Design impacts of cool roof coating, ventilation and thermal inertia on commercial low-rise building energy demand and summer comfort

Few studies focus on commercial low-rise buildings which are often characterized by low-cost constructions materials and weak energy performances. For these large volumes, the heat transfers with the roof and the ground are prevalent. In this article, we show how the analysis of heat transfers through both the roof and the ground can achieve their thermal performance. The roof design and its opening systems is a key factor of the thermal and lighting performance. Roof openings (skylight) and radiative properties of roof coating (cool roof) have a direct impact on solar gains, thermal losses and natural ventilation potential. The overall building thermal behavior depends both on the combination of these design parameters (solar reflectance, opening size, etc.) and weather conditions. Yet, the inertia of these lightweight structures is mainly given by the slab on the ground; and the performance of the roof design cannot be separated from the type of soil and slab which determine the dynamic behavior of these buildings. 
A simple and typical case study is presented and modeled and, an extensive parametric study (840 annual simu-lations) is performed to point out these key parameters impacts on building energy demand and comfort. The mixed use of efficient roof techniques (skylights and cool roof) combined with a high inertia of the building can be an adequate passive cooling solution in summer, with a 99.8% drop of degree hours above the discomfort temperature in summer. Nevertheless, we show that these passive strategies could not be totally efficient without taking care of the ground thermal inertia which account up to 58.6%.