Can window glass be smart?

As sunlight or temperature changes, smart energy-saving glass can adjust its color and light transmittance to achieve a certain degree of temperature control, thereby achieving energy-saving effects.

In other words, with this kind of glass, you can use less air conditioning in both summer and winter.

Recently, Researcher Cao Xun from the Shanghai Institute of Ceramics, in collaboration with Professor Yang Ronggui from Huazhong University of Science and Technology, has developed a new electrochromic structure that can be used for thermal management of windows, maximizing the use of visible and near-infrared solar radiation and radiative cooling from mid-infrared light.

This new material optimizes the full-band (visible light, near infrared, mid-infrared and far-infrared) light-heat exchange and can realize intelligent switching of multiple optical states within a wide wavelength range, achieving better energy-saving effects.

Outdoor experiments conducted by the research team in Shanghai and Sanya showed that under typical sunny weather, compared with traditional commercial Low-e windows, this window based on the new electrochromic structure can achieve continuous cooling throughout the day, with a maximum temperature reduction of up to 14°C.

Heat exchange simulation and experimental studies verify the universality and effectiveness of the model.

Simulations show that this new electrochromic device has higher energy savings than commercial low-e glass in most climate regions of the world. This discovery provides great opportunities for innovative smart energy-saving window designs, helping to achieve global carbon neutrality and sustainable development.

On May 14, the above research results were published online in the international academic journal Nature Sustainability under the title "Tri-band electrochromic smart window for energy savings in buildings".

In typical sunny weather, compared with traditional commercial Low-e windows, this window based on the new electrochromic structure can achieve continuous cooling throughout the day, with a maximum temperature reduction of up to 14°C.

The new electrochromic device proposed by the research team can achieve three-state transition based on the phase change of VO2 and WO3 thin films.

In this structure, by applying different external voltages, Li+ can diffuse into the monoclinic VO2 and WO3 layers respectively and complete two phase transitions .

The three optical states of the electrochromic structure can be maintained for more than 4 hours .

Among them, the tetragonal phase LixVO2 has the characteristics of a metallic phase, and its refractive index increases rapidly, resulting in a drastic change in the transmittance of near-infrared light; while LiyWO3 exhibits absorption of visible light and infrared parts, resulting in a rapid decrease in transmittance.

These two phase transitions can achieve three different optical states, thereby independently adjusting the visible light and near-infrared transmittance.

In addition, during the year-round thermal management of buildings, the outdoor environment and window surface temperatures are higher than those of indoor areas in summer. In order to reduce cooling energy consumption, it is necessary to reduce heat entry and reduce the amount of heat radiated from the outside through the windows. In winter, in order to reduce heat loss, it is necessary to reduce the amount of heat radiated from the indoor area to the windows, and it is also necessary to set a low emissivity on the inside of the windows.

The research team further minimized the radiative heat exchange between indoor and outdoor environments by optimizing the emissivity of the outer and inner electrochromic electrodes of the electrochromic structure.

Shao Zewei, a doctoral graduate from the Shanghai Institute of Ceramics, Huang Aibin, an associate researcher, and Cao Cuicui, a doctoral student, are the co-first authors of the above-mentioned newly published paper. The research work was funded and supported by the National Key R&D Program, the National Natural Science Foundation, the ANSO International Cooperation Project, and the Shanghai Natural Science Foundation Original Exploration Project.

Paper link: https://doi.org/10.1038/s41893-024-01349-z