Air conditioner and control method

Abstract

An air conditioner (1) comprises: an outdoor unit (200); an indoor unit (300); a liquid extension pipe (23) and a gas extension pipe (24) that connect the outdoor unit (200) and the indoor unit (300); and a control device (100). The outdoor unit (200) is provided with: a bypass valve (78) for opening or closing communication between the discharge side of a compressor (30) and the inflow side of an accumulator (70); and an injection port (79) for injecting liquid refrigerant into the accumulator (70). The control device (100) executes a first injection process for injecting the liquid refrigerant from the injection port (79) by opening the bypass valve (78) and opening the injection port (79) in a state in which the compressor (30) is operating.

Description

Air conditioner and control method

[0001] This disclosure relates to an air conditioner and a control method for controlling an air conditioner.

[0002] An air conditioner is configured to cool or heat a room by circulating a refrigerant between the outdoor unit and the indoor unit. A type of air conditioner known as a replacement multi-precharge unit comes with the outdoor unit pre-filled with refrigerant. When installing a replacement multi-precharge unit, the worker uses an automatic filling function to fill the outdoor unit with liquid refrigerant.

[0003] However, if liquid refrigerant is stored in the accumulator and then filled into the outdoor unit, the filling may be completed before the liquid refrigerant has completely flowed out of the accumulator, resulting in overfilling. In this regard, Japanese Patent Publication No. 2015-537186 ​​(Patent Document 1) and Japanese Patent Publication No. 2016-525666 (Patent Document 2) disclose a method in which the liquid refrigerant stored in the accumulator is evaporated and allowed to flow out of the accumulator before the liquid refrigerant is filled into the outdoor unit.

[0004] Special table 2015-537186 ​​publication Special table 2016-525666 publication

[0005] While the technology disclosed in Japanese Patent Publication No. 2015-537186 ​​and Japanese Patent Publication No. 2016-525666 can avoid overfilling with liquid refrigerant, it requires time to completely drain the liquid refrigerant from the accumulator, making it difficult for workers to efficiently fill the outdoor unit with liquid refrigerant. Therefore, there is a need for a technology that enables workers to efficiently fill the outdoor unit with liquid refrigerant.

[0006] This disclosure was made to solve the above-mentioned problems and aims to provide a technology that enables workers to efficiently fill outdoor units with liquid refrigerant in a short amount of time.

[0007] The air conditioner according to this disclosure comprises an outdoor unit equipped with a compressor, a condenser, and an accumulator; at least one indoor unit equipped with an expansion device and an evaporator; a liquid extension pipe connecting the outdoor unit and at least one indoor unit and allowing liquid refrigerant to pass through; a gas extension pipe connecting the outdoor unit and at least one indoor unit and allowing gaseous refrigerant to pass through; and a control device. In the path from the gas extension pipe of the outdoor unit to the liquid extension pipe, the accumulator, compressor, and condenser are connected in order. In the path from the liquid extension pipe of at least one indoor unit to the gas extension pipe, the expansion device and evaporator are connected in order. The outdoor unit further comprises a bypass valve for opening or closing the connection between the discharge side of the compressor and the inlet side of the accumulator, and an injection port for injecting liquid refrigerant into the accumulator. The control device performs a first injection process in which liquid refrigerant is injected from the injection port by opening the bypass valve and the injection port while the compressor is running.

[0008] The control method relating to this disclosure is a control method for controlling an air conditioner. The air conditioner comprises an outdoor unit equipped with a compressor, a condenser, and an accumulator; at least one indoor unit equipped with an expansion device and an evaporator; a liquid extension pipe connecting the outdoor unit and at least one indoor unit and allowing liquid refrigerant to pass through; and a gas extension pipe connecting the outdoor unit and at least one indoor unit and allowing gaseous refrigerant to pass through. In the path from the gas extension pipe of the outdoor unit to the liquid extension pipe, the accumulator, compressor, and condenser are connected in order. In the path from the liquid extension pipe of at least one indoor unit to the gas extension pipe, the expansion device and evaporator are connected in order. The outdoor unit further comprises a bypass valve for opening or closing the connection between the discharge side of the compressor and the inlet side of the accumulator, and an injection port for injecting liquid refrigerant into the accumulator. The control method includes, as a process executed by a computer, the steps of: estimating the amount of liquid refrigerant by opening the bypass valve and closing the injection port while the compressor is running; and injecting the amount of liquid refrigerant estimated in the estimation step by opening the bypass valve and the injection port while the compressor is running.

[0009] According to this disclosure, in an air conditioner, by opening the connection between the discharge side of the compressor and the inlet side of the accumulator with a bypass valve while the compressor is running, the liquid refrigerant stored in the accumulator can be evaporated by the high-temperature, high-pressure gaseous refrigerant from the compressor and allowed to flow out of the accumulator, while liquid refrigerant can be injected through the opened injection port. This allows workers to efficiently fill the outdoor unit with liquid refrigerant in a short amount of time.

[0010] This is a diagram showing the configuration of an air conditioning system according to an embodiment. This is a diagram showing the configuration of an air conditioner. This is a diagram illustrating the opening and closing of the bypass valve, the opening and closing of the injection port, and the number of indoor units in operation during the refrigerant charging process performed by the air conditioner. This is a timing chart illustrating the change in the amount of liquid refrigerant present in each component during the refrigerant charging process performed by the air conditioner. This is a diagram showing the distribution of liquid refrigerant at the time the air conditioner estimates the amount of additional refrigerant. This is a diagram showing the distribution of liquid refrigerant in the optimal state. This is a flowchart illustrating the refrigerant charging process performed by the air conditioner.

[0011] The embodiments of this disclosure will be described in detail below with reference to the drawings. While multiple embodiments will be described below, it has been intended from the outset that the configurations described in each embodiment may be combined as appropriate. In the drawings, the same or corresponding parts are denoted by the same reference numerals, and their descriptions will not be repeated.

[0012] [Configuration of the Air Conditioning System and Air Conditioner] The configuration of the air conditioning system 1000 according to the embodiment and the air conditioner 1 provided in the air conditioning system 1000 will be described with reference to Figures 1 and 2. Figure 1 is a diagram showing the configuration of the air conditioning system 1000 according to the embodiment. Note that Figure 1 functionally shows the connection relationships and arrangement of each component in the air conditioning system 1000 and does not necessarily show the arrangement in physical space. As shown in Figure 1, the air conditioning system 1000 includes an air conditioner 1 and a user device 500.

[0013] The user device 500 is configured to communicate with the air conditioner 1 via a network. The user device 500 is an information terminal used by a user, such as a worker. The user device 500 may be implemented as a general-purpose computer or as a dedicated computer for controlling the air conditioner 1. For example, the user device 500 may be an information terminal that performs predetermined information processing, such as a desktop PC (personal computer), a laptop PC, a smartphone, a smartwatch, a wearable device, a tablet PC, or a remote controller installed in a building. The worker may be able to control the air conditioner 1 using the user device 500, or they may be able to view data acquired from the air conditioner 1 on a display (not shown) provided by the user device 500.

[0014] The air conditioner 1 comprises a control device 100, an outdoor unit 200, and at least one indoor unit 300.

[0015] The air conditioner 1 adjusts the temperature and humidity of the air drawn in from the indoor space by circulating a refrigerant between the outdoor unit 200 and each of at least one indoor unit 300, and supplies the adjusted air to the indoor space. In the example in Figure 1, three indoor units 300A, 300B, and 300C are exemplified as at least one indoor unit 300. Hereafter, indoor units 300A, 300B, and 300C will be collectively referred to as "indoor unit 300". In the air conditioner 1, multiple indoor units 300 may be connected to one outdoor unit 200, or one indoor unit 300 may be connected to one outdoor unit 200.

[0016] Figure 2 shows the specific configuration of the air conditioner 1. Although only indoor unit 300A is shown in Figure 2 among the multiple indoor units 300 connected to the outdoor unit 200, the other indoor units 300B and 300C have the same configuration as indoor unit 300A.

[0017] As shown in Figure 2, the air conditioner 1 includes a refrigerant circuit 400 that includes an outdoor unit 200 and an indoor unit 300, and a control device 100 that controls the refrigerant circuit 400. In the path through which liquid refrigerant mainly passes in the refrigerant circuit 400, the outdoor unit 200 and the indoor unit 300 are connected via a valve 76 and a liquid extension pipe 23. In the path through which gaseous refrigerant (gaseous refrigerant) mainly passes in the refrigerant circuit 400, the outdoor unit 200 and the indoor unit 300 are connected via a valve 77 and a gas extension pipe 24.

[0018] Each of the valves 76 and 77 opens or closes the gap between the outdoor unit 200 and the indoor unit 300 according to the control of the control device 100.

[0019] The liquid extension pipe 23 connects the outdoor unit 200 and the indoor unit 300, allowing the liquid refrigerant flowing out of the outdoor unit 200 to pass through and into the indoor unit 300. The liquid refrigerant that flows out of the outdoor unit 200 and passes through the liquid extension pipe 23 flows into each indoor unit 300 via pipes (not shown) branching off from the liquid extension pipe 23.

[0020] The gas extension pipe 24 connects the outdoor unit 200 and the indoor unit 300, allowing the refrigerant gas flowing out of the indoor unit 300 to pass through and flow into the outdoor unit 200. The refrigerant gas flowing out of each indoor unit 300 flows into the outdoor unit 200 via piping (not shown) branching off from the gas extension pipe 24.

[0021] The outdoor unit 200 is generally installed outdoors, not in an area that is subject to air conditioning, and includes a four-way valve 40, a compressor 30, an outdoor heat exchanger 50, an outdoor fan 51, an expansion device 71, an accumulator 70, and a heat exchange circuit 22.

[0022] The four-way valve 40 includes a connection port 41, a connection port 42, a connection port 43, and a connection port 44. The connection port 41 of the four-way valve 40 is connected to the inflow side of the accumulator 70 via the pipe 19. The connection port 42 of the four-way valve 40 is connected to the outdoor heat exchanger 50 via the pipe 12. The connection port 43 of the four-way valve 40 is connected to the discharge port 32 of the compressor 30 via the pipe 11. The connection port 44 of the four-way valve 40 is connected to the indoor unit 300 via the pipes 18 and the gas extension pipe 24. The four-way valve 40 is configured to switch the internal communication state according to the control of the control device 100.

[0023] The compressor 30 is configured to operate and stop, and further change the rotational speed during operation according to the control of the control device 100. The control device 100 controls the compressor 30 to arbitrarily change the drive frequency of the compressor 30. The compressor 30 changes the number of rotations per unit time, that is, the rotational speed, according to the change in the drive frequency, thereby changing the discharge amount of the refrigerant. Various types of compressors 30 can be adopted, for example, a scroll type, a rotary type, a screw type, etc. can be adopted as the compressor 30.

[0024] The outdoor heat exchanger 50 performs heat exchange between the air sucked from the outside, that is, the outside air, and the refrigerant by the outdoor fan 51. One end side of the outdoor heat exchanger 50 is connected to the connection port 42 of the four-way valve 40 via the pipe 12. The other end side of the outdoor heat exchanger 50 is connected to the expansion device 71 via the pipe 13.

[0025] The outdoor fan 51 is configured to operate and stop, and further change the rotational speed during operation according to the control of the control device 100. The control device 100 controls the outdoor fan 51 to arbitrarily change the drive frequency of the outdoor fan 51. The outdoor fan 51 changes the number of rotations per unit time, that is, the rotational speed, according to the change in the drive frequency, thereby changing the amount of air sent to the outdoor heat exchanger 50.

[0026] The expansion device 71 is, for example, an electronic expansion valve whose opening degree is adjusted according to the control of the control device 100. The expansion device 71 reduces the pressure of the flowing-in refrigerant and allows the refrigerant obtained by decompression to flow out. The control device 100 can adjust the decompression amount of the refrigerant by adjusting the opening degree of the expansion device 71. Note that the expansion device 71 is not limited to an electronic expansion valve and may be a capillary tube. One end side of the expansion device 71 is connected to the outdoor heat exchanger 50 via the pipe 13. The other end side of the expansion device 71 is connected to the indoor unit 300 via the pipe 14 and the liquid extension pipe 23.

[0027] The accumulator 70 stores the liquid refrigerant in the lower part of a container (not shown) among the refrigerants flowing in via the pipe 19, while retaining the gas refrigerant in the upper part of the container, thereby separating the refrigerants flowing through the refrigerant circuit 400 into liquid refrigerant and gas refrigerant. One end side of the accumulator 70 is connected to the connection port 41 of the four-way valve 40 via the pipe 19. The other end side of the accumulator 70 is connected to the suction port 31 of the compressor 30 via the pipe 20. Hereinafter, the accumulator (Accumulator) 70 is also abbreviated as "ACC".

[0028] The heat exchange circuit 22 performs heat exchange between a part of the refrigerant flowing toward the inflow side of the accumulator 70 and the refrigerant flowing out from the expansion device 71 and flowing through the pipe 14. In the heat exchange circuit 22, the pipe 21 branched from the pipe 19 passes through, and the pipe 14 passes through in parallel with the pipe 21. That is, the heat exchange circuit 22 performs heat exchange between the refrigerant flowing through the pipe 21 and the refrigerant flowing through the pipe 14.

[0029] The refrigerant that has undergone heat exchange in the heat exchange circuit 22 flows out into the piping 14 via the expansion device 72. The expansion device 72 is, for example, an electronic expansion valve whose opening degree is adjusted according to the control of the control device 100. The expansion device 72 reduces the pressure of the incoming refrigerant and discharges the refrigerant obtained by the pressure reduction. The control device 100 can adjust the amount of refrigerant pressure reduction by adjusting the opening degree of the expansion device 72. Note that the expansion device 72 is not limited to an electronic expansion valve, but may also be a capillary tube. One end of the expansion device 72 is connected to the piping 21 that passes through the heat exchange circuit 22. The other end of the expansion device 72 is connected to the piping 14 that passes through the heat exchange circuit 22.

[0030] The indoor unit 300 is generally installed in an indoor space that is to be air-conditioned, and includes an expansion device 73, an indoor heat exchanger 60, and an indoor fan 61.

[0031] The expansion device 73 is, for example, an electronic expansion valve whose opening degree is adjusted according to the control of the control device 100. The expansion device 73 reduces the pressure of the incoming refrigerant and discharges the refrigerant obtained by the pressure reduction. The control device 100 can adjust the amount of refrigerant pressure reduction by adjusting the opening degree of the expansion device 73. Note that the expansion device 73 is not limited to an electronic expansion valve, but may also be a capillary tube. One end of the expansion device 73 is connected to the outdoor unit 200 via piping 15 and liquid extension piping 23. The other end of the expansion device 73 is connected to the indoor heat exchanger 60 via piping 16.

[0032] The indoor heat exchanger 60 performs heat exchange between the air drawn in from the room by the indoor fan 61 and the refrigerant. One end of the indoor heat exchanger 60 is connected to the expansion device 73 via piping 16. The other end of the indoor heat exchanger 60 is connected to the outdoor unit 200 via piping 17 and gas extension piping 24.

[0033] The indoor fan 61 is configured to operate and stop, and to change its rotational speed when operating, according to the control of the control device 100. The control device 100 controls the indoor fan 61 to arbitrarily change its drive frequency. The indoor fan 61 changes its rotational speed, i.e., the number of rotations per unit time, in accordance with the change in drive frequency, thereby changing the amount of air sent to the indoor heat exchanger 60.

[0034] The air conditioner 1 configured as described above is controlled to one of several operating modes, including a cooling operation mode for cooling the indoor space and a heating operation mode for heating the indoor space.

[0035] First, let's explain the operation of the air conditioner 1 in cooling mode. As shown by the solid line in Figure 1, in cooling mode, the internal communication state of the four-way valve 40 is such that connection port 41 communicates with connection port 44, and connection port 42 communicates with connection port 43. In other words, in cooling mode, the intake port 31 of the compressor 30 is connected to the indoor heat exchanger 60 side, and the discharge port 32 of the compressor 30 is connected to the outdoor heat exchanger 50 side.

[0036] The compressor 30 draws in the low-temperature, low-pressure gaseous refrigerant stored in the accumulator 70 and increases the pressure of the gaseous refrigerant by compressing it. The compressor 30 then discharges the high-temperature, high-pressure gaseous refrigerant obtained by compression to the outdoor heat exchanger 50.

[0037] In cooling operation mode, the outdoor heat exchanger 50 acts as a condenser. The outdoor heat exchanger 50 exchanges heat between the high-temperature, high-pressure gaseous refrigerant from the compressor 30 and the air drawn in from outside by the outdoor fan 51. The gaseous refrigerant that has released heat into the air through this heat exchange condenses inside the outdoor heat exchanger 50, changing into a high-temperature, high-pressure liquid refrigerant. The high-temperature, high-pressure liquid refrigerant obtained by the outdoor heat exchanger 50 flows out to the expansion device 71.

[0038] The expansion device 71 reduces the pressure of the high-temperature, high-pressure liquid refrigerant from the outdoor heat exchanger 50. The low-temperature, low-pressure gas-liquid two-phase refrigerant obtained by the pressure reduction in the expansion device 71 flows out into the heat exchange circuit 22.

[0039] The heat exchange circuit 22 performs heat exchange between a portion of the low-temperature, low-pressure gaseous refrigerant from the indoor heat exchanger 60 and the low-temperature, low-pressure gas-liquid two-phase refrigerant from the expansion device 71. The liquid refrigerant obtained by the heat exchange in the heat exchange circuit 22, passing through the piping 14, flows out to the indoor unit 300 via the valve 76 and the liquid extension piping 23. In addition, the low-temperature, low-pressure gas-liquid two-phase refrigerant obtained by the heat exchange in the heat exchange circuit 22, passing through the piping 21, is depressurized by the expansion device 72. The liquid refrigerant obtained by the depressurization in the expansion device 72 flows out to the indoor unit 300 via the valve 76 and the liquid extension piping 23.

[0040] In the indoor unit 300, the expansion device 73 reduces the pressure of the liquid refrigerant from the outdoor unit 200. The low-temperature, low-pressure gaseous two-phase refrigerant obtained by the pressure reduction of the expansion device 73 flows out to the indoor heat exchanger 60.

[0041] In cooling operation mode, the indoor heat exchanger 60 acts as an evaporator. The indoor heat exchanger 60 exchanges heat between the low-temperature, low-pressure gaseous two-phase refrigerant from the expansion device 73 and the air drawn in from the room by the indoor fan 61. The gaseous two-phase refrigerant that has absorbed heat from the air through this heat exchange evaporates inside the indoor heat exchanger 60, changing into a low-temperature, low-pressure gaseous refrigerant. The low-temperature, low-pressure gaseous refrigerant obtained from the indoor heat exchanger 60 flows out to the outdoor unit 200 via the gas extension pipe 24 and valve 77. The air that has absorbed heat from the gaseous refrigerant in the indoor heat exchanger 60 is sent back into the indoor space. As a result, the indoor space is cooled.

[0042] Thus, in cooling operation mode, the refrigerant flows in the following order: compressor 30, outdoor heat exchanger 50 (condenser), expansion device 71, heat exchange circuit 22, expansion device 73, indoor heat exchanger 60 (evaporator), and accumulator 70.

[0043] Next, the operation of the air conditioner 1 in heating mode will be explained. As shown by the dashed line in Figure 1, in heating mode, the internal communication state of the four-way valve 40 is such that connection port 41 communicates with connection port 42, and connection port 43 communicates with connection port 44. In other words, in heating mode, the intake port 31 of the compressor 30 is connected to the outdoor heat exchanger 50 side, and the discharge port 32 of the compressor 30 is connected to the indoor heat exchanger 60 side.

[0044] The compressor 30 draws in the low-temperature, low-pressure gaseous refrigerant stored in the accumulator 70 and increases the pressure of the gaseous refrigerant by compressing it. The compressor 30 then discharges the high-temperature, high-pressure gaseous refrigerant obtained by compression to the indoor heat exchanger 60.

[0045] In heating mode, the indoor heat exchanger 60 acts as a condenser. The indoor heat exchanger 60 exchanges heat between the high-temperature, high-pressure gaseous refrigerant from the compressor 30 and the air drawn in from the indoor space by the indoor fan 61. The gaseous refrigerant that has released heat into the air through this heat exchange condenses inside the indoor heat exchanger 60, changing into a high-temperature, high-pressure liquid refrigerant. The high-temperature, high-pressure liquid refrigerant obtained from the indoor heat exchanger 60 flows out to the expansion device 73. The air that has absorbed heat from the gaseous refrigerant in the indoor heat exchanger 60 is sent back into the indoor space. As a result, the indoor space is heated.

[0046] The expansion device 73 reduces the pressure of the high-temperature, high-pressure liquid refrigerant from the indoor heat exchanger 60. The low-temperature, low-pressure gas-liquid two-phase refrigerant obtained by the expansion device 73 flows out to the outdoor unit 200 via the liquid extension pipe 23 and valve 76.

[0047] In the outdoor unit 200, the heat exchange circuit 22 performs heat exchange between the low-temperature, low-pressure gaseous-liquid two-phase refrigerant from the indoor heat exchanger 60 and a portion of the low-temperature, low-pressure gaseous refrigerant from the outdoor heat exchanger 50. The liquid refrigerant obtained by the heat exchange in the heat exchange circuit 22 flows out through the piping 14 to the expansion device 71.

[0048] The expansion device 71 reduces the pressure of the liquid refrigerant from the heat exchange circuit 22. The low-temperature, low-pressure gas-liquid two-phase refrigerant obtained by the pressure reduction of the expansion device 71 flows out to the outdoor heat exchanger 50.

[0049] In heating mode, the outdoor heat exchanger 50 acts as an evaporator. The outdoor heat exchanger 50 exchanges heat between the low-temperature, low-pressure gaseous two-phase refrigerant from the expansion device 71 and the air drawn in from outside by the outdoor fan 51. The gaseous two-phase refrigerant that has absorbed heat from the air through this heat exchange evaporates inside the outdoor heat exchanger 50, changing into a low-temperature, low-pressure gaseous refrigerant. The low-temperature, low-pressure gaseous refrigerant obtained from the outdoor heat exchanger 50 flows out to the accumulator 70.

[0050] Thus, in heating operation mode, the refrigerant flows in the following order: compressor 30, indoor heat exchanger 60 (condenser), expansion device 73, heat exchange circuit 22, expansion device 71, outdoor heat exchanger 50 (evaporator), and accumulator 70.

[0051] Generally, in an air conditioner 1, the amount of refrigerant required during heating operation is less than the amount required during cooling operation. Therefore, the amount of refrigerant filled into the refrigerant circuit 400 of the air conditioner 1 is determined based on the amount of refrigerant required during cooling operation, and during heating operation, excess refrigerant that is not used for heating operation may be generated. Such excess refrigerant is stored by the accumulator 70.

[0052] The control device 100 comprises a control unit 101 and a storage unit 102. The control device 100 is capable of communicating with each actuator of the refrigerant circuit 400 in order to control each actuator of the refrigerant circuit 400, such as the compressor 30, outdoor fan 51, indoor fan 61, expansion devices 71, 72, 73, and valves 76, 77. The control device 100 may be mounted on either the outdoor unit 200 or the indoor unit 300, or it may be a separate unit from the outdoor unit 200 and the indoor unit 300.

[0053] The control unit 101 is a computing entity (computer) that executes predetermined processing. The control unit 101 is composed of a processor such as a CPU (Central Processing Unit), MPU (Micro-Processing Unit), TPU (Tensor Processing Unit), or GPU (Graphics Processing Unit). A processor, which is an example of the control unit 101, has the function of executing predetermined processing by executing a predetermined program, but some or all of these functions may be implemented using dedicated hardware circuits such as an ASIC (Application Specific Integrated Circuit) or FPGA (Field-Programmable Gate Array). The term "processor" is not limited to processors in the narrow sense that execute processing using a stored-program method, such as a CPU, MPU, TPU, or GPU, but may also include hardwired circuits such as ASICs or FPGAs. Furthermore, the control unit 101 is not limited to a von Neumann type computer such as a CPU or GPU, but may also be composed of a non-von Neumann type computer such as a quantum computer or an optical computer. The term "control unit 101" may also be read as "processing circuitry." The control unit 101 may consist of one chip or multiple chips. Furthermore, the processor and associated processing circuits may consist of multiple computers interconnected by wired or wireless connections via a local area network or wireless network. The processor and associated processing circuits may also consist of a cloud computer that remotely performs calculations based on input information and outputs the calculation results to other devices located at a distance.

[0054] The storage unit 102 provides a storage area for storing program code or work memory when the processor of the control unit 101 executes various programs. The storage unit 102 may be one or more non-transitory computer-readable media. Examples of the storage unit 102 include volatile memory such as DRAM (dynamic random access memory) and SRAM (static random access memory), or non-volatile memory such as ROM (Read Only Memory) and flash memory. The storage unit 102 may also be one or more computer-readable storage media. Examples of storage media include storage devices such as HDD (Hard Disk Drive) and SSD (Solid State Drive). The control unit 101 controls each actuator of the refrigerant circuit 400 by executing the programs stored in the storage unit 102.

[0055] If the air conditioner 1 is a replacement multi-precharge unit, the worker uses the automatic charging function to charge the outdoor unit 200 with liquid refrigerant. However, if the liquid refrigerant is charged to the outdoor unit 200 while it is stored in the accumulator 70, the charging may be completed before the liquid refrigerant has completely flowed out of the accumulator 70, resulting in overcharging. Alternatively, the liquid refrigerant stored in the accumulator 70 could be evaporated and allowed to flow out before being charged to the outdoor unit 200. However, in this case, time is required to allow the liquid refrigerant to completely flow out of the accumulator 70, making it difficult for the worker to charge the outdoor unit 200 efficiently in a short amount of time.

[0056] Therefore, as will be explained below, the air conditioner 1 is configured in such a way that workers can efficiently fill the outdoor unit 200 with liquid refrigerant in a short amount of time.

[0057] In the air conditioner 1, the outdoor unit 200 further includes a bypass valve 78 and an injection port 79.

[0058] The bypass valve 78 is connected to the discharge piping 11 of the compressor 30 and the inlet piping 19 of the accumulator 70, and opens or closes the path between the discharge side of the compressor 30 and the inlet side of the accumulator 70 according to the control of the control device 100.

[0059] The injection port 79 is connected to the inlet piping 19 of the accumulator 70 and is opened or closed according to the control of the control device 100. The injection port 79 can be connected to a refrigerant canister (not shown), and when the injection port 79 is open, a worker can automatically inject liquid refrigerant from the refrigerant canister into the outdoor unit 200.

[0060] [Specific Example of Refrigerant Charging Process] A specific example of the refrigerant charging process performed by the air conditioner 1 will be explained with reference to Figures 3 and 4. Figure 3 is a diagram illustrating the opening and closing of the bypass valve 78, the opening and closing of the injection port 79, and the number of indoor units 300 in operation during the refrigerant charging process performed by the air conditioner 1. As shown in Figure 3, the refrigerant charging process performed by the air conditioner 1 includes an estimation process, a first injection process, an outflow process, and a second injection process.

[0061] The estimation process is a process for estimating the amount of liquid refrigerant to be injected into the outdoor unit 200 in addition to the first injection process (hereinafter also referred to as the "additional refrigerant amount"). The first injection process is a process of injecting liquid refrigerant into the outdoor unit 200 from the injection port 79. The discharge process is a process of discharging the liquid refrigerant from the accumulator 70 until the accumulator 70 is empty, after the liquid refrigerant has been injected into the outdoor unit 200 in the first injection process. The second injection process is a process of injecting liquid refrigerant into the outdoor unit 200 again from the injection port 79.

[0062] In the estimation process, only some of the at least one indoor unit 300 of the air conditioner 1 are connected to the outdoor unit 200. The control device 100 operates the compressor 30 with only some of the indoor units 300 connected to the outdoor unit 200. In other words, in the estimation process, the air conditioner 1 is operated using fewer indoor units 300 than in full operation. For example, in the example in Figure 1, only indoor unit 300A of the three indoor units 300A, 300B, and 300C is connected to the outdoor unit 200, and the air conditioner 1 is operated using only indoor unit 300A. Furthermore, with the compressor 30 running, the control device 100 opens the bypass valve 78 and closes the injection port 79. In this state, the control device 100 estimates the amount of additional refrigerant needed to fill the outdoor unit 200.

[0063] In the estimation process, the air conditioner 1 is operated using only some of the indoor units 300 out of at least one indoor unit 300. Therefore, the number of indoor units 300 that the control device 100 needs to consider when estimating the amount of additional refrigerant can be reduced compared to when the air conditioner 1 is operated using all of the indoor units 300. This simplifies the calculation for estimating the amount of additional refrigerant. The amount of additional refrigerant estimated by the estimation process is displayed, for example, on the display of the user device 500 and notified to the operator.

[0064] After the amount of additional refrigerant is estimated by the estimation process, the air conditioner 1 performs a first injection process. In the first injection process, as in the estimation process, only some of the at least one indoor unit 300 of the air conditioner 1 is connected to the outdoor unit 200. The control device 100 operates the compressor 30 with some of the indoor units 300 connected to the outdoor unit 200. That is, in the first injection process, the air conditioner 1 is operated using the same number of indoor units 300 as the indoor units 300 connected to the outdoor unit 200 in the estimation process. Furthermore, with the compressor 30 running, the control device 100 opens the bypass valve 78 and the injection port 79. That is, from the state during the estimation process, the control device 100 continues to operate the compressor 30 and keeps the bypass valve 78 open while switching the injection port 79 from a closed state to an open state.

[0065] After the injection of liquid refrigerant is complete, the air conditioner 1 performs an outflow process. In the outflow process, as in the estimation process and the first injection process, only some of the at least one indoor unit 300 of the air conditioner 1 is connected to the outdoor unit 200. That is, in the outflow process, the air conditioner 1 is operated using the same number of indoor units 300 that were connected to the outdoor unit 200 in the estimation process and the first injection process. The control device 100 operates the compressor 30 with some of the indoor units 300 connected to the outdoor unit 200. Furthermore, with the compressor 30 running, the control device 100 opens the bypass valve 78 and closes the injection port 79. That is, from the state during the first injection process, the control device 100 continues to operate the compressor 30 and keeps the bypass valve 78 open while switching the injection port 79 from an open state to a closed state.

[0066] After the discharge process has expelled the liquid refrigerant stored in the accumulator 70 and emptied the accumulator 70, the air conditioner 1 performs a second injection process. In the second injection process, all indoor units 300 of the air conditioner 1 are connected to the outdoor unit 200. The control device 100 operates the compressor 30 with all indoor units 300 connected to the outdoor unit 200. For example, in the example shown in Figure 1, all three indoor units 300A, 300B, and 300C are connected to the outdoor unit 200, and the air conditioner 1 is operated using all indoor units 300. Furthermore, with the compressor 30 running, the control device 100 closes the bypass valve 78 and opens the injection port 79.

[0067] Figure 4 is a timing chart illustrating the changes in the amount of liquid refrigerant present in each component during the refrigerant charging process performed by the air conditioner 1. In Figure 4, the injected refrigerant amount indicates the amount of refrigerant injected into the outdoor unit 200. The condenser refrigerant amount indicates the amount of liquid refrigerant present in the condenser. The ACC refrigerant amount indicates the amount of liquid refrigerant present in the accumulator 70. The liquid extension piping refrigerant amount indicates the amount of liquid refrigerant present in the liquid extension piping 23. The evaporator refrigerant amount indicates the amount of liquid refrigerant present in the evaporator.

[0068] As shown in Figure 4, at timing t1, the control device 100 closes the bypass valve 78 and the injection port 79, and starts each actuator, including the compressor 30.

[0069] When the estimation process is executed at timing t2, the control device 100 opens the bypass valve 78 and closes the injection port 79. The compressor 30 continues to operate. At this time, the air conditioner 1 is operated using fewer indoor units 300 than when all units are in operation. As a result, the high-temperature, high-pressure gaseous refrigerant discharged from the compressor 30 flows into the accumulator 70 via the bypass valve 78 and the piping 19. The liquid refrigerant stored in the accumulator 70 is evaporated and gasified by the high-temperature, high-pressure gaseous refrigerant from the compressor 30 and accumulates at the top of the accumulator 70. When the compressor 30 operates, the gaseous refrigerant accumulated at the top of the accumulator 70 is sucked in by the compressor 30. As a result, the liquid refrigerant is expelled from the accumulator 70. Therefore, as shown in Figure 4, during the estimation process, the amount of ACC refrigerant decreases, and the amount of condenser refrigerant and liquid extension piping refrigerant increases.

[0070] When the first injection process is executed at timing t3, the control device 100 opens the bypass valve 78 and the injection port 79. The compressor 30 continues to operate. At this time, the air conditioner 1 is operated using fewer indoor units 300 than the number of units used for full operation. As a result, the high-temperature, high-pressure gaseous refrigerant discharged from the compressor 30 flows into the accumulator 70 via the bypass valve 78 and piping 19. The liquid refrigerant stored in the accumulator 70 is evaporated and gasified by the high-temperature, high-pressure gaseous refrigerant from the compressor 30 and accumulates at the top of the accumulator 70. As the compressor 30 operates, the gaseous refrigerant accumulated at the top of the accumulator 70 is sucked in by the compressor 30. As a result, the liquid refrigerant is expelled from the accumulator 70. Meanwhile, an additional amount of liquid refrigerant estimated by the estimation process is injected into the outdoor unit 200 from the injection port 79. Therefore, as shown in Figure 4, during the first injection process, the amount of injected refrigerant increases, the amount of ACC refrigerant decreases, and the amount of condenser refrigerant and liquid extension piping refrigerant increases.

[0071] In this way, the air conditioner 1 can inject liquid refrigerant from the injection port 79 while operating the compressor 30 to expel the liquid refrigerant stored in the accumulator 70 through the first injection process. This allows the outdoor unit 200 to be efficiently filled with liquid refrigerant in a short time while avoiding overfilling.

[0072] When the discharge process is executed at timing t4, the control device 100 opens the bypass valve 78 and closes the injection port 79. The compressor 30 continues to operate. At this time, the air conditioner 1 is operated using fewer indoor units 300 than when all units are in operation. As a result, the high-temperature, high-pressure gaseous refrigerant discharged from the compressor 30 flows into the accumulator 70 via the bypass valve 78 and piping 19. The liquid refrigerant stored in the accumulator 70 is evaporated and gasified by the high-temperature, high-pressure gaseous refrigerant from the compressor 30 and accumulates at the top of the accumulator 70. When the compressor 30 operates, the gaseous refrigerant accumulated at the top of the accumulator 70 is sucked in by the compressor 30. As a result, the liquid refrigerant is expelled from the accumulator 70. Therefore, as shown in Figure 4, during the discharge process, the amount of ACC refrigerant decreases, and the amount of condenser refrigerant and liquid extension piping refrigerant increases.

[0073] In this way, the air conditioner 1 operates the compressor 30 through the discharge process to expel the liquid refrigerant stored in the accumulator 70, so the accumulator 70 will eventually become empty at timing t5.

[0074] When the second injection process is executed at timing t5, the control device 100 closes the bypass valve 78 and opens the injection port 79. The compressor 30 continues to operate. At this time, all indoor units 300 of the air conditioner 1 are connected to the outdoor unit 200, and the air conditioner 1 is operated using all indoor units 300. As a result, considering that all indoor units 300 are operated at full capacity, liquid refrigerant is injected into the outdoor unit 200 from the injection port 79 until the amount of liquid refrigerant reaches the appropriate level before factory shipment. In this way, the air conditioner 1 can compensate for the shortage of liquid refrigerant injected in the first injection process by performing adjustment operation using all indoor units 300 during the second injection process. Therefore, as shown in Figure 4, during the second injection process, the amount of injected refrigerant increases, and the amount of refrigerant in the condenser and the amount of refrigerant in the liquid extension piping increase.

[0075] At timing t6, the control device 100 opens the bypass valve 78 and the injection port 79, and stops each actuator, including the compressor 30.

[0076] In this way, the air conditioner 1 can efficiently perform automatic charging of liquid refrigerant by controlling the bypass valve 78, injection port 79, and compressor 30 through the refrigerant charging process.

[0077] [Calculation Example for Estimating Additional Refrigerant Amount] Referring to Figures 5 and 6, an example of the calculation used by the air conditioner 1 when estimating the amount of additional refrigerant during the estimation process will be explained. Figure 5 is a diagram showing the distribution of liquid refrigerant at the time when the air conditioner 1 estimates the amount of additional refrigerant. Figure 6 is a diagram showing the distribution of liquid refrigerant in the optimal state.

[0078] As shown in Figure 5, the amount of condenser refrigerant at the time when the air conditioner 1 estimates the amount of additional refrigerant through estimation processing is M. ｃｏｎｄ＿ｔ , ACC refrigerant amount M ａｃｃ＿ｔ , the amount of refrigerant in the liquid extension pipe is M ｐｉｐｅ＿ｔ , the amount of evaporator refrigerant is M ｅｖａ＿ｔ As shown in Figure 6, the amount of condenser refrigerant in the proper condition is M. ｃｏｎｄ＿ｂ , ACC refrigerant amount M ａｃｃ＿ｂ , the amount of refrigerant in the liquid extension pipe is M ｐｉｐｅ＿ｂ , the amount of evaporator refrigerant is Mｅｖａ＿ｂ as shown in

[0079] Using each refrigerant amount as described above, the control device 100 can calculate (estimate) the additional refrigerant amount by the following formula (1).

[0080] In formula (1), the evaporator refrigerant amount M at the time of estimating the additional refrigerant amount ｅｖａ＿ｔ and the evaporator refrigerant amount M in the proper state ｅｖａ＿ｂ can be assumed to be the same. Also, the ACC refrigerant amount M in the proper state ａｃｃ＿ｂ can be assumed to be 0. Therefore, the control device 100 determines the condenser refrigerant amount M present in the condenser in the proper state ｃｏｎｄ＿ｂ and the liquid extension pipe refrigerant amount M present in the liquid extension pipe 23 in the proper state ｐｉｐｅ＿ｂ and calculates a first total value by adding them together, and the ACC refrigerant amount M present in the accumulator 70 ａｃｃ＿ｔ and the condenser refrigerant amount M present in the condenser ｃｏｎｄ＿ｔ and the liquid extension pipe refrigerant amount M present in the liquid extension pipe 23 ｐｉｐｅ＿ｔ and calculates a second total value by adding them together, and subtracts the second total value from the first total value to estimate the additional refrigerant amount injected by the first injection process.

[0081] Further, the condenser refrigerant amount M in the proper state ｃｏｎｄ＿ｂ is stored in the storage unit 102 in advance. Therefore, the control device 100 determines the condenser refrigerant amount M, the ACC refrigerant amount M ｃｏｎｄ＿ｔ and the liquid extension pipe refrigerant amount M at the time of estimating the additional refrigerant amount ａｃｃ＿ｔ and, and the liquid extension pipe refrigerant amount M in the proper state ｐｉｐｅ＿ｔ If calculated, the additional refrigerant amount can be calculated based on formula (1). ｐｉｐｅ＿ｂ

[0082] The condenser refrigerant amount M ｃｏｎｄ＿ｔ ｃｏｎｄ＿ｔ ｃｏｎｄ＿ｔRegarding this, the control device 100 utilizes the fact that the amount of refrigerant circulating through the condenser, obtained by subtracting the amount of refrigerant circulating through the bypass valve 78 from the amount of refrigerant circulating discharged from the compressor 30, is equal to the amount of refrigerant circulating through the expansion device 73 of the indoor unit 300. Using the dryness of the condenser outlet, the ratio of gas phase, two phase, and liquid phase areas, the average refrigerant density of each phase, the internal volume of the condenser, and the opening degree of the expansion device 73, the control device 100 calculates the condenser refrigerant amount M ｃｏｎｄ＿ｔ It is possible to calculate the amount of condenser refrigerant M. ｃｏｎｄ＿ｔ Since the opening of the expansion device 73 is used in the calculation, the fewer indoor units 300 operating during the estimation process, the better the control device 100 will be able to calculate the condenser refrigerant amount M. ｃｏｎｄ＿ｔ This allows for more accurate and easier calculation.

[0083] ACC refrigerant amount M ａｃｃ＿ｔ Regarding this, the control device 100 multiplies the liquid level height of the accumulator 70 corresponding to the superheating degree (or temperature) on the inlet side of the accumulator 70 and the superheating degree (or temperature) on the outlet side of the accumulator 70, and the internal volume of the accumulator 70, thereby determining the ACC refrigerant amount M ａｃｃ＿ｔ It is possible to calculate this.

[0084] Liquid extension pipe refrigerant amount M ｐｉｐｅ＿ｔ Regarding this, the control device 100 calculates the condenser refrigerant amount M from the amount of refrigerant pre-filled in the outdoor unit 200. ｃｏｎｄ＿ｔ , ACC refrigerant amount M ａｃｃ＿ｔ , and evaporator refrigerant amount M ｅｖａ＿ｔ By subtracting this, the amount of refrigerant in the liquid extension piping M ｐｉｐｅ＿ｔ This can be calculated. Note that the amount of evaporator refrigerant M ｅｖａ＿ｔ This can be determined by using the catalog value for air conditioner 1, or by multiplying the two-phase / liquid-phase area ratio, the average refrigerant density of each phase, and the internal volume of the evaporator.

[0085] Liquid extension pipe refrigerant amount M ｐｉｐｅ＿ｂ Regarding this, the control device 100 calculates the void fraction of the liquid extension pipe 23 corresponding to the dryness of the condenser outlet, and calculates the amount of liquid refrigerant when the void fraction is 0 (i.e., when the liquid extension pipe 23 is filled with liquid refrigerant), thereby determining the amount of liquid refrigerant in the liquid extension pipe M ｐｉｐｅ＿ｂ It is possible to calculate this.

[0086] The control device 100 calculates the amount of condenser refrigerant M as described above. ｃｏｎｄ＿ｔ , ACC refrigerant amount M ａｃｃ＿ｔ , liquid extension pipe refrigerant amount M ｐｉｐｅ＿ｔ , and liquid extension piping refrigerant amount M ｐｉｐｅ＿ｂ Using this method, the amount of additional refrigerant can be calculated based on equation (1). Note that the control device 100 may calculate (estimate) the amount of additional refrigerant using other calculation methods, not limited to the above example.

[0087] [Refrigerant Charging Process Flow] The refrigerant charging process flow will be explained with reference to Figure 7. Figure 7 is a flowchart illustrating the refrigerant charging process performed by the control device 100 of the air conditioner 1. In the figure, "S" is used as an abbreviation for "STEP".

[0088] As shown in Figure 7, the control device 100 closes the bypass valve 78 and the injection port 79 to activate each actuator, including the compressor 30 (S1). Subsequently, the control device 100 performs estimation processing.

[0089] In the estimation process, the control device 100 opens the bypass valve 78 and keeps the injection port 79 closed while only some of the indoor units 300 are connected to the outdoor unit 200 (S2). In this state, the control device 100 estimates the amount of additional refrigerant needed to fill the outdoor unit 200 (S3). After that, the control device 100 executes the first injection process.

[0090] In the first injection process, the control device 100 keeps the bypass valve 78 open and the injection port 79 open while only some of the indoor units 300 are connected to the outdoor unit 200 (S4). As a result, the high-temperature, high-pressure gaseous refrigerant discharged from the compressor 30 evaporates and gasifies the liquid refrigerant stored in the accumulator 70, and expels it from the accumulator 70. Furthermore, liquid refrigerant is injected from the injection port 79. That is, the control device 100 operates the compressor 30 to expel the liquid refrigerant stored in the accumulator 70 while injecting liquid refrigerant from the injection port 79. The control device 100 determines whether the additional amount of liquid refrigerant estimated by the estimation process has been injected (S5). If the liquid refrigerant injection is not complete (NO in S5), the control device 100 continues the liquid refrigerant injection and repeats the process in S5. On the other hand, if the liquid refrigerant injection is complete (YES in S5), the control device 100 performs the discharge process.

[0091] In the discharge process, the control device 100 keeps the bypass valve 78 open and closes the injection port 79 while only some of the indoor units 300 are connected to the outdoor unit 200 (S6). As a result, the liquid refrigerant stored in the accumulator 70 is evaporated and gasified by the high-temperature, high-pressure gaseous refrigerant discharged from the compressor 30 and expelled from the accumulator 70, while the injection of liquid refrigerant from the injection port 79 is stopped. The control device 100 determines whether the discharge of liquid refrigerant from the accumulator 70 is complete (S7). If the discharge of liquid refrigerant from the accumulator 70 is not complete (NO in S7), the control device 100 continues the discharge of liquid refrigerant from the accumulator 70 and repeats the process in S7. On the other hand, if the discharge of liquid refrigerant from the accumulator 70 is complete (YES in S7), the control device 100 executes the second injection process.

[0092] In the second injection process, with all indoor units 300 connected to the outdoor unit 200, the control device 100 closes the bypass valve 78 and opens the injection port 79 (S8). As a result, liquid refrigerant is injected from the injection port 79 with all indoor units 300 in operation. The control device 100 determines whether or not liquid refrigerant has been injected to the appropriate amount (S9). If the liquid refrigerant injection is not complete (NO in S9), the control device 100 continues the liquid refrigerant injection and repeats the process in S9.

[0093] On the other hand, when the injection of liquid refrigerant is complete (YES in S9), the control device 100 opens the bypass valve 78 and the injection port 79 to stop each actuator, including the compressor 30 (S10). After that, the control device 100 terminates this process.

[0094] As described above, the air conditioner 1, while the compressor 30 is running, opens the connection between the discharge side of the compressor 30 and the inlet side of the accumulator 70 with a bypass valve 78. This allows the high-temperature, high-pressure gaseous refrigerant from the compressor 30 to evaporate the liquid refrigerant stored in the accumulator 70, causing it to flow out of the accumulator 70, while liquid refrigerant is injected through the opened injection port 79. This allows workers to efficiently fill the outdoor unit 200 with liquid refrigerant in a short amount of time.

[0095] The embodiments disclosed herein should be considered in all respects to be illustrative and not restrictive. The scope of this disclosure is indicated by the claims rather than by the description of the embodiments above, and all modifications within the meaning and scope of the claims are intended to be included.

[0096] 1 Air conditioner, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21 Piping, 22 Heat exchange circuit, 23 Liquid extension piping, 24 Gas extension piping, 30 Compressor, 31 Intake port, 32 Discharge port, 40 Four-way valve, 41, 42, 43, 44 Connection port, 50 Outdoor heat exchanger, 51 Outdoor fan, 60 Indoor heat exchanger, 61 Indoor fan, 70 Accumulator, 71, 72, 73 Expansion device, 76, 77 Valve, 78 Bypass valve, 79 Injection port, 100 Control device, 101 Control unit, 102 Memory unit, 200 Outdoor unit, 300, 300A, 300B, 300C Indoor unit, 400 Refrigerant circuit, 500 User device, 1000 Air conditioning system.

Claims

1. An outdoor unit comprising a compressor, a condenser, and an accumulator; at least one indoor unit comprising an expansion device and an evaporator; a liquid extension pipe connecting the outdoor unit and the at least one indoor unit and through which liquid refrigerant passes; a gas extension pipe connecting the outdoor unit and the at least one indoor unit and through which gas refrigerant passes; and a control device, wherein the accumulator, the compressor, and the condenser are connected in order in a path from the gas extension pipe of the outdoor unit to the liquid extension pipe; the expansion device and the evaporator are connected in order in a path from the liquid extension pipe of the at least one indoor unit to the gas extension pipe; the outdoor unit further comprises a bypass valve for opening or closing the space between the discharge side of the compressor and the inlet side of the accumulator; and an injection port for injecting liquid refrigerant into the accumulator. The control device performs a first injection process in which liquid refrigerant is injected from the injection port by opening the bypass valve and the injection port while the compressor is in operation.

2. The air conditioner according to claim 1, wherein the control device opens the bypass valve and closes the injection port while the compressor is in operation, and performs an estimation process to estimate the amount of liquid refrigerant to be injected by the first injection process.

3. The air conditioner according to claim 2, wherein the control device performs the estimation process when some of the at least one indoor unit is connected to the outdoor unit.

4. The air conditioner according to claim 3, wherein the control device performs the first injection process while some of the indoor units are connected to the outdoor unit.

5. The air conditioner according to any one of claims 1 to 4, wherein the control device, after the first injection process is completed, opens the bypass valve and closes the injection port while the compressor is running, thereby performing an outflow process to discharge liquid refrigerant from the accumulator.

6. The air conditioner according to claim 5, wherein the control device, after the discharge process is completed, closes the bypass valve and opens the injection port while all of the at least one indoor unit is connected to the outdoor unit, thereby performing a second injection process in which liquid refrigerant is injected from the injection port.

7. The control device, in the estimation process, calculates a first summation value by adding the amount of liquid refrigerant present in the condenser in an appropriate state and the amount of liquid refrigerant present in the liquid extension piping in an appropriate state; calculates a second summation value by adding the amount of liquid refrigerant present in the accumulator, the amount of liquid refrigerant present in the condenser, and the amount of liquid refrigerant present in the liquid extension piping; and estimates the amount of liquid refrigerant to be injected by the first injection process by subtracting the second summation value from the first summation value, according to claim 2 or claim 3.

8. A control method for controlling an air conditioner, wherein the air conditioner comprises an outdoor unit having a compressor, a condenser, and an accumulator; at least one indoor unit having an expansion device and an evaporator; a liquid extension pipe connecting the outdoor unit and the at least one indoor unit and allowing liquid refrigerant to pass through; and a gas extension pipe connecting the outdoor unit and the at least one indoor unit and allowing gas refrigerant to pass through; the accumulator, the compressor, and the condenser are connected in order in a path from the gas extension pipe of the outdoor unit to the liquid extension pipe; the expansion device and the evaporator are connected in order in a path from the liquid extension pipe of the at least one indoor unit to the gas extension pipe; the outdoor unit further comprises a bypass valve for opening or closing the space between the discharge side of the compressor and the inlet side of the accumulator, and an injection port for injecting liquid refrigerant into the accumulator; and the process performed by a computer is as follows: A control method comprising the steps of: estimating the amount of liquid refrigerant by opening the bypass valve and closing the injection port while the compressor is in operation; and injecting liquid refrigerant from the injection port in an amount estimated by the estimation step by opening the bypass valve and opening the injection port while the compressor is in operation.

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