New All-Season Smart-Roof Coating Enables Year-Round Energy Savings


An all-season smart roof coating sample designed to keep your home warm during the winter and cool during the summer without consuming natural gas or electricity. The device looks like scotch tape and can be attached to hard surfaces such as rooftops. Research by scientists at the Lawrence Berkeley National Laboratory of the Department of Energy points to innovative technologies that outperform commercial cool roof systems in energy savings.Credits: Junqiao Wu, Lawrence Berkeley National Laboratory

Breakthrough technology regulates home temperature without consuming natural gas or electricity.

Scientists have developed an all-season smart roof coating that keeps the house warm during the winter and cool during the summer without consuming natural gas or electricity.Research results reported in the journal Chemistry It points out innovative technologies that are superior to commercial cool roof systems in terms of energy savings.

“Our all-season roof coating automatically switches from cool to warm, depending on the outside temperature. It combines all the energy and emission-free heating and cooling into one device. “Junqiao Wu, a scientist in the Materials Sciences Department at the Berkeley Institute and a professor of materials sciences and engineering at the University of California, Berkeley, who led the study, said.

Today’s cool roofing systems, such as reflective coatings, membranes, shingles, and tiles, have light or dark “cool” surfaces that reflect sunlight to cool the house. These systems also emit some of the absorbed solar heat as thermal infrared radiation. This natural process, known as radiative cooling, emits thermal infrared rays from the surface.

The problem with many cool roof systems on the market today is that they continue to radiate heat during the winter, which pushes up heating costs, Wu explained.

“Our new material, called temperature-adaptive radiative coating or TARC, can enable energy savings by automatically turning off radiative cooling in winter to overcome the problem of supercooling.” He said.

All-season roof

Metals are usually good conductors of electricity and heat. In 2017, Wu and his team discovered that vanadium dioxide electrons behave like metals to electricity, but like insulators to heat. “This behavior is in contrast to most other metals, where electrons conduct heat and electricity proportionally,” Wu explained.

TARC roof experiment

Setting up a rooftop experiment at the East Bay Hills. Experimental data was used to simulate how TARC works year-round in cities representing 15 different climatic zones across the Americas.Credit: Provided by Junqiao Wu

Vanadium dioxide below about 67 degrees Celsius (153 degrees Fahrenheit) Transmits (and therefore does not absorb) thermal infrared rays. However, when vanadium dioxide reaches 67 degrees Celsius, it switches to a metallic state and absorbs thermal infrared light. This ability to switch from one phase to another (in this case from an insulator to a metal) is characteristic of what is known as a phase change material.

To see how vanadium dioxide works in roofing systems, Wu and his team designed a 2 cm x 2 cm TARC thin film device.

“It looks like scotch tape and can be attached to a hard surface like a rooftop,” Wu said.

In a key experiment, co-lead author Kechao Tang conducted a rooftop experiment at his home in Wu’s East Bay last summer to demonstrate the feasibility of the technology in a real-world environment.

A radio measuring device installed on Wu’s balcony continuously recorded responses to direct sunlight and changes in outdoor temperature from TARC samples, commercially available dark roof samples, and commercially available white roof samples over several days. ..

How TARC is good at saving energy

Researchers then used experimental data to simulate how TARC works year-round in cities that represent 15 different climatic zones across the Americas.

Wu asked Ronnen Levinson, co-author of the study and leader of the Berkeley Institute’s heat island group in energy technology, to help improve the roof surface temperature model. Levinson has developed a method for estimating TARC’s energy savings from a set of over 100,000 building energy simulations previously performed by the Heat Island Group. Evaluate the benefits of cool roofs and cool walls All over the United States.

PLDTARC smart roof coating

Kaichen Dong (left) and Jiachen Li coordinate the pulsed laser deposition (PLD) device used in the development of TARC smart roof coatings. Credits: Thor Swift / Berkeley Lab

Finnegan Reichertz, 12th A primary school student at Auckland’s East Bay Innovation Academy, who worked remotely as Wu’s summer intern last year, said in each of the 15 cities, how TARC and other roofing materials work at specific times and on specific days throughout the year. Helped to simulate what to do. Or the climatic zone that the researcher studied for the dissertation.

Researchers have found that TARC saves energy in 12 of the 15 climatic zones, especially in areas with high temperature changes between day and night, such as the San Francisco Bay Area, or between winter and summer, such as New York. A city that has found to be superior to existing roof coatings.

“Installing TARC can save up to 10% on the average home in the United States,” said Tang, a postdoctoral fellow at Wu Labs at the time of the study. He is currently an assistant professor at Beijing University in Beijing, China.

A standard cool roof has high solar reflectance and high heat emissivity (the ability to dissipate heat by emitting thermal infrared radiation) even in cool weather.

Researchers have measured that TARC reflects about 75% of sunlight throughout the year, but has high thermal emissivity (about 90%) at high ambient temperatures (25 degrees Celsius or 77 degrees Fahrenheit or higher). Promotes heat loss. Sky. According to Levinson, in cool weather, TARC’s heat emissivity automatically drops, helping to absorb solar heat and retain heat from room heating.

The simulation was validated by the results of infrared spectroscopic experiments using advanced tools at Berkeley Lab’s Molecular Foundry.

“In simple physics, TARC was expected to work, but I was surprised that it worked very well,” Wu said. “Initially, we thought the switch from warming to cooling wasn’t that dramatic. Our simulations, outdoor experiments, and laboratory experiments proved not – it’s really exciting. “

Researchers are planning to develop a larger TARC prototype to further test its performance as a practical roof coating. According to Wu, TARC could also be a thermal protection coating to extend the battery life of smartphones and laptops and protect satellites and cars from extreme temperatures or temperatures. It can also be used to make tents, greenhouse covers, and even temperature control cloths for hats and jackets.

Reference: “Temperature Adaptation Radiation Coating for All-Season Home Heat Control” Kechao Tang, Kaichen Dong, Jiachen Li, Madeleine P. Gordon, Finnegan G. Reichertz, Hyungjin Kim, Yoonsoo Rho, Qingjun Wang, Chang-Yu Lin, Costas P. Grigoropoulos, Ali Javey, Jeffrey J. Urban, Jie Yao, Ronnen Levinson, Junqiao Wu, December 16, 2021 Chemistry..
DOI: 10.1126 / science.abf7136

The co-lead authors of this study were Kaichen Dong and Jiachen Li.

Molecular Foundry is a nanoscience user facility at Berkeley Labs.

This work was mainly supported by the DOE Science Department and the Bacar Fellowship.

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