Mirror, Mirror, On The Roof | Chemical & Engineering News
Volume 92 Issue 48 | p. 27 | Concentrates
Issue Date: December 1, 2014

Mirror, Mirror, On The Roof

Ultrathin, multilayered material keeps buildings cool by reflecting sunlight and by channeling interior warmth into outer space
Department: Science & Technology
News Channels: Environmental SCENE
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Stanford electrical engineers (from left) Linxiao Zhu, Fan, and Raman gaze upon their prototype high-tech mirror that sends beams of heat back into space.
Credit: Norbert von der Groeben/Stanford
Stanford engineers (from left) Linxiao Zhu, Shanhui Fan, Aaswath Raman gaze upon their prototype high-tech mirror that sends beams of heat directly into space.
 
Stanford electrical engineers (from left) Linxiao Zhu, Fan, and Raman gaze upon their prototype high-tech mirror that sends beams of heat back into space.
Credit: Norbert von der Groeben/Stanford

An ultrathin reflective material that can redirect sunlight and heat to cool buildings and other objects to a temperature that’s 5 °C below their ambient temperature has been developed by Shanhui Fan, Aaswath P. Raman, and colleagues at Stanford University (Nature 2014, DOI: 10.1038/nature13883). A device made using the material, which includes seven alternating layers of silicon dioxide and hafnium oxide atop a layer of silver, achieves passive cooling without electricity in two ways. First, the device reflects 97% of incoming sunlight, preventing solar heating. Second, it channels surrounding heat into outer space. The new material’s layers of varying thickness radiate infrared rays at a frequency that lets them pass through the atmosphere—it essentially soaks up the surrounding heat and sends it away. The prototype device is the size of a personal pizza, but Fan says the technology could be scaled up to create large panels necessary for cooling buildings.

 
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