Perfomance of a borehole heat exchanger: The influence of thermal properties estimation under tidal fluctuation

• Published in: Engineering science and technology, an international journal Vol. 30; p. 101057
• Main Authors: Moreira, Daniel, Macias, Jose, Hidalgo-Leon, Ruben, Jervis, Freddy X., Soriano, Guillermo
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 01.06.2022; Elsevier
• Subjects: Borehole heat exchanger; Phreatic level; Thermal properties of saturated soil; Thermal response test; Tidal effect; Phreatic level; Thermal response test; Borehole heat exchanger; Tidal effect; Thermal properties of saturated soil
• ISSN: 2215-0986; 2215-0986
• DOI: 10.1016/j.jestch.2021.09.003

This research assesses how groundwater flow induced by tide influences the performance of a borehole heat exchanger (BHE) using a case study in Guayaquil, Ecuador. The Thermal Response Test (TRT) was applied to determine the thermal properties of the ground. The experimental results of TRT showed periodic fluctuations in the response, presumably induced by the tide. An explanation of the effects of the tide on thermal performance was carried out systematically. Later, an analytical solution was proposed to estimate the phreatic level near the shore. A geometric mean model then predicted the thermal properties of the ground, given the groundwater level fluctuations. Consequently, a relationship between the effective thermal capacity of the soil and the phreatic level was found. Results show that thermal diffusivity is overpredicted by 50% and thermal conductivity by 8.8%. Finally, we evaluated the heat dissipation of a borehole heat exchanger using a TRNSYS simulation, revealing an overestimation of 12% in the heat rate capacity of the BHE when ignoring tidal effects. This overestimation shows how using standard thermal properties measurement methodologies may affect the design process resulting in substantial inaccuracies in performance and implementation costs.