Study on a design method for hybrid ground heat exchangers of ground-coupled heat pump system

The hybrid ground heat exchangers (GHEs) of ground-coupled heat pump (GCHP) systems refer to a GCHP system using both vertical and horizontal GHEs. With the proposed optimal load ratio of horizontal to vertical GHEs, three-dimensional numerical heat transfer GHE models were established using independent heat transfer calculation method, and a design method for hybrid GHEs of GCHP system was put forward and then applied in one project. A combined heat transfer calculation method considering the mixing outlet water temperature was proposed and validated by a built experimental platform, which shows an improvement in accuracy prediction compared to the independent heat transfer calculation. It indicates the mixing outlet water temperature plays an important role in calculation accuracy and should serve as the boundary condition in modelling. The heat transfer performance of GHEs can be characterized by the independent heat transfer results in a certain range of load ratio.