Evaluating Lubricants For Lower GWP Refrigerant Compressor Operations

Refrigerant Lubricants are an essential component to refrigerant and air conditioning compressor operation regardless of the refrigerant used. But to maintain reliable and efficient operation, the choice of lubricant can vary depending on the type of compressor, design of the system and especially the kind of refrigerant. Historically, refrigerants used in applications have changed over the period of time since the invention of refrigeration due to various reasons. Today the global warming potential (GWP) value that exists for each refrigerant are being scrutinized if the GWP value is deemed too high which could result in a negative environmental impact. One of the so called high GWP refrigerants is R-404A which is on the fast track to be minimized through regional and global phase downs and potential phase outs. Various replacement/substitute refrigerants exist today that have been evaluated or are currently being evaluated as lower GWP choices in place of R-404A refrigerant. For R-404A the typical lubricant of choice has been a synthetic lubricant such as a polyolester (POE) which meets certain criteria for refrigerant and lubricant interaction. Replacement/substitute lower GWP refrigerants for R-404A will vary in the type of lubricant chemistry that is satisfactory for effective operation resulting in numerous lubricant selections.   This paper will evaluate lower GWP refrigerant options and what lubricant chemistry is best suited. Various rules that apply to what testing is needed to make the appropriate conclusions will be outlined and results of refrigerant and lubricant interaction will be presented. This data will then be used to determine how the changes in lower GWP refrigerant properties will dictate these lubricant options. This type of information will allow for maintaining the required compressor performance parameters associated with the industry

20/20 Vision – Interaction Of Lubricants And Next Generation Refrigerants

The refrigeration and air conditioning industry still struggle on a global level to identify a unified direction on next generation lower global warming potential (GWP) refrigerants. This includes what to do for original equipment changeover and retrofit change outs. Refrigerant suppliers are scrambling today to introduce their options to the market, some refrigerants have gained a foothold while others are still being evaluated or developed. Issues like refrigerant flammability levels, charge size restrictions and overall stability have limited a timely and smooth transition to lower GWP options. Despite the unknown situation, lubricant suppliers need to be ready with whatever direction is initiated with the ability to maintain current levels of standards for energy efficiency and reliability. This paper will examine the market through the eyes of a lubricant supplier with focus on how interaction and stabilization of the refrigerant and lubricant within a system needs to be evaluated and potentially improved due to the choice of refrigerants. Emphasis will be placed on finding lubricant and lubricant additive combinations that help to maintain HFC like expected performance with next generation refrigerants in various applications. Lower GWP refrigerant candidates will be evaluated, along with approaches to identifying lubricant formulations that are fit to be used in numerous situations and applications. A variety of testing methods using specialized equipment and techniques will be outlined with various lower GWP refrigerants and lubricant chemistries

Lubricant Development To Meet Lower GWP Refrigerant Challenges

The HVAC&R industry continues to be in a wait and see mode regarding what refrigerants will be acceptable for the future. Concerns in safety, energy efficiency and environmental acceptance have clouded the direction of future refrigerant acceptance. This uncertainty has led to the development of what might be called the next lower global warming potential (GWP) refrigerant revolution of products. Manufacturers of refrigerants, environmentalist and government bodies are all trying to lay claim to what they perceive as acceptable for commercial sustainability, environmental sustainability, regulatory sustainability or economic sustainability. While various refrigerant products and chemistries jockey for position, a number of HVAC&R companies are allocating resources to make initial evaluations. They are hoping they make the right future choice regarding availability, safety regulations, energy efficiency standards and the next environmental mandates. Sometimes lost in all the uncertainty and position jockeying is how this outcome will affect the lubricant being used or the potential need for alternative lubricant options. Like in the past, changes to refrigerants have usually led to some type of change to the system or to the compressor and in particular changes to the lubricant. This is no different today with some of the lower GWP refrigerant options that are being investigated or with already established lower GWP such as hydrocarbons, carbon dioxide and ammonia refrigerants that could benefit from lubricant-refrigerant optimization. The improper choice of a lubricant for a certain refrigerant can lead to serious consequences in system performance and reliability. Conversely the proper choice of lubricant or choices that help to optimize system performance can benefit by minimizing the use of precious natural resources of energy. This paper will investigate some of the most critical lubricant and lower GWP refrigerant combinations that could potentially affect the future of the industry. These combinations will require optimization to enhance current lubricant options or because current lubricant options are inadequate. Some of the lubricant and refrigerant options that will be discussed are: - HFO-1234ze(E) – high solubility factor with current lubricants. - HFO-1234yf – stability with current lubricants. - R-32 – miscibility and working viscosity differences. - HFO blends – uncertainty to which refrigerants will be used and best lubricant candidates. - Ruling out lubricants that are not good candidates. - Evaluating a matrix of various HFO blends and different lubricant chemistries and viscosities. - Hydrocarbon refrigerants – optimization versus traditional mineral oil based lubricants. Exhaustive studies in miscibility, lubricant-refrigerant stability tests and pressure-viscosity-temperature (PVT) interactions will be discussed and illustrated to show how these techniques are vital to finding the correct lubricant for the corresponding refrigerant. Once the right combinations are identified compressor reliability and performance tests can be used to justify the lubricant selection. The lubricant and refrigerant testing will also be compared to current activities that are taking place in the HVAC&R industry regarding lower GWP compressor and system testing. Providing some insight to how lubricant optimization requirements for some of the lower GWP refrigerants under investigation and being tested could benefit the overall performance of the system

Evaluation of Lubricant Properties and Refrigerant Interaction

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

Investigation Of Low GWP Refrigerant Interaction With Various Lubricant Candidates

Refrigerants used in various air conditioning and refrigeration industries are going through changes today and continued changes into the near future. These changes are being driven by environmental and energy efficiency regulations and could result in the use of refrigerants that require the investigation of new lubricants. One such change is the use of refrigerants that carry a lower global warming potential (GWP) value then current refrigerants used in the market. Some of these refrigerants present certain challenges over current refrigerants such as changes in flammability requirements, higher pressures or stability of the refrigerant in system operation. These refrigerants and the changes they represent may require different lubricants in order to maintain system optimization ensuring that energy efficiency and reliable requirements are met. The interaction between the refrigerant and the lubricant in any air conditioning or refrigeration system is a vital piece of information that is required to make certain optimal performance is achieved. The lubricant in a system is crucial to operation and needs to adequately lubricate the moving components in a system and return to the compressor when circulated. These conditions can drastically be affected by the refrigerant and lubricant interaction with improper choices resulting in consequences from lowering the overall performance to complete failure. This paper will look at some of the current and proposed low GWP refrigerants and their interaction with various lubricants. Evaluations will be made and certain properties will be presented that are essential to system operation. Of particular interest will be the refrigerant solubility factor of low GWP refrigerant candidates that can affect system performance and reliability; the stability of newer low GWP refrigerant candidates that maintain comparable current refrigerant system requirements; the miscibility of low GWP refrigerants with lubricants that can affect oil circulation; and how chemistry changes to various lubricants can help increase energy efficiency in systems operated with low GWP refrigerants. The information in this paper and the presentation will be a timely look at current and future needs for lubricants for various refrigerants that will help manufacturers in the air conditioning and refrigerant industry to evaluate the choices that need to be made in order to maintain the required system performance