Mean radiant temperature in urban canyons from solar calculations, climate and surface properties – Theory, validation and ʽMr.Tʼ software

Abstract

Mean radiant temperature (Tmrt) is important for human thermal comfort indexes, but is difficult to determine. Tmrt was calculated from measured temperatures of buildings and vegetation surfaces in urban scenarios along with meteorological data (temperature, relative humidity and global radiation). The method can be used for experimental work in urban settings without the use of four-flux net radiometers. Tmrt for different positions in the urban canyon can be calculated. A software package named Mr.T was developed which allows determining Tmrt from data input manually or from EXCEL spreadsheets. The software was validated in two urban settings: in Tel Aviv University and a nearby urban canyon in summer and in the old city quarter of Beer Sheva at the end of winter. Results were close to those obtained with a four-flux net radiometer. Differences in calculated and measured fluxes are discussed as well as sources of errors in the calculations. Assumption of clear skies for the computation of atmospheric radiation did not introduce significant errors. A priori values of albedo and emissivity of the different urban surfaces can have large effects on fluxes and radiant temperatures, and the use of tables of those values is probably a large source of uncertainty when using the calculation procedure. In conclusion, the software developed can be a significant tool for the study of thermal comfort conditions in urban settings.