Measurement of the air change rate and ventilation characteristics during short term transient phenomena

Different measurement procedures are available for the experimental assessment of air change rates inside ventilated enclosures. These mainly consist of tracer gas techniques and can usually be applied to steady-state or moderately transient conditions and when a continuous mixing of the indoor air is assured throughout the test. However, due to the relatively slow response of the gas analysers, none of these procedures can usually be applied to fast transient phenomena that last 15 minutes or less. Moreover in many cases of natural ventilation strategies, the continuous mixing of the indoor air would compromise and interfere with the ongoing ventilation process. In this work, a modified tracer gas technique that is suitable to experimentally assess the transient features of the ventilation performances during these phenomena is proposed and tested for the case of buoyancy driven single-sided natural ventilation. The results are critically compared with the air flow rates assessed through anemometric measurements. The measurement features, limitations, shortcomings and uncertainties are also discussed.