Smart windows that take into account the sun鈥檚 height in the sky could adjust how much light gets in to your home over the course of the seasons, helping regulate the temperature and lower energy requirements for heating and cooling throughout the year.
Windows that block heat from the sun in the summer while allowing it through in the winter already exist, but Yi Long at Nanyang Technological University in China and her colleagues developed a new type of smart window that can also adjust for the height of the sun in the sky.
Many of the smart windows in development are made from vanadium dioxide, which has a changing molecular structure so it acts like a metal at temperatures above 68掳 C and as a ceramic at lower temperatures. The metal phase blocks near-infrared light, which carries the most heat with it, whereas the ceramic phase allows that heat through.
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It鈥檚 not just the temperature that changes between seasons, though, as the sun is higher in the sky in summer. To deal with this, the researchers used their material to 3D print a horizontal grating with ridges 0.2 millimetres wide that could placed over regular glass windows.
In winter, the sunlight can pass right between the ridges since it鈥檚 more likely to come from near the horizon, but in summer it hits them and is absorbed because it comes from overhead. On average, the grating let about 43 per cent of visible light through.
In simulations of how much energy these gratings could save in cities around the world including Athens in Greece, Guangzhou in China and Miami in the US, the researchers found that if all windows were fitted with gratings, it could make the windows about 23 per cent more energy efficient.
Advanced Optical Materials
