A hybrid ground source heat pump (HGSHP) system utilizes less-expensive heat sink (e.g., a dry cooler) or heat source (e.g., a solar thermal collector) to reduce the size of the more expensive GHEs. It thus has the potential to be more cost competitive than a conventional ground source heat pump system. Integrated with a thermal energy storage (TES) system, a HGSHP system could make full use of the available heating and cooling output from the less- expensive heat sink or heat source even when the GSHP is not running. The combination of HGSHP with a seasonal TES is also an effective solution to overcome the imbalance between the annual cooling and heating loads of a building. This paper presents a model of the integrated HGSHP and TES system, which is developed with the Modelica program. A preliminary simulation-based study was performed using the model to investigate on the effectiveness of the integrated HGSHP and TES system for a heating dominant residential building in Chicago, IL. Simulation results indicate that the integrated HGSHP and TES can significantly increase the entering water temperature of the ground source heat pump during heating operation and thus improve it operating efficiency, or it can reduce the size of the GHE for achieving the same energy efficiency as the conventional ground source heat pump system.