Chapter 6 Introduction to Refrigerants
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Zeotropic blends, however, have a range of tem-
peratures over which the blend may evaporate or con-
dense. As a result, temperature glide can be seen in
the pressure-enthalpy diagrams for zeotropic blends,
Figure 6-14. Unlike azeotropic blends and single
refrigerants, zeotropic blends have lines of constant
temperature that are slightly angled inside the satu-
ration curve. The lines of constant temperature are
angled to reflect the range of temperatures over which
a zeotropic blend changes phase. Using Figure 6-14 as
an example, you can see that the 100 psia line of pres-
sure crosses the saturated liquid line just above the 40°F
temperature line. However, by the time the 100 psia
pressure line cross the saturated vapor line, the zeo-
tropic blend has a temperature closer to the 60°F tem-
perature line.
6.5 Refrigerant Applications
Refrigerant applications are devised based on the
pressure, temperature, and heat properties of a refrig-
erant. The type of refrigerant to be used in a given sys-
tem is determined by the manufacturer. One type of
refrigerant may be used in a number of applications.
Several items are considered in the selection of the
refrigerant:
• Boiling point of the refrigerant.
• Latent heat of the refrigerant.
• Operating temperatures required.
• Operating pressures based on required temperatures.
• Size of the equipment.
The chart in Figure 6-15 shows some popular
refrigerants and their applications. The pressure-
enthalpy tables and diagrams for many of the refriger-
ants listed in the chart can be found in the Appendix. As
you read through the following sections, use this chart
as a convenient reference for identifying replacement
refrigerants, refrigerant boiling points, and refrigerant
operating pressures.
6.5.1 Phaseout of Refrigerants
The first refrigerants targeted for phaseout by
the Montreal Protocol were CFCs, such as R-12, due to
their large impact on the environment. The phaseout
of R-12 was completed in 1996 in developed countries
and in 2010 in all others. R-12 has been replaced with
R-134a, which is safer for the environment because
it has an ODP of zero. R-12 is no longer manufac-
tured and is not permitted to be used in new HVACR
equipment.
The next refrigerants targeted for phaseout are
HCFCs, such as R-22. In the United States, the phaseout
of R-22 will be completed in 2020, and it has been ille-
gal since 2010 to manufacture new equipment contain-
ing R-22. R-22 is being replaced by R-404A and R-407C.
The complete phaseout of all HCFC refrigerants will be
implemented by 2030.
Saturated vapor line
Saturated
liquid
line
100 psia
60°F
0°F 20°F 40°F
80°F
Pressure-Enthalpy Diagram for a Zeotropic Blend
Enthalpy (Btu/lb)
Pressure
(psia)
Goodheart-Willcox Publisher
Figure 6-14. This pressure-enthalpy diagram illustrates how temperature glide causes the lines of constant temperature to be
angled inside the saturation curve for a zeotropic blend.