CN117321352A

CN117321352A - Refrigeration cycle device

Info

Publication number: CN117321352A
Application number: CN202180098288.9A
Authority: CN
Inventors: 石川智隆; 有井悠介; 上田耕平; 早坂素
Original assignee: Mitsubishi Electric Corp
Current assignee: Mitsubishi Electric Corp
Priority date: 2021-05-25
Filing date: 2021-05-25
Publication date: 2023-12-29
Also published as: WO2022249288A1; JP7466771B2; JPWO2022249288A1; EP4350247A1

Abstract

A refrigeration cycle device is provided with: a control unit; a low-stage compressor that compresses a refrigerant from a 1 st pressure to an intermediate pressure higher than the 1 st pressure; a high-stage compressor that compresses an intermediate-pressure refrigerant from an intermediate pressure to a 2 nd pressure higher than the intermediate pressure; a condenser that exchanges heat between the air and the refrigerant having the 2 nd pressure; an INJ branching portion that branches the refrigerant flowing out from the condenser into a 1 st refrigerant and a 2 nd refrigerant; an expansion valve for expanding the 1 st refrigerant branched by the INJ branching portion to reduce the pressure to the 1 st pressure; an evaporator that exchanges heat between the 1 st refrigerant flowing out of the expansion valve and air, and that causes the 1 st refrigerant at the 1 st pressure to flow out toward the low-stage compressor; an INJ junction portion arranged between the discharge port of the low-stage compressor and the suction port of the high-stage compressor; and an injection circuit connected between the INJ branching portion and the INJ joining portion, for sucking the 2 nd refrigerant branched by the INJ branching portion into the high-stage compressor, the injection circuit comprising: an INJ expansion valve that expands the 2 nd refrigerant; and an accumulator for separating the 2 nd refrigerant expanded by the INJ expansion valve into a liquid refrigerant and a gas refrigerant and storing the liquid refrigerant, wherein the stored liquid refrigerant flows out toward the INJ junction, the control unit controls a ratio of a displacement of the high-stage compressor to a displacement of the low-stage compressor, the displacement of the low-stage compressor being a value obtained by multiplying a volume of the low-stage compressor by a rotational speed, and the displacement of the high-stage compressor being a value obtained by multiplying the volume of the high-stage compressor by the rotational speed.

Description

Refrigeration cycle device

Technical Field

The present disclosure relates to a refrigeration cycle apparatus having an injection circuit.

Background

A multi-stage compression refrigeration cycle apparatus having a low-stage compressor and a high-stage compressor and performing 2-stage compression is conventionally known (for example, refer to patent document 1).

In the refrigeration cycle apparatus described in patent document 1, a low-stage compressor, a high-stage compressor, a radiator, an internal heat exchanger, a 1 st expansion valve, and an evaporator are connected by refrigerant piping.

In addition, the refrigeration cycle apparatus described in patent document 1 is provided with an injection circuit for bypassing the intermediate-pressure refrigerant. One end of the injection circuit is connected between the radiator and the internal heat exchanger. The other end of the injection circuit is connected between the discharge port of the low-stage compressor and the suction port of the high-stage compressor. The injection circuit is provided with a 2 nd expansion valve, and the above-described internal heat exchanger is disposed downstream of the 2 nd expansion valve.

The low-stage compressor compresses a sucked refrigerant from a low pressure to an intermediate pressure. In addition, the high-stage compressor compresses the intermediate-pressure refrigerant discharged from the low-stage compressor to a high pressure. The refrigerant discharged from the high-stage compressor flows into the radiator. In the radiator, heat exchange is performed between the refrigerant and air, and the refrigerant is condensed. The refrigerant condensed by the radiator is supercooled in the internal heat exchanger. Hereinafter, the refrigerant to which supercooling is applied is referred to as a 1 st refrigerant.

On the other hand, a part of the refrigerant condensed by the radiator is branched to the injection circuit. In the injection circuit, the refrigerant flows into the internal heat exchanger after being depressurized by the 2 nd expansion valve. In the internal heat exchanger, the refrigerant supercools the 1 st refrigerant. Hereinafter, the supercooled refrigerant is referred to as a 2 nd refrigerant. Thereafter, the 2 nd refrigerant is guided to the discharge side of the low-stage compressor and the suction side of the high-stage compressor.

On the other hand, the 1 st refrigerant to which supercooling is applied by the internal heat exchanger is guided to the 1 st expansion valve. The 1 st refrigerant expanded by the 1 st expansion valve and having a low pressure flows into the evaporator. In the evaporator, heat exchange is performed between the 1 st refrigerant and air, and the 1 st refrigerant evaporates. The 1 st refrigerant evaporated by the evaporator is sucked into the low-stage compressor.

In the refrigeration cycle apparatus described in patent document 1, at the time of starting the refrigeration cycle apparatus, the rotation speeds of the low-stage compressor and the high-stage compressor are set to rotation speeds lower than the maximum rotation speed at which the maximum capacity is exhibited, and the operation is started, and the rotation speeds are increased stepwise.

Prior art literature

Patent literature

Patent document 1: japanese patent application laid-open No. 2012-247154

Disclosure of Invention

Problems to be solved by the invention

In the refrigeration cycle apparatus described in patent document 1, it is assumed that control is performed by increasing or decreasing the rotation speed of the advanced compressor when the value of the intermediate pressure is to be controlled. In the case where only the rotation speed of the high-stage compressor is increased in order to suppress the intermediate pressure, the condensing load of the radiator is increased, and the discharge pressure (i.e., high pressure) of the high-stage compressor may excessively rise.

The present disclosure has been made to solve the above-described problems, and an object thereof is to provide a refrigeration cycle device capable of suppressing excessive rise of high pressure while suppressing intermediate pressure.

Means for solving the problems

The refrigeration cycle device of the present disclosure includes: a control unit; a low-stage compressor that compresses a refrigerant from a 1 st pressure to an intermediate pressure higher than the 1 st pressure; a high-stage compressor that compresses the refrigerant of the intermediate pressure from the intermediate pressure to a 2 nd pressure higher than the intermediate pressure; a condenser that exchanges heat between the refrigerant having the 2 nd pressure and air; an INJ branching portion that branches the refrigerant flowing out from the condenser into a 1 st refrigerant and a 2 nd refrigerant; an expansion valve that expands the 1 st refrigerant branched by the INJ branching portion and reduces the pressure to the 1 st pressure; an evaporator that exchanges heat between the 1 st refrigerant flowing out of the expansion valve and air, and that causes the 1 st refrigerant at the 1 st pressure to flow out toward the low-stage compressor; an INJ junction portion disposed between a discharge port of the low-stage compressor and a suction port of the high-stage compressor; and an injection circuit connected between the INJ branching portion and the INJ joining portion, the injection circuit being configured to suck the 2 nd refrigerant branched by the INJ branching portion into the high-stage compressor, the injection circuit including: an INJ expansion valve that expands the 2 nd refrigerant; and an accumulator that separates the 2 nd refrigerant expanded by the INJ expansion valve into a liquid refrigerant and a gas refrigerant and stores the liquid refrigerant, wherein the stored liquid refrigerant flows out toward the INJ junction, and wherein the control unit controls a ratio of a displacement of the high-stage compressor to a displacement of the low-stage compressor, the displacement of the low-stage compressor being a value obtained by multiplying a volume of the low-stage compressor by a rotational speed, and the displacement of the high-stage compressor being a value obtained by multiplying the volume of the high-stage compressor by the rotational speed.

ADVANTAGEOUS EFFECTS OF INVENTION

According to the refrigeration cycle apparatus of the present disclosure, by providing the accumulator in the injection circuit, the displacement ratio of the high-stage compressor to the low-stage compressor is controlled, and thus the intermediate pressure, which is the pressure inside the accumulator, is controlled, and therefore, it is possible to suppress excessive rise in the high pressure, which is the discharge pressure of the high-stage compressor, while suppressing the intermediate pressure.

Drawings

Fig. 1 is a refrigerant circuit diagram showing the structure of the refrigeration cycle apparatus according to embodiment 1.

Fig. 2 is a perspective view showing an example of the structure of an internal heat exchanger (HIC) 30 provided in the refrigeration cycle apparatus of embodiment 1.

Fig. 3 shows that CO is used in the refrigeration cycle apparatus described in patent document 1 ₂ A p-h diagram of a refrigeration cycle in the case of a high-pressure supercritical refrigerant.

Fig. 4 is a flowchart showing a flow of processing of the control method (M1) in the refrigeration cycle apparatus according to embodiment 1.

Fig. 5 is a flowchart showing a flow of processing of the control method (M2) in the refrigeration cycle apparatus according to embodiment 1.

Fig. 6 is a p-h diagram showing a refrigeration cycle of the refrigeration cycle apparatus according to embodiment 1.

Detailed Description

Embodiments of a refrigeration cycle apparatus according to the present disclosure will be described below with reference to the accompanying drawings. The present disclosure is not limited to the following embodiments, and various modifications can be made without departing from the gist of the present disclosure. The present disclosure includes all combinations of combinable structures among the structures shown in the following embodiments and modifications thereof. In the drawings, the same or corresponding portions are denoted by the same reference numerals, and are common throughout the specification. In the drawings, the relative dimensional relationship, shape, and the like of the constituent members may be different from the actual ones.

Embodiment 1.

Fig. 1 is a refrigerant circuit diagram showing the structure of the refrigeration cycle apparatus according to embodiment 1. As shown in fig. 1, the refrigeration cycle apparatus includes a refrigerant circuit in which a compressor 10, a condenser 20, an internal heat exchanger (HIC (Heat Inter Changer)) 30, an expansion valve 40, and an evaporator 50 are connected by refrigerant pipes 60 as a main circuit. The compressor 10 has a high-stage compressor 11 and a low-stage compressor 12.

As shown in fig. 1, the refrigerant pipe 60 is provided with an INJ branching portion 61 and an INJ joining portion 62. The INJ branching portion 61 is disposed between the internal heat exchanger (HIC) 30 and the expansion valve 40. The INJ joining portion 62 is disposed between the discharge port of the low-stage compressor 12 and the suction port of the high-stage compressor 11.

Further, as shown in fig. 1, the refrigeration cycle apparatus has an injection circuit 70. The injection circuit 70 is for making an intermediate pressure P, which will be described later _M An intermediate pressure refrigerant bypass circuit for refrigerant flow. One end of the injection circuit 70 is connected to the INJ branching portion 61, and the other end of the injection circuit 70 is connected to the INJ joining portion 62.

The injection circuit 70 is configured by connecting an INJ expansion valve 71, a reservoir (receiver) 72, and a flow rate adjustment valve 73 by an injection pipe 76. In addition, an exhaust pipe 74 may be provided in the injection circuit 70. The exhaust pipe 74 is a bypass pipe connected to the reservoir 72 and the injection pipe 76. The exhaust pipe 74 may be provided with an on-off valve 75.

In the main circuit, the refrigerant flows through the refrigerant pipe 60 in the order of the low-stage compressor 12, the INJ junction 62, the high-stage compressor 11, the condenser 20, the internal heat exchanger (HIC) 30, the INJ branch 61, the expansion valve 40, and the evaporator 50.

In the injection circuit 70, the refrigerant flows in the injection pipe 76 in the order of the INJ branching portion 61, the INJ expansion valve 71, the accumulator 72, the flow rate adjustment valve 73, the internal heat exchanger (HIC) 30, and the INJ joining portion 62.

The configuration of each device constituting the refrigeration cycle apparatus shown in fig. 1 will be described below.

The low-stage compressor 12 discharges the sucked refrigerant from the low pressure P _L Compressed to an intermediate pressure P _M And is discharged. The low-stage compressor 12 is, for example, a variable-frequency compressor. When the low-stage compressor 12 is a variable-frequency compressor, the rotational speed may be arbitrarily changed by a drive circuit such as an inverter circuit, so that the capacity of the low-stage compressor 12 per unit time of the refrigerant to be sent may be changed. In this case, the driving circuit is controlled by the control section 90. In addition, low pressure P _L Is the 1 st preset pressure.

The high-stage compressor 11 discharges the intermediate pressure P from the low-stage compressor 12 _M And an intermediate pressure P flowing from the injection circuit 70 _M Is compressed to a high levelPressure P _H . The refrigerant discharged from the high-stage compressor 11 flows into the condenser 20. The advanced compressor 11 is, for example, a variable frequency compressor. In the case where the high-stage compressor 11 is a variable-frequency compressor, the rotation speed may be arbitrarily changed by a drive circuit such as an inverter circuit, so that the capacity of the high-stage compressor 11 per unit time of the refrigerant to be sent may be changed. In this case, the driving circuit is controlled by the control section 90. In addition, high pressure P _H Is the preset 2 nd pressure. The 2 nd pressure is greater than the 1 st pressure. In addition, intermediate pressure P _M Greater than the 1 st pressure and less than the 2 nd pressure.

The condenser 20 is disposed outdoors, for example. The condenser 20 is a heat exchanger that exchanges heat between the refrigerant flowing therein and air. The condenser 20 is, for example, a fin-tube heat exchanger. The refrigerant condensed and liquefied by the condenser 20 flows into an internal heat exchanger (HIC) 30.

The internal heat exchanger (HIC) 30 performs heat exchange between the refrigerants, and the other refrigerant cools one refrigerant. As shown in fig. 2, the internal heat exchanger (HIC) 30 is constituted by, for example, a double tube. Fig. 2 is a perspective view showing an example of the structure of an internal heat exchanger (HIC) 30 provided in the refrigeration cycle apparatus of embodiment 1. In fig. 2, for the sake of illustration, a part of the structure is illustrated by a broken line. In the example of fig. 2, the internal heat exchanger (HIC) 30 is constituted by an outer tube 31 disposed outside and an inner tube 32 disposed inside the outer tube 31. The refrigerant flowing out of the condenser 20 flows in the direction of arrow P1 in fig. 2in the outer tube 31, and the refrigerant flowing in the injection tube 76 flows in the direction of arrow P2 in fig. 2in the inner tube 32. As shown by the arrows in fig. 2, the flow direction of the refrigerant flowing through the outer tube 31 (the direction of the arrow P1) is opposite to the flow direction of the refrigerant flowing through the inner tube 32 (the direction of the arrow P2), and the flow of these refrigerants is a counter flow. The internal heat exchanger (HIC) 30 is not limited to the example of fig. 2. For example, the refrigerant flowing through the injection pipe 76 may flow through the outer pipe 31, and the refrigerant flowing out of the condenser 20 may flow through the inner pipe 32. In addition, the structure of the internal heat exchanger (HIC) 30 may be other structures.

In the internal heat exchanger (HIC) 30, the refrigerant flowing out of the accumulator 72 and flowing through the injection pipe 76 (refrigerant 2 described later) cools the refrigerant flowing out of the condenser 20 to be supercooled. The supercooled refrigerant (refrigerant 2) also flows through the injection pipe 76 after being applied, and is guided to the INJ joining portion 62. As described above, the INJ joining portion 62 is disposed on the discharge side of the low-stage compressor 12 and on the suction side of the high-stage compressor 11.

On the other hand, the refrigerant to which supercooling has been applied in the internal heat exchanger (HIC) 30 is branched into the 1 st refrigerant and the 2 nd refrigerant by the INJ branching portion 61. The 1 st refrigerant branched by the INJ branching portion 61 flows through the refrigerant pipe 60 and is guided to the expansion valve 40. The expansion valve 40 expands the 1 st refrigerant to reduce the pressure. Expand to become low pressure P _L The 1 st refrigerant of (2) flows into the evaporator 50. The expansion valve 40 is, for example, an electronic expansion valve. When the expansion valve 40 is constituted by an electronic expansion valve, the opening degree is adjusted by the control of the control unit 90.

The evaporator 50 is disposed in an indoor space, for example. The evaporator 50 is a heat exchanger that exchanges heat between the refrigerant flowing inside and air. The evaporator 50 is, for example, a fin-tube heat exchanger. In the evaporator 50, heat exchange is performed between the 1 st refrigerant and air, and the 1 st refrigerant evaporates. The 1 st refrigerant evaporated and gasified in the evaporator 50 is sucked into the low-stage compressor 12. The low-stage compressor 12 sucks the low pressure P flowing out of the evaporator 50 _L Is compressed to an intermediate pressure P _M And is discharged.

On the other hand, the 2 nd refrigerant branched by the INJ branching portion 61 flows through the injection pipe 76, and first flows into the INJ expansion valve 71.

The INJ expansion valve 71 expands the 2 nd refrigerant to reduce the pressure. Expand to become an intermediate pressure P _M And the 2 nd refrigerant flows into the accumulator 72. The INJ expansion valve 71 is, for example, an electronic expansion valve. When the INJ expansion valve 71 is constituted by an electronic expansion valve, the opening degree is adjusted by the control of the control unit 90.

The reservoir 72 is inflated by the INJ inflation valve 71 to an intermediate pressure P _M 2 nd refrigerant of (2). In storageIn the unit 72, the 2 nd refrigerant is separated into a liquid refrigerant and a gas refrigerant. The liquid refrigerant separated by the accumulator 72 flows into the inner tube 32 of the internal heat exchanger (HIC) 30 via the injection tube 76. The 2 nd refrigerant flowing through the inner pipe 32 exchanges heat with the refrigerant flowing through the outer pipe 31, and is then guided to the INJ junction 62. At this time, the 2 nd refrigerant cools the refrigerant flowing through the outer tube 31 in the internal heat exchanger (HIC) 30 to be supercooled. In addition, the internal heat exchanger (HIC) 30 is not necessarily provided, but may be provided only if necessary.

A flow rate adjustment valve 73 is provided in an injection pipe 76 between the reservoir 72 and the internal heat exchanger (HIC) 30. The flow rate of the 2 nd refrigerant (liquid refrigerant) flowing out of the accumulator 72 is adjusted by the opening degree of the flow rate adjustment valve 73. The flow rate adjustment valve 73 is, for example, an electronic adjustment valve. In this case, the opening degree of the flow rate adjustment valve 73 is controlled by the control unit 90.

In the INJ junction 62, an intermediate pressure P flowing in the injection pipe 76 _M Intermediate pressure P between refrigerant 2 and discharge of low-stage compressor 12 _M The 1 st refrigerant of (2) merges. The refrigerant merged by the INJ merging portion 62 is sucked into the high-stage compressor 11. Intermediate pressure P to be sucked by high-stage compressor 11 _M Is compressed to high pressure P _H And is discharged.

The exhaust pipe 74 is a bypass pipe connected between the reservoir 72 and the injection pipe 76. One end of the exhaust pipe 74 is connected to an upper portion of the reservoir 72, and the other end of the exhaust pipe 74 is connected between the flow rate adjustment valve 73 and the internal heat exchanger (HIC) 30. The gas discharge pipe 74 discharges the gas refrigerant in the accumulator 72 to the injection pipe 76 when the on-off valve 75 is opened, and stops the discharge of the gas refrigerant in the accumulator 72 when the on-off valve 75 is closed. This allows fine adjustment of the composition of the refrigerant flowing through the injection circuit 70, that is, the gas density in the refrigerant. However, the exhaust pipe 74 is not necessarily provided, and may be provided only if necessary.

The control unit 90 is constituted by a processing circuit. The processing circuitry is comprised of dedicated hardware or processors. The dedicated hardware is, for example, ASIC (Application Specific Integrated Circuit: application specific integrated circuit) or FPGA (Field Programmable Gate Array: field programmable gate array) or the like. The processor executes the program stored in the memory. A storage unit, not shown, provided in the control unit 90 is constituted by a memory. The Memory is a nonvolatile or volatile semiconductor Memory such as RAM (Random Access Memory: random access Memory), ROM (Read Only Memory), flash Memory, EPROM (Erasable Programmable ROM: erasable programmable Read Only Memory), or a disk such as a magnetic disk, a floppy disk, or an optical disk.

As shown in fig. 1, in embodiment 1, an intermediate pressure P is measured between the INJ expansion valve 71 and the reservoir 72 _M 1 st pressure sensor 81 of (2). Intermediate pressure P detected by 1 st pressure sensor 81 _M Is sent to the control section 90. Intermediate pressure P _M Is the pressure inside the reservoir 72.

As shown in fig. 1, in embodiment 1, a high-pressure P is measured between the discharge port of the high-stage compressor 11 and the condenser 20 _H 2 nd pressure sensor 82 of (a). High pressure P detected by pressure sensor 82 of No. 2 _H Is sent to the control section 90. High pressure P _H Is the discharge pressure of the high-stage compressor 11.

In the refrigeration cycle apparatus described in patent document 1, the use of CO is not assumed ₂ (carbon dioxide) and the like as the refrigerant. On the other hand, in the refrigeration cycle apparatus according to embodiment 1, CO can be used ₂ And (3) an equal-pressure supercritical refrigerant. It is assumed that CO is used in the refrigeration cycle apparatus described in patent document 1 ₂ In the case of a high-pressure supercritical refrigerant, the intermediate pressure may exceed the critical pressure.

Fig. 3 shows that CO is used in the refrigeration cycle apparatus described in patent document 1 ₂ A p-h diagram of a refrigeration cycle in the case of a high-pressure supercritical refrigerant. In fig. 3, the horizontal axis represents specific enthalpy, and the vertical axis represents pressure of the refrigerant. Further, a solid line 100 represents a saturated vapor line, and a solid line 101 represents a saturated liquid line. K is the intersection point of the saturated vapor line 100 and the saturated liquid line 101, and represents a critical point. P (P) _K Is the critical point KI.e. the critical pressure.

In fig. 3, T1 is the compression stroke of the advanced compressor, T2 is the condensation stroke of the radiator, and T3 is the heat exchange stroke of the internal heat exchanger. T4 is the expansion stroke of the 1 st expansion valve, T5 is the evaporation stroke of the evaporator, and T6 is the compression stroke of the low-stage compressor. T7 represents the expansion stroke of the 2 nd expansion valve, and T8 represents the heat exchange stroke of the internal heat exchanger.

In the refrigeration cycle apparatus described in patent document 1, the intermediate pressure P is to be controlled _M In this case, for example, the intermediate pressure P is controlled by increasing or decreasing the rotation speed of the high-stage compressor _M . At this time, in order to control the intermediate pressure P _M When only the rotation speed of the high-stage compressor is increased, the condensing load of the radiator downstream of the high-stage compressor increases. As a result, the high pressure P is the discharge pressure of the high-stage compressor _H May rise excessively. In this case, as shown in FIG. 3, the intermediate pressure P _M May exceed critical pressure P _K 。

In the refrigeration cycle apparatus according to embodiment 1, as shown in fig. 1, the accumulator 72 and the flow rate adjustment valve 73 are provided in the injection circuit 70. In the refrigeration cycle apparatus according to embodiment 1, the control unit 90 controls the accumulator 72 to have the intermediate pressure P as the internal pressure _M Is suppressed to critical pressure P _K The control is performed in the following manner. In addition, at this time, at high pressure P _H When the pressure rises excessively, the opening degree of the flow rate adjustment valve 73 is reduced, and the liquid refrigerant is stored in the accumulator 72, so that the high pressure P is generated _H And (3) lowering. Specifically, the intermediate pressure P is controlled using the following control method (M1) _M . Further, the following control method (M2) is used to control the high pressure P _H . In addition, the control of the control method (M2) is performed only when necessary.

Control method (M1): at an intermediate pressure P _M Becomes critical pressure P _K The control is performed in the following manner. Specifically, the intermediate pressure P is suppressed by increasing the ratio of the displacement of the high-stage compressor 11 to the displacement of the low-stage compressor 12 _M 。

Control method (M2): at high pressureP _H And is controlled so as not to exceed the design pressure of the advanced compressor 11. Specifically, the outflow amount of the liquid refrigerant flowing out of the accumulator 72 is suppressed, and the liquid refrigerant is stored in the accumulator 72 to have a high pressure P _H And (3) lowering.

[ concerning control method (M1) ]

First, a control method (M1) will be described. Fig. 4 is a flowchart showing a flow of processing of the control method (M1) in the refrigeration cycle apparatus according to embodiment 1. In FIG. 4, at an intermediate pressure P _M The control is performed so as to be equal to or less than the 1 st threshold.

As shown in fig. 4, in step S1, the control unit 90 obtains an intermediate pressure P from the 1 st pressure sensor 81 _M Is a detection value of (a).

Next, in step S2, the control unit 90 sets the intermediate pressure P _M And compared with the 1 st threshold. In the result of comparison as intermediate pressure P _M If the threshold value is greater than the 1 st threshold value, the process proceeds to step S3. On the other hand, the result of the comparison is the intermediate pressure P _M When the threshold value is equal to or less than the 1 st threshold value, the processing of the flow of fig. 4 is directly terminated.

In step S3, the control unit 90 sets the intermediate pressure P _M The following 1 st processing is performed so that the intermediate pressure P is set in advance _M The threshold value is 1 or less. Thereby, the intermediate pressure P _M And (3) lowering.

The 1 st threshold is, for example, critical pressure P _K . In embodiment 1, it is assumed that CO is used ₂ (carbon dioxide) as refrigerant, therefore, the 1 st threshold is, for example, CO ₂ Critical pressure P of (2) _K . Known CO ₂ Is 31.1 ℃, critical pressure P _K Is 7.1MPa. Thus, the 1 st threshold is, for example, 7.1MPa. Thus, CO ₂ Is capable of being at a critical temperature of 31.1 ℃ and a critical pressure P _K The refrigerant becomes a supercritical state under relatively mild conditions such as 7.1MPa.

As an example of the 1 st process, for example, the following process is given.

[ Displacement-based control ]

As the 1 st process, the control unit 90 increases the displacement ratio of the high-stage compressor 11 to the low-stage compressor 12. That is, the control unit 90 increases the ratio of the displacement of the high-stage compressor 11 to the displacement of the low-stage compressor 12. Here, the displacements of the low-stage compressor 12 and the high-stage compressor 11 are calculated by the following equation (2). That is, not only the rotation speed ratio of the low-stage compressor 12 to the high-stage compressor 11 but also the volume ratio of the low-stage compressor 12 to the high-stage compressor 11 are considered.

Displacement of low-stage compressor = volume of low-stage compressor x rotational speed of low-stage compressor

Displacement of advanced compressor = volume of advanced compressor x rotational speed of advanced compressor

(1)

The control unit 90 may increase the displacement ratio by a predetermined fixed amount, but may also increase the displacement ratio to the intermediate pressure P _M Corresponding to the value of (a). In this case, the intermediate pressure P is stored in advance in the storage unit of the control unit 90 _M A data table stored in correspondence with the amount of increase in the displacement ratio. Further, when the volumes of the low-stage compressor 12 and the high-stage compressor 11 are considered to be constant, the rotation speed ratio of the high-stage compressor 11 with respect to the low-stage compressor 12 may be increased. Specifically, at least one of the rotation speed of the low-stage compressor 12 and the rotation speed of the high-stage compressor 11 is controlled.

In this way, in step S3, the control unit 90 performs the 1 st processing set in advance. Thereby, the intermediate pressure P _M And (3) lowering. The control unit 90 repeats the processing of the flow of fig. 4 at a fixed cycle. Thereby, the intermediate pressure P can be used _M Becomes critical pressure P _K The intermediate pressure P is controlled in the following manner _M . Thus, by pressing the intermediate pressure P _M Always control to critical pressure P _K The following can reliably be set at the critical pressure P _K The liquid refrigerant is stored in the accumulator 72 as follows.

In step S3, as the 1 st process, the displacement ratio of the high-stage compressor 11 to the low-stage compressor 12 is increased instead of increasing only the displacement of the high-stage compressor 11. In the case of increasing only the displacement of the high-stage compressor 11, the condensing load of the condenser 20 increases, and the high pressure P _H May rise excessively. Therefore, in embodiment 1, the higher order is madeThe displacement ratio of the compressor 11 with respect to the low-stage compressor 12 increases. This can prevent an increase in the condensing load of the condenser 20, and thus can suppress the high pressure P _H Is excessively increased. Further, since an increase in the condensing load of the condenser 20 can be prevented, miniaturization (i.e., downsizing) of the condenser 20 is achieved, and accordingly, the manufacturing cost of the refrigeration cycle apparatus can be reduced.

Next, a control method (M2) will be described. Fig. 5 is a flowchart showing a flow of processing of the control method (M2) in the refrigeration cycle apparatus according to embodiment 1. In FIG. 5, at high pressure P _H The control is performed in such a manner that the design pressure Pcomp of the advanced compressor 11 is not exceeded.

In general, a design pressure Pcomp and a guaranteed pressure Pmax are set in the compressor. The design pressure Pcomp is a pressure value to be used as a reference in design calculation of the strength of the compressor. The design pressure Pcomp is set to a value equal to or higher than the maximum value of the internal pressure P of the compressor that can occur during the normal operation of the compressor. The design pressure Pcomp is obtained by multiplying the maximum value of the internal pressure P that can occur during normal operation of the compressor by a coefficient of 1 or more (for example, 1.1). Alternatively, the design pressure Pcomp is obtained by adding a certain value (for example, 0.1 Mpa) to the maximum value of the internal pressure P that can occur during the normal operation of the compressor.

The guaranteed pressure Pmax of the compressor is a legally prescribed value based on the design pressure Pcomp of the compressor. The assurance pressure Pmax is set to a value larger than the design pressure Pcomp of the compressor based on law.

Further, the breakage pressure Pbr at which the compressor may be broken is a value having a tolerance on the high pressure side with respect to the guaranteed pressure Pmax. That is, the breakage pressure Pbr is a value larger than the guaranteed pressure Pmax. When the pressure inside the compressor exceeds the breakage pressure Pbr, the pressure vessel constituting the casing of the compressor may be broken. The breakage pressure Pbr is obtained by a durability test of the compressor or the like.

In this way, the compressor is designed to ensure the legally prescribed assurance pressure Pmax based on the design pressure Pcomp. Thus, by operating at high pressure P _H The high-stage compressor 11 can be reliably prevented from being damaged by controlling the high-stage compressor 11 so as not to exceed the design pressure Pcomp.

As shown in fig. 5, in step S11, the control unit 90 acquires the high pressure P from the 2 nd pressure sensor 82 _H Is a detection value of (a).

Next, in step S12, the control unit 90 sets the high pressure P to _H And compared with threshold 2.In the result of comparison is high voltage P _H If the threshold value is greater than the 2 nd threshold value, the process proceeds to step S13. On the other hand, when the comparison result is high pressure P _H When the threshold is not more than the 2 nd threshold, the processing of the flow of fig. 5 is directly terminated.

In step S13, the control unit 90 sets the high pressure P to _H The following preset treatment 2 is performed to make the high pressure P _H The threshold value is 2 or less. Thereby, high pressure P _H And (3) lowering.

The 2 nd threshold value is, for example, the design pressure Pcomp of the advanced compressor 11. The design pressure Pcomp is obtained by multiplying the maximum value of the internal pressure P that can occur in the normal operation of the advanced compressor 11 by a coefficient of 1 or more (for example, 1.1). Alternatively, the design pressure Pcomp is obtained by adding a certain value (for example, 0.1 Mpa) to the maximum value of the internal pressure P that can occur in the normal operation of the high-stage compressor 11.

As an example of the 2 nd process, the following process is given.

[ control by flow control valve ]

As the 2 nd process, the control unit 90 decreases the opening degree of the flow rate adjustment valve 73.

The control unit 90 may decrease the opening degree of the flow rate adjustment valve 73 by a predetermined fixed amount, but may increase the opening degree of the flow rate adjustment valve 73 and the high pressure P _H Corresponding to the value of (a). In this case, the high pressure P is stored in advance in the storage unit of the control unit 90 _H A data table stored in correspondence with the amount of decrease in the opening of the flow rate adjustment valve 73.

In this way, in step S13, the control unit 90 performs the 2 nd processing set in advance. Thereby, high pressure P _H And (3) lowering. Control unit 90 performs processing of the flow of fig. 4The process of the flow of fig. 5 is repeated in parallel at a fixed cycle. However, it is desirable to delay the start timing of the process of the flow of fig. 5 by a predetermined time period from the start timing of the process of the flow of fig. 4. Therefore, specifically, for example, the process of the flow of fig. 4 and the process of the flow of fig. 5 are alternately performed. By performing the process of FIG. 5, the high pressure P can be used _H Control of the high pressure P in a manner not exceeding the design pressure Pcomp of the high-stage compressor 11 _H . Namely, can be at high pressure P _H Always satisfy high pressure P _H The relation of > 2 nd threshold value. Thus by applying a high pressure P _H The flat tube can be used as the heat transfer tube of the condenser 20 by controlling the temperature to be not more than the 2 nd threshold at all times. The flat tube has a smaller inner volume of the flow path (i.e., a cross-sectional area of the flow path) through which the refrigerant flows than the round tube. Thus, at high pressure P _H In the case of high, it is difficult to use a flat tube having a small flow path cross-sectional area. In embodiment 1, by storing the liquid refrigerant in the accumulator 72, the excess refrigerant in the accumulator 72 can be increased, and therefore, the high pressure P can be suppressed _H . As a result, the flat tube can be used as a heat transfer tube of the condenser 20. In embodiment 1, the high pressure P is applied _H By controlling the condenser 20 to always be equal to or smaller than the 2 nd threshold value, flat tubes can be used, and the condenser 20 and the refrigeration cycle apparatus can be miniaturized.

Fig. 6 is a p-h diagram showing a refrigeration cycle of the refrigeration cycle apparatus according to embodiment 1. In fig. 6, the horizontal axis represents specific enthalpy, and the vertical axis represents pressure of the refrigerant. Points a to J in fig. 6 correspond to points shown in the refrigerant circuit diagram of fig. 1. In fig. 6, point C is actually the same as point C1, but is slightly shifted for illustration.

First, the high-stage compressor 11 sucks the intermediate pressure P _M Is compressed to a high pressure P _H (the state of point a). The high-temperature and high-pressure gas refrigerant (in the state of the point a) discharged from the high-stage compressor 11 flows into the condenser 20. Then, in the condenser 20, the high-temperature and high-pressure gas refrigerant radiates heat to the air and condenses into a high-pressure P _H (state of point B). The high-pressure refrigerant passes through the internal heat exchanger (HIC) 30 in the direction of the arrow P1 in fig. 1, and the degree of supercooling is further increased (the point C and the point C1). A part of the refrigerant (state of point C1) having passed through the internal heat exchanger (HIC) 30 flows into the INJ expansion valve 71 via the INJ branching portion 61. In the INJ expansion valve 71, a high pressure P _H Is depressurized to an intermediate pressure P _M The refrigerant flows into the accumulator 72 and becomes a gas-liquid two-phase refrigerant (in the state of point H). Thereafter, the liquid refrigerant flowing out of the accumulator 72 passes through the internal heat exchanger (HIC) 30 in the direction of arrow P2 opposite to the just-described arrow P1. Thereby, the intermediate pressure P is increased in temperature _M Two-phase refrigerant (state of point I).

On the other hand, the remaining refrigerant (state of point C) having passed through the internal heat exchanger (HIC) 30 flows into the expansion valve 40. In the expansion valve 40, a high pressure P _H Is depressurized to a low pressure P _L The refrigerant becomes a gas-liquid two-phase refrigerant (point D state). Then, low pressure P _L The two-phase refrigerant (state of point D) flows into the evaporator 50. In the evaporator 50, a low pressure P _L The two-phase refrigerant of (2) absorbs heat from the air and evaporates to become a low pressure P _L (state of point E). The low pressure P _L Is introduced into the low-stage compressor 12. The low-stage compressor 12 draws in a low pressure P _L Is compressed to an intermediate pressure P _M (the state of point F). Intermediate pressure P discharged from low-stage compressor 12 _M And an intermediate pressure P flowing out of the internal heat exchanger (HIC) 30 in the direction of arrow P2 _M The two-phase refrigerant (state of point I) merges (state of point J). The refrigerant is sucked into the high-stage compressor 11, and the same cycle is repeated again.

As described above, the refrigeration cycle apparatus according to embodiment 1 includes the injection circuit 70 having the accumulator 72 and the flow rate adjustment valve 73. Further, the control unit 90 controls the displacement ratio of the high-stage compressor 11 to the low-stage compressor 12, even when CO is used ₂ In the case of a high-pressure supercritical refrigerant, the intermediate pressure P can be used _M Not exceeding critical pressure P _K Is controlled by way of the control system. Thereby, the pressure inside the reservoir 72 can be maintained to the critical pressure P _K Hereinafter, therefore, the liquid refrigerant can always be stored in the accumulator 72. Thus, in embodiment 1, even CO ₂ The refrigerant can also be reliably brought at least partially to the critical pressure P _K Hereinafter, the liquid refrigerant is stored in the accumulator 72. As a result, the high pressure P, which is the discharge pressure of the high-stage compressor 11, can be prevented _H Is able to suppress an increase in the condensing load of the condenser 20.

In embodiment 1, since the increase in the condensing load of the condenser 20 can be suppressed in this way, the condenser 20 can be miniaturized (reduced in size). In the case of miniaturizing the condenser 20, the manufacturing cost of the condenser 20 is reduced accordingly, and therefore, as a result, the manufacturing cost of the entire refrigeration cycle apparatus can be reduced.

In embodiment 1, the control unit 90 is based on the high pressure P _H Is controlled to control the opening degree of the flow rate adjustment valve 73 so that the high pressure P _H Not exceeding the design pressure Pcomp of the advanced compressor 11. This can suppress the outflow of the liquid refrigerant from the accumulator 72, and can store the liquid refrigerant in the accumulator 72. In this way, by suppressing the outflow amount of the liquid refrigerant flowing out of the accumulator 72, the amount of the refrigerant sucked by the high-stage compressor 11 is reduced, and therefore, the high pressure P, which is the discharge pressure of the high-stage compressor 11, can be reduced _H . In embodiment 1, by storing the liquid refrigerant in the accumulator 72, the high pressure P can be suppressed _H Therefore, in the condenser 20 provided downstream of the high-stage compressor 11, a flat tube having a small internal volume of the flow path can be used.

In addition, due to CO ₂ Is a supercritical refrigerant, and therefore, an intermediate pressure P is assumed _M Exceeding critical pressure P _K Is the case in (a). Therefore, the intermediate pressure P can be used _M Not exceeding critical pressure P _K In the refrigeration cycle apparatus according to embodiment 1in which the mode is controlled, CO is used ₂ Particularly effective as a refrigerant.

In the refrigeration cycle apparatus according to embodiment 1, since the internal heat exchanger (HIC) 30 is provided, supercooling can be increased, and therefore, the performance of the refrigeration cycle apparatus can be further improved.

Description of the reference numerals

10 compressor, 11 high-stage compressor, 12 low-stage compressor, 20 condenser, 31 outer tube, 32 inner tube, 40 expansion valve, 50 evaporator, 60 refrigerant piping, 61INJ branching portion, 62INJ joining portion, 70 injection circuit, 71INJ expansion valve, 72 accumulator, 73 flow rate adjusting valve, 74 discharge pipe, 75 opening and closing valve, 76 injection tube, 81 st pressure sensor, 82 nd pressure sensor, 90 control portion, 100 solid line (saturated vapor line), 101 solid line (saturated liquid line), K critical point, P internal pressure, P1 arrow, P2 arrow, P _H High pressure, P _K Critical pressure, P _L Low pressure, P _M Intermediate pressure, pbr breakage pressure, pcomp design pressure, pmax assurance pressure.

Claims

1. A refrigeration cycle apparatus, wherein,

the refrigeration cycle device is provided with:

a control unit;

a low-stage compressor that compresses a refrigerant from a 1 st pressure to an intermediate pressure higher than the 1 st pressure;

a high-stage compressor that compresses the refrigerant of the intermediate pressure from the intermediate pressure to a 2 nd pressure higher than the intermediate pressure;

a condenser that exchanges heat between the refrigerant having the 2 nd pressure and air;

an INJ branching portion that branches the refrigerant flowing out from the condenser into a 1 st refrigerant and a 2 nd refrigerant;

an expansion valve that expands the 1 st refrigerant branched by the INJ branching portion and reduces the pressure to the 1 st pressure;

an evaporator that exchanges heat between the 1 st refrigerant flowing out of the expansion valve and air, and that causes the 1 st refrigerant at the 1 st pressure to flow out toward the low-stage compressor;

an INJ junction portion disposed between a discharge port of the low-stage compressor and a suction port of the high-stage compressor; and

an injection circuit connected between the INJ branching portion and the INJ joining portion, for sucking the 2 nd refrigerant branched by the INJ branching portion into the high-stage compressor,

the injection circuit is provided with:

an INJ expansion valve that expands the 2 nd refrigerant; and

an accumulator for separating the 2 nd refrigerant expanded by the INJ expansion valve into a liquid refrigerant and a gas refrigerant and storing the liquid refrigerant, and flowing the stored liquid refrigerant out toward the INJ junction,

the control part controls a ratio of a displacement of the high-stage compressor to a displacement of the low-stage compressor,

the displacement of the low-stage compressor is a value obtained by multiplying the volume of the low-stage compressor by the rotational speed,

the displacement of the high-stage compressor is a value obtained by multiplying a volume of the high-stage compressor by a rotational speed.

2. The refrigeration cycle apparatus according to claim 1, wherein,

the control unit controls the intermediate pressure, which is the internal pressure of the accumulator, to be 1 st threshold or less by controlling the ratio of the displacement of the high-stage compressor to the displacement of the low-stage compressor.

3. The refrigeration cycle apparatus according to claim 2, wherein,

the control portion decreases the intermediate pressure by increasing a ratio of a displacement of the high-stage compressor to a displacement of the low-stage compressor.

4. A refrigeration cycle apparatus according to claim 2 or 3, wherein,

the 1 st threshold is a critical pressure, which is a pressure of a critical point of the refrigerant.

5. A refrigeration cycle apparatus according to any one of claims 1 to 4, wherein,

the refrigerant is carbon dioxide.

6. A refrigeration cycle apparatus according to any one of claims 1 to 5, wherein,

the injection circuit includes a flow rate adjustment valve disposed between the accumulator and the INJ junction portion, for adjusting an outflow amount of the liquid refrigerant flowing out from the accumulator,

the control unit controls the opening degree of the flow rate adjustment valve to control the 2 nd pressure to be equal to or lower than a 2 nd threshold value.

7. The refrigeration cycle apparatus according to claim 6, wherein,

the control unit decreases the 2 nd pressure by decreasing the opening degree of the flow rate adjustment valve.

8. A refrigeration cycle apparatus according to claim 6 or 7, wherein,

the 2 nd threshold is a design pressure of the advanced compressor.

9. The refrigeration cycle apparatus according to any one of claims 1 to 8, wherein,

the refrigeration cycle device includes an internal heat exchanger disposed between the condenser and the INJ branch portion, supercooling the refrigerant flowing out from the condenser,

the INJ branching portion branches the refrigerant flowing out from the internal heat exchanger into the 1 st refrigerant and the 2 nd refrigerant,

the accumulator causes the liquid refrigerant to flow out toward the INJ junction via the internal heat exchanger.

10. The refrigeration cycle apparatus according to claim 2 or any one of claims 3 to 9 when dependent on claim 2, wherein,

the refrigeration cycle device includes a 1 st pressure sensor disposed between the INJ expansion valve and the accumulator, the 1 st pressure sensor detecting the intermediate pressure as the internal pressure of the accumulator,

the control unit controls the intermediate pressure to be equal to or lower than a 1 st threshold value based on the intermediate pressure detected by the 1 st pressure sensor.

11. A refrigeration cycle apparatus according to any one of claims 6 to 8, wherein,

the refrigeration cycle device includes a 2 nd pressure sensor disposed on a discharge port side of the high-stage compressor, the 2 nd pressure sensor detecting the 2 nd pressure as a discharge pressure of the high-stage compressor,

the control unit controls the 2 nd pressure to be equal to or lower than a 2 nd threshold value based on the 2 nd pressure detected by the 2 nd pressure sensor.