112
Modern Refrigeration and Air Conditioning
refrigerants. Examples of HFC refrigerants are R-134a
and R-152a.
Although HFCs have an ODP of zero, some HFCs
still have a high GWP and are beginning to be replaced
by a variety of lower GWP alternatives, such as carbon
dioxide, hydrocarbons, and hydrofluoroolefins (HFOs).
HFOs are similar to HFCs because they contain hydro-
gen, fluorine, and carbon, but they have a slightly dif-
ferent chemical structure. HFOs, such as R-1234yf, have
a very low GWP and are beginning to be used in auto-
motive air conditioning systems. R-1234yf has a GWP
of four, which is 99% lower than the GWP of R-134a.
6.2.4 Refrigerant Blends
Refrigerant blends are mixtures of two or more
established refrigerants. Based on their thermodynamic
properties, they are split into the following groups:
azeotropes, zeotropes, and near-azeotropes.
Because they are made of other refrigerants, refrig-
erant blends fall into the same chemical classifications
as individual refrigerants. If a blend has a CFC, it is
classified as a CFC. If a blend contains an HFC and an
HCFC but no CFC, then it is an HCFC. If a blend con-
tains only HFCs, then it is an HFC. For example, R-500
is composed of R-12 and R-152a. R-152a is an HFC, but
because R-12 is a CFC, R-500 is considered a CFC.
Some refrigerants commonly mixed into these
blends include R-12, R-22, and R-134a. As equipment is
designed for newer, more ecologically friendly refrig-
erants, refrigerant blends that contain mixtures of
phased-out refrigerants, such as R-12 and R-22, are con-
sidered to be interim refrigerants. This is due to either
their high GWP or high ODP.
6.2.2 HCFC Refrigerants
Hydrochlorofluorocarbons (HCFCs) are refriger-
ants whose molecules are composed of hydrogen, chlo-
rine, fluorine, and carbon. HCFC molecules include
halogens combined with either methane (CH
4
) or eth-
ane (C2H6). Examples of HCFC refrigerants are R-22
and R-123.
Studies have indicated that HCFCs and certain
refrigerant blends have less impact on the ozone layer
than fully halogenated CFCs. CFCs are considered to
be fully halogenated because all the hydrogen atoms
in the original methane or ethane molecule have been
replaced by halogens, such as chlorine and fluorine.
In contrast, HCFCs are considered to be partially
halogenated because not all the hydrogen atoms have
been replaced by chlorine and fluorine, Figure 6-3.
As a result, HCFCs tend to break down in the lower
atmosphere and cause less ozone depletion than CFCs.
Although they have lower ODP levels than CFCs,
HCFCs still linger in the atmosphere for a long time
and have a high GWP. The EPA requires the complete
phaseout of HCFCs by the year 2030.
6.2.3 HFC Refrigerants
Hydrofluorocarbons (HFCs) are refrigerants that
contain hydrogen, fluorine, and carbon. They differ
from CFCs and HCFCs because they contain no chlo-
rine atoms. HFCs are considered to have zero ODP.
Like HCFCs, HFCs are partially halogenated, but they
have a lower ODP than HCFCs because they do not
contain chlorine atoms, refer to Figure 6-3. This makes
HFC refrigerants well suited to replace ozone depleting
Methane-based
molecule
(one carbon atom)
F
C C Cl Cl
Cl
Ethane-based
molecule
(two carbon atoms)
HFCs are partially
halogenated
Halogens
replace
hydrogen
H
H F C C F Cl
F
F
F F
H
Hydrogen atom
means HCFC is only
partially halogenated
HFCs contain no
chlorine
CFC (R-11) HCFC (R-22) HFC (R-134a)
Goodheart-Willcox Publisher
Figure 6-3. CFCs are fully halogenated refrigerants, whereas HCFCs and HFCs are not because they contain hydrogen.