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This paper presents a method to create a high-fidelity gearbox thermal model. A hybrid analytical-empirical model is presented, it is based on the thermal network approach and experiments are used to determine some unknown parameters of the model. A test campaign was led on a four stages helical gear unit and consisted of cooling measurements, no-load tests and loaded tests. These experiments were performed under different rotational speeds and loads. The results show that the developed thermal model provides an accurate prediction of the thermal behavior of different components of the gearbox (namely rolling element bearings and oil) by only using few thermal sensors. These results are corroborated by power losses measurements which demonstrate that the model can estimate the gear unit efficiency. [ABSTRACT FROM AUTHOR]

With the increasing importance of energy efficiency and sustainability, the demand for high-performance district heating networks is also on the rise. As traditional engineering methods were often no longer sufficient, several packages for numerical simulation have evolved. Many of them offer high accuracy at the cost of considerable manual preparation and computational effort. However, there is still no user-friendly software that is equally suitable for simplified studies in the early project phase, for the rapid optimisation of multiple concepts and for subsequent detailed planning and dimensioning. For this reason and in cooperation with some companies from the energy sector, we had conceived a novel, highly flexible modular approach, the so-called “quantum networks”, where all parts of the district heating network are appropriately abstracted into quantum elements. Now we present our recent implementation of this model in an object-oriented C++ library. Starting from a generalised base class and making use of the concepts of inheritance and polymorphism, the idea of different levels of detail for the same element type is directly realised and can always be further refined. In addition, as all elements are derived from the same base class, they all share the same outer appearance and can thus be easily combined or interchanged. Based on these prerequisites, a dedicated thermo-hydraulic solver has then been developed. Thanks to its recursive design requiring neither outer iterations nor matrix inversions, it proves to be extremely fast and is therefore suitable for rapid design or optimisation studies in which a vast number of configurations has to be computed. To conclude this part of the work, the developed C++ library was benchmarked on two use cases covering a full year of operation that can now be computed in approximately one second of runtime.

This study analyzes the potential for energy saving through the integration of a photovoltaic-thermal (PVT) system with a heat pump (HP) in a community with a small-scale thermal network. An empirical study was conducted in a community to analyze and compare the performance of a HP and small-scale thermal network with hub thermal energy storage system that utilizes the surplus thermal energy produced by a PVT system installed in a residential house from other buildings with that of an existing electric hot water boiler. The energy saving analysis of the proposed system revealed that the energy consumption could be reduced by more than 70 % compared to the existing system. The HP exhibited a COP ranging between 4.2 and 4.7. Throughout the experiment, the integrated system collected an average of 23.77 kWh of heat energy daily from the PVT units. The annual domestic hot water load coverage from PVT through the thermal network was found to be 50.4 %. These results indicate that PVT systems combined with thermal networks and HPs can effectively reduce energy consumption in individual buildings and enhance energy efficiency within communities.

The cost of manufacturing and electricity consumption are key considerations in encouraging the adoption of solar air heaters (SAH) in sunny and low‐income areas. These parameters can have a significant impact on promoting the use of these devices. In this study, solar air heating was designed with the objective of achieving the highest possible efficiency/cost ratio. It is a corrugated channel SAH whose structure is equipped with two barriers perforated with a sufficient number of holes for a good airflow distribution. A new model was developed to evaluate the qualitative parameters that describe the thermos‐energetic behavior of a heating system. These parameters were measured using experimental data obtained under real operating conditions. The thermal model assumes a uniform temperature for the glass, absorber, and insulation of the collector, while the temperature of the circulating air is assumed to vary linearly along the collector. To ensure that these assumptions were valid, the collector was cut into a number of 0.1 m sections in the direction of flow. By comparing the numerical results with the experimental data, the model was validated and then used to calculate the temperature profiles of the different elements of the collector, as well as to estimate the impact of certain operational parameters on its thermal performance. Relative percentage error values, between the numerical and the experimental results, of 1.7517%, 1.0750%, 0.8577%, 2.2371%, and 2.3637% for absorber plate temperature, outlet airflow temperature, useful power, thermal, and effective efficiencies, respectively, are recorded. [ABSTRACT FROM AUTHOR]

Gear transmission errors are influenced by temperature especially in the aerospace field. A model is proposed to investigate the influence of temperature on cylindrical gear transmission errors based on the thermal network (TETN). The gear temperature field distribution model is established based on the thermal network method, and gear thermal deformation can be calculated along the gear meshing line. Regarding the gear single-flank rolling process, the variation of gear transmission errors under temperature is determined. In numerical calculations in MATLAB, the variation of gear transmission errors at 100 ℃ compared to 20 ℃ is -4.20 μm, which decreases almost linearly while the thermal expansion coefficient of the gear material increases. The simulation of the gear transmission errors variation of temperatures using the finite element method (FEM) were carried out in Workbench software under Ansys and the average difference of the TETN model results between calculations and FEM for different temperatures was 0.24 μm. Experiments were carried out on the gear tester in temperatures ranging from 0℃ to 100℃, the TETN model results in calculations were compared with the results of the tester, and the average difference was -1.15 μm. The results show that the proposed TETN can be used as an algorithm to determine the variation of gear transmission errors under the influence of temperature. [ABSTRACT FROM AUTHOR]

Thermal interface materials (TIMs), as important materials for heat dissipation of insulated gate bipolar transistor (IGBT) modules, degrade under long-term thermal cycling, resulting in elevated junction temperatures and threatening the safe operation of IGBT modules. In consideration of the thermal coupling effect in IGBT modules, this paper proposes a three-dimensional thermal network model characterizing the TIM degradation. An IGBT module with the TIM is adopted to establish the finite element method (FEM) model, in which the TIM layer is divided into regular areas. The thermal network is established by simulating the heat transfer paths. The thermal impedance in each path is extracted according to the heat flow through its area considering the TIM degradation. Thereby, the impact of thermal coupling and TIM degradation on junction temperature of IGBT modules could be characterized. Furthermore, the proposed thermal network is verified by simulation from calculation accuracy of junction temperature and TIM temperature.

Copyright of Electric Machines & Control / Dianji Yu Kongzhi Xuebao is the property of Electric Machines & Control and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Abstract In order to more accurately and efficiently determine the loss and heating state of the magnetic pole area of a tubular hydro‐generator, this study establishes a comprehensive 3D electromagnetic field–thermal network analysis model of its pole area and implements calculations according to its rated symmetrical operating conditions. A 36 MW large tubular hydro‐generator is used as an example. Based on the measured results of the pole temperature and the use of the calculation hardware, the results are compared with the traditional electric circuit‐magnetic circuit‐thermal circuit method and 3D electromagnetic field‐temperature field finite‐element method. It is shown that the 3D electromagnetic field–thermal network model established in this study has several advantages, including high calculation accuracy, short calculation time, and low hardware consumption. These results have important value in improving the electromagnetic–temperature analysis and design of poles in large hydro‐generators.

Copyright of Bearing is the property of Bearing Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

In order to more accurately and efficiently determine the loss and heating state of the magnetic pole area of a tubular hydro‐generator, this study establishes a comprehensive 3D electromagnetic field–thermal network analysis model of its pole area and implements calculations according to its rated symmetrical operating conditions. A 36 MW large tubular hydro‐generator is used as an example. Based on the measured results of the pole temperature and the use of the calculation hardware, the results are compared with the traditional electric circuit‐magnetic circuit‐thermal circuit method and 3D electromagnetic field‐temperature field finite‐element method. It is shown that the 3D electromagnetic field–thermal network model established in this study has several advantages, including high calculation accuracy, short calculation time, and low hardware consumption. These results have important value in improving the electromagnetic–temperature analysis and design of poles in large hydro‐generators. [ABSTRACT FROM AUTHOR]

District cooling systems offer a promising alternative to conventional cooling, thanks to overall larger efficiencies and reduced carbon footprint. On the other hand they are characterized by large capital and operational costs that impede their diffusion. Optimizing the design and operation of these systems is therefore fundamental to fully exploit their potential. This paper proposes a novel optimization framework for the simultaneous optimization of design and operation of these systems. The model integrates a genetic algorithm at a master level with Mixed Integer Linear Programming models at a lower level. This approach enables the optimization of various aspects, including network topology, plant locations, supply temperatures and the selection of thermal storage technology. The study showed that in the specific case of Singapore, where the cost for space occupancy is significant, latent heat thermal storages are preferred. In addition, the results highlighted the cost benefits of thermal storage, as district cooling networks lacking it can be from 6.2% to 20.8% more expensive, depending on the scenario. Furthermore, the study demonstrated that the utilization of waste heat through absorption chillers enhances the economic feasibility of district cooling, lowering the payback time by up to 5 years. Lastly, it was observed that 3 °C increase of the indoor set point temperature could reduce the payback time by 3 years and increase the final net present value by 43%, as larger network supply temperatures allow chillers to operate with better performances. The developed model allows to estimate various crucial outcomes with few input parameters, representing a useful tool for both research and planning. • A hierarchical optimization model has been implemented. • NPV can be increased by 43% with an increase of 3 °C of indoor set point temperature. • When waste heat is available, payback time can decrease by up to 5 years. • District cooling without thermal storage is up to 20.8% more expensive. • Electricity cost influences the network topology and storage strategy. [ABSTRACT FROM AUTHOR]

The integration of renewable energy sources into existing district heating systems is imperative for the decarbonization of the global energy system. This transition is particularly challenging in existing systems that were originally supplied by fossil fuel plants and designed to operate with high supply temperatures. Reducing supply temperatures to facilitate the integration of low exergy heat may not be suitable for the existing infrastructure, due to both the heating devices or the thermal substations that may not support significant reductions or to the distribution infrastructure that can be unable to handle the required mass flow rate increases. To address these challenges, this paper focuses on the distribution infrastructure by introducing a physical-based approach to explore the current potential for supply temperature reduction of existing district heating infrastructures, taking into account the hydraulics of the system. Indeed, being able to identify the possible hydraulic bottlenecks arising in the network is essential to enable the transition of the networks and requires an accurate modelling of the fluid dynamic of the system. The methodology is fast and versatile, making it suitable for applications from small-scale to large-scale systems. An application to a real large-scale network is presented, proving the wide applicability of the methodology. Promising results in terms of temperature reduction are shown to be possible: the analyzed infrastructure is currently capable of shifting its operation from 120 °C to about 102 °C without considering invasive structural interventions on the network, and further reductions up to 90 °C are conceivable by assuming some adjustments to the system configuration. [ABSTRACT FROM AUTHOR]

It is important to have practical methods for constructing and learning a good mathematical model for a building's thermal system in the presence of unmeasured disturbances and using data from closed loop operation. With this goal in mind, this paper presents a mathematical framework that explains the asymptotic behavior of an estimated model under those conditions and that can aid in learning an accurate model. Some analytic results from the literature of system identification are extended and interpreted for building systems. A new identification approach for determining an accurate thermal network (RC) model for a multi-zone building is developed based on the analytic result, and its superior performance over a conventional grey-box modeling approach is demonstrated experimentally.

This article presents a high-efficient thermal analysis methodology and outlines a set of useful design guidelines for high-power linear ultrasonic motors. A thermal network modeling technique is introduced to rapidly calculate the temperature rise for a typical high-power linear ultrasonic motor with a V-shaped stator. First, a six-terminal equivalent circuit for Langevin piezoelectric transducer considering the prestress bolt loss and all three losses in piezoelectrics is proposed to calculate the stator loss. Then, the calculated losses along with the friction loss are used as inputs into the developed thermal network model to calculate the temperature rise of critical parts of the motor. Furthermore, an analytical mechanical model combined with the proposed thermal network is established to calculate the temporal–spatial distribution of the stator thermal stress for evaluating its fatigue under the heating-up process. Finally, some experimental measurements and finite-element simulations are conducted to validate the theoretical analyses. [ABSTRACT FROM AUTHOR]

Insulated gate bipolar transistor (IGBT) modules with multiple chips have wide range of applications, and the correct estimation for the thermal behaviors inside IGBT modules is becoming crucial. Thermal impedance matrix is one of the most adopted approaches to describe the thermal-coupling effect of IGBT module. For simplicity of analysis, the heatsink or ambient temperature is typically chosen as the reference node for the thermal-coupling impedance term, while the case temperature is simplified or ignored. This letter provides a thermal coupling model enabling case temperature as reference node. This proposed model decouples the thermal coupling impedances of IGBT module itself and external cooling condition, so that the modeling of cooling conditions outside device and inside the power module, can be separately considered. The characterization method and advantages of the proposed model are verified by an experimental demonstration, and the potential applications are further discussed. [ABSTRACT FROM AUTHOR]

The convective heat transfer characteristics of end-winding for a 10 kW external rotor PMSM with open end cap are studied in this paper. A coupling iterative method of CFD and thermal network (TN) is proposed to solve the motor temperatures and convective heat transfer coefficients (CHTC). The variation laws of the CHTCs and heat dissipation proportions of 10 kW motor walls with speed are analyzed. The heat dissipation capacities of the end-winding for motors with open and closed end cap are compared. Based on the CFD results, a fitting formula of end-winding CHTC for external rotor motor with open end cap is constructed, in which the Nusselt number is calculated by the dimensionless parameters composed of the geometric features of the open end cap. The validities of the proposed coupling iterative method and the fitting formula are verified by the temperature rise experiment of the 10 kW prototype. [ABSTRACT FROM AUTHOR]

Simulation and optimisation of district heating and cooling networks requires efficient and realistic models of the individual network elements in order to correctly represent heat losses or gains, temperature propagation and pressure drops. Due to more recent thermal networks incorporating meshing decentralised heat and cold sources, the system often has to deal with variable temperatures and mass flow rates, with flow reversal occurring more frequently. This paper presents the mathematical derivation and software implementation in Modelica of a thermo-hydraulic model for thermal networks that meets the above requirements and compares it to both experimental data and a commonly used model. Good correspondence between experimental data from a controlled test set-up and simulations using the presented model was found. Compared to measurement data from a real district heating network, the simulation results led to a larger error than in the controlled test set-up, but the general trend is still approximated closely and the model yields results similar to a pipe model from the Modelica Standard Library. However, the presented model simulates 1.7 (for low number of volumes) to 68 (for highly discretized pipes) times faster than a conventional model for a realistic test case. A working implementation of the presented model is made openly available within the IBPSA Modelica Library. The model is robust in the sense that grid size and time step do not need to be adapted to the flow rate, as is the case in finite volume models.

A temperature rise occurs when an electrical machine is fully loaded. The winding insulations of high-speed permanent magnet synchronous machines (PMSMs) are the most temperature-sensitive components, which can impact the machine's longevity. Thus, recently, prediction for high-speed PMSM winding temperature has been given more and more attention. Thermal analysis by numerical (computational fluid dynamics (CFD) and finite element method (FEM)) and analytical lumped parameter thermal network (LPTN) methods have been widely used to estimate the temperature of totally enclosed fan cooled axial ventilation system (TEFCAVS) machines. Although numerical methods have more accuracy, their computation wastes time. Therefore, LPTN is being utilized in this paper due to the fastness of its computation. Firstly, estimated losses of high-speed PMSM with TEFCAVS via electromagnetic analysis, including copper, iron, permanent magnet (PM) eddy current, sleeve eddy current, and mechanical, are coupled to the LPTN model, which acts as heat sources for temperature prediction. Moreover, analysis shows that slot windings' maximum temperature exceeds the winding insulation class with initial cooling configuration. Secondly, in order to mitigate slot winding temperature, the sensitivity study for liner conductivity, air gap's heat transfer and lamination to housing's contact is conducted by LPTN to identify which thermal parameter has more influence on mitigating the maximum temperature of the slot winding. Investigation shows that improving an air gap's heat transfer has more influence than other parameters for mitigating slot winding maximum temperature below its insulation class. Lastly, the machine is designed and tested with the best thermal-sensitive parameters. Then test results for the maximum temperature of the winding are compared with estimated results to ensure the proposed LPTN correctness, and the calibration process confirms LPTN accuracy. [ABSTRACT FROM AUTHOR]

This article summarizes the problems of the current high thermal conductivity polymer composite materials with boron nitride（BN） as the main filler, such as the agglomeration phenomenon of BN filler in the matrix and the high interface thermal resistance between BN particles and the matrix. In order to solve the above problems, three common methods are mainly used to modify the surface of boron nitride to make it functional, hybridize the filler particles, and construct a 3-dimensional boron nitride interconnection thermal network to achieve composite materials with lower BN loading, the high thermal conductivity. [ABSTRACT FROM AUTHOR]

Copyright of Tribologie und Schmierungstechnik is the property of Narr Francke Attempto Verlag GmbH & Co.KG and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

High-speed rolling element bearings for aircraft engines are custom-made components and operate under high temperature conditions owing to the elevated rotational speeds and loads. Therefore, assessing the various heat generation sources and mechanisms is worth investigating to accurately quantify the overall power loss within the bearing. In this context, a numerical parametric study was performed to determine and locate various power losses inside an aero-engine cylindrical roller bearing. Then, a thermal network model based on Ohm's law was developed to estimate the operating temperatures of the bearing elements. A series of experiments was carried out on a high-speed rolling element bearing test rig to validate the numerical predictions, such as bearing component temperatures and overall power loss at specific operating conditions. The numerical predictions based on a hybrid approach showed good agreement with the experimental data. [ABSTRACT FROM AUTHOR]

With an increasing penetration level of intermittent renewable energy sources and heterogeneous energy demands, the secure and economic operation of multi-energy microgrids (MEMGs) becomes more and more critical. Under this circumstance, this paper proposes an adaptive (two-layer) stochastic approach to obtain optimal MEMG operation decisions by taking advantage of distinct energy properties. First, rather than merely focusing on the active power economic dispatch, voltage/var control (VVC) scheme is involved to co-optimize the active and reactive power flow while guaranteeing voltage security; Second, a battery degradation model and a comprehensive thermal network model with thermal energy flow and transmission delay are presented to derive practical and efficient operations; Third, a conditional value-at-risk (CVaR)-based risk evaluation method is included to avoid over-optimistic solutions. The original nonlinear operation problem is reformulated as a mixed-integer linear programming (MILP) model to achieve high solution quality with acceptable computation performance. Finally, case studies are conducted to indicate that our proposed approach can effectively coordinate the dispatch of active/reactive power as well as thermal flow, thus ensuring system security with minimal operating costs and risks. [ABSTRACT FROM AUTHOR]

Based on the thermal network and the MATLAB artificial intelligence toolkit, a combustion optimization hybrid modelling of a 300 MW coal-fired power station boiler is carried out. The boiler is optimized for combustion, and the weight coefficient method is used to convert the multi-objective optimization problem into a single-objective optimization problem. The results show that the relative error average absolute value of the boiler thermal efficiency and NOx emission mass concentration calibration samples are 0.142% and 1.790%, the model has good accuracy and generalization ability. The weight coefficient method can select the corresponding weight coefficient according to the actual situation, with the boiler thermal efficiency or NOx emission mass concentration as the optimization focus, which has certain guiding significance for combustion optimization. [ABSTRACT FROM AUTHOR]

Copyright of Electric Power Automation Equipment / Dianli Zidonghua Shebei is the property of Electric Power Automation Equipment Press and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Electric Machines & Control / Dianji Yu Kongzhi Xuebao is the property of Electric Machines & Control and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

In order to make centrifugal blowers environmentally friendly, machines with a lighter weight and a more compact size are required. Thus, the axial length of the machine needs to be minimized within the diameter limit. However, in the design methodology, losses and thermal study become very significant; thus, losses increase significantly to achieve the desired output power when the volume is excessively reduced. Moreover, due to the machine’s compact size, heat is concentrated rapidly without adequate cooling. It might lead to a temperature rise of the critical part of the machine above the safe limit, such as winding, thereby affecting its lifespan. This study considers the 225 kW high-speed permanent magnet synchronous machine (HSPMSM) with the forced air cooling axial ventilation system (FACAVS) used in centrifugal blower applications. Firstly, four different analytical models (A2–A5) in the electromagnetic analysis are derived by minimizing the initial machine’s (A1) axial length to achieve a lighter weight and more compact size with better electromagnetic performance. The best among analytical models is chosen as the A4 model with a lighter weight and a more compact structure in addition to higher torque density than A1, A2, and A3 models, and higher efficiency than A1, A2, A3, and A5 models by HSPMSM’s, optimal geometric design, and optimal material choice, respectively. Secondly, LPTN is designed to predict the entire analytical model’s thermal behavior in the thermal analysis. Investigation shows that winding temperature rises from the A4 model is maintained below winding insulation by the determined optimal axial ventilation parameters from the sensitivity analysis. Finally, different analytical models are prototyped and tested. The comparisons between predicted electromagnetic performance, winding temperature rise, and test results were carried out, and the results were found to agree with each other consistently.

Frequency-domain modeling is a relatively new approach for thermal impedance description of power semiconductor devices, and it has shown promising advantages to analyze the multitimescale thermal dynamics of power semiconductor devices under complex mission profiles. However, parameters in the frequency-domain thermal model are still difficult to be accurately extracted, and sometimes the extraction process would be complicated and ambiguous depending on the construction of power devices and heat sink. This article proposes a new method to identify these key parameters of the frequency-domain thermal model for power semiconductors. The proposed approach utilizes the information of heat flowing out of device and only requires temperature responses of three different locations in the heat path of insulated-gate bipolar transistor (IGBT) module under a step power-loss. By the proposed approach, the critical frequencies in the frequency-domain thermal model of IGBT module can be extracted more easily and accurately. The effectiveness of the proposed method is also validated by simulations and experiments. [ABSTRACT FROM AUTHOR]

Featured Application: Dynamic simulation of Latent Heat Thermal Storage at system level; optimization of control strategies in multi-energy systems; investigation of Demand Side Management strategies. Nowadays, flexibility through energy storage constitutes a key feature for the optimal management of energy systems. Concerning thermal energy, Latent Heat Thermal Storage (LHTS) units are characterized by a significantly higher energy density with respect to sensible storage systems. For this reason, they represent an interesting solution where limited space is available. Nevertheless, their market development is limited by engineering issues and, most importantly, by scarce knowledge about LHTS integration in existing energy systems. This study presents a new modeling approach to quickly characterize the dynamic behavior of an LHTS unit. The thermal power released or absorbed by a LHTS module is expressed only as a function of the current and the initial state of charge. The proposed model allows simulating even partial charge and discharge processes. Results are fairly accurate when compared to a 2D finite volume model, although the computational effort is considerably lower. Summarizing, the proposed model could be used to investigate optimal LHTS control strategies at the system level. In this paper, two relevant case studies are presented: (a) the reduction of the morning thermal power peak in District Heating systems; and (b) the optimal energy supply schedule in multi-energy systems. [ABSTRACT FROM AUTHOR]

This study combines calorimetric measurement of power loss of an induction motor with inverse thermal mapping of its temperatures to segregate the net power loss into its constituent components. Constrained least square fitting is the tool used to achieve the inverse mapping. The lumped thermal network of the motor serves as the forward thermal model, establishing the physical relationship between the motor's power losses and its resultant temperature rises. The objective of the iterative minimisation is to find the actual loss components that correspond to the temperatures measured, and which sum up to the total loss of the motor that is measured with a calorimeter. Data ranges and constraints are imposed to attain a reasonable, unique solution. Each loss component predicted by the inverse mapping inherently includes the contribution from stray load losses as it is fitted to the measured temperatures of the motor. Given the challenges, this inverse thermal routine achieves the loss segregation in a fairly good fashion. [ABSTRACT FROM AUTHOR]

[Display omitted] • The nonlinear model of the thermal network was represented using the Taylor series expansion form. • A multi-layer control framework was defined by the dynamic temporal scales of different devices and processes in HE-IES. • The dynamic thermal storage processes of the thermal network were controlled with CGPC based on continuous time. • A hybrid continuous-discrete time resolution was proposed to reduce the computation complexity of the overall control model. The heat-electricity integrated energy system (HE-IES) presents a promising opportunity for increasing renewable energy generation by fully utilizing the dynamic heat storage capabilities of the thermal network (TN). However, the dynamic characteristics of the TN and the response characteristics of devices in the HE-IES present challenges to system operation and control. To address these challenges, this study proposes a novel multi-layer control strategy that divides the system based on the component response status. The first layer aims to minimize the operating costs of the HE-IES, disregarding any dynamic effects. The second layer optimizes the dynamic operation of thermal subsystems by employing a TN's Taylor expansion model and continuous-time generalized predictive control. The third layer focuses on optimizing the power subsystem to enhance the share of renewable energy generation, using discrete-time model predictive control. To the best of our knowledge, this is the first study that utilizes continuous time models to control the dynamic operation of TNs and their thermal subsystems. Through case analysis, the proposed model achieves a 34.5% reduction in operating costs compared to a single-layer control strategy and a 2.7% reduction compared to a discrete-time multi-layer control strategy. These findings highlight the favorable economic performance of the proposed model. Additionally, the utilization of continuous-time model allows for effective capturing dynamic performance of the TN and enhances its role in system operation. [ABSTRACT FROM AUTHOR]

Due to the flame resistance and lubricity of ethylene glycol solution, an ethylene glycol piston pump can be used as motion sources for extreme operating conditions. In this paper, a novel variable liquid-properties thermal network model (VLTNM) is proposed to analyze the thermodynamic characteristics of piston pump. The VLTNM considers the interaction between the changes in properties of liquid passing through piston pump and the heat generated by motion, and calculates the heat transfer between solid and liquid through a thermal network. A numerical calculation model for VLTNM is established in MATLAB using simscape language, and the results show that the temperature rise of outlet liquid can be reduced by 10.36%, when the thermal conductivity of shell is doubled. The working pressure has a positive effect on temperature variation, which is more significant in high-temperature environments, while the volume fraction of ethylene glycol solution has a negative effect. Additionally, a high load helps to improve the efficiency of piston pump, while the temperature rise caused by high pressure can also reduce the efficiency. When the working pressure increases from 6 MPa to 10 MPa, the efficiency decline of piston pump increased by 1.12%. Besides, comparing the two models of variable and non-variable liquid properties, there is a significant deviation in steady temperature of outlet liquid. The deviation in low temperature is more prominent, with a deviation of 6.1% when the temperature of air is 10 °C. Finally, the predicted steady temperature by VLTNM is in good agreement with the experimental data in reference, with a prediction error of less than 2.01%. [ABSTRACT FROM AUTHOR]

Increased use of energy in buildings and HVAC systems requires advanced control schemes like model-based control to improve energy efficiency, which in turn requires accurate thermodynamic models of buildings. The Resistive-Capacitive (RC) method is a popular and versatile approach for thermal modeling of buildings. Despite this, it is not easy to find practical solutions of implementation of the RC method. It is the goal of this paper to clarify the RC method and demonstrate simple implementation of this method, especially for multi-zone buildings, which have more potential for energy savings from use of model-based control. This paper provides two contributions. First is a detailed explanation of the RC method, focusing on its use for developing a structure of a model and first-principles approach for estimation of parameters of a model. Second is a demonstration of an algorithm that enables automatic development of the structure of a model from basic information about a building (layout, construction elements) and its combination with data-based parameter estimation. Use of the algorithm is presented with a case-study on industrial multi-zone building, for which such a grey-box model is developed and analyzed. The resulting model is rapidly developed and used in a simulation with the measured data. The outputs of the model are compared with the measured temperatures and they show good fit.

District cooling and heating methods that can utilize highly efficient heat pumps and various unused new and renewable types of energy are required to achieve low carbon emissions and zero energy usage in buildings and community units. The technical requirements for the implementation of decentralized thermal networks and heat trading are increasing, both for thermal networks in new buildings and for those remodeled based on existing centralized thermal networks. In this study, a conventional centralized thermal network was implemented as a decentralized thermal network and the possibility of heat prosumers feeding thermal networks was demonstrated experimentally. A real-scale plant was constructed by employing unused thermal energy facilities as prosumers in a school and childcare center based on the existing small-scale block heating and cooling thermal network. The decentralized thermal network and heat prosumer concepts were proven through operation experiments performed on the constructed system in summer and winter. An economic benefit can be achieved by increasing the peak power cost. The experimental results also showed that the proposed bi-directional heat trading reduced carbon emissions by 12.7% compared with conventional centralized thermal systems.

Improving the repair service system is becoming more and more important task in various industries. Damage from undersupply of heat energy to consumers is greatly reduced when decreasing time from the moment of damage occurrence in the centralized heat supply systems to detection and correction of this corruption. Thus, to reduce prejudice and for successful solution of problems of resource saving the time limit for the recovery period is of considerable importance. This is the urgency of the task. The work in the field of resource saving deployed in the Russian Federation in the past years makes the task of nationwide scale. The main aim of the study is to analyze the repair and maintenance documentation elements of the district heating of the large cities in the Russia Federation; classification of defects, creation and processing database of defectiveness. The methods used in the study. The authors have used the advanced statistical treatment of results and experimental studies; methods of probability theory and mathematical statistics. When developing the databases of damage and work with them the software packages Microsoft Access database and Excel, Autodesk AutoCAD, Statistica were used. The results. Based on the data collected by the heating system of the 21 cities in the Russian Federation the authors carried out a comprehensive analysis of damage: according to the terms of exploitation; on the elements of the heat supply system; for reasons of appearance, the elements and depending on the laying method. The "weak" points were identified and the causes of elements damage in the district heating systems were established.

The forced air cooling system plays an important role in the safe operation of power converters. Condition monitoring its health status can improve the reliability of power converter and reduce the cost of unscheduled maintenance due to over-heating. This letter proposed to use the natural frequency of thermal network as an indicator to monitor the aging process of cooling system. We show that the degradation of the cooling system can be monitored by detecting the variation of thermal network natural frequency. Experimental tests on a three-phase dc/ac converter with forced air cooling system are performed to verify the effectiveness of proposed method. This method is simple to implement and does not need to measure the power loss. Moreover, it enables the concurrent monitoring of multiple components in the cooling system. [ABSTRACT FROM AUTHOR]

The positioning precision of the ball screw system in machine tools is primarily affected by the thermal deformation of the screw. Hence, the adaptive prediction method must be established to calculate thermal errors of the ball screw system. First, based on heat transfer theory, a new adaptive moving thermal network model of the screw system with moving thermal excitation and varying operating conditions is proposed. The time-serial data of kinematic-pair representative temperatures and the time-serial position data of the moving nut are used as inputs. This adaptive model is used to determine the temperatures of the key elements in the supporting bearings and those of the moving nut and key points of the screw shaft. Further, the heat generation rate of each kinematic pair can be obtained simultaneously. Furthermore, a real-time prediction method of thermal errors of the screw system with moving thermal excitation under various operating conditions is presented. The effectiveness and robustness of the real-time prediction method of thermal errors was verified experimentally. This method is suitable for the rapid prediction of thermal errors of screw systems by monitoring the real-time kinematic-pair representative temperatures and real-time position of the moving nut. • A new adaptive moving thermal network model for a screw system is proposed. • Based on the moving network model, the real-time thermal error model is proposed. • The heat generation rates of the heat sources are simultaneously identified in real-time. • The presented model can be used for the multiple varying working conditions. • This model has self-adaptive ability and robustness. [ABSTRACT FROM AUTHOR]