Using Field Measurements to Assess Aging of Self-Cleaning High-Reflectance Paint

Abstract

Continuous field measurements were used to evaluate the aging of solar reflectance on self-cleaning coatings for roofs in comparison with conventional coatings that have no self-cleaning function. Solar reflectance on self-cleaning coatings decreases by about 6% per year with annual variations, due to the adhesion of dirt. On the other hand, solar reflectance on conventional coatings greatly decreases, by approximately 18% within four months of the coating's application, due to the adhesion of dirt. Then, it gradually recovers at a rate of about 4% per year, with annual variations, due to degradation of the coating. It is due to degradation of the conventional coating that the difference of solar reflectance between the self-cleaning coating and the conventional coating becomes almost zero in two years. Both the adhesion of dirt and coating degradation by chalking affect the temporal change of solar reflectance with annual variation.