Passive daytime radiative cooling (PDRC) is an emerging cooling technique of a sunshine-exposed terrestrial surface by dissipating excessive heat into the deep-cold outer space. It is a passive technique without fuel consumption and paves a promising way to overcome the issues of energy shortage and environmental pollution at the global scale. In the contemporary era, highly developed nanophotonic engineering allows spectrally precise emissivity/reflectivity of a thermal surface, significantly improving a PDRC structure's cooling power. Furthermore, scalable manufacturing techniques have also been successfully developed for PDRC material preparation at affordable costs, promoting their practical implementations. However, a comprehensive review of PDRC materials for real-world applications is still lacking. This work begins with the fundamentals of PDRC, continues with the power enhancement and scaling up process of PDRC materials, boosts with the advances of three typical types of scalable PDRC materials, including films, textiles, and bulk materials, and ends with an outlook that addresses the limitations and challenges on PDRC materials for extensive real-world applications. This review can help scientists and engineers carry forward the design and implementation of PDRC materials, promote the mitigation of global issues such as scorching and water shortage, and make the planet healthier and more comfortable. 

Passive daytime radiative cooling materials toward real-world applications

Experimental and numerical study on the potential of a new radiative cooling paint boosted by SiO2 microparticles for energy saving


 A high-performance adaptive radiative cooler comprising of multilayer filter and VO2-based Fabry-Perot (FP) cavity has been proposed. The bottom FP cavity adopts four layers of VO2/NaCl/PVC/Ag. Based on the phase transition of VO2, the average emissivity in the transparent window can be switched from 3.7% to 96.3%. Additionally, the average emissivity can also be adjusted with external strain to the PVC layer, providing another way to attain the desired cooling effect. The upper filter is included to block most of the solar radiation and provide a transmittance of 96.7% in the atmospheric window. At high temperature, the adaptive emitter automatically activates radiative cooling. The net cooling power is up to 156.4 W/m2 at an ambient temperature of 303 K. Our adaptive emitter still exhibits stable selective emissivity at different incident angle and heat transfer coefficient. At low temperature, the radiative cooling automatically deactivates, and the average emissivity decreases to only 3.8%. Therefore, our work not only provides new insights into the design of high-performance adaptive radiative coolers, but also advances the development of intelligent thermal management.

Realization of an adaptive radiative cooler with multilayer filter and VO2-based Fabry-Perot cavity

Switchable daytime radiative cooling and nighttime radiative warming by VO2

Thermal radiation represents a ubiquitous aspect of nature. As a main energy and entropy carrier, thermal radiation plays a fundamentally important role in a wide range of applications. In the emerging ﬁeld of thermal photonics , using thermal photonic structures (at least one of the structural features are at a wavelength or sub-wavelength scale) can reshape thermal radiation to be drastically different from conventional thermal emitters

Thermal photonics for sustainability


 Conventional static radiative coolers have an unadjustable cooling capacity, which often results in overcooling in low temperature environment. Therefore, there is a great need for an adaptive dynamic radiative cooler. However, such adaptive coolers usually require complex preparation processes. This paper proposes an adaptive radiative cooler based on a Fabry–Perot resonant cavity. By optimizing the structural parameters of the radiative cooler, this adaptive radiative cooler achieves a modulation rate of 0.909 in the atmospheric window band. The net radiative cooling performance difference between low and high temperatures is nearly eight times. Meanwhile, the device is easily prepared, has a high tolerance, and can effectively prevent W–VO2 oxidation. This study provides new insights into adaptive radiative cooling with potential for large-scale applications.

Theoretical study of a highly fault-tolerant and scalable adaptive radiative cooler

Abstract. Passive radiative cooling is an environmentally friendly and energy-free cooling method, but the practical application of radiative cooling materials is still limited by high costs and cumbersome preparation processes. Here, low-cost and chemically stable polyvinylidene fluoride (PVDF) was selected as the raw material and porous P-PVDF films for daytime radiative cooling were prepared by a simple phase separation method. A solar reflectivity of 95.6% and an atmospheric window emissivity of 99.1% were obtained, resulting in high-performance radiative cooling without a metal reflective layer. A cooling power of 69.43  W  ·  m  −  2 was achieved in direct sunlight, achieving sub-ambient cooling of 4.2°C. This work provides a unique solution for radiative cooling materials, which is expected to be implemented in practical applications of passive radiative cooling.

Low-cost and scalable sub-ambient radiative cooling porous films

Fossil fuel consumption for heating and cooling represents a considerable portion, approximately half, of the world's total energy use, thereby presenting a substantial challenge in diminishing dependence on these energy sources. Our study presents the design and fabrication of a zero-energy switchable radiative cooler (ZESRC) to address the global climate crisis by reducing energy consumption within buildings. ZESRC utilizes a simple morphology-driven method that exploits materials' differing thermal expansion coefficients, enabling a seamless switch between cooling and heating modes at any preset temperature point, enabling superior adaptive thermal management. Field experiments demonstrate that, relative to ambient temperature, ZESRC usage results in a maximum temperature decrease of 7.1°C during summer and a maximum increase of 7.5°C in winter. Furthermore, we developed an energy-efficiency map for different climate zones, showing the ZESRC's superiority over devices with only solar heating or radiative cooling, cutting building energy use by 14.3%. The results underscore the ZESRC's capability for net-zero energy consumption, significantly advancing global energy conservation and the 2050 net-zero carbon goal. 

Zero-energy switchable radiative cooler for enhanced building energy efficiency

Radiative cooling is an effective technology with zero energy consumption to alleviate climate warming and combat the urban heat island effect. At present, researchers often use foam boxes to isolate non-radiant heat exchange between the cooler and the environment through experiments, so as to achieve maximum cooling power. In practice, however, there are challenges in setting up foam boxes on a large scale, resulting in coolers that can be cooled below ambient only under low convection conditions. Based on polymer materials and nano-zinc oxide (nano-ZnO, refractive index > 2, the peak equivalent spherical diameter 500 nm), the manufacturing process of heat pump film (HPF) was proposed. The HPF (4.1 mm thick) consists of polyethylene (PE) bubble film (heat transfer coefficient 0.04 W/m/K, 4 mm thick) and Ethylene-1-octene copolymer (POE) cured nano-ZnO (solar reflectance ≈94% at 0.075 mm thick). Covering with HPF, the object achieves 7.15 °C decreasing in normal natural environment and 3.68 °C even under certain circumstances with high surface convective heat transfer (56.9 W/m2/K). HPF has advantages of cooling the covered object, certain strength (1.45 Mpa), scalable manufacturing with low cost, hydrophobic characteristics (the water contact angle, 150.6°), and meeting the basic requirements of various application scenarios.

/pdf/a-scalable-heat-pump-film-with-zero-energy-consumption-1qc10djk.pdf

A Scalable Heat Pump Film with Zero Energy Consumption

Equivalence ionisation effect of 1 MeV electron and proton space particles and γ-rays on optical silica

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Theoretical study of a highly fault-tolerant and scalable adaptive radiative cooler

Low-cost and scalable sub-ambient radiative cooling porous films

Zero-energy switchable radiative cooler for enhanced building energy efficiency

A Scalable Heat Pump Film with Zero Energy Consumption

Equivalence ionisation effect of 1 MeV electron and proton space particles and γ-rays on optical silica