Passive Thermal Management of Solar Heat Flux through Building Roof Structures

The impact of rising energy prices on household costs and the overall economy has increasingly become a focal point of public concern. During a typical summer day, solar radiation heats up a building for the majority of the day through the windows, walls, doors, and especially the roof. To maintain comfort in summer, the heat gained must be removed by a cooling system and similarly in winter, the heat lost must be replaced by a heating system. Heating and cooling are both major contributors to energy expenditures in most building structures, and as a result, energy savings focused on these sources need to be investigated. The objective of the research was to evaluate through analytic and experimental techniques a novel type of passive thermal management system by determining the impact of natural convective air gaps driven by buoyancy effects and evaluating the interactive thermal properties. The properties considered included the convection heat transfer coefficient, thermal conductivity, radiation emissivity, thermal resistance, and thermal capacitance of each system component. To meet this objective, the governing classical thermal and flow equations were used to create a predictive tool for the development of a scaled physical test model. This structural test model and its similar control unit were set up to evaluate the direct effects that convective cooling has on sunlit days. For these experiments, temperature and air speed measurements were observed in the experimental units and compared against the analytic predictions. To validate the design, experimental tests were performed and compared to the predictive results. In addition, the experimental results were used to validate the prediction model and to investigate alternative design settings, parametrically. This research assessed the thermal attributes of an add-on roof system for a single or multifamily residence or small business, with the goal of providing recommendations that can be employed in the design of new homes and businesses. Likewise, the roof system can be applied as a retro-fit to improve the efficiency of current home and business roof designs. The results of this evaluation show the effectiveness of the heat roof design for attic and home temperature reductions, as well as provide an experimentally based model for future roof design considerations