A2L Refrigerants, Vapor Injection, Compressor Modeling
The intent of this paper is to compare compressor performance of two low GWP refrigerants that are mildly flammable. Since there are limited test capabilities for compressors with flammable refrigerants, the compressor tests in this paper are based on a non-flammable refrigerant, in this case R513A. The tested compressor is an open type screw compressor that is driven by an external motor and is vapor injected. A physical compressor model is created from test data. This compressor model is not based on maps for efficiencies, capacity, or power consumption, but rather a basis of physical bulk elements, such as pressure drop from orifices (at suction, discharge and vapor injection), leakage orifices, volume ratio between the suction port and the vapor injection port as well as volume ratio between the suction port and the discharge port. The compressor displacement and speeds are the most fundamental inputs for both the model and the tests. For mechanical losses a friction coefficient and friction exponent, relative to the speed, are obtained from the developed compressor model. This model can predict the actual compressor operation with different refrigerants. This compressor model developed based on R513A testing is applied to predict the performance of R454A and R454C refrigerants that are potential candidates for low GWP transport refrigeration. R454A always gives higher capacity than R454C. For COP, R454A outperforms R454C in some conditions while R454C outperforms R454A in others.