Abstract The purpose of this study is to present the numerical modeling techniques for a Ground Source Heat Pump (GSHP): The Bolu case. Numerical modeling of the GSHP system with horizontal ground heat exchangers operating in heating (1.4 kW) mode was carried out for a room, with 9.68 m2 floor area, located in Bolu, Turkey. The GSHP simulation model is studied. The codes are written in the MATLAB program for solving the equations obtained from the model developed for the city of Bolu. In this program, additionally, state equations of cooling fluids, which calculate the thermodynamic properties of these fluids, are required. In literature, there are only state equations depending on many coefficients for R12, R22, and R502. So, state equations and table values of ASHRAE of R12, R22, and R502 are used in order to obtain the properties of R134a, R404a, and R410a by using the curve fitting method. The results show that COP values for R134a refrigerant are 3.33 and 3.28 for MATLAB program and Solkane Refrigerant Software program, respectively. The difference on COP was 0.05, i.e. approximately 1.52%. The results obtained from MATLAB program indicate that there was good agreement between Solkane Refrigerant Software program and MATLAB program.