Improved Design Methods for Ground Heat Exchangers

Abstract

As public awareness about energy conservation grows, so too does interest in alternative energy sources. Geothermal energy is an alternative energy source which consumers can access by installing a ground source heat pump (GSHP) system in the place of standard heating and cooling systems. A GSHP system can provide both heating and cooling and consists of one or more heat pumps, a ground heat exchanger (GHE), and circulating pumps. The GHE provides the heat source for heating and the heat sink for cooling. It is made up of a series of pipes installed in the ground in horizontal trenches or vertical bores. These pipes are filled with a working fluid that transfers heat to a building from the ground and vice versa. Specifying the appropriate size for the GHE is a key portion of the design for a GSHP system. The purpose of this study is to improve the design methods for ground heat exchangers by adding to and improving the GLHEPro design tool. A series of new models have been added to the program including � A finite line source model (FPFLS model) for modeling combinations of up to 30 inclined or vertical boreholes.� A method for calculating short circuiting resistance in vertical and inclined boreholes.� A method for modeling and sizing groundwater filled single U-tube boreholes.� A new global ground temperature database.� A Horizontal borehole model for straight trenches and horizontal slinky GHEImprovements to the g-function interpolation methods were also applied.It was found that these new models provided reasonable results and significant new features to GLHEPro V5.0. Several of the models implemented were previously validated: ground temperature model and the g-functions (temperature response functions) of the slinky model. A validation for the FPFLS model is included.