The effect of using a high-albedo material on the Universal Temperature Climate Index within a street canyon

This study investigates the effect of different high-albedo adaptation strategies on air temperature, mean radiant temperature and the Universal Temperature Climate Index (UTCI) for an idealized 2D street canyon. The used numerical model computes the heat transport in the canyon, and specifically takes into account the effect of multiple scattering of radiation. In general the mean radiant temperature has a much larger impact on the UTCI than the air temperature. Moreover, the mean radiant temperature exhibits strong spatial variations in the canyon due to its sensitivity to shading. The impact of albedo-differences on the UTCI is thus relatively small compared to the large shading effects. The best strategy to minimize the UTCI for the outdoor environment with building height to width ratio H/W = 0.5 is found to be a uniform albedo of 0.2. For H/W = 1.0, an albedo gradient from high at the bottom part to low at the top of the vertical walls showed the lowest UTCI. Although using high-albedo materials can mitigate the atmospheric urban heat island effect, it is very likely to increase pedestrian heat stress.