This study deals with the energetic and exergetic modeling of ground source heat pump (GSHP) systems for the system analysis and performance assessment. The analysis covers two various GSHPs, namely a solar assisted vertical GSHP and horizontal GSHP. The performances of both GSHP systems are evaluated using energy and exergy analysis method based on the experimental data. Energy and exergy specifications are also presented in tables. Some thermodynamic parameters, such as fuel depletion ratio, relative irreversibility, productivity lack and exergetic, factor, are investigated for both systems. The results obtained are discussed in terms of energetic and exergetic aspects. The values for COPHP ranged from 3.12 to 3.64, while those for COPsys varied between 2.72 and 3.43. The exergy efficiency peak values for both whole systems on a product/fuel basis were in the range of 80.7% and 86.13%. It is expected that the model presented here would be beneficial to everyone dealing with the design, simulation and testing of GSHP systems. (C) 2006 Elsevier B.V. All rights reserved.