Healthy Home Environments: Using Positive Pressure Ventilation Systems
Exploring ways to minimise construction and building waste is a passion for Dr Terri-Ann Berry, co-director of the newly formed Environmental Innovation Centre (EIC). Dr Berry has partnered with experienced Master Builder Nigel Benton to develop practical environmental solutions for the construction industry.
Ventilation systems that promote a healthy home environment.
Have you ever felt confused about how best to ventilate your home? There are so many options available. EIC have been keen to test air quality outcomes from the use of different systems. Here is one of our recent examples – time to get a little technical!
Positive pressure ventilation (PPV) systems are the most common form of mechanical ventilation available in New Zealand. These systems draw filtered air from within the roof cavity into the house through one or more ceiling vents, creating a positive pressure which forces air to leak out through gaps in the building envelope, particularly around windows and doors. The performance of these systems depends on the sizing of the fans, the distribution of the ceiling vents throughout the house, and the airtightness of the home. Most systems are fitted with filters, and the quality of the air entering the house can depend on whether these filters are regularly changed or cleaned.
Why Are These Systems Popular?
PPV systems are popular due to several advantages, including:
Lower initial costs: PPV systems are relatively cheap to purchase and install and do not require extensive ductwork.
Ease of installation: Everything can be mounted in the roof space, with a power source and a duct through the hallway ceiling or another central location.
Cost-effective operation: Powered by small fans, these systems in principal do not significantly increase the power bill.
Concerns About Air Quality
Air quality can be measured by determining the amount of tiny particles in the air called particulate matter or PM. These particles are measured over a range of sizes because some sizes have been linked with poorer health outcomes than others. For example PM2.5 means particles which measure 2.5mm or less and these particles are considered to impact human health more than PM10.
The air quality provided by PPV systems into the home has been questioned. One significant concern is that these systems draw air from the roof space, which may be contaminated. According to the G4 Ventilation code, ventilation systems should bring fresh air from outside into the house. PPV systems, however, typically draw air from the roof space, which is not considered fresh air, and may be contaminated with dust, dirt, mould, insect and rodent droppings, or even hazardous particles such as asbestos from asbestos cement roofing or sheet cladding.
Research Findings
Despite these concerns, there is a lack of published scientific evidence and studies to support or refute the claims about the air quality provided by these systems. To address this gap, our research aimed to determine the influence of air taken from the roof cavity on indoor air quality. We conducted a study involving ten houses across Auckland over seven to 14 days during winter. We tested air quality at three points: outdoor, indoor, and inside the roof cavity.
Our findings showed that in five of the houses, PM levels indoors were higher than those outdoors or in the roof. We also compared PM concentrations in the roof and found that in nine of the houses, these concentrations were lower in the roof cavity than outside. This suggests that the roof could actually act as a first filter for outdoor air before it is brought into the house and passed through an additional filter.
We also analysed patterns over the study period and observed that there is no clear relationship between the roof space and indoor pollution.
Furthermore, we analysed the patterns between indoor, roof, and outdoor air quality, as shown in the figure. We found a strong link between the roof and outdoor air quality, indicating that outdoor air significantly influences roof cavity air quality, see how similar the patterns are for these locations? However, we did not find a clear influence between roof and indoor pollution levels, suggesting that the additional filtering by the PPV system effectively reduces contaminants.
Conclusion
Our preliminary research suggests that taking air from the roof may be better than directly taking it from outdoors, as the roof cavity could act as a preliminary filter. However, further studies are necessary to investigate this on a larger scale and over longer periods.
Positive pressure ventilation systems offer several benefits, such as lower costs, easy installation, and cost-effective operation. However, concerns about air quality and the need for summer bypasses highlight the importance of regular maintenance and consideration of the specific conditions in each home. As with any ventilation system, it is crucial to ensure that it meets the necessary standards and provides a healthy living environment.
f you have any questions for the team that you would like answered in this column, please contact us.
This research forms a partial requirement for the PhD of German Hernandez, Universidad Politécnica de Madrid.