Abstract
Cool-roof coatings have received considerable attention worldwide as a solution for the “heat island” effect in urban areas. The solar reflectance of roofs coated with high-reflectance paint is reduced by dirt. We continuously measured the solar reflectance of a roof coated with high-reflectance paint with and without a self-cleaning function for more than two years. The solar reflectance of self-cleaning paint decreased by 0.5% per month over two years, due to the effect of dirt. The solar reflectance of conventional paint decreased by 4% per month over four months after coating and then reached a value similar to that for the self-cleaning paint for two years due to deterioration. With a slight decrease in solar reflectance, the self-cleaning function is effective in mitigating the heat island effect and obtaining continuous energy-savings. We applied the alkyl silicate system as self-cleaning for high-reflectance paint, the solar reflectance was measured continuously at 1 minute intervals, and the actual state of the fluctuation in reflectance over the short and long terms was analyzed with the influence of the altitude of the sun. The deterioration of the coating was also investigated by gloss retention and chalking test.
Highlights
High-reflectance paint is regarded as an important solution for the heat island effect in urban areas
It was considered that the decrease in initial reflectance of the conventional paint was due to dirt adhesion, and the reflectance increased due to whitening of chalking
The solar reflectance of a roof coated with high-reflectance paint with and without a self-cleaning function was continuously measured for more than two years
Summary
High-reflectance paint is regarded as an important solution for the heat island effect in urban areas. Many research results on residential [4] and non-residential buildings [5,6] have been reported regarding the effect of these high solar reflectance paints. Many important research about evaluation of building roofs with conventional and reflective coating, and the energy gain of building roof with many color type of waterproofing materials have been reported [7,8,9]. It has been reported that the solar reflectance greatly decreases in the first 1 to 2 years after painting [10,11,12]. It has been reported that this decrease in solar reflectance is due to dirt on the roof coating and the adhesion of organisms [13].The reduction in reflectance has been studied in exposure tests using various materials. Changes in solar reflectance are measured every three months and are affected by the location of exposure, it has been reported that the reflectance decreases by approximately 10% to 20% within 3 years [14,15]
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