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Can HVAC systems transmit COVID-19?

Peter Caulfield
Can HVAC systems transmit COVID-19?

A team of researchers at the University of Alberta (U of A) is investigating the possibility that heating, ventilation, and air conditioning (HVAC) systems might play a part in spreading airborne COVID-19, the illness caused by the novel coronavirus.

U of A assistant professor of mechanical engineering Lexuan Zhong  says the research team is studying HVAC design and operation to see if such variables as ventilation modes, air distribution patterns, pressure control, filtration and air cleaning technologies could affect the risk of virus transmission.

Zhong says the goal of the project is to develop non-pharmaceutical interventions for COVID-19 that use a building’s mechanical ventilation system. 

“Until now, it has been unclear how human-generated bioaerosols (suspended airborne particles) affect airborne virus transmission and how HVAC systems should be designed and operated to reduce the risk of transmission,”  said Zhong.

In addition to Zhong, the other principal investigators are Lisa Hartling and Brian Fleck.

The research team also has three engineers, two PhD students and three undergraduate trainees.

The project has an extensive to-do list.

It includes a review of building science literature related to airborne virus transmission;  an inventory and assessment of over 100 buildings with a variety of different ventilation systems; and, when the results of the research are in, a list of policy recommendations for building design and re-design.

Zhong says non-pharmaceutical intervention through HVAC systems is as valuable as vaccine research in the battle to tame the coronavirus.

“Improving mechanical ventilation systems in high-occupancy structures would be a critical way to contain the (COVID-19) pandemic,” she said. “Some buildings or cabins have a high density of occupants in enclosed spaces where the spread of airborne infections can have rapid and extensive consequences.”

Not everyone is convinced building ventilation is a significant transmitter of the novel coronavirus.

For example, the World Health Organization and other public-health bodies say the pathogen is spread almost entirely by droplets that are expelled when infected people cough or sneeze, and which fall to the ground within a short distance.

The two-metre/six-feet rule for social distancing and the reminders to wash hands after touching surfaces where the virus might be lurking are based on the droplet theory. However, says Zhong, the American Society of Heating, Refrigerating, and Air-Conditioning Engineers has said“Transmission of SARS-CoV-2 through the air is sufficiently likely that airborne exposure to the virus should be controlled.”

Some readers of a certain age might remember the outbreak of Legionnaires Disease in 1976.

More than 2,000 members of the American Legion attended a three-day convention, at a hotel in Philadelphia, to mark the U.S. bicentennial.

Soon a number of convention attendees were complaining of tiredness, chest pains, lung congestion and fever.

Within a week, more than 130 people had been hospitalized, and 25 had died.

A subsequent investigation by the U.S. Centers for Disease Control and Prevention found that the Legionella bacterium was breeding in the cooling tower of the hotel’s air conditioning system, which then spread it through the building. According to Wikipedia, this led to new regulations around the world for climate control systems.

Dinos Hadjiloizou, vice-president and general manager, Division 15 Mechanical Ltd in Surrey, B.C., says HVAC systems have features that detect smokes and smells and prevent their transmission, but they can’t detect viruses. 

“There are many well-designed HVAC systems that maintain air quality, especially those that have been built to LEED (Leadership in Energy and Environmental Design) specifications,” said Hadjiloizou. “Some things are measurable and can be controlled. But other things, such as viruses in the air, cannot be detected, at least not yet.”

Hadjiloizou says he “doesn’t have a clue” if the researchers’ hypothesis that the coronavirus could be spread by a building’s ventilation system is plausible or not.

“We don’t yet know the characteristics of the virus and how it spreads,” he said. “We need credible research that will give us more insight about the virus and how it spreads. Having said that, indoor air quality is, of course, very important.”

If the U of A researchers find that HVAC systems can, in fact, carry the virus, Hadjiloizou says how the ventilation systems need adjust depends on the spreading pattern of the virus.

“The fix could be simple, such as replacing the filters in the systems more frequently,” he said. “Or maybe the whole concept needs to be redesigned,  so that the air inside a building is not recirculated and fresh air is brought in from outside.”

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Terry Yap Image Terry Yap

The air conditioning concept as we know it is probably passed in view of the emergence of very infectious diseases.


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