lubricant, refrigerant, properties, methodology, selection
Lubricant selection for compressors used in the HVAC&R industry is typically tied to the refrigerant and subsequent properties understood to be desirable for effective system operation. Over the years refrigerants have changed, and with each change there has been a need for the reevaluation of the interaction with lubricants. In some cases, the existing lubricants can be utilized, however, in others, a there has been the need for new lubricants to be developed. Unfortunately, engineers have typically not challenged what constitutes good and have proceeded with outdated values for “good” or “desirable” properties of the lubricant-refrigerant mixture. Or, in some cases, the values have been tightened, not because the system or the industry required it, but rather because the refrigerants with their lubricants have become so “good” that there was not a way to distinguish between offerings. To differentiate products, engineers increased the severity of the tests and tightened the test result specification and that resulted in breaking what is the necessary properties for design. With the introduction of the lower GWP, unsaturated hydrofluorocarbon products (HFOs), hydrocarbons and CO2, the opportunity exists to assess potential changes to lubricant chemistries that still allow for acceptable use in air conditioning and refrigeration applications to offset the inherent instability of the refrigerant molecules, so we must return to an evaluation of what does the system require for durable, efficient operation. This paper will look at what current parameters are valued for a refrigeration lubricant, how these parameters are measured and why they are important. A focus will be put on looking at what is needed to be successful with next generation low GWP refrigerants and some examples of lubricant candidates for various low GWP refrigerants. Studies will be shown that investigate how we make evaluations and how some of the current approaches need to be revisited.