A vapor-compression chiller uses a refrigerant internally as its working fluid. Many refrigerants options are available; when selecting a chiller, the application cooling temperature requirements and refrigerant's cooling characteristics need to be matched. Important parameters to consider are the operating temperatures and pressures.

There are several environmental factors that concern refrigerants, and also affect the future availability for chiller applications. This is a key consideration in intermittent applications where a large chiller may last for 25 years or more. Ozone depletion potential (ODP) and global warming potential (GWP) of the refrigerant need to be considered. ODP and GWP data for some of the more common vapor-compression refrigerants:

Refrigerant	ODP	GWP
R134a	0	1300
R123	0.012	76
R22	0.05	1700
R290 (propane)	0	3
R401a	0.027	970
R404a	0	3260
R407a	0	???
R407c	0	1525
R408a	0.016	3020
R409a	0.039	1290
R410a	0	1725
R500	0.7	???
R502	0.18	5600
R717 (ammonia)	0	0

The refrigerants used in the chillers sold in Europe are mainly R410a (70%), R407c (20%) and R134a (10%).