Development, Verification, and Design Analysis of the Borehole Fluid Thermal Mass Model for Approximating Short Term Borehole Thermal Response

Abstract

The borehole fluid thermal mass (BFTM) model, described in this thesis, is an analytical model for the heat conduction in and around a borehole-type ground loop heat exchanger (GLHE). The advantage of the BFTM model over other analytical models is its ability to model the thermal mass of the circulating fluid. The thesis also applies the BFTM model to generating a non-dimensional representation of the short-time soil thermal resistance, called a g-function, which is used in the GLHE design software, GLHEPRO. The changes in required depth due to changing internal borehole properties are determined for peak-load and non-peak-load dominant buildings by performing 1440 sizing simulations in GLHEPRO. The performance of the BFTM model on an hourly basis was determined by comparing the BFTM model to a line source model using 6 hourly HVACSIM+ simulations. Six different methods for calculating the steady state borehole resistance are also reviewed in this thesis.