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Personal radiative cooling fabrics are a promising zero‐energy solution for creating a cool and comfortable microclimate for outdoor crowds. Despite significant progress, achieving efficient radiative cooling under some extreme situations, such as thermal shock and intensive physical activity, remains a challenge. Herein, a bioinspired metafabric with a dual‐gradient Janus design is reported for personal radiative and evaporative cooling. The hierarchical fiber structure allows for an excellent solar reflectance of 99.4% and mid‐infrared emittance of 0.94, inducing a skin temperature drop of 17.8 °C under intense sunlight. Mesoporous silica nanoparticles fixed in the fibrous network can store evaporative cooling capacity by atmospheric moisture‐absorption in the mild and humid nighttime and release such cooling capacity by moisture‐desorption in the hot daytime, providing an additional skin temperature drop of 2.5 °C. Dual‐gradient Janus design endows the metafabric with an outstanding sweat‐wicking effect and high‐performance sweat evaporative cooling capacity. In the steady‐state evaporation tests, a maximum sweat consumption of only 0.5 ml h−1 can cool the skin to a comfortable temperature, preventing harmful excessive sweating. Additionally, the bioinspired metafabric also possesses favorable wearability and color expansibility. Given these first‐rate features, the bioinspired metafabric will pave the way for the development of advanced functional fabrics. [ABSTRACT FROM AUTHOR]

Radiative cooling pigments offer new opportunities for sustainable carbon neutrality as zero‐energy and zero‐pollution functional materials. However, it is a challenge to prepare inorganic yellow pigments simultaneously with environmentally friendly, high color value, and weather resistance. In this study, a series of alkali metal‐doped γ‐Sm2S3 yellow pigments with near‐infrared reflectance were synthesized. The doping of alkali metal ions reduced synthesis temperature of Sm2S3 from 1300°C to 1000°C. The change in energy band structure induced by alkali metal doping allows the products to exhibit modifiable colors. Typical γ‐[Na]‐Sm2S3 pigment powders have a high near‐infrared reflectance and impressive colors (b* = 78.6, C* = 77.6). Furthermore, colored films made by prepared yellow powders with polyvinylidene fluoride in certain ratios had high near‐infrared reflectance and excellent environmental weathering, resulting in an effective cooling of 4–8°C in outdoor experiments. This work expands the range of options for energy‐efficient building and yellow colorant. [ABSTRACT FROM AUTHOR]

In this research, we designed a disc structure metamaterial emitter using silver and titanium dioxide for radiative cooling applications. We used COMSOL Multiphysics software for numerical simulations, considering temperature changes induced by atmospheric and surface radiation. The results of the numerical simulations demonstrated that the designed emitter had an average emissivity of 89.5% within the atmospheric transparency window, which spans from 8 to 13 µm. Furthermore, the designed emitter has the potential to achieve a radiative cooling power of 200.4 W/m2 at an ambient temperature of 300 K and can reach an equilibrium temperature of 268.25 K. Impressively, the designed emitter can cool down to 31.75 °C below the ambient temperature. Based on the results of our research, metamaterial emitter has the potential to be crucial components in the development of energy-efficient radiative cooling devices. Therefore, this work further contributes to the advancement of passive radiative coolers based on metal–dielectric–metal. [ABSTRACT FROM AUTHOR]

This paper investigates the theoretical and experimental cooling performance of textile materials utilizing radiative cooling technology. By applying Kirchhoff's law, the emissivity of surfaces is determined, revealing that materials with high transmission values can achieve comparable cooling performance to those with high reflection values. Notably, materials exhibiting moderate reflectance and transmittance in the solar range tend to absorb minimal solar radiation, thus offering high theoretical cooling performance. However, practical applications like building envelopes or clothing present challenges due to the impact of background radiation on overall cooling capacity. Despite their intrinsic cooling properties, a significant portion of solar radiation is transmitted, complicating matters as the background can significantly affect overall cooling performance. This study provides a solution that accounts for the influence of background materials. Based on spectral data, various background materials and their impact on different semi-transparent comparison materials can be considered, and cooling performance can be simulated. This enables the simulation of cooling performance for various application scenarios and facilitates comparisons between transparent, semi-transparent, and opaque textile materials. [ABSTRACT FROM AUTHOR]

In the continuous growth trend of global energy demand, the energy consumption of building cooling occupies a significant proportion. The utilization of alternative or partially alternative energy-input cooling methods in buildings, for example, the application of radiative cooling technology to building roofs, can effectively achieve better cooling performance. This has a positive impact on reducing energy consumption in the building field and slowing down global warming. This paper uses bibliometric analysis methods to systematically review the application of radiative cooling technology on building roofs. The development trajectory, hotspot issues, cutting-edge trends, and future research prospects in the research field over the past 20 years are analyzed and summarized. This study provides insights for the scaled application of radiative cooling technology in buildings and references for the application of radiative cooling technology in the field of architecture to reduce energy consumption, improve energy efficiency, achieve energy conservation, carbon reduction, and sustainable development. [ABSTRACT FROM AUTHOR]

Sophisticated infrared detection technology, operating through atmospheric transmission windows (usually between 3 and 5 μm and 8–13 μm), can detect an object by capturing its emitted thermal radiation, posing a threat to the survival of targeted objects. As per Wien's displacement law, the shift of peak wavelength towards shorter wavelengths as blackbody temperature rises, underscores the significance of the 3–5 μm range for ultra-high temperature objects (e.g., at 400 °C), emphasizing the crucial need to control this radiation for the objects' viability. Additionally, effective heat management is essential for ensuring the consistent operation of these ultrahot entities. In this study, based on a database with high-temperature resist materials, we introduced a material-informatics-based framework aimed at achieving the inverse design of simultaneous thermal camouflage (low emittance in the 3–5 μm range) and radiative cooling (high emittance in the non-atmospheric window 5–8 μm range) tailored for ultrahigh-temperature objects. Utilizing the transfer matrix method to calculate spectral properties and employing the particle swarm optimization algorithm, two optimized multilayer structures with desired spectral characteristics are obtained. The resulted structures demonstrate effective infrared camouflage at temperatures up to 250 °C and 500 °C, achieving reductions of 86.7 % and 63.7 % in the infrared signal, respectively. At equivalent heating power densities applied to the structure and aluminum, structure 1 demonstrates a temperature reduction of 29.4 °C at 0.75 W/cm2, while structure 2 attains a temperature reduction of 57.5 °C at 1.50 W/cm2 compared to aluminum, showcasing enhanced radiative cooling effects. This approach paves the way for attenuating infrared signals from ultrahigh-temperature objects and effectively managing their thermal conditions. [ABSTRACT FROM AUTHOR]

The pursuit of energy‐saving materials and technologies has garnered significant attention for their pivotal role in mitigating both energy consumption and carbon emissions. In particular, thermochromic windows in buildings offer energy‐saving potential by adjusting the transmittance of solar irradiation in response to temperature changes. Radiative cooling (RC), radiating thermal heat from an object surface to the cold outer space, also offers a potential way for cooling without energy consumption. Accordingly, smart window and RC technologies based on thermochromic materials can play a crucial role in improving energy efficiency and reducing energy consumption in buildings in response to the surrounding temperature. Vanadium dioxide (VO2) is a promising thermochromic material for energy‐saving smart windows and RC due to its reversible metal‐to‐insulator transition, accompanying large changes in its optical properties. This review provides a brief summary of synthesis methods of VO2 nanostructures based on nanoparticles and thin films. Moreover, this review emphasizes and summarizes modulation strategies focusing on doping, thermal processing, and structure manipulation to improve and regulate the thermochromic and emissivity performance of VO2 for smart window and RC applications. In last, the challenges and recent advances of VO2‐based smart window and RC applications are briefly presented. [ABSTRACT FROM AUTHOR]

A radiative cooling window is a type of energy-saving windows which is designed to emit radiation in the infrared atmospheric transparency window, while reflecting near-infrared light and transmitting visible light. Several radiative cooling windows based on film structures have been proposed, but the transmissivity of visible light or the reflectivity of near-infrared light needs to be improved. In this paper, a radiative cooling window with stacked multilayer structure is proposed. The film thickness and period number of SiO2/SiN periodic multilayer in the stacked structure are simultaneously optimized using genetic algorithm. Then the optimized stacked multilayer contain different periodic multilayer are also compared, and the spectral characteristic of the optimized stacked multilayer structure is further analyzed. An emissivity of 81% within the atmospheric window, a near-infrared reflectivity of 92% and a visible light transmissivity of 88% are obtained. Furthermore, the cooling performance of proposed stacked multilayer is studied, and a temperature drop of 32.2 K is realized when comparing it with a glass window with equal thickness. The proposed stacked multilayer structures could be used in radiative cooling windows for energy-saving of buildings and cars. [ABSTRACT FROM AUTHOR]

Static and dynamic metamaterials have been extensively studied for their ability to manipulate different physical fields and directed to broad applications. Because the governing equations of heat transfer consist of nonlinear terms with conservation of mass, momentum and energy, the equations can exhibit elliptical, parabolic, hyperbolic and hybrid configurations under different transfer modes. Such multi-mode transfer characteristics intrinsically make thermal metamaterials distinguish themselves from other metamaterials with unique static and dynamic manipulation mechanisms. Therefore, numerous studies have emerged that use the transformation theory and other methods to control static thermal metamaterials. It leads to the development of thermal cloaks, thermal concentrators, thermal diodes, and so on. Originating from the static style, the manipulation of heat transfer has expanded to dynamic systems in recent years. The introduction of hydrodynamics in metamaterial design leads to numerous novel physics effects, such as dynamic cloaking, zero-drag characteristics, topological heat transfer, nonreciprocal diffusion, and non-Hermitian physics. Moreover, the dynamic thermal metamaterials allow accurate control at both time and space dimensions, leading to exciting applications such as adjustable, reconfigurable, and intelligent thermal meta-devices. However, few studies have systematically analyzed thermal metamaterials from the perspective of static and dynamic manipulation. In this review, we aim at clarifying the connection and distinction of static and dynamic manipulation from the scopes of principle, application, and physical effects. We start with the development of static thermal metamaterials and its application. Subsequently, the development of dynamic thermal metamaterials is presented both in fundamental theory and application. Finally, we summarize the research directions and prospect future research challenges for static and dynamic thermal metamaterials. [ABSTRACT FROM AUTHOR]

In hot climates, the large amount of cooling load in electric vehicle (EV) results in a lot of battery energy consumption, leading the decrease of driving range. With the widespread application of windows in EV, the electrochromic glass (EC) shows great prospect in lowering the cooling load. However, researches on the application of EC in EV lack the consideration of both passive cooling measures and passenger comfort, which limits the further application of EC. In this paper, we proposed an idea combining the novel techniques of both electrochromism and radiative cooling. Computational fluid dynamics (CFD) is modeled to simulate the application of electrochromic and radiative cooling coupled smart windows in hot parking conditions, exploring the improvement effect of the window on the thermal environment, comfort and energy saving of the EV. The results indicate that, under the intense sunlight with an outdoor temperature of 33 °C, activating the air conditioning to maintain an average interior temperature of 26 °C, the coupled windows reduced the cooling capacity of the air conditioning by 762 W compared to regular windows, which can further increase the range of EV. Meanwhile, compared to simple electrochromic fully colored glass, the integration of radiative cooling technology can lower the window surface temperature by up to 10.7 °C. Moreover, compared to regular windows, the coupled windows lowered the standard effective temperature (SET*) for passengers by approximately 7 °C, significantly improving comfort. These research findings are expected to provide guidance for optimizing window design and enhancing the performance of EV. [ABSTRACT FROM AUTHOR]

Radiative cooling glass with spectral selectivity is an effective energy-saving strategy for buildings and vehicles. Nevertheless, the current research still has limitations; for example, the absorption of ultraviolet light by the glass results in a large amount of heat generated inside the space, which affects the radiative cooling performance. Herein, distinct spectral bands of solar radiation are precisely controlled through independently designing epsilon-near-zero (ENZ) regions within the hyperbolic metamaterials (HMMs) composed of Ag/SiO2 and Ag/TiO2 nanoscale-thick layers, which exhibit outstanding spectral regulation capability. The HMM glass features a high visible light transmittance (0.654), superior near-infrared reflectance (0.858), and good ultraviolet reflectance (0.576), while also possessing a high infrared emissivity of 95.6% in the atmospheric window. Outdoor simulation results suggest that with a convective heat transfer coefficient of 6 W/(m² K), the internal equilibrium temperature of the HMM glass can be reduced by 32.8°C compared to that of normal glass. Furthermore, the HMM glass can save up to 91.8-216.4 MJ/m² of cooling energy annually in China in comparison to normal glass. The radiative cooling glass showcased in this work, with its superior spectral regulation capabilities, plays a crucial role in energy conservation and fostering sustainable progress and thus makes it suitable for use in building glass curtain walls or roofs, vehicles windows, and so on. [ABSTRACT FROM AUTHOR]

Proper temperature regulation of photovoltaic (PV) modules increases their performance. Among various cooling techniques, phase change materials (PCMs) represent an effective thermal management route, thanks to their large latent heat at constant temperatures. Radiative cooling (RC) is also recently explored as a passive option for PV temperature regulation. In this paper, a heat sink (HS), phase change materials, and radiative cooling are integrated with photovoltaic modules to achieve low and uniform temperature distribution along the PV module and improved performance. Eight different combinations are considered for the proposed system, including HS, PCM, and RC, and their various combinations. The PCM is selected according to the environmental conditions of the selected location. A comprehensive 2-D model is developed and analyzed in COMSOL-Multiphysics software by solving the governing equations using the finite element method. The performance analysis is carried out for the climatic conditions of the Atacama Desert, having high solar radiation and ambient temperature. The effects of PCM height, ambient temperature, wind velocity, and solar radiation on the performance of the proposed system are studied. The performance of eight different configurations is also compared. The maximum reductions in PV temperature, maximum PV power, and a minimum drop in PV conversion efficiency are observed to be 22 oC, 152 W, and 14% using a combined heat sink and radiative cooling systems, among all other configurations. The findings of this study can be used to select the best PV cooling method among different configurations. [ABSTRACT FROM AUTHOR]

Passive daytime radiative cooling has emerged as a promising green technology for the thermal management of buildings, vehicles, textiles, and electronics. Typically, both high solar reflectance and high thermal emissivity are prerequisites to achieve sufficient daytime cooling. However, colored radiative cooling materials are facing the dilemma of introducing visible light absorption, leading to challenges in balancing cooling and aesthetic demands. Here, three colored bilayer radiative cooling coatings, each comprised of a white base layer and a colored top layer with fluorescence enhancement are fabricated. Three phosphors (Sr2Si5N8:Eu2+, Y3Al5O12:Ce3+, and (Ba,Sr)SiO4:Eu2+) are employed with respective photoluminescence quantum yields (PLQYs) of 81%, 95.8%, and 91.0% as the colored pigment in the top layer. To mitigate the contradiction between coloration and solar reflectance, SiO2 microspheres are introduced into the top layer and utilize their Mie‐resonance‐based multiple scattering to increase the photoluminescent (PL) properties of the phosphors, which jointly boosts the effective solar reflectance (ESR) of the top layer. As a result, the three bilayer coatings exhibit soft colors while achieving subambient cooling with temperature drops of up to 1.5 °C. This fluorescence‐enhancement strategy may pave the way for preparing highly efficient radiative cooling coatings with tunable colors. [ABSTRACT FROM AUTHOR]

To maintain a comfortable indoor living environment in low latitude or tropical regions, humans consume significant amounts of electrical energy in air conditioning, leading to substantial CO2 emissions. Passive daytime radiative cooling (PDRC) allows objects to cool down during the daytime without any energy consumption by dissipating heat through the atmospheric transparency window (8−13 µm) to outer space, which has garnered significant attention. However, the practical applications of common PDRC materials are hindered by their poor optical selectivity and high‐reflective silver backing. Additionally, the availability of artificial photon emitters with complex structures and excellent performance is also limited by their high cost. Herein, a novel multilayer prismatic photonic metamaterial film without any silver reflector, easily scalable and produced by a roll‐to‐roll method is demonstrated, which exhibits ≈96.4% sunlight reflectance (0.3−2.5 µm) and ≈97.2% emissivity in mid‐infrared (IR) (8−13 µm). At an average solar intensity of ≈920 W m−2, it is on average 6.8 °C below ambient temperature during the day and theoretically yields a radiative cooling power of 88.9 W m−2. Furthermore, the film exhibits excellent hydrophobicity, superior flexibility, and robust mechanical strength, providing an attractive and viable pathway for practical applications addressing the pressing challenges of climate and energy issues. [ABSTRACT FROM AUTHOR]

This study focuses on improving human thermal comfort in a high-temperature outdoor environment using vests with a radiative cooling coating. The effects of coating thickness on the radiative cooling performance were first evaluated, and an optimal thickness of 160 μm was achieved. Then, six subjects were recruited to evaluate the thermal comfort in two scenarios: wearing the vest with radiative cooling coatings, and wearing the standard vest. Compared with the standard vest, the coated vest decreases the maximum temperature at the vest inner surface and the outer surface by 5.54 °C and 4.37 °C, respectively. The results show that thermal comfort is improved by wearing radiative cooling vests. With an increase of wet bulb globe temperature (WBGT), the improving effects tend to decline. A significant improvement in human thermal comfort is observed at a WBGT of 26 °C. Specifically, the percentage of thermal sensation vote (TSV) wearing the cooling vest in the range of 0 to 1 increases from 29.2% to 66.7% compared with that of the untreated vest. At the same time, the average value of thermal comfort vote (TCV) increases from −0.5 to 0.2. [ABSTRACT FROM AUTHOR]

Achieving year‐round energy savings in buildings holds great significance toward reaching carbon neutrality and sustainability. Switchable thermal‐management materials offer an energy‐free solution to dynamically regulating internal building temperatures, by passively emitting heat into cold outer space in summer, and absorbing heat from hot sunlight in winter. In addition to dynamic thermal regulation, color display is another pursuit for addressing aesthetic considerations; however, most current dynamically switchable materials lack color options, due to an optical conflict between adaptive solar reflection and selective visible absorption, limiting their wide adoption in aesthetic scenarios such as commercial exterior walls. Herein, a colored temperature‐adaptive cloak (CTAC) that achieves dynamically switchable thermal management in an energy‐neutral way without sacrificing year‐round vibrant color display is reported. This is realized by decoupling solar reflectivity modulation and color display through the choice of two individual constituent components, including thermochromic microcapsules, and fluorescent dyes. Moreover, compared to single‐mode samples with similar colors, the CTAC with dual modes stays 5.6–3.4 °C warmer during cold winter and 14.9–7.9 °C cooler during hot summer (peak solar irradiance: ≈735 and 1030 W m−2, respectively), exhibiting a remarkable potential to achieve year‐round building energy savings. [ABSTRACT FROM AUTHOR]

Real-world passive radiative cooling requires highly emissive, selective, and omnidirectional thermal emitters to maintain the radiative cooler at a certain temperature below the ambient temperature while maximizing the net cooling power. Despite various selective thermal emitters have been demonstrated, it is still challenging to achieve these conditions simultaneously because of the extreme difficulty in controlling thermal emission of photonic structures in multidimension. Here we demonstrated hybrid polar dielectric metasurface thermal emitters with machine learning inverse design, enabling a high emissivity of ~0.92 within the atmospheric transparency window 8–13 μm, a large spectral selectivity of ~1.8 and a wide emission angle up to 80 degrees, simultaneously. This selective and omnidirectional thermal emitter has led to a new record of temperature reduction as large as ~15.4 °C under strong solar irradiation of ~800 W/m2, significantly surpassing the state-of-the-art results. The designed structures also show great potential in tackling the urban heat island effect, with modelling results suggesting a large energy saving and deployment area reduction. This research will make significant impact on passive radiative cooling, thermal energy photonics and tackling global climate change.

In recent years, passive radiative cooling has garnered considerable attention as a sustainable thermal regulation without relying on external energy sources, thus mitigating pollutants generation. However, an intrinsic limitation of these cooling systems lies in the reflective glare, often characterized by an ivory or silvery appearance. This drawback limits their practical application, especially where both functional efficiency and aesthetic appeal are pivotal. Herein, a biomimetic approach inspired by Saharan silver ants' thermoregulatory capabilities is adopted. These ants, equipped with distinctive triangular‐shaped hair, maintain body temperature lower than the ambient air. Leveraging insights from this natural model, a reusable silicon template is employed to fabricate a metasurface structural colored film with a triangular prism array structure using thermoplastic polyurethane (TPU) and the phase separation technique. The film demonstrates an average emissivity of 96% within the atmospheric window and an average solar reflectivity of 93%, leading to a maximum temperature reduction of 8.6 °C during daytime and 5.9 °C at night. Furthermore, the film displays stretchability and mechanical resilience, bolstered by the microscale prismatic structure enhancing superhydrophobicity. This work introduces a biomimetic strategy aimed at augmenting thermal emission while reconciling the challenge of achieving visual appealand high radiative cooling performance. [ABSTRACT FROM AUTHOR]

Passive daytime radiative cooling dissipates heat from surfaces by reflecting sunlight and emitting infrared radiation to the cold outer space, featuring a zero‐energy consumption. Polymer‐dielectric radiative cooling coatings have received significant attention because of their scalable preparation, low cost, and ease of use. However, current dielectric scatterers reveal limited solar reflectance in the polymer‐dielectric coatings due to the optical crowding, which reduces cooling effect and hinders practical application. Employing a scalable emulsion templated method, reversed yolk–shell dielectric scatterers (RYSS) are developed to alleviate optical crowding effects in polymer‐dielectric coatings. This results in coatings with a solar reflectance of ≈97.4% and an infrared emittance of ≈96.9%, while achieving a substantial reduction in scatterers content. Besides, simulation results show that RYSS outperforms core–shell, hollow, and solid scatterers in enhancing solar reflectance. Using phase change materials as emulsion templates, RYSS with high heat storage effectively enhance daytime cooling and reduce nighttime over‐cooling. Moreover, cooling experiments on concentrating photovoltaics demonstrate a temperature drop of 42 °C (≈26.2 times extension of lifetime) and a notable 22% increase in open‐circuit voltage. This work suggests that RYSS presents a promising solution to overcome the challenges of radiative cooling materials and pave the way for their practical applications. [ABSTRACT FROM AUTHOR]

[Display omitted] Outdoor radiative cooling is a passive method of cooling a surface that faces the sky. During the past decade, numbers of successful demonstrations of daytime radiative coolers have been reported. Because a daytime radiative cooler can be radiatively cooled both during the day and at night, it is always cooled and a temperature difference against the surroundings is generated. This temperature difference can be used to generate thermoelectric power throughout the day by placing a daytime radiative cooler on a thermoelectric module. However, such a device cannot harvest solar heat because sunlight is reflected by the daytime radiative cooler. In this study, a thermoelectric device that simultaneously harvests both radiative cooling and solar heating is presented. The essential component is a vertically placed thermoelectric module made of transparent thermoelectric thin films which allows radiatively cooled and solar heated surfaces to be co-planar. The outdoor and indoor measurements confirm that the device can harvest both radiative cooling and solar heating simultaneously during the day without offsetting each other, and can harvest radiative cooling at night. The co-planar design is an efficient method for simultaneously harvesting solar heating and radiative cooling, which could facilitate efficient energy harvesting and can be applied to a standalone power supply for off-grid sensor modules. [ABSTRACT FROM AUTHOR]

This study proposes the design of a novel Metal-Insulator-Metal (MIM) nano-infrared emitter that uses a unique diamond-shaped grating to achieve selective infrared absorption. Diamond-shaped nano emitter (DNE) structure exhibits four narrow resonant peaks within key absorption windows such as short-wave infrared (SWIR) mid-wave infrared (MWIR), alongside with a wide absorption band in the Non-Transmissive Infrared Range (NTIR) for thermal camouflage applications compatible with radiative cooling. Moreover, the proposed DNE is polarization insensitive as it has an in-plane symmetric design. Using the 3D Finite-Difference Time-Domain (FDTD) simulations, we demonstrate the nanoantenna's superior performance characterized by its high absorption rates and tuned effective impedance matching. As of our knowledge, the findings suggest that this is the first time that a MIM structure achieved multiple narrow resonance peaks, located in SWIR and MWIR simultaneously, with a wide absorption range in NTIR. Represented DNE stands as a significant innovation in the field of stealth technology, providing a tunable, high-efficiency solution for managing and controlling thermal emissions across diverse applications. [ABSTRACT FROM AUTHOR]

This paper proposes a temperature-adaptive radiative cooling (TARC) coating with simple preparation, cost effectiveness, and large-scale application based on a thermochromic powder. To determine the energy efficiency of the proposed TARC coating, the heat transfer on the surface of the TARC coating was analyzed. Then, a typical two-story residential building with a roof area of 258.43 m2 was modeled using EnergyPlus. Finally, the energy-saving potential and carbon emission reduction resulting from the application of the proposed TARC roof in buildings under different climates in China were discussed. The results showed that the average solar reflectivity under visible light wavelengths (0.38–0.78 μm) decreases from 0.71 to 0.37 when the TARC coating changes from cooling mode to heating mode. Furthermore, energy consumption can be reduced by approximately 17.8–43.0 MJ/m2 and 2.0–32.6 MJ/m2 for buildings with TARC roofs compared to those with asphalt shingle roofs and passive daytime radiative cooling (PDRC) roofs, respectively. This also leads to reductions in carbon emissions of 9.4–38.0 kgCO2/m2 and 1.0–28.9 kgCO2/m2 for the buildings located in the selected cities. To enhance building energy efficiency, TARC roofs and PDRC roofs are more suitable for use on buildings located in zones with high heating demands and high cooling demands, respectively. [ABSTRACT FROM AUTHOR]

Efficient heat transfer control is highly demanded for dynamic thermal management of equipment and buildings especially when the environmental temperature dramatically changes. Thermal switches, the current approach of heat transfer control, suffer from the issues of low switching ratios below eight and sharp state transition between "on" and "off". Herein, a continuously‐tuned thermal regulator with an ultrahigh thermal‐conductivity change ratio of 43 based on superaligned carbon nanotube aerogel is reported, which works on the regulation of both thermal interfacial resistance and conduction pathways by compressive deformation‐induced microstructure evolution. This thermal regulator can stabilize the device temperature at 25 °C when the environmental temperature varies by 7 and 11 °C under the natural convection and forced convection conditions, respectively. Toward practical application, the thermal regulator with flexibility is wrapped around a cylindrical lithium‐ion battery to control the operation temperature within the optimal range of 20–40 °C for enhanced discharging performance even at an environmental temperature of −20 °C. Besides, by combining the thermal regulator with radiative cooling film, the house model temperature can be lowered by 2.7 °C during daytime and raised by 1.1 °C during nighttime compared with the bare one. This efficient thermal regulation approach offers an effective solution for practical thermal management. [ABSTRACT FROM AUTHOR]

Personal protective clothing is designed to safeguard medical personnel from highly infectious diseases. However, it often compromises comfort, especially when worn outdoors during epidemics like the global COVID‐19 outbreak. This can lead to discomfort and even heatstroke. To tackle this issue, radiative cooling is incorporated into personal protective clothing by integrating hierarchically porous poly(vinylidene fluoride‐co‐hexafluoropropylene) (PVDF‐HFP) membranes into the fabric. These membranes possess a remarkable solar reflection rate of 96.9% and a strong mid‐infrared emittance of 95.2%. In practical scenarios, when exposed to clear sunny weather at midday, wearing radiative cooling personal protective clothing has the potential to reduce the temperature by 4.7 °C compared to commercially available personal protective clothing. Moreover, the lamination of porous PVDF‐HFP membranes enhances the protective capacity by increasing the synthetic blood penetration pressure from 7 to 20 kPa. The manufacturing process is straightforward, cost‐effective, and aligns with industry standards, making it suitable for large‐scale implementation in epidemic prevention and control. This technology offers comfortable protection while minimizing the risk of heatstroke. [ABSTRACT FROM AUTHOR]

Radiative Coolers (RCs) represent an emerging technology that has the potential to significantly reduce urban heat and improve indoor/outdoor thermal comfort in the built environment. Broadband and Selective Radiative Coolers (BRCs and SRCs, respectively) are the two main types of RCs that have been proposed for application in the built environment. Being both typically characterized by high solar reflectance, the former emits thermal radiation within the overall infrared spectrum, whilst the latter emits thermal radiation mainly within the Atmospheric Window (AW) waverange. A variety of both types of RCs have been developed and tested in both in‐lab and in‐field experimental campaigns. Yet, all experiments comprise small scale specimens that do not represent real‐life scale components of the built environment. In addition, no meso scale assessments have been performed with respect to the RCs' performance at a city scale. Here, for the first time, the thermo‐optical performance of both BRCs and SRCs is introduced and investigated in a multilayer Urban Canopy Model (UCM) coupled with extended Weather Research and Forecasting model (WRF) and we simulated 20 different scenarios representing the vast majority of urban layouts. The outcomes show that both types of RCs maintain lower surface temperature and air temperature at 2 m height inside the canyon, compared to conventional roofs. In addition, a city scale application of RCs has been found capable of decreasing ambient temperature up to 1.6°C as potentially experienced by pedestrians. [ABSTRACT FROM AUTHOR]

Radiative cooling, taking advantage of the coldness of the sky, has a potential to be a sustainable alternative to meet cooling needs. The performance of a radiative cooling device is fundamentally limited by the emissivity of the sky, therefore depends heavily on the regional weather conditions. Although the sky emissivity is known to increase with the dew point temperature, the feasibility of radiative cooling remains elusive in the equatorial tropical climate, where the weather is humid, cloudy, and constantly changing. It is pointed out that a high degree of thermal insulation of the radiative cooling system can be effective under such extreme weather conditions. A new method to characterize dynamic sky conditions is presented, namely to measure the sky window emissivity in the zenith direction. It is shown that a sub‐ambient cooling up to 8 °C is possible during daytime and that the cloud base is not a complete blackbody and can be used as a heat sink for radiative cooling. [ABSTRACT FROM AUTHOR]

Soaring solar cell temperature hindered photovoltaic (PV) efficiency, but a novel radiative cooling (RC) cover developed in this study offered a cost-effective solution. Using a randomly particle-doping structure, the radiative cooling cover achieved a high “sky window” emissivity of 95.3% while maintaining a high solar transmittance of 94.8%. The RC-PV system reached a peak power output of 147.6 W/m2. A field study to explore its potential in various provinces in China revealed significant efficiency improvements, with yearly electricity outputs surpassing those of ordinary PV systems by a relative improvement of 2.78%–3.72%. The largest increases were observed under clear skies and in dry, cool climates, highlighting the potential of RC-PV systems under real weather and environmental conditions. This work provided the theoretical foundation for designing scalable radiative cooling films for PV systems, unlocking the full potential of solar energy.

Abstract The dynamic regulation of thermal radiation in the mid‐infrared region is technologically important in diverse applications such as thermal management and camouflage. However, there is a notable lack of research on the combination of infrared radiators and memristors, which can maintain previous states or modes without extra power consumption. Here, a memristive mid‐infrared radiator, where graphene nanoribbon grating serves simultaneously as a floating gate for charge storage and a tunable infrared nanoantenna for thermal radiation is proposed. This design enables precise and fast modulation, low power consumption, and scalability. Even a small change of one attocoulomb in the stored charge can produce a 1‐µm peak shift in the absorption peak. This work provides a platform for a memristive infrared thermal radiator that can be further exploited for electrochromic glazing or on‐chip radiative cooling.

Passive thermoelectric devices that utilize radiative cooling and solar heating have witnessed significant advancements in power generation. However, their applications and promotions are limited due to the low and unsustainable output. In this study, we propose a compact passive thermoelectric device (TED) consisting of a thermoelectric generator (TEG) equipped with a radiative cooler (RCer) and a solar absorber (SAer) for 24-h electricity generation. The RCer is made of a high-scattering porous cellulose film with a thickness of 100 μm. It is coated onto the TEG's sky-facing terminal which serves as the cold end. The SAer is made of an aluminum substrate coated with black paint. It is attached to the opposite TEG terminal which serves as the hot end. By compactly integrating the RCer and SAer, the proposed TED can harvest energy from the space for continuous electric power generation with manageable implementations. Outdoor experiments have shown that during a clear daytime, the maximum temperature difference between the TEG ends reached 7.7°C, with an average of 2.8°C. During the nighttime, the maximum temperature difference between TEG ends could reach 1.7°C, with an average of 0.9°C. The maximum power outputs during daytime and nighttime are 351.6 mW·m−2 and 31.0 mW·m−2, respectively. This study introduces a conceptual design for a compact passive TED and lays the foundation for practical applications in powering outdoor microdevices.

Photovoltaic (PV) cells, widely adopted in solar energy applications, achieve a maximum efficiency of only 30 % and remain inactive during nighttime. In contrast, solar-thermal power generation has surpassed 50 % efficiency. To address these limitations, we introduce the Solar- Radiative cooling -Thermoelectric system (Solar-RC-TE), integrating solar energy, radiative cooling (RC), and thermoelectric power generation. This system enhances energy density, reduces consumption, lowers costs, and minimizes environmental impact while enabling nighttime power generation. For the optimization of the Solar-RC-TE model to further improve power generation efficiency, we employ the comprehensive three-dimensional methodology of COMSOL, considering material properties, structural configurations, and environmental factors. Research findings reveal that a 710 mm × 710 mm radiative cooling film can generate 386.12 mV of voltage on the thermoelectric generator (TEG). Environmental factors, such as increased solar irradiance, lead to temperature elevation, affecting efficiency. Overheating and higher wind speeds also contribute to decreased TEG efficiency. Regarding materials, improving the thermoelectric figure of merit (ZT) and film emissivity positively impact power generation efficiency. Elevating the film emissivity from 0.7 to 0.89 significantly enhances performance by 1.2 %. These outcomes provide a tangible and practical solution for addressing energy crises and environmental concerns.

Passive radiative cooling has emerged as a sustainable energy-saving solution, characterized by its energy-free operation and absence of carbon emissions. Conventional radiative coolers are designed with a skyward orientation, allowing for efficient heat dissipation to the cold heat sink. However, this design feature presents challenges when installed on vertical surfaces, as nearby objects obstruct heat release by blocking the cooler’s skyward view. Here, we introduce a directional radiative cooling glass (DRCG) designed to facilitate efficient heat dissipation through angular selective emission. The DRCG is constructed as a multilayer structure incorporating epsilon-near-zero materials, specifically Si3N4 and Al2O3, layered on an indium-tin-oxide thermal reflector. This innovative design restricts thermal emission to specific angular ranges, known as the Berreman mode. Additionally, the transparent layers enable a visible transmittance exceeding 84 %. Theoretical simulations validate the enhanced cooling performance of the DRCG, exhibiting a temperature reduction of over 1.5 °C compared with conventional glass in hot urban environments characterized by a nearby object temperature exceeding 60 °C and a sky view factor of 0.25. Furthermore, outdoor experiments demonstrate that employing the DRCG as a window enhances space-cooling performance by ∼1.5 °C. These findings underscore the potential of transparent energy-saving windows in mitigating the urban heat island effect.

Radiative cooling may serve as a promising option to reduce energy consumption for space cooling. Radiative cooling paints provide a cost-effective and scalable solution for diverse applications and attract great attention, but the state-of-art cooling paints generally use non-eco-friendly organic solvents and need large thicknesses (>400 μm) to realize high performance, which leads to high cost and environmental issues in implementation. This work aims to address these challenges by developing eco-friendly aqueous paints with low thickness (below 150 μm) by adopting a double-layer design based on a complementary spectrum strategy. The structure consists of a wide bandgap top layer to scatter short-wavelength light and a bottom layer with high reflectance to visible and near-infrared (NIR) irradiation. Effects of different design factors are studied using numerical simulation and experiments to attain the optimal design. The resulting Y2O3–ZnO paints show a strong reflectance of 95.4 % and a high atmospheric window emissivity of 0.93 at a low thickness of 150 μm. Field tests in the subtropic humid climate of Hong Kong demonstrated sub-ambient cooling of 2 °C at noon and 4 °C at night without shielding convection. The paints also show high robustness and excellent resistance to water and UV light attacks, rendering them promising for large-scale applications.

Passive daytime radiative cooling that could provide sub-ambient cooling emerges as a promising technology to reduce household energy consumption. Nonetheless, prevailing studies are predominantly focused on surface cooling, often overlooking its adaptability to enclosed spaces with active cooling technologies. Here we present a multilayer radiative cooling film (J-MRC) with Janus optical properties in the mid-infrared region, consisting of the nanoporous polyethylene films, the polyethylene oxide film, and silver nanowires. The top side of the J-MRC functions as a conventional radiative cooling material to supply sub-ambient surface cooling, while the bottom side with low mid-infrared emissivity transfers limited heat via thermal radiation to the low-temperature enclosures. Our experiments validate that the J-MRC possesses an enhanced space cooling performance in comparison to the conventional radiative cooling film. This work provides a valuable design concept for radiative cooling materials, thereby expanding their practical scenarios and contributing to reduce the carbon emission.

Many materials have been explored for the purpose of creating structures with high radiative cooling potential, such as nanocellulose-based structures and nanoparticle-based coatings, which have been reported with environmentally friendly attributes and high solar reflectance in current literature. They each have their own advantages and disadvantages in practice. It is worth noting that nanocellulose-based structures have an absorption peak in the UV wavelengths, which results in a lower total solar reflectance and, consequently, reduce radiative cooling capabilities. However, the interwoven-fiber structure of cellulose gives high mechanical strength, which promotes its application in different scenarios. The application of nanoplatelet-based coatings is limited due to the need for high volume of nanoparticles to reach their signature high solar reflectance. This requirement weakens the polymer matrix and results in more brittle structures. This work proposes a dual-layer system, comprising of a cellulose-based substrate as the bottom layer and a thin nanoparticle-based radiative cooling paint as the top layer, where both radiative cooling potential and mechanical strength can be maximized. Experimental and theoretical studies are conducted to investigate the relationship between thickness and reflectance in the top coating layer with a consistent thickness of the bottom layer. The saturation point is identified in this relationship and used to determine the optimal thickness for the top-layer to maximize material use efficiency. With the use of cotton paper painted with a 125 μm BaSO4-based layer, the cooling performance is enhanced to be 149.6 W/m2 achieved by the improved total solar reflectance from 80 % to 93 %.

Thermal radiation is a major dissipative pathway for heat generated by the human body and offers a significant thermoregulation mechanism over a wide range of conditions. We could use this in garment design to enhance personal cooling, which can improve the wearing comfort of garments or even result in energy savings in buildings. At present, however, radiative cooling has received insufficient attention in commercial design and production of textiles for wearable garments. Textiles that efficiently transmit the radiative heat were recently demonstrated, but either do not utilize standard weaving and knitting processes for wearable garments or require substantial process modifications. Here, we demonstrate the design and implementation of large-scale radiative cooling textiles for localized cooling management and enhanced thermal comfort using industry-standard particle-free nonporous micro-structured fibers that are fully compatible with standard textile materials and production methods. The micro-structured fibers, yarns and fabrics are part of a hierarchical photonic structure design that renders the textiles highly infrared transparent (up to > 0.8) while assuring visual opacity (up to 0.99). We design radiative cooling textiles with first-principles electromagnetic methods and fabricate them using commercial textile materials and formation facilities. Our “fabless” approach is confirmed by very good quantitative agreement between design and measurements. The resulting fabrics exhibit wearability properties expected of wearable textiles, and lower skin temperature by ≥ 3 °C compared to conventional textiles, which offers the potential for > 30 % energy savings in buildings and increases wearing comfort by significantly reducing the reliance on latent heat dissipation for thermoregulation.

This study explores the optical design of a daytime radiative cooler with near-ideal solar reflectance and longwave infrared (LWIR) emittance through materials selection and nanostructuring. Focusing on polymers as a materials platform, we introduce a bilayer architecture, comprising a porous poly(vinylidene fluoride-co-hexafluoropropene) (P(VdF-HFP)) topcoat that serves as a low-index LWIR emissive effective medium, over a nanofibrous, solar scattering polytetrafluoroethene underlayer. This novel configuration yields a superwhite coating with a near-ideal solar reflectance of >0.99, and a blackbody-like near-normal and hemispherical LWIR emittances of ∼0.98 and ∼0.96 respectively. Under humid and partially cloudy sky conditions unfavorable for radiative heat loss, these values enable the bilayer radiative cooler to achieve a sub-ambient of 2.3 °C. Given that the porous polymer bilayer uses scalable fabrication processes and commercially available materials, it holds significant promise for device-scale, as well as building thermoregulation applications.

Radiative cooling in smart windows using VO2 – a dynamic thermal management material, is of potential interest for enhancing energy savings in buildings due to its both solar and emittance tuneability in response to changing temperatures. However, studies related to the effects of VO2 thin film microstructure in a multilayer system on emissivity regulation are currently lacking. The present study addresses the thermochromic and emissivity performance of VO2/ZnSe/ITO/Glass Fabry−Perot (F–P) cavity thin film system, by manipulating the porosity in VO2 thin film. The device is fabricated by commercially feasible physical vapor deposition methods such as sputtering and thermal evaporation, most suitable for mass production. The optimized sample with porous VO2 delivers an enhanced long-wave infrared (LWIR) emissivity contrast of Δɛ LWIR ≥ 0.4 preserving a high visible transparency T lum(avg) of ∼41 % compared to dense VO2. Then finite difference time domain (FDTD) simulation is performed to further understand the effects of varying VO2 porosity and ZnSe thickness on the F–P cavity properties. The reduced low-temperature ɛ LWIR (0.1–0.2) gives this film better energy saving in regions where warming demand is dominant as simulated by EnergyPlus.

Radiative cooling, as a renewable cooling technology, is expected to mitigate growing global warming. However, the barrier when promoting radiative cooling from the laboratory to practice is still a blind spot and needs to be discussed right now. Here, on the basis of review for brief history, we propose a developing thread that the studies on radiative cooling arise from practice and in turn serves practice at the end. This perspective orderly elaborates fundamental limit in theory, realization of spectral-selective materials, practice on criteria for cooling performance, challenges and corresponding possible solutions in practice, and focusing on serving practice. We hope that the criticism for our own opinion could trigger researchers to deeply consider how to make achievement of radiative cooling better serving practice in the future.

With the increasing demand for energy worldwide, researchers from different fields have been striving to improve the sustainability and proper utilization of energy resources. Passive radiative cooling, as a natural energy transport method, can achieve cooling without additional external energy input. This review provides a comprehensive examination of passive radiative cooling, including its fundamental theories and latest development. A particular emphasis is placed on the diverse range of fields where passive radiative cooling has been applied, notably including but not limited to construction and architecture. The current state of applications, potential challenges that may arise with wider adaption and promising research directions for each field are thoroughly discussed. This review emphasizes the extensive potential and practical viability of passive radiative cooling in diverse applications and identifies pressing challenges and future research directions aimed at scaling up real-world implementation. [ABSTRACT FROM AUTHOR]

Radiative cooling and evaporative cooling are sustainable cooling techniques without additional energy input. However, radiative cooling lacks dynamic cooling ability, while evaporative cooling demands external water replenishment, hindering their applications. Herein, a smart radiative/evaporative cooling bilayer combining a polydimethylsiloxane (PDMS) upper layer with a hydrogel lower layer is presented for efficient all‐day dynamic passive cooling. The PDMS layer with high solar reflectivity (0.930) and emissivity (0.952) provides excellent all‐day radiative cooling and protects the hydrogel from solar exposure, while the hydrogel layer demonstrates remarkable water evaporation and absorption, achieving dynamic evaporative cooling. Thus, the synergy of the two layers significantly enhances the overall cooling performance. Specifically, the bilayer can achieve the peak cooling power values of 424.4 and 650.6 W m−2 as well as the maximum subambient cooling temperatures of 10.4 and 3.7 °C during sunny and cloudy mid‐days, respectively. Moreover, the bilayer obtains 3.2 °C warmer temperature compared with the PDMS alone during cold nighttime, while the two structures exhibit comparable cooling performance during hot nighttime, indicating the self‐adaptive cooling property of the bilayer. In addition, the bilayer can achieve good cooling performance even under continuous cloudy days, offering a promising strategy for efficient all‐day dynamic passive cooling. [ABSTRACT FROM AUTHOR]

Here, we present a novel protocol concept for quantifying the cooling performance of particle-based radiative cooling (PBRC). PBRC, known for its high flexibility and scalability, emerges as a promising method for practical applications. The cooling power, one of the cooling performance indexes, is the typical quantitative performance index, representing its cooling capability at the surface. One of the primary obstacles to predicting cooling power is the difficulty of simulating the non-uniform size and shape of micro-nanoparticles in the PBRC film. The present work aims to develop an accurate protocol for predicting the cooling power of PBRC film using image processing and regression analysis techniques. Specifically, the protocol considers the particle size distribution through circle object detection on SEM images and determines the probability density function based on a chi-square test. To validate the proposed protocol, a PBRC structure with PDMS/Al2O3 micro-nanoparticles is fabricated, and the proposed protocol precisely predicts the measured cooling power with a 7.8% error. Through this validation, the proposed protocol proves its potential and reliability for the design of PBRC. [ABSTRACT FROM AUTHOR]

We present a radiative cooling material capable of enhancing albedo while reducing ground surface temperatures beneath fielded bifacial solar panels. Electrospinning a layer of polyacrylonitrile nanofibers, or nanoPAN, onto a polymer-coated silver mirror yields a total solar reflectance of 99 %, an albedo of 0.96, and a thermal emittance of 0.80. The combination of high albedo and high emittance is enabled by wavelength-selective scattering induced by the hierarchical morphology of nanoPAN, which includes both thin fibers and bead-like structures. During outdoor testing, the material outperforms the radiative cooling power of a state-of-the-art control by ∼20 W/m2 and boosts the photocurrent produced by a commercial silicon cell by up to 6.4 mA/cm2 compared to sand. These experiments validate essential characteristics of a high-albedo radiative-cooling reflector with promising potential applications in thermal and light management of fielded bifacial panels. [ABSTRACT FROM AUTHOR]

Many materials have been explored for the purpose of creating structures with high radiative cooling potential, such as nanocellulose-based structures and nanoparticle-based coatings, which have been reported with environmentally friendly attributes and high solar reflectance in current literature. They each have their own advantages and disadvantages in practice. It is worth noting that nanocellulose-based structures have an absorption peak in the UV wavelengths, which results in a lower total solar reflectance and, consequently, reduce radiative cooling capabilities. However, the interwoven-fiber structure of cellulose gives high mechanical strength, which promotes its application in different scenarios. The application of nanoplatelet-based coatings is limited due to the need for high volume of nanoparticles to reach their signature high solar reflectance. This requirement weakens the polymer matrix and results in more brittle structures. This work proposes a dual-layer system, comprising of a cellulose-based substrate as the bottom layer and a thin nanoparticle-based radiative cooling paint as the top layer, where both radiative cooling potential and mechanical strength can be maximized. Experimental and theoretical studies are conducted to investigate the relationship between thickness and reflectance in the top coating layer with a consistent thickness of the bottom layer. The saturation point is identified in this relationship and used to determine the optimal thickness for the top-layer to maximize material use efficiency. With the use of cotton paper painted with a 125 μm BaSO4-based layer, the cooling performance is enhanced to be 149.6 W/m2 achieved by the improved total solar reflectance from 80 % to 93 %. [ABSTRACT FROM AUTHOR]

Radiative thermal management technologies that utilize thermal radiation from nano/microstructure for cooling and heating have gained significant attention in sustainable energy research. Passive radiative cooling and solar heating operate continuously, which may lead to additional heating or cooling energy consumption due to undesired cooling or heating during cold nighttime/winters or hot daytime/summers. To overcome the limitation, recent studies have focused on developing radiative thermal management technologies that can toggle radiative cooling on and off or possess switchable dual cooling and heating modes to realize sustainable and efficient thermal management. This review will explore the fundamental concepts of radiative thermal management and its switching mechanisms, utilizing novel systems composed of various materials and nano/microstructures. Additionally, we will delve into the potential future research directions in radiative thermal management technologies. [ABSTRACT FROM AUTHOR]

Passive radiative cooling is an energy-free cooling method by exchanging thermal radiation with the cold universe through the transparent atmospheric window. Spectrum tailoring of the radiative cooler is the key to daytime radiative cooling in previously reported works. In addition, radiative coolers with large-scale fabrication and self-cleaning characteristics should be further developed to improve their industrial applicability. Herein, we propose a bilayer radiative cooling coating with the superhydrophobic property and a scalable process, by covering TiO2/acrylic resin paint with a silica/poly(vinylidene fluoride-co-hexafluoropropylene) (SiO2/P(VdF-HFP)) composite masking layer. The strong Mie scattering in TiO2/acrylic resin paint contributes to high solar reflection, while the SiO2/P(VdF-HFP) masking layer is responsible for superhydrophobicity and synergetic solar reflection in the ultraviolet band, resulting in an effective solar reflectivity of 94.0 % with an average emissivity of 97.1 % and superhydrophobicity with a water contact angle of 158.9°. Moreover, the as-fabricated coating can be cooled to nearly 5.8 °C below the temperature of commercial white paint and 2.7 °C below the local ambient temperature under average solar irradiance of over 700 W m−2. In addition, yearly energy saving of 29.0 %–55.9 % can be achieved after the coating is applied to buildings in Phoenix, Hong Kong, Singapore, Guangzhou, and Riyadh. [ABSTRACT FROM AUTHOR]