Modeling façade degradation risks on a cubic building: The impact of spatial wetting- and drying patterns on the hygrothermal response

Abstract

HAM models have proven their value for analyzing moisture-related pathologies by assessing hygrothermal responses to environmental exposure. In this study, a coupling between CFD and HAM is developed to capture spatial wetting and drying effects, which allows to identify façade degradation patterns. Wind-driven rain (WDR) and evaporation significantly influence the hygrothermal performance and durability of façades, particularly in heritage and renovation. In traditional HAM modeling, WDR and convective heat transfer coefficients (CHTC) are often simplified by applying generic, uniform values across the façade. However, this approximation fails to account for the spatial and temporal variations in WDR and neglects the significant variations in CHTC due to the surrounding velocity flow field. These oversimplifications can limit the validity and accuracy of hygrothermal predictions. This study presents a novel approach by externally coupling CFD simulations with HAM modeling to capture the spatial distribution of WDR and CHTC on building façades. Steady Reynolds-averaged Navier-Stokes equations and Eulerian-multiphase simulations are performed to calculate the wind flow and the rain trajectories with turbulent dispersion of raindrops. Using a cubic low-rise building as a case, the coupled model evaluates the effects of wind and rain exposure on façade deterioration, including frost degradation, salt crystallization, and algae growth. Results indicate that conventional approaches tend to underestimate critical rain loads, while drying potential is overestimated. It highlights how spatial variations in WDR and drying influence degradation mechanisms, emphasizing the need for more detailed spatial analyses. This integrated method provides valuable insights into risks posed by moisture exposure and drying dynamics, offering practical applications for targeted renovation strategies and improved preservation of building materials.