Correlations for the forced convective heat transfer at a windward building façade with exterior louver blinds

Abstract

Exterior louver blinds are increasingly utilized to protect the building envelope from solar radiation. However, with the existing correlations from studies on a smooth flat/a surface of the bluff body, the convective heat exchange at louver blinds and the façade behind them will be underestimated and overestimated respectively. In this work, Computational Fluid Dynamic (CFD) simulations have been conducted to analyze the forced convective heat transfer at the windward façade with louver blinds, which are validated with wind-tunnel experiments. The 3D steady Reynolds-averaged Navier-Stokes (RANS) function with Low-Reynolds Number Modelling (LRNM) treatment has been employed for precision improvement. The theoretical simulations are performed for 5 louver angle φ (from 0° to 60°), 3 installing distance W (from 0.025H to 0.08H), 5 slat width B (from 0.02H to 0.10H), 8 temperature difference between the façade and blinds θ (from 1 to 7) and 5 reference wind velocity UH (from 2.56 m·s−1 to 4.27 m·s−1). It was found that the convective heat loss at the louver shows a positive correlation with the growth of φ, W and the reduction of B. Meanwhile, the convective heat loss on the façade behind is positive to B, W and negative to φ and θ. Finally, with some conversions of expressions, a group of correlations are established which can predict the surface-averaged Nu of the façade and louver blinds, of which relative errors are less than 13% compared that of simulation data.