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A landmark study by the City of Melbourne focused on three options to prevent the spread of Covid-19, while at the same time reducing energy use: open windows; in-ceiling HEPA air filters and a displacement ventilation system.

The BREATH project was conducted in partnership with Cbus Property, University of Melbourne, AG Coombs, SEED Engineering and Westaflex, with peer review by AURECON.

Over a span of three months the study, which is available on the City of Melbourne’s website, compared the energy use and performance of a number of ventilation retrofit options at full scale. 

Measurements were taken in a full-scale building in Melbourne’s CBD, namely Cbus Property’s soon-to-be redeveloped 423 Bourke Street, Melbourne, rather than in a lab.

City of Melbourne Lord Mayor Sally Capp said the study was important because the fear of infection remains a barrier for some city workers returning to the office.

“We encourage building owners, tenants and partners to take the BREATH findings on board, and to help us create more healthy and sustainable workspaces in the CBD.” 

The three options the study looked were:

The options were compared to a “business as usual” baseline, where there was no change in the building’s ventilation.

The displacement ventilation system, designed by AG Coombs, used a system of downpipes and diffusers to supply cold air from near the floor, rather than from the ceiling. 

The theory is that this setup will put the coldest air near the floor. As the air is heated by workstations, it rises up to air returns in the ceiling.

The in-ceiling HEPA air filters in the trial were similar in terms of power use and cleaning efficiency to portable systems, except they have the added benefits of being able to be tied to a building management system and can’t be accidentally moved by or turned off by staff. 

The good news is that all three ventilation options improved the safety of occupants, and reduced the chances of viruses being spread through the air when an infected person is in the building.

The study found that while the displacement ventilation system has a higher upfront cost, it performs the best in terms of limiting virus spread, reducing Covid transmission by 83 per cent. It also provides the lowest ongoing energy use, reducing it by around 20 per cent.

While open windows are great for safety (reducing transmission by 53 per cent), they perform poorly in terms of their energy use when a chiller is being used. Openable windows are also not always present in office buildings, and might not be a viable option in Melbourne’s climate.

Meanwhile, in-ceiling HEPA filters have a low upfront cost and only contribute a slight increase in power use. But the researchers warn that building owners need to constantly monitor and replace filters for them to be effective.

University of Melbourne head of mechanical engineering, Professor Jason Monty said that because most of the city energy cost goes to ventilating buildings, BREATH will improve our ability to reach net zero carbon faster.

“BREATH has given us the knowledge to predict the best type of retrofit to simultaneously reduce carbon footprint and infectious disease transmission,” Professor Monty said.

Meanwhile, Cbus Property’s chief executive, Adrian Pozzo, said the findings will help to keep his firm’s tenants safer by increasing levels of fresh air in the workplace.

“One of the key challenges with enhancing indoor air quality and mitigating potential transmission of airborne viruses such as Covid-19, is to balance that with the energy performance of our buildings.”

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