REFRIGERANTS are the working fluids in refrigeration@ air-conditioning@ and heat-pumping systems. They absorb heat from one area@ such as an air-conditioned space@ and reject it into another@ such as outdoors@ usually through evaporation and condensation@ respectively. These phase changes occur both in absorption and mechanical vapor compression systems@ but not in systems operating on a gas cycle using a fluid such as air. (See Chapter 1 for more information on refrigeration cycles.) The design of the refrigeration equipment depends strongly on the properties of the selected refrigerant. Tables 1 and 2 list standard refrigerant designations@ some properties@ and safety classifications from ASHRAE Standard 34.