Coronavirus and HVAC

Since the first case was detected in China in December 2019, the novel (new) coronavirus (2019-nCoV) has spread rapidly. On January 31, the World Health Organization (WHO) declared the novel coronavirus a public health emergency.

Although the vast majority of coronavirus patients have been in China, cases have been confirmed in Australia.

Not surprisingly, local HVAC practitioners are fielding queries from clients about whether any precautions need to be taken with regards to air conditioning and ventilation systems.

No action required – for now

The short answer is that until new information emerges, no specific actions are necessary for HVAC equipment in general-use areas.

Jeremy Stamkos, M.AIRAH is a Principal Consultant for Eronmor and an indoor environment quality expert. He confirms that at this stage in general-use buildings, there should not be a need to do anything from an HVAC perspective to help protect occupants.

“Following general guidance from health authorities is generally sufficient to protect against infection,” he says.

But he notes there are things to consider.

The exact dynamics of how the novel coronavirus is transmitted is yet to be determined. According to the Australian Government Department of Health it is most likely spread from person to person through direct contact, or through droplets when a person coughs or sneezes (or even talking). This may occur directly or via a surface where the droplet lands.

“Droplet nuclei are the small droplets of moisture that exit the mouth when someone coughs, sneezes or even talks,” says Stamkos. “These droplets can contain the infectious virus and, depending on the size of the droplet as well as the velocity and direction of the air, can stay airborne for a prolonged period – several minutes even – which can be inhaled by others causing infection.

“Many of these droplets will eventually settle onto surfaces, which can then be touched by people who can in turn become infected by touching their nose, mouth, etc.”

According to Stamkos, little credible research has been done to determine how long droplet nuclei can stay suspended or how far it can travel. The results of modelling conducted after the 2003 outbreak of SARS – another form of coronavirus – suggests it can travel quite far and infect people several stories away from the source.

He says that air filters could be upgraded to help catch the small droplet nuclei, and increasing outside air levels would help dilute airborne pollutants in the building. But such measures also increase energy use, and may introduce outdoor pollutants (such as smoke from bushfires).

“Consideration should be given to conducting a proper risk assessment to help determine if the measures are warranted,” Stamkos says.

Lessons from SARS

World-renowned expert on microbial control, Clive Broadbent AM, L.AIRAH, was heavily involved in addressing the SARS outbreak. In 2003 he flew to China at the request of the WHO to analyse the spread of the virus and produce guidelines on laboratory standards, hospital practices and appropriate ventilation for SARS patients.

Broadbent says that lessons learnt during that outbreak may be useful in facing the novel coronavirus.

“The evidence was that transmission of the SARS virus was overwhelmingly person-to-person in droplets arising from activities such as sneezing or coughing when the infected person was close to a susceptible host,” Broadbent says.

“This is a similar mode of transmission to that of other respiratory infections such as the common cold.

“It is possible that there is indirect transmission of such virus particles from contact with surfaces on which the virus may have landed shortly – say, within four hours – beforehand. There is little likelihood of this possibility occurring with the internal surfaces of air conditioning ductwork, for example, as infected droplets once landed are unlikely to become re-suspended in the air above such a surface without drying out rapidly down to an aerosol size.”

Broadbent notes that all usual maintenance of air conditioning plant should be observed as good practice. He also says that airflow, especially in hospital wards for infected patients, must be controlled appropriately.

“In short, negative pressure principles need to be followed for design, commissioning, operation and monitoring when there are patients within having highly contagious viral diseases,” he says. “A ward at positive pressure can be potentially lethal. Hospital rooms at positive pressure are needed, of course, for those patients not infected with the coronavirus and who are highly susceptible to infection from other rooms.

“Similar principles apply to other building types such as high-rise apartments.”

For general information and the latest updates on the novel coronavirus, please refer to the Department of Health website.

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