Air conditioning system

Abstract

This disclosure provides an air conditioning system that can stably maintain refrigerant injection and suppress noise caused by chattering of a check valve. [Solution] The air conditioning system in this disclosure includes an injection pipe that branches off from a liquid-side refrigerant pipe provided between an outdoor heat exchanger and an expansion valve, through which the refrigerant to be injected into the compressor flows; a subcooling heat exchanger that exchanges heat between the refrigerant in the injection pipe and the refrigerant in the liquid-side refrigerant pipe; an electronic expansion valve provided between the branching point of the injection pipe and the liquid-side refrigerant pipe and the subcooling heat exchanger; a branch pipe that branches off from the injection pipe and is connected to a gas-side refrigerant pipe on the suction side of the compressor; an on-off valve provided in the branch pipe; and a check valve that blocks the backflow of refrigerant from the compressor side to the injection pipe side, wherein when the on-off valve is closed, the opening of the electronic expansion valve is limited to an opening greater than or equal to a reference opening.

Description

Technical Field

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

Background Art

[0002] Patent Document 1 discloses a refrigeration device including a compressor capable of injecting refrigerant into an intermediate portion of a compression stroke. This refrigeration device includes an injection circuit having an injection pipe connected to an intermediate pressure portion of the compressor, an electronic expansion valve provided upstream of a subcooling coil in the injection circuit, and a solenoid valve that blocks the refrigerant injected into the compressor by being closed.

[0003] Patent Document 2 discloses a refrigeration cycle device including an injection flow path for sending refrigerant to a compressor. This refrigeration cycle device includes a third expansion valve provided at an injection flow path inlet, and a flow path switching portion capable of selecting either a suction port of the compressor or an intermediate pressure port of the compressor as a destination of the refrigerant flowing into the injection flow path.

[0004] Patent Document 3 discloses a refrigerator including an economizer. This refrigerator includes a branch pipe branched from a refrigerant pipe between a condenser and the economizer and connected to a cooling injection port of the compressor via the economizer, an economizer flow path opening / closing valve for opening and closing a flow path passing through the economizer, and expansion means provided upstream of the economizer in the branch pipe.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

[0006]

Patent Document 2

[0007] [Patent Document 3] Japanese Patent Publication No. 2017-198445 [Overview of the project] [Problems that the invention aims to solve]

[0008] This disclosure provides an air conditioning system that can stably maintain refrigerant injection from injection piping to the compressor and suppress noise caused by chattering of the check valve. [Means for solving the problem]

[0009] The air conditioning system in this disclosure includes a compressor, an outdoor heat exchanger, an expansion valve, and an indoor heat exchanger, and further comprises: an injection pipe branching from a liquid-side refrigerant pipe provided between the outdoor heat exchanger and the expansion valve, through which the refrigerant injected into the compressor flows; a subcooling heat exchanger for exchanging heat between the refrigerant in the injection pipe and the refrigerant in the liquid-side refrigerant pipe; an electronic expansion valve provided between the branching point of the injection pipe and the liquid-side refrigerant pipe and the subcooling heat exchanger; a branch pipe branching from the injection pipe and connected to a gas-side refrigerant pipe on the suction side of the compressor; an on-off valve provided in the branch pipe; and a check valve for blocking refrigerant from flowing back from the compressor side to the injection pipe side, wherein when the on-off valve is closed, the opening of the electronic expansion valve is limited to an opening greater than or equal to a reference opening. [Effects of the Invention]

[0010] The air conditioning system in this disclosure makes it easier to raise the pressure in the injection piping to a pressure higher than the intermediate pressure chamber pressure in the compressor when the on-off valve is closed. As a result, it becomes less likely for the pressure between the injection piping and the intermediate pressure chamber to reverse, which stably maintains the injection of refrigerant from the injection piping to the compressor and suppresses noise caused by chattering of the check valve. [Brief explanation of the drawing]

[0011] [Figure 1] Diagram showing the refrigerant circuit of the air conditioning system according to Embodiment 1. [Figure 2] Diagram showing the configuration of the control system for an air conditioning system. [Figure 3] Flowchart showing the operation of the control unit [Modes for carrying out the invention]

[0012] (Knowledge and other information that formed the basis of this disclosure) At the time the inventors conceived this disclosure, a technology was known in the field of air conditioning systems in which refrigerant that had passed through a condenser was branched into an injection pipe, depressurized by an electronic expansion valve, and then injected into the intermediate pressure chamber of a compressor. In this industry, backflow of refrigerant from the intermediate pressure chamber towards the injection pipe was a problem, and product designs sometimes included a check valve to prevent backflow of refrigerant. Under these circumstances, the inventors discovered that when the compressor was operated with the electronic expansion valve opened to a small degree or fully closed, the pressure in the injection pipe became almost equal to the pressure in the intermediate pressure chamber, and that the relative pressures of the intermediate pressure chamber and the injection pipe could repeatedly reverse due to fluctuations in the pressure in the intermediate pressure chamber accompanying the operation of the compressor. The inventors then discovered that the repeated reversal of the pressure levels in the intermediate pressure chamber and the injection piping caused the check valve to repeatedly open and close, resulting in chattering and potentially generating noise. To solve this problem, they arrived at the subject matter of this disclosure. Therefore, this disclosure provides an air conditioning system that can stably maintain refrigerant injection from injection piping to the compressor and suppress noise caused by chattering of the check valve.

[0013] The embodiments will be described in detail below with reference to the drawings. However, unnecessary details may be omitted. For example, detailed explanations of already well-known matters or redundant explanations of substantially identical configurations may be omitted. This is to avoid the following explanation becoming unnecessarily verbose and to facilitate understanding for those skilled in the art. Note that the accompanying drawings and the following description are provided to enable those skilled in the art to fully understand the present disclosure, and are not intended to limit the subject matter described in the claims.

[0014] (Embodiment 1) Hereinafter, Embodiment 1 will be described with reference to the drawings.

[0015] [1-1. Configuration] [1-1-1. Configuration of Refrigerant Circuit] FIG. 1 is a diagram showing a refrigerant circuit 1A of an air conditioner 1 according to Embodiment 1. The air conditioner 1 includes an indoor unit 2 and an outdoor unit 3. The indoor unit 2 is installed indoors and performs indoor air conditioning by blowing out warm air, cold air, or the like. The outdoor unit 3 is installed outdoors and is connected to the indoor unit 2 via a refrigerant pipe. In the present embodiment, the air conditioner  1 includes a plurality of indoor units 2 and a plurality of outdoor units 3. Note that the number of indoor units 2 and outdoor units 3 can be arbitrarily set as long as each is one or more.

[0016] The indoor unit 2 has an indoor heat exchanger 21. The indoor heat exchanger 21 is a heat exchanger that exchanges heat between the refrigerant flowing inside and the surrounding air. The indoor heat exchanger 21 is, for example, a fin-tube type heat exchanger.

[0017] Of the refrigerant flow paths of the indoor heat exchanger 21, an indoor side gas valve 22 is connected to one side of the inlet and outlet via a refrigerant pipe. The indoor side gas valve 22 is a valve connected to an internal and external connection gas pipe 4 that connects the indoor unit 2 and the outdoor unit 3. The internal and external connection gas pipe 4 is a refrigerant pipe through which a gas refrigerant flows inside.

[0018] The indoor unit 2 has an indoor expansion valve 23. The indoor expansion valve 23 is an expansion valve connected to the other side of the inlet and outlet of the refrigerant flow path of the indoor heat exchanger 21 via a refrigerant pipe. In the present embodiment, the indoor expansion valve 23 is configured to be able to adjust the opening degree by control. The indoor expansion valve 23 corresponds to an example of the "expansion valve" in the present disclosure.

[0019] The indoor expansion valve 23 is connected to the indoor liquid valve 24 via a refrigerant pipe. The indoor liquid valve 24 and the indoor gas valve 22 are valves connected to the internal and external connection liquid pipe 5 that connects the indoor unit 2 and the outdoor unit 3. The internal and external connection liquid pipe 5 is a refrigerant pipe through which liquid refrigerant flows inside.

[0020] The indoor unit 2 has an indoor blower 25. The indoor blower 25 can be a blower of any type, such as a cross-flow fan or a centrifugal fan, for example. The indoor blower 25 takes in indoor air into the housing of the indoor unit 2, exchanges heat with the refrigerant through the indoor heat exchanger 21, and blows out the air after heat exchange into the room.

[0021] The outdoor unit 3 has a compressor 31. The compressor 31 is a device that compresses the inhaled refrigerant and discharges it through the discharge port. The compressor 31 can be a compressor of any type, such as a scroll type or a rotary type, for example. The compressor 31 is provided with an injection port 31A, which is an opening that enables injection of refrigerant into the intermediate pressure chamber. The intermediate pressure chamber is a chamber in the compressor 31 where the pressure of the refrigerant is the intermediate pressure between the pressure of the inhaled refrigerant and the pressure of the discharged refrigerant. A check valve 31B is provided at the injection port 31A. The check valve 31B blocks the refrigerant from flowing back from the intermediate pressure chamber side of the compressor 31 to the injection pipe 50 side described later. The discharge port of the compressor 31 is connected to the discharge pipe 32. The discharge pipe 32 is a refrigerant pipe through which the high-temperature and high-pressure gas refrigerant discharged from the discharge port of the compressor 31 flows. A high-pressure switch HP is provided on the discharge pipe 32. The high-pressure switch HP is a pressure switch that detects whether the pressure of the refrigerant flowing inside the discharge pipe 32 is above a predetermined value.

[0022] The discharge pipe 32 is connected to the oil separator 33. The oil separator 33 separates and recovers the oil contained in the high-temperature, high-pressure refrigerant flowing through the discharge pipe 32. An oil pipe 33A is connected to the oil-side outlet of the oil separator 33. The oil pipe 33A is the piping through which the oil separated and recovered by the oil separator 33 mainly flows. The oil pipe 33A is connected to the oil separator 33 and to an intermediate section of the suction pipe 44, which will be described later. The oil pipe 33A is equipped with an oil recovery valve 33B that can be opened and closed by control. In addition, the oil pipe 33A is equipped with a check valve 33C between the oil recovery valve 33B and the oil separator 33 to block the flow of oil from the oil recovery valve 33B towards the oil separator 33. Furthermore, the portion of the oil pipe 33A between the oil recovery valve 33B and the check valve 33C is branched and connected to an oil valve 33D. The oil valve 33D is connected to the oil balance pipe 6. The oil balance pipe 6 is a pipe that connects the oil valves 33D installed on each outdoor unit 3 in parallel. The air conditioning system 1 adjusts the distribution of oil among the outdoor units 3 via the oil balance pipe 6.

[0023] A high-pressure gas pipe 34 is connected to the refrigerant outlet of the oil separator 33. The high-pressure gas pipe 34 is a refrigerant pipe that connects the oil separator 33 and the four-way valve 35. High-temperature, high-pressure gaseous refrigerant, from which the oil has been removed in the oil separator 33, flows through the inside of the high-pressure gas pipe 34. A high-pressure pressure sensor PS1 is provided in the high-pressure gas pipe 34 to measure the pressure of the refrigerant inside the high-pressure gas pipe 34.

[0024] A check valve 36 is provided in the high-pressure gas pipe 34. The check valve 36 blocks the flow of refrigerant in the high-pressure gas pipe 34 from the four-way valve 35 to the oil separator 33.

[0025] The four-way valve 35 is a valve that can switch the flow path of the refrigerant. The outdoor heat exchanger 37 and the outdoor gas valve 38 are connected to the four-way valve 35 via refrigerant piping. Furthermore, the low-pressure gas pipe 39 is connected to the four-way valve 35. The four-way valve 35 switches the operation of the air conditioning system 1 to cooling operation by connecting the high-pressure gas pipe 34 to the outdoor heat exchanger 37 and the outdoor gas valve 38 to the low-pressure gas pipe 39. The four-way valve 35 also switches the operation of the air conditioning system 1 to heating operation by connecting the high-pressure gas pipe 34 to the outdoor gas valve 38 and the outdoor heat exchanger 37 to the low-pressure gas pipe 39.

[0026] The outdoor heat exchanger 37 is a heat exchanger that exchanges heat between the refrigerant flowing inside and the outside air. The outdoor heat exchanger 37 can be any heat exchanger, such as a fin-tube type heat exchanger. The outdoor unit 3 is also provided with an outdoor fan 37A that takes in outside air into the housing of the outdoor unit 3 and exchanges heat with the refrigerant through the outdoor heat exchanger 37. Of the outdoor heat exchanger 37, the gas-side inlet and outlet of the refrigerant flow path are connected to a four-way valve 35 via refrigerant piping, and the liquid-side inlet and outlet of the refrigerant flow path are connected to liquid-side refrigerant piping 41 via an outdoor expansion valve 40. In this embodiment, the outdoor expansion valve 40 is an expansion valve whose opening degree can be adjusted by control.

[0027] The liquid-side refrigerant piping 41 is a refrigerant piping through which refrigerant, mainly in liquid form, flows. The liquid-side refrigerant piping 41 is connected to the outdoor expansion valve 40 and the outdoor liquid valve 42. The outdoor liquid valve 42 is a valve connected to the indoor-outdoor connecting liquid pipe 5. The indoor-outdoor connecting liquid pipe 5 connects the indoor liquid valve 24 of each indoor unit 2 in parallel to the outdoor liquid valve 42. In addition, the indoor-outdoor connecting liquid pipe 5 connects the outdoor liquid valve 42 of each outdoor unit 3 in parallel to the indoor liquid valve 24.

[0028] The outdoor gas valve 38 is a valve connected to the indoor-outdoor connecting gas pipe 4. The indoor-outdoor connecting gas pipe 4 connects the indoor gas valve 22 of each indoor unit 2 in parallel to the outdoor gas valve 38. In addition, the indoor-outdoor connecting gas pipe 4 connects the outdoor gas valve 38 of each outdoor unit 3 in parallel to the indoor gas valve 22.

[0029] The low-pressure gas pipe 39 is a refrigerant pipe connecting the four-way valve 35 and the accumulator 43. The low-pressure gas refrigerant that has evaporated from the indoor heat exchanger 21 and the outdoor heat exchanger 37, which functions as an evaporator, mainly flows through the low-pressure gas pipe 39. The low-pressure gas pipe 39 is equipped with a low-pressure pressure sensor PS2 that measures the pressure of the refrigerant inside the low-pressure gas pipe 39. The low-pressure gas pipe 39 corresponds to an example of the "gas-side refrigerant piping on the suction side of the compressor" in this disclosure.

[0030] The accumulator 43 allows only the gaseous refrigerant contained in the refrigerant of the low-pressure gas pipe 39 to flow into the suction pipe 44. The suction pipe 44 is a refrigerant pipe that connects the outlet of the gaseous refrigerant in the accumulator 43 to the inlet of the compressor 31. The compressor 31 draws in the gaseous refrigerant that has passed through the accumulator 43 via the suction pipe 44.

[0031] An injection pipe 50 is provided in the refrigerant circuit 1A. The injection pipe 50 is a refrigerant pipe that branches off from the liquid-side refrigerant pipe 41 and is connected to the injection port 31A of the compressor 31. An electronic expansion valve 51 is provided in the injection pipe 50. The electronic expansion valve 51 is an expansion valve whose opening degree can be controlled. The electronic expansion valve 51 reduces the pressure of the refrigerant in the injection pipe 50.

[0032] A subcooled heat exchanger 53 is provided in the refrigerant circuit 1A. The subcooled heat exchanger 53 is a heat exchanger that exchanges heat between the refrigerant flowing inside the injection piping 50 and the refrigerant flowing inside the liquid-side refrigerant piping 41. The subcooled heat exchanger 53 may be, for example, a plate-type heat exchanger. The subcooled heat exchanger 53 is located downstream of the electronic expansion valve 51 in the injection piping 50. In other words, the electronic expansion valve 51 is located in the injection piping 50 between the branching point 41A between the injection piping 50 and the liquid-side refrigerant piping 41 and the subcooled heat exchanger 53.

[0033] A branch pipe 55 is provided in the refrigerant circuit 1A. The branch pipe 55 is a refrigerant pipe that branches off from the injection pipe 50 and is connected to the low-pressure gas pipe 39. Specifically, the branch pipe 55 branches off from the injection pipe 50 between the subcooled heat exchanger 53 and the connection portion to the injection port 31A. An on-off valve 57 is also provided in the branch pipe 55. The on-off valve 57 is a valve that can be switched between an open state and a closed state by control. When the on-off valve 57 is in the open state, it allows the flow of refrigerant in the branch pipe 55, and when it is in the closed state, it blocks the flow of refrigerant in the branch pipe 55.

[0034] When the on-off valve 57 is open, the injection pipe 50 and the low-pressure gas pipe 39 are connected via the branch pipe 55, so the refrigerant pressure in the injection pipe 50 is lower than the refrigerant pressure in the intermediate pressure chamber of the compressor 31. For this reason, when the on-off valve 57 is open, the refrigerant in the injection pipe 50 is not injected into the compressor 31.

[0035] On the other hand, when the on-off valve 57 is closed, the injection piping 50 and the low-pressure gas pipe 39 are not connected via the branch piping 55. Therefore, if the opening of the electronic expansion valve 51 is greater than or equal to a predetermined opening, the pressure of the refrigerant in the injection piping 50 rises and becomes higher than the pressure of the refrigerant in the intermediate pressure chamber of the compressor 31. For this reason, when the on-off valve 57 is closed, the refrigerant in the injection piping 50 can be injected into the compressor 31 via the injection port 31A.

[0036] The outdoor unit 3 is equipped with an outdoor air temperature sensor TS1 that measures the temperature of the outside air. The outdoor air temperature sensor TS1 measures the temperature of the outside air. Specifically, the outdoor air temperature sensor TS1 is installed, for example, near the outside air intake port in the housing of the outdoor unit 3, and measures the temperature of the outside air drawn into the housing by the drive of the outdoor fan 37A.

[0037] The outdoor unit 3 is equipped with a gas-side temperature sensor TS2 and a liquid-side temperature sensor TS3. The gas-side temperature sensor TS2 measures the temperature of the refrigerant flowing near the gas-side inlet and outlet of the outdoor heat exchanger 37. The liquid-side temperature sensor TS3 measures the temperature of the refrigerant flowing near the liquid-side inlet and outlet of the outdoor heat exchanger 37.

[0038] The indoor unit 2 is equipped with an indoor temperature sensor TS4. The indoor temperature sensor TS4 measures the temperature of the refrigerant flowing near the liquid side inlet and outlet of the indoor heat exchanger 21.

[0039] [1-1-2. Control System Configuration] Figure 2 shows the configuration of the control system of the air conditioning unit 1. The air conditioning system 1 has a control unit 70. The control unit 70 is connected to various parts of the air conditioning system 1, such as the compressor 31, and controls these parts to perform various processes in the air conditioning system 1.

[0040] In this embodiment, the control unit 70 comprises a processor and a storage medium, and the processor reads and executes a program stored in the storage medium to perform various processing for the air conditioner 1. The processor that the control unit 70 may include is, for example, a CPU (Central Processing Unit) or an MPU (Micro-Processing Unit). The storage medium that the control unit 70 may include is, for example, a hard disk, flash memory, or optical disc. The control unit 70 may be installed in either the indoor unit 2 or the outdoor unit 3, or it may be installed outside the indoor unit 2 and the outdoor unit 3. Alternatively, the control unit 70 may function through the cooperation of the indoor unit 2, the outdoor unit 3, and a plurality of components, circuits, etc. installed outside them.

[0041] The control unit 70 controls the compressor 31 and adjusts its rotational speed. The control unit 70 is also configured to acquire the current value of the secondary current of the compressor 31. The secondary current is the current flowing through the motor of the compressor 31.

[0042] The control unit 70 controls the oil recovery valve 33B and the on / off valve 57, switching them individually between open and closed states. The control unit 70 controls the four-way valve 35, switching the operation of the air conditioner 1 between cooling and heating operation. The control unit 70 controls the indoor expansion valve 23, the outdoor expansion valve 40, and the electronic expansion valve 51, adjusting their respective opening degrees. The control unit 70 controls the rotation speed of the indoor blower 25 and the outdoor blower 37A, adjusting their respective airflow rates.

[0043] The control unit 70 acquires the measured values ​​from the high-pressure side pressure sensor PS1 and the low-pressure side pressure sensor PS2. The control unit 70 acquires the measured value from the high-pressure switch HP. The control unit 70 acquires the measured values ​​from the outside air temperature sensor TS1, the gas side temperature sensor TS2, the liquid side temperature sensor TS3, and the indoor side temperature sensor TS4.

[0044] [1-2. Operation] The operation of the air conditioning system 1, configured as described above, will be explained below.

[0045] Figure 3 is a flowchart showing the operation of the control unit 70, illustrating the operation of the control unit 70 when controlling the electronic expansion valve 51 and the on-off valve 57 during the operation of the air conditioning system 1. The operation of the control unit 70 shown in Figure 3 is repeatedly performed at predetermined time intervals during the operation of the air conditioning system 1. Note that the operation of the air conditioning system 1 means that the air conditioning system 1 drives at least the compressor 31, and includes, for example, cooling operation, heating operation, and dehumidification operation.

[0046] At the beginning of the operation shown in Figure 3, in step SA1, the control unit 70 determines whether the on-off valve 57 is in the open state. In other words, in step SA1, the control unit 70 determines whether or not refrigerant is being injected into the compressor 31.

[0047] If the control unit 70 determines in step SA1 that the on-off valve 57 is in the open state, that is, that no refrigerant has been injected into the compressor 31 (step SA1: YES), the control unit 70 proceeds to step SA2. If the control unit 70 determines in step SA1 that the on-off valve 57 is in the closed state, that is, that refrigerant has been injected into the compressor 31 (step SA1: NO), the control unit 70 proceeds to step SA7.

[0048] In step SA2, the control unit 70 determines whether the secondary current of the compressor 31 is less than or equal to a reference current value. Specifically, the control unit 70 obtains the current value of the secondary current of the compressor 31 and compares it with a reference current value stored in the storage medium.

[0049] According to the determination in step SA2, it is possible to determine whether the torque of the compressor 31 motor is less than or equal to the torque corresponding to the reference current value. In this way, in step SA2, the control unit 70 determines whether the motor torque and current will not become excessive even when refrigerant is injected into the compressor 31.

[0050] In step SA2, if the control unit 70 determines that the secondary current of the compressor 31 is less than or equal to the reference current value (step SA2: YES), the control unit 70 proceeds to step SA3. If the control unit 70 determines that the secondary current of the compressor 31 exceeds the reference current value (step SA2: NO), the control unit 70 proceeds to step SA8.

[0051] In step SA3, the control unit 70 determines whether the condensation temperature of the refrigerant in either the indoor heat exchanger 21 or the outdoor heat exchanger 37, which functions as a condenser, is below the reference condensation temperature. In both cooling and heating operations, the control unit 70 converts the pressure acquired by the high-pressure side pressure sensor PS1 to a saturation temperature and treats the converted value as the condensation temperature. The control unit 70 also compares the calculated condensation temperature with the reference condensation temperature stored in the storage medium.

[0052] When the condensation temperature of the refrigerant in the condenser is high, the torque of the compressor 31 motor tends to be higher than when the condensation temperature is low. In other words, the determination in step SA3, similar to the determination in step SA2, can indirectly determine whether the torque of the compressor 31 motor is less than or equal to the torque corresponding to the reference condensation temperature. Thus, in step SA3, the control unit 70 determines whether the motor torque and current will not become excessive even when refrigerant is injected into the compressor 31.

[0053] In step SA3, if the control unit 70 determines that the condensation temperature of the refrigerant in the condenser is below the reference condensation temperature (step SA3: YES), the control unit 70 proceeds to step SA4. If the control unit 70 determines that the condensation temperature of the refrigerant in the condenser exceeds the reference condensation temperature (step SA3: NO), the control unit 70 proceeds to step SA8.

[0054] In step SA4, the control unit 70 determines whether the outside air temperature is below the reference outside air temperature. The control unit 70 acquires the measured value of the outside air temperature from the outside air temperature sensor TS1 and compares the acquired measured value with the reference outside air temperature stored in the storage medium.

[0055] When the ambient temperature is high, the torque of the compressor 31 motor tends to be higher than when the ambient temperature is low. In other words, the determination in step SA4, similar to the determinations in steps SA2 and SA3, can indirectly determine whether the torque of the compressor 31 motor is less than or equal to the torque corresponding to the reference ambient temperature. Thus, in step SA4, the control unit 70 determines whether the motor torque and current will not become excessive even when refrigerant is injected into the compressor 31.

[0056] In step SA4, if the control unit 70 determines that the outside air temperature is below the reference outside air temperature (step SA4: YES), the operation of the control unit 70 proceeds to step SA5. If the control unit 70 determines that the outside air temperature exceeds the reference outside air temperature (step SA4: NO), the operation of the control unit 70 proceeds to step SA8.

[0057] In step SA5, the control unit 70 becomes capable of switching the on-off valve 57 from the open state to the closed state, and controls the on-off valve 57 to be either open or closed depending on the status of the refrigerant circuit 1A. In other words, in step SA5, the state of the on-off valve 57 is not limited to the open state, and the control unit 70 can inject refrigerant into the compressor 31 with the on-off valve 57 in the closed state. As described above, step SA5 is executed after confirming that the motor torque and current will not be excessive even if refrigerant is injected into the compressor 31 in steps SA2 to SA4. This suppresses excessive torque and current acting on the motor of the compressor 31, and stabilizes the operation of the air conditioning system 1. After the completion of step SA5, the operation of the control unit 70 moves on to step SA6.

[0058] In step SA6, the control unit 70 determines whether the on-off valve 57 is in the closed state. In other words, the control unit 70 determines whether refrigerant is being injected into the compressor 31.

[0059] If the control unit 70 determines in step SA6 that the on-off valve 57 is in a closed state (step SA6: YES), the control unit 70 proceeds to step SA7. If the control unit 70 determines that the on-off valve 57 is in an open state (step SA6: NO), the control unit 70 proceeds to step SA9.

[0060] In step SA7, the control unit 70 adjusts the opening of the electronic expansion valve 51 within a range limited to an opening greater than or equal to a reference opening. That is, when the on-off valve 57 is closed and refrigerant is injected into the compressor 31 (step SA1: NO, or step SA6: YES), the control unit 70 limits the opening of the electronic expansion valve 51 to greater than or equal to a reference opening.

[0061] As described above, when the on-off valve 57 is closed, the refrigerant in the injection piping 50 becomes more pressure than the intermediate pressure chamber of the compressor 31, and refrigerant is injected into the intermediate pressure chamber. At this time, if the opening of the electronic expansion valve 51 is too small, the flow rate of refrigerant downstream of the electronic expansion valve 51 in the injection piping 50 will be too small, and the pressure in the injection piping 50 and the pressure in the intermediate pressure chamber will be almost equal. When the compressor 31 is driven in this state, the pressure in the intermediate pressure chamber will fluctuate, and the pressure between the injection piping 50 and the intermediate pressure chamber may repeatedly reverse. In such a case, the check valve 31B provided in the injection port 31A will repeatedly open and close, causing chatter, and vibrations may be transmitted to the injection piping 50, etc., potentially generating noise. In contrast, in step SA7, while the on-off valve 57 is closed and refrigerant is being injected into the compressor 31, the opening of the electronic expansion valve 51 is limited to above the reference opening, thereby maintaining a state in which the injection piping 50 is at a higher pressure than the intermediate pressure chamber. This allows for stable injection of refrigerant from the injection piping 50 to the compressor 31, and suppresses noise and other issues associated with chattering of the check valve 31B.

[0062] In this embodiment, the reference opening is set to an opening of 10% or more and 40% or less, based on the maximum opening of the electronic expansion valve 51. By setting the reference opening within a range of 10% or more of the maximum opening, it is easier to stably maintain a state in which the injection piping 50 is at a higher pressure than the intermediate pressure chamber. Furthermore, by setting the reference opening within a range of 40% or less of the maximum opening, the range of opening of the electronic expansion valve 51 that can be adjusted by the control unit 70 in step SA7 can be made as wide as possible.

[0063] Furthermore, in this embodiment, the reference opening is variably set by the control unit 70 each time step SA7 is executed, within a range of 10% to 40% of the maximum opening, based on the rotational speed of the compressor 31, the suction pressure of the compressor 31, and the discharge pressure of the compressor 31 at the time of step SA7. The control unit 70 uses, for example, the measured value of the high-pressure side pressure sensor PS1 as the discharge pressure of the compressor 31. The control unit 70 uses, for example, the measured value of the low-pressure side pressure sensor PS2 as the suction pressure of the compressor 31.

[0064] The pressure in the intermediate pressure chamber of the compressor 31 can be determined using the rotational speed, suction pressure, and discharge pressure of the compressor 31. Furthermore, the pressure in the injection piping 50 becomes high when the opening of the electronic expansion valve 51 is large, and low when the opening of the electronic expansion valve 51 is small. Therefore, by setting the opening of the electronic expansion valve 51 to a reference opening that results in a sufficiently high pressure in the injection piping 50 relative to the intermediate pressure chamber pressure determined from the rotational speed, suction pressure, and discharge pressure of the compressor 31, a stable state of the injection piping 50 being at a higher pressure than the intermediate pressure chamber can be maintained. In this embodiment, the storage medium stores a table for converting the rotational speed, suction pressure, and discharge pressure of the compressor 31 to a reference opening. The control unit 70 reads and uses this table stored in the storage medium to convert the rotational speed, suction pressure, and discharge pressure of the compressor 31 to a reference opening.

[0065] Once the adjustment of the opening degree of the electronic expansion valve 51 is complete, the control unit 70 completes the operation of step SA7.

[0066] On the other hand, in step SA8, the control unit 70 maintains the on-off valve 57 in the open state. That is, in step SA8, the state of the on-off valve 57 is restricted to the open state, and the control unit 70 cannot inject refrigerant into the compressor 31 by closing the on-off valve 57. As described above, step SA8 is executed when it is determined in any of steps SA2 to SA4 that the motor torque and current may become excessive if refrigerant is injected into the compressor 31. Therefore, under conditions where the motor torque and current may become excessive, the injection of refrigerant into the compressor 31 can be restricted, and the operation of the air conditioning system 1 can be stabilized. After the completion of step SA8, the operation of the control unit 70 proceeds to step SA9.

[0067] In step SA9, the control unit 70 adjusts the opening degree of the electronic expansion valve 51. In this embodiment, in step SA9, the range of the opening degree of the electronic expansion valve 51 adjusted by the control unit 70 is not limited. That is, if the on-off valve 57 is open and no refrigerant is injected into the compressor 31 (steps SA2 to SA4: NO, or step SA6: NO), the control unit 70 does not limit the opening degree of the electronic expansion valve 51. When the on-off valve 57 is open, the pressure in the injection piping 50 is lower than the pressure in the intermediate pressure chamber of the compressor 31. Therefore, even if the opening degree of the electronic expansion valve 51 is made smaller than the reference opening degree, the pressure levels in the intermediate pressure chamber and the injection piping 50 will not repeatedly reverse. Consequently, in this case, noise due to chattering of the check valve 31B provided in the injection port 31A will not occur. Therefore, in step SA9, which is performed when the on-off valve 57 is in the open state, the control unit 70 is allowed to adjust the opening degree of the electronic expansion valve 51 to an opening degree smaller than the reference opening degree, depending on the status of the refrigerant circuit 1A, etc. Unlike this embodiment, in step SA9, similar to step SA7, the control unit 70 may be configured to adjust the opening of the electronic expansion valve 51 within a range limited to an opening greater than or equal to a reference opening. In this case, the range of possible openings for the electronic expansion valve 51 can be kept constant regardless of whether or not refrigerant is injected into the compressor 31, thus simplifying the control of the electronic expansion valve 51.

[0068] Once the adjustment of the opening degree of the electronic expansion valve 51 is complete, the control unit 70 completes the operation of step SA9.

[0069] After the completion of step SA7 or step SA9, the control unit 70 terminates the operation shown in Figure 3 and repeats the operation shown in Figure 3 from step SA1 after a predetermined time interval. This allows for appropriate control of the electronic expansion valve 51 and the on-off valve 57 while suppressing noise generation associated with chattering of the check valve 31B of the injection port 31A.

[0070] [1-3. Effects, etc.] As described above, in this embodiment, the air conditioning system 1 includes a compressor 31, an outdoor heat exchanger 37, an indoor expansion valve 23, an indoor heat exchanger 21, an injection pipe 50 through which the refrigerant injected into the compressor 31 flows, branching from a liquid-side refrigerant pipe 41 provided between the outdoor heat exchanger 37 and the indoor expansion valve 23, a subcooling heat exchanger 53 that exchanges heat between the refrigerant in the injection pipe 50 and the refrigerant in the liquid-side refrigerant pipe 41, and an injection pipe 50. The system may also be configured to include an electronic expansion valve 51 provided between the branching point 41A between pipe 50 and liquid-side refrigerant piping 41 and the subcooling heat exchanger 53, a branch pipe 55 that branches off from the injection piping 50 and is connected to the low-pressure gas pipe 39 on the suction side of the compressor 31, an on-off valve 57 provided on the branch pipe 55, and a check valve 31B that blocks refrigerant from flowing back from the compressor 31 side to the injection piping 50 side, wherein when the on-off valve 57 is closed, the opening of the electronic expansion valve 51 is limited to an opening greater than or equal to a reference opening. This makes it easier to raise the pressure in the injection piping 50 to a higher pressure than the intermediate pressure chamber in the compressor 31 when the on-off valve 57 is closed. As a result, the pressure between the injection piping 50 and the intermediate pressure chamber is less likely to reverse, and the injection of refrigerant from the injection piping 50 to the compressor 31 can be stably maintained. In particular, in this embodiment, the injection port 31A is provided with a check valve 31B that suppresses the backflow of refrigerant from the intermediate pressure chamber of 31 to the injection piping 50 side. As a result, by stably maintaining the injection of refrigerant from the injection piping 50 to the compressor 31, chattering of the check valve 31B can be suppressed, and the generation of noise associated with chattering can be suppressed. Also, in this embodiment, as in step SA9, the control unit 70 does not limit the range of the opening degree of the electronic expansion valve 51 when the on-off valve 57 is open. Therefore, in this embodiment, when injection is not performed in the compressor 31, the control unit 70 can increase the range of opening of the electronic expansion valve 51, which is adjustable.

[0071] As in this embodiment, the air conditioning system 1 may be configured such that the reference opening is set to an opening of 10% or more and 40% or less of the maximum opening of the electronic expansion valve 51. This makes it easier to raise the pressure in the injection piping 50 to a higher pressure than the intermediate pressure chamber in the compressor 31, while ensuring a degree of freedom in the opening of the electronic expansion valve 51 during injection. As a result, it becomes easier to maintain stable refrigerant injection from the injection piping 50 to the compressor 31, while also making it easier to set the opening of the electronic expansion valve 51 appropriately.

[0072] As in this embodiment, the air conditioning system 1 may be configured such that the reference opening is variably set based on at least one of the following: the discharge pressure of the compressor 31, the suction pressure of the compressor 31, and the rotational speed of the compressor 31. This allows the reference opening degree to be set appropriately. As a result, it becomes easier to maintain stable refrigerant injection from the injection piping 50 to the compressor 31, while also making it easier to set the opening degree of the electronic expansion valve 51 appropriately.

[0073] As in this embodiment, the air conditioning system 1 may be configured such that the on-off valve can be switched from an open state to a closed state when the secondary current of the compressor 31 is less than or equal to a reference current value. This allows refrigerant injection to the compressor 31 when the torque of the compressor 31 is unlikely to become excessive. Therefore, it is easier to stabilize the operation of the air conditioning system 1.

[0074] As in this embodiment, the air conditioning system 1 may be configured such that the on-off valve can be switched from an open state to a closed state when the condensation temperature in the outdoor heat exchanger 37 or the indoor heat exchanger 21 is below the reference condensation temperature. This allows refrigerant injection to the compressor 31 when the torque of the compressor 31 is unlikely to become excessive. Therefore, it is easier to stabilize the operation of the air conditioning system 1.

[0075] As in this embodiment, the air conditioning system 1 may be configured to switch the on / off valve from an open state to a closed state when the outside air temperature is below the standard outside air temperature. This allows refrigerant injection to the compressor 31 when the torque of the compressor 31 is unlikely to become excessive. Therefore, it is easier to stabilize the operation of the air conditioning system 1.

[0076] (Other embodiments) As described above, Embodiment 1 has been explained as an example of the technology disclosed in this application. However, the technology in this disclosure is not limited to this and can be applied to embodiments that have been modified, replaced, added, or omitted. Furthermore, it is possible to create new embodiments by combining the components described in Embodiment 1 above. Therefore, other embodiments are illustrated below.

[0077] In Embodiment 1, the indoor expansion valve 23 and the outdoor expansion valve 40 were described as having a configuration in which the opening degree can be adjusted by control, but this is just one example. The indoor expansion valve 23 and the outdoor expansion valve 40 do not have to be expansion valves in which the opening degree can be adjusted by control, and may be, for example, temperature-type expansion valves.

[0078] In Embodiment 1, the control unit 70 was described as including a processor and a storage medium, but this is just one example. The control unit 70 may, for example, use wired logic that cannot be rewritten. Using wired logic in the control unit 70 is effective in improving processing speed. Examples of wired logic include ASICs (Application Specific Integrated Circuits). The control unit 70 may also be implemented by combining a processor and wired logic. Implementing the control unit 70 by combining a processor and wired logic can improve processing speed while increasing the freedom of software design. Furthermore, the control unit 70 and a circuit having a different function from the control unit 70 may be configured with a single semiconductor element. Examples of circuits having a different function include A / D-D / A conversion circuits. The control unit 70 may also be configured with a single semiconductor element or with multiple semiconductor elements. When configured with multiple semiconductor elements, various controls may be implemented with different semiconductor elements. Moreover, the control unit 70 may be configured with a configuration including semiconductor elements and passive components such as resistors or capacitors.

[0079] In Embodiment 1, it was explained that the control unit 70 performs steps SA2, SA3, and SA4 to confirm that the motor torque does not become excessive even when refrigerant is injected into the compressor 31, but this is just one example. The control unit 70 only needs to perform at least one of steps SA2, SA3, and SA4.

[0080] In Embodiment 1, the branch pipe 55 was described as being connected to the low-pressure gas pipe 39, but this is just one example. The branch pipe 55 only needs to be connected to the refrigerant piping through which the gaseous refrigerant mainly flows on the suction side of the compressor 31. The refrigerant piping on the suction side of the compressor 31 refers to the refrigerant piping through which the refrigerant flows after passing through the evaporator of the indoor heat exchanger 21 and the outdoor heat exchanger 37. In other words, the refrigerant piping on the suction side of the compressor 31 only needs to be the refrigerant piping between the four-way valve 35 and the suction port of the compressor 31. For this reason, the branch pipe 55 may be configured to be connected to, for example, the suction pipe 44.

[0081] In Embodiment 1, it was explained that in step SA7, the reference opening is set by the control unit 70 based on the rotational speed of the compressor 31, the suction pressure of the compressor 31, and the discharge pressure of the compressor 31, but this is just one example. The reference opening can be set by the control unit 70 using one or more of the rotational speed of the compressor 31, the suction pressure of the compressor 31, and the discharge pressure of the compressor 31. In this case, for example, a table that converts one or more of the rotational speed of the compressor 31, the suction pressure of the compressor 31, and the discharge pressure of the compressor 31 into a value for the reference opening may be stored in a storage medium, and the control unit 70 may set the value obtained using the table as the reference opening.

[0082] In Embodiment 1, it was explained that a check valve 31B to prevent backflow of refrigerant from the intermediate pressure chamber side of the compressor 31 toward the injection piping 50 side is provided at the injection port of the compressor 31, but this is just one example. The check valve 31B may also be provided, for example, in the injection piping 50. In this case, the check valve 31B is provided, for example, on the side of the injection piping 50 that is closer to the connection portion with the injection port 31A than to the branch portion with the branch piping 55.

[0083] Since the embodiments described above are for illustrative purposes of the technology described herein, various modifications, substitutions, additions, omissions, etc., can be made within the claims or their equivalents.

[0084] (Note) Based on the above description of embodiments, the following technologies are disclosed.

[0085] (Technology 1) An air conditioning system comprising a compressor, an outdoor heat exchanger, an expansion valve, and an indoor heat exchanger, wherein the system includes an injection pipe that branches off from a liquid-side refrigerant pipe provided between the outdoor heat exchanger and the expansion valve and through which the refrigerant injected into the compressor flows, a subcooling heat exchanger that exchanges heat between the refrigerant in the injection pipe and the refrigerant in the liquid-side refrigerant pipe, an electronic expansion valve provided between the branching point of the injection pipe and the liquid-side refrigerant pipe and the subcooling heat exchanger, a branch pipe that branches off from the injection pipe and is connected to a gas-side refrigerant pipe on the suction side of the compressor, an on-off valve provided in the branch pipe, and a check valve that blocks the backflow of refrigerant from the compressor side to the injection pipe side, wherein when the on-off valve is closed, the opening of the electronic expansion valve is limited to an opening greater than or equal to a reference opening. This makes it easier to raise the pressure in the injection piping to a higher pressure than the intermediate pressure chamber in the compressor when the on-off valve is closed. As a result, it becomes less likely for the pressure between the injection piping and the intermediate pressure chamber to reverse, which helps to maintain stable refrigerant injection from the injection piping to the compressor and suppresses noise caused by chattering of the check valve.

[0086] (Technical 2) The air conditioning system according to Technical 1, wherein the reference opening is set to 10% or more and 40% or less of the maximum opening of the electronic expansion valve. This makes it easier to raise the pressure in the injection piping to a higher pressure than the intermediate pressure chamber in the compressor, while ensuring flexibility in the opening degree of the electronic expansion valve during injection. As a result, it becomes easier to maintain stable refrigerant injection from the injection piping to the compressor, while also making it easier to set the opening degree of the electronic expansion valve appropriately.

[0087] (Technical 3) The air conditioning system according to Technical 1 or 2, wherein the reference opening is set variably based on at least one of the discharge pressure of the compressor, the suction pressure of the compressor, and the rotational speed of the compressor. This allows for the appropriate setting of the reference opening. As a result, it becomes easier to maintain stable refrigerant injection from the injection piping to the compressor while also making it easier to set the opening of the electronic expansion valve appropriately.

[0088] (Technology 4) An air conditioning system according to any one of Techniques 1 to 3, wherein the on-off valve can be switched from an open state to a closed state when the secondary current of the compressor is less than or equal to a reference current value. This allows refrigerant injection into the compressor when the compressor torque is unlikely to become excessive. Therefore, it becomes easier to stabilize the operation of the air conditioning system.

[0089] (Technical 5) An air conditioning system according to any one of Technical 1 to 4, wherein the on / off valve can be switched from an open state to a closed state when the condensation temperature in the outdoor heat exchanger or the indoor heat exchanger is below a reference condensation temperature. This allows refrigerant injection into the compressor when the compressor torque is unlikely to become excessive. Therefore, it becomes easier to stabilize the operation of the air conditioning system.

[0090] (Technical 6) An air conditioning system according to any one of Technical 1 to 5, wherein the on / off valve can be switched from an open state to a closed state when the outside air temperature is below a standard outside air temperature. This allows refrigerant injection into the compressor when the compressor torque is unlikely to become excessive. Therefore, it becomes easier to stabilize the operation of the air conditioning system. [Industrial applicability]

[0091] This disclosure is applicable to air conditioning systems. Specifically, this disclosure is applicable to household air conditioning systems or commercial air conditioning systems, etc. [Explanation of Symbols]

[0092] 1. Air conditioning system 1A Refrigerant Circuit 2 Indoor unit 3 Outdoor unit 4. Internal and external gas pipes 5. Internal and external connecting liquid pipes 6. Oil balance pipe 21 Indoor heat exchanger 22 Indoor gas valve 23. Indoor expansion valve (expansion valve) 24 Indoor liquid valve 25 Indoor fan 31 Compressor 31A Injection Port 31B Check valve 32 Discharge pipe 33 Oil Separator 33A Oil pipe 33B Oil recovery valve 33C Check valve 33D Oil Valve 34 High-pressure gas pipe 35 Four-way valve 36 Check valve 37 Outdoor heat exchanger 37A outdoor blower 38 Outdoor gas valve 39. Low-pressure gas pipe (refrigerant piping on the gas side of the compressor's suction side) 40 Outdoor expansion valve 41 Liquid side refrigerant piping 41A Branch point 42 Outdoor liquid valve 43 Accumulator 44 Suction pipe 50 Injection Piping 51 Electronic expansion valve 53 Cooling heat exchanger 55 Branch piping 57 Shut-off valve 70 Control Unit HP High-Voltage Switch PS1 High-Pressure Side Pressure Sensor PS2 Low-Pressure Side Pressure Sensor TS1 Outdoor Temperature Sensor TS2 Gas-side temperature sensor TS3 Liquid-side temperature sensor TS4 Indoor Temperature Sensor

Claims

1. In an air conditioning system including a compressor, an outdoor heat exchanger, an expansion valve, and an indoor heat exchanger, An injection pipe is provided between the outdoor heat exchanger and the expansion valve, and branches off from the liquid-side refrigerant piping through which the refrigerant to be injected into the compressor flows. A subcooling heat exchanger that exchanges heat between the refrigerant in the injection piping and the refrigerant in the liquid-side refrigerant piping, An electronic expansion valve is provided between the injection piping and the liquid-side refrigerant piping at the branching point and the subcooling heat exchanger. A branch pipe that branches off from the injection piping and is connected to the gas-side refrigerant piping on the suction side of the compressor, A shut-off valve provided in the aforementioned branch piping, The system includes a check valve that blocks the flow of refrigerant back from the compressor side to the injection piping side, When the aforementioned on-off valve is in the closed state, the opening degree of the electronic expansion valve is limited to an opening degree equal to or greater than the reference opening degree. Air conditioning system.

2. The aforementioned reference opening is set to 10% or more and 40% or less of the maximum opening of the electronic expansion valve. The air conditioning device according to claim 1.

3. The reference opening is set variably based on at least one of the following: the discharge pressure of the compressor, the suction pressure of the compressor, and the rotational speed of the compressor. The air conditioning device according to claim 1.

4. The on-off valve can be switched from the open state to the closed state when the secondary current of the compressor is less than or equal to the reference current value. An air conditioning device according to any one of claims 1 to 3.

5. The on / off valve can be switched from the open state to the closed state when the condensation temperature in the outdoor heat exchanger or the indoor heat exchanger is below the reference condensation temperature. An air conditioning device according to any one of claims 1 to 3.

6. The on / off valve can be switched from the open state to the closed state when the outside air temperature is below the standard outside air temperature. An air conditioning device according to any one of claims 1 to 3.

Images