Heating Network Research Articles

Methodology for Fifth Generation District Heating and Cooling Network Simulation

5th generation district heating and cooling networks (5GDHC) will play a rolein the reduction of CO2 emissions and the resilience to global warming. Our analysis of the literature points out that no simulation study proposes a comprehensive enough description of such networks. The simulation solution presented in this article considers the intertwined influences between the thermal-hydraulic balance in the network, the behavior of the decentralized heat pumps and chillers at substations, and the thermal coupling with the ground. For a given simulation scenario, the 3 developed models are iteratively solved until convergence is reached. After showing how the latter is handled,we exhibit an original result about the influence of the differential pressure between the hot and cold pipes.

Evaluation of a Local Heating Network Supplied by a Pyrolysis Plant

In order to mitigate climate change, a wide range of negative emission technologies, such as pyrolytic carbon capture and storage, must be used in the future. This study therefore examines a specific application example for the energy supply with a pyrolysis plant that is operated with locally available biomass in the smallest district of the city of Freiburg. It is shown that such a supply concept is feasible and that the economic efficiency of the supply concept depends on the system output as well as the amount of local biomass and the revenues from the sale of the biochar. Of the six pyrolysis plants examined, two proved to be a promising alternative to the current wood chip boiler. By switching to an energy supply with a pyrolysis plant, the district could save several hundred tons of CO2 per year. The resulting total negative emissions would amount to almost 1200 tons of CO2 per year.

Survey of Industrial Excess Heat Potentials in Austria

In the research and service study for the Energy Transition 2050 program, the technical excess heat potentials for both energy-intensive and energy-extensive Austrian industry were surveyed. A bottom-up approach for most of the energy-intensive industry and a top-down approach for most of the energy-extensive industry were used by the consortium under the leadership of the Chair of Energy Network Technology EVT of Montanuniversität Leoben. The surveyed potentials were classified according to temperature level of excess heat, origin from the process, spatial occurrence and industry sectors. In order to estimate the future industrial excess heat potentials, a database of the innovation network "New Energy for Industry" (NEFI) was used. For the geographical localization, the results were integrated into the existing Austrian Heat Map, which enables a comparison with heat demand densities and existing heating networks. A technical excess heat potential of about 34 TWh could be identified. Thereof, about 300 companies of the energy-intensive industry, which were mainly calculated by the bottom-up method, account for a technical excess heat potential of about 26 TWh. For the energy-extensive industry, an excess heat potential of about 4 TWh was identified for more than 1500 companies using mostly the statistical top-down method. Due to existing know-how in the consortium, the technical excess heat potentials of more than 600 sewage treatment plants could also be estimated at approx. 4 TWh.

Planning Tools for Decentralized Heat Supply: Modeling the Effects of Volatile Renewable Energies

An increasing share of decentralized feed-in is necessary for the transition of district heating networks but it comes with various challenges. Software tools for modelling, simulation and optimization allow a theoretical examination of those challenges and possible solutions. Some of these have been used and further developed in the research project ZellFlex. One selected examination is the flexibility of supply temperatures by varying setpoint temperatures for a decentral solar thermal system (500 m²) integrated into an existing district heating network. The analysis of the supply temperature distribution in the network showed: A decrease of the solar thermal feed-in set point temperature by 5 K compared to the supply temperature of the central heat producer seemed acceptable in terms of security of supply, while a 10 K reduction comes with a high risk of undersupply. Furthermore, it was discovered that the points of time with the lowest supply temperatures at the consumers were just before and after they were provided with solar heat due to specific effects concerning temperature loss of the fluid.

Replacing Fossil-Fueled Combined Heat and Power Plants with Malta’s Pumped Heat Energy Storage Technology to Provide Clean Power and District Heat

This study analyzes the potential integration of a 100 MWel, 36-hour Malta Pumped Heat Energy Storage (PHES) system into the district heating network of the city of Hamburg, Germany, using energy from a nearby offshore wind farm that would otherwise be curtailed to charge the system. Publicly available data showing the times when curtailment instructions were given by the transmission system operator were used to determine the hours during which the storage system should be charged. Malta’s proprietary hourly performance model was used to simulate the behavior and performance of different plant configurations. It was shown that this configuration could avoid the curtailment of 227 GWhel of wind energy per year. The study showed that the system could provide 117 GWhel of electricity to the grid, as well as 72 GWhth of thermal energy for Hamburg’s district heating network, during periods where less renewable energy was available. This system could reduce the annual CO2 emissions by 101,400 tonnes compared to the coal-fired combined heat and power (CHP) plant that it would replace.

Day-ahead optimization of integrated electricity and thermal system combining multiple types of demand response strategies and situation awareness technology

Under the dual pressure of energy shortage and environmental pollution, relying only on increasing the installed capacity of units and line transmission capacity cannot cope with the conflict between the growth of power demand and the difficulty of grid expansion in the long run. Demand response conducts users to change their energy consumption habits through system-issued electricity prices or incentives, so that the demand of the load side can be adjusted flexibly, which can further enhance the consumption of wind power and improve system economics. Based on the background of diversified energy use, this paper proposes a day-ahead optimal scheduling strategy for integrated electricity and thermal system considering multiple types of demand response. Firstly, the dispatch framework of integrated electricity and thermal system with the situation awareness technology is constructed to address uncertainties of Renewable Energy Sources, thus helping system mitigate uncertain risks. Secondly, the demand response mechanism of power system and regional thermal inertia of thermal system are modeled, respectively, to uncover the principles of load regulation of different energy systems; Then, a day-ahead optimal scheduling model for the integrated thermal and electricity system is developed, and the consumption evaluation index is integrated to indicate energy utilization efficiency; Finally, a combined electric-heat system model with 39-node grid and 6-node heat network is developed, and the positive effects of considering multiple types of demand response and situation awareness technology on promoting the consumption of renewable energy and improving the energy efficiency of the system are verified through the case study.

Regulating Heat Networks: An Appraisal of the Energy Act 2023

Abstract Heat networks have the potential to deliver up to 20% of heat to homes in the UK by 2050 and are able to deliver significant reductions in carbon emissions contributing substantially to the UK’s 2050 net zero target. However, for many years the sector has been unregulated which means that some consumers of heat networks have been paying high prices for heating systems which may have been poorly constructed and which they do not understand. This analysis identifies three key problems that have arisen from a lack of regulation in the sector: higher prices for consumers, a lack of transparency and understanding of heat networks, and design and build problems, which have all served as barriers to realising low carbon heating in the UK. The recently enacted Energy Act 2023 will be analysed to determine the extent to which it will resolve these problems.

Washable and stable coaxial electrospinning fabric with superior electromagnetic interference shielding performance for multifunctional electronics

There is an urgent need for multifunctional and wearable smart devices to address the growing environmental impact on the human body, especially for pregnant women. However, it is big challenge to explore fabric combined multi-functions, such as EMI shielding, electrical therapy and biomotion detection while maintaining their intrinsic durability and washability. Here, we have employed an efficient coaxial electrospinning technique, followed by Ag precursor reduction and polydimethylsiloxane spraying to fabricate a multifunctional film which contains core–shell fibers with polyurethane/carbon nanotube (CNT) as core and polyurethane/Fe3O4 as shell. The CNT and the Ag nanoparticles (AgNPs) form double conductive network for EMI shielding, electrical heating and biological motion detection. The Fe3O4 provides magnetic loss and helps the fibers to provide rich attachment sites for AgNPs. The obtained film has an excellent combination of high EMI SE (110.0 dB in X-band), large Joule heating (up to 230 °C at 3 V), good sensing performance and large sensing range of 230 % strain. In addition, it showed an extremely superior durability and stability in complex conditions, good breathability and wash stability, ensuring the comfort wearing. This study offers an outstanding paradigm to construct next generation intelligent fabric combined versatility, stability and wearing comfort for protection of pregnant women and military solider.

Feasibility assessment of next-generation smart district heating networks by intelligent energy management strategies

Increasing flexibility of energy demand in a district heating network (DHN) results in both more possibility of interactions between the heating network and renewable resources and managing peak loads by shaving and shifting. This paper summarizes a series of tests performed in a large building complex that may drive future operational strategies for DHN. These novel strategies aim to impact selected customers with a specific range of heat consumption intensity to assess achievable flexibilities in heating demand without additional cost. The results show that a reduction in DHN supplied temperature by 6 °C does not significantly influence the heat consumption of customers equipped with radiators and thermostatic valves. However, its reduction by 10 °C, and 20 °C can impact users with higher consumed heat rates of approximately 0.2 and 0.1 [Unit/10min], respectively. Moreover, prolonging test periods until midday, when there is the highest probable outdoor temperature and solar irradiation may avoid sharp energy variations after tests.

Lumped‐element equivalent circuit modelling of district heating pipe in electromagnetic transients program

AbstractElectromagnetic transients program (EMTP) is widely used to analyze transients in power systems. With the increased interest in integrated energy systems (IESs), it would be beneficial to extend the application of EMTP to multi‐physics transients in integrated electrical and heating networks. In this paper, an accurate and efficient lumped‐element circuit model of the heating district pipe is developed in EMTP. The pipe is split into segments using spatial discretization. The application of the numerical discretization to the energy conservation equation gives the discretized pipe equation which is expressed in the form of a companion model of EMTP. In order to reduce the computational effort, the time‐varying terms in the admittance matrix of the companion model of pipe are eliminated. The modification of the admittance matrix is avoided. Furthermore, the internal nodes resulting from spatial discretization are eliminated, resulting in a lumped‐element circuit model with only two external nodes. Case studies are carried out to validate the proposed model in terms of accuracy and efficiency. The 2‐norm error of the proposed model is 0.0153%. With a pipe length of 100 m, the computational speed of the proposed model is increased by a factor of 2.94 compared with the existing distributed‐element circuit model. The implementation of the proposed pipe model in the EMTP‐type simulator enables the analysis of multi‐physics transients in a multi‐carrier energy system.

An Analytical Steady Heat Flow Calculation Method for District Heating Networks

An Analytical Steady Heat Flow Calculation Method for District Heating Networks

An Experimental Platform of Heating Network Similarity Model for Test of Integrated Energy Systems

An Experimental Platform of Heating Network Similarity Model for Test of Integrated Energy Systems

Multi-fault diagnosis of district heating system based on PCA_BP neural network

To diagnose multiple faults (blockage and leakage) of a district heating system (MFDHS) in a timely and accurate manner, a new multi-fault diagnosis method is proposed that considers fault diagnosis as a classification problem based on principal component analysis (PCA) and a Back Propagation (BP) neural network. Using this method, a simulation model of heating-network faults is constructed and fault experiments are conducted. Based on the simulation model and experiments, the experimental (ED) and model (MD) datasets are effectively constructed followed by the construction of substitute datasets(SD) that replaces the experimental data with model data. PCA and data standardization are then adopted to process all the datasets. Finally, three BP neural network classification models are trained and tested using the three datasets. To demonstrate the effectiveness of this method, four experimental heating networks, namely a single heat source and branch (SHB), single heat source and single loop (SHSL), double heat source and branch (DHB), and double heat source and double loop (DHDL), are discussed as case studies. The results show that the relative errors of the experimental and simulation data for the pressures and flow rates are less than 5%. The highest prediction accuracy is obtained when the fault to the normal data are 95–5% under training sets to testing sets of 70–30%, while for the four heating networks, the prediction accuracy of the method built with ED is 99.93%, 99.99%, 99.84%, and 99.66% respectively, whereas it reaches 99.99% for MD. The accuracies are 99.99%, 98.13%, 97.4%, and 99.99%, respectively, with MD serving as the training set while another 11400 sets of experimental data serve as the testing set. Accordingly, the accuracy ranges from 95.56% to 88.03%, 97.85–93.29%, 95.65–85.71%, and 100–84.82%, with SD serving as the training set and another 11400 sets of experimental data serving as the testing set.

Possibility assessment of the low-temperature district heating systems implementation in Ukraine

These researches concern the application of renewable energy sources in district heating systems. In Ukraine, district heating systems cover approximately 50% of the demand for thermal energy in the residential and communal sector. District heating systems 2G are most often used, which are characterized by high temperatures of the heat coolant, the lack of accounting for heat energy consumption during transportation of the heat coolant, and the use of fossil fuels. In the countries of the European Union, the introduction of district heating systems is considered one of the key directions for the transition to a decarbonized, environmentally safe and efficient energy system. The development of district heating systems technologies makes it possible to lower the temperature of the heat coolant in heat networks and increase the use of renewable energy sources. Ukraine will eventually become a full-fledged member of the European Union, and this determines the need to find ways to bring Ukraine's heat supply systems to the 4G level, in particular to low-temperature district heating systems with the most efficient use of renewable energy sources and waste heat. This article examines climatic, physical-geographical and social features, regulatory, technical and financial-economic opportunities and barriers to the implementation of low-temperature district heating systems in Ukraine. As a result of analytical studies, it was established that there are prerequisites for the introduction of low-temperature heat supply systems in Ukraine, however, a number of technical, regulatory, social and financial and economic measures need to be implemented to bring district heating systems up to 4G indicators. These studies allow establishing measures that require further research for the possibility of introducing low-temperature district heating systems in particular and environmental safety of heat supply systems in general.

Enhancing the Fermentation Process in Biogas Production from Animal and Plant Waste Substrates in the Southeastern Region of Bulgaria

Annually, a huge amount of waste from plant biomass and animal manure is produced from agriculture and animal farming. Many studies provide information on the biomethane potential of agricultural and livestock wastes, but only a few studies have investigated the application of the substrates in combination. The objective of the study is to enhance the fermentation process in the digester for biogas production, obtained from animal and plant waste substrates. In four batch processes for three months, the temperatures and the residence time of the substrates in the fermenter were analyzed. Simultaneously, electricity and thermal energy were produced via cogeneration units, which were exported to the public grid and city heating network. The plant substrate is a silage mixture of corn and wheat waste. The animal substrate is a mixture of beef and pig manure. Animal and vegetable waste raw materials are collected and transported to the site, located in the region of southeastern Bulgaria. The total annual consumption of animal and plant waste is 17,971 t/year. The enhancement of the process leads to the production of 1,506,000 Nm3 CH4/a of methane, the generation of which requires 299.63 MWh/a of electricity and 649.09 MWh/a thermal energy.

ANALYTICAL SOLUTION OF THE DIFFERENTIAL EQUATION OF HEAT CONDUCTIVITY FOR DAMAGED THERMAL INSULATION OF PIPELINES

For heat supply systems of Ukraine, the determination and forecasting of thermal energy losses during the transportation of heat carrier is an urgent problem. The thermal lines of the heating networks are long and its insulation is damaged. Installation of heat energy metering devices at all sources and all consumers (i.e. buildings) without exception allows determining and forecasting real heat losses in the heat network, but this is a difficult task, not all consumers and sources are actually covered by heat consumption accounting. The task of determining heat losses is also relevant for energy management systems of heat supply systems, energy companies and industry. The solution to the problem is proposed by a separate mathematical modeling of the temperature state of the section of the damaged insulating layer with the determination of the heat flow through it. It is proposed to solve the problem by the method of analytical solution of the differential equation of heat conduction with boundary conditions of the third kind. With the uniform distribution of characteristic damages along the total length of the pipeline, knowing the limits of damage influence, the share of insulation damage and the number of damages on the pipeline, it is possible to determine the real heat flow from the outer surface of the pipelines, including coefficient of increase of heat losses on the section of the heat pipe in relation to those determined by regulatory documents. Traditionally, one-dimensional models or determinations of the two-dimensional temperature field and actual heat fluxes in a cross-section to the axis of a characteristic damaged section of insulation are considered. But this does not take into account the two-dimensionality of the temperature field of the damaged layer of insulation along the length (that is, along the axis) of the pipeline. Therefore, the purpose of this work is to develop a methodology for determining heat losses through pipelines, taking into account the damage to their insulation and the distribution of characteristic damages along the length. The following simulation was carried out for one of the areas. Also, experimental and numerical studies using the finite difference method in combination with the method of running variable directions for similar models confirmed the coincidence of the analytical solution of the proposed model and the finite difference model within the permissible error.

THERMODYNAMIC IMPERATIVES THE MODERNIZATION OF THE ELECTRIC DRIVE OF PUMP UNITS OF THE CENTRALIZED HEAT SUPPLY NETWORK IN THE CONTEXT OF INCREASEING ENERGY EFFICIENCY

The relationship between thermodynamic and hydraulic parameters of the heat supply network has been established. The dependence of the electric power consumed by the electric drive of the pump unit on the pressure and supply of the coolant was determined. It is proved that the regulated electric drive system has advantages over the non-regulated electric drive system in the context of energy efficiency of the pumping unit and the district heating network in general. Approaches and criteria for the synthesis of a regulated electric drive system, including its automatic control system, were determined, regulation methods were analyzed, and the most acceptable version of the electric drive was chosen: a controlled frequency converter - an asynchronous motor with a short-circuited rotor, taking into account the above, an energy-saving mechanical system of a centralized heat supply network was synthesized. The peculiarity of this system is that the protection of parameters of hydraulic and temperature regimes in the network of centralized heat supply is ensured with the help of extreme automatic control systems. At the same time, the assignment of mode parameters is provided by the temperature controller of the heat exchange point of the network. Regulation of the pressure and productivity of the pumping unit is carried out by changing, according to a certain law, the frequency and power supply of the asynchronous motor.

Economic optimization and thermodynamic analysis of a novel nuclear district cooling system

“Yanlong” pool-type low-temperature heating reactor (DHR-400) stands at a highly promising nuclear heating technology. However, its annual utilization duration faces constraints when exclusively employed for winter heating. To cope with this challenge, a novel nuclear district cooling system driven by DHR-400 is proposed for the first time in this paper. As the core component of the proposed nuclear district cooling system, single-effect double-lift LiBr-H2O absorption refrigeration system (SDARS) can significantly increase the temperature difference between the supply and return of the primary heating network (PHN), thereby reducing the transmission energy consumption. Despite the significant potential, the optimization design of SDARS has received limited attention. An optimization model for SDARS with the annual cost (AC) as the objective function is developed. Focusing on a real district cooling scenario in Xi'an High-tech Zone, the heat transfer areas of all process units and the operating parameters of all streams in SDARS are optimized. Results demonstrate that the optimal annual average coefficient of performance (AACOP) is improved by 10.63 % and AC is reduced by 5.44 % compared with the Benchmark case. The dynamic payback period for the combined heating and cooling system driven by DHR-400 is reduced by 5.53 years compared to the heating-only system.

Heat Consumer Model for Robust and Fast Simulations of District Heating Networks Using Modelica

Dynamic thermo-hydraulic simulations of district heating networks (DHN) are essential to investigate novel concepts for their sustainable design and operation. To develop solutions for a particular case study, numerous long-term simulations are required. Therefore, computational effort for simulation is critical. Heat consumers (HC) are numerous and determine the dynamics of mass flows and return temperatures in the DHN. Thus, the way in which HCs are modeled has significant impact on the computational effort and the results of the simulation. This article presents a novel Modelica-based model for HCs that builds on an existing simplified modeling approach (open-loop design). The calculation of mass flow and return temperature is improved in terms of robustness, plausible behavior and low computational effort. In particular, the model reacts to limited differential pressure and supply temperatures to ensure plausible behavior across all operating conditions, including undersupply situations. The model is successfully tested using an exemplary DHN. The analysis proves that the HC model itself requires little time to simulate. Nevertheless, it significantly influences the simulation time for the entire DHN, which varies by a factor of five for the investigated system depending on the HC model. Fast dynamics, including a bypass in the model and correction of deviations between set point and actual heat load increase the simulation time, so users should sensibly choose how to use these options. HC models triggering many state events result in high computational effort. Compared to other simple HC models, the proposed model produces more plausible results while maintaining at least equal simulation performance (for models without bypass) or even improving it (for models with bypass, CPU time is reduced by at least 35%).

District heating system's development decarbonization strategy assessment by system dynamics modeling and multi-criteria analysis

The study introduces a hybrid model that integrates system dynamics modeling and multi-criteria analysis. Through the system dynamics model, the study examines energy, economic, and environmental indicators of a District Heating (DH) company, assessing its dynamics until 2050. Various decarbonization scenarios are explored, involving the transition of the DH system to a 4th generation DH (4GDH) system based on four strategies: utilizing at least (a) 50% Renewable Energy Sources (RES), (b) 50% waste heat, (c) 75% cogenerated heat, or (d) 50% of the combined aforementioned energy and heat. Additionally, development scenarios incorporate measures to enhance energy efficiency on the consumer side and within the heating networks. The sustainability of each scenario is evaluated using the multi-criteria analysis method TOPSIS. The hybrid model establishes a ranking of the transition pathways based on their sustainability scores and benchmarks the results of the developed scenarios against a carbon-neutral DH system. This model serves as a valuable guide for DH system developers and decision-makers. The study focuses on Riga as a practical case study.