CityComfort+: A simulation-based method for predicting mean radiant temperature in dense urban areas

Publication date: October 2014
Source:Building and Environment, Volume 80
Author(s): Jianxiang Huang , Jose Guillermo Cedeño-Laurent , John D. Spengler
This paper introduces CityComfort+, a new method to simulate the spatial variation of the mean radiant temperature (T mrt) in dense urban areas. This method derives the T mrt by modeling five components of radiation fluxes—direct solar radiation, diffuse solar radiation, reflected solar radiation, long-wave radiation from the atmosphere, and long-wave radiation from urban surfaces—each weighted by view factors. The novelty of CityComfort+ lies in a new algorithm to model surface temperature and associated long-wave radiation as well as the application of RADIANCE, a ray-tracing algorithm that can accurately simulate 3-D radiation fluxes in a complex urban space (Ward, et al, 1998). CityComfort+ was evaluated in field studies conducted in a dense urban courtyard (mean sky view factor of 0.4) in Boston, Massachusetts, USA under winter, spring, and summer (cold, warm, and hot) weather conditions. Simulation results yielded close agreement with measured T mrt. Also, predicted mean surface temperature agreed well with the measurement data. A sensitivity test using CityComfort+ revealed that T mrt on the study site will be mostly affected by the heat capacity and emissivity of surface material, not albedo. This study is subject to limitations from sensor accuracy and the thermal inertia of the grey ball thermometer, and the CityComfort+ method is still under development. The next step is to compare its performance with existing methods.