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Numeric study of geothermal borehole heat exchanger enhancement via phase change material macro encapsulation
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Advisor(s)
Abstract(s)
his article addresses the theoretical effect of using geothermal boreholes enhanced with macro-encapsulated
phase change materials (PCM) employed with a ground sourced heat pump (GSHP). The aim being the
improvement of the heat pump performance through soil temperature stabilisation, taking advantage from the
PCM inherent property of changing phase at a constant temperature, that can be matched with the temperature
of the surrounding soil, contributing as well to increase the energy storage capacity underground. The numeric
work studied different PCM thermal parameters with regards to their influence on the overall behaviour
of the heat pump, with different operation modes (On/Off and Inverter) changing the solidus and liquidus
temperatures and phase change enthalpy values. The CFD results showed that, while it underperformed having
0.15% difference in the best of cases (specifically the On/Off mode), it used in the best case scenario only 30%
of the stored energy in the PCM. The application of macro-encapsulation did provide a stabilising effect to the
soil and heap pump operation as it was originally intended to do, helping reduce energy expenditure by the
system. Significant modifications are needed in order to improve, both concerning geometry and encapsulation
techniques to overcome the PCM and other materials thermal limitations.
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Citation
Pássaro, J. Rebola, A. Coelho, L., & Conde, J. (2022). Numeric study of geothermal borehole heat exchanger enhancement via phase change material macro encapsulation. International Journal of Thermofluids, 16,100245