Increasing the Accuracy of Radiation Heat Transfer Estimation in a Lumped Parameter Urban Canopy Models

Abstract

Detailed simulation of urban microclimate momentum/energy exchanges can be attempted via Computational Fluid Dynamics (CFD). Developing and simulating a comprehensive CFD model of a realistic urban domain is, however, a monumental task. Furthermore, such a model cannot be used in a decision support framework where multiple parametric simulations are required. Simplified Urban Canopy Models (UCM) have gained in popularity over the past couple of decades. Some of the most notable ones are: Town Energy Balance (TEB), Square Prism Urban Canopy (SPUC), Urban Weather Generator (UWG), etc. The complexity and computational speed of these models is significantly reduced thanks to the implementation a simplified representation of momentum transfers. Concurrently, the spatial organization of the surfaces (slopes, orientations, shape factors), and their physical characteristics (albedo, emissivity, thermal conductivity) need to be simplified as well. In particular, the models often rely on very rough estimations of short-wave (solar) and long-wave (infrared) radiation heat transfer. In this study, we assess the comparative validity of the radiation heat transfer approximations proposed by the different simplified modelling approaches in comparison to exact solutions calculated for an actual urban district. The main contribution is the assessment of the impact of the improvement of an existing thermal lumped-parameter UCM by replacing the default radiation transfer calculations with much more accurate ones determined in consideration of the detailed geometry of a real urban district.