Dynamic thermal simulation of a tree-shaped district heating network based on discrete event simulation

The decentralisation of existing district heating systems by network separation is a promising approach for district heating transformation. A district heating network is separated into several smaller district heating network structures that can be individually adapted, e.g. in relation to the existing network structure or concerning the properties of the local buildings supplied, such as the temperature requirements of their heating systems. In this work, an approach for the optimal separation of existing district heating networks is expanded, which enables the decentralisation of a specific district heating system and the partial transformation of the separated network depending on the heat source utilised and the local district heating system conditions. The approach first identifies coherent network areas through community detection and aggregation, then optimises network separation and the installation of heat pumps, and finally evaluates the arising district heating network systems through district heating network simulations. The individual steps of this approach are adapted to be applicable to large district heating network structures, e.g. to handle the great number of separation options. The approach is applied to two existing district heating systems with over four thousand buildings supplied. Two types of utilised waste heat sources are investigated, a sewage plant with fluctuating temperatures and an electrolyser with a dynamic operation schedule. The results show favourable transformation alternatives for existing district heating networks, as the separated network areas are transformed by reducing supply temperatures depending on the heat source potential utilised and the temperature requirements of the buildings supplied. • Separating district heating networks facilitates the utilisation of heat sources. • An optimisation model reveals the optimal separation of district heating networks. • The network separation considers available heat capacity and temperature level. • Heat pumps are installed in the separated network to utilise low-temperature heat. • A subsequent simulation evaluates the separated district heating networks.

In Russia district heating (DH) systems are characterized by the high wear-out rate of key facilities, particularly energy distribution networks and plants, the inadequate reliability of operation, significant heat losses, and the polluting impact on the environment. The objective of this paper is to indicate the feasibility and advantage of the renovation on a traditional high-temperature DH network. All the calculations are performed in Zulu©, Russian commercial software for simulation of a district energy system’s behavior. Reference operational data for the DH system was obtained from database established by the local heat supply company in the form of Microsoft Office Excel spreadsheet file. The second idea (Case-2) envisages installing a heat pump and increasing the supply temperature in peak load periods during the heating season to limit a size of a heat pump. Case-3 and -4 are related to installing in-room terminal units and operating the system ‘as is’ respectively. Terminal units include consoles, fan-coils, blower coils, furnaces, chimneys, and radiant panels. The fifth option introduces low temperature district heating (LTDH) concept representing a paradigm shift in DH development and features a low supply temperature and smart control. When designing all errors should be less than local regulations allowable for each object. Presented research revealed that the issue of modernisation in Omsk, Russia cannot be easily and clear resolved. The future state-determination of results of DH network retrofitting is innovatively proposed in this paper.

Collaborative scheduling and flexibility assessment of integrated electricity and district heating systems utilizing thermal inertia of district heating network and aggregated buildings

Coordinated dispatch of electric power and district heating networks: A decentralized solution using optimality condition decomposition

Massive adoptions of combined heat and power (CHP) units necessitate the coordinated operation of the power system and district heating system (DHS). Exploiting the reconfigurable property of district heating networks (DHNs) provides a potentially cost-effective solution to enhance the flexibility of the power system by readjusting the configuration for heat supply, which has not been addressed in the literature. To address this issue, a unit commitment considering combined electricity and reconfigurable heating network (UC-CERHN) is proposed in this paper to coordinate the day-ahead scheduling of power system and DHS. The DHS is formulated as a nonlinear and mixed-integer model considering the reconfigurable DHN. To make the commitment problem tractable, an auxiliary heat quantity variable is introduced, and the DHS model is reformatted to a linear energy flow model by approximation of heat loss, where the computational burdens are significantly reduced. Extensive case studies are presented to validate the effectiveness and accuracy of the approximated model and illustrate the potential benefits of the proposed method with respect to congestion management and wind power accommodation.

Sizing distribution equipment of a district heating (DH) network is a complex yet decisive process to target techno-economic optimality for these systems. This paper describes and validates a framework that uses multi-objective optimization to support decisions regarding the sizing of a DH network. A genetic algorithm (NSGA2) is employed to generate optimal pipe diameters with respect to the operational and investment cost. This framework is then validated using an elementary toy problem consisting of a straight horizontal two-tube network, with a set of identical consumers equally distributed in the network and supplied by a unique heat source. We show that the framework, on the aforementioned problem, reaches very good convergence and diversity for the optimal solutions.This sizing method is then compared to typical local sizing method. We demonstrate a significant decrease of global cost by 40% by using DH network system simulation to take into account local interactions inside the DH system.

Metamorphoses of cogeneration-based district heating in Romania: A case study

Effects of the operation regulation modes of district heating system on an integrated heat and power dispatch system for wind power integration

The installation of heat pumps in district heating (DH) systems is one of the most promising technologies to increase the efficiency of heat supply by using renewable energy sources and reducing heat carrier temperatures in the networks. The possibilities of installing heat pumps in DH systems are very wide, but most often the main purpose of their application is to increase the temperature of the supplied heat carrier at the heat substations of individual consumers or their groups. This paper describes a study that analyzed the possibilities of integrating an individual heat pump at a heat substation in a building to reduce the temperature of the heat carrier in the return line. The results of the study revealed the dependences of the reduction of the heat demand of the building from the DH network, the power of the heat pump, the coefficient of performance (COP), and the reduction of the return temperature.

Policy instruments clearly influence the choice of production technologies and fuels in large energy systems, including district heating networks. Current Swedish policy instruments aim at promoting the use of biofuel in district heating systems, and at promoting electric power generation from renewable energy sources. However, there is increasing pressure to harmonize energy policy instruments within the EU. In addition, natural gas based combined cycle technology has emerged as the technology of choice in the power generation sector in the EU. This study aims at exploring the role of policy instruments for promoting the use of low CO2 emissions fuels in high performance combined heat and power systems in the district heating sector. The paper presents the results of a case study for a Swedish district heating network where new large size natural gas combined cycle (NGCC) combined heat and power (CHP) is being built. Given the aim of current Swedish energy policy, it is assumed that it could be of interest in the future to integrate a biofuel gasifier to the CHP plant and co-fire the gasified biofuel in the gas turbine unit, thereby reducing usage of fossil fuel. The goals of the study are to evaluate which policy instruments promote construction of the planned NGCC CHP unit, the technical performance of an integrated biofuelled pressurized gasifier with or without dryer on plant site, and which combination of policy instruments promote integration of a biofuel gasifier to the planned CHP unit. The power plant simulation program GateCycle was used for plant performance evaluation. The results show that current Swedish energy policy instruments favour investing in the NGCC CHP unit. The corresponding cost of electricity (COE) from the NGCC CHP unit is estimated at 253 SEK MWh−1, which is lower than the reference power price of 284 SEK MWh−1. Investing in the NGCC CHP unit is also shown to be attractive if a CO2 trading system is implemented. If the value of tradable emission permits (TEP) in such as system is 250 SEK tonne−1, COE is 353 SEK MWh−1 compared to the reference power price of 384 SEK MWh−1. It is possible to integrate a pressurized biofuel gasifier to the NGCC CHP plant without any major re-design of the combined cycle provided that the maximum degree of co-firing is limited to 27–38% (energy basis) product gas, depending on the design of the gasifier system. There are many parameters that affect the economic performance of an integrated biofuel gasifier for product gas co-firing of a NGCC CHP plant. The premium value of the co-generated renewable electricity and the value of TEPs are very important parameters. Assuming a future CO2 trading system with a TEP value of 250 SEK tonne−1 and a premium value of renewable electricity of 200 SEK MWh−1 COE from a CHP plant with an integrated biofuelled gasifier could be 336 SEK MWh−1, which is lower than both the reference market electric power price and COE for the plant operating on natural gas alone. Copyright © 2005 John Wiley & Sons, Ltd.

This paper presents an optimal production and distribution management for structural and operational optimization of the integrated district heating system (DHS) with multiple regional branches. A DHS consists of energy suppliers and consumers, district heating pipelines network and heat storage facilities in the covered region. In the optimal management system, production of heat and electric power, regional heat demand, electric power bidding and sales, transport and storage of heat at each regional DHS are taken into account. The optimal management system is formulated as a mixed integer linear programming (MILP) where the objectives is to minimize the overall cost of the integrated DHS while satisfying the operation constraints of heat units and networks as well as fulfilling heating demands from consumers. Piecewise linear formulation of the production cost function and stairwise formulation of the start-up cost function are used to compute nonlinear cost function approximately. Evaluation of the total overall cost is based on weekly operations at each district heat branches. Numerical simulations show the increase of energy efficiency due to the introduction of the present optimal management system.KeywordsHeat GenerationMixed Integer Linear ProgrammingUnit CommitmentHeat UnitHeat DemandThese keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.

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.

Model for optimal malfunction management in extended district heating networks

With the strengthening of carbon emission control, the development of clean renewable energy has become a unanimous choice for many countries. However, in the integrated electricity and district heating system (IEDHS), the tightly coupled relationship between heat and electricity will make the system lack the flexibility for wind power integration. A source-network-load-storage scheduling scheme considering thermal inertia (TI-based SNLS scheduling) is proposed to realize the coordinated operation of source, network, load, and storage in IEDHS. The simplified thermal inertia model of district heating network (DHN) and building, and the charging-discharging model of a solid regenerative electric boiler (SREB), are also introduced. Four comparative cases are conducted based on wind power data of Jilin Province for a day-ahead dispatch problem. The results indicate that the scheme achieves a 9.19% improvement on the regulation flexibility of the combined heat and power (CHP) units, and the wind curtailment rate is reduced by 16.14%. The research also finds that using thermal inertia can alleviate the contradiction between heat load and wind power curve, but the contribution from DHN is limited compared with buildings. SREB can directly absorb wind power to compensate for heating, which has considerable potential in promoting wind power utilization. Furthermore, the indicative calculation of financial payback time considering carbon trading income elucidates the economic feasibility of the case system.

Promoting efficient district heating in Estonia