Analytical and Numerical Modeling of Foundation Heat Exchangers

Abstract

Foundation heat exchangers (FHX) are an alternative to more costly ground heat exchangers utilized in ground-source heat pump (GSHP) systems serving detached or semi-detached houses. Simulation models of FHX are needed for design and energy calculations. This thesis looks at two approaches that have been used for development of simulation models for FHX: a detailed numerical model and a simplified monthly time-step analytical model used as a design tool. The numerical model is a two-dimensional finite volume model with hourly time steps, implemented in the HVACSIM+ environment. The simplified analytical model is based on superimposed line sources and sinks and uses a hybrid monthly time step. The numerical model is validated with experimental result for a period of ten months; data are collected from a two-story residual building, located in Oak Ridge, Tennessee. Both the FHX analytical model and FHX numerical model utilize Kusuda and Achenbach model (1965) to calculates the undisturbed ground temperature. However, the result of the Kusuda and Achenbach model depends on having the Kusuda and Achenbach parameters: annual average soil temperature, surface temperature amplitude and phase delay. Therefore, a simpler one-dimensional model that utilizes a 1D numerical model, with full surface heat balance coupled with TMY3 (Typical Meteorological Year 3) weather files (or other equivalent weather files), to estimate all three parameters has been developed. The 1D ground heat transfer model result is validated with experimental data of 11 locations within U.S..