A window that simultaneously blocks the sun and turns thermal heat into useful energy to reduce energy consumption in buildings!
Liquid window is an innovation from NTU researchers.
NTU researchers developed this ‘smart window’ by placing hydrogel-based liquid within glass panels.
They found that it can reduce up to 45% of energy consumption in buildings in simulations, compared to traditional glass windows.
And guess what?
It is 30% more energy-efficient than commercially available low-emissivity glass. It is also cheaper to make.
The research is supported by the National Research Foundation under its Campus for Research Excellence and Technological Enterprise (CREATE) programme, and the Sino-Singapore International Joint Research Institute.
Windows are a key component in a building design. However, they are also the least energy-efficient due to the ease with which heat can transfer through glass.
Windows thus have a significant impact on heating and cooling costs of a building.
A 2009 UN report said that buildings account for 40% of global energy usage and windows are responsible for half of that usage.
Difference between conventional windows with coatings and liquid window
Conventional windows with expensive coatings reduce infrared light passing into or out of a building. However, they do not regulate visible light, which is a major component of sunlight that causes buildings to heat up.
To overcome these limitations, the NTU researchers turned to water.
Water has the capacity to absorb a high amount of heat before it begins to get hot.
How the liquid window works
The liquid window uses a mixture of micro-hydrogel, water and a stabiliser. Thanks to the hydrogel, the liquid mixture turns opaque when exposed to heat, thus blocking sunlight. When cooled, it returns to its original ‘clear’ state.
The high heat capacity of water allows a large amount of thermal energy to be stored instead of getting transferred into the building. The heat is gradually cooled and released at night.
The window is fabricated by a simple process of pouring the mixture between two glass panels.
Dr Long Yi, lead author and Senior Lecturer at the School of Materials Science & Engineering said the fabrication process gives the window a unique advantage of high uniformity. It means the window can be created in any shape and size.
The research is published in the journal Joule.
Tests and simulations in hot and cold environments
Researchers have tested the smart window in outdoor hot (Singapore, Guangzhou) and cold (Beijing) environments.
Tests in Singapore revealed that the smart liquid window had a temperature of 50°C during the hottest time of the day. This compared to 84°C for a normal glass window. The Beijing tests showed that the room using the smart liquid window consumed 11% less energy to maintain the same temperature compared to the room with a normal glass window.
Simulations using an actual building model and weather data of four cities (Shanghai, Las Vegas, Riyadh, and Singapore) showed that the smart liquid window had the best energy-saving performance in all four cities when compared to regular glass windows and low emissivity windows.
The research team is now looking to collaborate with industry partners to commercialise the smart window.