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Open Access Publications from the University of California

Urban Microclimate, a Study of Energy Balance and Fluid Dynamics /

  • Author(s): Yaghoobian, Neda
  • et al.

Improvements in building energy use, air quality in urban canyons and in general urban microclimates requires understanding of the complex interaction between urban morphology, materials, and climate as well as their interaction with the flow dynamics in urban canyons. The review of the literature indicates that despite a long history of valuable urban microclimate studies, more comprehensive approaches of investigating energy, heat and flow in urban areas are needed. In this research an indoor -outdoor dynamically coupled urban model, the Temperature of Urban Facets Indoor-Outdoor Building Energy Simulator (TUF-IOBES), has been developed and carefully validated. It is a building-to-canopy model that simulates indoor and outdoor building surface temperatures and heat fluxes in an urban area to estimate cooling/heating loads and energy use in buildings. The effects of a large number of parameters such as different ground surface albedo, building condition, window size and type, seasonal climate, and canopy aspect ratio on building thermal loads were investigated. The results presented in this dissertation highlight the fact that the interaction of urban materials (e.g. reflective pavements) with surrounding buildings must be considered in the energy analysis of urban areas. Although reflective pavements have been proposed as a mitigation measure for urban heat island since they reduce urban air temperatures, the increased solar reflectivity which transports solar radiation into (through fenestrations) and onto adjacent buildings increases building energy use. To investigate a more comprehensive and realistic simulation of the diurnally varying street canyon flow and associated heat transport, TUF-IOBES three -dimensional surface heat flux distribution were used as thermal boundary conditions in large-eddy simulation (LES). Compared to previous analyses which used uniformly distributed thermal forcing on urban surfaces, the present analysis shows that non-uniform thermal forcing can result in complex local air flow patterns. Strong horizontal pressure gradients were detected in streamwise and spanwise canyons throughout the daytime which motivate larger turbulent velocity fluctuations in the horizontal directions rather than in the vertical direction. This dissertation demonstrates that only local simulations for specific neighborhoods and urban climates can elucidate specific effects of urban mitigation measures; with often surprising outcomes

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