Characteristic analysis of bleeding effect on standing column well (SCW) type geothermal heat exchanger

Thermal performance is the most important factor in the development of a borehole heat exchanger utilizing geothermal energy. The thermal performance is affected by many different design parameters and different operating conditions such as bleeding. This eventually determines the operation and cost efficiency of the borehole heat exchanger system. The thermal performance of an open standing column well (SCW) type geothermal heat exchanger was assessed under the influence of bleeding. For this, a thermal response test rig was established with line-source theory. The test rig also had a bleeding function by releasing fluid while taking additional underground water through the heat exchanger. The thermal response test was performed with an additional constant input heat source. Effective thermal conductivity and thermal resistance were obtained from the measured data. From the measurement, the effective thermal conductivity is found to have 1.47 times higher value when bleeding is applied. The thermal resistance also increases by 1.58 times compared to a non-bleeding case. This trend indicates enhanced heat transfer in the SCW type heat exchanger with a bleeding function. Bleeding, therefore, could be an effective method of achieving a high heat transfer rate in the SCW type heat exchanger with sufficient underground water supply.