Thermal Impact by Open-Loop Geothermal Heat Pump Systems in Two Different Local Underground Conditions on the Alluvial Fan of the Nagara River, Gifu City, Central Japan

An alluvial fan is a good area to install open-loop geothermal heat pump (GHP) systems due to shallower aquifers, faster groundwater flow, and fewer land subsidence risks. The natural temperature change in groundwater occurs in alluvial fans due to the recharge of river water and faster groundwater flow, and the thermal impact of the open-loop system has not been studied well in such areas. The purpose of this research is to understand the thermal impact of open-loop GHP systems on an alluvial fan. A regional 3D model of groundwater flow with heat transport was created to determine the distribution of flow velocity and temperature of groundwater. After that, two local models with different groundwater velocities were constructed to demonstrate the thermal impact of an open-loop GHP system using one extraction and one injection well. The results indicated that the local model with faster groundwater flow had a smaller thermal impact. The natural temperature change in groundwater causes groundwater temperature to be lower in the summer and higher in winter during the operation in the local model, with faster groundwater flow.

Automated summary

Alluvial fans are suitable areas for installing open-loop geothermal heat pump systems due to their shallower aquifers and faster groundwater flow. This research aims to understand the thermal impact of open-loop GHP systems on alluvial fans. The results from the models show that areas with faster groundwater flow have smaller thermal impacts.