Investigation on the optic-energy interaction between retro reflective façades and pavement in urban canyons

Retro-reflective (RR) materials, due to their ability to reflect most of the incident energy towards the same incoming direction, represent an opportunity to reduce UHI phenomenon. The optical properties of RR materials suggest that they could be effectively applied as coatings in order to reflect the solar radiation beyond the urban canyon. The RR behaviour depends on the angular distribution of the incident energy: for low incident angle the radiation is reflected mainly backward in the incoming direction; for high angles RR materials reflect the radiation symmetrically with respect to the perpendicular direction. To overtake the limit of RR materials of being mainly retroreflective only for low 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 an urban canyon layout with H/D equal to 2 is represented. 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 beige pavement for a non-perpendicular radiation, due to the interaction of optical properties of the materials.