HVAC Systems Design Handbook part 21

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HVAC Systems Design Handbook part 21

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The concept of indoor air quality (IAQ) is not new. Publications as far back as the early 1800s discuss the subject and suggest ventilation as the solution. These early writers mostly recommended a minimum of 5 ft3 /min of outdoor air per person, but later writers increased that number. The present ASHRAE Standard 62 value is 20 ft3 /min for normal situations.

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  1. Source: HVAC Systems Design Handbook Chapter Indoor Air Quality 21 21.1 Background The concept of indoor air quality (IAQ) is not new. Publications as far back as the early 1800s discuss the subject and suggest ventilation as the solution. These early writers mostly recommended a minimum of 5 ft3 /min of outdoor air per person, but later writers increased that number. The present ASHRAE Standard 62 value is 20 ft3 /min for normal situations. Most of this early work was done in England, where a number of public buildings were provided with heating and ventilating systems, including the House of Commons. Centrifugal fans were developed, using small steam engines for motive power. Schools were a prime target for ventilation, and by the early part of the twentieth century the schoolroom unit ventilator was developed and advertised. Electric motors were available by then. A three-story elementary school, built in 1916, included an outdoor air-ventilation system with a direct cur- rent motor-driven supply fan (rheostat control provided manual vari- able volume!) and cast iron steam-heating coils in the ventilation air for winter use. When the new science of air cooling came along, the value of introducing outdoor air through the cooling/heating system was obvious. And, as the material in the previous parts of this book shows, present technology allows us to control outdoor air ventilation very accurately. But there is a great deal more to improving IAQ than simply using outdoor air. Outdoor air is not necessarily ‘‘better’’ than indoor air, and simple ventilation is not enough. We must also control humidity; tem- perature; gaseous, particulate, bacterial and allergen contaminants; as well as air movement within occupied spaces in order to provide a comfortable and healthy environment. 501 Downloaded from Digital Engineering Library @ McGraw-Hill (www.digitalengineeringlibrary.com) Copyright © 2004 The McGraw-Hill Companies. All rights reserved. Any use is subject to the Terms of Use as given at the website.
  2. Indoor Air Quality 502 Chapter Twenty-One The subject of moisture in buildings is primarily the responsibility of the architect, but the HVAC designer must be aware of conditions that might lead to problems, such as mold, which might be aggravated or alleviated by HVAC design. 21.2 Negative Effects of Poor Air Quality Two terms are important: building related illness (BRI) and sick build- ing syndrome (SDS). BRI relates to individual illness due to poor IAQ. Much of this relates to allergens, to which some people are more sen- sitive than others. SBS means that many people become sick in the building environment, and this, of course, causes loss of production and, perhaps, lawsuits. In addition, there are problems with odors (including those caused by smoking) and problems with high or low humidity. High humidity may allow mold growth and deterioration of the building or furnishings. Excessive air movement (drafts) is a com- mon complaint. When people are sick or complaining, they are not producing. 21.3 Positive Effects of Air Quality Many studies have shown an increase in productivity of 10 percent or more, when the air quality and other environmental factors are opti- mized, and there is less time off for sickness and fewer complaints. Housekeeping and cleaning are made easier and less expensive. Thus, good IAQ is economically advantageous, and it improves the morale of the people who work and live in the building. 21.4 Sources of Poor Air Quality Air contaminants of importance in commercial buildings include par- ticulates, formaldehyde from cigarette smoke, chemicals emitted from building materials (carpet, wall coverings, finishes), chemicals from cleaning agents, emissions from people (methane, perfume, smoking), cooking odors, plus any similar contaminants brought in with the out- side air. There are many ‘‘war stories’’ about incinerators or trash rooms adjacent to outdoor air louvers. In one incident a high-rise office building became thoroughly contaminated when smoke from a nearby fire was brought in through the air system outside-air intake. High- humidity climates require special treatment of outdoor air. 21.5 Attaining Good IAQ: Responsibilities of the Designer It is obvious that the air-conditioning system must be designed to pro- vide good air quality when properly maintained and operated. So the Downloaded from Digital Engineering Library @ McGraw-Hill (www.digitalengineeringlibrary.com) Copyright © 2004 The McGraw-Hill Companies. All rights reserved. Any use is subject to the Terms of Use as given at the website.
  3. Indoor Air Quality Indoor Air Quality 503 primary responsibility resides with the designer. This book has dis- cussed all of the facets of designing a good HVAC system, but we have not talked about the other influences on air quality. As designers, we must also try to ascertain what types of interior finish are being used. If building materials, carpets, wall coverings, finishes, etc., contain materials that may ‘‘offgas,’’ and thus denigrate the air quality, we should raise the red flag. If we must cope with such a situation, then special filtration or irradiation may be required. For removal of the most common gases, adsorption filters are used. These use a filter of activated charcoal and potassium permanganate, which in combination will adsorb carbon dioxide and carbon monoxide, as well as ozone, some odors, and some other gases. Other adsorbents may also be used. See Ref. 1. Ultraviolet irradiation can be used, particularly for bacteria. This is an unusual and special treatment but effective when needed. When the outdoor air quality is poor, it may be desirable to use prefilters followed by high-efficiency filters to remove particulate mat- ter. Remember that no filter system is better than its mounting sys- tem. Leaks and bypassed air do not get filtered. Air washing may also be used but may require additional humidity control. When outdoor air is very humid, it may be desirable to use pretreat- ment of outdoor air to reduce the humidity before introducing it to the main air system. Avoid outside air-intake louver locations close to possible sources of gases, smoke, or odor. Check on the prevailing wind when making this investigation. It helps also to know something about airflow around buildings (which has not been discussed in this book). Properly de- signed and installed smoke detectors are essential in outdoor air or mixed-air ducts. It is necessary to control VAV systems to maintain minimum out- door air quantities over the entire range of supply air flow rates. Also, with VAV, supply air diffusers must be designed to provide good air distribution patterns at all air flow rates. Control systems will often require sensing of gaseous concentra- tions, particularly carbon monoxide, carbon dioxide, and formalde- hyde. This sensing may be used to increase or decrease outside air quantities or to warn of failure of the filtering, smoke detection, or irradiation systems. 21.5.1 Commissioning All of our design efforts are of no value if the IAQ system is not con- structed and commissioned as designed. See the section on commis- sioning in Chap. 14. This must include training of maintenance per- Downloaded from Digital Engineering Library @ McGraw-Hill (www.digitalengineeringlibrary.com) Copyright © 2004 The McGraw-Hill Companies. All rights reserved. Any use is subject to the Terms of Use as given at the website.
  4. Indoor Air Quality 504 Chapter Twenty-One sonnel in the maintenance and operation of equipment which, since these are new concepts, may be considered unusual or even exotic. 21.5.2 Maintenance and use Even though the IAQ system is properly designed and installed, and is functioning, it is essential that it be competently maintained and operated. This should result from the training at commissioning. One of the designer’s duties is to convince the owner of the necessity and value of these things. It is not always an easy task. One valuable argument is the research data which show that the cost of sick, un- well, or unhappy workers is much greater than the cost of doing the proper maintenance and operation. The owner should also be re- minded that poorly maintained equipment will not provide the ex- pected environment. References 1. ASHRAE Handbook, 1999 Applications, Chap. 44, ‘‘Control of Gaseous Indoor Air Contaminants.’’ 2. B. Donaldson and B. Nagengast, Heat and Cold, ASHRAE, 1994. 3. William J. Fisk, ‘‘How IEQ Affects Health, Productivity,’’ ASHRAE Journal, May 2002. 4. H. E. Barney Burroughs, ‘‘IAQ, An Environmental Factor in the Indoor Habitat,’’ Heating, Piping Air Conditioning, February 1997. 5. W. S. Cain, J. M. Samet, and M. Hodgson, ‘‘The Quest for Negligible Health Risk from Indoor Air,’’ ASHRAE Journal, July 1995. 6. Roy Kelley, ‘‘Room Air Circulation: The Missing Link to Good Air Quality,’’ Heating, Piping, Air Conditioning, September 1995. 7. Robert Scarry, ‘‘Looking Into Sick Buildings,’’ Heating, Piping, Air Conditioning, July 1994. 8. Federal Register, Regulations for Indoor Air in Workplaces. 9. Milton Meckler, ‘‘Indoor Air Quality from Commissioning Through Building Oper- ations,’’ ASHRAE Journal, November 1991. 10. S. M. Stewart, ‘‘Reaching Agreements on Indoor Air Quality,’’ ASHRAE Journal, August 1992. 11. R. P. Gaynor, ‘‘Developing an IAQ Management Plan for Commercial Buildings,’’ Heating Piping, Air Conditioning, August 1993. Downloaded from Digital Engineering Library @ McGraw-Hill (www.digitalengineeringlibrary.com) Copyright © 2004 The McGraw-Hill Companies. All rights reserved. Any use is subject to the Terms of Use as given at the website.
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