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Open AccessArticle

In Situ Experiment and Numerical Model Validation of a Borehole Heat Exchanger in Shallow Hard Crystalline Rock

1
Department of Civil Engineering, School of Engineering, Aalto University, P.O. Box 12100, FI-00076 AALTO, Espoo, Finland
2
Department of Physics, Helsinki University, P.O. Box 68, FI-00014 Helsingin Yliopisto, Helsinki, Finland
*
Author to whom correspondence should be addressed.
Energies 2018, 11(4), 963; https://doi.org/10.3390/en11040963
Received: 16 March 2018 / Revised: 13 April 2018 / Accepted: 15 April 2018 / Published: 17 April 2018
(This article belongs to the Special Issue Building renewable energy and thermal energy storage system 2018)
Accurate and fast numerical modelling of the borehole heat exchanger (BHE) is required for simulation of long-term thermal energy storage in rocks using boreholes. The goal of this study was to conduct an in situ experiment to validate the proposed numerical modelling approach. In the experiment, hot water was circulated for 21 days through a single U-tube BHE installed in an underground research tunnel located at a shallow depth in crystalline rock. The results of the simulations using the proposed model were validated against the measurements. The numerical model simulated the BHE’s behaviour accurately and compared well with two other modelling approaches from the literature. The model is capable of replicating the complex geometrical arrangement of the BHE and is considered to be more appropriate for simulations of BHE systems with complex geometries. The results of the sensitivity analysis of the proposed model have shown that low thermal conductivity, high density, and high heat capacity of rock are essential for maximising the storage efficiency of a borehole thermal energy storage system. Other characteristics of BHEs, such as a high thermal conductivity of the grout, a large radius of the pipe, and a large distance between the pipes, are also preferred for maximising efficiency. View Full-Text
Keywords: underground thermal energy storage; borehole heat exchanger; in situ experiment; numerical modelling; model validation; finite element method; COMSOL Multiphysics; crystalline rock underground thermal energy storage; borehole heat exchanger; in situ experiment; numerical modelling; model validation; finite element method; COMSOL Multiphysics; crystalline rock
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Janiszewski, M.; Caballero Hernández, E.; Siren, T.; Uotinen, L.; Kukkonen, I.; Rinne, M. In Situ Experiment and Numerical Model Validation of a Borehole Heat Exchanger in Shallow Hard Crystalline Rock. Energies 2018, 11, 963.

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