The development of an occupancy-controlled exhaust air ventilation system

Many dwellings with natural or gravity ventilation systems suffer from poor airchange rates. In Sweden, especially houses built in the 1960-ies and 1970-ies heated with electric resistance heating and thus without chimneys, are at risk. Improving the airchange rate in these houses is to some extent performed to decrease Radon gas concentrations where appropriate. For comfort, most homeowners learn to live with low airchange rates, accepting e.g. odours or window condensation and trying to compensate this with increased airing. They are often reluctant to install mechanical ventilation systems. This paper describes a new concept for an occupancy-controlled exhaust air ventilation system. The system features bedroom night-time ventilation, wet-room day-time ventilation and variable total air flow at a low installation cost. The system has since autumn 1994 been successfully installed in four houses and evaluated by air flow measurements, tracer gas tests, multizone airchange calculations etc. The homeowners are very pleased with the performance of the systems and the improved airchange rates.