Thermodynamic Performance Analysis of High Thermal Conductivity Materials in Borehole Heat Exchangers in the European Climate

While heat pumps have been acknowledged as a key enabling technology to achieve Net Zero goals, their uptake is limited by their performance and cost. In this paper, a simulation-based study is conducted to analyse the performance of ground source heat pumps (GSHPs) utilising high thermal conductivity materials for the borehole heat exchanger (BHE) pipe (1 W/mK) and grouting (3 W/mK) developed in the GEOCOND project. Exergy analysis is conducted to account for energy quantity and quality with a focus on BHE performance. An annual hourly simulation was performed using DesignBuilder V5.4 and Earth Energy Designer (EED4) for representative cool and hot locations in Europe—Stockholm and Valencia, respectively. For a constant BHE length, the results for Stockholm show that the high conductivity materials result in an increase of about 13% BHE exergy extraction compared to the standard grout and pipe, but no such improvement was observed for Valencia. The difference between outdoor temperature and its dynamic variation from the indoor setpoint is identified as a key factor in the overall GSHP exergetic performance. In future research, we propose a thorough life cycle analysis across diverse locations and varying indoor comfort criteria to pinpoint areas where the high thermal conductivity material can enable cost-effective, sustainable heating and cooling.

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