Liquid windows hold the key to the zero-energy buildings of the future

The groundbreaking technology is being tested in Sofia, Bulgaria as part of the InDeWaG project

An ordinary broken window may cut you. But how about a broken window that can make you wet, too?

Yes, such windows exist, although not on a mass production scale. Inside their panes a constant flow of water and glycol is maintained. And it is worth the effort, as they may hold the key to the "Nearly Zero Energy Buildings" of the future.   

Originating in Madrid, this technology has been developed by European architects and researchers under the InDeWaG project. InDeWaG is acronym of "Industrial Development of Water Flow Glazing Systems". It is an Innovation action project funded under Horizon 2020, a Public Private Partnership on "Buildings Design for New Highly Energy Performing Buildings".

The groundbraking technology is currently being efficiency-tested in a demonstration pavilion, built on the premises of the Bulgarian Academy of Sciences in Sofia, Bulgaria. Temperature and humidity are constantly monitored inside the building to see if energy can be produced and used long term or in very different climatic conditions.

Inside each window, there is a constant flow of 70 litres of distilled water and 30 litres of ethylene glycol, which serves as antifreeze. Each transparent panel acts as an individual solar collector. Using solar cells, the windows absorb solar radiation and turn it into thermal energy to heat the building's interior.

"The advantage of using liquids instead of air inside the glass is that water is denser, so it absorbs infrared light in a broader range", explains Associate Prof. Dr. Miglena Nikolaeva-Dimitrova, a physicist at the Bulgarian Academy of Sciences.

Ensuring energy efficiency, not just insulation

InDeWaG researchers want the water flow smart glazing system to guarantee energy efficiency, not to serve simply as a transparent insulator. So the system must be able to retain the maximum of solar heat during the winter and avoid overheating in the summer, acting exactly like animal skin that allows the whole body to thermo-regulate itself.

As the European Union seeks to dramatically increase the energy efficiency of new building designs, scientists think the new technology could be instrumental in the so-called "Nearly Zero Energy Buildings" of the future.

InDeWaG researchers say the Water Flow Glazing façades  technology is now ready to be installed in full-scale buildings. But while waiting for investors to come, measurements at the demonstration pavilion in Sofia will go on for the next 10 years.