Convective heat transfer coefficients at windward building facades: CFD simulations and new generalized expressions

The surface-averaged forced Convective Heat Transfer Coefficient (CHTC) distribution across the facades of a building is influenced by the complex interplay between a wide range of parameters including building geometry, position on the building facade, wind speed and wind direction. Existing CHTC expressions, however, consider the impact of these parameters either incompletely or not at all. Earlier studies have shown that this shortcoming can lead to significant errors in Building Energy Simulations. This paper, therefore, systematically investigates the combined effects of wind speed, building height and width, and wind direction on the surface-averaged forced CHTC for the windward facade of buildings and presents a new generalized CHTC expression as a function of these parameters. This expression is derived from high-resolution CFD simulations of wind flow and forced convective heat transfer for 70 different building geometries, 8 wind directions and 4 reference wind speed values. The 3D steady Reynolds-averaged Navier-Stokes equations are solved combining the high-Re number realizable k-e model and the low-Re number Wolfshtein model. The CFD simulations are based on a validation study with wind-tunnel measurements of surface temperature for a reduced-scale cubic model. The accuracy of the expression is confirmed by detailed in-sample and outof-sample evaluations.