Aging Roofs 3 Years in 3 Days

MONDAY, APRIL 20, 2015

BERKELEY, CA—A “cool roof time machine” developed at the Lawrence Berkeley National Laboratory could help dramatically speed the spread of cool-roof technology worldwide.

The technology has been approved as the standard protocol for rating solar reflectance levels of roofing products.

The lab method simulates natural soiling and weathering, allowing researchers to study the effect of three years of aging and soiling in just three days.

ASTM International recently approved the process as a standard practice for the industry, publishing ASTM D7897-15, Berkeley Lab announced Tuesday (April 14).

Boosting Cool-Roof Installs

"What we've created is essentially a cool roof time machine," explained Ronnen Levinson of Berkeley Lab's Heat Island Group.

"By reducing product rating time to three days from three years, our new ASTM standard practice will speed the introduction of high-performance cool roofs not only in the United States, but around the world."

Roof reflectance is rated on new substrates and after three years of outdoor exposure.

Surfaces with low solar reflectance absorb a large fraction of the incoming solar energy, which is either conducted into the buildings or convected to air (leading to higher air temperatures), ASTM said in its standard description.

Thus, use of materials with high solar-reflectance values may result in lower air-conditioning energy use and cooler cities and communities, according to ASTM.

Cool Roofs
City of New York

"By reducing product rating time to three days from three years, our new ASTM standard practice will speed the introduction of high-performance cool roofs not only in the United States, but around the world," according to Ronnen Levinson, of Berkeley Lab.

The team has applied the method to 25 different roof products, including single-ply membranes, coatings, tiles, and asphalt shingles, and has reproduced—in less than three days—the Cool Roof Rating Council's three-year aged values of solar reflectance, the team reported.

The Acceleration Process

On the first day, a piece of the roof material is placed in a commercial weathering apparatus, which exposes the material to cycles of heat, moisture, and ultraviolet light.

This process conditions the material before soiling, the scientists explain.

On the second day, a soiling apparatus sprays a calibrated aqueous soiling mixture of dust, soot, particulate organic matter, and salts onto the material.

Soiling a series of one to five test materials might take 10 minutes, Levinson said in an e-mail. Each specimen is sprayed for about 10-20 seconds, as needed to deposit the correct wet mass on the reference specimen, he added.

Aging diagram
Berkeley Lab Heat Island Group

The Berkeley Lab roof material aging process is completed in three days.

The material is then placed under a heat lamp to dry.

After it dries, it goes back in the weathering apparatus for one more day, to simulate the cleaning effects of dew and rain, according to Berkeley Lab.

Soiling By Site

The scientists note that the soiling concoctions mimic site-specific features of three environments: a hot and humid climate (Miami); a hot and dry climate (Phoenix); and a polluted atmosphere in a temperate climate (Cleveland, OH).

A fourth soiling mixture was devised to replicate the aged solar reflectance averaged over all three sites, which is the aged value reported by the CRRC on rated product labels, according to the scientists.

Collaboration, Training Scheduled

Berkeley Lab scientists and research associates, including Mohamad Sleiman, Hugo Destaillats, Sharon Chen, Thomas Kirchstetter, Haley Gilbert, Paul Berdahl, and Levinson, worked with Hashem Akbari at Concordia University, the CRRC, and more than 40 industrial partners to develop the protocol, Berkeley Lab reported.

The process was described in a paper in the journal Solar Energy Materials and Solar Cells last year and is explained in this video.

Representatives of 10 manufacturers, four independent testing laboratories, and several research institutions in Mexico and South Africa are expected to attend training on the practice April 21-22, in Berkeley, CA.

Funding for this research was provided by the Department of Energy, Energy Efficiency and Renewable Energy, Building Technologies Office.

Ongoing Research

Because the new ASTM standard has been endorsed by the CRRC, it is also accepted as part of California's building code, specifically California's Title 24 Building Energy Efficiency Standards, Berkeley Lab noted.

Research is underway to adapt the method for use in China, India, and Europe.


Tagged categories: Building Envelope; Coating types; Cool roof coatings; Cool Roof Rating Council (CRRC); Lawrence Berkeley National Laboratory; North America; Performance testing; Reflective roof coatings; Solar reflectance

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