Large-scale District Heating System Research Articles

Exergy Analysis of a District Heating System with a Predictive Model Based on Neural Network Algorithms

The article presents an exergy analysis of a district heating system (DHS) that incorporates a predictive model based on neural network algorithms. The study focuses on evaluating the thermodynamic efficiency of the DHS when these methods are applied, enabling the prediction of temperature changes and rapid adjustment of system parameters to enhance efficiency. The impact of increasing the number of connected consumers on the exergy efficiency of the DHS with the predictive model (DHPM) is examined. The use of neural network algorithms, such as LSTM, significantly enhances the system's ability to predict external temperature changes and respond promptly, resulting in optimized energy consumption and improved exergy efficiency, particularly at the beginning and end of the heating season. A comparative analysis of the exergy efficiency of traditional DHS and the system with the predictive model is included. The exergy analysis is based on modeling the system’s performance with varying numbers of consumers. The results indicate that an increase in the number of consumers leads to a rise in exergy efficiency due to better energy distribution management. The potential for significant thermal energy savings and reduced operational costs through the use of predictive methods is discussed. The study confirms that applying neural network algorithms in predictive models of DHS can substantially improve efficiency and reliability, leading to a more rational use of energy resources, cost reduction, and minimized environmental impact. The findings support the adoption of these methods in large-scale district heating systems for optimization and enhanced energy efficiency.

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.

Development of a white-box dynamic building thermal model integrated with a heating system

Development of a simplified building model can effectively mimic the transient building thermal behaviour which essentially depends on the weather profile and the building architecture under various operational strategies and occupant behaviour. This work presents the mathematical solution procedure based on the white-box physical building thermal model using resistance and capacitance network (i.e. lumped capacitance). The work takes into account the dynamic behaviour of radiator, and its heat flow adjustment via a thermostatic radiator valve, the solar heat gain (function of the time and location), the infiltration heat loss together with building model having multi-zone with multi-layer wall structure. The case study reveals that the integrated behaviour of the building components under a given control strategy paves the way for simulating different control strategies when large-scale district heating systems are considered.

Comparison of District Heating Supply Options for Different CHP Configurations

The article discusses the evaluation of potential heat production options for a large-scale district heating system in Narva (Estonia). Heat is currently generated at the Balti Power Plant’s CHP unit using local oil shale mixed with biomass. The CHP unit consists of two circulating fluidised bed boilers and a reheat steam turbine. According to the development strategy, the district heating system is expected to achieve carbon neutrality in the future. Various options and parameter variations should be analysed. The following scenarios were compared: (1) baseline scenario featuring an existing CHP extraction steam turbine; (2) alternative Scenario I featuring a CHP backpressure steam turbine; and (3) alternative Scenario II featuring a CHP gas turbine. To evaluate the above scenarios, a comprehensive energy/exergy analysis was performed, and economic indicators were calculated. The primary energy consumed, as well as the heat and electricity generated, were all taken into account. Based on this analysis, a scenario was selected using multiple-criteria decision-making that will improve energy efficiency and reliability of the system.

Techno-economic assessment of solar assisted precinct level heating systems with seasonal heat storage for Australian cities

District or precinct level heating systems are a promising way to incorporate solar for decarbonising the building heating sector. Despite growing interest in these technologies in Europe and China, there are no large-scale district heating systems in Australia. This study shows that a combined solar heat driven Domestic Hot Water (DHW) and Space Heating (SH) system with seasonal storage is technically and economically feasible for major Australian cities. A precinct scale solar-assisted domestic hot water and space heating system with seasonal heat storage has been designed and evaluated for Australian conditions. Technical performance was evaluated using solar fraction, storage efficiency and heat collection efficiency parameters. Economic performance was evaluated using the Levelized Cost of Heat for solar thermal (LCOHst) and whole system Levelized Cost of Heat (LCOH) with a combination of component cost data from China and Europe and energy cost data from Australia. A parametric study to identify optimal collector area and storage volume sizes shows that the proposed system could achieve technical and economic targets in all five Australian cities considered. The lowest LCOHst is 0.0597 USD/kWh in Hobart. Sydney and Perth could use nearly 100% solar energy to cover the heating demand with the proposed design.

Life Cycle Assessment of District Heating Systems in Europe: Case Study and Recommendations

District heating systems are a way to integrate renewable energies into the heating sector, with the primary aim of decarbonizing this final use. In such systems, renewable energy sources are centrally managed with cutting-edge technological equipment, efficient maintenance rates and service guarantees. Both the decarbonization effect and the centralization lead to environmental benefits, which can go beyond the climate change indicator. In this study, life cycle assessment was used to assess the environmental sustainability of district heating solutions compared to standalones. The study aimed to examine a diverse set of options for large-scale district heating systems across Europe and to compare them to different standalone solutions. Eight technologies (five district-level and three standalone solutions) were analyzed in two densities of habitats and four areas of Europe. This study aimed to understand the drivers of district heating environmental performance and to provide guidelines for accounting said performance. The analysis showed better performance for district heating scenarios compared to isotechnology standalones for every environmental impact category: the climate change impact category were reduced from 5 to 90%, while respiratory inorganics were reduced from 45 to 64%, depending on the considered climatic area. This statement was true under key parameters, both technical and methodological—efficiencies and complement rates, but also the neutral carbon principle for biomass energy accounting and allocation rules.

Techno-economic comparison of technology options for deep decarbonization and electrification of residential heating.

This study aims to provide detailed information on the key technologies that utilize renewables for decarbonization and electrification of the residential heating sector. To contextualize and compare the economics of the technologies, a levelized cost model is employed to perform a comparative analysis for a dense urban area in Switzerland. The outcome shows that decarbonization of the heat supply with a dominant share of renewables is feasible, but it is challenged by the high cost of some options. In the given context (current energy and CO2 prices, no coercive measures), the rapid shift from conventional boilers to electrification via decentralized heat pumps and/or the introduction of targeted small-scale thermal energy networks utilizing cheap local resources like industrial excess heat is the most viable option. The replacement of natural gas boilers with electrification technologies also is recommendable because it would result in a sixfold reduction in specific CO2 emissions. Wide-scale application of heat pumps may require significant electricity grid reinforcement which ultimately may escalate the costs. Large-scale district heating systems are currently relatively expensive due to the high network costs and require a sustainable financing mechanism. To speed up the energy transition, policy interventions by the government are urgently needed.

Design of a district heating roadmap for Hamburg

This paper presents a methodology for the development of a transformation strategy for large-scale district heating systems (DHSs). Using this methodology, a roadmap for Hamburg’s municipal DHS is derived with an exemplary scenario for a climate-neutral heat supply in 2050. The city of Hamburg is currently in the process of transforming its municipal DHS towards climate-neutrality until 2050. So far, a blueprint for the development of such a long-term strategy does not exist. The presented scenario is based on an analysis of the future heat demand and of the regional renewable heat potentials. In the resulting generation mix, the expected heat demand in 2050 can mainly be supplied by industrial surplus heat, large heat pumps and biomass. To meet the city’s climate goals, fossil fuels will have to phase out and even waste incineration needs to be reduced drastically. After the application to the DHS of Hamburg, the methodology and results are transformed into a general approach for municipal heat planning that can support the transfer to other cities. Most importantly, strategic heat planning should be integrated into municipal administration to guarantee a flexible planning process. The paper also reveals shortcomings of currently available methodologies and tools for strategic heat planning, such as spatially resolved forecasts of the heat demand and regional potentials for renewable heat sources, which should be tackled in future scientific research projects.

Longevity and power density of intermediate-to-deep geothermal wells in district heating applications

This paper assesses the potential of intermediate-to-deep geothermal wells for district heating purposes in non-hot spot regions as a means for replacing carbon-intensive heat sources. In analysing the problem of heat transfer from the bedrock to a flowing coolant in the well, we perform parameter scans to assess the longevity and power density of different-size wells and derive analytical estimates to explain salient characteristics of the well behaviour. The results are then utilized to illustrate how intermediate-to-deep geothermal wells would compare with the requirements of typical large-scale district heating systems, by using the city of Helsinki in Finland as an example.

Reduction analysis of building thermal models for simulation of heating accidents

When representing building thermal characteristics for a large-scale district heating (DH) system, the traditional 1-order model is easy to solve but has a nonnegligible delay when conditions change. High-order models are widely used in building simulation, but their complexity and high time cost prevent them from being applied in DH simulation. The purpose of this paper is to find out an appropriate building thermal model for heating accident simulation. An unoccupied residential building located in northeast China was tested for 72 h heating outage and subsequent 32 h recovery. Based on the lumped parameter method and state space model, a high order was established by 4240 mass points to describe the tested building. By integrating mass points, the low-order models reduced the orders to eight, three, and one respectively. Frequency domain analysis revealed the similarities and differences among the models. The 1-order model showed a large deviation from the other three models. The subsequent time domain analysis of the 1-order model also simulated a root mean square error (RMSE) of 1.69, a delay of 6 h, and the lowest temperature drop during a heating outage. In both frequency and time domain analyses, the 8-order and 3-order models showed similar results approaching the high-order model, with an RMSE of approximately 0.50, a delay of 1 h, and small deviation. The simpler 3-order model could be used to estimate the indoor air temperature during a heating accident in large-scale DH systems. The further study on integrating the 3-order model and system identification method may overcome the shortcomings of model reduction.

Agent-based distributed demand response in district heating systems

Current district heating systems are moving towards 4th generation district heating in which end-users play an active role in system operation. Research has shown that optimising buildings' heating demands can release network congestion and contribute to reducing primary energy usages. Coupled with end-user privacy concerns, an approach in which buildings jointly optimise their heating demands while preserving privacy needs to be investigated. In view of this need, we have developed a distributed demand response approach based on exchange ADMM to support distributed agent-based heating demand optimisation for the district heating system with minimal private information exchanges. This paper summarises mathematical derivation, simulation and implementation of the proposed approach. The results show that the proposed approach obtained the same results as its centralised counterpart proposed in the existing literature and the sensible information exchanges were substantially reduced. An implementation at multiple spatial scales and time scales on micro-controllers and a communication system validates the proposed approach in a practical context. In conclusion, the proposed approach is suitable for real-world implementation in a large-scale district heating system.

Methodology for Evaluation of District Heating Network Efficiency

The definition of overall district heating network performance indicators is under-investigated in the literature. This study reviews existing methods of performance estimation and develops a convenient methodology for an array of district heating networks applied to a Danish case study. Performances of the networks with state-of-art pipe transmission coefficients are compared to older traditional pipes using an effective average approach. The reported efficiencies and analysis of contributing factors show, that a single parameter is not sufficient to compare large-scale district heating systems and a multiparametric analysis must be employed. The effective average total heat transmission coefficient is evaluated based on the Technical Evaluation Factor and a multivariate regression is performed on typical sets of network parameters: pipe type, pipe series, pipe age, and operational temperature. The developed methodology is applied to testing an array of geographically independent district heating networks, pointing to possible performance bottlenecks, and discussing potential remedies.

Applied Problems and Methodological Approaches to Planning and Implementation of Operating Conditions at District Heating Systems

Problems in planning and implementation of the operating conditions for district heating systems (DHSs) are directly related to the controllability and permissibility of the conditions and the reliability, quality, and efficiency of the heat supply systems’ operation under various operating conditions. The operating conditions’ development should be aimed at minimizing operating costs related to implementing the operational modes taking into account the entire set of technical and technological restrictions. The decisive factor in implementing competent adjustment and planning DHS operating conditions is the performance of preliminary calculations directly by the operators. In this case, the condition-development engineer receives a computer model of the operating DHS at his disposal that allows justifying and conducting constant correction of the thermo-hydraulic conditions during the entire heating season under changing operational conditions. For example, when connecting new consumers, varying loads, and under forced changeovers caused by emergencies, they can calculate the postemergency modes and correct the control values when the operating variables exceed the permissible values. At the Institute for Energy Systems (Siberian Branch, Russian Academy of Sciences), a system of mathematical models and methods has been developed for calculating and analyzing the thermo-hydraulic conditions at DHSs. This system was implemented in the Angara-TS information–software package (ISP). The ISP an is integration of models, methods, and software with information technologies intended for automation of workplaces for condition-development engineers. Technology for developing operating conditions for large-scale DHSs that satisfy all technical restrictions, including the required heat supply level, is presented. The technology based on multilevel modeling has been verified when implementing the operating conditions of real DHSs in Irkutsk, Angarsk, Bratsk, Baykalsk, Petropavlovsk-Kamchatsky, and other cities. This article deals with the development of the operating conditions for the DHS of Cheremkhovo, a town in Irkutsk oblast, to supply heat power from a combined heat and power plant according to a new temperature schedule. Practical application of the technology developed for planning the real DHS operating conditions has revealed its great potential for energy saving and has significantly improved the quality of the heat supply. The operating conditions and adjustment measures developed using the Angara-TS information–software package allowed for a significant reduction in the circulating heating-medium flow rates, the consumption rate of the make-up water, the water drain by consumers, the energy consumed for transfer of the heating medium, and the cost of chemical water preparation and has ensured the required level of heat supply.

Optimal operation of novel hybrid district heating system driven by central and distributed variable speed pumps

The district heating system with distributed variable speed pumps can provide substantial energy savings, compared with the district heating system with conventional central circulating pump. However, for large-scale district heating systems, using distributed pumps at all substations leads to high pressures of the network terminals, which will increase the risk of pipe bursting and failure of heat supply. In this paper, the dilemma is overcome by combining the central circulating pump with distributed pumps to construct a novel hybrid district heating system, which can improve energy saving and reduce the network pressures of the district heating system. The optimal pressure control strategy for the new type of district heating network is developed to minimize the total pump power. In order to illustrate the feasibility and effectiveness of the proposed configuration, two cases were investigated regarding an existing district heating system with 1 heat source and 112 substations, including (I) varying the flow rate at all substations with the same relative rate, and (II) varying the flow rate at all substations with different relative rates. Analysis results show that compared with the conventional constant pressure difference control strategy, the hybrid system controlled by the optimal pressure control strategy ensures more stable operation conditions for the distributed pumps and can save 57% pump power when flow rate is 0.3.

Methodology for evaluating the transition process dynamics towards 4th generation district heating networks

Currently, the 4th Generation District Heating (4GDH) is an attractive topic in the energy field as it concerns a sustainable and efficient means of delivering heat to houses. The 4GDH concept is characterised by low temperatures, low heat distribution losses, renewable and excess energy utilisation, as well as high efficiency. As a result of implementing the 4GDH concept, existing district heating systems (DHS) are undergoing massive improvement. The barriers faced by existing DHS over the course of the transition process towards the 4th generation are reviewed in the paper; the methodology for the evaluation of the DHS transition process towards the 4th generation is also presented. This methodology allows to assess the transition process dynamics, as well as helps to focus on DHS characteristics, which need to be improved. A large-scale DHS in Tallinn (Estonia) was analysed with the help of the proposed methodology. Supply and return temperatures, the share of renewable energy, and network conditions demonstrated the highest potential for improvement and had the most notable impact on the Tallinn DHS transition process.

State space model and robust control of plate heat exchanger for dynamic performance improvement

Plate heat exchanger takes an important role in the modern industrial engineering. For large scale district heating system, plate heat exchanger is the key equipment in controlling the heat output from the heating substation. High performance control of plate heat exchanger is essential for stable and efficient operation of the heating substation. The governing equation of plate heat exchanger is a pair of partial differential equations, which is not suitable for model based control. In this work, a linear state space model was developed to describe the dynamic characteristic of plate heat exchanger. Validation results show that the proposed model can capture the dynamics of plate heat exchanger with satisfied accuracy. Based on the state space model, the two-degrees-of-freedom H∞ loop-shaping controller was designed for plate heat exchanger to enhance the control performance. The reference tracking and disturbance rejection performances of the proposed control algorithm were studied and compared with the PI control. Results show that the presented two-degrees-of-freedom H∞ loop-shaping control is superior to the PI control.

Optimal Hierarchical Decision-Making for Heat Source Selection of District Heating Systems

With the rapid development of China’s urbanization, the proportion between the heating consumption and the energy consumption of the whole society keeps rising in recent years. For a district heating system, the selection of the heat source makes significant impact on the energy efficiency and the pollutant emissions. By integrating the methods of the Analytic Hierarchy Process (AHP) and the Preference Ranking Organization Method for Enrichment Evaluation (PROMETHEE), a multiple-attribute decision-making scheme for the heat source selection of district heating systems is proposed in this paper. As a core part of this scheme, a comprehensive benefit index with hierarchical parallel structure is constructed. The economic benefit, environment benefit, and technical benefit can be reflected with a certain percentage in the comprehensive benefit index. To test the efficiency of the proposed scheme, a case study for a large-scale district heating system in Beijing is carried out, where five kinds of heat sources (water source heat pump, ground source heat pump, gas-fired boiler, coal-fired boiler, and oil-fired boiler) are taken into account. The analysis and instructions for the final sorting result are also demonstrated.

An Improved Method to Evaluate Energy Efficiency of Large-Scale District Heating System with Boiler Heat Source

Over 600 million square meter heating area use the district heating system in Beijing up to 2013. The construction and operation level of many heating systems are diverse. It leads to the difference in the heating energy consumption and cost. The obstacles that impacts on the energy efficiency improvement for the district heating system in Beijing were presented. The primary job to reduce the gross heating energy consumption is to evaluate the energy efficiency of the heating system, reasonably. The aim of the paper was to provide an improved method to evaluate the energy efficiency of a district heat system.The energy conversion between the different typical parts of a heating system was discussed: the source, the primary network, the secondary network, the heat exchanger station and the building. Also, six district heating system in Beijing was evaluated by the method to illustrate the proposed technique.

Life-Cycle Carbon from Waste Wood Used in District Heating and Other Alternatives

ABSTRACT Using wood wastes provides an opportunity to avoid fossil carbon emissions from the combustion of natural gas or other fossil fuels. Using a life-cycle assessment, a new biomass boiler sourced by forest residuals, sawmill residuals, and clean demolition material (CDM) was compared with an existing natural gas boiler for supplying heat to a large-scale district heating system. Potential alternative uses of these feedstocks, such as recycled or reprocessed products, and landfill alternatives were also evaluated for their relative impact on carbon emissions. We found a reduction in emissions from natural gas of 0.62 unit of carbon for every unit of carbon in the wood combusted. Temporary losses of forest carbon after initiating the collection of forest residuals were minimal over a short interval. These losses were more than offset by the joint production of wood products displacing fossil emissions. Carbon mitigation in the Pacific Northwest was increased from 5.5 metric tons/ha/y from the production of forest products with no collection of forest residuals to 6.5 metric tons/ha/y after completing the first rotation, an 18 percent reduction in fossil emissions per hectare of forest. The potential to recycle CDM into wood products may ultimately raise the efficiency in avoiding carbon emissions by 40 to 60 percent, although available wood quality and logistics currently favor use of CDM as biofuel feedstock. In the absence of any “incentives” or value for carbon mitigation, feedstock collection costs relative to low-cost fossil fuel will substantially limit the use of waste woods for biofuel or recycling alternatives.

Condensing boiler applications in the process industry

Major challenging issues such as climate change, energy prices and fuel security have focussed the attention of process industries on their energy efficiency and opportunities for improvement. The main objective of this research study was to investigate technologies needed to exploit the large amount of low grade heat available from a flue gas condensing system through industrial condensing boilers. The technology and application of industrial condensing boilers in various heating systems were extensively reviewed. As the condensers require site-specific engineering design, a case study was carried out to investigate the feasibility (technically and economically) of applying condensing boilers in a large scale district heating system (40MW). The study showed that by recovering the latent heat of water vapour in the flue gas through condensing boilers, the whole heating system could achieve significantly higher efficiency levels than conventional boilers. In addition to waste heat recovery, condensing boilers can also be optimised for emission abatement, especially for particle removal. Two technical barriers for the condensing boiler application are corrosion and return water temperatures. Highly corrosion-resistant material is required for condensing boiler manufacture. The thermal design of a “case study” single pass shell-and-tube condensing heat exchanger/condenser showed that a considerable amount of thermal resistance was on the shell-side. Based on the case study calculations, approximately 4900m2 of total heat transfer area was required, if stainless steel was used as a construction material. If the heat transfer area was made of carbon steel, then polypropylene could be used as the corrosion-resistant coating material outside the tubes. The addition of polypropylene coating increased the tube wall thermal resistance, hence the required heat transfer area was approximately 5800m2. Net Present Value (NPV) calculations showed that the choice of a carbon steel condenser ensured cash return in a relatively shorter period of time (i.e. 2years) when compared to a stainless steel condenser (i.e. 5–7years). Moreover, the NPV for the stainless steel was more sensitive to the change of the interest rate.