Investigating convective heat transfer coefficients of building surfaces under different thermal stratifications with non-isothermal inflow boundary conditions

Abstract

The convective heat transfer coefficient (CHTC) on building surfaces is crucial for understanding the thermal environment in urban areas, influencing building energy consumption and thermal performance. While previous studies have primarily focused on neutral inflow conditions and windward surfaces, the effects of non-isothermal inflows and surface-specific CHTC distributions remain insufficiently explored. This study investigates the CHTC distributions on building surfaces under different thermal stratifications using large-eddy simulation (LES). Eight inflow profiles, including one neutral and seven unstable cases, were generated via precursor simulations and applied to a 1:1:2 isolated building model. The results revealed that temperature differences have negligible effects under neutral inflow conditions but significantly influence CHTC distributions under non-isothermal inflow conditions, especially on lateral and leeward surfaces. A strong linear correlation was observed between CHTC and velocity for windward and top surfaces, consistent with findings under neutral inflow conditions, whereas lateral and leeward surfaces demonstrated greater sensitivity to temperature effects. The study develops novel correlations of CHTC with velocity, and normalized temperature differences for all building surfaces. Additionally, it provides relationships between the windward surface and other surfaces, showing that the lateral surface CHTC is approximately 85 % of the windward surface CHTC, the top surface CHTC is nearly equal to it, and corrections are required for the leeward surface. These findings contribute to improved accuracy in urban heat transfer modeling and more effective building energy efficiency evaluations.