An experimental technique based on globe thermometers for the measurement of mean radiant temperature in urban settings

Different variables concur to the outdoor comfort assessment and, among them, the Mean Radiant Temperature (T-mr) represents the most challenging one to experimentally evaluate. According to the scientific literature, the most accurate method for in-field T-mr calculation is integral radiation measurements with three net radiometers. Nevertheless, net radiometers are expensive sensors and their implementation on large scale may be hindered by their price. To provide a cost-effective alternative some researchers proposed the use of globe thermometers. Globe thermometers are affordable sensors but typically exploited indoors, and their accuracy in urban settings is still under investigation. The scope of this work is to provide information regarding the extent to which globe thermometers can substitute net radiometers in the evaluation of the T-mr in outdoor urban settings. To this purpose, an experimental comparison has been performed between the T-mr calculated using net radiometers, assumed as a reference, and using two different globe thermometers: a standard 150 mm black globe and a grey 50 mm globe. The results revealed that the black globe tends to overestimate the T-mr while the grey globe mainly underestimates it. Moreover, the analyses evidenced a wide fluctuation in the profile of the T-mr calculated using globe thermometers, due to the rapid variation of meteorological parameters and the globes' long response time. To improve the fit between globe thermometers and net radiometers' response, regressive functions have been proposed, resulting in a significant enhancement of the adherence between T-mr calculated using the standard black globe's measurements and the reference T-mr.