Developing tracer gas technique to determine interzonal air exchange rate.

The use of local exhaust is considered to be the most effective way to control pollutant dispersion from intense sources, such as in kitchens, in toilets, as well as in copy machine rooms. The optimum air exhaust rate required to prevent pollutants from escaping into the major occupant areas very much depends on the natural air exchange rate(AER) between the hooded room and the major room space. This paper presents a mathematical model and a test procedure of using tracer gas technique to quantify the AER. In this study, the mathematical model analyzes the balance of a tracer gas in two adjacent zones, and establishes two correlations between the dimensionless increaseldecay rates of the gas concentrations and the AER. The mathematical model reveals two alternative ways to determine the AER: a). Tracer gas concentrations in both rooms involved be monitored; b).Tracer gas concentration in one of the two spaces be monitored. The latter method was validated in a test for AER quantification between ceiling void and room in a test chamber. Finally the proper use of the two methods is discussed, and it is suggested that the techniques developed in this study can be used for estimating minimum exhaust rate requirement for ventilation system renovation in existing buildings.