Simulated and experimental performance of a solar-augmented heat pump

The Test Facility, located near Knoxville, Tennessee, is an unoccupied converted garage containing an instrumented experimental heating system. The heating system includes an air-heating solar collector array, an air-to-air heat pump, rock bed thermal storage, and an off-peak resistance heater. Hourly performance data from the system have been collected for the 1979-80 heating season by a computerized data acquisition system.

The heating system model was initially formulated using component models available as standard capability in the TRNSYS program. Several of the component models were extended and correlated with experimental performance to provide acceptable overall simulation accuracy. The modifications also produced an approximate 80% reduction in computer execution time as compared to the standard TRNSYS model.

Simulation and experimental results have been compared for a ten week period in midwinter 1979-80. The simulation model was found to produce accurate cost representations of total heat and power flows and average storage temperatures for the period.

Using complete heating season meteorological data, the performance of the experimental system and several alternatives has been simulated. An annual power cost analysis applied to the results indicates that the cost of peak period electricity must rise to at least six times the cost of off-peak electricity for the off-peak heating capability of the experimental system to become cost-effective. The solar portion of the experimental system was found to effectively conserve energy, but its cost effectiveness requires further capital cost analysis.