Preliminary study of radiative cooling in cooling season of the humid coastal area

Passive daytime radiative cooling provides cooling without energy input. This method is eco-friendly, which is beneficial, considering the increasing problems of global warming and urban heat islands. A poly(vinylidene fluoride) (PVDF) and polyurethane acrylate (PUA) matte white coating was prepared via photo-initiated free-radical polymerization. The porous polymeric coating without a metal-reflective layer exhibited an average emissivity of 0.9333 in the atmospheric window and an average solar reflectance of 0.9336 in the direct AM1.5 solar spectrum (888 W m −2 in the 0.3−2.5 μm region). The radiative cooling power of the fabricated radiative cooler with a thickness of 518 μm was 94.2 W m −2 . Furthermore, the radiative cooler demonstrated radiative cooling performance during both daytime and nighttime in Seoul, Korea, and Chiang Mai, Thailand. The PVDF/PUA matte white coating without a silver reflector can prevent solar absorption caused by the oxidation of silver and reduce the light pollution caused by the metallic film because of the antiglare surface of the matte coating.

Section: Resultsmentioning

confidence: 99%

Cross-Linked Porous Polymeric Coating without a Metal-Reflective Layer for Sub-Ambient Radiative Cooling

Son

Liu

Chae

et al. 2020

“…Owing to the existence of the gas environment, the atmosphere has its specific emissivity spectrum. − Figure a exhibits the effects of the thermal radiation absorptivity/emissivity and the sunlight absorptivity on cooling power, where the heating power is defined as a negative value. Higher thermal radiation absorptivity/emissivity and lower sunlight absorptivity are beneficial for higher cooling power.…”

Section: Resultsmentioning

confidence: 99%

Multifunctional Membrane for Thermal Management Applications

Song

Lei

Han

et al. 2021

Space cooling and heating consume a large proportion of global energy, so passive thermal management materials (i.e., without energy input), especially dual-mode materials including cooling and heating bifunctions, are becoming more and more attractive in many areas. Herein, a function-switchable Janus membrane between cooling and heating consisting of a multilayer structure of polyvinylidene fluoride nanofiber/zinc oxide nanosheet/carbon nanotube/Ag nanowire/polydimethylsiloxane was fabricated for comprehensive thermal management applications. In the cooling mode, the high thermal radiation emissivity (89.2%) and sunlight reflectivity (90.6%) of the Janus membrane resulted in huge temperature drops of 8.2–12.6, 9.0–14.0, and 10.9 °C for a substrate, a closed space, and a semiclosed space, respectively. When switching to the heating mode, temperature rises of 3.8–4.6, 4.0–4.8, and 12.5 °C for the substrate, closed space, and semiclosed space, respectively, were achieved owing to the high thermal radiation reflectivity (89.5%) and sunlight absorptivity (74.1%) of the membrane. Besides, the Janus membrane has outstanding comprehensive properties of the membrane, including infrared camouflaging/disguising, electromagnetic shielding (53.1 dB), solvent tolerance, waterproof properties, and high flexibility, which endow the membrane with promising application prospects.

“…The maximum net radiative cooling power occurs in Qinghai, with the value being 43.46 W/m 2 , which is attributed to the low relative humidity and thin atmosphere in this region . Considering that the average cooling load of energy-efficient residential buildings in most regions of China is less than 10 W/m 2 in the cooling season, passive radiative cooling technology with the NCF can cover the cooling demand in most regions of China.…”

Section: Resultsmentioning

confidence: 99%

Mechanically Robust and Spectrally Selective Convection Shield for Daytime Subambient Radiative Cooling

Zhang

Zhou

Tang

et al. 2021

Self Cite

As a passive cooling strategy, radiative cooling is becoming an appealing approach to dissipate heat from terrestrial emitters to the outer space. However, the currently achieved cooling performance is still underperforming due to considerable solar radiation absorbed by the emitter and nonradiative heat transferred from the surroundings. Here, we proposed a mechanically robust and spectrally selective convection shield composed of nanoporous composite fabric (NCF) to achieve daytime subambient radiative cooling. By selectively reflecting ∼95% solar radiation, transmitting ∼84% thermal radiation, and suppressing the nonradiative heat transferred from warmer surroundings, the NCF-based radiative cooler demonstrated an average daytime temperature reduction of ∼4.9 °C below the ambient temperature, resulting in an average net radiative cooling power of ∼48 W/m 2 over a 24 h measurement. In addition, we also modeled the potential cooling capacity of the NCF-based radiative cooler and demonstrated that it can cover the cooling demands of energy-efficient residential buildings in most regions of China. Excellent spectral selectivity, mechanical strength, and weatherability of the NCF cover enable a much broader selection for the emitters, which is promising in the real-world deployment of direct daytime subambient radiative cooling.