Liquid windows can turn opaque in the heat and save energy

You might not think of windows as objects in need of technological innovation — but they play an important part in saving energy through heat insulation. And now, a team of scientists has developed a “liquid window” panel which can change opacity to help conserve energy and keep people indoors more comfortable.

Researchers from Nanyang Technological University, Singapore (NTU) created their new window by taking two glass panels and placing a hydrogel-based liquid between them. This liquid changes its configuration based on its temperature, which means it can turn opaque and act as insulation to keep heat out on hot days, then revert to being clear on colder days.

The smart window turns opaque when exposed to heat, thus blocking sunlight, and, when cool, returns to its original 'clear' state.
The smart window turns opaque when exposed to heat, thus blocking sunlight, and, when cool, returns to its original ‘clear’ state. NTU Singapore

Wang Shancheng, Ph.D. student at NTU and first author of the study, explained: “Sound-blocking double glazed windows are made with two pieces of glass which are separated by an air gap. Our window is designed similarly, but in place of air, we fill the gap with the hydrogel-based liquid, which increases the sound insulation between the glass panels, thereby offering additional benefit not commonly found in current energy-saving windows.”

When testing their window panel, the researchers found a room fitted with the smart window used 11% less energy to keep the same temperature when compared to a normal glass window.

Members of the NTU research team include Dr Long Yi (left), Senior Lecturer at the School of Materials Science & Engineering, and PhD student Wang Shancheng (right).
Members of the NTU research team include Dr Long Yi (left), Senior Lecturer at the School of Materials Science & Engineering, and Ph.D. student Wang Shancheng (right). NTU Singapore

The windows have high heat capacity, which means they collect heat during the day and disperse it at night. The researchers think that these windows would be most useful in office buildings, where people use the building mostly during the day.

And the windows are relatively easy to manufacture to any required shape, according to Dr Long Yi, lead author and Senior Lecturer at the School of Materials Science & Engineering: “Our innovation combines the unique properties of both types of materials — hydrogel and water. By using a hydrogel-based liquid we simplify the fabrication process to pouring the mixture between two glass panels. This gives the window a unique advantage of high uniformity, which means the window can be created in any shape and size.”

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