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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. [ABSTRACT FROM AUTHOR]

This article presents an investigation on the impact of year-to-year weather variability on the optimal design of a system for heating and cooling a building using a ground-source heat pump. The designs of a boiler-ground-source heat pump hybrid and a cooling tower-ground-source heat pump hybrid were optimized using a typical meteorological year (TMY2) weather file and also using 15 years of actual weather data. The results indicate that a design based on a TMY2 weather file may be undersized for a severe weather year; this is particularly true if the severe weather year is encountered during the first year of system operation. A cooling tower-ground-source heat pump hybrid model was developed, which includes the use of a backup boiler placed on the building side (rather than the loop side) of the system. It was found that the use of a boiler backup mitigated much of the negative impact of a severe weather year. The boiler supplied the heating during periods of particularly severe weather so that the ground loop length could be maintained at a reasonable value. [ABSTRACT FROM AUTHOR]