Comparative study on thermal and economic performance of ground source heat pump systems utilizing vertical versus horizontal ground heat exchangers for building heating and cooling

This study presents a comparative evaluation of the thermal and economic performance of two ground source heat pump (GSHP) systems utilizing vertical U-tube and horizontal linear-type ground heat exchangers (GHEs). A high-resolution numerical model was developed to simulate system behavior under realistic operating conditions, incorporating annual hourly building load profiles, environmental fluctuations, and unsaturated soil characteristics. The lengths of both GHE configurations were determined using validated design equations and analytical methods, ensuring a technically sound and non-arbitrary comparison. Subsequently, a comprehensive techno-economic assessment framework was established, integrating initial capital, operational, and maintenance costs, along with key techno-economic indicators—levelized cost of energy (LCoE), net present value (NPV), and payback period (PP)—to rigorously evaluate economic efficiency. Sensitivity analyses were further conducted to examine the influence of input parameters on the relative performance gap between the two systems. Results demonstrate that the vertical GSHP system outperforms the horizontal counterpart in both thermal and economic terms, exhibiting smaller annual variations and higher average values in fluid outlet temperature, T f,o , heat pump coefficient of performance, COP hp , and system COP, COP sys , as well as lower initial and operational expenditures and favorable techno-economic indicators. Transitioning from horizontal to vertical GSHP system results in reductions of 61.96%, 46.94%, and 9.46% in the fluctuation ranges of T f,o , COP hp , and COP sys , increases of 1.48 °C, 0.26, and 0.24 in the annual average T f,o , COP hp , and COP sys , a reduction of 769.31 Chinese Yuan reduction in initial costs, a decrease of 0.02 CNY·kWh −1 in LCoE, an increase of 4428.05 CNY in NPV, and a reduction of 0.24 year in PP. The thermal-economic advantage of the vertical system is inversely related to unit drilling cost and horizontal GHE burial depth, while positively correlated with interest rate and the unit costs of excavation and pipe. Even at a burial depth of 3.00 m, the horizontal system remains inferior to the vertical system in both thermal efficiency and economic viability.