The air that we breathe

Mark Kaufmann, air conditioning and refrigeration engineer at ADK Kooling, on making air conditioning units safer for a post-coronavirus world.

Although scientists don’t know for certain, it seems likely that air conditioning units are helping COVID-19 to spread and infect more people.

In at least two events all fingers point to HVAC units, including at a restaurant in Guangzhou, China, where a diner is thought to have sat very close to an air conditioning unit. This is said to have carried viral particles in respiratory droplets, transporting them around the windowless room. Air conditioning is also thought to be one of the reasons why the virus spread so quickly on the Diamond Princess cruise ship back in early 2020.

It’s the coronavirus’s semi-airborne qualities that make air conditioning units such a tempting target for blame. The European Federation of Heating and Ventilation Engineers (REVHA) has put out guidelines that we can all implement to make our HVAC units safer, and virtually virus-free.

More, not less

To make an indoor environment safer from viruses, we need more air-conditioning, not less. We need to turn the power and settings up.

This may not make intuitive sense at first, but it does if you think about it, and it’s exactly the advice of REHVA. The internal air of indoor or confined spaces should be diluted with as much air as possible from air conditioning units, in order to swiftly remove or ‘blow away’ the viral particles before they can settle down on a surface.

What’s important is that the air con units are optimised to increase the rate of air that they can pull in from the outside, and to distribute this air rapidly throughout confined spaces for a frequent recycling and good exchange of air.

In short: if you can, you should reconfigure your air conditioning unit to run its recirculation mode on full outside air.

Can’t we just open the windows? Of course, it also helps to simply open the window. This


is fine during the warmer months and if practical, but for obvious reasons, no one will want the window open during the wintertime, or if the office or building is in a high- pollution urban area.

Yet even if conditions are perfect for open windows, a properly configured air conditioning unit will still be the much better, safer alternative for disposing of unwanted viruses.

HEPA’s impact

The safest and most efficient HVAC units of all come with high-efficiency particulate air (HEPA) filters. They are the units of choice for healthcare and the aeroplane industry. They work by quickly removing viruses, dust, fungi and other pathogens from the air, trapping them through millions of filter layers.

HEPA filtered air con units also typically have a rapid air exchange capable of completely switching up the air in a room anywhere between 20 and 30 times every hour. Though HEPA filters are not a common feature outside of ultra-specialised environments, that could soon change in the post-Coronavirus world, as we head into the ‘new normal’.

The biggest obstacle for the implementation of HEPA filters at the moment isn’t actually cost, it’s more technical: it’s about finding a way to implement them so that they seal properly. HEPA filters can also add ‘drag’ on, and therefore reduce the efficiency of conventional air conditioning units at present — which is another obstacle behind the rollout.

A safer indoors with air con

Until HEPA filters are an everyday reality, it’s important that we take care to optimise our air conditioning units. To keep safe from viral particles in the air, we need to counter them with a good amount of regularly occurring, freshly circulated air from the outside. In short, just tweak the settings and turn your air conditioning unit up.

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