Social distancing, face masks, shelter in place orders, rigorous hand washing; we are all well aware of the steps to mitigate the spread of COVID-19. While thorough hand washing and face masks may be with us for a while longer, shelter in place orders and social distancing are short-term brute force measures that are not intended as a permanent solution. As stay at home orders are lifted and people resume occupying shared spaces, engineers must consider long term solutions that can diminish risk in large buildings. COVID -19 is an airborne illness, so naturally a building’s HVAC system can play a vital role in reducing the spread of the coronavirus.
“Transmission of SARS-CoV-2 (COVID-19) through the air is sufficiently likely that airborne exposure to the virus should be controlled. Changes to building operations, including the operation of heating, ventilating, and air-conditioning systems, can reduce airborne exposures.” – This is the conclusion of ASHRAE, the American Society of Heating, Refrigerating and Air-Conditioning Engineers. For more information you can review ASHRAE’s guidance on reopening schools.
Properly applied, HVAC has the potential to break the chain of transmission of a virus as it attempts to move from host to host. Therefore heating, ventilating, and air-conditioning can have an effect on the number of people exposed to COVID-19. When applied properly, ventilation-related strategies such as dilution, airflow patterns, pressurization, temperature and humidity regulation and control, filtration, and UV and bi-polar ionization can mitigate, but not eliminate, the risk of transmission of infectious diseases through aerosols.
The consensus is that the ventilation and filtration provided by your building’s HVAC system will reduce the concentration of COVID-19 particles in the air and that thermal stress of unconditioned spaces may lower resistance to infection. For these reasons it is recommended you leave your HVAC system on. Making sure the building is positively pressurized ensures that all air in the building is being treated through the HVAC filtration system and not pulling in untreated outdoor air through windows, doors, or leaks in the building. Running the HVAC system 24/7 will ensure better dilution of any pathogens in the air.
It is also recommended that you increase filter efficiency (minimum efficiency reporting value (MERV)) if possible. Increasing your filters above the code required minimum will reduce the amount of particulates in the air-stream. However, increasing filter efficiency may have a negative effect on your HVAC system. Your air handling equipment should be evaluated prior to increasing filter performance to ensure the equipment can handle the higher pressure drop of these higher efficiency filters.
Prior to reoccupying any building, it is recommended that the building is fully flushed through the HVAC system and all filters are replaced.
There is evidence to suggest temperature and humidity can have an impact on the transmission of infectious agents such as COVID-19. However, the practical challenges and potential drawbacks raised by setting a uniformed climate setting in a building deserve careful consideration. Humidity between 40%-60% reflects the most unfavorable survival levels for microorganisms, so HVAC systems should remain on and operational as though the building is occupied to maintain optimal temperature and humidity levels.
Technologies such as UV Light and Bi-Polar Ionization (BPI) have been shown to kill and control viruses including SARS-CoV-2 (novel coronavirus) that causes COVID-19, because it apparently destroys the viruses’ DNA Bond (Larry Clark, HPAC Engineering 4/9/20). This is a relatively inexpensive technology that could be applied to new and existing air handling equipment to treat and kill the pathogens in the air-stream.
Another technique that should be considered is displacement ventilation. Traditional HVAC systems provide room air distribution and thermal comfort by thoroughly mixing the air in the space, in turn mixing all airborne contaminants. Displacement ventilation brings HVAC air into the space low and at low velocities, utilizing the buoyancy forces in a room generated by heat sources such as people, computers, equipment, etc. to remove heat and contaminants from the room without mixing. This type of approach would require a full evaluation of the space and system and would require a significant cost to retrofit.
New information is coming out almost daily as we learn more about this virus. As this develops, LAN will constantly update this list with the newest and best recommendations by the CDC and ASHRAE. HVAC mitigation factors should be viewed as part of a comprehensive strategy that includes common measures to protect against the spread, such as rigorous surface cleaning and limiting unnecessary contact.
We can absolutely help. If you have any questions about how to optimize your HVAC system to help mitigate the spread of COVID-19 contact LAN Associates.