A COVID-19 Update

With Covid-19 continuing to spread, understanding the proper procedures for air filtration and disinfection remains important. The National Air Filtration and the American Society of Heating, Refrigerating and Air Conditioning has provided helpful resources to guide your business and protect public health and safety.

HVAC Building Filtration and Maintenance
Heating, ventilation and air conditioning units can take part in managing migration of airborne particles, as some filters are able to remove particles that contain SARS-CoV-2 virus. ASHRAE recommends using a filter with a Minimum Efficiency Reporting Value (MERV) of 13 or better. Of course, the capabilities of the HVAC systems need to be taken into consideration. Generally, increasing filter efficiency leads to increased pressure drop, which can lead to reduced air flow through the HVAC system, more energy use for the fan to compensate for the increased resistance, or both. If a MERV 13 filter cannot be accommodated in the system, then use the highest MERV rating you can. Appropriate filters tested under the ISO 16890 Standard can also be used. The table below provides approximate relationships between ratings under the ASHRAE MERV and ISO 16890 test methods. The current recommendations would suggest using a filter with an ePM1 rating under ISO 16890. 

More information about SARS-CoV-2 Virus Size and Ventilation

Research has shown that the particle size of the SARS-CoV-2 virus is around 0.1 µm (micrometer). However, the virus does not travel through the air by itself. Since it is human generated, the virus is trapped in respiratory droplets and droplet nuclei (dried respiratory droplets) that are predominantly 1 µm in size and larger. ASHRAE currently recommends using a minimum MERV 13 filter, which is at least 85% efficient at capturing particles in 1 µm to 3 µm size range. A MERV 14 filter is at least 90% efficient at capturing those same particles. Thus, the recommended filters are significantly more efficient at capturing the particles of concern than a typical MERV 8 filter which is only around 20% efficient in the 1 µm to 3 µm size range. Filters with MERV ratings higher than 14 would capture an even higher percentage of the particles of concern. High-efficiency particulate air (HEPA) filters are even better at filtering human-generated infectious aerosols. By definition, a HEPA filter must be at least 99.97% efficient at capturing particles 0.3 µm in size. Thus, HEPA filters are more than 99.97% efficient at capturing airborne viral particles associated with SARS-CoV-2.
 

Recommended procedures for disinfecting HVAC equipment 

Neither ASHRAE nor CDC has posted guidance on the decontamination of HVAC systems (including air filtration systems) potentially exposed to SARS-CoV2. To date, there has not been compelling evidence to demonstrate that a viable virus is contaminating these systems. Should such systems actually become contaminated with viable viruses, the most likely scenario is believed to be that the virus would lose its viability naturally within hours to days, and thus, there is no guidance advocating proactive system shutdown for decontamination and/or filter exchange. If you choose to use chemical disinfectants, it is important to use them properly. There are no disinfectants approved specifically for use inside ventilation systems. If chemical disinfectants are used, they should only be applied with the HVAC system powered off. However, there are hundreds of EPA-registered disinfectants that are effective at killing human coronaviruses (see EPA List N). A good fact sheet on the use of disinfectants to control the COVID-19 virus from the National Pesticide Information Center can also be found here. It provides some tips for proper disinfectant usage, including surface types, understanding the label, and proper dwell or contact times. It is important to remember that most of these disinfectants, while effective at killing coronaviruses, do not continue killing long after they are applied, and would need to be reapplied. Also, disinfectants should not be applied to ventilation filters prior to continued use of the filters inside ventilation systems. The effects of the disinfectants on filter performance are unknown. Filters should only be treated with disinfectants when they are removed from service and discarded.

From The American Society of Heating, Refrigerating and Air-Conditioning Engineers. “Frequently Asked Questions and Glossary of Terms.” Filtration and Disinfection FAQ, The American Society of Heating, Refrigerating and Air-Conditioning Engineers, 2020, www.ashrae.org/technical-resources/filtration-and-disinfection-faq.

Precautions When Changing Filters

In general, it is sensible to assume that filters have active microbiological material on them. Whether this represents an important infectious disease risk from viruses is not known, but the precautionary principle would suggest that care should be taken. This becomes particularly important in any building (including a home) where there are known or likely cases of any infectious disease including COVID-19. This also extends to portable air cleaner filters and vehicle cabin air filters. Filters should be changed with the system turned off, while wearing gloves, with respiratory protection if available, outdoors if possible, and disposed of in a sealed bag.
 

From “COVID-19 (Corona Virus) and Air Filtration Frequently Asked Questions (FAQs).” National Air Filtration Association, 23 Sept. 2020, www.nafahq.org/covid-19-corona-virus-and-air-filtration-frequently-asked-questions-faqs/