Spatial Distribution of Wind Driving Rain and Drying on Façades and Associated Hygrothermal Response

Heat Air Moisture (HAM) transfer models have proven their added value in the renovation and restauration sector. These models allow to analyse the causes of moisture problems and the impact of renovation measures. Wind-driven rain (WDR) is one of the most important moisture sources, affecting the hygrothermal performance and durability of building components. In the traditional approach of HAM-modelling, the WDR and the convective heat transfer coefficient (CHTC) are implemented in a simplified manner, i.e., typically a generic value for one location is taken constant over the façade. However, WDR has a spatially and temporally discrete modus and the CHTC value varies highly across the windward façade. Therefore, the reliability of the traditional approach for hygrothermal response behaviour can be questioned. Within this paper, the spatial distribution of the catch ratio and CTHC are implemented in a response behaviour study. Steady Reynolds-average Navier-Stokes (RANS) equations and Eulerian multiphase CFD-simulations are performed for the CHTC and WDR, including the turbulent dispersion of raindrops. The approach is tested for a cubic low rise building and the effect of the spatial parameter is analysed for frost damage because this is of particular interest for decision frameworks for interior insulation strategies. The results show that critical rain loads are typically underestimated in practice. Next to that, the specific combination of rain loads and drying patterns entail unexpected freeze-thaw patterns.