A previous comparison of vertical ground heat exchanger design methods for geothermal heat pumps in residential applications found large disagreements in the sizes recommended by five commercially-available computer programs, even when consistent information was input to all five. The objective of this work is to repeat the comparison using updated versions of the five programs originally tested, and one new program which was not included in the previous comparison. Simulation models of two sites--one in a cooling dominated climate, and the other in a heating dominated climate--were calibrated to site-collected data and then driven with typical meteorological year data to produce consistent inputs for the six design programs. The results indicate that the programs are now much more consistent with one another. For the cooling dominated site, design lengths vary by about 7%, and for the heating dominated site the design lengths vary by 16%. Compared to the tests performed in 1996, there is now much more consistency among the various design algorithms.

Units: I-P