The role of a building’s HVAC system in controlling the spread of the virus suggests that building engineers could become ‘the hidden heroes of Britain’s Covid-19 recovery.’
The role of a building’s HVAC system in controlling the spread of Covid-19 has had commentators proposing building engineers as ‘the hidden heroes of Britain’s Covid-19 recovery.’
With virus particles able to pass through air conditioning filters, engineering specialists have expressed concern that temporary signage, the suspension of open-plan working and other activities designed to ensure building users’ sustain two-metre distancing, could be rendered pointless should those same buildings suffer from poor ventilation.
HVAC providers Vent-Axia supplied ventilation to several field hospitals, including the NHS Nightingale Hospital in London, Kent & Canterbury NHS Trust’s Covid-19 wards, and field hospitals at Bangor University and Deeside Leisure Centre. The firm was among those welcoming the government’s Covid-19 press briefing on 29 April at which Professor Jonathan Van-Tam, the UK’s deputy chief medical officer, said: “There is a definite truism across all of the science literature that ventilation is a most critical part of reducing transmission from respiratory viruses.”
This briefing added weight to a raft of global scientific evidence about the aerosol transmission of Covid -19; that it is riskier to be inside than outside a building because of the lack of airflow. It is thus vital to dilute the virus in the air inside buildings through effective ventilation and increased airflow.
On 11th May, ventilation was presented as a key element of the government’s Covid-19 return-to-work strategy, at which it was agreed that “the virus is less likely to be passed on in well-ventilated buildings and outdoors”.
The Chartered Institution of Building Services Engineers (CIBSE) said ventilation systems should be set at a higher volume flow rate, with recirculation or transfer of air from one room to another to be avoided as much as possible.
“We recommend increasing the rate of supply of outside air to occupants wherever it is practical as a precautionary measure. This is particularly important in poorly ventilated areas. Increasing the ventilation rate helps dilute any airborne contamination and reduces the risk of exposure for building users.”
All of which could mean cooler offices, with workers required to dress accordingly.
“General advice for now is to supply as much outside air as reasonably possible,” added Paul Lucas, managing director of Artic Building Services. “In buildings without mechanical ventilation, window airing can be used to boost ventilation. If in your building the number of employees has reduced, do not concentrate the remaining employees in smaller areas. Instead, maintain or enlarge the spacing among them in order to enhance the ventilation cleaning effect.
“Airborne contaminants can be minimised by correct filtration, regular plant maintenance and, where appropriate, cleaning of ventilation systems. We now have evidence that microbial contaminants will grow on filters in 14 days; these either need to be tackled by more regular filter changes or by increased cleaning.”
The role of humidification
Scientists from Harvard and Yale, in tandem with other immunobiology and infection control specialists, launched a global petition calling on the World Health Organization to establish global guidance on indoor air quality in public buildings. The aim is to establish clear guidance on the minimum lower limit of air humidity. The petition is targeted at the WHO because of its role in setting global guidelines for indoor air quality.
The move, said the scientists, “would reduce the spread of airborne bacteria and viruses in buildings and protect public health”, thus reducing seasonal respiratory illnesses, and comes in the wake of the Covid-19 crisis causing increased global awareness of the role indoor environmental quality plays in physical health. The scientists maintain that an indoor humidity level of between 40 per cent to 60 per cent relative humidity (RH) – is the optimum threshold for inhibiting the spread of respiratory viruses such as influenza. This is a threshold that many public buildings drop below every winter.
Dr Akiko Iwasaki PhD, the Waldemar Von Zedtwitz professor of immunobiology and professor of molecular, cellular and developmental biology at Yale, said: “When cold outdoor air with little moisture is heated indoors, the air’s relative humidity drops to about 20 per cent. This dry air provides a clear pathway for airborne viruses such as Covid-19. I recommend humidifiers during the winter, and feel the world would be a healthier place if all our public buildings kept their indoor air at 40 to 60 per cent RH.”
The scientists said there was good reason for maintaining 40-60 per cent RH in public buildings such as hospitals, care homes, schools and offices. When lower than 40 per cent, airborne droplets containing viruses shrink through evaporation, making them lighter. The particles then float for longer in the air, increasing the likelihood of infection.
Dr Stephanie Taylor, infection control consultant at Harvard Medical School, said: “It is time for regulators to place management of the built environment at the centre of disease control.”
Advice Sources: Next steps
Government advice – Legionella Risks During Coronavirus
CIBSE has recently issued documents to help building managers and operators preparing for an ease in lockdown.
CIBSE COVID-19 Ventilation Guidance includes the following key advice.
- Maintain higher ventilation rates and to consider increasing ventilation rates in toilets and circulation spaces such as stairwells.
- Increase the air supply and exhaust ventilation.
- Supply as much outside air as is reasonably possible to dilute and remove the virus as much as possible.
- Extend the operation times of supply and extract mechanical ventilation systems.
- Start ventilation at nominal speed at least two hours before building usage time.
- Switch to lower speed two hours after the building usage time.
- In demand-controlled ventilation systems, change the CO2 set-point lower to maintain operation at nominal speed.
- Keep ventilation on 24/7 with lower ventilation rates when people are absent. tinyurl.com/FacMag0620-cibse
Advice from the Federation of European Heating, Ventilation and Air Conditioning Associations (REHVA): tinyurl.com/FacMag0620-rehva