Effect of Aging on Solar Reflectance of White Cool Roof Coatings: Natural Weathering and the Influence on Building Energy Needs for Different Climate Conditions in Brazil

Abstract

The use of cool materials on the building envelope is one of the most cost-effective ways to increase indoor thermal comfort conditions in hot climates and decrease the cooling energy needs. Despite the benefit of reducing cooling loads, researches have demonstrated that aging of roof coatings changes the initial SR, which influences the long term building thermal and energy performance. Thus, this work presents preliminary natural weathering tests performed on samples of nine white coatings exposed to natural weathering for one year in the city of Sao Carlos, Brazil. Solar reflectances were measured with a spectrophotometer before and after exposure, every 3 months, for identifying the effect of aging along the time. The findings showed a decrease on the SR from 13% to 23% after one year of natural weathering, with higher decrease for rougher surfaces. The cleaning process restored from 90% to 100% of the original SR, which means maintenance can be an effective solution to restore the initial SR. Simulations indicated that roofs with higher SR increase indoor thermal comfort conditions and decrease the cooling energy need for buildings in hot climates, but the aging of white coatings increased the cooling energy needs along the time.

Durability of high reflective materials designed for building envelopes

“…In Brazil, several studies have been reported by [9,15,16,[25][26][27][28][29], with ongoing research being carried out by the members of the University of São Paulo and Federal University of Santa Catarina. In the studies proposed by [15], a white cool paint was exposed in 4 cities of the country (São Paulo, Pirassununga, Belém and São Sebastião) and presented different levels of degradation between the sites, caused by different weather conditions, microflora, and pollutants.…”