To maintain the building energy efficiency, the performance of exterior windows has always been a challenge. It was with this quandary in mind that a British scientist has created a new type of window – one that's filled with water. The biggest problem with conventional exterior windows is the loss of energy, especially in the winter and summer when the building’s furnace and cooling air conditioning have to go off and on frequently, resulting in high building energy consumption.

Dr. Matyas Gutai, a lecturer in architecture at Loughborough University in UK, believes that his “water-filled glass” windows can address these limitations. Each window contains a vertical sheet of water, sealed between two sheets of glass. When sunlight passes through the glass, it will heat the water to keep the room cooler than in other places. Once the temperature goes high enough, the water heated by sunlight will be circulated out of the window to the storage tank elsewhere in the building through the pipes in the wall. The cool water will be simultaneously pumped into the WFG window to replace the water pumped out.

When the outdoor temperature drops, the stored warm water can be back to the wall to reheat the room. In addition, this warm water can also be used as tap water in the building to reduce the need for a water heater. Although some electricity will be consumed to pump the water back and forth, Dr. Gutai claimed that his device uses much less energy than HVAC systems to keep the same room temperature under the same conditions.