The best energy efficient office building ventilation system to stop the spread of the virus

A landmark study by the City of Melbourne focused on three options for preventing the spread of Covid-19, while reducing energy use: opening windows; ceiling HEPA air filter and displacement ventilation system.

The BREATH project was carried out in partnership 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 City of Melbourne website, compared the energy use and performance of a number of full-scale ventilation retrofit options.

Measurements were made in a full-scale building in Melbourne’s CBD, namely 423 Bourke Street, Melbourne, which will soon be rebuilt by Cbus Property, not in a laboratory.

Melbourne City Mayor Sally Capp said the study was important because fears of infection remained a barrier for some city workers from returning to work.

“We encourage landlords, tenants and partners to embrace BREATH’s findings, and help us create healthier and more sustainable workspaces in the CBD.”

What does research learn?

The three options looked at in this study are:

• open the window
• HEPA air filter on ceiling
• displacement ventilation system

This option is compared to a “business as usual” basis, where there is no change to the ventilation of the building.

The displacement ventilation system, designed by AG Coombs, uses a system of downpipes and diffusers to supply cool air from near the floor, not from the ceiling.

The theory is that this setting will put the coldest air near the floor. As the air is heated by the work station, it rises into the air back at the ceiling.

Ceiling HEPA air filters in trials were similar in terms of power use and cleaning efficiency with portable systems, except they had the added benefit of being able to be strapped to the building management system and unable to be accidentally moved by or turned off by staff.

So how do the different options perform?

The good news is that all three ventilation options improve occupant safety, and reduce the chance of the virus spreading through the air when an infected person is inside the building.

The study found that while a displacement ventilation system had a higher up-front cost, it did its best to limit the spread of the virus, reducing Covid transmission by up to 83 percent. It also provides the lowest sustainable energy use, reducing it by about 20 percent.

While an open window is great for safety (reducing transmission by up to 53 percent), it performs poorly in terms of energy use when using the chiller. Openable windows are also not always present in office buildings, and may not be a viable option in Melbourne’s climate.

Meanwhile, the HEPA filter in the ceiling has a low initial cost and only slightly increases the power usage. But the researchers warn that building owners need to continue to monitor and replace filters to be effective.

The University of Melbourne’s head of mechanical engineering, Professor Jason Monty said that since a large part of the city’s energy costs are used to ventilate buildings, BREATH will increase our ability to achieve net zero carbon faster.

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

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

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

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