Research ArticleMATERIALS SCIENCE

High-performance subambient radiative cooling enabled by optically selective and thermally insulating polyethylene aerogel

See allHide authors and affiliations

Science Advances  30 Oct 2019:
Vol. 5, no. 10, eaat9480
DOI: 10.1126/sciadv.aat9480
  • Fig. 1 Schematic of the proposed approach.

    (A) Traditional approach to radiative cooling. An emitter facing the sky is exposed to solar irradiation and parasitic heat gain from the ambient air due to convection. (B) Proposed approach where an OSTI cover is placed on top of the emitter. This insulation reduces parasitic heat gain as well as the solar irradiation reaching the emitter, enabling lower emitter temperatures and higher subambient cooling power.

  • Fig. 2 Polyethylene aerogel.

    (A) Image of a 10-cm-diameter and 6-mm-thick PEA sample. The inset shows an SEM image at a magnification of ×1500. Photo credit: Arny Leroy, Massachusetts Institute of Technology. (B) Hemispherical transmittance and reflectance of a 6-mm-thick PEA sample along with the normalized AM1.5 solar spectrum and the atmospheric transmittance (U.S. Standard Atmosphere 1976).

  • Fig. 3 Performance of radiative coolers with PEA.

    (A) Daytime cooling performance of a semi-ideal selective emitter (Rsolar = 1 − αsolar = 0.97 and εIR = 0.9) at different temperatures (ΔT = TemitterTamb). The maximum cooling power is shown by a solid point for each emitter temperature curve. An optimal aerogel thickness exists to achieve the maximum cooling power at a given emitter temperature. The results shown were calculated based on the U.S. Standard Atmosphere 1976. Atmospheric conditions specific to a location and time, such as humidity and cloud cover, can considerably affect the results and should be accounted for accordingly (19). (B) Results for nighttime cooling performance. Higher cooling power and lower emitter temperatures can be achieved due to the absence of solar irradiation.

  • Fig. 4 Experimental setup.

    (A) Schematic of the radiative cooler. A PEA/emitter/heater assembly is placed on top of a vacuum insulation panel (VIP) that sits inside a thermally insulating foam (FOAMULAR 150) box. The box is covered with Tefzel-coated polished aluminum sheets to minimize solar heating. The emitter/heater consists of two separate parts—the main emitter/heater and the guard emitter/heater (see inset). (B) Picture of the setup consisting of two identical devices (left: device with PEA; right: device with no PEA). A DAQ (enclosed in an aluminum box) is also visible. More pictures showing details of the experimental location and setup are included in fig. S3. Photo credit: Arny Leroy, Massachusetts Institute of Technology.

  • Fig. 5 Stagnation temperature of radiative cooler.

    (A) Stagnation temperature of two devices (12-mm-thick PEA and no PEA) over a 24-hour period in early October in San Pedro de Atacama, Chile. The device with the PEA achieves 13°C subambient cooling around solar noon (30-min average around 13:22; GHI = 1123 W/m2) compared with 1.7°C without the PEA. (B) Wind speed and solar irradiation during the stagnation temperature experiment.

  • Fig. 6 Cooling performance of radiative cooler.

    (A) Measured emitter temperature of two devices (18-mm-thick PEA and no PEA) as well as the corresponding heater power and ambient temperature during the cooling power experiment. (B) Cooling power of the two devices as a function of the emitter subcooling in San Pedro de Atacama, Chile. The shaded area represents the range of cooling power and subambient temperatures made accessible by the PEA compared with an uninsulated emitter.

Supplementary Materials

  • Supplementary material for this article is available at http://advances.sciencemag.org/cgi/content/full/5/10/eaat9480/DC1

    Influence of emitter solar reflectivity and effective heat transfer coefficient

    Theoretical model for emitter cooling power

    Optical properties of PEA

    Fig. S1. Influence of system nonidealities.

    Fig. S2. Solar absorption at the emitter.

    Fig. S3. Experimental setup.

    Fig. S4. Selective emitter emissivity.

    Fig. S5. Influence of PEA thickness.

    Fig. S6. Cooling performance of radiative cooler in Cambridge, Massachusetts.

    Fig. S7. Experimental comparison of selective and black emitters with PEA.

    Fig. S8. Iterative process for cooling power modeling.

    Fig. S9. Optical properties of PEA.

    Reference (40)

  • Supplementary Materials

    This PDF file includes:

    • Influence of emitter solar reflectivity and effective heat transfer coefficient
    • Theoretical model for emitter cooling power
    • Optical properties of PEA
    • Fig. S1. Influence of system nonidealities.
    • Fig. S2. Solar absorption at the emitter.
    • Fig. S3. Experimental setup.
    • Fig. S4. Selective emitter emissivity.
    • Fig. S5. Influence of PEA thickness.
    • Fig. S6. Cooling performance of radiative cooler in Cambridge, Massachusetts.
    • Fig. S7. Experimental comparison of selective and black emitters with PEA.
    • Fig. S8. Iterative process for cooling power modeling.
    • Fig. S9. Optical properties of PEA.
    • Reference (40)

    Download PDF

    Files in this Data Supplement:

Stay Connected to Science Advances

Navigate This Article