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GRANT LAIDLAW
Grant Laidlaw is currently the owner of the Air Conditioning and Refrigeration Academy ( ACRA ) in Edenvale . He holds a Bachelor of Business Administration and an associate degree in educational administration . He has a National Technical Diploma and completed an apprenticeship with Transnet . He has dual-trades status : refrigeration and electrical . He has been involved with SAIRAC for over two decades and served on the Johannesburg committee as chairman and was also president between 2015 and 2018 . Currently he is the SAIRAC national treasurer .
REFRIGERANT CHANGES AND LUBRICANTS
By Grant Laidlaw
There are many changes as we move into a new natural refrigerant era . You will find that we have almost as many new oils on the market as there are refrigerants .
Gean asks : Grant , with all the changes with regards to refrigerants how does this affect the lubricants in the systems , aside from the older systems , are we even doing mineral oils ?
Hi Gean , let ’ s begin with the obvious : let the compressor manufacturers specify what oil to use in any application . If you are unsure of what oil to use , call the compressor manufacturer or use the specification data along with their performance curve literature . Having said that let us move on to the refrigerant oils . In refrigeration systems the purpose of the oil is to provide adequate lubrication between metal surfaces . Oil often serves as a seal to prevent refrigeration from leaking between high- and lowpressure regions of the compressor , on crankshaft seals and in the automotive sector in coating the rubber hoses . The oil can perform a cooling function that is significant in some compressors . In addition , oil can form an integral part of capacity control on larger compressors . Some oil will leave the compressor during the cooling cycle and circulate with the refrigerant through the system . The system should be piped to return this oil back to the compressor on a continual basis .
Refrigeration oils must have the correct properties required by the system . Other oils , such as those used to lubricate motor vehicle engines , or hydraulic systems , for example , do not have the correct properties and as such are not suitable for refrigeration systems . Care must be taken to use the correct oil when filling oil into a compressor . In refrigeration systems oil circulates with the refrigerant through the system . As the temperature and pressures vary greatly in the system , the oil must have very special characteristics .
Some of these are :
• At high temperature and pressures : º The oil must maintain its lubrication properties at condensing conditions . º The oil must not carbonise onto the valves , pistons , or other components due to the gas delivery temperatures in the compressor .
• At low temperature and pressures : º The oil must remain a fluid so that it can still lubricate . º The oil must not contain wax , which can form deposits at system operating temperatures .
• At all temperatures and pressures : º The oil must not react chemically with the refrigerant and any other materials used in the system . It must be compatible with the refrigerant and the system components , gaskets , and seals . Mineral oils were used for HCFC refrigerants but are not compatible with the HFC refrigerants due to their low solubility factors . Poly Ester oils are mostly used for the HFC refrigerants . ( However , the oil is hygroscopic and will readily absorb water ). º Some HC refrigerants may be used with mineral oils . º The oil must be very stable so that it lasts a long time . º The oil must be very dry ( contain the minimum amount of water ). º The oil must be miscible with the refrigerant .
The selection of the refrigeration oil depends on the operating conditions of the system , the type of refrigerant ( HCFC which requires mineral oil and HFC which requires polyester oil ) as well as the type of compressor .
www . hvacronline . co . za RACA Journal I February 2022 53