Sub-ambient non-evaporative fluid cooling with the sky


Cooling systems consume 15% of electricity generated globally and account for 10% of global greenhouse gas emissions. With demand for cooling expected to grow tenfold by 2050, improving the efficiency of cooling systems is a critical part of the twenty-first-century energy challenge. Building upon recent demonstrations of daytime radiative sky cooling, here we demonstrate fluid cooling panels that harness radiative sky cooling to cool fluids below the air temperature with zero evaporative losses, and use almost no electricity. Over three days of testing, we show that the panels cool water up to 5 C below the ambient air temperature at water flow rates of 0.2 l min−1 m−2, corresponding to an effective heat rejection flux of up to 70 W m−2. We further show through modelling that, when integrated on the condenser side of the cooling system of a two-storey office building in a hot dry climate (Las Vegas, USA), electricity consumption for cooling during the summer could be reduced by 21% (14.3 MWh).

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Figure 1: The fluid cooling panels.
Figure 2: Water cooling performance versus flow rate.
Figure 3: Extended testing over three days.
Figure 4: Modelling performance.
Figure 5: Fluid cooling performance and heat flows.
Figure 6: Modelling cooling system-level energy savings.


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This work is supported by the Advanced Research Projects Agency-Energy (ARPA-E), Department of Energy (Contract No. DE-AR0000316). We are grateful to Z. Weiner, D. Cotugno, R. Shrestha, E. D. de Maricourt and M. Metlitz for their help in fabricating the panels, and assisting with testing.

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E.A.G. and A.P.R. are co-first authors and contributed equally. All authors contributed to the conception and design of the experiments. E.A.G. and A.P.R. executed the experiments. All authors wrote the paper. A.P.R. and S.F. are co-corresponding authors.

Corresponding authors

Correspondence to Aaswath P. Raman or Shanhui Fan.

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Competing interests

The authors have founded a company, SkyCool Systems, seeking to commercialize the results reported in this paper.

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Goldstein, E., Raman, A. & Fan, S. Sub-ambient non-evaporative fluid cooling with the sky. Nat Energy 2, 17143 (2017).

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