Modelling Wind-Driven Rain Impact on Plastered Facades Using Direct Measurements, EN ISO 15927-3 Calculations and CFD

Abstract

Wind-driven rain (WDR) is a major moisture source for exterior walls and a key factor in the hygrothermal performance of unventilated facade systems, particularly those relying on moisture buffering. Accurate representation of WDR in hygrothermal modelling is essential, yet most approaches use vertical rain and wind data from meteorological stations processed according to EN ISO 15927-3. This study explores the use of locally measured climate data and directly measured WDR loads on vertical walls as inputs for Delphin simulations. Relationships between catch ratios for direct WDR measurement devices and actual wall were examined using computational fluid dynamics (CFD). The study compares WDR loads and the resulting hygrothermal performance of thick plaster system under different WDR input strategies. Results show that directly measured WDR loads correlate reasonably well with calculated loads but underestimate small WDR quantities. Hygrothermal simulations indicated that the closest agreement with the measured hygrothermal behaviour of the facade plaster was observed for the on-site weather station data and CFD-corrected direct WDR measurements.