GLHEPro has been validated against measured data from working ground heat exchangers and compared with the ASHRAE Handbook Method. Applying the measured loads on the ground heat exchanger as the design conditions and setting the actual peak temperatures as the user-specified design temperatures, the design methods should give us back the actual design.  GLHEPRO gave sizes within 5% of actual; the ASHRAE Handbook method gave designs substantially different from actual.  “Why” is explained in the paper cited below that details the comparison.

Cullin, J.R., J.D. Spitler, C. Montagud, F.  Ruiz-Calvo, S.J. Rees, S.S. Naicker, P. Konečný, and L.E. Southard. 2015. Validation of Vertical Ground Heat Exchanger Design Methodologies. Science and Technology for the Built Environment. 21(2):137-149.

The figure below shows the results of the comparison between sizing methods.