OZONE DEPLETION POTENTIAL
The ozone layer in our upper atmosphere provides a filter for ultraviolet radiation, which can be harmful to our health. Researchers found that the ozone layer was thinning, due to emissions into the atmosphere of CFCs, halons and bromides. The ozone depletion potential (ODP) of a refrigerant represents its effect
Table 3.1 Properties of refrigerants |
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Refrigerant |
Composition |
Application |
ODP (R11 = 1) |
HCFCs low chlorine |
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R22 |
CHCIFj |
HT, MT, LT |
0.05 |
R22 Blends |
R22 + HFCs |
MT |
0.03 to 0.05 |
R22 Blends |
R22 + HFCs |
LT |
0.02 to 0.03 |
HFCs chlorine free |
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R134a |
CF3CH0F |
HT, MT |
0 |
R404A |
R143a/125/134a |
LT |
0 |
R407C |
R32/125/134a |
HT |
0 |
R41OA |
R32/125 |
HT |
0 |
Other R32 blends |
R32 + HFCs |
LT |
0 |
Other R125 blends |
R125 + HFCs |
HT, MT, LT |
0 |
HCs halogen free |
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R290 |
CgHn propane |
HT, MT |
0 |
R1270 |
CgHR propylene |
LT |
0 |
R600a |
C4Hir) isobutane |
MT |
0 |
R290 blends |
R290 + HCs |
HT, LT, MT |
0 |
Other halogen free |
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R717 |
NH3 ammonia |
LT (MT, HT) |
0 |
R744 |
C02 carbon dioxide |
HT, MT, LT |
0 |
‘Triple point (5.2 bar abs). "At critical temperature 31 °C. |
1500 |
-41 |
19.4 |
970 to 1770 |
-33 to -35 |
13 to 14 |
1960 to 3570 |
-44 to -51 |
20 to 25 |
1300 |
-26 |
13.2 |
3260 |
-47 |
23.0 |
1525 |
-44 |
19.8 |
1725 |
-51 |
30.5 |
1770-2280 |
-46 to -48 |
21 to 23 |
1830-3300 |
-43 to -48 |
18 to 25 |
3 |
-42 |
17.1 |
3 |
-48 |
20.6 |
3 |
-12 |
6.8 |
3 |
-30 to -48 |
1 0 to 1 8 |
0 |
-33 |
20.3 |
1 |
-57* |
74** |
GWP(C02 = 1) |
Boiling point (°C) |
Vapour pressure at 50°C (bar abs) |
On atmospheric ozone, and the reference point usually adopted is ODP = 1 for the CFC R11.
After a series of rigorous meetings and negotiations, the Montreal Protocol on Substances that Deplete the Ozone Layer was finally agreed in 1987. Signatories agreed to phase out the production of these chemicals by 1995. Refrigerant emissions were only about 10% of the total, the remainder being made up of aerosol sprays, solvents and foam insulation. The refrigeration industry rapidly moved from CFCs to HCFCs; R22 and HCFC replacement blends. At subsequent revisions of the Protocol, a phase-out schedule for HCFCs was also set. R22, which is an HCFC, has a far lower ODP than the CFCs, but it was considered necessary to phase out all ozone depleting substances, and under the Protocol HCFCs will be eliminated by 2030. This signalled the end of R22. Moreover, the European Union drew up a far more stringent Regulation, 2037/2000, which banned all new HCFC equipment in 2004, banned the sale of new HCFC refrigerant for service in January 2010 and recycled refrigerant in 2015.
To replace the chlorine containing CFCs and HCFCs, the chemical companies developed a range of hydrofluorocarbons (HFCs). The HFCs tend to have slightly poorer thermodynamic properties than R22, and as single substances they generally do not exactly match the performance of the chemicals they are intended to replace. Whilst R134a, the first HFC to become available, is a close match to R12, the other HFC refrigerants now in wide use are blends of two or three HFCs (see Table 3.1). Figure 3.2 illustrates the ideal, or theoretical performance of some of the most widely used HFCs together with ammonia when evaporating at 5°C.
Theoretical COP (%R22) Condensing temperature Figure 3.2 Theoretical efficiency of replacement refrigerants at air conditioning conditions, relative to R22 |
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