Article | Published:

Sub-ambient non-evaporative fluid cooling with the sky

Nature Energy volume 2, Article number: 17143 (2017) | Download Citation


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).

Access optionsAccess options

Rent or Buy article

Get time limited or full article access on ReadCube.


All prices are NET prices.


  1. 1.

     & Modeling global residential sector energy demand for heating and air conditioning in the context of climate change. Energy Policy 37, 507–521 (2009).

  2. 2.

     & More intense, more frequent, and longer lasting heat waves in the 21st century. Science 305, 994–997 (2004).

  3. 3.

    Benefits of Water Cooled vs Air Cooled Equipment in Air Conditioning Applications Tech. Rep. (Cooling Technology Institute, 2011);

  4. 4.

    2016 ASHRAE Handbook: Heating, Ventilating, and Air-Conditioning: Systems and Equipment SI Edition (ASHRAE, 2016).

  5. 5.

    Total cost of ownership for air cooled and water-cooled chiller systems. ASHRAE J. 51, 42–48 (2009).

  6. 6.

    , ,  & Theoretical evaluation of night sky cooling in the Czech Republic. Energy Procedia 48, 645–653 (2014).

  7. 7.

    , , ,  & Potential energy savings by radiative cooling system for a building in tropical climate. Renew. Sustain. Energy Rev. 32, 642–650 (2014).

  8. 8.

     & Potentials of passive cooling for passive design of residential buildings in China. Energy Procedia 57, 1726–1732 (2014).

  9. 9.

     & Numerical simulation of combined solar passive heating and radiative cooling for a building. Build. Simul. 8, 239–253 (2015).

  10. 10.

    Thermal modelling of a night sky radiation cooling system. J. Energy Southern Afr. 16, 20–31 (2005).

  11. 11.

    ,  & A study of a polymer-based radiative cooling system. Sol. Energy 73, 403–417 (2002).

  12. 12.

    ,  & A night cold storage system enhanced by radiative cooling—a modified Australian cooling system. Appl. Therm. Eng. 19, 1013–1026 (1999).

  13. 13.

    , ,  & Daytime space cooling with phase change material ceiling panels discharged using rooftop photovoltaic/thermal panels and night-time ventilation. Sci. Technol. Built Environ. 22, 902–910 (2016).

  14. 14.

     & Radiative cooling during the day: simulations and experiments on pigmented polyethylene cover foils. Sol. Energy Mater. Sol. Cells 37, 93–118 (1995).

  15. 15.

    ,  & Ultrabroadband photonic structures to achieve high-performance daytime radiative cooling. Nano Lett. 13, 1457–1461 (2013).

  16. 16.

    , , ,  & Passive radiative cooling below ambient air temperature under direct sunlight. Nature 515, 540–544 (2014).

  17. 17.

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

  18. 18.

    , , ,  & Daytime radiative cooling using near-black infrared emitters. ACS Photon. 4, 626–630 (2017).

  19. 19.

     & A subambient open roof surface under the mid-summer sun. Adv. Sci. 2, 1500119 (2015).

  20. 20.

     & Users Manual for TMY3 Data Sets (National Renewable Energy Laboratory Golden, 2008).

  21. 21.

    , ,  & Energy Savings Potential of Radiative Cooling Technologies Tech. Rep. PNNL24904 (Pacific Northwest National Laboratory, 2015);

  22. 22.

    et al. US Department of Energy Commercial Reference Building Models of the National Building Stock Tech. Rep. NREL/TP-5500-46861 (National Renewable Energy Laboratory, 2011).

Download references


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.

Author information


  1. Edward L. Ginzton Laboratory, 348 Via Pueblo, Stanford University, Stanford, California 94305, USA

    • Eli A. Goldstein
    • , Aaswath P. Raman
    •  & Shanhui Fan


  1. Search for Eli A. Goldstein in:

  2. Search for Aaswath P. Raman in:

  3. Search for Shanhui Fan in:


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.

Competing interests

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

Corresponding authors

Correspondence to Aaswath P. Raman or Shanhui Fan.

About this article

Publication history





Further reading