Optimisation of district heating network separation: An extended approach for partial transformation of large-scale network structures

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.

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.

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.

District heating systems have an important role in increasing the efficiency of the heating and cooling sector, especially when coupled to combined heat and power plants. However, in the transition towards decarbonization, current systems show some challenges for the integration of Renewable Energy Sources and Waste Heat. In particular, a crucial aspect is represented by the operating temperatures of the network. This paper analyzes two different approaches for the decrease of operation temperatures of existing networks, which are often supplying old buildings with a low degree of insulation. A simulation model was applied to some case studies to evaluate how a low-temperature operation of an existing district heating system performs compared to the standard operation, by considering two different approaches: (1) a different control strategy involving nighttime operation to avoid the morning peak demand; and (2) the partial insulation of the buildings to decrease operation temperatures without the need of modifying the heating system of the users. Different temperatures were considered to evaluate a threshold based on the characteristics of the buildings supplied by the network. The results highlight an interesting potential for optimization of existing systems by tuning the control strategies and performing some energy efficiency operation. The network temperature can be decreased with a continuous operation of the system, or with energy efficiency intervention in buildings, and distributed heat pumps used as integration could provide significant advantages. Each solution has its own limitations and critical parameters, which are discussed in detail.

The use of computational modeling has become very popular and important in many engineering and physical fields, as it is considered a fast and inexpensive technique to support and often substitute experimental analysis. In fact system design and analysis can be carried out through computational studies instead of experiments, that are typically demanding in terms of cost and technical resources; sometimes the systems characteristics and the technical problems make the experiments impossible to perform and the use of computational tools is the only feasible option. Demand of resources for realistic simulation is increasing due to the interest in studying complex and large systems. In these framework smart modeling approaches and model reduction techniques play a crucial role for making complex and large system suitable for simulations. Moreover, it should be considered that often more than one simulation is requested in order to perform an analysis. For instance, if a heuristic method is applied to the optimization of a component, the model has to be run a certain number of times. The same problem arises when a certain level of uncertainty affect the system parameters; in this case also many simulation are required for obtaining the desired information. This is the reason why the use of technique that allows to obtain compact model is an interesting topic nowadays. In this PhD thesis different reduction approaches and strategies have been used in order to analyze three energetic systems involving large domain and long time, one for each reduction approach categories. In all the topic considered, a smart model has been adopted and, when data were available, tested using experimental data. All the model are characterized by large domain and the time involved in the analysis are high in all the cases, therefore a method for compact model achievement is used in all the cases. The considered topics are: • Groundwater temperature perturbations due to geothermal heat pump installations, analyzed trough a multi-level model. • District heating networks (DHN), studied from both the fluid-dynamic and thermal point of view and applied to one of the larger network in Europe, the Turin district heating system (DHS), trough a Proper Orthogonal Decomposition - Radial Basis Function model. • Forest fire propagation simulation carried out using a Proper Orthogonal Decomposition projection model.

Biomass-fired CHP and heat storage system simulations in existing district heating systems

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

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

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.

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.

Wind power integration could be restricted by inflexible operation of combined heat and power (CHP) units due to the strong linkage between power generation and heating supply in winter. Utilization of the heat storage capacity of existing district heating network (DHN) is a cost-effective measure to enhance power system operational flexibility to accommodate large amounts of variable wind power. In this paper, transmission-constrained unit commitment (UC) with combined electricity and district heating networks (UC-CEHN) is formulated with a linear DHN model to coordinate short-term operation of electric power and district heating systems. The heat storage capacity of the DHN is modeled by capturing the quasi-dynamics of pipeline temperature. Both deterministic and robust models are developed to incorporate UC with the linear DHN model. Case studies are carried out for two test systems to show the potential benefits of the proposed method in terms of wind power integration and efficient operation.

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

In order to maximise the share of biomass in the energy supplying system, the designers should adopt the appropriate changes to the traditional systems and become more familiar with the design details of the biomass heating systems. The aim of this study is to present the development of methodology and its associated implementation in software that is useful for the design of biomass thermal conversion systems linked with district heating (DH) systems, taking into consideration the types of building structures and urban settlement layout around the plant. The methodology is based on a completely parametric logic, providing an impact assessment of variations in one or more technical and/or economic parameters and thus, facilitating a quick conclusion on the viability of this particular energy system. The essential energy parameters are presented and discussed for the design of biomass power and heat production system which are in connection with DH network, as well as for its environmental and economic evaluation (i.e. selectivity and viability of the relevant investment). Emphasis has been placed upon the technical parameters of biomass logistics, energy system's design, the economic details of the selected technology (integrated cogeneration combined cycle or direct combustion boiler), the DH network and peripheral equipment (thermal substations) and the greenhouse gas emissions. The purpose of this implementation is the assessment of the pertinent investment financial viability taking into account the available biomass feedstock, the economical and market conditions, and the capital/operating costs. As long as biomass resources (forest wood and cultivation products) are available and close to the settlement, disposal and transportation costs of biomass, remain low assuring the sustainability of such energy systems.

It is in the DNA of district heating (DH) systems that low temperatures are crucial for efficiency, guaranteeing cost competitiveness and integrating alternative heat sources. The general conviction within the DH community is, that reduced temperatures have positive effects for the whole system and economic benefits can be expected. However, there is a lack in evidence-based data to evaluate these effects in monetary terms. The innovative approach of this work is to analyze key characteristics for different technologies by means of energy-economic assessments to show evidence-based energy-related and monetary benefits of reduced system temperatures. The proven benefits should increase the motivation and conviction of utilities and customers in low-temperature systems, both for reducing system temperatures in existing networks and for new networks. The key indicator cost reduction gradient (CRG), introduced in previous work, was applied for the energy-economic assessment of reduced system temperatures. In total, investigations of nine heat generation technologies, the DH network itself and four storage types are presented. The CRGs for the heat generation technologies varies from 0.08 to 0.67 €/(MWh·°C). In the case of alternative heat generation technologies such as heat pumps and solar thermal, a higher sensitivity of the monetary effects compared to traditional heat generation technologies can be observed. Here, higher economic benefits and monetary savings can be expected in future DH networks.

Comparative Analysis Between District Heating and Geothermal Heat Pump System