Numerical Study of Soil Saturation Effects on the Thermal Performance of a Horizontal Geothermal Heat Exchanger

The efficiency of horizontal ground heat exchangers (GHEs) is strongly influenced by soil saturation, which directly affects heat transfer rates and system stability. This study presents a numerical analysis of how soil moisture content impacts the thermal response of a horizontal GHE operating in heating mode over a one-month period. A finite element-based transient heat transfer model was developed to simulate dynamic interactions between the heat exchanger and surrounding soil, incorporating saturation-dependent soil properties and variable thermal conductivity to replicate realistic field conditions.

The results show that higher soil saturation enhances heat exchange efficiency by increasing effective thermal conductivity, reducing thermal resistance, and stabilizing temperature distribution around the pipes. Conversely, low saturation levels lead to greater temperature fluctuations and reduced heat transfer rates, negatively impacting system performance over time. The study further highlights the cyclic thermal behaviour of the heat exchanger, demonstrating how soil moisture content influences both daily and long-term thermal variations. These findings emphasize the critical role of soil moisture in optimizing geothermal heat exchanger design and operation.