How ‘fresh’ is your air?

Building managers should urgently review the way their ventilation systems are operating in light of the new restrictions announced by the government, according to David Frise, CEO of the Building Engineering Services Association (BESA).

The issue of air quality in commercial buildings has received widespread media coverage including a feature on BBC News, which advocated workers refusing to enter “stuffy” offices as these were most likely to pose a risk of a second spike in Covid-19 infections.

BESA has been advising members of the public, contractors and end users throughout the pandemic period with a consistent message to maximise the amount of outside air being introduced to buildings to dilute the airborne viral load.

Ventilation systems should be correctly set to maximise the amount of air being brought into the occupied spaces and should be regularly maintained. The Association recommends that systems are run for longer and at higher speeds than normal – starting two hours before occupation and kept running at lower speeds overnight and at weekends to purge the building.

Of course, this will increase the amount of electricity consumed, but health is more important than energy efficiency right now. The key task of the HVAC system is to keep up air change rates – even in partially occupied buildings – to minimise the risk of transmission of the airborne virus. Eventually, we will be able to return systems to their low energy modes, but for now some of our sustainability concerns must be on hold.

For now, systems that recirculate the air to improve energy efficiency should be switched to ‘full fresh air’ mode to minimise the risk of contaminated air re-entering the building. Recirculation dampers can usually be switched off manually or by using electronic controls. Return air from air handling units should be minimised and ‘purging’ carried out to avoid air moving from the extract side to the supply side of these units.

The lowest carbon emitting ventilation method is opening windows, however, it is not a good idea to rely on that despite what the fact that is what the BBC recommended. If there is little or no wind, the air will not naturally flow into a building from outside particularly if the temperature outside is colder than inside.  In that case the air will flow out rather than in so even less supply air is available to the occupants.

Another problem with opening windows is the risk of increasing the amount of polluted air entering the building, particularly in urban areas. There is a big difference between outside air and ‘fresh’ air.  Bringing in outside air may create other risks to health if it is full of pollutants. It needs to be filtered and air purification technologies could be used in some circumstances. The latter have been proving their worth in healthcare settings.

Another issue to consider is when offices have been re-configured to allow for social distancing with desks moved and partitions erected. This will change the way air moves around the space and, therefore, needs to be taken into account when reviewing whether the ventilation is still fit for purpose.

For all of these reasons it is, therefore, important to ensure mechanical ventilation and air conditioning systems are working as intended and are well maintained. Filters should be regularly checked and cleaned or replaced and maintenance staff should wear full protective clothing, gloves, respirators and goggles when carrying out this work.

Well maintained ventilation systems will play a critical role in reducing any future spread of the virus, but some news channels have also tried to imply that air conditioning is a source of contamination. Some referred to a study that examined a Covid-19 outbreak at a restaurant in China that was blamed on an air conditioning unit. However, it is simplistic to suggest this means mechanical building services systems pose a risk to occupants.

On the day in question, that particular restaurant was packed and its extract system used to remove stale or contaminated air was out of use. The only extractor was a small toilet fan at the opposite end of the room from where the diners were seated. The unit blamed for the spread was one of four units in operation and nobody close to the other three picked up the virus.

This was a flawed study that raised more questions than answers and the truth is that properly maintained air conditioning and ventilation systems can reduce the risk of a second wave by avoiding stale or stagnant air building up indoors.

However, if systems are not well looked after and/or there is no overall strategy for maintaining good indoor air quality, then there could be problems. That is self-evident.

David Frise is taking part in our ‘Indoor Climate Emergency’ webinar on October 29th.

Visit for more info.

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