For smart windows

Thermochromic Films

A buildings energy demand is greatly impacted by its windows. They usually represent the most vulnerable part of the building skin for radiator heat loss and show the highest interaction with sunlight and solar heat. Therefore, depending on the number of windows in a building’s façade, they are usually responsible for 30 – 40% of total energy loss. Energy-efficient windows commonly either focus on reducing radiator heat loss via increased insulation, or on reducing cooling demand via blocking of solar heat. Since these two functionalities are conflicting with each other, current energy-efficient glazing systems are only optimized for either hot or cold climates.

To solve this issue, we develop an energy-efficient window which is optimized for intermediate climes, where heating in winter is equally important as cooling in summer.

Thermochromic film

Thermochromic smart window

The thermochromic smart window is perfectly optimized for intermediate climates. It autonomously changes its solar heat gain depending on the outside temperature.

This enables the efficient use of solar heat in winter, to heat up a building, while shutting out solar heat in summer to keep the room temperature low.

The functional materials

The functional material in the interlayer is color neutral, while the switch in solar heat gain properties is autonomous, invisible to the human eye and optimized for highest total energy savings.

The material we developed is a nanometer sized thermochromic pigment based on VO2. The material autonomously changes its crystal structure at a temperature of 68°C. The change in crystal structure coincides with a change in electrical and optical properties. By adding a suitable dopant, we can lower this switching temperature to around 25°C, which is desired for the application.

After production, the thermochromic pigments are surface functionalized and integrated into PVB via masterbatch. After compounding, the pigmented polymer material is extruded via a pilot sized single screw extruded to provide pigmented polymer films. For perfect optical properties and low haze values, a good particle distribution in the polymer film without agglomeration is necessary.

The pigmented polymer films are used as interlayers for lamination of safety glass. This functional laminated glass is then integrated in an insulating glass unit (IGU) in combination with a low-e coated glass, to yield the final smart window. Within SUNOVATE we will demonstrate the smart window on pilot scale (1×1 m2).

Analysis and performance monitoring

For analysis and performance monitoring a new type of sensor will be integrated into the laminated glass. The sensor is made of thin glass fibers and is based on a Fiber Bragg grating. It enables fast, accurate and precise temperature and mechanical stress measurements. This improves the quality control and performance monitoring of our new development.

22% energy savings

This combination leads to a reduction in a buildings heating and cooling costs, simultaneously. Simulations show that it can lead to approximately 22% energy savings.

Technology demonstration and performance monitoring

Our pilot scale smart window demonstrators will be installed in test buildings at SolarBEAT in Eindhoven (NL) and at EnergyVille in Genk (VL). The demonstrators will be monitored and compared to standard laminated glass for one year while recording the most important parameters, such as performance, temperature and environmental stability. The aim of the project is to bring the technology to TRL 6.

Please contact us