Simulation of borehole thermal energy storage (BTES) systems using simplified methods

Abstract

This paper presents two complementary approaches for simulating the thermal performance of borehole thermal energy storage (BTES) systems. The first approach uses the concepts of heat exchange and storage efficiencies as a function of the state-of-charge of the BTES. The second method employs a technique similar to thermal response factors used to model bore fields in ground-source heat pump systems. It utilizes non-dimensional average storage temperatures and bore field thermal resistances of the BTES over time. The two methods rely on numerical experiments to obtain the required performance curves. As shown through examples, the two approaches are relatively simple to use, and it is shown that they are in good agreement with the well-known duct ground storage model. In one of the examples, it is suggested that the design of a BTES could be performed using three successive thermal pulses, similar to the approach used to determine the length of vertical ground heat exchangers in a ground-source heat pump systems.