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While the medical and scientific community is working hard to find answers to the bigger issues related to the spread and control of COVID-19, one of the more pressing questions that is increasingly being asked, especially as governments start the process of re-opening the economy, is about the potential role of HVAC systems in the transmission of the virus.

Some of the interest in assessing the role that air conditioning might play in the spread of COVID-19 follows the publication of a study in the journal Emerging Infectious Diseases.  The study, done by the Guangzhou Centre for Disease Control and Prevention, found that nine people in a restaurant in Guangzhou, China, were infected by the virus along a path that tracked the airflow of an air conditioning unit in the third-floor dining room.  The study concluded that the virus was spread by one asymptomatic diner who sat in front of the air conditioner.  Others sitting at three tables, each about one metre apart, were infected: “in this outbreak, droplet transmission was prompted by air-conditioned ventilation. The key factor for infection was the direction of the airflow.”  Researchers recommended that restaurants increase the distance between tables and improve ventilation to limit the spread of COVID-19.

The general consensus has been that the spread of the virus required larger droplets and would therefore be limited to closer proximities (hence the two meter guideline).  According to the World Health Organization, COVID-19 is primarily transmitted through respiratory droplets that land on people and surfaces.  There is no scientific consensus that airborne transmission of the virus, as described by the Guangzhou study, can spark an outbreak.

On April 14th, however, ASHRAE made the following statement regarding airborne transmission of SARS-CoV-2 (a.k.a. COVID-19):

Transmission of SARS-CoV-2 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.

ASHRAE further commented on the operation of HVAC systems as a means to reduce SARS-CoV-2 transmission:

Ventilation and filtration provided by heating, ventilating, and air-conditioning systems can reduce the airborne concentration of SARS-CoV-2 and thus the risk of transmission through the air. Unconditioned spaces can cause thermal stress to people that may be directly life threatening and that may also lower resistance to infection. In general, disabling of heating, ventilating, and air-conditioning systems is not a recommended measure to reduce the transmission of the virus.

ASHRAE’s Epidemic Task Force continues to assess scientific evidence related to this topic and will “maintain communication with members, industry partners, building owners, facility operators, government agencies, and the general public.”

Within the scientific community, it remains unclear how human-generated “bio-aerosols” affect airborne virus transmission and how HVAC systems should be optimally designed and operated to reduce the risk of transmission.  To assist in getting some answers, the Government of Canada is funding a study led by Dr. Lexuan Zhong, in the Department of Mechanical Engineering at the University of Alberta.  The research program “brings together experts in Engineering and Medical Sciences to develop Non-Pharmaceutical Interventions (NPI) related to mechanical ventilation systems in buildings.”  According to the research team,

These settings have high concentrations of humans in enclosed spaces where the spread of airborne infections can have rapid, extensive, and detrimental consequences in terms of morbidity, mortality, and ultimately productivity and costs.

This research program targets a key mechanism of COVID-19 transmission, that is, transport of the virus through heating, ventilation, and air conditioning (HVAC) systems with subsequent inhalation by other people.

The University of Alberta research initiative will include:

  1. A thorough review of building science literature related to airborne virus transmission;
  2. A policy directive for governing organizations who inform owners and operators of ventilation systems and building code bodies;
  3. An inventory and assessment of over 100 buildings with diverse ventilation systems; and
  4. An inventory and assessment procedure and protocol for other buildings.

The findings could provide some helpful guidance to the development of “evidence-based guidance and policy recommendations to inform the design/re-design of buildings.” This work has the potential for widespread impacts in terms of establishing policies and procedures that can be applied locally, nationally, and internationally.

Meanwhile, it was announced Wednesday that Public Health Ontario has asked the Canadian Agency for Drugs and Technologies in Health (CADTH) to assess whether air conditioning can further the transmission of the virus.  But CADTH spokespersons are saying the organization cannot commit to providing answers on this question as it appears to fall outside their scope of responsibility.  The independent agency has responsibility for reviewing the cost-effectiveness of prescription drugs and medical devices for provinces, to aid decisions about what products to make part of their publicly funded health-care systems.  According to CADTH’s Janis Bogart, Ontario’s request falls outside the agency’s normal scope of work, and it’s possible that it will only be able to provide the province with a literature review on the topic.

HRAI is following all of these developments carefully and is maintaining regular contact with ASHRAE and government health authorities.  HRAI is meeting with senior staff at Health Canada to ensure that the industry is properly consulted in the development of guidelines for the use and maintenance of HVAC systems.

HRAI is also in the process of developing a training program for contractors to create awareness about the potential role of HVAC technologies (ventilation, filtration, humidification, air cleaning) in potentially managing exposure to the virus, as well as the proper protocols for working safely and protecting customers.

For more information, contact Martin Luymes at 416-453-5899 or email mluymes@hrai.ca.