Numerical Simulation of Forced Convective Heat Transfer Coefficients on Shaded Roofs with Wind Circulation in Low-Rise Buildings
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Abstract
The convective heat transfer coefficient at the external wall of the building is an important variable in the calculation of heat transfer through the building envelope. The average value of this variable has been estimated from the empirical equation of the wind speed around the building. This research used computational fluid dynamics program (CFD), Phoenics 3.5, to compute the convective heat transfer coefficients as the shading device is fixed on the roof regarding the wind separation and recirculation around the building. The results of the coefficient of convective heat transfer derived from modeling a building with no shading device were compared with the experimental results in previous research works. The simulation results were validated in the simulated model with turbulent flow using Large Eddy Simulation (LES). After that, the model with LES approach known as the standard Smagorinsky model (SMG) was applied to the building models with shading device on the roof. The results of this research are the convection coefficient values at the roof surface for a 1.8 meter channel between the roof and shading device and a roof in the wind direction with a length of 8.0, 20.0 and 36.0 meters, representing a 2-storey house and 4-storey buildings. The derived coefficients are proposed as power-law functions of fixed points on the roof and shading device surfaces. The highest convective heat transfer is predicted at the sharp upstream edge, two span-wise rims for the 4-storey building and most of the area of the 2-storey house. Installing eaves or placing buffer zones around the top floor of building is recommended in addition to the shading device on the roof.
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