Scientists at Lawrence Berkeley National Laboratory are conducting research on cool roofs — roofs that reflect sunlight and deflect radiation to their surroundings — in China and found that these roofs reduced energy use and greenhouse gas emissions.
Researchers examined the function of cool roofs on buildings in Chinese cities that experienced hot summers. In addition to collaborating with Chinese researchers, Berkeley researchers are also working with scientists from Oak Ridge National Laboratory and the Dow Chemical Company.
“We want to improve energy efficiency in China to reduce the energy and carbon footprint of China,” said Ronnen Levinson, a scientist at the Berkeley lab who was lead author on the study’s recently published paper. “We had an opportunity to apply this well-developed energy-efficiency strategy to China, where it is not as well known.”
The project, which began with a meeting with the U.S. China Cool Roof Working Group in October 2010, is a five-year joint project among the researchers.
Cool roofs have contributed to cooling-energy savings in places such as the United States and around Europe. The roof is able to stay cooler in the sun by reducing the amount of heat flowing into the building and minimizing absorption and thermal radiation.
The cool roof helps in “cooling the planet by reducing the heating of the atmosphere,” Levinson added.
In comparison, most Chinese buildings have a structural concrete roof with a layer of waterproof coating that has a service life of five to 10 years. An aspect of the research involves developing a white, water-repellent roof coating to maintain high solar reflection, extend the lifetime of water-resistant coatings and resist microbial growth and water damage more efficiently.
“If we can integrate these materials in the spray-on cool roof coating, then high solar reflectance and the roof surface itself will last longer,” said Patrick Hughes, the buildings program director at Oak Ridge National Lab who is contributing to the research. “The goal is to double the energy savings by extending the surface life of the roof.”
But cool roofs are not recommended in northern China, where the costs of winter heating exceed energy savings from summer cooling.
The next steps of the research involve conducting year-round experiments to compare white, black and garden rooftops in two Chinese cities as well as pursuing similar research with counterparts in India. According to Levinson, China is beginning a program this month to test the performance of cool roofs in nine different locations in China.
“It’s been going very well,” Levinson said. “We’ve now demonstrated that cool roofs are a smart choice for both public and residential buildings in Chinese cities with hot summers.”