Thermodynamic Models for Predicting R-134a and R-1234yf Superheated Vapor Specific Entropies and Enthalpies for Evaluating Vehicle Air Conditioning

There is an urgent need to replace refrigerant fluids in use with new ones that have a lower global warming potential. In vehicle air conditioning systems, R-134a is mostly used, which despite not degrading the ozone layer, has a high global warming potential. R-1234yf is regarded as a strong candidate for replacing R-134a. However, a loss in the coefficient of performance is usually associated with this replacement. Process simulation is a powerful tool to assist in proposing alternative designs or operating points. However, proper thermodynamic models are needed to generate accurate simulation results. In this work, thermodynamic models are presented for the prediction of the specific enthalpies and entropies of the superheated vapor of R-134a and R-1234yf fluids. The postulated models show an excellent capacity for reproducing tabulated properties from the literature with prediction errors of less than 2%. They were further applied to simulate a typical vapor compression system operating with both refrigerant fluids. A loss in the coefficient of performance of up to 15% can be observed when replacing R-134a with R-1234yf and by simulating different operating scenarios an operating point having a loss of 5% in performance can be found.