Development and Validation of a Slinky Ground Heat Exchanger Model

Abstract

Ground source heat pump systems are an energy efficient heating and cooling technology for residential and commercial buildings. The main barrier to adoption is the higher investment cost compared to conventional systems. Where available land area permits, horizontal ground heat exchangers are generally less expensive than vertical borehole-type ground heat exchangers (GHXs). A further cost reduction can be made by using SlinkyTM ground heat exchangers, which require less trench space and hence reduce the installation cost, in many cases. It is desirable to formulate an accurate model for simulation purposes; such simulations can be used in both design tools and in energy analysis programs.The model formulated in this paper relies on analytical ring source solutions to compute temperature response functions for both horizontal and vertical SlinkyTM heat exchangers. The algorithm used to calculate the response factors have several features that significantly increase computation speed. The thermal effect of the detailed ground heat balance on the GHXs is considered by superimposing the undisturbed ground temperature calculated using a numerical model. For use in whole-building simulations where the GHX may be connected to other components, the model is formulated to calculate both heat transfer rate and exiting fluid temperature, given entering fluid temperature. The model has been validated against the previously published experimental data; and is implemented in a whole-building energy simulation program EnergyPlus.