Determining thermal conductivity of ground plays an important role in designing procedure of ground source heat pump (GSHP) systems. In this paper new modified 2D analytical models which are depending on thermal conductivity of ground are derived and results are compared with experimental ones. In an experimental study, a single borehole ground heat exchanger (GHE) with polyethylene U-tube pipe is considered for two different regions. Fluid is pumped into the pipes in a specific temperature and inlet and outlet temperatures are measured as well as volumetric flow rate. Analytical results curves are fitted to experimental one and thermal conductivities of ground are calculated for each region. Based on validated analytical models, long term performance of a single borehole GHE is determined. Additionally, temperature distributions around borehole GHE are investigated analytically in region 1 (N.D.B. residence region). Analytical models given in this study can easily help designers to evaluate thermal conductivity of ground and thermal performance of the borehole GHEs.