Study of Viral Filtration Performance of Residential HVAC Filters.

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From: ASHRAE Journal(Vol. 62, Issue 8)
Publisher: American Society of Heating, Refrigerating, and Air-Conditioning Engineers, Inc. (ASHRAE)
Document Type: Article
Length: 2,636 words
Lexile Measure: 1500L

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Researchers recently carried out an experimental study to understand the efficacy and effectiveness of residential HVAC filters at removing airborne virus particles in the airstream. It concluded that high-efficiency residential HVAC filters were effective at capturing airborne virus particles in the air passing through the filter.

Background

Studies have shown that droplets generated by coughing and sneezing can contain bacteria and virus, which covers a very wide particle size range. (1) Small droplets can suspend in the air, then dry to form fine particles, which can stay in the air for hours. SARS-CoV-2, which is the virus responsible for COVID-19, is known to transmit through droplets, contact and aerosols. Recent research (2) discovered that SARS-CoV-2 can be widely distributed in the air and on object surfaces.

Another study (3) concluded that airborne transmission, particularly via nascent aerosols from human atomization, is highly virulent and represents the dominant route for the transmission of this disease. In another study, (4) viable virus was detected in aerosols up to three hours post-aerosolization. The World Health Organization (5) recommended the use of airborne precautions whenever applicable in addition to standard, contact and droplet precautions. ASHRAE's Epidemic Task Force (6) recently issued COVID-19 position statements, which indicate that transmission of SARS-CoV-2 through air is sufficiently likely that airborne exposure to the virus should be controlled.

Removing bioaerosols by filters and other devices has been extensively studied by researchers in the past (see sidebar). This study focused on viral filtration of residential HVAC filters with different minimum efficiency rating values (MERV), e.g., MERV 5, MERV 12, MERV 13 and MERV 14.

Test Method

Figure 1 is a diagram of the test system. The single-pass viral filtration efficiency of residential HVAC filters was measured using a virus aerosol challenge, MS2 bacteriophage, in a horizontal stainless-steel test duct constructed per ASHRAE Standard 52.2-2017,7 Method of Testing General Ventilation Air-Cleaning Devices for Removal Efficiency by Particle Size. MS2 is one of the four bioaerosols recommended by the EPA (8) for air filtration tests. MS2 virus has approximately the same aerosol characteristics as a human virus and can serve as a surrogate for viruses of similar and larger size and shape. MS2 virion (viral particle) is about 27 nm in diameter, as determined by electron microscopy, (9) much smaller than the SARS-CoV-2 virion, which measures about 120 nm in diameter. (10,11)

Another test method used for evaluating the inactivation efficacy of an air cleaning device is ASHRAE Standard 185.1-2015, Lights for Use in Air-Handling Units or Air Ducts to Inactivate Airborne Microorganisms, which is developed for testing UV-C light devices in air-handling ducts for inactivation of airborne microorganisms. ASHRAE Standard 185.1-2015 uses Mycobacterium parafortuitum and Aspergillus sydowii as test microorganisms. In this study, MS2 bacteriophage was used as the test microorganism because it is safe to use and has the relevant size and shape to viruses that have significant public health concerns, such as the SARS-CoV-2 virus.

The tests were performed under positive pressure with a blower pushing air through...

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Gale Document Number: GALE|A689361068