – general........................................................................................ 290 5.41 Rotational moulding – reducing process heat losses ...................................................... 292 5.42 Rotational moulding – other process improvements........................................................ 294 5.43 Rotational moulding – where are you now? .................................................................... 296 5.44 EPS foam moulding – PCL and steam ........................................................................... 298 5.45 EPS foam moulding – process ....................................................................................... 300 5.46 EPS foam moulding – where are you now? .................................................................... 302 5.47 Compression moulding .................................................................................................. 304 5.48 Pultrusion....................................................................................................................... 306 5.49 Rubber – general ........................................................................................................... 308 5.50 Rubber – storage and mixing ......................................................................................... 310 5.51 Rubber – moulding......................................................................................................... 312 5.52 Regranulation – general................................................................................................. 314 5.53 Regranulation – processes............................................................................................. 316 Key tips .................................................................................................................................. 318

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Operations ......................................................................... 319 6.1 Operations – making it work ........................................................................................... 320 6.2 Setting, start-up, stand-by and shut-down ...................................................................... 322 6.3 Using interval data in operations .................................................................................... 324 6.4 Tool changeover and quality control ............................................................................... 326 6.5 Training and employee involvement ............................................................................... 328 6.6 The benefits of employee training................................................................................... 330 6.7 Processing operations – where are you now? ................................................................ 332 6.8 Maintenance .................................................................................................................. 334 6.9 Small power equipment.................................................................................................. 336 6.10 Small power equipment – where are you now?............................................................... 338 6.11 Process control .............................................................................................................. 340 6.12 Process control – where are you now? ........................................................................... 342 Key tips .................................................................................................................................. 344

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Buildings and offices............................................................. 345 7.1 Buildings and offices ...................................................................................................... 346 7.2 Lighting – general .......................................................................................................... 348 7.3 Lighting – controls and maintenance .............................................................................. 350 7.4 Lighting – where are you now?....................................................................................... 352 7.5 Heating – general........................................................................................................... 354 7.6 Heating – controls and maintenance .............................................................................. 356 7.7 Heating – where are you now? ....................................................................................... 358 7.8 Hot water – where are you now? .................................................................................... 360 7.9 Air conditioning .............................................................................................................. 362 7.10 Air conditioning – where are you now? ........................................................................... 364 7.11 Building fabric ................................................................................................................ 366 7.12 Building fabric – where are you now? ............................................................................. 368 Key tips .................................................................................................................................. 370

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Site surveys........................................................................ 371 8.1 A mini site survey – the energy walk-around (the treasure hunt) ..................................... 372 8.2 Preparing for a site survey – information ........................................................................ 374 8.3 Preparing for a site survey – tools .................................................................................. 376 8.4 Planning the initial site survey ........................................................................................ 378 8.5 Carrying out the initial site survey................................................................................... 380 8.6 Reporting the initial site survey....................................................................................... 382 8.7 Following up the initial site survey .................................................................................. 384 Key tips .................................................................................................................................. 386

9

Carbon footprinting .............................................................. 387 9.1 The basics of carbon footprinting.................................................................................... 388 9.2 Site carbon footprinting – Scope 1.................................................................................. 390 9.3 Site carbon footprinting – Scope 2.................................................................................. 392 9.4 Site carbon footprinting – Scope 3.................................................................................. 394 9.5 Site carbon footprinting – putting the scopes together..................................................... 396 9.6 Product carbon footprinting ............................................................................................ 398 9.7 Country plastics processing carbon footprints................................................................. 400 9.8 Carbon footprinting – where are you now? ..................................................................... 402 Key tips .................................................................................................................................. 404

Appendices .............................................................................. 405 Appendix 1 – Submitting site data ............................................................................................... 406 Appendix 2 – Submitting machine data ........................................................................................ 408

Postscript ................................................................................ 410 Abbreviations and acronyms ......................................................... 411

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Preface to the 3rd Edition

There have been many technical changes since the previous edition (2013) of this workbook and these continue to be both rapid and wide-reaching. Energy management and energy efficiency have continued to move up the management agenda for plastics processing companies. However, some processors think that they have ‘done’ energy management and that there is nothing more to do. Nothing could be further from the truth – energy management is a never-ending journey to reduce use and costs. In my work with companies around the world, it is apparent that there is a real divide. The companies that are moving fastest are those in Asia and Latin America. The reason for this is that the cost of energy is a ‘world cost’ and does not vary greatly around the world but the cost of labour is highly variable throughout the world. In low labour cost countries, the energy cost is a very high proportion of total costs and manager’s actions are focused by the size of the costs. Many companies in these areas are now not only benefiting from low labour costs but also from reduced energy costs. This is a real threat to Western plastics processors. This book provides a structured approach to energy management and covers the main topics for plastics processors. It is designed as a practical workbook and does not cover all aspects of the topics but focuses on the key energy issues for each topic. Each topic is dealt with in a single two-page spread and most can be read independently of each other – this is not a ‘cover-to-cover’ book. It should be easily Preface

understood and the actions recommended should be easily undertaken by most people in the plastics processing industry. Energy management is not ‘rocket science’; it is good management and engineering. The are two approaches to reducing the cost of energy are: • The ‘£/kWh’ approach which seeks to

reduce the cost of each kWh used. • The ‘kWh/kg’ approach which seeks to reduce the amount of energy used to process each kilogramme of material. Good purchasing can temporarily reduce the cost by up to 10% but good engineering and technology can remove the need to purchase the kWh – a permanent 100% saving. This is the approach generally used in this book. All data used in this book are real industry data from plastics processing sites around the world and has only been modified to prevent identification of the sites. All financial calculations are based on electricity prices of £0.10/kWh and gas prices of £0.03/kWh. Cost data are based on UK prices that are correct in 2017. I would like to dedicate this edition of the book to my first grandchild, Lucas Kent, but now I will have to write more books to make sure there is no favouritism. Robin Kent Hitchin, 2018 [email protected] www.tangram.co.uk Note: Additional resources are available at www.tangram.co.uk/energy.html. 1

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Chapter 1 Introduction to energy management

Energy efficiency is still one of the ‘hot’ topics of the 21st century and it is not going to get any easier in any area of the world. Many plastics processors are still trying to come to terms with this new world but lack guidance on where to turn and how to make real progress. It doesn’t matter whether a site is trying to reduce their energy use to improve their ‘green credentials’ or simply to reduce their costs – the issues are the same and the solutions are largely common. In the 1990s, energy management was a ‘minority sport’ and it was difficult attracting industry interest in energy management. When the first edition of this book was written (2008) the concept of energy management was rapidly gaining credibility but there was still little real information devoted to the particular concerns of plastics processors. Energy costs have now attracted the attention of every plastics processor and energy management is rising in importance as a business issue. However, this book still remains the sole text on energy management for plastics processors and is both widely quoted and plagiarised throughout the world. Perhaps this should be accepted as praise for some of the concepts developed in the First and Second Editions. Energy costs are now entrenched as the third largest variable cost (after materials and direct labour) and, in many low labour cost countries, energy is the second largest variable cost. This is not a ‘green’ issue, it is not a ‘carbon management’ issue, it is a real

business issue and in many cases is a survival issue. Getting energy management wrong can be fatal to a site. Energy prices have continued to increase and the desire to reduce greenhouse gas emissions has become even more critical (and political). Both factors have raised the profile of energy management in the plastics processing sector and this has prompted many sites into action. However, all too often the efforts have been poorly directed or ineffective. Sadly, this has led to some sites abandoning their efforts to improve energy management when the basic techniques are very simple and easily applied. Where sites have been well informed and have diligently applied the basics then the results have been exceptional – energy use reductions of 30% are not uncommon and some sites have achieved even greater reductions. Simple techniques can have dramatic results. This chapter looks at energy management in the broad sense so that use and cost reduction efforts can be effectively targeted. It is designed to provide the essentials of the management framework for energy management. Readers should not be tempted to rush into the practical engineering aspects of energy management without first understanding the management framework.

‘I am not a tree-hugger’. Jonathan Churchman-Davies

Energy Management in Plastics Processing https://doi.org/10.1016/B978-0-08-102507-9.50001-5, Copyright © 2018 Elsevier Ltd. All rights reserved.

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1.1

Where we are going

The destination Most plastics processing sites want to reduce energy use and costs and most have also made some efforts in this direction. The problem is that most sites do not have a structure for these efforts or any method of assessing the value of the ideas that they may have to reduce energy use. They also have no methods of assessing performance of either the site, the machines or the projects that they do carry out. The results are: • They cannot tell how efficient they are

already (at either the site or machine level). • They have no method of monitoring and targeting performance or they measure the wrong things. • They carry out projects with no idea if these projects are the best for the site. • Their main sources of advice are either suppliers who want to sell their products or consultants who do not know the processes. These sites then wonder why their efforts did not deliver significant benefits and they lose motivation to continue because it is ‘too hard’. The reality is that it is not too difficult for most plastics processors to reduce energy use by up to 30% within a period of 2–3 years even though there are still sites who proudly proclaim that they intend to reduce energy use by 5% in the next year. The major problem is that they know that they want to reduce energy use but they really have no idea of the steps that they have to take to get there. They set off on the journey with no real planning about where they want to go, how they are going to do it and how they will measure their progress (if any). Some sites install an ‘energy management system’ in the hope that this will reduce energy use, some install complex measuring systems, some install high-tech equipment and some appoint an ‘energy manager’ without giving them either the time or resources to actually do the job. All of these partial and disjointed measures will inevitably fail. Some will fail more miserably than others, but all will fail. 4

Before starting the journey to reduce energy use, every site needs a plan (a road-map) to define where they are and where they want to be. The figure opposite shows the major areas, the processes and tools used, the benefits from using the processes and tools and the overall results of a good energy management system.

Energy management could easily be the deciding factor in whether your company survives or not.

• Tip – Some sites install ISO 50001 (see

Section 1.5) and then wonder why the energy use does not automatically decrease. These are often the same sites who install ISO 9001 and wonder why quality does not automatically improve.

This is about the whole company A major issue is that energy is still sometimes seen as a ‘bolt-on’ to the other operations of the company. It is seen as a ‘good thing’ for the bad times but optional in the good times. The reality is that ‘energy management’ needs to permeate the complete operation of the company. It is not a ‘production’ issue, it is a management issue.

The road-map The road-map identifies the range of skills and activities necessary to reduce energy use and even this is limited by space. The road-map shows the type of things that you will have to do to achieve meaningful reductions in energy use and cost. It is not simply about management systems or any other single thing. Specifically, it is not only about production. It is about the whole company and it is about a mind-set that says ‘reducing energy use and costs is for everybody’ and that we are all responsible. The road-map covers all areas of a company’s operations from the management focus, people (and their training) through services, processing, operations, buildings and offices and how new profitable projects are identified and prioritised. Effective energy management impacts every aspect of a company’s operations. This is not for the fainthearted but the rewards are more than worth the effort. • Tip – None of the actions in the road-

map are ever completed. Get used to continual improvement. Chapter 1 – Introduction to energy management

The energy road-map Improving energy management is not difficult but it needs a road-map of the available processes, tools and actions to deliver the best results. Chapter 1 – Introduction to energy management

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1.2

The drivers for energy management

Changing times – changing issues The plastics processing industry in the developed world is highly focused on the cost of labour and sees the growth in volume of imported products as being due purely to the ‘lower labour costs of overseas suppliers’. In a previous book1, I looked at cost management and stated that the real issue was the change in the cost structure in plastics processing. It was not as simple as ‘lower labour costs’. The reality is that labour costs are now, and always have been, a minor component of the overall cost of most plastics products. The costs of materials and overheads are far more important in the total product cost, but Western industry still focuses overwhelmingly on the labour cost even as the overheads rise inexorably and the cost of energy approaches, or exceeds, the cost of direct labour. The approximate relative importance of the costs and the efforts that we spend are shown on the right. These may not be exactly correct for your site but they won’t be far out – we are directing the efforts in the wrong places and then simply seek to blame lower labour costs. In the East, however, they have already realised that the cost of energy is higher than the cost of labour and some of the most energy-efficient sites in the world are already in the East. This means that in addition to a labour cost advantage, they are also rapidly being assisted by an energy cost advantage.

Energy costs change on a daily basis but there is no reason to believe that they will decrease dramatically in the near future and every reason to believe that they will remain unstable for the foreseeable future.

Taxation The concerns with global warming have led governments across the world to impose rising taxes on energy use. These are financial instruments designed to internalise the effects of manufacturing on the environment. Previously industry was free to use resources and was not concerned with the societal impacts. These are now being internalised by legislation and taxation that raise costs.

‘The starting point for (UK) energy policy is to save energy. It is often the cheapest way for reducing carbon emissions, certainly in the short term. It can also contribute to security of supply, for example by reducing our need for energy imports, and reduce fuel poverty through lower bills.’ UK Energy White Paper (May 2007).

Supply shortages One major reason for historical energy cost increases was the high dependency of power generation on oil- and gas-based power stations but this has been mitigated by the ‘fracking revolution’ and this has stabilised oil and gas prices to some extent. Despite this, the world is still suffering from oil and gas resource depletion. In small words – the easily accessed supplies are rapidly running out.

This misdirection of our efforts continues to cost money and waste resources.

Financial and operational Rising costs Energy costs have risen dramatically in the last 15 years and this is the primary driver for increased interest in energy management. These rises have now levelled off to some extent as a result of geopolitical events but the world is only one misstep away from dramatic increases. It would be nice to think that the plastics processing industry is driven by a desire to be ‘greener’ but the way to attract attention in business is to affect the financial results and the increased cost of energy has attracted attention in the plastics processing industry. 6

The cost sources and where our efforts go Labour represents only about 10% of the cost of the product but the majority of our efforts still go into reducing the cost of direct labour. 75% of our efforts are in reducing labour costs and only 15% in reducing overhead costs. Chapter 1 – Introduction to energy management

This does not mean that we are necessarily running out of oil or gas – although this may be true. It simply means that the sources we are using now need more expensive technology to extract the oil and gas than the easily accessible sources that were available in the past. This is not simply a concern for the West, it is also a concern for sites all over the world. Energy is a world market and, whilst there are local variations, the cost of energy is essentially a global cost – sites all over the world are facing the same issues. In some areas the concern is not just with supply shortages in terms of the raw materials but with supply shortages in terms of the distribution network. In some rapidly developing Asian countries, the rate of expansion is so high that there are difficulties in providing the necessary supply network from the power stations to the users and this is creating a supply shortage at the point of use.

the environmental impact of operations. The concept of a ‘carbon footprint’ is becoming more relevant and customers (particularly consumer-oriented retailers) are beginning to demand information not only on the carbon footprint but also on action being taken to reduce this. Reducing energy use through effective energy management is a method of reducing the carbon footprint and improving the corporate social responsibility of any organisation.

Carbon Footprinting The process of carbon footprinting and establishing the carbon emissions of a site is rapidly becoming more important. This is more fully dealt with in Chapter 9.

• 1. Kent, R.J. 2017. ‘Cost Management in Plastics Processing’, Elsevier.

Security of supply The supply shortages are also driving the development of energy supplies from areas of the world that suffer from supply insecurity, either in terms of poor infrastructure development or in terms of national security issues from external or internal threats at the source or in the transport of the supply. It is no longer possible to consider energy supplies from many countries as stable and permanent.

Environmental CO2 emissions Most plastics processors pretend that they do not emit CO2 and will happily state that their CO2 emissions are zero. The reality is that plastics processing uses electrical energy and this is generated by power stations that emit CO2 on the processor’s behalf (unless they use nuclear or other renewable power sources). The fact that the CO2 is emitted at some distance from the processor is irrelevant in terms of the environmental impact. It is undeniable that CO2 levels are rising and that climate change is real. Efforts to reduce CO2 emissions will continue and this means that energy management will become increasingly important.

Corporate social responsibility Industry is slowly accepting that corporate social responsibility and simple good public relations require action to reduce

The benefits of energy management Energy management delivers reduced costs and improved profits for a site as well as improving working conditions at the site and reducing the environmental impact (the carbon footprint) of the site.

The new words: Global warming. Greenhouse effect. Carbon management. Carbon footprint. Sustainability. Life-cycle analysis. Corporate social responsibility. Stakeholders. Energy efficiency.

It doesn’t matter if you believe in any of these. It doesn’t matter if you believe in ‘anthropogenic global warming’ (man-made climate change). Motives don’t matter – survival does.

Chapter 1 – Introduction to energy management

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1.3

The importance of energy costs

The magnitude of the costs For the majority of plastics processing sites, the cost of energy is in the region of 6–8% of the turnover and, in many cases, this is approximately equal to the profit of the site. In some cases, particularly for processors in low-margin sectors, such as in packaging or automotive parts, the cost of energy can be greater than the profit margin. Savings in energy management can have a dramatic effect on profitability for many plastics processing sites.

The magnitude of the savings The possible savings from good energy management are in the region of 30% of the current energy spend for most plastics processing sites. This value varies with the status of the site but it will naturally be even higher for novice sites, i.e., those that have taken little action in the past and those that have little experience in energy management. In some cases, energy savings of up to 50% have been identified with little difficulty, although savings of this magnitude are rare. These savings can be delivered virtually irrespective of the industry sector or process used. It is not the case that any particular plastics process wastes more energy than another. The process appears to make little difference in the potential savings – it is the management that makes the difference.

building services (Chapter 7) can again produce energy savings of up to 10%. This includes small investments in technologies such as variable speed drive (VSD) control of water pumps and airhandling fans (this is now a ‘standard’ technology that is rapidly falling in implementation cost). We define a maintenance investment on the basis that the payback is < 1 year (irrespective of the amount required to achieve the saving). Such ‘investments’ would typically come from the revenue budget rather than the capital expenditure budget due to the rapid payback.

Energy costs can easily reach 8% of turnover. Do you spend this proportion of your time managing the cost of energy? Do you spend any time at all?

Capital investments The final 10% saving is possible through investment in energy-efficient processing technologies that reduce energy use in the process and, just as importantly, in the effective management of these. This includes investment in projects with longer paybacks such as completely new machines and technology. We define a capital investment on the basis that the payback is greater than 1 year (irrespective of the amount required to achieve the saving). Such investments would typically come from the capital expenditure budget rather than the revenue budget due to the longer payback.

Energy is a variable and a controllable cost.

Major savings are possible through simple improvements in management, maintenance and investment.

Management actions Simple recognition that the rules have changed and that managing energy use (in proportion to the management efforts that are expended in managing direct labour) can produce energy savings of up to 10%. This involves simple techniques such as monitoring and targeting (Chapter 3), improved process management (Chapter 5) and the creation of the relevant management control systems.

Maintenance actions Simple quick-fix actions such as controlling the use of services both in the process itself (Chapter 4) and in the 8

Energy cost reductions come from three basic areas Energy cost reductions typically come from three basic areas: management of the use, maintenance of the systems and investment in new technology. The first two generally require only no-cost and low-cost actions to reduce use and costs. Chapter 1 – Introduction to energy management

The payback The majority of the savings can therefore be delivered through a balanced combination of no-cost, low-cost and investment (maintenance or capital) actions. The average payback for all investments in energy management is, in our experience, in the region of 6–9 months. This is true even when the payback is calculated using nominal costs for internal management efforts using existing resources. This type of payback makes investment in energy management extremely attractive from a purely financial point of view. Not many capital investment projects achieve a payback of less than 1 year and continue to deliver the benefits virtually indefinitely. Yet many sites do not seem to accept or encourage investment in energy management because of the misguided view that energy costs are fixed and uncontrollable. Capital investment proposals are still primarily presented based on direct labour reductions and rarely put forward purely based on energy use reduction.

The source of the current costs Few sites are able to accurately allocate their energy consumption in terms of where energy is used, despite the fact that this is a relative easy task. A basic understanding of the reasons for energy use will inform a site as to where they should spend time and effort in energy use reduction efforts. Efforts at reduction should normally be relative to the size of the use and/or the ease of implementation. The simplest method to determine the approximate energy distribution at a site is to count the kW ratings of the main process motors, services and other major energy consumption areas (see Section 3.2 for further details of this ‘energy mapping’ process). Note: Lighting loads can be quantified by simply counting the number of tubes/lamps and associating the numbers with the energy use of each lamp. These kW values can be entered into a simple spreadsheet and factors applied for the relative use of the motor, service or lamp in terms of hours/year (or operational hours in the case of services such as compressors). This will give a first-pass approximation of the relative magnitude of the various areas of energy use at the site. The total of these values

should be subjected to a ‘reality check’ with the overall energy use of the site. Large discrepancies generally indicate motors that have been overlooked or loadings that have been miscalculated. The site results can be compared with the general approximate energy cost distribution for most plastics processing sites shown below. The exact percentages for each individual site will depend on the process used at the site, e.g., compressed air use is normally higher at blow moulding sites, cooling is normally higher at extrusion sites and sites with a large amount of assembly work will also generally use more compressed air. Despite these local variations, the ratios will be approximately correct for the majority of sites. • Tip – A simple walk around to identify

the major energy use areas will often identify hidden use that the site has never really considered before.

Low-cost energy efficiency measures can improve profits significantly.

Energy supplies are increasingly precarious. Energy supply has led to the greatest transfer of wealth the world has ever seen. Energy supply has driven major world political events and will drive more in the future.

• Tip – Many amateur energy surveyors

(or those not familiar with the plastics industry) get excited about lighting and heating. This is a sure sign that they have a lot to learn. The main energy use in plastics processing is in the machinery and services (92%). Lighting, heating and offices are minor costs (8%).

Earth First! We’ll drill the other planets later. Bumper sticker seen in Texas.

Offices Heating Lighting 1% 2% 5% Water pumps 5%

Chillers 11%

Compressed air 10%

Plastics processing 66%

Approximate energy cost distribution for plastics processing The main energy use and cost is in the plastics processing machinery and services (92%). Lighting, heating and offices are minor costs (8%). A sense of perspective is needed.

Chapter 1 – Introduction to energy management

9

The efforts, opportunities and obstacles

Straight to the bottom line In many cases, a site’s energy costs are almost a discretionary cost, i.e., the site effectively chooses to pay the cost of energy because it chooses not to do anything about it. Reducing the discretionary cost of energy at any site is directly geared to the profit of the site. Any cost saving due to energy management translates directly to the bottom line and is shown as a direct increase in profit. Work in energy management is as valuable as work to reduce direct labour and in many cases the savings are more easily achieved because previous work to reduce direct labour has already removed the easy wins. In fact, a large proportion of the cost of energy is a base load and can be reduced without affecting the site operations.

Better than increased sales Reducing the cost of energy is an extremely profitable activity. When the cost of energy is reduced it adds directly to the bottom line – something that increasing sales does not do. When energy costs are 5% of the turnover and the profit margin is 5% then reducing energy use by 30% is the same as adding 30% to the profit. To achieve the same results through increased sales would require an additional 30% of sales – not an easy task. What would your site do to gain new business that increased turnover and profit by 30% if you knew that: • Your competitors couldn’t stop you getting the business. • The business was effectively guaranteed. • The business required only internal

effort. • The business was low risk and had a payback of 6–9 months. • The business would continue into the

future and probably increase in value. • The business would make you look good to your stakeholders and the community. Most sites are enthusiastic about gaining new business through increased sales. Yet when shown the opportunity to reduce energy costs and achieve the same results at the profit line, the same sites react with huge indifference. The old saying is 10

‘turnover is vanity, profit is sanity’ and the sad reality is that many sites still prefer the vanity of increased turnover.

The efforts The current efforts at most sites are derisory in the extreme. Most sites are only too happy to complain about rising energy costs but take no interest in the management of the energy that they use. Finance complains but still pays the bill, manufacturing rarely sees the bill and accepts it as a fixed cost and the general management would rather increase sales than profits. It is rare to see any site take effective action to reduce the cost of energy other than sporadic actions to reduce the £/kWh at the annual tariff negotiations. The effective efforts are almost always taken at the grass-roots level by dedicated maintenance managers who make wise decisions that are rarely, if ever, understood or backed up by the top management. The real decisions on energy use never make it to the boardroom because the directors are more interested in discussing opportunities to increase sales by 5%.

Effective energy management can reduce costs and increase profits more economically than efforts to increase sales.

Investment in energy management can be the most effective investment a site can make.

Brick walls are a way of reminding you how much you want something. Randy Pausch

Gaining top management commitment to energy management is the key to real progress.

Sales value of £1 saved by energy management

100

80 Sales value (£)

1.4

60

40

20

0 0

2

4

6

8

10

12

14

16

18

20

Net margin (%)

Reducing energy costs is the equivalent of new sales If the net margin is 10% then every £1 saved by good energy management gives the same profit as £10 of new sales. If the net margin is 5% then every £1 saved is the equivalent of £20 of new sales. Savings from energy management are easier to get than new sales and provide easy opportunities for increased profits. Chapter 1 – Introduction to energy management

The opportunities and obstacles The opportunities and obstacles will vary in importance and difficulty with the site but should be separated and dealt with individually. The way to eat an elephant is one mouthful at a time. The only vital issue is top management commitment, once this is achieved all the rest follows.

Chapter 1 – Introduction to energy management

11

1.5

Energy management systems – the basics

Setting the structure This workbook contains detailed recommendations and actions that can be taken by most sites but they will not happen if they are carried out in isolation. After gaining top management commitment (see Section 1.4) a site needs to set up an energy management system to manage the process. Energy management is seen by many as the logical extension to the range of ‘management systems’ standards already developed for areas such as quality management (ISO 9001) and environmental management (ISO 14001). The rise of this ‘management systems’ approach and the reality of implementing these are discussed in Section 1.6 but at this stage we will consider the main requirements of an energy management system whether it nominally complies with ISO 50001 or not.

Policy Every site needs an energy policy giving: • A detailed statement of commitment from top management. • Performance targets from internal or external benchmarking. • Short-term site goals (1 year). • Medium-term objectives (3 years). • Long-term corporate goals (5 years).

This policy should be provided to all staff to raise awareness of the cost of energy and the benefits of improved energy management. The policy is the framework for developing and establishing good energy management practice and should establish the importance of energy management at all staff levels.

Personnel Operating the energy management system should be the clear responsibility of a nominated person, the ‘energy manager’, who will act as the facilitator, expert advisor and project manager for energy management projects. • Tip – This may not be a full-time role

but the responsibility and authority should be clear. • Tip – In the same way as the quality

manager is never the production 12

manager, it is best if the energy manager is not the person responsible for using the energy, i.e., the production manager.

Information Any management system needs information to operate and energy management is no different. Much of the required data are probably already being collected by most sites and this simply needs to be formatted so that it is easily used for energy management. Information is needed to allow monitoring, targeting and reporting (see Chapters 2 and 3). This is generally easily available but systems are needed that will regularly and automatically generate the information. The system should be targetbased and allow cost allocation and performance assessment. This will drive responsibility down to those who actually use the energy.

Planning the way energy management is organised is a senior executive responsibility which will determine the success or failure of the energy policy …

… this goes well beyond simply appointing an energy manager.

• Tip – Targeting is the key action. What

gets measured gets done. Information is also needed for project identification. At most sites, the opportunities to reduce energy use are greater than the resources, and actions must be prioritised for the quickest and easiest returns. Potential projects should be assessed in terms of the ease and cost of implementation and the size of the potential energy use reduction. This can be carried out using the information from Section 1.2 on the source of the current costs and using a simple decision grid (see Section 1.13). Projects should be prioritised for the maximum effect – there is no shame in starting with the ‘lowhanging fruit’.

Planning Project planning is needed even for simple projects. This should identify timings, resources and benefits to be achieved. The system must include a planning process, even at a basic level, so that projects are delivered as required.

Resources An energy management project is the same as any other project and planning will identify the resources needed (time and/or money) for the project to be completed. Sites need to allocate the

For details of simple methods of project management see Section 1.13 and Kent, R.J. 2017. ‘Cost Management in Plastics Processing’, Elsevier.

Chapter 1 – Introduction to energy management

necessary resources to achieve results. • Tip – Attempting to manage energy

without allocating adequate resources is doomed to failure. Energy management will almost certainly need more resources than currently available at most sites. However, given the magnitude of the rewards these can easily be financially justified.

Training Staff training is essential to implement an energy management system. The policy and other actions will have little effect unless the staff know the targets, the action being taken and how they can contribute. Staff training may be limited due to the automated nature of most plastics processing and the lack of ability of the staff to affect the outcomes. Training should be no longer than 40 minutes for existing staff and should be integrated with other induction procedures for new staff (see Section 6.5).

reports to initiate improvement actions – these must be closed out when completed (see Section 8.7). Non-conformance reports must lead to action.

Set the energy management structure …

Reporting An energy management system must also incorporate a reporting function (see Sections 3.6 and 3.7). Reporting should be to both management (to show the value of the work) and to staff (to show the progress being made). Reporting can also be to external stakeholders to show corporate social responsibility by reducing greenhouse gas emissions.

...then use the structure to set targets and implement projects to achieve the targets.

• Tip – Training sessions should be

followed by a ‘go-see’ exercise where the staff go to their area and identify energy improvements.

Auditing Any system needs auditing to ensure that progress continues to be made and that the system continues to operate. This is best achieved by regular site audits by site staff. This will ensure that the system is operating and will discover new areas for improvement. At least one person per site should be trained to a basic level in energy auditing to allow regular audits to be carried out. Internal auditors are carrying out two functions: • They are checking that the system is functioning as it was designed to. • They are looking for new profitable projects to implement. This workbook can be used as a primer for site audits and potential further improvements. Energy management is not a single task but a series of continuing actions; only continuous identification of new actions and resolving these issues will allow energy use and costs to be reduced. • Tip – Site audits should use standard

auditing methods. The audits should identify areas where actions do not meet the energy policy or where items from this workbook are noted. Site audits should also create non-conformance

The components of an energy management system An energy management system is needed to identify, plan and complete projects to deliver energy savings. Without a system, the energy management activities will be poorly coordinated and will eventually fall into disrepute.

Chapter 1 – Introduction to energy management

13

1.6

Energy management systems – the standard

ISO 50001 – the standard for energy management systems In 2011, ISO released ISO 50001 to provide organisations with guidance on implementing energy management. The standard is based on the ISO 9000 series model of ‘Plan–Do–Check–Act’. This allows many activities to be carried out in common with existing quality and environmental management systems. This also avoids a creating a stand-alone energy management system, makes use of existing structures and allows energy management to be seen as part of normal business.

What does ISO 50001 do? ISO 50001 provides a broad framework of requirements enabling any organisation to: • Develop a policy for more efficient use of energy. • Fix targets and objectives to meet the policy. • Use data to better understand and make decisions concerning energy use and consumption. • Measure the results.

• Provide techniques or tools to reduce

energy use. • Provide projects to reduce energy use.

What does ISO 50001 cover? The bulk of the current edition of ISO 50001 is covered in Section 4 of the standard but the complete standard covers the following elements:

1 Scope 2 Normative references

Before starting ISO 50001, ask yourself the critical question ‘Did ISO 9001 actually deliver quality to our company?’ If the answer is ‘No’ then ISO 50001 will probably not deliver energy management to your company.

3 Terms and definitions 4 Energy management system requirements 4.1 General requirements 4.2 Management responsibility 4.2.1 Top management 4.2.2 Management representative 4.3 Energy policy 4.4 Energy planning 4.4.1 General 4.4.2 Legal and other requirements 4.4.3 Energy review 4.4.4 Energy baseline

External systems are often used to justify an extraordinary amount of work for an infinitesimally small reward. Do not let this happen to you.

• Review the effectiveness of the policy. • Make continual improvements in energy

management. One of the major benefits of ISO 50001 is that it encourages setting up a permanent structure to manage energy use. In many sites, energy becomes a ‘flavour of the month’ when prices rise and then fades in importance as the site and management become used to the increased costs. This leads to random initiatives to reduce energy use but no long-lasting energy use reduction programme or focus. ISO 50001 provides the structure and processes for long-term work and long-term energy use and cost reductions.

What does ISO 50001 not do? As a broad framework for energy management that is equally applicable to all organisations, ISO 50001 does not: • Provide guidance for any specific

industry or sector. • Provide targets or benchmarks for any

specific industry or sector. 14

Plan

Input

Output

Check s& dard Stan edures proc

Continual improvement

The ‘Plan–Do–Check–Act’ cycle (the Deming Wheel) Plan–Do–Check–Act is part of the continuous improvement cycle where improvements are carried out in a cycle and then reinforced by internal standards to hold the gains made by the improvement. Chapter 1 – Introduction to energy management

4.4.5 Energy performance indicators 4.4.6 Energy objectives, energy targets and energy management action plans 4.5 Implementation and operation 4.5.1 General 4.5.2 Competence, training and awareness 4.5.3 Communication 4.5.4 Documentation 4.5.5 Operational control 4.5.6 Design 4.5.7 Procurement of energy services, products, equipment and energy 4.6 Checking 4.6.1 Monitoring, measurement and analysis 4.6.2 Evaluation of legal requirements and other requirements 4.6.3 Internal audit of the system 4.6.4 Nonconformities, correction, corrective and preventive action 4.6.5 Control of records 4.7 Management review 4.7.1 General 4.7.2 Input to management review 4.7.3 Output from management review

The systems approach ISO 50001 is an ‘external’ system, where the general requirements, but not the detail, of the system are specified. As for all external management systems, ISO 50001 follows the ‘Plan–Do–Check–Act’ (PDCA) model: • Plan – identify the requirements and set the policy. • Do – decide on the procedures needed and implement them. • Check – set targets and objectives, and

assess achievement. • Act – continually improve the system.

All external systems generally suffer from the same defects as internal systems, i.e., complexity and lack of clarity, but most have several additional defects that can actually prevent people from delivering the desired aim of the system. These are: • Inflexibility: ‘The standard requires this’. This is where the general requirements of the standard are translated into an edict that must be obeyed even when all concerned can see that the result is a system that either doesn’t deliver any benefit or, worse still, is detrimental to

the overall stated aim of the system. • Atrophy: ‘We can’t change this’. This is

where the interpreted requirements of the standard are regarded with an almost religious passion and become a dogma that cannot be changed. The result is a system that becomes engraved in stone, that nobody pays any attention to and eventually leads to disillusionment with the whole system. • Tick the boxes: ‘We have to show that we

have done this’. The system is acknowledged as not delivering, the management see no benefit in it but the threat of losing certification is worse than the alternative of attending meetings, producing reports and ticking all the required boxes. External systems can deliver excellent benefits provided companies have the courage to use them to the best effect, to modify or discard them if they are not working and to refuse to accept the boilerplate solutions that are commonly delivered to them. Companies need to: • Cut through the jargon and to use the systems to deliver real cost savings. • Use the systems that they already have. • Carry out a realistic business appraisal of the case for installing the external system or not. Systems are a business decision.

Actions and information for ISO 50001 • How much energy are we using? • When are we using energy? • Where are we using it? • Who influences energy use? • What are the energy use drivers? • What is our energy baseline? • What are our energy indicators? • Are there any legal or other requirements? • What are our objectives and targets? • What is our action plan? • Do we have the necessary resources and knowledge?

What to do? Choosing to obtain ISO 50001 may or may not reduce energy use but that is no reason not to start on the essential journey of reducing energy use.

Do they deliver? One issue that is largely absent from many of the discussions about ‘management systems’ standards is the answer to the unasked question ‘Do they deliver?’ Many companies are driven into the management systems standards approach by their own insecurity and need to present some external verification of their systems. In some companies, the introduction of the standards is primarily an exercise in ‘window-dressing’ where current and failing systems are simply documented and engraved in stone. This response will inevitably fail and the systems will not deliver. In other companies, the introduction of this type of standard forces a re-evaluation of the systems that are currently in place. This can be a powerful catalyst for change and improvement. The standard can act as a reference for ‘best practice’ and provide guidelines for the development of internal systems. Do they deliver? The answer depends on you.

Chapter 1 – Introduction to energy management

15

1.7

Energy management systems – the changing standard

All change with standards

ISO 50001 and ISO 14001

It will come as no surprise that there is now a ‘standard’ for management systems standards. Annex SL is the new standard high-level structure for all ISO management systems standards. It does not enforce any new requirements but simply makes the standards much more consistent in numbering, format and content.

ISO 50001 differs slightly from the other management systems standards in that it is much more data-driven and focuses on the numbers, i.e., it is much more quantitative than ISO 14001. ISO 14001 can certainly consider energy use and performance as environmental aspects and impacts but this consideration tends to be in a more qualitative manner.

All new and revised management systems standards will now conform to a common structure of the form:

If, as at many plastics processing sites, the major environmental aspect and impact is associated with energy use then ISO 50001 will provide a much more focused approach to environmental improvement. The fact that the cost of energy is also likely to be high for most plastics processors also means that any financial benefits of ISO 50001 are likely to be clearer.

• Clause 1: Scope. • Clause 2: Normative references. • Clause 3: Terms and definitions. • Clause 4: Context of the organisation. • Clause 5: Leadership. • Clause 6: Planning. • Clause 7: Support. • Clause 8: Operation. • Clause 9: Performance evaluation. • Clause 10: Improvement.

The Annex SL structure will make it much easier for sites with multiple management systems, e.g., ISO 9001, ISO 14001 and ISO 50001, to avoid duplication of effort and documentation. ISO 9001:2015 and ISO 14001:2015 have already been published in the Annex SL structure but the current version of ISO 50001 (as referred to in Sections 1.5 and 1.6) was written in 2011 in the ‘old’ management systems standard format. This is currently being re-written to conform to the Annex SL format with much the same changes in emphasis that were seen in ISO 9001 and ISO 14001. The release of the revised and new format ISO 50001 is planned for 2019 but there will be a 3-year transition period from the ‘old’ to the ‘new’ formats. A prediction of how the current ISO 50001:2011 clauses will map onto the ‘new’ format is shown on the right. The new format will increase the range of activities that are common to existing quality and environmental management systems. This can make use of existing structures and allows energy management to be seen as part of the normal business processes. 16

There is nothing to stop sites implementing both ISO 14001 and ISO 50001. The additional implementation cost is not likely to be large but the additional certification costs may be a barrier. • Tip – Some sites use ISO 14001 to

manage the overall environmental issues and ISO 50001 for specific energy issues. If this is done then the integration of the management systems standards can be used to minimise costs. • Tip – Do not think that implementing

ISO 50001 in any format will automatically reduce energy use. This needs projects to be identified, quantified and implemented.

Choosing to obtain ISO 50001 may or may not reduce energy use but that is no reason not to start on the essential journey of reducing energy use.

Free tools The US DoE has produced some excellent tools for implementing ISO 50001 and these are available at https:// save-energynow.org. Download the DOE ‘eGuide for ISO 50001’ or the ‘eGuide Lite’ for some excellent resources on how to implement ISO 50001. ENERGY STAR also has some excellent resources available at www.energystar.gov.

• Tip – Since the introduction of ISO

50001 in 2011, there has also been a range of new standards produced. These include: ISO 50002:2014 – Energy audits. Requirements with guidance for use. ISO 50003:2014 – Energy management systems. Requirements for bodies providing audit and certification of energy management systems. 

ISO 50001 requires actions to address risks and opportunities but the risk management requirements are likely to be far less stringent than in other management systems standards.

Chapter 1 – Introduction to energy management

Clause

ISO 50001:2011

0 1 2 3

Introduction Scope Normative references Terms & definitions

4

EnMS requirements

Clause 0 1 2 3 4

4.1 4.2 4.1

General requirements

4.3 4.2

Energy policy Management responsibility

4.4

Energy planning

4.4.3 4.4.2 4.4.4 4.4.5

Energy review Legal & other requirements Energy baseline Energy performance indicators

4.4.6

Energy objectives, targets & action plans

4.2.1 4.5.2

Top management Competence, training & awareness

4.5.3 4.5.4

Communication Documentation

4.5 4.5.1 4.5.6 4.5.7

Implementation & operation General Design Procurement of energy services, products, etc. Checking Monitoring, measurement & analysis

4.6 4.6.1 4.6.2 4.6.3

Evaluation of compliance with legal requirements and other requirements Internal audit of the EnMS

4.7 4.7.2 4.7.3

Management review Input to management review Output from management review

4.6.4

Nonconformities, correction, corrective action & preventive action

ISO 50001:2019 Introduction Scope Normative references Terms & definitions Context of the organisation

9.1.2

Understand the organisation & its context Understand the needs & expectations of interested parties Scope of the EnMS EnMS Leadership Leadership & commitment Energy policy Organisational roles, responsibilities & authorities Planning Actions to address risks & opportunities Energy review Legal & other requirements Energy baseline Energy performance indicators Planning action Energy objectives & planning Support Resources Competence Awareness Communication Documented information Creating & updating Control of documented information Operation Operation planning Design Procurement of energy services, products, etc. Performance evaluation Monitoring, measurement, analysis & evaluation Evaluation of compliance

9.2 9.2.2 9.3 9.3.2 9.3.3 10 10.2

Internal audit Internal audit programme Management review Management review inputs Management review outputs Improvement Nonconformity & corrective action

10.3

Continual improvement

4.3 4.4 5 5.1 5.2 5.3 6 6.1 6.1.2 6.1.3 6.1.4 6.1.5 6.1.6 6.2 7 7.1 7.2 7.3 7.4 7.5 7.5.2 7.5.3 8 8.1 8.2 8.3 9 9.1

Prediction of how ISO 50001:2011 will map to ISO 50001:2019 The exact requirements of ISO 50001:2019 will not be defined until 2018/2019 but it is highly likely that the requirements of ISO 50001:2011 will map as per previous management systems standards. It is also predicted that, in common with other standards, there will be increased emphasis on continual improvement, the introduction of risk-based thinking and the change from ‘documents’ to ‘documented information’. Chapter 1 – Introduction to energy management

17

1.8

Energy management – where are you now? To complete a column read the descriptions in the column cells and select the cell that is closest to the current situation at your site.

Where are we starting from? Understanding the current situation provides the basis for an improvement strategy and many of the basic actions necessary for successful implementation. The next sections in this chapter provide a series of self-assessment charts designed to assess your current position. The charts are easy to complete but we suggest copying the relevant pages before completing the forms.

Completing the chart Each chart has several columns which cover various aspects of the main topic.

It is unlikely that every part of the description in the cell will fully describe your specific situation but choose the cell that has the most appropriate description. This will give a score ranging from 0 to 4, mark this at the base of the column. After all the columns have been scored, transfer the scores to the radar chart for the relevant columns/axes. This gives a rapid visual assessment of the current situation for the specific topic.

Energy management Energy policy 4

If you don’t know where you are starting out from then it is unlikely that you will end up where you want to get to!

This is a team effort! Completing the chart on your own is not recommended. It is much better to either complete the chart as a group – you will be amazed at the divergence of opinions – or to get several people in the company to complete the chart separately and then to compare the results.

3 Investment

2

Organising

1 0

Marketing

Motivation

Assessing the results Ideally, a site would have balanced score with all columns/ axes in the same broad area. This is rare and in most cases, sites will show strengths in certain areas and weaknesses in others. The axes with low scores are the areas that the site needs to work on to improve the overall score.

Information systems Download the software

Use the scoring chart to assess where you are in energy management The numbers from the scoring chart can be transferred to the radar chart for a quick visual assessment of where you are in the basics of energy management. 18

This and similar charts are available as a downloadable spreadsheet at www.tangram.co. uk/energy.

Chapter 1 – Introduction to energy management

Energy management Level

4

3

2

Energy policy

Motivation

Information systems

Marketing

Formal & informal Comprehensive Marketing of Energy policy, Energy systems set energy efficiency action plan & management fully channels of targets, monitor & energy regular review integrated into communication have commitment regularly exploited consumption, management management identify faults, performance both of top structure. Clear by energy manager & energy quantify savings & internally & management as delegation of provide budget externally. part of an responsibility for staff at all levels. tracking. environmental energy strategy. consumption.

Investment Positive discrimination in favour of 'green' schemes with detailed investment appraisal of all opportunities.

Formal energy Monitoring & Programme of Same payback Energy manager Energy committee policy, but no used as main targeting reports staff awareness & criteria employed accountable to active commitment energy committee channel together regular publicity as for all other for individual premises are campaigns. investments. from top representing all with direct contact based on management. users, chaired by with major users. a member of the sub-metering, but savings not managing board. reported effectively to users. Unadopted energy Energy manager Contact with major policy set by in post, reporting users through adenergy manager or to ad-hoc hoc committee senior committee, but chaired by senior line management departmental departmental manager. & authority are manager. unclear.

An unwritten set of guidelines.

1

Some ad-hoc staff Investment using Monitoring & targeting reports awareness short-term based on supply training. payback criteria meter data. only. Energy unit has adhoc involvement in budget setting.

Energy Informal contacts Informal contacts Cost reporting management is between based on invoice used to promote engineering staff & the part-time energy efficiency. detail. Engineer compiles responsibility of a few users. reports for internal someone with limited authority or use within influence. technical department.

No explicit policy.

No energy management or any formal delegation of responsibility for energy consumption.

No contact with users.

x

x

x

0

Score

Organising

Chapter 1 – Introduction to energy management

Only low-cost measures taken.

No information No promotion of No investment in system. energy efficiency. increasing energy No accounting for efficiency. energy consumption.

x

x

x

19

1.9

Financial management – where are you now?

Without money it won’t happen Energy management is the same as any other project or process – starve the process of the appropriate investment and it will fail. All projects, even nominally nocost and low-cost projects need investment in staff time and much progress can be made in these areas. Eventually, the process will require financial investment of some magnitude and this must be justified before progress can be made.

standard investment hurdles and analysis that are in place at most sites. The main concern is that energy management receives the appropriate level of funding for the benefits that it can deliver.

Completing the chart

The financial aspects of investment in energy management are also covered in Chapter 3.

This chart is completed and assessed as for the previous chart.

Energy management does not require preferential funding. Most energy management projects can easily meet the

Financial management Identifying 4

3 Project funding

2

Exploiting

1

0

Management information systems

Human resources

Appraisal methods

Use the scoring chart to assess where you are in financial management The numbers from the scoring chart can be transferred to the radar chart for a quick visual assessment of where you are in the basics of financial management. 20

Areas of disagreement may show that there is something happening at the site that is not well known, i.e., the Finance function is actually keeping records but is not telling the Production function that they are doing so.

Chapter 1 – Introduction to energy management

Financial management Level

4

3

Identifying

Exploiting

Management information systems

Appraisal methods

Human resources

Board take a Detailed energy Formal Full MIS enabling Full discounting proactive surveys regularly requirement to identification of methods using approach to longupdated. identify the most internal rate of past savings & term investment Lists available of energy-efficient further return & ranking as part of a opportunities option. opportunities for priority projects as part of an ongoing detailed already costed & Decisions made investment investment environmental ready to proceed. on the basis of life meeting strategy. strategy in full cycle costs. organisation's support of the financial energy team. parameters. Energy surveys Energy staff are conducted by required to experienced staff comment on all or consultants projects. Energylikely to yield efficiency options largest savings. often approved but no account is taken of life cycle costs.

Energy staff Adequate notified of all management proposals that information affect energy available, but not usage. in the correct Proposals for format or easily energy savings are accessed in at risk when support of energycapital costs are saving proposals. reduced.

1

Informal ad-hoc energy walkabouts conducted by staff with checklists to identify energysaving measures.

Energy staff use Insufficient informal contacts information to to identify projects demonstrate where energy whether previous efficiency can be investment in improved at energy efficiency marginal cost. has been worthwhile.

0

Little or no No method used No-one in No mechanism or Energy efficiency not considered in information irrespective of the organisation resources to attractiveness of a identify energynew-build, available to promoting project. investment in saving refurbishment or develop a case for opportunities. plant replacement funding. energy efficiency. decisions.

Score

x

x

Projects compete equally with other areas. Full account taken of indirect benefits, e.g., marketing opportunities, environmental factors.

Promising Discounting Energy manager Projects compete proposals are methods using working well with for capital along presented to with other organisation's accounts/finance decision-makers specified discount department to business but insufficient rates. present wellopportunities, but information (e.g., argued cases to have to meet more sensitivity or risk stringent decision-makers. analysis) results in requirements for return on delays or investment. rejections.

Regular energy monitoring and analysis used to identify possible areas for saving.

2

Project funding

x

Chapter 1 – Introduction to energy management

Undiscounted appraisal methods, e.g., gross return on capital.

Occasional Energy projects proposals to not formally decision-makers considered for by energy funding from managers with capital budget, limited success & except when very only marginal short-term returns interest from are evident. decision-makers.

Simple payback Responsibility Funding only criteria are unclear & those available from involved lack time, revenue on lowapplied. No account taken expertise & risk projects with of lifetime of the resources to paybacks of less investment. identify projects & than one year. prepare proposals.

x

x

No funding available for energy projects. No funding in the past.

x 21

1.10

Technical management – where are you now?

The plant is the thing The distribution of energy use in plastics processing is very different to that in an office and Section 1.3 gives the relative magnitude of these costs for a typical plastics processor. The major energy users are the services and the plastics processing machinery and this is where the efforts must be concentrated. This requires good technical knowledge of the processes used and good technical management of the process itself.

Even when the majority of the operational plant was not originally designed with energy efficiency in mind there are many simple actions that can be taken to improve the energy efficiency of existing plant. These range from good maintenance actions, where simple low-cost tasks, such as the alignment of motor drives, can easily reduce energy use for existing plant through to involving the operators to reduce energy use.

Agreement by various people across the site shows consistency – a starting point for improvement.

Completing the chart This chart is completed and assessed as for those presented previously.

This chart tries to provide an assessment of these technical aspects of energy management.

Technical management

Existing plant 4 3 Operational methods

2

Plant replacement

1 0

Records

Maintenance

Use the scoring chart to assess where you are in technical management

Operators often know how to reduce energy use by changing operational methods. Despite this, their knowledge is routinely ignored in favour of the less relevant knowledge of someone in an office.

The numbers from the scoring chart can be transferred to the radar chart for a quick visual assessment of where you are in the basics of technical management.

An opportunity lost and a huge pity.

Operational knowledge

22

Chapter 1 – Introduction to energy management

Technical management Level

4

3

2

1

0

Score

Existing plant Majority of existing equipment uses best practice energy-efficient features, is correctly commissioned & well maintained.

Plant replacement

Maintenance

Operational knowledge

Records

Equipment chosen Maintenance is Staff know how Detailed is the most based on needs, their actions affect descriptions of appropriate for with condition energy efficiency systems, plant appraisal used for application. & take positive control & Life cycle costs & all equipment & steps to minimise operation. energy efficiency fabric elements energy use. Detailed are major factors affecting energy Staff have schedules of all targeted training in in selection. efficiency. plant, Results acted energy issues. instrumentation & upon. controls.

Operational methods Targets set by actual production volumes using historical performance. Monitored for actual usage by production area.

Equipment & plant Equipment is is appropriately appropriate for selected, energy- application with efficient, energy efficiency commissioned for considered. low energy Life cycle costs & consumption & energy efficiency well maintained. are evaluated.

Regular condition Staff are aware of Detailed surveys carried how they affect descriptions of out on equipment energy use & take plant control & & fabric elements all good operation, & affecting energy housekeeping outline systems. efficiency. measures to save Reasonable Action undertaken energy. schedules of all for most defects Training on a plant, identified. regular basis. instrumentation & controls.

Targets set by budgeted production volumes using historical performance. Monitored for actual usage by production area.

Most equipment is Equipment not specifically selected to be fit energy-efficient, for purpose, but either was bearing in mind commissioned or likely life cycle is being regularly costs & energy maintained for low efficiency factors. energy consumption.

Condition surveys carried out regularly on all equipment & fabric elements affecting energy efficiency. Remedial work constrained by budgets.

Targets set against realistic budgets, & maintained through financial procedures.

Most good housekeeping practices are adhered to in an attempt to reduce energy usage. Occasional energy efficiency training received.

Basic descriptions of plant control & operation. Basic plant, instrumentation & control schedules for most control systems.

Minimal or poor Equipment is not Power efficiency Condition surveys Energy-saving carried out energy-efficient, data on products techniques are plant control & obtained as part of occasionally, only adopted operation. but has been commissioned for selection process. prompted by plant where they can be Plant failure or safety easily instrumentation & economy & considerations. accommodated control schedules undergoes periodic Remedial work within traditional for only some of only carried out on working practices. the plant & control maintenance. major defects. systems.

Targets set by default through budget setting procedures.

Energy No consideration No regular surveys No consideration performance has of energy or maintenance is given to energy not been efficiency in plant carried out. efficiency during considered during equipment working the procurement, selection. operations. commissioning or maintenance of existing plant & equipment.

None available.

No targets set.

x

x

x

x

x

Chapter 1 – Introduction to energy management

x

23

1.11

Awareness and information – where are you now?

Knowledge is the key As with any new activity, there is a need to both specify what people are going to do and to ensure that they are aware of their responsibilities. One of the keys to energy management is to ‘show results to get resources’ and there is a need for clear reporting of successes in energy management to both get resources and to motivate the team. Equally there is a need to provide staff with training and development opportunities. A training course on variable-speed drives may appear a luxury but if it saves real money then it is a good investment in both the staff and the company. Further details of

the benefits of training and the resources to carry this out are given in Sections 6.5 and 6.6. Energy management is a rapidly developing field and there are very few people with experience or understanding of this area – keep staff well trained and up-to-date with the latest market developments.

Low scores are not bad but simply show areas with improvement potential.

Completing the chart This chart is completed and assessed as for those presented previously.

Awareness and information Energy management 4 3 Market awareness

2

Energy efficiency awareness

If you don’t know that you are doing it wrong then how can you hope to improve?

1 0

Training

Reporting

Performance review

Use the scoring chart to assess where you are in awareness & information The numbers from the scoring chart can be transferred to the radar chart for a quick visual assessment of where you are in the basics of awareness and information. 24

If you think training is expensive then consider the cost of ignorance.

Chapter 1 – Introduction to energy management

Awareness & information Level

4

3

2

Energy management

Energy efficiency awareness

Reporting

Training

Market awareness

Lists of responsibilities & their assignment exist & are comprehensive & regularly reviewed. All staff have responsibilities.

Energy efficiency Wide reporting of Progress regularly Training properly Keep abreast of current status resourced for technological performance reviewed. regularly given to compared with technical & developments by Performance all staff. best practice, on compared against premises staff. monitoring of trade regular basis & internal & external Active technical journals, literature Full use made of & other sources on publicity. geared at a range benchmarks. library. issues affecting All methods used of audiences. Ideas actively All staff have sought. access to energy energy efficiency. to promote new Full support to measures for public statements. efficiency saving energy. information.

Lists of responsibilities & their assignment exist for key energy staff & all departments.

Frequent energy Continuous Regular studies Energy efficiency Current status reports issued efficiency reviews professional carried out on status presented to all staff at least annually to using monitored development for trade journals, consumption & technical & literature & other annually. shareholders & cost data. premises staff. sources to assess Occasional but staff. Impartial reporting Analysis is regular, All staff are aware current widespread developments of performance to wide-ranging but of & have access publicity to impacting on staff & ritualistic. to an energy promote energy departments on a efficiency library. energy efficiency. saving. regular basis.

Some staff & Energy Occasional issue Occasional Technical & Trade journals, departments have of energy technical energy performance premises staff literature & other written presented to staff efficiency status efficiency reviews. development by sources scanned responsibilities. on a regular basis. reports. Regular cost professional & on an ad-hoc Occasional use of Concentrates on checks with technical journals. basis for information on the publicity to good news. exception Occasional promote energy reporting. initiatives to train latest Analysis of limited saving. staff in energy developments scope. efficiency. relating to energy efficiency. Unwritten set of responsibility assignments.

Energy Reports only Energy review issued if prompted activity based on performance occasionally by a business revenue costs. reported & known need. Limited exception to very few staff. Most reports will reporting only. Energy-saving contain only good measures are news. rarely promoted.

No evidence of assignment of energy efficiency tasks & duties.

No staff have explicit responsibilities or duties.

No reporting.

x

x

x

1

0

Score

Performance review

Chapter 1 – Introduction to energy management

Few staff have knowledge of energy efficiency techniques & facts. Little training in energy efficiency for staff.

Trade journals, literature & other sources studied for energy implications when a purchase is imminent.

Staff have little, if Energy efficiency No monitoring activity to underpin any, knowledge of not a review processes energy efficiency. consideration No attempt to when keeping up inform staff of to date on techniques & products or benefits of energy technology. efficiency.

x

x

x 25

1.12

Purchasing – where are you now?

Purchasing Purchasing any material or machine naturally affects the energy consumption of the process. Contracts for power supply naturally need to be examined carefully (see Chapter 4) but all contracts and projects potentially affect energy use and need to be examined with this in mind. New materials or additives may appear more expensive but may reduce the energy use during processing. New machinery may reduce labour costs but may lead to increased energy costs that outweigh the benefits. The attitude of regarding energy as a fixed cost and labour as a variable cost can lead to complex automation

projects that do not actually reduce costs overall. Purchasing at all levels and in all areas needs to be aware that purchases can potentially lock energy efficiency or energy inefficiency into the system.

Completing the chart

Energy efficiency in purchasing is not simply about the contracts to buy electricity or gas. It is about everything that you buy!

This chart is completed and assessed as for those presented previously.

Purchasing Contracts 4 3 2 1 Auditing

Potential suppliers

0

Buying the right machines and equipment will embed energy efficiency into a site for years to come.

Checking compliance

Use the scoring chart to assess where you are in purchasing The numbers from the scoring chart can be transferred to the radar chart for a quick visual assessment of where you are in the basics of purchasing. 26

Buying energyinefficient equipment will embed energy inefficiency into the site for years to come.

Chapter 1 – Introduction to energy management

Purchasing Level

4

Contracts

Potential suppliers

Checking compliance

Auditing

Rolling programme to ensure Whenever appropriate, Wherever appropriate, all existing contracts performance of suppliers is regular & methodical reviewed to see if they need evaluated against established checking by staff with to cover energy efficiency energy efficiency criteria. appropriate expertise. issues. Wherever necessary, only Corrective action identified & Where necessary, reference those meeting criteria invited subsequently monitored. to energy efficiency inserted to tender. Records maintained of in tendering procedures for supplier performance. contract renewal.

Wherever appropriate, completed contracts reviewed, with reporting of achieved levels of energy efficiency along with other critical aspects of supplier performance.

Agreed criteria for evaluating Periodic checking by suppliers exist & routinely experienced staff on most used to evaluate potential major contractors, identifying tenderers on most major corrective actions & issuing contracts. instructions accordingly.

Most major completed contracts reviewed, with reporting of energy performance as one of regular topics addressed.

Some ad-hoc action taken to Ad-hoc approach to Ad-hoc criteria exist & review whether major sometimes used to evaluate compliance checking against contracts need to cover suppliers of services & energy criteria only during energy efficiency issues. purchases. other general inspections of progress.

No general auditing but ad-hoc action to review energy efficiency only if & when performance audited for other purposes.

Most major contracts routinely reviewed to see whether they need to cover efficiency issues.

3

2

Informal & occasional Informal & occasional Informal consideration of Energy efficiency informally & auditing only on contracts energy efficiency issues only occasionally used to evaluate checking only on contracts in contracts specifically for potential suppliers only in specifically for energy goods specifically for energy goods energy goods or services. contracts specifically for or services. or services. energy goods or services.

1

0

Score

Little or nothing known about Little or nothing known about No attention paid during No attention paid during postinspections to issues relating contract auditing to issues the extent to which energy the ability of existing efficiency issues are dealt suppliers to deliver energyto energy efficiency. relating to energy efficiency. with in any of the efficient products or services organisation's current in practice. contracts.

x

x

Chapter 1 – Introduction to energy management

x

x 27

1.13

Project assessment and selection

Project management Energy use reduction will only come about through the successful identification and implementation of projects. Energy management is a change programme and the identification, assessment and successful completion of projects is at the heart of any change programme. This needs good project management to be effective.

Project selection A precursor to a successful project is good selection of the project to be undertaken. If this book succeeds in its aims then the reader will have a wide range of projects to choose from and will have to choose from the competing projects. It is best to choose a limited number of projects and succeed at these rather than to start many projects and never to complete any. Project selection is best based on a simple 2×2 ‘effort–reward’ matrix as shown in the diagram. Projects can be ranked quickly on the basis of: • The reward – the estimated size of the

energy use reduction.

exceptions to this otherwise staff will not know where to focus efforts or spending. • Never start projects that you cannot

finish no matter how attractive they may appear in terms of time or return. An unfinished project is a total waste of time. • If the resource bottleneck is finance-

related then insist that the energy management programme is totally selffunding. This should not be a problem if ‘A’ projects are started first and the savings are validated (see Section 3.9).

Project planning There are three approaches to project planning: • No planning – We’ll do it! • Simple planning methods. • Complex computer-based planning

methods. Project planning is essential for successful energy management but simple planning methods are far preferred. Energy management projects tend to be small in scale both in investment and time and the

• The effort – the ease of implementation.

Projects with a high reward and low effort are preferred and these will be in the A-segment of the matrix. These should be the first projects attempted. Projects in the D-segment of the matrix are realistically never going to start. When faced with a competing group of projects with comparable ‘effort–reward’ indices then the project with the shortest time to completion should be chosen.

B

A

D

C

Resource bottlenecks Every company has resource bottlenecks, these can be with regard to staff – there are always more things to do than there are time and people or with regard to finance – there are always more demands on capital than there is money in the bank. Whatever the particular resource bottleneck, follow these simple rules to get the best results: • Set a limit on the number of energy management projects that are allowed to be active at any time – do not open any new projects unless one of the current projects is closed or suspended. Make no 28

Low High Size of energy use reduction

Project selection for energy management Deciding which projects to carry out is the start of the energy management process. Rank potential projects according to the size of the reduction and the ease of implementation. Go for the greatest reductions and easiest implementations first. Chapter 1 – Introduction to energy management

planning process should match this. One excellent method is to use top-down planning using Post-it notes. This method is described in the box on the right and, despite the apparent simplicity, is a very powerful and flexible method for small project planning. The method encourages an open approach to planning where the whole process is visible, this is in contrast to the computer-based approaches where the project plan is controlled by the operator of the software. Whatever method of project planning is chosen, every project plan must have the following elements:

Aims and objectives These are the clearly stated aims and objectives of the project. These must be measurable and achievable to allow later performance assessment.

Milestones These are dates (from the actual start of the project, not from the date that approval was sought) that show when particular tasks are to be completed. Milestones enable assessment of project plan/time results.

• Project teams are assessed on their

results.

Meetings

Home truths of project management

• Project teams meet regularly.

• What you don’t know hurts you.

Schedules

• Any project can be accurately estimated for cost – after it is finished.

• Check progress (and slippage) against

agreed time and financial targets.

Communication • Project teams report on progress via an

agreed and pro-active reporting and communication plan. • One of the best methods is to communicate on one page and the OnePage Project Manager1 method is an excellent tool for both planning and reporting.

This section is adapted from Section 1.15 of Kent, R.J. 2017. ‘Cost management in plastics processing’, Elsevier.

• Nothing is impossible to the person who doesn’t have to do it. • What is not on paper has not been said. • If you can keep your head while all around you are losing theirs then you haven’t understood the plan.

• 1. Campbell, C.A. and Campbell, M. 2013. ‘The One-Page Project Manager’. Wiley.

Budget All projects should have an initial allocated budget.

Assessment Projects must be assessed after the aims and objectives have been completed or when the project manager decides that no more progress can be made. Assessment allows a review of the achievements against the previously agreed aims. • Tip – Assessment should not only

consider the financial aspects such as return on investment but also other nonfinancial benefits of the project.

Closure All projects should be formally closed after the assessment phase.

Project management Project teams • Project teams need a leader or ‘project

champion’. • Delegate control and accountability to the project manager. • Project teams can make decisions

without fear of being over-ruled later. • Project teams are free to innovate.

Project planning using Post-it notes Top-down project planning for cost management can be carried out using Post-it notes and a flip-chart. Write each task and the time to be allocated to it on a note. Move the notes around and group them according to the major tasks. Combine or divide tasks as the process continues. Leave the chart in view and add, subtract or move the notes around as the plan develops. Finally, move the notes to overlap activities that can be done at the same time and reduce the total time taken for the project (simultaneous engineering). The critical path is easily seen from the sum of the individual tasks.

Chapter 1 – Introduction to energy management

29

1.14

Energy management projects – where are you now?

The energy management process Choosing between energy management projects will always be difficult. There will always be too many projects competing for too few resources. Companies need to rapidly assess the potential gains and difficulty of implementing any potential project before rushing into a complex project that has a relatively low cost management potential. Project selection is a key to energy management. After projects have been selected then an effective project management system is an

essential to actually delivering the project and achieving the potential gains. Cross-functional teams are an invaluable tool for energy management due to the organisation of most companies.

Completing the chart This chart is completed and assessed as for the previous charts.

This section is adapted from Section 1.16 of Kent, R.J. 2017. ‘Cost management in plastics processing’, Elsevier.

Energy management projects Project selection 4

2 1

Project planning

Any potential new project had to pass a monthly review and to displace an existing project before it could be considered for action. Any displaced existing project was labelled as being ‘on hold’ and not considered for assessment.

0

Project resources

A Technical Manager reporting to me always had too many projects running at any one time and was judged to be ‘failing’. This was because the Managing Director constantly introduced new projects and changed the priorities. We set a limit of 8 projects that could be considered to be active at any one time.

3

Problem solving

Select your projects wisely – go for the big bucks and easy projects.

Project organisation

The Managing Director was therefore forced to prioritise the active projects and could not randomly introduce new projects. The results: • A more stable project list.

Use the chart to assess where you are in energy management projects The numbers from the self-assessment should be transferred to the radar chart for a quick visual guide to where you are in the basics of energy management projects. 30

• More completed projects. • A successful Technical Manager.

Chapter 1 – Introduction to energy management

Energy management projects Level

4

3

Project selection

1

0

Project organisation

All relevant energy Formal project Excellent energy reduction opportunities definition & project reduction project identified & prioritised plan necessary for any management system project. for action. used in all cases. Progress is regularly Projects have clearly reported & post-project defined management assessment is carried & energy/benefits. out.

Good energy reduction Most available energy Formal project reduction opportunities planning carried out for project management all projects but control, identified but not system but use is reporting & prioritised for action. variable. assessment are Good integration variable. across departments Failed projects are but many projects sometimes hidden & have poor no lessons learnt. energy/benefit definition.

Some energy reduction opportunities identified but no real planning process.

2

Project planning

Project resources

Problem solving

Firmly embedded Project resources defined & allocated culture of improvement before project start. & problem solving Projects are rarely through planning, delayed due to action & review. resource constraints. Root causes identified & resolved.

Project resources defined but not allocated at project start.

Problem solving is largely reactive with focus on solving root causes. Solutions developed but not always fully implemented.

Project planning carried out for most projects but control, reporting & assessment are poor or rarely carried out. Failed projects are often hidden & no lessons learnt.

Energy reduction project management system available but not used. Some integration of projects across departments & poor energy/benefit definition.

Project resources poorly defined at project start.

Problem solving is largely reactive; solutions are developed but rarely fully implemented. Focus on dealing with urgent effects & not on solving root causes.

Cursory & Few energy reduction opportunities identified undocumented project via unplanned process. planning but no formal project planning or monitoring. Projects can become dormant & remain unfinished.

No energy reduction project management system. Some integration of departments for projects that clearly cross departmental boundaries.

Project resources rarely considered at project start.

Problem solving is purely reactive & focused on dealing with urgent effects & not on solving the root cause.

Significant energy No effective project No energy reduction Projects often started Problems are ignored reduction opportunities planning. Actions are project management without adequate until they go away. ignored due to ‘urgent’ resources (due to poor ad hoc & driven by system. planning) or starved of Every project is daily pressures. events. Action is seen as more ‘different’. resources during important than Projects are run by project. planning. departments with little Urgency is rated more input from other highly than strategic departments. importance.

Score Chapter 1 – Introduction to energy management

31

Key tips • Energy costs are variable and there is no

reason to believe that they will stabilise in the near future. • The use of taxation and other financial

instruments will increase. • Supply and distribution shortages will

increase in the medium term.

managers take responsibility for the costs and action to reduce the costs. • The energy management system must cover: Energy policy. Personnel. 

Planning. Resources.

• Security of supply (at any cost) is a



rising issue. • Environmental issues are increasing in importance and public perception.



• Corporate social responsibility is

increasing in importance. • Energy management could easily be the

Training. Auditing.

 

Reporting.



• ISO 50001 is based on the Plan–Do–

Check–Act model.

deciding factor in whether your company survives or not. • Energy is a variable and a controllable cost.

• ISO 50001 can make use of existing

• Energy costs are reaching the same

• Management systems standards

magnitude as labour costs. • Energy costs are reaching the same magnitude as profits. • Energy use and costs can be reduced by over 30% in most cases and add directly to the site profits. • Energy costs can be reduced by management, maintenance and investment actions. • The payback for most investment in energy management is 6–9 months. • The sources of the current energy use in plastics processing can be established very quickly from readily available information. • The returns from efforts in energy management are quick, certain and need only internal effort. • Energy cost reductions are very highly geared and are often better for profits than additional sales. • Investment in energy management can be the most effective investment a site can make.

provide a framework for improvement but do not provide guidance on specific actions, targets, techniques or tools or projects to reduce energy use. • Sites should examine all the evidence before they commit to a management system standard. • Energy managers must show results to get resources. • Energy management is all about delivering completed projects and these need a good project selection and management system.

management standards processes in place for systems such as ISO 9001 and ISO 14001.

• Gaining top management commitment to

energy management is the key to real progress. • Implementing energy management

requires an energy management system. • An energy management system can be

based on ISO 50001 or can be an internal system, the important thing is that 32

Chapter 1 – Introduction to energy management

Chapter 2 Energy benchmarking

Despite the growing importance of energy management for plastics processors there is no established structure for measurement, assessment and prediction of energy use. This makes it difficult for companies to assess their energy use and to understand their relative competitiveness. Consequently, many companies are trying to measure the wrong things in the wrong ways. They then wonder why they get the wrong answers! This chapter describes and illustrates a consistent framework for measurement, assessment and prediction that can be used for most processes and plastics processing companies throughout the world. It looks at both internal and external benchmarking, at both the site level and at the machine level and how this information can provide real insights into how the site and the process are performing.

based on current practice but it does not provide a strong driving force for radical improvement or change. We will therefore finally look at external benchmarking on a site basis and the essentials of process rate dependency for the site. This is then extended to the machine level where we can also benchmark machines to look at the energy efficiency and process rate dependency for individual machines.

More importantly, the chapter looks at how this information can be used to improve both operations and performance and to correctly budget for energy use into the future. We firstly look at what controls or ‘drives’ energy use, then at internal benchmarking for the site to develop the concepts of ‘base’ and ‘process’ loads and then use these concepts to develop a simple method of assessing performance and predicting costs. Internal benchmarking is vital but it is based on the ‘status quo’, it can be used to provide a weak driving force for change

Note: For most plastics processes, the main energy source is electricity and unless otherwise noted all references to energy should be taken to refer to electrical energy supply.

Energy Management in Plastics Processing https://doi.org/10.1016/B978-0-08-102507-9.50002-7, Copyright © 2018 Elsevier Ltd. All rights reserved.

33

2.1

The framework and energy use drivers

The framework Energy management needs a basic framework for measurement and performance assessment (also known as monitoring and targeting or M&T). The basic framework for a consistent measurement system: • Looks at internal benchmarking of the site to provide a baseline for energy management improvements, a method of assessing performance and predicting costs. • Looks at external benchmarking of the

site to compare the performance with similar sites using similar processes. • Looks at external benchmarking of the machines to compare machine settings and performance with similar machines. This framework (shown in the box on the right) provides a wealth of information for site management to identify energy waste and to reduce energy use and costs by simple M&T techniques. Monitoring and targeting can be simply based on financial results, i.e., comparison of billing data with actual use and examination of billing data for inconsistencies or it can be based on physical values, i.e., production volume or other recorded data. Whilst pure financial data are useful in locating billing and other tariff-related errors, they do not provide any method of internal benchmarking or pressure for improvement. They are therefore solely a financial/budgetary control tool. This is a very useful exercise but the use of physical data is even more worthwhile and provides a real insight into site operations.

• A ‘condition’ driver is where the energy

use varies with an external influence, such as the weather. The measurement of a condition driver is generally externally specified. Understanding the effects of the relevant energy use drivers allows a site to analyse the energy use data to see how good the energy management is and more importantly to locate areas for potential energy use reductions.

Energy use can be related to either an ‘activity’ or a ‘condition’ driver or a combination these. • An ‘activity’ driver is where the energy

use is controlled by an internal activity, such as production volume (however defined or measured). 34

• ‘Activity’ drivers lead to energy use from internal activity. • ‘Condition’ drivers lead to energy use from an external influence.

When there is a single driver for energy use, it is possible to relate energy use directly to this driver. When there are multiple drivers then the situation is more complex.

Single drivers For a site with a single main process that

Internal benchmarking (Site)

Base and process loads

Assessing performance

Predicting costs

External benchmarking (Site)

Process dependency

Production rate dependency

External benchmarking (Machine)

Activity and condition drivers The energy use at any manufacturing site is not fixed and uncontrollable. Energy use is always controlled or driven by some external variable and understanding what drives energy use is a critical feature of any M&T programme.

Drivers

Process dependency

Production rate dependency

The energy management framework The energy management framework looks at internal benchmarking of the site, external benchmarking of the site and external benchmarking of the machines to provide a consistent and comparable view of the energy use at a site. Chapter 2 – Energy benchmarking

uses only electricity then it is possible to relate the electricity use to the single activity driver of production volume. This is the normal case for many plastics processing sites which use only a single process. For a site which uses gas only for heating then it is possible to relate the gas use to the single condition driver of Heating Degree Days (HDD = a measure of how cold it is). This is the normal case for site heating where gas is used only for heating. In both of these cases, the energy use is related to the driver (activity or condition) by the equation: kWh = A × Driver value + X. It is then relatively easy to predict energy use from the equation and the value of the relevant driver. It is also relatively easy to show the relationship using a simple graph (see box on the upper right).

not easy to show the relationship using a simple graph (see Section 2.10). Note 1: Driver 1 and Driver 2 can be either activity or condition drivers and typical examples might be: • kWh = A × Production volume

Process 1

+ B × Production volume Process 2 + X. • kWh = A × HDD Site + B × Production volume + X. where HDD = Heating Degree Days.

Understanding and using the key drivers to analyse energy use is an essential first step in energy management. Get the drivers wrong and you will be measuring the wrong thing.

• kWh = A × CDD

Site + B × Production volume + X. where CDD = Cooling Degree Days.

Note 2: It is also possible to have more than two energy use drivers and in this case the equation would be of the form: kWh = A × Driver 1 + B × Driver 2 + C × Driver 3 + …. + X.

Some sites are more complex and a single source of energy is used for two distinct purposes that are not metered separately. In these cases the total energy use is due to multiple drivers and some typical examples are: • Sites which have two processes taking place and where the processes have very different energy intensities, e.g., a site where both injection moulding and extrusion take place. Extrusion has a much lower energy intensity than injection moulding (see Section 2.4) and the energy use will be very different depending on the relative volumes of material processed.

kWh

Multiple drivers

Single activity driver When a single driver (activity or condition) controls energy use then it is relatively simple to visualise this on a conventional chart.

for the process but also for significant air conditioning loads. Some of the energy use will be due to the process (activity driven) and some due to the air conditioning (condition driven). • Sites where gas is used for process but also for the site heating. Some of the energy use will be due to the process (activity driven) and some due to the heating (condition driven). For sites with multiple drivers the energy use is related to the drivers (activity or condition) by the equation: kWh = A × Driver 1 + B × Driver 2 + X. In this case it is also easy to predict the energy use by knowing the equation and the value of the relevant drivers but it is Chapter 2 – Energy benchmarking

kWh

• Sites where electricity is used not only

Multiple activity drivers When multiple drivers (activity or condition) control energy use then it is much more difficult to visualise this on a conventional chart and alternative methods are needed. 35

2.2

The basic internal site data

Single drivers for simple sites Month

Energy use (kWh)

Production volume (kg)

1

425,643

182,421

2

463,772

197,897

The simple method

3

504,675

248,742

Assuming a single driver makes it possible to determine the base and the process loads for a site from simple, easily available energy use and production volume data. A site’s base and process loads can be estimated using the following simple method: • Record the site production volume (in kg) for a minimum of 12 months and record the energy use (in kWh) for the same periods. It is important that the production volume and energy use data measurement periods coincide. Typical industry data are shown in the table opposite for an injection moulding site but the method can be used for any plastics forming process.

4

437,307

204,228

5

492,613

212,716

6

518,940

225,239

7

532,322

217,864

8

469,029

207,615

9

676,008

347,845

10

711,119

343,468

11

671,962

311,174

12

409,526

147,378

For most plastics processing sites it is possible to allocate a single driver for energy use. For electricity use this will generally be production volume (in kg) and for gas use (heating only) this will generally be HDD (see Section 4.8).

Note: The production volume should be the ‘through the nozzles’ volume to include regrind and waste. It should not be simply the amount of good material sent to the warehouse or similar values.

The basic data The basic data to start managing energy at a site are easily obtained from the existing records. It is important that the measurement periods for the energy use and production volume coincide.

• Plot a scatter chart of the energy use (in

The equation of the line of best fit for the sample data shown on the right is: kWh = 1.5751 × Production volume + 152,440 where R2 = 0.9397 This is the Performance Characteristic Line (PCL) for the site. • The intersection of the linear line of best-

fit with the ‘Energy use’ axis is the ‘base 36

700,000

Energy use (kWh)

kWh) versus production level (in kg). This can be done in most spreadsheet packages. It is recommended that a minimum of 12 data points are used for the scatter chart. • Use the spreadsheet package to fit a linear line of best-fit to the data points and to find the equation of the linear line of best-fit. Where possible, extrapolate the linear line of best-fit back to the vertical axis.

Base and variable loads (injection moulding) 800,000

600,000 500,000 400,000 300,000 200,000 kWh = 1.5751 x Production volume + 152,440 R2 = 0.9397

100,000 0 0

50,000

100,000

150,000 200,000 250,000 Production volume (kg)

300,000

350,000

400,000

Finding the base and process loads A simple spreadsheet-generated scatter chart of the basic data provides valuable information on the base and process loads and is easily obtained from existing company energy use and production records. Chapter 2 – Energy benchmarking

load’ (in this case 152,440 kWh). This is the energy use when no effective production is taking place but machinery and services are available. • The slope of the linear line of best-fit is the ‘process load’ (in this case 1.5751 kWh/kg) and shows the average energy used to process a kilogramme of material. The R2 value is the ‘correlation coefficient’ for the linear line of best-fit. R2 can vary between 0 (no correlation between the two variables) and 1 (perfect correlation between the two variables). A high R2 value indicates good correlation between the variables and gives confidence that the equation describes the actual relationship. If the R2 value is less than 0.70 then there is either a problem with the data, e.g., the data collection periods for the energy use and the production volume are not the same or the energy use at the site is ‘out of control’. For the sample data the R2 value of 0.9397 indicates that the data set is very consistent with the line of best fit. This shows that the site is very consistent in energy use – this is not the same as good, it is simply consistent. The energy use at the example site therefore consists of: • A base load of 152,440 kWh. A process load of 1.5751 kWh/kg of plastic processed.

reducing overheads is always good.

The process load The process load information shows that the site uses approximately 1.5751 kWh/ kg of plastic processed and the cost for this is £0.15751/kg processed. The process load shows how efficient the site is at plastics processing. Reductions in the process load (reducing the slope of the graph) indicate improved process efficiency. This is often more difficult to achieve.

Dividing the loads Whilst separating the base and process loads may appear easy in theory, in practice it is often more difficult because many loads have both a fixed and a variable element. This is similar to accounting where costs can be nominally divided into fixed and variable costs but the reality is that most costs have both a fixed and a variable element. Despite this difficulty, the division of the loads by using a scatter chart can reveal profitable areas for improvement by site management and give excellent information on the site operations. Plastics processors need this type of information to enable correct targeting of energy use improvements for both the base and the process load. The actions required in each case are very different.

The base load The base load information implies that if there is no production then the site will consume approximately 152,440 kWh/ month. The total cost of the base load is approximately £15,244/month or £182,928/ year and the base load is approximately 30% of the company’s energy use – this is average for the plastics processing industry where the base load will typically be 20–40% (less is better). The base load is an energy ‘overhead’ and is generally due to machinery or services being left operational with no productive output, e.g. compressed air leaks, parasitic heat gain in cooling water piping, lights on with no production, conveyors operating with no production and motor losses. Reductions in the base load (translating the best-fit line downwards) can often be made without affecting production rates, quality or operations. These savings are very profitable because the base load is largely unrelated to production output and Chapter 2 – Energy benchmarking

Understanding the base and process loads is fundamental to understanding targets for energy management.

Reading the charts This type of simple data collection and chart can reveal a great deal about a company’s operations and further simple analysis can enable management to ‘see inside’ the process to target improvements.

R2 – a measure of the scatter R2 is the ‘correlation coefficient’ – it measures the scatter of the results. A high R2 shows low scatter.

The more complex method This method uses the Microsoft Excel ‘Analysis ToolPak’. This is generally available but must be installed with Excel. It can be activated by Tools > Add-Ins and checking the Analysis ToolPak box. This will activate the ToolPak. Go to Tools and this should now show the Data Analysis

option. Scroll down to ‘Regression’ and click to open the Options Box. Select the ‘Input Y Range’ to match the required data

(typically kWh). Select the ‘Input X Range’ to match the required data

(typically production volume or HDD) . Select the ‘Output Range’ as somewhere in the spreadsheet. Click ‘OK’ and a table of numbers will appear where the

Output Range was selected. The resulting table gives in numbers the same information

that results from the simple method (and a lot more statistical detail). In this case, the relevant numbers are the R Square, Intercept and X Variable 1. These can be compared to the values from the simple method. 37

The effect of management

Poor energy management and ‘out of control’ energy use will invariably show up very clearly on the scatter chart. At this type of site, the scatter chart shows a high base load, a lower than normal process load and high scatter (a low R2 value). The reasons for this are: • The base load will be high because processes and services are left on whether the site is producing any product or not. This will effectively raise costs because the energy use will remain high when production volumes are low. • The process load will be lower than normal because much of the normal process load will be effectively converted to base load, i.e., it is not seen by the analysis as a variable process load but as a fixed base load. • The high scatter will result from the poor linearity between energy use and production volume. Note: When the scatter is large it is also possible that the data collection periods for the energy use and production volume are not properly aligned. This should be checked first to ensure data integrity. This type of performance is generally indicative of poor management control of energy. This can be regarded as a ‘bad’ situation but it also indicates a high potential for improvement if the management of the site takes positive action. Base load energy use reductions are generally easy to make, low-cost and have rapid payback. Good energy management will also show up very clearly on the scatter chart. At this type of site, the scatter chart will show a low base load, a higher than normal process load and low scatter (a high R2 value). The reasons for this are: • The base load will be low because processes and services are turned off or not operated when the site is not producing any product. This will reduce overall costs because energy use will decrease very quickly when production volumes are low. • The process load will be higher than

normal because all of the process load will be seen as a variable load, i.e., very 38

little of the process load will be seen in the fixed base load. • The low scatter will result from the good

linearity between energy use and production volume. This type of performance is generally indicative of good management control of energy. Whilst initially very good this does

A high base load indicates good potential for easy management improvement and energy use reductions.

Base and variable loads (injection moulding) - Year 1 500,000

400,000 Energy use (kWh)

Management counts

300,000

200,000

100,000

0 0

50,000

100,000

150,000

200,000

250,000

300,000

Production volume (kg)

Poor energy management in injection moulding Poor management shows a low correlation between production volume and energy use. Fitting a PCL to this data is irrelevant due to the high scatter (R2 = 0.1155). Energy use is not being managed properly and large improvements are possible. Base and variable loads (injection moulding) - Year 3 500,000 Year 3 - Good management Year 1 - Poor management 400,000 Energy use (kWh)

2.3

300,000

200,000 Year 3 kWh = 1.5656 x Production volume + 56,918 2 R = 0.8594

100,000

0 0

50,000

100,000

150,000

200,000

250,000

300,000

Production volume (kg)

Good energy management in injection moulding After 2 years of improved management (no changes to facilities), the scatter is much decreased, the base load is effectively decreased and the site shows better control over the process. This type of improvement is possible at any site at no cost. Chapter 2 – Energy benchmarking

Changing the way a site operates Changing the way a site is run, i.e., management changes, can have a dramatic effect in terms of base and process loads and resulting costs. It is possible to reduce much of the base load through good management practices. This is shown in the results for an injection moulding site on the right. Initial analysis of the data showed a moderate scatter (R2 = 0.6748) and a high base load (46% of the average total load). Discussions revealed that at the end of Year 1, the entire management team was replaced with a new management team who were more concerned with energy management than their predecessors (and better at all types of management). No changes were made to the process, machines or other operations. These management changes were only operational, i.e., no investment or new technology, but they fundamentally changed the energy use profile of the site. The data were therefore separated into data for Year 1 and data for Year 2 and the PCL for each of the two years was found. The two data sets are very different and the effect of the management changes is dramatic. The base load has decreased considerably from 1,210,087 (Year 1) to 166,518 (Year 2) and whilst the process load has increased from 0.2081 (Year 1) to 1.0487 (Year 2) – it is now much more proportional to the production volume. The new management team were not using many of the techniques described in Chapter 2 – Energy benchmarking

Through management efforts, the base loads due to machinery being operational with no output have been eliminated and costs have been reduced. The site energy use now decreases considerably as production volumes decreases. At higher volumes it may appear that the new energy use profile will use more energy but having reduced the base load, the management team is already working to reduce the process load to rectify this.

How do your base and process loads relate to one another? A simple check may reveal potential for quick and low-cost improvement.

Base and variable loads (injection moulding) 2,500,000

2,000,000 Energy use (kWh)

The example shown on the upper left is for a site that had not started in energy management, the ‘Year 1’ data shows a very high scatter and little correlation between production volume and energy use. The ‘Year 3’ data shows the results of 2 years of improved energy management. This shows an energy use reduction of over 30% with no substantial changes in facilities or machines. This was all with the existing management team but simply with an improved focus on energy management and the use of the techniques described in this workbook.

the first edition of this workbook but had still made considerable progress.

1,500,000

1,000,000 Year 1 and 2 data kWh = 0.6712 x Production volume + 551,149 R2 = 0.6748

500,000

0 0

500,000

1,000,000

1,500,000

2,000,000

2,500,000

Production volume (kg)

Global data for injection moulding site The original data for an injection moulding site shows a wide scatter and indications of poor control. This data covers both Year 1 and Year 2 and the R2 value shows only moderate correlation of the data and gives some reasons for concern. Base and variable loads (injection moulding) 2,500,000 Year 1 kWh = 0.2081 x Production volume + 1,210,087 R2 = 0.2417

2,000,000 Energy use (kWh)

indicate a reduced potential for improvement. Management actions must be concentrated on the process loads, which generally require more fundamental and expensive process improvements to reduce.

1,500,000

1,000,000

Year 2 kWh = 1.0487 x Production volume + 166,518 R2 = 0.8280

500,000

0 0

500,000

1,000,000

1,500,000

2,000,000

2,500,000

Production volume (kg)

Management changes at the end of Year 1 Management changes at the end of Year 1 are revealed by the very different PCL. The new management has reduced the base load and there is now better linearity between production volume and energy use. 39

The effect of the process

The assessment method described in Sections 2.2 for base and process loads is independent of the process being assessed. The same method can be used for any process where the main driver for energy use is volume-related and energy is supplied from a single fuel source, e.g., electricity. Despite this, the results are highly process-dependent, particularly in terms of the process load. This is very relevant for plastics processing where different processes have different process loads. For a typical site, irrespective of process, the base load should lie in the range 20– 40% of the average total load. Any base load higher than 30% of the average total load generally indicates poor control of energy use and should be investigated. When reasonable efforts are made to control the base load, i.e., it is in the region of 20–30% of the average total load, then the process load (the slope of the PCL) will indicate the global energy efficiency of the underlying process. This will vary with the basic energy intensity of the process but it is possible to estimate typical values for individual processes.

Injection moulding The data shown in Section 2.2 are typical of industry data for injection moulding. This site has a base load of 30% of average total energy use and a process load of 1.5751 kWh/kg. This is generally representative of an injection moulding site that has not taken any action in energy management. A typical injection moulding site will have a process load in the region of 0.9–1.6 kWh/kg. This will vary with the size of the base load, i.e., a high base load as a proportion of the total load will generally result in a lower apparent process load. Despite this, for a site involved only in injection moulding, the process load should be in this region. Any site with values that are very different needs to investigate the causes.

Extrusion Injection moulding has a higher process energy requirement than extrusion and therefore it is to be expected that the 40

process loads will be significantly different. This is indeed the case. Typical data for an extrusion site shows a base load of 31% of the average total energy use and a process load of 0.4467 kWh/kg. This is again generally representative of an extrusion site that has not taken any action in energy management.

The slope of the PCL is the process load and will vary with the energy intensity of the basic process.

Base and variable loads (injection moulding) 800,000 700,000 600,000 Energy use (kWh)

Process dependency

500,000 400,000 300,000 200,000 kWh = 1.5751 x Production volume + 152,440 R2 = 0.9397

100,000 0 0

50,000

100,000

150,000 200,000 250,000 Production volume (kg)

300,000

350,000

400,000

Injection moulding site loads A typical injection moulding site will have a process load in the region of 0.9–1.6 kWh/kg. This will vary with the size of the base load, i.e., a high base load as a proportion of the total load will generally result in a lower apparent process load. Base and variable loads (extrusion) 600,000

500,000 Energy use (kWh)

2.4

400,000

300,000

200,000

kWh = 0.4467 x Production volume + 133,166 R2 = 0.9010

100,000

0 0

200,000

400,000 600,000 Production volume (kg)

800,000

1,000,000

Profile extrusion site loads A typical extrusion site will have a process load in the region of 0.4–0.7 kWh/kg. This will vary with the size of the base load, i.e., a high base load as a proportion of the total load will generally result in a lower apparent process load. Chapter 2 – Energy benchmarking

Film and other extrusion operations such as fibre extrusion are slightly less energyintensive than profile extrusion and the relevant process loads are also slightly less than those for profile extrusion.

Base and variable loads (extrusion blow moulding) 800,000 700,000

Energy use (kWh)

The injection moulding site and the profile extrusion site have broadly similar base loads (both in magnitude and in percentage terms) but the extrusion site has a process load only 30% of that of the injection moulding site (0.4467 kWh/kg compared to 1.5751 kWh/kg).

Typical process loads for other processes are: • Injection blow moulding (injection + blowing steps): 1.0–1.6 kWh/kg. • Thermoforming (sheet forming step only): 0.1–0.3 kWh/kg. • Thermoforming (including extrusion): 0.5–1.2 kWh/kg.

300,000

kWh = 1.3259 x Production volume + 145,790 R2 = 0.8448

0 0

100,000

200,000

300,000

400,000

500,000

Production volume (kg)

Extrusion blow moulding site loads A typical extrusion blow moulding site will have a process load in the region of 0.8–1.3 kWh/kg. This will vary with the size of the base load, i.e., a high base load as a proportion of the total load will generally result in a lower apparent process load. Base and variable loads (rotational moulding - electricity only) 120,000

Energy use (kWh)

100,000

80,000

60,000

40,000 kWh = 0.5016 x Production volume + 37,356 R2 = 0.8290

20,000

0 0

50,000

100,000

150,000

Production volume (kg) Base and variable loads (rotational moulding - gas only) 400,000 350,000 Energy use (kWh)

Other processes

400,000

100,000

Rotational moulding Rotational moulding uses both electricity and gas for the process and a PCL can be generated for both fuels. Typical data for a rotational moulding site shows a base load of 38% for electricity and 12% for gas. The gas base load is naturally less because the process generally uses no gas unless the ovens are firing. The typical data also shows a process load of 0.5016 kWh/kg for electricity and 2.2341 kWh/kg for gas.

500,000

200,000

Extrusion blow moulding Extrusion blow moulding is expected to show a process energy load somewhere in between injection moulding and extrusion. This is the case and typical data for an extrusion blow moulding site shows a base load of 25% of the average total energy use and a process load of 1.3259 kWh/kg. This is again generally representative of an extrusion blow moulding site that has not taken substantial energy management action. The extrusion blow moulding site has a broadly similar base load (both in magnitude and in percentage terms) to the injection moulding and profile extrusion sites and the extrusion blow moulding site has a process load between that of extrusion and injection moulding.

600,000

300,000 250,000 200,000 150,000 100,000 kWh = 2.2341 x Production volume + 28,547 R2 = 0.9243

50,000 0 0

50,000 100,000 Production volume (kg)

150,000

Rotational moulding site loads A typical rotational moulding site will have an electrical process load of 0.3–0.6 kWh/kg and a gas process load of 1.8 to 2.7 kWh/ kg. This will again vary with the size of the base load. Chapter 2 – Energy benchmarking

41

Variations on the site base and process loads

Alternative production measures In some cases, the data for production volume in kilogrammes is not available and the only measure of production volume is the number of parts produced in the week or the month. This is common in companies who regard themselves as ‘medical products companies’ or ‘automotive products companies’ rather than as being ‘plastics processing companies’. ‘Production volume’ for the PCL can be measured in terms of any driver that is related to the site activity. The production volume in ‘parts’ can be substituted for production volume in ‘kilograms’. Provided there is a reasonably consistent mix of part size, the use of ‘parts’ as a production driver still allows assessment of approximate base load and process loads. The use of parts (or similar) as a production driver will generally lead to higher scatter due to unavoidable variations in the product mix and this is shown on the right for an ‘automotive parts’ company. It is always preferable to establish the PCL in terms of the most appropriate production driver for the process. For all plastics processing, this is the production volume in terms of kilogrammes processed (through the nozzles).

energy use data at consistent times that are aligned with the production volume data collection period. Weekly data collection also allows the PCL to be created much faster (a PCL should be based on at least 12 data points for a valid PCL) and can be used to give faster feedback to production management on Base and variable loads (parts data)

400,000

Weekly data collection has the advantage that it is generally easier to collect production volume data from most production management systems, but requires regular weekly meter reading of 42

300,000

200,000

100,000

kWh = 0.084 x Number of parts + 189,075 R2 = 0.7516

0 0

500,000

1,000,000 1,500,000 2,000,000 2,500,000 3,000,000 3,500,000 Production volume (parts)

Production volume data in terms of ‘parts’ Production volume can be measured in terms of any ‘production driver’. For plastics processing, the best driver is production volume (in kilogrammes) but it is possible to use ‘parts’ where kilogramme data are not available. Base and variable loads (parts data) 500,000

Weekly data collection

400,000 Energy use (kWh)

All of the data presented so far have been in terms of monthly production volumes. It is, however, possible to use any convenient and consistent time period for data collection and determination of the PCL. Monthly data collection allows easy collection of energy billing data (normally monthly based) but may require some adjustment of production volume data if these are not collected on the same monthly basis. Monthly data collection has the disadvantage that it can take some time to collect enough data to allow a PCL to be generated with any confidence.

Weekly data collection gives many benefits and is generally preferred.

500,000

Energy use (kWh)

2.5

300,000

200,000

100,000

kWh = 0.9865 x Number of parts + 218,588 R2 = 0.5906

0 0

50,000 100,000 150,000 Production volume (parts in week)

200,000

Production volume data in terms of ‘weekly parts’ The timescale for data collection generally used is ‘months’. Collection of data on a ‘weeks’ basis gives faster data collection, allows the PCL to be created faster and gives faster feedback for production managers. Chapter 2 – Energy benchmarking

performance and quicker resolution of any concerns regarding excessive energy use. Whichever data period is used to generate the PCL it is important to recognise that the PCL generated is specific to the data collection period used and data collection periods must be fully aligned. • Tip – Daily data are available for some

The services were changed considerably at the start of Year 2 but these were not fully tuned to the operations of the site and actually increased the base load (despite what the supplier promised). This resulted in a distinct change in the base and process loads that can clearly be seen in the PCL for the 2 years.

sites but the natural variations in daily use will give low R2 values and the use of daily data is not recommended.

The site energy ‘fingerprint’ The PCL is unique to every site. It provides an operational signature of the site that is related to the way the site is run.

Long-term data collection

Process changes Despite this strong consistency over time, it is still possible to see some valuable information in the data collected over 8 years. The data for 2 years (Years 1 and 2) were extracted from the 8 years of data and whilst the global pattern remains distinctively that of the original site, the 2 years show discernible differences. Chapter 2 – Energy benchmarking

Base and variable loads (injection moulding)

800,000 700,000

Energy use (kWh)

600,000 500,000 400,000 300,000 200,000

All data (8 years) kWh = 1.1245 x Production volume + 124,422 R2 = 0.9141

100,000 0 0

100,000

200,000 300,000 400,000 Production volume in week (kg)

500,000

600,000

Long-term weekly data collection validates the PCL Weekly data collection over a period of 8 years (> 420 data points) shows that the PCL for the site has remained constant over the period despite significant changes to the site in terms of the number of machines used and production volume. Base and variable loads (injection moulding)

800,000 Year 2 kWh = 1.1206 x Production volume + 138,393 2 R = 0.8596

700,000

Energy use (kWh)

Most of the data used to generate the PCLs presented so far has been based on data collected over 12- or 24-month periods. Data collection and analysis over the longer term can be useful in revealing patterns in the energy consumption. Weekly energy use and production data collected over an 8-year period for an injection moulding site show a remarkable consistency of performance. The data show that the base and process loads have remained consistent over this period and the R2 value of 0.9141 indicates a very close correlation of the data to the PCL. During the 8-year period there were very significant changes at the site. The number of injection moulding machines nearly doubled from 32 to 57, production volume nearly doubled and the services increased considerably in scope and size. Despite these changes, the base and process loads were not greatly affected . There is a signature of ‘operational consistency’ in the data, i.e., this is how we run our processes and machines and these are the base and process loads that result from the decisions we have made. This is by no means an uncommon phenomenon and it is interesting to speculate that companies and their management have a ‘biological’ energy signature that is almost independent of conventional changes or the scale of the process. Significant changes in the energy signature appear to be only brought about by changes in energy management (see Section 2.3).

600,000 500,000 400,000 300,000 Year 1 kWh = 1.1622 x Production volume+ 102,471 R2 = 0.9456

200,000 100,000 0 0

100,000

200,000

300,000

400,000

500,000

600,000

Production volume in week (kg)

PCL data shows changes to the site performance Weekly PCL data collected over 2 separate years shows the effect on the site energy performance of changes to the services at the site. Whilst the performance remains broadly the same, the changes can be seen in the PCL. 43

2.6

What do we want to do?

Changing the PCL The PCL graph provides a simple graphical method to show the effect of a single driver and to visualise this as base and variable components. The objective of energy management is to reduce both types of load and it is useful to see how changing the base and variable loads affects the PCL. As noted in Section 2.2, most loads will have a mix of fixed and variable elements, although one of the types will generally dominate, e.g., operating a motor uses energy for the load but there are also some motor losses that are effectively fixed. This means that it is not always possible to identify a definitive physical meaning to the base or variable load element in a specific load.

Reducing only the base load In the ideal case of a pure base load, then a project that reduces the load will result in the PCL being translated downwards with no change in the slope of the PCL. The effect of this type of ideal project on the PCL is shown in the diagram on the upper right. A typical project that is close to the ideal might be reducing lighting loads in unused areas.

Reducing only the variable load In the ideal case of a pure variable load, then a project that reduces the load will result in the slope of the PCL being reduced with no change in the base load. The effect of this type of project on the PCL is shown in the diagram on the middle right. A typical project that is close to the ideal might be reducing barrel heater loads through insulation.

Reducing the base and variable load – ideal When only the base load is reduced the PCL will be translated downwards. When only the variable load is reduced then the slope of the PCL will be reduced.

PCL inal Orig

Reducing both loads simultaneously The process of energy management aims to reduce overall energy use. This means that a mix of projects is likely to be undertaken simultaneously and that both the base and the variable loads will also be reduced simultaneously. In the ideal case this will result in simultaneous translation of the PCL downwards and a reduction in the slope of the PCL. The effect of a mix of base and process load 44

Reducing both the base and variable loads – ideal When both the base and variable loads are reduced then the PCL is simultaneously translated downwards and the slope is reduced. Chapter 2 – Energy benchmarking

projects on the PCL is shown in the diagram on the lower left.

Base and variable loads (injection moulding) - Year 1 500,000

What really happens?

The introduction of good energy management practices and the completion of energy use reduction projects will not only reduce the base load but will also convert what was previously seen as base load into what is now seen as a true process load. In this case the base load will decrease BUT the process load will increase. A typical PCL for a site at this stage is shown in the diagram on the lower right. In this case the base load is approximately 20% (normal is 20 to 40%) and the process load is 1.57 kWh/kg (normal is 0.9 to 1.6 kWh/kg for injection moulding). This effect is often magnified by the fact that, in real life, the choice of projects and actions is more often driven by financial considerations (lowest cost and/or quickest payback) than by whether the load is fixed or variable. In most cases, the most profitable initial work will come from reducing base loads and these will be the loads that are reduced first. Sites should therefore be aware that apparent increases in the variable load are quite normal in the early stages of energy management.

Chapter 2 – Energy benchmarking

Energy use (kWh)

400,000

300,000

200,000

100,000

0 0

50,000

100,000

150,000

200,000

250,000

300,000

Production volume (kg) Base and variable loads (injection moulding) - Year 2 500,000

Energy use (kWh)

400,000

300,000

200,000 2009 kWh = 0.8688 x Production volume + 171,057 2 R = 0.6072

100,000

0 0

50,000

100,000 150,000 200,000 Production volume (kg)

250,000

300,000

Base and variable loads (injection moulding) - Year 3 500,000

400,000 Energy use (kWh)

At sites with poor energy management, e.g., where machines are left idling and services left operating, the majority of the load will appear to be fixed because large amounts of energy will be used whether production is taking place or not. At such sites, the PCL will have a poor relationship between production volume and energy use. A typical PCL for a site at this stage is shown in the diagram on the upper right. At the start of the energy management process, the first thing that will be seen is an improvement in the relationship between production volume and energy use. This indicates improved control but will still show a high apparent base load and a low apparent process load. A typical PCL for a site at this stage is shown in the diagram on the middle right. In this case the base load is approximately 60% (normal is 20 to 40%) and the process load is 0.87 kWh/kg (normal is 0.9 to 1.6 kWh/ kg for injection moulding).

300,000

200,000 2010 kWh = 1.5656 x Production volume + 56,918 2 R = 0.8594

100,000

0 0

50,000

100,000

150,000

200,000

250,000

300,000

Production volume (kg)

Changes in the PCL with energy management improvements As the energy management process is introduced and projects are completed then the PCL will change to show the improvements and reductions in energy use. A site with poor energy management will have a high apparent base load and a low apparent process load because a large amount of the process load is fixed by poor practices and is seen as a base load. Improved energy management will reduce the base load but will also appear to increase the variable (process) load. 45

2.7

Assessing site performance – internal benchmarking

Performance assessment The practically derived PCL can be used to assess the site performance relative to an internally generated standard. This can be on a monthly basis (or on a weekly basis if the data and equation are weekly). The equation of the PCL for an injection moulding site can be obtained for a specific year (Year 1 in the example shown on the right), this gives a PCL of:

months indicated in the PCL graph below. These have nearly identical production volumes (73,567 kg vs. 73,557 kg), yet the energy use differs by 27,201 kWh (153,690 kWh vs. 180,891 kWh). This is a 15% increase in energy use for no additional production volume. The site should investigate these differences because it has cost them £2,720 for the month.

Base and variable loads (injection moulding) - Year 1

kWh = 1.5551 × Production volume + 48,106 The PCL can then be used to predict and assess energy use for the site in Year 2.

kWh = 1.5551 × 70,000 + 48,106 = 156,963 kWh. The predicted energy use for a production volume of 70,000 kg in the month is therefore 156,963 kWh and predicted energy cost is £15,696. This simple approach enables the production of a performance table (shown on the lower right) for performance assessment and prediction of the monthly energy cost. Managers now have a direct and simple method for assessing energy use and assigning production accountability by the following method: • Set up a simple spreadsheet to calculate the predicted kWh for a given production volume using the PCL. • Determine the volume of material

processed in the past month and calculate the predicted energy use. • Determine the actual energy use for the

past month. • Compare the predicted energy use to the actual energy use. • If the actual energy use is less than the predicted energy use then the site performed better than it has done historically – find out what the site did right and do more of it. • If the actual energy use is more than the predicted energy use then the site performed worse than it has done historically – find out what the site did wrong and do less of it. An example of this would be the two 46

200,000 180,000 160,000 Energy use (kWh)

For example, if the production volume for the month is 70,000 kg, then the predicted energy use will be:

Energy use is no longer an uncontrolled and unknowable variable – it is directly related to the production volume of the site.

140,000 120,000 100,000 80,000 60,000 40,000

kWh = 1.5551 x Production volume + 48,106 R2 = 0.8104

20,000 0 0

10,000

20,000

30,000 40,000 50,000 60,000 Production volume (kg)

70,000

80,000

90,000

Base and variable loads for Year 1 The PCL is found by using the standard methods for Year 1. This gives an operating model for the site that can be used to predict the energy use in Year 2 for a given production volume and to assess the site performance based on previous performance.

Production volume (kg in month)

Predicted energy use (kWh in month)

£/month

0

48,106

£4,811

20,000

79,208

£7,921

30,000

94,759

£9,476

40,000

110,310

£11,031

50,000

125,861

£12,586

60,000

141,412

£14,141

70,000

156,963

£15,696

80,000

172,514

£17,251

90,000

188,065

£18,807

Assessing energy use in Year 2 from the Year 1 PCL It is simple to set up a spreadsheet using the PCL equation (kWh = 1.5551 x Production volume + 48,106 in this case) to provide a simple method of assessing performance on a monthly basis and targeting areas of excessive energy use and cost. Chapter 2 – Energy benchmarking

200,000

PCL can be generated for each area to allocate responsibility to the managers. When using the PCL to assess energy use and drive cost reduction it is best to use a weekly PCL for energy use and production volume. This gives faster feedback to the managers and gives closer control of the improvement process.

150,000

100,000 Actual use

50,000

Predicted use

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• Tip – If the site has sub-metering then a

Electricity use by month (kWh) - Year 2 250,000

Energy use (kWh)

The PCL is generally established for one year and then used to assess performance for the subsequent year. The PCL allows energy use targets to be set based on the production volume. These targets can be used to assess performance based on historical performance.

Month

CUSUM treatment of data

Predicted and actual energy use versus month

The normal method used to compare the predicted and actual energy use would be to plot and compare these on a monthly basis. This treatment is shown in the diagram on the upper right and can lead to misleading conclusions due to the similar sizes of the numbers, i.e., from the data it could be suggested that the site is operating near the predicted performance.

It is difficult to see the long-term performance from a plot of the predicted and actual energy use. This site might appear to be operating close to the predicted performance.

Chapter 2 – Energy benchmarking

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-30,000 Month CUSUM (injection moulding) - Year 2 100,000

CUSUM (kWh)

80,000

60,000

40,000

20,000

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that performance is stable. • A change in the slope of the curve indicates a change in the process or the management of the site that has affected the operating characteristic of the site. CUSUM data can also be used to set targets for energy use (see Section 3.5).

10,000

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• A flat (or substantially flat) curve shows

20,000

Ja

A far better method to identify trends is to use deviations and CUSUM. The deviation is the difference between the actual and the predicted energy use (Actual use − Predicted use) and this is shown in the diagram on the middle right. CUSUM calculates the Cumulative Sum of the deviations. This is easily carried out using a spreadsheet. A CUSUM plot quickly identifies trends and changes in actual relative to predicted performance. From the data it is now seen that things were getting worse – what was going wrong? The important thing with CUSUM charts is NOT the absolute value of the CUSUM; it is the slope of the curve and any changes in this slope. • A rising curve shows that use is consistently higher than predicted, i.e., performance is getting worse. • A falling curve shows that use is consistently better than predicted, i.e., performance is getting better.

Monthly deviation from target (injection moulding) - Year 2 30,000

Month

The deviation and CUSUM graphs These graphs clearly show that performance in Year 2 is significantly worse than in Year 1. The total cost of this poor performance was £7,203 or 3% of the energy cost for the site. 47

Assessing site performance – past performance

Where have we come from?

Base and variable loads - Year 2 3,000,000

PCL for Year 1

The base year (Year 1) The internal data for Year 1 are used to produce an initial PCL and this becomes the internal standard for performance assessment of Year 2. The graph on the upper right shows the PCL generated from Year 1 data as a solid line (no data points are shown for clarity) and the equation for this PCL.

48

PCL for Year 1 = Year 2 standard kWh = 1.404 x Production volume + 820,990 R2 = 0.6065

0 0

500,000 1,000,000 Production volume (kg)

1,500,000

Deviation from standard for month - Year 2 300,000

200,000 150,000 100,000 50,000

-100,000

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Deviation from standard (kWh)

250,000

-150,000 -200,000 Month CUSUM - Year 2 800,000 700,000 600,000 500,000 400,000 300,000 200,000 100,000

-200,000

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Note 1: If the site has performed better than Year 1 then ‘continual improvement’ requires that a new ‘improved’ PCL is used to assess Year 3. If the site has performed worse than in Year 1 then the Year 1 PCL should be retained to avoid slipping backwards. However, in this example we will recalculate the PCL each year.

1,000,000

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The cumulative performance is best seen by plotting the CUSUM (CUmulative SUM) of the deviations and this is done on the lower right. This shows that at the end of Year 2 the site had used 554,741 kWh more than the Year 1 standard and this cost the site an extra £55,474 at an energy cost of £0.10/kWh.

1,500,000

500,000

CUSUM from standard (kWh)

The individual monthly data for Year 2 can then be plotted on the graph on the upper right and the data points are shown. The Year 2 data could be interpreted as being broadly similar to the Year 1 PCL and it is difficult to see if the performance is better or not due to the relative size of the values (see Section 2.7). However, plotting the monthly deviation from the Year 1 standard for each month in Year 2 (graph at middle right) clearly shows 8 months in Year 2 where performance has been worse than the Year 1 standard and several where performance has been considerably worse than the Year 1 standard. Overall, the performance has been varied.

2,000,000

Ja

Year 2 assessment

Year 2 results

2,500,000

Energy use (kWh)

Changes in the PCL show the effect of site efforts in energy management and are useful for assessing the past performance of a site. This is best clarified with a worked example to show the detailed calculations. Sites should use their own internal data to produce similar charts for assessment of past performance.

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Month

Assessing energy use in Year 2 from the Year 1 PCL The PCL for Year 1 can be used as the standard for assessment of performance in Year 2. Assessment of past performance is best carried out using deviations and the CUSUM plot to show the values of the over- or under-spend. Chapter 2 – Energy benchmarking

Year 3 results

2,500,000

PCL for Year 2 2,000,000

1,500,000

1,000,000 PCL for Year 2 = Year 3 standard kWh = 1.5154 x Production volume + 741,640 R2 = 0.6034

500,000

0 0

500,000

Deviation from standard for month - Year 3

50,000

Note 2: Deciding if a point in a given month is ‘out-of-control’ and requires action needs the use of a regression control chart (see Section 3.5).

Chapter 2 – Energy benchmarking

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-100,000 -150,000 -200,000 -250,000 -300,000 -350,000

The PCL does not, of itself, drive improvement or provide external benchmarking. The PCL is based on the historical performance and only assesses the site against past internal performance.

1,500,000

100,000

Month

Summary

CUSUM - Year 3

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CUSUM from standard (kWh)

These sample data show an excellent set of results and the site has consistently reduced the base load from 820,990 kWh in Year 1, down to 741,640 in Year 2, down to 733,241 in Year 3 and then down to 482,450 in Year 4 (not shown). The site has also managed to maintain a virtually constant process load whereas, at most sites, the start of energy management sees a reduction in the base load but an increase in the process load (see Section 2.6).

1,000,000

Production volume (kg)

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The improved Year 3 performance can then be used to set a new (better) standard for Year 4 and the site data interpreted as above. For this site, the results for Year 4 were even better than in Year 3, indicating increased energy savings.

Base and variable loads - Year 3 3,000,000

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Note 3: As a challenge to readers, when did we visit the site and set up their energy management programme?

Energy use (kWh)

The Year 2 data can then be used to set a new standard for Year 3 and Year 3 performance assessed against this revised internal standard. This is done in the graph on the upper right where the PCL generated from Year 2 data is shown as a solid line (no data points shown for clarity) and the equation for the new PCL is also shown. The individual monthly data for Year 3 can then be plotted on the graph on the upper right (data points shown). The Year 3 data can be seen to be broadly less than the Year 2 standard and the Year 3 results look much better than the Year 2 standard. This can be more clearly seen in the monthly deviation (graph on the middle right). The monthly deviations are almost all negative (indicating energy savings relative to the standard) and the CUSUM for the year is shown in the graph on the lower right. This shows that at the end of Year 3 the site used 1,480,098 kWh less than the Year 2 standard and this saved the site £148,000 at an energy cost of £0.10/kWh.

Deviation from standard (kWh)

Year 3 assessment

-400,000 -600,000 -800,000 -1,000,000 -1,200,000 -1,400,000 -1,600,000

Month

Assessing energy use in Year 3 from the Year 2 PCL The PCL for Year 2 can then be used as the standard for assessment of performance in Year 3. As before, assessment of past performance is best carried out using deviations and the CUSUM plot to show the values of the over- or under-spend. 49

2.9

Budgeting for future site energy use

Predicting energy costs Another valuable, but less explored, use of the PCL is the forecasting of energy costs for budgeting purposes. Many companies have no formal procedure to budget for or predict the energy use or the costs of this use. This makes budgeting a case of ‘think of a number and add some contingency’ or some similar scientific approach. Using the PCL makes predicting energy use and the associated costs an easy task similar to that used for performance assessment.

• It allows rapid recalculation of the

predicted energy costs to the site in the event of changes in the cost of energy (£/ kWh) due to purchase contract or other changes. The PCL can now be used as a tool for the accurate prediction of the future energy use and cost of the site based simply on the historical energy use of the site corrected for production volume and the current energy prices – much more useful than any current method available.

The PCL allows accurate forecasting of use and costs based on the site activity.

Forecast monthly production volume (kg)

Forecast monthly energy use (kWh)

Forecast monthly energy cost (£)

January

79,000

170,959

£17,096

February

90,000

188,065

£18,807

March

110,000

219,167

£21,917

April

87,000

183,400

£18,340

energy use (kWh) using the PCL relationship between production volume (kg) and energy use (kWh). • The energy use is converted into the energy cost (£) using the current or future cost of energy. This can be estimated using the current contract cost and the forecast future contract cost. This is shown in the table on the right for the injection moulding site considered in Section 2.7 and shows that the total predicted energy cost for the site is £252,507 for the year.

May

103,000

208,281

£20,828

June

108,000

216,057

£21,606

July

100,000

203,616

£24,434

August

54,000

132,081

£15,850

September

101,000

205,171

£24,621

October

98,000

200,506

£24,061

November

99,000

202,061

£24,247

This method for energy cost budgeting provides several benefits over the existing methods used (if any):

December

80,000

172,514

£20,702

1,109,000

2,301,878

£252,507

The PCL and activity drivers The activity of the site is predicted from the sales forecast using the same PCL as is used for energy use assessment. This is carried out as follows: • The sales volume (in parts or other measures) is taken from the sales forecast. • The sales volume is converted into a monthly production volume (kg) for the site. • The production volume is converted into

Month

Totals

• The energy cost can now be seen by the

Finance function as being directly related to the production volume of the site. This will result in finance involvement in the control and management of energy costs that were previously seen as simply an allocation of a fixed cost. • It allows rapid recalculation of the

energy cost to the site with any changes in production volume. 50

Energy costs: £0.10/kWh for months 1 to 6. £0.12/kWh for months 7 to 12.

Budgeting for future energy use The historically derived PCL can be used with the sales forecasts (however accurate) to produce an energy use forecast for the year based on the real characteristics of the factory. The only variable is the cost of energy and this can be estimated from the current contract and future projected costs. Chapter 2 – Energy benchmarking

The information from this method also allows the Finance function to forecast the energy costs in absolute terms and as a % of sales revenue – to highlight the importance of energy management in overall cost management.

Using the PCL to forecast energy costs is the start of integrating energy into the full management accounts as a variable cost.

• Tip – This method makes energy cost

budgeting as accurate as the sales forecast. Not always a good thing in my experience where ‘Costs are certain but sales never are’. • Tip – Do not use the incremental cost

from the bill for a kWh for this type of calculation. The fixed costs for electricity supply (see Section 4.2) will also affect the cost of energy.

£300,000 £250,000 £200,000 £150,000 Forecast sales

£100,000

Forecast energy cost

£50,000

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Condition-driven energy use in plastics processing is less important than activitydriven energy use due to the lower magnitude of the use and costs. For most sites the only condition-driven energy use will be site heating or cooling and this is typically in the region of 2% of the total energy use. This makes energy management in the process industries very different to energy management in buildings. It is possible to use similar techniques (see Section 4.8) to budget for condition-driven energy use, primarily for heating, by considering the average temperatures for the site location. In this case the budget will need continual updating to reflect deviations from the average for the specific year or period.

Sales forecast/energy cost (£)

The PCL and condition drivers

Sales forecast and energy cost (injection moulding) £350,000

Month

The sales forecast and the energy costs The PCL can be used in calculations by the Finance function to forecast the cost of energy to the site from the sales forecast. This provides an accurate forecasting method based on real data rather than previous ‘guesstimates’. Energy cost as % of sales (injection moulding) 10%

Energy cost as % of sales

9% 8% 7% 6% 5% 4% 3% 2% 1%

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Energy cost as a % of sales The energy cost forecast from the PCL can be used with any forecast changes in the cost of energy to rapidly see the effect of energy prices changes on the profitability of the site and the sensitivity to energy costs. Chapter 2 – Energy benchmarking

51

2.10

Complex sites – multi-variate analysis

Multiple drivers

The relationship As discussed in Section 2.1, the equation of the PCL for a mixed load site will be of the form: kWh = A × Driver 1 + B × Driver 2 + X.

What do A, B and X mean? The values of A, B and X are similar in meaning to those in the equation for the single variable analysis: • The ‘A’ value is the load coefficient for Driver 1, i.e., the amount of energy used for each incremental increase in the driver. • The ‘B’ value is the load coefficient for Driver 2, i.e., the amount of energy used for each incremental increase in the driver. • The ‘X’ value is the ‘base load’ for the site, i.e., the energy use of the chosen source when no activity or condition is present. For an activity driver, such as production volume, this gives the amount of energy that will be used when no production is taking place but machinery and services are available. For a condition driver, such as the weather, this will generally be zero, i.e., no energy will be needed when the conditions do not require heating or air conditioning. It is important to realise that Driver 1 and Driver 2 can be either activity or condition drivers and typical examples are shown in Section 2.1.

52

Base and variable loads (mixed processes) 200,000

150,000 Energy use (kWh)

Where sites have a mixture of processes or other high loads from a common energy source then it is possible that there are multiple drivers for energy use (see Section 2.1). In this case, a simple scatter plot of the energy use and production volume data will generally show a lower R2 value (more scatter) because of changes in the relative effects of the activity drivers. The preferred method is to independently measure the energy use for each driver but this is not always possible and when this is the case then multi-variate analysis is needed.

100,000

kWh = 0.3639 x Production volume + 124,773 R2 = 0.4903

50,000

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40,000

80,000 Production volume (total)

120,000

160,000

Mixed process site loads Mixed processes will give a more variable process load and will generally show a low correlation coefficient (R2 is 0.4903) due to changes in the product mix and the energy intensity of the average site process with each month.

Calculating the values for multiple drivers There is no visual method for calculating the ‘A’, ‘B’ and ‘X’ values in the multiple driver case. This is only possible using a method similar to the more complex method shown in Section 2.2. This uses the Microsoft Excel ‘Analysis ToolPak’ or similar. It is assumed that the ToolPak has been activated. Go to Tools and this should now show the Data Analysis

option. Scroll down to ‘Regression’ and click to open the Options Box. Select the ‘Input Y Range’ to match the required data

(typically the kWh used in the month). Select the ‘Input X Range’ to match the required data. In this

case the range needs to be extended to cover both of the energy use drivers so it is easiest if they are next to one another in the spreadsheet. In many cases this will be the relevant production volume values but may also be the number of HDD or CDD for the month if one of the drivers is a condition driver (see Section 4.8 for further details on obtaining HDD or CDD data for a site). Select the ‘Output Range’ as somewhere in the relevant

spreadsheet. Click ‘OK’ and a table of numbers will appear where the

Output Range was selected. The Output Range table gives the relevant numbers for the

multiple driver equation: R Square (R2), Intercept (X), ‘X Variable 1’ (A) and ‘X Variable 2’ (B) values. These can then be fed into the multiple driver equation (kWh = A × Driver 1 + B × Driver 2 + X) to allow performance assessment and budgeting for future energy use as for the single driver case. Chapter 2 – Energy benchmarking

Multi-variate analysis makes it possible to separate the effects of the two drivers to allow monitoring and targeting of the individual drivers.

Blow moulding - energy use Injection moulding - energy use Base energy load

200,000 Energy use (kWh)

In this case, whilst it is possible to predict the energy use by knowing the equation and the value of the relevant drivers it is impossible to show the relationship on a simple graph of the PCL as for the single driver case.

Energy use by process 250,000

150,000

100,000

50,000

Mixed processes

In this case the PCL will be of the form: kWh = A × Production volume Injection + B × Production volume Blow moulding + X. Using the calculation method described in the box on the lower left the values for the coefficients for Year 1 can be calculated to give the full equation of:

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The PCL for the site shown on the left has a low correlation coefficient because the site has a mix of injection moulding and extrusion blow moulding processes. These have different energy intensities and the production volume for each process varies depending on the customer demand.

Month

Multi-variate analysis for two processes The analysis shows the relative contributions of the processes to the total energy use based on the relative production volumes. This also provides information for budgeting and cost allocation.

moulding

This is a global saving of 42,492 kWh but this cannot be allocated to a specific area without direct measurement of each area’s use. • Tip – It is possible to use multi-variate

analysis to separate the available data but sub-metering of the process areas is easier, more direct and more accurate. Chapter 2 – Energy benchmarking

10,000

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-20,000 -30,000 -40,000 -50,000 Month CUSUM (mixed processes) - Year 2 50,000 40,000 30,000 20,000 10,000

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One of the best methods to display multivariate results is to use a simple stacked bar chart and this is shown on the upper right. This shows the relative contribution of each process and is very useful for budgeting and cost allocation for energy costs to each area. As with the single driver case, it is best to examine performance by using the deviation from the standard for each month and a CUSUM plot to show the complete year results. This has been done in the graphs on the middle and lower right to show the site’s performance in Year 2 relative to the Year 1 standard. The results show that, despite a poor start to the year, the site recovered and ended the year 42,492 kWh under budget for the year and saved £4,249 relative to budget.

Deviation from standard (kWh)

Displaying the results

20,000

CUSUM from standard (kWh)

kWh = 1.473 × Production volume Injection moulding + 0.911 × Production volume Blow moulding + 34,942.

Deviation from standard for month (mixed processes) - Year 2 30,000

-30,000 -40,000 -50,000 Month

Assessing energy use in Year 2 from the Year 1 PCL The multi-variate PCL for Year 1 can be used to assess global performance in Year 2. Without direct measurement of each area, it is not possible to assess each area’s performance. 53

Site SEC and production volume

It is obvious that the simple monthly SEC measurement is affected by both the production volume and the base load. Two monthly results located on the same PCL and representing the same underlying energy performance will have highly different simple SEC measurements if the production volume is different. Increasing the production volume will automatically reduce the simple SEC 54

1.5

1.0

0.5

0.0

Month

Decreasing monthly SEC – a sign of improvements? The calculation of the SEC (kWh/kg) on a monthly basis can lead to errors. The graph shows a trend towards decreasing monthly SEC values and the site management appears to be improving energy efficiency in terms of kWh/kg produced. Production volume and SEC by month (extrusion and thermoforming) 1,000,000

5.0

800,000

4.0

600,000

3.0

400,000

2.0

200,000

SEC (kWh/kg)

This is easily explained by the PCL graph. In terms of the typical site PCL we can visualise the individual monthly measurement of SEC (kWh/kg) as finding the slope of the line drawn between the origin and an individual monthly data point. The slope of the line for each month will be the monthly SEC value (see upper graph on the opposite page).

2.0

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Consider the case shown on the upper right. The SEC (in kWh/kg) varies with the month but the overall trend is downwards and the energy efficiency is apparently increasing, i.e., it apparently takes less kWh to produce a kilogramme of finished product. The management team is feeling happy and being congratulated for their efforts in improving energy efficiency. Unfortunately, all is not as it seems. The production volume over the same period is also shown on the lower right and this can be seen to be again varying, but the overall trend is for increased production volume over the period. The SEC is also plotted on the same graph and it is obvious that the SEC value mirrors that of the production volume value, i.e., when the production volume is high the SEC is low and vice versa.

SEC (kWh/kg) by month (extrusion and thermoforming)

1.0

Production volume SEC

0

0.0

Ja n Fe ua r br y ua r M y ar ch A pr il M ay Ju ne Ju Au ly Se g pt ust em O ber c No to be ve r De mb ce e r m J a ber nu Fe a r br y ua r M y ar ch A pr il M ay Ju ne

A fundamentally flawed metric

Monitoring using monthly SEC values can lead to misleading conclusions.

2.5

SEC (kWh/kg)

Many sites (and also governments) take a simple approach to energy efficiency and calculate a single monthly Specific Energy Consumption (SEC) in terms of ‘kWh/kg’ as an assessment method. They calculate this from the kilogrammes processed in the month and simply divide by the kWh used in the month. This may provide a good snapshot of energy performance if production volume is constant but is very misleading if production volumes change.

because the base load will be amortised over a greater process load and lead to the impression that energy efficiency is improving. Raising the production volume decreases the kWh/kg value through

Ja nu Fe a ry br ua ry M ar ch

The pitfalls of simple kWh/kg

Production volume (kg)

2.11

Month

Production volume is increasing Over the same period as that shown above, the production volume for the site is also varying but shows a trend towards increased production volumes. This will inevitably affect the apparent energy efficiency of the site. The SEC value for the period is also shown and the SEC curve is the mirror of the production volume curve. When the production volume is high the SEC is low and vice versa. Chapter 2 – Energy benchmarking

• Tip – Do not use SEC as a monthly

monitoring and targeting metric for performance assessment or for comparison of sites. It is fundamentally flawed as a metric for these purposes.

not eliminate the effect of base load amortisation but it is marginally better than using a simple monthly SEC as a performance metric.

That explains it all! A colleague at a major company was using monthly SEC as his performance metric and was frustrated by the apparently random variations in SEC each month despite carrying out good work in energy management. When the reasons were explained he was overjoyed and found that his PCL was really excellent and actually showed the progress he was making.

Managers are happy to accept the apparent energy efficiency benefits of increasing production but may not be so happy if production levels decrease.

Base and variable loads (extrusion and thermoforming) 1,400,000 1,200,000 Energy use (kWh)

simple amortisation of the base load, i.e., high production volume = low kWh/kg and low production volume = high kWh/kg. Sites must therefore be careful in monitoring energy efficiency changes by simply comparing SEC values; these can be affected by simple changes in production volume rather than real changes in the energy efficiency of the process. This will be less significant where the base load is low in comparison to the process load but the simple number is almost always misleading. This is not a problem when production volumes are rising and the management team sees a continuously decreasing SEC. They are happy to accept congratulations from Head Office for doing nothing at all. When production volumes are decreasing and the SEC is increasing despite their efforts then they are less happy to accept the criticism.

1,000,000 800,000 Month 1: SEC = 2.20 kWh/kg

Month 18: SEC = 1.37 kWh/kg

600,000 400,000 kWh = 0.4260 x Production volume + 873,027 R2 = 0.3384

200,000

• Tip – SEC as a monthly performance

0

metric is only suitable for those people who can only hold one number in their head at a time. Do not be one of them!

0

200,000

400,000

600,000

800,000

1,000,000

Production volume (kg)

What are the alternatives?

What the monthly SEC represents

Many multi-national companies use the monthly SEC as their fundamental metric for energy efficiency but as a metric for progress it is worse than useless because it can reward bad behaviour and punish good behaviour – it all depends on which way the production volume is moving and the size of the base load for the site.

The monthly SEC is simply the slope of a line from the origin to the data point. As production volume increases the SEC will decrease with no underlying change in energy performance.

2.0 SEC (kWh/kg)

In this workbook we will use SEC as a metric but this is always qualified in terms of production volume or rate (see later in this section). So what are the alternatives:

SEC and production volume (extrusion and thermoforming) 2.5

1.5

1.0

• The most appropriate metric for M&T is

a site-based PCL as discussed in Section 2.7. This takes into account the specific nature of every site, i.e., the base load, the services and automatically corrects for production volume variations. • If companies are determined, against all arguments, to use monthly SEC then it is better to use a moving average over a period of at least 9 months to smooth out production volume variations. If production volumes are strongly increasing then even this method will Chapter 2 – Energy benchmarking

0.5

0.0 0

200,000

400,000 600,000 Production volume (kg)

800,000

1,000,000

Production volume and SEC The SEC will change with simple changes in production volume irrespective of any changes to the underlying energy performance. The simple PCL approach predicts this and it is possible to show how the SEC varies with production volume. 55

2.12

External site benchmarking – general

A global view The PCL and the information it provides are extremely useful but it is all based on the historical performance or the ‘status quo’ of a site. This approach does not provide any of the essential external benchmarking information that is necessary to drive very significant improvements in performance. This is only possible through external benchmarking with comparable sites.

Process information Only two sources of possible benchmarking process information are known to exist for energy use in plastics processing. These are: • The EURecipe report from a survey of European plastics processors in 2005.1 • Internal data collected by Tangram Technology Ltd. from site visits throughout the world over the past 19 years.2 Other available data are of limited use due to the small sample sizes.

Process dependency As shown in Section 2.4, plastics processes are not equally energy-intensive and each process therefore requires a different external benchmarking reference. However, sufficient data are really only currently available for injection moulding, extrusion, extrusion blow moulding and rotational moulding. Fortunately these processes account for the majority of the material processed and are relevant for the bulk of the industry.

the base load is included in the site SEC, whereas the process load mainly considers the processing energy use. Therefore these average values cannot be compared directly with the process load information given in Section 2.4.

Production rate dependency Energy use in any plastics processing method is rate-dependent due to the base load. This is analogous to the effect of production volume on the measurement of SEC (see Section 2.11). The base load remains constant whatever the production rate and must be amortised over the actual production volume. At low production rates, the process load is low and the fixed load dominates energy use,

Many industry bodies and government agencies have a fascination with using a single SEC value for any process. This is because of the simplicity of using a single number. However this is a fundamentally flawed value when comparing sites or progress towards energy efficiency objectives.

Average site SEC (kWh/kg) EURecipe1

Tangram2

Injection moulding

3.118

3.138

Extrusion

1.506

1.316

N/A

2.07

5.828

4.85 (all fuel)

Extrusion blow moulding Rotational moulding

Average site SEC for plastics processes Average site SEC from independent data sets shows good agreement but the site SEC must be corrected for production rate to allow site comparisons. Average SEC values are misleading.

Average site SEC data (which includes the base load) are available from these sources and are shown on the top right. Despite the geographical variations in the site locations and the inevitable wide variations in site performance, the data sets are consistent in terms of the average site SEC for the processes considered. It should be noted that these average values are not weighted in any manner for the production volume. They are a simple average of the SEC values for the sites that responded to the survey or were physically surveyed. The average site SEC is always higher than the process load because the effect of 56

The site base load is amortised over higher process loads at higher production rates Increasing production rates amortise the site base load over greater process loads and the apparent SEC of the site decreases. Chapter 2 – Energy benchmarking

i.e., the effective SEC of the process will appear high. At high production rates, the process load is high and the fixed load decreases in importance, i.e., the effective SEC of the process will appear low. This is again a simple amortisation of the base load into the process load and is shown in the figure on the lower left. The average site SEC as shown in the table on the left is therefore of limited use for external benchmarking of any specific site. The overall output rate affects the SEC dramatically and it is essential that the average SEC value for any process is clarified in terms of production rate.

correction for the production rate is therefore only possible with one set of process information. It is highly likely that the EURecipe data would show a similar pattern but it is not possible to verify this. • 1. EURecipe, 2005, ‘European Benchmarking Survey of Energy Consumption and Adoption of Best Practice’, www.eurecipe.com. • 2. Tangram Technology Ltd., Internal data from 154 injection moulding sites, 48 extrusion sites, 29 extrusion blow moulding sites and nine rotational moulding sites throughout the world.

Production rate versus power (model site system)

Power/machine = 1.5 x (Production rate) + 25

90 Power/machine (kW/machine)

Total site power (kW) = A × Production rate + B. The total load for this type of model system is shown on the upper right. At low production rates, the process load is low and the base load dominates the total load. At high production rates, the process load is high and the base load decreases in importance.

Being green can also be profitable. At the site level, running plastics processing machinery harder and increasing production volume increases the energy efficiency of the site.

100

The model It is possible to set up a model process with a total load (kW) consisting of a base load and a process load that is directly proportional to the production rate, i.e.

There is no conflict of interest.

80 70 60 50 40 30 20 10 0 0

10

20 30 Production rate (kg/h/machine)

40

50

The SEC for this model process is then given by:

Model system of site base and process loads

Site SEC (kWh/kg) = B × (Production rate)−1 + A. The SEC can be calculated over a range of production rates and this is shown at lower right (solid line) with the average site SEC also shown (dashed line). At low production rates the SEC of an actual site will appear higher than the average and at high production rates the SEC of an actual site will appear lower than the average. This is despite the site continuing to operate according to the simple and realistic model.

A model site system can be set up with a total load consisting of a base load and a process load that is directly proportional to the production rate, i.e., Total load = A × Production rate + B. This gives a total load versus production rate line as shown.

Chapter 2 – Energy benchmarking

Model site data Average site SEC

25

SEC = 25 x (Production rate)-1 + 1.5 SEC (kWh/kg)

It is immediately obvious that the ‘average SEC’ used by industry bodies and government agencies is not in any way representative of the model process. This means that quoting an ‘average’ SEC for any real process that is similar to the model process is irrelevant. This is, unfortunately, most of the processes used in general manufacturing and particularly for plastics processing. The EURecipe results1 provide no method of correcting for production rate. The Tangram results2 provide these data and

SEC versus production rate (model site system) 30

20

15

10

5

0 0

10

20 30 Production rate (kg/h/machine)

40

50

SEC for the model site system versus production rate The SEC for the model site system can be calculated for varying production rates and this gives the graph above. The effect of the base load on the apparent SEC of the model site is dramatic and the irrelevance of the ‘average’ SEC is clearly seen. 57

2.13

External site benchmarking – injection moulding

The benchmarking process A graph for power/machine versus production rate for injection moulding has been generated from data from 154 injection moulding sites throughout the world.1 This was done by: • Calculating the operating hours of the site over a full year. • Obtaining the total material processed

by the site over the year. • Defining the number of machines in

operation over the year. This required assessment of ‘part-machines’ if production was not continuous. • Calculating the global production rate

(in kg/h/machine) from the above. • Obtaining the total electricity use of the site over the full year and using this with the number of machines and the operating hours to calculate the average power/machine (kW/machine). • Plotting the average power/machine (kW/machine) versus the production rate (kg/h/machine) to give the graph shown on the upper right. • Fitting the data with a linear line of best fit to find the coefficients for the power graph of the form:

from the SEC benchmark curve. Individual sites can now carry out this process to benchmark themselves against the 154 sample sites around the world.

Cautionary notes Several points should be noted: • The benchmark SEC is a best fit value and some sites have a lower site SEC for the process, particularly in the area of lower production rates. • Achieving the benchmark SEC is not a

sign of good practice, only a sign of average practice. • The machines used at any site will be of

varying sizes but for this analysis the average consumption is assumed. This assumption does not appear to introduce any large anomalies. • A large degree of the scatter seen in the data points of the curve is due to machines being operated at differing levels of production efficiency, i.e., poor or good overall machine utilisation and variations in the base loads at the surveyed sites. • The polymer processed may be expected to have an effect but the data shows that this has little effect on the assessment.

Power = A × Production rate + B. • Using the coefficients from the power

graph to create the benchmark SEC curve of the form: Site SEC (kWh/kg) = B × (Production rate)−1 + A. This is the benchmark SEC curve shown on the lower right. This corrects the predicted SEC for production rate at injection moulding sites. It is now possible for an injection moulding site to benchmark itself against other similar sites. This can be done by: • Calculating the site global production

rate using the calculator on the right. • Finding the predicted site SEC from the

benchmark SEC curve at the global production rate. • Calculating the actual site SEC from the

total electricity use (kWh)/total material processed (kg). • Comparing the actual site SEC at the

given production rate with the prediction 58

These are site SEC data and take into account all the processes and services. They must not be confused with machine data which deal simply with the process.

• 1. Tangram Technology Ltd.: Internal data from 154 worldwide injection moulding sites.

Benchmarking any process must take into account the fixed loads of the process.

Want to submit your data? Sites are invited to submit their data to Tangram for inclusion in the benchmarking process. This is confidential and you will get feedback. See Appendix 1 for details of how to submit site data.

No. of hours/shift

No. of shifts/day

Days worked/week

Weeks worked/year

Total hours worked/year (hours): A Total site annual electricity use (kWh): B Total site annual polymer use (kilogrammes): C No. of machines on site: D Production rate (kg/hour/machine) = C/A/D Predicted site SEC in kWh/kg (read from the graph): Actual site SEC in kWh/kg = B/C

Site SEC benchmark calculator Compare the predicted and actual site SEC values to find the difference between actual and predicted performance for the site. Chapter 2 – Energy benchmarking

Site power graph for injection moulding 160

140

Power/machine (kW/machine)

120

100

80

60

40 kW = 1.39 x Production rate + 10.34 R2 = 0.8339 Sample size: 154 sites

20

0 0

10

20

30

40 50 60 Production rate (kg/h/machine)

70

80

90

100

Site power graph for injection moulding1 The average power graph matches the model in form and shows that for injection moulding the model is valid (R2 = 0.8341). The average power at an injection moulding site is defined by kW = 1.39 × Production rate + 10.19.

Site SEC for injection moulding 10 SEC = 10.34 x (Production rate)-1 + 1.39 Sample size: 154 sites 8 Benchmark curve

SEC (kWh/kg)

Average SEC 6

4

2

0 0

10

20

30

40

50

60

70

80

90

100

Production rate (kg/h/machine)

Site SEC for injection moulding1 The site SEC for injection moulding must be corrected for the production rate (kg/h/machine) but the resulting curve then allows rapid external benchmarking of a site against other sites around the world. It is easily seen that the ‘average’ value for the injection moulding process is a misleading value. Chapter 2 – Energy benchmarking

59

2.14

External site benchmarking – extrusion

The benchmarking process A similar analysis to that carried out for injection moulding is possible for extrusion. This has been done for 48 extrusion sites throughout the world to produce a benchmark SEC curve for SEC versus production rate for extrusion.1 The linear line of best fit to the global site power/machine (kW/machine) versus production rate (kg/h/machine) has been calculated using the same method as in Section 2.13 to produce the graph on the upper right. The coefficients from this graph have then been used to generate the SEC benchmark curve for SEC (kWh/kg) versus the production rate in kg/h/ machine (on the lower right). This benchmark SEC curve corrects for the effect of production rate in extrusion. It is now also possible for an extrusion site to benchmark itself against other similar sites. This can be done by: • Calculating the site global production rate using the calculator shown on the right. • Finding the predicted site SEC from the SEC benchmark curve at the global production rate.

appear to introduce any large anomalies. • A large degree of the scatter seen in the data points used for the creation of the power graph is due to machines being operated at differing levels of production efficiency, i.e., poor or good overall machine utilisation and variations in the base loads at the surveyed sites. • The polymer processed may be expected

to have some effect but the available data shows that this has little effect in the overall assessment. Note: This benchmark is relevant for all types of extrusion, e.g., film blowing, sheet forming, etc,, provided there is no substantial downstream processing such as thermoforming.

Cautionary notes

Sites are invited to submit their data to Tangram for inclusion in the benchmarking process. This is confidential and you will get feedback. • 1. Tangram Technology Ltd.: Internal data from 48 worldwide extrusion sites.

No. of shifts/day

Days worked/week

Weeks worked/year

Total hours worked/year (hours): A Total site annual electricity use (kWh): B

• The machines used at any site will

Site SEC benchmark calculator

60

See Appendix 1 for details of how to submit site data.

No. of hours/shift

Several points should be noted with regard to this analysis: • The benchmark SEC curve is a best fit value and some sites have a considerably lower site SEC for the process, particularly in the area of lower production rates. • Achieving the benchmark SEC is not a sign of good practice, only a sign of average practice. generally be of varying sizes but for this analysis the average consumption is assumed. This assumption does not

Benchmarking any process must take into account the fixed loads of the process.

Want to submit your data?

• Calculating the actual site SEC from the

total electricity use (kWh)/total material processed (kg)). • Comparing the actual site SEC at the given production rate with the prediction from the SEC benchmark curve. Individual sites can carry out this process to benchmark themselves against the 48 sample sites around the world.

These are site SEC data and take into account all the processes and services. They must not be confused with machine data which deal simply with the process.

Total site annual polymer use (kilogrammes): C No. of machines on site: D Production rate (kg/hour/machine) = C/A/D Predicted site SEC in kWh/kg (read from the graph): Actual site SEC in kWh/kg = B/C

Compare the predicted and actual site SEC values to find the difference between actual and predicted performance for the site. Chapter 2 – Energy benchmarking

Site power curve for extrusion 250

Power/machine (kW/machine)

200

150

100

kW = 0.49 x Production rate + 4.33 R2 = 0.9482 Sample size: 48 sites

50

0 0

50

100

150

200

250

300

350

400

450

500

Production rate (kg/h/machine)

Site power graph for extrusion1 The average power graph matches the model in form and shows that for extrusion the model is valid (R2 = 0.9480). The average power at an extrusion site is defined by kW = 0.49 × Production rate + 3.84.

Site SEC for extrusion 3.0 SEC = 4.33 x (Production rate)-1 + 0.49 Sample size: 48 sites 2.5

Benchmark curve Average SEC

SEC (kWh/kg)

2.0

1.5

1.0

0.5

0.0 0

50

100

150

200

250

300

350

400

450

500

Production rate (kg/h/machine)

Site SEC for extrusion1 The site SEC for extrusion must be corrected for the production rate (kg/h/machine) but the resulting curve then allows rapid external benchmarking of a site against other sites around the world. It is easily seen that the ‘average’ value for the process is a misleading value. Chapter 2 – Energy benchmarking

61

2.15

External site benchmarking – extrusion blow moulding

The benchmarking process A similar analysis to that carried out for injection moulding and extrusion is possible for extrusion blow moulding. This has been done for 29 extrusion blow moulding sites throughout the world to produce a benchmark SEC curve for SEC versus production rate for extrusion blow moulding.1 The linear line of best fit to the global site power/machine (kW/machine) versus production rate (kg/h/machine) has been calculated using the same method as in Section 2.13 to produce the graph on the upper right. The coefficients from this graph have then been used to generate the benchmark curve for SEC (kWh/kg) versus the production rate in kg/h/machine (on the lower right). This curve corrects the benchmark SEC for variations in production rate for extrusion blow moulding. It is now also possible for an extrusion blow moulding site to benchmark itself against other similar sites. This can be done by: • Calculating the site global production rate using the calculator shown on the right. • Finding the predicted site SEC from the benchmark SEC curve at the global production rate. • Calculating the actual site SEC from the total electricity use (kWh)/total material processed (kg)). • Comparing the actual site SEC at the given production rate with the prediction from the SEC benchmark curve. Individual sites can carry out this process to benchmark themselves against the 29 sample sites around the world.

Cautionary notes Several points should be noted with regard to this analysis: • The benchmark SEC curve is a best fit

value and some sites have a considerably lower site SEC for the process, particularly in the area of lower production rates. • Achieving the benchmark SEC is not a

sign of good practice, only a sign of average practice. 62

• The machines used at any site will

generally be of varying sizes but for this analysis the average consumption is assumed. This assumption does not appear to introduce any large anomalies. • A large degree of the scatter seen in the data points used for the creation of the power graph is due to machines being operated at differing levels of production efficiency, i.e., poor or good overall machine utilisation and variations in the base loads at the surveyed sites. • The polymer processed may be expected

to have some effect but the available data shows that this has little effect in the overall assessment.

These are site SEC data and take into account all the processes and services. They must not be confused with machine data which deal simply with the process.

Benchmarking any process must take into account the fixed loads of the process.

Want to submit your data? Sites are invited to submit their data to Tangram for inclusion in the benchmarking process. This is confidential and you will get feedback. • 1. Tangram Technology Ltd.: Internal data from 29 worldwide extrusion blow moulding sites.

See Appendix 1 for details of how to submit site data.

No. of hours/shift

No. of shifts/day

Days worked/week

Weeks worked/year

Total hours worked/year (hours): A Total site annual electricity use (kWh): B Total site annual polymer use (kilogrammes): C No. of machines on site: D Production rate (kg/hour/machine) = C/A/D Predicted site SEC in kWh/kg (read from the graph): Actual site SEC in kWh/kg = B/C

Site SEC benchmark calculator Compare the predicted and actual site SEC values to find the difference between actual and predicted performance for the site. Chapter 2 – Energy benchmarking

Site power curve for extrusion blow moulding 250

Power/machine (kW/machine)

200

150

100

kW = 1.58 x (Production rate) + 17.03 R2 = 0.8156 Sample size: 29 sites

50

0 0

20

40

60 80 Production rate (kg/h/machine)

100

120

140

Site power graph for extrusion blow moulding1 The average power graph matches the model in form and shows that for extrusion blow moulding the model is valid (R2 = 0.8156). The average power at an extrusion blow moulding site is defined by kW = 1.58 × Production rate + 17.03. Site SEC for extrusion blow moulding 5.0 SEC = 17.03 x (Production rate)-1 + 1.58 Sample size: 29 sites 4.0 Benchmark curve

SEC (kWh/kg)

Average SEC 3.0

2.0

1.0

0.0 0

20

40

60 80 Production rate (kg/h/machine)

100

120

140

Site SEC for extrusion blow moulding1 The site SEC for extrusion blow moulding must be corrected for the production rate (kg/h/machine) but the resulting curve then allows rapid external benchmarking of a site against other sites around the world. It is easily seen that the ‘average’ value for the process is a misleading value. Chapter 2 – Energy benchmarking

63

2.16

External site benchmarking – rotational moulding

The benchmarking process Rotational moulding uses both electricity and gas in the process and a similar analysis to that carried out for the previous processes has been carried out for rotational moulding for both electricity and gas. This has been done for nine rotational moulding sites throughout the world to produce a benchmark SEC curve for SEC versus production rate for rotational moulding1. The amount of site data is relatively low and caution should be taken in applying the benchmarks. It is now also possible for an rotational moulding site to benchmark itself against other similar sites for both electricity and gas use. This can be done by: • Calculating the site global production rate using the calculator shown on the right. • Finding the predicted site SEC for either electricity or gas from the relevant benchmark SEC curve at the global production rate. • Calculating the actual site SEC for electricity or gas from the total energy use of the relevant fuel (kWh)/total material processed (kg).

sign of good practice, only a sign of average practice. • The machines used at any site will

generally be of varying sizes but for this analysis the average consumption is assumed. This assumption does not appear to introduce any large anomalies. • A large degree of the scatter seen in the data points used for the creation of the power graph is due to machines being operated at differing levels of production efficiency, i.e., poor or good overall machine utilisation and variations in the base loads at the surveyed sites. • The polymer processed would be

expected to have some effect but the available data show that this has little effect in the overall assessment.

Want to submit your data? Sites are invited to submit their data to Tangram for inclusion in the benchmarking process. This is confidential and you will get feedback.

• Comparing the actual site SEC for the

relevant fuel at the given production rate with the prediction from the SEC benchmark curve. Individual sites can carry out this simple process to determine their ranking relative to the average performance of the nine sample sites around the world. The data shows that rotational moulding sites tend to have high base loads in both electricity and gas. This is likely to be related to the process, i.e., initially heating the oven and the losses associated with loading and unloading the oven.

• 1. Tangram Technology Ltd.: Internal data from nine worldwide rotational moulding sites.

No. of shifts/day

Days worked/week

Weeks worked/year

Total hours worked/year (hours): A Total site annual electricity (or gas) use (kWh): B Total site annual polymer use (kilogrammes): C No. of machines on site: D

Several points should be noted with regard to this analysis: • The benchmark SEC curve is a best fit value from a limited data set. Some sites have a considerably lower site SEC for the rotational moulding process, particularly in the area of lower production rates.

Production rate (kg/hour/machine) = C/A/D

64

See Appendix 1 for details of how to submit site data.

No. of hours/shift

Cautionary notes

• Achieving the benchmark SEC is not a

These are site SEC data and take into account all the processes and services. They must not be confused with machine data which deal simply with the process.

Predicted site SEC for electricity (or gas) in kWh/kg (read from the graph): Actual site SEC in kWh/kg = B/C

Site SEC benchmark calculator Compare the predicted and actual site SEC values to find the difference between actual and predicted performance for the site. Chapter 2 – Energy benchmarking

Site SEC for rotational moulding (electricity only) 2.0 SEC = 15.88 x (Production rate)-1 + 0.30 Sample size: 9 sites

Benchmark curve

1.5

SEC (kWh/kg)

Average SEC

1.0

0.5

0.0 0

20

40

60

80

100

120

Production rate (kg/h/machine)

Site SEC for electricity use rotational moulding1 The site SEC for electricity use in rotational moulding must be corrected for the production rate (kg/h/machine) but the resulting curve then allows rapid external benchmarking of a site against other sites around the world. It is easily seen that the ‘average’ value for the process is a misleading value. Site SEC for rotational moulding (gas only) 10.0 SEC = 59.35 x (Production rate)-1 + 2.32 Sample size: 9 sites 8.0 Benchmark SEC

SEC (kWh/kg)

Average SEC 6.0

4.0

2.0

0.0 0

20

40

60

80

100

120

Production rate (kg/h/machine)

Site SEC for gas use in rotational moulding1 The site SEC for gas use in rotational moulding must be corrected for the production rate (kg/h/machine) but the resulting curve then allows rapid external benchmarking of a site against other sites around the world. It is easily seen that the ‘average’ value for the process is a misleading value. Chapter 2 – Energy benchmarking

65

2.17

External machine benchmarking – general

The heart of the process The analysis of a site SEC corrected for production rate provides a vital external global benchmark for a site, but many sites would also like to be able to benchmark individual machines. This will enable them to determine which machine is the most energy-efficient under given operating conditions and to investigate machine settings to reduce energy consumption through correct machine setting.

volume. They are a simple average of the SEC values for the variety of machines that were physically surveyed. As with site SEC values the use of a simple average SEC for any process is not particularly useful due to the effect of production rate on the apparent SEC of the process.

Average machine SEC (kWh/kg)

Typical site process load (kWh/kg) (see Section 2.4)

Injection moulding (all machines)

1.91

0.9–1.6

Injection blow moulding

1.86

Insufficient data

Extrusion

0.53

0.4–0.7

Extrusion blow moulding

1.19

0.8–1.3

Thermoforming

0.20

Insufficient data

Process

Process information Machine energy consumption is available from a variety of sources but this is generally applicable for only a limited number of machines and is not generally ‘production’-oriented data, i.e., it is generally laboratory data which examines a limited range of machines. Tangram Technology has carried out detailed energy measurements on: • 330 injection moulding machines (291 hydraulic machines and 39 all-electric or hybrid machines). • 9 injection blow moulding machines. • 91 extruders. • 87 extrusion blow moulding machines. • 25 thermoforming machines (thin and

thick sheet models). These machines were all production machines producing commercial products in a variety of materials and were from a variety of manufacturers.

Comparing machine SEC values without taking production rate into account is meaningless.

Average machine SEC for various processes1 Average machine SEC values from machine data and typical process loads from PCL information (see Section 2.4) show some comparison but the machine SEC must be corrected for the production rate to correct for base loads and to allow machine comparisons. Average SEC values have very limited usefulness for assessment or comparison purposes.

Process dependency By this stage, it will come as no surprise that plastics processes are not equally energy-intensive. Therefore each process again requires a specific external benchmarking reference but sufficient data are not available for all production processes. Fortunately the data that are available cover the majority of the materials processed and are relevant to the bulk of the industry machines. Average machine SEC data across the range of machines surveyed (which includes any machine base load) has been calculated and this is shown on the upper right. These average values are not weighted in any manner for the number of machines surveyed or the production 66

The machine base load is amortised over higher process loads at higher production rates As with site performance, increasing machine production rates amortises the machine base load over greater process loads and the apparent SEC of the machine decreases. Chapter 2 – Energy benchmarking

Despite this, the values reinforce the strong process dependency of energy use in plastics processing, i.e., extrusion is significantly less energy-intensive at the machine level than injection moulding.

Total machine power (kW) = A × Production rate + B. and the SEC for this model machine will then be given by: Machine SEC (kWh/kg) = B × (Production rate)−1 + A. The power drawn and the SEC for the model system are shown on the upper and lower right, respectively. At low production rates the SEC of the model machine will appear high and at high production rates the SEC of the machine will appear low. This is despite the fact that most machines will continue to operate according to the model. Also plotted on the lower right is the ‘average’ of the SEC results for the model system. The average SEC is not representative of the system and any system behaving as predicted by the model, such as any plastics processing method, must be corrected for production rate to produce meaningful results. Therefore, any assessment or comparison of the energy efficiency of any production machine must take the production rate into account to be relevant in any way.

• 1. Tangram Technology Ltd., Internal data from 330 injection moulding machines (291 hydraulic machines and 39 all-electric or hybrid machines), 9 injection blow moulding machines, 91 extruders, 87 extrusion blow moulding machines and 25 thermoforming machines throughout the world.

Being green can also be profitable. As with sites, at the machine level, running plastics processing machinery harder increases the energy efficiency of the machine.

Production rate versus power (model machine system) 100 Power = 1.5 x (Production rate) + 25

90 80 70 Power (kW)

As with process dependency, it will come as no surprise that the energy use at the machine level for any plastics processing method is extremely rate-dependent due to the fixed size of any machine base load. As with sites, it is possible to set up a model production machine with a total load (kW) consisting of a base load and a process load that is directly proportional to the production rate (however defined), i.e.,

60 50 40 30 20 10 0 0

10

20 30 Production rate (kg/h)

40

50

Model system of machine base and process loads As with sites, a model machine system can be set up with a total load consisting of a base load and a process load that is directly proportional to the production rate, i.e., Total load = A × Production rate + B. This gives a total load versus production rate graph as shown. SEC versus production rate (model machine system) 30 Model machine data Average machine SEC

25

SEC = 25 x (Production rate)-1 + 1.5 SEC (kWh/kg)

Production rate dependency

There is no conflict of interest.

20

15

10

5

0 0

10

20 30 Production rate (kg/h)

40

50

SEC for the model system versus production rate The SEC for the model system can be calculated for varying production rates and this gives the plot as shown above. The effect of the base load on the apparent SEC of the model is dramatic. Chapter 2 – Energy benchmarking

67

2.18

External machine benchmarking – injection moulding

The benchmarking process Curves for machine SEC versus production rate for injection moulding have been generated from data from 291 hydraulic machines and 39 all-electric/ hybrid machines.1 This was done by the following method: • Monitoring the machine to determine the average power (kW) drawn. This is best calculated over a specific number of cycles to avoid measuring between the cycles or over a long time provided the machine operates continuously over the measurement time. • Measuring the shot weight per cycle (this

must include any sprues and runners as these have also been through the process) and using the cycle time or the measurement time to calculate the production rate (kg/h). • Plotting the average power (kW) versus the production rate (kg/h) to give the graph shown on the upper right. • Fitting the data with a linear line of best

fit to find the coefficients for the power graph of the form: Power = A × Production rate + B. • Using the coefficients from the power graph to create the benchmark SEC curve of the form: Machine SEC (kWh/kg) = B × (Production rate)−1 + A. This is the benchmark SEC curve shown on the lower right. This corrects the predicted SEC for production rate on injection moulding machines. This process has been carried out for both hydraulic and all-electric/hybrid machines because they are fundamentally different in energy terms. It is now possible for an injection moulding site to benchmark their individual machine/tool combinations against other typical machines/tool combinations. This can be done by: • Calculating the average machine production rate (kg/h). • Finding the predicted machine SEC from the relevant benchmark SEC curve (hydraulic or all-electric/hybrid) at the specific production rate. • Calculating the actual machine SEC

68

from the total electricity use (kWh)/total material processed (kg). • Comparing the actual machine SEC at

the given production rate with the SEC benchmark curve for the relevant machine type.

These are machine SEC data and take no account of the energy used by the services provided to the process.

Sites can now benchmark their machine/ tool energy performance relative to the average performance of the sample machine/tool combinations.

Cautionary notes Several points should be noted with regard to this analysis: • The benchmark machine SEC is an

average value and some machine/tool combinations have a considerably lower machine SEC, particularly in the area of lower production rates. • Achieving the benchmark machine SEC is not a sign of good practice, only a sign of average practice. • The machines used at any site will vary in size/clamp force but the method does not take this into account and appears reasonably consistent without any reference to the absolute machine size. • A large degree of the scatter in the curve is due to differing levels of machine utilisation. • The monitored machines are production machines and the results will be different from manufacturers’ results which will have been optimised.

Benchmarking any process must take into account the fixed loads of the process.

Energy rating of IMMs? The benchmarking data can be used for existing machines but how can a new machine be assessed? Euromap (www.euromap.org) introduced a rating scheme for new IMMs in January 2013. This rates IMMs by considering the effect of the screw diameter. This is an approximate equivalent of the production rate but this is not as relevant as directly measuring the absolute production rate. Industry needs a rating method but there is more work to be done to validate this approach for IMMs (see Section 5.14). • 1. Tangram Technology Ltd.: Internal data from 330 injection moulding machines throughout the world (291 hydraulic machines and 39 all-electric/hybrid machines).

Want to submit your data? Sites are invited to submit their machine data to Tangram for inclusion in the benchmarking process. This is confidential and you will get feedback. See Appendix 2 for details of how to submit machine data.

Chapter 2 – Energy benchmarking

Average machine power for injection moulding (Hydraulic + All-electric/hybrid) 200 Hydraulic machines All-electric/hybrid machines

kW = 0.75 x Production rate + 14.89 R2 = 0.7107 Sample size 291 hydraulic machines

Average power (kW)

150

100

50 kW = 0.62 x Production rate + 4.10 R2 = 0.8121 Sample size: 39 all-electric/hybrid machines 0 0

50

100 Production rate (kg/h)

150

200

Machine power graph for injection moulding1 The power graphs for both hydraulic and all-electric/hybrid machines match the model in form and show that for injection moulding the model is valid (R2 = 0.7107 for hydraulic machines and 0.8121 for all-electric /hybrid machines). Machine SEC for injection moulding (Hydraulic + All-electric/hybrid) 4.0

Hydraulic machines: –

SEC = 14.89 x (Production rate) 1 + 0.75 Sample size: 229 machines. All-electric/hybrid machines: SEC = 4.10 x (Production rate)–1 + 0.62 Sample size: 39 machines.

SEC (kWh/kg)

3.0

2.0

1.0

0.0 0

50

100

150

200

Production rate (kg/h)

Benchmark machine SEC for injection moulding1 The machine SEC for injection moulding must be corrected for the production rate (kg/h) but the curve then allows external benchmarking of a machine against other machines around the world. It is essential to choose the correct curve as hydraulic and all-electric/hybrid machines are fundamentally different. Chapter 2 – Energy benchmarking

69

2.19

External machine benchmarking – injection blow moulding

The benchmarking process A benchmarking curve for machine SEC versus production rate for injection blow moulding has been generated from data from nine injection blow moulding machines and tool combinations.1 It should be noted that these data are for the integrated injection blow process. They do not cover Injection Stretch Blow Moulding (ISBM), which has pre-form moulding and later blowing. This was done by the same method as for injection moulding to produce the coefficients of the power graph: Power = A × Production rate + B. (see on the upper right). These coefficients were used to create the SEC benchmark curve of the form: Machine SEC (kWh/kg) = B × (Production rate)−1 + A. This is the benchmark SEC curve shown on the lower right. This corrects the predicted SEC for production rate on injection blow moulding machines. It is now possible for injection blow moulding sites to benchmark their individual machine/tool combinations against other typical machines/tool combinations. This can be done by: • Calculating the average machine production rate. • Finding the predicted machine SEC from the SEC benchmark curve at the specific production rate.

should therefore use care in assessing machine performance using this benchmark. • The machine SEC benchmark curve is an average value and some machine/tool combinations have a considerably lower machine SEC, particularly in the area of lower production rates. • Achieving the machine SEC benchmark is not a sign of good practice, only a sign of average practice. • The machines used at any site will vary in size but the method does not take this into account and appears reasonably consistent without any reference to the absolute machine size.

These are machine SEC data and take no account of the energy used by the services provided to the process.

• The machines monitored were all

standard hydraulic machines; no ‘allelectric machine’ data have been used for injection blow moulding as no machines had been surveyed at the time of writing. All-electric machines are fundamentally different and similar data for all-electric machines are not yet available. • A large degree of the scatter in the curve is may be due to differing levels of machine utilisation but the number of data points is low and the correlation coefficient is also low. More reliable data are needed to verify the benchmark curve.

• Calculating the actual machine SEC

from the total electricity use (kWh)/total material processed (kg). • Comparing the actual machine SEC at

Want to submit your data?

the given production rate with the prediction from the machine SEC benchmark curve. Sites can now benchmark their machine/ tool energy performance relative to the average performance of the nine sample machine/tool combinations.

Sites are invited to submit their machine data to Tangram for inclusion in the benchmarking process. This is confidential and you will get feedback.

Cautionary notes Several points should be noted with regard to this analysis: • The lack of a substantial number of test

results makes the data less reliable than in the case of injection moulding. Sites 70

• 1. Tangram Technology Ltd.: Internal data from 9 injection blow moulding machines throughout the world.

See Appendix 2 for details of how to submit machine data.

Chapter 2 – Energy benchmarking

Average machine power for injection blow moulding 80

70

Average power (kW)

60

50

40

kW = 0.55 x Production rate + 26.48 R2 = 0.3801 Sample size: 9 machines

30

20

10

0 0

20

40

60

80

Production rate (kg/h)

Machine power graph for injection blow moulding1 The power graph for injection blow moulding machines suffers from a lack of data and is presented for information only at this stage. The low correlation coefficient (R2 = 0.3801) indicates considerable scatter in the results. Machine SEC for injection blow moulding 5

–1

SEC = 26.48 x (Production rate) Sample size: 9 machines

SEC (kWh/kg)

4

+ 0.55

3

2

1

0 0

20

40

60

80

Production rate (kg/h)

Benchmark machine SEC for injection blow moulding1 The machine SEC for injection blow moulding must be corrected for the production rate (kg/h) but the lack of data points may make the benchmark curve unreliable for external benchmarking.

Chapter 2 – Energy benchmarking

71

2.20

External machine benchmarking – extrusion

The benchmarking process A similar analysis to that carried out for injection moulding machines is possible for extruders. This has been done for 91 extruders throughout the world to produce an SEC benchmark curve for machine SEC (kWh/kg) versus production rate for extrusion.1 In the case of extrusion, the power drawn is substantially constant as there is no cycle to consider and output rate in kg/h is also substantially easier to evaluate. The same method as for injection moulding was used to produce the coefficients of the power graph: Power = A × Production rate + B. (see on the upper right). These coefficients were then used to create the benchmark SEC curve of the form: Machine SEC (kWh/kg) = B × (Production rate)−1 + A. This is the SEC benchmark curve shown on the lower right. This corrects the predicted SEC for production rate on extrusion machines. It is now possible for an extrusion site to benchmark individual machine/tool combinations against other typical machines/tool combinations. This can be done by: • Calculating the average machine

production rate. • Finding the predicted machine SEC from the SEC benchmark curve at the specific production rate. • Calculating the actual machine SEC from the total electricity use (kWh)/total material processed (kg). • Comparing the actual machine SEC at the given production rate with the prediction from the machine SEC benchmark curve. Sites can now benchmark their machine/ tool energy performance relative to the average performance of the 91 sample machine/tool combinations.

combinations have a considerably lower machine SEC, particularly in the area of lower production rates. • Achieving the machine SEC benchmark

is not a sign of good practice, only a sign of average practice. • The machines used at any site will generally be of varying sizes (barrel diameter and L/D ratio) and types (single screw and twin screw) but the method does not take this into account and appears reasonably consistent without any reference to the specific machine details. • A large degree of the scatter seen in the

data points of the operating curve is due to machines being operated at differing levels of production efficiency, i.e., poor or good overall machine utilisation. • The polymer processed would be expected to have some effect but the available data shows that this has little effect in the overall assessment. Dr Peter Cox2 has carried out over 60 tests on a variety of materials (PE-LD, PE-HD and PS) on a variety of extruder screw types (general purpose, mixing pin, barrier mixing and shallow). His results show some slight variations in materials and screw geometry but these are generally within the experimental error of the tests.

Want to submit your data?

Several points should be noted with regard to this analysis:

• 1. Tangram Technology Ltd.: Internal data from 91 extruders throughout the world.

• The machine SEC benchmark curve is

• 2. Dr Peter Cox: Private communication (2009).

72

Benchmarking any process must take into account the fixed loads of the process.

These benchmark data are not only relevant for profile extrusion but for any extrusion process provided there are no substantial downstream operations carried out, e.g., thermoforming.

Cautionary notes

an average value and some machine/tool

These are machine SEC data and take no account of the energy used by the services provided to the process.

Sites are invited to submit their data to Tangram for inclusion in the benchmarking process. This is confidential and you will get feedback. See Appendix 2 for details of how to submit machine data.

Chapter 2 – Energy benchmarking

Average machine power for extrusion 600

500

Average power (kW)

400

300

200

kW = 0.38 x Production rate + 2.31 R2 = 0.8728 Sample size: 91 machines

100

0 0

200

400

600 800 Production rate (kg/h)

1000

1200

1400

Machine power graph for extrusion1 The average power versus the production rate shows that extruders also fit a model of a fixed base load plus a variable process load with a good correlation coefficient. The high correlation coefficient (R2 = 0.8728) and the low base load (2.31 kW) demonstrate the inherent energy efficiency of extrusion. Machine SEC for extrusion 3.0

–1

SEC = 2.31 x (Production rate) Sample size: 91 machines

SEC (kWh/kg)

2.5

+ 0.38

2.0

1.5

1.0

0.5

0.0 0

200

400

600 800 Production rate (kg/h)

1000

1200

1400

Benchmark machine SEC for extrusion1 The machine SEC for extrusion must be corrected for the production rate (kg/h) but the operating curve then allows external benchmarking of a machine against other machines around the world.

Chapter 2 – Energy benchmarking

73

2.21

External machine benchmarking – extrusion blow moulding

The benchmarking process A similar analysis to that carried out for extrusion machines is possible for extrusion blow moulding machines. This has been done for 87 extrusion blow moulding machines throughout the world to produce an SEC benchmark curve for machine SEC (kWh/kg) versus production rate for extrusion blow moulding.1 The same method as for injection moulding was used to produce the coefficients of the power graph: Power = A × Production rate + B. (see upper right). These coefficients were then used to create an SEC benchmark curve of the form: Machine SEC (kWh/kg) = B × (Production rate)−1 + A. This is the SEC benchmark curve shown on the lower right. This corrects the predicted SEC for production rate on extrusion blow moulding machines. It is now possible for an extrusion blow moulding site to benchmark individual machine/tool combinations against other typical machines/tool combinations. This can be done by: • Calculating the average machine production rate.

• Achieving the machine SEC benchmark

is not a sign of good practice, only a sign of average practice. • The machines used at any site will generally be of varying sizes (barrel diameter and L/D ratio) and types but the method does not take this into account and appears reasonably consistent without any reference to the specific machine details. • A large degree of the scatter seen in the data points of the operating curve is due to machines being operated at differing levels of production efficiency, i.e., poor or good overall machine utilisation.

This is machine SEC data and takes no account of the energy used by the services provided to the process.

• The polymer processed would be

expected to have some effect but the available data show that this has little effect in the overall assessment.

Benchmarking any process must take into account the fixed loads of the process.

• Finding the predicted machine SEC from

the SEC benchmark curve at the specific production rate. • Calculating the actual machine SEC from the total electricity use (kWh)/total material processed (kg). • Comparing the actual machine SEC at the given production rate with the prediction from the machine SEC benchmark curve.

Want to submit your data?

Sites can now benchmark their machine/ tool energy performance relative to the average performance of the 87 sample machine/tool combinations.

Sites are invited to submit their data to Tangram for inclusion in the benchmarking process. This is confidential and you will get feedback.

Cautionary notes Several points should be noted with regard to this analysis: • The machine SEC benchmark is an

average value and some machine/tool combinations have a considerably lower machine SEC, particularly in the area of lower production rates. 74

• 1. Tangram Technology Ltd.: Internal data from 87 extrusion blow moulding machines throughout the world.

See Appendix 2 for details of how to submit machine data.

Chapter 2 – Energy benchmarking

Average machine power for extrusion blow moulding 180

160

140

Average power (kW)

120

100

80

60 kW = 0.27 x Production rate + 30.32 R2 = 0.6921 Sample size: 87 machines

40

20

0 0

50

100

150

200 250 Production rate (kg/h)

300

350

400

Machine power graph for extrusion blow moulding1 The average power versus the production rate shows that extrusion blow moulding machines also fit a model of a fixed base load plus a variable process load with a reasonable correlation coefficient. The high base load is a function of the blowing step as a result of the losses in the hydraulic system. Machine SEC for extrusion blow moulding 5

−1

SEC = 30.32 x (Production rate) Sample size: 87 machines

SEC (kWh/kg)

4

+ 0.27

3

2

1

0 0

50

100

150

200 Production rate (kg/h)

250

300

350

400

Benchmark machine SEC for extrusion blow moulding1 The machine SEC for extrusion blow moulding must be corrected for the production rate (kg/h) but the curve then allows external benchmarking of a machine against other machines around the world.

Chapter 2 – Energy benchmarking

75

2.22

External machine benchmarking – thermoforming

The benchmarking process A similar analysis to that carried out for injection moulding machines is possible for thermoforming machines. This has been done for 25 thermoforming machines throughout the world to produce a machine SEC benchmark curve for machine SEC (kWh/kg) versus production rate for thermoforming.1 The same method as for injection moulding was used to produce the coefficients of the power graph: Power = A × Production rate + B. (see upper right). These coefficients were then used to create the benchmark SEC curve of the form: Machine SEC (kWh/kg) = B × (Production rate)−1 + A. This is the SEC benchmark curve shown on the lower right. This corrects the predicted SEC for production rate on thermoforming machines. It is now possible for a thermoforming site to benchmark individual machine/tool combinations against other typical machines/tool combinations. This can be done by: • Calculating the average machine production rate. • Finding the predicted machine SEC from the SEC benchmark curve at the specific production rate. • Calculating the actual machine SEC from the total electricity use (kWh)/total material processed (kg). • Comparing the actual machine SEC at

the given production rate with the prediction from the machine SEC benchmark curve. Sites can now benchmark their machine/ tool energy performance relative to the average performance of the 25 sample machine/tool combinations.

gauge thermoforming (vacuum forming). These results show good consistency whatever the gauge of sheet being formed. • Some of the discrepancy in the data

points (low R2 value) is due to the inclusion of thermoformers where the thermoformer is physically linked to the extruder by the sheet, i.e., it is not fed from separate roll stock. In these cases the speed of the thermoformer operation is dictated by the output rate of the extruder and some inefficiencies can result. • The machine SEC benchmark is an

average value and some machine/tool combinations have a considerably lower machine SEC, particularly in the area of lower production rates. • Achieving the machine SEC benchmark is not a sign of good practice, only a sign of average practice. • The machines used at any site will generally be of varying sizes and heater types but the method does not take this into account and appears reasonably consistent without any reference to the specific machine details. • A large degree of the scatter seen in the data points of the operating curve is due to machines being operated at differing levels of production efficiency, i.e., poor or good overall machine utilisation. This is particularly true for several data points where the machine showed obvious utilisation issues.

• The data are for thin gauge and thick

76

Benchmarking any process must take into account the fixed loads of the process.

• The polymer processed would be

expected to have some effect but the available data shows that this has little effect in the overall assessment. Want to submit your data? Sites are invited to submit their data to Tangram for inclusion in the benchmarking process. This is confidential and you will get feedback.

Cautionary notes Several points should be noted with regard to this analysis: • The data are for the heating and thermoforming machine alone, i.e., they do not include any associated extrusion operation.

These are machine SEC data and take no account of the energy used by the services provided to the process.

• 1. Tangram Technology Ltd.: Internal data from 25 thermoformers throughout the world.

See Appendix 2 for details of how to submit machine data.

Chapter 2 – Energy benchmarking

Machine power for thermoforming 70

60

Power (kW)

50

40

30

20 kW = 0.0091 x Production rate + 33.86 R2 = 0.01600 Sample size: 25 machines

10

0 0

100

200

300

400

500

600

700

Production rate (kg/h)

Machine power graph for thermoforming1 The average power versus the production rate shows that thermoforming machines also fit a model of a fixed base load plus a variable process load but the correlation coefficient is very low. The high base load is a function of losses in the heating stage before thermoforming. Machine SEC for thermoforming 1.0 0.9

−1

SEC = 33.86 x (Production rate) Sample size: 25 machines

+ 0.0091

0.8

SEC (kWh/kg)

0.7 0.6 0.5 0.4 0.3 0.2 0.1 0.0 0

100

200

300

400

500

600

700

Production rate (kg/h)

Benchmark machine SEC for thermoforming1 The machine SEC for thermoforming must be corrected for the production rate (kg/h) but the curve then allows external benchmarking of a machine against other machines around the world.

Chapter 2 – Energy benchmarking

77

Key tips • Starting out in energy management

improvements.

requires both measurements and an understanding of the process. • Most of the initial measurements are very simple to obtain and can come from the standard accounts package. • The measurements need very little treatment to give vital information on the site and process operations. • The measurements give easy access to the key numbers from the Performance Characteristic Line (PCL) which reveals both the base load of the site and gives a good estimate of the relevant process load.

• The process load depends on the type of

• Energy use is not an uncontrolled and

efficiency measure will lead to inaccurate conclusions due to the effect of production volume changes. • The PCL can be used to internally benchmark a site against previous performance. • Deviations from standard and CUSUM treatment of data gives valuable insights into system changes and the effect of these on the energy use. • The PCL can be used to provide an accurate model for energy budgeting into the future. • Where energy use is driven by more than a single ‘driver’, it is possible to use multi-variate analysis to separate the effects of the drivers.

unknowable variable – it is directly related to the production volume of the site. • A low correlation coefficient (R2) indicates either data or management issues. For management issues, it indicates inconsistency in management practice and this can make it difficult to implement and control changes. • A high correlation coefficient (R2)

indicates consistency in management practice, it does not indicate good energy management but it does indicate that changes will be controlled. • The base load of a site is the ‘energy overhead’ and will typically range from 20–40% of the total load of the site. • A low base load generally indicates good management control of energy at the site. • A high base load generally indicates poor

management control of energy at the site. • Reducing the base load is easy to carry out, low-cost and has rapid payback. • Savings in the base load are very

profitable because the base load is largely a dead weight that is unrelated to production output. • The process load of a site is the energy needed to actually run the process (services and machines).

process being used at the site. • Whilst it is normal to use kg as a

reference for the production volume, it is also possible to use ‘parts’ or any other convenient measure of production. The kg value used should always be the kg processed (through the nozzles) and not the amount of material sent to the warehouse. • Weekly data collection gives faster feedback to production departments on how to improve. • Simply recording kWh/kg as a process

• It is possible to set up model systems for

both sites and machines to show how the energy usage of both sites and machines will vary with production rate. • Model systems open the way to effective

external benchmarking of both sites and machines. • External site benchmarking is possible using industry data but the results are only relevant for a specific process and production rate. • External machine benchmarking is possible using industry data but the results are only relevant for a specific process and production rate.

• Reducing the process load is more

difficult to achieve because it generally (but not always) requires more fundamental and expensive process 78

Chapter 2 – Energy benchmarking

Chapter 3 Targeting and controlling energy costs

The first two chapters of this book dealt with the management aspects of setting up an energy management system and benchmarking the current operations to identify areas for improvement and change. This chapter looks at understanding energy use and using some simple tools to assess where energy is actually being used at a site. This is not always a trivial question with an obvious answer. Assessing where use occurs is a vital first step in energy reduction efforts. We then look at the basics of integrating energy management into the management accounts of a site and how this can be achieved with relatively little effort. Integration into the accounts is an essential in treating energy management as simply another aspect of responsibly managing the company and not as a special one-off effort that can be safely ignored after a decent interval. We also look at monitoring and targeting (M&T) as an essential technique in controlling energy costs. This builds on the information obtained by benchmarking (see Chapter 2) and shows how simple information can be used to set achievable and realistic targets for energy use reduction. Targets are, by themselves, of limited use unless there is both reporting and accountability for achievement of the targets and we look at the basics of energy reporting systems that concisely report progress towards reducing the use and cost of energy. We also look at the methods of applying

for capital expenditure funds and how these can be used to highlight the on-going benefits of investing in energy management and energy-efficient technology. Involving the finance department and making the best use of their resources is a key to effective energy management. They can be a positive force for good but they need to understand that this is not only about being ‘green’, it is also about increasing profits. Finance departments also want to know that funds invested have been effective and this requires verification of the savings through measurement. None of this will happen unless it is driven by an ‘Energy Manager’ and the last part of this chapter considers what an Energy Manager needs to do to deliver costeffective energy management.

If it cannot be measured then it cannot be controlled. If it is not being measured then it is not being controlled.

Energy Management in Plastics Processing https://doi.org/10.1016/B978-0-08-102507-9.50003-9, Copyright © 2018 Elsevier Ltd. All rights reserved.

79

Understanding energy use – the basics

Before starting energy management and reducing use, it is necessary to understand the fundamentals of the use, i.e., where, when, why and how much energy is being used. This information provides the essential signposts for cost-effective energy efficiency improvements.

How much? The first step is to get a broad idea how much energy is costing the site. The simple measurements required for the creation of the PCL (see Chapter 2) can be easily extended to give a site valuable information on how much energy is being 80

9% 8% 7% 6% 5% 4% 3% 2% 1%

t Se pt em be r O ct ob er No ve m be r De ce m be r

Ju ly

Au gu s

Ju ne

ay M

Ap ril

0%

ar ch

The opportunity to easily reduce overall costs by between 1 and 3% deserves more attention than this and the involvement and integration of the Finance function in the process is vital to achieving real progress. This is a business problem and not simply a Production problem. Finance needs to take an active role in energy management and can assist Production by providing the essential targets and controls that are necessary to start to manage the use and therefore the costs. Energy management is often viewed as a complex and expensive exercise that is divorced from the mainstream management activities. This view is fundamentally flawed; energy management is simply part of the overall management of the business. It is management of a business resource that costs the site money and should be carried out as with any other management activity.

Energy cost as % of sales (injection moulding)

M

Energy costs are almost always treated as somebody else’s problem!

Energy management is the last great unexplored frontier of cost management.

10%

ry Fe br ua ry

Industry generally regards energy as an overhead and therefore as a fixed cost. This is untrue and Chapter 2 shows very clearly that energy is both a variable and a controllable cost. At many sites, the energy bill is sent directly to the Finance function, it is not critically questioned and is passed for payment without reference to the Production function. If it is passed to the Production function it is often given only cursory consideration and is also signed off with little critical examination.

used. This will allow assessment of the spend relative to production output and other cost variables. This then gives a site an idea of the magnitude of the efforts that should be spent on energy

Energy cost as % of sales

Reducing energy costs – the first steps

Ja nu a

3.1

Month

How much? Energy cost as a % of sales Energy cost data are easy to obtain and give a view of the magnitude of the efforts that should be expended in controlling the costs. The efforts expended should be in proportion to the costs involved.

Total energy use General services

Offices

Compressed air

3%

8% Processes

Chilled water

Process

6%

10%

Process

Plastics processing

Assembly

67%

77%

12%

Lighting

Lighting

4%

2%

Where? Site energy use map A simple site energy map (obviously more detailed than this example) will reveal areas of high energy use and allow targeting of improvement efforts in the most rewarding areas. The relative use values need only be estimates at this stage. Chapter 3 – Targeting and controlling energy costs

You don’t need a sophisticated automated system at the start. A simple picture of energy use based on easily available data can be very useful.

• Tip – Why are you paying to use so

much electricity in lunch breaks, production run changes, overnight, and weekends? • Tip – How much energy is being used in

non-productive periods? • Tip – Where is energy being used in non-

productive periods?

The minimum required The information listed above is the minimum required information but it can be used with the PCL (see Chapter 2) to start to integrate energy management into the full business accounting package. Only by this method will we start to drive energy management by the most effective means in any business – accounting and money.

Collecting the information should not be used as an excuse to ignore ‘easy wins’. Cheap and quick remedies should be targeted quickly. Take the money and run!

Half-hour consumption data for a single week (starting Wednesday) 800

600

Sunday

Saturday

700

500 400

200 100

Tuesday

300 Monday

The third basic step is to understand when energy is being used at the site. Energy use and costs are time-dependent and the total demand plotted versus time will give information on unexpected demand patterns (particularly when the site is not producing) and on how to reduce the timedependent energy costs. The data for this are generally easily available for free from the electricity supplier as part of their billing arrangements (see Sections 4.5 and 4.6). Interval data need to be examined for unusual peak variations from day to day

Concerted action to ‘turn off’ over the weekend reduced consumption and loads over the weekend by around 90% and saved £65,000 per year with no effect on production.

Friday

When?

• Compressors running just feed leaks.

Thursday

The second step is to determine where energy is being used on the site. The main energy consumption areas in plastics processing have already been briefly discussed (see Section 1.3) but a more detailed evaluation of the use of energy on a site is needed for effective targeting of action. A simple site energy map will show broadly where energy is being used. This is generally easily prepared by the site electrician and a typical map is shown on the lower left. Initially the use values can be estimates, the map only needs to be accurate enough to reflect the use of resources and initial targeting of efforts. At a later stage, the energy map can be refined and converted to a spreadsheet (see Section 3.2) to give further details and to identify and quantify detailed use. This can be used to evaluate the potential for sub-metering and the use of this to assign full management responsibility for energy use – area managers are responsible for the resources under their control (machines, materials and men). Energy is simply another resource that they should control – it is not a new responsibility, simply a new priority.

Energy is a variable and controllable cost.

• Heaters and air conditioning operating.

Wednesday

Where?

Do you have any of this vital information?

and particularly examined for energy use when there is no production. The site in the example shown below had no production on Saturday and Sunday but the average demand at this time is in the region of 30% of the normal production loads (this is good compared to some sites). Typical contributors to this weekend load were: • Machines left on for no reason.

kWh used in half-hour interval

management. Efforts at managing and controlling any cost should be related to the size of the cost and it is essential to keep the efforts in proportion. This is not a crusade, it is good management and the simple act of measuring energy costs will provide an estimate of the time that should be spent on controlling them. A general rule is that the potential energy savings are in the region of 30% of the total energy spend. Assuming a payback time of 1 year then the energy cost should give a rough idea of the potential investment ‘fund’ that should be made available for energy management efforts.

0 1

48

95

142

189

236

283

330

Half-hour reference number (48 per day)

When? Plotting site energy use Plotting the energy use versus time shows the use pattern of the site. Look for energy being used when there is no production and for unexplained peaks or troughs. In this example, there is no production on Saturday or Sunday so why is energy being used?

Chapter 3 – Targeting and controlling energy costs

81

3.2

Understanding energy use – the site energy map

Putting numbers on energy use At many sites, there is no actual submetering (see Section 4.7) and therefore little actual knowledge of the real energy use areas. A simple site energy map (see Section 3.1) will visually show where energy is being used but further detail can be provided by an energy map based on a spreadsheet. A typical example of an energy spreadsheet/map for an injection moulding site is shown on the right. The values in this map can be calculated by: • Determine the ‘nameplate’ values for the size of motors in the main services, main processes and other major energy consumption areas and counting the number and size of tubes/lamps used for lighting various areas. This will give the ‘nominal load’ of each area of use. • Apply a ‘duty’ factor to each load that is related to the amount of the nominal load that is actually needed, i.e., an injection moulding machine may have a motor of 45 kW but the actual average power drawn will most often be in the region of 45% of this value or ≈ 20 kW. • The product of these two values will give the ‘actual load’ of the service or process (this can be checked by the results of physical monitoring or sub-metering). • Calculate or determine the hours of use for each service or process. For services this will generally be the operational hours of the site and for processes this will generally be the operational hours of the process. • The product of the actual load and the hours will give a value for the kWh used by the service or process over a complete year.

• Tip – Large discrepancies generally

indicate services or processes that have been overlooked or loadings that have been miscalculated. • Tip – Sites should use actual results for

The estimated data in the energy map should be reinforced with real measurements where possible.

kW where possible. These can be obtained from portable monitoring equipment (see Section 8.3) or from submetering (see Section 4.7). • Tip – There is no consideration of

transformer losses in this method but this can be added if required (see Section 4.3). The energy map can be converted into an energy use distribution chart as shown in the chart below for a typical injection moulding site. Most sites should have a breakdown similar to this.

A sample energy map spreadsheet is available at www.tangram.co. uk/energy for modification.

• Tip – The percentages for individual

sites will depend on the process used, e.g., compressed air use is higher at blow moulding sites, cooling is higher at extrusion sites and sites with a large amount of assembly will use more compressed air. However, despite these variations, the ratios will be approximately correct for most sites. • Tip – The energy map and spreadsheet

provide information on where efforts should be targeted to achieve the best and quickest results.

The energy map spreadsheet starts to provide the real information on use and allows good estimates of potential savings from projects.

Site 7% Services 25%

• The total map value for the energy use of

the site can then be summed and subjected to a ‘reality check’ with the energy use of the site from billing data. For the sample injection moulding site the energy spreadsheet predicts a total electricity use of 7,463,233 kWh/year, a value that is 0.52% more than the actual use of 7,424,757 kWh. This map exercise generally takes less than 4 hours for a typical site where the information is readily available. 82

Plastics processing 68%

The site energy map divided into use areas (typical) The information from the site energy map can be used to see the areas of highest energy use at a site. Typical results for a plastics processing site are shown above. Most sites should have a breakdown similar to these values. Chapter 3 – Targeting and controlling energy costs

Full year

Nominal load (kW)

Duty (%)

Actual load (kW)

Hours

kWh/ year

Total (kWh/year)

78 10 1.5

100% 80% 80%

78 8 1.2

8760 8760 8760

683,280 70,080 10,512

763,872

5 3.7 22 7.5 5 18.6 6

100% 100% 100% 100% 100% 100% 100%

5 3.7 22 7.5 5 18.6 6

8760 8760 8760 8760 8760 8760 8760

43,800 32,412 192,720 65,700 43,800 162,936 52,560

593,928

92 22 3.7

35% 100% 100%

32.2 22 3.7

8760 8760 8760

282,072 192,720 32,412

507,204

Services Compressed air Compressor 1 Drier Extract fans Cooling water Tower fan (Tower 1) Pump to chiller Pump to process Pump to Tower 1 Tower fan (Tower 2) Pump to process Pump to Tower 2 Chilled water Chiller 1 System pumps (1 x 22 kW) Process pumps (1 x 3.7 kW) Services sub-total

1,865,004

Injection moulding Injection moulding machines Main motor 1x Heaters & MTC Main motor 8x Heaters & MTC Main motor 19x Heaters & MTC (4 x 5 kW) Main motor 12x Heaters & MTC (4 x 5 kW) Main motor 8x Heaters & MTC (4 x 5 kW) Main motor 1x Heaters & MTC (5 x 5 kW) Main motor 2x Heaters & MTC (5 x 5 kW) Main motor 3x Heaters & MTC (5 x 5 kW) Moulding sub-total

45 25.4 37 24.3 30 20 22 10.6 15 7.4 11 5.8 6.3 0.9 4.6 2.7

45% 10% 45% 10% 45% 10% 45% 10% 45% 10% 45% 10% 45% 10% 45% 10%

20.25 2.54 16.65 2.43 13.5 2 9.9 1.06 6.75 0.74 4.95 0.58 2.835 0.09 2.07 0.27

7488 7488 7488 7488 7488 7488 7488 7488

151,632 19,020 124,675 18,196 101,088 14,976 74,131 7,937 50,544 5,541 37,066 4,343 21,228 674 15,500 2,022

170,652 1,142,968 2,205,216 984,822 448,681 41,409 43,805 52,566 5,090,118

Site Offices Main office (first floor) Other offices Factory (all) Air conditioning A/C 1 A/C 2 Workshop A/C Site sub-total

30 15 25

45% 45% 100%

13.5 6.75 25

2982 2982 2982

40,257 20,129 74,550

134,936

46 46 14.5

40% 40% 40%

18.4 18.4 5.8

8760 8760 8760

161,184 161,184 50,808

373,176

Global total Reality check

Map value Actual value for year (from billing data) Difference

508,112 7,463,233 7,463,233 7,424,757 -0.52%

The site energy map converted to a spreadsheet The site energy map provides the basic information to quantify energy in various areas of a site. The map should always be subject to a ‘reality check’ against the actual site energy use. Chapter 3 – Targeting and controlling energy costs

83

3.3

Integrating energy into the accounts – monitoring and targeting

Accounting – a key function The potential energy savings from simple actions are known to be large but when sites attempt to reduce energy use the projects approved are often far fewer than those known to be possible and energy management does not deliver the potential results because projects are not approved. One of the major reasons is that energy management is seen simply as a ‘technology fix’ that has little to do with the financial aspects of the site. The activities are seen as involving the technical and production areas but are not rewarding enough for the other staff to get involved. Energy management is somehow seen as a ‘sideshow’ or as a ‘minority sport’. Nothing could be further from the truth and some of the most effective energy management efforts can come directly from the accounting function. So why is it that the accounting function pays little attention to energy efficiency and the positive benefits?

increasing energy efficiency. The efforts, risks and rewards of improving profits via energy management are entirely internal and within the control of the site. Increasing profits by 50% through the conventional external approaches means increasing sales by 50%, with the associated concerns of increasing production capacity and increasing risk.

Accountants can add value to a business by using their analytical skills to improve energy efficiency.

The standard procedures At many sites there are few controls on the energy spend. The energy bills are received by the accounts department, regarded as a fixed cost and paid. The people who control the expenditure (the Production function) rarely see the bills and in any case also regard them as part of the ‘cost of doing business’. This separation of authority and responsibility makes management and control of the energy spend nearly impossible and reduces the effectiveness of any efforts to reduce the costs. The spend

Nobody needs approval to spend money on energy. Everybody needs approval to spend money on saving energy. Does anybody see a fundamental disconnect here?

The magnitude of the costs The approximate magnitude of the cost of energy in plastics processing is shown on the right. The exact breakdown will vary with the site considered but for many products the cost of energy is already of the same magnitude as the cost of direct labour. For mass-produced volume parts the energy cost represents around 5.8% of the product cost and for complex technical parts it represents around 5.3% of the product cost. Good energy management can reduce these costs by up to 30% and therefore reduce the overall product cost by up to 1.5%. If the profit margin is low then the cost of energy is almost certainly higher than the profits of the site. A reduction in internal costs such as the cost of energy will translate into a significant increase in profits for no extra sales. This is typically 25% but can be up to 50% in some cases. Any internal low-risk activity that can raise profits by up to 50% should certainly attract attention at any site. Many sites do not hesitate to spend money on trying to increase sales but fail to see the benefits of spending money on increasing profits by 84

A general cost breakdown for plastics processing The detailed breakdown will vary with the site but energy costs are already of the same magnitude as the labour costs. Note: The labour element is the direct labour cost only and does not include support or indirect labour. Chapter 3 – Targeting and controlling energy costs

to reduce the costs is allocated to the maintenance department but the benefits of the spend are not seen by that department and even more rarely appreciated by anybody in management. When an activity receives all the costs but none of the benefits or recognition then it is not surprising that little gets done. Chapter 2 covered the variable nature of energy use where the PCL gives a relationship of the form: Total energy use = (Production volume × SEC) + Base load Accountants are familiar with calculating the total costs for a site from the fixed and variable components, where: Total cost = (Production volume × unit variable cost) + Fixed costs Therefore the use of a similar approach for energy management should hold no surprises for most accountants.

Measuring to manage These ideas allow energy management to be integrated into the accounts as with any other cost element and accounting for energy management can be treated in the same way as other items in the accounts systems. The overall aim is to achieve cost-effective energy management and integration of energy reporting into the accounting function allows energy to take its place on the management agenda as a part of the normal management of the site. In spite of this, the majority of sites have no active energy management programme or even reporting system. They consider that it is not central to their core business and are unaware of the potential for improvement or the substantial returns that can be made through small investments in energy efficiency. This needs to change to improve profitability.

locates opportunities for reducing energy consumption and cost. At most sites, the information needed for initial M&T can be taken from the existing Management Information System (MIS) and a large proportion of the benefits can be achieved by simple analysis of existing information. Basic historic data and a spreadsheet can be used to set up a simple system to start formal M&T. Gathering data will not, in itself, provide results. The potential benefits of energy efficiency cannot be achieved by collecting large amounts of data or preparing lengthy reports. Data are meaningless without careful analysis, and reports are useless if they are not targeted at people with the authority and the will to act. For any site, the amount of M&T needs to be appropriate to the energy spend. Effective M&T may need improved metering capability for accurate cost allocation but it is always worthwhile examining existing data to get a quick start on energy management.

Data are not the same thing as information. Data are simply a collection of numbers whereas information provides the basis for management action. Sites can be awash with data and still have little real information.

• Tip – The decision is not whether to

install meters to allow a breakdown of the usage and the costs, but how many meters and where to put them (see Section 4.7).

To integrate energy into the accounting function there is a need to establish the measures that will be used to assess performance and this requires both monitoring and targeting.

Monitoring & targeting (M&T) In energy management, the concept of M&T is used to focus attention on energy consumption and the identification of cost reduction opportunities with attractive returns on investment. M&T is the collection, interpretation and reporting of information on energy use. It measures and maintains performance and Chapter 3 – Targeting and controlling energy costs

85

3.4

Data collection and analysis

Data collection Measuring costs always involves data collection but there is no point in spending more money to collect data than can be saved by the useful application of that data. It is always necessary to assess the cost–benefit balance for data collection. It is also important to recognise that goodquality data are not necessarily the same thing as highly accurate data. The need is for enough relevant information to promote action – collect only the minimum amount of data necessary to produce the relevant information. Most of the core production data are probably already being gathered for cost and production control. This can often be used with minimal changes as part of an energy M&T system and sharing data may require only simple modifications to give a basic but effective system. Production data are either related to amounts (e.g., weight, volume, number of items) or are unrelated to amounts (e.g., density, moisture content). Amount-related data is ‘additive’ and information for a week can be obtained by adding the daily data. Data unrelated to amounts are ‘non-additive’ and can sometimes be difficult to summarise and use. Despite this, it may be difficult to establish an effective M&T system without recording some ‘nonadditive’ data (e.g., it may be difficult to assess energy use if there are large variations in moisture content and the drying process uses a significant amount of energy). Other data may require specific collection for M&T (e.g., regular meter readings) and this can be collected either manually or automatically (such as the half-hour meter readings referred to in Section 4.5).

The basic data The basic data needed for energy accounting fall into three categories:

Consumption data These are the most basic data of all and are collected via the site metering and billing system. There is a common misconception that M&T requires the installation of large numbers of meters. The use of sub-meters enables accurate allocation of costs (see below) and 86

substantial progress on M&T can be made with very small numbers of low-cost meters. The cost of meters has fallen dramatically in the past few years and even the smallest site can now afford to fit a basic sub-meter arrangement that will allow the process energy requirements (generally variable) to be separated from the building and utilities requirements (generally more fixed). Sub-metering is dealt with in more detail in Section 4.7.

Study the data before developing the system.

Cost data Money is the common language of business and only by expressing energy data in cost terms can integration into the accounting function take place. Cost data come from the supplier bills and must be part of the M&T system.

Driver data These are data about the factors that influence energy consumption and can be divided into ‘activity’ and ‘condition’ drivers: • Activity drivers are those where a feature of the site activity influences energy consumption. Activity driver data can generally be gathered from internal sources. The main activity driver in plastics processing is the production volume (see Chapter 2). • Condition drivers are those where the consumption is not affected by the activity but by external conditions. Condition driver data generally need to be gathered from external sources. The main condition driver in plastics processing is the weather (which influences heating loads on the site). ‘Degree days’ (a measure of how cold it is) should be directly related to the heating required for a site (see Section 4.8). As with all accounting, no cost is totally fixed or totally variable, e.g., the base load is essentially fixed but may also be affected by the weather (a condition driver) if the heating is electrical.

Converting data to information Data have no value unless they are converted into information; the simple presentation of data is not sufficient for energy management. It is information that

Energy management can be the difference between profit and loss for a company.

Chapter 3 – Targeting and controlling energy costs

has value. Producing information requires basic skills in data analysis and the techniques are generally well known to accountants and engineers. Typical analytical techniques, in order of preference, are: • Performance Characteristic Lines – the

PCL (as used in Chapter 2) provides excellent information on the performance of the site and allows performance assessment and budgeting. • Specific Energy Consumption – the SEC (see Chapter 2) provides benchmarks that are simple, easy to calculate and straightforward to communicate but must be used with care to ensure that they are not subject to production volume effects. • Deviations – deviations are frequently

used in accounting to show deviations between actual and predicted energy performance. Whilst useful for an overview, they do not identify areas for improvement or drive improvement. • CUSUM – CUmulative SUM of variance from standard charts is one of the most powerful methods of identifying and quantifying the impact of changes in energy use (see Section 2.7 and Section 3.5). • Control charts – these are similar to the typical control charts used in SPC and can highlight deviations from planned or standard performance. • Trend lines – these graphically show the

trend in energy use (preferably downward) over time. Trend lines can be produced using ‘moving averages’ to account for driver variation. • Lines of best fit – these are useful for producing simple relationships between drivers and energy consumption to aid prediction and to understand how various drivers affect consumption.

information it is necessary to assign the costs to create ownership. When monthly accounts are prepared for any business the operational costs are directly assigned to individuals who are responsible for the performance of that section of the operation. Energy costs should be treated in the monthly accounts package in the same manner. Methods of assigning accountability vary with the existing site process but typical methods are: • Energy Accountable Centres – these make managers accountable for the energy costs of their department. This involves allocating energy costs to departments and requiring them to operate within the allocated budget and to achieve agreed targets, generally based on a PCL approach. It depends on the ability to measure local energy consumption and requires direct control of the energy consumed. • Activity-Based Costing (ABC) – this recognises that income from manufacturing is determined by the price the market will accept but that income has to cover costs. Costs are added by ‘activities’, but some activities add value and others do not. ABC identifies activities that add more cost than value. Activities may be things people do or the resources that they need to do these things. • Quality-centred M&T – this is based on the requirement within quality and environmental management systems (ISO 9000, ISO 14000) for an information system and shares information with any existing similar systems. The advantage of applying energy accounting within such systems is that it uses existing management structures and is less likely to be marginalised as an activity.

• Energy profiles – these can be produced

using supplier data to reveal changes in consumption over short time periods. They are useful for identifying shortterm variations in energy use. Recent advances in ‘data mining’ can be used to discover relationships between multiple variables and to assess their relative effects on energy use.

Assigning the costs Cost reductions only happen if somebody is made directly responsible for them and after data have been converted into Chapter 3 – Targeting and controlling energy costs

In the UK, the government produced extensive information on data collection and analysis under various programmes. These are largely unavailable now but copies can possibly be obtained via the web. Try to get copies of: • Good Practice Guide 125 – Monitoring and targeting in small and mediumsized companies. • Good Practice Guide 231 – Introducing information systems for energy management. • Good Practice Guide 200 – A strategic approach to energy and environmental management.

An excellent introduction to Energy Management Information Systems is available free from Natural Resources Canada. Get a copy of their EMIS handbook from www.nrcan.gc.ca/ energy/efficiency/ industry/ cipec/5223. A great resource with good hints on setting up an EMIS.

87

Setting targets

The basics

Internal targets

Setting achievement targets is necessary for action but effective targets must be set to provide a real incentive for action. The characteristics of effective target measures are:1 • They should be clearly communicated to the employees: ‘I will succeed if you tell me what to do and where you want me to improve’.

When setting targets it is always best to use the internal data because then no-one can claim that this is special – it comes from their own internal performance. Fortunately the PCL techniques developed in Chapter 2 can be used to set challenging but achievable targets.

This is the type of target produced in the benchmark curves shown in Section 2.12 and following. These provide a simple value that the site may be expected to achieve based on external benchmarks for the specific process. They are not related to the historical or actual performance of the site. Managers will claim that their site and operations differ greatly from the industry standard – they are always special. 88

20,000

10,000

be r

ct ob er No ve m be r De ce m be r

-10,000

pt em

gu st

Ju ly

Au

Ju ne

M

ay

0

Se

External targets

Control chart of deviation from target (injection moulding)

Ap ril

Targets from data

The CUSUM for Year 1 (the year used to calculate the PCL) should give a CUSUM of zero at Month 12. This is a result of the method used to calculate the CUSUM.

30,000

ar ch

monitor and produce improvement rather than simple historic reporting: ‘OK, now I see where I can get better’. When setting targets it is essential that the target is set relative to the audience that is expected to achieve the target. Above all, targets should be challenging but achievable to provide a real incentive to improve but not be so difficult that the people required to deliver them become disenchanted with the targeting system. Targets therefore need to be derived from data that are relevant to the site.

M

• They should aim to teach rather than

Section 2.7 showed that deviations and the CUSUM chart can be used to assess site performance by comparing the actual energy use and the predicted energy use. These show the deviations and the overall effect of these but do not show which deviations are critical and outside the normal performance. It is possible to use a control chart (as for a standard control chart) to look for the significant deviations. There has been little work done on the use of control charts in regression analysis but Mandel2 established that it was possible to set control limits based on the standard deviation of the previous 12 months of results. To set the control limits, find the standard deviation (σ) of the previous 12 months of deviations and then use ±2σ as the control limits for the deviations. This will capture ≈ 95% of the results and any values outside the limits are highly likely

Ja nu ar y Fe br ua ry

used by all employees: ‘Tell me in terms I can understand’. • They should reflect the performance required at the location: ‘Give me something that is relevant’. • They should vary with time to reflect changing organisation goals: ‘I've got that right so let’s move on to the next priority’. • They should be simple and easy to use: ‘I understand that’. • They should be fast to give quick response and feedback: ‘Is today OK?’

Site staff are always interested in the effect that their work has on the environment and reporting in terms of CO2 relates directly to this concern.

Control charts

Deviation from target (kWh)

• They should be largely non-financial and

Targets set in terms of reductions of CO2 emissions can be very effective at the shop floor level.

O

3.5

-20,000 Deviation from predicted Upper Set Limit (USL) Lower Set Limit (LSL) -30,000 Month

Control chart for energy use A control chart of the deviation from the predicted performance clearly shows that the site has performed much worse than expected in January and July. The chart can also be scaled for cost (in £) to highlight the cost of excess use. Chapter 3 – Targeting and controlling energy costs

Challenging but achievable targets can be set using the PCL and the CUSUM chart. For the data shown in Section 2.7 the PCL was originally calculated using data for Year 1. These data show a sustained period of good performance from January to July (grey data points at upper right) when the actual use was consistently below the predicted use. These points can be used to generate a revised PCL based on the best historical performance of the site. The original and the revised PCL are shown (upper right) and the revised PCL has a much lower process load (although it does have a slightly higher base load). This revised PCL provides us with a new equation that is based on the best historical performance of the site. This has the following benefits: • The site cannot argue that they have ‘special circumstances’ because the revised PCL is based on their own data. • The site cannot argue that it is not achievable because they have already done it consistently for 7 months. All that is being asked is that they do again what they have demonstrably done in the past. The revised PCL can now be used as a ‘target PCL’ and an improved performance target generated from the production data. This also allows a revised CUSUM chart to be prepared (lower right). The long flat portion of the chart (January to July of Year 1) shows that the target is achievable because the site was performing to this standard for a period of 7 months. Note: Remember that a flat or substantially flat CUSUM curve shows that performance is stable and broadly matching the predicted values. The unfortunate thing in this case is that the site then consistently failed to perform to either the historically based prediction or to the historically based achievable

The PCL and CUSUM chart are extraordinarily powerful techniques for both setting targets and checking that they are being achieved. Readers are advised to further investigate their uses in a range of areas.

• 2. Mandel, B.J. 1969, ‘The regression control chart’, Journal of Quality Technology, Vol. 1 (No. 1), pp 1–9.

Base and variable loads (injection moulding) 200,000 Revised PCL based on best achieved performance kWh = 1.1752 x Production volume + 66,519 R2 = 0.9712

180,000 160,000 140,000 120,000 100,000 80,000

Original PCL based on all data kWh = 1.5551 x Production volume + 48,106 R2 = 0.8104

60,000 40,000 20,000 0 0

10,000

20,000

30,000

40,000

50,000

60,000

70,000

80,000

90,000

Production volume (kg)

Using the site data to set targets Periods where the site performs better than predicted can be used to create a revised PCL based on the best historical performance of the site. The revised PCL can then be used to set ‘aggressive but achievable’ targets for performance. CUSUM for injection moulding 400,000 350,000

CUSUM relative to original PCL CUSUM relative to revised PCL

300,000 250,000 200,000 150,000 100,000 50,000 0 Ja n Fe ua br ry ua M ry ar c Ap h ri M l ay Ju ne Ju A Se ug ly pt us em t O be c No to b r v e De em r ce be m r Ja be n r Fe ua br ry ua M ry ar ch Ap ri M l a Ju y ne Ju Se Aug ly pt us em t O be c No to b r v e De em r ce be m r be r

CUSUM setting

• 1. Maskell, B. 2009. ‘Making the numbers count’, Productivity Press.

Energy use (kWh)

Control charts do not set a direct improvement target but can reduce use by encouraging the site to achieve energy use below the prediction by highlighting any periods where the use is higher than predicted.

target for the next 16 months – at a total cost of £25,000 (15% of their bill for that period). Target setting using the PCL and CUSUM charts is a robust and defensible method of target setting that will challenge plants to do the best that they possibly can.

CUSUM (kWh)

to be the result of special causes rather than common causes. The control limits act as for a standard control chart, i.e., any points outside the control limits require investigation and corrective action.

-50,000

-100,000

Month

Using the CUSUM data to set targets The time where the site performs better than predicted (Months 1 to 7) is extracted to find a revised ‘challenging but achievable’ PCL and this is used to produce a revised CUSUM plot. The flat portion of the revised CUSUM shows the target is achievable.

Chapter 3 – Targeting and controlling energy costs

89

3.6

Reporting energy costs

The management action cycle Accounting, measuring and allocating the use of energy and the costs associated with this use does not necessarily reduce either the use or the cost. Energy use reduction only results from action. As with any information system, there is not only a need to set targets and to report the costs but even more importantly to use these reports to stimulate action. The management action cycle (see diagram on the right) provides a template for successful management.

with very basic numbers and then developing the spreadsheet and system as the needs grow. The type of report produced should match the needs of the audience to the information in the report:

The EMIS must be integrated with existing MIS systems to give the full benefits.

• Annual reports should provide top-level

performance information to show progress over the period.

If any action is to be successful the system should: • Have the full support and commitment

of senior management team. • Support the existing lines of authority

and responsibility. • Use analysis appropriate to the process

to ensure adequate control. • Involve the people it serves,

accommodating both their views and desires to offer solutions and have their performance judged on fair criteria.

The management action cycle Analysing data to provide information will not generate action unless there is a formal system for both reporting and taking action.

Monitoring and reporting

We will take no measurements without recording the results.

After targets for improvement have been agreed and set, it is necessary to report on progress to ensure that effective action has taken place. Any energy accounting report should support the targets set and meet the following requirements:

We will not record results without analysing them. We will not analyse results without acting on them. We will not act without measuring the results of our actions.

• The report should reach the manager

who controls the relevant resource. • The manager should be able to

understand what the report means to them. • There should be a minimum of extraneous information. • There should be some means of ensuring that action is taken when it is needed. • The reports should be integrated as far

as possible into the existing management information systems to make energy accounting a part of the normal operations of the site. As a general rule, it is more important that the Energy Management Information System (EMIS) does what the site needs rather than does many things that it does not require. In most cases, simple spreadsheets offer a method of starting 90

What information do recipients need? The same report is not needed for all the staff at the site. Reports need to be tailored to the needs of the audience and not everybody needs all the information. Be selective about distributing information otherwise people will turn off. Chapter 3 – Targeting and controlling energy costs

• Monthly reports should match the

format for conventional financial reporting and be incorporated into these. • Weekly reports should be more detailed and include operational target information to provide rapid feedback on operational issues. • Key indicator reports should be designed

for general consumption and produced as colour charts suitable for posting on notice boards. • Exception reports should be produced for Departmental Managers on areas where targets have not been met or for identification of areas for improvement.

Measure Ensure that production/climatic and energy measurement

periods coincide. Collect production volume data regularly and look for

irregularities in the data. Make sure that the meter reader is trained and train more

than one person. Preferably download the interval data from the supplier for

more complete data. Ensure that degree day information is collected as soon as

available.

Record

Distribution of reports is always a key area. Not all levels of staff require the same information and the reporting should vary to reflect the needs of the audience.

Only collect data that will be used.

Sustaining the system

Use familiar units for energy and production.

The greatest threat to any EMIS is where the system operates but no one takes any notice, there are four reasons for this: • Lack of authority – where the system does not have senior management support. • Lack of ownership – where the staff are servants of the system rather than vice versa. • Lack of accountability – when there is no clear linkage between responsibility and authority. • Lack of resolution – where the system highlights concerns that do not really exist or does not highlight concerns that do exist. Do not fall into any of these traps.

Analyse

Involve the accountants The accounting function can provide a range of tools and experience to target and control energy use. This is part of their function and they cannot disclaim responsibility. Energy information can be easily integrated into the conventional accounts package and the magnitude of the costs makes the accounting function negligent if they are not involved in this area.

Use simple straightforward forms. Perform simple checks to test data quality and validity. Read the meters at the same time each day/week/month.

When setting standards ensure that derived relationships are

reasonable and defensible. Analyse the data for each time period, as it is available and do

not wait too long. Use simple spreadsheets for simple and quick analysis –

most of the data are easy to handle and the analysis can be done on a standard PC. Use a ‘budget energy cost’ fixed at the start of the budget

period to avoid distortions created by fuel price changes during the year. Keep analysis simple to meet the needs of the site. Integrate the EMIS process with existing MIS systems. Issue reports in a timely fashion. Do not overload people with unnecessary information.

Act Discuss reports informally with the relevant staff after each

time period. Agree future plans for each period. Encourage discussion about future energy savings. Include energy in other management information discussions

(e.g., team briefings). Motivate to encourage action rather than reaction; it is better if

the production area is ahead of the game.

Control actions from the management action cycle Control actions should be consistent and follow the management action cycle format to be most effective. Simple easy-to-read reports are most effective at generating improvement action. When in doubt, leave it out – they can always ask. Chapter 3 – Targeting and controlling energy costs

91

3.7

The energy dashboard report

A simple report This section presents a sample ‘Energy Dashboard Report’ that can be used for general distribution and information. This contains the essential charts and management information for an overview of the energy management performance. It is mainly visual to show the trends and the actions that are being taken. The data used are the same as used in Section 3.5.

Electricity use (target and actual) The actual and target cost of electricity show the monthly cost of energy. Energy use must be shown in financial terms. The deviation between predicted and actual cost does not appear great due to the relative magnitude of the values. The production volume can also be included to validate and reinforce the relationship between production volume and energy use. The energy cost to this site is approximately £14,000 per month. Many companies are unhappy about actually revealing the numbers and this chart can also use simple kWh values.

Monthly deviation from predicted This shows the deviation from predicted energy use for each month and the ±2σ limits to act as a control chart. This highlights the months with the highest deviation from the predicted and also those that are outside the control chart limits. Corrective action was taken after the high deviation in July and the deviation for August is reduced.

Cumulative deviation from predicted and target The PCL for the site has been calculated from the Year 1 data and a target PCL calculated as described in Section 3.5. This shows that the cumulative deviation relative to the predicted has been getting steadily worse and the CUSUM relative to the target has also been getting worse (but at a relatively consistent rate). The final values of the CUSUM charts shows the energy ‘overuse’ relative to the predicted and target values.

92

Average SEC and benchmark SEC There is always a temptation to include a monthly graph of the SEC (kWh/kg) – I have done this myself and regretted it. Section 2.11 shows the effect of production volume on SEC and the changing production volume for the site means that a simple SEC will vary dramatically (from 1.92 to 2.43) due to nothing other than production volume changes. The monthly SEC is not a reliable indicator of any underlying changes in energy management and is therefore not included on a monthly basis but only as a global indicator for the year-to-date. This shows that the site has an average SEC of 2.24 kWh/kg compared to a benchmark SEC of 2.07 kWh/kg. This is 8% higher than average – the site must improve in order to become ‘average’.

The prime function of the EMIS is to support the overall strategy of the organisation.

The energy dashboard shows the energy performance of a site at a glance.

Project savings to date Projects are at the heart of energy management and only by successfully defining and completing projects will energy managers really save money. It is therefore essential to track the estimated savings from completed projects. This highlights the value of energy management to the business in terms of money saved.

Project review The project review is a list of the actions that the site is taking to reduce energy use. All projects have a start and completion date and an estimate of the potential energy cost saving. Note: Whilst all the other data are real, these are ‘dummy’ projects. Overall the dashboard report indicates that energy performance is not good (and is getting worse) but that corrective actions are in place to improve the energy management.

There are loads of resources on information dashboard design on the Internet but the classics on using graphics to reveal information are all by Edward Tufte. Get copies of: • Visual Display of Quantitative Information, 2nd Ed, 2001. • Envisioning Information, 1990. • Visual Explanations, 1997. • Beautiful Evidence, 2006. All are from Graphics Press and all are a delight to read and wonder at. I have copies of them all and sometimes just pull them out to look at them.

Chapter 3 – Targeting and controlling energy costs

Month: December 2017 Energy Use Report – Injection moulding Energy Indicators Electricity use (target and actual)

Deviation from predicted (kWh)

20,000

25,000

18,000

20,000

Electricity use (£)

16,000 15,000

14,000 10,000

12,000

5,000

6,000

-5,000

4,000

Actual use

2,000

Target use

-10,000

M ay Ju ne Ju l Au y g Se us pt em t b O er ct o No be ve r m De be ce r m be r

0

Ja nu Fe ary br ua ry M ar ch

8,000

Ap ril

kWh

10,000

-15,000 -20,000

Ju ly Au Se gu pt s t em be r O ct ob No er ve m b D ec er em be r

Ap ril M ay Ju ne

Ja nu a Fe ry br ua ry M ar ch

0

-25,000 Month

Month Cumulative deviation from predicted and target

Project savings to date (£)

300,000

CUSUM relative to revised PCL CUSUM from original PCL

250,000

90,000 80,000 70,000

200,000

Savings (£)

CUSUM (kWh)

100,000

150,000

100,000

60,000 50,000 40,000 30,000 20,000

50,000 10,000

t pt em be r O ct ob er N ov em b D ec er em be r

ly

gu s

Se

Au

ne

Ju

ay M

Ju

A

Ja nu a Fe ry br ua ry M ar ch

Au gu st pt em be r O ct o No ber ve m be D r ec em be r Se

Ju ly

ay

ne

M

Ju

h

ril Ap

ua ry

ar c M

Fe br

ar y Ja nu

pr il

0

0

Month

Month

Energy overspend (to predicted): £5,040

Average SEC (Year to date): 2.24 kWh/kg

Energy overspend (to target): £19,548

Benchmark SEC for site: 2.07 kWh/kg

Project Review No.

Project Name

Start-up and shut-down procedures 1 Compressed air leakage reduction 2 3 Compressed air generation cost reduction 4 Moulding machine insulation 5 Energy management system 6 Cooling water supply temperature & insulation VSD for water pumps 7 VSD for 2 injection moulders 8 Lighting review for moulding hall 9 10 Ancillaries linkage to injection moulders Potential cumulative savings from identified projects

Start

Completion

01-Jan 25-Jan 28-Jan 03-Feb 01-Jan 04-Apr 06-May 01-Jun 02-Jul 04-Aug

01-Feb 28-Feb 25-Feb 30-Mar 01-Feb 28-Apr 09-May 30-Jun 28-Jul 24-Aug

Estimated Cost Saving (£) £8,000 £3,300 £2,300 £8,580 £6,000 £4,000 £5,000 £8,000 £3,000 £2,500 £50,680

Energy dashboard report Not all the indicators are good but the report shows that there are projects in place to reduce use. Chapter 3 – Targeting and controlling energy costs

93

3.8

Capital expenditure and equipment selection

Changing the rules Many people think that energy efficiency is simply about turning out lights and turning down the heating. Though partially true, it is not the whole story. Energy efficiency is also about choosing cost-effective technology to permanently reduce a site's energy consumption. For example, changing the behaviour of people to turn out lights requires them to be motivated and constantly encouraged. Changing the light switch for a passive infrared (PIR) detector is quick, low-cost and effectively permanent. In many cases, it is easier to change the rules than to change the people. Whilst many energy management improvements are relatively low-cost and fall more properly into the management or expenditure budgets, there are often significant numbers of projects that need capital investment and it is worth investigating how energy efficiency projects are treated in terms of capital investment.

Capital expenditure – how to get it wrong Capital expenditure is ‘something on which a business spends money in order to earn more money’. This definition includes all the time and money we have tied up in the business. These investments are what we have put into the business or have at risk should the business fail. This is a broad definition of investment but it does reflect reality.

list when the available money runs out. Despite this perception, the business maintenance activities are often those that generate immediate cash for the least effort. Investment in business maintenance, mainly cost management, is proven to be the best source of internally generated investment funds, i.e., initial investment in business maintenance generates funds for later business development.

Purchasing energyefficient capital equipment will permanently change the energy efficiency of a company.

Financial appraisal The conventional accounting treatment of capital expenditure is largely based on methods such as Net Present Value, Return on Investment and Discounted Cash Flow. These methods enable ranking of competing investment opportunities and choosing between competing projects – they do not decide whether to invest in a specific project or not, that is the management function. Unfortunately, when looking at energy management improvement projects there is no ‘income’ associated with the project. The accounts department keeps records of expenditure but is not set up to keep accounts of money saved – especially as they regard the cost of energy as fixed. This makes it difficult to justify expenditure on energy improvements because the cost reductions are not recorded as being due to the investment. Fortunately, the CUSUM data already

Investment in energy management improvements can reduce the base load and/or the process load. Lighting upgrades would largely decrease the base load (use is unrelated to production volume), barrel insulation would reduce the process load (use is related to production volume) and improvements in cooling water would affect both base and process loads.

Capital expenditure is often unconsciously divided into two areas: • Business development – this is exciting and gets the most attention. • Business maintenance – this is routine

and gets ignored unless it is really large numbers. This division is shown on the right with the business maintenance activities further sub-divided into essential and discretionary expenditure. Expenditure on energy management and efficiency is typically seen as being a discretionary business maintenance expenditure. This is the lowest priority in the ranking of business expenditure and the necessary investment often falls off the bottom of the 94

Expenditure on energy management is seen as discretionary business maintenance expenditure This category is generally seen as the lowest priority in the ranking of business expenditure and it can be difficult to show an ‘income’ from business maintenance projects. Chapter 3 – Targeting and controlling energy costs

• Tip – Energy managers should maintain

a ‘capital return budget’ that identifies improvements, costs and effective income generated by the investments. This can be a valuable tool in justifying continued investment in energy efficiency.

Life cycle costing One aspect of capital investment is the difficult choice between competing products for capital equipment. It is easy to take the soft option and go for the lowest capital cost equipment without considering the total life cycle cost of the equipment. For most capital equipment, the cost of the energy used during the complete lifetime will be more than the initial capital cost. This will be true even for energy-efficient equipment but the energy cost will be even more for machines that are not energy-efficient. Energyefficient machines save money in the long term – an important factor when customers expect price decreases through the lifetime of a product. In the long term, and that is what capital expenditure is all about, it is cheaper to specify and purchase energy-efficient equipment at the start than to pay continuously for the energy inefficiency throughout the life of the equipment. The initial purchase cost should not dominate the decision-making process. The ‘whole life’ cost of the equipment (initial cost + operating costs) is the important cost for any plastics processor who wants to continue operating in the long term. Purchasing energy-efficient capital equipment is the simplest and easiest way to permanently improve a site’s overall energy efficiency and to reduce its energy costs. This is shown by the cumulative cost for two projects shown on the right. The initially more expensive project has lower energy costs and over a 10-year life cycle these are far greater than the initial purchase cost. The more energy-efficient but higher capital outlay project is by far the more attractive of the two projects.

• Tip – Make an ‘energy efficiency

assessment’ part of the capital expenditure approval process. If there is no assessment of energy use as part of the operational costs, then the capital expenditure should not be approved. • Tip – Ask suppliers for proof of the

energy efficiency of their products and check that it is applicable to the project. • Tip – Be prepared to pay slightly more

in initial purchase cost for long-term energy efficiency cost savings. • Tip – Look for projects where the rules

In the UK, the government produced extensive information on data collection and analysis under various programmes. These are largely unavailable now but copies can possibly be obtained via the web. Try to get a copy of: • Good Practice Guide 069 – Investment appraisal for industrial energy efficiency.

can be changed to the company's advantage and make energy saving automatic. • Tip – Beware of simple payback

calculations which do not include an assessment of the energy costs. • Tip – Look at the sensitivity of the costs

to potential energy price increases.

Projects Investing in energy efficiency can change the rules for plastics processing. New technology makes it possible to re-equip a site for energy savings and lower operating costs into the future. Many proven new technology projects have payback periods of less than 9 months. • Tip – Find these projects today and

improve the capital expenditure process to get them approved.

The cost of energy used during a machine's life will generally exceed the initial purchase cost. Energy-efficient machines and controls may cost more at the start, but they cost less in the long term.

Cumulative cost of investment 160,000 140,000 Initially more expensive 120,000 Cumulative cost (£)

being gathered (see Section 2.7) can be used to not only identify the time of any changes to the energy performance but also the magnitude of changes. Slope changes in the CUSUM graph will occur when an energy-saving investment is made and this can be assigned an ‘income’ value (actually a ‘negative expenditure value’) to justify the investment. CUSUM provides a tool for all seasons.

Initially cheaper

100,000 80,000 60,000 40,000 20,000 0 0

1

2

3

4

5

6

7

8

9

10

Year

Cumulative cost of an investment The ‘expensive’ project (£22,000 vs. £18,000) is more costeffective than the ‘cheaper’ project due to energy costs. For a 10year life the ‘expensive’ project is £36,000 cheaper – much more than the initial £4,000 difference in cost.

Chapter 3 – Targeting and controlling energy costs

95

3.9

Verifying energy savings – the theory

Verifying an absence?

The essentials

Energy savings from an energy management activity cannot be measured because they are an ‘absence’ of energy use rather than a measurable quantity. Therefore, the savings are calculated by comparing energy use before the activity with the energy use after the activity AFTER adjustments have been made for any changes in conditions.

The M&V programme must meet some essential requirements. It must be: • Accurate – M&V needs to be as accurate as possible but costs should still be small compared to the actual cost of the ECM. • Complete – M&V needs to consider all the effects of the project. These can be measured for significant effects but estimated for minor effects.

• Tip – In M&V language, an energy

management activity is termed an ‘Energy Conservation Measure’ (ECM). To avoid confusion, we will use this terminology for this section. The energy use before the ECM is termed the ‘baseline’ and the energy use after the ECM is termed the ‘post-installation’ or ‘performance’ period. The adjustments are to include changes that affect energy use but are not caused by the ECM. These adjustments can include consideration of changes such as production volume, weather or other factors. The equation to calculate the savings from an ECM is therefore:

• Conservative – M&V should be both

reasonable and conservative in estimating ECM savings.

‘Energy efficiency savings are the difference between the actual energy use under current conditions for the considered period compared to what it would have been under these conditions if the energy efficiency measures were not implemented.’ LJ Grobler

• Consistent – M&V should be consistent

in reporting savings for various types of projects, over different timescales and across the various disciplines involved in the project. • Relevant – M&V should measure the important values but can estimate less important values to reduce costs.

Savings = (baseline energy use − post installation energy use) ± Adjustments.

Rationale M&V can be used to: • Assess the energy savings from an ECM to justify the expenditure. • Assess the energy savings from an ECM to check that cost savings guarantees have been met. • Monitor equipment performance in the long and short term – this is important when installing new equipment (see Section 2.5). • Find additional savings from equipment. • Justify additional investment in ECMs. • Improve operations and maintenance by

highlighting operations and maintenance energy use issues. • Reduce uncertainties to reasonable

levels. • Allocate risks – this is important when

energy performance contracts are used for financing the ECM. 96

The basics of the M&V process M&V is actually quite simple and consists of five obvious steps. These are to establish the baseline (the before), complete the project and then to measure the results (the after). The real difficulty is in applying the routine and special adjustments. Chapter 3 – Targeting and controlling energy costs

• Transparent – M&V should be clearly

explained and documented so that an outside party can review the process.

Approaches M&V is a developing subject area and there are two main documents covering this area. These are: • IPMVP1 – this is the core guidance

document for the EVO work and provides an excellent framework for measuring, calculating, and reporting savings. It defines the key terms and outlines the issues that must be considered in developing an M&V plan but does not provide details of specific ECMs. There are also supporting documents and resources available for additional information. • ASHRAE2 – this is similar in outlook to the IPMVP approach but focuses more on the building aspects of M&V. It is less applicable to plastics processing where building issues are small in proportion to the process issues.

The M&V process The basic M&V process is outlined on the lower left. This is a five-step process to: • Define the ECM project, how it will reduce energy use and the measurement boundaries for the M&V plan. • Develop the M&V plan to include factors such as the measurement options, what measurements will be required and the adjustment methods to be used for M&V. • Gather the baseline data for the project. These data must be checked for validity, after the ECM is installed then the baseline will no longer exist and it will be impossible to revisit the baseline. • Complete the project and adjust for functional operation so that the system is working properly.

IPMVP options IPMVP gives four main options for IPMVP, divided into two main cases:

Retrofit only • Option A – Retrofit-isolation: Key

parameter measurement. Key parameters are measured (spot or short term) at the retrofit during both the baseline and reporting period. • Option B – Retrofit-isolation: All parameters measurement. All parameters are measured either periodically or continuously at the retrofit during both the baseline and reporting period.

Complete site • Option C – Complete site.

The M&V process is a robust process for assessing the savings from an ECM but the complete process must be followed to achieve meaningful results. • Tip – The definition and calculation of

the baseline is a critical point, unless you know where you are starting from then it will be impossible to know if you end up in a better place.

If the size of the reduction is small in relation to the overall energy use of the site then strongly consider retrofit-isolation to carry out M&V.

Savings are calculated from the main meter and measurements are continuous throughout the reporting period. • Option D – Complete site: Calibrated simulation. Savings are calculated only from simulation of the site, i.e., no direct measurement. These options are discussed in greater detail in Section 3.10. • 1. Efficiency Valuation Organisation, 2016. ‘Core concepts: International Performance Measurement and Verification Protocol’. Available from evo-world.org. • 2. ASHRAE Guideline 14-2014, 2014. ‘Measurement of Energy, Demand, and Water Savings’. Available from www.ashrae.org.

The complete site measurement boundary Options C & D

The retrofit measurement boundary Options A & B

• Report the savings by measuring the

post installation energy use and applying the previously defined routine and special adjustments to account for changes to conditions.

Choosing an M&V option needs to consider the size of the effect, e.g., installing a VSD will save money but the amounts may not be revealed in complete site results because of normal random variations in energy use.

Measurement at the main meter only

Measurement at sub-meter or portable meter

The differences between retrofit-isolation and complete site measurement Options A and B (retrofit-isolation) carry out M&V by measuring only the retrofit system but Options C and D (complete site) carry out M&V by measuring the complete site.

Chapter 3 – Targeting and controlling energy costs

97

3.10

Verifying energy savings – the practice

Measuring savings

option is best suited for ECMs where:

The four IPMVP options listed in Section 3.9 can all be used in plastics processing sites but the most common will be Options A, B and C.

• Full details of the ECM performance are

Retrofit-isolation In these cases, it is possible to isolate the retrofit from the remainder of the site and to isolate the effects of ECM from the normal random variations in site energy use. The options are:

Option A – Retrofit-isolation: Key parameter measurement With this option, only the key parameters are measured (spot or short term) at the retrofit boundary and these parameters are measured during both the baseline and reporting period. This option is best suited for ECMs where: • Full details of the performance of the ECM are not needed. • The load and/or the operating hours are constant. • The load and/or operating hours can be

reasonably assessed through spot/shortterm measurements. • Some uncertainty in savings calculations is acceptable. In Option A the equation for savings is reduced to:

needed, e.g., for performance contracts. • The load and/or operating hours are

variable. • The load and/or operating hours need

continuous measurement for assessment. • Uncertainty must be minimised. In Option B the equation for savings is reduced to: Savings = (baseline energy use − post installation energy use) Generally there are no special or routine adjustments required in this case. Typical examples of ECMs suitable for this option would be: • Motor improvements where the operating hours are variable, e.g., compressed air improvements. • Motor improvements where the load is variable, e.g., VSD installation and improvements. • Lighting improvements, e.g., control improvements. • Cooling/chilled water system improvements.

The cost of the M&V process should be related to the savings that are being measured. It is always worthwhile carrying out the M&V process but there needs to be a balance between the costs and the benefits.

• Individual machine improvements.

Savings = Operational hours × (baseline power drawn − post installation power drawn) Generally there are no special or routine adjustments required in this case. Typical examples of ECMs suitable for this option would be: • Motor improvements where the load is

constant. • Lighting improvements, e.g., LEDs.

The M&V process for this option should follow the process shown in Section 3.9 and demonstrating the savings is relatively simple.

Option B – Retrofit-isolation: All parameters measurement With this option, all the parameters are measured either periodically or continuously at the retrofit during both the baseline and reporting period. This 98

Baseline, adjusted baseline and actual energy use After implementation of the ECM the baseline is adjusted for changes in production volume (or other drivers) to give an adjusted baseline. This can be compared to the actual energy use to give an estimate of the savings resulting from the ECM. Chapter 3 – Targeting and controlling energy costs

The M&V process for this option should follow the process shown in Section 3.9 but demonstrating improvements is more complicated than Option A mainly because of the greater amount of data generated.

Complete site In this case the performance of the complete site is being assessed and this is generally because of difficulties in adequately isolating the ECM, e.g., improvements in start-up and shut-down or because multiple ECMs are being carried out at the same time. The options are:

Option C – Complete site With this option, the savings are calculated from the main site meter and measurement is continuous throughout the reporting period. This option is best suited for multiple ECMs where: • The only source of data is the main meter or a sub-meter covering a large area. • The projected savings are large in

relation to the normal random variations in site energy use, i.e., > 10% of the normal site energy use. • There is no requirement for individual assessment of the effectiveness of any individual ECM. In Option C the equation for savings is: Savings = (baseline energy use − post installation energy use) ± Routine Adjustments ± Special Adjustments. The difficulty in using this option is how to assess the baseline and the routine and special adjustments. In most cases this involves some type of regression analysis of the baseline data to find the drivers for adjusting the baseline. Fortunately for most plastics processors, the PCL techniques described in Chapter 2 already use regression analysis and give an immediate assessment of the effect of production volume changes (the main driver for energy use in plastics processing). Changes in the PCL allow rapid assessment of the effects of multiple ECMs on the energy use at a site and this was recommended in Chapter 2 as an assessment method. This is shown in the diagram on the right and the savings from multiple ECMs can easily be assessed using the techniques described in Section 2.8. It is simply a matter of:

• Calculating the PCL before the start of

the ECMs (the baseline). • Finding the PCL after the ECMs are

complete and assessing the difference between the PCL before the ECMs and the PCL after the ECMs on a monthly basis. This provides the adjustment for production volume and an assessment of the savings.

The techniques described in Chapter 2 already provide a solution to robust M&V for the complete site.

• The CUSUM of the differences (see

Section 2.8) since the implementation of the ECMs is therefore the savings achieved from the multiple ECMs. • Tip – If the projected savings are < 10%

of baseline energy use then it may be difficult to separate any changes from random variations. • Tip – In most cases, special adjustments

are not needed unless there are significant changes at a site, e.g., new production processes. If this is the case then estimates may need to be made for the special adjustments.

Option D – Calibrated simulation Option D uses calibrated modelling and simulation. Savings are calculated only from simulation of the site, i.e., there is no direct measurement of energy use. This option is widely used in the design of new buildings where good simulation models and data are available but it is not widely used in plastics processing.

Savings from ECMs at high production volume Savings from ECMs at low production volume

PCL before ECMs (baseline)

PCL after ECMs

Production volume

The PCL gives the baseline adjustment The PCL quantifies the effect of production volume as an energy use driver and allows rapid calculation of the baseline adjusted for production volume. Finding the difference between the PCL before and after the ECMs gives the adjustment

Chapter 3 – Targeting and controlling energy costs

99

3.11

The energy manager’s job

Driving improvement

Energy manager basics

Many sites either do not actually know who is responsible for energy management or they do not have a designated person responsible for energy management. When there is no central responsible person then progress in energy management is likely to be slow and fragmented.

Delivering good energy management involves a range of skills from basic management of the systems, e.g., ISO 50001, to the effective delivery of energy improvement projects. In many cases the energy manager will not be responsible for the actual work but will be responsible for the delivery, e.g., the energy manager will identify the need for a VSD project and plan the project, but it is highly likely that the maintenance manager will be responsible for the actual installation and commissioning.

To achieve the potential savings from good energy management there is a need for every site to have clarity about who is responsible for managing energy (the energy manager) and this should be the specific responsibility of only one person. The energy manager should act as the initiator, scorer, facilitator and project manager for energy improvements. They cannot (and should not) be responsible for the amount of energy used. This is the clear responsibility of the major energy users, e.g., production. • Tip – This is similar to the position of

the quality manager: The production manager is responsible for producing quality products; the quality manager is there to check that this is happening and to assist in the measurements. Poor quality is not the fault of the quality manager and poor energy use is not the fault of the energy manager. For large sites, the savings can justify a dedicated energy manager but smaller sites with an energy spend of < £1,000,000 will find this hard to justify in the long term. For small sites, the energy manager does not need to be a full-time role and it can be part of the responsibilities of another role. Some sites which have an environmental, health and safety manager (EHS) will assign energy to this role and others will assign energy management to the quality area. The important thing is that there is a dedicated person who is the central contact and who is responsible for energy management.

Energy managers have a wide responsibility. Energy is used across the organisation and the energy manager also needs to work across the organisation.

• Tip – The energy manager will be

responsible for delivering projects but they will need assistance from other technical/management people in the various areas.

The skills Energy management does not have a recognised career path and most energy managers have been trained in other disciplines, e.g., mechanical, electrical or polymer engineering. Despite the range of starting points for energy management, all energy managers at plastics processing sites should:

One site ‘hired’ an energy manager on the clear understanding that he had to deliver savings worth 3 x his salary to have a job at the end of the year. He is still there, is on permanent staff and is still saving money. Practical but brutal.

• Tip – If a site operates or intends to

operate ISO 50001 (see Section 1.5) then experience in operating this type of management system is invaluable. • Tip – If recruiting an energy manager

then a major skill is process knowledge. A ‘buildings’ energy manager will have a very different skill set to a ‘process’ energy manager. 100

Plan–Do–Check–Act Energy managers need to use the Plan–Do–Check–Act cycle (part of ISO 50001 and other management systems) to improve energy performance. The end result of the process is delivering a sustainable and verifiable improvement in energy use. Chapter 3 – Targeting and controlling energy costs

• Have an understanding of plastics

technology and general materials. • Have an understanding of the main

production processes in use at the site. • Have an understanding of the services in

use at the site. • Have knowledge of financial and energy management topics (see below). • Have good general management skills to

communicate with upper management. • Have good project management skills to deliver completed projects. • Have motivational skills to enthuse staff

in the importance of energy management.

Training Energy management is a relatively new skill set and there are not currently many people trained in the wide variety of skills needed. Many will be self-taught and training is invaluable in balancing and improving skills. There are a variety of formal and on-line courses available from organisations such as the Energy Institute (www.energyinst.org), the Energy Managers Association (www.theema.org.uk) and the Institute of Energy Professionals (www.theiep.org). All of these offer certification as an energy manager. • Tip – One of the best free access training

areas is the Schneider Energy University (www.schneideruniversities.com). This is an invaluable free access collection of over 200 e-learning courses in over 13 languages. Each course takes about 1 hour to complete and can lead to the Professional Energy Manager (PEM) certification offered by the Institute of Energy Professionals. I have used this myself for areas not central to my skills – invaluable! • Tip – Get your energy manager trained

to at least a basic level in energy management. Training will allow them to do their job better and save even more money.

Where do we find these people? The skills necessary for a good energy manager in plastics processing are not always easy to find. People with these skills are very rare and very valuable. Fortunately, the savings are generally so easy to find that a ‘novice’ energy manager can easily save money whilst learning the job – just be sure that they are not lured away by your competitors soon after!

What does the energy manager do? The typical activities of an energy manager are: Create, maintain and update the energy policy and overall

energy strategy. Manage the ISO 50001 management system (if applicable). Carry out (or arrange) energy surveys to identify profitable

projects and/or conformance to the energy policy. Identify and maintain a register of potential energy reduction

opportunities. Create a structured programme of energy reduction projects

with forecast implementation costs, energy use savings and cost savings. Manage the successful implementation of projects. Measure and verify savings achieved from implemented

projects. Regularly report on actual implementation costs, energy use

savings and cost savings delivered by implemented projects. Conduct and advise on energy assessment of new processes,

projects or equipment. Arrange staff training, awareness, motivation and other

schemes to involve staff in energy use reduction (including suggestions schemes and energy champions, where appropriate). Check energy bills for accuracy and completeness. Collect and examine interval data from suppliers to check and

validate bills. Collect and analyse internal meter readings, sub-metering or

logging data. Collect production volume, weather and other data to

correlate with energy use and to establish energy use drivers. Use energy use and driver correlations to analyse energy use

and detect exceptions or anomalous events. Investigate exceptions or anomalous events to prevent re-

occurrence. Collect data for benchmarking site, processes and machines. Regularly report on energy use and cost performance to

budget and forecast. Prepare energy budgets based on available data and

forecasts. Act as the central contact for the current energy supplier. Prepare tender documents for future energy contracts. Advise the purchasing department during tender and

negotiation of future energy contracts. Provide advice on legislation, price movements and other

aspects of the energy market likely to affect the site. Note 1: Some of these activities may be carried out by other people but the energy manager needs to have input to them. Note 2: This list is not exhaustive or prescriptive. Sites may add or delete activities from the list.

Chapter 3 – Targeting and controlling energy costs

101

3.12

Targeting and controlling – where are you now?

The initial steps in targeting and controlling As with the score charts shown earlier, this is a self-assessment exercise to allow a site to benchmark their current status. This will set the scene for planning improvements in the area of targeting and controlling. Targeting and controlling is primarily concerned with having operational systems in place to get data from reliable sources, administering and controlling the data gathering, analysing the data to produce information and reports and externally auditing the process to make sure that the data and reports are

accurate. The preceding sections have shown how to obtain and treat the data to provide real information on the performance of the site and how to use this information to both set targets and to assess performance.

Targeting the costs is the first step and controlling the costs is the second step. Information is the key to both steps.

Completing the chart This chart is completed and assessed as for those presented previously in Chapter 1. Data sources can be electrical meters, thermometers, scales for weighing materials use or any other method used to get data that are input to the system.

Targeting and controlling Operational 4 3 External audit

2

Data sources

1 0

Outputs

Administration

Analysis

Use the scoring chart to assess where you are in targeting and controlling The numbers from the scoring chart can be transferred to the radar chart for a quick visual assessment of where you are in terms of targeting and controlling. 102

The machine database contains information on the motors (sizes and ratings), heaters and other energy use areas of the machine. It provides the essential information on the energy use of the machine.

High scores in this chart indicate that a site has most of the relevant information to progress to selecting profitable energy management projects and measuring the profitability of these projects.

Chapter 3 – Targeting and controlling energy costs

Targeting and controlling Level

4

3

2

1

Operational

Data sources

Excellent data Regular data promptly obtained sources. & analysed. Updated machine Management & database. operational Driver data information (production provided promptly volumes and & in relevant temperatures) detail. routinely obtained.

Administration

Analysis

Outputs

External audit

Meter readings Energy use Concise reports Machine taken in analysis made on for managers to database, accordance with a energy costs, allow technical & instrument written plan, driver financial data to be calibration and production & other recorded volumes & other used. energy prices data collated & factors. Data normalised checked. combined with Targeting for comparison. Reports checked relevant trading & accuracy Impact of for trends & business data. assessed to uncertainties anomalies. business needs. defined.

All data obtained All data sources All meter readings Energy use Concise reports Machine database up to date & calibrated and taken regularly, analysis made on for managers to checked regularly analysed so as to reliable. driver & other energy costs, allow technical & for accuracy. Machine database financial data to be Instrumentation provide recorder data production OK. used, with management collated & volumes & other calibration verified. information in Production deviations from combined with factors. Market energy budget & adequate detail. volumes & energy relevant trading & Possible to prices checked. comparisons with use recorded by business data compare with shift. recording. previous periods. previous period.

Most data sources Provision of Most meter Energy use Reports prepared Machine database budget figures calibrated and readings taken analysis with for managers checked for frequently, driver & respect to energy based on use reliable. accuracy. giving both adjusted for Energy use other recorded costs, production technical & Ad-hoc cursory changes in base recorded on a data collated & volume & other financial data, check on reports & data (e.g., routine basis or combined with parameters deviations from comparison with production volume provided by relevant trading & undertaken as budget & previous year. supplier. business data required. comparisons with corrected). recording. previous period.

Provision of Records kept of Occasional meter Energy use Reports prepared Ad-hoc checks on budgetary figures consumption machine readings taken, analysis with & provided to database. based on use in based on bills from respect to energy managers driver & other corresponding suppliers. recorded data costs, production incorporating both Ad-hoc cursory check on reports & periods. collated & volume & other technical & combined with parameters carried financial data for comparison with previous year. relevant trading & out only in the period. business data response to recording. adverse trends.

No information of No measurements energy efficiency taken & no records or consumption kept. available.

Information not collected.

No energy No management analysis prepared. reports prepared.

No auditing function.

0

Score

x

x

x

Chapter 3 – Targeting and controlling energy costs

x

x

x 103

Key tips • A basic understanding of the energy use

at a site is possible using very little information and most of the information needed is easily available from either internal or external sources. • A basic energy map of the site is very easily prepared and reveals where most of the energy is being used at the site. • The energy map can be used to target efforts in the most rewarding areas and to decide on sub-metering arrangements. • A simple plot of energy use against time will reveal abnormal events and allow these to be investigated. • Integrating energy use into the

accounting system is a vital element of controlling energy costs. • Energy use and savings need to be expressed in terms that the accounts function can recognise and deal with. • The cost drivers for energy use can be ‘activity’ (generally related to production volume) or ‘condition’ (generally related to the weather) drivers. • Measuring and understanding the drivers allows cost assignment to the relevant areas and ownership of the costs can be created. Energy costs will no longer be seen as ‘somebody else’s problem’. • Monitoring and targeting can be used to set targets based on the PCL of the site. • Targets can be set on the basis of simple control charts, similar to those used for SPC. • The best method to assess performance is by using CUSUM charts which are very sensitive to changes in performance. • A ‘challenging but achievable’ performance target can be set from the data used to generate the PCL. This is effectively the best possible historic performance of the site. • The performance to predicted and target is best assessed using a CUSUM plot as these clearly show performance trends and exceptional events and allow these to be located in time. • Energy management needs a formal structure that ensures that the output of the system is translated into real financial performance improvements. 104

• Energy reporting must be adjusted for

the audience. • Simple graphical presentation of

information provides the key to attracting and retaining the audience’s attention. • Investment in improving energy use

performance can make energy cost reductions automatic and permanently improve the financial performance of the site. • Investment in improving energy efficiency is often neglected because of the lack of a recognisable income stream from the investment. • It is possible to use CUSUM data to

identify small energy use improvements and to produce a capital return budget that fully identifies the cost benefits of energy management. • Investment in capital equipment should consider the whole life cycle of the equipment and particularly the energy costs over the life cycle. • Measurement and verification are essential steps in the capital expenditure process. • After investing in capital projects, an assessment of the project return should always be made to check that the money has been well spent. • The methods of measurement and verification are well known and documented but you have to balance the costs and the benefits. • The role of the energy manager is new to most sites but they have a vital role to fulfil. • Energy managers need a variety of skills but they do not have to carry out all the tasks themselves and they are not responsible for energy use.

Chapter 3 – Targeting and controlling energy costs

Chapter 4 Services

As with any manufacturing industry, plastics processing is heavily dependent on the provision of services. This section covers the basics of services that are present at almost any manufacturing site, e.g., energy supply (electricity and gas), motors and compressed air, but also covers the services that are more specific to plastics processing, e.g., cooling water and drying plastics for plastics processing. Services, as opposed to the actual plastics processing and the buildings, are responsible for approximately 30% to 35% of the energy used in plastics processing and are a vital part of energy management in the sector. Services are also widely ignored by the sector and present some of the easiest and most exciting opportunities for energy use reduction.

As with any book, the decisions on what to include and what to omit have been difficult. This has been particularly so with regard to services as there is much background data that is simply not available to the typical site. The temptation is always to include such data but the size of any practical workbook is limited by the need to not frighten off the novice reader (and the limitations of the author’s own knowledge). Therefore the only the information on services included is that which is required to signpost, identify and undertake meaningful energy management activities. If the balance is wrong then please contact us and we will attempt to rectify this in future editions. As with energy management, this workbook is a ‘work-in-progress’.

This is not a section of the book to ignore because you consider services to be peripheral, boring and something that is dealt with by the maintenance manager or site engineer. It should be reiterated that this workbook is about energy management and not about the complete technology of plastics processing. Therefore the focus is on the energy management aspects and not on the basic technology except where it is necessary to understand the technology to reduce energy use. Using cooling as an example, the energy aspects of cooling are covered but not how to size a cooling system based on the throughput of the site. This is a specialist task that, whilst interesting and vital, is beyond the scope of this book. Energy Management in Plastics Processing https://doi.org/10.1016/B978-0-08-102507-9.50004-0, Copyright © 2018 Elsevier Ltd. All rights reserved.

105

4.1

Power supply – electricity terms

Understanding the bill Understanding the basis of electricity charges is necessary before any attempt can be made to manage the charges and costs. Many sites get an electricity bill and have little understanding of the factors that make up the total bill. This section attempts to explain the most common charges seen on an electricity bill. Bills are generally based on a combination of variable and fixed charges. The variable charges will be: • Standard power charges – these charges

will be in £/kWh and may include different rates for night, day, winter and summer use or a combination of these as defined by the supplier. • Reactive power charges – if levied, these charges will be £/kVArh and are charges for reactive power use (see below for information on reactive power and how it can be minimised). Reactive power charges will generally be in the region of 1/10th of the standard power charge. The fixed charges will be: • Available capacity charges – this is the

agreed maximum power (in kVA) that the site will draw from the supply (see below for further details). • Meter reading charges – this is often a

charge made for meter reading. In the UK, it is possible for companies to use their own meter reading company. • Site charges – this is generally a fixed amount per site. • Other charges such as: Environmental (carbon charges).



Local street lighting charges. ‘Green’ power levies. In addition to recording the simple kWh use (by charging period), the supplier will also generally record the following information as part of their metering arrangements: • Maximum Demand (MD). • Power Factor (PF).  

• Load Factor (LF).

Available capacity The available capacity is the agreed maximum power, in kVA, that the site can 106

draw from the supply. If the maximum demand of the site exceeds the available capacity then additional charges may be made and, in extreme cases, the site could be disconnected from the system by fuses or switchgear. If this happens then there will be an extended interruption to production while the supplier resets the switchgear and there will almost certainly be a substantial charge for this. The available capacity is generally first set when the building is connected to the supply and the supplier/developer sets this capacity based on the relevant distribution cables, transformers, substations and switchgear for the complete industrial estate. This may bear little relation to what the site actually needs. Over time the available capacity to the site may be changed by various occupiers depending on their specific needs and the capacity availability in the area. The result is that the actual available capacity may again bear little relation to the actual needs of the site and, in some cases, sites are paying far too much for available capacity that they are not using. The available capacity for a site can generally be changed up or down after consultation with the supplier.

The basis of this workbook is reducing the kWh/ kg rather than reducing the £/ kWh, but there is no point in paying for electricity and services that are avoidable or not being used.

Pulse output: Function of a meter which allows the consumption data to be transmitted externally via a 'pulsed' message.

• Tip – Discuss the available capacity

before renting a new property. If the current available capacity is insufficient then upgrading work will be very expensive and time-consuming.

Maximum demand (MD) The maximum demand, in kVA, but sometimes in kW, is the maximum load that is placed on a supply in the measurement period. In the UK, the MD is measured for each half-hour period and reset to zero at the end of the half-hour period, the highest MD for the complete billing period is recorded on the bill with the date and time of the MD. The maximum demand is just that, the maximum demanded by the site over the month. It doesn’t matter if your demand is very low for most of the month. A single half-hour period of high demand is what counts. Ideally the MD should be just below the available capacity (see Section 4.2).

Apparent power is measured in Volt Amperes (VA). Useful power is measured in Watts (W). Reactive power is measured in Volt Amperes reactive (VAr).

Chapter 4 – Services

Power factor (PF) Most electrical equipment, such as motors and fluorescent lighting, creates a phase shift between the supply voltage and the current due to the load. In a reactive load, the current produces a magnetic field and this magnetic field is the method of producing the actual power consumed. Therefore there are two components to the total power in a reactive load: • The useful power – which does the work and is measured in kW. • The reactive power – which is caused by

penalty rates are introduced for a power factor of less than 0.90.

Load factor (LF) Load factor (LF) is a measure of the number of hours a day that the site takes electricity from the supply expressed as a percentage. Suppliers prefer customers with a fairly constant demand profile as this makes generation easier, i.e., highly variable demand requires stand-by capacity to cover the short periods of peak demands. Suppliers will often set reduced charges for high load factors.

Energy efficiency measures can give a smoother, less ‘peaky’, electrical demand profile which will reduce charges based on maximum demand and power factor.

the magnetising current and is measured in kVAr. The total of these two components is the apparent power (kVA). Note: This is vector addition because the two types of power act at right angles to one another. The power factor is the ratio of the useful power (kW) used by a system to the apparent power (kVA) used by a system: PF = Useful power/Apparent power = kW/kVA = cos φ This might seem unduly complex but the origin and meaning of the power factor are clarified in the diagrams on the right. When all the loads are from equipment such as motors and transformers, i.e., reactive loads with some resistive load, then the phase shift is such that the current lags behind the voltage. In this case the load has a lagging power factor. This will be the case for most plastics processing sites where the major loads are from motors. When all the loads are resistive loads, such as those from heaters, there will be no phase shift and the power factor will be 1, i.e., they have no effect. When all the loads are from equipment such as fluorescent lights, i.e., capacitive loads, then the phase shift is such that the voltage lags behind the current. In this case the load has a leading power factor. This is rare for plastics processing sites. A good power factor for a plastics processing site will be in the region of 0.95 or above – this is normally only achievable with power factor correction equipment (see Section 4.2). Sites with a power factor of less than 0.80 will generally either be charged higher rates for each kWh or will have separate charges for reactive power. This is because such sites use a lot of network capacity. In some countries, Chapter 4 – Services

Mechanical analogy for power factor Imagine pulling a heavy load along a set of tracks. You are not able to pull it directly along the tracks but having to pull from one side of the tracks. The useful power is that required to move the load down the tracks. The apparent power is the power you actually need – this includes the ‘wasted’ power that is not really used to move the load down the tracks but is expended simply pulling against the side of the tracks.

Power factor in electrical supply The useful power (kW) is that actually required for the load, the apparent power (kVA) is that drawn from the supply and the reactive power (kVAr) is the useless or wasted power. The value of cos φ is the amount of the apparent power doing useful work. 107

4.2

Power supply – reducing electricity costs

The fixed charges Understanding the basics of the electricity bill enables companies to look for potential cost reductions. As with the bill, the reductions can come from two areas; the variable charges and the fixed charges. The majority of this workbook deals with reductions in the variable charges through managing and using fewer kWh. Variable charges (£/kWh) change rapidly depending on world energy prices. Our experience is that the actual variable charge depends more on the time the contract is signed than on the company that the contract is signed with. Despite this, there can also be opportunities to reduce the fixed charges and this section examines some of these.

Improve the power factor (PF) A low PF is charged for by the supplier either implicitly or explicitly. If there is no mention of reactive power charges in the contract or on the bill then the reactive power charges will simply be built into the £/kWh charge in the contract. The supplier can calculate the site’s PF from the meter data and will simply roll this up into the use charges. In this case, increasing the PF will not appear to have a direct cost benefit but the improved PF can be used to negotiate a reduction in the £/kWh charges at the next contract round. If the reactive power charges are itemised on the bill then it is easy to see the direct costs of a poor PF and the financial benefits of improving PF. The other benefits of improving the PF are: • The site’s useful power will be increased for no increase in the required available capacity. The table on the right shows the apparent power (available capacity) needed to provide useful power at various power factors. If the site needs useful power of 100 kW and has a PF of 0.95 then the site will need an available capacity of 105 kVA. If the PF decreases to 0.70 then the site will need an available capacity of 143 kVA to provide the same useful power. Increasing the PF from 0.70 to 0.95 will save £456/year in available capacity charges (@ ≈ £1.00/ 108

month/kVA). • The site’s supply voltage stability will

increase and voltage drops will be decreased. Voltage drops can cause motors to overheat and fail. • The site will be able to substantially

increase the current drawn before an upgraded supply connection is required. Fitting power factor correction equipment (PFC) is the best way to improve the PF. PFC equipment is basically a large bank of capacitors fitted into the power supply. These store and release energy to oppose the reactive loads. This balances the reactance with the capacitance to increase the PF. Most plastics processing sites need PFC to achieve a PF in the region of 0.95.

Many companies have no idea how to read their electricity bill. They have nobody who can even decipher the terms used on the bill let alone comment on whether the bill is accurate or not. It would be hard to write a better prescription to waste money.

• Tip – PFC is essentially passive and is

often forgotten in the plant room but still needs servicing and maintenance. Get PFC serviced regularly and mark the service intervals on the PFC cabinets. • Tip – Idling or lightly loaded motors

have a high phase shift and a very poor power factor. Minimise the use of lightly loaded motors. • Tip – Avoid using equipment above the

rated voltage. • Tip – Use high-efficiency motors

wherever possible (see Section 4.19). • Tip -– Read the electricity supply

contract! One company had been charged

Power

Power factor correction can be either local (at the machine) or plantwide (central location). Each method has advantages and disadvantages and expert advice is needed. Most sites will use plant-wide power factor correction.

Current

Power factor

Useful power (kW)

Apparent power (kVA)

Useful current (amps)

1.00

100

100

139

Magnetising current (amps) 0

0.95

100

105

139

45

146

0.90

100

111

139

67

155

0.85

100

118

139

86

164

0.80

100

125

139

104

174

0.75

100

133

139

123

186

0.70

100

143

139

142

199

Total current (amps) 139

The effect of the power factor If an element of the bill is calculated from the MD then as the power factor gets worse (lower) then the MD increases and the site will pay more for the electricity supply because of the increase in the wasted magnetising current. Chapter 4 – Services

for reactive power for a period of 5 years but their contract stated that there were no reactive power charges. A simple phone call got them £30,000 rebate and saved them £6,000 per year in incorrect charges. Know what you are paying for!

Reduce the maximum demand Most processing equipment has a high electrical demand at start-up and this can be 150 to 200% of the normal running demand. Starting all the machines at once can lead to a high transient maximum demand and therefore a higher available capacity than is actually required for normal operations. Staggering the startup of machinery will greatly reduce the maximum demand. • Tip – Motors have a very short transient

demand time but heaters have a much longer transient demand. • Tip – ‘Peak demand lopping’ is the use of

automatic controls to remove non-critical loads from the system if the demand approaches the available capacity. • Tip – If you can start the entire site’s

machines at one time and not exceed the available capacity then the available capacity is probably set too high.

company. Their maximum demand had never exceeded 120 kVA, they were located on an estate with spare capacity, they had no expansion plans and their available capacity was 400 kVA. A simple request to the supplier reduced their available capacity to 200 kVA and saved them £2,500/year. The supplier knew that the available capacity was too high but had not bothered to tell them for obvious reasons. • Tip – If building use has changed from

manufacturing to warehousing and the building has a separate supply then check the available capacity. Often the available capacity is not changed and the charges continue even though the demand is not there. We saved one company £16,000 per year simply by noting the change in use.

Negotiating tariffs Tariff negotiation is a specialised task and there are many companies who specialise in tariff selection and purchasing arrangements. Their fees can be flat rate or based on the savings made. The use of such companies can prove profitable but the first contact should be with the supplier to seek their advice.

Reduce the available capacity Once the PF is in the region of 0.95 or higher and start-up has been staggered it is useful to look at setting of the available capacity. Examine the maximum demand for several months and calculate the average (X) and the standard deviation (σ) of the numbers. Calculate X + 3σ to give the maximum demand that could reasonably be expected and the approximate available capacity needed if operations are not going to change very much in the future. The available capacity can then be adjusted to this value. Note: The available capacity for a site can generally be reduced easily but may be difficult to increase in the future. After a site has released available capacity, the supplier may sell this capacity to another customer on the same ring main. If the site wants to increase available capacity at a later date then it may not be available. Sites need to take a view on the development in the area, if manufacturing is decreasing then the capacity will probably be available but if manufacturing is increasing in the area then it may be difficult to increase capacity in the future. • Tip – We recently used this technique

with a small injection moulding Chapter 4 – Services

Most motors will have a cos φ value marked on them for various voltages. This is the ideal. Lightly loaded motors will have a much lower power factor.

‘Peak demand lopping’ can be very effective to reduce short peaks in the maximum demand.

‘Demand response’ programmes exist in various parts of the world. When the power system comes close to overloading, the site agrees to reduce demand (in return for financial incentives). These can be financially rewarding and in some areas the amount of disruption is small.

Key tips for reducing the cost of electricity Power Factor (PF) – Improve the power factor by: Using adequate and well-serviced PF correction equipment to

improve the PF. Running electric motors efficiently (high loads) to get power

factors closer to 1. Maximum Demand (MD) – Reduce the maximum demand by: Staggering machinery start-ups to smooth out high start-up

loads. Giving machinery time to stabilise before starting up new

processes. Using ‘peak demand lopping’ to reduce the MD. Improving the power factor.

Available capacity – Reduce the cost by: Matching the available capacity to the MD that is actually

required. Load Factor (LF) – Improve the load factor by: Running for longer than a single day shift. Carrying out some operations outside the main shift pattern.

109

4.3

Power supply – transformers

What do they do?

Transformer losses

Transformers are used at every plastics processing site and are also ignored at every plastics processing site. This is despite the fact that every transformer uses energy and has losses. Transformers transform electricity from one voltage to another. They allow energy to be transmitted on the main distribution network at high voltages and low currents and be converted to low voltages and higher currents at the point of use. The distribution network operates at differing voltages around the world but the main incomer to most plastics sites will be in the region of 11–25 kV and the site transformers will convert this to threephase voltages in the region of 230–415 V to operate the services and the machines. Transformers are made up of two or more coils of different sizes wound onto a magnetic core. The coil linked to the incomer is the ‘primary’ coil and the coil linked to the load is the ‘secondary’ coil. The coils are electrically isolated but magnetically linked by the core. The core forms a magnetic circuit between the primary and secondary coils and carries the magnetic flux that links two coils. The ratio of the numbers of turns in the primary coil to the number of turns in the secondary coil determines the ratio between the incoming and load voltages. Despite the common operating principle, transformers come in a wide variety of arrangements. The main types are either liquid-cooled (primarily oil-cooled) or drycooled (with either natural or forced air cooling). Liquid-cooled transformers can be located outdoors (ground-based or polebased) or indoors but dry-cooled transformers must always be located indoors for obvious reasons.

Whilst transformers are inert electrical equipment, all transformers will suffer from operating losses. These will be:

Transformers are a large capital cost but they last a long time and the savings will continue to be made far into the future.

• No-load losses (iron or core losses) –

these are due to the magnetising current and eddy current needed to flux the transformer core. They vary with the

Transformer losses versus % of loading (1,000 KVA conventional) 20

No-load losses 15

Load losses

Losses (kW)

Total losses

10

5

0 0%

10%

20%

30%

40%

50%

60%

70%

80%

90%

100%

% of rated capacity

Typical losses in transformers No-load losses are constant across the rated capacity but load losses vary with the square of the % of the rated capacity. For an old-style transformer, the total losses are therefore highest at full load. These are typical values only. Transformer losses versus % of loading (1,000 KVA) 20

Conventional transformer (total losses)

15 Losses (kW)

Low-loss transformer (total losses)

10

5

• Tip – Where transformers are located

indoors (liquid or dry) then the transformer room should be well ventilated using a temperaturecontrolled fan (either thermostat- or VSD-controlled) to keep the area at a maximum temperature of ≈ 35–40°C. • Tip – Transformers will always be rated

in kVA (see Section 4.1 for an explanation of kVA versus kW).

110

0 0%

10%

20%

30%

40%

50%

60%

70%

80%

90%

100%

% of rated capacity

The benefits of new-style transformers New low-loss transformers not only have lower no-load losses but also have lower load losses. They save money at all use levels but save the most at higher proportions of the rated capacity. These are typical values only. Chapter 4 – Services

core material and the magnetic circuit details (hysteresis and eddy currents). They are effectively constant across the operating range of the transformer. • Load losses (stray or copper losses) –

these are the losses from the primary and secondary windings. They vary and are proportional to the square of the overall load. Transformer manufactures will normally provide details of the no-load loss (Pno-load) and the full-load loss (Pload). The total losses from the transformer are: Ptotal = Pno-load + (% Load/100)2 × Pload or Ptotal = Pno-load + (Load kVA/Rated kVA)2 × Pload • Tip – Every transformer has losses. This

is why suppliers measure the energy used before the transformer – so that the customer pays for the transformer losses.

Low-loss transformers As with many technologies, new transformers have been developed using materials to reduce the no-load and the load losses. Typical new-generation technologies include: • Using amorphous cores instead of the conventional cold-rolled grain-oriented (CRGO) steel to reduce core hysteresis losses (and temperatures) by ≈ 75%. • Using aluminium instead of copper for the coil windings to give lower current densities and to reduce eddy losses by ≈ 40%. • Including automatic voltage optimisation and management capability in the transformer (see Section 4.4). These improvements now mean that replacing existing transformers with new low-loss transformers can be cost-effective.

These savings are based on the whole electricity use and will naturally increase if integral voltage management is included in the package (see Section 4.4). • Tip – Replacing a 15-year-old existing

transformer with a low loss transformer with automatic voltage optimisation can give savings of > £10,000/year for a 1,000 kVA transformer. • Tip – At 75% load (a typical load) the

Transformer tappings are simply alternative connections to the secondary coil to increase or reduce the output voltage. These are generally rated as a % of the rated output voltage.

pay-back time for installing a low loss transformer can be < 2 years.

It is going to be compulsory The size of losses from transformers and their pervasiveness in industry has led the EU to legislate on transformer efficiency and Tier 1 of the EU Ecodesign Directive for transformers was implemented in July 2015. This requires that all new transformers are low loss. The second phase of even more demanding requirements (Tier 2) which will reduce losses by a further 10% is planned for 2021. • Tip – Many suppliers already offer

transformers which meet the proposed 2021 Tier 2 standards and these are highly recommended for new transformer purchases. • Tip – A plastics processor had a

combined transformer capacity of 4,540 kVA and an average maximum demand of only 1,312 kVA, i.e., a utilisation of only 29% of the available transformer capacity and the no-load losses were higher than the load losses. The potential for savings in rationalising and upgrading the transformers was huge and this does not consider the enormous sunk capital cost in all the transformers and connecting them.

The EC estimates that ≈ 2.5% of all energy consumed in the EU is from transformer losses.

Typical savings The savings from replacing existing transformers with low-loss transformers varies with the age of the existing transformer, i.e., the technology, and the older the transformer being replaced then the greater the savings. Transformers tend to last a long time and it is not unusual for a transformer to be over 30 years old. Use the following as a guide only: • 1980’s transformer – 2.5% savings. • 1990’s transformer – 2.0 % savings. • 2000’s transformer – 1.5% savings.

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Transformer in the tropics Transformers get hot when the losses are converted to heat. Oil cooled transformers are normally around 40–50° when operating. It they are hotter then this can indicate possible concerns with the cooling. Check them with a thermal camera. 111

4.4

Power supply – voltage management

Site level energy use control The nominal supply voltage will vary across the world but in the EU this is nominally being ‘harmonised’ to the range 230 V ± 10% (207.0–253.0 V) for single phase. Most equipment will work at the lower range of this voltage and reducing the supply voltage may save energy for certain types of loads. In other areas of the world, the variation is not as large but there will always be a tolerance in the supply voltage of at least ± 6%. Correctly applied, savings in the range of 3–12% are reported for typical plastics processing sites through the use of voltage management techniques.

Types of load In electrical terms, there are three types of load: • Voltage-dependent loads – where the power drawn (P) is related to resistance (R) and voltage (V) by: P = V2/R For this type of load a 1% decrease in voltage will result in a 2% decrease in power drawn and energy used. • Voltage-independent loads – where the system is designed to give fixed output voltage whatever the supply voltage, e.g., most computer systems, high-frequency lighting systems and VSD-controlled motors. • Partially voltage-dependent loads – such as fixed-speed motors where, depending on the type of motor and the operating conditions, a 1% decrease in voltage will result in a 0–2% decrease in power drawn (higher if lightly loaded). Voltage management is only effective for voltage-dependent loads and the savings achieved will vary with the proportion of the load that is voltage-independent. This is not a simple ‘quick-fix’ and needs a detailed survey to assess the benefits and savings.

not achieve the full benefit. This is generally easy to carry out and it is normally possible to drop the overall voltage delivered to the site by around 5% with no ill effects.

The Carbon Trust (www.carbontrust. com) in the UK has prepared a guide to voltage management.

Voltage optimisation

Get a copy of ‘Voltage management’ (CTG045).

If voltage optimisation is provided sitewide it cannot be automatically assumed that there will be site-wide savings, e.g., if the site has high-frequency lighting or variable-speed drives there will not be a significant benefit for these loads. Older-style voltage optimisation equipment was generally of the fixedvoltage reduction type (fixed-ratio transformers) but the new generation provides dynamic voltage optimisation to continuously and automatically adjust the voltage reduction to a specified set-point.

Site assessment To determine if voltage reduction is an appropriate recommendation for a site it is necessary to carry out two assessments: • A voltage ‘survey’ is required. This should be undertaken at a suitable location at the site for at least one week. Single measurements or short timescale logging are not adequate to support a recommendation. If there are significant variations outside the statutory limits

UK (pre-1995)

EU

254 V

240 V

Harmonised EQS 253 V

+ 234 V 230 V

226 V

220 V

207 V

207 V

Adjust transformer tappings This is the lowest cost method (where possible) but this may be limited in effect where the tappings on the transformer do not allow any more than a 5–7.5% adjustment, i.e., the lowest tapping may 112

Voltage harmonisation (changing the numbers) The EU ‘harmonisation’ consisted of simply changing the boundaries to make the systems in each country acceptable. Nobody changed anything on the ground because it was too expensive and it was easier to just change the numbers. Chapter 4 – Services

then the electricity network should be involved. If a site is already running at less than 220 V (phase to neutral) then it is not wise to consider voltage reduction as an energy-saving measure. • A load assessment is required. This is to determine which loads will show savings from a reduced voltage and whether these loads might be changed in the near future, e.g., if old-style fluorescent lighting is a large load then is it possible that this will be replaced in the near future with modern high-frequency lighting.

Loads that will benefit Some loads definitely benefit from voltage optimisation and there will generally be energy savings from loads such as: • Old-style mains frequency fluorescent, discharge, tungsten halogen and LED lighting. However, this comes at the expense of a corresponding reduction in light output. This is often not a problem when adequate lighting has been provided but it is often better to introduce new high-frequency fittings with appropriate controls. • Standard AC induction motors will

where the air change is the controlling factor. • VSD-controlled motors will use the same

power and simply draw more current. • Modern high-frequency lighting. Note: Some specialist equipment can require full voltage and the use of voltage reduction techniques for this type of equipment is not recommended.

Other benefits of voltage optimisation Voltage optimisation can also have other benefits such as: • Suppression of harmonics to provide a cleaner power supply and improve the power quality. • Reduction of phase imbalances, allowing

many motors to run more efficiently. • Improvement of the power factor (but

this depends on the original power factor and the type of load present at the site).

Overview Voltage optimisation can provide good energy use savings in appropriate applications, but is not a universal panacea and needs thorough investigation.

generally benefit (to a variable extent) from reduced motor losses due to the reduced voltage. • IT equipment may benefit if the power supply is a switch mode but the savings are minimal and probably not worth the cost. • Old-style equipment with secondary transformers installed (to drop the voltage) will have reduced heat generation but if the transformer is a fixed ratio then this is not a large benefit and may affect system operation.

Note for UK sites Electrical equipment is designed to operate within a specified voltage range. If the supply is outside this range then the equipment may not operate correctly and could switch itself off, with possible safety implications. When changing the supply voltage across a site, it is essential to make sure that the supply is at an appropriate level to supply all machinery within the specified range but not higher. Identify any older equipment designed to operate at a voltage of 415/240 V ± 6% and take this into account when voltage reduction is considered.

Voltage management

Site level

Loads that will not benefit Voltage optimisation will reduce energy use in a resistive load but there are some loads that will not benefit from voltage reduction and there will generally be no savings from loads such as: • Heating loads will use less power and give out less heat, but the thermostats will compensate and the heaters will run longer to produce the same amount of heat. • Pumps or fans used to deliver a given

volume will simply run for longer to deliver the same amount of material (fluid or air). This will be the case for temperature-controlled ventilation fans Chapter 4 – Services

Transformer tappings

Machine level

Voltage optimisation

Fixed-voltage optimisation

Variablevoltage optimisation

Methods of adjusting the voltage There are a variety of methods for voltage management. Adjusting the transformer tappings is the simplest method but may not give the most benefits (and has some disadvantages). Variable voltage optimisation offers the most potential benefit but is not suitable for every site and depends on the type of loads. 113

Power supply – electricity supplier data

Getting the data

Plotting yearly data

For large users, the electricity supplier will provide a meter that continuously measures and records the energy use. These data are collected by the supplier either by a radio-link download or by a modem/phone line download. Whichever data collection method is used, the power supplier will almost certainly have detailed records of consumption versus time periods. In the UK, the time interval is every 30 minutes (½-hourly or HH data) but in other countries this can vary from every 10–15 minutes. The examples shown in this section use real ½-hourly data provided by a UK supplier. Similar data should be available in most other countries from the local supplier. These data are generally freely available from the supplier and are most often provided in the form of a spreadsheet download. Depending on the supplier it may be possible to get this information backdated for several years. Other suppliers provide a web-based portal arrangement where sites can not only download the historical data but also view the current data. For current data there is normally a time delay of 2–4 hours, i.e., the data will not be available until 2–4 hours after the period finishes.

The first action should be to look at the daily energy use for a long period, e.g., for a full year. This gives the overview of what the site is doing and an example is shown below. The yearly data clearly shows the weekend shut-downs and the Christmas break. Note the very small load over Christmas compared with that over a typical weekend.

Date

kWh kWh kWh 1 2 3 684.9 685

698.5 …..

647.0 654.9 661.5

10/11/17

674.8 671.6 680.7 …..

660.8 645.0 646.6

11/11/17

662.0 646.5 637.3 …..

95.6

96.4

96.2

12/11/17

97.9

95.3

97.8

…..

100.0 96.9

95.2

13/11/17

95.7

96.6

95.1

…..

673.1 649.0 650.5

14/11/17

687.1 672.1 683

…..

585.8 590.1 616.9

15/11/17

670.4 678.8 672.6 …..

655.0 622.8 626.4

Typical data set available from supplier half-hour data The supplier data are usually freely downloadable and give the number of kWh used in each half-hour period for every day. The data are usually available going back several years. This enables sites to examine consumption in a variety of ways.

114

Yearly consumption pattern (2017) 40,000 35,000

kWh used in day

30,000 25,000 20,000 15,000 10,000 5,000

01 -J an

Date

01 -D ec

01 -A ug 01 -S ep 01 -O ct

-J ul 01

01 -J un

ar 01 -A pr 01 -M ay

01 -M

01 -F eb

0

01 -J an

A typical sample data set is shown on the upper right and consists of one date per row and 48 columns of data (one per ½hour period) and the value given is the number of kWh consumed in the relevant ½-hour period. In some cases the value given is the maximum kW drawn in the period and some suppliers will also provide the value for kVAr or the power factor for the period.

kWh kWh kWh 46 47 48

09/11/17

Analysing the data It is possible to purchase spreadsheet software to analyse the data and most sites will find that this is very valuable for regular analysis, e.g., Energy Lens by Bizee (www.energylens.com) was used for all the charts in this section. However, for simple sites, analysis is possible through the use of the graphs and charts provided in a spreadsheet. The amount of data may be daunting but this is the penalty for getting good data resolution.

…..

Simple data analysis of the supplier ½-hour data gives an insight into when, where and how much energy is being used by the site.

01 -N ov

4.5

Daily energy use over the year Totalling the interval hour data for each day and then plotting this versus the day gives a clear summary of the energy use over the year. The weekend and Christmas closedown periods are clearly seen and November 2017 is highlighted. Chapter 4 – Services

The data can then be examined on a monthly basis and this is done for November in the graph on the upper right. This shows the weekend energy use clearly and it is obvious that Saturday uses more energy than Sunday for all the weekends.

Monthly consumption pattern (November 2017)

40,000 35,000 30,000 kWh used in day

Plotting monthly data

25,000 20,000 15,000

Plotting weekly data

The standard load of 100 kWh or £10 per ½-hour period (excluding the spike) is the ‘shut-down load’ for the site and is the load needed for maintenance services, i.e., security lighting and frost protection heating. There should be no other loads during this time. Instead, the average weekend use over the year is in the region of 20,000 kWh or 11% of the normal weekday energy use. This is a cost of £100,000/year to the site that could be reduced by 50% if the site were to actively manage energy and to shut-down to the levels achieved over the Christmas period.

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01 02-No - v 03 No v 04-No -N v 05 o v 06-No - v 07 No v 08-No - v 09 No v 10-No - v 11 No v 12-No - v 13 No v 14-No - v 15 No v 16-No - v 17 Nov 18 No - v 19 Nov 20 No - v 21 No v 22-No -N v 23 o v 24-No -N v 25 o v 26-No - v 27 No v 28-No - v 29 No v 30-No -N v ov

0

Day

Weekly consumption pattern for week starting 08 November 2017 900

700 600

Sunday

Saturday

800

500

Monday

100

Thursday

200

Friday

300

Tuesday

400 Wednesday

The data for the Sunday containing the spike event can be analysed in more detail to highlight and identify the time and magnitude of the spike event. This is shown in the chart on the lower right. The spike is now revealed as a rise in consumption from around 100 kWh per ½hour period to around 160 kWh per ½hour period. This spike lasted for nearly 16 hours and cost the site an additional £200 in energy costs. Investigations by the site failed to reveal the cause of the spike but it is suspected that this was a compressor cycling on and staying on for some time. The spike is a single event of excessive and wasteful energy consumption. The site can now work to identify the cause of the spike and take corrective action.

5,000

kWh used in half-hour interval

Plotting daily data

10,000

0 1

48

95

142

189

236

283

330

Half-hour reference number (48 per day)

Half-hour consumption data for Sunday 12 November 2017 900 800 kWh used in half-hour interval

The data can then be examined on a weekly basis to see the actual use over the week and this is shown in the chart on the middle right. The weekend is still clearly seen and it is obvious that there is a shutdown at around 08:00 on Saturday and a start-up at 08:00 on Monday. This matches with the shift patterns at the site. The Sunday data show significant energy use even though the site is empty and there is no production. There is also an anomalous spike in consumption on the Sunday when there was nobody at the site.

700 600 500 400 300 200 100 0 1 3 5 7 9 11 13 15 17 19 21 23 25 27 29 31 33 35 37 39 41 43 45 47 Half-hour reference number (48 per day)

Drilling down into interval data for various periods The interval data can be examined at various levels. The monthly view clearly shows the weekends and a partial shut-down on Saturday. The daily view shows the shut-down at around 08:00 on Saturday and a start-up at 08:00 on Monday. The large increase on Sunday can be seen in the daily view. This large increase cost £200 but there was nobody at the site. 115

Power supply – analysing interval data

116

Most companies are awash with data but data are just numbers. What is really needed is information and this is not the same thing. Only information allows management to take action.

Building 1: Energy use January to June 2012

50,000

40,000

30,000

20,000

10,000

01 -J un

01 -J ul

01 -J un

01 -J ul

ay 01 -M

01 -A pr

ar 01 -M

01 -F eb

0

Day Building 2: Energy use January to June 2012 35,000 30,000 25,000 20,000 15,000 10,000 5,000

ay 01 -M

01 -A pr

ar

0

01 -M

If Building 1 were to implement the same shut-down procedures as Building 2 and to reduce the average weekend daily working load to 38% of the average weekday working load then Building 1 would save a total of £170,000/year for no loss in production. Needless to say, the site recognised the

We need better information and not more data

60,000

01 -F eb

The two charts shown on the right are from a site that has two separate buildings (both injection moulding areas) but the areas have different managers. Both buildings operate 24/5 and have no production from 06:00 on Saturday until 06:00 on Monday. The graphs of the energy use at the two buildings is shown on the right. Try to ignore the absolute numbers, i.e., Building 1 uses about twice as much energy as Building 2 because it is a bigger area. The important thing is what happens at the weekend. It is immediately obvious from the shape of the graphs that Building 2 shuts down more machinery over the weekend than Building 1, i.e., the weekends are more clearly visible. The average weekend daily load (not producing) for Building 1 is 71% of the average weekday load (full production), whereas the average weekend daily load (not producing) for Building 2 is 38% of the average weekday load (full production). The only difference is in the management, the manager for Building 2 was more concerned about shut-down and had set up a scheme to check that the machines and services were correctly shut down at the end of the week whereas the manager for Building 1 was operating as he had for the last 15 years.

This is quite a common situation and in the worst case seen, the weekend load was

kWh used in day

Weekend shut-down 1

01 -J an

Many sites have, or have access to, interval data but do little to analyse the available data. These companies are ‘data rich, information poor’ and simple analysis of the available data can produce valuable management information. In this section we will review several examples of interval data analysis to illustrate how these data can be transformed into information and energy savings.

value of the information. The issue of shutting down machines over the weekend had previously been regarded as a low priority. The information clearly showed the magnitude of the possible savings from improved management control of the shutdown process. Work to reduce energy consumption over the weekend and closedown periods via simple no-cost management controls resulted in savings of approximately £150,000/year – a good return on simple work with a spreadsheet and simple management improvements.

kWh used in day

Data-rich, information-poor companies (DRIPs)

01 -J an

4.6

Day

Weekend shut-down counts If Building 1 simply performed as well as Building 2 then the site would save £170,000 in wasted energy. This is not even an aggressive target as the weekend loads in Building 2 are approximately 38% of the standard daily load. This is still high! Chapter 4 – Services

78% of the average week day load. This was not a site that was shut-down or on reduced activity – it was more abandoned and walked away from. • Tip – For a normal site with a good

weekend shut-down the average daily weekend load should be in the region of 10–15% and for a site with limited working this should be in the region of 30%.

approximately £17,000 with no impact on production.

Interval data analysis is powerful and can reveal unexpected trends and information.

Without using the interval data and converting it to real information, the managers had no idea of the cost of their decisions.

Do not ignore this valuable (and often free) data source.

Weekend shut-down 2

Saturday shut-down

kWh used in half-hour interval

250

200

150 Production finish 100

50

22 :0 0

20 :0 0

18 :0 0

16 :0 0

14 :0 0

12 :0 0

10 :0 0

08 :0 0

06 :0 0

04 :0 0

02 :0 0

0

00 :0 0

The interval data for this site are shown on the upper right and the good shut-down of the machinery is clear to see. The shut-down of the machines started at 03:00 and was complete by 04:00. After this there was no effective work at the site as all the machines were stopped and the site was inactive. The site manager was astounded by this as the shift did not actually finish until 06:00 and there were production orders left unfulfilled. The staff obviously shut the machines down early and had a good rest for 2 hours (or went home early for the weekend). Needless to say the site manager took strong action to rectify the situation.

Time

The site promptly changed the system to have the worker come in at 04:00 on Monday morning to start the machines. The machines were all warmed up in time for the production start and the site saved Chapter 4 – Services

The daily plot for the Saturday clearly shows that the production equipment (extruders) were all switched off around 03:00 and that the site was effectively inactive by 04:00. The only problem is that the shift did not finish until 06:00! Sunday start-up 180 160 140 120 100 Sunday

Monday

80 60 40 Production start

20

20 :0 0

16 :0 0

12 :0 0

08 :0 0

04 :0 0

00 :0 0

20 :0 0

16 :0 0

12 :0 0

08 :0 0

0

04 :0 0

It is obvious from the energy data that the machines were ready to start within 2 hours (this is typical for injection moulding machines) and for the rest of Sunday and Monday morning the machines were sitting there using energy for no production. Not only were the managers paying over £200 every Sunday for wasted energy, they were also paying the wages of the worker as he sat there watching the idle machines.

Early shut-down loses productive capacity

kWh used in half-hour interval

The interval data for this site are shown on the lower right and it is possible to see the start-up of the machines at between 19:00 and 20:00 on the Sunday evening. In this case, the site was also working 24/5 and actual production started at 06:00 on Monday morning. In order to start promptly, the management paid a maintenance technician to come in on Sunday evening at 19:00 to switch on all the machines so that they were ready for the production start 11 hours later.

00 :0 0

Start-up

Half-hour reference number (48 per day)

Early start-up costs money A daily plot over 2 days shows the machines starting at 19:00 on Sunday for an 06:00 start on Monday. This leads to idle machines simply using energy for over 9 hours. Simple changes to shift patterns saved over £17,000/year. 117

4.7

Power supply – sub-metering

Data at the process or machine level

generation of smart meters.

The interval data previously shown are based on the single meter for the complete incoming supply. This is because most sites have no formal electrical submetering facilities and consumption is only recorded by the supplier from the main meter. For most plastics processors this is not adequate given the size of the bills.

The new generation of smart meters can cost as little as £150/meter (although a site-wide system including the software will cost in the region of £6,000 for a small site) but provide a wealth of extra features. They can record energy information in real-time and then send this information to suitable software for analysis. These low-cost meters can be fitted and connected using wireless or Ethernet technology to give dynamic measurement and control of energy.

For most sites there will only be a single incoming supply meter and this will be the only source of interval data. At some sites, there are multiple incoming supply meters. The supplier will put the data from these meters together for the total bill but the interval data should be available for each supply point. Where this happens, the interval data for each supply can effectively provide a crude type of submetering but this is not a substitute for real sub-metering. All sites should consider introducing submetering to divide the consumption between areas, services and processes, particularly if there is more than one main process at the site. This allows division of the energy use between the areas and aids in monitoring and targeting. The energy map process (see Section 3.2) allocates a provisional energy use to areas, services and processes but the only way to verify the actual use is through submetering. Sub-metering allows calculation of the real energy cost for each area, service or process and continuous monitoring of areas of high energy use – a key factor in reducing energy costs. Whilst sub-meters do not actually save money, they are a very cost-effective method of getting the information needed to manage areas of high energy use.

Types of sub-metering Manual meters Manual read meters can cost as little as £50/meter and these are relatively easily fitted via current transformers to give a manual reading solution. These meters do not record the energy use and require manual reading at regular intervals. Simple manual meters are now generally regarded as being superseded by the next 118

Sub-metering, of itself, does not save money.

Smart meters

What it does, is provide data that can be transformed into information to identify and drive savings.

These new technologies give rise to the concept of aM&T (automated Monitoring and Targeting) and sites are advised to investigate these new technologies. Other benefits of modern internet-based sub-metering are: • The ability to quickly scan all the loads for significant events. • Excellent reporting ability to show progress in energy management. • Manual (or automatic) input of driver data for monitoring and targeting based on activity or condition drivers. • Benchmarking reports based on external or internal benchmarks. • Invoice validation via the tariff tables for the site. • Web-based reporting. • Automatic energy alarms via report, email or text message. • Automatic control of peak-demand lopping effective to reduce short peaks in the maximum demand. (see Section 4.2).

Sub-metering, when used with the techniques described elsewhere in this book, allows identification of waste and quantification of the benefits of energy management.

• Storage of all data in the ‘cloud’ for easy

remote access. Smart metering is a rapidly changing area of energy management and there are many systems available for web-enabled sub-metering and monitoring and targeting. Sites have a wide range of choices available and should carefully examine the alternatives.

Portable metering Permanent sub-metering provides the detailed data over long periods but may not be appropriate for small loads or for rapid assessment of the loads. In these

If an area, service, or process uses more than £50,000 of energy/year then sub-metering is recommended.

Chapter 4 – Services

cases, the use of portable metering is recommended. There is again a good selection of portable metering equipment available for use. This is primarily of the current transformer type and is normally supplied with analysis software. In the simplest case, this is a one-phase meter without a voltage reference for threephase supplies (this relies upon a balanced load) but three-phase current transformers taking reference voltage cost in the region of £1,000. The advantage of portable metering is the speed of installation (it is possible to scan the major loads at a site in less than a day) and the flexibility of the metering. The disadvantages are that it is not possible to collect large amounts of data or to use the data for exception reporting.

Specifying meters Sub-meters can either be connected as ‘whole current’ meters or as ‘current transformer’ meters. • Whole current meters are generally only

used for currents of less than 100 A and are directly connected in series with the supply. • Current transformer meters are the most common type of meter and use clip-on coils (Rogowski coils) to lower the current before measurement. The coils are not connected to the actual load (although reference voltage connections must be made) but care must still be used in connecting the coils. It is also essential that the coils are connected in the correct direction and to the correct phase when measuring three-phase loads. Care should always be taken in specifying and installing sub-meters to ensure that the measurement made is accurate and directly related to the actual load.

areas, services and process. As a general rule, any area, service or process using more than £50,000 of energy/year should be considered for sub-metering. Some sites will sub-meter all of the main processes irrespective of energy use but machines using less than £20,000 of energy/year are rarely worthwhile permanently monitoring for energy use. • Examine the distribution system to determine the potential location for submeters and to determine the type of meter to be used (whole current or current transformer). • Examine the competing products (there are many) to produce a check-list of features such as report format, remote access, web-based reporting, input from other meters (gas and water), general system architecture and scalable system architecture. • Obtain quotations from competing

systems. • Be prepared to pay 1–2% of the total

annual electricity bill for an effective sub-metering system. • Monitor, analyze, read and use the results to reduce costs.

Fast response local reporting (FRLR) The UK Building Research Establishment has developed FRLR – a simple but effective approach to metering to reduce the amount of data analysis and reporting. Meter points are provided with a pen, notebook and calculator. Meters are read regularly and the readings recorded in the notebook. If the energy used is within ± 5% of the expected value then no action is taken but if it is greater than this then action is taken. Fast response = fast action = reduced waste.

The process Sub-metering should follow the following process: • Produce an energy map (see Section 3.2) of the site to locate the major areas, services and processes for monitoring and improvement. This serves as the basis for designing a sub-metering system. • If there are any doubts or unknown areas then conduct a quick site survey using portable meters to gauge the real size of the loads. • Produce a prioritised list of the largest

Chapter 4 – Services

Basic meter layout for simple M&T Simply recording energy use from the main meter does not give the management information needed. A basic meter layout will allow cost allocation to the various process areas and assessment of the services load for cost allocation. Simple lowcost energy metering enables a site to allocate costs and responsibility based on the real energy use. Responsibility, assessment and recording drives real improvement. Note: The dedicated services for any specific process should be allocated directly to that process. 119

4.8

Power supply – gas

Gas use in plastics processing Gas use is not generally significant in the major plastics processing methods and is primarily used for space heating and the provision of hot water. The hot water load is a base load that would be expected to be relatively constant throughout the year. The space heating load is related to the weather conditions and the weather is the condition driver for space heating gas use (see Section 7.5). Where gas use is part of the process, e.g., rotational moulding or EPS moulding, and gas is also used for site heating then gas use will be driven by both the activity (production) and the condition (weather). In this case, the two drivers will need to be separated using multi-variate analysis (see Section 2.10), although the major user (and driver) will be the production volume.

Gas bill data The use of automated metering in gas supplies is not common in the plastics processing industry and gas billing data are rarely available to the level of detail available for electricity data. Due to the largely manual reading of meters, gas bills will rarely be provided for a calendar month and will quite often cover periods of differing lengths due to the manual reading. It is therefore often difficult to align the period of use and consumption data with driver data such as production volumes or weather conditions. In this case, approximations of use for days or months are necessary and this can lead to errors. • Tip – Where gas is used as part of the

process or is a major energy cost then the fitting of automated recording meters is strongly recommended. • Tip – Conventional gas meters can be

converted to automated recording meters if they are of the ‘pulse’ type. It is then possible to fit a ‘pulse reader’ to the meter and to use the output from this for automated reading and sub-metering (see Section 4.7). Gas bills are much easier to read and analyse than electricity bills. Apart from the irregular billing data, gas bills do not have as much detail as electricity bills and errors tend to be both less frequent and 120

more obvious. Despite this, gas bills should always be checked for accuracy and meters read regularly to avoid errors.

Process gas use Where sites do use gas for the processes then, as with sub-metering of electricity use, sub-metering of gas use will provide excellent insights into the use of gas at a site.

Gas use is relatively minor in most of the important plastics processing methods. Therefore it is treated in far less detail than electricity use.

• Tip – A rotational moulding site fitted

permanent recording gas meters to all of the rotational moulding ovens (6 off) and monitored the gas use during the cycle for each product and machine. As a result of the information, the process cycles were changed and gas use was reduced by 15%. The site manager stated that ‘fitting gas meters was the single most effective action’ that he had taken to reduce energy use. • Tip – It is possible to fit ‘portable’ non-

invasive gas flow meters to existing gas pipes. These operate using ultrasound technology to measure gas flow in pipes with no need to fit a permanent meter, no pressure drop over the meter, no shut-down necessary for fitting and no

Degree days – measuring how cold or how hot it is Degree days are a measure of how cold or how hot it is in a given time period. The greater the number of degree days (heating or cooling) in a period then the colder or hotter it is in the period. Cooling degree days (CDD) are mainly used for the assessment of air conditioning systems (see Section 7.9). Heating degree days (HDD) are used for the assessment of heating systems. Official degree days for the UK are generally worked out on a base temperature of 15.5oC. The base temperature is the outside temperature above which the heating system in a building would not generally operate. However, this is not a constant value for all buildings and some care needs to be used when selecting the base temperature because the value chosen depends on the building being assessed. As a simple example, if the outside temperature is 10.5oC for the whole day then the degree day value for the day would be (15.5–10.5) x 1 = 5 degree days. In reality this calculation should be carried out across the temperature profile of the whole day to provide a measure of the total heating demand for the day and then summed to provide the daily total. This is one of the beauties of degree day data, provided the base temperature is constant then daily data can be added up over longer periods to give weekly, monthly or yearly degree day values. Heating degree days cannot be negative, i.e., if the temperature is greater than 15.5oC then the heating degree days value is zero. Degree days provide a method of assessing the performance of space heating where weather is a condition driver and can be correlated with the space heating energy demand.

Chapter 4 – Services

Getting degree day data The best source of degree day data is www.degreedays.net. This gives free degree day data (both HDD and CDD) for almost anywhere in the world. The free download of the degree day data is limited to 36 months but this is more than enough for most sites to start working with historical degree day data and a site subscription gives access to longer periods of data.

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it is best to select an airport as the reference location. It may not be the closest weather station but the data will be more reliable.

Heating degree days and gas use for month 700

14,000 Heating Degree Days (HDD) Gas use (kWh)

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When gas is used for space heating and hot water only, the relevant condition driver is how cold it is and the measure used for this is the number of heating degree days (HDD) for the period (see box on the opposite page). The gas use and the degree days for a typical site are shown on the upper right and the relationship between the number of degree days (how cold it is) and the gas use is clearly seen. As with other drivers, it is possible to plot a scatter chart of the driver (HDD in the month) and the energy use to obtain a PCL for the energy use. This is shown on the lower right and the R2 value of 0.9559 shows an excellent correlation between the two variables. The PCL for the gas use at this site consists, unsurprisingly, of a very small base load (the hot water use for the site) and a variable load (the heating system use for the site). In this case, the hot water load has been effectively ignored by forcing the PCL to go through the intersection of the axes, i.e., 0,0. Using the techniques developed in Section 2, it is possible to use the PCL for the space heating to: • Assess the performance of the heating system for the site and to identify anomalous events where gas use is high. • Predict the gas use for the site based on the weather. • Assess the benefits and savings resulting from energy management or structural improvements. Not all sites will show results as good as this. Sites with poor control systems and old or poorly maintained heating systems will show considerable scatter. These are obviously areas for easy wins in energy management.

• Tip – When using www.degreedays.net

Heating Degree Days (HDD)

Heating gas use

The site also has some excellent articles on the use and abuse of degree day data and should be the first stop for any site wanting to analyse their data.

Month

Gas use and heating degree days over three years Plotting the gas use in a month and the degree days for the same month clearly shows that there is a relationship between the two. Colder months (higher degree days) means more gas use and higher gas costs. Heating degree days and gas use for month 12,000 kWh = 18.08 x HDD R2 = 0.9559

10,000

8,000 Gas use (kWh)

maintenance. This type of technology is ideal for process measurements on rotational moulding machines but is expensive for casual use (ca. £3,500).

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Line of best fit for degree days and gas use Plotting a simple scatter chart (see Section 2.2) makes it possible to find the PCL for the heating system at the site. The R2 value of 0.9559 shows that there is a good fit of the data and we can now use the PCL to both assess the performance of the heating system and to predict gas use. 121

4.9

Power supply – solar and wind

Renewables Some sites have taken action to use solar or wind-power to generate some of their own electricity in an attempt to reduce energy costs. The key word here is ‘some’ and for almost all plastics processing sites the use of on-site solar or wind will never be able to meet more than a small fraction of the demand. Solar and wind-power installation levels have greatly increased across the world in the last decade but, in most industrialised countries, solar and wind-power do not have sufficient power density to provide a viable alternative to other methods of generation.1

graphs highlight the main issues with solar generation, it will reduce energy use only when the sun is shining and this is unpredictable except in broad terms (more in summer and none at night). • Tip – If a site is operating only 24/5 and

has no large-scale battery storage to store excess electricity generated then

Do not be confused or misled by the use of the words ‘installed capacity’ for solar panels, this is always much more that the actual output of the panels.

Solar output on good and poor days – Southern UK, south facing) 0.005 Typical excellent day Typical poor day 0.004

Typical outputs Solar panels are rated in terms of the peak electricity output (kWp) which is assessed by a constant irradiance of 1,000/W/m2 in the plane of the panel. This is not the same thing as the actual electricity output as this will vary widely with the panel technology, the location, the installation conditions and other factors. For solar panels installed in the UK, the annual electricity output will be ≈ 100–180 kWh/ m2/year but this is highly variable. For a large plastics processing site some typical numbers are: • Total roof area: 24,000 m2.

0.002

0.001

0 00:00 02:00 04:00 06:00 08:00 10:00 12:00 14:00 16:00 18:00 20:00 22:00 Time

Solar output for excellent and poor days The difference between excellent (summer and a cloudless sky all day) and poor (winter and overcast most of the day) is dramatic. In winter, the days are also shorter and the opportunity to gather energy is much shorter. Solar output by day/m 2 – Southern UK, south facing 0.20

0.15

kWh/m 2

In assessing the viability of solar panels for a plastics processing site we will assume that the panels are to be mounted at the site. This immediately presents a concern as most sites are compact and do not have sufficient space for a large array (even if it were to be active all of the time). This means that for most sites, any solar module installation would be roofmounted.

kWh/m 2

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• Usable roof area allowing for orientation

• Total solar output: 2,520,000 kWh. • Actual electricity used: 14,000,000 kWh.

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and other effects: 75% = 18,000 m2. • Solar output: 140 kWh/m2/year.

Date

• Solar supply: 15.75% of requirements.

Solar output by day for a complete year

Typical solar outputs (kWh/m2) for an excellent day and a poor day are shown on the upper right and the output by day for a year is shown on the lower right. These

This is the actual solar output (kWh/m2) over a complete year. The difference in the generation output between summer and winter is stark. Obviously solar panels will be more beneficial in sunnier climates.

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these values will decrease and only 11% of the annual requirements will be met by the solar panels. • Tip – These values will increase for sites

in countries which receive higher annual solar radiation, i.e., nearer the equator.

Payback The payback on solar panels around the world is heavily dependent on government support via grants, rebates and feed-in tariffs (where the generation is subsidised by the government). These were initially very high to encourage the growth of the solar industry but have been dramatically reduced as the industry has grown larger. Depending on the location and the government support available the payback time is in the region of 7–9 years. This is normally well beyond the threshold of investment criteria for most plastics processing sites.

Summary Installing solar panels may well make a site feel good and look good in the annual sustainability report but there are many projects that are easier to carry out and are more financially attractive.

Wind As for solar power, we will assume that wind turbines are to be mounted at the site and this again presents the problem of the size of the site and the turbines and the amount of energy that can be generated by wind turbines. It is highly unlikely that any suitable wind turbine could be roof-mounted and a site therefore needs a large site area to make any meaningful difference in electricity generation terms. • Tip – In most parts of the world, off-

shore wind is more consistent and stronger than on-shore wind. Do not be confused by the generation yields for offshore wind.

Outputs For the UK, it is estimated that the power density for on-shore wind is ≈ 2 W/m2 of land area used.1 This assumes an average wind speed of 6 m/s in the UK (although this is much less for heavily populated areas of the UK) and typical windmill heights of 50 metres spaced at 5d where ‘d’ is the diameter of the windmill. If the site considered for solar energy (above) had a free area suitable for wind turbines equal to twice the roof area, i.e., Chapter 4 – Services

48,000 m2 then installing wind turbines would give a nominal output of 96 kW and over a year would generate 840,960 kWh or 6% of the annual requirements. Not many sites have this much free space or are located in areas where the average wind speed is as high as 6 m/s over the year.

Do not be confused or misled by the use of the words ‘peak capacity’ for wind turbines, this is always much more that the actual output of the turbine.

• Tip – A major issue with wind turbines

is the necessity for planning permission and this may be difficult to get for a substantial wind turbine farm. • Tip – As for solar systems, if a site is

operating only 24/5 and has no largescale battery storage to store excess electricity generated then these values will decrease and only 4.2% of the annual requirements will be met by the wind turbines.

Payback The payback on wind turbines is heavily dependent on government support but this is much less for on-shore generation and many countries make it difficult to install on-shore through planning constraints. Depending on the location and the government support/constraints the payback time is in the region of 5–6 years. This is normally well beyond the threshold of investment criteria for most plastics processing sites even if the physical space were available.

Summary Installing wind turbines may also make a site feel and look good but there are many projects that are easier to carry out and are more financially attractive.

Storage It might be argued that storage could change the arguments for solar or windpower but the current available output levels mean that most sites would use all the power available as it was generated.

The simple fact is that for most sites the use of solar or wind-power for on-site generation of electricity is not sufficiently large or financially attractive to make this a consideration.

Some sites with access to large areas of land close by are using this for solar, wind or anaerobic digestion plants. The power generated is then fed to the site and used to meet some of the demand (and reduce costs).

• 1. MacKay, D.J.C. 2008. ‘Sustainable Energy – without the hot air’. UIT. Available for purchase or free download at www.withouthotair.com.

Innovative thinking is needed to make local generation viable but it can be done to reduce the costs, although the payback will still be high.

Do we do it?

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4.10

Power supply – combined heat and power and tri-generation (CCHP)

Going off-grid Many people will be familiar with the concept of co-generation or combined heat and power (CHP), where a gas-fired turbine/generator is used to provide both electricity and heat (see diagram of the energy flow in CHP on the lower right). This technology is widely used in buildings and district heating schemes where both the electricity and heat can be used effectively. The generated electricity can run the lighting, services and machines and the waste heat can be used for heating or hot water. Whilst this is useful for buildings, most of the plastics processing industry needs cooling or chilled water more than it needs heat and CHP is not widely used in plastics processing.

Tri-generation Tri-generation or combined cooling, heat and power (CCHP) is similar to CHP in most respects but also different in how the waste heat is used. In CCHP, a gas turbine is used to produce electricity, a linked boiler is used to produce steam from the waste heat and the resulting steam is used either for heating or for the production of chilled water (see diagram of the energy flow in CCHP on the far right). All plastics processing sites use large amounts of chilled and cooling water for the process. Chilled and cooling water is normally provided by electrically powered chillers or cooling towers and these are very expensive to operate, particularly chillers. CCHP can generate power, heat (steam) and also chilled water to allow a site with access to good gas supplies to go off-grid for almost all the energy requirements. It is also relatively immune to power outages (see Section 4.11). In addition, removing the cooling demand from a site's electricity demand will dramatically reduce the electricity use by ≈ 11%. • Tip – It is the production of cooling and

chilled water that holds the key for sites to use almost all of the energy stored in the much cheaper raw gas input fuel. • Tip – It may seem strange that steam

can be used to produce cold water but the technology is well developed and 124

uses absorption cooling where steam is used instead of the expansion valve in a traditional chiller.

It can be partial CCHP does not have to meet the complete cooling needs of the site and can be sized according to the demand. A CCHP system can be sized to meet:

CCHP is not a new technology and is well known in Europe, the USA and Asia. Perhaps the future is bright for tri-generation for a multitude of reasons?

• The site electrical load – this would take

the site ‘off-grid’ in terms of electricity but may result in excess heat or cooling production depending on the exact balance. Note: The electricity output does not need to be the same as the current demand because of reduced chiller loading and would be ≈ 11% less. • The site heating load – for most sites this would still require a grid connection except with reduced demand. The system would meet all the heating needs in cold weather but only partially meet the cooling and electricity demand. • The site cooling load – for most sites this would still require a grid connection except with reduced demand. The system would meet all the cooling needs in hot weather and most likely all the heating

Absorption cooling can also use an ammonia–water cycle where ammonia is the refrigerant and water is the absorber

Absorption cooling systems have a low COP (however defined) but the low cost of the fuel, i.e., waste heat, can make systems very cost-effective.

Waste heat lost to atmosphere: 17.5%

Gas input 100%

Gas turbine/ generator (30% efficient)

Waste heat to boiler: 70%

Waste heat boiler (75% efficient)

Steam: for heating: 52.5%

Electricity output: 30% Plastics processing machines

The basics of CHP Combined heat and power (CHP) is uses a gas turbine to generate electricity and uses the waste heat to generate steam for heating. CHP is widely used for large buildings and district heating schemes where there is a use for the heat output. Chapter 4 – Services

needs in cold weather but only partially meet the electricity demand. Whichever size was chosen, with suitable controls a CCHP system for temperate climates would be set up as follows: • Hot seasons – the CCHP system is used to generate the maximum amount of cooling to take the maximum amount of load from the chillers. The system is not used for any heating. • Cold seasons – the CCHP system is used

to generate the maximum amount of heating to reduce heating gas use. Any remaining heat is used for cooling but the majority of the cooling load is met by air blast chillers (see Section 4.38) and any excess cooling load by chillers. • Intermediate seasons – the CCHP

system is flexed between heating and cooling depending on the heating and cooling loads.

What do we need to change? A CCHP system does not need changes to existing chilled or cooling water systems and can be set up as follows: • The CCHP system generates chilled water via absorption cooling and distributes this to the existing chilled and cooling water tanks. • Existing chillers remain in place but are set to switch on at high temperatures in the chilled water sump (≈ 20°C), i.e., in the event the CCHP system cannot generate enough chilled water. • Existing process pumps remain in place to distribute chilled water from the sump to the process and are VSD-controlled (see Section 4.40). • Existing system pumps, e.g., to towers and chillers, remain in place but are turned off and controlled to meet the cooling demand.

The basics of tri-generation (CCHP) CCHP uses a gas turbine to generate electricity and uses the waste heat to generate steam for either heating or cooling. CCHP is more suitable for plastics processing than CHP because there is more need for cooling than heating.

How does absorption cooling work? It may seem counter-intuitive to be able to use heat for cooling but gas-operated refrigerators have a long history (although they are no longer common). Cooling using absorption is similar to traditional vapour compression except that the compressor is replaced by a chemical cycle taking place between an absorber, a pump, and a regenerator. Absorption cooling dissolves a vapour in a liquid (the absorbent), pumps the solution to a higher pressure in the regenerator and then uses heat to evaporate the refrigerant vapour out of the solution.

What are the savings? The capital costs for CCHP with absorption cooling are currently high but falling rapidly. CCHP has advantages in terms of overall energy costs (gas is much cheaper than electricity) and insulating a site from power outages. • Tip – For sites with an unreliable grid

supply then the benefits of CCHP may be more than simply the energy aspects. • Tip – Find out more about tri-generation

and the benefits of going off-grid by carrying out a quick feasibility study to clarify the economics of CCHP. Chapter 4 – Services

Basic absorption cooling cycle The most common absorption cycle uses water as the refrigerant and lithium bromide (LiBr) as the absorber. These systems can be single, double or triple stage, where increasing the number of stages increases the efficiency but also the cost. The COP of an absorption chiller is in the region of 0.65 (single effect)–1.2 (double-effect) and the capital cost is higher than that of a conventional chiller. Despite this, if the heat source is very low cost, then the cost of providing process cooling can be very low compared to conventional chillers.

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4.11

Power supply – what to do when it fails (power outages)

Power interruptions – the ultimate energy saving Some parts of the world suffer from regular ‘power outages’ or unscheduled power losses where the grid is unable to supply energy to users. This is mainly in developing countries where the supply network has not kept up with the demand pattern and may even become a future problem in other countries, such as the UK, where green issues have led to premature closure of generation capacity. A power outage can almost be considered the ultimate in energy saving. The only problem is that you cannot process any plastic at all! So what can processors do to minimise the damage and get started again quicker?

very limited storage (they are only after all a rechargeable battery and a rectifier). Whilst UPS are simply not big enough for machines, they can be used for computers (and servers) to prevent data corruption and loss, e.g., I am running one right now on this computer to cover the rare event of a power outage in my area. A UPS will last a long time, is transparent in use and will protect data. • Tip – All office computers (and servers)

should be protected by UPS systems. This can be ‘system-wide’ or use an individual UPS for each computer. • Tip – Always gracefully shut-down the

computer as soon as possible after the power loss. Do not be tempted to keep working – the UPS will eventually drain and the computer will stop.

Minimising the damage

• Tip – Back-up, back-up and back-up

An unscheduled power outage is just that, it is unscheduled and the power simply stops. The primary actions to prepare for power outages are:

again. A power outage is a nuisance, data loss can be fatal. As a rule of thumb, back-ups should be stored off-site or at least the wing-span of a jumbo jet away from the machine. It is also strongly recommended that machine computers and controllers are also protected by a UPS. These should be wired in separately from the main supply inside the machine or using a ‘systemwide’ approach and low-voltage cabling (use the wiring diagrams to find where a UPS can be inserted to protect the computers and controllers). This will mean that the controller will still be active in the event of a power outage and prevent data loss or corruption BUT the machine must still be shut-down to prevent activation when the power comes back on.

• Set/adjust machines to ‘fail safe’ or ‘fail

to safe’ conditions. A power outage can leave machines in an unsafe or unstable condition. If it is possible, then setting all machines (don't forget the services) to ‘fail to safe’ is the prime action. • Prepare checklists and procedures for all actions in the event of a power outage, e.g., isolate machines, clear conveyors, clear assembly machines and set machines in correct condition for restart. • Identify any non-electrical energy users and decide the actions to be taken, e.g., if there are gas-fired ‘flamers’ for PP printing then these should be turned off. • Prevent data loss (or corruption) for all computers and controls. This was less critical in the 1980's when there was less dependence on computers but now a power outage can easily lead to loss of data and perhaps even damage to machines using computer controls. Uninterruptible power supplies (UPS) are a method of providing continued power for computers and controllers in the event of a power outage. They will never keep a plastics processing site operating in the event of a power outage because they have 126

• Tip – Fit small UPS to all machines to

Brownouts and blackouts are different things. Blackouts are a total failure of the supply. Brownouts are when the supply voltage or frequency fluctuates outside the normal tolerances of the site. These are actually a more common risk but are mostly hidden and sites need to be able to turn off non-core services or operations quickly.

The ability to cope with brownouts or blackouts is part of the overall business resilience or disaster recovery planning. Do not leave it too late to test systems and procedures.

Unpleasant (but vital) experience My main experience with power outages was whilst working in a rural area of the UK during the 1980's – our supply was extremely unstable and every month the power would fail (without fail). We were extruding PVC and when the power went off I would look at my watch and start counting. If the power went out for less than 30 seconds then we could get the site up and running again with only a loss of about 1 hour whilst we tried to get the machines stable again. If the power went off for over 4 minutes then it was ‘all hands on deck’ as we isolated machines to prevent start-up when the power came back on (thrust bearings tend to go when an extruder tries to move hard plastic), to strip and clean screws from barrels and to clean dies. For the next 8 hours we were committed to simply getting the site operational again. Those days are engraved in my memory and not in a good way.

Chapter 4 – Services

prevent data loss or corruption. • Tip – Gracefully shut-down machine

computers and controllers as soon as possible to prevent machine activation in the event of power being restored. • Tip – Make sure that you have back-up

copies of all machine settings and data. As with all back-ups, these should be stored away from the machine. • Tip – Robots present a specific problem

because they use higher power levels than controllers. If possible, set up a UPS to take robots to ‘safe’ position (and never enter the area unless the power is ‘locked out’). Assuming a power outage is going to happen then setting up systems to minimise the damage is the first thing to be done.

Getting started again faster After a power outage happens, then the main thing is to get running as quickly as possible after power has been restored. One of the key issues is the type of material being processed – materials that suffer from thermal degeneration or are very thermally sensitive, e.g., PVC, are much harder to deal with than materials which do not suffer from significant thermal degradation, e.g., PP. Processors using thermally sensitive materials already have the discipline of purging after a run and cleaning screws and barrels. After a power outage, these processors will need to strip barrels, screws and dies to clear any material present to avoid black spots and thermally degraded material. Processors running less thermally sensitive materials often simply shutdown a machine with no purging and start it up again by turning on the heaters, running for a few minutes to clean the screw/barrel and then starting production. Whilst not recommended, many processors still do this. After a power outage, these processors have a real advantage, they can set the machines to a safe position and when power is restored, provided they have a good UPS on the controller and have all the data, then they can start up again with few problems. It may not be painless, but it is still better than for processors of thermally sensitive materials. For almost all plastics processing, barrel insulation (see Section 5.10) is recommended as a method of reducing Chapter 4 – Services

energy use. In the event of a power outage, barrel insulation has other advantages, insulated barrels will cool down much slower and warm up much quicker than uninsulated barrels. For injection moulders, barrel insulation can not only reduce energy use but reduce the time taken to get processing again. Barrel insulation has an excellent payback (in energy savings alone) but if the speed of recovery is taken into account then a ‘nobrainer’ becomes almost essential.

We may complain about the cost of energy and try to minimise the use but when you have none at all then it gets very serious very quickly.

• Tip – Barrel insulation should be fitted

wherever possible.

Removing the problem Obviously, the best thing to do about power outages is to remove the problem but the removal of power outages involves some type of self-generation or going offgrid and this is expensive and needs high capital expenditure. Sections 4.9 and 4.10 discuss the use of renewables (solar or wind) and the newer concept of trigeneration, but some processors in badly affected areas use diesel generator sets (gensets) for back-up power. Gensets can be cost-effective for short periods or when they are used for ‘peak demand lopping’ but using them for any length of time is expensive due to the relatively low efficiency of the diesel generator, i.e., the heat output from the generator is lost to the atmosphere. Gensets can have start times from between 0.2 seconds to 2 minutes. As a general rule, the shorter the delay time then the more costly the generator set controls, but how long do you want a power outage in an operating room to be, especially if you are on the table? Power outages are disruptive to operations but with good planning plastics processors can take a range of actions to minimise their effects.

Over 80% of sites will experience an energy-related failure in most years. Some from ‘weather events’ and some from ‘equipment events’. It will happen to your site. It is only a matter of time.

127

4.12

Power supply – where are you now?

The initial steps in power supply As with the score charts shown earlier, this is a self-assessment exercise to allow a site to benchmark their status. This will set the scene for planning improvements in the area of power supply. Power supply basics are all about minimising the cost for energy and using the energy that you have paid for in the best possible manner.

supply measurements from sub-metering or the main meter can provide valuable information to manage energy use and reduce costs.

The electricity supply contract is the start of energy management. Get this right and you can minimise your costs.

Completing the chart This chart is completed and assessed as for those presented previously.

Getting the supply contract right for the site, getting the right information from the supplier and minimising the costs are basics in energy management. Simple

Power supply Supply contract 4

3

2 Maximum demand (kVA)

Meter reading & payment

1

0

PF correction

Sub-metering

Use the scoring chart to assess where you are in power supply The numbers from the scoring chart can be transferred to the radar chart for a quick visual assessment of where you are in terms of power supply. 128

In the UK, the maximum demand is a fixed cost that can be reduced to meet the site’s needs but care needs to be taken not to give away excess capacity if it will be needed in the near future.

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Power supply Level

Supply contract Supply contract sent out for competitive tender based on current & projected needs.

4

3

Adequate sub-metering Monthly checks of Supply contract sent Adequate PF Maximum demand correction equipment in tracked but no records for requirements. out for competitive meters made & tender but based consumption crossSystems used for place, adequately kept. checked against supply recording major simply on current maintained with PF > No concept of MD equipment & processes requirements. invoices. 0.95. monitoring. & consumption but little Invoices require approval of Production analysis carried out. Manager before payment.

Supply contract sent out for competitive tender but based on poor knowledge of requirements.

2

1

0

Score

Meter Sub-metering PF Maximum reading correction demand & payment (kVA) Excellent sub-metering Excellent PF correction Maximum demand Weekly checks of enables M & T for equipment in place, recorded as part of site meters & consumption cross-checked against major equipment & well maintained & facilities management. operating correctly with processes. invoices. Adequate but not Consumption data Interval data used to PF > 0.98. excessive MD capacity. detect trends or analysed to provide Peak lopping real information. exceptions. procedures in place. Invoices require approval of Production Manager.

Adequate PF Sporadic checks of Poor sub-metering for Maximum demand meters made but no requirements & no correction equipment in tracked intermittently analysis carried out on attempt to audit or place, poorly but no records kept. validate supply information available. maintained with PF > invoices against meter 0.85 but < 0.95. readings. Invoices require approval of Production Manager before payment.

No checks of meters Maximum demand Supply contract No deliberate subInadequate PF correction equipment in tracked only for supply renewed with current made. metering. Payment made on Limited sub-metering place. PF < 0.85. constraints. supplier with little tendering or negotiation No records kept. invoice. due to physical process. Copies sent to separation of site Production Manager for facilities. information only.

Supply contract Supply invoices are No sub-metering No PF correction renewed with current accepted without available to provide equipment in place & supplier with no validation & payment information. PF is < 0.80. tendering or negotiation made on invoice Data available from process. without reference to single main meter only. Production Department.

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x

x

x

Maximum demand not tracked & no records kept. No concept of MD monitoring.

x 129

4.13

Motors – understanding motor use and costs

The big demand

times the purchase cost of the motor.

Up to 66% of the energy costs in polymer processing are the result of electric motor use, yet motors are often neglected when considering energy use. The motors in the main processing equipment such as injection moulders and extruders are obvious when energy is considered but the majority of motors are ‘hidden’ in other equipment such as compressors, pumps and fans. Most plastics processors are relatively unaware of the cost of motors to the site and even the smallest motor at a site will use substantial amounts of energy over the operational year. There are many different types of motor and the main types are shown in the chart on the right. The most common type in industry is the three-phase squirrel cage rotor induction motor. Squirrel cage motors with electronic controls are now replacing many of the current applications of the wound rotor type of motor. Irrespective of the type of motor used, the cost of energy to run a motor of virtually any kW rating will generally exceed the purchase cost of the motor after 400 hours of continuous full-load operation. This is shown on the far right where the approximate operational costs for a variety of motor sizes are shown relative to the operating hours. A ‘small’ 22-kW motor will cost over £21,000/year to run and there are many of these at the average plastics processing site. When a typical cooling water installation can have up to 3 × 22-kW motors operating for the chilled water alone, the costs soon mount up. Failing to manage motors and taking short-term decisions to initially save small amounts is a very expensive decision to make. In most companies there is little thought given to motors and this can easily embed energy inefficiency into the system.

Motor basics

Motor efficiency is being addressed by governments around the world and this is forcing sites to think in terms of the ‘whole life cost’ of motors and the cost of inefficient motors. If the ‘whole life costs’ are considered then the cost of energy to run virtually any size of motor is over 200 130

Motors are a very complex subject that are well treated in many texts and freely available resources1,2,3 and as with most of this workbook we will deal only with the energy aspects of operating motors. The detailed aspects of motors will only be introduced as necessary to understand the methods for improving the energy management of motors. There are many methods for reducing the energy cost of motors, and whilst these are inevitably linked, they will be considered separately to provide a consistent structure for the development of a motor management programme. The full programme is outlined in Section 4.14.

Motor use and costs As with any energy management project, the use and cost of motors needs to be understood to assess the viability of any project. There are various methods for

The energy cost of a motor can exceed the purchase cost in just 400 hours of use.

Most of the focus in this section on motor will be on the standard AC induction motor (the most common type of motor). DC motors are not widely used in plastics processing except in extruders. These will be covered in Section 5.17.

Types of motor There are many different types of motor available and all have different characteristics. The most common motor used in industry (for pumps, fans, etc.) is the three-phase squirrel cage rotor induction motor. Chapter 4 – Services

assessing the cost of motors but it is possible to use a simple method to provide a rapid assessment of the cost of a motor. Assuming full load, the number of kWh used can be calculated by: kWh = kW × Operating hours η where: kW = Motor size in kW. η = Efficiency of motor (assume 0.85 unless other data are available). The cost of operating the motor can then be calculated from the electricity cost for the site. More sophisticated models are available to take account of the load factor but for general comparison the simplified model is adequate for a first approximation of the cost of operating a motor. • Tip – Take a walk around the site and

look at the kW ratings of various motors, you will soon be able to assess the kW rating from the physical size of a motor.

The life cost of a motor is often over 200 times the purchase cost.

Load factor

• 1. The US Department of Energy (DOE) has some excellent free books and publications on motors and drives. Some of the best are: Motor and Drive System Performance’ (2014).

■ ‘Premium

Efficiency Motor Selection and Application Guide’ (2014).

the cost of a 1-kW motor and use this as a standard for motors. For a site with a range of old and new motors the ‘best’ estimate of η is probably around 0.85 and a 1-kW motor operating for 8,760 hours/year at full load will use approximately 10,000 kWh and cost £1,000/year to operate. This gives an operating value of £1,000/kW for quick calculations and a 22-kW motor will therefore cost £22,000/year to operate. This is for quick calculations only. • Tip – Lightly loaded motors will have a

lower value of η but this depends on the motor and the load (see Section 4.19 for more details).

■ ‘Continuous

Energy Improvement in MotorDriven Systems’ (2014).

This is an estimation that needs some experience with real measurements of the motor’s power and needs to be used with care.

• 2. US Motors (www.usmotors.com) have some excellent training packages and calculators (all in Imperial units but still very good). • 3. ABB (www.abb.com) also has excellent resources but it is best to contact the local agent for most of these. ‘The Motor Guide’ is an invaluable reference. The cost of AC motors (2-pole motor @ IE3 minimum boundary) £90,000 £80,000

11 kW

55 kW

22 kW

90 kW

£70,000 Cost per year (£)

• Tip – For ease of calculation, work out

The load factor accounts for the fact that most motors do not actually operate at their full load for 100% of the time.

■ ‘Improving

• Tip – Use the simplified model to

estimate the energy use and cost for various processes. Be prepared for a shock when you realise how much some simple and unnecessary processes are costing you.

The simple method for calculation of the cost of a motor can be made more accurate by applying a ‘load factor’ to the calculation.

£60,000 £50,000 £40,000 £30,000 £20,000 £10,000 £0 0

1,000

2,000

3,000

4,000 5,000 Operating hours

6,000

7,000

8,000

9,000

The long-term operating cost of two-pole AC motors The operating costs of motors are high, whatever the operating hours. This graph shows the cost of operating motors using the simple model and the minimum efficiency for IE3 motors. Using older motors with lower efficiencies will increase the cost. Chapter 4 – Services

131

4.14

Motors – the programme

Reduce the demand and then optimise the supply Services should all follow the same basic programme for good energy management. Stage 1 of the programme is to assess and reduce the size of the demand before trying to optimise the system in any way. It is obviously not common sense to try to optimise the supply for an unrealistic or unnecessarily large demand. This demands a systems approach where the whole system is examined for areas of potential improvement. A typical ‘motor’ system is shown on the right and the programme aims to optimise the system rather than simply concentrate on a single element of the system. In this example the system losses accumulate so that only 62% of the input power is actually available to the process. This is a ‘good’ result and in some cases the losses are much higher. ‘Minimise the demand and then optimise the supply’ will become a common refrain in the energy management of services and we will return to this for most of the other services that are discussed in this chapter.

effective parts of the motor management programme. • Tip – Processors are always amazed

when we begin an energy survey by asking to see a ‘stopped’ machine but this inevitably finds motors running when they should be stopped. Instant energy savings are easy to find by stopping motors. • Tip – A simple walk around will identify

many hidden motors in fans, pumps, regranulators, etc. that are costing money by operating when not required. Simple controls and management action can significantly reduce use.

Reduce transmission losses Transmission losses are often a major component of the overall losses in the motor system and can easily exceed the losses in the motor itself. Improving the transmission method reduces the overall load on the motor and can be used to optimise the motor size.

The programme The overall motor programme is shown on the far right and this programme is designed to reduce motor energy costs throughout the motor system and not simply in the motor itself.

Stage 1: Minimise the demand The first stage of the motor management programme is to minimise the demand. The aim of this stage is to reduce the overall demand placed on the motor system so that it can later be optimised to provide the best service. Minimising the demand is not about removing services that are necessary for operation. It is about providing the appropriate service when needed.

Turn the motor off Obviously, the best method to reduce the cost of motors is to stop the motor operating when it is not required or producing valuable output. This completely removes the system from operation, saves 100% of the previous energy demand and is one of the most 132

The motor system Managing motors means looking at the complete system. The motor itself is only part of a system to drive a load and maintain the process. We do not want to optimise the parts but want to optimise the whole system for energy efficiency. Chapter 4 – Services

Reduce the driven load The actual process load on a motor can often be reduced through simple measures such as improving the control system, improving maintenance and examining the load to find methods of reducing the driven load.

be a sub-section of the overall site energy policy.

Managing the complete system is the only way to achieve real energy and cost savings.

Stage 2: Optimise the supply Get the right size motor The first step in reducing energy use in motors is to get the right size motor. Large motors always use more energy than small motors. What is not often recognised is that a lightly loaded motor is also less efficient than a motor operating at the design load, i.e., the value of η is less. This is a double incentive to choose the correct size motor.

Improve the motor efficiency The efficiency of a motor will vary with the motor type, the applied load and the demand profile. There are various methods of improving the efficiency of an AC motor, ranging from improving the basic motor specification to simply replacing an existing motor with a smaller motor or rewiring the existing motor connections.

Slow the motor down The majority of motors used in plastics processing are AC induction motors although DC motors are often used in mixing and extrusion. AC motors are generally low-cost and reliable but do suffer from the disadvantage of operating at a fixed rotational speed that is defined by the supply frequency and the design of the motor. Recent technology advances in inverter drives (VSDs) allow AC motors to operate at variable speeds but there are other methods for slowing down the motor to match the demand.

Maintenance and the motor management policy The results of the motor management programme also need maintenance actions to hold the benefits and a motor management policy to provide a framework for future actions. Guidelines on effective maintenance and setting up a motor management policy and what this should consist of and how to establish this are discussed further in Section 4.22. • Tip – The motor management policy can

Chapter 4 – Services

The motor management programme The motor management programme follows two stages and six steps to reduce motor energy use. Stage 1 must be completed and maintained before Stage 2 is started to get the full benefits of the programme.

Motor condition is important and motor temperature is a good indicator of motor health Motors get sick and show symptoms of ill-health before they fail. The classic test is to hold your hand on the motor. If it is too hot to touch with your hand then it is showing symptoms of ill-health (bad ventilation, potential bearing failure, etc.). Most operating AC motors should be in the region of 40–50°C. If a motor is too hot to put your hand on it for 2 minutes (> 60°C) then it is too hot and should be checked for clean fans and general maintenance. It is best to record temperatures with a thermal camera but the ‘hand test’ is quick and almost as accurate. Vibration analysis is also useful but this is a method that does need some experience. 133

4.15

Motors – minimise the demand: turn it off

The most effective method Operating a motor that is not required is a complete waste of energy and money. Despite this, it is very common at most sites to easily identify many motors operating when they are not needed and when they are doing no useful work. There are many low-cost methods for turning off motors and the method chosen depends on the application and the potential savings. The main barrier is not the technology; it is the simple lack of management attention to detail and the lack of realisation that operating motors costs money. This barrier is the hardest of all to overcome.

It’s OK to switch off! There is a common belief that stopping and starting motors damages the motor and costs money. Motors are designed to be switched on/off and the motor specification will state the maximum number of times the motor should be switched on/off per hour. Stay below this and you are OK. Starting a motor draws more power than operating but for most motors a start event uses less energy than 1 minute of operation. Do the numbers!

Methods for turning off motors Most sites only consider manual methods for turning off motors but there are a range of techniques for turning off motors when they are not needed. The method chosen depends on the application.

Techniques The available low-cost techniques are shown on the upper right and these are:

Manual Manual methods are the easiest to implement but are often the hardest to maintain and control. Changing staff attitudes is a difficult process, most people will react for a few months and then the old practices will creep back into action. This method is not recommended unless management control is strong. One of the biggest problems with manual methods is that switches are rarely conveniently located, are rarely labelled with what they control and there is never any guidance on what can be switched off. The result is that nobody does anything even when they know they should. • Tip – Relocate switches for easy access. • Tip – Clearly label all switches and

plugs so that everybody knows what the 134

Energy traffic light system for manual control Operators and other staff need clear and unambiguous guidance on what can and cannot be switched off. An energy traffic light system gives this clear guidance and management can then use this to enforce the process. Chapter 4 – Services

switch and plug controls. • Tip – Use traffic lights (see lower left) to

set a clear policy for action.

Timers Timers are a simple method for turning off motors and linking motor operation to production hours. Timers can be either the daily or 7-day programmable type (both should have a manual override facility) or of the simple push to operate type as commonly used in stairwell lighting controls. Timers enable improved control of motors that are regularly and predictably used for only part of the operational hours or are used sporadically and then left on because nobody can be bothered to switch them off, e.g., test equipment, small machines. Timers are particularly useful when the site does not operate at weekends and there is a risk that motors will be left on over the weekend. Unnecessary motors operating over the weekend will operate for nearly 2,500 hours/year, more than enough to pay for some simple timers. • Tip – Always ensure that timers leave

machines in a ‘safe’ condition. • Tip – Ensure that manual overrides are

present and that these are not actuated and left on! • Tip – As with manual switches, timers

need to be situated for easy access and clearly labelled so that everybody knows what the timer controls.

Condition sensors Condition sensors can be simple on/off controls that react to the site conditions. Simple examples are: • Linking roof ventilation fans to temperature sensors in the roof void. When the temperature reaches the setpoint, the fans come on and run until the temperature drops below the set-point. • Switching off cooling tower fans when the cooling water reaches the set point. • Tip – In many cases it is more cost-

effective to use a VSD (see Section 4.20) than to use a simple condition sensor.

Interlocked controls Interlocking motor controls to machine controls can be a very effective method of reducing motor use. Simple examples are: • Interlocking downstream equipment to

the machine. When the machine stops Chapter 4 – Services

operating then the downstream equipment runs to clear the line and then stops operating – there is no product coming out of the machine so why operate the downstream equipment? • Interlocking ventilation fans above extruders to the machine operation so that they only operate when the extruder is turned on and then overrun for a short time to vent the area after the extruder is turned off but still hot. • Interlocking isolation valves on supply pipes for cooling water and compressed air to the machine operation so that the machine is isolated from compressed air and cooling water when not operating. This will reduce motor energy use in motors remote from the machine.

At one site, we found a test machine running. It had not been used for 3 months but it was not turned it off because ‘it is only a small motor and we might need to use it again sometime’.

Sequenced operation Where a series of motors is used to provide services, e.g., there are multiple compressors or chillers, then sequencing the operation by staged switching on/off of the motors will allow a closer match of the demand to the supply and will greatly reduce motor use. Depending on the application, the sequencing can be controlled by flow rate variations, rises in pressure or other control variables.

The main problem is not ‘technology lacks’ but ‘conceptual locks’ After Stephen Jay Gould

• Tip – Motors and services do not operate

at peak efficiency at full load. Find the location of the peak efficiency of the system so that the sequencer can bring motors on line at the most energyefficient motor loading. • Tip – Sequencing can also be used to

rotate motor loading through a series of motors to equalise the use of the motors and prevent early failure, e.g., sequencing can rotate the load through a series of process and stand-by pumps.

Load sensing Sensors can be used to detect if a motor is operating under ‘no-load’ conditions and to switch off the motor after a set period of no-load operation. These can be used to stop motors automatically when idle. Simple examples are: • Regranulators operating with no material feed. • Hydraulic motors on injection moulding machines that have stopped operating due to faults, tool changeover or completion of the job. • Tip – Always ensure that sensors leave

machines in a ‘safe’ condition.

Soft starters If motors are likely to be switched on/ off regularly then ‘soft starters’ can be used. These ramp the supply voltage from zero to the operating value. This allows the motor to be switched on/off without damage. Most soft starters also include an energy optimiser to reduce the drop in motor efficiency for part load operation. Potential savings vary with the level of motor loading but can be marginal for part loads greater than 50% of the motor rating.

135

4.16

Motors – minimise the demand: reduce transmission losses

Get the power to the load

Improvement

It makes no sense to generate the power at the motor and then to waste this through poor transmission of the power to the actual load. Reducing transmission losses will also reduce the size of the apparent load to the motor and make motor optimisation an easier task.

High-efficiency helical bevel gearboxes are up to 30% more efficient than the traditional worm gearbox. Only use worm gears for motors of less than 7.5 kW.

Reduce transmission losses In plastics processing, motors drive loads and processes by one of two methods: • Directly by a mechanical connection such

as gearboxes, belts or chain drives. • Indirectly by a fluid connection such as a

hydraulic pump. Direct connection of the drive tends to be the most efficient method because of the reduced friction losses but it is still possible to increase the efficiency and to minimise the transmission losses (see Section 4.50 for discussion of how to reduce hydraulic system losses).

• Tip – Check the condition of any worm

Conveyors are a typical area where lubrication is often poor and the resulting friction increases the motor loading.

gearboxes and consider replacement with helical bevel gearboxes for any motors larger than 7.5 kW.

Belts Belt drives are used for large numbers of machines in the plastics processing industry such as cooling tower fans, ventilation fans and transmission systems for extrusion and extrusion blow moulding machines. Almost all of these applications use conventional V-belts and as long as the system continues to operate then little is done about them.

Maintenance counts Maintenance of existing systems will reduce energy use through simple good practice. Poor maintenance will increase transmission losses. No maintenance will increase it further (see Sections 4.22 and 6.8 for further details on the importance of maintenance). Reducing transmission losses is primarily about asking: Are we maintaining the system correctly and is there an alternative method of driving the system?

Gearboxes Most gearboxes do not require substantial maintenance but failure to regularly lubricate bearings and other components of the transmission system will increase frictional effects and motor loading. Typical actions to reduce transmission losses are:

Maintenance • Ensure that all gearboxes are well

lubricated with the correct lubricant and change it at the required interval. • Regularly inspect gearboxes for excessive wear or play in the gears. • Regularly inspect gearboxes for

lubrication and bearing wear. 136

An overview of transmission methods Transmissions are very diverse and only the main methods used in plastics processing are shown here. Note: There are many more types of gearbox and transmission methods that have been omitted for clarity. Chapter 4 – Services

Standard V-belts provide a transmission efficiency of 95–98% when first installed but they are subject to ageing, wear and slip or creep. These will rapidly decrease the transmission efficiency.

Maintenance • Use the right size belt for the pulley. If

the belt is too small it will sit too far into the pulley and if it is too big then it will not sit far enough into the pulley. Both conditions increase transmission losses. • Regularly check the condition of drive pulleys. They must be aligned correctly and be parallel and in the same plane with no offset.

belts with cogged or synchronous belts where they are suitable and it is possible. This can be done during a planned maintenance service.

Chain drives Chain drives are primarily used for product conveyors and handling but are not the main method of load transmission in plastics processing.

Maintenance • Regularly check and adjust chain

tension. • Regularly check chain condition and

grease chains at the correct interval.

• Regularly check belt condition for wear

• Regularly check the condition of drive

• Tip – If multiple belts are used they

should be matched sets and all be changed at the same time for belts from the same manufacturer. Preferably avoid multiple belts altogether. • Tip – Fit inspection windows to

machines so that the belt condition can be seen. Visual assessment of transmissions is quick and easy but the results can be limited. Ensure that the windows meet health and safety requirements. Checking for correct operation of V-belts is a specialist task that requires a stroboscopic tachometer and even then the guards must be removed for the test. Remote condition monitoring is possible using non-invasive technology and this type of equipment can reduce maintenance and improve performance.

Nobody had complained so we switched the motor off and claimed the savings.

• Use the right size chain for the pulley.

• Regularly check and adjust belt tension.

and the presence of hydraulic fluid or oil on the belt.

At one site, we found that all the belts on an HVAC fan had snapped and the motor was running without moving the fan.

sprockets. They must be aligned correctly and be parallel and in the same plane with no offset.

Couplings Where rigid couplings are used then the motor alignment is critical and poor alignment will result in damage to the motor or the coupling. Flexible couplings can accommodate some misalignment but should not be used as an excuse for poor alignment or lack of maintenance. Misalignment of flexible couplings can lead to excessive force on either the motor or the driven load. This can lead to failure of other components or large amounts of vibration. • Tip – Even if flexible couplings are used

the alignment of the motor and the load should be regularly checked.

A great resource for belt drives is ‘Preventive Maintenance & Safety for Belt Drives’. This is available free from www.gates.com.

Improvement The efficiency of standard V-belts will decrease over time from a peak of 95–98% to less than 93% due to ageing and failure to adjust the belt tension. Cogged belts have a greatly reduced bending resistance compared to standard V-belts and can be used on the same pulleys as equivalent Vbelts. They also need less maintenance, run cooler, last longer and are around 2% more efficient than standard V-belts. Synchronous belts are another alternative to standard V-belts, i.e., they are more efficient and retain their efficiency for longer, but they may not be suitable for all applications due to noise and a low tolerance for shock loading. • Tip – Replace existing traditional V-

Chapter 4 – Services

Cogged belts Cogged belts can easily be fitted to existing pulleys to improve transmission efficiency by up to 5% (typically 2–3%). Cogged belts may cost slightly more (20–30%) but they have a payback of less than 12 months. 137

4.17

Motors – minimise the demand: reduce the load at source

Lower loads to lower the power

Reduce the load at source

There are various techniques for reducing the driven load and these are shown on the lower right. The really important lesson here is that many motors are not actually contributing to productive output and that the loads can be eliminated or reduced through simple low-cost actions.

The savings from eliminating the load are total but the savings from reducing the load at source vary depending on the type of load. There are three basic load types, and these are classified by the relationship between torque, power and speed.

Eliminate the load at source

• Constant torque loads – these have a

Section 4.15 discussed methods of stopping motors when they had completed their essential work but this is about removing the load altogether because the load is not necessary. It may appear surprising, but significant numbers of motors do not actually perform a useful task, this can be because: • The task was once relevant but the need has been removed and nobody thought to stop the motor – after all it doesn’t cost anything does it? • The task was never relevant but again

the motor was free so why not use one? • The received wisdom is that the task is

necessary but the motor actually doesn’t perform the task (see sidebar of Section 4.16). A critical review of the site use of motors will always reveal areas for load elimination. Typical areas and examples for load source removal are: • Ventilation fans that operate even though the natural ventilation of the site/building is more than sufficient to provide the required air changes. • Personal cooling fans that operate whether people are there or not. At one site there were many small fans operating. The site manager stated that these were ‘to keep the operators cool’, but there were no people present because they were all on their lunch break.

Load reduction is often very costeffective. Many of the actions are lowcost and easy to carry out.

constant torque at all speeds and the power varies directly with the speed. Most applications, other than pumps and fans, are constant torque loads. Examples are positive displacement pumps and piston and screw compressors. For constant torque loads, reducing the speed by 50% will reduce the power needed by 50%. • Constant power loads – these have

higher values of torque at lower speeds, and lower values of torque at higher speeds. Examples are lathes, milling machines and drill presses. For constant power loads there is little that can be done to reduce the load. • Variable torque loads – with these loads

the torque varies as the square of the speed and the power varies as the cube of the speed. Examples include centrifugal pumps, turbine pumps, centrifugal blowers, fans and centrifugal compressors. Variable torque loads are

Do not operate motors at < 40% of the full rated load for long periods. This is very inefficient use of a motor. If possible replace the motor with a smaller one.

• Pumps for cooling water are often fitted

in parallel but this can degrade the system response. Ensure that the correct number of pumps is fitted for the need. Eliminating the load is simply a matter of asking: What does this motor do and do we need to do it? Ask this often enough and you will find motors that are not doing useful work and that can be eliminated. 138

Reducing the load can be achieved in many ways Load reduction is the third step in the energy management of motors. There are many methods available but the primary requirement is the realisation that many driven loads can be eliminated or reduced through simple low-cost actions. Chapter 4 – Services

the most rewarding loads to modify because of the cube relationship between the power and the speed. Reducing the load at source is a key action. Typical areas for load reduction are: • Dirt-encrusted fans will increase the motor load and cost more to run. Clean them regularly. • Automatically seal off extraction fans

from inoperative machinery to reduce extract fan loading. • Running cooling water systems at high pressures will increase the load on pumps and the losses in the system. Reducing system pressures (whilst monitoring cooling efficiency) can easily reduce pump motor loading.

• Checking that limit switches for

compressors are accurate and functioning. Fixed-speed compressors will have a control system that turns the compressor from off-load to on-load as the system pressure changes, these are often set very close together and the compressor effectively runs constantly. They are also not always accurate and can be improved in many cases. Control systems are about reducing motor energy use by ensuring that the motor works at the maximum efficiency (75–85% of full load) on the minimum load for the shortest possible time (and only when it is needed).

Reducing the load is also used in conjunction with many of the other techniques for motor management.

• Leaks in a compressed air system

increase the load on a compressor motor, reducing the leaks will reduce the load on the motor (see Section 4.26). • Conventional compressed air piping can

have high losses that are easily reduced using stainless steel or aluminium piping (see Section 4.30). • Blocked or dirty air inlet filters for compressors will increase the load necessary to feed air to the compressor and increase energy use. • Damaged or dirt-encrusted chillers will require more energy to transfer heat out of the system (see Section 4.36). • Blocked and dirty melt filters in extruders will increase the back pressure and cause the motor to run harder. Automatic screen changers are a wise investment for energy as well as for keeping the melt stream clean. Reducing the load at source is a matter of asking: What does this motor do and can we reduce the load? Ask this often enough and you will find loads that can be reduced for little effort.

Improve the control systems Many motor systems are effectively uncontrolled and simple controls can reduce the motor load. Some of these involve either switching the motor off (see Section 4.15) or slowing the motor down (see Section 4.20) but others involve ensuring that the system controls function and are effective. Typical areas for improved control systems are: • Ensuring that pump pressure switches

are accurate and functioning. Chapter 4 – Services

Motor loads vary in type and so do the energy savings The energy savings from reducing the load or the speed of the motor are not always the same. They depend on the characteristics of the load that is being driven. Variable torque loads offer the best opportunities because of the cube law. 139

Motors – optimise the supply: get the right size motor

Motor sizing Incorrect motor sizing costs real money and getting the right size motor is a critical decision that should never be taken lightly – bigger is not necessarily better and it is always more expensive in energy costs. Using a larger motor than necessary costs very little at the first purchase but the running cost is very different. A 15-kW motor costs only about £200–300 more than an 11-kW motor at the first purchase. However, a 15-kW motor will use an additional 41,224 kWh in the first year (based on 8,760 hours and η = 0.85). This is an additional cost of over £4,000 in the first year alone and over the typical 10-year lifetime of an AC motor the additional cost will be in the region of £41,000 (see graph on the lower right). This makes the additional purchase cost of £200–300 almost irrelevant. As noted in Section 4.13, the cost of motors is in the operation and not in the purchase.

Why do we choose big motors? There are a variety of reasons that sites and system designers select over-sized motors and the most common are: • Designers will generally over-specify motors (by rounding up to the next motor size) to provide a ‘safety factor’. • Designers are not generally concerned with the operating costs of a system as they are not responsible for this. This is an attitude that will only change when sites start to consider the ‘whole life cost’ of a project. • Motors are only available in a range of discrete sizes. It is therefore often difficult to exactly match the output to the demand and the next largest size is almost always chosen ‘just in case’. • Even relatively steady loads vary

slightly and it is often difficult to match the output to the process requirements. Therefore, designers will always work on the absolute maximum load even if this is only for 5% of the time. • Sites are tempted by the ‘bigger is

beautiful’ argument without considering the bigger energy costs that they load the site with. This type of routine decision-making 140

process often loads a site with motors and energy costs that are much larger than necessary (see the two boxes on the opposite page). This not only happens at the first purchase/system design. When a motor eventually fails, as they all must, it is often replaced with an even larger motor to ‘prevent failure in the future’. The result is that many motors in industry are larger than needed (up to twice as large in many cases), introduce excess costs to the site for no benefit, never reach their design load, and never run at optimum efficiency.

Fitting a large motor for a small load will cost money for the length of the motor life. Bigger is not better and size does matter.

• Tip – It is not uncommon to see a 22-kW

pump on a cooling water system when an 11-kW pump would be more than sufficient. What is an additional cost of ≈ £10,000/year between friends? • Tip – It is strongly recommended that

expert advice on motor sizing be sought to reduce costs. • Tip – Most motors can be temporarily

overloaded if they are allowed to cool down later by running at less than the rated load. • Tip – Review the size of all existing

installed motors by comparing the actual load to the rated load. If the two are very different, then replacing the existing Purchase and operating costs (11 kW vs. 15 kW motor) 120,000 11 kW 100,000 Purchase and operating cost (£)

4.18

15 kW

80,000

60,000

40,000

20,000

0 0

1

2

3

4

5

6

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Operating years

Typical AC motor operating costs over 10 years Many sites will choose a 15-kW motor over an 11-kW motor for ‘safety’ and ‘just in case’. The result of using a larger than necessary motor is an extreme (and unnecessary) financial penalty for the rest of the life of the motor. Chapter 4 – Services

motor with a smaller motor can be very profitable and pay back very quickly. Look at every motor and see if it can be replaced with a smaller motor – small changes can make a big difference. have a stock of replacement motors to get machines up and running in case of failure. This is acceptable for operational reasons but make sure it is a ‘temporary fix’ and that the correct motor size is fitted as soon as possible. • Tip – Where motors can be accurately

predicted to run at less than 33% of the rated output it is possible to reconfigure the motor from Delta to Star connection. This simple low-cost action can produce savings of up to 10%.

Motor efficiency Oversized motors not only use more energy but are also less efficient. Motors are most efficient when the load equals, or is slightly less than, the motor’s rated load and are highly inefficient when operating at a small proportion of their rated load (< 50%). The efficiency of any motor will vary with the applied load but this is not linear and two typical operating curves are shown on the top right. Both of these motors are most efficient when running at around 80– 90% of the rated load and both show a decrease in efficiency when the load is significantly lower than the rated load. The difference is that for older motors the efficiency decreases rapidly for loads of < 50% of the rated load, this decrease is much slower for new high-efficiency motors (see Section 4.19). • Tip – Using over-sized motors not only

increases energy costs but also means that the efficiency of the large motor decreases.

90 80 70 Efficiency (%)

• Tip – Maintenance departments may

Typical motor efficiency operating curve 100

60 50 Efficient (new)

40

Standard (old)

30 20 10 0 0

10

20

30

40

50

60

70

80

90

100

% of full load

Typical AC induction motor operating curve The efficiency of any motor is not constant over the full load range. Most motors are at their optimum efficiency at a load of 80% to 90% of the rated load. The efficiency of a motor falls off very quickly at loads below 50% of the rated load.

Motor sizing is important 1 At one site the cooling water pumps to the process from the two cooling towers were continuously operating fixed-speed pumps and for each tower there was a run and a stand-by pump. These were 30 HP (≈ 22 kW) for the run pump and 25 HP (≈ 18.5 kW) for the stand-by pump. The system worked perfectly well with the stand-by pump (18.5 kW) but the larger pump was always used, as it was the ‘run’ pump. This simple use of an oversized pump motor (22 kW instead of 18.5 kW) cost the site an extra US $4,000/year for each tower with no benefit in service. The site simply switched the pumps over so that the smaller pump for each tower was the ‘run’ and only used the larger pump as the ‘stand-by’. Instant savings of over US $8,000/year and enough to fund fitting VSDs to the ‘run’ pumps to save even more money.

Motor sizing is important 2 At another site, the sprue and runner regrinders on exactly the same machines producing exactly the same products were: Machine 1: 5.5-kW regrinder + 0.55-kW blower to the blender.

This system has a running cost of ≈ £6,235/year. Machine 2: 7.5-kW regrinder + 2.5-kW blower to the blender.

This system has a running cost of ≈ £10,306/year, i.e., ≈ £4,071/year more than Machine 1. There was no difference in the requirements but the site had the 7.5-kW regrinder + 2.5-kW blower available and simply used it without thinking about the energy cost of the larger motors. The savings from using the correct size regrinders and blowers were more than enough to pay for new, and correctly sized, equipment (with a payback of less than 6 months). This site had 25 regrinders so the potential was very large. Chapter 4 – Services

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4.19

Motors – optimise the supply: improve the motor efficiency

High-efficiency motors (HEMs) The importance of the energy use and the cost of motors has driven manufacturers to improve the efficiency of AC induction motors. These improvements are in the areas of: • More copper in the slots to reduce

electrical resistance. • Better-quality steel in the stator

laminations to improve magnetic fields. • Improved winding configurations. • Improved and reduced fan sizes to

improve cooling. • Improved bearings to reduce friction.

The broad classification of HEMs in the EU (EU MEPS) and in the USA and Canada (NEMA) is shown on the above right and this also includes the older CEMEP (European Committee of Manufacturers of Electrical Machines and Power Electronics) EU rating scheme based on Eff1, Eff2 and Eff3 (where Eff1 was the most efficient). This is no longer used but many motors with these designations will already be in service. The boundary limits for the four IEC ratings (two-pole motors @ 50 Hz) are shown on the right and the minimum efficiency limits vary with the size and type of the motor (the curves are slightly different for four-pole motors). Under EU MEPS and NEMA, motors must be labelled with the relevant efficiency class and governments around the world are starting to specify minimum motor efficiency levels based on these classifications: • In the EU, Directive 2009/125/EC

includes efficiency limits for motors and as of 1 January 2017, all motors with a 142

The efficiency standards for motors The efficiency of electric motors is increasing and what was regarded as ’high efficiency’ 10 years ago is now regarded as the standard efficiency level. The IEC standards are recognised world-wide but, in the USA, the NEMA standards apply. Efficiency boundaries for IE4, IE3, IE2 and IE1 2-pole motors 100%

Full load efficiency (%)

HEMs are up to 6% more efficient than standard motors (depending on the motor size and loading) and legislation in many parts of the world reflects these improvements. The International Electrotechnical Commission (IEC) sets world-wide standards for HEMs but in the USA, the standards are set by the National Electrical Manufacturers Association (NEMA). These standards are very similar but are not identical in all respects and care should be used in comparing motors.

90%

80%

IE4 minimum IE3 minimum IE2 minimum IE1 minimum

70%

IE5 (future) IE6 (future)

60% 0

20

40

60

80

100

120

140

160

180

200

Motor size (kW)

Boundary limits for IE grades of motors The development of HEMs continues and the current best motor (IE4) will soon be replaced by newer motors (IE 5 and better) that are not only more efficient but also retain their higher efficiency at lower part loads. Chapter 4 – Services

• In the USA, the Energy Independence

and Security Act (EISA) took effect on 1 June 2016 and requires a broad range of motors to meet the NEMA Premium standard. • Tip – This is for all new motors but does

not include: Motors that are completely integrated into equipment, e.g., pumps, fans and other new equipment. Motors that are made exclusively for operation with inverters (see Section 4.20). HEMs are widely available from all the main manufacturers and whilst they were initially more expensive than lowerefficiency motors, the price differential is being rapidly eroded. Any price differential will not matter in most cases because of the legal requirements. There is no legal requirement for existing motors to meet the higher efficiency levels but sites may choose to do this to reduce energy use and save money. For a 22-kW motor, an existing IE1 motor will have an efficiency of between 89.9 and 91.2% at 90% of the rated full load. An IE3 motor will have a minimum efficiency of 92.7% and an IE4 motor will have a minimum efficiency of 94.0% (these are the minimum efficiencies and individual motors may be better than this). These higher efficiencies are also generally achieved at a lower percentage of the rated load, i.e., around 75% of full load and the fall in efficiency at 50% load is much less in HEMs. These improvements may not sound much but the major cost for a motor is the operating cost and IE4 and IE3 motors have lower operating costs. For a 22-kW motor the efficiency difference between IE3 and IE2 is 1.5% at full load. This means that over a 10-year life cycle an IE2 motor will cost £3,200 more to run than an IE3 motor and will cost £6,000 more to run than an IE4 motor. At current costs, a 22-kW IE3 motor is only ≈ £150 more than an IE2 motor and a 22-kW IE4 motor is only ≈ £375 more than an IE2 motor. In the past it was not regarded as being cost-effective to replace an operating standard motor with a new IE4/IE3 motor until the old motor failed. This has now 

Chapter 4 – Services

changed. If the old motor has an efficiency of < 88% (a likely efficiency for an old motor) then the payback for replacing this with an IE4/IE3 motor will generally be less than a year (if the motor is operating at full load for 24/365).

HEMs have the same maintenance requirements as standard motors, are equally or more reliable and due to lower operating temperatures can have a longer operating life.

• Tip –Think about re-equipping the site

with IE4/IE3 motors now. • Tip – HEMs retain their efficiency at

lower loads ( 75%) they can actually increase the energy consumption.

This is a critical area as the smoother the DC output from the DC circuit, the cleaner the overall output from the drive. Finally, the inverter section of the drive inverts the DC waveform back into an AC waveform. This is generally carried out by pulse width modulation (PWM) using voltage pulses of constant magnitude but of varying length and frequency. These pulses create an effectively sinusoidal current that can be varied in frequency to vary the motor speed in response to the input control signal and the controller settings: Low frequency

Inverter Voltage Current High frequency

Note: The output AC waveform shown in the diagram is smooth but, in reality, the output waveform to the motor will often have harmonics in the main waveform.

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4.21

Motors – optimise the supply: the savings from slowing motors down

The savings depend on the load The savings that are achievable from slowing the motor down with VSDs vary with the type of load and loads vary in type depending on the application (see Section 4.18). This means that the energy savings also depend on the type of load.

with the cube of the speed (N3). Reducing the speed of a motor in a variable-torque application by 50% will reduce the power drawn (and energy use) by 88%. This is due to the ‘magic’ of the ‘Cube Law’ (also known as the ‘Affinity Laws’). Using VSDs in variable-torque applications can give substantial energy use reductions.

Constant-torque loads Typical constant-torque loads in plastics processing are: • Hydraulic power packs and systems.

• Mixers. • Positive-displacement pumps.

For this type of load, the torque required remains constant across the speed range and the savings from using a VSD are directly proportional to the speed reduction, i.e., kW = τ × N where: kW = kW drawn. τ = Torque. N = Motor speed. Reducing the speed of a motor in a constant-torque application by 50% will reduce the power drawn (and energy use) by 50%. This relationship is shown in the diagram on the upper right. Using VSDs to reduce the motor speed in constanttorque applications will reduce energy use but the real savings are in variable-torque loads.

Variable-torque loads Typical variable-torque loads in plastics processing are: • Cooling tower fans. • Cooling water pumps. • Chilled water pumps. • Compressors. • Vacuum pumps. • Air handling units.

80% Speed reduction (%)

• Conveyors.

90%

70% 60% 50% 40% 30% 20% 10% 0% 0%

20%

40%

60%

80%

100%

Energy use reduction (%)

Speed reduction for constant-torque loads The energy savings possible with VSDs are less significant for constant-torque loads and are directly proportional to the amount of speed reduction that can be achieved. A 20% reduction in motor speed will reduce energy use by 20%. VSD cost savings for variable-torque loads 100% 90% 80% Speed reduction (%)

• Piston and screw compressors.

VSD cost savings for constant-torque loads

100%

70% 60% 50% 40% 30% 20% 10% 0% 0%

20%

40% 60% Energy use reduction (%)

80%

100%

• Hot water circulation pumps.

Speed reduction for variable-torque loads

• Combustion blower fans.

The energy savings possible with VSDs are very significant with variable-torque loads even for small reductions in motor speed. A speed reduction of 20% reduces the energy used by 49% and a speed reduction of 50% reduces the energy used by 88%.

For variable-torque loads, the torque (τ) increases with the square of the speed (N2) and the power drawn therefore increases 146

Chapter 4 – Services

The 'Affinity Laws' for variabletorque loads The ‘Affinity Laws’ for variable-torque loads describe the impact of changes in speed or pressure on pumps or fans and can be used to predict the energy savings from installing VSDs. The basic Affinity Laws are:

Q new Q old

2.

=

of the impact of changes in motor speed and pressure but need to be used with care if the changes are large. • Tip – Pressure predictions need to

account for the effect of static head and the need to overcome this. You will not always save what is predicted – be conservative!

Parallel pumping The Affinity Laws mean that for certain applications it can be better to run two pumps at a slower speed than to run one pump at a high speed.

N new N old

2   N new   =   P old  N old 

VSD cost savings for variable-torque loads 100% 90%

P new

3   kW new N new  =    3. kW old  N old  where: Q = Flow rate (m3/min). N = Pump or fan speed. P = Pressure (meter or feet of head). kW = kW drawn. • Tip – The Affinity Laws can also be used

to: Predict the effect of impeller trimming. Convert pump curves produced for 60 Hz into the relevant curves for 50 Hz supplies. 

Pressure reduction (%)

1.

• Tip – The affinity laws allow prediction

80% 70% 60% 50% 40% 30% 20% 10% 0% 0%

20%

40%

60%

80%

100%

Energy use reduction (%)

Pressure reduction with variable-torque loads The energy savings possible with VSDs are less significant for pressure reductions but are still significant. A pressure reduction of 20% reduces the energy used by 28% and a pressure reduction of 50% reduces the energy used by 65%.

Speed reduction The effect of reducing the speed is calculated by transforming the third affinity law to the form: 3   N new   × kW kW new =  old   N old  This equation can be used to generate the graph for the energy savings that will result from speed decreases. This is shown on the lower left.

Pressure reduction The effect of reducing the pressure is calculated by transforming the second affinity law to the form: 3  Pnew  2 kW new =    P kW old  old 

This is what £145,000/year of pumps looks like

This equation can be used to generate the graph for the energy savings that will result from pump pressure decreases. This is shown on the upper right.

This set of pumps uses £145,000 of energy per year. There are no VSDs used and the system pressure is 7 bar. A reduction in system pressure to 4.5 bar with VSDs (35%) would save £75,000/year (48%) and give better process control.

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4.22

Motors – motor maintenance and management

Motor maintenance

Motor failure – replace/rewind?

Conventional AC induction motors are the workhorse of modern industry and will give excellent continuous operation for many years. However, they do need some basic maintenance to ensure that they continue to operate efficiently. Basic maintenance checks should include:

Even the best maintained motor will eventually fail and a decision is then needed whether to replace or to rewind. For motors of less than about 7.5 kW it is often cheaper and easier to replace the motor than to consider rewinding. For motors of greater than 7.5 kW, rewinding is often the instinctive answer because it is cheap, it is fast and it has always been done that way – but is it the best answer in the long term? Rewound and refurbished motors will inevitably suffer from a permanent energy efficiency reduction. When good practice is used this can be limited to 0.5% but the reduction can be up to 3.5% if the rewinding is poor. This efficiency reduction is permanent and if there is subsequent rewinding then the efficiency losses are likely to become additive, i.e., after two rewinds then the efficiency will have dropped by a minimum of 1% and could be up to 7% if poor practice is used. If the failed motor is a standard motor then this would increase the efficiency penalty for using the rewound standard motor versus a new HEM to over 10%.

• Check that the motor is well ventilated

and that air flow to the cooling fan is unobstructed. Do not allow the fan inlet to be blocked as this will cause the motor to overheat. • Check the condition of the bearings. • Tip – One of the easiest and quickest

methods of doing this is to use a vibration meter. The ultrasonic compressed air tool described in Section 8.3 can also be used for vibration testing but note that vibration testing is more for comparison than absolute measurement. • Check the motor electrical connections for the correct torque. • Tip – This is most easily carried out

using a thermal camera and this will also reveal any poor connections to the motor (see Section 8.3). • Check the electrical integrity of the

cables and motor insulation. • Check the overall cleanliness of the casing, the fan, the terminal box and any associated electronics such as soft starters and VSDs.

Note: This is based on a typical motor being rewound twice before replacement. If simple calculations of the effect of this loss of efficiency are carried out then for

Energy efficiency improvements from the development of VSDs and HEMs mean that companies must develop and implement a motor management policy for the purchase and operation of motors.

For every 10°C rise in winding temperature the life of the insulation is reduced by 50%. Keep motors cool to increase their life. Check the temperatures using the ‘hand test’ (see Section 4.14).

• Check the load transmission and

mechanical alignment of the motor to the load as detailed in Section 4.16. Simple basic maintenance will keep AC motors running for many years. One of the worst actions for energy efficiency and operational reliability is to allow an AC motor to run hot. All motors are certified for a specified temperature increase whilst running and will continue to operate within these limits. However, running motors at high temperature reduces their efficiency due to increasing winding resistance with temperature. This means that more current is dissipated as heat and the temperature rises even more. Running motors at excessive temperatures reduces the lifetime and reliability of the motor (see thermograph on the right). 148

Thermograph of motor casing at 113.3°C When a motor casing is at 113.3°C then motor failure is not far away. This motor is running a mission critical injection moulding machine and no spare is held on the site. This is an unhappy customer and a disaster waiting to happen. Chapter 4 – Services

any motor operating for more than 2,000 hours (in total and not per year) it is more cost-effective to purchase a new HEM than to rewind a failed motor. The replacement of failed standard motors with HEMs is simple economics. • Tip – There is a Good Practice Guide for

motor rewinding produced by the Association of Electrical and Mechanical Trades (www.aemt.co.uk). Check that your contractor complies with this or similar. Also see Appendix C of the US DoE publication1 for an excellent checklist to assess a motor contractor. • Tip – Motors that have been

mechanically damaged should always be replaced. • Tip – The failure of a motor is not

always due to it being undersized. Failure is not an opportunity to increase the size of the motor. It is an opportunity to review the size of the motor and to potentially replace the motor with a motor that is both more efficient but also of a more appropriate size, i.e., smaller. Care should be taken to consider the mounting of the motor if this is different for the smaller motor.

The motor management policy (MMP) Good motor maintenance and the replace/repair decision are components of an overall MMP. The greater importance of running costs over the initial purchase price means that sites need to change the way they look at motors. Traditionally the decision was made by the electrician on the spot and this was governed by the need to keep production running. In the future, decisions must be made on the ‘whole life cost’ of the motor where all purchase, maintenance, repair and operating costs are considered. An MMP can provide the rules for making the best financial decision. A well defined, effective and enforced MMP will allow a site to reduce costs by forcing the choice of the best motors and systems for the site.

Failing to set up and operate an effective MMP means that right now there are decisions being taken at your site that will affect your energy costs for the next 10 years. Are they the right ones? • Tip – Motor register. An essential part of

motor management is a motor register. This can be a simple spreadsheet listing:  The motor application.  

The nameplate details. The frame size.

The approximate running hours.  The repair history. 

The spares held for the motor.  The action to be taken in the event of failure, i.e., replace/repair? 

The motor register is also invaluable for the energy map (see Section 3.2). • Tip – It is now financially good to

At one site, the maintenance manager bought standard motors because they were £2,500 cheaper than IE3 motors. IE3 motors would have saved £2,500/year, a payback of 1 year. By saving ≈ £2,500 in purchase costs, the company has increased the energy costs by ≈ £25,000 over the next 10 years. He thought he was doing the right thing because nobody ever told him otherwise.

replace many motors with HEMs before failure. • Tip – Some sites have sub-contracted

their motor management. This is not a problem, simply include the MMP in the contract with the sub-contractor. • Tip – In some countries, the purchase of

HEMs qualifies for tax rebates or other financial assistance.

• 1. US Department of Energy (DOE). 2014. ‘Improving Motor and Drive System Performance’.

Replace with HEM

Repair

An MMP helps everybody and means that when a motor fails in the middle of the night then everybody knows exactly what to do, there is no confusion and the most economic decision is taken.

The motor management policy

This policy should include guidelines on repair and replacement based on lifetime costing and the specification of HEMs for all new purchases.

A motor management policy will make ‘repair or replace’ decisions easy and cost-effective. The simple decisions often cost the most money. As with any policies, failure to comply with the policy should be accompanied by appropriate sanctions.

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Size (kW)

149

4.23

Motors – where are you now?

The initial steps in motors As with the score charts shown earlier, this is a self-assessment exercise to allow a site to benchmark their current status. This will set the scene for planning improvements in the area of motors. Motors are the key to energy management in plastics processing due to the amount of electricity that is used in motors. Understanding where motors are used and adequately controlling their use is only part of motor management. It is just as important to ensure that a site has the right type of motors, i.e., energy-efficient motors, and uses these wisely through the use of VSDs when this is the appropriate

method of control. Above all, the easiest way to save energy with motors is to ensure that they are switched off when not being used. Motor management is crucial to successful energy management in plastics processing.

Control of motors is a combination of good management and good technical capabilities.

Completing the chart This chart is completed and assessed as for those presented previously.

Motors

Motor management 4 3 VSDs & HEMs

2

Motor information

1 0

Maintenance & repair

Motor sizing & speeds

Operations

Use the scoring matrix to assess where you are in motors The numbers can be transferred to the radar chart for a quick visual assessment of where you are in terms of controlling motors on the site. 150

Plastics processors ignore motors at their own cost. Some of the best and easiest energy management projects are in the field of motors.

Chapter 4 – Services

Motors Level

4

3

2

1

0

Score

Motor management

Motor information

Motor sizing & speeds

Motor management policy is widely available, widely publicised, approved by senior management & rigorously enforced.

Complete inventory of motors used at site & yearly running times. Detailed information available on motors using the most energy.

Detailed information on motor sizes & speed requirements available. Action taken to reduce all motor loads.

Motor management policy is widely available, widely publicised, approved by senior management but is not rigorously enforced.

List available of the major motors used at site & yearly running times. Some information available on motors using the most energy.

Motor management policy produced but not widely available, not publicised, not approved by senior management & not enforced.

Approximate Some information Policy of manual Poor or cursory Some application knowledge of the on motor sizes & switch off of motor of VSDs & HEMs largest motors on speed motors at job maintenance where specified the site & their requirements completion. carried out on all externally by running times but available. Policy enforced motors. suppliers. No action taken to variably & not well Virtually no spares no detailed information. reduce any motor adhered to. carried even for loads. ‘mission critical’ motors.

Operations

Excellent motor VSDs & HEMs maintenance used in all carried out on all applications where motors. appropriate. Critical spares carried for most motors & wide range of spares carried for ‘mission critical’ motors.

Information on Policy of manual motor sizes & switch off of speed motors at job requirements only completion. for limited number Policy strictly of motors. enforced & Some action taken adhered to. to reduce loads on large motors.

Fair motor VSDs & HEMs maintenance used in some carried out on applications but some motors. large numbers of Small range of critical applications spares carried but do not use the only for ‘mission latest technology. critical’ motors.

No motor No information on No knowledge of motors used at the motor sizing or management policy available. site. speeds available. All decisions are ad hoc, made at operational management level & inconsistent.

Chapter 4 – Services

x

VSDs & HEMs

Motors are electrically controlled to switch off when job is complete or not needed.

Unwritten motor Vague knowledge No information on No policy of management of the largest motor sizes & switching off speed policy established motors on the site. motors. Ad-hoc by maintenance requirements action taken by available. but often some staff. No action taken to Some motors left overridden by senior reduce any motor running management. loads. needlessly.

x

Maintenance & repair

x

Little motor maintenance carried out & little knowledge of maintenance requirements. No spares stocked.

Knowledge of the benefits of VSDs & HEMs but no use even where applications are suitable & can save substantial amounts of energy.

No policy of No motor No knowledge of maintenance & no the applications for switching off motors. knowledge of energy-efficient Many motors left maintenance VSDs or HEMs. running requirements. needlessly. No spares stocked. Maintenance carried out only when failed.

x

x

x 151

4.24

Compressed air – the system

System layout

Filters

Understanding the components and the layout of the compressed air system is necessary to start reducing energy use in compressed air. All systems contain the same fundamental components and have the same basic layout, although this may not initially seem the case when in the hot and noisy environment of the compressor room. A basic outline of a compressed air system is shown in the diagram on the right and can be used to identify the various components in the compressor house. The piping layout may appear complicated but much of the actual piping is ‘bypass’ piping designed to allow isolation and servicing of the main components without losing the supply of compressed air to the system. Do not be surprised if the site layout is slightly different to that illustrated; standards and layouts vary around the world. In some areas (particularly the USA) the air receivers tend to be located after the air treatment instead of before the air treatment as illustrated. This makes little difference to the operation of the system and similar variations are seen in most systems.

Filters are an essential part of the system and prevent contaminants from entering the distribution system. Filters are located throughout the system and are a vital but often overlooked component. The energy aspects of filters are dealt with in Section 4.29.

Compressors The main compressors are used to compress the cool inlet air and in most installations there will be two or more compressors. These provide the basic compressed air to the system. They may be arranged with one or more compressors actually supplying air or in single active compressor systems there will probably be another compressor acting as stand-by to provide air during the servicing of the main compressor. The compressors can be controlled individually or with a central controller. The energy aspects of the main compressor capacity are dealt with in Section 4.28.

Dryers Dryers are essential for the removal and disposal of the bulk of the water from the compressed air. Dryers are also often overlooked but dryer failure can lead to water contamination of the complete system. The energy aspects of dryers are dealt with in Section 4.29. 152

Receivers The receivers provide a store of compressed air for periods when the transient demand exceeds the instantaneous capacity of the compressors. They also act to cool the hot compressed air as it exits the compressors and enters the system. The energy aspects of receivers and their recommended capacity are dealt with in Section 4.30.

Most compressed air systems are similar in layout despite their apparent differences. Get to know your system components to reduce the energy consumption of the system.

Condensate drains Parallel to the compressed air system are the condensate drains and the water removal system. As the compressed air cools after exiting the compressor, there is considerable water condensation and this must be removed from the system. This condensate will also often be contaminated with oil and the condensate drains remove the oil/water mixture from the system and separate the oil from the water before disposing of the water to the drains and retaining the oil for safe disposal.

Distribution system After the compressed air is cleaned and dried, it is distributed to the site by the distribution system and this can either be a ring main or spur type distribution system. For sites with a large transient demand located at some distance from the compressor house, it is common to install additional local receivers close to the large transient demand. Regulators are commonly provided at various points on the drops to provide air at a reduced pressure. The energy aspects of distribution are dealt with in Section 4.30.

Chapter 4 – Services

The basic outline of a compressed air system showing the main components Most compressed air systems will be very similar to the typical layout shown above. There are naturally differences between individual systems, particularly in the actual compressor control system when multiple compressors are used. Some systems will not have a local receiver but will operate totally from the ring main and other systems will have no ring main but will operate from a spur type system. Chapter 4 – Services

153

Compressed air – the programme

It isn’t free! Compressed air is a convenient and often essential utility, but it is very expensive to produce. In fact, most of the energy used to compress air is turned into heat and then lost to the system and environment. At the point of use, compressed air costs more than ten times the equivalent quantity of electrical power, i.e., an equivalent cost of around £1.00/kWh. At this price, it should never be wasted and only be used when necessary. In addition to the generation costs, compressed air also needs to be treated to remove moisture, oil and dirt. It is obvious that the higher the air quality required, the greater the energy consumed by the treatment system. Reducing the cost of compressed air is one of the easiest energy management activities that a company can undertake. This is because most companies are very poor at managing compressed air and the potential gains are both easily quantified and easy to achieve. This is one of the first areas that any company should investigate for small investment and rapid payback. The cost of compressor ownership over 10 years is overwhelmingly made up of the cost of energy used to operate the compressor. At a typical site operating 24/7 (8,760 hours/year) day, a 90-kW compressor motor will use energy worth approximately £84,000/year. Even a relatively small 30-kW compressor (smaller than most compressors used in plastics processing factories) will cost over £29,000/year to run. This is far more than the capital cost of the compressor – saving money on the initial capital cost of a compressor by buying a product with poor energy efficiency is a very poor choice in the long term. At these cost levels, an energy-efficient system is highly costeffective, even if it costs much more to purchase.

The programme The cost of compressed air makes it an expensive resource and the way to achieve the best savings is to implement a full compressed air management programme. This is a structured programme designed 154

to reduce energy use at all stages of the compressed air process and is structured into two stages and five steps. These are followed in order to reduce the overall cost of energy. For the average company, a compressed air management programme can produce savings up to 50% in the cost of compressed air by inexpensive good housekeeping measures such as making end-users aware of the cost of generating compressed air and enlisting their help in reporting leaks.

Compressed air is an expensive resource. Minimise the demand and then optimise the supply.

Stage 1: Minimise the demand Minimising the demand is the first step in compressed air management and should be completed before any steps are taken to optimise the supply. It is not logical to optimise the supply for excessive demand based on excessive leakage or poor use.

Reduce leakage Leakage is a total waste to the system and must be minimised as the first step. Leakage rates in poorly maintained compressed air systems can reach as high as 50% and typical leakage rates are 30– 40% – this is 30–40% of wasted energy and for a small 30-kW compressor represents energy losses of £8,500/year.

Relative costs of compressor operation 100% 90% 80% 70% Cost division

4.25

60%

Capital 50%

Energy

40%

Maintenance

30% 20% 10% 0% 2000

5000 Operating hours per year

8000

The relative costs for compressor operation Even over low operating hours, the main cost of operating a compressor is in the energy used to operate the compressor motor. The capital and maintenance costs of operating a compressor are dwarfed by the operating costs. Chapter 4 – Services

Reduce use Compressed air is often misused because everyone assumes it is free. In reality it is one of the most expensive services that is provided to a factory. All applications of compressed air should be checked to see whether it they are essential or simply poor engineering for convenience.

Stage 2: Optimise the supply After the demand is minimised, it is then possible to start to optimise the supply to produce the required demand at the minimum energy use and cost.

Reduce generation costs Generation of the compressed air is the largest energy cost and simple measures can save considerable costs. The ultimate solution is to review the compressor specification to define the real needs.

versus the production output. A more valuable measurement is that of the air flow, an air flow meter can be used to determine the SEC of the compressed air process through the kWh/m3 of compressed air. • 1. The best resource book for all aspects of compressed air is the ‘Compressed Air Compendium’ (6th edition 2004) published by Boge. Some of the text is related to German customs and practice but it is still the best book around and it is available free from: www.drucklufttechnik.de/english. • 2. Atlas Copco produce a well-illustrated and well-written ‘Compressed Air Manual’. This seems to move around and it is best to search for it on the Internet. The current version is the 8th edition.

A compressed air programme can produce savings of up to 50% in the cost of compressed air.

Compressed air is a very expensive service. Only about 5% of the energy used at the compressor becomes available to do work at the point of use.

Reduce treatment costs Treatment of compressed air is an expensive operation that is often ignored even by companies who are good at managing compressed air. Again, simple measures can produce large and permanent savings.

Improve distribution The actual distribution piping and the condition of the distribution system have a large effect on the system losses and optimising the distribution system can produce large reductions in the cost of supplying compressed air.

The compressed air map One of the best tools to have in the management of compressed air is a ‘compressed air’ map of the site. This is a layout of the compressed air system with all the system components and the use listed on the map. This provides an overall guide to the system and guides leak reduction, use reduction and supply improvements and will inevitably reveal many areas where the process can be changed to reduce costs.

Monitoring & targeting The effectiveness of compressed air generation and use can be treated as for the energy consumption of the site. A kWh meter fitted to the compressor feed will enable hourly running costs to be determined and this can be plotted versus production volume (as in Section 2.2) to determine the cost of compressed air Chapter 4 – Services

The compressed air management programme The compressed air management programme follows two stages and five steps to reduce energy use in compressed air. Stage 1 must be completed and maintained before Stage 2 is started to get the full benefits of the programme.

Cost allocation is important As with any service, the users should pay for the service. In a company producing both injection stretch blow and extrusion blow mouldings the Managing Director noted that the injection stretch products were easy to sell but that the extrusion blow products always seemed expensive to the marketplace. Investigations showed that the injection stretch blow moulding was using a 40-bar compressed air supply costing approximately £300,000 per year but that the cost of this was being allocated over the complete company. The extrusion blow products (which used none of the 40-bar compressed air) were effectively subsidising the injection stretch blow products. This made the extrusion blow products more expensive and the injection stretch blow products cheaper. Sales were skewed because they were allocating costs incorrectly. 155

Compressed air – minimise the demand: reduce leakage

The invisible cost Reducing leakage is the first step in minimising demand. In the plastics processing industry, typical observed leak rates are of the order of 30–40% with an approximate average of 35%, i.e., 35% of the compressed air generating power is wasted in feeding leaks in the distribution system. Every system will have leaks and target leakage rates vary with the site: • For small sites, the leakage target

should be 5–7%. • For medium sites, the leakage target

should be 7–10%. • For large sites, the leakage target should

be 10–12%. Most plastics processing sites fall into the ‘medium’ category and should aim for a leakage rate of 7–10%. This means that the average site could save approximately 25% of the cost of compressed air simply by achieving the target leakage rate. Leakage is not only a direct source of waste; it is also an indirect contributor to operating costs. As leaks increase the system pressure drops and the most common solution is to increase the pressure to compensate for the losses and extra generating pressure costs money. The first step in leakage reduction is to recognise the costs involved and make a commitment to a site awareness programme. Regular, continuous attention to the compressed air system coupled with proper maintenance will lead to effective progress in minimising leaks.

The cost of leaks The cost of leakage in terms of equivalent mm in diameter at a pressure of 7 bar operating for 8,760 hours/year is shown on the right. A 3-mm hole in a system at 7 bar will leak about 11 litres/s and cost ≈ £1,800/year. In a system with numerous leaks, this cost will multiply rapidly. The limit of an audible leak is in the region of £200/year – this means that if the site is not operating and is quiet then any leak that is audible will be costing a minimum of £200/year. That ‘ssssssss’ noise you hear is not a normal operating condition, it is energy and money being wasted.

156

Note: The cost of leakage for a given leak will be greater if the system is running at a pressure of greater than 7 bar and less if the system is running at a pressure of less than 7 bar.

Compressed air leakage survey and programme Simple leak surveys and maintenance can produce dramatic cost reductions and, in some cases, leak reporting and repair has enabled companies to shut down some compressors for all or most of their operating time. A leak detection programme should be established to regularly survey the site to detect leaks and rectify these. Surveys can be made by finding audible leaks (during a shut-down period), using a solution of soap and water to find leaks during normal operation or using an ultrasonic detector at any time. Compressed air leakage control is not a single task that can ever be completed; it is a continuous rolling programme of leak detection and sealing that never ends. Sites are advised to use an ultrasonic detector and a programme of 2 hours per week for detection and rectification of leaks in specific area. Find a leak, tag a leak and seal a leak should be the process.

Many compressed air systems are set in bar and 1 bar = 100 kPa. We will use bar as this is most common in the industry. For sites using psi, 100 psi ≈ 7 bar.

Purchasing an ultrasonic detector is strongly recommended for any size of site. We use the EP542A detector + EP911 headphones costing ≈ £850. This is no longer available but similar detectors can be found from Logis-Tech Associates, www.logistech.co.uk.

Cost of compressed air leaks (8,760 hours/year @ 7bar) £20,000

£15,000 Cost per year (£)

4.26

£10,000

£5,000

£0 0

1

2

3

4

5

6

7

8

9

10

Size of leak (mm effective diameter)

The cost of compressed air leakage and poor use Leakage of compressed air is one of the greatest avoidable costs at many plastics processing sites. Simple recognition of the concern and rapid treatment can reduce operating costs significantly and quickly. Chapter 4 – Services

Leakage measurement

Where to look for leaks

It is only possible to carry out actual measurement of system leakage when all of the equipment that normally uses compressed air is completely shut down. This means that measurement must be outside normal operating hours, a difficult thing to do when operating 24/7.

Use the compressed air map (see Section 4.25) to plan the compressed air leakage survey. Look for leaks in:

Cycle timing method Close down all air-operated equipment. Start the compressor. When the system

has reached the set point, the compressor will switch off. As air leaks cause the pressure to fall below the set point it will switch on again. Record the average on-load time (T)

and average off-load time (t) over a minimum of at least five cycles. Establish the compressor delivery

capacity Q (in l/s or in m3/min) from the nameplate or other documentation.

Calculate total leakage from T, t, and

the total air capacity of the compressor Q in litres/second from:

Redundant spurs in the system. Condensate traps. Ageing pipe work. Fittings and flanges. Leaks are caused

by pipe strain due to inadequate supports, inadequate joints or twisting. Flexible hoses. Leaks can be caused

by abrasion, deterioration (e.g., heat sources) or mechanical impact. Use permanent fixings rather than worm drive fixings.

During an energy survey it was once discovered that the substantial compressor system was doing nothing but feed the leaks. The system had been installed, was maintained and was being paid for but the compressed air was not actually being used for anything. The only consumer of compressed air was the leakage of the system itself!

Isolate machinery, supply lines, even

whole buildings from the compressed air mains when not in production. This can be done automatically using electronic controllers. Regulators are often a source of

leakage and abuse by operators. Check all regulators for correct setting and operation and replace as required.

Leakage = Q × T/(T+t) If the capacity is not known then this

method can provide an estimate of the leakage as a percentage of the total compressor capacity.

A

B

C

D

Pressure decay If the compressor delivery capacity (Q) is not known or if it is a modulating compressor then the pressure decay method can be used. This is not as accurate as the cycle timing method at low pressures, e.g., 7 bar, but is sometimes the only method available: Calculate the volume of the

compressed air distribution system (V) in litres or m3 – this should include the volume of all piping over 25 mm in diameter and all receivers. Pump up the system to the set point

(P1) as recorded on the receiver pressure gauge. Isolate the receiver and the system

from the compressor. Using an accurate pressure gauge,

record the time (T) for the pressure to drop to P2 (at least 1 bar below P1) over a minimum of at least five tests. Calculate the total leakage from:

Leakage = V × (P1 − P2)/T Chapter 4 – Services

Terminating compressed air lines A: Electrical fitters use cable ties. B: Mechanical fitters use adhesive tape. C: Operators use anything that comes to hand. D: Smokers use a cigarette lighter. 157

4.27

Compressed air – minimise the demand: reduce use

The most expensive resource Most sites appear to have set up operations thinking that compressed air is free and use is, at best, poorly controlled and, at worst, totally uncontrolled. At these sites, compressed air is used for applications where it is preferable to use almost any other type of power. The simple realisation that compressed air is probably the most expensive method available for providing motive power should change the ideas of many sites.

Finding and classifying use – the compressed air map Much of the actual use of compressed air is the result of low-level uninformed ‘convenience’ decisions made with no consideration of the cost of compressed air. Vital use of compressed air for actuators, cylinders and slides often uses very little compressed air, i.e., the amount used in essential applications is normally only the volume of the cylinder or actuator and this is often trivial. The bulk of the compressed air use is ‘discretionary’, where air is freely discharged and the volumes are very large. In many cases, compressed air has been used as a ‘quick fix’ in the past and has now become standard practice that nobody notices or cares about. This is particularly true of open air lines used for cooling or motive power, these are effectively ‘leaks’ and cost the same as a leak (see Section 4.26). A survey of the use of compressed air at a site will inevitably reveal many areas where the process can be easily changed to reduce compressed air use and costs.

air is poorly used. The following typical examples of poor use may seem excessive but some of them are being used at your site now and are raising costs through excessive use of compressed air:

At the point of application, compressed air costs approximately 10 times (per kWh) as much as using direct electric power.

Cooling tools A site had problems with cracked water channels in a tool. Instead of fixing the tool, the site used compressed air through the tool to cool the product. Cost: £12,000/year. Note: Repairing the tooling cost £6,000.

Cooling motors

Fit a pressure regulator at each point of use and adjust it to the minimum pressure required for the application.

A site had an overheating extruder motor. Instead of fixing the problem, the site attached an open 10-mm ID air line to the motor inlet area. Cost: £20,000/year. Note: Replacing the motor cost £5,000.

Cooling chill rollers A site had sheet sticking to a chill roller. They ‘solved’ the problem with 2 × 5 mm ID open air lines in the separation area.

Use should be reduced wherever possible and other methods of motive power or process should be devised by re-engineering the process.

Cost: £6,400/year/machine. Note: The problem had actually gone away but the air lines were still there because they were absolutely necessary! They turned them off, nothing changed. • Tip – Solve the problem and not the symptoms.

Classification and action Application

Optional

Vital

Reengineered

Sites should carry out a complete survey of all the uses of compressed air on the site and categorise all uses as either ‘optional’ or ‘vital’. All ‘optional’ uses of compressed air should be re-engineered to remove the use – this is often not difficult when the cost of the current compressed air use is calculated.

Cooling motors





Cooling product





Note: Removing ‘optional’ uses of compressed air will also reduce site noise.

Use (or abuse) examples The range of optional uses of compressed air in plastics processing makes it difficult to identify all the areas where compressed 158



Actuators Testing





Bowl feeders





Hand tools





Granule movement





Typical applications of compressed air Listing applications of compressed air provides a checklist for reengineering to remove the optional uses of compressed air. Calculate the cost of compressed air used in each ‘optional’ application to provide a budget for the re-engineering process. Chapter 4 – Services

• Tip – Stop using compressed air for

ventilation or cooling – low-pressure, large-volume fans are cheaper and more effective.

Moving sheet A site producing sheet PVC used 4 × 3 mm air lines to direct cut sheet from the off-take area to one of two packing areas. Cost: £5,200/year/machine. Note: A simple mechanical guide cost £1,000 to manufacture and install.

Moving bottles A site used an open 3-mm ID air line to move PE bottles from one side of a conveyor to the other before a printer. Cost: £1,300/year/line. Note: A simple piece of metal cost less than £100 to make and install.

Moving parts – vibratory bowl feeders An assembly site used 5 × 3 mm air lines to orient parts in a bowl feeder because of problems with a previous part. These were totally unnecessary for most parts. Cost: £6,500/year/bowl feeder. Note: The air lines were turned off and no change was seen.

Moving parts – testing A site used an open 3-mm air line to test the movement of a hinged product after assembly. The air line operated whether there was product on the line or not. Cost: £1,300/year/line. Note: A mechanical alternative was devised for a cost of £800 and an operating cost of £150/year.

Compressed air blow guns Most sites have large numbers of compressed air blow guns at the machines and in general use. These are expensive to operate and energy-efficient models are easily available. • Tip – Fit high-efficiency air nozzles – the

payback can be as short as 4 months.

Hand tools In assembly areas, the use of compressed air hand tools is common. Compressed air hand tools may appear economic (no theft) but the total cost of ownership is high. • Tip – Use electric tools instead of

compressed air tools. Do not do any of these things!

Chapter 4 – Services

A flow chart for reducing compressed air use First create the compressed air map for all open air lines at the site, then follow the flow chart above for all open air lines at the site. Sites using this simple flow chart have reduced compressed air use by 30% within 6 months. 159

4.28

Compressed air – optimise the supply: improve generation

Simple changes Selecting the right compressor is a complex task and the choice depends on the pressure and amount of air required. The most popular compressors in the plastics processing industry are the piston and the screw types, both are positive displacement compressors but have very different configurations. • Piston compressors – air-cooled, single-

or two-stage piston compressors can provide 25–250 l/s of compressed air, for requirements of 250–1000 l/s then watercooled variants are generally used. • Screw compressors – single-stage screw compressors can provide from 25–250 l/s, for higher requirements, multi-stage screw compressors are used. Screw compressors have inter-coolers to improve overall efficiency. In both cases the compressed air is usually after-cooled to reduce the air temperature and to partially remove condensed water.

Intake air Air is a gas and follows the standard gas laws. Cold air is therefore denser and already more compressed than hot air and requires less energy to be compressed to the specified pressure. Compressor houses are often hot and using hot air for the intake decreases the efficiency of the compressor. Cool, clean, dry intake air will always lead to more efficient operation of the compressor and intake air should always be drawn from the coolest possible source (this is rarely from inside the compressor house) and colder outside air should be used wherever possible.

• Tip – Look at ways of minimising the

overall compressor room temperature, e.g., use partitions if compressors are located in boiler houses. The air intake filters to the compressor itself should also be clean and free of obstructions that could reduce the air flow to the compressor and increase generation costs. Blocked inlet filters can increase generation costs by up to 4%.

This workbook does not cover selecting a compressor as this is a specialist task.

• Tip – Inlet filter maintenance must be

part of the maintenance schedule.

Pressure setting The energy required to compress air to a specified pressure is not linear. The higher the pressure, the more expensive it is to provide the air. The cost of generation follows a ‘square law’, i.e. it costs four times as much to generate air at 8 bar as it does to generate air at 4 bar. Even small reductions in the pressure set point can result in significant energy cost reductions. A ‘rule of thumb’ is that 8% of the generation energy is saved for every 1 bar reduction in the set point. Most systems in the plastics processing industry are set at 7.0–7.5 bar but that is rarely the real need and most general systems can operate at 6.0–6.5 bar without any problems. Reducing the set

The approximate cost of running a compressor can be calculated from the simple calculation method shown in Section 4.13.

Switch off compressors during nonproductive hours. They are often only feeding leaks or creating them.

For every 3°C drop in intake air temperature there is a 1% increase in the efficiency of a compressor. For a 90-kW compressor costing £84,000/year to operate then a 3°C reduction in intake air temperature will produce savings of ≈ £840/year for virtually no cost. Greater temperature reductions are often possible. • Tip – Position air inlets outside if

possible – cold air is easier to compress. • Tip – Look at ways to minimise the

input air temperature, e.g., by ducting from outside, and consider the benefits of partially drying the input air before it is compressed rather than after. 160

Compressor types There are many different types of compressor available and the type chosen depends on the pressure and amount of air required by the site. In plastics processing the most common types are the screw and the reciprocating piston types. Chapter 4 – Services

• Tip – Investigate the set point on the

compressor. In many cases, the required pressure is less than the set point but nobody has ever asked what the real set point should be. Progressively and slowly reduce the set point whilst monitoring production quality and reviewing the actual applications to determine if this is creating any application concerns. Note: Do not forget to allow for piping losses at times of peak demand. • Tip – Make sure that the pressure is not

higher than it needs to be because of volume restrictions (see Section 4.30). • Tip – Higher than required set points

increase system leakage and increase use at open air lines. A decrease in the set point of 1 bar will decrease leakage and open air line use by around 15%. In many cases, a machine takes inlet air at 7 bar and then uses a regulator to reduce the pressure to ≈ 2 bar. A survey of the site should look not simply at the name plate requirements but also at the actual requirements inside the machine. It is sometimes possible to implement a dual compressed air system supplying a very limited number of machines with 7 bar air and supplying the bulk of the machines with 2–4 bar compressed air at a much reduced cost. • Tip – Where only one or two machines

require 7 bar then it may be possible to eliminate the 7 bar system completely and use a 2–3 bar system for the complete site with small local booster units close to the relevant processes.

VSDs and controls Fixed-speed compressors can be in one of three states: • On-load – generating compressed air. • Off-load – the motor is idling but no compressed air is being generated.

but VSD compressors are much more efficient as they eliminate off-load energy use. The payback times vary depending on the site but are generally less than 18 months. For large demands it is best to use continuously operating fixed-speed compressors to provide the base load demand and to use the VSD compressor to provide the variable demand. This does need a better control system and careful selection of compressors sizes but will provide the optimum solution.

If there is a machine or area that requires compressed air for longer than the rest of the factory, consider a dedicated compressor so that the main system can be switched off.

• Tip – Investigate VSD compressors. • Tip – Avoid off-load operation. • Tip – For compressors of < 1000 l/s with

a long off-load cycle, it may be possible to minimise off-load operation by turning the compressor off if the system demand is low and there is adequate receiver capacity. An automatic control can stop the compressor after a set period of offload running, and then restart the machine on demand for air. Note: Make sure that the number of stops and starts is within the recommended criteria for the motor. For installations with multiple compressors, the use of a simple cascade operation is not the most energy-efficient. Electronic sequencing controls can be used to optimise the operation of the compressors and to equalise wear. • Tip – Electronic sequencing minimises

compressors going on- and off-load.

VSD-controlled compressors are the best solution for almost all sites. For existing compressors, all sites should investigate the costs of retrofitting VSDs to existing compressors. For new purchases, buying a VSD compressor should be the only option.

Compressor energy use 250

200

150

Power (kW)

point by 1 bar can save ≈ £7,000/year for a 90-kW compressor.

Off-load power

100

• Stopped.

A compressor that is off-load is still drawing power and the plot on the right shows that this can easily be up to 70% of the on-load power use. This is for no effective compressed air generation. The current optimum solution for most sites is to use piston or screw compressors fitted with VSD motors and these offer many control and efficiency advantages. These can be new VSD compressors or retrofitted VSDs for existing compressors Chapter 4 – Services

50

0 00:00

00:20

00:40

01:00

01:20 01:40 Time (min:s)

02:00

02:20

02:40

03:00

Compressor energy use with time A compressor in the off-load condition (not generating compressed air) will use up to 70% of the energy of a compressor that is on-load (generating compressed air). VSD compressors will considerably reduce this load. 161

4.29

Compressed air – optimise the supply: optimise treatment

The right level Compressed air exiting the compressor needs treatment before it can be safely distributed around the system and used because the quality of the air has a significant effect on the maintenance and reliability of the system. Compressing air not only compresses the air but also concentrates airborne contaminants such as water vapour, oil vapour, pollutants and micro-organisms. The compressor itself often adds oil to the air and the piping network may be contaminated with dirt, rust and water. Compressed air treatment systems such as dryers and filters consume energy directly and usually create a restriction to flow and a pressure drop that increases the energy used in supplying compressed air. Most dryers are not considered after installation but poor or inadequate maintenance of dryers will consume excessive energy.

Get the right air quality The energy costs for air treatment depend directly upon the air quality specified but many companies have no idea of their application requirements or the specification to which they are producing compressed air. ISO 8573-1 specifies various classes for particles (specified in terms of number and mass concentration), water (specified in terms of dew point and g/m3) and oil (specified in terms of mg/m3). The quality class required varies with the application and specifying too high a quality obviously costs more. Sites must establish the following:

quality (Class 3 or above) is both unnecessary and expensive. • Tip – Use the minimum quality air

needed. The higher the quality the higher the energy cost. It is possible that specific applications at a site may require high-quality air and in these cases the site can consider reducing the treatment quality of the bulk air supply to Class 4 and upgrading the quality as necessary at the point of use. This minimises treatment costs for the bulk air but still provides the required quality when required.

Leaving condensate drains open is not a substitute for good drying – it is a waste and can increase air demand by up to 5%.

• Tip – Don’t create problems for yourself.

Try to get the inlet air as clean as possible before it gets to the compressor and make sure that the compressor air inlet filters are clean.

Drying Ambient air typically contains 12.5 g of water for 1 m3 of free saturated air at 15°C. If a compressor produces 500 litres/s, the compressed air produced each hour will contain 22.5 litres of water. The rise in air temperature in the compressor initially prevents condensation, but as the air passes through the compressor after-

• What quality class is the system is

nominally producing to? • What quality class is the system actually

producing to? This is relatively easy to establish but does require specialist equipment. • What quality class is actually required by the applications? Guidance on quality class requirements for a variety of applications is given in table on the opposite page. For most general applications in plastics processing, Class 4 is sufficient and treating all the compressed air to a higher 162

The potential contaminants Untreated compressed air contains a range of potential contaminants that must be removed before it is released to the distribution system. Failure to treat compressed air correctly can contaminate the system but over-treatment is very expensive. Chapter 4 – Services

cooler up to 90% of the water condenses and can be removed. Some water will, however, remain as vapour but if the air temperature falls below its starting temperature (i.e., 15°C) there will be further condensation. There are several different types of dryer available but the two most common types of dryer used in plastics processing are: • Desiccant dryers (up to Class 1 air quality) – a desiccant dryer consumes up to 15% of the compressor power for heated regeneration and causes pressure drops on the system of up to 1.5 bar but can produce air with a pressure dewpoint between −20°C and −80°C. • Refrigeration dryers (up to Class 4 air

quality) – this is the most common type of dryer and is widely used in most industries. Refrigeration dryers typically have an energy use of 5% of the energy use of the compressor and can produce air with a pressure dew-point between 3°C and 5°C. Whichever type of dryer is used there will be a specified compressed air flow rate and exceeding this can lead to poor air drying and water contamination of the system.

• Tip – Manual condensate traps are

often deliberately left open (it is only compressed air) and act as leaks. Replace any manual condensate traps with electronically controlled traps.

• Tip – Check the air dryness against

specification, and refurbish as necessary. • Tip – Check that the condensate

collection system is not constantly bleeding air. • Tip – If possible, arrange distribution

pipe work to slope downwards to drain points (fitted with automatic traps).

Filtration Filters cause pressure drops and to save energy it is recommended that only the minimum filtration requirement is met. Filters should be adequately sized for the duty and should be regularly checked for cleanliness. • Tip – Treat the bulk of air to the

minimum quality necessary, 40-micron filters are usually sufficient and specifying 5-micron filters will increase the filter purchase cost, the replacement frequency, and the pressure drop for minimal extra gain in most cases. • Tip – Test filters regularly – measure

Chapter 4 – Services

Filters cost money to run. They create a differential pressure that must be made up by the compressor. The average filter costs around £500/ year to run.

Typical Quality Class required

Application

Oil

Particles

Water

Air agitation

3

5

3

Air bearings

2

2

3

Air gauging

2

3

3

Air motors

4

1-4

5

General workshop air

4

4

5

Hand air tools

4

4-5

4-5

Machine part cleaning

4

4

4

Machine tools

4

3

5

Pneumatic cylinders

3

3

5

Pneumatic tools

4

4

4

Process control instruments

2

2

3

Paint spraying

3

3

3

Welding machines

4

4

5

• Tip – Make sure that air inlet to the

dryer does not exceed 35°C and that dryer room temperature is within 5°C of the outside ambient temperature. Dryers as well as compressors benefit from a cool environment.

Dryers cost money to run. A small dryer (5 kW) will cost around £5,000/year to run.

the pressure drop at full demand across the dryer pre- and after-filters (this should not be greater than 0.4 bar) and across the dryer itself (this should not exceed 0.3 bar) and refurbish as necessary. If the pressure drops are higher than this then replace the filters. The cost of the energy to overcome a pressure drop of greater than 0.4 bar is usually greater than the cost of a filter. Blocked filters can cost real money.

Pneurop guidance on quality class required for various applications (www.pneurop.org) The required air quality varies with the application and specifying too high a quality for the application uses energy and costs money. 163

4.30

Compressed air – optimise the supply: improve distribution

Getting it there Generating compressed air and treating it to the correct quality level is only half the job. The compressed air system must also deliver adequate volumes of the treated air to the point of use at the correct (and stable) operating pressure and at the lowest possible cost. This is the function of the distribution system and this is perhaps the most overlooked of all the system components.

Receivers Most compressed air systems have at least one receiver in the system and many have more than one. The receiver has four main functions: • It provides storage capacity to reduce cycling of the compressor to meet demand. The compressor tops up the receiver and can then go off-load and stay off-load whilst the receiver supplies the demand. • It smoothes out transient demand

fluctuations and high peak demands to reduce compressor loads. • It creates more stable pressure conditions. Compressors, especially piston compressors, produce a pulsing volume flow and this can affect instruments and control circuits. Receivers dampen pulsations and prevent it from being transferred into the main distribution system. • It acts as a secondary cooler. The warm air from the compressor interacts with the large surface area of the receiver to cool down and some of the water in the compressed air will condense out on the surface of the receiver.

• Tip – Receivers are required by

This workbook does not cover sizing receivers or piping as this is a specialist task.

legislation to have safety valves fitted. • Tip – Receivers should have a working

pressure gauge fitted. Large distribution systems with high transient demands at some distance from the main receiver will often be fitted with a series of local receivers to reduce system fluctuations and to provide a constant pressure for applications that are remote from the compressors.

Distribution systems design and maintenance Compressed air is a fluid and as with any fluid in a piping system, it will suffer from a pressure drop over the length of the distribution system. The longer the compressed air pipework, the greater the pressure loss over the pipework and the greater the cost to generate the compressed air to feed the system and the lower the pressure at the point of use. Compressed air distribution systems also have a habit of growing (but rarely do they shrink) and at many sites the compressed air distribution system is actually an unknown quantity to the site managers.

As a ‘rule of thumb’, a correctly sized receiver should be able to store about 8 litres of air for every l/s of free air delivery (FAD) at 7 bar. VSD compressors can reduce the size of the receiver substantially because the VSD will buffer the system.

If you want a really quick method: multiply the size of the compressor (in kW) by 25. This should be the minimum receiver size (in litres).

• Tip – Receivers must be sized correctly

for the system; a receiver that is too small for the system will result in excessive cycling of the compressor. • Tip – Receivers should be in a cool place

to encourage condensation and to reduce the energy load on the dryer. • Tip – Receivers are pressure vessels and

are covered by various regulations that require periodic inspections. These must be carried out, and it is recommended that the receiver be physically marked with the date and result of the last inspection. 164

Basic compressed air distribution layouts The two basic layouts are the ring and spur systems. The ring main is far preferred because it evens out pressure fluctuations and allows better isolation. In practice most sites will have a combination of ring and spur systems. Chapter 4 – Services

They simply do not know where the piping goes and what most of it is for. One of the first tasks in managing the system is therefore to produce a map of the system to record the location, size and condition of the mains and distribution piping. This will enable identification and removal (or total isolation) of any redundant spurs or branches and identification and removal of unnecessary restrictions to flow. If the map reveals that the system is actually a spur arrangement running from a central hub then the site should strongly consider modifying this to a ring main system as this is the most effective type of distribution system.

General piping • Tip – Locate the compressor as close to

the process as possible. • Tip – Use a ring main arrangement in

each building – air can converge from two directions. This arrangement reduces the pressure drops and makes changes to the system easier. • Tip – Distribution systems should

source of leaks. Replacement of corroded pipework will not only improve the system but also improve system safety. • Tip – Flexible hoses are often used to

make connections between the rigid pipe network and use points. Leaks can be caused by abrasion, deterioration (e.g., heat sources) or mechanical impact.

Junctions, spurs and corners • Tip – Avoid sharp corners and elbows in

pipework as they cause turbulence and high pressure drops. • Tip – Check pressure drops across

valves and fittings, and replace or refurbish if excessive. • Tip – Investigate the system for

redundant spurs that can be permanently sealed off. Low-use areas should be fitted with isolation valves to allow complete sealing when not used. • Tip – Leaks are common at fittings and

flanges; these are frequently caused by pipe strain due to inadequate supports, inadequate joints or twisting.

always be designed for zone isolation to enable areas that are not being used to be isolated and shut down. • Tip – Increase pipe diameters to reduce

• Tip – A large-diameter piping system

has lower distribution losses and the high capacity of the distribution piping can effectively act as a secondary receiver to smooth demand fluctuations. • Tip – Smooth-bore stainless steel or

aluminium piping for compressed air distribution costs more initially but lasts longer and has much lower transmission losses. Conventional steel-threaded pipes are very quick to fit and easy to work with but have a high flow resistance and give large pressure drops.

Many sites run at a high pressure (> 7 bar) because they have a poor distribution system with volume and pressure restrictions. They then increase the pressure and the cost to alleviate these rather than solving the problem at the source. In the long term it is cheaper to fix the m 3/min problem than to pay for the higher generation pressure.

Equivalent pipe length in metres Component

Internal pipe diameter (d) 25 mm

100 mm

90o angle

1.5

6.0

T (through flow)

0.3

2.0

T (side flow)

1.5

6.0

0.4

1.6

Elbow (R = 2d)

0.3

1.2

Ball valve (full flow)

0.3

1.3–20

R

the pressure drop to a minimum. Small piping increases the resistance to flow and causes unnecessary pressure drops.

It is always cheaper to fit goodquality distribution piping in the long term. Pressure losses will be less, corrosion will be much reduced and the overall lifetime cost will be reduced.

Elbow (R = d)

• Tip – The air velocity in the piping

should not exceed 6 m/s in main sections and the pressure drop between the receiver and the point of use should be a maximum of 0.1–0.2 bar at full load. • Tip – Check and drain piping at

appropriate intervals to prevent the build-up of water, oil, and other contaminants. • Tip – Older systems can often benefit

greatly from joining existing spurs to create a ring main. • Tip – Old and corroded piping is a prime

Chapter 4 – Services

d

Fittings are not neutral Every fitting in the compressed air distribution system has an effect on the distribution losses. The above table shows the equivalent pipe length of various fittings. Increasing the radius of an elbow decreases the resistance to flow – smooth is better! 165

Compressed air – heat recovery

Heating for free Over 90% of the energy input to compressors is rejected in the form of heat. This is usually relatively low-grade heat at temperatures in the region of 50°C and is commonly directly rejected to the atmosphere via air or water cooling (depending on the compressor type). Whilst these are not high temperatures, it is possible to recover this rejected heat for use in building services and various other applications. Heat recovery systems can use hot air or water from the compressor for building services such as space heating and hot water supplies. Installation costs vary depending on the application but payback periods of between one and two years are typical where the heat recovered can be fully utilised. The amount of heat available from typical compressor sizes is shown on the right. This is reported in terms of the value of the available heat if it were to be provided by either gas or electrical heating. If a site uses electrical heating then a compressor of 22 kW can provide heating that would otherwise cost £18,000/year if electrical heating is used or £5,500 if gas heating is used. In general, the heat recovered cannot always be fully utilised and this needs to be taken into account in the payback calculations. Heat recovery possibilities should only be investigated after the rest of the compressed air management programme has been carried out (see Section 4.25). Correct management of compressed air will reduce the use and therefore the heat generated and any financial calculations should be based on the optimised system. The heat generated by compressed air systems can be recovered to provide any or all of the following:

Space heating The warm outlet air from the compressor is generally vented to the atmosphere via ducting or via simple grills. Where the compressor house is located close to the production area then the heat generated can easily be ducted into the production area to provide free heating. Most plastics processing sites are very warm in summer due to the process heat and heating of the 166

production area is not required for the full year. Ducting should be fitted with a thermostatically operated flapper by-pass to divert the heat into the building in the winter and out to the atmosphere to prevent the factory becoming too hot in summer. Thermographic photographs of both poor and good use of the heat generated from compressors are shown on the far right. The upper photographs show heat being vented directly to the atmosphere in winter when the site was using heating for the production area. The lower photographs show a site using ducting to use the compressor heat as space heating for the site in winter.

Whilst heat recovery from compressors is important, it should not interfere with the normal and efficient operation of the compressor. Heat recovery is a by-product and not the main function.

• Tip – Air filters and silencers should be

installed in the ducting between the compressor and the heated area when the factory is sensitive to dust or noise. • Tip – Ensure that the compressor

exhaust fans can cope with the pressure drops over the ducting length. Too long a duct and the fans may not have enough power to exhaust and cool the compressor. • Tip – For small compressor installations

the use of ducting may not be necessary. Simply use a ‘hole-in-the-wall’ fan to draw the reject hot air into the factory in Value of heat available from compressors 200,000 180,000 Gas heating

160,000 Value of available heat (£)

4.31

Electrical heating

140,000 120,000 100,000 80,000 60,000 40,000 20,000 0 0

20

40

60

80

100

120

140

160

180

200

Size of compressor (kW)

Value of available heat rejected from compressors Even for a small compressor the value of the rejected heat from the compressor is significant. If the site uses electrical heating then a compressor of 22 kW rejects heat worth over £18,000/ year. This is worth recovering. Chapter 4 – Services

the winter and an alternative fan to draw the reject hot air to the atmosphere in the summer. Link the fans and control them with a thermostat that is based on the factory internal temperature. Drawing the air out of the compressor house will also encourage the inflow of colder air and improve the efficiency of the compressor (see Section 4.28).

Regeneration of desiccant dryers If desiccant dryers are used for hygroscopic polymers then the desiccant requires drying between the cycles. Supplying warm dry air from the compressor can reduce regeneration costs for desiccant dryers.

Hot water

Other projects

Simple air to water plate heat exchangers can be used to provide hot water for the site for staff washing and other purposes. This water can be provided at general domestic hot water temperatures (up to 60°C) but requires storage and control systems to get the full benefits.

The heat rejected from compressors can also be used to: • Dry inlet air for the compressor itself. • Provide warm dry air for paint processes. • Provide warm dry air for extrusion blow-

off instead of the conventional use of airknives.

EPS products When producing EPS products the main energy use is in steam generation for the pre-blow and blowing processes. The rejected heat from the compressor can be used to pre-heat the boiler combustion air to greatly reduce the boiler energy use and heating costs. It is also possible to use the rejected heat from the compressor to pre-heat the boiler feed water. Pre-heating the boiler inlet water to 60°C will also reduce boiler energy use and heating costs.

Thermoforming When thermoforming is off-line from roll stock, thermoforming sheet is often prewarmed (see Section 5.38) before entering the thermoformer itself to reduce the cycle time. All plastics take a long time to warm due to their poor thermal conductivity, particularly when in roll form, prewarming to 50°C enables the pre-warmers to be run at a much lower temperatures and still get the sheet to the required temperature. Pre-warming with hot air from the compressors can also reduce costs and can decrease cycle times.

Heat loss at compressor outlet to the building exterior Heat is being ducted from the compressor outlet to the exterior of the building in winter. Meanwhile gas heating is being used to warm the site. This is wasting the heat from the compressors when it could be used to heat the site.

Materials drying Drying is often a high energy user in plastics processing (see Section 4.42). Correct storage in a warm environment can reduce the amount of drying needed for hygroscopic polymers and remove the need for any drying at all of nonhygroscopic polymers. If the compressor house is near the raw materials storage area then heating the storage area with compressor exhaust air can reduce drying costs.

Chapter 4 – Services

Heat use at compressor outlet to the building interior Heat is being ducted from the compressor outlet to the interior of the building in winter to warm the site. This is good use of the recovered heat from the compressors and reduces the site heating costs. 167

4.32

Compressed air – where are you now?

The initial steps in compressed air As with the score charts shown earlier, this is a self-assessment exercise to allow a site to benchmark their current status. This will set the scene for planning improvements in the area of compressed air.

(see Section 4.25) is an easy and very structured method of reducing energy usage and costs.

Completing the chart This chart is completed and assessed as for those presented previously.

Compressed air is one of the most expensive services provided to a site and getting the system right is vital to energy management. Compressed air is also one of the easiest services to target for reducing costs due to the huge amount of wastage in the area. Following the compressed air management programme

Compressed air Leakage 4 3 Maintenance & operations

2

Use

1 0

Distribution

Generation

Treatment

Use the scoring chart to assess where you are in compressed air The numbers from the scoring chart can be transferred to the radar chart for a quick visual assessment of where you are in terms of compressed air. 168

Leakage and poor use are the main offenders in excess energy use for compressed air. Reduce these and the costs will decrease considerably.

Chapter 4 – Services

Compressed air Level

4

3

2

1

0

Score

Leakage

Use

Excellent High level of awareness of cost awareness of the of leakage. compressed air Regular surveys cost. (no-load testing) Only used for applications where carried out. absolutely Leaks identified, tagged & promptly necessary. Little chance of sealed. use reduction. Good awareness of cost of leakage. Surveys carried out sporadically. Leaks identified but sealing action is sporadic.

Generation

Treatment

Distribution

Maintenance & operations

System sized & Regular Air treated to Ring main lowest acceptable distribution used & controlled to preventative minimise cycling & level. under constant maintenance & filter replacement. control pressure. Local treatment review. used when Spurs can be Waste heat Minimum system demand known & needed. isolated. recovered. delivered. Well controlled Excellent system Automatic condition & condensate traps Good air receiver drying practice & capacity. condensate pressure drops checked. collection. measured to find concerns.

Good awareness System size OK Air treated to low System regularly Regular of use. reviewed. maintenance but poor control. level with no local Some small items Minimum system Spurs are capable checks & treatment. Adequate drying & of isolation when occasional action. use compressed demand air. condensate not in use but Low-level approximately Use monitored but known but poorly collection but few never actually preventative controls in place. isolated. maintenance so no substantive controlled. that system Good drying action taken. Adequate air continues to pressures & receiver capacity. operate. temperatures.

Moderate System correctly Moderate air Moderate awareness of cost consideration of sized but poor quality provided of leakage. use. control & cycling irrespective of Surveys rarely need. High number of when not required. carried out. items use System demand Poor drying & Leaks identified on compressed air. only vaguely condensate known. collection with no an ad-hoc basis Compressed air is only. monitored but no Poor air receiver controls in place. action taken. capacity. High pressure Sealing action is drops at dryers. rarely taken.

System review is Maintenance over 12 months checks carried out old. regularly but little action taken. Maintenance only to ensure that system continues to operate, i.e servicing only.

Low awareness of Little consideration System badly cost of leakage. of use. sized & poorly controlled, cycling No leakage High use for surveys carried motive power, when not required. out. drying & cleaning. System demand Misuse of unknown. compressed air is Air receiver discouraged but inadequate for accepted. demand.

System review is over 3 years old. Large number of redundant spurs with no isolation. Distribution system in poor condition (visible distortion & corrosion.

Sporadic maintenance of filter systems (when problem is noted with the system).

Distribution system not reviewed since installed. Many redundant spurs with no isolation. System is old, corroded & has many sharp bends & corners.

Components dirty & not cleaned. No maintenance of treatment system. Filters clogged. Manual condensate traps jammed open & not maintained.

x

x

High leakage rate & no awareness of cost. No leakage surveys carried out, significant air leakage identified on cursory inspection but no action taken.

No consideration of use. Many items use compressed air for motive power, drying & cleaning. Misuse of compressed air is common & ignored.

x

x

Chapter 4 – Services

High air quality provided irrespective of need. Little control of drying & condensate collection. Excessive pressure drop across dryers.

System oversize, Highest air quality idling when not provided required & cycling irrespective of due to poor need. controls. System demand & minimum pressure needed unknown. Warm air intake.

x

x

169

4.33

Cooling water – the programme

Introduction Plastics processing uses large amounts of energy to heat raw materials and to form these into products and there is also a need to remove this heat from the process to solidify the plastic and complete the process. This means that the provision of a reliable and consistent source of cooling water is essential for fast and repeatable process times in all sectors of the plastics processing industry. Whilst there is a great deal of emphasis in the plastics industry on energy-efficient heating and processing of the plastic, there is much less emphasis on energy-efficient cooling – a process that uses as much, if not more, energy and a process with huge opportunities for energy improvements. Cooling and refrigeration plant uses between 11% and 16% of the energy used in plastics processing but implementing good practice and proven technology can significantly reduce this expenditure.

• Cooling towers – These are conventional

cooling towers of the type seen in many other industries. Cooling towers are considered further in Section 4.37. • Free cooling: This is a sealed circuit

which passes the water through a series of radiators that are cooled by fans and the ambient air. Free cooling is also sometimes called ‘air blast cooling’ and this is considered further in Section 4.38. • Ground water – This is a ‘once through’

Another hidden energy cost When was the last time anybody at your site looked at the cooling system? Savings of up to 25% are possible with little technical risk.

system, taking water from a ground source, using it for cooling and then returning it to the source. This option is rapidly disappearing in many countries due to environmental issues and the fact that the cooling water temperature is limited to that of the extracted ground water. Ground water cooling is considered further in Section 4.39.

Cooling methods

Chilled water or cooling water? A typical cooling system for plastics processing will have separate systems for chilled water and cooling water. These operate at different temperatures and generally use different technologies. For clarity we will define these as follows: • Chilled water is water at < 15°C and is used mainly for moulds and tools. This is generally provided by a chiller and can include a free cooler to use low ambient winter or overnight temperatures to reduce the chiller load. • Cooling water is water at > 15°C and is used mainly for machine hydraulics, compressor cooling or chiller cooling. This is generally provided either by cooling towers or by a free cooler.

Chilled water

Chillers

Stand-alone Free cooling assisted

Ground water

Rivers

Lakes

Bore holes

Cooling towers

Rivers

The main cooling methods are shown on the right and these are:

Free cooling

Lakes

• Chillers – These are generally vapour

Ground water

Bore holes

Cooling water

Cooling water systems

compression chillers operating on a sealed circuit. Chillers are generally compact and the refrigeration cycle can deliver lower temperatures than other methods but generally at a higher energy cost. Chillers are considered further in Section 4.36.

170

Cooling methods for plastics processing Plastics processing almost always needs cooling as part of the process. The methods used depend on the process being cooled and the desired flow temperatures. The options vary greatly in their energy efficiency. Chapter 4 – Services

Although the cooling methods are fundamentally different, there are certain common basic components, i.e., pumps, fans, pipes, insulation and controls. Many sites use a combination of the various methods to meet their overall cooling demand.

Pumping water through the distribution system is a considerable cost and simple solutions can reduce costs considerably.

The programme

The cooling water map

The cost of providing cooling to a site makes it an expensive resource and the way to achieve the best savings is to implement a full cooling water management programme. This programme is shown on the right and is structured into two stages and four steps. For the average site, the programme can deliver savings of up to 25%, mainly by inexpensive measures.

Mapping the distribution network for the site provides one of the best tools for the programme. This is a layout of the cooling system with the system components and the use listed on the map. This provides an overall guide to cooling system improvements and will inevitably reveal areas where the system can be changed to reduce costs.

Stage 1: Minimise the demand Minimising the demand is the first step in cooling management and should be completed before any steps are taken to optimise the supply. It is not sensible to optimise the supply for an excessive cooling load that can easily be reduced by changes to the temperatures or use.

Reduce heat gains It makes little sense to use energy to chill water to low temperatures and then to let the water suffer from parasitic heat gain or to circulate the cool water through inoperative machines. The heat gains of the water should be limited to those where it is actually performing useful heat removal.

ultimate solution is to review the complete cooling system to define the real needs.

Reduce distribution costs

• Tip – Include portable chillers on the

cooling water map. • Tip – Changes in the system often mean

that pipework has been changed without considering the resulting change in pump efficiency at the new pressures. The pipework and pumps need to be sized for the current demands.

Monitoring & targeting The effectiveness of cooling water generation and use can be treated as for the energy consumption of the site. A kWh meter fitted to the cooling water system main feed will enable hourly running costs to be determined and this can be plotted versus production volume (as in Section 2.2) to determine the cost of providing cooling water versus the production output and the prevailing weather.

Increase temperatures Running cooling systems at lower temperatures than are needed is poor energy management – cooling water temperatures should be maximised as the second step. Cooling water temperatures at many sites are both poorly understood and poorly controlled. Increasing system temperatures can improve reliability and dramatically reduce costs, especially with chiller systems.

Stage 2: Optimise the supply After the demand is minimised it is then possible to optimise the supply to deliver the cooling demand for the minimum energy use.

Reduce cooling costs The cooling process is often the largest energy cost in the cooling system and simple measures can reduce costs. The Chapter 4 – Services

The topic of cooling water systems is seldom approached scientifically. Most sites agree that cooling water is needed, and that it is important that the temperature is constant to maintain production quality. Beyond that, there is little consensus on temperature or quantity needed per unit production.

Cooling plant is reliable and tends to be ignored unless there is a problem. Regular analysis of performance data is recommended to enable any loss of efficiency to be detected before complete loss of service.

Cooling plant efficiency can be improved by a multitude of measures; the main task is to decide between the competing measures.

Minimise the demand

Optimise the supply

Step 1 Reduce heat gains

Step 3 Reduce cooling costs

Step 2 Increase temperatures

Step 4 Reduce distribution costs

Stage 1

Stage 2

The cooling water management programme The cooling water management programme follows two stages and four steps to reduce the energy used in cooling. Stage 1 must be completed and maintained before Stage 2 is started to get the full benefits of the programme. 171

4.34

Cooling water – minimise the demand: reduce heat gains

Cooling load Minimising the cooling load will have a large impact on the running costs of cooling installations and identifying the loads and reducing these is critical to improving energy efficiency. For many chilled water systems, a major part of the load is due to ‘parasitic heat gain’. This is heat gained by the chilled water due to differences in temperature between the chilled water and the atmosphere and poor insulation of the system. Chillers are set to output a given temperature of water but what really matters is the temperature of the water delivered to the process. Any heat gained by the water between the chiller and the process means that the chiller must be set at a lower temperature to achieve the required water temperature at the process (and use more energy). At many sites, the temperature of the chiller output needs to be set at ≈ 2°C less than the temperature needed at the process to achieve the correct temperature at the actual process. For most chiller systems decreasing the temperature by 1°C results in a 3% increase in operating costs, this means that parasitic heat gains could be increasing the cost of chilled water by 6%. • Tip – Insulation is rarely needed on

cooling water pipework because the temperatures are not as critical and they are also closer to ambient.

Failed insulation on chiller parts The insulation here has become water-logged and totally ineffective. Water is a good conductor of heat and this insulation is increasing the parasitic heat gain at the start of the process.

Uninsulated chilled water tank First we cool it down and then we store it in an uninsulated container so that it heats up again. Parasitic heat gain must be avoided at all stages of the process.

Reducing parasitic heat gain Parasitic loads should be minimised by insulation of pipes, tanks and most other components. This is particularly relevant where chilled water pipes and pumps are in, or go through, service blocks containing compressors or other hot equipment but heat gains can occur on any long pipe run where there is inadequate insulation. • Tip – Most chilled water insulation

projects are easy to complete with lowcost insulation and have a payback of less than 12 months. • Tip – If you can see condensation on any

part of the chilled water distribution system then this is due to parasitic heat gain. The site is paying money to condense the water out of the air. 172

Uninsulated chilled water piping The uninsulated chilled water piping is suffering from parasitic heat gain. Note the difference in the temperature of the uninsulated piping (black) and insulated piping (grey). Chapter 4 – Services

Condensation is a sure sign of poor insulation. • Tip – Look for condensation underneath

uninsulated pipes. The wet area is actually money on the floor. A minimised cooling load allows a realistic assessment of the cooling system design, particularly in the way the system responds to part load operations.

Chiller parts The manufacturer will insulate most chiller parts but if these are water-logged then the insulation is ineffective and needs replacement.

Storage tanks Where storage tanks or sumps are used then these should be insulated to prevent parasitic heat gain. The thermograph on the middle left clearly shows the water level in the tank and there is condensation on the surface of the tank up to this level.

Uninsulated drops from main pipe work Even when the main pipe work is well insulated, it is rare to find any effective insulation on the drops from the main pipe work. The tubing may be rubber (a good insulator) but there is still significant parasitic heat gain. Metal piping is even worse.

Main pipework All main chilled water pipe work should be well insulated to prevent parasitic heat gain. The thermograph on the lower left clearly shows the difference in temperature between the insulated and uninsulated pipework.

Drops from the main pipework Insulation needs to continue from the main drops through to the machine. The thermograph on the upper right clearly shows the chilled water tubing. Rubber tubing is good but insulation reduces heat gains on pipe (particularly metal pipes).

Local distribution piping

Local distribution piping Even if the distribution piping is insulated, the local tubing is often PVC and is almost always uninsulated. Note how the site has used cable ties to tidy the area by locking the cold feed and warm return together (to encourage parasitic heat gain?).

Where flexible tubes are used then the cold feed and hot return are often strapped together to tidy the area. This increases the heat transfer and heats the feed water more than the simple ambient temperature.

Machine internals Machine internals should not be neglected. Most processes will benefit from low-cost insulation on mould surfaces and between moulds and the machine platens.

Isolate areas Providing cooling water to areas where it is not needed adds to the cooling load. • Tip – Use isolation valves to prevent the

supply of cooling water to areas, machines and tooling that are not being used. Chapter 4 – Services

Moulds and tools are almost never insulated In most processes there is a cold mould and a hot process. Sheet insulation on the cold surfaces of the mould and between the mould and the main machine will reduce parasitic heat gain and remove heat from the process and not the surrounding air. 173

4.35

Cooling water – minimise the demand: increase temperatures

Get the temperatures up After the parasitic heat gain load has been minimised (see Section 4.34) it should be possible to increase the set-point of the chillers by ≈ 2°C and still retain the same temperature at the process. It is then possible to investigate increasing the set-point again to further reduce cooling costs. To reduce costs, the correct and maximum temperature of chilled water should be used to minimise the load on the chiller. As noted in Section 4.34, every 1°C temperature rise in the chiller flow temperature will reduce the energy required for cooling by approximately 3%. For a site running a small 200-kW output chiller at 24/7 then a 2°C increase in chilled water flow temperature will save ≈ £2,500/year for little technical risk. Running chilled water systems at very low temperatures is not free but costs money and overcooling is a large factor in excessive chilled water energy use. The chilled water temperature should be set to the maximum needed for the process instead of the lowest setting on the chiller. In many cases, the chilled water temperature can be increased to 15°C with no effect on the process and substantial reductions in energy costs.

included in any of the cost benefits even though it may be the largest saving. • Tip – This applies to cooling towers as

well. Although tower cooling is very low cost, increasing the temperatures will lead to fans operating less frequently (although pumps may operate more to deliver the required cooling to the machines).

At many sites there is resistance to increasing the chilled water temperatures on the basis that this might increase cycle times. It is simply stated that ‘colder is better’ although this is generally unproven and unsubstantiated for specific tools and sites. Cooling time is important in injection moulding and is generally in the region of 40–60% of the total cycle time. Perhaps more importantly, cooling time is ≈ proportional to the square of the wall thickness, i.e., increasing the wall thickness by a factor of 2 increases the cooling time by a factor of 4. Reducing the wall thickness will have a greater effect on cooling time than decreasing the chilled water flow temperature.

always mean that the part cools faster. If moulding or extruding thick-walled parts then a very cold mould will freeze off the outer surface but because most plastics are good thermal insulators this will warm up again as the heat transfers from the warmer internal material. This can lead to warpage for some parts, i.e., you use more energy and still end up with faulty parts. • Tip – Increasing the temperatures

increases the amount of time that free cooling (see Section 4.38) can operate over the year. This can have a dramatic effect on chiller operating costs but is not

174

This is real money that is being spent.

• Tip – Increasing the water flow volume

is better than reducing the temperature, increasing the flow rate increases the

The savings from increasing chiller water flow temperatures (Standard motor @ IE3/IE2 boundary) £10,000 +2°C Savings/year (£) 200-kW chiller @ 70% load factor

• Tip – Colder chilled water doesn’t

Many sites are unaware of what this acceptance costs.

Injection moulding

• Tip – If you do have a small number of

moulds or processes that demonstrate a real need for lower temperatures then a small portable chiller can often be more economic than running the whole chiller system at a lower temperature.

We accept the current chilled water temperatures with little critical assessment of the need for low temperatures.

+4°C £8,000

+6°C +8°C

£6,000

£4,000

£2,000

£0 0

1,000

2,000

3,000

4,000 5,000 6,000 Operational hours

7,000

8,000

9,000 10,000

The savings from increasing the chilled water flow temperature A 200-kW output chiller is relatively small but even for this size of chiller the savings from a 2°C increase in chilled water flow temperature will be ≈ £2,500/year. Chapter 4 – Services

turbulence and increasing turbulence can hugely increase heat transfer rates. • Tip – Consider decreasing the ∆T (the

difference between the flow and the return water) across moulds from ≈ 5°C to ≈ 3°C by increasing the chilled water flow rate. This has some implications for pump use (see Section 4.40). • Tip – Moulds that are too cold can suffer

from premature melt freezing during the fill stage. Running very cold moulds is not always good. • Tip – Check that the size and location of

the chilled water circuits in the mould meet good design guidelines. Poor design of chilled water circuits needs lower temperature to remove heat from the mould. Optimising cooling circuit design will reduce cooling times far more than reducing the temperature of the chilled water. • Tip – Hot runners should only be used

where necessary as 80% of the energy input to hot runner systems must be removed by the cooling system. • Tip – New technologies such as pulsed

cooling (see Section 5.12) can be used to give even greater reductions in cooling time than reducing the temperature of the chilled water. • Tip – When using semi-crystalline

thermoplastics (most polyolefins) then cycle time can be reduced by using the lowest recommended melt temperature. The injection pressure may need to be raised to compensate for the higher viscosity. This will reduce the cooling time and also reduce thermal stresses from contact with the mould surface. A lower melt temperature will also reduce start-up times and heating energy use. • Tip – Higher mould surface

temperatures will often not only save energy but also improve the surface finish of the moulding. • Tip – Increasing the flow temperature

will decrease the difference between the chilled water temperature and the ambient temperature and will therefore decrease parasitic heat gain (but it is still better to insulate the pipework). • Tip – Increasing the chilled water flow

temperature also decreases the risk of ‘mould sweating’ from cold moulds.

speed and then fail to use the chilled water correctly. Extrusion needs good turbulent water flow to efficiently remove heat from the profile and simply flushing the system does not provide enough turbulence. Systems using a fine mist and other spray methods can be more effective than full immersion in chilled water. Even when the water is distributed correctly to the profile, the use of very cold chilled water is not always the best for extrusion and can be responsible for concerns such as: • Heat sinks, low gloss/matte finish, scratches or drag lines and plate-out if the first calibrator is too cold. • Chatter if the water is too cold and the

profile is shrinking too fast. To overcome these concerns, some extrusion sites throttle the water flow rather than increase the water temperature.

Try it, what have you got to lose?

Water has a better cooling efficiency than air, bubbles in the cooling water will decrease the efficiency of the cooling. Seal and degas the water cooling system where possible to allow even greater increases in flow temperature.

What to do next? • Increase the set point on the chillers by

0.1°C and note the results in production. • Check for any problems with machines or processes. • Investigate and solve any problems with machines or processes. • Wait 1 week and then increase the set point by 0.1°C again. • Investigate and solve any problems with machines or processes. • Continue until maximised. • Tip – Don’t tell anyone that you have

increased the chiller water temperatures. If you do then everything that goes wrong in the next 6 months will be blamed on the temperature increase.

Although this section is primarily concerned with chilled water it is also good to operate cooling water at the highest possible temperature (except where cooling water is supplied to refrigerant condensers).

Why is it set that low? At one site, the chilled water temperature was set at 6.4°C for all the moulds and machines. When questioned, none of the management team knew what the set-points were or why they were set as low as this. Similar sites were using 14°C and having no problems with quality or cycle times. Eventually it was found that the chillers were set at 6.4°C because that was how the last service technician had left them.

Profile extrusion

The chilled water flow temperature was increased to 10°C immediately and there were no concerns. A subsequent increase to 14°C showed a minor concern with one mould and this was rectified after a short visit to the toolmaker.

Many profile extrusion sites use very cold water in an attempt to increase the line

This simple action saved the site nearly 23% of the cost for chilled water.

Chapter 4 – Services

175

4.36

Cooling water – optimise the supply: reduce cooling costs with chillers

Chiller cooling Many plastics processing plants have conventional chiller installations to provide chilled water and in these installations the biggest energy user is the chiller itself. Every chiller is basically a compressor that is pumping refrigerant and for every 100 kW of output cooling capacity a chiller needs approximately 30 to 40 kW input of electricity for the chiller alone. Even a small site can have a 200kW output chiller. This will need ≈ 60–80 kW input power and for an IE3 motor and 24/7 operation this will cost ≈ £42,000/ year. As with many energy-intensive systems, the total cost of ownership is far greater than the initial purchase cost. For a typical water chiller operating full time over a 10-year life cycle the energy costs will be over 90% of the total cost and the initial capital cost will be less than 9% of the total cost. Despite the fact that chillers use large amounts of energy they tend to be ignored as simply providing a ‘service’ to the factory. The energy efficiency of existing installations can easily be improved through simple maintenance and process improvements.

effect on the compressor performance. The recovered heat can then be used for process heating or feeding space heaters. • Warm air discharged from the chiller at

about 10°C above ambient can be directly used for space heating if it is ducted to appropriate areas. • If heat recovery systems are to be used,

it is still important that chillers are well ventilated to provide good airflow over condensers. • It is often possible to use a retrofitted air blast cooling system (see Section 4.38) to use low ambient temperature conditions to pre-cool water before it enters the chiller. • Some sites use discrete chillers rather than a central system. This provides increased flexibility and lower cost at start-up but can be more expensive in the long-term in both capital and running costs. • Some sites use a single pipe system for both moulds and machines and use the thermo-regulators on the machines to control the water temperature. This is very energy-intensive. Machines are best cooled by cooling towers or free cooling because of the higher water temperatures.

Measures of performance: Energy efficiency ratio (EER), is the ratio of the cooling output to the power input at full load. It is classified in A–G bands with different boundaries for air and water-cooled chillers. This should not be considered in isolation as most chillers do not operate at full load. An ‘A’-rated, aircooled, chiller has an EER of ≥ 3.1. European seasonal energy efficiency ratio (ESEER) measures the energy efficiency of the chiller under defined part loads. It is effectively the European equivalent of the US Integrated Part Load Value (see www.euroventcertification.com).

Systems A minimised cooling load allows a realistic assessment of the cooling system design, particularly in the way the system responds to part load operations. Areas for improvement are:

Cooling load (see Sections 4.34 and 4.35)

• Optimisation of the existing chiller

system is a key to reducing energy use and in many cases changes have taken place in the system since it was first installed. Systems should use the most suitable refrigerant and be optimised for high part load and winter efficiency. This is important where additional chillers have been added to the system to provide multi-chiller capacity. • Pumps and the chillers should be balanced and matched to the normal load with controls to match a variable load via multi-chiller capacity. • Chillers generate large amounts of heat.

This heat can be recovered from the compressors by de-superheaters with no 176

Systems Reducing chiller costs Components

Operation and Maintenance

Chiller costs can be reduced by a variety of measures Chiller costs can be reduced by working on the various aspects of the system. Simply concentrating on a single aspect may ignore other areas where there are easier savings to be made. Work to the programme to consider every area. Chapter 4 – Services

Components Component selection is a key to energyefficient operations and areas for improvement are: • New-technology chillers use more efficient scroll and screw compressors and refrigerant gases. These can be considered as direct replacements for existing chillers subject to cooling load and systems investigations. When sizing the compressor to match the cooling load, avoid running the compressor at low load to maximise efficient operation. • Turbocor centrifugal compressors are oil-

free, VSD-controlled and run on magnetic frictionless bearings. They are extremely efficient at part load and simplify systems design. In some cases it is possible to retrofit Turbocor compressors to existing installations. • VSDs can be used with standard motors to drive screw compressors and to provide a variable response to variable demand. When used with standard fixedspeed chillers (to provide the base load), VSD-driven chillers offer substantial energy savings especially when part loads are anticipated. When used with free cooling (see Section 4.38) the savings can be dramatic. • Where VSDs are not possible and part

loads are a realistic requirement, e.g., when using air blast cooling, then multicompressor chillers (which perform better under part loads) should be considered. • Condensers for air-cooled chillers should be located where they have good air flow with cool air. The compressor room is not the ideal place for obvious reasons.

• Systems should be gas-tight and have

the correct charge of the correct refrigerant. Refrigerant charge is critical – a 20% refrigerant undercharge can cause a 50% efficiency loss. • Condenser heat exchange surfaces must be kept clean. Dirty air-cooled condensers are inefficient because the compressor absorbs more power at higher condensing temperatures and condenser fans use more electricity because they will operate longer. Watercooled condensers must be kept clean and free of fouling. • Dirty evaporator surfaces are inefficient and these should be cleaned regularly to maintain efficiency. Small levels of scale on an evaporator coil will dramatically increase operating costs, i.e., 1 mm of scale will reduce heat transfer by ≈ 50%. • Analyse the compressor oil at least

annually for contaminants. • All systems components should be

automatically turned off when not in use – this is the most cost-effective way of saving energy. • There are increasing world-wide restrictions on the use of the hydrofluorocarbons (HFCs) that are used as refrigerant gases in most chillers. Sites with existing equipment need to be aware of the ‘life span’ of these chillers and have a strategic plan to conform to the regulations. Sites buying new chillers need to plan for F-gas phase-out and select suitable gases for the future.

Greenhouse gases (GHGs) The EU has passed the F-gas regulation (842/2006) that came into effect on 16 April 2014. These regulations plan for a 79% reduction in the use of some gases between 2015 and 2030.

New refrigerants (to replace older refrigerants that are now restricted) are more efficient and can reduce chiller operating costs by between 12 and 30%.

Whichever refrigerant is being used the refrigerant loss should be monitored and any leaks repaired. Under EU Regulations it is required that all refrigeration equipment containing more than 3 kg of gas must be leak tested at least annually.

Operation and maintenance It is common for cooling systems to be operating at well below their potential efficiency due to neglect in carrying out routine maintenance tasks. Areas for improvement are: • Records should be kept of plant conditions to identify trends. • Regular servicing (such as purging of

condensers) should be carried out to maintain efficient operation. • Regular checks on flow and return temperatures. Flow rates should be checked so that these are kept at the correct and optimum settings. These can also act as an early warning of degradation in compressor efficiency. Chapter 4 – Services

Chiller mistakes Dirty and blocked condensers decrease the heat transfer and make chillers less efficient. This is actually the condenser of a chiller that is thoroughly blocked with dirt and dust. Simple maintenance can reduce energy costs in chilled water supply. 177

4.37

Cooling water – optimise the supply: reduce cooling costs with cooling towers

Simple cooling

General good practice tips

Cooling towers are one of the simplest cooling mechanisms known and can be very economic to use and run. Those used in the plastics processing industry are primarily the mechanical draught wet cooling type. These use evaporative cooling in a semi-closed circuit to cool water to slightly above the ambient wetbulb temperature.

Water distribution

Operation The mechanical draught in the cooling tower is created using fans: • Towers with fans at the discharge end

are ‘induced draught’ towers, i.e., the fan draws moist air out of the tower and ambient air into the tower via an induced draught to produce high exit speeds and low entrance speeds. • Towers with fans at the intake end of the

cooling tower are ‘forced draught’ towers, i.e., the fan blows air into the tower and this forces the moist air out of the tower to produce low exit speeds and high entrance speeds. Forced draught towers typically require larger motors to maintain the air flow through the tower. Evaporation is fundamental to the cooling performance of a cooling tower and can only occur at the water surface. Therefore, one of the aims of cooling towers is to maximise the water surface presented to the air flow through the tower. To do this, the warm water is distributed by spray nozzles over a fill material inside the tower before going through the tower. A good distribution over the fill and the evaporation of a relatively small amount of water contribute to 80% of the cooling load with the remaining 20% being achieved by heat transfer to air. The flow temperature possible with cooling towers is dependent on the ambient wet-bulb temperature and water can be cooled to 4–6°C higher than the wet-bulb temperature of the entering air. The temperature difference between the return and the flow temperature ranges from 3.5–11°C depending on the system. Adequately treated water and regular testing can ensure that there are few concerns with modern cooling towers.

178

Dry-bulb and wet-bulb temperature

Evaporation is maximised by a large water surface area and it is important that re-circulated water is evenly distributed over the entire tower fill and that the fill is correctly stacked and undamaged. • Tip – Watch out for scale deposits on the

surface of the fill as this can reduce the heat transfer and effectiveness of the tower. • Tip – Scale and debris can clog the spray

nozzles and give uneven water flow over the fill and reduced heat transfer. Clean spray nozzles periodically to avoid this. • Tip – Cooling towers are ‘dust collectors’

and will collect dust and debris from the air. This debris will build up and reduce the cooling performance unless removed. Towers and the fill should be cleaned regularly.

Air access and distribution Air access to the cooling tower air inlets should be unobstructed. Do not stack or build anything in front of the air inlets that will obstruct air access. Air inlet louvres should be clean and free of obstructions to allow unobstructed air passage to the fill material. The fill should be free of obstructions and thoroughly cleaned periodically to ensure correct air and water distribution.

A

Dry-bulb temperature is the air temperature measured by a thermometer freely exposed to the air but protected from radiation and moisture. Wet-bulb temperature is the temperature measured by a thermometer that has the bulb wrapped in a wet cloth. If the RH is < 100%, water evaporates from the cloth to cool the bulb below the drybulb temperature. The lower the RH, the greater the evaporation and the greater the difference between the dry-bulb and wet-bulb temperatures. The wet-bulb temperature is always less than or equal to the drybulb temperature.

B

Cooling towers come in all shapes and sizes A: Probably the oldest cooling tower we have ever seen but still giving sterling service. B: The USA has a tendency to mount cooling towers high to get good airflow and to use the area underneath for parking. Chapter 4 – Services

Water treatment

temperature.

The water evaporation leaves behind any solids that are in the water, i.e., salts and minerals, and these can build up on the tower surfaces to reduce the heat transfer effectiveness giving decreased cooling capacity and increased energy consumption. Good water treatment (water softening, pH adjustment, corrosion inhibition, etc.), filtering and regular water draw off will prevent the build up of solids and also prevent concerns such as Legionella (see box on the right).

• Tip – When using any temperature

Temperature control Cooling towers are designed to achieve a specific amount of cooling at a design drybulb/wet-bulb temperature but for most of the year the ambient temperatures will be below this. If temperature controls are not used then the system will deliver variable temperature water and this can affect process control, process stability and energy use. • Tip – Deliver water at the highest

possible temperature for the process. If small users need lower temperatures then look at a separate chiller system as a stand-alone or as a top-up for the tower water. • Tip – Good temperature control is an

excellent energy-saving opportunity. • Tip – When tower water is being used

for water cooling of a chiller or compressor then the temperatures should be as low as possible to improve the efficiency of the chiller or compressor. • Tip – Operation of towers should only be

during production hours. As always, unnecessary operation should be avoided. • Tip – In cold climates, trace heating and

sump immersion heaters may be needed to prevent freezing.

Cooling towers – opportunities The main energy management opportunities for cooling towers are in the control of the fans and the pumps.

Fans The amount of cooling delivered by a cooling tower can be controlled by varying the fan speed according to the sump water temperature. Reduced process loads or cold ambient conditions allow fans to be controlled according to the required flow Chapter 4 – Services

control, the thermostat should be regularly checked for correct operation. The simplest method of controlling the fans is to turn them off during cold weather but automatic controls are far better. It is possible to use a thermostat to cycle the fans on/off according to the sump water temperature but this can lead to concerns with short cycle times and wear and tear on the fans or with long cycle times causing excessive temperature cycling of the flow water. Using a VSD is preferable.

The temperature of cooling water delivered from a cooling tower will vary between 2°C and 30°C over the year in the UK.

• Tip – Use a VSD to control the fan speed

with a signal taken from the sump water temperature. This will slow the fan down when the water is cold and speed it up when the water is hot. As well as reducing energy use this will give better control of the cooling water temperature and reduce the noise from the cooling tower. • Tip – Many cooling tower fans use V-

belts for operation due to the speed of operation. Check for the possible use of cogged belts (see Section 4.16). • Tip – If you can operate a cooling tower

in ‘cascade’ mode only during winter, i.e., with the fans turned off, then install temperature controls for the fans.

Cooling towers act as ‘air filters’ by removing all the dust and debris from the air. As this collects, the performance of the tower will degrade. Regular cleaning should be carried out to keep towers in good condition.

Legionnaires’ disease Legionnaires’ disease is a potentially fatal form of pneumonia. It was named after an outbreak of pneumonia at a 1976 American Legion convention in Philadelphia where 34 people died and 221 were infected. Legionella outbreaks are generally accompanied by significant death rates and survivors can suffer from extensive lung and other damage. The disease is spread by inhaling tiny water droplets from a Legionella-contaminated source. The disease is caused by the bacterium Legionella pneumophila and related bacteria that are common in almost all natural water sources but are usually only present in low numbers and infection rates are very low. The bacterium thrives in warm environments (25–45°C) with optimum growth rates at 35°C. Cooling towers can therefore provide very favourable conditions for the rapid growth and dispersal of the bacterium. Control measures for Legionella make it possible to greatly reduce the possibility of infection and there are approved control measures around the world. These include biocide treatment of the cooling water, microbiological monitoring (dip slides) on a weekly basis and routine testing at least quarterly and more often if the bacteria have been previously identified as being present in significant amounts. Legionella is a serious but controllable risk. Any site using cooling towers must ensure that control systems are present and complied with. 179

4.38

Cooling water – optimise the supply: reduce cooling costs with free cooling

Free cooling Standard chilled water systems are not generally configured to take full advantage of cold ambient weather conditions and constantly use energy to provide the cooling. In temperate or cold climates it is possible to use low ambient winter or overnight temperatures to precool the return water from the process and to considerably reduce the chiller load and energy use. Low ambient temperatures are experienced for a large part of the year in the many temperate climates, and in the UK, the ambient temperature is below 15°C for almost 75% of the year. During these periods free cooling can be used to considerably reduce energy costs (see diagram on the right). Free cooling is particularly suitable for use in the plastics processing industry because the ambient and flow temperatures involved in plastics processing are relatively similar and free cooling can be used to its best advantage. This is particularly true for injection moulding sites where the chillers are providing chilled water at ≈ 12–14°C for both tooling and machine hydraulics. Installation of a free cooler into the cooling system can produce significant energy savings for minimal additional capital costs.

Free cooling theory The installation and operation of free coolers as a pre-cooling or total cooling system is straightforward and a typical installation of a free cooler is shown on the lower right on the opposite page. If the ambient temperature falls to 1°C or more below the return water temperature then free cooling can become effective and the automatic three-way motorised valve operates to divert the return water through the free cooler section. This precools the water, reducing the load on the main chiller and therefore reduces the energy use and cost. The lower the ambient temperature falls below the return water temperature, the greater the free cooling effect. When the ambient temperature is as little as 3°C below the return water temperature, the pre-cooling achieved is generally sufficient 180

to meet the system demands. The free cooler then provides the total cooling load and the cooling water does not enter the chiller at all but is diverted direct to the process by another three-way motorised valve. It is then possible to switch the main chiller off completely and the chiller load is reduced to zero. The only energy consumed at this stage is that used to drive the fan motors of the free cooler. This means that at ambient temperatures of below ≈ 9–11°C the main chillers would become inactive. Raising the flow temperature for the chilled water system to 15°C would mean that at external temperatures below 12°C the main chiller would become inactive. This is ≈ 72% of the year in most temperate climates such as the UK, Europe and much of the USA.

Free cooling in practice The physical layout of a free cooler consists of a finned copper tube, an aluminium fin matrix and a three-way valve with an electronic microprocessor control that follows the external ambient temperature to control the switching of the return water to the free cooler when ambient conditions allow it to be effective. Varying the fan speed or progressively cycling the fans according to the ambient temperature controls the amount of cooling achieved by the free cooler. Free cooling provides extremely low-cost

Free cooling works off the dry-bulb temperature. This is always greater than or equal to the wet-bulb temperature.

Free cooling is sometimes called air-blast cooling. They are the same thing.

If operating cooling towers, it is also possible to divert the chilled water return through a heat exchanger in the cooling tower sump to provide pre-chilled water when the cooling tower water is cold enough. This will act as a pre-cooler in the same way as a free cooler does and take a load off the chiller system.

Free cooling only, 72%

Chiller only, 5%

Free cooling + chiller, 23%

Percentage of year that free cooling is active for temperate climates Free cooling will not be active for the whole year in many parts of the world and will need chiller assistance, or complete chiller operation, for some parts of the year. Chapter 4 – Services

chilled and/or cooling water and the energy savings generated by reducing or eliminating chiller use have a typical payback period less than 2 years and can be as little as 12 months in many cases. Installation of a free cooler also increases the potential life of the main chiller unit by reducing use and acting as a stand-by for the main chiller system. Free coolers can be supplied as standard equipment for new chiller installations or they can be retrofitted as an additional cooling loop to existing cooling systems to improve their energy efficiency. For new systems, free cooling is generally available as a factory-fitted option and for space saving it can be incorporated within a conventional air-cooled chiller. In this case, the air-cooled chiller contains two coils. The first inner coil is the conventional condenser and the second outer coil is the free cooler. For retrofitting, the free cooler is fitted to the return water flow to provide low-cost precooling for the existing chiller system. Whether new or retrofitted the free cooler only operates when the ambient conditions are right and it then provides low-cost precooling to enable reductions in chiller operating costs. In the case of a retrofit installation it should be established that the existing chiller can run at part load in order to achieve the full benefits of free cooling.

Adiabatic cooling If lower temperatures are required it is possible to fit a free cooler with a water mist system to provide additional cooling capacity. The evaporation of the water mist then provides extra cooling of the radiators. The spray system is only activated when ambient temperatures are at a maximum and the operation uses minimal water to provide the additional cooling reserve.

• Tip – The size of the overall chiller

package should be capable of providing the total cooling load to cope with the short periods when free cooling is not operational. • Tip – As for chillers, radiator surfaces

should be cleaned regularly to maintain efficiency. • Tip – In hot climates, free cooling often

In the case of a retrofit installation it should be established that the existing chiller can run efficiently at part loads in order to achieve the full benefits of air blast cooling.

cannot provide enough cooling for chilled water but can be used for cooling water instead of cooling towers to avoid any concerns with Legionella.

Three-way valve Return Free cooler Three-way valve

Chiller

Flow

Schematic of free cooling installation Free cooling is simple to install and provides automatic free cooling when the external temperature is low. A free cooler can be supplied new or retrofitted to a suitable existing chiller installation.

Good practice tips • Tip – Chillers with new or retrofitted

free cooling circuits can show large reductions in operating costs. • Tip – Chillers with free cooling circuits

have lower chiller running times, lower maintenance costs and extended chiller life. • Tip – Free coolers are available for

capacities as low as 5 kW with no effective upper limit as units can be linked together to provide greater cooling capacity. Chapter 4 – Services

Typical large-scale free cooling installation Free cooling installations can individually be quite small and can be linked together to provide the required cooling capacity or they can be large-scale installations to cover a complete site. This installation covers a complete site for free cooling. 181

4.39

Cooling water – optimise the supply: reduce cooling costs with ground water

Ground water cooling Ground water cooling is not often used in plastics processing yet it is one of the options that can be exceptionally rewarding in energy terms. Cooling of this type is used extensively for nuclear power installations where large amounts of excess heat are channelled to the sea or large lakes, which is why most nuclear power stations are located on the coast. Ground water is a ‘once through’ system, disposing of the process heat to the ground water which is then returned to the source. There are several different sources of stable low-temperature water for ground water cooling.

Rivers River water temperature is very stable throughout the year at ≈ 10–12°C in many parts of the world and can provide a virtually unlimited cooling source. A site in Germany1 uses this method to provide all the chilled and cooling water for their injection moulding operation. The cooling system consists of two heat exchangers (one for chilled water and one for cooling water) submerged in an adjacent river. The heat exchangers prevent any contact between the water in the cooling system, which contains glycol, and the river water. The system, shown on the right, pumps the process return water through the heat exchangers where it is cooled to ≈ 12°C and then pumped back to the process. The river water temperature is very stable throughout the year but the site also has two chillers ready to run if the water flow in the river decreases in the summer. The cooling water heat exchanger was positioned downstream from the chilled water heat exchanger in case the water was heated by the cooling water. In practice, the uplift in the river water temperature is < 0.1°C at the heat exchangers and not measurable at 12 m from the heat exchangers. Periodic cleaning of the heat exchangers is necessary to reduce any build-up of algae or other growths attracted by the warm heat exchangers. A radical alternative, used in Spain, is to concentrate the heat removed in one area 182

and to use the warmer water as a fish farm/hatchery where small fish are grown to be later distributed to rivers in partnership with the local environmental agency for stocking rivers. Whilst some areas may have environmental regulations that will prevent new systems of this type, there are environmental benefits in terms of reduced energy use and greatly reduced carbon footprint (see Section 9.1).

This option is disappearing in many countries but if it can be used the benefits are huge and it reduces energy use and carbon emissions significantly.

• Tip – Look outside the site for a nearby

river and consider using this as a source of cooling. For new applications this will require liaison with the local environmental authorities but can be very rewarding financially.

Lakes Large lakes are used by nuclear facilities for heat dispersal but they must be large enough to have sufficient heat capacity.

Bore holes In many areas of the world there are plentiful supplies of groundwater at temperatures in the region of 9–11°C (depending on the location and depth of the source). Where permission can be gained to tap into these aquifers then these can provide a very stable source of

Using river water to extract process heat Simple low-cost heat exchangers submerged in a river can provide almost unlimited free cooling for only the cost of the pumps. The heat exchangers prevent any contact between the water in the cooling system and the river water. Chapter 4 – Services

cooling. Projects of this type have been carried out in Denmark2 and the USA3,4 and have shown excellent results. As with river water cooling, the bore hole water is passed through heat exchangers to extract the process heat. The water is then pumped back into the aquifer via a second bore hole located at some distance from the extract bore hole. This avoids long-term heating of the area surrounding the extract bore hole and warming of the intake water. This type of application is slightly more difficult than river water cooling because the extracted water needs to be pumped through a heat exchanger and must therefore be filtered to remove contaminants that might affect the system over time. Apart from filtering, the ground water is completely isolated from the cooling system. In some systems, cold winter weather is used to cool the return water before it is pumped into the bore hole. This minimises any heating of the area near the return bore hole. This can involve separate plant or, in the case of the Tangram client, the use of a large storage pond that naturally cooled the water over the winter. The alternative is to simply increase the distance between the flow and return bore holes to minimise heat transfer between the two. • Tip – The Danish2 scheme set the

pressure of the bore hole water in the heat exchanger higher than the pressure of the process water to prevent any contamination of the bore hole water with process water in the event of a system failure, i.e., the leak goes from the bore hole water into the process water.

large well (10 m diameter and 45 m deep) as a heat sink. Water is drawn from the bottom of the well for the process cooling and simply returned to the top of the well after extracting the heat. The hot water sits at the top of the well and the temperature of the water at the bottom of the well has varied by no more than 0.1°C over a period of nearly 20 years.

Cooling is a very large cost and some lateral thinking is necessary to reduce the costs. Do not dismiss these ideas until you have calculated the cost of running chillers 24/7.

• 1. Tangram client. • 2. EURECIPE Case Study: Energy savings with groundwater cooling (www.eurecipe.com) • 3. Multifilm Case Study: (www.multifilm.com/ sustainability.htm). • 4. Tangram client. • 5. Tangram client.

Process (chilled water)

• Tip – Groundwater cooling is very

effective and removes the need for chillers. If the temperature is low enough then there will be no need for back-up chillers because the water temperature will be constant throughout the year. • Tip – The payback for this type of

scheme is likely to be in the order of 2–5 years but will reduce cooling costs for many years.

Return bore hole

Flow bore hole

300 m Warmed area

Wells

Using bore hole water to extract process heat

It is also possible to use large wells as heat sumps and this is done in Portugal for a mould trial site where machine use is relatively limited.5 The site uses a very

Where aquifers (and regulations) allow, it is possible to use ground water at 9–11°C to provide cooling. The flow bore hole and the return bore hole should be separated by some distance to avoid long-term heating of the ground and the flow water.

Chapter 4 – Services

183

4.40

Cooling water – optimise the supply: reduce distribution costs

More than you think The typical cooling system at a plastics processing site has a large number of pumps and the energy cost for distribution is always high. For a simple split system with separate chilled and cooling water circuits and both chilled and cooling water sumps there will be the following pumps: • Chilled water process pumps – There

will be a minimum of two pumps (run and stand-by) and often more. • Chilled water system pumps – There will be a minimum of two pumps (run and stand-by) and often more. • Cooling water process pumps – There

will be a minimum of two pumps (run and stand-by) and often more. • Cooling water system pumps – There will be a minimum of two pumps (run and stand-by) and often more. In addition to these standard pumps, there may be additional pumps such as: • Water-cooled chiller pumps. • Water-cooled air compressor pumps. These pumps will, in total, use 5–8% of the total site energy. Pumps driven by AC motors are very reliable and it is very easy to ignore them and to concentrate on the visible areas such as lighting, which uses less than 5% of the total site energy. This is foolish as the availability of VSDs means that pump projects are low-cost, easy to carry out and deliver excellent savings. The majority of pumps used in cooling are oversized and use fixed-speed motors. This increases energy consumption because the pump supply is not matched to the demand. Using VSDs allows matching of the supply to the demand and a 20% reduction in pump speed gives a 50% reduction in energy use (see Section 4.21) as well as matching the pump output to the process demand. • Tip – Get the pump size right first.

Large pumps operating at low loads will be less efficient than small pumps operating closer to the maximum load. • Tip – Pumps should always be firmly

located on stable footings. • Tip – Pumps should always be fitted

with a ‘soft start’ but most VSDs will 184

have this in the control system.

A ‘no-brainer’

• Tip – Pump shafts should be aligned

with the motor and well lubricated. • Tip – It takes more energy to pump

water through small pipes than through large pipes. Make sure that the pipes are the correct size for the system.

Map the pumps One of the first steps of the cooling water management programme is to set up a cooling water map (see Section 4.33). This should list all the pumps and their motor sizes and forms the basis for energy management in cooling water distribution. • Tip – The cooling water map should list

all the pumps, their size, their function and their location.

VSDs are probably the easiest and best method to reduce energy use. The savings are proven and easily calculated. Developments in VSD technology have reduced the cost of VSDs so that the payback is almost always < 1 year and often < 6 months. This type of project is a ‘no-brainer’.

• Tip – Check the system layout before

taking any action. Follow the actual pipes and do not trust old drawings. The system has probably been changed. • Tip – Check that the ‘run’ and ‘stand-by’

pumps are the same size. If they are not then use the smallest as the main pump (see Section 4.18). • Tip – Install a cross-over switch between

the ‘run’ and the ‘stand-by’ pumps to allow quick switching of the pumps.

System pumps System pumps are a good application of VSDs but some care is needed if VSDs are planned for retro-fitting on chiller system pumps.

Chilled water Chilled water pumps to the system (chillers or air-blast pre-coolers) are

For further excellent information on pumps get a copy of ‘Improving Pumping System Performance: A Sourcebook for Industry’ (2006), available for free from the USA DOE.

Affinity laws for centrifugal pumps The affinity laws tell you how a centrifugal pump responds to changes in conditions (see Section 4.21). They are very simple: Flow is directly proportional to the speed of the of the pump in

revolutions/min. If you double the speed of the pump then you double the flow. The pressure developed by the pump is related to the square

of the speed of the pump in revolutions/min. If you double the speed of the pump then you multiply the pressure by 4. The power drawn by the pump is related to the cube of the

speed of the pump in revolutions/min. If you double the speed of the pump then you multiply the power drawn by 8 (23). Chapter 4 – Services

sometimes not suitable for VSDs but it depends on the design of the chiller. Some chillers do not operate efficiently at part load, i.e., it is best for the chiller to temporarily turn off when the set-point temperature in the sump is reached rather than to run at a reduced load. New design chillers, particularly those with Turbocor compressors, operate better at part load but most of these should already have VSDs fitted to the system pumps. • Tip – Check with your supplier if it

possible and recommended to fit a VSD to the chilled water system pump.

Cooling water Pumps to cooling towers should be fitted with VSDs to control the pump speed based on the temperature of the cooling tower sump (see Section 4.37). • Tip – If the cooling water has had glycol

added for anti-freeze then this will increase the viscosity of the fluid. This increases the energy required to circulate the same volume of coolant and decreases the heat transfer efficiency.

Process pumps Process pumps are the ideal candidate for application of VSDs.

Chilled water The chilled water process pumps should be fitted with a VSD control to control either the ∆T or the pressure of the system. One method is to measure the return temperature of the chilled water and to control the pump speed to maintain a constant return water temperature. This reduces energy use and improves the chilled water temperature stability.

Cooling water

Pressure gauges at the inlet and the outlet of a pump allow the pressure developed by the pump to be measured.

The cooling water process pumps should be fitted with a VSD control to control the ∆T or the pressure of the system. As for chilled water process pumps, the control signal can be the temperature or the pressure of the return water from the process. The notes for chilled water process pumps are also relevant for cooling water process pumps.

The pump curve can then be used to give the flow rate of the pump.

Pumps to water-cooled chillers or air compressors should be fitted with VSDs to control the pump speed based on the temperature of the chiller or compressor.

Isolate the process In most cases chilled and cooling water supply to the process is left open when the main machine is stopped. Simple shut-off valves (preferably automatic and linked to the main machine) can be used to isolate the supply of cooling or chilled water when it is not needed. Isolating moulds and machines will reduce both parasitic and process heat gain and therefore the ∆T of the chilled and cooling water. When VSDs are used this will be part of the signal to slow the pump down and save energy. • Tip – Fit solenoid/timer valves and link

these to the main machine to automatically switch off the supply.

The efficiency of the pump can then be checked by closing the outlet valve and checking the developed pressure with the zero flow pressure on the pump curve. If the pressure is less than that given by the pump curve then maintenance is needed.

Parallel pumping Think about running two pumps at a slower speed than running one pump at a high speed. It can save energy.

100% Head/flow

Resistance curve

• Tip – Depending on the system there

may be a need for a second control point to ensure that the system pressure does not fall below a set level, e.g., 2.5 or 4 bar.

Power

• Tip – For multiple pump systems, it is

possible to use VSDs to control all the pumps. These will control the multiple pumps and even rotate pump use to give even use. As an alternative, it is possible to fit a VSD to only one pump, the fixedspeed pumps then provide the base load for the system and the VSD-controlled pump provides the variable load. The second method is to control the pump speed from the system pressure to maintain a constant system pressure. This should be as low as possible to maximise the savings (see box on the left). Chapter 4 – Services

Efficiency

0%

100% % Flow

Typical pump performance curve The pump performance curve tells you all you need to know about a pump. As the flow (m3/min) increases so does the resistance and the power needed. The pump efficiency is at a maximum in the middle area of the curve. 185

4.41

Cooling water – where are you now?

The initial steps in cooling water As with the score charts shown earlier, this is a self-assessment exercise to allow a site to benchmark their current status. This will set the scene for planning improvements in the area of cooling water. The temperature setting of cooling water is often justified on the basis of improved throughput but rarely do we see a true cost–benefit calculation of the justification and often this is simply a case of ‘what gets measured gets done and what doesn’t get measured is ignored’. Production rates get measured and energy costs don’t – guess which gets done?

In some processes, the provision of cooling water is one of the largest avoidable costs in the process and simple actions can reduce the costs considerably.

Completing the chart This chart is completed and assessed as for those presented previously.

Poor maintenance of cooling water systems is another hidden source of energy wastage in plastics processing.

Cooling water Cooling load 4 3 Heat recovery

2

Systems

1 0

Air blast cooling

Components

Operation & maintenance

Use the scoring chart to assess where you are in cooling water The numbers from the scoring chart can be transferred to the radar chart for a quick visual assessment of where you are in terms of cooling water. 186

Cooling water is often set at too low a temperature for the real needs of the process.

Chapter 4 – Services

Cooling water Level

4

3

2

1

0

Score

Cooling load

Air blast cooling

Heat recovery

System optimised New technology Cooling load Records of plant for current loading. (scroll & screw) minimised & condition & Pipework & pumps maximum compressors service. reviewed within 12 temperature used. Regular check on possible used. months & well All pumps & fans flow & return Pipework & all suited for current sized correctly & temps, gas IE4 & VSD pumps areas well loading. tightness & insulated against Good ventilation & fans used to refrigerant charge. parasitic loads. over chiller parts. match process Clean heat demands. exchanger surfaces.

Air blast cooling used for major cooling load.

Heat recovery from cooling system used extensively for space & water preheating.

Good attempt to System review is minimise parasitic over 12 months loads but poor old. control of Moderate maximum ventilation over temperature chiller parts. required for the system.

Air blast cooling installed as trial before full implementation.

Heat recovered from cooling system used partially & effectively.

Some attempt to minimise parasitic loads but not extensive. Cooling load only vaguely known & maximum temperature not minimised.

Systems

Components

Operation & maintenance

Majority of Good regulatory equipment is new records kept & technology (scroll good service records. & screw compressors, IE3 Regular checks on & VSD pumps & system temps & heat exchanger fans). surfaces. Programme to replace old equipment.

System review is Most equipment is Minimum Air blast cooling old & operates regulatory records over 3 years old. planned for excessively & Large amount of kept & some poor installation in short old piping & poor irrespective of service records. term. process demand. insulation. Few checks on Distribution Recognition of system temps & system has visible upgrades available heat exchanger distortion & & action being surfaces. corrosion present. taken on rolling basis.

Heat recovered from cooling system used partially but ineffectively.

Heat recovery System not All equipment is Only regulatory Air blast cooling Poor attempt to minimise parasitic optimised or old. Fixed-speed records kept (leak considered & still considered but not loads. High reviewed since pumps & fans testing for under attempted. parasitic loads, installation. operate refrigerants). consideration. Poor ventilation irrespective of No other records e.g., badly insulated pipes. over chiller parts. demand. available. No idea of Recognition of No checks on upgrades available system temps or maximum temperature but no action. heat exchanger needed. surfaces. No attempt to minimise high parasitic loads, e.g., badly insulated pipes. Cooling is supplied to many areas with no idea of maximum temperature.

System not optimised or reviewed since installation. Very poor ventilation over chiller parts.

x

x

Chapter 4 – Services

All equipment is No records of Air blast cooling meeting regulatory not known of & not old. Fixed-speed requirements. considered. pumps & fans No regular operate maintenance irrespective of carried out. process demand. System in poor No recognition of overall condition. possible upgrades available.

x

x

x

Heat recovery possibilities not known or considered.

x 187

4.42

Drying – the programme

A processing essential? Drying of plastics is not always necessary and many sites have no drying equipment at all. However, for successful processing of hygroscopic polymers, drying is always necessary and it can be useful for the repeatable processing of some nonhygroscopic polymers (see Section 4.43). If wet polymers are not dried then any moisture inside or on the surface of the plastics granules will be converted to steam during processing and this may show as an internal void, as a surface imperfection or a plane of weakness in the product. Hydrolysis can also take place during processing and this can result in chain scission, reduced molecular weight and large decreases in mechanical properties. Where drying is needed as part of the process, it will generally account for ≈ 10– 15% of the total site energy use. Using an optimised process and new technologies, this can be reduced by up to 50%. This is a considerable saving in energy and cost.

Drying basics The moisture content of any polymer will depend not only on the type of polymer but also on the specific grade of polymer, the current weather conditions and on the history of the particular sample of polymer. The effectiveness and energy requirements of the drying process will also depend on these factors and good materials handling can improve drying effectiveness and reduce energy use. There are a wide variety of competing technologies available to dry polymers and developments in the area have been very rapid. Whichever method is used, all seek to reduce the residual moisture content to below ≈ 0.02% (≈ 0.003% in the case of PET) and all have process-specific advantages and disadvantages. It is very difficult to directly compare the effectiveness and performance of competing drying technologies due to the variations in materials and conditions, e.g., some methods are very well suited to small volumes and others are very well suited to high-volume production. Ideally standard test procedures should be used but some of the new technologies are very specific to the process requirements. 188

• Tip – Drying is a hidden cost. Find out

Absorb and Adsorb

the time taken, the optimum temperature, the energy used and the real cost of drying. This will prompt action to reduce the cost of drying. • Tip – Most drying systems have ‘hidden’

Absorption = The penetration of a substance into the body of another.

motors for blowers, fans, etc. Correct specification and motor management practices can considerably reduce costs (see Section 4.14).

Adsorption = The taking up of one substance at the surface of another.

The programme The cost of providing drying to those sites that need it makes it an expensive resource and the way to achieve the best savings is to implement a full drying management programme. This programme is shown below and is structured into two stages and four steps. For the average site, the programme can deliver savings of up to 25% mainly by inexpensive measures.

Stage 1: Minimise the demand Minimising the demand is the first step in drying management and should be completed before any steps are taken to optimise the supply. As for any service, it is not sensible to optimise the supply for an excessive drying load that can easily be reduced.

The difference is very well defined, a desiccant takes water out of the air to dry it and adsorbs it – there is no penetration of the water removed from the air into the body of the desiccant so the desiccant does not absorb the moisture. All the moisture is on the surface of the desiccant.

Dry the right materials It makes little sense to use energy to dry materials that do not need drying in the

Minimise the demand

Optimise the supply

Step 1 Dry the right materials

Step 3 Improve control systems

Step 2 Store materials correctly

Step 4 Reduce drying costs

Stage 1

Stage 2

The drying management programme The drying management programme follows two stages and four steps to reduce the energy used in cooling. Stage 1 must be completed and maintained before Stage 2 is started to get the full benefits of the programme. Chapter 4 – Services

first place. Drying should be limited to those materials that need drying for successful processing.

Failure to dry plastics properly can lead to a variety of concerns such as:

Store materials correctly

• Splay.

After the correct materials have been dried, they will take up moisture from the atmosphere if they are left in contact with normal moisture-laden air. Processes and systems are needed either to use dried materials immediately after drying or to keep them in a dry condition and prevent re-absorption or re-adsorption of moisture.

• Silver streak. • Internal bubbles. • Surface defects. • Poor melt flow. • Reduced impact strength.

Stage 2: Optimise the supply

• Reduced tensile strength.

Only after the demand is minimised should the supply be optimised. It is not logical to optimise the supply based on excessive demand.

• Reduced elongation at break. Getting it wrong can be very costly.

Improve control systems and insulation

Rating dryers?

Drying has been traditionally very difficult to control but advances in control methods have been rapid and now offer some of the best opportunities for large and automatic energy use reductions. This is an exciting and rapidly moving area for energy management.

Wittmann Group (www.wittmangroup.com) has developed a rating system for dryers that models dryers in a similar manner to that of Section 2.17.

Reduce drying costs

Progress at last?

The actual drying process is the largest energy cost in the drying process and simple measures can reduce costs. The focus of this book is on rapid payback and incremental improvements but the ultimate solution is to review the complete drying system to define the real needs and to match these exactly. The range of methods available makes the choice difficult.

Monitoring & targeting The energy map (see Section 3.2) can be used to estimate the cost of drying to a site but it is more accurate to fit a kWh meter to the drying system main feed to allow hourly running costs to be measured. This can be plotted versus production volume (as in Section 2.2) for monitoring and targeting. • Tip – A formal drying management

program does not cost much to set up and the only cost will be the labour and time needed to establish the system. For most sites the potential savings from a dryer management programme will be in the region of 5–8% of the energy cost. These savings are unlikely to be achieved without a formal programme. Chapter 4 – Services

Drying methods There are many different methods for polymer drying and they have widely varying energy loads. Each has advantages and disadvantages and some are only suitable for specific polymers or processes. The choice is difficult. 189

4.43

Drying – minimise the demand: dry the right materials

Hygroscopic materials Hygroscopic polymers absorb moisture to an equilibrium level in normal atmosphere and this will vary with the water content of the atmosphere. The moisture will penetrate into the body of the polymer and will be bonded to the polymer by polar hydrogen bonds – this is not a surface effect and will not be immediately obvious by any moisture on the surface of the plastic granules. Typical hygroscopic materials are PET, PA and PC (see the table on the opposite page for a more complete list). In these materials, the water molecules are absorbed and are intimately bonded or trapped inside the material and are not easily removed. Drying is essential before processing hygroscopic materials. Processing undried hygroscopic polymers can result in hydrolysis (chain scission) during processing. This will affect the quality of the finished moulding and moulding defects and premature part failure are almost inevitable. When drying hygroscopic materials the supplier’s detailed data should be checked for the drying requirements.

moisture due to poor materials handling. In some cases, such as PP with high levels of talc fillers or PE with high carbon black loadings, a nominally non-hygroscopic material (PP or PE) may need to be dried to remove moisture absorbed by the filler (talc) or colourant (carbon black). If this is not done ‘silver streak’ may form on the surface of the mouldings.

Drying is an expensive process Define the materials that you must dry before processing and only dry these materials.

• Tip – There are other causes of ‘silver

streak’ that are not associated with moisture, e.g., poor tool venting, excess shear (also known as ‘shear splay’) or gas trapping at intersecting material flow fronts. It is far preferable to work to eliminate these possible causes before committing the site to drying all PP + talc blends. • Tip – Some sites use drying (at great

cost) when the real solution is to improve the process conditions. Some sites pre-heat all materials on the anecdotal basis that this gives improved cycling and increased production rates. In these cases, the drying is really ‘insurance’ against lost production that may have

• Tip – Supplier’s data will generally be

based on the ‘worst-case scenario’ and can be reduced if good materials handling is followed or in hot, dry weather. It is more energy-efficient to use good controls than to follow a timebased value (see Section 4.45).

Non-hygroscopic materials Non-hygroscopic materials do not absorb water into the bulk of the material but they adsorb water at the surface by simple condensation if the materials handling is not good, i.e., bringing materials from a cold warehouse area into a warm production area. These may not strictly require drying but poor handling may mean that they can carry surface moisture that should be removed before processing. Typical non-hygroscopic materials are non-polar polymers such as PE, PP, and PVC (see the table on the opposite page for a more complete list). • Tip – Drying of non-hygroscopic

materials is a waste of dryer energy unless these materials have picked up 190

Hygroscopic and non-hygroscopic polymers Drying requirements vary with the polymer, hygroscopic polymers always need drying but non-hygroscopic polymers may only need the removal of surface moisture. Compounds, e.g., PP + talc, may need drying to remove moisture from the additives. Chapter 4 – Services

been more expensive than the drying cost.

Base polymer

• Tip – Avoid ‘insurance’ drying of non-

hygroscopic materials and improve materials handling instead (see Section 4.44). Increasing energy costs make this an expensive insurance policy and it is worthwhile making a careful study of the actual needs of the polymers, the time taken, the temperature required and the kWh used. • Tip – Care should be taken with over-

drying of any material as this may result in volatile additives being driven out of the material. • Tip – Simply defining the materials that

need to be dried for reliable processing can considerably reduce the cost of drying. • Tip – Define the materials that it is

absolutely necessary to dry and dry to the absolute minimum.

Hygroscopic (Yes/No)

ABS

Yes

ABS/PC

Yes

ABS/PVC

Yes

Acetal (copolymer)

Yes

Acetal (homopolymer)

No

CAB

Yes

PA 6

Yes

PA 6/6

Yes

PA 6/12

Yes

PA 11, 12

Yes

PBT

Yes

PBT/PET

Yes

PC

Yes

PE-HD

No

PE-HD + 3% Black

Yes

PE-HD + 35% Black

Yes

PE-LD

No

PE-LD + 3% Black

Yes

PE-LD + 35% Black

Yes

PEEK

Yes

PET

Yes

PET-G

Yes

PES

Yes

PP

No

PPS

Yes

PS-GP

No

PS-HI

Yes

PVC

No

SAN

Yes

Hygroscopic and non-hygroscopic polymers This is table is for guidance only. Actual results are depend not only on the base polymer but also on the additives, e.g., PP is non-hygroscopic but PP + talc is hygroscopic because the talc is hygroscopic. Always check with the supplier for detailed data. Chapter 4 – Services

191

4.44

Drying – minimise the demand: store materials correctly

Materials handling counts

Hygroscopic materials

Hygroscopic polymers will absorb moisture during manufacture, transportation and when in storage. Correctly minimising this moisture absorption will reduce the amount of drying necessary. Non-hygroscopic polymers will not adsorb moisture during manufacture or transportation, but they may become wet during storage if poorly stored and may suffer from surface condensation if moved from a cold storage area to a warm processing area.

Hygroscopic materials will generally be supplied in sealed bags to reduce moisture absorption but even sealed bags will pick up moisture if stored in a moist cold area.

In both cases, good storage and handling can reduce the drying load and must be implemented before reviewing the drying process. In the case of non-hygroscopic materials, good storage of polymers can eliminate drying altogether. Minimising the load is always the first step.

• Tip – Drying parameters set by resin

companies usually assume a certain initial moisture level. Improving materials handling procedures can reduce the drying load for little cost. • Tip – Polymers will require less drying

General good practice

• Tip – All opened polymer bags or

in warm dry weather and cycle times can be adjusted to reduce energy use. containers should be promptly (and effectively) resealed after use and stored in warm dry areas to reduce the amount of moisture take up before being dried.

Materials suppliers give drying guidelines for all materials but these will often include non-hygroscopic resins where the guidelines are sometimes given purely as insurance. It is essential that sites pay attention to the moisture characteristics of the material that they are drying to avoid drying the wrong materials (see Section 4.43).

• Tip – An opened bag of hygroscopic

Good storage of unused polymers in a warm dry environment will reduce their moisture content before drying and reduce the amount of condensation formed when they are processed in a warm environment.

• Tip – Unopened bags of some

stored in warm, dry areas. • Tip – Investigate warming the materials

in storage areas using any waste heat rejected from compressors (see Section 4.31), chillers or other processes. These can provide large quantities of warm dry air to an area for very little cost. • Tip – Ambient weather conditions affect

the amount of drying needed. Good realtime weather data (particularly relative humidity) can be used to set drying conditions. 192

Keep the material dry and keep it as warm as possible.

If the material is stored improperly and moisture levels get too high, it will take additional energy to achieve the desired moisture content. A modest investment in proper storage and handling can lead to big energy savings at the dryer provided the site is set up to adjust drying based on the real moisture content of the material rather than simply working from the time-based rules given by the supplier.

It is estimated that simple management improvements in materials handling could reduce the drying energy use by approximately 10%.

• Tip – Ensure that all materials are

Good storage is simple common sense.

material (even if resealed) should be regarded as ‘wet’ material. • Tip – Hygroscopic material supplied in

sealed bags from the supplier should be regarded as potentially ‘wet’ as the history is not known. hygroscopic polymers can absorb water over long periods. Check packaging for information such as ‘Should be dried before use if not used before XX/XX/XX’.

Seal the drying system Drying is carried out to achieve the correct moisture content at the relevant machine not as the material exits the dryer. Air leaks in the materials handling system will allow hygroscopic materials to pick up moisture after drying and will either create processing defects or require drying to a much lower level to get the correct moisture content at the machine (which is what counts anyway). Chapter 4 – Services

It makes little sense to expend energy on drying of plastics if dried materials are not stored and handled correctly to minimise moisture take up after drying. After drying any material should be kept in a sealed container or be conveyed by a sealed system. All components of the materials handling system from the dryers to the machines should be checked for leaks and sealed to remove moisture absorption after drying. Drying a material and then allowing it to absorb moisture after drying is simply a waste of energy and will increase energy costs unnecessarily. Sealing of the materials handling system is relatively easy (it can also reduce the materials handling costs). • Tip – Check the materials handling

system for leaks that will allow dried materials to reabsorb moisture after drying. • Tip – Seal any leaks found. • Tip – Do not think that the process of

moisture absorption is slow and that short exposure times to ambient air do not matter. Hygroscopic materials can pick up substantial amounts of moisture in 30 minutes or less. Most will take much longer than this, e.g., PA will take some days to reach equilibrium, but some absorb water very quickly. • Tip – If material is left in a machine

warm up before processing. • Tip – If materials are stored internally

then keep the area as warm as possible to reduce the possibility of condensation when the material is transferred to the processing area.

When will condensation occur? Condensation of atmospheric moisture on a surface will only occur when the ‘dew point’ temperature of the air in contact with the surface exceeds the temperature of the surface itself. Condensation can therefore be controlled by either: • Reducing the humidity of the air

(lowering the dew point). • Raising the temperature of the surface.

The simple approximation (see sidebar on the right) can be used to calculate the dew point in the processing area to predict if condensation will occur on the surface of any polymer when it is brought from a cold storage area to a warm processing area. • Tip – As a ‘rule of thumb’, under normal

processing area conditions (20–25°C and 30–40% RH), if the temperature difference between the storage area and the processing area is > 15°C, i.e., the storage area is < 5–10°C, then there may be a concern with condensation if material is not given time to warm up before processing.

Dew point The dew point is an important value in drying. The dew point is the temperature below which the water vapour in a volume of air at a constant pressure will condense into liquid water. It is the temperature at which the air is saturated with moisture. Calculating the dew point accurately is complex but a simple approximation is:  100 −RH   5  

Tdp = T −

where: • Tdp is the dew point temperature. • T is the dry-bulb temperature. • RH is the relative humidity. This is accurate to within ± 1°C provided the RH is > 50% (this is quite high).

hopper then it should be covered with a ‘blanket’ of dry air to prevent moisture absorption.

Non-hygroscopic materials Non-hygroscopic materials will, by definition, not absorb moisture but may suffer from surface moisture if they are stored in cold areas and then brought into a warm areas before processing. This is particularly important in winter where the temperature differential between the storage area and the processing area can be higher. It is even more important in cold climates where external silos are used and the plastic can be very cold before processing. Storage of non-hygroscopic polymers should be in dry areas that are preferably at the same temperature as the processing area to minimise any condensation. • Tip – If material is stored in external

‘cold’ silos then consider transferring the material to internal ‘day bins’ around 24 hours before processing to allow it to

Chapter 4 – Services

193

4.45

Drying – optimise the supply: improve control systems and insulation

Control at last Drying has traditionally been a difficult process to control. In the past, control systems were primarily time-based and it was not possible to directly measure the moisture content of the material in realtime. Measurement was only possible via the dew-point of the process air. Whilst this is related to the moisture content of the material, it is not a direct measurement and does not give the best control. New developments now make direct real-time measurement of material moisture content possible and this is an exciting development. Improved computer control systems and computer modelling technology have also improved control of the drying process.

Improve control systems Improved control is needed to both reduce energy use and also to avoid overheating of materials. Traditional temperature/time controls are serviceable but not energyefficient. What is important is the moisture content after drying not the temperature and time in the dryer. Computer control gives better control and allows drying to a pre-set moisture content rather than to a temperature/time specification that may have nothing to do with the actual moisture content and will most likely over-dry the material. Using good control systems to monitor moisture content can help to save energy and reduce running costs by optimising the process to eliminate over- or underdrying. They also provide a more consistent material to the process. • Tip – Improved controls in drying are an

area that can have rapid payback. • Tip – Investigate methods of improving

control of the drying system to dry the material to a moisture content and not to a simple temperature/time specification. • Tip – Establish controls to ensure that

the system is operating at the correct temperature and is able to maintain the temperature and dew point accurately.

performance, especially for older dryers with poor control systems. These not only allow operators to monitor the process but also to set the required dew point for the air to the drier and to control the system to achieve this. Other controls measure the dew point of the exhaust air as a measure of the amount of drying already achieved and give better process control.

Direct material control An important recent development is the introduction of real-time measurement of the moisture content of the actual material. Systems have been developed by Bry-Air Prokon (www.pro-kon.ch), Moretto (www.moretto.com) and others based on measuring material properties to calculate the actual water content of the material. These systems are capable of measuring water content in the range 0.015% to 0.050% with an accuracy of ± 0.001% and have the potential to change the way dryers are operated and to achieve complete control of the drying process.

Rather than worry about which of the many new processes is most energy-efficient, it can be more profitable to work with what you have got. All it takes is some basic process analysis, some basic controls and most current systems could be improved by > 25% for little financial outlay.

Reduce timings in summer The drying recommendations for most hygroscopic materials are of the form ‘Dry for X hours at Y°C’. Manufacturers give these recommendations to achieve a specific moisture content for the plastic. However, drying should be to a moisture content and not to a time. The times and temperatures given by the manufacturer are based on an average to achieve the required moisture content. Good storage conditions (see Section 4.44) mean that the plastic should not need as much drying. This is particularly true in warm dry climates where it is possible to reduce drying times and still achieve the required moisture content.

Install VSD controls on fans and blowers. Airflow control in dryers is sometimes achieved by dampers on the flow from a fan which is usually working at full load. VSD-controlled fans are much more energyefficient.

• Tip – Drying to a time is easy to do but

it can lead to times and temperatures that are greater than those needed. Using knowledge of the actual ambient conditions can easily reduce drying times with no effect on the condition of the plastic at the machine.

Dew point control

• Tip – Reduce drying times in warm, dry

Dew point controls can be added to any dryer system to measure the air dew point and to dramatically improve dryer

• Tip – Record the storage conditions

194

Process control offers some of the best and simplest improvements for the drying process.

conditions to reduce energy costs. (temperature and RH) of the material as a guide to the amount of drying needed.

Direct material control has not been possible in the past but the solution may be in sight.

Chapter 4 – Services

Use ‘set-back’ temperatures Controls allow materials to be dried and kept in the ‘ready-to-use’ condition with little further energy use. After a material has been dried it does not need further heating to keep it dry provided it is kept warm in a sealed container. Simple controls can be used to define a ‘set-back’ temperature condition, i.e., 35°C, for the material. The same controls can be used to switch dryers off when no material is required. Over-drying (keeping the material at the drying temperature for longer than is necessary) can actually degrade the mechanical properties of the material. It is not simply wasting energy but can also lead to product failure. • Tip – Use simple controls to put dryers

into a ‘set-back’ condition when the drying cycle is complete. • Tip – Set-back should be used with

caution if the material is to be used soon, i.e., the reduced material temperature may need to be made up at the machine and increase energy use at the machine. It is all a question of timing.

breakdowns and poor insulation on hoppers and hoses (air inlet and air delivery hoses are rarely insulated). These will all increase temperatures in the processing area and increase the cost of operating the dryer. Heat should be applied where it is needed and not lost. • Tip – An infra-red camera will reveal

leaks and failed insulation. Check dryers for insulation leaks and breakdowns (particularly at inspection port seals). • Tip – Seal any leaks and rectify any

failed insulation. • Tip – Insulate air inlet and air delivery

hoses to reduce heat losses. • Tip – Do not insulate return air hoses

from the top of the hopper to the desiccant bed. If the return air from the hopper is hot then the desiccant can heat up and this will reduce its ability to remove moisture from the air (that is why there is often an aftercooler on the return air line). It is more efficient for the process if these hoses lose heat. • Tip – Dryers can be insulated using

hopper covers to reduce heat losses (see www.insul-vest.com).

Keep the heat in the dryer Check where the hot air (and heat) is going after it exits the dryer. If it is being vented to the site then consider using a heat exchanger to recover the heat to pre-warm air to the system or to heat water. You have already paid for the heat. It is worse if the air is vented to an airconditioned site – you will pay for it twice then. Once to heat it up and the next time to cool it down with the A/C.

Dryers are hot and checking by hand is not recommended.

• Tip – Use simple controls (linked to the

main machine) to turn dryers off when there is no demand for material, e.g., over weekends and shut-downs. • Tip – Check the drying cycle to see if

dryers are operating at full power after the drying cycle has been completed. Note: The dryers may need to be restarted a short time before the production start to remove any moisture picked up during the shut-down period and to ensure that the material is in the correct condition for use.

VSDs for blowers and fans All drying systems have blower and fan motors for air or materials movement and these have traditionally been fixed-speed motors that simply ‘damped’ as a control mechanism. These motors are prime candidates for the application of VSDs and suitable controls (see Section 4.52). • Tip – Blower and fan motors are very

suitable for VSDs and can normally improve the control and stability of the process as well as saving energy.

Sealing and insulation

Heat losses at dryers

Dryers are designed to be hot and often suffer from heat leaks that increase energy use and operating costs. Most goodquality dryers are well insulated but it is common to find leaks, insulation

The heat losses at dryers from either breaching of the insulation with fixtures (upper pictures) or poor sealing on apertures such as doors or inspection ports (lower pictures). Improved thermal insulation and good maintenance of seals is important.

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4.46

Drying – optimise the supply: reduce drying costs with desiccant drying

The industry standard Desiccant drying using dehumidified air is probably the most widely used drying technique in the plastics industry and a typical desiccant dryer layout is shown on the right. This is for information only and actual installations may vary considerably in actual layout. Most systems consist of a battery of individual dryers but it is also possible to use a central desiccant dryer feeding dry air to a range of individual hoppers – this reduces floor space and can reduce costs but each dryer must still be individually controlled according to the specific material and the material flow rate required. Desiccant dryers work by passing moisture-laden air through a canister containing desiccant beads. The strongly hygroscopic desiccant adsorbs moisture from the feed air to produce dry air, which is then heated and passed through the drying hopper containing the plastic granules. The warm dry air removes moisture from the granules and the returning wet cooler air is recycled back to the dryer through a closed loop system for further drying and use. The desiccant canister is regularly removed from the drying stream for high heat regeneration (≈ 300°C) to remove adsorped moisture. A typical dryer uses either indexing desiccant canisters or valve arrangements to regularly cycle the desiccant through the drying and regeneration stages to avoid overloading the desiccant and degrading the process efficiency. The regeneration cycle can be determined either through a simple timer (which is not energy-efficient) or when the output dry air dew point reaches a set point (to indicate the need for regenerated desiccant). The most efficient method is to either measure or predict the moisture content of the material to determine the regeneration cycle time. The regeneration stage is completely separate from the drying stage but it is common for the heat used during regeneration to be recycled into heating the process air before it is sent to the drying hopper. The typical cycle time for drying using desiccant is in the region of 4–6 hours depending on the type of material being dried and the initial moisture content. The 196

most commonly used desiccant is crystalline alumino-silicate molecular sieve because it has a high affinity for moisture at very low dew points.

Dew point – lower is better

Desiccant wheel drying Conventional desiccant dryers use canisters packed with desiccant to dry the air. These have a large thermal mass and regeneration demands large amounts of energy. Desiccant wheel dryers are based on a wheel which has desiccant crystals impregnated and grown on a fibreglass substrate. The lightweight wheel has a high surface area to air flow ratio and has a much smaller thermal mass than the conventional canister. In operation, the wheel rotates continuously and the desiccant passes through the adsorption, regeneration and cooling cycles every 4–5 minutes. Drying air is continuously regenerated in a closed loop circuit. Hot regeneration air passes through the desiccant media and the released moisture is then purged to the atmosphere. No ambient air is introduced to the process as desiccant cooling is done using dry air. The desired dew point is

All air contains some water vapour. The dew point is an indicator of how much water vapour is present. In drying terms, the lower the dew point (in °C) the drier the air. For most polymer drying a dew point of −40°C is used, although this may not be required in all cases.

Typical desiccant dryer layout A typical desiccant dryer showing the primary process (drying the polymer) on the left and the secondary process (regenerating the desiccant) on the right. The desiccant beds are rotated so that the active bed is always capable of drying the polymer. Chapter 4 – Services

achieved by changing the rotational speed and other dryer variables without overdrying of thermally sensitive materials. The low thermal mass of the wheel allows the use of lower regeneration temperatures than conventional desiccant drying systems whilst still achieving the required overall temperature for effective regeneration. The structure also produces a lower pressure drop to both the process and regeneration blowers, allowing the use of smaller, energy-efficient blowers.

Desiccant drying – heat exchangers and heat recovery Conventional desiccant dryers rarely attempt to recover the substantial amount of heat lost from the dryer during the process and often incur cooling costs. This process also suffers from considerable energy losses whilst transferring the heated dry air to the drying bin because of the high temperatures of the feed air. These features lead to considerable heat and energy losses and a relatively inefficient process. A conventional desiccant dryer has a thermal efficiency of approximately 34%, i.e., only 34% of the total input energy is used to actually heat and dry the polymer. The rest of the input energy is lost before or after drying the polymer. New developments to the process use integral heat exchangers to recover heat from the exhaust air and recycle this heat back into pre-heating the cooler dried air from the desiccant dryer before it is heated to the required temperature at the inlet to the drying bin to heat and dry the polymer. The heat balance for a drying system using a heat exchanger to recover heat from the exhaust air has a thermal efficiency of up to 56%, i.e., 56% of the input energy is used to actually dry the polymer. Some of the benefit of this method is not due to heat recovery but to the use of localised heating of process air at the drying bin – this reduces the transit heat losses and increases the overall energy saved and cannot be directly attributed to the heat exchange process. Additional developments in this area involve bleeding some of the hot exhaust air directly into the process airline immediately before the air is heated. This has particular advantages at low materials throughput but may not be an Chapter 4 – Services

advantage when the dryer is heavily loaded. This technology can be retrofitted to existing dryers to reduce energy and improve material quality.

Desiccant drying – good practice tips • Tip – Units that have automatic

Desiccant gets old and breaks down under the heating and cooling cycle. Test the desiccant regularly and replace after 18 months to keep the system in good condition.

desiccant regeneration controlled by dew point sensors or preferably by material moisture content are technically preferred because they are more consistent in operation. • Tip – Optimise cycle times for the

desiccant during drying to avoid overloading the desiccant and thus reducing process efficiency. • Tip – The lower the dew point of the air

supplied the quicker the drying time but a balance must be made between the acceptable dew point and the energy used in the regeneration process. • Tip – The smaller the plastic granule the

quicker the drying time due to the shorter diffusion path through the granule. • Tip – Smaller spherical desiccant sieve

sizes give quicker reactivation and greater adsorption because the greater ratio of surface area to mass gives quicker heating and cooling. • Tip – High desiccant reactivation

temperatures improve desiccant reactivation and give greater adsorption in use after cooling but may use more energy in reactivation.

Most conventional desiccant dryers use electricity for heating the process air and regeneration. It is also possible to use gas for heating and for regeneration and this can be an economical alternative. Gas costs less per kWh than electricity and while the process efficiency is not as high, the savings can be very substantial. As with all energy management – do the numbers.

• Tip – Desiccant drying systems should

be ‘closed loop’ systems to exclude ambient air and to get the lowest dew point from the process. • Tip – Reactivated desiccant must be

cooled after reactivation and a cooling stage (either passive or active) should be present before use. Ideally, this should not use ambient moisture-containing air. • Tip – Desiccant systems need to be

correctly sized for the demand. • Tip – Well insulated material hoppers,

desiccant beds and piping can reduce heat losses from the process. • Tip – Material that has been sufficiently

dried should be reduced to a ‘set-back’ temperature if not immediately needed.

Dew point measurement is possible with small hand-held dew point meters or meters fitted to the dryer. These can be linked to external meters which measure the wetbulb temperature and the enthalpy of the outside air to maximise the free cooling potential of the ambient air.

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4.47

Drying – optimise the supply: reduce drying costs with other methods

Manual and hot air drying Manual oven drying is not recommended for any polymer processing operation. Whilst initially cheap, it has high energy costs and high batch-to-batch variations in material moisture content. Hot air or hopper drying is only really suitable for non-hygroscopic polymers where the only moisture present is on the surface of the granules. Even in these cases it should be reduced by good materials handling (see Section 4.44). The energy efficiency of drying using dehumidified air exceeds that of oven or hopper dryers by a factor of > 5.

Compressed air drying Compressed air drying uses conventional compressed air from the standard site system. The polymer is first heated with hot air and then compressed air at 7 bar and with a dew point in the region of 5°C) is fed into the bottom of the dryer and allowed to expand to atmospheric pressure. The expansion process greatly reduces the dew point of the hot air to approximately −20°C which is adequate for the drying of many polymers. The hot, dry air then flows up through the hopper to remove moisture. If additional drying capacity is required then it is possible to upgrade compressed air dryers with a moisture removal membrane to further dry the polymer. Compressed air dryers have no moving parts, no desiccant, no regeneration of desiccant and are very low maintenance. When combined with good heat recovery from both the compressor (see Section 4.31) and from the drying process, the use of compressed air dryers can be very effective for relatively low-volume throughput. • Tip – If considering compressed air

dryers then make sure that the cost of generating the compressed air is used in the costing of the drying process. It is often forgotten. • Tip – If considering compressed air

dryers then make sure that the site has adequate compressed air generating capacity and that the compressed air dryers are adequate to produce large quantities of dry air. 198

• Tip – Standard compressed air dryers

can be good for hygroscopic resins that do not need very low moisture content but will almost certainly need the membrane upgrade for use with PET and even then need to be treated with some caution.

Low-pressure drying Low-pressure drying (LPD) uses a vacuum applied to a dryer cabinet to accelerate the drying process. The process uses three canisters of polymer mounted on an indexing carousel.

New technologies are being developed in response to the need to reduce energy consumption in drying. Processors should examine the new technologies to determine if these are suitable for their operations.

• In the first stage the granules are

automatically loaded into the canister. The canister and contents are then heated. After reaching the required temperature the canister is indexed to the second stage. • In the second stage the canister is sealed and a strong vacuum is applied. The vacuum reduces the boiling point of any moisture present from 100°C to around 56°C and the water vapour is rapidly driven out of the granules, evacuated to the ambient air and removed by the vacuum. • In the third stage the canister is indexed

to allow dry material delivery by vacuum loader direct to the required machine. Using vacuum as a driving force reduces the drying time by up to 80% and reduces the direct energy use (including the energy for the vacuum) by 50–80%. It also simplifies the process plant needed for drying, as desiccants are eliminated and no longer need to be regenerated and replaced. This provides a further opportunity to save money and energy. The system can be used for a wide range of both hygroscopic and non-hygroscopic materials but is particularly suited to the machine-side drying of materials where processors need rapid material changes. The shorter drying time enables rapid start up from cold, the use of smaller batches of material reduces clean down and materials changeover times so that machine utilisation and production efficiency can be increased. In many cases, a material colour changeover can be carried out ‘on-the-fly’ with virtually no interruption of the process cycle.

As the pressure decreases, the boiling point of water also decreases. Water boils at a temperature of ≈ 71°C at the top of Mt. Everest – not great for cooking or a warming cup of tea as any climber will tell you.

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The use of smaller batches of material treated in a shorter time enables the process to match the throughput of machines operating on larger batches of material and the direct delivery to the machine reduces any opportunity for the polymer to pick up further moisture after the drying cycle has been completed. The use of the vacuum-assisted drying reduces the heating cycle to between 20 to 30 minutes and the temperatures experienced by the polymer are reduced. These factors greatly reduce the risk of any thermal degradation of the polymer in the drying process. LPD is suitable for low- to medium-volume throughput.

Infrared drying Infrared drying (IR) uses the energy from IR radiation to directly heat the bulk material of the polymer granule/flake. The delivered energy is applied directly to the granule with no other transfer medium. The applied energy causes internal heating and molecular oscillation and therefore heats the bulk material of the granule and any internal moisture. A stream of cooler ambient air surrounds the granule and the internal heat drives the moisture out into the cooler air stream that removes it from the process. The driving force for IR drying is the difference in temperature between the vaporised water and the ambient air stream: this creates a partial pressure gradient from the inside of the granule to the outside and a strong driving force for moisture removal.

These systems can be used for drying both hygroscopic and non-hygroscopic materials but are particularly suited to the drying of reprocessed PET. PET processing uses crystalline granules but the material becomes amorphous during processing – therefore PET regrind is amorphous and must be recrystallised before it can be processed again. Historically a separate recrystallisation process was used prior to drying and processing. In IR drying processes, the PET is raised above Tg and continuously agitated during the process, this effectively combines recrystallisation and drying in one pass.

IR systems (drum or IR + vacuum) offer dramatic improvements in energy efficiency. Combine these with direct moisture measurement of the polymer (see Section 4.45) and significant energy use reductions in drying are possible.

Drying times for many hygroscopic materials can be dramatically reduced and, in the case of PET reprocessing, the recrystallisation process can be performed at the same time. The MOBY process (IR + vacuum) also provides a cleaning action to provide high-quality reprocessed PET for direct processing (‘Super-Clean’ for food applications) and can also be set up to improve the intrinsic viscosity (IV) of the PET from the system. The drum system is fully continuous but the IR + vacuum system does need a buffer hopper. The direct energy application at the point of use provides reduced process times and energy consumption is claimed to be 72– 120 W/kg for PET recrystallisation and drying to final moisture contents of less than 0.005%. This is much lower than that achieved with traditional drying methods. IR drying (either type) is suitable for highvolume throughput.

Rotating drum This system uses a horizontal drum containing an internal spiral feed which transports and agitates the material as it is carried along the drum underneath the IR heaters. The final moisture content of the polymer is determined by the power rating of the IR heaters and the residence time in the system. These can be finely controlled by the rotation rate of the drum and the power applied to the heaters.

Infrared + vacuum This system uses not only IR heaters but an additional applied high vacuum (down to −980 mbar). The IR provides material heating and the vacuum further draws the water out of the material (as with standard LPD drying). This increases the process efficiency and reduces energy use. Chapter 4 – Services

Infrared drying + vacuum (MOBY) process The MOBY process uses not only infrared but also vacuum to further accelerate drying of the plastic. Source: SB Plastics Machinery (www.sbplastics.it) 199

4.48

Drying – where are you now?

The initial steps in drying As with the score charts shown earlier, this is a self-assessment exercise to allow a site to benchmark their current status. This will set the scene for planning improvements in the area of drying. Drying is another hidden service that uses large amounts of energy to operate and is frequently misused or overused. Drying is rarely considered in the average site but at sites where drying takes place it is one of the significant energy use areas.

worry about it) and drying cycles are rarely adjusted for the weather conditions. Simple techniques are easily implemented to reduce the amount of drying carried out at most sites.

Insurance drying is an expensive insurance policy to make up for poor storage and handling.

Completing the chart This chart is completed and assessed as for those presented previously.

Drying is weather-dependent yet most sites take no account of the weather in the storage and handling of raw materials (it is all going to be dried anyway so why

Polymer drying Drying load 4 3 Heat recovery

2

Drying parameters

1 0

New technology

Systems & components

Operation & maintenance

Use the scoring chart to assess where you are in drying The numbers from the scoring chart can be transferred to the radar chart for a quick visual assessment of where you are in terms of drying. 200

New technologies are being developed to reduce drying costs and many of these are already available to plastics processors.

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Drying Level

4

3

Drying load

Good attempt to Drying parameters Systems based on good performance adjusted for minimise drying load but weather & partial for current use made of unsuccessful due requirements. to poor storage & natural conditions. Dew point of handling. Materials dried drying air poorly according to need. controlled.

2

0

Score

Systems & components

Operation & maintenance

Excellent practice Drying parameters Systems based on Full preventative adjusted for best performance maintenance in minimising weather & full use drying load by for current programme in requirements. place for all excellent storage made of natural Dew point of system & handling. conditions. drying air well components. Materials dried controlled for according to need. optimum drying energy use.

Poor attempt to minimise drying load.

1

Drying parameters

New technology

Heat recovery

New technologies Heat recovered investigated & from drying installed where system & used appropriate. extensively for preheating.

Good New technologies Heat recovered fully investigated & maintenance from drying based on actual found appropriate system & partially performance of but not installed. used for predrying system & heating. triggered by alarms for potential failure.

Drying parameters Systems based on Poor maintenance New technologies adjusted for previous based on annual partially investigated but no weather. requirements. maintenance Drying parameters Dew point of schedule only, conclusions made. adjusted for drying air irrespective of material to be measured but not operations. dried. controlled.

Heat recovered from drying system used partially but ineffectively.

Aware of Heat recovery Unaware of need Drying parameters Systems selected No maintenance to minimise drying not adjusted for based on previous unless production possibilities of new considered but not load. weather. requirements & problems seen. technologies but attempted. Drying parameters poor for current No attempt to not investigated. minimise drying adjusted for requirements. load by material to be Dew point of appropriate drying air dried. considered but not storage & handling. measured.

Unaware of the Drying parameters Systems selected need to minimise not adjusted for based on previous drying load. weather. requirements & All materials dried Drying load is unsuitable for increased by as part of normal current inappropriate procedure. requirements. storage & Dew point of handling. drying air not considered or measured.

x

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x

x

No maintenance even when production problems seen.

Possibility of new technologies unknown & not investigated.

Heat recovery possibilities not known or considered.

x

x

x 201

4.49

Vacuum generation

Vacuum isn’t free either One of the most common methods of generating a vacuum is through the use of compressed air but there are several different methods of generating a vacuum and each has specific operating characteristics. The method chosen depends on the application requirements and the general operating characteristics of three different methods of generating vacuum are shown on the diagram on the far right. Whichever method is chosen, high flow rates and high vacuum levels will result in high energy costs and vacuum, like compressed air, is not free.

Vacuum pumps Vacuum pumps provide high vacuum levels at moderate volume flow rates, i.e., they have a low suction capacity, and are very suitable for many plastics processing applications. The most common type of pump currently used is the liquid ring vacuum pump (LRVP) using water as a liquid ring and these can be expensive to operate in terms of water use if a oncethrough water system is used. Other types of pumps available are dry-running (rotary claw, Roots and scroll or screw types) or oil-lubricated types. Vacuum pumps are often used for drying, extrusion degassing, extrusion calibration, vacuum forming or thermoforming with vacuum assist.

sized for the demand. Consider using two smaller pumps (rather than one large pump) with one as the main routine vacuum supply and the second as the back up capacity which is automatically started when necessary.

Vacuum blowers Vacuum blowers provide low vacuum levels at a high-volume flow rate, i.e., they have a high suction capacity. Vacuum blowers are also termed ‘side channel compressors’ and transfer the kinetic energy of a wheel to the air converting the rotary motion into pressure and hence vacuum. Blowers are generally oil- and lubrication-free, produce no pulsation in the output and are very quiet. Vacuum blowers are most often used for granule and powder transport in raw materials handling systems. • Tip – Fit vacuum blowers with VSDs to

ensure that the blower is only generating the required level of vacuum. • Tip – For new vacuum blowers, only

purchase blowers with VSDs.

Vacuum leaks tend not to have the low ‘ssssssss’ noise of compressed air leaks. A vacuum leak gives more of a high-pitched whistle. Try it and see – or more accurately, hear.

The main decisions in specifying vacuum systems are: • What flow rate is needed? • What vacuum level is needed? This will define the technology needed to produce the vacuum.

• Tip – Look at converting any once-

through water seals on LRVPs with a recirculating water seal. The feasibility of this will depend on the amount of contamination in the liquid seal. • Tip – Fit LRVPs with VSDs to ensure

that the pump is only generating the required level of vacuum. • Tip – Ensure that the liquid ring

temperature is minimised to keep LRVP operating at the highest capacity and vacuum pressure. • Tip – Look at replacing LRVP with dry-

running vacuum pumps, e.g., screw or rotary claw types, to reduce water and energy use. • Tip – Vacuum pumps are often over-

sized for the demand. Investigate the motor sizing for all vacuum pumps. • Tip – Vacuum pumps are often over-

202

Vacuum and pressure in context Measurement of vacuum and pressure can be either relative to an absolute or perfect vacuum or relative to the atmospheric pressure. Absolute pressures are always positive, whereas relative pressures can be either positive or negative (vacuum). Chapter 4 – Services

Ejectors Ejectors provide high vacuum levels at relatively low-volume flow rates. This vacuum is not generated by a motor or blower but by the use of the ‘venturi’ effect and a feed of compressed air. A stream of compressed air flows through a drive nozzle and the velocity differential creates a lower pressure at the inlet. Ejectors have no moving parts and therefore require no maintenance and never wear out. They generate no heat, can be very small, and permit the implementation of very short cycle times. Ejectors can be fitted with sophisticated controls to regulate the vacuum generated by modulating the compressed air supply. Ejectors are primarily used to generate vacuum for robotic grippers, packaging and localised vacuum generation. • Tip – Ejectors should include rapid shut-

off of the compressed air. • Tip – Ejector systems are often a source

of compressed air leakage and must be included in the leak survey programme. • Tip – Ejectors are a substantial user of

compressed air and costings for ejector use must include not only the first installation cost but also the high operational cost of compressed air used in this type of vacuum equipment. • Tip – Suction cup leakage is a

contributor to the high operating cost of ejectors and suction cups must be selected carefully and kept in good condition to reduce energy use.

Systems The level of vacuum to be achieved by the system is a large factor in the running cost of the system and setting the minimum vacuum level possible for the actual system demand will have a significant effect on the energy use of the system. • Tip – Check the application demand and

set the system to deliver this and no greater. The demand should be checked in terms of both the volume flow rate and the level of vacuum needed. Vacuum systems should be regularly checked for leaks. Leakage into the vacuum system is one of the most common reasons for inefficient operation. Vacuum is expensive to produce and detection of leaks is more difficult than for compressed air. Vacuum leaks can be detected with an ultrasonic detector but detection is more difficult and it can be difficult to pinpoint the exact location of the leak. Sensitivity Chapter 4 – Services

is also relatively low unless at very close range. Despite this, an ultrasonic detector is probably the best tool available given that the only cheaper alternatives are listening or the use of a smoke gun, both of which are only suitable at close range and both of which can be difficult to use at the typical site. • Tip – Every system should have a

vacuum checking programme to locate and seal leaks in the system.

Ejector systems often operate at quite low pressures – look out for pressure regulators (reducing valves) close to ejectors. The compressed air pressure is often as low as 2 bar.

• Tip – Open vacuum ports are effectively

a leak in the system and increase energy use. Systems should be regularly checked for system integrity and start-up procedures should include a check on vacuum systems before a machine is released to production. • Tip – Materials transport systems often

have small leaks and should be included in the vacuum checking programme.

Distributed or central systems? Ejector systems can be very expensive to operate and there are good arguments for the use of a central vacuum system for the provision of vacuum to robot grippers (see Section 4.51). A vacuum pump uses far less energy and vacuum distribution can be with light-weight piping. • Tip – Investigate and cost the concept of

using a central system for vacuum. In the right circumstances this can reduce energy use and costs substantially.

Always specify HEMs for vacuum pump motors (see Section 4.19). Where vacuum pump motors are cycling (as in materials feed systems) ensure that there is a softstart fitted to reduce the start-up spike in the power drawn.

Vacuum pumps

Ejectors

Vacuum blowers

Volume flow rate

Approximate operating characteristics of various vacuum generation methods The three methods of generating vacuum all have different operating characteristics. The method of generating vacuum must look at the application requirements. 203

4.50

Hydraulics systems

Fluid power Hydraulics systems are one of the largest energy users in injection moulding (see Section 5.13) but they are also used for many other small and large applications in plastics processing. The high power density available from hydraulics systems makes them extremely suitable for a variety of applications such as stuffers or crammers for recycling or regranulation and for various testing equipment. Excluding their use in injection moulding machines, it is estimated the hydraulics applications account for some 3% of the energy used in plastics processing. This is primarily through the use of small individual machines that are often overlooked and ignored.

Basic theory Energy management and efficiency in hydraulics requires an understanding of some simple concepts: • Energy transmission by hydraulics has two effective variables, the pressure and the flow rate. • The system pressure is defined by the load reacting to the output. • Energy losses are a function of the flow rate and the magnitude of the pressure drop through which the flow occurs. • Energy losses can be minimised by avoiding passing any flow rate through a pressure drop without doing work on the load. The flow rate is generally fixed by the load and therefore the main opportunity is to reduce the system pressure drop. To minimise energy losses the following should be minimised in any hydraulic system: • Large numbers of fittings.

Note: If the peak demand is only for a very short time then the design flow rate may be adjusted downwards slightly.

The type of oil used can affect the energy efficiency of the system.

Hydraulic systems The main components of a hydraulic system are: • Pump – various pumps types are available and these have varying operational efficiencies (see table below).

Some oils are better than others.

• Accumulator – accumulators act in

hydraulic systems in much the same way as receivers do for compressed air systems. They can store energy as hydraulic fluid under pressure and allow a short-term high flow rate of fluid. Low delivery rate pumps can charge the accumulator over a long period of time for rapid delivery when needed. As with compressed air receivers, they also dampen delivery pulsations and pressure surges in the circuit. IMMs with accumulators can often run at lower peak power due to the accumulator. • Piping/valves and control circuits – these are used to transfer and control the energy stored in the accumulator to the actuator where the actual work of the circuit is carried out. • Actuators – actuators are used to convert the energy of the fluid back into mechanical power. The three basic types are linear (conventional hydraulic cylinder), continuous rotation (hydraulic

The effect of choosing the correct hydraulic oil on the energy efficiency of IMMs is dealt with in Section 5.13.

Volumetric Efficiency (%)

Overall Efficiency (%)

Plunger

99

95

• Small inside diameters of any fittings.

Radial

95

90

• Flow-through relief valves.

Axial

95

90

Pump Type Piston:

• Excessive flow controls.

Precision gear pump

95

90

• Small directional control valves.

Vane pump

90

80

• Leakage at cylinder seals.

For constant flow rate systems the sizing of components is relatively easy but where the system is a ‘demand flow’ system then the sizing of the components should be based on the maximum system flow rate. 204

Hydraulic pump types – typical efficiencies There are a range of types of hydraulic pumps and both the volumetric and overall efficiency will vary with the pump type. The main type of pump used in hydraulic circuits is the positive displacement type. Chapter 4 – Services

motor) and limited rotation (semi-rotary actuator). • Hydraulic fluids – hydraulic fluids link

all the other components and are the driver of the complete system. They are classified by letter symbols allocated according to the composition and properties of the fluid (ISO 6743-4). The classification covers properties such as specific gravity, viscosity and viscosity index, pour point (the temperature 3°C above that at which the fluid ceases to flow) and compressibility.

Good practice tips Once designed and installed, most hydraulic systems are fixed and changes are rarely made to the system. Maintenance is generally not carried out except on breakdown and then simple replacement parts are used. Maintenance does matter and simple preventative maintenance (PM) can easily maintain energy-efficient operation of hydraulic systems. Good maintenance is the major factor in energy savings for hydraulic systems. Issues to be aware of are: • Hydraulic pumps – reciprocating pumps will suffer significantly in efficiency terms if they are not maintained properly and an effective PM programme is necessary to maintain efficiency. Rotary and screw pumps also need an effective PM programme but do not generally suffer from efficiency deterioration as rapidly. • Hydraulic oil and system cleanliness – most concerns and failures in hydraulic systems are either directly or indirectly related to contamination of the hydraulic fluid. • Tip – Checking and replacing filters at

regular intervals will mean that you may replace too early or too late. Measure the pressure drop across the filter (using a differential pressure gauge) to know exactly when to change the filter and prevent excessive pressure drops. • Tip – Get the filters in the right place so

that the hydraulic pump is ‘pumping’ to the filter and not ‘sucking’ from it. • Tip – Hydraulic fluid quality should be

regularly checked for cleanliness and replaced at regular intervals with the hydraulic fluid specified for the system. Sampling can be carried out via sampling points where there is relatively constant flow. Chapter 4 – Services

Note: Contamination can be analysed by particle count or by chemical analysis. • Tip – Hydraulic fluid will suffer from air

bubbles (aeration) that will cause noise and vibration, increase wear of system components, reduce cooler efficiency and decrease fluid life. De-aeration can be carried out off-line or on-line to remove air bubbles. The Quicktoron from Triple R (www.triple-r-europe.com) is great for in-line de-aeration and also improves filter performance. • Internal leaks – these are rarely seen and even more rarely effectively dealt with. Excessive internal leakage reduces the efficiency of the system and can cause hydraulic fluid deterioration through heat generation.

De-aerate hydraulic oil on a regular basis to improve the efficiency of the hydraulic system.

Note: Most systems have some designed leakage to provide for component lubrication. • External leaks – these are very visible

and often present a health and safety slip hazard. They are also very expensive to both clean up and to replace the lost hydraulic fluid. One of the most common causes of leaks is deterioration of the hydraulic seals as a result of contaminated fluid or excessive temperatures. Mechanical impact damage can also cause leakage. • System controls – as with any system, operating the hydraulics system when not loaded is a total waste of energy. Systems should be fitted with timers or other controls to automatically switch them off when they are not required or after excessive periods of no load operation.

Keep hydraulic fluid at a steady temperature to improve control of the process and prolong the life of the oil. Some sites use chilled water to cool hydraulic oil. This is generally unnecessary and very expensive. It may also cause the hydraulic oil to be too cold and lead to rapid changes in viscosity giving less stable control and quality problems.

Hydraulic filters The majority of problems with hydraulics systems are the result of dirty or old hydraulic oil and inefficient or ineffective filtering of the hydraulic oil. Fitting additional or more effective oil filters is one simple method of improving oil quality and reducing problems. Additional filters will: Increase the operational life of the oil. Reduce wear on all components. Reduce oil contamination. Reduce maintenance costs. Reduce breakdown times.

Fitting additional filters (and maintaining them properly) can reduce energy use. 205

4.51

Robots

The rise of the robots In the constant (but possibly misguided) search to reduce labour costs, robots are increasing being used for part removal, degating, assembly, quality control and handling in plastics processing. This is another rapidly developing field and the simple Cartesian robots or even the more advanced SCARA (Selective Compliant Articulated/Assembly Robot Arms) robots are increasingly being replaced by fully articulated six-axis robots. Robots are flexible tools but sites should be aware that any additional ancillary component such as a robot will increase energy use. Robots are neither free to purchase nor free to maintain and operate. A full six-axis robot may actually be one of the few items where the energy costs during the lifetime do not exceed the purchase cost but energy will still be a significant cost factor. Even though they do not individually use large amounts of energy, the total energy used by robots is significant at many sites. Reducing energy use in robots can be focused on the energy used in movement and the energy used in gripping. These areas offer the potential to decrease the energy used in robots by up to 50% through a range of simple measures.

robot. Recuperative braking (energy collection during the braking phase to recover the energy from acceleration) is excellent but reducing the need for braking saves even more energy. • Tip – Robots that accelerate to the speed

of a bullet for 50 cm, are then braked to a halt over the next 10 cm and then wait for 10 seconds before the next operation are candidates for slowing down and saving energy. Cartesian robots are also good candidates for slowing down. • Tip – Good timing to avoid abrupt

The word robot comes from the Czech word ‘robota’ meaning forced labour or serf. It was first used in reference to what we now consider to be robots by the Czech writer Karel Čapek in his play R.U.R. (Rossum's Universal Robots) in 1920.

movements will not only save energy but will also reduce stresses on the robot and reduce maintenance costs. • All movements should follow a smooth

trajectory to minimise directional changes and excessive energy use (see diagram below). It is not difficult to see that a smooth trajectory will reduce energy use compared to an abrupt trajectory. Set robots to follow a smooth trajectory to reduce energy use. • As with motors, robots should be turned off when not required. For newgeneration robots this can be achieved by setting the robot into the ‘sleep’ mode in the same way that a computer can be put

Energy use in movement There are several basics to reducing energy use in robot movement and these are: • Every movement of a robot uses energy

and minimising the number of moves that the robot makes reduces energy use. This requires careful path planning, especially if multiple robots are working in the same area, but reduces energy use. • Sporadic or rapid movement of a robot increases the energy required for acceleration and deceleration. All movements should be planned to avoid excessive acceleration and braking. The cycle timing should be such that the robot is in the correct position at the correct time and not as soon as possible. This applies even if recuperative braking, i.e., energy recovery from braking, is available on the selected 206

Trajectories matter Try this quiz: Which trajectory do you think uses less energy – the smooth trajectory or the abrupt trajectory? Sometimes the answer is easy and intuitive. All you have to do is ask the right questions to save energy. Chapter 4 – Services

into ‘sleep’ mode. If there is a ‘sleep’ mode available on the robot controller then activate this. As for plastics processing, there is an energy signature for every robot operation and these can be used to optimise energy use in robot movement. Energy savings of up to 50% have been recorded from path optimisation and other improvements to robot movement.1

Energy use in gripping A robot itself can do no real work unless it is equipped with some type of end-of-arm tooling (EOAT) and this is potentially the largest energy user in robot operations, although not necessarily at the actual robot. Most EOAT will grip the product with either mechanical grippers or with vacuum grippers. Mechanical grippers will normally use compressed air operated actuators. These use compressed air operated pistons to move the gripper fingers and to hold them either open or closed, i.e., there is no continuous compressed air discharge and the amount of air used is limited to that needed to move the piston. This is the cheapest method of gripping from an energy viewpoint, although the design, production and installation may initially be more expensive. • Tip – The operating costs of mechanical

grippers are much less than the operating costs of venturi grippers. It is the whole life cost that is important and not simply the purchase cost.

grippers. The compressed air should start to flow just before the cup touches the product and not at the start of the cycle. Small changes in the cycle timing can make big differences in compressed air use. This is easy to check by simply listening to the cycle and noting where the arm is. • Tip – Venturis on robots will be in

constant motion and a prime source of compressed air leaks. Check them regularly and seal any leaks (see Section 4.26). At sites using large amounts of venturi grippers, these can be the largest user of compressed air and the cost will be substantial but often unrecognised. • Tip – Using a central vacuum generation

station with a vacuum pump (see Section 4.49) and distributing vacuum instead of compressed air can greatly reduce the cost of generating vacuum but does need a separate vacuum system.

Do we need to use them? Robots are excellent when absolute part orientation is needed but product designers need to be aware of the operational costs of robots. When designing products they should not assume that they will always use a robot for part handling. Just because the robots are there it doesn’t mean that they have to be used on every job. Some sites have robots on every machine and these are used for part removal of even very simple products where gravity (it is still free and untaxed) could be used just as effectively.

• Tip – Use mechanical grippers if at all

• Tip – Do not assume that robots are

possible. Although mechanical grippers are much cheaper to operate, in plastics processing the most common gripping method is compressed air generated vacuum (via venturi). A venturi gripper is effectively a controlled compressed air leak and will inevitably use large amounts of compressed air because the compressed air discharge must be continuous to provide the vacuum.

• Tip – Robots are also often used for

The main robot types There are many types of robots but the main ones are: • Cartesian robots, can only make linear movements in the X, Y and Z axes. • SCARA robots can move in the X, Y and Z axes like Cartesians, but the arms are linked and the movement is primarily rotational about the linkages. They can also include movements in the Θ (theta) end of the Z plane to rotate end-of-arm tooling (EOAT). • Six-axis robots move forward and back, up and down, and can yaw, pitch, and roll to offer more directional control than SCARAs.

necessary. Check if they are performing a useful value-adding function that could not be done more simply with gravity. If they don’t save you time/money then turn them off! degating and sprue removal. There is a temptation to use the robot to recycle the sprues and runners simply because it is there. Regranulation costs money and using a robot adds to the cost.

• Tip – The graph in Section 4.26 can be

used to estimate the cost of venturi gripping. Be prepared for a surprise. • Tip – The design and selection of venturi

cups is a complex topic and it pays to spend some time getting this correct for the application. • Tip – Examine the timing of venturi

Chapter 4 – Services

• 1. AREUS Project (Automation and Robotics for European Sustainable manufacturing), www.areus-project.eu.

In the automotive sector, it is estimated that robots account for nearly 50% of the energy used to assemble a car body.

207

4.52

Fans

Air movers

Legislation

Fans are simply a method of moving air around a site, but fan engineers have come up with a remarkable array of methods to achieve this. This not only includes a wide variety of blade configurations (see diagram on the lower right) but also a wide variety of motor types such as many of those noted in Section 4.13. Fans are used in plastics processing for all types of air movement from heat, fume and dust extraction to more complex fans that are part of a system such as those used in air handling units (AHU) and purification systems for clean rooms.

Since 1 January 2015, fan installations with input powers of 125 W–500 kW in the EU have been covered by the Energy Related Products Directive (ErP). This regulation covers most types of fans and applies if the fan is installed as an individual product or if it is installed as part of a larger installation, e.g., an AHU or an HVAC system.

Fan performance The various types of fan shown in the diagram on the right all have differing performance characteristics, e.g., radial blade fans are very good for dirty air streams. The choice of a specific fan type is part of the design process and will not be covered in this workbook. Whichever type of fan is chosen, many fan installations are oversized for the system requirements and the US EPA estimates that 60% of fans are oversized. Over-sizing not only degrades the system performance (see below) but also increases energy use.

The directive requires fan manufacturers to measure the efficiency of the fan system and to declare this as a Fan Motor Efficiency Grade (FMEG) and to label this on the fan/system. It is possible to comply with the 2015 requirements using an AC motor + VSD but these requirements are not static and the directive is forecast to increase the requirements in 2018.

New purchases The 2018 requirements may mean that an AC motor + VSD solution is not capable of meeting the requirements and there is a current drive towards the use of EC

Most fans have a total system efficiency of between 30 and 40%. This is a very low efficiency and indicates a lot of room for improvement.

Fan costs can be large for sites using large amounts of AC or cooling. The savings are good for simple actions.

Affinity laws Fans are subject to the affinity laws and as shown in Section 4.20, these state that: • Air flow is proportional to the fan rotational speed and slowing a fan to 50% speed also reduces the air flow to 50%. • The differential air pressure is proportional to the square of the rotational speed and slowing a fan to 50% speed reduces the differential air pressure to 25%. • The power drawn is proportional to the cube of the rotational speed and slowing a fan to 50% speed reduces the power used to 12.5%. The affinity laws offer as the same benefits in fan operation as in pump operation but many current AHUs or HVAC systems are not designed to make use of the affinity laws. • Tip – Use the affinity laws to save

energy and money. 208

The bewildering array of fan types Fans come in a wide variety of configurations. This is just the configuration of the fan blades and the motors used to turn the fans are just as varied. Every type of fan has advantages and disadvantages but the centrifugal type is the most widely used. Chapter 4 – Services

motors for fan applications. In this case EC does not stand for European Community but for ‘Electronically Commutated’. This is a DC motor which does not have commutators in the traditional sense but uses integrated electronics to commutate the AC power to DC. This provides integrated speed control similar to that achieved with a VSD and also benefits from the affinity laws. EC motors have a much flatter efficiency curve than AC motors and use permanent magnet technology (see Section 5.17) to remove rotor copper and slip losses and improve the motor efficiency. • Tip – The available range of EC motors

is rapidly expanding and EC motors should be strongly considered for all new fan applications.

Retro-fit actions The majority of fan systems are not very efficient (see sidebar on the upper right) and can benefit from simple retro-fit actions to reduce energy use. A sample of these are: • Get the motor size right – many fan motors are oversized and can be replaced with smaller motors. Oversized motors can result in: Noise and vibration. Increased fan maintenance. Unstable fan operation. Low fan load factors. Bigger is not always better, especially with fans. • If replacing existing motors then always use high-efficiency motors of IE3 or greater. • Look for dampers that are being used to control air flow – dampers will reduce air flow in the system but will not reduce energy use, all they will do is increase the back-pressure on the fan. If dampers are used to control the air flow then fit VSDs to the existing fan motors (if suitable). The affinity laws allow VSDs on fans to save large amounts of energy. • Optimise the system air flow by adjusting the fan speed – minimise the use of balancing dampers and preferably have any dampers in the open position. • Examine the ductwork for streamlined

flow – losses due to poorly aligned ductwork will increase energy use. Look also at the fan entry and discharge areas for obstructions and blockages, e.g., materials and products. Chapter 4 – Services

• If using a central system for many areas

then check that the system is not running hard to meet the needs of a single area – if this is the case then check if the area can be fitted with an independent system to reduce energy use across the complete system. • Use the methods listed in Section 4.15 to

stop fans operating when they are not needed – consider using either PIRs or other control methods so that systems only operate when needed.

The cost differential between EC and AC fans is dropping rapidly. EC motor replacements for AC motors can have a payback of less than 2.5 years as well as making the system area tidier and more compact.

Maintenance actions Whichever type of fan is used and whether it is old or new, there are some essential maintenance actions that a site can take to reduce the energy use in fans. The essential maintenance actions are: • Check for noise and vibration – excessive noise and vibration are always a good sign that something else is not correct. • Check and adjust belt drives regularly for the correct operating tension – fans will often use belt drives and the use of cogged belts will improve energy performance (see Section 4.16). • Tip – When adjusting belt drives also

check for pulley alignment. • Clean and lubricate all fan components – check bearings for wear or contamination. Obviously do not lubricate drive belts! • Check fan blades for dust and other contaminants – these can build up on fan blades (some more than others) and will increase drag and energy use. • Check fan blades for wear and

degradation that will affect performance. • Clean air inlet filters and replace if required – dirty filters will increase the fan load and energy use. • Clean all distribution ductwork – dust build-up will increase the energy required to move the air around. • Seal any leaks in the ductwork or other

components – leaks will simply vent air to places where it is not needed and also waste the heating or cooling energy input to the air. • Inspect fans regularly and carry out PM on the complete system to maintain peak performance. • Tip – Inefficiencies in fan systems can be

costly to rectify but the payback times are quite good for most actions.

EC motors can avoid belt drives altogether and reduce the losses even further.

209

Key tips • Understanding the energy consumption

(electricity and gas) is a key task. • Simply knowing how to read the energy bills can save money. • Improving the power factor, reducing the

maximum demand and reducing the available capacity will reduce energy costs. • Suppliers’ interval data are a vital tool

and can provide important information. • The rule for the provision of any service is to minimise demand and then optimise supply. • Motors are the largest energy user in

plastics processing. • Turning motors off (by any means possible) is one of the most effective methods of reducing energy use. • Operating motors at the maximum

efficiency means getting the size right. • New high-efficiency motors offer significant energy savings over the life of the motor. • VSDs allow motors to be slowed down to match the demand and offer energy savings and improved process control. • VSDs are one of the most important tools

available to plastics processing to reduce energy use and costs. • Motor management is a necessity for modern plastics processing. This should allow sites to make the repair/replace decision before the motor fails. • Compressed air is NOT free, it is an expensive resource. • Compressed air leakage is an avoidable

waste. • Compressed air use should be reduced by

using other means of power where possible. Almost any other method of doing a job will be cheaper than using compressed air. • Compressed air generation, treatment and distribution offer many low-cost areas for energy use reduction. • Generate compressed air at the lowest possible pressure to reduce generation costs. • Heat from compressors is often wasted

• Cooling water (chilled and cool) is a

major hidden cost for plastics processing. • Insulate machines and chilled water

piping wherever possible. • Simply increasing the chilled or cooling

water temperatures can have a major effect on energy costs. • Chillers are basically compressors at

heart and simple maintenance techniques can reduce energy use significantly. • Cooling towers offer low-cost cool water

and offer good opportunities for energy saving through low-cost actions. • Legionella controls are an essential for cooling towers. • Free cooling removes the need for

cooling towers and can be used with chillers to reduce operating costs when the external temperatures are low. • Drying of many polymers is not needed if good materials handling practice is used. Insurance drying is not free – it costs money. • Drying to the correct level is essential, over drying increases energy use and costs and can damage material. • Desiccant drying is the traditional method of drying and can be very effective if good practice is used. • New technologies exist for drying that can be more effective in certain circumstances. • Vacuum is often poorly generated,

poorly used and poorly distributed. • Operating at the minimum vacuum level will reduce costs. • Hydraulics systems are widely used but

often poorly maintained. • Simple actions can improve the

reliability and energy efficiency of hydraulic systems. • Robots can use a large amount of

energy but improving the movement and gripping method can easily reduce energy use. • Fans offer a range of options to reduce

energy use.

but can be recovered and used in a variety of applications. 210

Chapter 4 – Services

Chapter 5 Processing

The actual processing of the plastic uses the greatest amount of energy but in some ways it is also the most difficult area in which to reduce energy use. The services are an easy target because in most cases they are a base load and can be reduced by improving management and some relatively low-cost capital investment. The basic processing technology is effectively fixed when the major capital investment is made and in most cases it is difficult to reduce the process energy use after this critical investment has been committed. This must not be interpreted as implying that progress with energy management is impossible. It is simply more difficult and is generally reliant upon capital investment in process equipment. The capital investment can be substantial but it is often matched by the rewards – reducing the process load can be the most rewarding task in energy management (both intellectually and financially). Reducing the process load can change the way a site works. The changes can also permanently change the process economics for a site and provide a substantial and permanent competitive advantage. Using the most appropriate technology can be the edge that a site needs to succeed. This chapter considers energy management for most of the major plastics processing methods in detail, but obviously considers injection moulding and extrusion in the greatest detail due to their importance in terms of processing volume and because that is where most of the practical work has been carried out. This is not a textbook on plastics

processing methods, it is assumed that the reader is familiar with the basic processes and these are therefore not described except as necessary to indicate where energy use can be minimised. Where a processing method is not covered it is not implied that there are no energy improvements to be made – simply that the improvements are either covered as part of one of the other processes or that they can be reasonably inferred from the details given for one of the other processes. If there are significant omissions then please let us know and we will update the text for future editions.

‘The future is already here, it is just not evenly distributed’.

Energy Management in Plastics Processing https://doi.org/10.1016/B978-0-08-102507-9.50005-2, Copyright © 2018 Elsevier Ltd. All rights reserved.

William Gibson 211

5.1

Processing – where are we going?

A changing world The cost of energy is changing the priorities of process development. Thirty years ago consideration of the energy efficiency of plastics processing equipment was minimal. Machinery and processes were designed with total disregard to the energy use because the energy was effectively free. All this has changed and many of the new developments in machinery or processes are focussed on reducing energy use.

Process

Injection moulding

Extrusion blow moulding

Process improvements The average energy intensity of the main plastics processes was calculated by EURecipe1 from a postal survey and this is shown on the lower right. This matches well with the Tangram measured data where comparison is possible (see Section 2.12). The average energy intensity of the main process (at site level) has not changed dramatically since 1996, primarily due to the installed machine base and the effect of other contributors to energy use such as services and site loads (in fact site loads have increased due to the increased use of air conditioning). Note: The average energy intensity should not be used for benchmarking for obvious reasons (see Section 2.12). 212

Injection blow moulding

Energy use in 2017 (kWh/kg) (to 1996 base of 100%)

Hydraulic

65%

All-electric

60%

Extrusion

Machine improvements A simple examination of the claims by machinery manufacturers shows that energy efficiency has risen considerably in status – they are responding to the needs of the market. This is reflected in the energy use (in kWh/kg) of the most common processing methods. Since 1996 all of the main processing methods have shown large relative decreases in the amount of energy used in the process. A best estimate of the improvements is shown on the upper right. These are necessarily best estimates because of the relative lack of data from 1996 and the continuing lack of benchmarking data for processes and machines. Energy use in kWh/kg has certainly decreased but the rate of change needs to increase to meet the needs of the industry. If machine manufacturers wish to attract the attention of customers then they must continue work in this area.

Technology

70% Hydraulic

80%

All-electric

70%

Hydraulic

75%

All-electric

70%

Thermoforming

70%

EPS

75%

Pultrusion

80%

Energy use improvements in the main processes Energy use in plastics processing has improved with time and the above are best estimates of the magnitude of the improvements. These are best estimates only because there is not much data from 1996.

Process

Average site SEC1 (kWh/kg)

Thermoforming

6.179

Rotational moulding

5.828

Compression moulding

3.168

Injection moulding

3.118

Profile extrusion

1.506

Film extrusion

1.346

Fibre extrusion

0.850

Compounding

0.631

Average

2.811

EURecipe average site SEC for various processes1 EURecipe provides average site SEC values for a range of processes but these are not correlated to production rate. These data provides an estimate of the general process energy intensity but should not be used for benchmarking (see Chapter 2). Chapter 5 – Processing

The challenges

Where are we going?

In previous editions of this book we discussed the future challenges for the plastics processing industry in terms of energy efficiency. These were largely the result of a Faraday Plastics Partnership workshop held in 2003 to generate a ‘Technology Road Map for Low Energy Polymer Processing’.2 This road-map covered the strategic directions (e.g., defining priorities and targets, defining and developing best practice and designing processes for energy minimisation) and the R&D programmes necessary to deliver these (e.g., increased understanding of energy balances, computer modelling, robust measurement techniques, additive development and weight minimisation).

The changes in the industry in the near future will be more rapid. Processes such as ‘rapid prototyping’ are metamorphosing into ‘additive manufacturing’ where products are made without high tooling costs, i.e., direct from 3D files and are mass customised. There are a variety of approaches to this but they all have the potential to change our concept of plastics processing forever. We all now own a private printing press (computer + printer) and in the future we may all own a private plastics processing factory (computer + 3D printer). Things are already getting interesting.3

Progress since 2003 in all of these areas has been good but there is still much to be done despite the work undertaken by academia and the machine manufacturers.

It is with some reluctance that I quote from studies made in the early 2000’s but there have been no equivalent studies in recent years. Time for an update?

No industry is guaranteed a future and technology can change everything.

The reality Unfortunately, the take up of this advanced technology by the industry is still slow and industry needs to start to make use of the technology to make real changes. It is with a sense of despair that there is still a great deal of work to do (at a very basic and simple level) in the plastics processing industry to improve energy use in both services (see Chapter 4) and processes (see this chapter). The challenges for the future are not simply for machinery manufacturers and process developers. The industry has to use the technology for it to be effective. Therefore this section of the workbook will not deal with the very necessary R&D programmes that can reduce energy use. In common with previous sections, it will deal with simple and practical but highly effective actions that can be easily understood and easily taken at the majority of plastic processing sites. This is a workbook for industry not for research.

Good practice is inexpensive and reduces all costs – not just energy costs.

• 1. EURecipe, 2005, ‘European Benchmarking Survey of Energy Consumption and Adoption of Best Practice’, www.eurecipe.com • 2. Faraday Plastics Partnership, 2003, ‘Technology Road Map for Low Energy Polymer Processing’, available from www.eurecipe.com. • 3. Kent, R.J. 2017. ‘Cost management in plastics processing’, Elsevier. Section 5.27.

Technology changed the world of the sailing ship builder and the slide rule manufacturer. It has the potential to change the world of the plastics processor too.

Where have we come from? The photograph on the right shows a hydraulic injection moulding machine manufactured in 1971 and, despite the obvious cosmetic differences (new machines hide all the piping behind pretty exteriors), the basic operation of the machine has not changed very much in the 47 years since this machine was manufactured. Chapter 5 – Processing

Where we came from Injection moulding machine from 1971. It may look crude today but this was advanced technology at the time. In 2050 the injection moulding machine will probably not exist anymore (if it lasts that long – still it was fun while it lasted). 213

5.2

Injection moulding – where does all the energy go?

Real energy Injection moulding is one of the most common plastics forming processes and has made considerable technical advances in recent years. Despite this, only ≈ 5–10% of the energy used by conventional hydraulic injection moulding machines (IMM) is actually input to the plastic, the remaining ≈ 90–95% is used to operate the machine. It would be used whether plastic was being processed or not due to the fixed costs of operating the machine. The importance of getting the right machine for the job is paramount (see Section 5.4) in minimising the machine energy use. The relatively low amount of energy that is actually input to the material in injection moulding is one of the reasons for the low sensitivity of the process SEC to the type of plastic processed, i.e., even large changes in the materials properties will give small changes in the overall process load (see Section 2.18).

Main process/detailed services/ site The services energy use can also be divided according to the service provided and, for the typical site, this is done in the lower chart (see below). This is very similar to the chart for a general plastics processing site (see Section 1.3).

Services 32.3%

Main process 62.5%

Site 5.3%

Where does it go? Main process/services/site The energy use at a typical injection moulding site by the main process (injection moulding and assembly), services (compressed air, chillers, etc.) and site (lighting and offices) is shown on the upper right and this will approximately match the energy use distribution in most injection moulding sites. Note: These are typical data for an injection moulding site with some limited assembly and can also be compared with a similar example given in Section 3.2. • Tip – There will be differences between

individual sites depending on the exact process, products and machines, e.g., sites with high amounts of assembly will have higher compressed air use and therefore higher services use. However, a site should start to worry if it is very far away from the indicative ratios of:

Energy use at a typical injection moulding site (global) The main process uses the most energy but the services energy use is also significant (see Chapter 4). This division will vary with every site depending on the details of the specific process, e.g., products and tolerances, machine type and utilisation.

Lighting 3.9%

Heat/cool 1.1%

Offices/IT 0.2%

Water pumps 8.1%

Compressed air 9.0%

Chillers and cooling water 15.2%

Main process 62.5%

Main process: 65%.



Services: 30%. Site: 5%.

 

• Tip – For guidance on what to include

under ‘main process’, ‘services’ and ‘site’ see the energy spreadsheet example in Section 3.2. 214

Energy use at a typical injection moulding site A breakdown of main services use shows the importance of energy management as a complete process involving all areas of the site. These are the same data as used above but the services energy use is presented in more detail. Chapter 5 – Processing

IMM by consumption area The main process is the largest energy user at any site and in injection moulding this is primarily in the IMMs. However, the energy used in an IMM is not totally consumed by the main motor and the typical split of the energy use in an IMM is shown on the upper right. Note: This is for a typical IMM only (480 T running on a 38 s automatic cycle @ 100 kg/hour). The main motor is the largest user but the contribution from heating, ancillaries and control is a significant proportion of the energy use. Every IMM will have different proportions depending on the exact configuration of motors, heating and ancillaries. The actual measured energy use will depend on how the IMM is wired. In some cases the hot runners are wired separately and must also be measured separately.

• Tip – Do not confuse a high power peak

with high energy use. The time the power is drawn is also important.

Ancillaries and downstream 10%

Robots 2%

Heating (incl. hot runners) 35%

IMM motors 51%

The important point is that the main motor uses 61% of the energy but the other components use 39% and these should not be ignored in reducing energy use.

IMM by moulding cycle The energy use in a typical IMM can also be divided by the section of the moulding cycle taking place, e.g., injection, hold etc., A typical example of this division is shown on the lower right for a typical IMM. Note: This is for a typical IMM only and is for the same machine as in the upper chart, e.g., 480 T running on a 38 s automatic cycle @ 100 kg/hour. The surprising element of this chart is the high amount of energy nominally used in plasticising. The energy use in many IMMs is complicated by the fact that some elements of the moulding cycle happen at the same time (see Section 5.3). It then becomes extremely difficult to accurately segregate energy use by the specific moulding cycle element. • Tip – Any division by moulding cycle

phase must be treated with some caution. Another complication is that the energy used is defined by the area under the power graph, i.e., it is the integral of the power graph. This means that a very high and rapid power peak, e.g., injection, may actually use less overall energy than a lower power peak over a longer time, e.g., plasticising. Chapter 5 – Processing

IMM control 2%

Energy use on a typical IMM (by consumption area) The major energy use is in the main motor(s) and this can use up to 80% of the total energy (depending on the process, screw, machine settings and other variables). Sites need to understand the relative energy use to understand where to take action. Closing 5%

Heating 29%

Injection 21%

Hold 1% Ejection 1% Opening 5% Plasticising 38%

Energy use on a typical IMM (by moulding cycle) The energy use by phase shows the importance of plasticising. This is often the main energy user despite the high power drawn during injection. The difference is that injection is high power but brief but plasticising will be lower power for longer. 215

5.3

Injection moulding – the basics

Energy use in the process Injection moulding is a cyclic process with a constant variation in energy use throughout the cycle. The total energy used depends on the part design, the plastic being processed, the machine type and the process parameter settings. Manufacture of a part actually takes two cycles to complete. The material that is plasticised in one cycle is injected in the next cycle, while the material for the next cycle is being plasticised. Cooling starts the moment that injection is taking place and is complete at the end of the hold section of the cycle. The components of the conventional hydraulic IMM are: • Power pack and associated cooling – provides rotary and linear motion from the hydraulic pump. Oil cooling is needed to remove ≈ 50% of the power input to the power pack which is lost as heat to the cooling system. • Feed and injection unit – the drive mechanism for the screw (both rotational and forward/back) and the nozzle and shut-off valve. • Barrel heaters – needed to input heat to melt the solid plastic. • Clamp unit – holds the mould, closes the mould before injection takes place and holds the mould closed during cooling. It also opens the mould after cooling and ejects the part.

Energy use in the moulding cycle Typical energy use in an injection moulding cycle is shown below. This shows five cycles of a typical 600 T hydraulic machine operating on an automatic cycle of ≈ 28 s. The cycle is clearly seen and the peak is the injection phase of the cycle (almost always the highest power drawn in the cycle but not necessarily the highest energy user). It is important to note the ‘base load’ of the cycle for this IMM. This is the minimum power drawn and occurs at any time when the hydraulic motor is not required to do any work but is simply idling and most of the hydraulic oil is diverted back to the tank via the relief valve, e.g., throughout most of the cooling time. In this case the base load is 52 kW and this is 63% of the average load for the cycle (82 kW). This is low for a typical IMM. The base load is only 30% of the maximum power drawn during the injection phase (176 kW). We will return to the importance of the base load in Section 5.4. This curve is specific to the IMM, the mould and the settings used. The trace Energy use in the moulding cycle 200

1 cycle 150

machine movements. temperature and flow at the mould and remove sprues and runners. Energy is input via the hydraulic power pack and the barrel heaters and removed via the power pack cooling system, the mould cooling system and a much smaller amount as the warm finished part. It is possible to calculate an energy balance for the process and, as noted in Section 5.2, only a relatively small amount of energy input (≈ 5–10%) is actually required for the melting and forming of the plastics. The machine losses in the hydraulic system and the associated thermal losses are the major energy users in the process. 216

Power (kW)

• Control system – controls all the • Hot runner (when used) – to control

Only 5–10% of an IMMs energy use is input to the plastic.

100

50

Base load 0 00:00

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00:40

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02:00

02:20

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03:00

Instantaneous power use in the moulding cycle The instantaneous energy use during the injection moulding cycle fluctuates through the cycle and it is possible to see the machine movements that consume energy. Similar plots can be obtained directly from many modern machines or by using a simple data logger and meter arrangement. Each plot provides a unique signature of the machine, machine settings and mould. Chapter 5 – Processing

A typical cycle from the same machine has been expanded on the lower right and the cycle is clearly seen with the base load again being obvious. Experienced moulders will be able to see the cycle and the machine movements simply from the energy used. This type of measurement only takes minutes to make using a simple data logger but most moulders are astounded at the information that can be gained from the measurements and the ability to see inside the cycle. • Tip – Monitor machine energy use to

establish the fingerprint of the process for each machine/mould combination and to identify changes in the machine condition. • Tip – Good maintenance can give

significant energy savings. Look at areas such as temperature controllers, hydraulic valves, hydraulic oil viscosity (see Section 5.13) and screw wear.

Machine purchasing As with most machines, the initial cost of an IMM will be less than the cost of energy used during its lifetime but the energy cost will be even more for IMMs that are not energy-efficient. Energy efficient IMMs may cost more initially but will save money in the long term – an important factor when customers are beginning to expect price decreases through the lifetime of a product. In this market it is important to use a ‘whole life costing’ approach when purchasing new IMMs and to include the energy costs in these calculations. Machinery suppliers are aware of these changes in the market and new-generation IMMs will almost always have improved energy efficiency. In some instances this can reduce product costs by over 3%. Where the basic IMM is not energy-efficient, many machinery suppliers can provide additional equipment to reduce energy consumption. This will increase initial costs but produce long-term savings. • Tip – Ask for data on IMM energy use as

part of the purchasing process. The peak power requirement of an IMM is often the deciding factor in selection of the machine size. In conventional IMMs this is almost always only needed for a short time during injection but it determines the size and pressure settings of the main Chapter 5 – Processing

hydraulic power pack which is therefore overrated for most of the time. Accumulators can be used to store energy for rapid release during injection. This allows a size reduction in the hydraulic system and lower pressure settings. Both actions reduce energy use. • Tip – Sites are advised to investigate

and consider the use of accumulators. ‘All-electric’ machines are much more energy-efficient (see Section 5.9) and are a natural purchase decision in most cases.

Get machines set right, record the settings and do not change them unless absolutely necessary. Do not allow ‘tweaking’ of machines by operators and use Statistical Process Control (SPC) to control machine settings and performance.

Starting up Controlling the start-up sequence of IMMs can significantly reduce energy costs. Starting multiple machines simultaneously will increase the maximum demand (MD) and the cost of energy (see Section 6.3). • Tip – Plan and control the start-up

sequence to limit MD. This will not reduce energy use but will reduce MD and available capacity charges (if applicable). • Tip – Fit a warning device to sound or

flash when the MD approaches the allowable limit.

Instantaneous energy use in the moulding cycle 200

1 cycle 150

Power (kW)

provides a unique ‘fingerprint’ of the process.

100

50

Base load 0 00:00

00:05

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00:15 00:20 Time (min:s)

00:25

00:30

00:35

Inside a single cycle Using a simple data logger (see Section 8.3) it is possible to examine the instantaneous energy use for a single cycle. This gives the cost for each second of operation of the IMM and can be totalled to give the energy cost for a single cycle. 217

5.4

Injection moulding – machine selection

Idling is not free

Machine selection

The IMM measured in Section 5.3 was not operating when monitoring started and this is seen in the power trace on the upper right. The long horizontal trace before the peaks shows the idling motor base load. When producing product, this machine costs £10.44/hour in energy but during the idling period it costs £6.58/hour – for no production and no return. Leaving hydraulic machines with the main motor running is a very expensive activity. All hydraulic IMMs use energy when idling; the actual amount used varies with the machine but can range from 50–97.5% of the production energy consumption. An idling machine is not ‘free’; it is costing large amounts of money. This makes it vital that the main motor of a hydraulic IMM is switched off as soon as possible after production is stopped for any reason.

Selecting the right machine for the job is vital for good energy management and machine capacity should be closely matched to the product need. Using large machines for small products is very energy-inefficient and raises the cost of the product. Starting an IMM 200

Power (kW)

150

100

50

• Tip – Set up automatic systems (based

• Tip – Switch off the main motor of an

IMM as soon as possible after the platens have stopped moving.

0 00:00

Base load 02:00

04:00

06:00

08:00 10:00 Time (min:s)

12:00

14:00

16:00

18:00

The base load for an IMM The IMM measured in Section 5.3 was not producing when monitoring started. The main motor was operating but the platens were not moving. This is clearly seen and the cost of idling the machine is 63% of the cost of actually operating the machine. Energy use in the moulding cycle 15

10 Power (kW)

on the controls) to automatically switch off the main motors if the platens have not moved for more than 5 minutes. Idling machines not only use energy in the main motor but also in ancillaries and services such as heaters, conveyors, sprue regranulators and blowers, compressed air, chilled water and cooling water. Machines should be set to an idling mode if they are not going to be used for more than 20–45 minutes. This can be made automatic with simple control systems. Machines that are not going to be used for more than 2–3 hours should be turned off altogether, as it will almost certainly be cheaper to switch off and restart.

Simple monitoring can provide excellent information on the selection and performance of IMMs.

Base load 5

• Tip – Define, document and implement

an ‘idling’ mode for machines that will not be used for more than 20–45 minutes – motor off, barrel heaters reduced to ‘set-back’, downstream equipment off, services (air, chilled water and cooling water) off and compressed air off. • Tip – Switch off barrel heaters and

cooling fans between runs. • Tip – Design handling systems to

operate ‘on-demand’ only. 218

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02:00

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IMM with average base load (65–75% of average) A well selected and set hydraulic IMM should have base load in the region of 65–75% of the average load. This machine has a base load of 73% and shows a consistent cycle with a regular peak load and a regular cycle. Chapter 5 – Processing

This means that the operation of the hydraulic motor and the losses in the hydraulic system (for no platen movement of the platens) uses 65–75% of the energy involved in the moulding. The actual moulding process, including platen movement, only uses 27% of the total energy used. The hydraulic and system losses in platen movement means that only 5–10% of the energy input to the process is actually being input to the plastic for the moulding process.

High base load An IMM with a high base load is shown on the upper right. This machine was operating on a 19.40 s cycle and has a base load of 93%. This is very high for an IMM (although we have recorded base loads of up to 97.5%) and indicates that the machine used is too large for the part. For this moulding, 93% of the energy cost is simply due to the machine losses (motor and hydraulic system). These were fixed when the machine was selected. The actual process of melting the plastic and filling the mould probably uses < 2% of the total energy used.

Low base load An IMM with a low base load is shown on the lower right. This machine was operating on a 15.60 s cycle and has a base load of only 53%. This is low for an IMM and the trace shows increasing variability. It is probable that this IMM is marginally too small for the part and is finding it difficult to cope with the requirements. If the machine is too small for the part or if the cycle time is too short then the trace becomes increasingly random and can indicate potential quality concerns.

• Tip – All-electric machines also have a

base load but this is mainly small and comes from areas such as the control cabinet and machine/motor losses whilst running. They do not suffer from the same degree of losses whilst idling. • Tip – Use as much of the machine

injection unit capacity as possible (aim for ≈ 80%) and run the machine hard. It reduces the kWh/kg.

• Tip – Check that all jobs are on the

appropriate machines. • Tip – Not all screws are equal: Fit the

Chapter 5 – Processing

Variable-delivery hydraulic pumps reduce energy use by slowing down when not needed.

Energy use in the moulding cycle

40

30

Base load

20

10

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IMM with high base load (93%) This machine has a very high base load and most of the energy cost for the part has been set by the machine selection. Most of the energy is lost in the machine operation. Actual moulding of the part only adds 7% of the energy used in the process. Energy use in the moulding cycle 150

100

50

• Tip – Large motors at part load are less

efficient than small motors at full load. IMMs are most efficient near their design load and total machine energy efficiency decreases as the operating conditions move away from the original design conditions.

Using large machines for small mouldings greatly increases the fixed energy cost.

50

Power (kW)

A typical IMM power trace is shown on the lower left. This machine was operating on a 15.53 s cycle and has a base load of 73%. This is typical for a well set and selected hydraulic IMM where the base load should be 65–75% of the average.

correct screw for the material to give the best processing results and energy efficiency.

Power (kW)

Typical base load

Base load 0 00:00

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IMM with low base load (53%) Machines with a low base load can show a more variable power trace. This can indicate incorrect machine selection (too small for the part) and potential quality concerns in the future. Reducing the base load can reduce cost but introduce other problems. 219

5.5

Injection moulding – machine monitoring

Machine monitoring For simple measurements on individual machines, a hand-held clamp meter (costing between £50 and £100) can give very basic current measurements while a machine is in production. The load of an injection moulding machine fluctuates considerably during each cycle and an accurate view of the average load needs some judgement by the operator. The machine movements and energy load follow a regular pattern but the barrel heaters are switched by their individual controllers and can cause some irregularity. The heater load will fluctuate as individual heaters are switched by their thermostats but an average can be observed over 10–15 minutes.

Making your own measurements Machine monitoring is a vital tool in reducing energy use in injection moulding. It uses low-cost equipment, is simple and quick to carry out, requires little training and yet provides vital process information from relatively easy analysis. Typically, an IMM is fed by a three-phase supply into a control cabinet. This is split into feeds for motor, heaters and other ancillaries such as granulators and conveyors. Measurement of the separate feeds is usually possible from the control cabinet but sometimes common wiring is used and access can be difficult (or dangerous).

• Tip – Always check for multiple

conductors. In some cabinets the wiring uses two or more wires in parallel to reduce the current carried and increase cable flexibility. Measure one wire and multiply by the number of conductors. • Tip – Always check for multiple motors,

bi-injection barrels and for electric screws which may not be visible at first site. As a general rule measuring as close to the supply as possible will capture most of the load. • Tip – Measurements can be made of the

complete machine or the various components but always record what was actually measured. • Tip – Track where the wires go to

understand the internal layout of the machine before touching anything or making any measurements. Look carefully for equipment that is not wired into the main IMM, e.g., hot runners are often wired direct to the main supply and are not fed from the IMM. • Tip – This is electricity, it can kill. Be

very safe and follow standard precautions. Keep one hand in your pocket at all times! The motor demand will vary rapidly during the cycle and it will not be possible to manually read this. Heater demand is

Some machine manufacturers are building energy analysis tools into their machines, e.g., Krauss Maffei have an Energy Analysis Tool (EAT) that can be retrofitted to machines to collect energy data and find the most efficient machine settings. It is also possible to fit commercial analysis packs to machines but the response rate must be high to be able to ‘see inside’ the cycle.

Energy use in heater bands 100

80

Power (kW)

• Tip – Depending on the site electrical

layout, it may only be possible to measure the complete machine from the site distribution board but note should be taken of possible voltage drops if the cabling is very long, i.e., the voltage at the machine may be reduced from the voltage at the distribution board.

Process energy measurement and analysis quickly and easily shows that machine selection and operation can dramatically affect profitability.

60

40

20

• Tip – Some clamp meters work across

only a single phase of the three-phase supply. If using this type of meter then check that the phases are balanced before making measurements. This is not always the case and results may need adjustment. Three-phase meters that do not depend on a balanced load and take a reference voltage from the supply are far preferred. 220

0 00:00

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02:00

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03:00

Energy use in heater bands Barrel heaters use a constant power and are cycled on/off to maintain the correct temperature. When measuring heater bands alone, the power trace will be striated and show the cycling of the heaters. In this case, the heaters were ≈ 18 kW each. Chapter 5 – Processing

much more cyclic and can often be seen as a stepped increase/decrease in demand as the heater bands cycle on/off. • Tip – Whilst a hand-held clamp meter

can be used to get a rough estimate, the rapid changes in demand for IMMs generally make a data logger clamp meter necessary for accurate readings (see Section 8.3). Machine monitoring can take as little as 5 minutes, is non-invasive and analysis can take as little as 20 minutes. Production staff are always amazed at the amount of information that is easily available in minutes. Seeing where the energy and costs go is a rewarding experience for most production staff. • Tip – Production staff and operators will

be interested in seeing the results of monitoring. Share the results with them and get them involved.

Analysing the results Main motors Typical monitoring results for main motors (or complete machines) were shown previously in Sections 5.3 and 5.4 and these are the main output of most monitoring. Depending on the machine and settings, the main cycle should be easily visible and it should be possible to identify the cycle time of the machine. • Tip – Never try to take measurements

over a single cycle, the results will always vary slightly with each cycle (even with the best machines). Measure over a minimum of 10 cycles and preferably over 20 cycles to get a good view of what the IMM is actually doing in the long term.

Heater bands Heater bands have a fixed power output and are cycled on/off by the controllers. If the heater band feed is monitored then the trace will be very similar to that shown on the left. This has a very striated appearance that results from the individual bands being turned on/off. In this case the striations are at ≈ 18 kW, indicating this is the power input by each heater band. Note: Not all heater band traces are as clear as this because the bands may be cycling at various times.

Unclear cycles When the main motor power trace is unclear (see below) this indicates that the machine is either too small for the product or has been set incorrectly (primarily cycle time too short). The very sporadic pattern of energy use also indicates a high potential for greater than normal product variation and has potentially greater concerns with quality issues. • Tip – Machine monitoring offers an

opportunity to ‘see inside’ the cycle. • Tip – Machine monitoring allows an

assessment of machine setting and can be used to reduce energy use and assess improvements/changes. • Tip – Machine monitoring can be used

as an early warning of the need for machine maintenance, i.e., it is a good indicator of screw or barrel wear.

• Tip – Always measure the shot weight

(including any sprues and runners) to assess the amount of material processed during the monitoring. • Tip – Check for full cavitation (or partial

cavitation) in the mould. Blocked cavities will reduce the material processed each shot and affect the process efficiency. Chapter 5 – Processing

Measure the cavity pressure to see when the gate has frozen and reduce the hold pressure at this time or eject the part.

Unclear cycle 250

1 cycle? 200

Power (kW)

• Tip – If using monitoring to detect

energy use changes from changing the settings (see Section 5.6) then always allow the machine time to settle down before taking measurements. IMMs can take some time to settle down after setting changes (up to 30 minutes). It is better to wait some time to check that part quality has not been affected and to get good results.

When cell-based manufacturing is used the IMM is often linked to other machines and the cycle time can be adjusted to balance the line. In this case the overall efficiency of the cell may well take precedence over the actual energy efficiency of the IMM. Decisions such as this need to be economically justified.

150

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Unclear cycle forecasts quality concerns When the cycle is difficult to identify and inconsistent, the machine will suffer from higher variation and greater quality concerns. This is an older machine with potentially poor setting practice. 221

5.6

Injection moulding – process setting

Process setting Process setting has an obvious and direct influence on energy use but there has been very little work carried out to link the two. Scientific methods are available to improve setting for increased reliability and productivity (see Section 6.2) but no method currently includes an assessment of the process energy use. Optimising the process through setting will minimise energy use in many areas, i.e., it will minimise cycle times and the cooling required, but reducing energy use is currently seen as a by-product rather than as a specific aim of the process.

Scientific moulding One of the greatest advances in injection moulding in the past 20 years has been the use of what is termed by some as ‘scientific’ moulding, where the injection moulding process is effectively broken down into three stages: • The filling stage of ≈ 95% of the volume of the mould which is controlled by the ram/screw velocity. • The packing stage of the remaining ≈ 5% of the volume of the mould which is controlled by the packing pressure. • The cooling stage after gate seal where no more material can enter the mould and the packing pressure can be released as the product is simply cooling before ejection. The recognition that these were separate stages allows separate optimisation of the stages to give better process control and potentially reduced energy use. An idealised graph of the cavity pressure and the hydraulic pressure (for a hydraulic machine) is shown on the right. The curves are not exactly aligned because of time delays in signalling and valve switching. Note: The curve will be different for amorphous and semi-crystalline plastics.

The stages of moulding Velocity-controlled filling This controls the majority of the cavity filling and sets the basic shape of the product. Changes to the fill speed can be used to control orientation, crystallinity, appearance and other aspects at the 222

surface of the product. Excessive speeds can result in jetting (in the early stages), flash formation and even mould damage. After the mould is nearly filled, control is changed from velocity control to pressure control. This changeover point will be set using a closed-loop system based on a signal from screw position, hydraulic pressure, cavity pressure or cavity temperature. • Tip – Cavity pressure is also used to

The theoretical and practical setting of IMMs has advanced hugely in the past 20 years. ‘Scientific moulding’ is a general term for using a defined set of tests to fully determine the moulding settings in a logical manner.

control valve gates for multi-cavity tools.

Pressure-controlled packing After changeover, the packing pressure is used to fully compress the plastic as it cools and shrinks in the mould. Changes to the packing pressure will control the compression of the melt along the flow path. Insufficient packing pressure can result in voids, short shots, excessive shrinkage on ejection, warping and other filling defects.

Maximum hydraulic pressure

Cavity pressure Hydraulic pressure

Maximum cavity pressure

Changeover point

Gate seal Time

Velocity controlled

Pressure controlled

Cooling

An idealised cavity and hydraulic pressure curve for injection moulding (not to scale) The cavity and hydraulic pressures will change throughout the cycle, most noticeably near the changeover point and as the gate seals. After gate seal, the hydraulic pressure can be removed. Chapter 5 – Processing

Cooling The cooling stage, whilst one of the longest stages, is simply waiting for the material to cool sufficiently for successful ejection without significant post-ejection warping. • Tip – If the cavity is fully filled then the

experience of the melt during cavity filling (temperature and pressure) is a major factor in product quality. • Tip – If a cavity pressure sensor shows a

significant drop at ejection then it is likely that the gate has not yet fully sealed. More details on scientific moulding can be found in the references.1, 2, 3

Reducing energy use through process setting Scientific moulding provides a robust process that is more consistent in production and improves product consistency and quality but adjusting settings can also reduce energy use in the process. Areas to examine in setting are: • Barrel temperatures set too high – any heat put into the material at the barrel must be removed by the cooling system and this increases the cycle time and the energy used in the process. High barrel temperatures will also decrease the melt viscosity at the barrel wall and decrease the effect of shear heating. Shear heating is a more effective heating method than electrical heating. • Back pressure set too high – back

pressure is vital for mixing and compression but excess back pressure will use excess energy. A high back pressure may be used during setting but this should be reduced to a minimum afterwards. A high back pressure will increase shear heating and decrease heat input from barrel heaters but high back pressures will still use excess energy. • Clamp force set too high – the clamping force must be enough to keep the mould closed during injection and early cooling. After the gate has frozen then the clamp force can be reduced. Note: This is not an issue when mechanical toggles are used. • Packing pressure too high – a high packing pressure is necessary during pressure-controlled packing and during initial cooling and shrinkage but this can be reduced to zero after the gate has frozen (gate seal). Keeping the pressure high after gate seal uses excess energy. Chapter 5 – Processing

Note: Excessive packing pressure can also lead to over-packing of the mould. • Hold time too long – the packing pressure can be released soon after gate seal has taken place. Keeping the packing pressure on after gate seal serves no real purpose and uses excess energy. • Cooling time too long – the cooling time

needs to be sufficient to allow ejection without damaging the part. This is governed by the cooling system but excess cooling times will increase the cycle and use excess energy. The rate of cooling is determined by the need to avoid residual stress and sink marks. • Screw-back time – the plasticising of the melt is affected by the screw speed and this phase of the cycle uses a large proportion of the total energy. The screw-back time should be set to use ≈ 80% of the necessary cooling time. In practical tests using an IMM with a cooling time of 35 s, changing the screwback time from 6 s to 28 s (or 80% of the total cooling time) reduced the energy use by 8% for no other changes to the process and did not change the product quality. • Fully automatic operation – IMMs on fully automatic operation produce more consistent parts and have no time between the cycles where the machine is idling waiting for the operator and using excess energy. Sites should ensure that they have good controls on all settings and preferably operate SPC on the process.

Scientific moulding is a complex subject and the reader is referred to one of the references given for further details. This workbook concentrates on the energy aspects of plastics processing and scientific moulding is a valuable tool to not only reduce energy use but also to improve injection moulding quality.

• 1. Routsis, A. 2015. ‘Injection Molding Reference Guide’. An excellent general guide that is available free from www.traininteractive.com. • 2. Kulkani, S. 2010. ‘Robust process development and scientific molding’. Hanser. • 3. Kazmer, D. 2009. ‘Plastics Manufacturing Systems Engineering’. Hanser.

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5.7

Injection moulding – motors

The biggest contribution The motor (or motors) of IMMs are the largest energy user in the system and progress in controlling these has been rapid and diverse over the last 30 years. Prospective purchasers of IMMs are now faced with a bewildering choice of options and this section reviews the main options for controlling IMM motor energy use.

Hydraulic Hydraulic IMMs are the traditional approach and most of the installed IMMs have hydraulic power systems. The new developments in this area are mainly concerned with slowing the motor down when hydraulic oil is not needed. The various options are shown on the right but not all are commercially available and only the main types will be discussed.

Fixed-speed motor/variablevolume pump This type of system was common from some manufacturers but is now rapidly being superseded by new technology. It uses variable-volume pumps to provide improved control of the amount of oil generated. Whilst much more energyefficient than fixed-volume pumps, these machines are still not fully energyefficient. The variable-volume pump works by adjusting the swash plate of the pump to deliver the required oil volume. The efficiency of this type of IMM can be increased by adding motor speed control (if applicable) as well as pump volume control, i.e., it is more effective to reduce the speed of the motor than to reduce the output volume of the pump. Retrofitted

Most of the new technologies for hydraulic injection moulding are concerned with reducing the amount of oil flowing when the machine is not under full load.

Fixed-speed motor/fixed-volume pump The typical energy demand through the cycle varies continuously (see Section 5.3) but, despite this, a fixed-speed motor/fixed-volume pump will continue to deliver a fixed volume of hydraulic fluid. This volume will be such that enough fluid is delivered for the maximum transient demand (generally during injection). At other times, any excess hydraulic fluid is diverted back to the sump via the relief valve and the pump’s energy use is largely wasted. This means that the pump motor is delivering excess hydraulic fluid for all but the maximum demand period and using excess energy for all but the maximum demand period. This type of IMM is no longer manufactured but examples will exist at sites with older IMMs. This very old type of system has a low efficiency (η) particularly during the hold and cooling phases and much of the energy input during these phases is wasted (as shown on the right on the opposite page). Existing IMMs of this type can be considered for retrofitted VSDs (see Section 5.8) but if they are not suitable for retrofitting then these are very energyinefficient machines due to the overproduction of oil when it is not needed.

224

Some of the options for IMM main power There are many options for improving the motor energy use in IMMs. There is a bewildering array of methods but not all are currently used on commercial IMMs. The current trend for hydraulic IMMs is towards the servo motor technology. Chapter 5 – Processing

VSDs (see Section 5.8) can therefore still reduce the energy used by this type of machine and further reduce energy use. VSD-controlled machines are considered in greater detail in Section 5.8.

Variable-speed motor/variablevolume pump This type of system uses a combination of VSD and pump technology to optimise both the motor speed and the pump volume to deliver the oil required in the most efficient combination of motor and pump speeds. As with other technologies the speed of the pump is greatly reduced in the hold and cooling phases. When the volume demand at low pressure is high the system will move the swash plate to generate more volume at low pressure rather than increase the motor speed as this is a more efficient option. Machines using this technology have reported energy use of 15–45% less than standard hydraulic machines and the cost is ≈ 12% more than standard hydraulic machines.

Servo motor/fixed-volume pump The use of servo motors to drive pumps is rapidly gaining acceptance and is now being used by many manufacturers due to recent falls in servo motor prices. These tend to be toggle clamp machines where the servo motor is used as a variablespeed drive for a fixed-volume pump (piston or gear pumps are both used). This type of system can be set up to slow down or stop if no oil is required and because it is a servo motor it can actually reverse direction. This is one of the most promising of the new technologies for new machines and also available as a retrofit but has made little impact in this area so far. Machines using this technology have reported energy use of 40–60% less than standard hydraulic machines but the cost is only ≈ 5% more than standard hydraulic toggle machines due to the simple nature and low cost of gear pumps.

All-electric All-electric IMMs use servo motors to directly drive the machine motions. Very early models were limited in shot capacity for a given clamp force, limited in injection rate, nozzle touch force and ejector force and used energy during Chapter 5 – Processing

holding. These issues have largely been resolved by developments such as pulsing motors on/ off to reduce over-heating or by using electromagnetic braking to prevent the screw from backing off during pack/hold time without needing force from motor. All-electric machines are considered in greater detail in Section 5.9.

Hydraulic machines are rapidly increasing in efficiency and in some cases are not far away from achieving allelectric standards of energy use.

Hybrid Some manufacturers use a hybrid technology combining both electric and hydraulic operation for specific applications. This allows moulders to benefit from the advantages of both electric and hydraulic operations. Hybrid machines may not achieve all of the benefits of fully all-electric machines. Hybrids come in a range of options and most use a servo motor (as for all-electric IMMs) to control the screw drive and use hydraulics for other machine movements such as clamping and holding and sometimes for very high injection rates. The hydraulics tend to be energy-efficient and use either variable-speed drives or variable-volume pumps to achieve energy savings in the hydraulics.

Qmax

Qact

Pump delivery volume

Required delivery volume Useful power Actual pressure required Pact

Delivery pressure Pmax

Pressure (P)

The fundamental problem for hydraulic IMMs Using a fixed-speed motor/pump and throttling the output results in wasted energy. In the example above, the useful power is only 36.5% of the total generated power. The system therefore has an efficiency of only 36.5%. 225

Injection moulding – new and retrofitted VSDs

Fixed-speed motors and VSDs As for many other motors (see Section 4.21), it is possible to fit a VSD to an IMM to control the motor speed based on the actual demand for oil rather than allowing the motor to run constantly at full speed. Some manufacturers offer this as a factory-fitted option. Where the process has a long cycle time (> 25 s) and where this is available, it is an excellent addition to the machine to reduce energy costs into the future. The typical results for a factory-fitted VSD are shown on the lower left and this reduced the energy costs for the machine and moulding by 25%. Although the other new technologies for IMM motors (see Section 5.7) are being rolled out across the world, the primary concern for most sites is ‘What can we do with our existing machine stock?’ For many sites with suitable IMMs and products, a cost-effective way of meeting the variable demand is via retrofitted VSDs. Retrofitted VSDs can significantly reduce energy costs by matching the output of the hydraulic pump to the changing demand of the injection moulding cycle. The major benefit of VSDs is in the hold or packing phase of the cycle where the pump delivers relatively little hydraulic fluid and is simply holding the pressure and slightly packing the polymer in the mould as it shrinks. The VSD will slow the motor down to keep the required pressure but not the constant volume that is normally supplied. In other phases of the cycle, a VSD will closely match the supply of hydraulic fluid to the demand but the savings are not as great.

The savings achievable with retrofitted VSDs depend on the machine size and the specific cycle, etc., but typical savings vary from 35–60%. In general, this will give payback times of ≈ 1.5 years.

VSDs and IMM There are many suppliers and installers of VSDs but a VSD of the type used for fan or pump control is not the best solution for IMMs. The energy savings depend on the ability of the inverter to rapidly and accurately match the output speed to the demand. Slow or poor tracking of the real demand will reduce the energy savings. Purchasing assessment can be difficult due to suppliers providing different information and in different formats. • Tip – Ask for the energy savings to be

specified as part of the purchase contract. Do not simply accept ‘savings achieved elsewhere were….’

Retrofitted VSDs should not be confused with motor voltage regulators (MVR): this is a different technology. MVR varies the supply voltage to improve the motor operating efficiency by reducing motor losses. It does not change the supply frequency or change the motor speed. MVR has limited application in IMM but can reduce energy consumption for certain stages of the cycle.

• Tip – Ask for performance-backed

guarantees so that if the equipment does not perform as predicted then it can be returned at no cost. • Tip – Ask for relevant industry

experience. Do not simply accept one case study or reference. Factory-fitted VSD (650T) 150 VSD off VSD on

1 cycle

1 cycle

100 Power (kW)

5.8

50

The savings

226

0 00 :0 0 00 :2 0 00 :4 0 01 :0 0 01 :2 0 01 :4 0 02 :0 0 02 :2 0 02 :4 0 03 :0 0 03 :2 0 03 :4 0 04 :0 0 04 :2 0 04 :4 0 05 :0 0 05 :2 0 05 :4 0 06 :0 0 06 :2 0 06 :4 0

The results of retrofitting a 1000 T IMM are shown on the upper right on the opposite page. The first section of the power trace is with the VSD turned off and the second section is with the VSD turned on. The reduction is primarily in the hold and cooling phases with little difference during the injection phase when the full capacity of the motor is needed. For this machine the average power has decreased from 87.9 kW to 46.4 kW, a decrease of 41.5 kW or 47.2%.

Time (min:s)

The effect of factory-fitted VSDs This machine was a 650 T IMM operating on an automatic cycle of ≈ 88 s and fitted with a factory-fitted VSD. The VSD is not operating for the first section of the trace and is switched on for the second section of the trace. The average power for one cycle has decreased from 50.0 kW to 37.5 kW. This is a decrease in the average power of 12.5 kW – a reduction of 25.0%. Chapter 5 – Processing

• Tip – Implement on a suitable machine

Effect of retro-fit VSD (SynchroSpeed)

as a trial and then roll out to all applicable machines.

250 VSD off VSD on

• Tip – Most VSDs for IMMs can be

• Fixed/variable displacement, vane or

gear type pump. • > 37-kW motors. • > 25-second cycle time. • > 5000 operating hours/year.

50

96 10 5 11 5 12 4 13 3 14 3 15 2 16 2 17 1 18 0 19 0 19 9 20 8 21 8 22 7

77 87

0 58 68

Retrofit VSD technology is not suitable for all IMMs and the benefits achieved depend on the machine and product. The minimum general conditions for effective operation of retrofit VSD are:

100

40 49

Suitable machines

150

21 30

to be overloaded for a short time to cope with a transient peak demand (provided it can be slowed down and cooled down at a later stage in the cycle).

Power (kW)

• Tip – A VSD also allows an IMM motor

1 cycle

200

0 11

simply taken out of the supply in the event of failure and the machine will run as normal, i.e., as pre-VSD installation.

1 cycle

Time (s)

The effect of retrofit VSDs A 1000 T IMM on an automatic cycle of ≈ 62 s with retrofitted VSD. The VSD is not operating for the first section of the trace and is switched on for the second section of the trace. The average power has decreased from 87.9 kW to 46.4 kW. This is a decrease of 41.5 kW – a reduction of 47.2%. Source data modified for presentation purposes only. Source: www.ccstech.co.uk

If these conditions are not met then it is unlikely that fitting a retrofit VSD will have an attractive payback. The full benefits will be achieved when the conditions are: • > 55-kW motors. • > 40-second cycle time. • > 6000 operating hours/year. This is shown diagrammatically on the right. Follow the diagram to determine if a machine/product is suitable.

Variable-volume pumps It was previously assumed that variablevolume pumps were not suitable for retrofitted VSDs but recent work1 has shown that even with modern variablevolume pumps the savings can be ≈ 10– 30%. These savings result in longer payback periods but are an opportunity for moulders with this type of machine.

Retrofitted VSDs are not suitable for all IMMs

• 1. Pratt, F. 2012. ‘The drive for energy savings’, Injection World, September 2012.

Chapter 5 – Processing

The use of retrofitted VSDs is not recommended for all types of hydraulic IMM. The chart above gives a selection matrix for deciding if a retrofit is suitable. The payback will depend on how close the operations are to the ideal. 227

5.9

Injection moulding – all electric machines

A mature technology All-electric injection moulding machines have seen a rapid rise in application in many parts of the world, primarily because of their energy efficiency. Early all-electric machines had a significant initial purchase cost differential compared to conventional hydraulic machines (in the order of 50%) but, as with any new technology, this differential has decreased rapidly and is now much lower, i.e., ≈ 10–20%. As noted earlier, the initial purchase should not be the deciding factor and the important cost is the ‘whole life cost’ of the machine (initial cost + operating costs).

Machine size All-electric machines are also rapidly increasing in size and clamp force. When first introduced, the maximum clamp pressure available was approximately 30 tonnes. This has now increased to > 1000 tonnes and continues to rise with technology improvements. A decrease in the inertia of servomotors has also allowed faster reaction times during the injection phase and higher speeds during the clamping phase.

The benefits All-electric machines have many benefits that are independent of the specific manufacturer and these are:

Energy savings All-electric injection machines have the potential to reduce the energy use in injection moulding by between 30 and 60% depending on the particular moulding and the all-electric machine being used (see Section 2.18). Energy profiles through the moulding cycle show that energy is saved during all the phases of the moulding cycle due to large reductions in the base load compared to hydraulic machines. Controlled trials carried out by suppliers show significant energy savings across a broad range of materials (from PS to PC). These energy savings can be achieved even if the cycle time is kept at that required for the conventional machine. On hydraulic machines, the hydraulic system only provides peak power for a very short part of the cycle and is 228

overrated for much of the time. Receivers or accumulators can be used as storage for rapid hydraulic energy release to reduce the energy consumption but the hydraulic system is generally overrated. In contrast, all-electric machines use only the power needed and at the time it is needed.

Operations Removing the hydraulic system from the machine is one of the major effects with all-electric machines and this removes a significant variable from the process. This has a multitude of benefits: • No hydraulic system present, means no requirement for hydraulic oil to be stocked, provided, filtered, changed or disposed off – all operations that take time, cost money and use energy. • There is no hydraulic oil present to

contaminate the area or environment. • No hydraulic system means no waiting for the hydraulic oil temperature to stabilise and quicker start-ups. • There is no need for hydraulic oil cooling and both the equipment and the energy use associated with this. The improved performance of servomotors gives greatly improved process control and a process that is easier to set up, is easier to adjust and calibrate and is more stable in series production. Typical all-electric

Application Medical product (inhaler) Medical product component

All-electric or hybrid? Some manufacturers use a hybrid technology combining both electric and hydraulic operation for specific applications (see Section 5.7). This allows moulders to benefit from the advantages of both electric and hydraulic operations. Hybrid machines may not achieve all of the benefits of fully all-electric machines.

All-electric machines show energy efficiency during all phases of the injection cycle.

Typical recorded energy saving 58% 60% in PS (53% in PC)

Automotive product (connector)

62%

Household product (shower panel)

55%

Cap stack tool Garden product (flower pot)

Between 28% and 64% 40%

Typical recorded energy savings for all-electric machines in a variety of applications All-electric machines show energy savings over a range of product categories and materials. The savings are consistent and significant in operational and cost terms. Chapter 5 – Processing

• All-electric machines are directly driven

– the motor directly controls the machine movements – unlike a hydraulic machine where the drive from the motor is indirect and via the hydraulic system. The reduced system inertia (there are no valves to open or close) makes operations quicker, more direct and more controllable. • Hydraulic machines tend to carry out operations in series due to limitations in oil volume and pressure. All-electric machines can carry out operations in parallel (such as clamping and injection and opening and ejection) to reduce cycle times, energy consumption and increase productivity. Using all-electric machines and optimised cycle times maximises the energy saving and productivity of the machine and can lead to significant cycle time reductions (up to 30%) without any degradation of product quality.

Secondary operations Hydraulic control of cores on existing moulds that are currently powered from the machine’s hydraulic system is easily possible on all-electric machines by the use of a small hydraulic power pack. This allows existing tooling to be used on allelectric machines with no modification. When using new tooling, electrical core pulling devices are readily available to make the complete tool electric.

Installation Installation of all-electric machines is generally easier and cheaper than the installation of hydraulic machines because there is no need for plumbing, cooling and filling of hydraulic oil systems.

Maintenance One of the benefits of all-electric machines is the reduced maintenance load of the machines. Hydraulic systems account for a large proportion of the maintenance requirements of hydraulic machines and the removal of the hydraulic system Chapter 5 – Processing

significantly reduces the maintenance load of the machine: • There are no consumables such as oil

and filters to carry, with the result that the maintenance stockholding is greatly simplified and reduced.

All-electric machines can control machine settings more accurately to the set point.

• No hydraulic system means no need for

cleaning and servicing and no oil leaks. • The reduced number of operating parts

means fewer parts to service and replace. Servicing is also reduced in complexity, time and cost but may require more highly qualified service technicians. Overall, all-electric machines have a reduced risk of failure and can be more easily used in ‘lights out’ operations than conventional machines.

Costs All-electric machines can have a significant benefit in overall energy cost terms for moulders (see table on the lower left). The improved cycle times, increased reproducibility and precision results in improved productivity, reduced production capacity requirements, and can lead to significant overall cost reductions. All-electric machines also have a reduced heat output because more of the energy used is applied directly to the process, this is important in clean rooms where there is a reduced load on the A/C and filtration plant and a subsequent reduction in energy costs.

The evidence is clear If you can buy an all-electric machine and choose not to then you are permanently building an energy cost into the site’s operations.

All-electric (200T) 100

1 cycle 80

Power (kW)

machines can control machine movements and shot weights up to 10 times better than hydraulic machines. This accurate control of the machine optimises the amount of material used and the energy used to process it, as well as significantly reducing rejects and improving reproducibility. All-electric machines can also reduce the cycle time for many products:

60

40

20

0 00:00

00:20

00:40

01:00

01:20 01:40 Time (min:s)

02:00

02:20

02:40

03:00

All-electric IMM with base load of 10% of average load Most pure all-electric IMMs have a very low base load of 5–25% of the average load. This is mainly from the control cabinet and attached ancillaries. Not all machines show a trace this clear as parallel machine movements can make the cycle unclear. 229

5.10

Injection moulding – heating

Keeping it in Barrel heating is a fundamental part of injection moulding and, depending on the machine and part, takes 15–40% of the energy input to the IMM. The percentage is actually higher for all-electric machines because the motor use is much lower (see Section 5.8). Getting the heating right is a key issue in reducing energy use in injection moulding. The heat losses from barrel heaters are significant (see on the right below). This not only uses excessive energy but is also a health and safety concern and makes the site hotter.

Heat transfer from heaters Conventional heater bands need good contact with the surface of the barrel to give the best heat transfer from the heater band to the barrel. Heat transfer from heater bands can be maximised and evenly distributed by good seating to the barrel and the use of a conductive metal compound. • Tip – Heater bands should be ‘bedded-in’

by repeatedly tightening and loosening the heater band to get a good seating. • Tip – Use a conductive metal compound

between the heater band and the IMM barrel to maximise the heat transfer.

Heater bands The use of integrally insulated barrel heaters should be considered as they can reduce energy consumption used in heating by up to 17% depending on the machine and application. The majority of heater bands used in the industry are of the mica or ceramic knuckle-type. These can easily be replaced with mineral insulated heater bands. Insulated heater bands have a thin layer of highly conductive material between the heating element and a backing layer of insulation to direct heat inwards towards the barrel.

benefits of replacing these with insulated heater bands.

Barrel insulation Barrel insulation is a proven method of reducing energy losses in plastics processing and producing a more stable process bringing quality and output improvement. This has been validated in significant numbers of research studies and in significant numbers of monitored test installations. Conventional barrel insulation uses an insulating blanket with cut-outs for electrical connections (to avoid overheating) and/or monitoring equipment. The exterior surface is normally Teflon-coated to reduce dirt and staining. The sections of the blanket are wrapped around the heater bands and fastened with Velcro fixing strips. Most systems have cover strips to close the gaps between individual sections. Several systems combine barrel heater and barrel insulation into a single integrated system. Barrel insulation reduces the energy used in heating by up to 50% and the overall energy use of an IMM by between 10–25% (depending on the type of machine and the original proportion of the load that was due to heating). The positive aspects of insulation are: • Greatly reduced heat loss and energy consumption (and cooler sites).

Barrel insulation can have payback periods of less than a year. This is not an investment, it is simple revenue expenditure.

For moulders running machines in air-conditioned (A/C) areas the benefits can be almost doubled. Less heat emitted by the machines means less heat to be removed by the A/C system. A double benefit but rarely quantified or considered.

• Tip – Mineral insulated heater bands

reduce heat loss, decrease energy use and can also decrease start-up times because they are able to withstand a greater current density than standard heaters. • Tip – Sites should check the types and

numbers of heater band they are currently using and calculate the costs/ 230

Thermograph of guarded but uninsulated IMM barrel The barrel shows a peak temperature of 244°C and an average temperature of around 180°C. This has safety implications, but is also energy leaking into the surroundings and heating the site. Is it any wonder the site needs A/C in summer? Chapter 5 – Processing

• Start-up times are reduced as the barrel

gets to temperature quicker (provided the temperature controllers are set correctly). • Processing consistency is improved and

part weight and tensile stress variations can decrease. • A more stable environment is created –

machines are not affected by draughts or other cold air flows. • The health and safety concerns associated with unprotected hot areas/ heater bands are eliminated. • Rapid payback of ≈ 1 year depending on

the local costs. The negative aspects of insulation are: • Barrel insulation can take time to fix and set up in the initial stages but this is generally a once-off time penalty. • Barrel insulation can be damaged during normal operations and changeovers if treated poorly. • Barrel insulation can increase the time for barrels to cool down when changing materials but this can be minimised by unwrapping the fasteners during cooling down. The benefits of barrel insulation are maximised when using modern IMMs with heater band tuning to get the best out of the barrel heaters.

and reduced time lag. This provides excellent control of heating and energy use reductions. The units have the benefits of barrel insulation and also have the option of using a fan assist to blow cold air into the gap between the heaters and the barrel to provide selective barrel cooling and improved control (see www.insulvest.com).

38 mm of ceramic barrel insulation will reduce barrel heat losses by nearly 95%.

Induction heating This uses induction heating to generate heat directly in the barrel wall via eddy currents. This is therefore a non-contact system. The system also includes thermal insulation to reduce heat loss. The systems claim up to 70% savings for barrel heating but we have not validated this (see www.xaloy.com).

• Tip – Checks on insulation condition and

fitting should be part of the set-up process. • Tip – Ensure that the barrel heating

controls are linked to a thermostat to prevent overheating.

Conventional barrel insulation fitted to an IMM The barrel of this IMM has been fitted with a conventional barrel insulation blanket on top of the barrel heaters. Fitting is rapid and uses Velcro fixing strips. The insulation not only reduces heat losses but also makes operations safer.

• Tip – Barrel insulation can be affected

by nozzle drool, fit a special nozzle area cover or do not insulate the nozzle area. • Tip – The savings may appear more (in

% terms) for all-electric machines as barrel heating is a larger percentage of the load for these machines.

New technologies Combined heating and insulation This combines barrel heating, barrel insulation and optional barrel cooling in one unit. This is shown on the lower right and uses cast insulation material to carry infrared heating elements slightly off the barrel of the IMM. The fast response time of infrared means that heating is supplied direct to the barrel without having to first heat up a heater band and they can also be rapidly cycled to provide better control Chapter 5 – Processing

New-generation barrel insulation with integral infrared heating elements and option for cooling fans The new generation of barrel insulation not only insulates the barrel but also removes the need for heater bands by using infrared heating elements to directly heat the IMM barrel. Source: www.insul-vest.com 231

5.11

Injection moulding – mould temperature controllers

Mould heating or mould temperature control? Not all mould tools need cooling with chilled water for operation. Some mould tools are heated to reduce cycle times, to improve quality by reducing the formation of moulded-in stresses, to aid ejection from the tool by encouraging and controlling shrinkage away from restrictions and to pre-heat the tool to the operating temperature for faster start-up and less start-up scrap. Some sites use no mould temperature controllers (MTCs) at all and other sites producing similar parts use them extensively. There appears to be no consistent decision-making in the process and some sites use considerable amounts of energy on MTCs when the benefits for their site are doubtful.

risk of overflow and flooding. The temperature is limited to under 100°C to avoid Health and Safety concerns with steam escape. These are relatively ‘old’-technology MTCs. Indirect cooling uses a sealed cooling coil or heat exchanger through which cooling water circulates to cool the heat transfer medium (water or oil). The cooling water can be air-cooled or chilled using an integral chiller. These have a lower cooling capacity and are more expensive to run than direct systems. Indirect cooling uses less water and the water can be treated with anti-scale and corrosion inhibitors. The tank can be sealed to



Correct sizing of MTCs is necessary to get the right MTC. This is a relatively simple matter but should be done for all MTCs. Tool-Temp have produced an excellent guide to MTCs and sizing (‘Perfect your process’). It is difficult to find but worthwhile for a good introduction.

• Tip – Just because they are there doesn’t

mean that you have to use them on every job. Check if MTCs are really necessary on each job and that they are performing a useful function. If they don’t save you time/money then turn them off! Most MTCs function primarily as heaters but it is wrong to think only in terms of heating capacity – controllers are often also required to cool the mould to keep it at a constant temperature. • Tip – The kWh (heating) rating of the

controller is not the only factor – cooling capacity and flow rate are important too.

Types of MTC MTCs come in a range of types and an outline of the operational principles is shown on the right. • Open systems can provide heating up to ≈ 95°C for water systems or ≈ 150°C for oil-based systems. The cooling in open systems can be either direct or indirect: Direct cooling uses a simple tank with inlet and outlet valves to flush hot water out of the tank and to refill the tank with cold inlet water. These have high cooling capacity at low temperature differences and are small and cheap to run but can use large amounts of water. There are also potential concerns with circulating untreated water through a mould (corrosion and scale build-up) and the 232

Operation of MTCs Outline flow diagrams for the various types of MTCs. These are simplified diagrams to show the principles only and omit some essential control circuits and safety features, particularly for closed systems when pressurised. Chapter 5 – Processing

reduce the risk of overflow and flooding.

use, i.e., they are there so why not turn them on?

• Closed (pressurised) systems can provide

• Tip – Sites should ensure that MTCs are

heating up to ≈ 140°C (and sometimes higher) for water-based systems and significantly higher for oil-based systems, but pressurised oil systems are rarely used in plastics processing. Pressurised systems may be open until the temperature reaches ≈ 85°C and then closed for safety. This type of system needs significantly more consideration of safety issues in terms of piping and operation and may require certification if they are ‘pressure vessels’. Indirect and closed MTCs can use either oil or water as the heat transfer medium. Both have advantages and disadvantages but the main advantage of water from an energy perspective is that it is a far more effective heat transfer medium than oil (approximately three times better).

only used when they are actually needed for the particular job and only turned on when they are being used. Running an MTC will heat up the site (most have an integral chiller to provide the required cooling) and use energy even if the MTC is performing no useful mould temperature control.

• Tip – Heat transfer in water or oil is

degraded by air bubbles in the fluid. Make sure that the heat transfer medium does not contain bubbles and that oil, if used, is de-aerated on a regular basis.

Flow rate The temperature of the MTC fluid is not the only issue. The flow rate through the mould is also important and must be such that the heat transfer to/from the mould is correct. There will be natural temperature gradients across the mould that depend on the heat transfer to/from the various parts of the mould that are cycling at different temperatures. The MTC must maintain the correct temperature gradient by delivering the correct temperature and flow rate to all areas of the tool. VSDcontrolled pumps can not only reduce energy use but also deliver flow rates that are matched to the fluid and mould requirements.

MTCs rarely have any substantial insulation on any of the piping connecting the MTC and the mould. These can be substantial runs of piping and are always subject to parasitic heat gain when cooling or heat loss when heating the tool. • Tip – Piping between MTCs and the

mould should be insulated as far as is practically possible. The temperatures involved are generally relatively low and high-temperature insulation is rarely needed. Hot water piping is insulated in your house, why not at the site?

If hot runners are used in the mould then do not forget to include these in the cooling capacity calculations.

It is possible to control the pumping of the cooling fluid to match the needs of the IMM. Stopping and starting the flow can reduce energy use and also decrease cycle times (see www.singletemp.de for details of the Ecotemp system).

• Tip – Be careful when using automatic

shut-off quick-release couplings with ‘leakstoppers’ on temperature control units. The ‘leakstopper’ mode may activate the shut-off and seal the mould. • Tip – Where there is an integral chiller

then older units may contain greenhouse gases such as R22 as the refrigerant. These need control and potentially replacement with new refrigerants. • Tip – If the MTC has a large chiller unit

then it may be covered by regulations for GHG monitoring and control (see Section 4.36).

Regloplas (www.regloplas. com) produce an excellent book ‘Temperature control by means of fluid media’ on all aspects of MTCs for all conceivable applications. Copies are available from the local Regloplas representative.

• Tip – VSD-controlled pumps on MTCs

can not only save energy but also improve temperature control, although the pumps will generally be quite small (< 5 kW). • Tip – Control systems should indicate if

there is a blockage of the cooling pipes that restricts flow.

Energy saving with MTCs Whichever type of MTC is used, the energy use will be significant and at most sites both hidden and ignored. The first issue with MTCs is that of indiscriminate Chapter 5 – Processing

Thermograph of uninsulated MTC hoses These uninsulated hoses are emitting heat to the production area. This increases the energy use of the heaters, raises the temperature of the production area and increases A/C energy use at the site. 233

5.12

Injection moulding – mould design

A new frontier

and increased cycle times and energy use.

Energy management and efficiency in the design of moulds has not really been an issue in the past and many existing moulds are not designed to be energyefficient. This is changing rapidly and much of the research work on mould design is now concerned with methods to reduce energy use. Some of these techniques are in the development stages and others are already being used.

• Tip – Check cooling channel

Cooling the mould Cooling is one of the critical elements of energy-efficient mould design because the cooling time effectively determines the cycle time and the energy use. There are two key variables in improving cooling efficiency at the mould design level, cooling channel location and the mould material.

Cooling channel location Cooling channels should be located as close to the surface of the mould as possible to minimise the amount of energy used to cool the mould itself and to maximise the amount of energy that is being used to cool the part. Cooling is about getting the part solid as soon as possible. Using cooling effectively not only reduces the cycle time but also reduces energy use.

effectiveness by checking the pressure drop across the mould. Any deviation will indicate possible blockage of the cooling channels and ineffective cooling. Take the initial reading from the new mould or after thorough cleaning. • Tip – Before storing a mould, always

flush cooling channels with detergent or cleaning agents and dry moulds with hot air to remove all traces of water.

Mould material Improving the thermal conductivity of the mould material is an effective method of reducing the energy needed for cooling. Aluminium has a much lower thermal mass and a higher thermal conductivity than steel. Using aluminium can significantly reduce the cooling loads and energy use and also reduce the overall mould construction cost because aluminium is easier to machine. Unfortunately aluminium also has a much lower wear resistance than steel and

Designing products with thin walls to minimise materials use will also minimise the energy used. Reducing wall thickness is probably one of the most energyefficient actions that can be taken. It reduces material use, reduces cycle time and reduces energy use in the process.

Conformal cooling has the potential to reduce cycle times by up to 35% and energy use by up to 20% but the results depend on the specific mould.

• Tip – Cool the part and not the mould. The spacing of the cooling channels in the mould is also important, but less important than the distance from the surface. • Tip – Getting cooling channels close to

the surface is the most important factor. New techniques such as conformal cooling and pulsed cooling allow cooling channels to be more effectively spaced around the mould and to reduce cooling loads, cooling times and cycle times. Conformal cooling can also be combined with evaporative cooling to greatly reduce the cooling load. • Tip – Mould designers should look at

cooling techniques such as conformal, pulsed and evaporative cooling. Cooling channels should be kept clean and free from deposits such as scale, sludge and rust. These can build up and block the channels to give reduced cooling capacity 234

Mould design affects energy use in many ways Energy efficiency can be designed into mould tooling but it is best implemented at the mould design stage before the major decisions are made and it should be considered as part of a programme to reduce overall energy use. Chapter 5 – Processing

mould lifetime is significantly shorter. Hard coating of aluminium shows good potential for increasing the life of the moulds to make it a viable material for small to medium-sized run moulds. • Tip – If the part requirements are low

then consider using aluminium tooling to reduce construction and operating costs.

Sprues and runners Sizing There is a tendency to regard increasing the sprue and runner size as a simple mould-side solution to some moulding defects such as sink marks, short shots and voids. This action may decrease the occurrence of these defects but when conventional sprue and runner systems are used it will increase the amount of material processed and increase the amount of material that needs to be regranulated. • Tip – Minimise the size of sprues and

runners. The material may be recycled but the energy is lost forever. Regranulation of sprues and runners is not free and machine-side regranulation of sprues and runners can be very expensive. A small regranulator can cost over £14,000/year to run (see Section 5.53) and if the volume of sprues and runners is low then it can be costly to regranulate at the machine. The operating cost of a regranulator is effectively fixed and, for low material volumes, the cost of regranulation can be very high, i.e., for some machines it costs over £0.80/kg to regranulate the material at the machine. • Tip – Consider handling and disposal of

sprues and runners during mould design. It is not free.

Hot runners Hot runners remove conventional sprues and runners but the hot runners are not free. There is very little work on the energy use in hot runners but at some sites this is a significant power load and is rarely considered. There is a need for more work in this area, particularly in the effect of hot runners on the use of cooling water when they are flood cooled.

Part ejection Ejection of parts from moulds is sometimes assisted by compressed air, especially with a shallow draft product, where a vacuum can form between the part and the mould. The compressed air Chapter 5 – Processing

overcomes the vacuum and prevents the part being caught in the mould and being damaged. The compressed air should be limited to a short blast to break the adhesion – it should not be a continuous stream of free compressed air. • Tip – If compressed air is used as part of

the ejection system then limit the time that air is injected into the cavity to that absolutely necessary to break the vacuum. Preferably use an alternative method to release the vacuum between the part and the mould.

Current mould design procedures, even highly developed software approaches, take little specific account of energy use. Energy is not currently an explicit part of the design criteria.

Part removal Ejection of parts from the tool is one step in getting the product out of the machine and the second step is removing the part after it has been ejected from the mould. Robots are increasingly being used for this to maintain absolute part orientation control (see Section 4.51) but traditional, low-cost methods of simply ejecting onto an out-take chute are still widely used. In some cases this is accompanied by a burst or continuous flow of compressed air to move the part from the chute to a conveyor. This use of compressed air is highly variable. Some sites use large amounts of compressed air to move parts, whereas others use no compressed air but simply use gravity to move the parts. In fact, the use of compressed air is variable within sites and in a single site it is possible to find compressed air used on some moulds and not on others – with no apparent logic used in the decision process. • Tip – Gravity is free throughout the

world. The use of open compressed air lines to move parts from the out-take chute to a conveyor is wasteful, costs money and is rarely necessary. • Tip – Check the methods used to move

products from the out-take chutes to the conveyors. If they use compressed air then use engineering to remove the use of compressed air (see Section 4.27).

Keep the heat (or the cold) where it is designed to be and insulate the mould from the huge heat sink called the machine. Low-cost, hightemperature insulation material can be mounted between the mould and the platens to insulate the mould and reduce heat transfer. See products such as Brandenburger insulation (www.brandenburg erisoliertechnik.com).

235

5.13

Injection moulding – hydraulic fluid

The lifeblood of hydraulics Section 4.50 covered the basics of good practice with hydraulics systems for general purpose uses, e.g., stuffers, crammers, EBMM mould movement and other small-scale equipment. This section concentrates on conventional hydraulic IMMs where the hydraulic system and oil are essential to the operation of the machine. This is an easy topic to overlook because the cost of hydraulic fluid is typically < 1% of the operating costs of a site but the hydraulic fluid is literally the lifeblood of a hydraulic IMM. Choosing a good hydraulic fluid can not only protect the hydraulic systems but also reduce energy use in the IMM.

temperature. • Tip – The viscosity of a hydraulic fluid

will also change with time as the fluid molecules break down in service. A mineral oil will have a wider range of molecule sizes than a synthetic oil and the larger molecules will break down faster, leading to greater changes in viscosity with time for a mineral oil.

Viscosity index (VI) The viscosity index (VI) is an arbitrary measure of the change in viscosity with temperature of a fluid devised by the Society of Automotive Engineers (SAE) for lubricating oil but applies to hydraulic fluids as well: • A low VI means a high change in

In this section we are talking about ‘hydraulic fluids’ and not about ‘lubricants’. They are both oils but hydraulic fluids do not simply lubricate, their main function is to transmit power from the hydraulic pump to provide the essential machine motions. There is a world of difference and you would never use a lubricating oil as a hydraulic fluid!

viscosity with temperature.

Viscosity of hydraulic fluids

• A high VI means a low change in

Viscosity is the resistance of a fluid to deformation by shear stress and in nonscientific terms it is a measure of the ‘thickness’ of the fluid: • High-viscosity fluids are ‘thick’ fluids, e.g., honey or treacle. • Low-viscosity fluids are ‘thin’ fluids, e.g., water or petrol. There are several different types of viscosity that can be measured (dynamic, kinematic and bulk) but for hydraulic fluids the important viscosity measurement is the ‘kinematic viscosity’ which is the ratio of the dynamic viscosity to the density of the fluid.

viscosity with temperature. This is important for hydraulic fluids because a high VI fluid will not change viscosity as much with temperature (see diagram below). An IMM using a high VI fluid will be more stable with any changes in fluid temperature, can start production quicker because the fluid gets to the required viscosity quicker, is easier to pump at low temperatures but does not get too thin (and lose lubricating ability)

• Tip – The kinematic viscosity is

represented by ‘ν’ (this is the Greek letter ‘nu’ and not a v, although you may need a magnifying glass to see the difference). The units of ν are m2/s. For most fluids, and particularly for hydraulic fluids, the viscosity will decrease with increasing temperature, i.e., the fluid will get thinner and flow more easily. • Tip – Viscosity is important for sites

with hydraulic IMMs because unless the fluid is at the correct viscosity, i.e., at the correct temperature, then the machine will not operate as specified and if the temperature of the fluid is not stable then the machine will not be stable. That is why sites spend hours and a great deal of energy getting the fluid up to the right 236

Hydraulic fluid change in viscosity with temperature The viscosity of hydraulic fluids decreases with increasing temperature. Viscosity improvers (VIs) reduce the amount of change with temperature. This means decreased losses at low temperatures and better wear protection at high temperatures. Chapter 5 – Processing

at high temperatures. • Tip – The original VI scale ranged from

0 to a maximum of 100 but the introduction of new synthetic oils and VIs (see below) means that the scale now goes as high as 400.

Viscosity index improvers The VI of a hydraulic fluid can be improved by the use of VI improvers, these are typically high-molecular-weight polymer additives that are added to a base hydraulic fluid and which expand or contract with temperature. These polymers minimise the effect of temperature on the viscosity: • At high temperatures, the polymer additive expands and increases the viscosity of the compounded fluid. • At low temperatures, the polymer

additive contracts and the viscosity of the compounded fluid is dominated by the viscosity of the base fluid. VI improvers increase the VI of the resulting fluid to give a fluid with a much more consistent and optimised viscosity across a wider temperature range. A relatively constant viscosity is vital for hydraulic IMMs because decreases in hydraulic fluid viscosity will result in decreased pump efficiency and decreased IMM energy efficiency. • Tip – A higher and more consistent

viscosity will increase the volumetric efficiency of the pump, increase the volume output and can improve the system response time. This can potentially reduce cycle times for highspeed IMMs where the system response time is the limiting factor. • Tip – VI improvers can also improve the

shear stability of the compounded fluid and increase the oil change interval as well as protecting the system.

Energy savings with VI improvers There are two competing sources for VI improvers with IMMs, these are: • Dynavis from Evonik – this is a polymer additive licensed to several hydraulic fluid suppliers. • Exxon Mobil DTE 10 – this is a complete

solution available direct from Exxon Mobil for IMMs. The energy savings reported from using high VI hydraulic fluids are typically in the range 4–10% of the energy used by the Chapter 5 – Processing

hydraulic pump. These savings will naturally vary with the machine, the application and other factors, and sites are advised to verify the savings through controlled trials. • Tip – Energy savings of 4–10% through

a change in the hydraulic fluid are too good to be ignored. Sites using hydraulic IMMs are strongly recommended to examine their hydraulic fluid and to use fluids containing VI improvers wherever possible. The changeover can be gradual and does not have to be site-wide. This can be a planned maintenance change to improve energy efficiency.

Protecting your oil In addition to looking at improving the quality of the hydraulic fluid used, sites should also look at maintaining the fluids that are in use. Oil analysis should be used to check not only the fluid and keep it in good condition but also as a diagnostic tool to assess the health of the overall IMM. Fluid breakdown will occur as a result of high temperatures, high pressures and shear stresses. This will reduce the viscosity of the fluid and increase costs as well as decreasing the protective properties of the fluid.

‘Afternoon fade’ Some processors will notice ‘afternoon fade’ – this is where as the day goes on the oil gets hotter than normal. This decreases the viscosity giving a decrease in the volumetric efficiency of the pump, decreased volume output and a slower system response speed. This is not a good result and it is telling you that the hydraulic fluid may not be correct or in good health.

• Tip – Most of the major oil suppliers

offer oil analysis services. Sites should use these to make sure that their hydraulic IMMs are operating correctly. • Tip – Do not forget to assess the

environmental impact of the hydraulic fluid used. Some of the synthetic fluids can have environmental benefits too. • Tip – As noted in Section 4.50, Triple R

(www.triple-r-europe.com) make some great equipment for removing water and air from hydraulic fluids. These can reduce fluid oxidation, improve filter efficiency and are great at maintaining oil quality. When using hydraulic IMMs the condition of the hydraulic oil is an important factor. Keep the oil clean through continuous filtration, and monitor the condition of the oil regularly. Look after the hydraulic oil and it will look after you.

237

5.14

Injection moulding – IMM energy rating

Why rate machines?

EUROMAP 60.1: Machine related

The data presented in Section 2.18 allows an operating IMM to be assessed for energy use in operation and compared to a benchmark for various types of machine. This method is for ‘production’ IMMs and includes other factors, e.g., machine utilisation and setting. It does not, however, help purchasers in the selection of new machines. This needs an assessment method that is independent of external factors and this is provided by the EUROMAP (European Plastics and Rubber Machinery) technical recommendations in EUROMAP 60.

EUROMAP 60.1 specifies standard test conditions and energy measurement protocols to determine the energy used in IMMs for either standard and fast running machines. The output of the testing is a value for the kWh/kg of the machine under the test conditions.

EUROMAP 60 EUROMAP 60 (2009) provided a method to calculate the specific energy consumption (SEC) for IMMs over three cycle types using standard measurement equipment, standard materials and a standard cycle. This provided a value for the SEC under standard conditions and was reported in the form: Specific machine related energy consumption (EUROMAP 60), Cycle ll, 0.95 kWh/kg, 20 kW, 30 s, cos φ = 0.95. Unfortunately, this did not provide any method of assessing the relative energy efficiency of machines and prevented EUROMAP 60 from achieving the recognition that it deserved and from acting as a market transformation tool. In 2012, Tangram proposed a method and system using the EUROMAP 60 standard test cycles and the data shown in Section 2.18 to provide a simple A–G rating for IMMs.1 This proposed using an energy rating label similar to those seen on domestic appliances and the object of the scheme was to drive market transformation by the elimination of inefficient IMMs.

EUROMAP 60.1 and 60.2 Euromap also recognised this need for a relative assessment of energy efficiency in IMMs and in 2013 revised EUROMAP 60 and split it into two parts: • 60.1: Determination of Machine Related

Energy Efficiency Class. • 60.2: Determination of Product Related

Energy Consumption. 238

Energy rating of any product should be “fair, accurate and credible”. There should be no reference to correction factors that may influence the results.

This SEC is converted into an energy rating in the range 1–10 (where 1 is the least energy-efficient and 10 is the most energy-efficient) using energy efficiency classes based on the kWh/kg value. EUROMAP 60.1 uses a two-part class assessment based on the screw diameter: • For screw diameters of ≥ 25 mm the calculated kWh/kg is used directly to assign a class rating based on the value, e.g., to be Class 10 (the best) for a screw diameter ≥ 25 mm the SEC must be ≤ 0.25 kWh/kg. • For screw diameters of < 25 mm the efficiency class boundary is multiplied by a correction factor (f) based on the diameter of the screw. This is based on the screw diameter because “Small machines mostly have a higher energy specific consumption than big ones due to technical reasons. This shall be taken into account for screw diameters < 25 mm by a applying the following factor f = (25 mm/d)2 to the class boards given in table 2.”2 Therefore, for a screw diameter of 10 mm the class boundary (≤ 0.25 kWh/kg) is multiplied by 6.25 to give a class boundary of 1.56 kWh/kg, i.e., for a screw diameter of 10 mm the SEC must be ≤ 1.56 kWh/kg to be Class 10. EUROMAP 60.1 provides a table (Table 3) to convert the class boundaries for various screw diameters in the range 4– 24 mm. This method assumes that for screw diameters of ≥ 25 mm then the SEC (kWh/ kg) is constant for all production rates and can be used to rate the machine. Our results (see Section 2.18) show that this is not true and that the SEC is dependent on the production rate (kg/h) for all production rates. The SEC does approach a limit for both hydraulic and all-electric IMMs at high production rates as the base

EUROMAP 90: Energy efficiency label IMMs tested and certified to EUROMAP 60.1 can be marked with a EUROMAP energy rating label and the formant and contents of the label are given in EUROMAP 90.

Chapter 5 – Processing

load is amortised into the increasing process load. However, EUROMAP 60.1 gives no reason why this is based on the screw diameter as opposed to the more relevant and easily calculated production rate. Equally, for screw diameters of < 25 mm, the EUROMAP 60.1 method assumes that the governing factor is the screw diameter and adjusts the class boundaries by large amounts (the f-factor) based on the screw diameter. Our results show that for small machines the SEC is more sensitive to the production rate (kg/h) due to the higher effect of any base load. This is easily demonstrated and there is no need to invoke an arbitrary screw diameter correction.

The chart below also includes several data points from manufacturer’s testing to EUROMAP 60.1 for a set of all-electric IMMs and these results show that most of the machines would be B-rated with at least two being in the C-rating area. A B-rating for an all-electric IMM may appear harsh but rating schemes should always attempt to provide space for technology improvements. This is to avoid the need for the introduction of A+ and A++ grades in the near future.

Tangram was responsible for the establishment of the British Fenestration Rating Council, the certification body for energy rating of windows and fenestration products in the UK.

• Tip – Given consistent technology, then

theoretically and practically the major factor influencing variation in the SEC in an IMM is the production output rate (kg/h). • Tip – If you want to get a good rating for

any size of machine then run it hard and the rating will improve irrespective of the screw diameter, e.g., manufacturers who test machines at high production rates will gain better ratings than would otherwise be achieved.

EUROMAP 60.2: Product related EUROMAP 60.2 specifies a method for testing and measuring the absolute amount of energy used in manufacturing a specific product on a specific machine to allow comparison of machines and settings. The measured energy use is not compared relative to any standard or rating but simply reported to the customer.

• 1. Kent, R. J. 2012. ‘Making a case for energy rating’, Injection World, September 2012. • 2. EUROMAP 60.1, Version 3.0 January 2013. ‘Determination of Machine Related Energy Efficiency Class’, www.euromap.org (accessed 13 December 2017). Sample of manufacturer's data and rating values 200 Manufacturer's data to Euromap 60 for a range of all-electric machines

• Tip – EUROMAP provides a very useful

Real machines Section 2.17 shows that small machines will always have a higher SEC due to the greater effect of the base load at their lower production rate. Section 2.18 shows that this is validated by actual monitoring of production machines. The data from Section 2.18 can easily be used to create an A–G series of rating bands (as shown on the right) simply based on the production rate and no reference to the screw diameter is needed. Previously1 this rating method used parallel rating bands but these have been revised to avoid inconsistencies at low production rates. Chapter 5 – Processing

150 Average power (kW)

template for reporting results to EUROMAP 60.2.

G-rated 100

50

A-rated 0 0

50

100 Production rate (kg/h)

150

200

Rating boundaries to benchmark IMMs An alternative to EUROMAP 60.1 which rates machines using the familiar A–G bands, the production rate and the average power. The data points are actual manufacturer’s data (for allelectrics) to EUROMAP 60.1. Most would be B-rated. 239

5.15

Injection moulding – where are you now? been improved.

The initial steps in injection moulding As with the score charts shown earlier, this is a self-assessment exercise to allow sites to benchmark their current status for injection moulding. Injection moulding is one of the most common processing methods and significant improvements have been made in recent years in both the understanding of the process and in technologies to reduce energy use. Setting is now a science rather than an art, barrel insulation is now a proven technology, allelectric machines continue to develop in size and accuracy and ancillaries have also

Companies in the injection moulding sector have a wide variety of possible actions available to reduce energy use and to establish a competitive advantage.

Completing the chart This chart is completed and assessed as for those presented previously.

Energy use in injection moulding can be improved by a variety of methods. Processors need to critically examine their operations to minimise energy use.

Injection moulding Monitoring & setting 4 3 Tool design

2

Barrel insulation

1 0

Mould temperature controllers

Retrofit VSDs

All-electric machines

Use the scoring chart to assess where you are in injection moulding The numbers from the scoring chart can be transferred to the radar chart for a quick visual assessment of where you are in terms of injection moulding. 240

Progress in energy management in injection moulding has been more rapid than in many other areas because of the size of the market.

Chapter 5 – Processing

Injection moulding Level

4

3

2

1

0

Monitoring & setting

Barrel insulation

Retrofit VSDs

All-electric machines

Mould Tool temperature design controllers MTCs only used Tool design takes All-electric machines are over when absolutely energy into 50% of applicable necessary. account in all machines & are Use is controlled areas. default purchase by setting sheets. Compressed air option for all new All hoses are well usage is small & machines. insulated to controlled. reduce heat Good control & transfer. use of cooling.

Machine settings Full barrel checked & insulation in good validated against condition. best practice. New-generation Most machines barrel insulation monitored for used. energy efficiency Very little heat lost & performance. to the surrounding area.

Retrofit VSD drives fitted to over 50% of applicable machines.

Very few machine Full barrel settings show insulation in poor deviations from condition with good practice. visible degradation of insulation Some machines material. monitored for energy efficiency & performance.

Retrofit VSD drives fitted to under 50% of applicable machines.

MTCs theoretically All-electric machines are only used when less than 50% of necessary but actual use is poor. applicable machines. All hoses are well Purchase of insulated to all-electric reduce heat machines is still transfer. subject regarded as 'advanced'.

Small number of Partial barrel machine settings insulation in good show deviations condition. Reduced amounts from good practice. of heat lost to No machines surrounding area. monitored for energy efficiency & performance.

Retrofit VSD drives under evaluation for selected machines.

MTCs theoretically Tool design is All-electric only used when machine under good for necessary but evaluation as test productivity & has actual use is poor. small sprues & before full implementation. No insulation on runners (or hot hoses & heat runners) but poor for energy through transfer is significant. the poor use of services.

Tool design takes productivity & energy into account but there is some poor use of services in the process.

Significant number Energy efficiency Partial barrel Retrofit VSD All-electric MTCs used on of machine insulation in poor drives considered is minor some tools & use machines settings show condition. consideration in but not purchased. considered but not is uncontrolled. tooling. Tool deviations from Moderate amounts purchased. Large heat losses through the use of design has large good practice. of heat lost to general site area. uninsulated & sprues & runners poorly chosen & uses services hoses. very poorly.

Most machine settings show deviation from good practice or recommended values.

Barrel guarding but no barrel insulation. Large amounts of heat lost from uninsulated barrel to site.

Retrofit VSD All-electric MTCs used on drives not machines not most tools & use considered & not considered despite is uncontrolled. aware of being applicable Large heat losses possibilities. for the operations. through the use of uninsulated & poorly chosen hoses.

Energy not considered in tooling. Mould heating & cooling work against one another. Tool uses compressed air for many actions.

Score Chapter 5 – Processing

241

5.16

Extrusion – general

The key process Extrusion is not simply a final forming process for profiles such as pipes, tubes, etc. but is also an intermediate process for transporting and preparing material in many other processing techniques such as injection moulding, blow moulding and film blowing. Energy-efficient extrusion operation is an essential to much of the plastics processing industry. Fortunately, extrusion is a very energy-efficient process and has one of the lowest SEC values for all of the plastics processing methods. Most of the energy use when extrusion is the prime process is in operating the extruder itself and the main variations in sites occur after the actual extruder, i.e., operating the calibrators for profiles, operating the rollers for sheet and in operating the ovens for BOPP. The energy use at a typical profile extrusion site is shown on the upper right and ≈ 50% of the total energy is used to drive the extruders with the remaining energy being used for items such as services and ancillaries. Whilst these data are for a profile extrusion site, the same type of energy use split is seen at most sites where extrusion is the main process. The energy use of a typical profile extrusion machine is shown on the lower right. At the machine level, the main energy use is in the main motor followed by heating and vacuum (generally specific for profile extrusion). This will naturally vary depending on the specific process.

AC motors for speed control. The use of ‘direct torque’ motors, e.g., permanent magnet or PM motors, is now the most advanced technology and this is highly recommended for investigation (see Section 5.17).

Extrusion is a key forming process and is integral to many other processes.

• Tip – Sites should consider energy

efficiency at the purchase decision stage.

Lighting 5% Water pumps 5%

Heating Offices 2% 1%

Compressed air 11%

Extruder 50%

Chillers 26%

Energy use at a typical profile extrusion site The extruders use the most energy but chillers and compressed air use nearly as much. Minimise the demand for these three key elements to reduce costs. Whilst the extruders are the most important, the other areas may provide easier savings.

Vacuum 5%

Heating (barrel and other) 25%

Product The energy use will also depend on the specific product. Products with many critical tolerances, such as window profiles, will inevitably use more energy than products with few or no critical tolerances such as cover strips. This has implications not only on the cost of energy but on the overall cost of production.

The extruder The initial cost of energy-efficient extruders may be higher but they will give rapid returns on the extra investment. Most older extruders used DC motors to provide the required speed control of the extruder screw. New extruders now almost exclusively use a VSD-controlled 242

Others (material feed, etc.) 5%

Main motor 65%

Energy use on a typical profile extrusion machine The major energy use is in the main motor and this can use up to 80% of the total energy (depending on the process, screw, machine settings and other variables). Sites need to understand the relative energy use to understand where to take action. Chapter 5 – Processing

Whatever the motor type, the first essential is to get the right extruder for the job. The extruder and screw design should be checked to make sure they are right for the polymer and product.

• Tip – Fans can be VSD-controlled to

• Tip – Always use the correct extruder for

Simple measurements on individual machines are possible and the measurement is easier for extrusion because of the relatively constant motor loads. This means that a simple clamp meter will give reasonably accurate measurements during production (but a data logger meter is still better). Monitoring and analysis follow the same principles as injection moulding (see Section 5.5) but are again often considerably easier because of the relatively constant loads. Simple measurement and analysis can provide information that is vital for: • Machine scheduling, i.e., which machine is used for a specific job. • Machine purchasing, i.e., comparison of prospective machine purchases. • Machine maintenance, i.e., SEC is a good indicator of screw or barrel wear. • Machine setting, i.e., use setting to reduce energy use and assess changes. Some new machines are being fitted with integral energy monitoring equipment as part of the control system and this is an excellent option for future monitoring.

the material. This has wider implications than simply the energy aspects. Extruders run most efficiently (not only in energy terms) when operating at the design conditions. As far as is possible, the extruder should be set to run at the maximum design speed, as this is usually the most efficient speed for production efficiency and for heating (see Section 5.18). The screw speed should be controlled to give an extrusion rate as close to the design speed as possible and still produce good product. • Tip – Using large extruders for small

profiles wastes energy and costs money. Extruder motors run most efficiently close to their design output and the motor should be sized and controlled to match the torque needed by the screw. • Tip – Investigate the option of switching

extruder motors to match the job. This may seem a strange idea at first glance but can make a substantial difference. Cost the time taken to switch motors and the energy saved. The calculations sometimes show that switching the motor is a very cost-effective operation.

reduce energy use by using the exhaust area temperature as a signal.

Machine monitoring

For an excellent short review of the basic principles of extrusion, see ‘Words of Wisdom: The 10 (11) key principles of extrusion’ by Allan Griff, www.plasticstoday. com/articles/wordswisdom-10-11-keyprinciplesextrusion. Read this again and again until you understand all the implications of what he is saying!

Energy use in an extruder is a sensitive measure of the extruder condition and can be used as a diagnostic tool. Increasing energy consumption is an early warning of deterioration of the machine condition and the need for maintenance.

Downstream Downstream equipment is very processspecific but the wise use of services is a common theme for most applications (see Chapter 4). Some of the easiest savings are in the area of services and this should be an area for detailed examination. Downstream heating is a large cost at most extrusion sites and needs careful treatment to ensure that heating is only applied where needed and is used to heat the product and not the atmosphere.

General notes Ventilation/extract fans Many extrusion machines will have exhaust fans fitted above the die area to remove hot air and fumes created during processing. These will be fixed-speed and controls are rarely conveniently located. • Tip – Link ventilation/extract fans to the

main drive so that when the main extruder drive is stopped then the fan automatically stops after a pre-set time (to vent the area while it is still hot). Chapter 5 – Processing

The range of extruder types The range of screw types used for extrusion has grown enormously since the original single-screw extruder. The selection of screw type is based on the format of the raw material, the throughput and the shape/complexity of the product. 243

5.17

Extrusion – motors

Extruder motors

Main motor 250

200

Power (kW)

The extruder motor uses ≈ 65% of the power input to the extruder and it is essential to get the choice right. The traditional choice was a DC drive to give the variable speed needed for extrusion but, as for IMMs, the range of options has now greatly increased. The current options are shown on the lower right.

150

100

DC motors The traditional option has been to use a DC drive for speed control but this has now been superseded by AC technology.

AC motors + VSDs New machines The widespread availability of VSDcontrolled AC motors now makes this the preferred option for new machines and most manufacturers have removed DC motors from their product range to only offer AC motors + VSD drives. VSDs can be used to adjust motors to run at the lowest possible speed (within the allowable torque values) to reduce the energy used to a minimum. The reported achieved savings vary widely. In our validated tests the savings were ≈ 7–10% but savings of 5–20% are widely reported. The exact savings depend on the machine type and speed and, as a general rule, the savings decrease with increasing screw speed. Some tests report even greater savings of more than 30% but this depends on the load and speed.

50

0 00:00

00:20

00:40

01:00

01:20 01:40 Time (min:s)

02:00

02:20

02:40

03:00

kW trace for main extruder motor Extruders have a relatively consistent energy use over time. There is no machine cycle and extruders can be simply monitored over a specified time. This machine draws an average power of 221 kW for a motor rated at 345 kW (64%).

• Tip – Sites should always ask for an AC

motor + VSD in new extrusion machines. Motors should be IE3 (or better) rated. • Tip – One of the biggest savings in using

AC motors + VSDs is the greatly reduced maintenance load of AC motors.

Retrofitting AC motors + VSDs AC motors + VSDs can easily be retrofitted to most extruders and this is a recommended action. The energy savings will generally be ≈ 5–20% but reductions in maintenance costs are very significant. The payback should be ≈ 1–2 years. • Tip – Sites should strongly consider

retrofitting AC motors + VSD for existing DC motors. Motors should be IE3 rated or better. 244

The drive options The drive system options have expanded rapidly in the last 15 years. Most extrusion machines from before 2000 will be fitted with DC motors but the efficiency and lower maintenance of alternative drive systems is improving rapidly. Chapter 5 – Processing

Direct drives – permanent magnet synchronous motors This is the newest development in extrusion machine motors and uses new motor technology to connect the motor directly to the screw (often with no need for a gearbox at all). These are advanced systems but offer considerable advantages over existing systems. They are: • More energy-efficient and the reported

savings using direct drives are ≈ 12–15% compared to AC motor + VSDs. • Quieter than DC or AC motor + VSDs. • Small and less complex than DC or AC motor + VSDs. The direct drive system is definitely the system for the future.

Gearboxes/belt drives When a gearbox is used to connect the motor to the load then this must be treated with care. Gearboxes will give excellent service but do need regular maintenance. • Tip – Do not exceed the maximum

torque allowance of the gearbox. • Tip – Make sure that gearbox oil is the

correct temperature. If it is too hot then there is a problem with the gearbox or the lubrication system. If it is too cold then lubrication will be ineffective. • Tip – Do not mix synthetic oil with

• Tip – Where pulleys are used this can be

as simple as using pulleys of different diameter but always get the alignment correct when changing or using pulleys.

Gear pumps Gear pumps control the output of the screw to the die. Gear pumps use a set of rotating gears to control the melt pressure and output volume to the die within very tight tolerances (< 1%) with little or no pulsation of the melt flow. This isolates the die from any upstream fluctuation such as surging in the screw area due to material or machine variations.

• Tip – Check gear pumps regularly and

monitor the pump for changes in power use as this can act as an early warning for many gear pump problems. • Tip – Herringbone geared gear pumps

tend to have a lower pressure fluctuation than standard spur gears. Gear pumps can also be used to raise the melt pressure. This will lower the screw pressure, the melt temperature and potentially increase the output of the extruder.

motor to the screw uses belts then optimise the belts (see Section 4.16).

Gear ratios Extruder motors commonly run at high speeds and are geared down to the required screw rotational speed. When the existing gear ratios are not correct for the job, the motor will not be operating at the correct speed, the energy use will be high and the torque generated will be well below the maximum level. Changing the drive ratio can be a simple project to optimise motor use. • Tip – Check the loading on extruder

motors and modify the gear ratios to optimise motor energy use. Chapter 5 – Processing

Getting the right motor and drive system is critical to energy-efficient extrusion. It is the basic and most important action.

Summary of the AC and DC drive options DC motors

• Tip – Excessive vibration is always a

• Tip – Where the transmission from the

It is always preferable to measure the melt pressure directly and to include over-load protection on the motor.

Gear pumps can be driven by AC or DC motors but accurate speed control is essential.

mineral oil. good indicator of potential problems. Where a belt drive is used to connect the motor to the load then a simple project is to replace the standard V-belts with more efficient belts.

Monitoring the motor load is not the same thing as monitoring the melt pressure.

For

Against

Accurate, fast and direct

torque control.

Low motor reliability. High initial motor cost.

Good speed response.

High maintenance costs.

Simple control systems. High accuracy of speed and

torque control. Flat speed versus torque

profile.

AC motors + VSD For Small, light and robust. Simple design. Lower initial motor cost. Lower maintenance cost.

Against More complex control

system. High motor controller cost. Variable torque versus

speed profile.

Reduced operating cost. Improves site power factor.

245

5.18

Extrusion – heating

Heating in extrusion

processing. The energy use by extrusion machine heater bands is therefore often considerably less than for IMMs and in many cases the heaters are dual-purpose and need to have the ability to cool (fan blowers) as well as heat. The power trace for ancillaries feed of the extruder shown in Section 5.17 is shown on the upper right. This is typical of the ancillaries load and will normally be striated as various heaters/blowers turn on and off. For this machine the main motor load was 221 kW and the average heater and ancillaries load was 39 kW or 17.5% of the main motor load. In most cases, the drive energy is more efficiently transferred into the material by shear heating rather than by external heating from barrel heaters which acts only on the outer layer of the material at the barrel interface. • Tip – Shear heating should be used to

provide the bulk of the heating in the central sections of an extruder. The rear barrel and feed throat areas (where cold material enters) will generally need heating due to the entrance of cold material and the lack of sufficient shearing. • Tip – Cooling the barrel with fan

blowers not only removes excess heat from the barrel but can also aid the extruder operation by increasing the friction at the plastic/barrel interface and encouraging mixing and forward movement. 246

Power (kW)

80

60

40

20

0 00:00

00:20

00:40

01:00

01:20

01:40

02:00

02:20

02:40

03:00

Time (min:s)

kW trace for ancillaries feed This trace includes heaters and blowers and shows a very banded appearance because of the heater bands cycling on/off load. The ancillaries draw an average power of 39 kW for an installed power of 49 kW (79%). Total energy input to extrusion line (% of motor rated power) 150% Screw power input Heating power input Cooling power input Power required for process Total power input

125%

100%

Heating required

Cooling required

Operating window

• To adjust the barrel temperatures during

Ancillaries 100

kW (% of motor rated power)

Heating in extruders is more complex than in IMMs. In extrusion, most of the thermal energy involved in plasticising and heating the material comes from frictional heat developed by shearing of the plastic as it is being moved by the interaction between the screw and the barrel. The barrel heaters do not provide the bulk of the heat input to the plastic. The main reasons for barrel heaters are: • To melt the polymer at the start-up phase. • To provide the initial melt.

75%

50%

25%

0% 0%

10%

20%

30%

40% 50% 60% Screw speed (%)

70%

80%

90%

100%

Energy inputs for extrusion (simple model) At low speeds the screw power input is low and heaters are needed to provide the main power input for the process. As the screw speed increases, the screw power input increases and the heater input decreases until the processing window is reached. At this stage the energy requirements of the process will be supplied mainly by the screw (90–95%) with the rest of the energy (5–10%) being supplied by heaters to adjust temperatures along the barrel. If the screw speed continues to increase, the power input by the screw will exceed that required for the process and the melt temperature could increase above the processing window. At this stage, cooling will be needed for process stability. This will increase the total power required by the process. Chapter 5 – Processing

Extruder speed and heating Optimising the extruder speed maximises the heat from mechanical work and minimises the amount of electrical energy needed to heat the plastic (see figure on the lower left). Provided the downstream equipment does not limit the output, the energy consumption of an extruder per kilogram of processed polymer can be decreased by nearly 50% by doubling the rotational speed of the screw. • Tip – Insulation is effective on extruder

barrels but not in all sections or for all applications. Where shear heating is low then it is effective in reducing the energy input needed from barrel heaters. It reduces energy use, temperature fluctuations and health and safety concerns. It has a payback of ≈ 1 year. • Tip – If insulation is not used then

to the die. They are always heated to keep the melt at the correct temperature and are rarely insulated to prevent excessive heat loss. New-generation screen changers feature insulation to reduce energy use in the heating (www.gneuss.com).

The barrel heaters do not provide the bulk of the heat input to the plastic.

• Tip – Investigate insulation for screen

changers.

Die heating Extrusion dies are always heated and rarely insulated despite the obvious benefits in energy saving and also in removing a potential health and safety concern. • Tip – Extrusion dies should always be

insulated with either flexible insulation (see below) or with board-type insulation.

Check the barrel heater ammeters. If the heater is constantly on then the shear heating is not providing all the heating required and insulation could well be beneficial.

extruder barrels must be adequately safety guarded. • Tip – Installing insulation at all sections

of an extruder barrel can lead to a ‘runaway process’. Good extrusion requires that the plastic is kept at the optimum temperature whilst at the same time prevented from overheating. Depending on the material, the operating or processing window is small and overheating from shearing is common unless accurate temperature control is present. Accurate temperature control will produce good product and minimise energy costs. • Tip – Check extruder controls to make

sure that the heating and cooling are working efficiently together and not competing with one another.

Thermograph of uninsulated extrusion die head The uninsulated die head is at ≈ 134°C and has very little shear heating. In addition to the high energy losses from the die head, the exposed hot surface has significant health and safety implications.

Downstream from the screw Downstream from the screw tips there is very little shear heating because the flow is mainly through channels with low shearing. In these areas, heating is provided by band heaters and insulation is vital to reduce energy use and as a health and safety measure.

Transfer pipes Transfer pipes are used to move the melt from the barrel to the gear pump (if used), the screen changer/melt filters and finally the die. These should all be insulated (see Section 5.21 for an example).

Screen changers/melt filters Screen changers/melt filters are designed to filter the melt and provide a clean melt Chapter 5 – Processing

Thermograph of insulated extrusion die head This is a similar die head to that shown above. The simple application of the insulation reduces the exposed surface temperature to ≈ 20°C. This greatly reduces energy losses and removes any health and safety implications. 247

5.19

Extrusion – profiles

Perfect profile Profile extrusion is one of the largest volume processes for plastics processing and is used for products from pipes through to windows and medical tubing. The variety of products means that the process also has many variations and this section only attempts to describe actions that can be taken in the majority of cases. Extrusion sites are advised to review their process using this section as a guide but not as a prescription.

Screw design Machine and screw manufacturers are introducing computer-aided design procedures to reduce energy use in the basic screw extrusion process. • Tip – Check that the basic screw is

optimised both for the material and for energy use. • Tip – Failing to select the correct screw

will lead to variable product as well as poor energy efficiency.

Machine setting Setting of the extruder is critical to reducing energy use and many sites pay little attention to correct setting – as long as the profile is acceptable then it is assumed that the extruder is set correctly. It is only when concerns appear that the extruder settings are examined. Sites need to examine the setting process carefully to maximise the heat input from shear heating and minimise the operation of the heater bands.

then consider reducing the temperature at the die. • Tip – Accurate temperature control will

produce good product and minimise energy costs. Check thermocouples regularly.

Profile extrusion (including pipes) is one of the largest volume users of plastics.

Barrel insulation Insulation is not generally required on the complete length of profile extruder barrels because the shear heating from the screws should provide enough heat for the process (see Section 5.18). There are, however, some notable exceptions: • Extruders will always need heaters for the start-up of the machine. • The rear section of the screw will often need almost continuous heating due to the inflow of the cold material before it has undergone any shearing. • The front of the barrel may need heating

due to reduced shearing in this area. Monitoring of the barrel heaters and blowers will enable an understanding of the exact heat flows in a specific process. Monitoring of the heaters and blowers will show when they are coming on and off load (preferably not at the same time). If the heaters are on at all times then the motor is not providing enough shear heating for the process and there are two choices: • The main extruder can be run harder to increase the shear heating and decrease

If oil heating is used for dies and downstream parts then do not forget to insulate the oil pipes.

• Tip – If the motor is drawing excessive

current then the screw speed may be set too high for the die. • Tip – If the profile shows a grainy

surface then the melt temperature may be too high and the barrel temperatures could be reduced. A balanced die is essential for good profile dimensional control. When die balance is lost for a previously good die then this is generally the result of the die being too hot for the process. This is often due to a failure of the thermocouples to control the die temperature adequately. • Tip – If die balance is lost then check the

thermocouples for the complete system (barrel and die). If these are all good 248

Main profile extrusion machine with barrel insulation on the screw section This window profile extruder is running relatively slowly for quality reasons and shear heating does not provide all the heat required. The barrel section is therefore insulated to reduce energy use. Chapter 5 – Processing

the need for the heater bands. This may not be an option if the output is limited by the calibration process or the haul-off. • The barrel can be fitted with insulation to reduce heat losses. • Tip – If heaters are operating at all

times then increase the screw speed before trying insulation on the barrel. • Tip – Turn off barrel heaters and cooling

fans between runs when the time between runs is sufficient and after barrels have been purged (if required by the polymer being used, i.e., PVC).

Downstream from the screw As with most other types of extrusion, there is little shear heating downstream of the screw tips and heaters will be required to provide the majority of the heat necessary to keep the plastic at the correct temperature in breaker plates, adapters, transfer lines and dies. This is particularly important for hollow profiles where the mandrel is held in place by spiders and full rewelding of the melt stream must take place after the material passes the spiders (otherwise weaknesses will result). Heating is generally necessary for all areas downstream from the screw tip and heat losses will be significant. Insulation will reduce heat losses and energy use in these areas as well as reducing health and safety concerns.

Piggy-back co-extruder with no insulation Piggy-back co-extruders will often run very slowly to match the main extruder speed and these will often benefit from barrel insulation due to the low amount of shear heating. The transfer pipes to the main die should also be insulated.

• Tip – All areas downstream of the screw

tip will generally benefit from insulation to reduce temperature changes and energy use (see Section 5.18).

Co-extruders Small piggy-back co-extruders are often used to attach soft sections (lips and gaskets) or different colours to the main profile (see photograph on the upper right). These will often be run slowly because of the small amount of material being applied. In these cases, the shear heating will be very low and barrel insulation can save energy.

Thermograph of hot profile extrusion die head The extrudate is at 203°C but large areas of the uninsulated die head are > 200°C and could benefit from insulation to reduce heat losses. Using insulation also reduces any health and safety concerns.

• Tip – As noted in Section 5.18, check the

heater ammeters. If the heaters are constantly on then barrel insulation can reduce energy use.

Thermograph of extruder barrel using fan blowers The barrel is at 213°C largely as a result of shear heating and needs some additional cooling to keep the plastic in the processing window. In this case the additional load of the cooling increases the energy use of the process. Chapter 5 – Processing

249

5.20

Extrusion – profiles: calibration and cooling

Calibration and cooling Calibration and cooling take place at the same time although there are several different methods used. For simple profiles, the calibration may be a single metal plate calibrator followed by immersion in a chilled water bath, whereas for complex PVC-U window profiles, calibration is usually by multiple metal plate calibrators in a full chilled water bath or in a spray bath.

Cooling

outer surface has frozen the heat transfer rate is more determined by the properties of the polymer than by the ∆T). This means that decreasing the chilled water temperature further will have no effect (see Section 4.35). Significant improvements in the energy used in calibration and cooling can be made by simple good management of the services. • Tip – Turn off the chilled water flow to

the calibrators as soon as the machine is idle, i.e., when the screw stops turning.

Profile extrusion typically uses large quantities of chilled water that flows freely over the extrudate as it passes through the cooling bath (which, depending on the profile, may or may not also contain extrusion calibrators). After passing over the extrudate, the water is returned to a large sump, generally by gravity flow. The rate of heat removal from the extrudate depends on the temperature difference between the extrudate and the chilled water, the water exchange rate and the amount of contact between the extrudate and the water.

• Tip – Check that chilled water is not

In many cases, the rate of heat removal from the extrudate is actually the limiting factor in the line speed, i.e., the extrudate must be solid enough to have fixed dimensions and cool enough to handle at the end of the water bath. The extrusion speed may therefore be defined by the water bath length and the rate of heat removal in the water bath. If the cooling is ineffective then the line speed must be slowed down with obvious implications for energy use (see Section 5.18).

made from stainless steel then consider insulating them to prevent parasitic heat gain to the chilled water. For window profiles, the traditional approach was to use solid metal vacuum calibrators cooled with chilled water. The high specific heat capacity of the metal calibrators provided rapid heat transfer

Cooling of pipe and hollow profile extrusion can also be improved by forcing cool air into the profile to increase the cooling rate and therefore the production rate. An example of this is efficient air cooling or EAC (www.battenfeldcincinnati.com).

circulating through idle calibrators (see below and lower photograph on the right). • Tip – Check that chilled water is

treated, chilled and distributed efficiently (see Chapter 4). • Tip – Find the maximum acceptable

extrudate temperature after cooling and set the maximum chilled water temperature to achieve this. Do not overcool the product, it is simply a waste. • Tip – When the calibration baths are

Vacuum pumps for calibration tables need to be able to handle air/water mixtures and often large water flows.

Cooling rates may be increased by: • Good contact between the profile and the calibrators – this is desirable not only for the calibration but also improves heat transfer because the metal removes heat quickly. • Turbulent water flow around the profile. • Removal of air bubbles from the water

bath – air bubbles on the extrudate surface will greatly reduce the cooling rate and it is common to seal the water bath and to apply a vacuum to remove air from the system. • Increasing the ∆T between the extrudate

and the chilled water (although once the 250

Non-productive calibrator set This extrusion machine was stopped (and had been for 24 hours). Despite this, the chilled water was still flowing to the inactive calibration tanks and all the vacuum pumps were still operating on open calibrators. Chapter 5 – Processing

away from the extrudate provided there was good contact between the calibrators and the plastic. This approach is largely superseded by the use of ‘floating calibrators’ consisting of thin metal plates in a water bath. The cooling water is then applied either through full immersion or as a water spray (which moves the warm water away from the extrudate quicker and provides better cooling). This type of calibrator also makes setting the line easier. Although there are a range of practical options, a number of general theories and considerable numbers of empirical rules; few have been subject to thorough testing for validity. At sites, actual is variable; water use is highly variable, temperatures, pressures, filtration standards and flow rates depend on the site’s experience and there are few definitive rules for the actual requirements and the energy really necessary to provide the cooling. What is certain, however, is that the theoretical cooling requirements are almost always exceeded by the actual use in the process.

ensure that the tanks are sealed correctly and the seals are in good condition and do not allow air ingress. Check seals regularly, they will age. • Tip – Use VSDs on vacuum pumps to

control the vacuum achieved to the minimum actually required. • Tip – Check that the vacuum supply is

generated and distributed efficiently.

Extrusion often uses a number of small vacuum pumps near to the point of use, rather than a central utility. In most cases the motors are oversized, are run lightly loaded and are inefficient.

• Tip – Check that the vacuum supply is

switched off when it is not needed.

After the calibrators After cooling, the extrudate is removed from the water bath and cut or coiled to length. • Tip – Do not use open compressed air

lines as air knives to remove water from the extrudate. Use venturi units or air intensifiers where possible.

Some suppliers (www.greinerextrusion.at) have introduced vacuum control systems to cut the energy use by up to 80%. It is actually quite easy when you care.

• Tip – Make the maximum use of natural

cooling by using a large sump and by using artificial cooling as little as possible. • Tip – Use VSDs to control pumps to

produce a constant pressure or flow rate. Use thermostatic controls to vary the flow rate based on the cooling demand rather than the pump’s fixed output. • Tip – Cooling is a major expense in

profile extrusion and yet little information is available to assess the energy efficiency of the competing cooling methods or their effect on the process economics.

Chilled water temperature of 13.6°C ‘This site cannot work with a water temperature higher than 9°C’ said the Site Manager. Meanwhile, the water temperature was showing as 13.6°C and the site was at full production. I didn’t understand it either and raised the chilled water set-point.

Vacuum use in calibration For any profile in a water bath, air bubbles on the extrudate greatly reduce the rate of cooling and some cooling baths are sealed (nominally) and fitted with vacuum pumps to provide a reduced pressure and to encourage air removal and close contact between the extrudate and the calibrators. The vacuum pumps are expensive to operate, are generally larger than needed and often the cooling baths do not have good seals to prevent air ingress, i.e., the vacuum pumps are being overworked. • Tip – If vacuum pumps are being used to

remove air from the cooling bath then Chapter 5 – Processing

Thermograph of non-productive calibrator set The non-productive (and uninsulated) calibrator area is fully operational (chilled water flowing and vacuum on) but the machine has been non-productive for > 36 hours. Turn off the chilled water flow and insulate the calibrators. 251

5.21

Extrusion – sheet

Extrusion of sheet

Co-extruders

Sheet extrusion for later thermoforming (see Section 5.36) is a major process in the plastics industry and large volumes of material are processed using sheet extrusion.

In many cases a sheet will be produced using a co-extruder to produce a sheet of the A–B–A format where A and B are different materials. Where co-extruders are only used occasionally these should be subject to good purging and shut down.

Process Sheet extrusion differs from film blowing (see Section 5.22) in that the resulting material is thicker and is generally an intermediate material rather than the final product. The process involves extrusion through a slit die directly onto sizing rollers which control the overall sheet thickness. There is no conventional water-cooled calibration bath as for profile extrusion and the rollers provide both the thickness control and the cooling. Sheet extrusion can be either for solid sheets, e.g., PP, PVC or PET, which are extruded as flat sheets straight onto the cooling rollers, or for foam sheets, e.g., PS and other foam materials, which are extruded as a tube that is slit and flattened before rolling into reels.

• Tip – Co-extruders are often left at heat

even when no run is planned. These should be purged and shut down if they are not going to be used for over 3 hours.

For foam sheet extrusion, cooling of the foam is sometimes provided by the expansion of compressed air – a very expensive method of providing cooling.

Transfer lines Transfer lines between co-extruders or the main feed and the die are rarely insulated except in the best factories. There is no

Extruders and dies Die preparation At some sites it is common to pre-warm a die so that it is ready for later production. If this is carried out by connecting the die heaters then the energy use will be considerable. This can easily be reduced by using a ‘tea cosy’ of insulation during the pre-warming.

Oil transfer piping In this extruder, oil provides additional heating at 148°C due to the low shear heating in the barrel. Insulation applied to the oil transfer pipe will reduce energy use and health and safety concerns.

• Tip – If pre-warming is carried out then

use insulation to reduce energy use and health and safety concerns.

Heating Die and barrel heating can be either via conventional band heaters or via hot oil heaters. Hot oil heaters are shown on the upper right and are similar to mould heaters in injection moulding. • Tip – Where hot oil heaters are used

then all the oil transfer piping should be insulated to reduce heat losses, to reduce any health and safety issues with hot oil lines and to reduce the temperature in the area. Heaters must also be adequately controlled to prevent overheating. 252

Good insulation on transfer lines There is very little shear heating in transfer pipes and heaters are needed to keep the plastic molten. This thermograph shows excellent use of insulation in a transfer pipe to reduce energy use. Chapter 5 – Processing

shear heating in these areas and heater bands are used to keep the plastic molten. • Tip – Transfer lines should be fitted

with insulation to reduce heat losses (see photographs on the lower left).

Barrel insulation and heating As noted in Section 5.18, insulation is not always needed on extruders but may be needed on sheet dies if the output is low (see photograph on the upper right). • Tip – Check the ammeters to see if the

barrel heaters are operating during normal use. If so, consider simple barrel insulation. • Tip – Insulation has low risks but

temperature controllers should be checked to ensure that they can tune the heaters to the required levels.

Die insulation

Good barrel insulation on a sheet extrusion machine When a sheet extruder is linked to a downstream thermoformer the output may be ‘throttled’ to match the thermoformer output. In this case the lower speed means that shear heating does not provide all the heat. Insulation of this barrel saves energy.

Heat losses can be significant on uninsulated dies. There is again no shear heating in this area and heaters are used to keep the plastic molten. Insulation can reduce energy use (see middle and lower photographs on the right). • Tip – Dies should be insulated to reduce

heat losses. Note: Ensure that the heaters are controlled to prevent overheating.

Cooling rollers Cooling rollers are cooled by chilled water. • Tip – Increase water temperatures to

the maximum required by the process. • Tip – Ensure that turbulent flow is

taking place in the rollers.

Edge trim regranulation

Good insulation on the rear of a sheet die There is little shear heating in the sheet die and heaters are needed to keep the plastic molten. This photograph shows excellent use of insulation at the rear of a sheet extrusion die to reduce energy use.

On most sheet lines, the sheet is trimmed to width and the edge trim is recycled (sometimes in a closed loop) back into the process. This reduces material use but sites need to calculate the energy cost of this recycling. If edge trim volumes are small then recycling of the edge trim may not be financially viable. • Tip – Sites should calculate all the costs

of recycling edge trim (energy costs and handling costs) to see if the recycling operation is actually saving money. Whilst recycling is good, if it is not profitable then either change the process to make it profitable or stop recycling. • Tip – Investigate edge trim volume

reduction at the line with later regranulation for a cheaper alternative.

Chapter 5 – Processing

Good insulation on the rear of a sheet die This sheet die has thicker insulation but it is a standard ‘blanket’ and the coverage is not as good as with the purpose-made insulation cover shown above. However, it still reduces the energy used in the heating of the die. 253

5.22

Extrusion – blown film

Blown film The blown film process uses extrusion to produce a homogeneous melt that is fed into a circular die head and fed with pressurised air to form a bubble that is cooled, slit, wound and possibly posttreated depending on the specific application of the product. For blown film production, energy is the second largest cost (after material) and good energy management is critical to profitability.

Speed Running faster will increase the energy efficiency of the base extruder but this must be balanced against a potential increase in downstream concerns, e.g., decreases in gauge consistency and decreases in bubble and web stability. The overall energy efficiency of the site is based on good product and if running faster simply increases material use and production concerns then the gains may be outweighed by the losses. • Tip – Running faster is not always

better for overall productivity.

The cooling rate of the film is the limiting factor in process speed and cooling is assisted by blowing cold air onto the inside (internal bubble cooling) and outside surfaces of the bubble. As the extrusion speed increases the chill or frost line (where solidification of the extrudate takes place) will be higher on the bubble and the bubble can become unstable. Increasing the air flow rate can increase cooling but if the air flow rate is too high then the bubble can become distorted and again unstable. The correct chilling of the blown film in the bubble is therefore critical to good production and the temperature and volume of the air are varied to get the chill line at the correct location on the bubble. This can be controlled by the use of fans with VSDs that are controlled by the chill line location. New technology can vary the amount of cooling air delivered to each area of the perimeter of the bubble to control the rate of stretch around the bubble and to produce very even bubble thickness and reduce thick spots on the bubble. This requires sophisticated control of the air

Edge trim On most lines, the film is trimmed to width and the trim is recycled. This reduces material usage but sites should calculate the energy cost of this recycling. At one site, the regranulators were all very large so that complete rolls could be reground when needed but most of the time they were only used for trim and were running unloaded. Replacing the large regranulators with smaller trim regranulators for normal use and dedicating a large regranulator for roll regrinding, saved large amounts of energy.

Extruders and dies The residence time of the melt in the die head is a critical issue for film blowing and this can be reduced by reducing the melt volume in the die head through good die design. As with any extrusion die there is little shear heat input after the screw tips and most of the heat is input from electrical heaters. A large amount of this energy is lost to the environment (or transferred to air cooling lines). It is possible to greatly reduce this energy loss by die insulation (see upper photograph on the opposite page). This reduces heat losses from the die (see middle photograph on the opposite page). • Tip – Fit die insulation to blown film

dies to reduce the heating energy required for the die.

Cooling For film extrusion, the high surface area to volume ratio of the extruded film means that cooling is achieved using cold air rather than cooling water. The cold air is provided by the cooling system to chill the film as it exits the annular die. 254

A typical small film blowing line with off-take reels Extrusion is not simply used for profiles and sheet but also for the production of blown film. The extruder feeds a ring die to produce a bubble that is cooled, slit and wound onto reels. Post fabrication is used for the production of bags and other items. Chapter 5 – Processing

flow through each segment of the air ring (via control valves). • Tip – Check that the chill line is even

around the bubble as an indicator of any mismatch in the effectiveness of the cooling. • Tip – Ensure that all air cooling lines

are well insulated to prevent parasitic heat gain (see middle photograph on the right). • Tip – Keep air cooling lines as far away

as possible from hot components and make them all the same length to keep pressure drops the same. • Tip – Use VSD-controlled fans for bubble

size control blowers (see lower photograph on the right). • Tip – Use VSD-controlled fans for

chilling the bubble to locate the chill line. • Tip – Use VSD-controlled air ring fans

Insulation of blown film die area Simple insulation of the die area of the extruder reduces heat losses to the area. It would be even better to include insulation of the chilled air tubing to prevent parasitic heat gain to the chilled air tubing from the hot environment.

for the best location and control of the bubble. • Tip – Some blown film sites will suffer

from large amounts of dirt and condensed volatile materials (depending on the product). This can condense on motor and fan cooling areas and reduce their efficiency. Keep these areas clean through regular maintenance.

Winders After cooling, the bubble is flattened, trimmed to size and wound. These processes use much less energy than the main extruder but poor maintenance can lead to variations in speed and product quality. • Tip – Good maintenance of winder

motors, gearboxes and controllers is essential for good control and minimising energy use.

Thermograph of blown film bubble The decrease in temperature of the blown film as it moves away from the die is clearly seen. The close proximity of the hot extrusion die and the cold chilled air tubing leads to parasitic heat gain in both areas. Both areas should be insulated.

Post-treatment Depending on the process, tempering ovens may be used to post-treat films to get the correct properties. In common with many ovens, these are often inadequately insulated and sealed to reduce energy use. • Tip – Post-treatment ovens should be

well sealed and insulated at all openings (doors, etc.) and all surfaces. • Tip – The cycle times used for post-

treatment ovens are often not well controlled or optimised. Simple controls can reduce energy use in post-treatment ovens.

Chapter 5 – Processing

Bubble control The bubble size is controlled by blowing air into the bubble. In this case, the blower was controlled by ‘damping’ or adjusting the location of a piece of cardboard! A VSD reduced the motor speed by > 80% and operating cost by 95% with a payback of 6 days. 255

5.23

Extrusion – oriented film

Oriented films Oriented film uses a very different production process to blown films and the process has developed rapidly since the late 1990s. Biaxial films can be produced from a wide range of standard polymers including PP, PA, PE, PS, PET, PETG and PVC but PP is the largest in volume production. Oriented films are now widely used as a replacement for cellophane, paper and aluminium. Production of oriented film involves extrusion of a basic sheet. The sheet is then rapidly stretched to reduce the thickness and strongly orient the polymer chains. This gives a very thin sheet with excellent mechanical properties (such as good tear strength) and also excellent optical properties (transparency and gloss). The ability to produce multiple layers enables the inclusion of barrier layers and the resulting film has excellent properties for packaging applications. ‘Oriented film’ actually covers a range of processes such as: • Mono-axial orientation where the orientation is only applied in either the longitudinal or transverse directions. • Sequential biaxial orientation where the orientation is first applied in the longitudinal direction and then in the transverse direction (see outline drawing on the lower right). • Simultaneous biaxial orientation where the orientation is applied in both the longitudinal and transverse directions at the same time.

5. Secondary slitting and/or metallisation of the film.

Extrusion The extrusion section of an oriented film line is very similar to any other extrusion operation. When multi-layer films are produced, the extrusion machines tend to be widely separated with long transfer pipes to the co-extrusion die. • Tip – Insulate extrudate transfer pipes

as for other extrusion operations (see upper photograph on the opposite page). The co-extrusion die is heated but is rarely insulated. • Tip – Insulate the co-extrusion die

where possible to reduce heat losses (see middle photograph on the opposite page).

Orientation Longitudinal orientation Longitudinal orientation is generally carried out with little external heating but the sheet constantly loses heat to the atmosphere and there is generally little

If steam is used to heat the ovens then all steam pipes should be well insulated.

The sequential biaxial orientation process is the most common process and BOPP (biaxially oriented polypropylene) is the most common product.

Basic process Sequential BOPP (or any other biaxially oriented material) is produced in five steps: 1. Co-extrusion of the initial multi-layer sheet. 2. Orientation of the sheet in the longitudinal direction. 3. Orientation of the sheet in the transverse direction. 4. Primary slitting of the film. 256

Outline of sequential orientation production line Sequential orientation is the most common process and involves longitudinal stretching followed by transverse stretching. The process is highly energy-intensive compared to other extrusion processes due to the downstream heating required. Chapter 5 – Processing

effort made to retain the heat from the extrusion operation. • Tip – Consider insulation or cabinets to

retain the heat in the sheet during the longitudinal stretching operation. The stretched sheet is transferred to the oven for transverse stretching. This transfer distance is often substantial and the sheet continues to radiate heat. • Tip – Consider insulation or cabinets to

retain the heat in the sheet during the transfer to the transverse stretching oven from the longitudinal stretch operation.

Transverse orientation

Extrusion section of BOPP line

The sheet enters the transverse stretching oven via a large entry slot prior to reheating to ≈ 110°C for transverse stretching.

The extrusion section of this BOPP line has 5 extruders feeding a co-extrusion die. In order to have space for the individual extrusion machines they are widely spaced with long transfer pipes to the co-extrusion die. These all need insulation.

• Tip – The entry slot is often very large

compared to the thickness of the sheet. Reduce the slot size to just over the thickness of the sheet to prevent heat losses from the oven (see lower photograph on the right). Ovens are often poorly sealed and insulated. This results in heat loss to the atmosphere and increased operating costs. • Tip – The outer surface should not be

hot to the touch otherwise the insulation is not adequate. • Tip – Carry out a thermographic survey

of all areas of the ovens and improve insulation or maintenance of seals to reduce heat losses. • Tip – Where leaks are substantial these

will be visible from discolouration of the oven surface. The ovens often have poor heat recovery from the hot air used to heat them (this must be vented to provide contaminant free air). This is a waste to the site and heat recovery should be used to reduce the heating load of any oven.

Die section of BOPP line The co-extrusion die combines the output of the individual extruders to form the multi-layer sheet. The die is uninsulated and radiating heat at ≈ 250°C. Simple insulation of the die would reduce this energy loss and reduce A/C costs for the site.

• Tip – Use heat exchangers to recover as

much heat as possible from exhaust air.

Slitting Slitting is a relatively low energy user in the orientation process compared to the other elements.

Oven entrance for BOPP line The transit distance between the longitudinal stretch area and the oven is very long and the sheet loses heat which must be replaced by the oven. The sheet enters the stretching oven via a large aperture despite the fact that the sheet is very thin. Chapter 5 – Processing

257

5.24

Extrusion – other processes

A multitude of processes Extrusion is not only used for the production of solid profiles, sheets and film but also for a variety of other processes such as recycling (pelletising), and ram extrusion. Recycling uses the basic screw extrusion process and many of the issues for these are common to those discussed previously, but ram extrusion is a different process and does not involve an extruder screw.

Recycling Post-consumer recycling has grown in importance as both the economics have improved and as the pressure on resources has increased. The sorting and preparation process can be complex depending on the plastic being recycled but generally consists of granulation, washing and sorting (flotation or other methods) to produce a clean plastic flake. This is then extruded to produce a specific grade of raw material that can be reused. Energy use at recycling sites will generally be slightly higher than at standard extrusion sites due to the extra energy used in the sorting and washing process and in the extrusion process (if this is a two-stage process). At the extruder level, it is possible to use the standard extrusion benchmarking data.

Washing Washing involves agitation, scrubbing and cleaning of the raw material. Where this involves pumps for water then the use of VSDs to control the pumps is a natural energy use reduction project.

Lack of transfer pipe insulation This transfer pipe is easily accessible for fitting insulation to reduce energy use and to remove a potential health and safety concern.

Lack of adaptor plate insulation This adaptor plate is uninsulated but safety-guarded. The cost of the guard (to remove the health and safety concern) is not much less than the cost of insulation which would also save energy.

• Tip – When water pumps are used for

washing and/or flotation tanks then VSDs should be fitted to all the pumps for better control of the process. • Tip – VSDs can also be used for

materials transfer and vacuum pumps. • Tip – Where conveyors are used to feed

regranulators and extruders then these can be fitted with controls to maintain a constant feed rate to the regranulators.

Extrusion

Lack of die head insulation

The extrusion process used in recycling is similar to other extrusion processes. Motor improvements and insulation are the key actions to be taken.

The die area of this recycling extruder is uninsulated. This uses excessive energy (radiated to the atmosphere) and is a potential health and safety concern.

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Chapter 5 – Processing

• Tip – Motors should be examined for

improvements (see Section 5.17). • Tip – Insulation is easily possible at

many areas of the recycling process and will reduce energy use as well as protecting staff from hot areas and removing any health and safety concerns. Some typical areas for potential applications are shown on the left.

a denser product. Sintering closes the voids and produces a compact solid product with a very low permeability to liquids and gases.

Extrusion can also be used for rubber production (see Section 5.52).

• Tip – Sintering ovens should be well

sealed and insulated at all openings (doors, etc.) and all surfaces.

• Tip – Recycling will often have high

levels of volatiles (printing inks, etc.) and extract fans should be fitted with VSDs to reduce energy costs. Extract fans should also be fitted with controls to prevent operation when the main extrusion machine is not operating. • Tip – Where water baths are used to cool

the recycled granules then the water temperature of the bath should be maximised to reduce the load on chillers, preferably the temperatures should be high enough that air cooling or cooling towers can provide the required cooling.

Ram extrusion Whilst the majority of polymer extrusion is carried out using screw extruders, there are some plastics that simply cannot be extruded using this method. For polymers that have a very low coefficient of friction or are otherwise difficult to extrude because of their high melt viscosity, screw extrusion is not possible and ram extrusion is used. Plastics such as PE-UHMW and PTFE are typical of these ‘non-melt processable polymers’ and they are generally processed by ram extrusion where the pressures that can be attained are much higher. The basic layout of a ram extruder is shown on the right. Depending on the material, the extrudate can be a solid material or a paste that is later sintered and dried to form the final product. Unlike conventional extrusion, which takes place at high temperatures and uses a polymer melt, ram extrusion takes place at slightly above room temperature (generally in the region of 40–60°C). When a paste is produced this is then drawn through a drying/sintering furnace where the necessary processing aids are driven off by heating the extrudate above the volatilisation temperature of the additives. If the application requires a fully coalesced product then the extrudate is sintered at higher temperatures (300– 330°C) to remove any voids and to produce

Chapter 5 – Processing

The basic principle of ram extrusion Ram extrusion is used for materials with low coefficients of friction. These materials cannot be processed by a conventional screw extruder. The extrusion is generally at low temperatures with post-processing of the extrudate. 259

5.25

Extrusion – where are you now?

The initial steps in extrusion As with the score charts shown earlier, this is a self-assessment exercise to allow a site to benchmark their current status. Extrusion is a key process in plastics processing and forms the basis for a wide variety of distinct sectors. Progress has not been as rapid as in injection moulding but sites using extruders still have a wide variety of possible improvement actions available to reduce energy use. The correct setting of machines, the use of insulation in areas where shear heating is not providing the required heat input, the increasing application of AC motors and VSDs on main extruder drives and the

wider application of AC motors and VSDs in the control of ancillaries all provide fertile ground for improvements in extrusion.

Completing the chart

The extrusion process can easily be improved by carrying out simple measurements and acting on these.

This chart is completed and assessed as for those presented previously.

Extrusion

Monitoring & setting 4 3 Films

2

Barrel blowers & insulation

1 0

Tool & die insulation

Sheet

Profiles

Use the scoring chart to assess where you are in extrusion The numbers from the scoring chart can be transferred to the radar chart for a quick visual assessment of where you are in terms of extrusion. 260

Extrusion is ready for significant energy use reductions through fundamental motor and drive improvements.

Chapter 5 – Processing

Extrusion Level

4

3

Monitoring & setting Machine settings checked & validated against best practice. Most machines monitored for energy efficiency & performance.

2

0

Tool Profiles Sheet Films & die insulation Full insulation on Excellent match of Excellent control Excellent use of motor & gear hot areas of co-extruder. VSDs in all downstream from ratios to profile. Automation of applicable areas. Excellent control screw tip & sheet thickness Post-treatment uses no excessive of vacuum insulation in good control. condition. generation & use Ventilation VSD- energy, e.g., good insulation & closed (no leaks). Very low heat controlled. Cooling water well energy use. losses. Edge trim controlled. regranulators automatic 'off'.

Very few machine Full insulation Full insulation on Motor & gear Good control of Good use of VSDs in most applicable settings show upstream from hot areas ratios well co-extruders. areas. deviations from screw tip where downstream from matched to profile. Automated sheet good practice. applicable or screw tip & in Vacuum thickness control. Post-treatment uses excessive Some machines insulation present good condition. generation & use Ventilation good. automatic 'off'. energy, e.g., monitored for & in good Reduced heat energy efficiency condition. losses. Cooling water Edge trim moderate regranulators insulation & & performance. Reduced heat distribution & partially closed losses. contact good. automatic 'off'. energy use.

Small number of machine settings show deviations from good practice.

1

Barrel blowers & insulation Full insulation in good condition upstream from screw tip where applicable. New-generation heater/blowers. Very low heat losses & good heating control.

Partial insulation Partial insulation Motor & gear Good control of Moderate use of upstream from VSDs in some on hot areas ratios poorly co-extruders. screw tip where downstream from matched to profile. Better manual areas. applicable, e.g., screw tip or Vacuum control of sheet Post-treatment materials feed uses excessive insulation present generation & use thickness (SPC). Ventilation manual energy, e.g., low area or insulation but in poor good. present but in poor condition. Cooling water 'off'. insulation or Edge trim partially open condition. Moderate heat distribution & Moderate heat losses. contact good. regranulators energy use. manual 'off'. losses.

Significant number Safety guarding Safety guarding Motor & gear Poor control of co- Low use of VSDs of machine present for hot present for hot ratios poorly extruders. in few areas. settings show areas upstream areas downstream matched to profile. Good manual Post-treatment deviations from from screw tip but from screw tip but Vacuum control of sheet uses highly excessive energy, good practice. no insulation on no insulation on generation & use thickness. Ventilation manual e.g., low insulation any hot area. any hot area. poor. Large heat losses. Large heat losses. Cooling water 'off'. or open energy distribution & Edge trim use. contact good. regranulators manual 'off'.

Most machine No safety guarding settings show present for hot deviations from areas upstream good practice or from screw tip. recommended Risk of contact values. with hot surfaces. Large heat losses.

No safety guarding Motor & gear Poor control of copresent for hot ratios poorly extruders. areas downstream matched to profile. Poor manual from screw tip. Vacuum control of sheet Risk of contact generation & use thickness. with hot surfaces. poor. Ventilation Large heat losses. Cooling water permanently on. distribution & Edge trim contact poor. regranulators permanently on.

No use of VSDs. Post-treatment carried out poorly with highly excessive energy use, e.g., poor insulation or open energy use.

Score Chapter 5 – Processing

261

5.26

Extrusion blow moulding – general

A step up from extrusion EBM is much smaller in volume than either injection moulding or extrusion but still represents just under 10% of the processed polymers by weight and uses approximately 10% of the total energy used in plastics processing. EBM is a two-step process:

The regrinding use for ‘tops and tails’ regrinding (see Section 5.29) is also substantial (≈ 4%) and this is often ignored and considered to be insignificant.

Machine monitoring Machine monitoring can be carried out as for injection moulders and extruders but the extrusion blow moulding process uses

• The first step is the extrusion of the

Cooling water 13%

parison and this is very similar to simple extrusion. • The second step is the trapping and blowing of the parison in the mould to form the final product. This is similar in many ways to injection moulding. The process energy intensity at the site level is an average of 2.13 kWh/kg and this is, unsurprisingly, approximately midway between the process energy intensity for injection moulding and extrusion (see Section 2.12 and Section 2.17).

Sites considering new EBMMs should seriously consider the purchase of allelectric machines. Most machine manufacturers now make them.

Compressed air 16%

Water pumps 5% Lighting 1% Offices/IT 1%

Processing 64%

Site energy use The energy use breakdown at a typical EBM site is shown on the upper right and the processing load (the actual EBM machines) is obviously the highest load. The services loads, particularly compressed air, are generally higher at an EBM site due to the use of compressed air in the blowing process. The services are particularly productive areas for improvement projects at most EBM sites. This is particularly the case for compressed air use, an area that EBM sites do not appear to manage well at all.

Energy use breakdown at a typical EBM site The processing uses the most power at an EBM site but the services loads are generally higher than at an injection moulding or extrusion site. This is due to the much higher use of compressed air at an EBM site. Regrinding 4% Heating 12%

Machine energy use The energy use breakdown for a typical EBM machine (EBMM) is shown on the lower right and the extrusion area is by far the largest area of energy use. Note: This is only the machine and does not include centrally provided services such as air and water. The high energy use for motion (≈ 28%) is the result of constantly moving and holding the mould platens. These are often heavy and the hydraulic systems are equally large to move them quickly and accurately but are rarely well controlled in most machines.

262

Extrusion 56% Motion 28%

Energy use breakdown for a typical EBMM At the machine level, the extrusion element is far higher than any other demand. The motion (mainly hydraulics for platen movement) uses ≈ 28%, a value that comes as a surprise to most sites. Chapter 5 – Processing

large amounts of compressed air and cooling. The energy use of these services not easily allocated and accounted for at the machine level but should be accounted for in the total assessment of the process.

The base load A typical power trace for an EBMM is shown on the upper right and this shows a strong similarity with the injection moulding traces seen in Section 5.3. The pattern repeats with each cycle of the EBMM and there is an obvious base load, similar to that seen in injection moulding. In EBM, the base load is mainly due to: • The constant operation of the extruder. • The losses in the hydraulic system.

electric IMMs but have all the many advantages of all-electric machines described in Section 5.9. Most manufacturers now produce allelectric EBMMs and the energy savings in these machines are claimed to be in the region of 30–40%. This is what would be expected from experience with all-electric IMMs. However, these are still relatively rare in the installed machine base and we do not have enough direct monitoring data to fully validate this. EBM – shuttle 100

80

• Tip – Check EBMMs for excessively

large extrusion capacity (relative to parison size), large hydraulic pump size and large regrinders as a first step to understanding where the power is used.

Power (kW)

• The constant operation of the regrinders.

This base load differs from the base load seen in injection moulding where the base load is present even if the IMM is stopped. In EBM, stopping the extruder removes much of the base load. The base load for an EBMM is generally in the area of 65– 75% as shown on the upper right. The trace on the lower right shows an EBMM with a base load of ≈ 90%. This is high for an EBMM and indicates a machine that is over-sized for the application. The machine may be oversized in any of the areas listed above and these should be investigated as a first step.

PCLs can be easily be generated for EBM and machine operating curves for EBM machines are shown in Section 2.21.

60

40

Base load 20

0 00:00

00:20

00:40

01:00

01:20 01:40 Time (min:s)

02:00

02:20

02:40

03:00

Power cycle for a typical EBM machine As with IMMs, EBMs have a pattern that repeats with each cycle and a base load for the process (primarily the extruder load and the hydraulic losses). In this case the base load is ≈ 65% of the total load. This is average for an EBM machine. EBM – shuttle 100

The process load

All-electric machines As with injection moulding, the introduction of all-electric extrusion blow moulding machines has changed the basis of energy use in EBM. These new machines are still not as common as allChapter 5 – Processing

80

Power (kW)

As for injection moulding the power traces for EBM show a cyclic process load but for EBM the cyclic process load is primarily the additional load on the hydraulic system as it moves the platens. Large platens have a high inertia and require a large hydraulic system for movement and clamping. • Tip – Check the hydraulic system size and the platen size (mass and inertia) for potential projects to reduce the process load.

Base load

60

40

20

0 00:00

00:20

00:40

01:00

01:20 01:40 Time (min:s)

02:00

02:20

02:40

03:00

Power cycle for an over-sized EBMM In this case the base load (from the extruder load and the hydraulic losses) is ≈ 90% of the total load. This is high for an EBMM and indicates that the machine is perhaps over-sized for the specific job. 263

5.27

Extrusion blow moulding – extrusion and blowing

Extrusion step The major single energy use in EBM is the extruder and this typically uses 56% of the total energy supplied to the machine (see Section 5.26). Many of the actions for standard extrusion apply equally to EBM and these will not be discussed again. EBMMs generally use more externally applied heat than standard extruders but much of the heat is still generated mechanically by the extrusion process. The additional heat that is required from barrel heaters should be optimised and evenly distributed by good seating of the heaters to the barrel and the use of conductive metal compounds between the heater and the barrel. The energy use can also be reduced and controlled by using barrel insulation (see Section 5.18). The power drawn by a stopped EBM machine is shown on the lower right and this is substantial due to the large area available for heat dissipation.

thickness and parison length and will improve energy efficiency and materials usage. Controllers that are capable of varying the parison thickness to allow for differential stretching during the blow phase will optimise the wall thickness (see diagram on the opposite page). Failing to control the parison thickness will increase material and energy costs. Dynamic variation of the wall thickness will minimise uneven wall thinning and can

Good process control minimises material and energy use. They are always a good investment.

• Tip – Check the ammeters of the heater

bands. If they are constantly on then the barrel may well benefit from barrel insulation (see Section 5.18). Most of the heat put into the material during the extrusion stage must be removed before the product can be released from the mould. Product cooling time is about 50% of the cycle time and minimisation of the extrusion melt temperature will save energy in both heating and cooling as well as reducing the cycle time.

Parison formation in EBM The parison is extruded from the heads before the blow step. In this case, the material is at ≈ 200°C and the heads are all individually heated to much the same temperature to allow extrusion. EBM – not producing 100

80

temperature it actually needs to form the parison and provide the surface detail needed. • Tip – Lower the required melt

temperature by using more efficient screw profiles. This can cut parison temperatures by up to 10°C and save energy in both heating and cooling. Good process parameter control will give more efficient operation and reduce the costs of operation in all areas, not simply in terms of energy efficiency. Simple process controller improvements can give good paybacks and it is often worthwhile investigating upgrades to machines. Improved process control will give controlled, accurate and minimised wall 264

Power (kW)

• Tip – Set the polymer at the minimum 60

40

20

0 00:00

00:20

00:40

01:00

01:20 01:40 Time (min:s)

02:00

02:20

02:40

03:00

Stopped machines still use power in EBM This machine was stopped (non-productive) but all heater bands were still on and at temperature. The only thing that was actually stopped was the main motor. The energy use is mainly for the heater bands (note the striated pattern) but is still substantial. Chapter 5 – Processing

reduce material use by up to 7%. An additional benefit is that a consistent wall thickness allows faster cooling and a higher demoulding temperature by eliminating differential shrinkage.

• Tip – Excessive compressed air pressure

• Tip – Process controller improvements

contact applications the compressed air must be clean and dry. Leak testing using pressure decay will use large amounts of compressed air and the test pressure should be the minimum possible to still run the equipment and check the product in the time available.

give controlled, accurate and minimised wall thickness and parison length. They will decrease energy and material use. • Tip – Parison length control and top and

tail management are vital issues for extrusion blow moulding (see Section 5.29). Improved control of the parison and final product size will improve energy and process efficiency.

Blowing step The blowing step is typically responsible for ≈ 28% of the energy use in EBMMs (primarily for machine movements) but it also uses substantial amounts of services that are cannot be allocated directly to the machine (e.g., compressed air and chilled water). The hydraulic forces for mould closing and holding should be matched to the actual process demand, i.e., blowing pressure × projected area, to reduce the hydraulic pressure needed. • Tip – If at all possible then move the

parison to the mould rather than the mould to the parison (the mould is heavier than the parison) but a cost/ benefit analysis should be carried out for the cost of suitable robots versus the cost of traversing clamp units.

for the blowing or holding times wastes energy. Pressures should be reduced to the minimum required. • Tip – For all EBM products in food

Controls As with other processes, start-up, stand-by and shut-down procedures should be developed for EBM machines. These should bring the energy demands online at the latest possible time during start-up, set the machines in stand-by mode (hydraulics, barrel heaters and cooling fans off and services isolated) between runs and to shut-down the machine so that the energy-intensive areas of the machine are turned off as soon as possible (see Section 6.2).

Reducing the blow pressure will reduce compressed air costs.

Hydraulic accumulators can allow smaller motors to still deliver the required amount of movement. They can store energy when the movement is not required and the motor would otherwise be wasting energy.

• Tip – Look for opportunities to reduce

heating time, cooling time and other cycle stages to save energy. The control of process parameters gives huge savings and good practice is that only just enough energy is used at each stage to complete the stage.

Reducing the platen clamp force will reduce hydraulic system use in the cooling step.

• Tip – The demands on the hydraulic

system are much less complicated on EBMMs than on IMMs. This is an ideal application for VSDs but nobody seems to be producing retrofit hydraulic kits for EBMMs. Why not? The formation of the blown parison in the mould must be complete before the outside surface chills and stops surface texture formation. This can mean large transient requirements for compressed air at high pressures. • Tip – Investigate the use of

accumulators to cope with high transient demands for compressed air. During the blowing phase the compressed air pressure should be sufficient to get full contact of the parison with the mould surface but should not be excessive. After blowing is complete, the compressed air pressure can be reduced so that it is just sufficient to hold the product against the mould to get the best cooling rate. Chapter 5 – Processing

The principle of parison control in EBM Good parison control is the key to reducing product weight by changing material distribution in the part. Not all areas are blown to the same extent and the wall thickness can vary widely across the part. Parison control puts the material where it is needed. 265

5.28

Extrusion blow moulding – heating and cooling

Extrusion heating EBMMs tend to produce less shear heating than conventional extruders and will generally benefit more from barrel insulation than conventional extrusion machines (see Section 5.18). As with conventional extrusion machines, shear heat will be negligible downstream of the screw tips and almost all of the material flow components downstream of the screw tips will benefit from insulation. One issue with EBMMs is that the area downstream of the screw tips is often crowded with other equipment and insulation is both difficult to fix and retain in position. Sites should therefore take a pragmatic approach and only attempt to insulate areas that are easy to access and have sufficient space for insulation. A typical example is shown on the lower right where the adaptor plate is clearly radiating heat (it is at 184°C) and where insulation could be easily applied. • Tip – Only attempt insulation where it

is easy and practical to apply. One area that is worthwhile investigating is the thermal isolation of the parison extrusion heads from the main EBMM body. When the heads are not thermally isolated then considerable heat will be lost to the main machine body by simple conduction through the metal fastenings. • Tip – Check the thermal isolation of the

extruder heads from the main machine body and improve if possible.

should check the temperatures in the area before attempting insulation and select an insulation material that can withstand the temperature. • Tip – Insulate cooling water hoses where

this can be done easily and safely. EBM dies are cooled with chilled water and are rarely insulated to prevent parasitic heat gain from the atmosphere. Dies can gain considerable amounts of heat from the atmosphere or from the rest of the machine. Heat gain from the atmosphere is illustrated in the middle photograph on the opposite page. This shows the effect of cooling the entire die block to provide cooling for the blown product. The entire platen is at ≈ 12°C and this is suffering from parasitic heat gain from the atmosphere which was 28°C in this case. This raises the cooling load on the chillers and increases energy use. Simple, flat insulation on the outer faces of the die block can dramatically decrease the amount of parasitic heat gain to the cooling water system. • Tip – Insulate flat surfaces of the die

block with flat insulation board to reduce parasitic heat gain to the chilled water system. The die block will not only gain heat from the atmosphere but also from the main machine via the rear platen if the die block is not insulated from the rear platen. Heat transfer will occur between the

Cooling of the product will define the cycle time for EBM (as with many other processes). It pays to get it right.

EUROMAP (see Section 5.14) has produced: • EUROMAP 46.1 (Determination of Machine Related Energy Efficiency Class) for EBMMs. • EUROMAP 46.2 (Determination of Product Related Energy Consumption) for blow mouldings. These recommendations are much more robust than those for IMMs.

Cooling Reducing parasitic heat gain In addition to heat losses from the hot components, EBMMs tend to suffer from heat gains to the process cooling water and again little is done because the machines tend to have little space for improvements. Reducing parasitic heat gain will not affect the energy use at the EBMM but will reduce services use in cooling water. Cooling water hoses are rarely insulated and will suffer from parasitic heat gain (see upper photograph on the opposite page). Standard insulation of these hoses may not have sufficient heat resistance due to the temperature of the area. Sites

266

Uninsulated and hot extrusion adapter on EBMM There will be very little shear heating forward of the screw tip and all the adapter plates and feeds to the parison heads will be electrically heated. Insulation applied here can save energy and make the site cooler. Chapter 5 – Processing

cooled die block and the machine platens. This is shown in the lower photograph on the right. • Tip – Use insulation between the die

block and the machine platens to prevent heat transfer between the cold die block and the machine. • Tip – Brandenburger makes excellent

products to insulate the die from the machine and for external die insulation (see ks.brandenburger.de/images/ download/iso-fachartikel/ Kunststoffe_Int_PE_5_09.pdf).

Cooling efficiency The process efficiency of the mould cooling affects both the time taken and the energy used in the process and can be a major barrier to increased productivity. Despite this, cooling the mould too much can be counter productive – a mould that is too cold can give rise to condensation in the mould and water marks on the surface of the product. A general minimum mould temperature of ≈ 5°C is recommended.

Uninsulated cooling water hoses on EBMM The cooling water pipes for the dies are rarely insulated even thought they are in a very hot area. Simple low-cost insulation on these lines will reduce parasitic heat gain and save energy at the chillers.

• Tip – Increase the demoulding

temperature until the maximum for good product is reached – with good parison control there will be limited differential shrinkage and de-moulding is possible at higher temperatures. • Tip – It is possible to demould quickly

from the main mould and use postcooling with water-cooled contour clamps in critical areas.

Uninsulated dies on EBMM The dies are large masses of metal that are cooled with chilled water. These often show condensation due to their low temperature. Simple insulation on the exposed faces of the die will reduce parasitic heat gain and save energy at the chillers.

Side view of uninsulated die on EBMM The chilled section of the die is clearly visible but the rear platen is also very cold due to heat transfer. Insulating the tool from the rest of the machine will reduce the cooling load on the system. This die could also easily be insulated on the exposed faces. Chapter 5 – Processing

267

Extrusion blow moulding – tops and tails management

• Tip – Continue to monitor the weight of

tops and tails on a regular basis. • Tip – Do not be confused by the low

volume of the tops and tails versus the high volume of the actual product. Tops and tails are solid whereas the product is largely air. Measure the weights of the tops and tails and the actual product to get the real values.

Taking action If the site result for tops and tails is over 30% then action needs to be taken to reduce the amount of tops and tails.

Step 1 Use the calculated tops and tails values (see above) to find the minimum achieved at the site. Set this minimum as the target for all future production on all future machines. This has already been achieved by the site and can be regarded as a realistic target. Note: All machines and dies are different Tops and tails (% of extrusion weight) 40% 35%

The industry average for tops and tails is between 30–40% (relative to the total volume of extruded plastic) and the global relative industry performance for tops and tails is shown on the right.

30%

268

Sample size: 87 EBM machines

25% 20% 15% 10% 5%

% 90 –1 00

80 –9 0%

70 –8 0%

60 –7 0%

10 %

0% 0–

This shows that a substantial amount of the industry (26%) achieves under 30% tops and tails and some have reduced this to under 10%. Tops and tails cannot be eliminated entirely (5–10% is a realistic lower limit) but for companies that are average (≈ 35%) or above average in terms of tops and tails management there is much that can be done to improve productivity and performance. Achieving reasonable levels of tops and tails (in the region of 10%) will result in an average increase in productivity of

% of machines

The magnitude of the problem

50 –6 0%

Although a certain amount of tops and tails are necessary for the EBM process, minimising the amount produced will prevent energy being used to heat and process plastic that is not incorporated into the finished product and will therefore improve the energy efficiency of the process.

tails being produced by each machine and tool combination. Be prepared for a surprise at some of the high levels of tops and tails.

40 –5 0%

This recycling argument is fundamentally flawed at many levels: • It costs money to operate the machine. • It costs money to heat, process and cool the material in the tops and tails even if the material itself is recycled. • It costs money to regranulate the material because conveyors, granulators, blowers, pumps and blenders do not operate for free. The material may well be recycled and recovered but the energy and production time used to produce these is lost forever. Energy and production time cannot be recycled. Large tops and tails cost real money even if the material is recycled.

Large tops and tails represent a loss of productive capacity to a site.

• Tip – Calculate the amount of tops and

30 –4 0%

Tops and tails are an easily overlooked opportunity for increasing the energy efficiency of EBM. In most companies, they are considered to be ‘part of the process’ and any discussion about tops and tails is usually cut short by the comment that ‘it is all recycled anyway’.

around 30% and an energy use decrease of an equivalent amount for a substantial part of the process.

20 –3 0%

Process waste

10 –2 0%

5.29

Tops and tails as % of total extrusion weight

Tops and tails by weight The amount of tops and tails produced varies with the site. The chart gives the best estimate of the industry performance of tops and tails as a % of the total extruded weight. Sites should check their performance against this benchmark for tops and tails. Chapter 5 – Processing

but you need to start somewhere and targets should be aggressive but achievable. • Tip – Specify the allowable weight of

tops and tails on the basis of the current minimum achieved.

Step 2 After all machines have achieved the target then reduce the target tops and tails weight and start again with a global target of < 20%. Process changes and development may be necessary to improve the tops and tails weight. Many current machines and processes are not optimised for reducing tops and tails because the machine manufacturers do not appear to be worried by tops and tails. In fact, some machines demand large tops and tails for product transport. The process for this type of machine needs to be critically examined. • Tip – Process development may be

necessary but if you want to be the same as all of your competitors then don’t worry about it. Setting sheets for EBM must include the specification and measurement of the amount of tops and tails produced. It is not enough for a setter to simply get a machine running; the amount of tops and tails produced is a key economic indicator of the process performance and must be part of the setting process and part of the assessment of the machine and process performance. • Tip – Tops and tails weights must be

part of the control measurements for the process.

Machine side regranulators for EBM will typically have a minimum of a 1-kW conveyor, a 7–11-kW grinder and a 2.2-kW blower for transfer to the regrind bin and blending with the virgin material – a total of approximately 14 kW and an operating cost of approximately £1.40/hour. Reducing tops and tails to the 10% level means that it can cost over £0.89/kg to recycle the tops and tails (see table below for an example calculation). At these cost levels the site can choose between two options: • Centrally regrind at night to take advantage of lower energy costs and to reduce energy costs by full machine utilisation. The regrind can then be used in specific products or fed back into the process on the next run. • Sell the tops and tails at commercial prices to a contractor and remove the regranulation process entirely from the site. Either choice will enable a site to be tidied up, energy consumption to be reduced and productivity to be increased.

Tops and tails management in EBM is critical to both energy use and productivity. It is not accurate to think that because all the tops and tails are ‘recycled’ that there is no waste in the process.

Reduce and then recycle.

Note: Regranulators are rarely linked to machine operations and will normally be continuously on even when the machine is not running so that true cost of running the regranulator will probably be higher than indicated (see Section 5.52 for more details of reducing energy use in regranulation). • Tip – Tops and tails management is a

topic that any EBM site should investigate with some urgency for all machines.

• Tip – Improved parison control (see

Section 5.27) is a key to improving and reducing tops and tails. Thin the parison in the tops and tails areas to reduce the material used?

Product

Top and tails must be minimised to reduce energy use and improve productivity.

Recycling cost (£)

• Tip – Measure the weight of the parison

and the tops and tails and control these using SPC.

Machine-side regranulation One ignored aspect of tops and tails management is that as the amount of tops and tails decreases it becomes less economic to recycle the tops and tails at the side of the machine. This almost paradoxical result comes from the fact that operating a regranulator has an almost constant cost and as the material throughput deceases then the unit cost/kg of regrind increases. Chapter 5 – Processing

Product (kg)

Tops Material Cost of % tops Cost of and recycled regranulaand recycling tails per hour tor tails (£/kg) (kg) (kg) (£/hour)

0.120

0.080

40%

9.60

1.40

0.1458

0.120

0.013

10%

1.56

1.40

0.8974

Reducing the amount of top and tails Reducing the amount of tops and tails decreases the throughput of the regranulation area but the cost of regranulation remains the same. The cost of recycling starts to approach the cost of virgin material and changes the approach to regranulation. 269

5.30

Extrusion blow moulding – where are you now?

The initial steps in extrusion blow moulding

moulding and will affect the whole basis of energy use in the sector.

As with the score charts shown earlier, this is a self-assessment exercise to allow a site to benchmark their current status in extrusion blow moulding.

Completing the chart This chart is completed and assessed as for those presented previously.

Transport of finished EBM products should also be considered for energy reduction activities. The products tend to be light but bulky and it is always tempting to use compressed air for product movement.

Extrusion blow moulding needs many of the controls associated with conventional extrusion but good parison control and careful process setting to minimise tops and tails are the keys to both minimising energy use and maximising process productivity.

Don’t!

All-electric machines are also now becoming available for extrusion blow

Extrusion blow moulding Monitoring & setting 4 3 2 Blowing & cooling

Barrel insulation

1 0

Tops & tails management

All-electric machines If a polyolefin EBM product is to be printed then pretreatment will be necessary.

Use the scoring chart to assess where you are in extrusion blow moulding The numbers from the scoring chart can be transferred to the radar chart for a quick visual assessment of where you are in terms of extrusion blow moulding. 270

Flamers (if used) should be well controlled to minimise gas use.

Chapter 5 – Processing

Extrusion blow moulding Level

4

3

2

Monitoring & setting

Barrel insulation

All-electric machines

Score

Blowing & cooling

Machine settings checked & validated against best practice. Most machines monitored for energy efficiency & performance.

Full barrel insulation in All-electric machines Tops & tails minimised & recorded for all good condition. are over 50% of New-generation barrel applicable machines & products before job released. insulation used. are default purchase Setters have close Very little heat lost to option for all new the surrounding area. machines. targets for tops & tails. No job released until targets met.

Very few machine settings show deviations from good practice. Some machines monitored for energy efficiency & performance.

Full barrel insulation in All-electric machines Tops & tails minimised Accumulators minimise poor condition with are less than 50% of for most products transient air demands. visible degradation of applicable machines. before job released. Blow & hold pressures insulation material. Purchase of all-electric Setters given targets reduced. but often overridden by Increased demould machines is still subject regarded as desire to get job into temperature. 'advanced'. production.

Partial barrel insulation Small number of machine settings show in good condition. deviations from good Reduced amounts of heat lost to surrounding practice. No machines area. monitored for energy efficiency & performance.

Accumulators minimise transient air demands. Blow & hold pressures checked & minimised. Optimum demould temperature.

All-electric machine under evaluation as test before full implementation.

Tops & tails minimised Small accumulator – for some products large transient air before job released. demands. Setters given targets Blow & hold pressures but not controlled or reduced. recorded. Moderate demould temperature.

Significant number of Partial barrel insulation All-electric machines machine settings show in poor condition. considered but not deviations from good Moderate amounts of purchased. heat lost to general site practice. area.

Tops & tails No accumulator – high management transient air demands. considered but not Blow & hold pressures implemented. reduced. Tops & tails Low demould uncontrolled. temperature used. Setters look at tops & tails but main task is starting machine.

1

0

Tops & tails management

Most machine settings Barrel guarding but no All-electric machines No concept of tops & not considered despite show deviation from barrel insulation. tails management. good practice or Large amounts of heat being applicable for the Tops & tails recommended values. lost from uninsulated operations. uncontrolled. barrel to site. Setters task is to simply get the job running.

x

Chapter 5 – Processing

x

x

x

No accumulator – high transient air demands. High blow & hold pressures used. Very low demould temperature used.

x 271

5.31

Injection blow moulding

A growing market Injection blow moulding (IBM) is a growing market due to the increasing popularity of the process for pharmaceutical and cosmetics containers.

reliability because of the small number of machines measured. The available data shows the same type of SEC variation with production rate as do all of the other

As with other processes, the introduction of all-electric injection blow moulding machines (IBMMs) has changed the basis of energy use in IBM. All-electric IBMMs are not yet as common as all-electric IMMs but have all the advantages of allelectric IMMs described in Section 5.9. Most manufacturers of IBMMs now offer an all-electric option and sites should investigate these. • Tip – Purchase all-electric IBMMs when

they are suitable for the product.

PCLs, SEC and benchmarking

Integrated IBM process IBM is often carried out on a three-station rotary turntable. The turntable can produce multiple products (only one is shown for clarity). After pre-form injection, the turntable is rotated for the blow operation and then rotated again for part removal. Power drawn in IBM 80

60

Power (kW)

The basic IBM process is an integrated three-step process generally carried out on a rotating table. The first step is the injection moulding of a pre-form to the basic shape of the container. The table then rotates the pre-forms and the second step is the blowing of the pre-form in the final mould to form the product. The table rotates again and the third step is the removal of the finished product. This process is shown on the upper right. The integration of the process so that the pre-form is blown immediately after the injection phase considerably reduces the energy required for the process because the pre-form is still hot from the injection process and does not need a large energy input to heat it up prior to blowing. IBM has an advantage over EBM for small products because no tops and tails are produced in the IBM process, i.e., all of the injection moulded parison is used for the final product.

40

There is little industry data available for the IBM process at the site level because many sites use both IBM and injection moulding. It is therefore difficult to separate the effects of the two processes. However, it is estimated that the process load at the site level is in the region of 2.4 kWh/kg although this has a low reliability.

IBMM with average base load (72% of average load)

There is equally a poor amount of industry data for the IBM process at the machine level. The best available data are shown in Section 2.19 but this also has a low

IBMMs are very similar to IMMs and a typical hydraulic IBMM has a base load in the region of 70–80% of the average load. This machine has a base load of 72% and shows a consistent cycle with a regular peak load and a regular cycle.

272

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Base load 0 00:00

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Chapter 5 – Processing

processes examined but the scatter is larger. The available data also shows that IBMMs perform very much as do IMMs and can be fitted to the IMM benchmark curve. This is understandable as most of the energy use in the process is in the operation of the injection unit. • Tip – There is a need for more industry

data for IBM. Use Appendix 1 to contribute your site and machine data.

Process energy use Measurements made on IBMMs show similar traces to that of IMMs and a typical trace is show on the lower left. This shows a very similar trace to that of an IMM with a base load of 72% (typical for an IMM) and a regular cyclic load as the injection phase takes place. The base load for an IBMM would be expected to be slightly higher than that of an IMM because of the higher base load of operating the blowing process and associated heating.

Uninsulated barrel of IBMM Despite the presence of the safety guarding, the heat and energy losses on the barrel of this machine are clearly seen in the thermograph. These will be significant and will increase energy use and costs.

Barrel insulation As with conventional injection moulding (see Section 5.10), the use of barrel insulation is highly recommended for IBMMs and the effect of insulation is shown in the upper and middle photographs on the right for the IBM process. The uninsulated barrel is safety guarded but is emitting large amounts of heat to the atmosphere. The insulated barrel is much cooler and will not use as much energy in the process heating. • Tip – Barrel insulation of IBMMs is

strongly recommended.

Insulated barrel of IBMM Energy is being saved by the presence of insulation and losses are only seen at the junctions of the insulation. This machine will be more energy-efficient. Note that no safety guarding is necessary when insulation is used.

Temperature control The IBM process often uses heated moulds for the pre-form blowing phase to avoid cooling of the part and difficulty in blowing the product. These are normally conventional MTCs running oil for heating at ≈ 125°. These are very hot and often uninsulated (see Section 5.11). • Tip – Insulate MTC pipes to reduce the

energy used in mould heating. MTCs are not the only area in IBM where heat is used poorly. Sites often have heating and cooling in the same area and do not manage the heat well. Insulation and good process control are needed. • Tip – Heat management should be

improved at most IBM sites.

Chapter 5 – Processing

Uninsulated oil MTCs for IBM The mould temperature controllers use oil to keep the mould hot at ≈ 125°C. These pipes are not only a waste of energy but also a health and safety concern. Fit insulation to all pipes such as these. 273

5.32

Injection blow moulding – where are you now?

The initial steps in injection blow moulding As with the score charts shown earlier, this is a self-assessment exercise to allow a site to benchmark their current status in IBM. IBM shares many technological characteristics with conventional injection moulding. Many of the techniques for reducing energy use in injection moulding can be simply and directly transferred to IBM. These include improved setting, barrel insulation, improved motors and drives, all-electric machines, improved control of ancillaries and improvements in tool design. The additional blowing step

needs control but does not add much to the direct energy use of the machine, although it adds it through the increased use of services such as compressed air for blowing.

Completing the chart This chart is completed and assessed as for those presented previously.

IBM is primarily a process used for packaging and the margins are very low. Even small improvements in energy use can affect a site’s profitability.

Injection blow moulding

Monitoring & setting 4 3 2 Tool design

Barrel insulation

1 0

Mould temperature controllers

All-electric machines

Use the scoring chart to assess where you are in IBM The numbers from the scoring chart can be transferred to the radar chart for a quick visual assessment of where you are in terms of IBM. 274

Some suppliers have decided to avoid all-electric and to go for a servo approach to run the hydraulics. This can also reduce energy use significantly in the IBM process.

Chapter 5 – Processing

Injection blow moulding Level

4

3

2

Monitoring & setting

Machine settings checked & validated against best practice. Most machines monitored for energy efficiency & performance.

Very few machine settings show deviations from good practice. Some machines monitored for energy efficiency & performance.

Barrel insulation

All-electric machines

Mould Tool temperature design controllers Full barrel insulation in All-electric machines MTCs only used when Tool design takes good condition. are over 50% of absolutely necessary. energy into account in New-generation barrel applicable machines & Use is controlled by all areas. insulation used. are default purchase setting sheets. Compressed air use is Very little heat lost to option for all new All hoses are well small & controlled. the surrounding area. machines. insulated to reduce Good control & use of heat transfer. cooling.

Full barrel insulation in All-electric machines MTCs theoretically only Tool design takes poor condition with are less than 50% of used when necessary productivity & energy visible degradation of applicable machines. but actual use is poor. into account but there insulation material. Purchase of all-electric All hoses are well is some poor use of machines is still insulated to reduce services in the process. subject regarded as heat transfer. 'advanced'.

Partial barrel insulation Small number of machine settings show in good condition. deviations from good Reduced amounts of heat lost to surrounding practice. No machines area. monitored for energy efficiency & performance.

All-electric machine under evaluation as test before full implementation.

Significant number of Partial barrel insulation All-electric machines machine settings show in poor condition. considered but not deviations from good Moderate amounts of purchased. heat lost to general site practice. area.

MTCs used on some tools & use is uncontrolled. Large heat losses through the use of uninsulated & poorly chosen hoses.

Energy efficiency is minor consideration in tooling. Tool design uses services very poorly.

Most machine settings Barrel guarding but no All-electric machines not considered despite barrel insulation. show deviation from good practice or Large amounts of heat being applicable for the recommended values. lost from uninsulated operations. barrel to site.

MTCs used on most tools & use is uncontrolled. Large heat losses through the use of uninsulated & poorly chosen hoses.

Energy not considered in tooling. Mould heating & cooling work against one another. Tool uses compressed air for many actions.

x

x

1

0

Score

MTCs theoretically only Tool design is good for used when necessary productivity but poor for but actual use is poor. energy through the No insulation on hoses poor use of services. & heat transfer is significant.

x

Chapter 5 – Processing

x

x

275

5.33

Injection stretch blow moulding – general and moulding

Clearly better Injection stretch blow moulding is a growing market due to the increasing popularity of the process for crystal-clear drinks containers, although it is now also being used for a variety of other products such as food containers. The basic ISBM process is a two-step process that is discontinuous, i.e., there is no linking of the two steps. The first step is the injection moulding of a ‘pre-form’ to the basic shape of the container (including the threaded top of the container). The second step is the heating of the body of the pre-form (generally with infrared heaters) and the use of a core rod and high-pressure air to stretch and blow the hot pre-form in the final mould. ISBM is similar to IBM in that no tops and tails are produced in the process. All of the material injection moulded into the pre-form is used for the final product.

needed for energy use minimisation. This energy distribution is only for the main IMM and drying and does not include centrally provided services such as compressed air (low or high pressure) and chilled water. Drying may be carried out by the machine or centrally and has been included here at the IMM level to show

IMMs 20%

Driers 6% Chillers 11%

Blowing machines 25%

Other 2% Compressed air (high pressure) 30%

Compressed air (low pressure) 6%

Site energy use The energy use breakdown at a typical ISBM site producing complete bottles is shown on the upper right. The processing load (the actual injection and blowing machines) is significant and is ≈ 45% of the total energy use. However, the services loads are even higher, particularly for high-pressure compressed air (30–40 bar) which can use up to 30% of the total site energy. The services are particularly productive for improvement projects at most ISBM sites. This is particularly the case for high-pressure compressed air where small efficiency improvements can have a large effect.

Energy use breakdown at a typical ISBM site Processing (moulding and blowing) uses a lot of energy at an ISBM site but the total of the services loads is higher than these. This is due to the high energy use in the production of highpressure air for the blowing step.

Dryer regeneration 2%

Mould dehumidifier 3%

Drier operation 24%

Machine energy use The energy use breakdown for a typical IMM producing PET pre-forms is shown on the lower right and the IMM is the largest energy use. Moulding of the pre-forms needs dried PET and the drying load in pre-form production is significant. The high use of energy for drying (≈ 26% including regeneration of the desiccant when desiccant dryers are used) is a result of the very low moisture level needed to process PET and good control of dryers is 276

Hot runner controller 10%

IMM 61%

Energy use breakdown for a typical PET pre-form IMM At the IMM level, the loads for drying and the hot runner controllers are very significant and represents 36% of the total machine load. Effective control of dryers and hot runners is essential to minimise energy use. Chapter 5 – Processing

the high energy demand of drying.

Pre-form production Pre-form production is a standard injection moulding operation but the production rates are typically very much higher (in kg/h) than standard injection moulding. This makes the machines appear very energy-efficient in comparison to standard IMMs because the base load of the IMM is amortised into a very large process load.

step can be carried out using the data provided in Section 2.18 and the IMMs used will normally appear very efficient using this benchmark because of the high production rates. In fact, in some cases, the production rates are so high that the conventional benchmarking process fails to predict the actual SEC of these machines.

As with conventional IMMs (see Section 5.9), all-electric IMMs are now available for pre-form production and these are considerably more energy-efficient than conventional hydraulic IMMs.

Power drawn for dryers (including regeneration) for ISBM 80 70

• Tip – Sites should carry out all of the

Dryer loads The dryer load for PET pre-form production is very high and a typical dryer power load is shown in the chart on the upper right. This chart is for the complete dryer load and includes the transition from desiccant regeneration (the left section of the chart) to conventional operation (the right section of the chart). Regeneration will take ≈ 25% of the cycle time and will add significantly to the dryer load, in the example shown it adds ≈ 6 kW or 14% of the load. Good management of the drying process is essential for energy-efficient ISBM.

60

Power (kW)

energy use reduction activities for standard injection moulding (see Sections 5.2 to 5.14).

Recycled PET scrap can easily be reground for reuse but the material needs to be recrystallised before re-use. Recrystallisation and drying can be combined by the use of infrared drying (see Section 4.47) to reduce energy use.

50 40 30 20 10 0 00:00

05:00 Time (min:s)

10:00

Power drawn for dryers in ISBM The power drawn for the complete dryer operation in ISBM is significant but is not constant. In this example, the average load is ≈ 48 kW. Note the transition from regeneration (left) to standard operation (right) at around 5 minutes.

• Tip – Sites should carry out all of the

Power drawn for hot runners for ISBM

energy use reduction activities for drying (see Sections 4.42 to 4.48).

40

• Tip – Dryer operation also sometimes

has very short and high power spikes at operating cycle transitions. Most IMMs used for ISBM will need to be fitted with hot runners. A typical chart of the power drawn by hot runners is shown on the lower right. The size of the hot runners needed means that these will add significantly to the total operating load (typically 10%). Good management of hot runners is essential for energy-efficient ISBM. • Tip – Sites should look at the

management of hot runners to minimise energy use in ISBM.

Benchmarking Benchmarking of the pre-form production Chapter 5 – Processing

Power (kW)

Hot runners

30

20

10

0 00:00 05:00 10:00 15:00 20:00 25:00 30:00 35:00 40:00 45:00 50:00 55:00 Time (min:s)

Power drawn for hot runners in ISBM The power drawn for hot runners in ISBM is significant in ISBM and this fluctuates with time. In this example, the hot runners draw an average of 19 kW but this peaks at ≈ 31 kW. This is not a negligible load (and is 10% of the total). 277

Injection stretch blow moulding – blowing

Blowing step The blowing step is discontinuous and the pre-forms are normally produced, stored and later reheated/conditioned before stretching and blowing. In some cases, the pre-forms are transported to another site before blowing to reduce transport costs. Blowing is carried out by heating the preform to ≈ 100°C and applying highpressure compressed air (30–40 bar) before cooling and despatch.

Blowing machines The blowing step uses infrared heating to re-heat the pre-form and allow it to be blown to the required shape. The heaters are the main energy use in the actual blow machine because these have to have enough output to adequately warm the pre-form rapidly and uniformly. Power traces for these machines will not show a cyclic demand due to the high production speeds and the continuous nature of the process. This is typically a minimum of 4,500 bottles/hour with some blowers capable of operating at more than 25,000 bottles/hour. A typical power graph is shown on the right for a blower operating at 22,000 bottles/hour. The graph shows some noncyclic variation due to natural machine and heater variations – this is not the same as the injection moulding cycle. The later section of the graph shows the blower operating, i.e., producing bottles. In the production state, the blower drew an average of ≈ 151 kW (machine and IR heaters only). The initial section of the chart shows a blower that is dry cycling, i.e., machine running but no product present. In the non-production dry cycling state the blower drew an average of ≈ 50 kW. • Tip – Dry cycling is not free and costs

real money. Despite this obvious truth, many ISBM sites routinely dry cycle blowers with no thought about the cost of running the machine and IR heaters. For the blower shown on the right the energy used was 6.86 Wh/bottle (excluding services use). The value is given in Wh/ bottle because of measurement uncertainties in the mass of material processed. This is slightly higher than 278

other machines where the average energy required is closer to 5.00 Wh/bottle. Obviously the size of the bottle has an effect in the amount of IR heating required but sites can use this as an approximate benchmark for the blowing step (excluding services use).

Optimisation of the pre-form reheating process before blowing can reduce energy use by up to 20%.

• Tip – IR heaters should be optimised for

the material. New-generation reflector lamps can reduce heating costs by up to 18%.

Benchmarking There is very little industry data available for the blowing step at the machine level but monitored results indicate an energy intensity of ≈ 0.25 kWh/kg for the blowing step alone. This is generally much the same as the energy intensity of the injection step for ISBM. A lack of production rate-related data and the fact that no comparable information in any other literature has been found makes it impossible to produce an operating curve at either the process or the machine level. It is still considered that energy use (SEC) in the blowing process, at the machine level, will be production rate sensitive but the available data do not allow verification of this. • Tip – There is a need for more industry

Dry cycling of blowing machines is very expensive, especially if the infrared lamps are left on.

Power drawn for blow step in ISBM (dry cycling and running) 180 160 140 120 Power (kW)

5.34

100 80 60 40 20 0 00:00

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25:00

30:00

35:00

Power drawn for a blowing machine The power drawn for a blowing machine is relatively constant due to the rapid cycle time of the process. The cost of dry cycling a blowing machine will be significant (left section of the graph) and will be up to 30% of the cost of productive operations. Chapter 5 – Processing

data for ISBM. Use Appendix 1 to contribute your site and machine data.

Compressed air in blowing The blow step of ISBM requires compressed air at 30–40 bar and this is therefore much more costly than conventional low-pressure compressed air at 6–8 bar because compressed air costs more to generate at higher pressure (see Section 4.28). The cost of the highpressure compressed air is ≈ 30% of the energy cost for an ISBM site (see Section 5.33). High-pressure compressors are more complex than low-pressure compressors and often have several ‘stages’ as the pressure of the air is increased. Despite this, high-pressure compressors still suffer from operating ‘on-load’ and ‘off-load’ as do standard low-pressure systems. The chart on the right shows a typical high-pressure compressor operating at 35 bar. The cycling of the system is easily seen and the compressor draws an average of 244 kW over the period. The ‘on-load’ demand is 321 kW but the ‘off-load’ demand is 98 kW for ≈ 10% of the time. As for low-pressure systems, it is possible to fit VSDs to highpressure systems either as original equipment or as retro-fit packs. These slow the compressor down to match the demand and save energy and money. Note 1: For the site considered a retro-fit VSD would have a pay-back of 2 years. Note 2: For the site considered there was also a 132-kW high-pressure compressor operating ‘off-load’ all the time and consistently drawing 30 kW. A good VSD and control system would totally eliminate this load.

all the hoses and fittings and these should only be worked on if the system is completely discharged. Health and safety precautions must be followed. • Tip – Leakage is generally less of a

problem with high-pressure systems. These systems are managed by professionals and leaks are so obvious that they tend to be fixed quickly. Sites need to allocate compressed air costs correctly if ISBM is being carried out at sites where there are other processes and the ISBM process must bear the costs of the high-pressure compressed air generation for accurate cost allocation (see Section 4.25). used for ISBM are correctly allocated to give correct costings.

Integrated processing The two-step ISBM process has been modified by various companies to provide a continuous one-step process, e.g., Aoki, ASB Nissei, Cypet. These produce PET containers in a single step, as does the new process of compression blow forming (CBF) developed by Sacmi. These all claim to use less energy for the same product. Perhaps the most innovative approach is LiquiForm, developed by Amcor and Sidel, which removes the use of compressed air for the blow step and uses the incompressible fill liquid to blow and fill the bottle at the same time. Great idea and a potential game changer for ISBM. High-pressure compressor cycling in ISBM 400 350

Power (kW)

300 250 200 150

• Tip – VSDs and good control systems are

100

needed to minimise energy use and cost in the production of high-pressure compressed air for the blowing step.

50

• Tip – Sites should carry out all of the

energy use reduction activities for compressed air (see Sections 4.24 to 4.31) to minimise the cost of high-pressure compressed air. • Tip – High-pressure compressed air is

extremely dangerous and must be treated with great caution. This includes Chapter 5 – Processing

This could be one of the most valuable actions to take in ISBM.

• Tip – Ensure that the costs of services

• Tip – It is possible to recover the high-

pressure blow air for use in other areas of the machine as low-pressure air. • Tip – Local receivers at blowing machines will minimise transient pressure fluctuations.

Investigate the use of VSDs (new or retrofit) for highpressure compressors in ISBM.

0 00:00

01:00

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04:00

05:00

On-load and off-load high-pressure blowing compressor This high-pressure compressor draws an average of 244 kW but this conceals the fact that it draws 98 kW when off-load and producing no compressed air for the blow step. 279

5.35

Injection stretch blow moulding – where are you now?

The initial steps in injection blow moulding As with the score charts shown earlier, this is a self-assessment exercise to allow a site to benchmark their current status in ISBM. ISBM shares many technology characteristics with conventional injection moulding. Many of the techniques for reducing energy use in injection moulding can be simply and directly transferred to ISBM. These include improved setting, barrel insulation and all-electric machines.

energy management improvements ranging from how blow air is generated and used through to how the IR heaters are specified and controlled. When injection blow moulding PET, the regranulation and recrystallisation of the regranulated material can be improved by new drying methods that combine the two processes.

Completing the chart This chart is completed and assessed as for those presented previously.

The blow step of ISBM is also an area for

Injection stretch blow moulding Polymer drying 4 3 Regranulation & recrystallisation (PET)

2

Barrel insulation

1 0

Blowing & cooling

Monitoring & setting

Blowing machines in the ISBM process will often give off large amounts of rejected heat through exhausts.

Compressed air generation

Use the scoring chart to assess where you are in ISBM The numbers from the scoring chart can be transferred to the radar chart for a quick visual assessment of where you are in terms of ISBM. 280

The fans need to be controlled and the possibility of recovering the excess heat (air to air heat exchangers) for pre-warming of the pre-forms should be investigated.

Chapter 5 – Processing

Injection stretch blow moulding Level

4

3

2

1

0

Polymer drying

Barrel insulation

Monitoring & setting

Compressed air generation

Systems based on Full barrel Machine settings System sized & best performance insulation in good checked & controlled to for current condition. validated against minimise cycling & requirements. New-generation best practice. control pressure. Dew point of barrel insulation Most machines Minimum system drying air well used. demand known & monitored for Very little heat lost energy efficiency controlled for delivered. optimum drying to the surrounding & performance. Good air receiver energy use. capacity. area.

Regranulation & recrystallisation (PET) Accumulators Regranulation minimise transient automatically air demands. controlled to operate only when Blow & hold pressures checked needed. & minimised. Drying & recrystallisation are combined in one-step process. Blowing & cooling

Systems based on Very few machine System size OK Full barrel Accumulators Regranulation good performance insulation in poor settings show but poor control. minimise transient manually operated only when needed for current condition with air demands. deviations from Minimum system visible degradation good practice. requirements. demand Blow & hold & controls are Dew point of of insulation pressures Some machines approximately good. drying air poorly material. reduced. Drying & monitored for known but poorly controlled. energy efficiency controlled. recrystallisation & performance. Adequate air are combined in receiver capacity. one-step process.

Systems based on Partial barrel Small number of System correctly Small accumulator Regranulation previous insulation in good machine settings – large transient manually operated sized but poor only when needed requirements. condition. show deviations control & cycling air demands. Reduced amounts Dew point of & controls are from good when not required. Blow & hold drying air good. of heat lost to practice. System demand pressures measured but not surrounding area. No machines only vaguely Drying process reduced. controlled. separate from monitored for known. recrystallisation energy efficiency Poor air receiver & performance. capacity. process.

Significant number Systems selected System badly Partial barrel No accumulator – Regranulator based on previous insulation in poor of machine sized & poorly high transient air manually operated controlled, cycling only when needed settings show requirements & condition. demands. poor for current Moderate amounts deviations from when not required. Blow & hold but controls are good practice. requirements. System demand pressures poor. of heat lost to Dew point of general site area. unknown. reduced. Drying process drying air Air receiver separate from considered but not inadequate for recrystallisation measured. demand. process.

Systems selected Barrel guarding based on previous but no barrel requirements & insulation. unsuitable for Large amounts of current heat lost from requirements. uninsulated barrel Dew point of to site. drying air not considered or measured.

Most machine settings show deviation from good practice or recommended values.

System oversize, No accumulator – Regranulator idling when not high transient air operates required & cycling demands. continuously due to poor High blow & hold whether needed or controls. pressures used. not. System demand & Drying process minimum pressure separate from needed unknown. recrystallisation Warm air intake. process.

Score Chapter 5 – Processing

281

5.36

Thermoforming – general and pre-heating

An energy-intensive process Only the basic thermoforming operation is considered in these sections and the extrusion of the basic sheet is covered in Section 5.21. Thermoforming is an energyintensive process wherever the boundaries are set, the process heats the extruded sheet, forms the sheet in matched moulds and then crops the forms from the sheet stock. Approximately 90% of the energy input to thermoformers will be used to heat the sheet before forming, and control of the heating sections is a major task for thermoformers. As with any energyintensive capital equipment, the cost of the energy used in the lifetime of a thermoforming line will far exceed the initial capital cost of the line. The basic process options are shown below; these are similar in the main heating area and differ only in the presence or absence of pre-heating and the option of thermoforming direct from the extrusion line or from roll stock. • Tip – EUROMAP is currently working

on EUROMAP 100 to define the energy efficiency of thermoforming machines. This will allow thermoformers to be rated as for IMMs (see Section 5.14).

Simple thermographic examination of prewarming cabinets, heater banks and other heating areas will show where heat losses are occurring and enable targeting of improved sealing and insulation.

Material preparation An area that is often neglected by thermoformers is the basic preparation of the feedstock. When using roll stock, it is essential that the roll stock is at a consistent temperature and moisture content before processing. This may involve ‘conditioning’ for several days at the room temperature of the thermoforming line due to the poor thermal transfer characteristics of most plastics. When the production line is linked to the extruder then material preparation is minimal because the heat from extrusion is retained in the sheet.

Check temperatures of heater banks regularly. If these can be reduced even by a small amount then energy costs at both the heating and cooling stages will be reduced.

• Tip – Cold materials should be brought

in to the production area several days before processing to ensure that the material temperature is consistent.

od Pr Ed

ge

t uc

trim

od Pr Ed g

t uc

et rim

Thermoforming options Thermoforming can be from cold roll stock through a pre-warming oven and then to the heater banks before forming (1) or direct to the heater banks from either the extruder or from cold roll stock (2). In either of the options the process suffers from large heat losses due to generally poorly sealed and insulated process equipment. There are many areas where simple engineering actions can reduce energy use. 282

Chapter 5 – Processing

• Tip – If using hygroscopic sheet

materials, the sheets should be separated to allow all the sheets to reach equilibrium (temperature and moisture). • Tip – Pre-warming will reduce

temperature variations across the sheet and reduce concerns such as gloss variations across the sheet.

Pre-warming of roll stock In some cases (see diagram on the left), the cold roll stock is run through prewarming cabinets to warm the sheet prior to entering the full heater banks. Prewarming cabinets will add to the total energy load of the line but will provide a more uniform feedstock to the heating area and will increase production rates. This will lead to an overall reduction in the SEC (kWh/kg) for the process. Despite this, there are many ways the effectiveness of pre-warming cabinets can be increased to further reduce the SEC of the process. Pre-warming cabinets are often poorly insulated and have large entrance and exit slots that are not sized to the sheet being warmed. This can lead to high heat losses from pre-warming cabinets as shown on the right.

Entrance to pre-warming cabinets Cold sheet is pre-warmed in a heated oven to ≈ 125°C. Poor insulation and excessive gaps at the inlet and outlet slots allow heat to be lost to the atmosphere. This warms the site and wastes energy.

• Tip – Sealing can be improved on many

pre-warming cabinets to minimise heat losses at the input and output slots. These often have large slots for the thin sheets and unobstructed gaps at the top, bottom and sides of the sheet. These gaps can easily be reduced by simple adjustable baffles and guards to prevent heat escaping. This would have no effect on the product but would reduce energy use in every pre-warming cabinet. There are no risks with improving the sealing of the heating cabinets as they are thermostatically controlled. Reducing heat loss will simply reduce the energy input to reach the set point of the controller.

Entrance to pre-warming cabinets The open slot is much wider than the sheet and allows heat to escape. This area can be sealed and adjusted to the size of the sheet to avoid excessive heat loss through the slots. This is a simple engineering project.

• Tip – Insulation of pre-warming cabinets

is an easy way to reduce heat losses and reduce energy use. This is a simple engineering task using commercial insulation. This will also reduce heat output from the cabinets and reduce the temperature of the site in summer. • Tip – Where pre-warming cabinets have

gaskets on access doors then these should be well maintained and in good condition.

Chapter 5 – Processing

Insulation and seals on pre-warming cabinets The leakage at door seals and perimeters is clearly seen in the thermographic photograph. Maintenance of seals and doors is essential to keeping the heat where it is needed, in the sheet and not in the atmosphere. 283

5.37

Thermoforming – heat losses

Input and output sealing of heater banks Whether pre-warming cabinets are used or not, the sheet is eventually fed into the main heater banks. These are often poorly sealed at entrances (see photograph on the upper right), exits and sides. There are often large openings in these areas and, when the heater banks are contained in clamshell holders there is often poor sealing of the clamshell joints. These all allow heat to escape continuously during running and idling, particularly when running narrow-width sheets. Heat loss through these openings is considerable. • Tip – Improved sealing is recommended

for all areas around the heater banks, e.g., entrances, exits, open sides to the heater banks and joints to clamshells. Open holes can be blanked off to the minimum size possible, joints should be adequately sealed and aligned correctly with the thermoforming press to reduce heat leakage. These are simple engineering projects with rapid payback. Ensure that the heating controls are linked to a thermostat to prevent overheating in the forming area.

Entrance to main heater bank The large gaps at the entrance to the heater bank allow large amounts of heat to escape. Reducing the gap size to match the sheet size is a simple engineering project.

Insulation of heater banks When using clamshell heater banks the tops, sides and bottoms of the heater banks often become very hot and lose large amounts of heat (see photograph on the middle right). These are often partially insulated but can become hot enough to present a health and safety concern. Additional insulation will not only reduce heat losses from clamshell heater banks but also remove any health and safety concerns with hot surfaces.

Heat losses Heat being lost from the top of the thermoforming heating area. The radiant heaters are vented to the atmosphere and lose large amounts of heat. Simple insulation would reduce heat losses.

• Tip – Investigate the costs and benefits

of improving insulation levels around clamshell heater banks. A typical easily fitted insulation blanket on a thermoformer is shown on the lower right. Insulation and sealing is primarily an issue with the older coiled wire type of heater. In many cases these have been replaced with more efficient heaters that are tuned to the specific sheet material and product.

284

Simple insulation to reduce heat losses Simple insulation laid on top to the heating area reduces heat losses and improves the efficiency of the heating process and prevents the loss of large amounts of heat. Chapter 5 – Processing

Reflection and radiation heaters Even tuned radiation heating can suffer from significant heat losses through simple radiation and convection. The typical heat losses from other types of heating element are shown in the photographs and thermographs on the right. • Tip – Heating elements will radiate heat

in all directions and reflectors are needed to ensure that the energy is being directed to where it is needed. • Tip – Reflectors are needed to prevent

the radiation heating the machine or the site. Additional sealing or reflection of radiated heat back to the sheet to be thermoformed can result in considerable energy savings and a reduction in heat losses from the heater area. The photograph on the lower right shows how radiated heat has damaged the protective plastic panel indicating high amounts of radiated heat and a potential health and safety concern. This is common when reflectors are not used. Reflectors will give better heat distribution across the sheet. Without reflectors, the edges of the sheet will be colder than the centre of the sheet because the edge of the sheet is only being heated from one direction. • Tip – Simple metal reflectors reradiate

heat back towards the sheet, reduce energy use, reduce heat losses and reduce health and safety concerns. Reflectors can be manufactured from a variety of materials such as aluminium tape, aluminium sheet, plated or galvanised steel, or even simple aluminium spray on the thermoformer frame. Each method has advantages and disadvantages but all will reduce energy use.

Heat losses from the top of a thermoformer Heat being lost from the top of the thermoforming heating area. The radiant heaters are vented to the atmosphere and lose large amounts of heat. Simple flat solid insulation would reduce heat losses significantly.

Heat losses from the top of a thermoformer Heat is lost from the complete length of the thermoformer heating elements. Investigate insulation or tuning of the heaters to control the amount of heat generated at the sheet heating area and insulation or methods of directing the heat to the sheet.

• Tip – Good use of reflectors can decrease

energy use by up to 30%. • Tip – Most types of reflectors need

maintenance to maintain the reflection properties of the material. Keep the reflectors clean for the most efficient operation, do not simply increase the temperature. • Tip – Monitoring the energy use of the

machine can be an effective way of measuring the efficiency of the reflectors. Increasing energy use indicates that the reflectors need maintenance. Chapter 5 – Processing

Excessive heat lost from the process In this case the heat radiated from the process heaters has damaged the protective panels. The exterior temperature of the panels was ≈ 70°C. At this temperature there is a potential health and safety concern. 285

Thermoforming – heating and cooling

The heating elements used in the heater banks are a critical factor in energyefficient operation. Plastics have poor thermal transfer characteristics and can take some time to heat up when simply placed in a warm environment. Radiation heating is entirely different to heating by conduction or convection and these are totally separate methods of heat transfer. Radiation is the primary method of heating in modern heater banks as this is the most efficient heat transfer method. Infrared radiation heating works by emitters producing electromagnetic energy as radiation in the infrared range which is then absorbed by the contacting surface and converted into heat inside the material. Infrared radiation is the same as any other radiation, it can be absorbed, reflected or simply transmitted and all three mechanisms must be considered when working with infrared radiation. The effectiveness of heating a material by radiation depends on the wavelength of the radiation source and the wavelength of radiation absorbed by the material. For most plastics the absorption wavelength is in the region of 0.8 to 10 micron (µm) but this will also be affected by the thickness and the colour of the plastic. Infrared radiators used for thermoforming are mainly ceramic, quartz, gas or halogen emitters and all emit radiation over a range of wavelengths in the 0.8 to 10 micron (µm) region. Ceramic and quartz are the most common types of emitters but gas and halogen also have significant advantages in certain cases. • Tip – Control systems may need

updating for infrared radiation. • Tip – Radiant heating is more effective

as there is less convective heat to be lost from the process – the heat ends up where you want it and not where it wants to go. Radiant heat gives far fewer concerns with heat losses because it is mostly used to heat the sheet.

Ceramic and quartz infrared heaters Ceramic and quartz infrared radiators can provide up to 40% improvement in the energy use compared to older-style 286

convective rod heaters but this depends on the specific absorption characteristics of the material being formed. The better response time of these elements also makes control much easier and it is possible to zone the heater banks to get the best heat distribution profile across the sheet and to control this heating

Use a thermographic camera to see where the heat is going and to optimise the process.

Thermoformer power trace 100

80

Power (kW)

Getting the right heat

60

40

20

0 00:00

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00:40

01:00

01:20 01:40 Time (min:s)

02:00

02:20

02:40

03:00

Power use in a thermoformer Some thermoformers show an almost constant power use with no significant indication of a cycle at all. This is common on machines which are not fully integrated, i.e., they are made up of components rather than a full machine. Thermoformer power trace 120

100

80 Power (kW)

5.38

60

40

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0 00:00

00:20

00:40

01:00

01:20 01:40 Time (min:s)

02:00

02:20

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03:00

Power use in a thermoformer Some thermoformers show a variable power use and there is a visible cycle, although this is not often related to the production cycle of the machine. In this case the machine cycle was ≈ 5 s but the large cycle in the power trace is ≈ 20 s. Chapter 5 – Processing

profile within tight parameters (see www.ceramicx.co.uk). • Tip – Selection of the specific heater is

dependent on the material being processed and sites are advised to seek expert advice on the selection of the heater to match the material. The supplier will need to know the main material being processed (they all have different absorption characteristics between about 0.8 and 10 microns [µm]), any other materials that will be processed on the machine, the general processing characteristics of the material and other details. This is a specialist job but getting it right is worthwhile and very profitable. • Tip – Matching the infrared heater

emissivity to the absorption characteristics of the material being processed will reduce energy costs significantly. Sites are advised to evaluate the heaters and materials to get the best match. • Tip – The surface condition of the

heating element will have a large effect on the effectiveness of the elements. Look after the elements and have them cleaned and serviced regularly. • Tip – Most emitters will decline in

efficiency with time and have a specific lifetime. Failing to maintain emitters will lead to excess energy use.

Gas infrared panels Radiant panels using catalytic flameless heaters can be used to transform the calorific energy of gas directly into infrared energy. These heaters operate without flame and the only by-products are CO2 and H2O. They transform all the gas into useful energy and have high efficiency factors. The infrared wavelengths generated can be set between 3–6 microns to give good radiation absorption by most plastics. These are NOT gas burners, there is no flame and there is no risk of explosion (see catalyticovens.com).

Halogen lamps Halogen lamps give off most radiation in the region of 1 micron (µm). This tends to penetrate the sheet and heat the material quickly from the inside rather than from the outside (which is typical of higher wavelengths). Halogen lamps have a very quick response time and can improve productivity depending on the limiting factor for the Chapter 5 – Processing

process, i.e., for thick sheets the heating time may be the limiting factor. Halogen lamps are an emerging technology and have a high capital cost but energy savings of up to 20% are reported. • Tip – Halogen lamps may heat the

outside of the sheet too quickly and lead to surface damage. Take care with this as it may only appear on later weathering.

Most machine manufacturers show no enthusiasm for energy reduction even if it only raises the machine cost marginally. Is this because they don’t have to pay for the energy?

Cooling The material must not only be heated to the forming temperature but also cooled to below the heat distortion temperature to allow the product to be removed from the tool. These processes are linked and must take place within the same part of the cycle. In many cases the cooling time is the limiting factor and an efficient mould cooling system is the key to reducing cycle times and decreasing energy use. • Tip – Do not forget that cooling can be

the limiting factor in decreasing cycle times. • Tip – Overheating the sheet may make

forming easy but will need more time for cooling and will increase the overall cycle time.

In-line thermoforming The use of in-line thermoforming, i.e. extrusion of sheet direct to the input of the thermoformer (see Section 5.36) can significantly reduce the energy used in thermoforming. In-line thermoforming reduces energy use by removing a heating/cooling cycle. Instead of heating and cooling to form the roll stock and then heating and cooling to produce the thermoformed article, the material is still warm from the extrusion process when it enters the thermoformer. This requires less energy and can reduce the overall energy used by the process by up to 50%. • Tip – In-line thermoforming can reduce

energy use but also needs better controls due to the inter-linked nature of the process. • Tip – In-line thermoforming reduces

space requirements, materials handling and productivity but the extruder is dedicated to a single thermoformer and can increase investment requirements and decrease flexibility. • Tip – The output rate of the extruder is

limited by the thermoformer and it may therefore appear less efficient.

Other opportunities • If using vacuumassist then use VSD-controlled vacuum pumps to reduce the vacuum to the required level and use controls to turn them off when not needed. • Thermoforming can produce a significant amount of dust and sites often have dust extraction equipment. These are perfect opportunities for the use of VSD controls on motors using the air-flow volume as a control signal. • Thermoforming sites will often have many regranulators (generally one per thermoformer for web waste and another larger one for bulk stock). Good regranulator management is required (see Section 5.54) for energy-efficient operation. • Thermoforming uses large amounts of services, e.g., chilled water, compressed air and vacuum. Management of the services in thermoforming is critical to reducing energy use (see Chapter 4).

287

5.39

Thermoforming – where are you now?

The initial steps in thermoforming

Completing the chart

As with the score charts shown earlier, this is a self-assessment exercise to allow a site to benchmark their current status in thermoforming.

This chart is completed and assessed as for those presented previously.

Thermoforming is a widely used process but, in contrast to other processes, the technical advances for energy management in the process have not been either rapid or widely distributed throughout the industry. There are still many areas where the industry can reduce energy use and improve competitiveness with relative ease. There is still much to be done in the industry.

Thermoformed PET containers are a rapidly growing market and it is possible to use rPET (recycled PET) directly in the process using an energy-efficient integrated cleaning and recrystallisation process.

Thermoforming Heavy-gauge thermoforming?

Pre-warmers 4

Most thermoforming is thin-gauge but as the gauge thickness rises then it can become ‘vacuum forming’.

3 2

Vacuum forming is far less automated than thin-gauge thermoforming but almost all of the comments in these sections can be applied to vacuum forming.

Heater bank sealing

Cooling 1 0

Heating method

Heater bank insulation

Use the scoring chart to assess where you are in thermoforming The numbers from the scoring chart can be transferred to the radar chart for a quick visual assessment of where you are in terms of thermoforming. 288

Getting the heating stage of thermoforming right is the key to energy-efficient operation and the heaters must be chosen carefully and well maintained.

Chapter 5 – Processing

Thermoforming Level

4

3

2

1

0

Score

Pre-warmers

Heater Heater Heating Cooling bank bank method sealing insulation Pre-warmers have Heater banks have Heater banks have Heater emissivity Excellent tool cooling excellent seals at matched to material with good arrangement excellent seals at excellent insulation & entrances & exits & are & operation. entrances & exits. absorption. radiation protection. Very low heat losses at Very low heat losses at Ceramic/quartz heaters Cooling optimised for fully insulated. Door seals in excellent heater bank entrances minimum cycle time. heater banks from used & serviced conduction, convection condition. & exits. regularly. Pre-warmers have & radiation. New technologies negligible heat losses. investigated & implemented if appropriate. Pre-warmers have Heater banks have Heater banks have No matching of heater Good tool cooling with excellent seals at some limited good seals at good insulation & emissivity & material entrances & exits & entrances & exits. radiation protection. absorption. optimisation of cooling arrangement. some insulation. Low heat losses at Low heat losses at Ceramic/quartz heaters used but irregularly Good cycle times. Door seals in good heater bank entrances heater banks from conduction, convection condition. & exits. serviced. New technologies not Pre-warmers have low & radiation. investigated. heat losses.

Pre-warmers have good seals at entrances & exits & some insulation. Door seals in good condition. Pre-warmers have average heat losses.

Heater banks have Heater banks have No matching of heater Acceptable tool cooling average seals at some insulation & emissivity & material arrangements. entrances & exits. radiation protection. absorption. Average cooling & Moderate heat losses Moderate heat losses Ceramic/quartz heaters cycle times. at heater banks from at heater bank used but rarely conduction, convection entrances & exits. serviced. & radiation.

Pre-warmers have Heater banks have Heater banks have little No matching of heater Tool cooling poorly poor seals at entrances insulation or radiation emissivity & material arranged & operated. average seals at entrances & exits & are protection. & exits. absorption. Average cooling & High heat losses at High heat losses at Ceramic/quartz heaters poorly insulated. cycle times. heater banks from Door seals in poor heater bank entrances used but never conduction, convection condition. & exits. serviced. Pre-warmers have high & radiation. heat losses.

Pre-warmers have poor Heater banks have no Heater banks have no Convective rod heaters seals at entrances & seals at entrances & insulation or radiation used & not matched to exits & are poorly exits. protection. material. insulated. Very high heat losses Very high heat losses Poor servicing of Door seals visibly at heater bank at heater banks from heaters. conduction, convection degraded or missing. entrances & exits. Pre-warmers have very & radiation. high heat losses.

x

Chapter 5 – Processing

x

x

x

Tool cooling not optimised. Poor cooling & high cycle times.

x 289

Rotational moulding – general

PCLs in rotational moulding Rotational moulding uses gas as the primary energy source and in many ways this is an advantage as gas costs are generally far less than electricity costs. For rotational moulding, the performance characteristic line (PCL) can be found not only for electricity but also for gas. The methods of Chapter 2 can be applied to both energy sources and these are shown on the right for a typical site. Both the gas and electricity use are linked to production volume and a PCL can be found for each energy source. For electricity use: kWh = 0.4022 × Production volume + 19,184. For gas use: kWh = 2.0078 × Production volume + 57,096. In both cases there is a clear distinction between the fixed base load and the variable process load. The two energy sources can be combined to give total energy use and a total PCL can be developed to predict the total costs. However, splitting the data by the energy source provides excellent guidance on how actions to reduce energy use with each fuel source can be targeted.

data due to the poor cost and energy data collection at most rotational moulding sites. Interval gas data are not often recorded despite the high value that such information has in rotational moulding. Gas use is ≈ 4% of the total costs3 but most

Base and variable electricity loads (rotational moulding) 80,000 70,000 60,000 50,000 40,000 30,000 kWh = 0.4022 x Production volume + 19,184 R2 = 0.7912

20,000 10,000 0 0

20,000

40,000

60,000

80,000

100,000

120,000

140,000

Production volume (kg)

Electrical energy use for rotational moulding The electrical energy use for rotational moulding is very consistent with production volume (R2 = 0.7912) and the PCL can be used to assess and predict electricity use in a similar manner to that described in Chapter 2.

SEC and benchmarks

Base and variable gas loads (rotational moulding) 350,000 300,000 Energy use (kWh)

Lack of production rate-related data makes it difficult to produce reliable operating curves for the process. EURecipe1 indicates an average SEC for rotational moulding (unadjusted for production rate) of 5.828 kWh/kg but it is not clear if this energy use is electricity, gas or combined energy use. The Tangram2 data (see Section 2.16) covers only nine sites but indicate an average SEC of 0.70 kWh/kg for electricity and an average SEC of 4.15 kWh/kg for gas. This must be corrected for production rate and the relevant operating curves are shown in Section 2.16.

If the heat can be got into the plastic faster then the process will be faster.

Gas

Energy use (kWh)

5.40

250,000 200,000 150,000 kWh = 2.0078 x Production volume + 57,096 R2 = 0.8718

100,000 50,000 0 0

20,000

40,000

60,000

80,000

100,000

120,000

140,000

Production volume (kg)

Site energy data

Gas energy use for rotational moulding

A provisional cost breakdown of the rotational moulding process is shown on the upper right on the opposite page3 but this cannot be validated from our own

The gas energy use for rotational moulding is very consistent with production volume (R2 = 0.8718) and the PCL can be used to assess and predict gas use in a similar manner to that described in Chapter 2.

290

Chapter 5 – Processing

sites think that manual reading of the gas meter on an irregular basis is an acceptable way to manage costs. The technology is available for interval metering with data logging and this gives invaluable information. • Tip – Fit an interval for the site main

gas supply to monitor site gas use.

Electricity See Section 4.5 for the use of interval data with electricity.

Machine energy data

on the lower right and Section 4.15).

Rotational moulding is ready for change, the process has not been subjected to the same technological advances seen in other areas of plastics processing.

• 1. EURecipe, 2005, ‘European Benchmarking Survey of Energy Consumption and Adoption of Best Practice’, www.eurecipe.com. • 2. Tangram Technology Ltd., Internal data from 9 rotational moulding sites throughout the world. • 3. STP Rotomachinery Group, 2012, ‘Rotomoulding machines & energy savings opportunities’, ARMA Rotomould, Melbourne, Australia.

Gas No individual machine gas use data are available because, to date, no sites surveyed have had individual gas meters on machines and none surveyed have had access to machine interval data. This is a major failing for an industry which claims to be interested in energy use.

Gas 4%

The best solution for any site would be to install low-cost individual gas meters on each rotational moulding machine (≈ £350/ machine). These can be used to provide downloadable information on each machine and provide the site with energy use information for various machines and show trends and use of the ovens. • Tip – Fit gas meters on large machines

to enable true metering of the gas use. • Tip – Record gas use for individual

machines to allow machine selection based on the most effective machine.

Labour 10%

Material 82%

Machine and mould amortisation 3% Electricity 1%

Cost breakdown of rotational moulding The material is overwhelmingly the largest cost in rotational moulding. Energy use is low in cost terms but is increasing in importance as costs rise. Source: STP RotomachineryGroup

Electricity

• Tip – Permanent sub-metering of

individual rotational moulding machines may not be financially viable but the use of portable sub-meters (see Section 4.7) is extremely worthwhile. • Tip – Fit soft-starts on rotor motors to

avoid high starting loads (see power use Chapter 5 – Processing

Rotational moulding machine power trace 100

Power (kW)

80

60

40

20

0

00 :0 0 01 :0 0 02 :0 0 03 :0 0 04 :0 0 05 :0 0 06 :0 0 07 :0 0 08 :0 0 09 :0 0 10 :0 0 11 :0 0 12 :0 0 13 :0 0 14 :0 0 15 :0 0

Electrical power use is also not often available for rotational moulding machines but the results of monitoring a typical rotational moulding machine are shown on the lower right. This shows consistent power use during operation and the two lower areas are almost certainly at times when the main rotation arm is not working, i.e., during loading and unloading. It is expected that most machines would show a similar pattern, although the magnitude will vary. As would be expected this is relatively low compared to most of the other processes considered.

Time (min:s)

Power use in a rotational moulding machine This trace shows two distinct levels of consumption, i.e., when rotation is taking place (the high level) and when rotation is not taking place (the low level). The spikes are probably due to high start-up loads on the arms. The average power use was 33 kW. 291

5.41

Rotational moulding – reducing process heat losses

Keeping it in (again) Rotational moulding uses energy to get the oven up to temperature and open or poorly insulated areas will inevitably increase heat losses and increase energy use. Reducing oven loss is a key area in minimising energy use in rotational moulding but current machines do not appear to have taken this issue seriously and, as a result, heat losses are large on many ovens. Reducing heat losses from ovens also reduces any health and safety concerns with hot surfaces. Simple improvements in the sealing and insulation of ovens can improve energy performance for relatively low cost. Thermographic examination of rotational moulding ovens is strongly recommended as a method of quickly identifying areas of large heat loss in rotational moulding and of deciding the necessary action.

insulation will reduce heating loads and gas use. These areas also generally do not have a large thermal mass and therefore both cool down and heat up quickly. Increasing insulation levels around the oven to increase the thermal mass will reduce the heating time for the ovens by keeping them at a higher temperature whilst the mould is cycled into or out of the oven.

It is estimated that oven gas use can be reduced by up to 10% from simple engineering improvements.

• Tip – Improving insulation of rotational

moulding ovens is easy and retrofitting additional insulation should be considered to reduce heat losses. • Tip – Thermographic examination will

quickly show areas where the insulation

Simply replacing seals and reducing heat losses at one site reduced the cycle time and gas use by over 30%.

Sealing Ovens are generally poorly sealed, this inevitably loses large amounts of heat to the atmosphere and raises the energy cost. This is particularly true in the door areas and where arms enter the oven; seals in these areas need to be flexible and have low compression set at high temperatures. • Tip – Machines should be specified with

good-quality and effective seals in the door areas. • Tip – The area where the drive shaft

enters the oven is often a large heat loss area. Improved sealing in this area will reduce heat losses and energy use (see photographs on the right).

Heat loss at doors and entrance to an oven Heat is being lost at many areas of the perimeter of the closed doors due to poor sealing of the oven when the mould is in the oven. This is both a design and a maintenance issue that needs attention.

• Tip – Some ovens have inspection

windows that are open to the atmosphere. Install simple sealing arrangements and ensure that they are used (see photograph on the right). • Tip – Thermographic examination will

quickly show areas where the sealing of the oven has broken down or was initially inadequate (it often is).

Insulation The side and other panels of ovens are often not well insulated and as a result are often very hot. If the side of an oven is hot to the touch then the site is paying too much to heat the oven. Improved oven 292

Heat loss at doors and entrance to an oven Heat continues to be lost due to poor sealing even when the mould is not in the oven. A permanently open inspection hatch is arrowed. This is again both a design and a maintenance issue that needs attention. Chapter 5 – Processing

of the oven has broken down or was initially inadequate.

Maintenance Whatever the condition of the oven as delivered it is essential that regular maintenance is carried out on seals and gaskets to ensure that the seals continue to operate effectively. Ovens need flexible and tight fitting seals to be energyefficient. Seals should be inspected at regular intervals and replaced as soon as wear is evident. This is particularly true where the arms enter or leave the oven and on all door perimeters. Traditional seals used on machines tend to wear or take on a compression set and eventually become ineffective. • Tip – Burn marks around the oven will

indicate areas where seals are failing or are inadequate (see middle photograph on the right). Our houses are sealed to keep heat in. Why don’t we do the same thing with ovens?

Heat loss at rear of doors on an oven Heat is being lost at the rear door seals on this oven due to damaged and worn seals on the doors (dark areas indicated by arrow). Simple maintenance and/or replacement of the door seals will reduce gas use.

• Tip – Renovate and maintain the sealing

of all areas of the ovens. Seals may become brittle with age and need maintenance. • Tip – Silicon rubber seals (with working

temperatures of up to 300°C) can provide a flexible seal and also significantly reduce heat losses. • Tip – Thermographic examination will

quickly show worn or inadequate seals. In addition to the seals, the insulation and joining of the oven panels should be regularly inspected. Movement of panels and failure of the internal insulation can lead to large heat losses even in nominally sealed areas (see photographs on the middle and lower right).

Heat loss at rear of an oven Heat is being lost due to poor maintenance of the oven. The failed sealing area is clearly seen from the burn marks (dark areas indicated by arrow) and the 147°C temperature in the area. This is a hidden cost to the site in gas use.

• Tip – Thermographic examination and

burn marks around the oven will indicate areas where panels and internal insulation have failed. • Tip – Do not try to assess the condition

of the seals, the insulation or maintenance issues by hand. These areas can be very hot! • Tip – Improving the sealing, insulation

and maintenance of rotational moulding ovens can remove significant health and safety concerns from the site. If you don’t do it to save energy and money then do it to reduce the health and safety concerns.

Chapter 5 – Processing

Heat loss at panels on an oven Heat is being lost due to broken and leaking panel seals. The panels have deflected and opened up a leakage path. The burn marks (dark areas indicated by arrow) on the lower panel are a good indication that the sealing of the panels has failed. 293

5.42

Rotational moulding – other process improvements

Process controls

Process control

Process control improvements in rotational moulding can also be used to reduce heat losses. The process loses large amounts of heat every time the oven doors are opened. On some machines this heat is recycled inside the oven when the doors are open but large losses still occur due to the low thermal mass of most ovens. Machines should be adjusted to minimise the door opening time and the heat losses during opening. In many cases, the doors open completely to allow the mould to load and exit despite the fact that the mould does not occupy the whole height/depth of the oven.

Some of the best process control tools are currently being developed by 493K Ltd., a technology spin-off from engineering research and development carried out at the Rotational Moulding Research Centre, Queen’s University, Belfast (www.493K.com).

• Tip – Modify and optimise cycle

programmes to open the doors (or move the oven) the minimum amount necessary to remove the mould and then to close doors as soon and as quickly as possible after mould removal. • Tip – Investigate methods of splitting

doors/openings so that only a part of the oven is open during loading/unloading. Some machines do not use a product on all arms and the cycle may consist of a drycycle on one or more of the arms. This can involve opening the oven doors and releasing all the heat when no product is present. • Tip – Optimise cycles to avoid

unnecessary heat loss.

Process improvements The rotational moulding process does not require a hot mould, simply a hot plastic that will flow inside and around the mould. From a basic process analysis, rotational moulding is a very energyintensive process and involves externally heating the complete mould to melt the internal plastic and allow it to take up the internal mould form and then cooling the complete mould to cool the molten plastic so that it can be removed from the mould. The energy used depends on the heat transfer rate through both the mould and the polymer and the heat capacity of the mould and the polymer. There are significant opportunities for process controls to improve the heat flow and energy efficiency. 294

They have developed a range of products for rotational moulding process control at various stages of the process, e.g., K-Face to determine when the mould is ready to be removed from the oven and K-Kontrol to continuously measure the mould temperature during heating and cooling. These are excellent devices to optimise the rotational moulding process and reduce energy use. These and alternative products are needed to allow the process to be optimised – a task which is rarely carried out in rotational moulding.

Simple energy engineering (from basic principles) does not appear to have been carried out for rotational moulding because gas has always been very cheap. Easy actions could reduce energy costs by an estimated 15% and reduce cycle times by 15%.

Pre-heat materials Polymer powder can be pre-heated before placing it in the tool by the rejected process heat (or from compressors if located nearby). All plastics have a low heat transfer coefficient and take time to heat up. Pre-heating even by a small amount will reduce the energy input necessary and therefore the cycle time. Polymer could even be pre-heated by infrared heaters before the cycle begins. • Tip – Process waste heat (see below) can

Rotational moulding is a process with considerable health and safety concerns. Any adjustments to the process must be carried out safely and with appropriate precautions.

Heat loss at exhaust stack of oven Venting hot air at more than 127°C is a simple waste. The site has paid for all this energy and is then blowing it up into the atmosphere. Sites should use good process engineering to reduce this heat loss and to recycle or reuse the heat. Chapter 5 – Processing

also be used to heat the material and the mould to reduce cycle times by up to 18% (but it is better not to waste it in the first place).

Reduce the mould thermal mass Moulds should have the lowest possible thermal mass. This can be achieved by using materials with high heat transfer rates, e.g., aluminium, or by the use of thin-walled moulds where mechanical strength is provided by fins on the mould.

• Tip – Investigate if waste heat can be

used to pre-heat the material/mould before entering the oven. • Tip – Use controls to stop the exhaust

fans when they are not needed. They will only vent useful heat to the atmosphere and waste energy.

Recirculation fans

Heat pipes can be used to increase the heat transfer rate to the interior of the mould and the polymer.

Recirculation fans will often be allowed to operate when the oven doors are open. This blows heat out of the oven and operates the fans unnecessarily. Fan controls should be interlocked to the cycle to slow them down via VSD controls (or stop them) when the cycle opens the oven doors (see Section 4.21 on the savings possible with VSDs).

Burners

• Tip – Use controls and VSDs on all

Heat pipes

Burner efficiency should be monitored and controlled to ensure that full combustion is taking place. This is a simple maintenance task but should be carried out at least every 6 months. • Tip – Burner efficiency is critical to any

combustion process and must be monitored. • Tip – Check for any unburnt gas in the

exhaust stack using a flue gas analyser and adjust the burners as required. • Tip – Modulated burners will minimise

gas use for the same results. • Tip – Keep burners clean, maintain

them well and tune them properly. If there are still high exhaust temperatures then the burner may need to be de-rated.

recirculation fans to reduce energy use. • Tip – Fitting VSDs will also allow the

recirculation fan speed to be adjusted to control the process speed.

Cooling fans Fans cool the mould after exit from the oven. These are fixed-speed fans with simple controls operated as part of the cycle. Fan operation can be controlled by the surface temperature of the tool (determined via infrared sensing) and/or linked to the mass of polymer/tooling being cooled. VSD controls can be used to slow down/turn off the fans when the tool has reached a specified temperature. fans to control the cooling rate and reduce energy use.

Water pumps

Exhaust fans are generally operated from fixed-speed motors irrespective of the actual need or use a damper to provide control. These should be VSD-controlled from the exhaust gas temperature so that the fan slows down when the cycle does not require operation (see Section 4.21 on the savings possible with VSDs). Potentially even worse than using the fan when it is not needed is venting hot air to the atmosphere (see photograph on the left). This is a simple waste and should be avoided.

Cooling is often water-assisted by blowing a water mist onto the tool; this is similar to using adiabatic cooling with free coolers (see Section 4.38). Cooling water pumps are fixed-speed and this is an ideal application for VSD-controlled pumps. The control signal can be similar to that used for the cooling fans, i.e., infrared sensing.

locate areas of heat waste such as those shown. • Tip – An air-to-air heat exchanger can

be used in this type of application to preheat the incoming air to the burners. Chapter 5 – Processing

Processors need to understand the heat transfer and temperature inside the mould to correctly manage the process. The temperature of the oven is NOT the same thing as the internal temperature of the air inside the tool and the process is effectively controlled by the peak internal air temperature (PIAT).

• Tip – Use VSDs and controls on cooling

Exhaust fans

• Tip – Use a thermographic camera to

Process control in rotational moulding needs to be improved greatly (and rapidly).

• Tip – Use VSDs and controls on water

pumps to control the cooling process and reduce energy use.

For an entirely new approach to rotational moulding look at SRM (Solar Rotational Moulding) which uses direct solar energy via heliostats to concentrate solar energy. The process is not applicable to much of the Western world but is viable for some developing countries (see lm.solar for further details).

295

5.43

Rotational moulding – where are you now?

The initial steps in rotational moulding As with the score charts shown earlier, this is a self-assessment exercise to allow a site to benchmark their current status in rotational moulding. Rotational moulding is an energyintensive process but recent work has greatly improved the potential for process control and improvement. The tools and techniques are now available to significantly reduce the energy and cycle times of the process and to transform the economics of rotational moulding. Some of these improvements are the simple application of existing tools such as VSDs

and good insulation but others are more advanced process controls such as monitoring the internal air temperature of the mould. Sites need to examine all of these techniques to reduce energy use and remain competitive.

Reducing heat losses will also decrease the cycle time and increase productivity.

Completing the chart This chart is completed and assessed as for those presented previously.

Rotational moulding

Gas burners 4 3 2 Process controls

1

Fans (recirculation & exhaust)

0

Tooling

If we were inventing new processes then rotational moulding as it is today would probably not make it onto the radar simply because of the energy intensity.

Oven leakage & insulation

Use the scoring chart to assess where you are in rotational moulding The numbers from the scoring chart can be transferred to the radar chart for a quick visual assessment of where you are in terms of rotational moulding. 296

It can be improved greatly but many sites are not that worried about it – by the time they are it may be too late for them.

Chapter 5 – Processing

Rotational moulding Level

4

3

2

1

0

Score

Gas burners

Fans Oven leakage Tooling (recirculation & insulation & exhaust) Burner effectiveness Variable-speed drives Minimal oven leakage. All tooling is aluminium automatically controlled on all fans to optimise Excellent insulation of or thin sheet steel for for full combustion. fan operation. ovens. reduced thermal mass. Regular thermographic Regular preventative maintenance. surveys carried out to New burner technology identify changes in & techniques leakage or insulation. investigated.

Process controls Cycle optimised for all products to minimise door/oven movement & opening times. Process optimised to minimise heat losses during the cycle.

Optimisation of cycle to Regular manual flue Variable-speed drives Minimal oven leakage. Most tooling is aluminium or thin sheet minimise door/oven gas measurement. control recirculation Good insulation of Gas burners rarely steel for reduced fans to optimise fan ovens. movement & opening examined or cleaned. thermal mass. times undertaken for operation. Sporadic Burner maintenance on Fixed-speed exhaust thermographic surveys Programme in place to majority of products. long maintenance fans operate whether carried out to identify upgrade remaining Reduced heat losses during the cycle. cycle. needed or not. changes in leakage or tooling to reduce insulation. thermal mass.

Fixed-speed Regular manual flue recirculation fans gas measurement. Gas burners rarely controlled by machine examined or cleaned. cycle. Burner maintenance on Variable-speed drives long maintenance control exhaust fans cycle. depending on conditions.

Optimisation of cycle to Moderate oven Some tooling of leakage. reduced thermal mass minimise door/oven Moderate insulation of & some of high thermal movement & opening ovens. mass. times undertaken for No thermographic No action being taken minority of products. survey carried out to to upgrade tooling to Moderate heat losses assess oven reduce thermal mass. during the cycle. performance.

Flue gas measurement Fixed-speed motors on High oven leakage at rarely made. all fans controlled by several areas. Gas burners rarely machine cycle. Poor insulation of examined. ovens. Burner maintenance on No thermographic breakdown only. survey carried out to assess oven performance.

Most tooling is solid Optimisation of cycle to steel & has high minimise door/oven thermal mass. movement & opening No action being taken times considered but to upgrade tooling to little action taken. reduce thermal mass. High heat losses during the cycle.

No concept of flue gas Fixed-speed motors on Excessive oven All tooling is steel & all fans & operating leakage at many areas. has high thermal mass. measurement. Gas burners in ‘as whether required or Very poor insulation of No action being taken installed’ state. not. ovens. to upgrade tooling to Poor burner No thermographic reduce thermal mass. maintenance. survey carried out to assess oven performance.

x

Chapter 5 – Processing

x

x

x

Optimisation of cycle to minimise door/oven movement & opening times not considered. Very high heat losses during the cycle.

x 297

EPS foam moulding – PCL and steam

PCLs in EPS foam moulding The largest energy use in EPS foam production is the gas or other fuel used to produce the steam needed for expansion. A performance characteristic line (PCL) can be found not only for the steam fuel but also for electricity. The methods of Chapter 2 can be applied to both energy sources and these are shown on the right for a typical site (using gas for steam production). Both the gas and electricity use are linked to production volume and a PCL can be found for each energy source. For electricity use: kWh = 0.8685 × Production volume + 21,394. For gas use: kWh = 10.878 × Production volume + 8,620. In both cases there is a clear distinction between the fixed base load and the variable process load (although the gas base load is low in the case shown). The two energy sources can be combined to give total energy use and a total PCL can be developed to predict the total costs. However, splitting the data by the energy source provides better guidance on how to target actions to reduce energy use.

Steam generation and distribution Heat mapping The major energy cost for EPS foam moulding is for steam boiler fuel and sites need to investigate every possible opportunity to reduce steam generation

Base and variable electricity loads (EPS)

60,000 50,000 40,000 30,000 20,000 kWh = 0.8685 x Production volume + 21,394 R2 = 0.5867

10,000 0 0

10,000

• Tip – Sites should fit steam meters for

the complete site and on large machines to enable true metering of the steam use. 298

20,000 30,000 Production volume (kg)

40,000

50,000

Electrical energy use for EPS foam moulding The electrical energy use relationship with production volume for foam moulding is not very consistent at this site (R2 = 0.5867) but the PCL can still be used to assess and predict electricity use as described in Chapter 2.

SEC and benchmarks

Base and variable gas loads (EPS) 600,000

500,000 Energy use (kWh)

A lack of production rate-related data makes it difficult to produce operating curves for the process and no comparable information has been found in any other literature. The Tangram1 data covers only four sites but indicate an average SEC of 12.49 kWh/kg for gas alone. All the sites have very similar production rates and these data cannot be used to produce an operating curve to correct for production rate. The site data show that the SEC for EPS foam moulding is production rate sensitive but the available data do not allow quantification of this. Equally no machine data are available because none of the sites surveyed had steam meters on individual machines or access to machinelevel use data.

Whilst this section specifically covers EPS, many of the comments are relevant for other types of foam production.

70,000

Energy use (kWh)

5.44

400,000

300,000

200,000

kWh = 10.878 x Production volume + 8,620 R2 = 0.6121

100,000

0 0

10,000

20,000

30,000

40,000

50,000

Production volume

Gas energy use for EPS foam moulding The gas energy use relationship to production volume for EPS foam moulding is slightly better than for that of the electricity use (R2 = 0.6121) and the PCL can be used to assess and predict gas use as described in Chapter 2. Chapter 5 – Processing

costs, to minimise heat losses during steam transport and to maximise opportunities for heat recovery, e.g., from the waste water system. This requires a knowledge of the existing system (which has probably changed since installation) and the best tool is a heat distribution map. This is a simple map of where heat is generated, how it is transported (pipe insulation conditions), where it is used and where it is disposed off.

• Tip – Check the actual steam pressure

• Tip – Prepare a heat distribution map as

Simple checks and management of boilers can easily reduce steam costs by 10% for little or no cost.

soon as possible. • Tip – Use the map to identify redundant

piping or spurs and remove or isolate these. • Tip – Carry out a full steam audit (boiler

room and site) as a first step in reducing energy use. Heat exchangers are a proven technology but appear to be rarely used in the EPS industry in comparison to the available possibilities. When used correctly they always provide excellent results. • Tip – The heat distribution map should

locate areas where heat is lost to the system. These are candidates for heat recovery using simple and proven heat exchanger technology, e.g., pre-warming boiler feed water. Heat must be managed to minimise the cost of generation and use and this should be the first action at any EPS site.

Steam generation The high cost of steam generation means that even small improvements in efficiency are very cost-effective. Suggested areas for examination are:

needed by the process and slowly reduce steam pressure until it just operates the process. • Tip – Regularly check steam-traps. • Tip – Check the flue and if this is fan-

assisted then investigate the use of a VSD for the fan motor. • Tip – Check for adequate ventilation in

the boiler area.

Steam must be managed to minimise the cost of generation and use. As with any other service, the provision of steam should be subject to the rule of ‘minimise the demand and then optimise the supply’.

Distribution Steam distribution systems are rarely well insulated on either the straight pipes or other exposed areas, e.g., valves, flanges and joints. Uninsulated piping will provide ‘free’ heating for the site but this is uncontrolled and wastes energy. Lack of insulation will decrease the effectiveness of the steam distribution system due to parasitic heat losses. Thermographic inspection of the complete system is the easiest way to quickly reveal heat losses and areas for potential insulation improvements such as boiler rooms, pre-blow areas, main distribution pipes, around blow machines. Simple insulation of major pipes and distribution valves is a once-off cost that can reduce fuel consumption by up to 10% by reducing the boiler load. • Tip – Start to insulate the easier access

areas with low-cost insulation. • 1. Tangram Technology Ltd., Internal data from 4 EPS sites throughout the world.

EPS has been renamed ‘airpop’ or ‘engineered air’ but we will continue to use EPS as the name for expanded polystyrene.

• Tip – Monitor boiler output efficiency in

term of kg steam/kWh of energy input. • Tip – Monitor boiler feed water

condition. • Tip – Monitor and review blow down

levels. • Tip – Monitor and review condensate

return levels. • Tip – Regularly check burner

combustion efficiency. • Tip – Check that boiler firing controls

and sequencing (for multiple boiler installations) are matched to the demand for optimum efficiency. • Tip – Fit a flue gas thermometer and

monitor the flue gas temperature. If this is more than 4°C greater than that of the last service then get another service.

Chapter 5 – Processing

Steam piping without insulation loses heat and uses energy A lack of insulation on steam piping causes excessive heat losses and excessive energy use to create the correct amount of steam at the point of use. 299

5.45

EPS foam moulding – process

The white stuff The EPS process is effectively a two-step process consisting of pre-blowing of the initial resin to form the partially blown beads and then a steam blowing in the final mould to form the final product. These two steps can be considered separately.

Pre-blow Pre-blow is generally carried out in bulk before delivery to the final blow process.

Process settings The pre-blow area is a major energy user but the energy use is largely fixed by the sequencing and monitoring of the process. Staff have little control over the process, which is generally highly automated, but process setting needs to be good to reduce process timings and energy use. Improved process controls will inevitably reduce costs. • Tip – Energy use should be initially

monitored on a batch basis to enable target setting. • Tip – Targets should be set for

improvement in pre-blow energy use. In most cases there are not many variables in the pre-blow process and it will be possible to carry out some limited experiments to locate quick improvements in cycle time and energy use. As a critical area, even small improvements will have a large effect on the energy use. Taguchi techniques (Design of Experiments) can be used for simple experiment design to locate the optimum process settings. The energy use can be a setting factor in the Taguchi analysis.

production needs uniform density of both the final product and of the pre-blown beads. Density variations in the pre-blown beads affect both the product function and material use and hence energy and cost. Good pre-blown beads have a narrow density range and the fully moulded product will have properties similar to the lowest densities in the EPS. The narrower the density range in the pre-blown bead, the lower the mean product density can be and still produce a moulding with the specified properties. This requires a consistent pre-blow process and uniformly pre-blown beads. Photomicrographs of pre-blow beads can often show a wide range of diameters and therefore probably densities (see photomicrograph below). Reducing the density variation at pre-blow will reduce energy costs both at pre-blow and at final processing. Density checking of pre-blown beads is an excellent quality control check to detect and reduce variation in the process and can be used to control the process.

EPS sites show the same relationship between production volume and SEC as do other processes. SEC is an unreliable metric for energy performance for any process.

• Tip – Checking the density of incoming

materials and pre-blown beads can be used to ensure that the pre-blow process is working efficiently and can be used to monitor the effectiveness of the pre-blow process. The process can then be controlled by SPC to reduce product variation and energy use.

• Tip – Sites should learn about Taguchi

methods for the design of simple multivariate experiments and then use these to set the process parameters. A selection of easy-to-understand books on the subject can be found on the Internet. Simple experiments can save up to 5% of the steam consumption at very little cost.

Quality control The automated nature of the pre-blow process means that there are often few quality control checks of the process or intermediate product. Efficient EPS 300

Pre-blow bead size consistency is an important process parameter The pre-blow bead size should be consistent to give good blowing and mould-filling characteristics. These pre-blown beads show a wide range of sizes and therefore probably densities. Chapter 5 – Processing

• Tip – Carry out simple experiments to

reduce the variability of the output product (pre-blown beads). • Tip – Low-cost USB microscopes, e.g.,

Dino-Lite, are available for less than £50 and can be used to measure and monitor pre-blow size at regular intervals. Effective control of the pre-blow density can save up to 5% of the steam consumption at very little cost.

Blowing Setting sheets and set-up times Most EPS producers carry out a significant number of tooling changes due to their order pattern and storage capacity. This makes control of the machine set-up process an important variable for the industry. The use of welldefined setting sheets (see Section 6.2) and the full implementation of a set-up time reduction programme (see Section 6.4) will reduce energy use in the main process.

EPS recyclers All sites should have an EPS recycler that will compact any EPS scrap before final disposal. These will have reasonable size motors for the hydraulic pumps and need good controls to ensure that staff do not simply leave them running at all times.

Check the density and size of incoming material. It is the key to a good process but rarely done.

Simple recognition of the cost of running the machines can lead to easy and rapid cost reductions. Allowing these to run under no load is simply wasteful. • Tip – Use a simple management fix – stack any reject products in the area of the recycler, wait until there is enough build-up of product, regrind and compress them and then switch the machine off. • Tip – Fit controls to switch recyclers off

after a set period of no-load running.

• Tip – Use full setting sheets. • Tip – Implement a set-up time reduction

programme (see Section 6.4).

Pressure switch settings The pressure switch setting for the blow process is critical to energy use and a successful process. If the setting is too high this can lead to excessive pressure being applied and burning of the product, and if the setting is too low then there can be incomplete fusion of the beads. Pressure switch settings need to be monitored and recorded to ensure that they are both correct and optimised. • Tip – Check the monitoring of the

pressure switches and ensure that these are set (as part of the set-up process) and monitored (as part of the process controls) to the optimum setting for both the energy use and the process requirements.

Services Water use Water use is high in the EPS process and sites should not only monitor the amount of water used but also ensure that they are not being charged too much for water discharge to the sewers as part of their water charging. • Tip – Check that water that evaporates

as part of the process is not being charged for in the sewerage charges. Chapter 5 – Processing

Use a recycler for scrap product even if only for volume reduction.

301

5.46

EPS foam moulding – where are you now?

The initial steps in EPS foam moulding

Completing the chart

As with the score charts shown earlier, this is a self-assessment exercise to allow a site to benchmark their current status in EPS foam moulding.

This chart is completed and assessed as for those presented previously.

EPS foam moulding is unique in plastics processing in the use of steam as the major process energy use. As for any service, this must be managed (minimise the demand and then optimise the supply). Steam management a major task in reducing energy use in EPS moulding. This is not a skill normally associated with plastics processing but can make all the difference with EPS foam moulding.

EPS foam moulding

Boiler selection 4 3 2 Process controls

Multiple boilers

1 0

Distribution & pipe work

Pumps

Use the scoring chart to assess where you are in EPS foam moulding The numbers from the scoring chart can be transferred to the radar chart for a quick visual assessment of where you are in terms of EPS foam moulding. 302

If you are not getting a discount on the water bill for evaporated water (not discharged to the sewers) then you are paying too much money.

Chapter 5 – Processing

EPS foam moulding Level

Boiler selection

Multiple boilers

Very low standing loss boilers – typically less than 0.5% of rated output.

All items below are satisfied & formal documentation exists on design intent & control settings.

4

3

2

Low standing loss Heat losses from idle boilers with losses boilers are down to 0.75% of rated automatically output, common minimised by reducing primary pump. or restricting the water flow through boilers that are not firing.

Score

Distribution & pipe work

Variable-speed All pipe-work insulated controlled from at all areas (straight representative load, sections & valve areas) reducing pump & well sealed. differential pressure Distribution system in with demand. excellent condition. Records kept of pump All redundant spurs control & operation. isolated.

Variable-speed controlled from representative load, reducing pump differential pressure with demand.

Process controls Excellent monitoring & control of steam quality & use. Heat exchangers used to recover heat where applicable. Excellent control of heat use.

Most straight pipe-work Good monitoring & control of steam quality insulated. & use. Distribution system in very good condition. Several heat exchangers used in All redundant spurs system. isolated. Good control of heat use.

High standing loss boilers with losses in the range of 2% to 5% of rated output, fully isolated & cold when off line.

Boiler operation dictated by automatic sequence controls. Redundant capacity capable of manual isolation.

Variable-speed pumps Some straight pipeSome monitoring & control of steam quality controlled at constant work insulated. pump differential Distribution system in & use. Some heat exchangers pressure. good condition. Records kept of pump Few redundant spurs used in system. that are not isolated. control & operation. Good control of heat use.

High standing loss boilers with losses greater than 5% of rated output, isolated & cold when off line.

Conditions can be manually altered to change boiler sequencing.

Variable-speed pumps Pipe-work is No monitoring or control of steam quality controlled at constant uninsulated. & use. pump differential Distribution system in pressure. poor condition (visible Some heat exchangers distortion & corrosion). used in system. Some redundant spurs Good control of heat with no isolation. use.

1

0

Pumps

High standing loss Operation of multiple boilers greater than 7% boilers does not of rated output, not change with changes in isolated when off line. demand – warm return water is circulated through idle boilers & flow rates are constant.

x

Chapter 5 – Processing

x

Fixed-speed pumps.

x

Pipe-work is No monitoring or uninsulated & shows control of steam quality leakage. & use. Distribution system is No heat exchangers old & has many sharp used at any point in bends & corners. system. Many redundant spurs Poor control of heat with no isolation. use.

x

x 303

5.47

Compression moulding

The original process Compression moulding is the original plastics processing method and was initially used for early polymers such as horn and rubber. With the advent of thermosetting materials such as the phenol-formaldehydes and ureaformaldehydes the natural processing choice was compression moulding. Compression moulding is now also used for materials such as fibre reinforced polyester resins in the form of Bulk Moulding Compound (BMC) or Sheet Moulding Compound (SMC). Compression moulding can also be used for thermoplastics and this is mainly for high-temperature materials such as polyimide, PPS and PEEK. Compression moulding of thermoplastics will not be covered in this section. Compression moulding of thermosetting materials differs from moulding thermoplastics in two main areas: • The mould is heated (instead of cooled) to cure the material. • The cycle time required for the process is substantially longer than for conventional injection moulding, i.e., in the order of 10 times longer, to allow for adequate curing of the material. These differences mean that energy use in compression moulding is often higher (in kWh/kg) than in injection moulding.

reduced substantially during the curing phase. There is no need for high pressure to ensure full mould packing or to wait for gate seal. After the initial forming, the pressure requirement is simply to account for volumetric expansion as the material temperature increases. This means that motor control in the hydraulic system is critical to reducing energy use in compression moulding. The energy use in a typical BMC compression moulding cycle is shown below. This is an older-type machine with no motor speed control and is operating on a cycle time of 104 s. The machine shows a very high base load and this indicates that the motor (and heaters) are almost certainly operating constantly.

Compression moulding is undergoing a renaissance in some areas of production and it is now possible to compression mould thermoplastic caps and closures. These machines use an extruder to produce a hot thermoplastic pellet which is placed in a rotating turret for compression moulding. The process uses lower pressures and temperatures than injection moulding, has very low tooling costs and is very energy efficient (see www.sacmi.com).

• Tip – Motor speed control based on

whether movement of the platens is needed can reduce energy use on older compression moulding machines. The cycle times are not generally as rapid as in IMMs and conventional VSDs can cope with the speed changes needed.

These are not the type of machines discussed in this section.

• Tip – New compression moulding

presses often have the option to use electric drives for the main press operation. This obviously stops the motor when there is no movement required but continues to hold the pressure on the platens. Energy use in the compression moulding cycle 90

Hydraulic systems

Compression moulding presses tend to have a lower tonnage and power than IMMs because, although the pressure required for forming is high, it is not as high as the pressures generated during injection in IMMs. The mould closing pressure must be initially very high to form the material but this can often be 304

80 70

5 cycles

60 Power (kW)

Operation of the compression press has traditionally been by hydraulic systems which are required to move the mould long distances and to keep the mould closed for a substantial part of the moulding cycle. Some systems use a combination of lowand high-pressure pumps and use low pressure/high volume to move the platens large distances quickly and then use high pressure/low volume to carry out the actual compression moulding.

50 40 30 20 10 0 00:00

01:00

02:00

03:00

04:00

05:00 06:00 Time (min:s)

07:00

08:00

09:00

10:00

The compression moulding cycle This machine has a cycle time of 104 s and a base load of ≈ 33 kW compared to an average load of 34.8 kW. This is a base load of 95% which is very high and shows the effect of the consistently high hydraulic loads and the lack of insulation. Chapter 5 – Processing

Mould insulation

Compression moulding machines do not always use electrical heating of the moulds. Some systems use oil heating to allow mould temperatures to be varied through the cycle but the benefits of mould insulation and machine bed isolation still remain.

Compression moulding of thermosetting materials requires the continuous application of heat to cure the resin and this requires a mould heated to the range 150–200°C. The photographs and thermographs on the lower right show the amount of heat lost to the atmosphere during mould pre-heating (upper) and through uninsulated moulds (lower). In the lower photograph and thermograph the mould had insulation initially fitted but this was allowed to fall into disrepair through poor maintenance. In both instances, the amount of heat being lost from the mould is excessive and can easily be reduced. • Tip – Mould insulation for compression

moulds will have a rapid payback as well as making the site cooler. Suitable insulation materials are easily found, e.g., www.brandenburger.de. • Tip – Mould insulation has the same

positive aspects as barrel insulation (see Section 5.10) but is generally easier to fit. • Tip – Mould insulation will also give a

more consistent and stable mould temperature. • Tip – At this site, the previous good

practice of mould insulation needs to be reinstated as soon as possible.

Machine bed isolation It is not only important to insulate the mould but, due to the temperature difference between ambient and the mould, it is also important to thermally isolate the machines bed from the hot mould. This will prevent the machine bed acting as a large heat sink for the heated mould and reduce the energy used in unnecessarily heating the machine bed. This is relatively easy to do using highpressure sheet insulation, e.g., see Brandenburger (above).

Heat emitted from mould at 122.9°C This non-operational compression mould is being warmed up and is not producing parts. The mould and the press act as large radiators. Moulds should be insulated and thermally isolated from the press bed with insulation.

• Tip – The temperature differences

involved make machine bed isolation more important for compression moulding than for injection moulding. • Tip – Tool and bed insulation has the

same positive aspects as barrel insulation (see Section 5.10) but is generally easier to fit.

Heat emitted from uninsulated mould at 120.5oC This operating compression mould shows the remnants of previous insulation (this is the dark cooler area arrowed in both photographs). The insulation of the other areas has either been removed or fallen off due to poor maintenance of the tool.

Chapter 5 – Processing

305

5.48

Pultrusion

Pultrusion

data indicates values of:

Pultrusion is a continuous process utilising glass or other fibrous reinforcement in a polyester or other resin matrix.

• Electricity – 0.32 kWh/kg.

For simple profiles (see diagram on the upper right), the reinforcement material is drawn through a resin bath where it is impregnated with the liquid thermosetting resin. The wet fibrous laminate is formed to the desired geometric shape and pulled into a heated steel die.

• Gas – 0.99 kWh/kg.

These values cannot be corrected for production rate or machine utilisation due to a lack of sufficient relevant data but are valid for a production rate of 564 kg/hour/ machine.

Once in the die, resin setting is initiated by heat so that the laminate solidifies in the exact shape of the cavity of the die as it is being continuously pulled by the pultruder.

Mat

The haul-off equipment used is either a conventional caterpillar belt puller (as used in extrusion) or a hand-over-hand reciprocating clamp type. The caterpillar type is a cheaper solution because no motion sequencing is involved but it can be expensive to produce the large number of gripper pads necessary for each profile. The caterpillar type also has the disadvantage that the gripping force cannot be isolated from the pulling force and for large profiles this can damage the profile. Hollow profiles are also possible via the pultrusion process and require a mandrel to be used inside the die as for conventional extrusion. For large sheets (see diagram on the lower right), an initial external lower liner is evenly coated with a mixture of resin and rovings (short glass fibres) and then a final external upper layer is applied to seal and contain the resin and rovings. This composite sheet is formed to the desired shape and pulled through formers in a heated oven to initiate and complete the resin setting.

Roving Resin bath

Heated die

Haul-off

Formers

Schematic of the pultrusion process for small profiles The pultrusion process for small profiles (rods, tubes and custom extrusions) involves dipping the reinforcement in the resin to wet the reinforcement, forming the composite through shaped formers and then curing the composite in an oven or heated die.

Upper liner

Resin Spreader Rovings plate Lower liner

Formers and curing oven Haul-off

Energy use Where the process uses externally applied heat this can be either by electrically heated dies (for simple pultrusions) or by gas-fired heated ovens (for large sheet pultrusions). The small number of sites surveyed for pultrusions does not allow an accurate benchmark of energy use but the limited 306

Schematic of the pultrusion process for larger profiles, e.g., roofing sheets For large sheets an upper and lower liner are used to contain the resin and chopped glass rovings before the composite is passed through a gas-heated oven to cure the resin. Chapter 5 – Processing

Dies

air plate heat exchangers.

Electrically heated dies typically use similar heating elements to those used in extrusion. Insulation of the outer face of the heated die areas reduces heat losses and can provide a more consistent and controllable application of heat to the profile.

It is also possible to provide the required curing heat through gas-fired catalytic infrared heaters that can be finely tuned to the absorption band of the resin system and this can reduce costs considerably for many sites (see Section 5.38).

• Tip – Use insulation on heated dies to

infrared heaters as an alternative to simple gas combustion. Oven temperatures should be carefully monitored and controlled to prevent ‘hunting’.

reduce heat losses.

Ovens Gas-fired ovens for large sheets are often poorly sealed against heat leakage and poorly insulated even when the low temperatures involved are considered.

• Tip – Investigate gas-fired catalytic

Simple thermographic examination of dies and ovens will show where heat losses are occurring and enable targeting of improved sealing and insulation.

• Tip – Improved process controls will

often reduce energy use.

This is often particularly the case where sheets enter the oven. As with pre-heaters for thermoforming, the entrance and exit areas of ovens are large and there is virtually no attempt to reduce heat leakage out of the curing oven. Simple actions to improve insulation and seal curing ovens can reduce energy costs by over 25%. • Tip – For large sheets ensure that any

oven entrance and exit areas are profiled to match the sheet and as small as possible to reduce heat losses. • Tip – Curing ovens generally use low

temperatures but this is no excuse for poor insulation of any heated area. Many ovens have poor insulation and significant areas where there is no insulation. All possible areas of curing ovens (sides, top and underneath) should be insulated to reduce heat losses and any inspection or other access ports should be provided with adequate seals to reduce heat losses. • Tip – Where access ports are provided

with latches or other closures then these should always be sealed before starting production. • Tip – Check that the seals on all access

ports and hatches are in good condition and seal correctly. Refurbish and maintain to give a good seal. Where ovens are used then exhaust stacks will be used to remove the hot combustion gases from the oven. These will result in heat being lost from the process. This heat can be used in two ways: • To improve combustion efficiency by pre-

heating the combustion air as with regenerative heating in ceramics kilns. • To provide factory heating in colder

months through the use of simple air-toChapter 5 – Processing

307

5.49

Rubber – general

Looking at the history Rubber is not a thermoplastic but, when compounded with suitable cross-linking agents effectively becomes a thermosetting product, i.e., it can be moulded, extruded and otherwise processed as for thermoplastic materials but it must also be cured (or vulcanised) to create the final product. The curing can take place during the process, e.g., most moulding methods include a curing step, or curing can take place afterwards, e.g., most extrusion methods use a separate curing step. There are few reliable indicators of the cost of energy to rubber manufacturers but data from the British Rubber Manufacturers’ Association1 (now part of the British Rubber & Polyurethane Products Association) indicates that in 1999 the energy costs varied widely, indicative vales were: • Mixing: 1.7–2.6% of turnover. • Mixing and General Rubber Goods (GRG): 2.7–3.2% of turnover. • General Rubber Goods: 2.2–3.2% of turnover. Due to cost increases since 1999, it is estimated that these cost percentages have approximately doubled and that the ranges are now in the region of 3.4–6.4% of the turnover.

vulcanise the rubber and create the crosslinks that give rubber its unique properties. This means that, in common with the processing of other thermosetting materials, there is a high use of heat to promote the vulcanisation process and heat management (in the form of steam or other sources) is a key skill in minimising energy use in rubber processing.

Energy use Performance characteristic line

There is no particular reason for rubber to be included in this workbook. However, after you have had carbon black under your fingernails, eyelids and in every other conceivable bodily orifice (as I did for several years) then you develop a strange affinity for the material.

Energy use in any rubber process can be linked to the production volume using

Rubber processing Rubber is processed using a variety of methods (see diagram on the right) and many of these processes were the precursors for the original plastics processing methods, e.g., transfer moulding and compression moulding were developed for rubbers and were later used for processing the early thermoplastics. This means that most of the topics in this workbook can be usefully read and applied by rubber processors. The information in Section 5.47 on the compression moulding of thermoplastics can be applied to the compression moulding of rubber and most of the rest of the workbook on topics such as monitoring and targeting can also be applied by rubber processors. There are, however, significant differences between rubber processing and the processing of thermoplastics. Rubber processing uses heat and sulphur to 308

Rubber manufacturing is not a single process The variety of methods used to process rubber is as wide as those used for plastics processing. In this workbook we will only cover mixing and compounding, moulding and extrusion. Tyre manufacturing is very specialised and will not be covered. Chapter 5 – Processing

methods such as those illustrated in Chapter 2. The PCL for rubber injection moulding (electricity only) and for curing gas use of extruded products are shown on the upper and lower right. Note: These PCLs are based on weekly production volumes and using monthly data will give different results. In both cases the data show relatively poor R2 values due to the lack of good energy management practice at the sites. This is particularly evident in the gas use for curing where the site had very poor control of steam generation and distribution.

• 1. British Rubber Manufacturers’ Association. 2001. ‘Rubber manufacturing: a guide to best practice’. Now out of print. Base and variable loads for rubber injection moulding (electricity only)

External benchmarking

Machine SEC (kWh/kg) = B × (Production rate)−1 + A As for plastics processing, this means that quoting a ‘benchmark’ SEC for either a site or a machine is largely irrelevant unless the production rate is taken into consideration. There are various values available for the SEC at the site level for some rubber processing techniques but none of these refer to the production rate and they are therefore of limited use. Despite this, some generally accepted indicative values for the site SEC (without reference to the production rate) are: • Moulding – a site SEC of 6–10 kWh/kg is

achievable by most sites but this depends on the exact process being used. • Extrusion – a site SEC of 1–2 kWh/kg achievable by most sites but this again depends on the exact process being used. As with plastics processing, this shows a lower SEC for extruded products. Sites should not be tempted to place too much emphasis on achieving these values and instead should use the PCL method to carry out internal benchmarking.

Chapter 5 – Processing

Electricity use (kWh)

Site SEC (kWh/kg) = B × (Production rate)−1 + A • The machine SEC (kWh/kg) is related to the machine production rate by an equation of the form:

100,000

80,000

60,000

40,000 kWh = 3.266 x Production volume + 60,179

20,000

2

R = 0.6547

0 0

2,000

4,000

6,000 8,000 10,000 Production volume (kg)

12,000

14,000

Base and variable loads for rubber injection moulding This PCL is based on weekly data but still shows a reasonable R2 value for the process. The high process load (3.266 kWh/kg) is mainly due to the long cycle time required by curing in the mould and the lack of mould insulation. Base and variable loads for rubber extrusion curing (gas only) 60,000

50,000

Gas use (kWh)

There is not sufficient relevant data for rubber processing to create external benchmark curves of the type created for plastics processing (see Chapter 2) but the available data show the same trends. • The site SEC (kWh/kg) is related to the global production rate by an equation of the form:

120,000

40,000

30,000

20,000 kWh = 1.769 x Production volume + 12,269

10,000

2

R = 0.4754

0 0

5,000

10,000 15,000 Production volume (kg)

20,000

25,000

Base and variable loads for steam curing of rubber extrusions This PCL is based on weekly data and shows a very poor R2 value for the process due to poor management practices at the site. 309

5.50

Rubber – storage and mixing

Storage and mixing

reduce heating costs.

The mixing phase of rubber processing is essential to create the compound that is later processed. This is a large cost to any site but, whichever method of mixing is used, there is a range of simple activities that can reduce energy use and costs dramatically.

• Tip – This will involve piping costs and

Materials storage Preheat Energy saving for pre-heat systems focuses mainly on warm rooms. These are likely to need more careful management than the more compact and probably wellinsulated autoclaves.

Insulation Savings of up to 50% can often be achieved by good insulation of walls and ceilings and draught-proofing of the door.

Bale spacing Spacing out the bales and arranging successive layers at right angles can increase the surface area by more than 100%. Spacing out reduces the capacity but increases the heating rate and this decreases the need for large volumes. Savings can then be made by reducing the warm room size (using insulating panels) and reducing the standing loss.

will only be economical for factories operating on a three-shift basis. • Tip – Microwave preheating eliminates

standing losses but has a high capital cost and will only be economical if the site is already using it for other processes and has spare capacity. • Tip – Use waste heat to preheat

extender oil and reduce the viscosity before pumping. If extender oil is a large proportion of batch volume, it may be better to cool the oil so that it acts as part of the process cooling system. This can be useful where high batch temperatures result in multi-stage operations and the extra cooling can enable a switch to single-stage operation.

Control of additions Controlling additions is the key to good compounding and accurate weighing systems will quickly pay for themselves through improvements in product quality and consistency and in energy savings through a reduced need to rework offspecification material. Using detailed energy (kWh) and power (kW) recordings of production allows much closer control of batch conditions and also the optimisation of additions timing.

• Tip – The important thing is the

throughput of the warm room, not the volume capacity.

Dispersive mixing peak

Reducing stratification Warm air stratifies in any room and temperature differences of up to 15oC between the floor and the ceiling can result. Using fans to move the air will substantially reduce heat losses. • Tip – Thermostats should be properly

maintained and able to achieve control with a minimum dead band.

Extender oil addition

Rubber viscosity reduction

Dispersive mixing

Filler addition

• Tip – To prevent heat loss, preheated

bales should be repacked into a closefitting mass when removed from preheating.

Heat recovery Transferring waste heat from other site operations (e.g., flash steam, heat from air compressor cooling operations, heat from mixer/mill cooling) to the warm room will 310

Time

Power-versus-time profile for conventional singlestage mixing cycle The power required is not constant through the mixing cycle and sites should consider using VSDs to vary the speed of the motor through the cycle. Chapter 5 – Processing

Incorporating this information into batch controls also contributes to product quality and consistency. The savings from optimised energy use can give payback periods of less than one year. • Tip – The same information also allows

batch comparison and can be used for preventive maintenance systems by monitoring changes in machine performance in terms of kWh/kg batch (on-load).

• Tip – Cooling water distribution should

be as clean as possible to prevent the formation and deposition of rust and scale on cooling surfaces. • Tip – Insulate extender oil systems and

use either steam or fossil fuel-based heating systems rather than electricity.

• Tip – Reliable measuring systems are

essential to allow project energy savings to be verified to justify further investment. The capital costs of better monitoring systems can often be justified on the grounds of energy saving alone. In many instances, switching off equipment when it is not in use for significant periods (as during shift changes and meal breaks) can be highlighted as an easy method of saving energy. • Tip – Better measurement on mills,

related to throughput and separated into on- and off-load kWh, will reveal other opportunities for savings and short payback investment.

Control and maintenance Energy for motors in mixing, pumps, dust extraction, etc., is a major cost and using variable-speed drives and motor controllers/soft starts can significantly reduce energy use in internal mixing and milling. Some areas for improved control are: • Water cooling pumps and cooling tower fans both use significant amounts of energy. Using good and flexible control systems to vary flow rates and keep cooling water supply temperatures constant not only reduces energy use but also improves product consistency and quality. • Festoon coolers need high volumes of air crossing the rubber sheet. Designs using counter-current flow and minimum airflows are best but the main savings come from ensuring that fans are switched off when not in use. • Tip – Use a photocell at the inlet to the

festoon cooler to sense when product is no longer entering the box. Use this to activate a timer to shut-down the fans as the sheet passes through the cooler. • Tip – For dust extraction systems,

minimise the volume of air extracted at the point of use by employing highvelocity/low-volume collection systems. Chapter 5 – Processing

311

5.51

Rubber – moulding

Moulding The theoretical machine SEC required to mould rubber is ≈ 0.1 kWh/kg but actual results range from 0.3 kWh/kg to 2 kWh/ kg. These are efficiencies of only 33% and 5%, respectively, and most of this energy is used to heat the machinery and the surroundings.

Process design Process design based on energy efficiency can produce plant at a capital cost of not much more than for inefficient plant – if energy efficiency is included at the start of process. In addition, it can provide savings in maintenance, improved reliability, throughput and product quality.

Insulation Heat loss is a major source of inefficiency in rubber moulding but it can be reduced by good insulation. Surfaces such as moulds, injection press barrels, autoclave doors and flanges can be easily insulated.

curing plant losses occur and minimises the energy needed for curing. High cure temperatures and rates also maximise the machine throughput. After the shortest cure cycle consistent with product quality has been found, the SEC can be reduced by: • Accurate temperature control. • Accurate cure period timing. • Accurate cure pressure control. Cure temperatures, pressures or times above or below the optimum use excess energy, reduce throughput or increase scrap, all of which increase energy use and costs.

Moulding can be by compression moulding (see Section 5.47 for more actions to take), injection moulding (see Section 5.2 and following for more actions to take) or by transfer moulding.

Cure temperature control In many electrically heated presses, simple thermostats do not provide accurate temperature control. This is best achieved using proportional integral and derivative (PID) control systems that

• Tip – Insulate easily accessible mould

surfaces with board insulation (see Section 5.47). This has a 1- to 2-year payback period. • Tip – Insulate heated moulds from the

press platen using suitable board insulation (see Section 5.47). This has a 1- to 2-year payback period. Insulation saves the most money at sites with large exposed mould areas operating long hours at high temperatures but will always reduce energy use and often reduce the maximum demand (see Section 4.1). If steam is used for heating there will be smaller steam supply requirements for steam plant and savings in gas use. Safety and comfort for operators are improved, heat-up times are shorter, and temperature distribution is more even, reducing ventilation or air-conditioning costs.

Cure controls The energy needed to heat a compound increases with the cure temperature (the heat losses also increase) but the cure rate acceleration more than compensates for the increased rate of heat loss. • Tip – Curing at the highest possible

temperature reduces the time over which 312

Heat losses from uninsulated moulds As with compression moulding, the high temperatures needed to cure injection moulded rubber means hot moulds. These operating moulds show high heat losses from the moulds and no insulation to prevent or reduce this. Chapter 5 – Processing

quickly reach set-point with low overshoot and final offset to reduce the heat loss and energy cost and provide consistency for reduced cure times.

Cure time control Curing plant can take a long time to warm up before the working shift can begin and may be left to run for longer than necessary. In small factories, simple timers can make dramatic savings at low cost but these must be reprogrammed when there is a change in plant use. • Tip – At many sites the cure time has a

‘safety factor’ of up to 25% to allow for raw material variations. Sites should assess the variations and what causes them, reduce/eliminate them and then reduce any safety factors to reduce energy use. • Tip – Computerised cure prediction and

machine control give quick determination of settings for curing plant and good cure cycle control.

Cure pressure control The minimum moulding pressure consistent with product quality should be used to reduce the pump energy and to reduce flash and rubber waste. • Tip – New curing plants using central

computer control have achieved 50% energy savings.

Hydraulic systems Hydraulic plant can consume as much as 50% of the energy used, especially when systems are operated at flows, pressures and loads significantly different from their design capacity. • Tip – Staggering of cure cycles will

reduce the maximum fluid demand and the size or number of pumps required. • Tip – Use accumulators to smooth

intermittent demand from presses and allow the use of smaller pumps. • Tip – A hydraulic network with

oversized, undersized or redundant pipes will waste energy. • Tip – Use booster pumps if ‘spot’

pressures higher than the system pressure are needed. This is cheaper than running a high-pressure system and using reducing valves. • Tip – Servo electric drives can be used

as substitutes for hydraulic systems to reduce energy costs and improve performance (see Section 5.7). • Tip – Using throttling or by-pass valves

Chapter 5 – Processing

to control pressure is very inefficient. In new installations, savings can be made by replacing control valves with pressure-controlled pump motors. • Tip – Heat transfer from the press to the

See Section 5.44 for additional methods to reduce energy use in steam systems.

hydraulic system often means that cooling systems are needed. Improved platen to back-plate insulation will reduce heat transfer and the cooling load.

Steam use Efficiently generated and well-controlled steam is a far cheaper heat source than electricity, especially where good utilisation gives high boiler and distribution system efficiencies. As with any service, it is best to ‘minimise the demand before optimising the supply’. This means: • Minimising the curing heat required. • Minimising heat losses from the process

plant. • Maximising the heat transfer efficiency by prevention and removal of scale, corrosion, air ingress and condensate flooding of heat exchangers. • Maximising the amount of condensate recovered and minimising temperature and pressure losses. • Tip – At sites where steam use has

decreased, the system is often too large for the demand. This gives very high standing losses, maintenance and manning costs. It can be economic to decentralise the steam supply using local gas or electric boilers. • Tip – Very low efficiency may indicate a

need for system improvements or decentralisation of heat supply.

Low-pressure curing Electrical heating methods convert 100% of the electricity supplied into heat, but transfer to the rubber is slow because of the very low thermal conductivity of rubber. The transfer of energy to rubber can be improved with appropriate conversion techniques such as electromagnetic radiation, conduction or convection in liquid or gas curing media. Processes for low-pressure curing are: • Microwave heating. • Infrared heating. • Induction heating. • High-power density resistance heating of

electric ovens.

Eliminate steam leaks, in addition to being a health and safety issue, a steam plume of 1 metre will cost ≈ £1,000/year in energy costs.

313

Regranulation – general

Reused material, lost energy As with tops and tails in EBM, the regranulation of internally generated scrap reuses the actual material but the energy used in processing the material is lost forever. In these sections on regranulation, we will consider regranulation of process waste and not shredding or size reduction before recycling. The principle may be the same but the machines are very different. Energy-efficient regranulator operation is essential but it is even more essential to regranulate as little material as possible. At one site, the site manager was worried about the fact that the regranulator was using too much energy and wanted to know how to reduce the energy use. This was a fine objective but it was even more important that the site not produce as much material for regrinding in the first place. The site manager needed to concentrate on minimising the amount of regrind produced before he concentrated on optimising the method of regranulation. • Tip – Remember the golden rule

‘minimise and then optimise’ for all services. This is also true for regranulation.

The need for regranulators However efficient the site, there will be a need for some type of regranulation to allow the reuse of waste produced by the process, even if it is only the start-up scrap, either for reuse in the process (preferably) or for size reduction before disposal. Most sites have no controls over the use of regranulators and this costs significant amounts of money – regranulators running in the background are common at plastics processing site and, much like compressed air leaks, are taken to be part of the environment. The cost of a small regranulator is shown on the right and even a small machine can be costing over £10,000 per year to operate. Failure to control regranulators will use large amounts of energy and gaining control of regranulators can be a very rewarding exercise. The machine selection will depend on the 314

material to be regranulated and the intended use of the regranulate, i.e., is it to be fed directly back into the process, will it be treated before reuse or is it a simple volume reduction exercise prior to disposal. Whatever the type of machine chosen, the management controls are as important as the type of regranulator.

At one company their scrap rate was classed as zero because ‘all the material was recycled’. Anybody spot the disconnect?

General regranulator tips Regranulators are designed to be sturdy workhorses but irrespective of the process the following general tips should be noted: • Tip – Make sure that the regranulator is

the smallest size possible for the job. Never use the largest regranulator you have just because it is there (see Section 4.18). Regranulator or regrinder?

• Tip – Use soft-start and other motor

controllers to prevent high starting currents (see Section 4.15).

There doesn't seem to be any consistency in the use of the words ‘regranulator’ and ‘regrinder’ in the plastics processing industry.

• Tip – Sharp blades are needed for

efficient operation and good regranulation. Sharpen them regularly to reduce energy, noise and fines. • Tip – Always check and maintain the

gap between the rotating and fixed knives (it should be ≈ 0.2–0.3 mm).

At risk of exposing my own ignorance, I will use ‘regranulator’ for both.

• Tip – Do not overfeed regranulators.

Overfeeding will increase current spikes and can jam the regranulator.

The cost of running a regranulator with a total load of 14 kW (motor + conveyor + fan blowers) £16,000 £14,000 £12,000 Cost per year (£)

5.52

£10,000 £8,000 £6,000 £4,000 £2,000 £0 0

1,000

2,000

3,000

4,000

5,000

6,000

7,000

8,000

9,000

Operating hours

Operating cost for a 14-kW regranulator + blower The small regranulator in the corner probably has a 14-kW load (1-kW conveyor + 7–11 kW-regranulator + 2.2-kW blower) and can be costing over £14,000/year to operate if it is left on 24/7. These costs add up rapidly for even a small factory. Chapter 5 – Processing

• Tip – Check the drive mechanism. If it

uses V-belts then consider replacing these with alternative belts (see Section 4.16). If they are not replaced then at least make sure that the alignment is correct and that the tension is adjusted correctly. • Tip – Make sure the motor is an HEM

and possibly replace it if it isn’t (see Section 4.19). • Tip – Regranulation is a very dusty

process and bearings are subject to dirt and dust collection. Clean and lubricate bearings regularly. • Tip – If the regranulator is not

automatically emptied then always make sure that the collection bin is regularly emptied. Full collection bins will back up and the regranulator will eventually fail.

fit kit for around £800. A simple kit such as this can greatly reduce energy use. • Tip – This is a kit but most sites could

easily introduce similar controls to their regranulators and save energy (see Section 5.53 for alternative methods). The Watt Watcher (and similar automation approaches) are one method of controlling regranulators but strong management and good staff training can have equally effective results (see Section 5.53). • Tip – Train the staff to recognise that

Regranulators almost always have: • Large motors. • High starting currents. • High idling power use. • Low power factors. Management of regranulators is important.

regranulator use is not ‘free’ and provide them with the techniques and tools to minimise energy use in regranulators.

• Tip – Automatic feeding (see Section

5.53) will control peaks in regranulator use and avoid overloading the regranulator.

Regranulator energy use

It is possible to fit most types of regranulators with controls to automatically turn them off when they are not needed. One of these is the Watt Watcher produced by IMS (www.imscompany.com) which uses vibration detection as a signal to turn off a regranulator when the vibration indicates that it is simply idling. This also can be linked to a timer (20 seconds to 2 minutes) to further delay the shut-down and ensure that the regranulator throat is clear. Start-up is controlled by a photocell which detects feeding of the regranulator. Simple, effective and available as a retroChapter 5 – Processing

Regranulator power trace 10 9 8 7 Power (kW)

Controlling regranulators

Controlling regranulators is easy and can be very effective in reducing energy use.

6 5 4 3 2 1 0

00 :0 0 00 :0 5 00 :1 0 00 :1 5 00 :2 0 00 :2 5 00 :3 0 00 :3 5 00 :4 0 00 :4 5 00 :5 0 00 :5 5 01 :0 0 01 :0 5 01 :1 0 01 :1 5 01 :2 0 01 :2 5 01 :3 0

The power trace of a typical small regranulator is shown on the right and it is seen that for most of the 1½ hours of monitoring the regranulator was idling and doing no effective work. The full load power was ≈ 8 kW but this was only for 10–15 minutes. The idling load was ≈ 3.8 kW and this was drawn for the complete period, even when the machine was doing no productive work. This is a classic case of the site failing to ‘minimise and then optimise’ for this service. Carrying out all of the general tips above would simply optimise the wasteful use. In this case, the need is to minimise the use and the site needs to introduce either technology or management controls to reduce regranulator use.

Time (min:s)

Power trace for central regranulator This regranulator is used sporadically but is always running. It draws an average power of 3.8 kW and costs £0.38/hour to operate but for most of the time it is not actually doing anything other than use energy. Simple controls can give rapid results. 315

5.53

Regranulation – processes

Injection moulding Regranulation in injection moulding is required for any scrap product (hopefully minimised) and for sprues and runners. This regranulation can be either closed loop with machine side regranulation feeding the material directly back into the process or the waste can simply be stored and centrally regranulated. As with the closed loop recycling of tops and tails in EBM, the cost of closed loop regranulation for injection moulding needs to be critically examined. The cost of running the regranulator is largely fixed and reducing the amount of sprues and runners can make closed loop recycling very expensive. In one case, the cost of the closed loop recycling was £0.80/kg and this excluded the investment and operational cost of the sprue picker/robot. • Tip – Sites should calculate the cost of

running closed loop recycling, especially when the sprues and runners are small and the regranulator is large, and compare this to the cost of the material being recycled. It may well be more economic in energy and cost terms to centrally regranulate at night when energy costs are lower. Removing the machine-side regranulators can also tidy up the site and allow better access to the machine. The continuous operation of machine-side regranulators for small amounts of sprues and runners, often as low as 1 kg/hour, can make it more economic to turn the regranulator off, collect the sprues and runners until an economic amount is collected and then run the regranulator for a short time to clear the backlog. • Tip – Sites should investigate if it is

more economic to collect sprues and runners at the machine side and then regranulate in a batch. This a management solution approach: Set up a small holding area (similar to a JIT area) where scrap is stored until enough material has accumulated to operate the regranulator. The operator then switches on and operates the regranulator until the holding area is empty and then switches the machine off. The holding area is then clear until it 316

fills up again and the regranulator is run again. This is a management solution to a management problem. • Tip – Regranulators should also be

linked to the machine motions so that when the machine stops operating then the regranulator runs on for a small time to clear the machine throat and then switches off. Equally the machine can be set to only start when the machine motions start – it will be up to full speed before the first material enters the throat and the risk of jamming due to a very high start-up torque is low.

There are generally few risks associated with correctly managing regranulators but as with any engineering project, health and safety aspects of any change should be investigated as part of any project.

• Tip – Regranulation of purgings has

always been a problem but the ‘Purging Recovery System’ from Maguire (www.maguire.com) uses a unique system to shave purgings down to a size where they can be regranulated. Think of a power plane mounted upside down and being run over the purging. This is a unique system and worth a look to recover purgings.

Profile extrusion Bulk regranulation of profile extrusions needs a hopper or process to allow the feeding of long lengths directly into the regranulator and this can be conveyor- or gravity-fed. • Tip – Conveyor feed speeds can be

adjusted by a VSD controlled by the amps drawn by the regranulator motor. As the amps rise then the feed conveyor slows down (and vice versa) and at very low amps then the motor shuts down completely until manually restarted.

Failure to specify or control regranulators At a blown film site, each film line had a large regranulator (55 kW) and associated blower (22 kW) despite the fact that most of the time the regranulators were dealing simply with the film edge trim. The site wanted to be able to regrind large reels at start-up and the regranulators for each film line were sized for this. For almost all of the time the regranulators were effectively idling under no load. This energy-inefficient system was replaced with a series of small regranulators (2 kW each) for the edge trim and a central large regranulator for intermittent use with the larger start-up reels (as for the original regranulators). The payback was less than 5 months. Chapter 5 – Processing

• Tip – The JIT approach (see above)

should be investigated. If regranulators need to be operated continuously then the process is being poorly controlled! • Tip – The Maguire ‘Purging Recovery

System’ (see above) can also be used to recover head waste from start-up.

Film and sheet extrusion The production of film or sheet generally needs continuous regranulation for edge trim and a separate bulk regranulation facility for large roll stock regranulation (see box on the left). The two issues should not be confused or there will be excessive energy use. • Tip – Edge trim regranulator operating

costs should be examined in terms of the real cost of recycling the raw material. • Tip – Edge trim regranulators do not

need to operate if the line is not working. Link them to the process to slow down or stop when the extruder is not running. These machines can also be fitted with VSD drives to adjust their speed to the line speed but ensure that the regranulator operates correctly at low rotational speeds. • Tip – If management is not strong

enough, then bulk reel or sheet regranulators can be fitted with simple timers and photo sensors to detect the presence of product for regranulation (see Section 5.53). A signal can be taken from the current drawn by the regranulator motor, when this drops below a set point then the timer can start operation (to clear the throat) and switch the machine off after a defined time. Photo sensors can be used to detect the presence of material and if no material is present then the timer can start. • Tip – Bulk regranulators should be

subject to the JIT type of approach (see above). • Tip – Edge trim regranulator motors

will often be in the range of 6–7 kW even when the amount of edge trim is minimal. A simple motor change to 3–4 kW can greatly reduce energy costs for lightly loaded motors. • Tip – Instead of operating a

regranulator for each side of the edge trim, consider how the edge trim can be moved across or under the line to one central regranulator for the complete line. This can reduce the cost of regranulation by 50% through some Chapter 5 – Processing

simple engineering. • Tip – Instead of using conventional

regranulators for film consider using small multi-cutters or in-line granulators of the type developed by Kongskilde (www.kongskilde.com). These are much smaller (0.75–1.5 kW) but are adequate for most film lines. • Tip – For sheet edge trim investigate the

use of chippers or guillotines that reduce the size of the edge trim to allow easy transport before later regranulation (see www.rapidgranulator.com for details of their guillotine system). Film edge trim regranulation can use compressed air to feed the thin film into the regranulator; this is a huge waste of compressed air and alternatives exist. • Tip – Do not use compressed air to feed

film edge trim to regranulators. This is very expensive. Examine all the other methods before using compressed air.

Regranulators are very noisy and hearing protection should always be used when close to them. On the first day at a one site I saw the regranulator operator working without hearing protection and questioned the site manager about this. The site manager replied ‘It is OK because he is registered deaf and likes the job because nobody bothers him’. Equal opportunity hiring!

Extrusion blow moulding The treatment of tops and tails for EBM is an essential for the process and minimising the tops and tails was considered in Section 5.29. However, tops and tails are an inevitable part of the process even when minimised and management of the regranulators is an essential part of the process. • Tip – Use the methods listed for

injection moulding and other processes to reduce regranulation energy use in EBM.

Thermoforming Thermoforming inevitably produces waste and regranulators will operate continuously to regranulate the skeletal waste. In this case it is possible to use the JIT approach with the skeletal waste but sometimes every thermoformer will have a machine side regranulator. These machines can be subjected to a range of controls (see above) to reduce energy use. Thermoforming sites will also use bulk regranulators for either collected skeletal waste or for large roll regranulation and many of the controls suggested above are applicable.

Transport of regrind should not be neglected in considering regranulation. The regrind material is always transported somewhere by blowers or similar. Look at these to make sure they are the correct size and managed correctly, i.e., turned off when not needed.

317

Key tips • Plastic processing technology is

improving in energy efficiency. Old machines are inevitably less energyefficient than new machines. • Processors using old machinery are not

‘saving money’, they may well be putting themselves at a permanent cost disadvantage. • The rate of change in improvement needs to accelerate and the machinery manufacturers need to recognise this. • Most processing methods offer opportunities for energy management and energy efficiency improvements. • Sites need to investigate the energy use

of all machinery before new purchases. • Look for large motors that are not used

to their design specification on small machines. • Idling machines in any process are not free – they are costing large amounts of money but are often ignored by the site management. • Machine monitoring can be rapid and low-cost. • IMMs have made a huge leap in efficiency with the introduction of allelectric machines and these can give processors a permanent advantage over competitors using conventional hydraulic machines. • Machine monitoring will enable processors to see inside the IMM cycle and to adjust the settings to get the most energy-efficient settings for the job. • There is no conflict between energyefficiency and productivity – they can both be achieved. • Barrel heating in IMM is a major energy user and can easily be reduced by the use of barrel insulation. • Barrel insulation also reduces health and safety concerns with hot surfaces. • New technologies exist for improved barrel heating and insulation. • All-electric IMMs are a ‘no-brainer’.

• Initial mould design can affect energy

use and designers need to be aware of the cost of their decisions. • Extrusion costs can be reduced by using

VSDs and AC motors instead of DC motors. • Barrel insulation in extrusion is not

always needed but can be useful in certain areas where shear heating is low. • Gear ratios can be changed in extruders to improve energy efficiency. • Cooling water is a major energy user in

profile extrusion and the controls need to be good. • The economics of edge-trim recycling in sheet extrusion need careful examination. • Tops and tails management is a key energy issue in extrusion blow moulding. • Compressed air use is a key energy issue in injection blow moulding. • Thermoforming machinery should be examined for sealing and insulation improvements. • Rotational moulding is ready for change in a variety of areas and energy efficiency can be improved considerably. • Steam generation efficiency in EPS foam moulding is the key issue and can be improved at many sites. • Regranulation is a hidden cost at most sites and little attention is paid to the process economics. • Regranulation energy use can be improved by management action and improved controls.

• Retrofitting VSDs to hydraulic machines

is very cost-effective if the machine parameters are right. • MTCs are a hidden cost in injection

moulding and need to be examined carefully. 318

Chapter 5 – Processing

Chapter 6 Operations

Operations are at the heart of energy management. This is where all the improvements in services and processes come together (or not) and where real changes can be made for very little financial cost. In the immortal phrase ‘it is where the rubber meets the road’. The information on energy benchmarking (see Section 2.3) showed that the operational management of a site can change the energy performance of a site dramatically with few changes in the physical components or layout of the site. The key issues are the dedication and enthusiasm of the site management.

failure. Operationally the task is still the same – get the best out of what you are given and prioritise your efforts to get the best out of your time and efforts. If that means spending more time on energy management and less time on labour concerns then that is what must happen. As always, site managers must go for the most economic allocation of the resources at their disposal – no more and no less.

Site managers have complained about this ‘new’ task of energy management and how much time it was taking. Site managers have always been given resources (men, machines, materials and energy) and have always been tasked with utilising these to the best of their ability to get the best out of the site. This has not changed, site managers are still being given resources and are still being tasked with utilising these to get the best out of them. There is no new task, simply that the rise in the cost of energy means that it is now higher up the management agenda than previously. The fact that site managers could ignore energy in the past is not an excuse for ignoring it in the future and is no reason to call it a new task – it was always there and it always will be. Thinking of energy management as a new task is a fallacy that can only lead to Energy Management in Plastics Processing https://doi.org/10.1016/B978-0-08-102507-9.50006-4, Copyright © 2018 Elsevier Ltd. All rights reserved.

319

Operations – making it work

320

Relative process energy intensity (raw material to finished product) 16 14 12 10 8 6 4

Process

Mixing and compounding

EPS foam

Pultrusion

Extrusion – Film

Extrusion – Profile

Recycling (to (pellet

0

Extrusion blow moulding

2

Injection Moulding

The choice of processing method is rarely based on the energy intensity of the competing processes. It is made on the basis of the complete process economics: this is a complex decision based on the part design, the size and number of parts to be produced, the likelihood of further demand and a variety of other factors. Comparing the energy intensity of the various processing methods is therefore of limited practical use to processors who are tied to a specific processing method. Comparisons are also extremely difficult because, as seen in Chapter 2, the energy

However, it is worthwhile examining the relative energy intensities of some of the main plastics processing methods, at least at the qualitative level. This is shown below and in all cases the energy intensity is for the ‘raw material to finished product’ operation, i.e., for thermoforming this includes mixing of the resin, extrusion of the sheet and final thermoforming.

Compression moulding

Choice of process

easy to define, raw material enters and is converted to a finished product. • Thermoforming – This is more difficult to define. Should the energy intensity be that of the complete process from raw material to finished product, i.e., including extrusion of the reel stock or should it simply be the thermoforming operation from reel stock to the finished product? The amounts of energy used are very different.

Rotational moulding

The main business priority of any site is to make money and energy management can be a key contributor to increasing profits and increasing margins. It is not an additional responsibility at the management or at any other level. Most site managers react very quickly when they see direct labour being idle or deliberately wasting production materials but the same urgency is not present if the actions or inactions of direct labour use excessive energy. If direct labour arrives late for work, their pay is reduced but once they arrive they can switch on all the machines and nobody will say anything at all – which costs more money and why are we doing nothing about it? This must change because they are all resources and money, they are all potential profits being wasted and they are all controlled by the actions or inactions of the staff. Site managers must be strong and consistent to fully implement and sustain operational changes. That is, after all is considered, what they are paid for.

• Injection moulding – This is relatively

Injection blow moulding

The previous chapters have dealt primarily with the technical aspects of energy management and these are effective, relatively trouble-free and easy to implement and maintain. On the other hand, operational improvements are very dependent on people. Whilst these may be the cheapest method of reducing energy use, they are also the most difficult to implement and are definitely the most difficult to maintain in the medium to long term.

intensity of the main processes is dependent on the processing rate. Comparing the energy intensity is also difficult because of the range of processes. This is not simply a matter of different processes but also a matter of where the boundaries are drawn, for example:

Energy intensity

The people process

Thermoforming (incl. extrusion)

6.1

Relative energy intensity of processing methods This table presents a qualitative indication only. No values (kWh/ kg) are attached to the rankings as the relative energy intensity of most plastics processing methods is strongly dependent on the processing rate. Chapter 6 – Operations

Choice of machine Only a small proportion of the energy input into most plastics processing machinery is actually used to melt and form the plastic. The majority is lost from losses in the machinery (motor losses, friction, etc.) or as rejected heat from the heating and cooling processes. This is the base load for the process and acts in much the same way as other base loads. Selecting the correct machine for the job to work the machine at it’s design limits and to therefore minimise the energy use is a key decision in reducing operational energy use. For ‘in-house’ processors, the machine size can generally be predicted from sales figures and schedules although, even here, small products may be run on large machines. For trade or contract processors the decision is less easy and often jobs are run on large machines because smaller machines are not available. These difficult choices will inevitably increase energy use and reduce profits. Processors need to have a defined selection procedure for machines that takes energy use into account and minimises it. This requires a knowledge of the machines, the options and the costs associated with each. • Tip – A large machine producing small

operator involvement and this needs a workforce that is: • Informed – the operators must know

what the programme is, what the potential is, what the current performance is, what the company is doing and how they can contribute. • Motivated – operators must receive recognition for their efforts. This does not have to be money, but can be recognition in the form of publicity or a simple thanks. Here is a thought – instead of looking for somebody doing something wrong so that you can yell at them, try to find somebody doing something right so that you can thank them. Difficult, but very rewarding for both you and the person. • Empowered – operators must feel that they have the power to change things for the better and that they have the responsibility and resources to improve their area. • Tip – What are you doing, specifically, to

make sure that your operators are informed, motivated and empowered? • Tip – Every operator knows their

machine better than you do. They know how to reduce energy costs – they have simply never been asked. Wouldn’t it be good to get the benefit of their experience?

At one site, extruder motors were changed depending on the job running on the extruder: small products had small motors fitted and large products had larger motors fitted. Changing the extruder motor was treated as part of the normal set-up for the job. Initially, this was a radical proposal but all it took to gain acceptance was quantifying the cost of the changeover versus the cost of operating a large machine for a small job. Put numbers on it and the decision can be clear and rational rather than based on prejudice and ‘what we have always done’.

products will always use more energy than a smaller correctly sized machine. • Tip – Producing to a higher specification

than required will waste energy. • Tip – Heavy tooling is often moved

around a site but sites rarely consider the option of changing motors, barrels or other machine components to optimise the machine for the job.

I

or nf

m

ed

• Tip – Look for large motors that are not

used to their design specification on small machines. • Tip – Most plastics processing uses

screws to move the plastic. A ‘generalpurpose’ screw is more correctly a ‘nopurpose’ screw because it is not correct for any material. Materials-specific screws are always better (when used with the correct material).

Operator involvement Operator involvement (and harnessing their common sense) is the key to lasting operational improvements. This will require operator training in some form (see Section 6.5) but the real key is in Chapter 6 – Operations

The building blocks of operator involvement All levels of staff, but particularly operators, need to be involved if operational improvements are to reduce energy use. The three elements of this are information, motivation and empowerment. Site managers need to provide all three elements. 321

6.2

Setting, start-up, stand-by and shut-down

Cool running Optimising machine settings in any process is an essential step in reducing energy use but many companies have few procedures for optimising the process. Get the settings wrong at the start and both energy and money will be wasted whenever the settings are used. Get them right and the energy use and cost are minimised for high-quality output.

Initial machine setting The initial setting process is rarely managed correctly to produce optimised settings. After tooling acceptance (a fairly random process in many companies), the initial setting process is often as follows: • The tooling is set using traditional settings that the setter has used before for similar materials and tools. It doesn’t matter if they were the best – ‘they worked then so we’ll try them again’. • The setter plays with the settings to

reduce cycle times and to find the local best settings without changing the initial settings too much. • The setter runs out of time, gets bored or

decides that he has found the ‘best’ settings for the tool and the machine. • These settings are recorded on the machine or setting sheet. This is the process optimisation equivalent of Brownian motion (a ‘random walk in space’) and is not the way to go about it.1 This is not a serious problem because these settings will never be used – shifts, operators and setters will all establish their own settings and use them when nobody is looking. Correct setting must follow a defined procedure to optimise the machine and tool combination. For injection moulding, a good example of this is PRO-OP from RJG Technologies Ltd (www.rjginc.co.uk) which takes a scientific approach to getting the global best setting for the machine and tool. Similar setting techniques are available for other processes but all should include the following elements: • Tooling and machines must be set using

correctly designed experiments. • Machines and materials used must be

322

the same as the production machine and material. • Optimised settings must be fully recorded. • The initial parameters should be used to

calculate control chart parameters for SPC charts. • Initial trial settings should be programmed into the machine and locked out to prevent changes. • Initial trial settings should be used for

all runs of the machine and tool unless changes are authorised by a senior person.

Start-up After recording the settings, it is relatively easy to control the process but start-up

I have lost track of the number of machines that I have seen set incorrectly. This includes machines running standard PP injection mouldings at 280°C (with no barrel insulation) ‘because we have always done it that way’. Get your machines set right, record the settings and do not change them unless absolutely necessary.

Setting sheets Setting sheets should include all the details necessary to get the job running and to be sure that it is producing the right product to the right specification. Typical details to be recorded are: Machine and tooling specification, i.e., all details of machine

set- up, including serial numbers of machines, dies and other ancillary equipment. Machine settings, i.e., all variable settings for the machine

should be specified including insulation fitment as required. Tooling settings, i.e., all variable settings of the tool should be

specified including cooling water connections or other mould temperature control settings. Material specification, i.e., all details of type, supplier, grade,

colour, additional additives required, moisture content and drying time (if required). Tools needed for setting up the machine/tool. Set-up time specification (good product to good product) and

set-up scrap allowance. Start-up sequence for all machine areas, tool and ancillaries. Production rate required. Product specification and control chart/inspection information.

This should also include details of any allowance for scrap product. These details should allow anybody to set up a machine/tool and get it running to specification. No changes to the settings sheets are allowed unless the changes are authorised by senior production management and quality personnel. Disciplinary action should be taken if unauthorised changes are made to the setting of the machine/tool. Chapter 6 – Operations

must be firmly and consistently controlled to ensure that the settings are actually used. If modifications are needed, then they must be approved and recorded on a revised setting sheet. Even when setting sheets are used, they rarely take energy use into account and it is common to see machines being set up where the procedure is as follows: • 0:00 – Switch everything on (machine,

motors, heaters, ancillaries, downstream equipment, lights, etc.). • 0:05 – Go away and wait until the machine warms up. Time for coffee. • 0:45 – Return when everything is hot

and set the machine. • 0:65 – Start machine.

This is simply not energy-efficient and setting sheets should also include a startup sequence for all machines, tool and ancillaries. This can be a simple time-line for when the various areas/items are to be switched on: • 0:00 – Switch on main heaters. • 0:45 – Adjust machine settings. • 0:55 – Switch on motor. • 0:60 – Switch on downstream equipment. • 0:65 – Start machine. This time-line approach provides setters with firm guidance on what to switch on when and also gives guidance on the setup timings. • Tip – Take a walk around the site, look

for the setting sheets and check that the actual machine and tool settings match those on the setting sheets. If not, then where are the records, reasons and signatures for the changes? These unauthorised changes are probably costing money and energy. Do not ask about this, you will always be told that they are correct and being used – check it physically in the production area. • Tip – Setting sheets should also include

a ‘Special Notes’ section for details of safety issues or notes. • Tip – Setting sheets provide the basis for

reducing set-up times and the start-up time-line referred to above needs to be kept up-to-date with reductions in set-up times.

Stand-by Machines are often left in a fully operational condition because it is believed that this is more economic than turning them off. For most IMMs, if the machine is Chapter 6 – Operations

not going to be used for over 2–3 hours then it is more energy-efficient to turn the machine off and then turn it back on again when it is needed. Each machine will have an optimum time (depending on the size and the heaters) but most are in the region of 1–2 hours and some are considerably shorter. Other plastics processing machinery has similar times for economic turning off. If the machines are not going to be used within the economic turn-off time then the machine should be completely turned off. If the machine is going to be used again within the economic turn-off time then the machine should be put into the stand-by condition. This is the condition with all unnecessary items switched off, heaters banked down to a holding temperature (< 130°C) and services isolated. • Tip – Sites should determine their own

values for economic turn off times. This is relatively easy, use a monitor (see Section 8.3) to determine the start-up energy used and compare this to the stand-by cost to determine the optimum turn off time. In practice, it is best to add a small safety margin to allow for the effort of turning off. Economic turn-off times should be part of the setting/ operating instructions. • Tip – Sites should establish stand-by

conditions for every machine and these should be part of the setting sheets. • Tip – It is best if the stand-by settings

are automatically actuated, i.e., when the machine has not been operating for a specific time then it automatically goes into stand-by mode. This is particularly applicable for IMMs, when the platens stop moving for 3–5 minutes then the hydraulic motor should automatically power down.

Shut-down Economic shut-down is the opposite of the start-up process and follows on from the stand-by condition. All items using energy should be shut down in a logical sequence that stops them using energy as soon as possible. As with stand-by, it is best if this can be automated to remove the human element. • Tip – Use interval data (see Section 6.3)

to examine the effectiveness of the shutdown process. • 1. Kent, R.J. 2017. ‘Cost management in plastics processing’, Elsevier. Section 5.12.

Tweaking of machines by individual operators (to get more production) causes more lost time and energy than almost any other cause.

During a survey at an injection moulding site, everything was going well. Their services were excellent and after the first day we could find almost nothing to improve but their energy use was still well above the benchmarks. The second day revealed all – the site had 28 machines, 14 were running and the other 14 were ready to go – all motors were running, all barrels were at temperature and all services were connected and open. This was 14 machines simply sitting there using energy. Initially we thought that it was lucky that they were using PP and not a thermal history sensitive material such as PVC. On reflection, it became obvious that people brought up using materials such as PVC would simply never have left machines in that condition. Sometimes the hard lessons are worth it.

323

6.3

Using interval data in operations This is typical of the standard weekend shut-down for this site.

Getting every last bit of information Interval data from the supplier were discussed in Sections 4.5 and 4.6 as a method of looking at the general site operations but they can also provide an invaluable insight into the effectiveness of start-up, stand-by and shut-down.

The calendar chart The calendar chart is a simple chart of the energy use (by interval and by day) over a month. This is quickly generated using Energy Lens (www.energylens.com) and a sample output is shown below for a typical site operating 24/5. This shows: • A shut-down starting on Saturday 17 December 2016 with the site shut-down by 03:45. The site is then shut-down for 48 hours until start-up at 04:45 on Monday 19 December. During this period the site uses an average of 180 kWh/15 minutes or 17,760 kWh/day (£1,776/day).

• A shut-down starting on Friday 23

December 2016 with the site shut-down by 22:00. The site is then shut-down for several days until start-up in the New Year. During this period the site uses an average of 90 kWh/15 minutes or 8,640 kWh/day (£864/day). The energy use for the different levels of shut-down is clearly visible in the highlighted sections of the calendar chart (below). These two shut-downs were nominally identical according to the site, i.e., the site was shut-down with no production, but the difference between an ineffective shutdown and an effective shut-down is £864/ day. Over a full year (50 weekends/year or 100 days), then simply achieving the effectiveness of the Christmas shut-down would save the site £86,400/year with no effect on operations.

We need better information and not more data Most companies are awash with data but data are just numbers. What is really needed is information and this is not the same thing. Only information allows management to take action.

Thu, 1 Dec 16

Fri, 2 Dec 16

Sat, 3 Dec 16

Sun, 4 Dec 16

Mon, 5 Dec 16

Tue, 6 Dec 16

Wed, 7 Dec 16

Thu, 8 Dec 16

Fri, 9 Dec 16

Sat, 10 Dec 16

Sun, 11 Dec 16

Mon, 12 Dec 16

Tue, 13 Dec 16

Wed, 14 Dec 16

Thu, 15 Dec 16

Fri, 16 Dec 16

Sat, 17 Dec 16

Sun, 18 Dec 16

Mon, 19 Dec 16

Tue, 20 Dec 16

Wed, 21 Dec 16

Thu, 22 Dec 16

Fri, 23 Dec 16

Sat, 24 Dec 16

Sun, 25 Dec 16

Mon, 26 Dec 16

Tue, 27 Dec 16

Wed, 28 Dec 16

Thu, 29 Dec 16

Fri, 30 Dec 16

Sat, 31 Dec 16

Calendar chart – weekend shut-down counts This is a calendar chart for a site operating 24/5 and shows the power drawn every 15 minutes over the day. The chart clearly shows the ineffective weekend shut-downs, the start-ups and more revealingly the effective Christmas shut-down. Simply replicating the effectiveness of the Christmas shut-down for the weekend shutdown would save the site ≈ £86,400/year. Ineffective shut-downs cost real money. 324

Chapter 6 – Operations

Note: The site was also given a target to reduce the cost of shut-down to £500/day to further reduce the cost of shut-down. • Tip – At every shut-down, inspect the

site (with checklists) to check that all equipment is shut-down.

The start-up overshoot The calendar chart also shows the start-up of the site on three Mondays. Each startup shows a ‘start-up overshoot’ (see arrow on chart on the left) and this is also shown in more detail in the chart on the upper right. The shut-down consumption level rapidly increases at start-up and overshoots the normal level. This is an indication that the site is starting up as per the standard method where all the machines are turned on at once and draw a large load whilst they are heating up but not actually being used. This is wasted energy and increases the power drawn. Interval data can be used to identify and manage start-up overshoot to reduce energy use, but more importantly to reduce high peaks in the power drawn.

400

350

kWh (per 15-minute interval)

In this case, the site should inspect all operations (with checklists) at every shutdown. If it cost £100 for the inspection at every shut-down to check that the site is fully shut-down then the site would still save £750/day of shut-down.

Single day profile: Mon, 19 Dec 2016 450

300

250

200

150

100

50

0

00 :0 0 01 :0 0 02 :0 0 03 :0 0 04 :0 0 05 :0 0 06 :0 0 07 :0 0 08 :0 0 09 :0 0 10 :0 0 11 :0 0 12 :0 0 13 :0 0 14 :0 0 15 :0 0 16 :0 0 17 :0 0 18 :0 0 19 :0 0 20 :0 0 21 :0 0 22 :0 0 23 :0 0

These results clearly show that there is still considerably more equipment operating during the site’s conventional shut-down than during the Christmas shut-down. There is a need to improve the shut-down process throughout the year and to ensure that all non-essential services and machines are turned off during every shut-down.

Time (15-minute intervals)

Start-up overshoot This indicates that all the machines are turned on at once with no time-line approach. This can easily be reduced by starting machines in a programmed order to reduce overshoot and maximum demand. 00:30

02:30

04:30 06:30 120-140

08:30

100-120 80-100

10:30

60-80 40-60

12:30

20-40 0-20

14:30

• Tip – Use timelines (see Section 6.2) to

16:30

save energy at start-up. 18:30

The heat map

• Tip – This is a simple surface plot in a

spreadsheet. Changing the values can give insight into energy use and times. Chapter 6 – Operations

20:30 22:30 1 12 6 4 8 00

01 /0 03 1 /1 /0 6 05 1 /1 /0 6 07 1 /1 /0 6 09 1 /1 /0 6 11 1 /1 /0 6 13 1 /1 /0 6 15 1 /1 /0 6 17 1 /1 /0 6 19 1 /1 /0 6 21 1 /1 /0 6 23 1 /1 /0 6 25 1 /1 /0 6 27 1 /1 /0 6 29 1 /1 /0 6 31 1 /1 /0 6 1/ 16

A variation on the standard methods of analysing interval data is the heat map and an example is shown on the right. A heat map uses a 3D plot of the energy use and is similar to contour lines on a map where each contour (or colour in this case) represents a level of energy use by day and time. In the example, the peak energy use times are clearly highlighted and the operations staff can then investigate the reasons for the high use.

Heat plots A heat plot is simply a method of looking at a complete month of data in one graph to see when the highest energy demands occur. The heat map can rapidly find the times of maximum demand and allow action to be taken. 325

6.4

Tool changeover and quality control

Tool changeover

• Standard base plates.

Whilst tool changeover may not appear to be directly related to energy use, most setups happen while the machine is live and using energy. The cost of the set-up therefore includes the cost of the energy use during the set-up and reducing the set-up time automatically reduces the amount of energy used. Reducing set-up times also reduces the importance of the concept of Economic Batch Quantity (EBQ) because the whole concept of EBQ is driven by the need to amortise and recover the production lost due to the time taken to set up the process. EBQ also drives excessive inventory and the possibility of redundant or damaged stock, and loss of the energy that has been used to produce the product.

• Combining handed tooling. • Parallel operations. • Set-up sheets for all variables.

External set-up operations – Improve by: • Pre-setting of tooling. Provide tool kits

for each tooling set. • Standardise on all screws, bolts and

Reducing the set-up time Set-up time reduction works by accepting that some operations can happen while the machine is running (external set-up operations) and others require the machine to be stopped and access to the machine (internal set-up operations). The aim is to carry out all the external actions before the machine has finished the current run, stop the machine, carry out the internal actions and start the machine again. This greatly reduces the down time from good product to good product. The sequence is:

Step 1 Establish a ‘set-up time reduction team’ from the shop floor. One of the best methods of ‘capturing’ the current method is to video the operation. Watch the video with the team to see the times where people and machines are doing nothing. This exercise will generate many suggestions for improvement. Analyse the existing set-up times. Try putting these on a chalkboard to show the employees what is important. There will be an immediate improvement.

Step 2 Divide the total set-up time into internal and external set-up operations and reduce these. This is done as follows: Internal set-up operations – Improve by: • Quick-change tooling/connections.

326

The set-up time reduction process1 The basic outline of the set-up time reduction process. The process is not a once-and-for-all process but continues as part of the continual improvement programme. Reducing set-up times will reduce energy use by reducing waste in the process. Chapter 6 – Operations

fixtures to be used in tooling. • Pre-kit all gauges and inspection equipment ready for immediate use. • Provide tool kits beside the machine for

all operations. • Make all special equipment available. • Use standard base plates and

connectors.

Step 3 Convert internal operations to external operations that can be done before stopping the machine.

see the effects in the energy use of these sites. The cost of quality is not just the cost of inspection and scrap materials; it is the total cost of not getting the product ‘right first time’. It includes the energy used to produce the rejected product that is lost forever even if the material can be recovered by in-house recycling. This is not insignificant in some companies. • Tip – Always include the cost of the

Start again.

energy lost in the cost of quality calculations for the company. The true cost of quality is always higher than that first estimated by most sites, i.e., the cost of their Quality Control Department. For the average plastics processing site, the true cost of quality is somewhere between 5 and 25% of their turnover. At a nominal value of 10%, this is higher than the profit margin for most sites. Most of this cost is preventable and yet many sites have yet to seriously try to reduce this avoidable cost.

• Tip – Reducing set-up time is not only

• Tip – Quality costs have not gone away

Step 4 Reduce and speed up internal operations further through experience.

Step 5 Reduce and speed up external operations further through experience.

Step 6

good for energy use but also for productivity.

During one of our trials with set-up time reduction we wanted a benchmark on the current times to prove improvements. We set up a chalkboard and started to note the times. No sooner had we started than the setters started a competition to improve the set-up (they didn’t tell us). Before we started the formal process the set-up time had been halved from 8 hours to under 4 hours. When asked how they had done it they replied: ‘It was easy – but we never knew you cared so we never made an effort!’

and at many sites there is still much work to be done!

Quality control It is still with a sense of disappointment that a section on quality needs to be included in a book about energy management but many sites have not seen the obvious link between getting a product right first time and the excessive use of energy. One of the basic financial benefits of quality management (and that is not the same as inspection) is that it is cheaper to prevent defects being produced than it is to detect them after you have made them. Prevention reduces waste of all types, including the energy used to produce the defective products, reduces costs, gains orders and either increases profits or increases sales by reduced prices or by greater customer satisfaction. The results of defect prevention and defect detection are shown on the right. Quality is not an abstract theory but a vital tool in managing any site. Some sites have made the transition to defect prevention and quality is no longer an issue – it is simply part of the environment in which they operate. These sites also have good control of their energy use. Despite this, inspection and product rejection are still used at many sites as the standard method of quality control. This accepts energy use for the production of defective products and it is possible to Chapter 6 – Operations

• 1. Kent, R.J. 2017. ‘Cost Management in Plastics Processing’, Elsevier. Section 5.17. • 2. Kent, R.J. 2016. ‘Quality Management in Plastics Processing’, Elsevier. Section 5.1.

Detection versus prevention Detection (after the event)

Prevention (before the event)

Tolerates waste

Avoids waste

Raises cost

Lowers cost

Loses orders

Gains orders

Destroys jobs

Protects jobs

Two approaches to quality2 Would you prefer defect prevention or defect detection? Defect detection tolerates waste. It may not lose material if the defect is caught in time and the material recycled but it does lose all the time and energy used in producing the rejected material. 327

6.5

Training and employee involvement

Involve everybody Staff can only assist in the achievement of the energy management targets if they are aware of the effects of their actions and the true cost to the company. This awareness can only be achieved by training. Buy-in from employees, at all levels, is essential. Effective training is necessary to get this.

Training for the role The type of training to be delivered varies with the position in the company and whilst everybody has a role to play in energy management, they do not need the same information or training: • Directors need to provide top-level support to the operations so that the people on the ground can actually get on with the job. • Line managers need to provide resources

(time and money) to carry out the actions and, contrary to expectations, time is often the limiting resource. • Operational staff are the people who will carry out the real work and, in most cases, they need little other than being freed from the current restrictions placed on them. • External specialists will provide the essential detailed technical advice for energy management and are a resource that can be tapped by any level of the company. The roles of the various positions are shown on the right.

• The benefits of reducing energy use

(reduced emissions, reduced costs and increased job security). • What we want to achieve and what we

can actually achieve. Awareness training should be limited due to the automated nature of most plastics processing methods and the limited ability of many staff to affect the outcomes. The training should be approximately 40 minutes long for existing staff and should be integrated with other induction procedures for new staff, i.e., all staff receive a health and safety induction and should receive energy awareness training at the same time. Energy awareness training should be delivered to all staff at the site.

Be conservative in the targets, staff involvement is retained when targets are achieved – better to ‘under-promise and over-deliver’ than to ‘overpromise and underdeliver’.

• Tip – Nobody wants to explain to their

children why they waste energy at work but they will be proud to explain how they are reducing energy use and CO2 emissions. • Tip – Create a short general awareness

training programme based on the company energy policy (see Section 1.5)

If you think the cost of training is high, consider the cost of ignorance!

The important issues to be addressed are: • Why we should save energy (preferably

presented in terms of CO2 emissions). 328

re d er gy

Awareness training is not technical-based but emotion-based. All staff will be aware of climate change issues and the need for reductions in energy use as part of climate change reduction actions. They want to reduce energy use at home because of cost and emissions and this should be linked to their actions at work.

En

Awareness training

s ce ur so Re

The training delivered should be relevant and specific to the role and can be divided into three basic types.

uc ti o n

Training specifics

The role in energy management varies with position All staff must accept that their role will be different in implementing effective energy management. External specialists will often be necessary to achieve the full potential savings by providing expert advice on potential projects. Chapter 6 – Operations

and use this as part of normal staff training process.

Policy and financial training Training on the policy and financial aspects of energy management is best presented as a ‘Management Briefing’ rather than as formal training. This should focus on the financial benefits of energy management and the need for a site policy. The important issues to be addressed are: • Energy use as a rapidly rising variable and controllable cost. • Potential profit improvements as a result

of energy management (see Section 1.4). This is best presented as the profit equivalent of increased sales. • The rapid payback from most energy management actions and the continued return on investment into the future. Policy and financial training should be designed to get senior management support for energy management and agreement to set the policy and provide the resources. Policy and financial training should be delivered to directors and senior managers.

Tools training This should be process and product specific and developed by the process manager. This workbook can be used to highlight the important issues for the relevant process. The important issues to be addressed are:

should be taken as soon as possible to show good faith with the operator’s recommendations.

As example of employee involvement: An advertising sales person was recruited by a publisher to save a failing magazine. She agreed to accept 5% of her advertising sales as salary. She was very successful and saved the magazine. The problem was that her 5% became so high that her salary was actually more than some of the company directors. Despite the fact that she was paid on results and the company got 95% of what she brought in, the directors were not happy and they limited her salary so that it was less than theirs.

Employee involvement Training is the start of employee involvement and will naturally raise employee expectations of both action and results. Energy management can easily become another ‘management initiative’ unless the site continues to progress and, more importantly, reports this progress to the employees on successes and achievement of targets. This can be done by area, by process or by site but must be done regularly to retain employee involvement (see Section 3.7). Many sites are concerned about reporting financial savings – if the operations staff save money then they may want some of it back in their pay packet – but is that unreasonable if they save more money than you give them? • Tip – If reporting financial savings is a

real concern then sites can easily report energy savings in terms of CO2 emission reductions. • Tip – Know where you want to get to –

She left.

the ultimate aim is to make energy management as integral to the process as ‘quality’. The discussions about quality are rapidly fading into the background – it is no longer a debateable issue, it is simply part of the environment. The end point is when energy management reaches this stage.

The magazine failed. They didn’t get their 95% of the sales. The company is no more. I wonder why?

• What do we do in the process? • Where do we use energy in the process?

Tools training should be delivered to all line managers and operational staff. • Tip – Part of the tools training should

always be a ‘go-see’ exercise and this should be carried out during the training. Operators and employees are taken to a production area other than their own and asked to identify five areas where they could reduce energy use. It is important that this is not their area otherwise they will be blinded by their current practices. They are then taken to their own production area and carry out the same exercise. The results can be astounding. • Tip – A ‘go-see’ exercise will identify a

lot of common areas (lighting will always be an issue because they can see it) but ideas should be recorded and action Chapter 6 – Operations

Topic Awareness

Policy and financial

Directors/senior managers





Line managers







Operational staff







Tools 

Energy training varies with the level in the company All staff need basic awareness training, directors need to understand the policy and financial aspects to generate the highlevel support but the line managers and the operational staff need to understand the tools for practical energy management. 329

The benefits of employee training

It can be proven

Performance assessment – Year 1 1,200,000 Year 1 results 1,000,000 Energy use (kWh)

The charts on the right show the energy performance of a plastics processing site (injection moulding, injection blow moulding and assembly).

There was no new equipment, no new processes, no monitoring and targeting and no other management intervention. The clear benefits continued into Year 2 and the performance for Year 2 is shown 330

800,000

No v

600,000

De c 400,000 Year 0 kWh = 2.1792 x Production volume + 305,471

200,000

R2 = 0.8011

Note: If in any doubt, Section 2.8 shows how to read these charts.

0 0

100,000

200,000

300,000

400,000

Production volume (kg) Deviation from standard for month – Year 1 150,000

50,000

ct -1 6 N ov -1 6 De c16

O

l-1 6 Au g16 Se p16

Ju

Ju n16

6

ay -1 6 M

6

ar -1 M

Fe b1

-50,000

6

0

Ja n16

Deviation from standard (kWh)

100,000

-100,000 -150,000 -200,000 -250,000 Month

CUSUM – Year 1 200,000 150,000 100,000 50,000

De c16

No v16

Ju l-1 6 A ug -1 6 Se p16 O ct -1 6

Ju n16

Ap r16 M ay -1 6

M

ar -1 6

0 -50,000

Fe b16

CUSUM from standard (kWh)

The site shows consistent performance to the Year 0 PCL for most of Year 1 until November. In November and December the energy use decreased by over 20% compared to the PCL prediction. This is shown clearly in the deviation from standard graph shown on the middle right where performance suddenly improved and both months were ≈ 185,000 kWh better than predicted. This result is also seen in the CUSUM graph shown on the lower right where the performance was 137,800 kWh worse than predicted until November when it suddenly changed and by the end of the year the CUSUM graph was 235,000 kWh better than predicted. There was an obvious sudden improvement in the energy performance of the site in October but what actually happened? The reality is that the recently hired energy manager delivered an energy management training session to every employee over a period of 3 weeks. As recommended in Section 6.5, this was a 40 minute training session followed by ‘gosee’ exercise. The innovative aspect of the training was that exactly the same session was delivered to every single person on the site from the CEO to the floor sweepers. This included all the shifts and even included the contract labour so that everybody had the same information. Nothing else changed.

PCL for Year 0

Ja n16

Staff training is often asserted to be beneficial to a company’s profits but there is often difficulty in proving and quantifying the exact benefits. This is not the case for staff training in energy management. The benefits are both provable and quantifiable.

Ap r-1

6.6

-100,000 -150,000 -200,000 -250,000 -300,000 Month

The effect of training A simple 40-minute training session (carried out in September and October) can be seen to change the results for this site. The training gave a 20% reduction in energy use almost immediately as the staff took notice and action. Chapter 6 – Operations

in the graphs on the right.

Performance assessment – Year 2 1,200,000

• Tip – Energy training has provable and

800,000

600,000

400,000

• Tip – It is possible to do this in any site

0

100,000

200,000

300,000

400,000

Production volume (kg) Deviation from standard for month – Year 2

De c17

No v17

17

ct -1 7 O

17

Se p-

Au g-

Ju l-1 7

n17 Ju

ay -1 7 M

7

A

7

ar -1 M

Fe b1

n17 Ja

Deviation from standard (kWh)

-20,000

pr -1 7

0

It has to be repeated

-40,000

-60,000

-80,000

-100,000

-120,000

-140,000 Month

• Tip – Energy training should be

CUSUM – Year 2

CUSUM from standard (kWh)

De c17

N ov -1 7

17

ct -1 7 O

Se p-

17 ug A

Ju l-1 7

n17 Ju

7

ar -1

Ap r- 1 7 M ay -1 7

-100,000

M

Ja

n17

integrated with other induction procedures for new staff.

7

0

Fe b1

quickly and can be used to reduce energy costs whilst all the technical and structural actions are taking place. The technical and structural actions can then be used to lock the savings in place.

Year 0 kWh = 2.1792 x Production volume + 305,471 2 R = 0.8011

0

and the source materials for this training session are available for free download from www.tangram.co.uk/ energy.

• Tip – Training can get things moving

PCL for Year 0

200,000

quantifiable benefits.

One issue with training is that it has to be repeated to continue to be effective. Although it is not visible from the data shown, our experience is that this type of exercise has a ‘half-life’ and the benefits decrease with time. Sites will then need to repeat the training or take other actions.

Year 2 results

1,000,000 Energy use (kWh)

Note: We have kept the PCL for Year 0 to show the magnitude of the improvement. The performance relative to the PCL is shown on the upper right and the improvement is marked. This carries through in the monthly deviation (data were only available up to July 2017) and the CUSUM graph shows that by July 2017 the site had saved 656,000 kWh (£65,600) relative to the predicted performance. Combined with the 2016 savings for November and December, this is a total saving of 891,000 kWh (£89,100) over 9 months.

-200,000

-300,000

-400,000

-500,000

-600,000

-700,000 Month

The continued effect of training The benefits of the training continued into the future and gave continued savings. However, training suffers from a ‘half-life’ and the benefits will gradually fade away as people forget or change. The training will need repeating in the future. Chapter 6 – Operations

331

6.7

Processing operations – where are you now?

The initial steps in processing operations As with the score charts shown earlier, this is a self-assessment exercise to allow a site to benchmark their current status. This will set the scene for planning improvements in the area of processing operations.

plastics processing sites, the weakness of the management is reflected in excessive energy use.

Completing the chart This chart is completed and assessed as for those presented previously.

How sites are run, in human terms, is naturally important in terms of energy management. Simple rules for managing the operations can ensure that energy use is reduced considerably. This is real management of the process and gaining control of the process through management action. In far too many

Poor management of processing and simply ignoring the issue will not make excessive energy use go away. We are watching and have the tools to measure performance.

Processing operations

Set-up 4 3 Operator training & awareness

2

Stand-by

1 0

Tool changeover

Shut-down Management is about managing the process rather than simply administering the results.

Quality control

Use the scoring chart to assess where you are in processing operations The numbers from the scoring chart can be transferred to the radar chart for a quick visual assessment of where you are in terms of processing operations. 332

If you want to be an administrator then be prepared to be paid as one (it is generally much less than a manager).

Chapter 6 – Operations

Processing operations Level

4

Set-up

1

0

Score

Shut-down

Quality control

Tool changeover

Set-up sheets Minimal stand-by Shut-down sheets Full SPC systems available to all implemented. available to all operation. staff, sheets used Machines staff, sheets used Capability studies to start machines. switched off on to shut-down carried out before machines in project start. Sheets updated job completion regularly with unless next job is energy-efficient Control charts latest data. ready to start. manner. Sheets used for critical parameters. Data sheets for updated regularly stand-by settings with latest data. available & used.

OTED implemented.

Set-up sheets available but use is restricted & some are out of date.

SMED implemented.

3

2

Stand-by

Stand-by instructions available to operators but more management action needed to enforce implementation.

Shut-down sheets available but use is restricted & some are out of date.

Limited SPC on specific products for specific customers. SPC carried out as a duty or customer service rather than as a normal part of the operations.

Operator training & awareness Excellent operator training (general & job-specific). Structured general training & certification to national standard & internal jobspecific training.

Extensive jobspecific training for operators but little structure & most is ad-hoc.

Moderate ad-hoc Set-up sheets Stand-by Shut-down sheets Complex ‘end of Set-up time not job-specific available but use instructions available but use line’ inspection relevant for most used (AQL products training for is optional & available in theory is optional & majority of many out of date. but little concrete many out of date. approach). (constant running) management Limited attempt to or set-up time operators. gain control of the reduction carried action taken to out to basic level enforce in process. operations. for majority of products.

Simple ‘end of Set-up sheets No information on Shut-down sheets held by stand-by held by line’ inspection. management & Quality based on management & operations not used by available. not used by rejecting the bad Some machines setters. rather than setters. Many out of date. controlling the Many out of date. are switched off but most on standprocess to by for no apparent prevent reason. production of bad products.

Set-up time reduction carried out to basic level for minimal number of products.

Limited ad-hoc job-specific training carried out for some operators.

No setup sheets No information on available or used. stand-by operations available. All machines set to ‘stand-by’ or left operational when not being used.

x

Chapter 6 – Operations

x

No shut down sheets available or used.

No visible inspection.

No consideration of changeover time reduction. EBQ dominates production thinking but no action taken to reduce.

No structured operator training available in either general or jobspecific topics. Training uses the 'sit by Nellie' approach.

x

x

x

x 333

6.8

Maintenance

Maintenance matters

is used at a significant minority of sites.

Maintenance may appear to have only a tenuous connection with energy management but the two are actually intimately related. Poor maintenance will result in inefficient machines (in any sense of the word) and, in the context of this workbook, will result in energyinefficient machines. The SEC (kWh/kg) of a machine inevitably decreases with poor maintenance: • For any machine, worn components and bearings will increase energy use before the wear results in failure. • For extruders and injection moulding machines, screw wear will increase energy use for the same output and this is a sensitive indicator of screw wear. Machines that fail through poor maintenance cause many problems to a site such as: • Lead times increase and sometimes cannot be reduced if the machine is a bottleneck for the site. • Scrap and re-work are increased.

Planned preventative maintenance (PPM)

• Production planning becomes very

difficult, if not impossible. A maintenance programme of some description is a necessary requirement for removing unscheduled stoppages and increasing machine availability. The aim of the maintenance programme is to ensure that unscheduled stoppages do not occur and to minimise energy use.

PPM involves regular maintenance of specific identified areas and can reduce energy use provided the correct items are serviced at the correct time. Sometimes the schedule will identify maintenance areas where there is really no need for maintenance at the specified time (cautious) and sometimes the schedule will fail to identify items that do need maintenance (reckless). The difficulty is that often the maintenance is cursory and concentrates simply on those items on the schedule. This type of system is used at the majority of plastics processing sites.

Predictive maintenance (PM) PM is often referred to as ‘condition monitoring’ as it actually measures the machine’s condition to predict and prevent failure. Typical techniques used are: • Vibration analysis and monitoring. Some ultrasonic leak detectors (see Section 8.3) also include vibration monitoring capability but these need to be used carefully for full PM work. • Energy use analysis can be used to predict the need for maintenance.

Poor

The various strategies for maintenance range from non-existent (breakdown maintenance) to complex and sophisticated systems that monitor machine condition and prevent breakdowns occurring.

Condition monitoring

Total productive maintenance (TPM)

Breakdown maintenance

334

Reactive or breakdown maintenance

Planned preventative maintenance (PPM)

Strategies for maintenance

Breakdown maintenance will run machines until they fail. The machines will use excessive energy and will eventually fail (and always at the worst possible time) and cause customers problems. A machine that is subject to breakdown maintenance is shown on the far right. This is not so much a strategy as a lack of imagination and a lack of management control. This type of system

Maintenance is not an option in a ‘world-class’ business. It is simply a method of improving the return on capital employed (ROCE) and of being sure that you can meet the customer’s requirements.

Best

Reliability-centred maintenance (RCM)

Maintenance strategies range from the non-existent to complex and sophisticated systems Maintenance systems affect energy management. Machines that are poorly maintained will not operate efficiently (in any sense of the word). Costs will increase and productivity will decrease. Chapter 6 – Operations

PM can be used effectively but not all areas can be monitored and PM should be used in conjunction with other techniques.

Total productive maintenance (TPM) TPM is the maintenance equivalent of total quality management (TQM) and as with TQM is a complete strategy and a framework that covers other topics that will not be dealt with in this workbook.1 A key measurement in TPM is the overall equipment effectiveness (OEE), which is used to quantify the performance of equipment. The OEE is found from: OEE (%) = Availability (%) × Performance rate (%) × Quality rate (%). TPM requires that: • Maintenance is planned into the

production schedule. • Machines are designed for fast repair.

• Tip – Regularly inspect all critical

bearings for wear by measuring the temperature of the bearing. This is an ‘after the event’ check as temperature rises only occur after significant wear has occurred. It is better to use vibration monitoring but this needs interpretation and it is best to use contractors to get the best results. • Tip – Regularly inspect electrical

insulation and terminals for integrity. Many sites have regular thermographic surveys of the electrical installations. • Tip – Regularly inspect commutators,

slip rings and brushes for potential breakdown. • Tip – Poor maintenance will often be

revealed by load increases on motors. Regularly inspect motors and drives for load increases and identify maintenance actions for load reduction (see Section 4.22).

• Basic preventive maintenance is

decentralised to operator level. • Stocks are carried of trouble-prone items

or machines are designed to avoid them. • Predictions are made for machine

breakdown via a written history and performance measurements. • Maintenance problems are designed out of the machines. TPM has some significant advantages over other methods but is currently used at a minority of plastics processing sites (particularly the more advanced sites).

Maintenance is an investment that protects existing and future production capability. Poor maintenance costs money and energy.

This section concentrates on machinery maintenance only. Services maintenance, e.g., dealing with compressed air leaks or the condition of insulation, is dealt with in the respective sections for the service. These also need maintenance and should be built into the overall maintenance schedule.

• 1. Kent, R.J. 2017. ‘Cost Management in Plastics Processing’, Elsevier. Section 5.14. • 2. Kent, R.J. 2017. ‘Cost Management in Plastics Processing’, Elsevier. Section 4.25.

Reliability-centred maintenance (RCM) RCM takes a slightly different view and concentrates on preserving a system's function by selecting and applying effective preventive maintenance tasks. In contrast to other approaches, RCM is characterised by a focus on preserving the system function, identifying failure modes that cause functional failure, prioritising the failure modes and identifying maintenance tasks to prevent each failure mode. RCM uses an approach similar to any other risk assessment process but uses this for maintenance tasks.2

Maintenance basics Whichever method is used the same basic areas should be covered to reduce energy use at plastics processing sites: • Tip – Regularly inspect screws and

barrels for wear and alignment. Chapter 6 – Operations

Maintenance does matter in energy efficiency The internal view of this machine shows the results of poor maintenance. Uncontrolled air leaks, uncontrolled vacuum leaks, increased probability of failure and difficulty in repairing stoppages all contribute to higher than expected energy use. 335

6.9

Small power equipment

Do sweat the small stuff Small power equipment is a category that covers all of the other machinery and energy sinks that are located around the site. This does not include the main services or processing machinery but includes the ancillary equipment used for separating, packing, printing and treating the product before it is delivered to the customer. This type of equipment will generally account for ≈ 5% of the energy use at a site and is very diverse in nature. Some small power equipment will be ‘home-made’ to solve a specific concern and this type of equipment is rarely energy-efficient because it was ‘designed’ (although in most cases this is overstating the process) to solve a specific concern and energy was the last thing on the mind of the ‘designer’. In other cases, the equipment will be purchased for a specific need but will be used incorrectly or poorly controlled. Sites need to view everything that uses energy as a potential subject for improvement. They must look critically at every aspect of the process to find poor use of energy and potential actions for energy reduction. Some typical examples of poor use of small power equipment are given below but every site is different and there are more opportunities in most sites.

Heaters Any heater application should be examined for the potential to improve the process by either improved control or insulation to prevent heat losses. A typical example is shown on the upper right. This is a heater box designed to anneal an extrudate (later punched to produce gaskets) immediately after extrusion. The box is ‘home-made’ from two uncontrolled hot air blowers (2 × 2 kW). These have no thermostat control and the temperature is allowed to fluctuate depending on the use of the box. The ‘annealer’ is never switched off and constantly vents hot air to the site which is air-conditioned in summer. This is an opportunity to implement a simple thermostat control for the heaters to control the heat input based on the 336

temperature of the box and to switch off the blowers when the extruder is not operating. It is also easily possible to insulate the exterior of the box to reduce heat losses and to reduce the inlet and outlet slots to reduce heat losses from air being blown out of the box. These are simple measures with a direct impact and no impact on production.

Sorters When the output of an IMM (product + sprues) is dropped onto a conveyor it is often necessary to sort the sprues from the product for recycling of the sprues. This is carried out with a rotating drum sorter as

Look around, feel the air for heat, feel the area for draughts, smell the area for burning and question everything. The opportunities are everywhere but are rarely found, i.e., ‘there are none so blind as those who will not see’.

‘Home-made’ extrudate heater Heating of an extrudate using two uncontrolled hot air blowers. They do not switch off when the extruder is stopped, are not temperature-controlled and blow into an uninsulated box with large entrances and exits. This should be re-engineered.

Sprue/product separator continuously operating This sprue/product separator is continuously operating even when the IMM has stopped. It is easy to link the machines and stop the separator when there is no product being produced. Simple relays can work wonders! Chapter 6 – Operations

shown on the lower left. This is a good solution except for the fact that the sorter is operating all the time whether the IMM is producing or not. It is uncontrolled and simply left on because nobody can be bothered to switch it off. This is an opportunity to link the sorter to the main IMM controls so that when the platens stop moving the sorter continues for 5 minutes (to clear the conveyors) and then stops automatically. This is a simple measure with a direct impact and no effect on production.

Flamers When printing on polyolefins it is necessary to treat the surface to get good print adhesion. This can be carried out by a variety of methods but one of the most common is to use a ‘flamer’ which activates the surface by applying a flame. The flamer shown on the upper right consists of eight gas jets to ‘flame’ the surface of an injection blow moulded product as it falls onto the printing conveyor. There is no control on the flamer, it operates from the moment it is switched on until the end of the week, whether product is being printed or not. Perhaps worse it is totally unprotected and open to the staff at the site. Simple control measures can be used to reduce the gas flow or turn off the gas when the IBMM is not operating (about 50% of the time) and an auto-ignition device can be used to turn the flamer on when the IBMM starts up. In addition there is a health and safety risk to staff from the naked flames which are difficult to see.

with this oven are: • Reduce the inlet and outlet slots to the

minimum required for the product. • Increase the insulation of the oven to

reduce heat losses from the oven. • Enclose and insulate the conveyor belt on the return so that it does not cool down during the return journey underneath the oven.

Small power equipment covers a multitude of machinery and energy sinks around a site.

These are simple measures with a direct impact and no impact on production.

Summary These examples are not the only things that can be found, they are simply typical of the operational activities that become ‘part of the scenery’. Energy management is too vital to let this happen. Look for the small power equipment and save money and energy.

Flamer control for pre-print surface treatment Product dropping through a ‘ring of fire’ to surface treat the material before printing. This is not linked to a sensor or the IBMM and is constantly operating using gas, heating the site and putting an extra load on the A/C system.

Packaging equipment Packaging of many products is carried out by shrink-sleeving the product and the same type of process is used to apply sleeves to ISBM products that are not going to be printed. A typical shrink oven is shown on the lower right. As for the annealing oven (see above), this has poor insulation and large entrance and exit slots. This is perhaps even worse because the metal belt used to transport the product is heated by the oven and then exits the oven and returns underneath the oven so that it has cooled down completely before it picks up the product again and is heated again. This is a tragic waste of energy. The opportunities Chapter 6 – Operations

Heat losses at packing machine aperture The gaps at the entrance and exit of this machine are larger than required for the product and are poorly sealed. The gaps should be closed and the oven fitted with a thermostat. These actions will reduce energy use and the load on the A/C system. 337

6.10

Small power equipment – where are you now?

The initial steps in small power equipment As with the score charts shown earlier, this is a self-assessment exercise to allow a site to benchmark their current status. This will set the scene for planning improvements in the area of small power equipment. In seeking to improve management of the main plastics processing machinery it is very easy to overlook all the other small power equipment that is inevitably located throughout the site. Typical examples are: • Ancillary equipment that is not part of the main processing lines.

• Test equipment in the QC laboratory. • Equipment and machines in

maintenance workshops and tool rooms. Small power equipment is everywhere in the factory and often overlooked despite the considerable amounts of energy that it uses and the easy savings potential of simple management techniques.

Completing the chart This chart is completed and assessed as for those presented previously.

• Test equipment throughout the site.

Small power equipment Purchasing 4 3 2 Energy saving features

1

Operation

0

Audit

Operational compliance

Use the scoring chart to assess where you are in small power equipment The numbers from the scoring chart can be transferred to the radar chart for a quick visual assessment of where you are in terms of small power equipment. 338

Chapter 6 – Operations

Small power equipment Level

4

3

Purchasing Equipment selected to be the most appropriate to the application, bearing in mind life cycle costs & energy efficiency. Energy-saving features a major consideration in product selection.

Equipment selected to be energy-efficient. High energy-label products selected (where appropriate). Energy-saving features taken into consideration in product selection.

Operation

Operational compliance

Initial & regular Regular checking of assessment to time switches & determine most energy- automatic controls to efficient operating ensure equipment mode commensurate powered down to with business needs. lowest consumption Time switches & other mode whenever devices installed where possible. appropriate.

Initial assessment of each situation to determine the most energy-efficient operating mode commensurate with business needs.

Energy saving features Documented routine of All energy-saving regular checks to features (e.g., ensure equipment only automatically reverting powered up when to stand-by after prenecessary. determined time) are enabled & optimised. Audit

Equipment only There is a routine of All energy-saving features are enabled & switched on when regular checks to ensure equipment only reviewed against likely needed. Power-saving set-ups powered up when criteria for efficient employed whenever operation. necessary. possible to minimise waste.

Equipment switched off Equipment selected to Departmental Checks regularly Energy savings responsibilities exist for settings are enabled for be suitable for the when not needed. carried out to determine whether application, bearing in ensuring that equipment with high mind life cycle costs & equipment is switched equipment is switched electricity consumption. off out of hours. energy efficiency. off when not in use.

2

Power efficiency data Users instructed to only All equipment switched Ad-hoc checks carried Some energy-saving have equipment on at start of day & out to determine features are enabled on products obtained switched on when remains on whenever whether equipment is but there is no clear as part of selection strategy, & settings are process. required. building occupied. switched off out of hours. ad hoc & diverse.

1

No consideration of energy efficiency in product selection.

No policy for ensuring Equipment frequently equipment switched off left running even when when not in use. building unoccupied.

No checks to determine whether equipment is left on even when building is unoccupied.

Pre-delivery settings are unchanged by users.

x

x

0

Score

x

Chapter 6 – Operations

x

x

339

6.11

Process control

Improvements The availability and application of process control in plastics processing has improved immensely in the past 10 years. Processors using inefficient process control systems are not only failing to manage their energy consumption but also failing to manage many other aspects of their business. Many of the energy management techniques discussed in this book rely upon improved process control. Technical improvements such as varying the flow rate or pressure in a cooling water system via a VSD regulated by the current water temperature or pressure are, at their most basic, a process control issue and rely on the basic control loop for process control as shown on the right. Equally, many of the more advanced factory production monitoring systems are effectively process control systems, although in some cases they rely on manual intervention in the event of measurements indicating control failure.

Simple process control – on/off Very simple on/off control systems in injection moulding can be established to minimise energy use in injection moulding. Typical examples might be:

e.g., sprue regranulators, conveyors, printers and materials handling. Note: With sprue regranulators it is advisable to allow a short time delay to clear the regranulator throat of material to avoid excessive torque on restart. Equally simple on/off control systems can be used for other processing methods and the examples for injection moulding can easily be adapted to extrusion, blow moulding, etc. for both upstream and downstream services and equipment. This is the simplest type of control system as there is no real proportionality between the detected signal and the output. The control system simply determines whether the service is required or not and takes the appropriate action.

Change the system and not the people – it is generally easier and more permanent. As we used to say in the automotive industry: ‘If you can’t change the people then change the people.’

Proportional process control Proportional process control uses the measured output of the control parameter to provide a variable control signal to the regulator to influence the process. Typical examples might be: • Most pumps and fans can use VSD

drives and proportional control loops for motor speed control and reduced energy consumption (see Section 4.20).

Industry 4.0 is all about improving process control and data management. These concepts will have a huge impact on energy management in the future.

• Sense the machine movements from the

control signals – if no machine movement is detected for a set period of time then use a control signal to shut down the motor. This is only really relevant for hydraulic machines as allelectric machines will not be using energy when the motor is not operating. • Sense the machine movements from the control signals – if no machine movement is detected for a set period of time then use a control signal to shut down all the upstream services, e.g., use actuators to close off compressed air, cooling water and other services. Note: Ensure that shutting down upstream services does not allow machines to overheat. • Sense the machine movements from the control signals – if no machine movement is detected for a set period of time then use a control signal to shut down all the downstream ancillaries, 340

The basic single-loop feedback control of a process A basic control loop has four components – the process being controlled, a method of measuring the process output, a method of comparing the measured with the desired output and a method of adjusting the process to match measured and desired outputs. Chapter 6 – Operations

• Conveyor-fed regranulators can use

proportional process control to sense the current drawn by the motor and use this as a control signal to vary the conveyor belt speed to keep the current drawn below excessive levels. This can be combined with optical sensors on the conveyor and regranulator throat (to detect the presence of material) and completely control the regranulator operation. • For film blowing, automatic film

thickness measurement is commonly used to control the extrusion parameters and the downstream equipment (such as the haul-off speed) to control the film thickness. • One area of process control that is frequently overlooked in plastics processing is control of the drying process. Drying aims to achieve a set point in terms of moisture content of the polymer but most dryers are set to run for a specific time rather than to actually achieve the desired moisture content of the polymer. It is assumed that at the end of the specified time that the polymer will be dry despite the varying moisture content of raw materials depending on prior handling. In most cases, at the end of the specified time the polymer will actually be either too dry (having used excessive energy in the drying process) or not dry enough. Simple feedback loops to measure the moisture content of the polymer (or the moisture content of the output drying air) can be used to reduce the drying energy use and to ‘hold’ the dried polymer once the desired set point has been achieved (see Section 4.45). This application of good process control not only reduces energy consumed in ‘overdrying’ but also provides a final product that is more consistent in terms of moisture content.

changes in processing conditions and/or changes in machine performance through wear or other degradation. Simple and consistent measurement of the SEC of the process will very quickly reveal potential maintenance and control issues and allow action before defective product is produced or machine failure occurs.

Improvements in process control can also improve throughput by between 2% and 5% and reduce the incidence of quality problems by up to 50%.

The benefits

Source: The Carbon Trust (www.carbontrust. com).

Simple on/off or proportional control systems offer a unique opportunity to embed energy management into plastics processing. They can be relatively lowtechnology but once implemented become automatic and require only maintenance to continue to deliver cost savings. They do not require initial or continued operator training, operator intervention or management of the process. Implementation of simple process control systems changes the system rather than attempting to change the people. Much more effective and permanent.

Controlling the process – SEC as an indicator The specific energy consumption (SEC) for a process is a sensitive indicator of the overall efficiency of the process and not simply the energy efficiency. Whilst the SEC will vary from product to product and machine to machine, the SEC for a specific product on a specific machine should remain constant with constant machine settings. Changes in the SEC under these conditions are a sensitive indicator of Chapter 6 – Operations

Improving control systems The process for improving control systems is similar to the operation of a control system itself. Investigate the current systems, find out how far they are away from the desired performance and improve the system to meet the requirements. 341

6.12

Process control – where are you now?

The initial steps in process control As with the score charts shown earlier, this is a self-assessment exercise to allow a site to benchmark their current status. This will set the scene for planning improvements in the area of process control.

control allows better tuning of equipment to produce the required output at the least possible cost.

Completing the chart

Process control is not an optional extra. It is a fundamental requirement.

This chart is completed and assessed as for those presented previously.

Process control is all about using the best available control techniques for machinery and processing control. The range of control techniques has improved dramatically in the recent past and sites that are not taking advantage of these improvements will inevitably be inefficient in their use of energy. Improved process

Process control

Management 4 3 Training

2

Knowledge

1 0

Plant

Projects

Funding

Use the scoring chart to assess where you are in process control The numbers from the scoring chart can be transferred to the radar chart for a quick visual assessment of where you are in terms of process control. 342

Chapter 6 – Operations

Process control Level

4

3

Management

Knowledge

Projects

Process control improvement policy has top management commitment as part of improvement strategy.

Benefits of Benefits analyses process control carried out improvement are frequently & regularly updated. appreciated & supported at top Profit opportunities management identified, costed level. & ready to proceed.

Process control improvement policy available, with senior management responsible.

Senior Experienced staff management or consultants support present for conduct process process control control improvement. improvement surveys of plants most likely to yield largest savings.

Funding

Plant

Training

Majority of plant Training provided Improvement projects compete incorporates best for all technical & operating staff. equally with other practice process control, correctly investments. Account is taken commissioned & of benefits with no well maintained. direct cost return, Problems rectified quickly. e.g., environmental.

Projects compete Some more for capital funding advanced control with other systems & action business taken for most opportunities, but problems have to meet identified. stiffer investment returns.

Process control improvement policy set by local management.

Middle management is responsible for process control improvement.

Infrequent monitoring to identify possible savings.

Control improvement is a part-time responsibility of someone with limited authority & influence.

Limited in-house knowledge of process control.

Surveys of Revenue funding Control systems process control only on low-risk not best for effectiveness are projects with short- efficient operation. rarely made. term returns. Budget limits restrict improvement.

No policy or delegation of responsibility for improvement.

No in-house expertise in control. Contracted out maintenance.

No resources available to identify profit opportunities.

No funding for process control improvement.

x

x

x

x

Some control awareness & process control improvement training for staff.

Control Control systems Technical staff improvements are are simple but well development is only considered maintained. mainly via with payback of 6 professional & months, or less. technical journals.

2

1

Few staff have knowledge of process control techniques.

Breakdown No training maintenance only. available for staff in process control.

0

Score

Chapter 6 – Operations

x

x 343

Key tips • Operations is an area where the

• Maintenance is a key issue in achieving

technical improvements are put into practice – it is where the ‘rubber meets the road’. • Operations are dependent on people and improvements are cheap but can be difficult to implement and sustain. • Choosing the process is often not an option but the various processes have different energy intensities. • Choosing the right machine is a key to reducing energy use in any process.

and sustaining the energy efficiency of machines. • Improved maintenance reduces both operating costs and energy costs. • Small power equipment is located all

around plastics processing sites. The skill is in finding it and producing good projects for energy use reduction. • Process control improvements can reduce energy use at a range of levels.

• Initial setting of processes needs a

scientific approach to get the best results. • Initial optimised settings must be adequately recorded and used to be effective. • Do not allow anybody to change settings without justification and high-level approval. • Start-up should follow the setting sheets at all times. • Starting up in the correct sequence and following a simple time-line can dramatically reduce energy use. • Machines should be set into stand-by only when they are not going to be operated for a short time – if they are not going to be operated for a long time then they should be shut down. • Stand-by settings should be defined and machines should go into stand-by automatically after a pre-set period if not operating. • Shut-down should follow a logical sequence to take the high energy loads off-line as soon as possible. • Fast tool changeover can reduce energy costs from standing machines. • Quality costs should include the energy

lost as a result of reject products. • Training is needed to explain the process

and to motivate staff at all levels. • Training needs to be relevant to the role of the staff. • Training will save energy. This is

provable and quantifiable. • Training has a ‘half-life’ and needs to be

repeated at regular intervals to maintain effectiveness. 344

Chapter 6 – Operations

Chapter 7 Buildings and offices

The previous chapters have concentrated primarily on services, production and other process-related energy uses. These are largely activity-driven and depend on the process intensity of the forming process being used. The energy use in buildings is largely condition-driven and depends on the weather, the building fabric and to a lesser extent the user activities. Both types of load have a variable and a fixed element. Buildings-related energy use is often seen as a secondary issue, but it can represent up to 10% of total energy costs for a plastics processing site and is often an easy area to make energy savings because changes do not impact on production rate, production capacity, quality or other issues. Building-related energy management and process energy management should be seen as complementary parts of an integrated energy management programme for a site. In temperate climates, the building energy load is generally quite low in plastics processing compared to other industries. This is because of the generally poor insulation levels used in the processes and the high amounts of heat that are extracted and lost from the process to warm the production areas. As a result, production areas are almost always warm in the winter months and often very hot in the summer months. This is reflected in the office heating costs when offices are located adjacent to the production area, i.e., heating costs are generally low in the winter but air-conditioning costs are high in the summer.

In hot climates, the building energy load depends largely on the degree of air conditioning used at the site. Air conditioning is not generally used in the production area but can be used extensively in offices and become a significant part of the overall energy use of a site. Whatever the climate, much of the energy used in the building fabric can be regarded as discretionary use and can be reduced by over 20% through simple no-cost and lowcost actions. In many areas it is the staff attitude that makes the difference and staff training and motivation are more important in this area than in most of the process-related areas where the solutions can be more technical in nature. Most of the information in this section relates to buildings located in temperate climates. For readers located in very hot or very cold climates the information may need modification and appropriate notes are provided.

Note: This chapter concentrates on industrial buildings and the small offices located in these. It does not cover pure office buildings or large office areas.

Energy Management in Plastics Processing https://doi.org/10.1016/B978-0-08-102507-9.50007-6, Copyright © 2018 Elsevier Ltd. All rights reserved.

345

7.1

Buildings and offices

Standing costs Process-related energy use is extremely important in plastics processing and building energy use is sometimes totally ignored. One of the main reasons for this is that building energy use is primarily conditiondriven, i.e., the energy use is a function of the weather, and is sometimes seen to be even less controllable than process energy use. Building energy use is a large part of the base load of any site and is therefore a profitable area to make energy savings because any changes have no impact on production or quality. For all industries, recent years have seen vast improvements in factory buildings and working conditions. This has delivered significant improvements in buildings energy use but many technical developments mean that there are still significant energy-saving opportunities in areas such as lighting, heating and air conditioning.

Monitoring and targeting (M&T) For building services where there are definable condition drivers such as external temperature, the techniques described earlier in Chapters 2 and 3 for process monitoring and targeting can easily be adapted to assessing building energy performance (see Section 4.8). These can be used to produce a ‘building energy signature’ for the site and to assess the performance of building services such as heating and air conditioning. As with process M&T, the production of a PCL for a building enables identification of times or events when the systems are not operating correctly and where improvements can be made. This is particularly true when metering can be improved to allow a time-based assessment of the services. • Tip – Most heating in the plastics

processing industry is gas-fired and the use of improved meters to give a timebased use (as is available from electricity interval data) will greatly improve the ability to monitor and target energy use and costs. Targeting can again be internal (based on 346

Energy use in buildings and small offices The energy use in buildings and offices is primarily in the control of temperature. The relative proportions of energy used will vary with the climate – in temperate climates air conditioning is low but in hot climates it may be a major energy use.

Acceptable Type

Unsatisfactory

Electricity Gas Electricity Gas (kWh/m2/y) (kWh/m2/y) (kWh/m2/y) (kWh/m2/y)

Light industry

< 43

< 175

> 70

> 300

Storage and distribution

< 29

< 135

> 43

> 185

Office in factory

< 72

< 150

> 100

> 225

Separate office building

< 95

< 120

> 110

> 200

Approximate energy benchmarks for industrial buildings and small offices These values are typical energy benchmarks for industrial buildings and offices located in them. They are for temperate climates and need to be adjusted for hot or cold climates. Chapter 7 – Buildings and offices

the previous internal records and performance of the site) or external (based on the performance of similar buildings). Internal targeting is carried out as already described in Chapter 3 and is fairly easy to do on a simple comparison basis. External targeting for buildings is often considerably more difficult due to the wide range of building construction types, building use patterns and local weather conditions. • Tip – There is a great deal of

information available on energy use in buildings but for plastics processors this is not as important because of the size of the actual process loads.

Benchmarking

Office equipment This workbook concentrates on plastics processing and not on general energy efficiency. However, office equipment is used at every site and the following tips are given for general guidance. General tips: Tip – Make sure that all office equipment such as computers

and photocopiers is switched off rather than simply left in stand-by mode. Electrical appliances in stand-by use up to 50% of their operating power. Tip – Select ‘Energy Star’-rated equipment at purchase to

ensure that the whole life energy costs are reduced (see www.eu-energystar.org for more information). Tip – Set up energy-saving features such as stand-by to

reduce energy use by up to 95%. Most features are easily set up and once done will operate for the life of the machine.

For offices in temperate climates, approximate benchmarks are given on the lower left. These indicative values must obviously be corrected for occupancy and degree days in the year. These include a limited allowance for air conditioning and sites in hot climates may need to adjust these for the greater air-conditioning load of offices.

Tip – Monitor out-of-hours use and be sure to switch off all

• Tip – M&T for buildings energy use is

Turn monitors off if they are not going to be used for more

strongly recommended for all sites.

Management The key to reducing energy costs in buildings is the same as in many other areas. Simple good management will reduce costs, no-cost measures can be very effective and low-cost investment will give further reductions in costs generally with rapid pay back periods. • Tip – Prepare a company energy policy

for buildings and ensure that it is followed. • Tip – Set up a property database or

spreadsheet to document the condition of the building and the settings of all the building services. • Tip – The starting point in reducing

building energy use is an audit of the buildings and systems. This is similar to the general energy walk-around but concentrates on the buildings element. • Tip – An audit of your building energy

use is always worthwhile.

equipment at the end of the day. The argument that computers can fail if frequently switched on and off is false. Computers: Tip – Screen savers were designed to prevent an image

burning itself into CRT monitors – they do not save energy and they are not generally required with modern flat screen monitors. Disable them. than 10 minutes but still set monitors to go into stand-by mode after a set period in case users forget to turn monitors off. Flat screen monitors free up valuable desk real estate and

also use only about 30% of the energy of an old-style CRT monitor. If you are still using any of these then upgrade them – the users will thank you and you will save money. Win–win. Set computers to power down hard discs if not used for a set

period. Simple settings can make a big difference. Photocopiers and printers: Photocopiers and printers are large energy users and effectively controlling them can give good rewards: Tip – Many printers and copiers have stand-by modes. Learn

about them and set them up. Tip – Fit 7-day timers to photocopiers to stop them being left

on when not being used. Printers are ‘personal’ and people tend to turn them off. Photocopiers are ‘communal’ – nobody is responsible so nobody turns them off. Tip – Photocopiers and printers can give off a lot of heat – try

to locate them in colder areas that are not air-conditioned. Vending machines: Tip – Use 7-day timers for drinks vending machines and water

machines with heaters (coffee machines, etc.). These generally have a small heater inside to keep water near the use temperature and 7-day timers can save up to 75% of the energy used by these machines. Tip – For food machines that are chilled, check if the

temperature can be increased without affecting the food quality or safety. Chapter 7 – Buildings and offices

347

7.2

Lighting – general

A visible commitment Although it is only a relatively small part of the overall energy use, lighting offers easily seen and demonstrable opportunities to save energy. Lighting is an extremely emotive and visible issue for staff. When the topic of energy management is first raised at any site, lighting is the first issue that everybody focuses on. It is the one that everybody sees and therefore starts with. Lighting control is also a very visible sign of the company’s commitment to energy management. The savings are easily achieved and send a message that the company is serious about energy management. At many sites, the first action of the energy manager is to put up self-adhesive stickers that exhort staff to ‘turn out lights’ when leaving the room or when they are not needed. This is a waste of time. Initially there may be some slight improvement in performance but after about 4 months the impetus will have gone from the campaign, the stickers will be dirty and hanging off the wall and the energy use will not have changed at all. This type of action tries to change the behaviour of the staff, when actually it is far easier and more permanent to change the system. The installation of suitable controls is easier, quicker, more permanent and saves more energy. Energy management of lighting is primarily a series of small additive actions that individually are not significant but will cumulatively add up to reasonable energy use reductions and savings.

Ambient and task lighting One of the key lessons to be learnt in lighting is the distinction between task and ambient lighting: • Ambient lighting is the amount of light that is needed to move safely around the site, to be able to see potential hazards and to take appropriate action. • Task lighting is the amount of lighting that is needed to carry out a specific task or operation and the amount of lighting varies with the task to be carried out. • Tip – A site with reasonable levels of

ambient lighting for circulation and non348

critical tasks and well-designed task lighting is actually more comfortable to work in than one with exceptionally high levels of ambient lighting and no effective task lighting. A general guide to the lighting levels required for some specific tasks is given in the box below. Some sites have the complete site lit to very high levels because they fail to recognise the difference between these two very different lighting needs.

A lighting audit is the first step in reducing lighting costs. As with other services, minimise the demand and then optimise the supply.

The lighting map The first step is to gain an element of understanding of the operations. A ‘lighting map’ of the site showing the position and size of lighting and the position/extent of the controls is necessary to start this process. The lighting map should include the size of all the current lamps and the current power use of the lighting. After this is complete, it is possible to prepare a structured programme for the site lighting. The lighting map provides the basis for creating ‘Action Lists’ for the installation of energy-efficient controls at the site.

Lighting – general The main factors influencing the type and amount of lighting are: • Light level (illuminance) – this is the density of luminous flux on a surface (amount of light per unit area at the point of use) and is measured in lux where 1 lux = 1 lumen/m2.

Location/activity

Many lights are on simply because nobody knows how to switch them off. This is always true when the switches are not labelled and do not operate logically.

Lux

Packing work, passages

150–300

Offices and computer work stations

300–500

Visual work at production line

300–750

Inspection work

750–1500

Small parts assembly line

1000–2000

Approximate light levels required for various activities The lighting level required is dependent on the activity and the needs of task lighting should never be confused with the needs of ambient lighting. Good use of task lighting can reduce lighting costs considerably. There may be legal limits for lighting levels! Chapter 7 – Buildings and offices

• Colour temperature (K) – this is a

measure of the appearance of the light given off by a source. It is given in units of temperature because this is the temperature at which a heated blackbody radiator matches the colour of the light source. Colour temperature is a simple method of characterising the spectral properties of a light source, in reality every light source has a spectral curve but the colour temperature measurement effectively summarizes this curve. Low colour temperatures (< 3,300K) are warmer and more yellow/red whilst high colour temperatures (>5,300K) are colder and more blue. Daylight might be expected to have a constant colour temperature but has a varying colour temperature throughout the day, i.e., it is low in the morning and higher during the day. Colour temperature is important because this gives an idea of the visual effect of the light emitted from a source. • Colour rendering index (CRI) – this is the ability of the light source to accurately reproduce colours and is measured by the colour rendering index (CRI). CRI will vary from 100 (excellent colour rendering) to values of near 60 for a standard cool white fluorescent lamp. It is the average of a number of measurements and whilst a good general measure of colour it is not always fully accurate, particularly with light sources which have very concentrated emission spectra. • Lamp life – this is a measure of the

average operating life of a lamp. This is very important when high-bay lighting is used because short lamp life will lead to frequent and often awkward lamp changes. • Warm-up time – this is a measure of how long it takes a lamp to reach 80% of the maximum output from a cold start. This is important when dealing with controls because lamps with a long warm-up time can be unsuitable for some types of controls. • Re-strike time – when some lamps are momentarily turned off then they must be left for a time to cool down before they can be switched on again. The re-strike time is a measure of how long it takes a lamp to reach 80% of the maximum output from a warm start. There are a wide range of lighting sources available but these vary widely in how Chapter 7 – Buildings and offices

efficiently they convert electricity to light and the quality of the light produced in terms of colour rendering. The main types of light source are: • High-pressure sodium. • High-pressure mercury. • High –pressure metal halide.

The lighting map provides the key to the lighting audit. It enables clarity of thought to see the issue of lighting in the context of the complete site.

• Fluorescent – tubular, compact. • Tungsten halogen. • Light emitting diodes (LED). • Daylight (often forgotten but nothing is

cheaper).

General good practice In lighting, simple measures can save money easily and a well-designed lighting system can be a permanent energy-saving feature for a site. • Tip – Many major lamp manufacturers

also offer free advice and contract consultancy on lighting. Use it. • Tip – Use natural daylight where

possible and keep skylights clean to reduce the amount of lighting needed. • Tip – Lighting switched on in the

morning will rarely be switched off until the evening – whatever the changes in daylight levels. Controls can solve this. • Tip – Replacing standard incandescent

bulbs with LEDs will save money in the long term. Although they initially cost much more, LEDs use only 20% of the energy of standard bulbs and last at least 10 times longer. Reduced maintenance costs, especially for lights in high-bay fitments that are difficult to access, can easily fund the extra purchase costs.

In the UK, the Carbon Trust (www.carbontrust .com) produces extensive information on lighting. Get copies of: • CTL 163 – How to implement lighting refurbishments. • CTL 164 – How to implement LED lighting. • CTL 165 – How to implement T5 retrofits.

• Tip – ‘Delamping’ is the removal of

individual lamps from a given luminaire. This reduces light output and energy use. It is not the same as leaving a nonworking lamp in the luminaire, it is removing the complete lamp to reduce lighting levels in little-used areas or areas where the lighting is excessive, e.g., only ambient lighting is required.

Metamerism is where the same colour appears different under different light sources. This is critical when dealing with consumer goods and a light cabinet is necessary to get consistent light and colour matching. With some pearlescent paints it is also possible to have geometric metamerism where the viewing angle affects the perceived colour.

349

7.3

Lighting – controls and maintenance

Setting the strategy The primary method used to reduce energy use in lighting is to modify fittings, controls and operations to improve the efficiency of existing lighting. This type of action can be very cost-effective at plastics processing sites. • Tip – The development of LEDs and T5

fluorescent lamps can make re-lamping of large areas very economic. These lamps give much improved control and when considered as part of a programme of lighting refurbishment can be extremely effective. Sites should examine the opportunities for using LEDs or T5 lamps and obtain quotations for re-lamping with improved controls.

is not necessary and simple lighting presence detectors (passive infrared = PIR) can reduce energy use considerably. PIRs can be used with almost all fluorescent lamps (fitted with suitable ballasts) in areas where lights are potentially on continuously, e.g., offices, toilets, canteens, workshops and services rooms. PIRs can generally be adjusted for:

If PIRs in toilets turn off then they have been in there too long! If PIRs turn off in the Board Room then at least they get a good sleep!

• The distance, angle and size of activation

movement required. • The time that the lamp will remain lit

after activation. • The ambient light level below which the

sensor will be activated. PIRs are available in ceiling mount, surface mount, wall mount and a variety

Controls Controls are at the heart of reducing energy use in lighting and a good control system makes energy use reduction automatic. Lighting controls can be manual, automatic or part of an overall Building Energy Management System (BEMS). Manual methods require strong management and good housekeeping and generally fall into disuse after a short time. BEMS are broader than simply lighting and control the complete range of building services. They were expensive but prices are dropping rapidly. They are not widely used in plastics processing (despite some strong advantages in the long term). Local automatic methods probably offer the best combination of ease of installation and rapid payback. • Tip – The site ‘lighting map’ (see Section

7.2) should be used to create ‘Action Lists’ for the installation of suitable controls to be carried out by site maintenance staff. Note: Lighting controls should never create a situation of unsafe working, i.e., they should never power down whilst operations or maintenance are taking place.

Lighting presence detectors (PIR) There is a common myth that the energy needed to restart fluorescent tubes is high but starting a modern fluorescent tube uses only the same energy as leaving it on for a few seconds. Leaving modern fluorescent lamps on for extended periods 350

Basic outline of lighting controls The range of available lighting controls allows lighting to be varied according to the ambient conditions and the presence of people. Simple controls provide excellent opportunities for energy usage reduction. Chapter 7 – Buildings and offices

of other fittings and can be directed to detect the appropriate movement. Installation is generally easy, simple and quick. • Tip – PIRs can also be supplied with

ambient light detectors and integral dimmers (subject to the ballast or the lamp being suitable) to dim the lamp as the ambient lighting level increases.

Daylight detectors A number of areas where lights are potentially on 24/7 can benefit from simple light-level detectors to switch off when ambient light is sufficient. General site external lighting should always be fitted with simple daylight detectors. • Tip – The re-strike time for the lamps

used should be considered in setting the limits for the detectors. This is a particular issues for high-pressure lamps.

Timer switches Simple timer switches (push to operate) can provide better control for some areas. These are generally where short-term task lighting is required and passing traffic could trip PIRs, e.g., assembly areas.

Zoning and switching Zoning is an important concept in lighting and controls/switching should recognise that different areas have different needs. A single control/switch to turn on all the lighting is bound to be inefficient. When good zoning is used then all the controls/ switches should be labelled to enable staff to see which switch controls which light. • Tip – Lighting circuits should be

arranged to allow lights near windows to be controlled separately to those far away from windows that do not receive daylight.

Maintenance Cleaning The surfaces of luminaires, particularly reflectors, require regular cleaning and when lamps are not protected by a luminaire, the lamps themselves should be cleaned. If high-level lamps do not have reflectors then these should be fitted to increase light levels for no increase in energy use. This can often mean that the number of lamps can be reduced with no effect on the apparent lighting level. Skylights provide useful free lighting but only when regularly cleaned to allow light to enter. This is particularly important Chapter 7 – Buildings and offices

when using dimmer controls – dirty skylights will result in higher energy costs than necessary. • Tip – Light outputs can be increased for

no increase in cost by regular cleaning.

Replacement Replacement should never be on a simple like-for-like basis – lamp failure is an opportunity to upgrade the installation. Refurbishment using controls, modern LEDs and T5s can result in energy savings as well as improved lighting. Failed lamps should always be replaced (or the control circuits disabled), as they may continue to use energy in the control gear even with no light output.

Calculating the cost of lighting is relatively easy. Simply total the number of lamps and their ratings and multiply by the number of hours of operation. This gives the lighting energy use and can be used to quantify the costs and potential savings from the use of controls or alternative lamp types.

• Tip – Always use the correct IP rating

for the application. • Tip – Replace existing low- frequency

ballasts with high-frequency ballasts and T5 lamps to decrease costs in the long term. These use up to 30% less energy, provide more light and have a better power factor. • Tip – When using fluorescent lamps

near rotating machinery it is important to use high-frequency ballasts to avoid strobe effects. • Tip – The light output and life of

fluorescent lamps reduces at high ambient temperatures. • Tip – Older opal diffusers or prismatic

controllers can be effectively replaced with new prismatic controllers (preferably using LED or T5 lamps and improved control systems) to increase light output by 30 to 60% and allow delamping.

In the UK, the Carbon Trust (www.carbontrust .com) produces extensive information on lighting. Get copies of: • CTL 161 – How to implement lighting controls. • CTL 162 – How to implement external lighting.

IP ratings The amount of protection given by various lamp enclosures is given by the IP rating system (to EN 60529). This is a two figure rating system where the first figure gives a rating from 0 to 6 for protection against solid objects (higher is better protection) and the second figure gives a rating from 0 to 8 for protection against liquids (higher is better). Examples: IP 00 = No protection against solid objects and no protection against liquids. IP 44 = Protected against solid objects over 1 mm and protected against water sprayed from all directions (with limited ingress). IP 68 = Totally protected against dust and protected against long periods of immersion under pressure. Lamps should be selected for the IP rating for the application. 351

7.4

Lighting – where are you now?

The initial steps in lighting As with the score charts shown earlier, this is a self-assessment exercise to allow a site to benchmark their current status. This will set the scene for planning improvements in the area of site lighting. Lighting is a difficult topic to assess due to the widely varying needs of different areas. Offices require an entirely different lighting strategy to factories because of the greatly different needs. The assessment is broad-ranging but deals primarily with installing lighting that can be adequately controlled to provide the right lighting levels at the lowest possible overall cost to the site. Lighting is also an

extremely emotive subject – staff are interested in the very visible commitment that a company will make in terms of lighting but will also vigorously challenge any changes that are made that appear to reduce lighting levels.

Lighting is an area where technical improvements are possible that will fundamentally change the cost base of the site.

Completing the chart This chart is completed and assessed as for those presented previously.

Lighting Factory lighting 4 3 Operation

2

Office lighting

1

Sites should investigate the potential for LED lighting retro-fit projects.

0

Diffusers & shades

The introduction of LED lamps has changed the lighting landscape and can give excellent energysaving projects that reduce costs and improve the quality of the lighting.

Switching equipment

Replacement policy

Use the scoring chart to assess where you are in lighting The numbers from the scoring chart can be transferred to the radar chart for a quick visual assessment of where you are in terms of lighting. 352

Lighting is a base load that can be reduced.

Chapter 7 – Buildings and offices

Lighting Level

4

3

2

Factory lighting

Office lighting

Replacement policy

Lights are Light fittings, Factory lighting All lights are 16mm diameter (T5) switched in banks including diffusers, with fully tubes or LEDs. & switches match reflectors & controlled 16-mm triphosphor-coated activity & daylight. ballasts, are T5 tubes or LEDs. Switches are updated on a labelled to show planned basis. which lamps they Specular reflectors operate. are widely used.

High-pressure sodium lamps used throughout due to no need for good colour rendering. Task lighting used when good colour rendering is needed.

Mix of 16-mm diameter (T5) tubes & 26-mm diameter (T8) tubes.

Diffusers & shades

Operation

Diffusers & shades Lights operate are selected for only as required. their high Where daylight is utilisation factor & available, lighting are cleaned on a is adjusted to scheduled basis. requirement. Routine exists for regularly checking lighting use.

Diffusers & shades Lights are Light fittings, including diffusers, are selected for switched in separate rows & reflectors & their high utilisation factor & switches located ballasts are near the lights periodically are cleaned they operate. upgraded when occasionally. Switches are opportunities clearly labelled. allow.

Lighting levels & hours of operation are well controlled. Checks are undertaken on an ad-hoc basis. Cleaners light current working area only.

Diffusers & shades Lighting levels High-pressure All lights are 26Lights are Light fittings, metal halide used mm diameter (T8) switched in rows & including diffusers, are of high partially controlled. throughout due to utilisation factor, Lights are tubes. switches located reflectors & need for good near the lights ballasts are but are not switched on when upgraded on an adcolour rendering. regularly they are required, they operate. & switched off Rows not aligned hoc basis. maintained. when not. with daylight, No routine for switches not checking use. labelled.

High-pressure mercury lamps used throughout.

Mix of 26-mm diameter (T8) tubes & 38-mm diameter (T12) tubes.

Tungsten halogen or tungsten filament lighting throughout.

All lights are 38mm diameter (T12) tubes.

x

x

1

0

Score

Switching equipment

Chapter 7 – Buildings and offices

Lights have the potential to be switched on in banks, but in practice all go on together.

Lamps & ballasts Diffusers & shades Lighting levels are sometimes are of fair partially controlled. upgraded to high- translucency but Lights switched on efficiency types are rarely cleaned. at start & operate continuously when when they are building occupied, replaced. whether needed or not.

Diffusers & shades Lights are Lamps are switched from replaced upon are not selected central locations & failure with ‘like-forfor all go on together. like’ lamp types. translucency/lighttransmitting properties. There is no programme for cleaning.

x

x

x

Lighting levels are uncontrolled. Lighting is frequently left on 24 hours per day whether the building is occupied or not.

x 353

7.5

Heating – general

Cool it down Heating is generally a lower cost for plastics processors than for many other industries due to the rejected process heat that can be used to provide heating. This is a poor source of heating and it is far better to insulate the process than to try to use it to heat a building – this is not what plastics processing machinery was designed for. Heating by this method is uncontrolled, very costly and can lead to excessive heating in the summer. Insulate the process and heat the building using purpose-designed and controlled systems. Heating is still required in many plastics processing sites in temperate climates in the winter and will inevitably add to the energy costs of the site, although in most cases this will be through gas use rather than through electricity use. At many sites, the heating system is effectively ignored, poorly understood, poorly maintained, poorly adjusted and has rarely been changed since the first installation (despite subsequent changes to the building fabric and use). In cases such as this, it is often easy to reduce heating costs by 30% through simple actions. One of the keys to efficient heating is to reduce the heating load by reducing uncontrolled air leakage and improving the thermal insulation of the building fabric (see Section 7.11). Reducing heat losses makes it possible for smaller heating systems to provide the required heating and reduces energy use and costs. • Tip – Reducing the heating load is a first

priority. As for any service, the rule is to reduce the demand and then optimise the supply. • Tip – Reducing the set-point

temperature by 1°C will reduce heating costs by about 8%.

Heating – general Reducing the heating load and the energy used depends on two main factors: • The heating quality requirements – these are usually the storage temperature requirements for materials and products and are not to be confused with the humidity requirements which may be needed for raw materials (see 354

Section 4.44) or packaging (see below). • The comfort requirements – these are

the temperatures required by people for comfortable working. Some recommended design values for air temperature are shown below and these temperatures should be held within ± 2°C for most of the working period. Simply determining whether the requirements are quality (materials) or comfort (people) and making a clear difference between these requirements can clarify many of the issues regarding heating and enable sites to set heating at the most economic level.

Heating systems There are a bewildering number of types of heating system used at plastics processing sites around the world. Systems can be operated by gas, oil, electricity or steam (generated by gas boilers). In most cases, the reasons for using a specific system are now irrelevant or have been forgotten. It is rarely economic to change the complete heating system and site managers will most often

Type of activity

Recovering heat Many services and plastics forming processes generate excess heat and it is worth investigating if this heat can be used for other purposes, such as space heating on colder days by general or local heating or preferably energy recycling through a heat exchanger. Heat recovery from compressors is probably the best example (see Section 4.31).

Air temperature (°C)

Factory production area – occupied Sedentary work (seated bench work)

19–21

Light work (light bench work)

16–19

Heavy work (heavy bench work)

13–19

Stores and warehouses

10–12

Factory production area – unoccupied or night setting Minimum for frost protection

5

Minimum for condensation protection

10

Office areas General

19–21

Some typical recommended temperatures for various activity levels The temperature of a zone should reflect the activity being carried out in the zone. Heavy activities require a lower zone temperature than light or sedentary activities. Chapter 7 – Buildings and offices

have to simply find the most economic method of operating the system that they have been left with.

Area considerations Specific areas have specific needs and site managers need to have a basic understanding of these to effectively manage and operate the heating system. The basics of controls and zoning are dealt with in Section 7.6.

Production areas Provided that materials are stored adequately, production areas most often simply need comfort heating for staff. In these areas the set point rarely needs to be above 19°C. At most plastics processing sites, the temperature can actually be much lower.

Warehouses (raw materials and finished goods) Most warehouses for plastics products do not require full heating systems, they only require dehumidification to prevent dampness effects on raw materials or packaging and a minimum temperature for frost prevention on sprinkler systems. • Tip – Do not heat lightly occupied areas

when all that is required is humidity control. Dehumidification and thermal clothing for staff are lower-cost options. • Tip – Make sure that warehouses are

sealed and that windows and doors close automatically after access. • Tip – Consider ‘trace heating’ for

sprinkler systems in warehouses to provide frost protection for the pipes rather than heat the whole warehouse. It will be a lot cheaper.

Offices Offices are always a heating ‘danger area’ because staff often have very different expectations. They will constantly adjust settings, open windows (because they are ‘too hot’) and bring in additional heaters (because they are ‘too cold’). Accept that you will never get it right! This is an area for staff training and motivation provided that issues raised are resolved quickly and effectively. • Tip – Raise staff awareness of the cost of

heating and actively encourage their involvement in solving heating issues. Do not let them take their own measures – it will cost you money. • Tip – If an area is too cold then

additional electric heating is very Chapter 7 – Buildings and offices

expensive (up to five times as much) compared to a correctly set and operating gas-fired boiler. • Tip – If an area is too hot then do not

open a window – inform maintenance or adjust the set-point.

Monitoring and targeting (M&T) Monitoring and targeting of heating systems is only really possible if the system uses a different fuel to that of the main production, i.e., it is not electrical, or if there is a separate feed for the heating system. In these cases, the use of simple M&T techniques can reveal if the heating system is operating correctly (see Section 4.8). A simple chart of use versus degree days can provide valuable information for heating system management. Where heating and hot water use the same fuel and are on the same system it is reasonable to assume 80–85% of the load is heating. This can be verified by examining consumption during the summer months when hot water is likely to be the only load. This will give an approximate split of the heating and hot waters loads for the system.

Irrespective of how the building is heated, if you are using radiators then installing heat reflectors to the walls behind radiators will improve their efficiency at very low cost.

Hot water Hot water is a low energy use in most plastics processing and is primarily used for hygiene and personal washing. However hot water is used at every site and the following tips are given for general guidance. Tip – Fit time controllers to all hot water boilers. Tip – Condensing boilers are the best option for new or

replacement small hot water systems. Tip – Check the water storage temperature if storage is some

distance from point of use. The storage temperature should be 60–65°C but no higher otherwise heat losses will be higher. Tip – Check that all hot water storage tanks and pipework are

adequately and fully insulated. Fit lagging to all local hot water storage tanks if insulation is not present. Tip – Ensure that no hot water taps are leaking and preferably

fit automatic sensor controlled taps. This will also save water. Tip – Check tap water temperature regularly. This should be

the minimum temperature consistent with Legionella control (if applicable). The tap temperature should be 55–60°C but no higher otherwise heat losses will be higher. Tip – Consider fitting local ‘on-demand’ hot water heaters to

avoid long pipe runs. These can reduce energy use considerably, especially in summer when other demands on a centralised system are low. 355

7.6

Heating – controls and maintenance

Comfort control As with lighting, the primary method used to reduce energy use in heating is to modify controls and operations to improve the efficiency of the existing heating system. However, in seeking to improve the efficiency of the heating system and reduce costs it is easy to lose sight of the prime objective. Heating should make working areas comfortable and acceptable to the staff – reducing heating levels too much is not productive.

Controls Most heating systems will have at least basic thermostat temperature controls but these can easily be improved by the use of additional controls to vary timing and other aspects of the system. The controls can be simple or complex depending on the occupation and needs of the site. Even simple time controls can save money – every extra hour of heating a building adds at least 4% to the heating costs. Good controllers can get a building up to temperature quicker than poor controllers but when a building has been unheated for a long time then it needs to be pre-heated for longer. Optimum start controllers are best for this. Interlocked controls should be fitted to prevent heating and cooling systems operating at the same time.

change them – people can be very ingenious at times! • Tip – Leave old thermostats on the wall

but disconnect them from the system. Staff can then ‘adjust’ the temperature as much as they like. It makes them feel good but does nothing to the system settings – a ‘win–win’ result. • Tip – Thermostats should be calibrated

annually to ensure they are accurate. • Tip – Where radiators are used, install

thermostatic radiator valves (TRVs) to all radiators but do not install TRVs when there is also a room thermostat. If specific areas are too cold then the radiator system may need to be rebalanced to equalise the system flow.

Time control Simple time controls enable the system to operate only when occupied and prevent operation when not needed. Time controls should be used in conjunction with thermostats and should be set to provide pre-heating of the area so that it is at the correct temperature before occupancy. • Tip – Use 7-day timers for control of

temperatures when occupancy varies widely over the week, particularly when there is no working over weekends. Check the settings regularly or prevent changes being made – people will change them if they are accessible.

Thermostats

Zone control

Thermostats are the most basic control of all and should be set as recommended in Section 7.5. Thermostats prevent overheating and produce a good working environment. However, they must be set and located correctly to provide the best temperature profile for the activity taking place in the area. Locate thermostats away from radiators, office equipment, draughts and direct sunlight to prevent false readings being obtained. One negative aspect of thermostats is the tendency of people to change them because of their personal preferences.

Section 7.5 gives temperature settings for various activities. Zoning of the building can considerably reduce energy use by providing the right amount of heating at the right time for specific activities. Zoning allows the differing needs and building fabric of various areas to be controlled separately and effectively.

• Tip – Install tamper-proof thermostats

and controllers to stop staff changing them. • Tip – Check thermostat settings

regularly in case staff find a way to

356

Whatever heating control method is used, do not let staff bring their own electric heaters into work. They are inefficient, can overload circuits, mask problems with the heating system and create a fire hazard.

Areas of similar activity levels should preferably be in the same control zone but this may not always be possible due to the site layout.

Optimum start controls Where installations are greater than 50 kW then optimum start controls are recommended (they are required in the UK) and these should be set so that the building temperature increases from the set-back temperature to the occupancy

BEMS Building Energy Management Systems (BEMS) are very well developed because of the importance of energy management in large buildings. They are not often used in plastics processing because of the generally small amount of offices present at plastics processing sites. However, they are great at what they do and can provide real insight into how and when buildings use energy. It is generally more effective to invest in a process energy management system and use this to monitor the buildings as well.

Chapter 7 – Buildings and offices

temperature in time for occupancy and not before. • Tip – Make sure that the controllers are

set to the actual occupancy times and not before.

Building Energy Management Systems (BEMS) For larger sites, BEMS are extremely effective at controlling temperatures without staff intervention, but sensors must be located correctly.

• Tip – If heating is provided by a boiler

that was once used for process heating then it is likely that this will be very inefficient if used simply for building heating. • Tip – Old boilers (> 15 years old) will

have efficiencies in the region of 60% compared to modern boilers which have efficiencies of greater than 90%. Upgrading these systems can be financially viable simply due to energy efficiency improvements.

• Tip – Review temperature and control

settings at least annually and ensure that controls reflect the seasons, i.e., summer control settings should differ from winter control settings.

Night set-back temperature is the temperature setting for when the building is unoccupied. This should be set in the region of 10°C.

If using radiators then insulation on the pipe work will reduce losses in ceilings or under floors. Get the heat where it is needed.

• Tip – Check the sequencing and cycling

of boilers. • Tip – Pumps and fans should only

operate when the system is active. • Tip – Pumps and fans should use VSDs

to control the flow rather than dampers or restrictor valves. • Tip – Check that all controls are

operating and set correctly. • Tip – Where radiators are used, fit

reflectors behind the radiator and do not block the front of the radiator.

Maintenance Poorly maintained heating systems can increase heating costs by up to 30% and poor maintenance increases the probability of failure, which always occurs at the coldest part of the year! It is important to have a maintenance schedule for the complete heating system. • Tip – Produce a checklist/diary of

actions to be taken by the site during the ‘heating year’, i.e., get the boilers serviced in summer to ensure that systems are ready for the winter. • Tip – Servicing boilers and heating

systems is a specialist job, especially when gas-fired units are involved. In most cases, this can only be legally carried out by a certified contractor. Be sure to comply with local regulations when getting heating systems serviced. Burners in direct-fired units should have twice-yearly maintenance servicing and checks to ensure correct combustion and continued reliability. • Tip – When gas-fired boilers are checked

then the service should include a combustion efficiency report to show any improvements in the boiler. Chapter 7 – Buildings and offices

Simple 7-day timer Simple 7-day timers can be programmed to control the energy use of office equipment, lighting and heating according to the occupancy levels of the site. The model shown is a plug-in model but similar models can easily be wired into the control circuits.

Heating loads are not automatic Whilst carrying out a site survey a very large warehouse was found to be heated throughout the year. The product did not need temperature control and the staff were mainly forklift truck drivers who were constantly driving in and out of the open roller shutter doors. The site manager explained that the heating wasn’t on for either of these reasons but simply to ensure that in the winter the fire sprinkler system did not freeze up. The simple application of insulation and electrical trace heating/ frost protection with a temperature controller on the fire mains and sprinkler systems allowed the heating for the complete warehouse to be switched off and provided complete protection to the satisfaction of the insurers down to external temperatures of −20°C. The warehouse energy use was reduced by over 85% and the installation had a payback of less than 12 months. 357

7.7

Heating – where are you now?

The initial steps in heating As with the score charts shown earlier, this is a self-assessment exercise to allow a site to benchmark their current status. This will set the scene for planning improvements in the area of site heating. In plastics processing, heating the production area is relatively low cost but heating the offices and other areas is often inefficient and poorly controlled. Improved controls and distribution can often pay good dividends in reducing energy use. Personal comfort is important but there is no reason for everybody in the office to come to work in polo shirts just because somebody else is paying the bill – they

don’t do this at home, so why should they expect you to pay the bills for them to do this at work!

Completing the chart This chart is completed and assessed as for those presented previously.

Heating use is a condition-driven variable. Correlating heating use to degree days will give good information on heating demands and efficiency.

Heating Time control 4 3 Zoning

2

Boiler output controls Rejected process heat from plastics processing machinery will warm the site in winter but this is inefficient for site heating and will make the site too warm in summer.

1 0

Heating levels & balance

Use the scoring chart to assess where you are in heating

It is more efficient to insulate the machines to minimise and retain the process heat where it is needed and to use wellcontrolled site heating. If you wanted to heat your home you would not buy an injection moulding machine or an extruder.

The numbers from the scoring chart can be transferred to the radar chart for a quick visual assessment of where you are in terms of heating.

Do not be seduced by this concept.

Heat emitters

System operation

358

Chapter 7 – Buildings and offices

Heating Level

4

3

2

1

0

Score

Boiler Heating Heat System output levels & Zoning emitters operation controls balance Space heating is Effective Radiators have Rigorous checking Temperatures are Zoning for of controls even throughout occupancy, solar controlled by automatic control thermostatic system of boiler standing valves, fan function, settings the building (18°– gain, equipment programmed for losses. convectors have & system balance gain, structure, 20°C) when individual controls annually. non-working days Only required etc., where occupied, & with selfboilers are hot, all & different areas Documented appropriate. otherwise reducing procedures & learning optimum others cold or of the building Adequate means to lower have internal results recorded. start & stop. cooling. for controlling temperatures. Boilers & thermostats. temperature in manifolds well each zone. insulated. Time control

Optimum start controller varies start time of heating from outside temperatures & optimum stop at the end of the day.

Effective manual Radiators & fan isolation of boilers convectors have to reduce standing individually losses when full operated controls. output is not Temperature of required. radiators varies Boiler & manifold with the season. well insulated.

Full yearly check of controls, settings & system balance. Documented procedure for each check. Some results recorded.

Temperatures are Extensive zoning, even throughout approximately the building, but in reflecting some parts they occupancy time & are > 20°C during temperature spring or autumn. requirements. 20°C maintained Controls exist for each zone. only during occupancy.

Optimum start Boilers become Radiators have Informal checking Temperatures are Limited zoning, individual controls controller fitted to hot only when > 20°C during due to building of controls & the heating boiler output is expansion, but but water system balance spring & autumn, temperature is the carried out once system. required. & the building is zones Holiday periods Boilers are cold at warm for more approximately same all year per year. reflect the need for can be all other times round. Schedule exists than an hour programmed in (e.g., overnight). before or after distinct occupancy but no records. advance. occupancy. times & temperatures.

Heating system has an easily set simple timer. Timer settings are adjusted manually to suit season.

Boilers remain hot Radiators have Annual functional during pre-heat & basic controls & checks carried out building there is only one but not recorded. occupation hours internal during summer & temperature winter. sensor to control them.

Temperatures vary Limited zoning or & they are inappropriate frequently > 20°C zoning. for long periods – including periods of no occupancy.

Timer in poor state Boilers remain hot Radiators have no Maintenance is on Building of repair & cannot regardless of controls & get hot breakdown basis temperatures are be easily adjusted. whether or not together. & controls are frequently too hot there is a demand The controller Radiator checked only for much of the does not for heating. temperatures when problems building, recognise days of appear to be the occur. particularly in the week. same all year spring & autumn. round.

x

x

Chapter 7 – Buildings and offices

x

x

x

No zoning.

x 359

7.8

Hot water – where are you now?

The initial steps in hot water As with the score charts shown earlier, this is a self-assessment exercise to allow a site to benchmark their current status. This will set the scene for planning improvements in the area of hot water supply. Most hot water use in plastics processing is for personal use and process use is generally low. Despite this, hot water can be quite costly and the chance to reduce energy use and costs by simple good practice should not be missed. As with lighting and heating, the use of good controls is a key to minimising hot water costs – delivery of the correct amount of

water at the correct temperatures is all that is required.

Completing the chart This chart is completed and assessed as for those presented previously.

Rejected heat from compressors (see Section 4.31) can often be used via a heat exchanger for simple pre-heating of hot water for use in the production area.

Hot water Installation type 4 3 2 Tap water temperature

Timer or programmer settings

1 0

Pipework insulation

Hot water boiler

Use the scoring chart to assess where you are in hot water The numbers from the scoring chart can be transferred to the radar chart for a quick visual assessment of where you are in terms of hot water. 360

Central hot water boilers can often be replaced by simple point of use systems at low cost and these also have the advantage of low transport losses.

Chapter 7 – Buildings and offices

Hot water Level

4

Timer or Tap Pipework programmer Hot water boiler water insulation settings temperature Instantaneous point of Two or more visual & The hot water boiler is Water circulation All pipework is well use water heaters or temperatures are hot functional checks correctly sized, insulated & both appropriately located & insulation & reflective throughout (> 50°C) & water heaters with made each year localised storage & against a formal designed to eliminate coatings or waterproof where there is risk of scalding, outlets are time controls. document & results stratification. finishes are in prime recorded. Insulated to the condition. fitted with blenders to No pump or heating optimum thickness. Flanges, valves & other mix with cold water for fuel used when building fittings are insulated. comfort. is unoccupied. Installation type

Instantaneous point of use water heaters or water heaters with localised storage without time controls.

Annual visual checks Hot water boiler is All pipework in both made using formal correctly sized & unheated & heated spaces is well insulated procedures & results insulated to an recorded. economic thickness & insulation feels cool No pump power or calculated using local to the touch. heating fuel used when Flanges, valves & other criteria. building is unoccupied. Located to meet fittings are insulated. demand for hot water.

Water circulation temperatures are hot throughout (> 50°C) & some automatic blenders are fitted to mix with cold water for comfort.

Times of availability Hot water boiler is well All pipework in both Hot water is provided closely matched to insulated with unheated & heated from dedicated central demand. plant with seven-day insulation known to be spaces is well insulated timer/programmer that Regular checks on time & insulation feels cool more than 50 mm allows heating & hot to the touch. switch settings. thick. water services to operate independently.

Water circulation temperatures are hot throughout (> 50°C). Water temperature at the taps is hand hot & cold water has to be added regularly for comfort.

3

2

Hot water is provided Times of availability not Hot water boiler is Pipework in unheated Water temperature at from central plant, with specifically checked. insulated with 25–50 spaces is well insulated the taps is variable & is timer/programmer & cool to the touch. often < 50°C or > 60°C. mm insulation. serving both heating system & hot water.

1

The only controls are Times of availability not Hot water boiler is on/off & the primary specifically checked. incompletely insulated circuit thermostat. Strong possibility of & is subject to availability when significant heat loss. building unoccupied.

Pipework generally is not insulated or the insulation is thin, damaged or in poor condition.

Water temperature at the taps is regularly < 50°C or > 60°C.

x

x

0

Score

x

Chapter 7 – Buildings and offices

x

x

361

7.9

Air conditioning

Comfort cooling Air conditioning (A/C) is more expensive than heating and can use more energy. It is also one of the fastest rising users of energy in temperate climates where it is used more for comfort cooling than for actual air conditioning. In the past, the major electrical energy demand was in winter for heating but this is changing rapidly and the summer peak is rising due to the use of air conditioning. In some parts of the USA, the summer electricity demand is already higher than the winter demand – winter heating is largely by oil but summer cooling is mainly by electricity for air conditioning. In temperate climates there are actually very few days where the temperature is over 28°C (the level at which comfort cooling can be justified) and cooling for these few days can cost as much as heating for the entire winter. It is important to recognise the difference between air conditioning and simple ventilation – natural ventilation is cheaper and when properly controlled can greatly reduce air-conditioning loads. • Tip – The use of air conditioning is

primarily a staff issue and staff training and awareness of the effects of their actions are key issues in the control of air conditioning.

as air blast cooling for chillers (see Section 4.38) – when the outside air temperature is below the return water temperature then the compressors are shut down and the free cooling cuts in. Free cooling is more energy-efficient when external temperatures are lower than the set-point. This is particularly true in summer where night cooling (ventilating the building with cool air) can lower the building temperature overnight and reduce building heat build up. • Tip – Investigate free cooling for air-

conditioning units.

Offices Poorly controlled air conditioning can easily double the energy costs of even a small office and one of the key issues is to avoid having the heating and air conditioning competing with one another. The operational temperatures for the two systems should be separated by as much as possible. This gap is known as the ‘dead band’ and should be maximised for maximum efficiency, e.g., the air conditioning should be set not to operate until 25°C and the heating should be set to turn off at 19°C. The larger the dead band the better because this increases the temperature range for which neither heating nor cooling will be operating.

Types of air conditioning Air conditioning is a chiller by another name and all air conditioning therefore has a compressor of some type in the unit. There are two basic types of layout: • Centralised system where cooling is carried out at a central plant room and cool air is ducted to the point of use. • Local split systems where the cooling is carried out locally with an external condenser. This is the most common type in offices that have been retrofitted for comfort cooling and the type most commonly used in small office applications in the plastics processing sector. The two basic systems can be combined to have partial centralised cooling with further cooling at the point of use. Some air-conditioning units have free cooling coils that operate in the same way 362

Air conditioning equipment does what it says on the label, i.e., condition the air to specific standards of temperature, humidity and purity. Many systems are simply ‘air-cooling’ units and can be more accurately described as ‘comfort coolers’ – make sure you know what you are buying.

Air conditioning 35%

Hot water 5%

Lighting 15%

Heating 25% Office equipment 20%

Energy use in an average air-conditioned office Even when well controlled, air conditioning will make up approximately 35% of the energy demand of the average office. Poorly controlled air conditioning will use much more energy and can be over 50% of the energy use. Chapter 7 – Buildings and offices

Air conditioning in offices is often used when the need could be adequately satisfied by simple air movement and adequate ventilation. Avoid ‘comfort cooling’ and consider switching off air conditioning and using fans and opening windows (depending on the external temperature and the insulation of the building) to get more energy-efficient cooling through simple air movement. • Tip – Cooling demand will increase as

the cooling load rises so minimise the load by reducing heat generated by lighting and office equipment (see Sections 7.1 to 7.3). • Tip – Cooling load can be reduced by

improvements to the building fabric (see Section 7.11). This is particularly true with shading or blinds to reduce solar heat gain. The cost of installing external shading is rapidly paid back by the reduced use of air-conditioning plant. • Tip – Keeping windows closed is just as

important for air conditioning as it is for heating. Opening windows means that the air conditioner has to work harder to try to cool down the whole world – this is not a solution to global warming!

Production areas Air conditioning should only be used for offices, for production areas the real need is for ventilation. In temperate climates there is no reason for air conditioning of production areas. In very hot climates, the use of air conditioning for production areas should be seriously questioned. It is a very expensive option where fans or blowers can provide a cooling air flow that is much cheaper and just as effective.

to the outside temperature. Staff will dress for this weather and the office temperature can reflect this. • Tip – Reducing the delivered air

volumes can reduce costs. • Tip – Look at the air conditioner to see if

there are humidity controls that are increasing the energy consumption. • Tip – Leaving air conditioning on

overnight does not save energy. Energy use is minimised by turning off (unless night cooling controls are activated) and restarting in the morning. Use controls to turn air conditioning off overnight. • Tip – Always ask suppliers about

operating costs before purchasing. If the unit also has a heating coil then check that the controls can be set with a large dead-band to prevent heating and air conditioning operating at the same time.

HVAC A combined heating and cooling system is probably more accurately described as a HVAC (heating, ventilation and air conditioning) system and these systems control the complete building environment from heating in winter through to cooling in summer. These systems are used extensively in office buildings but not often in industrial buildings.

Maintenance issues Maintenance is just as important for air conditioning as it is for any service and poor maintenance will cost money. If maintenance is not carried out regularly and effectively then energy use can be up to 30% higher than necessary. • Tip – Keep grilles, chiller parts

(condensing and evaporating surfaces) and ducting dust-free and unobstructed. • Tip – Air conditioning is a specialist

subject and units should only be serviced by trained people to get the best energy efficiency. In most cases, a maintenance contract is recommended.

Splits and HVAC systems are a major location of greenhouse gases (GHGs). There are regulations covering these and servicing should take these into account.

• Tip – ‘Mould sweating’ is sometimes

used as a justification for airconditioning use. Try local dehumidification instead. It is normally cheaper.

Operation and controls Operation of air conditioning is often left to the staff and they will adjust the equipment to suit their personal preferences rather than your need to reduce costs. Set the system correctly and install tamper-proof controls to prevent staff adjusting them. • Tip – Turning thermostats down does

not cool the building quicker. An air conditioner has a fixed output and cannot cool faster than this. • Tip – Cooling levels should be adjusted

Chapter 7 – Buildings and offices

Plastics processing in hot climates Whilst surveying several injection moulding sites in the USA, it became apparent that the production areas were effectively ‘sealed boxes’ that were totally air-conditioned. The production areas were enclosed (through poorly sealed doors and poorly sealed building fabric) and kept at a very pleasant 21°C day and night. Every kW of heat lost by the machines (uninsulated barrels) and product was balanced by a kW of cooling from the air-conditioning units that were removing the heat and keeping the sealed box at 21°C. The site management wondered why their energy bills were so high. Despite this, when confronted with the evidence they continued to air condition the complete production area. As a counterpoint, similar sites in Asia, Australia, Spain and Italy simply opened the doors. I wonder why their costs were significantly less? 363

7.10

Air conditioning – where are you now?

The initial steps in air conditioning As with the score charts shown earlier, this is a self-assessment exercise to allow a site to benchmark their current status. This will set the scene for planning improvements in air conditioning. Air conditioning is a rapidly rising cost throughout the world and equally so in the plastics processing industry. Hot production areas often lead to airconditioned offices immediately adjacent to hot machines. Energy management in air conditioning is a combination of good controls and staff management to ensure that air conditioning is cooling the

minimum volume for the minimum time. Air-conditioned areas should always have controlled access and self-closing doors should be fitted to avoid inadvertent ‘cooling’ of the production area.

Air conditioning is often misused when all that is needed is really air movement.

Completing the chart This chart is completed and assessed as for those presented previously.

Air conditioning System selection 4 3 2 Cooling systems

System design

1 0

Fan power

System control

Use the scoring chart to assess where you are in air conditioning The numbers from the scoring chart can be transferred to the radar chart for a quick visual assessment of where you are in terms of air conditioning. 364

Avoid over-cooling in summer to minimise airconditioning costs.

Chapter 7 – Buildings and offices

Air-conditioning systems Level

4

3

2

System selection

System design

Appropriate system System design well Wide deadband for with delivered air control setpoints for matched to needs & temperature & humidity volumes to match building type. need. Temperature & (where apropriate). humidity controlled with System includes Occupancy-based energy-saving features minimum energy control with good such as heat recovery consumption. operator facilities. or controlled partial recirculation based on air quality.

Fan power

Cooling systems

High-efficiency fans used & system designed for low pressure loss along ductwork. Control by VSD.

Efficient means for providing cooling. Chillers have variablespeed compressors. Flow rates and/or temperature of cooling medium are variable depending on demand.

Automatically Appropriate system Good fan selection & Efficient means for Good system design with carefully delivered controlled but variable good ductwork design. cooling, e.g., good use with all expected conditions for common air volumes to match System uses VSD made of evaporative energy efficiency measures, such as free the need. supply ducts. and/or high-efficiency cooling. Energy-saving features cooling control & night Chillers selected & Modern electronic motor. purge during summer. controls. sequenced to match such as run-around Temperature & Communication demand across load coils for heat recovery. humidity requirements between controllers. range. achieved.

Designed to Air conditioning reasonable standard necessary but inappropriate systems but lacks energy and/or features efficiency other than limited measures, e.g., selected. Excessive air change free cooling control. rates & unnecessary cooling or humidity control.

Cooling provided using Fixed common supply Reasonable fan duct conditions to limit selection & ductwork efficient chillers. Outputs chosen to duty on terminal units design, but energy but no optimisation of efficiency was not a minimise energy consumption, energy performance. prominent factor during particularly over the full Modern controls with selection. time programming. range of operating loads. Fixed delivery temperature.

Air conditioning necessary for parts of building but other areas are air-conditioned.

Poorly designed & oversized plant with lack of energy efficiency measures such as free cooling control. Reasonable functional control of plant.

Reasonable chiller Very close control of Oversized fans or poor ductwork design. performance, but poor heating & cooling. performance Stand-alone time characteristics at low control without facility operating loads. for shut-down during unoccupied periods. Fixed delivery temperature, lower than required.

Air conditioning not necessary, yet presence is significant.

Very poor design & likely to be oversized for application. No energy-saving features.

Close control of heating & cooling in space & within supply ducts (to within less than 1°C, 5% RH) where not appropriate. Poor time control of plant.

Oversized, poorly selected fans, poor ductwork design.

Poor chiller performance, providing a constant temperature output, at a much lower level than necessary.

x

x

x

x

x

1

0

Score

System control

Chapter 7 – Buildings and offices

365

7.11

Building fabric

Reducing the load

Air leakage and ventilation

Building fabric improvements have greatly reduced the heat losses and gains in modern buildings, but much of the older building stock still has considerable opportunities for improvements. Heating and air conditioning have been discussed in Sections 7.5 to 7.9 and can be considered as being services to provide the correct temperature in the building. As with any service, reducing the load is the first step and for temperature control this means reducing the heating or cooling load by making the building as thermally efficient and as airtight as possible.

Air leakage (draughts) in a building should never be confused with ventilation. Air leakage is uncontrolled, accidental (due to poor design or maintenance) and is never needed. Ventilation is controlled by the needs of the process, deliberate and is needed to remove heat, smells, dust and other contaminants. Air leakage is not a substitute for ventilation. Air leakage should always be reduced to a minimum so that the ventilation system can function correctly.

When considering heating it is obvious that insulation and leakage are key issues but this is sometimes less clear for cooling. A well-insulated and well-sealed building will not only lose less heat in cold weather to reduce heating costs but will also gain less heat in hot weather and reduce cooling costs. For plastics processing, the rejected process heat may provide free heating during winter but this is uncontrolled and will make the building excessively hot in the summer. It is best to solve the problem at the source rather than to attempt to mitigate the symptoms – insulate the process (see Chapter 5) to reduce the uncontrolled heat entering the building and then adjust the temperature.

Building energy costs can be a significant percentage of the total energy costs.

• Tip – Reduce the demand for ventilation

by reducing unwanted heat gains from the process and by turning off unproductive processing equipment. This can double the savings. • Tip – Minimise the use of ventilation by

the use of controls to operate ventilation only when needed and fit VSD drives to continuously vary the speed according to the actual demand.

Improving the energy efficiency of existing buildings can be very costeffective and easy to do and not only reduces costs but also improves staff comfort and work output.

Existing buildings Many of the issues for industrial buildings are similar to those seen in domestic buildings and in most cases the things that you would do in your own home to reduce energy use can be replicated in industrial buildings. It is simply that the costs and benefits are larger. The starting point is an audit of the buildings and heating/cooling systems. One of the best tools for examining large buildings is an infrared thermography survey. This will reveal areas of poor or water-logged insulation, thermal bridging and areas of air leakage. As a method for building assessment, thermography is superb – it is rapid, visual and shows the real state of the building. • Tip – Review building insulation

thickness and ensure that this meets the current best practice.

366

Energy losses from building fabric The energy/heat losses from a typical industrial building come from a variety of areas. Typical industrial buildings in a temperate climate will lose up to 75% of the heat through the building fabric. Improvements are generally low-cost and easy to implement. Chapter 7 – Buildings and offices

Windows and pedestrian doors Reducing air leakage at windows and doors is a key issue and simple measures can have dramatic effects on comfort and energy use. • Tip – Draught-proofing doors and

windows is cheap but can be very effective. Even a small gap will cause draughts and heat losses. You would not accept it at home so why accept it at work – except for the fact that it isn’t your money! • Tip – Ensure that doors and windows

are maintained properly. • Tip – Permanently seal unused doors

and windows. • Tip – Fit automatic closers on all

internal doors in the factory and do not allow staff to block them open. This is particularly important if offices are heated or cooled and are adjacent to areas of different temperatures. Air conditioning operating with doors open is a simple waste of energy. • Tip – Keep windows and doors closed to

reduce draughts – adjust the controls instead. Let the heating or airconditioning system do the job that it was designed for. • Tip – Do not heat areas where you have

windows or outside doors open. Improving the building fabric by replacing windows and doors can have a long payback but will improve energy efficiency and comfort. • Tip – Double glazing will reduce heat

loss and improve comfort. Modern windows with improved glass, gas filling and warm edge systems are far more efficient than standard double glazing. If it is not possible to justify replacement windows then simple secondary glazing can reduce draughts and improve comfort but it is not as energy-efficient. For offices with large expanses of glass, solar gain may be good in winter but cause overheating in summer. Simple external blinds or ‘brise-soleil’ are an excellent method of preventing solar energy from getting into the building where it will only increase the cooling costs.

Vehicle doors Vehicle doors are for vehicles to go through, not to produce uncontrolled draughts and a route for warm/cool air to escape or enter. • Tip – Separating vehicle and pedestrian

Chapter 7 – Buildings and offices

access allows large doors to be kept shut and is safer. • Tip – Automatic fast-acting roller

shutters are more effective than plastic strip doors and reduce draughts at vehicle doors. It is even better if air locks are used and interlocked so that the two doors cannot be open at the same time. • Tip – Interlock temperature controls

with large vehicle doors so that ‘door open = heating/cooling off’. The message is very direct and behaviour will change.

Walls and roof areas Cavity wall and roof insulation will greatly reduce heat loss in these areas. Cavity walls should be insulated if they are present and roof areas should be fitted with 300 mm deep insulation if possible. This is equally important for ‘internal’ offices where the temperature is different to that of the main area. • Tip – Restrict the size of temperature-

Measuring heat loss Heat loss from buildings and building components is measured by the U-value. A low U-value means reduced thermal transmission through the component. In the past, building regulations have specified maximum U-values for each component but the new European methods for building energy performance assess the energy performance of the whole building.

controlled areas by using insulated partitions or local systems. Do not heat or cool the whole building simply for a few small areas. • Tip – High ceilings can increase heating

costs simply because heat rises. False ceilings can restrict this and destratification fans can be used to blow hot air down from the roof space to the production area (see www.airius.co.uk for typical units).

New buildings/refurbishment A new building or a major refurbishment programme is an ideal time to reduce long-term costs for relatively low additional costs. New and refurbished buildings must meet local building regulations or codes and the requirements are increasing all over the world. Meeting the requirements is simply the minimum; it is not best practice – improving the energy efficiency to greater than the minimum at the design and construction stage is much more cost-effective than later retrofitting. • Tip – When adding new buildings look

at designs with energy-efficient windows, improved insulation, passive solar heating, passive ventilation, added thermal mass, ‘brise-soleil’ and natural lighting. Contractors and designers must be asked for these options. • Tip – Recladding of old buildings will not

only improve the look of the building but improve the insulation as well.

In the USA, the measurement of thermal transmission is given by the Rvalue. This is effectively the inverse of the Uvalue (except the units are different) but the good thing about the R-value is that it increases as the component gets better. It somehow seems more logical that bigger is better!

367

7.12

Building fabric – where are you now?

The initial steps in building fabric As with the score charts shown earlier, this is a self-assessment exercise to allow a site to benchmark their current status. This will set the scene for planning improvements in the area of building fabric. The condition of the building fabric controls the use of both heating and air conditioning and a high-quality building fabric can minimise both costs. The energy efficiency of the building fabric has increased dramatically in the recent past as developers and owners have recognised the need to decrease the energy use in

buildings. Many of the older buildings in the plastics processing industry could be cost-effectively overhauled to improve comfort and convenience and at the same time reduce energy use.

Completing the chart This chart is completed and assessed as for those presented previously.

The building fabric contributes to the base load for energy use. Improvements in this area can permanently reduce the base load.

Building fabric Windows 4 3 2 1 Natural ventilation

External doors

0

Roof insulation

Use the scoring chart to assess where you are in building fabric The numbers from the scoring chart can be transferred to the radar chart for a quick visual assessment of where you are in terms of building fabric. 368

The rise of double glazing and other ‘home’ improvements has not been mirrored by a similar rise in their use in industry. Comfort and convenience at home are not mirrored by comfort and convenience at work.

Chapter 7 – Buildings and offices

Building fabric Level

Windows All windows double-glazed & draughtstripped. Window operating gear holds them tightly shut.

4

3

External doors

Roof insulation

Natural ventilation

Roof insulation is at least 150 Users have control over All external doors mm thick & continuous over ventilation, providing draughtstripped with operating self-closing whole roof area. adequate ventilation during occupancy. devices. Much reduced overnight & Draught lobbies provided for frequently operated doors. weekend ventilation serving only to prevent condensation.

All windows double-glazed & Most external doors are well- Roof insulation is at least 100 draughtstripped. fitting & draughtstripped with mm thick & continuous over operating self-closing whole roof area. devices. Door locks hold them tightly closed.

Reasonable degree of user control over natural ventilation. Adequate ventilation during occupancy, with significantly reduced air changes outside of working hours.

Windows generally singleglazed & draughtstripped. Window operating gear holds them tightly shut.

External doors well-fitting & generally draughtstripped.

Roof insulation is 150 mm to Some degree of user control 100 mm thick generally, but over ventilation rates during visible gaps in the insulation. occupancy, although excessive during winter & inadequate during summer.

Windows single-glazed but fit well with minimal draughts.

External doors fit well.

Parts of the roof are insulated.

Higher than necessary rates of ventilation during occupied periods, with minimal reduction outside of occupancy.

Windows single-glazed & poorly fitting with gaps visible around the edges.

External doors are poorly fitting & gaps are visible around the edges.

There is no roof insulation installed.

Unnecessarily high air change rates with no variation between air change rates inside & outside of occupancy.

x

x

x

x

2

1

0

Score

Chapter 7 – Buildings and offices

369

Key tips • Improving building energy efficiency

reduces costs and also improves staff comfort and work output. • Building energy costs are a significant

percentage of the total energy costs but often use a different fuel to process energy use. • Monitoring and targeting for buildings

energy use is largely ‘condition’-driven (by the weather) and can be benchmarked both internally and externally. • The energy use of office equipment is a small percentage of total energy use but can be reduced through simple staff measures. • Lighting may not use a large amount of energy but is a very visible sign of a site’s commitment to energy management. • The primary reason for lighting is to provide a safe environment. • Ambient and task lighting are very different. Recognising this and taking action to separate the two can reduce costs. • Producing a ‘lighting map’ is a key action in reducing energy use in lighting.

• Maintenance of heating is important in

reducing energy use. • Hot water is best provided by local

generation from ‘on-demand’ heaters. • Air conditioning is a rapidly rising

energy user but is mostly comfort cooling for a few days of the year. It can cost as much as the yearly heating bill to operate air conditioning for these few days. • Air-conditioning controls are often

tampered with by staff. • Building fabric improvements can reduce the heating and air-conditioning loads and reduce costs in these areas. • Simple building fabric improvements can

reduce energy use. • The main tasks are to reduce air leakage and to improve building insulation. • Air leakage is not the same thing as ventilation. • Insulation can be improved through simple local measures.

• Developments in lighting have produced

products that can greatly reduce lighting costs. • Controls provide an opportunity to automatically reduce lighting use without affecting product or lighting quality. • Maintenance of lighting can be a large

cost but will return the investment. • The primary reason for heating is to

provide a comfortable working environment for the staff. • Reducing the heating load is the first

task. • Heating can be either quality or comfort

related – these have very different requirements. Recognising this and taking action to separate the two can reduce costs. • Heating levels should be set to match the activity in the area. • Heating controls can reduce heating

costs but must be set correctly and secured against tampering. 370

Chapter 7 – Buildings and offices

Chapter 8 Site surveys

Carrying out a site survey is an essential starting point for energy management. The site survey is at the heart of finding cost-effective opportunities for energy use reduction and is one of the most useful tools available for any site. Starting energy management without a full site survey can easily lead to starting projects that are not completed because they do not fit into an overall plan. The site survey provides a planning mechanism and a global plan for improvements in energy management. A site survey is not difficult to carry out but experience with the process is necessary to get the best out of a site survey. The best tools for a site survey are an inquisitive mind, good senses of smell, hearing and observation and above all a refusal to accept that ‘because we have always done it that way’ means that it is the best, or only way to run the process or operation. Many sites will choose to outsource the site survey and this can provide the essential external viewpoint on the site. The right consultant will have the right equipment, will know how to carry out a survey quickly, will have the specialist knowledge of energy management, will know what works and what doesn’t, will treat the results objectively and will prepare a complete plan for the site. Equally, reports from the ‘wrong’ external consultants, who have no process experience, will mainly contain recommendations for lighting projects (despite the fact that lighting is only ≈ 5% of the energy use). If the report focuses on

lighting then you have got the wrong consultant. Internal resources may be influenced by pre-determined solutions, may not be fully impartial and be reluctant to identify areas where they themselves are part of the problem. They may also be limited in time and knowledge of the topic of energy management. Despite this, many sites will want to carry out their own survey, if only to verify the potential savings and to see if an external consultant would be valuable. Whichever way you decide to go, it is essential that you start somewhere. While you are thinking about the topic, there is money being thrown on the production floor. The time to do this is now.

If you don’t know where you are starting from then it is highly unlikely that you will get to where you want to end up.

Energy Management in Plastics Processing https://doi.org/10.1016/B978-0-08-102507-9.50008-8, Copyright © 2018 Elsevier Ltd. All rights reserved.

371

8.1

A mini site survey – the energy walkaround (the treasure hunt)

The precursor to the site survey It is doubtful that any reader will have got to this point without being convinced of the need for a full site energy survey but it is often useful to carry out a mini site survey or an energy walk-around to verify that a full site survey will be productive. This is easily carried out by any member of staff and should take only 2–3 hours. Take a walk around the site at about mid-

shift and simply look for potential areas where the energy is being poorly used or wasted. The check sheets on this page are not all that you can look for, they simply provide a focus for some things to observe during the walk-around. The walk-around also provides an opportunity to check on simple maintenance measures and to question accepted practices.

In doubt about whether you need a full site survey or not? Take this quick test to see if there are any significant opportunities for improvement.

Yes

General

No

Can you easily identify the areas with the largest electrical load?

Look for the largest machines on the site. They will most likely also have the largest motors or heaters and create the largest load, when they are used. Can you see machines or equipment that are not in production but have motors, heaters

or downstream ancillary equipment running? Typical examples are barrel heaters, pumps, fans, conveyors and granulators – Note any energy use where no productive work is being carried out. Look for machines operating during lunch breaks and after normal hours. Can you see or hear water, hydraulic fluid, steam or compressed air leaks on any

machinery (operating or not)? Look for areas of energy use where no productive work is being carried out and yet machines are running and using energy. This is particularly important after the factory has stopped operation for the day or week. Can you see any ‘accepted’ practices that are wasting energy and can these be

modified at no cost at all? Look for areas where simple changes can save energy such as batching of reject parts for regranulation or using regranulators only at night. Can you see any good, simple maintenance measures that can be introduced to reduce

energy use? Look for areas where a lack of maintenance raises energy use, e.g., blocked filters (air or water), kinked pipes or poor insulation due to age and ‘wear and tear’.

Motors Are machines kept idling to be ready for the next production run?

Look for idling machines and keep asking ‘why?’ until you get to the real answer. The first reason given is often an excuse for inaction and not a real reason. Are the motors the right size for the job?

Look for motors that are larger than normal motors compared to similar equipment. Are the motors the right type for the job?

Motors that are in constant use should be a minimum of IE3 motors efficiency. Check the motor information from the data plate on the motor. Is the demand on the motors variable?

If the demand is variable then the speed of the motor can be changed using a VSD.

Compressed air Can you hear any compressed air leaks?

The hissing noise from compressed air leaks (or use) is costing real money. If there is no production being carried out why is the compressed air allowed to leak?

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Chapter 8 – Site surveys

Yes

No

Is compressed air being used for applications where other cheaper methods can be

used? Compressed air is a very expensive method of powering any process. It is especially expensive when open air lines are used for positioning, cleaning, drying or cooling. Does the compressed air pressure need to be so high?

Reducing the compressed air pressure reduces the amount of leakage and also reduces the cost of any leaks in the system.

Chillers/cooling towers Are chillers or cooling towers being operated when there is no production or is cooling

water being fed through machines that are not operating? Running chillers or cooling towers with no production simply recirculates the water, allowing it to pick up needless heat from the system that is then removed by the chiller or the cooling tower. Running cooling water through inoperative machines picks up needless heat that must be removed by the chiller or the cooling tower. Are cooling water pumps still running when there is no production?

Circulating water through an inoperative system is simply a waste of energy.

Machines Is thermal insulation present on all the machines?

Most plastics processing involves applying heat to the plastic. Allowing this heat to escape to the atmosphere is very expensive. If there is no insulation then it should be fitted. If there is insulation then it should be in good condition. Are there clear setting instructions for all machines and products and if present are they

being followed? Setting instructions should ensure that machines are in the most economical production state and must be documented and followed. Is there a shut-down procedure to specify the longest time that machines are to be left

idling? Idling machines cost real money. Shut-down procedures formalise the process and provide the rules to minimise energy use.

Building fabric Is the lighting dirty or not operating?

Dirty lighting costs the same to run but gives less lighting efficiency. Lighting that is not operating can still be costing money. Can natural daylight be used to reduce the need for artificial lighting?

Good natural daylight is not only the best lighting but it is also free. Use it as much as possible. Are there any automatic lighting controls that sense ambient light levels and building

occupancy? Good automatic controls take the human element out of lighting levels and can be used to maximise the use of natural daylight. Do you have automatic fast-acting roller shutters on external access doors?

Automatic doors will reduce heating energy use in the winter and keep the buildings at a more constant temperature. Are the windows and doors for all office areas draughtproofed?

Draughtproofing is effective and used in most houses. Use it to reduce the heating costs. Are you heating (and lighting) lightly occupied warehouses?

Many warehouses simply need ambient lighting and trace heating for sprinklers. If you answered ‘Yes’ to more than 11 of these 23 questions then there is a real need for a full survey of the energy use at the site. The site has some good opportunities for real energy use savings. Chapter 8 – Site surveys

373

8.2

Preparing for a site survey – information

Get the basic energy data Preparing for a site survey is an essential part of the process and good preparation makes a site survey much more useful. Getting basic internal site data is the first step in preparing for the site survey. The surveyor needs to understand the basics of the energy use at the site before it is possible to recommend cost-effective improvements.

Analyse the basic energy data The simple calculation of the PCL and analysis of the base and variable loads against the expected values for the process provides a first look at where energy management might be improved at a site. Large base loads, low correlation between the data points and a process energy load outside the expected range are all indicators of areas for possible improvement. Equally the PCL gives indications of where not to look, i.e., where it would not be profitable to spend time. Sensible analysis of these data can save time later in the survey.

Analyse the completed SER forms Analysis of the completed SER forms will rapidly show where the site is weak in the critical areas of services and processing. The surveyor can then concentrate on the lowest-scoring areas to identify the improvements that are necessary and to set out the programme for improvement. In the first instance, it is not wise to try to improve all the areas of the radar charts that are low-scoring. Sites should attempt to improve the scores in the lowest rating areas only. Select one aspect for each chart (the lowest rating aspect) and set out a programme to improve this area. Complete the programme and improve the score for this area. Start again with the next low-scoring area. This will provide the essential long-term programme for improvements at the site.

Complete the ‘Where are you now?’ sheets Throughout this book there is a series of ‘Where are you now?’ sheets presented in the individual sections for which they are relevant. These can be combined into a ‘Site Energy Review’ (SER) to provide a comprehensive diagnostic assessment of the status of the site with respect to a variety of energy issues. Simply carrying out the assessments necessary to complete the SER sheets will prompt the site to question many of the accepted practices within the site and this will identify areas for improvements. A downloadable spreadsheet containing all the SER sheets is available from www.tangram.co.uk/energy.

374

Starting a site survey without adequate information is a futile process.

Base and variable loads (injection moulding)

Make an energy map of the site

800,000 700,000

Energy use (kWh)

The site energy map (see Section 3.2) is an invaluable tool in a site survey. A detailed energy map will give information on the largest energy use areas and these are the areas to spend time on during the survey. Energy management is always about allocating appropriate resources.

An initial site survey is a key starting point for energy saving.

600,000 500,000 400,000 300,000 200,000 kWh = 1.5751 x Production volume + 152,440 R2 = 0.9397

100,000 0 0

50,000

100,000

150,000 200,000 250,000 Production volume (kg)

300,000

350,000

400,000

The PCL gives vital information for the site survey The good correlation of the data (R2 = 0.9397) indicates a site that is in good control of energy use. The base load is ≈ 30% of the typical load (average for plastics processing) and the process load is 1.5751 kWh/kg (slightly high for injection moulding). The site survey should look for easy wins in base load reductions (lighting, compressed air leakage, etc.) and also for some easy wins in process load reductions (lack of barrel insulation, processing temperatures too high, etc.) This information starts to tell you where to look in the site survey for useful reductions in energy consumption. Chapter 8 – Site surveys

Motors

Power supply

Motor management 4

Supply contract 4

3

3 2

Maximum demand (kVA)

1

VSDs & HEMs Meter reading & payment

2

Motor information

1 0

0

Maintenance & repair PF Correction

Motor sizing & speeds

Sub-metering

Operations

Cooling water

Compressed air

Cooling load 4

Leakage 4

3 Maintenance & operations

2

3 Use

Heat recovery

1

0

Generation

Treatment

Systems

1

0

Distribution

2

Air blast cooling

Components

Operation & maintenance

Typical ‘Where are you now?’ radar charts provide vital information on how to improve energy management at a site. Four typical radar charts produced from the ‘Where are you now?’ data (see Sections 4.12, 4.23, 4.32 and 4.41 for the blank scoring forms). These examples indicate: Power supply: This site appears strong in contract negotiation but weak in most other areas of power supply management. Administrative efforts need to be made in recording the use and maximum demand and the site installation needs to be improved in both PF correction and sub-metering information. Motors: This site has made little progress in controlling motors in any way. Efforts in this area need considerable improvement and there are many opportunities for improvement. Compressed air: This site is almost certainly not in control of compressed air at any part of the process. There will be many obvious opportunities for improvement in compressed air management. Cooling water: This site appears to have made good efforts in controlling and managing chilled water. It does not appear that there are many opportunities in this area. The radar charts start to tell you where to look in the site survey for a useful reduction in energy consumption. Chapter 8 – Site surveys

375

8.3

Preparing for a site survey – tools

The basics It is possible to carry out a site survey, at the basic level, without any physical tools other than a notebook and pen to record the results. It is, however, far better to have a simple tool kit that will extend the range of the survey and allow the surveyor to present the results in a far more effective manner. The human hand is also a great tool: • If a motor is hot to the touch then it needs some maintenance. • If a pipe is cold to the touch then it probably needs insulation. • If a pipe is hot to the touch then it

probably needs insulation.

Ultrasonic leak tester Compressed air leaks emit ultrasound, with an ultrasonic leak detector it is possible to find compressed air leaks even on a noisy site (for example, see www.logis-tech.co.uk).

The basic tool kit The basic tool kit for a site survey is: • The information listed in Section 8.2. • A camera to record the practices that you

see on the site. This is really the basics – with these simple tools it is possible to carry out a basic survey. This means that compressed air leaks will be detected by hand, hot surfaces will be detected by touch (preferably approaching but not touching) and no electrical measurements will be made.

The advanced tool kit The advanced tool kit will allow a surveyor to not only detect more possible improvements but will allow exceptional events to be documented far more clearly and graphically. The advanced tool kit (in no particular order) is: • Ultrasonic compressed air leak detector – this is listed as an advanced item but the cost is so low (≈ £1,000) that it should actually be regarded as standard equipment for any site using compressed air. Ultrasonic leak detectors can find air leaks in noisy environments. Using this type of equipment it is possible to detect leaks from a distance of up to 5 m. This allows high-level distribution systems to be checked at the same time as the floorlevel system. Surveyors also need tags to mark detected leaks – if it is possible to mark leaks in terms of m3/min or in terms of £/year, always choose the latter. 376

Thermal cameras A thermal camera reveals areas of possible electrical failure and areas with poor insulation (hot or cold) very quickly (for example, see www.flir.com).

Environmental meter A multi-function environmental meter measures noise levels, light levels, temperature (ambient and thermocouple probe) and relative humidity. Chapter 8 – Site surveys

• Thermal camera – the cost of thermal

cameras has dropped dramatically and a thermal camera that attaches to a mobile phone now only costs in the region of £200. The use of a thermal camera enables detection of process hot spots ((generally due to poor insulation), overheating motors and potential electrical failure points. Many companies already use thermographic analysis for electrical systems and should extend this to process analysis. • Environmental meter – a simple multi-

function environmental meter capable of measuring light, noise, relative humidity and temperature (either ambient or via a thermocouple). This type of tool costs ≈ £80. • Clamp meter – a standard clamp meter allows non-intrusive measurement of electrical data but is generally for ‘point’ data only. This type of tool costs ≈ £25. • Clamp meter data logger – clamp meters can also be data loggers and store measurements. These tools can take measurements at intervals of between 1 s and 1 day and then download these direct to analysis software via USB. This allows long-term analysis of systems such as compressors or short-term analysis of rapidly changing systems such as IMMs. These cost ≈ £300 for a single-phase meter or £1,000 for a threephase meter. • A small portable weather station – these provide a multitude of measurements in a single small unit. This type of tool costs ≈ £300. • Thermometer (thermocouple and infrared remote thermometer) – a simple infrared remote sensing thermometer provides an easy method of taking spot temperature measurements in areas such as roof voids to determine the amount of stratification of heating. This type of tool costs ≈ £25.

Single-phase data logger clamp meter A data logger clamp meter allows measurements to be taken at intervals and then downloaded via USB to a PC for later analysis. All the power traces shown in this book were taken with similar meters (for example, see www.spcloggers.com).

Three-phase data logger clamp meter A single-phase meter relies on balanced phases but for full threephase measurement a three-phase meter is needed. All the power traces shown in this book were taken with similar meters (for example, see www.spcloggers.com).

• Torch – for reading nameplates and

other information in dark areas. • Stopwatch – for timing operating cycles. • Panel keys – for machine control panel access. The advanced tool kit will allow a full survey to be carried out with detailed measurements of machine or services energy use and selected environmental measurements.

Chapter 8 – Site surveys

Portable weather station Portable weather stations can measure wind speed, wind chill, air flow (volume), dew point, relative humidity, both wet- and drybulb temperatures as well as altitude and heat intensity – all in one small unit (for example, see www.kestrelmeters.com). 377

8.4

Planning the initial site survey

Objectives In most cases, the objectives of the site survey are: • To gain an overview of the general site energy use. • To identify a basic programme of no-cost

and low-cost improvements that can be made to reduce costs. • To identify an advanced programme of

higher cost investment opportunities that can be made to reduce costs. In a very practical sense, it is simply a walk around the site with an ‘energy management’ hat on – auditors are looking for opportunities to reduce energy use and to save money.

Defining the survey A key issue in site surveys is defining the parameters of the survey. Decisions need to be made on: • Who is going to carry out the survey? Surveys can be ‘internal’ using internal staff or ‘external’ using consultants. Consultants may be expensive but they can provide insights and experience that internal staff do not have. They are less likely to adopt the ‘we’ve always done it that way’ approach and can challenge barriers to improvement.

assess or rank potential improvement projects without good information and the auditor can easily end up recommending projects that are either ineffective or do not save large amounts of money. The information listed in Sections 8.1 and 8.2 should be gathered as soon as possible and preferably before carrying out the site survey.

Low-cost energy efficiency measures can improve profits significantly.

• Tip – Energy surveys and audits must

be ‘data-driven’. Starting work without all the required data is not sensible and will potentially give misleading results and projects. • Tip – Information is the key. Collect

every piece of data that is available before the survey. It makes it easier to plan and carry out the survey and will be useful when doing the analysis and reporting.

When to carry out a site survey The site survey should be carried out as soon as possible – if energy is being wasted now, it is costing you money now. Get the information, carry out the analysis

• Tip – Consultants should always have

process knowledge, if they don’t know the process then it is difficult for them to recommend good projects. • What is the survey scope? Surveys can be broad and cover all the site processes or be very specific in scope. This workbook gives information on all areas but a site might decide to limit the scope to a specific area such as ‘compressed air’ to get more detailed outputs. • Tip – An initial site-wide survey will

identify and prioritise projects that might need additional surveys, e.g., if a site-wide survey identifies ‘compressed air’ as an issue then there might be a need for additional surveys in this area.

Information is the key Carrying out a site survey without the essential information (see Section 8.2) is not an effective process. It is impossible to 378

Energy use in plastics processing Energy is used at all stages of polymer processing. The major use is in motors, heating, cooling and services such as compressed air. The site survey should look at all these areas to locate potential savings and areas for cost management. Chapter 8 – Site surveys

and make an unannounced survey of the site at around mid-shift – try to include at least one meal break so that you can see what happens during these breaks. Any individual site survey is only a snapshot of the operations of the site – no single survey can ever hope to identify all the opportunities. • Tip – It may be necessary to carry out

concentrate on the visible (but less important) areas such as lighting. • Tip – Checklists and good planning focus

the site survey on the important areas. • Tip – The energy map (see Section 3.2) is

an invaluable resource for a site survey but you may not be able to get all of the information before the survey.

One of the most productive surveys I have ever carried out was on a Sunday afternoon – my dedication knows no bounds.

several site surveys to be confident that all of the improvement opportunities have been captured. When planning a schedule for a site survey it is also profitable to carry out at least one site survey when there is no production activity, i.e., during the night if there is no night shift or during the weekend if you do not work at the weekend. Surveys during non-production times inevitably identify areas of base load use, e.g., compressors left switched on and machinery idling with no production. Be prepared for a shock when you find what has been left on during these times!

Planning time allocation The site energy map (see Section 3.2) provides a view of how much time should be spent in each area of the site. If lighting uses only 5% of the energy at the site then ≈ 5% of the site survey time should be spent on lighting topics. Equally at most plastics processing sites, the actual plastics processing machinery will use over 60% of the energy and this should be the prime focus of the site survey. The diagram on the left shows the basic process steps and the main areas of energy input in most plastics processing operations. This can be used to identify the potential areas for investigation. Use this as a guide during the survey to look for areas of high or unnecessary energy use. It is useful to prepare a similar process map for the site being surveyed. • Tip – If process maps have been created

as part of ISO 9001 then these can be used to plan a survey. Process maps can be translated into a series of checklists to ensure that the site survey covers all the areas of energy use. It is very easy during a site survey to be sidetracked by the discovery of potential opportunities and the use of a preprepared checklists ensures that all the areas are covered. It is also very easy during a site survey to forget to look at the hidden (but important) processes, particularly the services, and to

Chapter 8 – Site surveys

Planning the site survey The time spent in an area during the survey should reflect the amount of energy used in that area. Planning the site survey should be logical and appropriate. Try to complete the survey of one area or group before moving on to another area. 379

8.5

Carrying out the initial site survey

Boots on the ground The initial planning carried out in Section 8.4 provides the essential preparation needed to carry out a survey but conducting a good survey involves more than simply checklists and time allocation. This is where the process moves from a ‘desk-based’ assessment to ‘boots on the ground’. It is where the surveyor swaps a mouse and spreadsheet for measuring equipment and safety boots. • Tip – We always use the phrase ‘site

survey’ rather than ‘site audit’ because ‘audit’ can create a negative image and imply that the site is doing something wrong and will be punished as a result of the survey. A site survey should be a positive experience and a chance for the site to learn how to reduce costs and improve operations.

Starting out right Select a survey team All good surveys need site staff to provide assistance and information during the survey. The site should provide a ‘survey team’ to guide, assist and help carry out the survey. The survey team will normally be operational managers and will be familiar with the detailed operations of the site as well as being broad in experience and responsibility. This is an opportunity for the surveyor to collect real operational information and to learn how the site works. A good survey team will reinforce each other’s knowledge and generate an ‘esprit de corps’ in energy management.

potential opportunities and the potential financial benefits of improved energy management. It should be designed to not only inform but also to generate enthusiasm for the survey process.

Observe what is happening – not what you think should be happening.

• Tip – Do not forget to mention improved

financial performance and improved job security in the briefing.

Walk the site Unless this is an internal survey, it is recommended that an external surveyor ‘walks the site’ to get an overview of the scale, operations and complexity of the site. Preferably the site walk will follow the product as it flows through the site. • Tip – The site walk allows an external

surveyor to adjust timings (see below) if there are areas that have not been included in the initial scoping of the site.

Follow the survey plan The survey plan (see Section 8.4) should be followed to cover the complete site. The basic questions that need to be asked (and answered) for each process are:

Site surveys should be fun and the surveyor should learn as much as the site does. This is a two-way process.

• Tip – If the survey is being carried out

by an external surveyor then this is an ideal opportunity for the survey team to be trained in the surveying and in how to look for energy-saving opportunities. • Tip – The Maintenance Manager is a

‘must have’ on the survey team. They will know about the services and machines and will also be responsible for many of the actions even if the site has an Energy Manager.

Brief the site management The site management should be clearly briefed on the survey process and timings. A good initial briefing will cover the broad 380

Energy losses All manufacturing processes need an energy input as well as a material input. The survey process is designed to find and quantify the non-productive energy use (losses) in a process. This can be in the services or in the main process. Chapter 8 – Site surveys

• What is the function of this system/

operation? • How does the system/operation do this? • How much energy does the system/

operation use? • How can the energy used by the system/

operation be reduced? • Who is responsible for maintaining and improving the system/operation? The answers to these questions will immediately start to generate a range of potential energy management projects.

Collect data The survey process is essentially a data collection process where the surveyor attempts to collect as much data as possible in a short time. The checklist generated as a result of the process flow maps (see Section 8.4) will provide the basis for much of the data collection but it is essential that the surveyor makes comprehensive notes, takes photographs and, where necessary, takes measurements during the survey. There is nothing more frustrating than completing a survey and starting to write the report only to find that a small but vital piece of information has not been recorded. Record and document everything that is seen or measured; this should include good practice as well as bad practice – the final survey report should not only give suggestions for improvement but also note good practices and record these. Give credit where credit is due. • Tip – Count the motors, their size and

how hot they are. • Tip – Count the lights, the type and

their control systems. • Tip – Use the tools (see Section 8.3) to

make measurements at every opportunity. No measurement is ever wasted, it may not be used but it will serve to build up a picture of the site operations. • Tip – Collect samples of the product for

later examination. They can be invaluable reference information. • Tip – It is often unnecessary to measure

every machine and process – look for the typical examples and areas where improvements can be made. • Tip – Photograph everything, it doesn’t

cost anything so why not take as many as you can? They will be invaluable in remembering what was happening if the notes are confusing. Chapter 8 – Site surveys

• Tip – Use video as well as conventional

photographs – nothing is as powerful as a video of a machine operating with no product being produced.

Question everything Surveyors should always question everything and follow the ‘5 Whys’ method to find out what really happens and why. A lot of the energy losses in a site are due to ‘We have always done it that way’. Energy surveyors are there to challenge this type of thinking and only by being sceptical (but courteous) will the survey find the opportunities for real improvement.

There are several good resources available on the Internet about carrying out site surveys. Unfortunately, many of these are ‘buildings-oriented’ rather than ‘process-oriented’ and are not really suitable for plastics processing sites.

• Tip – Never accept the first answer to

any question. Always probe for the background reasons.

Keep to the time plan The time allocation plan (see Section 8.4) gives approximate timings for surveying a plastics processing site and it is important to keep to the time plan to ensure that every element of the site is covered. An orderly approach to the site survey requires the completion of one aspect of the survey before proceeding to the next aspect of the survey. This means that all the items concerned with power supply should be completed before moving on to compressed air. The only exceptions to this are the delivery of the services at the machines, i.e., compressed air is treated in the general sense first (generation and treatment) but monitoring of compressed air leaks is treated as part of the machine survey topic. • Tip – If there is a potential project

identified then spend extra time gathering data.

Finish off right The final step in an energy survey is the ‘exit debrief’. This is where the site is presented with the preliminary findings of the survey and some of the potential measures (with preliminary savings values). • Tip – The final survey report should not

come as a surprise to the site. The exit debrief is the chance to give a preview of what the survey report will contain. • Tip – The initial site survey is a first

pass at finding opportunities. There is always an opportunity to carry out another survey.

Suppliers are not consultants, they are suppliers. They can be used for some aspects of a survey but remember that they are there to make money from selling something. It may (or may not) save energy at the site but it will definitely make money for them. Use supplier surveys with caution.

381

8.6

Reporting the initial site survey

Turning the site survey into information A site survey is useless unless action is taken to reduce energy consumption as a result of the findings. Following a site survey, a survey report should be produced to detail the findings, suggest projects and, above all else, to drive action. Reporting should be clear, concise and prompt to produce action rather than to simply sit on a shelf.

The site survey report Site survey reports should focus on generating discrete projects. It is not enough to state that the energy management at the site is ‘poor’, it is essential to specify the actions and preferably projects that the site needs to complete to get better.

Discrete projects that the site can carry out are the best method for generating action. Projects must be specific, costed, timed and targeted to generate concrete actions.

The big picture The front of the site survey report should be a simple summary of identified projects and the broad financial details. A typical example of a site survey summary is shown below and this includes all the relevant financial details on one sheet for easy reference. • Tip – Leave the full financial details and

calculations to the ‘Survey Project Sheets’ or to the text of the report. • Tip – Most energy management projects

have a very positive financial impact. It is possible to do ROI and other

Annual savings Recommendation

If a consultant (paid or free) looks at the lighting for a long time and if most of the recommendations are about lighting then you know that he is not the right person for the job. He doesn’t know the process and he will have missed the most valuable opportunities.

Estimated project cost (£)

Payback (years)

Cost (£)

Energy (kWh)

CO2e

Energy management system

7,601

83,522

43.2

4,000

0.53

Staff energy management training

7,601

83,522

43.2

3,000

0.39

Available capacity reduction

16,669

0

0.0

500

0.03

Compressed air – leak reduction

17,197

188,953

97.7

4,000

0.23

Compressed air – use reduction

42,992

472,383

244.1

20,000

0.47

Compressed air – generation

17,938

197,100

101.9

1,500

0.08

Chilled water – increase temperatures

14,351

157,680

81.5

2,000

0.14

Chilled water to process pumps – resize and VSD

44,527

489,249

252.8

4,000

0.09

Stand-by and shut-down

10,135

111,363

57.6

10,000

0.99

Regranulator control

32,369

355,656

183.8

8,000

0.25

Auditor training and energy audits

7,601

83,522

43.2

3,500

0.46

218,981

2,222,950

1,149.0

60,500

0.28

43.2%

39.9%

38.4%

TOTALS %

Reporting the big picture of a site survey This is a typical format for reporting the big picture of a site survey. This should be the first thing that the site management sees in the report. It does not give the details of each identified project but gives the simple financial, energy and environmental benefits of each project. The format is designed to attract management attention to the benefits of energy management and to stimulate action. 382

Chapter 8 – Site surveys

calculations but a simple payback calculation is often more appropriate.

The ‘Survey Project Sheets’ A suggested format for a ‘Survey Project Sheet’ is shown on the right; this is designed to contain all the essential information necessary for the site to start and complete a specific project. The complete site survey report is a collection of ‘Project Sheets’ for the site to work on.

• Tip – The energy survey may start out

as part of ‘sustainability’ or ‘production’ but rapidly becomes ‘financial’ when the size of the numbers becomes apparent. Be prepared for interest from the financial people – you may find that you acquire new friends.

• Tip – Try to keep the Survey Project

Sheet to a single page. If it is longer than this then many people will lose interest. The financial details in the project sheet will initially be estimates (to be confirmed before starting the project) and, for a first site survey, the simple payback on most projects should be less than 18 months. • Tip – The prime aim of the Survey

Project Sheet is to stimulate action. Many managers will not read beyond the financial details before deciding on whether to proceed or not. If the financials look good then most managers will not even read the rest of the sheet. Survey Project Sheets should provide details of the proposed project and the basis for the financial calculations as well as an assessment of the risks involved in the project. It is also useful to include an outline of the necessary next steps. This is not a project plan (see Section 1.13) but simply an outline of what happens when the project is approved. If there is any difficulty in identifying projects, the Site Energy Review process (see Section 8.2) provides a good method for identifying potential projects. A series of completed SER sheets attached to the site survey report will provide top management with a good visual record of where the site is in terms of energy management and serve as a ‘road-map’ for further improvements.

Distribute the report widely The distribution of the site survey report is also vital. When carried out correctly, a site survey will identify significant savings to the site and this becomes a business issue. The report should therefore go to all the directors of the company. This must include the Managing Director and the Finance Director as well as the Operations Director and the Production Director. Toplevel understanding of the results of the survey (expressed in financial terms) is essential to getting the resources and backing necessary to complete projects. Chapter 8 – Site surveys

Reporting the details of a site survey This is a typical format for reporting on an opportunity identified during a site survey. The form contains all the important information needed to assess and control the project. Identification is easy – implementation is the only important thing. 383

8.7

Following up the initial site survey

Turning the site survey into action The initial site survey report should prompt action but this must be targeted to get the best results. As a general rule, a site should be given no more than 15 projects to work on at any one time. Energy management is not the only job that most people have and keeping the number of projects manageable increases the chances of completing the projects. It is not the number of projects you start that save money – it is the number of projects that you complete.

Plan the process There is always a temptation to start work on identified projects as soon as possible but this is not recommended. However attractive the payback on projects, it will be impossible to deliver all the identified projects immediately. This means that some type of project plan is necessary to control the order in which projects are to be carried out, when they are to be started and when they are due to be finished. Whilst this is a separate activity to the actual survey report, the Survey Project Sheets can be used to give a rough approximation of the relative timings for projects (see Section 8.6).

hanging fruit) that are so simple and easy to deliver that they should not wait for a complete project plan, e.g., sealing compressed air leaks should start the moment they are found. At one site, the management had a team of three people follow me around sealing the compressed air leaks even before I had completed the tag. Sites can then use the global and detailed plans to control and complete the projects identified in the initial site survey.

The cost savings possible from energy efficiency will only be achieved if there is a management commitment to actually carry out the work necessary and save the money.

• Tip – Always close out projects as they

are completed and all closed out projects should be subject to a verification process (see Section 3.9) to verify that they have delivered the identified savings. • Tip – Completed and verified projects

should be fed back into the monitoring and targeting process (see Chapter 3) to reflect improvement in targets. The gains should be locked into the system. • Tip – Completed projects are good news

and should be communicated widely to generate continued enthusiasm for energy management. Do not hesitate to celebrate success.

The Survey Project Sheets will need management approval and only after this is given can a site start to plan the process. The priority of any approved project in the plan can be based on a variety of criteria but preference should be given to projects that are easiest to implement and give the largest energy use reduction (see Section 1.13). Sites should prepare an overall global project plan (as shown on the right) to provide an overview of projects and time. This should refer to the plans for each individual project and these can be created relatively quickly using Post-it notes (see Section 1.13). • Tip – Planning is an essential part of

delivering completed and successful energy-saving projects. Neglect it at your peril. • Tip – Whilst planning is essential, there

will always be some projects (the low384

Global project planning from a site survey report The Survey Project Sheets should be assessed and a global project plan developed. This will provide an overall plan for the site’s efforts to reduce energy use and allow progress in energy management to be seen quickly. Chapter 8 – Site surveys

Repeat the site survey The initial site survey provides a selection of projects for reducing energy costs but this is not the end of the process. The initial projects will inevitably be the easiest to find and implement but repeated site surveys at regular intervals by trained auditors will continue to discover new improvement projects for existing processes and products. New processes, products and proposed capital expenditure will also need assessment and investigation to identify opportunities for energy savings. Energy management is not a single task but a programme of continuing actions. Only by continual identification and completion of new projects will energy use and costs be reduced. Sites should:

the site money and should be taken very seriously.

The process of repeating site surveys is part of continual improvement in energy management. This is not a single task but a continual effort to reduce energy use and costs.

• Use the site survey process to train a

suitable person to a basic level in site energy surveying. • Carry out regular site surveys using standard auditing methods (as for health and safety and quality audits). • Use the regular site surveys to identify current projects that are not completed or are not on schedule. • Use repeated site surveys to identify new projects for action.

Driving action Most sites will already have an ISO 9001 Quality Management System and will be familiar with the concept of ‘nonconformance’ reports. Under ISO 9001 these are issued when an auditor finds something that does not conform to the system or when there is potential for quality concerns to happen. It is recommended that sites use their existing system of non-conformance reports to drive action. Non-conformance reports will stimulate continued action for existing projects or improvement where a non-conformance is not part of an existing project. A suggested format for a nonconformance report is shown on the right and this identifies that the Production Manager has not taken action to seal identified air leaks within the allowed time limit. • Tip – Non-conformance reports must be

closed out when completed and must lead to action. • Tip – Failure to take action on non-

conformance reports is directly costing Chapter 8 – Site surveys

Non-conformance reports must follow surveys This is a typical format for reporting on lack of action by the production department. Auditing is only effective if it leads to action. Non-conformance reports should be issued if action is not taken and followed up until the action is closed out. 385

Key tips • Site surveys are a key part of energy

management. • An initial site survey establishes where a

subject to non-conformance reports if progress is not to schedule or if action is not being taken.

site is in terms of energy management and serves as a reference point for future progress. • A mini site survey (an energy walk-

around) will rapidly establish the need for a full site survey. • Information is the key to an effective site

survey. • Basic energy consumption data, an

energy map of the site and a completed Site Energy Review are necessary for an effective site survey. These allow targeting of areas on the site which will be most rewarding for the survey process. • The equipment needed for a basic site survey is minimal and it is possible to carry out a site survey with virtually no equipment. • The equipment needed for an advanced

site survey is still relatively inexpensive but allows the survey to be extended and to add more value to the site. • Site surveys should be well planned to get the most benefit. • Site surveys should be carried out during

normal production and also, if possible, during shut-down periods. • Site surveys should be targeted to the heaviest energy use areas to provide the greatest rewards. • Site surveys should record all the information obtained during the survey. • Reporting on site surveys should drive action to reduce energy use. • Reporting on site surveys should produce

a range of clearly defined projects that will pay back rapidly. • Reporting on site surveys should be in financial terms to motivate top management to support the improvement projects. • Site surveys should be repeated at regular intervals to check progress with existing projects, to report success of previous projects, to close out completed projects and to generate new projects for completion. • Progress on existing projects should be

386

Chapter 8 – Site surveys

Chapter 9 Carbon footprinting

Energy management focuses on reducing the use and cost of energy but an inevitable result of this will be a reduction in the carbon footprint of the site. Whilst reducing the use and cost of energy is the main objective of this workbook, reducing the carbon footprint of a site can have significant benefits both in terms of public relations but also in terms of conforming to the range of government regulations that are appearing around the world. Establishing a site carbon footprint is not difficult and this chapter gives details of how to do this. Simply gathering the information necessary for good energy management will result in gathering much of the information necessary to produce a carbon footprint. There is also a need for some additional information but this is generally easily obtained and only needs to be formatted correctly to produce a site carbon footprint. A site carbon footprint can be used to communicate progress in energy management, to set and meet external targets from customers and to set and meet external targets from government regulators. It is also a useful tool to concentrate minds on one of the reasons for reducing energy use by energy management.

countries are also introducing legislation that requires environmental reporting of greenhouse gas emissions, i.e., reporting the carbon footprint. In addition, many large customers, particularly retailers, are encouraging suppliers to calculate their carbon footprint. This will eventually be cascaded down the supply chain to the plastics processors who supply these retailers directly or indirectly. At the consumer level there is also interest in carbon footprints but at this level the interest is more on the product carbon footprint. This is a much more difficult proposition than a site carbon footprint. Most plastics processors produce a component and do not produce a complete product. They therefore cannot produce a complete product carbon footprint. Despite this, they do need to know how these are calculated so that they can take part in the information gathering that is necessary for a product carbon footprint. This chapter also gives broad details of product carbon footprinting but does not cover this in detail.

At present, calculating a site carbon footprint is optional in most parts of the world but this may not remain so for much longer. Initiatives such as ‘carbon trading’ and ‘carbon taxes’ are being discussed in most countries and these discussions will inevitably mean that site carbon footprinting will be necessary. Many Energy Management in Plastics Processing https://doi.org/10.1016/B978-0-08-102507-9.50009-X, Copyright © 2018 Elsevier Ltd. All rights reserved.

387

9.1

The basics of carbon footprinting

Site or product?

Emission types (scopes)

A carbon footprint can refer to either a specific site or to a complete product and these are very different. The boundaries for a site and product carbon footprint are shown below. A site carbon footprint does not include any embodied energy of the raw materials – this is calculated by the raw materials suppliers from their individual site carbon footprints. A product carbon footprint is the total of all the site carbon footprints for the complete supply chain (cradle to grave) and includes all the embodied energy of the raw materials.

Emissions are grouped by the level of control that a site or organization has over them. This gives a 3-part classification:

At this stage, we will concentrate on the production of a site carbon footprint. Carbon footprinting involves collecting data on all the carbon emissions either directly from a site or as a result of the site activities. These emissions are expressed in terms of the mass of CO2 emissions. In some cases the actual gas emitted is not CO2 but is another greenhouse gas (GHG) such as methane (CH4) or nitrous oxide (N2O). Emissions of these gases are given as CO2 equivalents (CO2e) to allow a total equivalent CO2e to be calculated. These are calculated using Global Warming Potential (GWP) factors from the Intergovernmental Panel on Climate Change (IPCC) 5th Assessment Report (AR5, 2014), e.g., the GWP for CH4 = 28 and the GWP for N2O = 265). There are a range of reporting methods, some are web-based, some are specific to a country or area, some are designed for industry and some are designed for domestic/consumer use. Most of these methods are based on the GHG Protocol (www.ghgprotocol.org) which gives a standard format for classifying and reporting emissions. Many of the rules of the GHG Protocol are similar to accounting rules. These are designed to ensure that emissions can be added up across the supply chain without double-counting and to ensure that emissions are correctly allocated to the appropriate corporate entity, i.e., how emissions are treated for joint ventures etc. At the site level, we can ignore this issue and calculate the emissions within a site’s control. 388

Scope 1: Direct emissions Direct emissions cover emissions that a site directly causes and controls. In this case, the CO2e is actually emitted either at the site or by an asset that the site controls.

Scope 2: Indirect emissions from imported utilities All sites import utilities, e.g., electricity, and Scope 2 covers emissions from purchased electricity or other utilities such as imported heat or steam. In this case, the CO2e is emitted at some distance from the site by the power station that has generated the electricity, heat or steam.

Scope 3: Indirect emissions Indirect emissions are emissions that a site causes to occur but where it does not control the asset. Common types of

One of our clients had paid a consulting company $42,000 to provide a carbon footprint – it took 3 consultants 3 weeks. We had the energy data (as part of the site survey) and carried out the other data gathering on the back of a place mat over a steak and a beer. Our numbers were different by 0.5%, i.e., well within the potential error of the calculation. It is not that difficult and the numbers are relatively easy to either estimate or calculate.

Plastic raw materials

Other raw materials

Other raw materials

Manufacture of plastic component

Manufacture and assembly

Manufacture

Site carbon footprint for plastics product

Distribution

Use

Disposal Product carbon footprint for plastics product

The boundaries for site and product carbon footprints The site carbon footprint for most plastics processing sites will only be part of the total product carbon footprint. The contributions from each of the product life cycle stages can be added up to give the product carbon footprint. Chapter 9 – Carbon footprinting

indirect emissions include emissions from transport in vehicles owned by other organisations or emissions from outsourced activities or the supply chain. For a very basic carbon footprint not all these emissions are calculated. In most cases, the focus is on the common emissions from Scope 1 and Scope 2 which can be easily and consistently measured. Some standards regard coverage of Scope 3 emissions as optional depending on the scale of the site and the availability of the data.

Emission sources

from vehicles which are used by the company or their employees on company business but are not owned by the site (e.g., personal cars or short-term hire cars) are included in Scope 3.

Getting the data

Carbon footprinting requires good data collection but is not difficult (despite what many highly paid consultants will tell you).

Preparing an initial carbon footprint will necessarily involve estimations and approximations because some of the data will not be easily available. After a site has prepared the initial carbon footprint the data collection should become part of the normal operations. It is much easier if the data are collected continuously. • Tip – Sites should record and refine

The table below gives a list of common emission sources listed by Scope. One of the major areas of confusion is whether to allocate an emission into Scope 1 or Scope 3. The key issue is whether the site has control of the asset or not and actual ownership is less important than control. As an example: Emissions from vehicles which are either owned by the site or for which the site has long-term hire contracts (e.g., company-owned or leased cars) are included in Scope 1. Emissions

carbon emissions to quantify the carbon footprint. This will inevitably become an issue for customers as they attempt to reduce their own carbon footprint.

Reporting the data Carbon footprints should be reported for a complete year in terms as ‘tonnes of CO2e’. The year chosen can be either the company reporting year or a calendar year, but consistency is important. The reporting period should be both declared in the footprint and consistent.

One of the best and simplest explanations of how to measure and report is the UK government publication ‘Guidance on how to measure and report your greenhouse gas emissions’.

Scope 1

Scope 2

Scope 3

Direct emissions (site has control of the asset)

Indirect emissions from imported utilities

Indirect emissions (site does not have control of the asset)

Gas (process or heating).

Emissions from the purchase of

electricity.

Oil (process or heating). Bottled liquid or gaseous fuels

Employee business travel –

personal car.

Emissions from the import of heat Employee business travel – train,

(e.g., LPG for fork lift trucks). Other fossil fuel. Owned or leased cars, buses,

trucks or other vehicles. Process emissions. Refrigerant emissions (e.g.,

replacement of losses due to leakage). Other direct emissions.

or steam.

bus and other means. Employee business travel –

plane. Employee business travel –

rental car. Employee business travel – taxi. Employee commuting. Water. Product transport – contract

transport. Waste disposal and/or recycling.

The scopes for carbon footprinting The scopes of the emissions are used to assess the total emissions from a site. The objective is to be consistent in collecting information and much of the published guidance is on how to report the available data so that they can be compared with other sites and avoid issues such as ‘double counting’ in the production of a product carbon footprint. These conventions can then be used to build up a product carbon footprint (see Section 9.6). Chapter 9 – Carbon footprinting

389

9.2

Site carbon footprinting – Scope 1

Direct emissions (controlled assets) Scope 1 covers the direct emissions at a site, i.e., the emissions that a site directly causes and controls. This can be divided into the various emission sources and these will be covered individually for a typical plastics processing site. A typical report format is shown at the bottom of the opposite page. Some sites will not have all the emissions discussed.

Purchased fuels The CO2e for fuels purchased for use on site can be calculated using the tables in Annex 1 of DBE&IS (see box on the right for details of DBE&IS). This is simply a matter of deciding on the relevant measure (tonnes, litres or kWh) and using the conversion factor to calculate the CO2e resulting from this factor. These values are relatively independent of the application and location. The results are a function of basic chemistry and assume full combustion of the fuel.

Gas (heating and process) Gas when purchased via a mains feed will be invoiced either by mass (tonnes), by volume (litres) or by energy (gross calorific value or net calorific value). The gas supply for the year should be available from the billing data and this can be easily converted into CO2e using DBE&IS. The only difficulty is when the supplier quotes ‘kWh’ (see upper sidebar). In most cases the kWh quoted will be the gross CV but this should be clarified with the supplier to ensure that the correct factor is used. • Tip – Check that you are using the

correct table in DBE&IS. There is a large difference between gross CV and net CV.

Fuel oil (heating and process) As with gas, fuel oil can be purchased in a variety of ways but in most cases this will be in litres. The amount of fuel oil can be converted to CO2e using DBE&IS.

Fork lift truck gas Where fork lift trucks (FLTs) are gaspowered the gas will generally be LPG and will be delivered by bottle. The use can be 390

calculated from the litres delivered in the year. If the data are not available then a reasonable use of a FLT will be ≈ 6,000 litres/year. Obviously, if electric FLTs are used then this can be ignored.

Other fossil fuel DBE&IS lists a wide range of fuel types and can be used to convert almost any fuel use into CO2e.

Owned cars Owned cars includes all company cars provided for use to employees. It does not matter if the car is leased or owned. The important issue is the control of the vehicle. If the site has control of the vehicle then it is counted here. DBE&IS has conversion factors for a wide range of vehicles. The input data are in terms of distance travelled (in miles or km). • Tip – The only time I haven’t been able

to find a relevant conversion factor was in Brazil where the vehicles used ethanol as fuel. • Tip – If data are available in terms of

the amount of fuel used then the ‘fuels’ tab will give more accurate results.

Gross calorific value (gross CV) is the calorific value under laboratory conditions and will be higher than the net calorific value (net CV) which is the useful calorific value that will be obtained in the real world. Suppliers will usually quote gross CV but this should be checked.

The absolute value of CO2e is generally reported in tonnes as tCO2e. This is the metric ton or metric tonne and is equal to 1,000 kg.

Conversion factors for emissions There are a variety of sources for data on emissions such as those published by the GHG Protocol and various organisations around the world. The most reliable, consistent and comprehensive set of data is that published by the UK government (‘Greenhouse gas reporting – Conversion factors’). This is produced by the Department for Business, Energy & Industrial Strategy and is updated yearly. At the time of writing, the latest edition is 31 July 2017. The conversion factors are supported by a Methodology Paper (‘2017 Government GHG Conversion Factors for Company Reporting: Methodology Paper for Emission Factors’) that gives background data on how the factors were calculated and how they should be used. All conversion factors used in this chapter are taken from the 2017 edition of this document. This document includes not only the CO2 emissions but also allowances for CH4 and N2O emissions. For convenience we will refer to the 2017 version of this document as ‘DBE&IS’. Readers are advised to check for updates and extensions to DBE&IS. Chapter 9 – Carbon footprinting

Owned trucks or vehicles

Method 1

Some sites will lease or own trucks, vans, buses or other vehicles and the data for these are available in DBE&IS for both passenger and goods vehicles.

The most accurate method is to record the amount and type of GHG used to service the equipment each year. This will also be the amount and type of refrigerant lost to the atmosphere and can be used with the factors in DBE&IS to give a CO2e value.

As with owned cars, there are a variety of options and it is simply a matter of choosing the correct activity measure and conversion factor. • Tip – If company trucks are used to

collect goods from suppliers or to deliver to customers then this is where the emissions are collected. If suppliers deliver goods or customers collect them then they are NOT included as part of the site carbon footprint.

Process emissions Few plastics processing operations have actual process emissions and this is not normally relevant. If, however, the site uses a foaming process and vents a gas to atmosphere then the GWP (if any) of the gas should be calculated and inserted in this area.

Method 2 The easiest initial method is to produce a ‘GHG List’ for the site. This is a list of the location, application, volume and type of each GHG. The total volume of each type of GHG present at the site can then be calculated. The loss of refrigerant can be calculated by assuming a loss factor for each item of equipment. DBE&IS gives full details of this method and typical loss factors. • Tip – If in doubt about leakage then

apply a leakage factor of 3% for most industrial chiller systems. The GHG leakage (in kg) for each refrigerant type can then be used with the factors in DBE&IS to give a CO2e value. • Tip – Whichever method is used the

Refrigerant emissions Most sites will have chillers, compressed air dryers and A/C units. These will all contain refrigerant gases and most of these are GHGs. These will all leak slight amounts of refrigerant gas to the atmosphere and these emissions should be calculated.

Emission type

losses should be calculated over a whole year.

Other direct emissions This is not normally relevant for most plastics processing sites.

Emission source

There are separate factors for GHG emissions for installation and disposal. These should be used when installing or disposing of equipment.

Emission Tonne CO2e

%*

2.85

0.08%

Billing data.

Fuel oil (heating and process)

0

0.00%

N/A.

Fork lift truck gas

0

0.00%

Electric FLTs.

Other fossil fuel

0

0.00%

N/A.

20.25

0.60%

Distance travelled.

Owned trucks or vehicles

0

0.00%

N/A.

Process emissions

0

0.00%

N/A.

Refrigerant emissions

3.84

0.11%

Refrigerant data.

Other direct emissions

0

0.00%

N/A.

26.94

0.79%

Gas (heating and process)

Scope 1: Direct emissions (controlled assets)

The GHG List can also serve as part of the control process to remove GHGs from the site (see Section 4.36).

Owned cars

Sub-Total

Notes

Typical reporting of Scope 1 emissions This is a typical format for reporting Scope 1 emissions (all conversion factors taken from DBE&IS). Data for fuel use are taken from the billing or delivery data. Data for cars and trucks are taken from the distance travelled DBE&IS tables. * This is the percentage of total emissions from all three scopes. Chapter 9 – Carbon footprinting

391

9.3

Site carbon footprinting – Scope 2

Indirect emissions (imported utilities)

Country

kg CO2/kWh

South Africa

0.8573

India

0.8291

Australia

0.8136

Poland

0.7739

Indonesia

0.7584

Saudi Arabia

0.7529

People's Rep. of China

0.7525

Malaysia

0.7218

Emissions from electricity use

Czech Republic

0.5919

The generation of electricity will inevitably result in CO2e emissions but the size of these emissions depends on the generation method. Nuclear, thermal or hydroelectric generation result in low CO2e emissions, whereas coal, gas and other fossil fuels result in high CO2e emissions. Each country will have a mix of generation for grid electricity that will therefore affect the total emissions. This is also true at the supplier level, i.e., a supplier can have a different emission factor to the country as a whole if their generation profile is significantly different to the country profile.

South Korea

0.5518

Japan

0.5294

Thailand

0.5249

United States

0.4985

Germany

0.4718

Turkey

0.4644

United Kingdom

0.4622

Egypt

0.4542

Russia

0.4498

Mexico

0.4484

Italy

0.3990

Netherlands

0.3990

Pakistan

0.3945

Spain

0.2891

Belgium

0.1894

Canada

0.1640

Generation, transmission and consumption emissions

Brazil

0.0693

Grid electricity is generated at the power station and this results in emissions, but the transmission and distribution of the electricity to the user also results in losses, i.e., transmission and distribution losses. The emission factor at the point of consumption is therefore higher than the

France

0.0586

Scope 2 covers indirect emissions from imported utilities and the most common of these is the purchase and use of electricity. Some sites also purchase steam or heat from external sources and this is also covered under Scope 2. The data needed are simply the total number of kWh used in the year and the relevant carbon intensity factor for the supply country. The number of kWh used in the year should be easily available from the electricity bills and the interval data (see Section 4.5).

For example, a country generating a large proportion of grid electricity from nuclear sources or renewable energy will have a lower CO2e emissions factor than a country generating a large proportion of grid electricity from coal or other carbonbased fuels. The factors for any specific country will change with time as the generation pattern changes. • Tip – Always use the latest data for

emissions factors to account for changing generation patterns.

392

Scope 2 carbon intensity by country The carbon intensity (kg CO2e/kWh) varies widely across the world depending on the generation method. These data includes emissions from all Scopes and is the 5-year rolling average. Source: DBE&IS 2015. Chapter 9 – Carbon footprinting

emission factor at the point of generation and Emission factor (consumed) = Emission factor (generated) + Emission factor (losses). • Tip – Generation emissions are recorded

under Scope 2 but loss emissions are recorded under Scope 3 (see Section 9.4).

Supplier data The most accurate value for the emission factor will be from the specific supplier because this will reflect their generation profile. Most suppliers should be able to supply this on request. • Tip – If requesting data from suppliers

then be sure to get the generation emission factor and check if it is CO2e data and not simply CO2 data. If it is only CO2 data then note this in any reporting. • Tip – The carbon intensity for any

supplier will change with time as their generation profile changes. The best value to use is either the most current year or an average for the last 5 years.

Country data If the supplier cannot supply a generation emission factor then it is possible to use a country emission factor but this will not be as accurate. Until 2015, country emission data for a wide range of countries were given in DBE&IS and the table on the left gives the 2015 consumption emission factors for selected countries (DBE&IS 2015) and shows the range of emission factors around the world. The countries with the highest emission factors, e.g., South Africa, India, Australia and Poland, mainly use coal for electricity generation. The countries with low emission factors, e.g., Brazil and France, use low-carbon electricity generation

methods such as hydro or nuclear. After 2015, DBE&IS stopped giving this information but this is now available for purchase from the International Energy Agency (IEA). The IEA data are for the electricity supplied to the grid and does not include emissions from losses. These are still provided by DBE&IS and should be included in Scope 3. • Tip – Always use the emission factor for

The imported utilities, i.e., electricity, will almost always be the largest part of the carbon footprint for plastics processors. It is essential to get the right data for this Scope.

electricity generation and not for consumption in Scope 2.

US regional data In the USA, the size and diversity of the electricity generation capacity means that the global single country value from the DCBE&IS is not really relevant for most of the country. For a more accurate approach it is possible to use the eGRID data produced by the US Environmental Protection Agency. The USA is divided into 26 sub-regions for which detailed emissions data are available. The latest version of the data was released in January 2017 and is for 2014. This site also has an excellent Frequently Asked Questions section and summary tables for quick reference. • Tip – The US eGRID data are sometimes

difficult to work with because the subregion boundaries do not align with physical state boundaries. Try to get supplier data before using eGRID.

Emissions from imported heat or steam Importing heat or steam from local generators is rare in plastics processing. If heat or steam is imported then DBE&IS provides UK data but if the site is located outside the UK then the emission factor should be calculated by the generator of the heat or steam.

Emission type

Emission source

Scope 2: Indirect emissions (imported power)

Electricity Sub-Total

Emission Tonne CO2e

%

Notes

2,484.57

73.11%

Supplier CO2e data.

2,484.57

73.11%

Typical reporting of Scope 2 emissions This is a typical format for reporting Scope 2 emissions. The data for actual fuel use are taken from the billing or interval data. The emissions factor is taken from supplier data. * This is the percentage of total emissions from all three scopes.

Chapter 9 – Carbon footprinting

393

9.4

Site carbon footprinting – Scope 3

Direct emissions (not controlled assets)

Employee business travel

Scope 3 covers the direct emissions that a site uses but does not control. As an example: An employee has to fly to visit a customer. The flight has direct emissions but the site does not control the asset (the aeroplane) and is not responsible for the complete emissions of the flight. The site therefore takes a share of these emissions based on the distance flown.

Private car

Data for Scope 3 emissions are sometimes difficult to obtain and the errors can be high. In many cases, Scope 3 emissions are not calculated and this is unfortunate because it is usually possible to estimate them quickly using available information. For most plastics processing sites, Scope 3 emissions will be < 10% of the total emissions. Even large estimation errors will not affect the total emissions greatly but including Scope 3 emissions provides a better estimate of the total site carbon footprint than totally ignoring them. Scope 3 can be divided into various emission sources and these will be covered individually for a typical plastics processing site. A typical report format is shown on the lower right on the opposite page. Some sites will not have all the emissions discussed.

Business travel has several elements: If employees use their private cars for company business then this is included here. This may be calculated from company payments for private car use with the emission factor for the car type taken from DBE&IS. If in doubt then use the ‘average car/unknown fuel’ factor. • Tip – A quick method is to estimate how

many people use their car for business and then to estimate the average distance travelled/year.

Scope 3 calculations will always have greater errors than other scopes due to the diverse nature of the components. This is no excuse for not estimating the magnitude of the Scope 3 emissions. There are quick methods for estimating many of the Scope 3 effects.

Rail/bus Most sites make little use of rail or bus but these can be calculated from DBE&IS.

Flights Emission factors for air travel vary for short- and long-haul travel and also for the various travel classes, i.e., first class has higher emissions than economy class. DBE&IS gives the relevant emission factors for both short and long haul and for a range of classes. The total emissions can be calculated from travel records and the distances travelled by each flight. The numbers needed here are the number of passenger km travelled/

Transport and distribution losses (T&D) As noted in Section 9.3, transport and distribution losses for electricity are recorded in Scope 3. DBE&IS 2017 has continued to give T&D values for many countries and these can be used with the electricity consumption (kWh) to calculated emissions from T&D losses.

Well-to-tank losses (WTT) The production of electricity involves wellto-tank losses. These are the emissions from the extraction, refining and transportation of fuels before they are used in electricity generation. WTT loses are given in DBE&IS 2017 for many countries and these can be used with the electricity consumption (kWh) to calculated emissions from WTT losses. • Tip – DBE&IS gives separate WTT

factors for generation and T&D losses. 394

Indirect labour (15 miles)

Site Direct labour (10 miles)

Estimating commuting mileage The quickest way to estimate commuting mileage is to identify the average distance travelled by direct labour and by indirect labour. The indirect labour will travel further because they are better paid. Chapter 9 – Carbon footprinting

year in the relevant categories.

then other tables in DBE&IS can be used to estimate the resulting emissions.

• Tip – The distance travelled for flights

can be found on the Internet. • Tip – A quick method is to estimate how

many people fly for business and then to estimate their typical journey.

Rental cars/taxis This can be accurately found from travel records (employee expense claims) and using DBE&IS. If in doubt then use the ‘average car/unknown fuel’ factor. • Tip – Rental cars and taxis are mainly

used for travel at the start and end of flights. • Tip – A quick method is to use the flight

Product transport In most cases, product transport is by contractors who control the vehicle. DBE&IS has tables for all types of transport from trucks to air freight. When calculating the product transport emissions by road there is a choice of: • Calculating emissions as if the complete vehicle was used, i.e., all the emissions are taken by the site. In this case the data needed are the number of loads and the average distance to the customer. • Calculating the emissions as if only part

of the vehicle was use, i.e., the site only takes a part of the emissions. In this case the data needed are the number of tonne.km. This is the distance travelled (km) by each tonne of product.

numbers (see above) and to allocate some taxi and rental car use to each flight.

Employee commuting This can be difficult to calculate accurately. Some sites use staff surveys but the quickest method is to assume that each employee travels an average distance to the site. The average distance will be greater for indirect labour than for direct labour. This average distance can be used with the number of days worked/year and the ‘average car/unknown fuel’ factor. • Tip – When car sharing is used then the

values should be decreased.

Sites should assess their transport method and use the appropriate tables. • Tip – A quick method is to estimate the

average distance to the customer for each transport method and the amount of product transported by this method. This gives a rapid estimate of the emissions from product transport. • Tip – If the customer collects the

• Tip – If commuting is by train or bus

Emission type

products then the carbon emissions are allocated to them and not to the site.

Emission source

These can be used to calculate the emissions due to water supply and treatment.

‘Travelmath’ is good for finding driving and flight distances.

DBE&IS also gives emission factors for material use and waste. These can be used to calculate the emissions due to basic material use and to waste disposal and recycling.

Emission Tonne CO2e

%

T&D losses

212.44

6.25

DBE&IS data.

WTT losses (generation/T&D)

376.36

11.07%

DBE&IS data.

0

0.00%

Estimated.

Employee travel – air transport

4.34

0.13%

Estimated.

Employee travel – taxi

1.73

0.05%

Estimated.

Employee travel – rental car

0.37

0.01%

Estimated.

Employee travel – commuting

10.78

0.32%

Estimated.

Product transport

274.20

8.07%

Estimated.

Water use

0.38

0.01%

Estimated.

Waste disposal

6.41

0.19%

Estimated.

855.78

25.41%

Employee travel – own car

Scope 3: Direct emissions (not controlled assets)

DBE&IS also gives emission factors for water supply and treatment.

Sub-Total

Notes

Typical reporting of Scope 3 emissions This is a typical format for reporting Scope 3 emissions. The data can be based on estimates if no accurate data are available. The relevant emission factors are taken from DCF. * This is the percentage of total emissions from all three scopes.

Chapter 9 – Carbon footprinting

395

9.5

Site carbon footprinting – putting the scopes together

The site carbon footprint Calculating the effects of the various scopes (see Sections 9.2 to 9.4) allows an estimate of the various elements of the total site carbon footprint. These are put together into the complete site carbon footprint on the opposite page and for this typical site the total CO2e emissions are estimated at 3,749.54 tonnes/year. There is naturally an error associated with this value and this is normally in the region of ± 2%. The methods used to gather the data will affect this error value and this may increase if estimates are used extensively. It is also useful for most sites to look at the relative effects of the various scopes and this is shown in the pie chart on the lower right. This distribution of the carbon emissions is typical for a plastics processing site where the emission factor for electricity is in the region of 0.3–0.6 kg CO2e/kWh, i.e., most of Europe and the USA. The reason for this is the high use of electricity in plastics processing as a source of energy.

Assessing the carbon footprint The absolute value of the site carbon footprint in tonnes/year is useful as a reporting measure but fluctuating production volume will obviously affect this value because of the relationship between production volume and electricity use. It is therefore common to report the carbon footprint in terms of a relative measure such as ‘tonne of CO2e/tonne of product’ or ‘tonne of CO2e/product’. These relative measures can provide a measure of progress towards carbon reduction targets but they will also suffer from the same problems as using kWh/kg as a metric (see Section 2.11). For any site there will be a ‘base carbon load’ from heating, lighting and other fixed loads and a ‘process carbon load’ from productionrelated loads. This is analogous to the base and process loads discussed in Chapter 2. Despite this, if the assessment is taken over a reporting period of at least 12 months then the effect becomes small. Comparing carbon footprints between countries is possible but the large variations in emission factors between 396

countries can make this comparison more dependent on the country emission factor than on how the site operates.

Reporting Calculating a site carbon footprint is not the end of the story. The carbon footprint provides a convenient metric for the following actions: • Reporting progress in carbon reduction to staff, customers, stakeholders and external bodies such as government. This can be via the annual report or via notice boards/staff newsletters.

For sources that are less than 1% of the total it is sensible to use estimates rather than spend resources calculating the data for accurate calculation. The aim is to have good data for ≈ 95% of the emissions.

• Setting targets for carbon reduction (via

an energy management programme as electricity is key to the carbon footprint). • Providing customers with data for incorporation into product carbon footprints (see Section 9.6). This is becoming more important as major customers demand these data for their own products. • Tip – One of the most respected ways of

externally reporting carbon footprints and progress in carbon reduction is via the Carbon Disclosure Project (www.cdp.net). This is an open access database of freely disclosed carbon data from many of the world’s major companies. Scope 1: Direct emissions (controlled assets) 0.79%

Scope 3: Other indirect emissions (not controlled assets) 26.10%

Scope 2: Indirect emissions (imported power) 73.11%

The carbon footprint by scope As with many plastics processing sites, Scope 2 is the largest contributor to the carbon footprint. This is simply a reflection of the heavy dependence of the industry on electricity as a source of energy. Chapter 9 – Carbon footprinting

Period: 2016 Emission Emission type

Emission source Tonne CO2e

%

2.85

0.08%

Billing data.

Fuel oil (heating and process)

0

0.00%

N/A.

Fork lift truck gas

0

0.00%

Electric FLTs.

Other fossil fuel

0

0.00%

N/A.

20.25

0.60%

Distance travelled.

Owned trucks or vehicles

0

0.00%

N/A.

Process emissions

0

0.00%

N/A.

Refrigerant emissions

3.84

0.11%

Refrigerant data.

Other direct emissions

0

0.00%

N/A.

26.94

0.79%

2,484.57

73.11%

2,484.57

73.11%

T&D losses

212.44

6.25

DBE&IS data.

WTT losses (generation/T&D)

376.36

11.07%

DBE&IS data.

0

0.00%

Estimated.

Employee travel – air transport

4.34

0.13%

Estimated.

Employee travel – taxi

1.73

0.05%

Estimated.

Employee travel – rental car

0.37

0.01%

Estimated.

Employee travel – commuting

10.78

0.32%

Estimated.

Product transport

274.20

8.07%

Estimated.

Water use

0.38

0.01%

Estimated.

Waste disposal

6.41

0.19%

Estimated.

855.78

25.41%

3,749.54

100%

Gas (heating and process)

Scope 1: Direct emissions (controlled assets)

Owned cars

Sub-Total

Scope 2: Indirect emissions (imported power)

Electricity Sub-Total

Employee travel – own car

Scope 3: Indirect emissions (not controlled assets)

Sub-Total Total

Notes

Supplier CO2e data.

The complete site carbon footprint (all scopes) This is a typical format for reporting a complete site carbon footprint. It is important to specify the period of the calculation. This is a typical calculation only.

Chapter 9 – Carbon footprinting

397

9.6

Product carbon footprinting

The complete life cycle A product carbon footprint (PCF) is designed to allow companies and consumers to understand the environmental impact of a product over the complete life cycle from the raw materials to disposal and/or recycling. The theory is that this will allow companies to measure, monitor and manage energy use, set targets for emission reductions, reduce costs and communicate with stakeholders. The PCF concept has generated many schemes and systems and there are currently over 20 schemes around the world that are used to measure PCFs. Whilst the methods are all broadly similar they can vary in the details. The two most robust current methods for developing a PCF are: • ‘PAS 2050: 2011’ – developed in the UK by BSI and the UK Government. • ‘Product Life Cycle Accounting and

Reporting Standard’ (2011) – developed by the GHG Protocol, WBCSD and WRI. The methodology for both of these is very similar and they are both freely available (see sidebar on the lower right). They were essentially developed together and are broadly compatible, although they vary in some details of the requirements, primarily in the areas of recording and public reporting. A similar and compatible approach was also used to develop ISO/TS 14067:2013 ‘Greenhouse gases – Carbon footprint of products – Requirements and guidelines for quantification and communication’.

Steps to calculating a PCF Whichever scheme is chosen, the steps to calculating a PCF are broadly similar. These are:

Step 1 – Build a process map The first step in defining the PCF is to create a process map of the product life cycle. A basic example process map is shown on the right and when fully completed this gives details of all the materials, activities and processes in the complete product lifecycle. These may be very different for nominally similar products. 398

Step 2 – Assess boundaries and determine priorities (materiality) The process map is used to assess the boundaries (the limits of the life cycle that are being considered) and to calculate an initial overview PCF to locate the ‘hot spots’ of high emissions. At this stage the ‘materiality’ is also considered – this is to minimise the effort of data collection. If a single source contributes < 1% of the total footprint then it can be excluded provided that the total of all the exclusions is not > 5% of the total PCF. This allows an initial high-level PCF calculation to establish high emission areas where data collection accuracy is important.

Step 3 – Collect data Two type of data are needed for a PCF: • Activity data – these are the measurable materials and energy used in each of the life cycle stages. Ideally these would be data derived from meters or invoices. • Emission factors – these are the GHG emissions associated with each unit of the activity data. These can come from databases such as DCF or other accredited databases.

There is not complete agreement on the benefits, efficiency or even accuracy of product carbon footprinting. There are considerable criticisms of the methodology and application of the results.

Most PCFs are suitable for comparing the impact of changes to materials, processes, etc. over time but do not provide the level of detail or accuracy necessary for product comparison.

Step 4 – Calculate the footprint The activity data are multiplied by the emission factors (as for the site carbon footprint) to calculate the actual emissions for each stage of the life cycle.

Step 5 – Check uncertainty Uncertainty is critical in producing a robust PCF, i.e., if the uncertainty is high then the PCF is not robust. The GHG Product Standard specifically requires a statement of the uncertainty in the report but PAS 2050 notes this only as guidance to use data that will reduce uncertainty.

Step 6 – Verify the footprint The PCF should be verified and this can be by simple self-certification, by a third party or by an accredited verification company. The choice depends on costs and how the PCF is going to be used • Tip – For most plastics processors, a

PCF will be unnecessary but processors should be aware that their site carbon footprint data may be requested by customers as part of their PCF.

The best (and easiest to understand) documents on product carbon footprinting are: • PAS 2050:2011 ‘Specification for the assessment of the life cycle greenhouse gas emissions of goods and services’. Available free from BSI: shop.bsigroup.co m/en/forms/PASs/ PAS-2050. • ‘Product Life Cycle Accounting and Reporting Standard’. Available free from GHG Protocol: www.ghgprotocol. org.

Chapter 9 – Carbon footprinting

Chapter 9 – Carbon footprinting

Process map for a plastic vacuum flask Raw materials

Glass raw materials

Manufacture

Distribution

Glass furnace

Warehouse Internally recycled

Forming

Use

Disposal

Consumer use

Transport

Transport

Scrap

Recycled

Landfill Ceramic pads

Silver solution

Assembly

Glass manufacture

Distribution centre

Silvering Transport Sealing

Packaging

Packing

Bulk packaging

Transport

Plastic and assembly EPS

Stopper assembly

Retailer

Key Returns

Stopper

Transport packaging

Individual site boundary Assembly

PP

Injection moulding

Transport Distribution centre

Outer

Packing

Site function

Landfill

Internally recycled

Transport

Stopper assembly

Operation

Scrap Packaging

Product and bulk packaging

Transport

Recycled

The basic process map for the life cycle of a plastic vacuum flask 399

The process map is the start of creating a PCF. It defines the basic processes and enables the emissions ‘hot spots’ to be identified.

Movement

9.7

Country plastics processing carbon footprints

The global level Section 9.3 gave the relative carbon intensity for electricity generation in a variety of countries and Section 9.4 discussed the effect of transport and distribution (T&D) losses and well-to-tank (WTT) losses. Under the standard carbon footprinting conventions, these carbon emissions are reported separately in Scopes 2 and 3 but they can be combined to give a country total carbon emission for electricity consumed that will include all the emissions. Tangram Technology has developed a simple model which: • Takes the total processed plastics production for a country.1 • Divides this into the various types of

plastics based on general world-wide trends for plastics production. • Divides each type of plastic into the various production methods used to process the material based on the general world-wide trends for plastics processing. • Totals each type of plastic used for each

process to give a total volume of processed plastic by process. • Assigns an average site process energy to each specific process (kWh/kg). • Calculates the total process energy (kWh) for each specific process. • Calculates the total country energy use for all plastics processing methods (kWh). • Uses the total country energy use for plastics processing and the country total carbon emissions as a result of electricity use to estimate the total country CO2 emissions as a result of plastics processing. • Uses an average electricity cost of £0.10/ kWh to estimate the total energy cost (in £) for the country.

footprint, i.e., they are only for the plastics processing operation.

Error estimation This process is based on a series of estimations and inevitably contains errors. We have compared the model results with other similar estimates and the results are within ± 7% in all cases. This is regarded as an acceptable error given the assumptions necessary to make the estimates, i.e., not every country will have the same proportion of plastics processed and not all processing will use energy with the same carbon intensity as the general country carbon intensity.

Plastics processing is an energyintensive operation wherever it is carried out.

Therefore these estimates are provided for guidance only.

Country plastics processing carbon footprints The top three countries, in terms of processed volume, electricity used, carbon emissions resulting from plastic processing and energy cost are China, USA and India. For the 27 countries considered, the total electricity used is estimated to be ≈ 454,188 GWh, the total cost is estimated to be ≈ £45.4 billion and the total carbon emissions are estimated to be ≈ 342 million tonnes. The table only lists the major plastics processing countries but this is estimated to capture ≈ 95% of the total world-wide volume of plastics processed.

The results of this process for 27 countries are shown in the table on the right. • Tip – These calculations do not include

the embodied energy of the plastics processed, i.e., the energy used to produce the actual plastic. • Tip – These calculations do not include

any consideration of the product carbon 400

• 1. Processed volume values from ‘Plastics Resin Production and Consumption in 63 Countries Worldwide’, 2016, Euromap (www.euromap.org).

Chapter 9 – Carbon footprinting

T&D + 2015 Energy Generation Total Electricity WTT Processed CO2e cost (kg CO2e/ (kg CO2e/ used (kg CO2e/ volume1 (Mtonnes) kWh) kWh) (Million £) (GWh) kWh) (tonnes) Belgium

0.1894

0.0402

0.2296

1,938,000

4,204

0.97

420

Brazil

0.0693

0.0266

0.0959

6,314,000

13,696

1.31

1,370

Canada

0.1640

0.0421

0.2061

2,846,000

6,173

1.27

617

Czech Rep.

0.5919

0.1414

0.7334

1,201,000

2,605

1.91

261

Egypt

0.4542

0.1382

0.5924

1,386,000

3,006

1.78

301

France

0.0586

0.0149

0.0735

4,180,000

9,067

0.67

907

Germany

0.4718

0.0979

0.5698

7,591,000

16,466

9.38

1,647

India

0.8291

0.3394

1.1685

12,903,000

27,988

32.71

2,799

Indonesia

0.7584

0.2056

0.9640

4,377,000

9,494

9.15

949

Italy

0.3990

0.0939

0.4929

5,633,000

3,137

1.55

314

Japan

0.5294

0.1114

0.6408

8,348,000

18,108

11.60

1,811

Malaysia

0.7218

0.1686

0.8904

2,327,000

5,048

4.49

505

Mexico

0.4484

0.1681

0.6164

5,538,000

12,013

7.40

1,201

Netherlands

0.3990

0.0807

0.4797

1,446,000

3,137

1.50

314

Pakistan

0.3945

0.1577

0.5521

1,207,000

2,618

1.45

262

China

0.7525

0.1765

0.9290

79,595,000

172,652

160.39

17,265

Poland

0.7739

0.1982

0.9721

2,712,000

5,883

5.72

588

Russia

0.4498

0.1439

0.5937

5,488,000

11,904

7.07

1,190

Saudi Arabia

0.7529

0.2053

0.9583

2,942,000

6,382

6.12

638

South Africa

0.8573

0.2439

1.1012

1,360,000

2,950

3.25

295

South Korea

0.5518

0.1077

0.6595

6,719,000

14,574

9.61

1,457

Spain

0.2891

0.0801

0.3691

2,877,000

6,241

2.30

624

Thailand

0.5249

0.1163

0.6412

4,150,000

9,002

5.77

900

Turkey

0.4644

0.1704

0.6348

5,950,000

12,906

8.19

1,291

UK

0.4622

0.1127

0.5749

3,136,000

6,802

3.91

680

USA

0.4985

0.1181

0.6165

30,162,000

65,425

40.34

6,543

454,188

342.51

45,419

Total

Country carbon footprints of major plastics processing countries The relative total electricity carbon intensity for a country can be combined with the production volume for the country and the various processing methods to give a total country carbon footprint for the plastics processing industry in that country. Note: This is for the processing only and does not include any embodied carbon in the basic polymer production. Chapter 9 – Carbon footprinting

401

9.8

Carbon footprinting – where are you now?

Assessing the impact Carbon footprinting assesses the impact that a site or organisation has on the atmosphere and is a performance metric that is growing in importance. External organisations are increasingly asking suppliers for access to carbon footprint calculations and every site should be assessing this impact. Good energy management for plastics processing companies will not only reduce the amount of energy used and the cost of this but will also reduce the carbon footprint. Companies may embark on energy management primarily for the cost benefits but calculating and monitoring

the carbon footprint will also reveal the benefits to society of good energy management. As with the score charts shown earlier, this is a self-assessment exercise to allow a site to benchmark their current status in terms of carbon footprinting.

Completing the chart

Most of the data needed for carbon footprinting will be generated automatically as part of energy management. There is very little extra work involved.

This chart is completed and assessed as for those presented previously.

Carbon footprinting Scope 1 data 4 3 2 External declaration

Scope 2 data

1 0

Complete site carbon footprint

Scope 3 data

Use the scoring chart to assess where you are in carbon footprinting The numbers from the scoring chart can be transferred to the radar chart for a quick visual assessment of where you are in terms of carbon footprinting. 402

Calculate your carbon footprint now so that it is ready for when your customers ask for it. Being pro-active is far better than being reactive.

Chapter 9 – Carbon footprinting

Carbon footprinting Level

4

Scope 1 data

Scope 2 data

Scope 3 data

Complete site carbon footprint

External declaration

All relevant Scope 1 data collected on a monthly basis using existing accounting systems for greater accuracy.

Scope 2 emissions from electricity calculated using supplier’s current specific carbon intensity for generation.

All relevant Scope 3 data collected on a regular basis using existing accounting systems for greater accuracy.

All relevant data for Full external declaration of Scopes 1 to 3 combined on a monthly organisation carbon basis using existing footprint for Scopes 1 accounting systems for to 3. greater accuracy.

All relevant Scope 1 data collected on an annual basis using existing accounting systems.

Scope 2 emissions from electricity calculated using area or region carbon intensity for generation.

All relevant Scope 3 data collected on an annual basis using existing accounting systems.

All relevant data for Scopes 1 to 3 combined on an annual basis using existing accounting systems.

All relevant Scope 1 data estimated on an annual basis.

Scope 2 emissions Full external All relevant Scope 3 All relevant data for from electricity data estimated on an Scopes 1 to 3 declaration of combined on an annual organisation carbon calculated using annual basis. general country carbon footprint for Scopes 1 & basis using good estimates for a number intensity for generation. 2. of factors.

Full external declaration of site carbon footprint for Scopes 1 to 3.

3

2

Some relevant Scope 1 data not calculated at all.

Scope 2 emissions from electricity calculated using unvalidated carbon intensity factor for generation.

No calculation of Scope 1 data.

No calculation of Scope 2 data.

No calculation of Scope 3 data.

No complete site carbon footprint prepared.

No external declaration of organisation or site carbon footprint.

X

X

X

X

X

1

Some relevant Scope 3 Scope 1 & 2 data data not calculated at combined for partial all. carbon footprint but no Scope 3 data estimated or included.

Full external declaration of site carbon footprint for Scopes 1 & 2.

0

Score

Chapter 9 – Carbon footprinting

403

Key tips • Sites should record and refine carbon

emissions to quantify their carbon footprint. This will inevitably become an issue for customers as they attempt to reduce their own carbon footprint. • Check that you are using the correct tables in any database. This is particularly true for gas use – there is a large difference between gross CV and net CV. • If in doubt about leakage of GHGs from chillers then apply a leakage factor of 3% of the total volume of GHG in the chiller and calculate the losses over the whole year. • Always use the latest data for emissions

factors to account for changing generation patterns. • When calculating emissions as a result of electricity use then always use the emission factor for the generation and then calculate the other losses separately. • If requesting data from suppliers then be sure to get the generation emission factor. • If requesting data from suppliers then check that they are total CO2e data and not simply CO2 data. They are very different. • The carbon intensity for any supplier will change with time as their generation profile changes. The best value to use is either the most current year or an average for the last 5 years. • For US electricity emission calculations the eGRID data are sometimes difficult to work with because the sub-region boundaries do not align with physical state boundaries. Try to get supplier data before using eGRID.

journey. • For rental car and taxi use, a quick method is to assume that rental cars and taxis are used mainly for travel at the start and end of flights. Use the flight numbers and allocate some taxi and rental car use to each flight. • For commuting when car sharing takes place then the values should be decreased appropriately.

Carbon footprinting is going to become more important in the future.

• Product transport emissions can be

This is about market pressures – you can either be part of it or out of the market.

quickly estimated from the average distance to the customer for each transport method and the amount of product transported by this method. • If the customer collects the products then the carbon emissions are allocated to the customer and not to the site. • One of the most respected ways of externally reporting carbon footprints and progress in carbon reduction is via the Carbon Disclosure Project. This is an open access database of freely disclosed carbon data from many of the world’s major companies. • For most plastics processors, a product carbon footprint (PCF) will be unnecessary but processors should be aware that their site carbon footprint data may be requested by customers as part of their PCF.

It doesn’t matter if you believe in ‘anthropogenic global warming’ (manmade climate change) or not.

• When calculating emissions for private

car use, a quick method is to estimate how many people use their car for business and then to estimate the average distance travelled/year. • For flight distance the distance travelled

can easily be found on the Internet but be sure to get the flight distance and not the road distance. They are different. • For flight emissions, a quick method is to

estimate how many people fly for business and then estimate their typical 404

Chapter 9 – Carbon footprinting

Appendices

Appendices

405

Appendix 1

Submitting site data

Take part in the surveys and contribute to the industry The lack of comparative industry data makes it very difficult to effectively benchmark sites. If you have used the site benchmarking data in this book and would like to contribute your data then we would be pleased to update the industry data. All information will be treated in strictest confidence and you will receive updates of

406

the performance curves as these are revised. Copy the forms on these pages, complete the data for each site and then email them to us ([email protected]). Please include an email address so that we can email updated performance curves to you.

Appendix 1 – Site energy survey form

Appendix 1 – Site energy survey form

407

Appendix 2

Submitting machine data

Take part in the surveys and contribute to the industry

the performance curves as these are revised.

The lack of comparative industry data makes it very difficult to effectively benchmark machines. If you have used the machine benchmarking data in this book and would like to contribute your data then we would be pleased to update the industry data.

Copy the forms on these pages, complete the data for each machine and then email them to us ([email protected]). Please include an email address so that we can email updated performance curves to you.

All information will be treated in strictest confidence and you will receive updates of

408

Appendix 2 – Machine energy survey form

Appendix 2 – Machine energy survey form

409

Postscript

As with any book, there is an element of ‘a labour of love’ in the creation of this workbook. Some of the information in the book is obtainable from other sources but it is invariably general and not specific to plastics processing. This makes it difficult for managers in the plastics industry to access the information and to assess how relevant it is to their operations. My experience and efforts in energy management in plastics processing are driven by a desire to improve competitiveness in the industry but also a desire to make a real difference in terms of energy consumption in both the developed and the developing world. Whatever happens with ‘climate change’, the security of supply of fossil fuels will continue to be variable and the generation and supply of energy based on these fuels will become more expensive in the future. In a very real sense, ‘we are not building a brick wall – we are building a cathedral’. This is a workbook and not a sacred text, it is designed for real use in real plastics processing companies. Please use and abuse it as such. All of the concepts and projects discussed in the book will work in practice but it can never be comprehensive in scope or coverage. If you have some good projects that work really well then let me know and I can include them in the next edition. Equally, if you have projects that do not work out then let me know and I can include them in the next edition! When the first edition of this book was planned, over 10 years ago, it was going to be a ‘small’ introduction to energy but rapidly grew into a whole book. In the 10 410

years since then the field has grown considerably and this edition is even larger to reflect this. As always, I dread the thought of producing the next edition. The variety of the plastics processing industry means that this can never be a definitive work – space and time do not permit this. Much of the information is informed by my own experiences in the field and if I have no practical experience with a specific process then the data are necessarily reduced. If there are significant omissions then please let me know and I will attempt to update the text for future editions. I have acknowledged as many of the sources as possible in the text but it is impossible to acknowledge all those people who contributed practical assistance and ideas (good and bad) during my time in the plastics industry. Many of these people are the unrecognised heroes of energy management; they are the facilities and maintenance managers around the world who daily strive to reduce energy use at their sites. I would like to thank all these people for their continued tolerance and enthusiasm in delivering sustainable change. They are the people who make the difference.

A final thought from H. L. Mencken: ‘For every complex problem, there is a solution that is simple, neat, and wrong.’ Postscript

Abbreviations and acronyms AC – Alternating Current A/C – Air Conditioning AHU – Air Handling Unit AMR – Automatic Meter Reading aM&T – Automatic Monitoring and Targeting AQL – Acceptable Quality Level BEMS – Building Energy Management System BMC – Bulk Moulding Compound BOPP – Biaxially Oriented Polypropylene BSI – British Standards Institution CDD – Cooling Degree Days CEMEP – European Committee of Manufacturers of Electrical Machines and Power Electronics CFL – Compact Fluorescent Lamps CHP – Combined Heat and Power CO2e – Equivalent CO2 emission CUSUM – Cumulative Sum of Deviations CV – Calorific Value DC – Direct Current DBE&IS – Conversion factor document published by DBE&IS DECC – UK Department of Energy and Climate Change DEFRA – UK Department for Environment, Food and Rural Affairs EBM – Extrusion Blow Moulding EBQ – Economic Batch Quantity EC – Electronically Commutated ECM – Energy Conservation Measure EHS – Environment, Health and Safety EISA – Energy Independence and Security Act (USA) EMIS – Energy Management Information System EOAT – End Of Arm Tooling EU MEPS – European Minimum Energy Performance Standard FLT – Fork Lift Truck FRP – Fibre Reinforced Plastics GHG – Greenhouse Gas GRG – General Rubber Goods GWP – Global Warming Potential HDD – Heating Degree Days HEM – High-Efficiency Motor HVAC – Heating, Ventilation and Air Conditioning IBM – Injection Blow Moulding IEC – International Electrotechnical Commission IMM – Injection Moulding Machine Inverter – Also known as VSD or VFD IPCC – Intergovernmental Panel on Climate Change Abbreviations and acronyms

IR – Infrared ISBM – Injection Stretch Blow Moulding ISO – International Standards Organisation JIT – Just-In-Time LF – Load Factor LPG – Liquid Petroleum Gas LRVP – Liquid Ring Vacuum Pump M&T – Monitoring and Targeting M&V – Measurement and Verification MD – Maximum Demand MIS – Management Information System MMP – Motor Management Policy MTC – Mould Temperature Controllers NEMA – National Electrical Manufacturers Association (USA) OEE – Overall Equipment Effectiveness OTED – One Touch Exchange of Dies PCF – Product Carbon Footprint PCL – Performance Characteristic Line PIR – Passive Infrared PF – Power Factor PFC – Power Factor Correction PM – Predictive Maintenance PPM – Planned Preventative Maintenance RCM – Reliability-Centred Maintenance RH – Relative Humidity SAE – Society of Automotive Engineers SEC – Specific Energy Consumption SER – Site Energy Review SMC – Sheet Moulding Compound SMED – Single Minute Exchange of Dies SPC – Statistical Process Control T&D – Transport and Distribution losses TPM – Total Productive Maintenance TQM – Total Quality Management UPS - Uninterruptible Power Supply VFD – Variable-Frequency Drive: also known as VSD VI – Viscosity Index VSD – Variable-Speed Drive: also known as VFD WBCSD – World Business Council for Sustainable Development WRI – World Resources Institute

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