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ABSTRACT

A detailed borehole heat exchanger model is presented, cast as a TRNSYS component model, for use in ground source heat pump system simulations with optimization of system subcomponents. The proposed borehole heat exchanger model is based on non-dimensionalized short time step response factors, and includes a time-dependent borehole thermal resistance that is due to transient responses from the surrounding ground and short time-step thermal storage effects of the borehole grout and heat carrier fluid. These effects have been accounted for by developing a finite element model of a borehole heat exchanger where the fully transient borehole thermal response is modeled and coupled to a short time step ground response factor model. Furthermore, each response factor function (g-function), describing the thermal response of a particular borehole field to a unit heat pulse is developed to allow for varying borehole spacing-to-depth ratios so that borehole spacing is independent of the borehole depth. The model is developed with the specific objective use in optimization problems for hybrid ground source heat pumps systems. A detailed model validation and sensitivity analyses are presented and discussed.