Air conditioning device

Abstract

This air conditioning device (1) includes: an outdoor unit (2) having a compressor (10), an accumulator (50), and an outdoor heat exchanger (30); an indoor unit (4) having an indoor heat exchanger (80); and a relay (3) that relays or blocks circulation of a refrigerant between the outdoor unit (2) and the indoor unit (4), wherein the outdoor unit (2) and the relay (4) are connected by a low-pressure gas main pipe (101), a high-pressure gas main pipe (102), and a liquid main pipe (103), the relay (3) and the indoor unit (4) are connected by a gas branch pipe (104) and a liquid branch pipe (105), and the relay (3) has a relay gas pipe (301) having a high-pressure gas branched pipe (302) and a low-pressure gas branched pipe (303), a relay liquid pipe (304), a bypass pipe (305) connecting the high-pressure gas branched pipe (301) and the relay liquid pipe (304), and a bypass valve (60) that that is provided to the bypass pipe (305) and has a function for switching between an open state for allowing circulation of the refrigerant and a closed state for blocking circulation of the refrigerant.

Description

air conditioning equipment

[0001] The present disclosure relates to an air conditioner having an accumulator.

[0002] In heat pump air conditioners, when heating is performed at low outdoor temperatures, frost forms on the surface of the outdoor heat exchanger, requiring periodic defrosting. Generally, refrigerant liquid remaining in the heat exchanger and piping during heating operation flows into the outdoor unit's accumulator (liquid backflow) when defrosting is initiated. If the amount of backflowing refrigerant liquid exceeds the accumulator capacity, the overflowing refrigerant liquid flows into the compressor, diluting the lubricating oil and potentially causing compressor failure.

[0003] Therefore, Patent Document 1 discloses a three-pipe simultaneous heating and cooling operation system that controls the opening / closing or direction of a valve so that the refrigerant liquid that flows toward the accumulator during defrosting operation flows through the pipes that have been warmed during heating operation. As a result, the air conditioner of Patent Document 1 has the refrigerant liquid absorb the heat of the pipes that have been warmed by the high-temperature refrigerant gas during heating operation and evaporate the refrigerant during defrosting operation, thereby suppressing liquid backflow into the accumulator.

[0004] Japanese Patent Application Laid-Open No. 2017-026171

[0005] However, since the pipes cool gradually during defrosting operation, the defrosting operation of Patent Document 1 may have a reduced effect of suppressing liquid backflow if a large amount of frost is formed and a long defrosting operation is required.

[0006] The present disclosure has been made to solve the above-mentioned problems, and aims to provide an air conditioning apparatus in which liquid backflow during defrosting operation is continuously suppressed, even when a large amount of frost has formed and a long defrosting operation is required.

[0007] The air conditioning apparatus according to the present disclosure includes an outdoor unit having a compressor that compresses a refrigerant, an accumulator that stores the refrigerant, and an outdoor heat exchanger that exchanges heat between the refrigerant and air, an indoor unit having an indoor heat exchanger that exchanges heat between the refrigerant and air, a relay unit that relays or blocks the flow of refrigerant between the outdoor unit and the indoor unit, the outdoor unit and the relay unit being connected by a low-pressure gas main pipe through which gas refrigerant flows, a high-pressure gas main pipe through which gas refrigerant at a higher pressure than the gas refrigerant flowing in the low-pressure gas main pipe flows, and a liquid main pipe through which liquid refrigerant flows, and the relay unit and the indoor unit are connected by a gas refrigerant exchanger through which the gas refrigerant flows, The relay unit connects the gas branch pipes to the high-pressure gas main pipe and the low-pressure gas main pipe, and includes a relay gas pipe having a high-pressure gas branch pipe connected to the high-pressure gas main pipe and a low-pressure gas branch pipe connected to the low-pressure gas main pipe, a relay liquid pipe connecting the liquid main pipe and the liquid branch pipe, a bypass pipe connecting the high-pressure gas branch pipe and the relay liquid pipe, and a bypass valve provided in the bypass pipe and having the function of switching between an open state that allows the refrigerant to flow through the bypass pipe and a closed state that blocks the refrigerant to flow through the bypass pipe.

[0008] The air conditioning apparatus of the present disclosure has a bypass valve provided in the bypass pipe. Therefore, in the air conditioning apparatus of the present disclosure, by opening the bypass valve during defrosting operation and further blocking the flow of refrigerant to the indoor unit, high-temperature refrigerant can be allowed to flow into the outdoor heat exchanger while refrigerant liquid remains in the indoor unit. In other words, in the defrosting operation of the air conditioning apparatus of the present disclosure, liquid backflow is suppressed without utilizing the heat of the piping warmed by the high-temperature refrigerant gas during heating operation. Therefore, the air conditioning apparatus of the present disclosure can continuously suppress liquid backflow to the accumulator during defrosting operation.

[0009] 1 is a refrigerant circuit diagram of an air conditioner according to embodiment 1. FIG. 2 is a hardware configuration diagram showing an example configuration of a control device according to embodiment 1. FIG. 3 is a hardware configuration diagram showing an example configuration of a control device according to embodiment 1. FIG. 4 is a functional block diagram showing an air conditioner according to embodiment 1. FIG. 5 is a diagram for explaining heating operation of an air conditioner according to embodiment 1. FIG. 6 is a diagram for explaining defrosting operation of an air conditioner according to embodiment 1. FIG. 7 is a diagram for explaining cooling operation of an air conditioner according to embodiment 1. FIG. 8 is a diagram for explaining liquid draining operation of an air conditioner according to embodiment 1. FIG. 9 is a flowchart showing the operation of a control device for an air conditioner according to embodiment 1. FIG. 10 is a refrigerant circuit diagram of an air conditioner according to embodiment 2. FIG. 11 is a functional block diagram showing an air conditioner according to embodiment 2. FIG. 12 is a diagram for explaining heating operation of an air conditioner according to embodiment 2. FIG. 13 is a diagram for explaining defrosting operation of an air conditioner according to embodiment 2. FIG. 14 is a diagram for explaining cooling operation of an air conditioner according to embodiment 2. FIG. 15 is a diagram for explaining liquid draining operation of an air conditioner according to embodiment 2. FIG. 16 is a refrigerant circuit diagram of an air conditioner according to embodiment 3. FIG. 17 is a functional block diagram showing an air conditioner according to embodiment 3. FIG. 18 is a diagram for explaining heating operation of an air conditioner according to embodiment 3. 1 is a diagram for explaining the defrosting operation of an air conditioner according to Embodiment 3. FIG. 2 is a refrigerant circuit diagram of an air conditioner according to Embodiment 4. FIG. 3 is a functional block diagram showing an air conditioner according to Embodiment 4. FIG. 4 is a diagram for explaining the heating operation of an air conditioner according to Embodiment 4. FIG. 5 is a diagram for explaining the defrosting operation of an air conditioner according to Embodiment 4. FIG. 6 is a refrigerant circuit diagram of an air conditioner according to Embodiment 5. FIG. 7 is a diagram for explaining the heating operation of an air conditioner according to Embodiment 5. FIG. 8 is a diagram for explaining the defrosting operation of an air conditioner according to Embodiment 5. FIG. 9 is a diagram for explaining the cooling operation of an air conditioner according to Embodiment 5. FIG. 10 is a diagram for explaining the liquid draining operation of an air conditioner according to Embodiment 5. FIG. 11 is a refrigerant circuit diagram of an air conditioner according to Embodiment 6. FIG. 11 is a diagram for explaining the heating operation of an air conditioner according to Embodiment 6.FIG. 10 is a diagram for explaining the defrosting operation of an air conditioning apparatus according to embodiment 6. FIG. 11 is a diagram for explaining the cooling operation of an air conditioning apparatus according to embodiment 6. FIG. 12 is a diagram for explaining the liquid draining operation of an air conditioning apparatus according to embodiment 6. FIG. 13 is a refrigerant circuit diagram of an air conditioning apparatus according to embodiment 7. FIG. 14 is a diagram for explaining the heating operation of an air conditioning apparatus according to embodiment 7. FIG. 15 is a diagram for explaining the defrosting operation of an air conditioning apparatus according to embodiment 7. FIG. 16 is a refrigerant circuit diagram of an air conditioning apparatus according to embodiment 8. FIG. 17 is a diagram for explaining the heating operation of an air conditioning apparatus according to embodiment 8. FIG. 18 is a diagram for explaining the defrosting operation of an air conditioning apparatus according to embodiment 8.

[0010] Hereinafter, an air conditioning apparatus according to an embodiment will be described with reference to the drawings. In the drawings, identical components are denoted by the same reference numerals, and repeated description will be given only when necessary. The present disclosure may include any combination of configurations that can be combined among the configurations described in the following embodiments. The configurations of the components shown in the entire specification are merely examples and are not limited to the configurations described in the specification. In particular, the combinations of the components are not limited to the combinations in each embodiment, and components described in other embodiments may be applied to other embodiments.

[0011] Embodiment 1. Fig. 1 is a refrigerant circuit diagram of an air conditioner 1 according to embodiment 1. As shown in Fig. 1, the air conditioner 1 has an outdoor unit 2, a relay unit 3, a first indoor unit 4a, and a second indoor unit 4b.

[0012] The outdoor unit 2 and the relay unit 3 are connected by three pipes: a low-pressure gas main pipe 101, a high-pressure gas main pipe 102, and a liquid main pipe 103. Gas refrigerant that flows out of the relay unit 3 and flows into the outdoor unit 2 during cooling operation passes through the low-pressure gas main pipe 101. Gas refrigerant that flows out of the outdoor unit 2 and flows into the relay unit 3 during heating operation passes through the high-pressure gas main pipe 102. A gas refrigerant with a higher pressure than the gas refrigerant flowing through the low-pressure gas main pipe 101 flows through the high-pressure gas main pipe 102. Refrigerant that flows out of the relay unit 3 and flows into the outdoor unit 2 during heating operation passes through the liquid main pipe 103, and refrigerant that flows out of the outdoor unit 2 and flows into the relay unit 3 during cooling operation passes through the liquid main pipe 103. The low-pressure gas main pipe 101, the high-pressure gas main pipe 102, and the low-pressure liquid main pipe 103 branch off from the part that connects the outdoor unit 2 and the relay unit 3. The branches of the low-pressure gas main pipe 101, the high-pressure gas main pipe 102, and the liquid main pipe 103 may be connected to a relay unit other than the relay unit 3 or an indoor unit.

[0013] The relay unit 3 and the first indoor unit 4a are connected by a first gas branch pipe 104a and a first liquid branch pipe 105a. The relay unit 3 and the second indoor unit 4b are connected by a second gas branch pipe 104b and a second liquid branch pipe 105b. Gas refrigerant flows through the first gas branch pipe 104a and the second gas branch pipe 104b. Liquid refrigerant flows through the first liquid branch pipe 105a and the second liquid branch pipe 105b.

[0014] The outdoor unit 2 is a device that supplies hot or cold heat to the first indoor unit 4a and the second indoor unit 4b. The outdoor unit 2 has outdoor piping 201 to 204, a suction pipe 206, and a discharge pipe 207. The outdoor unit 2 includes a compressor 10, a heat exchanger-side flow switching device 21, an outdoor heat exchanger 30, an outdoor expansion valve 40, and an accumulator 50.

[0015] The outdoor pipe 201 connects the heat exchanger-side flow switching device 21 and the low-pressure gas main pipe 101. The outdoor pipe 202 connects the heat exchanger-side flow switching device 21, the outdoor heat exchanger 30, the outdoor expansion valve 40, and the liquid main pipe 103. The outdoor pipe 203 branches off from the outdoor pipe 201 and connects to the accumulator 50. The outdoor pipe 204 connects the discharge pipe 207 and the high-pressure gas main pipe 102. The suction pipe 206 connects the accumulator 50 and the compressor 10. The discharge pipe 207 connects the compressor 10 and the heat exchanger-side flow switching device 21.

[0016] The compressor 10 draws in low-temperature, low-pressure refrigerant, compresses it, and discharges it as high-temperature, high-pressure refrigerant. The heat exchanger-side flow switching device 21 is, for example, a four-way valve. The heat exchanger-side flow switching device 21 switches between connecting the outdoor heat exchanger 30 to the compressor 10 and connecting the outdoor heat exchanger 30 to the accumulator 50. This changes the flow direction of the refrigerant in the refrigerant circuit. The outdoor heat exchanger 30 exchanges heat between the refrigerant and outdoor air. The outdoor heat exchanger 30 functions as a condenser during cooling operation and as an evaporator during heating operation. The outdoor expansion valve 40 reduces the pressure of the refrigerant and expands it, and is, for example, an electronic expansion valve with an adjustable opening. The accumulator 50 is a device for storing excess refrigerant circulating through the outdoor unit 2.

[0017] The relay unit 3 is a device that relays or blocks the refrigerant flowing between the outdoor unit 2 and the first and second indoor units 4a, 4b. The relay unit 3 has a relay gas pipe 301, a relay liquid pipe 304, and a bypass pipe 305. The relay unit 3 is equipped with a bypass valve 60, a first low-pressure valve 71a, a second low-pressure valve 71b, a first high-pressure valve 72a, and a second high-pressure valve 72b.

[0018] The relay gas pipe 301 connects the first gas branch pipe 104a and the second gas branch pipe 104b with the high-pressure gas main pipe 102 and the low-pressure gas main pipe 101. The relay gas pipe 301 is a pipe that branches into a high-pressure side and a low-pressure side, and has a high-pressure gas branch pipe 302 and a low-pressure gas branch pipe 303. The high-pressure gas branch pipe 302 is a pipe that connects the branched portion of the relay gas pipe 301 with the high-pressure gas main pipe 102. The low-pressure gas branch pipe 303 is a pipe that connects the branched portion of the relay gas pipe 301 with the low-pressure gas main pipe 101. The high-pressure gas branch pipe 302 branches out corresponding to the first indoor unit 4a and the second indoor unit 4b. Similarly, the low-pressure gas branch pipe 303 branches out corresponding to the first indoor unit 4a and the second indoor unit 4b. The relay liquid pipe 304 branches out corresponding to the first indoor unit 4a and the second indoor unit 4b, and connects the main liquid pipe 103 to the first liquid branch pipe 105a and the second liquid branch pipe 105b. The bypass pipe 305 connects the high-pressure gas branch pipe 302 and the relay liquid pipe 304.

[0019] The bypass valve 60 is provided in the bypass pipe 305 and has the function of switching between an open state that allows the refrigerant to flow through the bypass pipe 305 and a closed state that blocks the refrigerant from flowing through the bypass pipe 305.

[0020] The first low-pressure valve 71a is provided at a position corresponding to the first indoor unit 4a in the low-pressure gas branch pipe 303 that branches to the first indoor unit 4a and the second indoor unit 4b. The first low-pressure valve 71a has a function of switching between an open state that allows refrigerant to flow through a region of the low-pressure gas branch pipe 303 that corresponds to the first indoor unit 4a and a closed state that blocks refrigerant from flowing through a region of the low-pressure gas branch pipe 303 that corresponds to the first indoor unit 4a. The second low-pressure valve 71b is provided at a position corresponding to the second indoor unit 4b in the low-pressure gas branch pipe 303 that branches to the first indoor unit 4a and the second indoor unit 4b. The second low-pressure valve 71b has a function of switching between an open state that allows refrigerant to flow through a region of the low-pressure gas branch pipe 303 that corresponds to the second indoor unit 4b and a closed state that blocks refrigerant from flowing through a region of the low-pressure gas branch pipe 303 that corresponds to the second indoor unit 4b.

[0021] The first high-pressure valve 72a is provided at a position corresponding to the first indoor unit 4a in the high-pressure gas branch pipe 302 that branches into the first indoor unit 4a and the second indoor unit 4b. The first high-pressure valve 72a has a function of switching between an open state, which allows refrigerant to flow through a region of the high-pressure gas branch pipe 302 that corresponds to the first indoor unit 4a, and a closed state, which blocks refrigerant from flowing through a region of the high-pressure gas branch pipe 302 that corresponds to the first indoor unit 4a. The second high-pressure valve 72b is provided at a position corresponding to the second indoor unit 4b in the high-pressure gas branch pipe 302 that branches into the first indoor unit 4a and the second indoor unit 4b. The second high-pressure valve 72b has a function of switching between an open state, which allows refrigerant to flow through a region of the high-pressure gas branch pipe 302 that corresponds to the second indoor unit 4b, and a closed state, which blocks refrigerant from flowing through a region of the high-pressure gas branch pipe 302 that corresponds to the second indoor unit 4b.

[0022] The bypass valve 60, the first low-pressure valve 71 a, the second low-pressure valve 71 b, the first high-pressure valve 72 a, and the second high-pressure valve 72 b are not limited to any particular type as long as they have mechanisms that allow or block the flow of refrigerant. Therefore, these valves may be, for example, on-off valves or expansion valves.

[0023] The first indoor unit 4a and the second indoor unit 4b are devices for supplying hot or cold heat to the room. The first indoor unit 4a has a first indoor piping 401a. The first indoor unit 4a is equipped with a first indoor heat exchanger 80a and a first indoor expansion valve 90a. The second indoor unit 4b has a second indoor piping 401b. The second indoor unit 4b is equipped with a second indoor heat exchanger 80b and a second indoor expansion valve 90b. The first indoor piping 401a connects the first gas branch pipe 104a, the first indoor heat exchanger 80a, the first indoor expansion valve 90a, and the first liquid branch pipe 105a. The second indoor piping 401b connects the second gas branch pipe 104b, the second indoor heat exchanger 80b, the second indoor expansion valve 90b, and the second liquid branch pipe 105b. The first indoor heat exchanger 80a and the second indoor heat exchanger 80b exchange heat between the indoor air and the refrigerant. The first indoor heat exchanger 80a and the second indoor heat exchanger 80b function as evaporators during cooling operation and as condensers during heating operation. The first indoor expansion valve 90a and the second indoor expansion valve 90b reduce the pressure of the refrigerant to expand it, and are, for example, electronic expansion valves with adjustable opening.

[0024] The number of indoor units in the air conditioning apparatus 1 is not limited to two, and may be one, or three or more. In the following description, when the indoor units and the components corresponding to the indoor units are not particularly distinguished, they may be referred to as follows. That is, when the first indoor unit 4a and the second indoor unit 4b are not distinguished, they are referred to as the indoor unit 4. When the first gas branch pipe 104a and the second gas branch pipe 104b are not distinguished, they are referred to as the gas branch pipe 104. When the first liquid branch pipe 105a and the second liquid branch pipe 105b are not distinguished, they are referred to as the liquid branch pipe 105. When the first low-pressure valve 71a and the second low-pressure valve 71b are not distinguished, they are referred to as the low-pressure valve 71. When the first high-pressure valve 72a and the second high-pressure valve 72b are not distinguished, they are referred to as the high-pressure valve 72. When the first indoor pipe 401a and the second indoor pipe 401b are not distinguished, they are referred to as the indoor pipe 401. When there is no need to distinguish between the first indoor heat exchanger 80a and the second indoor heat exchanger 80b, they will be referred to as the indoor heat exchanger 80. When there is no need to distinguish between the first indoor expansion valve 90a and the second indoor expansion valve 90b, they will be referred to as the indoor expansion valve 90.

[0025] The air conditioning apparatus 1 has a control device 5 that controls each device included in the outdoor unit 2, relay unit 3, and indoor unit 4. The control device 5 controls switching between various operation modes and the execution of each operation mode. The operation modes executed by the air conditioning apparatus 1 of embodiment 1 include heating operation, defrosting operation, cooling operation, and liquid draining operation. The user commands the execution of heating operation and cooling operation using a remote control (not shown). The defrosting operation is an operation mode for removing frost that has formed on the outdoor heat exchanger 30 during heating operation. The liquid draining operation is an operation mode for draining liquid that has accumulated in the high-pressure gas main pipe 102 during cooling operation.

[0026] Here, an example of hardware of the control device 5 will be described. FIG. 2 is a hardware configuration diagram showing an example of the configuration of the control device 5 according to the first embodiment. When each function of the control device 5 is executed by hardware, the control device 5 is configured by a processing circuit 501 as shown in FIG. 2. The processing circuit 501 is, for example, a single circuit, a composite circuit, a programmed processor 502, a parallel programmed processor 502, an ASIC (Application Specific Integrated Circuit), an FPGA (Field-Programmable Gate Array), or a combination thereof. Each function realized by the processing circuit 501 may be realized by separate hardware, or each function may be realized by a single piece of hardware.

[0027] Another example of hardware for the control device 5 will now be described. FIG. 3 is a hardware configuration diagram showing an example of the configuration of the control device 5 according to the first embodiment. When each function of the control device 5 is executed by software, the control device 5 is configured by a processor 502 such as a CPU and a memory 503, as shown in FIG. 3. FIG. 3 shows that the processor 502 and the memory 503 are communicably connected to each other via a bus 504. Each function of the control device 5 is realized by software, firmware, or a combination of software and firmware. The software and firmware are written as programs and stored in the memory 503. The processor 502 realizes the functions of each means by reading and executing the programs stored in the memory 503.

[0028] The memory 503 may be a non-volatile semiconductor memory such as a read-only memory (ROM), a flash memory, an erasable and programmable ROM (EPROM), or an electrically erasable and programmable ROM (EEPROM). Alternatively, the memory 503 may be a volatile semiconductor memory such as a random access memory (RAM). Alternatively, the memory 503 may be a removable recording medium such as a magnetic disk, a flexible disk, an optical disk, a compact disc (CD), a mini disc (MD), or a digital versatile disc (DVD). It should be noted that some of the functions of the processing circuit 501 may be realized by dedicated hardware, and other functions may be realized by software or firmware.

[0029] Fig. 4 is a functional block diagram showing the air conditioning apparatus 1 according to Embodiment 1. As shown in Fig. 4, the control device 5 controls the compressor 10, heat exchanger-side flow switching device 21, and outdoor expansion valve 40 of the outdoor unit 2 according to the operation mode. The control device 5 also controls the bypass valve 60, low-pressure valve 71, and high-pressure valve 72 of the relay unit 3 according to the operation mode. The control device 5 controls the first indoor expansion valve 90a of the indoor unit 4 according to the operation mode.

[0030] The control device 5 controls the execution of the defrosting operation and the liquid draining operation based on the measurement results of the frost detection device 6, the defrost detection device 7, and the liquid accumulation detection device 8. The frost detection device 6 is a sensor for detecting frost formation on the outdoor heat exchanger 30, such as a pressure sensor. The frost detection device 6 is not particularly limited, but may be disposed, for example, on a pipe between the outdoor heat exchanger 30 and the compressor 10. The frost detection device 6 transmits its measurement results to the control device 5. When the control device 5 determines, based on the measurement results of the frost detection device 27, that frost has formed in the outdoor heat exchanger 23 to the extent that defrosting is required, the control device 5 transitions the operation mode from heating operation to defrosting operation. For example, when the refrigerant pressure measured by the frost detection device 27 is lower than a predetermined threshold, the control device 5 determines that frost has formed in the outdoor heat exchanger 23 to the extent that defrosting is required. The defrost detection means is a sensor for detecting defrost from the outdoor heat exchanger 30, such as a temperature sensor. The defrost detection device 7 is disposed on a pipe between the outdoor heat exchanger 30 and the compressor 10. The defrost detection device 7 transmits a measurement result to the control device 5. When the control device 5 determines that defrosting of the outdoor heat exchanger 23 is completed based on the measurement result of the defrost detection device 28, the control device 5 transitions the operation mode from the defrosting operation to the heating operation. For example, when the refrigerant temperature measured by the defrost detection device 28 exceeds a predetermined threshold, the control device 5 determines that defrosting of the outdoor heat exchanger 23 is completed.

[0031] The liquid pool detection device 8 is a sensor or timer for detecting the occurrence and removal of a liquid pool, which is a pool of liquid refrigerant in the high-pressure gas main pipe 102. For example, the liquid pool may be a temperature sensor, a pressure sensor, or an integrating timer, or a combination of these. The liquid pool occurs when gas refrigerant accumulating in the high-pressure gas main pipe 102 condenses during cooling operation. Because this gas refrigerant has a pressure equivalent to the discharge pressure of the compressor 10 and a saturated gas temperature higher than the ambient air temperature, it gradually condenses as cooling operation continues. The occurrence of a liquid pool during cooling operation can result in a refrigerant shortage. The liquid pool detection device 8 is not particularly limited, but may be disposed, for example, in the high-pressure gas main pipe 102. The liquid pool detection device 8 transmits measurement results to the control device 5. When the control device 5 determines, based on the measurement results of the liquid pool detection device 8, that a liquid pool that needs to be removed has occurred in the high-pressure gas main pipe 102, the control device 5 transitions the operating mode from cooling operation to liquid draining operation. For example, if the refrigerant temperature and pressure measured by the liquid pool detection device 8 are below predetermined threshold ranges, the control device 5 determines that a liquid pool that needs to be eliminated has occurred in the high-pressure gas main pipe 102. Furthermore, if the control device 5 determines that the elimination of the liquid pool in the high-pressure gas main pipe 102 has been completed based on the measurement results of the liquid pool detection device 8, it transitions the operating mode from liquid draining operation to cooling operation. For example, the control device 5 determines that the liquid pool in the high-pressure gas main pipe 102 has been eliminated if the duration of the liquid draining operation measured by the integrating timer exceeds a predetermined threshold range.

[0032] The state of each device and the flow of refrigerant in each operation mode will be described. First, heating operation will be described. FIG. 5 is a diagram for explaining the heating operation of the air conditioning apparatus 1 according to Embodiment 1. In FIG. 5, arrows indicate the direction of refrigerant flow. When performing heating operation, the control device 5 switches the heat exchanger-side flow switching device 21 to a direction that connects the outdoor heat exchanger 30 and the accumulator 50. The control device 5 also closes the bypass valve 60, closes the low-pressure valve 71, and opens the high-pressure valve 72. Furthermore, the control device 5 opens the indoor expansion valve 90 and the outdoor expansion valve 40.

[0033] During heating operation, the refrigerant drawn into the compressor 10 is compressed by the compressor 10 and discharged in a high-temperature, high-pressure gas state. The high-temperature, high-pressure gas refrigerant discharged from the compressor 10 passes through the high-pressure gas main pipe 102 and flows into the relay unit 3. The refrigerant flowing into the relay unit 3 passes through the high-pressure gas branch pipe 302, which is equipped with the high-pressure valve 72, and the gas branch pipe 104, before flowing into the indoor unit 4. The refrigerant flowing into the indoor unit 4 passes through the indoor heat exchanger 80, which functions as a condenser. The refrigerant passing through the indoor heat exchanger 80 exchanges heat with the indoor air, condensing and liquefying. During this process, the indoor air is heated, thereby heating the room. The liquid refrigerant passes through the indoor expansion valve 90, where it is decompressed and expanded to become a low-temperature, low-pressure, two-phase gas-liquid refrigerant. The two-phase gas-liquid refrigerant flows through the liquid branch pipe 105, the relay liquid pipe 304, and the main liquid pipe 103, before flowing into the outdoor unit 2. The refrigerant that flows into the outdoor unit 2 passes through the outdoor expansion valve 40, where it is further decompressed and expanded, and then passes through the outdoor heat exchanger 30, which functions as an evaporator. The refrigerant that passes through the outdoor heat exchanger 30 exchanges heat with the outdoor air, evaporating and gasifying. The evaporated refrigerant, now in a low-temperature, low-pressure gas state, then passes through the heat exchanger-side flow switching device 21 and the accumulator 50, and is again drawn into the compressor 10 and circulated.

[0034] Next, the defrosting operation will be described. Fig. 6 is a diagram for explaining the defrosting operation of the air conditioning apparatus 1 according to Embodiment 1. In Fig. 6, arrows indicate the direction of refrigerant flow. When performing the defrosting operation, the control device 5 switches the heat exchanger-side flow switching device 21 to a direction that connects the outdoor heat exchanger 30 and the accumulator 50. The control device 5 also opens the bypass valve 60, closes the low-pressure valve 71, and opens the high-pressure valve 72. Furthermore, the control device 5 closes the indoor expansion valve 90 and opens the outdoor expansion valve 40.

[0035] During defrosting operation, refrigerant drawn into the compressor 10 is compressed by the compressor 10 and discharged in a high-temperature, high-pressure gas state. The high-temperature, high-pressure gas refrigerant discharged from the compressor 10 passes through the high-pressure main gas pipe 102 and flows into the relay unit 3. The refrigerant that flows into the relay unit 3 passes through a portion of the high-pressure gas branch pipe 302, a bypass pipe 305 provided with a bypass valve 60, a portion of the relay liquid pipe 304, and the main liquid pipe 103, before flowing back into the outdoor unit 2. The high-temperature, high-pressure gas refrigerant that flows into the outdoor unit 2 passes through the outdoor expansion valve 40 and the outdoor heat exchanger 30, which functions as an evaporator. The high-temperature, low-pressure gas refrigerant passing through the outdoor heat exchanger 30 exchanges heat with frost adhering to the outdoor heat exchanger 30, condenses, and becomes a low-temperature, low-pressure gas. At this time, the outdoor heat exchanger 30 is defrosted. The low-temperature, low-pressure gas refrigerant then passes through the heat exchanger-side flow switching device 21 and the accumulator 50, and is again drawn into the compressor 10 to circulate. During defrosting operation, the low-pressure valve 71 is closed, and the indoor expansion valve 90 is also closed. This blocks the flow of refrigerant to the indoor unit 4, and the liquid refrigerant is stored in the indoor unit 4.

[0036] Next, cooling operation will be described. Fig. 7 is a diagram for explaining the cooling operation of the air conditioning apparatus 1 according to Embodiment 1. In Fig. 7, arrows indicate the direction of refrigerant flow. When performing cooling operation, the control device 5 switches the heat exchanger-side flow switching device 21 to a direction that connects the compressor 10 and the outdoor heat exchanger 30. The control device 5 also closes the bypass valve 60, closes the high-pressure valve 72, and opens the low-pressure valve 71. Furthermore, the control device 5 opens the indoor expansion valve 90 and the outdoor expansion valve 40.

[0037] During cooling operation, the refrigerant drawn into the compressor 10 is compressed by the compressor 10 and discharged in a high-temperature, high-pressure gas state. The high-temperature, high-pressure gas refrigerant discharged from the compressor 10 passes through the heat exchanger-side flow switching device 21 and the outdoor heat exchanger 30. The refrigerant passing through the outdoor heat exchanger 30 exchanges heat with outdoor air, condenses, and liquefies. The liquid refrigerant passes through the outdoor expansion valve 40, where it is reduced in pressure and expanded. The liquid refrigerant passes through the main liquid pipe 103 and flows into the relay unit 3. The refrigerant that has flowed into the relay unit 3 passes through the relay liquid pipe 304 and the liquid branch pipe 105 and flows into the indoor unit 4. The refrigerant that has flowed into the indoor unit 4 is further reduced in pressure and expanded by the indoor expansion valve 90, becoming a low-temperature, low-pressure, two-phase refrigerant in a gas-liquid state. The low-temperature, low-pressure, two-phase refrigerant in a gas-liquid state passes through the indoor heat exchanger 80, where it exchanges heat with indoor air, evaporates, and gasifies. At this time, the indoor air is cooled, and cooling is performed in the room. The gaseous refrigerant passes through the gas branch pipe 104 and flows into the relay unit 3. The refrigerant that has flowed into the relay unit 3 passes through the low-pressure gas branch pipe 303, which is provided with the low-pressure valve 71 of the relay gas pipe 301, and the low-pressure gas main pipe 101, and flows into the outdoor unit 2. The refrigerant that has flowed into the outdoor unit 2 passes through the accumulator 50 and is again sucked into the compressor 10 and circulates.

[0038] Next, the liquid draining operation will be described. Fig. 8 is a diagram for explaining the liquid draining operation of the air conditioning apparatus 1 according to Embodiment 1. In Fig. 8, the arrows indicate the direction of refrigerant flow. When performing the liquid draining operation, the control device 5 switches the heat exchanger-side flow switching device 21 to a direction that connects the compressor 10 and the outdoor heat exchanger 30. The control device 5 also opens the bypass valve 60, closes the high-pressure valve 72, and opens the low-pressure valve 71. Furthermore, the control device 5 opens the indoor expansion valve 90 and the outdoor expansion valve 40.

[0039] During liquid drainage operation, a main circuit and a bypass circuit are formed. Refrigerant flows through the main circuit in the same manner as in cooling operation. In the bypass circuit, high-temperature, high-pressure gas refrigerant discharged from the compressor 10 passes through the high-pressure gas main pipe 102 and flows into the relay unit 3. The refrigerant that flows into the relay unit 3 passes through a portion of the high-pressure gas branch pipe 302 and the bypass pipe 305 equipped with the bypass valve 60, flows into the relay liquid pipe 304, and merges into the main circuit. As the refrigerant flows through the bypass circuit, the liquid refrigerant that had accumulated in the high-pressure gas main pipe 102 flows and merges into the main circuit. This eliminates liquid accumulation in the high-pressure gas main pipe 102. The flow of refrigerant to the indoor unit 4 is blocked, and the liquid refrigerant is stored within the indoor unit 4. Furthermore, the liquid refrigerant that merges into the main circuit passes through the indoor expansion valve 90 and the indoor heat exchanger 80 and is gasified. This prevents liquid from flowing back into the accumulator 50.

[0040] The operation of the control device 5 will now be described. Figures 9 and 10 are flowcharts showing the operation of the control device 5 of the air conditioning apparatus 1 according to embodiment 1. First, the execution of defrosting operation will be described with reference to Figure 9. During heating operation, the control device 5 determines whether defrosting of the outdoor heat exchanger 30 is necessary based on the measurement results of the frost detection device 6 (step S1). If it is determined that defrosting of the outdoor heat exchanger 30 is not necessary (step S1: NO), the process of step S1 is repeated until it is determined that defrosting of the outdoor heat exchanger 30 is necessary. If it is determined that defrosting of the outdoor heat exchanger 30 is necessary (step S1: YES), the operation mode is transitioned from heating operation to defrosting operation (step S2).

[0041] During the defrosting operation, the control device 5 determines whether defrosting of the outdoor heat exchanger 30 has been completed based on the measurement result of the defrost detection device 7 (step S3). If it is determined that defrosting of the outdoor heat exchanger 30 has not been completed (step S3: NO), the control device 5 repeats the processing of step S3 until it is determined that defrosting of the outdoor heat exchanger 30 has been completed. If it is determined that defrosting of the outdoor heat exchanger 30 has been completed (step S3: YES), the control device 5 transitions the operation mode from the defrosting operation to the heating operation (step S4).

[0042] Next, the execution of the liquid draining operation will be described with reference to Fig. 10. During cooling operation, the control device 5 determines whether or not it is necessary to remove the liquid pool in the high-pressure gas main pipe 102 based on the measurement results of the liquid pool detection device 8 (step S11). If it is determined that it is not necessary to remove the liquid pool in the high-pressure gas main pipe 102 (step S11: NO), the process of step S11 is repeated until it is determined that it is necessary to remove the liquid pool in the high-pressure gas main pipe 102. If it is determined that it is necessary to remove the liquid pool in the high-pressure gas main pipe 102 (step S11: YES), the operation mode is transitioned from cooling operation to liquid draining operation (step S12).

[0043] During the liquid draining operation, the control device 5 determines whether or not the elimination of the liquid pool in the high-pressure gas main pipe 102 has been completed based on the measurement results of the liquid pool detection device 8 (step S13). If it is determined that the elimination of the liquid pool in the high-pressure gas main pipe 102 has not been completed (step S13: NO), the process of step S13 is repeated until it is determined that the elimination of the liquid pool in the high-pressure gas main pipe 102 has been completed. If it is determined that the elimination of the liquid pool in the high-pressure gas main pipe 102 has been completed (step S13: YES), the operation mode is transitioned from the liquid draining operation to the cooling operation (step S14).

[0044] As described above, according to the first embodiment, the air conditioning apparatus 1 includes the bypass valve 60 provided in the bypass pipe 305. Therefore, in the air conditioning apparatus 1 of the first embodiment, the bypass valve 60 is opened during defrost operation, and the flow of refrigerant to the indoor unit 4 is blocked, allowing high-temperature refrigerant to flow into the outdoor heat exchanger 30 while the refrigerant liquid remains in the indoor unit 4. In other words, in the defrost operation of the air conditioning apparatus 1 of the present disclosure, liquid backflow is suppressed without utilizing the heat of the piping warmed by the high-temperature refrigerant gas during heating operation. Therefore, the air conditioning apparatus 1 of the first embodiment can continuously suppress liquid backflow into the accumulator 50 during defrost operation. Furthermore, in the air conditioning apparatus 1 of the first embodiment, the high-pressure gas main pipe 102 and the liquid main pipe 103 do not cool during defrost operation, allowing for an early return to heating mode.

[0045] Embodiment 2. Figure 11 is a refrigerant circuit diagram of an air conditioning apparatus 1A according to embodiment 2. As shown in Figure 11, embodiment 2 differs from embodiment 1 in that the outdoor unit 2 has a high-pressure pipe side flow switching device 22. In embodiment 2, the same parts as those in embodiment 1 are given the same reference numerals and their description will be omitted, and the description will focus on the differences from embodiment 1.

[0046] The outdoor unit 2 further has an outdoor pipe 205. The outdoor unit 2 also has a high-pressure pipe-side flow path switching device 22. The outdoor pipe 205 connects the high-pressure pipe-side flow path switching device 22 and the outdoor pipe 201. The high-pressure pipe-side flow path switching device 22 is provided on the outdoor pipe 204. The high-pressure pipe-side flow path switching device 22 switches between an orientation in which the high-pressure gas main pipe 102 and the compressor 10 are connected and an orientation in which the high-pressure gas main pipe 102 and the accumulator 50 are connected.

[0047] Fig. 12 is a functional block diagram showing an air conditioning apparatus 1A pertaining to Embodiment 2. As shown in Fig. 12, the control device 5 controls the compressor 10, heat exchanger-side flow switching device 21, high-pressure pipe-side flow switching device 22, and outdoor expansion valve 40 of the outdoor unit 2 according to the operation mode. The control device 5 also controls the bypass valve 60, low-pressure valve 71, and high-pressure valve 72 of the relay unit 3 according to the operation mode. The control device 5 controls the first indoor expansion valve 90a of the indoor unit 4 according to the operation mode.

[0048] The state of each device and the flow of refrigerant in each operation mode will be described. First, heating operation will be described. FIG. 13 is a diagram illustrating the heating operation of the air conditioning apparatus 1A according to Embodiment 2. In FIG. 13, arrows indicate the direction of refrigerant flow. When performing heating operation, the control device 5 switches the heat exchanger-side flow switching device 21 to a direction connecting the outdoor heat exchanger 30 and the accumulator 50, and switches the high-pressure pipe-side flow switching device 22 to a direction connecting the compressor 10 and the high-pressure gas main pipe 102. The control device 5 also closes the bypass valve 60, closes the low-pressure valve 71, and opens the high-pressure valve 72. Furthermore, the control device 5 opens the indoor expansion valve 90 and the outdoor expansion valve 40.

[0049] During heating operation, the refrigerant drawn into the compressor 10 is compressed by the compressor 10 and discharged in a high-temperature, high-pressure gas state. The high-temperature, high-pressure gas refrigerant discharged from the compressor 10 passes through the high-pressure pipe-side flow switching device 22, the high-pressure gas main pipe 102, and into the relay unit 3. The refrigerant flowing into the relay unit 3 passes through the high-pressure gas branch pipe 302 equipped with the high-pressure valve 72 and the gas branch pipe 104, and then into the indoor unit 4. The refrigerant flowing into the indoor unit 4 passes through the indoor heat exchanger 80, which functions as a condenser. The refrigerant passing through the indoor heat exchanger 80 exchanges heat with the indoor air, condenses, and liquefies. At this time, the indoor air is heated, and heating is performed in the room. The liquid refrigerant passes through the indoor expansion valve 90, where it is decompressed and expanded to become a low-temperature, low-pressure, two-phase gas-liquid refrigerant. The refrigerant in a gas-liquid two-phase state passes through the liquid branch pipe 105, the relay liquid pipe 304, and the main liquid pipe 103, and flows into the outdoor unit 2. The refrigerant that flows into the outdoor unit 2 passes through the outdoor expansion valve 40, where it is further decompressed and expanded, and then passes through the outdoor heat exchanger 30, which functions as an evaporator. The refrigerant that passes through the outdoor heat exchanger 30 exchanges heat with the outdoor air, evaporating and gasifying. The evaporated refrigerant, now in a low-temperature, low-pressure gas state, then passes through the heat exchanger-side flow switching device 21 and the accumulator 50, and is again drawn into the compressor 10 and circulated.

[0050] Next, the defrosting operation will be described. Fig. 14 is a diagram illustrating the defrosting operation of the air conditioning apparatus 1A according to the second embodiment. In Fig. 14, arrows indicate the direction of refrigerant flow. When performing the defrosting operation, the control device 5 switches the heat exchanger-side flow switching device 21 to a direction connecting the outdoor heat exchanger 30 and the accumulator 50, and switches the high-pressure pipe-side flow switching device 22 to a direction connecting the compressor 10 and the high-pressure gas main pipe 102. The control device 5 also opens the bypass valve 60, closes the low-pressure valve 71, and opens the high-pressure valve 72. Furthermore, the control device 5 closes the indoor expansion valve 90 and opens the outdoor expansion valve 40.

[0051] During defrosting operation, refrigerant drawn into the compressor 10 is compressed by the compressor 10 and discharged in a high-temperature, high-pressure gas state. The high-temperature, high-pressure gas refrigerant discharged from the compressor 10 passes through the high-pressure pipe-side flow switching device 22, the high-pressure gas main pipe 102, and into the relay unit 3. The refrigerant that flows into the relay unit 3 passes through a portion of the high-pressure gas branch pipe 302, the bypass pipe 305 provided with the bypass valve 60, a portion of the relay liquid pipe 304, and the main liquid pipe 103, before flowing back into the outdoor unit 2. The high-temperature, high-pressure gas refrigerant that flows into the outdoor unit 2 passes through the outdoor expansion valve 40 and the outdoor heat exchanger 30, which functions as an evaporator. The high-temperature, low-pressure gas refrigerant passing through the outdoor heat exchanger 30 exchanges heat with frost adhering to the outdoor heat exchanger 30, condenses, and becomes a low-temperature, low-pressure gas. At this time, the outdoor heat exchanger 30 is defrosted. The low-temperature, low-pressure gas refrigerant then passes through the heat exchanger-side flow switching device 21 and the accumulator 50, and is again drawn into the compressor 10 to circulate. During defrosting operation, the low-pressure valve 71 is closed, and the indoor expansion valve 90 is also closed. This blocks the flow of refrigerant to the indoor unit 4, and the liquid refrigerant is stored in the indoor unit 4.

[0052] Next, cooling operation will be described. FIG. 15 is a diagram illustrating the cooling operation of the air conditioning apparatus 1A according to Embodiment 2. In FIG. 15, arrows indicate the direction of refrigerant flow. When performing cooling operation, the control device 5 switches the heat exchanger-side flow switching device 21 to a direction connecting the compressor 10 and the outdoor heat exchanger 30, and switches the high-pressure pipe-side flow switching device 22 to a direction connecting the accumulator 50 and the high-pressure gas main pipe 102. The control device 5 also closes the bypass valve 60, closes the high-pressure valve 72, and opens the low-pressure valve 71. Furthermore, the control device 5 opens the indoor expansion valve 90 and the outdoor expansion valve 40.

[0053] During cooling operation, the refrigerant drawn into the compressor 10 is compressed by the compressor 10 and discharged in a high-temperature, high-pressure gas state. The high-temperature, high-pressure gas refrigerant discharged from the compressor 10 passes through the heat exchanger-side flow switching device 21 and the outdoor heat exchanger 30. The refrigerant passing through the outdoor heat exchanger 30 exchanges heat with outdoor air, condenses, and liquefies. The liquid refrigerant passes through the outdoor expansion valve 40, where it is reduced in pressure and expanded. The liquid refrigerant passes through the main liquid pipe 103 and flows into the relay unit 3. The refrigerant that has flowed into the relay unit 3 passes through the relay liquid pipe 304 and the liquid branch pipe 105 and flows into the indoor unit 4. The refrigerant that has flowed into the indoor unit 4 is further reduced in pressure and expanded by the indoor expansion valve 90, becoming a low-temperature, low-pressure, two-phase refrigerant in a gas-liquid state. The low-temperature, low-pressure, two-phase refrigerant in a gas-liquid state passes through the indoor heat exchanger 80, where it exchanges heat with indoor air, evaporates, and gasifies. At this time, the indoor air is cooled, and cooling is performed in the room. The gaseous refrigerant passes through the gas branch pipe 104 and flows into the relay unit 3. The refrigerant that has flowed into the relay unit 3 passes through the low-pressure gas branch pipe 303, which is provided with the low-pressure valve 71 of the relay gas pipe 301, and the low-pressure gas main pipe 101, and flows into the outdoor unit 2. The refrigerant that has flowed into the outdoor unit 2 passes through the accumulator 50 and is again sucked into the compressor 10 and circulates.

[0054] Next, the liquid draining operation will be described. Figure 16 is a diagram illustrating the liquid draining operation of the air conditioning apparatus 1A according to the second embodiment. In Figure 16, arrows indicate the direction of refrigerant flow. When performing the liquid draining operation, the control device 5 switches the heat exchanger-side flow switching device 21 to a direction connecting the compressor 10 and the outdoor heat exchanger 30, and switches the high-pressure pipe-side flow switching device 22 to a direction connecting the accumulator 50 and the high-pressure gas main pipe 102. The control device 5 also opens the bypass valve 60, closes the high-pressure valve 72, and opens the low-pressure valve 71. Furthermore, the control device 5 opens the indoor expansion valve 90 and the outdoor expansion valve 40.

[0055] During liquid drainage operation, a main circuit and a bypass circuit are formed. Refrigerant flows through the main circuit in the same manner as in cooling operation. In the bypass circuit, high-temperature, high-pressure gas refrigerant discharged from the compressor 10 passes through the high-pressure gas main pipe 102 and flows into the relay unit 3. The refrigerant that flows into the relay unit 3 passes through a portion of the high-pressure gas branch pipe 302 and the bypass pipe 305 equipped with the bypass valve 60, flows into the relay liquid pipe 304, and merges into the main circuit. As the refrigerant flows through the bypass circuit, the liquid refrigerant that had accumulated in the high-pressure gas main pipe 102 flows and merges into the main circuit. This eliminates liquid accumulation in the high-pressure gas main pipe 102. The flow of refrigerant to the indoor unit 4 is blocked, and the liquid refrigerant is stored within the indoor unit 4. Furthermore, the liquid refrigerant that merges into the main circuit passes through the indoor expansion valve 90 and the indoor heat exchanger 80 and is gasified. This prevents liquid from flowing back into the accumulator 50.

[0056] As described above, according to the second embodiment, similar to the first embodiment, the air conditioning apparatus 1A includes the bypass valve 60 provided in the bypass pipe 305. Therefore, in the air conditioning apparatus 1A of the second embodiment, the bypass valve 60 is opened during defrost operation, and the flow of refrigerant to the indoor unit 4 is blocked, allowing high-temperature refrigerant to flow into the outdoor heat exchanger 30 while the refrigerant liquid remains in the indoor unit 4. In other words, in the defrost operation of the air conditioning apparatus 1A of the present disclosure, liquid backflow is suppressed without utilizing the heat of the piping warmed by the high-temperature refrigerant gas during heating operation. Therefore, the air conditioning apparatus 1A of the second embodiment can continuously suppress liquid backflow into the accumulator 50 during defrost operation. Furthermore, in the air conditioning apparatus 1A of the second embodiment, the high-pressure gas main pipe 102 and the liquid main pipe 103 are not cooled during defrost operation, allowing for an early return to heating operation.

[0057] Embodiment 3. Figure 17 is a refrigerant circuit diagram of an air conditioning apparatus 1B pertaining to embodiment 3. As shown in Figure 17, embodiment 3 differs from embodiment 1 in that the relay unit 3 has a first medium-pressure valve 73a and a second medium-pressure valve 73b. In embodiment 3, the same parts as in embodiment 1 are given the same reference numerals and their description will be omitted, and the description will focus on the differences from embodiment 1.

[0058] The relay unit 3 has a first medium pressure valve 73a and a second medium pressure valve 73b. The first medium pressure valve 73a and the second medium pressure valve 73b are provided in the relay liquid pipe 304 between the connection portion of the bypass pipe 305 and the connection portion of the liquid branch pipe 105. The first medium pressure valve 73a is provided in the relay liquid pipe 304 that branches to the first indoor unit 4a and the second indoor unit 4b, at a position corresponding to the first indoor unit 4a. The first medium pressure valve 73a has the function of switching between an open state that allows refrigerant to flow through the section of the relay liquid pipe 304 that corresponds to the first indoor unit 4a, and a closed state that blocks refrigerant from flowing through the section of the relay liquid pipe 304 that corresponds to the first indoor unit 4a. The second medium pressure valve 73b is provided in the relay liquid pipe 304 that branches to the first indoor unit 4a and the second indoor unit 4b, at a position corresponding to the second indoor unit 4b. The second intermediate pressure valve 73b has the function of switching between an open state, which allows the flow of refrigerant through the region of the relay liquid pipe 304 corresponding to the second indoor unit 4b, and a closed state, which blocks the flow of refrigerant through the region of the relay liquid pipe 304 corresponding to the second indoor unit 4b. In the following description, when there is no need to distinguish between the first intermediate pressure valve 73a and the second intermediate pressure valve 73b, they may be referred to as the intermediate pressure valve 73. Note that the type of intermediate pressure valve 73 is not limited as long as it has a mechanism that can switch between allowing and blocking the flow of refrigerant. Therefore, the intermediate pressure valve 73 may be, for example, an on-off valve or an expansion valve.

[0059] Figure 18 is a functional block diagram showing an air conditioning apparatus 1B pertaining to Embodiment 3. As shown in Figure 18, the control device 5 controls the compressor 10, heat exchanger-side flow switching device 21, and outdoor expansion valve 40 of the outdoor unit 2 according to the operation mode. The control device 5 also controls the bypass valve 60, low-pressure valve 71, high-pressure valve 72, and medium-pressure valve 73 of the relay unit 3 according to the operation mode. The control device 5 controls the first indoor expansion valve 90a of the indoor unit 4 according to the operation mode.

[0060] The state of each device and the flow of refrigerant in each operation mode will be described. The cooling operation and liquid drainage operation are the same as those in embodiment 1, and therefore will not be described here. First, the heating operation will be described. FIG. 19 is a diagram illustrating the heating operation of the air conditioning apparatus 1B according to embodiment 3. In FIG. 19, the arrows indicate the direction of refrigerant flow. When performing the heating operation, the control device 5 switches the heat exchanger-side flow switching device 21 to a direction that connects the outdoor heat exchanger 30 and the accumulator 50. The control device 5 also closes the bypass valve 60, closes the low-pressure valve 71, opens the high-pressure valve 72, and opens the intermediate-pressure valve 73. Furthermore, the control device 5 opens the indoor expansion valve 90 and the outdoor expansion valve 40.

[0061] During heating operation, the refrigerant drawn into the compressor 10 is compressed by the compressor 10 and discharged in a high-temperature, high-pressure gas state. The high-temperature, high-pressure gas refrigerant discharged from the compressor 10 passes through the high-pressure gas main pipe 102 and flows into the relay unit 3. The refrigerant that flows into the relay unit 3 passes through the high-pressure gas branch pipe 302, which is equipped with the high-pressure valve 72, and the gas branch pipe 104, before flowing into the indoor unit 4. The refrigerant that flows into the indoor unit 4 passes through the indoor heat exchanger 80, which functions as a condenser. The refrigerant that passes through the indoor heat exchanger 80 exchanges heat with the indoor air, condenses, and liquefies. At this time, the indoor air is warmed, and heating is performed in the room. The liquid refrigerant passes through the indoor expansion valve 90, where it is decompressed and expanded to become low-temperature, low-pressure, two-phase gas-liquid refrigerant. The refrigerant in a gas-liquid two-phase state passes through the liquid branch pipe 105, the relay liquid pipe 304 provided with the intermediate pressure valve 73, and the main liquid pipe 103, and flows into the outdoor unit 2. The refrigerant that flows into the outdoor unit 2 passes through the outdoor expansion valve 40, where it is further reduced in pressure and expanded, and passes through the outdoor heat exchanger 30, which functions as an evaporator. The refrigerant passing through the outdoor heat exchanger 30 exchanges heat with the outdoor air, evaporating and gasifying. The evaporated refrigerant, now in a low-temperature, low-pressure gas state, then passes through the heat exchanger-side flow switching device 21 and the accumulator 50, and is again drawn into the compressor 10 and circulated.

[0062] Next, the defrosting operation will be described. FIG. 20 is a diagram illustrating the defrosting operation of the air conditioning apparatus 1B according to Embodiment 3. In FIG. 20, arrows indicate the direction of refrigerant flow. When performing the defrosting operation, the control device 5 switches the heat exchanger-side flow switching device 21 to a direction that connects the outdoor heat exchanger 30 and the accumulator 50. The control device 5 also opens the bypass valve 60, closes the low-pressure valve 71, opens the high-pressure valve 72, and closes the intermediate-pressure valve 73. Furthermore, the control device 5 opens the indoor expansion valve 90 and the outdoor expansion valve 40. Note that the indoor expansion valve 90 may also be closed.

[0063] During defrosting operation, refrigerant drawn into the compressor 10 is compressed by the compressor 10 and discharged in a high-temperature, high-pressure gas state. The high-temperature, high-pressure gas refrigerant discharged from the compressor 10 passes through the high-pressure main gas pipe 102 and flows into the relay unit 3. The refrigerant that flows into the relay unit 3 passes through a portion of the high-pressure gas branch pipe 302, a bypass pipe 305 provided with a bypass valve 60, a portion of the relay liquid pipe 304, and the main liquid pipe 103, before flowing back into the outdoor unit 2. The high-temperature, high-pressure gas refrigerant that flows into the outdoor unit 2 passes through the outdoor expansion valve 40 and the outdoor heat exchanger 30, which functions as an evaporator. The high-temperature, low-pressure gas refrigerant passing through the outdoor heat exchanger 30 exchanges heat with frost adhering to the outdoor heat exchanger 30, condenses, and becomes a low-temperature, low-pressure gas. At this time, the outdoor heat exchanger 30 is defrosted. The low-temperature, low-pressure gas refrigerant then passes through the heat exchanger-side flow switching device 21 and the accumulator 50, and is again drawn into the compressor 10 to circulate. During defrosting operation, the low-pressure valve 71 is closed, and the indoor expansion valve 90 is also closed. This blocks the flow of refrigerant to the indoor unit 4, and the liquid refrigerant is stored in the indoor unit 4.

[0064] As described above, according to the third embodiment, similar to the first embodiment, the air conditioning apparatus 1B includes the bypass valve 60 provided in the bypass pipe 305. Therefore, in the air conditioning apparatus 1B of the third embodiment, the bypass valve 60 is opened during defrosting operation, and the flow of refrigerant to the indoor unit 4 is blocked, allowing high-temperature refrigerant to flow into the outdoor heat exchanger 30 while the refrigerant liquid remains in the indoor unit 4. In other words, in the defrosting operation of the air conditioning apparatus 1B of the present disclosure, liquid backflow is suppressed without utilizing the heat of the piping warmed by the high-temperature refrigerant gas during heating operation. Therefore, the air conditioning apparatus 1B of the third embodiment can continuously suppress liquid backflow into the accumulator 50 during defrosting operation. Furthermore, in the air conditioning apparatus 1B of the third embodiment, the high-pressure gas main pipe 102 and the liquid main pipe 103 do not cool during defrosting operation, allowing for an early return to heating operation.

[0065] Embodiment 4. Figure 21 is a refrigerant circuit diagram of an air conditioning apparatus 1C according to embodiment 4. As shown in Figure 21, embodiment 4 differs from embodiment 1 in that the outdoor unit 2 has a high-pressure pipe-side flow switching device 22 and the relay unit 3 has a first intermediate pressure valve 73a and a second intermediate pressure valve 73b. In other words, embodiment 4 corresponds to a combination of embodiment 2 and embodiment 3. In embodiment 4, the same parts as in embodiment 1 are assigned the same reference numerals and their description will be omitted, and the description will focus on the differences from embodiment 1.

[0066] The outdoor unit 2 further has an outdoor pipe 205. The outdoor unit 2 also has a high-pressure pipe-side flow path switching device 22. The outdoor pipe 205 connects the high-pressure pipe-side flow path switching device 22 and the outdoor pipe 201. The high-pressure pipe-side flow path switching device 22 is provided on the outdoor pipe 204. The high-pressure pipe-side flow path switching device 22 switches between an orientation in which the high-pressure gas main pipe 102 and the compressor 10 are connected and an orientation in which the high-pressure gas main pipe 102 and the accumulator 50 are connected.

[0067] The relay unit 3 has a first medium pressure valve 73a and a second medium pressure valve 73b. The first medium pressure valve 73a and the second medium pressure valve 73b are provided in the relay liquid pipe 304 between the connection portion of the bypass pipe 305 and the connection portion of the liquid branch pipe 105. The first medium pressure valve 73a is provided in the relay liquid pipe 304 that branches to the first indoor unit 4a and the second indoor unit 4b, at a position corresponding to the first indoor unit 4a. The first medium pressure valve 73a has the function of switching between an open state that allows refrigerant to flow through the section of the relay liquid pipe 304 that corresponds to the first indoor unit 4a, and a closed state that blocks refrigerant from flowing through the section of the relay liquid pipe 304 that corresponds to the first indoor unit 4a. The second medium pressure valve 73b is provided in the relay liquid pipe 304 that branches to the first indoor unit 4a and the second indoor unit 4b, at a position corresponding to the second indoor unit 4b. The second intermediate pressure valve 73b has the function of switching between an open state, which allows the flow of refrigerant through the region of the relay liquid pipe 304 corresponding to the second indoor unit 4b, and a closed state, which blocks the flow of refrigerant through the region of the relay liquid pipe 304 corresponding to the second indoor unit 4b. In the following description, when there is no need to distinguish between the first intermediate pressure valve 73a and the second intermediate pressure valve 73b, they may be referred to as the intermediate pressure valve 73. Note that the type of intermediate pressure valve 73 is not limited as long as it has a mechanism that can switch between allowing and blocking the flow of refrigerant. Therefore, the intermediate pressure valve 73 may be, for example, an on-off valve or an expansion valve.

[0068] Figure 22 is a functional block diagram showing an air conditioning apparatus 1C pertaining to Embodiment 4. As shown in Figure 22, the control device 5 controls the compressor 10, heat exchanger-side flow switching device 21, high-pressure pipe-side flow switching device 22, and outdoor expansion valve 40 of the outdoor unit 2 according to the operation mode. The control device 5 also controls the bypass valve 60, low-pressure valve 71, high-pressure valve 72, and medium-pressure valve 73 of the relay unit 3 according to the operation mode. The control device 5 controls the first indoor expansion valve 90a of the indoor unit 4 according to the operation mode.

[0069] The state of each device and the flow of refrigerant in each operating mode will be described. The cooling operation and liquid drainage operation are the same as those in the first embodiment, and therefore will not be described here. First, the heating operation will be described. FIG. 23 is a diagram illustrating the heating operation of the air conditioning apparatus 1C according to the fourth embodiment. In FIG. 23, arrows indicate the direction of refrigerant flow. When performing the heating operation, the control device 5 switches the heat exchanger-side flow switching device 21 to connect the outdoor heat exchanger 30 and the accumulator 50, and switches the high-pressure pipe-side flow switching device 22 to connect the compressor 10 and the high-pressure gas main pipe 102. The control device 5 also closes the bypass valve 60, closes the low-pressure valve 71, opens the high-pressure valve 72, and opens the intermediate-pressure valve 73. Furthermore, the control device 5 opens the indoor expansion valve 90 and the outdoor expansion valve 40.

[0070] During heating operation, the refrigerant drawn into the compressor 10 is compressed by the compressor 10 and discharged in a high-temperature, high-pressure gas state. The high-temperature, high-pressure gas refrigerant discharged from the compressor 10 passes through the high-pressure pipe-side flow switching device 22, the high-pressure gas main pipe 102, and into the relay unit 3. The refrigerant flowing into the relay unit 3 passes through the high-pressure gas branch pipe 302 equipped with the high-pressure valve 72 and the gas branch pipe 104, and then into the indoor unit 4. The refrigerant flowing into the indoor unit 4 passes through the indoor heat exchanger 80, which functions as a condenser. The refrigerant passing through the indoor heat exchanger 80 exchanges heat with the indoor air, condenses, and liquefies. At this time, the indoor air is heated, and heating is performed in the room. The liquid refrigerant passes through the indoor expansion valve 90, where it is decompressed and expanded to become a low-temperature, low-pressure, two-phase gas-liquid refrigerant. The refrigerant in a gas-liquid two-phase state passes through the liquid branch pipe 105, the relay liquid pipe 304 provided with the intermediate pressure valve 73, and the main liquid pipe 103, and flows into the outdoor unit 2. The refrigerant that flows into the outdoor unit 2 passes through the outdoor expansion valve 40, where it is further reduced in pressure and expanded, and passes through the outdoor heat exchanger 30, which functions as an evaporator. The refrigerant passing through the outdoor heat exchanger 30 exchanges heat with the outdoor air, evaporating and gasifying. The evaporated refrigerant, now in a low-temperature, low-pressure gas state, then passes through the heat exchanger-side flow switching device 21 and the accumulator 50, and is again drawn into the compressor 10 and circulated.

[0071] Next, the defrosting operation will be described. FIG. 24 is a diagram illustrating the defrosting operation of the air conditioning apparatus 1C according to the fourth embodiment. In FIG. 24, arrows indicate the direction of refrigerant flow. When performing the defrosting operation, the control device 5 switches the heat exchanger-side flow switching device 21 to a direction connecting the outdoor heat exchanger 30 and the accumulator 50, and switches the high-pressure pipe-side flow switching device 22 to a direction connecting the compressor 10 and the high-pressure gas main pipe 102. The control device 5 also opens the bypass valve 60, closes the low-pressure valve 71, opens the high-pressure valve 72, and closes the intermediate-pressure valve 73. The control device 5 also opens the indoor expansion valve 90 and the outdoor expansion valve 40. Note that the indoor expansion valve 90 may be closed.

[0072] During defrosting operation, refrigerant drawn into the compressor 10 is compressed by the compressor 10 and discharged in a high-temperature, high-pressure gas state. The high-temperature, high-pressure gas refrigerant discharged from the compressor 10 passes through the high-pressure pipe-side flow switching device 22, the high-pressure gas main pipe 102, and into the relay unit 3. The refrigerant that flows into the relay unit 3 passes through a portion of the high-pressure gas branch pipe 302, the bypass pipe 305 provided with the bypass valve 60, a portion of the relay liquid pipe 304, and the main liquid pipe 103, before flowing back into the outdoor unit 2. The high-temperature, high-pressure gas refrigerant that flows into the outdoor unit 2 passes through the outdoor expansion valve 40 and the outdoor heat exchanger 30, which functions as an evaporator. The high-temperature, low-pressure gas refrigerant passing through the outdoor heat exchanger 30 exchanges heat with frost adhering to the outdoor heat exchanger 30, condenses, and becomes a low-temperature, low-pressure gas. At this time, the outdoor heat exchanger 30 is defrosted. The low-temperature, low-pressure gas refrigerant then passes through the heat exchanger-side flow switching device 21 and the accumulator 50, and is again drawn into the compressor 10 to circulate. During defrosting operation, the low-pressure valve 71 is closed, and the medium-pressure valve 73 is also closed. This blocks the flow of refrigerant to the indoor unit 4, and the liquid refrigerant is stored in the indoor unit 4.

[0073] As described above, according to the fourth embodiment, similar to the first embodiment, the air conditioning apparatus 1C includes the bypass valve 60 provided in the bypass pipe 305. Therefore, in the air conditioning apparatus 1C of the fourth embodiment, the bypass valve 60 is opened during defrosting operation, and the flow of refrigerant to the indoor unit 4 is blocked, allowing high-temperature refrigerant to flow into the outdoor heat exchanger 30 while the refrigerant liquid remains in the indoor unit 4. In other words, in the defrosting operation of the air conditioning apparatus 1C of the present disclosure, liquid backflow is suppressed without utilizing the heat of the piping warmed by the high-temperature refrigerant gas during heating operation. Therefore, the air conditioning apparatus 1C of the fourth embodiment can continuously suppress liquid backflow into the accumulator 50 during defrosting operation. Furthermore, in the air conditioning apparatus 1C of the fourth embodiment, the high-pressure gas main pipe 102 and the liquid main pipe 103 are not cooled during defrosting operation, allowing for an early return to heating mode.

[0074] Embodiment 5. Figure 25 is a refrigerant circuit diagram of an air conditioning apparatus 1D pertaining to embodiment 5. As shown in Figure 25, embodiment 5 differs from embodiment 1 in that it has a first outdoor unit 2a and a second outdoor unit 2b. In embodiment 5, the same parts as in embodiment 1 are given the same reference numerals and their description will be omitted, and the description will focus on the differences from embodiment 1.

[0075] The first outdoor unit 2a and the second outdoor unit 2b have the same configuration as the outdoor unit 2 described in the first embodiment. That is, the first outdoor unit 2a includes a first compressor 10a, a first heat-exchanger-side flow switching device 21a, a first outdoor heat exchanger 30a, a first outdoor expansion valve 40a, and a first accumulator 50a. The first compressor 10a draws in low-temperature, low-pressure refrigerant, compresses the drawn refrigerant, and discharges it into high-temperature, high-pressure refrigerant. The first heat-exchanger-side flow switching device 21a is, for example, a four-way valve. The first heat-exchanger-side flow switching device 21a switches between a direction in which the first outdoor heat exchanger 30a and the first compressor 10a are connected and a direction in which the first outdoor heat exchanger 30a and the first accumulator 50a are connected. This switches the flow direction of the refrigerant in the refrigerant circuit. The first outdoor heat exchanger 30a exchanges heat between the refrigerant and outdoor air. The first outdoor expansion valve 40a reduces the pressure of the refrigerant to expand it, and is, for example, an electronic expansion valve with an adjustable opening. The first accumulator 50a stores excess refrigerant circulating through the first outdoor unit 2a.

[0076] Similarly, the second outdoor unit 2b includes a second compressor 10b, a second heat exchanger-side flow switching device 21b, a second outdoor heat exchanger 30b, a second outdoor expansion valve 40b, and a second accumulator 50b. The second compressor 10b draws in low-temperature, low-pressure refrigerant, compresses it, and discharges it into high-temperature, high-pressure refrigerant. The second heat exchanger-side flow switching device 21b is, for example, a four-way valve. The second heat exchanger-side flow switching device 21b switches between a connection between the second outdoor heat exchanger 30b and the second compressor 10b and a connection between the second outdoor heat exchanger 30b and the second accumulator 50b. This changes the flow direction of the refrigerant in the refrigerant circuit. The second outdoor heat exchanger 30b exchanges heat between the refrigerant and outdoor air. The second outdoor expansion valve 40b reduces the pressure of the refrigerant to expand it, and is, for example, an electronic expansion valve with an adjustable opening. The second accumulator 50b is a device for storing excess refrigerant circulating through the second outdoor unit 2b.

[0077] The number of outdoor units 2 in the air conditioning apparatus 1D is not limited to one or two, but may be three or more. In the following description, when the outdoor units and the components corresponding to the outdoor units are not particularly distinguished, they may be referred to as in the same manner as in Embodiment 1, as follows. That is, when the first outdoor unit 2a and the second outdoor unit 2b are not distinguished, they are referred to as the outdoor units 2. When the first compressor 10a and the second compressor 10b are not distinguished, they are referred to as the compressors 10. When the first heat exchanger-side flow switching device 21a and the second heat exchanger-side flow switching device 21b are not distinguished, they are referred to as the heat exchanger-side flow switching device 21. When the first outdoor heat exchanger 30a and the second outdoor heat exchanger 30b are not distinguished, they are referred to as the outdoor heat exchanger 30. When the first outdoor expansion valve 40a and the second outdoor expansion valve 40b are not distinguished, they are referred to as the outdoor expansion valves 40. When there is no need to distinguish between the first accumulator 50a and the second accumulator 50b, they will be referred to as accumulators 50.

[0078] 4 of the first embodiment, the control device 5 controls the compressor 10, the heat exchanger-side flow switching device 21, and the outdoor expansion valve 40 of the outdoor unit 2 according to the operation mode. The control device 5 also controls the bypass valve 60, the low-pressure valve 71, and the high-pressure valve 72 of the relay unit 3 according to the operation mode. The control device 5 controls the first indoor expansion valve 90a of the indoor unit 4 according to the operation mode.

[0079] The state of each device and the flow of refrigerant in each operation mode will be described. First, heating operation will be described. FIG. 26 is a diagram for explaining the heating operation of the air conditioning apparatus 1D according to embodiment 5. In FIG. 26, arrows indicate the direction of refrigerant flow. When performing heating operation, the control device 5 switches the heat exchanger-side flow switching device 21 to a direction that connects the outdoor heat exchanger 30 and the accumulator 50. The control device 5 also closes the bypass valve 60, closes the low-pressure valve 71, and opens the high-pressure valve 72. Furthermore, the control device 5 opens the indoor expansion valve 90 and the outdoor expansion valve 40.

[0080] During heating operation, the refrigerant drawn into the first compressor 10a is compressed by the first compressor 10a and discharged in a high-temperature, high-pressure gas state. The high-temperature, high-pressure gas refrigerant discharged from the first compressor 10a passes through the high-pressure gas main pipe 102 and flows into the relay unit 3. The refrigerant flowing into the relay unit 3 passes through the high-pressure gas branch pipe 302, which is equipped with the high-pressure valve 72, and the gas branch pipe 104, before flowing into the indoor unit 4. The refrigerant flowing into the indoor unit 4 passes through the indoor heat exchanger 80, which functions as a condenser. The refrigerant passing through the indoor heat exchanger 80 exchanges heat with the indoor air, condensing and liquefying. At this time, the indoor air is heated, and heating is performed in the room. The liquid refrigerant passes through the indoor expansion valve 90, where it is decompressed and expanded to become a low-temperature, low-pressure, two-phase gas-liquid refrigerant. The refrigerant in a gas-liquid two-phase state passes through the liquid branch pipe 105, the relay liquid pipe 304, and the main liquid pipe 103 and flows into the first outdoor unit 2a. The refrigerant that flows into the first outdoor unit 2a passes through the outdoor expansion valve 40, where it is further decompressed and expanded, and then passes through the first outdoor heat exchanger 30a, which functions as an evaporator. The refrigerant that passes through the first outdoor heat exchanger 30a exchanges heat with outdoor air and evaporates, becoming gasified. The evaporated refrigerant then passes through the first heat exchanger-side flow switching device 21a and the accumulator 50, and is again drawn into the first compressor 10a.

[0081] The refrigerant drawn into the second compressor 10b is compressed by the second compressor 10b and discharged in a high-temperature, high-pressure gas state. The high-temperature, high-pressure gas refrigerant discharged from the second compressor 10b flows into the high-pressure gas main pipe 102 and joins the refrigerant flowing between the first outdoor unit 2a and the relay unit 3. The refrigerant in a gas-liquid two-phase state flowing through the main liquid pipe 103 branches off from the refrigerant flowing between the first outdoor unit 2a and the relay unit 3 and flows into the second outdoor unit 2b. The refrigerant that flows into the second outdoor unit 2b passes through the outdoor expansion valve 40, where it is further decompressed and expanded, and then passes through the second outdoor heat exchanger 30b, which functions as an evaporator. The refrigerant passing through the second outdoor heat exchanger 30b exchanges heat with the outdoor air, evaporating and gasifying. Thereafter, the evaporated low-temperature, low-pressure gaseous refrigerant passes through the second heat exchanger side flow switching device 21b and the accumulator 50, and is again sucked into the second compressor 10b.

[0082] Next, the defrosting operation will be described. Fig. 27 is a diagram for explaining the defrosting operation of the air conditioning apparatus 1D according to Embodiment 5. In Fig. 27, arrows indicate the direction of refrigerant flow. When performing the defrosting operation, the control device 5 switches the heat exchanger-side flow switching device 21 to a direction that connects the outdoor heat exchanger 30 and the accumulator 50. The control device 5 also opens the bypass valve 60, closes the low-pressure valve 71, and opens the high-pressure valve 72. Furthermore, the control device 5 closes the indoor expansion valve 90 and opens the outdoor expansion valve 40.

[0083] During defrosting operation, refrigerant drawn into the first compressor 10a is compressed by the first compressor 10a and discharged in a high-temperature, high-pressure gas state. The high-temperature, high-pressure gas refrigerant discharged from the first compressor 10a passes through the high-pressure gas main pipe 102 and flows into the relay unit 3. The refrigerant that flows into the relay unit 3 passes through a portion of the high-pressure gas branch pipe 302, a bypass pipe 305 provided with a bypass valve 60, a portion of the relay liquid pipe 304, and the main liquid pipe 103, before flowing back into the first outdoor unit 2a. The high-temperature, high-pressure gas refrigerant that flows into the first outdoor unit 2a passes through the outdoor expansion valve 40 and the first outdoor heat exchanger 30a, which functions as an evaporator. The high-temperature, low-pressure gas refrigerant passing through the first outdoor heat exchanger 30a exchanges heat with frost adhering to the first outdoor heat exchanger 30a, condenses, and becomes a low-temperature, low-pressure gas. At this time, the first outdoor heat exchanger 30a is defrosted. The low-temperature, low-pressure gaseous refrigerant then passes through the first heat exchanger-side flow switching device 21a and the accumulator 50, and is again drawn into the first compressor 10a. During defrosting operation, the low-pressure valve 71 is closed, and the indoor expansion valve 90 is also closed. This blocks the flow of refrigerant to the indoor unit 4, and the liquid refrigerant is stored in the indoor unit 4.

[0084] The refrigerant drawn into the second compressor 10b is compressed by the second compressor 10b and discharged in a high-temperature, high-pressure gas state. The high-temperature, high-pressure gas refrigerant discharged from the second compressor 10b flows into the high-pressure gas main pipe 102 and joins the refrigerant flowing between the first outdoor unit 2a and the relay unit 3. The refrigerant in a gas-liquid two-phase state flowing through the main liquid pipe 103 branches off from the refrigerant flowing between the first outdoor unit 2a and the relay unit 3 and flows into the second outdoor unit 2b. The refrigerant that flows into the second outdoor unit 2b passes through the outdoor expansion valve 40, where it is further decompressed and expanded, and then passes through the second outdoor heat exchanger 30b, which functions as an evaporator. The refrigerant passing through the second outdoor heat exchanger 30b exchanges heat with the outdoor air, evaporating and gasifying. Thereafter, the evaporated low-temperature, low-pressure gaseous refrigerant passes through the second heat exchanger side flow switching device 21b and the accumulator 50, and is again sucked into the second compressor 10b.

[0085] Next, cooling operation will be described. Fig. 28 is a diagram for explaining the cooling operation of the air conditioning apparatus 1D according to Embodiment 5. In Fig. 28, arrows indicate the direction of refrigerant flow. When performing cooling operation, the control device 5 switches the heat exchanger-side flow switching device 21 to a direction that connects the compressor 10 and the outdoor heat exchanger 30. The control device 5 also closes the bypass valve 60, closes the high-pressure valve 72, and opens the low-pressure valve 71. Furthermore, the control device 5 opens the indoor expansion valve 90 and the outdoor expansion valve 40.

[0086] During cooling operation, the refrigerant drawn into the first compressor 10a is compressed by the first compressor 10a and discharged in a high-temperature, high-pressure gas state. The high-temperature, high-pressure gas refrigerant discharged from the first compressor 10a passes through the first heat exchanger-side flow switching device 21a and the first outdoor heat exchanger 30a. The refrigerant passing through the first outdoor heat exchanger 30a exchanges heat with outdoor air, condenses, and liquefies. The liquid refrigerant passes through the outdoor expansion valve 40, where it is reduced in pressure and expanded. The liquid refrigerant passes through the main liquid pipe 103 and flows into the relay unit 3. The refrigerant that has flowed into the relay unit 3 passes through the relay liquid pipe 304 and the liquid branch pipe 105 and flows into the indoor unit 4. The refrigerant that has flowed into the indoor unit 4 is further reduced in pressure and expanded by the indoor expansion valve 90, becoming a low-temperature, low-pressure, two-phase gas-liquid refrigerant. The low-temperature, low-pressure refrigerant in a gas-liquid two-phase state passes through the indoor heat exchanger 80, where it exchanges heat with the indoor air, evaporating and gasifying. During this process, the indoor air is cooled, and the room is cooled. The gaseous refrigerant passes through the gas branch pipe 104 and flows into the relay unit 3. The refrigerant that has flowed into the relay unit 3 passes through the low-pressure gas branch pipe 303, which is provided with the low-pressure valve 71 of the relay gas pipe 301, and the low-pressure gas main pipe 101, and flows into the first outdoor unit 2a. The refrigerant that has flowed into the first outdoor unit 2a passes through the accumulator 50 and is again drawn into the first compressor 10a.

[0087] The refrigerant drawn into the second compressor 10b is compressed by the second compressor 10b and discharged in a high-temperature, high-pressure gas state. The high-temperature, high-pressure gas refrigerant discharged from the second compressor 10b passes through the second heat exchanger-side flow switching device 21b and then through the second outdoor heat exchanger 30b. The refrigerant passing through the second outdoor heat exchanger 30b exchanges heat with outdoor air, condenses, and liquefies. The liquid refrigerant passes through the outdoor expansion valve 40, where it is reduced in pressure and expanded. The liquid refrigerant flows into the liquid main pipe 103 and joins the refrigerant flowing between the first outdoor unit 2a and the relay unit 3. The refrigerant flowing through the low-pressure gas main pipe 101 branches off from the refrigerant flowing between the first outdoor unit 2a and the relay unit 3 and flows into the second outdoor unit 2b. The refrigerant that has flowed into the second outdoor unit 2b passes through the accumulator 50 and is again sucked into the second compressor 10b.

[0088] Next, the liquid draining operation will be described. Figure 29 is a diagram for explaining the liquid draining operation of the air conditioning apparatus 1D according to Embodiment 5. In Figure 29, arrows indicate the direction of refrigerant flow. When performing the liquid draining operation, the control device 5 switches the heat exchanger-side flow switching device 21 to a direction that connects the compressor 10 and the outdoor heat exchanger 30. The control device 5 also opens the bypass valve 60, closes the high-pressure valve 72, and opens the low-pressure valve 71. Furthermore, the control device 5 opens the indoor expansion valve 90 and the outdoor expansion valve 40.

[0089] During liquid drainage operation, a main circuit and a bypass circuit are formed. Refrigerant flows through the main circuit in the same manner as in cooling operation. In the bypass circuit, high-temperature, high-pressure gas refrigerant discharged from the first compressor 10a passes through the high-pressure gas main pipe 102 and flows into the relay unit 3. The refrigerant that flows into the relay unit 3 passes through a portion of the high-pressure gas branch pipe 302 and the bypass pipe 305 equipped with the bypass valve 60, flows into the relay liquid pipe 304, and merges into the main circuit. As the refrigerant flows through the bypass circuit, the liquid refrigerant that had accumulated in the high-pressure gas main pipe 102 flows and merges into the main circuit. This eliminates liquid accumulation in the high-pressure gas main pipe 102. The flow of refrigerant to the indoor unit 4 is blocked, and the liquid refrigerant is stored within the indoor unit 4. Furthermore, the liquid refrigerant that merges into the main circuit passes through the indoor expansion valve 90 and the indoor heat exchanger 80 and is gasified. This prevents liquid from flowing back into the accumulator 50.

[0090] The refrigerant drawn into the second compressor 10b is compressed by the second compressor 10b and discharged in a high-temperature, high-pressure gas state. The high-temperature, high-pressure gas refrigerant discharged from the second compressor 10b passes through the second heat exchanger-side flow switching device 21b and then through the second outdoor heat exchanger 30b. The refrigerant passing through the second outdoor heat exchanger 30b exchanges heat with outdoor air, condenses, and liquefies. The liquid refrigerant passes through the outdoor expansion valve 40, where it is reduced in pressure and expanded. The liquid refrigerant flows into the liquid main pipe 103 and joins the refrigerant flowing between the first outdoor unit 2a and the relay unit 3. The refrigerant flowing through the low-pressure gas main pipe 101 branches off from the refrigerant flowing between the first outdoor unit 2a and the relay unit 3 and flows into the second outdoor unit 2b. The refrigerant that has flowed into the second outdoor unit 2b passes through the accumulator 50 and is again sucked into the second compressor 10b.

[0091] As described above, according to the fifth embodiment, similar to the first embodiment, the air conditioning apparatus 1D includes the bypass valve 60 provided in the bypass pipe 305. Therefore, in the air conditioning apparatus 1D of the fifth embodiment, the bypass valve 60 is opened during defrosting operation, and the flow of refrigerant to the indoor unit 4 is blocked, allowing high-temperature refrigerant to flow into the outdoor heat exchanger 30 while the refrigerant liquid remains in the indoor unit 4. In other words, in the defrosting operation of the air conditioning apparatus 1D of the present disclosure, liquid backflow is suppressed without utilizing the heat of the piping warmed by the high-temperature refrigerant gas during heating operation. Therefore, the air conditioning apparatus 1D of the fifth embodiment can continuously suppress liquid backflow into the accumulator 50 during defrosting operation. Furthermore, in the air conditioning apparatus 1D of the fifth embodiment, the high-pressure gas main pipe 102 and the liquid main pipe 103 do not cool during defrosting operation, allowing for an early return to heating mode.

[0092] Embodiment 6. Figure 30 is a refrigerant circuit diagram of an air conditioning apparatus 1E pertaining to embodiment 6. As shown in Figure 30, embodiment 6 differs from embodiment 2 in that it has a first outdoor unit 2a and a second outdoor unit 2b, as explained in embodiment 5. In embodiment 6, the same parts as in embodiment 2 are given the same reference numerals and explanations thereof will be omitted, and the explanation will focus on the differences from embodiment 2.

[0093] The second outdoor unit 2b has a second high-pressure pipe-side flow path switching device 22b. The second high-pressure pipe-side flow path switching device 22b switches between an orientation in which the high-pressure gas main pipe 102 is connected to the second compressor 10b and an orientation in which the high-pressure gas main pipe 102 is connected to the second accumulator 50b. In the following description, when there is no need to distinguish between the first high-pressure pipe-side flow path switching device 22a and the second high-pressure pipe-side flow path switching device 22b, they may be referred to as high-pressure pipe-side flow path switching devices 22.

[0094] The state of each device in each operating mode will be described. The refrigerant flow in Embodiment 6 differs from Embodiment 2 only in that, as described in Embodiment 5, the refrigerant flow between the first compressor 10a and the relay unit 3 and the refrigerant flow between the second compressor 10b and the relay unit 3 are parallel, and therefore will not be described here. First, heating operation will be described. FIG. 31 is a diagram illustrating the heating operation of the air conditioning apparatus 1E according to Embodiment 6. In FIG. 31 , arrows indicate the direction of refrigerant flow. When performing heating operation, the control device 5 switches the heat exchanger-side flow switching device 21 to connect the outdoor heat exchanger 30 and the accumulator 50, and switches the high-pressure pipe-side flow switching device 22 to connect the compressor 10 and the high-pressure gas main pipe 102. The control device 5 also closes the bypass valve 60, closes the low-pressure valve 71, and opens the high-pressure valve 72. Furthermore, the control device 5 opens the indoor expansion valve 90 and the outdoor expansion valve 40.

[0095] Next, the defrosting operation will be described. FIG. 32 is a diagram illustrating the defrosting operation of the air conditioning apparatus 1E according to Embodiment 6. In FIG. 32, arrows indicate the direction of refrigerant flow. When performing the defrosting operation, the control device 5 switches the heat exchanger-side flow switching device 21 to a direction connecting the outdoor heat exchanger 30 and the accumulator 50, and switches the high-pressure pipe-side flow switching device 22 to a direction connecting the compressor 10 and the high-pressure gas main pipe 102. The control device 5 also opens the bypass valve 60, closes the low-pressure valve 71, and opens the high-pressure valve 72. Furthermore, the control device 5 closes the indoor expansion valve 90 and opens the outdoor expansion valve 40.

[0096] Next, cooling operation will be described. Figure 33 is a diagram for explaining the cooling operation of the air conditioning apparatus 1E according to Embodiment 6. In Figure 33, arrows indicate the direction of refrigerant flow. When performing cooling operation, the control device 5 switches the heat exchanger-side flow switching device 21 to a direction connecting the compressor 10 and the outdoor heat exchanger 30, and switches the high-pressure pipe-side flow switching device 22 to a direction connecting the accumulator 50 and the high-pressure gas main pipe 102. The control device 5 also closes the bypass valve 60, closes the high-pressure valve 72, and opens the low-pressure valve 71. Furthermore, the control device 5 opens the indoor expansion valve 90 and the outdoor expansion valve 40.

[0097] Next, the liquid draining operation will be described. Figure 34 is a diagram for explaining the liquid draining operation of the air conditioning apparatus 1E according to Embodiment 6. In Figure 34, arrows indicate the direction of refrigerant flow. When performing the liquid draining operation, the control device 5 switches the heat exchanger-side flow switching device 21 to a direction connecting the compressor 10 and the outdoor heat exchanger 30, and switches the high-pressure pipe-side flow switching device 22 to a direction connecting the accumulator 50 and the high-pressure gas main pipe 102. The control device 5 also opens the bypass valve 60, closes the high-pressure valve 72, and opens the low-pressure valve 71. Furthermore, the control device 5 opens the indoor expansion valve 90 and the outdoor expansion valve 40.

[0098] As described above, according to the sixth embodiment, similar to the second embodiment, the air conditioning apparatus 1E includes the bypass valve 60 provided in the bypass pipe 305. Therefore, in the air conditioning apparatus 1E of the sixth embodiment, the bypass valve 60 is opened during defrosting operation, and the flow of refrigerant to the indoor unit 4 is blocked, allowing high-temperature refrigerant to flow into the outdoor heat exchanger 30 while the refrigerant liquid remains in the indoor unit 4. In other words, in the defrosting operation of the air conditioning apparatus 1E of the present disclosure, liquid backflow is suppressed without utilizing the heat of the piping warmed by the high-temperature refrigerant gas during heating operation. Therefore, the air conditioning apparatus 1E of the sixth embodiment can continuously suppress liquid backflow into the accumulator 50 during defrosting operation. Furthermore, in the air conditioning apparatus 1E of the sixth embodiment, the high-pressure gas main pipe 102 and the liquid main pipe 103 are not cooled during defrosting operation, allowing for an early return to heating mode.

[0099] Embodiment 7. Figure 35 is a refrigerant circuit diagram of an air conditioning apparatus 1F pertaining to embodiment 7. As shown in Figure 35, embodiment 7 differs from embodiment 3 in that it has a first outdoor unit 2a and a second outdoor unit 2b, as explained in embodiment 5. In embodiment 7, the same parts as in embodiment 3 are given the same reference numerals and explanations thereof will be omitted, and the explanation will focus on the differences from embodiment 3.

[0100] The state of each device in each operating mode will be described. Regarding the refrigerant flow in the seventh embodiment, as described in the fifth embodiment, the only difference from the third embodiment is that the refrigerant flow between the first compressor 10a and the relay unit 3 is parallel to the refrigerant flow between the second compressor 10b and the relay unit 3. Therefore, a description thereof will be omitted. Furthermore, the cooling operation and the liquid draining operation are the same as those in the fifth embodiment, and therefore a description thereof will be omitted. First, the heating operation will be described. FIG. 36 is a diagram illustrating the heating operation of the air conditioning apparatus 1F according to the seventh embodiment. In FIG. 36, the arrows indicate the direction of refrigerant flow. When performing the heating operation, the control device 5 switches the heat exchanger-side flow switching device 21 to connect the outdoor heat exchanger 30 and the accumulator 50. Furthermore, the control device 5 closes the bypass valve 60, closes the low-pressure valve 71, opens the high-pressure valve 72, and opens the intermediate-pressure valve 73. Furthermore, the control device 5 opens the indoor expansion valve 90 and the outdoor expansion valve 40.

[0101] Next, the defrosting operation will be described. FIG. 37 is a diagram for explaining the defrosting operation of the air conditioning apparatus 1F according to Embodiment 7. In FIG. 37 , arrows indicate the direction of refrigerant flow. When performing the defrosting operation, the control device 5 switches the heat exchanger-side flow switching device 21 to a direction that connects the outdoor heat exchanger 30 and the accumulator 50. The control device 5 also opens the bypass valve 60, closes the low-pressure valve 71, opens the high-pressure valve 72, and closes the intermediate-pressure valve 73. Furthermore, the control device 5 opens the indoor expansion valve 90 and the outdoor expansion valve 40. Note that the indoor expansion valve 90 may also be closed.

[0102] As described above, according to the seventh embodiment, similar to the third embodiment, the air conditioning apparatus 1F includes the bypass valve 60 provided in the bypass pipe 305. Therefore, in the air conditioning apparatus 1F of the seventh embodiment, the bypass valve 60 is opened during defrosting operation, and the flow of refrigerant to the indoor unit 4 is blocked, allowing high-temperature refrigerant to flow into the outdoor heat exchanger 30 while the refrigerant liquid remains in the indoor unit 4. In other words, in the defrosting operation of the air conditioning apparatus 1F of the present disclosure, liquid backflow is suppressed without utilizing the heat of the piping warmed by the high-temperature refrigerant gas during heating operation. Therefore, the air conditioning apparatus 1F of the seventh embodiment can continuously suppress liquid backflow into the accumulator 50 during defrosting operation. Furthermore, in the air conditioning apparatus 1F of the seventh embodiment, the high-pressure gas main pipe 102 and the liquid main pipe 103 do not cool during defrosting operation, allowing for an early return to heating operation.

[0103] Embodiment 8. Figure 38 is a refrigerant circuit diagram of an air conditioning apparatus 1G according to embodiment 8. As shown in Figure 38, embodiment 8 differs from embodiment 1 in that it has a first outdoor unit 2a and a second outdoor unit 2b, as explained in embodiment 5. In embodiment 8, the same parts as in embodiment 4 are given the same reference numerals and explanations thereof will be omitted, and the explanation will focus on the differences from embodiment 4.

[0104] The state of each device in each operation mode will be described. As described in the fifth embodiment, the refrigerant flow in the eighth embodiment differs from the fourth embodiment only in that the refrigerant flow between the first compressor 10a and the relay unit 3 and the refrigerant flow between the second compressor 10b and the relay unit 3 run parallel to each other. Therefore, a description thereof will be omitted. Furthermore, the cooling operation and the liquid draining operation are the same as those in the fifth embodiment, and therefore a description thereof will be omitted. First, the heating operation will be described. FIG. 39 is a diagram illustrating the heating operation of the air conditioning apparatus 1G according to the eighth embodiment. In FIG. 39, the arrows indicate the direction of refrigerant flow. When performing the heating operation, the control device 5 switches the heat exchanger-side flow switching device 21 to connect the outdoor heat exchanger 30 and the accumulator 50, and switches the high-pressure pipe-side flow switching device 22 to connect the compressor 10 and the high-pressure gas main pipe 102. The control device 5 also closes the bypass valve 60, closes the low-pressure valve 71, opens the high-pressure valve 72, and opens the intermediate-pressure valve 73. Furthermore, the control device 5 opens the indoor expansion valve 90 and the outdoor expansion valve 40.

[0105] Next, the defrosting operation will be described. FIG. 40 is a diagram illustrating the defrosting operation of the air conditioning apparatus 1G according to the eighth embodiment. In FIG. 40, arrows indicate the direction of refrigerant flow. When performing the defrosting operation, the control device 5 switches the heat exchanger-side flow switching device 21 to a direction connecting the outdoor heat exchanger 30 and the accumulator 50, and switches the high-pressure pipe-side flow switching device 22 to a direction connecting the compressor 10 and the high-pressure gas main pipe 102. The control device 5 also opens the bypass valve 60, closes the low-pressure valve 71, opens the high-pressure valve 72, and closes the intermediate-pressure valve 73. The control device 5 also opens the indoor expansion valve 90 and the outdoor expansion valve 40. Note that the indoor expansion valve 90 may be closed.

[0106] As described above, according to the eighth embodiment, similar to the fourth embodiment, the air conditioning apparatus 1G of the eighth embodiment includes the bypass valve 60 provided in the bypass pipe 305. Therefore, in the air conditioning apparatus 1G of the eighth embodiment, the bypass valve 60 is opened during defrosting operation, and the flow of refrigerant to the indoor unit 4 is blocked, allowing high-temperature refrigerant to flow into the outdoor heat exchanger 30 while the refrigerant liquid remains in the indoor unit 4. In other words, in the defrosting operation of the air conditioning apparatus 1G of the present disclosure, liquid backflow is suppressed without utilizing the heat of the piping warmed by the high-temperature refrigerant gas during heating operation. Therefore, the air conditioning apparatus 1G of the eighth embodiment can continuously suppress liquid backflow into the accumulator 50 during defrosting operation. Furthermore, in the air conditioning apparatus 1G of the eighth embodiment, the high-pressure gas main pipe 102 and the liquid main pipe 103 do not cool during defrosting operation, allowing for an early return to heating mode.

[0107] The above is a description of the embodiments of the present disclosure. However, the present disclosure is not limited to the configurations of the above embodiments and various modifications and combinations are possible within the scope of the technical concept. For example, the liquid draining operation may be performed not only based on the measurement results of the liquid pool detection device 8 but also at predetermined time intervals. Alternatively, instead of performing the liquid draining operation based on the measurement results of the liquid pool detection device 8, the liquid draining operation may be performed at predetermined time intervals. Furthermore, although an example has been described in which all indoor units 4 perform heating and cooling operations, simultaneous heating and cooling operation may be performed in which one indoor unit 4 performs cooling operation and the other indoor unit 4 performs heating operation. Furthermore, although the present disclosure has been described in which a defrosting operation is performed after heating operation and a liquid draining operation is performed after cooling operation, the order of the operating modes is not limited to this.

[0108] 1 Air conditioner, 1A Air conditioner, 1B Air conditioner, 1C Air conditioner, 1D Air conditioner, 1E Air conditioner, 1F Air conditioner, 1G Air conditioner, 2 Outdoor unit, 2a First outdoor unit, 2b Second outdoor unit, 3 Relay unit, 4 Indoor unit, 4a First indoor unit, 4b Second indoor unit, 5 Control device, 6 Frost detection device, 7 Defrost detection device, 8 Liquid accumulation detection device, 10 Compressor, 10a First compressor, 10b Second compressor, 21 Heat exchanger side flow path switching device, 21a First heat exchanger side flow path switching device, 21b Second heat exchanger side flow path switching device, 22 High-pressure pipe side flow path switching device, 22a First high-pressure pipe side flow path switching device, 22b Second high-pressure pipe side flow path switching device, 30 Outdoor heat exchanger, 30a First outdoor heat exchanger, 30b Second outdoor heat exchanger, 40 Outdoor expansion valve, 40a First outdoor expansion valve, 40b Second outdoor expansion valve, 50 Accumulator, 50a First accumulator, 50b Second accumulator, 60 Bypass valve, 71 Low pressure valve, 71a First low pressure valve, 71b Second low pressure valve, 72 High pressure valve, 72a First high pressure valve, 72b Second high pressure valve, 73 Intermediate pressure valve, 73a First intermediate pressure valve, 73b Second intermediate pressure valve, 80 Indoor heat exchanger, 80a First indoor heat exchanger, 80b Second indoor heat exchanger, 90 Indoor expansion valve, 90a First indoor expansion valve, 90b Second indoor expansion valve, 101 Low pressure gas main pipe, 102 High pressure gas main pipe, 103 Liquid main pipe, 104 Gas branch pipe, 104a First gas branch pipe, 104b Second gas branch pipe, 105 liquid branch pipe, 105a first liquid branch pipe, 105b second liquid branch pipe, 201 outdoor pipe, 202 outdoor pipe, 203 outdoor pipe, 204 outdoor pipe, 205 outdoor pipe, 206 suction pipe, 207 discharge pipe, 301 relay gas pipe, 302 high-pressure gas branch pipe, 303 low-pressure gas branch pipe, 304 relay liquid pipe, 305 bypass pipe, 401a first indoor pipe, 401b second indoor pipe, 501 processing circuit, 502 processor, 503 memory, 504 bus.

Claims

1. an outdoor unit having a compressor that compresses a refrigerant, an accumulator that stores the refrigerant, an outdoor heat exchanger that exchanges heat between the refrigerant and air, an outdoor expansion valve that expands the refrigerant, and a heat exchanger side flow path switching device that switches between a direction in which the outdoor heat exchanger and the compressor are connected and a direction in which the outdoor heat exchanger and the accumulator are connected; an indoor unit having an indoor heat exchanger that exchanges heat between a refrigerant and air and an indoor expansion valve that expands the refrigerant; A relay unit that relays or blocks the flow of a refrigerant between the outdoor unit and the indoor unit; A control device that controls the execution of a cooling operation and a heating operation, The outdoor unit and the relay unit are connected by a low-pressure gas main pipe through which a gas refrigerant flows, a high-pressure gas main pipe through which a gas refrigerant having a higher pressure than the gas refrigerant flowing through the low-pressure gas main pipe flows, and a liquid main pipe through which a liquid refrigerant flows, The relay unit and the indoor unit are connected by a gas branch pipe through which a gas refrigerant flows and a liquid branch pipe through which a liquid refrigerant flows, The repeater is a relay gas pipe that connects the gas branch pipe to the high-pressure gas main pipe and the low-pressure gas main pipe, the relay gas pipe having a high-pressure gas branch pipe that is connected to the high-pressure gas main pipe and a low-pressure gas branch pipe that is connected to the low-pressure gas main pipe; a relay liquid pipe connecting the main liquid pipe and the branch liquid pipe; a bypass pipe connecting the high-pressure gas branch pipe and the relay liquid pipe; a bypass valve provided in the bypass pipe and having a function of switching between an open state in which the refrigerant flows through the bypass pipe and a closed state in which the refrigerant flows through the bypass pipe; a high-pressure valve provided in the high-pressure gas branch pipe and having a function of switching between an open state that allows the flow of the refrigerant through the high-pressure gas branch pipe and a closed state that blocks the flow of the refrigerant through the high-pressure gas branch pipe; a low pressure valve provided in the low pressure gas branch pipe and having a function of switching between an open state in which the refrigerant flows through the low pressure gas branch pipe and a closed state in which the refrigerant flows through the low pressure gas branch pipe, The control device includes: Controlling execution of a defrosting operation for removing frost on the outdoor heat exchanger during the heating operation; In the defrosting operation, The heat exchange side flow switching device is controlled to an orientation in which the outdoor heat exchanger and the accumulator are connected, The bypass valve is opened, The outdoor expansion valve is opened, The indoor expansion valve is closed. The low pressure valve is closed. Air conditioning units.

2. An outdoor unit having a compressor that compresses a refrigerant, an accumulator that stores the refrigerant, an outdoor heat exchanger that exchanges heat between the refrigerant and air, an outdoor expansion valve that expands the refrigerant, and a heat exchange side flow path switching device that switches between a direction in which the outdoor heat exchanger and the compressor are connected and a direction in which the outdoor heat exchanger and the accumulator are connected; an indoor unit having an indoor heat exchanger that exchanges heat between a refrigerant and air and an indoor expansion valve that expands the refrigerant; A relay unit that relays or blocks the flow of a refrigerant between the outdoor unit and the indoor unit; A control device that controls the execution of a cooling operation and a heating operation, The outdoor unit and the relay unit are connected by a low-pressure gas main pipe through which a gas refrigerant flows, a high-pressure gas main pipe through which a gas refrigerant having a higher pressure than the gas refrigerant flowing through the low-pressure gas main pipe flows, and a liquid main pipe through which a liquid refrigerant flows, The relay unit and the indoor unit are connected by a gas branch pipe through which a gas refrigerant flows and a liquid branch pipe through which a liquid refrigerant flows, The outdoor unit is Further comprising a high-pressure pipe side flow path switching device that switches between an orientation in which the high-pressure gas main pipe and the compressor are connected and an orientation in which the high-pressure gas main pipe and the accumulator are connected, The repeater is a relay gas pipe that connects the gas branch pipe to the high-pressure gas main pipe and the low-pressure gas main pipe, the relay gas pipe having a high-pressure gas branch pipe that is connected to the high-pressure gas main pipe and a low-pressure gas branch pipe that is connected to the low-pressure gas main pipe; a relay liquid pipe connecting the main liquid pipe and the branch liquid pipe; a bypass pipe connecting the high-pressure gas branch pipe and the relay liquid pipe; a bypass valve provided in the bypass pipe and having a function of switching between an open state in which the refrigerant flows through the bypass pipe and a closed state in which the refrigerant flows through the bypass pipe; a high-pressure valve provided in the high-pressure gas branch pipe and having a function of switching between an open state that allows the flow of the refrigerant through the high-pressure gas branch pipe and a closed state that blocks the flow of the refrigerant through the high-pressure gas branch pipe; a low pressure valve provided in the low pressure gas branch pipe and having a function of switching between an open state in which the refrigerant flows through the low pressure gas branch pipe and a closed state in which the refrigerant flows through the low pressure gas branch pipe, The control device includes: Controlling execution of a defrosting operation for removing frost on the outdoor heat exchanger during the heating operation; In the defrosting operation, The heat exchange side flow switching device is controlled to an orientation in which the outdoor heat exchanger and the accumulator are connected, The high-pressure pipe side flow path switching device is controlled to an orientation in which the high-pressure gas main pipe and the compressor are connected, The bypass valve is opened, The outdoor expansion valve is opened, The indoor expansion valve is closed. The low pressure valve is closed. Air conditioning equipment.

3. An outdoor unit having a compressor that compresses a refrigerant, an accumulator that stores the refrigerant, an outdoor heat exchanger that exchanges heat between the refrigerant and air, an outdoor expansion valve that expands the refrigerant, and a heat exchange side flow path switching device that switches between a direction in which the outdoor heat exchanger and the compressor are connected and a direction in which the outdoor heat exchanger and the accumulator are connected; an indoor unit having an indoor heat exchanger that exchanges heat between a refrigerant and air and an indoor expansion valve that expands the refrigerant; A relay unit that relays or blocks the flow of a refrigerant between the outdoor unit and the indoor unit; A control device that controls the execution of a cooling operation and a heating operation, The outdoor unit and the relay unit are connected by a low-pressure gas main pipe through which a gas refrigerant flows, a high-pressure gas main pipe through which a gas refrigerant having a higher pressure than the gas refrigerant flowing through the low-pressure gas main pipe flows, and a liquid main pipe through which a liquid refrigerant flows, The relay unit and the indoor unit are connected by a gas branch pipe through which a gas refrigerant flows and a liquid branch pipe through which a liquid refrigerant flows, The repeater is a relay gas pipe that connects the gas branch pipe to the high-pressure gas main pipe and the low-pressure gas main pipe, the relay gas pipe having a high-pressure gas branch pipe that is connected to the high-pressure gas main pipe and a low-pressure gas branch pipe that is connected to the low-pressure gas main pipe; a relay liquid pipe connecting the main liquid pipe and the branch liquid pipe; a bypass pipe connecting the high-pressure gas branch pipe and the relay liquid pipe; a bypass valve provided in the bypass pipe and having a function of switching between an open state in which the refrigerant flows through the bypass pipe and a closed state in which the refrigerant flows through the bypass pipe; a high-pressure valve provided in the high-pressure gas branch pipe and having a function of switching between an open state that allows the flow of the refrigerant through the high-pressure gas branch pipe and a closed state that blocks the flow of the refrigerant through the high-pressure gas branch pipe; a low pressure valve provided in the low pressure gas branch pipe and having a function of switching between an open state that allows the refrigerant to flow through the low pressure gas branch pipe and a closed state that blocks the refrigerant from flowing through the low pressure gas branch pipe; a medium pressure valve provided in the relay liquid pipe between a connection portion of the bypass pipe and a connection portion of the liquid branch pipe, the medium pressure valve having a function of switching between an open state that allows the refrigerant to flow through the relay liquid pipe and a closed state that blocks the refrigerant from flowing through the relay liquid pipe. Air conditioning equipment.

4. An outdoor unit having a compressor that compresses a refrigerant, an accumulator that stores the refrigerant, an outdoor heat exchanger that exchanges heat between the refrigerant and air, an outdoor expansion valve that expands the refrigerant, and a heat exchange side flow path switching device that switches between a direction in which the outdoor heat exchanger and the compressor are connected and a direction in which the outdoor heat exchanger and the accumulator are connected; an indoor unit having an indoor heat exchanger that exchanges heat between a refrigerant and air and an indoor expansion valve that expands the refrigerant; A relay unit that relays or blocks the flow of a refrigerant between the outdoor unit and the indoor unit; A control device that controls the execution of a cooling operation and a heating operation, The outdoor unit and the relay unit are connected by a low-pressure gas main pipe through which a gas refrigerant flows, a high-pressure gas main pipe through which a gas refrigerant having a higher pressure than the gas refrigerant flowing through the low-pressure gas main pipe flows, and a liquid main pipe through which a liquid refrigerant flows, The relay unit and the indoor unit are connected by a gas branch pipe through which a gas refrigerant flows and a liquid branch pipe through which a liquid refrigerant flows, The repeater is a relay gas pipe that connects the gas branch pipe to the high-pressure gas main pipe and the low-pressure gas main pipe, the relay gas pipe having a high-pressure gas branch pipe that is connected to the high-pressure gas main pipe and a low-pressure gas branch pipe that is connected to the low-pressure gas main pipe; a relay liquid pipe connecting the main liquid pipe and the branch liquid pipe; a bypass pipe connecting the high-pressure gas branch pipe and the relay liquid pipe; a bypass valve provided in the bypass pipe and having a function of switching between an open state in which the refrigerant flows through the bypass pipe and a closed state in which the refrigerant flows through the bypass pipe; a high-pressure valve provided in the high-pressure gas branch pipe and having a function of switching between an open state that allows the flow of the refrigerant through the high-pressure gas branch pipe and a closed state that blocks the flow of the refrigerant through the high-pressure gas branch pipe; a low pressure valve provided in the low pressure gas branch pipe and having a function of switching between an open state in which the refrigerant flows through the low pressure gas branch pipe and a closed state in which the refrigerant flows through the low pressure gas branch pipe, The control device includes: In the cooling operation, the high-pressure valve is closed, When liquid accumulation in the high-pressure gas main pipe is detected during the cooling operation, the bypass valve is opened to perform a liquid draining operation for draining the liquid accumulated in the high-pressure gas main pipe. Air conditioning equipment.

5. An outdoor unit having a compressor that compresses a refrigerant, an accumulator that stores the refrigerant, an outdoor heat exchanger that exchanges heat between the refrigerant and air, an outdoor expansion valve that expands the refrigerant, and a heat exchange side flow path switching device that switches between a direction in which the outdoor heat exchanger and the compressor are connected and a direction in which the outdoor heat exchanger and the accumulator are connected; an indoor unit having an indoor heat exchanger that exchanges heat between a refrigerant and air and an indoor expansion valve that expands the refrigerant; A relay unit that relays or blocks the flow of a refrigerant between the outdoor unit and the indoor unit; A control device that controls the execution of a cooling operation and a heating operation, The outdoor unit and the relay unit are connected by a low-pressure gas main pipe through which a gas refrigerant flows, a high-pressure gas main pipe through which a gas refrigerant having a higher pressure than the gas refrigerant flowing through the low-pressure gas main pipe flows, and a liquid main pipe through which a liquid refrigerant flows, The relay unit and the indoor unit are connected by a gas branch pipe through which a gas refrigerant flows and a liquid branch pipe through which a liquid refrigerant flows, The repeater is a relay gas pipe that connects the gas branch pipe to the high-pressure gas main pipe and the low-pressure gas main pipe, the relay gas pipe having a high-pressure gas branch pipe that is connected to the high-pressure gas main pipe and a low-pressure gas branch pipe that is connected to the low-pressure gas main pipe; a relay liquid pipe connecting the main liquid pipe and the branch liquid pipe; a bypass pipe connecting the high-pressure gas branch pipe and the relay liquid pipe; a bypass valve provided in the bypass pipe and having a function of switching between an open state in which the refrigerant flows through the bypass pipe and a closed state in which the refrigerant flows through the bypass pipe; a high-pressure valve provided in the high-pressure gas branch pipe and having a function of switching between an open state that allows the flow of the refrigerant through the high-pressure gas branch pipe and a closed state that blocks the flow of the refrigerant through the high-pressure gas branch pipe; a low pressure valve provided in the low pressure gas branch pipe and having a function of switching between an open state in which the refrigerant flows through the low pressure gas branch pipe and a closed state in which the refrigerant flows through the low pressure gas branch pipe, The control device includes: During the cooling operation, the high-pressure valve is closed, and the bypass valve is opened at predetermined time intervals to perform a liquid draining operation for draining the liquid accumulated in the high-pressure gas main pipe. Air conditioning equipment.

6. When all of the indoor units are performing the heating operation, the refrigerant circulates in the order of the compressor, the high-pressure valve, the indoor heat exchanger, the indoor expansion valve, the outdoor expansion valve, the outdoor heat exchanger, the heat exchange side flow switching device, and the accumulator, When all of the indoor units are performing the cooling operation, the refrigerant circulates in the order of the compressor, the heat exchanger side flow switching device, the outdoor heat exchanger, the outdoor expansion valve, the indoor expansion valve, the indoor heat exchanger, the low pressure valve, and the accumulator. An air conditioning apparatus according to any one of claims 1 or 3 to 5.

7. The outdoor unit further includes a high-pressure pipe side flow path switching device that switches between an orientation in which the high-pressure gas main pipe and the compressor are connected and an orientation in which the high-pressure gas main pipe and the accumulator are connected. The air conditioner according to any one of claims 3 to 5.

8. When all of the indoor units are performing the heating operation, the refrigerant circulates in the order of the compressor, the high-pressure pipe side flow switching device, the high-pressure valve, the indoor heat exchanger, the indoor expansion valve, the outdoor expansion valve, the outdoor heat exchanger, the heat exchange side flow switching device, and the accumulator, When all of the indoor units are performing the cooling operation, the refrigerant circulates in the order of the compressor, the heat exchanger side flow switching device, the outdoor heat exchanger, the outdoor expansion valve, the indoor expansion valve, the indoor heat exchanger, the low pressure valve, and the accumulator. The air conditioning apparatus according to claim 7.

9. The control device includes: Controlling execution of a defrosting operation for removing frost on the outdoor heat exchanger during the heating operation; In the defrosting operation, The heat exchange side flow switching device is controlled to an orientation in which the outdoor heat exchanger and the accumulator are connected, The bypass valve is opened, The outdoor expansion valve is opened, The medium pressure valve is closed, The low pressure valve is closed. The air conditioning apparatus according to claim 3.

10. The outdoor unit further has a high-pressure pipe side flow path switching device that switches between an orientation in which the high-pressure gas main pipe and the compressor are connected and an orientation in which the high-pressure gas main pipe and the accumulator are connected; The control device includes: Controlling execution of a defrosting operation for removing frost on the outdoor heat exchanger during the heating operation; In the defrosting operation, The heat exchange side flow switching device is controlled to an orientation in which the outdoor heat exchanger and the accumulator are connected, The high-pressure pipe side flow path switching device is controlled to a direction in which the high-pressure gas main pipe and the compressor are connected, The bypass valve is opened, The outdoor expansion valve is opened, The medium pressure valve is closed, The low pressure valve is closed.

4. The air conditioning system according to claim 3.

11. The control device includes: In the cooling operation, the high-pressure valve is closed.

3. An air conditioning apparatus according to claim 1 or 2.