Variation of Wind-Driven Rain Intensity with Building Orientation

One of the primary functions of the external envelope of a building is to protect its inside from wind and rain and to give a desirable environment to its occupants. It is important that building envelopes should be adequately designed to resist water penetration due to rainstorms. Unfortunately, many buildings, even relatively new ones, are subjected to water leakage problems. There are many reasons for the poor performance of a building envelope (e.g., workmanship, poor design, and poor understanding of the problem). Water leakage is directly related to wind-driven rain (WDR), and a good understanding of the WDR process will minimize the water leakage problems. WDR around a building is a complex phenomenon. This paper describes a numerical approach to calculate the WDR intensity on the faces of a building. This method first obtains the wind flow pattern around a building by using a computational fluid dynamics technique. It then solves for the raindrop trajectories for the different raindrop sizes, and, finally, the intensity of WDR impinging on the building is calculated. This method is used to study the WDR phenomenon and the governing factors affecting the process. The effects of building geometry, orientation (relative to the wind), and wind speed are studied. It is found that wind speed is one of the major controlling factors, and the intensity of WDR on different locations of a building face also can be very different.