A BREATH OF FRESH AIR: HOW CAN PASSIVE HOUSE IMPROVE INDOOR AIR QUALITY?

The COVID-19 pandemic has thrown a spotlight on the importance of having clean, healthy air in our homes, offices and public indoor spaces. Passivblog spoke to air quality specialists about what to look out for, and how the Passive House standard helps people breathe easier.

So what is indoor air quality?

Julien Colangelo, President of the Indoor Air Quality Association of Australia, says it’s important to understand and control indoor air pollutants as they can affect people’s health, comfort and wellbeing. “Common causes of poor indoor air quality and indoor air pollution include fuel-burning and combustion, excess moisture, mould, bacteria and viruses, poor ventilation, cleaning chemicals and building materials,” he says. Julien adds that a focus on energy efficiency has reduced the amount of fresh air entering homes and buildings, which can lead to a build-up of indoor contaminants. Passive House certified buildings achieve energy savings using high performance building materials, insulation and design, but use mechanical ventilation with heat recovery (MVHR) to provide a steady flow of clean air.
“The building is constructed with an airtight design to minimise uncontrolled outdoor air leakage, and a highly energy efficient heat recovery ventilation unit to supply constant fresh air to remove indoor pollutants without causing uncomfortable drafts,” Julien says.
Australian Passive House Association Chairperson Kate Nason says mould and energy efficiency are both prominent issues in the Australian construction industry. “With exponentially rising energy prices, the Passive House standard can provide comfortable and healthy indoor conditions with minimal energy required. It can also prevent a lot of moisture and condensation issues that cause mould,” she says.

How do we know how healthy our air is?

Certified Passive House Designer Cameron Munro from Passive Analytics says there’s an acute lack of awareness among the public and building industry about the levels of pollutants in our indoor environments because we don’t monitor the air quality. But he says certified Passive House buildings maintain a good quality of air regardless of what occupants do, within reasonable limits.
“With a normal house, you’re winging it,” he says.
For example, open windows may not provide adequate ventilation if they are not open wide enough, or if it is not windy enough to provide good air flow.
Cameron says carbon dioxide is easy to measure, and can be used as a general indicator of indoor air quality. Outside, carbon dioxide levels are typically around 420 parts per million (ppm). Inside, trapped carbon dioxide from heating, cooking and breathing can lead to much higher levels. This can temporarily affect concentration and problem-solving ability, and make people feel tired.
“The World Health Organisation guidelines say that it needs to be below 1,000 ppm for good indoor air quality,” Cameron says.
In a typical home in winter, carbon dioxide levels can be highly variable, with spikes reaching 2,000, and even 3,000 ppm. But in a certified Passive House with MVHR, the level is consistently below 1,000 ppm.

*Carbon Dioxide Study at Thornleigh Passive House*

What about cooking and heating?

Cameron says that burning fuel inside is another source of indoor air pollutants. For example, in gas cooking and heating, and fireplaces. Passive House buildings use highly efficient systems to complement the heat recovery from MVHR, typically reverse-cycle split systems which do not produce indoor pollutants and can also help to control humidity. To keep dust from building up in split systems, the filters should be changed regularly.
To remove cooking odours while maintaining airtightness, Passive House buildings often use an internally recirculating range hood with a carbon filter.

*Zehnder Whole Home Ventilation System.*

What about smoke, pollen and dust?

As well as trapped pollutants from indoor activities, indoor air quality can be affected by pollutants such as pollen, smoke and dust, which can come in through windows or gaps from outside the building, or from underfloor, roof or wall cavities.
Cameron explains that Passive House buildings provide a filtered pathway into the house, with all fresh air coming through the ventilation system when windows and doors are closed.
“The standard F7 filter picks out pollen and larger pieces of dust. It also removes some smoke, but not all,” he says, adding that smoke levels are two thirds to half of those in typical houses with closed doors and windows.
Turning off the MVHR for a few hours can help if there is a sudden influx of smoke. But to reduce smoke infiltration further, buildings need to upgrade to a high-efficiency particulate air (HEPA) filter, similar to those used for air purification in hospitals.
“The airtightness of Passive House means a single HEPA filter on the mechanical ventilation inlet can radically reduce smoke infiltration to healthy levels throughout the building. It’d be almost impossible to achieve that level of air quality in a conventional, leaky building” says Cameron.

How can the construction industry help?

In the aftermath of the pandemic, Julien says building occupants are calling for major improvements when it comes to indoor air safety.
“That means architects, engineers, builders, consultants and air quality professionals need to come together to solve and prevent indoor environmental problems for the benefit of everyone,” he says.
Kate adds that the Passive House standard – especially the meticulous attention to airtightness and controlled ventilation – provide a new way of solving indoor air quality issues, particularly in the residential sector.
“We have typically relied on extract-only systems to control moisture and open windows and gaps under doors to control air quality. Neither is working perfectly or predictably as intended, and neither helping us control temperature for reduced energy demand,” she says.

This is the first in a three part series on the role of Passive House in improving and maintaining indoor air quality. Next, we’ll be looking at how Passive House is helping keep children and young people healthy in their schools and classrooms.

Photography by Marnie Hawson Photography, with PurePassiv Passive House and carbon dioxide study at Thornleigh Passive House by Envirotecture.

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