Several factors that are HVAC-related might be of significance when it comes to the way COVID-19 is spread. That spread can be minimized through enhanced humidification, increased filtration, improved ventilation, and upgraded mechanical hygiene. General guidance was issued by ASHRAE for HVAC operations during the pandemic. This article will break down what we know about SARS-CoV-2 (a.k.a. COVID-19), including the virus that caused it. We will also go over other viruses, and the role that HVAC plays to control and spread infection.

Airborne Transmission Significance

Respiratory infections transmitted through air could result in immediate contact (within 3 m). Until it becomes inactivated (degraded), COVID-19 is infectious. How long it stays infectious while in the air remains to be seen, though. Since viruses typically come with minimum doses capable of causing infection (as per the dose-reaction relationship), health risks are associated with air concentration and exposure duration. Such factors remain unknown for COVID-19.

SARS-CoV-2 response guidelines set forth by the WHO and CDC assume that critical transmission routes involve direct contact made with patients, droplet exposure at short ranges, and transfers from surfaces in places where aerosols are settled. As per this assumption, public health agencies have recommended certain response measures, which are generally restricted to surface sanitization, handwashing, face coverings, and social distancing. With that said, evidence suggests small aerosols stay suspended while airborne. In doing so, occupants are exposed to them (airborne transmission).

Chinese and Australian researchers believe there is significant proof of SARS-CoV-2 being transmitted through the air. As such, improvement of filtration and ventilation systems are justified, as doing so could minimize the exposure to COVID-19. This position has been adopted by ASHRAE. Environmental epidemiology establishes how important airborne transmission is when COVID-19 is being spread. It also establishes efficient measures to minimize airborne exposure.

Health scientists, environmental epidemiologists, and engineers are encouraged to collaborate in order to gauge the timing and location of cases, as well as the conditions that are associated with them.

Examples of Poorly operational HVAC system

A comprehensive engineering assessment was conducted involving conditions when an outbreak of COVID-19 happened (at a China-based restaurant). After case locations were mapped out, conditions that were experienced by unaffected and infected staff and customers were considered. The role that various transmission routes played was assessed by contrasting factors. Study findings included the following:

• 10 of 73 restaurant patrons were infected.
• The ten infected individuals were sitting down at a few adjacent tables situated on a single side of a dining room (about 3 feet to 16 feet, or 1 meter to 5 meters) from an individual who had recently arrived from the city of Wuhan. This happened before the spread throughout the remainder of China happened.
• HVAC was comprised of 5 FCUs (fan coil units) without any exhaust fans or outside air. If exhaust fans were present, they were switched on at that time.
• Filtration and ventilation rates were measured and prioritized by magnitude below the ASHRAE standard of 62.1-2019.
• Airflow pattern modeling determined that one “bubble” was created by each fan coil unit, separating the room directly into five divided zones, which contained contaminants that were released back into that very zone.
• There were three tables impacted, and all of them were inside of the exact same zone.
• Results from the modeling also indicated that a fan coil unit’s discharge directed air toward breathing zones between customers.
• Air transmitted from the zone that was contaminated didn’t integrate with the remainder of that room. As such, no other customers became infected that were in hotspot areas of the room.
• Surveillance footage revealed how close proximities between people – as well as fomite contact – weren’t significant.
• Some waiters had been in contact with customers that were infected, albeit briefly. It wasn’t enough time for these workers to become infected, though.