Definition

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A Thermal Grid, colloquially known as 'district heating' or 'district cooling', serves for the pipeline-based transmission of thermal energy via a fluid for direct or indirect use. Due to the spatial separation between the supplier and the consumer, transportation is necessary, which typically results in a loss of the transmitted thermal energy. Spatial separation occurs when the building identification (EGID) and thus, the location of the heat source/sink and at least one consumer differ.

Importance

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Space heating, domestic hot water production, process heat and cooling applications are drivers of a significant portion of the national energy demand. Altogether this accounts for 45% of Switzerland's total energy consumption and constitutes 35% of Switzerland's greenhouse gas emissions. 1450 thermal grids are employed in Switzerland in 2024 to supply various building types with thermal energy mainly for heating. Currently only few grids can also provide cooling, but those systems are expanding rapidly. In view of the goal set for 2050 of achieving net-zero emissions, thermal grids play an important role in decarbonising heating and cooling (see also history and classification of thermal grids).

Potential

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Until 2050, the use of thermal grids is foretold to increase from 5% to 40%, which, according to current calculations, should save five million tonnes of CO₂ emissions. Compared to other alternatives, thermal grids allow integration of large-scale renewable energy sources, which is key to decarbonisation. For example, the thermal energy available in Swiss lakes can easily be fed into thermal grids, which is proven by many successful systems. Additionally, the use of waste heat, e.g. from data centres, can be utilised through thermal grids. As illustrated by these examples, thermal grids can make use and reuse of a variety of energy sources. With the development of new, previously untapped thermal energy sources, thermal grids also have high economic potential. Not only do thermal grids offer new opportunities when it comes to tapping into new, previously unused energy sources, but also by utilising lower temperatures within the network, energy loss is minimised. In summary, thermal grids have the potential to even further support the decarbonisation of Swiss heating energy demands while being on track towards establishing a valuable technology for cooling energy. Thermal grids offer unique synergies allowing use of recycled thermal energy and large-scale renewable energy technologies harnessing ambient, solar and geothermal energy sources.

References

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[1]: N. Vetterli, M. Sulzer, and U. P. Menti: Energy monitoring of a low temperature heating and cooling district network, in Energy Procedia, Elsevier Ltd, 2017, pp. 62–67. doi: 10.1016/j.egypro.2017.07.289.
[2]: M. Sulzer, S. Werner, S. Mennel, and M. Wetter: Vocabulary for the fourth generation of district heating and cooling, Smart Energy, vol. 1, Feb. 2021, doi: 10.1016/j.segy.2021.100003.
[3]: T. Sommer, S. Mennel, and M. Sulzer: Lowering the pressure in district heating and cooling networks by alternating the connection of the expansion vessel, Energy, vol. 172, pp. 991–996, Apr. 2019, doi: 10.1016/j.energy.2019.02.010.
[4]: M. Sulzer, A. Sotnikov, and T. Sommer: Reservoir-Niedertemperatur Netztopologie für die Vermaschung von thermischen Netzen, in Status-Seminar, 2018. [Online]. Available: www.empa.ch
[5]: T. Sommer et al.: Hydrothermal challenges in low-temperature networks with distributed heat pumps, Energy, vol. 257, Oct. 2022, doi: 10.1016/j.energy.2022.124527.
[6]: A. Maccarini, A. Sotnikov, T. Sommer, M. Wetter, M. Sulzer, and A. Afshari: Influence of building heat distribution temperatures on the energy performance and sizing of 5th generation district heating and cooling networks, Energy, vol. 275, Jul. 2023, doi: 10.1016/j.energy.2023.127457.
[7]: A. Sotnikov, E. Sandmeier, M. Sulzer, T. Sergi, S. Mennel, and T. Sommer: Thermal stability and heat transfer in the reservoir low-temperature network, in Journal of Physics: Conference Series, 2019.
[8]: T. Sommer, A. Sotnikov, E. Sandmeier, C. Stettler, S. Mennel, and M. Sulzer: Optimization of low-temperature networks by new hydraulic concepts, in Journal of Physics: Conference Series, 2019.
[9]: T. Sommer, M. Sulzer, M. Wetter, A. Sotnikov, S. Mennel, and C. Stettler: The reservoir network: A new network topology for district heating and cooling, Energy, vol. 199, p. 117418, May 2020, doi: 10.1016/j.energy.2020.117418.
[10]: A. Sotnikov, T. Sommer, C. Stettler, and T. Schluck: Hydraulic Simulations of Low Temperature Networks, in International Sustainable Energy Conference, 2018.
[11]: C. Stettler and A. Sotnikov: Efficiency Increase in Low Temperature Networks with Decentralised Feed Pumps, in Proceedings of Building Simulation 2019: 16th Conference of IBPSA, IBPSA, Mar. 2020, pp. 1794–1801. doi: 10.26868/25222708.2019.210362.