Filter efficiency of selected HVAC filters

Air quality begins with good engineering air handling system (HVAC) controls. Air handler filters should remove the major particulate matter from incoming ambient air. A study of various NIOSH air handler bag filters was conducted to determine their filter efficiency against submicrometer particles (0.03-0.4 micrometers), since submicrometer particles are the most penetrating. Aerosol penetration measurements show an extremely large range of filter efficiency. New filter aerosol penetration ranged from less than one percent to greater than ten percent with penetration depending on flow rate, media surface area, and challenge agent particle size and state (liquid versus solid). Exposed filters (from air handler) showed a significant increase in submicrometer particle filter penetration and a shift in most penetrating aerosol particle size toward the larger particle size range. Both mechanical and electrostatic filters are used in HVAC applications. The electrostatic filters showed significant filter efficiency reduction over the filters expected service lifetime.