Abstract

The use of roofing with high solar radiation reflectance has proven effective in improving buildings’ thermal and energy performance, especially in hot climates. However, performance declines over time due to the natural aging of surfaces. Another issue identified in relation to passive techniques, such as cool roofs, is the difficulty in quantifying their benefits in buildings without air conditioning. This study aimed to investigate the impact of aging and restoration (achieved through a cleaning process) on cool roofs in terms of thermal, energy, and economic performance. The method applied was capable of assessing the economic benefits of cool roofs in buildings without air conditioning. The surfaces were evaluated by exposing samples of white-painted fiber cement tiles for two years in three Brazilian cities: Florianópolis, São Paulo, and Manaus. The samples’ thermal emittance and solar reflectance were measured in three conditions: new, aged, and restored, after the first and second years of exposure. With the results measured in the laboratory, a computer simulation was performed using the EnergyPlus software for a thermoenergetic evaluation. Finally, an analysis of the economic benefits of cool roofs in a residential building without air conditioning was carried out. Thermal emittance did not show significant changes due to natural aging and restoration. Conversely, the solar reflectance of the surfaces underwent significant changes in the aging process. It was observed that the cool roofs’ greatest performance was in the first year of exposure (reduction of up to 40% in reflectance), and the restoration process proved to be efficient for most samples, returning to the initial reflectance value for some of them. A few paints did not perform well over time, proving to be unsuitable for the proposed purpose. A benefit of up to US$2.87 per square meter was found when considering the use of cool roofs for the city of São Paulo.

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