Sunday, December 6th, 2009
Nick Orf, one of the team of students, demonstrates Thermeleon.
Most modern homes have black roofing shingles that absorb energy from the summer sun leading to higher cooling bills and wasted energy. This is offset somewhat in the winter with the sun’s energy being absorbed by the roof and reducing heating bills but the sun is most intense in the summer and thus the problem. One solution is to paint your roof white. While this solves the problem in the summer what about that energy that you could be absorbing in the winter? What if you could do both – reflect the sun’s energy in the summer and absorb it in the winter?
Using a phase changing polymer gel we are able to control the light energy transmission properties of our roofing material. On a hot day the material becomes white, reflecting all wavelengths of light. On a cool day the material is transparent which allows our heat absorbing backing to conduct heat into the home. We have filed a provisional patent on our technology and are exploring commercialization options.
Our roofing system is based on a polymer gel which phase separates at a pre-determined temperature. Although most of our testing has been done with a gel that transitions around room temperature, we are able to select from a wide variety of transition temperatures ranging from approximately 0 to 100 degrees Celsius and beyond. When the polymer phase separates from the gel, the solution becomes a mixture of polymer and solvent and because the polymer and solvent have different refractive indices the mixture becomes strongly scattering (white colored). When the mixture cools below the transition temperature the polymer re-dissolves in the liquid and the solution is clear and colorless. The pictures below illustrate the change in color when the tile is subjected to hot and cold temperatures.
The polymer gel is sealed in a container (usually made out of weather-resistant plastic) with a transparent top and black bottom. When the polymer gel is above the transition temperature the scattering it produces reflects over 80% of the incident light whereas below the transition temperature (when it’s cool outside) the gel is transparent and the 70% of the sun’s energy is absorbed by the black backing.
The simplicity of the design and the use of commodity materials leads to an inexpensive, robust system. We have thus far demonstrated a hard tile (glass front / plastic back), a flexible tile (plastic front and back), and a paintable system (for application onto black roofing tiles or other materials). We are currently developing our system and are looking forward to doing some long-term environmental testing (heat/UV/humidity) to determine the anticipated lifespan of our design.
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