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

Abstract

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.

Ideal spectral emissivity for radiative cooling of earthbound objects

“…The spectrally-selective and single-band based ideal coolers outperform other non-ideal coolers by many degrees for small h c . Even for h c = 2 W/(m 2 K) that is practically realizable even without vacuum sealing 26 , the ideal cooler shows noticeable advantage.…”

“…This aspect was not fully investigated in previous studies. Two types of emissivity patterns were usually considered as optimal: a broadband emissivity pattern for above-ambient cooling and a rectangular (1 over 8–13 μm and 0 for other wavelengths) emissivity pattern for below-ambient cooling 6 , 7 , 14 , 22 – 26 . However, the actual spectral regions contributing to cooling and heating via radiation change dramatically as the temperature drops below the ambient temperature.…”

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

“…With the acceleration of global warming, the environment is being seriously threatened [ 1 ], and thus environmentally friendly cooling methods are highly desired. Passive radiative cooling has attracted much attention in recent years for its properties of considerable cooling performance without energy consumption [ 2 , 3 , 4 , 5 , 6 ]. This technology involves the physical process that objects cool themselves by transferring thermal radiation to the environment through the mid-infrared atmospheric transparency window [ 5 , 7 ].…”

“…Cooling power density of 40.1 W/m 2 and temperature reduction of 4.9 °C below ambient temperature was realized with a 2-μm-thick multilayer films. Subsequently, many daytime radiative cooling methods have been proposed, such as polymers [ 6 , 15 ] and metamaterials [ 5 , 7 ]. Although polymers exhibit great potential in radiative cooling according to their visible transparent and infrared emissive characteristics, the degradation of most polymers in outdoor conditions is difficult to restore [ 16 ].…”

Continuously variable emission for mechanical deformation induced radiative cooling

“…Consequently, several metamaterials that successfully achieve the daytime radiative cooling with an equilibrium temperature below the ambient have been experimentally investigated, such as silica-polymer hybrid metamaterial 6 , hierarchically porous paint-like materials 7 , and woodbased structural materials 8 . Other materials like nanophotonic structures 9,10 , infrared transparent aerogel 11 , and polymer nanofiber 12 also provide various alternatives for daytime radiative cooling. These materials pave the way for applications of radiative cooling to energy-saving buildings, energy harvesting, and temperature regulation without energy consumption and achieving sustainable cooling throughout the day.…”