Zero-ODP refrigerants for low tonnage centrifugal chiller systems

This paper investigates the use of several zero-ozone depleting potential (zero-ODP) HFC refrigerants, including HFC-134a, HFC-227ca, HFC-227ea, HFC-236ea, HFC236cb, HFC-236fa, HFC-245cb, and HFC-254cb for centrifugal chiller applications. The authors took into account the thermodynamic properties of the refrigerant and aerodynamic characteristics of the impeller compression process in this evaluation. For a given operating temperature lift, there are significant differences in the enthalpy rise required by each refrigerant and this variation in enthalpy rise directly affects compressor size, efficiency, and performance. A comparison of the HFC refrigerant candidates with CFC-114 shows that HFC-236ea, HFC-227ca and HFC-227ea are viable alternatives for centrifugal water chillers. HFC-236ea has properties closest to CFC-114, and will result in compatible performance, but will require a slightly larger impeller and a purge system. Using HFC-227ca or HFC-227ea results in a significantly lower enthalpy rise requirement, potentially allowing single-stage compression, however, wet compression could be a problem. Single-stage compression gives an overall performance advantage over CFC-114 (operating with 3-5°C of liquid subcooling), and when considering thermodynamics and aerodynamics, as is necessary in centrifugal applications, they find that HFC-227ca and HFC-227ea have additional advantages over HFC-236ea and CFC-114