Calculation of the driving rain wall factor using ray tracing

The current study presents a simplified method towards the improvement of the ISO Standard for the wind driven rain (WDR) assessment; given that the corresponding semi-empirical ISO model only provides wall factor values for a limited number of facade configurations, potential variations along the building facades such as protrusion of windowsills, extrusions or roof overhangs are only partially accounted for and as a result, significant overestimations of driving rain impingement at the respective spots, located in the 'rain shadow' may occur. In order to encounter this limitation for areas in the rain shadow, the present study proposes the use of the ray tracing method so as generate a building specific wall factor at a significantly low computational cost. Both validation and application results showed that the method can capture the distinct effect of the overhang and the windowsills in terms of rain sheltering while on the other hand, dynamic characteristics of the wind and more complex phenomena cannot be handled.