Semi-Analytical Method for g-Function Calculation of bore fields with series- and parallel-connected boreholes

A semi-analytical method for the calculation of g-functions of bore fields with mixed arrangements of series- and parallel-connected boreholes is presented. Borehole wall temperature variations are obtained from the temporal and spatial superposition of the finite line source (FLS) solution. The FLS solution is coupled to a quasi-steady-state solution of the fluid temperature profiles in the boreholes, considering the piping connections between the boreholes. The dimensionless borehole wall temperatures in the bore field and the inlet fluid temperature are obtained from the simultaneous solution of the heat transfer inside and outside the boreholes. The effective borehole wall temperature (i.e., the g-function) is defined based on the dimensionless inlet fluid temperature and a newly introduced effective bore field thermal resistance. The g-function evaluation method is validated against the DST model and its use is demonstrated in a sample simulation of a seasonal thermal energy storage system.