EP4679009A1

EP4679009A1 - Refrigeration cycle device

Info

Publication number: EP4679009A1
Application number: EP23927321.2A
Authority: EP
Inventors: Takurou MATSUO; Motoki Takagi; Yasunori TABAYASHI
Original assignee: Daikin Europe NV; Daikin Industries Ltd
Current assignee: Daikin Europe NV; Daikin Industries Ltd
Priority date: 2023-03-10
Filing date: 2023-03-10
Publication date: 2026-01-14
Also published as: WO2024189697A1; JPWO2024189697A1; EP4679009A4

Abstract

The present disclosure provides a refrigeration cycle apparatus that can accurately determine the state of a refrigerant in an evaporator even when an internal heat exchanger is provided. The refrigeration cycle apparatus including: a refrigerant circuit including a compressor, a radiator, a decompression means, an internal heat exchanger, and an evaporator; and a temperature detection unit that detects the temperature of the refrigerant, in which the refrigerant circuit is charged with a non-azeotropic mixture refrigerant, the internal heat exchanger causes heat exchange between the refrigerant flowing from the evaporator to the compressor, and the refrigerant flowing from the radiator to the evaporator, and the temperature detection unit detects the temperature of the refrigerant flowing out of the evaporator and before flowing into the internal heat exchanger.

Description

TECHNICAL FIELD

The present disclosure relates to a refrigeration cycle apparatus.

BACKGROUND ART

Patent Literature 1 ( JP 2009-085568 A ) discloses a refrigeration cycle apparatus (refrigeration circuit) that includes a refrigerant circuit including a compressor, a condenser, an evaporator, an internal heat exchanger, and an expansion mechanism, and in which a non-azeotropic mixture refrigerant is charged in the refrigerant circuit.
Aside from this, a technology is known that determines the state of the refrigerant in the evaporator based on the temperature of the refrigerant measured by a temperature sensor provided near a suction part of the compressor.

SUMMARY OF THE INVENTION

As in the refrigeration cycle apparatus disclosed in Patent Literature 1, when the refrigerant circuit includes the internal heat exchanger, the refrigerant that flows out of the condenser exchanges heat when passing through the internal heat exchanger. Therefore, it is difficult to accurately determine the state of the refrigerant in the evaporator based on the temperature of the refrigerant measured by the temperature sensor.
The present disclosure provides a refrigeration cycle apparatus that can accurately determine the state of the refrigerant in the evaporator, even when the refrigerant circuit includes the internal heat exchanger.

A refrigeration cycle apparatus of a first aspect includes a refrigerant circuit and a temperature detection unit.
The refrigerant circuit includes a compressor, a radiator, a decompression means, an internal heat exchanger, and an evaporator. The temperature detection unit detects the temperature of a refrigerant.
The refrigerant circuit is charged with a non-azeotropic mixture refrigerant.
The internal heat exchanger causes heat exchange between the refrigerant flowing from the evaporator to the compressor and the refrigerant flowing from the radiator to the evaporator. The temperature detection unit detects the temperature of the refrigerant flowing out of the evaporator and before flowing into the internal heat exchanger.
The refrigeration cycle apparatus can detect the temperature of the refrigerant flowing out of the evaporator, before flowing into the internal heat exchanger. Therefore, the refrigeration cycle apparatus, even when provided with the internal heat exchanger, can accurately determine the state of the refrigerant in the evaporator.
The refrigeration cycle apparatus of a second aspect is the refrigeration cycle apparatus of the first aspect, further including a pressure detection unit that detects the pressure of the refrigerant flowing out of the internal heat exchanger and before flowing into the compressor.
The refrigeration cycle apparatus can more accurately determine the state of the refrigerant in the evaporator by taking into account the pressure of the refrigerant before flowing into the compressor together with the temperature of the refrigerant detected by the temperature detection unit.
The refrigeration cycle apparatus of a third aspect is the refrigeration cycle apparatus of the second aspect, further including a control unit that calculates wetness of the refrigerant before flowing into the internal heat exchanger based on detection results of the temperature detection unit and the pressure detection unit.
The control unit can calculate the wetness of the refrigerant before flowing into the internal heat exchanger based on two detection results obtained from the temperature detection unit and the pressure detection unit.
The refrigeration cycle apparatus of a fourth aspect is the refrigeration cycle apparatus of the third aspect, in which the decompression means decompresses the refrigerant flowing from the radiator to the evaporator. The control unit controls the opening degree of the decompression means based on the wetness.
By allowing the gas-liquid two-phase refrigerant with low wetness to flow into the internal heat exchanger, the control unit can efficiently cause heat exchange of the refrigerant in the internal heat exchanger by using the temperature glide. Therefore, the refrigeration cycle apparatus can perform the heating operation and the cooling operation efficiently.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic configuration diagram of a refrigeration cycle apparatus 1.
FIG. 2 is a block diagram of a control unit 100.
FIG. 3 is a Mollier diagram showing a relationship among temperature T, pressure P, and specific enthalpy H.

DESCRIPTION OF EMBODIMENTS

(1) Overall configuration

FIG. 1 is a schematic configuration diagram of a refrigeration cycle apparatus 1 according to one embodiment.
The refrigeration cycle apparatus 1 includes a refrigerant circuit 90 and a control unit 100. The refrigerant circuit 90 mainly includes a compressor 10, a switching mechanism 20, a first decompression means 41, a second decompression means 42, a bridge circuit 50, a first heat exchanger 61, a second heat exchanger 62, an internal heat exchanger 63, an economizer heat exchanger 64, an accumulator 80, a liquid refrigerant flow path 71, an injection flow path 72, a first branch flow path 73, and a second branch flow path 74.
The refrigeration cycle apparatus 1 performs the heating operation and the cooling operation. In more detail, the refrigeration cycle apparatus 1 causes the refrigerant circuit 90 to perform a refrigeration cycle to heat or cool water circulating in a water circuit 200, performing the heating operation and the cooling operation for a target space (not shown) by using this water.

(2) Detailed configuration

(2-1) Refrigerant circuit 90

The refrigerant circuit 90 is charged with a non-azeotropic mixture refrigerant as a refrigerant. Although not limited thereto, the refrigerant circuit 90 is charged with R454C.

(2-1-1) Compressor 10

The compressor 10 compresses a low-pressure refrigerant to a high-pressure refrigerant in the refrigeration cycle. In more detail, the compressor 10 is a two-stage compressor that suctions the low-pressure refrigerant in the refrigeration cycle, compresses the refrigerant to intermediate pressure in the refrigeration cycle, and then further compresses the intermediate-pressure refrigerant to high pressure for discharge.
The compressor 10 includes a casing 10a, a first compression element 10b, a second compression element 10c, a drive motor 10d, a first suction part 10e, a second suction part 10f, and a discharge part 10g.
The casing 10a accommodates the first compression element 10b and the second compression element 10c. The first compression element 10b and the second compression element 10c are coupled to a single drive shaft (not shown). During the operation of the compressor 10, the drive motor 10d rotationally drives the first compression element 10b and the second compression element 10c via the drive shaft. In other words, the compressor 10 has a single-shaft two-stage compression structure. The number of rotations of the drive motor 10d is controlled by the control unit 100.
The first suction part 10e suctions the low-pressure refrigerant from the refrigerant circuit 90. The second suction part 10f suctions the intermediate-pressure refrigerant from the refrigerant circuit 90. The discharge part 10g discharges the high-pressure refrigerant to the refrigerant circuit 90. The second suction part 10f is one example of a suction part.
The first compression element 10b compresses the refrigerant suctioned by the first suction part 10e to the intermediate pressure and discharges the compressed refrigerant to the second compression element 10c. The second compression element 10c compresses both the intermediate-pressure refrigerant discharged by the first compression element 10b and the intermediate-pressure refrigerant suctioned by the second suction part 10f to high pressure and discharges the compressed refrigerant to the discharge part 10g.
The structure of the compressor 10 is not limited to the single-shaft two-stage compression structure. The structure of the compressor 10 may include, for example, a compression element driven by another drive motor.

(2-1-2) Switching mechanism 20

The switching mechanism 20 switches the direction in which the refrigerant flows in the refrigerant circuit 90 between two states. The switching mechanism 20 is a four-way switching valve. The switching mechanism 20 includes a first port P1, a second port P2, a third port P3, and a fourth port P4.
The switching mechanism 20 switches between a first state (state indicated by the broken lines in FIG. 1) and a second state (state indicated by the solid lines in FIG. 1). In the first state, the switching mechanism 20 allows communication between the first port P1 and the second port P2, and allows communication between the third port P3 and the fourth port P4. In the second state, the switching mechanism 20 allows communication between the first port P1 and the fourth port P4, and allows communication between the second port P2 and the third port P3. The state of the switching mechanism 20 is controlled by the control unit 100.
The switching mechanism 20 is not limited to the four-way switching valve. The switching mechanism 22 may be configured by combining a plurality of electromagnetic valves and refrigerant flow paths.

(2-1-3) First heat exchanger 61 and second heat exchanger 62

The first heat exchanger 61 causes mutual heat exchange between the refrigerant flowing through the refrigerant circuit 90 and the water circulating through the water circuit 200. The first heat exchanger 61 functions as a radiator for the refrigerant in the heating operation, and as an evaporator for the refrigerant in the cooling operation. The first heat exchanger 61 includes a refrigerant flow path 61a and a water flow path 61b. Note that FIG. 1 shows only a part of the water circuit 200.
The refrigerant flow path 61a is provided in the refrigerant circuit 90. The water flow path 61b is provided in the water circuit 200. The refrigerant flowing through the refrigerant flow path 61a causes mutual heat exchange with the water flowing through the water flow path 61b. The water that has exchanged heat with the refrigerant circulates through the water circuit 200 to heat or cool the air in the target space.
Hereinafter, for convenience of description, in the cooling operation, the end of the refrigerant flow path 61a into which the refrigerant flows is referred to as a first end 61aa, and the end of the refrigerant flow path 61a from which the refrigerant flows out is referred to as a second end 61ab.
The second heat exchanger 62 causes mutual heat exchange between the refrigerant flowing through the refrigerant circuit 90 and the air at the installation location of the second heat exchanger 62. The second heat exchanger 62 functions as an evaporator for the refrigerant in the heating operation, and as a radiator for the refrigerant in the cooling operation. The second heat exchanger 62 includes a refrigerant flow path (not shown) 62a.
The second heat exchanger 62 is provided in the refrigerant circuit 90. The refrigerant flowing through the refrigerant flow path of the second heat exchanger 62 causes mutual heat exchange with the air at the installation location of the second heat exchanger 62.
Hereinafter, for convenience of description, in the heating operation, the end of the refrigerant flow path of the second heat exchanger 62 into which the refrigerant flows is referred to as a first end 62aa, and the end of the refrigerant flow path 61a from which the refrigerant flows out is referred to as a second end 62ab.
Hereinafter, for convenience of description, the first heat exchanger 61 and the second heat exchanger 62 may collectively be referred to as a main heat exchanger 60.

(2-1-4) Bridge circuit 50

The bridge circuit 50 causes the refrigerant that flows out of the first heat exchanger 61 and the second heat exchanger 62 and flows through the liquid refrigerant flow path 71 to flow into the first branch flow path 73. The bridge circuit 50 causes the refrigerant that flows out of the internal heat exchanger 63 and flows through the second branch flow path 74 to flow into the liquid refrigerant flow path 71. The bridge circuit 50 includes a first check valve 51, a second check valve 52, a third check valve 53, and a fourth check valve 54.
The first check valve 51 has an outlet side connected to an outlet side of the second check valve 52, and an inlet side connected to an outlet side of the fourth check valve 54. The third check valve 53 has an outlet side connected to an inlet side of the second check valve 52, and an inlet side connected to an inlet side of the fourth check valve 54.
Hereinafter, for convenience of description, a connection part between the outlet side of the first check valve 51 and the outlet side of the second check valve 52 is referred to as a first connection part C1. A connection part between the inlet side of the second check valve 52 and the outlet side of the third check valve 53 is referred to as a second connection part C2. A connection part between the inlet side of the third check valve 53 and the inlet side of the fourth check valve 54 is referred to as a third connection part C3. A connection part between the outlet side of the fourth check valve 54 and the inlet side of the first check valve 51 is referred to as a fourth connection part C4.

(2-1-5) Liquid refrigerant flow path 71

The liquid refrigerant flow path 71 is a refrigerant flow path that connects each of the first end 61aa of the refrigerant flow path 61a of the first heat exchanger 61 and the first end 62aa of the refrigerant flow path of the second heat exchanger 62 to the bridge circuit 50. The liquid refrigerant flow path 71 includes a first part 71a and a second part 71b.
The first part 71a connects the first end 61aa of the first heat exchanger 61 to the second connection part C2 of the bridge circuit 50. The second part 71b connects the first end 62aa of the second heat exchanger 62 to the fourth connection part C4 of the bridge circuit 50.

(2-1-6) Internal heat exchanger 63

The internal heat exchanger 63 is a precooling heat exchanger that cools the refrigerant flowing from the main heat exchanger 60 that functions as a radiator to the main heat exchanger 60 that functions as an evaporator. The internal heat exchanger 63 includes a first heat transfer tube 63a and a second heat transfer tube 63b. The internal heat exchanger 63 causes mutual heat exchange between the refrigerant passing through the first heat transfer tube 63a and the refrigerant passing through the second heat transfer tube 63b.
The refrigerant flowing from the main heat exchanger 60 that functions as an evaporator to the first suction part 10e of the compressor 10 passes through the first heat transfer tube 63a. One end of the first heat transfer tube 63a is connected to the third port P3 of the switching mechanism 20. The other end of the first heat transfer tube 63a is connected to the first suction part 10e of the compressor 10 via the accumulator 80.
The refrigerant flowing from the main heat exchanger 60 that functions as a radiator to the main heat exchanger 60 that functions as an evaporator passes through the second heat transfer tube 63b. One end of the second heat transfer tube 63b is connected to the third connection part C3 of the bridge circuit 50. The other end of the second heat transfer tube 63b is connected to the first connection part C1 of the bridge circuit 50.

(2-1-7) First branch flow path 73 and second branch flow path 74

Each of the first branch flow path 73 and the second branch flow path 74 is a refrigerant flow path that branches from the liquid refrigerant flow path 71 via the bridge circuit 50, and is connected to the second heat transfer tube 63b.
One end of the first branch flow path 73 is connected to the first connection part C1 of the bridge circuit 50. The other end of the first branch flow path 73 is connected to the second heat transfer tube 63b. A second heat transfer tube 64b (described later) of the economizer heat exchanger 64 is provided in the middle of the first branch flow path 73.
One end of the second branch flow path 74 is connected to the third connection part C3 of the bridge circuit 50. The other end of the second branch flow path 74 is connected to the end of the second heat transfer tube 63b on the opposite side of the first branch flow path 73.

(2-1-8) First decompression means 41

The first decompression means 41 decompresses the refrigerant flowing from the main heat exchanger 60 that functions as a radiator to the main heat exchanger 60 that functions as an evaporator to low pressure. The first decompression means 41 is provided in the middle of the second branch flow path 74. The opening degree of the first decompression means 41 is controlled by the control unit 100. The first decompression means 41 is one example of a decompression means.
Although not limited thereto, the first decompression means 41 is an electric expansion valve.

(2-1-9) Injection flow path 72

The injection flow path 72 is a refrigerant flow path that branches from a portion of the first branch flow path 73 between the economizer heat exchanger 64 and the second heat transfer tube 63b of the internal heat exchanger 63, and connects to the second suction part 10f of the compressor 10. As will be described in detail later, a first heat transfer tube 64a (described later) of the economizer heat exchanger 64 is provided in the middle of the injection flow path 72.

(2-1-10) Second decompression means 42

The second decompression means 42 decompresses the passing refrigerant to intermediate pressure. The second decompression means 42 is provided in the middle of the injection flow path 72. In more detail, the second decompression means 42 is provided between the connection part of the injection flow path 72 to the first branch flow path 73, and the connection part of the injection flow path 72 to the economizer heat exchanger 64. The opening degree of the second decompression means 42 is controlled by the control unit 100.
Although not limited thereto, the second decompression means 42 is an electric expansion valve.

(2-1-11) Economizer heat exchanger 64

The economizer heat exchanger 64 causes mutual heat exchange between the refrigerant that has passed through the injection flow path 72 and has been decompressed by the second decompression means 42, and the refrigerant flowing from the main heat exchanger 60 that functions as a radiator to the main heat exchanger 60 that functions as an evaporator. The economizer heat exchanger 64 includes the first heat transfer tube 64a and a second heat transfer tube 64b. The economizer heat exchanger 64 causes mutual heat exchange between the refrigerant passing through the first heat transfer tube 64a and the refrigerant passing through the second heat transfer tube 64b.
The refrigerant that flows through the injection flow path 72 passes through the first heat transfer tube 64a. The first heat transfer tube 64a is provided in the injection flow path 72. One end of the first heat transfer tube 64a is connected to the second decompression means 42 and the first branch flow path 73 via the injection flow path 72. The other end of the first heat transfer tube 64a is connected to the second suction part 10f of the compressor 10 via the injection flow path 72.
The refrigerant that flows through the first branch flow path 73 passes through the second heat transfer tube 64b. The second heat transfer tube 64b is provided in the first branch flow path 73. One end of the second heat transfer tube 64b is connected to the first connection part C1 of the bridge circuit 50 via the first branch flow path 73. The other end of the second heat transfer tube 64b is connected to the second heat transfer tube 63b of the internal heat exchanger 63 via the first branch flow path 73.

(2-1-12) Accumulator 80

The accumulator 80 separates the refrigerant flowing out of the first heat transfer tube 63a and flowing into the first suction part 10e of the compressor 10 into a gas refrigerant and a liquid refrigerant. The accumulator 80 is provided in a refrigerant flow path that connects the other end of the first heat transfer tube 63a to the first suction part 10e of the compressor 10.

(2-1-13) Temperature detection unit 81

A temperature detection unit 81 detects the temperature T of the refrigerant flowing out of the main heat exchanger 60 that functions as an evaporator and before flowing into the first heat transfer tube 63a of the internal heat exchanger 63. The temperature detection unit 81 is provided in the refrigerant flow path that connects one end of the first heat transfer tube 63a to the third port P3 of the switching mechanism 20.
The control unit 100 acquires the temperature of the refrigerant detected by the temperature detection unit 81. Although not limited thereto, the temperature detection unit 81 is a thermistor.

(2-1-14) Pressure detection unit 82

A pressure detection unit 82 detects the pressure P of the refrigerant flowing out of the first heat transfer tube 63a of the internal heat exchanger 63 and before flowing into the first suction part 10e of the compressor 10. The pressure detection unit 82 is provided in the refrigerant flow path that connects the accumulator 80 to the first suction part 10e of the compressor 10.
The control unit 100 acquires the pressure of the refrigerant detected by the pressure detection unit 82.

(2-2) Control unit 100

FIG. 2 is a block diagram of the control unit 100. The control unit 100 controls each device of the refrigerant circuit 90 to cause the refrigerant circuit 90 to perform the refrigeration cycle. The control unit 100 is electrically connected to the compressor 10, the switching mechanism 20, the first decompression means 41, the second decompression means 42, the temperature detection unit 81, and the pressure detection unit 82 to allow transmission and reception of signals.
The control unit 100 is implemented by a computer. The control unit 100 includes a control arithmetic device and a storage device (both not shown). A processor such as a CPU or a GPU can be used for the control arithmetic device. The control arithmetic device reads a program stored in the storage device and performs predetermined arithmetic processing according to the program. Furthermore, the control arithmetic device can write an arithmetic result in the storage device and read information stored in the storage device according to the program.

(3) Overall operation

The control unit 100 controls each device in the heating operation and the cooling operation, as will be described next.

(3-1) Heating operation

When execution of the heating operation is instructed for the refrigeration cycle apparatus 1, the control unit 100 controls each part of the refrigerant circuit 90 as follows.
The control unit 100 causes the compressor 10 to start operations, and controls the number of rotations of the drive motor 10d. The switching mechanism 20 is controlled to be in the first state. The opening degree of the first decompression means 41 is controlled based on the temperature detection unit 81 and the pressure detection unit 82. Details of the control of the first decompression means 41 will be described later. The opening degree of the second decompression means 42 is controlled. For example, the control unit 100 controls the opening degree of the second decompression means 42 such that the degree of superheating of the refrigerant flowing out of the second decompression means 42 approaches a predetermined target degree of superheating.
When the compressor 10 starts operations, the low-pressure gas refrigerant in the refrigeration cycle is suctioned from the first suction part 10e, and the intermediate-pressure gas refrigerant in the refrigeration cycle is suctioned from the second suction part 10f. The first compression element 10b compresses the low-pressure refrigerant suctioned by the first suction part 10e to the intermediate pressure and discharges the compressed refrigerant to the second compression element 10c. The second compression element 10c compresses both the intermediate-pressure refrigerant discharged from the first compression element 10b and the intermediate-pressure refrigerant suctioned by the second suction part 10f to high pressure in the refrigeration cycle, and discharges the compressed refrigerant as a gas refrigerant to the discharge part 10g.
The high-pressure gas refrigerant that has flowed out of the discharge part 10g passes through the switching mechanism 22 in the order of the first port P1 and the second port P2, and then flows into the refrigerant flow path 61a of the first heat exchanger 61 from the second end 61ab. The refrigerant that flows into the first heat exchanger 61 causes mutual heat exchange with the water flowing through the water flow path 61b and condenses, becomes a high-pressure liquid refrigerant, and flows out of the first end 61aa. In other words, the first heat exchanger 61 functions as a radiator.
The high-pressure refrigerant that has flowed out of the first heat exchanger 61 flows through the first part 71a of the liquid refrigerant flow path 71. The refrigerant that flows through the first part 71a of the liquid refrigerant flow path 71 flows into the bridge circuit 50 from the second connection part C2. The refrigerant that has flowed into the bridge circuit 50 passes through the second check valve 52 and the first connection part C1, and flows into the first branch flow path 73.
The refrigerant that has flowed into the first branch flow path 73 flows into the second heat transfer tube 64b of the economizer heat exchanger 64. The refrigerant that has flowed into the second heat transfer tube 64b of the economizer heat exchanger 64 causes mutual heat exchange with the refrigerant passing through the first heat transfer tube 64a of the economizer heat exchanger 64, and then flows out of the second heat transfer tube 64b. A portion of the refrigerant that has flowed out of the second heat transfer tube 64b flows into the injection flow path 72, while the remainder passes through the first branch flow path 73 and flows into the second heat transfer tube 63b of the internal heat exchanger 63.
The refrigerant that has flowed into the injection flow path 72 is decompressed to intermediate pressure when flowing through the second decompression means 42. The intermediate-pressure refrigerant flows into the first heat transfer tube 64a of the economizer heat exchanger 64, causes mutual heat exchange with the refrigerant passing through the second heat transfer tube 64b of the economizer heat exchanger 64, and then flows out of the first heat transfer tube 64a. The refrigerant that has flowed out of the first heat transfer tube 64a is again suctioned into the compressor 10 from the second suction part 10f.
The refrigerant that has flowed into the second heat transfer tube 63b of the internal heat exchanger 63 causes mutual heat exchange with the refrigerant passing through the first heat transfer tube 63a of the internal heat exchanger 63, and then flows out to the second branch flow path 74. The refrigerant that has flowed out to the second branch flow path 74 passes through the first decompression means 41 and flows into the bridge circuit 50 from the third connection part C3. The refrigerant that has passed through the first decompression means 41 is decompressed to low pressure and becomes a refrigerant of a gas-liquid two-phase state.
The refrigerant that has flowed into the bridge circuit 50 branches at the third connection part C3 into the third check valve 53 and the fourth check valve 54. The refrigerant that has flowed into the third check valve 53 passes through the second connection part C2 and flows into the second check valve 52. The refrigerant that has flowed into the second check valve 52 passes through the first connection part C1 and flows into the first branch flow path 73, as described above. The refrigerant that has flowed into the fourth check valve 54 passes through the fourth connection part C4 and flows into the second part 71b of the liquid refrigerant flow path 71.
The refrigerant that has flowed into the liquid refrigerant flow path 71 flows into the refrigerant flow path of the second heat exchanger 62 from the first end 62aa. The refrigerant that has flowed into the second heat exchanger 62 evaporates by mutual heat exchange with the air at the installation location of the second heat exchanger 62, becomes a low-pressure gas refrigerant, and flows out of the second end 62ab. In other words, the second heat exchanger 62 functions as an evaporator.
The low-pressure refrigerant that has flowed out of the second heat exchanger 62 passes through the switching mechanism 22 in the order of the fourth port P4 and the third port P3, and then flows into the first heat transfer tube 63a of the internal heat exchanger 63. The refrigerant that has flowed into the first heat transfer tube 63a causes mutual heat exchange with the refrigerant passing through the second heat transfer tube 63b of the internal heat exchanger 63, and then flows out of the first heat transfer tube 63a. The refrigerant that has flowed out of the first heat transfer tube 63a passes through the accumulator 80 and is again suctioned into the compressor 10 from the first suction part 10e.

(3-2) Cooling operation

When execution of the cooling operation is instructed for the refrigeration cycle apparatus 1, the control unit 100 controls each part of the refrigerant circuit 90 as follows.
The control unit 100 causes the compressor 10 to start operations, and controls the number of rotations of the drive motor 10d. The switching mechanism 20 is controlled to be in the second state. The control unit 100 controls the opening degree of the first decompression means 41 based on the temperature detection unit 81 and the pressure detection unit 82. Details of the control of the first decompression means 41 will be described later. The opening degree of the second decompression means 42 is controlled. For example, the control unit 100 controls the opening degree of the second decompression means 42 such that the degree of superheating of the refrigerant flowing out of the second decompression means 42 approaches a predetermined target degree of superheating.
When the compressor 10 starts operations, the low-pressure gas refrigerant in the refrigeration cycle is suctioned from the first suction part 10e, and the intermediate-pressure gas refrigerant in the refrigeration cycle is suctioned from the second suction part 10f. The first compression element 10b compresses the low-pressure refrigerant suctioned by the first suction part 10e to the intermediate pressure and discharges the compressed refrigerant to the second compression element 10c. The second compression element 10c compresses both the intermediate-pressure refrigerant discharged from the first compression element 10b and the intermediate-pressure refrigerant suctioned by the second suction part 10f to high pressure in the refrigeration cycle, and discharges the compressed refrigerant as a gas refrigerant to the discharge part 10g.
The high-pressure gas refrigerant that has flowed out of the discharge part 10g passes through the switching mechanism 22 in the order of the first port P1 and the fourth port P4, and flows into the refrigerant flow path of the second heat exchanger 62 from the second end 62ab. The refrigerant that has flowed into the second heat exchanger 62 condenses by mutual heat exchange with the air at the installation location of the second heat exchanger 62, becomes a high-pressure liquid refrigerant, and flows out of the first end 62aa. In other words, the second heat exchanger 62 functions as a radiator.
The high-pressure refrigerant that has flowed out of the second heat exchanger 62 flows through the second part 71b of the liquid refrigerant flow path 71, and then flows into the bridge circuit 50 from the fourth connection part C4. The refrigerant that has flowed into the bridge circuit 50 passes through the first check valve 51 and the first connection part C1, and flows into the first branch flow path 73.
The refrigerant that has flowed into the first branch flow path 73 flows into the second heat transfer tube 64b of the economizer heat exchanger 64. The refrigerant that has flowed into the second heat transfer tube 64b of the economizer heat exchanger 64 causes mutual heat exchange with the refrigerant passing through the first heat transfer tube 64a of the economizer heat exchanger 64, and then flows out of the second heat transfer tube 64b. A portion of the refrigerant that has flowed out of the second heat transfer tube 64b flows into the injection flow path 72, while the remainder passes through the first branch flow path 73 and flows into the second heat transfer tube 63b of the internal heat exchanger 63.
The refrigerant that has flowed into the injection flow path 72 is decompressed to intermediate pressure when flowing through the second decompression means 42. The intermediate-pressure refrigerant flows into the first heat transfer tube 64a of the economizer heat exchanger 64, causes mutual heat exchange with the refrigerant passing through the second heat transfer tube 64b of the economizer heat exchanger 64, and then flows out of the first heat transfer tube 64a. The refrigerant that has flowed out of the first heat transfer tube 64a is again suctioned into the compressor 10 from the second suction part 10f.
The refrigerant that has flowed into the second heat transfer tube 63b of the internal heat exchanger 63 causes mutual heat exchange with the refrigerant passing through the first heat transfer tube 63a of the internal heat exchanger 63, and then flows out to the second branch flow path 74. The refrigerant that has flowed out to the second branch flow path 74 passes through the first decompression means 41 and flows into the bridge circuit 50 from the third connection part C3. The refrigerant that has passed through the first decompression means 41 is decompressed to low pressure and becomes a refrigerant of a gas-liquid two-phase state.
The refrigerant that has flowed into the bridge circuit 50 branches at the third connection part C3 into the third check valve 53 and the fourth check valve 54. The refrigerant that has flowed into the fourth check valve 54 passes through the fourth connection part C4 and flows into the first check valve 51. The refrigerant that has flowed into the first check valve 51 passes through the first connection part C1 and flows into the first branch flow path 73, as described above. The refrigerant that has flowed into the third check valve 53 passes through the second connection part C2 and flows into the first part 71a of the liquid refrigerant flow path 71.
The refrigerant that has flowed into the liquid refrigerant flow path 71 flows into the refrigerant flow path 61a of the first heat exchanger 61 from the first end 61aa. The refrigerant that has flowed into the first heat exchanger 61 causes mutual heat exchange with the water flowing through the water flow path 61b and evaporates, becomes a low-pressure gas refrigerant, and flows out of the second end 61ab. In other words, the first heat exchanger 61 functions as an evaporator.
The low-pressure refrigerant that has flowed out of the first heat exchanger 61 passes through the switching mechanism 22 in the order of the second port P2 and the third port P3, and then flows into the first heat transfer tube 63a of the internal heat exchanger 63. The refrigerant that has flowed out of the first heat transfer tube 63a passes through the accumulator 80 and is again suctioned into the compressor 10 from the first suction part 10e.

(3-3) Control of opening degree of first decompression means 41

The control unit 100 calculates wetness W of the refrigerant before flowing into the first heat transfer tube 63a of the internal heat exchanger 63 based on detection results of the temperature detection unit 18 and the pressure detection unit 82. The control unit 100 controls the opening degree of the first decompression means 41 based on the calculated wetness W. For example, the control unit 100 can increase the opening degree of the first decompression means 41 when the wetness W increases, and can decrease the opening degree of the first decompression means 41 when the wetness W decreases.
The refrigeration cycle apparatus 1 utilizes the temperature glide characteristics of the non-azeotropic mixture refrigerant to efficiently cause heat exchange of the refrigerant in the internal heat exchanger 63. Therefore, it is preferable that a gas-liquid two-phase refrigerant having low wetness W flows into the first heat transfer tube 63a. Therefore, the control unit 100 controls the opening degree of the first decompression means 41 such that the wetness W of the refrigerant before flowing into the first heat transfer tube 63a becomes predetermined target wetness W (for example, about 0.2).
Specifically, in the Mollier diagram of the refrigerant charged in the refrigerant circuit 90, the control unit 100 determines the specific enthalpy H from the position where the isotherm of the temperature T that is a detection result of the temperature detection unit 81 intersects with the isobar of the pressure P that is a detection result of the pressure detection unit 82. Thereafter, the control unit 100 calculates the wetness W by using this specific enthalpy H. FIG. 3 is a Mollier diagram showing a relationship among temperature T, pressure P, and specific enthalpy H.
As shown in FIG. 3, the isotherm of the non-azeotropic mixture refrigerant having temperature glide characteristics is inclined with respect to the isobar in the gas-liquid two-phase state. Therefore, for the refrigerant in the gas-liquid two-phase state, the control unit 100 can determine one specific enthalpy H based on one set of temperature T and pressure P, and can calculate the wetness W of the refrigerant before flowing into the first heat transfer tube 63a by using this specific enthalpy H.
Note that the isotherm of a single-component refrigerant that does not have temperature glide characteristics is substantially parallel to the isobar in the gas-liquid two-phase state. Therefore, for the refrigerant circuit charged with a single-component refrigerant, it is not possible to determine one specific enthalpy H for the refrigerant in the gas-liquid two-phase state based on one set of temperature T and pressure P, and to calculate the wetness W.

(4) Characteristics

(4-1)
The refrigeration cycle apparatus 1 includes the refrigerant circuit 90 and the temperature detection unit 81. The refrigerant circuit 90 includes the compressor 10, the main heat exchangers 60 that function as a radiator and an evaporator (specifically, first heat exchanger 61 and second heat exchanger 62), the first decompression means 41, and the internal heat exchanger 63. The temperature detection unit 81 detects the temperature of the refrigerant.
The refrigerant circuit 90 is charged with a non-azeotropic mixture refrigerant. The internal heat exchanger 63 causes heat exchange between the refrigerant flowing from the main heat exchanger 60 that functions as an evaporator to the compressor 10, and the refrigerant flowing from the main heat exchanger 60 that functions as a radiator to the main heat exchanger 60 that functions as an evaporator. The temperature detection unit 81 detects the temperature of the refrigerant flowing out of the main heat exchanger 60 that functions as an evaporator and before flowing into the internal heat exchanger 63.
The refrigeration cycle apparatus 1 can detect the temperature of the refrigerant flowing out of the main heat exchanger 60 that functions as an evaporator, before flowing into the internal heat exchanger 63. Therefore, the refrigeration cycle apparatus 1, even when provided with the internal heat exchanger 63, can accurately determine the state of the refrigerant in the evaporator.
(4-2)
The refrigeration cycle apparatus 1 further includes the pressure detection unit 82. The pressure detection unit 82 detects the pressure of the refrigerant flowing out of the internal heat exchanger 63 and before flowing into the compressor 10.
The refrigeration cycle apparatus 1 can more accurately determine the state of the refrigerant in the evaporator by taking into account the pressure of the refrigerant before flowing into the compressor 10 together with the temperature of the refrigerant detected by the temperature detection unit 81.
(4-3)
The refrigeration cycle apparatus 1 further includes the control unit 100. The control unit 100 calculates the wetness of the refrigerant before flowing into the internal heat exchanger 63 based on detection results of the temperature detection unit 81 and the pressure detection unit 82.
The control unit 100 can calculate the wetness of the refrigerant before flowing into the internal heat exchanger 63 based on two detection results (temperature T and pressure P) obtained from the temperature detection unit 81 and the pressure detection unit 82.
(4-4)
The first decompression means 41 decompresses the refrigerant flowing from the main heat exchanger 60 that functions as a radiator to the main heat exchanger 60 that functions as an evaporator. The control unit 100 controls the opening degree of the first decompression means 41 based on the wetness W.
By allowing the gas-liquid two-phase refrigerant with low wetness W to flow into the internal heat exchanger 63, the control unit 100 can efficiently cause heat exchange of the refrigerant in the internal heat exchanger 63 by using the temperature glide. Therefore, the refrigeration cycle apparatus 1 can perform the heating operation and the cooling operation efficiently.

(5) Modification examples

(5-1)
The heat source with which the refrigerant flowing through the refrigerant flow path 61a exchanges heat is not limited to water; for example, heat may be exchanged with air in the target space. In this case, the first heat exchanger 61 can be disposed in the target space.
(5-2)
The refrigerant to be charged in the refrigerant circuit 90 is not limited to R454C if the refrigerant is a non-azeotropic mixture refrigerant.

While the embodiments according to the present disclosure have been described above, it will be understood that various changes in forms and details can be made without departing from the gist and scope of the present disclosure recited in the claims.

REFERENCE SIGNS LIST

1: refrigeration cycle apparatus
10: compressor
20: switching mechanism
41: first decompression means (decompression means)
61: first heat exchanger (radiator or evaporator)
62: second heat exchanger (radiator or evaporator)
63: internal heat exchanger
63a: first heat transfer tube
63b: second heat transfer tube
81: temperature detection unit
82: pressure detection unit
90: refrigerant circuit
100: control unit
P: pressure
T: temperature
W: wetness

CITATION LIST

PATENT LITERATURE

Patent Literature 1: JP 2009-085568 A

Claims

A refrigeration cycle apparatus comprising:
a refrigerant circuit (90) including a compressor (10), a radiator (61, 62), a decompression means (41), an internal heat exchanger (63), and an evaporator (61, 62); and

a temperature detection unit (81) that detects a temperature of a refrigerant,

wherein the refrigerant circuit is charged with a non-azeotropic mixture refrigerant,

the internal heat exchanger causes heat exchange between the refrigerant flowing from the evaporator to the compressor, and the refrigerant flowing from the radiator to the evaporator, and

the temperature detection unit detects the temperature of the refrigerant flowing out of the evaporator and before flowing into the internal heat exchanger.
The refrigeration cycle apparatus according to claim 1, further comprising
a pressure detection unit (82) that detects pressure of the refrigerant flowing out of the internal heat exchanger and before flowing into the compressor.
The refrigeration cycle apparatus according to claim 2, further comprising
a control unit (100) that calculates wetness (W) of the refrigerant before flowing into the internal heat exchanger based on detection results of the temperature detection unit and the pressure detection unit.
The refrigeration cycle apparatus according to claim 3, wherein
the decompression means decompresses the refrigerant flowing from the radiator to the evaporator, and

the control unit controls an opening degree of the decompression means based on the wetness.