Refrigeration cycle device

Abstract

A refrigeration cycle device (1) is provided with a refrigerant circuit (RC), detection devices (10, 11), and a control device (100). The refrigerant circuit (RC) includes a compressor (2) into which oil capable of dissolving a non-azeotropic refrigerant mixture is placed, a first heat exchanger (4), an expansion valve (5), a second heat exchanger (6), and an accumulator (20). The detection devices (10, 11) detect the composition of the liquid phase in the accumulator (20). The control device (100) uses the detection results from the detection devices (10, 11) to control the rotational speed of the compressor (2) such that the flow rate of the gas refrigerant circulating in the refrigerant circuit (RC) is higher than a zero-rate speed.

Description

Refrigeration Cycle Equipment

[0001] The present disclosure relates to a refrigeration cycle device.

[0002] Japanese Patent Laid-Open Publication No. 7-98161 (Patent Document 1) discloses a refrigeration cycle apparatus that uses a mixed refrigerant, which is a mixture of multiple refrigerants with different components, as the refrigeration cycle refrigerant. This refrigeration cycle apparatus includes a refrigerant circuit including a compressor, a first heat exchanger, a pressure reducing device, a second heat exchanger, and a storage container. The storage container contains refrigeration oil in which the mixed refrigerant is soluble. The refrigeration cycle apparatus also includes an adjustment device (an on-off valve and a heating device) for adjusting the pressure and temperature within the storage container. By adjusting the pressure and temperature within the storage container, the refrigeration cycle apparatus controls the refrigerant composition ratio dissolved in the refrigeration oil in the storage container. This allows the composition ratio of the refrigerant circulating within the refrigerant circuit to be controlled by utilizing the differences in the solubility of each refrigerant in the refrigeration oil (hereinafter also referred to as "selective solubility"), thereby enabling operation with a refrigerant suitable for the operating conditions.

[0003] Japanese Patent Application Publication No. 7-98161

[0004] The compressor included in the refrigerant circuit of a refrigeration cycle system contains refrigerant oil, which acts as a lubricant within the compressor. The refrigerant oil in the compressor is discharged from the compressor together with the refrigerant and circulates within the refrigerant circuit depending on the operating state. Therefore, the composition ratio of the refrigerant circulating within the refrigerant circuit cannot be accurately controlled without taking into account the effect of refrigerant dissolution into the refrigerant oil discharged from the compressor and circulating within the refrigerant circuit.

[0005] As described above, the refrigeration cycle device disclosed in Japanese Patent Laid-Open No. 7-98161 (Patent Document 1) controls only the refrigerant composition ratio dissolved in the refrigerating machine oil in the storage container by adjusting the pressure and temperature in the storage container. In other words, the refrigeration cycle device disclosed in Japanese Patent Laid-Open No. 7-98161 (Patent Document 1) only considers the effect of refrigerant dissolution in the refrigerating machine oil in the storage container, and does not consider the effect of refrigerant dissolution in the refrigerating machine oil discharged from the compressor and circulating in the refrigerant circuit, making it difficult to perform optimal operation.

[0006] Generally, refrigerant mixtures are classified into azeotropic and non-azeotropic refrigerant mixtures. In a refrigeration cycle system using a non-azeotropic refrigerant mixture, if the non-azeotropic refrigerant mixture has selective solubility in refrigerating machine oil, the solubility (amount) of each refrigerant component in the non-azeotropic refrigerant mixture changes independently depending on the operating state and environmental conditions. This affects the composition of the circulating gas refrigerant circulating in the refrigerant circuit. When the composition of the circulating gas refrigerant changes, the density of the circulating gas refrigerant changes, which in turn affects the flow rate of the circulating gas refrigerant. This can result in refrigerating machine oil remaining in the refrigerant circuit without returning to the compressor, potentially leading to a deterioration in reliability.

[0007] The present disclosure has been made to solve the above-mentioned problems, and its purpose is to appropriately suppress refrigeration oil from accumulating in a refrigerant circuit in a refrigeration cycle device that uses a non-azeotropic refrigerant mixture.

[0008] The refrigeration cycle device according to the present disclosure is a refrigeration cycle device that uses a non-azeotropic refrigerant mixture, and includes a refrigerant circuit including a compressor filled with oil in which the non-azeotropic refrigerant mixture is soluble, a first heat exchanger, an expansion valve, a second heat exchanger, and a gas-liquid separator, a detection device for detecting the composition of the liquid phase in the gas-liquid separator, and a control device that uses the detection results of the detection device to control the rotational speed of the compressor so that the flow velocity of the circulating gas refrigerant, which is the gas refrigerant circulating in the refrigerant circuit, is higher than the zero penetration speed.

[0009] According to the present disclosure, in a refrigeration cycle device that uses a non-azeotropic refrigerant mixture, it is possible to appropriately prevent refrigerating machine oil from accumulating in a refrigerant circuit.

[0010] 1 is a diagram (part 1) schematically showing an example of the overall configuration of a refrigeration cycle device; FIG. 2 is a diagram showing an example of the arrangement position of a capacitance type sensor inside an accumulator; FIG. 3 is a diagram showing an example of how the flow state of refrigeration oil changes depending on the circulating gas refrigerant flow velocity V; FIG. 4 is a flowchart (part 1) showing an example of the processing procedure of a control device; FIG. 5 is a diagram showing an example of the correspondence relationship between the liquid phase dielectric constant e and the refrigerant mixing ratio X; FIG. 6 is a diagram showing an example of the correspondence relationship between the dielectric constant eref of a non-azeotropic mixed refrigerant and the first refrigerant composition ratio x; FIG. 7 is a diagram (part 2) schematically showing an example of the overall configuration of a refrigeration cycle device; FIG. 8 is a diagram showing an example of the arrangement position of a capacitance type sensor inside an oil separator; and FIG. 9 is a flowchart (part 2) showing an example of the processing procedure of a control device.

[0011] Hereinafter, embodiments of the present disclosure will be described in detail with reference to the drawings. In the drawings, the same or corresponding parts are designated by the same reference numerals, and description thereof will not be repeated.

[0012] 1 is a diagram schematically illustrating an example of the overall configuration of a refrigeration cycle apparatus 1 according to this embodiment. The refrigeration cycle apparatus 1 includes a refrigerant circuit RC through which a non-azeotropic refrigerant mixture circulates, a capacitance-type sensor 10, temperature sensors 11 and 12, and a control device 100. The refrigerant circuit RC includes a compressor 2, a four-way valve 3, a first heat exchanger 4, an expansion valve 5, a second heat exchanger 6, an accumulator 20, and pipes 31 to 37 connecting these components.

[0013] The compressor 2 draws in low-pressure refrigerant, compresses it, and discharges it as high-pressure refrigerant. The compressor 2 discharges refrigerant at a flow rate that corresponds to its frequency (rotational speed). The compressor 2 is, for example, an inverter compressor whose frequency (rotational speed) is variable. The flow rate of refrigerant circulating within the refrigerant circuit RC is controlled by adjusting the frequency of the compressor 2.

[0014] The compressor 2 contains refrigeration oil capable of dissolving each refrigerant contained in the non-azeotropic refrigerant mixture. The refrigeration oil in the compressor 2 acts as a lubricant within the compressor 2. The refrigeration oil in the compressor 2 is discharged from the compressor 2 together with the non-azeotropic refrigerant mixture and circulates within the refrigerant circuit RC depending on the operating state of the refrigeration cycle apparatus 1. The non-azeotropic refrigerant mixture used in the refrigeration cycle apparatus 1 according to this embodiment has selective solubility in the refrigeration oil (difference in solubility of each refrigerant).

[0015] The first heat exchanger 4 is a heat exchanger having a flow path through which the refrigerant flows. In the first heat exchanger 4, heat is exchanged between the refrigerant flowing inside the flow path and the air outside the flow path.

[0016] The expansion valve 5 is a pressure reducing device that reduces the pressure of the high-pressure refrigerant. As the expansion valve 5, for example, an electronically controlled expansion valve having a valve element whose opening degree can be adjusted can be used.

[0017] The second heat exchanger 6 is a heat exchanger having a flow path through which the refrigerant flows. In the second heat exchanger 6, heat is exchanged between the refrigerant flowing inside the flow path and the air outside the flow path.

[0018] The accumulator 20 is a container that stores the non-azeotropic refrigerant mixture therein, and the non-azeotropic refrigerant mixture is separated into gas and liquid phases inside the accumulator 20. The accumulator 20 corresponds to an example of a "gas-liquid separator" in the present disclosure. The gas refrigerant separated into gas and liquid phases in the accumulator 20 is returned to the compressor 2 through a pipe 37.

[0019] The refrigeration cycle device 1 can be operated in a first mode (cooling mode) and a second mode (heating mode) by switching the state of the four-way valve 3 .

[0020] The four-way valve 3 is provided on the discharge side of the compressor 2. The four-way valve 3 is configured to be able to switch the discharge destination of the compressor 2 between a first heat exchanger 4 and a second heat exchanger 6. The four-way valve 3 is selectively controlled to either a "first state" in which the discharge side of the compressor 2 is connected to the first heat exchanger 4 and the suction side of the compressor 2 is connected to the second heat exchanger 6, or a "second state" in which the discharge side of the compressor 2 is connected to the second heat exchanger 6 and the suction side of the compressor 2 is connected to the first heat exchanger 4. Note that FIG. 1 shows an example in which the four-way valve 3 is controlled to the "first state."

[0021] In the first mode, the four-way valve 3 is set to the first state, and the discharge side of the compressor 2 is connected to the first heat exchanger 4. In the first mode, the first heat exchanger 4 functions as a condenser, and the second heat exchanger 6 functions as an evaporator. The refrigerant that has undergone heat exchange in the second heat exchanger 6 flows through the pipe 35, the four-way valve 3, and the pipe 36 in this order, and enters the accumulator 20, where it is separated into gas and liquid. The gas refrigerant in the accumulator 20 is drawn into the compressor 2 through the pipe 37.

[0022] In the second mode, the four-way valve 3 is set to the second state, and the discharge side of the compressor 2 is connected to the second heat exchanger 6. In the second mode, the first heat exchanger 4 functions as an evaporator, and the second heat exchanger 6 functions as a condenser. The refrigerant that has undergone heat exchange in the first heat exchanger 4 passes through the pipe 32, the four-way valve 3, and the pipe 36 in this order, and flows into the accumulator 20, where it is separated into gas and liquid. The gas refrigerant in the accumulator 20 passes through the pipe 37 and is drawn into the compressor 2.

[0023] The capacitance-type sensor 10 is disposed in a liquid phase portion located vertically below the accumulator 20, and detects the capacitance of the liquid phase (hereinafter also referred to as "liquid-phase capacitance C") in the accumulator 20. The capacitance-type sensor 10 outputs the detection result (liquid-phase capacitance C) to the control device 100.

[0024] 2 is a diagram showing an example of the arrangement position of the capacitance type sensor 10 inside the accumulator 20. The refrigerant flows into the accumulator 20 from a pipe 36 and is returned to the compressor 2 through a pipe 37. The pipe 36 extends in an I-shape inside the accumulator 20. On the other hand, the pipe 37 extends in a J-shape inside the accumulator 20.

[0025] The tip of the pipe 37 (the inlet for the gas refrigerant) is located at a height in the gas phase (vapor phase) that is located vertically above the liquid phase. The lower end of the pipe 37 is located at a height in the liquid phase. An oil return hole 23 is formed at the lower end of the pipe 37 to return refrigeration oil contained in the liquid phase to the compressor 2.

[0026] It is desirable to install the capacitance sensor 10 at a height where the inside of the accumulator 20 is in a single liquid phase so that the capacitance sensor 10 can reliably detect the liquid-phase capacitance C. Therefore, in this embodiment, the capacitance sensor 10 is placed at a position vertically below the oil return hole 23 inside the accumulator 20.

[0027] Returning to Fig. 1 , temperature sensor 11 is disposed in pipe 37 through which refrigerant flows to be sucked from accumulator 20 to compressor 2, and detects the temperature of pipe 37 (hereinafter also referred to as "suction pipe temperature T"). Temperature sensor 11 outputs the detection result (suction pipe temperature T) to control device 100. Note that, because pipe 37 is close to the liquid phase in accumulator 20, in this embodiment, the suction pipe temperature T detected by temperature sensor 11 is used as a temperature correlated to the temperature of the liquid phase in accumulator 20.

[0028] In this embodiment, the capacitance sensor 10 and the temperature sensor 11 function as a detection device for detecting the composition of the liquid phase in the accumulator 20. If a temperature sensor that directly detects the liquid phase temperature in the accumulator 20 is available, that temperature sensor may be used instead of the temperature sensor 11.

[0029] The temperature sensor 12 is disposed in the pipe 31 through which the refrigerant discharged from the compressor 2 to the four-way valve 3 flows, and detects the temperature of the pipe 31 (hereinafter also referred to as the "discharge pipe temperature"). The temperature sensor 12 outputs the detection result to the control device 100.

[0030] The control device 100 includes a CPU (Central Processing Unit), memory, and input / output ports for inputting and outputting various signals. The control device 100 controls the components of the refrigeration cycle device 1 (such as the compressor 2, four-way valve 3, and expansion valve 5) based on signals from the sensors (such as the capacitance sensor 10 and temperature sensors 11 and 12) and the components, as well as programs stored in the memory. Note that the control performed by the control device 100 is not limited to software processing, and can also be performed by dedicated hardware (electronic circuits).

[0031] <Zero Penetration Speed> Next, the limit refrigerant flow velocity of oil return (refrigerating machine oil return) to the compressor 2 will be described. Generally, in the piping of the refrigerant circuit, refrigerant and oil flow in two phases of gas and liquid, and in the upward flow in particular, the flow state of the refrigerating machine oil (liquid) changes depending on the flow velocity of the gas refrigerant (gas). When the flow velocity of the gas refrigerant (hereinafter also referred to as "circulating gas refrigerant") circulating in the piping of the refrigerant circuit is high, the refrigerating machine oil is also lifted up by the flow of the circulating gas refrigerant and rises, and when the flow velocity of the circulating gas refrigerant decreases, the refrigerating machine oil stops rising. The flow velocity of the circulating gas refrigerant when the refrigerating machine oil stops rising is called the "zero penetration speed", and is the limit refrigerant flow velocity of oil return to the compressor 2. The zero penetration speed is defined as V Ｚ Then, the zero penetration speed V Ｚ can be calculated as in the following formula (1).

[0032]

[0033] In formula (1), "g" represents the gravitational acceleration (unit: m / s ２ ), "d" is the inner diameter of the pipe (unit: m), "D ｒｅｆ＿ｇ " is the circulating gas refrigerant density (unit: kg / m ３ ), "D ｏｉｌ " is the density of the refrigerating machine oil (unit: kg / m３ ), and "C" is a constant determined by the refrigerant and the shape of the piping.

[0034] On the other hand, if the flow velocity of the circulating gas refrigerant is defined as "circulating gas refrigerant flow velocity V", the circulating gas refrigerant flow velocity V can be calculated as shown in the following formula (2).

[0035]

[0036] In formula (2), "G ｒ " is the refrigerant circulation rate (unit: kg / h), "A" is the cross-sectional area of ​​the pipe (unit: m ２ )

[0037] 3 is a diagram schematically showing how the flow state of refrigerating machine oil changes depending on the circulating gas refrigerant flow velocity V. The piping shown in FIG. 3 corresponds to any one of the piping 31 to 37 shown in FIG. 1.

[0038] The circulating gas refrigerant flow velocity V is the zero penetration velocity V Ｚ When the temperature is higher than 100°C, the refrigerating machine oil flows together with the circulating gas refrigerant, as shown on the left side of Figure 3, so the refrigerating machine oil circulates without accumulating in the piping. This allows the oil to be returned to the compressor 2, ensuring the reliability of the compressor 2.

[0039] On the other hand, the circulating gas refrigerant flow velocity V is equal to the zero penetration velocity V Ｚ When the temperature is lower than the reference temperature, the refrigerating machine oil does not flow even when the circulating gas refrigerant flows, as shown on the right side of Figure 3, so the amount of refrigerating machine oil remaining in the piping increases rapidly. This reduces the amount of oil returned to the compressor 2, and there is a risk that the compressor 2 will run out of oil.

[0040] Therefore, in this embodiment, as will be described below, taking into consideration the influence of the selective solubility of the non-azeotropic refrigerant mixture in the refrigerating machine oil, the circulating gas refrigerant flow velocity V is set to be equal to the zero penetration velocity V Ｚ The frequency (rotation speed) of the compressor 2 is controlled so that the above value is satisfied. This ensures the amount of oil returned to the compressor 2, and oil depletion in the compressor 2 can be appropriately suppressed.

[0041] <Frequency control of compressor 2> When a non-azeotropic refrigerant mixture has selective solubility in refrigerating machine oil as in the refrigeration cycle device 1 according to this embodiment, the amount of each refrigerant dissolved in the refrigerating machine oil changes depending on the operating state and environmental conditions of the refrigeration cycle device 1, which in turn changes the composition ratio of the circulating gas refrigerant. When the composition ratio of the circulating gas refrigerant changes, the density of the circulating gas refrigerant changes, and the circulating gas refrigerant flow velocity V changes. As a result, the circulating gas refrigerant flow velocity V becomes lower than the zero penetration velocity V. Ｚ If the temperature is lower than this, the oil return to the compressor 2 will be deteriorated, and the refrigerating machine oil will accumulate in the refrigerant circuit RC, which may lead to a deterioration in reliability.

[0042] It is also known that when an excess amount of non-azeotropic refrigerant mixture becomes liquid and accumulates in accumulator 20, a larger amount of refrigerant with a high boiling point dissolves in the liquid phase of accumulator 20. Therefore, the greater the amount of excess refrigerant in accumulator 20, the greater the composition ratio of the circulating gas refrigerant becomes, with the composition ratio of refrigerant with a low boiling point increasing. For example, when a non-azeotropic refrigerant mixture of R32 and R1234yf is used, the greater the amount of excess refrigerant in accumulator 20, the greater the amount of R1234yf with a high boiling point that dissolves in the excess refrigerant, and therefore the circulating gas refrigerant contains a correspondingly larger amount of R32 with a low boiling point.

[0043] Furthermore, the liquid phase in the accumulator 20 contains not only the non-azeotropic refrigerant mixture but also refrigerating machine oil. Therefore, the composition of the liquid phase in the accumulator 20 changes due to the selective solubility (difference in solubility) of each refrigerant in the refrigerating machine oil in the liquid phase in the accumulator 20, and this may affect the composition of the circulating gas refrigerant.

[0044] In consideration of the above, the refrigeration cycle apparatus 1 according to this embodiment includes a capacitance sensor 10 and a temperature sensor 11 as detection devices for detecting the composition of the liquid phase in the accumulator 20. The control device 100 calculates the refrigerant composition ratio in the liquid phase in the accumulator 20 using the detection results of the capacitance sensor 10 and the temperature sensor 11, thereby accurately calculating the composition of the circulating gas refrigerant, taking into account the amount of excess refrigerant in the accumulator 20 and the selective solubility of each refrigerant. The control device 100 then uses the calculated composition of the circulating gas refrigerant to calculate the circulating gas refrigerant flow velocity V when the circulating gas refrigerant flow velocity V reaches the zero penetration velocity V. Ｚ The frequency (rotation speed) of the compressor 2 is controlled so that the frequency (rotation speed) of the compressor 2 is equal to or greater than the above. This makes it possible to appropriately prevent the depletion of refrigerating machine oil in the compressor 2, while lowering the frequency of the compressor 2 and reducing the power consumption of the compressor 2.

[0045] 4 is a flowchart showing an example of a processing procedure of the control device 100. This flowchart is repeatedly executed every time a predetermined condition is met.

[0046] The control device 100 measures the dielectric constant of the liquid phase in the accumulator 20 (hereinafter also referred to as the "liquid-phase dielectric constant e") based on the liquid-phase capacitance C detected by the capacitance-type sensor 10 (step S10). The liquid-phase dielectric constant e can be measured, for example, by the following method. The liquid-phase capacitance C is expressed by the following equation (3):

[0047] C = e ０ ×e ｓ × (S / L) = e × (S / L) (3) In the formula (3), "e ０ " is the dielectric constant in a vacuum (generally 8.854 x 10 －１２ ), "e ｓ " is the relative dielectric constant of the liquid phase, "S" is the electrode area of ​​the capacitance-type sensor 10, and "L" is the distance between the electrodes of the capacitance-type sensor 10. Since S and L are constants, the control device 100 can calculate the liquid phase dielectric constant e (= e ０ ×e ｓ ) can be measured.

[0048] Next, the control device 100 acquires the suction pipe temperature T detected by the temperature sensor 11 as a temperature correlated with the temperature of the liquid phase in the accumulator 20 (step S11).

[0049] Next, the control device 100 calculates the refrigerant composition ratio in the liquid phase in the accumulator 20 using the liquid phase dielectric constant e measured in step S10 and the suction pipe temperature T acquired in step S11 (step S12).

[0050] An example of a method for calculating the refrigerant composition ratio in the liquid phase within accumulator 20 will be described below in detail. A non-azeotropic refrigerant mixture of a first refrigerant and a second refrigerant having different components will be described below as an example of a non-azeotropic refrigerant mixture. Furthermore, an example of the refrigerant composition ratio in the liquid phase within accumulator 20 will be described below in which the ratio of the first refrigerant (the sum of the first refrigerant not dissolved in the refrigerating machine oil and the first refrigerant and the second refrigerant dissolved in the refrigerating machine oil) to the total refrigerant, when the total refrigerant contained in the liquid phase (the sum of the first refrigerant and the second refrigerant not dissolved in the refrigerating machine oil and the first refrigerant and the second refrigerant dissolved in the refrigerating machine oil) is set to "1." This example calculates the ratio as "first refrigerant composition ratio x."

[0051] 5 is a diagram schematically showing the correspondence relationship between the liquid phase dielectric constant e and the refrigerant mixing ratio X. The refrigerant mixing ratio X is the ratio of the non-azeotropic refrigerant mixture to the entire liquid phase, where the entire liquid phase in the accumulator 20 is set to "1." As shown in FIG. 5, the refrigerant mixing ratio X varies not only with the liquid phase dielectric constant e but also with the refrigerant temperature (suction pipe temperature T) a°C, b°C, c°C, and so on.

[0052] Liquid phase dielectric constant e ｓ can be expressed by the following approximate formula (4). In formula (4), "e ｏｉｌ " is the dielectric constant of the refrigerating machine oil, "e ｒｅｆ " is the dielectric constant of the non-azeotropic refrigerant mixture, and "f" is a coefficient.

[0053] e ｓ = e ｏｉｌ (1-X) + e ｒｅｆ X + f ... (4) Dielectric constant e of refrigerating machine oil ｏｉｌ is the dielectric constant e of the non-azeotropic refrigerant mixtureｒｅｆ It is known to be small compared to the above and has no temperature dependency, so it can be considered a constant determined by the type of oil.

[0054] Furthermore, the dielectric constant e of the non-azeotropic refrigerant mixture ｒｅｆ can be expressed by the following equation (5) using the liquid phase dielectric constant e and the refrigerant mixing ratio X.

[0055] e ｒｅｆ = eX (5) Figure 6 shows the dielectric constant e of non-azeotropic refrigerant mixtures. ｒｅｆ 6 is a diagram showing a correspondence relationship between the dielectric constant (= eX) and the first refrigerant composition ratio x. As shown in Fig. 6, the first refrigerant composition ratio x changes depending not only on the dielectric constant of the first refrigerant in the liquid phase but also on the temperature of the first refrigerant.

[0056] Furthermore, the dielectric constant e of the non-azeotropic refrigerant mixture ｒｅｆ is the dielectric constant of the first refrigerant in the liquid phase, e Ａ and the dielectric constant of the second refrigerant is e Ｂ Then, it can be expressed by the following approximate formula (6).

[0057] e ｒｅｆ = e Ａ x + e Ｂ (1-x) ... (6) Furthermore, the dielectric constant e of each refrigerant Ａ , e Ｂ Since k changes depending on the refrigerant temperature, it can be expressed by the following equations (7) and (8), respectively. １ ~k ４ is a constant in the approximation formula.

[0058] e Ａ = k １ T+k ２ …(7) e Ｂ = k ３ T+k ４ ...(8) The control device 100 calculates the first refrigerant composition ratio x (the refrigerant composition ratio in the liquid phase in the accumulator 20) using the liquid phase dielectric constant e measured in step S10, the suction pipe temperature T acquired in step S11, and the above equations (4) to (8).

[0059] Next, the control device 100 determines whether the refrigerant composition ratio in the liquid phase in the accumulator 20 has stabilized (step S13). For example, the control device 100 determines that the refrigerant composition ratio in the liquid phase has stabilized if the fluctuation range of the refrigerant composition ratio in the liquid phase calculated within the most recent predetermined time period is smaller than a predetermined reference value. If the refrigerant composition ratio in the liquid phase is not stable (NO in step S13), the control device 100 returns to step S10 and repeats steps S10 to S13 until the refrigerant composition ratio in the liquid phase has stabilized.

[0060] If the refrigerant composition ratio in the liquid phase is stable (YES in step S13), the control device 100 calculates the refrigerant composition in the gas phase in the accumulator 20 as the composition of the circulating gas refrigerant from the gas-liquid equilibrium relationship based on the refrigerant composition ratio in the liquid phase calculated in step S12 (step S14).

[0061] Next, the control device 100 calculates the circulating gas refrigerant density D based on the composition of the circulating gas refrigerant calculated in step S14. ｒｅｆ＿ｇ is calculated (step S15).

[0062] Next, the control device 100 calculates the circulating gas refrigerant density D ｒｅｆ＿ｇ Using the above equation (1), the zero penetration speed V Ｚ is calculated (step S16).

[0063] Next, the control device 100 calculates the circulating gas refrigerant density D ｒｅｆ＿ｇ and the refrigerant circulation amount G calculated from the frequency of the compressor 2. ｒ and the above formula (2), the circulation gas refrigerant flow velocity V is calculated (step S17).

[0064] Next, the control device 100 determines whether the circulating gas refrigerant flow velocity V is equal to or greater than the zero penetration velocity V Ｚ It is determined whether it is higher than (step S18).

[0065] The circulating gas refrigerant flow velocity V is the zero penetration velocity V ＺIf the flow velocity V of the circulating gas refrigerant is lower than the zero penetration velocity V (NO in step S18), the control device 100 increases the frequency of the compressor 2 by a predetermined amount (step S19). Ｚ The process of increasing the frequency of the compressor 2 by a predetermined amount is repeated until the frequency becomes higher than the predetermined value. This improves the oil return to the compressor 2, and makes it possible to appropriately suppress depletion of refrigeration oil in the compressor 2.

[0066] On the other hand, the circulating gas refrigerant flow velocity V is equal to the zero penetration velocity V Ｚ If the frequency is higher than the predetermined value (YES in step S18), the control device 100 reduces the frequency of the compressor 2 by a predetermined amount (step S20). This reduces the frequency of the compressor 2 to a degree that ensures oil return to the compressor 2, thereby reducing the power consumption of the compressor 2.

[0067] As described above, according to the refrigeration cycle device 1 of this embodiment, even if the amount of excess refrigerant in the accumulator 20 changes and each refrigerant contained in the non-azeotropic refrigerant mixture has selective solubility in the refrigerating machine oil, the circulating gas refrigerant flow velocity V and the zero penetration velocity V are adjusted according to the change in the circulating gas refrigerant composition. Ｚ is calculated, and the circulating gas refrigerant flow velocity V is the zero penetration velocity V Ｚ The frequency of the compressor 2 is controlled so that the above value is satisfied. This makes it possible to prevent refrigerating machine oil from accumulating in the piping of the refrigerant circuit, thereby improving the oil return property of the refrigerating machine oil to the compressor 2.

[0068] 7 is a diagram schematically illustrating an example of the overall configuration of a refrigeration cycle apparatus 1A according to this modification. The refrigeration cycle apparatus 1A is configured by adding an oil separator 30 and an oil return pipe 33 to the above-described refrigeration cycle apparatus 1, and further providing a capacitance-type sensor 10A instead of the capacitance-type sensor 10. The other configuration of the refrigeration cycle apparatus 1A is the same as that of the above-described refrigeration cycle apparatus 1.

[0069] The oil separator 30 is disposed on a pipe 31 connecting the discharge port of the compressor 2 and the four-way valve 3, and separates the gas refrigerant compressed by the compressor 2 from the refrigerating machine oil (liquid) discharged from the compressor 2 together with the gas refrigerant. An oil return pipe 33 is connected to a lower portion of the oil separator 30 and the pipe 36. The refrigerating machine oil separated from the gas refrigerant in the oil separator 30 is returned to the pipe 36 through the oil return pipe 33.

[0070] The capacitance sensor 10A is disposed in a liquid phase (oil phase) portion located vertically below the oil separator 30, and detects the capacitance of the liquid phase within the oil separator 30. The capacitance sensor 10A outputs the detection result to the control device 100.

[0071] 8 is a diagram showing an example of the arrangement position of the capacitance sensor 10A inside the oil separator 30. As described above, the oil separator 30 is arranged on the pipe 31 and separates the gas refrigerant from the refrigerating machine oil (liquid). The refrigerating machine oil separated by the oil separator 30 accumulates in the liquid phase (oil phase) located vertically below the oil separator 30. The oil return pipe 33 is connected to the lower end of the oil separator 30.

[0072] The capacitance sensor 10A is disposed at the lower end portion within the oil separator 30 so as to be able to reliably detect the capacitance of the liquid phase within the oil separator 30.

[0073] As described above, when there is a gas-liquid separator such as the oil separator 30 that separates the gas refrigerant and the refrigeration oil, the capacitance sensor 10A may be provided in the lower liquid phase portion (oil retention portion) within the oil separator 30.

[0074] The oil separator 30 according to this modification corresponds to an example of a "gas-liquid separator" of the present disclosure. Furthermore, since the pipe 31 is close to the liquid phase in the oil separator 30, in this modification, the temperature of the pipe 31 (discharge pipe temperature) detected by the temperature sensor 12 is used as a temperature correlated with the temperature of the liquid phase in the oil separator 30. That is, in this modification, the capacitance-type sensor 10A and the temperature sensor 12 function as detection devices for detecting the composition of the liquid phase in the oil separator 30. Note that, if a temperature sensor that directly detects the liquid phase temperature in the oil separator 30 is available, that temperature sensor may be used in place of the temperature sensor 12.

[0075] Fig. 9 is a flowchart showing an example of the processing procedure of control device 100 according to this modification. In this flowchart, steps S10 to S14 of the flowchart shown in Fig. 4 described above are replaced with steps S10A to S14A. The other steps in the flowchart of Fig. 9 (the steps having the same numbers as the steps shown in Fig. 4 described above) have already been described, and therefore detailed description thereof will not be repeated here.

[0076] The control device 100 measures the liquid-phase dielectric constant in the oil separator 30 based on the liquid-phase capacitance in the oil separator 30 detected by the capacitance sensor 10A (step S10A). The liquid-phase dielectric constant in the oil separator 30 can be measured using a method similar to the method for measuring the liquid-phase dielectric constant e in the accumulator 20.

[0077] Next, the control device 100 acquires the discharge pipe temperature detected by the temperature sensor 12 as a temperature correlated with the temperature of the liquid phase in the oil separator 30 (step S11A).

[0078] Next, the control device 100 calculates (step S12A) the refrigerant composition ratio in the liquid phase in the oil separator 30 using the liquid phase dielectric constant measured in step S10A and the discharge pipe temperature acquired in step S11A. The refrigerant composition ratio in the liquid phase in the oil separator 30 can be calculated in the same manner as the refrigerant composition ratio in the liquid phase in the accumulator 20.

[0079] Next, the control device 100 determines whether the refrigerant composition ratio in the liquid phase in the oil separator 30 is stable (step S13A). If the refrigerant composition ratio in the liquid phase is not stable (NO in step S13A), the control device 100 returns to step S10A and repeats steps S10A to S13A until the refrigerant composition ratio in the liquid phase is stable.

[0080] If the refrigerant composition ratio in the liquid phase is stable (NO in step S13A), the control device 100 calculates the refrigerant composition in the gas phase in the oil separator 30 as the composition of the circulating gas refrigerant from the gas-liquid equilibrium relationship based on the refrigerant composition ratio in the liquid phase calculated in step S12A (step S14A).

[0081] The process from step S15 onwards is the same as that in the above-described embodiment. That is, the control device 100 calculates the zero penetration speed V using the composition of the circulating gas refrigerant calculated in step S14A. Ｚ and the circulating gas refrigerant flow velocity V is calculated (steps S15 to S17), and the circulating gas refrigerant flow velocity V is equal to or greater than the zero penetration velocity V Ｚ The frequency of the compressor 2 is increased or decreased depending on whether it is higher than the reference temperature (steps S18 to S20).

[0082] As described above, when the oil separator 30 that separates the gas refrigerant and the refrigeration oil is provided in the refrigerant circuit, the composition of the gas refrigerant (circulating gas refrigerant) that is not dissolved in the liquid phase in the oil separator 30 can be calculated more accurately by measuring the composition of the refrigerant dissolved in the liquid phase (refrigeration oil) in the oil separator 30. As a result, it is possible to achieve the same effects as the above-described embodiment while improving control responsiveness compared to the above-described embodiment.

[0083] The embodiments disclosed herein should be considered to be illustrative in all respects and not restrictive. The scope of the present disclosure is defined by the claims, not the above description, and is intended to include all modifications within the meaning and scope of the claims.

[0084] 1, 1A refrigeration cycle device, 2 compressor, 3 four-way valve, 4 first heat exchanger, 5 expansion valve, 6 second heat exchanger, 10, 10A capacitance type sensor, 11, 12 temperature sensor, 20 accumulator, 23 oil return hole, 30 oil separator, 31 to 37 piping, 33 oil return pipe, 100 control device.

Claims

1. A refrigeration cycle device that uses a non-azeotropic refrigerant, comprising: a compressor filled with oil in which the non-azeotropic refrigerant is soluble; a refrigerant circuit including a first heat exchanger, an expansion valve, a second heat exchanger, and a gas-liquid separator; a detection device for detecting the composition of the liquid phase in the gas-liquid separator; and a control device that uses the detection result of the detection device to control the rotational speed of the compressor so that the flow velocity of a circulating gas refrigerant, which is a gas refrigerant circulating within the refrigerant circuit, is higher than the zero penetration speed.

2. A refrigeration cycle apparatus as described in claim 1, wherein the detection device includes a capacitance sensor that detects the capacitance of the liquid phase in the gas-liquid separator, and a temperature sensor that detects the temperature of the liquid phase in the gas-liquid separator or a temperature correlated to the temperature of the liquid phase in the gas-liquid separator.

3. The refrigeration cycle apparatus of claim 2, wherein the control device calculates a refrigerant composition ratio in the liquid phase in the gas-liquid separator using the detection result of the detection device, calculates a composition ratio of the circulating gas refrigerant using the refrigerant composition ratio in the liquid phase in the gas-liquid separator, calculates a density of the circulating gas refrigerant using the composition ratio of the circulating gas refrigerant, calculates a zero penetration speed using the density of the circulating gas refrigerant, calculates a flow velocity of the circulating gas refrigerant using the density of the circulating gas refrigerant and a frequency of the compressor, and increases the frequency of the compressor when the flow velocity of the circulating gas refrigerant is lower than the zero penetration speed.

4. The refrigeration cycle apparatus of claim 3, wherein the control device calculates a mixing ratio of refrigerant and oil in the liquid phase in the gas-liquid separator using the detection result of the detection device, and calculates a refrigerant composition ratio in the liquid phase in the gas-liquid separator using the detection result of the detection device and the mixing ratio.

5. The refrigeration cycle apparatus of claim 2, wherein the gas-liquid separator is an accumulator connected to an intake port of the compressor, the accumulator has an oil return hole for returning oil in the liquid phase within the accumulator to the compressor, and the capacitance type sensor is installed at a position vertically below the oil return hole in the accumulator.

6. The refrigeration cycle apparatus according to claim 2, wherein the gas-liquid separator is an oil separator connected to the discharge port of the compressor, a lower end of the oil separator is connected to an oil return pipe for returning oil in the oil separator to the compressor, and the capacitance sensor is installed at the lower end of the oil separator.

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