Detailed heat, air and moisture transport modelling in cavity walls

% Cavity walls are a widely used external wall type in North-western Europe. In this paper a cavity wall configuration was analysed with a heat and moisture transport model for porous materials integrated into a computational fluid dynamics solver. The studied wall is a wood frame wall with a brick veneer as outside leaf. Four cases were analysed in detail: drying of the outside or inside cavity leaf when initially saturated, both for summer and winter conditions. The model was compared with a widely used simulation tool for building envelope analysis (WUFI (R)). This simulation tool uses a simplified modelling approach for the convection in the cavity. The study showed that these simplifications are not always justified. The simplified model overestimates the drying and moistening rates of the cavity wall compared to the detailed model. Both models showed that the drying of the outer leaf is mainly determined by the outside conditions and the outside leaf dries out mainly to the outside and not to the cavity. The cavity ventilation in this case is of less importance. For the inside leaf this cavity ventilation is of mayor importance for drying. The largest discrepancies between both models were found for this inner cavity leaf.

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