In-situ response test of various borehole depths and heat injection rates at standing column well geothermal heat exchanger systems

Comparative Analysis of Geothermal Energy in Korea Based on Closed Borehole and Single- and Two-Well Standing Column Well Geothermal Heat Exchange Systems

“…Using the highest error for the flowmeter taken from Table 4 of ±2.03%, the total uncertainty in the heat balance equation was computed as Total Error = (±0.0165) 2 + (±0.0203)ˆ2 ≈ 2.62%. Figure 6 shows the average temperature and the difference of inlet/outlet temperatures over time for alluvial deposit, gneiss, and granite rocks using a ground heat exchanger system with a borehole depth of 200 m using a closed loop borehole heat exchanger system [3,6,13,41,49,53]. The initial groundwater temperature from the three types of rock was approximately 15-16 • C, with an average temperature distribution of approximately 28-35 • C during the test period.…”

“…In the future, the effect of groundwater flow on the effective thermal conductivity of underground heat exchangers will be studied. Figures 8 and 9 show the evaluation results of thermal performance by temperature for a ground heat exchanger with the return pipe positioned as shown in Figure 5b, using an SCW underground heat exchanger with a borehole depth of 400 m, as shown in References [31][32][33][34][35][36][37][38][39][40][41]. This study analyzed the characteristics of this in accordance with the effective thermal conductivity and thermal resistance as a study on the heat transfer characteristics according to a position above the submerged pump [52,56,57,60].…”

“…In this study, the characteristics of single-well and two-well underground heat exchangers were compared. We also evaluate the thermal performance of a two-well system and a single-well system underground heat exchanger when there is no discharge rate and when returning from the inlet and re-injecting the discharge into the wells [40][41][42]. Figure 3 consists of the trailer-type transport system used in this study [52][53][54][55][56].…”

“…The groundwater heat pump system using groundwater extracted from the same well hole and being recovered into the same well hole in a semi-open loop arrangement was widely known as the SCW (standing column well) system. The ground heat exchangers in these systems consist of vertical boreholes filled with groundwater up to the groundwater level [40,41]. In an open-loop pipe circuit, water is circulated from the well through a heat pump to return to the same well, and, for most of the year, the system works by recirculating water between the well and the heat pump.…”

“…In an open-loop pipe circuit, water is circulated from the well through a heat pump to return to the same well, and, for most of the year, the system works by recirculating water between the well and the heat pump. However, during the peak temperature period, only a portion of the flow can be returned to the well, and the rest can be drained to "bleed" some water from the system [41]. This leads to groundwater flow from the surrounding formation to the well.…”