Thermal analysis of flat roof systems with regards to their thermal insulation and exterior surface emissivity coefficient

In this study, a numerical analysis of the thermal performance of a flat roof system is presented. The dynamic thermal behaviour of this system is assessed with regards to the effects produced by an insulation layer and the thermal emissivity of the exterior surface exposed to the outdoor environment thermal conditions, such as the ambient air temperature and radiation (short-wave and long-wave). Analysed building components correspond to insulated and noninsulated flat roof assemblies formed by reinforced concrete. For their exterior surface, a varying value of its thermal emissivity is assumed. In this context, the aim of this investigation is to assess the dynamic thermal behaviour of multi-layered roof configurations in terms of thermal flux through their construction; this allows us to determine the overall heat exchange in a daily basis, in the aspect of the above-mentioned parameters. In order to analyse the thermal response of the flat roof located in the Greek region, during the cooling period, a FEM model is introduced (one-dimensional model). Results underline the significance to consider the thickness of the thermal insulation layer, as well as the effect of various emissivity coefficients on heat transfer processes.