A window that can automatically switch from blocking heat from the sun to letting it pass through has shown promise in real-world conditions during preliminary pilot tests, said the Netherlands Organization for Applied Scientific Research (TNO).

The “smart window” is being developed by TNO and partners in Project Sunovate, which focuses on increasing the energy efficiency in buildings through heat management in windows and solar panels. The window is optimized to reduce energy consumption in moderate climates with cold winters and warm summers, said TNO.

The tests show that the window “transitions from an infrared transparent to blocking state as soon as direct sunlight hits the window and ambient temperatures are above 20°C. The transition back to the infrared transparent state usually happens overnight when the glass surface cools down. This ensures an optimized use of solar heat leading to reduced energy demand for heating and cooling simultaneously. This can lead to additional energy and cost savings of up to 8% per year.”

The active material in the window is thermochromic, which means that it changes optical properties at a specific temperature. The window is optimized for energy savings while remaining completely transparent. The switch happens autonomously and is intrinsic to the laminated glass, so the window can be installed in regular frames without special installation requirements.

The goal is to reduce heating demand in the winter and cooling demand in the summer. The window will adapt its solar heat gain to seasonal changes. TNO hopes to introduce the window into the market within the next two to three years.