JP2010060179A - Control device, air conditioner and refrigerating device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent a wet operation by surely detecting a wet state. <P>SOLUTION: A controller 20 of a refrigerant circuit 3 constituted by connecting a two-stage compressor 31, a condenser 32, an economizer heat exchanger 33, an evaporator 35 and an intermediate injection circuit 4, controls a second expansion valve 41 in such a state that a high-pressure discharge gas superheat degree in intermediate saturation which is a superheat degree of a high-pressure discharge gas when a refrigerant of an intermediate injection section becomes a saturated gas, calculated on the basis of a pressure of the high-pressure discharge gas discharged from the compressor 31, measured by a high-pressure pressure sensor 21, a pressure of an intermediate-pressure discharge gas discharged from the economizer heat exchanger 33 to the intermediate injection circuit 4, measured by the intermediate-pressure pressure sensor 22, and a temperature of the intermediate injection section detected by the intermediate injection section temperature sensor 23, is a lower limit of the superheat degree of the high-pressure discharge gas. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a control device that controls components of a refrigerant circuit, and an air conditioner and a refrigeration apparatus using the control device.

  If the discharge gas temperature of the compressor constituting the refrigerant circuit is excessively increased, the protection circuit may be activated to make the operation of the compressor unstable. In order to prevent such a situation, a liquid injection method is known as means for suppressing the discharge gas temperature (see, for example, Patent Documents 1 and 2). In the liquid injection system, the liquid injection circuit is branched from the liquid side piping of the refrigerant circuit, and a part of the liquid refrigerant is returned to the compressor and evaporated, whereby the compressor is cooled and the discharge gas temperature is suppressed. ing.

  In the liquid injection method, a part of the refrigerant is returned to the compressor without passing through the evaporator, so that the refrigerating capacity is lowered. In order to improve this, there is also a method in which a part of the liquid refrigerant is diverted from the liquid side pipe to form a diverted refrigerant, heat exchange is performed with the liquid refrigerant in the economizer heat exchanger, and then the diverted refrigerant is injected into the compressor. Are known.

  In this system, an economizer heat exchanger is provided between the condenser and the evaporator in the refrigerant circuit, and a part of the liquid refrigerant that has passed through the economizer heat exchanger is diverted. The diverted refrigerant which has been diverted is decompressed by the expansion valve, and is led to the economizer heat exchanger in a state where the temperature is lowered. In the economizer heat exchanger, the liquid refrigerant is cooled by exchanging heat with the liquid refrigerant, and the degree of supercooling is increased.

  Therefore, since the refrigeration capacity is improved by reducing the specific enthalpy of the refrigerant flowing through the evaporator, it is possible to compensate for the decrease in the refrigeration capacity due to the reduced amount of refrigerant. Therefore, it is possible to suppress a decrease in the refrigerating capacity and to suppress the discharge gas temperature of the compressor.

  In any case, when the compressor is cooled by providing an injection circuit, the compressor may be in a wet operation in which the compressor is operated in a wet state with liquid refrigerant inside. When the wet operation occurs, the compressor is likely to be damaged particularly when the wet state and the overheated state are repeated. Therefore, it is necessary to perform so-called wetness control in which the wet operation is avoided by controlling the injection amount.

In the conventional refrigerant circuit control device, the temperature of the high-pressure refrigerant gas discharged from the compressor is measured, and the wet state is detected by calculating the degree of superheat using the temperature, and the wetness control is performed. Yes. That is, since the difference between the actual discharge gas temperature and the temperature when the discharge gas is saturated is the superheat degree, when the discharge gas superheat degree becomes negative, the superheat degree becomes positive when the discharge gas superheat degree becomes negative. Wet control is performed by controlling the operation of the refrigerant circuit. The discharge gas temperature is measured by measuring the temperature of the discharge pipe through which the discharge gas passes and setting the discharge pipe temperature as the discharge gas temperature.
JP 7-127925 A Japanese Patent Laid-Open No. 8-200247

  However, the responsiveness of the measured value of the discharge pipe temperature is poor with respect to the actual discharge gas temperature. Therefore, in the conventional control device, the degree of superheat calculated using the discharge gas temperature obtained by measuring the temperature of the discharge pipe is positive even though the actual degree of superheat is negative. Therefore, there is a problem that the detection of the wet state may be delayed.

  The present invention has been made in order to solve such a conventional technical problem, and performs control to reliably detect the wet state of the compressor constituting the refrigerant circuit and avoid the wet operation of the compressor. An object is to provide an apparatus.

  A control device according to one aspect of the present invention includes a compressor having a two-stage compression mechanism of a low pressure side and a high pressure side, a condenser, an economizer heat exchanger, an evaporator, and the economizer heat. An intermediate injection circuit for returning a part of the refrigerant discharged from the exchanger to an intermediate injection portion that is intermediate between the low pressure side and the high pressure side of the compressor, the controller for the refrigerant circuit, A high pressure sensor for measuring the pressure of the high pressure discharge gas discharged from the intermediate pressure sensor, an intermediate pressure sensor for measuring the pressure of the intermediate pressure discharge gas discharged from the economizer heat exchanger to the intermediate injection circuit, and the intermediate injection section The intermediate injection part temperature sensor for detecting the temperature of the gas, the high pressure discharge gas pressure, the intermediate pressure discharge gas pressure, and the intermediate injection part temperature are used. Calculating the high pressure discharge gas superheat degree at the time of intermediate saturation, which is the superheat degree of the high pressure discharge gas when the refrigerant in the intermediate injection section becomes the saturated gas, and calculating the high pressure discharge gas superheat degree at the time of intermediate saturation of the high pressure discharge gas. Control means for controlling the intermediate injection circuit as a lower limit of the degree of superheat (Claim 1).

  The high pressure discharge gas superheat degree at the time of intermediate saturation is smaller than the superheat degree calculated from the temperature of the high pressure discharge gas when the refrigerant in the intermediate injection section is dry and outside the saturated vapor line, that is, in the superheated state. That is, the detection point of the superheat degree used for wetness control can be made closer to the temperature when the discharge gas is saturated than the conventional control device.

  Moreover, the high pressure discharge gas superheat degree at the time of intermediate saturation is the superheat degree of the high pressure discharge gas when the refrigerant of the intermediate injection portion becomes a saturated gas, and the temperature of the intermediate injection portion at this time is on the isothermal line, The temperature measurement error is small compared to the case of measuring the discharge pipe temperature of the high-pressure discharge section with poor temperature response and large error.

  Therefore, the superheat degree of the high pressure discharge gas is calculated using the discharge pipe temperature of the high pressure discharge section, and the wet state of the compressor is more reliably detected than when the lower limit of the superheat degree of the high pressure discharge gas is used. Therefore, the wetness control of the compressor is more reliably performed.

In the above configuration, the control means includes
High pressure discharge gas pressure: HP
Intermediate pressure discharge gas pressure: MP
Intermediate injection part temperature: Tms
Polytropic index when the compression process is polytropic change: n
Temperature when the high-pressure discharge gas becomes saturated gas: Ths
And when
Tpms = Tms × ((HP) / (MP)) ^ ((n−1) / n)
SHps = Tpms-Ths
The degree of superheat of the high-pressure discharge gas at the time of intermediate saturation can be calculated using the equation (2).

  According to this configuration, the intermediate saturation high-pressure discharge gas temperature that can be easily calculated is calculated, and used to calculate the calculated intermediate saturation high-pressure discharge gas superheat degree. Therefore, the degree of superheat of the high-pressure discharge gas during intermediate saturation can be easily calculated.

  An air conditioner or a refrigeration apparatus according to another aspect of the present invention includes a compressor having a two-stage compression mechanism of a low pressure side and a high pressure side, a condenser, an economizer heat exchanger, an evaporator, An intermediate injection circuit for returning a part of the refrigerant discharged from the economizer heat exchanger to an intermediate injection section that is intermediate between the low pressure side and the high pressure side of the compressor, and a refrigerant circuit connected to the compressor circuit A high pressure sensor for measuring the pressure of the discharged high pressure discharge gas, an intermediate pressure sensor for measuring the pressure of the intermediate pressure discharge gas discharged from the economizer heat exchanger to the intermediate injection circuit, and the intermediate injection section An intermediate injection part temperature sensor for detecting temperature, the high pressure discharge gas pressure, the intermediate pressure discharge gas pressure, and the intermediate injection part temperature Is used to calculate the high pressure discharge gas superheat degree during intermediate saturation, which is the superheat degree of the high pressure discharge gas when the refrigerant in the intermediate injection section becomes saturated gas, and the high pressure discharge gas superheat degree during intermediate saturation is calculated as high pressure discharge. The intermediate injection circuit is controlled as a lower limit of the degree of superheating of the gas (claims 3 and 4).

  According to this structure, it is avoided that the compressor which comprises the refrigerant circuit of an air conditioner or a freezing apparatus receives damage by wet operation.

  According to the control device of the present invention, the detection of the wet state of the compressor is performed more reliably than in the conventional control device, and the wetness control of the compressor is more reliably performed. Therefore, the wet operation of the compressor is reliably avoided and one of the failure factors of the compressor can be prevented, so that the maintenance cost and the life of the refrigerant circuit including the compressor can be reduced.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

  FIG. 1 is a schematic diagram of a refrigeration apparatus 1 including a control device 2 according to an embodiment of the present invention. FIG. 2 is a Mollier diagram (pressure-specific enthalpy diagram) showing a refrigeration cycle in the refrigeration apparatus 1. (ph diagram).

  The refrigeration apparatus 1 executes the refrigeration cycle by the control device 2 controlling the refrigerant circuit 3. The refrigerant circuit 3 includes a compressor 31, a condenser 32, an economizer heat exchanger 33, a first expansion valve 34, an evaporator 35, and an intermediate injection circuit 4.

  The compressor 31 is, for example, a two-stage compressor that includes a scroll-type compression mechanism and includes a two-stage compression mechanism of a low-pressure side compression mechanism 31a and a high-pressure side compression mechanism 31b in order to increase compression efficiency. The compressor 31 compresses the low-temperature / low-pressure refrigerant vapor sent from the evaporator 35 into a high-temperature / high-pressure refrigerant vapor (from point A to point D in FIG. 2).

  The condenser 32 is, for example, a cross-fin type air-cooled heat exchanger in which fins are attached to the outside of the cooling pipe through which the refrigerant flows, and is discharged from the compressor 31 by exchanging heat between the outdoor air and the refrigerant. The high-temperature and high-pressure refrigerant is cooled to obtain a supercooled high-pressure liquid refrigerant (from point D to point E in FIG. 2).

  The high-pressure liquid refrigerant liquefied in the condenser 32 passes through the economizer heat exchanger 33. Part of the high-pressure liquid refrigerant that has passed through the economizer heat exchanger 33 is diverted to the intermediate injection pipe 4.

  The intermediate injection pipe 4 is branched from the refrigerant circuit 3 between the economizer heat exchanger 33 and the first expansion valve 34, and the low pressure of the compressor 31 is passed through the economizer heat exchanger 33 with this branch point as a starting point. It is connected to an intermediate injection portion that is intermediate between the side compression mechanism 31a and the high-pressure side compression mechanism 31b. A second expansion valve 41 is provided between the branch portion of the intermediate injection circuit and the economizer heat exchanger 33.

  The second expansion valve 41 is a pulse motor drive type electronic expansion valve, for example, and the opening degree can be freely adjusted. The diverted refrigerant divided into the intermediate injection circuit is decompressed by the second expansion valve 41 before entering the economizer heat exchanger 33, and the temperature is lowered (from point F to point G in FIG. 2).

  The economizer heat exchanger 33 is, for example, a plate heat exchanger, and performs heat exchange between the branch refrigerant and the high-pressure liquid refrigerant. As a result, the shunt refrigerant exchanges heat with the high-pressure liquid refrigerant and absorbs heat from the high-pressure liquid refrigerant (point G to point C in FIG. 2), thereby increasing the degree of supercooling of the high-pressure liquid refrigerant (FIG. 2). From point E to point F), the specific enthalpy of the high-pressure liquid refrigerant decreases. Therefore, the refrigeration capacity of the refrigeration apparatus 1 is improved.

  The first expansion valve 34 is, for example, an electronic expansion valve, and the opening degree can be freely adjusted. By the expansion of the first expansion valve 34, the high-pressure liquid refrigerant becomes a low-temperature and low-pressure refrigerant (from point F to point H in FIG. 2) and is sent to the evaporator 35. The first expansion valve 34 also adjusts the flow rate of the refrigerant sent to the evaporator 35 according to the refrigeration load of the evaporator 35.

  The evaporator 35 is, for example, a cross-fin type air-cooled heat exchanger, and exchanges heat between indoor air and the refrigerant. As a result, the refrigerant takes heat from the room air and evaporates, and the room air is cooled. The evaporated refrigerant becomes superheated steam that is slightly overheated from the saturation temperature (from point H in FIG. 2 to point A) and travels to the compressor 31.

  FIG. 3 is a block diagram illustrating a functional configuration of the control device 2. The control device 2 includes a high pressure sensor 21, an intermediate pressure sensor 22, an intermediate injection part temperature sensor 23, and a controller 20 (control means).

  The high pressure sensor 21 is provided in the refrigerant discharge part of the high pressure side compression mechanism 31b of the compressor 31, and measures the high pressure discharge gas pressure which is the pressure of the discharged refrigerant gas.

  The intermediate pressure sensor 22 is provided in the intermediate injection part, and measures the pressure of the intermediate pressure discharge gas discharged from the economizer heat exchanger 33 to the intermediate injection part through the intermediate injection circuit 4.

  The intermediate injection part temperature sensor 23 is provided in the intermediate injection part and detects the temperature of the intermediate injection part.

  The controller 20 includes a microcomputer including a CPU (Central Processing Unit), and functions to include a system control unit 201 and a calculation unit 202.

  The system control unit 201 performs overall control of the refrigeration apparatus 1. Further, the system control unit 201 adjusts the injection amount by controlling the second expansion valve 41 so that the intermediate saturation high pressure discharge gas superheat degree calculated by the calculation unit 202 becomes the lower limit of the high pressure discharge gas superheat degree. To do. The high pressure discharge gas superheat degree at the time of intermediate saturation is the superheat degree of the high pressure discharge gas when the refrigerant in the intermediate injection section becomes a saturated gas.

  The calculation unit 202 calculates the intermediate saturation high pressure discharge gas superheat degree using the high pressure discharge gas pressure, the intermediate pressure discharge gas pressure, and the intermediate injection portion temperature.

  A method of calculating the intermediate saturation high pressure discharge gas superheat degree in the calculation unit 202 will be described with reference to FIG.

  In the conventional control device, the wet state is detected by measuring the temperature of the discharge pipe through which the high-pressure discharge refrigerant gas discharged from the compressor 31 passes, and calculating the degree of superheat using the discharge pipe temperature as the discharge gas temperature. And wet control was performed.

Since the degree of superheat is the difference between the actual discharge gas temperature (Thh) and the temperature (Ths) when the discharge gas is saturated, the degree of superheat (SHp) is defined by the following equation.
SHp = Thh-Ths

  That is, if the refrigerant circuit is controlled so that SHp> 0 ° C., wetting control can be performed. In the conventional control device, the discharge pipe temperature is used as Thh. However, the responsiveness of the measured value of the discharge pipe temperature is poor with respect to the actual discharge gas temperature. Therefore, in the conventional control device, although Thh ≦ Ths, in fact, Thh> Ths obtained by measuring the temperature of the discharge pipe, and apparently SHp> 0 ° C., and the wet state May be delayed.

  By the way, even if an attempt is made to calculate the superheat degree of the intermediate injection part in order to perform wetness control, the superheat degree of the intermediate injection part cannot be accurately calculated when the intermediate injection part is in a saturated state, that is, in a wet state.

  That is, when the intermediate injection part is in a saturated state (between point G and point I in FIG. 2), the intermediate injection part is in an isothermal and equal pressure state, so that the pressure and temperature of the intermediate injection part are measured. However, the superheat degree of the intermediate injection part cannot be calculated accurately. Therefore, it becomes difficult to accurately control the wetness.

  In order to solve the above problems, in the control device 2 according to the present embodiment, the intermediate saturation high pressure discharge gas superheat degree, which is the superheat degree of the high pressure discharge gas when the refrigerant in the intermediate injection section becomes the saturated gas, is set. Wet control is performed by calculating and controlling the second expansion valve 41 so that the high pressure discharge gas superheat degree at the time of intermediate saturation becomes the lower limit of the superheat degree of the high pressure discharge gas.

The high pressure discharge gas superheat degree (SHps) at the time of intermediate saturation is defined by the following equation.
SHps = Tpms-Ths

  Here, Tpms is the high-pressure discharge gas temperature (high-pressure discharge gas temperature during intermediate saturation) when the refrigerant in the intermediate injection section becomes a saturated gas (temperature at the point K in FIG. 2), and Ths is the high-pressure discharge gas This is the high-pressure discharge gas temperature when it becomes saturated gas (temperature at point J in FIG. 2).

Tpms when the compression process in the compressor 31 is regarded as a polytropic change can be calculated from the following equation.
Tpms = Tms × ((HP) / (MP)) ^ ((n−1) / n)

  Here, Tms is the temperature of the intermediate injection part (temperature at point I in FIG. 2), HP is the pressure of the high-pressure discharge gas, MP is the pressure of the intermediate injection part, and n is the polytropic index in the compression process. As described above, when the intermediate injection portion is in a saturated state (between point G and point I in FIG. 2), the intermediate injection portion is in an isothermal and equal pressure state, so Tms is constant. Measurement errors are reduced. Moreover, Tpms is calculated as the compression process starting from point I.

  Since Ths is a value that is uniquely determined with respect to pressure, SHps can be calculated by calculating Tpms.

  The compression process when the superheat degree of the high-pressure discharge gas is SHps is a process indicated by a broken line between points I and K in FIG. Since there is no polytropic change, the process is shown by the solid line between point C and point D in FIG. Since the high-pressure discharge gas temperature at the point D is Thh and Thh> Tpms, the high-pressure discharge gas superheat degree (SHp) when the refrigerant in the intermediate injection section is in an overheated state is always higher than SHps. Therefore, if this SHps is set as the lower limit of the superheat degree of the high-pressure discharge gas, the damp operation can be prevented.

  FIG. 4 is a flowchart for explaining wetness control in the refrigeration apparatus 1 according to the embodiment of the present invention.

  When the refrigeration apparatus 1 is activated, the calculation unit 202 calculates SHps (step S1). If SHps> 0 ° C., the discharge gas is in an overheated state, and if SHps ≦ 0, the discharge gas is in a saturated state, that is, the compressor 31 is in a wet operation.

  If SHps> 0 ° C. (YES in step S2), the process proceeds to step S4. If SHps ≦ 0 ° C. (NO in step S2), since the compressor 31 is in a wet operation, the opening degree of the second expansion valve 41 is reduced by the system control unit 201, and the injection amount is reduced (step S3). .

  In step S <b> 4, the calculation unit 202 determines whether SHps is within a predetermined degree of superheat, for example, 20 ° C.

  If SHps ≦ 20 ° C. (NO in step S4), since the discharge gas temperature of the compressor is appropriate, the opening degree of the second expansion valve 41 is maintained by the system control unit 201, and the injection amount is maintained ( Step S5).

  If SHps> 20 ° C. (YES in step S4), the discharge gas temperature of the compressor is excessively increased, so that the opening of the second expansion valve 41 is increased by the system control unit 201, and the injection amount is increased. (Step S6).

  As a result of calculating SHps by the calculation unit 202 (step S1), the process proceeds to one of step S3, step S5, and step S6. In either case, returning to step S1 again, steps S1 to S6 are repeated, and the injection amount is adjusted at any time.

  According to the refrigeration apparatus 1 including the control device 2 according to the present embodiment described above, the calculation unit 202 calculates SHps, and the system control unit 201 adjusts the opening of the second expansion valve 41 based on the SHps. Adjust the injection amount. Compared to conventional control devices, the superheat detection point used for wetness control can be brought closer to the temperature when the discharge gas is saturated, and the discharge of a high-pressure discharge section with poor temperature response and large error Compared with the case of measuring the tube temperature, Tms with a small temperature measurement error is used for calculating the degree of superheat, so that the wet state of the compressor 31 is reliably detected and the wetness control of the compressor 31 is more reliable. To be made.

  The refrigeration apparatus 1 according to the embodiment of the present invention has been described above, but the present invention is not limited to this, and for example, the following modified embodiment can be taken.

  (1) In the above embodiment, SHps> 0 ° C. is used as the condition for wetness control. However, the discharge pipe temperature sensor is further added to measure the high-pressure gas discharge temperature, and the wetness control is performed so that SHp> SHps. It is good also as conditions.

  When the intermediate injection part is in a saturated state (between point G and point I in FIG. 2), there is a possibility that the wet operation of Thh ≦ Ths, that is, SHp ≦ 0 ° C. As described for the conventional control device, when the discharge pipe temperature is used as Thh, detection of the wet state may be delayed. However, when Tms, HP, and MP measured in the above embodiment are used in addition to the conventional discharge pipe temperature, as shown in FIG. 2, since Tpms> Ths in theory, SHp> SHps. Is set as a condition for wet control, the wet state can be detected on the safer side. Therefore, even if a discharge pipe temperature having a poor responsiveness to a measured value is used with respect to the actual discharge gas temperature, the wet control condition can be set on the overheat side, so that SHp> SHps is satisfied. It can be.

  (2) In the above-described embodiment, the control device 2 is applied to the refrigeration device 1, but the control device 2 can be widely applied to all air conditioners including the refrigeration device.

It is a schematic diagram of the freezing apparatus provided with the control apparatus which concerns on one Embodiment of this invention. It is a Mollier diagram which shows the refrigerating cycle in the freezing apparatus which concerns on one Embodiment of this invention. It is a block diagram which shows the functional structure of the control apparatus which concerns on one Embodiment of this invention. It is a flowchart for demonstrating the wetness control in the freezing apparatus which concerns on one Embodiment of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Refrigeration apparatus 2 Control apparatus 20 Controller (control means)
201 System Control Unit 202 Arithmetic Unit 3 Refrigerant Circuit 31 Compressor 31a Low Pressure Side Compression Mechanism 31b High Pressure Side Compression Mechanism 32 Condenser 33 Economizer Heat Exchanger 35 Evaporator 4 Intermediate Injection Circuit 41 Second Expansion Valve

Claims (4)

Compressor (31) having a two-stage compression mechanism of a low pressure side and a high pressure side, a condenser (32), an economizer heat exchanger (33), an evaporator (35), and the economizer heat A refrigerant circuit (4) connected to an intermediate injection circuit (4) for returning a part of the refrigerant discharged from the exchanger (33) to an intermediate injection section that is intermediate between the low pressure side and the high pressure side of the compressor (31). 3) a control device,
A high pressure sensor (21) for measuring the pressure of the high pressure discharge gas discharged from the compressor (31);
An intermediate pressure sensor (22) for measuring the pressure of the intermediate pressure discharge gas discharged from the economizer heat exchanger (33) to the intermediate injection circuit (4);
An intermediate injection part temperature sensor (23) for detecting the temperature of the intermediate injection part;
High pressure at intermediate saturation that is the degree of superheat of the high-pressure discharge gas when the refrigerant in the intermediate injection section becomes a saturated gas using the high-pressure discharge gas pressure, the intermediate pressure discharge gas pressure, and the intermediate injection section temperature And a control means (20) for calculating the discharge gas superheat degree and controlling the intermediate injection circuit (4) using the intermediate saturation high pressure discharge gas superheat degree as a lower limit of the superheat degree of the high pressure discharge gas. High pressure discharge gas pressure: HP
Intermediate pressure discharge gas pressure: MP
Intermediate injection part temperature: Tms
Polytropic index when the compression process is polytropic change: n
Temperature when the high-pressure discharge gas becomes saturated gas: Ths
And when
The control means includes
Tpms = Tms × ((HP) / (MP)) ^ ((n−1) / n)
SHps = Tpms-Ths
The control device according to claim 1, wherein the superheat degree of the high-pressure discharge gas at the time of intermediate saturation is calculated using the formula Compressor (31) having a two-stage compression mechanism of a low pressure side and a high pressure side, a condenser (32), an economizer heat exchanger (33), an evaporator (35), and the economizer heat A refrigerant circuit (4) connected to an intermediate injection circuit (4) for returning a part of the refrigerant discharged from the exchanger (33) to an intermediate injection section that is intermediate between the low pressure side and the high pressure side of the compressor (31). 3) and
A high pressure sensor (21) for measuring the pressure of the high pressure discharge gas discharged from the compressor (31);
An intermediate pressure sensor (22) for measuring the pressure of the intermediate pressure discharge gas discharged from the economizer heat exchanger (33) to the intermediate injection circuit (4);
An intermediate injection part temperature sensor (23) for detecting the temperature of the intermediate injection part,
High pressure at intermediate saturation that is the degree of superheat of the high-pressure discharge gas when the refrigerant in the intermediate injection section becomes a saturated gas using the high-pressure discharge gas pressure, the intermediate pressure discharge gas pressure, and the intermediate injection section temperature An air conditioner that calculates a discharge gas superheat degree and controls the intermediate injection circuit (4) with the high pressure discharge gas superheat degree during intermediate saturation as a lower limit of the superheat degree of the high pressure discharge gas. Compressor (31) having a two-stage compression mechanism of a low pressure side and a high pressure side, a condenser (32), an economizer heat exchanger (33), an evaporator (35), and the economizer heat A refrigerant circuit (4) connected to an intermediate injection circuit (4) for returning a part of the refrigerant discharged from the exchanger (33) to an intermediate injection section that is intermediate between the low pressure side and the high pressure side of the compressor (31). 3) and
A high pressure sensor (21) for measuring the pressure of the high pressure discharge gas discharged from the compressor (31);
An intermediate pressure sensor (22) for measuring the pressure of the intermediate pressure discharge gas discharged from the economizer heat exchanger (33) to the intermediate injection circuit (4);
An intermediate injection part temperature sensor (23) for detecting the temperature of the intermediate injection part,
High pressure at intermediate saturation that is the degree of superheat of the high-pressure discharge gas when the refrigerant in the intermediate injection section becomes a saturated gas using the high-pressure discharge gas pressure, the intermediate pressure discharge gas pressure, and the intermediate injection section temperature A refrigeration apparatus that calculates a discharge gas superheat degree, and controls the intermediate injection circuit (4) with the high pressure discharge gas superheat degree during intermediate saturation as a lower limit of the superheat degree of the high pressure discharge gas.

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