FRACTIONAL AEROSOL FILTRATION EFFICIENCY OF IN-DUCT VENTILATION AIR CLEANERS

The filtration efficiency of ventilation air cleaners is highly partic le-size dependent over the 0.01 to 3 mu m diameter size range. Current standardized test methods, which determine only overall efficiencies for ambient aerosol or other test aerosols, provide data of limited ut ility. Because particles in this range are respirable and can remain a irborne for prolonged time periods, measurement of air cleaner fractio nal efficiency is required for application to indoor air quality issue s. The objectives of this work have been to 1) develop a test apparatu s and procedure to quantify the the fractional filtration efficiency o f air cleaners over the 0.01 to 3 mu m diameter size range and 2) quan tify the fractional efficiency of several induct air cleaners typical of those used in residential and office ventilation systems. Results s how that efficiency is highly dependent on particle size, flow rate, a nd dust load present on the air cleaner. A minimum in efficiency was o ften observed in the 0.1 to 0.5 mu m diameter size range. The presence of a dust load frequently increased an air cleaner's efficiency; howe ver, some air cleaners showed little change or a decrease in efficienc y with dust loading. The common furnace filter had fractional efficien cy values of less than 10% over much of the measurement size range.