Impact of combined dilution and pressurisation effects of ventilation air on indoor contaminant concentration.

When outdoor air is the main source of pollutants indoors, mechanical air ventilation can be viewed as having two fronts of action in controlling indoor air quality. The first is its capacity to remove indoor air pollutants by dilution, and the second is its capability to prevent, through its pressurisation effect, the pollutant source (i.e. untreated outdoor air) from infiltrating, through the building envelope, to the occupied space. This paper discusses the impact of combined dilution and pressurisation potentials of ventilation air on indoor contaminant concentration when outdoor air is the main source of pollutants. Utilising an airflow model in conjunction with a one-compartment indoor air quality model, contaminant concentration behaviour within a single zone enclosure is predicted at various enclosure air leakage, system characteristics and pressurisation levels. Results from this study are indicative of the appreciable impact of the pressurisation effect of ventilation air which needs to be considered for a better assessment of ventilation air effectiveness and further enhancement of indoor air quality control.