Concerns raised about certain aircons

Air-conditioning units that recirculate the same air should be switched off or only used with open windows, experts urge, after the World Health Organisation pointed to “emerging evidence” of airborne transmission of the coronavirus.

Experts said air-conditioning units that only used recirculated air could exacerbate the spread of virus particles if someone was infected with Covid-19.

Dr Shaun Fitzgerald, a fellow at the Royal Academy of Engineering, said there were two types of air-conditioning units — ones that take air in from outside and expel it, or those that recirculate the same air.

This second type, known as a “split” unit, draws air in, passes it over cooling coils and sends it back out.

Guidance from the Chartered Institute of Building Service Engineers warns that split air-conditioning units that do not have a “dedicated source of outside air supply into a room ... could be responsible for recirculating and spreading airborne viral particles into the path of socially distanced users”.

Fitzgerald said opening a window while operating the unit was the best way to mitigate risk.

“The recommended strategy now, if you have one of these split units, is to throw the window open.

“If there is a modicum of wind it will move the air around. If you can’t open a window, turn the unit off.”

Experts have been concerned about air-conditioning units since the publication of a study in the journal Emerging Infectious Diseases that looked at an outbreak of coronavirus among 10 diners at a restaurant in Guangzhou, China.

The diners were seated at three separate tables and researchers believe airflow from an air-conditioning unit could have spread droplets between the three groups. The question over how the disease is transmitted was given added urgency in recent days after the WHO released a new scientific brief that acknowledged “emerging evidence” of airborne transmission of Covid-19.

Existing WHO guidelines say the virus is spread primarily through droplets from the nose or mouth — and the best preventive strategies are hand washing and social distancing.

It said restaurants, nightclubs and places of worship where people may be shouting, talking or singing and where there was poor ventilation, were a risk for airborne transmission.