When the Spanish Flu pandemic started in 1918, cities which carried on as normal were hit with a huge upward curve of cases. Cities which cancelled their public events and told people to stay at home had a much flatter curve and as a result, their health care systems weren’t overloaded and a lot more people received treatment and survived.
That’s what it means to ‘flatten the curve’. We’re already looking at ways to stop the spread through public health directives like social distancing and wearing masks.
But what else can we do to mitigate the risk of transmission? The answer may lie in alternative Heating, Ventilating, and Air Conditioning (HVAC) system designs.
SARS-CoV-2 (COVID-19) is highly contagious and spreads readily via person-to-person transmission, with over 18 million infections and nearly 690,000 fatalities worldwide.
There are three main modes of person-to-person transmission:
It’s the third mode of transmission where HVAC systems become critical. Research indicates that you are 20 times more likely to catch the virus if you are indoors versus being outdoors.
Virus particles can also stay airborne and travel significant distances through airborne transport or through recirculation via the HVAC system. Tiny water droplets from coughing, sneezing or even talking can travel reasonable distances.
The issue with traditional ducted air conditioning systems is that they can be effective at picking up the smaller aerosols and circulating them.
Firstly, the supply air comes into a room via an air diffuser which is designed to mix with the air already in the room so that the occupants don't feel cold draughts. This means if somebody in the room is infectious, people in the vicinity of the infectious person are breathing in the mixed air and possibly the infected aerosols.
Secondly, traditional HVAC systems are designed to return air from the room to the unit and then redistribute it. This creates the potential for the system to recirculate the infected aerosols throughout the areas served by the system, further spreading the infected aerosols.
Alternative systems like Passive Chilled Beams (PCB) and underfloor systems can act to minimise viral transmission simply because they’re not designed to mix the room air to the same extent.
PCB systems are based on convective air currents, while underfloor systems are designed to push out contaminated room air. Although these are two different ways of making a HVAC system work, both can act to minimise the infection risk associated with the spread of airborne contaminants.
Part of the reason these alternative systems were developed in the first place was to improve indoor air quality and reduce sick building syndrome. It’s only logical that these systems can help with minimising transmission of COVID-19 as well.
With recirculating type HVAC systems, the potential for spread can be reduced by increasing outside air rates to dilute the return air. Where practical, system designs using 100% outside air are best practice.
What we must do moving forward is pick up learnings from the global research into best practices and apply these design techniques both in new building designs and throughout our existing building stock.
At Arcadis Australia Pacific, we’re undertaking a new series of studies in conjunction with internationally prominent researchers to develop practical guidelines for HVAC systems.
As well as alternative HVAC systems for new buildings, we are also investigating new ways that existing systems can be altered to reduce viral transmission.
But that’s just one piece of the puzzle.
We also have teams across the globe working to improve the way the virus is tracked via the wastewater systems, smarter ways of disinfecting spaces, researching viral-resistant surface coatings and developing better government models for social distancing in public spaces.
Our ultimate goal is to combine our findings to reduce the spread in the short term and eventually stamp out the virus altogether. It's a fascinating journey, and I’d like to think that we have a lot to be proud of given the work we’re doing.
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