Ground heat exchangers are key component of ground-coupled heat pump systems, and their thermal response is therefore very important for ground-coupled heat pump system design and operation. This paper proposes a new hourly simulation method, and uses it to study the performance improvement potential for the ground-coupled heat pump system. First, with an effective U-pipe shank spacing determined by the calculated and measured borehole thermal resistance, a reasonable and accurate fluid temperature prediction method is developed, and the hourly energy performance simulation method is also proposed accordingly with the Fast Fourier Transform superposition algorithm. This hourly simulation method is validated using experimental data collected from a well-designed ground-coupled heat pump experiment platform, which shows that the maximum absolute error for the predicted fluid temperature is smaller than 1.04 degrees C. Second, using the proposed hourly simulation method, a framework for the energy performance simulation of an office building served by the ground-coupled heat pump system is developed. Impact factors on ground-coupled heat pump system performance are systematically analyzed using this simulation method, and the results show that performance can be improved with shorter operation schedules and lower heat fluxes. (C) 2018 Elsevier Ltd. All rights reserved.