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.
Highlights
Ground-source heat pump (GSHP) systems have attracted international attention as one of the most energy-efficient systems for providing space-heating/cooling, snow-melting, hot water supply, and more [1,2]
These columns illustrate that the shallow subsurface stratigraphy of the Aizu Basin is composed of gravel, sand, and mud strata
The northern and southern basin areas correspond to an alluvial fan region with steeper surface gradients, which indicated the existence of preferable aquifers with higher groundwater flow velocities
Summary
Ground-source heat pump (GSHP) systems have attracted international attention as one of the most energy-efficient systems for providing space-heating/cooling, snow-melting, hot water supply, and more [1,2]. The installation of GSHP systems has increased worldwide especially in the United. In Japan, GSHP systems have installed increasingly since the year around 2000. The most popular GSHP system in Japan (87%) is the closed-loop system using ground heat exchangers (GHEs) while open-loop and a combination of both systems constitute 12% and 1%, respectively [4]. The number of installations in Japan remains limited when compared with the other named countries due largely to uncertainties regarding subsurface information (e.g., geology, groundwater flow, and thermal temperatures) that is required to plan optimal GSHP systems as well as the higher drilling costs associated with GHEs. The heat exchange rates of GHEs are strongly influenced by the ground effective thermal conductivity (i.e., geological structure) and heat advection
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