Development and validation of a Slinky™ ground heat exchanger model

• A Slinky™ GHX model intended for use in building simulation programs is developed.
• A response function (g-function) method is used to model Slinky™ GHX.
• A full surface heat balance is adopted to model the effect of ground surface.
• The model has been validated against experimental data.

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 Slinky™ GHXs, 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 Slinky™ heat exchangers. The algorithms used to calculate the response factors have several features that significantly increase computation speed. The thermal effect of the ground surface temperature variation on the GHXs is considered by superimposing the undisturbed ground temperature, which is calculated using the numerical approach. For use in system 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 field test data.