Scalable-manufactured randomized glass-polymer hybrid metamaterial for daytime radiative cooling

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Science  10 Mar 2017:
Vol. 355, Issue 6329, pp. 1062-1066
DOI: 10.1126/science.aai7899

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  • Cooling power can be improved by overlaying metamaterials
    • Yoshiyasu Takefuji, Professor, Keio University
    • Other Contributors:
      • Takashi Sasaki, inventor/CEO, Niigata-Techno

    During the solar radiation peaks, Fig.4C shows that cooling power of the proposed method (1) dramatically decreases. It is because the volume of the hybrid metamaterial is not sufficient. Fig.S2A in the supplementary material indicates that the maximum refractive index is about 22 degree (arctangent((80cm/2)/100cm)=21.8). Because of 90/21.8=4.1, overlaying five films should make less likely to become hot. Because of 22-(22*5-90)=2, the near-perfect reflection can be achieved. In other words, cooling power can be improved by overlaying metamaterials.

    1. Yao Zhai, et al., Scalable-manufactured randomized glass-polymer hybrid metamaterial for daytime radiative cooling, Science 355, 1062–1066 (2017)

    Competing Interests: None declared.
  • RE: Use of glass polymer hybrid for cooling buildings

    I'm not a Science subscriber so haven't read the full article, just the Abstract and the summary published in The Economist. I noted that The Economist stated that a pump would be required to circulate water in a practical application of this technology to cooling buildings. In fact, since the warming part of the water circuit is at the bottom (the rooms) and the cooling part of the water circuit is at the top (the roof), a pump may not be required, as the thermosiphon effect will circulate the water naturally. This would require careful design and, probably, larger pipe diameters in parts of the circuit than a pumped system, but would offer substantial benefits in running costs, maintenance and reliability.

    Competing Interests: None declared.

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