Project partners
This research activity was a three-year, multi-partner project between the NRC-IRC, INSPQ, the Centre Hospitalier Universitaire du Québec (CHUQ) and Canada Mortgage and Housing Corporation (CMHC). The Ministère de la Santé et des Services sociaux du Québec and Health Canada were also partners.
INSPQ was responsible for coordinating the activities in the field, recruiting the participants and monitoring the health of asthmatic children. NRC was responsible for characterizing the environmental conditions, especially the IAQ and the ventilation scenario. A task group on ventilation, which was led by CMHC and included members from NRC and INSPQ, was responsible for the design and implementation of the ventilation interventions.
A field study investigating the impact of residential ventilation rates on indoor air quality (IAQ) and the respiratory health of asthmatic children in Québec City, was recently completed by the NRC Institute for Research in Construction (NRC-IRC) and the Institut national de santé publique du Québec (INSPQ). The objectives of this study were threefold: to determine whether an increase in ventilation would lead to a corresponding decrease in the children’s asthma symptoms; to correlate ventilation rates with IAQ; and to support research for determining health-based ventilation rates.
The study showed that in many homes, and particularly children’s bedrooms, ventilation rates did not meet the objectives of the building code. Through either the installation of a Heat Recovery Ventilator (HRV) or an Energy Recovery Ventilator (ERV), or the optimization of existing ventilation equipment, the ventilation rates were sufficiently increased. By pre-heating or pre-cooling the incoming air as required, HRVs or ERVs enable an increased volume of outside air coming into the home while minimizing the heating/cooling costs normally associated with natural or traditional mechanical ventilation.
In a large number of homes, the relative humidity (RH) was found to be too low in winter. Low RH levels are often associated with a negative impact on occupants’ comfort and might also aggravate respiratory symptoms. Because introducing more cold outside air in winter further reduces RH, low-RH homes were chosen for the installation of the ERVs (instead of HRVs) to increase the ventilation rate. The ERV membrane allows the transfer of moisture from the outgoing air to the incoming air, thus preventing the home from becoming too dry. Whether contaminants, like formaldehyde from the indoor air, are re-circulated with the water vapour through the membranes, is not fully understood yet.
Dust collected in a specialized vacuum is analyzed for semi-volatile organic and biological compounds related to the presence of mould and bacteria.
Equipment used to measure the ventilation rate in the home (large black box on the left of the table), to sample volatile organic compounds in air (two small black rectangular devices in the centre) and measure the concentration and number of aerosols (blue and white box on the right).
Preliminary results showed that increased ventilation improved the IAQ, demonstrated by the reduced concentrations of volatile organic compounds (VOCs) and airborne mould spores. Before the interventions, about a third of the homes exceeded the Health Canada guideline of 50 µg/m3 during the winter season. By increasing the ventilation rate, a decrease of the formaldehyde concentrations by 35% on average was observed, with the result that all homes met the HC formaldehyde guideline.
Study design
Asthmatic children were recruited through the Centre Hospitalier Universitaire du Québec. The homes were visited twice during the heating season and once in summer, both before and after the intervention, for a total of six visits. At the end of the three visits during the pre-intervention phase, HRVs or ERVs were introduced in 50% of the homes selected at random, keeping the other 50% as controls. The same set of parameters was measured during the three post-intervention visits. NRC staff was responsible for measuring a comprehensive set of IAQ-relevant physical, chemical and microbiological parameters.
In summer, formaldehyde concentrations were found to be generally much higher, with 64% of the homes exceeding the guidelines before the intervention. However, through improving the ventilation rate, this percentage was significantly reduced. Formaldehyde in the air is a known irritant and can potentially trigger asthma. Some of the measured VOCs are also suspected to pose health hazards.
For more information
Data on the improvement of respiratory health through this intervention will be available in Summer 2012. For more information, contact Hans Schleibinger hans.schleibinger@nrc-cnrc.gc.ca at 613-993-9702.
