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

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Refrigerants
Selecting the refrigerant
Originally when the modern refrigerating system concept was
developed in the middle of the 19th Century, a small number
of fluids were used as the working fluid, or “refrigerant”. These
included ammonia (NH3, R717), carbon dioxide (CO2, R744),
sulphur dioxide, methyl chloride and ethyl ether. However, because
of the combination of toxicity, flammability and pressure issues,
these refrigerants were largely replaced with to a “new” group of
fluorinated chemicals which exhibited little reactivity, low-toxicity
and no flammability. However, during the 1980s, it was found that
these chemicals contributed to the depletion of the ozone layer,
which lead to the development of the Montreal Protocol in 1987.
The Montreal Protocol requires the cessation of the consumption
and production of all chlorofluorocarbons (CFCs) and
hydrochlorofluorocarbons (HCFCs) and since its introduction, the
refrigeration and air conditioning (RAC) industry has been engaged
with the chemical community to establish substitutes for ozone
depleting refrigerants. Throughout this time a large number of
refrigerants have been introduced worldwide, of which some are
long term alternatives, and others are “transitional” substances.
With the increasing attention paid to the issue of global warming
and climate change, there is now a stronger push towards adopting
alternative refrigerants with low or no global warming potential
(GWP), as well as zero ozone depleting potential (ODP).
With the continued attention on replacement refrigerants, coupled
with the ever growing market for RAC, there are now several
hundred refrigerants that are currently commercially available. Such
a diversity of refrigerants and their variety of different characteristics
can create difficulties in handling and servicing practices for many
RAC technicians. This section aims to introduce an overview of
refrigerants and their characteristics, classifications, applications,
identification and lubricants.
There are usually two situations that necessitate refrigerant selection,
the first being for manufacture of systems, and the second being
equipment servicing. For manufacturing RAC equipment, the
refrigerant selection process is theoretically complex, involving the
CHAPITRE 2
consideration of huge number parameters.
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THERMODYNAMIC
AND TRANSPORT
PROPERTIES
CHEMICAL
PROPERTIES
AND STABILITY
SELECTION CRITERIA
ALTERNATIVES
COST
AND
AVAILABILITY
34
OPERATING
PRESSURES
SAFETY
CHARACTERISTICS