Published on October 11th, 2009 | by Susan Kraemer10
MIT Roof Tiles Save Energy in All Climates
A team of students at MIT has just developed a temperature sensitive roof tile that turns black and absorbs heat in cold weather, and turns white, reflecting heat away when it’s hot.
In cold weather, the polymer stays dissolved and the black backing shows through, but exposed to heat, tiny droplets form and scatter the light back to produce a white appearance. The tiles reflected 80% of the sunlight falling on them when white, and only 30% when black.
The cooling needs would then be reduced 20%.
Dark-roofed houses absorb more heat, requiring more air conditioning use in the summer for cooling, which in turn means using more energy for running air conditioners, which emits more greenhouse gases. Steven Chu at the DOE famously recommends “cool” white roofing for the sunny states – mentioning California, Florida and Georgia. Cool roofs reduce energy costs associated with air conditioning.
There are already special energy efficient elastomeric roof paints, rated by the independent cool roof council through coolroofs.org for how well each one reflects heat. California Energy Commissioner Athur Rosenfeld probably originated the idea to use “white roofs” for sunny climates, where air conditioning costs outpace heating costs for energy use.
In summer, the white roofed house is reflecting heat away. lowering energy costs. But for climates that get both extremes of heat and cold winters, there has not been a solution till now. Their carbon emitting energy use goes up summer and winter.
The MIT team that came up with this tile were the winning competitors in the Making and Designing Materials Engineering Contest (MADMEC) that this year has been focused on energy efficiency. They have the marketing down. They’ve named their reversible black/white tile the Thermeleon, which rhymes with chameleon.
They used a common commercial polymer like that used in hair gels in a water solution, encapsulated between flexible plastic layers with a dark layer at the back.
The materials they used were common and cheap, so commercial viability would not be an issue, though they have more testing to do on durability. The students plan to develop it into a commercial enterprise with a simple white paint that would still have their color changing properties, but can be painted over dark roofs.