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Developing a new passive tracer gas test for air change rate measurement

Sarah L. Paralovo, Maarten Spruyt, Joris Lauwers, Borislav Lazarov, Marianne Stranger, Jelle Laverge, 2019
ventilation | air change rate | indoor air quality | Tracer gas test | passive sampling
Bibliographic info: 40th AIVC - 8th TightVent - 6th venticool Conference - Ghent, Belgium - 15-16 October 2019
Languages: English Pages (count): 10

Ventilation is critical in interpreting indoor air quality (IAQ), yet few IAQ assessments report ventilation rates; even when they do, the measurement method is often not fully described. Most ventilation assessments use a tracer gas test (TGT) to measure total air change rate. In a TGT, the indoor air is marked with an easily identifiable gas (tracer) and the air change rate (ACH) is inferred by monitoring the tracer’s injection rate and concentration. Passive sampling (adsorptive/absorptive samplers) is mostly preferred to monitor tracer concentration for its simplicity, practicality and affordability. Such samplers are commercialized by a range of companies and are widely used in IAQ studies to assess pollutants levels. Currently used passive TGTs present three major limitations: (1) disconnection from IAQ analysis (providing ACH data in a different time-scale than IAQ data), (2) employment of inadequate substances as tracers and (3) tendency to bias arising from the perfect-mixing assumption. Thus, this paper proposes a new approach on the passive TGT method, employing as tracer a suitable gas that can be co-captured and co-analysed using commercial passive samplers employed in common IAQ studies and which includes a more careful planning phase to account for imperfect mixing. A literature review was carried out in pursuit of such a gas, and the gases considered as possible tracers were the volatile organic compounds (VOCs) capable of being captured by the samplers commercialized by Radiello®. Radiello® samplers are composed by activated charcoal, which captures all VOCs in the targeted molar mass range by adsorption. The info-sheets for these samplers were consulted. Two options for alternative tracer gas are currently under consideration: 2-butoxyethyl acetate (EGBEA) and deuterated decane (D-decane). Both present low-reactivity, usually negligible background indoor concentration, generally low toxicity and no links to chronic health effects. A preliminary field test was carried out in order to check EGBEA’s measurability, and results showed insignificant background EGBEA concentration and good measurability by the Radiello® sampler. A total of six chamber tests were performed to evaluate the behaviour of EGBEA and D-decane under standard conditions and to optimize a source design: three in stainless steel chambers (TCP1, 2 and 3) and three in glass chambers (GCP1, 2 and 3). Results from these chamber tests indicate emission rates stability and enabled incremental enhancements to the source design. Further chamber tests will be performed to evaluate the behaviour of the potential tracers under varying conditions and to further optimize the source design. Future work also includes simulation of TGTs in imperfectly-mixed zones to study the effects of source/samplers positioning on the accuracy of the resulting ACH calculations.   

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