District Heating Supply Research Articles

Techno-economics of solar re-powering and retro-fitting an existing district heating network

Most of the district heating systems today use higher operating temperatures than those in new-built systems, possibly limiting compatibility with solar energy. This study evaluates the cost-effectiveness in terms of unit heat cost of integrating solar heating into an existing district heating system compared to not using solar energy, under changing economic boundary conditions such as collector and fuel cost, in addition to discount rate. This is investigated for both a scenario where the solar heating and a boiler replacement is done concurrently, as well as a scenario where solar heating is added to an existing system without replacing the boiler. A theoretical district heating supply of 3 MW is modelled and simulated based on a real system and load profile. The heat supply is varied to include storage with or without solar heating. Results for a 3 % discount rate indicate that; Replacing a 3 MW boiler with a slightly smaller boiler of 2.5 MW and adding a storage is cost effective and yields a unit heat cost of 58.0 EUR/MWh (16.1 EUR/TJ) which is a reduction of about 6 %. Installing solar heating together with the boiler replacement yields a unit heat cost as low as 55.7 EUR/MWh (15.4 EUR/GJ) which is a reduction of about 8 %. When replacing the boiler, all system configurations have similar unit heat costs compared to a boiler-only system, so factors such as emission reductions due to solar heating are relevant when considering alternatives. Furthermore, adding solar flat plate collectors corresponding to a 13 % solar fraction without replacing the boiler can reduce the unit heat cost as low as 34.8 EUR/MWh (9.7 EUR/TJ), which is 32 % lower than without solar. Evacuated tube collectors can increase this solar fraction to 17 % with similar system size, although at a higher cost. At a discount rate of 5 % solar heating is cost-competitive when fuel cost is above 26 EUR/MWh (7.2 EUR/TJ) and at 7 % competitive when fuel cost is above 32 EUR/MWh (8.9 EUR/TJ). Increasing solar heating system size reduces the backup-boiler fuel use during summer maintenance and makes fuel type less relevant for the overall unit heat cost.

Integrating district heating potentials into European energy system modelling: An assessment of cost advantages of renewable and excess heat

This paper takes a novel modelling approach by considering high spatial resolution heat generation potentials for district heating and integrating them into a European energy system model. Subsequently, a modelling analysis of an integrated energy system including district heating, electricity and hydrogen supply for 25 EU Member States and the year 2050 is carried out. In contrast to existing approaches, the modelling approach captures the heterogeneous resource availability in district heating. The results show multivalent district heating networks based on a wide range of renewable and excess heat sources used directly or in combination with large-scale heat pumps. The high spatial resolution of the heat generation potentials allows a detailed cost comparison of different possible future technology mixes in district heating. The paper finds that the use of heat pumps, geothermal energy and industrial excess heat offer slight cost advantages for the energy system as a whole. Geothermal heat can also provide cost advantages for district heating generation.

Booster heat pump with drop-in zeotropic mixtures applied in ultra-low temperature district heating system

The pursuit of sustainable district heating solutions has driven a growing interest in ultra-low temperature district heating (ULTDH) systems, where booster heat pumps (BHPs) play a pivotal role despite challenges posed by their efficiency limitations under large temperature glide conditions. This paper investigates the potential of drop-in R-1234yf/R-32 zeotropic mixtures in BHPs compared to a baseline R-134a system, within the context of a ULTDH framework. This study focused on the viability of the mixtures of R-1234yf/R-32 with the composition ratio of 80 %/20 % and 90 %/10 %. The investigation reveals disparities in compressor efficiency and heat exchanger pressure drop at the component level. Device-level analysis unveils increased COP for R-1234yf/R-32 mixtures, alongside with maximum second-law efficiencies reaching 0.32. A remarkable enhancement in heating capacity up to 58 % was found. System-level analysis demonstrated exergetic efficiencies and identified preferable district heating temperatures. Exergetic efficiencies of 0.47, 0.55, and 0.59 were achieved for domestic hot water preparation at district heating supply temperatures of 30 °C, 35 °C, and 40 °C, with a subsequent shift in optimal district heating temperatures as central heating station efficiency decreased. Temperature profile analysis underscored challenges stemming from excessive subcooling, highlighting the need for configuration refinements.

Strategies for decarbonizing European district heating: Evaluation of their effectiveness in Sweden, France, Germany, and Poland

Decarbonizing the EU's district heating is crucial for meeting climate goals and securing a sustainable energy future. Currently, district heating suffers from inefficiency, high operating temperatures, significant distribution losses, and reliance on fossil fuels. Literature highlights strategies for reducing emissions, including integrating low-carbon heat sources, lowering supply temperatures, and employing efficient technologies like heat pumps and combined heat and power (CHP). However, the individual effectiveness of these strategies in reducing emissions within existing networks remains unassessed. This study addresses the gap by applying a comprehensive model that evaluates energy and emissions across the district heating supply chain, coupled with a derivative-based sensitivity analysis. We apply this methodology to the national-level district heating systems of Sweden, France, Germany, and Poland. Results indicate that the impact of decarbonization strategies on district heating emissions varies significantly by the system's characteristics, i.e., the energy mix in power and district heating supply and the presence of CHP plants. Primarily, incorporating more low-carbon heat sources emerges as the most effective method for emission reduction across nearly all examined countries. A 1 % increase in the share of low-carbon heat sources can potentially cut emissions by 0.8–1.3 kg CO2e per GJ of heat. In countries like Sweden and France, where the power generation already relies heavily on low-carbon resources, technologies which convert electricity to heat—such as heat pumps and electric boilers—rank as the second most effective approach. In contrast, for countries like Germany and Poland, with their moderate to low use of low-carbon power, reducing distribution losses and decreasing heat demand prove more effective, with emission reductions ranging between 0.8-1.3 and 0.7–1.2 kg CO2e per GJ in these countries, respectively. Additionally, cutting down power generation in fossil fuel-based CHP plants significantly reduces emissions in these regions. While green hydrogen and carbon capture and storage (CCS) also contribute to emission reductions, a 1 % increase in green hydrogen's share might decrease emissions by just 0.3–0.5 kg CO2e per GJ of heat, highlighting their lower effectiveness compared to the aforementioned strategies. These insights hold value for both district heating operators and for technology suppliers seeking decarbonization pathways. This is also true for policymakers focused on climate change mitigation, guiding the distribution of subsidies and R&D investments.

Attracting Customers to District Heat Supply: The Case of Riga

District heating will be important in achieving future climate goals. Possibilities of using waste heat from different sources, e.g. subways, hospitals, shops, data centers, rivers are often discussed. Many district heating companies face the challenge of sufficient coverage of connected consumers in a city or region. To expand the operating area, companies should initially attract objects which are close to heat networks to lower the connection costs. The research question is how to attract existing buildings under construction to the district heating system. The present work uses system dynamics modeling for studying the possibilities of the Riga district heat supply company to increase consumer network. Modeling is based on historical data of residential buildings. The results show that old buildings choose to connect to the district heat supply when these are being renovated, or the individual heat supply equipment is out of order. The older the buildings, the more likely these will be connected to the district heating, however this decision may take at least 70 years. Renovation increases the probability of connection to the district heating, so the impact of subsidies for renovation is important. Regulation that requires connection to the district heating as a priority choice in case of renovation is also important.

Use of an Absorption Heat Pump to Lift the District Cooling Waste Heat Temperature for the District Heating Supply in Tallinn: a Technical and Economic Analysis

Absorption heat pumps can lift a lower temperature waste heat source to a higher temperature useful output. In that process, it uses less electricity as an input compared to heat pumps with electrical compressors. Therefore, in some cases, it can be used to lift a lower temperature waste heat source to a higher temperature useful output with less electricity consumption. Absorption heat pumps are not very widely spread in district heating, mostly because there aren’t many suitable waste heat sources or conditions needed to run them. Tallinn has a district heating system with an annual generation of more than 2 TWh and a goal to make it an entirely carbon neutral district heating system by 2030. Tallinn has also started to develop a district cooling network, and by the end of 2023, the installed capacity was about 6 MW. District cooling capacity is estimated to grow to around 100 MW in 2030. This paper investigates different types of absorption heat pumps and the possibilities of integrating an absorption heat pump to a district cooling plant with the purpose of using waste heat from the cooling plant for renewable heat generation, that can be used in district heating. Different technical aspects are examined to find a suitable production solution, are presented as results. From an economical point of view, the cost of heat to cover peaks with an absorption heat pump is calculated. The effect of reducing fossil fuel use in the Tallinn district heating network with an absorption heat pump is estimated.

Design and safety features of SALUS-100: A long fuel-cycled Sodium-cooled fast reactor

The paper introduces the innovative development of an SFR-based Small Modular Reactor (SMR) known as SALUS-100, with a 100 MWe electrical output, developed by KAERI. This innovative design, derived from the previous TRU transmutation burner SFR concept, represents a significant step forward in establishing a new model for SMRs and offers diverse applications, including on– and off-grid electricity generation, district heating, and industrial heat supply. The reactor features of SALUS-100 incorporate an integrated pool-type primary system configuration and a long fuel-cycle core concept with a metallic alloy nuclear fuel. Its design concept prioritizes preventing severe accidents by capitalizing on the inherent safety and reliability features achieved through emphasizing passive design characteristics. The paper describes the engineering design and safety analyses of SALUS-100, highlighting advanced design concepts in reactor core, fuel, materials, and systems. Additionally, the key research and development endeavors, focusing on vital areas such as enhancing system design capability, validating designs, demonstrating safety, and innovating in metal fuel technology, are briefly discussed, emphasizing the potential of SALUS-100 in revolutionizing the SMR market and utilizing efficient nuclear energy in the future.

Integrated Gasification of Biomass Residues (IBGCC)

A comprehensive outline of a new approach in integrated gasification of biomass residues including the material flow management in urban areas being targeted on the generation of electricity and district heating is presented. The feedstock is derived from civilian material by fully automated collection, sorting and separation. Thereby an outward transfer of inerts is executed, such as minerals, metals, glass and electronic scrap as well as sorted plastics being object to recycling. Finally a ligno cellulosic and a non-lignocellulosic fraction are gained. The for mer one is suitable for thermochemical conversion, the latter one for biological conversion into fuel gases which subsequently are oxidised completely at low air excess in a horizontally arranged cyclone combustion chamber. The heat recovered from the flue gases in the utility boiler is used to generate steam scooping in the supply of electricity and district heating. The basic design is scaled to an overall thermal capacity of 2-5 MW. This type is most capable of utilising renewable energy by converting the organic fractions of civilian material flows. The power plant is based on a reliable technology representing an on-site integrated biomass gasification combined cycle system including peripheral units specified for the treatment of complementary materials.

Use of Absorption Heat Pumps to Raise District Cooling Waste Heat Temperature for District Heating Supply in Tallinn: Technical and Economic Analysis

Abstract Decarbonisation of District Heating (DH) networks is essential to achieving the European Union’s climate goals. In this context, there is growing interest among DH stakeholders in the recovery and reuse of underutilised heat sources. Waste heat recovery from district cooling (DC) networks offers a compelling option that can be used as input for various heat pump integrated DH solutions. In this regard, absorption heat pumps (AHP) showcase a promising solution to elevate a lower-temperature waste heat source with reduced electricity consumption. However, AHPs are not widely applied in DH context, primarily due to the lack of suitable waste heat sources or the necessary conditions for their effective operation. This article aims to explore various configurations of AHP and their potential integration with DC plant waste heat for DH application. The potential for adopting AHPs to boost efficiency and lower carbon emissions is evaluated through a techno-economic examination of three distinct technological configurations. For Tallinn case study, it was observed that AHPs can be more efficient, reduce energy consumption, and achieve a lower LCOH while being combined with HP condenser cooling. This study is expected to provide a theoretical support for the positive impact of using AHPs to reduce the usage of fossil fuels in the Tallinn DH network.

Exploring the location and use of baseload district heating supply. What can current heat sources tell us about future opportunities?

The decentralization of energy production and recovery of excess heat (EH) to reach climate targets is essential for renewable and fully decarbonized heating systems. This paper identifies current and potential industrial EH sources providing baseload capacity for district heating (DH) systems. These sources are evaluated by sector and process for supplying baseload capacities explored for current 3rd generation district heating (3GDH) and 4th generation district heating (4GDH) systems with lower grid temperatures and losses, with and without expansions. The method combines geographical analysis and available baseload capacity estimations for 360 Danish DH systems scenario-making and an additional sensitivity analysis evaluating baseload capacity full-load hours. It is found that 80 % of Danish DH systems have an unmet baseload capacity of 50 % or higher. Half of the systems have geothermal capacity available and up to 20 % of industrial EH baseload capacity potential, which sums up to 5 PJ of EH potential within a 2 km distance. The findings also suggest that there is an additional opportunity for the placement of future energy infrastructure able to supply EH, which is highly contextual and strategic in heat planning, particularly considering the future development of sustainable and energy-efficient DH systems.

Valorisation of Waste Heat in Existing and Future District Heating Systems

To recover thermal energy from different sources, its quality and possibilities for utilisation are essential. The wide range of engineering solutions includes a direct connection to the district heating (DH) system and the integration of low-quality heat using heat pumps to increase the temperature level of recoverable heat. Therefore, this article compares waste heat valorisation strategies for integration into existing DH networks, low-temperature DH, and ultra-low heat supply systems using the multi-criteria assessment method. In addition, a local scale assessment was performed to identify the waste heat role in existing RES-based DH systems. The results show that the highest waste heat valorisation rate could be reached when integrated into low-temperature DH systems due to high waste heat potential and suitable temperature conditions. However, a local scale assessment shows a significant impact on the already implemented solar technologies, as waste heat could cover around 70% of the summer heat load.

Optimizing Solar Energy Harvesting through Integrated Organic Rankine Cycle–Reverse Osmosis Systems: A Techno–Economic Analysis

When it comes to seawater desalination in the small- to medium-electricity ranges, the organic Rankine cycle (ORC) powered by solar energy stands out as the most energy-efficient technology currently available. Various solar techniques have been developed to capture and absorb solar energy. Among them, the parabolic trough collector (PTC) has gained recognition as a low-cost solar thermal collector with a long operating life. This study investigates the thermodynamic performance and economic parameters of a PTC-powered ORC using Dowtherm A and toluene as working fluids for the solar cycle and ORC cycle, respectively. Thermo-economic multi-objective optimization and decision-making techniques are applied to assess the system’s performance. Four key parameters are analyzed for their impact on exergy efficiency and total hourly cost. Using TOPSIS decision-making, the best solution from the Pareto frontier is identified, featuring an ORC exergy efficiency of 30.39% and a total hourly cost of 39.38 US$/h. The system parameters include a mass flow rate of fresh water at 137.7 m3/h, a total output net power of 577.9 kJ/kg, and a district heating supply of 1074 kJ/kg. The cost analysis reveals that the solar collector represents approximately 68% of the total hourly cost at 26.77 US$/h, followed by the turbine, thermoelectric generator, and reverse osmosis (RO) unit.

Methodology to compare and optimize district heating and decentralized heat supply for energy transformation on a municipality level

The determination of the optimal energy supply system and the selection of energy producers are two major challenges in the energy transformation of districts. This paper addresses these issues, presenting a holistic approach to compare and optimize district heating supply and decentralized heat supply, which is applicable to arbitrary districts. For this purpose, load profiles for space heating, domestic hot water and electricity are generated utilizing an archetype approach and statistical data. To identify the most economic supply variant, optimization models are created, using the Open Energy Modelling Framework. The optimization results are compared and the most economic supply variant is identified. The method is demonstrated with a case study of a district with a heat density of 491.15kWh/(m2a), considering different emission reduction targets and energy costs. The results show that, for a district with these properties, district heating has lower levelized costs of heating than decentralized heat supply for 94% of the investigated variants. The difference lies between 0.002€/kWh and 0.135€/kWh, depending on energy prices and emission reduction target. In the future, the developed method will be used to investigate the influence of various district characteristics on the economic efficiency of supply variants.

Carbon capture from combined heat and power plants – Impact on the supply and cost of electricity and district heating in cities

The capture and storage of biogenic CO2 emissions from large point sources, such as biomass-combusting combined heat and power (CHP) plants, can contribute to climate change mitigation and provide carbon-negative electricity while supplying district heating in urban areas. This work investigates the impact of retrofitting CO2 capture processes to CHP plants in a city energy system context. An energy system optimization model is applied to a case study of the city Västerås, Sweden, with scenarios involving two existing CHP plants in the city, retrofitted with either a heat-driven (MEA) or an electricity-driven (HPC) carbon capture process. The results show that the CHP plants might be retrofitted with either option without significantly impacting the district heating system operation or the marginal costs of electricity and district heating in the city. The MEA process mainly causes a reduction in district heating output (up to 30% decrease on an annual basis), which can be offset by heat recovery from the capture unit. The electrified HPC process does not impact the CHP plant steam cycle but implies increased import of electricity to the city (up to 44% increase annually) compared to a reference scenario.

To the problem of the need to install thermoregulators on heating appliances in buildings with district heat supply

The article is devoted to the question of the degree of expediency of installing automatic thermostats on heating appliances in buildings with centralized heat supply. The data of actual temperature measurements and the feeling of thermal comfort are given.

Potential for supply temperature reduction of existing district heating substations

Reducing operating temperatures is a crucial goal for transforming district heating networks into sustainable systems as it allows the integration of low exergy heat (e.g. renewable, waste heat). Many criticalities arise when reducing operating temperatures in existing networks that are not designed to operate in these conditions. The criticalities occur at different levels: in the building, in the thermal substations, in the pipelines and in the production plants. In this paper, the reduction of supply temperature in existing district heating substations is analyzed. A methodology including a model of the thermal substation and a data analysis software is developed to estimate the potential temperature reduction that could be applied to existing substations. The application of the model to an existing large-scale district heating network in Northern Italy shows that all the analyzed substations are currently able to shift their operation from 120 °C to 104 °C, and that district heating supply temperatures around 90 °C can be realistically achieved with few improvements on the system.

The effect of low-carbon processes on industrial excess heat potentials for district heating in the EU: A GIS-based analysis

Excess heat from industrial processes can be utilized in district heating networks, thereby reducing the primary energy demand and possibly the CO2 emissions for generating district heating. Numerous studies found a substantial potential of industrial excess heat, but have not systematically considered future changes in the energy system that will affect its utilization potential. Industrial production is set to transform to low-carbon processes and district heating needs to be generated without the use of fossil fuels. We quantify industrial excess heat using spatial matching for the EU-27, and considering the impact of the transformation to a climate-neutral energy system. The first step identifies excess heat potentials from energy-intensive industries as point sources, and considers process changes. The subsequent step spatially matches these excess heat potentials to district heating areas using a GIS-based approach. The results show that the amount of available excess heat will decrease significantly due to industry transformation. At the same time, the utilization could be increased due to lower district heating system temperatures and expanding district heating areas, resulting in 3–36 TWh per year. At local level, industrial excess heat can make a significant contribution to the supply of district heating in the future, but the major share will need to come from renewables.

ANALYSIS OF HOT WATER HEATERS FOR INDIVIDUAL HEATING STATION WHEN THE TEMPERATURE CHART OF THE DISTRIBUTION HEAT NETWORK IS CHANGED

The aspects of the functioning of centralized heating systems of residential urban districts after additional insulation of this district existing buildings were considered. The influence of the heat carrier temperature in the district distribution heating network on the heat transfer surface of the heat exchangers that are installed in the individual heat station schemes for hot water supplying was analyzed. Estimates were made for single-stage connection of the heat exchangers to the heating systems. When determining the heat transfer surface, known criterion equations for plate heat exchangers of heat supply systems were used. The range of changes in the heat transfer surface of hot water heaters and the consumption of network water is determined depending on the selected temperature chart of the distribution heat network. The proposed recommendations can be useful in developing a heat supply quality control schedule for a district buildings heating systems in a district when the building thermal insulation process is completed. Possible approaches to the thermal design of heat exchangers of the hot water supply system for insulated buildings individual heating stations are considered when changing the temperature chart of the district heating supply system of the residential urban districts. Estimates were made to understand the influence of the reduced temperature chart for heat supply of the districts on the network water consumption for hot water heating and the surface of heat exchangers of insulated buildings heaters. It was shown that the increase in network water consumption for building hot water supply can be 1.5 to 3 times higher. The analysis presented for the surface of the heat exchangers of heating installations for insulated buildings hot water supply shows that it can be even double increase of heaters heat transfer surface depending on the temperature chart. The results obtained should be taken into account when planning the temperature chart of the heat carrier for a distribution heating network. Keywords: district heating, heat supply systems reforming, individual heating station, hot water heaters, plate heat exchanger, heat exchanger thermal design.

Decarbonization of district heating and deep retrofits of buildings as competing or synergetic strategies for the implementation of the efficiency first principle

This paper discusses the compatibility of district heating (DH) networks with deep retrofits of buildings under various European climate conditions and city typologies. The study analyses five cities with different DH market shares, climate zones, population densities, and transferability potentials. First, we have forecasted population, heated floor area, and share of floor area per construction period until 2050, and then calculated three different heat demand scenarios for varying building refurbishment rates of 1%, 2%, and 3% of the total floor area. Second, future suitable DH regions with min 25 GWh/km2 networks were identified. By applying a bottom-up GIS model, based on the type of city area, number of buildings, street length, and heat density, the DH distribution capital and operation costs were calculated. Lastly, to compare the total cost of heat supply for each scenario, the cost of individual heat per building type was calculated.The results show that even in the scenarios with high refurbishment rates of 3%, high percentage of the built-up areas, between 23% and 68% depending on the city typology, are suitable for DH supply in 2050. The share of DH from the total heat supply varies between 49% and 83%. An increase of the DH price between 14% and 35%, depending on the scenario and case study can be expected due to the reduced heat densities compared to the current ones. Nevertheless, maximizing the DH connection rates in the identified regions leads to lower total cost of heat in almost all the analysed case studies.

Peak Shaving of a District Heated Office Building with Short-Term Thermal Energy Storage in Finland

Short-term thermal energy storage techniques can be effective to reduce peak power and accommodate more intermittent renewable energies in district heating systems. Centralized storage has been the most widely applied type. However, in conventional high-temperature district heating networks, substations are typically not equipped with short-term thermal energy storage. Therefore, this paper investigated its peak shaving potential. A 5 m3 thermal storage tank directly charged by the district heating supply water was integrated into a substation of a Finnish office building. The substation with the stratified storage tank and the office building were modeled and simulated by IDA ICE. Different storage tank temperature control curves were designed to charge the tank during off-peak hours and discharge to reduce the high-peak-period heating power. Moreover, the peak power was further dimensioned by reducing the mass flow of the primary district heating supply water. The results indicate that the storage tank application significantly decreases the office building daily peak power caused by the ventilation system’s morning start during the heating season. It reflected a higher peak shaving potential for colder days with 31.5% of maximum peak power decrease. Cutting the mass flow by up to 30% provides an additional peak power reduction without sacrificing thermal comfort.