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A refrigeration system (20A) comprises an evaporator (27) for evaporating a refrigerant, a two-stage compressor (32) for compressing the refrigerant, a single-stage compressor (34) for compressing the refrigerant, a heat rejecting heat exchanger (24) for cooling the refrigerant, a first economizer c

A refrigeration system (20A) comprises an evaporator (27) for evaporating a refrigerant, a two-stage compressor (32) for compressing the refrigerant, a single-stage compressor (34) for compressing the refrigerant, a heat rejecting heat exchanger (24) for cooling the refrigerant, a first economizer circuit (25A), and a second economizer circuit (25B). The first economizer circuit (25A) is configured to inject refrigerant into an interstage port (48) of the two-stage compressor (32). The second economizer circuit (25B) is configured to inject refrigerant into a suction port (52) of the single-stage compressor (34). The single-stage compressor (34) is configured to discharge into the interstage port (48) of the two-stage compressor (32).

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1. A refrigeration system comprising: an evaporator,a two-stage compressor for compressing a refrigerant, the two-stage compressor having a suction port, an interstage port, and a discharge port;a first single-stage compressor for compressing the refrigerant, the first single-stage compressor having

1. A refrigeration system comprising: an evaporator,a two-stage compressor for compressing a refrigerant, the two-stage compressor having a suction port, an interstage port, and a discharge port;a first single-stage compressor for compressing the refrigerant, the first single-stage compressor having a suction port and a discharge port, wherein the first single-stage compressor is configured to discharge into the interstage port of the two-stage compressor;a heat rejecting heat exchanger for cooling the refrigerant;a first economizer circuit configured to inject refrigerant into the interstage port of the two-stage compressor, the first economizer circuit having an economizer heat exchanger and an expansion valve; anda second economizer circuit configured to inject refrigerant into the suction port of the first single-stage compressor, the second economizer circuit having an economizer heat exchanger and an expansion valve. 2. The refrigeration system of claim 1, and further comprising: a second single-stage compressor for compressing the refrigerant, the second single-stage compressor having a suction port and a discharge port; anda third economizer circuit configured to inject refrigerant into the suction port of the second single-stage compressor. 3. The refrigeration system of claim 2, wherein the second single-stage compressor is configured to discharge into the interstage port of the two-stage compressor. 4. The refrigeration system of claim 1, wherein the two-stage compressor and the first single-stage compressor are part of a single, multi-cylinder compressor unit. 5. The refrigeration system of claim 1, wherein the heat rejecting heat exchanger is a condenser. 6. The refrigeration system of claim 1, wherein the heat rejecting heat exchanger is a gas cooler. 7. The refrigeration system of claim 1, wherein the refrigerant is carbon dioxide. 8. The refrigeration system of claim 1, wherein the economizer heat exchangers of the first and second economizer circuits form a brazed plate heat exchanger. 9. The refrigeration system of claim 1, wherein the economizer heat exchangers of the first and second economizer circuits are flash tanks. 10. The refrigeration system of claim 1, wherein the expansion valves of the first and second economizer circuits are thermal expansion valves. 11. The refrigeration system of claim 1, wherein the expansion valves of the first and second economizer circuits are electronic expansion valves. 12. A refrigeration system comprising: an evaporator;a two-stage compressor for compressing a refrigerant, the two-stage compressor having a suction port, an interstage port, and a discharge port;a plurality of single-stage compressors for compressing the refrigerant, wherein one or more of the compressors is configured to discharge into the interstage port of the two-stage compressor;a heat rejecting heat exchanger for cooling the refrigerant;an interstage economizer heat exchanger configured to discharge into the interstage port of the two-stage compressor; anda plurality of parallel economizer heat exchangers, wherein each of the parallel economizer heat exchangers is configured to discharge into one of the plurality of single-stage compressors. 13. The refrigeration system of claim 12, wherein the two-stage compressor and the single-stage compressors are part of a single, multi-cylinder compressor unit. 14. The refrigeration system of claim 12, wherein the refrigerant is carbon dioxide. 15. The refrigeration system of claim 12, wherein the interstage and parallel economizer heat exchangers each include an expansion valve. 16. The refrigeration system of claim 15, wherein the expansion valve is a thermal expansion valve. 17. The refrigeration system of claim 15, wherein the expansion valve is an electronic expansion valve. 18. A method of operating a refrigeration system, the method comprising: evaporating a refrigerant;compressing the refrigerant from a lower pressure to a higher pressure in a plurality of compressors, the plurality of compressors including a two-stage compressor and at least one single-stage compressor;cooling the refrigerant;directing the refrigerant through a plurality of economizer heat exchangers each having a main path and an economized path;injecting a first portion of the refrigerant from the economized path of one of the economizer heat exchangers into an interstage port of the two-stage compressor,injecting a second portion of the refrigerant from the economized path of another one of the economizer heat exchangers into a suction port of one of the single-stage compressors; anddischarging the second portion of the refrigerant into the interstage port of the two-stage compressor. 19. The method of claim 18, wherein the refrigerant is carbon dioxide. 20. The method of claim 18, wherein the compressors are part of a single, multi-cylinder compressor unit.