Refrigeration cycle apparatus

Abstract

A refrigeration cycle apparatus comprising: a plurality of turbo compressors installed in the same refrigeration cycle; and a flow path switching device for switching flow paths of refrigerant flowing through the plurality of turbo compressors. Each of the plurality of turbo compressors has a single-stage impeller or a plurality of stages of impellers. The flow path switching device is capable of switching the flow paths such that the impellers of the plurality of turbo compressors are connected in series or in parallel.

Description

Refrigeration Cycle Equipment

[0001] The present disclosure relates to a refrigeration cycle device having a plurality of turbo compressors.

[0002] Patent Document 1 describes a configuration in which the number of centrifugal compressors connected in series within the same refrigeration cycle is controlled.

[0003] Japanese Unexamined Patent Publication No. 63-055397

[0004] A positive displacement compressor compresses a refrigerant in a nearly sealed compression chamber created by contacting metal surfaces. Since the efficiency and product life of a positive displacement compressor would be significantly reduced if lubricating oil were not used, many positive displacement compressors use refrigeration oil. However, because refrigeration oil circulates through the refrigeration cycle together with the refrigerant, when multiple compressors connected to the same refrigeration cycle are controlled, uneven oil volume can occur between the compressors, potentially resulting in poor lubrication.

[0005] On the other hand, turbo compressors do not require metal surfaces to contact each other to seal the compression chamber, so they can be configured without using refrigeration oil. However, due to problems such as surging and choke, turbo compressors have difficulty adjusting the refrigeration capacity by controlling the rotation speed while maintaining the compression ratio, as is the case with positive displacement compressors. Therefore, when using turbo compressors, there is a problem that the range of operable conditions is narrowed.

[0006] The present disclosure has been made to solve the above-mentioned problems, and has an object to provide a refrigeration cycle device that uses a turbo compressor and can be operated efficiently under a wide range of operating conditions.

[0007] The refrigeration cycle device according to the present disclosure includes a plurality of turbo compressors installed in the same refrigeration cycle, and a flow path switch that switches the flow path of the refrigerant flowing to the plurality of turbo compressors, each of the plurality of turbo compressors having a single-stage or multi-stage impeller, and the flow path switch is capable of switching the flow path so that the impellers of the plurality of turbo compressors are connected in series or in parallel.

[0008] According to the present disclosure, a turbo compressor can be used to operate efficiently under a wide range of operating conditions.

[0009] FIG. 1 is a schematic configuration diagram of a refrigeration cycle device according to embodiment 1. FIG. 2 is a schematic configuration diagram of the inside of a compressor of the refrigeration cycle device according to embodiment 1. FIG. 3 is a schematic configuration diagram of a refrigeration cycle device according to modified example 1 of embodiment 1. FIG. 4 is a graph comparing the operating condition ranges of a positive displacement compressor and a turbo compressor. FIG. 5 is a graph comparing the operating condition ranges of a positive displacement compressor and a turbo compressor. FIG. 6 is a graph comparing the operating condition ranges of a positive displacement compressor and a turbo compressor. FIG. 7 is a schematic configuration diagram of a refrigeration cycle device according to modified example 2 of embodiment 1. FIG. 8 is a schematic configuration diagram of a refrigeration cycle device according to embodiment 2. FIG. 9 is a schematic configuration diagram of a refrigeration cycle device according to embodiment 3. FIG. 10 is a schematic configuration diagram of a refrigeration cycle device according to embodiment 4. FIG. 11 is a schematic configuration diagram of a refrigeration cycle device according to modified example 1 of embodiment 4. FIG. 12 is a schematic configuration diagram of a refrigeration cycle device according to modified example 2 of embodiment 4. FIG. 13 is a schematic configuration diagram of a refrigeration cycle device according to modified example 3 of embodiment 4. FIG. 14 is a schematic configuration diagram of a refrigeration cycle device according to embodiment 5.

[0010] Embodiments of the present disclosure will be described below with reference to the drawings. The present disclosure is not limited to the following embodiments and can be modified in various ways without departing from the spirit and scope of the present disclosure. Furthermore, the present disclosure includes all possible combinations of the configurations shown in the following embodiments. In particular, the combinations of components are not limited to the combinations in each embodiment; components described in one embodiment can be applied to another embodiment. In the following description, directional terms (e.g., "up," "down," "right," "left," "front," "rear," etc.) are used as appropriate to facilitate understanding, but these are for explanatory purposes and do not limit the present disclosure. In each drawing, components designated with the same reference numerals are identical or equivalent, and this applies throughout the entire specification. Note that the relative dimensional relationships or shapes of each component in each drawing may differ from those in actuality.

[0011] Embodiment 1. A refrigeration cycle apparatus according to embodiment 1 will be described. FIG. 1 is a schematic diagram of a refrigeration cycle apparatus 100 according to this embodiment. In the diagram, thick lines connecting each component indicate refrigerant piping. Dashed lines connecting each component indicate electrical wiring. Arrows at the end points of the thick lines always indicate the direction of refrigerant flow. Thin solid arrows, dotted arrows, and dashed-dotted arrows drawn parallel to the thick lines each indicate the direction of refrigerant flow when the flow path is switched. Descriptions of cases where the route of the refrigerant flowing through a heat exchanger or the like is switched, such as between heating and cooling operations of an air conditioner, will be omitted.

[0012] 1 , the refrigeration cycle apparatus 100 includes a first compressor 1A, a second compressor 1B, a discharge-side flow path switch 3, a condenser 4, an expansion valve 5, an evaporator 6, a suction-side flow path switch 2, a first power supply unit 7A, a second power supply unit 7B, and a controller 8. The first compressor 1A, the second compressor 1B, the discharge-side flow path switch 3, the condenser 4, the expansion valve 5, the evaporator 6, and the suction-side flow path switch 2 are connected in this order via refrigerant piping in a circular configuration, thereby forming a refrigerant circuit in which the refrigerant circulates.

[0013] The first compressor 1A is a turbo compressor having a first impeller 1Aa and a second impeller 1Ab therein. The first impeller 1Aa and the second impeller 1Ab are arranged in series with respect to the refrigerant flow inside the first compressor 1A. The second compressor 1B is a turbo compressor having a first impeller 1Ba and a second impeller 1Bb therein. The first impeller 1Ba and the second impeller 1Bb are arranged in series with respect to the refrigerant flow inside the second compressor 1B.

[0014] The refrigerant suction sides of the first compressor 1A and the second compressor 1B are connected via refrigerant piping to a suction-side flow switching device 2. The refrigerant discharge sides of the first compressor 1A and the second compressor 1B are connected via refrigerant piping to a discharge-side flow switching device 3.

[0015] The evaporator 6 and the suction side flow path switcher 2 are connected via a low-pressure refrigerant flow path 31. The discharge side flow path switcher 3 and the condenser 4 are connected via a high-pressure refrigerant flow path 32. The suction side flow path switcher 2 and the discharge side flow path switcher 3 are connected via three flow paths: a first flow path 21, a second flow path 22, and a third flow path 23. A first compressor 1A is provided in the first flow path 21. A second compressor 1B is provided in the third flow path 23. No compressor is provided in the second flow path 22. In this embodiment, when the number of compressors is n, the number of flow paths connecting the suction side flow path switch 2 and the discharge side flow path switch 3 is 2n-1.

[0016] The suction side flow path switch 2 and the discharge side flow path switch 3 are each connected to the controller 8 via electrical wiring. The suction side flow path switch 2 and the discharge side flow path switch 3 are configured to switch the flow paths in response to a signal issued by the controller 8. By switching the flow path, the refrigerant that has flowed from the evaporator 6 into the suction side flow path switch 2 flows serially through the compressors 1A and 1B in this order or in the reverse order, flows in parallel through the compressors 1A and 1B, or flows only through one of the compressors 1A and 1B.

[0017] 1 represent the flow paths of the refrigerant when it flows serially through the first compressor 1A and the second compressor 1B in this order. In this state, the flow paths of the suction-side flow path switch 2 are switched so that the low-pressure refrigerant flow path 31 communicates with the first flow path 21 and the second flow path 22 communicates with the third flow path 23. The flow paths of the discharge-side flow path switch 3 are switched so that the first flow path 21 communicates with the second flow path 22 and the third flow path 23 communicates with the high-pressure refrigerant flow path 32.

[0018] 1 indicate the flow paths when the refrigerant flows in parallel through the first compressor 1A and the second compressor 1B. In this state, the flow paths of the suction-side flow path switch 2 are switched so that the low-pressure refrigerant flow path 31 communicates with the first flow path 21 and the third flow path 23. The flow paths of the discharge-side flow path switch 3 are switched so that the first flow path 21 and the third flow path 23 communicate with the high-pressure refrigerant flow path 32.

[0019] 1 indicate the flow paths of the refrigerant flowing through only the first compressor 1A. In this state, the flow paths of the suction-side flow path switch 2 are switched so that the low-pressure refrigerant flow path 31 communicates with the first flow path 21. The flow paths of the discharge-side flow path switch 3 are switched so that the first flow path 21 communicates with the high-pressure refrigerant flow path 32.

[0020] The first compressor 1A is connected to the controller 8 via an electric wiring through a first power supply unit 7A. The second compressor 1B is connected to the controller 8 via an electric wiring through a second power supply unit 7B. The controller 8 is configured to start and stop each compressor and control the motor rotation speed of each compressor. The controller 8 may be configured by a microcomputer or dedicated hardware.

[0021] 2 is a schematic diagram of the inside of a compressor of a refrigeration cycle apparatus 100 according to this embodiment. Arrows in the figure indicate the flow direction of refrigerant vapor. In this embodiment, the first compressor 1A and the second compressor 1B have the same configuration. Therefore, in the following description, the first compressor 1A and the second compressor 1B may each be simply referred to as compressor 1. Similarly, the first impeller 1Aa and the first impeller 1Ba may each be referred to as first impeller 1a, and the second impeller 1Ab and the second impeller 1Bb may each be referred to as second impeller 1b.

[0022] As shown in Fig. 2, the compressor 1 has therein a motor 9, a bearing 10, a first impeller 1a, and a second impeller 1b. The motor 9, the bearing 10, the first impeller 1a, and the second impeller 1b are connected coaxially. The first impeller 1a is provided on one end of the motor 9 in the axial direction. The second impeller 2a is provided on the other end of the motor 9 in the axial direction. The first impeller 1a and the second impeller 1b are connected to the motor 9 via a common rotation shaft. The first impeller 1a and the second impeller 1b are mounted symmetrically with respect to the axial direction.

[0023] The motor 9 is connected via electrical wiring to a power supply unit 7 external to the compressor 1. The motor 9 is rotated by the power supplied from the power supply unit 7. The first impeller 1a and the second impeller 1b are rotated by the rotational power of the motor 9 and compress the refrigerant vapor. The first impeller 1a and the second impeller 1b are connected in series in the flow of the refrigerant.

[0024] The refrigerant vapor that flows into the compressor 1 first flows into the first impeller 1a and is compressed by the application of force. The refrigerant vapor compressed by the first impeller 1a flows into the second impeller 1b and is further compressed by the application of force again before being discharged from the compressor 1.

[0025] The bearing 10 is configured to support axial forces in the radial and axial directions so that the rotating shaft does not whirl due to the rotational power of the motor 9 and the forces applied to the refrigerant vapor by the first impeller 1 a and the second impeller 1 b. It is preferable to use a magnetic bearing, gas bearing, or the like for the bearing 10, which can support the axial force without seizing even without using lubricating oil.

[0026] The first impeller 1a and the second impeller 1b are each subjected to a large axial force due to the reaction of the force applied to the refrigerant vapor, the pressure on their back surfaces from the refrigerant that has been pressurized after compression, etc. For this reason, it is desirable to install the first impeller 1a and the second impeller 1b in opposite axial directions as shown in Figure 2 so that the axial forces in the axial direction can be offset.

[0027] 3 is a schematic diagram of a refrigeration cycle apparatus 101 according to a first modified example of this embodiment. The thick lines connecting the components in the diagram indicate refrigerant piping. The arrows at the end points of the thick lines indicate the direction of refrigerant flow at all times. The thin solid arrows and dotted arrows drawn parallel to the thick lines indicate the direction of refrigerant flow when the flow path is switched, respectively. The electrical wiring shown in FIG. 1 and the devices connected thereby are omitted.

[0028] The suction-side flow path switch 2 and the discharge-side flow path switch 3 are connected via five flow paths: a first flow path 21, a second flow path 22, a third flow path 23, a fourth flow path 24, and a fifth flow path 25. A first compressor 1A is provided in the first flow path 21. A second compressor 1B is provided in the third flow path 23. A third compressor 1C is provided in the fifth flow path 25. No compressors are provided in the second flow path 22 and the fourth flow path 24.

[0029] The first compressor 1A has a first impeller 1Aa, a second impeller 1Ab, and a third impeller 1Ac inside. The first impeller 1Aa, the second impeller 1Ab, and the third impeller 1Ac are connected in series in the refrigerant flow inside the first compressor 1A. The second compressor 1B has a first impeller 1Ba, a second impeller 1Bb, and a third impeller 1Bc inside. The first impeller 1Ba, the second impeller 1Bb, and the third impeller 1Bc are connected in series in the refrigerant flow inside the second compressor 1B. The third compressor 1C has a first impeller 1Ca, a second impeller 1Cb, and a third impeller 1Cc inside. The first impeller 1Ca, the second impeller 1Cb, and the third impeller 1Cc are connected in series in the refrigerant flow inside the third compressor 1C.

[0030] While Fig. 1 illustrates the refrigeration cycle apparatus 100 including two compressors each having a two-stage impeller, the refrigeration cycle apparatus 101 shown in Fig. 3 includes three compressors each having a three-stage impeller. In this manner, the refrigeration cycle apparatus may include three or more compressors. Each compressor may have three or more stages of impellers, or may have a single-stage impeller.

[0031] The suction-side flow path switch 2 and the discharge-side flow path switch 3 are configured to switch their flow paths in response to a signal from the controller 8. The thin solid arrows in Fig. 3 represent the flow paths when the refrigerant flows serially through the first compressor 1A, the second compressor 1B, and the third compressor 1C in this order. In this state, the flow paths of the suction-side flow path switch 2 are switched so that the low-pressure refrigerant flow path 31 communicates with the first flow path 21, the second flow path 22 communicates with the third flow path 23, and the fourth flow path 24 communicates with the fifth flow path 25. The flow paths of the discharge-side flow path switch 3 are switched so that the first flow path 21 communicates with the second flow path 22, the third flow path 23 communicates with the fourth flow path 24, and the fifth flow path 25 communicates with the high-pressure refrigerant flow path 32.

[0032] 3 indicate the flow paths of the refrigerant when it flows in parallel through the first compressor 1A, the second compressor 1B, and the third compressor 1C. In this state, the flow paths of the suction-side flow path switch 2 are switched so that the low-pressure refrigerant flow path 31 communicates with the first flow path 21, the third flow path 23, and the fifth flow path 25. The flow paths of the discharge-side flow path switch 3 are switched so that the first flow path 21, the third flow path 23, and the fifth flow path 25 communicate with the high-pressure refrigerant flow path 32.

[0033] Next, a description will be given of the operation of the refrigeration cycle apparatus 100. The refrigeration cycle apparatus 100 operates to transfer heat from the evaporator 6 side to the condenser 4 side so as to warm the environment on the condenser 4 side or cool the environment on the evaporator 6 side. In the refrigeration cycle apparatus 100, the operating state of each compressor and the refrigerant flow path of each flow path switch change depending on the surrounding environment and load conditions.

[0034] The refrigerant vapor flowing out from the discharge side flow path switch 3 releases heat to the surrounding environment through the condenser 4 and is condensed. The refrigerant liquid flowing out from the condenser 4 is decompressed in the expansion valve 5, and a portion of it becomes refrigerant vapor, expands, and its temperature drops. The refrigerant flowing out from the expansion valve 5 absorbs heat from the surrounding environment through the evaporator 6 and is evaporated. The refrigerant vapor flowing out from the evaporator 6 flows into the suction side flow path switch 2. The operations up to this point are common to the refrigeration cycle devices of each embodiment. In cases where the heat exchanger responsible for the condenser 4 and the heat exchanger responsible for the evaporator 6 are switched, such as in an air conditioner that can switch between cooling and heating, the refrigerant flow path from the discharge side flow path switch 3 to the suction side flow path switch 2 may be configured to be switchable.

[0035] In this embodiment, the refrigerant flow path from the suction side flow path switch 2 to the discharge side flow path switch 3 until the refrigerant vapor is compressed in each compressor, and the rotation speed of each compressor are controlled by the controller 8 according to conditions such as the surrounding environment and load situation.

[0036] Figures 4 to 6 are graphs comparing the operating condition ranges of a positive displacement compressor and a turbo compressor. Figure 4 shows the operating condition range under conditions where the volumetric flow rate of the refrigerant circulating through the refrigeration cycle is small. Figure 5 shows the operating condition range under conditions where the volumetric flow rate of the refrigerant circulating through the refrigeration cycle is intermediate. Figure 6 shows the operating condition range under conditions where the volumetric flow rate of the refrigerant circulating through the refrigeration cycle is large. In Figures 4 to 6, the horizontal axis represents suction pressure, and the vertical axis represents discharge pressure. The hatched areas in Figures 4 to 6 represent the operable condition range for a positive displacement compressor at the same rotation speed. The solid lines represent the operable condition range for a turbo compressor at the same rotation speed.

[0037] As shown in Figures 4 to 6, in a refrigeration cycle system using a positive displacement compressor, the volumetric flow rate depends almost entirely on the rotational speed, so an operating range from low to high volumetric flow rates can be covered by controlling only the rotational speed. In contrast, in a refrigeration cycle system using a single turbo compressor, the volumetric flow rate also depends on the compression ratio. Therefore, increasing the rotational speed also increases the compression ratio, changing the pressure limits of the suction pressure and discharge pressure at which surging and choking occur. Therefore, when using a turbo compressor, it is difficult to cover the same wide operating range as a positive displacement compressor by controlling the rotational speed alone. In this embodiment, by controlling not only the rotational speed but also the number of compressors 1, a wide operating range equivalent to or greater than that of a positive displacement compressor is achieved using a turbo compressor.

[0038] For example, as the condition for a smaller volumetric flow rate at the same compression ratio increases, the flow paths are switched so that the number of compressors 1 connected in series increases, and the suction-side flow path switch 2 and the discharge-side flow path switch 3 are controlled to reduce the average rotation speed of each compressor 1, as shown in Fig. 4. On the other hand, as the condition for a larger volumetric flow rate at the same compression ratio increases, the flow paths are switched so that the number of compressors 1 connected in parallel increases, and the suction-side flow path switch 2 and the discharge-side flow path switch 3 are controlled to reduce the average rotation speed of each compressor 1, as shown in Fig. 6.

[0039] Furthermore, as the compression ratio becomes lower at the same volumetric flow rate, the suction-side flow path switch 2 and the discharge-side flow path switch 3 are controlled to decrease the number of compressors 1 connected in series or increase the number of compressors 1 connected in parallel while relatively lowering the average rotation speed of each compressor 1. On the other hand, as the compression ratio becomes higher at the same volumetric flow rate, the suction-side flow path switch 2 and the discharge-side flow path switch 3 are controlled to increase the number of compressors 1 connected in series or decrease the number of compressors 1 connected in parallel while relatively raising the average rotation speed of each compressor 1.

[0040] In some cases, the number of compressors 1 connected in series or the number of compressors 1 connected in parallel may be controlled in stages depending on the conditions as described above, thereby achieving a wide operating range.

[0041] In positive displacement compressors, such as reciprocating, rotary, scroll, and screw types, refrigerant is compressed in a nearly sealed compression chamber created by contacting metal surfaces. Without lubricating oil, positive displacement compressors often suffer from refrigerant leakage and seizure between metal surfaces, significantly reducing efficiency and product life. For this reason, many positive displacement compressors use refrigeration oil. However, because refrigeration oil circulates through the refrigerant cycle, controlling multiple compressors connected to the same refrigeration cycle can lead to uneven oil levels among the compressors, resulting in poor lubrication. Connecting multiple positive displacement compressors in series and connecting them in parallel requires different methods for ensuring sufficient oil within each compressor. In both cases, the refrigerant circuit and control system become more complex.

[0042] On the other hand, turbo compressors do not require metal surfaces to contact each other to seal the compression chamber, making it possible to configure them without using refrigeration oil. However, unlike positive displacement compressors, the volumetric flow rate of turbo compressors does not depend almost solely on the rotational speed; the volumetric flow rate also varies depending on the compression ratio. For this reason, controlling the rotational speed while maintaining the compression ratio in turbo compressors is difficult due to problems such as surging and choking. Therefore, when using turbo compressors, the range of operable conditions is narrow.

[0043] In this embodiment, multiple turbo compressors are connected within the same refrigeration cycle, and the refrigerant flow path can be switched between series and parallel flow through each compressor depending on the operating conditions. This allows the compression stages to be switched between series and parallel without using oil. This embodiment eliminates the risk of poor lubrication, as occurs with positive displacement compressors, and does not require complex measures to prevent oil imbalance, such as an oil separation circuit. Furthermore, the use of oil does not result in a decrease in efficiency. Furthermore, by controlling the number of operating compressors and switching the connection of each compressor between series and parallel, turbo compressors can be used efficiently over a wide range of operating conditions without causing surging or choking. Furthermore, the use of refrigeration oil suppresses deterioration of each component, thereby extending the product life and maintaining high efficiency for a long period of time.

[0044] When simply controlling the number of compressors connected in series or in parallel, increasing the number of control stages depending on conditions and loads results in a corresponding increase in the number of compressors. In contrast, this embodiment not only controls the number of compressors, but also switches the compressor connection between series and parallel. Therefore, the number of control stages can be increased depending on conditions and loads without increasing the number of compressors. Furthermore, since it is possible to reduce the total number of compressor motors used in the refrigeration cycle device, the number of compressor power supplies, etc. can be reduced, simplifying the system.

[0045] 2, inside each compressor 1, the first impeller 1a and the second impeller 1b are installed facing opposite directions with the motor 9 in between. This cancels out the axial forces applied to the first impeller 1a and the second impeller 1b, reducing the stress load applied to the bearing 10 and enabling the motor 9 to be controlled at a higher rotation speed. This further widens the range of operable conditions of the refrigeration cycle device.

[0046] As shown in Figure 1, a refrigeration cycle apparatus 100 including a first compressor 1A and a second compressor 1B, each equipped with two impellers, has the simplest configuration and has an operable condition range equal to or greater than that of a refrigeration cycle apparatus using a positive displacement compressor. To further widen the operable condition range, the number of compressors may be increased as shown in Figure 3. To increase the operable compression ratio, the number of impellers inside the compressors may be increased as shown in Figure 3. Conversely, if a narrower operable compression ratio is acceptable, the number of impellers inside the compressors may be reduced to one.

[0047] FIG. 7 is a schematic diagram of a refrigeration cycle apparatus 102 according to a second modification of this embodiment. The thick lines connecting the components in the diagram indicate refrigerant piping. The arrows at the end points of the thick lines always indicate the direction of refrigerant flow. The thin solid arrows drawn parallel to the thick lines indicate the direction of refrigerant flow. The electrical wiring shown in FIG. 1 and the devices connected thereby are not shown here. This modification can also switch the refrigerant flow direction to that shown by the thin solid arrows and dotted arrows in FIG. 3.

[0048] In the state shown in Figure 7, the refrigerant flows in parallel through the first compressor 1A and the third compressor 1C, is compressed, and then the flows merge and are further compressed by the second compressor 1B. When three or more compressors are used in this manner, the flow paths may be switched so that the refrigerant flows in parallel through some compressors and in series through other compressors. The number, combination, and order of parallel and series compressors may be freely set according to the operating environment and conditions.

[0049] For example, under conditions of a small flow rate and a high compression ratio, when the flow rate of the compressors in the subsequent stages is insufficient or excessively high, but not enough to connect all the compressors in series, it is preferable to control as shown in Fig. 7. Also, under conditions of a large flow rate and a low compression ratio, when the flow rate of the compressors in the subsequent stages is insufficient or excessively high, but not enough to connect all the compressors in parallel, it is preferable to control as shown in Fig. 7.

[0050] In this modification, the combination of series and parallel connections can be changed for each compressor, allowing for more precise adjustment of the refrigerant flow rate into each impeller. This allows for a wider operating range, prevents damage to each impeller, and realizes a refrigeration cycle device with reduced efficiency degradation.

[0051] As described above, the refrigeration cycle apparatus according to this embodiment includes the first compressor 1A, the second compressor 1B, and the third compressor 1C, as well as the suction-side flow path switch 2 and the discharge-side flow path switch 3. The first compressor 1A, the second compressor 1B, and the third compressor 1C are installed in the same refrigeration cycle. The suction-side flow path switch 2 and the discharge-side flow path switch 3 are configured to switch the flow path of the refrigerant flowing through the first compressor 1A, the second compressor 1B, and the third compressor 1C. Each of the first compressor 1A, the second compressor 1B, and the third compressor 1C has a single-stage or multi-stage impeller. The suction-side flow path switch 2 and the discharge-side flow path switch 3 can switch the flow path so that the impellers of the first compressor 1A, the second compressor 1B, and the third compressor 1C are connected in series or in parallel. Here, the first compressor 1A, the second compressor 1B, and the third compressor 1C are an example of a plurality of turbo compressors. The suction side flow path switch 2 and the discharge side flow path switch 3 are examples of a flow path switch.

[0052] This configuration allows for efficient use over a wide range of operating conditions while suppressing surging and choking. Furthermore, this configuration eliminates the need for refrigeration oil, minimizing the deterioration of each component. This extends the product's lifespan and allows for high efficiency to be maintained for a long time.

[0053] The refrigeration cycle apparatus according to this embodiment further includes a controller 8 that controls the first compressor 1A, the second compressor 1B, the third compressor 1C, the suction-side flow path switch 2, and the discharge-side flow path switch 3. The controller 8 controls the suction-side flow path switch 2 and the discharge-side flow path switch 3 so that the number of impellers connected in series increases as the low-flow-rate, high-compression-ratio condition increases. The controller 8 controls the suction-side flow path switch 2 and the discharge-side flow path switch 3 so that the number of impellers connected in parallel increases as the high-flow-rate, low-compression-ratio condition increases. This configuration allows for efficient use over a wide range of operating conditions while suppressing the occurrence of surging, choking, and the like.

[0054] In the refrigeration cycle apparatus according to this embodiment, the number of turbo compressors is two. Each of the first compressor 1A and the second compressor 1B has a two-stage impeller. The two-stage impellers are mounted symmetrically with respect to the axial direction. With this configuration, the number of impellers can be reduced, and therefore the total number of motors that drive the impellers can be reduced. Furthermore, because the two-stage impellers are mounted symmetrically with respect to the axial direction, the axial load on the bearings can be reduced.

[0055] In a refrigeration cycle apparatus according to a second modification of the present embodiment, the number of turbo compressors is three or more. The suction-side flow path switch 2 and the discharge-side flow path switch 3 are capable of switching the flow paths so that the first compressor 1A and the third compressor 1C are connected in parallel and the second compressor 1B is connected in series with the first compressor 1A and the third compressor 1C. This configuration allows for more precise capacity control, thereby more reliably preventing the occurrence of surging, choking, and the like and improving operating efficiency.

[0056] In the refrigeration cycle apparatus according to this embodiment, the flow path switcher includes a suction side flow path switcher 2 and a discharge side flow path switcher 3. The suction side flow path switcher 2 is provided between the evaporator 6 and the first and second compressors 1A and 1B. The discharge side flow path switcher 3 is provided between the first and second compressors 1A and 1B and the condenser 4. The evaporator 6 is connected to the suction side flow path switcher 2 via a low-pressure refrigerant flow path 31. The discharge side flow path switcher 3 is connected to the condenser 4 via a high-pressure refrigerant flow path 32. The suction side flow path switcher 2 and the discharge side flow path switcher 3 are connected via a first flow path 21, a second flow path 22, and a third flow path 23. The first compressor 1A is provided in the first flow path 21. The second compressor 1B is provided in the third flow path 23. In the suction side flow path switch 2, the low-pressure refrigerant flow path 31 can be communicated with the first flow path 21, and the second flow path 22 can be communicated with the third flow path 23. In the discharge side flow path switch 3, the first flow path 21 can be communicated with the second flow path 22, and the third flow path 23 can be communicated with the high-pressure refrigerant flow path 32. When the flow paths of the suction side flow path switch 2 and the discharge side flow path switch 3 are set in this manner, the first compressor 1A and the second compressor 1B are connected in series. In the suction side flow path switch 2, the low-pressure refrigerant flow path 31 can be communicated with the first flow path 21 and the third flow path 23. In the discharge side flow path switch 3, the first flow path 21 and the third flow path 23 can be communicated with the high-pressure refrigerant flow path 32. When the flow paths of the suction side flow path switch 2 and the discharge side flow path switch 3 are set in this manner, the first compressor 1A and the second compressor 1B are connected in parallel.

[0057] According to this configuration, the series connection and parallel connection of the first compressor 1A and the second compressor 1B can be switched with a simpler configuration.

[0058] Embodiment 2. A refrigeration cycle device according to embodiment 2 will be described. Fig. 8 is a schematic diagram of a refrigeration cycle device 103 according to this embodiment. The thick lines connecting the components in the figure indicate refrigerant piping. The arrows at the end points of the thick lines indicate the direction in which the refrigerant always flows. The thin solid arrows and dotted arrows drawn parallel to the thick lines indicate the direction in which the refrigerant flows when the flow path is switched, respectively. The electrical wiring shown in Fig. 1 and the devices connected thereby will not be shown again.

[0059] The first compressor 1A has a first impeller 1Aa and a second impeller 1Ab therein. The first impeller 1Aa and the second impeller 1Ab are arranged in series in the refrigerant flow inside the first compressor 1A. The first impeller 1Aa is arranged upstream of the second impeller 1Ab. The sizes of the first impeller 1Aa and the second impeller 1Ab are adjusted so that the inlet cross-sectional area of ​​the first impeller 1Aa is larger than the inlet cross-sectional area of ​​the second impeller 1Ab.

[0060] The second compressor 1B has a first impeller 1Ba and a second impeller 1Bb therein. The first impeller 1Ba and the second impeller 1Bb are arranged in series in the refrigerant flow inside the second compressor 1B. The first impeller 1Ba is arranged upstream of the second impeller 1Bb. The sizes of the first impeller 1Ba and the second impeller 1Bb are adjusted so that the inlet cross-sectional area of ​​the first impeller 1Ba is larger than the inlet cross-sectional area of ​​the second impeller 1Bb.

[0061] Furthermore, the inlet cross-sectional area of ​​the second impeller 1Ab of the first compressor 1A is larger than the inlet cross-sectional area of ​​the first impeller 1Ba of the second compressor 1B. In this embodiment, when the first compressor 1A and the second compressor 1B are connected in series, the first compressor 1A is disposed upstream of the second compressor 1B, and the first impeller 1Aa, the second impeller 1Ab, the first impeller 1Ba, and the second impeller 1Bb are disposed in this order. As a result, the inlet cross-sectional area of ​​the upstream impeller is larger than the inlet cross-sectional area of ​​the impeller further downstream.

[0062] Even when controlling the operation of one compressor alone, the output may be changed by operating either the first compressor 1A or the second compressor 1B depending on the surrounding environmental conditions and the load. For example, when the load is slightly higher than the intermediate condition, only the first compressor 1A, which has a larger inlet cross-sectional area of ​​the internal impeller, is operated. When the load is slightly lower than the intermediate condition, only the second compressor 1B, which has a smaller inlet cross-sectional area of ​​the internal impeller, is operated.

[0063] As shown in FIG. 3 , the same operation can be performed when three or more compressors are used, or when three or more impellers are used inside each compressor. That is, when compressors are connected in series to compress, it is preferable to make the inlet cross-sectional area of ​​the upstream impeller larger than that of the downstream impeller. Furthermore, when three or more compressors are used, whether connected in series or in parallel, the number of control stages can be increased by changing the combination pattern of operating and unused compressors depending on the surrounding environmental conditions and load. For example, even if the number of operating compressors is the same, when the load is slightly higher, it is preferable to prioritize the combination of compressors with larger inlet cross-sectional areas of their internal impellers. Even when using a single compressor, it is preferable to select a compressor with a larger inlet cross-sectional area of ​​its impeller as the load increases.

[0064] In a series connection, the density of the refrigerant compressed by the upstream impeller increases, resulting in a decrease in volumetric flow rate. When a refrigerant with a small volumetric flow rate flows into the impeller, the main flow velocity around the blades slows, making surging more likely to occur. However, because the inlet cross-sectional area of ​​the downstream impeller is smaller, the main flow velocity around the blades does not slow down even when a refrigerant with a small volumetric flow rate flows in, thereby avoiding surging. By avoiding surging, impeller failure can be prevented and the operating range can be broadened. Since there is no need to excessively increase the refrigerant flow rate into the upstream impeller to avoid surging in the downstream impeller, choking and a decrease in compression efficiency in the upstream impeller can be prevented, resulting in a more efficient refrigeration cycle device.

[0065] Furthermore, even when operating a compressor alone or in parallel, the combination of compressors to be used and compressors to be stopped can be changed to control the system to maximize efficiency according to the load, thereby providing a more efficient refrigeration cycle device.

[0066] As described above, in the refrigeration cycle apparatus according to the present embodiment, when the impellers are connected in series, the inlet cross-sectional area of ​​the impellers becomes smaller toward the downstream side. This configuration makes it possible to more reliably suppress the occurrence of surging and choking.

[0067] In the refrigeration cycle apparatus according to this embodiment, when the first compressor 1A and the second compressor 1B are connected in parallel, the controller 8 stops one compressor as follows. That is, the controller 8 stops the compressor having an impeller with a smaller inlet cross-sectional area when the flow rate is higher, and stops the compressor having an impeller with a larger inlet cross-sectional area when the flow rate is lower. This configuration allows for more precise capacity control, thereby improving operating efficiency.

[0068] Third Embodiment A refrigeration cycle device according to a third embodiment will be described. Fig. 9 is a schematic diagram of a refrigeration cycle device 104 according to this embodiment. Thick lines connecting the components in the figure indicate refrigerant piping. Arrows at the end points of the thick lines indicate the direction in which the refrigerant always flows. Thin solid arrows and dotted arrows drawn parallel to the thick lines indicate the direction in which the refrigerant flows when the flow path is switched, respectively. The electrical wiring shown in Fig. 1 and the devices connected thereby will not be shown again.

[0069] The suction side flow path switch 2 of the refrigeration cycle apparatus 104 is provided with a flow rate adjustment valve 13a. When the refrigerant flows in series from the first compressor 1A to the second compressor 1B, the refrigerant discharged from the first compressor 1A passes through the discharge side flow path switch 3 and the third flow path 23 and returns to the suction side flow path switch 2. When the flow rate adjustment valve 13a is open, the refrigerant returning to the suction side flow path switch 2 is split by the suction side flow path switch 2, with a portion flowing back into the first compressor 1A and the remaining main flow flowing to the second compressor 1B. The flow rate of the refrigerant flowing back into the first compressor 1A from the suction side flow path switch 2 is adjusted by the flow rate adjustment valve 13a.

[0070] Such an operating pattern may be used, for example, in conditions where the overall temperature is low and the compression ratio is low, and even if an appropriate amount of refrigerant flows into the second compressor 1B, the flow rate of refrigerant flowing into the first compressor 1A is low or the refrigerant liquid is likely to mix. This operating pattern may also be used immediately before starting the refrigeration cycle device 104 after it has been stopped for a while, because the environment around the compressor is low. In cases where such operating conditions are expected that the refrigerant liquid is likely to mix and flow into the first compressor 1A, an accumulator 11 may be installed on the outlet side of the evaporator 6, or an accumulator 12 may be installed on the suction side of the first compressor 1A, as shown in FIG. 9 .

[0071] In conditions where the overall temperature is low and the compression ratio is low, even if an appropriate amount of refrigerant flows into the second compressor 1B, the flow rate of the refrigerant flowing into the first compressor 1A may be low, or the refrigerant flowing into the first compressor 1A may be easily mixed with liquid refrigerant. In such cases, in this embodiment, a portion of the refrigerant discharged from the first compressor 1A is returned to the first compressor 1A, thereby increasing the refrigerant flow rate into the first compressor 1A. Furthermore, because a portion of the high-temperature refrigerant compressed by the first compressor 1A is returned to the first compressor 1A, the liquid refrigerant flowing into the first compressor 1A is heated and evaporated. This prevents liquid refrigerant from flowing into the first compressor 1A. As a result, impeller failure due to surging and other factors can be prevented, and the operating range can be further expanded. Similar effects can be achieved even when the refrigeration cycle apparatus 104 is started up after being shut down for a while.

[0072] 9 , the discharge-side flow path switch 3 may be provided with a flow rate adjustment valve 13b. When the refrigerant flows in series from the first compressor 1A to the second compressor 1B, the refrigerant discharged from the second compressor 1B flows into the discharge-side flow path switch 3. When the flow rate adjustment valve 13b is open, the refrigerant is divided by the discharge-side flow path switch 3, and a portion of the refrigerant passes through the second flow path 22 and the suction-side flow path switch 2 and flows back into the second compressor 1B, while the remaining main flow flows to the condenser 4. The flow rate of the refrigerant flowing back into the second compressor 1B is adjusted by the flow rate adjustment valve 13b.

[0073] When operating with this operating pattern, for example, in conditions where the overall environment is low temperature and the compression ratio is high, even if an appropriate amount of refrigerant flows into the first compressor 1A, the flow rate of refrigerant flowing into the second compressor 1B is low.

[0074] Under conditions where the compression ratio is high, the density of the refrigerant after compression by the first compressor 1A increases, and the volumetric flow rate of the refrigerant flowing into the second compressor 1B decreases. In this embodiment, a portion of the refrigerant discharged from the second compressor 1B flows back into the second compressor 1B, thereby increasing the volumetric flow rate of the refrigerant flowing into the second compressor 1B. This prevents damage to the impeller of the second compressor 1B due to surging and further expands the operable range.

[0075] In addition, since a portion of the high-temperature refrigerant compressed by the second compressor 1B is returned to the second compressor 1B, the temperature of the refrigerant vapor flowing into the second compressor 1B increases. For this reason, this embodiment is more effective when operating in an environment with a low temperature overall.

[0076] In this embodiment, the refrigeration cycle apparatus 104 is illustrated as having two compressors, each having two stages of impellers. However, the configuration and operation of this embodiment can also be applied to a refrigeration cycle apparatus having multiple compressors, each having one or more stages of impellers, such as the refrigeration cycle apparatus shown in FIG.

[0077] As described above, in the refrigeration cycle apparatus according to the present embodiment, when the first compressor 1A and the second compressor 1B are connected in series, the suction-side flow path switch 2 can further connect the second flow path 22 and the first flow path 21. The suction-side flow path switch 2 has the flow control valve 13a between the second flow path 22 and the first flow path 21. Here, the flow control valve 13a is an example of a first flow control valve. With this configuration, the volumetric flow rate of the refrigerant flowing into the second compressor 1B can be increased, thereby preventing failure of the impeller of the second compressor 1B and further expanding the operable range.

[0078] Fourth Embodiment A refrigeration cycle apparatus according to a fourth embodiment will be described. Fig. 10 is a schematic diagram of a refrigeration cycle apparatus 105 according to this embodiment. Thick lines connecting the components in the figure indicate refrigerant piping. Arrows at the end points of the thick lines indicate the direction in which the refrigerant always flows. Thin solid arrows and dotted arrows drawn parallel to the thick lines indicate the direction in which the refrigerant flows when the flow path is switched, respectively. The electrical wiring shown in Fig. 1 and the devices connected thereby will not be shown again.

[0079] The refrigeration cycle device 105 is provided with an upstream expansion valve 5a and a downstream expansion valve 5b as expansion valves. A gas-liquid separator 14 is provided between the upstream expansion valve 5a and the downstream expansion valve 5b. A steam outlet of the gas-liquid separator 14 is connected to the second flow path 22 via a sixth flow path 26. A flow rate adjustment valve 15 is provided in the sixth flow path 26.

[0080] When refrigerant flows in series from the first compressor 1A to the second compressor 1B, the refrigerant condensed in the condenser 4 is decompressed to a certain extent by the upstream expansion valve 5a and then flows into the gas-liquid separator 14 to be separated into refrigerant liquid and refrigerant vapor. The refrigerant liquid flows out from a liquid outlet of the gas-liquid separator 14, is further decompressed by the downstream expansion valve 5b, and flows into the evaporator 6. On the other hand, when the flow control valve 15 is open, the refrigerant vapor flows out from a vapor outlet of the gas-liquid separator 14, passes through the flow control valve 15, merges with the second flow path 22, passes through the suction side flow path switch 2, and flows into the second compressor 1B.

[0081] When operating with this operating pattern, for example, in conditions where the overall environment is high and the compression ratio is high, even if an appropriate amount of refrigerant flows into the first compressor 1A, the flow rate of refrigerant flowing into the second compressor 1B is low.

[0082] Under conditions of a high compression ratio, the density of the refrigerant compressed by the first compressor 1A increases, resulting in a reduced volumetric flow rate of the refrigerant flowing into the second compressor 1B. In this embodiment, the refrigerant vapor separated by the gas-liquid separator 14 merges with the refrigerant discharged from the first compressor 1A and flows into the second compressor 1B, increasing the volumetric flow rate of the refrigerant flowing through the second compressor 1B. This prevents damage to the impeller of the second compressor 1B due to surging and further expands the operable range. Furthermore, the low-temperature refrigerant vapor separated by the gas-liquid separator 14 merges with the high-temperature refrigerant vapor discharged from the first compressor 1A and flows into the second compressor 1B. This reduces the temperature of the refrigerant vapor flowing into the second compressor 1B, improving the compression efficiency of the second compressor 1B. In other words, a refrigeration cycle apparatus can be provided that prevents damage to the second compressor 1B while suppressing a decrease in efficiency.

[0083] Fig. 11 is a schematic diagram of a refrigeration cycle device 106 according to a first modified example of this embodiment. The thick lines connecting the components in the figure indicate refrigerant piping. The arrows at the end points of the thick lines indicate the direction in which the refrigerant always flows. The thin solid arrows and dotted arrows drawn parallel to the thick lines indicate the direction in which the refrigerant flows when the flow path is switched, respectively. The electrical wiring shown in Fig. 1 and the devices connected thereby are omitted here.

[0084] The second flow path 22 is connected to a portion between the condenser 4 and the expansion valve 5 in the refrigerant circuit of the refrigeration cycle device 106 via a seventh flow path 27. The seventh flow path 27 is provided with a flow control valve 16 and an economizer 17. When the flow control valve 16 is open, a portion of the refrigerant is diverted to the seventh flow path 27.

[0085] When the refrigerant flows in series from the first compressor 1A to the second compressor 1B, the refrigerant condensed in the condenser 4 branches into two flows between the condenser 4 and the expansion valve 5. The main flow of the refrigerant flows into the expansion valve 5, where it is reduced in pressure, and then flows into the evaporator 6. The other branch flow is reduced in pressure to a certain extent by the flow control valve 16, and then exchanges heat with the high-temperature main flow in the economizer 17. The other branch flow passes through the seventh flow path 27, the second flow path 22, and the suction-side flow switch 2, and then flows into the second compressor 1B again.

[0086] When operating with this operating pattern, for example, in conditions where the overall environment is high and the compression ratio is high, even if an appropriate amount of refrigerant flows into the first compressor 1A, the flow rate of refrigerant flowing into the second compressor 1B is low.

[0087] In this modification, the branch flow of the refrigerant liquid, which has been reduced in pressure by the flow control valve 16 and reduced in temperature, is heated and vaporized by receiving heat from the high-temperature refrigerant before the branch in the economizer 17. This provides the same effects as the configuration in Fig. 10. That is, it is possible to provide a refrigeration cycle apparatus that prevents damage to the second compressor 1B and suppresses a decrease in efficiency.

[0088] FIG. 12 is a schematic diagram of a refrigeration cycle apparatus 107 according to a second modification of the present embodiment. The refrigeration cycle apparatus 107 shown in FIG. 12 is a further modification of the refrigeration cycle apparatus 105 shown in FIG. Two branch flow paths 26a and 26b branch off from the sixth flow path 26. The branch flow path 26a connects the sixth flow path 26 to a flow path between the first impeller 1Aa and the second impeller 1Ab inside the first compressor 1A. The branch flow path 26a is provided with a flow control valve 18a. The branch flow path 26b connects the sixth flow path 26 to a flow path between the first impeller 1Ba and the second impeller 1Bb inside the second compressor 1B. The branch flow path 26b is provided with a flow control valve 18b.

[0089] As a result, a portion of the refrigerant vapor separated in the gas-liquid separator 14 flows through the flow control valve 18a into the space between the first impeller 1Aa and the second impeller 1Ab inside the first compressor 1A. Also, a portion of the refrigerant vapor separated in the gas-liquid separator 14 flows through the flow control valve 18b into the space between the first impeller 1Ba and the second impeller 1Bb inside the second compressor 1B.

[0090] 10 , the sixth flow path 26 may be connected to the second flow path 22. In this case, when the first compressor 1A and the second compressor 1B are connected in series, a portion of the refrigerant vapor separated in the gas-liquid separator 14 can be merged with the second flow path 22 via the flow control valve 18c and can be made to flow into the second compressor 1B via the suction-side flow path switch 2.

[0091] FIG. 13 is a schematic diagram of a refrigeration cycle apparatus 108 according to a third modification of the present embodiment. The refrigeration cycle apparatus 108 shown in FIG. 13 is a further modification of the refrigeration cycle apparatus 106 shown in FIG. 11. Two branch flow paths 27a and 27b branch off from the seventh flow path 27. The branch flow path 27a connects the seventh flow path 27 to a flow path between the first impeller 1Aa and the second impeller 1Ab inside the first compressor 1A. The branch flow path 27a is provided with a flow control valve 18a. The branch flow path 27b connects the seventh flow path 27 to a flow path between the first impeller 1Ba and the second impeller 1Bb inside the second compressor 1B. The branch flow path 27b is provided with a flow control valve 18b.

[0092] As a result, the refrigerant diverted to the seventh flow path 27 is decompressed to a certain extent by the flow control valve 16 and heated by the economizer 17 to become refrigerant vapor. A portion of the refrigerant vapor flows through the flow control valve 18a into the space between the first impeller 1Aa and the second impeller 1Ab inside the first compressor 1A. A portion of the refrigerant vapor flows through the flow control valve 18b into the space between the first impeller 1Ba and the second impeller 1Bb inside the second compressor 1B.

[0093] 11 , the seventh flow path 27 may be connected to the second flow path 22. In this case, when the first compressor 1A and the second compressor 1B are connected in series, a portion of the refrigerant vapor diverted to the seventh flow path 27 can be merged with the second flow path 22 via the flow control valve 18c and can be made to flow into the second compressor 1B via the suction side flow path switch 2.

[0094] Unlike the refrigeration cycle devices 105 and 106, the refrigeration cycle devices 107 and 108 can be used not only when the compressors are connected in series, but also when the compressors are connected in parallel and when the compressor is used alone.

[0095] The refrigeration cycle devices 107 and 108 are capable of adjusting the flow rate of refrigerant flowing into not only each compressor but also the impeller of each compressor, allowing for more detailed control than the refrigeration cycle devices 105 and 106. Therefore, it is possible to provide a refrigeration cycle device that can further expand the operable range, prevent damage to each impeller, and suppress a decrease in efficiency.

[0096] As described above, in the refrigeration cycle apparatus according to this embodiment, the upstream expansion valve 5a and the downstream expansion valve 5b, and the gas-liquid separator 14 disposed between the upstream expansion valve 5a and the downstream expansion valve 5b are provided downstream of the condenser 4 and upstream of the evaporator 6. The gas-liquid separator 14 and the second flow path 22 are connected via the sixth flow path 26. The sixth flow path 26 is provided with the flow control valve 15. Here, the sixth flow path 26 is an example of a first refrigerant flow path. The flow control valve 15 is an example of a second flow control valve. With this configuration, when the first compressor 1A and the second compressor 1B are connected in series, the refrigerant flow rate flowing into the downstream second compressor 1B can be increased. This prevents damage to the impeller of the second compressor 1B and further expands the operable range.

[0097] In the refrigeration cycle apparatus according to this embodiment, an expansion valve 5 is provided downstream of the condenser 4 and upstream of the evaporator 6. The condenser 4, the expansion valve 5, and the second flow path 22 are connected via a seventh flow path 27. The seventh flow path 27 is provided with a flow control valve 16 and an economizer 17. Here, the seventh flow path 27 is an example of a second refrigerant flow path. The flow control valve 16 is an example of a third flow control valve. With this configuration, when the first compressor 1A and the second compressor 1B are connected in series, the flow rate of refrigerant flowing into the downstream second compressor 1B can be increased. This prevents damage to the impeller of the second compressor 1B and further expands the operable range.

[0098] Fifth embodiment. A refrigeration cycle apparatus according to a fifth embodiment will be described. Fig. 14 is a schematic diagram of a refrigeration cycle apparatus 109 according to this embodiment. Thick lines connecting the components in the figure indicate refrigerant piping. Arrows at the end points of the thick lines indicate the direction in which the refrigerant always flows. Thin solid arrows and dotted arrows drawn parallel to the thick lines indicate the direction in which the refrigerant flows when the flow path is switched, respectively. The electrical wiring shown in Fig. 1 and the devices connected thereby will not be shown again.

[0099] The refrigeration cycle apparatus 109 has an eighth flow path 28 and a ninth flow path 29. The eighth flow path 28 branches off from a flow path between the first impeller 1Aa and the second impeller 1Ab inside the first compressor 1A, and is connected to the discharge-side flow path switch 3. The ninth flow path 29 branches off from a flow path between the first impeller 1Ba and the second impeller 1Bb inside the second compressor 1B, and is connected to the discharge-side flow path switch 3.

[0100] The suction-side flow path switch 2 and the discharge-side flow path switch 3 are switched between the flow paths indicated by the thin solid arrows and the flow paths indicated by the dotted arrows in Fig. 14. When the flow paths of the suction-side flow path switch 2 and the discharge-side flow path switch 3 are switched as indicated by the thin solid arrows, the refrigerant compressed by the first impeller 1Aa of the first compressor 1A is divided into two flows. One refrigerant is compressed by the second impeller 1Ab and flows toward the condenser 4 via the discharge-side flow path switch 3. The other refrigerant flows into the second compressor 1B via the eighth flow path 28, the discharge-side flow path switch 3, the second flow path 22, and the suction-side flow path switch 2, is compressed by the first impeller 1Ba and the second impeller 1Bb in this order, and then flows toward the condenser 4 via the discharge-side flow path switch 3.

[0101] The conditions for such control are preferably, for example, when the load is high but the flow rate is not so high that the compressors need to be connected in parallel, and the compression ratio is low and the volumetric flow rate of the refrigerant immediately after the first impeller 1Aa is large.

[0102] When the flow paths of the suction side flow path switch 2 and the discharge side flow path switch 3 are switched as shown by the dotted arrows, the refrigerant flowing out of the evaporator 6 is split into two by the suction side flow path switch 2. One refrigerant flows into the first compressor 1A and is compressed by the first impeller 1Aa. The other refrigerant flows into the second compressor 1B and is compressed by the first impeller 1Ba and the second impeller 1Bb, respectively, and then merges with the first refrigerant in the flow path between the first impeller 1Aa and the second impeller 1Ab inside the first compressor 1A via the discharge side flow path switch 3. The merged refrigerant is compressed by the second impeller 1Ab and flows toward the condenser 4 via the discharge side flow path switch 3.

[0103] The conditions for such control are preferably, for example, when the load is high but the flow rate is not so high that the compressors need to be connected in parallel, and the volumetric flow rate of the refrigerant flowing into the second impeller 1Ab is small at a high compression ratio.

[0104] 14 shows a case where the refrigerant branches between the first impeller 1Aa and the second impeller 1Ab in the flow indicated by the thin solid arrows, and merges between the first impeller 1Aa and the second impeller 1Ab in the flow indicated by the dotted arrows. However, the flow direction may be controlled by switching the first compressor 1A and the second compressor 1B, or, as shown in FIG. 3, operation may be controlled so as to change the combination of impellers connected in series and impellers connected in parallel in three or more compressors.

[0105] In this embodiment, the combination of series and parallel connections can be changed not only for each compressor but also for each impeller, which allows for more precise adjustment of the refrigerant flow rate into each impeller. This allows for a wider operating range, prevents damage to each impeller, and provides a refrigeration cycle device that suppresses a decrease in efficiency.

[0106] As described above, in the refrigeration cycle apparatus according to this embodiment, the suction-side flow path switch 2 and the discharge-side flow path switch 3 can switch the flow paths as follows. That is, the impeller 1Aa is connected in parallel with the impellers 1Ba and 1Bb, and the remaining impeller 1Ab is connected in series with these. This configuration allows for more precise capacity control, which more reliably prevents surging, choking, and the like, and improves operating efficiency.

[0107] 1 Compressor, 1A First compressor, 1Aa First impeller, 1Ab Second impeller, 1Ac Third impeller, 1B Second compressor, 1Ba First impeller, 1Bb Second impeller, 1Bc Third impeller, 1C Third compressor, 1Ca First impeller, 1Cb Second impeller, 1Cc Third impeller, 1a First impeller, 1b Second impeller, 2 Suction side flow path switch, 3 Discharge side flow path switch, 4 Condenser, 5 Expansion valve, 5a Upstream expansion valve, 5b Downstream expansion valve, 6 Evaporator, 7 Power supply unit, 7A First power supply unit, 7B Second power supply unit, 8 Controller, 9 Motor, 10 Bearing, 11 Accumulator, 12 Accumulator, 13a Flow control valve, 13b Flow control valve, 14 Gas-liquid separator, 15 Flow rate control valve, 16 Flow rate control valve, 17 Economizer, 18a Flow rate control valve, 18b Flow rate control valve, 18c Flow rate control valve, 21 First flow path, 22 Second flow path, 23 Third flow path, 24 Fourth flow path, 25 Fifth flow path, 26 Sixth flow path, 26a Branch flow path, 26b Branch flow path, 27 Seventh flow path, 27a Branch flow path, 27b Branch flow path, 28 Eighth flow path, 29 Ninth flow path, 31 Low-pressure refrigerant flow path, 32 High-pressure refrigerant flow path, 100 Refrigeration cycle device, 101 Refrigeration cycle device, 102 Refrigeration cycle device, 103 Refrigeration cycle device, 104 Refrigeration cycle device, 105 Refrigeration cycle device, 106 Refrigeration cycle device, 107 Refrigeration cycle device, 108 Refrigeration cycle device, 109 Refrigeration cycle device.

Claims

1. A refrigeration cycle device comprising: a plurality of turbo compressors installed in the same refrigeration cycle; and a flow path switcher that switches the flow path of refrigerant flowing to the plurality of turbo compressors, wherein each of the plurality of turbo compressors has a single-stage or multi-stage impeller, and the flow path switcher is capable of switching the flow path so that the impellers of the plurality of turbo compressors are connected in series or in parallel.

2. The refrigeration cycle device according to claim 1, further comprising a controller for controlling the plurality of turbo compressors and the flow path switch, wherein the controller controls the flow path switch so that the number of impellers connected in series increases as the condition of a low flow rate and a high compression ratio becomes higher, and the controller controls the flow path switch so that the number of impellers connected in parallel increases as the condition of a high flow rate and a low compression ratio becomes higher.

3. A refrigeration cycle device according to claim 1 or claim 2, wherein the number of the plurality of turbo compressors is two, each of the plurality of turbo compressors has a two-stage impeller, and the two-stage impellers are mounted symmetrically with respect to the axial direction.

4. A refrigeration cycle device according to claim 1 or claim 2, wherein the number of the plurality of turbo-type compressors is three or more, and the flow path switch is capable of switching the flow paths so that some of the plurality of turbo-type compressors are connected in parallel and the remaining turbo-type compressors of the plurality of turbo-type compressors are connected in series with some of the turbo-type compressors.

5. A refrigeration cycle device according to any one of claims 1 to 4, wherein when the impellers are connected in series, the inlet cross-sectional area of ​​the impellers becomes smaller towards the later stage.

6. A refrigeration cycle device according to claim 5, further comprising a controller for controlling the plurality of turbo-type compressors and the flow path switch, wherein when the plurality of turbo-type compressors are connected in parallel, the controller, when stopping some of the turbo-type compressors among the plurality of turbo-type compressors, stops the turbo-type compressor having an impeller with a smaller inlet cross-sectional area as the flow rate condition increases, and stops the turbo-type compressor having an impeller with a larger inlet cross-sectional area as the flow rate condition decreases.

7. The flow path switch has a suction side flow path switch provided between an evaporator and the plurality of turbo-type compressors, and a discharge side flow path switch provided between the plurality of turbo-type compressors and a condenser, the evaporator and the suction side flow path switch are connected via a low-pressure refrigerant flow path, the discharge side flow path switch and the condenser are connected via a high-pressure refrigerant flow path, the suction side flow path switch and the discharge side flow path switch are connected via a first flow path, a second flow path and a third flow path, the plurality of turbo-type compressors have a first compressor and a second compressor, the first compressor is provided in the first flow path, and the second compressor is provided in the third flow path, 7. The refrigeration cycle apparatus according to claim 1, wherein, in the suction side flow path switcher, when the low-pressure refrigerant flow path and the first flow path are communicated with each other and the second flow path and the third flow path are communicated with each other, and in the discharge side flow path switcher, when the first flow path and the second flow path are communicated with each other and the third flow path is communicated with the high-pressure refrigerant flow path, the first compressor and the second compressor are connected in series; and when, in the suction side flow path switcher, the low-pressure refrigerant flow path and the first flow path and the third flow path are communicated with each other, and in the discharge side flow path switcher, the first compressor and the second compressor are connected in parallel.

8. A refrigeration cycle device as described in claim 7, wherein when the first compressor and the second compressor are connected in series, the suction side flow path switch is capable of further connecting the second flow path and the first flow path, and the suction side flow path switch has a first flow control valve between the second flow path and the first flow path.

9. A refrigeration cycle device as described in claim 7 or claim 8, wherein an upstream expansion valve and a downstream expansion valve, and a gas-liquid separator arranged between the upstream expansion valve and the downstream expansion valve are provided downstream of the condenser and upstream of the evaporator, the gas-liquid separator and the second flow path are connected via a first refrigerant flow path, and a second flow control valve is provided in the first refrigerant flow path.

10. A refrigeration cycle device as described in claim 7 or claim 8, wherein an expansion valve is provided downstream of the condenser and upstream of the evaporator, the condenser and the expansion valve are connected to the second flow path via a second refrigerant flow path, and a third flow control valve and an economizer are provided in the second refrigerant flow path.

11. A refrigeration cycle device according to any one of claims 1 to 10, wherein the flow path switch is capable of switching flow paths so that some of the impellers of the plurality of turbo-type compressors are connected in parallel and the remaining impellers of the plurality of turbo-type compressors are connected in series with the some of the impellers.

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