First Generation of District Heating Technology (1GDH)

---

The first commercial district heating systems were implemented in the United States in 1880, based on the steam distribution results obtained in 1876-1877 by Birdsill Holly in his pioneering Lockport experiments. This steam distribution technology, although considered outdated to this day, is still used in two major district heating systems: the Manhattan system in New York and the Paris system. Both urban areas are extremely dense and offer very favourable conditions for low heat distribution costs. In fact, Paris has the best conditions for efficient heat distribution in the entire European Union (Persson & Werner, 2011)[6]. Therefore, both systems can afford to use the first generation of outdated district heating technologies in their current operations.

Second-generation district heating technology (2GDH)

---

The first commercial European district heating systems were introduced in Germany in the 1920s, initially with steam distribution. However, several German engineers disputed the choice of steam as the heat carrier and argued for the need to use water as the heat carrier to increase the efficiency of the system. These engineers became early adopters of second-generation technology when they implemented their new ideas in new district heating systems. However, rather high supply temperatures (above 100 °C) were applied, with a large temperature difference between supply and return, so that smaller diameter pipes could be used. This second-generation technology was recognised as the best technology available between 1930 and 1980. Second-generation technology was also applied in the USSR during the introduction and expansion of district heating in the 1930s and 1950s. Russian experiences and methods were later transferred and used in China when district heating was first introduced in the 1950s and 1960s.

Third-generation district heating technology (3GDH)

---

The two international oil crises of the 1970s sparked increased interest in Europe in using district heating systems as a general means of reducing dependence on fuel oil imports. This was especially the case in the three Nordic countries: Denmark, Sweden, and Finland. Engineers in these three countries advocated lower supply temperatures (below 100 °C) to improve system efficiency. At the same time, other productivity gains were achieved by using prefabricated and pre-insulated pipes together with prefabricated substations. This third-generation technology has been recognised as the best technology available since about 1980 and it is currently being used in the expansion of all European district heating systems. This technology is also used in Russia and China for expansion of existing systems.

Fourth Generation District Heating Technology (4GDH)

---

The awareness of global warming that emerged in the 1990s with the creation of the UNFCCC (United Nations Framework Convention on Climate Change) in 1992 and the Kyoto Protocol in 1997 created a renewed interest in district heating systems as a means of replacing fossil fuels using renewables and various low-temperature heat sources. Early adopters of low-temperature district heating were engineers who designed several pilot solar district heating systems in Sweden, Denmark, and Germany. These experiences flowed into the Marstal system in Denmark, where seasonal heat storage was introduced for the first time in a European district heating system. The development of the Marstal system was supported by Sunstore projects, funded by European research programs. The conditions and corresponding five expected capacities of 4GDH were defined by (Lund et al., 2014)[5]. This definition paper was written by a group of researchers affiliated with the 4GDH research center in Aalborg (Denmark), with core funding from Innovation Fund Denmark. The five skills identified are:

• the ability to provide low-temperature district heating for space heating and domestic hot water;
• the ability to distribute heat with low network losses;
• the ability to recycle heat from low temperature sources;
• the ability to integrate thermal networks into a smart energy system; and
• the ability to ensure adequate facilities for planning, cost, and motivation.

The purpose of developing 4GDH systems is to find a technology that can be harmonised for European conditions and support the expansion of district heating in European countries with low district heating penetration. It is expected that this new district heating technology will play the same role that 3GDH has played in the expansion of district heating in the Nordic countries.

Fifth Generation District Heating and Cooling Technology (5GDHC)

---

(Boesten et al., 2019) provide a definition for 5GDHC and show how this concept differs from the concept of 4GDH, since 5GDHC are decentralised, bidirectional, close to ground temperature networks that use direct exchange of warm and cold return flows and thermal storage to balance thermal demand as much as possible [3]. Also (Boesten et al., 2019) underline the novelty of 5GDHC and the different possible topology, comprising decentralised heat pumps rather than a single large energy centre, giving opportunities for sharing (prosuming) heating and cooling across a very low temperature loop [3]. The concept of 5GDHC runs alongside the increasingly popular and interesting technology of heat pumps, which can very efficiently provide heating and cooling to buildings.

References

---

[1]: S. Frederiksen and S. Werner: District heating and cooling, Studentlitteratur Lund, 2013. [Online].
[2]: S. Buffa, M. Cozzini, M. D’Antoni, M. Baratieri, and R. Fedrizzi: 5th generation district heating and cooling systems: A review of existing cases in Europe, Renew. Sustain. Energy Rev., vol. 104, pp. 504–522, Apr. 2019, doi: 10.1016/J.RSER.2018.12.059.
[3]: S. Boesten, W. Ivens, S. C. Dekker, and H. Eijdems: 5th generation district heating and cooling systems as a solution for renewable urban thermal energy supply, Adv. Geosci., vol. 49, pp. 129–136, Sep. 2019, doi: 10.5194/adgeo-49-129-2019.
[4]: P. Caputo, G. Ferla, M. Belliardi, and N. Cereghetti: District thermal systems: State of the art and promising evolutive scenarios. A focus on Italy and Switzerland, Sustain. Cities Soc., vol. 65, p. 102579, Feb. 2021, doi: 10.1016/J.SCS.2020.102579.
[5]: H. Lund et al.: 4th Generation District Heating (4GDH). Integrating smart thermal grids into future sustainable energy systems, Energy, vol. 68. pp. 1–11, 2014. doi: 10.1016/j.energy.2014.02.089.
[6]: U. Persson and S. Werner: Heat distribution and the future competitiveness of district heating, Appl. Energy, vol. 88, no. 3, pp. 568–576, Mar. 2011, doi: 10.1016/j.apenergy.2010.09.020.