Among many new and renewable energy technologies, a ground source heat pump system has been declared as an energy efficient and an environmentally friendly system in meeting the thermal energy demands for residential and commercial applications. One major drawback for ground source heat pump system is the high initial cost and a relatively longer payback period of the system. In this study, a numerical analysis and an experimental investigation were carried out on the effects of the heat pump performance and the building load for a ground loop heat exchanger design. A decrease of heat pump unit fluid flow rate and an increment of COP for the heat pump unit resulted in the reduction of the ground loop heat exchanger size in the cooling mode. It was observed that reducing the peak load of building has the potential for reduction in the ground loop heat exchanger length. Matching the heat pump capacity with the building peak load variation, a decrease of 40% in the cooling and heating peak load resulted in a decrease of 44.5% and 69.2% in the total ground loop heat exchangers required in the cooling and heating mode, respectively. (C) 2016 Elsevier B.V. All rights reserved.