How air filters change with use: Testing new and used filters
Air filters are designed to collect dust as they are used. It has long been understood that this use changes the efficiency and pressure drop for the filters over time. However, there has been little carefully-collected, publically-available data on these changes. While the collected dust may be readily visible, the efficiency and pressure drop require equipment to measure. For repeatable measurements laboratory data collected under controlled conditions are usually needed.
To address these needs, RTI led an ASHRAE research project (1360-RP) to investigate how filter performance changes over time in real use and how these data compare to standardized testing on the same filters when new.
To investigate filter performance change with use, specific types of residential (uncharged, nominally MERV 7 and charged MERV 11) and commercial filters (uncharged MERV 15) were sent to volunteers in four cities. The volunteers installed the filters in their HVAC ducts then returned the filters at prescribed time intervals for laboratory testing to determine efficiency, weight gain and pressure drop.