Fine and ultrafine particle removal efficiency of new residential HVAC filters

Abstract

Particle air filters used in central residential forced‐air systems are most commonly evaluated for their size‐resolved removal efficiency for particles 0.3‐10 µm using laboratory tests. Little information exists on the removal efficiency of commercially available residential filters for particles smaller than 0.3 µm or for integral measures of mass‐based aerosol concentrations (eg, PM2.5) or total number concentrations (eg, ultrafine particles, or UFPs) that are commonly used in regulatory monitoring and building measurements. Here, we measure the size‐resolved removal efficiency of 50 new commercially available residential HVAC filters installed in a recirculating central air‐handling unit in an unoccupied apartment unit using alternating upstream/downstream measurements with incense and NaCl as particle sources. Size‐resolved removal efficiencies are then used to estimate integral measures of PM2.5 and total UFP removal efficiency for the filters assuming they are challenged by 201 residential indoor particle size distributions (PSDs) gathered from the literature. Total UFP and PM2.5 removal efficiencies generally increased with manufacturer‐reported filter ratings and with filter thickness, albeit with numerous exceptions. PM2.5 removal efficiencies were more influenced by the assumption for indoor PSD than total UFP removal efficiencies. Filters with the same ratings but from different manufacturers often had different removal efficiencies for PM2.5 and total UFPs.

In situ efficiency of filters in residential central HVAC systems

“…However, the efficiency was generally low for ultrafine particles (UFP) with a diameter smaller than 100 nm and decreased for particles smaller than 30 nm for some filters. This trend is consistent with other studies on electret or non-electret particle filters (eg, 5,9,15,23,24 exists around filters which allows upstream particles to travel around the filter to downstream and this phenomenon is discussed in more detail in the Discussion. Another possibility is that fine particles were generated in the air handling unit or resuspended from the surfaces of the heat exchangers and cooling coils during the efficiency tests.…”

“…However, the efficiency was generally low for ultrafine particles (UFP) with a diameter smaller than 100 nm and decreased for particles smaller than 30 nm for some filters. This trend is consistent with other studies on electret or non‐electret particle filters (eg,). One possible explanation for the low efficiency for UFPs is the relatively high media face velocity.…”

Transmission of SARS‐CoV‐2 by inhalation of respiratory aerosol in the Skagit Valley Chorale superspreading event

“…The furnace is also outfitted with a MERV 11 filter, which has a single-pass efficiency of ≥ 30-65% for airborne particles of diameter 1 µm or larger. 22,23 Modeling Airborne Infection Risk…”

Assessment and mitigation of aerosol airborne SARS-CoV-2 transmission in laboratory and office environments

“…0:2 (MERV8) to f ! 0:95 (MERV16) in the particle size range 1-3 mm, leading to much higher penetration values (Fazli et al 2019;ASHRAE 2017). Our treatment of HEPA-filtered recirculation can be directly applied to MERVfiltered recirculation by substituting the value of f appropriate to the relevant MERV standard.…”