Assessing the variability of the air change rate through tracer gas measurements

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The increasing energy concerns across the European Union enhanced the importance of buildings ventilation and pointed out the reduction of energy for ventilation as one of the targets. The measurement of ventilation and leakage rates are therefore necessary to understand buildings performance, especially in mild climate countries where often dwellings ventilation is adventitious and highly influenced by user behaviour. In mild climate countries, natural ventilation is the most common strategy. The air movement is therefore a combined result of pressure differences produced by wind and buoyancy forces, which are both time-dependent. Under these circumstances, one-time measurements of the air change rate, made over short periods, may not be an accurate indicator. An experimental campaign for the evaluation of the air change rate in a Portuguese dwelling was conducted over a period of two months. During this period, tracer gas measurements were performed in two compartments: (R1) living room; and (R2) bedroom. In each, two different boundary conditions were tested: (i) door closed; and (ii) door opened. A total of 132 tests were carried out. The decay technique was used for the quantification of the air change rate. Simultaneously, indoor and outdoor conditions were continuously monitored. The results highlighted the importance of performing several measurements as some variability was found, especially for the open door scenarios. Moreover, the importance of wind speed was also confirmed as the main trigger mechanism in naturally ventilated buildings, especially in the mid-season period where the indoor/outdoor temperature difference is not significant.




Almeida, R. M. S. F., Barreira, E., & Moreira, P. (2017). Assessing the variability of the air change rate through tracer gas measurements. In Energy Procedia (Vol. 132, pp. 831–836). Elsevier Ltd.

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