One building block for a sustainable future is the EU Energy Performance of Buildings Directive that targets a full zero-emission building stock all over Europe before 2050.
Glazing in buildings accounts for up to 60% of energy transfer through modern building envelopes. In winter, heat is emitted to the outside, while in summer, solar radiation heats the building interior which increases the demand for air-conditioning and cooling. Large windows and glass façades – a common design element in modern and large buildings – worsen this effect.
Today, mechanical window blinds and jalousies are used to control solar radiation dependent on the time of day, temperature and sunlight intensity. However, they strongly affect (or impair) comfort and light conditions inside the building. In glass façade buildings, such window blinds – if installed at all – disturb the architectural design and require heavy mounts and profiles.
Smart and switchable glass solutions have the potential to replace mechanical window blinds in the future. However, they are currently optimized towards aesthetic requirements, and not energy saving, are very expensive and hard to come by. The EU-funded initiative Switch2Save aims to overcome these limitations by combining and maturing EC and TC systems to create lightweight Energy Smart Insulating Glass Units (IGUs) suitable for large windows and glass-façades. EC switching relies on materials that change their light transmittance by applying a low electrical voltage; TC cells are based on materials that change their infrared reflection properties with increasing temperature.
The Switch2Save consortium includes leading universities, research institutes and industries from six EU countries. Within the next four years, the partners will collectively develop a combination of EC and TC cells – with optimized maximum energy saving potential – based on a switchable total energy transmittance (g-value). They will scale the manufacturing technologies for increased availability and cost-effectiveness, assess the performance of the innovative IGUs, and demonstrate the heating and cooling energy saving potential and the lighting comfort in two operational buildings in Greece and Sweden.
“Experts estimated that energy demand for air-conditioning and cooling of buildings will more than double by 2050," said Project Coordinator Dr. John Fahlteich, Fraunhofer FEP. "Furthermore, large glass façade buildings (e. g. shopping centers, airports, office buildings) require as much as 35% more energy for heating and up to five times more energy for cooling than modern buildings with small windows. The Switch2Save solution will be able to reduce the total annual heating and cooling energy demand of such large glass buildings by up to 44%. This will be achieved through smart switching protocols based on local, real-time weather and temperature data and the illumination conditions in the building.”
The Switch2Save EC and TC modules are based on nanoscaled thin film stacks that are applied to plastic webs or ultra-thin glass films by using a large-area vacuum and atmospheric pressure deposition techniques. The modules have a specific weight of less than one kg per square meter – much less than even a single glass pane in a window. They are easily integrated into IGUs by a lamination step to allow window and glass façade manufacturing with well-established processes – a key requirement for acceptance of the novel technology by construction companies. The integration of wireless switching and standard interfaces directly into the building automation systems will satisfy the needs of building owners and provide maximum energy saving when in operation.
Switch2Save will demonstrate the potential in two representative buildings – Greece’s second-largest hospital in Athens and an operational office building in Uppsala, Sweden. The Switch2Save consortium will replace 50 windows and 200 m² glass façade area with the smart glass solution and will perform a full “before-after” comparison of the energy demand for a one-year cycle in both buildings. The findings will accelerate the widespread implementation of energy smart glass and significantly contribute to the goal of CO2-neutral building stock in the EU before 2050.