Modelling as a Tool to Evaluate Continuously Measured Concentration Value of Gaseous Indoor Air Pollutants
Results from studies of air quality in buildings are often difficult to interpret and evaluate and, in order to avoid erroneous conclusions, special evaluating tools may be needed. Modelling in various forms can be used as a method of evaluating measured values from such investigations. This thesis discusses modelling of gaseous pollutant concentrations in indoor air with the focus on identification of the sources of the pollutants.
The results are mainly obtained by field measurements and the data are analysed by use of a mass balance equation. One of the basic requirements for using the method described, is that continuously monitored concentration values are available from measurements obtained, for both supply air and exhaust air of the room or building studied. Modelling applied to continuosly monitored concentration values can reveal whether the pollutants originate outdoors or indoors. The strength of the indoor pollutant source or sink can also be determined.
The modelling described can be applied at the design stage of a building in order to calculate the ventilation rate required to overcome the concentration of gaseous pollutants. The effect of different ventilation strategies, for example airflow rate control, can also be investigated in this way.
It is essential to have knowledge about the air change rate when investigating the indoor air quality. The air change rate of a room or a building can be determined in several ways. A new method is suggested for determining the air change rate, which unlike conventional tracer gas methods does not require the supply of an additional tracer gas. Instead, the air change rate is determined by measuring the normal CO concentration in both the supply air and the exhaust air, thereby eliminating the necessity for further measurements. The calculated exhaust air concentration values of CO are compared to the measured values for various air change rates. The air change rate that gives the best correlation between calculated and measured values provides a good estimate of the air change rate.
The modelling described in the thesis has proved to be a useful tool when evaluating field measurements of pollutant concentrations in indoor air. The method gives adequate accuracy which makes it suitable for many different situations, omitting the need for tedious calculations.