Environmental impact of CFCs
Chlorofluorocarbons (CFCs) are chemical compounds which have been developed for use as refrigerants. Their molecular structure is based on either methane or ethane; one or more of the hydrogen atoms is substituted by chlorine or fluorine.
The CFC refrigerants soon replaced most other refrigerants except ammonia, which is still in use today. Other products made from CFCs were then used for aerosols, expanded foam processes and degreasing agents.
One desirable property of the compounds which appealed to manufacturers of refrigerants is their chemical stability. It is this long term stability which contributes to the pollution of the atmosphere. Once released, CFCs remain in the atmosphere for years. At low altitudes this does not present a problem. However, when they reach the upper atmosphere CFCs, like ozone, are broken down by ultraviolet light. This results in the release of free radical chlorine atoms, which interfere with the normal formation of ozone and contribute to the greenhouse effect (about 10 15 per cent).
There are now restrictions imposed upon manufacturers of certain CFCs by the Montreal Protocol, an international agreement which came into force in January 1989. Within ten years, production of CFCs should have been reduced to 50 per cent of the 1986 levels.
Refrigeration service and installation engineers can assist in reducing the emission of CFCs. Design engineers can ensure that systems are constructed so that emissions are minimal when various forms of maintenance or repairs are necessary.
Good refrigeration practice for CFC systems
It is a well known fact that an engineer required to work on an ammonia system will be very careful not to allow undue discharges of refrigerant because of its toxicity. Since CFCs are non-toxic it has been common practice to discharge them to atmosphere. This must now be regarded as malpractice and cease forthwith.
Evacuation
It was also past practice to use the dilution or triple evacuation method, in which a small amount of refrigerant is used to dilute the atmosphere within the system, discharging between evacuations. This method can still be employed, but instead of releasing the refrigerant to atmosphere it should be reclaimed by decanting to a cooled refrigerant cylinder.
Alternatively, the more practical deep evacuation method should be adopted.
Cleaning condensers
The practice of cleaning condensers with a refrigerant should be discontinued. Proprietary brands of degreasing and cleansing agents which are environment friendly are readily available.
Should it be necessary to apply pressure to ensure penetration to fins and pipework, then nitrogen should be used.
Decanting re rigerant
Special care must be taken not to overfill the cylinder, and to use only those which are free from any contamination by oil, acid or moisture.
Do not mix grades of refrigerants. Always use a cylinder for the specific refrigerant for which it is designated.
Removal o re rigerant rom sealed systems
This can be achieved by fitting a line tap valve to the system and connecting to a recovery cylinder.
Removal o contaminated re rigerant
Contaminated refrigerant which may have resulted from a compressor burnout or a water cooled condenser leak must not be used to recharge the system. It must be recovered and sent away for reprocessing or disposal.
It should be decanted into special recovery cylinders available from the manufacturers or suppliers of refrigerants. Never use service cylinders for reclaiming contaminated refrigerants.
When removing refrigerant charges or decanting from systems, adequate protective clothing and goggles must be worn. All safety procedures must be observed.
It is advisable to include an isolating hand shut-off valve at the cylinder end of the charging line to minimize purging. Ensure that the valve is open before discharging from the system. Use charging lines without the Schraeder inserts.