Berkeley Lab Touts Pilot Credit for Cool Walls
The Lawrence Berkeley National Laboratory recently confirmed that the U.S. Green Building Council is piloting a new credit for the installation of cool exterior walls in new homes, schools and commercial buildings for the purpose of mitigating urban heat islands.
Berkeley notes that with the pilot credit, this is a test integration for cool walls into the USGBC’s LEED ratings for buildings. The credit was written by Berkeley Lab scientist Ronnen Levinson based on peer-reviewed research by the University of South California and Berkeley Lab. That study found that reflective walls could lower urban air temperature much like reflective “cool roofs.”
The newly issued pilot credit means buildings that satisfy specific cool wall requirements will earn an innovation point in LEED. After a trial period, USGBC will decide whether to add the pilot credit to its permanent library.
“LEED has long recognized the heat island reduction benefits of cool roofs and pavements. This pilot credit also acknowledges the urban cooling that can be delivered by reflective walls,” said Levinson, leader of Berkeley Lab’s Heat Island Group.
“Cool wall materials, such as light-colored paints, are available today at no extra cost. Choosing them for new construction or routine repainting is an easy and affordable way to make our cities cooler and safer while lowering your energy bill.”
Berkeley notes that idea is to surface exterior walls with a solar-reflective paint or cladding. Reflecting sunlight out of the city reduces urban heat. To qualify for the LEED pilot credit, buildings must cover 75% of a building’s exterior with a cool wall material that reflects at least 60% of sunlight, among other specifications.
Berkeley’s Cool Studies
In July 2019, Berkeley Lab researchers found that in many climates in the United States, the use of “cool” exterior walls can save building owners as much or more energy than cool roofs.
“Cool walls provide energy cost savings and emission reductions across California and the southern half of the United States,” said Levinson, who co-authored the study, published in the journal Energy & Buildings. “In these climates, cool walls can save as much or more energy than the same size cool roof.”
The report analyzed more than 100,000 building simulations and modeled several different types and ages of homes, retail stores and office buildings in cities across California and the rest of the U.S.
Levinson explained at the time that, while walls receive less intense sunlight than roofs, they’re also less insulated.
According to Berkeley, about 40% to 60% of all buildings in the U.S. were built before 1980, when building codes generally specified much less wall insulation than today. As a result, cool-wall savings in these older buildings could be three to six times greater than those for new buildings, the study found.
“Repainting the exterior walls of pre-1980 buildings—whether homes or office buildings or stores—with cool paint offers the greatest benefit because they have the least insulation,” Levinson said. “And that’s not difficult to do. There are many light-colored cool paints in local home supply stores.”
In warm U.S. cities such as Miami, Florida, and Albuquerque, New Mexico, researchers found that cool walls could lead to annual heating, ventilation and air conditioning energy cost savings up to 11% for stand-alone retail stores, 8.3% for single-family homes and 4.6% for medium-sized office buildings. And for single-family homes across all California climates, the study found potential energy cost savings could range from 4–27%.
The study was supported by the Electric Performance Investment Charge program of the California Energy Commission and by the U.S. Department of Energy’s Office of Energy Efficiency and Renewable Energy.
A month later, Berkeley issued another study, this time focusing back on cool roofs—more specifically California’s use of cool roofs.
The study, “Interacting Implications of Climate Change, Population Dynamics and Urban Heat Mitigation for Future Exposure to Heat Extremes,” was published in the journal Environmental Research Letters.
“The researchers predict that heat waves are likely to become two to 10 times more frequent across the state by mid-century,” according to Berkeley’s press release. “But if cool roofs were adopted throughout California’s most populous areas—the San Francisco Bay Area, Los Angeles, San Diego and Sacramento—by 2050 these reflective roofs could bring down heat wave exposures (defined as each time a person experiences a heat wave) by 35 million each year, compared to an estimated 80 million heat wave cases in 2050 with no increase in cool roof adoption.”
In the study, researchers had two goals, according to the lab: They wanted to predict heat wave occurrences across California’s 29 major counties between now and 2050, and they wanted to analyze the effectiveness of cool roofs in mitigating heat wave impact.
Researchers used regional climate conditions between 2001-15 as a starting point to simulate the climate under two scenarios (with and without cool roofs). Combining those conditions with high-resolution satellite images is what allowed them to look at buildings, roads and vegetation, which absorb and release heat.
Then, they used population estimates for 2050 to assess population exposure to heat waves.
“We wanted to gain a better picture of future climate change risks for California’s urban environments and adaptation options,” said Andrew Jones, a scientist in Berkeley Lab’s Climate and Ecosystem Sciences Division and co-author of the study. “Making such refined and realistic predictions can help urban planners and citizens prepare for heat events in an increasingly warming future.”
The study found heat waves with temperatures exceeding 95 F and lasting three consecutive days to become two to 10 times more frequent under the estimated scenarios. The researchers expect that there will be 80 million heat wave exposure cases in California each year, more than double what is currently seen.
They found that white-coated roofs or the installation of sun-reflecting could be a helpful answer.
To analyze the effectiveness of the cool roofs, the team repeated the simulations, but replaced all the existing building roofs with cool roofs.
They found that if every building in California sported cool roofs by 2050, it could bring down the annual number of heat wave exposures in California to 45 million from 80 million, according to the lab.
“Although a small percentage of California’s land is urban, I was surprised at how effective cool roofs could be in pushing back risks of heat extremes,” Jones said.
The researchers acknowledge, however, that the retrofitting of existing buildings needed to accomplish the every-building goal is a difficult task, so the next step is finding the minimum cool-roof coverage needed to accrue similar benefits.