Polyolester Oils: Handling the New Lubricant in R-410A Systems
April 20, 2009
With the approach of 2010, the industry will be faced with a shift in both refrigerants and system lubricants. The impending phaseout of chlorine-based refrigerants mandates that the industry move to lubricants that work satisfactorily with the new hydrofluorocarbon (HFC) refrigerants. These lubricants must have levels of reliability and performance as good as - or better than - those previously experienced with traditional mineral oils used with chlorine-containing refrigerants.
Instead of the mineral oils commonly used with R-22 systems, synthetic polyolester (POE) oils meet this requirement and will be utilized more universally, with virtually all R-410A systems. As a result, contractors need to be aware of the benefits of POE oils and the differences between handling POE oils and mineral oils, as improper handling of POE oils could lead to premature system failure. POE oils must be handled differently than mineral oil.
POE OILSPOE oils are a family of synthetic lubricants. Unlike natural mineral oils, POE oils are completely wax-free and are the best choice of lubricants for use with the new generation of chlorine-free HFC refrigerants, such as R-410A. This is because they provide superior lubrication, offer better thermal stability, and are more miscible in HFC refrigerants than mineral oils. POE oils are also highly biodegradable.
Another positive aspect of POE oils is that they can be designed to meet lubricity requirements equivalent to those of mineral oils used with chlorofluorocarbons (CFCs) and hydrochlorofluorocarbons (HCFCs), and their miscibility with refrigerants can be matched easily to that of mineral oil in R-12, R-502, or R-22. Thus, POE oils should have all of the oil-return characteristics similar to mineral oils with conventional chlorine-containing refrigerants.
POE oils offer the greatest level of flexibility because they are compatible with most commonly used refrigerants being introduced into the market. This flexibility should help reduce confusion over exactly which lubricants and refrigerants are compatible.
There are many types and grades of POE oils, so it is important to understand that not all POE oils are the same. Areas of differences include lubricity, miscibility with refrigerants, viscosity, additive packages, pour point, and moisture content. Always check with the compressor manufacturer or system OEM to find the grade of POE oil recommended before adding or changing the oil. Appropriately specified POE oils often times do not require lubricity additives. Although POE oils offer a variety of benefits for use with R-410A systems, it is important to handle, install, and service them properly.
HANDLING POE OILSPOE oils are more hygroscopic than mineral oils, so exposing POE oils to air will result in their absorbing moisture more quickly than mineral oils. When POE oils are exposed to moisture and heat, they may react, forming acid that is harmful to the system. If a POE system is open for the same amount of time service technicians are used to having mineral oil systems open, there is a much greater chance of moisture contamination of the oil and, consequently, downstream system concerns.
As a result, it is imperative that contractors keep containers of POE oils sealed, except when the oils are actually being dispensed. POE oils should also be stored properly in their original container because many plastics used to package oils are permeable to moisture. It is also important to keep compressors and systems closed, except when work is actually being done on the equipment, and to filter out undesirable contaminants. This can be achieved with proper installation and service techniques as well as the use of correct filters and driers.
When an R-22 system using mineral oil as a lubricant is being retrofitted with an HFC refrigerant of similar vapor pressure characteristics (such as R-407C), a new oil suitable for that refrigerant should be used. Moreover, it is suggested that the newly POE-charged system contain no more than 5 percent by volume residual mineral oil for most applications. Following this guideline by flushing the system prior to charging will mitigate mineral oil insolubility concerns. Guidelines are available from Emerson Climate Technologies Inc.
Our actual industry experience relating to the stability of POE oils over the years (given today’s current state of POE oil handling) has been extremely encouraging. Warranty ppm rates for oil-related compressor returns are insignificant. OEM warranty rates for HFC/POE compressors are lower than comparable R-22/mineral oil compressors.
FILTER DRIERS AND MOISTURE INDICATORS FOR POE OILSContractors should also use high water capacity filter driers in any new system. When compared to R-22-optimized driers, R-410A-optimized filter driers use less activated alumina and more molecular sieve for increased water capacity. It is important to follow OEM recommendations, if provided.
These filter driers remove moisture circulating through the refrigeration system and then hold that moisture to prevent it from contaminating the expansion device, evaporator, compressor, or oil. The use of driers is a good practice regardless of oil type to prevent ice formation inside the system. The filter separates particulate contamination from the refrigerant flow, preventing clogging of the expansion device, and the desiccant removes moisture from the refrigerant, preventing it from interacting with the POE oil. An R-410A optimized moisture-indicating sight glass can be used to ensure moisture levels are maintained at safe levels.
With the new regulations approaching, POE oils are the optimal lubricant choice for use with the new generation of chlorine-free HFC refrigerants, particularly R-410A. With proper installation and service techniques, as well as the use of the correct filter driers and moisture indicators, contractors can successfully work with and benefit from the many advantages that POE oils provide.
Publication date: 04/20/2009