An energetic and exergetic modeling of a solar-assisted vertical ground-source heat pump (GSHP) greenhouse heating system (SAGSHPGHS) for system analysis and performance assessment is presented in this study. Energy (heating coefficient of performance 'COP') and exergy efficiencies at various reference and entering water temperatures are also determined. The actual thermal data collected are utilized for the model calculations at different reference temperature values in the range of -0.69 to 25 degrees C. Furthermore, the performance of a SAGSHPGHS, installed in Solar Energy Institute of Ege University, Izmir, Turkey, is evaluated to show, how energy and exergy efficiencies values change with system. The exergy destructions in the overall SAGSHPGHS are quantified, particularly for a reference temperature of -0.69 degrees C on 7 January 2004 for comparison purposes. Based upon the measurements made in the heating mode from the 16th of December 2003 till 31st of March 2004, average heating CON of the GSHP unit and the overall system are obtained to be 2.84 and 2.27, respectively. The best (peak) COP of the GSHP and system were found to be 3.14 and 2.79 on 7 January 2004, respectively. Average exergy efficiency of the system is determined to be 68.11%, while the best exergy efficiency peak values for the GSHP unit and the whole system on a product/fuel basis are obtained to be 76.2% and 75.6%, respectively. (c) 2005 Elsevier Ltd. All rights reserved.