Full-Building Radiation Shielding for Climate Control John Abraham Camille George Solar 2007 Cleveland, Ohio November 22, 2018
Introduction During 2005, a faculty-led student team traveled to Mali, Africa. The purpose of the trip was to investigate the use of full-building solar shields for cooling buildings. Solar 2007 Cleveland, Ohio November 22, 2018
Introduction The shields were employed on a wide range of building structures including small, single room dwellings to large, multi-room buildings. Extensive experiments show the effect of shielding on reducing the thermal load to the building. Analytical calculations were verified by experimental results. Solar 2007 Cleveland, Ohio November 22, 2018
Buildings in Mali Photograph of a large, multi-room building with dual-roof structure. Solar 2007 Cleveland, Ohio November 22, 2018
Buildings in Mali A smaller, single-room building with corrugated metal roof. Solar 2007 Cleveland, Ohio November 22, 2018
Heat Transfer Processes High rates of heat pass through roofs, walls, and windows. Very little shade leads to highly intense incident solar radiation. Unreliable electric grid and expensive air conditioning are not appropriate in Mali. Cooling efforts are directed at lowering the incident solar influx. Solar 2007 Cleveland, Ohio November 22, 2018
Heat Transfer Processes Heat transfer through opaque walls involves radiation and convective exchanges external and internal to the space. Solar 2007 Cleveland, Ohio November 22, 2018
Heat Transfer Processes An energy balance begins the analysis Solar 2007 Cleveland, Ohio November 22, 2018
Heat Transfer Processes Radiation transfer includes absorbed, reflected, and transmitted components. Solar 2007 Cleveland, Ohio November 22, 2018
Heat Transfer Processes Schematic showing the combined convection and radiant heat transfer rates. Solar 2007 Cleveland, Ohio November 22, 2018
Heat Transfer Processes Final form of the energy balance. - Absorbed radiation includes a direct solar contribution and a diffuse contribution. - Radiant losses from the wall to the interior space is treated with a linearized transfer coefficient. Solar 2007 Cleveland, Ohio November 22, 2018
Heat Transfer Processes The uncovered roof was a dull, oxidized metal. The roof was covered with a highly reflective metallic foil sheet. Solar 2007 Cleveland, Ohio November 22, 2018
Heat Transfer Processes The emerging results are: Troof = 332 K = 138 oF (no barrier) Troof = 311 K = 100 oF (with barrier) Solar 2007 Cleveland, Ohio November 22, 2018
Heat Transfer Processes – Double Roof Two coupled energy equations must be solved simultaneously Solar 2007 Cleveland, Ohio November 22, 2018
Heat Transfer Processes – Double Roof The emerging results are: Upper Roof Troof = 346 K = 163 oF (no barrier) Troof = 320 K = 116 oF (with barrier) Lower Roof: Troof = 319 K = 114 oF (no barrier) Troof = 312 K = 102 oF (with barrier) Solar 2007 Cleveland, Ohio November 22, 2018
Experimental Verification Extensive experiments were carried out on shielded and un-shielded roofs. Results are shown for the upper portion of a double-roof structure. Solar 2007 Cleveland, Ohio November 22, 2018
Comparison of Results Temperature (K) No Barrier Barrier Single Roof 334 (332) NA (311) Double Roof (Upper) 351 (346) 316 (320) Double Roof (Lower) 321 (319) 311 (312) Excellent agreement is seen between experimental and calculated results. Solar 2007 Cleveland, Ohio November 22, 2018
Heat Load to Building Interior The reduction in the heat load transferred to the building interior can be determined. Heat Flux in Building (W/m2) No Barrier Barrier Single Roof 145 Double Roof 64 6 Solar 2007 Cleveland, Ohio November 22, 2018
Remaining Issues The results indicate that a highly reflective solar barrier can reduce the rate of heat transfer into buildings. The solar barrier must be rugged in order to withstand weathering. Reflective barrier should be built into construction rather than added afterwards. Solar 2007 Cleveland, Ohio November 22, 2018