Simultaneous hygrothermal performance assessment of an air volume and surrounding highly hygroscopic walls

Abstract

Heat and mass transfers are becoming increasingly important in the field of building physics. They should be considered to predict building performance, especially for a wall containing highly hygroscopic materials. The moisture balance at the room scale is influenced by air leakage and moisture sources, by the vapour transfer within the material and by the interaction between the wall and the air volume. Therefore, to study the impact of mass transfers on the indoor climate, experimental data at different scales of study are needed. The present study adopts this approach to validate hygrothermal prediction. At the material scale, the hygric properties of wooden panels are estimated using an inverse method algorithm with transient experimental data. The phenomena within the wall and the interactions between the wall and the air volume are studied by designing an experimental device and characterising it in terms of air leakage to validate predictions obtained with model. The values of the material properties are validated at the wall scale by correctly simulating the hygrothermal behaviour before characterising the exchange between the wall surface and the air volume by estimating the convective transfer coefficient. Using this information, the indoor moisture level is correctly predicted by the developed model as well as the heat and mass flows through the walls. Finally, this numerical model highlights that taking into account coupled transfers has only a slight effect on the average energy consumed, while the heating power at the beginning of moisture steps is greatly decreased due to moisture adsorption.