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Modeling Packaged Heat Pumps in a Quasi-steady State Energy Simulation Program

Tang, Chih Chien
The purpose of this study is to validate steady-state heat pump models implemented in EnergyPlus. The heat pump models include air-to-air, water-to-air heat and water-to-water. Part load models are used to adjust the models' full load outputs to part load conditions. New curve-fit heat pump models are proposed and compared to existing parameter estimation based models using experimental data. Uncertainties in the models are analyzed and quantified. A short study is also conducted on the compressor shell heat loss that is often neglected by the manufacturer. The EnergyPlus heat pump models agree with experimental data with an error of less than 12%. Most of the errors are attributed to the discrepancies between the catalog and the experimental measurement. The curve-fit models in EnergyPlus agree with detailed and parameter estimation based models within 6%. Curve-fit heat pump models also allow extrapolation beyond the catalog data without catastrophic error and require less computation time and are more robust than parameter estimation based models. The current drawback of curve-fit models is the inability to simulate the degradation effect of antifreeze on water source heat pump performance. The heat pump component models in EnergyPlus have been validated but the control algorithm and system interactions still require further validation with measured data.