Professor Claes-Göran Granqvist and colleagues at Uppsala University in Sweden have recently received about 2 million euros from the European Research Council to develop new materials making buildings more energy efficient. The researchers have mostly worked on materials for windows that adjust to the environment so we can use less heating and air conditioning in our buildings. However, they are also improving sensors for air quality measurements and want to use photocatalytic material in windows. Through photocatalysis the material can remove bacteria and pollution in the air which can reduce the ventilation need. “The window is generally the weak link in the building’s energy system. Either we get in too much solar energy and then we have to remove it by air conditioning or too much heat goes out through the windows so we need to heat. We need to have windows that can control the amount of solar energy and visual light that we can bring in. We developed what is known as electrochromic or smart windows and that is a technology that I pioneered myself.
It’s something that we started about 25 years ago. The idea is to use electricity to vary how much solar energy and light that we bring in. Essentially it’s like a battery. In a battery you have an anode and a cathode and an electrolyte in between and think of these as micrometer thick layers on the glass or on plastic foil attached to the window. With the anode and the cathode as the right materials when you charge this battery, both the anode and the cathode get dark. When you discharge it they both become transparent. By charging and discharging these coatings applied to the window you can control how much light and solar energy that goes through. The control strategy is very important for the energy efficiency you get. When somebody is in the room it’s very important this person can control the transparency of the windows, but when there’s nobody in the room, there’s no reason why we should let in a lot of energy that we just remove by air conditioning. An outflow of the research group here is the company ChromoGenics which is now making prototypes up to about 0.8 times 1.8 meters, so it’s full window size. ChromoGenics technology can be a very low cost technology.” he said.
The group has also developed thermochromic windows which change their transparency when the temperature changes. They are cheaper, but not as flexible. The researchers plan to combine the electrochromic and the thermochromic technologies to improve energy efficiency.
If these windows will be used on a large scale Granqvist thinks that the energy savings can be huge.” We know that about 40 percent of the total energy in the world is used for heating, cooling, ventilation and lighting of buildings. With proper technologies it’s possible to get very substantial savings. It depends very much on the buildings, but it would be possible to reduce a building’s energy consumption by 30 to 40 percent. This is a very important ingredient in eco-buildings. The Lawrence Berkeley National Laboratory in the U.S. found that if this technology is implemented on a large scale the energy consumption in the U.S. can be reduced by several percent up to five percent,” he said.
So far no full scale tests of buildings containing these smart windows have been made. However, detailed computer models on energy use in buildings, where the influence of smart windows has been modeled, show promising results when it comes to reducing buildings’ energy consumption.