An international research team led by scientists from Nanyang Technological University, Singapore (NTU Singapore) has developed a material that, when coated on a glass window panel, can effectively adapt to heat or cool rooms in different climate zones around the world, helping to reduce energy consumption.
Developed by NTU researchers and reported in top scientific journal Science, the first glass of its kind automatically reacts to temperature changes by switching between heating and cooling.
Self-adaptive glass is developed using composite layers of vanadium dioxide nanoparticles, poly(methyl methacrylate) (PMMA) and a low-e coating to form a unique structure that could simultaneously modulate the heating and cooling.
The newly developed glass, which has no electrical components, works by harnessing light spectra responsible for heating and cooling.
During the summer, glass suppresses solar heating (near infrared light), while increasing radiative cooling (long wave infrared) – a natural phenomenon where heat radiates through surfaces to the cold universe – to cool the room. In winter, it does the opposite to warm the room.
In laboratory tests using an infrared camera to visualize the results, the glass allowed a controlled amount of heat to emit under various conditions (ambient temperature – above 70°C), proving its ability to react dynamically to weather conditions changing.
New glass regulates both heating and cooling
Windows are one of the key elements of a building’s design, but they are also the least energy efficient and most complicated part. In the United States alone, the energy consumption associated with windows (heating and cooling) in buildings represents approximately 4% of their total primary energy consumption each year, according to an estimate based on data available from the United States Department of energy.
While scientists elsewhere have developed sustainable innovations to mitigate this energy demand – such as the use of low-emissivity coatings to prevent heat transfer and electrochromic glass that regulate solar transmission from entering the room by tinting – none of the solutions have been able to modulate both heating and cooling at the same time, so far.
The principal investigator of the study, Dr. Long Yi from NTU School of Materials Science and Engineering (MSE) said: “Most energy-saving windows today address the portion of solar heat gain caused by visible and near-infrared sunlight. However, researchers often overlook radiative cooling in the long-wavelength infrared. While innovations focused on radiative cooling have been used on walls and roofs, this feature becomes undesirable in winter. Our team demonstrated for the first time a lens that can respond favorably to both wavelengths, meaning it can continuously adapt to react to a change in temperature in all seasons.
With these features, the NTU research team believe their innovation offers a practical way to save energy in buildings, as it does not rely on any moving components, electrical mechanisms or blocking views to operate.
To improve window performance, simultaneous modulation of solar transmittance and radiative cooling is crucial, the co-authors said. Professor Gang Tan from the University of Wyoming, USA, and Professor Ronggui Yang of Huazhong University of Science and Technology, Wuhan, China, who led the building’s energy-saving simulation.
“This innovation fills the missing gap between traditional smart windows and radiative cooling by opening up a new research direction to minimize energy consumption,” said Professor Gang Tan.
The study is an example of groundbreaking research that supports the NTU 2025 strategic plan, which seeks to address humanity’s grand sustainability challenges and accelerate the translation of research discoveries into innovations that lessen human impact on the environment.
A useful innovation for a wide range of climate types
As a proof of concept, the scientists tested the energy-saving performance of their invention using simulations of climate data covering all populated regions of the globe (seven climate zones).
The team found that the glass they developed exhibited energy savings in both hot and cold seasons, with a energy saving performance up to 9.5%, or ~330,000 kWh per year (estimated energy required to power 60 households in Singapore for one year) less than commercially available low-e glass in a simulated mid-rise office building.
First author of the study Wang Shancheng, who is a researcher and former doctoral student of Dr. Long Yi, said, “The results prove the viability of applying our glass in all types of climates, as it is able to help reduce energy consumption regardless of regardless of seasonal hot and cold temperature fluctuations. This distinguishes our invention from current energy saving windows which tend to find limited use in regions with less seasonal variation.
What’s more, the heating and cooling performance of their glass can be customized to meet the needs of the market and region for which it is intended.
“We can do this by simply adjusting the structure and composition of a special nanocomposite coating applied to the glass panel, allowing our innovation to potentially be used in a wide range of heat control applications, not limited to windows”, Dr. Long Yi noted.
Provide an independent perspective Professor Liangbing Hu, Herbert Rabin Distinguished Professor, Director of the Center for Materials Innovation at the University of Maryland, USA, said, “Long and his colleagues originally developed smart windows capable of regulating near-infrared sunlight and long-wave infrared heat. The use of this smart window could be very important for energy saving and decarbonization of buildings. »
A Singapore patent has been filed for the innovation. In the next steps, the research team aims to achieve even higher energy saving performance by working on their nanocomposite coating design.
The international research team also includes scientists from Nanjing Tech University, China. The study is supported by the Singapore-HUJ Alliance for Research and Enterprise (SHARE), under the Campus for Research Excellence and Technological Enterprise (CREATE) program, the Minster of Education Research Fund Tier 1 and Sino -Singapore International Joint Research Institute.
Notes to Editor:
Article titled “Scalable Thermochromic Smart Windows with Passive Control of Radiative Cooling”, Posted in Science, December 17, 2021.
 E.S. Lee, X. Pang, S. Hoffmann, H. Goudey, A. Thanachareonkit, “An Empirical Study of a Large-Scale Polymer Thermochromic Window and Its Implications for Materials Science Development Goals,” (Lawrence Berkeley National Laboratory, 2013).
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Scalable thermochromic smart windows with passive radiative cooling control
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