More study is required to establish if HVAC systems are capable of transmitting the infection of COVID-19. Further study will also be necessary to determine if changes to HVAC systems can actually control the spread. There is little-to-no detail about such information at the time of writing.
Airborne Transmission
There haven’t been enough samples taken to establish that COVID-19 is airborne. There are also very few samples suggesting that it can expose occupants past 7 feet (2 m), though exposure doesn’t necessarily mean infection. Recent findings have established that SARS-CoV-2 is capable of circulating through various HVAC systems. Although multiple SARS-CoV-2 infection outbreaks have implied airborne transmission, it is typically in spaces with minimal ventilation. That may be because building ventilation dilution (as per building code requirements) hinders transmission of disease.
Ventilation
The increase of outdoor air can dilute SARS-CoV-2’s concentration if it’s airborne. Minimum ventilation rates haven’t been established yet for building operations where infected people might be present. With that said, it hasn’t been determined whether the increase of ventilation rates over ASHRAE minimums could actually reduce the transmission of disease. National ventilation hasn’t been evaluated for SARS-CoV-2.
Distribution of Air
Research suggests that air, once discharged, that circulates inside spaces could establish if exposure is enough to stimulate disease. For instance, FCUs that are wall-mounted are capable of discharging air into breathing zones, which could direct the virus to another occupant. Relative pressurization is also capable of spreading or containing contamination. There is a lack of field data about the effect of air distribution when it comes to exposure of COVID-19.
Filtration
Reports of sampled surfaces within HVAC systems that were recirculating were recently reported. According to the data, a pre-filter (MERV 10) minimized the quantity of COVID-19 that was deposited by almost 70%. Also, a final filter (MERV 15) might not remove extra viruses. Field data was insufficient with regards to filter selection and COVID-19. However, filtration inside an area (for instance, compact HEPA units) can minimize virus exposure inside local spaces with appropriate placement and design.
Ultraviolet Disinfection
While ultraviolet light can potentially minimize virus exposure inside certain situations, a lack of data is available to back up widespread application.
Control of Humidity
Coronaviruses have the potential to survive longer. Occupants are therefore more vulnerable to respiratory infections inside dry conditions. While SARS-CoV-2 initially spread within areas with dry conditions (such as during winter), community spread also happened in humid places (like southern hemispheres and tropical climates in the summertime). Continuous high COVID-19 rates in the USA this past summer suggest that levels of humidity are not a relevant factor. The available information doesn’t support humidification if the RH happens to be under 40%, as far as controlling COVID-19 goes.
Sewage
COVID-19 was discovered in urine and feces, making sewage and sewer gas a potential exposure source. Further studies are required to establish impactful strategies capable of preventing occupants from becoming infected.
Mechanical Hygiene
COVID-19 was found on surfaces within HVAC systems that were recirculating air. However, it is unclear if the virus is capable of contaminating the airstream.