An empirical model for outdoor contaminant transmission into residential buildings and experimental verification

This study presents an empirical model for outdoor air contaminant transmission into residential buildings. It has been found that the air exchange rate plays an important role in the rate of transmission of outdoor air contaminants into the indoor environment. The model shows that the air exchange rate appears as a factor in an exponential term which influences the ratio of the integrated average indoor and outdoor contaminant levels. Two empirically fitted parameters related to the transport characteristics have been identified from the model. Experiments were conducted on site to verify the model. Five homes in Hong Kong were selected for the measurement from April of 1998 to January of 1999 and PM2.5 was chosen as the target pollutant in the study. A significant portion of PM2.5 in the ambient air in Hong Kong comes from vehicle emission, which is a common and serious problem in many highly populated cities. Detailed PM2.5 measurements were conducted in the homes and ventilation rates were concurrently measured to investigate the relationship between the ratio of the indoor/outdoor pollutant levels and the air exchange rates. Two ventilation modes, window-open and window-closed, were considered in the study. Mechanical ventilation was not operating during the measurement. Ratio of indoor PM2.5 and outdoor PM2.5 level was plotted against the air exchange rate. It was found that the indoor and outdoor levels were almost the same when the air change was higher than 4 h−1 and the model was valid for moderate air exchange rates.