Extension of generalized forced convective heat transfer coefficient expressions for isolated buildings taking into account oblique wind directions

The surface-averaged forced Convective Heat Transfer Coefficient (CHTC_avg) at a windward building facade is influenced by the complex interaction between a wide range of parameters. 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. In this paper, therefore, the combined impacts of wind speed (U₁₀), building height (H) and width (W), and wind direction (θ) on the CHTC_avg for the windward facade of buildings are systematically investigated. High-resolution CFD simulations of wind flow and forced convective heat transfer, validated with wind-tunnel measurements, are performed for 64 building geometries (10 m ≤ H and W ≤ 80 m), 8 wind directions (0° ≤ θ ≤ 78.75°) and 4 reference wind speeds (1 m/s ≤ U₁₀ ≤ 4 m/s). The 3D steady RANS equations with the realizable k-ε turbulence model and the low-Re number Wolfshtein model are used. The results show that for a given building geometry and U₁₀, the CHTC_avg decreases as θ increases from 0° to 78.75°. The maximum reduction of about 42% occurs for the building with H = 8W = 80 m. In addition, for a given θ and U₁₀, by increasing H, the CHTC_avg increases, while increasing W has the opposite impact on the CHTC_avg. Finally, a new generalized CHTC expression is presented as a function of U₁₀, H, W and θ and its accuracy is confirmed by detailed in-sample and out-of-sample evaluations.