Due to aesthetics, most US homeowners won’t buy a light colored roof, even if it reduces their air conditioning bills by reflecting, instead of absorbing, solar heat. So the question for scientists interested in increasing energy efficiency is, can one make a roof that is both cool and dark?
Hashem Akbari, Paul Berdahl, and Ronnen Levinson of Lawrence Berkeley National Laboratory (LBNL), and their collaborators in US industry have tackled that question with breakthrough results. They’ve developed a complete toolkit—a database, software, and novel manufacturing methods—for developing heat-reflective roofing products in any color, dark or light. The toolkit is called Cool Color Roofs. Roofing developed with Cool Color Roofs uses pigments that selectively reflect the invisible, near-infrared component of sunlight, making energy-saving roofing available in a wide range of colors. Berkeley Lab research estimates that applying cool-colored roofs to residences in U.S. cities could achieve a net energy savings in the U.S. worth over $400 million per year.
To develop Cool Color Roofs, the LBNL scientists used pigment spectroscopy to identify pigments of different colors that reflect the near-infrared component of sunlight and wrote software for the design of cool color coatings. They collaborated with a consortium of U.S. pigment, coating and roofing manufacturers to develop novel methods to manufacture asphalt shingle, clay tile, concrete tile, and metal roofing in a wide palette of cool colors.
Berkeley Lab’s industrial partners manufactured the prototypes and products, while colleagues at Oak Ridge National Laboratory performed some of the demonstration work, measuring both the energy savings achieved by the use of cool colored roofing, and the extent to which exposure over time changes the appearance and performance of cool colored roofing. All of LBNL’s sixteen industrial partners have introduced, or plan to introduce, cool color roof products or components (e.g., pigments, coatings, or colored granules). The consortium includes most of the major roofing manufacturers.
The price difference between cool roofs and conventional roof is typically paid back in air conditioning savings within a few years. Cool Color Roofing reduces a home’s solar heat gain and air-conditioning energy consumption in a warm climate by about 10 to 20%. These roofs also lower a home’s peak-hour cooling power demand by about 10 to 20%, helping prevent blackouts and brownouts on hot summer afternoons.
In addition, when a sufficiently large number of home and commercial building owners adopt cool roofs regionally, urban air temperatures will decrease, slowing the rate of smog formation. This improves public health, and helps cities meet federal clean air requirements.
The LBNL research team is now working with the automobile industry to develop cool colored coatings for car exterior metal and plastic surfaces. This will allow car manufacturers to install lighter, lower capacity air conditioning units that operate with greater efficiency. The cool color pigments also can be used in clothing, to produce dark uniforms that stay cooler in the sun for example, and in a wide variety of coatings, including those applied to furniture, machinery, tools, or camping gear.