ABSTRACT
Driving rain must be taken into account when designing building envelope components and systems. The rain intensities on vertical facades depend on the wind flow characteristics and the rain drop size distributions. In this article a simplified wind flow model, based on potential flow, is validated against field measurements. The model estimates the catch ratio for different rain drop sizes. The catch ratio gives the ratio between the amount of drops hitting the ground and the facade, for a given drop radius. A modified catch ratio is introduced in order to account for the free driving rain, i.e. driving rain on an imaginary facade, far away from the building, as a first approximation for the catch ratio. The in-situ microclimate measurements were carried out at the field station of Chalmers University of Technology located in Fiskebäck, Göteborg, on the West Coast of Sweden from January 1998 to December 1999. The building of the field station is situated 5 meters above the sea level and 50 meters from the seacoast. It has a rectangular form with following dimensions, length 22.1 m, with 7.2 m and 4.3 m high. Driving rain gauges, tipping bucket (conventional), measured the amount of driving rain striking the Southwest wall. Also wind speed, wind direction, and precipitation on a horizontal surface were obtained at the field station.
