Lubricants, Refrigerants, HFO, Optimization, Sustainability
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.