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Types of district cooling and heating networks (classification)

Heat networks differ mainly in terms of their flow and return temperatures. On this page, you find a classification of heating and cooling networks based on a scientific study.

What types of heat networks exist?

The network type with the lowest supply and return temperatures is the ice network, which is primarily used for cooling purposes. Here, the high enthalpy of fusion is used to increase the cooling capacity compared to ordinary cooling networks. This type of network is not yet widely used. Alternatively, conventional cooling networks with supply temperatures of around 6 °C can be installed to provide cooling. The low temperature difference between supply and return leads to high volume flows and high pumping work, which reduce the efficiency of this type of network. 5th generation district heating and cooling (5GDHC) networks include the network types source network and, to some extent, the alternating-warm heat network. Modern "warm" heat networks are low-temperature networks with flow temperatures of around 70-90 °C. They are also referred to as 4th generation district heating networks (heating network 4.0). Hot heat networks with flow temperatures above 100 °C are considered outdated. However, these are currently the most common type of network. They are also referred to as 3rd generation heat networks. Steam networks (1st generation heat networks) are considered obsolete. The last two network types have high heat losses and can only be operated with fossil fuels (gas, coal, etc.). Finally, it should be mentioned that this classification is not unambiguous and should therefore be understood as exemplary. Alternatively, heat networks can be classified according to different heat network generations (1st to 5th generation).

In the nPro tool, district energy systems with conventional warm/hot heat networks and 5GDHC networks can be simulated.
Table 1: Classification of heat networks, adapted from [1].
Network type Temperatures
Ice network 0 °C / 12 °C little widespread, more efficient than conventional cooling network
Cooling network 6 °C / 12 °C large volume flows
Source network 6 °C - 15 °C /
3 °C - 6 °C
"classic" 5GDHC network, little heat losses (but heat gains!)
Alternating-warm heat network 25 °C - 45 °C /
10 °C - 25 °C
is operated in winter as a normal heat network, in summer also cold supply
Low-temperature heat network (4th generation district heating) 70 °C - 90 °C /
50 °C - 70 °C
often in combination with solar thermal or central heat pump, "modern" heat network
High-temperature heat network (3rd generation district heating) > 100 °C currently (still) most widespread type of heat network, inefficient, difficult to decarbonize
Steam network (1st generation district heating) < 200 °C obsolete technology, but still in use in some cases, inefficient


  1. Seethermie - Innovative Wärmeversorgung aus Tagebaurestseen (Schlussbericht). Stefan Böttger, Bernd Felgentreff, Dr. Gerold Hesse, Martin-Joseph Hloucal, Dr. Dieter Leßmann, Sebastian Mix, Dr. Kersten Roselt, Dr. Mathias Safarik, Jörg Schmidt, Christoph Steffan, Dr. Wilfried Uhlmann, 2021.

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