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

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.

Posted in Refrigeration and Air Conditioning