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TY - THES AU - Düber, Stephan TI - Modelling of borehole heat exchangers and heat transfer along horizontal connection pipes PB - Rheinisch-Westfälische Technische Hochschule Aachen VL - Dissertation CY - Aachen M1 - RWTH-2024-09789 SP - 1 Online-Ressource : Illustrationen PY - 2024 N1 - Veröffentlicht auf dem Publikationsserver der RWTH Aachen University 2025 N1 - Dissertation, Rheinisch-Westfälische Technische Hochschule Aachen, 2024 AB - 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. LB - PUB:(DE-HGF)11 DO - DOI:10.18154/RWTH-2024-09789 UR - https://publications.rwth-aachen.de/record/995213 ER -