Fraunhofer researchers have developed a smart coating for glazing that darkens in sunlight. This uses electrochromic and thermochromic materials that react to electricity and heat. In buildings with large glass facades, it prevents rooms from overheating due to solar radiation, reducing the need for energy-intensive air conditioning.
The construction industry is one of the largest emitters of greenhouse gases. According to the German Environment Agency, buildings account for about 30% of the country's CO2 emissions and 35% of its energy consumption. Buildings with large glass facades and roofs, such as the office buildings that dominate modern cities, are particularly problematic. They get hot in the sun, especially in summer. However, the use of blinds and blinds to provide shade is generally undesirable because they detract from the aesthetics of the glass and interfere with views outside. Instead, the interior is cooled with air conditioning, which requires a lot of electricity and increases the building's carbon footprint.
The Fraunhofer Institute for Silicate Research ISC in Wurzburg and the Fraunhofer Institute for Organic Electron, Electron Beam and Plasma Technology FEP in Dresden have developed a complex solution to this question. In the Switch2Save project, researchers have been working on clear coatings for windows and glass facades using electrochromic and thermochromic materials. These add a variable, transparent dark hue to the outside of the window, keeping the room cool. The Fraunhofer Institute has collaborated with university and industrial partners in six EU countries on this EU-funded research project.
The electrochromic coating is applied to a transparent conductive film, which can then be "turned on". Applying a voltage triggers the transfer of ions and electrons that darken the coating and tint the window. Thermochromic coatings, on the other hand, work by reflecting thermal radiation from the sun when a certain ambient temperature is reached, explains Dr. Marco Schott, group manager of Fraunhofer ISC Electrochromic Systems.
With electrochromic elements, sensors can be used to measure factors such as brightness and temperature and send the results to a control system. This sends a current or voltage pulse to the conductive film, triggering the darkening of the window. Whenever the temperature or brightness gets too high, the glass surface will gradually darken. This prevents the room from overheating and reduces the need for air conditioning, which is especially useful in sunny climates and buildings with large glass facades. It also acts as anti-glare protection on sunny days. The windows will stay bright on cloudy days and at night.
The Fraunhofer researchers also considered whether the technology is suitable for everyday use. The windows don't dim suddenly, but gradually dim over a few minutes, with very low energy consumption, Schott explained. In the preferred case, the electrochromic film requires electricity only during the switching process, and very low voltages are sufficient to initiate the coloring process. Thermochromic materials do not require electricity at all, but passively respond to the heat generated by the sun. They can be used to complement switchable systems or as an alternative where switchable solutions are not required.
Switch2Save promises significant energy savings in areas with high outdoor temperatures (i.e. southern regions) by reducing the use of air conditioning systems or eliminating the need for them altogether. Dr. John Fahlteich, project coordinator and research group leader at Fraunhofer FEP's Switch2Save, explained that in warmer regions of Europe, the cooling and heating energy requirements of modern buildings can be reduced by up to 70 percent. In cooler northern regions, the savings aren't huge, but the system can also be used here as anti-glare protection from direct sunlight.
In principle, the combination of electrochromic and thermochromic layers in composite windows offers the greatest possible flexibility. By using it, architects and developers can provide individual solutions for various areas and buildings. We are installing the technology in the pediatric clinic of the second largest hospital in Athens, Greece, and an office building in Uppsala, Sweden. In both buildings, energy consumption will be monitored and compared for a full year before and after new windows are installed. By doing so, we can demonstrate the actual performance of the Switch2Save technology and can continue to test and improve the technology for different climate zones, Fahlteich said.
The researchers also tackled manufacturing challenges. Electrochromic coatings are applied to polymer-based film substrates. Thermochromic coatings, on the other hand, use thin glass substrates. Wet chemical and vacuum coating processes are used for cost-effective roll-to-roll manufacturing systems. The switchable assembly is then vacuum laminated to 4mm thick window glass, which is then integrated into the insulating glass unit. The coating process is also economically feasible on an industrial scale. Electrochromic and thermochromic switchable elements are only a few hundred microns thick and less than 500 grams per square meter. As a result, they add hardly any weight to the windows, which means they can be retrofitted in existing buildings without changing the building structure.
The project consortium is currently working to further improve the technology. For example, teams of experts are investigating how to combine electrochromic and thermochromic elements in composite windows to better exploit the technology's potential. Further research goals include adapting the coating to curved glass forms and adding more colour to the existing blue and grey options.
World warming and the goals of the European Green Deal will significantly increase demand for energy-efficient building technologies in the coming years – all buildings in the EU are expected to be carbon neutral by 2050. The EU's Switch2Save project for electrochromic and thermochromic windows can make an important contribution to this.
- Transferred from China Glass Network
