Modelling indoor air pollutant concentrations considering air mixing conditions.

Modelling of indoor pollutant concentrations that varies in time can be a useful tool forestimation of the strength of internal sources and sinks. Usually the modelling has beencarried out using one zone, i.e. with the assumption that the air is well mixed [1,2,3]. Thepresent paper demonstrates that the methodology may be modified to fit multizone situations.By studying the decay of a tracer gas, a correct model can be obtained for a specific volume ina building. For each zone in the volume, the model will include one exponential function.Once the correct model is obtained it can be used to determine the strength and the origin of apollutant source or sink. This method will increase the agreement between the measured andcalculated indoor concentration of the pollutant studied.As pointea out in this paper, the well mixed assumption with one zone can not be used in allbuildings. In a specific case, which was created in a test chamber, the total volume had to bedivided into three zones, with different airchange rates to achieve a satisfactory agreementwith measured data. A two zone model was sufficient to study fast variations in concentration,but to study slow changes a three zone model was needed. A similar situation, like the onecreated in the test chamber, may arise in buildings in operation when the supply air devicesand the exhaust air devices are incorrectly installed and as a result there is a short circuit,which divides the volume into two or more zones with different airchange rates.