Effect of soil type and moisture content on ground heat pump performance

Abstract Three different soils (sand, silty loam and silty clay) with five different degrees of saturation (0, 12.5, 25, 50 and 100%) were used in computer simulations. The performance of a ground heat pump system was found to depend strongly on the moisture content and the soil type (mineralogical composition). Alteration of soil moisture content from complete dryness to 12.5% of saturation strongly influences the ground heat pump performance, and any decrease of soil moisture in this range has a devastating effect on the coefficient of performance (COP). Therefore, it is beneficial to keep the soil moisture value as high as possible above dry soil conditions. Soil moisture content above the quarter saturation state leads to a much better heat pump performance. It was found, however, that the effect of moisture content variation above 50% of saturation on ground heat pump performance is relatively insignificant.