Ventilation is a key component in an efficient, healthy home. When improving the energy performance of homes – often with increased envelope tightness and insulation – selecting ventilation systems is not always straightforward. There is a lack of research to support better performing residential mechanical ventilation systems, such as balanced ventilation compared to exhaust-only ventilation. Building codes and standards do not attempt to address delivery of outdoor air to each space or forced air circulation/distribution of ventilation air. Instead, an assumption is made that for all ventilation system situations, the entire house is a single, well-mixed zone and the focus is only on the annual average exposure of contaminants. With this assumption as the basis for ventilation design, the ventilation rate must be high enough to accommodate the worst performing system, which is exhaust-only ventilation.
In 2016, National Research Council (NRC) researchers, led by Principle investigator Boualem Ouazia, initiated a study on the in-situ impacts of two ventilation systems with various indoor mixing scenarios: no mixing, partial mixing and continuous mixing, including the impacts of indoor pressure, ventilation effectiveness (whole-house air change rate) and air change rate between living space zones. The project involved a side-by-side testing of the twin single detached test houses located at the NRC's Canadian Centre for Housing Technology.
Exhaust-only ventilation testing showed lower whole-house air change rate, lower uniformity of air exchange rate between indoor spaces, higher concentrations of formaldehyde and volatile organic compounds (VOCs) and higher whole-house energy consumption than did the balanced energy recovery ventilation system. The exhaust-only system depressurized the house (-2 to -4 Pa) and the balanced energy recovery ventilator system was able to slightly pressurize the house (1 to 3 Pa). This showed that the single-point exhaust ventilation system was inferior as a whole-house ventilation strategy, due to the uncontrolled source of outdoor air not directly from outside (the ventilation air was not distributed) and because no provision existed for filtration. In contrast, the balanced ventilation system showed that there is a significant benefit to drawing outside air from a known outside location, and filtering and fully distributing that air.
The balanced ventilation system reduced formaldehyde by 37% to 70% in winter and by 6% to 34% in summer. It also, reduced the VOCs, alpha-Pinene by 26% to 89% and Toluene-d8 by 8% to 76% in winter. The summer data showed a reduction the VOCs; alpha-Pinene by 87% to 339%, Toluene-d8 by 45% to 88%, Heptane by 40% to 91% and Benzaldehyde by 35% to 406%. The data analysis showed that residential balanced ventilation systems improved the whole-house air change rate by 6% to 34%. This showed that exhaust-only ventilation was inferior as a whole-house ventilation strategy, because the source of outside air was not directly from outside, the ventilation air was not distributed, and no air filtration was provided.
In contrast, the balanced ventilation system showed that there is a significant benefit to drawing outside air from a known outside location, and filtering and fully distributing that air. The balanced ventilation confirmed the energy saving benefit by reducing the average weekly whole-house heating/cooling and ventilation energy consumption from 2.1% to 8.5%.
This research project demonstrates that a depressurized home will experience unknown air paths or sources of outside air, since the exhaust-only ventilation system can cause indoor air to be more contaminated depending on what contaminants are picked up on the way in.
Residential balanced ventilation system effectiveness and IAQ Impacts. Report # A1-009760.1 is under review and will be available by spring 2019
Residential balanced ventilation and its impact on indoor pressure and air quality. Paper presented and published at the 39th AIVC Conference on smart ventilation for buildings 2018