The range of refrigeration lubricants being offered today is much broader than ten years ago. This is partly due to the increased use of enviro-friendly refrigerants such as the chlorine-free hydrofluorocarbons. But is also due to a desire by original equipment manufacturers and end users to improve the efficiency and reliability of their refrigeration systems. These influences and others have been quietly changing the requirements and number of lubricants available since refrigeration compressors were first introduced.
Traditional lubricants for refrigeration systems have been based on mineral oils. Major changes over the years has been in the quality of their refining and sometimes the use of additives. Naphthenic oils have been used for almost every type of refrigeration application. They are relatively inexpensive, have had desirable solution characteristics with halocarbon refrigerants, are reasonably stable and have been widely available. Additives have sometimes been used to help improve lubricity or stability. In general, these lubricants have provided adequate service, if not the best, for most systems. Most changes with these oils have been due to external influences such as availability of crude oil supplies or environmental concerns.
Periodic shortages of naphthenic crude oil supplies and concerns over the toxicity of certain aromatic materials have resulted in these oils becoming more cyclo-parrafinic than aromatic. This has had both good and bad consequences. These oils , such as the CPI Refrigeration Oil (RO) series, tend to be much more stable than their predecessors. Their lower miscibility with highly fluorinated refrigerants caused concerns over oil return from evaporators, particularly at low temperatures. Lubricant professionals and equipment manufacturers had to improve their knowledge over application selection of various oils with the particular refrigerant to be used. The result was a better understanding of the properties required, and an increase in the number of types of these oils being specified.
The potential short comings of naphthenic oils also led to the development of other types of refrigeration lubricants. Paraffinic oils, with a lower cost, are now known to be acceptable for a wide number of applications. This is largely due to improved refining techniques which remove impurities. These lubricants have better low temperature properties and improved stability over those previously offered. Improvements have been made in ammonia systems where paraffinic oils have been traditionally used. Our CP-1009 -68 is a severely refined hydrotreated oil, sometimes called semi-synthetic, which has been found to greatly improve the efficiency and reliability of these systems. Secondary refining techniques can reduce oil consumption in some systems by as much as ninety percent. The result is greater cost effectiveness. The same type of oils have superior stability with R-12, a CFC which is now being eliminated from use.
Alkyl benzene type synthetic oils, such as our CP-4700 series, also found their beginning from the potential deficiency of naphthenic oils. This type of synthetic is based on hydrocarbon chemistry and is similar to a high aromatic containing naphthenic oil. The major advantage of this material is that it is more miscible and more stable than its naphthenic counterpart and has low toxicity. It is not uncommon to find partial synthetic refrigeration oils which contain alkyl benzene to improve on the mineral oil’s properties. One such product is our LENOIL. Some types of alkyl benzene oils have the necessary properties for use with some HFC refrigerants. They have been found to be acceptable with HFC-123, and very low viscosity grades are being investigated for use with HFC-134a in appliance and certain fractional horsepower applications.
Polyalphaolefin types of synthetic hydrocarbon fluids are similar to a very stable paraffinic with no wax content. These fluids have excellent viscosity temperature characteristics. The major use of PAOs in refrigeration has been in ammonia applications or in halocarbon applications where miscibility is not a concern. Our CP-4600 series have been specialty designed for these severe conditions. These products are being used worldwide in applications with evaporator temperatures below -60oC in ammonia systems and at below -100oC with certain halocarbons. Systems generally have direct exchange evaporators but occasionally flooded systems with specialty oil recovery systems are used.
The most common type of synthetic lubricant being used with HFC refrigerants is the polyolester or POE. Our SOLEST series has been accepted by dozens of OEMs and package system suppliers. Polyalkylene glycols, or PAGs, such as our RPAG series are the second most common and have been primarily limited to automotive air-conditioning applications. There are many varieties of these synthetics based on individual manufacturer’s technology. At this time, POE lubricants have been classified in the categories of linear, branched or mixed. This actually is a description of the type of fatty acids used to synthesize the polymer. Other differences include the type of alcohol used to make the ester. Most suppliers of these lubricants are now offering a range of products which are classified as highly miscible (such as our SOLEST LT series, or moderately miscible. These products meet the requirements of various original equipment manufacturers.
Major differences between the POEs being marketed today are derived from their formulation technology which is likely to be covered by current or future patents. The way POEs behave with different refrigerants is dependent on their chemistry, particularly on the ratio of the amount and type of the alcohols and acids being used. In some cases a difference as little as five percent of one component will enable the POE to be miscible with a particular HFC or HFC blend.
POEs are not a new type of synthetic lubricant. They have been used since World War II for a diverse number of applications ranging from aircraft turbine engines to high temperature oven chains. Applications generally result for a need for a lubricant which operates at environmental extremes. It is only the formulation chemistry that has been developed to meet the needs of HFC refrigerant compressors and systems. These products have even been used in halocarbon refrigeration applications. They were first examined in the 1950s for use with R-12 due to shortages in available mineral oils. By the early 1980s, our CP-4214 series became commercial for use with R-22, R-502 and R-503. This made CPI the first company to offer a POE refrigeration oil in the US and many other parts of the world. Thus these products have been used with CFCs, HCFCs and blends of HCFCs with HFCs. The majority of applications for use of POEs were to achieve better low temperature miscibility or to provide energy savings. The later is still a common practice for several original equipment manufacturers. For example, POEs have been developed which provide very high viscosity (up to ISO VG 320) in the compression area of rotary compressors, and which are very miscible for ease of removal from evaporators. The result is very good compression and adiabatic efficiency. The major difference of today’s POE from those used fifteen years ago is improved miscibility and lubricity in HFC compressor systems.
The end user is likely to be introduced to a number of new lubricants. Nearly a dozen distinct types of lubricants exist today and it is likely that others are under development. We are already testing several. These include new chemistry hydrocarbon oils and some interesting new types of synthetics. We have commercially introduced several lubricants which are soluble or miscible with ammonia – allowing the use of DX evaporators. The result is remarkable improvements in heat transfer efficiency. This makes it possible to use ammonia in several applications where halocarbons were previously used. The environmental friendly ammonia refrigerant is one of the most efficient alternatives to CFC and HCFC refrigerants. We have also developed lower cost alternatives for HFC refrigerants which are now being tested for their suitability in various laboratory and field tests. CPI has taken our efforts several steps further to insure reliable performance, ease of handling and an efficient transition to the new refrigerants and lubricants. The emphasis of original equipment manufacturers is to qualify each lubricant for each type of compressor. Quality lubricant manufacturers such as CPI are also testing their products with a variety of compressors. It is the responsibility of both types of manufacturer to provide information on how to apply the lubricant and which lubricant is acceptable for each type of compressor. Through this type of cooperation, the end user will ultimately receive the benefit of a reliable efficient compressor system.