Modeling and numerical investigation for hygrothermal behavior of porous building envelope subjected to the wind driven rain

Abstract

Wind driven rain (WDR) may have serious effect on the heat transfer through exterior wall, optimal design of envelope, and building energy consumption simulation. Accurate evaluation of the impact of WDR on the hygrothermal performance of building envelope is important for energy-saving design of buildings. This work presented the numerical model and analysis method for the hygrothermal behavior of building wall exposed to the WDR. A capillary pressure based coupled heat and moisture (CHM) transfer model applicable to the high humidity condition was established and validated. The ISO15927-3 method of WDR was improved based on the previous experimental results. WDR on four orientation walls were investigated use the improved ISO method and weather station data between November 2017 and October 2018 in the representative city of Changsha. Dynamic simulation of hygrothermal performance for external wall is conducted under three calculation conditions: the transient heat conduction (TH), CHM (no rain) and CHM (WDR) models. The results show that total cooling load transmitted through the east, south, west and north orientation walls calculated with CHM (no rain) model is predicted to increase 8.5%, 8.6%, 5.3% and 10.3% compared to the TH model. But total cooling load transmitted through the four orientation walls calculated with CHM (WDR) model separately increases −2.5%, 1.8%, −7.9% and −46.1% in contrast with TH model. Total heating load transmitted through the four orientation walls calculated with CHM (WDR) model is predicted to separately increase 3.2%, 3.2%, 63.3% and 71.5% compared to the TH model. The results indicate that WDR has significant influence on the hygrothermal performance of building wall. It is essential to incorporate the WDR into the hygrothermal transfer model for the validity of optimal design and the accuracy of building energy simulation in rainy areas.