Passive House Design: Planning and Design of Energy-Efficient Buildings [1 ed.] 9783955532215, 9783955532208

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Passive House Design

Edition ∂ Green Books

Passive House Design Planning and design of energy-efficient buildings

Roberto Gonzalo Rainer Vallentin

Imprint

Authors: Roberto Gonzalo, Dr.-Ing. Architekt Rainer Vallentin, Dr.-Ing. Architekt Co-author (building services): Wolfgang Nowak, Prof. Dr.-Ing. Project management and editorial work: Jakob Schoof, Dipl.-Ing. Editorial work and layout: Jana Rackwitz, Dipl.-Ing. Jakob Schoof, Dipl.-Ing. Illustrations: Ralph Donhauser, Dipl.-Ing. (FH) Cover design: Cornelia Hellstern, Dipl.-Ing. (FH) Translation: Sharon Heidenreich, Dipl.-Ing. (FH) English proofreading: J. Roderick O’Donovan, B. Arch.

This work is subject to copyright. All rights are reserved, whether the whole or part of the material is concerned, specifically the rights of translation, reprinting, recitation, re-use of illustrations and tables, broadcasting, reproduction on microfilms or in other ways, and storage in data banks. Duplication of this publication is only permitted under the provisions of the German Copyright Law in its current version. A copyright fee must always be paid. Violations are liable for prosecution under the German Copyright Law.

DTP & layout: Roswitha Siegler Reproduction: ludwig:media, Zell am See Print: GCC Grafisches Centrum Cuno, Calbe 1st edition 2014 Institut für internationale Architektur-Dokumentation GmbH & Co. KG Hackerbrücke 6, D-80335 München Telephone: +49/89/38 16 20-0 Telefax: +49/89/39 86 70 www.detail.de © 2014 Institut für internationale Architektur-Dokumentation GmbH & Co. KG, Munich A specialist book from Redaktion DETAIL ISBN: 978-3-95553-220-8

The FSC-certified paper used for this book is manufactured from fibres proved to originate from environmentally and socially compatible sources.

Contents

Urban design Impact of energy-related aspects on the urban design Design principles of compact and solar building Model urban design guidelines Reference projects Completed Passive House developments

68

76

18

Non-residential building Passive House principles in non-residential buildings Energy balance Features of different building typologies

Passive House planning Main principles and comparison with other standards Passive house criteria Passive House Planning Package (PHPP) Certified building components Certification of Passive House buildings Certified Passive House designers EnerPHit standard Minergie-P standard 2000-Watt Society – SIA D 216 Net-zero energy standard

22

Reference buildings – non-residential

84

22 22 24 28 28 28 28 30 31 31

Passive House refurbishment Conditions for an energy efficiency refurbishment Refurbishment standards and strategies Energy balance and individual measures Outlook

100

Reference buildings – Passive House refurbishments

106

Design and planning principles General design issues Passive House design principles Principle of thermal envelope and form factor Principle of homogeneity Solar building design in Passive Houses The importance of window placement Basic principles of Passive House building services Design-based energy balance Impact of regional and urban climate Coordination of individual aspects Residential projects

32 32 34 34 36 38 40 42 44 46 46 46

Building envelope components Significance of the building envelope Opaque envelope constructions Transparent components Other construction elements and special components Building methods and construction systems

126 126 126 129

Building services Ventilation Space heating Heat supply concepts Energy-efficient cooling systems

134 134 139 140 143

Reference buildings – residential

48

Outlook

144

Appendix

146

Introduction

6

Principles Concept approach: energy efficiency Definition of the Passive House standard Passive House components How does a Passive House work at different times of the year? Thermal comfort and wellbeing Scope and field of application Economy Energy-related sustainability and climate protection

8 8 8 8 10 12 14 16

68 69 72 73 74

76 77 80

100 102 103 105

131 132

Introduction

Designing energy efficiency This book is all about the design of Passive House buildings. Unlike many other books published, the design concept is considered not only from the viewpoint of construction technology, energy efficiency or building physics, but deliberately takes a holistic approach from the viewpoint of an architect and urban planner. On the other hand, the book is not intended to be a complete and academic design tool for energy-efficient building. Instead it is designed to illustrate how theoretical and practical experience with Passive House buildings can help contribute to the clarification of as yet unresolved issues. In this context, it is particularly interesting to determine the extent as to which design principles of solar and energy-efficient building are expedient or, as individual features, even mandatory to meet Passive House standard. Naturally, these considerations question the principles and even provoke the assessment of improvement strategies in the design process. One aspect, in particular, has become apparent in the short period of approximately 20 years in which the Passive House standard has been around: the design and planning strategies have always been closely linked to the energy-efficient technologies available at the time of construction. The further development of these technologies has invariably affected the corresponding design approach. And yet, a large variety of design strategies can lead to successful outcomes so long as the overall energy-related target is kept in mind, which is to design urban quarters, residential housing estates and buildings that are sustainable from an energy point of view – also in terms of the long-term, very ambitious climate protection goals. 6

Target groups There is an increasing interest in Passive Houses, also among architects. However, this is not due to clever marketing, but simply because it is one of the most scientifically sophisticated and practical energy efficiency standards for buildings currently available. This book is therefore addressed to all architects, urban and specialist planners who want to find out more about the Passive House concept or who are just about to design their first Passive House dwelling or Passive House housing estate. The contents will also provide new insight for those architects and planners already familiar with the Passive House standard. Among other things, it includes the future assessment of Passive House buildings with regard to their energy sustainability, and explains the impact this has on design. Clients interested in the topic will find the many reference projects and insights into the design work of architects and specialist planners very worthwhile reading. Passive House concept and design The Passive House concept is based on very clear and well-established energyrelated requirements and the verification thereof using the specially developed assessment tool: the Passive House Planning Package (PHPP). The concept is designed to give architects a high degree of flexibility as to how target values can be reached, since precise rules are deliberately avoided. It is fascinating to see how designers, step by step, have taken advantage of this freedom and gradually extended the scope of application. And, in our opinion, it is precisely this exploration of possibilities that makes the architects’ contribution towards the further development of the Passive House standard so substantive.

Strict criteria One question that often arises in the context of Passive Houses is whether the limit imposed on the space heat demand – it should be no greater than 15 kWh / m2a – must really be quite so strict. There are several ways to answer this question: • The target values of the Passive House standard and the constructional and technical approaches have proven successful in practice. Together they provide a well-balanced mix of high comfort and performance in terms of building physics, which is reflected in economic and functional efficiency. • The space heat demand is the most important value in defining the energy performance of a building. It follows that it also evaluates the architectural design in terms of the overall energy efficiency achieved. • The principal design features and properties of Passive House buildings are based on the extremely low space heat demand and the very small heat load. Among these are excellent thermal comfort in winter, the elimination of draughts and very good indoor air quality, the absence of otherwise required radiators beneath windows, as well as the simple arrangement of building services in a core zone. • User behaviour also varies quite considerably in Passive House homes. Different residents require different room temperatures, ranging from 18 to 24°C; some like to open windows in winter to air the interior. The space heat demand measured in identical dwelling units can therefore vary between 3 and more than 40 kWh/m²a. Thus, the building services concept of Passive House buildings should be designed in such a way that even very different user

Energy-efficient building design

demands can be fulfilled in terms of heating performance and perfect comfort. If one were to increase the space heat demand to, for example, 20 kWh / m²a, the very basic heating system, commonly used in Passive House buildings, would no longer suffice to meet the demands. Open approach versus “laissez faire” This book takes a very open approach to the design of energy-efficient buildings. The energy balance, using certified calculation programs and simulations, has been identified as the only really reliable tool. Those who verify their design using this tool but, at the same time, for good reasons, extend, replace or dispense with the undoubtedly very effective planning principles are very welcome to do so. However, this procedure requires a great deal of discipline, because each creative exceedance demands a sound knowledge of principles and their implications. This approach is therefore the exact opposite of a “laissez faire” attitude. Simply because of its low reserve capacity, the Passive House is less tolerant than buildings with lavishly dimensioned heating and cooling systems. Book contents The structure of this book is based on the planning process of a Passive

House. It starts with an explanation of fundamental aspects including the definition of standards, project design, building physics and building services. The topical focus is on architecturerelated design issues. This is followed by insights into the application of Passive House principles in urban planning, since this is regarded as the basis for the meaningful development of energyefficient buildings. A separate chapter focuses on non-residential buildings completed according to Passive House standard. In this field especially, there is an increasing variety of typologies, ranging from schools, to museums and indoor swimming pools. The weighting of factors in the energy balance varies according to type and use. Nevertheless, in the case of these buildings, too, the design and construction have a significant impact on the overall efficiency. In recent times, energy efficiency upgrades have become an important field of application for Passive House components. However, the difficult circumstances often encountered in these schemes mean that not all elements can be improved sufficiently to meet the Passive House standard of a new build. Further limitations are frequently added, such as the sensitivity of a scheme (building conservation), issues concerning space and building approval, as

well as demands to perform refurbishments in stages rather than in a single step. With the introduction of the EnerPHit standard, the Passive House Institute has developed a fine-tuned and practical planning concept for energy efficiency upgrades. Passive House projects A range of completed Passive House projects in this book illustrate the exemplary implementation of the principles for energy-efficient and solar building. The projects have generally been built with an average budget and ordinary user requirements. The selected examples present a wide range of building typologies, spatial configurations and structural concepts, as well as different solutions concerning building services. The Passive House standard referred to in this book is the “classic” Passive House concept as determined by the German Passive House Institute. In order to present the Passive House developments taking place in other countries (e.g. the Swiss Minergie-P standard), the projects selected also include some buildings that marginally exceed Passive House standard. 1.1 Residential estate in Frankfurt am Main (D) 2008, Stefan Forster Architekten. Development of a building with a mixed-use concept, including living, shopping and dining, on the former site of a tram depot in the city centre.

1.1

7

Principles

• Concept approach: energy efficiency • Definition of the Passive House standard • Passive House components • How does a Passive House work at different times of the year? • Thermal comfort and wellbeing • Scope and field of application • Economy • Energy-related sustainability and climate protection

Concept approach: energy efficiency The Passive House concept is based on a scientific, objective method and is characterised by consistency and transparency. Its energy-related targets define a clearly determined framework within which the design of the Passive House takes place. How the targets are actually met is quite purposely left to the designer. Thus, there are no predetermined design principles, construction methods or building services solutions. The only crucial factor is the energy performance of the building and its constructional and technical components. The criteria are simple and wellfounded. Complicated interdependencies of the target values between, for example, the size and compactness of the building or the type of building are deliberately avoided. The overriding concept is extremely simple: nobody is interested in a wasteful consumption of energies and resources as an end in itself. Everybody is far more interested in the result and comfort that can be achieved through its consumption. Among the energy services expected are, for example, a comfortable workplace or home which is warm in winter and sufficiently cool in summer. There should always be an adequate supply of fresh air in the interior without, however, having to sit in a draught. Furthermore, we need facilities in buildings for washing, bathing and showering, for washing and drying laundry, storing and preparing food and the opportunity to call on these according to our daily routines, which can occasionally be very spontaneous. It must also be possible to compensate for a lack of daylight, either in a room or at a certain time of day, by providing a suitable amount of artificial light in order to perform each and every task at any time. 8

This list more or less includes our entire sphere of life and all of the economic, public and private activities involved. Most of these services can be rendered with a much lower use of energy than is usual practice today. The Passive House concept is designed to implement this efficiency standard consequently in the proposal, planning, development and operation of buildings. For economic and practical reasons, it begins with components that are generally required in every building anyway. These are further developed in such a way that, in relation to the small additional constructional and technical effort required, superior results and comfort are achieved in total.

Definition of the Passive House standard To begin with, the energy consumption in a Passive House is reduced with passive measures to such a low level that the building hardly requires any heating, cooling, humidification or dehumidification to meet the predetermined climate and comfort conditions. Among the passive measures, the most substantial contribution is made by the thermal insulation of the building. Most of the heat demand in winter can be covered by passive heat sources, such as the sun, the occupants, office or household appliances and the heat extracted from the exhaust air. The thermal insulation also helps to reduce heat gains inside a building in summer. Further passive measures, such as shading devices, natural ventilation, easily accessible storage mass, as well as a systematic reduction of internal heat loads, either suffice to keep the building cool on their own or are able to reduce the cooling load sufficiently so that it can

be covered with the use of very little energy. The application of technical equipment is therefore limited to the active ventilation of the interior space. This should include heat recovery and possibly also the recovery of moisture. Furthermore, the Passive House concept is designed to provide a controlled supply of the very small space heat demand, and if necessary also cooling demand, according to the individual requirements of the residents or users.

Passive House components The Passive House concept represents the state-of-the-art technical solution for energy-efficient building. The aim has been to improve the constructional and building services components in building,s in terms of their energy efficiency, to such a degree that the heating system can be downsized considerably. The main components of a Passive House building include: Excellent thermal insulation The most obvious feature of a Passive House building is the excellent thermal insulation of the entire building envelope. The opaque elements (exterior walls, roofs, ground and ceiling slabs) have, depending on the form factor of the building and the quality of the other constructional and technical components, U-values ranging between 0.08 and 0.18 W / m2K. In order to provide a high level of thermal comfort, the U-values of the windows are below 0.80 W / m2K. This requires insulated frames and the use of triple thermal protection glazing. Avoiding thermal bridges; air and windtight construction of the building envelope Good thermal insulation includes excellent detailing of all junctions. This is nec-

Passive House components

essary not only from an energy point of view but also in terms of building physics (fig. 2.4, p. 10): • In order to avoid the thermal insulation of plane surfaces simply ending at junctions, it is necessary to make sure that all thermal bridges are prevented or at least minimised. • An airtight construction of the building envelope is necessary to eliminate draughts, leak-induced damage and ventilation heat loss. • The wind-tight construction of the building envelope avoids the thermal insulation from being wind-washed, i.e. air penetrating into and around the insulation, and thus reducing its effectiveness. Coordinated passive solar components High solar contributions to the heating can be made by using Passive Housesuitable windows and glazing systems. And this does not even require an excessively large solar aperture area, i.e. even a moderate window area can suffice. The size and number of glazed areas can be selected according to other aspects, such as daylight autonomy, the desired indoor/outdoor connection or designrelated considerations. The solar gain through windows can only provide a substantial contribution towards the space

heating if the heat loss of the window frames and window panes is kept to an absolute minimum. For summer conditions, it is essential, like in all buildings, to limit the solar aperture to the size necessary in terms of lighting and the connection to the exterior space, or to provide controllable shading devices. Depending on the design of the building, different window quantities (e.g. window sizes) and qualities (U-value of the window and g-value of the glass) must be checked and assessed according to the impact they have on the performance both in summer and winter conditions. Alongside affecting the energy balance, these considerations have a significant impact on the appearance and the user friendliness of the building. High-performance ventilation unit Alongside the reduction of transmission heat loss, the minimization of ventilation heat loss, through the installation of a mechanical ventilation unit with a heat recovery system, is a key aspect of a Passive House building’s low space heat demand. All rooms within the thermal envelope of a Passive House are therefore provided with fresh air using a comfort ventilation system with heat recovery and a controlled supply and extraction of

air. The main aspect here is to ensure the air exchange necessary from a hygiene point of view. The effective heat supply rate of the mechanical ventilation unit should be at least 75 % in order to provide a suitable degree of efficiency and comfort. Adapted heating and cooling systems A Passive House requires heating and cooling systems that are suitable to match the low heating and cooling demands of the building. Generally speaking, any conventional type of heating system can be used. In many cases, though, Passive House buildings can be heated using the supply air only. Additional heating surfaces, if at all required, do not necessarily have to be placed beneath windows, which was previously the case. This has the effect of simplifying and reducing the installation work, which frees up the additional expenditure for the heat recovery system of the mechanical ventilation unit. These aspects have a considerable impact on the economic efficiency of the Passive House concept.

2.1 School for speech correction in Griesheim (D) 2011, Ramona Buxbaum Architekten. The new build includes three separate, compact pavilions built as timber frame structures.

2.1

9

Principles

20 °C

-5°C 35 W/m2

U = 1.40 W/m2K

Building stock

8 W/m2

U = 0.30 W/m2K

EnEV

3 W/m2

U = 0.12 W/m2K

Passive House 2.2

outside air

extract air

0°C

Energy-efficient electrical installations The use of power-efficient devices, work or household appliances and lighting, as well as all other service facilities (e.g. elevators) and electronic devices (e.g. communication technology) is a fundamental aspect of the Passive House concept (fig. 2.5). However, the implementation of this aspect is often disregarded by architects and consultants since it is not considered to be within the scope of normal services. Its impact on the primary energy balance, the greenhouse gas emissions and comfort conditions in summer is quite considerable though. It is for this reason that all power consumers are accounted for and assessed in the electricity balance of the primary energy criterion.

20 °C

How does a Passive House work at different times of the year? Heat exchanger ηHR = 90 %

exhaust air

supply air

3°C

18 °C

Annual space heat demand [kWh/m2a]

2.3 35 30

28.2

25 19.8

20

17.1 15.0

15

13.5

Passive House limit

10 5 0

Primary energy (non-renewable) [kWh/m2a]

3.0

1.5

1.0

0.6 0.3 n50 pressure test factor

150

120

Passive House limit

2.4 household electricity aux. power hot water heating

100 90 50 25 50

15

10

5

25

25

25

20

20

20

average power efficiency today

improved

efficient

0

2.5

10

The functional principles of a Passive House are explained below. The exemplary illustrations are based on a singleunit dwelling in a Central European climate and take into account the residents’ lifestyle. The ventilation concept and performance, which is adapted to the corresponding season, is of central importance. Winter Fresh outside air is drawn into the building through a central opening or structure with an integrated filter and transported to the core element of the mechanical ventilation unit, the heat exchanger, with the help of energy-saving fans. At the same time, a second fan extracts waste air from rooms where moisture and pollutants are most often generated (e.g. kitchen, bathroom, utility room). The heat contained in the extract air is transferred to the outside air in the heat exchanger (fig. 2.3). The preheated air is continuously supplied to the living spaces (e.g. living room, bedrooms). A high quality of supply air is ensured by the steady and permanent exchange of air. While it is not necessary to open windows for ventilation purposes, this can be done if required, for example in the case of a party or where cooler bedrooms are preferred at night. The excellent insulation of the building envelope and the controlled air exchange provided by the mechanical ventilation unit with heat recovery reduce the heat loss to a minimum. The high quality glazing even ensures high solar heat gain in the middle of winter. The

remaining heat demand can be covered solely by the preheated supply air, and possibly a few additional, carefully placed radiators. It is also possible to completely separate the ventilation and heating system and control them individually. The heating period in a Passive House lasts from November to March and is therefore much shorter than that of a conventional building. In-between seasons In the in-between seasons, autumn and spring, the Passive House does not need to be heated, provided the heat recovery system of the mechanical ventilation unit is still being operated. It is fairly easy to adjust the temperature in the interior of a Passive House by opening the windows for short periods of time to get rid of excess heat due to, for example, undesirable solar heat gains. Because of the high radiation of the low standing sun, the use of shading devices and glare control is especially important on very sunny days. Summer In summer, Passive House buildings are very similar to conventional buildings of similar construction. Contrary to popular belief, the very good thermal insulation actually helps to keep rooms cool. This is especially true for attic storeys, which are often uncomfortable to use in summer due to overheating. By using windows with forced ventilation and adjustable shading devices at the most important openings, the residents have some very effective passive cooling strategies at their disposal. However, the conditions for their installation must already be made at the design stage, including the perfect arrangement of windows to provide cross ventilation, possibly involving several storeys, as well as the integration of shading devices. The mechanical ventilation unit is often also operated in summer purely to provide better thermal comfort. In this case, however, the heat recovery system must be circumvented, either by installing a bypass or by exchanging it for a summer casette. The use of energy-efficient electrical appliances is fundamental for good comfort conditions in summer since this prevents the build up of critical heat loads in the interior space. Opening of windows in Passive Houses In contrast to the common misconception that you are not allowed to open windows in a Passive House, window

100

space heating

internal heat gains

solar heat gains

transmission

Frequency of overtemperature h (δ > 25 °C) [%]

Annual space heating energy balance [kWh/m2a]

How does a Passive House work at different times of the year?

ventilation

90 without ventilation heat recovery without ground heat exchanger

80 70 ventilation heat recovery 80% ground heat exchanger 20%

60 50

5.9 13%

40

23.2 50%

30

40.4 87%

8.1 18%

20 10

24.5 35 %

29.2 42 %

8.5 12 % 40.4 58 %

36.6 53 %

15 32%

0

25

20

15

10

5

0

Gains

Losses Passive House

Gains Losses Passive House without heat recovery

frequent

average

infrequent

2.6 3

2.7

6 1

4 2

5 25

21 24 22

23

13

20

8

18

9

17 16

supply air

21

supply air

7 19

waste air 19

10 15 12

11

14

26

2.2 Heat flow through an exterior wall dependent on the U-value of the construction 2.3 Performance of the highly efficient heat recovery system (with ηHR = 90 %) 2.4 Annual space heat demand of a Passive House dependent on the airtightness measured by the blower door pressure test 2.5 Primary energy value of a Passive House dependent on the efficiency of electrical systems (household appliances, communication electronics, lighting, pumps, fans) 2.6 Impact of ventilation heat recovery on the energy balance of a Passive House. The annual space heat demand would rise from 15 to almost 40 kWh/m2a without heat recovery. 2.7 Impact of residents opening windows for ventilation purposes to improve summer ther-

mal comfort (frequency of indoor temperature rising above 25 °C). 2.8 Overview of the most important Passive House components and their interaction in a schematic section. 1 air intake with filter (F 7 filter) 2 frost protection coil 3 heat exchange chamber 4 support fan (intake duct) 5 support fan (exhaust duct) 6 exhaust air outlet (e.g. deflector hood) 7 fireproof dampers 8 supply air terminal in dwelling unit 9 secondary heating coil 10 waste air fan 11 bathroom radiator 12 optional additional heating surface

2.8 13 central core with fire resistant ventilation ducts (F 90) 14 sanitary rooms arranged around the central core 15 waste air filter 16 insulated exterior wall 17 wind-tight layer (e.g. external rendering) 18 airtight layer (e.g. internal plastering) 19 Passive House window with triple glazing 20 blind box integrated into insulation layer 21 fixed overhang (e.g. balcony slab) as a shading device for the south-facing facade 22 balcony set in front of the structure (only point-fixed to building) 23 window ventilation (tilt position) 24 window ventilation (cross ventilation in summer) 25 roof overhang to provide shading of south facade 26 bottom block course made of aerated concrete

11

Principles

The starting point of energy-efficient design is the human being. In order for a person to feel comfortable in an interior

In the case of “slightly naive” empirical analyses, there are, dependent on the building culture and the corresponding construction method, large differences in buildings in regard of the prevailing comfort levels. It is easy in this respect to draw the wrong conclusion and assume that comfort requirements are influenced by culture. If one however performs detailed systematic surveys, there are hardly any cultural differences worth mentioning. Even the climate zones (tropical, subtropical, temperate, cold) are irrelevant. This is an extremely important discovery that was made by Ole Fanger [2], whereby the human being and its bodyheat balance function as an objective, because biology related, criterion for comfort levels. The following factors are of significance in this case: • the activity and the generation of body heat it involves

Predicted percentage of dissatisfied (PPD) [%]

Predicted percentage of dissatisfied (PPD) [%]

Conclusion The functional principles and energy performance of a Passive House enable the design and development of buildings with a high degree of thermal comfort without having to resort to a high consumption of energy and elaborate technical installations. The energy demand of Passive House buildings does not, however, equal zero. This is, on the one hand, due to economic factors and, on the other hand, in order to provide sufficient flexibility in case of periods of absence, the arrival of new residents or changes in building use. The installed heating system is intended to cater for the individual temperature requirements of residents and balances, in addition to the mechanical ventilation system, the heat loss through opening windows at the height of winter.

space, the temperature and humidity levels must be within a certain range and balanced throughout the space and day. Thermal comfort is, in this case, of great significance. It is dependent on a number of parameters, which can be narrowed down fairly precisely with the help of scientific and statistical methods [1]. The thresholds of sensitivity differ considerably according to the parameter used. In addition, individual preferences play an important role, making them an important component of the comfort definition. The room climate can be, in good approximation, determined by four parameters that affect a person present in a room. These are listed according to their degree of significance: • radiation temperature of the surrounding surfaces • room temperature • relative air velocity close to the human body • humidity.

Thermal comfort and wellbeing

30

winter

25

20

15 DIN EN ISO 7730 (PPD = 10%) 10 (PPD = 6%) 5 0

ASHRAE “A“

12

b

summer

25

20

15 DIN EN ISO 7730 (PPD = 10%) 10

Thermal comfort Concerning homes and offices, the comfort levels, at which at least 90 – 95 % of those questioned felt comfortable, can be determined as follows [1, 2, 3]: • The air temperature should be set at around 21 °C (± 1 Kelvin) with the possibility of being adjusted to between 18 and 24 °C. Temperatures higher than 24 °C (± 2 Kelvin) can be tolerated in summer by adapting the clothing accordingly (fig. 2.9). • The average surface temperature should not differ from the air temperature by more than 2 – 3 Kelvin; the difference between component surfaces should not exceed 3 – 4 Kelvin. Floor temperatures are perceived as comfortable at between 19 and 26 °C. • Both in winter and summer, the temperature difference between head and foot (sedentary activity) should not exceed 2 Kelvin. • The relative air humidity should be between 40 and 70 %. From a medical point of view, relative humidity levels below 30 % are regarded as unhealthy. • The air movement indoors should not exceed 0.08 m/s in habitable rooms (danger of draughts). • In summer, however, at operative temperatures above 25 °C, an increased air velocity can help to readjust thermal perception and make occupants feel more comfortable. • At high operative temperatures (> 25 °C), all radiating heat sources (radiation temperature > 25 °C, e.g. overhead rooflights) are considered very unpleasant. 34

without cooling

with cooling

30

26

22

(PPD = 6%) 18

5 0

16.4 17.3 18.2 19.1 20 20.9 21.8 22.7 23.6 Operative temperature [°C] a

30

• the clothing, in particular the thermal resistance and wind-tightness • physical processes, such as thermal conduction, thermal radiation, convection and evaporation in and on the body and in interaction with the surroundings.

Operative room temperature [°C]

ventilation actually plays a central role. In winter, there is no need to open windows since the mechanical ventilation unit is responsible for the air exchange necessary in terms of hygiene. Residents are in agreement that this actually eases the burden and increases comfort levels. In all other seasons, window ventilation is absolutely essential to generate comfortable temperatures in the interior space. Measurements in residential buildings during the height of summer have shown that different temperatures are metered according to different window opening habits: whereas rooms with frequently opened windows stay quite cool, the temperature in rooms where windows are opened only sporadically rises significantly during heat waves (fig. 2.7, p. 11).

ASHRAE “A“ 20.7 21.6 22.5 23.4 24.3 25.2 26.1 27 27.9 Operative temperature [°C] 2.9

14 -5

0 5 10 15 20 25 30 35 Moving average of outdoor temperature [°C] 2.10

Thermal comfort and wellbeing

• At high temperatures (> 30 °C) and high humidity levels (> 50 % relative humidity), the heat regulation capacity of the body is reduced to such a degree that countermeasures must be taken (cooling, dehumidification). Adaptive model Whereas the requirements for high thermal comfort in winter are not disputed, there are different approaches to achieve comfortable conditions, independent of clothing and cooling strategies, in the inbetween seasons and summer (fig. 2.9 and 2.10). Clothing in summer is lighter, which means that the temperature perceived as comfortable increases. Especially during spells of hot weather, greater air movement is not considered a nuisance. It is also a fact that, under certain conditions (no dress code, individual regulation of window ventilation and shading devices), building users accept higher operative temperatures during hot weather periods. From a design point of view, these findings increase the scope of using passive cooling strategies without an active cooling system so long as air conditioning, which would not be controlled by the building users individually, is avoided in agreement with the client and consultants (fig. 2.10). Passive House concept – winter time Thanks to the very good thermal insulation, in winter surface temperatures throughout a Passive House are sufficiently high. The quality of window frames and window panes is extremely important for the provision of thermal comfort since this is the only way to achieve even surface temperatures indoors and limit the cold air drop at windows. In order to ensure the same comfort in buildings with floor-to-ceiling glazing (approx. 3 m high), Passive House-certified windows must achieve a

whole window U-value of ≤ 0.85 W / m2K. This is the only solution which ensures that radiators beneath windows can be omitted. In Passive House buildings it is possible to keep the air movement in living rooms within a comfortable range of