Air conditioner and control method

Abstract

This air conditioner comprising a refrigerant circuit, indoor units, and an outdoor unit comprises: liquid piping which enables a refrigerant to flow between an outdoor heat exchanger and indoor unit expansion valves; a bypass pipe which is for bypassing of the refrigerant from the liquid piping to an accumulator; a supercooling heat exchanger which is provided to the liquid piping and is configured to exchange heat between the refrigerant flowing through the bypass pipe and the refrigerant flowing through the liquid piping; a supercooling expansion valve which is provided to the bypass pipe and is capable of adjusting the flow rate of the refrigerant flowing from the liquid piping to the supercooling heat exchanger; a liquid-side shutoff valve which is provided to the liquid piping between the supercooling heat exchanger and indoor heat exchangers; an discharge pressure sensor which detects the discharge pressure of the refrigerant that is discharged from a compressor; and a control part which controls operation of the air conditioner. Upon receiving a refrigerant leakage detection signal from a refrigerant leakage sensor, the control part: closes the liquid-side shutoff valve; performs a refrigerant recovery operation for moving the refrigerant, which is circulating in the refrigerant circuit, to the outdoor unit; and, during the refrigerant recovery operation, changes the opening degree of the supercooling expansion valve according to a detection value of the discharge pressure sensor.

Description

Air conditioner and control method

[0001] The present disclosure relates to an air conditioner and a control method.

[0002] In air conditioners with a large amount of refrigerant sealed in the refrigerant circuit, such as when a large number of indoor units are connected to one outdoor unit or when the connecting piping connecting the indoor and outdoor units is long, a refrigerant recovery operation (pump-down operation) may be performed to detect a refrigerant leak and recover the refrigerant to the outdoor unit. For example, a refrigeration cycle device has been disclosed that, during the refrigerant recovery operation, detects that the outdoor heat exchanger is close to a liquid seal state, opens a subcooling expansion valve, and transfers the refrigerant to an accumulator via a bypass pipe (see, for example, Patent Document 1).

[0003] International Publication No. 2018 / 167811

[0004] During the refrigerant recovery operation described above, the refrigerant recovered from the indoor unit to the outdoor unit passes through the four-way valve, then passes through the accumulator and is drawn into the compressor. When the subcooling expansion valve is opened while the outdoor heat exchanger is close to liquid ring, liquid refrigerant flows from the outdoor heat exchanger into the accumulator all at once through the bypass pipe. This can result in a higher proportion of refrigerant drawn from the accumulator into the compressor than refrigerant recovered from the indoor unit. This can reduce the amount of refrigerant recovered from the indoor unit, resulting in a longer refrigerant recovery operation. The refrigerant recovery operation must be completed as quickly as possible to reduce refrigerant leakage into the room. Therefore, it is necessary to prevent the outdoor heat exchanger from becoming liquid ring and to minimize the prolongation of the refrigerant recovery operation.

[0005] The present disclosure has been made in consideration of the above-mentioned circumstances, and one of its objects is to provide an air conditioner and a control method that, when a refrigerant leak is detected, prevents the outdoor heat exchanger from becoming liquid-sealed during refrigerant recovery operation, which recovers refrigerant from the refrigerant circuit to the outdoor unit, and suppresses the extension of the refrigerant recovery operation.

[0006] An air conditioner according to the present disclosure is an air conditioner comprising: a refrigerant circuit that circulates a refrigerant through a compressor, a four-way valve, an outdoor heat exchanger, an indoor unit expansion valve, an indoor heat exchanger, and an accumulator; an indoor unit equipped with the indoor heat exchanger; and an outdoor unit equipped with the compressor, the four-way valve, the outdoor heat exchanger, and the accumulator, and further comprising: a liquid pipe that enables refrigerant to flow between the outdoor heat exchanger and the indoor unit expansion valve; a bypass pipe that bypasses refrigerant from the liquid pipe to the accumulator; and a subcooling heat exchanger that is provided in the liquid pipe and configured to exchange heat between the refrigerant flowing in the bypass pipe and the refrigerant flowing in the liquid pipe. a subcooling expansion valve provided in the bypass pipe and capable of adjusting the flow rate of refrigerant flowing from the liquid piping to the subcooling heat exchanger; a liquid-side shut-off valve provided in the liquid piping between the subcooling heat exchanger and the indoor heat exchanger; a discharge pressure sensor that detects the discharge pressure of the refrigerant discharged from the compressor; and a control unit that controls the operation of the air conditioner, wherein when the control unit receives a refrigerant leakage detection signal from the refrigerant leakage sensor, it closes the liquid-side shut-off valve and performs a refrigerant recovery operation to move the refrigerant circulating in the refrigerant circuit to the outdoor unit, and during the refrigerant recovery operation, it changes the opening of the subcooling expansion valve according to the detection value of the discharge pressure sensor.

[0007] Further, a control method for an air conditioner according to the present disclosure includes a refrigerant circuit that circulates a refrigerant through a compressor, a four-way valve, an outdoor heat exchanger, an indoor unit expansion valve, an indoor heat exchanger, and an accumulator, an indoor unit equipped with the indoor heat exchanger, an outdoor unit equipped with the compressor, the four-way valve, the outdoor heat exchanger, and the accumulator, a liquid pipe that enables refrigerant to flow between the outdoor heat exchanger and the indoor unit expansion valve, a bypass pipe that bypasses refrigerant from the liquid pipe to the accumulator, a subcooling heat exchanger that is provided in the liquid pipe and configured to exchange heat between the refrigerant flowing in the bypass pipe and the refrigerant flowing in the liquid pipe, and a subcooling heat exchanger that is provided in the bypass pipe and A control method for an air conditioner equipped with a subcooling expansion valve capable of adjusting the flow rate of refrigerant flowing from the liquid piping to the subcooling heat exchanger, a liquid-side shut-off valve provided in the liquid piping between the subcooling heat exchanger and the indoor heat exchanger, and a discharge pressure sensor that detects the discharge pressure of refrigerant discharged from the compressor, the control method including the steps of: when a control unit that controls the operation of the air conditioner receives a refrigerant leakage detection signal from a refrigerant leakage sensor, closing the liquid-side shut-off valve and performing a refrigerant recovery operation in which the refrigerant circulating in the refrigerant circuit is moved to the outdoor unit; and during the refrigerant recovery operation, changing the opening degree of the subcooling expansion valve in accordance with the detection value of the discharge pressure sensor.

[0008] According to the present disclosure, when a refrigerant leak is detected, during refrigerant recovery operation in which refrigerant in the refrigerant circuit is recovered to the outdoor unit, it is possible to prevent the outdoor heat exchanger from becoming liquid-sealed while suppressing the extension of the refrigerant recovery operation.

[0009] Fig. 1 is a diagram showing an example of a refrigerant circuit of an air conditioner according to a first embodiment. Fig. 2 is a flowchart showing the processing of a refrigerant recovery operation according to a second embodiment. Fig. 3 is a flowchart showing the processing of a refrigerant recovery operation according to a third embodiment. Fig. 4 is a flowchart showing the processing of a refrigerant recovery operation according to a fourth embodiment.

[0010] Hereinafter, embodiments will be described with reference to the drawings. First Embodiment First, the first embodiment will be described.

[0011] [Configuration of the refrigerant circuit of the air conditioner] Fig. 1 is a diagram showing an example of a refrigerant circuit of an air conditioner according to this embodiment. The illustrated air conditioner 1 is configured to include an outdoor unit 100 and a plurality of indoor units 200.

[0012] The outdoor unit 100 includes a compressor 101, a four-way valve 102, an outdoor heat exchanger 103, a subcooling expansion valve 104, a liquid-side shutoff valve 105, a gas-side shutoff valve 106, an accumulator 107, a discharge pressure sensor 108, a suction pressure sensor 109, a subcooling heat exchanger 10a, a bypass pipe 10b, and an outdoor unit control unit 115. Here, the liquid-side shutoff valve 105 and the gas-side shutoff valve 106 may be configured to be built into the outdoor unit 100, or may be configured to be externally attached as separate components from the outdoor unit 100.

[0013] Indoor unit 210 and indoor unit 220 represent indoor units included in a plurality of indoor units 200 connected to outdoor unit 100 via a refrigerant circuit. While two indoor units 200, indoor unit 210 and indoor unit 220, are shown in this figure, three or more indoor units may be used. Indoor units 210 and 220 are equipped with indoor unit expansion valves 211 and 221, indoor heat exchangers 212 and 222, refrigerant leak sensors 213 and 223, indoor fans 214 and 224, and indoor unit control units 215 and 225. The refrigerant leak sensors 213 and 223 may be built into indoor units 210 and 220, or may be externally mounted components separate from indoor units 210 and 220. The indoor expansion valves 211 and 221 may be built into indoor units 210 and 220, or may be externally mounted components separate from indoor units 210 and 220.

[0014] The outdoor unit 100 and each of the multiple indoor units 200 (indoor units 210 and 220) are connected as a refrigerant circuit that circulates the refrigerant via gas piping 10 and liquid piping 20 through which the refrigerant flows. The gas piping 10 enables the refrigerant to flow between the four-way valve 102 and the indoor heat exchangers 212, 222. The liquid piping 20 enables the refrigerant to flow between the outdoor heat exchanger 103 and the indoor unit expansion valves 211, 221.

[0015] The outdoor unit control unit 115 and the indoor unit control units 215, 225 are control units that control the operation of the air conditioner 1. The outdoor unit control unit 115 is configured to include a CPU (Central Processing Unit), memory (storage unit), etc., and controls the various units of the outdoor unit 100. The indoor unit control units 215, 225 are configured to include a CPU, memory (storage unit), etc., and control the various units of the indoor unit control units 215, 225. Information about each device is also communicated between the outdoor unit control unit 115 and the indoor unit control units 215, 225.

[0016] The compressor 101 compresses and outputs refrigerant gas. The output of the compressor 101 is adjusted by changing the operating frequency of the compressor 101 using a control signal from the outdoor unit control unit 115. The compressor 101 may be of various types, such as a rotary type (scroll type, rotary type, screw type, etc.) or a reciprocating type.

[0017] Suction pressure sensor 109 detects the suction pressure of the refrigerant sucked into compressor 101. In Fig. 1, suction pressure sensor 109 is installed between four-way valve 102 and accumulator 107, but it may be installed between accumulator 107 and compressor 101. Discharge pressure sensor 108 detects the discharge pressure of the refrigerant discharged from compressor 101.

[0018] The four-way valve 102 switches the refrigerant circulation direction between cooling operation and heating operation in response to a control signal from the outdoor unit control unit 115. In cooling operation, the four-way valve 102 switches the connection of the refrigerant circuit so that the refrigerant circulates in the following order: compressor 101, outdoor heat exchanger 103, subcooling heat exchanger 10a, liquid-side shutoff valve 105, indoor unit expansion valve 211, indoor heat exchanger 212 (or indoor unit expansion valve 221, indoor heat exchanger 222), gas-side shutoff valve 106, and accumulator 107.

[0019] During heating operation, the four-way valve 102 switches the connection of the refrigerant circuit so that the refrigerant circulates in the following order: compressor 101, gas-side shut-off valve 106, indoor heat exchanger 212, indoor unit expansion valve 211 (or indoor heat exchanger 222, indoor unit expansion valve 221), liquid-side shut-off valve 105, subcooling heat exchanger 10a, outdoor heat exchanger 103, and accumulator 107.

[0020] The liquid-side shutoff valve 105 is a shutoff valve provided in the liquid piping 20 between the subcooling heat exchanger 10a and the indoor expansion valves 211, 221. That is, the liquid-side shutoff valve 105 is provided in the liquid piping 20 between the subcooling heat exchanger 10a and the indoor heat exchangers 212, 222. The gas-side shutoff valve 106 is a shutoff valve provided in the gas piping 10 between the four-way valve 102 and the indoor heat exchangers 212, 222.

[0021] The outdoor heat exchanger 103 exchanges heat between the refrigerant inside it and the surrounding air (outside air). During cooling operation, the refrigerant gas compressed by the compressor 101 is converted into a liquid refrigerant through heat exchange in the outdoor heat exchanger 103, and flows through the liquid piping 20 and the indoor unit expansion valves 211, 221 to the indoor heat exchangers 212, 222. During heating operation, the liquid refrigerant that flows from the indoor heat exchangers 212, 222 through the indoor unit expansion valves 211, 221 and the liquid piping 20 is converted into a refrigerant gas through heat exchange in the outdoor heat exchanger 103, and flows through the four-way valve 102 to the compressor 101.

[0022] The accumulator 107 is provided in the piping on the suction side of the compressor 101. The accumulator 107 separates the drawn refrigerant into liquid refrigerant and gas refrigerant, and draws only the gas refrigerant into the compressor 101. The accumulator 107 prevents the compressor 101 from drawing in liquid refrigerant, thereby avoiding breakdown of the compressor 101 due to liquid compression, and also functions as a liquid reservoir for storing excess refrigerant.

[0023] The bypass pipe 10b is a pipe that bypasses the refrigerant from the liquid pipe 20 to the accumulator 107. The subcooling heat exchanger 10a is provided in the liquid pipe 20 and is configured to exchange heat between the refrigerant flowing through the bypass pipe 10b and the refrigerant flowing through the liquid pipe 20.

[0024] The subcooling expansion valve 104 is provided in the bypass pipe 10b and is capable of adjusting the flow rate of the refrigerant flowing from the liquid pipe 20 to the subcooling heat exchanger 10a. For example, the subcooling expansion valve 104 is a linear expansion valve (LEV) that can open and close the valve using the force of an electromagnet. The subcooling expansion valve 104 changes the valve opening (LEV opening) according to a control signal from the outdoor unit control unit 115.

[0025] Each of the indoor unit expansion valves 211, 221 is provided between each of the indoor heat exchangers 212, 222 and the liquid piping 20, and is capable of adjusting the flow rate of refrigerant flowing from the indoor heat exchangers 212, 222 to the liquid piping 20 or the flow rate of refrigerant flowing from the liquid piping 20 to the indoor heat exchangers 212, 222.

[0026] The indoor heat exchangers 212, 222 exchange heat between the refrigerant inside them and the surrounding air (indoor air). During cooling operation, the liquid refrigerant that flows into the indoor heat exchangers 212, 222 through the liquid piping 20 and the indoor unit expansion valves 211, 221 turns into refrigerant gas through heat exchange in the indoor heat exchangers 212, 222, and flows through the gas piping 10, the four-way valve 102, and the accumulator 107 to the compressor 101. During heating operation, the gas refrigerant that flows in from the gas piping 10 turns into liquid refrigerant through heat exchange in the indoor heat exchangers 212, 222, and flows through the indoor unit expansion valves 211, 221 and the liquid piping 20 to the outdoor heat exchanger 103.

[0027] The indoor fans 214, 224 are blowers that blow into the room the air that has exchanged heat with the refrigerant in the indoor heat exchangers 212, 222. The indoor fans 214, 224 rotate or stop rotating in response to control signals from the indoor unit control units 215, 225. The indoor fans 214, 224 also change their rotation speed (change airflow) in response to control signals from the indoor unit control units 215, 225.

[0028] The refrigerant leakage sensors 213, 223 are sensors that detect refrigerant leakage. The refrigerant leakage sensor 213 is provided in the indoor unit 210 and detects refrigerant leakage in the indoor unit 210. The refrigerant leakage sensor 223 is provided in the indoor unit 220 and detects refrigerant leakage in the indoor unit 220. When the refrigerant leakage sensors 213, 223 detect a refrigerant leakage, they transmit a detected refrigerant leakage detection signal indicating that a refrigerant leakage has been detected.

[0029] In addition, each of the refrigerant leak sensors 213, 223 may be built into each of the indoor units 210, 220 as part of the air conditioner 1, or may be an external refrigerant leak detection alarm device that can be attached to each of the indoor units 210, 220 as a separate part from the air conditioner 1.

[0030] Next, the refrigerant recovery operation in the air conditioner 1 will be described. When the indoor unit control unit 215 or the indoor unit control unit 225 receives a refrigerant leak detection signal from the refrigerant leak sensor 213 or the refrigerant leak sensor 223, it notifies the outdoor unit control unit 115 that the refrigerant leak sensor 213, 223 has detected a refrigerant leak. Then, when a refrigerant leak is detected in at least one of the indoor units 210 and 220, the air conditioner 1 (the outdoor unit control unit 115 and the indoor unit control units 215, 225) starts a refrigerant recovery operation. For example, when a refrigerant leak is detected, the outdoor unit control unit 115 closes the liquid-side shutoff valve 105 and performs a refrigerant recovery operation to move the refrigerant circulating in the refrigerant circuit to the outdoor unit 100.

[0031] Because the refrigerant recovery operation accumulates refrigerant in the outdoor heat exchanger 103, there is a risk of liquid seal if the total amount of refrigerant charged in the air conditioner 1 is large. To prevent liquid seal, the air conditioner 1 is designed to perform a high-pressure cut (abnormal shutdown) when the discharge pressure of the compressor 101 exceeds a threshold. If the high-pressure cut is performed, the refrigerant recovery operation is interrupted, and the amount of refrigerant leakage continues to increase even while the operation is interrupted.

[0032] Therefore, to prevent a high-pressure cut, immediately after starting the refrigerant recovery operation, the air conditioner 1 starts feedback control of the subcooling expansion valve 104. In this feedback control of the subcooling expansion valve 104, the outdoor unit control unit 115 changes the opening degree of the subcooling expansion valve 104 in accordance with the discharge pressure of the compressor 101 detected by the discharge pressure sensor 108.

[0033] As refrigerant accumulates in the outdoor heat exchanger 103, the discharge pressure of the compressor 101 gradually increases. Therefore, the outdoor unit control unit 115 can detect the degree of refrigerant accumulation in the outdoor heat exchanger 103 by monitoring the discharge pressure of the compressor 101. For example, the outdoor unit control unit 115 opens the subcooling expansion valve 104 when the discharge pressure of the compressor 101 is high, and throttles the subcooling expansion valve 104 when the discharge pressure is low.

[0034] When the subcooling expansion valve 104 opens, the refrigerant accumulated in the outdoor heat exchanger 103 moves to the accumulator 107 via the bypass piping 10b, preventing liquid sealing. However, the amount of refrigerant recovered from the indoor unit 200 decreases as the amount of refrigerant bypassed and moved to the accumulator 107 increases. Therefore, in order to prevent a delay in the refrigerant recovery operation due to the opening of the subcooling expansion valve 104, the outdoor unit control unit 115 throttles the subcooling expansion valve 104 when the discharge pressure of the compressor 101 is low, thereby reducing the amount of refrigerant bypassed and moved to the accumulator 107. In this way, the outdoor unit control unit 115 prevents a decrease in the amount of refrigerant recovered from the indoor unit 200.

[0035] Next, the operation of the refrigerant recovery operation process in the air conditioner 1 will be described with reference to Fig. 2. Fig. 2 is a flowchart showing the refrigerant recovery operation process according to this embodiment.

[0036] (Step S101) The air conditioner 1 detects a refrigerant leak using the refrigerant leak sensors 213, 223. For example, when the indoor unit control unit 215 or the indoor unit control unit 225 receives a refrigerant leak detection signal from the refrigerant leak sensor 213 or the refrigerant leak sensor 223, it notifies the outdoor unit control unit 115 that the refrigerant leak sensor 213, 223 has detected a refrigerant leak. Then, the process proceeds to step S103.

[0037] (Step S103) When the air conditioner 1 detects a refrigerant leak, it starts a refrigerant recovery operation. For example, the outdoor unit control unit 115 fixes the rotation speed of the compressor 101 to a given rotation speed and closes the liquid-side shutoff valve 105. As an example, when the given rotation speed of the compressor 101 is 65 Hz, the outdoor unit control unit 115 fixes the rotation speed of the compressor 101 to 65 Hz during the refrigerant recovery operation, regardless of whether the compressor 101 is operating or stopped. Then, the process proceeds to step S105.

[0038] (Step S105) The air conditioner 1 starts feedback control of the subcooling expansion valve 104. Then, the process proceeds to step S111.

[0039] (Step S111) In feedback control of the subcooling expansion valve 104, the air conditioner 1 determines a target opening degree of the subcooling expansion valve 104 according to the discharge pressure of the compressor 101. For example, the outdoor unit control unit 115 determines the target opening degree based on the detection results from the discharge pressure sensor 108 so that the subcooling expansion valve 104 opens when the discharge pressure of the compressor 101 is high and throttles when the discharge pressure is low. Then, the process proceeds to step S113.

[0040] (Step S113) The air conditioner 1 sets the opening degree of the subcooling expansion valve 104 to the target opening degree determined in step S111. For example, the outdoor unit control unit 115 opens the subcooling expansion valve 104 when the discharge pressure of the compressor 101 is high, and throttles the subcooling expansion valve 104 when the discharge pressure is low. Then, the process proceeds to step S121.

[0041] (Step S121) The air conditioner 1 determines whether or not the termination conditions have been met. For example, the termination conditions may be when the suction pressure of the compressor 101 falls below a predetermined threshold or when the refrigerant recovery operation time exceeds a predetermined threshold. Note that when the suction pressure of the compressor 101 falls below the predetermined threshold or when the refrigerant recovery operation time exceeds the predetermined threshold, this corresponds to the recovery of refrigerant having progressed to the point where further recovery is no longer necessary. If the air conditioner 1 determines that the termination conditions have not been met (NO), it returns to step S111 and continues the refrigerant recovery operation. On the other hand, if the air conditioner 1 determines that the termination conditions have been met (YES), it proceeds to step S123.

[0042] (Step S123) If the air conditioner 1 determines in step S121 that the termination condition is satisfied, the air conditioner 1 performs an operation to terminate the refrigerant recovery operation. For example, the outdoor unit control unit 115 stops the compressor 101 and closes the gas-side shutoff valve 106 to confine the refrigerant within the outdoor unit 100 and terminate the refrigerant recovery operation.

[0043] In this way, the air conditioner 1 can prevent high-pressure cuts and delays in refrigerant recovery operation by changing and adjusting the opening of the subcooling expansion valve 104 according to the discharge pressure of the compressor 101. This allows the air conditioner 1 to perform refrigerant recovery operation more efficiently, reducing the amount of refrigerant leaking into the room.

[0044] As described above, the air conditioner 1 according to this embodiment includes a refrigerant circuit that circulates a refrigerant through a compressor 101, a four-way valve 102, an outdoor heat exchanger 103, indoor unit expansion valves 211, 221, indoor heat exchangers 212, 222, and an accumulator 107, an indoor unit 200 (indoor units 210, 220) that includes the indoor heat exchangers 212, 222, and an outdoor unit that includes the compressor 101, the four-way valve 102, the outdoor heat exchanger 103, and the accumulator 107. The air conditioner 1 also includes a liquid piping 20, a bypass piping 10b (an example of a bypass pipe), a subcooling heat exchanger 10a, a subcooling expansion valve 104, a liquid-side shutoff valve 105, a discharge pressure sensor 108, and an outdoor unit control unit 115 and indoor unit control units 215, 225 that control the operation of the air conditioner 1.

[0045] The liquid piping 20 enables refrigerant to flow between the outdoor heat exchanger 103 and the indoor unit expansion valves 211, 221. The bypass piping 10b bypasses refrigerant from the liquid piping 20 to the accumulator 107. The subcooling heat exchanger 10a is provided in the liquid piping 20 and is configured to exchange heat between the refrigerant flowing through the bypass piping 10b and the refrigerant flowing through the liquid piping 20. The subcooling expansion valve 104 is provided in the bypass piping 10b and is capable of adjusting the flow rate of refrigerant flowing from the liquid piping 20 to the subcooling heat exchanger 10a. The liquid-side shut-off valve 105 is provided in the liquid piping 20 between the subcooling heat exchanger 10a and the indoor heat exchangers 212, 222. The discharge pressure sensor 108 detects the discharge pressure of the refrigerant discharged from the compressor 101.

[0046] When the indoor unit control units 215, 225 receive a refrigerant leakage detection signal from the refrigerant leakage sensors 213, 223, the outdoor unit control unit 115 closes the liquid-side shutoff valve 105 and performs a refrigerant recovery operation to move the refrigerant circulating in the refrigerant circuit to the outdoor unit 100. Furthermore, during the refrigerant recovery operation, the outdoor unit control unit 115 changes the opening degree of the subcooling expansion valve 104 in accordance with the detection value of the discharge pressure sensor 108.

[0047] In this way, the air conditioner 1 monitors the amount of refrigerant accumulated in the outdoor heat exchanger 103 based on the detection value of the discharge pressure sensor 108 (the discharge pressure of the compressor 101), and changes the opening of the subcooling expansion valve 104 according to this detection value. This allows the air conditioner 1 to adjust the amount of refrigerant flowing from the outdoor heat exchanger 103 to the accumulator 107, thereby controlling the discharge pressure of the compressor 101 to a target value and preventing liquid sealing of the outdoor heat exchanger. Furthermore, because the air conditioner 1 can also accumulate refrigerant in the accumulator 107, the amount of refrigerant that can be recovered to the outdoor unit 100 increases.

[0048] Furthermore, because the air conditioner 1 adjusts the amount of refrigerant flowing from the outdoor heat exchanger 103 into the accumulator 107 according to the discharge pressure of the compressor 101, the amount of refrigerant flowing from the outdoor heat exchanger 103 into the accumulator 107 does not become extremely greater than the amount of refrigerant flowing from the indoor unit 200 into the accumulator 107 via the four-way valve 102. Therefore, in the air conditioner 1, the refrigerant that flows into the accumulator 107 from the indoor unit 200 is also appropriately drawn into the compressor 101, making it possible to prevent the refrigerant recovery operation from being extended.

[0049] Therefore, when the air conditioner 1 detects a refrigerant leak, during refrigerant recovery operation in which the refrigerant in the refrigerant circuit is recovered to the outdoor unit 100, the air conditioner 1 can prevent the outdoor heat exchanger 103 from becoming liquid-sealed while suppressing the extension of the refrigerant recovery operation.

[0050] Furthermore, the control method in the air conditioner 1 according to this embodiment includes the steps of: when the indoor unit control units 215, 225 receive a refrigerant leakage detection signal from the refrigerant leakage sensors 213, 223, the outdoor unit control unit 115 closes the liquid-side shut-off valve 105 and performs a refrigerant recovery operation in which the refrigerant circulating in the refrigerant circuit is moved to the outdoor unit 100; and during the refrigerant recovery operation, changing the opening of the subcooling expansion valve 104 in accordance with the detection value of the discharge pressure sensor 108.

[0051] As a result, as described above, the control method in the air conditioner 1 can prevent the outdoor heat exchanger 103 from becoming liquid-sealed during refrigerant recovery operation in which refrigerant from the refrigerant circuit is recovered to the outdoor unit 100 when a refrigerant leak is detected, while suppressing the extension of the refrigerant recovery operation.

[0052] As described above, the air conditioner 1 includes an outdoor unit 100 and an indoor unit 200, each equipped with an accumulator 107, a bypass pipe 10b for bypassing refrigerant from the outdoor heat exchanger 103 to the accumulator 107, and a subcooling expansion valve 104. The air conditioner 1 and the control method thereof adjust the opening of the subcooling expansion valve 104 according to the discharge pressure of the compressor 101, thereby storing refrigerant not only in the outdoor heat exchanger 103 but also in the accumulator 107 and preventing liquid sealing. Simply opening the subcooling expansion valve 104 increases the amount of bypass to the accumulator 107, reducing the amount of refrigerant recovered from the indoor unit 200, leading to a delay in the refrigerant recovery operation. Therefore, the air conditioner 1 and the control method thereof throttle the subcooling expansion valve 104 when the discharge pressure of the compressor 101 is low, thereby suppressing a delay in the refrigerant recovery operation.

[0053] Second Embodiment Next, a second embodiment will be described. In the refrigerant recovery operation in the first embodiment, the opening degree of the subcooling expansion valve 104 is adjusted according to the discharge pressure of the compressor 101. However, in this embodiment, proportional control may be used in the feedback control of the subcooling expansion valve 104.

[0054] In this embodiment, the air conditioner 1 determines the target opening degree of the subcooling expansion valve 104, for example, using the following formula 1.

[0055] Target LEV opening=Current LEV opening−Kp×(Target discharge pressure−Current discharge pressure) (Equation 1) Target LEV opening: Target opening of the subcooling expansion valve 104 Current LEV opening: Current opening of the subcooling expansion valve 104 Kp: Proportional coefficient

[0056] If the current discharge pressure of the subcooling expansion valve 104 is higher than the preset target discharge pressure, the air conditioner 1 sets "target LEV opening ≧ current LEV opening" because refrigerant is accumulating in the outdoor heat exchanger 103. On the other hand, if the current discharge pressure is lower than the target discharge pressure, the air conditioner 1 sets "target LEV opening ≦ current LEV opening" because little refrigerant is accumulating in the outdoor heat exchanger 103.

[0057] That is, during the refrigerant recovery operation, if the current detection value (current discharge pressure) of the discharge pressure sensor 108 is higher than the preset target detection value (target discharge pressure), the outdoor unit control unit 115 increases the opening of the subcooling expansion valve 104. On the other hand, during the refrigerant recovery operation, if the current detection value (current discharge pressure) of the discharge pressure sensor 108 is lower than the preset target detection value (target discharge pressure), the outdoor unit control unit 115 decreases the opening of the subcooling expansion valve 104.

[0058] Next, the operation of the refrigerant recovery operation process when proportional control is used in the feedback control of the subcooling expansion valve 104 will be described with reference to Fig. 3. Fig. 3 is a flowchart showing the refrigerant recovery operation process according to this embodiment.

[0059] The processes of steps S201, S203, and S205 in Fig. 3 are the same as the processes of steps S101, S103, and S105 in Fig. 2. When the air conditioner 1 detects a refrigerant leak, it starts a refrigerant recovery operation and starts feedback control of the subcooling expansion valve 104. Then, the process proceeds to step S211.

[0060] (Step S211) The air conditioner 1 determines the target opening degree (target LEV opening degree) of the subcooling expansion valve 104 according to the following formula.

[0061] Target LEV opening = current LEV opening - Kp x (target discharge pressure - current discharge pressure)

[0062] In other words, if the current discharge pressure of the subcooling expansion valve 104 is higher than the preset target discharge pressure, the air conditioner 1 sets "target LEV opening ≧ current LEV opening" because refrigerant is accumulating in the outdoor heat exchanger 103. On the other hand, if the current discharge pressure is lower than the target discharge pressure, the air conditioner 1 sets "target LEV opening ≦ current LEV opening" because little refrigerant is accumulating in the outdoor heat exchanger 103. Then, the process proceeds to step S213.

[0063] (Step S213) The air conditioner 1 sets the opening of the subcooling expansion valve 104 to the target opening determined in step S211. For example, if the current detection value (current discharge pressure) of the discharge pressure sensor 108 is higher than a preset target detection value (target discharge pressure), the outdoor unit control unit 115 increases the opening of the subcooling expansion valve 104. On the other hand, if the current detection value of the discharge pressure sensor 108 is lower than the preset target detection value, the outdoor unit control unit 115 decreases the opening of the subcooling expansion valve 104. Then, the process proceeds to step S221.

[0064] The subsequent processes of steps S221 and S223 are the same as the processes of steps S121 and S123 in Fig. 2. If the air conditioner 1 determines that the termination conditions are not satisfied, it continues the refrigerant recovery operation, and if it determines that the termination conditions are satisfied, it performs an operation to terminate the refrigerant recovery operation. For example, the outdoor unit control unit 115 stops the compressor 101 and closes the gas-side shutoff valve 106 to confine the refrigerant within the outdoor unit 100 and terminate the refrigerant recovery operation.

[0065] In this way, the air conditioner 1 controls the subcooling expansion valve 104 so that the discharge pressure of the compressor 101 becomes the target discharge pressure. As a result, the air conditioner 1 can prevent the outdoor heat exchanger 103 from becoming liquid-sealed, while suppressing the occurrence of a phenomenon in which refrigerant suddenly flows into the bypass from the outdoor heat exchanger 103 to the accumulator 107, and can suppress the extension of the refrigerant recovery operation.

[0066] As described above, in the air conditioner 1 according to this embodiment, when the current detection value (current discharge pressure) of the discharge pressure sensor 108 is higher than the preset target detection value (target discharge pressure) during refrigerant recovery operation, the outdoor unit control unit 115 increases the opening of the subcooling expansion valve 104. On the other hand, when the current detection value (current discharge pressure) of the discharge pressure sensor 108 is lower than the preset target detection value (target discharge pressure) during refrigerant recovery operation, the outdoor unit control unit 115 decreases the opening of the subcooling expansion valve 104.

[0067] As a result, the air conditioner 1 can control the discharge pressure of the compressor 101 to the target discharge pressure by adjusting the opening degree of the subcooling expansion valve 104, thereby preventing the outdoor heat exchanger 103 from becoming liquid-sealed and preventing the occurrence of a phenomenon in which refrigerant suddenly flows from the outdoor heat exchanger 103 into the accumulator 107, thereby suppressing the extension of the refrigerant recovery operation.

[0068] Third Embodiment Next, a third embodiment will be described. In the refrigerant recovery operation in the first and second embodiments, the subcooling expansion valve 104 is adjusted according to the discharge pressure of the compressor 101. However, in this embodiment, the opening degree of the subcooling expansion valve 104 may be set to either an upper limit or a lower limit, or both.

[0069] Here, the lower limit opening degree of the subcooling expansion valve 104 is referred to as "LEV_1." The upper limit opening degree of the subcooling expansion valve 104 is referred to as "LEV_2." The upper limit opening degree (LEV_2) is set to an opening degree that is greater than the lower limit opening degree (LEV_1) of the subcooling expansion valve 104 and smaller than the maximum opening degree.

[0070] At the start of the refrigerant recovery operation, the outdoor unit control unit 115 first controls the opening degree of the subcooling expansion valve 104 to a predetermined initial opening degree. For example, the initial opening degree is set to the lower limit opening degree (LEV_1).

[0071] During the refrigerant recovery operation, the outdoor unit control unit 115 changes the opening degree of the subcooling expansion valve 104 between the upper limit opening degree (LEV_2) and the lower limit opening degree (LEV_1) of the subcooling expansion valve 104.

[0072] 4, a description will be given of the operation of the refrigerant recovery operation when an upper limit opening degree and a lower limit opening degree are set in the feedback control of the subcooling expansion valve 104. FIG. 4 is a flowchart showing the refrigerant recovery operation process according to this embodiment.

[0073] The processes of steps S301, S303, and S305 in Fig. 4 are the same as the processes of steps S101, S103, and S105 in Fig. 2. When the air conditioner 1 detects a refrigerant leak, it starts a refrigerant recovery operation, but in step S304 it controls the opening of the subcooling expansion valve 104 to a predetermined initial opening before proceeding to step S305.

[0074] (Step S304) The air conditioner 1 controls the opening of the subcooling expansion valve 104 to the initial opening. For example, the outdoor unit control unit 115 sets the target LEV opening of the initial opening to the lower limit opening (LEV_1) (target LEV opening = LEV_1).

[0075] That is, the air conditioner 1 (outdoor unit control unit 115) sets the initial opening of the subcooling expansion valve 104 to the lower limit opening (LEV_1), then proceeds to step S305 and starts feedback control of the subcooling expansion valve 104. Then, proceeds to step S311.

[0076] (Step S311) In feedback control of the subcooling expansion valve 104, the air conditioner 1 (outdoor unit control unit 115) determines the target opening of the subcooling expansion valve 104 according to the discharge pressure of the compressor 101. For example, based on the detection results from the discharge pressure sensor 108, the outdoor unit control unit 115 determines the target opening (target LEV opening) so that the subcooling expansion valve 104 opens when the discharge pressure of the compressor 101 is high and throttles down when the discharge pressure is low. Then, the process proceeds to step S313.

[0077] (Step S313) The outdoor unit control unit 115 determines whether the target opening (target LEV opening) of the subcooling expansion valve 104 determined in step S311 is below the lower limit opening (LEV_1). If the outdoor unit control unit 115 determines that the target opening (target LEV opening) of the subcooling expansion valve 104 is below the lower limit opening (LEV_1) (YES), the outdoor unit control unit 115 proceeds to step S314 and sets the target opening (target LEV opening) of the subcooling expansion valve 104 to the lower limit opening (LEV_1) (target LEV opening = LEV_1). Then, the outdoor unit control unit 115 proceeds to step S317. On the other hand, if the outdoor unit control unit 115 determines that the target opening (target LEV opening) of the subcooling expansion valve 104 is not below the lower limit opening (LEV_1) (NO), the outdoor unit control unit 115 proceeds to step S315.

[0078] (Step S315) The outdoor unit control unit 115 determines whether the target opening (target LEV opening) of the subcooling expansion valve 104 determined in step S311 exceeds the upper limit opening (LEV_2). If the outdoor unit control unit 115 determines that the target opening (target LEV opening) of the subcooling expansion valve 104 exceeds the upper limit opening (LEV_2) (YES), the outdoor unit control unit 115 proceeds to step S316, where it sets the target opening (target LEV opening) of the subcooling expansion valve 104 to the upper limit opening (LEV_2) (target LEV opening = LEV_2). Then, it proceeds to step S317. In addition, if the outdoor unit control unit 115 determines that the target opening (target LEV opening) of the subcooling expansion valve 104 does not exceed the upper limit opening (LEV_2) (NO), it adopts the target opening (target LEV opening) of the subcooling expansion valve 104 determined in step S311 and proceeds to step S317.

[0079] (Step S317) The outdoor unit control unit 115 sets the opening of the subcooling expansion valve 104 to the target opening determined in steps S311 to S316. That is, during the refrigerant recovery operation, the outdoor unit control unit 115 sets the opening of the subcooling expansion valve 104 between the upper limit opening (LEV_2) and the lower limit opening (LEV_1) of the subcooling expansion valve 104. Then, the process proceeds to step S321.

[0080] The subsequent processes of steps S321 and S323 are the same as the processes of steps S121 and S123 in Fig. 2. If the air conditioner 1 determines that the termination conditions are not satisfied, it continues the refrigerant recovery operation, and if it determines that the termination conditions are satisfied, it performs an operation to terminate the refrigerant recovery operation. For example, the outdoor unit control unit 115 stops the compressor 101 and closes the gas-side shutoff valve 106 to confine the refrigerant within the outdoor unit 100 and terminate the refrigerant recovery operation.

[0081] In this way, the air conditioner 1 has the following advantages by providing a lower limit opening degree and an upper limit opening degree when adjusting the opening degree of the subcooling expansion valve 104.

[0082] (Advantages of Setting a Lower Limit Opening) Due to refrigerant distribution before the refrigerant recovery operation, a large amount of refrigerant may accumulate in the outdoor heat exchanger 103 immediately after the refrigerant recovery operation, causing a sudden rise in the discharge pressure of the compressor 101. This may prevent feedback control of the subcooling expansion valve 104 from keeping up, resulting in a high-pressure cut. Therefore, by setting a lower limit opening when adjusting the opening of the subcooling expansion valve 104, the air conditioner 1 can always release a constant amount of refrigerant to the accumulator 107, preventing the occurrence of a high-pressure cut. Furthermore, if a lower limit opening is not set, the opening would have to be increased from a fully closed state. However, by setting a lower limit opening when adjusting the opening of the subcooling expansion valve 104, the air conditioner 1 can shorten the time required to increase the opening to a predetermined opening compared to when a lower limit opening is not set, thereby efficiently performing feedback control of the subcooling expansion valve 104.

[0083] (Advantages of Setting an Upper Limit of Opening Degree) Although it depends on the flow characteristics of the subcooling expansion valve 104, if the maximum opening degree is too large, the amount of refrigerant bypassed and flowing to the accumulator 107 will increase too much, resulting in a decrease in the amount of refrigerant recovered from the indoor unit 200. By setting an upper limit of opening degree when adjusting the opening degree of the subcooling expansion valve 104, the air conditioner 1 can prevent a large amount of refrigerant from flowing from the outdoor heat exchanger 103 into the accumulator 107 in a short period of time, and can suppress delays in the refrigerant recovery operation.

[0084] As described above, in the air conditioner 1 according to this embodiment, the outdoor unit control unit 115 controls the opening of the subcooling expansion valve 104 to a predetermined initial opening (an example of a first opening, for example, a lower limit opening) at the start of the refrigerant recovery operation. During the refrigerant recovery operation, the outdoor unit control unit 115 changes the opening of the subcooling expansion valve 104 between an upper limit opening (an example of a second opening) that is greater than the initial opening (an example of the first opening, for example, a lower limit opening) and less than the maximum opening, and the initial opening (an example of the first opening, for example, a lower limit opening).

[0085] As a result, the air conditioner 1 opens the subcooling expansion valve 104 at an initial opening (for example, about 20%) from the start of refrigerant recovery operation, so that even if there is a temporary sudden increase in the amount of refrigerant recovered, the refrigerant can be released into the accumulator 107, thereby mitigating the pressure increase in the outdoor heat exchanger 103 and preventing high-pressure cuts (forced shutdown due to pressure abnormalities) from occurring.

[0086] Furthermore, in refrigerant recovery operation, the air conditioner 1 can reduce the time required to increase the opening of the subcooling expansion valve 104 to a predetermined opening compared to increasing the opening from a fully closed state. Therefore, when increasing the opening of the subcooling expansion valve 104 in accordance with the discharge pressure of the compressor 101, the air conditioner 1 can quickly change to the predetermined opening, and can bypass the refrigerant accumulated in the outdoor heat exchanger 103 to the accumulator 107 before a high-pressure cut occurs even if the discharge pressure suddenly increases.

[0087] In addition, in the air conditioner 1, the maximum opening during refrigerant recovery operation is the upper limit opening, which is smaller than the maximum opening (fully open) of the subcooling expansion valve, so it is possible to prevent a large amount of refrigerant from flowing from the outdoor heat exchanger 103 into the accumulator 107 in a short period of time, and to suppress the extension of the refrigerant recovery operation.

[0088] Fourth Embodiment Next, a fourth embodiment will be described. In the refrigerant recovery operation in the first to third embodiments described above, feedback control of the subcooling expansion valve 104 is performed according to the discharge pressure, but in addition, the fans of all indoor units 200 (indoor fans 214, 224) may be driven at maximum rotation speeds when the refrigerant recovery operation starts.

[0089] For example, when the refrigerant recovery operation starts, the indoor unit control units 215, 225 drive the indoor fans 214, 224 of the indoor units 210, 220 connected to the outdoor unit 100 at maximum rotation speed, regardless of the operating mode of the air conditioner 1 before the refrigerant recovery operation starts.

[0090] 5, a description will be given of the processing of the refrigerant recovery operation in the case where the fans of all the indoor units 200 are driven at the maximum rotation speed at the start of the refrigerant recovery operation in feedback control of the subcooling expansion valve 104. Fig. 5 is a flowchart showing the processing of the refrigerant recovery operation according to this embodiment.

[0091] The processes of steps S401, S403, and S405 in Fig. 5 are the same as the processes of steps S101, S103, and S105 in Fig. 2. When the air conditioner 1 detects a refrigerant leak, it starts a refrigerant recovery operation, but in step S404 it drives the fans of all indoor units 200 (indoor fans 214, 224) to their maximum rotation speeds before proceeding to step S405.

[0092] For example, in step S404, immediately after the start of the refrigerant recovery operation, the indoor unit control units 215, 225 drive the indoor fans 214, 224 of the indoor units 210, 220 connected to the outdoor unit 100 at the maximum rotation speed, regardless of the operation mode of the air conditioner 1 before the start of the refrigerant recovery operation. The air conditioner 1 then proceeds to step S405 and starts feedback control of the subcooling expansion valve 104. The air conditioner 1 then proceeds to step S411.

[0093] The processes of steps S411 and S413 are the same as the processes of steps S311 and S315 in Fig. 2. In the feedback control of the subcooling expansion valve 104, the air conditioner 1 determines and sets the target opening degree of the subcooling expansion valve 104 in accordance with the discharge pressure of the compressor 101.

[0094] Note that instead of the processes of steps S411 and S413, the target opening degree of the subcooling expansion valve 104 may be determined and set by the processes of steps S211 and S213 in FIG. 3 or the processes of S311 to S316 in FIG.

[0095] The subsequent processes of steps S421 and S423 are the same as the processes of steps S121 and S123 in Fig. 2. If the air conditioner 1 determines that the termination conditions are not satisfied, it continues the refrigerant recovery operation, and if it determines that the termination conditions are satisfied, it performs an operation to terminate the refrigerant recovery operation. For example, the outdoor unit control unit 115 stops the compressor 101 and closes the gas-side shutoff valve 106 to confine the refrigerant within the outdoor unit 100 and terminate the refrigerant recovery operation.

[0096] In this way, the air conditioner 1 drives the indoor fans of all indoor units 200 (for example, indoor fans 214, 224 of indoor units 210, 220) at maximum rotation speed during refrigerant recovery operation, thereby promoting gasification of the refrigerant in the indoor heat exchangers 212, 222 and enabling the refrigerant to be recovered to the outdoor unit 100 more efficiently.

[0097] Furthermore, in the first to third embodiments, the air conditioner 1 implements feedback control of the subcooling expansion valve 104 as a countermeasure against liquid sealing, but this also leads to a delay in the refrigerant recovery operation. Therefore, the air conditioner 1 can suppress delays in the refrigerant recovery operation by driving the indoor fans 214, 224 at the maximum rotation speed during the refrigerant recovery operation.

[0098] As described above, in the air conditioner 1 according to this embodiment, the indoor units 210, 220 (an example of an indoor unit) are equipped with indoor fans 214, 224 (an example of a fan). At the start of the refrigerant recovery operation, the indoor unit control units 215, 225 drive the indoor fans 214, 224 of the indoor units 210, 220 connected to the outdoor unit 100 at the maximum rotation speed, regardless of the operation mode of the air conditioner 1 before the start of the refrigerant recovery operation.

[0099] As a result, the air conditioner 1 can gasify the refrigerant in the indoor heat exchangers 212, 222 by rotating the indoor fans 214, 224 of the indoor units 210, 220, and more efficiently recover the refrigerant to the outdoor unit 100. Furthermore, by rotating the fans of all of the indoor units 200 connected to the outdoor unit 100 at this time, the air conditioner 1 can more efficiently recover the refrigerant and suppress delays in the refrigerant recovery operation.

[0100] Each embodiment has been described above in detail with reference to the drawings, but the specific configuration is not limited to these embodiments, and it is possible to combine the embodiments, or to modify or omit the embodiments as appropriate.

[0101] For example, in the configuration of the air conditioner 1 shown in Figure 1, two indoor units 200, an indoor unit 210 and an indoor unit 220, are shown, but the number of indoor units 200 may be three or more, or may be just one.

[0102] Note that a program for realizing the functions of the outdoor unit control unit 115 and the indoor unit control units 215, 225 may be recorded on a computer-readable recording medium, and the program recorded on this recording medium may be read into a computer system and executed to perform the processing of the outdoor unit control unit 115 and the indoor unit control units 215, 225. Note that the term "computer system" here includes hardware such as the OS and peripheral devices.

[0103] Furthermore, "computer-readable recording media" refers to portable media such as flexible disks, optical magnetic disks, ROMs, and CD-ROMs, as well as storage devices such as hard disks built into computer systems. Furthermore, "computer-readable recording media" also includes devices that dynamically store programs for a short period of time, such as communication lines used when transmitting programs over networks like the Internet or communication lines like telephone lines, and devices that store programs for a fixed period of time, such as volatile memory within computer systems that serve as servers or clients. The programs may also be programs that implement some of the aforementioned functions, or may be programs that can achieve the aforementioned functions in combination with programs already stored in the computer system. The programs may also be stored on a designated server and distributed (e.g., downloaded) over communication lines in response to requests from other devices.

[0104] Furthermore, some or all of the functions of the outdoor unit control unit 115 and the indoor unit control units 215, 225 may be implemented as an integrated circuit such as an LSI (Large Scale Integration). Each function may be implemented as a separate processor, or some or all of the functions may be integrated into a processor. The integrated circuit implementation method is not limited to LSI, and may be implemented using a dedicated circuit or a general-purpose processor. Furthermore, if an integrated circuit technology that can replace LSI emerges due to advances in semiconductor technology, an integrated circuit based on that technology may be used.

[0105] 1 Air conditioner 10 Gas piping 20 Liquid piping 100 Outdoor unit 101 Compressor 102 Four-way valve 103 Outdoor heat exchanger 104 Subcooling expansion valve 105 Liquid-side shutoff valve 106 Gas-side shutoff valve 107 Accumulator 108 Discharge pressure sensor 109 Suction pressure sensor 10a Subcooling heat exchanger 10b Bypass piping 115 Outdoor unit control unit 200 Indoor unit 210, 220 Each indoor unit 211, 221 Indoor unit expansion valve 212, 222 Indoor heat exchanger 213, 223 Refrigerant leakage sensor 214, 224 Indoor fan 215, 225 Indoor unit control unit

Claims

1. An air conditioner comprising a refrigerant circuit that circulates a refrigerant via a compressor, a four-way valve, an outdoor heat exchanger, an indoor unit expansion valve, an indoor heat exchanger, and an accumulator; an indoor unit equipped with the indoor heat exchanger; and an outdoor unit equipped with the compressor, the four-way valve, the outdoor heat exchanger, and the accumulator, A liquid piping that enables the flow of refrigerant between the outdoor heat exchanger and the indoor unit expansion valve, A bypass pipe that bypasses the refrigerant from the liquid piping to the accumulator, A subcooling heat exchanger is provided in the liquid piping and configured to exchange heat between the refrigerant flowing through the bypass pipe and the refrigerant flowing through the liquid piping, A subcooling expansion valve is provided in the bypass pipe and is capable of adjusting the flow rate of refrigerant from the liquid piping to the subcooling heat exchanger, A liquid-side shut-off valve is provided between the subcooled heat exchanger and the indoor heat exchanger in the liquid piping, A discharge pressure sensor for detecting the discharge pressure of the refrigerant discharged from the compressor, A control unit that controls the operation of the air conditioner, Equipped with, The control unit, Upon receiving a refrigerant leak detection signal from the refrigerant leak sensor, the liquid-side shut-off valve is closed, and a refrigerant recovery operation is performed to move the refrigerant circulating in the refrigerant circuit to the outdoor unit. During the refrigerant recovery operation, if the current detected value of the discharge pressure sensor is higher than a preset target detected value, the opening of the subcooling expansion valve is increased, and if the current detected value of the discharge pressure sensor is lower than the target detected value, the opening of the subcooling expansion valve is decreased, thereby providing feedback control of the subcooling expansion valve. Perform At the start of the refrigerant recovery operation, the opening degree of the subcooling expansion valve is set to the lower limit opening degree, and then the feedback control is started. In the feedback control performed during the refrigerant recovery operation, the opening of the subcooling expansion valve is changed between an upper limit opening that is greater than the lower limit opening and less than the maximum opening, and the lower limit opening. Air conditioner.

2. The aforementioned indoor unit is equipped with a fan, The control unit, At the start of the refrigerant recovery operation, regardless of the operating mode of the air conditioner prior to the start of the refrigerant recovery operation, all fans of the indoor units connected to the outdoor unit are driven at their maximum rotational speed. The air conditioner according to claim 1.

3. A control method for an air conditioner comprising: a refrigerant circuit that circulates a refrigerant via a compressor, a four-way valve, an outdoor heat exchanger, an indoor unit expansion valve, an indoor heat exchanger, and an accumulator; an indoor unit equipped with the indoor heat exchanger; an outdoor unit equipped with the compressor, the four-way valve, the outdoor heat exchanger, and the accumulator; liquid piping that enables the flow of refrigerant between the outdoor heat exchanger and the indoor unit expansion valve; a bypass pipe that bypasses the refrigerant from the liquid piping to the accumulator; a subcooling heat exchanger provided in the liquid piping and configured to exchange heat between the refrigerant flowing through the bypass pipe and the refrigerant flowing through the liquid piping; a subcooling expansion valve provided in the bypass pipe and capable of adjusting the flow rate of refrigerant flowing from the liquid piping to the subcooling heat exchanger; a liquid-side shut-off valve provided between the subcooling heat exchanger and the indoor heat exchanger in the liquid piping; and a discharge pressure sensor that detects the discharge pressure of the refrigerant discharged from the compressor, wherein The control unit that controls the operation of the air conditioner, Upon receiving a refrigerant leak detection signal from the refrigerant leak sensor, the liquid side shut-off valve is closed, and a refrigerant recovery operation is performed to move the refrigerant circulating in the refrigerant circuit to the outdoor unit. During the refrigerant recovery operation, if the current detected value of the discharge pressure sensor is higher than a preset target detected value, the opening of the subcooling expansion valve is increased, and if the current detected value of the discharge pressure sensor is lower than the target detected value, the opening of the subcooling expansion valve is decreased, thereby performing feedback control of the subcooling expansion valve. Includes, At the start of the refrigerant recovery operation, the opening degree of the subcooling expansion valve is set to the lower limit opening degree, and then the feedback control is started. In the feedback control performed during the refrigerant recovery operation, the opening of the subcooling expansion valve is changed between an upper limit opening that is greater than the lower limit opening and less than the maximum opening, and the lower limit opening. Control method.