A darker roof will absorb more heat from the sun and help to heat a
house in winter; a lighter-colored roof will reflect the light and help keep a
home cooler in the summer, Yu said.
About 40 percent of an average building’s energy use and expense
comes from heating and cooling, Yu said, making the changeable roof system
potentially a money-saving innovation for homeowners and businesses alike. Buildings
also use about 30 percent of the world’s electricity, much of it still
generated from fossil fuels.
Yu—and collaborator Jianying Hu, a former postdoctoral researcher at Case Western Reserve now at Southeastern University—experimented with various colors and materials in different climate situations. In addition, they are testing another system to more efficiently scatter or concentrate collected light particles to increase the efficiency of the material.
The system has not yet been tried on residential or commercial
roofs, but computer models across climates in seven U.S. geographic regions projected
success rates of varying degrees.
On average, the coatings could lead to a 5.4 percent reduction in
energy demand in winter and 13.3 percent reduction in summer, their modeling
showed. The simulations and energy analysis were run on U.S. Department of
thermochromic roof system was most effective in San Francisco, showing a combined
savings of more than 47 percent in heating and cooling over the course of a
Yu came up with the idea as a way to improve upon the U.S. Department of Energy’s “Cool Roof” program, which advocates for roofs painted white to reflect light and heat in warmer areas of the country, which helps reduce the phenomenon in bigger cities known as the “urban heat island effect”. “In a world of climate change, you have areas experiencing wilder swings in temperature,” Yu said, “so having a roof that reacts to both heat and cold could be beneficial no matter the time of year.”