Improving thermal performance of the roof enclosure of heavy construction buildings

High heat flux through the enclosures of heavy building constructions during summer and winter seasons is of great concern with respect to energy-related economics and environmental issues. This paper demonstrates the importance of quantitative evaluation of enclosure design and proves the potential for substantial energy savings by minor alterations of conventional roof designs. These modifications include adding insulation layer(s), removing construction details and obstructing fluid flow within the attic cavity by partial or full vertical partition within the cavity. The CFD approach adopted for this purpose is based on a numerical study of steady, conjugate natural convection in the cavity of an attic of heavy construction buildings. Because of the flow characteristics, laminar and turbulent models were employed for summer and winter day boundary conditions, respectively. Steady state results based on the finite-volume method were obtained for Rayleigh number in the range 108-1010. Representative results illustrating the effects of the proposed design modifications on the local and total Nusselt numbers at the indoor surfaces are presented and discussed for summer and winter day boundary conditions. The results show that considerable energy saving may be achieved via relatively simple design changes. It is also shown that adding an insulation layer does not necessarily translate into energy conservation, and that eliminating a minor design detail might have significant rewards in terms of energy savings.