A geospatial assessment of the installation potential of shallow geothermal systems in a graben basin

Abstract

The installation potential of a ground source heat pump (GSHP) system was highly affected by site geological conditions. A certain type of geological unit maintains similar geological settings geospatially. It is of importance to demonstrate a case to characterize the geological background and the associated geothermal potential to properly plan and sustainable development of geothermal resources. In this paper, the installation of GSHP system in a graben basin was assessed by considering the geospatial variation in the soil types. The results show that the graben basin was composed of an alluvial area and a piedmont area in which the alluvial area expresses a higher potential for a GWHP system than the piedmont area. Within the alluvial area, the upper alluvial reaches attain the highest heat extraction rate of 5.26 kW/m, followed by the middle reaches at 3.16 kW/m and the lower reaches at 1.58 kW/m. More specially, the ground-coupled heat pump (GCHP) system realizes a higher exploitable energy density than the GWHP system in all areas due to the dense layout of borehole heat exchangers (BHEs). By further considering the savings-to-investment (STI) ratio and environmental impacts, the GWHP system was considered the first priority in alluvial areas II-a and II-b. Installation of the GCHP system was recommended in alluvial area II-c and the piedmont area.