Ice-Grid - Implementation of ice storage tanks into 5GDHC networks as seasonal storage or load shifting element

According to the Energy Strategy 2050+, the share of district heating (DH) in Switzerland’s heat supply
is set to rise sharply to around 30 %. An increasingly popular type of district heating (DH) network is
the anergy network, which distributes energy from a low-temperature source to decentralized heat pumps
installed in buildings. Many low-temperature energy sources available in Switzerland have limitations, either
in their power output (e.g., waste heat from sewage treatment plants) or in their availability during cold
winter days, if at all (e.g., solar thermal energy). Due to the high amount of energy released (or absorbed)
during the liquid/solid phase transition of water, ice storage are suitable for storing large amounts of energy at
temperatures near 0 °C. For this reason, ice storages are being used in buildings as an energy source for heat
pumps in Switzerland, in so-called solar-ice systems. However, until now, there has been a lack of analysis
on integrating large-scale ice storage into district heating networks. In IceGrids, we explored the energetic
feasibility and economic viability of integrating ice storages into low-temperature district heating networks,
also known as 5th generation district heating and cooling (5GDHC). As a case study, our investigation focused
on the Jona energy network, which utilizes waste heat from a waste water treatment plant (WWTP) to supply
decentralized heat pumps, making the heat usable. Ice storage tanks can be easily integrated into 5GDHC
networks that employ an antifreeze heat transfer fluid, as the Jona network. However, freezing of the heat
exchanger on the sewage treatment plant side must be prevented by a partial re-circulation from the flow pipe.
Based on the results in this study, the following findings emmerge: In combination with power limited waste
heat sources, even small ice storage volumes are sufficient to bridge power peaks in winter. As a lot of surplus
waste heat is readily available for regenerating ice storage systems during the transition period, ice storage
systems can more than double the capacity of such sources. When combining ice storage tanks with scalable
seasonal heat sources (e.g.outdoor air or solarthermal energy), ice storage sizes of approx. 0.6m3/MWh are
required to enable year-round operation of the network at 0 °C.