A Study on Passive Cooling Methods by Evaporation and Solar Reflection on Rooftops in a Temperate Climate Region

Abstract

A number of studies have been carried out on the passive cooling of the outer surface of buildings for the purpose of conserving energy without resorting to fossil fuels, while simultaneously improving the indoor thermal comfort. In addition, the heat island phenomenon has been regarded as a problem. Thus, it is necessary to strive to reduce the thermal load of buildings on the urban environment. In this study, an outdoor experiment was conducted using test specimens with a focus on passive cooling on rooftop surfaces in summertime to clarify the cooling effect of various types of passive rooftop cooling. The influence of rooftop cooling on the indoor heat load, and the heat load of the atmospheric side were also clarified. A total of 10 types of data were collected; case 1 is an AR surface, Cases 2–5 are watered AR surfaces, Cases 6 and 7 are ceramic tiles, with and without water coating or white paint respectively, and finally, Cases 8 and 9 are perforated bricks, with and without a coat of white paint respectively. (1) Results of data analysis for Cases 6–10 show that because these types can reduce the load on the air during the day, they are effective. For Cases 7 and 9 and during the day, the heat island effect is suppressed. For Cases 6–9, the tropical night phenomenon can be prevented. (2) In order to reduce the cooling load in summer, the roof slab insulation to reduce heat load in the atmosphere is essential in order to employ an effective passive cooling method. (3) For the insulation standards of the next generation of solar radiation and the evaporation coefficients of 0.5 or 2 and more, 0.1 or 2 can be applied.