抄録
For reducing the initial cost of geothermal heat pump (GeoHP) systems, the existence of groundwater flow is considered important since the advection effect of groundwater flow can significantly enhance the heat exchange rate at ground heat exchangers (GHEs). In most of the planes of Japan, however, the advection effect cannot be utilized due to the slowness of the groundwater flow. In this study, therefore, we carried out field tests and numerical simulations to evaluate the effects of groundwater pumping, which could generate artificial groundwater flow around the GHEs and hence enhance the heat exchange rates.
In the field tests, we carried out four thermal response tests (TRTs) in two types GHEs drilled in Hirosaki City, Japan. The results of TRTs showed that the grouting with permeable materials is more preferable than the grouting with impermeable materials in terms of heat exchange rates since the use of the permeable grouting material allows a closer contact between the heat exchange pipes and the groundwater flow. The effect of groundwater pumping was not clearly observed in the TRTs due to the existence of natural groundwater flow.
In the next step, a 3D numerical simulation model was developed to simulate the heat exchange performance of the GHEs with groundwater pumping and was validated using TRT results. Sensitivity studies using the simulation model showed that groundwater pumping can remarkably enhance heat exchange rates in case groundwater flow is slow, though the effect tended to decrease as groundwater flow becomes faster. Cost calculations were also carried out on the basis on the sensitivity studies to conclude that the application groundwater pumping in GHEs could remarkably improve the feasibility of GeoHP systems.
