Method for Assessing Thermal and Economic Benefits of Cool Roofs in Unconditioned Buildings

The use of cool roofs is a passive technique to reduce the cooling load of buildings in hot climates, moreover, it is use has the potential to mitigate the heat island phenomenon. This study presents a method to quantify and monetize the benefits of applying the cool roof passive technique in buildings without air conditioning. The proposed method can be adapted to other passive techniques. For this study, an experimental step was carried out to measure the thermal emittance and reflectance of fiber cement tile samples. The study also presents a thermoenergetic performance analysis using EnergyPlus simulations. The last part highlights the innovation of this method in relation to other studies, which consists of monetizing the thermal benefits of the cool roof passive technique. The analysis contemplates a single-family residential building model for three cities in different regions of Brazil (Florianópolis/SC, São Paulo/SP and Manaus/AM). Fiber cement tiles in their natural color were considered and painted white, representing a cool roof. The solar reflectance of the white-painted samples was around 50% higher than that of the conventional (unpainted) samples. When comparing conventional and cool roofs, the reduction in heat flow through the roof was over 80 % for all three cities. Although the building analyzed does not have air conditioning, the proposed method makes it possible to quantify the thermal load that the passive technique could avoid. The most significant results were in Manaus, resulting in a possible saving of US 4.2/m² per year.