2017 Volume 39 Issue 2 Pages 81-92
Ground Source Heat Pump (GSHP) systems directly exploit geothermal energy to meet the heating and cooling demands of buildings. However, despite being one of the commonest applications of geothermal energy, this technology is rarely used in Japan due to the high drilling costs. This paper introduces a new semi-open loop GSHP system that increases the heat transfer rate of Ground Heat Exchangers (GHEs) by water-pumping and injection inside the GHE wells. The effect of water-pumping and injection on the system performance was evaluated in four field tests on a GSHP system constructed at Akita University Campus, Japan. Based on geological data at the system location, a numerical model was constructed and validated by comparisons with experimental data. The system performance under different groundwater velocities and operating conditions was then evaluated in sensitivity analyses. The semi-open loop system improved the coefficient of performance (COP) by only 5%, relative to base case. The sensitivity studies showed that in formations with fast groundwater flow, the maximum enhancements of the COP and system coefficient of performance (SCOP) are 12% and 9%, respectively. In the absence of groundwater flow, the COP and SCOP improved by 40% and 20%, respectively, with significantly increased system capacity. Therefore, the performance improvement was limited by the groundwater flow.
