Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Cool roofs in China offer enhanced benefits during heat waves

23.12.2015

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.


The greater urban area of Guangzhou is outlined in the center of each figure. A midday urban heat island effect is clearly visible. The results of increased roof albedos are shown in the bottom row.

Credit: Berkeley Lab

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.lbl.gov.

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.

Media Contact

Julie Chao
jhchao@lbl.gov
510-486-6491

 @BerkeleyLab

http://www.lbl.gov 

Julie Chao | EurekAlert!

Further reports about: Cool roofs Energy Research heat waves temperature waves

More articles from Earth Sciences:

nachricht Modeling magma to find copper
13.01.2017 | Université de Genève

nachricht What makes erionite carcinogenic?
13.01.2017 | Friedrich-Schiller-Universität Jena

All articles from Earth Sciences >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: Designing Architecture with Solar Building Envelopes

Among the general public, solar thermal energy is currently associated with dark blue, rectangular collectors on building roofs. Technologies are needed for aesthetically high quality architecture which offer the architect more room for manoeuvre when it comes to low- and plus-energy buildings. With the “ArKol” project, researchers at Fraunhofer ISE together with partners are currently developing two façade collectors for solar thermal energy generation, which permit a high degree of design flexibility: a strip collector for opaque façade sections and a solar thermal blind for transparent sections. The current state of the two developments will be presented at the BAU 2017 trade fair.

As part of the “ArKol – development of architecturally highly integrated façade collectors with heat pipes” project, Fraunhofer ISE together with its partners...

Im Focus: How to inflate a hardened concrete shell with a weight of 80 t

At TU Wien, an alternative for resource intensive formwork for the construction of concrete domes was developed. It is now used in a test dome for the Austrian Federal Railways Infrastructure (ÖBB Infrastruktur).

Concrete shells are efficient structures, but not very resource efficient. The formwork for the construction of concrete domes alone requires a high amount of...

Im Focus: Bacterial Pac Man molecule snaps at sugar

Many pathogens use certain sugar compounds from their host to help conceal themselves against the immune system. Scientists at the University of Bonn have now, in cooperation with researchers at the University of York in the United Kingdom, analyzed the dynamics of a bacterial molecule that is involved in this process. They demonstrate that the protein grabs onto the sugar molecule with a Pac Man-like chewing motion and holds it until it can be used. Their results could help design therapeutics that could make the protein poorer at grabbing and holding and hence compromise the pathogen in the host. The study has now been published in “Biophysical Journal”.

The cells of the mouth, nose and intestinal mucosa produce large quantities of a chemical called sialic acid. Many bacteria possess a special transport system...

Im Focus: Newly proposed reference datasets improve weather satellite data quality

UMD, NOAA collaboration demonstrates suitability of in-orbit datasets for weather satellite calibration

"Traffic and weather, together on the hour!" blasts your local radio station, while your smartphone knows the weather halfway across the world. A network of...

Im Focus: Repairing defects in fiber-reinforced plastics more efficiently

Fiber-reinforced plastics (FRP) are frequently used in the aeronautic and automobile industry. However, the repair of workpieces made of these composite materials is often less profitable than exchanging the part. In order to increase the lifetime of FRP parts and to make them more eco-efficient, the Laser Zentrum Hannover e.V. (LZH) and the Apodius GmbH want to combine a new measuring device for fiber layer orientation with an innovative laser-based repair process.

Defects in FRP pieces may be production or operation-related. Whether or not repair is cost-effective depends on the geometry of the defective area, the tools...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

12V, 48V, high-voltage – trends in E/E automotive architecture

10.01.2017 | Event News

2nd Conference on Non-Textual Information on 10 and 11 May 2017 in Hannover

09.01.2017 | Event News

Nothing will happen without batteries making it happen!

05.01.2017 | Event News

 
Latest News

Multiregional brain on a chip

16.01.2017 | Power and Electrical Engineering

New technology enables 5-D imaging in live animals, humans

16.01.2017 | Information Technology

Researchers develop environmentally friendly soy air filter

16.01.2017 | Power and Electrical Engineering

VideoLinks
B2B-VideoLinks
More VideoLinks >>>