The best energy efficient ventilation systems for office buildings to stop the spread of viruses

A groundbreaking study by the City of Melbourne focused on three options for preventing the spread of Covid-19 while reducing energy consumption: open windows; HEPA air filters in the ceiling and a displacement ventilation system.

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

Over a three-month period, the study which is available on the Melbourne City websitecompared the energy consumption and performance of a number of ventilation retrofit options at full scale.

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

Melbourne City Mayor Sally Capp said the investigation was important as fears of infection remain a barrier for some city workers returning to the office.

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

What the study looked at

The three options the study looked at were:

  • open windows
  • HEPA Ceiling Mount Air Filters
  • a displacement ventilation system

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

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

The theory is that this arrangement will bring the coldest air near the floor. Since the air is heated by workstations, it rises to air returns in the ceiling.

The HEPA in-ceiling air filters in the trial were comparable to portable systems in power consumption and cleaning efficiency, except they have the added benefits of being able to be linked into a building management system and not accidentally moved or turned off by personnel.

So how did the different options perform?

The good news is that all three ventilation options have improved residents’ safety and reduced the chances of spreading viruses through the air when an infected person is in the building.

The study found that while the displacement ventilation system has a higher initial cost, it performs the best in terms of limiting the spread of viruses, reducing Covid transmission by 83 percent. It also offers the lowest continuous energy consumption, with a reduction of about 20 percent.

While open windows are great for safety (reduces transmission by 53 percent), they perform poorly in terms of energy consumption when a chiller is in use. Public windows are also not always present in office buildings and may not be a viable option in Melbourne’s climate.

Meanwhile, ceiling mount HEPA filters have a low initial cost and only contribute to a slight increase in power consumption. But the researchers warn that building owners must constantly monitor and replace filters to be effective.

Professor Jason Monty, head of mechanical engineering at the University of Melbourne, said that because most of the city’s energy costs go into 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,” said Professor Monty.

Meanwhile, Adrian Pozzo, CEO of Cbus Property, said the findings will help keep his company’s tenants safer by increasing the amount of fresh air in the workplace.

“One of the key challenges in improving indoor air quality and reducing potential transmission of airborne viruses, such as Covid-19, is balancing that with the energy performance of our buildings.”

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