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Superinsulating BNNS/PVA Composite Aerogels with High solar reflectance for Energy-Efficient Buildings

Nano-Micro Letters 2022年第3期14卷 292-307页

作者： Jie Yang Kit‑Ying Chan Harun Venkatesan Eunyoung Kim Miracle Hope Adegun Jeng‑Hun Lee Xi Shen Jang‐Kyo Kim Department of Mechanical and Aerospace Engineering The Hong Kong University of Science and TechnologyClear Water BayKowloonHong KongPeople’s Republic of China Department of Aeronautical and Aviation Engineering The Hong Kong Polytechnic UniversityHung HomKowloonHong KongPeople’s Republic of China

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.

关键词： Boron nitride nanosheets Solvent-assisted freeze-casting Thermally insulating aerogel solar reflectance Energy-saving buildings

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Thin paints for durable and scalable radiative cooling

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Journal of Energy Chemistry 2024年第3期90卷 176-182,I0006页

作者： Shanquan Liu Fei Zhang Xingyu Chen Hongjie Yan Wei Chen Meijie Chen School of Energy Science and Engineering Central South UniversityChangsha 410083HunanChina School of Intelligent Manufacturing Ecosystem Xi'an Jiaotong-Liverpool UniversitySuzhou 215400JiangsuChina

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.

关键词： Radiative cooling Heat dissipation solar reflectance Thermal emittance Contact angle

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

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Building Simulation 2023年第12期16卷 2245-2259页

作者： Guangpeng Zhang Huijun Wu Jia Liu Jianming Yang Huakun Huang Yujie Ding Lei Xie School of Civil Engineering Guangzhou UniversityGuangzhou 510006China Guangdong Provincial Key Laboratory of Building Energy Efficiency and Application Technologies Guangzhou 510006China School of Automation Guangdong Polytechnic Normal UniversityGuangzhou 510665China School of Computer Science and Cyber Engineering Guangzhou UniversityGuangzhou 510006China

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.

关键词： reflective and insulative composite coating exterior wall building insulation solar reflectance thermal conductivity

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

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Advanced Fiber Materials 2022年第5期4卷 1058-1068页

作者： Bo Xiang Rong Zhang Xujia Zeng Yanlong Luo Zhenyang Luo College of Science Nanjing Forestry UniversityNanjing 210037People’s Republic of China Department of Materials Science and Engineering Collaborative Innovation Center of Advanced MicrostructuresJiangsu Key Laboratory of Artificial Functional MaterialsCollege of Engineering and Applied SciencesNanjing UniversityNanjing 210093People’s Republic of China

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.

关键词： Radiative cooling solar heating solar reflectance Infrared emittance Daytime outdoor thermal management

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

Energy and Built Environment

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Energy and Built Environment 2022年第3期3卷 327-347页

作者： Mohan Rawat R.N.Singh School of Energy and Environment Studies Devi Ahilya UniversityTakshashila CampusKhandwa RoadIndore452001Madhya PradeshIndia

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.

关键词： Cool roof Building envelope Heat gain solar reflectance Thermal comfort

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