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A transcritical vapor compression system includes a fluid circuit circulating a refrigerant in a closed loop. The fluid circuit has operably disposed therein, in serial order, a compressor, a first heat exchanger, at least one non-variable expansion device and a second heat exchanger. The compressor

A transcritical vapor compression system includes a fluid circuit circulating a refrigerant in a closed loop. The fluid circuit has operably disposed therein, in serial order, a compressor, a first heat exchanger, at least one non-variable expansion device and a second heat exchanger. The compressor compresses the refrigerant from a low pressure to a supercritical pressure. The first heat exchanger is positioned in a high pressure side of the fluid circuit. The second heat exchanger is positioned in a low pressure side of the fluid circuit. The at least one non-variable expansion device reduces the pressure of the refrigerant from a supercritical pressure to a relatively lower pressure. A refrigerant storage vessel is in fluid communication with the fluid circuit and contains a variable mass of refrigerant whereby the capacity of the system may be controlled.

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What is claimed is: 1. A transcritical vapor compression system comprising: a fluid circuit circulating a refrigerant in a closed loop, said fluid circuit having operably disposed therein, in serial order, a compressor, a first heat exchanger, at least one non-variable expansion device and a second

What is claimed is: 1. A transcritical vapor compression system comprising: a fluid circuit circulating a refrigerant in a closed loop, said fluid circuit having operably disposed therein, in serial order, a compressor, a first heat exchanger, at least one non-variable expansion device and a second heat exchanger wherein said compressor compresses the refrigerant from a low pressure to a supercritical pressure, said first heat exchanger is positioned in a high pressure side of said fluid circuit and contains refrigerant at a first supercritical pressure and said second heat exchanger is positioned in a low pressure side of said fluid circuit and contains refrigerant at a second subcritical pressure, said at least one non-variable expansion device reducing the pressure of the refrigerant from a supercritical pressure to a relatively lower subcritical pressure wherein said at least one non-variable expansion device defines a pressure reduction substantially equivalent to the pressure difference between said first pressure and said second pressure; a refrigerant storage vessel in fluid communication with said fluid circuit via an open fluid conduit which provides both outflow and inflow of refrigerant to and from said refrigerant vessel and said fluid circuit, said refrigerant storage vessel having a variable mass of refrigerant stored therein; and a thermal control device disposed in thermal exchange relationship with said refrigerant storage vessel, wherein the mass of refrigerant within said refrigerant storage vessel is adjustable with said thermal control device to in turn adjust the mass of refrigerant in said fluid circuit. 2. The system of claim 1 wherein said refrigerant storage vessel is in communication with said fluid circuit between said first heat exchanger and said at least one non-variable expansion device. 3. The system of claim 1 wherein said at least one non-variable expansion device comprises two non-variable expansion devices disposed in said fluid circuit between said first and second heat exchangers, said refrigerant storage vessel being disposed in fluid communication with the fluid circuit between said non-variable expansion devices. 4. The system of claim 1 wherein said non-variable expansion device comprises at least one capillary tube. 5. The system of claim 1 wherein said non-variable expansion device comprises at least one fixed orifice expansion device. 6. The system of claim 1 wherein said thermal control device comprises a third heat exchanger disposed between said second heat exchanger and said compressor. 7. The system of claim 6 wherein said thermal control device further comprises an air moving device configured to move air across said third heat exchanger and toward said refrigerant storage vessel. 8. The system of claim 1 wherein said compressor is a two stage compressor having a first compressor mechanism compressing the refrigerant from the low pressure to an intermediate pressure and a second compressor mechanism compressing the refrigerant from the intermediate pressure to a supercritical pressure, said fluid circuit further including a fluid line providing communication from said refrigerant storage vessel to a location in said fluid circuit between said first and second compressor mechanisms. 9. The system of claim 8 wherein said at least one non-variable expansion device comprises two non-variable expansion devices, said refrigerant storage vessel being disposed in fluid communication with the fluid circuit between said non-variable expansion devices. 10. The system of claim 1 wherein said thermal control device comprises a heating element. 11. The system of claim 1 wherein said thermal control device comprises a conduit containing a fluid, the fluid in thermal exchange relationship with the refrigerant. 12. The system of claim 1 wherein said refrigerant storage vessel is in fluid communication with said fluid circuit via a single conduit. 13. A transcritical vapor compression system comprising: a fluid circuit circulating a refrigerant in a closed loop, said fluid circuit having operably disposed therein, in serial order, a compressor, a first heat exchanger, at least one non-variable expansion device and a second heat exchanger wherein said compressor compresses the refrigerant from a low pressure to a supercritical pressure, said first heat exchanger is positioned in a high pressure side of said fluid circuit and contains refrigerant at a first supercritical pressure and said second heat exchanger is positioned in a low pressure side of said fluid circuit and contains refrigerant at a second subcritical pressure, said at least one non-variable expansion device reducing the pressure of the refrigerant from a supercritical pressure to a relatively lower pressure wherein said at least one non-variable expansion device defines a pressure reduction substantially equivalent to the pressure difference between said first pressure and said second pressure; a refrigerant storage vessel in fluid communication with said fluid circuit between said first and second heat exchangers; and a temperature adjustment device disposed in thermal exchange with said refrigerant storage vessel, said temperature adjustment device operable to transfer heat to refrigerant in said storage vessel and to remove heat from refrigerant in said storage vessel wherein a temperature of refrigerant in said refrigerant storage vessel is adjustable with said temperature adjustment device. 14. The system of claim 13 wherein said temperature adjustment device comprises an air moving device configured to move air across said refrigerant storage vessel. 15. The system of claim 14 wherein said temperature adjustment device further comprises a third heat exchanger disposed between said second heat exchanger and said compressor, said air moving device moving air across said third heat exchanger toward said refrigerant storage vessel. 16. The system of claim 13 wherein selective operation of said temperature adjustment device controls the mass of the refrigerant in said refrigerant storage vessel. 17. The system of claim 13 wherein said refrigerant storage vessel is in communication with said fluid circuit between said first heat exchanger and said at least one non-variable expansion device. 18. The system of claim 13 wherein said at least one non-variable expansion device comprises two non-variable expansion devices disposed in said fluid circuit between said first and second heat exchangers, said refrigerant storage vessel being disposed in communication with the fluid circuit between said non-variable expansion devices. 19. The system of claim 13 wherein said compressor is a two stage compressor having a first compressor mechanism compressing the refrigerant from the low pressure to an intermediate pressure and a second compressor mechanism compressing the refrigerant from the intermediate pressure to a supercritical pressure, said fluid circuit further including a fluid line providing communication from said refrigerant storage vessel to a location in said fluid circuit between said first and second compressor mechanisms. 20. The system of claim 19 wherein said at least one non-variable expansion device comprises two non-variable expansion devices, said refrigerant storage vessel being disposed in communication with the fluid circuit between said non-variable expansion devices. 21. The system of claim 13 wherein said temperature adjustment device comprises a heating element. 22. The system of claim 13 wherein said temperature adjustment device comprises a conduit containing a fluid, the fluid in thermal exchange relationship with the refrigerant. 23. The system of claim 13 wherein said refrigerant storage vessel is in fluid communication with said fluid circuit via a single conduit. 24. A method of controlling a transcritical vapor compression system, said method comprising: providing a fluid circuit circulating a refrigerant in a closed loop, the fluid circuit having operably disposed therein, in serial order, a compressor, a first heat exchanger, at least one non-variable expansion device and a second heat exchanger; compressing the refrigerant from a low pressure to a supercritical pressure in the compressor; removing thermal energy from the refrigerant in the first heat exchanger; reducing the pressure of the refrigerant in the at least one non-variable expansion device wherein said at least one non-variable expansion device defines a pressure reduction substantially equivalent to a pressure difference between a first supercritical pressure of the refrigerant within the first heat exchanger and a second subcritical pressure of the refrigerant within the second heat exchanger; adding thermal energy to the refrigerant in the second heat exchanger; providing a refrigerant storage vessel in fluid communication with said fluid circuit via an open fluid conduit which provides both outflow and inflow of refrigerant to and from the refrigerant storage vessel and the fluid circuit; providing a thermal control device in thermal exchange relationship with the refrigerant storage vessel; and controlling the mass of refrigerant in the refrigerant storage vessel with the thermal control device to thereby control the mass of refrigerant in the fluid circuit and thereby regulate the capacity of the system. 25. The method of claim 24 wherein the step of controlling the mass of refrigerant in the refrigerant storage vessel comprises controlling the temperature of the refrigerant in the refrigerant storage vessel. 26. The method of claim 24 wherein reducing the pressure of the refrigerant in the at least one non-variable expansion device comprises reducing the pressure of the refrigerant in two non-variable expansion devices. 27. The method of claim 24 wherein the compressor comprises a first compressor mechanism compressing the refrigerant from the low pressure to an intermediate pressure, a second compressor mechanism compressing the refrigerant from the intermediate pressure to the supercritical pressure, and a first fluid line communicating refrigerant from the first compressor mechanism to the second compressor mechanism, the method further comprising providing the fluid circuit with a second fluid line communicating refrigerant from the refrigerant storage vessel to the first fluid line. 28. The method of claim 27 wherein reducing the pressure of the refrigerant in the at least one non-variable expansion device comprises reducing the pressure of the refrigerant in two non-variable expansion devices and the refrigerant storage vessel is disposed in communication with the fluid circuit between the two non-variable expansion devices. 29. A compression system comprising: a fluid circuit circulating a refrigerant in a closed loop, said fluid circuit having operably disposed therein, in serial order, a compressor, a first heat exchanger, at least one expansion device and a second heat exchanger wherein said compressor compresses the refrigerant from a low pressure to a high pressure, said first heat exchanger is positioned in a high pressure side of said fluid circuit and contains refrigerant at the high pressure and said second heat exchanger is positioned in a low pressure side of said fluid circuit and contains refrigerant at the low pressure, said at least one expansion device reducing the pressure of the refrigerant from the high pressure to the low pressure and defining a pressure reduction substantially equivalent to the pressure difference between the low pressure and the high pressure; a refrigerant storage vessel in fluid communication with said fluid circuit, said refrigerant storage vessel having a variable mass of refrigerant therein; and a thermal control device disposed in thermal exchange relationship with said refrigerant storage vessel, said temperature adjustment device operable to transfer heat to refrigerant in said storage vessel and to remove heat from refrigerant in said storage vessel wherein the mass of refrigerant within said refrigerant storage vessel is adjustable with said thermal control device to in turn adjust the mass of refrigerant in said fluid circuit. 30. The system of claim 29 wherein said thermal control device comprises a heating element. 31. The system of claim 29 wherein said thermal control device comprises an air moving device configured to move air across said refrigerant storage vessel. 32. The system of claim 29 wherein said thermal control device comprises a conduit containing a fluid, the fluid in thermal exchange relationship with the refrigerant. 33. The system of claim 29 wherein said refrigerant storage vessel is in fluid communication with said fluid circuit via a single conduit. 34. A transcritical vapor compression system comprising: a fluid circuit circulating a refrigerant in a closed loop, said fluid circuit having operably disposed therein, in serial order, a compressor, a first heat exchanger, at least one non-variable expansion device and a second heat exchanger wherein said compressor compresses the refrigerant from a low pressure to a supercritical pressure, said first heat exchanger is positioned in a high pressure side of said fluid circuit and contains refrigerant at a first supercritical pressure and said second heat exchanger is positioned in a low pressure side of said fluid circuit and contains refrigerant at a second subcritical pressure, said at least one non-variable expansion device reducing the pressure of the refrigerant from a supercritical pressure to a relatively lower subcritical pressure wherein said at least one non-variable expansion device defines a pressure reduction substantially equivalent to the pressure difference between said first pressure and said second pressure; a refrigerant storage vessel in fluid communication with said fluid circuit, said refrigerant storage vessel having a variable mass of refrigerant stored therein; and a thermal control device disposed in thermal exchange relationship with said refrigerant storage vessel, wherein the mass of refrigerant within said refrigerant storage vessel is adjustable with said thermal control device to in turn adjust the mass of refrigerant in said fluid circuit, wherein said thermal control device comprises an air moving device configured to move air across said refrigerant storage vessel.