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@PHDTHESIS{Dber:995213,
      author       = {Düber, Stephan},
      othercontributors = {Fuentes Gutierrez, Raul and Vardon, Phil},
      title        = {{M}odelling of borehole heat exchangers and heat transfer
                      along horizontal connection pipes},
      school       = {Rheinisch-Westfälische Technische Hochschule Aachen},
      type         = {Dissertation},
      address      = {Aachen},
      publisher    = {RWTH Aachen University},
      reportid     = {RWTH-2024-09789},
      pages        = {1 Online-Ressource : Illustrationen},
      year         = {2024},
      note         = {Veröffentlicht auf dem Publikationsserver der RWTH Aachen
                      University 2025; Dissertation, Rheinisch-Westfälische
                      Technische Hochschule Aachen, 2024},
      abstract     = {The use of geothermal energy with shallow borehole heat
                      exchangers (BHEs) is growing steadily. BHEs are the
                      underground components of heat pump systems that uses the
                      ground as source or sink of thermal energy for conditioning
                      of buildings. Larger systems with tens to hundreds of
                      boreholes are being built. Analytical calculation approaches
                      are successfully used for the design of such systems and
                      mechanical plants. To simulate and optimise the actual
                      operating conditions, more complex models that take into
                      account transient conditions may be required. In addition,
                      large BHE fields often require hundreds of meters of
                      horizontal connection pipes to connect the BHE to the
                      manifolds and the building. Heat transfer along these pipes
                      is often neglected. This thesis presents a hybrid simulation
                      approach for BHEs based on a novel combination of existing
                      solutions for the simulation of heat transfer processes
                      within the borehole and the surrounding ground. Heat
                      transfer is modelled using a combination of analytically
                      determinedg-functions and a borehole thermal resistance
                      capacity model. The computational efficiency of long-term
                      simulations is drastically increased by dividing the
                      simulation time into multiple periods, where the influence
                      of past periods on future periods is calculated using the
                      FastFourier Transform. Based on monitoring data from a BHE
                      field with 40 BHEs and a combined connection pipe length of
                      900 m, heat transfer along connection pipes is investigated.
                      The heat transfer alongthe connection pipes is correlated
                      with parameters such as surface types or solar radiation
                      above the pipes using multiple linear regression analysis,
                      showing that solar radiation above the pipes has the
                      greatest effect. A comparison of three soil and three pipe
                      models of varying complexity is carried out to investigate
                      their suitability in the context of connection pipes and BHE
                      simulation. Basedon the results, a computationally efficient
                      approach is proposed using a novel combination of
                      established steady-state models for the BHE and the
                      connection pipes. The model isused to investigate the effect
                      of horizontal connection pipes attached to a BHE for the
                      25most representative climate zones. The consideration of
                      the connection pipes leads to thebiggest BHE load reduction
                      in tropical climates, followed by temperate, arid and
                      continentalclimates. In the case of existing BHE fields
                      where the connection pipes have not been considered in the
                      design, various options for the subsequent use of heat gains
                      along the pipes are investigated. The study explores the
                      potential of extended operation, increased loads and an
                      optimised operating strategy to exploit the idle capacity
                      gain from the horizontal connection pipes. Finally, a simple
                      and fast methodology to account for changing thermal
                      properties by using the g-function method is presented. The
                      simulation time is divided into periods according to the
                      changes in thermal properties. By transforming the
                      temperature response from one period to the next and
                      subsequent superposition, any changes in the thermal
                      conductivity properties can be taken into account. The
                      computational time is significantly shorter than comparable
                      numerical simulations.},
      cin          = {314310},
      ddc          = {624},
      cid          = {$I:(DE-82)314310_20140620$},
      typ          = {PUB:(DE-HGF)11},
      doi          = {10.18154/RWTH-2024-09789},
      url          = {https://publications.rwth-aachen.de/record/995213},
}