What is district heating? Definition, types and benefits __

District heating is becoming increasingly important for towns, neighbourhoods and larger buildings. It can efficiently combine the supply of heating, hot water and integrate different energy sources into a single system. At the same time, important questions arise for local authorities, operators and building owners: What types of district heating are there? What are the advantages and disadvantages of district heating? And what role will it play in the future of heat supply? This article clearly explains the key fundamentals and provides a concise overview of technical and international developments.

What is district heating?

District heating means that heat is generated outside the buildings being supplied and distributed to multiple consumers, via well-insulated pipework. It is not a source of energy in its own right, but rather a form of heat supply. The heat required can come from fossil fuels, renewable energy sources or industrial waste heat, amongst other sources.

In contrast to local heat supply – such as that provided by individual boilers in each house – with district heating, the heat required is generated in large combined heat and power plants or energy centres. From there, it is usually delivered as hot water to the connected buildings, where it is used for space heating and domestic hot water. District heating is therefore primarily used in neighbourhoods, districts and densely populated areas.

This distinguishes it fundamentally from decentralised heating solutions, in which heat is generated directly within the building. When planning district heating – whether centrally or decentrally – the area of application and the supply structure determine which concept is suitable. The difference between district heating and local heating lies primarily in the range, size and complexity of the supply system.

The basic principle of district heating supply

District heating is based on a clearly structured technical process, ranging from central heat generation to heat transfer within the building. How district heating works can be explained in three successive steps:

• Central heat generation: Heat is generated in combined heat and power (CHP) plants, heating plants or other centralised facilities. Typically, combined heat and power (CHP) is used, whereby the combustion of fuels – such as natural gas or biomass – simultaneously produces electricity and usable heat. Waste incineration plants and industrial waste heat are also utilised as heat sources. The heat is usually supplied in the form of hot water, and less commonly as steam, for transport.
• Transport via the primary network: The hot water or steam is transported to the connected buildings via an extensive, predominantly underground pipework system. The pipes are thermally insulated to minimise heat loss from the district heating system on its way to the consumer. The distance between the generator and the consumer can be several kilometres. Pre-insulated pipework systems help to ensure that heat is transported with as little loss as possible.
• Building connection and heat transfer: The connection to the building is made via a service pipe. The district heating transfer station usually transfers the supplied heat to the building’s internal heating system, via a heat exchanger and hydraulically separates the two circuits from one another. Depending on the design, it regulates pressure, temperature and flow rate, and measures the amount of heat supplied for billing purposes. Safety and control devices ensure trouble-free operation. The cooled water flows back to the generation plant via the return pipe and is reheated.

With this technical infrastructure, district heating enables a reliable and convenient supply of space heating and hot water to buildings, particularly in urban areas and for larger properties.

What types of district heating are there?

District heating can be divided into different categories, depending on the energy source used. The choice of heat source has a significant impact on the economic and environmental performance of the supply. Individual sources may be used, or several heat sources may be combined within a single system. The composition of a district heating system depends, amongst other things, on regional conditions and available resources.

Fossil-fuel-based district heating

Traditionally, a large proportion of district heating supply has been based on fossil fuels such as natural gas and coal. These fuels are burnt in central heating plants or combined heat and power (CHP) plants to generate heat, and often electricity through combined heat and power generation. Fossil-fuel-based district heating is widespread but, depending on the fuel used, causes significant CO₂ emissions. The decarbonisation of district heating therefore aims to gradually replace fossil fuel sources or reduce their share.

District heating from renewable energy sources

The share of renewable energy in district heating supply is growing steadily. In the case of green district heating, a significant proportion of the heat comes from renewable heat sources or usable waste heat. The most important renewable heat sources include:

• Biomass: The combustion of wood, pellets or other organic waste materials can provide renewable heat. Its environmental impact depends, amongst other things, on the origin, processing and transport of the biomass.
• Geothermal energy: Deep geothermal systems utilise natural geothermal heat, to provide hot water. Particularly in regions with suitable geological conditions, geothermal energy can provide a continuous supply of heat.
• Solar thermal energy: Large-scale solar collectors convert solar energy into heat, which is fed into the grid. In combination with seasonal heat storage systems, solar thermal energy can cover a significant proportion of annual heat demand.

Which renewable heat sources are used, or combined with one another, depends on regional conditions and the existing infrastructure.

District heating from waste heat

The integration of industrial waste heat offers further significant potential. Many industrial processes generate surplus heat, that cannot be fully utilised on site. Waste heat from data centres can also be harnessed for heat supply. If it is fed into the supply system, the need for additional energy generation is reduced and the efficiency of the overall system can increase. The use of industrial waste heat is a key component in the transformation of the heat supply.

District heating: an overview of the advantages and disadvantages

District heating can be an efficient and convenient form of heat supply. However, the advantages and disadvantages of district heating depend on the heat sources used, the local infrastructure, the supplier and the terms of the contract. It is therefore not possible to make a blanket assessment.

Advantages of district heating

District heating combines technical efficiency and user comfort, with the possibility of integrating renewable energy and waste heat into the heat supply. An overview of the key advantages of district heating:

• Energy efficiency through centralised generation: Heat is often generated in large combined heat and power (CHP) plants. This process produces electricity at the same time as heat. Thanks to this combined production, the fuel used is utilised efficiently and a high overall efficiency can be achieved.
• Integration of different heat sources: District heating systems can integrate various energy sources, ranging from biomass and geothermal energy to industrial waste heat. This allows fossil fuel sources to be gradually supplemented or replaced.
• Potential for reducing CO₂ emissions: If renewable energy sources or previously unused waste heat are utilised, district heating can help to reduce CO₂ emissions. However, the actual carbon footprint depends on the heat sources used and the efficiency of the overall system.
• Minimal space requirements in buildings: Compared with traditional heating systems, district heating transfer stations require very little space. Boilers, fuel storage facilities and chimneys are generally not required. This is particularly advantageous in densely built-up or urban areas.
• Security of supply and reduced maintenance requirements: Centralised control and monitoring by the operator ensures a high level of operational reliability. Faults can be detected and dealt with centrally. End users are spared the need to source their own fuel and maintain a boiler. However, the transfer station and the in-house heating system must still be inspected and maintained.
• Regional value creation: Where local heat sources are utilised and municipal or regional operators are involved, value creation and investment can remain within the region.

The extent to which these advantages of district heating are realised, depends on the type of heat generation, the technical infrastructure, and local conditions.

Disadvantages of district heating and further challenges

District heating can only be used if a connection is available at the relevant location, or if it is technically feasible to establish one. The initial connection often involves investment in network development, the building service pipe, and the transfer station. How quickly these costs are recouped depends on the building and local conditions.

In many regions, there is only one local supplier available. It is therefore usually not possible to switch suppliers. Added to this, in some cases, are long-term contractual commitments and pricing arrangements, which depend on the terms and conditions of the respective supplier.

Cost-effectiveness is also influenced by connection density and building density. District heating is suitable for densely populated areas and larger properties, whilst the cost per connection can rise in sparsely populated regions. The environmental impact is not automatically positive either, but depends largely on the heat sources used and the efficiency of the overall system.

A comparison of the advantages and disadvantages of district heating

The key aspects can therefore be compared as follows:

District heating in an international comparison

District heating is an established part of the heating supply worldwide. According to the International Energy Agency (IEA), it supplies more than 600 million people and accounts for around ten per cent of global final energy consumption for heating. It is particularly widespread in Europe, China, Russia and parts of Central Asia.

However, there are significant regional differences. Several northern European countries are already making greater use of bioenergy, waste heat and heat pumps. In China and parts of Eastern Europe, by contrast, district heating continues to be dominated by existing coal- and gas-fired plants. Due to its geological conditions, Iceland relies almost entirely on geothermal energy for its heating supply.

Key international development priorities and challenges

The types of district heating used depend on regional resources, existing infrastructure and the political framework. The IEA identifies large-scale heat pumps, solar thermal energy, geothermal energy, thermal storage and the use of industrial or urban waste heat as key approaches to decarbonising district heating.

The IEA cites Denmark as an example, where large solar thermal plants are combined with seasonal heat storage systems. In Germany and the Netherlands, solar thermal energy, storage and waste heat are integrated. In the USA, the Department of Energy supports municipal and neighbourhood-based geothermal projects.

High initial investment costs, long payback periods, and outdated infrastructure are holding back expansion. At the same time, one of the advantages of district heating is that different heat sources can be brought together within a single system, and local waste heat potential can be utilised. This requires a suitable regulatory framework and coordinated planning.

Collaboration on district heating projects

District heating projects involve a wide range of stakeholders and decision-makers. Their implementation requires close coordination between public and private sector actors as well as early clarification of the technical, economic and regulatory framework.

Local and regional authorities take on responsibilities in heating planning and establish the planning framework. Municipal utilities, energy suppliers and network operators are responsible for planning, financing, construction and operation. Political decision-makers and regulatory authorities set overarching guidelines and ensure transparency and consumer protection.

Housing associations, operators of large property portfolios, public institutions, and industrial and commercial enterprises contribute their requirements as heat consumers. Companies with usable waste heat may also play a role as heat suppliers. The interaction between these stakeholders influences how district heating projects are planned and implemented.

District heating in practice: the Veksoe project

In Veksoe, north of Copenhagen in Denmark, around 400 homes are connected to the local district heating plant. The pipework system, which is over 15 kilometres long, distributes the heated water within the housing estate. Effective insulation of the underground pipes helps to limit heat loss and keep the heating plant’s energy requirements as low as possible.

The operators therefore opted for aquatherm energy. In this system, the PP-R or PP-RCT service pipes are factory-insulated with PUR foam and encased in an HDPE outer pipe.

Technical advantages of pre-insulated PP-R pipe systems for district heating

Pre-insulated polypropylene pipe systems, such as those made from PP-R and PP-RCT, offer several application-specific advantages during installation and operation:

• Thermal conductivity: The material’s low thermal conductivity helps to limit heat loss during transport (aquatherm energy: thermal conductivity < 0.027 W/mK).
• Corrosion behaviour: The pipes are corrosion-resistant and do not exhibit any material-related corrosion. This can reduce maintenance costs.
• Hydraulic properties: The smooth inner surface of the pipes contributes to favourable flow conditions and low pressure losses.
• Installation: The pipes’ low weight and flexibility make them easy to handle and can facilitate rapid installation.

For the pipe system, which is more than 15 kilometres long, the low thermal conductivity, corrosion resistance and ease of handling during installation were particularly relevant.

Conclusion: District heating as a cornerstone of heat supply

District heating combines the generation and distribution of heat and primarily supplies towns, neighbourhoods and larger properties with space heating and hot water. Different heat sources can be integrated into a single supply system. International trends show that this form of heat supply is being expanded and further developed technically in many regions.

A holistically planned district heating system, in which various energy sources are efficiently combined, can unlock significant potential for savings in heat generation. Coordinated planning and pipework systems that meet the technical requirements of the specific project are crucial to its implementation.