Investigating Instantaneous Wind-Driven Infiltration Rates using the CO2 Concentration Decay Method

Carbon dioxide has already been recognized as a potential tracer gas for estimating the mean air exchange rates of a room or building. The wind direction and mean wind velocity have also been identified as critical factors that affect the air infiltration. In this paper, the indoor CO2 concentration has been logged at three specific points in an office room for seven selected measurement-periods. The decay method was used to estimate the infiltration rates (ac/h). In parallel, an ultrasonic anemometer was used outdoors for monitoring wind characteristics such as the direction angle and the instantaneous velocity components. The results of the calculated ac/h varied from 0.32 h-1 to 0.75 h-1 from measurement to measurement and thus an investigation was carried out from the perspective of unsteady wind conditions. The wind direction angle and the relevant velocity components seem inadequate to entirely explain the differences in ac/h and thus the wind turbulence intensity was calculated and a spectral analysis of the wind measurements was applied. The corresponding power spectra Syy(f) were correlated to the mean ac/h of the room, giving a better understanding of wind-driven infiltration and depicting the role of the wind fluctuation frequency. In addition, a hypothesis of using the indoor spatial distribution of CO2 concentration as an airflow pattern tracer is presented respective to the location of the leakages. Finally, the local CO2 fluctuations are discussed and the respective standard deviations are presented as indicators of leakage detection.