A first and a second expansion and compression machine (30, 40) having different volume ratios (Vc/Ve) are connected in parallel to a refrigerant circuit (10) of a refrigeration apparatus. Expanders (31, 41) of the expansion and compression machines (30, 40) are connected in parallel. Compressors (3
A first and a second expansion and compression machine (30, 40) having different volume ratios (Vc/Ve) are connected in parallel to a refrigerant circuit (10) of a refrigeration apparatus. Expanders (31, 41) of the expansion and compression machines (30, 40) are connected in parallel. Compressors (32, 42) of the expansion and compression machines (30, 40) are also connected in parallel. Upon variation in the operating condition of the refrigeration apparatus, the ratio of rotation speed between the expansion and compression machines (30, 40) is controlled by a controller (60). This, as a result, allows the refrigeration apparatus to operate at a COP close to an ideal condition.
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What is claimed is: 1. A refrigeration apparatus comprising a refrigerant circuit in which a refrigeration cycle is performed by circulation of refrigerant therethrough and a fluid machine connected to the refrigerant circuit, the fluid machine including an expander, a compressor, and a rotation sh
What is claimed is: 1. A refrigeration apparatus comprising a refrigerant circuit in which a refrigeration cycle is performed by circulation of refrigerant therethrough and a fluid machine connected to the refrigerant circuit, the fluid machine including an expander, a compressor, and a rotation shaft for coupling together the expander and the compressor; wherein a plurality of the fluid machines are connected to the refrigerant circuit; wherein the expanders of the fluid machines are mutually connected in parallel; and wherein the compressors of the fluid machines are also mutually connected in parallel, wherein, where the suction volume of refrigerant drawn into the compressor per one rotation of the rotation shaft of each of the plurality of the fluid machines is expressed by Vc and the inflow volume of refrigerant flowing into the expander per one rotation of the rotation shaft of each of the plurality of the fluid machines is expressed by Ve, the plurality of the fluid machines are configured such that they differ from each other in the volume ratio, Vc/Ve, of the suction volume Vc to the inflow volume Ve. 2. The refrigeration apparatus of claim 1, further comprising: a controller which provides individual control of the rotation speed of each of the rotation shafts of the plurality of the fluid machines. 3. The refrigeration apparatus of claim 1, wherein the plurality of the fluid machines are configured such that they have the same value for the suction volume Vc. 4. The refrigeration apparatus of claim 1, wherein the refrigerant circuit is provided with an expansion valve which is disposed on the inflow side of the expander of only one of the plural fluid machines that has the largest value for the volume ratio Vc/Ve thereamong. 5. The refrigeration apparatus of any one of claims 1-4, wherein the refrigerant in the refrigerant circuit is CO2. 6. The refrigeration apparatus of claim 2, further comprising: a temperature sensor sensing at least one of an outdoor temperature and refrigerant evaporation temperature, wherein the controller controls the rotation speed based on the sensed temperature. 7. The refrigeration apparatus of claim 2, further comprising: a pressure sensor configured to measure a high pressure and a low pressure of the refrigerant. 8. The refrigeration apparatus of claim 6, wherein the controller controls a first fluid machine of the plurality of fluid machines to operate at a first rotation speed while controlling all others of the plurality of fluid machines to stop when the sensed temperature is at a first design point, the controller controls a second fluid machine of the plurality of fluid machines to operate at a second rotation speed while controlling all others of the plurality of fluid machines to stop when the sensed temperature is at a second design point, and the controller controls the first fluid machine and the second fluid machine to operate at a third rotation speed and a fourth rotation speed, respectively, when the sensed temperature is between the first design point and the second design point. 9. The refrigeration apparatus of claim 1, wherein the inflow volume of each expander of the plurality of the fluid machines is different than all other expanders. 10. The refrigeration apparatus of claim 9, wherein the inflow volume of a first expander is 5 cc, and the inflow volume of a second expander is 1.33 cc. 11. The refrigeration apparatus of claim 9, wherein the suction volume of each compressor of the plurality of fluid machines is 20 cc. 12. The refrigeration apparatus of claim 1, wherein a first fluid machine of the plurality of fluid machines satisfies Vc/Ve=de1/dc1, where de1 is expander inflow refrigerant density at a first operating condition, and dc1 is compressor suction refrigerant density at the first operating condition, and a second fluid machine of the plurality of fluid machines satisfies Vc/Ve=de2/dc2, where de2 is expander inflow refrigerant density at a second operating condition, and dc2 is compressor suction refrigerant density at the second operating condition. 13. The refrigeration apparatus of claim 12, wherein the first fluid machine of the plurality of fluid machines has a ratio of Vc/Ve equal to 20, and the second fluid machine of the plurality of fluid machines has a ratio of Vc/Ve equal to 4. 14. The refrigeration apparatus of claim 1, further comprising: a controller which controls a ratio of rotation speed between the plurality of the fluid machines in response to an operating condition when the plurality of the fluid machines are simultaneously operated.
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