Thermal evaluation of building roofs with conventional and reflective coatings

Abstract This chapter discusses the thermal performance of slab type building roofs with different coatings. A setup with two outdoor test boxes in which the roofs can be exchanged was monitored to evaluate three small-scale roof samples. A conventional gray roof was used as the reference, while the other two roof samples were covered with a white reflective and a black coating, respectively. Two comparative tests (gray-white and gray-black) were carried out in a city in Mexico with mild weather. The results show that during the hours with sunlight, the white roof remained up to 11.1°C cooler than the gray roof, and the black roof remained up to 18.2°C hotter than the gray roof. To evaluate the roofs under different weather conditions, a numerical model of the building roof was built and validated with experimental data. The results provided by the numerical model had a maximum deviation of 5.5% and 4.6% from experimental data for the gray and white roofs, respectively. Further, a building room model located in a city with warm weather was studied. For this evaluation, the validated roof model and a numerical model of a building room were coupled to determine how a roof coating influences the indoor thermal comfort of the room. It was found that the white reflective roof improved the indoor thermal comfort by around 6 and 8°C compared with the gray and the black roof, respectively. It was also found that the room with the white roof had a daily heat gain 9% smaller than the room with the gray roof, and the room with the black roof had a daily heat gain 5% higher than the room with the gray roof.