Refrigerant vapor compression system with flash tank economizer

A refrigerant vapor compression system comprising:

• a primary refrigerant circuit including a refrigerant compression device, a refrigerant heat rejection heat exchanger for passing refrigerant received from said compression device at a high pressure in heat exchange relationship with a cooling medium, a refrigerant heat absorption heat exchanger for passing refrigerant at a low pressure refrigerant in heat exchange relationship with a heating medium, and a primary expansion device interdisposed in the primary refrigerant circuit downstream of said refrigerant cooling heat exchanger and upstream of said refrigerant heating heat exchanger;
• a flash tank disposed in the primary refrigerant circuit downstream of the refrigerant heat rejection heat exchanger and upstream of said primary expansion device, said flash tank defining a separation chamber wherein refrigerant in a liquid state collects in a lower portion of said separation chamber and refrigerant in a vapor state in a portion of said separation chamber above the liquid refrigerant;
• a secondary expansion device disposed in the primary refrigerant circuit in operative association with and upstream with of said flash tank;
• a refrigerant vapor line establishing refrigerant flow communication between an upper portion of said separation chamber and an intermediate pressure stage of said compression device and a suction pressure portion of said primary refrigerant circuit;
• a refrigerant liquid line establishing refrigerant flow communication between a lower portion of said separation chamber and an intermediate pressure stage of said compression device and a suction pressure portion of said primary refrigerant circuit;
• and
• a refrigerant-to-refrigerant heat exchanger operative to transfer heat from refrigerant flowing through the primary refrigerant circuit to refrigerant flowing through said refrigerant vapor line;
• wherein said refrigerant-to-refrigerant heat exchanger has a first refrigerant pass and a second refrigerant pass disposed in heat exchange relationship, the first refrigerant pass interdisposed in the primary refrigerant circuit intermediate the refrigerant heat rejection heat exchanger and said secondary expansion valve, the second refrigerant pass in refrigerant flow communication with said refrigerant vapor line;
• a first economizer flow control device interdisposed in said refrigerant vapor line intermediate said flash tank and an intermediate stage of said compression device;
• a refrigerant bypass line establishing refrigerant flow communication between said refrigerant vapor line at a point upstream with respect to refrigerant flow and said refrigerant vapor line at a point downstream with respect to refrigerant flow, the second refrigerant pass of said refrigerant-to-refrigerant heat exchanger interdisposed in said refrigerant bypass line;
• a second economizer flow control device interdisposed in said refrigerant bypass line upstream with respect to refrigerant flow of the second refrigerant pass of said refrigerant-to-refrigerant heat exchanger;
• a third flow control device interdisposed in an upstream portion of said refrigerant liquid line;
• a fourth flow control device disposed upstream with respect to refrigerant flow of said intermediate pressure stage of said compression device and downstream with respect to refrigerant flow of both said first economizer flow control device and said second economizer flow control device and said third flow control device;
• and
• a fifth flow control device disposed upstream with respect to refrigerant flow of said suction pressure portion of said primary refrigerant circuit and downstream with respect to refrigerant flow of both said first economizer flow control device and said second economizer flow control device and said third flow control device.