WO2012004987A1 - Two-stage pressure buildup refrigeration cycle system - Google Patents

Abstract

Disclosed is a two-stage pressure buildup refrigeration cycle system which includes a higher-stage compressor mechanism (11a) and a lower-stage compressor mechanism (12a), the refrigerant delivery capacities of which are independently controllable. The refrigerant delivery capacity of the lower-stage compressor mechanism (12a) is determined on the basis of an outside air temperature (Tam), an air temperature (Tfr), and a temperature setting (Tset). The refrigerant delivery capacity of the higher-stage compressor mechanism (11a) is determined based on the determined refrigerant delivery capacity of the lower-stage compressor mechanism (12a) so that the effective capacity ratio is equal to or greater than one and equal to or less than three. This simplified construction and control can provide an improved COP for the two-stage pressure buildup refrigeration cycle system.

Description

Two-stage boost refrigeration cycle equipment Cross-reference of related applications

This application is based on Japanese Patent Application 2010-154680 filed on July 7, 2010, the disclosure of which is incorporated herein by reference.

The present invention relates to a two-stage boosting refrigeration cycle apparatus that includes a low-stage compression mechanism and a high-stage compression mechanism and boosts refrigerant in multiple stages.

Conventionally, in Patent Document 1, a low-stage side compression mechanism that compresses and discharges low-pressure refrigerant until it becomes intermediate-pressure refrigerant, and an intermediate-pressure refrigerant discharged from the low-stage side compression mechanism is compressed and discharged until it becomes high-pressure refrigerant. A two-stage booster type refrigeration cycle apparatus that includes a high-stage compression mechanism that boosts the refrigerant in multiple stages is disclosed.

More specifically, the two-stage booster type refrigeration cycle apparatus of Patent Document 1 includes a radiator that radiates high-pressure refrigerant discharged from the high-stage compression mechanism, and a part of the high-pressure refrigerant that has flowed out of the radiator is an intermediate-pressure refrigerant. An intermediate pressure expansion valve is provided that decompresses and expands to the end, and is configured as a so-called economizer refrigeration cycle apparatus that guides the intermediate pressure refrigerant decompressed by the intermediate pressure expansion valve to the suction side of the high-stage compression mechanism.

In this type of economizer refrigeration cycle apparatus, a high-stage compression mechanism is caused to suck a mixed refrigerant of intermediate-pressure refrigerant decompressed by an intermediate-pressure expansion valve and intermediate-pressure refrigerant discharged from a low-stage compression mechanism. Can do. As a result, the mixed refrigerant having a lower temperature can be sucked into the high stage side compression mechanism than when the intermediate pressure refrigerant discharged from the low stage side compression mechanism is sucked. Efficiency can be improved.

Further, the economizer refrigeration cycle apparatus employs compression mechanisms having the same compression ratio as the high-stage compression mechanism and the low-stage compression mechanism, and the pressure of the intermediate pressure refrigerant (intermediate refrigerant pressure) is changed to the pressure of the high pressure refrigerant (high pressure). The coefficient of performance (COP) of the cycle can be improved by approaching the target intermediate refrigerant pressure defined by the geometric mean of the pressure of the refrigerant on the side (low-pressure refrigerant) and the pressure of the low-pressure refrigerant (low-pressure refrigerant pressure).

Therefore, in the two-stage booster type refrigeration cycle apparatus of Patent Document 1, the throttle opening of the intermediate pressure expansion valve is changed so as to bring the intermediate refrigerant pressure closer to the target intermediate refrigerant pressure, thereby aiming to improve COP.

However, since the target intermediate refrigerant pressure is determined based on both the high-pressure side refrigerant pressure and the low-pressure side refrigerant pressure in the two-stage boosting type refrigeration cycle apparatus disclosed in Japanese Patent Application Laid-Open No. 2006-242557. Pressure detecting means for detecting the refrigerant pressure of both the pressure and the low-pressure side refrigerant pressure must be provided. Therefore, the manufacturing cost of the two-stage booster refrigeration cycle apparatus tends to increase.

Furthermore, if the throttle opening of the intermediate pressure expansion valve is changed so that the intermediate refrigerant pressure approaches the target intermediate refrigerant pressure, the high-pressure side refrigerant pressure and the low-pressure side refrigerant pressure also change. The control for stabilizing (converging) the ability is also complicated.

Moreover, the intermediate pressure refrigerant flowing out of the intermediate pressure expansion valve is in a liquid phase state or a gas-liquid two phase state simply by changing the throttle opening of the intermediate pressure expansion valve so that the intermediate refrigerant pressure approaches the target intermediate refrigerant pressure. It may become. As a result, the problem of liquid compression that the high-stage compression mechanism compresses the incompressible fluid occurs, and the reliability of the high-stage compression mechanism, that is, the reliability of the entire two-stage booster refrigeration cycle apparatus is impaired. Is concerned.

In view of the above points, the first object of the present invention is to provide a two-stage boost type refrigeration cycle apparatus capable of improving COP with a simple configuration and control.

The second object of the present invention is to provide a highly reliable two-stage boost refrigeration cycle apparatus with a simple configuration and control.

In order to achieve the above object, in the two-stage boost type refrigeration cycle apparatus of the first example of the present invention, a low-stage compression mechanism that compresses and discharges low-pressure refrigerant until it becomes intermediate-pressure refrigerant, and a low-stage compression mechanism A high-stage compression mechanism that compresses and discharges the discharged intermediate-pressure refrigerant until it becomes a high-pressure refrigerant, a radiator that heats the high-pressure refrigerant discharged from the high-stage compression mechanism with heat from the outdoor air, and heat dissipation Low-pressure expansion valve that decompresses and expands the high-pressure refrigerant that has flowed out of the radiator until it becomes intermediate-pressure refrigerant, and flows out to the suction side of the high-stage compression mechanism, and low-pressure that expands the high-pressure refrigerant that has flowed out of the radiator to low-pressure refrigerant An expansion valve, and an evaporator for evaporating the low-pressure refrigerant decompressed and expanded by the low-pressure expansion valve through heat exchange with the blown air blown into the space to be cooled and flowing out to the low-stage compression mechanism suction side are provided. Furthermore, the two-stage booster type refrigeration cycle apparatus has at least one of the outdoor air temperature of the outdoor air that exchanges heat with the high-pressure refrigerant in the radiator and the air temperature of the blown air that exchanges heat with the low-pressure refrigerant in the evaporator. Along with the rise, the first discharge capacity control unit that determines to increase the refrigerant discharge capacity of one of the high-stage compression mechanism and the low-stage compression mechanism, and the refrigerant discharge capacity of one compression mechanism And a second discharge capacity control unit that determines the refrigerant discharge capacity of the other compression mechanism. Further, the second discharge capacity control unit sets the discharge capacity of the high-stage compression mechanism to V1, the rotation speed of the high-stage compression mechanism to N1, the discharge capacity of the low-stage compression mechanism to V2, and the rotation of the low-stage compression mechanism. When the number is N2, the refrigerant discharge capacity of the other compression mechanism is determined so that the effective capacity ratio defined by N2 * V2 / N1 * V1 is a value within a predetermined reference range.

According to this, the 1st discharge capacity control part determines the refrigerant discharge capacity of one compression mechanism based on at least one value among outside temperature and air temperature, and also the 2nd discharge capacity control part Since the refrigerant discharge capacity of the other compression mechanism is determined based on the refrigerant discharge capacity of one compression mechanism, the refrigerant discharge capacity of each compression mechanism can be easily determined.

At this time, since the second discharge capacity control unit determines the refrigerant discharge capacity of the other compression mechanism so that the effective volume ratio becomes a value within a predetermined reference range, only the reference range is set appropriately. Thus, the intermediate refrigerant pressure can be substantially brought close to a value corresponding to the geometric mean of the high-pressure side refrigerant pressure and the low-pressure side refrigerant pressure.

Therefore, it is possible to improve the COP of the two-stage booster type refrigeration cycle apparatus with a simple configuration that does not require an expensive pressure detection means and extremely easy control.

Furthermore, since the throttle opening degree of the intermediate pressure expansion valve can be determined regardless of the refrigerant discharge capacity of each compression mechanism, the intermediate pressure refrigerant flowing out from the intermediate pressure expansion valve is used as a gas-phase refrigerant to perform high-stage compression. The problem of liquid compression of the mechanism can be avoided.

Therefore, it is possible to improve the reliability of the high-stage compression mechanism with a simple configuration, that is, the reliability of the entire two-stage booster refrigeration cycle apparatus. The discharge capacity of the compression mechanism is a theoretical flow rate that the compression mechanism discharges per rotation and is a geometrically calculated flow rate.

For example, in the two-stage booster type refrigeration cycle apparatus of the second example of the present invention, the intermediate pressure expansion valve decompresses and expands one of the high-pressure refrigerants branched at the branching part that branches the flow of the high-pressure refrigerant flowing out of the radiator. The low-pressure expansion valve decompresses and expands the other high-pressure refrigerant branched at the branch portion, and further, the low-pressure refrigerant decompressed and expanded at the intermediate pressure expansion valve and the other high-pressure refrigerant branched at the branch portion An intermediate heat exchanger for exchanging heat is provided.

Since the intermediate heat exchanger is provided, the intermediate-pressure refrigerant flowing out from the intermediate-pressure expansion valve can be easily heated to be a gas-phase refrigerant. As a result, the reliability of the two-stage booster refrigeration cycle apparatus can be improved more reliably.

In addition, the other high-pressure refrigerant branched at the branching section is cooled, the enthalpy difference between the enthalpy of the evaporator inlet side refrigerant and the enthalpy of the outlet side refrigerant is expanded, and the refrigerating capacity exhibited in the evaporator is increased. Can be increased. As a result, the COP of the two-stage booster refrigeration cycle apparatus can be further improved.

For example, in the second-stage booster type refrigeration cycle apparatus of the third example of the present invention, one compression mechanism may be a low-stage compression mechanism and the other compression mechanism may be a high-stage compression mechanism.

According to this, the first discharge capacity control unit determines the refrigerant discharge capacity of the low-stage compression mechanism based on at least one of the outside air temperature and the air temperature, and directly sets the refrigerant evaporation pressure of the evaporator. Can be controlled. Therefore, it is easy to adjust the air temperature of the blown air blown into the cooling target space to a desired temperature.

In the second-stage booster type refrigeration cycle apparatus of the fourth example of the present invention, the second discharge capacity control unit is configured such that the absolute value of the temperature difference between the air temperature and the target cooling temperature of the cooling target space is equal to or less than a predetermined reference temperature difference. When it becomes, based on the refrigerant | coolant discharge capability of one compression mechanism, you may determine the refrigerant | coolant discharge capability of the other compression mechanism.

In this case, the second discharge capacity control unit performs the refrigerant discharge capacity of the other compression mechanism until the absolute value of the temperature difference between the air temperature and the target cooling temperature of the cooling target space is equal to or less than a predetermined reference temperature difference. Can be controlled regardless of the refrigerant discharge capacity of one of the compression mechanisms. Therefore, for example, it is possible to execute an operation mode in which the space to be cooled is rapidly cooled when the two-stage booster type refrigeration cycle apparatus is started.

In the two-stage booster type refrigeration cycle apparatus of the fifth example of the present invention, the air temperature is higher than the target cooling temperature, and the second discharge capacity control unit is configured to target the air temperature and the space to be cooled. When the absolute value of the temperature difference with the cooling temperature is equal to or less than a predetermined reference temperature difference, the refrigerant discharge capacity of the other compression mechanism may be determined based on the refrigerant discharge capacity of the one compression mechanism. Good. In this case, capacity control of both compression functions can be performed effectively.

Moreover, in the two-stage booster type refrigeration cycle apparatus of the sixth example of the present invention, the high-stage compression mechanism and the low-stage compression mechanism are composed of a fixed capacity type compression mechanism having a fixed discharge capacity, A high-stage electric motor that rotationally drives the high-stage compression mechanism and a low-stage electric motor that rotationally drives the low-stage compression mechanism, and the rotational speed of the high-stage electric motor and the low-stage electric motor The number of rotations may be configured to be controllable independently of each other.

In this case, since the discharge capacity of the high-stage compression mechanism and the discharge capacity of the low-stage compression mechanism are constant values, at least one of the rotation speed of the high-stage compression mechanism and the rotation speed of the low-stage compression mechanism The effective capacity ratio can be easily set to the reference range simply by changing the value.

In the two-stage booster type refrigeration cycle apparatus of the seventh example of the present invention, the high-stage compression mechanism and the low-stage compression mechanism are composed of variable displacement compression mechanisms whose discharge capacity can be changed. The discharge capacity of the stage side compression mechanism and the discharge capacity of the low stage side compression mechanism may be configured to be changeable independently of each other.

In this case, since the discharge capacity of the high-stage compression mechanism and the discharge capacity of the low-stage compression mechanism can be changed independently, the effective capacity ratio can be easily set even if the rotation speeds of both compression mechanisms are the same. It can be a reference range. Therefore, both compression mechanisms can be driven by a common driving means.

Furthermore, in any one of the above-described two-stage booster type refrigeration cycle apparatuses, the second discharge capacity control unit has an effective capacity ratio of 1 ≦ N2 × V2 / N1 × V1 ≦ 3.
In other words, the refrigerant discharge capacity of the other compression mechanism may be determined.

1 is an overall configuration diagram of a two-stage boost type refrigeration cycle apparatus according to a first embodiment. It is a flowchart which shows the control processing of the two-stage pressure | voltage rise refrigerating-cycle apparatus of 1st Embodiment. It is a graph which shows the change of COP ratio with respect to the change of an effective volume ratio, (a) is a graph in the predetermined condition A, (b) is a graph in another condition B. It is a whole block diagram of the 2 step | paragraph pressure | voltage rise type refrigerating-cycle apparatus of 2nd Embodiment.

(First embodiment)
A first embodiment of the present invention will be described with reference to FIGS. FIG. 1 is an overall configuration diagram of a two-stage booster refrigeration cycle apparatus 10 of the present embodiment. The two-stage booster type refrigeration cycle apparatus 10 is applied to a refrigerator and has a function of cooling the blown air blown into a freezer, which is a space to be cooled, to an extremely low temperature of about −30 ° C. to −10 ° C. Fulfill.

First, as shown in FIG. 1, the two-stage booster refrigeration cycle apparatus 10 includes two compressors, a high-stage compressor 11 and a low-stage compressor 12, and the refrigerant circulating through the cycle is multistage. It is designed to boost the pressure. In addition, as this refrigerant | coolant, a normal freon-type refrigerant | coolant (for example, R404A) is employable. Further, the refrigerant is mixed with refrigerating machine oil (oil) for lubricating the sliding parts in the low-stage compressor 12 and the high-stage compressor 11, and a part of the refrigerating machine oil is cycled together with the refrigerant. It is circulating.

First, the low-stage compressor 12 includes a low-stage compression mechanism 12a that compresses and discharges the low-pressure refrigerant until it becomes an intermediate-pressure refrigerant, and a low-stage electric motor 12b that rotationally drives the low-stage compression mechanism 12a. It is an electric compressor having. The low-stage compression mechanism 12a is composed of a fixed capacity type compression mechanism with a fixed discharge capacity V2, and specifically, various types such as a scroll type compression mechanism, a vane type compression mechanism, a rolling piston type compression mechanism, and the like. A compression mechanism can be adopted.

The low-stage electric motor 12b is an AC motor whose operation (number of rotations) is controlled by an alternating current output from the low-stage inverter 22. Moreover, the low stage side inverter 22 outputs the alternating current of the frequency according to the control signal output from the refrigerator control apparatus 20 mentioned later. And by this frequency control, the refrigerant | coolant discharge capability of the low stage side compressor 12 (specifically, the low stage side compression mechanism 12a) is changed.

Therefore, in the present embodiment, the low stage electric motor 12b constitutes the discharge capacity changing means of the low stage compressor 12. Of course, a DC motor may be employed as the low-stage electric motor 12b, and the rotation speed may be controlled by a control voltage output from the refrigerator control device 20. Further, the suction port side of the high-stage compressor 11 is connected to the discharge port of the low-stage compressor 12 (specifically, the low-stage compression mechanism 12a).

The basic configuration of the high stage compressor 11 is the same as that of the low stage compressor 12. Accordingly, the high-stage compressor 11 includes a high-stage compression mechanism 11a that compresses and discharges the intermediate-pressure refrigerant discharged from the low-stage compressor 12 until it becomes a high-pressure refrigerant, and a high-stage electric motor 11b. It is an electric compressor having.

Further, the high-stage compression mechanism 11a is a fixed-capacity compression mechanism with a fixed discharge capacity V1, and the high-stage electric motor 11b has a rotational speed controlled by an alternating current output from the high-stage inverter 21. Is done. Further, the compression ratio of the high-stage compression mechanism 11a and the compression ratio of the low-stage compression mechanism 12a of the present embodiment are substantially the same.

The refrigerant inlet side of the radiator 13 is connected to the discharge port of the high stage compressor 11 (specifically, the high stage compression mechanism 11a). The heat dissipator 13 is a heat dissipating member that dissipates and cools the high-pressure refrigerant by heat-exchanging the high-pressure refrigerant discharged from the high-stage compressor 11 and the outside air (outdoor air) blown by the cooling fan 13a. It is a heat exchanger.

The cooling fan 13a is an electric blower in which the number of rotations (the amount of blown air) is controlled by a control voltage output from the refrigerator control device 20. In the two-stage boost type refrigeration cycle apparatus 10 of the present embodiment, a refrigerant is used as a refrigerant, and a subcritical refrigeration cycle in which the high-pressure side refrigerant pressure does not exceed the critical pressure of the refrigerant is configured. Reference numeral 13 functions as a condenser for condensing the refrigerant.

A branching portion 14 for branching the flow of the refrigerant flowing out of the radiator 13 is connected to the refrigerant outlet of the radiator 13. The branch portion 14 has a three-way joint structure having three inflow / outflow ports, and one of the inflow / outflow ports is a refrigerant inflow port and two of the inflow / outlet ports are refrigerant outflow ports. Such a branch part 14 may be configured by joining pipes, or may be configured by providing a plurality of refrigerant passages in a metal block or a resin block.

The inlet side of the intermediate pressure expansion valve 15 is connected to one refrigerant outlet of the branch part 14, and the inlet side of the high-pressure refrigerant flow path 16 a of the intermediate heat exchanger 16 is connected to the other refrigerant outlet of the branch part 14. The intermediate pressure expansion valve 15 is a temperature type expansion valve that decompresses and expands the high-pressure refrigerant flowing out of the radiator 13 until it becomes an intermediate-pressure refrigerant.

More specifically, the intermediate pressure expansion valve 15 has a temperature sensing portion disposed on the outlet side of the intermediate pressure refrigerant channel 16b of the intermediate heat exchanger 16, and the temperature of the refrigerant on the outlet side of the intermediate pressure refrigerant channel 16b. The degree of superheat of the refrigerant on the outlet side of the intermediate pressure refrigerant flow path 16b is detected based on the pressure, and the valve opening degree (refrigerant flow rate) is adjusted by a mechanical mechanism so that the degree of superheat becomes a predetermined value set in advance. It has become. Further, the outlet side of the intermediate pressure expansion valve 15 is connected to the inlet side of the intermediate pressure refrigerant flow path 16b.

The intermediate heat exchanger 16 includes an intermediate pressure refrigerant decompressed and expanded by the intermediate pressure expansion valve 15 flowing through the intermediate pressure refrigerant flow path 16b, and the other branch branched by the branch portion 14 flowing through the high pressure refrigerant flow path 16a. Heat exchange is performed with the high-pressure refrigerant. Since the temperature of the high-pressure refrigerant is reduced by reducing the pressure, in the intermediate heat exchanger 16, the intermediate-pressure refrigerant flowing through the intermediate-pressure refrigerant channel 16b is heated, and the high-pressure refrigerant flowing through the high-pressure refrigerant channel 16a is cooled. Will be.

Further, as a specific configuration of the intermediate heat exchanger 16, a plurality of plate-like heat transfer plate members are stacked and the intermediate pressure refrigerant flow path 16b and the high pressure refrigerant flow path 16a are alternately arranged between the heat transfer plate members. A plate-type heat exchanger that is formed and exchanges heat between the high-pressure refrigerant and the intermediate-pressure refrigerant through the heat transfer plate is employed.

Alternatively, a double-pipe heat exchanger configuration in which an inner tube that forms the intermediate-pressure refrigerant channel 16b is arranged inside an outer tube that forms the high-pressure refrigerant channel 16a may be adopted. Of course, the high-pressure refrigerant channel 16a may be an inner tube and the intermediate-pressure refrigerant channel 16b may be an outer tube. Furthermore, the structure etc. which join the refrigerant | coolant piping which forms the high pressure refrigerant flow path 16a and the intermediate pressure refrigerant flow path 16b, and heat-exchange may be employ | adopted.

In the intermediate heat exchanger 16 shown in FIG. 1, the flow direction of the high-pressure refrigerant flowing through the high-pressure refrigerant flow path 16a and the flow direction of the intermediate pressure refrigerant flowing through the intermediate-pressure refrigerant flow path 16b are the same. Although a heat exchanger is adopted, of course, the flow direction of the high-pressure refrigerant flowing through the high-pressure refrigerant channel 16a and the flow direction of the intermediate-pressure refrigerant flowing through the intermediate-pressure refrigerant channel 16b are opposite to each other. A heat exchanger may be employed.

The outlet of the intermediate pressure refrigerant flow path 16b of the intermediate heat exchanger 16 is sucked into the high-stage compressor 11 (specifically, the high-stage compression mechanism 11a) via a check valve (not shown). The mouth side is connected. Therefore, in the high-stage compression mechanism 11a of the present embodiment, a mixed refrigerant of the intermediate-pressure refrigerant flowing out from the intermediate-pressure refrigerant flow path 16b and the intermediate-pressure refrigerant discharged from the low-stage compressor 12 is sucked.

On the other hand, the inlet side of the low-pressure expansion valve 17 is connected to the outlet side of the high-pressure refrigerant channel 16a of the intermediate heat exchanger 16. The low-pressure expansion valve 17 is a temperature type expansion valve that decompresses and expands the high-pressure refrigerant flowing out of the radiator 13 until it becomes a low-pressure refrigerant. The basic configuration of the low pressure expansion valve 17 is the same as that of the intermediate pressure expansion valve 15.

More specifically, the low-pressure expansion valve 17 has a temperature sensing portion arranged on the refrigerant outlet side of the evaporator 18 described later, and the evaporator 18 is based on the temperature and pressure of the refrigerant on the outlet side of the evaporator 18. The degree of superheat of the outlet side refrigerant is detected, and the valve opening degree (refrigerant flow rate) is adjusted by a mechanical mechanism so that the degree of superheat becomes a predetermined value set in advance.

The refrigerant inlet side of the evaporator 18 is connected to the outlet side of the low pressure expansion valve 17. The evaporator 18 evaporates the low-pressure refrigerant and exhibits an endothermic effect by exchanging heat between the low-pressure refrigerant decompressed and expanded by the low-pressure expansion valve 17 and the blown air circulated through the freezer by the blower fan 18a. This is an endothermic heat exchanger. The blower fan 18 a is an electric blower in which the rotation speed (the amount of blown air) is controlled by a control voltage output from the refrigerator control device 20.

Furthermore, the refrigerant outlet of the evaporator 18 is connected to the suction port side of the low-stage compressor 12 (specifically, the low-stage compression mechanism 12a).

Next, the electric control unit of this embodiment will be described. The refrigerator control device 20 outputs a control signal or control voltage to a well-known microcomputer including a CPU that performs control processing and arithmetic processing, and a storage circuit such as ROM and RAM that stores programs and data, and various control target devices. Output circuit, an input circuit to which detection signals of various sensors are input, a power supply circuit, and the like.

The output side of the refrigerator control device 20 is connected to the above-described low-stage inverter 22, high-stage inverter 21, cooling fan 13a, blower fan 18a, and the like as control target devices. Controls the operation of controlled devices.

In addition, although the control means which controls the action | operation of these control object apparatuses is integrated, the refrigerator control apparatus 20 controls the action | operation of each control object apparatus among the refrigerator control apparatuses 20. FIG. The configuration (hardware and software) constitutes control means for each control target device.

In the present embodiment, the configuration (hardware and software) for controlling the refrigerant discharge capacity of the low-stage compression mechanism 12a by controlling the operation of the low-stage inverter 22 is the first discharge capacity controller 20a, and the high-stage inverter A configuration (hardware and software) that controls the operation of 21 to control the refrigerant discharge capacity of the high-stage compression mechanism 11a is defined as a second discharge capacity control unit 20b.

Accordingly, the rotation speed of the low-stage side electric motor 12b and the rotation speed of the high-stage side electric motor 11b can be controlled independently of each other by the first discharge capacity control unit 20a and the second discharge capacity control unit 20b, respectively. ing. Of course, you may comprise the 1st, 2nd discharge capacity control parts 20a and 20b as a separate control apparatus with respect to the refrigerator control apparatus 20, respectively.

On the other hand, on the input side of the refrigerator control device 20, an outside air temperature sensor 23 which is an outside air temperature detecting means for detecting the outside air temperature Tam of the outside air (outdoor air) which exchanges heat with the high-pressure refrigerant by the radiator 13, an evaporation An internal temperature sensor 24 that is an internal temperature detection means for detecting the air temperature Tfr of the blown air that exchanges heat with the low-pressure refrigerant in the cooler 18 is connected, and detection signals from these sensors are input to the refrigerator control device 20. Is done.

Furthermore, an operation panel 30 is connected to the input side of the refrigerator control device 20. The operation panel 30 has an operation / stop switch as a request signal output means for outputting an operation request signal or a stop request signal for the refrigerator, and a temperature as a target temperature setting means for setting the internal temperature (target cooling temperature) Tset. Setting switches and the like are provided, and operation signals of these switches are input to the refrigerator control device 20.

Next, the operation of the two-stage step-up refrigeration cycle apparatus 10 of the present embodiment having the above configuration will be described with reference to FIG. First, FIG. 2 is a flowchart showing a control process executed by the refrigerator control device 20. This control process starts when the operation request signal is output after the operation / stop switch of the operation panel 30 is turned on.

First, in step S1, flags, timers, and the like are initialized, and in the next step S2, detection signals detected by the outside air temperature sensor 23 and the inside temperature sensor 24, and operation signals such as a temperature setting switch of the operation panel 30 are displayed. The operation mode is determined according to Tset set by reading and the temperature setting switch. Specifically, if the target cooling temperature Tset is −10 ° C. or higher, a chilled mode is performed in which refrigeration is performed at a temperature suitable for suppressing a decrease in freshness of fresh foods, and the target cooling Tset is lower than −10 ° C. If there is, set the frozen mode to freeze.

Subsequently, the process proceeds to step S3 to determine the control mode. Since the control mode is common to both the chilled mode and the frozen mode, description for each operation mode is omitted.

Specifically, in step S3, the temperature difference ΔT, which is a value obtained by subtracting the target cooling temperature Tset set by the temperature setting switch from the air temperature Tfr read in step S2, is based on a predetermined reference temperature difference ΔKT. When the temperature difference is large, it is determined that a large capacity is necessary. When the temperature difference ΔT is equal to or less than a predetermined reference temperature difference ΔKT, the internal temperature is close to the set temperature Tset, and fine capacity control is performed. Is determined to be necessary.

In most cases, immediately after the start-up of the refrigerator, the internal temperature, which is the space to be cooled, is higher than the target cooling temperature Tset. Therefore, in this embodiment, a value obtained by subtracting the target cooling temperature Tset from the air temperature Tfr is used as the temperature difference ΔT. Of course, a value obtained by subtracting the air temperature Tfr from the target cooling temperature Tset as the temperature difference ΔT. The absolute value of may be adopted.

If it is determined in step S3 that a large capacity is necessary, the process proceeds to step S4, and operation is performed in the cool-down mode. In step S4, the rotational speeds of the high-stage electric motor 11b and the low-stage electric motor 12b are determined so that the refrigerant discharge capacity of the low-stage compressor 12 and the refrigerant discharge capacity of the high-stage compressor 11 are substantially maximized. .

In the subsequent step S5, the control state of other control target devices in the cool-down mode of the refrigerator is determined. For example, for the cooling fan 13a and the blower fan 18a, the number of rotations is determined so that the blower capacity is substantially maximized, and the process proceeds to step S9.

On the other hand, if it is determined in step S3 that fine capacity control of the refrigerator is necessary, the process proceeds to step S6, and operation is performed in the capacity control mode. In step S6, the refrigerant discharge capacity of the low-stage compressor 12 is determined based on the detection signal and the operation signal read in step S2 this time.

More specifically, in step S6, the rotational speed of the low-stage side electric motor 12b, that is, the rotational speed N2 of the low-stage side compression mechanism 12a is determined based on elements of deviation, integration, and differentiation between the control temperature and the set temperature. To do.

In subsequent step S7, the refrigerant discharge capacity of the high stage compressor 11 is determined based on the refrigerant discharge capacity of the low stage compressor 12 determined in step S6.

Specifically, in step S7, the rotational speed N1 of the high-stage compression mechanism 11a is determined so that the effective volume ratio defined by the following formula F1 is a value within a predetermined reference range shown by the following formula F2. To do.
Effective volume ratio = N2 × V2 / N1 × V1 (F1)
1 ≦ N2 × V2 / N1 × V1 ≦ 3 (F2)
V1 is the discharge capacity of the high-stage compression mechanism 11a, N1 is the rotational speed of the high-stage compression mechanism 11a, V2 is the discharge capacity of the low-stage compression mechanism 12a, and N2 is the low-stage compression mechanism. This is the rotational speed of the mechanism 12a.

In subsequent step S8, the control state of the other control target device is determined. For example, for the cooling fan 13a and the blower fan 18a, the rotational speed is determined so that the blowing capacity increases as the rotational speed N2 of the low-stage compression mechanism 12a determined in step S6 increases. Proceed to step S9.

Next, in step S9, a control signal is output from the refrigerator control device 20 to the control target device connected to the output side so that the control state determined in steps S4 to S8 is obtained. Proceed to step S10.

In step S10, when the stop request signal from the operation panel 30 is output to the refrigerator control device 20, the operation of each control target device is stopped and the entire system of the refrigerator is stopped. On the other hand, if the stop request signal is not output, the process returns to step S2 after waiting for a predetermined control period τ.

Therefore, when the operation / stop switch of the operation panel 30 is turned on, in the two-stage booster type refrigeration cycle apparatus 10, the high-stage compressor 11 causes the intermediate-pressure refrigerant discharged from the low-stage compressor 12 and the intermediate heat to be discharged. The mixed refrigerant with the intermediate pressure refrigerant flowing out from the intermediate pressure refrigerant flow path 16b of the exchanger 16 is sucked, compressed and discharged.

The high-temperature and high-pressure refrigerant discharged from the high-stage compressor 11 flows into the radiator 13 and is cooled by exchanging heat with outside air blown by the cooling fan 13a. The flow of the high-pressure refrigerant that has flowed out of the radiator 13 is branched at the branching section 14. Then, the high-pressure refrigerant that has flowed into the intermediate pressure expansion valve 15 from the branch portion 14 is decompressed and expanded until it becomes an intermediate pressure refrigerant.

At this time, the throttle opening of the intermediate pressure expansion valve 15 is adjusted so that the degree of superheat of the intermediate pressure refrigerant passage 16b outlet side refrigerant of the intermediate heat exchanger 16 becomes a predetermined value. Further, the intermediate pressure refrigerant decompressed by the intermediate pressure expansion valve 15 flows into the intermediate pressure refrigerant flow path 16b of the intermediate heat exchanger 16, and flows from the branch portion 14 to the high pressure refrigerant flow path 16a of the intermediate heat exchanger 16. Heat exchanged with the high-pressure refrigerant that has flowed in is heated and sucked into the high-stage compressor 11.

On the other hand, the high-pressure refrigerant that has flowed into the high-pressure refrigerant flow path 16a of the intermediate heat exchanger 16 from the branch portion 14 is cooled by the intermediate heat exchanger 16. The high-pressure refrigerant that has flowed out of the high-pressure refrigerant channel 16a flows into the low-pressure expansion valve 17 and is decompressed and expanded until it becomes a low-pressure refrigerant. At this time, the throttle opening degree of the low-pressure expansion valve 17 is adjusted so that the degree of superheat of the refrigerant on the outlet side of the evaporator 18 becomes a predetermined value.

Further, the low-pressure refrigerant decompressed by the low-pressure expansion valve 17 flows into the evaporator 18 and absorbs heat from the blown air circulated by the blower fan 18a to evaporate. Thereby, the ventilation air sent in the freezer which is space to be cooled is cooled. The refrigerant that has flowed out of the evaporator 18 is sucked into the low-stage compressor 12.

Since the two-stage booster refrigeration cycle apparatus 10 of the present embodiment operates as described above, not only can the above-described economizer refrigeration cycle apparatus be configured to improve the compression efficiency of the high-stage compression mechanism, The following excellent effects can be exhibited.

First, in the present embodiment, the refrigerant discharge capacity of the low-stage compression mechanism 12a is determined based on the outside air temperature Tam, the air temperature Tfr, and the set temperature Tset, and the refrigerant discharge of the determined low-stage compression mechanism 12a is further determined. Based on the capability, the refrigerant discharge capability of the high-stage compression mechanism 11a is determined. Therefore, the refrigerant discharge capacities of the respective compression mechanisms 11b and 12b can be easily determined.

At this time, since the refrigerant discharge capacity of the high-stage compression mechanism 11a is determined so that the effective volume ratio satisfies the above formula F2, the high-pressure side refrigerant pressure, the intermediate refrigerant pressure, or the low-pressure side refrigerant pressure is detected. The coefficient of performance (COP) of the cycle can be improved with a simple configuration that does not require the pressure detection means and extremely easy control.

This will be described in more detail with reference to FIG. FIG. 3 is a graph showing a change in the COP ratio with respect to a change in the effective volume ratio, and FIG. 3A is a graph in the condition A where the outside air temperature Tam = 38 ° C. and the set temperature Tset = −10 ° C. FIG. 3B is a graph in Condition B where the outside air temperature Tam = 10 ° C. and the set temperature Tset = −25 ° C.

The COP ratio is the COP of the two-stage boost refrigeration cycle apparatus 10 of the present embodiment relative to the COP when the intermediate refrigerant pressure is set to a predetermined value different from the geometric mean of the high-pressure side refrigerant pressure and the low-pressure side refrigerant pressure. Is the ratio.

As is clear from FIG. 3, a peak appears in the COP ratio in the range where the effective volume ratio is 1 or more and 3 or less under any condition. This means that the intermediate refrigerant pressure can be made close to the geometric mean of the high-pressure side refrigerant pressure and the low-pressure side refrigerant pressure by setting the effective volume ratio in the range of 1 or more and 3 or less.

Therefore, according to the two-stage boost type refrigeration cycle apparatus 10 of the present embodiment, COP can be improved with a simple configuration and extremely easy control. Note that the peak value of the COP ratio is present in the vicinity of the effective volume ratio of 2 under any of the conditions. Therefore, in the control step S7, the effective volume ratio is set within the range of 1.5 to 2.5. Thus, the COP can be further improved.

Further, in the refrigeration cycle applied to the refrigerator as in the present embodiment, for example, the pressure difference between the high-pressure side refrigerant pressure and the low-pressure side refrigerant pressure is larger than the refrigeration cycle applied to the air conditioner. The power consumption of the compressor tends to increase. Therefore, it is extremely effective to improve COP in a refrigeration cycle applied to a refrigerator.

Further, in the present embodiment, the refrigerant on the outlet side of the intermediate pressure refrigerant flow path 16b of the intermediate heat exchanger 16 has a superheat degree regardless of the refrigerant discharge capacity of the high stage compression mechanism 11a and the low stage compression mechanism 12a. Since the throttle opening degree of the intermediate pressure expansion valve 15 is adjusted, the problem of liquid compression of the high stage side compression mechanism 11a can be avoided. Moreover, since the throttle opening degree of the low-pressure expansion valve 17 is adjusted so that the refrigerant on the outlet side of the evaporator 18 has a superheat degree, the problem of liquid compression of the low-stage compression mechanism 12a can be avoided.

Therefore, it is possible to improve the reliability of the high-stage compression mechanism 11a and the low-stage compression mechanism 12a with a simple structure, that is, the reliability of the entire two-stage booster refrigeration cycle apparatus.

In this embodiment, since the refrigerant discharge capacity of the low-stage compression mechanism 12a is determined based on the outside air temperature Tam or the like, the refrigerant evaporation pressure of the evaporator 18 is directly set based on the outside air temperature Tam or the like. Can be determined. Therefore, the air temperature Tfr of the blown air blown into the freezer is easily brought close to the set temperature Tset.

Further, since the two-stage booster type refrigeration cycle apparatus 10 of the present embodiment includes the intermediate heat exchanger 16, the intermediate pressure refrigerant that has flowed out of the intermediate pressure expansion valve 15 is separated by the high-pressure refrigerant that is branched at the branch portion 14. It can be heated and easily converted into a gas phase refrigerant. As a result, the reliability of the two-stage booster refrigeration cycle apparatus can be improved more reliably.

Furthermore, since the high-pressure refrigerant branched by the branching section 14 can be cooled by the intermediate-pressure refrigerant flowing out from the intermediate-pressure expansion valve 15, the enthalpy difference between the enthalpy of the evaporator 18 inlet side refrigerant and the enthalpy of the outlet side refrigerant is increased. Thus, the refrigerating capacity exhibited by the evaporator 18 can be increased. As a result, the COP of the two-stage booster refrigeration cycle apparatus can be further improved.

Moreover, in this embodiment, when it determines with it not being immediately after starting of a refrigerator in control step S3, the refrigerant | coolant discharge capability of the high stage compression mechanism 11a is based on the refrigerant | coolant discharge capability of the low stage compression mechanism 12a. To decide. Accordingly, immediately after starting the refrigerator, the operation mode for rapidly cooling the cooling target space is executed with the refrigerant discharge capacity of the low-stage compression mechanism 12a and the refrigerant discharge capacity of the high-stage compression mechanism 11a being substantially maximized. Can do.

Further, in the present embodiment, since the fixed displacement type compression mechanism is adopted as the high stage side compression mechanism 11a and the low stage side compression mechanism 12a, the respective discharge capacities V1 and V2 can be set to constant values. Therefore, after determining the rotational speed N2 of the low-stage compression mechanism 12a, the effective capacity ratio can be easily set to a value within a desired range by simply adjusting the rotational speed N1 of the high-stage compression mechanism 11a. .

(Second Embodiment)
In the second embodiment, as shown in the overall configuration diagram of FIG. 4, an example in which the high-stage compression mechanism 11a and the low-stage compression mechanism 12a are configured with a variable displacement compression mechanism is described with respect to the first embodiment. To do. Furthermore, in this embodiment, the high stage side electric motor 11b and the low stage side electric motor 12b are abolished, and both compression mechanisms 11a and 12a are rotationally driven by the common electric motor 19. In FIG. 4, the same or equivalent parts as those in the first embodiment are denoted by the same reference numerals.

More specifically, in this embodiment, a swash plate type variable displacement compression mechanism is employed as the high-stage compression mechanism 11a and the low-stage compression mechanism 12a. The swash plate type variable displacement compression mechanism is a swash plate type compression mechanism in which the control angle Pc in the swash plate chamber is changed to change the tilt angle of the swash plate to change the stroke of the piston. Is continuously changed in a range of approximately 0% to 100%.

The control pressure Pc in the swash plate chamber of the high-stage compression mechanism 11a and the low-stage compression mechanism 12a is a high pressure refrigerant and a low pressure introduced into the swash plate chamber by changing the valve opening degree of the electromagnetic capacity control valves 11c and 12c, respectively. It is adjusted by changing the introduction ratio of the refrigerant. The operation of the electromagnetic capacity control valves 11c and 12c is controlled by control currents output from the first and second discharge capacity control units 20a and 20b of the refrigerator control device 20, respectively.

The electric motor 19 is an AC motor whose operation (number of rotations) is controlled by an AC current output from the inverter 25, similarly to the high-stage electric motor 11b and the low-stage electric motor 12b of the first embodiment. is there. The inverter 25 outputs an alternating current having a frequency corresponding to the control signal output from the refrigerator control device 20.

Furthermore, the rotational driving force output from the electric motor 19 of the present embodiment is transmitted to both compression mechanisms 11a and 12a via pulleys and belts. Therefore, the rotational speed ratio N2 / N1 between the rotational speed N2 of the low-stage compression mechanism 12a and the rotational speed N1 of the high-stage compression mechanism 11a of the present embodiment is always a constant value. In the present embodiment, the rotational speed ratio N2 / N1 is set to approximately 1, and the rotational speed N2 of the low-stage compression mechanism 12a is made equal to the rotational speed N1 of the high-stage compression mechanism 11a.

Other configurations and operations are the same as those in the first embodiment. Therefore, also in the two-stage boost type refrigeration cycle apparatus 10 of the present embodiment, the coefficient of performance (COP) of the cycle can be improved with a simple configuration and extremely easy control as in the first embodiment. it can. Furthermore, the reliability of the high-stage compression mechanism 11a and the low-stage compression mechanism 12a, that is, the reliability of the entire two-stage booster refrigeration cycle apparatus can be improved with a simple configuration.

In the present embodiment, since variable displacement compression mechanisms are employed as the high-stage compression mechanism 11a and the low-stage compression mechanism 12a, the discharge capacities V1 and V2 of the respective compression mechanisms 11a and 12a are independently set. Can be changed. Accordingly, the effective capacity ratio (N2 × V2 / N1 × V1) can be easily changed to a desired value even if the rotational speeds N1 and N2 of both the compression mechanisms 11a and 12a have the same value.

Furthermore, since both the compression mechanisms 11a and 12a can be driven by a common drive source (electric motor 19), the cycle configuration can be further simplified.

(Other embodiments)
The present invention is not limited to the above-described embodiment, and can be variously modified as follows without departing from the spirit of the present invention.

(1) In the above-described embodiment, the cycle configuration employing the intermediate heat exchanger 16 has been described, but the cycle configuration of the two-stage booster refrigeration cycle apparatus of the present invention is not limited to this. For example, the intermediate heat exchanger 16 may be eliminated, and an intermediate gas-liquid separator that separates the gas-liquid refrigerant flowing out from the intermediate-pressure expansion valve 15 may be provided.

Then, the gas-phase refrigerant separated by the intermediate gas-liquid separator may be sucked into the high-stage compressor 11. In this case, the intermediate pressure expansion valve 15 may be eliminated and a fixed throttle may be employed. Further, the economizer type refrigeration cycle apparatus may be configured such that the liquid phase refrigerant separated by the intermediate gas-liquid separator is made to flow into the low-pressure expansion valve 17 by eliminating the branch portion 14.

(2) In the above-described embodiment, the refrigerant discharge capacity of the low-stage compressor 12 is determined based on the outside air temperature Tam or the like in the control step S6 of FIG. Although the example which determined the refrigerant | coolant discharge capability of the high stage side compressor 11 based on the refrigerant | coolant discharge capability of the compressor 12 was demonstrated, of course, similarly, the refrigerant | coolant discharge capability of the high stage side compressor 11 is similarly in control step S6. In step S7, the refrigerant discharge capacity of the low-stage compressor 12 may be determined.

Furthermore, in the control step S6, the example in which the refrigerant discharge capacity of the low-stage compressor 12 is determined based on the outside air temperature Tam, the air temperature Tfr, and the set temperature Tset has been described. However, the outside air temperature Tam, the air temperature Tfr, the setting The refrigerant discharge capacity of the low-stage compressor 12 may be determined using at least one of the temperatures Tset.

(3) In the above-described embodiment, the example in which the temperature type expansion valve is used as the intermediate pressure expansion valve 15 and the low pressure expansion valve 17 has been described. However, as the intermediate pressure expansion valve 15 and the low pressure expansion valve 17, the electric expansion valve is used. May be adopted.

For example, detection means for detecting the temperature and pressure of the refrigerant on the outlet side of the intermediate pressure refrigerant flow path 16b is added so that the degree of superheat of the refrigerant on the outlet side of the intermediate pressure refrigerant flow path 16b becomes a predetermined value set in advance. In addition, the operation of the intermediate pressure expansion valve 15 may be controlled. Further, detection means for detecting the temperature and pressure of the refrigerant on the outlet side of the evaporator 18 is added to operate the low pressure expansion valve 17 so that the superheat degree of the refrigerant on the outlet side of the evaporator 18 becomes a predetermined value. You may control.

(4) In the above-described embodiment, the example in which the two-stage boost type refrigeration cycle apparatus 10 of the present invention is applied to a refrigerator has been described, but the application of the present invention is not limited to this. For example, you may apply to an air conditioner, a refrigerator, etc. Furthermore, the present invention may be applied to refrigerated / frozen containers such as mobile bodies (vehicles, ships).

In stationary air conditioners and refrigerators / freezers, it is easy to obtain driving energy for the compressors 11 and 12 from a commercial power source or the like. However, in a refrigerator / freezer container applied to this type of mobile body, the driving energy is limited. Therefore, it is effective that the COP can be improved as in the two-stage boost type refrigeration cycle apparatus 10 of the present invention.

(5) In the control step S3 described above, an example has been described in which it is determined whether or not a large capacity is necessary by comparing the temperature difference ΔT and the reference temperature difference ΔKT, but the determination method is not limited to this.

For example, after the operation / stop switch is turned on (ON), first, in the control mode in which the rotational speeds of both the compression mechanisms 11a and 12a are determined so that the difference between the air temperature Tfr and the target cooling temperature Tset is reduced. When the temperature change amount ΔTfr of the air temperature Tfr per unit time is larger than the predetermined reference temperature change amount ΔKTfr, it is determined that the refrigerator has just been started, and ΔTfr is equal to or less than the predetermined reference temperature change amount ΔKTfr. When it is, it may be determined that the refrigerator is in a steady state.
(6) When an azeotropic refrigerant or a pseudo-azeotropic refrigerant is used as the refrigerant, the temperature difference between the inlet side refrigerant temperature of the intermediate pressure refrigerant flow path 16b and the outlet side refrigerant temperature of the intermediate pressure refrigerant flow path 16b is detected, and this temperature The valve opening degree (refrigerant flow rate) of the intermediate pressure expansion valve 15 may be adjusted so that the difference becomes a predetermined value set in advance.

Also, as the refrigerant temperature, the surface temperature of the refrigerant pipe connecting the intermediate pressure refrigerant flow path 16b and another device may be used.

(7) In the first embodiment described above, in step S5 and step S7, control of the other devices (the cooling fan 13a and the blower fan 18a) other than the low-stage compressor and the high-stage compressor is performed according to the control mode. However, it may be configured to control these devices according to the operation mode. For example, the cooling fan 13a and the blower fan 18a may be controlled to be substantially maximized in the chilled mode, and the blower fan 13a and the blower fan 18a may be controlled to have a low air volume in the frozen mode. .

(8) In the above-described embodiment, the mode in which the rotation speed of the low-stage electric motor 12b is controlled by the so-called PID control using the control temperature and the set temperature in Step 6 has been described, but the outside air temperature Tam, the air temperature With reference to the control map stored in advance in the storage circuit of the refrigerator control device 20 based on the Tfr and the set temperature Tset, as the outside air temperature Tam rises, the air temperature Tfr rises, and further, the set temperature Tset falls Thus, the rotational speed of the low-stage electric motor 12b, that is, the rotational speed N2 of the low-stage compression mechanism 12a may be determined so that the refrigerant discharge capacity of the low-stage compressor 12 is increased.

(9) In the above-described second embodiment, an example in which both the high-stage compression mechanism 11a and the low-stage compression mechanism 12a are driven using one electric motor 19 as a drive unit has been described. Separate mechanisms may be employed for the mechanisms 11a and 12a, and an engine (internal combustion engine) may be employed as the mechanism.

Claims (8)

1. A low-stage compression mechanism (12a) that compresses and discharges the low-pressure refrigerant until it becomes an intermediate-pressure refrigerant;
   A high-stage compression mechanism (11a) that compresses and discharges the intermediate-pressure refrigerant discharged from the low-stage compression mechanism (12a) until it becomes a high-pressure refrigerant;
   A radiator (13) for exchanging heat by exchanging heat between the high-pressure refrigerant discharged from the high-stage compression mechanism (11a) and outdoor air;
   An intermediate pressure expansion valve (15) that decompresses and expands the high-pressure refrigerant flowing out of the radiator (13) until it becomes an intermediate-pressure refrigerant, and flows out to the suction side of the high-stage compression mechanism (11a);
   A low-pressure expansion valve (17) for decompressing and expanding the high-pressure refrigerant flowing out of the radiator (13) until it becomes a low-pressure refrigerant;
   The low pressure refrigerant decompressed and expanded by the low pressure expansion valve (17) is evaporated by exchanging heat with the blown air blown into the space to be cooled and flowing out to the suction side of the low stage compression mechanism (12a) ( 18) a two-stage boost type refrigeration cycle apparatus comprising:
   The outdoor air temperature (Tam) of the outdoor air that exchanges heat with the high-pressure refrigerant in the radiator (13) and the air temperature (Tfr) of the blown air that exchanges heat with the low-pressure refrigerant in the evaporator (18). Of these, as the temperature rises, at least one of the high-stage compression mechanism (11a) and the low-stage compression mechanism (12a) is determined to increase the refrigerant discharge capacity of one of the compression mechanisms. A discharge capacity controller (20a);
   A second discharge capacity control unit (20b) that determines the refrigerant discharge capacity of the other compression mechanism based on the refrigerant discharge capacity of the one compression mechanism;
   The second discharge capacity control unit (20b) has a discharge capacity of the high-stage compression mechanism (11a) as V1, a rotation speed of the high-stage compression mechanism (11a) as N1, and the low-stage compression mechanism (12a). ) Discharge capacity is V2, and the rotation speed of the low-stage compression mechanism (12a) is N2, the effective capacity ratio defined by N2 × V2 / N1 × V1 is a value within a predetermined reference range. Thus, the two-stage boosting type refrigeration cycle apparatus is characterized in that the refrigerant discharge capacity of the other compression mechanism is determined.
2. The intermediate pressure expansion valve (15) decompresses and expands one of the high-pressure refrigerants branched at the branching part (14) that branches the flow of the high-pressure refrigerant flowing out of the radiator (13),
   The low-pressure expansion valve (17) decompresses and expands the other high-pressure refrigerant branched at the branch portion (14),
   And an intermediate heat exchanger (16) for exchanging heat between the low pressure refrigerant decompressed and expanded by the intermediate pressure expansion valve (15) and the other high pressure refrigerant branched by the branch section (14). The two-stage booster type refrigeration cycle apparatus according to claim 1, wherein
3. The one compression mechanism is the low-stage compression mechanism (12a),
   The two-stage booster type refrigeration cycle apparatus according to claim 1 or 2, wherein the other compression mechanism is the high-stage compression mechanism (11a).
4. The second discharge capacity control unit (20b) has a reference temperature difference (ΔKT) in which an absolute value of a temperature difference (ΔT) between the air temperature (Tfr) and a target cooling temperature (Tset) of the space to be cooled is predetermined. 4. The refrigerant discharge capacity of the other compression mechanism is determined based on the refrigerant discharge capacity of the one compression mechanism when it becomes the following. 5. Two-stage booster refrigeration cycle equipment.
5. The air temperature (Tfr) is higher than the target cooling temperature (Tset), and the second discharge capacity control unit (20b) determines the air temperature (Tfr) and the target cooling temperature (Tset) of the space to be cooled. ), When the absolute value of the temperature difference (ΔT) is equal to or less than a predetermined reference temperature difference (ΔKT), the refrigerant discharge capacity of the other compression mechanism is based on the refrigerant discharge capacity of the one compression mechanism. The two-stage booster type refrigeration cycle apparatus according to claim 4, wherein:
6. The high-stage compression mechanism (11a) and the low-stage compression mechanism (12a) are configured by a fixed capacity compression mechanism having a fixed discharge capacity (V2, V1).
   Furthermore, a high-stage electric motor (11a) that rotationally drives the high-stage compression mechanism (11a),
   A low-stage electric motor (12b) that rotationally drives the low-stage compression mechanism (12a),
   The rotational speed of the high stage side electric motor (11a) and the rotational speed of the low stage side electric motor (12b) are configured to be controllable independently of each other. The two-stage booster type refrigeration cycle apparatus according to claim 1.
7. The high-stage compression mechanism (11a) and the low-stage compression mechanism (12a) are composed of variable displacement compression mechanisms that can change their discharge capacities (V2, V1).
   The discharge capacity (V1) of the high-stage compression mechanism (11a) and the discharge capacity (V2) of the low-stage compression mechanism (12a) are configured to be controllable independently of each other. Item 6. The two-stage boost type refrigeration cycle apparatus according to any one of Items 1 to 5.
8. The second discharge capacity control unit (20b) has an effective capacity ratio of
   1 ≦ N2 × V2 / N1 × V1 ≦ 3
   The two-stage booster type refrigeration cycle apparatus according to any one of claims 1 to 7, wherein the refrigerant discharge capacity of the other compression mechanism is determined so that
   

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