refrigerant, lubricant, POE, solution properties, R-404A equivalent
Lubricants are important components of almost all air conditioning and refrigeration systems. Their primary function is to lubricate the compressor, provide sealing of clearances between low and high pressure sides of the compressor and remove frictional heat. But the lubricant is in contact with refrigerant at all times in the refrigeration cycle and plays a thermo-fluidic role that can impact both system capacity and coefficient of performance (COP). Lubricants can influence capacity by altering the refrigerant-side heat transfer coefficients, and increasing pressure drop required to maintain set point temperatures. Lubricants can also affect the isentropic efficiency of the compressor.Â Recent research has conclusively demonstrated that the optimization of lubricant/refrigerant properties can provide improvements in energy efficiency and COP.Â Examples of optimization of refrigerant/lubricant properties for improved energy efficiency have been demonstrated for pure refrigerants such as R-32, R-744 and R-290.Â This paper discusses the extension of our previous techniques for refrigerant/lubricant optimization to low global warming potential refrigerant blends; in particular, to mildly flammable alternatives to R-404A (GWP= 3952) with GWP < 150.Â The first part of the presentation is a comparison between refrigerant/lubricant solution property data for R-404A and various low GWP candidate replacement refrigerants with a commercial ISO 32 polyol ester (POE) compressor lubricant. The second part summarizes a study of solution phase behavior and solution property data for one low GWP R-404A candidate refrigerant in combination with a number of POE lubricants of varied chemical structure and correspondingly varied solubility/miscibility with the refrigerant. The trends in solution viscosities and composition are correlated to performance in full system tests that are presented in a separate paper. The results suggest that there are opportunities to improve system performance through proper matching of lubricant chemical structure and compatibility with the refrigerant.