Poor indoor-air quality (IAQ) is more than just a nuisance; it is costly. For example, total costs to the U.S. economy because of poor IAQ reach as high as $168 billion per year.1 Part of those costs comes from direct medical care and absenteeism, while other costs are related to “presenteeism” — a problem that occurs when employees go to work sick and suffer productivity losses as a result.
Poor IAQ significantly influences the occurrence of communicable respiratory illnesses and allergy, asthma, and sick-building symptoms. Some of the airborne triggers for these illnesses include microorganisms; respirable particles such as dust and smoke; volatile organic compounds; and allergens.
Ideally, these triggers are eliminated or reduced significantly by the air filters in a building's HVAC system. Advances in air filtration have led to the development of systems that provide superior IAQ while reducing energy costs and helping commercial and institutional buildings achieve green-building milestones.
AIR FILTRATION AND IAQ
The average human breathes in about 16,000 qt of air, which contain about 70,000 visible and invisible particles, each day. The U.S. Environmental Protection Agency (EPA) notes that indoor air often is two to five times more polluted than outdoor air. Most of the “respirable” dust and other particles people breathe into their lungs are a fraction of the size of a grain of sand (Figure 1).
Removal of all airborne contaminants is not practical in most facilities. Therefore, once problematic pollutants are identified, it is time to look at filter efficiency. Filtration efficiency is defined by how well a filter cleans indoor air by removing airborne particles. Low-efficiency filters — those that are 25-percent-efficient in removing particles 3 to 10 µm in size — typically are used to keep lint and dust from clogging the heating and cooling coils of HVAC systems. Medium- and high-efficiency filters — those that are up to 95-percent-efficienct in removing particles measuring 3 to 10 µm in size — typically are used to remove mold, pollen, soot, and other small particles.
Effective air filtration provides the primary defense against such pollutants. But just what is effective air filtration? The American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE) has a test standard that quantifies the air-cleaning performance of HVAC filters. ASHRAE Standard 52.2-2007, Method of Testing General Ventilation Air-Cleaning Devices for Removal Efficiency by Particle Size, measures a filter's ability to remove airborne particles 0.3 and 10 µm in size. A minimum-efficiency reporting value (MERV) is assigned to a filter based on its efficiency in three different particle-size ranges (0.3 to 1 µm, 1 to 3 µm, and 3 to 10 µm). The higher the MERV, the greater the ability to remove high quantities of small particles from air (Table 1).
FILTERS AND ENERGY CONSERVATION
While HVAC filters play an important role in removing airborne contaminants and protecting HVAC equipment from dust that can cause coil fouling and increase operating costs, they also play a significant role in minimizing the energy consumed to operate an HVAC system. The amount of energy consumed is based on the level of resistance to air passing through a filter. There lies the opportunity for filters to be used as a method of energy conservation, as the lower a filter's resistance to airflow, the lesser the amount of energy consumed.
Filter media — the material inside a filter frame that captures particles — actually has the largest impact on airflow resistance, energy consumption, and energy costs. The composition (e.g., fiberglass or polymer-based synthetics) and structure (i.e., the shape and size of individual fibers and how they combine) of filter media impact airflow resistance. When an HVAC motor has to work harder to deliver the required airflow, energy consumption and costs increase.
Many users think of HVAC filters and filter media as commodity products with little difference in performance. Recent advances in filtration-media technology, however, show that is not the case. With price typically the determining factor in choice of filter and media type, it is important to understand that ensuing energy costs can far outweigh initial filter price. Because they control the majority of an HVAC air-handling system's energy consumption and, thus, a majority of its operating costs, filters should be perceived as a means to conserve energy.
To use a filter as an energy-conservation tool, consider the total life-cycle cost of the filter and the long-term impact it will have on energy costs. More-energy-efficient filters do not necessarily cost more, so energy savings often can be achieved without an additional investment. Life-cycle costs, energy costs, and a filter's resistance to airflow should come into play during the filter-selection process.
The three major components of life-cycle costs for HVAC filters are initial investment and maintenance, energy consumption, and disposal. On average, energy costs account for 81 percent of a filter system's total life-cycle cost. Initial investment and maintenance account for 18 percent, while disposal accounts for 1 percent.3
To apply the life-cycle costs of filters to energy efficiency, consider a filter's resistance to airflow as measured by Standard 52.2-2007. Development of new materials has given the filter industry a chance to produce filtration media with lower airflow resistance while maintaining high particle-capture efficiencies, thereby providing the ability to improve IAQ and reduce energy costs simultaneously.
Switching to filters with low airflow resistance is one of the easiest ways to reduce energy costs, as with less airflow resistance, an HVAC-system motor does not have to work as hard to deliver required airflow.
Table 2 illustrates the effect of a filter's airflow resistance on annual energy costs. Filters A and B are identical, except for their initial airflow resistance. Filter A provides less initial and average airflow resistance, saving about $29 in energy costs per filter annually.
From a macroscale standpoint, the overall impact of energy consumed by commercial-building HVAC systems can be estimated by considering that commercial buildings account for just over 30 percent of the energy consumed in the United States and that heating and cooling account for 40 percent of a commercial building's total electricity bill. At an average cost of 8 cents per kilowatt-hour, commercial buildings in the United States consume about $65 billion in energy per year — $26 billion of which comes from HVAC-system operation.
A change in a filter's airflow resistance can affect total energy consumption. This can be estimated by assuming that average airflow resistance can be reduced by 0.025 in. wg with the use of a commercial building filter. For example, assume that it is reduced from 0.700 to 0.675 in. wg. By applying a simple ratio to an energy formula — 325 billion kwh ÷ 0.700 in. wg equals × ÷ 0.675 in. wg — the total energy used is 313 billion kwh. At a cost of 8 cents per kilowatt-hour, this results in a savings of 12 billion kwh, which translates to a savings of $960 million. To put this into perspective, filter manufacturers and distributors would have to reduce filter prices by approximately 50 percent to provide this level of savings.
USING FILTERS TO ACHIEVE LEED CREDITS
HVAC filter systems provide an often-overlooked way to earn credits under the U.S. Green Building Council's (USGBC's) Leadership in Energy and Environmental Design (LEED) Green Building Rating System. While no individual product or system can be LEED-certified, a proper HVAC air-filtration system and strategy can help contribute to the completion of LEED for Existing Buildings (LEED-EB) prerequisites and credits. Filters have a direct impact on Indoor Environmental Quality (IEQ) Credit 3, Construction IAQ Management Plan, and IEQ Credit 5, Indoor Chemical and Pollutant Source Control. However, filters also support LEED principles in other ways — especially in the areas of reducing energy costs and waste, eliminating sources of indoor pollution, and improving building IAQ (Table 3).
CLEANER AIR IS GREENER AIR
In addition to providing for superior IAQ and reducing energy consumption, HVAC filter selection has a direct effect on a number of green-building issues, including:
Greenhouse-gas emissions: A 0.05-in.-wg reduction in a filter's initial airflow resistance can reduce carbon-dioxide (CO2) emissions by up to 4 percent, or 120 lb per filter. A 0.20-in.-wg reduction in a filter's initial airflow resistance can reduce CO2 emissions by up to 9 percent, or 480 lb per filter.
Raw-material use: Some filters provide better performance using less media than other filters. In addition, filter media can be made with recycled polymer from manufacturing waste streams.
Waste output: High-capacity pleated filters can extend filter life and reduce changeouts. Extended filter life can reduce waste streams while minimizing resistance to airflow.
Careful selection of HVAC filters and filter media can improve IAQ, save money, and reduce waste while helping to earn LEED credits.
Fisk, W.J., & Rosenfeld, A.H. (1997). Estimates of improved productivity and health from better indoor environments. Indoor Air, 7, 158-172.
NAFA user's guide for ANSI/ASHRAE 52.2-1999: Method of testing general ventilation air-cleaning devices for removal efficiency by particle size. (n.d.). Retrieved from http://www.nafahq.org/Articles/Article006.htm
Carlsson, T. (2001). Indoor air filtration: Why use polymer based filter media. Filtration+Separation, 38, 30-32.
David Matela, CAFS, is a market manager with Kimberly-Clark Filtration Products, a supplier of HVAC filter media. He has worked for the company for 11 years, during which he has been involved in consumer-product development and nonwoven-material and process development, areas in which he holds eight patents. He can be contacted at email@example.com.