Experimental assessment of the combined effect of retroreflective façades and pavement in urban canyons

Abstract

Retro-reflective (RR) materials represent an opportunity to reduce UHI phenomenon due to their ability to reflect most of the incident energy towards the same incoming direction. The RR behaviour depends on the angular distribution of the incident energy: for small incident angle the radiation is reflected mainly backward in the incoming direction; for large angles RR materials reflect the radiation symmetrically with respect to the surface normal. To overtake the limit of RR materials of being mainly retroreflective only for small angles of incidence, the investigation is focused on the optic interaction between vertical and horizontal RR surfaces. Therefore, the aim of this paper is to investigate the synergic effect of RR pavements and façades on a physical model in which urban canyon layouts with H/W equal to 1 and 2 are represented. To evaluate the global cooling effect of RR pavements and façades, a new parameter, called equivalent albedo, is introduced and calculated over the canyon’s ceiling. The results show that a canyon with RR vertical surfaces and RR pavement reflects outward more radiation than a canyon with RR vertical surfaces and diffusive pavement due to the interaction of optical properties of the materials.