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District heating enables the supply of cost-effective and environmentally friendly heat for heating and hot water to multiple buildings, apartment blocks, or even entire cities. With this type of heat generation, hot water is not produced on-site within the building itself, but in a nearby central power or heating plant. In our blog, you can find out how this system works, the advantages it offers in terms of costs and sustainability, and what to consider regarding the district heating pipeline.
District heating is a system for the central generation and distribution of heat for heating buildings and providing hot water. The heat generated is transported to the connected consumers via a network of insulated pipelines, known as the heating network.
The main difference between district heating and local heating systems lies in the geographical distribution and the type of heat generation. District heating networks are usually targeted at 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 both systems is the same.
In a combined heat and power plant, heat is generated by combustion, such as the burning of fossil fuels like natural gas or hard coal. However, heat generated during waste incineration or industrial processes is also used as district heating. The use of renewable energies makes district heating more environmentally friendly. For example, geothermal and solar thermal energy, as well as environmental heat, which is made usable with the help of large heat pumps, are already integrated into district heating systems.
An evaluation by the German Federal Statistical Office provides the following data on heat generators for district heating:
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 in combined heat and power (CHP), meaning they not only produce heat but also generate electricity in the same process. It works like this: Water vapor is generated by combustion and passed through a turbine. The steam drives a turbine shaft, creating mechanical energy, which is then converted into electrical energy with the help of a generator. This principle saves fuel compared to separate electricity and heat generation, which in turn reduces the carbon dioxide emissions of district heating.
The use of waste heat, such as from waste incineration and renewable energies, further contributes to district heating being an environmentally friendly heating method. 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 will save an additional 39 million tonnes of CO2 emissions in the building sector by 2030 – equivalent to the CO2 footprint of 6.5 million people per year. Additionally, the share of district heating in the heating demand of buildings can be increased to 30 percent. Currently, district heating is used in about 14 percent of buildings. Therefore, district heating is a future-proof building solution for the heating transition.
Other advantages offered by district heating? It's
After being generated from the combined heat and power plant, the hot water must reach the customer – ideally with minimal heat loss over several kilometres. This is important because the higher the heat losses, the more energy is required to generate district heating, which negatively affects both the CO2 footprint and costs.
Water is transported through the so-called heating network, a pipeline network designed as a closed circuit. The system transports the hot water to the building, where 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 reheated.
The pipe system is usually installed underground, but in some cases, such as when structural obstacles are present, it may be necessary to install it above ground. In any case, insulation of the pipes is essential to prevent heat loss during transport.
Almost exclusively, pre-insulated pipes are used. This means the thermal insulation is already applied to the pipe at the manufacturer, and only the system is connected on site. This not only saves time on the construction site but also ensures consistently high insulation quality. Polyurethane foam (PUR) insulation is commonly used, as it has excellent insulating properties and a low thermal conductivity compared to other materials like mineral wool (lambda value 0.022 - 0.029 W/mK). Typically, plastic or steel is used for the medium pipes in district heating systems. Unlike metal, plastic pipes do not corrode. Their light weight makes them easier to assemble on-site, and they also offer excellent thermal insulation properties that minimise heat or cold loss during transport. Additionally, plastic pipes are 100% recyclable and have a CO2 balance that is more than 50% better than metallic systems.
The Gateshead energy centre in England demonstrates how district heating can reduce energy costs and save carbon dioxide. Here, the existing heating network was expanded to supply 5,000 households with cost-effective and more environmentally friendly heating. Instead of using steel piping, the city of Gateshead opted for polypropylene pipes for the district heating pipeline expansion. As a result, an estimated cost saving of around 460 euros per metre of installed pipeline was achieved. Read more about it here.
District heating will continue to advance the heating transition in a future-proof and sustainable way. The key factors are the production of heat in the combined heat and power plant and the distribution of the hot water through a thermally insulated pipe system. Ultimately, the efficiency of district heating depends on choosing 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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