New Berkeley Lab study uses regional climate model to compare heat waves to normal summer conditions
It is well established that white roofs can help mitigate the urban heat island effect, reflecting the sun's energy back into space and reducing a city's temperature under normal weather conditions. In a new study of Guangzhou, China, Lawrence Berkeley National Laboratory (Berkeley Lab) researchers working with Chinese scientists found that during a heat wave, the effect is significantly more pronounced.
Using a regional climate model combined with an urban model that allowed researchers to adjust roof reflectance, they found that the average urban midday temperature was lowered by 1.2 degrees Celsius (2.2 degrees Fahrenheit) during heat waves, or 50 percent more than the 0.8 degrees Celsius reduction for typical summer conditions.
The study, "Cool Roofs in Guangzhou, China: Outdoor Air Temperature Reductions during Heat Waves and Typical Summer Conditions," was published recently in the journal Environmental Science & Technology. The authors were Berkeley Lab researchers Dev Millstein, Ronnen Levinson, and Pablo Rosado; and Meichun Cao and Zhaohui Lin of the Institute of Atmospheric Physics, Chinese Academy of Sciences, Beijing.
"The hotter it is, the more cooling you get with cool roofs--and it is a significant difference, compared to the margin of error," said Millstein. "We found that the stagnant conditions of a heat wave, where the air is just sitting over the city, was one of the main factors."
Reflective roofs, also called cool roofs, save energy by keeping buildings cooler, thus reducing the need for air conditioning. Hot surfaces such as dark roofs that warm the outside air contribute to the urban heat island effect. Previous Berkeley Lab research in China found that cool roofs could substantially reducing energy use and greenhouse gas emissions in climate zones with hot summers.
The reasons for studying heat waves have to do with both health and energy. "That's when reducing the hottest temperatures can have the most health benefit," Millstein said. "It's also when the electric grid is the most stressed. Air conditioners are running at full speed and with no break, so a small change on the margin can have a bigger impact."
In addition to reducing city temperatures more during a heat wave, the researchers also found that cool roofs can decrease the intensity of the urban heat island effect more during extreme conditions. "Looking at the average difference in temperature between every grid cell in the city and the adjacent rural area, cool roofs had a more dramatic effect during heat waves," Millstein said.
Guangzhou is a sprawling megacity in southern China, near Hong Kong, with a population of more than 8.5 million. Researchers simulated conditions from six of the strongest historical heat waves over the last decade, and compared them to 25 typical summer weeks between 2004 and 2008.
For the purposes of the study, the researchers made all the roofs in the city as reflective as an aged white roof. While it is unlikely that will ever occur, it was necessary to have a statistically significant signal. A government policy, Millstein said, would likely be necessary to encourage use of cool roofs.
"It wouldn't have to be all at once, just as they're replaced," he said. "That's one of the reasons we think so much about cool roofs--because it's free or inexpensive to put a cool roof on when you're putting a new roof on anyway."
The research was funded by DOE's Building Technologies Office, through the U.S.-China Clean Energy Research Center Building Energy Efficiency (CERC-BEE), the Chinese Academy of Sciences, and the National Natural Science Foundation of China. The researchers used the computing facilities of the National Energy Research Scientific Computing Center (NERSC), a DOE Office of Science User Facility.
Lawrence Berkeley National Laboratory addresses the world's most urgent scientific challenges by advancing sustainable energy, protecting human health, creating new materials, and revealing the origin and fate of the universe. Founded in 1931, Berkeley Lab's scientific expertise has been recognized with 13 Nobel prizes. The University of California manages Berkeley Lab for the U.S. Department of Energy's Office of Science. For more, visit http://www.
DOE's Office of Science is the single largest supporter of basic research in the physical sciences in the United States, and is working to address some of the most pressing challenges of our time. For more information, please visit science.energy.gov.
Julie Chao | EurekAlert!
How much biomass grows in the savannah?
16.02.2017 | Friedrich-Schiller-Universität Jena
Canadian glaciers now major contributor to sea level change, UCI study shows
15.02.2017 | University of California - Irvine
In the field of nanoscience, an international team of physicists with participants from Konstanz has achieved a breakthrough in understanding heat transport
Cells need to repair damaged DNA in our genes to prevent the development of cancer and other diseases. Our cells therefore activate and send “repair-proteins”...
The Fraunhofer IWS Dresden and Technische Universität Dresden inaugurated their jointly operated Center for Additive Manufacturing Dresden (AMCD) with a festive ceremony on February 7, 2017. Scientists from various disciplines perform research on materials, additive manufacturing processes and innovative technologies, which build up components in a layer by layer process. This technology opens up new horizons for component design and combinations of functions. For example during fabrication, electrical conductors and sensors are already able to be additively manufactured into components. They provide information about stress conditions of a product during operation.
The 3D-printing technology, or additive manufacturing as it is often called, has long made the step out of scientific research laboratories into industrial...
Nature does amazing things with limited design materials. Grass, for example, can support its own weight, resist strong wind loads, and recover after being...
Nanometer-scale magnetic perforated grids could create new possibilities for computing. Together with international colleagues, scientists from the Helmholtz Zentrum Dresden-Rossendorf (HZDR) have shown how a cobalt grid can be reliably programmed at room temperature. In addition they discovered that for every hole ("antidot") three magnetic states can be configured. The results have been published in the journal "Scientific Reports".
Physicist Dr. Rantej Bali from the HZDR, together with scientists from Singapore and Australia, designed a special grid structure in a thin layer of cobalt in...
13.02.2017 | Event News
10.02.2017 | Event News
09.02.2017 | Event News
17.02.2017 | Medical Engineering
17.02.2017 | Medical Engineering
17.02.2017 | Health and Medicine