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 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.

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.

The Analysis of Modifications in Cooling Systems for High-Performance Data Centers. A Case Study

2017 ◽  
Author(s):  
Artur Rusowicz ◽  
Adam Ruciński ◽  
Rafał Laskowski
Keyword(s):  
Air Conditioning ◽  
High Performance ◽  
Energy Savings ◽  
Cooling System ◽  
Capital Expenditure ◽  
Cooling Power ◽  
Power Demand ◽  
Excessive Heat ◽  
Refrigeration Equipment ◽  
Payback Time

One of main issues concerning server room operation is appropriate cooling of electronic modules to prevent excessive heat generation resulting in their damage. Since high cooling powers are required, precision air conditioning systems are used that are specially designed for cooling server and equipment rooms, server cabinets, etc. These devices require very large energy supplies. The paper proposes an upgrade of a cooling system for three server rooms in which refrigeration equipment with a cooling power of 1.873 MW is installed. The average actual cooling power demand is 890 kW, and some units work as a standby. Thir-eight direct-evaporation air-conditioning cabinets are installed. The refrigerant is R407C. The devices have been operated for 14 years; therefore, the refrigeration equipment should be replaced with modern units. The paper compares three approaches: replacing the units with similar ones based on newer technology, introducing contained aisle configurations of rack cabinets and units based on newer technology with additional EconoPhase modules. The application of free cooling was not analyzed since mounting additional heat exchangers was impossible (due to the lack of space and limited roof loading capacity). The paper provides capital and operating costs of the solutions. The introduction of up-to-date units and replacing condensers resulted in lowering the electric power demand by 16%. The simple payback time (SPBT) of this solution is 18.8 years. The energy savings achieved through the second solution (contained aisle configurations of rack cabinets) amount to 37.8%, with SPBT equal to 8.38 years. Variant III, consisting in using modern units with additional EconoPhase modules, significantly improves energy savings (48.3%) but it requires large capital expenditure, with simple payback time of 12.1 years.

scholarly journals A Pragmatic and High-Performance Radiative Cooling Coating with Near-Ideal Selective Emissive Spectrum for Passive Cooling

Coatings ◽  
2020 ◽  
Vol 10 (2) ◽  
pp. 144 ◽  
Author(s):  
Mingxue Chen ◽  
Wenqing Li ◽  
Shuang Tao ◽  
Zhenggang Fang ◽  
Chunhua Lu ◽  
...  
Keyword(s):  
High Performance ◽  
Large Scale ◽  
Low Cost ◽  
Passive Cooling ◽  
Radiative Cooling ◽  
Test Results ◽  
External Energy ◽  
Functional Nanoparticles ◽  
Space Cooling ◽  
The Universe

Radiative cooling is a passive cooling technology that can cool a space without any external energy by reflecting sunlight and radiating heat to the universe. Current reported radiative cooling techniques can present good outside test results, however, manufacturing an efficient radiative material which can be applied to the market for large-scale application is still a huge challenge. Here, an effective radiative cooling coating with a near-ideal selective emissive spectrum is prepared based on the molecular vibrations of SiOx, mica, rare earth silicate, and molybdate functional nanoparticles. The radiative cooling coating can theoretically cool 45 °C below the ambient temperature in the nighttime. Polyethylene terephthalate (PET) aluminized film was selected as the coating substrate for its flexibility, low cost, and extensive production. As opposed to the usual investigations that measure the substrate temperature, the radiative cooling coating was made into a cubic box to test its space cooling performance on a rooftop. Results showed that a temperature reduction of 4 ± 0.5 °C was obtained in the nighttime and 1 ± 0.2 °C was achieved in the daytime. Furthermore, the radiative cooling coating is resistant to weathering, fouling, and ultraviolet radiation, and is capable of self-cleaning due to its hydrophobicity. This practical coating may have a significant impact on global energy consumption.

scholarly journals Biologically inspired flexible photonic films for efficient passive radiative cooling

2020 ◽  
Vol 117 (26) ◽  
pp. 14657-14666 ◽  
Author(s):  
Haiwen Zhang ◽  
Kally C. S. Ly ◽  
Xianghui Liu ◽  
Zhihan Chen ◽  
Max Yan ◽  
...  
Keyword(s):  
High Throughput ◽  
High Performance ◽  
Low Cost ◽  
Cooling Power ◽  
Radiative Cooling ◽  
Fundamental Parameter ◽  
Photonic Materials ◽  
Biologically Inspired ◽  
Thermoregulatory Function ◽  
Wearable Products

Temperature is a fundamental parameter for all forms of lives. Natural evolution has resulted in organisms which have excellent thermoregulation capabilities in extreme climates. Bioinspired materials that mimic biological solution for thermoregulation have proven promising for passive radiative cooling. However, scalable production of artificial photonic radiators with complex structures, outstanding properties, high throughput, and low cost is still challenging. Herein, we design and demonstrate biologically inspired photonic materials for passive radiative cooling, after discovery of longicorn beetles’ excellent thermoregulatory function with their dual-scale fluffs. The natural fluffs exhibit a finely structured triangular cross-section with two thermoregulatory effects which effectively reflects sunlight and emits thermal radiation, thereby decreasing the beetles’ body temperature. Inspired by the finding, a photonic film consisting of a micropyramid-arrayed polymer matrix with random ceramic particles is fabricated with high throughput. The film reflects ∼95% of solar irradiance and exhibits an infrared emissivity >0.96. The effective cooling power is found to be ∼90.8 W⋅m−2and a temperature decrease of up to 5.1 °C is recorded under direct sunlight. Additionally, the film exhibits hydrophobicity, superior flexibility, and strong mechanical strength, which is promising for thermal management in various electronic devices and wearable products. Our work paves the way for designing and fabrication of high-performance thermal regulation materials.

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 High-Performance Multilayer Radiative Cooling Films Designed with Flexible Hybrid Optimization Strategy

Materials ◽  
2020 ◽  
Vol 13 (13) ◽  
pp. 2885
Author(s):  
Peng You ◽  
Xiong Li ◽  
Yijia Huang ◽  
Xiaoliang Ma ◽  
Mingbo Pu ◽  
...  
Keyword(s):  
Power Density ◽  
High Performance ◽  
Silver Film ◽  
Hybrid Optimization ◽  
Electromagnetic Properties ◽  
Cooling Power ◽  
Radiative Cooling ◽  
Optimization Strategy ◽  
Special Significance ◽  
Traditional Design

Despite their great potential for energy-saving applications, it is still challenging to design passive radiative cooling (RC) materials with simultaneous high performance and simple structures based on traditional design philosophy. To solve the contradiction between optimization speed and corresponding performance, we present a flexible hybrid optimization strategy based on a genetic algorithm (GA) in conjunction with the transfer matrix method and introducing the calculation of radiative cooling power density in the evaluation function of the GA. As a demonstration, an optimized coating with 1.5-μm-overlapping MgF2 and Si3N4 layers on top of a silver film was numerically designed. Based on a detailed analysis of the material’s electromagnetic properties and cooling performance, this coating achieved a radiative cooling power density of 62 W/m2 and a temperature reduction of 6.8 °C at an ambient temperature of 300 K. Our optimization strategy may have special significance in the design of high-performance RC materials or other multi-spectral engineering materials with simple structures.

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 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.

scholarly journals Passive Cooling of Surfaces

2018 ◽  
Vol 2 (1) ◽  
pp. 10-15
Author(s):  
Imtiaz Ahmad ◽  
E. E. Khawaja
Keyword(s):  
Ambient Temperature ◽  
Spectral Region ◽  
Film Surface ◽  
Silicon Monoxide ◽  
Suitable Condition ◽  
Passive Cooling ◽  
Radiative Cooling ◽  
Thin Film Surface ◽  
Infrared Transmittance ◽  
Atmospheric Window

Radiative cooling of surfaces without applying an energy source has been suggested in the literature. The basis for radiative cooling is the infrared transmittance of the atmosphere. The spectral transparency (i.e. low absorption) of the atmosphere in the wavelength range of 8 to 13 μm is generally termed the atmospheric window. If the humidity and cloudiness are low, then the downward thermal radiation from the atmosphere in the spectral region of the atmospheric window are expected to be low. A temperature between 15 oC and 25 oC below ambient temperature has been achieved as a result of radiative cooling.Spectrally selective radiating material, which is defined as a material with high emittance in the spectral region of the atmospheric window and high reflectance in the rest of the spectral range, can be used as an essential means in a sky radiator for passive cooling of the material. Silicon monoxide film on highly reflective substrate (aluminum coated glass) was used in the present work. It was found that the temperature of the thin film surface was about 12 oC lower than that of ambient temperature under suitable condition of radiative cooling. Cooling is expected to be more efficient in performance if it is carried out in desert places.

Sign in / Sign up

Export Citation Format

Share Document