District heating describes a water-based heating system where there is a considerable distance between the place the heat is generated (power plant) and the place the heat is used (the building).
District heating has become more and more popular all over the world, and is found in the majority of larger cities.
At the power plants, flue gas undergoes an exceptionally advanced treatment before being released. This has become an important factor in improving air quality in cities.
A district heating system consists of:
- a generation system (power plant)
- a distribution system (underground pipes)
- a user solution (individual heating system at the user)
The heat is traditionally produced at the power plants, where fossil fuel (coal, oil, etc) or alternative fuels (straw, wood chips, etc) is burned. A few power plants also have solar energy systems.
Heat generation is often combined with the generation of electricity in the same power plant.
From the power plant, the heat is sent through transmission piping to heat exchanger substations. The heat is traditionally distributed between the power plant and the heat exchanger substation at a flow temperature of up to 120°C. In the heat exchanger substation, it is usually exchanged down to around 90°C .
The heat is then transferred through the distribution system (pipes) to the users.
One of the drawbacks with district heating is that the long distances between the power plant and user causes relatively large heat losses.
Connection to district heating can take place either directly or through an indirect system.