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MAY • 2008
VOL. 11 • NO. 5
Diffuser Models For Airflow Simulation Effective Humidity Measuring Systems Airborne Security
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DIFFUSER MODELS FOR AIRFLOW SIMULATION
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Jelena Srebric, Ph.D., Qingyan Chen, Ph.D., and Andrew Manning
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POINT OF VIEW
J.E.J. (Ned) Gravel
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Controlled Environments Magazine® (ISSN1097-167X) is published eleven times per year, by Vicon Publishing, Inc., 4 Limbo Lane, Amherst, NH 03031. USPS 021-493 Periodicals Postage Paid at Amherst, NH 03031 and at additional mailing office. A requester publication, Controlled Environments Magazine® is distributed free to qualified subscribers in the US and Canada. Non-qualified subscription rates in the U.S and Canada: $120 per year. All other countries: $180 per year, payable in U.S. funds. Back issues may be purchased at a cost of $15 each in the U.S. and $20 elsewhere. While every attempt is made to ensure the accuracy of the information contained herein, the publisher and its employees cannot accept responsibility for the correctness of information supplied, advertisements, or opinions expressed. POSTMASTER: Send address changes to Controlled Environments Magazine, PO Box 1273, Skokie, IL 60076. ©2008 Controlled Environments Magazine® by Vicon Publishing, Inc. All rights reserved. No part of this publication may be reproduced without permission from the publisher. Permission is granted for those registered with the Copyright Clearance Center, Inc. (CCC), 222 Rosewood Drive, Danvers, MA 01923 (phone: 978-750-8400; fax: 978-750-4470) to photocopy articles for a base fee of $1 per copy of the article plus $.35 per page. Canada Agreement number: PM40063731, Return Undeliverable Canadian Addresses to: Station A , PO Box 54, Windsor, ON N9A 6J5, Email: [email protected]
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POINT OF VIEW
NED GRAVEL
Leadership vs. Management I recently delivered a leadership course, and one of the pieces of feedback I received was about the necessity for acquiring a leadership skillset in the first place. The question was, “If I am a trained and experienced manager, why do I need to learn about leadership?” The simple answer to that question is really: “You don’t. Unless…” And this is where it gets tricky. We have all read something of Peter Drucker’s regarding the science of management. He is the modern day guru and it is primarily because he pushed it into the realm of a learned/acquired set of rules that we are able to quantify what it takes to manage something. I define management as “the science of planning, organizing, directing, and controlling resources to achieve an organizational goal.” This is a very straightforward definition and combines most of elements used by many very knowledgeable folks. I define leadership as “the art of motivating people to achieve a common goal.” I am not certain if most people can appreciate the differences between these two definitions but, for me, the science deals with resources and the art deals with people. In my opinion, people are not resources; they are people. Under an approach using management science, we will consider people (human resources) as another set of variables and resources to apply to the project we have been assigned. If we treat people as resources we may get maximum “use” of them, but we will not get maximum “benefit” from them. And that is the single biggest reason why the management approach may not be good enough for managers. Maximum use is not the same as maximum benefit. I can already hear some managers ringing up cost/benefit analyses from this statement and I guess that is OK, but those that do may run into some resistance from the people on their teams. People can sense when they are being sized up to produce more with less. The real paradigm shift that managers should experience at this point is the realization that, just like themselves, the people on their teams can “contribute” to the success of the team or organization whereas resources can only be used in attaining such successes. Resources do not contribute to such successes, only people can do that.
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I define leadership as “the art of motivating people to achieve a common goal.”
Managers who do not understand this believe that the only person who is contributing to group success is his or her self — and no other. For these folks, people truly are “resources.” I think such managers should consider restricting the practice of their science to processes, plant, and other inanimate resources. But what should a person do, if they really want to get maximum benefit from the folks on their team — the team they have been appointed to “manage?” If such a manager understands that people are not resources, they have taken the first emotionally-risky step in becoming a true leader. They will learn to concentrate on providing motivation to their team members, individually and collectively. They will learn that team success is dependent on the success of everyone else on the team. They will learn that their own personal success is based on the success of everyone else on the team. They will be practicing the art. In short, when we switch our concentration away from our own resource allocation work to the work of our team members — we are changing from managers to leaders. When we understand that leadership is more about how we (personally) do things and management is more about how resources are aligned, we can start to get more from the people who are our team members. People do not really need to be managed, but they really want good leadership from us. If we give them what they need, they can provide the real contribution to the success of the team and our organization. The approach we use is entirely up to us, but the results will depend on our team members. J.E.J. (Ned) Gravel, P.Eng., CA-LS, CAE, is the Manager, Quality and Training for the Canadian Association for Environmental Analytical Laboratories (CAEAL). www.caeal.ca
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Diffuser Models for Airflow Simulation Accurate simulation of the airflow and heat transfer in cleanrooms is highly dependent on the diffuser, yet diffusers have traditionally been very difficult to model.
Jelena Srebric, Ph.D., Qingyan Chen, Ph.D., and Andrew Manning
The airflow in and around diffusers is particularly important in cleanrooms because diffusers play a vital role in the isolation and flushing strategies that are commonly used to meet performance requirements. An isolation strategy may involve the use of air curtains at entrance or to isolate specific areas of the cleanroom. On the other hand, a flushing strategy might involve the use of a raised floor arrayed with diffusers while the returns are located in the ceiling. In either case, a precision tool is required to deliver the airflow in the right locations and avoid generating flow where it could have a negative impact. Simulation is required in nearly every cleanroom project to meet today’s challenging cleanroom performance requirements. However, diffuser modeling has posed difficulties in the past. The key information that is normally required is the crosssectional velocity profile of the diffuser at its outlet for use as a boundary condition in a computational fluid dynamics (CFD) simulation. However, the CFD software used to model airflow in cleanrooms is generally not easy for modeling
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diffusers because of their small physical size and high flow velocities. The traditional way to model diffusers is to build a CFD model that matches the physical tests performed by the diffuser manufacturer. Then the diffuser boundary conditions are adjusted through a trial and error process until the simulation results match the diffuser manufacturer’s test results. This is a long and tedious process that substantially drives up the amount of time required to simulate airflow. While working in the Building Technology Program for the Massachusetts Institute of Technology’s (MIT) Department of Architecture, we identified a method for modeling diffuser airflow that eliminates the need for this trial and error process.1 We used the momentum method to develop a model that predicts the diffuser boundary conditions based on a few parameters such as the type of diffuser, dimensions, flow rate, supply temperature, deflection angle, and effective area. We performed extensive physical testing that demonstrates that this model accurately predicts the boundary conditions over a wide range of applications. CFD software sup- ➤ May 2008 쩤 11
pliers have developed web macros that enable users to simply type in a few parameters and then the macro generates the correct grid geometry and constraints required to accurately model the diffuser.
CHALLENGE OF MODELING DIFFUSERS CFD modeling provides the ability to accurately model air flow and heat transfer within a building, enabling heating and cooling systems to be optimized in the form of a software prototype without the expense and time involved in making changes to the actual building. The greatest challenge in CFD is often modeling the diffusers because they have a major effect on the airflow in the building yet they are difficult to model with conventional CFD software. The difficulty with modeling diffusers arises from the fact that they are small compared to the size of a building and have very high flow velocities. To model detailed diffuser geometry would require millions of grid cells which would require large amounts of computer capacity. On the other hand, to model the diffuser at the same grid density as the room would ignore details that could introduce errors into the numerical simulation. What needs to be known for an accurate CFD simulation is generally the boundary conditions consisting of the velocity and temperature cross-sectional profile at the diffuser outlet. Manufacturers of diffusers typically perform tests on their products, installing the diffuser in a room and measuring airflow in the room. Until recently, the most accurate way for CFD users to model diffusers has been to build a model that duplicates the tests performed by the diffuser manufacturer, then adjust the diffuser boundary conditions until the airflow in the room matches the test results. There are several weaknesses to this approach. One is that a considerable amount of time is required to create the room model and the other is that the boundary conditions determined by this method are only completely accurate for rooms that match the room used in the diffuser manufacturer’s test. Several years ago, while at MIT, we set out to find a faster and easier method to determine the boundary conditions for common diffusers. We looked at several possible methods of determining boundary conditions for different types of diffusers. We identified the momentum method, which de-couples the momentum and mass flow in the CFD simulations of room airflow, as the most promising.
terms of the conversation equations over the real diffuser area. The air supply velocity for the momentum source term is calculated as follows: • U0 m A0 where: U0 is the centerline or maximum jet velocity in m/s m• is the mass flow rate in kg/s is the air density in kg/m3 A0 is the diffuser effective area in m2 The momentum method requires the following data when it is used in CFD simulations: • airflow rate • discharge jet velocity or effective diffuser area • supply turbulence properties, and • supply temperature and contaminate concentration. This approach is easy to use, which is an important advantage when using CFD for indoor air distribution design.
PHYSICAL TESTING APPARATUS The airflow pattern and the distributions of air velocity and temperature were measured in a full-scale environmental test facility as shown in Figure 1. The facility consists of a well-insulated box (thermal resistance = 30 ft2 °F h/Btu or 5.3 m2K/W) with a partition wall that divides the box into a test chamber and a climate chamber. Each chamber has a separate air-handling system. The wall between the test and climate chambers has a double-glazing window as wide as the room. The temperature, relative humidity, and air supply rate was controlled in both chambers. The climate chamber was used to simulate the outdoor climate. The test chamber, 17 ft (5.16 m) long, 12 ft (3.65 m) wide, and 8 ft (2.43 m) high, simulates the indoor environment. The six diffusers were installed in the test chamber at positions shown in Figure 1, where
HOW THE MOMENTUM METHOD WORKS The momentum method uses the initial jet momentum, M0, and diffuser mass flow rate, m• , as boundary conditions for the diffuser simulations. The diffuser is represented in the CFD study with an opening that has the same gross area, mass flux, and momentum flux as a real diffuser. The model enables specification of the source
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Figure 1: Test Chamber
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the dashed lines denote cross sections of middle planes in the chamber. In the present study, the major measuring equipment of the test facility includes: • a flow visualization system by smoke for observing airflow patterns • a hot-sphere anemometer system for air velocity and temperature measurements • a thermocouple system for measuring wall and air temperatures, and • a tracer-gas system for measuring concentrations.
Figure 3 provides a comparison of the calculated and measured air velocities at five positions in the room. The results show that the air velocities are low — lower than 0.35 m/s or 70 fpm, even in the jet region. In the other parts of the room, the air velocities are mostly lower than 0.1 m/s (20 fpm). Since there are slow and unsteady recirculations in the lower part of the room, it was difficult to measure and calculate reliable velocities in the area. Nevertheless, the agreement between the computed and measured results is reasonably good. Since the low velocities would not cause a draft problem, it is impor- ➤
DISPLACEMENT DIFFUSER We used the momentum method to study eight types of commonly used diffusers. One of these was the displacement diffuser, which has a very low momentum from the air supply. The buoyancy force is the same order of magnitude as the momentum force, so the airflow pattern from the jet does not correspond to a classic catalogue of jets defined in textbooks. Textbook cases show the jet changes its shape rapidly as shown in Figure 2. The jet also depends strongly on the heat sources in the room. The airflow is discharged horizontally from the front surface. The supply air velocity is 0.35 m/s (70 fpm), the airflow rate is 0.0768 kg/s (135 cfm), and the temperature is 13.0°C (55°F). In the experiment, the supply air temperature was adjusted to be very low in order to study how the low supply temperature can affect the thermal comfort in the occupied zone.
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tant to correctly predict room air temperature stratification in displacement ventilation system design. The data shows a very good agreement between the calculated and measured air temperatures. This is especially evident in the jet region.
Figure 2: Development of wall jet from displacement diffuser.
GRILLE DIFFUSER
Figure 3: The comparison of calculated and measured velocity profiles for the displacement diffuser at five positions in the room.
We also studied the grille diffuser. The vanes in the grille diffuser were adjusted to discharge a jet normal to the grille surface. The resulting jet was shifted 5° in the horizontal plane towards the sidewall. The reason for the deflection is probably due to a very short straight duct behind the diffuser that did not allow the full development of the flow in the duct. Another possible reason is the impact of the asymmetric room geometry. The calculated and measured velocities are shown in Figure 4. The figure also shows that the results with the momentum method are better than an alternative method known as the box method. The accuracy of the box method depends on the velocity direction obtained from the smoke visualization. A flow direction with such a small deflection angle (5-10°) is difficult to observe. On the other hand, the measurements for the slot diffuser did not have such a problem, since the jet deflection angles were much larger (30-60°). It is more reliable to estimate the jet discharge angles at the diffuser surface for the momentum method than to present the angels at the surfaces for the box method.
WEB MACROS SIMPLIFY USE OF MOMENTUM METHOD
Figure 4: Calculated and measured velocities for the grille diffuser.
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The methods we developed have the potential to substantially improve building modeling by substantially reducing the amount of time and effort required to model diffusers. However, even after the validity of this approach has been demonstrated, a considerable effort was required to make them practical for use. The momentum method directly affects the calculation of the partial differential equations used to determine the fluid flow and heat transfer within the building. The vast majority of simulation users rely on commercial software that makes it virtually impossible for the user to modify these calculations. However, developers of CFD software for heating and ventilation system design have developed methods that simplify the use of these techniques. Web macros enable the users to model diffusers simply by entering a few parameters such as a type of diffuser, length, height, width, depth, flow rate, supply temperature, horizontal deflection angle, vertical deflection angle, and effective area into a web site. The ➤ Controlled Environments 쩤 www.cemag.us
Goodness Marge, How do you get your cleanroom so darn spotless? Controlled Environments Magazine ® provides current information on everything from pure materials through protective packaging, from state-of-the-art facility construction through day-to-day cleaning, and control challenges affecting quality and yield. Apply today for a FREE subscription!
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ods. She published extensively in the field, and received several remacros are used to implement the momentum method search awards including one form the International Academy of by de-coupling momentum and mass flow in the CFD Indoor Air Sciences. Dr. Srebric is an editorial board member of five simulations from the room airflow. This method uses the international journals, and an associate editor of HVAC&R Research Journal published by the American Society of Heating, Ventiinitial momentum and mass flow rate from a diffuser lating and Air Conditioning Engineers (ASHRAE). as boundary conditions for the diffusers. The built-in intelligence of the new web macros eliminates what used to be a difficult and time-consuming task. The models produced by the new web macros dramatically reduce the time required to accurately model diffusers. CONTROLLED CONTAMINATION SERVICES, LLC Another advantage of web macros is that they automatically generate the correct grid geometry and constraints, which helps avoid errors. References 1. Chen, Q. and Srebric, J. "Simplified diffuser boundary conditions for numerical room airflow models," 2000. Final Report for ASHRAE RP1009, 181 pages, Department of Architecture, Massachusetts Institute of Technology, Cambridge, MA. Figures © 2001, American Society of Heating, Refrigerating and Air-Conditioning Engineers, Inc. (www.ashrae.org). Reprinted by permission from ASHRAE RP-1009, Sponsored by ASHRAE TC 4.10, Indoor Environmental Modeling and TC 5.3, Room Air Diffusion. This material may not be copied nor distributed in either paper or digital form without ASHRAE’s permission. Andrew Manning is Director of Thermal Engineering for Flomerics, Inc., US Headquarters at 4 Mount Royal Ave., Suite 450, Marlborough, MA. Flomerics has incorporated the more accurate diffuser models described in this article into its Flovent Computational Fluid Dynamics (CFD) software. www.flovent.com Dr. Qingyan Chen is a professor of mechanical engineering at Purdue University and a Principal Director of the Air Transportation Center of Excellence for Airliner Cabin Environment Research (ACER). He also serves as the Editor-in-Chief of “Building and Environment,” the international journal of building science and its application. His current research topics include indoor environment, aircraft cabin environment, and energy-efficient, healthy, and sustainable building design and analysis. Chen has published two books and nearly 200 journal and conference papers, and has been invited to deliver more than 80 lectures internationally. Dr. Jelena Srebric is an Associate Professor of Architectural Engineering and an Adjunct Professor of Mechanical and Nuclear Engineering at The Pennsylvania State University (PSU). Dr. Srebric conducts research and teaches in the field of building energy consumption, air quality, and ventilation meth-
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May 2008 쩤 17
Catching the Drift Knowing what to look for in product specifications can initiate incisive questioning of manufacturers about the effectiveness of their humidity measuring systems.
Kevin Bull
One of the hardest parameters to accurately measure, relative humidity (RH) is a pivotal factor across a broad spectrum of industries and often entails the potential to impact critical applications and public safety. In calibration, stability testing, or quality assurance processes, the intrinsic uncertainty of humidity measurement can be a major source of unnecessary cost, skewed data, and lost revenues.
FACT: ALL HUMIDITY SENSORS DRIFT It’s an immutable law of RH measurement; relative humidity sensors drift. They do so for the simple reason that they are “air breathers.” Unlike temperature sensors, the internal structure of the humidity sensor must be in direct contact with the environment, which is constantly changing temperature and contains countless airborne contaminants. Both fluctu-
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ating temperatures and contaminants significantly affect the accuracy of any RH sensor, more so over time. This is why, even if the calibration process were perfect (it isn’t), once exposed to the real world, the measurement accuracy inevitably degrades.
A TALE OF TWO CALIBRATIONS There are two key accuracy values that must be considered when looking at any RH measuring device’s product specifications. The first is “initial accuracy”; the other is one year accuracy. Initial accuracy should factor in all known uncertainties, including: • calibration uncertainty • temperature effect and mathematical fit • hysteresis • measurement resolution
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If you don’t see these variables on a product’s specifications, they may or may not have been included in calculating that device’s accuracy.
ONE YEAR LATER: HOW LONG HAVE YOU BEEN OUT OF SPEC? One year accuracy is the accuracy of the device after a year of normal use, one year being the typical interval between calibrations. Although a critical value, a device’s projected accuracy value after exposure to the environment is rarely included on product specifications for humidity measuring instruments. However, this percentage is actually more important than initial accuracy because all data gathered since the last calibration is based solely on its accuracy upon re-calibration. For example, if your RH measurement device is found out-of-spec when you go to re-calibrate, you will be faced with some hard questions. What products or tests were affected and to what extent?
SEEK AND YE SHALL FIND You may be able to find specs on the accuracy of an RH measuring device after a year of typical use and over a wide temperature range, but you’ll have to know what to look for. You may have to just ask the sales representative. However, this comes with a proviso; the man-
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ufacturer should provide documentation that shows the accuracy values of their devices at the end of the calibration cycle, before re-calibrating. The question is: why is the inclusion of these values on product specifications uncommon within the industry? To answer, it’s vital to understand the three main elements that determine sensor accuracy: • sensor characteristics • calibration • sensor measurement system (electronics) A device may have the best RH sensor available; however, as already stated, all RH sensors drift. To maximize overall accuracy, it is crucial to reduce errors that occur during the calibration process and within the sensor measurement system. These elements, well controlled, will create a bit of room for the device to drift. In other words, to anticipate the drift of a device, you must achieve optimal accuracy in the calibration and the sensor measurement system. In effect, you need to reduce or virtually eliminate all other sources of error in the manufacture and maintenance of the device.
OTHER SOURCES OF ERROR Calibration Uncertainty All humidity calibration chambers have an associated uncertainty, a major source of which is temperature non-
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uniformity, which must be factored into a measuring device’s accuracy specification. Before humidity calibration, manufacturers of humidity data recorders must perform a high-accuracy temperature calibration. Each recorder’s measured temperature is then able to compensate for chamber non-uniformity during RH calibration — greatly reducing this source of error. Inside some data recorders, the temperature sensor is placed right beside the RH sensor. This proximity allows both sensors to read the same environment, eliminating discrepancies between their measurements. Temperature Effect and Mathematical Fit Most RH measuring devices are calibrated to measure at one specific temperature (typically 25ºC). But, unless the device will only be used to measure humidity at that temperature, there can be significant temperature-related inaccuracies. To solve this, a manufacturer could include tables that correlate humidity measurement over a wide range of calibrated temperatures in the memory of the device. Ideally, no two data recorders have the same set of tables because each set is calibrated to the unique components of every recorder. This creates an “intelligent” device, because the tables contain explicit information on how to measure humidity over a wide temperature range. This is particularly important in the case of ICH (stability) applications. Hysteresis Hysteresis is the tendency of measuring devices to not return completely to their original state after a change has been measured. It’s also a major source of error. Unfortunately, despite its ubiquity, too few data sheets include hysteresis as a factor in their accuracy values. If it appears at all, it’s often de-emphasized by being placed far apart from the total accuracy specification. Hysteresis unmentioned or disconnected from an accuracy value should be considered product data misrepresentation. Measurement Resolution Resolution is simply the smallest measurable increment that the device can detect. A good device will feature a 12-bit high-resolution system that detects changes of as small as 0.05%RH. Electronics A significant element that affects a device’s accuracy is its electronic components. Electronics systems are greatly impacted by temperature, which in turn affects overall
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accuracy. One challenge that manufacturers face is trying to get the electronic system to remain stable over wide temperature ranges.
CONCLUSION Product specifications, often one of the key pieces of information decision makers use to select a suitable system, must be explicit, easy-to-understand, and straightforward. All of the known influences and sources of error — calibration uncertainty, temperature effect, measurement resolution, and hysteresis — should be included in the accuracy value stated on any data sheet. If these values are not mentioned on a product data sheet, the consumer is left to ask: have they been included in that product’s stated accuracy? Until consumers are better informed on other factors that contribute to inaccuracy in humidity measuring devices, manufacturers confronted with their own out-of-spec devices upon re-calibration, can always blame drift. Kevin Bull, CEO, Veriteq Instruments, Inc., 13775 Commerce Parkway, Richmond, BC, V6V 2V4; 1-800-683-8374. For further information, please contact [email protected].
Plascore Semiconductor and Pharmaceutical Walls, Doors and Ceiling systems are specifically designed to meet the needs of today’s demanding Cleanroom applications.
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May 2008 쩤 21
Airborne Security Particles in a cleanroom environment must be removed. Particles that can reproduce themselves can become a difficult part of the problem to address.
Frank Stamatatos and Aaron Ayer
Cleanroom environments place extreme demands on the control of airborne contaminants. HEPA and other higher-end filters provide effective means of removing particulates — but don’t address destruction of biologicals in that airstream. Living organisms can represent major problems in maintaining an adequate manufacturing environment. Ultraviolet applications can be applied, but are expensive and efficacy can be difficult to quantify. A new form of electrically enhanced air purification offers an approach that captures and kills a variety of organisms. Even the most robust air filtration systems are just that — filters designed to capture airborne matter. Pathogens however, remain alive and the filters can become a fertile breeding ground. What happens when a technician raises a ceiling panel that was wetted long ago and previously quiescent mold spores get aerosolized? The ones that do get captured in current filtration technologies can take on a self-sustaining life of their own. Multiplying germs can dislodge from the filters and re-enter the sur-
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rounding air. As air is recirculated, pathogens have easy access to the entire building.
CAPTURE-ONLY TECHNOLOGY Almost all current filtration technologies are evaluated on the concept of “capture” rate, measuring the amount of particulates captured on the first pass through the filtration device. The higher the efficiency of a filtration device, the greater the number of particles captured. HEPA filters have a capture rate of 99.97 percent. HEPA and other high-end filters use dense filter media to capture particles physically; the denser the filter media, the more particles captured. Today’s high efficiency filtration technologies do not solve the airborne pathogen problem. Although offering excellent capture rates, they still do not kill or inactivate the organisms they collect. Once captured on an HVAC or portable filtration system, pathogens have a breeding ground for colony formation, which can lead to the spread of ➤ May 2008 쩤 23
Ionization Array
Upstream Field Electrode
An electric field is applied with simple electrodes across a filter. Ionization array applies an electrical charge to passing particles.
microorganisms and possibly their endotoxins. Dust, dead skin cells, and other matter collected on the filter provide nutrients for trapped organisms to grow and thrive. During the course of their life cycle, many of these microorganisms also produce waste products, which can be carried downstream in the airflow. Certain bacteria, for example, produce endotoxins to which many people are highly allergic. As long as the bacteria are alive, this process continues. Killing or inactivating these bacteria is the only way to stop the spread of harmful organisms and their waste products in the air stream. In addition, certain environmental conditions, such as high humidity common to HVAC systems in certain parts of the country, actually enable organisms to multiply and grow through filters; a phenomenon known by the unsavory term, “filter ripening.” Even in high-end
Charged particles stick to the polarized filter material with a strong bond.
24 쩤 May 2008
Upstream Field Electrode
Filter Media
Downstream Electrode
The electrostatic field established across the filter, polarizes the fibers.
HEPA systems, pathogens can grow and are then pushed into the airstream by the HVAC blower system. These pathogens can be present in the air stream in far higher numbers than they might have been without the filter’s intermediation. Mold or other fungi growing on a filter will generate high numbers of spores, which are then carried throughout the indoor environment and can be inhaled by the occupants. Finally, in addition to the airborne threat posed by pathogens growing on and through the filter media, additional spores or colony-bred pathogens trapped on the filter pose a threat to anyone encountering the contaminated filter media. Routine maintenance, disposal, or inspection of the filter can expose personnel to any of the original active, captured pathogens as well as any colonies breeding on the filter.
In the inhospitable environment of the enhanced filter, living organisms are inactivated.
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UV FILTRATION Ultraviolet light and other state of the art germicidal technologies also do not fully address the pathogen problem. Currently, the only viable approach for inactivating microbiologicals is through the use of combined UV and filtration systems, which employs strong ultraviolet lights to cause DNA strand damage within the organism before capture in a filter. UV filter systems have certain drawbacks. UV light efficacy on moving air streams can be difficult to reliably quantify. In addition, UV systems only affect the surfaces on which the UV light falls; it relies on residence and exposure time to inactivate an organism. UV light does not kill the root organism; it only inactivates an organism’s replication. This inactivation is not always assured if an organism is traveling on a particle, in a droplet, or hidden by surface matter, water, or other material that can shield the organism from the UV light. Spores and hardy viruses have evolved to survive in harsh environments, and many have become resistant to UV filter systems.
while the downstream electrode is grounded, creating a strong electrostatic field across the filter. This field causes the negative and positive charges within each filter fiber to separate and migrate to opposite sides of the fiber (polarization). Particles entering the filter are similarly polarized, which in combination with the polarized fibers increases the particle capture effectiveness. As organisms are captured on the filter, they are exposed to both electrical field and current generated by the arrays. The combination of stresses on the ➤
ELECTRICALLY ENHANCED FILTRATION Based on research commissioned originally by the United States Department of Energy for the Lawrence Livermore National Laboratory, electrically enhanced filtration technology utilizes a low resistance mechanical filter that efficiently captures airborne particles, and creates a highly inhospitable environment for biologicals. Particles traveling in the air stream move through an ionization array where an electric field charges the passing particles. The particles then enter and are captured on a mechanical filter which is sandwiched between two metal electrodes. The upstream electrode is charged with a high DC voltage,
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May 2008 쩤 25
Organism
Lab
Date
Kill
Spore Forming
Bacillus subtilis (Anthrax surrogate)
Univ. of Colorado
July 2005
97 percent in 24 hours
Gram Positive
Mycobacterium Parafortuitum (Tuberculosis surrogate)
Univ. of Colorado
July 2005
99.9 percent in 24 hours
Staphlococcus aureaus
LMS Technologies
April 2004
97.5 percent at 6 and 100 percent at 12 hours
Serratia marcescens
Univ. of Colorado
October 2005
99.9 percent
LMS Technologies
April 2004
96.6 percent within one hour and 100 percent at 6 hours
Pseudomonas aeruginosa
Univ. of Colorado
October 2005
99.9 percent in 24 hours
Aspergillus versicolor Morbillivirus (Measles)
Univ. of Colorado
July 2005
99 percent in 24 hours
November 2005 Southwest Foundation January 2006 for Biomedical Research
99.9 percent after 45 minutes 94.8 percent after two hours. 96.9 percent after 12 hours.
Physiology Bacteria
Gram Negative
Fungi Virus
Vaccinia (Smallpox surrogate)
Endotoxin
Univ. of Colorado
July 2006
Vaccinia (Smallpox surrogate)
Univ. of Colorado
SARS
Southwest Foundation July 2006 for Biomedical Research
Influenza Wild Type A
Univ. of Colorado
99.9 percent after 18 hours 96 percent after 1 hour and below detectable limits after 2 hours
January 2007
99 percent after 50 minutes
Human Influenza (Wild) Univ. of Colorado
May 2007
99 percent after 100 minutes
Avian Influenza (Wild)
Univ. of Colorado
May 2007
99.9 percent after 200 minutes
Encephalomyocarditis picornaviridae (Human cold virus surrogate)
Univ. of Colorado
Sept 2007
99.99 percent after 6 hours
Serratia marcescens
Univ. of Colorado
August 2006
84 percent after 24 hours
Escherichia Coli
Univ. of Colorado
August 2006
46 percent after 24 hours
Table 1: Inactivation results for tested organisms
26 쩤 May 2008
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microorganism has been shown to effectively inactivate the organism and in some cases rupture the cell membrane. There is evidence of the destruction of endotoxins — allergenic and asthmatic remnants of destroyed microbes — present on the filter. With the collocation of filtration and germicidal mechanisms, even the toughest organisms are exposed long-term to the destructive fields.
EFFECTIVENESS OF ELECTRICALLY ENHANCED FILTRATION Like other pathogens, such as bacteria and fungi, individual viruses vary in their degrees of hardiness and the amount of inactivating force needed to kill them. This filtration technology has been subjected to extensive third-party testing, confirming high germicidal efficiency. Results include: • against Aspergillus, 99 percent destruction was achieved within 24 hours • against Staphylococcus Aureaus, 100 percent inactivation was observed within 12 hours • against Vaccinia spores (a Smallpox surrogate), a 94.8 percent reduction was achieved after two hours and a 96.9 percent reduction after 12 hours In September 2007, Dr. Mark Hernandez from the University of Colorado at Boulder, Dept. of Civil, Environmental and Architectural Engineering in conjunction with
the CDC presented test results of Avian Influenza virus, H5N1, using this filtration technology at the American Association for Aerosol Research annual conference. The results showed a 99.9 percent inactivation of the Avian Influenza virus in 200 minutes. A number of other organisms have been tested and had similar inactivation results (Table 1).
CONCLUSION Although the electrically enhanced filtration technology was initially developed as a general commercial and healthcare air purification technology, it has been implemented in high security facilities and employed as a means to enhance operational effectiveness in clean environments. This technology presents a potential solution to the airborne pathogen and particle threat, deploying new air sanitization technology that both captures and inactivates harmful microorganisms and other dangerous objects in the air stream. It is applicable for whole building, manufacturing facilities, or spot security placements. Electrically enhanced filtration not only captures but inactivates dangerous pathogens, providing air sanitization and protection to facilities. Aaron Ayer is Vice President of Marketing and Frank Stamatatos is Manager, Strategic Partners & Business Development, both for StrionAir Corporation in Louisville, CO. www.strion.com
IN THE NEWS NEW DEVELOPMENT CENTER AND ASEPTIC FACILITY OPENS NEAR BALTIMORE PII (Pharmaceutics International, Inc.) has opened a new 30,000 sq. ft. development, aseptic filling facility, and cGMP manufacturing plant near Baltimore, MD. The new Beaver Court complex complements the three existing PII facilities in Hunt Valley and Pharmaterials in the UK. As part of PII’s growth, the development work has moved to dedicated manufacturing space in the new building. The area consists of multiple manufacturing and containment suites to handle development projects. This area will support projects prior to moving to cGMP production.
ISPE LAUNCHES GAMP® 5 TECHNICAL DOCUMENT ISPE, a global association of pharmaceutical manufacturing professionals, has issued the launch of GAMP® 5: A Risk-Based Approach to Compliant GXP Computerized Systems. The document is the fifth revision of the original document published in 1994. In this major upgrade,
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GAMP® 5 addresses the entire lifecycle of a computerized system, and the principles are applicable to a wide range of information systems, lab equipment, integrated manufacturing systems, and IT infrastructure.
COMPOSITE NANOTECHNOLOGY SLOWS TUMOR GROWTH In laboratory studies conducted at Roswell Park Cancer Institute, researchers discovered that nanocomposite particles carrying radioactive gold directly to tumors reduced cancer growth by 45% in just eight days. This research was published in a recent issue of the Journal of Nanomedicine: Nanotechnology, Biology and Medicine and provides first evidence of the therapeutic use of tumor targeted radioactive nanodevices. The researchers who created the radioactive gold composite nanodevices (CNDs) used nanobrachytherapy to deliver them directly into prostate tumors in laboratory models. The single injection resulted in a statistically significant reduction in tumor volume, when compared to an untreated group and a group injected with a nanodevice without radioactive gold. No clinical toxicity was observed during the experiments.
May 2008 쩤 27
PRODUCT NEWS BENCH TOP LAB The M-110P processor is a bench top lab machine that requires no compressed air or cooling water for hydraulics. The portable processor requires only a standard electrical outlet and can be incorporated into any laboratory setting. It enables the production of nano-suspensions and nano-emulsions, as well as liposomal encapsulation and cell disruption. Microfluidics www.microfluidicscorp.com
FUME HOOD PANELS The oversized FRP Fume Hood Panels are chemical, fume, and smoke resistant that meet or exceed SEFA, UL, and ASTM standards. The panels feature a smooth white interior surface that is durable, easy to clean, and provides high light reflectivity. They also resist staining and discoloration. MFG Composite Systems www.moldedfiberglass.com
OXYGEN ABSORBERS CLASS 100 CLEANROOM OVEN No. 970 is a 500ºF (~260ºC) electrically-heated, Class 100 cleanroom oven that can be used for sterilizing, depyrogenation, curing, and drying workloads. It features a stainless steel powered forced exhauster, two HEPA recirculating air filters, digital and manual reset temperature controller, and recirculating blower airflow safety switch. The Grieve Corporation www.grievecorp.com
The StabilOx® family of specialty oxygen absorbers reduce oxygen levels within the packaged environment to decrease the rate of oxidative degradation, while maintaining relative humidity. It is available in a variety of delivery formats, including packets, labels, canisters, and solid forms. Additionally, it preserves formulation stability and efficacy throughout drug product shelf life. Multisorb Technologies www.multisorb.com
LINEAR SLIDES DOWNFLOW WORKSTATIONS The DWS range of downflow workstations increase operator safety when routine work is being carried out. They were designed to provide a small bench mounted unit with unrestricted access for operations that are difficult to perform in a conventional fume hood. The main filter can be chosen from 14 different types of carbon. Air Science USA www.air-science.com
PLATINUM CURED TUBING
PIPETTE MAINTENANCE
The Class VIA platinum cured tubing has a 50A durometer and various I.D. and O.D. options for biotechnical, medical, and pharmaceutical applications. The tubing has smooth surfaces, few leachables, high clarity, and low protein bonding. It can withstand repeated compressions for consistent, dependable performance. Qosina www.qosina.com
This total care service provides calibration, repair, and preventive maintenance services on over 800 models of pipettors. The service meets or exceeds laboratory GLP requirements, including ISO 8655 compliant calibration and repair. Custom calibration services are available upon request. It ensures that pipettes will perform accurately and precisely. PipetteMD www.pipettemd.com
TRANSMITTING DATA LOGGER The TrackSense® Pro Sky Transmitting Data Logger allows users to view real time data, statistics, and lethality calculations. The Data Logger has a temperature range of -80 to 140°C and a transmission range of 50 ft. It features low setup time, accuracy, stability, the elimination of slip rings, and vessel integrity. Ellab www.ellab.com
28 쩤 May 2008
The RGSW and RGSWX Series Slides were designed for packaging, assembly, medical and life sciences, semiconductor manufacturing, and factory automation. Both series offer thick wide bases and direct sensor mounting systems. Requiring no maintenance or lubrication, the anti-backlash slides can be manufactured in lengths up to eight feet. Kerk Motion Products www.kerkmotion.com
FILTERS The Protec® RM filter is available in 0.2 µm, 0.3 µm, and 0.5 µm ratings. They combine an outer layer of borosilicate glass microfiber media with an inner layer of hydrophilic PVDF membrame. The filters protect downstream membrane filters and equipment, while removing colloids, aggregated and non-product proteins, lipids, and other particles. Meissner Filtration Products www.meissner.com
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P R O D U C T F O C U S BENCHES, STORAGE, FURNITURE
MODULAR DRAWER STORAGE These modular drawer cabinets have a large storage capacity and provide safe and secure storage of valuable laboratory equipment, glassware, and instruments. The modular casework protects objects from dirt and other elements, and allows a variety of differently sized and shaped items to be stored. LISTA INTERNATIONAL www.listaintl.com
STORAGE LOCKERS These storage cabinets are specifically designed to provide the sheltered clean space necessary for the storage of tools, instruments, clean parts, garments, glassware, or any other critical materials used in the cleanroom. Options include HEPA filtration, pass-thru chambers, and garment disposal receptacles. Constructed in stainless steel, epoxy painted steel, and plastics. ATMOS-TECH INDUSTRIES www.atmostech.com
CLEANROOM BENCHES AND TABLES Clean benches are offered in a variety of models for controlling airborne contamination within small spaces. Transfer carts provide HEPA filtered air while transporting components. Cleanroom tables are offered with laminate work surface or all stainless steel construction, swivel casters with brakes, and 600 lb. capacity. CLEAN ROOMS INTERNATIONAL www.cleanroomsint.com
GARMENT STORAGE CABINET The model 7200MH Motorized HEPA filtered garment storage cabinet is manufactured in 3/4" novaply laminated in high pressure white plastic. Garments are bathed in Class 100 (ISO 5) clean air. The cabinets feature a plexiglass door, overlapping closure, and chrome plated hinges and leg levelers. LIBERTY INDUSTRIES www.liberty-ind.com
STAINLESS STEEL WORK BENCH The OpenTop™ Perforated Top benches feature hidden reinforcements that minimize dead spots and eliminate deflection bounce-back. The benches have a one-piece bullnose for worker comfort that increases vertical laminar airflow without welds or cracks. The rod tops feature rods floating in a non-outgassing elastomer that dampens noise and vibration. TERRA UNIVERSAL www.terrauniversal.com
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May 2008 쩤 29
31 Mitchell Road Pittsfield, New York 14543-2301 Tel: 585-264-9430 Fax: 585-264-9522 31 Mitchell Road, Pittsford, New York 14543-2301 [email protected]
Tel. 585-264-9430 • Fax. 585-264-9522
e-mail: [email protected] www.cleanroom-consulting.com
www.cleanroom-consulting.com
Principal, Scott E. Mackler Principal, Scott E. Mackler
30 쩤 May 2008
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This informative book by John Durkee Ph.D., P.E., covers all aspects of modern cleaning technologies, including environmental regulations.
Howard Siegerman, Ph.D. Consulting Services • Contamination Control • Facility Audits • Precision Cleaning • Training Seminars • Analytical Chemistry • Test Method Development • Strategic Planning
Siegerman and Associates, LLC Telephone: 201.666.2977 e-mail: [email protected]
PrecisionCleaning.com
PENCIL IT IN... May 4-7, 2008 ESTECH 2008 Bloomingdale, IL www.iest.org
May 7-8, 2008
Best Practices for an Effective Cleaning Validation Program Costa Mesa, CA www.cfpie.com
May 13-15, 2008
SLC Europe 2008 Swissôtel Düsseldorf, Germany www.supplychain.eu.com
May 14, 2008
European Supply Chain Distinction Awards 2008 Swissôtel Düsseldorf, Germany www.supplychainawards.com
May 14-15, 2008
Free Humidity Measurement Training Seminar Detroit, MI www.vaisala.com/seminars
June 1-5, 2008 Nanotech 2008 Boston, MA www.nsti.org
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June 10-11, 2008
Sterilization Procedures: Technology, Equipment, and Validation Malvern PA www.cfpie.com
June 11-12, 2008
Free Humidity Measurement Training Seminar Baltimore, MD www.vaisala.com/seminars
July 15-17, 2008 SEMICON West 2008 San Francisco, CA www.semiconwest.org
September 8-12, 2008 2008 PDA/FDA Joint Regulatory Conference Washington, DC www.pda.org
June 12-13, 2008
September 15-18, 2008
Cleanroom Microbiology for the Non-Microbiologist Malvern, PA www.cfpie.com
ISPE Conference on Quality By Design/Design Space Manchester, UK www.ispe.org
June 23-25, 2008
September 17-18, 2008
Technical Tutorial for Latchup/ ESD-Device Design and ESD-Test. ESD Association and Fraunhofer Institute for Reliability and Microintegration IZM Munich, Germany www.esda.org
July 14-16, 2008
AGS Annual Conference Daytona, FL www.gloveboxsociety.org
DISKCON 2008 USA Santa Clara, CA www.idema.org
October 8, 2008 ISPE Boston Area Chapter Product Showcase and Seminars Foxborough, MA www.ispe.org
October 26-29, 2008 ISPE Annual Meeting Boca Raton, FL www.ispe.org
May 2008 쩤 31
CRITICAL CLEANING FOR CONTAMINATION CONTROL JOHN DURKEE, Ph.D., P.E.
High Solubility or Low Surface Tension — Take Your Pick This column is about compromise — why it’s chemically impossible to have the solvent you want. In critical cleaning, we want solvents with low surface tension, say less than 15 dynes/cm, so that the liquid can penetrate between particles and the surfaces they are contaminating. In critical cleaning, or any cleaning, we want solvents which dissolve the soils about which we have concern, such as adhesives used in the manufacture of disk drives. The problem is we can’t have both. This column is about why that is so.
A TIME FOR SIMPLICITY Briefly, one needs intermolecular forces to dissolve soils, and intermolecular forces produce surface tension forces.
THE SCIENCE OF SOLUBILITY Ideas of Professor Joel Henry Hildebrand (1881-1983, University of California, Berkeley), and the work derived from them, allowed development of a useful system of solubility characterization. Hildebrand’s basic idea was that dissolution (or solubility) occurs when there is an energy match within a fluid. Specifically, the attractive interaction energy of the solvent molecules must approximate the attractive intermolecular energy in the solute (soil). Hildebrand showed that these energy requirements were at a minimum if the solute (soil) and solvent exerted the same forces upon one another. Hildebrand created a parameter, named after him, which quantifies the level of intermolecular force so that solvents can be matched with soils. Higher values of the Hildebrand Solubility Parameter (HSP) have higher values of intermolecular force — what’s often wanted in cleaning operations.
er inside the liquid, and much less so by the molecules in the adjacent medium (vacuum, air, a solid surface, or another liquid). Molecules at a boundary have fewer neighbors than interior molecules. They exist in a higher state of energy. Minimization of solvent energy, at a given temperature and pressure, means minimization of the number of surface molecules. In other words, the thermodynamic state of minimum energy requires a minimum of surface area — the surface with the “smoothest” curvature. So, solvents with high levels of intermolecular forces have high values surface tension — what’s not wanted in cleaning operations.
A TIME FOR COMPROMISE A plot of the Hildebrand Solubility Parameter vs. surface tension is shown in Figure 1. Solvents such as PFCs, paraffins, HFCs, HFEs, and CFCs have low levels of intermolecular force, low values of HSP, and low values of surface tension. They will therefore match up with soils which share that condition — for which no adhesives need apply. So is the opposite true, as is shown by Figure 1. Nmethyl pyrrolidone, used to remove adhesives from disk drive components, has a surface tension of 40.7 dynes/cm. Water, the “perfect” solvent (it’s not, but that’s
THE SCIENCE OF SURFACE TENSION Surface tension is another effect of the intermolecular forces within solvent molecules. It may seem trivial, but there is no surface tension in the bulk mass of a fluid. It is only at a surface where there is an unbalanced force. At a liquid surface, solvent molecules are pulled inwards by other molecules deep-
32 쩤 May 2008
Figure 1: Total Solubility Parameter vs Surface Tension
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NOW AVAILABLE another column), has a surface tension value of 71.4 dynes/cm. Next time you want to wash particles from surfaces with water, and use no mechanical force with sonic transducers, or want to clean soils having high levels of hydrogen-bonding with HFEs, you’ll know why you’re unlikely to be successful doing either one. 1. A benchmark reference about intermolecular forces and energy transfers within solvents is: Hildebrand, J. and Scott, R.L., Regular Solutions, Prentice-Hall, Englewood Cliffs, NJ, 1962. 2. A commonly used and numerically equivalent unit for surface tension is mili-Newton/meter (mN/m).
ON AMAZON.COM
John Durkee is the author of the book Management of Industrial Cleaning Technology and Processes, published by Elsevier (ISBN 00804-48887). He is the author of the forthcoming book Solvent Cleaning for the 21st Century, also to be published by Elsevier, and is an independent consultant specializing in critical cleaning.You can contact him at PO Box 847, Hunt, TX 78024 or 122 Ridge Road West, Hunt, TX 78024; 830-238-7610; Fax 612-677-3170; or [email protected].
A D V E RT I S E R I N D E X COMPANY
PAGE
ARAMARK Cleanroom Services .......................................7 American Glovebox Society Annual Conference ..............25 Berkshire Corporation .....................................................2 Biotest Diagnostics Corporation......................................35 Clean Air Solutions, Inc.................................................30 Clean Air Technology Inc...............................................30 Clean Rooms International, Inc.........................................4 Cleanroom Consulting ..................................................30 Controlled Contamination Services, LLC ..........................17 Crest Ultrasonics Corp ..................................................30 IDEMA ........................................................................20 KNF CleanRoom Products Corp........................................6 Monroe Electronics .......................................................30 Noblemen International...................................................5 Pegasus Cleanroom Services, Inc. ..................................30 Perfex Corporation .........................................................9 Plascore, Inc. ...............................................................21 S-Curve Technologies ....................................................30 SEMICON West...........................................................15 Siegerman and Associates.............................................31 Terra Universal, Inc. ......................................................36 TSI ...............................................................................6 Ultratape Industries, Inc.................................................30 Vaisala, Inc. ................................................................13 Veltek Associates, Inc. ...............................................3, 30
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Wiping Surfaces Clean: a concise, practical guide to removing surface contamination
Howard Siegerman, Ph.D., shares his technical expertise and explains this important element of successful contamination control. This essential working reference helps controlled environments professionals develop effective cleaning protocols and techniques.
Order Your Copy Today! Only $49.95 (+shipping)
May 2008 쩤 33
CONTAMINATION CONTROL
IN
AND
OUT OF THE CLEANROOM
Are the Cleaning Agents Clean Enough? PART II: WATER BARBARA KANEGSBERG AND ED KANEGSBERG
Water is the most common cleaning solvent for manufacturing processes. Water purity determines the quality of the final product. However, selecting the appropriate water for the application may not be readily apparent.
filtering, distillation, and deionization (DI). Reverse osmosis (RO) is a commonly employed filtering process, one that is frequently combined with ion removal processes.
TAP WATER
We hear medical device manufacturers assert, “We’re OK; we use USP Purified Water (PW) or Water for Injection (WFI).” These designations do not insure that this is pure enough for all critical cleaning applications; the water may still contain undesirable amounts of inorganics. USP PW and WFI are defined by Section of the United States Pharmacopeia (USP). To meet the concerns of chlorine and microbial contamination, PW must meet the EPA NPDWR and also Total Organic Carbon (TOC) and electrical conductivity specifications. The conductivity spec is lower than a single-pass RO but not as low as DI. WFI is the same as PW with an additional microbial endotoxin specification.
Too many manufacturing cleaning operations use tap water. It is important to keep in mind that the requirements and goals of municipalities and manufacturers differ. Community health is the primary driver of drinking water specifications. Manufacturers need to acquire desired surface qualities. Tap water must comply with the EPA National Primary Drinking Water Regulations (NPDWR). Municipalities may add further requirements. Drinking water may contain solid, organic, and dissolved substances that can interfere with industrial processes. Most localities purposefully add chlorine or chloramines as disinfectants; some add fluorides. The quality of water can vary greatly from location to location, and seasonally in a given location. This lack of control and consistency makes tap water undesirable for industrial applications.
ION CONTENT One measure of ion content is electrical conductivity. The highest purity water has a conductivity of 0.055 micro-Siemens per centimeter, (S/cm). For low conductivities (