Experimental Comparison of Heat Flow Through Concrete Roofing Flagstones with Different Coatings

The predominant climate in most of Mexico is hot and sunny, divided between humid in the southern coastal areas and dry in the north. One of the most common materials used to build roofs today is reinforced concrete. This material allows a better use of the available space, but its thermal insulation characteristics are inadequate. This causes the levels of comfort inside the houses to be much worse than the minimum required. The current tendency to make better use of energy in buildings has led to the development of a new generation of roof coatings that offer a greater resistance to heat transfer. Thus, there is now a need for experimental mechanisms capable of evaluating the thermal behaviour of these products. In a hot and sunny climate, the effect of solar radiation reaching the roof is very important. In summer, under a clear sky, up to 1,000 W/m can reach the roof of any given house. Depending on the reflectivity of the roof surface, between 10% and 95% of the incident radiation is absorbed and converted to heat. This adds to the convective heat transfer generated by the temperature difference between the interior and exterior air. This work presents the results of a series of experiments in which 12 different roof coating systems commonly used in Mexico were subjected to identical operating conditions. For this, we built an experimental shed whose roof was designed to hold 12 concrete test-probes, insulated from each other, and coated with the substances to be tested. The coated testprobes were subject to the same exterior weather conditions, with the inside of the shed under constant airconditioning. Temperature measurements were taken on both faces of each slab, which made it possible to compare their heat transfer rates and thus the performance of each coating. The system was monitored over several weeks, with simultaneous measurements taken every two minutes. The results show that applying a few millimeter coating of white acrylic paint with polymer microspheres has the same effect as insulating the slab with 1" of polyurethane foam covered with conventional red acrylic paint. We also compared the heat flows obtained with the 12 different coatings during the day and night.