JP2022181837A - Multistage compression refrigeration device - Google Patents

Abstract

To provide a refrigeration device capable of operating stably over a wide range of operation conditions while improving efficiency of a refrigeration cycle due to increase of the number of compression stages.SOLUTION: A refrigeration device comprises: a compression unit including a multi-stage compression mechanism, where a stage number N is 3 or more; a first heat exchanger that radiates the heat of a refrigerant discharged from the compression unit to outside air; a decompression unit including a plurality of decompression mechanisms provided to each of the multiple stages; a second heat exchanger that causes the refrigerant having passed through the decompression unit to absorb heat from a heat load; a plurality of gas-liquid separators provided between the decompression mechanisms; a plurality of intermediate-pressure injection flow paths that corresponds to the plurality of gas-liquid separators, and supplies a gas-phase refrigerant from the corresponding gas-liquid separators between the compression mechanisms; and a valve provided in at least one of the plurality of intermediate-pressure injection flow paths. Upon operating the valve, the effective number of stages through which the refrigerant circulates is changed.SELECTED DRAWING: Figure 1

Description

The present disclosure relates to a refrigeration system that compresses refrigerant in multiple stages.

Patent Literature 1 discloses a refrigeration system with a two-stage compression mechanism. Such a refrigeration system includes an electric compressor having a low-stage compression mechanism and a high-stage compression mechanism in a closed housing, a radiator, a high-pressure expansion valve, a gas-liquid separator, a low-pressure expansion valve, an evaporator, It is equipped with gas injection piping. The gas refrigerant introduced from the gas-liquid separator into the housing of the electric compressor is sucked into the high-stage compression mechanism together with the refrigerant discharged into the housing from the low-stage compression mechanism.

JP 2017-44420 A

A refrigerant with a low GWP is adopted for the purpose of reducing the global warming potential (GWP) and improving the energy consumption efficiency (COP; Coefficient of Performance). Development and commercialization are underway.
When a refrigerant containing _CO2 is used as the refrigerant, in order to keep the high refrigerant discharge temperature within the permissible limit due to high-pressure operation, the high pressure set for the radiator and the low pressure set for the evaporator must be maintained. It is effective to introduce intermediate-pressure gas refrigerant from the gas-liquid separator between the low-stage compression mechanism and the high-stage compression mechanism (intermediate-pressure gas injection). According to such a configuration, the discharge temperature can be suppressed by injecting gas refrigerant having a temperature lower than that of the refrigerant discharged from the low-stage compression mechanism. In addition, since the liquid refrigerant is supplied from the gas-liquid separator to the low-pressure expansion valve, the enthalpy obtained by the evaporator is expanded compared to the case of single-stage compression, so the refrigeration capacity is increased and the COP is improved. be able to.

In a refrigerating device that employs a refrigerant with a low GWP, it is desired to realize a refrigerating device that increases the COP while suppressing the discharge temperature from the compressor by further increasing the number of stages of the compression mechanism. . However, according to test research by the inventors of the present disclosure, a refrigeration system in which the number of stages of the compression mechanism is increased to, for example, "4" does not operate stably depending on the operating conditions such as the outside air temperature. Such a refrigeration system includes N compression mechanisms, N expansion valves, N−1 gas-liquid separators, and N−1 gas injection pipes.

In view of the above, an object of the present disclosure is to provide a refrigeration system that can stably operate over a wide range of operating conditions while improving the efficiency of the refrigeration cycle by increasing the number of compression stages.

The present disclosure is a refrigerating device that circulates a refrigerant by a refrigerating cycle, includes a plurality of stages of compression mechanisms that are connected in series and each compresses a refrigerant, a compression section having three or more stages, and a low stage due to the compression section. A first heat exchanger for releasing heat to the outside air from the refrigerant that is compressed over a plurality of steps from to a high stage and discharged from the compression unit, and a plurality of pressure reducing mechanisms provided to each of the plurality of stages. Provided between the pressure reducing unit that reduces the pressure of the refrigerant that has passed through the first heat exchanger over a plurality of steps, the second heat exchanger that causes the refrigerant that has passed through the pressure reducing unit to absorb heat from the heat load, and the pressure reducing mechanism and the pressure reducing mechanism a plurality of gas-liquid separators each corresponding to the plurality of gas-liquid separators, and a plurality of intermediate-pressure injection passages for supplying gas-phase refrigerant from the corresponding gas-liquid separators between the compression mechanisms. and a valve provided in at least one of the plurality of intermediate pressure injection flow paths. Such a refrigeration system is configured such that the effective number of stages in which the refrigerant circulates is variable by operating valves.
In the present invention, the valve provided in the intermediate pressure injection flow path can be opened and closed during operation of the refrigeration system according to operating conditions for the purpose of stably operating the refrigeration system. In addition to this, closing the valve for other purposes, for example to prevent migration of the refrigerant when the refrigeration system is shut down, is not prevented.

According to the refrigeration system of the present disclosure, the number of effective stages in which the refrigerant circulates is variable by switching between opening and closing the valve provided in at least one of the plurality of intermediate pressure injection passages. Therefore, while improving the COP by the refrigeration cycle with the maximum number of stages, if the operating state becomes unstable when operating with the maximum number of stages, the valve is closed during operation to reduce the effective number of stages with respect to the maximum number of stages. As a result, the refrigeration system can be stably operated.
According to the present disclosure, by changing the number of effective stages by opening and closing the valve, it is possible to easily realize a cycle that adapts to each state of the refrigerant under various operating conditions, so that stable operation is possible over a wide range of operating conditions. It is possible to provide a multi-stage compression refrigeration system.

It is a figure which shows the circuit structure of the refrigeration apparatus which concerns on 1st Embodiment. 2 is a Moliere diagram in a normal operation mode of the refrigeration system shown in FIG. 1; FIG. 2 is a Moliere diagram in the high outside air temperature mode of the refrigeration system shown in FIG. 1. FIG. It is a figure which shows the circuit structure of the refrigeration apparatus based on the modification of 1st Embodiment. It is a figure which shows the circuit structure of the refrigeration apparatus which concerns on 2nd Embodiment. 6 is a Moliere diagram in the low outside air temperature mode of the refrigeration system shown in FIG. 5; FIG. It is a figure which shows the circuit structure of the refrigeration apparatus which concerns on a modification.

An embodiment of the present disclosure will be described below with reference to the accompanying drawings.
[First embodiment]
(Basic elements of refrigeration cycle)
The multi-stage compression refrigerating apparatus 1 shown in FIG. 1 circulates a refrigerant in a refrigerating cycle to cool an appropriate heat load (for example, the air in the apparatus housing and stored items) using outside air as a heat source.
The refrigerating apparatus 1 includes, as basic elements forming a refrigerating cycle, a compression section 10 for compressing the refrigerant, a radiator E1 (first heat exchanger) for releasing heat from the refrigerant to the outside air, and a decompression section 20 for reducing the pressure of the refrigerant. and a heat absorber E2 (second heat exchanger) that absorbs heat from the heat load to the refrigerant. The refrigerant compressed by compression section 10 flows through radiator E<b>1 , decompression section 20 , and heat absorber E<b>2 in this order, and is sucked into compression section 10 .

The refrigerant circuit of the refrigeration apparatus 1 of the present embodiment is filled with a refrigerant containing carbon dioxide (CO ₂ ) at least in part. Such a refrigerant corresponds to a single refrigerant of CO ₂ or a mixed refrigerant in which CO ₂ is mixed with, for example, R32 refrigerant at a ratio of about 10 to 20%. The GWP of carbon dioxide is "1". The critical temperature of carbon dioxide is lower than that of other refrigerants such as HFC (Hydro Fluoro Carbon). Therefore, in the normal operation mode of the refrigeration system 1, the refrigerant of the present embodiment is compressed to a pressure exceeding the critical pressure P _C by the compression section 10 that compresses the refrigerant in multiple stages, and the pressure is higher than when other refrigerants are used. It is operated in a state where the set pressure on the high pressure side H is high.

(multi-stage compression mechanism/decompression mechanism)
Compression unit 10 includes a plurality of compression mechanisms 11 to 14 connected in series. The first-stage compression mechanism 11, the second-stage compression mechanism 12, the third-stage compression mechanism 13, and the fourth-stage compression mechanism 14 sequentially compress the refrigerant from the low-pressure side L to the high-pressure side H over a plurality of steps. The number of stages N of the compression unit 10 is 3 or more, and as an example, the number of stages N is "4". The first to fourth stages are indicated by the symbols n1, n2, n3 and n4.

As will be described later, the number of stages N is changed according to the operation mode of the refrigeration system 1 . FIG. 2 is a Moliere diagram showing the relationship between refrigerant pressure and specific enthalpy assumed in the normal operation mode. The symbols r1, r2, etc. shown in FIG. 2 correspond to the same symbols shown in FIG.

The refrigeration system 1 of this embodiment includes two electric compressors 101 and 102, a control device 15 capable of controlling the operation of the electric motors and expansion valves of the electric compressors 101 and 102, and the electric compressors 101 and 102. and an intermediate cooling heat exchanger 16 provided between.
The first electric compressor 101 rotates the first stage compression mechanism 11 and the second stage compression mechanism 12 that are connected in series, a housing 101A that houses the compression mechanisms 11 and 12, and the compression mechanisms 11 and 12. and an electric motor 101B.
The second electric compressor 102 rotates the third stage compression mechanism 13 and the fourth stage compression mechanism 14 that are connected in series, a housing 102A that houses the compression mechanisms 13 and 14, and the compression mechanisms 13 and 14. and an electric motor 102B.

Combining two electric compressors 101 and 102 each having a multi-stage compression mechanism driven by the same electric motor realizes a multi-stage compression refrigeration system 1 having N stages. Therefore, the control device 15 may control the respective rotation speeds of the two electric motors 101B and 102B. Therefore, the control of the refrigeration system 1 is easier than when the compression mechanisms 11 to 14 in each stage are individually driven by corresponding electric motors. In addition, the size and weight of the refrigeration apparatus 1 can be reduced compared to the case where the compression section 10 is composed of four compressors each having a compression mechanism, an electric motor, and a housing.

The intermediate cooling heat exchanger 16 cools the refrigerant discharged from the second-stage compression mechanism 12 by radiating heat to the outside air, and supplies the refrigerant to the suction portion of the third-stage compression mechanism 13 (operating points r4 to r5 in FIG. 2). What).

The first stage compression mechanism 11 corresponds to, for example, a rotary compression mechanism including a piston rotor and a cylinder. The third stage compression mechanism 13 is also the same. The second stage compression mechanism 12 corresponds to, for example, a scroll compression mechanism including a pair of scroll members. The same applies to the fourth stage compression mechanism 14 .

Corresponding to the fact that the compression unit 10 is composed of multiple stages of compression mechanisms 11 to 14, the decompression unit 20 has the same number of decompression mechanisms 21 as the number of compression stages N provided to each stage (n1, n2, n3, n4). ~24 included. Each of the decompression mechanisms 21-24 may be an expansion valve, a capillary tube, or the like. The fourth stage decompression mechanism 24, the third stage decompression mechanism 23, the second stage decompression mechanism 22, and the first stage decompression mechanism 21 sequentially reduce the pressure of the refrigerant that has passed through the radiator E1 in a plurality of steps in this order. Let

As shown in FIG. 2, the pressure of the refrigerant increases stepwise as the refrigerant is compressed by the multi-stage compression mechanisms 11-14 of n1, n2, n3, and n4. Along with this, the discharge temperature of the refrigerant rises.
By lowering the temperature of the refrigerant by the action of the intermediate cooling heat exchanger 16 that releases the heat of the refrigerant to the outside air (see arrow A1 in FIG. 2), it is possible to contribute to the suppression of the discharge temperature of the compression section 10 as a whole. .

The pressure between the suction pressure to the first stage n1 and the discharge pressure from the second stage n2 is called the first intermediate pressure _P1 . Similarly, the pressure between the suction pressure to the second stage n2 and the discharge pressure from the third stage n3 is called a second intermediate pressure _P2 , and the pressure from the suction pressure to the third stage n3 and the pressure from the fourth stage n4 is The pressure between it and the discharge pressure is called a third intermediate pressure _P3 . A relationship of P ₁ <P ₂ <P ₃ holds.
Each stage n1, n2, n3 determined from the set pressure P _H of the radiator E1 on the high pressure side H, the set pressure P _L of the heat sink E2 on the low pressure side L, and the intermediate pressures (P ₁ , P ₂ , P ₃ ) , n4, the refrigerant circulates in the refrigerant circuit of the refrigeration system 1 while changing the pressure and enthalpy with a phase change.

(intermediate pressure gas injection)
In the refrigeration system 1, intermediate-pressure gas refrigerant obtained by gas-liquid separation of the refrigerant between the stages of the first to fourth stage pressure reducing mechanisms 21 to 24 is transferred to the first to fourth stage compression mechanisms 11 to 14. Perform gas injection to supply between each. Therefore, the refrigerating apparatus 1 corresponds to N−1 gas-liquid separators 31 to 33 provided between the first to fourth stage pressure reducing mechanisms 21 to 24, respectively, and the gas-liquid separators 31 to 33, respectively. It has N−1 intermediate pressure injection flow paths 41 to 43 .

In the normal operation mode, the pressure (r12, r13, r14) of the refrigerant discharged from the fourth stage compression mechanism 14 and passed through the radiator E1 and the fourth stage decompression mechanism 24, that is, the third intermediate pressure _P3 is the critical pressure P Stay below _C.
The third intermediate-pressure gas-liquid separator 33 (liquid receiver) receives the refrigerant from the fourth stage decompression mechanism 24 into the storage tank 33A and separates it into a gas phase and a liquid phase. This corresponds to the state change from r12 to r13 and r14 as shown in FIG.
Inside the storage tank 33A, the refrigerant is separated into a gas phase and a liquid phase based on the density difference. A third intermediate pressure injection channel 43 is connected to the gas phase region 33B above the liquid surface.

The third intermediate pressure injection passage 43 supplies the gas refrigerant at the third intermediate pressure _P3 from the gas phase region 33B to the suction portion of the fourth stage compression mechanism 14 (from r13 to r8). The temperature of the gas refrigerant supplied to the fourth stage compression mechanism 14 through the third intermediate pressure injection passage 43 is lower than the temperature of the refrigerant discharged from the third stage compression mechanism 13 . Therefore, the temperature of the refrigerant to be sucked into the fourth stage compression mechanism 14 is lowered (r7 to r8). As a result, the temperature of the refrigerant discharged from the fourth stage compression mechanism 14 also drops, so the intermediate pressure gas injection contributes to the reduction of the discharge temperature.

On the other hand, the liquid refrigerant at the third intermediate pressure P3 stored in the storage tank _33A flows out of the storage tank 33A and is decompressed by the third stage decompression mechanism 23 (from r14 to r15). By supplying the liquid refrigerant to the decompression mechanisms 21 to 23 including the decompression mechanism 23, the enthalpy corresponding to the evaporation process in the heat absorber E2 is expanded (see arrow A2 in FIG. 2 for the third stage decompression mechanism 23). ), which can improve the COP.

The reduction in discharge temperature and the improvement in efficiency due to the expansion of enthalpy described above can be said for each of the third intermediate pressure P ₃ , the second intermediate pressure P ₂ , and the first intermediate pressure P ₁ . By increasing the number of stages N to five or six instead of four in the present embodiment, it is possible to enhance the effect of reducing the discharge temperature and improving the efficiency.

The gas injection for each of the second intermediate pressure _P2 and the first intermediate pressure _P1 is the same as the gas injection for the third intermediate pressure _P3 described above.
The refrigerant that has passed through the third stage pressure reducing mechanism 23 is received by the second intermediate pressure gas-liquid separator 32 and separated into a gas phase and a liquid phase in the same manner as the third intermediate pressure gas-liquid separator 33 . This corresponds to a state change from r15 to r16 and r17.

A second intermediate pressure injection channel 42 is connected to the gas phase region of the second intermediate pressure gas-liquid separator 32 . When the second intermediate pressure injection flow path 42 supplies the gas refrigerant at the second intermediate pressure _P2 to the intake portion of the third stage compression mechanism 13 (from r16 to r6), it flows out of the intermediate cooling heat exchanger 16 and The temperature of the refrigerant sucked into the third stage compression mechanism 13 decreases (from r5 to r6). Between the second-stage compression mechanism 12 and the third-stage compression mechanism 13, in addition to the injection action of the intermediate pressure _P2 , the third-stage compression mechanism is also affected by the action of the intermediate cooling heat exchanger 16 (from r4 to r5). Since the intake temperature to 13 is lowered, the discharge temperature can be further suppressed.
The second intermediate pressure _P2 liquid refrigerant flowing out of the second intermediate pressure gas-liquid separator 32 is decompressed by the second stage decompression mechanism 22 (from r17 to r18).

After passing through the second pressure reducing mechanism 22, the refrigerant is received by the first intermediate pressure gas-liquid separator 31 and separated into a gas phase and a liquid phase. This corresponds to a state change from r18 to r19 and r20.
When the first intermediate pressure injection passage 41 connected to the gas phase region of the first intermediate pressure gas-liquid separator 31 supplies the gas refrigerant at the first intermediate pressure _P1 to the suction portion of the second stage compression mechanism 12 ( from r18 to r3), the temperature of the refrigerant sucked into the second stage compression mechanism 12 decreases (from r2 to r3).
The first intermediate pressure _P1 liquid refrigerant flowing out of the first intermediate pressure gas-liquid separator 31 is decompressed by the first stage decompression mechanism 21 (from r20 to r21). The refrigerant that has passed through the first stage pressure reducing mechanism 21 is evaporated by absorbing heat from the heat load by the heat absorber E2, and is sucked into the first stage compression mechanism 11 (from r21 to r22, r1).

When the refrigerating device 1 is operated in the normal operation mode set by the control device 15, compression, expansion, and intermediate pressure injection are performed for the number of stages N included in the refrigerating device 1, whereby the low GWP refrigerant The refrigerating apparatus 1 can be operated stably while improving the COP while using , and maintaining the discharge temperature below the allowable limit.
However, for example, when the outside temperature is excessively high relative to the outside temperature range assumed in the normal operation mode, operating the refrigeration system 1 with the maximum number of stages N may cause the operating state to become unstable, and the refrigerant will It may not be possible to circulate.
Even if it is permissible for the temperature of the _CO2 refrigerant discharged from the compression section 10 through multi-stage compression to exceed the critical pressure PC, the amount of heat released by the radiator _E1 decreases as the outside air temperature rises. , the third intermediate pressure P ₃ (r12, r13, r14) exceeds the critical pressure P _C , since the refrigerant does not condense in the third intermediate pressure gas-liquid separator 33, gas-liquid separation cannot be performed. Since the behavior of the refrigerant in the critical state is unstable, it is difficult to perform stable control. It is difficult to predict the pressure, temperature, flow rate, etc. of the supercritical fluid and stabilize the operating state.

Therefore, in order to stably operate the refrigerating apparatus 1 over a wide range including operating conditions in which the outside air temperature is excessive or other operating conditions, the refrigerating apparatus 1 is arbitrarily selected from the intermediate pressure injection passages 41 to 43. A valve (V3) is provided in at least one selected.
The refrigerating apparatus 1 of this embodiment includes a third intermediate pressure valve V3 provided in the third intermediate pressure injection passage 43 on the highest pressure side H. As shown in FIG.
The third intermediate pressure valve V3 is an electromagnetic valve and is switched between open and closed based on a command issued from the control device 15.

In the normal operation mode, the refrigerating apparatus 1 applies the first to third intermediate pressures P ₁ , P ₂ , . . . While performing injection of _P3 , operation is performed while changing the pressure and enthalpy of the refrigerant as shown in FIG. At this time, the number of effective stages _NA as the number of stages in which the refrigerant is circulating is "4" corresponding to the total number N of stages provided in the refrigerating apparatus 1 .

(high ambient temperature mode)
When the outside air temperature is so high that the refrigerant exceeds the critical pressure, the control device 15 closes the third intermediate pressure valve V3 to operate only the first intermediate pressure injection passage 41 and the second intermediate pressure injection passage 42. , the operation mode of the refrigeration system 1 is switched to the high outside air temperature mode in which intermediate pressure injection is performed. In the high outside air temperature mode, the refrigerant in the supercritical state after passing through the fourth stage pressure reducing mechanism 24 passes through the storage tank 33A of the third intermediate pressure gas-liquid separator 33 and is reduced in pressure by the third stage pressure reducing mechanism 23. After that, it flows into the second intermediate pressure gas-liquid separator 32 (from r12, r13, r14 to r15). At this time, no liquid refrigerant is stored in the storage tank 33A (corresponding to the state inside the storage tank 33A shown in FIG. 4).

When the third intermediate pressure valve V3 is closed, the refrigerant does not flow through the third intermediate pressure injection passage 43, so the third stage n3 and the fourth stage n4 in the normal operation mode are combined into one stage in the compression/expansion process. The effective stage number N is reduced to "3". As shown in FIG. 3, the state of the refrigerant in the high outside air temperature mode, the refrigeration system 1 is operated in a three-stage compression/three-stage expansion cycle of n1 to n3. Since the pressure of the supercritical refrigerant is reduced by the third stage pressure reducing mechanism 23 (from r12, r13, r14 to r15), the second intermediate pressure _P2 is maintained below the critical pressure _PC . Therefore, the refrigeration system 1 is stably operated.

In the normal operation mode, the controller 15 detects the outside temperature by using, for example, map data indicating the correspondence between the outside temperature and the set pressure of the high pressure side H and the outside temperature detected by the temperature sensor 17. It is determined whether or not the high-pressure side H pressure on the map data corresponding to the result is higher than the first threshold pressure T ₁ (FIG. 3) set lower than the critical pressure P _C with allowance for margin. When the high-pressure side H pressure on the map data corresponding to the detection result of the outside air temperature is larger than the first threshold pressure _T1 , the control device 15 closes the third intermediate pressure valve V3 to exit the normal operation mode. Shift to high outside temperature mode.
The outside temperature is continuously monitored even in the high outside temperature mode, and for example, the high pressure side H pressure on the map data corresponding to the outside temperature detection result reaches the second threshold pressure _{T2 which} is lower than the first threshold pressure T1. On the other hand, if it is smaller, the controller 15 opens the third intermediate pressure valve V3 to return from the high outside air temperature mode to the normal operation mode.

According to the refrigeration system 1 of the first embodiment described above, by switching between opening and closing the valve V3 provided in at least one of the intermediate pressure injection passages 41 to 43, the effective number of stages N _A in which the refrigerant circulates. are variably configured. Therefore, in the normal operation mode, while the COP is improved by the refrigeration cycle with the maximum number of stages N, when the outside air temperature rises to such an extent that the intermediate pressure on the high-pressure side H exceeds the critical pressure _PC , the intermediate pressure on the high-pressure side H By closing the valve V3 provided in the pressure injection flow path 43 to reduce the number of effective stages _NA , the refrigeration system 1 can be stably operated.
In other words, according to the present embodiment, even though the refrigerant compressed to the supercritical state is handled, difficult control based on the prediction of the behavior of the refrigerant in the supercritical state is not required. By changing the _NA , it is possible to easily realize a cycle suitable for each state of the refrigerant under various operating conditions. Therefore, it is possible to provide a multi-stage compression refrigeration system 1 that can stably operate over a wide range of operating conditions.

The refrigeration system 1 may include valves provided in the other intermediate pressure injection flow paths 42 and 41 in addition to the valve V3 provided in the third intermediate pressure injection flow path 43 . For example, as shown in FIG. 4, the second intermediate pressure injection flow path 42 may also be provided with a valve V2 that can be opened and closed by the control device 15. As shown in FIG. In the high outside air temperature mode shown in FIG. 4, of the intermediate pressure valves V2 and V3, only the third intermediate pressure valve V3 shown in black is closed.

[Second embodiment]
Next, a second embodiment will be described with reference to FIGS. 5 and 6. FIG. The following description focuses on matters that are different from the first embodiment. The same symbols are given to the same components as in the first embodiment.
The refrigerating apparatus 1-2 shown in FIG. 5 has a first intermediate pressure valve V1 in the first intermediate pressure injection passage 41 in order to cope with operating conditions different from those of the refrigerating apparatus 1 of the first embodiment. The refrigerating device 1-2 also includes a third intermediate pressure valve V3 provided in the third intermediate pressure injection passage 43, like the refrigerating device 1 of the first embodiment. A refrigerating device 1-2 of the second embodiment is configured in the same manner as the refrigerating device 1 of the first embodiment, except that it includes a first intermediate pressure valve V1.

Since the refrigerating device 1-2 has the third intermediate pressure valve V1 as in the refrigerating device 1, only the third intermediate pressure valve V3 of the intermediate pressure valves V1 and V3 is closed to set the effective stage number _NA to "3. , the high ambient temperature mode described above can be performed.

Contrary to the high outside air temperature mode, when the outside air temperature is low, the pressure ratio between the set pressure PH on the high pressure side _H and the set pressure PL on the low pressure side _L becomes small. Since the pressure ratio is apportioned to each stage, if the maximum stage number N is used as in the normal operation mode, the pressure ratios of the stages n1, n2, n3, and n4 become smaller. When the outside air temperature is low enough that the pressure ratio of each stage is insufficient for the pressure ratio required to convey the refrigerant from the gas-liquid separators 31 to 33 to the compression mechanisms 12 to 14, respectively, Refrigerant cannot be circulated.
In this case, the control device 15 closes both the first intermediate pressure valve V1 and the third intermediate pressure valve V3 to switch the refrigeration system 1 from the normal operation mode to the low outside air temperature mode (low pressure ratio operation mode). - Switch between two operating modes. In the low outside air temperature mode, intermediate pressure injection is performed only through the second intermediate pressure injection passage 42 .

FIG. 6 shows the state of the refrigerant in the low outside temperature mode. By closing the first intermediate pressure valve V1 and the third intermediate pressure valve V3, the number of effective stages _NA is reduced to "2". be driven. As the number of effective stages N _A decreases with respect to the total number of stages N, the pressure sufficient for conveying the refrigerant from each of the gas-liquid separators 31 to 33 to the compression mechanisms 12 to 14 is ensured in each stage. 1 operates stably.

In the normal operation mode, the control device 15 uses, for example, map data indicating the correspondence between the outside air temperature and the pressure ratio of each stage, and the outside temperature detected by the temperature sensor 17 to obtain the outside temperature detection result. is larger or smaller than the first pressure ratio _R1 of each stage considering the pressure ratio of each stage required for intermediate pressure injection. When the pressure ratio of each stage on the map data corresponding to the detection result of the outside air temperature is smaller than the first pressure ratio _R1 of each stage, the control device 15 controls the first intermediate pressure valve V1 and the third intermediate pressure valve V1. The valve V3 is closed to shift from the normal operation mode to the low outside air temperature mode.
The outside air temperature is continuously monitored, and for example, the pressure ratio of each stage on the map data corresponding to the detection result of the outside air temperature is larger than the second pressure ratio R ₂ (R ₁ <R ₂ ) of each stage. In this case, the control device 15 opens the intermediate pressure valves V1 and V3 to return from the low outside air temperature mode to the normal operation mode.

According to the refrigeration system 1-2 of the second embodiment described above, at least the third intermediate pressure valve V3 among the intermediate pressure valves V1 and V3 provided one each on the high pressure side H and the low pressure side L is closed, the number of effective stages N _A can be changed to 3 stages and 2 stages for the total number of stages of 4 stages. By doing so, the refrigerating device 1-2 can be stably operated over a wider range of operating conditions than the refrigerating device 1 of the first embodiment.

From the viewpoint of reducing the effective stage number _NA , only one of the intermediate pressure valves V1 and V3 of the second embodiment can be closed in the low outside air temperature mode. For example, only the third intermediate pressure valve V3 is closed, and a pressure ratio sufficient for performing intermediate pressure injection by the first intermediate pressure injection channel 41 and the second intermediate pressure injection channel 42 is secured in each stage n1, n2, n3. is the case. While detecting the outside air temperature, for example, among the intermediate pressure valves V1 to V3, all are open (four stages), only the intermediate pressure valve V3 is closed (three stages), and the intermediate pressure valves V1 and V3 are closed (three stages). The refrigerating device 1-2 can be operated at the most stable number of stages in the state where both are closed (two stages).
Alternatively, only the first intermediate pressure valve V1 is closed, and a pressure ratio sufficient for performing intermediate pressure injection by the third intermediate pressure injection passage 43 and the second intermediate pressure injection passage 42 is secured in each stage n2, n3, n4. You may In the latter case, if the refrigeration system 1-2 is not used in an environment where the outside air temperature is so high that the third intermediate pressure _P3 exceeds the critical pressure _Pc , the intermediate pressure valve to the third intermediate pressure injection passage 43 is Installation of V3 can be omitted.

In the second embodiment, the second intermediate pressure injection flow path 42 may also be provided with an on-off valve. However, in the above-described second embodiment, the two-stage compression/two-stage expansion cycle is maintained by always performing intermediate pressure injection through the second intermediate pressure injection passage 42 in all operating modes including the low outside air temperature mode. Therefore, by not installing an intermediate pressure valve in the second intermediate pressure injection passage 42, the device cost can be suppressed.

Even if the total number of stages N is more than "4", for example, "5" or "6", the refrigeration system can be operated by reducing the number of stages N as in the second embodiment. can be done.
For example, when the stage number N is "5", the refrigeration system includes an intermediate pressure valve provided in at least one of the fourth intermediate pressure injection channel and the third intermediate pressure injection channel on the high pressure side H; an intermediate pressure valve provided in at least one of the fourth intermediate pressure injection channel and the third intermediate pressure injection channel on side H;
In this case, assuming that the refrigeration system includes a fourth intermediate pressure valve V4, a third intermediate pressure valve V3, a second intermediate pressure valve V2, and a first intermediate pressure valve V1, in the low outside air temperature mode, For example, the first intermediate pressure valve V1, the third intermediate pressure valve V3, and the fourth intermediate pressure valve V4 are closed to operate in a two-stage cycle, or the first intermediate pressure valve V1 and the fourth intermediate pressure valve V4 are closed. It is possible to close it and operate it in a three-stage cycle. That is, the number of effective stages _NA can be changed to "2" or "3".

[Modification]
Although not shown, intermediate pressure valves may be provided for each of the first to third intermediate pressure injection channels 41 to 43, that is, for all intermediate pressure injection channels 41 to 43. FIG. In this case, closing all of the three intermediate pressure valves V1, V2, V3 provided in the refrigeration system can reduce the effective number of stages _NA to "1".
In addition, by keeping one or two of the three intermediate pressure valves V1, V2, and V3 provided in the refrigeration system open at all times, and opening and closing only the remaining intermediate pressure valves, it is possible to meet various required operating conditions. Refrigeration equipment can be adapted. At this time, even the valves that are normally open can be closed according to the operation mode depending on the operating conditions such as the refrigerant used in the refrigeration system and the outside air temperature range suitable for the region where the refrigeration system is used. In other words, the same refrigerant circuit can be applied to multiple products with different refrigerants, operating environment temperatures, or uses.

The refrigerating apparatus 1-3 shown in FIG. 7 does not have a multi-stage electric compressor (101, 102 in FIG. 1). Each of the compression mechanisms 11-13 provided in the refrigerating device 1-3 is configured as a single-stage compressor together with an electric motor 10M and a housing 10H.
The refrigerating device 1-3 includes a second intermediate pressure valve V2 in a second intermediate pressure injection channel 42 on the high pressure side H of the first and second intermediate pressure injection channels 41 and 42, and a second intermediate pressure valve V2 on the low pressure side L A first intermediate pressure valve V1 is provided in the first intermediate pressure injection flow path 41 of .

If the second intermediate pressure _P2 exceeds the critical pressure _PC when intermediate pressure injection is performed using both the first and second intermediate pressure injection passages 41 and 42 because the outside air temperature is high, By closing the second intermediate pressure valve V2 on the highest pressure side H, the refrigeration system 1-3 may be operated in a two-stage compression/two-stage expansion cycle.
Also, if the outside air temperature is low and both the first and second intermediate pressure injection passages 41 and 42 are used to carry out intermediate pressure injection, the pressure ratio of each stage will be insufficient. For this reason, it is preferable to operate the refrigeration system 1-3 in a two-stage compression/two-stage expansion cycle or a one-stage compression/expansion cycle by closing one or both of the intermediate pressure valves V1 and V2.

Refrigeration system 1-3 does not include intermediate cooling heat exchanger 16 (FIG. 1), but in order to reduce the discharge temperature, at least one between compression mechanisms 11 and 12 and/or between compression mechanisms 12 and 13 is provided. An intercooling heat exchanger 16 may be provided.
In the refrigerating apparatuses 1 and 1-2 described above, it is sufficient if the intermediate cooling heat exchanger 16 is provided as necessary.

In addition to the above, it is possible to select the configurations mentioned in the above embodiments, or to change them to other configurations as appropriate.
For example, in each of the embodiments described above, liquid level sensors can be provided in the gas-liquid separators 31-33 in order to protect the compression mechanisms 11-14. If the liquid level sensor detects that an excessive amount of liquid refrigerant is stored in the storage tank, the controller 15 may close the intermediate pressure valve of the corresponding intermediate pressure injection passage. By doing so, it is possible to prevent damage to the compression mechanism due to the inflow of the liquid refrigerant.

[Appendix]
The refrigeration system described above is understood as follows.
[1] The refrigerating devices 1, 1-2, 1-3 that circulate the refrigerant by the refrigerating cycle include multiple stages of compression mechanisms 11 to 14 that are connected in series and each compresses the refrigerant, and the number of stages N is 3 or more. a compression unit 10, a first heat exchanger (E1) that releases the refrigerant discharged from the compression unit 10 after being compressed in a plurality of steps from a low stage to a high stage by the compression unit 10, to the outside air; A decompression unit 20 that includes a plurality of decompression mechanisms 21 to 24 provided to each of the multiple stages and reduces the pressure of the refrigerant that has passed through the first heat exchanger (E1) over a plurality of steps, and the refrigerant that has passed through the decompression unit 20. A second heat exchanger (E2) that absorbs heat from the heat load, a plurality of gas-liquid separators 31 to 33 respectively provided between the pressure reducing mechanisms of the pressure reducing mechanisms 21 to 24, and a plurality of gas-liquid separators 31 to 33, and a plurality of intermediate pressure injection passages 41 to 43 that supply gas-phase refrigerant between the compression mechanisms of the compression mechanisms 11 to 14 from the corresponding gas-liquid separators 31 to 33, and a plurality of intermediate pressure injection passages 41 to 43. and valves V1, V2, and V3 provided in at least one of the pressure injection flow paths 41-43. By operating the valves V1, V2 and V3, the number of effective stages _NA through which the refrigerant circulates is made variable.
[2] The valve V3 is provided in the intermediate pressure injection passages 41-43 having the highest pressure among the plurality of intermediate pressure injection passages 41-43.
[3] The refrigerant contains at least a portion of carbon dioxide.
[4] The number of stages N is 4 or more, and the valves V1, V2, and V3 are connected to at least one of the intermediate pressure injection passages 41 to 43 on the high pressure side and the low pressure injection passages 41 to 43. It is provided in at least one of the intermediate pressure injection flow paths 41 to 43 on the side.
[5] The refrigerating devices 1, 1-2, and 1-3 exchange heat with the outside air in the refrigerant discharged from the low-pressure side compression mechanism as one of the compression mechanisms 11 to 14, and is connected in series with the low-pressure side compression mechanism. It has an intercooling heat exchanger 16 that flows into a high-pressure side compression mechanism as a connected compression mechanism.
[6] The compression unit 10 includes a plurality of compression mechanisms 11, 12 (or 13, 14) connected in series and a housing (101A, etc.) that accommodates the plurality of compression mechanisms 11, 12 (or 13, 14). , and an electric motor (101B, etc.) that drives a plurality of compression mechanisms 11, 12 (or 13, 14).
[7] The refrigerating devices 1, 1-2, 1-3 are provided with a control device 15 that generates a command to operate the valves V1, V2, V3, and the control device 15 generates a command according to the temperature of the outside air. Thus, the number of effective stages _NA is changed.

1, 1-2, 1-3 Refrigerating device 10 Compression unit 10H Housing 10M Electric motor 11 First stage compression mechanism 12 Second stage compression mechanism 13 Third stage compression mechanism 14 Fourth stage compression mechanism 15 Control device 16 Intermediate cooling heat exchange vessel (intermediate heat exchanger)
17 temperature sensor 20 decompression section 21 first stage decompression mechanism 22 second stage decompression mechanism 23 third stage decompression mechanism 24 fourth stage decompression mechanism 31 first intermediate pressure gas-liquid separator 32 second intermediate pressure gas-liquid separator 33 third intermediate Pressure gas-liquid separator 33A Storage tank 33B Gas phase region 41 First intermediate pressure injection channel 42 Second intermediate pressure injection channel 43 Third intermediate pressure injection channel 101 First electric compressor (multi-stage electric compressor)
101A housing 101B electric motor 102 second electric compressor (multi-stage electric compressor)
102A housing 102B electric motor E1 radiator (first heat exchanger)
E2 heat absorber (second heat exchanger)
H High pressure side L Low pressure side N Number of stages _NA Effective number of stages P ₁ First intermediate pressure P ₂ Second intermediate pressure P ₃ Third intermediate pressure _PC Critical pressure _PH , _PL Set pressure R ₁ , R ₂ Pressure ratio T ₁ 1st threshold pressure T ₂ 2nd threshold pressure V1 1st intermediate pressure valve V2 2nd intermediate pressure valve V3 3rd intermediate pressure valve n1~n4 stage r1~r22 operating point

Claims (7)

A refrigeration device that circulates a refrigerant by a refrigeration cycle,
a compression unit including a plurality of stages of compression mechanisms that are connected in series and each compresses the refrigerant, and has three or more stages;
a first heat exchanger for releasing heat to the outside air from the refrigerant that has been compressed in a plurality of steps from a low stage to a high stage by the compression section and discharged from the compression section;
a decompression unit that includes a plurality of decompression mechanisms provided to each of the plurality of stages and reduces the pressure of the refrigerant that has passed through the first heat exchanger in a plurality of steps;
a second heat exchanger that causes the refrigerant that has passed through the decompression unit to absorb heat from a heat load;
a plurality of gas-liquid separators respectively provided between the decompression mechanism and the decompression mechanism;
a plurality of intermediate-pressure injection passages corresponding to the plurality of gas-liquid separators, and supplying the gas-phase refrigerant between the compression mechanism and the compression mechanism from the corresponding gas-liquid separator;
a valve provided in at least one of the plurality of intermediate pressure injection flow paths,
By operating the valve, the number of effective stages in which the refrigerant circulates is variable.
refrigeration equipment. The valve is provided in the intermediate-pressure injection channel having the highest pressure among the plurality of intermediate-pressure injection channels,
Refrigeration equipment according to claim 1 . The refrigerant contains at least a portion of carbon dioxide,
3. The refrigeration system according to claim 1 or 2. The number of steps is 4 or more,
The valve is provided in at least one of the intermediate-pressure injection channels on the high-pressure side and at least one of the intermediate-pressure injection channels on the low-pressure side among the plurality of intermediate-pressure injection channels.
4. A refrigeration system according to any one of claims 1 to 3. A high-pressure side compression mechanism as the compression mechanism connected in series with the low-stage side compression mechanism by heat-exchanging the refrigerant discharged from the low-stage side compression mechanism as the compression mechanism with the outside air. comprising an intermediate heat exchanger feeding into
A refrigeration system according to any one of claims 1 to 4. The compressing section is
A multi-stage electric compressor comprising a plurality of the compression mechanisms connected in series, a housing accommodating the plurality of compression mechanisms, and an electric motor driving the plurality of compression mechanisms,
A refrigeration system according to any one of claims 1 to 5. A control device that generates a command to operate the valve,
The control device changes the number of effective stages by generating the command according to the temperature of the outside air.
A refrigeration apparatus according to any one of claims 1 to 6.

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