Analysis of shallow subsurface geological structures and ground effective thermal conductivity for the evaluation of ground-source heat pump system installation in the Aizu Basin, Northeast Japan

Abstract

Shallow subsurface geological structure mapping combined with ground effective thermal conductivity values at the basin scale provide an appropriate method to evaluate the installation potential of ground-source heat pump systems. This study analyzed the geological structure of the Aizu Basin (Northeast Japan) using sedimentary cores and boring log and mapped the distribution of average ground effective thermal conductivity in the range from -10 m to -100 m depth calculated from cores and logs. Gravel layers dominate in alluvial fans of the northern and southern basin areas, which are found to be associated with higher average ground effective thermal conductivity values, 1.3-1.4 W/m/K, while central and western floodplain areas show lower values of 1.0-1.3 W/m/K due to the existence of thick mud layers in the shallow subsurface. The results indicate that the conventional closed-loop systems are more feasible in northern and southern basin areas than in the central and western areas. Evaluation for the installation potential of the ground-source heat pump systems using depth-based distribution maps of average ground effective thermal conductivity is the originality of this study. This approach is valuable and proper for the simple assessment of the system installation in different sedimentary plains and basins in Japan and other countries.