Refrigeration cycle equipment

Abstract

When performing oil return operation in a multi-type air conditioner, if moisture is detected in the compressor's suction piping and then the expansion valve of the indoor unit is throttled, the distance from the expansion valve to the compressor can cause even more moist refrigerant to flow into the compressor, potentially resulting in liquid compression. [Solution] The refrigeration cycle device 1 comprises a heat source side unit 2, a first user side unit group G1, a second user side unit group G2, and a control device 3. The first user side unit group G1 includes at least a user side unit U1 as the first user side unit. The control device 3 performs an oil return operation to return lubricating oil that has leaked out of the compressor 21 to the compressor 21. In the oil return operation, the control device 3 makes the opening degree of the user side expansion valve 101 of user side unit U1 belonging to the first user side unit group G1 different from the opening degrees of the user side expansion valves 201, 301, and 401 of user side units U2, U3, and U4 belonging to the second user side unit group G2.

Description

Technical Field

[0001] It relates to a refrigeration cycle device.

Background Art

[0002] There has conventionally been a multi-type air conditioner that circulates refrigerant only in a specific indoor unit and does not circulate refrigerant in other indoor units when performing a defrost operation, which is an abnormal operation (Patent Document 1 (Japanese Patent Application Laid-Open No. 2002-147879)).

Summary of the Invention

Problems to be Solved by the Invention

[0003] When performing an oil return operation, which is an abnormal operation, in a multi-type air conditioner, when the expansion valve of an indoor unit is throttled after detecting moisture in the suction pipe of the compressor, there is a distance from the expansion valve to the compressor, so there is a problem that more moist refrigerant may flow into the compressor and liquid compression may occur.

Means for Solving the Problems

[0004] The refrigeration cycle device of the first aspect includes a heat source side unit, a first utilization side unit group, a second utilization side unit group, and a control unit. The heat source side unit has a compressor. The first utilization side unit group includes at least a first utilization side unit. The control unit performs an oil return operation to return the lubricating oil flowing out of the compressor to the compressor. Each utilization side unit belonging to the first utilization side unit group and the second utilization side unit group has an expansion valve. The control unit makes the opening degree of the expansion valve of the utilization side unit belonging to the first utilization side unit group different from the opening degree of the expansion valve of the utilization side unit belonging to the second utilization side unit group in the oil return operation.

[0005] In this refrigeration cycle device, it is possible to reduce the opening degree of the expansion valve of the utilization side unit where there is a high risk that refrigerant gas with a high degree of moisture will return to the heat source side unit, and increase the opening degree of the expansion valves of other utilization side units. Therefore, while suppressing liquid compression in the compressor, it is possible to shorten the time required for oil return.

[0006] The refrigeration cycle apparatus in the second aspect is the apparatus in the first aspect, and each user unit belonging to the first user-side unit group and the second user-side unit group comprises a user-side heat exchanger, a detection unit, It has the following features. The detection unit detects the state of the refrigerant at the outlet of the heat exchanger on the user side.

[0007] In this refrigeration cycle system, by detecting the state of the refrigerant at the outlet of the heat exchanger on the user side, it is possible to identify user-side units that are highly likely to have refrigerant gas with a high degree of humidity returning to the heat source-side units.

[0008] The refrigeration cycle device in the third aspect is the device in the first or second aspect, and the control unit controls the opening degree of the expansion valve based on the state of the refrigerant at the outlet of the heat exchanger on the utilization side.

[0009] In this refrigeration cycle system, the degree of moisture content of the refrigerant gas returning to the heat source unit can be adjusted by controlling the opening of the expansion valve based on the state of the refrigerant at the outlet of the heat exchanger on the user side.

[0010] The refrigeration cycle device of the fourth aspect is a device of the first, second, or third aspect, wherein the control unit reduces the opening degree of the expansion valve of any of the user-side units belonging to the first user-side unit group and the second user-side unit, and then increases the opening degree of the expansion valve after a predetermined time has elapsed.

[0011] In this refrigeration cycle system, by reducing the opening of the expansion valve, the refrigerant flow rate in a user-side unit is reduced. After a predetermined time has elapsed, the opening of the expansion valve is increased to prevent the refrigerant flow rate in a specific user-side unit from becoming too low.

[0012] A refrigeration cycle device according to the fifth aspect is a device according to the third or fourth aspect, further comprising an accumulator. The accumulator is positioned between the utilization-side heat exchanger and the compressor's intake port and stores refrigerant in its internal space. The control unit controls the opening degree of the expansion valve based on the state of the refrigerant exiting the accumulator and being drawn into the compressor.

[0013] In this refrigeration cycle system, the opening degree of the expansion valve is controlled based on the state of the refrigerant exiting the accumulator and being drawn into the compressor, thereby preventing excessive accumulation of liquid refrigerant in the accumulator. [Brief explanation of the drawing]

[0014] [Figure 1] This is a schematic diagram of the refrigeration cycle device according to this embodiment. [Figure 2] This is a block diagram of the control device for the refrigeration cycle system according to this embodiment. [Figure 3] This flowchart shows the process of oil return operation during air conditioning. [Figure 4] This flowchart shows the process for oil return operation during heating. [Modes for carrying out the invention]

[0015] Embodiments of this disclosure will be described below with reference to the drawings.

[0016] (1) Overall structure Figure 1 is a schematic diagram of the refrigeration cycle device 1 according to this embodiment.

[0017] The refrigeration cycle unit 1 is an air conditioning system that cools / heats a target space by performing a vapor compression type refrigerant cycle. The refrigeration cycle unit 1 performs normal operation and abnormal operation. Normal operation is the cooling and heating operation of the refrigeration cycle unit 1. Abnormal operation is the oil return operation.

[0018] The refrigeration cycle apparatus 1 includes a heat source side unit 2, a first utilization side unit group G1, a second utilization side unit group G2, and a control device (control unit) 3. In other words, the refrigeration cycle apparatus 1 mainly includes one heat source side unit 2, a plurality of (four in this embodiment) utilization side units U1, U2, U3, U4 connected in parallel to the heat source side unit 2, a liquid refrigerant connection pipe 5, a gas refrigerant connection pipe 6, and a control device 3. The first utilization side unit group G1 includes at least a first utilization side unit. The liquid refrigerant connection pipe 5 and the gas refrigerant connection pipe 6 are pipes that connect the heat source side unit 2 and the utilization units U1, U2, U3, U4. The control device 3 controls the operations of various devices of the heat source side unit 2 and the utilization units U1, U2, U3, U4.

[0019] The refrigeration cycle apparatus 1 is a multi-type that includes a plurality of utilization side units U1 to U4 for one heat source unit 2.

[0020] In this embodiment, the refrigeration cycle apparatus 1 has four utilization side units, but the number of utilization units is not limited to four. The refrigeration cycle apparatus 1 may have two or three utilization side units, or may have four or more utilization side units.

[0021] The heat source side unit 2 and the utilization units U1, U2, U3, U4 are connected via the liquid refrigerant connection pipe 5 and the gas refrigerant connection pipe 6 to constitute a refrigerant circuit 10 in which the refrigerant circulates.

[0022] The refrigerant used in the refrigeration cycle apparatus 1 is, for example, a refrigerant such as R32, although it is not limited.

[0023] The refrigeration cycle device 1 has, as operation modes, a cooling operation mode for executing a cooling operation and a heating operation mode for executing a heating operation. The cooling operation is an operation in which the refrigerant circulates in the refrigerant circuit 10 to realize a refrigeration cycle, and the air in the target space where the utilization-side units U1, U2, U3, and U4 are installed is cooled. The heating operation is an operation in which the refrigerant circulates in the refrigerant circuit 10 to realize a heating cycle, and the air in the target space where the utilization-side units U1, U2, U3, and U4 are installed is heated.

[0024] In addition to the cooling operation and the heating operation, the refrigeration cycle device 1 executes an oil return operation.

[0025] (2) Detailed configuration (2-1) Utilization-side unit The utilization-side units U1, U2, U3, and U4 are units installed in a target space such as a building interior. For example, the utilization-side units U1, U2, U3, and U4 are ceiling-embedded units installed in the ceiling. However, the utilization-side units U1, U2, U3, and U4 are not limited to ceiling-embedded units, and may be ceiling-suspended units suspended from the ceiling, wall-mounted units installed on the wall, or floor-standing units installed on the floor.

[0026] The utilization-side units U1, U2, U3, and U4 are each connected to the heat source unit 2 via the liquid refrigerant connection pipe 5 and the gas refrigerant connection pipe 6, and constitute a part of the refrigerant circuit 10.

[0027] The utilization-side unit U1 has a utilization-side refrigerant circuit 10a, a utilization-side fan 103, various sensors, and a utilization-side control unit 107.

[0028] The utilization-side refrigerant circuit 10a constitutes a part of the refrigerant circuit 10. The utilization-side refrigerant circuit 10a mainly has a utilization-side expansion valve 101 and a utilization-side heat exchanger 102.

[0029] The utilization-side fan 103 is driven by a motor 103a.

[0030] The various sensors in the user-side unit U1 include a liquid-side temperature sensor 104, a gas-side temperature sensor 105, and a target space temperature sensor 106.

[0031] The user-side unit U2 includes a user-side refrigerant circuit 10b, a user-side fan 203, various sensors, and a user-side control unit 207.

[0032] The user-side refrigerant circuit 10b constitutes a part of the refrigerant circuit 10. The user-side refrigerant circuit 10b mainly comprises a user-side expansion valve 201 and a user-side heat exchanger 202.

[0033] The user-side fan 203 is driven by motor 203a.

[0034] The various sensors in the user-side unit U2 include a liquid-side temperature sensor 204, a gas-side temperature sensor 205, and a target space temperature sensor 206.

[0035] The user-side unit U3 includes a user-side refrigerant circuit 10c, a user-side fan 303, various sensors, and a user-side control unit 307.

[0036] The user-side refrigerant circuit 10c constitutes a part of the refrigerant circuit 10. The user-side refrigerant circuit 10c mainly comprises a user-side expansion valve 301 and a user-side heat exchanger 302.

[0037] The user-side fan 303 is driven by motor 303a.

[0038] The various sensors in the user-side unit U3 include a liquid-side temperature sensor 304, a gas-side temperature sensor 305, and a target space temperature sensor 306.

[0039] The user-side unit U4 includes a user-side refrigerant circuit 10d, a user-side fan 403, various sensors, and a user-side control unit 407.

[0040] The user-side refrigerant circuit 10d constitutes a part of the refrigerant circuit 10. The user-side refrigerant circuit 10d mainly comprises a user-side expansion valve 401 and a user-side heat exchanger 402.

[0041] The user-side fan 403 is driven by motor 403a.

[0042] The various sensors in the user-side unit U4 include a liquid-side temperature sensor 404, a gas-side temperature sensor 405, and a target space temperature sensor 406.

[0043] The configurations of the user-side units U2, U3, and U4 are the same as the corresponding configurations of the user-side unit U1. Therefore, below, only the configurations of the user-side unit U1 will be described, and the descriptions of the user-side units U2, U3, and U4 will be omitted unless specifically necessary.

[0044] (2-1-1) User-side heat exchanger The user-side heat exchanger 102 performs heat exchange between the refrigerant flowing inside the user-side heat exchanger 102 and the air in the target space passing over the surface of the user-side heat exchanger 102.

[0045] One end of the user-side heat exchanger 102 is connected to the liquid refrigerant connecting pipe 5 via refrigerant piping. The other end of the user-side heat exchanger 102 is connected to the gas refrigerant connecting pipe 6 via refrigerant piping.

[0046] The user-side heat exchanger 102 is not limited to a specific type, but for example, it is a cross-fin type fin-and-tube heat exchanger composed of heat transfer tubes (not shown) and a large number of fins (not shown).

[0047] The heat exchanger 102 on the user side functions as an evaporator during cooling operation. The heat exchanger 102 on the user side functions as a condenser during heating operation.

[0048] (2-1-2) User-side expansion valve The user-side expansion valve 101 adjusts the pressure and flow rate of the refrigerant flowing through the user-side refrigerant circuit 10a. The user-side expansion valve 101 is installed in the refrigerant piping that connects the liquid side of the user-side heat exchanger 102 and the liquid refrigerant connecting pipe 5. The user-side expansion valve 101 is, for example, an electronically operated expansion valve with a variable opening.

[0049] (2-1-3) User-side fan The user-side fan 103 draws air from the target space into the user-side unit U1, supplies it to the user-side heat exchanger 102, and blows the air that has exchanged heat with the refrigerant in the user-side heat exchanger 102 back into the target space. The user-side fan 103 is, for example, a sirocco fan. However, the type of user-side fan 103 is not limited to a sirocco fan and can be selected as appropriate. The user-side fan 103 is driven by a motor 103a. The user-side fan 103 is a variable-speed fan driven by a motor 103a whose rotational speed can be changed.

[0050] (2-1-4) Sensor The user-side unit U1 has a liquid-side temperature sensor 104, a gas-side temperature sensor 105, and a target space temperature sensor 106 as sensors. The user-side unit U1 does not necessarily have to have all of the above sensors 104, 105, and 106; it may have only some of them.

[0051] The liquid-side temperature sensor 104 is installed in the refrigerant piping that connects the liquid side of the user-side heat exchanger 102 to the liquid refrigerant connecting pipe 5. The liquid-side temperature sensor 104 measures the temperature of the refrigerant flowing through the refrigerant piping on the liquid side of the user-side heat exchanger 102.

[0052] The gas-side temperature sensor 105 is installed in the refrigerant piping that connects the gas side of the user-side heat exchanger 102 to the gas-refrigerant communication pipe 6. The gas-side temperature sensor 105 measures the temperature of the refrigerant flowing through the refrigerant piping on the gas side of the user-side heat exchanger 102.

[0053] The target space temperature sensor 106 is installed on the intake side of the target space air of the user-side unit U1. The target space temperature sensor 46 detects the temperature of the target space air (target space temperature Tr) flowing into the user-side unit U1.

[0054] Although not limited to the type of sensor, in this embodiment, the liquid-side temperature sensor 104, the gas-side temperature sensor 105, and the target space temperature sensor 106 are thermistors.

[0055] (2-1-5) User-side control unit The user-side control unit 107 controls the operation of each part that constitutes the user-side unit U1.

[0056] The user-side control unit 107 is implemented by a microcomputer and memory, etc. The microcomputer comprises a control arithmetic unit and a memory device. A processor such as a CPU or GPU can be used for the control arithmetic unit. The control arithmetic unit reads a program stored in the memory device and performs predetermined arithmetic processing according to this program. Furthermore, the control arithmetic unit can write the calculation results to the memory device or read information stored in the memory device according to the program.

[0057] The user-side control unit 107 is electrically connected to the user-side expansion valve 101, user-side fan 103, liquid-side temperature sensor 104, gas-side temperature sensor 105, and target space temperature sensor 106 of the user-side unit U1 so as to enable the transmission and reception of control signals and information. Furthermore, the user-side control unit 107 is connected to the heat source-side control unit 37 (described later) of the heat source-side unit 2 via a transmission line 8a so as to enable the transmission and reception of control signals, etc. Note that the user-side control unit 107 and the heat source-side control unit 37 do not necessarily have to be connected by a physical transmission line. The user-side control unit 107 and the heat source-side control unit 37 may also be connected wirelessly for communication. The user-side control unit 107 is configured to receive various signals transmitted from a remote control (not shown) for operating the user-side unit U1. These various signals include signals related to the operation / stop of the user-side unit U1 and signals related to various settings. Signals related to various settings include, for example, the operating mode switching signal and the target temperature (set temperature Trs) for cooling and heating operations.

[0058] The user-side control unit 107 and the heat source-side control unit 37 work together to function as a control device 3. The functions of the control device 3 will be described later.

[0059] (2-2) Heat source side unit The heat source unit 2 is installed, for example, outside the building where the refrigeration cycle device 1 is installed.

[0060] The heat source unit 2 is connected to the user units U1, U2, U3, and U4 via the liquid refrigerant connecting pipe 5 and the gas refrigerant connecting pipe 6. The heat source unit 2, together with the user units U1, U2, U3, and U4, constitutes the refrigerant circuit 10.

[0061] The heat source unit 2 includes a heat source side refrigerant circuit 10e, a heat source side fan 28, various sensors, and a heat source side control unit 37.

[0062] The heat source side refrigerant circuit 10e constitutes a part of the refrigerant circuit 10. The heat source side refrigerant circuit 10e mainly includes a compressor 21, a four-way switching valve 22, a heat source side heat exchanger 23, a heat source side expansion valve 38, an accumulator 24, a liquid side shut-off valve 26, a gas side shut-off valve 27, an intake pipe 11a, a discharge pipe 11b, a first gas refrigerant pipe 11c, a liquid refrigerant pipe 11d, and a second gas refrigerant pipe 11e.

[0063] The suction pipe 11a connects the four-way switching valve 22 to the suction side of the compressor 21. An accumulator 24 is provided in the suction pipe 11a.

[0064] The discharge pipe 11b connects the discharge side of the compressor 21 to the four-way switching valve 22.

[0065] The first gas refrigerant pipe 11c connects the four-way switching valve 22 to the gas side of the heat source side heat exchanger 23.

[0066] The liquid refrigerant pipe 11d connects the liquid side of the heat source side heat exchanger 23 to the liquid refrigerant connecting pipe 5. The liquid refrigerant pipe 11d is equipped with a heat source side expansion valve 38. A liquid side shut-off valve 26 is provided at the connection point between the liquid refrigerant pipe 11d and the liquid refrigerant connecting pipe 5.

[0067] The second gas refrigerant pipe 11e connects the four-way switching valve 22 and the gas refrigerant connecting pipe 6. A gas-side shut-off valve 27 is provided at the connection point between the second gas refrigerant pipe 11e and the gas refrigerant connecting pipe 6.

[0068] The main components of the heat source unit 2 will be explained further below.

[0069] (2-2-1) Compressor The compressor 21 compresses the low-pressure refrigerant drawn in from the suction pipe 11a using a compression mechanism (not shown) and discharges it to the discharge pipe 11b. In this embodiment, the heat source unit 2 has only one compressor 21, but the number of compressors 21 is not limited to one. The heat source unit 2 may have multiple compressors 21 connected in parallel. Also, if the heat source unit 2 compresses the refrigerant in multiple stages, the heat source unit 2 may have multiple compressors 21 connected in series.

[0070] The compressor 21 is not limited to any particular type, but it is a positive displacement compressor such as a rotary or scroll type. The compression mechanism of the compressor 21 is driven by the motor 21a. The compression mechanism is driven by the motor 21a, which compresses the refrigerant. Here, the motor 21a is a motor whose rotational speed can be controlled by an inverter. The capacity of the compressor 21 is controlled by controlling the rotational speed (operating frequency) of the motor 21a.

[0071] (2-2-2) Four-way switching valve The four-way switching valve 22 switches the direction of refrigerant circulation by switching the direction of refrigerant flow.

[0072] During cooling operation, the flow direction of the refrigerant discharged from the compressor 21 is switched by the four-way switching valve 22 to the connection state shown by the solid line in Figure 1. The four-way switching valve 22 connects the suction pipe 11a to the second gas refrigerant pipe 11e and the discharge pipe 11b to the first gas refrigerant pipe 11c (see the solid line in the four-way switching valve 22 in Figure 1). The refrigerant discharged from the compressor 21 flows through the refrigerant circuit 10 in the following order: heat source side heat exchanger 23, heat source side expansion valve 38, utilization side expansion valves 101, 201, 301, 401, utilization side heat exchangers 102, 202, 302, 402, and returns to the compressor 21. This realizes the cooling cycle.

[0073] During heating operation, the flow direction of the refrigerant discharged from the compressor 21 is switched by the four-way switching valve 22 to the connection state shown by the dashed line in Figure 1. The four-way switching valve 22 connects the suction pipe 11a to the first gas refrigerant pipe 11c and the discharge pipe 11b to the second gas refrigerant pipe 11e (see the dashed line in the four-way switching valve 22 in Figure 1). The refrigerant discharged from the compressor 21 flows through the refrigerant circuit 10 in the following order: user-side heat exchangers 102, 202, 302, 402, user-side expansion valves 101, 201, 301, 401, heat source-side expansion valve 38, heat source-side heat exchanger 23, and returns to the compressor 21. This realizes the heating cycle.

[0074] (2-2-3) Heat source side heat exchanger The heat source side heat exchanger 23 performs heat exchange between the refrigerant flowing inside the heat source side heat exchanger 23 and the air at the installation location of the heat source side unit 2 (referred to as heat source air) that passes over the surface of the heat source side heat exchanger 23. If the heat source side unit 2 is installed outdoors, the heat source side heat exchanger 23 performs heat exchange between the refrigerant flowing inside and the outdoor air.

[0075] One end of the heat source side heat exchanger 23 is connected to the liquid refrigerant pipe 11d. The other end of the heat source side heat exchanger 23 is connected to the first gas refrigerant pipe 11c.

[0076] The heat source side heat exchanger 23 is not limited to a specific type, but for example, it is a fin-and-tube type heat exchanger having heat transfer tubes (not shown) and a number of fins (not shown).

[0077] The heat source side heat exchanger 23 functions as an evaporator during heating operation. On the other hand, during cooling operation, the heat source side heat exchanger 23 functions as a condenser (radiator).

[0078] (2-2-4) Heat source side expansion valve The heat source side expansion valve 38 is installed in the refrigerant circuit 10 between the heat source side heat exchanger 23 and the utilization side heat exchangers 42, 52, and 62. Specifically, the heat source side expansion valve 38 is installed in the liquid refrigerant pipe 11d between the heat source side heat exchanger 23 and the liquid side shut-off valve 26.

[0079] The heat source-side expansion valve 38 regulates the pressure and flow rate of the refrigerant flowing through the liquid refrigerant pipe 11d. The heat source-side expansion valve 38 is, for example, an electronically operated expansion valve with a variable opening.

[0080] (2-2-5) Accumulator The accumulator 24 separates the incoming refrigerant into gaseous refrigerant and liquid refrigerant. The accumulator 24 also has a function of storing excess refrigerant that is generated in response to fluctuations in the operating load of the user-side units U1, U2, U3, and U4. The accumulator 24 is installed in the suction pipe 11a. In other words, the accumulator 21 is positioned between the user-side heat exchangers 102, 202, 302, and 402 and the suction port of the compressor 21 during the cooling cycle, and stores refrigerant in its internal space. The refrigerant flowing into the accumulator 24 is collected in the upper space as gaseous refrigerant and in the lower space as liquid refrigerant. The gaseous refrigerant collected in the upper space flows out to the compressor 21.

[0081] (2-2-6) Liquid side shut-off valve and gas side shut-off valve The liquid-side shut-off valve 26 is a valve provided at the connection point between the liquid refrigerant pipe 11d and the liquid refrigerant connecting pipe 5. The gas-side shut-off valve 27 is a valve provided at the connection point between the second gas refrigerant pipe 11e and the gas refrigerant connecting pipe 6. The liquid-side shut-off valve 26 and the gas-side shut-off valve 27 are, for example, valves that are operated manually.

[0082] (2-2-7) Heat source side fan The heat source side fan 28 is a fan that draws in heat source air from outside the heat source side unit 2 into the heat source side unit 2 and supplies it to the heat source side heat exchanger 23, and discharges the air that has exchanged heat with the refrigerant in the heat source side heat exchanger 23 to the outside of the heat source side unit 2.

[0083] The heat source side fan 28 is, for example, a propeller fan. However, the type of fan for the heat source side fan 28 is not limited to a propeller fan and may be selected as appropriate.

[0084] The heat source side fan 28 is driven by motor 28a. While not limited to this, motor 28a is a motor whose rotational speed can be controlled by an inverter. The heat source side fan 28 is a fan with variable airflow, controlled by the rotational speed of motor 28a.

[0085] (2-2-8) Sensor The heat source unit 2 is equipped with various sensors. For example, the heat source unit 2 has the following temperature sensor and pressure sensor. The types of temperature and pressure sensors can be selected as appropriate.

[0086] The sensors in the heat source unit 2 include an intake pressure sensor 29, a discharge pressure sensor 30, an intake temperature sensor 31, a discharge temperature sensor 32, and a heat exchanger temperature sensor 33. The heat source unit 2 does not necessarily have to have all of the sensors 29-33 described above; it may have only some of them. Furthermore, the heat source unit 2 may have sensors other than those described above.

[0087] The suction pressure sensor 29 is installed in the suction pipe 11a. The suction pressure sensor 29 is a sensor that measures the suction pressure Ps. The suction pressure Ps is the low-pressure value of the refrigerant cycle.

[0088] The discharge pressure sensor 30 is installed in the discharge pipe 11b. The discharge pressure sensor 30 is a sensor that measures the discharge pressure Pd. The discharge pressure Pd is the high-pressure value of the refrigerant cycle.

[0089] The intake temperature sensor 31 is installed in the intake pipe 11a. The intake temperature sensor 31 is a sensor that measures the intake temperature Ts.

[0090] The discharge temperature sensor 32 is installed in the discharge pipe 11b. The discharge temperature sensor 32 is a sensor that measures the discharge temperature Td.

[0091] The heat exchanger temperature sensor 33 is installed in the heat source side heat exchanger 23. The heat exchanger temperature sensor 33 measures the temperature of the refrigerant flowing through the heat source side heat exchanger 23. During cooling operation, the heat exchanger temperature sensor 33 measures the refrigerant temperature corresponding to the condensation temperature Tc, and during heating operation, it measures the refrigerant temperature corresponding to the evaporation temperature Te.

[0092] (2-2-9) Heat source side control unit The heat source side control unit 37 controls the operation of each part that constitutes the heat source side unit 2.

[0093] The heat source side control unit 37 is implemented by a microcomputer and memory, etc. The microcomputer comprises a control arithmetic unit and a memory device. A processor such as a CPU or GPU can be used for the control arithmetic unit. The control arithmetic unit reads a program stored in the memory device and performs predetermined arithmetic processing according to this program. Furthermore, the control arithmetic unit can write the calculation results to the memory device or read information stored in the memory device according to the program.

[0094] The heat source side control unit 37 is electrically connected to the heat source side unit 2, specifically the compressor 21, four-way switching valve 22, heat source side expansion mechanism 38, heat source side fan 28, suction pressure sensor 29, discharge pressure sensor 30, suction temperature sensor 31, discharge temperature sensor 32, and heat exchanger temperature sensor 33, to enable the transmission and reception of control signals and information. Furthermore, the heat source side control unit 37 is connected to the user side control units 107, 207, 307, and 407 of the user side units U1, U2, U3, and U4 via a transmission line 8a to enable the transmission and reception of control signals and other information.

[0095] The heat source side control unit 37 and the user side control units 107, 207, 307, and 407 of the user side units U1, U2, U3, and U4 work together to function as a control device 3 that controls the operation of the refrigeration cycle device 1. The functions of the control device 3 will be described later.

[0096] (2-3) Refrigerant connecting piping The refrigeration cycle unit 1 includes a liquid refrigerant connecting pipe 5 and a gas refrigerant connecting pipe 6 as refrigerant connecting pipes. The liquid refrigerant connecting pipe 5 and the gas refrigerant connecting pipe 6 are pipes that are installed at the installation site of the refrigeration cycle unit 1 when the refrigeration cycle unit 1 is installed. Various lengths and diameters of pipes are used for the liquid refrigerant connecting pipe 5 and the gas refrigerant connecting pipe 6 depending on the installation conditions such as the installation site and the combination of the heat source side unit and the user side unit.

[0097] The user-side refrigerant circuits 10a, 10b, 10c, and 10d of user-side units U1, U2, U3, and U4, and the heat source-side refrigerant circuit 10e of heat source-side unit 2 are connected by liquid refrigerant connecting pipe 5 and gas refrigerant connecting pipe 6, thereby forming the refrigerant circuit 10 of the refrigeration cycle device 1.

[0098] (2-4) Control device Figure 2 is a block diagram of the control unit (control unit) 3. The control unit 3 is configured such that the heat source side control unit 37 of the heat source side unit 2 and the user side control units 107, 207, 307, and 407 of the user side units U1, U2, U3, and U4 are connected via a transmission line 8a to enable the transmission and reception of control signals and the like. The control unit 3 is realized when the microcomputers of the heat source side control unit 37 and the user side control units 107, 207, 307, and 407 execute programs stored in memory.

[0099] It should be noted that the control device 3 in this embodiment is merely one example. Functions similar to those performed by the control device 3 may be realized by hardware such as logic circuits, or by a combination of hardware and software.

[0100] Furthermore, while the control device 3 is configured with the heat source side control unit 37 and the user side control units 107, 207, 307, and 407, it is not limited to this configuration. For example, the refrigeration cycle device 1 may have, in addition to the heat source side control unit 37 and the user side control units 107, 207, 307, and 407, or instead of the heat source side control unit 37 and the user side control units 107, 207, 307, and 407, a control device provided separately from the heat source side unit 2 and user side units U1, U2, U3, and U4 that implement some or all of the functions of the control unit 3 described below.

[0101] Furthermore, the control device 3 of the refrigeration cycle device 1 does not necessarily have to have some or all of the functions described below. For example, some or all of the functions of the control device 3 described below may be implemented by a central controller or the like installed in a location separate from the refrigeration cycle device 1. In other words, the functions of the control device 3 do not have to be performed solely by the refrigeration cycle device 1, and may be implemented by a central controller or the like (not shown) installed separately from the refrigeration cycle device 1. Also, the central controller and the heat source side control unit 37 of the heat source side unit 2 may control the user side expansion valves 101, 102, 301, 401, etc. of the user side units U1, U2, U3, U4.

[0102] As shown in Figure 2, the control device 3 is connected to the heat source side unit 2, which includes user-side expansion valves 101, 201, 301, 401, compressor 21, four-way switching valve 22, heat source side expansion valve 38, user-side fans 103, 203, 303, 403, and heat source side fan 28, and the user-side units U1, U2, U3, U4, enabling it to send and receive control signals and the like. Furthermore, as shown in Figure 2, the control unit 3 is connected to the liquid-side temperature sensors 104, 204, 304, 404, gas-side temperature sensors 105, 205, 305, 405, target space temperature sensors 106, 206, 306, 406, suction pressure sensor 29, discharge pressure sensor 30, suction temperature sensor 31, discharge temperature sensor 32, and heat exchanger temperature sensor 33, enabling it to send and receive control signals and the like.

[0103] The control device 3 performs an oil return operation to return the lubricating oil that has leaked out of the compressor 21 to the compressor 21. In the oil return operation, the control device 3 makes the opening degree of the expansion valve of the user-side unit belonging to the first user-side unit group G1 and the opening degree of the expansion valve of the user-side unit belonging to the second user-side unit group G2 different.

[0104] The control device 3 controls the opening degree of the user-side expansion valves 101, 201, 301, and 401 based on the state of the refrigerant at the outlets of the user-side heat exchangers 102, 202, 302, and 402.

[0105] Conventionally, during oil return operation, the heat source unit and the user unit communicate once every 20 seconds. However, in the refrigeration cycle device 1 of this embodiment, during oil return operation, the heat source unit 2 and user units U1 to U4 communicate once every 10 seconds. Furthermore, conventionally, during normal operation, the heat source unit and the user unit communicate once every minute. However, in the refrigeration cycle device 1, during normal operation, the heat source unit 2 and user units U1 to U4 communicate once every 30 seconds. Thus, in the refrigeration cycle device 1, the communication frequency between the heat source unit 2 and user units U1 to U4 is higher than in conventional systems.

[0106] In this embodiment, user-side units U1 to U4 transmit the measured values ​​of the liquid-side temperature sensors 104, 204, 304, 404 or the gas-side temperature sensors 105, 205, 305, 405 to the heat source-side control unit 37 of the heat source unit 2, and the heat source-side control unit 37 of the heat source unit 2 instructs user-side units U1 to U4 to control the opening degree of the user-side expansion valves 101, 201, 301, 401. Furthermore, during oil return operation in cooling mode, the heat source-side control unit 37 of the heat source-side unit 2 instructs user-side units U1 to U4 to set the target superheat level SHrs for oil return operation.

[0107] The control device 3 mainly comprises a setting unit 12a, a storage unit 12b, and a timer unit 12c as its functional units.

[0108] (2-4-1) Settings section The setting unit 12a sets which of the user-side units U1 to U4 of the refrigeration cycle device 1 belongs to the first user-side unit group G1 or the second user-side unit group G2. The setting unit 12a sets user-side units U1 and U2, which have longer liquid refrigerant connecting pipes 5 and gas refrigerant connecting pipes 6 to the heat source-side unit 2, as user-side units belonging to the first user-side unit group G1, and user-side units U3 and U4, which have shorter liquid refrigerant connecting pipes 5 and gas refrigerant connecting pipes 6 to the heat source-side unit 2 than user-side units U1 and U2, as user-side units belonging to the second user-side unit group G2. The setting of user-side units belonging to user-side unit groups is not limited to setting based on the length of the connecting pipes.

[0109] Furthermore, the number of user units belonging to the first user unit group G1 and the second user unit group G2 is not limited to two; it may be one or three or more. Also, the number of user units belonging to the first user unit group G1 and the number of user units belonging to the second user unit group G2 may be the same or different. In addition, although the refrigeration cycle device 1 has two user unit groups, the number of user unit groups is not limited to two; it may be three or more.

[0110] The setting unit 12a sets the target superheat level SHrs during the oil return operation in cooling operation. Conventionally, in the oil return operation during cooling operation, the target superheat level SHrs was set to the same value for all user-side units. In the oil return operation during cooling operation of the refrigeration cycle device 1 of this embodiment, the setting unit 12a sets the target superheat level Shrs during the oil return operation differently depending on the user-side unit group.

[0111] (2-4-2) Storage section The memory unit 12b stores whether each user-side unit of the refrigeration cycle device 1 is configured as a user-side unit belonging to the first user-side unit group G1 or as a user-side unit belonging to the second user-side unit group G2. In this embodiment, it stores that user-side units U1 and U2 are configured as user-side units belonging to the first user-side unit group G1. It also stores that user-side units U3 and U4 are configured as user-side units belonging to the second user-side unit group G2.

[0112] Furthermore, the memory unit 12b stores the target superheat level SHrs set during the oil return operation when the oil return operation is performed during cooling operation.

[0113] (2-4-3) Timer section The timer unit 12c measures the time during which the refrigeration cycle unit 1 is in normal operation. This allows the control device 3 to calculate the cumulative time during which the refrigeration cycle unit 1 has been in normal operation since the end of the previous oil return operation.

[0114] Furthermore, the timer unit 12c measures the time during which the oil return operation of the refrigeration cycle device 1 is continuously performed.

[0115] (3) Operation of the refrigeration cycle The operation of the refrigeration cycle unit 1 during cooling operation, heating operation, and oil return operation will be described below.

[0116] (3-1) Cooling operation When the remote control instructs the refrigeration cycle unit 1 to perform cooling operation, the control device 3 sets the operating mode of the refrigeration cycle unit 1 to the cooling operation mode. When the predetermined conditions for starting cooling operation are met in the cooling operation mode, the four-way switching valve 22 is switched to the cooling operation state (the state shown by the solid line of the four-way switching valve 22 in Figure 1), and the compressor 21, heat source side fan 28, and user side fans 43, 53, and 63 are operated to start cooling operation.

[0117] In the refrigerant circuit 10, the low-pressure gaseous refrigerant in the refrigerant cycle is drawn into the compressor 21, where it is compressed to become the high-pressure gaseous refrigerant in the refrigerant cycle. The high-pressure gaseous refrigerant is sent to the heat source side heat exchanger 23 via the four-way switching valve 22, where it exchanges heat with the heat source air supplied by the heat source side fan 28 and condenses to become the high-pressure liquid refrigerant.

[0118] The high-pressure liquid refrigerant flows through the liquid refrigerant pipe 11d and passes through the heat source side expansion valve 38. The high-pressure liquid refrigerant is sent to the user side units U1, U2, U3, and U4 via the liquid refrigerant connecting pipe 5. The high-pressure liquid refrigerant sent to user side units U1, U2, U3, and U4 is reduced in pressure to near the suction pressure of the compressor 21 at the user side expansion valves 101, 201, 301, and 401, becoming a gas-liquid two-phase refrigerant and sent to the user side heat exchangers 102, 202, 302, and 402.

[0119] The gaseous two-phase refrigerant evaporates in the user-side heat exchangers 102, 202, 302, and 402, where it exchanges heat with the air in the target space supplied to the user-side heat exchangers 102, 202, 302, and 402 by the user-side fans 103, 203, 303, and 403, becoming a low-pressure gaseous refrigerant. The low-pressure gaseous refrigerant is sent to the heat source-side unit 2 via the gaseous refrigerant communication pipe 6 and flows into the accumulator 24 via the four-way switching valve 22. The low-pressure gaseous refrigerant that flows into the accumulator 24 is then drawn back into the compressor 21.

[0120] (3-2) Heating operation When the remote control instructs the refrigeration cycle unit 1 to perform heating operation, the control device 3 sets the operating mode of the refrigeration cycle unit 1 to heating operation mode. When the predetermined heating operation start conditions are met in heating operation mode, the four-way switching valve 22 is switched to the heating operation state (the state shown by the dashed line on the four-way switching valve 22 in Figure 1), and heating operation is started by operating the compressor 21, the heat source side fan 28, and the user side fans 103, 203, 303, and 403.

[0121] In the refrigerant circuit 10, the low-pressure gaseous refrigerant in the refrigerant cycle is drawn into the compressor 21, where it is compressed to become the high-pressure gaseous refrigerant in the refrigerant cycle. The high-pressure gaseous refrigerant is sent to the user-side heat exchangers 102, 202, 302, and 402 via the four-way switching valve 22, where it exchanges heat with the air in the target space supplied by the user-side fans 103, 203, 303, and 403, condenses, and becomes the high-pressure liquid refrigerant.

[0122] The high-pressure liquid refrigerant is reduced in pressure as it passes through the user-side expansion valves 101, 201, 301, and 401. The refrigerant reduced in pressure at the user-side expansion valves 101, 201, 301, and 401 is sent to the heat source-side unit 2 via the liquid refrigerant connecting pipe 5 and flows into the liquid refrigerant pipe 11d. The refrigerant flowing through the liquid refrigerant pipe 11d is reduced in pressure to near the suction pressure of the compressor 21 as it passes through the heat source-side expansion valve 38, becoming a gas-liquid two-phase refrigerant and sent to the heat source-side heat exchanger 23.

[0123] The two-phase gaseous refrigerant evaporates in the heat source side heat exchanger 23 through heat exchange with the heat source air supplied to the heat source side heat exchanger 23 by the heat source side fan 28, becoming a low-pressure gaseous refrigerant. The low-pressure gaseous refrigerant flows into the accumulator 24 via the four-way switching valve 22. The low-pressure gaseous refrigerant that flows into the accumulator 24 is then drawn back into the compressor 21.

[0124] (3-3) Oil return operation The oil return operation is an operation to forcibly return the refrigerant oil that has flowed out of the compressor 21 and accumulated in the refrigerant circuit 10 other than the compressor 21 back to the compressor 21.

[0125] The oil return operation during cooling will now be explained. During the oil return operation during cooling, when the predetermined oil return start conditions are met, the four-way switching valve 22 is in the cooling operation state (shown by the solid line of the four-way switching valve 22 in Figure 1), and the opening of the user-side expansion valves 101, 201, 301, and 401 is increased to perform the oil return operation.

[0126] The predetermined oil return start condition is a condition under which it is desirable to return the refrigeration oil to the compressor 21. For example, the control device 3 determines that the oil return start condition has been met when the cumulative value of the time during which the refrigeration cycle device 1 has been in normal operation since the end of the previous oil return operation exceeds a predetermined threshold. Alternatively, the control device 3 may determine that the oil return start condition has been met when the amount of oil coming up from the compressor 21 since the end of the previous oil return operation exceeds a predetermined threshold.

[0127] The amount of oil leaked is the amount of refrigerant oil that leaked out of the compressor 21 during normal operation of the refrigeration cycle unit 1. The amount of oil leaked is calculated, for example, based on the rotational speed of the compressor 21 during normal operation and the cumulative time during which normal operation was performed.

[0128] In the refrigerant circuit 10, the low-pressure gaseous refrigerant in the refrigerant cycle is drawn into the compressor 21, where it is compressed to become the high-pressure gaseous refrigerant in the refrigerant cycle. The high-pressure gaseous refrigerant is sent to the heat source side heat exchanger 23 via the four-way switching valve 22, where it exchanges heat with the heat source air supplied by the heat source side fan 28 and condenses to become the high-pressure liquid refrigerant.

[0129] The high-pressure liquid refrigerant flows through the liquid refrigerant pipe 11d and passes through the heat source side expansion valve 38. The high-pressure liquid refrigerant is sent to the user side units U1, U2, U3, and U4 via the liquid refrigerant connecting pipe 5. The high-pressure liquid refrigerant sent to user side units U1, U2, U3, and U4 is reduced in pressure to near the suction pressure of the compressor 21 at the user side expansion valves 101, 201, 301, and 401, becoming a gas-liquid two-phase refrigerant and sent to the user side heat exchangers 102, 202, 302, and 402. The larger the opening of the user side expansion valves 101, 201, 301, and 401, the larger the amount of refrigerant sent to the user side heat exchangers 102, 202, 302, and 402.

[0130] The gaseous two-phase refrigerant evaporates in the user-side heat exchangers 102, 202, 302, and 402, where it exchanges heat with the air in the target space supplied to the user-side heat exchangers 102, 202, 302, and 402 by the user-side fans 103, 203, 303, and 403, becoming a low-pressure gaseous refrigerant. The low-pressure gaseous refrigerant is sent to the heat source-side unit 2 via the gaseous refrigerant communication pipe 6 and flows into the accumulator 24 via the four-way switching valve 22. The low-pressure gaseous refrigerant that flows into the accumulator 24 is then drawn back into the compressor 21.

[0131] The control device 3 terminates the oil return operation if it determines that the oil return termination condition has been met during the oil return operation. The control device 3 determines that the oil return termination condition has been met when the time during which the oil return operation has been continuously performed exceeds a predetermined threshold. Note that the oil return termination condition is not limited to the above condition. For example, the control device 3 may determine that the oil return termination condition has been met when a predetermined amount of refrigerant oil has been returned to the compressor 21.

[0132] (4) Processing when performing oil return operation during cooling Figure 3 is a flowchart showing the process of oil return operation during cooling.

[0133] In step S1, start the cooling operation.

[0134] In step S2, the control device 3 determines whether the oil return start condition is met. In this embodiment, the control device 3 determines that the oil return start condition is met when the cumulative value of the time during which the refrigeration cycle device 1 has been in normal operation since the end of the previous oil return operation, as measured by the timer unit 12c, exceeds a predetermined threshold. If the oil return start condition is met (Yes in step S2), the process proceeds to step S3.

[0135] In step S3, the setting unit 12a sets the user units belonging to the user unit group. In this embodiment, the setting unit 12a sets user units U1 and U2, which have longer liquid refrigerant connecting pipes 5 and gas refrigerant connecting pipes 6 to the heat source unit 2, as user units belonging to the first user unit group G1, and user units U3 and U4, which have shorter liquid refrigerant connecting pipes 5 and gas refrigerant connecting pipes 6 to the heat source unit 2 than user units U1 and U2, as user units belonging to the second user unit group G2.

[0136] In step S4, the control device 3 sets the target superheat SHrs for the oil return operation. For example, the target superheat SHrs for user units U1 and U2 belonging to the first user unit group G1 are set to "+2". Also, the target superheat SHrs for user units U3 and U4 belonging to the second user unit group G2 are set to "+0.1". Note that the value of the target superheat SHrs for the oil return operation is not limited to these, but user units belonging to the same user unit group are set to have the same target superheat SHrs. Furthermore, the value of the target superheat SHrs for the oil return operation is set differently for each user unit group.

[0137] In step S5, the oil return operation is started. The control device 3 increases the opening of the user-side expansion valves 101, 201, 301, and 401 when the four-way switching valve 22 is in the cooling operation state (shown by the solid line of the four-way switching valve 22 in Figure 1) and performs the oil return operation.

[0138] In step S6, the control device 3 controls the opening degree of the user-side expansion valves 101, 201, 301, and 401. The control device 3 controls the opening degree of the user-side expansion valves 101, 201, 301, and 401 so that the superheat degree SHr of the refrigerant at the gas-side outlets of the user-side heat exchangers 102, 202, 302, and 402 becomes a predetermined target superheat degree SHrs. In this embodiment, the control device 3 controls the opening degree of the user-side expansion valves 101 and 201 so that the superheat degree SHr of the refrigerant at the gas-side outlets of the user-side heat exchangers 102 and 202 becomes "+2", which is the target superheat degree SHrs during oil return operation. In addition, the control device 3 controls the opening degree of the user-side expansion valves 301 and 401 so that the superheat degree SHr of the refrigerant at the gas-side outlets of the user-side heat exchangers 302 and 402 becomes "+0.1", which is the target superheat degree SHrs during oil return operation. This makes it possible to perform oil return operations in which user-side units with the user-side expansion valve slightly closed and user-side units with the user-side expansion valve slightly open are mixed together.

[0139] The gas-side temperature sensors (detection units) 105, 205, 305, 405 and the liquid-side temperature sensors (detection units) 104, 204, 304, 404 detect the state of the refrigerant at the outlets of the user-side heat exchangers 102, 202, 302, 402. The superheat degree SHr of the refrigerant at the gas-side outlets of each of the user-side heat exchangers 102, 202, 302, 402 is calculated, for example, by subtracting the evaporation temperature Te, which is converted from the measurement value of the suction pressure sensor 29 (suction pressure Ps), from the measurement value of the gas-side temperature sensors 105, 205, 305, 405. Alternatively, the superheat degree SHr of the refrigerant may be calculated by subtracting the measurement value of the liquid-side temperature sensors 104, 204, 304, 404, which corresponds to the evaporation temperature Te, from the measurement value of the gas-side temperature sensors 105, 205, 305, 405.

[0140] In step S7, the control device 3 determines whether the oil return termination condition is met. In this embodiment, the control device 3 determines that the oil return termination condition is met when the time for which the oil return operation has been continuously performed, as measured by the timer unit 12c, exceeds a predetermined threshold.

[0141] If the condition for completing the oil return process is met (Yes in step S8), proceed to step S8.

[0142] In step S8, the oil return operation is terminated.

[0143] (5) Characteristics (5-1) The refrigeration cycle device 1 according to this embodiment comprises a heat source side unit 2, a first user side unit group G1, a second user side unit group G2, and a control device 3. The heat source side unit 2 has a compressor 21. The first user side unit group G1 includes at least a user side unit U1 as the first user side unit. The control device 3 performs an oil return operation to return lubricating oil that has leaked out of the compressor 21 to the compressor 21. Each user side unit U1 to U4 belonging to the first user side unit group G1 and the second user side unit group G2 has user side expansion valves 101, 201, 301, and 401. In the oil return operation, the control device 3 makes the opening degree of the user side expansion valve 101 of user side unit U1 belonging to the first user side unit group G1 different from the opening degrees of the user side expansion valves 201, 301, and 401 of user side units U2, U3, and U4 belonging to the second user side unit group G2.

[0144] In oil return operation, a special operation, the opening of the indoor unit expansion valve (utilization-side expansion valve) is increased compared to normal operation to moisten the refrigerant returning to the compressor, and the refrigerant oil remaining in the refrigerant system is mixed with the refrigerant and recovered. When oil return operation is performed on an air conditioner with an expansion valve on the indoor unit side, such as a multi-type air conditioner, if the indoor unit expansion valve is closed after detecting the moisture of the refrigerant flowing through the suction piping in the outdoor unit, there is a distance from the indoor unit expansion valve to the compressor, so even more moistened refrigerant may flow into the compressor, and liquid compression may occur inside the compressor.

[0145] In this refrigeration cycle device 1, the heat source unit 2 issues instructions to individual user-side units U1 to U4 to control the opening degree of the user-side expansion valves 101, 201, 301, and 401, thereby reducing compressor 21 failures caused by refrigerants with a high degree of humidity.

[0146] In this refrigeration cycle device 1, the opening of the expansion valve of the user-side unit, which is at high risk of highly humid refrigerant gas returning to the heat source-side unit 2, can be reduced, while the opening of the expansion valves of other user-side units can be increased. This allows for reduced liquid compression in the compressor 21 while shortening the time required for oil return.

[0147] (5-2) In the refrigeration cycle device 1 according to this embodiment, each user unit U1 to U4 belonging to the first user-side unit group G1 and the second user-side unit group G2 has user-side heat exchangers 102, 202, 302, and 402, and gas-side temperature sensors 105, 205, 305, and 306. During the oil return operation in cooling, the gas-side temperature sensors 105, 205, 305, and 306 detect the state of the refrigerant at the outlet of the user-side heat exchangers 102, 202, 302, and 402.

[0148] In this refrigeration cycle device 1, by detecting the state of the refrigerant at the outlets of the user-side heat exchangers 102, 202, 302, and 402, it is possible to identify user-side units that are highly likely to have refrigerant gas with a high degree of humidity returning to the heat source-side unit 2.

[0149] (5-3) In the refrigeration cycle device 1 according to this embodiment, the control device 3 controls the opening degree of the expansion valve based on the state of the refrigerant at the outlets of the utilization-side heat exchangers 102, 202, 302, and 402.

[0150] In this refrigeration cycle system, the degree of humidity of the refrigerant gas returning to the heat source unit 2 can be adjusted by controlling the opening of the user-side expansion valves 101, 201, 301, and 401 based on the state of the refrigerant at the outlets of the user-side heat exchangers 102, 202, 302, and 402.

[0151] (6) Variant (6-1) Variation 1A The control device 3 may, after a predetermined time has elapsed, reduce the opening degree of the expansion valve in any of the user units belonging to the first user unit group G1 and the second user unit G2, and then increase the opening degree of the expansion valve.

[0152] For example, if the user-side unit U1 is a user-side unit where there is a high risk that a refrigerant gas with a high degree of humidity will return to the heat source-side unit 2, then by reducing the opening of the user-side expansion valve 101 of the user-side unit U1, the flow rate of the refrigerant in the user-side unit U1 decreases, and after a predetermined time has elapsed, the opening of the user-side expansion valve 101 of the user-side unit U1 is increased.

[0153] In modified example 1A, by reducing the opening of the expansion valve, the refrigerant flow rate of a user-side unit is reduced. After a predetermined time has elapsed, the opening of the expansion valve is increased to prevent the refrigerant flow rate of a specific user-side unit from becoming too low.

[0154] (6-2) Variation 1B The control device 3 may also control the opening degree of the user-side expansion valves 101, 201, 301, and 401 based on the state of the refrigerant that exits the accumulator 24 and is drawn into the compressor 21.

[0155] The state of the refrigerant flowing out of the accumulator 24 and being drawn into the compressor 21 may be detected by sensing the liquid level of the known accumulator 24. Alternatively, the state of the refrigerant flowing out of the accumulator 24 and being drawn into the compressor 21 may be detected by sensing the discharge temperature of the compressor 21.

[0156] For example, during oil return operation in cooling mode, if the control device 3 detects that a large amount of liquid refrigerant is contained in the refrigerant coming out of the accumulator 24 and being drawn into the compressor 21 based on the discharge temperature of the compressor 21 detected by the discharge temperature sensor 32, the control device 3 calculates the superheat degree SHr of the refrigerant at the outlets of the user-side heat exchangers 102, 202, 302, and 402. The control device 3 may then control the opening degree of the user-side expansion valves 101, 201, 301, and 401 based on the state of the refrigerant at the outlets of the user-side heat exchangers 102, 202, 302, and 402.

[0157] In modified example 1B, the opening degree of the user-side expansion valves 101, 201, 301, and 401 is controlled based on the state of the refrigerant exiting the accumulator 24 and being drawn into the compressor 21, thereby preventing excessive accumulation of liquid refrigerant in the accumulator 24.

[0158] (6-3) Modification 1C In this embodiment, the process for oil return operation during cooling has been described, but oil return operation may also be performed during heating.

[0159] Figure 4 is a flowchart showing the process of oil return operation during heating.

[0160] Step S2, which determines whether the conditions for starting oil return are met; step S3, which sets the user-side units belonging to the user-side unit group; step S7, which determines whether the conditions for ending oil return are met; and step S8, which ends the oil return operation are the same as the oil return operation process during cooling shown in Figure 3, so a detailed explanation is omitted.

[0161] In step S11, start the heating operation.

[0162] In step S12, the control device 3 sets the target subcooling degree SCrs during the oil return operation. In the modified example 1C, the target subcooling degree SCrs during the oil return operation for user units U1 and U2 belonging to the first user unit group G1 are set to the same value. In addition, the target subcooling degree SCrs during the oil return operation for user units U3 and U4 belonging to the second user unit group G2 are set to the same value.

[0163] In step S13, the oil return operation is started. The control device 3 increases the opening of the user-side expansion valves 101, 201, 301, and 401 when the four-way switching valve 22 is in the heating operation state (shown by the dashed line of the four-way switching valve 22 in Figure 1) and performs the oil return operation.

[0164] In step S14, the control device 3 controls the opening degree of the user-side expansion valves 101, 201, 301, and 401. The control device 3 controls the opening degree of the user-side expansion valves 101, 201, 301, and 401 so that the degree of subcooling SCr of the refrigerant at the liquid-side outlet of each of the user-side heat exchangers 102, 202, 302, and 402 becomes a predetermined target degree of subcooling SCrs.

[0165] The degree of refrigerant subcooling SCr at the liquid-side outlet of each of the user-side heat exchangers 102, 202, 302, and 402 may be calculated, for example, by subtracting the measured values ​​of the liquid-side temperature sensors 104, 204, 304, and 404 from the condensation temperature Tc, which is calculated from the measured value (discharge pressure Pd) of the discharge pressure sensor 30.

[0166] (6-4) While embodiments of this disclosure have been described above, it should be understood that various modifications to the form and details are possible without departing from the spirit and scope of this disclosure as described in the claims. [Explanation of Symbols]

[0167] 1. Refrigeration cycle system 2 Heat source side unit 3. Control device (control unit) G1 First user-side unit group G2 Second user-side unit group U1~U4 User Units 21 Compressor 23 Heat source side heat exchanger 24 Accumulators 29. Intake pressure sensor 30 Discharge pressure sensor 31. Intake temperature sensor 32 Discharge temperature sensor 33 Heat exchanger temperature sensor 101, 201, 301, 401 User-side expansion valve (expansion valve) 102, 202, 302, 402 User side heat exchanger 103, 203, 303, 403 User-side fans 104, 204, 304, 404 Liquid-side temperature sensor (detection unit) 105, 205, 305, 405 Gas-side temperature sensor (detection unit) 106, 206, 306, 406 Target space temperature sensor [Prior art documents] [Patent Documents]

[0168] [Patent Document 1] Japanese Patent Publication No. 2002-147879

Claims

1. A heat source side unit (2) having a compressor (21), A first group of user units (G1) including at least a first user unit, The second group of user-side units (G2), A control unit (3) performs an oil return operation to return the lubricating oil that has leaked out of the compressor back to the compressor, Equipped with, Each user-side unit belonging to the first user-side unit group and the second user-side unit group has an expansion valve (101, 201, 301, 401), The control unit, in the oil return operation, makes the opening degree of the expansion valve of the user-side unit belonging to the first user-side unit group and the opening degree of the expansion valve of the user-side unit belonging to the second user-side unit group different. Refrigeration cycle device.

2. Each user unit belonging to the first user unit group and the second user unit group is: The heat exchangers on the user side (102, 202, 302, 402) and The detection units (104, 204, 304, 404, 105, 205, 305, 405) detect the state of the refrigerant at the outlet of the heat exchanger on the user side, Having, The refrigeration cycle apparatus according to claim 1.

3. The control unit controls the opening degree of the expansion valve based on the state of the refrigerant at the outlet of the heat exchanger on the user side. A refrigeration cycle apparatus according to claim 1 or 2.

4. The control unit reduces the opening degree of the expansion valve in any of the user units belonging to the first user unit group and the second user unit, and after a predetermined time has elapsed, increases the opening degree of the expansion valve. A refrigeration cycle apparatus according to claim 1 or 2.

5. An accumulator (24) is positioned between the heat exchanger on the utilization side and the suction port of the compressor, and stores the refrigerant in its internal space. Furthermore, The control unit controls the opening degree of the expansion valve based on the state of the refrigerant that exits the accumulator and is drawn into the compressor. The refrigeration cycle apparatus according to claim 3.

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