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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]

• This study focuses on optimization of an air source transcritical CO 2 heat pump. • Factors influencing the optimal discharge pressure were examined experimentally. • A correlation formula for the optimal discharge pressure was determined. • Compared with the experimental results, the maximum error was less than 10%. • A control strategy for based on degree of superheat correction was proposed. The compressor discharge pressure is an important parameter for optimizing the performance of a transcritical CO 2 heat pump system. In this study, the factors influencing the optimal compressor discharge pressure of an air source transcritical CO 2 heat pump system were examined experimentally. The results showed that the optimal compressor discharge pressure is affected by the gas cooler water inlet temperature and gas cooler CO 2 outlet temperature. Consequently, a correlation formula for the optimal compressor discharge pressure appropriate for a more comprehensive temperature range and higher prediction accuracy was determined based on the experimental data. Compared with the experimental results, the maximum error was less than 10%, which is minor considering the lower gas cooler CO 2 outlet temperature. In addition, a control strategy for the optimal compressor discharge pressure based on the degree of superheat correction was proposed. Subsequently, under variable operating conditions, the air source transcritical CO 2 heat pump crude oil heating system was continuously operated based on this control strategy. The results showed that the compressor discharge pressure agreed with the optimal compressor discharge pressure calculated using the new correlation formula. Compared with the control strategy of constant opening under a variable frequency mode, the results showed that the system could operate under the control strategy proposed in this paper, the thermodynamic perfection of the system being higher. [ABSTRACT FROM AUTHOR]

The use of solar heaters for space and water heating applications in energy efficient buildings is one of the most promising applications of solar energy, particularly in heating-dominated areas. In this paper, six different cases have been compared for an integrated solar space and water heating system, according to results based on the variation in terms of predicted solar fraction and collector efficiency. These models are developed from the combination of two simulation models (configuration 1 and configuration 2) based on different operational strategies and control schemes within the load-side loop and six methods of implementing the properties of different solar collectors, varying thermal energy storage systems (sensible and latent), and selecting optimum PCMs within latent thermal energy storage (LTES). A system operating under configuration 2 (C-2) energized with an evacuated tube collector (ETC) can offer more than 12 % higher solar fraction than a system operating under configuration 1 (C-1) energized with a flat plate collector (FPC). Furthermore, it is anticipated that incorporating optimum PCMs can significantly enhance the thermal energy storage capacity and significantly further enhance the solar fraction depending upon the working schedules and heating requirements. The detailed financial feasibility analysis concludes that the payback period of such a system is up to 5.9 years without considering financial incentives. Moreover, a 60 % reduction in greenhouse gas (GHG) emissions is achieved compared to a base system powered by electricity. • Techno-economic analysis of an integrated solar space and water-heating system is proposed. • The evacuated tube collector offers up to 22 % higher useful energy gain than the flat plate collector. • The solar fraction difference between LTES and STES rises by operating the system in non-peak sun hours. • The payback period is estimated to be 5.9 years without considering any financial incentives. [ABSTRACT FROM AUTHOR]

Heat recovery in industry is limited by thermodynamic and economic factors. Increased heat recovery in an existing heat exchanger calls for higher costs in terms of capital and pumping due to increased exchanger size and pressure drop. One design option to offset the rapid growth of surface area to meet the upgraded heat load is to seek strategies to increase the heat recovery by increasing the heat transfer coefficient with a moderate increase on pressure drop. Compabloc heat exchangers have the construction features that make them suitable for such purposes. This paper presents a new design methodology for this type of exchanger and discusses its application in retrofit projects. The approach exploits the use of utility paths as the simplest and more practical way of identifying energy savings projects. The importance of analysing and quantifying temperature disturbance propagations is discussed. Applications to two case studies demonstrate the economic viability of using compabloc exchangers to achieve large energy recovery and savings. It is demonstrated that with an additional pumping cost of $66,776.12 USD/year, a total surface area of 1140.8 m2 and capital investment of $1062,272.0 USD, 24.8 MW of additional energy can be recovered, saving $5339,675.52 USD/year, giving a payback of 2.8 months. • A practical approach to the use of compabloc heat exchangers in retrofit applications is introduced. • Compabloc exchangers are sized using a new design methodology and new generalised thermohydraulic correlations. • Utility paths and temperature disturbance propagation are important aspects of the approach. • Compabloc exchanger can achieve high heat recovery, energy savings and short payback periods. [ABSTRACT FROM AUTHOR]

Hydrogen is increasingly being positioned as an essential part of low-carbon transitions. While the role of hydrogen in decarbonising industrial processes and transportation has received growing attention in recent years, very little research has focused on hydrogen as a fuel for homes. This paper uses theories of social practice to illustrate how the physical and chemical properties of hydrogen may disrupt domestic practices of cooking and heating. It focuses on one specific characteristic of hydrogen, that it burns with a near-invisible flame, and reports on a research project that investigated how one hundred people in the North East of England believed this would change their sensorially mediated social practices of heating and cooking. Participants imagined their practices of cooking would be severely disrupted while their practices of heating would be largely unaffected. The paper concludes by summarising the implications of the research for policy, industry, and researchers interested in hydrogen transitions; that these two key home domestic practices have potentially different transition pathways. • Utilises social practice theory to conceptualise how hydrogen transitions will take place in homes. • Focuses on the use of hydrogen for cooking and heating, and how gas-energised practices are sensorially mediated. • Finds that the near-invisibility of hydrogen's flame may be a disruption to cooking, but not heating. • Develops implications for policy, industry, and social science researchers interested in hydrogen transitions. [ABSTRACT FROM AUTHOR]

• Development of medium and low temperature solar thermal utilization systems is discussed. • Experimental tests are carried out in different thermal boundary conditions. • Influence of the boundary conditions on the solar storage is explored. Solar thermal utilization is an important part of renewable energy applications, and its development and application have received extensive attention. Based on the development status of medium and low temperature solar thermal utilization systems, this paper first introduces the application and performance research on subsystems of the solar system including heat collection, heat storage and heat utilization units. It then introduces the theoretical and experimental development of matching relationships and dynamic performance of the medium and low temperature thermal utilization systems. Lastly, a case study analysis of a solar thermal system performance was carried out under different thermal boundary conditions. The influence of the boundary conditions of the heat storage system and the actual weather conditions on its performance is explored. The results showed that the boundary conditions of constant temperature and the boundary conditions of constant heat flow density have their own advantages. The heat source conditions provided by heat transfer medium are similar to the constant heat flux boundary condition. The work of this paper provided a theoretical basis for the subsequent application and performance study of solar medium and low temperature thermal utilization systems. [ABSTRACT FROM AUTHOR]

Paper presents a comparison between a traditional district heating system with conventional boilers as a source of heat and electricity purchases from power utilities and a low temperature DH system incorporating the CHP with organic Rankine Cycle providing electricity and local heat pump raising the temperature of the DH fluid to the required temperature in the dwelling, meaning that both heat and electricity are produced within the system. Additionally, such "island" system may feature or not the heat pump. Comparisons are made based on the results obtained using a developed simple analytical model enabling calculations of the efficiency of respective systems. The analyses have a general character and can be used in studies of complex networks however presented in the paper simple examples show merely the fundamental capabilities of the developed tool. The objective of the heat pump in the system is to increase temperature of hot water to the required level locally at the dwelling and provide the heating in such way, contrary to the traditional system, where water heating is considered by the use of electric heaters to increase parameters of water for central heating purposes and preparation of utility hot water. Presence of the heat pump in the system allows for significantly lower temperatures of distributed in the network heat carrier. • Comparison between a traditional DH with conventional boilers and a LTDH system with ORC CHP and local heat pump. • Heat pump to locally raise temperature to the required values. • Simple analytical model enabling calculations of the efficiency of respective systems. • Heat pump in the system allows for significantly lower temperatures of water in DH. [ABSTRACT FROM AUTHOR]

• Heat extraction and storage models for deep borehole heat exchanger systems are presented. • The effects of heat storage on the heating power of deep borehole heat exchangers are quantified. • The thermal recovery of rock and soil under different heat storage conditions is revealed. • A novel design method for the threshold inlet water temperature of heat storage is proposed. The heating capacity of deep borehole heat exchanger (DBHE) systems gradually attenuates due to the cold accumulation of rock and soil during long-term operation. Therefore, heat storage in rock and soil is crucial to alleviate thermal attenuation and ensure stable operation. However, the mechanism and design methods for heat storage are unclear. In this paper, heat extraction and storage models for DBHE systems are established, the effects of heat storage on system operation are revealed, and a design method for the threshold inlet water temperature of heat storage is proposed. The results show that the fluid in the DBHE should inflow from the inner pipe to release more heat into the rock and soil when adopting heat storage. The heat storage power under fluid inflow from the inner pipe is 10.81 kW higher than that from the annular space under the same operating conditions. Increasing the inlet water temperature is more beneficial than increasing the flow rate to enhance the heat storage power. After 2880 h of operation, the heating power of the DBHE is increased by 3.44% for the next heating season when the storage flow rate is increased from 8 m3/h to 38 m3/h. Thus, a high heat storage inlet temperature with a low flow rate should be adopted during the heat storage period. Furthermore, the threshold inlet water temperature of heat storage is highly dependent on the depth of the DBHE and the geothermal gradient, with percentage contributions of 57.14% and 39.26%, respectively. The multiple linear regression model (R 2 = 0.972) has shown high predictive accuracy in the assessment of threshold inlet water temperatures, with a maximum relative error of −5.60%. The findings of this paper provide technical support for designing heat storage using DBHE systems. [ABSTRACT FROM AUTHOR]

• The optimization problem of EPS and flexibility-enhanced DHSis formulated. • The DHS is retrofitted with BCT and uses a variable mass flow operation strategy. • A conditional-DRO is employed to hedge against the uncertainty of renewable energy. • Propose adouble-layer distributed algorithm to achieve the distributed solution. In an integrated electricity and heating system (IEHS), building flexibility-enhanced district heating systems (DHSs) that use advanced flexibility-enhanced technologies are effective for promoting renewable energy accommodation. However, it is challenging to comprehensively utilize these flexibility-enhanced technologies in IEHS dispatch. This paper proposes a distributed conditional-distributionally robust coordination method for an electrical power and flexibility-enhanced DHS. The DHS is retrofitted with bypass compensation technology and uses a variable mass flow operation strategy to enhance its flexibility and promote renewable energy accommodation. Moreover, conditional-distributionally robust optimization is used to consider the inherent dependency between the forecasting error of a wind farm and the forecast output information, which goes beyond the state-of-the-art models. Additionally, a novel reformulation method is adopted to transform the problem with random variables and bilinear constraints into a more tractable programming problem, yielding a conservative approximative model of the original model that guarantees feasibility. Finally, to protect the privacy of electrical power system and DHS operators, this paper proposes a double-layer distributed algorithm to solve the problem in a distributed fashion while guaranteeing feasibility. Case studies demonstrate that the proposed model with flexibility-enhanced DHSs significantly promotes renewable energy accommodation and reduces dispatch costs, and the proposed double-layer distributed algorithm effectively solves the dispatch problem in a distributed fashion and guarantees the feasibility of dispatch results. [ABSTRACT FROM AUTHOR]

[Display omitted] • Localized heating systems are a proper solution for providing thermal comfort. • Providing personalized heating by radiation or conduction is more convenient, so the inhaled air is kept cool and pleasant. • Local radiant heating systems directly heat the body without heating the environment, leading to lower energy consumption. • With local radiant heating systems, proper thermal comfort and sensation can be achieved even at low air temperatures. Localized heating systems are a proper solution for providing thermal comfort while lowering energy consumption in cold environments. Local radiant heating systems provide thermal comfort at lower air temperatures than convective systems which heats air, resulting in cool and pleasant inhalation air. This paper reviews experimental studies regarding local radiant heating systems considering thermal sensation and comfort. These systems can heat body directly, often with a big view factor toward the body. They do not necessarily heat the air and environment, leading to lower energy consumption. Other types of heating systems combined with local radiant heating systems are also reviewed in this paper. According to reviewed studies, localized methods improved thermal comfort, and the same thermal sensation could be achieved in lower air temperatures, especially when using local radiant heating systems. To design local radiant heating systems properly, improvement of existing local thermal comfort and sensation modeling based on radiant heat transfer is needed. [ABSTRACT FROM AUTHOR]

Urban cities have a great potential for the sewage wastewater (WW) and treated WW but this heat resource is still underutilised in many European cities, including the three Baltic capitals of Tallinn, Riga, and Vilnius. The aim of this paper was to evaluate the integration of waste heat (WH) into a district heating (DH) system via absorption heat pumps by using key performance indicators (KPIs) in the fields of energy, environment, economy and social sphere in the three Baltic capitals. The paper presents a three-step methodology that develops an innovative multi-dimensional approach to energy poverty analysis and includes the three main drivers of energy poverty: fuel prices, household income, and energy efficiency. The paper shows that the integration of WH is economically feasible from the consumer's point of view and reduces energy poverty, especially when the price of fuel increases. • Multidimensional energy poverty approach is used for the methodology of treated wastewater. • The potential of treated wastewater is evaluated in Tallinn, Riga and Vilnius. • Economic benefits of incorporating wastewater heat into the DH system is assessed. [ABSTRACT FROM AUTHOR]

[Display omitted] • Nano graphene Silver coated heater was manufactured. • Graphene is increased the heat transfer. • Working voltage for graphene Silver coating was determines as 0.70 V. • Pure silver coating increased the energy consumption about 5 times against the graphene silver coating. In this paper, thermal and surface properties of silver and silver-graphene thin film heaters were investigated. Especially heat transfer ratios to a media from the heater surface (heat transfer gradient) were investigated. A novelty of the study is determine the velocity of energy transfer. Graphene increased the heat transfer gradient about five times. Silver nanoparticles and silver nano fiber are intensively researched materials to produce the heater, and graphene doped or stacked silver coatings are promising materials to be manufacture a heaters. Silver-graphene coating is preferred for relatively low voltage. In the paper, applied voltage was adjusted in the range of 0.15–0.70 V for silver-graphene, and 0.50–1.50 V used for silver coating. These values are very low voltage value against the literature. The heaters were deposited onto polyvinyl chloride by a thermionic vacuum arc (TVA) deposition system. The heaters were used to heat a calorimeter box and it was found that silver-graphene heaters are promising materials and transfer the heat energy to air was very fast against the silver coated sample. To investigate the surface properties of coated layers, field emission scanning electron microscopy (FESEM) images were obtained and the extended intersection regions (EIR) between the collapsed regions were detected. EIR has the crack, space and volumes. Two dimensional plates are observed in Ag-Gr coated surfaces. Cyclic-voltammetry and Tafel graphs were obtained for the coated samples. Corrosion years were calculated as 3.19 × 103 and 2.31 × 105 years for 1 mm corrosion layer. Finally, coated silver-graphene coating is promising material for the surface heating. It found that surface topography plays a key role in transferring the heat energy. As a result, Graphene doped Ag thin films are proper for the high performance heater design and heat energy transfer. [ABSTRACT FROM AUTHOR]

• A two-layer framework is proposed for building HVAC and associated multi-energy consumption optimization. • 100% renewable complementarities are proposed for building multi-energy supplies. • A R-C thermodynamic network is formulated to model the building HVAC. • AC slow charging and DC fast charging types of EVs are considered and managed via a novel real-time supply–demand pricing. Building heating, ventilation, and air conditioning (HVAC) and associated energy consumption make up the more and more important part of the world, whose reduction provides a cost-effective path to the "dual carbon" goal. This paper proposes a two-layer management of HVAC-based multi-energy buildings under proactive demand response of fast/slow-charging electric vehicles (EVs). In this paper, the building HVAC is mathematically formulated via a R-C thermodynamic model, which coordinates with multi-energy converters and storages to form a 100% renewable building. The building management is a challenging optimization problem due to its severe constraints and strong spatio-temporal couplings. In the first layer, a day-ahead multi-energy dispatch is formulated to economically optimize the electrical, heat, gas energy carriers. In the second layer, alternating current (AC) slow charging and direct current (DC) fast charging types of EVs are considered and managed via a novel real-time supply–demand pricing mechanism. After acquiring the economical dispatch references in the first layer, the second layer implements a model predictive control (MPC)-based real-time scheduling to handle the multi-energy supply–demand fluctuations. The original two-layer optimization is further handled via mixed-integer linear program (MILP) reformulation for high-efficient solving. Comparisons have shown the advantageous performances of the proposed two-layer optimization over economics and practicability. Simulations results show that the overall system operating cost can be reduced by at most 3.01% with a higher operational flexibility in building management. [ABSTRACT FROM AUTHOR]

In this paper, we consider a family of simultaneous distributed-boundary optimal control problems (P α) on the internal energy and the heat flux for a system governed by a mixed elliptic variational equality with a parameter α > 0 (the heat transfer coefficient on a portion of the boundary of the domain) and a simultaneous distributed-boundary optimal control problem (P) governed also by an elliptic variational equality with a Dirichlet boundary condition on the same portion of the boundary. We formulate discrete approximations P h α and P h of the optimal control problems P α and (P) respectively, for each h > 0 and for each α > 0 , through the finite element method with Lagrange's triangles of type 1 with parameter h (the longest side of the triangles). The goal of this paper is to study the convergence of this family of discrete simultaneous distributed-boundary mixed elliptic optimal control problems P h α when the parameters α goes to infinity and the parameter h goes to zero simultaneously. We prove the convergence of the family of discrete problems P h α to the discrete problem P h when α → + ∞ , for each h > 0 , in adequate functional spaces. We study the convergence of the discrete problems P h α and P h , for each α > 0 , when h → 0 + obtaining a commutative diagram which relates the continuous and discrete simultaneous distributed-boundary mixed elliptic optimal control problems P h α , P α , P h and (P) by taking the limits h → 0 + and α → + ∞ respectively. We also study the double convergence of P h α to (P) when (h , α) → (0 + , + ∞) which represents the diagonal convergence in the above commutative diagram. [ABSTRACT FROM AUTHOR]

• Combining deep reinforcement learning DRL and Computational Fluid Dynamics CFD • Control and optimization of two and three dimension conjugate heat transfer applications • Loss function engineering as a key aspect for a good optimization • Policy-Based Optimization improved the temperature homogeneity during heating Gas furnaces are the most widely used means of heating in industry, and with the growing concern for environmental issues, and a global energy crisis at our doorstep, the optimization of the processes related to them becomes a key challenge. This paper aims at introducing a new way of practicing gas furnace control involving simulations, virtual sensors and deep reinforcement learning (DRL) techniques. In order to do so we designed a set of simulations of conjugate heat transfer systems governed by the coupled Navier–Stokes and heat equations for single-step control. The DRL algorithm used in this paper is the policy-based optimization (PBO) algorithm specialized in single-step (or open-loop) control. We explore its ability to find global maxima in different situations and under various constraints. Therefore, various 2D and 3D cases are tackled, in which the position of the work piece, the flow rate, and other parameters are controlled. The obtained results highlight the potential of the DRL framework combined with computational fluid dynamics (CFD) conjugate heat transfer systems for optimizing searches in large parameter spaces. For the 2D case, PPO achieved an increase of 89 % in temperature homogeneity, and for the 3D case an increase of 7 % in final temperature with the same total input. [ABSTRACT FROM AUTHOR]

The simultaneous energy and food resources management can be a challenging problem for researchers working in this field. Solar dryers are equipment that can employ solar energy in order to dry degradable food for long-term storage. However, these systems should also utilize an auxiliary energy source because of non-availability of continuous access to the solar radiation. In this paper, a cabin solar dryer equipped with a heating element as an auxiliary heat source has been used to dry four types of products. The tested products consist of apple, kiwi, banana slices, as well as quince julienne strips. The experiments were performed in four days during autumn, when the solar energy had a low level intensity and the heating element was employed for aiding the energy supply. Temperature and humidity have been measured using temperature and humidity sensors mounted at the inlet and outlet of the collector and dryer cabin. Then the thermal efficiency of the collector and the cabin is investigated via the energy and exergy analysis, and the thermal performance of the system is analyzed. Lastly, an economic analysis is presented to calculate the production cost of per kilogram of products. The results show that thermal efficiency, drying process exergy, produced exergy and specific moisture evaporation rate (SMER) of julienne strips of quince are higher than those of other products. Although banana slices have better conditions in terms of these parameters among the sliced products. Due to the results, it was found that the quince julienne strips have the highest cost about 1.137 $/kg and the lowest drying rate about 0.188 kg/h. On the contrary, the minimum cost belongs to the apple slices about 0.478 $/kg and the maximum drying rate about 0.3224 kg/h. • Hybrid dryer combined with spiral solar air heater and auxiliary heating system is used. • Four types of products are dried. • The tested products consist of apple, kiwi and banana slices and quince julienne strips. • Energy, exergy and economic analysis are performed. • Thermal performance and the cost of production per kilogram of product are estimated. [ABSTRACT FROM AUTHOR]

The construction sector accounts for 40% of total energy consumption and is increasing. To reduce energy consumption of heating and cooling systems during peak demand while maintaining thermal comfort, phase change materials (PCMs) are used more and more. Appropriate application of PCM and design of latent heat thermal energy storage (LHTES) requires in practice an in-depth knowledge of the thermal properties of PCMs. The aim of the paper is to present the results of experimental determination of the properties of two commercially available, organic PCMs – RT22HC and RT28 HC, using T-history method and pipe Poensgen apparatus. Results of experimental tests showed that these low-temperature PCMs could effectivity store heat and cold in a narrow temperature range of approx. 7 K for RT22 HC and about 3–4 K for RT28 HC. The average measured latent heat values are 190 kJ/kg for RT22 HC and 244 kJ/kg for RT28 HC. The distribution of energy stored in RT22 HC shows the peak in the temperature range of 21–23 °C (with 20–50 kJ/kgK for heating, 22–71 kJ/kgK for cooling). For RT28 HC this range is 27–28 °C (75–130 kJ/kgK for heating, 40–125 kJ/kgK for cooling). The diagrams of enthalpy present small hysteresis (0.5–1 K) in these materials. Thermal conductivity measurements using pipe Poensgen apparatus demonstrated that these PCMs have a low conductivity of 0.12–0.33 W/mK. The presented experimental research is intended to provide the data necessary for the correct design of LHTES with RT22 HC or RT28 HC intended to use in heating and cooling systems and to maintain thermal comfort in buildings. • RT22 HC and RT28 HC were tested using T-history method and pipe Poensgen apparatus. • The average measured latent heat is 190 kJ/kg for RT22 HC, 244 kJ/kg for RT28 HC. • Results of T-history method and three-layer calorimeter are in good agreement. • Pipe Poensgen apparatus was used to determine thermal conductivity of PCMs. • Tested PCMs confirmed their potential to reduce peak energy consumption. [ABSTRACT FROM AUTHOR]

This paper is presented a concept of thermochemical recuperation of waste heat based on hydrogen extraction from liquid organic hydrogen carriers (LOHC), on the example of methylcyclohexane-toluene system. The advantages of this concept is described, for example, a possibility to use a moderate low temperature of waste heat for generation high-exergy "green" hydrogen fuel. To understand the effect of operating parameters on the energy and mass balance, the thermodynamic analysis was performed. The chemical system for hydrogen generation was analyzed via Gibbs free energy minimization method. The thermodynamic analysis was conducted under various operating conditions: temperature of 100–400 °C, pressure of 1–4 bar. Aspen HYSYS software was used for the energy and mass conservation analysis. Sankey diagram for the energy flows is depicted. The results showed that the maximum energy efficiency the thermochemical waste heat recuperation system have in the temperature range above 300–350 °C. In this temperature range, the effect of pressure on the energy balance is negligible and it is recommended for the thermochemical recuperation system to use LOHC with a pressure of 1.5–2 bar. Based on the analysis, it was concluded that the temperature potential of waste heat for about 300–350 °C is enough for the investigated concept. An analysis of a mass balance showed that the decreasing in condensation temperature leads to a significant increasing in the share of condensed toluene from toluene-hydrogen mixture after a reactor. If temperature of a hydrogen-toluene mixture of 20 °C at pressure above 2 bar about 96% of toluene can be condensed after the first condenser. • Concept of thermochemical recuperation based on liquid organic hydrogen carriers (LOHC). • Effect of pressure and temperature on energy and mass balance is studied. • Temperature of waste heat for efficient using of LOHC is 300–350 °C. • Effect of pressure on energy balance of the thermochemical recuperation system is negligible. [ABSTRACT FROM AUTHOR]

This paper elaborates experimental analysis of cardboard/sawdust briquettes as a viable option for biomass fuel. Physical–mechanical and thermal characteristics of cardboard/sawdust briquettes were investigated. The influence of the main parameters on heating content was also examined through an ANOVA and regression analysis, i.e. pressure influence (that was applied in a punch-and-die process), cardboard/sawdust ratio influence and finally drying temperature influence. In order to find the maximum heating value, minimum ash content and maximum compressive strength optimization were done. The optimal values obtained for the studied briquetting process parameters are a compression force of 588.6 kN, a sawdust mass of 46.66% and a drying temperature of 22 °C. According to the mathematical model obtained, these optimal values give a maximum higher heating value of 17.41 MJ/kg, a minimum ash content of 6.62% and a maximum compressive strength of 149.54 N/mm. Finally, Cardboard/sawdust briquettes showed potential for application as viable biomass fuel. [ABSTRACT FROM AUTHOR]

The heat pump operated single-stage humidification-dehumidification desalination system, configured with a subcooler and a heat regenerator, has been proven highly effective in improving both freshwater productivity and energy efficiency. To investigate the potential benefits of increasing the number of humidification stages, this paper presents a heat pump operated two-stage humidification-dehumidification desalination system by adding a pre-humidifier. Subcooler and condenser of the heat pump are used as the heat sources of the main humidifier and the pre-humidifier, respectively. Through parametric studies, a comparative analysis is conducted on the thermodynamic and economic performances of both the heat pump operated single-stage system and two-stage system at various operating conditions. The results show that such system modification can greatly improve system performances. Compared to the single-stage system, the maximum freshwater productivity of the two-stage system is 42.89 kg/h, increased by 19.77 %; the peak gain output ratio is 7.93, up by 9.53 %; and the lowest specific electricity consumption is 79.34 kWh/m3, reduced by 15.15 %. Furthermore, the freshwater production cost for the two-stage system, ranging from 7.78 to 13.33 $/m3, is also superior that of the single-stage system, further demonstrating its substantial value in practical product development and market promotion. • A heat pump operated two-stage humidification-dehumidification system is proposed. • Performances of single and two-stage systems are compared at identical conditions. • Freshwater production costs of the two-stage system range from 7.78 to 13.33 $/m3. • The two-stage system is significantly more efficient than the single-stage system. [ABSTRACT FROM AUTHOR]

In this paper, we give a computational approach of work and heat for any quantum systems. We use the strategy that the part of energy exchange with the von Neumann entropy unchanging is defined as work, and the part with the von Neumann entropy changing is defined as heat. We define the work and heat and they are formulated. This method is suitable for the study of any quantum systems (not only bipartite quantum systems, but also single-body, and multi-body quantum systems). As examples, firstly we investigate a bipartite model whose dynamics can be rigorously solved by using the Bloch equation, and secondly, we study two single-body models by using the numerical method of master equation of Redfield form. • Decompose quantum dissipative processes into pure work and pure heat processes. • In a pure heat process the von Neumann entropy is changed, in a pure work process the entropy is unchanged. • In a pure heat processes the eigenvectors remain unchanged, in a pure work process the eigenvalues remain unchanged. [ABSTRACT FROM AUTHOR]

Packed-bed latent heat storage (PBLHS) system has been widely studied in the solar energy application area due to its properties of solving the time-space mismatch of energy supply and demand. The paper delves into the cyclic thermal performance of PBLHS tanks, seamlessly integrated with flat-plate collectors, to manage building heat loads effectively. A 1D transient mathematic model of PBLHS integrated with the solar collector for a building is established using MATLAB which is validated with the experimental results from the literature. Based on this model, the effect of different sizes, flow rates, inlet temperature thresholds and different heating months are discussed. The results show that: 1). Building heat load can have a significant influence on the thermal performance of the PBLHS system. 2). The optimal size of the tank for a 96 m2 house is 1.0*1.0 m and the optimal flow rate is 0.05 kg/s 3). The weather data can significantly affect the thermal performance of PBLHS, the storage tank heating durations for one week in different heating months are 108.4h, 73.6h,70.8h and 81.7h. These insights are pivotal for the optimal design of PBLHS tanks, paving the way for more efficient building heating solutions. • PBLHS tank integrated with a flat plate operating under heat load is modelled. • Energetic and thermal performance assessments of a PBLHS tank are obtained. • The cyclic operation of the PBLHS system under long-term intermittent loads is presented. • Influences of different mass flow rates, inlet temperature limits and different size tanks are evaluated. • The operation of the PBLHS system under heating seasons is analyzed. [ABSTRACT FROM AUTHOR]

Accurate heating load prediction is essential to supply-demand collaboration in district heating systems and energy sustainability. With the development of the Internet of Things technology, massive monitoring data is collected that provides abundant data sources for the prediction models. However, the missing data from equipment anomalies, network transmissions and the complexity of heat load changing cause difficulty in realizing accurate heat load prediction. Therefore, the hybrid model based on bidirectional long short-term memory network and temporal convolutional network proposed in this paper to improve the accuracy of the heat load prediction from the aspects of reconstruction of missing values and extraction of complex features. The bidirectional long short-term memory algorithm imputes missing values based on bi-directional features of existing data and provides solid data foundation for subsequent training of predictive models. The temporal convolutional network achieves high-level feature extraction and parallel computation, which contributes to the effective modeling of complex changes in heat load and the realization of accurate heat load prediction. Comparative study was conducted with four heat exchange stations of actual environment to evaluate the performance of the prediction model. The results showed the mean absolute percentage error of the hybrid model decreased to 2.47% which is lower than the State-of-the-Art models, such as long short-term memory, temporal convolutional network, and support vector regression etc. The superior results further validated the feasibility of this hybrid model in heat load prediction. • The missing values in heating system were reconstructed by deep learning model. • A hybrid heating load prediction model was proposed considering missing values. • Detailed experiments were conducted to validate the model's superiority. [ABSTRACT FROM AUTHOR]

Hydrogen propulsion is generally treated as the ultimate net zero-emission option for aviation, therein liquid hydrogen storage appears to provide the only feasible solution for aircraft with the constraints imposed by aircraft weight and volume. Hydrogen liquefaction consumes a great amount of energy, which significantly boosts the cost of hydrogen as an aviation fuel. Besides the H 2 chemical exergy for combustion to provide thrust, the H 2 physical exergy in the form of cold energy is also a kind of high-quality clean energy to produce power output, which offers great opportunities to achieve cost-effective use of hydrogen fuel. Thus, this paper presents a Rankine cycle and H 2 direct expansion cycle (RC-DEC) combined power generation thermal management system for the simultaneous utilization of exhaust gas heat exergy and hydrogen fuel cold exergy from the liquid hydrogen-fueled turbojet engine. In the Rankine cycle, the transcritical mode is applied on the hot side while the liquid separation condensation concept is adopted on the cold side to achieve better thermal matchings with heat and cold sources. The hydrocarbon/inert gas binary mixture is proposed as the working fluid of the Rankine cycle. The effects of key thermodynamic parameters and the influence of Para-Ortho hydrogen conversion on system performance are discussed, then a comparison of the mixture working fluid is conducted. Results show that there exists an optimal separation temperature ratio and condensation pressure of RC to obtain maximum total net power output. As the DEC expander inlet pressure increases, the total net power output first increases and then levels off. The introduction of the Para-Ortho hydrogen conversion has a negligible impact on net power output but leads to a significant reduction in the exergy efficiency, which is attributed to the cold energy release nature of Para-Ortho hydrogen conversion. The results of the working fluid comparison indicate that the optimal inert gas retardant for CH 4 is Kr, while those for C 2 H 6 and C 3 H 8 are Xe to achieve the maximum net power output and exergy efficiency of the proposed power generation system. Among them, C 2 H 6 /Xe(0.6/0.4) obtains the maximum net power output of 2717.9 kW and maximum exergy efficiency of 33.1%, which suggests an opportunity to provide megawatts of electrical power for the aircraft in place of the APU. • RC-DEC combined thermal management system is proposed for LH 2 turbojet engine. • The hydrocarbon/inert gas binary mixture is proposed for LH 2 cold exergy recovery. • The influence of the Para-Ortho hydrogen conversion on the system is revealed. • The optimal inert gas retardant for the selected hydrocarbons is determined. [ABSTRACT FROM AUTHOR]

As the coupling between power distribution systems (PDSs) and district heating systems (DHSs) becomes tighter, it is critical to develop a coordinated strategy for load restoration in integrated electric and heating systems (IEHSs) after natural catastrophes. Similar to PDS reconfiguration, DHSs can modify network topology by remotely operating the ties and sectionalizing valves. A coordinated reconfiguration with soft open points (SOPs) is proposed in this paper for resilience-oriented restoration in IEHSs, which mitigates the fault propagation during fault isolation and explores the flexibility of network topology variation with SOPs for load restoration. To guarantee the privacy of electric and heating systems, we propose an adaptive alternating direction method of multipliers (ADMM), which divides the original problem into PDS and DHS subproblems. The proposed algorithm can intelligently dispatch SOPs and switches in the PDS sub-problem and valves in the DHS subproblem. Comprehensive case studies are carried out to illustrate the effectiveness of coordinated reconfiguration with SOPs for load restoration and verify the proposed algorithm. When considering coordinated reconfiguration with SOPs under the PDS fault scenario, the resilience metrics value increases by 9.6% compared to only PDS reconfiguration. • A Distributed coordinated load restoration strategy in integrated electric and heating systems is proposed. • Soft Open Point flexibility is fully exploited to improve load restoration levels. • Coordinated reconfiguration of the PDS and DHS is provided to improve service restoration level. • The adaptive ADMM is utilized to guarantee the privacy security of electric and heating systems. [ABSTRACT FROM AUTHOR]

• A two-layer control method is proposed to deal with calculation complexity. • The clustered temperature transfer processes of bitumen tanks are analyzed. • A data-driven method is introduced to enhance computational efficiency. • A real-time predictive control method is developed to deal with uncertainties. Uncertainties and computational complexity are two growing challenges in scheduling industrial heating loads. In this paper, a data-driven real-time predictive control approach is proposed to deal with these challenges in the industrial scheduling of bitumen tanks. Specifically, predictive control technology is utilized to leverage the updated information to mitigate the negative impact of past uncertainties in equipment parameters and external environmental factors, which may lead to temperature constraint violations in the bitumen tank operation processes. Meanwhile, a data-driven method using artificial neural networks (ANN) is developed to ensure efficient computation for real-time predictive control. Moreover, a two-layer control method is devised to reduce the calculation time for day-ahead optimal scheduling of a large scale of bitumen tanks, aiming to generate sufficient high-quality data for training ANN. In the two-layer control method, the clustered temperature transfer processes of bitumen tanks are analyzed and modeled for the first time. Simulation results indicate that the two-layer control method can significantly reduce the computational time required for the day-ahead optimal scheduling of bitumen tanks, facilitating the generation of a large amount of high-quality data for training ANN. Subsequently, the application of ANN enables real-time predictive control, helping to eliminate the negative impact of uncertainties. [ABSTRACT FROM AUTHOR]

Agricultural greenhouses play a crucial role in addressing the threat of climate change to agricultural systems. The greenhouse systems control exhibits nonlinear characteristics and large lag, both affecting the regulation of the greenhouse thermal environment. In this paper, a control strategy was designed to set the dynamic reference value of the control objective of the greenhouse model, considering factors such as solar radiation and the heating capacity of water body. A complete greenhouse model was developed using TRNSYS, and then the model predictive control building and optimization were implemented through MATLAB. The control effects of traditional proportional-integral-differentiation control, initial model predictive control, and optimized model predictive control were compared. The results showed that the regulation of greenhouse temperature was improved by 10.6 % in the coldest mouth compared to the conventional proportional-integral-differentiation control by the optimized model predictive control. During a typical cold month, the violation of constraints was reduced by 29.7 % by dynamically setting the target of the greenhouse with the optimized model predictive control. The performance of greenhouse climate control is enhanced by the proposed optimized model predictive control method, ensuring a stable regulation of the crop growth environment. [ABSTRACT FROM AUTHOR]

[Display omitted] • Combining global simplified and local turbulence models to calculate flow details. • Analysis of the low-pressure heater pipe failure causes. • Simulate the low-pressure heater with the porous medium model. • Obtained flow information in the damaged local area. Low-pressure heaters are critical heat exchange equipment in thermal and nuclear power generation. The high-speed steam flow in the low-pressure heaters induces pipe vibration, causing pipe failure. The large size and complex flow make it hard to calculate directly. This paper employs a combined method of the porous medium and local models by substituting the boundary to calculate and prove steam flow trajectory and velocity are consistent with the actual situation. The analysis of the turbulent kinetic energy exhibits that the primary causes of pipe vibration are the periodic vortex shedding and the impact of the impingement plate on the pipes. The stress analysis indicates that the loosening of the pipes leads to a 368 times amplification of the shear stress by 0.1 MPa. The most crucial step in solving such a problem is to strengthen the fixation of the pipes, especially near the shell region. [ABSTRACT FROM AUTHOR]

Solar thermal energy is one of the important sources of renewable energy. The solar thermal energy gives clean energy which can be utilized for industrial applications. Industrial heaters which require heat energy for many industrial uses can be attained using these solar thermal absorbers. The solar thermal absorber is designed using a layer design that consists of material compositions of Titanium (Ti) and Stannic selenide (SnSe 2) for ground and substrate sections respectively. A graphene layer which has the good properties to be used in solar absorbers is added between the Aluminum and SnSe 2 material. A thin graphene section is inserted above the SnSe 2 substrate and below the Ti resonator. To catch the good absorption in the current design, the best four wavelengths (micrometer) have been attached such as 0.22, 0.8, 2.46, and 2.85. This design's contribution can be studied in 4-atm regimes (from UV, V to NIR, and MIR). According to the wavelength and bandwidth ranges, the current absorption explores more than 97% (97.4%) in between 2.4 and 3 μm (600 nm) bandwidth and exceeds 95% (95.2%) from 0.2 to 1 μm (800 nm) respectively. To the overall range of design, it extracts 90.3% for the 2800 nm band between 0.2 and 3 wavelength regime. The flow of the presentation of the proposed paper is (i) Introduction (ii) Design and Parameters, and (iii) Results and Discussions. The explored absorber can be effective in water heating and swimming pool heating for homes. Moreover, it can also be applied in large industries as a solar thermal absorber for heating applications. [ABSTRACT FROM AUTHOR]

Clarifying the aging characteristics of aluminum alloys during continuous heating is crucial for formulating isothermal and non-isothermal aging (continuous heating aging) processes. This paper investigates the stress relaxation characteristics of an Al-Cu-Mg-Ag alloy under three-point bending during continuous heating. Taking into account the mechanical properties and precipitate analysis, it demonstrates the feasibility of using the stress relaxation method to determine the peak aging temperature during continuous heating. This approach is efficient, requires minimal sample, and yields continuous data. The peak aging temperature of the sample increases from 260 °C to 305 °C when the heating rate increases from 1 to 3 °C/min with the same initial load (3 N). The peak aging temperature is around 280 ℃, when the initial load increases from 1 N to 9 N with the same heating rate (2 °C/min). Under low temperatures (25 ℃∼ 200 ℃), the sample displays the presence of GP zones, and a few Ω precipitates during the continuous heating process of 2 ℃/min. As the temperature increases, the GP zones dissolve and transform into the Ω precipitates. A large number of Ω precipitates appear in the matrix in a continuous precipitation manner when the temperature reaches 235 °C. The precipitation strengthening effect is strongest at 280 °C, and the Ω precipitates begin to coarsen as the temperature exceeds 280 °C. [Display omitted] • A method to determine the continuous heating peak aging temperature of aluminum alloys was proposed. • The peak aging temperature of Al-Cu-Mg-Ag alloy was related to the heating rate. • The evolution of the precipitates during continuous heating aging of Al-Cu-Mg-Ag alloy was obtained. [ABSTRACT FROM AUTHOR]

Integrating renewable energies into district heating systems has a large potential to reduce CO 2 -emissions in the heating sector. As district heating systems offer the possibility of incorporating renewable energies into the heat supply, new systems have to be built and the existing networks must be maintained. This study investigates ways to optimize existing district heating systems in order to ensure economic sustainability in the long-term. Previous case studies have elaborated on a variety of optimization measures. However, to date, these measures have neither been collected nor consistently assessed for a wider application range. Therefore, in the study presented here a system for assessing the ecological and economic benefits of optimization measures was developed and applied. The assessment method utilized showed that optimization of district heating consumer substations and adding of a central buffer storage tank has a high optimization potential in comparison to intermittent operation strategy, which has a significantly lower optimization potential. From this information and the transferability data, a district heating operator can determine which optimization measure should be prioritized, which is shown at the end of the paper on an example case. • A method was developed to assess benefits of optimizing district heating systems. • A survey was conducted to assess the ecological and economic value. • Optimization measures for DH systems were compared using the new method. • A guideline is provided to offer operators a suggested approach to take. [ABSTRACT FROM AUTHOR]

• A defect model modification method with surface heat flux identification is proposed for thermal protection system. • Levenberg–Marquardt method is adopted to identify surface heat flux, and whether the defect has occurred is determined. • A defect model modification method is proposed from the knowledge of the identified heat flux. • An experiment is designed to prove good accuracy of the proposed method. Thermal protection systems (TPS) have become a key issue in ensuring the reliability of hypersonic flights. Aimed at monitoring the thermal loads and possible defects for TPS, a defect model modification method with surface heat flux identification is proposed in this paper. Firstly, by the measured temperature from a distributed sensor network and the initial TPS model, the surface heat flux was identified with the Levenberg–Marquardt Method (LMM). If there existed outliers in the identified heat flux distribution, it can be visually indicated that the defect occurred. Then, defects were represented by shape parameters and can be determined by the model modification from the knowledge of the identified heat flux and the measured temperature. The effectiveness of the proposed method was verified numerically using TPS containing a surface defect. Meanwhile, the effects of various factors on the identified results were investigated in detail, such as defect sizes, defect shapes, sensor locations, and real aerodynamic heating. Finally, the proposed method was successfully applied to an experiment, and results demonstrated that the proposed method can achieve good identification results by experimentally measured temperature. [ABSTRACT FROM AUTHOR]

Cleaner end-uses of energy, including electrified heating, represent a cornerstone of a decarbonised energy transition. On the other hand, many governments have adopted measures to mitigate energy poverty and facilitate access to modern energy services, including heating. Both objectives may be interrelated, since energy poor people are less likely to use cleaner (and costlier) heating fuels. This paper analyses the impact of energy poverty on the decision to use different heating sources and identifies whether the events of COVID and the Ukraine war have affected this decision. Thus, a multinomial probit model is estimated using information from a large database of Spanish households in 2019, 2021 and 2022. The results show that being energy poor increases the probability to use carbon-intensive energy sources for heating compared to electricity, and that COVID and the war in Ukraine have affected this relationship. The increase in energy poverty over those years has negatively affected the decarbonisation goal with respect to heating choices. The influence of those events on the probability to use electric heating depends on some household and dwelling features. Therefore, mitigating energy poverty increases the welfare of energy poor people while supporting the choice of cleaner heating. [ABSTRACT FROM AUTHOR]

Industrial steam heating is a significant aspect of energy consumption in China, playing a crucial role in industrial energy efficiency. Historically, demand response research has predominantly focused on the electricity sector, with limited emphasis on steam supply. This study explores a novel Time-of-Use pricing approach for steam heating systems, anchored in the demand response theory of price incentives. It develops a peak-valley segmentation method by considering both the load differences between supply and demand and the thermal storage capacity of the pipeline system. Additionally, the paper delves into user response characteristics to formulate an optimized Time-of-Use pricing model for steam heating systems. Implemented in a Jiangsu-based case study, the model demonstrates significant efficiency improvements: it reduces the peak-valley load difference by up to 68.3% and cuts steam purchasing costs by ¥135,000. Furthermore, the alignment between the users' total steam load curve and the heat source's steam supply is enhanced by 18.8%, illustrating the model's effectiveness in balancing demand and supply. • Cluster analysis to extract steam user load characteristics. • Divide peak/valley times based on network storage and user traits. • Create a multi-objective Time-of-Use model for steam pricing optimization. • Carry out a case validation in an actual industrial park in Jiangsu. [ABSTRACT FROM AUTHOR]

In this paper, TRNSYS is used to simulate the heating systems of air-cooling concentrating photovoltaic/thermal (CPVT) coupled air source heat pump and water-cooling CPVT coupled air source heat pump. Besides, Grasshopper is adopted for multi-objective optimization of air-cooling system. This study not only proposed two hybrid systems and enriched the research of CPVT coupled air source heat pump, but also proposed a multi-objective optimization method, which uses Grasshopper to invoke TRNSYS. Compared with the air source heat pump system, the annual average COP of heat pump in the air-cooling system increases by 22.8%, and that of the water-cooling system decreases by 6%. The primary energy saving rate of the air-cooling system is 1.06 times and 6.67 times that of the water-cooling system and the air source heat pump system. The optimized air-cooling system reduces the annual total cost by 2.83%, and increases the energy utilization coefficient by 4.76%. The proposed air-cooling system has obvious advantages in energy saving and improving COP of heat pump. This study is useful for the cost savings and energy conservation of air-cooling concentrating photovoltaic/thermal (CPVT) coupled air source heat pump systems based on urban public buildings. • Models of different CPVT coupled ASHP systems are established in TRNSYS. • The optimization method integrates the advantages of TRNSYS simulation and the advantages of GH parameterization. • The systems are analyzed and compared from energy utilization coefficient, exergy efficiency, primary energy saving rate, annual total cost and net present value. • The ACPVT-ASHP system performance is best when the ASHP capacity is 9.9 kW and the length of PV cells is 1.819 m. [ABSTRACT FROM AUTHOR]

• Efficient operating range of the original district heating substation is below 1℃. • Proposed system formed by original components operates efficiently in whole winter. • Control strategies are based on the lowest primary return water temperature. • The proposed system has advantages in energy and economic performance. With the rapid development of heating technology, heating terminals are developing toward low temperatures and diversification, resulting in the simultaneous presence of different temperature demands in district heating systems. To reduce the primary return water temperature and satisfy the temperatures of different terminals, a dual-temperature district heating substation supplying dual temperatures of hot water with two absorption heat pumps and two heat exchangers has been proposed based on the design conditions. However, whether the dual-temperature district heating substation can operate and how to control this system during the entire heating period have not been explored. In this paper, the models for the substation with two absorption heat pumps and two heat exchangers and its subsystems were established to analyze and compare the operational conditions for the substation and its subsystems at different outdoor temperatures. By comparing the primary return water temperatures of all subsystems, control strategies and a combined system for efficient operation during the heating season were determined. Then a case study and analysis of the combined system were conducted under the proposed control strategies and compared with two other systems – two heat exchangers and two absorption heat exchangers – used in dual-temperature heating stations. Results show that 1) The original system with two absorption heat pumps and two heat exchangers could only operate when the outdoor temperature was −8–1℃. 2) The subsystem with a high-temperature absorption heat pump and two heat exchangers and the subsystem with two heat exchangers which could achieve efficient operation under outdoor temperature ranges of 1–7 °C and 7–11 °C respectively were considered in the combined system to broaden the operating range of the original system. 3) The combined system had the lowest return water temperature (23.8℃) and the highest coefficient of performance (6.60) during the entire heating season. The payback period of the combined system was 1.54 years. This study provides a reference for the efficient operation of dual-temperature district heating substations at different ambient temperatures during the heating season. [ABSTRACT FROM AUTHOR]

• The main thermal-hydraulic parameters of the ITER IBED PHTS have been assessed under selected operational scenarios. • The Fathom model of the ITER IBED PHTS has been revised and updated. • Three scenarios are presented, i.e. one that simulates hot standby conditions and the other two that simulate the normal operation. • The study confirms the correct operation of the system while highlighting some potential criticalities. One of the key elements for the success of ITER is the efficient removal of the thermal power generated by the deuterium-tritium fusion reaction within the confined plasma. The Integrated Blanket ELM/VS Coils and Divertor (IBED) Primary Heat Transport System (PHTS) is a pressurized, closed-loop cooling system designed to supply cooling water to the in-Vessel components. To support process design of the IBED PHTS, a thermal-hydraulic research campaign has been conducted to analyse the proper operation of the system during selected operational scenarios. The work has been carried out using the commercially available thermal-hydraulic software AFT Fathom, performing steady-state hydraulic and heat transfer analyses of complex hydraulic systems. The present paper summarizes the research activity, describing the computational model used and the scenarios investigated, as well as the results obtained and their critical discussion. [ABSTRACT FROM AUTHOR]

• Soft stimulation of the sedimentary reservoir. • Chemical stimulation successfully increased the injectivity by 4 – 10 times. • Precise placement and dosing of stimulation fluid is important. • Low lateral expansion of the sandstone layers at reservoir depth, mineral precipitation and biofilm formation cause clogging. Geothermal energy projects often lack sufficient permeability for a sustainable operation. If natural permeability is low, it can be enhanced by stimulation treatments. These can be of thermal, hydraulic or chemical nature. The challenge is to stimulate the reservoir successfully and at the same time to do it in an environmentally safe way. This is called soft stimulation and was extensively tested in the context of the EU-Horizon2020 DESTRESS project at several geothermal sites worldwide. This paper describes the successful thermal and chemical stimulation of a geothermal doublet in Mezőberény (Hungary), targeting a sandstone reservoir at 2000 m depth. A geothermal system was constructed in 2011–2012 aimed at exploiting the geothermal potential in the Békés Basin for a district heating system. The system with one production well and one reinjection well faced a severe injectivity drop during a 3-week operational period at the end of 2012, so that the operation had to be stopped. Historical data analysis, well logging, sampling and eventually a tailored stimulation program was designed in a 'soft' manner, according to standards developed in the DESTRESS project. The stimulation successfully increased the injectivity by 4 – 10 times, so that the system is ready to go into operation again. [ABSTRACT FROM AUTHOR]

The new generation of the district heating system (DHS) has attracted much attention due to its high efficiency. A precise and fast dynamic simulation is the foundation of the optimization and control strategy of a DHS. As a type of heterogeneous system, the DHS has internal components with multiple time scales, which limits accuracy of simulations. However, current studies have either chosen pseudo-dynamic models or have not considered the effect of the internal time scale on the simulation. To solve above problems, a dynamic multi-rate simulation method based on the individual-based model (IBM) is proposed in this paper. According to IBM, a complex system is decoupled into individuals, who interact with each other to form the whole system from bottom-up. During the process of modeling, equations of individuals indicating their dynamic behaviors are all converted into a system of ordinary differential equations (ODEs). And then the ODEs are solved from system level using multi-rate simulation methods. The case study illustrates that the proposed method takes 36.59 s for the 72 h long-term simulation of the DHS containing three components commonly involved and a district heating network, which provides good decision-making information for the optimal control of the system. • Individual-based multi-rate dynamic analysis method for heterogeneous systems. • Abstraction-based programming framework for IBM dynamic simulation. • Short-term simulation verification of a real DHN and long-term dynamic behavior analysis of a virtual DHS. • Compared with the forward Euler method, the proposed method is accurate and fast. [ABSTRACT FROM AUTHOR]

In the long-term operation of a geothermal heat pump system, when the cooling load is high, the temperature rise in the ground due to heat accumulation occurs. Changes in ground temperature hinder recovery of the temperature on the heat source side of the heat pump, and the performance of the geothermal system deteriorates because the heat exchange efficiency of the circulating water decreases. This problem can be solved by operating a hybrid geothermal system composed of an additional heat source system to the geothermal system. Therefore, in this paper, a method for operating a hybrid geothermal heat pump system was proposed to solve the degradation of system performance due to the temperature rise in the ground due to heat accumulation. The operating conditions for starting the operation of the hybrid geothermal heat pump system were derived, and the coefficient of performance prediction model was proposed for flow rate control considering the energy of the pump and the heat pump system. In addition, the proposed control method was evaluated for energy saving and performance improvement through simulation, and was also evaluated in terms of economic feasibility. [ABSTRACT FROM AUTHOR]

For the current molten salt storage heat to medium and high frequency electromagnetic coupling heating mainly, there are problems such as high failure rates and difficulties in achieving high-voltages and high-power. This paper proposes a power-frequency electromagnetic coupling direct heating technology that can realize high-voltage and high-power heating of molten salt. According to the theory of electromagnetic induction heating and the working principle of transformer, a power frequency electromagnetic coupling heating molten salt heat storage system that can achieve uniform heating effect is designed. By studying the influence of different heating power and different heat storage materials on parameters such as heat storage time, heat storage performance, and heat storage uniformity, a theoretical basis is provided for the system to determine a reasonable heating power and scope of application. A heat exchange tube layout scheme was proposed for the two operating modes of heat release, and simulation analysis was conducted. And the results show that the heat energy can be transferred outward quickly and uniformly. Through theoretical calculation and simulation experiments, the system can realize uniform heating and heat release of molten salt, and proposes a new solution to the current technical problems in the field of high-voltage and high-power direct heating of molten salt heat storage systems. [ABSTRACT FROM AUTHOR]

• Design of variable temperature BRDF measurement system up to 1000℃. • BRDF scanning measurements for hemispherical spaces of highly reflective surfaces. • BRDF measurements during two heating processes on a stainless-steel sample. Bidirectional Reflectance Distribution Function (BRDF) under variable temperature conditions is important for target identification and stealth in aerospace applications of highly reflective materials. In this paper, a variable temperature BRDF measurement system based on a robotic arm with an ingenious heater is designed. For BRDF measurements of highly reflective surfaces, a scanning strategy with variable angle intervals in continuous space is proposed to improve the resolution near the maximum BRDF and to reduce the measurement time. An ingenious heater is designed to be mounted on the robotic arm to move in space and heat a sample. The measurement uncertainty of the proposed variable temperature BRDF of highly reflective materials is discussed, which has been divided into the components of laser intensity fluctuations, scanning speed and heating stability. The effectiveness of the measurement system was verified by the variable temperature BRDF measurements during two heating processes on a highly reflective stainless-steel sample. [ABSTRACT FROM AUTHOR]

The EU's industrial sector discards about 18.9% of its energy as waste heat, much of which has the potential for recovery. This study addresses the challenge by focusing on the advancement of latent heat thermal energy storage (LHTES) using phase change materials (PCMs) encapsulated within industrial waste foundry sand (WFS). WFS, a problematic by-product, is repurposed as a supportive matrix for NaNO 3 and solar salt PCMs, tailored for effective integration into high-temperature industrial processes. The paper provides a thorough mechanical and thermal examination of the WFS-salt PCMs, highlighting their improved thermal stability, performance, and compatibility with direct thermal energy systems. The composite PCMs demonstrated melting points well-suited for industrial waste heat applications and achieved an energy density of 542.0 ± 8.3 kJ/kg for NaNO 3 and 516.0 ± 4.5 kJ/kg for solar salt, An experimental cascade PBLHS, based on these CPCMs, with a capacity of 262 MJ, designed to mimic an industrial heat source at 450 °C, was systematically tested to assess its energy density and efficiency over repeated charging/discharging and free cooling cycles. Its overall system efficiency is found to be 68.5%. These findings position WFS-salt PCMs as a promising and environmentally beneficial approach to enhance industrial energy efficiency and utilisation. [Display omitted] • Novel use case for waste foundry sand (WFS) is presented. • Composite phase change materials (CPCMs) based on WFS and molten NaNO 3 /SS are presented. • CPCM energy density is 542 kJ/kg for NaNO 3 and 516 kJ/kg for SS (25–450 °C). • A packed bed latent heat storage system based on WFS-CPCMs is presented. • The system with a capacity of 262 MJ has an overall efficiency of 68.4%. [ABSTRACT FROM AUTHOR]

For multi-family buildings with radiator heating system (MFBRHS) in China, on-demand heating is an important route to achieve energy saving, emission reduction, and improve user satisfaction. The current researchs are mainly focused on load forecasting and achieving heat balance by adjusting supply temperature or flow rate. However, the time-delay of disturbances factors and control parameters caused by the building envelopes and hydraulic coupling of the network is often ignored, which results in the failure to truly achieve heat balance. In this paper, a linearization method is proposed for the MFBRHS, and the frequency domain approach was employed as an analytical tool to gain a deeper understanding of the dynamic characteristics of the system. The results show that the selected building is equivalent to a low-pass filter. The average response speed of supply temperature and flow rate is slower than that of the solar radiation and outdoor temperature, which indicates that each control parameter should be delayed for adjustment to truly achieve heat balance. Additionally, the uncertainty of the building envelope only affects the magnitude of the disturbances while has a limited effect on its response speed. • The linearization method for multi-family buildings. • System controllability analysis in the frequency domain. • Impact of disturbances under uncertainty in thermal parameters of the building envelopes. [ABSTRACT FROM AUTHOR]

To achieve low-carbon goals, long-distance district heating (LDH) systems are widely applied, which utilize the waste heats from renewable energy power plants and waste incineration plants. The hydraulic oscillations induced by pump-stopping in LDH systems may give rise to critical incidents, such as pipeline ruptures and heating disruptions. The systematic analysis of hydraulic oscillations induced by pump-stopping and the subsequent revelation of critical factors that mitigate their intensity are fundamental prerequisites for ensuring the safety and reliability of LDH system. In this paper, firstly, a pump-stopping hydraulic transient model of the LDH system is established based on the distributed parameter method. Then, combining the method of characteristics (MOC) and the Newton iteration method, the numerical solution scheme for this model is proposed. Finally, taking a 20 km LDH system as an example, the characteristics of hydraulic oscillations induced by pump-stopping is analyzed, and the key factors influencing the intensity of these hydraulic oscillations are investigated. In addition, the differences between hydraulic oscillations induced by pump-stopping and those induced by sudden faults on pipelines are also analyzed. The results indicate that an optimal pump inertia moment value and a properly sized bypass pipe at the pump significantly mitigate hydraulic oscillations, while the influence of constant pressure at the heat source inlet on hydraulic oscillations can be negligible. Our study has important reference value for improving the safe and reliable operation of LDH systems. • 1.A pump-stopping hydraulic transient model of the LDH system is established. • A numerical solution scheme combined MOC and Newton iteration method is proposed. • Too small pump inertia moments intensify pump-stopping-induced hydraulic oscillation. • Bypass pipe reduces the pressure oscillation at the outlet of the heat source. [ABSTRACT FROM AUTHOR]

• The effects of three parameters were evaluated in terms of the system performance. • Factors affecting performance: filling ratio, cooling fluid flow rate and temperature. • 90 % of heat transfer resistance is between evaporator wall and ground. • Improving evaporator-ground heat transfer resistance most effective for performance. • Combining geothermal thermosiphons and heat/energy recovery ventilators. Geothermal thermosiphons (GTs) and Heat/Energy Recovery Ventilators (HRV/ERV) are two technologies, commonly used in buildings in cold climates to fulfill separate duties. GTs are primarily used to maintain the integrity of buildings/foundations built over permafrost, while HRV/ERV are used to meet indoor air quality requirements and reducing energy consumption within buildings. Operating separately, HRV/ERV is subject to frosting, which consumes energy, while the heat extracted by the GT is rejected in the environment. Such practice, plagued with a double penalty of inefficiency and energy waste, needs to be upgraded. In this paper, a new application is proposed where the heat extracted by GTs is no longer rejected to the atmosphere but is rather recovered to preheat the incoming fresh air of HRV/ERV units. An experimental GT test bench filled with CO 2 and fully instrumented was constructed to investigate the system's thermal performance. The effects of filling ratio, cooling fluid flow rate and temperature on GT operation were examined and discussed. The results indicated that the heat transfer resistance between the evaporator outer wall and the ground accounted for 90 % versus 10 % for the internal thermosiphon resistance, a fact which highlights the elevated overall thermal conductivity of this device. As a result, reducing the heat transfer resistance between the evaporator and the ground is most effective for improved heat transfer performance of the GT system. Furthermore, in the range of the selected tests conditions, heat transfer rate values per unit length of the GT ranged between 24.5 W/m and 61.6 W/m. [ABSTRACT FROM AUTHOR]