? NTU scientists develop energy-saving “liquid window”

Scientists from Nanyang Technological University, Singapore (NTU Singapore) have developed a liquid window panel that can simultaneously block the sun to regulate solar transmission, trapping thermal heat that can be released during the day and night, helping to reduce the energy consumption in buildings.

NTU researchers developed their “smart window” by placing a hydrogel-based liquid inside glass panels and found that it can reduce energy consumption in buildings in simulations by up to 45%, compared to traditional windows in the building. glass. It is also about 30% more energy efficient than commercially available low-emissivity (energy-efficient) glass, while being cheaper to produce.

The “smart window” is the first example reported in a scientific journal of energy-saving smart windows made with liquids and supports the vision of NTU Smart Campus which aims to develop technologically advanced solutions for a sustainable future.

Windows are a key component in the design of a building, but they are also the least energy efficient part. Due to the ease with which heat can transfer through glass, windows have a significant impact on a building’s heating and cooling costs. According to a 2009 UN report, buildings account for 40% of global energy consumption and windows are responsible for half of that energy consumption.

Traditional low-e energy-saving windows are made with expensive coatings that reduce the infrared light entering or leaving a building, thus helping to reduce the demand for heating and cooling. However, they do not regulate visible light, which is an important component of sunlight that causes buildings to heat up.

To develop a window to overcome these limitations, NTU researchers turned to water, which absorbs a large amount of heat before it starts to heat up, a phenomenon known as high specific heat capacity.

They created a blend of micro-hydrogel, water and a stabilizer and discovered through experiments and simulations that it can effectively reduce energy consumption in a variety of climates, thanks to its ability to respond to a change in temperature. Thanks to the hydrogel, the liquid mixture becomes opaque when exposed to heat, thus blocking the sunlight and, once cold, it returns to its original “clear” state.

“Liquid window” best suited for office buildings

At the same time, the high heat capacity of the water allows a large amount of heat energy to be stored instead of being transferred through the glass and into the building during the hot hours of the day. The heat will then be gradually cooled and released during the night.

Dr. Long Yi, lead author of the research study published in Joule journal and senior lecturer at the School of Materials Science & Engineering said, “Our innovation combines the unique properties of both types of materials: hydrogel and water. Using a hydrogel to liquid based we simplify the manufacturing process to pour the mixture between two glass panels. This gives the window a unique advantage of high uniformity, which means that the window can be created in any shape and size. “

As a result of these characteristics, the NTU research team believes their innovation is more suitable for use in office buildings, where operating hours are mostly during the day.

To demonstrate the concept, scientists conducted outdoor tests in hot (Singapore, Guangzhou) and cold (Beijing) environments.

The Singapore test revealed that the smart liquid window had a lower temperature (50 ° C) during the hottest hours of the day (noon) than a normal glass window (84 ° C). Tests in Beijing showed that the room using the smart liquid window consumed 11% less energy to maintain the same temperature than the room with a regular glass window.

Smart window moves electrical load peak, blocks noise

The scientists also measured when the day’s highest stored thermal energy occurred.

This “temperature spike” in the normal glass window was at 12:00 and in the smart liquid window it was moved to 14:00. If this change in temperature spike results in a change in the time a building needs to draw electricity to cool or heat the building, it should result in lower energy rates for users.

Simulations using an actual building model and weather data from four cities (Shanghai, Las Vegas, Riyadh and Singapore) showed that the smart liquid window has the best energy saving performance in all four cities compared to normal windows in low-emissivity glass and windows.

Soundproofing tests also suggested that the smart liquid window reduces noise by 15% more effectively than double-glazed windows.

Study first author Wang Shancheng, who is project leader at the School of Materials Science & Engineering, said: “Soundproof double-glazed windows are made of two pieces of glass separated by an air gap. Our window is designed similarly, but instead of air, we fill the void with hydrogel-based liquid, which increases the sound insulation between the glass panels, thus offering additional benefits not commonly found in current energy-saving windows “.

The other first author, Dr. Zhou Yang, was a PhD student in NTU and is currently an associate professor at the China University of Petroleum-Beijing (CUPB).

Providing an independent point of view, Professor Ronggui Yang, Huazhong University of Science and Technology, China, winner of the 2020 Nukiyama Memorial Award in Thermal Science and Engineering and expert in thermal and energy systems, said: “This is the first example of a hydrogel-based liquid smart window, and takes us away from conventional glass design. Disruptive innovation leads to solar regulation and heat storage, which together make for outstanding energy saving performance. “

The research team is now looking to work with industry partners to commercialize the smart window.

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The research is supported by the National Research Foundation, the Prime Minister’s Office, Singapore, as part of its Campus for Research Excellence and Technological Enterprise (CREATE) program and the Sino-Singapore International Joint Research Institute.