Experimental validation of a ground heat exchanger model in a hybrid ground source heat pump

Abstract

This article provides an overview of short time-scale validation of the duct storage model (Hellström 1989) for the simulation of ground source heat pump performance using experimental data acquired from two operational systems. The error in the temperature change across the ground heat exchanger in the first system was within measurement error, but it was larger than the measurement error in the second sytem due to uncertainty in the thermal properties of the ground. A sensitivity study determined that the thermal conductivity and heat capacity have the greatest impact on the model accuracy. An assessment of the error in the model using ASHRAE handbook (ASHRAE 2007) values for thermal conductivity and heat capacity provided a measure of acceptable error. The difficulties of using real-world operational systems for model validation are discussed.

Acknowledgments

This study was funded by NIST and the DOE. The authors would like to thank the personnel and tenants at both Site 1 and Site 2 for their cooperation in letting data be collected at their homes and places of business. We also thank Dan Cautley at the Energy Center of Wisconsin for assistance in the experimental data collection and Jeff Thornton of TESS for his modeling input.

Amanda Pertzborn, Fellow ASHRAE, is Research Assistant. Scott Hackel, PE, LEED AP, Member ASHRAE, is Senior Project Manager. Greg Nellis, PhD, Member ASHRAE, is Associate Professor. Sanford Klein, PhD, Member ASHRAE, is Ouweneel-Bascom Professor.