Coupled CFD, radiation and building energy model for studying heat fluxes in an urban environment with generic building configurations

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In the past decades cities have been continuously growing. The microclimate in urban areas differs significantly from the microclimate in rural areas. The temperatures in urban areas are most of the time higher due to the urban heat island (UHI) effect and the wind speeds are lower due to wind sheltering. The local microclimate strongly influences the space cooling and heating demand of buildings and the human comfort and health in urban areas. The mechanisms causing the UHI effect have to be understood in detail to be able to improve the sustainability of (future) cities and the human comfort in urban areas. Wind driven ventilation is one of the most efficient ways of removing heat from urban areas. Knowledge of the heat fluxes caused by wind driven ventilation is important to be able to optimize the design of urban areas in terms of heat removal. The heat removal by wind and buoyancy can be increased by choosing optimal building geometries. In this study the urban heat fluxes are studied for six generic urban morphologies. Coupled CFD (computational fluid dynamics) and building energy simulations are conducted. This approach has the advantage of having highly spatially resolved temperature and flow fields and therefore being able of determining heat fluxes. Turbulent and convective heat fluxes are considered. The results show the importance of buoyancy for low wind speed cases and the strong influence of buildings upstream on the heat fluxes and temperatures further downstream.