Semi-Empirical Screw Compressor Chiller Model

A screw chiller model which is based on a first principles, semi-empirical analysis that describes the system performance based on observations of the thermodynamic processes is developed. This model is a modified method to empirically derive the system irreversibilities of the Gordon-Ng first principles approach and is applied to a screw chiller. The irreversibilities were combined into one effect based on the refrigerant temperature difference between the condenser and evaporator and the water temperature difference between the outlet and inlet of the evaporator. The required measured parameters of the model are the evaporator water inlet and outlet temperatures and mass flow, the refrigerant temperature in the condenser and evaporator, and the input power. The similarity in the results generated by the Gordon-Ng model and the semi-empirical model effectively verified both calculation methods. The semi-empirical chiller model simulated outputs were the input power, coefficient of performance and kW/ton with an accuracy of 4-7% when compared to the 4,104 data points acquired from a screw chiller system. The semi-empirical chiller model results were also compared to the Gordon-Ng model predictions as a function of the percentage chiller loading