Criteria are described for ideal working substances in centrifugal chillers. Chlorine-free fluorinated ethers and hydrocarbons are being considered as potential replacements for R-11, R-12 and R-114. Comparisons are made in terms of ecological and thermophysical properties and standard air-conditioning parameters for working substances which can be used without change of system design. R-245ca and E-245fa are promising alternatives to R-11 for the low-capacity range, and R-134a is the best retrofit refrigerant for R-12 in the medium-capacity range. R-236ea, R-236ca, R-236fa, R-236cb, and E-134 are promising refrigerants for replacing R-114 in centrifugal chillers for the high-capacity range.