Design factors affecting the passive release of tracer gas for ventilation measurements

The ventilation rate is an important parameter for assessing indoor air quality and energy efficiency. In occupied buildings, ventilation measurements utilising passive methods are preferable to active methods due to their simplicity and less intrusive nature. The perfluorocarbon tracer method can be used to measure long-term ventilation rates for this purpose. This method requires the passive release of a tracer gas which is often a liquid chemical diffusing out of a vial. The tracer gas emission rate is a key parameter of the vial design as if it is too low, the sampler will not be able to detect the tracer gas. If the emission rate is too high, the sampler can become saturated. Both scenarios will lead to inaccurate ventilation results. There is wide variability in vial design but little information about the relative impact of each design factor. Thus, the aim of this study was to compare the emission rate of a common tracer gas, perfluoromethylcyclohexane, using different vials designs i.e. capping styles, septa materials, and fill levels. Samples were kept in an incubator and gravimetric analysis was carried out using a semi-microbalance (resolution: 0.01 mg). The results demonstrate that the emission rate is significantly affected by capping style but not by fill level.