Introduction

Refrigeration oil plays a crucial role in maintaining the efficiency and longevity of a refrigeration system. Refrigeration oil must not only provide lubrication to the compressor and system components, it needs to be compatible with the selected refrigerant and the system operating conditions.

CFC and HCFC Refrigerants: Traditional vs. Synthetic Oils

Previously with CFC and HCFC refrigerants, traditional mineral oil met the performance requirements for both lubrication and miscibility. Alkylbenzene oil was a synthetic oil that was also compatible with CFC and HCFC refrigerants. Alkylbenzenes offered better thermal stability than mineral oils at higher compressor temperatures, contained no wax and provided better miscibility at low temperatures. The downside is they are slightly more hygroscopic than mineral oil.

Transition to HFCs

As the industry transitioned to HFC’s there was a need to develop a new compressor oil that would be miscible with these new refrigerants. The first of these oils was PAG (Polyalkylene Glycol) and POE (Polyolester), both synthetic oils. While less hygroscopic POE oil was unsuitable for the Automotive industry due to its incompatibility with the rubber used in hoses and shaft seals.

The Latest Advancement: PVE (Poly Vinyl Ether) Oil

The most recent development in refrigeration Oils is PVE (Poly Vinyl Ether). PVE oil offers better stability and miscibility than POE oil. It is compatible with all HFC refrigerants, refrigerant oils, and process fluids. Perhaps most importantly, because PVE oil is ether-based it will not hydrolyse in the presence of water. This means it will not cause blocked capillaries or form acids like POE oils. The downside is PVE oil has a higher surface tension than POE oil.

Challenges with PVE Oil: System Evacuation

Because of the high surface tension, PVE oil adds to the challenge of system evacuation. Typically, down to 2000 microns, evacuation times will be similar to like-sized equipment. From 2000 microns the vacuum stalls as moisture and refrigerant are held in the oil. Applying heat will help release moisture and refrigerant but it is not uncommon for this last 1800 microns and below to take another 24hrs to evacuate.

Conclusion: PVE Oils in Refrigeration Compressors

While more common in Air Conditioning systems PVE oil is slowly being adopted by refrigeration compressor manufacturers.