In the early days of vapour compression refrigeration, many different working fluids were used. More recently, ammonia (R717) and halocarbons (R12, R22 and R502) have mainly been used.
Ammonia is generally used in larger plants and the halocarbons are used for smaller installations. The halocarbons are, in many respects, ideal refrigerants. Recently serious drawbacks were discovered. Some of halocarbons, known as CFC's and HCFC's, were causing breakdowns in the ozone layer round the Earth which protects the lower atmosphere from excess UV radiation. In addition the chemicals were suspected of causing global warming.
Because of the drawbacks it has been agreed internationally to phase out the production and use of CFC's by 1995 and HCFC's by 2020. The 1987 international agreement is known as the Montreal Protocol. In addition, the EC has introduced stricter timetables for phasing-out the refrigerants.
The most likely strategy to meet the phase-out is an increased use of ammonia, coupled with the introduction of newer halocarbon refrigerants, HFC's, either separately or in
Because of the uncertainties about the halocarbons, it is advisable to use ammonia for all plants of 7kW or greater. Although the CFC's are still available (l994) and the HCFC's are due to be available until early next century, it is now important to ensure that any refrigerant chosen will be available during the life of the plant. Both ammonia and the alternative refrigerants require skilled personnel to service them, so training is always necessary.
If anything, the phase-out timetable is likely to be shortened. During the period of phase-out it is likely that the practical problems of using the newer refrigerants will be resolved. It is also possible however that some of the non-halocarbon fluids previously used will come back into use. It is therefore important to seek advice on the choice of refrigerant from a reputable refrigeration engineer.