This article is devoted to verification of VGHEs (Vertical Ground Heat Exchangers) used as a low temperature energy source for heat pumps. The aim and objective of the study was to obtain practical knowledge of temperatures of rock mass and heat transfer fluids which affect the life cycle of the low temperature sources and the effectiveness of heat pump systems. The objective was also to gain knowledge of specific thermal energy and power extracted by these exchangers which are relevant to the evaluation of frequently used configurations of VGHEs. The results of the operational tests of two active boreholes with different arrangements, namely a single U exchanger (A), a double U exchanger (B) - and the reference (inactive) borehole (R). The tests were performed in the years 2012-2014 and involved 2 heating seasons and 2 exchanger stagnation periods. Results of the tests showed that exchanger B is more effective than exchanger A in terms of temperatures and particularly specific heat power and energies. The average specific thermal power in the heating periods were 23.11 Wm(-1) and 26.57 Wm(-1) for exchanger B and 16.88 Wm(-1) and 20.66Wm(-1)for exchanger A. Total specific energies transferred from the massif during the heating periods were higher by 6.05 kWhm(-1) and 6.94 kWhm(-1) at exchanger B than at exchanger A. (C) 2017 Elsevier B.V. All rights reserved.