Heat Distribution
After generation, the heat is distributed to the customer via a network of insulated pipes. District heating systems consists of feed and return lines. Usually the pipes are installed underground but there are also systems with overground pipes. Within the system heat storages may be installed to even out peak load demands.
The common medium used for heat distribution is water, but steam is also used. The advantage of steam is that in addition to heating purposes it can be used in industrial processes due to its higher temperature. The disadvantage of steam is a higher heat loss due to the high temperature. Also, the thermal efficiency of cogeneration plants is significantly lower if the cooling medium is high temperature steam, causing smaller electric power generation. Heat transfer oils are generally not used for district heating, although they have higher heat capacities than water, as they are expensive, and have environmental issues.
At customer level the heat network is usually connected to the central heating of the dwellings by heat exchangers (heat substations). The water (or the steam) used in the district heating system is not mixed with the water of the central heating system of the dwelling. In the Odense system direct connection is used.
Typical annual loss of thermal energy through distribution is around 10%, as seen in Norway's district heating network.
Read more about this topic: District Heating
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