GB2603246A

GB2603246A - Air conditioning device

Info

Publication number: GB2603246A
Application number: GB2115484.4A
Authority: GB
Inventors: Morishita Yuya
Original assignee: Mitsubishi Electric Corp
Current assignee: Mitsubishi Electric Corp
Priority date: 2019-07-01
Filing date: 2019-07-01
Publication date: 2022-08-03
Anticipated expiration: 2039-07-01
Also published as: GB2603246B; WO2021001869A1; CN114008393A; GB202115484D0; CN114008393B

Abstract

This air conditioning device comprises a relay that has a first decompression device. The relay has a flow path switching valve that is provided to first refrigerant piping connected between a compressor and a load-side heat exchanger, and bypass piping that is connected to the flow path switching valve at one end, and at the other end is connected to second refrigerant piping connected between the first decompression device and a heat source-side heat exchanger. The flow path switching valve has, as internal flow paths, a first flow path communicating the first refrigerant piping and the bypass piping, and a second flow path communicating the compressor and the load-side heat exchanger via the first refrigerant piping, and switches the internal flow paths such that one internal flow path among the first flow path and the second flow path is open while the other internal flow path is closed.

Description

DESCRIPTION Title of Invention

AIR-CONDITIONING APPARATUS

Technical Field

[0001] The present disclosure relates to an air-conditioning apparatus including a relay unit

Background Art

[0002] Patent Literature 1 discloses an air-conditioning apparatus including a relay unit that connects an outdoor unit and indoor units. The relay unit of the air-conditioning apparatus in Patent Literature 1 accommodates a pressure reducing device. The air-conditioning apparatus in Patent Literature 1 includes multiple indoor units connected to the relay unit, and the multiple indoor units can independently be turned on or off.

Citation List Patent Literature [0003] Patent Literature 1: Japanese Unexamined Patent Application Publication No. 2015-135196

Summary of Invention

Technical Problem [0004] In some cases, an air-conditioning apparatus temporarily increases the amount of circulating refrigerant to maintain the operation capacity of an outdoor unit. In such a case, to maintain the amount of refrigerant circulating through indoor units in operation, the air-conditioning apparatus in Patent Literature 1 may also circulate refrigerant temporarily through an indoor unit that is stopped. In this case, the opening degree of the pressure reducing device connected to an indoor unit that is stopped is controlled so as to be smaller than the opening degree of the pressure reducing device connected to an indoor unit in operation and to be a minimum opening degree. This control is performed to reduce a temperature variation in a space where the indoor unit that is stopped is installed. However, if the opening degree of the pressure reducing device is controlled in this way, a noise is generated when refrigerant flows through the pressure reducing device, and there is a possibility that the degree of quietness of the relay unit is degraded.

[0005] The present disclosure has been made in order to address the above problem and is aimed at providing an air-conditioning apparatus capable of maintaining quietness of a relay unit.

Solution to Problem [0006] An air-conditioning apparatus of one embodiment of the present disclosure includes an outdoor unit including a heat-source-side heat exchanger and a compressor connected to the heat-source-side heat exchanger, a plurality of indoor units each including a load-side heat exchanger, and a relay unit that includes a first pressure reducing device connected to the heat-source-side heat exchanger and that is connected to one or more but not all of the plurality of indoor units. The relay unit includes a first refrigerant pipe connected between the compressor and the load-side heat exchangers, a second refrigerant pipe connected between the first pressure reducing device and the heat-source-side heat exchanger, a flow switching valve installed into the first refrigerant pipe, and a bypass pipe that is connected to the flow switching valve on one end and that is connected to the second refrigerant pipe on the other end. The flow switching valve includes as internal passages a first passage through which the first refrigerant pipe on the compressor side and the bypass pipe are in fluid communication and a second passage through which the first refrigerant pipe on the compressor side and the first refrigerant pipe on the load-side heat exchangers side are in fluid communication. The internal passages are switched to open one passage of the first and second passages and to close the other passage.

Advantageous Effects of Invention [0007] The air-conditioning apparatus of one embodiment of the present disclosure includes the relay unit, which includes the flow switching valve and the bypass pipe. Accordingly, while the indoor unit is stopped, the internal passages of the flow switching valve are switched to prevent refrigerant from flowing into the indoor unit, and refrigerant can be rerouted to the bypass pipe. In other words, the air-conditioning apparatus of one embodiment of the present disclosure enables flow passages to be switched so that refrigerant does not flow through the first pressure reducing device while the indoor unit is stopped. Thus, since the air-conditioning apparatus of one embodiment of the present disclosure includes the relay unit, which includes the flow switching valve and the bypass pipe, a noise generated by refrigerant flowing through the first pressure reducing device is reduced, and the air-conditioning apparatus capable of maintaining quietness of the relay unit can be provided.

Brief Description of Drawings

[0008] [Fig. 1] Fig. 1 is a schematic diagram depicting an example of the air-conditioning apparatus according to Embodiment 1.

[Fig. 2] Fig. 2 is a schematic refrigerant-circuit diagram depicting a portion of the air-conditioning apparatus in Fig. 1.

[Fig. 3] Fig. 3 is a flowchart depicting a control process of the flow switching valve and the first pressure reducing devices during a defrosting operation according to Embodiment 1.

[Fig. 4] Fig. 4 is a flowchart depicting a control process of the flow switching valve and the first pressure reducing devices during an oil-recovery operation according to Embodiment 2.

[Fig. 5] Fig. 5 is a schematic refrigerant-circuit diagram depicting an example of the refrigerant circuit of the air-conditioning apparatus according to Embodiment 3.

[Fig. 6] Fig. 6 is a flowchart depicting a control process of the flow switching valve and the first pressure reducing devices in the case of refrigerant-leak detection according to Embodiment 3.

[Fig. 7] Fig. 7 is a schematic refrigerant-circuit diagram depicting an example of a refrigerant circuit of the air-conditioning apparatus according to Embodiment 4.

[Fig. 8] Fig. 8 is a flowchart depicting a control process of the flow switching valve and the first pressure reducing devices in the case where the indoor unit is stopped according to Embodiment 4.

[Fig. 9] Fig. 9 is a schematic refrigerant-circuit diagram depicting an example of a refrigerant circuit of the air-conditioning apparatus according to Embodiment 5.

[Fig. 10] Fig. 10 is a flowchart depicting a control process of the flow switching valve, the first pressure reducing devices, and the second pressure reducing device during a heating operation of the air-conditioning apparatus according to Embodiment 5.

[Fig. 11] Fig. 11 is a schematic refrigerant-circuit diagram depicting an example of a refrigerant circuit of the air-conditioning apparatus according to Embodiment 6.

[Fig. 12] Fig. 12 is an enlarged view of the branch pipe in Fig. 11.

[Fig. 13] Fig. 13 is an enlarged view of the flow switching valve and the bypass pipe disposed in a refrigerant circuit of the air-conditioning apparatus according to Embodiment 6.

Description of Embodiments

[0009] Embodiment 1 The air-conditioning apparatus 100 according to Embodiment 1 will be described.

Fig. 1 is a schematic diagram depicting an example of the air-conditioning apparatus 100 according to Embodiment 1. Fig. 2 is a schematic refrigerant-circuit diagram depicting a portion of the air-conditioning apparatus 100 in Fig. 1. Relative sizes and shapes of components illustrated in the following drawings sometimes differ from actual relative sizes and shapes of the components. Further, in the following drawings, components or portions that are the same or that have the same function are denoted by the same symbol, or no symbol is attached to those components or portions.

[0010] As depicted in Fig. 1, the air-conditioning apparatus 100 includes an outdoor unit 10, multiple indoor units 20, and the relay unit 30. The outdoor unit 10 and the relay unit 30 are connected by using refrigerant pipes. Some of the multiple indoor units 20 are connected to the outdoor unit 10 with the relay unit 30 interposed therebetween, and the rest of the multiple indoor units 20 are directly connected to the outdoor unit 10 without the relay unit 30 interposed therebetween. For example, the relay unit 30 is connected to the indoor unit 20 installed in a space where quietness is required, such as a president room, a meeting room, or an office. The indoor unit 20 installed in a space where quietness is not required, such as an elevator lobby or a storage room, is directly connected to the outdoor unit 10 without the relay unit 30 interposed therebetween. In Fig. 1, only one outdoor unit 10 and one relay unit 30 are depicted, but multiple outdoor units and/or multiple relay units may be installed. In addition, the number of the indoor units 20 connected to the relay unit 30 may be one. Further, existing refrigerant pipes in premises where the air-conditioning apparatus 100 is installed may be used, or new refrigerant pipes may be installed when the air-conditioning apparatus 100 is installed.

[0011] In the following description, a "cooling operation" indicates an operation mode of the air-conditioning apparatus 100 that causes low-temperature and low-pressure two-phase refrigerant to flow into the indoor units 20. A "heating operation" indicates an operation mode of the air-conditioning apparatus 100 that causes high-temperature and high-pressure gas-phase refrigerant to flow into the indoor units 20.

[0012] The outdoor unit 10 includes a compressor 1, a refrigerant-flow switching device 2, and a heat-source-side heat exchanger 3. The compressor 1 and the heat-sourceside heat exchanger 3 are connected by using a refrigerant pipe, and the refrigerant- flow switching device 2 is interposed between the compressor 1 and the heat-source-side heat exchanger 3 in the outdoor unit 10.

[0013] The compressor 1 is a fluid machine that compresses suctioned low-pressure refrigerant and that discharges the compressed refrigerant as high-pressure refrigerant, and a variable-capacity compressor, such as a reciprocating compressor, a rotary cornpressor, or a scroll compressor, is used.

[0014] The refrigerant-flow switching device 2 is an electric device that switches refrigerant passages inside the refrigerant-flow switching device 2 based on an electric signal in accordance with switching from a cooling operation to a heating operation of the air-conditioning apparatus 100 or switching from a heating operation to a cooling operation of the air-conditioning apparatus 100. In Fig. 2, the refrigerant passage inside the refrigerant-flow switching device 2 during a cooling operation is represented by dotted lines, and the refrigerant passage inside the refrigerant-flow switching device 2 during a heating operation is represented by solid lines. Examples of the refrigerant-flow switching device 2 include a four-way valve for which an operation of a solenoid valve is adapted. Alternatively, the refrigerant-flow switching device 2 may be a switching device formed by a combination of two-way valves or three-way valves. If the air-conditioning apparatus 100 performs only one of a cooling operation and a heating operation, the refrigerant-flow switching device 2 may be removed.

[0015] The heat-source-side heat exchanger 3 is a heat transfer device that moves and exchanges heat energy between two fluids having different heat energy. The heat-source-side heat exchanger 3 functions as a condenser during a cooling operation and functions as an evaporator during a heating operation. Examples of the heat-sourceside heat exchanger 3 include an air-cooled heat exchanger, such as a fin-and-tube type heat exchanger or a plate-fin type heat exchanger, and a water-cooled heat exchanger, such as a shell-and-tube type heat exchanger, a plate heat exchanger, or a double-tube type heat exchanger. A condenser of the air-conditioning apparatus 100 is sometimes referred to as a radiator.

[0016] An indoor unit 20 includes a load-side heat exchanger 4. Similarly to the heatsource-side heat exchanger 3, which is described above, the load-side heat exchanger 4 is a heat transfer device that moves and exchanges heat energy between two fluids having different heat energy. The load-side heat exchanger 4 functions as an evaporator during a cooling operation and functions as a condenser during a heating operation. Examples of the load-side heat exchanger 4 include an air-cooled heat exchanger, such as a fin-and-tube type heat exchanger or a plate-fin type heat exchanger.

[0017] The relay unit 30 is connected between the outdoor unit 10 and the indoor units 20 by using refrigerant pipes. The relay unit 30 includes a first refrigerant pipe 5a and a second refrigerant pipe 5b. The first refrigerant pipe 5a is one of the refrigerant pipes that connect the compressor 1 and the load-side heat exchangers 4, and the second refrigerant pipe 5b is a portion of a refrigerant pipe connected to the heat-source-side heat exchanger 3. A group of branch refrigerant pipes is connected to the first refrigerant pipe 5a, and another group of branch refrigerant pipes is connected to the second refrigerant pipe 5b. The number of branch refrigerant pipes in each group corresponds to the number of the load-side heat exchangers 4 of the indoor units 20.

The relay unit 30 includes a first pressure reducing device 6, a capillary tube 7, and a strainer 8.

[0018] The first pressure reducing device 6 is an expansion device that expands high-pressure liquid-phase refrigerant and reduces the pressure of the refrigerant.

Examples of the first pressure reducing device 6 include an expander, a temperature-type automatic expansion valve, and a linear electronic expansion valve. An expander is a mechanical expansion valve that uses a diaphragm as a pressure-receiving unit. A temperature-type automatic expansion valve is an expansion device that controls the amount of refrigerant in accordance with the degree of superheat of gas-phase refrigerant on the suction side of the compressor 1. A linear electronic expansion valve is an expansion device that can control the opening degree in a step-wise manner or continuously and is also abbreviated to LEV. The first pressure reducing devices 6 are each installed into the corresponding branch refrigerant pipe connected to the second refrigerant pipe 5b.

[0019] The capillary tube 7 is a refrigerant pipe that has a capillary-like shape and that is made of a long thin copper tube. The capillary tube 7 has a pipe resistance to allow a required amount of refrigerant to flow through the capillary tube 7 and reduces the pressure of the refrigerant. The capillary tubes 7 are each connected to the corresponding branch refrigerant pipe in series with one of the first pressure reducing devices 6, the corresponding branch refrigerant pipe being connected to the second refrigerant pipe 5b. The capillary tubes 7 are installed into the branch refrigerant pipes on the indoor units 20 side of the first pressure reducing devices 6. The capillary tubes 7 are installed to assist the pressure reducing function of the first pressure reducing devices 6 and may be removed in the air-conditioning apparatus 100.

[0020] The strainer 8 is a filter to filter out dust particles, impurities, or the like, such as sludge, generated in refrigerant during the operation of the compressor 1. The strainers 8 are installed to prevent the first pressure reducing devices 6 and the capillary tubes 7 to be clogged. The strainers 8 are installed one each into the second refrigerant pipe 5b and into each of the branch refrigerant pipes connected to the second refrigerant pipe 5b so that the refrigerant pipes into which the first pressure reducing devices 6 and the capillary tubes 7 are installed are interposed between the strainers 8. For example, if the compressor 1 is capable of preventing sludge to be generated, the strainers 8 may be removed.

[0021] The air-conditioning apparatus 100 may have a configuration that differs from the configuration described above. For example, the air-conditioning apparatus 100 may include a unit other than the units described above, for example, a subcooling heat exchanger, an accumulator, or an oil separator. The indoor unit 20 may include multiple load-side heat exchangers 4.

[0022] In the air-conditioning apparatus 100, the compressor 1, the heat-source-side heat exchanger 3, the first pressure reducing devices 6, and the load-side heat exchangers 4 are connected by pipes, and a refrigerant circuit through which refrigerant circulates is formed. An operation of the refrigerant circuit of the air-conditioning apparatus 100 during a cooling operation will schematically be described herein. [0023] During a cooling operation, the refrigerant-flow switching device 2 performs passage control of refrigerant passages inside the refrigerant-flow switching device 2 as represented by the dotted lines in Fig. 2.

[0024] In the outdoor unit 10, high-temperature and high-pressure gas-phase refrigerant discharged from the compressor 1 flows into the heat-source-side heat exchanger 3 via the refrigerant passages inside the refrigerant-flow switching device 2. The heatsource-side heat exchanger 3 functions as a condenser during a cooling operation. The high-temperature and high-pressure gas-phase refrigerant that flows into the heatsource-side heat exchanger 3 exchanges heat with a heat medium, such as outdoor air, in the heat-source-side heat exchanger 3 and flows out of the heat-source-side heat exchanger 3 as high-pressure liquid-phase refrigerant. The high-pressure liquid-phase refrigerant that flows out of the heat-source-side heat exchanger 3 flows out of the outdoor unit 10 and flows into the relay unit 30.

[0025] The high-pressure liquid-phase refrigerant that flows into the relay unit 30 flows into the first pressure reducing device 6 via the second refrigerant pipe 5b. The high-pressure gas-phase refrigerant that flows into the first pressure reducing device 6 is expanded in the first pressure reducing device 6 with the pressure reduced and flows out of the first pressure reducing device 6 as low-temperature and low-pressure two-phase refrigerant. The low-temperature and low-pressure two-phase refrigerant that flows out of the first pressure reducing device 6 flows out of the relay unit 30 and flows into the indoor unit 20.

[0026] The low-temperature and low-pressure two-phase refrigerant that flows into the indoor unit 20 flows into the load-side heat exchanger 4. The load-side heat exchanger 4 functions as an evaporator during a cooling operation. The low-pressure two-phase refrigerant that flows into the load-side heat exchanger 4 exchanges heat with a heat medium, such as indoor air, in the load-side heat exchanger 4, and flows out of the load-side heat exchanger 4 as low-pressure gas-phase refrigerant. Refrigerant that flows out of the load-side heat exchanger 4 is sometimes low-pressure two-phase refrigerant having a high quality. The low-pressure gas-phase refrigerant that flows out of the load-side heat exchanger 4 flows out of the indoor unit 20 and flows into the outdoor unit 10 via the first refrigerant pipe 5a of the relay unit 30.

[0027] The low-pressure gas-phase refrigerant that flows into the outdoor unit 10 is suctioned by the compressor 1 via the refrigerant passages inside the refrigerant-flow switching device 2. The low-pressure gas-phase refrigerant suctioned by the compressor 1 is compressed by the compressor 1 and discharged from the compressor 1 as high-temperature and high-pressure gas-phase refrigerant. The above cycle is repeated during a cooling operation of the air-conditioning apparatus 100.

[0028] An operation of the refrigerant circuit of the air-conditioning apparatus 100 during a heating operation will schematically be described. During a heating operation, the refrigerant-flow switching device 2 performs passage control of the refrigerant passages inside the refrigerant-flow switching device 2 as represented by the solid lines in Fig. 2.

[0029] High-temperature and high-pressure gas-phase refrigerant discharged from the compressor 1 flows out of the outdoor unit 10 via the refrigerant passages inside the refrigerant-flow switching device 2 and flows into the indoor unit 20 via the first refrigerant pipe 5a of the relay unit 30.

[0030] The high-temperature and high-pressure gas-phase refrigerant that flows into the indoor unit 20 flows into the load-side heat exchanger 4. The load-side heat exchanger 4 functions as a condenser during a heating operation. The high-temperature and high-pressure gas-phase refrigerant that flows into the load-side heat exchanger 4 exchanges heat with a heat medium, such as indoor air, in the load-side heat exchanger 4, and flows out of the load-side heat exchanger 4 as high-pressure liquid-phase refrigerant. The high-pressure liquid-phase refrigerant that flows out of the load-side heat exchanger 4 flows out of the indoor unit 20 and flows into the relay unit 30.

[0031] The high-pressure liquid-phase refrigerant that flows into the relay unit 30 flows into the first pressure reducing device 6. The high-pressure liquid-phase refrigerant that flows into the first pressure reducing device 6 is expanded in the first pressure reducing device 6 with the pressure reduced and flows out of the first pressure reducing device 6 as low-temperature and low-pressure two-phase refrigerant. The low-temperature and low-pressure two-phase refrigerant that flows out of the first pressure reducing device 6 flows out of the relay unit 30 via the second refrigerant pipe 5b and flows into the outdoor unit 10.

[0032] The low-temperature and low-pressure two-phase refrigerant that flows into the outdoor unit 10 flows into the heat-source-side heat exchanger 3. The heat-sourceside heat exchanger 3 functions as an evaporator during a heating operation. The low-temperature and low-pressure two-phase refrigerant that flows into the heat-source-side heat exchanger 3 exchanges heat with a heat medium, such as outdoor air, in the heat-source-side heat exchanger 3 and flows out of the heat-source-side heat exchanger 3 as low-pressure gas-phase refrigerant. Refrigerant that flows out of the heat-sourceside heat exchanger 3 is sometimes low-pressure two-phase refrigerant having a high quality.

[0033] The low-pressure gas-phase refrigerant that flows out of the heat-source-side heat exchanger 3 is suctioned by the compressor 1 via the refrigerant passages inside the refrigerant-flow switching device 2. The low-pressure gas-phase refrigerant suctioned by the compressor 1 is compressed by the compressor 1 and discharged from the compressor 1 as high-temperature and high-pressure gas-phase refrigerant The above cycle is repeated during a heating operation of the air-conditioning apparatus 100.

[0034] Next, a bypass circuit of the relay unit 30 will be described. The relay unit 30 includes a bypass circuit formed by the flow switching valve 50 and the bypass pipe 52.

[0035] The flow switching valve 50 is disposed in the middle of the first refrigerant pipe 5a and is an electric device that switches between the refrigerant circuit and the bypass circuit in accordance with an electric signal. The flow switching valve 50 includes a first port 50a, a second port 50b, and a third port 50c. The first port 50a is connected to the first refrigerant pipe 5a on the outdoor unit 10 side, the second port 50b is connected to the first refrigerant pipe 5a on the indoor units 20 side, and the third port 50c is connected to one end of the bypass pipe 52. The flow switching valve 50 includes as internal passages a first passage through which the first port 50a and the third port 50c are in fluid communication and a second passage through which the first port 50a and the second port 50b are in fluid communication. When the first passage is opened and the second passage is closed in the flow switching valve 50, a refrigerant passage through which the first refrigerant pipe 5a on the outdoor unit 10 side and the bypass pipe 52 are in fluid communication is established. Further, when the first passage is closed and the second passage is opened in the flow switching valve 50, a refrigerant passage through which the first refrigerant pipe 5a on the outdoor unit 10 side and the first refrigerant pipe 5a on the indoor units 20 side are in fluid communication is established. Examples of the flow switching valve 50 include a three-way valve for which an operation of a solenoid valve is adapted. The flow switching valve 50 may be an electric device formed by a four-way valve with one port closed or an electric device formed by a combination of two-way valves.

[0036] One end of the bypass pipe 52 is connected to the third port 50c of the flow switching valve 50, and the other end of the bypass pipe 52 is connected to the second refrigerant pipe 5b. Since the relay unit 30 only includes small electric devices, such as the first pressure reducing devices 6, downsizing the relay unit 30 is easier than downsizing the outdoor unit 10 or the indoor units 20. Accordingly, the first refrigerant pipe 5a and the second refrigerant pipe 5b can be placed close to each other inside the relay unit 30, and thus the bypass pipe 52 can be designed to be short.

[0037] The relay unit 30 includes the flow switching valve 50 and the bypass pipe 52. Accordingly, while all the indoor units 20 are stopped, refrigerant can be rerouted to the bypass pipe 52 by opening the first passage of the flow switching valve 50 and closing the second passage of the flow switching valve 50. In other words, this configuration enables flow passages to be switched so that refrigerant flows through none of the first pressure reducing devices 6 while all the indoor units 20 are stopped, reducing a noise generated by refrigerant flowing through the first pressure reducing devices 6. Thus, the air-conditioning apparatus 100, which is capable of maintaining quietness of the relay unit 30, can be provided.

[0038] Next, a control process of the flow switching valve 50 will be described. The air-conditioning apparatus 100 includes a controller 70, and the controller 70 switches internal passages of the flow switching valve 50.

[0039] The controller 70 is formed by dedicated hardware, a microcomputer, or a micro-processing unit. The microcomputer or the micro-processing unit includes a central computing device, a memory, or similar components. The controller 70 is formed, for example, as a built-in control circuit board and disposed in an electric component box of the outdoor unit 10. The controller 70 is connected to first temperature sensors 72a, the compressor 1, the refrigerant-flow switching device 2, the first pressure reducing devices 6, and the flow switching valve 50 via wireline or wireless communication. The controller 70 may be installed in only one of the units, which include the outdoor unit 10, the indoor units 20, and the relay unit 30, in the air-conditioning apparatus 100. Alternatively, multiple controllers 70 may be installed one each in two or more of the units, which include the outdoor unit 10, the indoor units 20, and the relay unit 30, in the air-conditioning apparatus 100, and the multiple controllers 70 may bi-directionally communicate with each other via wireline or wireless communication. No wireline or wireless communication line connecting to the controller 70 is depicted in Fig. 2 and the figures that follow.

[0040] The controller 70 transmits to the flow switching valve 50 a control signal to switch internal passages of the flow switching valve 50 to open one passage of the first and second passages of the flow switching valve 50 and to close the other passage. The controller 70 also transmits to the first pressure reducing devices 6 control signals to control the opening degrees of the first pressure reducing devices 6. It is assumed that the controller 70 includes the entire electrical circuit that transmits signals to control the opening degrees of the first pressure reducing devices 6 and to switch the internal passages of the flow switching valve 50.

[0041] The controller 70 receives information regarding temperatures sensed by a first temperature sensors 72a. The first temperature sensors 72a sense the temperatures of refrigerant to be suctioned by the compressor 1 during a cooling operation or the temperatures of refrigerant discharged from the compressor 1 during a heating operation. Examples of the first temperature sensors 72a include sensors made of a semiconductor material such as a thermistor or a metal material such as a temperature-measuring resistor.

[0042] The controller 70 can also be configured to perform frequency control of the compressor 1, internal passage control of the refrigerant-flow switching device 2 when cooling and heating operations are switched, or the start and stop of the air-conditioning apparatus 100.

[0043] Fig. 3 is a flowchart depicting a control process of the flow switching valve 50 and the first pressure reducing devices 6 during a defrosting operation according to Embodiment 1. A "defrosting operation" indicates an operation mode in which high-temperature and high-pressure refrigerant is supplied to the heat-source-side heat exchanger 3 to prevent the heat-source-side heat exchanger 3 to be frosted, and the defrosting operation is mainly performed before a heating operation starts or during a heating operation. The defrosting operation is performed, for example, by switching the internal passage of the refrigerant-flow switching device 2 to the internal passage for a cooling operation while a heating operation is performed. The defrosting operation may also be performed by supplying high-temperature and high-pressure refrigerant to the heat-source-side heat exchanger 3 from the compressor 1 via a bypass circuit without switching the refrigerant-flow switching device 2. The control process in Fig. 3 can be set to be performed at regular intervals, for example, every 30 minutes. It is assumed that the internal passages of the flow switching valve 50 are in a state in which the first passage is closed and the second passage is opened during a normal heating operation before the control process is performed.

[0044] In step S11, the controller 70 determines whether to operate the air-conditioning apparatus 100 in the defrosting operation mode. Whether to operate in the defrosting operation mode is determined, for example, based on the temperature of the heatsource-side heat exchanger 3. If it is determined not to operate in the defrosting operation mode, the control process ends.

[0045] If it is determined in step S11 to operate in the defrosting operation mode, the controller 70 performs control in step S12 to open the first passage of the flow switching valve 50, close the second passage of the flow switching valve 50, and cause the opening degrees of the first pressure reducing devices 6 to be fully closed. In Fig. 2, the refrigerant flow that occurs in response to the control process in step 512 is represented by arrows. In such a case, since high-temperature gas-phase refrigerant stops flowing through the indoor unit 20 in a normal operation, for example, a thermostat operation, in which air is only blown over the load-side heat exchanger 4, is performed. High-pressure liquid-phase refrigerant returns to the outdoor unit 10 from the relay unit 30 via the bypass pipe 52, but it is possible to perform control so that low-pressure gas-phase refrigerant is suctioned by the compressor 1 since the high-pressure liquid-phase refrigerant mixes with refrigerant that returns from other indoor units 20.

[0046] The amount of refrigerant discharged from the compressor 1 temporarily becomes larger during the defrosting operation of the air-conditioning apparatus 100 than during a heating operation, and the amount of refrigerant flowing into the relay unit 30, to which the indoor units 20 that are stopped are connected, also increases. However, according to this control process, since refrigerant that is discharged from the compressor 1 and that flows into the heat-source-side heat exchanger 3 returns to the outdoor unit 10 via the bypass pipe 52, the first pressure reducing devices 6 need not be opened when the amount of refrigerant inflow increases. Thus, according to this control process, a noise generated by refrigerant flowing through the first pressure reducing devices 6 can be reduced, and the air-conditioning apparatus 100, which is capable of maintaining quietness of the relay unit 30, can be provided.

[0047] Further, according to this control process, it is not necessary to open the first pressure reducing devices 6 when the amount of refrigerant inflow increases, and thus refrigerant does not flow into the indoor units 20 that are stopped. Accordingly, a temperature drop in an air-conditioned space where the indoor unit 20 that is stopped is installed can be prevented, and the degree of comfort provided by the air-conditioned space can be maintained.

[0048] If multiple relay units 30 are connected in the air-conditioning apparatus 100, the controller 70 may perform the control process in step S12 for one relay unit 30 having the smallest total operating capacity of the indoor units 20 connected to the relay unit 30. The controller 70 may also be configured to determine after step S11 and before the control process in step S12 whether each of the multiple relay units 30 satisfies a criterion for stopping operation and to perform the control process in step S12 for one or more of the multiple relay units 30 that satisfy the criterion for stopping operation. The criterion for stopping operation may be determined, for example, based on a threshold value of the operation capacity of the indoor units 20 connected to the relay unit 30. For example, the controller 70 may be configured to determine that the criterion for stopping operation is satisfied when all the indoor units 20 connected to the relay unit 30 are stopped.

[0049] Embodiment 2 In Embodiment 2, a control process of the flow switching valve 50 and the first pressure reducing devices 6 during an oil-recovery operation will be described with reference to Fig. 4. Fig. 4 is a flowchart depicting the control process of the flow switching valve 50 and the first pressure reducing devices 6 during the oil-recovery operation according to Embodiment 2. An air-conditioning apparatus 100 is configured in the same manner as in Embodiment 1 and will not be described.

[0050] The "oil-recovery operation" indicates an operation mode of the air-conditioning apparatus 100 that recovers lubricant discharged from a compressor 1 together with refrigerant and that returns the lubricant to the inside of the compressor 1. When a cooling operation is performed for a long time and with a low load, lubricant discharged from the compressor 1 together with refrigerant accumulates in what is called a liquid-side pipe. A liquid-side pipe is a portion of the refrigerant pipes connecting the outdoor unit 10 and a relay unit 30 and particularly indicates a portion disposed between the heat-source-side heat exchanger 3 and the first pressure reducing devices 6.

Lubricant accumulates in the liquid-side pipe because the flow speed of liquid-phase refrigerant flowing in the liquid-side pipe is slower than the flow speed of gas-phase refrigerant and liquid lubricant contained in liquid-phase refrigerant more easily precipitates in refrigerant pipes than gas lubricant contained in gas-phase refrigerant. The oil-recovery operation is performed to recover lubricant that has accumulated outside the compressor 1, and thus the driving frequency of the compressor 1 is increased from the driving frequency for a normal cooling operation. The control process in Fig. 4 can be set to be performed when the air-conditioning apparatus 100 has operated for a long time, for example, five hours or more with a frequency lower than the frequency for a normal operation. It is assumed that the internal passages of the flow switching valve 50 are in a state in which the first passage is closed and the second passage is opened during a normal cooling operation before the control process is performed.

[0051] In step 521, the controller 70 determines whether to operate the air-conditioning apparatus 100 in the oil-recovery operation mode. Whether to operate in the oil-recovery operation mode is determined, for example, in accordance with a criterion determined in advance based on the entire load of the air-conditioning apparatus 100 and an operation time of the air-conditioning apparatus 100 with the load. If it is determined not to operate in the oil-recovery operation mode, the control process ends. [0052] If it is determined in step S21 to operate in the oil-recovery operation mode, the controller 70 performs control in step 522 to open the first passage of the flow switching valve 50, close the second passage of the flow switching valve 50, and cause the opening degrees of the first pressure reducing devices 6 to be fully closed. The refrigerant flow that occurs in response to the control process in step S22 is in the direction represented by arrows in Fig. 2 as in Embodiment 1. In such a case, since low-temperature and low-pressure two-phase refrigerant stops flowing through the indoor unit 20 in a normal operation, for example, a thermostat operation, in which air is only blown over the load-side heat exchanger 4, is performed. High-pressure liquid-phase refrigerant returns to the outdoor unit 10 from the relay unit 30 via the bypass pipe 52, but it is possible to perform control so that low-pressure gas-phase refrigerant is suctioned by the compressor 1 since the high-pressure liquid-phase refrigerant mixes with refrigerant that returns from other indoor units 20.

[0053] Since the driving frequency of the compressor 1 is increased during the oil-recovery operation of the air-conditioning apparatus 100, the amount of refrigerant discharged from the compressor 1 temporarily becomes larger than during a normal cooling operation, and the amount of refrigerant flowing into the relay unit 30, to which the indoor units 20 that are stopped are connected, also increases. However, according to this control process, since refrigerant that is discharged from the compressor 1 and that flows into the heat-source-side heat exchanger 3 returns to the outdoor unit 10 via the bypass pipe 52, the first pressure reducing devices 6 need not be opened when the amount of refrigerant inflow increases. Thus, according to this control process, a noise generated by refrigerant flowing through the first pressure reducing devices 6 can be reduced, and the air-conditioning apparatus 100, which is capable of maintaining quietness of the relay unit 30, can be provided.

[0054] Further, according to this control process, it is not necessary to open the first pressure reducing devices 6 when the amount of refrigerant inflow increases, and thus refrigerant does not flow into the indoor units 20 that are stopped. Accordingly, a temperature drop in an air-conditioned space where the indoor unit 20 that is stopped is installed can be prevented, and the degree of comfort provided by the air-conditioned space can be maintained.

[0055] If multiple relay units 30 are connected in the air-conditioning apparatus 100, the controller 70 may perform the control process in step S22 for one relay unit 30 having the smallest total operating capacity of the indoor units 20 connected to the relay unit 30. The controller 70 may also be configured to determine after step S21 and before the control process in step S22 whether each of the multiple relay units 30 satisfies a criterion for stopping operation and to perform the control process in step S22 for one or more of the multiple relay units 30 that satisfy the criterion for stopping operation. The criterion for stopping operation may be determined, for example, based on a threshold value of the operation capacity of the indoor units 20 connected to the relay unit 30. For example, the controller 70 may be configured to determine that the criterion for stopping operation is satisfied when all the indoor units 20 connected to the relay unit 30 are stopped.

[0056] Embodiment 3 A configuration of the air-conditioning apparatus 100 according to Embodiment 3 will be described with reference to Fig. 5. Fig. 5 is a schematic refrigerant-circuit diagram depicting an example of a refrigerant circuit of the air-conditioning apparatus 100 according to Embodiment 3. A refrigerant-leak detection device 74 is installed into the indoor unit 20 in the air-conditioning apparatus 100 according to Embodiment 3. The controller 70 receives from the refrigerant-leak detection device 74 information regarding detection of a refrigerant leak. For example, a refrigerant-leak detection sensor is installed as the refrigerant-leak detection device 74. Examples of a refrigerant-leak detection sensor include a gas sensor such as a semiconductor gas sensor, a hot-wire-type semiconductor gas sensor, or an infrared-light gas sensor. Alternatively, a refrigerant-leak detection sensor may be an oxygen-concentration gas sensor that detects a decrease in the oxygen concentration or a flammable-gas detection sensor that detects flammable gas. The refrigerant-leak detection device 74 may be installed into a device, such as a remote controller, used to input information into the indoor unit 20. The refrigerant-leak detection device 74 is not limited to a refrigerant-leak detection sensor and, for example, may indirectly detect a refrigerant leak based on an anomaly in the temperature of a refrigerant pipe of the indoor unit 20. Other portions of the air-conditioning apparatus 100 are configured in the same manner as in Embodiment 1 and Embodiment 2 and will not be described.

[0057] Fig. 6 is a flowchart depicting a control process of the flow switching valve 50 and the first pressure reducing devices 6 in the case of refrigerant-leak detection according to Embodiment 3. The control process in Fig. 6 can be set to be performed at regular intervals, for example, every 5 minutes. It is assumed that the internal passages of the flow switching valve 50 are in a state in which the first passage is closed and the second passage is opened during a normal cooling or heating operation before the control process is performed.

[0058] In step S31, the controller 70 determines whether a refrigerant leak is detected in the indoor unit 20. If it is determined that a refrigerant leak is not detected, the control process ends. If it is determined in step S31 that a refrigerant leak is detected in the indoor unit 20, the controller 70 performs control in step S32 to open the first passage of the flow switching valve 50, close the second passage of the flow switching valve 50, and cause the opening degrees of the first pressure reducing devices 6 to be fully closed. The refrigerant flow that occurs in response to the control process in step S32 is in the direction represented by dotted arrows in Fig. 5 during a cooling operation and in the direction represented by solid arrows in Fig. 5 during a heating operation. It is possible to perform control so that low-pressure gas-phase refrigerant is suctioned by a compressor 1 since refrigerant that returns to the outdoor unit 10 from the relay unit 30 via a bypass pipe 52 mixes with refrigerant that returns from other indoor units 20. [0059] According to this control process, refrigerant discharged from the compressor 1 does not flow into the indoor units 20 and returns to the outdoor unit 10 via the bypass pipe 52, and thus a refrigerant leak from the indoor units 20 can be prevented.

[0060] Embodiment 4 A configuration of the air-conditioning apparatus 100 according to Embodiment 4 will be described with reference to Fig. 7. Fig. 7 is a schematic refrigerant-circuit diagram depicting an example of a refrigerant circuit of the air-conditioning apparatus 100 according to Embodiment 4. A second temperature sensor 72b and a third temperature sensor 72c are installed into the indoor unit 20 in the air-conditioning apparatus 100 according to Embodiment 4. The second temperature sensor 72b is used to measure the temperature of the air after being subjected to heat exchange by the heat-source-side heat exchanger 3 and functions as a room-temperature sensor. The third temperature sensor 72c is used to measure the temperature of high-pressure liquid-phase or two-phase refrigerant during a heating operation and functions as a subcooling temperature sensor The controller 70 receives from the second temperature sensor 72b and the third temperature sensor 72c information regarding detection of a refrigerant leak. Examples of the second temperature sensor 72b and the third temperature sensor 72c include sensors made of a semiconductor material such as a thermistor or a metal material such as a temperature-measuring resistor. Other portions of the air-conditioning apparatus 100 are configured in the same manner as in Embodiment 1 and Embodiment 2 and will not be described. One of the second and third temperature sensors 72b and 72c may be removed from the air-conditioning apparatus 100.

[0061] Fig. 8 is a flowchart depicting a control process of the flow switching valve 50 and the first pressure reducing devices 6 in the case where the indoor unit 20 is stopped according to Embodiment 4. The control process in Fig. 8 can be set to be performed at regular intervals, for example, every 30 minutes during a heating operation of the air-conditioning apparatus 100. It is assumed that the internal passages of the flow switching valve 50 are in a state in which the first passage is closed and the second passage is opened during a normal heating operation before the control process is performed.

[0062] In step S41, the controller 70 determines whether refrigerant has accumulated in the indoor unit 20. For example, when the temperature sensed by the second temperature sensor 72b keeps at 30 degrees Celsius for three minutes, it is determined that refrigerant in a two-phase state has accumulated in the heat-source-side heat exchanger 3. Alternatively, when the temperature sensed by the third temperature sensor 72c keeps unchanged for three minutes after increasing, it is determined that refrigerant in a two-phase state has accumulated in the heat-source-side heat exchanger 3. If it is determined that refrigerant has not accumulated, the control process ends.

[0063] If it is determined in step S41 that refrigerant has accumulated in the indoor unit 20, the controller 70 performs control in step S42 to open the first passage of the flow switching valve 50, close the second passage of the flow switching valve 50, and cause the opening degrees of the first pressure reducing devices 6 to be fully open. The refrigerant flow that occurs in response to the control process in step S42 is in the direction represented by arrows in Fig. 7. It is possible to perform control so that low-pressure gas-phase refrigerant is suctioned by a compressor 1 since refrigerant that returns to the outdoor unit 10 from the relay unit 30 via the bypass pipe 52 mixes with refrigerant that returns from other indoor units 20.

[0064] According to this control process, refrigerant discharged from the compressor 1 does not flow into the indoor unit 20 and returns to the outdoor unit 10 via the bypass pipe 52. Thus, according to this control process, a temperature rise can be reduced in an air-conditioned space where the indoor unit 20, which is stopped, is installed. In addition, a refrigerant flow that returns to the outdoor unit 10 via the bypass pipe 52 induces refrigerant that has accumulated in the indoor unit 20 to return to the outdoor unit 10. Consequently, a decrease in the amount of refrigerant in the indoor unit 20 caused by the accumulation of refrigerant in the indoor unit 20 can be prevented, and a necessary amount of refrigerant to restart a heating operation of the indoor unit 20 is secured. [0065] Embodiment 5 A configuration of the air-conditioning apparatus 100 according to Embodiment 5 will be described with reference to Fig. 9. Fig. 9 is a schematic refrigerant-circuit diagram depicting an example of a refrigerant circuit of the air-conditioning apparatus 100 according to Embodiment 5. The second pressure reducing device 54 is installed into the bypass pipe 52 in the air-conditioning apparatus 100 according to Embodiment 5. The second pressure reducing device 54 is an expansion device that expands high-pressure refrigerant and that reduces the pressure of the refrigerant. For example, a linear electronic expansion valve is used as the second pressure reducing device 54. Other portions of the air-conditioning apparatus 100 are configured in the same manner as in Embodiment 1 and Embodiment 2 and will not be described.

[0066] Fig. 10 is a flowchart depicting a control process of the flow switching valve 50, the first pressure reducing devices 6, and the second pressure reducing device 54 during a heating operation of the air-conditioning apparatus 100 according to Embodiment 5. The control process in Fig. 10 can be set to be performed at regular intervals, for example, every 30 minutes during a heating operation of the air-conditioning apparatus 100. It is assumed that the internal passages of the flow switching valve 50 are in a state in which the first passage is closed and the second passage is opened during a normal heating operation before the control process is performed.

[0067] In step S51, the controller 70 determines whether the indoor units 20 connected to the relay unit 30 are stopped. If it is determined that at least one of the indoor units 20 is not stopped, the control process ends. If it is determined in step S51 that the indoor units 20 are stopped, the controller 70 performs control in step S52 to open the first passage of the flow switching valve 50, close the second passage of the flow switching valve 50, and cause the opening degrees of the first pressure reducing devices 6 to be fully closed. In step S53, the controller 70 controls the opening degree of the second pressure reducing device 54 so that high-pressure gas-phase refrigerant flowing into the bypass pipe 52 flows out as low-pressure gas-phase refrigerant. The refrigerant flow that occurs in response to the control processes in steps S52 and S53 is in the direction represented by arrows in Fig. 9. It is possible to perform control so that low-pressure gas-phase refrigerant is suctioned by a compressor 1 since refrigerant that returns to an outdoor unit 10 from the relay unit 30 via the bypass pipe 52 mixes with refrigerant that returns from other indoor units 20.

[0068] According to this control process, refrigerant discharged from the compressor 1 does not flow into the indoor units 20, which are stopped, and returns to the outdoor unit 10 via the bypass pipe 52. Thus, according to this control process, temperature rises can be reduced in air-conditioned spaces where the indoor units 20, which are stopped, are installed, and the accumulation of refrigerant in the indoor units 20, which are stopped, can be prevented from occurring. In addition, although a sound caused by refrigerant flowing through the first pressure reducing devices 6 intermittently occurs in some cases in Embodiment 4, a sound caused by flowing refrigerant can be avoided in Embodiment 5 because the first pressure reducing devices 6 are closed.

[0069] Embodiment 6 A configuration of the air-conditioning apparatus 100 according to Embodiment 6 will be described with reference to Figs. 11 to 13. Fig. 11 is a schematic refrigerant-circuit diagram depicting an example of a refrigerant circuit of the air-conditioning apparatus 100 according to Embodiment 6. Branch pipes 90 having three opening ports are installed one each into a first refrigerant pipe 5a and a second refrigerant pipe 5b in the air-conditioning apparatus 100 according to Embodiment 6. Fig. 12 is an enlarged view of one of the branch pipes 90 in Fig. 11. Two of the three opening ports of the branch pipe 90 installed into the first refrigerant pipe 5a are connected to the first refrigerant pipe 5a, for example, by brazing. A cap 92 is attached to the remaining opening port of the branch pipe 90, for example, by brazing to close the opening. The branch pipe 90 installed into the second refrigerant pipe 5b is also disposed in the same manner Fig. 13 is an enlarged view of the flow switching valve 50 and the bypass pipe 52 disposed in the refrigerant circuit of the air-conditioning apparatus 100 according to Embodiment 6. The branch pipe 90 installed into the first refrigerant pipe 5a in the air-conditioning apparatus 100 can be removed by melting, for example, the brazed portion, and the flow switching valve 50 can be installed, for example, by brazing. In addition, the cap 92 of the branch pipe 90 installed into the second refrigerant pipe 5b in the air-conditioning apparatus 100 can be removed by melting, for example, the brazed portion, and the bypass pipe 52 can be installed between the branch pipe 90 and the flow switching valve 50, for example, by brazing. Other portions of the air-conditioning apparatus 100 are configured in the same manner as in Embodiment 1 and Embodiment 2 and will not be described.

[0070] As described above, the flow switching valve 50 and the bypass pipe 52 can detachably be attached to the air-conditioning apparatus 100. Since this configuration enables the flow switching valve 50 and the bypass pipe 52 to be retrofitted into a relay unit 30 when a noise is generated, it is possible to simplify the structure of the relay unit 30 and to reduce material cost.

[0071] Other Embodiments The present disclosure is not limited to the embodiments described above, and various modifications are possible as long as they do not depart from the spirit of the disclosure. For example, the bypass pipe 52 in Embodiment 6, which is described above, may be the bypass pipe 52 into which the second pressure reducing device 54 is installed. The bypass pipe 52 into which the second pressure reducing device 54 is not installed may be replaced with the bypass pipe 52 into which the second pressure reducing device 54 is installed, or vice versa.

[0072] Further, the embodiments described above may be combined with each other.

Reference Signs List [0073] 1: compressor, 2: refrigerant-flow switching device, 3: heat-source-side heat exchanger, 4: load-side heat exchanger, 5a: first refrigerant pipe, 5b: second refrigerant pipe, 6: first pressure reducing device, 7: capillary tube, 8: strainer, 10: outdoor unit, 20: indoor unit, 30: relay unit, 50: flow switching valve, 50a: first port, 50b: second port, 50c: third port, 52: bypass pipe, 54: second pressure reducing device, 70: controller, 72a: first temperature sensor, 72b: second temperature sensor, 72c: third temperature sensor, 74: refrigerant-leak detection device, 90: branch pipe, 92: cap, 100: air-conditioning apparatus

Claims

CLAIMS[Claim 1] An air-conditioning apparatus comprising: an outdoor unit including a heat-source-side heat exchanger and a compressor connected to the heat-source-side heat exchanger; a plurality of indoor units each including a load-side heat exchanger; and a relay unit that includes a first pressure reducing device connected to the heatsource-side heat exchanger and that is connected to one or more but not all of the plurality of indoor units, wherein the relay unit includes a first refrigerant pipe connected between the compressor and the load-side heat exchangers, a second refrigerant pipe connected between the first pressure reducing device and the heat-source-side heat exchanger, a flow switching valve installed into the first refrigerant pipe, and a bypass pipe that is connected to the flow switching valve on one end of the bypass pipe and that is connected to the second refrigerant pipe on an other end, wherein the flow switching valve includes as internal passages a first passage through which the first refrigerant pipe on the compressor side and the bypass pipe are in fluid communication, and a second passage through which the first refrigerant pipe on the compressor side and the first refrigerant pipe on the load-side heat exchangers side are in fluid communication, and wherein the internal passages are switched to open one passage of the first and second passages and to close an other passage.[Claim 2] The air-conditioning apparatus of claim 1, further comprising: a controller configured to control an opening degree of the first pressure reducing device and to switch the internal passages of the flow switching valve.[Claim 3] The air-conditioning apparatus of claim 2, wherein the controller is configured to during a defrosting operation in which high-temperature and high-pressure refrigerant is supplied to the heat-source-side heat exchanger, open the first passage, close the second passage, and cause the opening degree of the first pressure reducing device to be fully closed.[Claim 4] The air-conditioning apparatus of claim 2 or claim 3, wherein the compressor is a variable-capacity compressor, and the controller is configured to during an oil-recovery operation in which lubricant discharged from the compressor together with refrigerant is recovered and returned to inside of the compressor, open the first passage, close the second passage, and cause the opening degree of the first pressure reducing device to be fully closed.[Claim 5] The air-conditioning apparatus of any one of claims 2 to 4, wherein the one or more but not all of the plurality of indoor units each includes a refrigerant-leak detection device, and the controller is configured to in response to a refrigerant leak being detected by the refrigerant-leak detection device, open the first passage, close the second passage, and cause the opening degree of the first pressure reducing device to be fully closed.[Claim 6] The air-conditioning apparatus of any one of claims 2 to 5, wherein the controller is configured to during a heating operation in which high-temperature and high-pressure refrigerant is supplied to the heat-source-side heat exchanger, open the first passage, close the second passage, and cause the opening degree of the first pressure reducing device to be fully open in a case where all the indoor units connected to the relay unit are stopped and refrigerant has accumulated in one or more of the indoor units.[Claim 7] The air-conditioning apparatus of any one of claims 2 to 6, wherein the relay unit includes a second pressure reducing device installed into the bypass pipe, and wherein the controller is configured to during a heating operation in which high-temperature and high-pressure refrigerant is supplied to the heat-source-side heat exchanger, open the first passage, close the second passage, and cause the opening degree of the first pressure reducing device to be fully closed in a case where the indoor units connected to the relay unit are stopped, and control an opening degree of the second pressure reducing device so that pressure of refrigerant flowing out of the bypass pipe is lower than pressure of refrigerant flowing into the bypass pipe.[Claim 8] The air-conditioning apparatus of any one of claims 1 to 7, wherein the flow switching valve and the bypass pipe are detachably attached.