Modern Engineering Thermodynamics

14.8 CFCs and the Ozone Layer 553
HOW WERE CFCs CONTROLLED?
1978: The U.S. Environmental Protection Agency (EPA) banned the use of CFCs in all nonessential aerosol cans. This
action alone cut the U.S. consumption of CFCs by 50%.
1980: The European Community limited CFC production and use in aerosols.
1985: The Ozone Hole is discovered in the Antarctic.
1987: The Montreal Protocol is signed by 43 nations to decrease overall production of CFCs by 50% by 1999.
1990: Title VI of the Clean Air Act (Stratospheric Ozone Protection) is passed into law in the United States.
1992: The signers of the Montreal Protocol agree to a phase-out schedule for all HCFCs (including R-123) by the
year 2030.
The financial investment in existing refrigeration and air conditioning systems is massive, so the replacement
refrigerants must have very similar thermodynamic properties to R-11 and R-12, so that they can be used in the
same operating equipment with minimal modifications. Today, R-123 is temporarily 4 replacing R-11, and
R-134a is replacing R-12. By the end of 1995, EPA banned most production and import of R-12. However, the
use of R-12 is still permitted until supplies are depleted. Figures 14.15 and 14.16 show the p–h diagrams for
these refrigerants and their replacements.
R-123 is CHCl 2 CF 3 and is called a hydrochlorofluorocarbon (HCFC). While it still contains chlorine, it is 50 times
less detrimental to the ozone layer than R-11. Consequently, it is viewed as a temporary replacement for R-11,
since it too must be phased out by the year 2030. The ultimate replacement for R-11 may be R-245fa
(CF 2 HCF 2 CFH 2 ), a propane-based halocarbon that does not contain chlorine. R-134a is CH 2 FCF 3 and is called a
hydrofluorocarbon (HFC). It contains no chlorine and will not damage the ozone layer. The other common refrigerant
in use in large-scale air conditioning and heat pump systems is R-22 (CHClF 2 ). It is also an HCFC, and
1000
500
R−11
1000
500
R−12
R−134a
200
R−123
200
100
100
Pressure (psia)
50
20
Pressure (psia)
50
20
10
10
5
5
2
2
1 0 20 40 60 80 100 120 140
Enthalpy (Btu/lbm)
1 0 20 40 60 80 100 120 140
Enthalpy (Btu/lbm)
FIGURE 14.15
Superimposed p–h diagrams for R-11 and R-123, showing the
thermodynamic similarities between these two refrigerants.
FIGURE 14.16
Superimposed p–h diagrams for R-12 and R-134a, showing the
thermodynamic similarities between these two refrigerants.
4 R-123 is scheduled to be phased out in 2020 in new equipment.