Improvement of radiation modelling in Simplified Urban Canopy Representations

Abstract

Detailed modelling of the interaction between buildings and the urban environment is best implemented using Computational Fluid Dynamics (CFD). However, due to the often exorbitant computational cost of CFD models of a realistic urban domain, a number of simplified Urban Canopy Models (UCM) have been proposed since 2000 including Town Energy Balance (TEB), Square Prism Urban Canopy (SPUC), Temperatures of Urban Facets in 3D (TUF3D), Urban Weather Generator (UWG), etc. These models are a lot faster than CFD models. However, the spatial organization of the surfaces (slopes, orientations, shape factors), and their physical characteristics (albedo, emissivity, thermal conductivity) need to be simplified as well thereby affecting the accuracy of the outcome. The models necessarily rely on overly simplified representations of short-wave (solar) and long-wave (infrared) radiation heat transfer. This study assesses the comparative validity of the radiation heat transfer approximations proposed by the different simplified approaches in comparison to exact solutions calculated for an actual urban district. In this research, it proposes to improve existing simplified urban canopy models by replacing their approximate radiation transfer calculations with much more accurate ones determined by reference to the detailed geometry of the urban district under consideration. Part of this study is the evaluation of the impact of the proposed radiation models implemented in UWG on the UHI and on the energy consumption of buildings estimated by EnergyPlus. This approach is validated using the case of a district in downtown Abu Dhabi.

Date of Award	Dec 2017
Original language	American English