4th Generation District Heating Research Articles

Adsorption Desalination and Cooling Systems: Advances in Design, Modeling and Performance

The increase in energy efficiency, reducing energy demand, greenhouse gas emissions and the use of waste, renewable and recycled heat from low-temperature sources are significant challenges today and are key parts of the idea of the 4th Generation District Heating (4GDH) [...]

Operational optimization of a 4th generation district heating network with mixed integer quadratically constrained programming

Decreasing CO2-Emissions is a common goal for efficient energy system design and operation. An efficient design for the heating sector are 4th-generation district heating networks with waste heat integration. This paper focuses on operational optimization of a 4th-generation district heating network with regards to temperatures and use of thermal inertia in the network and in thermal energy storages. A case study is presented, where the system is formulated as a Mixed-Integer Quadratically Constrained Program. The quadratic formulations allow to simultaneously optimize energy balances and temperatures, with regards to efficiency correlations and temperature thresholds of components. The case study consists of seven consumers with heat pumps and thermal energy storages, which are supplied by waste heat from a nearby high-performance computer. The case study is solved for eight representative days. The results show, that savings in operational costs up to 18.2% compared to a reference system with constant temperatures are possible. All in all, this paper demonstrates the use and limitations of quadratic formulations in an operational optimization and emphasizes the possibility of temperature optimizations in operation of 4th-generation district heating.

Distinguish between the economic optimal and lowest distribution temperatures for heat-prosumer-based district heating systems with short-term thermal energy storage

Decreasing distribution temperature is the key driving force for energy-efficient and economic-competitive district heating (DH) systems, powering the transition from the 1st generation high-temperature steam-based DH systems to the 4th generation low-temperature water-based DH systems. However, for heat prosumers integrated with thermal energy storages (TESs), the decreasing distribution temperature may lower the peak load shaving capability of TESs and raise the peak-load-related heating costs, due to decreased charging temperature. This study, therefore, aimed to investigate the overall impacts of distribution temperature and to identify the economic optimal distribution temperature for heat-prosumer-based DH systems integrated with short-term TES. Firstly, an economic optimization problem was developed. Afterwards, distribution temperatures were optimized within the feasible regions of individual scenarios, including three benchmark scenarios representing the 2nd, 3rd, and 4th generation DH and an improved scenario featured high feasibility in distribution temperature. A campus DH system in Norway was used as the case study. Results revealed that the improved scenario's economic optimal distribution temperature was significantly distinct from the 4th generation DH scenario's lowest distribution temperature, both in terms of distribution range and annual average level. Finally, broad conclusions were reached by discussing the impacts of crucial factors on economic optimal distribution temperatures.

Low-temperature operation of heating systems to enable 4th generation district heating: A review

District heating networks increasingly rely on heat pumps, condensing biomass boilers, and excess heat in the transition to sustainable energy systems. Accordingly, district heating operators seek to reduce their networks’ supply and return temperatures to maximise production efficiencies, minimise heat losses from distribution pipes and allow greater utilisation of renewable heat sources and excess heat. Experts have predicted that investing in solutions that reduce heating temperatures in buildings will yield a return on investment of 300% for district heating operators. Therefore, expecting incentives, building operators should identify methods to reduce supply and return temperatures to enable a rapid, widespread transition to low-temperature district heating. Ample research has investigated and documented the feasibility of low-temperature heating in buildings, and this paper presents the first comprehensive review. It synthesises available literature and adds new perspectives to help guide future implementation, research and development of low-temperature heating. The energy and temperature demands of various heating systems provides a background, leading to a review of typical malfunctions and their impacts. The article subsequently reviews the obtainable supply and return temperatures before and after renovating the building envelope and heating systems. It further identifies and summarises vital measures for decreasing heating system temperatures. Ultimately, the authors recommend minimising heating system temperatures using automatic balancing of space heating and ventilation systems, novel solutions for safe domestic hot water supply, and digitally-enabled performance monitoring and optimal control.

Integrating a Heat Pump into a 4th Generation District Heating (4gdh) System - Two-Mode Configuration Inputting Operational Data

Integrating a Heat Pump into a 4th Generation District Heating (4gdh) System - Two-Mode Configuration Inputting Operational Data

A multivalent supply concept: 4th Generation District Heating in Moosburg an der Isar

With regard to the decarbonisation of the heating sector, district heating is of paramount importance considering its potential for the efficient utilisation of renewable energies and waste heat sources. Against this background, the transformation and expansion of an existing heating network in the city of Moosburg an der Isar (Germany) is planned within the “District Heating 4.0” funding programme of the German Federal Office of Economic Affairs and Export Control.The innovative concept involves a heat supply based entirely on renewable energies and industrial waste heat. In particular, the integration of unused waste heat from mechanical and chemical industrial processes enables an ecologically and economically optimal supply concept. Depending on the temperature level, the waste heat is fed into the grid directly or by an intermediate heat pump. In addition, solar thermal systems on roofs are integrated into the grid and optimised in terms of efficiency by using a heat storage. Biomass boilers operated by woodchips of waste wood cover peak loads as well as part of the base load and guarantee the security of supply.Considering the overall system behaviour, the multivalent concept is designed to maximise the share of renewable fuel-free heat sources and capitalise on the beneficial marginal costs of waste heat and solar thermal energy. A profitability analysis shows that low heat generation costs can be realised, not least because of the funding of investment costs. In addition to the technical design process and the economic evaluation, the analysis of legal aspects is a key element of this first phase of the project. In further project phases, the implementation of the heating network, the monitoring of the energy flows and the ongoing acquisition of new customers will be carried out.

How do business models for prosumers in the district energy sector capture flexibility?

The apparent usefulness of prosumers in the district energy (DE) grid, with the transition to 4th generation district heating (4GDH) and smart energy system is beginning to be realized. Similarly, there is a burgeoning interest in the exploitation of flexibility in the DE grid. But, whether the business models for prosumers also capture the flexibility provided by the prosumers is doubtful. Our current study ponders on: what are the business models for prosumers in the heating sector? do they capture flexibility? And, if so, how do they capture flexibility? A directed Content Analysis of systematically selected scientific literature is analyzed to investigate the business models for prosumer integration in the DE sector, and how they capture flexibility. Fifteen scientific articles were chosen through a systematic selection process. The selected literature was analyzed under the following categories: research objectives or research questions, methodology used, key actors considered, key technologies, pricing logic of heat, control of the prosumer system, computation of benefits and flexibility consideration. The findings from the selected articles show that when looking at how prosumers can supply peak heat, most studies consider the marginal cost of heat supply as an important parameter in the price logic. Similarly, the benefits are computed in a system-wide manner as the difference between the marginal cost of heat either through production from DE system or through production from the prosumer. In calculating the marginal cost of heat investment costs are not considered, which is not conducive for positive decision-making by the potential prosumer looking to invest in heat pumps or excess-heat exploiting technologies.

Synergies between buildings retrofit and district heating. The role of DH in a decarbonized scenario for the city of Milano

The goal of this work is to present challenges and opportunities for the development of 4th generation district heating in future decarbonized scenarios for the Italian city of Milano. The work has been developed in the framework of a Climate-KIC project to support Milano municipality in developing decarbonization measures. The first part of the work consists in the evaluation of a geographical distribution of the civil sector heat demand according to a bottom-up approach based on open data. Thanks to this statistical tool, also buildings retrofit can be analysed. Three retrofit scenarios are simulated according to policy goals for 2030 and 2050, foreseeing a retrofit priority of worst energy performances buildings, resulting in 8.8TWh, for the first two scenarios, and 9.4TWh for the last one. The areas characterized by the majority of retrofit can be identified as the most suitable for low temperature district heating development. Renewables and low temperature waste heat sources are also assessed, resulting in 9.8TWh of available heat. The application of district heating in combination with the identified renewables is assessed in these scenarios with a clustering approach. The evaluation of potential diffusion of 4GDH is based on the comparison between the overall cost of district heating and the competing individual systems costs: district heating is considered feasible only in retrofitted buildings where district heating cost is lower than individual systems cost (about 0.7TWh in each scenarios). The retrofitting scenarios combined with the diffusion of renewable based 4GDH are assessed also in terms of environmental impact. The current greenhouse gas emissions related to the actual heating systems, evaluated through the Thermal Systems Regional Cadastre database, is compared to the district heating development scenarios and to individual heat pump system scenarios. The results show the highest reduction of emission in the district heating scenarios (65%).

Analysis of heat losses during heat supply of an urban-type settlement using a heat pump

Centralized heat supply systems include a network of pipelines connecting buildings and structures in such a way that entire districts and quarters are supplied with a heat carrier from a single boiler plant. District heating is a well-studied part of the energy system. Despite this, low temperature district heating is still underdeveloped, although it is one of the key technologies for energy efficient urban heating. Low-temperature heat supply systems are the basis of 4th generation district heating systems, since they can significantly reduce heat losses during transportation of the heat carrier to the heat energy consumer and allow the use of heat from renewable sources, for example, heat pumps. The study focuses on analyzing the heat loss of a district heating system by comparing simulation results at a standard flow temperature and at a temperature typical of the 4th generation heat supply schedule. On the basis of the created model, the calculation of heat and hydraulic losses of the low-temperature district heating system was carried out, as well as a comparative analysis in comparison with the standard heat supply system.

Drivers and barriers for prosumer integration in the Swedish district heating sector

Despite the apparent usefulness of prosumers in the DH grid, there has not been a systematic investigation into why Sweden has not seen a general uptake in prosumer integration in the district heating (DH) sector. The transition to 4th generation district heating (4GDH) and smart energy system concepts are conducive to prosumer integration. Nonetheless, the integration of heat prosumers has been slow in Sweden. Our current study investigates the drivers and barriers for prosumer integration in the Swedish DH sector and looks at if and how rules, regulations and policies may affect the enabling of prosumer integration. The research questions posed in this study are: what are the drivers and barriers for prosumer integration in the DH sector in Sweden, and, what are the rules, regulations and policies that can affect the enabling of prosumer integration in the DH sector in Sweden. A directed Content Analysis of systematically selected scientific and industry-related literature is analyzed to investigate the drivers and barriers for prosumer integration in the Swedish DH sector. The drivers for prosumer integration can be broadly categorized as DH-side drivers, prosumer side drivers and macro-trend drivers. In terms of the DH-side, costs savings, more flexibility, increasing the environmental and commercial profile of the company and increasing the effective use of energy are the main drivers. Similarly, for the prosumers, it is additional income, increased self-sufficiency and raising the environmental profile which are the main drivers. In the barriers side, not up-to-date policies and regulations about the energy use and required energy efficiency for buildings, and conflicting regulations about accounting of energy use disincentivize prosumer integration in the Swedish DH sector. There are barriers on both the DH-side and prosumers’ side hindering the integration of prosumers in the DH sector. These barriers are also enhanced by ambiguous policies, which hinder the prosumer integration in the Swedish DH sector.

Increasing flexibility towards a virtual district heating network

The development over the last decade of the district heating (DH) network of Gleisdorf (Austria) represents an innovative example for a transition to a 4th generation DH network (4GDH). The local DH operator has strong ambitions towards implementing a highly efficient, nearly 100% renewable DH system using local resources. These goals will be achieved by the development and implementation of a novel control strategy, namely a “Virtual Heating Plant” (VHP) control concept. The VHP concept is an intelligent high level control system using operating data for real time calculations and a 24h prediction to optimise the overall DH network. The VHP control is fully implemented into the DH system and led to an improved and more flexible unit commitment, higher solar yields and more stable operating conditions. This paves the way to integrate multiple decentralised local heat sources and existing boiler units as well as other systemic approaches (e.g. sector coupling with waste water treatment plant, cascading heat supply out of the return pipe, stepwise system temperature reduction, implementation of an intelligent, decentral storage concept) and non-technical measures (e.g. user and stakeholder integration).

District heating in 100% renewable energy systems: Combining industrial excess heat and heat pumps

The literature emphasizes the important role of industrial excess heat (IEH) and heat pumps (HP) in future 4th generation district heating and smart energy systems. However, they can potentially have negative or positive effects on the integration of renewable energy sources (RES). It is necessary to find a trade-off between IEH and HP in the transition towards a 100% renewable energy system yet has not been discussed in the literature. This paper presents a comprehensive techno-economic analysis for the optimal district heating (DH) strategy in a 100% renewable energy system. It is conducted based on a novel hybrid methodology framework that couples hourly smart energy system simulation, multi-objective optimization, and multiple-criteria decision making. The optimal share between IEH and HP and associated RES capacity can be determined considering the preferences of policymakers. A scenario for 2050 for Aalborg Municipality in Denmark is used as a case study. Results show that an appropriate mix of IEH and HP, 40% and 20% respectively in the DH supply, should be employed to obtain a balanced near carbon–neutral system with the least cost. Also, the cross-sector effective interactivities between the DH network, power grid, and gas grid are revealed in the smart energy system context. The proposed framework is designed in a general way that can be used in other cities, regions, or countries.

Linking energy efficiency policies toward 4th generation district heating system

Implementation of 4th or 5th generation district heating system needs a complex solution as it involves an energy source, a heating network and consumers. Retrofitting of buildings and energy efficiency level have been the main factors defining an implementation of the low temperature heat solutions. When evaluating the national heat supply system, it is difficult to evaluate the readiness of buildings to accept lower temperature heat carriers. Therefore, the system dynamics modelling approach has been used to determine the links between different elements of 4th generation district heating system in the long-term perspective. The developed system dynamic model allows evaluating whether the allocated financial support is sufficient for reaching the set energy efficiency goals, as well as to achieve the desired performance of district heating systems. The study analysed various policy measures and their long-term effects. The modelling results show that support in the form of subsidies has a greater impact on key targets than tax increases. In the combined policy scenario with increased fossil fuel tax and subsidies for RES technologies it is possible to achieve the share of RES up to 80% in DH and 62% in individual heat supply.

Sizing and optimizing the operation of thermal energy storage units in combined heat and power plants: An integrated modeling approach

Thermal energy storage technologies are of great importance for the power and heating sector. They have received much recent attention due to the essential role that combined heat and power plants with thermal stores will play in the transition from conventional district heating systems to 4th and 5th generation district heating systems. This paper presents a novel decision support method for sizing and optimizing the operation of thermal energy storage units in combined heat and power plants. To achieve this goal, the method in this paper comprises three steps. The first step provides an approximation of the storage capacity based on the characterization of the thermal load. The second step extends the applicability of the method by enabling the evaluation of the hourly operation of the combined heat and power plant with thermal storage. The third step evaluates the long-term economic effects of retrofitting the combined heat and power plant with a heat storage option. The applicability of the method is illustrated using the example of a coal-fired combined heat and power plant and the study of two scenarios. The analysis of the scenarios shows that the utilization of the energy storage enhances the operational flexibility of the system by increasing the number of hours in which the combined heat and power plant operates at its maximum electrical output and, at the same time, reduces the thermal contribution of the heat-only boilers. The method developed in this work can be applied to carry out the financial analysis of an energy storage project.

Techno-economic evaluation of electricity price-driven heat production of a river water heat pump in a German district heating system

Large scale heat pumps (HP) are an important technology that will link district heating (DH) systems to the electricity sector in future smart energy systems. This paper examines the feasibility of the integration of a river water HP at a combined heat and power plant in Germany. It is part of a more extensive study about the transformation of a DH system in an urban district towards a 4th generation DH system. The focus is on operational characteristics and economic efficiency of electricity price-driven heat production. A novel method for estimating the coefficient of performance (COP) of two-stage ammonia HPs based on the difference between sink and source temperature is presented. The HP achieves a seasonal COP in the range of 3.4 to 3.7. The 15-year simulation with the software energyPRO shows that electricity-price driven operation is especially relevant for lower heat loads during the non-heating season. The correlation between volatility of electricity market price change and flexible operation is analysed. Finally, the levelized cost of heat for four designs with heat outputs of the HP from 4.7 MWth to 6.1 MWth and increasing storage sizes are compared. The results indicate that electricity costs are reduced in more flexible systems, but cost parity to the minimum dimensioning is not yet reached with the underlying economic framework conditions. However, the parameters that benefit the economic efficiency of more flexible systems are discussed.

Improving CHP flexibility by integrating thermal energy storage and power-to-heat technologies into the energy system

Smart energy grids include smart thermal and electrical grids. One of the links between them is the combined heat and power (CHP) plant, which supplies both heat and power to the grid. CHPs are designed for stable heat and electric loads and their ability to cope with peaks and lows needs to be improved. This paper explores technical solutions aimed at improving CHP flexibility, considering the potential transition to the 4th generation district heating (4GDH). CHP flexibility extends its operating time and improves the energy efficiency of the system. The solutions examined include coupling CHPs with electric boilers and TES, which will help balance heat and power loads and allow to introduce RES to the system. In this study, these technical solutions are compared in terms of natural gas consumption, heat rejection reduction, and the share of heat supplied to the system by the CHP. The results of this study show that when 150 000 m3 TES and 40 MW electric boiler are integrated into the Tallinn DH system, natural gas consumption can be reduced by 36% and heat rejection by 38%.

Impact of Legionella regulation on a 4th generation district heating substation energy use and cost: the case of a Swiss single-family household

4th Generation District Heating (4GDH) systems can have a supply temperature lower than 50 °C to decrease losses and to favour the integration of renewable and waste heat. As the temperature requirement for space heating in new and retrofitted buildings is around 35 °C or lower, they would be suitable for 4GDH. However, Domestic Hot Water (DHW) is a significant barrier in district heating, because the temperature needs to be maintained above the standard Legionella growing range (25 °C–55 °C), even if 45 °C would be sufficient for comfort. Nonetheless, current regulations vary widely across countries in Europe, especially for small buildings. This paper aims to study the effect of different Legionella regulations on the DHW energy use, and on the substation cost of a Swiss single-family household connected to a 4GDH network. The Swiss standard is confronted with the requirements of the Danish regulation and the German “3-litre rule”. Results demonstrated that a relaxation of the current Swiss regulation could present energy and economic savings. The “3-litre rule” resulted in an annual heat consumption reduction of 13% while the Danish standard achieved the lowest annual running cost and annualized total cost.

Utilizing excess heat through a wholesale day ahead heat market – The DARKO model

District heating has already proven to be a suitable solution for the decarbonisation of the most energy intensive energy sector in Europe, heating and cooling. However, to achieve this, it needs to incorporate renewable and sustainable energy sources into the generation mix which is still dominated by fossil fuels in many countries. Alongside traditional renewables like solar thermal, geothermal and biomass, excess heat from the industrial and service sector has a high untapped potential. Nonetheless, to utilize it in district heating, third party access must be granted. For that reason, a wholesale day ahead heat market has been modelled in this study and validated on a case study in the city of Sisak in Croatia. The idea was twofold: to evaluate the functionality of such a heat market and its effect on the existing system, as well as to analyse the integration of high and low temperature excess heat sources in different conditions, including the use of thermal storage, as well as the competition with low-cost renewables, i.e. solar thermal. The results have shown that the introduction of a wholesale day ahead heat market would ensure the positive total welfare in all the scenarios. The benefit for the demand side and the total welfare would increase even more if excess heat sources are integrated in the system and especially if they are combined with a thermal storage to increase their capacity factor, which would also decrease the competing effect of solar thermal. Finally, it was shown that low temperature excess heat is not feasible in the high temperature district heating and the transfer to the 4th generation district heating is required to feasibly utilise low temperature sources.

Design optimization of a heating network with multiple heat pumps using mixed integer quadratically constrained programming

District heating is a state of the art technology for efficient supply of heat. Modern 4th generation and 5th generation district heating networks can be used to integrate sources of waste heat, which allows efficient operation. The design of such heating networks is subject of many optimization models. Most optimization models focus on energy flows and result in Mixed Integer Linear Programs. This requires simplifications, where temperatures and mass flow rates are neglected or simplified. This work presents a Mixed Integer Quadratically Constrained Program with temperature constraints. A case study is presented, where the integration of low temperature waste heat in a district heating network is optimized. In this case study the positioning of heat pumps at the supply or at the consumers influences network operation. The results show a trade-off between economical and ecological optimal solutions with a range of total annualized costs from 120,000 EUR/a to 307,000 EUR/a and a range of CO2-Emissions from 193 t/a to 605 t/a. Furthermore, the influence of design decisions on the optimal operation is demonstrated. All in all, the quadratic model formulation stresses the influence of temperatures on the optimization outcome and offers pareto optimal solutions for the design of the presented case study.

The role of 4th generation district heating (4GDH) in a highly electrified hydropower dominated energy system

District heating (DH) is considered an important component in a future highly renewable European energy system. With the turn towards developing 4th generation district heating (4GDH), the integral role of district heating in fully renewable energy systems is emphasized further. Norway is a country that is expected to play a significant role in the transition of the European energy system due to its high shares of flexible hydropower in the electricity sector. While the country is moving towards electrification in all sectors and higher shares of variable renewable electricity generation, district heating could potentially decrease the need for electric generation and grid capacity expansion and increase the flexibility of the system. In this paper we investigate the role of 4GDH in a highly electrified future Norwegian energy system. A highly electrified scenario for the Norwegian energy system is constructed based on a step-by-step approach, implementing measures towards electrification and expansion of renewable electricity generation. Then, a 4GDH scenario is constructed for the purpose of analysing the role of 4GDH in a highly electrified hydropower based energy system. EnergyPLAN is used for simulation. Results show that an expansion of 4GDH will increase the total system efficiency of the Norwegian energy system. However, the positive effects are only seen in relation to the introduction of efficiency measures such as heat savings, more efficient heating solutions and integration of low-temperature excess heat. Implementation of heat savings and highly efficient heat pumps in individual based heating systems show a similar effect, but does not allow for excess heat integration. In the modelled DH scenario, the introduction of large heat storages has no influence on the operation of the energy system, due to the logic behind the EnergyPLAN model and the national energy system analysis approach chosen, and thus the effect of implementing 4GDH may be underestimated.