Application of retro-reflective materials in urban canyon at different geographical locations

Retro-reflective materials (RRMs) reflect incoming radiation toward the incident direction. The present paper estimates the cooling potential (as the decrease of energy kept inside the canyon) of retro-reflective (RR) colored plasters at different latitudes, longitudes and canyon's orientations, through the use of an analytic model developed in MATLAB R2019b, in 8 different geographical locations. The energy reflected outside the canyon with respect to the incident energy (%) is reported for 5 combinations of RR/diffusive materials and for aspect ratios from 1 to 5. Results show that at latitudes near the Equator, from March to September, RRMs have no sensible effect in the energy circulating inside the canyon, with South-oriented façade. At low latitudes, better values are obtained in narrow canyons with East-oriented façade (+30.6%, aspect ratio equal to 5). Appreciable positive effects occur in other months, especially for narrow canyons (in January, increase in the energy sent outside the canyon with respect to diffusive materials: +29.5%). At middle latitudes, RR use is suggested especially for narrow canyons. At high latitudes, the effect of RRMs is stronger for narrow canyons during summer, while in other months it does not depend on the canyon's geometry. RRMs behavior is not affected by longitude. Generally, RRMs have a significant cooling effect in cities at middle/high latitudes while seem not to bring benefits with respect to diffusive materials in cities like Abu Dhabi or Singapore. Deeper insight should be devoted to the evaluation of the heating demand penalties during cold seasons.