IAQ Trends: Clearing The [Indoor] Air On Improving IAQ
By Andrew Persily, Ph.D., Fellow ASHRAE
Published in the November 2009 issue of Today’s Facility Manager
Few people are aware that levels of many indoor air pollutants can be several times higher than the levels outside. As a result, building occupants frequently inhale about 30 pounds of air each day (but only drink about four pounds of water and eat about two pounds of food). Oddly enough, most people worry much more about the quality of the water they drink and the food they eat than the air they breathe.
Over the last several decades, much progress has been made towards improving air quality outdoors. During this same time, there hasn’t been as much attention on indoor air. In fact, things may actually be worse, as new contaminants are introduced into the indoor environment and a lack of maintenance leads to lower ventilation rates.
Buildings are expected to fulfill a variety of requirements as defined by their intended function and by applicable codes and standards. Indoor air quality (IAQ) is typically addressed through compliance with minimum code requirements, which are based on industry consensus standards such as ASHRAE Standard 62.1, Ventilation for Acceptable Indoor Air Quality. Yet, IAQ affects occupant health, comfort, productivity, and in some cases even building usability, all of which can have significant economic impacts for owners, facility managers (fms), and building occupants.
IAQ Compromises Can Be Risky Business
While facility owners and managers may recognize the importance of IAQ, they often do not appreciate how routine design, construction, and operation decisions can result in IAQ problems. Additionally, they may assume that achieving a high level of IAQ is associated with premium costs and novel or even risky technical solutions. In other cases, they may employ individual measures thought to provide good IAQ, such as increased outdoor air ventilation rates or specification of lower emitting materials, without a sound understanding of the actual impacts of these measures or a systematic assessment of IAQ priorities.
While serious IAQ problems do occur in buildings, information exists to achieve good IAQ without incurring excessive costs or employing practices that are beyond the current capabilities of building professionals.
One source of information is a new guide written by six leading organizations in the building community. The guide presents best practices for design, construction, and commissioning.
The Indoor Air Quality Guide, Best Practices for Design, Construction, and Commissioning, slated for publication in the fourth quarter of 2009, serves as a comprehensive and practical resource aimed at helping achieve better IAQ in commercial and institutional buildings.
The book was written by a team of IAQ experts coordinated by the American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE), American Institute of Architects (AIA), Building Owners and Managers Association International (BOMA), U.S. Environmental Protection Agency (EPA), Sheet Metal and Air Conditioning Contractors’ National Association (SMACNA), and U.S. Green Building Council (USGBC).
The information in this guide is based on the IAQ problems that have been occurring in commercial and institutional buildings for several decades. It builds on the authors’ experiences in investigating, resolving, and avoiding these problems. These problems relate to issues in several major categories, which are used to organize the information contained in the guide.
Important Aspects Of IAQ Issues
What follows is a breakdown and brief description of the key sections of the guide.
IAQ during design and construction. Many problems are the result of IAQ not being considered at the beginning of the design process. Basic design decisions related to site selection, building orientation, location of outdoor air intakes, and how the building will be heated, cooled, and ventilated are of critical importance to providing good IAQ. Efforts to achieve high levels of building performance without diligent consideration of IAQ at the beginning of the design process can lead to problems and represent missed opportunities to ensure good IAQ.
Lack of building commissioning. While a good design is critical to providing good IAQ, improper installation or commissioning can seriously compromise indoor air conditions. Therefore, a key factor in achieving good IAQ is a serious commitment to a comprehensive commissioning effort that starts in the design phase and continues well into occupancy. This effort should include a focus on commissioning of systems and assemblies critical to good IAQ.
Moisture in building assemblies. There have been many notable cases of IAQ problems associated with excessive levels of moisture in building assemblies, particularly in the building envelope. Such situations can lead to mold growth that can be very difficult to fix without major renovation efforts and costs. Moisture problems arise for a variety of reasons, including roof leaks; rain penetration through leaky windows; envelope design and construction defects (such as low permeability wall coverings in hot and humid climates); and poor building pressure control. These problems are largely avoidable, but they require an understanding of building moisture movement, attention to detail in envelope design and construction, and awareness of mechanical system selection, installation, and operation.
Poor outdoor air quality. The traditional means of dealing with IAQ is through outdoor air ventilation. And while this can be an effective way to dilute indoor contaminants, it assumes the outdoor air is cleaner than what’s inside. In many scenarios, this is not the case, and insufficiently treated ventilation air can actually make IAQ worse. Poor exterior air quality includes regionally elevated outdoor contaminant levels as well as local sources (such as motor vehicle exhaust from nearby roadways) and contaminants generated by activities in adjacent buildings. Some programs to encourage higher levels of building performance recommend increasing outdoor air ventilation rates, but such recommendations need to consider the potential impacts of poor outdoor air quality. It should be noted that ASHRAE Standard 62.1 requires the assessment of outdoor air quality in the vicinity of a building and requires outdoor air cleaning under some circumstances.
Moisture and dirt in ventilation systems. Dirt accumulation in ventilation systems, combined with poor management of water, can lead to biological growth and serious IAQ problems. These conditions generally result from inadequate levels of particle filtration, poor filter maintenance, and problems with cooling coil condensate or other moisture sources. ASHRAE Standard 62.1 contains several requirements related to dirt and moisture management in ventilation systems. The new guide addresses the topic in more detail, given the seriousness of the problems that can result.
Indoor contaminant sources. Many IAQ problems are associated with indoor contaminant sources that are unusually strong or otherwise cannot be handled by typical or code compliant levels of outdoor air ventilation. Many contaminants are released by normal building materials and furnishings, especially when new, along with materials and substances brought into the building during occupancy. Unusual, unexpected, or high contaminant emissions from indoor sources are associated with many IAQ problems, and the guide addresses the issue of material selection, cleaning, and other indoor source concerns.
Contaminants from indoor equipment and activities. The wide range of occupancies and activities in commercial and institutional buildings involve many different types of equipment and activities. Many IAQ problems can be avoided through proper equipment operation, adequate exhaust ventilation, and careful choices of materials used in these activities.
Inadequate ventilation rates. While building codes and standards have addressed outdoor air ventilation for decades, many buildings and spaces are poorly ventilated, which increases the likelihood of IAQ problems. There are a variety of reasons for inadequate ventilation rates, including: lack of compliance with applicable codes and standards; installation or maintenance problems that lead to the failure of the design ventilation rate in practice; and space use changes without an assessment of the need for updated ventilation rates. Also, system level outdoor air intake rates may be adequate, but air distribution problems can lead to certain areas in the building being poorly ventilated. While ASHRAE Standard 62.1 covers the determination of design ventilation rates, additional guidance can be very helpful in addressing these issues.
Ineffective filtration and air cleaning. Filtration and air cleaning are effective means of controlling many indoor air pollutants, particularly those associated with poor outdoor air quality. Filtration or cleaning can therefore provide an important adjunct, and in some cases, a substitute for outdoor air ventilation. The guide provides alternatives which, when properly maintained, can improve IAQ and energy performance.
The health and comfort of building occupants is vital. IAQ should never be considered a mere afterthought. There is a vast amount of experience out there to help facility professionals avoid IAQ problems in buildings, ensuring that occupants have access to excellent indoor air. In the end, everyone will breathe a little easier.
Persily, Ph.D., Fellow ASHRAE, is chair of ASHRAE’s Advanced Indoor Air Quality Design Guide Steering Committee and formerly served as chair of the Standard 62.1 committee, Ventilation and Indoor Air Quality.