Challenges and opportunities arising from different ventilation approaches: controlled experiments conducted at the Canadian Centre for Housing Technology

The ingress of naturally occurring radioactive radon gas from the soil into buildings can occur both by convection through any openings in the foundations as a result of pressure differentials and by diffusion across an airtight barrier (World Health Organization 2009). Residential ventilation systems and exhaust devices can affect indoor radon concentrations if they result in depressurization of the conditioned spaced relative to the outdoors or to the soil below the foundations or if they supply outdoor air directly. Balanced mechanical supply and exhaust ventilation (MSEV) systems tend to dilute the indoor radon concentration; however, some depressurization of the lower level can result from the air distribution if air is primarily supplied to upper level rooms and exhausted from lower level rooms. Mechanical exhaust only ventilation (MEV) systems depressurize the conditioned space and rely on the resulting infiltration of air across the building envelope that can be above and below grade. Higher indoor radon concentrations have been reported for the larger depressurization of 5-9 Pa in MEV houses relative to 2-3 Pa in MSEV houses (Arvela et al. 2014). In this study, indoor radon concentrations were measured in the National Research Council (NRC) Canadian Centre for Housing Technology (CCHT) semi-detached net-zero energy-ready smart house during depressurization testing using a duct blaster, and the depressurization resulting from typical exhaust devices was evaluated. Indoor radon concentrations were also measured during depressurization testing in a smaller NRC test house.