Determination of local mean ages of air by the homogeneous injection tracer gas technique.

The paper describes the application of a new tracer gas technique for studying ventilation. The technique is called the homogeneous injection technique, since it relies on the continuous injection of tracer gas in all parts of a zone-divided ventilated system, with tracer injection rates, which are strictly proportional to the zone volumes. The steady state concentrations of tracer gas in the different zones are proportional to the local mean ages of air. The technique is demonstrated and compared with other tracer gas techniques in an indoor test house with controlled ventilation under different conditions of air mixing and door opening. It is shown that the homogeneous injection technique is easy to use and has some attractive advantages, compared to the tracer decay technique. It is shown that reliable results are obtained even without artificial mixing of the air.