A method for exchanging heat in a vapor compression heat transfer system having a working fluid circulating therethrough, comprising the steps of: (a) circulating a working fluid to an inlet of a first tube of an internal heat exchanger, through the internal heat exchanger and to an outlet thereof; (b) circulating the working fluid from the outlet of the first tube of the internal heat exchanger to an inlet of an evaporator, through the evaporator to evaporate the working fluid, thereby convert it Into a gaseous working fluid, and through an outlet of the evaporator; (c) circulating the working fluid from the outlet of the evaporator to an inlet of a second tube of the internal heat exchanger to transfer heat from the liquid working fluid from the condenser to the gaseous working fluid from the evaporator, through the internal heat exchanger, and to an outlet of the second tube; (d) circulating the working fluid from the outlet of the second tube of the internal heat exchanger to an inlet of a compressor, through the compressor to compress the gaseous working fluid, and to an outlet of the compressor; (e) circulating the working fluid from the outlet of the compressor to an inlet of a condenser and through the condenser to condense the compressed gaseous working fluid into a liquid, and to an outlet of the condenser; (f) circulating the working fluid from the outlet of the condenser to an inlet of the first tube of the internal heat exchanger to transfer heat from the liquid from the condenser to the gas from the evaporator, and to an outlet of the first tube; and (g) circulating the working fluid from the outlet of the first tube of the internal heat exchanger back to the evaporator, characterized in that the working fluid comprises HFC-1234yf and wherein the first tube has a larger diameter than the second tube, and the second tube is disposed concentrically in the first tube, and a hot liquid in the first tube surrounds a cool gas in the second tube. (a) circulating a working fluid to an inlet of a first tube of an internal heat exchanger, through the internal heat exchanger and to an outlet thereof; (b) circulating the working fluid from the outlet of the first tube of the internal heat exchanger to an inlet of an evaporator, through the evaporator to evaporate the working fluid, thereby convert it Into a gaseous working fluid, and through an outlet of the evaporator; (c) circulating the working fluid from the outlet of the evaporator to an inlet of a second tube of the internal heat exchanger to transfer heat from the liquid working fluid from the condenser to the gaseous working fluid from the evaporator, through the internal heat exchanger, and to an outlet of the second tube; (d) circulating the working fluid from the outlet of the second tube of the internal heat exchanger to an inlet of a compressor, through the compressor to compress the gaseous working fluid, and to an outlet of the compressor; (e) circulating the working fluid from the outlet of the compressor to an inlet of a condenser and through the condenser to condense the compressed gaseous working fluid into a liquid, and to an outlet of the condenser; (f) circulating the working fluid from the outlet of the condenser to an inlet of the first tube of the internal heat exchanger to transfer heat from the liquid from the condenser to the gas from the evaporator, and to an outlet of the first tube; and (g) circulating the working fluid from the outlet of the first tube of the internal heat exchanger back to the evaporator, characterized in that the working fluid comprises HFC-1234yf and wherein the first tube has a larger diameter than the second tube, and the second tube is disposed concentrically in the first tube, and a hot liquid in the first tube surrounds a cool gas in the second tube.