Covid link to poor air supply a major concern for AC planning

Use of AC systems during the current pandemic must be considered as part of a holistic indoor air quality strategy that factors in both air movement and end user behaviour, a government advisor has argued.

Professor Cath Noakes from the University of Leeds’ School of Civil Engineering, who sits on the government’s SAGE (Scientific Advisory Group for Emergencies) committee, said that emerging evidence about the potential for airborne transmission of Covid-19 meant that careful planning of all air movement systems being used in enclosed spaces was required.

She said, “Given what we know about air conditioning, I think I would be very cautious about using these systems in poorly ventilated spaces. If the space is well ventilated, the risk is probably relatively low. But in poorly ventilated areas, I would be a bit worried about [the risk of] maintaining aerosols in that space for longer period of times.”

The comments were made during a recent BESA webinar that focused on ventilation and the importance of air quality in managing the risk of Covid-19 transmission. A main argument made by Professor Noakes during the webinar was on the importance of considering how end users interact with specific systems.

She noted, “It’s no-good saying, ‘yes, this system can deliver’ if people in a space shut the windows or turn it off. We need to make sure people know why they need to use ventilation effectively.”

This same principle should also apply to air conditioning and purification technologies, especially with how they are being used with other building systems, said Professor Noakes.

Since the beginning of the pandemic, HVAC experts have been calling on building operators and FM specialists to ensure there is a high rate of ventilation to provide constant external air into a space as a means to safeguard against Covid-19 outbreaks. The industry has also been advised over the same period to ensure systems are not recirculating air.

Professor Noakes said that this advice remained important as most cases of significant airborne transmission that had been identified over the last year were recorded in spaces with lower ventilation rates of one to three litres per second per person.

She added, “There is very little evidence to suggest that airborne transmission is happening, for example, where there is 10 litres per second per person in a space.”

However, she added that each application had to be judged individually, given that rates of aerosol transmission varied from person to person, and so occupants and the nature of the building had to be factored in.

Concerns about how air conditioning and ventilation systems are used to manage pollutants and contaminants within enclosed spaces are anticipated to be a long-term issue for the HVACR sector that will extend beyond the present pandemic.

Trade bodies have warned that a shift in public perception about air supply and quality in public and private spaces as a result of Covid-19 will significantly impact how AC specifiers and manufacturers now provide solutions.