Researchers Create Climate-Friendly Window Coating
A group of researchers has recently published a study on a new transparent window coating that could be utilized to lower the temperature inside buildings.
The study, “High-Performance Transparent Radiative Cooler Designed by Quantum Computing,” has since been published in a journal issued by the American Chemical Society, ACS Energy Letters.
Window Coating Research
According to previous research, it has been estimated that cooling in buildings accounts for 15% of global energy consumption. To avoid having to expend energy watts for cooling, scientists have pondered window coatings capable of blocking the sun’s ultraviolet and near-infrared light.
In taking cooling options a step further, scientists have also observed how window coatings could radiate heat from a window’s surface at a wavelength that passes through the atmosphere into outer space.
However, these same scientists further shared that combining these coating criteria simultaneously is difficult because of the need to allow transmission of visible light or an interference with a person’s view from inside said structures.
To mitigate this issue, Eungkyu Lee, Tengfei Luo and colleagues set out to design a “transparent radiative cooler” (TRC) using advanced computing technology and artificial intelligence.
In the study’s abstract, researchers described that the TRC was developed on the basis of layered photonic structures using a quantum computing-assisted active learning scheme, which combines active data production, machine learning, and quantum annealing in an iterative loop.
By alternating thin layers of common materials like silicon dioxide, silicon nitride, aluminum oxide or titanium dioxide on a glass base topped with a film of polydimethylsiloxane, researchers said they were able to optimize a coating design that, when fabricated, beat the performance of conventionally designed TRCs.
In addition, the team wrote that the resulting coating design performed better than one of best commercial heat-reduction glasses on the market.
The formulation was developed through an iterative approach where various types, orders and combinations of layers were tested with the assistance of machine learning and quantum computing, which stored data using subatomic particles.
The team shared that the computing method of testing the various coating formulations enabled them to carry out optimization faster and better than conventional computers because it could efficiently test all possible combinations in a fraction of a second.
The best-performing TRC developed from the study has the potential to reduce cooling energy consumption by 31% compared with conventional windows, according to the study authors. The coating also has the potential to be utilized in other applications, such as car and truck windows.
The team further concluded that its quantum computing-enabled optimization technique could be used to design other types of composite materials.
The authors acknowledge support from the National Research Foundation of Korea and the Notre Dame Center for Research Computing for its findings.
Other Window Coating Studies
Earlier this year, in January, a team of researchers from the Penn State Department of Architectural Engineering found that coating windows, particularly single-pane windows, with a translucent metallic film capable of absorbing some solar heat were a more economical option than replacing the windows with double-panes.
While double-pane windows are still ultimately more energy efficient than single-pane, or single-panes with a translucent metallic film coating, Penn State researchers believe that with the help of nanotechnology, the coating could help elevate the thermal performance to that of double-pane windows in winter.
By examining the energy-saving properties of a coating comprising nanoscale components, the team defined which components would reduce heat loss and better absorb heat. According to Julian Wang, associate professor of architectural engineering, near-infrared light—a portion of solar light that humans feel as heat but cannot see—can activate unique light-to-heat effects on certain metallic nanoparticle. This action thus enhances how heat flows inward through a window.
For the research, the team first developed a model to estimate how much heat from sunlight would be reflected, absorbed into or transferred through a window coated with metallic nanoparticles that incorporated a photothermal compound. The compound was chosen for its ability to absorb the sun’s near-infrared light, while still allowing for ample visible light transmission.
By testing a single-pane window, the researchers were able to confirm that when coated with the nanoparticles under simulated sunlight in the laboratory, more heat was absorbed through the window and reflected less near-infrared light or heat than most other coating types. The researchers also noted that there was a significant rise in temperature on the side of the window coated with the nanoparticles, thus indicating that the coating could pull heat from sunlight inside to compensate for internal heat lost.
After making this discovery, the team then implemented their data into a larger-scale simulation to analyze the energy savings for an entire building with coated windows across different climates. According to their findings, near-infrared absorption resulted in a roughly 12% to 20% reduction in heat loss compared to the other coatings and an overall building energy-saving potential of up to around 20% when compared to a building with no coatings on single-pane windows.
However, while better heat transmissivity is a vital feature for the winter months, in the summer it could become a drawback. To account for seasonal changes, Wang and her team implemented awnings into their building-scale simulation, which blocked more direct sunlight. While this mitigated the new heat issue, the team is continuing its research into other designs, including dynamic window systems, to fulfill seasonal heating and cooling needs.
Back in 2020, researchers from RMIT University (Melbourne, Australia) developed a coating that was reported to have the potential to bring down the cost of energy-saving windows and become a standard in new builds and retrofits.
The spray-on coating was described as “ultra-thin, cost-effective and rival[s] the performance of current industry standards for transparent electrodes.”
The current process for such a coating relies heavily on raw materials and is made through a time-consuming process, according to RMIT. This new method, however, is fast, scalable and “based on cheaper materials that are readily available.”
“Smart windows and low-E glass can help regulate temperatures inside a building, delivering major environmental benefits and financial savings, but they remain expensive and challenging to manufacture,” said Della Gaspera, a senior lecturer and Australian Research Council DECRA Fellow at RMIT, at the time.
“We’re keen to collaborate with industry to further develop this innovative type of coating. The ultimate aim is to make smart windows much more widely accessible, cutting energy costs and reducing the carbon footprint of new and retrofitted buildings.”
Researchers say the method could both simplify the fabrication of smart windows as well as low-emissivity glass.
First author Jaewon Kim, a PhD researcher in Applied Chemistry at RMIT, said the next steps in the research are developing precursors that will decompose at lower temperatures, allowing the coatings to be deposited on plastics and used in flexible electronics, as well as producing larger prototypes by scaling up the deposition.