On investigating instantaneous wind-driven infiltration rates using CO2 decay method

Carbon dioxide has been already recognized as a potential tracer gas towards estimation of the mean air exchange rates (ACH) of a room or building. The wind direction and mean wind velocity have been also clarified as critical factors that affect the air infiltration. In this study, the indoor CO2 concentration is detected and logged at three specific points in an office room for seven selected measurement-periods. The decay method is used to estimate the leakage rates. In parallel, an ultrasonic anemometer is used outdoors for monitoring wind characteristics, as the direction angle and the instantaneous velocity components, while the turbulence intensity is calculated. The results of ACH vary from 0,32h-1 to 0,75h-1 from measurement to measurement and thus an investigation is carried out from the perspective of unsteady windy conditions. A spectral analysis of the wind measurements is applied and the corresponding power spectra Svv(f) are correlated to the mean ACH of the room, giving a better understanding of wind-driven infiltration and depicting the role of the wind fluctuations frequency. In addition, a hypothesis of using the spatial distribution of CO2 concentration indoors as airflow pattern tracer is presented respect to the location of the leakages and the local [CO2] fluctuations are discussed as an indicator of leakage detection.