Refrigeration cycle device and refrigeration cycle device control method

Abstract

A refrigeration cycle device (100) according to a certain aspect of the present disclosure comprises a refrigerant circuit (50), a bypass pipe (70), a first valve (60), a second valve (80), and a control device (90). The refrigerant circuit is configured such that a refrigerant circulates through a compressor (10), a first heat exchanger (20), a decompression mechanism (30), and a second heat exchanger (40) in this order. The bypass pipe connects a suction port (10B) and a discharge port (10A) of the compressor. The first valve is provided between the discharge port and the first heat exchanger. The second valve is provided in the bypass pipe. The control device for controlling the first valve and the second valve closes the first valve and opens the second valve when the compressor has stopped operating.

Description

Refrigeration cycle device and control method for refrigeration cycle device 【0001】 The present disclosure relates to a refrigeration cycle device and a control method for a refrigeration cycle device. More specifically, it relates to a technique for preventing a decrease in the capacity of a compressor in a refrigeration cycle device. 【0002】 Generally, when a refrigeration cycle device starts up, if the pressure difference between the refrigerant pressure on the suction side of the compressor and the refrigerant pressure on the discharge side of the compressor is large, it is known that the capacity of the compressor may decrease or a failure may occur. 【0003】 As a measure for preventing such a failure of the compressor, for example, Japanese Patent Application Laid-Open No. 2000-55484 (Patent Document 1) discloses a refrigeration cycle device that controls an on-off valve on a bypass circuit that connects the discharge side and the suction side of the compressor in response to the stop of the compressor. 【0004】 The refrigeration cycle device of Patent Document 1 can equalize the refrigerant pressure on the suction side of the compressor and the refrigerant pressure on the discharge side of the compressor by opening the on-off valve on the bypass circuit when the compressor stops. By doing so, the pressure difference between the refrigerant pressure on the suction side of the compressor and the refrigerant pressure on the discharge side of the compressor when the refrigeration cycle device starts up next can be reduced. 【0005】 Japanese Patent Application Laid-Open No. 2000-55484 【0006】 However, when the compressor stops after operating for a relatively short time, since the amount of gaseous refrigerant discharged from the compressor is relatively small, the liquid refrigerant may remain on the discharge side of the compressor. Therefore, when the valve on the bypass circuit is opened in this state, the liquid refrigerant on the discharge side may move to the suction side of the compressor via the bypass circuit and may enter the inside of the compressor when the compressor starts up next time. In this case, the oil concentration of the refrigerant oil inside the compressor may decrease due to the infiltrated liquid refrigerant, and there is a risk of causing a decrease in the capacity of the compressor when the compressor starts up. 【0007】 The present disclosure has been made to solve the above problems, and an object thereof is to prevent a decrease in the capacity of a compressor in a refrigeration cycle device. 【0008】A refrigeration cycle device according to a certain aspect of the present disclosure comprises a refrigerant circuit, bypass piping, a first valve, a second valve, and a control device. The refrigerant circuit is configured to circulate the refrigerant in the order of a compressor, a first heat exchanger, a pressure reducing mechanism, and a second heat exchanger. The bypass piping connects the suction port and discharge port of the compressor. The first valve is provided between the discharge port and the first heat exchanger. The second valve is provided in the bypass piping. The control device that controls the first valve and the second valve closes the first valve and opens the second valve when the operation of the compressor stops. 【0009】 A control method for a refrigeration cycle system relating to another aspect of this disclosure relates to a control method for a refrigeration cycle system comprising a refrigerant circuit, bypass piping, a first valve, and a second valve. The refrigerant circuit is configured to circulate the refrigerant in the order of a compressor, a first heat exchanger, a pressure reducing mechanism, and a second heat exchanger. The bypass piping connects the suction port and discharge port of the compressor. The first valve is provided between the discharge port and the first heat exchanger. The second valve is provided in the bypass piping. The control method includes the steps of determining that the operation of the compressor has stopped, and, if the operation of the compressor has stopped, closing the first valve and opening the second valve. 【0010】 According to the refrigeration cycle device of this disclosure, it is possible to prevent liquid refrigerant from moving from the discharge side to the suction side of the compressor via a bypass circuit during the pressure equalization process. This prevents liquid refrigerant from entering the compressor while equalizing the refrigerant pressure between the suction side and the discharge side of the compressor. Therefore, it is possible to prevent a decrease in the compressor's capacity in the refrigeration cycle device. 【0011】 This is a diagram showing an example of the configuration of a refrigeration cycle system. This is a diagram showing an example of the hardware configuration of the control device in the refrigeration cycle system. This is a functional block diagram of the control device in the refrigeration cycle system. This is a flowchart showing the processes executed in the control device of the refrigeration cycle system according to Embodiment 1. This is a table showing a method for identifying the state of the refrigeration cycle system according to Embodiment 2. This is a flowchart showing the processes executed in the control device of the refrigeration cycle system according to Embodiment 2. 【0012】This embodiment will be described below with reference to the drawings. In the following description, identical parts are denoted by the same reference numerals. Their names and functions are also the same. Therefore, detailed descriptions of them will not be repeated. 【0013】 Embodiment 1. [Configuration of Refrigeration Cycle Device] Figure 1 is a diagram showing an example of the configuration of a refrigeration cycle device 100. The refrigeration cycle device 100 functions, for example, as an air conditioning device. As shown in Figure 1, the refrigeration cycle device 100 includes a refrigerant circuit 50, bypass piping 70, a control valve 80, a control device 90, temperature sensors 116, 118, and pressure sensors 112, 114, 115. 【0014】 The refrigerant circuit 50 constitutes a circulation path through which the refrigerant circulates. The refrigerant circuit 50 includes a compressor 10, heat exchangers 20 and 40, a pressure reducing mechanism 30, and a shut-off valve 60. 【0015】 The compressor 10 includes an intake port 10B for drawing in refrigerant and a discharge port 10A for discharging refrigerant. The compressor 10 draws in refrigerant from the intake port 10B, compresses it, changes the state of the refrigerant to a high-temperature, high-pressure gaseous state, and discharges it from the discharge port 10A. The compressor 10 discharges refrigerant at a flow rate corresponding to its rotational speed. In other words, by adjusting the rotational speed of the compressor 10, the flow rate of refrigerant circulating within the refrigeration cycle device 100 can be controlled. 【0016】 The compressor 10 includes a drive circuit (not shown), and the frequency of the voltage applied to the compressor 10 may be changed according to the control of the control device 90, thereby changing the rotational speed of the compressor 10. The compressor 10 can be variably adjusted in frequency, for example, by inverter control. The operating state of the compressor 10 is transmitted to the control device 90. The operating state of the compressor 10 is the state of the compressor 10, whether it is running or stopped. 【0017】 The discharge port 10A of the compressor 10 is connected to one end of the heat exchanger 20 by piping. The heat exchanger 20 has a flow path through which a refrigerant flows, and performs heat exchange between the refrigerant flowing through the flow path and the air outside the flow path. The heat exchanger 20 corresponds to the "first heat exchanger" in this disclosure. 【0018】 The other end of the heat exchanger 20 is connected by piping to one end of the pressure reducing mechanism 30. The pressure reducing mechanism 30 reduces the pressure of the refrigerant, which is in a high-temperature, high-pressure gas-liquid mixture state, and changes it into a low-temperature, low-pressure gas-liquid mixture state. 【0019】 For example, the pressure reducing mechanism 30 is an electronically controlled expansion valve with an adjustable opening. Alternatively, the pressure reducing mechanism 30 may be a capillary tube or an orifice. The pressure reducing mechanism 30 includes a drive circuit and may be switched between open and closed according to the control of the control device 90. 【0020】 The other end of the pressure reducing mechanism 30 is connected by piping to one end of the heat exchanger 40. The heat exchanger 40 has a flow path through which the refrigerant flows, and is a heat exchanger that performs heat exchange between the refrigerant flowing through the flow path and the air outside the flow path. The other end of the heat exchanger 40 is connected to the suction port 10B of the compressor 10. The refrigerant flowing out from the other end of the heat exchanger 40 is drawn into the compressor 10 from the suction port 10B of the compressor 10. The heat exchanger 40 corresponds to the "second heat exchanger" in this disclosure. 【0021】 The shut-off valve 60 is located between the discharge port 10A of the compressor 10 and the heat exchanger 20. The shut-off valve 60 shuts off the refrigerant flowing between the discharge port 10A of the compressor 10 and the heat exchanger 20. The shut-off valve 60 includes a drive circuit and is switched between open and closed according to the control of the control device 90. The shut-off valve 60 corresponds to the “first valve” in this disclosure. 【0022】 The bypass piping 70 connects the discharge port 10A and the suction port 10B of the compressor 10. Specifically, one end 70A of the bypass piping 70 is connected between the discharge port 10A of the compressor 10 and the shut-off valve 60. More specifically, the other end 70B of the bypass piping 70 is connected between the suction port 10B of the compressor 10 and the heat exchanger 40. 【0023】 The control valve 80 is located on the bypass piping 70. The control valve 80 shuts off the refrigerant flowing through the bypass piping 70. The control valve 80 includes a drive circuit and is switched open and closed according to the control of the control device 90. The control valve 80 corresponds to the “second valve” in this disclosure. 【0024】 Temperature sensor 116 is located on the discharge side of the compressor 10. Temperature sensor 116 measures the refrigerant temperature on the discharge side of the compressor 10. Temperature sensor 118 is located on the outlet side of the heat exchanger 20. Temperature sensor 118 measures the refrigerant temperature on the outlet side of the heat exchanger 20. The measured values ​​from temperature sensors 116 and 118 are transmitted to the control device 90. Temperature sensors 116 and 118 are, for example, thermistors. Temperature sensors 116 and 118 correspond to the "first temperature sensor" and the "second temperature sensor" in this disclosure, respectively. 【0025】 Pressure sensor 112 is located on the discharge side of the compressor 10. Pressure sensor 112 measures the refrigerant pressure on the discharge side of the compressor 10. Pressure sensor 114 is located at the suction port 10B of the compressor 10. Pressure sensor 114 measures the refrigerant pressure on the suction side of the compressor 10. Pressure sensors 112 and 114 correspond to the "first pressure sensor" and "second pressure sensor" in this disclosure, respectively. 【0026】 The pressure sensor 115 is located on the outlet side of the heat exchanger 20. The pressure sensor 115 measures the refrigerant pressure on the outlet side of the heat exchanger 20. The measured values ​​from the pressure sensors 112, 114, and 115 are transmitted to the control device 90. 【0027】 The control device 90 controls the entire refrigeration cycle system 100 based on the measured values ​​from the temperature sensors 116 and 118 and the pressure sensors 112, 114, and 115, as well as programs stored in memory. The control performed by the control device 90 is not limited to software processing; some or all of it can be processed by dedicated hardware. For example, dedicated hardware may be electronic circuits. 【0028】 [Control device configuration] Figure 2 shows an example of the hardware configuration of the control device 90 in the refrigeration cycle device 100. As shown in Figure 2, the control device 90 includes a memory 92, a processor 94, and a communication interface 96, all connected to each other via a communication bus. 【0029】The communication interface 96 receives the measured values ​​from the temperature sensors 116, 118 and pressure sensors 112, 114, 115 of the refrigeration cycle device 100, as well as the operating status of the compressor 10. The communication interface 96 also transmits control signals for driving the shut-off valve 60, the control valve 80, and the pressure reducing mechanism 30. 【0030】 The memory 92 stores the measured values ​​of the temperature sensors 116, 118 and pressure sensors 112, 114, 115 of the refrigeration cycle unit 100, the operating status of the compressor 10, the operating system, and application programs. The memory 92 is composed of, for example, ROM (Read Only Memory), RAM (Random Access Memory), and flash memory. In addition to the memory 92, a large-capacity storage device such as an HDD (Hard Disk Drive) or SSD (Solid State Drive) may also be provided. 【0031】 The processor 94 controls each device of the refrigeration cycle device 100 based on data stored in memory 92 and data obtained from the communication interface 96. For example, the processor 94 is a processing unit such as a CPU (Central Processing Unit) and an MPU (Micro Processing Unit). 【0032】 [Functions of the control device] Figure 3 is a functional block diagram of the control device 90 in the refrigeration cycle device 100. As shown in Figure 3, the control device 90 comprises a state determination unit 164, a valve control unit 174, and a pressure reduction mechanism control unit 176. 【0033】The state determination unit 164 acquires the measured value from the pressure sensor 112 located on the discharge side of the compressor 10. The state determination unit 164 also acquires the measured value from the pressure sensor 114 located on the suction side of the compressor 10. The state determination unit 164 also acquires the measured value from the pressure sensor 115 located on the outlet side of the heat exchanger 20. The state determination unit 164 also acquires the measured value from the temperature sensor 116 located on the discharge side of the compressor 10. The state determination unit 164 also acquires the measured value from the temperature sensor 118 located on the outlet side of the heat exchanger 20. The state determination unit 164 also acquires the measured value from the timer 122 built into the control device 90. 【0034】 The state determination unit 164 determines the state of the refrigeration cycle device 100 based on the measured values ​​from the pressure sensors 112, 114, 115, the temperature sensors 116, 118, and the timer 122. Specifically, if a sufficient amount of time has elapsed since the compressor 10 started operation, the state determination unit 164 determines that the refrigeration cycle device 100 is in a steady state. On the other hand, if a sufficient amount of time has not elapsed since the compressor 10 started operation, the state determination unit 164 determines that the state of the refrigeration cycle device 100 is in a transient state. 【0035】 The valve control unit 174 controls the shut-off valve 60 of the refrigerant circuit 50 based on the operating state of the compressor 10. The valve control unit 174 also controls the control valve 80 on the bypass piping 70 based on the operating state of the compressor 10 and the state of the refrigeration cycle device 100 determined by the state determination unit 164. 【0036】 The pressure reduction mechanism control unit 176 controls the pressure reduction mechanism 30 based on the operating state of the compressor 10 and the state of the refrigeration cycle device 100 determined by the state determination unit 164. 【0037】 [Refrigerant Distribution] After sufficient time has passed since the compressor 10 stopped, the refrigerant in the piping from the compressor 10 to the heat exchanger 20 is cooled by the outside air and becomes liquid refrigerant. When the compressor 10 is restarted, high-temperature, high-pressure gaseous refrigerant is discharged from the discharge port 10A of the compressor 10. The liquid refrigerant in the piping from the compressor 10 to the heat exchanger 20 is gradually moved to the heat exchanger 20 by the gaseous refrigerant. 【0038】 Thus, for a period of time after the compressor 10 starts operation, the refrigerant in the piping from the compressor 10 to the heat exchanger 20 is in a gas-liquid mixture state of liquid and gas. In this specification, the state of the refrigeration cycle device 100 when the refrigerant in the piping from the compressor 10 to the heat exchanger 20 is in a gas-liquid mixture state of liquid and gas is referred to as a "transient state". 【0039】 After a certain period of time has elapsed since the compressor 10 started operating, all of the liquid refrigerant in the piping from the compressor 10 to the heat exchanger 20 moves to the heat exchanger 20. In other words, after a certain period of time has elapsed since the compressor 10 started operating, all of the refrigerant in the piping from the compressor 10 to the heat exchanger 20 becomes gaseous. 【0040】 In this specification, the state of the refrigeration cycle system 100 when the refrigerant in the piping from the compressor 10 to the heat exchanger 20 is entirely in a gaseous state is referred to as the "steady state." When the refrigeration cycle system 100 is in a steady state, a relatively large amount of liquid refrigerant in the refrigerant circuit 50 accumulates in the piping from the heat exchanger 20 to the pressure reducing mechanism 30. 【0041】 [Pressure Equalization] The compressor 10 draws in refrigerant from the inlet 10B, pressurizes it, and discharges it into the piping from the discharge port 10A. Therefore, during the operation of the compressor 10, a pressure difference occurs between the refrigerant pressure on the suction side of the compressor 10 and the refrigerant pressure on the discharge side of the compressor 10. 【0042】 When the compressor 10 is stopped, the refrigerant in the refrigerant circuit 50 moves to where the refrigerant with lower temperature and / or pressure is located. If the refrigeration cycle device 100 does not have a bypass pipe 70 and a control valve 80, when the compressor 10 is stopped, the refrigerant flows gradually through the refrigerant circuit 50 from the discharge side of the compressor 10 where the high-temperature, high-pressure refrigerant is located to the heat exchanger 20, the pressure reducing mechanism 30, and the heat exchanger 40 where the low-temperature, low-pressure refrigerant is located. In this way, the refrigerant pressure on the suction side of the compressor 10 and the refrigerant pressure on the discharge side of the compressor 10 are gradually equalized. 【0043】However, when the time from when the compressor 10 stops to when its operation restarts is short, the operation of the compressor 10 restarts before the refrigerant pressures on the suction side and the discharge side of the compressor 10 equalize. 【0044】 That is, the operation of the compressor 10 restarts in a state where the pressure difference between the refrigerant pressure on the suction side of the compressor 10 and the refrigerant pressure on the discharge side of the compressor 10 is relatively large. At this time, in order to discharge the refrigerant from the compressor 10, it is necessary to make the pressure of the refrigerant discharged from the compressor 10 higher than the high-pressure refrigerant in the discharge piping. 【0045】 Particularly immediately after the compressor 10 starts, since the compressor 10 starts from a low rotation speed, a larger driving torque is required to discharge refrigerant at a pressure higher than the refrigerant in the discharge piping. In order to achieve a large driving torque, an excessively large current needs to flow through the compressor 10. Such a high-load operation can cause capacity reduction and failures due to being a factor in the deterioration of the compressor 10. 【0046】 To prevent this, the refrigeration cycle device 100 of the present embodiment includes a bypass pipe 70 and an adjustment valve 80. When the compressor 10 stops, by opening the adjustment valve 80 by the control device 90, the refrigerant pressures on the suction side and the discharge side of the compressor 10 can be equalized in a short time. 【0047】 [Invasion prevention] Also, due to this equalization process, the refrigerant existing in the piping from the discharge port 10A of the compressor 10 to the heat exchanger 20 flows in the order of one end 70A of the bypass pipe 70 and the other end 70B of the bypass pipe 70, and flows toward the suction port 10B of the compressor 10. Then, when there is liquid refrigerant on the discharge side, the liquid refrigerant may invade from the suction port 10B of the compressor 10 into the inside of the compressor 10. 【0048】 Then, due to the invaded liquid refrigerant, the oil concentration and viscosity of the refrigeration machine oil inside the compressor 10 decrease, and capacity reduction of the compressor 10 may occur due to reasons such as seizure of the bearing due to insufficient lubrication or insufficient pressurization due to insufficient sealing. 【0049】 To prevent this, the refrigeration cycle device 100 of this disclosure is equipped with a shut-off valve 60 in the path from the compressor 10 to the heat exchanger 20. When the compressor 10 is stopped, the control device 90 closes the shut-off valve 60, preventing the liquid refrigerant present in the piping from the shut-off valve 60 to the heat exchanger 20 from moving to the suction side of the compressor 10 through the bypass piping 70, thereby preventing it from entering the inside of the compressor 10. 【0050】 As described above, when the operation of the compressor 10 is stopped, the refrigeration cycle device 100 can prevent liquid refrigerant from entering the compressor 10 while equalizing the refrigerant pressure on the suction side and the refrigerant pressure on the discharge side of the compressor 10 by closing the shut-off valve 60 and opening the control valve 80. Therefore, the refrigeration cycle device 100 can prevent a decrease in the capacity of the compressor 10. 【0051】 Furthermore, the liquid refrigerant in the piping from the shut-off valve 60 to the heat exchanger 20 flows toward the compressor 10 from the moment the control valve 80 is opened. Therefore, it is desirable to open the control valve 80 simultaneously with the closing of the shut-off valve 60, or after the closing of the shut-off valve 60. 【0052】 While closing the shut-off valve 60 can prevent liquid refrigerant from entering the compressor 10 through the piping from the shut-off valve 60 to the heat exchanger 20, it cannot prevent liquid refrigerant from entering the compressor 10 through the piping from the discharge port 10A of the compressor 10 to the shut-off valve 60. Therefore, it is preferable that the shut-off valve 60 be installed as close as possible to the discharge port 10A of the compressor 10. 【0053】 [Processing in Embodiment 1] Figure 4 is a flowchart showing the processing performed in the control device 90 of the refrigeration cycle device 100 according to Embodiment 1. The flowchart in Figure 4 is repeatedly executed during the operation of the compressor 10 whenever a predetermined condition is met, for example, at specific cycles. 【0054】First, the control device 90 determines whether or not the compressor 10 is stopped (step S1). If the compressor 10 is stopped (YES in step S1), the control device 90 closes the shut-off valve 60 and opens the control valve 80 (step S2). 【0055】 On the other hand, if the compressor 10 is restarted (NO in step S1), the control device 90 opens the shut-off valve 60 (step S3). This allows the circulation of refrigerant in the refrigerant circuit 50 to be restarted. Note that the control valve 80 is also used to adjust the cooling capacity of the refrigeration cycle device 100, so it may remain open even after the compressor 10 is restarted. 【0056】 By performing control according to the above process, when the operation of the compressor 10 is stopped, the refrigeration cycle device 100 can prevent liquid refrigerant from entering the compressor 10 while equalizing the refrigerant pressure on the suction side and the refrigerant pressure on the discharge side of the compressor 10 by closing the shut-off valve 60 and opening the adjustment valve 80. Therefore, the refrigeration cycle device 100 can prevent a decrease in the capacity of the compressor 10. 【0057】 Embodiment 2. In Embodiment 2, in addition to the processing in Embodiment 1, a configuration in which the pressure reduction mechanism 30 is controlled according to the state of the refrigeration cycle device 100 will be described. 【0058】 When the refrigeration cycle system 100 is in a transient state, the period since the start of operation of the compressor 10 is short. Therefore, generally, compared to when the refrigeration cycle system 100 is in a steady state, there is more liquid refrigerant in the piping from the compressor 10 to the heat exchanger 20 than in the piping from the heat exchanger 20 to the pressure reducing mechanism 30. 【0059】 Therefore, when the refrigeration cycle system 100 is in a transient state, the likelihood of refrigerant present in the piping from the compressor 10 to the heat exchanger 20 flowing into the compressor 10 through the pressure reduction mechanism 30 and the heat exchanger 40 is lower than when the refrigeration cycle system 100 is in a steady state. 【0060】On the other hand, when the refrigeration cycle system 100 is in a transient state, the liquid refrigerant in the piping from the compressor 10 to the heat exchanger 20 is more likely to flow through the bypass piping 70 into the suction port 10B of the compressor 10 compared to when the refrigeration cycle system 100 is in a steady state. 【0061】 Therefore, when the operation of the compressor 10 is stopped while the refrigeration cycle device 100 is in a transient state, the refrigeration cycle device 100 closes the shut-off valve 60 and opens the control valve 80, similar to the process in Embodiment 1, thereby preventing liquid refrigerant from entering the compressor 10 while equalizing the refrigerant pressure on the suction side and the refrigerant pressure on the discharge side of the compressor 10. Thus, the refrigeration cycle device 100 can prevent a decrease in the capacity of the compressor 10. 【0062】 On the other hand, when the refrigeration cycle system 100 is in a steady state, the refrigerant in the piping from the discharge side of the compressor 10 to the heat exchanger 20 becomes high temperature and high pressure due to the compressor 10 and turns into a gaseous state. Therefore, liquid refrigerant is present in relatively large quantities in the piping from the heat exchanger 20 to the pressure reduction mechanism 30. 【0063】 In this state, when the compressor 10 is stopped and the control valve 80 is opened, the liquid refrigerant present in the piping from the heat exchanger 20 to the pressure reducing mechanism 30 flows through the heat exchanger 20 to the discharge side of the compressor 10, and also flows towards the heat exchanger 40, which is low temperature and low pressure. 【0064】 Therefore, even when the refrigeration cycle device 100 is in a steady state, the liquid refrigerant flowing to the discharge side of the compressor 10 is blocked by closing the shut-off valve 60, similar to the process in Embodiment 1. Furthermore, the liquid refrigerant flowing toward the heat exchanger 40 is blocked by closing the pressure reduction mechanism 30. As a result, in Embodiment 2, liquid refrigerant flowing into the suction side of the compressor 10 via the heat exchanger 40 can be further prevented, thus preventing liquid refrigerant from entering the compressor 10 while equalizing the refrigerant pressure on the suction side and the refrigerant pressure on the discharge side of the compressor 10. Consequently, the refrigeration cycle device 100 can prevent a decrease in the capacity of the compressor 10. 【0065】Furthermore, if the control device 90 opens the regulating valve 80, the liquid refrigerant in the piping from the heat exchanger 20 to the pressure reducing mechanism 30 will quickly flow towards the discharge side of the compressor 10 or the heat exchanger 40. Therefore, the shut-off valve 60 is closed first, and then the pressure reducing mechanism 30 is closed to confine the refrigerant in the piping from the shut-off valve 60 to the pressure reducing mechanism 30, after which the regulating valve 80 is opened. Alternatively, the control device 90 simultaneously closes the shut-off valve 60, closes the pressure reducing mechanism 30, and opens the regulating valve 80. 【0066】 [State of Refrigeration Cycle Device] Next, a method for determining whether the refrigeration cycle device 100 is in a steady state or a transient state will be described using Figure 5. Figure 5 is a table showing a method for identifying the state of the refrigeration cycle device 100 according to Embodiment 2. As shown in Figure 5, mainly the first to fourth examples can be used as methods for determining the state of the refrigeration cycle device 100 in Embodiment 2. 【0067】 As explained in Figure 1, when sufficient time has elapsed since the start of operation of the compressor 10, the control device 90 determines that the state of the refrigeration cycle device 100 is in a steady state. The control device 90 determines that sufficient time has elapsed since the start of operation of the compressor 10 by the fact that the target parameter is greater than a threshold value. The control device 90 calculates the parameter based on the measured values ​​of each sensor or timer. 【0068】 In the first example, the control device 90 determines the state of the refrigeration cycle device 100 using pressure sensors 112 and 114. The control device 90 obtains the refrigerant pressure on the discharge side of the compressor 10 from pressure sensor 112. The control device 90 also obtains the refrigerant pressure on the suction side of the compressor 10 from pressure sensor 114. 【0069】 The control device 90 calculates the difference between the refrigerant pressure on the discharge side of the compressor 10 and the refrigerant pressure on the suction side of the compressor 10. The control device 90 may, for example, calculate the absolute difference between the refrigerant pressure on the discharge side of the compressor 10 and the refrigerant pressure on the suction side of the compressor 10 as the difference value. 【0070】The control device 90 compares a parameter called a difference value with a threshold value corresponding to that difference value. The threshold value is, for example, the difference between the refrigerant pressure on the discharge side of the compressor 10 and the refrigerant pressure on the suction side of the compressor 10 after a certain amount of time has elapsed since the compressor 10 was started. 【0071】 As described above regarding pressure equalization, when the compressor 10 is stopped, the refrigerant pressure on the suction side of the compressor 10 and the refrigerant pressure on the discharge side of the compressor 10 become equalized. In other words, when the compressor 10 is stopped, the difference between the refrigerant pressure on the suction side of the compressor 10 and the refrigerant pressure on the discharge side of the compressor 10 approaches zero. 【0072】 When the compressor 10 restarts operation, it draws in refrigerant from the suction port 10B, compresses the refrigerant, and discharges it into the piping from the discharge port 10A. Therefore, while the compressor 10 is operating, the difference between the refrigerant pressure on the suction side of the compressor 10 and the refrigerant pressure on the discharge side of the compressor 10 increases until the refrigeration cycle device 100 reaches a steady state. 【0073】 Therefore, if the compressor 10 is operating and the difference between the refrigerant pressure on the suction side of the compressor 10 and the refrigerant pressure on the discharge side of the compressor 10 is less than a threshold, it can be determined that the compressor 10 has just started operating. Thus, the control device 90 determines that the state of the refrigeration cycle device 100 is a transient state. 【0074】 On the other hand, if the difference between the refrigerant pressure on the suction side of the compressor 10 and the refrigerant pressure on the discharge side of the compressor 10 is greater than or equal to a threshold, it can be seen that the compressor 10 has been operating for a certain period of time. Therefore, the control device 90 determines that the state of the refrigeration cycle device 100 is a steady state. 【0075】 In the second example, the control device 90 uses the timer 122 to determine the state of the refrigeration cycle device 100. The control device 90 obtains the operating time of the compressor 10 from the timer 122. The operating time of the compressor 10 is, for example, the time from when the operation of the compressor 10 starts until when the operation of the compressor 10 ends. 【0076】The control device 90 compares the operating time of the compressor 10, which is a parameter, with a threshold value corresponding to that operating time. If the operating time of the compressor 10 is less than the threshold value, the control device 90 determines that the state of the refrigeration cycle system 100 is a transient state. On the other hand, if the operating time of the compressor 10 is equal to or greater than the threshold value, the control device 90 determines that the state of the refrigeration cycle system 100 is a steady state. 【0077】 In the third example, the control device 90 determines the state of the refrigeration cycle device 100 using the temperature sensor 116. The control device 90 obtains the refrigerant temperature on the discharge side of the compressor 10 from the temperature sensor 116. The control device 90 also obtains the refrigerant pressure on the discharge side of the compressor 10 from the pressure sensor 112. The control device 90 calculates the degree of superheating of the refrigerant, which is the difference between the refrigerant temperature on the discharge side of the compressor 10 and the saturation temperature at the refrigerant pressure on the discharge side of the compressor 10. 【0078】 The control device 90 compares the superheating degree of the refrigerant, which is a parameter, with a threshold value corresponding to that superheating degree. The control device 90 determines that the state of the refrigeration cycle system 100 is a transient state if the superheating degree of the refrigerant on the discharge side of the compressor 10 is less than the threshold value. On the other hand, the control device 90 determines that the state of the refrigeration cycle system 100 is a steady state if the superheating degree of the refrigerant on the discharge side of the compressor 10 is equal to or greater than the threshold value. 【0079】 In the fourth example, the control device 90 uses the temperature sensor 118 to determine the state of the refrigeration cycle device 100. The control device 90 obtains the refrigerant temperature at the outlet side of the heat exchanger 20 from the temperature sensor 118. The control device 90 also obtains the refrigerant pressure at the outlet side of the heat exchanger 20 from the pressure sensor 115. The control device 90 calculates the degree of subcooling of the refrigerant, which is the difference between the refrigerant temperature at the outlet side of the heat exchanger 20 and the saturation temperature at the refrigerant pressure at the outlet side of the heat exchanger 20. 【0080】The control device 90 compares the parameter, the degree of subcooling of the refrigerant, with a threshold value corresponding to that degree of subcooling. The control device 90 determines that the state of the refrigeration cycle system 100 is a transient state if the degree of subcooling of the refrigerant on the outlet side of the heat exchanger 20 is less than the threshold value. On the other hand, the control device 90 determines that the state of the refrigeration cycle system 100 is a steady state if the degree of subcooling of the refrigerant on the outlet side of the heat exchanger 20 is equal to or greater than the threshold value. 【0081】 [Processing in Embodiment 2] Figure 6 is a flowchart showing the processing performed in the control device 90 of the refrigeration cycle device 100 according to Embodiment 2. The flowchart in Figure 6 is repeatedly executed during the operation of the compressor 10 whenever a predetermined condition is met, for example, at specific cycles. 【0082】 As explained with reference to Figure 5, the control device 90 determines the state of the refrigeration cycle device 100 based on the detection results from each sensor or timer 122 (step S11). Next, the control device 90 determines whether or not the compressor 10 is stopped, similar to the process in Embodiment 1 (step S12). 【0083】 If the compressor 10 is operating (NO in step S12), the control device 90 opens the shut-off valve 60 and the pressure reducing mechanism 30 (step S16). The control valve 80 may be closed or left open, as it may also be used to adjust the cooling capacity of the refrigeration cycle device 100. 【0084】 On the other hand, if the compressor 10 is stopped (YES in step S12), the control device 90 determines whether the state of the refrigeration cycle device 100 determined in step S1 is in a steady state or not (step S13). 【0085】 If the refrigeration cycle device 100 is in a transient state (NO in step S13), the control device 90 closes the shut-off valve 60 and opens the control valve 80 (step S15). When the refrigeration cycle device 100 is in a transient state, the refrigerant in the piping from the compressor 10 to the heat exchanger 20 is not in a gaseous state as it is when the refrigeration cycle device 100 is in a steady state, but is a two-phase mixture. 【0086】 On the other hand, if the refrigeration cycle device 100 is in a steady state (YES in step S13), the control device 90 closes the shut-off valve 60 and the pressure reducing mechanism 30, and opens the control valve 80 (step S14). 【0087】 Similar to the process in Embodiment 1, the control device 90 can equalize the refrigerant pressure on the suction side of the compressor 10 and the refrigerant pressure on the discharge side of the compressor 10 by opening the adjustment valve 80 prior to the ingress prevention process. 【0088】 In this way, the refrigeration cycle device 100 can prevent liquid refrigerant from entering the compressor 10 while equalizing the refrigerant pressure on the suction side and the refrigerant pressure on the discharge side of the compressor 10. Therefore, the refrigeration cycle device 100 can prevent a decrease in the performance of the compressor 10. 【0089】 The embodiments disclosed herein should be considered in all respects to be illustrative and not restrictive. The scope of this disclosure is indicated by the claims and not by the foregoing description, and all modifications within the meaning and scope of the claims are intended to be included. 【0090】 10 Compressor, 10A Discharge port, 10B Inlet port, 20 Heat exchanger, 30 Pressure reducing mechanism, 40 Heat exchanger, 50 Refrigerant circuit, 60 Shut-off valve, 70 Bypass piping, 70A one end, 70B the other end, 80 Control valve, 90 Control device, 92 Memory, 94 Processor, 96 Communication interface, 100 Refrigeration cycle device, 112, 114, 115 Pressure sensors, 116, 118 Temperature sensors, 122 Timer, 164 State determination unit, 174 Valve control unit, 176 Pressure reducing mechanism control unit.

Claims

1. A refrigeration cycle device comprising: a refrigerant circuit configured to circulate a refrigerant in the order of a compressor, a first heat exchanger, a pressure reducing mechanism, and a second heat exchanger; a bypass pipe connecting the inlet and outlet of the compressor; a first valve provided between the outlet and the first heat exchanger; a second valve provided in the bypass pipe; and a control device for controlling the first valve and the second valve, wherein the control device closes the first valve and opens the second valve when the operation of the compressor stops.

2. The refrigeration cycle apparatus according to claim 1, wherein the control device closes the first valve and the pressure reducing mechanism and opens the second valve when the operation of the compressor is stopped and the state of the refrigeration cycle apparatus is in a steady state, and the steady state is a state in which the refrigerant in the refrigerant circuit from the compressor to the first heat exchanger is in a gaseous state.

3. The refrigeration cycle apparatus according to claim 1, wherein the control device closes the first valve and then opens the second valve when the operation of the compressor stops.

4. The refrigeration cycle apparatus according to claim 3, wherein, when the operation of the compressor is stopped and the state of the refrigeration cycle apparatus is in a steady state, the control device closes the first valve and the pressure reducing mechanism, and then opens the second valve, the steady state being a state in which the refrigerant in the refrigerant circuit from the compressor to the first heat exchanger is in a gaseous state.

5. The refrigeration cycle apparatus according to claim 2 or 4, wherein the control device determines that the state of the refrigeration cycle apparatus is the steady state when a parameter indicating the state of the refrigeration cycle apparatus is greater than a threshold corresponding to the parameter.

6. The refrigeration cycle apparatus according to claim 5, further comprising a first pressure sensor for measuring a first pressure value of the refrigerant on the discharge side of the compressor, and a second pressure sensor for measuring a second pressure value of the refrigerant on the suction side of the compressor, wherein the parameter includes the difference between the first pressure value and the second pressure value.

7. The refrigeration cycle apparatus according to claim 5 or 6, wherein the parameters include the operating time of the compressor.

8. The refrigeration cycle apparatus according to any one of claims 5 to 7, further comprising a first temperature sensor for measuring the temperature of the refrigerant on the discharge side of the compressor, wherein the parameter includes a degree of superheating calculated based on the measurement value of the first temperature sensor.

9. The refrigeration cycle apparatus according to any one of claims 5 to 8, further comprising a second temperature sensor for measuring the temperature of the refrigerant on the outlet side of the first heat exchanger, wherein the parameter includes a degree of subcooling calculated based on the measurement value of the second temperature sensor.

10. A method for controlling a refrigeration cycle device, wherein the refrigeration cycle device includes a refrigerant circuit configured to circulate a refrigerant in the order of a compressor, a first heat exchanger, a pressure reducing mechanism, and a second heat exchanger; a bypass pipe connecting the inlet and outlet of the compressor in the refrigerant circuit; a first valve provided between the outlet and the first heat exchanger; and a second valve provided in the bypass pipe, the control method comprising the steps of determining that the operation of the compressor has stopped, and, when the operation of the compressor has stopped, closing the first valve and opening the second valve.

Images