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Different heating processes were applied to pretreat the pulp and paper mill sludge to enhance the hydrolysis stage. Hot air oven, autoclave, microwave and water bath were used for comparison. Chemical analyses exposed that all the pretreatment methods have shown improvement in solubilisation of organic matter. Among the pretreatments studied, heat transfer through hot air (80 °C for 90 min) mode had the highest impact on sludge solubilisation. There was an increase in cellulose (P = 0.0096), acid soluble (P = 0.0053) and insoluble lignin (P = 0.0012), but decrease in hemicellulose (P = 0.0009) content after pretreatment. The XRD and FT-IR spectroscopic characterisation shows the development of aliphatic, unsaturated and carbonyl carbon functionalities in the pretreated samples at higher severities. FESEM picture also confirms the change in structure after pretreatment. Thus, pretreatments contribute to disruption of the lignocellulosic structure making the cellulose easily accessible to acidogenic microorganisms. [ABSTRACT FROM AUTHOR]

Pyrolysis process of coffee paper cup samples was investigated in a flow stream of nitrogen at different heating rates (10, 20, 30 and 40°Cmin−1), using thermo-analytical techniques. It was found that second pyrolysis stage can be described by Šesták-Berggren (SB) autocatalytic model, with mechanism function f(α)=α0.011(1−α)1.459. Based on analysis of SB kinetic exponents (designated by M and N), it was found that second pyrolysis stage is mainly controlled by chemical process, involving reactions with reaction-order (n) higher than unity. Applying specific statistical analysis, in order to obtain precise distribution of reactivity, the discrete (binomial) distribution has shown that there are two important areas of current distribution for corresponding energy outcomes, within the apparent activation energy as random variable. The first "concentration" area of energy outcomes corresponds to start of chain end depolymerization reaction forming levoglucosan at high enough temperature region, while second "concentration" area of energy outcomes includes occurrence of macro-radicals in liquid phase propagate with radical addition on unsaturated C-C bonds, with cross-linking and formation of small chemical species. It was found that further elevating of temperature (above 340°C), will leads to fact that rate of tar-forming reactions increases and formation of char decreases. [ABSTRACT FROM AUTHOR]

A solution-processed conductive paper heater (CPH) with metallic features is used as a new class of low voltage ignitor of nanoenergetic materials (nEMs). In contrast to conventional electrothermal ignition techniques that typically require high operating voltages, the combustion of a paper substrate with a relatively low ignition point generates high thermal energy instantaneously, which makes it possible to ignite nEMs even at low voltages as low as ∼1 V. In addition, the ignition and explosion properties of CPH-based low voltage ignitors are highly controllable and reproducible, mainly due to their simple fabrication and reliable electrical properties. Based on the low voltage ignition property, a compact remote ignition system is demonstrated by integrating wireless a switching circuit, portable batteries, and heater mounter in a small plastic package and operated remotely to ignite the nEMs. [ABSTRACT FROM AUTHOR]

Abstract Inkjet printed electronic devices, as a new kind of thin film electronics, have got much attention due to their advantages of fast manufacturing, flexibility and cost saving. The challenge of this field is efficient sintering at low temperature, which is necessary for the wearable and flexible electronic application, especially on heat-sensitive substrates, e.g. papers and plastics. To solve the cracking phenomenon at high-temperature sintering which is a common problem for photo paper substrate, we proposed an effective multiple-step method combining acetone washing with LED-assisted low-temperature heating. The sintering temperature was reduced dramatically through using this method, with the resistivity of silver tracks treated at 70 °C equal to that treated by thermal sintering at 150 °C. Thus, we broke through the bottleneck resulting from high-temperature sintering of cracking of long conductive tracks. The mechanisms of the capping agents' removal and LED-assisted low-temperature sintering were investigated by X-ray photoelectron spectra (XPS). Besides, the size of silver nanoparticles (NPs) was well controlled by adjusting the dropping speed of the solution, which helped improve the electrical performance of the ink. The surface properties including morphologic roughness, bonding strength and flexibility were also investigated. By combining inkjet-printing and post-processing method, we showed exemplary applications of paper electronics with fast-manufactured, no-mask-required, pattern-programmable and precisely-controlled characteristics. Our results provide a simple and convenient approach for developing high-performance flexible thin-film electronic devices based on inkjet printing technology. Highlights • Substrate-harmless low-temperature sintering for paper electronics • High-yield silver nanoparticles with controlled size • Applications of flexible electronic circuits, 3D RFID antenna and strain sensor • Good mechanical performance of printed tracks withstanding 1000 bending cycles [ABSTRACT FROM AUTHOR]

• Paper-based microfluidic device combined with a graphene heater for silicon nanodots synthesis. • Total carbohydrates determination based on fluorescence intensity of the silicon nanodots. • Heater temperature controlled by portable electronic system with wireless communication. We report a simple, rapid, low-resource and one-step method for formation of fluorescent silicon nanodots (SNDs) in a microfluidic paper-based analytical device (μPAD) incorporated in a reusable, portable and flexible heater for determination of total carbohydrates. The synthesis of SNDs is based on the redox reaction between (3-aminopropyl) triethoxysilane (APTS) reagent and carbohydrates, which act as a reducer. The graphene-based heater was fabricated by laser ablation of Kapton polyimide. Thereby, the developed system heat the μPAD during the synthesis of SNDs at 80 °C for 30 min. The blue emitting SNDs formed have an emission peak wavelength at 475 nm. We used a digital camera and smartphone for the quantitative analysis of total carbohydrates expressed such as index of glucose or fructose with grey scale value as the analytical parameter. Under the optimal conditions, the method has a low detection limit (0.80 μM for glucose and 0.51 μM for fructose, respectively), and a linear response (10–200 μM for glucose and 10–100 μM for fructose). The method has been applied to the determination of glucose in biological fluids (serum and urine samples). In addition, determination of total carbohydrates in commercial juices and teas have been carried out. [ABSTRACT FROM AUTHOR]

Ultrafast high-temperature heating methods based on the Joule heating of carbon heaters can dramatically shorten the time required for material synthesis/sintering. However, commonly used porous carbon heaters cannot provide stable high temperatures in air, limiting their applicability to the processing of atmosphere-sensitive materials. In this study, we present a novel configuration for ultrafast high-temperature heating in air using commercial graphite paper. This configuration enables stable high temperatures of ~1330–2230 °C in air, on the time-scale of minutes, and ultrafast heating rates, reaching ~104 oC/min. We describe the mechanism behind the excellent performance of our proposed configuration, and further demonstrate its flexibility and controllability by considering ultrafast high-temperature sintering of ZnO ceramics with tunable microstructures using different heating profiles. Our configuration provides a complementary approach to simplifying the ultrafast high-temperature heating process, reducing costs, and meeting the requirements of synthesis/sintering in air. [ABSTRACT FROM AUTHOR]

Recent advances in renewable energy research have suggested the fuel cell as a promising future energy source. Compared to the conventional power generation process, which has multiple-step conversion, a fuel cell is a single-step conversion process and produces power and sometimes heat. The efficiency of the individual existing conventional system is increased by integrating with fuel cells. The purpose of hybridization is to fulfill the demand and supply of power and heat. This paper starts with the historical development of fuel cell proceed with different categorize of hybrid systems. Discuss the possibilities of integration of existing fuel cell with other existing technologies such as SOFC-PEMFC, FC-CHP, FC-GT-ST, FC-Hybrid Vehicle, FC-PV/Battery. Numerical modeling can be done for each hybrid system considering mass balance, energy-exergy balance. At the end of the paper a discussion on the technical, economical, and commercial challenges and their solutions with future possibilities is presented. [Display omitted] • Study the integration potential of fuel cell with other power generating systems. • Fuel-cell hybrid configurations are analyzed. • Modelling aspect of various fuel cell hybrid configurations were summarized. • Fuel cell behavior with power and heat generation is presented. [ABSTRACT FROM AUTHOR]

In this paper, we generalize a fast Fourier transforms (FFTs) based preconditioner and propose a novel α -absolute value preconditioner for all-at-once systems from heat equations. Our preconditioner is symmetric positive definite and can also be computed efficiently using fast Fourier transforms or discrete sine transforms (DSTs). Furthermore, we prove that the corresponding preconditioned matrix has a unitary-plus-low-rank decomposition, and the eigenvalues of the preconditioned matrix are clustered at ±1, which leads to fast convergence rate of the preconditioned MINRES method. Finally, numerical examples on all-at-once systems from heat equations with different discretization scheme demonstrate the effectiveness of our new preconditioner. [ABSTRACT FROM AUTHOR]

Waste heat is one of the major problems associated with the energy system. This paper discusses an energy, exergy, and emissions approach for the hybrid system by utilizing waste heat to the maximum extent. A thermoelectric generator (TEG) is incorporated to utilize the low-temperature waste heat from a hybrid model of a solid oxide fuel cell (SOFC) and a combined heat and power (CHP) system. SOFC is an electrochemical cell that generates power at high temperatures through an electrochemical reaction. The high-temperature, unutilized fuel leaves the SOFC, which is burned in the afterburner. The afterburner temperature controls the operating temperature of SOFC. Here, three recuperators are used to utilize this high-temperature waste heat to improve the performance of SOFC and simultaneously generate heat power from the water or gas recuperator. TEG is an auxiliary power production technology that converts waste heat into energy. A novel integration of TEG with SOFC–CHP hybrid system to utilize the low temperature waste heat, is employed. The main goal of this study is to analyze a novel SOFC–CHP-TEG hybrid system in terms of its thermodynamics and emissions. A Two stage TEG is integrated with the SOFC–CHP hybrid system. The simulation model of high temperature fuel cell (SOFC) is developed on MATLAB and validated with published results. This study analyses the impact of pressure ratio and afterburner temperature on the performance of SOFC–CHP-TEG. To do this, perform energy and exergy assessments using the principles of the first and second laws of thermodynamics. A novel exergy-based sustainability index with emissions analysis for the proposed SOFC–CHP is presented. The achieved overall energy efficiency is 62.54% at a pressure ratio of 12 and an afterburner temperature of 1000 K. With an increase in pressure ratio and temperature, the level of CO emissions reduces significantly. [Display omitted] • A novel energy exergy for SOFC–CHP-TEG system is presented. • Exergy based performance is compared and achieve 56.62. • Utilization of waste heat via TEG. • Energy efficiency of SOFC–CHP-TEG is 62.54% at rp = 12 and afterburner temperature of 900 K. [ABSTRACT FROM AUTHOR]

Self-heating of sensing elements on gas sensors is an effective solution to avoid using external heaters. In this paper, a self-heated hydrogen gas sensor is presented. The sensor was created using the DC sputtering method, which involved fabricating it on a thermal-insulating Kapton flexible substrate. This process utilized a thin film of SnO 2 with thick 50 nm that was modified with nanoclusters of Pt, serving as the sensing material. The SnO 2 /Pt material film was analyzed for microstructure and composition by SEM, XRD, and XPS analysis. Infrared images show that the self-heating effect is mainly concentrated in the strip of gas-sensitive material. It showed many good performances, such as high sensitivity (able to detect down to 50 ppm of H 2), good selectivity (poor response to CO, NH 3 , H 2 S, and NO 2), the sensor's performance is little changed by environmental humidity, and low power consumption (89 μW at 5V). The sensor is also stable and low-cost, suitable for portable H 2 detection devices due to its low generated heat and small size. • The SnO 2 /Pt thin film sensor was fabricated on flexible substrate (Kapton). • The sensor showed good performance to H 2 gas (able to detect down to 50 ppm H 2). • The sensor showed good selectivity (poor response to CO, NH 3 , H 2 S, and NO 2). • The self-heated sensors consume ultralow power (89 μW at 5 V). • The fabricated sensor slightly reduced its sensitivity at ambient humidity of above 90% R.H.. [ABSTRACT FROM AUTHOR]

The present paper deals with the influence of different hydrogen enrichment on oxy-fuel combustion of natural gas, enabling important insights regarding decarbonization of high-temperature processes. Experiments were conducted using a high-impulse multifuel burner for industrial applications for hydrogen contents between 0 and 100%. The fuel input varied between 100 and 140 kW, while water-cooled lances were used to simulatethermal loads. The analysis included temperature measurement points, atomic and energy balances and the cooling capacity of the thermal load for steady-state operation. The obtained results show that the flue gas temperature decreases by up to 126 K for pure hydrogen, while the cooling capacities of the thermal load increased by up to 16.3% at constant calorific energy input. The flames for different hydrogen enrichments were also compared visually. Overall, all investigated fuel blends were highly interchangeable with the investigated burner and showed high potential for a timely decarbonization of industrial heating. • Oxy-fuel combustion of hydrogen-enriched natural gas with 0–100% H 2. • Experimental analysis of a semi-industrial scale furnace at steady state conditions. • How the flame length, heat distribution and flow rates depend on H 2 content in NG. • Analysis of mass and energy fluxes with positive pressure within the furnace. • Promising solution for timely CO 2 reduction in high-temperature processes. [ABSTRACT FROM AUTHOR]

• A new finned tube heater used for household frost-free refrigerator is proposed. • The duration of the defrosting cycle is shortened by 12%. • The overall energy consumption is reduced by 0.025 kW·h (10.4%). • FC temperature rise decreases by 2.4 °C. For frost-free refrigerators, the tubular metal sheathed type defrosting heater installed at the downstream of the evaporator is usually stainless steel circular tube defrosting heater (CTDH). During the defrosting process, a large part of the heat leaks into the cabinets of the refrigerator, causing the cabinet temperature to rise. This paper proposes a finned tube defrosting heater (FTDH) by using an aluminum alloy finned square tube as the metal sleeve of the defrosting heater. The external surface area of the defrosting heater is greatly increased due to the existence of the fins, thus strengthening the natural convection between the air and the defrosting heater and shortening the defrosting duration. The defrosting performance (defrosting duration, temperature rise, energy consumption) between FTDH and CTDH are compared experimentally. Results show that the whole defrosting cycle duration is shortened by 12%, while the freezer cabinets (FCs) temperature rise is reduced by 2.1 °C and the maximum FC temperature is reduced by 2.4 °C. In addition, the shorter defrosting operation cycle and the lower FC maximum temperature result in a 10.4% reduction in energy consumption of the whole defrosting cycle. In conclusion, FTDH is promising in refrigerators for reducing the FC temperature rise, shortening the duration and decreasing energy consumption during the defrosting cycle. [ABSTRACT FROM AUTHOR]

The surface faceting of metals has been studied for several decades, typically using experimental methods such as low-energy electron diffraction. In the current paper, surface faceting of tungsten pellets was studied during in situ heating inside an environmental scanning electron microscope (ESEM), which allowed for direct, high-fidelity observation of morphological changes in response to high-temperature annealing under a moderate vacuum (0.8 Torr). Additionally, a second set of tungsten samples was annealed in an ultrahigh vacuum chamber (10−8 Torr), albeit without direct observation via ESEM. This study revealed that oxygen plays a crucial role in tungsten surface faceting and in a morphological transition to vertex rounding. Furthermore, this paper discusses relevant techniques for identifying the crystallographic indices of surface facets. It is demonstrated that a combination of electron backscatter diffraction, tilted-sample imaging from multiple angles, and serial sectioning in a focused ion beam system can be effectively deployed to determine the geometry of faceting, which in turn can be verified with the aid of software for generating Wulff shapes. The influence of processing environment on tungsten surface faceting enables the possibility of designing and controlling the morphology and crystallographic facets of tungsten surfaces. • ESEM annealing of W at 0.8 Torr resulted in oxide sublimation and surface faceting. • The surfaces of samples annealed under UHV remained flat and smooth. • Temperature and grain orientation influence W surface facet size and sharpness. • SEM tilted-sample imaging and serial sectioning tomography aided facet indexing. • Wulffmaker software helped determine relative surface energies of low-index facets. [ABSTRACT FROM AUTHOR]

• Saturated-wave theory for snubber modeling is modified to fix three conceptual errors. • The equivalent resistance and inductance of the snubber are recalculated. • Calculating the thickness of eddy-current region no longer relies on external circuit. • The current rise of the model is nearly the same as the experiment with about 10 % over-estimated peak shorting current. Core snubber is a common device used for breakdown protection in auxiliary heating systems. It absorbs energy from the high-voltage power supply to protect the load. The existing snubber models are based on saturation-wave theory, but the theory still has several conceptual problems. In this paper, an improved saturated-wave theory is presented. We consider that the eddy current region of the tape needs to be layered and that there is an unsaturated region in the tape which enables the snubber to be equated to an inductor. Then we divided the working process of snubber into 4 stages and rederived the circuit model of the snubber. The comparison with the existing simulation model shows that the new model in this paper is closer to the experimental data, especially in the rising phase of short-circuit current. It can more accurately analyze the conditions within a few microseconds after breakdown, and give a useful reference for the design of breakdown protection and power supply systems. [ABSTRACT FROM AUTHOR]

Decarbonising the heating sector is one of the key elements to realizing the ambitious dual carbon goals of China, which is the largest carbon emitter and energy consumer globally. Currently, district heating (DH) systems have penetrated approximately 88% of the urban heating areas in Northern China. Nevertheless, around 90% of the heating demand in China still relies on fossil fuels. A larger scale integration of renewable energy and waste heat sources into the DH systems is critical for decarbonising the entire heating sector in China. However, a deeper level of comprehension is required to harness its full potential. This paper provides a thorough investigation of the status, potential, and national policy schemes of renewable energy and waste heat recovery in the DH systems of China. Combined with a critical review of recent literature on relevant areas published in both international and Chinese domestic sources, the trends, challenges, and future perspectives are discussed from scientific research and practical implementation aspects. This paper highlights the synergy of the integration of renewable energy and waste heat sources in DH, the energy efficiency improvements as well as the use of thermal storage technologies through the implementation of 4th generation district heating and smart energy systems that could offer a more economically viable pathway forward. • Focus on renewable energy and waste heat (REWH) in the district heating (DH) systems in China. • A systematic review of REWH in Chinese DH systems from status, policy, and literature aspects. • Identification of research gaps based on the review of both international and Chinese journals. • Policy recommendations proposed to promote REWH in Chinese DH systems. • The introduction of international experiences on REWH in DH for analysis in the Chinese context. [ABSTRACT FROM AUTHOR]

Increasing the demand for water and energy resources as well as the clean energy policies and the need for pollution emission reduction has developed the research on the renewable energy resources. This paper reviews the recent advances in multi-generation units for heat, electricity, and desalinated water production. It tries to investigate the new papers in this arena which were not mentioned in the previous reviews. The main parts of this work introduce the co-generation systems for the production of "water and electricity", "heat and water", and "electricity, water, and heat". The results show that among the solar energy receiving devices, Photovoltaic/Thermal panels (PV/Ts) and parabolic trough solar collectors are the most used in co-generation systems. On the other hand, a combination of solar collectors and power cycles makes them a suitable choice for the establishment of a large-scale co-generation plant. Therefore, solar collector-based electricity and water co-generation systems have at least 10 times more output capacity than PV- or PV/T-based systems. On the other hand, most heat and water co-generation systems can achieve an output temperature of 60 °C or more and produce around 10000 kg/year of freshwater based on system size. Examining the co-generation systems of water, electricity and heat also shows that these systems have a high production capacity compared to other co-generation systems. Systems based on heliostat solar tower can produce maximum powers of more than 18 MW and fresh water of 90 kg/s. • Recent advances in solar multi-generation units are reviewed. • PV/Ts and parabolic trough solar collectors are most used collectors in cogeneration systems. • RO and MED have more applications in solar-based co-generation units. • Using waste heat can increase technical and economic performance of system. [ABSTRACT FROM AUTHOR]

Loop heat pipes, as a type of two-phase thermal control device, can not only eliminate the reliance on pump transportation technology in single-phase fluid circuits, but also utilize the structural features of gas-liquid pipeline separation to reasonably achieve the evaporation and condensation process. Considering that the loop heat pipes have good application prospects in the field of heat dissipation system in space environment, the condensation pipeline layout on its heat dissipation plate has been optimized in this paper to achieve lightweight while meeting the operational constraints. Based on previous research results, different static surrogate model training methods were compared and combined with genetic algorithms to complete preliminary optimization. After observing insufficient accuracy from static surrogate model, dynamic surrogate model technology was introduced. The results show that the dynamic surrogate model based on hybrid update strategy proposed in this paper can balance the local prediction accuracy, the global convergence ability, and the optimization calculation efficiency, which was more efficient and accurate in lightweight optimization. • Lightweight optimization was performed for radiation radiator by surrogate models. • A dynamic surrogate model based on hybrid update strategy was proposed. • The proposed method has good prediction accuracy and convergence. [ABSTRACT FROM AUTHOR]

• Thermal saturation occurs at bore field center due to the confined boreholes in the interior region. • Boreholes at the bore field center are less efficient boreholes. • Shorter boreholes in the interior region, and deeper ones in perimeter could reduce the total BHE-length. • Total BHE-length savings of this design are affected by the borehole spacing. Most studies about vertical borehole heat exchangers (BHEs) tended to focus on optimizing total borehole length with all boreholes having the same depth. This is mainly because most of the vertical BHEs design tools do not have the feature of designing mixed borehole depths at the same bore field. Because thermal saturation occurs over time at the center of the field due to thermal interaction between the confined boreholes in the interior region, reducing depth of these less efficient boreholes is a desired goal. This paper studies the effects of mixed borehole depths where shorter boreholes are designed to be in the interior region, and deeper ones in the perimeter. The python package pygfunction has been adapted in this paper to generate the thermal response factor of a bore field with mixed borehole depths and to simulate its performance in difference design scenarios. The results reveal that total BHE-length could be decreased by up to 10 % in some cases of mixed borehole depths compared with the case of same-depth boreholes. However, since the total BHE-length could increase in few cases, careful examination is crucial when applying mixed borehole depths. [ABSTRACT FROM AUTHOR]

HFC refrigerants as R134a, R404A, R407C and R410A are commonly used in heating, air conditioning and refrigeration (HACR) systems since Kyoto protocol. However, they are phased-out due to their high global warming potential (GWP). There are various options to replace high GWP refrigerants, among all hydrofluorolefin (HFO) fluids, such as R1234yf, represents an excellent alternative. With GWP <1, R1234yf is a promising substitute for R134a. This paper presents the most relevant researches concerning the application of R1234yf in the last decade. This review paper regroups experimental and theoretical studies which assess the performance of pure R1234yf as working fluid of the compression systems such as mobile and residential air conditioning, air and water heat pump, domestic refrigerator and freezer. Studies depict that R1234yf can be recommended for small-scale systems instead of R134a, but an optimization process is necessary to achieve the optimum operating conditions. [ABSTRACT FROM AUTHOR]

In the debate on the decarbonisation of heat, renewable electricity tends to play a much more dominant role than green gases, despite the potential advantages of gas in terms of utilising existing transportation networks and end-use appliances. Informed comparisons are hampered by information asymmetry; the renewable electricity has seen a huge grid level deployment whereas low-carbon hydrogen or bio-methane have been limited to some small, stand-alone trials. This paper explores the regulatory and commercial challenges of implementing the first UK neighbourhood level 100% low-carbon hydrogen demonstration project. We draw on existing literature and action research to identify the key practical barriers currently hindering the ability of strategically important actors to accelerate the substitution of natural gas with low carbon hydrogen in local gas networks. This paper adds much needed contextual depth to existing generic and theoretical understandings of low-carbon hydrogen for heat transition feasibility. The learnings from pilot projects, about the exclusion of hydrogen calorific value from the Local Distribution Zone calorific value calculation, Special Purpose Vehicle companies, holding of liability and future costs to consumers, need to be quickly transferred into resilient operational practice, or gas repurposing projects will continue to be less desirable than electrification using existing regulations, and with more rapid delivery. • This paper explores barriers for the first UK 100% hydrogen distribution project. • Learnings from pilot projects need to be transferred into UK operational practice. • Existing regulations present barriers to gas distribution innovation projects. [ABSTRACT FROM AUTHOR]

Uncertain parameters and factors substantially impact the operational performances of combined cooling, heating, and power (CCHP) systems. This paper constructs a chance-constrained programming model for system design and energy dispatch management of a hybrid solar CCHP system under the uncertainties of solar energy and building loads. The uncertain scenarios with probability distributions are generated in the Latin hypercube sampling and clustering methods. The chance-constrained model transforms stochastic optimization into deterministic optimization based on these scenarios. Then, the multi-objective optimization model of CCHP system considering the performances of economic, energy, emission, and flexibility is established, and the modified ε -constraint method is employed to obtain Pareto solutions. A case study validates the proposed model. The capacities and operational strategies of components in the hybrid CCHP system are optimized, and the impacts of the confidence level of probability distributions of uncertain factors on the optimization results are discussed. The results indicate that the photovoltaic capacity in the hybrid CCHP system declines by 87.5% when the confidence level increases from 0.50 to 0.99. But other components' capacities are raised, and the gas turbine capacity as the key component rises by 10.49%. The energetic and environmental performances of the CCHP system rise with the confidence level, and the operation safety is improved. [ABSTRACT FROM AUTHOR]

Integrated Energy Systems (IES) serve as an effective solution to address grid fluctuations. However, mainstream IES still adhere to established supply strategies such as thermal and electrical non-conversion (TENC), heat determined by power (HDP), and power determined by heat (PDH). These strategies overlook the additional flexibility generated by the synergy between electricity and heat, preventing the full realization of their advantages in supporting the grid. This paper proposes a Flexible Scheduling (FS) operational strategy for IES that maximizes the utilization of flexibility resources to meet the demands of heating, cooling, and electricity while maintaining grid stability. The superiority of this strategy is analyzed through an IES multi-objective optimization scheduling model and a comprehensive flexibility margin model. The results of a case study indicate that the FS strategy reduces total costs by 19.9% compared to TENC, 16.6% compared to HDP, and 5.2% compared to PDH. It exhibits the strongest support for the grid, increasing the overall flexibility margin of IES by 40.5% compared to TENC, 12.7% compared to HDP, and 8.2% compared to PDH. The FS-based IES operational strategy proposed in this paper contributes significantly to the flexible and economical operation of IES. • Established a multi-objective optimization scheduling model for integrated energy systems that considers both economic and environmental factors. • Established a model for the flexibility margin of system electricity and heat. • Proposed the system's "flexible scheduling" operating strategy and validated it. [ABSTRACT FROM AUTHOR]

• Establish an optimization scheduling strategy for electrothermal joint operation. • Increase wind power consumption with electric boiler & heat storage tank. • Simulation shows 87 % wind power absorption rate with electric boiler & heat storage tank. • Combined use of electric boiler & heat storage lowers system operating costs. The intermittency and volatility of wind power and the characteristics of the operating mode of cogeneration units pose certain challenges to the wind power consumption of the power grid. To optimize the performance of the power and heat combined operation system and maximize the wind power consumption, this paper establishes a mathematical model for each component of the cogeneration system, including the thermal dynamic characteristics of the heat network, buildings, cogeneration units, electric boiler, and heat storage tank. At the same time, a scheduling optimization model is proposed, which considers the power load demand, and wind power output of the regional heating system. The research results provide insights and optimal dispatching strategies for ensuring the reliable operation of the power system and heating system and realizing the efficient utilization of wind power. This paper verifies the effectiveness and feasibility of optimizing the cogeneration system and provides a practical solution to the challenge of cogeneration economics. [ABSTRACT FROM AUTHOR]

Traditional flat PV heat pumps has low irradiation density, large PV area, and the PV evaporators are always fixed, causing large area occupation and lots of irradiation missing, which limit the application and system efficiency. To solve the problems, a novel concentrated PV-air dual-source heat pump system (CPV-DSHP) was proposed in the previous paper, but the annual performance and economic comparison with flat PV-DSHP (FPV-DSHP) are still blank, which are extremely concerning to researchers. Besides, the paper also fills related content about the impact of irradiation composition on the system performance and economics, as well as the irradiation comparison on tracking CPV and fixed FPV surface. From the calculation of the validated model, it's found that the CPV-DSHP system could capture 6098 MJ and 2213 MJ more solar energy, and produce 282.21 kWh and 100.16 kWh more electricity in Garze and Hefei in a year. The annual concentration efficiency is 82.73 % in Garze where direct irradiation accounts for 68.89 %, which is only 73.15 % in Hefei with 39.84 %.The COP PVT is annually lifted by 0.40 in Garze. Although the two systems could both get payback in 5∼6 years, the CPV-DSHP only shows economic advantages in places with good direct irradiation conditions like Garze. • A novel concentrated PV-air dual-source heat pump system (CPV-DSHP) is presented. • The annual performance and economic comparison in different cities are supplemented. • The CPV-DSHP could produce 282.21 kWh more electricity in Garze in a year. • The annual concentration efficiency is 82.73 % in Garze with better direct irradiation. • Payback time is 5∼6 years but CPV-DSHP only shows economic advantage in Garze. [ABSTRACT FROM AUTHOR]

• Carbon capturing technology is widely used in fossil fuel power generation sector to reduce the greenhouse gas emissions. • This paper presents a feasibility study of implementing carbon capturing technology on building heating systems. • It evaluates life cycle environmental impacts and costs of implementing carbon capturing on building heating systems and introduces a decision-making framework. • The paper shows carbon capturing technologies have the potential to be implemented in building heating systems compared to other greenhouse gas emissions mitigations technologies. Buildings are responsible for 40 % of the global energy consumption, thus leading to significant climate change and other environmental impacts. Adopting carbon capturing, storage, and utilization technologies (CCSU) can be a solution for reducing greenhouse gas (GHG) emissions from natural gas building heating systems. However, the current knowledge base lacks definitive knowledge on the possibilities and impacts of building level CCSU. The goal of this study is to investigate the feasibility of implementing CCSU technologies in natural gas building heating systems. A comparative performance assessment framework was developed to evaluate the environmental and economic performance of building-level CCSU technologies over their life cycle. These performances were then compared against alternative GHG emissions mitigation methods used for building heating systems. The results obtained by a case study indicated that adopting CCSU technologies in residential buildings is not economically and environmentally competitive against electricity-based heating systems when the regional electricity is generated using renewable energy sources and nuclear energy. However, there is a potential for the building-level CCSU in regions that depend on fossil fuels to generate electricity. The research outcomes will further develop and improve building-level carbon capturing technologies and will provide confidence to stakeholders to invest. [Display omitted] [ABSTRACT FROM AUTHOR]

Although fully automated, operation of the District Heating Systems (DHS) is considered reactive and simplistic since control decisions are most often made based on the real-time ambient temperature. The research presented in this paper is aiming at facilitating proactive DHS control, by using predictive modeling techniques based on modern Artificial Intelligence (AI) architectures, namely the Deep Learning (DL)-based multivariate time-series forecasting. Proactive approach involves controlling fluid temperature in the DHS supply line, based on relevant meteorological features, heat demand in the past and weather forecast. In this paper, we evaluate state-of-the-art DL architectures for multivariate one-step and multi-step prediction based on Long-Short Term Memory (LSTM) approach, namely, stacked LSTM, bi-directional LSTM, encoder-decoder and attention models. The initial results of forecasting heat demand and local explanations are provided for the case of small 8MW DHS. For local explanations, Local Interpretable Model-agnostic Explanations (LIME) was successfully validated. [ABSTRACT FROM AUTHOR]

• Historic library indoor microclimate campaign, methodology and results. • Heritage microclimate risk and prediction risk damage application to a heritage building. • Monitoring and alert protocol. This paper aims to illustrate and give an interpretation of the results emerged from a pilot activity developed within the ROCK project, by the Department of Architecture of the University of Bologna, Alma Mater Studiorum. Through this activity, we studied the indoor microclimate of the University Library of Bologna (BUB), in the Archive and in the Lecture Hall, with the aim to detect how these spaces are affected by the influence of factors such as the outdoor climate and the cooling and heating systems. Moreover, the paper presents the customisation of the probes' alert system and of the probes itself, used for a one-year monitoring campaign started on the 20th of December 2018. In addition, we calculated the Heritage Microclimate Risk index, to verify the level of risk to which the heritage in the Library is exposed due to the indoor microclimate, and the Predicted Risk of Damage index, that evaluate the more specific risks of damage to which precise objects hosted in there are exposed. Therefore, this paper enriches the research field of Historic Indoor Microclimate, started in 2013, which concerns issues as preventive conservation and restoration in historic buildings. The new insights about the Bologna University Library facilitate the possibility to draw up a specific 'Indoor Microclimate Management Protocol (IMMP)' aimed at the preventive conservation of manuscripts and books in historical libraries. [ABSTRACT FROM AUTHOR]

Primary and secondary sludges originating from kraft pulp mill effluent treatment plants represent an environmental challenge. Their final disposal mainly includes landfill or burning in the mill's biomass boiler. Seeking energy self-sufficiency and better environmental outcomes, the pulp industry is looking to develop new waste management strategies. Biogas production is a millennial technology already applied in many fields, but still behind in terms of pulp and paper mill sludges. Due to the high moisture content of sludge, anaerobic digestion shows great potential. This paper aimed to study biogas production using kraft pulp mill primary and secondary sludges under thermophilic conditions, coupling laboratory experiments with mathematical modeling. Methane production was estimated through the Biochemical Methane Potential (BMP). The Process Simulation Model developed by Rajendran et al. [1] was calibrated for kraft pulp mill sludge based on the BMP results. Cumulative methane production from the secondary sludge reached 46.9 NmL CH 4 /g VS in 30 days. In addition, the Rajendran et al. [1] model was shown to be suitable for simulating the methane yield from bleached kraft pulp mill secondary sludge after minor adjustments. The energy balance showed that the anaerobic digestion process under thermophilic condition for kraft pulp mill secondary sludge still is not feasible on large scale, since the heat produced by biogas was smaller than the heat demanded for heating the reactors. [ABSTRACT FROM AUTHOR]

The majority of small district heating systems (DHS) in Poland are supplied with coal and do not have a status of efficient ones according to Energy Efficiency Directive. They should transform into efficient ones by taking an appropriate measures by the end of 2035. At the same time, a significant reduction of CO 2 emissions is expected in this sector. One of the possible solution for such systems is to apply unites fueled with fuels alternative to coal such as biomass. Cost benefits analysis of implementation a biomass ORC (Organic Rankine Cycle) cogeneration unit in municipal district heating system of 22 MW thermal capacity is the subject of the paper. The research included building configuration scenarios of a heat source regarding ORC size and operation modes. Different economic inputs such as electricity, fuel and European Union Allowance (EUA) for CO 2 prices as well as financial support mechanisms were considered. Economic indexes (Net Present Value, Internal Rate of Return and payback times) have been derived for both Polish and German conditions. [ABSTRACT FROM AUTHOR]

In this paper, we study the diffusive limit of the steady state radiative heat transfer system for non-homogeneous Dirichlet boundary conditions in a bounded domain with flat boundaries. By taking account of the boundary layers, a composite approximate solution is constructed using asymptotic analysis. The convergence to the composite approximate solution in the diffusive limit is proved using a Banach fixed point theorem. The major difficulty lies in the nonlinear coupling between elliptic and kinetic transport equations. To overcome this difficulty, a spectral assumption is proposed to ensure the linear stability of boundary layers. Moreover, a combined L 2 - L ∞ estimate and the Banach fixed point theorem are used to obtain the convergence proof. This result extends our previous work [6] for the well-prepared boundary data case to the general boundary date. [ABSTRACT FROM AUTHOR]

• Combination of the absorption and vapor compression heat pump. • Maximum performance enhancements for heating is 45.8%. • Maximum performance enhancements for cooling is 18.9%. • Power savings for heating and cooling are 16.0% and 31.4%, respectively. • Lower the heat-driven temperature for absorption to 60 °C. Decarbonizing the energy sector becomes a key topic to solving man-made climate change. For achieving indoor thermal comfort conditions, conventional heating, ventilating, and air-conditioning systems consume so much energy in both residential and public buildings. In this paper, a novel solar-assisted absorption-compression system for both heating and cooling is proposed to utilize solar thermal energy throughout the year for the heating/cooling supply. The experimental prototype was built and operational modes including solar-assisted heating/cooling mode and vapor compression individual heating/cooling mode. The performance enhanced by assisted heat input of the proposed system is evaluated by comparing it with air-source heat pumps operated under the same ambient conditions. Performance indices consisting of COP ele increment, power-saving ratio (PSR) and energy-saving ratio (ESR) are presented. The results indicate that the combination of the absorption heat pump subsystem and the vapor compression subsystem lowers the heat-driven temperature to 60 °C and thus makes higher solar collection efficiency possible. The maximum of the COP ele increment and the PSR under solar-assisted heating mode are achieved at conditions with 80 °C hot water temperature, of 45.8% and 31.4%, respectively, and the corresponding value for solar-assisted cooling mode are 18.9% and 16.0%. The speed of compressor as well as fan frequency of terminal has a greater influence on heating performance that on cooling performance due to the different coupling mechanisms. [ABSTRACT FROM AUTHOR]

• A photovoltaic-thermal road assisted ground source heat pump system is proposed. • The system could be applied to the buildings far away from heat supply network. • The system performance for building heating is studied by a 10-year simulation. • Influence of design parameters on the long-term operation performance is studied. • The matching relationship between heat exchanger length and road area is optimized. The photovoltaic-thermal (PVT)-ground source heat pump (GSHP) system has been proved to have great potential in improving building energy efficiency, but ordinary PVT collector requires a large installation area and limits the popularization of PVT. In this paper, a novel solar energy collector, called photovoltaic-thermal road (PVTR), is proposed to replace the traditional PVT collector, and a novel energy system that is PVTR-GSHP system is proposed. In order to study the system performance, taking a typical expressway service accommodation building in Beijing as an example, a 10-year simulation is carried out to analyze the heating operation characteristics of the proposed system. Moreover, the effects of the PVTR area, the length and layout of ground heat exchanger (GHE) on the system performance are also discussed. Results show that, when the length of GHE is 5000 m, and the number of boreholes is 25 and the borehole depth is 100 m, the minimum area of PVTR satisfying the soil heat balance and meeting the system power consumption are 187.2 m2 and 216 m2, respectively. When the PVTR area is 216 m2, the minimum GHE length satisfying the soil heat balance is 4000 m. Finally, to realize system zero energy consumption and soil heat balance, the best combination of GHE length and PVTR area is 4000 m and 216 m2 under the cases of this paper. And in this case, the average COP HP and COP sys in ten years are 5.59 and 2.31 respectively. [ABSTRACT FROM AUTHOR]

This paper experimentally investigates the effect of increasing ice thickness at a heater's edge on the thermal energy required to de-ice ice at the leading's edge. A correlation between ice thickness at the stagnation line and ice thickness at the heater edge is developed for the leading edge of a cylinder surface. An experimental approach is used to investigate whether the increase in ice thickness at the heater's edge is linked to the increase in ice thickness at the stagnation line. The de-icing investigation shows that as ice thickness at the heater's edge grows, the de-icing duration significantly increases. The results of this paper suggest that employing a correlation between the ice thickness at both the stagnation line and the heater's edge can help reduce the thermal energy required to remove ice from the leading edge of an airfoil or cylindrical surface. • Defining the ice thickness relationship at the stagnation line and heater edge for cylindrical ice accumulation. • Examining the impact of ice thickness at the heater edge on the thermal energy required for de-icing. • Using imaging techniques to measure accumulated ice on a cylindrical surface. • Using thermal imaging to analyze the behavior of ice during the de-icing process. [ABSTRACT FROM AUTHOR]

In this paper the aerothermal heating of a reusable launch vehicle is reconstructed on the basis of temperature measurements taken in the thermal protection system of this vehicle. The discussed integrated thermal protection system is composed of three layers. Mathematical model, describing the problem, takes into account the dependence on temperature of the material parameters as well as the thermal resistances occurring in the contact zones of the layers, which is a novelty in the proposed approach. For solving the direct problem, the implicit scheme of the finite difference method is applied. Next, by using the solution of the direct problem, the Tikhonov functional is created, which describes the error of the current approximate solution. Whereas for determining the solution of the inverse problem the Levenberg-Marquardt method, modified and adapted to the Tikhonov functional, is used. The paper presents the mathematical model of the problem and the method of solution together with the selected examples illustrating its exactness and stability. In order to better examination of the solution method some various values of parameters are taken in the demonstrated examples. • Reconstructing an aerothermal heating in space vehicle protection system with temperature dependent material properties. • Reconstructing an aerothermal heating taking into account the thermal resistance between layers. • Solving the problem for three layers model of the thermal protection system. • Inverse problem solved for input data taken from NASA measurements. • Heat flux measured by NASA reconstructed with good precision and stability. [ABSTRACT FROM AUTHOR]

• Analysis of 12 decarbonisation scenarios via the electrification of space heating. • Innovative modelling approach that combines two highly detailed models. • Building stock and upstream supply sector of whole EU are covered. • Electrification via heat pumps leads to 11% lower system costs compared to hydrogen. • Heat pumps are cost-efficient in decentralised and in district heating systems. This paper analyses different levels and means of the electrification of space and hot water heating using an explorative modelling approach. The analysis provides guidance to the ongoing discussion on favourable pathways for heating buildings and the role of secondary energy carriers such as hydrogen or synthetic fuels. In total, 12 different scenarios were modelled with decarbonisation pathways until 2050, which cover all 27 member states of the European Union. Two highly detailed optimisation models were combined to cover the building stock and the upstream energy supply sector. The analysis shows that decarbonisation pathways for space and water heating based on large shares of heat pumps have at least 11% lower system costs in 2050 than pathways with large shares of hydrogen or synthetic fuels. This translates into system cost savings of around €70 bn. Heat pumps are cost-efficient in decentralised systems and in centralised district heating systems. Hence, heat pumps should be the favoured option to achieve a cost-optimal solution for heating buildings. Accordingly, the paper makes a novel and significant contribution to understanding suitable and cost-efficient decarbonisation pathways for space and hot water heating via electrification. The results of the paper can provide robust guidance for policymakers. [ABSTRACT FROM AUTHOR]

The problem addressed in this work is the enhancement of energy efficiency in buildings, primarily focused on heating control. The paper highlights the importance of addressing this challenge, given that HVAC systems are responsible for over 60% of total energy consumption in buildings, making them the largest energy consumers in both the residential and nonresidential sectors. This paper presents a methodology for developing a model predictive control (MPC) system based on artificial neural network (ANN) models, with the aim of improving the energy efficiency of buildings. This approach involves the creation of a training dataset using dynamic thermal simulation tools, enabling the learning of the ANN model that is responsible for predicting future states within an MPC optimization loop. Additionally, the implementation leverages advanced technologies such as Field-Programmable Gate Arrays (FPGAs), specifically the PYNQ board, Wi-Fi modules, and MQTT communication to enhance scalability, deployment, and adaptability. The study evaluates the proposed Neural Network Model Predictive Control (NNMPC) strategy implemented on the PYNQ, reporting a substantial reduction of 38.53% in heating energy consumption in buildings compared to a basic On/Off control approach for 24-hour simulation. This outcome underscores the solutions significant potential for energy savings in building heating systems. [ABSTRACT FROM AUTHOR]

Subgrade frost heave is the main reason that affects the safe operation and comfort of trains during the cold season. Solar heating system based on heat pipe technology is a promising method to mitigate the frost heave by raising the subgrade temperature. In this paper, a field experiment was conducted to evaluate the heating performance of the solar heating system based on heat pipe technology in the cold season. In addition, the heat collection performance and stability of the system are compared with other solar heating systems. Finally, its applicability is discussed. Experimental results revealed that the solar heating system based on heat pipe technology can effectively raising the soil temperature and mitigate the frost heave of subgrade. During the experiment period, the soil temperature at the depth of −0.5 m in the experiment site was 5 °C higher than that of the comparison site, and the maximum freezing depth was 0.4 m, which was 56 % lower than that of the comparison site. The mean daily temperature of heat collection units (HCUs)fluctuated around 30 °C, and the mean daily temperature of the two-phase closed thermosyphons (TPCTs) fluctuated between 15 °C and 30 °C. The heat transfer efficiency of System 1 and System 2 is greater than 0.5, and the total effective heat transfer during the experiment period is 512 MJ and 283 MJ, respectively, and the heat transfer difference is about 2 times. Compared with other solar heating systems, the system proposed in this paper has good heat collection performance and more superior system stability. The mean daily heat transfer of System 1 and System 2 is 6.4 MJ and 3.71 MJ, respectively, which is 62.9 % higher and 5.6 % lower than the mean daily heat loss of subgrade of 3.93 MJ, respectively. The system has the application prospect of low maintenance cost and good long-term anti-frost heave effect. • A solar heating system based on heat pipe technology was proposed for mitigating subgrade frost heave. • The soil temperature can be effectively increased under the heating effect of the system. • The system can provide effective heat transfer higher than 62.9 % of the mean daily heat loss of subgrade. • To provide a reference of using solar energy and heat pipe technology for mitigating subgrade frost heave. [ABSTRACT FROM AUTHOR]

• Abnormal heating of cable grounding line near three-phase reactor by finite element analysis. • Investigation into the impact of cable burial depth and cable laying on temperature elevation. • Effective shielding and safety assurance for the slot box. Cable termination near to three-phase dry-type air- core reactor (DAR) is prone to abnormal heating. In response to this problem, this paper firstly establishes the finite element model of the reactor and the cable and calculates the electromagnetic field distribution to obtain the current of the grounding wire of the cable armor layer. It is analyzed that the main reason for the abnormal temperature of the cable terminal is the eddy current in the grounding wire of the cable armor layer, which is caused by the leakage magnetic field of the reactor. Meanwhile, the influence of cable laying mode near the reactor on the current of armored grounding wire is further discussed. Secondly, the finite element model of the cable terminal is established and the temperature of the cable terminal is obtained by calculating the current-fluid-thermal coupling field. Considering the influence of adding shielding to reactor operation, the scheme of adding laminated silicon steel sheet slot box to cable is put forward and simulated. After adding slot box, the grounding wire current of armor layer is reduced by about 87% ∼ 89%. The test results show that when the input voltage of the coil is constant, the eddy current measured after installing the slot box decreases significantly, and with the increase of the coil voltage, the suppression effect of installing the slot box on the induced circulating current is better. This paper provides a certain reference value for the laying of cables near three-phase DAR in substations and the solutions to the abnormal heating of cable terminals. [ABSTRACT FROM AUTHOR]

District heat load forecasting is a challenging task that involves predicting future heat demand based on historical data and various influencing factors. Accurate forecasting is essential for optimizing energy production and distribution in district heating systems. However, most existing forecasting models lack transparency and interpretability and fail to capture the spatial–temporal dependencies in the data. Moreover, they often require a large amount of annotated data for training, which can be costly and time-consuming to obtain. In this paper, we present a novel approach to district heat load forecasting, which involves predicting future heat demand based on historical data and various influencing factors. The proposed approach is based on an Active Graph Recurrent Network (Ac-GRN), which leverages the strengths of active deep learning and graph neural networks to capture the complex spatial–temporal dependencies in the data. The approach also provides explainability for its predictions by using correlation-based attribution methods. The active deep learning component can effectively select the most informative and representative samples from a large pool of data, reducing the frequency and cost of data collection and human effort. The graph neural network component can model both linear and nonlinear relationships among heat meters using bidirectional recurrent connections, enhancing the accuracy and robustness of the predictions. We conduct extensive experiments and compare our approach with eleven state-of-the-art models on a real-world dataset of district heating consumption data from Danish residential buildings. Our results show that our approach outperforms other models in terms of accuracy, robustness, reliability, and computational efficiency for multi-horizon multi-step district heat load forecasting. Our approach also provides meaningful explanations for its predictions by highlighting the most influential factors and heat meters for each prediction. This paper makes a novel contribution to district heat load forecasting with explainability. • Novel approach for district heat load forecasting with active deep learning and graph neural networks. • Explainable predictions using gradient-based attribution methods. • Outperforms state-of-the-art models in accuracy and robustness. • Evaluates on real-world district heating data and conducts ablation studies. [ABSTRACT FROM AUTHOR]

Electrified Vehicles (xEVs) often rely on complex thermal systems to meet energy efficiency and performance targets. These systems are typically made up of multiple interacting loops, such as coolant loop, oil loop, and refrigerant loop which can be highly nonlinear, strongly coupled, and teemed with multiple sources of uncertainties and disturbances. Designing effective control strategies for such complex thermal systems is a difficult and crucial task. This paper proposes three advanced Model-Based Control (MBC) strategies for the cabin active heating thermal system of an EV, namely, a Nonlinear Model Predictive Control (NMPC), a Model Predictive Control via Value Function Approximation (MPC-VFA), and a Linear-Quadratic Regulator (LQR). For this purpose, a physics-based model of the aforementioned thermal system is derived and validated using data generated from a high-fidelity thermal plant model created in GT-suite software. The parameters of the physics-based model are identified using the particle swarm optimization algorithm and it is shown that the nonlinear dynamics of the thermal system has been accurately captured. A comprehensive test study is performed and the performance of the proposed MBC approaches is evaluated using various indicators, such as reference tracking, energy consumption, robustness, computation time, and implementation complexity. Experimental data has been also utilized to validate the high-fidelity thermal plant model. The results of the test study demonstrate a high performance and efficiency of the proposed control strategies, offering significant advancements in thermal system control of Electrified Vehicles. • This paper proposes three advanced Model-Based Control (MBC) strategies for the cabin active heating system of an EV. • A physics-based model of the thermal system is derived and validated using test data. • Experimental data has been also utilized to validate the high-fidelity thermal plant model. • The performance of the proposed MBC approaches is evaluated using various indicators. [ABSTRACT FROM AUTHOR]

The district heating system (DHS) is one of the essential carriers for coordinating renewable energy with fossil energy and achieving flexible energy consumption. Considering the uncertainty of both the renewable energy units' power and the consumers' aggregate loads impact the transport process of the DHS, the thermal characteristics of the DHS transportation and the node temperature response under the source-load uncertainty need to be quantified and analyzed. This paper proposed a method to calculate the nodes' temperature dynamic response of the DHS under multiple source-load uncertainty scenarios. The prediction and combination methods of supply and demand probability intervals of source and load nodes under varying credibility levels were investigated. Additionally, the effects of source-load uncertainty boundary conditions on the DHS transport process were analyzed. The temperature response of the nodes was calculated based on the established dynamic DHS model under multiple source-load uncertainty scenarios. A DHS in Beijing was selected for case validation and analysis, and it has 90 nodes and 109 pipes. The simulation results showed that the relative average error of node flow rate in the dynamic DHS model was 3.02%, and the average difference in node temperature was 1 °C. The probability distribution semi-analytical method and the Bayesian credible interval calculation method can accurately describe the uncertainty on both source and load sides. The models and algorithms proposed in this paper could effectively quantify the nodes' dynamic temperature response under the source-load uncertainty. • Proposed uncertainty quantification models for the source and load nodes of DHS. • Developed a novel credible interval calculation method for nodes' thermal power. • Quantified nodes' temperature dynamic response considering source-load uncertainty. [ABSTRACT FROM AUTHOR]

In the context of carbon neutrality, energy conservation and carbon reduction in the heating industry have become the focus of attention. However, severe heat loss is currently occurring in the secondary heating system due to hydraulic imbalance, which is unable to supply heat according to users' needs. In view of this, a thermodynamic-hydraulic model of users' demand for heat and flow rate for the heating system is established. Then, a novel method to regulate hydraulic imbalance is proposed, with the dynamic heat demand satisfied by regulating the valve opening based on NSGA-II. The optimization results show that the comprehensive hydraulic imbalance coefficient has been reduced from 23.08 to less than 0.019, which means that almost 100% of users can get heat supplies corresponding to their needs, while the energy consumption is reduced by about 30%. Additionally, when there are 1000 population and iteration steps, good convergence and high speed are presented using this method. In summary, an on-demand optimized model of hydraulic balance for the secondary heating network is put forward, which provides powerful engineering support and guidance for intelligent heating construction. • This paper presents a method to regulate the hydraulic balance of network using NSGA-II according to the heat demand. • This paper combines the demand flow regulation of users with the resistance analysis of the heating network. • The hydraulic balance can be implemented greatly by using the hydraulic imbalance coefficient as the optimization goal. • The number of iteration steps in the algorithm has an effect on the optimization results. [ABSTRACT FROM AUTHOR]

Drones and UAVs are gaining worldwide popularity and are now considered a popular choice for both military and commercial applications. Icing poses tremendous safety and performance concerns for the operation of all types of drones. This paper is part of a project that studies icing effects on the hovering 0.66 m diameter Bell APT70 drone rotor and the development of potential ice protection systems. The objective of this paper is to investigate the use of electrothermal heaters with severe icing conditions and to characterize the energy efficiency of anti-icing or de-icing regimes. Rotor speeds of 3880, 4440 and 4950 RPM were used while two air temperatures, −5 and −12 °C, were also tested. The heat transfer profile on the blade was studied using dry run tests where the rotor operated with heating but without water spray. Anti-icing tests with variable heating power were tested to determine the location of the initial ice accumulation as well as the minimum heating power requirement to protect the leading edge. Moreover, anti-icing tests with constant heating rates were done and compared to previous tests of unprotected blades, under similar condition. On the other hand, de-icing tests with various heating cycles were also carried out. Results indicate that although de-icing requires significantly less heating energy compared to anti-icing, there is clear trade-off on rotor stable aerodynamic output, electrical power consumption and vibration levels, depending on the adopted de-icing mode. Future work is about investigating the rise of secondary effects, such as shed ice impact due to de-icing. Work is also planned for a hybrid ice protection system that combines electro-thermal heaters with icophobic or superhydrophobic coatings. [ABSTRACT FROM AUTHOR]

The ideal non-collapse heated oil shale reservoir may lead to the maximum preservation of pores and fractures. However, the previous research on the pore evolution during heating in oil shale reservoirs has focused only on the analysis of capillary pores, ignoring the supercapillary pores (including fractures) that can provide the free flow of fluid. Through open thermal system experiments, combined with multi-scale visual statistics and quantitative testing, this paper reveals that the surface porosity of supercapillary pores increased from 0.27% to 15.95% and the porosity of capillary pores and microcapillary pores increased from 0% to 39.55%, in which the contribution rate of organic matter pores increased from 2.36% to 87.46%. From the perspective of the trap, we propose that the displacement pressure, breakdown pressure and overburden pressure of surrounding rock determine the pressure of injected CO 2. Regarding the adsorption and free state, through an improved formula for carbon storage potentials, the maximum theoretical CO 2 storage per unit volume for the Minhe depleted oil shale reservoir was estimated to be approximately 0.261 × 109 t/km3. Thus, a depleted oil shale reservoir is a suitable place for CO 2 storage owing to the large storage potential. [ABSTRACT FROM AUTHOR]

• A Stirling heat pump with a temperature gradient in the heat exchanger is studied. • The heat exchanger with a temperature gradient achieves cascade output of energy. • Negative effect due to the mix of gases at different temperatures is insignificant. • Considering economy and efficiency, single large heat pump is also a good choice. The free-piston Stirling heat pump (FPSHP) is efficient, environmentally friendly and has a wide available temperature range, making it a promising device for building heating. The temperature of the external heat-carrying fluid is different at the inlet and outlet of the heating heat exchanger, so there is a temperature gradient in the heating heat exchanger. The larger the scale of the FPSHP, the more pronounced the temperature gradient. However, the influence of such a temperature gradient on system performance has not been investigated so far. This paper therefore presents a detailed study of the FPSHP with a circumferential temperature gradient in the heating heat exchanger. The calculation results show that a cascade output of energy can be achieved when there is a circumferential temperature gradient in the heating heat exchanger. With the same outlet temperature, the larger the temperature difference between the inlet and outlet of the heating heat exchanger, the higher the COP. However, due to the mixing of internal working gases with different temperatures in the compression space, part of the high temperature heat is directly transferred to the low temperature module and output at a lower level, adversely affecting system efficiency. Fortunately, this adverse effect is found to be insignificant when compared with multiple independent small FPSHPs without circumferential temperature gradients. Considering the higher investment cost of multiple small FPSHPs, a single large FPSHP is also a good choice for large heating capacity demand. [ABSTRACT FROM AUTHOR]

Reducing building energy consumption and increasing the use of renewable energy are essential to energy conservation. Photovoltaic thermoelectric heat pumps have been considered as a sustainable measure to supply detached houses with hot water, especially those that even do not have access to the power grid. This paper investigates a stand-alone photovoltaic/thermal integrated thermoelectric water heating system (PV/T-TEWH). A dynamic model of PV/T-TEWH is developed and validated. The performance of the system in Lhasa, Beijing, Changsha and Guangzhou is simulated and analyzed respectively, and the economics of the system are compared. Results show that PV/T-TEWH can rely on the electric energy it generates without additional power supply when the current is less than or equal to 1.4 A in Lhasa and 1.0 A in Beijing, Changsha and Guangzhou. The annual total heat gain of the PV/T-TEWH system increases as the operating current increases, but the COP of the system falls with the rise of operating current. When the system is operating at the currents of 0.6 A, 1.0 A, 1.4 A, and 1.8 A, the payback period shortens with the increase of current. Lhasa has the shortest payback period among four cities and it is only 2.2 years when the working current is 1.8 A. The PV/T-TEWH system provides a new method for building hot water supply, especially for detached houses in remote areas. • This paper proposes and investigates a photovoltaic/thermal integrated thermoelectric water heating system (PV/T-TEWH). • A dynamic model suitable for simulating the PV/T-TEWH system is developed and validated. • The annual performance of the system in Lhasa, Beijing, Changsha and Guangzhou is simulated and analyzed. • The economics of the system in different cities are compared. [ABSTRACT FROM AUTHOR]

• An automatic energy leakage detection for district heating systems based on UAV Infrared (IR) images is presented. • A deep learning-based model and 8 different ML classifiers have been developed and evaluated for detection of leakages. • A region extraction algorithm has been incorporated to extract potential leakages enabling the ML analysis. • The proposed ML methods have been applied to ca. 13.4 million image patches and achieved an actual detection rate of 98.6%. In this paper, we propose automatic energy leakage detection in underground pipes of district heating systems based on Infrared (IR) images, captured by an Unmanned Aerial Vehicle (UAV). Hot water or steam is distributed to homes and industries through underground pipes from a central power plan. Leakages in underground pipes pose a very common problem, which can occur for many reasons, e.g. unprofessional installation and end of service life. Potentially, a leakage remains undiscovered for a very long period of time. Therefore, it is of great interest for power supply companies to monitor district heating networks to identify leakages. In this paper, the original IR images are captured in a 16 bit format by a UAV. On ground, potential leakages are extracted using a region extraction algorithm. Thereafter a Convolutional Neural Network (CNN) as well as eight conventional Machine Learning (ML) classifiers are applied on these regions to classify whether or not it is a leakage. In total, twelve UAV sequences are captured at different cities in Denmark. Based on these, around 13.4 million samples of image patches of district heating systems are extracted. Eleven sequences are used for training and the remaining one for testing. This was performed on all splits in the leave-one-out testing. The deep learning CNN achieved an average weighted accuracy of 0.872 with a false positive and negative rate of 12.7 % and 10.4 %, respectively. This CNN model detected around 98.6 % of the true leakages. In comparison, conventional ML classifiers, i.e. Adaboost (AB), Random Forest (RF), etc. provide lower average weighted accuracy, but on the other hand they require less computational resources. We have compared our method with a state-of-art method and the result shows that the proposed method is very competitive. [ABSTRACT FROM AUTHOR]

In this paper, the influence of measurement uncertainties on the key performance indicators f sav and F S C in solar-assisted heating systems is investigated. The impact of temperature, volumetric flow rate, and irradiance sensors with different measurement accuracies is analysed with a combination of Gaussian error propagation and Monte Carlo Analysis. To identify the sensor equipment with best cost–benefit-ratio (BCBR), different sensor combinations are investigated. If f sav and F S C are to be measured, additional sensors must be installed. The resulting costs range from 250 € for an inexpensive equipment to 330 € for recommended BCBR equipment and up to 780 € for the maximum accuracy equipment. For smaller economically dimensioned systems the use of inexpensive sensors results in large uncertainties, e.g. f ˆ sav = (15. 2 ± 13. 7) %. The uncertainties for larger systems are significantly lower, e.g. f ˆ sav = (56. 7 ± 6. 3) %. This is true as well if better sensors are used. Regardless of the system's size, with the BCBR sensor equipment the resulting expanded uncertainties can be reduced by 60 % (relative) compared to the results with the inexpensive sensor equipment. With maximum accuracy sensor equipment the resulting expanded uncertainties can even be reduced by 77 % (relative). The results show the importance of a carefully selected sensor equipment and the influence of the system's size. Inexpensive sensors can lead to large uncertainty ranges for the important key performance indicators f sav and F S C. Thus, these key figures effectively cannot be used for assessing the performance of a solar-assisted heating system. • Accuracy of f sav and FSC strongly depends on installed sensor qualities. • Analysis based on Monte-Carlo method and Gaussian Error Propagation. • Most influential sensors: temperatures in auxiliary and space heating loop. • Commonly used, inexpensive sensors result in very imprecise performance indicators. • Cost-efficient sensor equipment reduces uncertainties by 60% (fsav) and 45% (FSC). [ABSTRACT FROM AUTHOR]