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Design optimization of a district heating and cooling system with a borehole seasonal thermal energy storage

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  • Massimo Fiorentini
  • Philipp Heer, Swiss Federal Laboratories for Materials Science and Technology (Empa)
  • ,
  • Luca Baldini, Zurich University of Applied Sciences

The optimal design of borehole thermal energy storage systems can ensure their techno-economical goals are met. Current design optimization methods either employ detailed modelling unsuitable for numerical optimization or use simplified models that do not consider operational conditions. This paper proposes an optimization-oriented model and a non-convex optimization formulation that, differently from other studies in the literature, can consider the influence of the seasonal storage size and temperature on its capacity, losses, heat transfer rate, and efficiency of connected heat pumps or chillers. This methodology was applied to a case study, considering two scenarios: storing only the rejected heat from cooling and integrating solar thermal generation. Results show that, with varying boundary conditions such as the electricity CO2 intensity profile, cooling demand, and price of carbon emissions, not only the optimal seasonal storage size changes but also its optimal operating conditions. The potential reduction of CO2 emissions was found, under standard boundary conditions, to be limited (up to 6.7%), but an increase in cooling demand and an enhancement of the CO2 intensity seasonal variation led to a reduction of 27.1%. Integration of solar generation further improved it to 43.7%, with a comparably small increase in annual cost, up to 6.1%.

Original languageEnglish
Article number125464
Publication statusPublished - Jan 2023
Externally publishedYes

Bibliographical note

Funding Information:
The authors thank K. Orehounig for her insights on the energy hub approach and relevant applications to seasonal thermal energy storage, and acknowledge the financial support of the Swiss Federal Office of Energy SFOE grant No. SI/501938 .

Publisher Copyright:
© 2022 The Author(s)

    Research areas

  • CO emissions reduction, Energy optimization, Multi-energy systems, Renewable energy, Seasonal thermal energy storage

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