Development of an Integrated Building Load-Ground Source Heat Pump Model as a Test Bed to Assess Short- and Long-Term Heat Pump and Ground Loop Performance

Abstract

An integrated building load-ground source heat pump model is developed in this paper to serve as a test bed for assessing the short- and long-term performance of GSHP and HGSHP systems with vertical boreholes. The model uses the Simulink/Matlab environment to take advantage of their built-in functionality, allowing for full coupling of the component building load, heat pump, ground loop, and supplemental heat rejection models at every time step The building load model uses the HAMBASE thermal program which can model residential and commercial buildings. The heat pump model uses available data provided by GSHP manufacturers and sensible heat corrections to accurately model operation across a wide range of input conditions. The vertical borehole ground loop model is based on Eskillsons g-function model, but includes a one-dimensional numerical model by Xu to calculate the short-term thermal response of the borehole and ground. The supplemental heat rejection section allows various techniques to be tested. The integrated model captures system performance over a wide range of time scales from seconds to 10–20 years. Results of a 15-year simulation are presented to illustrate the different time scale information that reveal the slow degradation in system performance due to the effects of ground heating.