An analytical approach to evaluating the effect of thermal interaction of geothermal heat exchangers on ground heat pump efficiency

• The interaction between multiple boreholes is presented as an arising issue.
• Thermal interaction among boreholes in long-term system operation is examined.
• Effect of thermal interaction on heat pump COP is examined.
• Borehole stores/removes heat in the ground under a periodic ground heat profile.
• The analytical model is validated with a numerical finite volume approach.

A semi-analytical model that couples a model outside the borehole with one inside the borehole is proposed. To examine the effect of temperature rise in the soil surrounding a vertical ground heat exchanger on the performance of an associated ground heat pump, the heat pump model should be coupled to the model inside the borehole and the conduction heat transfer model outside the borehole. The running fluid temperature, the borehole wall temperature and the heat load profile are the main coupling parameters between the three models. The results of the analytical model are compared with ones of a finite volume numerical model.