Reduce Building Energy Consumption Research Articles

A case study of multi-objective design optimization of a healthy building in Shanghai, China

Energy efficient healthy buildings design is important in achieving carbon neutrality and occupants’ health, yet not sufficiently explored. This paper aims to optimize a healthy building in Shanghai, China, based on energy consumption, indoor air quality and visual comfort. A four-step optimization method was proposed. Firstly, Latin Hypercube-Soubert sampling method was used to generate 375 design samples and performance data through computer simulation and calculation. Secondly, five different machine learning approaches were applied for prediction model development. Thirdly, the best prediction models were coupled with eleven optimization algorithms to find Pareto solutions. Finally, optimization on different combinations of design parameters were conducted. It was found that the back propagation neural network and Pareto Envelope-based Selection Algorithm II were the best prediction models and optimization algorithm. The average reduction of building energy consumption, visual discomfort, and improper indoor air quality hours were found to be 25.73 %, 46.24 %, and 38.34 %, respectively. The recommended windows to wall ratios of the east, south, west and north walls, absorptance of solar radiation and filter types are in the range of 20%–35 %, 10%–45 %, 10%–30 %, 10%–40 %, 0.7–0.9, and S7-S9, respectively. This study contributes to enrich the case study of healthy buildings, provide a quick design optimization approach and analysis on the importance of each design parameter. Its originality lies in the optimization methodology, comparative analysis of prediction models, optimization algorithms, and combination effects of design parameters. The outcomes can guide the building designers in performing energy efficient design while maximizing indoor air quality and visual comfort.

Solar chimney design in rural areas of Anhui, China: CFD simulation, energy and carbon footprint assessment

China is currently undergoing a large-scale renovation of rural buildings. The solar chimney, a passive solar system, emerges as a cost-effective and easily implementable solution, particularly suitable for rural regions. This study designs a solar chimney in the Hui architectural style for renovating residential buildings in rural areas of Anhui province. A selected pilot building serves as the testbed for the solar chimney implementation, with plans to extend the design to other local renovation projects. Computational Fluid Dynamics (CFD) simulations are employed to compare various solar chimney configurations and identify the optimal design for the case study. Results from the CFD simulations highlight the optimal configurations for the pilot building's solar chimney design. Additionally, a comparative analysis of heating and cooling energy consumption is conducted between buildings with and without solar chimneys to assess the energy-saving potential. Furthermore, a life cycle assessment evaluates the environmental impacts of solar chimney construction and the environmental benefits during operation. It is revealed that the solar chimney can reduce building energy consumption. The greenhouse gas emissions associated with solar chimney construction can be offset within one year. The study presents an effect diagram illustrating the renovated building with a solar chimney. This study provides valuable insights into the application of solar chimneys in developing rural areas to enhance indoor comfort and promote energy savings. Additionally, it offers guidance for exploring optimal solar chimney configurations for specific geographical regions areas.

A Framework for Adaptive Façade Optimization Design Based on Building Envelope Performance Characteristics

The adaptive façades serve as the interface between the indoor and outdoor energy of the building. Adaptive façade optimization design can improve daylighting performance, the thermal environment, view performance, and solar energy utilization efficiency, thus reducing building energy consumption. However, traditional design frameworks often neglect the influence of building envelope performance characteristics on adaptive façade optimization design. This paper aims to reveal the potential functional relationship between building façade performance characteristics and adaptive façade design. It proposes an adaptive façade optimization design framework based on building envelope performance characteristics. The method was then applied to a typical office building in northern China. This framework utilizes a K-means clustering algorithm to analyze building envelope performance characteristics, establish a link to adaptive façade design, and use the optimization algorithm and machine learning to make multi-objective optimization predictions. Finally, Pearson’s correlation analysis and visual decision tools were employed to explore the optimization potential of adaptive façades concerning indoor daylighting performance, view performance, and solar energy utilization. The results showed that the optimized adaptive façade design enhances useful daylight illuminance (UDI) by 0.52%, quality of view (QV) by 5.36%, and beneficial solar radiation energy (BSR) by 14.93% compared to traditional blinds. In addition, each office unit can generate 309.94 KWh of photovoltaic power per year using photovoltaic shading systems. The framework provides new perspectives and methods for adaptive façade optimization design, which helps to achieve multiple performance objectives for buildings.

Simulation of low energy building thermal energy cycle in IoT smart city planning based on environmental sensors and deep learning

With the intensification of global climate change, the reduction of building energy consumption has become an important goal of smart city development. By optimizing the thermal energy circulation system, low energy buildings can not only reduce energy consumption, but also improve living comfort. In recent years, with the help of environmental sensors and deep learning technology, the intelligent management of building heat energy cycle has become a research hotspot. The research constructs an intelligent thermal energy circulation system that integrates multiple environmental sensors for real-time monitoring of indoor and outdoor temperature, humidity and other key environmental parameters. A deep learning algorithm is used to analyze the collected data to optimize the control strategy of the thermal energy cycle. Through simulation, the energy efficiency performance of the scheme under different climatic conditions and building types was evaluated. The experimental results show that the control strategy based on environmental sensors and deep learning can significantly improve the thermal energy utilization efficiency of low-energy buildings, and the average energy consumption is greatly reduced compared with the traditional management mode. The system shows good adaptability and stability under different climate conditions. Therefore, the application of environmental sensors and deep learning technology in the thermal energy cycle of low-energy buildings can effectively promote the energy efficiency management of smart cities.

Performance analysis of a fresh air and indoor air co-treatment parallel-loop exhaust air heat pump for buildings

To reduce building energy consumption and solve the problem that the power of traditional exhaust air heat pump is limited by exhaust air volume, an innovative fresh air and indoor air co-treatment parallel-loop exhaust air heat pump (CPEAHP) was proposed, and three operating modes of the CPEAHP were studied. The results showed that the co-treatment mode not only increased the flexibility of system regulation, but also improved the heating performance of the system at low temperature in winter. When the winter outdoor temperature was higher than 0 °C, the temperature efficiency of the co-treatment mode was higher than 100 %, and that efficiency was higher than 100 % under all outdoor temperature conditions in summer. At a winter outdoor temperature of −15 °C, the co-treatment mode could increase the temperature of fresh air by 20.4 °C and increase the temperature of indoor air by 3.1 °C, the heating capacity of the system was 6.3 kW and the COP was 8.7 at this time. At an outdoor temperature of 42 °C in summer, the co-treatment mode could decrease the temperature of fresh air by 22.8 °C and decrease the temperature of indoor air by 3.1 °C, the cooling capacity of the system was 7.3 kW and the COP was 4.5 at this time. These results demonstrated the excellent performance of CPEAHP system, and the application of CPEAHP system was expected to reduce building energy consumption and promote carbon neutrality in the construction industry.

Optimizing Window Configurations for Energy-Efficient Buildings with Aluminum Alloy Frames and Helium-Filled Insulating Glazing

This research investigates building energy consumption in the Fujian region of China, characterized by warm winters and hot summers. The study focuses on window configurations and their impact on heat exchange and solar gain management. Initially examining three aluminum alloy window frames, the study utilizes the Multi-Quality Metric Calculator (MQMC) software V1 to assess the benefits of filled insulating glass. The reference values for the heat transfer coefficient, visible transmittance, and sun shading coefficient are established. Subsequently, Ecotect software V5.6 is employed to conduct a comprehensive year-round energy consumption simulation analysis, identifying an optimal window layout tailored to Fujian’s climate. In the Fuzhou simulation, aluminum–plastic co-extruded windows exhibit the lowest cooling energy consumption, while aluminum alloy windows have the highest. Summer cooling energy consumption, comprising about 75% of the total annual energy usage in hot summer and warm winter regions, significantly influences overall energy consumption. Windows made of aluminum–plastic co-extruded material with superior thermal insulation qualities can greatly reduce building energy consumption. The results contribute valuable insights to sustainable building practices and energy-conscious designs in regions characterized by warm winters and hot summers.

Dynamic insulation technology in buildings subject to intermittent heating and cooling, Part A: Iraqi case

In harsh climates like Iraq, characterized by extreme temperatures and energy shortages, dynamic insulation technology holds great potential to significantly reduce energy consumption and enhance thermal comfort. Dynamic insulation technology reduces building energy consumption by adjusting thermal conductivity based on climate changes. This article reviews existing literature and numerically evaluates the effectiveness of dynamic insulation technology in buildings subject to harsh climates, specifically focusing on the case of Iraq. The first part of our articles aims to provide a comprehensive overview of dynamic insulation technology and its potential effectiveness in Iraqi structures subject to intermittent heating and cooling. The collected data guides the design and implementation of future studies and experiments. The study predicts the dynamic insulation performance of an office in Baghdad compared to conventional insulation, considering factors such as lighting, number of residents, equipment, and solar gains. The results indicate that applying dynamic insulation techniques in Iraqi buildings can reduce energy consumption by 28% during the heating season and 11% during the cooling season. Implementing this technology can make a significant contribution towards creating a more sustainable and comfortable environment in harsh climates, examined in Iraqi buildings, as a model case. Practical Applications: The study contributes to the evaluation of dynamic insulation technology in Iraqi buildings. Focusing on Iraq's harsh climate provides valuable insights into the effectiveness of this technology. Scientifically based recommendations guide the design of buildings in such environments. In addition, the study investigates the performance of intermittent cooling and heating, ensuring practicality. Overall, it enables professionals to create sustainable and efficient built environments in Iraq.

Bio-based composite phase change material utilizing wood fiber and coconut oil for thermal management in building envelopes

Bio-based materials are attracting substantial attention for their eco-friendly attributes within the construction field, where they facilitate energy saving and emissions reduction. However, the performance of it, such as thermal properties, needs to be improved. Fully utilizing bio-based materials, we developed a novel composite phase change material (PCM), A-WF/CO/h-BN, with high thermal storage properties designed for application in building envelopes. It incorporates coconut oil (CO) as the PCM featuring an optimal phase change temperature. Hexagonal boron nitride (h-BN) was chosen to enhance the thermal conductivity. Acetylated wood fiber (A-WF) was employed as the supporting material. The prepared A-WF/CO/h-BN sample exhibits excellent and rapid heat storage and exothermic capabilities. In the experiment of thermal performance evaluation, the cold end of the A-WF/CO/h-BN sample is cooler than that of the A-WF when both hot ends are heated. Results indicate that the proposed A-WF/CO/h-BN sample can effectively delay the heat transfer and inhibit the temperature rise and fall. For these superior properties, when the A-WF/CO/h-BN sample is applied in building envelopes, it can minimize the heat transfer from the envelope to the interior and inhibit indoor temperature fluctuation. Thus, it can reduce building energy consumption and carbon emissions while achieving indoor thermal comfort.

Improving energy consumption for dynamic intake and exhaust FAÇADES: A new setup design: Part B

Dynamic insulation technology adjusts thermal resistance to reduce building energy consumption in response to climate changes. Sustainable building practices prioritize optimizing the building envelope to enhance energy efficiency and regulate the interaction between indoor and outdoor environments. The previous part of this study (Part A) provided an overview of dynamic insulation technology and its potential effectiveness in Iraqi structures with intermittent heating and cooling. The successful implementation of dynamic thermal insulation necessitates careful planning and design solutions that balance performance and efficiency. This paper (Part B) three wall models (static, dynamic, modified dynamic) to evaluate their thermal performance during the heating season. The results demonstrate that the intake facade achieves a preheating efficiency of 77% for the dynamic wall and 81.8% for the modified dynamic wall at the maximum permissible fresh air limit. This improvement in efficiency enhances the quality and conditions of fresh air intake. Additionally, the modified dynamic wall exhibits a notable 50% reduction in pressure loss compared to the dynamic wall, resulting in lower intake or exhaust fan power and thus energy consumption. The results of this paper will guide the presentation of cooling season results and the experimental aspect of future work, offering valuable insights for further exploration. Practical applications This study aims to enhance the efficiency of dynamic facades by investigating the physical phenomena within wall layers. The paper delves into the determination of optimal airflow patterns within facades, the assessment of airflow path modifications, and the evaluation of energy efficiency achieved by implementing dynamic insulation at the intake and exhaust facades during the heating season. The findings contribute to streamlining design complexities and expanding design options for specific climates, thereby ensuring the pragmatic implementation of this technology.

Application of multi-stage ionic wind technology in glass curtain walls for enhanced thermal insulation performance

Glass curtain walls are widely used in architecture due to their aesthetic appeal and brightness. However, their thermal insulation performance is relatively poor, with natural convection within the cavity contributing significantly to overall heat transfer. To enhance the thermal insulation of double glazing curtain walls and reduce building energy consumption, we propose installing a multi-stage ionic wind generator on the curtain wall to weaken natural convection using ionic wind.In this paper, we introduce an ionic wind generator based on a wire-plate electrode configuration arranged in a plane, demonstrating that it follows the same discharge laws as electrodes arranged in space. An experimental platform was established to investigate the effect of multi-stage ionic wind on reducing natural convection within the cavity. The results indicate that ionic wind interference effectively weakens natural convection, thereby improving the thermal insulation of the glass curtain wall. Specifically, when voltages of 10 kV, 15 kV, and 20 kV are applied, the overall heat transfer coefficient of the double glazing cavity decreases by 5.56 %, 10.35 %, and 14.39 %, respectively. Numerical simulations visually record the process of weakening natural convection and provide electric field data for ionic wind. Additionally, we evaluated the Coefficient of Performance (COP) of the experimental cavity, which reached a maximum of 2.4 in our experiments. Future research can focus on optimizing energy efficiency. This study innovatively explores the feasibility of improving the thermal insulation of glass curtain walls using ionic wind, contributing to reducing building operational energy consumption and mitigating global warming.

Assessment of photovoltaic power generation and radiative cooling potentials in old residential districts: A case study of Shenzhen

Building-integrated photovoltaic (PV) and radiative cooling (RC) are promising technologies for attaining the zero-carbon target in building industry. The PV and RC materials can be utilized for energy-saving renovations in building envelopes of existing residential districts. Nowadays, it is common practice to add thermal insulation to old residential districts to reduce building energy consumption. Whereas the development of PV and RC technologies provide opportunities of renewable energy utilization on building envelops in old residential districts renovation. The space for installing PV and RC materials on the roofs and facades is restricted. Hence, assessing and contrasting the efficacy of PV and RC materials in different sections of building envelopes is important from both energy and economic aspects consideration.This study employed the Rhino-Grasshopper platform to assess the energy and economic performances of PV and RC technologies when installed on roofs and facades with varying orientations. A typical old residential district in Shenzhen was employed as an example. The objective was to enhance the allocation of PV and RC components to attain optimal energy and economic outcomes. The life-cycle equivalent energy saving was used as economic indicator. Results demonstrated that PV is more suitable on roofs application, whereas RC is more suitable for facades. It is profitable to apply RC on the north facade whereas PV can be profitable when applied to the other envelops. By applying PV and RC to all old residential districts in Shenzhen, the annual PV power generation and cooling energy saving from RC are as high as 5299 GWh and 277 GWh. This study demonstrated that PV and RC are promising technologies in energy-saving renovation of old residential districts. The developed methodology can be applied in renovation projects to achieve optimized designs.

Research on geometry optimization of park office buildings with the goal of zero energy

At the conceptual design stage, the building geometry design can predict the building load demand and renewable energy application potential to some extent. Geometry design interventions are critical to efficiently achieving the goal of zero-energy buildings. In the existing studies, the typicality and representativeness of the object geometry in the practice project are not high, and the influence of different geometry indices on energy savings and photovoltaic (PV) utilization potential under the same type of plane shape is rarely considered. In addition, the surrounding building shading situations considered are single. There is still significant room for improvement in the typical geometries selection and optimization condition settings. This paper presents a study of three typical park office building geometries in hot summer and cold winter regions. An optimization method based on the genetic algorithm and energy consumption simulation is proposed that takes into account both building energy savings and PV utilization potential improvements. The geometry-related indices of each typical geometry are then optimized under different PV layout scenarios and surrounding shading situations, and suitable geometry design strategies for typical office buildings are proposed under each optimization scenario. Geometry optimization can significantly reduce building energy consumption (the building energy-saving rate is 1.3–10.7 %) and increase PV generation (enhancement of 13.37–66.67 % for PV generation potential), thus lowering the net energy consumption of buildings. The findings of this study can be used to guide the design of park office building geometries in hot summer and cold winter regions with the goal of zero energy, as well as to promote the practice of zero-energy office buildings at the regional and national levels.

On-site evaluation of indoor thermal comfort and energy performance of a liquid-desiccant assisted air-conditioning system in a high-latent-load building

Indoor humidity control is increasingly important because indoor sensible heat ratio decreases to reduce building energy consumption. However, reference vapor compression cooling systems exhibit energy inefficiency and limitations in maintaining indoor thermal comfort. Therefore, this study proposes an alternative heat-pump-driven liquid-desiccant air-conditioning system, independently controlling air temperature and humidity. The reference and proposed systems are applied to a high-latent-load building to investigate their onsite indoor thermal comfort and energy performance empirically and simultaneously under various outdoor summer conditions. The reference system exhibits a thermal comfort satisfaction ratio of 97% only under limited hot and dry weather. Conversely, the thermal comfort satisfaction ratio sharply drops to 2% or less under humid weather. The proposed system consistently achieves a high thermal comfort satisfaction ratio exceeding 90% under various outdoor summer conditions. In empirical comparisons, the proposed system can maintain a thermally comfortable room for an hour while achieving energy savings exceeding 92.4% and 12.1% under warm and humid (rainy season) and hot and humid outdoor conditions, respectively. The proposed system is concluded to consistently maintain indoor thermal comfort while using energy efficiently, demonstrating its widespread applicability for general high-latent-load buildings characterized by low indoor sensible heat ratio values of 0.56 on average.

Multi-objective optimization of building integrated photovoltaic windows in office building

Building-Integrated Photovoltaics (BIPV) offer a promising solution to enhance building energy efficiency and reduce building energy consumption. Among the various application of BIPV, BIPV windows stand out as an intriguing and notable example. This paper investigates an office building with BIPV windows in five different climatic cities in China. The study considers four variables, including building orientation (BO), window size (WZ), window visible light transmittance (VLT), and type of PV (TOPV). The objective is to minimize both the annual net electricity cost (ANEC) and the extra investment cost of BIPV windows. To simulate the design variables and objective functions, the jEPlus software is employed. Additionally, the jEPlus + EA software uses the SRC and Morris algorithms for sensitivity analysis of design parameters. The multi-objective problem is addressed using the NSGA-II. By conducting optimization, a set of Pareto optimal solutions were obtained. The results demonstrate that the building with BIPV windows can save a minimum of 6.83 % annual electricity costs. Moreover, the static investment payback period for all cities ranges from 7 to 14 years, indicating the economic feasibility of implementing BIPV windows.

Layered laser-engraved wood-based composite capable of photothermal conversion and energy storage for indoor thermal management in buildings

Wood is used more and more in building. Phase change materials (PCM) with automatic temperature regulation and heat storage function have been widely concerned in the field of building energy conservation. However, phase-change materials have poor light induction and cannot absorb sunlight during the day in time, resulting in limited heat storage effect. For the purpose of achieving efficient energy collection and utilization, a laser-engraved method was employed in this study to directly generate a three-dimensional grid structure on the surface of wood. Then, the eutectic mixture of capric acid (CA) and stearic acid (SA) and nano-SiO2 composite PCM (CPCM) was impregnated into the supporting substrate with photothermal conversion capability. The obtained laser-engraved wood (LEW) loaded with CA-SA/Nano-SiO2 showed a latent heat of 64.706 J/g, a thermal conductivity of 0.732 W/(m⋅K) and a photothermal conversion efficiency of 64.46 %. Additionally, the three-dimensional porous structure of wood and the addition of nano-silica set up a double barrier for the leakage of PCM. Therefore, CPCM have prospective applications as indoor thermal insulation materials. In this research, a simple laser engraving method was adopted to endow the wooden substrate with photothermal conversion ability, which provides an idea to expand the application of photothermal conversion materials in the field of phase-change energy storage. In addition, the building simulation software validated the potential of CPCM in stabilizing indoor temperatures and reducing building energy consumption.

Weathering resistance of novel sustainable prefabricated thermal insulation wall

External walls, serving as the primary medium for heat exchange between the building and the external environment, has its thermal loss comprising the largest proportion of building energy consumption. Therefore, enhancing the thermal insulation capacity of the wall is of great significance in reducing building energy consumption. In this paper, a novel sustainable prefabricated expanded polystyrene (EPS) thermal insulation wall panel with irregular column frame structures was developed. And weathering tests combined with finite element simulations were conducted to investigate its weathering performance and degradation patterns. The results revealed that In the weathering test, the panel surfaces did not exhibit apparent water seepage cracks, powdering, hollowing, peeling, etc. There was no occurrence of facing brick detachment or damage. The outer surface concrete of the wall panel experienced resistance during normal thermal expansion and contraction, generating compressive stress during expansion and tensile stress when contracted. In addition, the bond strength of the specimens decreased by 8.1% after the thermal-rain cycles, 5.1% after the thermal-cold cycles, and 12.1% after the freeze-thaw cycles. In the numerical simulations, the temperature stress at various positions on the concrete wall had a noticeable mutual restraining effect on the force deformation of the nearby concrete. There was a significant risk of cracking in the middle and around the opening, particularly in the lower part of the wall panel. This study serves as a basis for the degradation analyses and optimization design of the sandwich insulation wall panels for sustainability.

A novel biogenic porous core/shell-based shape-stabilized phase change material for building energy saving

The application of phase change materials (PCMs) for thermal storage in construction can effectively reduce building energy consumption. However, high costs and vulnerability to leaks have hindered their application. The present study proposes two approaches for the synthesis of porous supporting matrices derived from rice husk, resulting in the formation of rice husk silica (RHS) and rice husk carbon (RHC). Then, n-octadecane and the porous materials were combined by vacuum impregnation, while the leakage resistance performance of the composite PCMs was enhanced by applying epoxy resin coating to create a shell-core structure. The results show that the n-octadecane/RHS and n-octadecane/RHC composite PCMs exhibit high latent heat potential of 106.5 J/g and 116.3 J/g, respectively. Both porous supporting structures provided the PCMs with robust structural stability and exceptional thermal conductivity. The thermal conductivity of the n-octadecane/RHS composite PCMs and n-octadecane/RHC composite PCMs reached 0.52 W/(m K) and 0.41 W/(m K), respectively. The thermal properties of the biogenic porous core/shell-based shape-stabilized PCMs were characterized by an analog T-history method, and the results demonstrated that the composite PCMs exhibited excellent and rapid heat storage and exothermic capabilities. After undergoing 300 complete heating and cooling cycles, the composite PCMs demonstrate exceptional thermal reliability and possess a high enthalpy capacity. Finally, the impact of the pore structure of RHS and RHC on the crystallization behavior of n-octadecane was discussed. Both composite PCMs can be regarded as environmentally friendly construction materials with promising thermal and acoustic properties.

Experimental and numerical study on the shear performance of stainless steel-GFRP connectors for use in precast concrete sandwich panels

Precast Concrete Sandwich Panel (PCSP) is composed of concrete load-bearing panels, thermal insulation panels, and decorative panels, which are assembled through connectors, integrating load-bearing, thermal insulation, and decorative functions. The connector bears the main shear force between the wall panels, and the shear resistance and insulation performance of the connector largely determine the mechanical stability and insulation effect of the wall panels, which is a key component in PCSPs. The current common practice is to cross assemble stainless steel insulation (SSI) connectors and Glass-Fiber-Reinforced Plastic (GFRP) connectors into PCSPs, which can reduce building energy consumption and save resources while meeting strength and insulation requirements. A large-scale pull-out test on a PCSP with intersecting SSI-GFRP connectors was conducted in this paper. The damage process and damage pattern of PCSP were observed and the shear performance of SSI-GFRP connectors was analyzed. Secondly, a numerical analysis model of the test PCSP was built using ABAQUS finite element software and its validity was verified through the test data. In addition, parameters such as connector diameter, connector number ratio and concrete strength were analyzed for their effect on the shear performance of SSI-GFRP connectors and it was found that connector diameter and connector number ratio had a significant effect. Finally, it is found that there are some differences between the classical theory for calculating the shear performance of SSI-GFRP connectors and the actual results. A theoretical correction factor (ζ) is given to improve the accuracy of the calculation of the classical theory, and its influencing factors and changing rules are investigated.

Dimensionless resolutions for heat flux decrement factor and time lag of the wall during cyclic variations in outdoor air temperature

The heat flux decrement factor (DF) and time lag (TL) are two vital indicators for assessing wall dynamic thermal performance. However, computing these indicators involves complex variables such as material thermal properties, wall thickness, and others. Therefore, exploring the inherent relation between these two indicators and the influencing parameters is an urgent problem for reducing building energy consumption. To this end, an analytical method based on the auxiliary function was employed to calculate the heat flux DF and TL of a single-layer wall. Then, the impact of the influencing factors on heat flux DF and TL were evaluated. The results showed that heat flux DF and TL are only determined by two dimensionless parameters: diffusion length and thermal efficiency coefficient. The heat flux DF decreases by at least 5 times as the diffusion length varies from 0 to 2. Besides, it is also affected by the diffusion length when the thermal efficiency coefficient (ε) is less than 5, and the smaller the ε, the smaller the heat flux DF. On the other hand, the heat flux TL increases linearly with the diffusion length initially but declines precipitously as the diffusion length approaches 6–7. When the diffusion length is the same, the heat flux TL slightly decreases as the thermal efficiency coefficient increases.

In situ carbothermal reduction of oxygen vacancies in monoclinic WO3-x film for dual-band electrochromic windows

Dual-band electrochromic windows have emerged as a promising approach to reduce building energy consumption. However, developing facile and effective method for preparing single-component dual-band electrochromic material remains a challenge. Herein, an in situ carbothermal reduction strategy was utilized to fabricate monoclinic oxygen-deficient tungsten oxide (WO3-x) for high-performance dual-band electrochromism. Polyvinylpyrrolidone (PVP–K90) underwent transformation into amorphous carbon at high temperature, serving as the reducing agent embedded in the tungsten oxide film, and in situ inducing the formation of oxygen vacancies during annealing treatment. Lastly, the amorphous carbon was gasified without weakening the transmittance of WO3-x film. The content of oxygen vacancies in WO3-x could be modulated by controlling the added amount of PVP-K90. The intrinsic generation of oxygen vacancies not only obtained a strong local surface plasmon resonance (LSPR) absorption in near-infrared (NIR) range, but also improved lithium ion (Li+) diffusion in WO3-x film. The WO3-x electrochromic film exhibited excellent dual-band electrochromic performance in optical modulation, switching time, coloring efficiency, bistability, and cycle stability. Furthermore, the WO3-x film was applied to electrochromic window to verify its available regulation in solar illumination and heat, indicating that the designed modification strategy has potential for developing a single-component dual-band electrochromic window with outstanding performance.