Tracer studies of airflow and air exchange

Release of a tracer gas, typically SF6, can enable airflows through buildings to be quantified and identified when other methods such as pressure differential testing or smoke testing cannot perform adequately.

Tracer decay testing permits measurement of the outdoor air exchange in the building, measured in air changes per hour (ACH). Once all spaces in the building have uniform concentration of tracer, the outdoor intake is opened and the levels of tracer measured as they decline. The slope of the curve is the air changes per hour.

In the test on the right, the initial equalization can be seen, along with the slow decrease of tracer from outdoor air infiltration, followed by the rapid drop in tracer concentration once the outdoor air intake is opened. Each ACH can be calculated to determine if the space is being adequately ventilated.