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District heating makes it possible to supply several buildings, apartment blocks or entire cities with cost-effective and sustainable heat for heating and hot water. In this type of heat generation, hot water is not produced on site in the building itself, but in a central power or heating plant nearby. You can find out how this works, what advantages it brings in terms of costs and sustainability, and what needs to be considered when it comes to district heating pipelines in our blog.
In a combined heat and power plant, the heat is generated by combustion, for example from fossil fuels such as natural gas or hard coal. However, heat generated during waste incineration or industrial processes is also used as district heating. The share of renewable energies in district heating is growing steadily. For instance, geothermal and solar thermal energy as well as environmental heat, which is made usable with the help of large-scale heat pumps, are already fed into district heating systems.
An evaluation by the German Federal Statistical Office provides the following data on heat generators for district heating:
The main difference between district heating and local heating systems lies in the geographical distribution and the way in which heat is generated. District heating networks are usually geared towards urban areas, where they supply heat from a central source to numerous households and businesses. Local heating networks, on the other hand, are more likely to be found in rural areas or neighbourhoods where the heat source is closer to the consumers. The technology behind the two systems is the same.
District cooling is when buildings are supplied with cooling via a pipeline. This is not only used for air conditioning rooms, but is also used in the food industry, gastronomy and data centres.
Learn more about piping systems for district and local heating or cooling
The combined heat and power plants are operated by combined heat and power (CHP). This means that they not only produce heat, but also electricity in the same process. Here's how it works: Combustion generates steam and passes it through a turbine. The steam sets a turbine shaft in motion – mechanical energy is generated. This is converted into electrical energy with the help of a generator. This principle saves fuel compared to separate electricity and heat generation, which in turn has a positive effect on carbon dioxide emissions.
The use of waste heat, for example from waste incineration, as well as renewable energies also means that district heating is seen as a climate-friendly type of heating. In its current study "Perspective of District Heating", the Energy Efficiency Association for Heating, Cooling and Combined Heat and Power (AGFW) shows that the continuous expansion and conversion of district heating in Germany by 2030 will save an additional 39 million tonnes of CO2 emissions in the building sector – as much as the CO2 footprint of 6.5 million people per year – and increase the share of district heating in the heating demand of buildings to 30 percent. Currently, district heating is used in about 14 percent of the buildings. District heating is therefore an important building block for the heat transition.
Other advantages offered by district heating? It's
After being produced from the combined heat and power plant, the hot water must reach the customer – and if possible in such a way that it arrives several kilometres away with little heat loss. This is because the higher the heat losses, the more energy has to be used to generate the district heating, which has a negative impact on the CO2 footprint and costs.
Water is transported with the help of the so-called heating network, a pipeline network that is designed as a closed circuit. The system transports the hot water to the building. There, a heat exchanger extracts the heat from the water, but the water remains in the pipe. The cooled water then flows back to the combined heat and power plant via the return flow and is heated again.
The pipe system is usually laid underground, but in some cases, for instance due to structural obstacles, above-ground installation is a good idea. In any case, the insulation of the pipe is necessary to avoid heat loss during transport.
Pre-insulated pipes are used almost exclusively. This means that the thermal insulation is already attached to the pipe at the manufacturer's site, while the system is only connected on the construction site. On the one hand, this saves time on the construction site, and on the other hand, the quality of the insulation remains consistently high. Insulation made of polyurethane foam (PUR) has proven its worth. Polyurethane has very good insulating properties and has a low thermal conductivity (lambda value 0.022 - 0.029 W/mK) compared to other insulating materials such as mineral wool. As a rule, systems made of plastic or steel are used as medium pipes for district heating pipes. Unlike metal, plastic pipes have the advantage that they do not corrode. The light weight is also an advantage and makes it easier to assemble on the construction site. Plastic pipes also offer very good thermal insulation properties, which minimise heat or cold loss during transport. They also score points in terms of sustainability: they are 100% recyclable and have a more than 50 % better CO2 balance than metallic systems.
How district heating can be used to reduce energy costs and save carbon dioxide is demonstrated by the Gateshead Energy Centre in England. Here, the existing heating network has been expanded so that 5000 households can be supplied with low-cost electricity. Instead of steel piping, the city of Gateshead relied on pipes made of polypropylene for the extension of the district heating pipeline. As a result, it achieved an estimated cost saving of around 460 euros per metre of installed piping. Read more about it here.
District heating is an important topic for the future that is driving the heat transition. Just as important as the production of heat in the combined heat and power plant is the distribution of the hot water via a thermally insulated pipe system. After all, district heating can only be operated efficiently by selecting the right system.
With its product aquatherm energy, aquatherm offers a piping system consisting of pre-insulated polypropylene pipes as well as fittings and joints. All medium pipes and fittings used for aquatherm energy are made of the corrosion-resistant plastic fusiolen PP-R/PP-RCT.
Learn more about aquatherm energy
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