Impact of semi-empirical methods implemented in heat, air, and moisture (HAM) models on predicted wind-driven rain (WDR) loads and hygrothermal responses

Abstract

The amount, duration, and intensity of wind-driven rain (WDR) are instrumental to the durability and sustainability of building components. Semi-empirical methods implemented in heat, air, and moisture (HAM) models have proved to be a practical and efficient approach to quantify WDR exposure of building components and to examine WDR's influence on hygrothermal responses of building envelopes. However, specific assumptions and simplifications in the implementations can cause discrepancies in WDR calculations and hygrothermal responses. While measured datasets or computational fluid dynamics (CFD) predictions are employed to validate WDR calculations in previous studies, few address the further influence on hygrothermal responses, particularly confronted with full-scale experimental datasets. This paper starts with a general formulation of semi-empirical methods for WDR calculation and elaborates the ASHRAE and ISO standards implemented in two representative HAM models, WUFI and DELPHIN. In the first phase of simulations, two full-scale experimental datasets at Leuven (Belgium) and Eindhoven (the Netherlands) are reproduced by the two models to compare predicted WDR loads. In the second phase, the predicted and measured WDR loads are imposed as boundary conditions of different scenarios of one benchmark case to further analyze the influence on the hygrothermal responses. The results indicate that both models roughly reproduce the semi-empirical methods. Because of disparity in algorithms and implementations and differences in weather and building conditions, the simulated WDR loads show similar trends with deviations to the measured datasets. The predicted hygrothermal responses show deviations to different extents, presumably due to disparity in WDR load predictions during certain periods.