2 FM quick reads on Air filtration
1. Air Filter Improvements Help Efficiency Efforts
Today's tip is to be aware of changes in the air-filtration industry. Manufacturers have created new products that not only have improved indoor air quality but also have reduced the cost of installing and operating air-filtration equipment.
As maintenance and engineering managers continue to focus on IAQ and its impact on their facilities and occupants, manufacturers are providing them with more efficient HVAC systems and components, including air filters. This technology reduces pressure drops and improves filter efficiency.
ASHRAE has been promoting the minimum efficiency reporting value system to standardize definitions. MERV measures a filter's arrestance (ability to remove large airborne particles from the air) and dust-spot efficiency (ability to remove small airborne particles). Common commercial HVAC systems include:
Fiberglass filter. This throwaway air filter is the most common type. Layered fiberglass fibers form the filter media and typically are reinforced with a metal grating that supports the fiberglass.
Polyester and pleated filters. These filters are similar to fiberglass filters but typically have a higher resistance to airflow and a superior dust-stopping ability.
High efficiency particulate arrestance (HEPA) filters. These units filter the air passing through them at a very fine scale. The U.S. Department of Energy and its contractors use HEPA filters that meet DOE standard STD-3020-97 to filter 99.97 percent of all particles 0.3 microns or larger.
Washable air filters. These products are not as common and rely on the build-up of dust along the cloth to improve the efficiency of the filter. Industrial processes involving high volumes of coarse dust are typical applications.
All filters cause some pressure loss as air flows across them. The longer a filter has been in use, the greater the pressure loss because build-up reduces airflow; and energy demand increases as fans work harder.
The situation has improved in recent years, however. The most important design improvements involve placing more folds in the filter media and creating valleys to increase surface area. Also, the filter can be rotated so it is not perpendicular to the airstream, which may require minor changes to the filter bay.