Intercomparison of calculation models for wind-driven rain on buildings

Three different calculation models for wind-driven rain (WDR) on buildings are compared by applying them to four idealised, isolated building configurations. The three models are the semi-empirical model in the European Standard Draft for WDR assessment (ESD), the semi-empirical model by Straube and Burnett (SB) and the CFD model by Choi. The buildings are a low-rise cubic building, a low-rise wide building, a high-rise wide building and a tower building. The calculations are made for steady-state conditions of wind and rain. Validation of the CFD wind flow simulations and of the WDR simulations was performed in earlier studies. The CFD simulations of the WDR coefficient are considered as the reference case, and the performance of the two semi-empirical models is evaluated by comparison with these CFD results based on two criteria: (1) the ability to model the wind-blocking effect on the WDR coefficient; and (2) the ability to model the variation of the WDR coefficient with horizontal rainfall intensity Rh. It is shown that the ESD and SB model, as opposed to the CFD model, can not reproduce the wind-blocking effect. In addition, the ESD model provides WDR coefficients that are independent of Rh, while the SB model shows a dependency that is opposite to that by CFD. Future improvements to semi-empirical models should take into account these rather fundamental differences.