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Why our HVAC and buildings can’t always keep us safe

Last updated: 05-04-2021

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Why our HVAC and buildings can’t always keep us safe

OXYGEN FILES: In recent weeks, air quality in Sydney and Brisbane, and in many regional areas, has ranged from bad to extremely hazardous because of bushfire smoke. With health experts telling people to stay indoors because no amount of exposure to the smoke is safe, a deeper issue is emerging: most of our buildings can’t block the pollution.

On Tuesday, when Sydneysiders struggled to breathe because of unprecedented levels of bushfire smoke, director of sustainable business consultancy Action Sustainability, Alistair Coulstock, emailed his staff about hazardous air quality outdoors and potentially indoors.

A monitor inside Coulstock’s “leaky” 1960s Frenches Forest brick veneer home alerted him to the problem. It indicated excessive particulate pollution inside his house, including extremely dangerous PM 2.5 and PM1 particles, even when all doors and windows were closed, he told The Fifth Estate. The house has a split system airconditioner but it is rarely used, he says.

A second dwelling being built on the block according to Passive House design principles will have a fully-sealed building envelope and a heat exchange ventilation system for the bedrooms to supply fresh outdoor air.

However, Coulstock says the filters in many ventilation systems used for Passive House homes might not filter out the micro particulates that are most dangerous to our health, unless the filter is HEPA grade.

Australian Institute of Refrigeration, and Heating(AIRAH) fellow and HVAC consultant, Vincent Aherne, who is based at Port Macquarie, has been experiencing fire and smoke impacts at close range.

He told The Fifth Estate it would be “very rare” for a commercial HVAC filtration system to be designed for the level of air pollution generated by the recent bushfires.

“Residential systems are generally provided to a very low or minimum filtration performance, commercial systems would meet a higher standard, none would be designed for recent air contamination levels,” he says.

Aherne says most typical residential systems have a “rock catcher” filter that allows most micro-particulates to pass through.

Large ducted residential and light commercial systems would generally meet a slightly better filter specification, but performance will depend on the amount of time between change-outs or inspections.

Most contemporary filter systems are media-based particulate filters that “sieve” the air and collect the particulate of the target size.

Now that smoking has been banned in public and commercial spaces, some filters, such as electrostatic filters, are rarely used. However, they would be more effective at removing bushfire smoke particulates than other kinds of filters.

Increased use of HVAC systems during this smoky season will have pushed up energy use, not only because more people are relying on mechanical ventilation, but because as particulates build up in filters, HVAC fans use more energy to push the air through. Refrigeration compressors may also have to work harder.

There is also a risk air filtration system that could totally fail if particulates continue to build up. Building managers and homeowners need to clean filters more often.

There are other problems, too. Buildings that do not have natural ventilation must have an outdoor air intake. But many naturally ventilated buildings – such as homes and apartments – have split system airconditioning that does not have outdoor air input.

Aherne says people tend to close the natural ventilation openings to preserve the cooling effect. But that means no fresh air circulates within the space, putting people at risk of inhaling contaminated air.

“This practice of airconditioning a naturally ventilated building complies with building codes because the occupants are able to control their ventilation needs by opening windows,” Aherne says.

“Good design requires that the outdoor ventilation and the airconditioning system are integrated, either by combining the two in a single system or having a separate outdoor air ventilation system to compliment the air conditioner.”

Current smoke levels call into question the popular wisdom that homes need to be airy in this climate.

In fact, if heating or cooling is required, occupants need to be able to seal a building tightly to reduce the energy required to maintain thermal comfort.

However, there are systemic problems across design, specification, construction and compliance inspections that leave homes leaky.

Coulstock says it highlights another reason state and federal governments must work to improve existing dwellings. It will make buildings safer in the event of air pollution or extreme heat events, and will help cut carbon emissions and energy bills.

When it comes to new buildings, we need to spend a little more on construction to reap the benefits of operational energy use and occupant safety and wellbeing.

“Action is well overdue in terms of improving the quality of our built assets,” Coulstock says.

If you have more insights in this area please get in touch at editorial@thefifthestate.com.au and let us know.


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