Pavements Designed to Fight Climate Change Could Increase Energy Consumption in Surrounding Buildings

Maybe this would be beneficial in places that have a lot of cold weather.

http://www.jacobsschool.ucsd.edu/news/news_releases/release.sfe?id=1281

Nov. 6, 2012 -- A push to replace old, heat-trapping paving materials with new, cooler materials could actually lead to higher electricity bills for surrounding buildings, engineers at the University of California, San Diego, have found. Researchers published their findings Oct. 29 in the new Journal of Urban Climate.

The new paving materials are designed to lower the overall temperature of the areas where they are used—something that the study, which was focused on local solar radiation and energy consumption, was not designed to measure.

The study sounds a note of caution at a time when both federal and state legislatures have been pushing for increased use of the new highly reflective pavement materials. Assembly Bill 296, which became law in California this year, is designed to advance cool pavement practices in the state and requires the compilation of a Cool Pavement Handbook. The federal Heat Island and Smog Reduction Act of 2011, currently under consideration in Congress, would specifically require paving materials with higher solar reflectivity.

“Our findings suggested that some benefits associated with reflective pavements are tied to the environment where they’re used,” said Jan Kleissl, a professor of environmental engineering at the Jacobs School of Engineering at UC San Diego. “More studies are needed to determine where these new materials would be most beneficial.”

The new materials could have a positive effect in areas where buildings can automatically respond to additional sunlight because they are equipped with smart lighting solutions, such as dimmers run by photo-sensitive cells.

However, buildings without these features do not fare as well. The increases in consumption of cooling energy due to the new pavements ranged anywhere from 4.5 to 9.5 percent for typical newer, and better insulated, buildings; and from 5 to 11 percent for older structures. That’s because the new paving materials stay cool by reflecting significantly more of the sun’s rays than traditional pavements. Many rays are reflected back into space, helping to cool surrounding areas—and the planet. However, a portion of these rays gets reflected onto the windows of nearby buildings. In the researchers’ study, windows facing the reflective pavements got 40 percent more daily sunshine in summer as windows facing more traditional paving surfaces (in winter the difference was only 12 percent). That in turn increases temperatures inside the building, especially if the windows do not have solar-control coating. So the buildings’ occupants turn up the air conditioning. Meanwhile, office buildings that have smart lighting or energy-conscious occupants may actually benefit from the additional sunlight by being able to reduce energy use due to artificial lighting.

The worst-case scenario is when these new cooler pavements are used in office park settings with many mid-rise buildings with large window areas. The best-case scenario would be to use the new paving materials near buildings without windows; on roads or large parking lots that are not surrounded by buildings; or in warehouse districts where structures don’t have air conditioning, Kleissl said.