A fast method for evaluating the performance of complex arrangements of borehole heat exchangers

Abstract

Ground coupled heat pumps are systems combining a heat pump with a ground heat exchanger for building heating and cooling purposes. Borehole heat exchangers (BHE) are the most frequently adopted solution for ground-assisted heat pump applications, and in most installations, they represent the most important cost item. For this reasons, a careful design analysis is needed to either assure long-time performance or reduce the payback period, both parameters related to overall BHE length. The required approach for such a problem is a transient analysis of ground response to different heat loads at different time scales. A computationally efficient way to tackle the problem is the recursive calculation of a basic thermal response factor for given different heat pulses representing the building energy demand. In this article, a review of the existing response factor models for BHE analysis is performed, and the finite line source model is employed to develop and test new simplified solutions suitable for fast spatial and temporal superposition and for generating thermal response factors for arbitrary BHE arrangements.

Acknowledgments

Marco Fossa, PhD, is Associate Professor.