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Mastering building airtightness is essential to meet the requirements of current and future building codes, not only for saving energy but also for ensuring moisture safety. Perfect airtightness is difficult to achieve: failures are often observed, due to bad design or poor workmanship. Some published investigations proved that leaking air mostly flows through porous material and thin air channels, due to material imperfections and construction tolerances. In addition, air inlet and outlet are not necessarily close to each other, which makes air leakage paths through the building envelope multidimensional and difficult to map. Very few existing models enable such complex air leakage geometries to be dealt with.
In this article, a recently developed detailed model coupling heat air and moisture (HAM) transfer is presented and used to analyse moist air flows due to airtightness defects. The model is able to deal with anisothermal airflow through complex 2D building assemblies, including both air permeable porous materials and thin air channels. The model is then applied on a 2D air leakage configuration subjected to infiltration and exfiltration scenarii. Results are analysed in terms of moisture risk and energy impact. A parametric study on boundary conditions is carried out. The results show higher moisture risk in case of air exfiltration through the airtightness defect.