Thermal comfort of pedestrians in an urban street canyon is affected by increasing albedo of building walls.

Numerical simulations based on the ENVI-met model were carried out for an E-W street canyon in the city of Stuttgart (Southwest Germany) to analyse the effect of increased albedo of building walls on outdoor human thermal comfort. It was quantified by air temperature (Ta), mean radiant temperature (Tmrt) and physiologically equivalent temperature (PET). The simulations were conducted on 4 August 2003 as a heat wave day that represents a typical scenario for future summer weather in Central Europe. The simulation results presented for 13 CET and averaged over the period 10-16 CET are focused on pedestrians on both sidewalks. For the initial situation, i.e. albedo of 0.2, human heat stress indicated by mean PET is by 26% lower on the N-facing than on the S-facing sidewalk, while this reduction amounts to 42% for mean Tmrt. Mean Ta does not show any spatial differentiation. The systematic albedo increment by 0.2 from 0.2 to 0.8 leads to a linear increase of outdoor human heat stress in terms of Tmrt and PET. For both variables, this increase is more pronounced on the N-facing than on the S-facing sidewalk. Mean relative Ta shows the tendency of a minimal increase with rising albedo. The results were achieved for the usual standardised human-biometeorological reference person. Its substitution by two other types of male and female pedestrians, respectively, which are statistically characteristic of human conditions in Germany, does not reveal any significant change in the results.