Short indicates other issues that need to be considered include thermal stability, volatility and compatibility with other materials used in the refrigeration system. He says, « Both the thermal stability and volatility of the lubricant must be considered based on the application. Lubricants must be compatible with components such as metals, coatings and elastomers that are used in the refrigeration system. It is also desirable for the lubricant to have thermal conductivity to promote effective cooling. »
Wei provides other items that must be considered when recommending a lubricant: « Above all, the lubricant must provide lubricity and be stable enough over the lifetime of the compressor. Contaminants such as water, impurities and total acid number (TAN) must be kept to an absolute minimum so that the problems such as capillary plugging cannot occur. Viscosity is also an important consideration because this parameter must be low enough to provide less drag (better energy efficiency) and good oil return properties. »
One other element that is becoming more important is retrofitting of compressor refrigeration systems with newer refrigerants that exhibit no ozone depletion and low global warming potential (GWP). In moving lo a new refrigerant, measures must be taken to ensure that the lubricant is compatible and stable.
Jeff Berge, manager of R&D for Ingersoll Rand Climate Control Technologies, furnishes an end-user perspective on the testing that is conducted in choosing a lubricant for a specific application. He says, « The first step in our evaluation involves physical and chemical testing of the lubricant: color, viscosity, moisture level, acid number, particulate count and FTIR analysis.