Modern Building Services

MODERN BUILDING SERVICES JULY 2022 25 FEATURE INDOOR AIR QUALITY Efficiency versus effectiveness It is well established that efficient and effective filtration is one of the foundational pillars of any well-designed building heating, ventilating, and air conditioning (HVAC) system. With regard to air filters and cleaners, efficiency is a term that refers to the ability of a collectingmedium to capture contaminants from the airstream that passes through it. The effectiveness of an air cleaner refers to its ability to reduce particulate concentrations in a space. The US Environmental Protection Agency (EPA) tells us “It should be noted that expected removal efficiencies for air cleaning devices are not the same as the effectiveness of the unit in actual use. Efficiency onlymeasures the percent removal of contaminants in the air that flows through the air cleaning device. Effectiveness in use depends on howmuch of the interior air actually goes through the unit in a given time period”. 1 If space contaminants in the air do not pass through the air filter that is tasked with their removal, the effectiveness (actual contaminants removed) may be less than expected regardless of the filter’s rated efficiency. Simply put, a filter described as very efficient may not be all that effective in actual use. Rating filter efficiency The American Society of Heating, Refrigerating and Air Conditioning Engineers (ASHRAE) Standard 52.2 Method of testing general ventilation air-cleaning devices for removal efficiency by particle size has established a test procedure for evaluating the performance of air-cleaning devices (filters) as a function of particle size. This standard describes a method of laboratory testing to measure the performance of general ventilation air-cleaning devices using a test apparatus like the one shown in figure 1. By David Schurk , Director of Healthcare and Applied Engineering Markets for Global Plasma Solutions and lecturer for ASHRAE. Expectation versus reality - examining air filter performance Figure 1. Schematic of test duct - ASHRAE Std 52.1-2017