Wind-driven rain on buildings: Accuracy of the ISO semi-empirical model

Abstract

Previous studies have shown that the accuracy of the ISO semi-empirical wind-driven rain (WDR) model can be improved by applying more detailed wall factors determined based on high-resolution field measurements. However, discrepancies between measurements and predictions still exist. The availability of high-resolution WDR field data collected over a long period of time makes a detailed analysis possible. Field measurements of WDR on two mid-rise and one high-rise buildings in three Canadian regions over a year and a half were analyzed. Two main factors that can significantly improve the ISO WDR model were identified, i.e. the time resolution (5 ​min data vs. hourly data) and the correction of difference in wind speed and wind direction between the building site and weather station using hourly data. It is recommended to take WDR measurements at shorter-duration and calculate wall factors using both shorter-duration records and hourly averaged data. In general, the ISO model works well if all the differences in wind conditions between site and the weather station can be taken into account. The observed discrepancy can be reduced to within 2% for façades facing the prevailing wind-direction, while to about 60% for façades off the prevailing wind direction in complex urban settings.