Effect of incident flow conditions on convective heat transfer from the inclined windward roof of a low-rise building with application to photovoltaic-thermal systems

Steady RANS CFD simulations were used to evaluate convective heat transfer from the roof of a low-rise building immersed in an atmospheric boundary layer for different terrain, with relevance to photovoltaic-thermal (PV/T) systems. Dimensionless correlations for the exterior convective heat transfer coefficient (CHTC), expressed as Nusselt number (Nu), were developed for the windward roof, based on Reynolds number and incident turbulence intensity at eaves height, thereby quantifying the strong influence of incident turbulence on the CHTC. Simulations were also performed for a generic flat plate of the same streamwise length so as to provide further insight into the effects of incident turbulence on the windward roof boundary layer. The CHTC values for the windward roof and, hence, the correlations presented here, for a given terrain, are largely insensitive (less than 5% change) to variations in roof slope (from 20 to 45°) or small changes in wind direction (up to 20° from the normal to the eaves). Mixed convection simulations for conditions with significant buoyancy forces (Richardson numbers from 0.9 to 7) show that the CHTC values can be up to 14% higher than those based on forced convection only.