Spatial distribution of material degradation. Can we predict spatial risks based on wetting and drying patterns?

Heat Air Moisture (HAM) transfer models have proven their added value in the renovation industry. These models allow to analyze the causes of moisture problems and the impact of renovation measures. Wind driven rain (WDR) is one of the most important moisture source, affecting the hygrothermal performance and durability of buildings. 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 an hourly-average value for one location on the façade. However, in reality 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 behavior can be questioned. Within this paper, the spatial distribution of the catch ratio and CTHC are implemented in a response behavior 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 the parliament case study in Ottawa (Canada), with a focus on the windward façade. The effect of the spatial parameter is analyzed for frost damage because the retrofit strategy (with additional interior insulation) could increase the number of freeze-thaw cycles. The results show the importance of the spatial parameter of the building façade as well as the combined effect of a variable WDR and CHTC on the wall. This spatial approach could help in mapping deterioration patterns of facades and pinpointing critical areas.