Working Fluid

According to DIN EN 378-1, the working medium is a "fluid used for heat transfer in a refrigeration system which absorbs heat at low temperature and low pressure and releases heat at higher temperature and pressure, with changes in the state of the fluid usually taking place."

Fluids that are gaseous at working temperature and can be liquefied by moderate pressure increase are particularly effective. This makes it possible to use the heat of vaporization for heat transport.