DOE EERE Research Reports

Electrically-Driven Heat Pumps

Fluids Development

Historically, chloro-fluorocarbons have been used as the working fluids in vapor compression systems because they have thermodynamic properties that correspond to the temperature ranges experienced in refrigeration and space conditioning applications. They also have thermophysical properties that contribute to high efficiency and enable them to be used with common construction materials.

Typically, pure working fluids have been used which evaporate or condense at constant temperature and pressure. Mixtures of refrigerants that change temperature as they change from liquid to vapor or back theoretically have more efficient heat transfer and heat pumps, air conditioners, or refrigerators using these non-azeotropic refrigerant mixtures could be more efficient than systems using pure refrigerants. R&D projects sought to demonstrate and to quantify these theoretical improvements.

Discoveries in the 1970's and 1980's revealed that chloro-fluorocarbon refrigerants in the upper atmosphere were significant factors in depletion of the stratospheric ozone layer. An international effort under the auspices of the United Nations Environment Programme led to the Montreal Protocol and a complete phase-out of the manufacture and use of CFC's and hydro-chloro-fluorocarbons. Research was undertaken to identify safe and efficient alternatives to CFC's and HCFC's for use in heat pumps, air conditioners, refrigerators, and commercial refrigeration systems.

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