By Barney Richardson
Practitioners must be aware of safety and changes in design concepts and the phase-out of HCFC and HFC refrigerants and use of new refrigerants in refrigeration.
The requirements of the SAQCC Gas registration revolve around the safe handling of refrigerant gases by practitioners. The training being followed with the new SARACCA training manual provides an understanding of the Pressure Equipment Regulations, SABS standards and good engineering practice in refrigeration.
There is also continuing training and education in new design concepts, the phase out of HCFCs and HFCs and the procedures for natural refrigerants such as hydrocarbon, carbon dioxide and ammonia refrigerants.
The handling of refrigerants includes the proper pressure testing and leak detection procedures to safely be followed. The training not only gives a basic understanding of refrigeration and refrigerants but also the procedures for recovery of refrigerant, leak detection, repair, pressure testing and charging of the system.
For existing refrigeration systems where a leak is suspected this is usually indicated by lower system pressures and poor performance. The leak must be found and pinpointed. The common methods used would be a visual check first then to use a soap solution to see if any bubbles come up on joints etc. A halogen or electronic detector can also be used.
To repair a leak or the replacement of a faulty component the remaining refrigerant must be recovered into a service cylinder. It is important to avoid leaking refrigerant into the atmosphere. The refrigerant must be recovered into an approved service cylinder with indication of the recommended capacities for common refrigerants in kilograms.
Cylinders have different capacities for refrigerants, for example a cylinder rated for R134a at a capacity of 12.6 Kg will be rated at 9.8Kg for R404. The cylinder must be empty and free of other refrigerant types. Use an accurate scale and fill to the capacity shown. Do not over fill. It is advised to fill only to 80% of the capacity – this allows for expansion if the temperature rises for any reason.
The recovered refrigerant should be tested for contaminants and purity. Always avoid mixing refrigerants. There are several substances that could contaminate the recovered refrigerant. These could be water vapour, acid or metal particles from the moving parts of the compressor left over from installation activity.
There could also be non-condensable gases like nitrogen, carbon dioxide and air that may have been introduced during installation or previous service work. Remember that if the refrigerant was such as a Zeotropic blend, the leak could have resulted in a loss of one of components in the blend in which case new refrigerant will have to be used.
Refrigerants can be recycled after the contaminants are filtered out and removed. This may be difficult to do on site unless a specialist is brought in to do this. In most cases it is advised that the gas is sent to a supplier who has the laboratory facilities to do this. These specialist suppliers can analyse and process a used refrigerant through a reclamation procedure.
This process usually applies to larger capacity systems. The smaller recovered quantities would need to be checked for contamination before being accumulated and recycled through the reclamation process.
Pressure testing after a new installation or repair is always undertaken using dry Nitrogen before pulling a vacuum. Evacuation is an important part of the refrigeration system commissioning process. The pulling of a vacuum lowers the boiling point of water, which if present will evaporate and can then be extracted through the vacuum pump. The lower the pressure in the system, the lower to boiling point it will be.
Therefore, it is advisable that the evacuation should be to an absolute pressure of 5000 microns. An electronic pressure monitoring device should be used to ensure a complete evacuation and removal of moisture. Great care must be taken when connecting and disconnecting the vacuum pump and hoses to avoid losing the vacuum. This procedure is explained in the SARACCA training manual.
When it come to charging, accuracy is important. If oil is to be charged this must be done first and be warm to avoid the refrigerant combining with the oil. Some refrigerants should be charged in liquid form e.g. the 400 group of refrigerants known a Zeotropic refrigerant.
Charging can be done preferably by weighing using an electronic scale for accuracy or by sight glass as a reference until it shows a clear flow of refrigerant. The temperature and pressures need to be monitored carefully until the system is running satisfactorily and to specification.
About the author
Barney Richardson is the director of South African Refrigeration and Air Conditioning Contractors Association (SARACCA) and sits on various other boards within the HVAC industry, including the South African Qualifications and Certifications Committee for Gas (SAQCC) Gas.