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Massimo Fiorentini

Control-oriented modelling and operational optimization of a borehole thermal energy storage

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Seasonal thermal energy storage is an effective measure to enable a low carbon future through the integration of renewables into the energy system. Borehole thermal energy storage (BTES) provides a solution for long-term thermal energy storage and its operational optimization is crucial for fully exploiting its potential. This paper presents a novel linearized control-oriented model of a BTES, describing the storage temperature dynamics under varying operating conditions, such as inlet temperature, mass-flow rate and borehole connection layouts (e.g. in-series, in-parallel or mixed). It supports an optimization framework, which was employed to determine the best operating conditions for a heat pump-driven BTES, subject to different CO2 intensity profiles of the electricity. It was demonstrated that this boundary condition, due to its seasonal variation, is critical for the optimal operation of the system, as increasing heat pump efficiency in winter while accepting a lower one in summer can be beneficial. Results for an exemplary district case, subject to two different CO2 intensity profiles, show that a lower relative intensity in summer compared to the one in winter leads to a higher optimal operating temperature of the storage. The district system studied is heating-dominated, effectively enabling the BTES to cover only 20% of the total heat demand, leading to limited total yearly CO2 emissions savings of 2.2% to 4.3%. When calculating the benefits associated with the heating and cooling demand handled by the BTES, a higher CO2 emission reduction in the range of 12.8%–19.9% was found. This highlights the BTES potential when subject to more balanced loads.

Original languageEnglish
Article number117518
JournalApplied Thermal Engineering
Publication statusPublished - 25 Nov 2021
Externally publishedYes

Bibliographical note

Funding Information:
We acknowledge the assistance with the TRNSYS simulations as well as valuable insights and guidance of our colleague R. Weber. This research work was financially supported by the Swiss Federal Office of Energy SFOE, Switzerland grant Nr. SI/501938-01 .

Publisher Copyright:
© 2021 The Authors

    Research areas

  • Borehole thermal energy storage, CO2 emissions reduction, Energy flexibility, Operational optimization, Seasonal load shift, Seasonal thermal energy storage

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