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

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Refrigerants
Carbon dioxide (CO2, R744)
Carbon dioxide contains carbon and oxygen, and is widely used
within many industries. It had been extensively applied as a
refrigerant since the mid-1800s, but this also ceased with the
advent of the CFCs and HCFCs. From the later 1990s, its has reemerged
as a refrigerant and its use is currently increasing within
industrial refrigeration, cold storage, commercial refrigeration and
hot-water heat pumps, amongst others. R744 is chemically stable,
and does not react under most conditions, and is compatible
with many materials. The pressure-temperature characteristic of
R744 are different from most conventional refrigerants, in that it
operates at pressures, for example, approximately seven times
higher than R22, which necessitates the system to be designed with
special consideration to high pressures. In addition, it has a low
critical temperature, such that when ambient temperatures exceed
about +25°C, a special system design is required. Otherwise, it’s
thermodynamic and transport properties are excellent, leading
to potentially highly efficient systems within cooler climates. Due
to its lower toxicity and non-flammability, it has an A1 safety
classification. Unlike the fluorinated gases, it has no impact on the
ozone layer so is not controlled by the Montreal Protocol. However,
despite it having a GWP of 1, it is included within the Kyoto
Protocol, but its use it not restricted as a result of this. R744 is very
cheap and widely available from specialist retailers.
Refrigerant numbering
Chemical names of typical refrigerants are generally long and
complex. In order to create a more simple way to designated
refrigerants a method of identifying them by number was
developed. IIR’s note on classification of refrigerants that describes
the basic rules for adopting the number of the refrigerant (see
www.iifiir.org/en/doc/1034.pdf). The classification is based on the
standard ASHRAE 34 and makes it possible to name all refrigerants
used in a clear and internationally recognised way by classifying
them according to their chemical composition. Basically an
identifying number is assigned to each refrigerant. It consists of a
prefix made up of letters and a suffix made up of digits. The prefix
is composed of the letter R (for refrigerant). Examples: R22, R134a,
R600a, R717. Blended refrigerants, whether they are zeotropic or
azeotropic, always being with R4xx or R5xx, respectively.
Refrigerant blends characteristics and pros and cons:
Lubricants properties and choices:
Refrigerant blends 4
Lubricants 4
Once you have explored these characteristics the next button introduces
refrigerants and their appropriate use:
Using Refrigerant Blends 4
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