Application of glass beads as retro-reflective facades for urban heat island mitigation: Experimental investigation and simulation analysis

Glass beads are the common main component of retro-reflective (RR) material applied to building envelopes for urban heat island (UHI) mitigation. In order to evaluate the influence of glass bead RR materials on the UHI mitigation, two glass bead RR samples with refractive index of 1.9 and 1.5 in white reflective layer, one prism RR sample and one white diffusive sample for comparison were produced for this study. Their RR angular distributions of reflection intensity were investigated by an emitting-receiving optical fiber system developed in our laboratory. Their solar reflectance at different incident angles was measured by thermal balance theory in the outdoor environment. Furthermore, the influence of these developed samples on UHI mitigation potential was evaluated at an example location of Osaka, Japan using a 2-D analytic model. It showed that the glass bead RR sample with refractive index of 1.9 is more effective for mitigating the UHI phenomenon, both increasing the urban albedo and reducing the proportion of solar radiation absorbed by urban canyons.