High-entropy rare earth stannate ceramics:Acid corrosion resistant radiative cooling materials with high atmospheric transparency window emissivity and high near-infrared solar reflectivity

In response to the development of the concepts of“carbon neutrality”and“carbon peak”,it is critical to developing materials with high near-infrared(NIR)solar reflectivity and high emissivity in the atmospheric transparency window(ATW;8–13μm)to advance zero energy consumption radiative cooling technology.To regulate emission and reflection properties,a series of high-entropy rare earth stannate ceramics(HE-RE_(2)Sn_(2)O_(7):(Y_(0.2)La_(0.2)Nd_(0.2)Eu_(0.2)Gd_(0.2))_(2)Sn_(2)O_(7),(Y_(0.2)La_(0.2)Sm_(0.2)Eu_(0.2)Lu_(0.2))_(2)Sn_(2)O_(7),and(Y_(0.2)La_(0.2)Gd_(0.2)Yb_(0.2)Lu_(0.2))_(2)Sn_(2)O_(7))with severe lattice distortion were prepared using a solid phase reaction followed by a pressureless sintering method for the first time.Lattice distortion is accomplished by introducing rare earth elements with different cation radii and mass.The as-synthesized HE-RE_(2)Sn_(2)O_(7)ceramics possess high ATW emissivity(91.38%–95.41%),high NIR solar reflectivity(92.74%–97.62%),low thermal conductivity(1.080–1.619 W·m^(−1)·K^(−1)),and excellent chemical stability.On the one hand,the lattice distortion intensifies the asymmetry of the structural unit to cause a notable alteration in the electric dipole moment,ultimately enlarging the ATW emissivity.On the other hand,by selecting difficult excitation elements,HE-RE_(2)Sn_(2)O_(7),which has a wide band gap(Eg),exhibits high NIR solar reflectivity.Hence,the multi-component design can effectively enhance radiative cooling ability of HE-RE_(2)Sn_(2)O_(7)and provide a novel strategy for developing radiative cooling materials.

Thin paints for durable and scalable radiative cooling

Passive daytime radiative cooling(PDRC) is environment-friendly without energy input by enhancing the coating's solar reflectance(R_(solar)) and thermal emittance(ε_(LWIR)) in the atmosphere's long-wave infrared transmission window.However,high R_(solar) is usually achieved by increasing the coating's thickness,which not only increases materials' cost but also impairs heat transfer.Additionally,the desired high R_(solar) is vulnerable to dust pollution in the outdoors.In this work,a thin paint was designed by mixing hBN plates,PFOTS,and IPA. R_(solar)=0.963 and ε_(LWIR)=0.927 was achieved at a thickness of 150 μm due to the high backscattering ability of scatters.A high through-plane thermal conductivity(~1.82 W m^(-1) K^(-1)) also can be obtained.In addition,the porous structure coupled with the binder PFOTS resulted in a contact angle of 154°,demonstrating excellent durability under dust contamination.Outdoor experiments showed that the thin paint can obtain a 2.3℃ lower temperature for sub-ambient cooling than the reference PDRC coating in the daytime.Furtherly,the above-ambient heat dissipation performance can be enhanced by spraying the thin paint on a 3D heat sink,which was 15.7℃ lower than the reference 1D structure,demonstrating excellent performance for durable and scalable PDRC applications.

Kubelka-Munk Revised Theory for High Solar Reflectance and High Long-wave Emissivity Coatings Designing

The Kubelka-Munk revised theory was adopted to derive the mix design theory of high solar reflectance and high emissivity coatings.When the concentration of each colorant is within 20%,and the width of the coating is more than 200 μm,each colorant has enough covering power in visible and near-infrared spectral range.It can be assumed that the addition of colorants in coatings can only change the solar spectral absorption ratio rather than solar spectral scattering coefficient.The spectral scattering coefficient of coatings tends to a constant.The spectral absorption-scattering property of each colorant can be characterized through one parameter.The spectral absorption-scattering coefficient of coatings can be calculated with the multivariate linear relationship of each pigment.Moreover,the results can be expanded for high solar reflectivity and high long-wave emissivity coating preparation.The accuracy of Kubelka-Munk revised theory has been tested and verified through comparison between the calculated value and tested value of coating reflectance.

Superinsulating BNNS/PVA Composite Aerogels with High Solar Reflectance for Energy-Efficient Buildings

With the mandate of worldwide carbon neutralization,pursuing comfortable living environment while consuming less energy is an enticing and unavoidable choice.Novel composite aerogels with super thermal insulation and high sunlight reflection are developed for energy-efficient buildings.A solvent-assisted freeze-casting strategy is used to produce boron nitride nanosheet/polyvinyl alcohol(BNNS/PVA)composite aerogels with a tailored alignment channel structure.The effects of acetone and BNNS fillers on microstructures and multifunctional properties of aerogels are investigated.The acetone in the PVA suspension enlarges the cell walls to suppress the shrinkage,giving rise to a lower density and a higher porosity,accompanied with much diminished heat conduction throughout the whole product.The addition of BNNS fillers creates whiskers in place of disconnected transverse ligaments between adjacent cell walls,further ameliorating the thermal insulation transverse to the cell wall direction.The resultant BNNS/PVA aerogel delivers an ultralow thermal conductivity of 23.5 mW m^(−1) K^(−1) in the transverse direction.The superinsulating aerogel presents both an infrared stealthy capability and a high solar reflectance of 93.8%over the whole sunlight wave-length,far outperforming commercial expanded polystyrene foams with reflective coatings.The anisotropic BNNS/PVA composite aerogel presents great potential for application in energy-saving buildings.

Effect of Aging on Solar Reflectance of White Cool Roof Coatings:Natural Weathering and the Influence on Building Energy Needs for Different Climate Conditions in Brazil

The use of cool materials on the building envelope is one of the most cost-effective ways to increase indoor thermal comfort conditions in hot climates and decrease the cooling energy needs.Despite the benefit of reducing cooling loads,researches have demonstrated that aging of roof coatings changes the initial solar reflectance(SR),which influences the long term building thermal and energy performance.Thus,this work presents preliminary natural weathering tests performed on samples of nine white coatings exposed to natural weathering for one year in the city of Sao Carlos,Brazil.Solar reflectances were measured with a spectrophotometer before and after exposure,every 3 months,for identifying the effect of aging along the time.The findings showed changes of 13%to 23%on SR after one year of natural weathering,with higher decrease on SR for rougher surfaces.The cleaning process restored from 90%to 100%of the original SR,which means maintenance can be an effective solution to restore the initial SR.Simulations indicated that roofs with higher solar reflectance increase indoor thermal comfort conditions and decrease the cooling energy need for buildings in hot climates,but the aging of white coatings increased the cooling energy needs along the time.

Bionic Leaves Imitating the Transpiration and Solar Spectrum Reflection Characteristics of Natural Leaves

A novel thin film organic bionic leaf was prepared by a solution-casting method to simulate the thermal effect of transpi- ration and solar spectrum reflection characteristics of plant leaves. The main components of the bionic leaf are polyvinyl alcohol （PVA）, lithium chloride （LiCl） and chromium sesquioxide （Cr2O3）. The thin film was modified by chemical cross-linking, and its surface was modified by alkylsilane to prevent excessive swelling. The thin film can simulate the thermal effect of natural leaf transpiration because that the hygroscopic PVA and LiCI can absorb and desorb water due to the high and low humidity of the ambient air at night and day, respectively. The thin film has the similar solar spectrum reflection characteristics to those of plant leaves due to the Cr2O3 and the water content of the hygroscopic materials. The measured diurnal maximum radiation temperature difference between the organic bionic leaf and the Osmanthus fragrans leaf was only 0.55 ℃. In addition, the solar spectrum reflection measurements revealed that the organic bionic leaf could precisely simulate the key solar spectrum reflec- tion characteristics of plant leaves.

Nanoparticles-modified polymer-based solar-reflective coating as a cooling overlay for asphalt pavement

The phenomenon of rutting is one of the most serious problems on asphalt pavements.Decreasing the surface temperature of the asphalt pavement is an effective method to solve the rutting problem on asphalt pavements.In this study,a nano-sized-particlesfilled polymer composite was developed as an overlay to reflect solar energy and decrease the surface temperature of asphalt pavements.The overlay was composed of acrylic or epoxy resin filled with nano TiO_(2) or nano TiNO_(2).The solar reflection of the nanoparticle-filled polymers was tested,and the results showed that solar reflection effectiveness of the TiO_(2)/acrylic composite reached the highest value.The results of outdoor temperature tests indicate that the solar-reflective overlay could decrease the surface temperature of asphalt pavements by about 10℃ when the pavement temperature is about 60℃.

Biomimetic Material Simulating Solar Spectrum Reflection Characteristics of Yellow Leaf

To counter the threat of hyperspectral detection, it is necessary to develop biomimetic materials to simulate the solar spectral re- flection characteristics of plant leaf accurately. Two kinds ofmembranaceous yellow biomimetic materials were prepared by dispersing the particles of chrome titanium yellow and iron oxide yellow as fillers in polyvinyl alcohol films respectively. Reflectance and transmittance of the biomimetic materials were measured, and absorption and scattering coefficients of the biomimetic materials were inverted with a four-flux model. Results indicate that the biomimetic material adopting chrome titanium yellow particles can simulate the solar spectrum reflection characteristics of yellow leaf because of the similar absorption and scattering characteristics. The biomimetic material adopting iron oxide yellow particles cannot simulate the spectrum reflection characteristics of yellow leaf near the wavelength of 900 nm due to the characteristic absorption of the iron oxide. When the volume fraction of the chrome titanium yellow particles is lower than 2.12%, the absorption and scattering coefficients both increase approximately linearly with the volume fraction, indicating that the particles can scatter radiation independently. Therefore, the reflectance of the biomimetic material can be regulated through linearly changing of the volume fraction of the chrome titanium yellow particles.

Mo/Si multilayers used for the EUV normal incidence solar telescope

This paper first reviews an EUV normal incidence solar telescope that we have developed in our lab. The telescope is composed of four EUV telescopes and the operation wavelengths are 13.0 nm, 17.1 nm, 19.5 nm, and 30.4 nm. These four wavelengths, fundamental to the research of the solar activity and the atmosphere dynamics, are always chosen by the EUV normal incidence solar telescope. In the EUV region, almost all materials have strong absorption, so optics used in this region must be coated by the multilayer. The Mo/Si multilayers used for the EUV normal incidence solar telescope are designed and fabricated by the magnetron sputtering coating machine. The characteristics of these multilayers, such as reflectivity and thermal stability at wavelengths of 13.0 nm, 17.1 nm, 19.5 nm and 30.4 nm, are also described. All the multilayers were measured by a hard X-ray diffractometer (XRD) and an EUV/soft X-ray reflectometer (EXRR) before and after heating (in a vacuum chamber) at 100℃ for 24 hours and at 200℃ for 1 hour and 4 hours. The results show that Mo/Si multilayers have high reflectivity at 13.0 nm, 17.1 nm, and 19.5 nm but low at 30.4 nm. We found no change in the reflectivity and center wavelength of these multilayers by comparing the reflectivity curves before and after heating. This suggests the thermal stability of Mo/Si multilayers may meet our requirement in future solar observation missions.

Long-Term Consistent Recalibration of VIRR Solar Reflectance Data Record for Fengyun Polar-Orbiting Satellites

The visible infrared radiometer(VIRR)is the first instrument with longest measurements equipped on the Fengyun(FY)polar-orbiting satellites.Through re-processing of the historic VIRR measurements,long-term(over 20 yr)global data can be integrated from multiple participating VIRRs on a consistent radiometric scale,which are valuable to climate and climate change studies.Due to lack of an onboard calibration system for VIRR,the reflective solar bands must be vicariously calibrated.This study applied the multi-site vicarious approach for consistent calibration of the VIRR visible(VIS)and near-infrared(NIR)data,and produced calibration coefficients for five VIRRs on FY-1 C/D and FY-3 A/B/C.The data quality was then evaluated with observations.The reflectance predicted by using the radiative transfer model over multiple invariant desert and ocean targets was used to derive the calibration slope via a weighted fitting scheme,in which the weights are the inverse of the variance from a radiative transfer simulation evaluated with reference to Aqua moderate resolution imaging spectroradiometer(MODIS).The sensor-specific calibration coefficients were derived on a daily basis by using piecewise polynomials.The calibration reference of the VIRR solar band record was further traced to the Aqua MODIS Collection 6.1 reference calibration with a systematic correction derived from the Libya4 desert.The VIRR record was compared with the Aqua MODIS C6.1 calibration over the polar region based on simultaneous nadir overpass observations.The lifetime relative difference for each sensor are within 3.3%and 4.5%for channels 1 and 2.Invariant deserts were also employed to evaluate the stability and consistency of the VIRR record.In general,the means of the directional and spectral corrected reflectance for each sensor are within 1%of the 20-yr average,implying that the VIRR reflectance of the invariant targets is consistent to within 1%among the sensors for channels 1 and 2.The VIRR data thus derived are reliable.

THE TEKOA BOYS’HOME A Melding of Vision,Functionality,and Sustainability

INTRODUCTION Community Housing Partners(CHP)is a 501(c)(3)community development corporation that serves the needs of low-income and low-wealth individuals and families in the southeast.CHP’s mission is to create affordable,green,sustainable housing opportunities and services for the people and communities they serve.Since 1975,CHP has served over 206,000 people,including the elderly,women and children in transition,formerly homeless people,single female heads-of-household.

Boosting daytime radiative cooling performance with nanoporous polyethylene film

Radiative cooling without energy consumption and environmental pollution holds great promise as the next-generation cooling technology.To date,daytime radiative cooling performance is still slightly low,especially in humid areas.In this work,we demonstrated that nanoporous polyethylene(Nano PE)film can improve solar reflectivity from 96%to 99%,thus boosting radiative cooling performance.Moreover,the experimental results in humid areas indicate that Nano PE films can improve radiative cooling performance by∼76%in a clear day and 120%in a day with few clouds.Additionally,compared with ordinary PE films,thin Nano PE films have significantly higher weather fastness and mechanical strength.More importantly,nano PE films can scatter part of visible light,thus suppressing the generation of light pollution in practical applications.Lastly,the modeling results reveal that with Nano PE films,more than 95%of China’s areas can achieve daytime cooling performance.Our work can boost the development of radiative cooling technology with a very low cost.

Dynamic performance and energy efficiency of reflective and insulative composite coating on building exterior wall

Reflective and insulative composite coatings are a new energy-saving material with high solar reflectance and extremely low thermal conductivity for buildings.The optimization and impact of high solar reflectance and low thermal conductivity on the insulating capacity of walls remain uncertain.This work investigates the dynamic thermal performance and energy efficiency of a reflective and insulative composite coating in regions with hot summer and warm winter.A simplified thermal resistance-heat capacitance model of an exterior building wall is established to predict thermal performance.The dynamic temperature and heat flow of the wall are predicted to reduce heat loss through the interior surface of the wall and compared to the conventional coating.The specific impact of the thermal conductivity and solar reflectance of the coating on the heat loss is further investigated to minimize heat loss of the wall.This research shows that the composite coating shows better performance on adjusting outdoor climate change than the other coating.Compared with cement,it reduces the maximum temperature of the exterior surface of the wall by 7.45°C,and the heat loss through the interior surface of the wall by 38%.The heat loss is reduced with the increase of solar reflectance and the reduction of thermal conductivity.The results can provide a useful reference and guidance for the application of reflective and insulative composite coating on building exterior wall to promote their energy-saving use on building envelopes.

Bright-white hydrogels for on-demand passive cooling

Passive cooling permits thermal management of near-zero energy consumption and low CO_(2)emissions.Despite significant progress of passive radiative coolers,comfortable and steady temperatures can hardly be achieved due to their inadequate daytime cooling power(below 0.2 k W m^(-2))yet over-cooling at night.Here,we provide a bright-white hydrogel that enables ondemand passive cooling by virtue of adaptive water evaporation and high solar reflectance up to 86.1%.Notably,theoretical cooling power determined by the evaporating rate can reach 1.25 k W m^(-2)in daytime but decreases dramatically at night.Hence sub-ambient temperature reduction of 11-13℃at noon yet nearly none at night are realized,with the diurnal temperature difference narrowed significantly.Moreover,effective cooling using colored hydrogels,and transition from evaporative cooling to solar heating have been demonstrated.This novel evaporative cooling approach will pave the way for smart passive coolers of high efficiency,colorful appearance,and low cost.

An Easy‑to‑Prepare Flexible Dual‑Mode Fiber Membrane for Daytime Outdoor Thermal Management

Excellent outdoor thermal management is vital for public health and safety.However,the ever-changing and uncontrol-lable outdoor environmental conditions,such as irrepressible sunlight and drastic temperature fluctuations,bring majestic challenges to outdoor thermal management.Here,we report a significant advancement toward designing and fabricating a novel fiber membrane with a dual-function of radiative cooling and solar heating for an efficient daytime outdoor thermal management.Unlike the reported dual-mode thermal management materials,which are usually fabricated by compounding organic polymers and metal/inorganic non-metal materials,our fiber-based membrane is composed of only two polymers,i.e.,poly(vinylidene fluoride-co-hexafluoropropene)(PVDF-HFP)and polypyrrole(PPy).The resulting membrane presents outstanding outdoor thermoregulation capacity,with a practically attainable sun-ambient cooling temperature of~4.5℃,super-ambient heating temperature of~35.8℃,in an outdoor environment,under solar intensity(Isolar)of~850 W m^(-2).Fabrication process is simple and cost-effective,which offers the possibility of preparing large-scale products.Owing to the scalable and simple fabrication process,and the exceptional outdoor thermoregulation ability,this dual-mode fiber membrane has great potential to maintain a comfortable outdoor environment for human activities and industrial operations.

Utilization of irradiance ratios for calculating the effect of reflections from obstructions in building energy simulation

The ability to take into account reflections from obstructions is of fundamental importance in building energy simulation (BES), because reflections can have a substantial influence on solar gains. In BES tools, this ability is often implemented duplicating functionalities that have already been solved efficiently in lighting simulation tools. This happens because importing those functionalities from a lighting simulation tool (source) into a BES tool (target) is usually a complex operation producing non-portable results. This article demonstrates that this ability can be imported modularly and portably without intervening in the internals of the two tools. This can be obtained by: (1) creating, in the source tool, pairs of models which are analogue-on the one hand-to the original model in the target tool, and-on the other hand-to the model in the target tool hypothetically enriched with some predictive ability only available in the source tool;(2) measuring, at each time step, the ratio between the performances predicted by the source tool as regards the two analogue models;(3) re-scaling, at each time-step, the performance predicted by the target tool on the basis of that ratio. When appropriate analogue models are utilized, this strategy enables distinct simulation tools to work like an integrated computing unit.

A study on the comparative review of cool roof thermal performance in various regions

Energy demand is growing significantly worldwide to create thermal comfort in buildings.Air-conditioning is contributing to energy consumption at a massive scale in the residential and commercial sectors.The roof is one of the most critical components of the building envelopes,and it achieved maximum heat gain in summer,and it covered nearly 20-25%of overall urban surface areas.In this respect,cool roofs are considered one of the sustainable solutions to maintain thermal comfort in buildings.The results achieved from the literature review indicate that cool roof application reduced energy use in the buildings and a useful tool to mitigate Urban Heat Island(UHI)effect.This paper summarizes cool roof thermal performance with different types of surface coatings in different climatic zones for buildings with additional benefits,limitations,and recommendations for future research work.The results of this review can be helpful for engineers,researchers,dwellers,and architectures to have a good understanding of the benefits of cool roofs to mitigate energy consumption demand in dwelling in a sustainable,cost-effective,and energy-efficient way.The average energy-saving effect of the roof is expressed from 15%to 35.7%in different climatic zones(Temperate,Tropical,Composite,Hot and Warm-Humid)as per the literature survey results.Also,the average roof surface temperature reduction is possible from 1.4℃ to up to 4.7℃ using cool roof technology.