Numerical determination and treatment of convective heat transfer coefficient in the coupled building energy and CFD simulation

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The integration of building energy simulation (ES) and computational fluid dynamics (CFD) programs eliminates many assumptions employed in the separate applications, resulting in more accurate predictions of building performance. This paper discusses the methods used to determine convective heat transfer on interior surfaces of building envelope, which is the key linkage between ES with CFD programs. The study found that the size of the first grid near a wall in CFD is crucial for the correct prediction of the convective heat. A finer grid resolution in CFD does not always lead to a more accurate solution when using zero-equation turbulence models. Through numerical experiments, the paper suggests a universal first grid size at 0.005 m for natural convection room airflows and 0.1 m for forced convection indoor airflows. The investigation also found that negative convective heat transfer coefficients may cause divergence and instability of the coupled simulation.