1. Full-Building Radiation Shielding for Climate Control
John Abraham
Camille George
Solar 2007
Cleveland, Ohio
November 22, 2018

2. 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

3. 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

4. Buildings in Mali
Photograph of a large, multi-room building with dual-roof structure.
Solar 2007
Cleveland, Ohio
November 22, 2018

5. Buildings in Mali
A smaller, single-room building with corrugated metal roof.
Solar 2007
Cleveland, Ohio
November 22, 2018

6. 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

7. 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

8. Heat Transfer Processes
An energy balance begins the analysis
Solar 2007
Cleveland, Ohio
November 22, 2018

9. Heat Transfer Processes
Radiation transfer includes absorbed, reflected, and transmitted components.
Solar 2007
Cleveland, Ohio
November 22, 2018

10. Heat Transfer Processes
Schematic showing the combined convection and radiant heat transfer rates.
Solar 2007
Cleveland, Ohio
November 22, 2018

11. 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

12. 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

13. 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

14. Heat Transfer Processes – Double Roof
Two coupled energy equations must be solved simultaneously
Solar 2007
Cleveland, Ohio
November 22, 2018

15. 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

16. 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

17. 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

18. 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

19. 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