JP2018044725A - Refrigerant circuit device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a refrigerant circuit device enabling stable control of a water level of a gas liquid separator used for the refrigerant circuit device including a two-stage compression two-stage expansion cycle by using a simple configuration.SOLUTION: A refrigerant circuit device includes: an evaporator 12 for evaporating a low-pressure refrigerant; a low-stage compressor 1 for compressing the low-pressure refrigerant to intermediate pressure; a high-stage compressor 2 for compressing an intermediate-pressure refrigerant to high pressure; a condenser 3 for condensing a high-pressure refrigerant; a high-stage expansion valve 5 for decompressing and expanding the high-pressure refrigerant condensed by the condenser 3 to an intermediate pressure; a gas liquid separator 7 for performing gas-liquid separation of the intermediate-pressure refrigerant introduced from the high-stage expansion valve 5; intermediate piping 9 for introducing the intermediate-pressure refrigerant introduced from a gas phase side outlet of the gas liquid separator 7 to between a discharge port of the low-stage compressor 1 and a suction port of the high-stage compressor 2; and a low-stage side expansion valve 10 for decompressing and expanding the intermediate-pressure refrigerant introduced from a liquid phase side outlet of the gas liquid separator 7 to low-pressure and leading out the low-pressure refrigerant to the evaporator 12. The refrigerant circuit device further includes a control section C for controlling rotational frequency of the low-stage compressor 1 in accordance with dryness of the refrigerant introduce to the gas liquid separator 7.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a refrigerant circuit device capable of stably controlling the water level of a gas-liquid separator used in a refrigerant circuit device having a two-stage compression / two-stage expansion cycle with a simple configuration.

  In the two-stage compression and two-stage expansion cycle, the compression ratio per single stage of the compressor can be reduced by using two stages of compression, and when operating as a heat pump, the refrigerant flow on the low stage side is minimized. As a result, the compression power on the lower stage side can be minimized, so that the efficiency can be increased as compared with the single stage cycle.

  Patent Document 1 describes a two-stage compression heat pump type heating apparatus provided with two compressors, a low-stage compressor and a high-stage compressor. This heat pump type heating device is provided with a first pressure reducing device, a second pressure reducing device, a gas-liquid separator, and an injection pipe, thereby improving the heating capacity with a simple configuration.

JP 2014-119157 A

  By the way, in a two-stage compression two-stage expansion cycle, generally, a gas-liquid separator is used to separate an intermediate-pressure refrigerant gas-phase refrigerant, and the separated intermediate-pressure refrigerant and the refrigerant discharged from the low-stage compressor are combined. It is installed on the inlet side of the high stage compressor. The gas-liquid separator controls the water level and separates the gas-phase refrigerant and the liquid-phase refrigerant with high efficiency. However, if the water level changes greatly, the gas-liquid separator greatly affects the two-stage compression / two-stage expansion cycle. Conventionally, a water level meter that actually measures the water level in the gas-liquid separator has been provided. However, if the water level meter is provided, the configuration of the gas-liquid separator that requires pressure resistance becomes complicated and expensive.

  The present invention has been made in view of the above, and a refrigerant circuit capable of stably controlling the water level of a gas-liquid separator used in a refrigerant circuit device having a two-stage compression / two-stage expansion cycle with a simple configuration. An object is to provide an apparatus.

  In order to solve the above-described problems and achieve the object, a refrigerant circuit device according to the present invention includes an evaporator that evaporates low-pressure refrigerant and low-stage compression that compresses low-pressure refrigerant introduced from the evaporator to an intermediate pressure. A high-pressure compressor that compresses the intermediate-pressure refrigerant compressed by the low-stage compressor to a high pressure, a condenser that condenses the high-pressure refrigerant compressed by the high-stage compressor, and a condenser that is condensed by the condenser A high-stage expansion valve that decompresses and expands the high-pressure refrigerant to the intermediate pressure, a gas-liquid separator that gas-liquid separates the intermediate-pressure refrigerant introduced from the high-stage expansion valve, and a gas phase of the gas-liquid separator An intermediate pipe for introducing intermediate pressure refrigerant introduced from the side outlet between the discharge port of the low stage compressor and the suction port of the high stage compressor, and introduced from the liquid phase side outlet of the gas-liquid separator. A low-stage expansion valve that expands the intermediate pressure refrigerant under reduced pressure to reduce the pressure to the evaporator. And a refrigerant circuit device, characterized by comprising a control unit for controlling the rotational speed of the low-stage compressor in accordance with the dryness of the refrigerant introduced into the gas-liquid separator.

  In the refrigerant circuit device according to the present invention, in the above invention, the control unit decreases the rotational speed of the low-stage compressor when the dryness of the refrigerant is equal to or higher than a target value, and the dryness of the refrigerant. When the value is less than the target value, the rotational speed of the low-stage compressor is increased.

  Further, the refrigerant circuit device according to the present invention is the above-described invention, wherein the temperature detector that detects the temperature of the high-pressure refrigerant between the condenser and the high stage expansion valve, the condenser, and the high stage expansion valve. A high-pressure detector that detects the pressure of the high-pressure refrigerant, and the pressure or temperature of the intermediate-pressure refrigerant between the high-stage expansion valve and the gas-liquid separator or the intermediate-pressure refrigerant in the intermediate pipe An intermediate-pressure refrigerant state detecting unit, and the control unit is configured to control the refrigerant introduced into the gas-liquid separator based on the temperature and pressure of the high-pressure refrigerant and the pressure or temperature of the intermediate-pressure refrigerant. The dryness is calculated.

  In the refrigerant circuit device according to the present invention as set forth in the invention described above, the control unit includes a high-stage refrigerant circulation amount sucked into the high-stage compressor and a low-stage refrigerant circulation sucked into the low-stage compressor. The dryness is obtained from the amount.

  In the refrigerant circuit device according to the present invention, in the above invention, a high-stage intake temperature detection unit that detects a refrigerant temperature on the intake side of the high-stage compressor, and a refrigerant on the intake side of the high-stage compressor. A high-stage suction pressure detection unit that detects pressure, and the control unit detects a temperature detected by the high-stage suction temperature detection unit, a pressure detected by the high-stage suction pressure detection unit, and the high-stage compressor The high-stage refrigerant circulation amount is calculated from the number of rotations.

  In the refrigerant circuit device according to the present invention, in the above invention, a high-stage flow rate detection unit is provided between the high-stage compressor and the gas-liquid separator, and the high-stage refrigerant circulation amount is detected. It is characterized by.

  In the refrigerant circuit device according to the present invention, in the above invention, a low-stage intake temperature detection unit that detects a refrigerant temperature on the intake side of the low-stage compressor, and a refrigerant on the intake side of the low-stage compressor. A low-stage intake pressure detection unit that detects pressure, and the control unit detects the temperature detected by the low-stage intake temperature detection unit, the pressure detected by the low-stage intake pressure detection unit, and the low-stage compressor The low-stage refrigerant circulation amount is calculated from the number of rotations of the engine.

  In the refrigerant circuit device according to the present invention, in the above invention, a low-stage flow rate detection unit is provided between the liquid-phase outlet of the gas-liquid separator and the low-stage compressor, and the low-stage refrigerant circulation is provided. It is characterized by detecting the quantity.

  Further, in the refrigerant circuit device according to the present invention, in the above invention, the control unit has a startup liquid level control mode and a normal liquid level control mode. When the refrigerant dryness is equal to or higher than the first target value, the rotational speed of the low-stage compressor is decreased, and when the refrigerant dryness is lower than the first target value, the rotational speed of the low-stage compressor is decreased. In the normal liquid level control mode, the control unit decreases the rotational speed of the low-stage compressor when the dryness of the refrigerant is equal to or higher than a second target value, and the dryness of the refrigerant is increased. The number of revolutions of the low-stage compressor is increased when the value is less than the second target value, and the first target value is set to be smaller than the second target value.

  In the refrigerant circuit device according to the present invention, in the above invention, the control unit is in the startup liquid level control mode when the refrigerant circuit device is activated, and a predetermined time has elapsed after the refrigerant circuit device is activated. And shifting to the normal liquid level control mode.

  In the refrigerant circuit device according to the present invention, in the above invention, the target value is an amount of refrigerant flowing out from a liquid-phase side outlet of the gas-liquid separator rather than an amount of liquid-phase refrigerant flowing into the gas-liquid separator. The intermediate pipe has a heating means for heating the intermediate pressure refrigerant introduced from the gas phase outlet of the gas-liquid separator.

  According to the present invention, the water level can be stably controlled without providing a water level gauge in the gas-liquid separator used in the refrigerant circuit device having the two-stage compression / two-stage expansion cycle.

FIG. 1 is a circuit diagram showing a configuration of a refrigerant circuit device according to Embodiment 1 of the present invention. FIG. 2 is a ph diagram of the refrigerant circuit device shown in FIG. FIG. 3 is a flowchart illustrating a water level control processing procedure by the control unit according to the first embodiment of the present invention. FIG. 4 is a flowchart showing a water level control processing procedure by the control unit according to the second embodiment of the present invention. FIG. 5 is a circuit diagram showing a configuration of a refrigerant circuit device according to Embodiment 3 of the present invention. FIG. 6 is a flowchart showing a water level control processing procedure by the control unit according to the third embodiment of the present invention. FIG. 7 is a circuit diagram showing a configuration of a refrigerant circuit device according to Embodiment 5 of the present invention. FIG. 8 is a circuit diagram showing a configuration of a refrigerant circuit device according to Embodiment 6 of the present invention. FIG. 9 is a flowchart showing a water level control processing procedure by the control unit according to the sixth embodiment of the present invention.

  DESCRIPTION OF EMBODIMENTS Hereinafter, embodiments for carrying out the present invention will be described with reference to the accompanying drawings.

(Embodiment 1)
FIG. 1 is a circuit diagram showing a configuration of a refrigerant circuit device according to Embodiment 1 of the present invention. FIG. 2 is a ph diagram of the refrigerant circuit device shown in FIG. This refrigerant circuit device is a two-stage compression two-stage expansion cycle.

  As shown in FIG. 1, the compressor is a two-stage compressor having a low-stage compressor 1 and a high-stage compressor 2. As shown in FIGS. 1 and 2, the high-stage compressor 2 generates a high-pressure refrigerant RH having a high-stage refrigerant circulation amount GH and introduces it into the condenser 3 (from the point P2 to the point P3 in FIG. 2). The high-pressure refrigerant RH is radiated and condensed by the condenser 3 and cooled (from point P3 to point P4 in FIG. 2). The condenser 3 heats water to be heated for generating steam, for example. Thereafter, the high-pressure refrigerant RH is decompressed and expanded by the high-stage expansion valve 5 (from the point P4 to the point P5 in FIG. 2), becomes an intermediate-pressure refrigerant RM, and is introduced into the gas-liquid separator 7. Among the intermediate pressure refrigerant RM, the intermediate pressure refrigerant RM1 having a refrigerant circulation amount GM in a gas state is interposed between the discharge port of the low stage compressor 1 and the suction port of the high stage compressor 2 via the intermediate pipe 9. It is introduced (point P2 in FIG. 2).

  On the other hand, the intermediate-pressure refrigerant RM2 in the low-stage refrigerant circulation amount GL in the liquid state in the intermediate-pressure refrigerant RM is decompressed and expanded by the low-stage expansion valve 10 (from point P6 to point P7 in FIG. 2), and the low-pressure refrigerant RL And introduced into the evaporator 12. The evaporator 4 heats and evaporates the low-pressure refrigerant RL (from the point P7 to the point P1 in FIG. 2) and introduces it into the low-stage compressor 1 (the point P1 in FIG. 2). The low-stage compressor 1 compresses the introduced low-pressure refrigerant RL to an intermediate-pressure refrigerant. The high stage compressor 2 compresses the intermediate pressure refrigerant of the low stage refrigerant circulation amount GL compressed by the low stage compressor 1 and the intermediate pressure refrigerant RM1 of the refrigerant circulation amount GM introduced via the intermediate pipe 9. Then, the high-pressure refrigerant RH having the high-stage refrigerant circulation amount GH is derived.

  In the first embodiment, the temperature detector T11 that detects the temperature of the high-pressure refrigerant RH between the condenser 3 and the high stage expansion valve 5 and the high pressure between the condenser 3 and the high stage expansion valve 5 are used. A high pressure detection unit P11 that detects the pressure of the refrigerant RH and an intermediate pressure refrigerant state detection unit P12 that detects the pressure of the intermediate pressure refrigerant RM between the high stage expansion valve 5 and the gas-liquid separator 7 are provided.

  The control unit C receives detection results from the temperature detection unit T11, the high pressure detection unit P11, and the intermediate pressure refrigerant state detection unit P12, and based on the detection results, the refrigerant introduced into the gas-liquid separator 7 is detected. Calculate dryness x. Then, when the dryness x is equal to or higher than the target value xt, the control unit C decreases the rotational speed of the low-stage compressor 1 via the inverter 21. When the dryness x is lower than the target value xt, Control is performed to increase the rotational speed of the low-stage compressor 1 via the inverter 21. This control is performed by, for example, PID control.

  The target value xt is the degree of dryness when the gas-phase separator outlet of the gas-liquid separator 7 is above the water level LV and only the intermediate pressure refrigerant RM1 in the gaseous state reaches the water level LV led to the intermediate pipe 9. Corresponding and predetermined.

  As shown in FIG. 2, the dryness x represents a specific enthalpy difference between the intersection PP1 between the intermediate pressure PM and the saturated liquid line PW and the intersection PP2 between the intermediate pressure PM and the dry saturated airline PD “1”. Is a value corresponding to the specific enthalpy difference between the point P5 and the intersection PP1, and indicates the mass ratio of the gas-phase refrigerant contained in the gas-liquid two-phase intermediate pressure refrigerant.

  The control unit C calculates the point P4 based on the temperature of the high-pressure refrigerant RH detected by the temperature detection unit T11 and the pressure of the high-pressure refrigerant RH detected by the high-pressure detection unit P11, and the intermediate-pressure refrigerant state detection unit P12 detects The dryness x is calculated by obtaining a point P5 having the same specific enthalpy as the point P4 with the pressure PM of the intermediate pressure refrigerant RM.

  Here, with reference to the flowchart shown in FIG. 3, the water level control process procedure by the control part C of Embodiment 1 is demonstrated. First, as described above, the control unit C calculates the current dryness x using the temperature and pressure of the high-pressure refrigerant RH and the pressure PM of the intermediate-pressure refrigerant RM (Step S101).

  Thereafter, the controller C determines whether or not the dryness x is equal to or greater than the target value xt (step S102). When the dryness x is equal to or greater than the target value xt (step S102, Yes), the rotational speed of the low-stage compressor 1 is decreased via the inverter 21 (step S103), and this process is terminated. On the other hand, when the dryness x is not equal to or greater than the target value xt (No at Step S102), the rotational speed of the low-stage compressor 1 is increased via the inverter 21 (Step S104), and this process is terminated. And the process mentioned above is repeated for every predetermined control time.

  In the first embodiment, the water level LV of the gas-liquid separator 7 can be controlled based on the calculated dryness x of the gas-liquid separator 7 without providing a water level meter in the gas-liquid separator 7. The water level of the liquid separator 7 can be stably controlled with a simple configuration.

  The intermediate pressure refrigerant state detection unit P12 described above may detect the pressure of the intermediate pressure refrigerant RM1 in the intermediate pipe 9. Further, the intermediate pressure refrigerant state detection unit P12 may detect the temperature of the intermediate pressure refrigerant RM. In this case, the control unit C obtains the point P5 using the isotherm LT instead of the intermediate pressure PM shown in FIG. 2, and calculates the current dryness x.

(Embodiment 2)
In the first embodiment described above, the control unit C performs the water level control process in the normal state (steady state) after startup. However, in the second embodiment, the liquid phase is contained in the gas-liquid separator 7. In the start-up from the state where no refrigerant exists, different water level control processes are performed in the normal state after the start-up and after the start-up. The controller C enters the startup liquid level control mode at the time of startup, and enters the normal liquid level control mode when a predetermined time has elapsed after startup.

  Here, with reference to the flowchart shown in FIG. 4, the water level control process procedure by the control part C of Embodiment 2 is demonstrated. First, as described above, the control unit C calculates the current dryness x using the temperature and pressure of the high-pressure refrigerant RH and the pressure PM of the intermediate-pressure refrigerant RM (Step S201).

  Thereafter, the control unit C determines whether the current mode is the startup liquid level control mode or the normal liquid level control mode (step S202). When the current mode is the startup liquid level control mode (step S202, startup liquid level control mode), it is determined whether or not the dryness x is equal to or higher than the first target value xt1 (step S203). Here, the first target value xt1 is set so that the amount of liquid-phase refrigerant flowing into the gas-liquid separator 7 is larger than the amount of refrigerant flowing out from the liquid-phase outlet of the gas-liquid separator 7, and unit time The water level rising speed in the gas-liquid separator 7 is controlled to be constant. When the dryness x is equal to or greater than the first target value xt1 (step S203, Yes), the rotational speed of the low-stage compressor 1 is decreased via the inverter 21 (step S204), and the process proceeds to step S206. To do. On the other hand, when the dryness x is not equal to or greater than the first target value xt1 (No at Step S203), the rotational speed of the low-stage compressor 1 is increased via the inverter 21 (Step S205), and the process goes to Step S206. Transition.

  In step S206, it is determined whether or not a predetermined time has elapsed after activation. If a predetermined time has elapsed after the start (step S206, Yes), the process proceeds to the normal liquid level control mode (step S207), and this process ends. On the other hand, if the predetermined time has not passed since the start (step S206, No), this processing is ended as it is.

  On the other hand, when the current mode is the normal liquid level control mode (step S202, normal liquid level control mode), it is determined whether or not the dryness x is equal to or greater than the second target value xt2 (step S208). The second target value xt2 is larger than the first target value xt1, and the amount of liquid-phase refrigerant flowing into the gas-liquid separator 7 and the amount of refrigerant flowing out from the liquid-phase outlet of the gas-liquid separator 7 Is preferably set so that they are substantially the same. When the dryness x is equal to or greater than the second target value xt2 (step S208, Yes), the rotational speed of the low-stage compressor 1 is decreased via the inverter 21 (step S209), and this process is terminated. To do. On the other hand, when the dryness x is not equal to or greater than the second target value xt2 (No at Step S208), the rotational speed of the low-stage compressor 1 is increased via the inverter 21 (Step S210), and this process is performed. finish. And the process mentioned above is repeated for every predetermined control time.

  In the second embodiment, even when the water level in the gas-liquid separator 7 is started from zero at the time of startup, the water level is raised to the target level by the startup liquid level control mode, and then the normal liquid level control mode is shifted to. be able to.

(Embodiment 3)
In the first and second embodiments described above, the dryness x is calculated using the ph diagram of the two-stage compression / two-stage expansion cycle shown in FIG. 2, but in the third embodiment, the dryness is calculated. x is calculated using the high-stage refrigerant circulation amount GH and the low-stage refrigerant circulation amount GL.

Here, the relationship between the dryness x, the high-stage refrigerant circulation amount GH, and the low-stage refrigerant circulation amount GL is expressed by the following equation (1).
1-x = GL / GH (1)
Therefore, the dryness x is expressed by the following equation (2).
x = 1- (GL / GH) (2)
As a result, the dryness x can be calculated using the high-stage refrigerant circulation amount GH and the low-stage refrigerant circulation amount GL.

  FIG. 5 is a circuit diagram showing a configuration of a refrigerant circuit device according to Embodiment 3 of the present invention. As shown in FIG. 5, in the third embodiment, the high-stage suction temperature detection unit T <b> 21 that detects the temperature of the refrigerant on the suction side of the high-stage compressor 2, and the pressure of the refrigerant on the suction side of the high-stage compressor 2. A high-stage suction pressure detection unit P21 that detects the refrigerant, a low-stage suction temperature detection unit T22 that detects the temperature of the refrigerant on the suction side of the low-stage compressor 1, and a pressure of the refrigerant on the suction side of the low-stage compressor 1 And a low stage suction pressure detection unit P22.

  The control unit C is discharged from the discharge port of the high stage compressor 2 based on the temperature detected by the high stage suction temperature detection unit T21, the pressure detected by the high stage suction pressure detection unit P21, and the rotation speed of the high stage compressor 2. The low-stage compressor 1 is calculated from the temperature detected by the low-stage intake temperature detection unit T22, the pressure detected by the low-stage intake pressure detection unit P22, and the rotation speed of the low-stage compressor 1. The low-stage refrigerant circulation amount GL sucked into the suction port is calculated. And the control part C calculates dryness x based on the high stage refrigerant | coolant circulation amount GH and the low stage refrigerant | coolant circulation amount GL using Formula (2).

  Here, with reference to the flowchart shown in FIG. 6, the water level control process procedure by the control part C of Embodiment 3 is demonstrated. First, as described above, the control unit C determines the high stage compressor from the temperature detected by the high stage suction temperature detection unit T21, the pressure detected by the high stage suction pressure detection unit P21, and the rotation speed of the high stage compressor 2. The high-stage refrigerant circulation amount GH discharged from the second discharge port is calculated (step S301). Further, the control unit C supplies the suction port of the low stage compressor 1 from the temperature detected by the low stage suction temperature detection unit T22, the pressure detected by the low stage suction pressure detection unit P22, and the rotation speed of the low stage compressor 1. The low-stage refrigerant circulation amount GL to be sucked is calculated (step S302). And the control part C calculates dryness x using Formula (2) (step S303).

  Thereafter, the control unit C determines whether or not the dryness x is equal to or greater than the target value xt (step S304). If the dryness x is equal to or greater than the target value xt (step S304, Yes), the rotational speed of the low-stage compressor 1 is decreased via the inverter 21 (step S305), and this process is terminated. On the other hand, when the dryness x is not equal to or higher than the target value xt (No at Step S304), the rotational speed of the low-stage compressor 1 is increased via the inverter 21 (Step S306), and this process is terminated. And the process mentioned above is repeated for every predetermined control time.

  In the third embodiment, the dryness x is calculated using only the existing temperature detection means and pressure detection means used for normal operation control without providing a water level meter in the gas-liquid separator 7 to calculate the gas-liquid. Since the water level LV of the separator 7 can be controlled, the water level of the gas-liquid separator 7 can be stably controlled with a simple configuration.

(Embodiment 4)
In the first to third embodiments, the liquid-liquid refrigerant amount flowing into the gas-liquid separator 7 and the refrigerant amount flowing out from the liquid-phase side outlet of the gas-liquid separator 7 are set to be substantially the same. The water level LV of the separator 7 is controlled to be constant. On the other hand, when operating under special conditions such as a very high compression ratio of the compressor, the volumetric efficiency becomes worse, so the error between the calculated theoretical value and the actual value increases, and the water level fluctuates. There is a risk of doing. Normally, the refrigerant charge amount in the refrigerant circuit is determined so that the maximum operation efficiency is achieved at the water level LV in the gas-liquid separator 7 determined in advance at the time of design. Therefore, it is desirable to always maintain a constant water level during operation. .

  For this reason, in the fourth embodiment, the target value xt is set so that the refrigerant amount flowing out from the liquid-phase side outlet of the gas-liquid separator 7 becomes larger than the liquid-phase refrigerant amount flowing into the gas-liquid separator 7. Yes. Here, it is desirable that the target value xt is set so that the difference between the amount of liquid-phase refrigerant flowing into the gas-liquid separator 7 and the amount of refrigerant flowing out from the liquid-phase outlet of the gas-liquid separator 7 is minimized.

  By operating at such a setting, excessive gas-liquid two-phase refrigerant is separated from gas-liquid while preventing the influence of changes in operating conditions by always maintaining the water level of the gas-liquid separator 7 at zero level. It is also possible to prevent the efficiency from deteriorating due to outflow from the liquid phase side outlet of the vessel 7.

(Embodiment 5)
In the fifth embodiment, the target value xt is set so that the refrigerant amount flowing out from the liquid-phase side outlet of the gas-liquid separator 7 is smaller than the liquid-phase refrigerant amount flowing into the gas-liquid separator 7. Here, it is desirable that the target value xt is set so that the difference between the amount of liquid-phase refrigerant flowing into the gas-liquid separator 7 and the amount of refrigerant flowing out from the liquid-phase outlet of the gas-liquid separator 7 is minimized. As shown in FIG. 7, the intermediate pipe 9 is provided with a heating unit 8 that heats the intermediate pressure refrigerant RM <b> 1 introduced from the gas phase side outlet of the gas-liquid separator 7. The heating unit 8 converts the gas-liquid two-phase refrigerant flowing out from the gas-phase side outlet of the gas-liquid separator 7 into a gas-phase refrigerant. For example, a heat exchanger can be used as the heating unit 8, and a high-pressure refrigerant discharged from a condenser or an external heat source can be used as a heat source.

  By operating in such a setting, an excess of the gas-liquid two-phase refrigerant is kept in the gas-liquid separator 7 while always keeping the water level of the gas-liquid separator 7 at the same level as the gas-phase outlet of the gas-liquid separator 7. It is possible to prevent the efficiency from deteriorating due to outflow from the gas phase outlet. Furthermore, even when a liquid-phase refrigerant is mixed into the refrigerant flowing out from the gas-phase-side outlet of the gas-liquid separator 7, it can be completely vaporized by the heating unit 8 and then sucked into the high-stage compressor 2. Liquid back in the high stage compressor can be prevented.

(Embodiment 6)
FIG. 8 is a circuit diagram showing a configuration of a refrigerant circuit device according to Embodiment 6 of the present invention. As shown in FIG. 8, in the sixth embodiment, a high-stage refrigerant circulation amount GH provided between the high-stage compressor 2 and the gas-liquid separator 7 and discharged from the discharge port of the high-stage compressor 2. The low-stage refrigerant that is provided between the high-stage flow rate detection unit F11 for detecting the gas and the gas-liquid separator 7 from the liquid-phase side outlet to the low-stage compressor 1 and sucked into the suction port of the low-stage compressor 1 A low-stage flow rate detection unit F12 that detects the circulation amount GL.

  The control unit C calculates the dryness x based on the high-stage refrigerant circulation amount GH detected by the high-stage side flow rate detection unit F11 and the low-stage refrigerant circulation amount GL detected by the low-stage side flow rate detection unit F12. .

  Here, with reference to the flowchart shown in FIG. 9, the water level control process procedure by the control part C of Embodiment 6 is demonstrated. First, as described above, the control unit C detects the high stage refrigerant circulation amount GH by the high stage side flow rate detection unit F11 (step S401). Further, the control unit C detects the low-stage refrigerant circulation amount GL by the low-stage side flow rate detection unit F12 (step S402). And the control part C calculates dryness x using Formula (2) (step S403).

  Thereafter, the control unit C determines whether or not the dryness x is equal to or greater than the target value xt (step S404). When the dryness x is equal to or greater than the target value xt (step S404, Yes), the rotational speed of the low-stage compressor 1 is decreased via the inverter 21 (step S405), and this process is terminated. On the other hand, when the dryness x is not equal to or greater than the target value xt (No at Step S404), the rotational speed of the low-stage compressor 1 is increased via the inverter 21 (Step S406), and this process is terminated. And the process mentioned above is repeated for every predetermined control time.

  In Embodiment 6, the water level LV of the gas-liquid separator 7 is calculated by calculating the dryness x using an existing flow meter used for conventional output control or the like without providing a water level meter in the gas-liquid separator 7. Therefore, the water level of the gas-liquid separator 7 can be stably controlled with a simple configuration.

  In addition, each component of Embodiment 1-6 mentioned above can be combined suitably, and a duplication combination is possible. For example, when the overlapping combination of Embodiments 1 and 2 is performed, the control unit C may control the average value of the dryness x calculated by each as the dryness x. Thus, by using together the dryness calculated by the several method, an error can be made smaller and a water level can be stabilized more.

DESCRIPTION OF SYMBOLS 1 Low stage compressor 2 High stage compressor 3 Condenser 5 High stage expansion valve 7 Gas-liquid separator 8 Heating part 9 Intermediate piping 10 Low stage expansion valve 12 Evaporator 21 Inverter C Control part F11 High stage side flow rate detection part F12 Low-stage flow rate detection unit GH High-stage refrigerant circulation amount GL Low-stage refrigerant circulation amount GM Refrigerant circulation amount LT Isothermal line LV Water levels P1 to P7 Point P11 High-pressure detection unit P12 Intermediate-pressure refrigerant state detection unit P21 High-stage intake pressure detection unit P22 Low stage suction pressure detection part PD Dry saturated air line PP1, PP2 Intersection PW Saturated liquid line RH High pressure refrigerant RL Low pressure refrigerant RM, RM1, RM2 Intermediate pressure refrigerant T11 Temperature detection part T21 High stage suction temperature detection part T22 Low stage suction temperature Detection unit x Dryness xt, xt1, xt2 Target value

Claims (11)

An evaporator that evaporates low-pressure refrigerant, a low-stage compressor that compresses low-pressure refrigerant introduced from the evaporator to an intermediate pressure, and a high-stage compression that compresses intermediate-pressure refrigerant compressed by the low-stage compressor to a high pressure A condenser for condensing the high-pressure refrigerant compressed by the high-stage compressor, a high-stage expansion valve for decompressing and expanding the high-pressure refrigerant condensed by the condenser to the intermediate pressure, and the high-stage expansion A gas-liquid separator that gas-liquid separates the intermediate-pressure refrigerant introduced from the valve; and an intermediate-pressure refrigerant introduced from the gas-phase-side outlet of the gas-liquid separator, the discharge port of the low-stage compressor and the high-stage compression An intermediate pipe introduced between the suction port of the compressor and a low-stage expansion valve for decompressing and expanding the intermediate pressure refrigerant introduced from the liquid phase side outlet of the gas-liquid separator to a low pressure A refrigerant circuit device comprising:
A refrigerant circuit device comprising a control unit that controls the number of revolutions of the low-stage compressor in accordance with the dryness of the refrigerant introduced into the gas-liquid separator.   The control unit decreases the rotational speed of the low-stage compressor when the dryness of the refrigerant is equal to or higher than a target value, and decreases the rotational speed of the low-stage compressor when the dryness of the refrigerant is less than the target value. The refrigerant circuit device according to claim 1, wherein the refrigerant circuit device is increased. A temperature detector for detecting the temperature of the high-pressure refrigerant between the condenser and the high stage expansion valve;
A high-pressure detector that detects the pressure of the high-pressure refrigerant between the condenser and the high-stage expansion valve;
An intermediate pressure refrigerant state detection unit for detecting the pressure or temperature of the intermediate pressure refrigerant between the high stage expansion valve and the gas-liquid separator or the intermediate pressure refrigerant in the intermediate pipe;
With
The said control part calculates the dryness of the refrigerant | coolant introduce | transduced into the said gas-liquid separator based on the temperature and pressure of the said high pressure refrigerant | coolant, and the pressure or temperature of the said intermediate pressure refrigerant | coolant. The refrigerant circuit device according to 1 or 2. The controller is
The dryness is obtained from a high-stage refrigerant circulation amount sucked into the high-stage compressor and a low-stage refrigerant circulation amount sucked into the low-stage compressor. Refrigerant circuit device. A high stage suction temperature detection unit for detecting the temperature of the refrigerant on the suction side of the high stage compressor;
A high stage suction pressure detection unit for detecting the pressure of refrigerant on the suction side of the high stage compressor;
With
The controller is
The high-stage refrigerant circulation amount is calculated from the temperature detected by the high-stage intake temperature detection unit, the pressure detected by the high-stage intake pressure detection unit, and the rotation speed of the high-stage compressor. 5. The refrigerant circuit device according to 4.   5. The refrigerant circuit device according to claim 4, further comprising a high-stage-side flow rate detection unit between the high-stage compressor and the gas-liquid separator, and detecting the high-stage refrigerant circulation amount. A low-stage intake temperature detector that detects the temperature of the refrigerant on the intake side of the low-stage compressor;
A low-stage suction pressure detector that detects the pressure of refrigerant on the suction side of the low-stage compressor;
With
The controller is
The low-stage refrigerant circulation amount is calculated from the temperature detected by the low-stage intake temperature detection unit, the pressure detected by the low-stage intake pressure detection unit, and the rotation speed of the low-stage compressor. The refrigerant circuit device according to any one of 4 to 6.   The low-stage side flow rate detection unit is provided between the liquid-phase side outlet of the gas-liquid separator and the low-stage compressor, and the low-stage refrigerant circulation amount is detected. The refrigerant circuit device according to claim 1. The control unit has a startup liquid level control mode and a normal liquid level control mode,
The controller, as the starting liquid level control mode, reduces the rotational speed of the low-stage compressor when the dryness of the refrigerant is equal to or higher than a first target value, and the dryness of the refrigerant is set to the first dryness level control mode. Increase the number of rotations of the low-stage compressor when less than the target value,
In the normal liquid level control mode, the control unit decreases the rotation speed of the low-stage compressor when the dryness of the refrigerant is equal to or higher than a second target value, and the dryness of the refrigerant is set to the second level. Increase the number of rotations of the low-stage compressor when less than the target value,
The refrigerant circuit device according to any one of claims 1 to 8, wherein the first target value is set smaller than the second target value.   The control unit is in the startup liquid level control mode when the refrigerant circuit device is activated, and shifts to the normal liquid level control mode when a predetermined time has elapsed after the refrigerant circuit device is activated. Item 10. The refrigerant circuit device according to Item 9.   The target value is set so that the amount of refrigerant flowing out from the liquid-phase side outlet of the gas-liquid separator is smaller than the amount of liquid-phase refrigerant flowing into the gas-liquid separator. The refrigerant circuit device according to any one of claims 1 to 8, further comprising a heating unit that heats the intermediate pressure refrigerant introduced from a gas phase side outlet of the separator.

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