Low GWP R134a replacements for small refrigeration (plug-in) applications
This paper presents a performance evaluation of two low global warming potential (GWP) refrigerants, R1234yf and R1234ze(E), as replacements for R134a. A theoretical comparison is first presented based on the thermodynamic properties of the refrigerants. Tests are carried out in a representative vending machine system (cassette) at two representative outdoor ambient temperatures of 32.2°C (efficiency test), and 40.5°C (capacity test) and return air temperatures of 2°C, 20°C and 38°C. Under drop-in conditions, R1234yf shows performance similar to R134a. For R1234ze(E), a refrigerant with lower volumetric cooling capacity, testing was done using a larger compressor to obtain capacity recovery. A simulation model is used to analyze the system design changes, which can lead to further improvement in the performance of low GWP refrigerants. Overall, the results indicate that with minor design changes, such as use of a suction-line/liquid-line heat exchanger and modifications to the refrigerant circuitry, these refrigerants can match the performance of R134a.