Insulating window frames and vertical enclosures in buildings, is a central issue in the design of new architecture and reducing energy requirements to heat or cool enclosed spaces. British startup Water-Filled Glass has developed on this wave the prototype of a new window composed of water-filled glass panes that harness sunlight to power an energy-saving system.

Founded in 2020 by Loughborough University architecture lecturer Matyas Gutai and his colleagues Daniel Schinagl and Abolfazl Ganji Kheybari, Water-Filled Glass aims to use patented technology to make even buildings with a strong presence of glass in the facade sustainable.

The windows envisioned contain a thin layer of water between the glass panes, which absorbs heat from sunlight or other radiation, such as heat coming out of a room. The heated water is then pumped through low-pressure sealed pipes to cooler areas of the building, either through a floor system or a thermal storage tank. By absorbing heat energy, the new device also reduces the need for air conditioning in hot climates.

WFG estimates that, depending on a building’s climate and window-to-wall ratio, its technology can reduce energy bills by about 25 percent compared to standard windows. The startup's first commercial projects, an industrial building in Hungary and an apartment complex in the United States, are under construction.

Currently, two prototype buildings using the technology have been completed, named Water House 1.0, a small cabin in Hungary, and Water House 2.0, a pavilion at Feng Chia University in Taiwan.