Application of a passive tracer gas technique in naturally and mechanically ventilated school buildings.

The homogeneous emission passive tracer gas technique is described. This technique relies on an even distribution of constant tracer gas emission rate within the object to be measured, so that the emission rate per volume unit is constant. The local steady state concentration of the tracer gas is directly proportional to the local mean age of air and the emission rate per volume unit. The technique was applied in 10 school buildings, of which 4 were newly constructed naturally ventilated buildings, 2 were old naturally ventilated buildings, 2 were old mechanically ventilated buildings and 2 were newly constructed supply and exhaust ventilated buildings. The result shows that the ventilation rates in naturally ventilated schools are relatively low compared to required standards. It demonstrates the importance of not only rely on the naturally induced ventilation rate, but also to use other means for improving the air quality during or between lessons, like window opening.