Glass that regulates both heating and cooling

SINGAPORE: Scientists claim to have developed a coating for windows that can switch between heating and cooling in response to changing temperatures.

The international research team led by scientists from Nanyang Technological University (NTU), Singapore, says that the material, when coated on a glass window panel, can effectively self-adapt to heat or cool rooms across different climate zones in the world, helping to cut energy usage.

The self-adaptive glass is developed using layers of vanadium dioxide nanoparticles composite, the transparent thermoplastic PMMA, and low-emissivity coating to form a novel structure which could modulate heating and cooling simultaneously. 

The glass has no electrical components and works by exploiting the spectrums of light responsible for heating and cooling. During summer, the glass suppresses solar heating (near infrared light), while boosting radiative cooling (long-wave infrared). In the winter, it does the opposite to warm up the room. 

Lab tests using an infrared camera is said to have shown that the glass allowed a controlled amount of heat to emit in various conditions (room temperature – above 70°C), proving its ability to react dynamically to changing weather conditions. 

The team argues that, while scientists elsewhere have developed sustainable innovations such as low emissivity coatings to prevent heat transfer and electrochromic glass that regulate solar transmission from entering the room by becoming tinted, none of the solutions have been able to modulate both heating and cooling at the same time, until now. 

“Most energy-saving windows today tackle the part of solar heat gain caused by visible and near infrared sunlight. However, researchers often overlook the radiative cooling in the long wavelength infrared. While innovations focusing on radiative cooling have been used on walls and roofs, this function becomes undesirable during winter,” said Dr Long Yi of the NTU School of Materials Science and Engineering (MSE) and principal investigator of the study.

“Our team has demonstrated for the first time a glass that can respond favourably to both wavelengths, meaning that it can continuously self-tune to react to a changing temperature across all seasons.” 

The scientists also tested the energy-saving performance of their invention using simulations of climate data fro seven climate zones covering all populated parts of the globe. Overall energy saving performance for both warm and cool seasons was found to be up to 9.5% better than commercially available low emissivity glass in a simulated medium sized office building. 

The heating and cooling performance of the glass can be customised to suit the needs of the market and region for which it is intended by simply adjusting the structure and composition of special nano-composite coating layered onto the glass panel.

A Singapore patent has been filed for the innovation. As the next steps, the research team is aiming to achieve even higher energy-saving performance by working on the design of their nano-composite coating. 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) programme, Minster of Education Research Fund Tier 1, and the Sino-Singapore International Joint Research Institute.