JP5028481B2 - Multistage compressor unit for refrigeration system - Google Patents

Description

  The present invention relates generally to compressors used in refrigeration systems. More particularly, the present invention relates to a multi-stage compressor unit for a refrigeration system that includes at least one two-stage compressor subunit.

  A typical refrigeration system includes an evaporator, a compressor, a condenser, and a throttle valve. A refrigerant, such as hydrofluorocarbon (HFC), typically enters the evaporator as a two-phase liquid-vapor mixture. In the evaporator, as a result of heat transfer to the refrigerant, the liquid portion of the refrigerant changes phase from liquid to vapor. The refrigerant is then compressed in the compressor, thereby increasing the refrigerant pressure. The refrigerant then passes through the condenser where it changes phase from vapor to liquid while being cooled. Finally, the refrigerant expands as it passes through the throttle valve, resulting in a decrease in pressure and a phase change from a liquid to a two-phase liquid-vapor mixture.

  Recently, natural refrigerants such as carbon dioxide have been proposed as an alternative to the currently used HFCs, but the high side pressure of carbon dioxide generally ends up in the supercritical region, where there is a high pressure refrigerant. There is no vapor-to-liquid transition when the is cooled. Therefore, in a normal single-stage vapor compression cycle, the efficiency is degraded due to losses during the subcritical isothermal condensation process and the relatively high residual enthalpy of supercritical carbon dioxide at the normal higher temperature.

  Accordingly, there is a need for a compressor unit for a refrigeration system that can utilize any refrigerant, including a transcritical refrigerant, while facilitating maintaining the efficiency of the refrigeration system at a high level.

  The present invention is a multi-stage compressor unit for a refrigeration system configured to circulate refrigerant. The multi-stage compressor unit includes a first compressor subunit having a first stage and a second stage, and a second compressor sub having a first stage in parallel with the first compressor subunit. A unit. Each of the first and second stages of the first compressor subunit has a suction port and a discharge port. The first compressor subunit is configured to receive and compress a first portion of refrigerant from the evaporator. The first stage of the second compressor subunit has a suction port and a discharge port. The second compressor subunit is configured to compress the second portion of the refrigerant.

Schematic illustrating a first alternative embodiment of a multi-stage compressor unit connected to a refrigeration system. 1B is a graph relating the enthalpy of the refrigeration system of FIG. 1A to pressure. Schematic illustrating a second alternative embodiment of a multi-stage compressor unit connected to a refrigeration system. 2B is a graph relating the enthalpy of the refrigeration system of FIG. 2A to pressure. Schematic illustrating a third alternative embodiment of a multi-stage compressor unit connected to a refrigeration system. FIG. 3B is a graph relating the enthalpy of the refrigeration system of FIG. 3A to pressure. Schematic illustrating a fourth alternative embodiment of a multi-stage compressor unit connected to a refrigeration system. 4B is a graph relating the enthalpy of the refrigeration system of FIG. 4A to pressure. Schematic illustrating a fifth alternative embodiment of a multi-stage compressor unit connected to a refrigeration system. FIG. 5B is a graph relating the enthalpy of the refrigeration system of FIG. 5A to pressure. Schematic illustrating a sixth alternative embodiment of a multi-stage compressor unit connected to a refrigeration system. FIG. 6B is a graph relating the enthalpy of the refrigeration system of FIG. 6A to pressure.

  FIG. 1A illustrates a schematic diagram of a multi-stage compressor unit 10A connected to a refrigeration system 20A. The refrigeration system 20A includes a heat removal heat exchanger 24, a first economizer circuit 25A, a main expansion valve 26, and an evaporator 27. And a detector 31. The first economizer circuit 25A includes a first economizer heat exchanger 28A, an expansion valve 30A, and a detector 31A. Although the first economizer heat exchanger 28A is illustrated as a tube-in-tube co-current heat exchanger, the multistage compressor unit 10A is limited. Although not necessarily, a counter-current heat exchanger in which the pipe is arranged in a pipe, a shell-in-tube heat exchanger in which the pipe is arranged in a shell, a flash tank, a brazing plate heat exchanger It is also useful in refrigeration systems that use other types of economizer heat exchangers, including

  The multistage compressor unit 10 </ b> A includes a two-stage compressor subunit 32 and a one-stage compressor subunit 34. As shown in FIG. 1, the two-stage compressor subunit 32 is a reciprocating compressor, and includes cylinders 36A and 36B connected in series. Similarly, the single-stage compressor subunit 34 is also a reciprocating compressor and includes a cylinder 36C. Although the two-stage compressor subunit 32 and the one-stage compressor subunit 34 are illustrated as reciprocating compressors, they are not limited to scrolls, screws, rotary vanes, fixed vanes, variable speeds, and sealed types. Other types of compressors (in various combinations) can be used, including open drive compressors. However, by way of example, the embodiments of the present invention will be described as including a multi-stage reciprocating compressor unit represented by a compression cylinder.

  In the refrigeration system 20A, two separate refrigerant paths are formed by connecting various elements in the system. The main refrigerant path is formed by a loop defined by positions 1, 2, 3, 4, and 5. A first economy refrigerant path is formed by a loop defined by positions 4A, 5A, 6A, and 7A. These paths are all closed paths, and it goes without saying that these closed paths allow a continuous flow of refrigerant through the refrigeration system 20A.

  In relation to the main refrigerant path, the refrigerant loses heat in the heat removal heat exchanger 24 and is low after flowing out of the two-stage compressor subunit 32 through the discharge port 39 at high pressure and enthalpy (position 3). Out of heat removal heat exchanger 24 with enthalpy and high pressure (position 4A). The refrigerant then splits into two flow paths 40A, 42A before entering the first economizer heat exchanger 28A. The main path continues along path 40A and passes through first economizer heat exchanger 28A (position 4). The refrigerant in the path 40A is cooled by the refrigerant in the path 42A of the first economize path while passing through the first economizer heat exchanger 28A.

  Next, the refrigerant from the path 40 </ b> A is throttled in the main expansion valve 26. The main expansion valve 26 is preferably a thermal expansion valve (TXV) or an electronic expansion valve (EXV) together with the economizer expansion valve 30A. After passing through the expansion process in the main expansion valve 26 (position 5), the refrigerant is a two-phase liquid-vapor mixture and goes to the evaporator 27. After the remaining liquid has evaporated (position 1), the refrigerant flows into the two-stage compressor subunit 32 through the suction port 37. The refrigerant is compressed in the cylinder 36A, which is the first stage of the two-stage compressor subunit 32, and then discharged from the discharge port 50 (position 2). The refrigerant is discharged through the discharge port 39 after the second stage of compression (position 3).

  In connection with the first economy path, the refrigerant exits the heat removal heat exchanger 24 with low enthalpy and high pressure (position 4A) and is divided into two flow paths 40A, 42A before the first economy path. Continues along path 42A. In the path 42A, the refrigerant is throttled to a lower pressure by the economizer expansion valve 30A (position 5A) before passing through the first economizer heat exchanger 28A. The refrigerant that has passed through the first economizer heat exchanger 28A from path 42A (position 6A) is then flowed along the economizer return path 46A and is compressed in the single stage compressor subunit 34 for compression within the single stage compressor subunit 34. It is sent to the suction port 52. The refrigerant is compressed in the single-stage compressor subunit 34 and then discharged through the discharge port 54 (position 7A), where it is mixed with the refrigerant discharged from the two-stage compressor subunit 32.

  The refrigeration system 20A also includes a detector 31 disposed along the main refrigerant path between the evaporator 27 and the multistage compressor unit 10A. In general, the detector 31 operates together with the expansion valve 26 to detect the temperature of the refrigerant flowing out of the evaporator 27 and the pressure of the refrigerant in the evaporator 27, and maintains the combination of temperature and pressure within a certain range. In the preferred embodiment, expansion valve 26 is an electronic expansion valve and detector 31 is a temperature transducer such as a thermocouple or thermistor. In another embodiment, expansion valve 26 is a mechanical thermal expansion valve, and detector 31 includes a small tube that terminates in a pressure vessel filled with a refrigerant other than the refrigerant flowing through refrigeration system 20A. When the refrigerant from the evaporator 27 flows through the detector 31 while flowing toward the multistage compressor unit 10A, the pressure vessel is heated or cooled, so that the pressure in the pressure vessel changes. As the pressure in the pressure vessel changes, detector 31 sends a signal to expansion valve 26 that changes the pressure drop across expansion valve 26. Similarly, in the case of an electronic expansion valve, the detector 31 sends an electrical signal to the expansion valve 26 that responds similarly to regulate the refrigerant flow. For example, when the return gas coming from the evaporator 27 is too hot, the detector 31 is heated and sends a signal to the expansion valve 26 to increase the opening of the valve, and the refrigerant flowing through the evaporator 27 per unit time is increased. The temperature of the refrigerant flowing out from 27 is lowered.

  The economizer circuit 25 also includes a detector 31A that operates similarly to the detector 31. Instead, however, detector 31A detects the temperature along economizer return path 46A and operates with expansion valve 30A to control the pressure drop within expansion valve 30A. It should also be noted that detectors other than those previously described can be replaced with detectors 31, 31A.

  By controlling the expansion valves 26 and 30A, the operation of the refrigeration system 20A can be adjusted so as to satisfy cooling requirements and achieve optimum efficiency. In addition to adjusting the pressure drop associated with the expansion valves 26, 30A, the displacement of the cylinders 36A, 36B, 36C can also be adjusted to help achieve optimal efficiency of the refrigeration system 20A.

  FIG. 1B illustrates a graph relating the enthalpy of the refrigeration system 20A of FIG. 1A to pressure. The vapor dome V is formed by a saturated liquid line and a saturated vapor line, and defines the state of the refrigerant at various positions along the refrigeration cycle. Under the vapor dome V all states contain both liquid and vapor coexisting at the same time. The uppermost part of the steam dome V is a critical point. The critical point is defined as the highest pressure at which the saturated liquid and saturated vapor coexist. In general, the compressed liquid is located on the left side of the vapor dome V, and the superheated vapor is located on the right side of the vapor dome V.

  In FIG. 1B again, the main refrigerant path is a loop defined by positions 1, 2, 3, 4, and 5, and the first economy path is a loop defined by positions 4A, 5A, 6A, and 7A. The main path cycle begins at position 1, where the refrigerant is at low pressure and high enthalpy before entering the multi-stage compressor unit 10A. After the first stage of compression in the cylinder 36A of the two-stage compressor subunit 32, both enthalpy and pressure increase as shown in position 2. After the second stage of compression in the cylinder 36B, the refrigerant exits the multi-stage compressor unit 10A at high pressure and higher enthalpy as shown in position 3. Then, as the refrigerant passes through the heat removal heat exchanger 24, the enthalpy decreases while the pressure remains constant. Before the refrigerant flows into the first economizer heat exchanger 28A, the refrigerant is divided into a main portion and a first economizer portion as indicated by a position 4A. The main part is then throttled at the main expansion valve 26 and the pressure drops as shown in position 5. Finally, the main part of the refrigerant evaporates with a higher enthalpy as shown in position 1 and flows out of the evaporator 27.

  As mentioned earlier, the first economy portion is separated from the main portion as indicated by position 4A. The first economy portion is throttled to a lower pressure at the expansion valve 30A as shown at position 5A. The first economized portion of the refrigerant then exchanges heat with the main portion of the refrigerant in the first economizer heat exchanger 28A to cool the main portion as indicated by position 4, and the temperature is increased as indicated by position 6A. To rise. The first economy portion is then compressed in the single stage compressor subunit 34 and mixed with the main portion of the refrigerant discharged from the two stage compressor subunit 32 as shown at position 7A.

  As shown in FIG. 1B, the cylinders 36A, 36B, 36C of the multistage compressor unit 10A are configured to receive the refrigerant and compress it to various pressures. In particular, cylinder 36A receives refrigerant from the main refrigerant path and compresses it to an intermediate pressure as indicated by position 2. Cylinder 36B then receives the refrigerant and compresses it from the intermediate pressure to the outlet pressure as indicated by position 3. Similarly, cylinder 36C receives refrigerant from the first economize refrigerant path and compresses it to outlet pressure as indicated by position 7A. As shown in FIG. 1B, the outlet pressure of cylinder 36C is substantially equal to the outlet pressure of cylinder 36B. In the refrigeration system 20A, these outlet pressures are determined by the inlet pressure required by the heat removal heat exchanger 24.

  FIG. 2A illustrates a schematic diagram of a multi-stage compressor unit 10B connected to the refrigeration system 20B. The multistage compressor unit 10B is the same as the multistage compressor 10A. However, as will be described in more detail below, the two-stage compressor subunit 32 is further configured to receive refrigerant from the economizer circuit to cool the refrigerant in the main refrigerant path prior to the second stage of compression. An intermediate port 48 is included. The refrigeration system 20B is similar to the refrigeration system 20A, but further includes a second economizer circuit 25B. The second economizer circuit 25B includes a second economizer heat exchanger 28B, an expansion valve 30B, and a detector 31B.

  In the refrigeration system 20B, three separate refrigerant paths are formed by connecting various elements in the system. The main refrigerant path is formed by a loop defined by positions 1, 2, 3, 4, 5, 6. A first economy refrigerant path is formed by a loop defined by positions 5A, 6A, 7A, 3, and 4. Finally, the second economy refrigerant path is formed by the loop defined by the positions 5B, 6B, 7B, and 8B.

  In relation to the main refrigerant path, the refrigerant loses heat in the heat removal heat exchanger 24 and is low after flowing out of the two-stage compressor subunit 32 through the discharge port 39 at high pressure and enthalpy (position 4). Out of heat removal heat exchanger 24 with enthalpy and high pressure (position 5A). The refrigerant then splits into two flow paths 40A, 42A before entering the first economizer heat exchanger 28A. The main path continues along the paths 40A and 40B and passes through the first economizer heat exchanger 28A (position 5B) and the second economizer heat exchanger 28B (position 5), respectively. The refrigerant in the path 40A is cooled by the refrigerant in the path 42A of the first economize path while passing through the first economizer heat exchanger 28A. Similarly, the refrigerant in the path 40B is cooled by the refrigerant in the path 42B of the second economize path while passing through the second economizer heat exchanger 28B.

  Next, the refrigerant from the path 40 </ b> B is throttled in the main expansion valve 26. After passing through the expansion process in the main expansion valve 26 (position 6), the refrigerant is a two-phase liquid-vapor mixture and goes to the evaporator 27. After the remaining liquid has evaporated (position 1), the refrigerant flows into the two-stage compressor subunit 32 through the suction port 37. The refrigerant is compressed in the cylinder 36A, which is the first stage of the two-stage compressor subunit 32, and then discharged from the discharge port 50 (position 2) where it is fed from the economizer return path 46A that is fed into the intermediate port 48. Mixed with low temperature refrigerant (position 3). Thus, the refrigerant from the economizer return path 46A functions to cool the refrigerant discharged from the cylinder 36A before the second stage of compression in the cylinder 36B. The refrigerant is discharged through the discharge port 39 after the second stage of compression (position 4).

  In connection with the first economy path, the refrigerant exits the heat removal heat exchanger 24 with low enthalpy and high pressure (position 5A) and is divided into two flow paths 40A, 42A before the first economy path. Continues along path 42A. In the path 42A, the refrigerant is throttled to a lower pressure by the economizer expansion valve 30A (position 6A) before passing through the first economizer heat exchanger 28A. The refrigerant that has passed through the first economizer heat exchanger 28A (path 7A) from the path 42A is then flowed along the economizer return path 46A and is sent to the intermediate port 48 of the two-stage compressor subunit 32 where it passes through the main path. Mixed with the flowing refrigerant, cools the refrigerant before the second stage of compression in the cylinder 36B (position 3).

  In relation to the second economize path, the refrigerant in path 40A is split in two flow paths 40B, 42B after being cooled in higher pressure first economizer heat exchanger 28A (position 5B). The second economize path continues along the flow path 42B where the refrigerant is throttled to a lower pressure by the economizer expansion valve 30B before passing through the second economizer heat exchanger 28B (position 6B). The refrigerant that has passed through the second economizer heat exchanger 28B from path 42B (position 7B) is then flowed along the economizer return path 46B and is compressed in the single stage compressor subunit 34 for compression within the single stage compressor subunit 34. It is sent to the suction port 52. The refrigerant is compressed in the one-stage compressor subunit 34 and then discharged through the discharge port 54 (position 8B), where it is mixed with the refrigerant discharged from the two-stage compressor subunit 32.

  FIG. 2B illustrates a graph relating the enthalpy of the refrigeration system 20B of FIG. 2A to pressure. As shown in FIG. 2B, the main refrigerant path is a loop defined by positions 1, 2, 3, 4, 5, 6, and the first economy path is defined by positions 5A, 6A, 7A, 3, 4. The second economy path is a loop defined by positions 5B, 6B, 7B, and 8B.

  As shown in FIG. 2B, the cylinders 36A, 36B, 36C of the multi-stage compressor unit 10B are configured to receive the refrigerant and compress it to various pressures. In particular, cylinder 36A receives refrigerant from the main refrigerant path and compresses it to an intermediate pressure as indicated by position 2. Cylinder 36B then receives refrigerant from the main refrigerant path and the first economy path and compresses it from the intermediate pressure to the outlet pressure as indicated by position 4. Similarly, cylinder 36C receives refrigerant from the second economy refrigerant path and compresses it to outlet pressure as indicated by position 8B. As shown in FIG. 2B, the outlet pressure of cylinder 36C is substantially equal to the outlet pressure of cylinder 36B.

  FIG. 3A illustrates a schematic diagram of a multi-stage compressor unit 10C connected to the refrigeration system 20C. The multistage compressor unit 10C is the same as the multistage compressor 10B. However, as will be described in more detail below, the single stage compressor subunit 34 is not connected to the first economizer return path instead of being discharged into the heat removal heat exchanger 24 as shown in the multistage compressor unit 10B of FIG. 2A. It is configured to be discharged into 46A.

  In the refrigeration system 20C, three separate refrigerant paths are formed by connecting various elements in the system. The main refrigerant path is formed by a loop defined by positions 1, 2, 3, 4, 5, 6. A first economy refrigerant path is formed by a loop defined by positions 5A, 6A, 7A, 3, and 4. Finally, the second economy refrigerant path is formed by the loop defined by the positions 5B, 6B, 7B, 8B, 3, and 4.

  In relation to the main refrigerant path, the refrigerant loses heat in the heat removal heat exchanger 24 and is low after flowing out of the two-stage compressor subunit 32 through the discharge port 39 at high pressure and enthalpy (position 4). Out of heat removal heat exchanger 24 with enthalpy and high pressure (position 5A). The refrigerant then splits into two flow paths 40A, 42A before entering the first economizer heat exchanger 28A. The main path continues along the paths 40A and 40B and passes through the first economizer heat exchanger 28A (position 5B) and the second economizer heat exchanger 28B (position 5), respectively. The refrigerant in the path 40A is cooled by the refrigerant in the path 42A of the first economize path while passing through the first economizer heat exchanger 28A. Similarly, the refrigerant in the path 40B is cooled by the refrigerant in the path 42B of the second economize path while passing through the second economizer heat exchanger 28B.

  Next, the refrigerant from the path 40 </ b> B is throttled in the main expansion valve 26. After passing through the expansion process in the main expansion valve 26 (position 6), the refrigerant is a two-phase liquid-vapor mixture and goes to the evaporator 27. After the remaining liquid has evaporated (position 1), the refrigerant flows into the two-stage compressor subunit 32 through the suction port 37. The refrigerant is compressed in the cylinder 36A, which is the first stage of the two-stage compressor subunit 32, and then discharged from the discharge port 50 (position 2) where it is fed from the economizer return path 46A that is fed into the intermediate port 48. Mixed with low temperature refrigerant (position 3). Thus, the refrigerant from the economizer return path 46A functions to cool the refrigerant discharged from the cylinder 36A before the second stage of compression in the cylinder 36B. The refrigerant is discharged through the discharge port 39 after the second stage of compression (position 4).

  In connection with the first economy path, the refrigerant exits the heat removal heat exchanger 24 with low enthalpy and high pressure (position 5A) and is divided into two flow paths 40A, 42A before the first economy path. Continues along path 42A. In the path 42A, the refrigerant is throttled to a lower pressure by the economizer expansion valve 30A (position 6A) before passing through the first economizer heat exchanger 28A. The refrigerant that has passed through the first economizer heat exchanger 28A (path 7A) from the path 42A is then flowed along the economizer return path 46A and is sent to the intermediate port 48 of the two-stage compressor subunit 32 where it passes through the main path. Mixed with the flowing refrigerant, cools the refrigerant before the second stage of compression in the cylinder 36B (position 3).

  In relation to the second economize path, the refrigerant in path 40A is split in two flow paths 40B, 42B after being cooled in higher pressure first economizer heat exchanger 28A (position 5B). The second economize path continues along the flow path 42B where the refrigerant is throttled to a lower pressure by the economizer expansion valve 30B before passing through the second economizer heat exchanger 28B (position 6B). The refrigerant that has passed through the second economizer heat exchanger 28B from path 42B (position 7B) is then flowed along the economizer return path 46B and is compressed in the single stage compressor subunit 34 for compression within the single stage compressor subunit 34. It is sent to the suction port 52. The refrigerant is compressed in the first stage compressor subunit 34 and then discharged through the discharge port 54, where it is sent to the intermediate port 48 of the second stage compressor subunit 32 (position 3) before being placed in the economizer return path 46A. Mixed with refrigerant (position 8B).

  FIG. 3B illustrates a graph relating the enthalpy of the refrigeration system 20C of FIG. 3A to pressure. As shown in FIG. 3B, the main refrigerant path is a loop defined by positions 1, 2, 3, 4, 5, 6, and the first economy path is defined by positions 5A, 6A, 7A, 3, 4. The second economy path is a loop defined by positions 5B, 6B, 7B, 8B, 3, and 4.

  As shown in FIG. 3B, the cylinders 36A, 36B, 36C of the multi-stage compressor unit 10C are configured to receive the refrigerant and compress it to various pressures. In particular, cylinder 36A receives refrigerant from the main refrigerant path and compresses it to an intermediate pressure as indicated by position 2. Similarly, cylinder 36C receives refrigerant from the second economy refrigerant path and compresses it to outlet pressure as indicated by position 8B. Cylinder 36B then receives refrigerant from the main refrigerant path, the first economy path and the second economy path and compresses it to the outlet pressure as indicated by position 4. As shown in FIG. 3B, the outlet pressure of the cylinder 36C is substantially equal to the intermediate pressure of the cylinder 36A.

  FIG. 4A illustrates a schematic diagram of a multi-stage compressor unit 10D connected to the refrigeration system 20D. The multistage compressor unit 10D is the same as the multistage compressor unit 10A. However, the multi-stage compressor unit 10D further includes a single-stage compressor subunit 35 having a cylinder 36D. The refrigeration system 20D is similar to the refrigeration system 20C except that the intermediate port 48 is replaced by an intermediate cooler 49, which is the first compressor for compression within the two-stage compressor subunit 32. It is configured to cool the main part of the refrigerant between the second stage.

  In the refrigeration system 20D, three separate refrigerant paths are formed by connecting various elements in the system. The main refrigerant path is formed by a loop defined by positions 1, 2, 3, 4, 5, 6. The first economy refrigerant path is formed by a loop defined by positions 5A, 6A, 7A, and 8A. Finally, the second economy refrigerant path is formed by the loop defined by the positions 5B, 6B, 7B, and 8B.

  In relation to the main refrigerant path, the refrigerant loses heat in the heat removal heat exchanger 24 and is low after flowing out of the two-stage compressor subunit 32 through the discharge port 39 at high pressure and enthalpy (position 4). Out of heat removal heat exchanger 24 with enthalpy and high pressure (position 5A). The refrigerant then splits into two flow paths 40A, 42A before entering the first economizer heat exchanger 28A. The main path continues along the paths 40A and 40B and passes through the first economizer heat exchanger 28A (position 5B) and the second economizer heat exchanger 28B (position 5), respectively. The refrigerant in the path 40A is cooled by the refrigerant in the path 42A of the first economize path while passing through the first economizer heat exchanger 28A. Similarly, the refrigerant in the path 40B is cooled by the refrigerant in the path 42B of the second economize path while passing through the second economizer heat exchanger 28B.

  Next, the refrigerant from the path 40 </ b> B is throttled in the main expansion valve 26. After passing through the expansion process in the main expansion valve 26 (position 6), the refrigerant is a two-phase liquid-vapor mixture and goes to the evaporator 27. After the remaining liquid has evaporated (position 1), the refrigerant flows into the two-stage compressor subunit 32 through the suction port 37. The refrigerant is compressed in the cylinder 36A, the first stage of the two-stage compressor subunit 32, and then discharged from the discharge port 50 (position 2), where it precedes the second stage of compression in the cylinder 36B. The intermediate cooler 49 is passed. The intermediate cooler 49 is configured to cool the refrigerant discharged from the cylinder 36A before the second stage of compression in the cylinder 36B. The refrigerant is discharged through the discharge port 39 after the second stage of compression (position 4).

  In connection with the first economy path, the refrigerant exits the heat removal heat exchanger 24 with low enthalpy and high pressure (position 5A) and is divided into two flow paths 40A, 42A before the first economy path. Continues along path 42A. In the path 42A, the refrigerant is throttled to a lower pressure by the economizer expansion valve 30A (position 6A) before passing through the first economizer heat exchanger 28A. The refrigerant that has passed through the first economizer heat exchanger 28A from path 42A (position 7A) is then flowed along the economizer return path 46A and is compressed in the single stage compressor subunit 34 for compression within the single stage compressor subunit 34. It is sent to the suction port 52. The refrigerant is compressed in the single-stage compressor subunit 34 and then discharged through the discharge port 54 (position 8A), where it is mixed with the refrigerant discharged from the two-stage compressor subunit 32 and the single-stage compressor subunit 35. The

  In relation to the second economize path, the refrigerant in path 40A is split in two flow paths 40B, 42B after being cooled in higher pressure first economizer heat exchanger 28A (position 5B). The second economize path continues along the flow path 42B where the refrigerant is throttled to a lower pressure by the economizer expansion valve 30B before passing through the second economizer heat exchanger 28B (position 6B). The refrigerant that has passed through the second economizer heat exchanger 28B from the path 42B (position 7B) is then flowed along the economizer return path 46B and in the single stage compressor subunit 35 for compression within the single stage compressor subunit 35. It is sent to the suction port 56. The refrigerant is compressed in the single-stage compressor subunit 35 and then discharged through the discharge port 58 (position 8B), where it is mixed with the refrigerant discharged from the two-stage compressor subunit 32 and the single-stage compressor subunit 34. The

  FIG. 4B illustrates a graph relating the enthalpy of the refrigeration system 20D of FIG. 4A to pressure. As shown in FIG. 4B, the main refrigerant path is a loop defined by positions 1, 2, 3, 4, 5, 6, and the first economy path is a loop defined by positions 5A, 6A, 7A, 8A. The second economy path is a loop defined by the positions 5B, 6B, 7B, and 8B.

  As shown in FIG. 4B, the cylinders 36A, 36B, 36C, 36D of the multi-stage compressor unit 10D are configured to receive the refrigerant and compress it to various pressures. In particular, cylinder 36A receives refrigerant from the main refrigerant path and compresses it to an intermediate pressure as indicated by position 2. Cylinder 36B receives the refrigerant after it has been cooled in intermediate cooler 49 from the main refrigerant path and compresses it from the intermediate pressure to the outlet pressure as indicated by position 4. Cylinder 36C receives refrigerant from the first economize refrigerant path and compresses it to outlet pressure as indicated by position 8A. Similarly, cylinder 36D receives refrigerant from the second economy refrigerant path and compresses it to outlet pressure as indicated by position 8B. As shown in FIG. 4B, the outlet pressure of the cylinders 36C, 36D is substantially equal to the outlet pressure of the cylinder 36B.

  FIG. 5A illustrates a schematic diagram of a multi-stage compressor unit 10E connected to the refrigeration system 20E. The multistage compressor unit 10 </ b> E includes a two-stage compressor subunit 70 in addition to the two-stage compressor subunit 32. The two-stage compressor subunit 70 includes cylinders 36E and 36F connected in series. The refrigeration system 20E is the same as the refrigeration system 20D except that a third economizer circuit 25C is added to the system.

  In the refrigeration system 20E, four separate refrigerant paths are formed by connecting various elements in the system. The main refrigerant path is formed by a loop defined by positions 1, 2, 3, 4, 5, 6. A first economy refrigerant path is formed by a loop defined by positions 5A, 6A, 7A, 3, and 4. A second economy refrigerant path is formed by a loop defined by positions 5B, 6B, 7B, 9, and 10. Finally, the third economy refrigerant path is formed by the loop defined by the positions 5C, 6C, 7C, 8C, 9, and 10.

  In relation to the main refrigerant path, the refrigerant loses heat in the heat removal heat exchanger 24 and is low after flowing out of the two-stage compressor subunit 32 through the discharge port 39 at high pressure and enthalpy (position 4). Out of heat removal heat exchanger 24 with enthalpy and high pressure (position 5A). The refrigerant then splits into two flow paths 40A, 42A before entering the first economizer heat exchanger 28A. The main path continues along paths 40A, 40B, and 40C, and the first economizer heat exchanger 28A (position 5B), the second economizer heat exchanger 28B (position 5C), and the third economizer heat exchanger 28C, respectively. Go through (position 5). The refrigerant in the path 40A is cooled by the refrigerant in the path 42A of the first economize path while passing through the first economizer heat exchanger 28A. The refrigerant in the path 40B is cooled by the refrigerant in the path 42B of the second economize path while passing through the second economizer heat exchanger 28B. Finally, the refrigerant in the path 40C is cooled by the refrigerant in the path 42C of the third economize path while passing through the third economizer heat exchanger 28C.

  Next, the refrigerant from the path 40 </ b> C is throttled in the main expansion valve 26. After passing through the expansion process in the main expansion valve 26 (position 6), the refrigerant is a two-phase liquid-vapor mixture and goes to the evaporator 27. After the remaining liquid has evaporated (position 1), the refrigerant flows into the two-stage compressor subunit 32 through the suction port 37. The refrigerant is compressed in the cylinder 36A, which is the first stage of the two-stage compressor subunit 32, and then discharged from the discharge port 50 (position 2) where it is fed from the economizer return path 46A that is fed into the intermediate port 48. Mixed with low temperature refrigerant (position 3). Thus, the refrigerant from the economizer return path 46A functions to cool the refrigerant discharged from the cylinder 36A before the second stage of compression in the cylinder 36B. The refrigerant is discharged through the discharge port 39 after the second stage of compression (position 4).

  In connection with the first economy path, the refrigerant exits the heat removal heat exchanger 24 with low enthalpy and high pressure (position 5A) and is divided into two flow paths 40A, 42A before the first economy path. Continues along path 42A. In the path 42A, the refrigerant is throttled to a lower pressure by the economizer expansion valve 30A (position 6A) before passing through the first economizer heat exchanger 28A. The refrigerant that has passed through the first economizer heat exchanger 28A (path 7A) from the path 42A is then flowed along the economizer return path 46A and is sent to the intermediate port 48 of the two-stage compressor subunit 32 where it passes through the main path. Mixed with the flowing refrigerant, cools the refrigerant before the second stage of compression in the cylinder 36B (position 3).

  In relation to the second economize path, the refrigerant in path 40A is split in two flow paths 40B, 42B after being cooled in higher pressure first economizer heat exchanger 28A (position 5B). The second economize path continues along the flow path 42B where the refrigerant is throttled to a lower pressure by the economizer expansion valve 30B before passing through the second economizer heat exchanger 28B (position 6B). The refrigerant that has passed through the second economizer heat exchanger 28B from the path 42B (position 7B) then flows along the economizer return path 46B and is sent to the intermediate port 72 of the two-stage compressor subunit 70, where it is at the discharge port 74. The refrigerant is mixed with the refrigerant flowing out of the cylinder 36F to cool the refrigerant before the second stage of compression in the cylinder 36F (position 9).

  In connection with the third economize path, the refrigerant in path 40B is split in two flow paths 40C, 42C after being cooled in the higher pressure second economizer heat exchanger 28B (position 5C). The third economize path continues along the flow path 42C where the refrigerant is throttled to a lower pressure by the economizer expansion valve 30C (position 6C) before passing through the third economizer heat exchanger 28C. The refrigerant that has passed through the third economizer heat exchanger 28C from the path 42C (position 7C) then flows along the economizer return path 46C and is sent to the suction port 76 of the two-stage compressor subunit 70. The refrigerant is cooled by the refrigerant sent to the intermediate port 72 from the economizer return path 46B after the first stage of compression in the cylinder 36E (position 8C) and before the second stage of compression. The refrigerant is discharged through the discharge port 78 after the second stage of compression in the cylinder 36F (position 10) where it is mixed with the compressed refrigerant discharged from the two-stage compressor subunit 32.

  FIG. 5B illustrates a graph relating the enthalpy of the refrigeration system 20E of FIG. 5A to pressure. As shown in FIG. 5B, the main refrigerant path is a loop defined by positions 1, 2, 3, 4, 5, 6, and the first economy path is defined by positions 5A, 6A, 7A, 3, 4. The second economy path is a loop defined by the positions 5B, 6B, 7B, 9, 10 and the third economy path is defined by the positions 5C, 6C, 7C, 8C, 9, 10 Loop.

  As shown in FIG. 5B, the cylinders 36A, 36B, 36E, 36F of the multistage compressor unit 10E are configured to receive the refrigerant and compress it to various pressures. In particular, cylinder 36A receives refrigerant from the main refrigerant path and compresses it to an intermediate pressure as indicated by position 2. Cylinder 36B then receives refrigerant from the main refrigerant path and the first economy path and compresses it from the intermediate pressure to the outlet pressure as indicated by position 4. Similarly, cylinder 36E receives refrigerant from the third economy refrigerant path and compresses it to an intermediate pressure as indicated by position 8C. Cylinder 36F then receives refrigerant from the second and third economy paths and compresses it from the intermediate pressure to the outlet pressure as indicated by position 10. As shown in FIG. 5B, the outlet pressure of cylinder 36B is substantially equal to the outlet pressure of cylinder 36F.

  Although each embodiment of the multi-stage compressor unit described and illustrated above is connected to a refrigeration system that includes one or more economizer circuits, the multi-stage compressor unit of the present invention can also be used in a refrigeration system that does not include an economizer circuit. . FIG. 6A illustrates a schematic diagram of a multi-stage compressor unit 10F connected to the refrigeration system 20F. The refrigeration system 20F includes a heat removal heat exchanger 24, a first expansion valve 26, a first evaporator 27, a first evaporator 1 detector 31, second expansion valve 126, second evaporator 127, and second detector 131. The multistage compressor unit 10F includes a two-stage compressor subunit 32 and a one-stage compressor subunit 34. The two-stage compressor subunit 32 includes cylinders 36A and 36B connected in series, and the one-stage compressor subunit 34 includes a cylinder 36C.

  In the refrigeration system 20F, two separate refrigerant paths are formed by connecting various elements in the system. The first main refrigerant path is formed by a loop defined by positions 1, 2, 3, 4, and 5. The second main refrigerant path is formed by a loop defined by positions 4, 5A, 6A, and 7A.

  In connection with the first main refrigerant path, the refrigerant flows from the two-stage compressor subunit 32 through the discharge port 39 at high pressure and enthalpy (position 3) and then heats in the heat removal heat exchanger 24. Loss and exits the heat removal heat exchanger 24 with low enthalpy and high pressure (position 4). The refrigerant in the main path is then throttled at the first expansion valve 26. The refrigerant is a two-phase liquid-vapor mixture after going through the expansion process in the first main expansion valve 26 (position 5), and goes to the first evaporator 27. After the remaining liquid has evaporated (position 1), the refrigerant flows into the two-stage compressor subunit 32 through the suction port 37. The refrigerant is compressed in the cylinder 36A, which is the first stage of the two-stage compressor subunit 32, and then discharged from the discharge port 50 (position 2). The refrigerant is discharged through the discharge port 39 after the second stage of compression in the cylinder 36B (position 3).

  In relation to the second main refrigerant path, the refrigerant is throttled at the second expansion valve 126 after flowing out of the heat removal heat exchanger 24. After passing through the expansion process in the second main expansion valve 126 (position 5A), the refrigerant is a two-phase liquid-vapor mixture and goes to the second evaporator 127. The refrigerant evaporates in the second evaporator 127 (position 6A), and then flows into the first-stage compressor subunit 34 through the suction port 52. The refrigerant is compressed in the cylinder 36C and then discharged from the discharge port 54 (position 7A), where it is mixed with the refrigerant discharged through the discharge port 39 of the two-stage compressor subunit 32.

  FIG. 6B illustrates a graph relating the enthalpy of the refrigeration system 20F of FIG. 6A to pressure. As shown in FIG. 6B, the first main refrigerant path is a loop defined by positions 1, 2, 3, 4, and 5, and the second main refrigerant path is defined by positions 4, 5A, 6A, and 7A. Loop.

  As shown in FIG. 6B, the cylinders 36A, 36B, 36C of the multi-stage compressor unit 10F are configured to receive the refrigerant and compress it to various pressures. In particular, cylinder 36A receives refrigerant from the first main refrigerant path and compresses it to an intermediate pressure as indicated by position 2. Cylinder 36B then receives the refrigerant and compresses it from the intermediate pressure to the outlet pressure as indicated by position 3. Similarly, cylinder 36C receives refrigerant from the second main refrigerant path and compresses it to outlet pressure as indicated by position 7A. As shown in FIG. 6B, the outlet pressure of cylinder 36C is substantially equal to the outlet pressure of cylinder 36B.

  Alternative embodiments of multi-stage compressor units have been described as including a number of compressor subunits in the range of 2-3, but multi-stage compressor units having four or more compressor subunits are also contemplated by the present invention. Needless to say, it is included in the range. Furthermore, although the embodiment of the multi-stage compressor unit has been described to include exclusively single-stage and two-stage compressor subunits, three or more stages of compressor subunits are also within the intended scope of the present invention. Accordingly, the illustration of the single and two stage compressor subunits is for illustration only and not for limitation. Alternate embodiments are also contemplated that include compressor subunits connected in various combinations other than those described above.

  The multistage compressor unit of the present invention is useful for improving system efficiency in a refrigeration system using any kind of refrigerant, but is particularly useful in a refrigeration system using a transcritical refrigerant such as carbon dioxide. Since carbon dioxide is a refrigerant having such a low critical temperature, a refrigeration system using carbon dioxide generally operates in a transcritical state. In addition, because carbon dioxide is such a high-pressure refrigerant, multiple economizers and multiple compressor cylinders are provided between the high and low pressure sections of the circuit, each contributing to system efficiency. More opportunities to do so. Thus, the multi-stage compressor unit of the present invention can be used to improve the efficiency of a system using a transcritical refrigerant such as carbon dioxide, and to compare the efficiency with the normal efficiency. However, the multi-stage compressor unit of the present invention is useful for improving efficiency in a refrigeration system using any refrigerant, including a system that operates at a subcritical level and a system that operates at a transcritical level.

  Although the present invention has been described with reference to preferred embodiments, workers skilled in the art will recognize that changes may be made in form and detail without departing from the spirit and scope of the invention.

Claims (16)

A multi-stage compressor unit for a refrigeration system configured to circulate refrigerant,
A first compressor subunit having a first stage and a second stage;
A second compressor subunit in parallel with the first compressor subunit and having a first stage;
Each of the first and second stages of the first compressor subunit has a suction port and a discharge port, and the first compressor subunit removes the first portion of refrigerant from the evaporator. Configured to receive and compress, the first stage of the second compressor subunit has a suction port and a discharge port, and the second compressor subunit compresses the second portion of the refrigerant The compressed and compressed second portion is mixed with the compressed first portion;
The first stage of the second compressor subunit is configured to receive a second portion of refrigerant from the first economizer circuit ;
The first economizer circuit branches the refrigerant to the main portion and economizer section, characterized that you heat exchange refrigerant decompressed refrigerant and the main part economizer parts by the economizer heat exchanger, the multi-stage compressor unit. The first compressor subunit further comprises an intermediate port disposed between the first stage discharge port and the second stage suction port, the intermediate port from the second economizer circuit. The second economizer circuit is configured to receive the third part, and the second economizer circuit branches the refrigerant into the main part and the economizer part, and exchanges heat between the refrigerant decompressed by the economizer part and the main part refrigerant in the economizer heat exchanger. The multistage compressor unit according to claim 1, wherein   The multi-stage compressor unit according to claim 1, wherein the first compressor subunit and the second compressor subunit comprise a reciprocating compressor.   The multistage compressor unit according to claim 1, wherein the refrigerant is a transcritical refrigerant.   The intercooler configured to cool a first portion of refrigerant between the first stage and the second stage of the first compressor subunit. Multistage compressor unit.   The multistage compressor unit according to claim 1, wherein the second compressor subunit is configured to discharge to an intermediate port of the first compressor subunit.   The second compressor subunit further includes a second stage having a suction port and a discharge port, and the first stage and the second stage of the second compressor subunit are connected in series. The multistage compressor unit according to claim 1, wherein A multi-stage compressor unit for a refrigeration system configured to circulate refrigerant and having a first economizer circuit,
A first compressor subunit having a first stage and a second stage;
A second compressor subunit in parallel with the first compressor subunit;
The first compressor subunit is configured to receive and compress the first portion of refrigerant from the evaporator, and the second compressor subunit is configured to receive refrigerant first from the first economizer circuit. The compressed second part is mixed with the compressed first part, and is configured to compress the two parts ;
The first economizer circuit branches the refrigerant to the main portion and economizer section, characterized that you heat exchange refrigerant decompressed refrigerant and the main part economizer parts by the economizer heat exchanger, the multi-stage compressor unit. The first compressor first subunit stage and according to claim 8, further comprising an intermediate cooler configured to cool a first portion of the refrigerant between the second stage Multistage compressor unit. The first compressor subunit is configured to discharge refrigerant at a first outlet pressure, and the second compressor subunit is configured to discharge refrigerant at a second outlet pressure. The multistage compressor unit according to claim 8 . Multi-stage compressor unit of claim 1 0, wherein the first outlet pressure and the second outlet pressure, characterized in that substantially equal. The first compressor subunit is an intermediate port disposed between the first stage and the second stage and is configured to receive a third portion of the refrigerant from the second economizer circuit And a second stage of the first compressor subunit is configured to compress the mixture of the first and third portions of refrigerant, and the second economizer circuit includes the refrigerant as a main portion. branches to the economizer section, multi-stage compressor unit of claim 8, wherein that you heat exchange refrigerant decompressed refrigerant and the main part economizer parts by the economizer heat exchanger. The multi-stage compressor unit according to claim 8, wherein the second compressor subunit is a single-stage compressor. 9. The multi-stage compressor unit according to claim 8, wherein the second compressor subunit is a two-stage compressor. The second compressor subunit further comprises an intermediate port configured to receive a fourth portion of the refrigerant from the third economizer circuit, the third economizer circuit branching the refrigerant into the main portion and the economizer portion. and, a multistage compressor unit according to claim 1 4, wherein that you heat exchange refrigerant decompressed refrigerant and the main part economizer parts by the economizer heat exchanger. A multi-stage compressor unit for a refrigeration system configured to circulate refrigerant,
A first compressor subunit having a first stage, a second stage, and an intermediate port disposed between the first stage and the second stage;
A second compressor subunit having a first stage;
Wherein the first stage of the first compressor subunit is configured to compress the first portion of the refrigerant to an intermediate pressure, and the second stage of the first compressor subunit is The first portion is configured to compress to the outlet pressure of the first compressor subunit, and the second compressor subunit is configured to reduce the second portion of refrigerant to the outlet pressure of the second compressor subunit. The compressed second portion configured to compress is mixed with the compressed first portion ;
The second compressor subunit discharges the second portion of refrigerant to the intermediate port of the first compressor subunit, and the outlet pressure of the second compressor subunit is the first compressor subunit's outlet pressure. A multi-stage compressor unit, characterized in that it is substantially equal to the intermediate pressure .

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