scholarly journals A Pragmatic Bilayer Selective Emitter for Efficient Radiative Cooling under Direct Sunlight

Materials ◽  
2019 ◽  
Vol 12 (8) ◽  
pp. 1208 ◽  
Author(s):  
Liu ◽  
Bai ◽  
Fang ◽  
Ni ◽  
Lu ◽  
...  
Keyword(s):  
Photonic Crystal ◽  
Ambient Temperature ◽  
High Efficiency ◽  
Volume Fraction ◽  
Ambient Air ◽  
Radiative Cooling ◽  
Direct Sunlight ◽  
Cooling Performance ◽  
Selective Emitter ◽  
Functional Nanoparticles

Radiative cooling can make the selective emitter cool below ambient temperature without any external energy. Recent advances in photonic crystal and metamaterial technology made a high-efficiency selective emitter achievable by precisely controlling the emitter’s Infrared emission spectrum. However, the high cost of the photonic crystals and meta-materials limit their application. Herein, an efficient bilayer selective emitter is prepared based on the molecular vibrations of functional nanoparticles. By optimizing the volume fraction of the functional nanoparticles, the bilayer selective emitter can theoretically cool 36.7 °C and 25.5 °C below the ambient temperature in the nighttime and daytime, respectively. Such an efficient cooling performance is comparable with the published photonic crystal and metamaterial selective emitters. The rooftop measurements show that the bilayer selective emitter is effective in the ambient air even under direct sunlight. The relatively low cost and excellent cooling performance enable the bilayer selective emitter to have great potential for a practical purpose.

Potential for Passive Radiative Cooling by PDMS Selective Emitters

2017 ◽  
Author(s):  
Braden Czapla ◽  
Arvind Srinivasan ◽  
Qingtian Yin ◽  
Arvind Narayanaswamy
Keyword(s):  
Thin Films ◽  
Ambient Temperature ◽  
Passive Cooling ◽  
Radiative Cooling ◽  
Polydimethyl Siloxane ◽  
Selective Emitter ◽  
The Cost ◽  
Aluminum Substrates ◽  
Selective Emitters ◽  
Fabrication Costs

The scalability and implementation of selective emitters in passive radiative cooling applications are limited by the high fabrication costs due to the complexity of these structures. The usage of commercially available polymers in selective emitters holds potential in lowering the cost of radiative cooling solutions. In this work, we demonstrate that thin films of polydimethyl-siloxane (PDMS) on aluminum substrates act as radiative coolers by selectively emitting in the wavelength range of 8 μm to 13 μm, where the Earth’s atmosphere is highly transparent. We also show that our device can achieve passive cooling up to 12 °C below the ambient temperature under the night sky. This suggests that PDMS, especially due to its ease of deposition, may be a viable selective emitter in passive radiative cooling applications.

scholarly journals Highly suppressed solar absorption in a daytime radiative cooler designed by genetic algorithm

Nanophotonics ◽  
2021 ◽  
Vol 0 (0) ◽  
Author(s):  
Sunae So ◽  
Younghwan Yang ◽  
Soomin Son ◽  
Dasol Lee ◽  
Dongwoo Chae ◽  
...  
Keyword(s):  
Genetic Algorithm ◽  
High Performance ◽  
Degrees Of Freedom ◽  
Wavelength Region ◽  
Solar Irradiation ◽  
Maximum Temperature ◽  
Radiative Cooling ◽  
Direct Sunlight ◽  
Solar Absorption ◽  
Selective Emitter

Abstract Here, we report a selective multilayer emitter for eco-friendly daytime passive radiative cooling. The types of materials and thickness of up to 10 layers of the multilayer structure are optimized by a genetic algorithm. The passive radiative cooler is designed to mainly target low solar absorption, which allows sub-ambient cooling under direct sunlight. We used a custom objective function in the solar region to achieve high-performance daytime radiative cooling to minimize solar absorption. The designed structure minimizes solar absorption with an average absorptivity of 5.0% in the solar region (0.3–2.5 μm) while strongly emitting thermal radiation with an average emissivity of 86.0% in the atmospheric transparency window (8–13 μm). The designed and fabricated structure achieves daytime net cooling flux of 84.8 W m−2 and 70.6 W m−2, respectively, under the direct AM 1.5 solar irradiation (SI) (total heat flux of 892 W m−2 in the 0.3–2.5 μm wavelength region). Finally, we experimentally demonstrate a passive radiative cooling of the fabricated selective emitter through a 72-hour day-night cycle, showing an average and maximum temperature reduction of 3.1 °C and 6.0 °C, respectively. Our approach provides additional degrees of freedom by designing both materials and thickness and thereby is expected to allow high-performance daytime radiative cooling.

RADIATIVE COOLING OF WATER TO SUB-AMBIENT TEMPERATURE UNDER DIRECT SUNLIGHT

2018 ◽  
Author(s):  
Dongliang Zhao ◽  
Yao Zhai ◽  
Gang Tan ◽  
Xiaobo Yin ◽  
Ronggui Yang
Keyword(s):  
Ambient Temperature ◽  
Radiative Cooling ◽  
Direct Sunlight

scholarly journals Mirroring Solar Radiation Emitting Heat Toward the Universe: Design, Production, and Preliminary Testing of a Metamaterial Based Daytime Passive Radiative Cooler

Energies ◽  
2020 ◽  
Vol 13 (16) ◽  
pp. 4192
Author(s):  
Anna Castaldo ◽  
Giuseppe Vitiello ◽  
Emilia Gambale ◽  
Michela Lanchi ◽  
Manuela Ferrara ◽  
...  
Keyword(s):  
Solar Radiation ◽  
Ambient Temperature ◽  
Noble Gas ◽  
Low Cost ◽  
Ambient Air ◽  
Radiative Cooling ◽  
Proof Of Concept ◽  
Selective Coating ◽  
Positive Effects ◽  
The Universe

A radiative cooling device, based on a metamaterial able to mirror solar radiation and emit heat toward the universe by the transparency window of the atmosphere (8–13 µm), reaching and maintaining temperatures below ambient air, without any electricity input (passive), could have a significant impact on energy consumption of buildings and positive effects on the global warming prevention. A similar device is expected to properly work if exposed to the nocturnal sky, but during the daytime, its efficacy could be affected by its own heating under direct sunlight. In scientific literature, there are only few evidences of lab scale devices, acting as passive radiative cooling at daytime, and remaining few degrees below ambient air. This work describes the proof of concept of a daytime passive radiative cooler, entirely developed in ENEA labs, capable to reach well 12 °C under ambient temperature. In particular, the prototypal device is an acrylic box case, filled with noble gas, whose top face is a metamaterial deposited on a metal substrate covered with a transparent polymeric film. The metamaterial here tested, obtained by means of a semi-empirical approach, is a spectrally selective coating based on low cost materials, deposited as thin films by sputtering on the metallic substrate, that emits selectively in the 8–13 µm region, reflecting elsewhere UV_VIS_NIR_IR electromagnetic radiation. The prototype during the daytime sky could reach temperatures well beyond ambient temperature. However, the proof of concept experiment performed in a bright clear June day has evidenced some limitations. A critical analysis of the obtained experimental results has done, in order to individuate design revisions for the device and to identify future metamaterial improvements.

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

2019 ◽  
Vol 5 (10) ◽  
pp. eaat9480 ◽  
Author(s):  
A. Leroy ◽  
B. Bhatia ◽  
C. C. Kelsall ◽  
A. Castillejo-Cuberos ◽  
M. Di Capua H. ◽  
...  
Keyword(s):  
Ambient Temperature ◽  
Air Conditioning ◽  
High Performance ◽  
Recent Progress ◽  
Passive Cooling ◽  
Cooling Power ◽  
Radiative Cooling ◽  
Direct Sunlight ◽  
Solar Absorption ◽  
Solar Noon

Recent progress in passive radiative cooling technologies has substantially improved cooling performance under direct sunlight. Yet, experimental demonstrations of daytime radiative cooling still severely underperform in comparison with the theoretical potential due to considerable solar absorption and poor thermal insulation at the emitter. In this work, we developed polyethylene aerogel (PEA)—a solar-reflecting (92.2% solar weighted reflectance at 6 mm thick), infrared-transparent (79.9% transmittance between 8 and 13 μm at 6 mm thick), and low-thermal-conductivity (kPEA = 28 mW/mK) material that can be integrated with existing emitters to address these challenges. Using an experimental setup that includes the custom-fabricated PEA, we demonstrate a daytime ambient temperature cooling power of 96 W/m2 and passive cooling up to 13°C below ambient temperature around solar noon. This work could greatly improve the performance of existing passive radiative coolers for air conditioning and portable refrigeration applications.

scholarly journals Vapor condensation with daytime radiative cooling

2021 ◽  
Vol 118 (14) ◽  
pp. e2019292118
Author(s):  
Ming Zhou ◽  
Haomin Song ◽  
Xingyu Xu ◽  
Alireza Shahsafi ◽  
Yurui Qu ◽  
...  
Keyword(s):  
Air Temperature ◽  
Liquid Water ◽  
Infrared Radiation ◽  
Ambient Air ◽  
Vapor Condensation ◽  
Passive Cooling ◽  
Radiative Cooling ◽  
Direct Sunlight ◽  
Produce Water ◽  
Extraction And Purification

A radiative vapor condenser sheds heat in the form of infrared radiation and cools itself to below the ambient air temperature to produce liquid water from vapor. This effect has been known for centuries, and is exploited by some insects to survive in dry deserts. Humans have also been using radiative condensation for dew collection. However, all existing radiative vapor condensers must operate during the nighttime. Here, we develop daytime radiative condensers that continue to operate 24 h a day. These daytime radiative condensers can produce water from vapor under direct sunlight, without active consumption of energy. Combined with traditional passive cooling via convection and conduction, radiative cooling can substantially increase the performance of passive vapor condensation, which can be used for passive water extraction and purification technologies.

scholarly journals A Multilayer Emitter Close to Ideal Solar Reflectance for Efficient Daytime Radiative Cooling

Polymers ◽  
2019 ◽  
Vol 11 (7) ◽  
pp. 1203 ◽  
Author(s):  
Yeqing Zhu ◽  
Dong Wang ◽  
Cheng Fang ◽  
Ping He ◽  
Yong-Hong Ye
Keyword(s):  
Air Temperature ◽  
Physical Vapor Deposition ◽  
Ambient Air ◽  
Film Structure ◽  
Radiative Cooling ◽  
Atmospheric Conditions ◽  
Cooling Performance ◽  
Average Temperature ◽  
Ambient Air Temperature ◽  
Solar Reflectance

A passive radiative cooling method has a significant influence on thermal management applications because it can cool without any energy input. This work both experimentally and theoretically demonstrates a multilayer thin film structure with high solar reflectance, which can be applied to passive daytime radiative cooling. The combination of physical vapor deposition and spin-coating prepared the samples, which were also characterized experimentally by spectrometers. On-site measured results show that the emitter can effectively achieve daytime radiative cooling, and the cooling performance can be further improved with the increase of the ambient air temperature. When the emitter is exposed to direct solar radiation (AM1.5) of about 880 W/m2 on a rooftop under dry air conditions, it can achieve an average temperature reduction of about 12.6 °C from the ambient air temperature with nonradiative heat transfer (11 a.m.–1 p.m.). Theoretical simulations reveal that the emitter can still have a certain cooling performance in the presence of significant nonradiative heat exchange and nonideal atmospheric conditions. The influence of ambient air temperature on the cooling performance of the emitter is also theoretically analyzed.

Passive radiative cooling below ambient air temperature under direct sunlight

Nature ◽  
2014 ◽  
Vol 515 (7528) ◽  
pp. 540-544 ◽  
Author(s):  
Aaswath P. Raman ◽  
Marc Abou Anoma ◽  
Linxiao Zhu ◽  
Eden Rephaeli ◽  
Shanhui Fan
Keyword(s):  
Air Temperature ◽  
Ambient Air ◽  
Radiative Cooling ◽  
Direct Sunlight ◽  
Ambient Air Temperature

scholarly journals Changes in ambient temperature increase hospital outpatient visits for allergic rhinitis in Xinxiang, China

2021 ◽  
Vol 21 (1) ◽  
Author(s):  
Jianhui Gao ◽  
Mengxue Lu ◽  
Yinzhen Sun ◽  
Jingyao Wang ◽  
Zhen An ◽  
...  
Keyword(s):  
Allergic Rhinitis ◽  
Ambient Temperature ◽  
Positive Association ◽  
Ambient Air ◽  
Ambient Air Pollution ◽  
Hospital Outpatient ◽  
Distributed Lag ◽  
Outpatient Visits ◽  
Daily Data ◽  
The Relationship

Abstract Background The effect of ambient temperature on allergic rhinitis (AR) remains unclear. Accordingly, this study aimed to explore the relationship between ambient temperature and the risk of AR outpatients in Xinxiang, China. Method Daily data of outpatients for AR, meteorological conditions, and ambient air pollution in Xinxiang, China were collected from 2015 to 2018. The lag-exposure-response relationship between daily mean temperature and the number of hospital outpatient visits for AR was analyzed by distributed lag non-linear model (DLNM). Humidity, long-time trends, day of the week, public holidays, and air pollutants including sulfur dioxide (SO2), and nitrogen dioxide (NO2) were controlled as covariates simultaneously. Results A total of 14,965 AR outpatient records were collected. The relationship between ambient temperature and AR outpatients was generally M-shaped. There was a higher risk of AR outpatient when the temperature was 1.6–9.3 °C, at a lag of 0–7 days. Additionally, the positive association became significant when the temperature rose to 23.5–28.5 °C, at lag 0–3 days. The effects were strongest at the 25th (7 °C) percentile, at lag of 0–7 days (RR: 1.32, 95% confidence intervals (CI): 1.05–1.67), and at the 75th (25 °C) percentile at a lag of 0–3 days (RR: 1.15, 95% CI: 1.02–1.29), respectively. Furthermore, men were more sensitive to temperature changes than women, and the younger groups appeared to be more influenced. Conclusions Both mild cold and mild hot temperatures may significantly increase the risk of AR outpatients in Xinxiang, China. These findings could have important public health implications for the occurrence and prevention of AR.

Improving cabin thermal environment of parked vehicles under direct sunlight using a daytime radiative cooling cover

2021 ◽  
Vol 190 ◽  
pp. 116776
Author(s):  
Yinyan Lv ◽  
Anchong Huang ◽  
Jian Yang ◽  
Jingtao Xu ◽  
Ronggui Yang
Keyword(s):  
Thermal Environment ◽  
Radiative Cooling ◽  
Direct Sunlight
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