Pollutant dispersion simulated with tracer gas in a naturally ventilated test house.

The New Zealand Building Code has kept with tradition in allowing residential building ventilationdesigns based entirely on openable window areas. Working against this tradition, however, is a trend inNew Zealand towards more airtight construction and declining reliance on open windows. Contributingto this trend are changing patterns of occupancy with fewer people at home during the working week,along with developing concerns for personal security. The research described in this paper is developingnew ventilation strategies for single family residential buildings based on combinations of passive andsimple mechanical systems. A series of measurements are described which used a tracer gas to simulatepollutant dispersion in a multi-room test house. The tracer was released at a constant rate in kitchen andbathroom locations with natural and mechanically assisted ventilation strategies in place. The buildingwas operated in four modes reflecting two levels of building airtightness and with internal doors eitheropen or closed. Results are expressed in terms of the mean age of air and the mean age of the pollutantaveraged over periods of several days.The first order effect of the different ventilation strategies was to control tracer concentrations about aseffectively as a dilution ventilation system. While concentration differences were seen in the differentrooms at breathing height, these were generally smaller than would have been expected to develop understatic driving forces and with limited internal mixing, and are not overly significant in the context oflimiting pollutant exposures within the building. Pollutant removal in the house is presented as a relativecontaminant removal effectiveness averaging over the air volume and over time periods of at least a day.It is clear that the constantly changing driving forces of infiltration reduce some of the potentialcontaminant removal efficiencies that might be anticipated and that closed internal doors effectivelypartition the building into multiple zones. Although only one building has been examined, the resultssignal some simplifications in the way natural and single point mechanical ventilation systems are sizedto meet ventilation requirements in code documents.