R-744 system with hot gas defrost by the transcritical compressors

1. A transcritical R-744 refrigeration system ( 50 ) with a transcritical medium temperature section ( 52 ) having a plurality of circuits, at least one medium temperature evaporator ( 11 ) receiving an R-744 refrigerant in a medium-pressure liquid state from a receiver ( 8 ) and feeding at least one medium temperature compressor ( 1 ) to compress the R-744 refrigerant from a low-pressure gaseous state into a high-pressure gaseous state to feed a gas cooler ( 5 ) and a pressure reducing device ( 7 ) to partially condense the R-744 refrigerant into a medium-pressure gaseous-liquid state, the system ( 50 ) comprising:

a pressure reducing valve ( 41 ) directly connected to a discharge conduit ( 2 ) of the at least one medium temperature compressor ( 1 ) and directly feeding a portion of said R-744 refrigerant in hot gas phase to a defrost manifold ( 19 , 18 ) to defrost one of the plurality of circuits of the transcritical medium temperature section ( 52 ) or one of a plurality of circuits of a subcritical low temperature section ( 54 );

said pressure reducing valve ( 41 ) reducing a pressure of said portion of said R-744 refrigerant in hot gas phase flowing therethrough and being fed to said defrost manifold ( 19 , 18 ) to a pressure value less than or equal to a maximum operating pressure of the at least one medium temperature evaporator ( 11 ) or of at least one low temperature evaporator ( 12 ) of the subcritical low temperature section ( 54 ), respectively.

2. The transcritical R-744 refrigeration system ( 50 ) of claim 1 , further comprising a heat exchanger ( 43 ) downstream of said pressure reducing valve ( 41 ), said heat exchanger ( 43 ) transferring heat from the high-pressure gaseous state of said R-744 refrigerant from the at least one medium temperature compressor ( 1 ) and fed to the gas cooler ( 5 ) to the hot gas phase of said portion of said R-744 refrigerant exiting said pressure reducing valve ( 41 ).

3. The transcritical R-744 refrigeration system ( 50 ) of claim 1 , wherein the receiver ( 8 ) is a flash tank.

4. The transcritical R-744 refrigeration system ( 50 ) of claim 1 , wherein the refrigerant exiting the at least one medium temperature compressor ( 1 ) passes through an oil separator ( 3 ) before reaching said pressure reducing valve ( 41 ).

5. The transcritical R-744 refrigeration system ( 50 ) of claim 1 , further comprising an additional defrost manifold ( 27 ) in the transcritical medium temperature section ( 52 ) between said at least one medium temperature evaporator ( 11 ) and the receiver ( 8 ).

6. The transcritical R-744 refrigeration system ( 50 ) of claim 5 , further comprising a pressure regulating valve ( 29 ) to regulate the pressure of the refrigerant in said additional defrost manifold ( 27 ) before entering the receiver ( 8 ).

7. The transcritical R-744 refrigeration system ( 50 ) of claim 1 , further comprising a plurality of check valves ( 36 , 39 ) to prevent any hot gas phase of said portion of said R-744 refrigerant from entering a liquid line.

8. The transcritical R-744 refrigeration system ( 50 ) of claim 1 , further comprising a safety valve ( 46 ) connected to said defrost manifold ( 19 ).

9. The transcritical R-744 refrigeration system ( 50 ) of claim 1 , wherein said at least one low temperature evaporator ( 12 ) receiving the R-744 refrigerant from the receiver ( 8 ) and feeding at least one low temperature compressor ( 20 ).

10. The transcritical R-744 refrigeration system ( 50 ) of claim 9 , further comprising an additional defrost manifold ( 26 ) in the subcritical low temperature section ( 54 ) between said at least one low temperature evaporator ( 12 ) and the receiver ( 8 ).