Seasonal variation in monthly average air change rates using passive tracer gas measurements

Indoor air quality in dwellings is largely determined by the air change rate (ACR) and the magnitude of indoor air pollution sources. Concurrently, great efforts are made to make buildings energy efficient, which may result in low ACRs. In the present study, the monthly ACR averages were measured in five dwellings in Greater Copenhagen, Denmark. A passive tracer gas technique (Perfluorocarbon) was used to measure ACR in a seven-month period. Considerable differences were observed between the dwellings with monthly ACRs ranging from 0.21 to 1.75 h^-1. Only smaller seasonal variations, generally less than 30% of the overall average, were observed within the same dwellings, except during the warmest summer period, when ACR was generally higher. This suggests that a single measurement of the average ACR is a good indicator of the general situation, except for the summer period, and that varying driving forces for natural ventilation is partially compensated by changed occupant behaviour.