Sub-ambient radiative cooling with wind cover

Liu, Junwei; Ji, Zhiming; Zhang, Debao; Jiao, Shifei; Xing, Jincheng; Tang, Huajie; Zhang, Ying; Li, Shuai; Zhou, Zhihua; Zuo, Jian

doi:10.1016/j.rser.2020.109935

Cited by 51 publications

(17 citation statements)

References 45 publications

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“…NP mixture RC with a molecular ratio of 2:2:1 (Al 2 O 3 /SiO 2 /Si 3 N 4 ) and incorporation of 5 wt % DPHA based on the total NP weight was selected based on the results shown in Figures S7 and S8 and listed in Tables S1 and S2, respectively, by considering the maximization of the calculated P net . To calculate P net in Tables S1 and S2, we used the standard condition of AT in Figure S1a, the solar power density in Figure S2a, T amb = 300 K, and h c = 6 W m –2 K –1 , as reported previously. − In Figure S7 and Table S1, the composition of the lower Si 3 N 4 content, which induces an increase in α avg , was selected. In Figure S8 and Table S2, we included DPHA in the NP mixture to increase binding adhesion between NPs and emissivity in the atmospheric transparency window according to the high extinction coefficient of DPHA presented in Figure S9.…”

Section: Resultsmentioning

confidence: 99%

Spectrally Selective Nanoparticle Mixture Coating for Passive Daytime Radiative Cooling

Chae

Lim

et al. 2021

ACS Appl. Mater. Interfaces

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Passive daytime radiative cooling, which is a process that removes excess heat to cold space as an infinite heat sink, is an emerging technology for applications that require thermal control. Among the different structures of radiative coolers, multilayerand photonic-structured radiative coolers that are composed of inorganic layers still need to be simple to fabricate. Herein, we describe the fabrication of a nanoparticle-mixture-based radiative cooler that exhibits highly selective infrared emission and low solar absorption. Al 2 O 3 , SiO 2 , and Si 3 N 4 nanoparticles exhibit intrinsic absorption in parts of the atmospheric transparency window; facile one-step spin coating of a mixture of these nanoparticles generates a surface with selective infrared emission, which can provide a more powerful cooling effect compared to broadband emitters. The nanoparticle-based radiative cooler exhibits an extremely low solar absorption of 4% and a highly selective emissivity of 88.7% within the atmospheric transparency window owing to the synergy of the optical properties of the material. The nanoparticle mixture radiative cooler produces subambient cooling of 2.8 °C for surface cooling and 1.0 °C for space cooling, whereas the Ag film exhibits an above-ambient cooling of 1.1 °C for surface cooling and 3.4 °C for space cooling under direct sunlight.

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Section: Resultsmentioning

confidence: 99%

Spectrally Selective Nanoparticle Mixture Coating for Passive Daytime Radiative Cooling

Chae

Lim

et al. 2021

ACS Appl. Mater. Interfaces

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“…The discrepancy between ∆ T and the equilibrium temperature differences between the cooler and the reference is attributed not only to the fundamental difference between the static and dynamic cases, but also to the non‐ideal measurement conditions such as the measured solar irradiance that is smaller than the AM1.5d, high relative humidity, and high dew point (see Section S3, Supporting Information) that degrade radiative cooling. [ 46,47 ]…”

Section: Resultsmentioning

confidence: 99%

Visibly Transparent Radiative Cooler under Direct Sunlight

Kim

Lee

Son

et al. 2021

Advanced Optical Materials

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Transparency is an important characteristic in practical applications of radiative cooling, but the transmitted sunlight trapped in an inner space is generally the main cause of the increasing temperature. A transparent radiative cooler that can lower a temperature during the daytime by transmitting visible light, reflecting near‐infrared (NIR) light, and radiating thermal energy through the atmospheric window is proposed. In contrast to transparent selective emitters that transmit most of the incoming solar irradiance under direct sunlight and opaque radiative coolers that reflect all solar energy, the proposed cooler achieves transparency and the cooling effect simultaneously by selectively blocking solar absorption in the NIR regime. Outdoor rooftop measurements confirm that the cooler can reduce i) the inner temperature of an absorbing system and ii) its own temperature when combined with commercially available paints. During daytime, the cooler provides a temperature reduction of a maximum 14.4 °C and 10.1 °C for the inner and own temperature, respectively, and of an average 5.2 °C and 4.3 °C, respectively, in comparison to the transparent selective emitter. The proposed cooler can reduce the temperature during the daytime while maintaining transparency, confirming its possibilities in practical applications such as passive diurnal cooling of vehicles or buildings and compatibility with current paint technologies for aesthetic use.

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“…A Petri dish covered by a polyethylene foil was used as an enclosure (Figure a) to reduce the convection losses. On the basis of previous studies with similar experimental setups, we assumed the value of thermal coefficient for the parasitic nonradiative contribution ( h c ) to be 10 W m –2 K –1 . ,, Strategically placed Pt100 sensors were used to measure the inner ambient temperature of the enclosure and the sample temperature (see the Experimental Section for details). During the experiment the effect of wind remained negligible as can be verified from the wind velocity measurement plot in Figure d.…”

Section: Resultsmentioning

confidence: 99%

Efficient Thin Polymer Coating as a Selective Thermal Emitter for Passive Daytime Radiative Cooling

Banik¹,

Agrawal²,

Meddeb³

et al. 2021

ACS Appl. Mater. Interfaces

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Radiative cooling to subambient temperatures can be efficiently achieved through spectrally selective emission, which until now has only been realized by using complex nanoengineered structures. Here, a simple dip-coated planar polymer emitter derived from polysilazane, which exhibits strong selective emissivity in the atmospheric transparency window of 8–13 μm, is demonstrated. The 5 μm thin silicon oxycarbonitride coating has an emissivity of 0.86 in this spectral range because of alignment of the frequencies of bond vibrations arising from the polymer. Furthermore, atmospheric heat absorption is suppressed due to its low emissivity outside the atmospheric transparency window. The reported structure with the highly transparent polymer and underlying silver mirror reflects 97% of the incoming solar irradiation. A temperature reduction of 6.8 °C below ambient temperature was achieved by the structure under direct sunlight, yielding a cooling power of 93.7 W m–2. The structural simplicity, durability, easy applicability, and high selectivity make polysilazane a unique emitter for efficient prospective passive daytime radiative cooling structures.

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Sub-ambient radiative cooling with wind cover

Cited by 51 publications

References 45 publications

Spectrally Selective Nanoparticle Mixture Coating for Passive Daytime Radiative Cooling

Spectrally Selective Nanoparticle Mixture Coating for Passive Daytime Radiative Cooling

Visibly Transparent Radiative Cooler under Direct Sunlight

Efficient Thin Polymer Coating as a Selective Thermal Emitter for Passive Daytime Radiative Cooling

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