Local wind speed near exterior building surfaces for convective transfer coefficients

Exterior convective heat and mass transfer coefficients at building surfaces are to a large extent determined by the local wind speed. Usually, empirical formulae are used to relate the reference wind speed at a meteorological station to the local wind speed near the building surface and to relate the local wind speed to surface transfer coefficients. These formulae however are based on a limited number of measurements. Little is known about the actual value and the variability of local wind speed and surface transfer coefficients across facades of different building geometries. In this paper, a validated Computational Fluid Dynamics (CFD) model is used to calculate the local wind speed near the exterior surface of a cubic building model as a function of wind speed, wind direction and the position on the facade. It is shown that the variation of the local wind speed across the facade is very pronounced and that using the available empirical formulae can yield large errors in HAM (Heat-Air-Moisture) calculations.