Operation Of District Heating System Research Articles

Integrating Low Temperature Waste Heat in District Heating Systems. Legal Framework and Pricing Mechanisms

ABSTRACT:Decarbonisation the heating sector is a key challenge for the European Union to achieve its ambitious goals of becoming the first climate - neutral continent in 2050. Decarbonising the heating sector is about reducing fossil fuel consumption and finding new scenarios based on renewables and restructuring the operation of district heating system. Recovering and integration waste heat into the district heating system has an enormous potential to meet the heating needs of households through non – combustion technologies while reducing carbon emissions. The heat from urban sources of waste heat is advantageous because the heat sources are, close to district heating networks and close to areas with high heat demand. However, there is still no legal or regulatory framework for the use of waste heat and no incentives for its use in district heating in the Member States of EU.This paper has two main objectives: firstly, to consider different pricing and cost determination scenarios when the waste heat is integrated into the district heating system. The heat tariff calculation model is based on the approved Latvian heat tariff calculation methodology. Secondly – to consider a mathematical model for the pricing of waste heat. The waste heat integration strategies are tested on the Case study of district heating system in Salaspils, Latvia. Simplified model of a waste heat recovery system that recovers heat energy from a wastewater treatment plant through heat pump integration is developed.

Heat exchanger control: Using deep-Q network

To achieve stable operation of district heating systems and improve the performance of heat exchange station control systems, this paper explores the application of intelligent control algorithms for controlling district heating systems. Initially, a heat exchanger neural network model is established. Secondly, a mass regulation controller based on a deep reinforcement learning algorithm is designed to accurately track the desired outlet temperature of the secondary side set point. Finally, the performance of the controller in terms of tracking response and disturbance suppression is verified using an example of a district heating system. The experimental results demonstrate that the controller exhibits minimal overshoot, with the outlet temperature of the secondary side deviating by less than 1 % when the controller setting value changes. Additionally, during disturbance suppression response, the deviation of the outlet temperature of the secondary side remains within ±2 °C. Compared to other controllers, the designed controller exhibits superior dynamic performance across various operating points and under different disturbances. Additionally, it outperforms traditional control methods in terms of stability and disturbance rejection capabilities.

Carbon capture from combined heat and power plants – Impact on the supply and cost of electricity and district heating in cities

The capture and storage of biogenic CO2 emissions from large point sources, such as biomass-combusting combined heat and power (CHP) plants, can contribute to climate change mitigation and provide carbon-negative electricity while supplying district heating in urban areas. This work investigates the impact of retrofitting CO2 capture processes to CHP plants in a city energy system context. An energy system optimization model is applied to a case study of the city Västerås, Sweden, with scenarios involving two existing CHP plants in the city, retrofitted with either a heat-driven (MEA) or an electricity-driven (HPC) carbon capture process. The results show that the CHP plants might be retrofitted with either option without significantly impacting the district heating system operation or the marginal costs of electricity and district heating in the city. The MEA process mainly causes a reduction in district heating output (up to 30% decrease on an annual basis), which can be offset by heat recovery from the capture unit. The electrified HPC process does not impact the CHP plant steam cycle but implies increased import of electricity to the city (up to 44% increase annually) compared to a reference scenario.

Identifying supply-demand mismatches in district heating system based on association rule mining

Supply-demand mismatches in district heating system (DHS) may affect system's safe and stable operation without reasonable regulation actions in time. The accurate identification of supply-demand matching states is the prerequisite for heat balance regulation. However, this job is quite difficult and time-consuming, as DHS is typically a large time delay system and operates under various conditions. This paper proposes an association rule mining-based method to identify supply-demand mismatch from DHS operation data. Considering DHS's thermal inertia and fault-tolerance, the supply-demand mismatch rate is firstly defined along with its quantitative evaluation model. Then the theoretical intervals of the heating parameters are obtained by establishing association rules and rules post-processing. And a reasonable error band is decided by comparing the occurrence times of mismatches to balance identification accuracy and sensitivity. The proposed method is tested and verified in a typical DHS. The rules between primary supply temperature and relevant operation parameters are mined. An error band of ±7.5% is determined by comparison with historical operation data. The supply-demand mismatch rate is calculated to be −10%–15%. The identification results are validated by analyzing the heat substations' operation data including supply and return temperature, flow rate, and valve opening.

Benefit allocation for combined heat and power dispatch considering mutual trust

Combined heat and power dispatch (CHPD) has attracted wide attention recently, which exploits the potential flexibility in the district heating system (DHS) and provides an economic-effective solution for better wind accommodation. However, DHS operators bear extra operation cost in CHPD, which is proved theoretically in this paper, so that they have insufficient incentive to coordinate with electrical power system. To cope with this issue, a cost allocation strategy based on the Aumann-Shapley value method is proposed, which can rationally allocate the benefit among multiple agents. And a new solution scheme with the Gauss-Legendre quadrature formula is developed to enhance computation efficiency. Also, considering the potential malicious behavior of dishonest agents in the process of allocation, the blockchain framework with Proof of Solution consensus mechanism is introduced to ensure mutual trust among multiple agents. Numerical simulations based on different cases demonstrate the effectiveness of the proposed method of benefit allocation among multiple agents. In addition, the validity of the proposed blockchain framework in preventing malicious behavior when CHPD is verified.

ИССЛЕДОВАНИЕ РАБОТЫ ЦЕНТРАЛИЗОВАННЫХ СИСТЕМ ТЕПЛОСНАБЖЕНИЯ В УСЛОВИЯХ СЕЛИТЕБНОЙ ЗАСТРОЙКИ

The article considers methods to improve the modes of operation of district heating systems in residential areas. The authors identify the problem of heat carrier heat supply to the final consumer and describe the main factors that influence the deviation of the design parameters of the heat carrier. The concept and example of the application of the heat supply scheme for residential developments is given. The paper demonstrates methods of regulating the heat carrier and their effect on the operation of the heating network. The authors give schematic diagrams with the peculiarities of each method operation in case of deviation of parameters of supply of quality heat carrier to the final customer. The operation of control valves with different variations of their installation in the heat supply system is shown graphically. It can be concluded that there is a need to revise the provisions of the concept of district heating concerning the regulation of heat loads and the structure of coverage of heat loads of consumers.

Optimal quantity, location and capacity allocation of the additional renewable energy stations in a large-scale district heating system and comprehensive case analyses

Integrating the combined heat and power (CHP) plants with distributed renewable energy stations (RESs) is an important way to promote the low-carbon development of district heating system (DHS) and to further achieve “carbon neutrality” goal in the future. However, when the total capacity of power-to-heat devices is determined by district energy planning, different configurations (quantity, location, and installed capacity allocation) of additional RESs show various energy-saving potential in the long-term operation of DHS. In this study, an integrated optimization model consisting two independent optimization modules is proposed, aiming at maximizing the comprehensive economic benefits of distributed RESs. A novel virtual split method is also introduced to simplify the operating optimization of DHS. In addition, to ensure the reliability and accuracy of optimization calculation, a heuristic optimization tool (genetic algorithm) is applied to solve these non-linear optimization problems. Case studies from a real trans-regional DHS indicate that a reasonable configuration of additional RESs optimizes and equalizes the distribution of pressure and flow in the primary DHN, and the heat dissipation of flow energy in regulating valves and transmission pipelines can be reduced considerably. The proposed integrated optimization model and its solving processes can be migrated to other similar projects worldwide.

Experimental research of electrical characteristics combined solar-electric air heater

Poor water quality in district heating systems leads to failure of boilers and pipelines in heating networks. The main reason for this is corrosion and scale deposits. The presence of these factors shows the low efficiency of water treatment systems. The article presents the results of the introduction of non-traditional water treatment technologies for district heating systems based on the experience of the Zhytomyrteplokommunenergo utility company of the Zhytomyr City Council in 2007-2021. In the boiler houses of the enterprise, water treatment systems were modernized, and the production chemical service was reorganized. In particular, chemical deaeration was launched in combination with traditional sodium cationization, as well as chemical deaeration in combination with complexonate water treatment against the classical water treatment technology - ion exchange. Installed magnetic sludge separators with magnetic inserts. The technology of water softening with anti-corrosion protection using Redox filters has been introduced. Gravimetric corrosion sensors of our own design have been developed and installed. The database of processing and statistical analysis Access "Corrosion damage of pipelines of heat networks" was created and put into operation. The experience of modernizing the water treatment system has shown that work in this direction increases the reliability of operation of district heating systems by reducing the consumption of energy carriers and material resources. In addition, the problem of improving the operational reliability of the heat exchange equipment of thermal stations needs to be solved. The projected start of the use of heat recovery devices on water heating boilers in operation, in condensation or partially condensation modes, will also bring with it a number of problems with the neutralization of condensate and its return to the heat supply system. The end result is an increase in production reliability, environmental friendliness and a reduction in the cost of heat for district heating systems.

Day-ahead heat load forecasting during the off-season in the district heating system using Generalized Additive model

The paper presents the results of heat demand forecasting during the off-season (summertime and transitional period) in a real district heating system. The hourly heat demand in the analyzed system ranges from 16 to 28 MW, depending on the month and hour of the day. Short-term prediction of the heat demand in the day-ahead horizon is needed for effective operation of production units in the Cogeneration Heat and Power Plant (CHP). The method of an hourly heat load predictions using a data-driven model is presented. The algorithm is based on the Generalized Additive Model with hour of the day, day of the week and day of the year as predictors. A way of increasing the accuracy of forecasts using the autoregressive model for residuals of the model was discussed. The influence of the training dataset size on the model error was also examined. The several versions of the model were evaluated by comparing forecasted results with real values during the district heating system's operation from June to the end of August. For the most accurate one, Root Mean Square and Mean Average Percentage Error were 0.84 MW and 3.3 %, respectively.

Design optimization and granularity analysis of district heating systems for distributed solar heating access

In the low-carbon transition process of district heating systems (DHS), the need for widespread access to renewable energy and lower carbon emissions conflict with the existing structure of large centralized DHS. This paper proposes an optimized design of the DHS based on granularity analysis methodology to harness distributed solar energy. This study applies a hierarchical clustering method to get the possible scheme set based on the given geometrical information of an area with distributed solar heating system (SHS). This study further carries out pipe network routings and the pipeline sizing optimization to implement the scheme with the best economic performance. To disclose the relationship between granularity and SHS access ratio, we propose a quantitative granularity estimation method considering the spatial distribution of heat in the sense of Manhattan distance. This study calculates optimal schemes' total annual cost (TAC) and potential operation instability (PRI) under a series of SHS access ratios. A real DHS covering a heating area of 164300 m2, and 21 buildings is selected for a case study. At a granularity of 4.50%, TAC is reduced by 16.04%, and PRI by 58.06% compared to the existing design where granularity is not considered and one substation covering the entire area. As the SHS access ratio increases from 0 to 12%, the optimal granularity value increases from 4.50% to 16.84%, indicating a higher granularity is necessary to utilize solar energy. Our work shows that a proper selection of granularity in the design stage is essential to the economic and stable operation of DHS with renewable energy access. The result from this study is also meaningful to the design and operation control of district energy systems and integrated energy systems.

Study of an Integrated Control Method for Heating Substations Based on Prediction of Water-Supply Temperature and Indoor Temperature

The refined control of heating substations is of great significance for on-demand heating provision and for the efficient operation of district heating systems (DHSs). This paper proposes an integrated control strategy for substations based on the prediction of the water-supply temperature and indoor temperature. Firstly, online sequential extreme learning machine (OS-ELM) is used to predict the water-supply temperature. Then, a linear prediction model is established to predict the indoor temperature. Finally, the integrated regulation strategy is established with the goal of minimizing operational costs, aiming at ensuring heating quality and meeting the limits of the flow rate and of the supply- and return-water temperatures. The heat-saving rate, power-saving rate and indoor-temperature satisfactory rate are introduced to evaluate the regulation effect of the proposed method. The field study results show that the performance index of operation executed with the regulation strategy proposed in this paper is 9.31%, 16.33% and 20.87% higher than that without our energy-saving regulation strategy respectively. The fluctuations in the water-supply pressure and differential pressure of the secondary network are significantly reduced, and the energy-saving effect is obvious.

Improving a heat supply system by increasing the efficiency of the heat pump unit

The reliability and efficiency of the operation of district heating systems is largely determined by the efficiency of preparation of heating network water. In open heat supply systems, make-up water, among other things, compensates for the water intake in hot water supply systems. A number of technologies have been developed that increase the efficiency of an open heat supply system by reducing the water consumption in the supply pipeline of the heating network, increasing the operating time of the heat pump, and increasing the specific generation of electricity for heat consumption at the CHP plant due to additional cooling of the network water in the return pipe of the heating network.

Some aspects of ecological engineering in modern heating systems of cities

This article outlines the results of a study of some aspects of implementation and use of ecological engineering elements in the heat supply systems of large urban agglomerations of the Russian Federation. It considers important problems associated with the definition of the term ecological engineering, defines the elements of ecological engineering that can be introduced into the sphere of heat supply of large urban agglomerations. It provides the data on heat energy losses in some subjects of the Russian Federation with harsh climatic conditions, in which heat supply to the large cities lasts for over 9 months a year. The article also identifies the main challenges the heat supply systems used in large metropolitan agglomerations of the Russian Federation face related to the modernization and digital transformation of the heat supply sector of Russian cities. It designates the main problems and opportunities of ecological engineering, which will allow, if widely implemented, providing remote control of the operation of district heating systems, controlling their temperature regime and pressure in pipelines, carrying out the necessary engineering calculations of the functioning of the systems relative to the topography of a particular urban agglomeration. In addition, the study outlines important components of the digitalization of district heating systems in cities to ensure their efficient, effective and, most importantly, safe for the ecosystems of large urban agglomerations, functioning. It has been established that ecological engineering in the district heating industry of large urban agglomerations has to be directed at conservation and restoration of the reserves of natural thermal resources, as well as the natural environment as a whole, by reducing the intensity of operation and emissions into the atmosphere that are produced during the processing of fuel resources.

Leak detection of long-distance district heating pipeline: A hydraulic transient model-based approach

Long-distance district heating pipelines (LDHPs) are important infrastructures in large scale district heating (DH) system. Their safety and stability are crucial for stable and efficient operation of the whole DH system. Pipeline leakage is a common accident in the operation of DH system, accurate and fast leak detection technique is an indispensable measure for ensuring efficient repair and avoiding large-area heating failure. In this paper, a fast and accurate leak detection technique for LDHPs is proposed. The technique utilizes the numerical hydraulic transient model of the LDHP and the particle swarm optimization (PSO) algorithm to find the leak point. A pressure wave velocity identification procedure is also established for the leak detection. Simulation tests are conducted on a 20 km LDHP to investigate the influences of instrumental error and sampling frequency of measured data on the accuracy of the leak detection. Results show that when the sampling frequency is higher than 0.1 Hz, the relative errors of the detected leak point areas and leak point positions can be less than 2.73 % and 2.40 %, respectively. Effective leak detection of LDHPs can be therefore conducted through the proposed leak detection technique and measuring instruments with high precision and proper sampling frequency.

Improvement of methods of comprehensive assessment of the operation efficiency of centralized heat supply systems in municipal heat power engineering

The possibility of a comprehensive assessment of the efficiency of the operation of a district heating system based on the indicator of the overall efficiency of the equipment OEE (overall equipment efficiency) and its extension to the system as a whole is considered. The disunity of the direction of existing approaches in assessing the efficiency of operation of district heating systems does not allow a comprehensive assessment of the overall efficiency of the functioning of the technological sequence of the entire system. It is proposed to consider efficiency as the probability of full functioning of all elements of the heat supply system. It is shown that the heat output of the boiler house is proportional to the power consumption of the boiler house and is approximated by a periodic function. It is shown that the main element of the heat supply system, which determines its efficiency, is the heat-generating source. As a result of the study, it is determined that the efficiency of the heat-generating source functioning increases as the maximum value of its efficiency is reached. Numerical modeling has shown that the flexible use of the installed heat generator capacity contributes to an increase in the efficiency factor from 0.53 to 0.70 and the overall efficiency of the heat supply system can be increased by more than 30 %. When designing a boiler house, it was recommended to provide for the installation of capacities with gradation 1; 0.5; 0.25. It is shown that the OEE indicator allows one to characterize the efficiency of both the heat supply system as a whole and its individual components, and can be used in the design and analysis of the operation of systems

Landscape of district heating systems in Germany – Status quo and categorization

Abstract Studies on decarbonizing district heating systems are either system specific or use artificial district heating systems. In contrast to the liberalized electricity sector, there are no disclosure obligations in the district heating sector. This paper offers eight district heating system categories, representing the landscape of district heating systems in Germany as of 31st December 2019. As a basis, the German district heating systems and their heat generation technologies were researched using public power plant lists, notices and approvals by the authorities, press releases, plant brochures, and operator websites. The collected data was validated through individual contact and information gathered by the AGFW, the German District Heating Association. Key figures based on economic and operational anticipated behavior are formed and evaluated for 82 district heating systems with an installed thermal capacity each greater than 50 MWth. Those key figures are then used in an agglomerative clustering algorithm to form the presented categories. By publishing the key figures, the inaccessibility of data is overcome, and the complexity in models for studies on a national level can be reduced. Possible transformation pathways can be derived per category and district heating system operators can transfer the results to their own systems.

INVESTIGATION OF THE FREQUENCY OF DAMAGE TO HEATING NETWORKS

This article is devoted to improving the efficiency of planning the consumption of material and technical and labor resources and their appropriate planning for heating and non-heating periods, by months of the year based on the calculation of the estimated number of damage to heating pipes, based on the obtained dependences of failure rate. This task is modern and relevant especially in conditions of limited funding of engineering systems. The object of study - the district heating system. The subject of research - pipelines of thermal networks. The purpose of the work is to determine the distribution of damage to the heating network pipelines by months. The research method is statistical modeling of damages of heating network pipelines by months of the year for different terms of their operation. Currently, the reliable operation of district heating systems and their heating networks is one of the main factors in the livelihood of settlements. The reliability of heating network pipelines is determined by the reliability indicators obtained on the basis of data on the damage of heating pipelines. Studying the distribution of the number of damages of heating network pipelines by months depending on the service life of heating pipelines is necessary for effective planning of material, technical and labor resources. In order to increase the efficiency of planning of material and technical and labor resources, it is advisable to calculate the number of damages for the heating and unheated periods, by months of the year, by decades. The calculated dependences of the distribution of damage to the pipelines of heating networks for the heating and non-heating periods on a monthly basis, decadally, should take into account the service life of the pipelines. The results of the above research will save material, technical, labor and energy resources.

Hierarchical dispatch method for integrated heat and power systems considering the heat transfer process

The coordinated operation of integrated heat and power systems (IHPSs) is a promising solution for accommodating renewable energy and improving energy efficiency. A practical, effective dispatch method that coordinates the electric power system (EPS) and district heating system (DHS) is of great concern. This paper proposes a practical, non-iterative hierarchical dispatch method that introduces the concepts of the feasible region of boundary variables (FRBV) and optimal function of boundary variables (OFBV). In the proposed method, the private information of the DHS is protected in both the FRBV and OFBV. Moreover, they are transmitted between the EPS and the DHS operators only once to reduce communication overhead. This paper further proposes a method to conservatively estimate the FRBV and OFBV of the DHSs when the heat transfer process is considered in the model. Case studies are presented for an actual IHPS located in a northern city in China, and the results show that: 1) The heat generation capacity is over-estimated when the heat transfer process is not considered. 2) The hierarchical dispatch method obtains a larger regulating range of the combined heat and power units compared to those of the traditional “heat-led” operation mode and reduces the total coal consumption and the curtailed wind power by 4.46% and 38.50%, respectively. 3) The approximation-based hierarchical dispatch method obtains a solution that is less optimal than the exact method, but this difference in optimal value is less than 1%.

Bi-level modeling of district heating systems with prosumers

The paper deals with the actual problem of the functioning and development of district heating systems in the framework of the transition to intelligent energy, in which the active consumers (prosumers) holds the key place. The paper proposes an optimization mathematical model for management the operation of district heating systems taking into account prosumers based on the bi-level modeling method (bi-level programming). The proposed mathematical model allows taking into account the technical and economic characteristics of heat sources and heat networks, the interests of participants in the process of heat supply to consumers and determining the optimal conditions for management the operation of district heating systems.

GMM clustering for heating load patterns in-depth identification and prediction model accuracy improvement of district heating system

The identification of heating load patterns, also known as load profiles, is of vital importance to effective management and operation of district heating system (DHS). Clustering algorithms have been successfully applied in identifying heating load patterns. In this paper, we propose that the heating load patterns should be analyzed more specifically, and Gaussian Mixture Model (GMM) clustering is selected to extract sub-patterns. The novelty of this paper is that a new GMM clustering is applied to identify temperature related sub-pattern and people behavior related sub-pattern, and the clustering result is further utilized to improve the accuracy of prediction models. An energy station in Tianjin is used as case studies and four typical operation patterns are found with their characteristic of occur time and energy signature, which are defined as working pattern, on-duty pattern, daytime–nighttime pattern and nighttime–daytime pattern. The results reveal that this proposed method can make an in-depth identification of heating load patterns and also proves that the prediction accuracies of regression and artificial intelligence model are significantly improved by utilizing the GMM clustering results.