Numerical Evaluation of the Long-Term Performance of KIGAM Geothermal Heat Pump System

Temperature change of the ground in the vicinity of borehole heat exchangers (BHEs) is important for the longterm operation of geothermal heat pump (GHP) systems. If there are differences between injected energy from heat pumps to BHEs in cooling season and rejected energy from heat pumps to BHEs in heating season and heat transfer is not sufficiently fast in the ground, temperature change of the ground affects on the performance of the GHP system. Vertical closed-loop GHP systems and monitoring systems were installed at the building of the Earthquake Research Center in Korea Institute of Geoscience and Mineral (KIGAM) in Daejeon, Korea. To evaluate the long-term performance of KIGAM GHP system where there are differences between injected energy from heat pumps to BHEs in cooling season and rejected energy from heat pumps to BHEs in heating season, numerical simulations are performed by using three-dimensional numerical model that can simulate temperature changes in the BHE with circulating fluid through the U-tubes as well as it computes groundwater flow and aquifer temperature changes. Temperature of the ground in the vicinity of BHEs is gradually increased during 25 years operation. The efficiency of the GHP system is decreased in the cooling season and increased in the heating season.