Coronavirus has been a catalyst for new conversations about air quality in buildings. Stantec’s Patrick Chambers has an innovative solution that could be as simple as monitoring noise levels.
While the scientific body of knowledge about air quality, indoor environments and sick building syndrome has grown considerably in recent decades, corresponding innovation in the ventilation space has been “relatively limited,” says Stantec’s mechanical projects engineer, Chambers.
Indoor air quality is typically maintained by forcing outside air into buildings via mechanical ventilation. This strategy is underpinned by the process of dilution, to reduce concentrations of airborne contaminants to safe levels.
“It’s the simplest solution but not necessarily the smartest.” Why? One reason is that the practice assumes that the outside air is clean – but we know, with growing urban pollution and increasing instances of extreme weather events (such as the 2020 Black Summer bushfire season) that this is not always the case.
“Bringing huge quantities of outside air into a building also takes enormous amounts of energy to heat and cool that air,” Chambers adds.
The baseline for how much fresh air is circulated in a building is typically determined by occupancy, and the “rule of thumb” is 10 litres of outside per person, per second. “In an auditorium packed with 500 people, that’s 5,000 litres of outside air every second,” Chambers explains.
This 10-litre benchmark has been around for around a century and is based on sound body of epidemiological evidence. Sick building symptoms surged during the energy crisis of the 1970s, for instance, when ventilation rates were lowered to save money.
COVID-19 has brought a new dimension to the air quality debate, Chambers adds. “The industry is recognising that one of the most important sources of harmful indoor contaminants are from people themselves.”
Stantec is currently collaborating with several universities to explore how to better balance outside and recirculated air. One of those projects, in partnership with physicist Professor Lidia Morawska from Queensland University of Technology, is investigating how sensors could be deployed to monitor aerosol emission.
Morawska alongside more than 200 other experts from 32 countries, co-authored an open letter to the World Health Organization in July which argued that aerosol transmission could spread COVID-19. WHO guidance states that COVID-19 is transmitted primarily between people through respiratory droplets and contact. Aerosol transmission involves microscopic respiratory particles that can hang in the air for long periods and can be transmitted over distances greater than one metre.
Morawska has demonstrated that viruses are released when we breathe, talk and cough, and she has tested various vocal activities that have “determined that talking loudly, for instance, emits more aerosols,” Chambers explains.
“If instead of being transfixed on increasing dilution rates in buildings, we focussed on exhausting from the point of aerosol release, we could maintain safer base-line levels of indoor pollution/contaminant, without having to significantly increase the quantity of outside air that being processed by the mechanical ventilation system”.
The power behind the strategy is smart sensing technology, which is already being installed in buildings around Australia.
“More research is needed. But a simple way could be to use sensors to identify when people are talking loudly, and for a local exhaust system to automatically switch on at that point and discharge the air to atmosphere.”
Stantec is currently developing tools to model the effectiveness of this strategy, and Chambers points out that most buildings already use supplementary exhaust systems to address air quality issues at their source.
“We know printers are sources of volatile organic compounds, for example, so we install exhaust grills over printers to get rid of those VOCs at the source.
“If we are trying to achieve low concentrations of infectious aerosols in buildings, we can either significantly increase dilution, or exhaust aerosols at the point of release. The latter is considerably easier and doesn’t come with a huge energy penalty.”
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