Netherlands-based Researchers Develop Budding Smart Window

The Netherlands-based research center, TNO, has developed a smart window using thermochromic smart glass. They partnered with Sunnovate on the Interreg project to achieve this latest innovation. The window is designed to switch between absorbing heat or letting it pass through.  

What is Smart Window Technology? 

The smart window has a thermochromic active material. It can automatically change its optical properties at a certain temperature, around 20⁰C. As the temperature increases, the glass changes its infrared transmittance when the sun hits it. When this occurs, its transparency changes and the window becomes less transparent to solar heat.

This effect happens in the infrared part of the solar spectrum, making the window transparent to the human eyes. The transition back to the infrared transparent state usually happens overnight and in cooler temperatures when the glass surface cools down. The switch happens automatically and is built into the laminated glass. This makes it possible to install the smart window without special installation requirements.

In simple terms, the window blocks the heat from the sun when outdoor temperatures are high and absorbs heat in lower outdoor temperatures. 

Speaking to Journalists, researcher Paskal Buskens explained,  ‘VO2 changes its crystal structure at a certain temperature. With this change in the crystal structure, also the electrical and optical properties change, which means that the material absorbs more infrared light in the high-temperature crystal phase and the absorbed solar energy is not transmitted into the building.’

Vanadium dioxide (VO2) is a functional material in the pigmented polymer film coating. It changes its crystal structure and optical properties at high temperatures, which makes it suitable for the technology. A standard low-emission coated glass was used in the thermochromic coating.

Buskens said, ‘Thermochromics can switch their infrared modulating properties from transmissive to blocking depending on the glazing temperature. The integration of VO2  into a film or coating for application in smart thermochromic windows can lead to a significant reduction in energy consumption for heating and cooling of buildings in an intermediate climate.’

In January, the Netherlands Organisation for Applied Scientific Research(TNO) and partners began pilot testing on the smart window to examine the properties and performance in a real environment. They implemented Two 1m2-sized smart window demonstrators at the SolarBEAT test facilities in Eindhoven, making it the first time testing the adaptive thermochromic effect in real-world conditions. The results have been positive, and the demonstration will continue till the end of the year to obtain information across all four seasons. 

The optimal switching temperature is around 20⁰C but can be adjusted via metal ion doping for optimum energy savings. The researchers claim the smart window can ensure energy savings of up to 8% compared to the state of the art HR++ windows in free-standing buildings, duplexes, and terrace houses.

While the price is not confirmed, Busken said that the final costs depend on the glass companies selling the product. ‘But due to the low costs for the material itself and the large potential saving an attractive business case is ensured, whilst keeping the return on investment for end-users at an acceptable level of around seven years.’

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