WO2015001613A1 - Refrigeration cycle device - Google Patents

Abstract

A refrigeration cycle device that performs injection in a compressor, and that is equipped with: a flow volume adjuster that adjusts the injection amount of a refrigerant flowing into the compressor from an injection pipe; and a control device that controls the degree of opening of the flow volume adjuster. The control device controls the degree of opening of the flow volume adjuster such that the degree of dryness is 1 or greater at a convergence section where the refrigerant drawn in from the intake side of the compressor and the refrigerant supplied from the injection pipe converge.

Description

Refrigeration cycle equipment

The present invention relates to a refrigeration cycle apparatus that injects into a compressor.

In a refrigeration cycle in which a compressor, a condenser, an expansion valve, and an evaporator are connected in order, one that injects into the compressor is known (see, for example, Patent Documents 1-5). In Patent Documents 1 and 2, an injection pipe (bypass) is provided between the condenser and the expansion valve, which reaches the middle of the compression process in the compressor, and a flow regulator such as an on-off valve of the injection pipe is controlled. An air conditioner that controls the amount of injection is disclosed. In particular, Patent Document 1 uses R32 refrigerant as the refrigerant, and Patent Document 3 discloses that the specific heat ratio of the R32 refrigerant is 1.51.

Patent Document 4 discloses an air conditioner that calculates the temperature of an intermediate injection unit based on a polytropic index and controls the injection amount based on the calculated temperature. Patent Document 5 has a second bypass path from the condenser and the expansion valve to the suction of the compressor, and a second capillary and a second on-off valve are provided on the second bypass path. A refrigerating apparatus having a control device that controls the opening degree of a second on-off valve of the on-off valve is disclosed.

International Publication No. 2013/001572 (paragraph 0132-0135) JP 2004-183913 A (FIG. 1) JP 2001-304699 A (paragraph 0006) JP 2010-60179 A (paragraph 0046) JP-A-9-159288

In the case of Patent Document 1, the injection amount is controlled so that the R32 refrigerant immediately after joining is in the vicinity of the saturated gas, that is, the dryness is between 0.9 and 0.99. In addition, when liquid injection is performed using a refrigerant other than the R32 refrigerant described above, generally, the smaller the injection amount, the better the performance, and the injection amount is defined by the reliability of the compressor (discharge gas temperature). Has been. However, it is desired to perform more efficient operation while ensuring the reliability of the compressor than Patent Documents 1-5.

The present invention has been made to solve the above-described problems. Even when a refrigerant having a high specific heat ratio is used, efficient operation can be performed while ensuring the reliability of the compressor. An object of the present invention is to provide a refrigeration cycle apparatus that can be used.

The refrigeration cycle apparatus of the present invention is a refrigeration cycle apparatus in which a refrigeration cycle in which a compressor, a condenser, an expansion valve, and an evaporator are connected in order is formed, and refrigerant is introduced into the compressor from between the condenser and the expansion valve. A flow injection pipe, a flow rate regulator that is arranged in the injection pipe and adjusts the injection amount of the refrigerant flowing from the injection pipe into the compressor, and a control device that controls the opening degree of the flow regulator, and a refrigerant polytropic index Is equal to or greater than 1.28, and the control device controls the flow regulator so that the dryness of the merged portion between the refrigerant sucked from the suction side of the compressor and the refrigerant supplied from the injection pipe is 1 or more. The opening degree is controlled.

According to the refrigeration cycle apparatus of the present invention, when a refrigerant having a polytropic index of 1.28 or more is used, the injection amount is controlled so that the dryness at the junction is 1 or more. Even when a refrigerant having a large specific heat ratio and a large temperature rise is used, high efficiency and high reliability can be realized.

It is a refrigerant circuit figure which shows Embodiment 1 of the refrigerating-cycle apparatus of this invention. FIG. 2 is a graph showing a Ph diagram during injection in the compressor of the refrigeration cycle apparatus of FIG. 1. In the refrigeration cycle apparatus of FIG. 1, it is a graph which shows the relationship between the dryness of the confluence | merging part for every kind of refrigerant | coolant, and COP.

Hereinafter, embodiments of the refrigeration cycle apparatus of the present invention will be described with reference to the drawings. FIG. 1 is a refrigerant circuit diagram showing Embodiment 1 of the refrigeration cycle apparatus of the present invention. The refrigeration cycle apparatus 1 will be described with reference to FIG. The refrigeration cycle apparatus 1 forms a refrigeration cycle in which a compressor 2, a condenser 3, an expansion valve 4, and an evaporator 5 are connected by piping. As the refrigerant flowing through the refrigeration cycle apparatus 1, a refrigerant having a polytropic index of 1.28 or more (specific heat ratio is 1.2 or more) is used, for example, a single refrigerant of R32 refrigerant or a mixed refrigerant containing R32 refrigerant is used. It has been.

The compressor 2 sucks the refrigerant, compresses the refrigerant, and discharges it in a high temperature / high pressure state. The condenser 3 performs heat exchange between the refrigerant discharged from the compressor 2 and air (outside air). For example, the condenser 3 is between a heat transfer tube through which the refrigerant passes and between the refrigerant flowing through the heat transfer tube and the outside air. It has a structure provided with fins for increasing the heat transfer area. The expansion valve 4 adjusts the pressure of the refrigerant passing through the evaporator 7. The evaporator 5 performs heat exchange between the refrigerant and air (outside air). For example, the evaporator 5 increases the heat transfer area between the heat transfer tube that passes the refrigerant and the refrigerant that flows through the heat transfer tube and the outside air. And a fin for the purpose.

In addition, the refrigeration cycle apparatus 1 is disposed in an injection pipe (bypass) 11 through which refrigerant flows from between the condenser 3 and the expansion valve 4 into the compressor 2, and the injection pipe 11. _And a flow rate adjuster 12 for adjusting the injection amount G _inj flowing into the. Here, the compressor 2 is a two-stage compressor having, for example, a low-stage side compression unit and a rear-stage side compression unit, and compresses the intermediate pressure by the low-pressure side compression unit and compresses the maximum pressure by the high-pressure side compression unit. It has a function to do. The injection pipe 11 is connected to the merging section 2 a between the low pressure side compression section and the high pressure side compression section in the compressor 2, and the refrigerant that has flowed into the compressor 2 from the injection pipe 11 is contained in the compressor 2. In the middle of the compression process in the compression mechanism, the refrigerant discharged from the low-pressure side compression section merges at the merge section 2a.

Next, the refrigerant flow in the refrigeration cycle apparatus 1 will be described. First, the low-pressure gas refrigerant is compressed in the compressor 2 to be in a high-temperature and high-pressure gas state. The refrigerant in the high-pressure gas state is heat-exchanged with the outside air in the condenser 3 and is condensed by transferring the energy of the refrigerant to a heat source (air or water) to become a high-pressure liquid refrigerant. Thereafter, the refrigerant is depressurized by the expansion valve 4 to be in a low-pressure two-phase state and enters the evaporator 5. In the evaporator 5, the refrigerant absorbs air energy and evaporates to become low-pressure gas. At this time, water or air that has been heat exchanged with the refrigerant is cooled. Thereafter, the refrigerant flowing out of the evaporator 5 is again sucked into the compressor 2.

At this time, a part of the high-pressure and low-temperature liquid refrigerant branches from between the condenser 3 and the expansion valve 4 and flows to the injection pipe 11 side. The refrigerant in the injection pipe 11 is depressurized while being adjusted in flow rate by the flow rate regulator 12 and becomes a two-phase intermediate pressure, and merges at the merging portion 2a in the compressor 2, and the merged refrigerant is compressed on the high-pressure side in the compressor 2 Compressed at the part and discharged.

The injection amount (bypass amount) G _inj of the refrigerant flowing through the injection pipe 11 described above is controlled by the flow rate regulator 12, and the opening degree of the flow rate regulator 12 is controlled by the control device 30 based on the outputs of the sensors 21 to 25. It is controlled. Specifically, the refrigeration cycle apparatus 1 includes a discharge temperature sensor 21, a suction temperature sensor 22, an intermediate temperature sensor 23, a discharge pressure sensor 24, and a suction pressure sensor 25. The discharge temperature sensor 21 is provided on the discharge side of the compressor 2 and detects the discharge temperature of the refrigerant discharged from the compressor 2. The suction temperature sensor 22 is provided on the suction side of the compressor 2 and detects the suction temperature of the refrigerant sucked into the compressor 2. The intermediate temperature sensor 23 is provided on the injection pipe 11 and detects the intermediate temperature of the refrigerant flowing through the injection pipe 11. The discharge pressure sensor 24 is disposed on the discharge side (high pressure side) of the compressor 2 and detects the discharge pressure of the refrigerant discharged from the compressor 2. The suction pressure sensor 25 is disposed on the suction side (low pressure side) of the compressor 2 and detects the suction pressure of the refrigerant sucked into the compressor 2.

The control device 30 has a dryness calculating means 31 and an opening degree adjusting means 32. The dryness calculating means 31 uses the suction temperature, the discharge temperature, the suction pressure, the discharge pressure, and the operation frequency (the number of rotations) of the compressor 2 detected by each of the sensors 21 to 25, so that The dryness Xin is calculated. For example, the dryness calculating means 31 has a table or function in which the relationship between the suction pressure, the discharge pressure, the rotation speed of the compressor 2 and the compressor efficiency is stored in advance, and is detected by each sensor 21-25. The compressor efficiency is derived from the suction pressure, the discharge pressure, and the rotation speed of the compressor 2. At the same time, the dryness calculating means 31 calculates a saturation pressure from the intermediate temperature. Since the refrigerant flowing in the injection pipe 11 is in the gas-liquid two-phase state and the intermediate temperature is the refrigerant temperature in the gas-liquid two-phase state, the saturation pressure can be calculated from the intermediate temperature. Then, the dryness calculating means 31 calculates the dryness Xin in the junction 2a from the detected discharge side pressure and discharge temperature, the calculated saturation pressure Tm, and the compressor efficiency η.

The dryness Xin may be calculated by, for example, storing a table with the above parameters as an argument in advance and referring to the table, or by calculating from an approximate expression using the above parameters as an argument. May be. Further, the case of calculating the dryness Xin based on the detection results of the sensors 21 to 25 is illustrated, but in order to improve the calculation accuracy, parameters (arguments) such as the suction temperature may be increased, Various other known methods can be used.

The opening degree adjusting means 32 controls the opening degree of the flow rate regulator 12 based on the dryness degree Xin calculated by the dryness degree calculating means 31 so that the dryness degree Xin becomes 1 or more. Specifically, the opening degree adjusting means 32 has a difference (Xin−) between the dryness Xin of one or more targets (for example, the lower limit target dryness = 1.0, the upper limit target dryness = 1.1) and the dryness Xin. Xref) is calculated, and the difference (Xin−Xref) is multiplied by a predetermined coefficient to calculate the increase / decrease amount of the excess / deficiency injection amount G _inj (opening). The opening degree adjusting means 32 controls the current opening degree of the flow rate regulator 12 according to the calculated increase / decrease amount. For example, when the dryness Xin is less than 1.0, the opening degree adjusting means 32 controls the flow rate regulator 12 in the direction to open the opening degree, and when the dryness degree Xin is larger than the dryness degree 1.1, the opening degree adjusting means 32. Controls the flow regulator 12 in a direction to close the opening.

Thus, for example, when a refrigerant having a high specific heat ratio κ and a high discharge temperature, such as an R32 refrigerant, is used, reliability is controlled by controlling the injection amount G _inj so that the dryness Xin is 1 or more. High-efficiency operation can be performed while maintaining In particular, high-efficiency operation can be performed in high-compression ratio operation where the discharge gas temperature increases.

Hereinafter, for example, when a refrigerant having a polytropic index of 1.28 or more (specific heat ratio of 1.2 or more) such as R32 refrigerant is used, the reason for controlling the injection amount G _inj so that the dryness becomes 1 or more is described. explain. First, in general, the smaller the compressor input W, which is the power required to drive the compressor 2, the higher the COP. FIG. 2 is a PH diagram showing a state in the compressor of FIG. In FIG. 2, there is a case where there is an injection amount G _inj with a solid line, and a broken line is a case where there is no injection amount G _inj . In the following, it is assumed that the capacity is constant and the high pressure, low pressure, intermediate pressure, and suction temperature do not change.

When there is injection from the injection pipe 11, the compressor input W is expressed by the following formula (1). In the equation (1), Delta] hl the enthalpy difference of the compressor 2 of the low-stage, [Delta] h2 is the enthalpy difference of the compressor 2 of the high-stage after injection has been made, the G _e from the suction side of the compressor 2 The refrigerant flow rate, G _inj , indicates the amount of injection that flows into the compressor 2 from the injection pipe 11.

On the other hand, when there is no injection, the compressor input Wo is expressed by the following equation (2). Incidentally, [Delta] h2 ₀ represents the enthalpy difference of the compressor 2 of the high-stage in the absence of injection (discharge side).

The compressor input W injected from the above formulas (1) and (2) can be expressed as the following formula (3).

In Expression (3), the second term on the right side indicates the amount of increase in the compressor input W due to the injection amount G _inj , and the third term on the right side indicates the amount of decrease in the compressor input W due to the injection of the high- _stage compressor 2. ing. That is, the compressor input W changes due to the change in the injection amount G _inj , and when the injection amount G _inj increases, the second term on the right side increases and the third term on the right side decreases monotonously.

Moreover, the change of the input of the compressor 2 with respect to the injection amount is _represented by the following equation (4) obtained by differentiating the equation (3) by the injection amount G _inj .

In Expression (4), the enthalpy difference Δh2 on the high stage side of the first term on the right side is a positive value (Δh2> 0), but monotonously decreases as the injection amount G _inj increases. The second term on the right side is a negative value, but monotonously increases with increasing injection amount G _{inj and gradually approaches} 0.

Incidentally, as shown in the equation (4), the compressor input W and the change in the enthalpy h in the compressor 2 (enthalpy difference Δh2) are closely related. This enthalpy can be expressed as the following formula (5) in the case of an ideal gas. In the formula (5), Cp is the low pressure specific heat. As shown in equation (5), enthalpy h is expressed as a function of temperature T.

[Equation 5]
h = Cp · T (5)
(Δh = Cp · ΔT)

The compression process in the compressor 2 is adiabatic compression, and the temperature change can be expressed by the following equation (6). In equation (6), κ represents the specific heat ratio of the refrigerant.

Furthermore, the polytropic change considering the actual change is expressed by the following formula (7), where n is the polytropic index.

As shown in the equations (6) and (7), the enthalpy h (enthalpy change Δh) depends on the specific heat ratio κ or the polytropic index n of the refrigerant. That is, if the specific heat ratio κ or the polytropic index n of the refrigerant is small, the temperature change is small and the enthalpy change Δh is also small. On the other hand, if the specific heat ratio κ or the polytropic index n of the refrigerant is large, the temperature change increases and the enthalpy change Δh also increases. Further, as shown in the equations (1) to (4), the change of the compressor input W with respect to the injection amount G _inj depends on the enthalpy change Δh. Therefore, the change of the compressor input W depends on the specific heat ratio κ and the polytropic index n.

The specific heat ratio κ and the polytropic index n are different depending on the type of refrigerant as shown in Table 1 below, and the R32 refrigerant has a specific heat ratio κ and a polytropic index n larger than those of the R404A refrigerant.

First, the case where general R404A is adopted as the refrigerant flowing through the refrigeration cycle will be described. As shown in Table 1, the R404A refrigerant has a small specific heat ratio κ and a relatively small temperature change ΔT during adiabatic compression. Further, if the temperature change ΔT is small, the enthalpy change Δh is also small. For this reason, the first term on the right side of Equation (4) is always a positive value, whereas the second term on the right side is always a small value. For this reason, the change rate δW / δG _inj > 0 of the compressor input W in the equation (4) regardless of the injection amount G _inj . This means that the compressor input W monotonously increases as the injection amount G _inj increases. Therefore, in order to minimize the compressor input W when the R404A refrigerant is used, the opening degree adjusting means 32 controls the flow rate regulator 12 so that the injection amount G _inj is minimized. Thereby, highly efficient operation can be realized within a wide operation range while ensuring the reliability of the compressor 2 by performing injection.
When the behavior when the R404A refrigerant is used is shown in FIG. 3, an increase in the injection amount G _{inj results in} a decrease in the dryness of the merging portion 2a, and an increase in compressor input results in a decrease in COP. Since it cannot be operated in a state higher than the dryness determined by the reliability limitation of the compressor (discharge gas temperature), the COP is determined at the same time.

Next, the case of R32 refrigerant will be described. As shown in Table 1, the R32 refrigerant has a large specific heat ratio κ and a relatively large temperature change during adiabatic compression. When the temperature change ΔT is large, the enthalpy change Δh is also large. Therefore, the second term on the right side of the equation (4) changes greatly as the injection amount G _inj increases.

Specifically, in the range from the injection amount G _inj to the first predetermined value from zero, the relationship | first term on the right side |> | second term | W change rate δW / δG _inj > 0. On the other hand, in the range from the first predetermined value to the second predetermined value, the injection amount G _inj becomes | the first term on the right side | <| the second term on the right side |, and the change rate δW / δG _inj < 0. Further, when the injection amount G _inj is larger than the second predetermined value, the first term on the right side |> | the second term on the right side is again obtained, and the change rate δW / δG _inj > 0 of the compressor input W is obtained. Therefore, the compressor input W of the expression (3) increases until the injection amount G _inj reaches zero from the first predetermined value, decreases from the first predetermined value to the second predetermined value, and becomes the second predetermined value. It increases when it becomes larger than the value. Thus, the minimum value (minimum value) of the compressor input W is the case where the injection amount G _inj = 0 or the second predetermined value.

Among them, when the injection amount G _{inj = 0,} the reliability of the operation of the compressor 2 may be greatly decreased by an increase in discharge temperature. Therefore, the injection amount G _inj is controlled to be the second predetermined value. This second predetermined value is a point at which the change in the enthalpy difference Δh2 on the higher stage side becomes insensitive, and the refrigerant in the merging portion 2a is in a state where it becomes a saturated gas (dryness Xin = 1). Therefore, the compressor input W is minimized when the refrigerant dryness Xin = 1 at the junction 2a. Therefore, the opening degree adjusting means 32 can minimize the compressor input W while ensuring the reliability of the compressor 2 by controlling the flow rate regulator 12 so that the dryness Xin becomes 1 or more. .

When the behavior when the R32 refrigerant is used is shown in FIG. 3, an increase in the injection amount G _{inj results in} a decrease in the dryness of the merging portion 2a, and an increase in compressor input results in a decrease in COP. When the injection amount G _inj = 0 changes to the second predetermined value, the dryness of the merging portion 2a decreases from 1.15 or more to 1.1 and is small but COP decreases monotonously. When the injection amount G _inj changes from the second predetermined value to the first predetermined value, the dryness of the merging portion 2a decreases from 1.1 or more to 1, which is small but the COP increases monotonously. When the injection amount G _inj further decreases from the first predetermined value, the dryness of the joining portion 2a further decreases from 1, the COP decreases monotonously, and the decrease amount is large.

In addition, although it is a case where control is performed so that the dryness = 1, it is actually difficult to control to one value, and control is performed while allowing a certain range. In this case, if the dryness is 1 or less, the COP decrease is remarkable, which is not preferable. If the dryness is allowed to be between 1 and 1.1, the change from the COP maximum is small, and the operation can be stably performed in the high COP state.

As described above, the R404A refrigerant and the R32 refrigerant have been exemplified and described. However, if the COP such as the R32 refrigerant has the characteristic of a refrigerant that maximizes the compressor input W (minimum compressor input W), the junction 2a What is necessary is just to control so that the dryness Xin of becomes 1 or more. The conditions under which this COP has a maximum value are formulated below.

First, in the refrigeration cycle apparatus 1, a certain state A is compared with a state B in which the injection amount G _inj is decreased from the state A by ΔG. The energy balance at the junction 2a of the compressor 2 in the state A can be expressed as the following formula (8). In Equation (8), H _mix is the enthalpy of the merging section 2a, H _liq is the injection enthalpy before merging, Δh1 is the difference in enthalpy of the compressor 2 on the low stage side (before suction-merging), and h1 is the compressor suction The enthalpies in are shown respectively.

On the other hand, the energy balance at the junction 2a in the state B can be expressed as the following formula (9). In equation (9), ΔG is the amount of decrease in the injection amount G _inj , ΔH is the amount of change in the enthalpy of the merging 2a, and Δh ^* is the amount of change in the enthalpy difference of the compressor 2 on the low stage side (before suction-merging). Show.

Formula (10) is established from Formula (8) and Formula (9).

On the other hand, the following equation (11) is established from the equation of state. In equation (11), ρ represents the density of the joining portion 2a, Δρ represents a density difference accompanying a state change, ΔP represents a pressure difference associated with the state change, and ΔT represents a temperature difference associated with the state change.

Further, the enthalpy difference Δh1 of the low-stage compressor 2 in the equation (8) can be expressed by the following equation (12). In Formula (12), P1 is the suction pressure of the compressor 2, and P2 is the pressure of the merging portion 2a.

Similarly, the enthalpy difference Δh1 + Δh ^* of the low-stage compressor 2 in the equation (9) can be expressed by the following equation (13).

From the expression (12) and the expression (13), the following expression (14) is established.

Substituting ΔH = Cp · ΔT and Equations (10) and (11) shown in Equation (5) into Equation (14) gives Equation (15).

That is, when the injection amount change ΔG decreases (ΔG <0), the pressure change ΔP increases (ΔP> 0) when the condition of the following equation (16) is satisfied.

In the case of a refrigerant having a polytropic index n (specific heat ratio κ) satisfying the above equation (16), COP has a maximum value, and therefore, if the control is performed so that the dryness Xin of the joining portion 2a is 1 or more, the maximum is obtained. The driving efficiency can be obtained. The polytropic index n ≧ 1.28 or the specific heat ratio κ ≧ 1.2 satisfies the equation (16).

According to the above-described embodiment, when the injection amount G _inj increases as in the conventional case, the COP does not decrease, but in the refrigerant with a high discharge temperature, the injection amount G _inj at which the dryness Xin of the joining portion 2a becomes 1 or more Utilizing the characteristic that COP is sometimes maximized, high-efficiency operation can be performed, and reliability can be maintained.

That is, in refrigeration applications, the ratio of high pressure to low pressure (compression ratio) increases, and the temperature of the refrigerant coming out of the compressor 2 increases. When the temperature of the refrigerant is high, an excessive load is generated on the compression mechanism due to a difference in expansion coefficient between members, abnormal wear due to a decrease in the viscosity of the refrigerating machine oil due to a temperature rise, The reliability such as deterioration of the internal resin member, generation of sludge, etc. is lowered, and further, the performance is lowered due to damage to the compressor 2. For this reason, supplying the liquid refrigerant from the injection pipe 11 to the compression process allows the latent heat to cool the inside of the compressor 2. Therefore, a temperature rise inside the compressor 2 can be prevented and reliability can be ensured. Note that the refrigerant entering the injection pipe 11 may be a supercooled liquid or a two-phase refrigerant.

Further, in the restriction of a refrigerant having a high discharge temperature that satisfies a polytropic index ≧ 1.28, a high-efficiency operation is performed by utilizing the feature that the injection amount G _{inj at} which the dryness Xin of the joining portion 2a is 1 or more is the maximum COP. Can be implemented. Further, it can be determined by the refrigerant physical property value in the operation state of the polytropic index n or the specific heat ratio κ and the compressor performance characteristic in the operation state. Furthermore, characteristics due to specification differences can be taken into consideration, and determination can be made with high accuracy.

DESCRIPTION OF SYMBOLS 1 Refrigeration cycle apparatus, 2 Compressor, 2a Merge part, 3 Condenser, 4 Expansion valve, 5 Evaporator, 11 Injection piping, 12 Flow regulator, 21 Discharge temperature sensor, 22 Intake temperature sensor, 23 Intermediate temperature sensor, 24 Discharge pressure sensor, 25 Suction pressure sensor, 30 Control device, 31 Dryness calculation means, 32 _Opening adjustment means, G _inj injection amount, h enthalpy, Δh1, Δh2 Enthalpy difference, Δh ^* Lower stage side (before suction-merging) Change of enthalpy difference of compressor, n polytropic index, Tm saturation pressure, W, Wo compressor input, Xin dryness, Xref target dryness, ΔG injection amount change, Δh enthalpy change, ΔP pressure change, P1 compression Machine suction pressure, pressure at P2 junction, ΔT temperature change, η compressor efficiency, κ specific heat ratio.

Claims (5)

A refrigeration cycle apparatus in which a refrigeration cycle in which a compressor, a condenser, an expansion valve, and an evaporator are connected in order is formed,
An injection pipe through which refrigerant flows into the compressor from between the condenser and the expansion valve;
A flow rate regulator that is disposed in the injection pipe and adjusts the injection amount of the refrigerant flowing from the injection pipe into the compressor;
A control device for controlling the opening of the flow regulator;
With
The refrigerant polytropic index is 1.28 or more,
The control device controls the opening degree of the flow rate regulator so that the dryness of the joining portion of the refrigerant sucked from the suction side of the compressor and the refrigerant supplied from the injection pipe becomes 1 or more. A refrigeration cycle apparatus characterized by being a thing. The control device is configured so that the dryness of the junction of the refrigerant sucked from the suction side of the compressor and the refrigerant supplied from the injection pipe is between 1 and 1.1. The refrigeration cycle apparatus according to claim 1, wherein the opening degree is controlled. 3. The refrigeration cycle apparatus according to claim 1, wherein a specific heat ratio of the refrigerant is 1.2 or more. 4. The refrigeration cycle apparatus according to claim 1, wherein the refrigerant is a single refrigerant of R32 refrigerant or a mixed refrigerant containing R32 refrigerant. An intake temperature sensor for detecting an intake temperature of the refrigerant on the intake side of the compressor;
A discharge temperature sensor for detecting the discharge temperature of the refrigerant on the discharge side of the compressor;
An intermediate temperature sensor for detecting an intermediate temperature of the refrigerant flowing through the injection pipe;
A suction pressure sensor for detecting the suction pressure of the refrigerant on the suction side of the compressor;
A discharge pressure sensor for detecting a discharge pressure of the refrigerant on the discharge side of the compressor;
The controller is
A dryness calculating means for calculating a dryness in the merging section using the suction temperature, the discharge temperature, the intermediate temperature, the suction pressure, the discharge pressure, and an operating frequency of the compressor;
The opening degree adjusting means for controlling the opening degree of the flow rate regulator so that the dryness calculated by the dryness calculating means becomes 1 or more. The refrigeration cycle apparatus according to any one of the above.

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