Method for selecting lubricants for heat pumps

A method of introducing a refrigerant and a lubricant into a vapor compression refrigeration device system, comprising: a. to provide a vapor compression refrigeration device comprising a heat transfer circuit, a compressor having an inlet side and an outlet side, and a refrigerant and lubricant reservoir, wherein said reservoir is in fluid communication with the inlet side of the compressor and with said heat transfer circuit, and said heat transfer circuit is in fluid communication with said outlet side of the compressor; b. determining a lower operating temperature range for a vapor compression refrigeration device; c. determine an upper operating temperature range of the vapor compression refrigeration device; d. selecting a coolant comprising at least one C3 to C4 fluoroalkene in a first concentration and selecting a lubricant comprising at least one polyol or polyalkylene glycol ester in a second concentration to produce a fluid system having a coolant-rich phase and a coolant-rich phase in lubricant at a first temperature within said lower operating temperature range and at a second temperature within said lower operating temperature range. superior performance, provided that said second temperature is higher than said first temperature, wherein the refrigerant-rich phase is denser relative to the lubricant-rich phase at said first temperature, wherein the lubricant-rich phase is denser dense relative to the refrigerant-rich phase at said second temperature, and wherein the difference in density between the refrigerant-rich phase and the lubricant-rich phase is 20% or less; and e. introducing said refrigerant and lubricant into the vapor compression refrigeration device.