Existing District Heating System Research Articles

Optimization of the operation of existing district heating systems

AbstractThis study examines the economic optimisation of existing district heating systems. A new approach has been taken to solving a long-standing problem. The authors describe the input-output model of the system, the balance equations for the thermal equilibrium of the system, and the heat transfer system. From the balance equations of the series-connected system elements, the resultant heat transfer balance equation and the resultant power transmission equation are derived. In an example, the authors detailed how perturbations in some input variables can be corrected with other variables. The equations presented and the concepts introduced form absolutely new scientific results.

Corrigendum to: Optimization of the operation of existing district heating systems

Corrigendum to: Optimization of the operation of existing district heating systems

Exploring opportunities for temperature reduction in existing district heating infrastructures

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.

Optimisation of district heating network separation for the utilisation of heat source potentials

Integrating sustainable heat sources into district heating systems is crucial to reduce the mainly fossil-based heat supply in the building sector. However, integrating a heat source into an existing district heating system can be challenging due to non-matching temperature levels or unfavourable availability of the heat source intended for utilisation. To avoid the problems associated with heat source integration, i.e. utilisation in an existing district heating system, an alternative approach is to separate the district heating network into two independent networks. Thus, the separated network forms a standalone district heating system, which is supplied by the utilised heat source and can be individually transformed depending on the characteristics of the utilised heat source and the supplied buildings. In this way, complex design and control adaptions for the entire district heating system are avoided.This work presents a method for the automatic determination of optimal district heating separation depending on the given district heating network structure and the heat source that should be utilised. For this purpose, an optimisation model determines the separation based on predefined coherent areas in the network, while considering the potential of the heat source and the heat requirements of the buildings. The application of the presented method shows various network separations depending on the heat source conditions and the focused optimisation objectives. The subsequent network simulation identifies critical areas for insufficient heat supply from which various necessary measures could be derived.

AbSolut - Integration of Absorption Technologies in District Heating and Cooling Systems for Enhanced Economic and Ecological Impact

District heating (DH) systems play a crucial role in meeting heating demands across the European Union (EU) and Austria, with significant potential for energy efficiency improvements and decarbonization. However, the transition towards climate neutrality by 2040 poses significant challenges, particularly in decarbonizing existing DH systems and integrating renewable energy sources. This work explores the application of absorption technologies, specifically absorption heat exchangers (AHX), absorption chillers (AC), and absorption heat pumps (AHP), in optimizing DH systems. The study investigates the utilization of AHX as transfer substations to increase heat capacity within existing grids by up to 30%, facilitating the integration of renewables and reducing distribution heat losses. Additionally, AC implementation for cooling supply demonstrates efficiency improvements through dynamic operation modes, renewable energy integration, and reduced electricity demand. Furthermore, AHP for waste heat utilization in DH power plants showcases environmental benefits, cost savings, and enhanced energy security. Through detailed techno-economic analyses and case studies, the paper evaluates the viability and economic feasibility of absorption technologies in DH applications. Challenges such as system integration, spatial requirements, and driving energy optimization are addressed, offering insights into overcoming barriers to adoption. Overall, the research highlights the transformative potential of absorption technologies in enhancing the efficiency, sustainability, and resilience of DH systems. By leveraging these technologies, DH operators and stakeholders can navigate the transition towards climate neutrality, while ensuring reliable and cost-effective heating and cooling solutions for urban areas.

Small-scale district heating system as heat storage for decentralized solar thermal collectors during non-heating period

Solar thermal energy usage in the Baltic countries is currently low, so there is a need to find technically and economically feasible solutions to increase the appeal of this technology. Integration of solar energy into existing district heating systems is a way to increase the share of renewable energy sources while utilizing the existing infrastructure, thereby reducing capital investments, as well as mitigating the risk of solar collector overheating and eliminating the need for local storage tanks in buildings. This study presents a parametric study for evaluating the effectiveness of using a district heating system to store heat produced by decentralized solar thermal collectors and comparing the district solution to the traditional local solution. The TRNSYS 18 model was developed for this purpose. The model investigates the impact of different hot tap water demand profiles as well as pipeline diameters and lengths on system energy efficiency, showing a statistically significant difference (p < 0.05) between installing solar collectors on residential and restaurant or office roofs, and no significant difference (p = 0.24) between restaurant and office. The model shows that solar energy can be shared within a 500 m distance between neighborhoods and that a larger main pipeline diameter can increase overall system efficiency.

Development and application of a guideline for assessing optimization potentials for district heating systems

Integrating renewable energies into district heating systems has a large potential to reduce CO2-emissions in the heating sector. As district heating systems offer the possibility of incorporating renewable energies into the heat supply, new systems have to be built and the existing networks must be maintained. This study investigates ways to optimize existing district heating systems in order to ensure economic sustainability in the long-term. Previous case studies have elaborated on a variety of optimization measures. However, to date, these measures have neither been collected nor consistently assessed for a wider application range. Therefore, in the study presented here a system for assessing the ecological and economic benefits of optimization measures was developed and applied. The assessment method utilized showed that optimization of district heating consumer substations and adding of a central buffer storage tank has a high optimization potential in comparison to intermittent operation strategy, which has a significantly lower optimization potential. From this information and the transferability data, a district heating operator can determine which optimization measure should be prioritized, which is shown at the end of the paper on an example case.

The role of the Emission Trading Scheme in the decarbonization of existing district heating systems

ABSTRACT The FitFor55 legislative package sets ambitious targets to make Europe the first climate-neutral continent by 2050. Within it, the EU Emission Trading Scheme is mandatory for energy operators with an installed capacity higher than 20 MW, calculated by considering units with a rated thermal input under 3 MW. The paper highlights the impact of the Emission Trading Scheme on the investment choices made by district heating systems operators, considering both current regulations and the potential extension of the Emission Trading Scheme to encompass lower energy capacities. The analysis concerns the simulation of four revamping scenarios (two fueled by natural gas and two partially by renewables) within an existing district heating system located in Italy. The economic analysis shows that an extension of the Emission Trading Scheme alone is not effective in hindering scenarios based on natural gas production. A reform of the power exchange market is necessary to drive decarbonization and encourage investment in renewable generation plants.

Approach to Modernizing Residential-Dominated District Heating Systems to Enhance Their Flexibility, Energy Efficiency, and Environmental Friendliness

The need to modernize existing district heating systems is due to increased requirements for their flexibility, energy efficiency, and environmental friendliness. The technical policy on district heating pursued in different countries centers on the listed goals and takes account of historical, climatic, and regional features of the resource, technology, and economic availability of various thermal energy sources. This study aims to analyze methods designed to improve the flexibility, energy efficiency, and environmental friendliness of district heating systems. The focus of the study is district heating system, which provides heating and hot water supply to consumers and consists of various types of thermal energy sources. The work shows the possibility for the heating system to transition from the third generation to the fourth one, which differ in their level of intellectualization. The establishment of an intelligent control system will ensure the interaction of various heat sources, but this is a separate strand of research. In this study, a model and a methodology were developed to optimize the structure of thermal energy sources and their operating conditions when covering the heat load curve of a territory with a predominance of household consumers. Gas-reciprocating and gas-turbine cogeneration plants are considered as the main thermal energy sources, whose efficiency is boosted through their joint operation with electric boilers, thermal energy storage systems, low-grade heat sources, and absorption chillers. The primary emphasis of the study is on the assessment of the environmental benefit to be gained by using cogeneration plants as a factor of enhancing the investment appeal of the district heating systems. The findings suggest that the transition of district heating systems to the next generation is impossible without changing the institutional environment, strengthening the role of active consumers, and introducing intelligent control for district heating systems.

Aerial urban observation to enhance energy assessment and planning towards climate-neutrality: A pilot application to the city of Turin

Based on the central role of cities in the decarbonisation process, this study aims at providing a novel methodology to assess and optimize the building energy demand and photovoltaic producibility at city scale. This is done by exploring the potential of aerial acquisition of local-scale thermographic data to integrate the existing database on building Energy Performance Certificates, on which the EU energy assessment and retrofit policies are based, on a dedicated GIS platform. Once the method is validated through testing the reliability of the resulting energy classification of buildings, the approach is used to esteem the energy demand and potential energy production in the current state and two alternative retrofit scenarios for a large district in Turin, Italy. For the analysed scenarios, potential savings are quantified up to 20 GWh and 5000 tCO2 yearly, decreasing by more than 70 % primary energy and CO2 emissions when photovoltaic panels and heat pumps are optimally used and integrated to the existing district heating system. Conclusions remark the potential of this tool to support urban policy making and governance, also with the future perspective of a thematic urban digital twin for planning energy retrofit intervention and large scale implementation of Renewable Energy Communities.

Design approach to extend and decarbonise existing district heating systems - case study for German cities

This paper aims to present an approach for the planning of carbon low heat supply in a future district heating system based on open data for German cities with existing district heating networks. One focus is on the integration of industrial waste heat and the uncertainty of future waste heat sources as well as restrictions on the use of biomass. For that purpose, knowledge about the energy demand is necessary. In a first step it is shown how the demand around a heating network is estimated with spatial data and a load profile is generated. Local available heat sources are examined according to their suitability and their kind of integration in the heating network. As heat production from different units are optimised, the development of a simulation model will be presented. The simulation is based on the optimisation of the operational costs of the used technologies for heating supply. Different scenarios covering various technologies and economic assumptions are applied. The results show the levelized costs of heating as well as the ecological performance. A sensitivity analysis shows the importance of uncertainties for the economic assumptions. The results showing levelized costs of heating as well as the ecological performance underlining the advantage of excess heat integration.

Modelling of waste heat integration into an existing district heating network operating at different supply temperatures

A promising way to make use of waste heat sources is to distribute the heat to nearby buildings via district heating systems to cover the heat demands of the buildings. The integration of a waste heat source into an existing district heating system must be studied in advance to avoid difficulties in network operation and to ensure the required heat supply to all connected buildings. Simultaneously, supply temperature reduction can improve the overall system efficiency and should also be considered for a sustainable transformation of existing district heating systems.In this paper, we develop a district heating model with multiple supplying heat sources to study the influence of an additional integrated heat source and the effects of reduced supply temperatures on the network conditions. With the developed model, we investigate the waste heat integration into an existing district heating system at a German research facility campus. Therefore, we test different integrated waste heat shares to identify arising bottlenecks and to check for the sufficient heat supply to the connected consumers. Furthermore, we test the opportunity to additionally lowering the supply temperatures in the district heating network. The simulation results show that waste heat integration is possible at the investigated district heating system up to 40%. However, simultaneously lowering the supply temperature leads to greater challenges as more bottlenecks arise and additional buildings are affected by insufficient supply.

Modeling and validation of a novel load model considering uncertain thermal disturbance in the district heating system

To accomplish precise heating, district heating systems need to understand the demand of heat users comprehensively. Most current heating load prediction models were built on energy center control, with only a few involving user-side control. Thermal disturbance factors differ depending on the type of heat user. This work established a novel heating load model (BHLP-UN model) for the user side in an existing district heating system. The uncertain thermal disturbances were identified and integrated into the base model (BHLP model) with hybrid mechanisms and deep learning methods. The model was calibrated and validated using actual operational data from different types of heat users during multiple heating seasons. The findings showed that the mean absolute percentage error of the BHLP-UN model was decreased by 53.512% −65.338% for different types of heat users compared with the BHLP model, which only considered the meteorological factors and the thermal inertia. Indoor temperature was set as an input variable to effectively analyze the time-varying property of user demand for temperature. When the indoor temperature was 22℃ / 18℃ (working /non-working), the annual load could decrease to 26.501% − 28.572%. The model achieves long-term load trends with short-term forecast accuracy.

An inexact multiple-recourse hybrid-fuel management model with considering carbon reduction requirement for a biofuel-penetrated heating system

In China’s goal of reaching carbon neutrality by 2060, the blending-biofuel-based heating technique is being used to reduce CO2 and air-pollutant emissions in existing district heating systems in northern China. This brings a series of new system components, complex interactions, and multiple-polymorphic uncertainties to the heating systems, making it difficult for the heating-system manager to improve the traditional fuel management mode while considering the demands of society, economy, policy, environment, and system operation. To address this issue, this study proposes an inexact multi-recourse hybrid-fuel management model for a biofuel-penetrated district heating system (BDHS). The model minimizes the total heating cost by optimizing the biofuel blending ratio, coal and biofuel deficit-recourse pattern among different heating sources, and selecting the optimal CO2 reduction mode under uncertainties. An application of the model to a BDHS case in Dalian City shows that the 5% biofuel blending ratio is suitable for both main heating sources and that the 0 deficit of high-quality coal can be up to [2.48, 2.69] × 103 tonne with the “cold-degree” changing from “mild” to “cold”. The results also indicate that the proposed model can ensure biofuels and high-quality coal are not overused or misused, but instead consumed responsibly. Additionally, most of the CO2 produced in the pulverized coal boiler is traded, while most of the CO2 sourced from the circulating fluid bed boiler is treated by the chemical absorption equipment. Finally, the model reveals that a high system cost (up to [84.73, 96.83] × 106 CNY) and low CO2 emission (down to [66.13, 78.07] × 103 tonne) can be obtained at a high thermalization coefficient through the tradeoff analysis.

Retrofitting of the District Heating System Based on the Application of Heat Pumps Operating with Natural Refrigerants

The implementation of renewable energy sources and heat pumps with natural refrigerants in the existing 3rd-generation district heating (DH) systems is a promising technology for the conversion to a 4th-generation DH system. This paper aims to investigate this transition through a case study for the existing DH system in Croatia. The district of Rijeka, which is considered in the case study, has an existing 3rd-generation DH system with a capacity of 9.2 MW, which was originally designed for a temperature regime of 130/70 °C and produces thermal energy from natural gas. In order to use heat pumps efficiently in such a system, the temperature of the distribution system and the energy consumption should be reduced. Trnsys software was used to perform complete dynamic simulations of the DH system. Used baseline models were validated according to the actual energy consumption reported by the heat supplier. The application of heat pumps with natural refrigerants in combination with on-site electricity production (PV system) can almost eliminate system CO2 emissions, reduce primary energy consumption and lower operation costs. Simulations were performed for 18 different scenarios that included 2 different building envelope variants. The results were compared, then discussed and conclusions were drawn.

Optimal Installation of Heat Pumps in Large District Heating Networks

Power-to-heat technology represents a promising solution for the decarbonization of the energy sector. The installation of large-scale heat pumps within district heating systems is widely recognized to be a cost-effective and competitive way to provide flexibility to the electric system, enhancing the use of intermittent renewable energy sources. The goal of this paper is to show how the economic and environmental benefits provided by the installation of a large-scale heat pump in existing district heating systems vary according to the installation location in different scenarios. To do that, an integrated methodology is developed. This includes a physical model of the thermo-fluid dynamic of the district heating network and a detailed modeling of the heat pump. To compare the different positions and also the different operating conditions, an approach based on exergy analysis is adopted. Moreover, a specific control strategy of the mass-flow rate is analyzed to further reduce greenhouse gas emissions. The application to a real large-scale district heating network shows that reductions in CO2 emissions of almost 4% can be obtained by installing a single heat pump of about 4 MWe (over a total thermal load of about 305 MWt), while this positive effect can be reduced by up to 63% if placing the heat pump at non-optimal locations.

Організація централізованого теплопостачання в окремих населених пунктах і напрями формування регіональних ринків теплоенергії

The aim of the article is to study individual settlements from the point of view of organization of their heat supply and to develop on this basis a set of models of regional heat energy markets. The article analyzes a sample of 838 settlements in Ukraine that have centralized heat supply systems. The respective analysis of the sample showed that in the regions of Ukraine there are enterprises of various organizational and legal forms of management, namely: the State-owned and municipal enterprises (including non-profit organizations), business associations, private enterprises and individual entrepreneurs. It is a common phenomenon that the supply of heat energy is carried out by an industrial or energy enterprise, for which this type of activity is not the main one. Different forms of ownership have a certain impact on the organization of relationships between suppliers, local governments and consumers of heat energy. The carried out research allowed to allocate several typical options for the organization of relationships in the field of district heating. It is determined that the organization of these relationships is influenced by the following specific features of an individual settlement and the existing heat supply systems: the number and density of population; provision of the settlement with social facilities; the nature of the predominant buildings; the dimensions of the existing district heating system; presence or absence of mainline and distribution networks for the transportation of heat energy; structure of heat consumption in the context of individual groups of users. The advantages and disadvantages of each of the identified options are analyzed and recommendations for their improvement are elaborated. On this basis, various models of organization of regional heat energy markets and the scope of their use have been proposed. The developed models take into account the specific features of individual settlements and determine the main directions of reforming the relations between suppliers and consumers of heat energy. The implementation of the developed models is aimed at the formation of competitive regional heat markets.

Methods for the reliability optimization of district-distributed heating systems with prosumers

District-distributed heating systems are considered as the result of the development of existing district heating systems, in which various energy technologies are integrated to achieve maximum efficiency of the heating to consumers. The distributed sector in these systems is associated, first of all, with the implementation of prosumers. The problem statement is determining such values of reliability parameters of components (in particular, failure rates) of studied system that provide the required level of reliability of heating to consumers at the minimum cost for ensuring this level of reliability taking into account the redundancy of prosumers. A methodology is based on the nodal probability of failure-free operation index, the Markov random process, the laws of heat transfer processes in heat supply, and some other methods. A case example is considered, an analysis of the results obtained is carried out, and directions for further research are formulated.

Framework for the Automated Identification of Possible District Heating Separations to Utilise Present Heat Sources Based on Existing Network Topology

The ambitious climate targets of the European Union emphasise the necessity to reduce carbon dioxide emissions in the building sector. Therefore, various sustainable heat sources should be used in existing district heating systems to cover the heat demands of buildings. However, integrating on-site heat sources into large existing district heating networks could be challenging due to temperature or capacity limitations since such large district heating systems are often supplied by large fossil-based heating plants. Most sustainable heat sources that should be utilised in district heating systems differ in their geographical locations or have limited heat capacities and, therefore, cannot easily replace conventional heating plants. The resulting difficulty of integrating limited heat sources into large district heating networks could be tackled by separating the existing network structure into two independent heat distribution networks. In this study, we present a developed framework that automatically recommends which network parts of an existing district heating system could be hydraulically separated in order to utilise a present heat source that is not yet in use. In this way, a second, standalone district heating system, supplied by the utilised heat source, could be established. The framework applies a community detection algorithm to the existing district heating network to first identify communities in the structure. Neighbouring communities are aggregated to larger network areas, taking into account that these areas could be supplied with the available amount of heat. These network areas are classified as possible areas for separation if the shortest connection path to the utilised heat source is within a certain distance. Subsequently, the found possibilities for network separation are simulated to test a feasible district heating operation and to evaluate the environmental and economic impacts. The presented framework is tested with a meshed and a spanning-tree network structure. Overall, the developed framework presents an approach to utilise present heat sources in separated network structures by automatically identifying, testing and evaluating possible network separations.

Optimal Planning of Future District Heating Systems—A Review

This article provides the state-of-the-art on the optimal planning and design of future district heating (DH) systems. The purpose is to provide practical information of first-step actions for countries with a low DH market share for heating and cooling supply. Previous research showed that for those countries, establishing a heat atlas with accurate geographical data is an essential prerequisite to promote the development of DH systems. In this review, essential techniques for building a high-quality heat atlas are elaborated. This includes a review of methodologies for district thermal energy demand prediction and the status of the integration of sustainable resources in DH systems. In the meanwhile, technical barriers for the implementation of various sustainable heat sources are identified. Furthermore, technologies for the optimal planning of DH systems are discussed. This includes the review of current approaches for the optimal planning of DH systems, discussions on various novel configurations which have been actively investigated recently, and common upgrading measures for existing DH systems.