Hot Topic at Berkeley Lab: Cool Walls

Monday, January 8, 2018

Ronnen Levinson, Hugo Destaillats and Haley Gilbert recently hosted an industry and research team meeting to review the latest news and information regarding "Cool Walls," a technology that improves the energy-efficiency of homes and other buildings.

Cool Walls Workshop

The workshop was attended by a wide variety of scientists and industry professionals interested in the technology, and by representatives of the California Energy Commission, California and U.S. Environmental Protection Agencies and PG&E.

Robert Martuch, environmental health and safety manager at Sherwin Williams paint company, attended the workshop to keep up with cool-wall trends.

"We recognize that cool roofs were in the forefront and cool walls are now the beckoning technology of the future," Martuch said. As a paint company, Sherwin Williams wants to be "in the know" on the latest developments at Lawrence Berkeley National Lab, so they can anticipate what will happen next in the marketplace and make the best decisions to help consumers.

Martuch said there is a learning curve for industry executives and customers to ultimately "buy in" to new technologies like cool walls. Often, when the public finds out about money and energy that can be saved, they'll get on board.

Cool roofs and cool walls are a major research area for Levinson and his team, the Heat Island Group at Berkeley Lab. The group also partners with the University of Southern California and UC San Diego.

Attendees at the workshop included researchers and industry partners from Germany, Japan, China and France.

Cool roofs and walls reflect more sunlight than ordinary roofs and walls, reducing heat conduction into the building. Some cool wall materials could also direct reflected sunlight skyward, away from other buildings and people in the city.

Historically, cool walls have been either white or some other light color. Now, however, walls and roofs can be painted in a variety of shades that will stay cool in the sun.

Most of the roofs in the United States are dark-colored. In full sun, the surface temperature of a black roof can rise about 80 °F (44 °C) over the ambient temperature, reaching about 180 °F (82 °C) on a typical summer afternoon. While walls receive less sun than roofs, they are also less insulated. This lets the energy savings from cool walls often exceed those from cool roofs.

The workshop, entitled "Solar-Reflective "Cool" Walls: Benefits, Technologies and Implementation," was held on October 25, 2017 at Berkeley Lab.

Discussion items included:
• The ability of cool walls to reduce heating, ventilation, and air conditioning (HVAC) loads in residential and commercial buildings
• Urban climate impacts of cool walls
• Self-cleaning, fluorescent, and retroreflective wall materials
• Advancing cool wall adoption through standards, incentive programs, and application guidelines

Building simulations indicate that cool walls can save energy and reduce emissions of greenhouse gases (CO2) and criteria pollutants (NOx, SO2) throughout California and the warmer U.S. climate zones. Meanwhile, urban climate simulations predict that cool walls can lower outside air temperature in the Los Angeles Basin. Outdoor trials conducted at six sites across the United States show that cool wall reflectance does not drop substantially over the first year of exposure, and that some soil-resistant or self-cleaning products perform especially well. The researchers have also produced some novel cool materials, including red, blue, and green coatings that use fluorescence (absorption of light at one wavelength, followed by emission of light at another wavelength) to help stay cool in the sun.

"Now that we have shown that making walls more reflective can save energy and cool cities, we will work with manufacturers, utilities, and the state of California to create the infrastructure needed to advance the climate-appropriate use of cool walls," Levinson said. "This includes application guidelines, a product rating system, incentives in building energy efficiency standards, and utility rebates."