08 February 2021
During a BESA webinar, Professor Cath Noakes spoke to highlight the importance of engineering solutions to take ventilation systems beyond current building requirements after the Covid-19 pandemic. She suggested that a collaborative approach between engineers, researchers and policymakers was needed to form bespoke solutions that would address several important factors.
Noakes told the Building Engineering Services Association’s (BESA) David Frise that there are still uncertainties of what is required in terms of ventilation to control Covid-19; however, there has been a low correlation of high transmission in well ventilated spaces. It is commonly known that ventilation is a beneficial factor for people’s health and wellbeing and should remain a priority to design accordingly as some buildings still do not have any ventilation at all.
Professor Noakes is one of two engineer members of the Scientific Advisory Group for Emergencies (SAGE) and Professor of Environmental Engineering for Buildings at the University of Leeds. She has been providing advice on airborne transmission to the NHS and the government throughout the pandemic. She has also chaired SAGE’s Environment and Modelling Group (EMG) – helping the NHS, Public Health England and government officials understand how the virus survives in the built environment.
“This is a very complex issue, and it will take years to build up the amount of data needed to make sure we can do better”, said Noakes. “ However, as a rule of thumb, we should aim for [air change rate] 10 litres per second per person and CO2 concentrations of 800 parts per million.” She also confirmed that studies had shown the risk of infection was higher indoors when ventilation served less than 3 litres per second, with Covid-19 thriving in cool, dry, dark conditions.
Mechanical and Electrical
Discussing how mechanical and electrical components within a building contribute to transmission rates, Noakes said that recent studies have shown larger water droplets are suspended in the air longer when air conditioning is being used and cautioned against using in unventilated areas.
In response to a recent increase in air-cleaning devices, she said that these methods were not a reason to ventilate less. And there was very little ‘real-world’ evidence to prove the effectiveness as the performance data had come from laboratory-based studies. They may increase indoor air quality by removing other airborne pollutants, but people should be aware that they could be exposed to blue light and other secondary pollutants. They “should be used where you can’t ventilate effectively” and that a deeper understanding of the technology is required if they were to be more widely deployed.
According to Noakes, engineering controls should sit above the measures that rely on human behaviour such as distancing and wearing face coverings in any “hierarchy of risk control”. Building managers should address source control before studying ventilation requirements. This approach would not necessarily lead to increasing ventilation rates.
“This is not just about flow rates as it depends on the size of the space. 10l/s per person is ideal, but if people are close together and for an extended period, we may need more flow rate. You can also have quite a lot of people in a large space with lower ventilation rates.”
She said all these variables showed the need for caution about setting hard and fast rules; suggesting the bespoke solutions should be linked to the relative risk of exposure to the virus. Concentrations of CO2 could be used as a “canary in a cage” to demonstrate whether appropriate ventilation rates were being achieved.
For the future, the industry will have to find ways of proving it is delivering the ventilation performance required in buildings and demonstrate its compliance with the standards that will emerge. Part F of the Building Regulations, which is currently under review, could be used to improve on the IAQ measures likely to be introduced in the forthcoming Environment Bill, the BESA webinar heard.
“The gap is between what we write down as a standard and how we deliver. There are buildings out there that don’t have any controlled ventilation at all – they don’t meet any building standards, but we can’t just close them down,” Noakes explained.
The government will have to find a balance between its ambition for a net zero carbon built environment and one that achieves good health outcomes for people, she added.
“I hope that people have recognised early enough that ventilation is really important. There is a risk that we try to deal with net zero by sealing [buildings] up more. The problem is that it is always much easier to measure energy performance than ventilation effectiveness – we have to address that too.”
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