Quantifying cooling benefits of cool roofs and walls applied in building clusters by scaled outdoor experiments

Abstract

Cool coating on building surfaces is a promising technique for cooling cities in summer. However, field measurements considering building clusters coupling cool roofs and/or cool vertical walls are rare. We conducted new-type scaled outdoor experiments in a suburb of Guangzhou, China (23°1′N, 113°25′E) to quantify the impacts of various reflective coatings on overall urban albedo, roof and wall temperature (Troof and Twall), and street air temperature (Tair) in three-dimensional high-rise building clusters. These experiments involved (a) high/low reflective roofs with a plan area index λp=0.25/0.44 (street width W = 0.5 m/0.25 m, building height H = 1.2 m) and (b) different cool coating modes with white coating as λp=0.44, i.e., roof coating (R-type), wall coating (W-type), both roof and wall coating (RW-type). As λp=0.25/0.44, cool roofs increase daytime average albedo αa from 0.16/0.19 to 0.26/0.34 reducing Troof by ∼8.0 °C on average for both urban densities. When λp=0.44, the RW-type increases αa (∼0.18–0.20) by 138.9%, significantly more than the R-type (88.9%) and W-type (20.0%). However, Twall (z/H < 0.5) is minimally affected by all three coating modes and Tair remains largely unchanged. This study provides valuable insights into the efficacy of cool coatings in urban environments and offers high-quality experimental data for validating related numerical simulations.