GB2563170A

GB2563170A - Air conditioner

Info

Publication number: GB2563170A
Application number: GB1814397.4A
Authority: GB
Inventors: Azuma Koji; Morimoto Osamu; Takahashi Hiroki
Original assignee: Mitsubishi Electric Corp
Current assignee: Mitsubishi Electric Corp
Priority date: 2016-03-31
Filing date: 2016-03-31
Publication date: 2018-12-05
Anticipated expiration: 2036-03-31
Also published as: JPWO2017168681A1; JP6644131B2; GB201814397D0; GB2563170B; WO2017168681A1; GB2563170C

Abstract

Provided is an air-conditioner provided with a heat source unit, a plurality of indoor units, a relay unit, a state detector, and a control unit. The relay unit has: a plurality of cooling electromagnetic valves connected in parallel to each other, the cooler electromagnetic valves having one end connected to a gas branch pipe and the other end connected to a first connection pipe, and being opened during a cooling operation and closed during a heating operation; and a heating electromagnetic valve having one end connected to a gas branch pipe and the other end connected to a second connection pipe, and being opened during a heating operation and closed during a cooling operation. The control unit has: a valve control means for controlling the opening/closing of the plurality of cooling electromagnetic valves; a determining means for determining whether or not a flow sound will be generated on the basis of the state of a refrigerant detected by the state detector when the refrigerant is channeled through the cooling electromagnetic valves; and a timing control means for controlling the valve control means so as to open one of the plurality of cooling electromagnetic valves when the indoor unit is switched from a heating operation to a cooling operation, and controlling the valve control means so as to open one of the closed cooling electromagnetic valves when the determining means determines that a refrigerant flow sound will be generated.

Description

DESCRIPTION

Title of Invention

AIR-CONDITIONING APPARATUS

Technical Field [0001]

The present invention relates to an air-conditioning apparatus including a relay unit that distributes refrigerant supplied from a heat source unit to a plurality of indoor units.

Background Art [0002]

An air-conditioning apparatus having a plurality of indoor units that individually execute a heating operation or a cooling operation includes a refrigerant circuit and a structure that efficiently supply a plurality of loads with heating energy or cooling energy generated in a heat source unit or both the heating energy and the cooling energy, for example. Such an air-conditioning apparatus is applied to a multi-airconditioning apparatus for a building, for example. An existing air-conditioning apparatus, such as a multi-air-conditioning apparatus for a building, circulates refrigerant between the indoor units disposed indoors and an outdoor unit disposed outdoors as the heat source unit, for example, to thereby execute the cooling operation or the heating operation. Specifically, an air-conditioned space is cooled by air cooled with heat received by the refrigerant, or is heated by air heated with heat transferred from the refrigerant. For example, HFC-based refrigerant, that is, hydrofluorocarbon-based refrigerant is often employed as the refrigerant for use in such an air-conditioning apparatus. Further, an air-conditioning apparatus employing natural refrigerant such as carbon dioxide, that is, CO2 has also been proposed.

[0003]

There has been proposed an air-conditioning apparatus in which a heat source unit and a plurality of indoor units are connected to supply refrigerant from the heat source unit to the plurality of indoor units and execute a simultaneous cooling and heating operation. An air-conditioning apparatus described in Patent Literature 1 includes a first connecting pipe, a first branching unit formed as three-way switching valves connected to the first connecting pipe and a second connecting pipe to be switchable therebetween, and a second branching unit that connects the second connecting pipe with indoor unit-side second connecting pipes via six check valves. [0004]

In the air-conditioning apparatus described in Patent Literature 1, the three-way switching valves of the first branching unit switch refrigerant flowing into the indoor units performing the heating operation and refrigerant flowing from the indoor units performing the cooling operation. Further, the check valves forming the second branching unit allow the refrigerant to flow in one direction depending on the switching of the refrigerant in the first branching unit. When one of the indoor units performs the cooling operation, therefore, a first connecting port of the three-way switching valve is closed, and a second connecting port and a third connecting port of the threeway switching valve are open. Further, when the indoor unit performs the heating operation, the second connecting port of the three-way switching valve is closed, and the first connecting port and the third connecting port of the three-way switching valve are open.

[0005]

Further, when the indoor unit performs the cooling operation, the refrigerant has a low pressure in the first connecting pipe and a high pressure in the second connecting pipe. Therefore, the refrigerant has a high pressure in a connecting pipe on the side of the first connecting port of the three-way switching valve, and has a low pressure in a connecting pipe on the side of the second connecting port of the threeway switching valve and a connecting pipe on the side of the third connecting port of the three-way switching valve. Further, during the cooling operation, the refrigerant is controlled based on a superheat amount on an outlet side of an indoor-side heat exchanger, and low-pressure gas-state refrigerant flows through an indoor unit-side first connecting pipe.

[0006]

Further, when the indoor unit performs the heating operation, the refrigerant has a low pressure in the first connecting pipe and a high pressure in the second connecting pipe. Therefore, the refrigerant has a high pressure in the connecting pipe on the side of the first connecting port of the three-way switching valve, a low pressure in the connecting pipe on the side of the second connecting port of the three-way switching valve, and a high pressure in the connecting pipe on the side of the third connecting port of the three-way switching valve. Further, during the heating operation, the refrigerant is controlled based on a subcool amount on the outlet side of the indoor-side heat exchanger, and high-temperature, high-pressure gas-state refrigerant flows through the indoor unit-side first connecting pipe. Herein, high-temperature, high-pressure liquid-state refrigerant is in the indoor-side heat exchanger and a connecting pipe from the indoor-side heat exchanger to a first flow rate control device.

[0007]

When the operation of the indoor unit is switched from the heating operation to the cooling operation, therefore, the high-temperature, high-pressure gas refrigerant and the high-temperature, high-pressure liquid refrigerant flowing during the heating operation pass through the three-way switching valve and flow into the first connecting pipe, in which the pressure is low. In this process, flow sound of the refrigerant is generated in the three-way switching valve depending on the balance between high pressure and low pressure of the refrigerant passing through the threeway switching valve. Particularly, the flow sound of the high-temperature, highpressure liquid refrigerant is increased.

[0008]

In view of the above, an air-conditioning apparatus has been proposed in which the three-way switching valves are replaced by solenoid valves, particularly opening and closing solenoid valves. An air-conditioning apparatus described in Patent Literature 2 uses a second solenoid valve for heating and a first solenoid valve and a third solenoid valve, which is provided with an orifice function, for cooling, and allows the refrigerant to flow through the first solenoid valve and the third solenoid valve in a phased manner during the switch from the heating operation to the cooling operation. The air-conditioning apparatus described in Patent Literature 2 is thus configured to reduce the flow sound of the high-temperature, high-pressure liquid refrigerant. Further, in the air-conditioning apparatus described in Patent Literature 2, a flow rate control device is reduced in opening diameter and subjected to pulse control, and the third solenoid valve is reduced in opening diameter to reduce the flow sound of the refrigerant. Further, another air-conditioning apparatus has been proposed which employs solenoid valves, particularly opening and closing solenoid valves, to reduce the size of the air-conditioning apparatus. This air-conditioning apparatus uses a second solenoid valve for heating and a first solenoid valve, a third solenoid valve, and an orifice for cooling. Herein, the orifice forms a bypass between a highpressure-side pressure and a low-pressure-side pressure to equalize the pressure in a high-pressure-side pipe and the pressure in a low-pressure-side pipe and reduce the flow sound of the refrigerant. That is, the air-conditioning apparatus allows the refrigerant to flow through the orifice, the third solenoid valve, and the first solenoid valve in a phased manner during the switch from the heating operation to the cooling operation. The air-conditioning apparatus is thus configured to reduce the flow sound of the high-temperature, high-pressure liquid refrigerant.

Citation List

Patent Literature [0009]

Patent Literature 1: Japanese Patent No. 4350836

Patent Literature 2: Japanese Unexamined Patent Application Publication No. 09-042804

Summary of Invention

Technical Problem [0010]

The above-described air-conditioning apparatus, however, requires three solenoid valves and three orifices for one indoor unit. Each of the branching units therefore requires three solenoid valves and three orifices for each of the indoor units.

As described above, each of the orifices forms a bypass between a pipe connected to the corresponding indoor unit and a pipe connected to the heat source unit. In terms of refrigerant leakage, this structure makes it difficult to prevent the refrigerant from leaking into indoor unit pipes in the branching units.

[0011]

The present invention has been made to address the above-described issues, and provides an air-conditioning apparatus with an improved function of preventing refrigerant leakage and reduced flow sound of the refrigerant.

Solution to Problem [0012]

An air-conditioning apparatus according to an embodiment of the present invention includes: a heat source unit including a compressor and a heat source-side heat exchanger; a plurality of indoor units each including a first flow rate control device and an indoor-side heat exchanger, and configured to perform a cooling operation or a heating operation; a relay unit connected to the heat source unit by a first connecting pipe and a second connecting pipe, connected to the plurality of indoor units by a plurality of gas branch pipes and a plurality of liquid branch pipes, and configured to distribute refrigerant supplied from the heat source unit to the plurality of indoor units; a state detecting unit configured to detect a state of the refrigerant flowing through the plurality of gas branch pipes; and a control unit configured to control an operation of the relay unit. The relay unit includes: a plurality of cooling solenoid valves connected in parallel, having respective one sides connected to the plurality of gas branch pipes and respective other sides connected to the first connecting pipe, and configured to be open during the cooling operation and closed during the heating operation; and heating solenoid valves having respective one sides connected to the plurality of gas branch pipes and respective other sides connected to the second connecting pipe, and configured to be open during the heating operation and closed during the cooling operation. The control unit includes: a valve control unit configured to control opening and closing of the plurality of cooling solenoid valves; a determining unit configured to determine, based on the state of the refrigerant detected by the state detecting unit, whether or not flow sound is generated when the refrigerant flows through one of the plurality of cooling solenoid valves; and a timing control unit configured to control the valve control unit to open one of the plurality of cooling solenoid valves when one of the plurality of indoor units is switched from the heating operation to the cooling operation, and control the valve control unit to open one of the plurality of cooling solenoid valves in a closed state when it is determined by the determining unit that the flow sound of the refrigerant is generated.

Advantageous Effects of Invention [0013]

According to the present invention, when one of the plurality of indoor units is switched from the heating operation to the cooling operation, the timing control unit controls the valve control unit to open one of the plurality of cooling solenoid valves. Further, when it is determined that the flow sound of the refrigerant is generated, the timing control unit controls the valve control unit to open one of the plurality of cooling solenoid valves in the closed state. Since the plurality of cooling solenoid valves are thus opened in a phased manner, it is possible to reduce the flow sound of the refrigerant without using an orifice. Accordingly, it is possible to improve the function of preventing the refrigerant leakage and reduce the flow sound of the refrigerant. Brief Description of Drawings [0014] [Fig. 1] Fig. 1 is a circuit diagram illustrating an air-conditioning apparatus 100 according to Embodiment 1 of the present invention.

[Fig. 2] Fig. 2 is a block diagram illustrating a control unit 70 of the airconditioning apparatus 100 according to Embodiment 1 of the present invention.

[Fig. 3] Fig. 3 is a circuit diagram illustrating a state of the air-conditioning apparatus 100 according to Embodiment 1 of the present invention in a cooling only operation.

[Fig. 4] Fig. 4 is a circuit diagram illustrating a state of the air-conditioning apparatus 100 according to Embodiment 1 of the present invention in a heating only operation.

[Fig. 5] Fig. 5 is a circuit diagram illustrating a state of the air-conditioning 5 apparatus 100 according to Embodiment 1 of the present invention in a cooling main operation.

[Fig. 6] Fig. 6 is a circuit diagram illustrating a state of the air-conditioning apparatus 100 according to Embodiment 1 of the present invention in a heating main operation.

[Fig. 7] Fig. 7 is a flowchart illustrating an operation of the air-conditioning apparatus 100 according to Embodiment 1 of the present invention.

[Fig. 8] Fig. 8 is a flowchart illustrating the operation of the air-conditioning apparatus 100 according to Embodiment 1 of the present invention.

[Fig. 9] Fig. 9 is a circuit diagram illustrating an existing air-conditioning 15 apparatus 200.

[Fig. 10] Fig. 10 is a flowchart illustrating an operation of the air-conditioning apparatus 100 according to Modified Example 1 of Embodiment 1 of the present invention.

[Fig. 11] Fig. 11 is a flowchart illustrating an operation of the air-conditioning 20 apparatus 100 according to Modified Example 2 of Embodiment 1 of the present invention.

[Fig. 12] Fig. 12 is a flowchart illustrating an operation of the air-conditioning apparatus 100 according to Modified Example 3 of Embodiment 1 of the present invention.

Description of Embodiments [0015]

Embodiment 1

Embodiment 1 of an air-conditioning apparatus according to the present invention will be described below with reference to the drawings. Fig. 1 is a circuit diagram illustrating an air-conditioning apparatus 100 according to Embodiment 1 of the present invention. The air-conditioning apparatus 100 will be described based on this Fig. 1. As illustrated in Fig. 1, the air-conditioning apparatus 100 includes a heat source unit A, a plurality of indoor units B, C, and D, a relay unit E, and a control unit 70. In Embodiment 1, a description will be given of an example in which the three indoor units B, C, and D are connected to the single heat source unit A. However, the number of heat source units A may be two or more. Further, the number of indoor units may be three or more.

[0016]

As illustrated in Fig. 1, the air-conditioning apparatus 100 is configured to have the heat source unit A, the indoor units B, C, and D, and the relay unit E connected together. The heat source unit A has a function of supplying heating energy or cooling energy to the three indoor units B, C, and D. The three indoor units B, C, and D are connected in parallel and have the same configuration. The indoor units B, C, and D have a function of heating or cooling an air-conditioned space, such as an indoor space, with the heating energy or cooling energy supplied from the heat source unit A. The relay unit E is interposed between the heat source unit A and the indoor units B, C, and D, and has a function of switching a flow of refrigerant supplied from the heat source unit A in response to requests from the indoor units B, C, and D. The air-conditioning apparatus 100 further includes a state detecting unit 80 that detects the state of the refrigerant. The state detecting unit 80 includes gas pipe temperature detecting sensors 53, liquid pipe temperature detecting sensors 54, a liquid outflow pressure detecting sensor 25, a downstream-side liquid outflow pressure detecting sensor 26, a confluence pressure detecting sensor 56, and a discharge pressure detecting sensor 18.

[0017] (Heat Source Unit A)

The heat source unit A includes a compressor 1 having a variable capacity, a flow switching valve 2 that switches a refrigerant flow direction in the heat source unit A, a heat source-side heat exchange unit 3 that functions as an evaporator or a condenser, an accumulator 4 connected to a suction side of the compressor 1 via the flow switching valve 2, and a heat source-side flow control unit 40 that limits the flow direction of the refrigerant. The heat source unit A has a function of supplying the heating energy or the cooling energy to the indoor units B, C, and D. The flow switching valve 2 is a four-way valve in the illustrated example, but may be formed as a combination of two-way valves or three-way valves, for example.

[0018]

The heat source-side heat exchange unit 3 includes a first heat source-side heat exchanger 41, a second heat source-side heat exchanger 42, a heat source-side bypass passage 43, a first opening and closing solenoid valve 44, a second opening and closing solenoid valve 45, a third opening and closing solenoid valve 46, a fourth opening and closing solenoid valve 47, a fifth opening and closing solenoid valve 48, and a heat source-side fan 20.

[0019]

The first heat source-side heat exchanger 41 and the second heat source-side heat exchanger 42 have the same heat transfer area, and are connected in parallel. The heat source-side bypass passage 43 is connected in parallel to the first heat source-side heat exchanger 41 and the second heat source-side heat exchanger 42. The refrigerant flowing through the heat source-side bypass passage 43 does not pass through the first heat source-side heat exchanger 41 and the second heat source-side heat exchanger 42, and thus does not perform heat exchange.

[0020]

The first opening and closing solenoid valve 44 is provided on one end side of the first heat source-side heat exchanger 41. The second opening and closing solenoid valve 45 is provided on the other end side of the first heat source-side heat exchanger 41. The third opening and closing solenoid valve 46 is provided on one end side of the second heat source-side heat exchanger 42. The fourth opening and closing solenoid valve 47 is provided on the other end side of the second heat source-side heat exchanger 42. The fifth opening and closing solenoid valve 48 is provided on the heat source-side bypass passage 43.

[0021]

The heat source-side flow control unit 40 includes a third check valve 32, a fourth check valve 33, a fifth check valve 34, and a sixth check valve 35. The third check valve 32 is provided on a pipe connecting the heat source-side heat exchange unit 3 and the second connecting pipe 7 to allow the refrigerant to flow from the heat source-side heat exchange unit 3 toward the second connecting pipe 7. The fourth check valve 33 is provided on a pipe connecting the flow switching valve 2 of the heat source unit A and the first connecting pipe 6 to allow the refrigerant to pass flow the first connecting pipe 6 toward the flow switching valve 2. The fifth check valve 34 is provided on a pipe connecting the flow switching valve 2 of the heat source unit A and the second connecting pipe 7 to allow the refrigerant to flow from the flow switching valve 2 toward the second connecting pipe 7. The sixth check valve 35 is provided on a pipe connecting the heat source-side heat exchange unit 3 and the first connecting pipe 6 to allow the refrigerant to flow from the first connecting pipe 6 toward the heat source-side heat exchange unit 3.

[0022]

Further, the heat source unit A is provided with the discharge pressure detecting sensor 18. The discharge pressure detecting sensor 18 is provided on a pipe connecting the flow switching valve 2 and a discharge side of the compressor 1 to detect a discharge pressure of the compressor 1. The heat source-side fan 20 controls a heat exchange capacity by changing an air supply amount of air to be supplied to the heat source-side heat exchange unit 3.

[0023] (Indoor Units B, C, and D)

Each of the indoor units B, C, and D includes an indoor-side heat exchanger 5 functioning as a condenser or an evaporator and a first flow rate control device 9, and has a function of heating or cooling the air-conditioned space, such as the indoor space, with the heating energy or cooling energy supplied from the heat source unit A. During cooling, the first flow rate control device 9 is controlled based on a superheat amount on an outlet side of the indoor-side heat exchanger 5. Further, during heating, the first flow rate control device 9 is controlled based on a subcool amount on the outlet side of the indoor-side heat exchanger 5.

[0024]

The indoor units B, C, and D are provided with the gas pipe temperature detecting sensors 53 and the liquid pipe temperature detecting sensors 54. The gas pipe temperature detecting sensors 53 are provided between the indoor-side heat exchangers 5 and the relay unit E to detect the respective temperatures of the refrigerant flows flowing through the gas branch pipes 6b, 6c, and 6d connecting the indoor-side heat exchangers 5 and the relay unit E. The liquid pipe temperature detecting sensors 54 are provided between the indoor-side heat exchangers 5 and the first flow rate control devices 9 to detect the respective temperatures of the refrigerant flows flowing through the liquid branch pipes 7b, 7c, and 7d connecting the indoor-side heat exchangers 5 and the first flow rate control devices 9.

[0025] (Relay Unit E)

The relay unit E includes a first branching unit 10, a second flow rate control device 13, a second branching unit 11, a gas-liquid separating device 12, a heat exchange unit 8, and a third flow rate control device 15. The relay unit E is interposed between the heat source unit A and the indoor units B, C, and D, and has a function of switching the flow of refrigerant supplied from the heat source unit A in response to requests from the indoor units B, C, and D and distributing the refrigerant supplied from the heat source unit A to the plurality of indoor units B, C, and D.

[0026]

Herein, the flow switching valve 2 of the heat source unit A and the relay unit E are connected by the first connecting pipe 6. The indoor-side heat exchangers 5 of the indoor units B, C, and D and the relay unit E are connected by the gas branch pipes 6b, 6c, and 6d on the side of the indoor units B, C, and D corresponding to the first connecting pipe 6. The heat source-side heat exchange unit 3 of the heat source unit A and the relay unit E are connected by the second connecting pipe 7 smaller in diameter than the first connecting pipe 6. The indoor-side heat exchangers 5 of the indoor units B, C, and D and the relay unit E are connected via the first connecting pipe 6, and are connected by the liquid branch pipes 7b, 7c, and 7d on the side of the indoor units B, C, and D corresponding to the second connecting pipe 7.

[0027]

The first branching unit 10 has one side connected to the gas branch pipes 6b, 6c, and 6d and the other side connected to the first connecting pipe 6 and the second connecting pipe 7. In the first branching unit 10, the flow direction of the refrigerant during the cooling operation is different from the flow direction of the refrigerant during the heating operation. The first branching unit 10 includes first cooling solenoid valves 31a, second cooling solenoid valves 31b, and heating solenoid valves 30.

Each of the first cooling solenoid valves 31a and the corresponding second cooling solenoid valve 31 b are connected in parallel. The first cooling solenoid valve 31 a and the second cooling solenoid valve 31b have one side connected to the gas branch pipe 6b, 6c, or 6d and the other side connected to the first connecting pipe 6, and are open during the cooling operation and closed during the heating operation. [0028]

Further, each of the heating solenoid valves 30 has one side connected to the gas branch pipe 6b, 6c, or 6d and the other side connected to the second connecting pipe 7, and is open during the heating operation and closed during the cooling operation. Hereinafter, the first cooling solenoid valve 31a and the second cooling solenoid valve 31 b connected to each of the indoor units B, C, and D may be collectively referred to as the cooling solenoid valves 31. The number of the cooling solenoid valves 31 is not limited to two, and three or more cooling solenoid valves 31 may be provided. Further, the first cooling solenoid valve 31a and the second cooling solenoid valve 31 b may have equal or different Cv values. Further, the cooling solenoid valves 31 connected to the indoor units B, C, and D may have equal or different Cv values.

[0029]

The second branching unit 11 has one side connected to the liquid branch pipes 7b, 7c, and 7d and the other side connected to the first connecting pipe 6 and the second connecting pipe 7. In the second branching unit 11, the flow direction of the refrigerant during the cooling operation is different from the flow direction of the refrigerant during the heating operation. The second branching unit 11 includes first check valves 50b, 50c, and 50d and second check valves 52b, 52c, and 52d.

[0030]

The number of the first check valves 50b, 50c, and 50d provided corresponds to the number of the indoor units B, C, and D. The first check valves 50b, 50c, and 50d are provided on the liquid branch pipes 7b, 7c, and 7d, respectively, to allow the refrigerant to flow from the second connecting pipe 7 toward the liquid branch pipes 7b, 7c, and 7d.

[0031]

The number of the second check valves 52b, 52c, and 52d provided corresponds to the number of the indoor units B, C, and D. On the liquid branch pipes 7b, 7c, and 7d, the second check valves 52b, 52c, and 52d are connected in parallel to the first check valves 50b, 50c, and 50d, respectively, to allow the refrigerant to flow from the liquid branch pipes 7b, 7c, and 7d toward the second connecting pipe 7.

[0032]

The gas-liquid separating device 12 separates gas-state refrigerant and liquidstate refrigerant from each other, and has an inflow side connected to the second connecting pipe 7, a gas outflow side connected to the first branching unit 10, and a liquid outflow side connected to the second branching unit 11.

[0033]

The heat exchange unit 8 includes a first heat exchange unit 19 and a second heat exchange unit 16. The second flow rate control device 13 is formed as an openable and closable electric expansion valve, for example. Herein, the gas-liquid separating device 12 and the second branching unit 11 are connected via the first heat exchange unit 19, the second flow rate control device 13, and the second heat exchange unit 16. Further, the second branching unit 11 and the first connecting pipe 6 are connected by the first bypass pipe 14. The third flow rate control device 15 is provided on the first bypass pipe 14, and is formed as an openable and closable electric expansion valve, for example. Herein, the second branching unit 11 and the first connecting pipe 6 are connected via the third flow rate control device 15, the second heat exchange unit 16, and the first heat exchange unit 19.

[0034]

That is, the first heat exchange unit 19 exchanges heat between an upstream side of the second flow rate control device 13 on the second connecting pipe 7 and a downstream side of the second heat exchange unit 16 on the first bypass pipe 14. Further, the second heat exchange unit 16 exchanges heat between a downstream side of the second flow rate control device 13 on the second connecting pipe 7 and a downstream side of the third flow rate control device 15 on the first bypass pipe 14. [0035]

Downstream sides of the first check valves 50b, 50c, and 50d on the liquid branch pipes 7b, 7c, and 7d, the downstream side of the second flow rate control device 13 on the second connecting pipe 7, and an upstream side of the second heat exchange unit 16 are connected by a second bypass pipe 51. Further, a pipe of the second bypass pipe 51 connected to the liquid branch pipes 7b, 7c, and 7d and a pipe of the second bypass pipe 51 connected to the second connecting pipe 7 merge together at an intermediate position therebetween.

[0036]

Further, the second check valves 52b, 52c, and 52d are provided upstream of a merging part of the pipe of the second bypass pipe 51 connected to the liquid branch pipes 7b, 7c, and 7d and the pipe of the second bypass pipe 51 connected to the second connecting pipe 7. A flow passage from the second connecting pipe 7 to the first flow rate control devices 9 via the liquid branch pipes 7b, 7c, and 7d provided with the first check valves 50b, 50c, and 50d form a first refrigerant flow passage. A flow passage from the first flow rate control devices 9 to the second connecting pipe 7 via the liquid branch pipes 7b, 7c, and 7d and the second bypass pipe 51 provided with the second check valves 52b, 52c, and 52d form a second refrigerant flow passage.

[0037]

Further, the relay unit E is provided with the liquid outflow pressure detecting sensor 25, the downstream-side liquid outflow pressure detecting sensor 26, and the confluence pressure detecting sensor 56. The liquid outflow pressure detecting sensor 25 is provided between the first heat exchange unit 19 and the second flow rate control device 13 on the second connecting pipe 7 to detect the pressure of the refrigerant on the liquid outflow side of the gas-liquid separating device 12. The downstream-side liquid outflow pressure detecting sensor 26 is provided between the second flow rate control device 13 and the second heat exchange unit 16 on the second connecting pipe 7 to detect the pressure of the refrigerant between the second flow rate control device 13 and the second heat exchange unit 16. That is, the downstream-side liquid outflow pressure detecting sensor 26 detects the pressure of the refrigerant flowing into the merging part of the plurality of liquid branch pipes 7b, 7c, and 7d. The confluence pressure detecting sensor 56 is provided to a connecting part of the first connecting pipe 6 and the first bypass pipe 14 to detect the pressure of the refrigerant flowing through a connecting part of the liquid branch pipes 7b, 7c, and 7d and the first connecting pipe 6.

[0038] (Refrigerant)

In the air-conditioning apparatus 100, the interior of pipes is filled with the refrigerant. For example, natural refrigerant, such as carbon dioxide (CO2), hydrocarbon, or helium, chlorofluorocarbon substitute refrigerant not containing chlorine, such as HFC410A, HFC407C, orHFC404A, or chlorofluorocarbon-based refrigerant used in existing products, such as R22 or R134a, is used as the refrigerant. HFC407C is a zeotropic refrigerant mixture in which R32, R125, and R134a of HFC are mixed at a ratio of 23 wt%: 25 wt%: 52 wt%, respectively.

Further, the interior of the pipes in the air-conditioning apparatus 100 may be filled with a heat medium in place of the refrigerant. The heat medium is water or brine, for example.

[0039] (Control Unit 70)

The control unit 70 controls the entire system of the air-conditioning apparatus 100. Specifically, based on detected information received from the gas pipe temperature detecting sensors 53, the liquid pipe temperature detecting sensors 54, the liquid outflow pressure detecting sensor 25, the downstream-side liquid outflow pressure detecting sensor 26, the confluence pressure detecting sensor 56, and the discharge pressure detecting sensor 18 and an instruction from a remote controller (not illustrated), the control unit 70 controls, for example, the driving frequency of the compressor 1, the rotation speeds of the heat source-side fan 20 and fans provided to the indoor-side heat exchangers 5 (not illustrated), the switching of the flow switching valve 2, the opening and closing of the first opening and closing solenoid valve 44, the second opening and closing solenoid valve 45, the third opening and closing solenoid valve 46, the fourth opening and closing solenoid valve 47, the fifth opening and closing solenoid valve 48, the first cooling solenoid valves 31a, the second cooling solenoid valves 31b, and the heating solenoid valves 30, and the opening degrees of the first flow rate control devices 9, the second flow rate control device 13, and the third flow rate control device 15.

[0040]

The control unit 70 may be provided in one or all of the heat source unit A, the indoor units B, C, and D, and the relay unit E. Further, the control unit 70 may be provided separately from the heat source unit A, the indoor units B, C, and D, and the relay unit E. Further, if the air-conditioning apparatus 100 includes a plurality of control units 70, the control units 70 are connected to each other by wire or wirelessly to be able to communicate with each other.

[0041]

Fig. 2 is a block diagram illustrating the control unit 70 of the air-conditioning apparatus 100 according to Embodiment 1 of the present invention. As illustrated in

Fig. 2, the control unit 70 includes a valve control unit 71, a determining unit 72, and a timing control unit 73. The valve control unit 71 controls the opening and closing of the plurality of cooling solenoid valves 31. Further, when one of the indoor units B,

C, and D is switched from the heating operation to the cooling operation, the valve control unit 71 operates to maintain the opening degree of the corresponding first flow rate control device 9 at a constant opening degree. For example, the valve control unit 71 opens one of the corresponding first cooling solenoid valve 31a and the corresponding second cooling solenoid valve 31b.

[0042]

The determining unit 72 determines whether or not the flow sound is generated when the refrigerant flows through one of the cooling solenoid valves 31 based on the state of the refrigerant detected by the state detecting unit 80. Specifically, the determining unit 72 determines that the flow sound of the refrigerant is generated when the difference in pressure between the front side and the rear side of the cooling solenoid valve 31, which is obtained from the pressure of the refrigerant detected by the downstream-side liquid outflow pressure detecting sensor 26 and the pressure of the refrigerant detected by the confluence pressure detecting sensor 56, is equal to or greater than a threshold. In the above-described example, the state of the refrigerant flowing into the cooling solenoid valve 31 is determined based on the detected information from the confluence pressure detecting sensor 56. However, the information to be used is not limited thereto, and information from another detecting unit may be used, as described below.

[0043]

For example, the state of the refrigerant flowing into the cooling solenoid valve 31 may be determined through prediction of a differential pressure value between an inlet and an outlet of the cooling solenoid valve 31 based on the information from the confluence pressure detecting sensor 56 and the corresponding gas pipe temperature detecting sensor 53. Further, the state of the refrigerant flowing into the cooling solenoid valve 31 may be determined from an outlet subcool value of the indoor-side heat exchanger 5 performing the heating operation and having yet to be switched to the cooling operation. Further, the state of the refrigerant flowing into the cooling solenoid valve 31 may be determined through prediction of the state of the refrigerant in the stopped indoor unit from the time elapsed since the stop of the heating. Furthermore, the state of the refrigerant flowing into a fourth flow rate control device 55 may be determined by a combination of the above-described methods.

[0044]

The timing control unit 73 controls the valve control unit 71 to open one of the plurality of cooling solenoid valves 31 when one of the indoor units B, C, and D is switched from the heating operation to the cooling operation. Further, the timing control unit 73 controls the valve control unit 71 to open one of the cooling solenoid valves 31 in a closed state when it is determined by the determining unit 72 that the flow sound of the refrigerant is generated. Further, the timing control unit 73 may control the valve control unit 71 such that, when a threshold open time elapses since the opening of one of the cooling solenoid valves 31 in the closed state, the valve control unit 71 opens another one of the cooling solenoid valves 31 in the closed state. For example, the timing control unit 73 controls the valve control unit 71 to open the second cooling solenoid valves 31b when the threshold open time elapses since the opening of the first cooling solenoid valve 31 a by the valve control unit 71. [0045]

If the indoor units B and C are switched from the heating operation to the cooling operation, the valve control unit 71 may open any of the following cooling solenoid valves 31 of the first cooling solenoid valve 31a and the second cooling solenoid valve 31b connected to the indoor unit B and the first cooling solenoid valve 31 a and the second cooling solenoid valve 31 b connected to the indoor unit C. For example, the timing control unit 73 may control the valve control unit 71 to first open one of the cooling solenoid valves 31 connected to the indoor unit B, which has the newest address, for example. The order of opening the cooling solenoid valves 31 is not limited.

[0046]

Further, if the first cooling solenoid valve 31a connected to the indoor unit B is opened by the valve control unit 71, the timing control unit 73 may control the valve control unit 71 to open the second cooling solenoid valve 31b connected to the indoor unit B, the first cooling solenoid valve 31a connected to the indoor unit C, or the second cooling solenoid valve 31 b connected to the indoor unit C. That is, the timing control unit 73 may control the valve control unit 71 to open the other cooling solenoid valve 31 connected to the indoor unit B connected to the cooling solenoid valve 31 opened by the valve control unit 71, or to open another cooling solenoid valve 31 connected to the indoor unit C.

[0047]

According to Embodiment 1, in the indoor units B, C, and D switched from the heating operation to the cooling operation, the first cooling solenoid valve 31a connected to the indoor unit B having the newer address is opened, and thereafter the second cooling solenoid valve 31 b connected to the indoor unit B is opened. If the Cv value of the first cooling solenoid valve 31 a is greater than the Cv value of the second cooling solenoid valve 31b, the second cooling solenoid valve 31b is opened first. Further, if the second cooling solenoid valves 31 b connected to the indoor units B, C, and D have different Cv values, one of the second cooling solenoid valves 31 b having the minimum Cv value is opened. In Embodiment 1, a description will be given of an example in which the second cooling solenoid valve 31b connected to the indoor unit B is first opened by the valve control unit 71.

[0048]

An operation of the air-conditioning apparatus 100 will now be described. Operation modes of the air-conditioning apparatus 100 include cooling only operation, heating only operation, cooling main operation, and heating main operation. The cooling only operation refers to a mode in which all of the indoor units B, C, and D perform the cooling operation. The heating only operation refers to a mode in which all of the indoor units B, C, and D perform the heating operation. The cooling main operation refers to a mode in which the capacity of the cooling operation exceeds the capacity of the heating operation in the simultaneous cooling and heating operation.

The heating main operation refers to a mode in which the capacity of the heating operation exceeds the capacity of the cooling operation in the simultaneous cooling and heating operation.

[0049] (Cooling Only Operation)

Fig. 3 is a circuit diagram illustrating a state of the air-conditioning apparatus 100 according to Embodiment 1 of the present invention during the cooling only operation. The cooling only operation will first be described. In the air-conditioning apparatus 100, all of the indoor units B, C, and D are performing the cooling operation. As illustrated in Fig. 3, high-temperature, high-pressure gas refrigerant discharged from the compressor 1 passes through the flow switching valve 2, and is condensed and liquified in the heat source-side heat exchange unit 3 through heat exchange with the air supplied by the heat source-side fan 20 having a variable air supply amount. Thereafter, the refrigerant flows through the third check valve 32, the second connecting pipe 7, the gas-liquid separating device 12, and the second flow rate control device 13 in this order, passes through the second branching unit 11 and the liquid branch pipes 7b, 7c, and 7d, and flows into the indoor units B, C, and D.

[0050]

The refrigerant flowing into the indoor units B, C, and D is reduced in pressure to a low pressure by the first flow rate control devices 9 controlled based on the respective superheat amounts at the outlet sides of the indoor-side heat exchangers 5. The refrigerant with the reduced pressure flows into the indoor-side heat exchangers 5, and is evaporated and gasified in the indoor-side heat exchangers 5 through heat exchange with indoor air. During this process, the respective indoor spaces are cooled. The refrigerant brought into the gas state is then suctioned into the compressor 1 via the gas branch pipes 6b, 6c, and 6d, the first cooling solenoid valves 31a and the second cooling solenoid valves 31b of the first branching unit 10, the first connecting pipe 6, the fourth check valve 33, and the flow switching valve 2 and the accumulator 4 of the heat source unit A.

[0051]

In the cooling only operation, all of the heating solenoid valves 30 are closed. Further, all of the first cooling solenoid valves 31 a and the second cooling solenoid valves 31 b are open. Further, the pressure is low in the first connecting pipe 6 and high in the second connecting pipe 7, and thus the refrigerant flows into the third check valve 32 and the fourth check valve 33.

[0052]

Further, in this circulation cycle, a part of the refrigerant having passed through the second flow rate control device 13 flows into the first bypass pipe 14. Then, the refrigerant is reduced in pressure to a low pressure by the third flow rate control device 15, and thereafter is evaporated in the second heat exchange unit 16 through heat exchange with the refrigerant having passed through the second flow rate control device 13, that is, the refrigerant having yet to branch into the first bypass pipe

14. Further, the refrigerant is evaporated in the first heat exchange unit 19 through heat exchange with the refrigerant having yet to flow into the second flow rate control device 13. The evaporated refrigerant flows into the first connecting pipe 6 and the fourth check valve 33, and is suctioned into the compressor 1 via the flow switching valve 2 and the accumulator 4 of the heat source unit A.

[0053]

Meanwhile, the refrigerant sufficiently subcooled in the first heat exchange unit and the second heat exchange unit 16 by cooling through heat exchange with the refrigerant flowing into the first bypass pipe 14 and reduced in pressure to a low pressure by the third flow rate control device 15 passes through the first check valves 50b, 50c, and 50d of the second branching unit 11 and flows into the indoor units B,

C, and D, which are to be cooled. Herein, the control unit 70 adjusts the variable capacity of the compressor 1 and the air supply amount of the heat source-side fan such that evaporating temperatures of the indoor units B, C, and D and a condensing temperature of the heat source-side heat exchange unit 3 equal respective predetermined target temperatures. Accordingly, it is possible to obtain intended cooling capacity in each of the indoor units B, C, and D. The condensing temperature of the heat source-side heat exchange unit 3 is obtained as the saturation temperature for the pressure detected by the discharge pressure detecting sensor 18.

[0054] (Heating Only Operation)

Fig. 4 is a circuit diagram illustrating a state of the air-conditioning apparatus 100 according to Embodiment 1 of the present invention in the heating only operation. The heating only operation will now be described. In the air-conditioning apparatus 100, all of the indoor units B, C, and D are performing the heating operation. As illustrated in Fig. 4, the high-temperature, high-pressure gas refrigerant discharged from the compressor 1 passes through the flow switching valve 2, the fifth check valve 34, the second connecting pipe 7, the gas-liquid separating device 12, the heating solenoid valves 30 of the first branching unit 10, and the gas branch pipes 6b, 6c, and 6d in this order, and flows into the indoor units B, C, and D. The refrigerant flowing into the indoor units B, C, and D is condensed and liquified through heat exchange with the indoor air. During this process, the respective indoor spaces are heated. Then, the refrigerant in this state passes through the first flow rate control devices 9 controlled based on the respective subcool amounts on the outlet sides of the indoor-side heat exchangers 5.

[0055]

The refrigerant flows having passed through the first flow rate control devices 9 flow into the second branching unit 11 from the liquid branch pipes 7b, 7c, and 7d, pass through the second check valves 52b, 52c, and 52d, and thereafter merge together. The refrigerant flows merging together in the second branching unit 11 are further guided into between the second flow rate control device 13 and the second heat exchange unit 16 on the second connecting pipe 7, and pass through the third flow rate control device 15. Further, the refrigerant is reduced in pressure by the first flow rate control devices 9 and the third flow rate control device 15 into a lowpressure, two-phase gas-liquid state.

[0056]

The refrigerant reduced in pressure to a low pressure passes through the sixth check valve 35 of the heat source unit A via the first connecting pipe 6, flows into the heat source-side heat exchange unit 3, and is evaporated through heat exchange with the air supplied by the heat source-side fan 20 having the variable air supply amount. The evaporated and gasified refrigerant is suctioned into the compressor 1 via the flow switching valve 2 and the accumulator 4.

[0057]

In the heating only operation, all of the heating solenoid valves 30 are open. Further, all of the first cooling solenoid valves 31 a and the second cooling solenoid valves 31 b are closed.

[0058]

Further, in this circulation cycle, the pressure is low in the first connecting pipe 6 and high in the second connecting pipe 7, and thus the refrigerant flows into the fifth check valve 34 and the sixth check valve 35. Further, the pressure is higher in the liquid branch pipes 7b, 7c, and 7d than in the second connecting pipe 7, and thus the refrigerant does not pass through the first check valves 50b, 50c, and 50d. Herein, the control unit 70 adjusts the variable capacity of the compressor 1 and the air supply amount of the heat source-side fan 20 such that condensing temperatures of the indoor units B, C, and D and an evaporating temperature of the heat source-side heat exchange unit 3 equal respective predetermined target temperatures. Accordingly, it is possible to obtain intended heating capacity in each of the indoor units B, C, and D.

[0059] (Cooling Main Operation)

Fig. 5 is a circuit diagram illustrating a state of the air-conditioning apparatus 100 according to Embodiment 1 of the present invention in the cooling main operation. The cooling main operation will now be described. In the airconditioning apparatus 100, there are a cooling request from each of the indoor units B and C and a heating request from the indoor unit D. As illustrated in Fig. 5, the high-temperature, high-pressure gas refrigerant discharged from the compressor 1 flows into the heat source-side heat exchange unit 3 via the flow switching valve 2, and is brought into a two-phase, high-temperature, high-pressure state through heat exchange with the air supplied by the heat source-side fan 20 having the variable air supply amount.

[0060]

Herein, the control unit 70 adjusts the variable capacity of the compressor 1 and the air supply amount of the heat source-side fan 20 such that the evaporating temperatures of the indoor units B and C and the condensing temperature of the indoor unit D equal respective predetermined target temperatures. The control unit 70 further adjusts the heat transfer area by opening or closing the first opening and closing solenoid valve 44 and the second opening and closing solenoid valve 45 on opposite ends of the first heat source-side heat exchanger 41 and the third opening and closing solenoid valve 46 and the fourth opening and closing solenoid valve 47 on opposite ends of the second heat source-side heat exchanger 42. The control unit 70 further adjusts the flow rate of the refrigerant flowing through the first heat source-side heat exchanger 41 and the second heat source-side heat exchanger 42 by opening and closing the fifth opening and closing solenoid valve 48 on the heat source-side bypass passage 43. Thereby, a desired heat exchange amount is obtained in the heat source-side heat exchange unit 3, and it is possible to obtain intended heating or cooling capacity in each of the indoor units B, C, and D.

[0061]

The two-phase, high-temperature, high-pressure refrigerant is sent to the gasliquid separating device 12 of the relay unit E via the third check valve 32 and the second connecting pipe 7, and is separated into gas refrigerant and liquid refrigerant. Then, the gas refrigerant separated from the two-phase, high-temperature, highpressure refrigerant by the gas-liquid separating device 12 passes through the corresponding heating solenoid valve 30 of the first branching unit 10 and the gas branch pipe 6d in this order, flows into the indoor unit D, which is to be heated, and is condensed and liquified in the corresponding indoor-side heat exchanger 5 through heat exchange with the indoor air. During this process, the indoor unit D heats the corresponding indoor space. Further, the refrigerant flowing from the indoor-side heat exchanger 5 passes through the corresponding first flow rate control device 9, which is controlled based on the subcool amount on the outlet side of the indoor-side heat exchanger 5 of the indoor unit D, to be reduced in pressure by a small amount, and flows into the second branching unit 11. The refrigerant passes through the second bypass pipe 51 having the second check valve 52d, and flows into the downstream side of the second flow rate control device 13 on the second connecting pipe 7.

[0062]

Meanwhile, the liquid refrigerant separated from the two-phase, hightemperature, high-pressure refrigerant by the gas-liquid separating device 12 passes through the second flow rate control device 13 controlled based on the pressure detected by the liquid outflow pressure detecting sensor 25 and the pressure detected by the downstream-side liquid outflow pressure detecting sensor 26, and merges with the refrigerant having passed through the indoor unit D, which is to be heated. Thereafter, the refrigerant flows into the second heat exchange unit 16, and is cooled in the second heat exchange unit 16.

[0063]

Then, a part of the refrigerant cooled in the second heat exchange unit 16 passes through the first check valves 50b and 50c and the liquid branch pipes 7b and 7c, and flows into the indoor units B and C, which are to be cooled. The refrigerant flowing into the indoor units B and C flows into the corresponding first flow rate control devices 9, which are controlled based on the respective superheat amounts on the outlet sides of the indoor-side heat exchangers 5 of the indoor units B and C, to be reduced in pressure, and thereafter flows into the indoor-side heat exchangers 5 and is evaporated and gasified through heat exchange. During this process, the indoor units B and C cool the respective indoor spaces. Thereafter, the refrigerant flows into the first connecting pipe 6 via the corresponding first cooling solenoid valves 31a and the corresponding second cooling solenoid valves 31b.

[0064]

Meanwhile, the remaining part of the refrigerant cooled in the second heat exchange unit 16 passes through the third flow rate control device 15 controlled such that the pressure difference between the pressure detected by the liquid outflow pressure detecting sensor 25 and the pressure detected by the downstream-side liquid outflow pressure detecting sensor 26 falls within a predetermined range. The refrigerant is thereafter evaporated through heat exchange in the second heat exchange unit 16 and the first heat exchange unit 19, and then flows into the first connecting pipe 6 and merges with the refrigerant having passed through the indoor units B and C. The refrigerant flows having merged together in the first connecting pipe 6 are suctioned into the compressor 1 via the fourth check valve 33, the flow switching valve 2, and the accumulator 4 of the heat source unit A.

[0065]

In the cooling main operation, the heating solenoid valves 30 connected to the indoor units B and C are closed. Further, the heating solenoid valve 30 connected to the indoor unit D is open. Further, the first cooling solenoid valves 31a and the second cooling solenoid valves 31b connected to the indoor units B and C are open. Furthermore, the first cooling solenoid valve 31a and the second cooling solenoid valve 31 b connected to the indoor unit D are closed.

[0066]

Further, the pressure is low in the first connecting pipe 6 and high in the second connecting pipe 7, and thus the refrigerant flows into the third check valve 32 and the fourth check valve 33. Further, the pressure is lower in the liquid branch pipes 7b and 7c than in the second connecting pipe 7, and thus the refrigerant does not pass through the second check valves 52b and 52c. Furthermore, the pressure is higher in the liquid branch pipe 7d than in the second connecting pipe 7, and thus the refrigerant does not pass through the first check valve 50d. The first check valves 50 and the second check valves 52 prevent the refrigerant having passed through the indoor unit D, which has issued the heating request, from flowing into the indoor units B and C, which have issued the cooling request, without passing through the second heat exchange unit 16 and thus without being sufficiently subcooled.

[0067] (Heating Main Operation)

Fig. 6 is a circuit diagram illustrating a state of the air-conditioning apparatus 100 according to Embodiment 1 of the present invention in the heating main operation. The heating main operation will now be described. In the airconditioning apparatus 100, there are a heating request from each of the indoor units B and C and a cooling request from the indoor unit D. As illustrated in Fig. 6, the high-temperature, high-pressure gas refrigerant discharged from the compressor 1 is sent to the relay unit E through the flow switching valve 2, the fifth check valve 34, and the second connecting pipe 7, and passes through the gas-liquid separating device 12. The refrigerant having passed through the gas-liquid separating device 12 passes through the corresponding heating solenoid valves 30 of the first branching unit 10 and the gas branch pipes 6b and 6c in this order, flows into the indoor units B and C, which are to be heated, and is condensed and liquified in the corresponding indoor-side heat exchangers 5 through heat exchange with the indoor air. During this process, the indoor units B and C heat the respective indoor spaces. The condensed and liquified refrigerant passes through the corresponding first flow rate control devices 9, which are controlled based on the respective subcool amounts on the outlet sides of the indoor-side heat exchangers 5 of the indoor units C and D, to be reduced in pressure by a small amount, and flows into the second branching unit 11.

[0068]

The refrigerant flowing into the second branching unit 11 passes through the second bypass pipe 51 having the second check valves 52b and 52c, merges with the refrigerant flowing through the second connecting pipe 7, and is cooled in the second heat exchange unit 16. A part of the refrigerant cooled in the second heat exchange unit 16 passes through the first check valve 50d and the liquid branch pipe 7d, and flows into the indoor unit D, which is to be cooled. The refrigerant flowing into the indoor unit D then flows into the corresponding first flow rate control device 9, which is controlled based on the superheat amount on the outlet side of the corresponding indoor-side heat exchanger 5, to be reduced in pressure, and thereafter flows into the indoor-side heat exchanger 5 and is evaporated and gasified through heat exchange. During this process, the indoor unit D cools the corresponding indoor space. Thereafter, the refrigerant flows into the first connecting pipe 6 via the corresponding first cooling solenoid valve 31a and the corresponding second cooling solenoid valve 31b.

[0069]

Meanwhile, the remaining part of the refrigerant cooled in the second heat exchange unit 16 passes through the third flow rate control device 15 controlled such that the pressure difference between the pressure detected by the liquid outflow pressure detecting sensor 25 and the pressure detected by the downstream-side liquid outflow pressure detecting sensor 26 falls within a predetermined range. The refrigerant having passed through the third flow rate control device 15 is evaporated in the second heat exchange unit 16 through heat exchange with the refrigerant flowing from the indoor units B and C. Thereafter, the refrigerant merges with the refrigerant having passed through the indoor unit D, which is to be cooled, and flows into the sixth check valve 35 and the heat source-side heat exchange unit 3 of the heat source unit A via the first connecting pipe 6. The refrigerant flowing into the heat source-side heat exchange unit 3 is evaporated and gasified through heat exchange with the air supplied by the heat source-side fan 20 having the variable air supply amount.

[0070]

Herein, the control unit 70 adjusts the variable capacity of the compressor 1 and the air supply amount of the heat source-side fan 20 such that the evaporating temperature of the indoor unit D having issued the cooling request and the condensing temperatures of the indoor units B and C having issued the heating request equal respective predetermined target temperatures. The control unit 70 further adjusts the heat transfer area by opening or closing the first opening and closing solenoid valve 44 and the second opening and closing solenoid valve 45 on the opposite ends of the first heat source-side heat exchanger 41 and the third opening and closing solenoid valve 46 and the fourth opening and closing solenoid valve 47 on the opposite ends of the second heat source-side heat exchanger 42.

The control unit 70 further adjusts the flow rate of the refrigerant flowing through the first heat source-side heat exchanger 41 and the second heat source-side heat exchanger 42 by opening and closing the fifth opening and closing solenoid valve 48 on the heat source-side bypass passage 43. Thereby, a desired heat exchange amount is obtained in the heat source-side heat exchange unit 3, and it is possible to obtain intended heating or cooling capacity in each of the indoor units B, C, and D. The refrigerant is then suctioned into the compressor 1 via the flow switching valve 2 and the accumulator 4 of the heat source unit A.

[0071]

In the heating main operation, the heating solenoid valves 30 connected to the indoor units B and C are open. Further, the heating solenoid valve 30 connected to the indoor unit D is closed. Further, the first cooling solenoid valves 31a and the second cooling solenoid valves 31b connected to the indoor units B and C are closed. Furthermore, the first cooling solenoid valve 31a and the second cooling solenoid valve 31 b connected to the indoor unit D are open.

[0072]

Further, the pressure is low in the first connecting pipe 6 and high in the second connecting pipe 7, and thus the refrigerant flows into the fifth check valve 34 and the sixth check valve 35. The second flow rate control device 13 is closed. Further, the pressure is higher in the liquid branch pipes 7b and 7c than in the second connecting pipe 7, and thus the refrigerant does not pass through the first check valves 50b and 50c. Further, the pressure is lower in the liquid branch pipe 7d than in the second connecting pipe 7, and thus the refrigerant does not pass through the second check valve 52d. The first check valves 50 and the second check valves 52 prevent the refrigerant having passed through the indoor units B and C, which have issued the heating request, from flowing into the indoor unit D, which has issued the cooling request, without passing through the second heat exchange unit 16 and thus without being sufficiently subcooled.

[0073]

Fig. 7 is a flowchart illustrating an operation of the air-conditioning apparatus 100 according to Embodiment 1 of the present invention. An operation of the control unit 70 will now be described. When one of the indoor units B, C, and D is switched from the heating operation to the cooling operation, the high-temperature, highpressure gas refrigerant and the high-temperature, high-pressure liquid refrigerant flowing during the heating pass through the corresponding first cooling solenoid valve 31a and the corresponding second cooling solenoid valve 31b, and flow into the first connecting pipe 6, in which the pressure is low during the cooling. Consequently, a large difference in pressure arises between the front side and the rear side of the cooling solenoid valves 31, causing a possibility that the flow sound of the refrigerant may be generated from around the cooling solenoid valves 31. In Embodiment 1, the control unit 70 suppresses the flow sound of the refrigerant generated from the relay unit E including the cooling solenoid valves 31. It is assumed in Embodiment 1 that the indoor units B, C, and D have the newest address, the second newest address, and the third newest address, respectively.

[0074]

As illustrated in Fig. 7, when the indoor units B and C are switched from the heating operation to the cooling operation, for example, the timing control unit 73 controls the valve control unit 71 to maintain the opening degree of each of the corresponding first flow rate control devices 9 at a constant opening degree (step ST1). Thereby, the pressure in the first connecting pipe 6 is released to the second connecting pipe 7. Therefore, the pressure is reduced on one sides of the first cooling solenoid valves 31a and the second cooling solenoid valves 31b close to the first connecting pipe 6, and the pressure in the first connecting pipe 6 and the pressure in the second connecting pipe 7 approach each other to become equal.

The timing control unit 73 further controls the valve control unit 71 to open the first cooling solenoid valve 31a connected to the indoor unit B (step ST2).

[0075]

Fig. 8 is a flowchart illustrating the operation of the air-conditioning apparatus 100 according to Embodiment 1 of the present invention. Then, based on the state of the refrigerant detected by the state detecting unit 80, the determining unit 72 determines whether or not the flow sound is generated when the refrigerant flows through the second cooling solenoid valve 31b opened by the valve control unit 71 (step ST3). Specifically, as illustrated in Fig. 8, the determining unit 72 determines whether or not a pressure P of the refrigerant detected by the confluence pressure detecting sensor 56 is equal to or greater than a pressure threshold Po (step ST31). As illustrated in Fig. 7, if the pressure P of the refrigerant is less than the pressure threshold Po (No at step ST3), the difference between the pressure in the first connecting pipe 6 and the pressure in the second connecting pipe 7 is small. Therefore, it is determined that the flow sound of the refrigerant will not be generated, and the procedure returns to a normal operation. Meanwhile, if the pressure P of the refrigerant is equal to or greater than the pressure threshold Po (Yes at step ST3), the difference between the pressure in the first connecting pipe 6 and the pressure in the second connecting pipe 7 is large. Therefore, it is determined that the flow sound of the refrigerant may be generated, and the procedure proceeds to step ST4. The determining unit 72 may determine that the flow sound of the refrigerant is generated when the difference in pressure between the front side and the rear side of the cooling solenoid valve 31, which is obtained from the pressure of the refrigerant detected by the downstream-side liquid outflow pressure detecting sensor 26 and the pressure of the refrigerant detected by the confluence pressure detecting sensor 56, is equal to or greater than a threshold.

[0076]

At step ST4, the timing control unit 73 checks whether the threshold open time has elapsed since the opening of the second cooling solenoid valve 31 b. If the threshold open time has not elapsed (No at step ST4), step ST4 is repeated. If the threshold open time has elapsed (Yes at step ST4), the timing control unit 73 selects the second cooling solenoid valve 31b connected to the indoor unit B having the newest address (step ST5). Thereafter, the selected second cooling solenoid valve b is opened (step ST6). Thereby, the plurality of cooling solenoid valves 31 are not opened at the same time. Accordingly, it is possible to prevent the refrigerant from gushing into the first connecting pipe 6. Thereafter, it is determined whether or not there is a closed cooling solenoid valve 31 in any of the indoor units having issued the cooling request (step ST7). If there is a closed cooling solenoid valve 31 (Yes at step ST7), the procedure returns to step ST3. Meanwhile, if there is no closed cooling solenoid valve 31 (No at step ST7). The control is completed.

[0077]

Herein, as well as the indoor unit B, the indoor unit C has issued the cooling request in Embodiment 1. At step ST7, therefore, there is a closed cooling solenoid valve 31, and the procedure returns to step ST3. Then, if the pressure P of the refrigerant is still equal to or greater than the pressure threshold Po, the procedure proceeds to step ST4. Herein, the second cooling solenoid valve 31 b connected to the indoor unit C, for example, is selected. Then, it is checked whether the threshold open time has elapsed since the opening of the second cooling solenoid valve 31b connected to the indoor unit B forming another branch (step ST5). If the threshold open time has elapsed, the selected second cooling solenoid valve 31b connected to the indoor unit C is opened (step ST6).

[0078]

Since the second cooling solenoid valve 31b connected to the indoor unit D is closed, the procedure returns again to step ST3 from step ST7. Then, if the pressure P of the refrigerant is still equal to or greater than the pressure threshold Po, the procedure proceeds to step ST4. Herein, the second cooling solenoid valve 31 b connected to the indoor unit D is selected. Then, it is checked whether the threshold open time has elapsed since the opening of the second cooling solenoid valve 31b connected to the indoor unit D and closed immediately before (step ST5). If the threshold open time has elapsed, the selected second cooling solenoid valve 31b connected to the indoor unit D is opened, (step ST6). Then, there is no closed cooling solenoid valve 31 at step ST7, and thus the control is completed.

[0079]

According to Embodiment 1, when one of the indoor units B, C, and D is switched from the heating operation to the cooling operation, the timing control unit 73 controls the valve control unit 71 to open one of the plurality of cooling solenoid valves 31. Further, if it is determined that the flow sound of the refrigerant is generated, the timing control unit 73 controls the valve control unit 71 to open one of the cooling solenoid valves 31 in the closed state. The plurality of cooling solenoid valves 31 are thus opened in the phased manner. It is therefore possible to reduce the flow sound of the refrigerant without using an orifice. Accordingly, it is possible to improve the function of preventing the refrigerant leakage and reduce the flow sound of the refrigerant.

[0080]

Fig. 9 is a circuit diagram illustrating an existing air-conditioning apparatus 200. As illustrated in Fig. 9, in the existing air-conditioning apparatus 200, a first branching unit 110 includes first cooling solenoid valves a, second cooling solenoid valves c, orifices d, and heating solenoid valves b. When the heating operation is switched to the cooling operation in the existing air-conditioning apparatus 200, the refrigerant flows through the orifices d, the first cooling solenoid valves a, and the second cooling solenoid valves c in this order in a phased manner, to thereby reduce the flow sound of the refrigerant. However, each of the orifices d forms a bypass between a highpressure-side pressure and a low-pressure-side pressure to equalize the pressure in a high-pressure-side pipe and the pressure in a low-pressure-side pipe and reduce the flow sound of the refrigerant. The orifices d therefore bypass the refrigerant supplied to the indoor units during the heating operation, and thus the function of preventing the refrigerant leakage deteriorates.

[0081]

By contrast, in Embodiment 1, the valve control unit 71 opens one of the plurality of cooling solenoid valves 31, and the timing control unit 73 controls the valve control unit 71 to open one of the cooling solenoid valves 31 in the closed state if it is determined that the flow sound of the refrigerant is generated. It is therefore possible to reduce the flow sound of the refrigerant without using an orifice.

Accordingly, it is possible to improve the function of preventing the refrigerant leakage and reduce the flow sound of the refrigerant.

[0082]

Further, when one of the indoor units B, C, and D is switched from the heating operation to the cooling operation, the valve control unit 71 operates to maintain the opening degree of the corresponding first flow rate control device 9 at a constant opening degree. Thereby, the pressure in the first connecting pipe 6 and the pressure in the second connecting pipe 7 are equalized. Accordingly, the gush of the refrigerant is suppressed.

[0083]

Further, when the threshold open time elapses since the opening of the one of the cooling solenoid valves 31 in the closed state, the timing control unit 73 controls the valve control unit 71 to open another one of the cooling solenoid valves 31 in the closed state. Therefore, the gush of the refrigerant is suppressed. Accordingly, it is possible to further reduce the flow sound of the refrigerant.

[0084]

Furthermore, the state detecting unit 80 includes the confluence pressure detecting sensor 56 that detects the pressure of the refrigerant flowing through the connecting part of the liquid branch pipes 7b, 7c, and 7d and the first connecting pipe 6 and the downstream-side liquid outflow pressure detecting sensor 26 that detects the pressure of the refrigerant flowing through the merging part of the plurality of liquid branch pipes 7b, 7c, and 7d. The determining unit 72 determines that the flow sound of the refrigerant is generated when the difference between the pressure of the refrigerant detected by the confluence pressure detecting sensor 56 and the pressure of the refrigerant detected by the downstream-side liquid outflow pressure detecting sensor 26 is equal to or greater than the threshold. It is thereby possible to normalize the pressure in the first connecting pipe 6. Accordingly, it is possible to further reduce the flow sound of the refrigerant.

[0085] (Modified Example 1)

Fig. 10 is a flowchart illustrating an operation of the air-conditioning apparatus 100 according to Modified Example 1 of Embodiment 1 of the present invention. Modified Example 1 of Embodiment 1 will now be described. Modified Example 1 is different from Embodiment 1 in the operation at step ST3 in Fig. 7, and the determining unit 72 determines whether or not the flow sound of the refrigerant is generated based on the difference between the pressure at one side of the cooling solenoid valve 31 and the pressure at the other side of the cooling solenoid valve 31. [0086]

As illustrated in Fig. 10, the determining unit 72 determines whether or not a difference APa between the pressure at one side of the first cooling solenoid valve 31 a or the second cooling solenoid valve 31 b and the pressure at the other side of the first cooling solenoid valve 31a or the second cooling solenoid valve 31b is equal to or greater than a pressure difference threshold ΔΡο (step ST41). Specifically, when the difference APa between the pressure of the refrigerant detected by the confluence pressure detecting sensor 56 and the pressure of the refrigerant corresponding to the temperature of the refrigerant detected by the corresponding gas pipe temperature detecting sensor 53 is equal to or greater than the pressure difference threshold ΔΡο, the determining unit 72 determines that the flow sound of the refrigerant is generated. That is, the pressure at the one side of the first cooling solenoid valve 31a or the second cooling solenoid valve 31b is detected by the confluence pressure detecting sensor 56. Further, the pressure at the other side of the first cooling solenoid valve 31a or the second cooling solenoid valve 31b is calculated based on the saturation temperature detected by the gas pipe temperature detecting sensor 53. As illustrated in Fig. 7, if the difference ΔΡ in pressure is less than the pressure difference threshold ΔΡο (No at step ST3), the procedure returns to the normal operation. Meanwhile, if the difference ΔΡ in pressure is equal to or greater than the pressure difference threshold ΔΡο (Yes at step ST3), the procedure proceeds to step ST4.

[0087]

As described above, in Modified Example 1, the state detecting unit 80 includes the confluence pressure detecting sensor 56 that detects the pressure of the refrigerant flowing through the connecting part of the liquid branch pipes 7b, 7c, and 7d and the first connecting pipe 6 and the gas pipe temperature detecting sensors 53 that detect the respective temperatures of the refrigerant flows flowing through the gas branch pipes 6b, 6c, and 6d. The determining unit 72 determines that the flow sound of the refrigerant is generated when the difference between the pressure of the refrigerant detected by the confluence pressure detecting sensor 56 and the pressure of the refrigerant corresponding to the temperature of the refrigerant detected by one of the gas pipe temperature detecting sensors 53 is equal to or greater than the pressure difference threshold. Modified Example 1 also has effects similar to those of Embodiment 1.

[0088] (Modified Example 2)

Fig. 11 is a flowchart illustrating an operation of the air-conditioning apparatus 100 according to Modified Example 2 of Embodiment 1 of the present invention. Modified Example 2 of Embodiment 1 will now be described. Modified Example 2 is different from Embodiment 1 in the operation at step ST3 in Fig. 7, and the determining unit 72 determines whether or not the flow sound of the refrigerant is generated based on the subcool value on the outlet side of the indoor-side heat exchanger 5 included in the indoor unit performing the heating operation.

[0089]

As illustrated in Fig. 11, the determining unit 72 determines whether or not a subcool value SCa on the outlet side of the indoor-side heat exchanger 5 included in the indoor unit performing the heating operation is equal to or greater than a subcool threshold SCo (step ST51). The subcool value SCa is calculated based on the saturation temperature of the indoor unit during the heating operation and the temperature of the refrigerant detected by the corresponding liquid pipe temperature detecting sensor 54. The saturation temperature of the indoor unit during the heating operation is calculated based on the pressure detected by the liquid outflow pressure detecting sensor 25. As illustrated in Fig. 7, if the subcool value SCa is less than the subcool threshold SCo (No at step ST3), there is a small amount of liquid refrigerant. It is therefore determined that the flow sound of the refrigerant will not be generated, and the procedure returns to the normal operation. Meanwhile, if the subcool value SCa is equal to or greater than the subcool threshold SCo (Yes at step ST3), there is a large amount of liquid refrigerant. It is therefore determined that the flow sound of the refrigerant is generated, and the procedure proceeds to step ST4.

[0090]

As described above, in Modified Example 2, the relay unit E further includes the gas-liquid separating device 12, which has the inflow side connected to the second connecting pipe 7, the gas outflow side connected to the heating solenoid valves 30, and the liquid outflow side connected to the liquid branch pipes 7b, 7c, and 7d, and which separates the gas refrigerant and the liquid refrigerant from each other. The state detecting unit 80 includes the liquid outflow pressure detecting sensor 25 that detects the pressure of the refrigerant on the liquid outflow side of the gas-liquid separating device 12 and the liquid pipe temperature detecting sensors 54 that detect the respective temperatures of the refrigerant flows flowing through the liquid branch pipes 7b, 7c, and 7d. The determining unit 72 determines that the flow sound of the refrigerant is generated when the subcool value on the outlet side of the indoor-side heat exchanger 5 calculated based on the temperature of the refrigerant corresponding to the pressure of the refrigerant detected by the liquid outflow pressure detecting sensor 25 and the temperature of the refrigerant detected by the corresponding liquid pipe temperature detecting sensor 54 is equal to or greater than the subcool threshold. Modified Example 2 also has effects similar to those of Embodiment 1.

[0091] (Modified Example 3)

Fig. 12 is a flowchart illustrating an operation of the air-conditioning apparatus 100 according to Modified Example 3 of Embodiment 1 of the present invention.

Modified Example 3 of Embodiment 1 will now be described. Modified Example 3 is different from Embodiment 1 in the operation at step ST3 in Fig. 7, and the determining unit 72 determines whether or not the flow sound of the refrigerant is generated based on whether or not a threshold stop time has elapsed since the stop of the indoor-side heat exchanger 5 included in the indoor unit performing the heating operation.

[0092]

As illustrated in Fig. 12, the determining unit 72 determines whether or not an elapsed time Ta elapsed since the stop of the indoor-side heat exchanger 5 included in the indoor unit performing the heating operation is equal to or shorter than a threshold elapsed time To (step ST61). As illustrated in Fig. 7, if the elapsed time Ta is equal to or longer than the threshold elapsed time To (No at step ST3), the difference between the pressure in the first connecting pipe 6 and the pressure in the second connecting pipe 7 has been reduced. It is therefore determined that the flow sound of the refrigerant will not be generated, and the procedure returns to the normal operation. Meanwhile, if the elapsed time Ta is shorter than the threshold elapsed time To (Yes at step ST3), the difference between the pressure in the first connecting pipe 6 and the pressure in the second connecting pipe 7 is still large. It is therefore determined that the flow sound of the refrigerant is generated, and the procedure proceeds to step ST4.

[0093]

As described above, in Modified Example 3, the determining unit 72 determines that the flow sound of the refrigerant is generated until the threshold stop time elapses since the stop of the indoor-side heat exchanger 5 included in the indoor unit B, C, or D performing the heating operation. Modified Example 3 also has effects similar to those of Embodiment 1.

Reference Signs List [0094]

1: compressor: 2: flow switching valve: 3: heat source-side heat exchange unit: 4: accumulator: 5: indoor-side heat exchanger: 6: first connecting pipe: 6b, 6c, 6d: gas branch pipe: 7: second connecting pipe: 7b, 7c, 7d: liquid branch pipe: 8: heat exchange unit: 9: first flow rate control device: 10: first branching unit: 11: second branching unit: 12: gas-liquid separating device: 13: second flow rate control device: 14: first bypass pipe:

15: third flow rate control device: 16: second heat exchange unit: 18: discharge pressure detecting sensor: 19: first heat exchange unit: 20: heat source-side fan: 25: liquid outflow pressure detecting sensor: 26: downstreamside liquid outflow pressure detecting sensor: 30: heating solenoid valve: 31: cooling solenoid valve: 31a: first cooling solenoid valve: 31b: second cooling solenoid valve: 32: third check valve: 33: fourth check valve: 34: fifth check valve: 35: sixth check valve: 40: heat source-side flow control unit: 41: first heat source-side heat exchanger: 42: second heat source-side heat exchanger:

43: heat source-side bypass passage: 44: first opening and closing solenoid valve: 45: second opening and closing solenoid valve: 46: third opening and closing solenoid valve: 47: fourth opening and closing solenoid valve: 48: fifth opening and closing solenoid valve: 50b: first check valve: 50c: first check valve: 50d: first check valve: 51: second bypass pipe: 52b: second check valve: 52c: second check valve: 52d: second check valve: 53: gas pipe temperature detecting sensor: 54: liquid pipe temperature detecting sensor: 56: confluence pressure detecting sensor: 70: control unit: 71: valve control unit:

72: determining unit: 73: timing control unit: 80: state detecting unit: 100: air-conditioning apparatus: 110: first branching unit: 111: second branching unit: 112: gas-liquid separating device: 113: second flow rate control device: 115: third flow rate control device: 116: second heat exchange unit: 119: first heat exchange unit: 200: air-conditioning apparatus: A: heat source unit: B: indoor unit: C: indoor unit: D: indoor unit: E: relay unit

Claims

CLAIMS [Claim 1]

An air-conditioning apparatus comprising:

a heat source unit including a compressor and a heat source-side heat exchanger;

a plurality of indoor units each including a first flow rate control device and an indoor-side heat exchanger, and configured to perform a cooling operation or a heating operation;

a relay unit connected to the heat source unit by a first connecting pipe and a second connecting pipe, connected to the plurality of indoor units by a plurality of gas branch pipes and a plurality of liquid branch pipes, and configured to distribute refrigerant supplied from the heat source unit to the plurality of indoor units;

a state detecting unit configured to detect a state of the refrigerant flowing through the plurality of gas branch pipes; and a control unit configured to control an operation of the relay unit, wherein the relay unit includes a plurality of cooling solenoid valves connected in parallel, having respective one sides connected to the plurality of gas branch pipes and respective other sides connected to the first connecting pipe, and configured to be open during the cooling operation and closed during the heating operation, and heating solenoid valves having respective one sides connected to the plurality of gas branch pipes and respective other sides connected to the second connecting pipe, and configured to be open during the heating operation and closed during the cooling operation, and wherein the control unit includes a valve control unit configured to control opening and closing of the plurality of cooling solenoid valves, a determining unit configured to determine, based on the state of the refrigerant detected by the state detecting unit, whether or not flow sound is generated when the refrigerant flows through one of the plurality of cooling solenoid valves, and a timing control unit configured to control the valve control unit to open one of the plurality of cooling solenoid valves when one of the plurality of indoor units is switched from the heating operation to the cooling operation, and control the valve control unit to open another one of the plurality of cooling solenoid valves in a closed state when it is determined by the determining unit that the flow sound of the refrigerant is generated.
[Claim 2]

The air-conditioning apparatus of claim 1, wherein when the another one of the plurality of indoor units is switched from the heating operation to the cooling operation, the valve control unit operates to maintain an opening degree of the first flow rate control device at a constant opening degree.
[Claim 3]

The air-conditioning apparatus of claim 1 or 2, wherein when it is determined by the determining unit that the flow sound of the refrigerant is generated, the timing control unit controls the valve control unit to open yet another one of the plurality of cooling solenoid valves in the closed state and a threshold open time elapses since the opening of the another one of the plurality of cooling solenoid valves in the closed state.
[Claim 4]

The air-conditioning apparatus of one of claims 1 to 3, wherein the state detecting unit includes a confluence pressure detecting sensor configured to detect a pressure of the refrigerant flowing through a connecting part of the plurality of liquid branch pipes and the first connecting pipe, and a downstream-side liquid outflow pressure detecting sensor configured to detect a pressure of the refrigerant flowing through a merging part of the plurality of liquid branch pipes, and wherein when a difference between the pressure of the refrigerant detected by the confluence pressure detecting sensor and the pressure of the refrigerant detected by the downstream-side liquid outflow pressure detecting sensor is equal to or greater than a threshold, the determining unit determines that the flow sound of the refrigerant is generated.
[Claim 5]

The air-conditioning apparatus of one of claims 1 to 4, wherein the relay unit further includes a gas-liquid separating device having an inflow side connected to the second connecting pipe, a gas outflow side connected to the heating solenoid valves, and a liquid outflow side connected to the plurality of liquid branch pipes, and configured to separate gas refrigerant and liquid refrigerant from each other, wherein the state detecting unit includes a liquid outflow pressure detecting sensor configured to detect a pressure of the refrigerant on the liquid outflow side of the gas-liquid separating device, and a liquid pipe temperature detecting sensor configured to detect a temperature of the refrigerant flowing through the plurality of liquid branch pipes, and wherein when a subcool value on an outlet side of the indoor-side heat exchanger is equal to or greater than a subcool threshold, the determining unit determines that the flow sound of the refrigerant is generated, with the subcool value being calculated based on a temperature of the refrigerant corresponding to the pressure of the refrigerant detected by the liquid outflow pressure detecting sensor and the temperature of the refrigerant detected by the liquid pipe temperature detecting sensor.
[Claim 6]

The air-conditioning apparatus of one of claims 1 to 5, wherein the state detecting unit includes a confluence pressure detecting sensor configured to detect a pressure of the refrigerant flowing through a connecting part of the plurality of liquid branch pipes and the first connecting pipe, and a gas pipe temperature detecting sensor configured to detect a temperature of the refrigerant flowing through the plurality of gas branch pipes, and wherein when a difference between the pressure of the refrigerant detected by the confluence pressure detecting sensor and a pressure of the refrigerant corresponding to the temperature of the refrigerant detected by the gas pipe temperature detecting sensor is equal to or greater than a pressure difference

5 threshold, the determining unit determines that the flow sound of the refrigerant is generated.
[Claim 7]

The air-conditioning apparatus of one of claims 1 to 6, wherein the determining unit determines that the flow sound of the refrigerant is generated until a threshold

10 stop time elapses since stop of the indoor-side heat exchanger included in one of the plurality of indoor units performing the heating operation.