Manual for Refrigeration Servicing Technicians - UNEP - Division of ...

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Refrigerants
Natural refrigerants
Various hydrocarbons, ammonia and carbon dioxide belong to a group
named “natural refrigerants”. All natural refrigerants exist in material cycles
present in the nature even without human interference. They have zero ODP
and zero or negligible GWP. Evolutions and technological innovations have
helped in the consideration of “natural refrigerants” as a safe and economic
solution for applications in many sectors. Because of minimal environmental
impacts and for being more appropriated in a sustainable technological
development perspective, refrigeration systems with natural refrigerants
could have an important role in the future in many applications.
Ammonia (NH3, R717)
Ammonia contains nitrogen and hydrogen, and is widely used
within many industries. It has been used widely as a refrigerant
since the late 1800’s, and is currently in common use in industrial
refrigeration, cold storage and food process cooling, and
more recently is being used for commercial refrigeration and
chillers. R717 is chemically stable, but will react under certain
conditions, for example when it is in contact with carbon dioxide,
or water and copper. Otherwise, compatibility in steel systems
and correctly chosen oils is good. The pressure-temperature
characteristic of R717 is broadly similar to that of R22. However,
it’s thermodynamic and transport properties are excellent, leading
to potentially highly efficient systems. Due to its higher toxicity
and lower flammability, it has a B2 safety classification. Unlike the
fluorinated gases, it has no impact on the ozone layer and has a
zero GWP, so it is controlled by neither the Kyoto Protocol nor the
Montreal Protocol. R717 is very cheap and widely available from
specialist retailers.
Hydrocarbons (HCs)
Hydrocarbons contain hydrogen and carbon, and are widely used
within many industries. The most commonly used for refrigeration
purposes are isobutane (C4H12, R600a) and propane (C3H8,
R290), propylene (C3H6, R1270), and blends thereof. Within
industrial applications, a variety of other HCs are widely used.
In general, HCs had been widely used a refrigerant since the
late 1800s until 1930s, and has been re-applied since the early
1990s. Apart from industrial applications, HCs have been used in
domestic refrigeration, commercial refrigeration, air conditioners
and chillers. HCs are chemically stable, and exhibit similar
compatibility to the CFCs and HCFCs. Across the range of HCs,
there are a variety of pressure-temperature characteristics. They
also have excellent thermodynamic and transport properties,
leading to potentially very efficient systems. Due to their higher
flammability, all HCs have an A3 safety classification. As with
R717, they have no impact on the ozone layer and have a
negligible GWP, so are controlled by neither the Kyoto Protocol
nor the Montreal Protocol. R600a and R290 are fairly cheap but
availability is disparate, depending upon the country.
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