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Comparison of various refrigerant alternatives, including the natural refrigerants (ammonia, CO 2, water), with emphasis on water (R718) centrifugal refrigeration compressors is realized in this chapter. The possibilities for replacement of the refrigerant in an existing refrigeration system, as well as the range of suitable and successful application of various refrigerants in centrifugal refrigeration units, mainly depend on refrigerant molecular mass, normal boiling temperature, and refrigerant specific cooling capacity. The required pressure ratio for a given temperature lift is lower for refrigerants with lower normal boiling temperature. A centrifugal stage working with these refrigerants attains a high pressure ratio with relatively low peripheral speed. CFCs, HCFCs, HFCs, and HFEs are compounds with large molecular mass. The characteristics of refrigeration centrifugal compressors mainly depend on refrigerant normal boiling temperature, molecular mass, and specific cooling capacity (specific compressor displacement). The thermodynamic properties of the refrigerant and the operating conditions of the refrigeration/heat pump system determine the peculiarities of the refrigeration centrifugal compressors. Ĺ arevski PhD, in Water (R718) Turbo Compressor and Ejector Refrigeration / Heat Pump Technology, 2016 2.8 Conclusions