Analysis of numerical simulations and semi-empirical models on distribution characteristics of wind-driven rain on low-rise building facades

Abstract

Wind-driven rain (WDR) is a significant contributor to indoor moisture in buildings, directly impacting the thermal and moisture performance of facades. Previous research on WDR in China focused on a limited number of low-rise pilot buildings, whose materials, shapes, and environmental settings are not entirely representative of typical applications. Aim to improve the accuracy of WDR predictions on low-rise building facades, there is a need for assessing different WDR calculation methods under various rain events. The paper presented high-resolution WDR measurements from a low-rise concrete building in Chongqing to investigate the distribution of WDR on building facades under local meteorological conditions. The study compared the performance of numerical simulations and two semi-empirical models with different meteorological data averaging techniques. The results indicated that Computational Fluid Dynamics (CFD) simulations using the Eulerian multiphase (EM) model more closely matched the actual catch ratio across various locations and the WDR amount across the facade, with errors ranging between 10%-25 % and 2%–23 %, respectively. Furthermore, the ISO model with weighted averaging (WA) technique outperformed others in estimating catch ratios at various locations and the WDR amount across the facade, particularly when estimating the midline catch ratio. When considering both cumuliform and stratiform rainfall, the arithmetic averaging (AA) technique was a viable method for the ASHRAE model to forecast WDR. The ISO model's predictions corresponded to 54%–81 % of the field measurements, while the ASHRAE model's estimates varied more widely, ranging from 33 % to 229 % of the measured values.