Refrigeration cycle system

Abstract

To suppress lubrication failure in a compressor, even in the case where an environmental temperature becomes a temperature where the density of lubrication oil and the density of refrigerant in a liquid state are reversed.SOLUTION: A refrigeration cycle system includes: a compressor lubricated by a lubrication oil and for compressing refrigerant; an evaporator for, after compression by the compressor, allowing the refrigerant which has released heat and been decompressed to pass and for performing heat exchange between the passing refrigerant and an object; and a storage container provided in a space from the evaporator to the compressor, and capable of storing the refrigerant and the lubrication oil. Even in the case where an environmental temperature where the storage container is installed becomes a reverse temperature in which the density of the lubrication oil and the density of the refrigerant in a liquid state are reversed, the lubrication oil stored in the storage container can be supplied to the compressor.SELECTED DRAWING: Figure 2

Description

Technical Field

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

Background Art

[0002] Patent Document 1 describes a liquid return prevention device for a refrigeration apparatus in which a low-pressure receiver is disposed between a compressor and an evaporator in a refrigerant circulation system. An oil return opening for returning lubricating oil accumulated in the low-pressure receiver to the compressor is formed in a refrigerant pipe on the compressor side of the low-pressure receiver, and a communication pipe for flowing down the liquid refrigerant accumulated in the low-pressure receiver to the evaporator when the compressor stops operating is provided between the bottom surface of the low-pressure receiver and the evaporator.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] For example, in a refrigeration cycle system, a storage container capable of storing a refrigerant in a liquid state (sometimes referred to as "liquid refrigerant") may be provided on a circuit through which the refrigerant circulates, such as the low-pressure receiver described in Patent Document 1. In such a storage container, lubricating oil that circulates through the circuit together with the refrigerant is also stored in order to ensure lubrication in the compressor. When the liquid refrigerant and the lubricating oil are immiscible, they are separated into an upper layer and a lower layer in the storage container, and the lubricating oil is supplied to the compressor by an oil supply mechanism such as the oil return opening of Patent Document 1. Here, depending on the combination of the liquid refrigerant and the lubricating oil, their densities may reverse at a certain temperature, causing the upper and lower layers to swap. When the upper and lower layers swap, it becomes difficult to supply oil to the compressor with a conventional oil supply mechanism, resulting in poor lubrication in the compressor. The present disclosure proposes a refrigeration cycle system that suppresses poor lubrication in a compressor even when the ambient temperature reaches a temperature at which the density of the lubricating oil and the density of the refrigerant in a liquid state are reversed.

Means for Solving the Problems

[0005] The refrigeration cycle system of the first aspect includes a compressor lubricated by lubricating oil and compressing a refrigerant, A radiator that allows the refrigerant compressed by the compressor to pass through and extracts heat from the passing refrigerant for heat dissipation; an evaporator that allows the refrigerant compressed by the compressor to pass through, radiates heat and decompresses, and exchanges heat between the passing refrigerant and an object, An electric valve disposed between the radiator and the evaporator and that adjusts the pressure of the refrigerant passing through the evaporator; a storage container provided between the evaporator and the compressor and capable of storing the refrigerant and the lubricating oil, A control unit that controls the state of the refrigerant; and is characterized in that The control unit: when the ambient temperature at which the storage container is installed reaches a reverse temperature at which the density of the lubricating oil and the density of the refrigerant in a liquid state are reversed Reduces the opening degree of the electric valve In this case, even when the ambient temperature reaches a temperature at which the density of the lubricating oil and the density of the refrigerant in a liquid state are reversed, poor lubrication in the compressor is suppressed. The refrigeration cycle system of the second aspect is the refrigeration cycle system of the first aspect, and the control unit can control the frequency of the movement for compression in the compressor to be higher than before the control for adding superheat to the refrigerant flowing into the storage container. The refrigeration cycle system of the third aspect is A refrigeration cycle system from a first perspective or a second perspective, characterized by including a temperature sensor that measures the environmental temperature where the storage container is installed. The refrigeration cycle system of the fourth aspect is A refrigeration cycle system from a third perspective, characterized in that the control unit reduces the opening degree of the electric valve based on the measured value of the temperature sensor. The refrigeration cycle system of the fifth aspect is From the first perspective or the second perspective A refrigeration cycle system, characterized in that the lubricating oil is polyalkylene glycol.

Brief Description of the Drawings

[0006]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Mode for Carrying Out the Invention

[0007] <First Embodiment> (Air Conditioning System 1) FIG. 1 is a diagram showing a schematic configuration example of an air conditioning system 1 to which this embodiment is applied. As shown in the figure, the air conditioning system 1 to which this embodiment is applied includes an air conditioning unit 10 including a refrigerant circuit in which the refrigerant circulates, and a control unit 90 that controls various devices (described later with reference to FIG. 2) included in the air conditioning unit 10. Note that the control unit 90 is connected to each device of the air conditioning unit 10 by wire or wirelessly, and can transmit a control signal to each device. Note that the air conditioning system 1 is an example of the refrigeration cycle system in this embodiment.

[0008] The air conditioning system 1 provides a cooling function for cooling the space by cooling the taken-in air and supplying it as cold air to the space. More specifically, the air conditioning system 1 extracts heat from the air by heat exchange between the refrigerant passing through the heat exchanger (described later with reference to FIG. 2) provided in the air conditioning unit 10 and the air which is an example of the object, thereby cooling the air. Then, the cooled air is supplied as cold air to the space from the air outlet of the indoor unit (described later with reference to FIG. 2) or the like to cool the space. In addition, the air conditioning system 1 provides a heating function for heating a space by heating the intake air and supplying it as warm air to the space. More specifically, the air conditioning system 1 heats the air by giving heat to the air through heat exchange between the refrigerant passing through the heat exchanger included in the air conditioning unit 10 and the air. Then, the heated air is supplied as heating from the air outlet of the indoor unit or the like to the space to heat the space.

[0009] (Control unit 90) The control unit 90 controls various devices included in the air conditioning unit 10 by transmitting control signals to the devices included in the air conditioning unit 10. Additionally, according to the control of various devices by the control unit 90, the state of the refrigerant circulating in the refrigerant circuit of the air conditioning unit 10 is controlled. The control unit 90 performs control, for example, according to the measured value of a temperature sensor (to be described later with reference to FIG. 2) included in the air conditioning unit 10. In addition, the control unit 90 may perform control according to operation inputs such as temperature setting and air volume setting from the user, which are input via an operation panel or a controller that receives operations from the user. Furthermore, control may be performed according to the measured value of a temperature sensor that measures the temperature of the space where cooling / heating is performed. The control unit 90 may acquire information related to operations such as the effective value of the operation with respect to the control value for each device included in the air conditioning unit 10, and perform control according to the acquired information. Also, the amount of cold air / warm air supplied by the air conditioning system 1 to the space, the wind direction, etc. may be controlled.

[0010] (Configuration of the air conditioning unit 10) FIG. 2 is a diagram showing a configuration example of the air conditioning unit 10 according to the present embodiment. As shown in the figure, the air conditioning unit 10 of the air conditioning system 1 according to the present embodiment includes a first refrigerant circuit 31 and a second refrigerant circuit 32. The first refrigerant circuit 31 is arranged across the indoor unit 20 and the outdoor unit 30.

[0011] The indoor unit 20 includes an indoor heat exchanger 21. During heating operation, the indoor heat exchanger 21 functions as a radiator that heats the object of heat exchange by dissipating heat from the refrigerant, heating the air that is the object of heat exchange to produce warm air. During cooling operation, it functions as a cooler that cools the object of heat exchange by absorbing heat with the refrigerant, cooling the air that is the object of heat exchange to produce cold air. Additionally, when functioning as a radiator, since the refrigerant dissipates heat, the refrigerant itself is cooled, and when functioning as a cooler, since the refrigerant absorbs heat, the refrigerant is heated. Note that the indoor heat exchanger 21 is an example of an evaporator that exchanges heat between the passing refrigerant and the object. In addition, the indoor unit 20 may include an indoor fan (not shown) or the like.

[0012] The first refrigerant circuit 31 is connected to the indoor unit 20 by piping having a first shutoff valve 47 and a second shutoff valve 48 respectively. The second refrigerant circuit 32 functions as an assist circuit that enhances the capacity of the first refrigerant circuit 31. In the first refrigerant circuit 31 according to the present embodiment, carbon dioxide is circulated as an example of the refrigerant. In the second refrigerant circuit 32, propane is circulated as an example of the refrigerant.

[0013] The first refrigerant circuit 31 is configured by sequentially connecting a first compressor 41, a first sub-accumulator 42, a four-way switching valve 43, a first outdoor heat exchanger 44, a cascade heat exchanger 45 shared with the second refrigerant circuit 32, a first electric valve 46, a first shutoff valve 47, the indoor heat exchanger 21, a second shutoff valve 48, and a low-pressure receiver 100. The second refrigerant circuit 32 is configured by sequentially connecting a second compressor 51, a second sub-accumulator 52, a cascade heat exchanger 45 shared with the first refrigerant circuit 31, a second outdoor heat exchanger 53, and a second electric valve 54. Note that the first refrigerant circuit 31 and the second refrigerant circuit 32 are not limited to the above-described configuration. For example, the first refrigerant circuit 31 and the second refrigerant circuit 32 may be configured to include a filter, a heat sink, an oil separator, etc. Also, they may be configured to include a pressure sensor / temperature sensor that detects the pressure / temperature of the refrigerant at various locations in the circuit, a high-pressure pressure switch that is a protective detector, etc.

[0014] The first compressor 41 has its discharge side connected to the first port (P1) of the four-way switching valve 43, and its suction side connected to the first sub-accumulator 42. The first sub-accumulator 42 separates the refrigerant into gas and liquid, and only allows the gaseous refrigerant to be sucked into the first compressor 41. The first compressor 41 compresses the sucked gaseous refrigerant and discharges it from the discharge side. Note that the temperature of the discharged refrigerant rises due to the acquisition of compression heat associated with compression (sometimes referred to as "heating compression"). In addition, the first compressor 41 according to the present embodiment is controlled according to a control signal from the control unit 90, for example, the operating frequency, the amount of refrigerant sucked / discharged, etc. are controlled. Note that the "operating frequency" is the frequency of the movement (operation) of the component for compressing the refrigerant, which is performed inside the compressor. Specifically, for example, it is the frequency of the swing of the swing body in a swing compressor, or the frequency of the rotation of the rotating body in a scroll compressor or a rotary compressor. Note that the first compressor 41 is lubricated by the lubricating oil described later. More specifically, lubrication is ensured by the lubricating oil so as not to hinder the movement of the components for compressing the refrigerant described above. Examples of the lubricating oil include polyalkylene glycol (PAG).

[0015] The four-way switching valve 43 includes a first port (P1), a second port (P2), a third port (P3), and a fourth port (P4), and can switch between a state where the first port (P1) and the second port (P2) communicate with each other and the third port (P3) and the fourth port (P4) communicate with each other, and a state where the first port (P1) and the fourth port (P4) communicate with each other and the second port (P2) and the third port (P3) communicate with each other. During the cooling operation, the four-way switching valve 43 is in a state where the first port (P1) and the second port (P2) communicate with each other and the third port (P3) and the fourth port (P4) communicate with each other, and during the heating operation, it switches to a state where the first port (P1) and the fourth port (P4) communicate with each other and the second port (P2) and the third port (P3) communicate with each other.

[0016] The first outdoor heat exchanger 44 performs heat exchange between the refrigerant and the outside air. The first outdoor heat exchanger 44 functions as a cooler during heating operation and as a radiator during cooling operation. The first outdoor heat exchanger 44 may be configured to include an outdoor fan or the like. Note that the first outdoor heat exchanger 44 is an example of an evaporator that exchanges heat between the passing refrigerant and an object. The cascade heat exchanger 45 performs heat exchange between the first refrigerant circuit 31 and the second refrigerant circuit 32. The cascade heat exchanger 45 is, for example, a double-pipe heat exchanger in which two pipes with different diameters are combined in a double structure of inner and outer. Also, the cascade heat exchanger 45 may be another type of heat exchanger such as a plate heat exchanger.

[0017] The first electric valve 46 is configured to include, for example, a valve such as a ball valve and a motor that drives the valve. By the motor adjusting the opening degree of the valve, the pressure of the passing refrigerant is adjusted. More specifically, the first electric valve 46 is provided between the pipe on the cascade heat exchanger 45 side and the pipe on the first shut-off valve 47 side. The refrigerant flowing in from one pipe is throttled and expanded according to the opening degree of the valve to reduce the pressure, and then flowed to the other pipe. Note that the temperature of the refrigerant flowing to the other pipe decreases as the pressure decreases due to throttling expansion (sometimes referred to as "pressure reduction and temperature drop"). The opening degree of the first electric valve 46 is adjusted by driving and controlling each motor according to a control signal from the control unit 90. Note that, as a valve whose opening degree can be controlled by the control unit 90, in addition to the electric valve, an electromagnetic valve that drives the valve by a solenoid or the like may be used.

[0018] The low-pressure receiver 100 is a container capable of storing the inflowing refrigerant. It stores the liquid refrigerant among the inflowing refrigerant and discharges the gaseous refrigerant (sometimes referred to as "gas refrigerant") for recirculation. In the first compressor 41 described above, if the liquid refrigerant is inhaled and compressed, it will cause a decrease in compression efficiency and malfunction. Therefore, the low-pressure receiver 100 separates the inflowing refrigerant into liquid refrigerant and gas refrigerant and stores the liquid refrigerant, thereby suppressing the inhalation of liquid refrigerant into the first compressor 41. The low-pressure receiver 100 is an example of the storage container according to the present embodiment. Here, the outdoor unit 30 according to the present embodiment includes a temperature sensor 101 that measures the temperature of the environment in which the low-pressure receiver 100 is installed (hereinafter sometimes referred to as "ambient temperature"). In FIG. 2, schematically, the state in which the low-pressure receiver 100 and the temperature sensor 101 are arranged side by side inside the outdoor unit 30 is shown, but the arrangement of the temperature sensor 101 is not limited. The temperature sensor 101 may be attached, for example, outside the casing / housing of the outdoor unit 30. Further, as the temperature sensor 101, for example, a thermistor can be used. The low-pressure receiver 100 and the temperature sensor 101 will be described in detail later.

[0019] The second compressor 51, the second sub-accumulator 52, the second outdoor heat exchanger 53, and the second electric valve 54 in the second refrigerant circuit 32 each have the same configuration as the first compressor 41, the first sub-accumulator 42, the first outdoor heat exchanger 44, and the first electric valve 46 in the first refrigerant circuit 31.

[0020] (Flow of refrigerant during cooling operation) An example during the cooling operation will be described for the flow of the refrigerant in the first refrigerant circuit 31 and the second refrigerant circuit 32. During the cooling operation, the four-way switching valve 43 is in a state where the first port (P1) and the second port (P2) are in communication, and the third port (P3) and the fourth port (P4) are in communication.

[0021] In the first refrigerant circuit 31, the refrigerant is first compressed by the first compressor 41. The compressed refrigerant passes through the four-way switching valve 43 and enters the first outdoor heat exchanger 44. The first outdoor heat exchanger 44 functions as a radiator during the cooling operation. The refrigerant that exits the first outdoor heat exchanger 44 enters the cascade heat exchanger 45. During the cooling operation, the cascade heat exchanger 45 functions as a radiator in the first refrigerant circuit 31. The refrigerant that exits the cascade heat exchanger 45 is depressurized when passing through the first motor-operated valve 46 and enters the indoor heat exchanger 21 through the first shutoff valve 47. The indoor heat exchanger 21 functions as a cooler during the cooling operation. The refrigerant that exits the indoor heat exchanger 21 passes through the second shutoff valve 48, the four-way switching valve 43, the low-pressure receiver 100, and the first sub-accumulator 42, and enters the first compressor 41 again.

[0022] The flow of the refrigerant in the second refrigerant circuit 32 will be described. In the second refrigerant circuit 32, the refrigerant is first compressed by the second compressor 51. The compressed refrigerant enters the second outdoor heat exchanger 53. The second outdoor heat exchanger 53 functions as a radiator during the cooling operation. The refrigerant that exits the second outdoor heat exchanger 53 is depressurized when passing through the second motor-operated valve 54 and enters the cascade heat exchanger 45. During the cooling operation, the cascade heat exchanger 45 functions as a cooler in the second refrigerant circuit 32. The refrigerant that exits the cascade heat exchanger 45 passes through the second sub-accumulator 52 and enters the second compressor 51 again.

[0023] The air conditioner 10 according to the present embodiment constitutes a binary circuit by the first refrigerant circuit 31 and the second refrigerant circuit 32. More specifically, in the air conditioner 10 during the cooling operation, the cascade heat exchanger 45 has the function of a radiator in the first refrigerant circuit 31 and the function of a cooler in the second refrigerant circuit 32. In this case, the refrigerant flowing through the first refrigerant circuit 31 is heated and compressed by the first compressor 41, then cooled by the first outdoor heat exchanger 44, further cooled by the cascade heat exchanger 45, depressurized and cooled in temperature by the first motor-operated valve 46, and cools the air in the indoor heat exchanger 21.

[0024] (Refrigerant flow during heating operation) Next, the flow of the refrigerant in the first refrigerant circuit 31 and the second refrigerant circuit 32 during the heating operation will be described. The four-way switching valve 43 is in a state where the first port (P1) and the fourth port (P4) communicate with each other, and the second port (P2) and the third port (P3) communicate with each other during the heating operation.

[0025] In the first refrigerant circuit 31, the refrigerant is first heated and compressed by the first compressor 41. The compressed refrigerant passes through the four-way switching valve 43 and the second shut-off valve 48 and enters the indoor heat exchanger 21. The indoor heat exchanger 21 functions as a radiator during the heating operation. The refrigerant that has exited the indoor heat exchanger 21 enters the indoor unit 20 through the first shut-off valve 47 and is depressurized and cooled when passing through the first electric valve 46. The depressurized refrigerant passes through the cascade heat exchanger 45 and enters the first outdoor heat exchanger 44. The first outdoor heat exchanger 44 functions as a cooler during the heating operation. The refrigerant that has exited the first outdoor heat exchanger 44 passes through the four-way switching valve 43, the low-pressure receiver 100, and the first sub-accumulator 42 and enters the first compressor 41 again. Note that, even during the heating operation, a configuration in which heat exchange is performed by the cascade heat exchanger 45 may be adopted. In this case, the cascade heat exchanger 45 functions as a cooler in the first refrigerant circuit 31.

[0026] (Reservoir of Lubricating Oil) By the way, in the first refrigerant circuit 31, lubricating oil for ensuring lubrication in the first compressor 41 circulates together with the refrigerant. Therefore, the lubricating oil that has flowed into the low-pressure receiver 100 together with the liquid refrigerant is stored therein. If the inflow and storage of the lubricating oil continue without the lubricating oil stored in the low-pressure receiver 100 being taken out, the lubricating oil supplied to the first compressor 41 gradually decreases. Eventually, it becomes difficult to supply oil to the first compressor 41, and lubrication failure may occur in the first compressor 41. For this reason, it is necessary to provide an oil supply mechanism in the low-pressure receiver 100 that can take out the stored lubricating oil and supply it to the first compressor 41. On the other hand, as described above with reference to FIG. 2, it is not preferable for the liquid refrigerant to be sucked into the first compressor 41. Therefore, in the oil supply mechanism, it is good if the lubricating oil can be taken out and the extraction of the liquid refrigerant can be suppressed.

[0027] Here, when the liquid refrigerant and the lubricating oil are immiscible, they separate into an upper layer and a lower layer in the low-pressure receiver 100. And depending on the combination of the liquid refrigerant and the lubricating oil, at a certain temperature (which may be called the "inversion temperature"), their densities reverse, and the upper layer and the lower layer are interchanged.

[0028] FIG. 3 is a diagram showing the relationship between the temperature and density of the liquid refrigerant and the lubricating oil. In FIG. 3, the horizontal axis represents the temperature (°C), and the vertical axis represents the density (kg / m 3 ). In FIG. 3, an example is shown in the case where carbon dioxide is used as the liquid refrigerant and polyalkylene glycol is used as the lubricating oil. As shown in FIG. 3, at temperatures higher than -20°C, the density of the lubricating oil is greater than the density of the liquid refrigerant, and the liquid refrigerant is in the upper layer and the lubricating oil is in the lower layer. On the other hand, at -20°C or lower, the density of the lubricating oil is smaller than the density of the liquid refrigerant, and the lubricating oil is in the upper layer and the liquid refrigerant is in the lower layer. Note that -20°C is an example of the inversion temperature.

[0029] In this specification, "immiscible" does not mean that the liquid refrigerant and the lubricating oil are completely insoluble in each other, but rather refers to the fact that they are hardly soluble in each other to the extent that they separate as layers at least in the low-pressure receiver 100. Also, it is not limited to being immiscible in all temperature ranges, and it is sufficient if they are immiscible at the normally assumed environmental temperature.

[0030] The air conditioning system 1 to which the present embodiment is applied is configured to be able to supply the lubricating oil stored in the low-pressure receiver 100 to the first compressor 41 even when the environmental temperature becomes -20°C or lower.

[0031] Using FIGS. 1 to 4, a configuration example 100-1, 100-2 of the low-pressure receiver 100 and the extraction of the lubricating oil stored in the low-pressure receiver 100 will be described. Hereinafter, the configuration examples 100-1, 100-2 of the low-pressure receiver 100 may be referred to as the "low-pressure receiver 100" without distinction. Also, unless otherwise specified, the cooling operation of the air conditioning unit 10 will be described as an example. FIG. 4 is a diagram for explaining the extraction of the lubricating oil stored in the low-pressure receiver 100. (a) is a schematic diagram of the low-pressure receiver 100-1 provided with an oil return pipe 140, and (b) is a schematic diagram of the low-pressure receiver 100-2 provided with an oil return hole 151 in the middle of the compressor side pipe 150. In the low-pressure receiver 100-2, for the same configuration as the low-pressure receiver 100-1, the common name and reference numerals may be given and the description may be omitted.

[0032] As shown in FIG. 4(a), the low-pressure receiver 100-1 includes a storage unit 110 capable of storing liquid refrigerant, a heat exchanger side pipe 120 for allowing the refrigerant flowing from the indoor heat exchanger 21 side to flow into the storage unit 110, a compressor side pipe 130 for discharging the gas refrigerant in the storage unit 110 to the first compressor 41 side, and an oil return pipe 140 provided at the bottom surface of the storage unit 110. As shown in the "non-reversed state" on the left side of the paper surface of FIG. 4(a), when the environmental temperature of the low-pressure receiver 100-1 is higher than -20°C and the reversal of the liquid refrigerant and the lubricating oil has not occurred, the oil return pipe 140 can suck out the lubricating oil in the lower layer and supply it to the first compressor 41. However, when the environmental temperature is -20°C or lower and the density reversal has occurred, if it is not configured to be able to supply the stored lubricating oil to the first compressor 41, as shown in the "reversed state" on the right side of the paper surface, the lubricating oil becomes the upper layer, making it difficult to suck out by the oil return pipe 140 and difficult to supply to the first compressor 41.

[0033] Further, as shown in FIG. 4(b), the low-pressure receiver 100-2 includes a storage section 110, a heat exchanger side pipe 120, and a compressor side pipe 150 that extends through the vicinity of the bottom surface of the storage section 110. Further, in the compressor side pipe 150, an oil return hole 151 is provided at a portion passing through the vicinity of the bottom surface of the storage section 110. As shown in the "non-reversed state" on the left side of the drawing of FIG. 4(b), when the environmental temperature is higher than -20°C and the reversal of the liquid refrigerant and the lubricating oil does not occur, the low-pressure receiver 100-2 can suck out the lubricating oil in the lower layer through the oil return hole 151 and supply it to the first compressor 41. However, when the environmental temperature is -20°C or lower and the density reversal occurs, if it does not have a configuration capable of supplying the stored lubricating oil to the first compressor 41, as shown in the "reversed state" on the right side of the drawing, the lubricating oil becomes the upper layer, making it difficult to suck out through the oil return hole 151, and it becomes difficult to supply it to the first compressor 41.

[0034] Thus, when it does not have a configuration capable of supplying the lubricating oil stored at an environmental temperature of -20°C or lower to the first compressor 41, when the environmental temperature becomes -20°C or lower, it may become difficult to take out the lubricating oil. Therefore, in the air conditioning system 1 of the present embodiment, even when the environmental temperature becomes -20°C or lower, as a configuration capable of supplying the lubricating oil stored in the low-pressure receiver 100 to the first compressor 41, the control unit 90 can be controlled so that the refrigerant flowing into the low-pressure receiver 100 has superheat when the environmental temperature becomes -20°C or lower.

[0035] The control unit 90 according to the present embodiment, for example, in response to the measured value of the temperature sensor 101 becoming -20°C or lower, reduces the opening degree of the first electric valve 46 to be smaller than before it became -20°C or lower, increases the pressure of the refrigerant passing through the indoor heat exchanger 21, and increases the temperature of the refrigerant. Thereby, superheat can be added to the refrigerant, and the refrigerant flowing into the low-pressure receiver 100 can be made into a gas refrigerant. For example, when the measured value of the temperature sensor 101 reaches -20°C or lower, the control unit 90 increases the operating frequency of the first compressor 41 to be higher than before it reached -20°C or lower, increases the pressure of the refrigerant passing through the indoor heat exchanger 21, and raises the temperature of the refrigerant. Similarly, by such control, superheat can be added to the refrigerant, and the refrigerant flowing into the low-pressure receiver 100 can be made into a gas refrigerant.

[0036] (Switching of control modes) In the present embodiment, the control of various devices included in the air conditioner 10 by the control unit 90 includes a normal control mode and a reverse control mode. When no reverse occurs between the liquid refrigerant and the lubricating oil in the low-pressure receiver 100, the control unit 90 controls various devices in the normal control mode. On the other hand, for example, when the ambient temperature reaches -20°C or lower and reverse between the liquid refrigerant and the lubricating oil may occur, the control unit 90 controls various devices in the reverse control mode. In the reverse control mode, the control unit 90 controls so as to add superheat to the refrigerant flowing into the low-pressure receiver 100. Hereinafter, the switching between the normal control mode and the reverse control mode will be described with reference to FIG. 5.

[0037] FIG. 5 is a flowchart showing an example of switching between the normal control mode and the reverse control mode according to the present embodiment. When the operation of the air conditioner 10 is started, the control unit 90 controls various devices included in the air conditioner 10 in the normal control mode (step S1001). In the normal control mode, the control unit 90 controls various devices included in the air conditioner 10 so that, for example, the outlet temperature of the first outdoor heat exchanger 44 that functions as a radiator during the cooling operation becomes constant.

[0038] Next, the control unit 90 determines whether the measured value of the temperature sensor 101 is equal to or lower than the reverse temperature (step S1002). If the measured value of the temperature sensor 101 is higher than the reverse temperature (NO in step S1002), the process returns to step S1001, and the control unit 90 controls various devices included in the air conditioner 10 in the normal control mode.

[0039] On the other hand, when the measured value of the temperature sensor 101 is equal to or lower than the inversion temperature (YES in step S1002), the control unit 90 switches the operation mode and controls various devices included in the air conditioner unit 10 in the inversion control mode (step S1003). The control unit 90 performs control so that superheat is added to the refrigerant flowing into the low-pressure receiver 100, for example, by reducing the opening degree of the first motor-operated valve 46.

[0040] Next, the control unit 90 determines whether or not the measured value of the temperature sensor 101 is equal to or lower than the inversion temperature (step S1004). When the measured value of the temperature sensor 101 is equal to or lower than the inversion temperature (YES in step S1004), the process returns to step S1003, and the control unit 90 controls various devices included in the air conditioner unit 10 in the inversion control mode. On the other hand, when the measured value of the temperature sensor 101 is higher than the inversion temperature (NO in step S1004), the control unit 90 switches the operation mode and controls various devices included in the air conditioner unit 10 in the normal control mode (step S1005).

[0041] As described above, when the measured value of the temperature sensor 101 becomes equal to or lower than the inversion temperature, the control unit 90 according to the present embodiment performs control so that superheat is added to the refrigerant flowing into the low-pressure receiver 100. As a result, since the gas refrigerant flows into the low-pressure receiver 100, it becomes difficult for the liquid refrigerant to be stored, and even when the measured value of the temperature sensor 101 is equal to or lower than the inversion temperature, it becomes possible to suck out the lubricating oil through the oil return pipe 140 and the oil return hole 151.

[0042] In FIG. 5, the condition for switching the control mode is set based on the measured value of the temperature sensor 101, but the present invention is not limited to this. For example, the control unit 90 may switch the control mode based on the low-pressure of the refrigerant, the suction temperature, or the like. Further, the above-described control is an example of control for adding superheat to the refrigerant flowing into the low-pressure receiver 100, and other control may be performed.

[0043] <Second Embodiment> The second embodiment has an oil suction mechanism capable of sucking out lubricating oil stored in the low-pressure receiver 100 and supplying it to the first compressor 41 even when the environmental temperature is -20°C or lower, and even when the liquid refrigerant forms a layer below the lubricating oil in the low-pressure receiver 100, so that the lubricating oil can be supplied to the first compressor 41.

[0044] For example, the outdoor unit 30 according to the second embodiment has a configuration capable of sucking out both the liquid refrigerant and the lubricating oil in the low-pressure receiver 100. More specifically, for example, in the low-pressure receiver 100-2 shown in FIG. 4(b), on the compressor-side pipe 150, there are a plurality of holes with different heights from the bottom surface of the storage portion 110, including an oil return hole 151, and by sucking out from these plurality of holes, it is possible to suck out the liquid refrigerant and the lubricating oil. The sucked liquid refrigerant and lubricating oil perform heat exchange in the air conditioning system 1 between at least a high-temperature portion having a temperature higher than -20°C, more preferably, a high-temperature portion having a temperature higher than the evaporation temperature of the sucked liquid refrigerant, and are supplied to the first compressor 41. Thereby, lubricating oil is supplied to the first compressor 41, and the suction of the liquid refrigerant in the first compressor 41 can be suppressed.

[0045] <The third embodiment> The third embodiment has a configuration capable of raising the temperature of the liquid refrigerant and the lubricating oil stored in the low-pressure receiver 100 and eliminating reverse rotation, so that the lubricating oil stored in the low-pressure receiver 100 can be supplied to the first compressor 41 even when the environmental temperature is -20°C or lower.

[0046] For example, the outdoor unit 30 according to the third embodiment has a heater capable of raising the temperature of the liquid stored inside the low-pressure receiver 100. The heater is provided, for example, so as to be close to or in contact with the side portion or the bottom surface of the storage portion 110 of the low-pressure receiver 100. The heater is turned on according to the control of the control unit 90, and heats and raises the temperature of the liquid stored inside the low-pressure receiver 100 until at least the inversion temperature is exceeded. In this case, the control unit 90 may turn on the heater, for example, in response to the measured value of the temperature sensor 101 becoming -20°C or lower. Thereby, it becomes possible to raise the temperature of the liquid refrigerant and the lubricating oil stored in the low-pressure receiver 100 and eliminate the inversion.

[0047] Also, for example, the outdoor unit 30 according to the third embodiment may heat-exchange the refrigerant compressed by the first compressor 41 with the liquid refrigerant stored in the low-pressure receiver 100 or the low-pressure receiver 100 to raise the temperature of the stored liquid refrigerant. More specifically, the pipe from the first compressor 41 to the four-way switching valve 43 is extended, and the extended pipe is brought into contact with or wound around the storage portion 110 of the low-pressure receiver 100 so that heat exchange is performed between the refrigerant compressed by the first compressor 41 and the low-pressure receiver 100. Also, a part of the pipe may be inserted into the storage portion 110 so that the extended pipe passes through the inside of the storage portion 110 of the low-pressure receiver 100, and heat exchange may be performed between the refrigerant compressed by the first compressor 41 and the low-pressure receiver 100. Furthermore, for example, the outdoor unit 30 according to the third embodiment may heat-exchange the low-pressure receiver 100 or the liquid refrigerant stored in the low-pressure receiver 100 with the exhaust heat from the first compressor 41 or the second compressor 51 to raise the temperature of the stored liquid refrigerant. With these configurations as well, the heat acquired by the liquid refrigerant due to heat exchange can be used to raise the temperature of the liquid refrigerant and the lubricating oil stored in the low-pressure receiver 100. When heat-exchanging the refrigerant compressed by the first compressor 41 with the liquid refrigerant stored in the low-pressure receiver 100 or the low-pressure receiver 100, a temperature sensor such as a thermistor may be provided inside the storage portion 110 of the low-pressure receiver 100 in order to enable measurement of the temperature of the liquid refrigerant stored in the low-pressure receiver 100.

[0048] <Others> In the above-described embodiments, the case where the refrigeration cycle system is applied to the air conditioning system 1 has been described as an example, but the application range is not limited. By utilizing the heat absorption in the cooler, it may be applied to various devices for cooling an object, such as a refrigerated warehouse, a refrigerator, an ice maker, etc. Also, by utilizing the heat dissipation in the radiator, it may be applied to various devices for heating an object, such as a heating appliance, a water heater, a water supply heater, etc.

[0049] Also, as an example of the refrigerant circulating in each refrigerant circuit, carbon dioxide and propane have been exemplified, but the type of refrigerant is not limited. For example, in the first refrigerant circuit 31, a mixed refrigerant in which carbon dioxide and other components are mixed may be used, or a single refrigerant or a mixed refrigerant not containing carbon dioxide may be used. However, it is assumed that the refrigerant circulating in the first refrigerant circuit 31 is immiscible with the lubricating oil of the first compressor 41. It should be noted that since the inversion temperature is determined according to the combination of the refrigerant and the lubricating oil, it is not limited to the -20°C described above.

[0050] Furthermore, in the above-described embodiments, an example in which the liquid refrigerant is in the upper layer and the lubricating oil is in the lower layer at a temperature higher than the inversion temperature has been described. However, depending on the combination of the refrigerant and the lubricating oil, conversely, an example in which the lubricating oil is in the upper layer and the liquid refrigerant is in the lower layer at a temperature higher than the inversion temperature may also occur. Also in this case, by applying the above-described embodiments, a configuration in which the lubricating oil can be supplied to the first compressor 41 even at a temperature below the inversion temperature can be achieved.

[0051] Furthermore, although the air conditioning unit 10 has been described as constituting a binary circuit, for example, it may be configured as a single unit circuit without providing the second refrigerant circuit 32 and the cascade heat exchanger 45. It should be noted that the configuration of each refrigerant circuit is not limited to the above-described one, and other configurations may be adopted.

[0052] Also, in the above-described embodiment, an example using the first motor-operated valve 46 has been described in order to enable the control of the opening degree by the control unit 90. When the control by the control unit 90 is not performed, a capillary tube, an orifice plate, or the like may be used instead of the first motor-operated valve 46.

[0053] Although the embodiments have been described above, it will be understood that various changes in form and detail are possible without departing from the gist and scope of the claims. For example, a part of each configuration may be omitted, or other functions may be added to each configuration. Also, for example, the configurations included in one configuration example and the configurations included in another configuration example may be interchanged, or the configurations included in one configuration example may be added to another configuration example.

Explanation of Reference Numerals

[0054] 1...Air conditioning system, 10...Air conditioning unit, 21...Indoor heat exchanger, 31...First refrigerant circuit, 32...Second refrigerant circuit, 90...Control unit, 100...Low-pressure receiver, 101...Temperature sensor

Claims

1. A compressor lubricated by lubricating oil and compressing a refrigerant, a radiator that allows the refrigerant compressed by the compressor to pass through, extracts heat from the passing refrigerant, and dissipates heat, an evaporator that allows the refrigerant compressed by the compressor to pass through after heat dissipation and decompression, and exchanges heat between the passing refrigerant and an object, an electric valve disposed between the radiator and the evaporator and adjusting the pressure of the refrigerant passing through the evaporator, a storage container provided between the evaporator and the compressor and capable of storing the refrigerant and the lubricating oil, a control unit for controlling the state of the refrigerant, The control unit reduces the opening degree of the electric valve when the environmental temperature at which the storage container is installed becomes a reversal temperature at which the density of the lubricating oil and the density of the refrigerant in the liquid state are reversed, and controls the refrigerant flowing into the storage container to become a gas refrigerant. A refrigeration cycle system characterized by this.

2. The control unit is capable of controlling the frequency of the movement for compression in the compressor to be greater than before the control for adding superheat as control for adding superheat to the refrigerant flowing into the storage container. The refrigeration cycle system according to Claim 1, characterized by this.

3. The refrigeration cycle system according to Claim 1 or 2, characterized by including a temperature sensor that measures the environmental temperature at which the storage container is installed.

4. The control unit reduces the opening degree of the electric valve based on the measured value of the temperature sensor. The refrigeration cycle system according to Claim 3, characterized by this.

5. The lubricating oil is polyalkylene glycol. The refrigeration cycle system according to Claim 1 or 2, characterized by this.

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