Assessing cooling loads from roofs with attics: Modeling versus field experiments

T.C. Quevedo, A.P. Melo, R. Lamberts

The use of low-emissivity materials in roofing offers a low-cost solution to reduce the demand for cooling in countries with hot climates. The performance of radiant barriers is often evaluated through simulations and the type of modeling employed influences the results. This study evaluates different modeling approaches to simulate radiant barriers in attics. First, the influence of the temperature and emissivity of materials on the thermal resistance of air chambers were evaluated. Then, the heat flow and thermal load values were obtained with the simulation of three different models. Simulation results were compared with actual tests and results in the literature. The emissivity of the materials resulted in strength variations of up to 4%. The simulation model that adopted the energy management system (EMS) and thermal resistance calculated according to ISO 6946 2017 was the closest results to experimental tests and literature. These provide maximum differences of 7% in the downward heat flow and thermal load. The model that included the attic underestimated by 20% the reduction in heat flow compared to bench tests. Finally, thermal resistance values to be adopted in attic simulations with low-emissivity materials in hot climates are proposed.