Refrigeration cycle system

Abstract

Even if the ambient temperature becomes a temperature at which the density of the lubricating oil and the density of the refrigerant in the liquid state are reversed, poor lubrication in the compressor can be suppressed. A refrigeration cycle system is provided with: a compressor which is lubricated by a lubricating oil and which compresses a refrigerant; an evaporator through which the refrigerant compressed by the compressor and subjected to heat dissipation and pressure reduction passes and which exchanges heat with an object; and a storage container which is provided between the evaporator and the compressor, can store the refrigerant and the lubricating oil, and can supply the lubricating oil stored in the storage container to the compressor even if the ambient temperature in which the storage container is provided becomes an inversion temperature at which the density of the lubricating oil and the density of the refrigerant in a liquid state invert.

Description

Technical Field

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

[0002] In Patent Document 1, a liquid return prevention device for a refrigeration apparatus is described. In this refrigeration apparatus, a low-pressure storage tank is disposed between a compressor and an evaporator in a refrigerant circulation system. Regarding the liquid return prevention device, in the refrigeration apparatus, an oil return opening for returning lubricating oil accumulated in the low-pressure storage tank to the compressor is formed in a refrigerant pipe on the compressor side of the low-pressure storage tank, and a communication pipe for allowing liquid refrigerant accumulated in the low-pressure storage tank to flow down to the evaporator is provided between the bottom surface of the low-pressure storage tank and the evaporator when the compressor stops operating.

[0003] Prior Art Documents

[0004] Patent Documents

[0005] Patent Document 1: Japanese Patent Laid-Open No. 63-172870 Summary of the Invention

[0006] Problems to be Solved by the Invention

[0007] For example, in a refrigeration cycle system, like the low-pressure storage tank described in Patent Document 1, a storage container capable of storing refrigerant in a liquid state (sometimes referred to as "liquid refrigerant") may be provided in a refrigerant circulation path. In such a storage container, lubricating oil that circulates in the path together with the refrigerant is also stored to ensure lubrication in the compressor. And, when the liquid refrigerant and the lubricating oil are immiscible, they separate into an upper layer and a lower layer in the storage container, and the lubricating oil is supplied to the compressor through an oil supply mechanism such as the oil return opening of Patent Document 1.

[0008] Here, depending on the combination of the liquid refrigerant and the lubricating oil, their densities reverse at a certain temperature, and the upper layer and the lower layer are swapped. If the upper layer and the lower layer are swapped, it becomes difficult to supply oil to the compressor in the conventional oil supply mechanism, resulting in poor lubrication in the compressor.

[0009] The present disclosure provides a refrigeration cycle system that can suppress 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 liquid-state refrigerant reverse.

[0010] Means for Solving the Problems

[0011] The refrigeration cycle system of the first aspect is characterized in that the refrigeration cycle system includes: a compressor lubricated by lubricating oil that compresses a refrigerant; an evaporator through which the refrigerant that has been cooled and depressurized after being compressed by the compressor passes, and the passing refrigerant exchanges heat with an object; and a storage container disposed between the evaporator and the compressor that can store the refrigerant and the lubricating oil, and can supply the lubricating oil stored in the storage container to the compressor even when the ambient temperature at the location of the storage container reaches the inversion temperature at which the density of the lubricating oil and the density of the refrigerant in the liquid state are reversed. In this case, even when the ambient temperature reaches the temperature at which the density of the lubricating oil and the density of the refrigerant in the liquid state are reversed, poor lubrication in the compressor can be suppressed.

[0012] The refrigeration cycle system of the second aspect is characterized in that, based on the refrigeration cycle system of the first aspect, the refrigeration cycle system includes a control unit that controls the state of the refrigerant, and the control unit can control in such a manner that the refrigerant flowing into the storage container is superheated when the ambient temperature reaches the inversion temperature. In this case, compared with the case where no superheat control is applied, the lubricating oil is more easily supplied to the compressor.

[0013] The refrigeration cycle system of the third aspect is characterized in that, based on the refrigeration cycle system of the second aspect, the refrigeration cycle system includes an electric valve that adjusts the pressure of the refrigerant passing through the evaporator. As control for superheating the refrigerant flowing into the storage container, the control unit can control the opening degree of the electric valve to be smaller than before the superheat control.

[0014] The refrigeration cycle system of the fourth aspect is characterized in that, based on the refrigeration cycle system of the second aspect, as control for superheating the refrigerant flowing into the storage container, the control unit can control the frequency of the compression motion in the compressor to be higher than before the superheat control.

[0015] The refrigeration cycle system of the fifth aspect is characterized in that, based on the refrigeration cycle system of any one of the first to fourth aspects, the storage container has an oil suction mechanism that can suck out and supply the lubricating oil to the compressor even when the ambient temperature reaches the inversion temperature and the refrigerant in the liquid state in the storage container forms a layer below the lubricating oil. In this case, even when the lubricating oil layer becomes the lower layer, poor lubrication in the compressor can be suppressed.

[0016] The refrigeration cycle system of the sixth aspect is characterized in that, based on the refrigeration cycle system of the fifth aspect, the oil suction mechanism has a plurality of holes on the pipe with different heights from the bottom surface of the storage container, wherein the pipe sucks the lubricating oil in the storage container, and through the plurality of holes, the refrigerant and the lubricating oil in the liquid state can be sucked out. After the sucked refrigerant and lubricating oil in the liquid state are heat-exchanged with a high-temperature part in the refrigeration cycle system whose temperature is higher than the inversion temperature, they are supplied to the compressor. In this case, compared with the case where there is no heat exchange with the high-temperature part, the load applied to the compressor due to the inflow of the refrigerant in the liquid state can be reduced.

[0017] The refrigeration cycle system of the seventh aspect is characterized in that, based on the refrigeration cycle system of any one of the first to sixth aspects, even when the ambient temperature becomes the inversion temperature, the refrigerant and the lubricating oil in the liquid state stored in the storage container can be heated up to eliminate the density inversion. In this case, compared with the case where there is no heating, the lubricating oil is more easily supplied to the compressor.

[0018] The refrigeration cycle system of the eighth aspect is characterized in that, based on the refrigeration cycle system of any one of the first to seventh aspects, the refrigeration cycle system has a heater, and the heater is installed on the storage container and can heat up the refrigerant and the lubricating oil in the liquid state stored in the storage container.

[0019] The refrigeration cycle system of the ninth aspect is characterized in that, based on the refrigeration cycle system of any one of the first to eighth aspects, the refrigeration cycle system is equipped with a radiator, and the radiator allows the refrigerant compressed by the compressor to pass through, extracts heat from the passing refrigerant and dissipates heat, and can perform heat exchange between the storage container or the refrigerant in the liquid state in the storage container and the refrigerant passing through the radiator. In this case, compared with the case where there is no radiator, the refrigeration capacity of the refrigeration cycle system is improved.

[0020] The refrigeration cycle system of the tenth aspect is characterized in that, based on the refrigeration cycle system of any one of the first to ninth aspects, heat exchange can be performed between the storage container or the refrigerant in the liquid state in the storage container and the waste heat of the compressor. In this case, the waste heat of the compressor can be reused.

[0021] The refrigeration cycle system of the eleventh aspect is characterized in that, based on the refrigeration cycle system of any one of the first to tenth aspects, the lubricating oil is polyalkylene glycol. Description of the Drawings

[0022] Figure 1 This is a diagram showing a schematic configuration example of the air conditioning system to which the present embodiment is applied.

[0023] Figure 2 This is a diagram showing a configuration example of the air conditioning unit of the present embodiment.

[0024] Figure 3 This is a diagram showing the relationship between the temperature and density of the liquid refrigerant and lubricating oil.

[0025] Figure 4 This is a diagram for explaining the suction of the lubricating oil stored in the low-pressure storage tank. (a) is a schematic diagram of the low-pressure storage tank equipped with a return oil pipe, and (b) is a schematic diagram of the low-pressure storage tank equipped with an oil return hole in the middle of the compressor side piping.

[0026] Figure 5 This is a flowchart showing an example of the switching between the normal control mode and the control mode during inversion of the present embodiment. Detailed Embodiment

[0027] <First Embodiment>

[0028] (Air Conditioning System 1)

[0029] Figure 1 This is a diagram showing a schematic configuration example of the air conditioning system 1 to which the present embodiment is applied.

[0030] As shown in the figure, the air conditioning system 1 to which the present embodiment is applied includes: an air conditioning unit 10 including a refrigerant circuit through which a refrigerant circulates; and a control unit 90 that controls various devices included in the air conditioning unit 10 (to be described later). In addition, the control unit 90 is connected to each device of the air conditioning unit 10 by wire or wirelessly, and can send control signals to each device. Figure 2 In addition, the air conditioning system 1 is an example of the refrigeration cycle system in the present embodiment.

[0031] In addition, the air conditioning system 1 is an example of the refrigeration cycle system in the present embodiment.

[0032] The air conditioning system 1 provides a refrigeration 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 uses the heat exchange between the refrigerant passing through the heat exchanger (to be described later) included in the air conditioning unit 10 and the air as an example of the object to take out heat from the air, thereby cooling the air. Then, the cooled air is supplied as cold air from the air outlet of the indoor unit (to be described later) to the space, thereby cooling the space. Figure 2 In addition, the air conditioning system 1 is an example of the refrigeration cycle system in the present embodiment. Figure 2 In addition, the air conditioning system 1 is an example of the refrigeration cycle system in the present embodiment.

[0033] 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 performing heat exchange between the refrigerant passing through the heat exchanger provided in the air conditioning unit 10 and the air, thereby heating the air. Then, the heated air is supplied as warm air to the space from the air outlet of the indoor unit or the like, thereby heating the space.

[0034] (Control unit 90)

[0035] The control unit 90 controls various devices included in the air conditioning unit 10 by sending control signals to each device provided in the air conditioning unit 10. In addition, 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 controls, for example, based on the measured value of the temperature sensor (used Figure 2 described later) provided in the air conditioning unit 10.

[0036] In addition, the control unit 90 may also perform control based on operation inputs from the user, such as temperature setting or air volume setting, input via an operation panel or a controller that accepts operations from the user. And it may also perform control based on the measured value of the temperature sensor that measures the temperature of the space for cooling / heating.

[0037] The control unit 90 may also 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 based on the acquired information. In addition, the air conditioning system 1 may also control the amount, direction, etc. of the cold air / warm air supplied to the space.

[0038] (Structure of the air conditioning unit 10)

[0039] Figure 2 is a diagram showing a configuration example of the air conditioning unit 10 of the present embodiment.

[0040] As shown in the figure, the air conditioning unit 10 of the air conditioning system 1 of the present embodiment includes a first refrigerant circuit 31 and a second refrigerant circuit 32. The first refrigerant circuit 31 is arranged throughout the indoor unit 20 and the outdoor unit 30.

[0041] The indoor unit 20 includes an indoor heat exchanger 21.

[0042] The indoor heat exchanger 21 functions as a radiator that heats the object of heat exchange by dissipating heat from the refrigerant during the heating operation, heating the air that is the object of heat exchange to form warm air. Further, during the cooling operation, it functions as a cooler that cools the object of heat exchange by absorbing heat from the refrigerant, cooling the air that is the object of heat exchange to form cold air. In other words, when functioning as a radiator, the refrigerant dissipates heat, so the refrigerant itself is cooled, and when functioning as a cooler, the refrigerant absorbs heat, so the refrigerant is heated. Further, the indoor heat exchanger 21 is an example of an evaporator that causes the refrigerant passing therethrough to exchange heat with an object.

[0043] In addition, the indoor unit 20 may also include an indoor fan (not shown) or the like.

[0044] The first refrigerant circuit 31 is connected to the indoor unit 20 through pipes respectively having a first stop valve 47 and a second stop valve 48. The second refrigerant circuit 32 functions as an auxiliary circuit for enhancing the capacity of the first refrigerant circuit 31.

[0045] In the present embodiment, the first refrigerant circuit 31 circulates carbon dioxide as an example of a refrigerant. The second refrigerant circuit 32 circulates propane as an example of a refrigerant.

[0046] The first refrigerant circuit 31 is constituted by sequentially connecting a first compressor 41, a first sub-liquid receiver 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 stop valve 47, an indoor heat exchanger 21, a second stop valve 48, and a low-pressure storage tank 100.

[0047] The second refrigerant circuit 32 is constituted by sequentially connecting a second compressor 51, a second sub-liquid receiver 52, the cascade heat exchanger 45 shared with the first refrigerant circuit 31, a second outdoor heat exchanger 53, and a second electric valve 54.

[0048] Further, the first refrigerant circuit 31 and the second refrigerant circuit 32 are not limited to the above structures. For example, the first refrigerant circuit 31 and the second refrigerant circuit 32 may also be configured to include a filter, a heat sink, an oil separator, etc. Further, they may also 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 as a protective detector, etc.

[0049] The discharge side of the first compressor 41 is connected to the first port (P1) of the four-way switching valve 43, and its suction side is connected to the first auxiliary accumulator 42. The first auxiliary 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. In addition, the discharged refrigerant rises in temperature due to the compression heat accompanying the compression (sometimes referred to as "heating compression").

[0050] In addition, regarding the first compressor 41 of the present embodiment, according to the control signal from the control unit 90, for example, the operating frequency, the amount of refrigerant sucked / discharged, etc. are controlled. In addition, the "operating frequency" refers to the frequency of the movement (action) of the component for compressing the refrigerant inside the compressor. Specifically, for example, it is the swing frequency of the swing body in a swing compressor, or the rotation frequency of the rotating body in a scroll compressor or a rotary compressor.

[0051] Furthermore, the first compressor 41 is lubricated by the lubricating oil described later. More specifically, in order not to hinder the movement of the above-mentioned components for compressing the refrigerant, lubrication is ensured by the lubricating oil. As the lubricating oil, for example, polyalkylene glycol (PAG) can be cited.

[0052] The four-way switching valve 43 has a first port (P1), a second port (P2), a third port (P3), and a fourth port (P4), and can switch between the following states: a state where the first port (P1) communicates with the second port (P2) and the third port (P3) communicates with the fourth port (P4); and a state where the first port (P1) communicates with the fourth port (P4) and the second port (P2) communicates with the third port (P3).

[0053] During the refrigeration operation, the four-way switching valve 43 is in a state where the first port (P1) communicates with the second port (P2) and the third port (P3) communicates with the fourth port (P4), and during the heating operation, it switches to a state where the first port (P1) communicates with the fourth port (P4) and the second port (P2) communicates with the third port (P3).

[0054] The first outdoor heat exchanger 44 exchanges heat between the refrigerant and the external air. The first outdoor heat exchanger 44 functions as a cooler during the heating operation and as a radiator during the refrigeration operation. The first outdoor heat exchanger 44 may also be configured to include an outdoor fan, etc. In addition, the first outdoor heat exchanger 44 is an example of an evaporator that exchanges heat between the refrigerant passing through it and the object.

[0055] The cascade heat exchanger 45 exchanges heat 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 into a double layer on the inner and outer sides. In addition, the cascade heat exchanger 45 may also be a heat exchanger in other forms such as a plate heat exchanger.

[0056] The first electric valve 46 is configured to include, for example, a valve such as a ball valve and a motor for driving the valve. The motor adjusts the opening degree of the valve, thereby adjusting the pressure of the flowing refrigerant. More specifically, the first electric valve 46 is provided between the pipe on the side of the cascade heat exchanger 45 and the pipe on the side of the first stop valve 47. The refrigerant flowing in from one pipe is throttled and expanded corresponding to the opening degree of the valve to reduce the pressure, and the refrigerant is made to flow to the other pipe. It should be noted that the refrigerant flowing to the other pipe decreases in temperature due to the pressure reduction caused by the throttling expansion (sometimes referred to as "pressure reduction and temperature reduction").

[0057] 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. In addition, as a valve whose opening degree can be controlled by the control unit 90, in addition to the electric valve, an electromagnetic valve in which the valve is driven by a solenoid can also be used.

[0058] The low-pressure storage tank 100 is a container capable of storing the flowing refrigerant. It stores the liquid refrigerant in the flowing refrigerant and discharges the gaseous refrigerant (sometimes referred to as "gaseous refrigerant") and makes it circulate again. In the above-mentioned first compressor 41, if the liquid refrigerant is sucked in and compressed, it will cause a reduction in compression efficiency or poor operation. Therefore, the low-pressure storage tank 100 divides the flowing refrigerant into liquid refrigerant and gaseous refrigerant and stores the liquid refrigerant, thereby suppressing the liquid refrigerant from being sucked into the first compressor 41. The low-pressure storage tank 100 is an example of the storage container in this embodiment.

[0059] Here, the outdoor unit 30 of this embodiment is equipped with a temperature sensor 101 for measuring the temperature of the environment where the low-pressure storage tank 100 is installed (hereinafter, sometimes referred to as "ambient temperature"). In addition, in Figure 2 it schematically shows the situation where the low-pressure storage tank 100 and the temperature sensor 101 are arranged horizontally side by side inside the outdoor unit 30, but the arrangement of the temperature sensor 101 is not limited. The temperature sensor 101 can also be installed, for example, outside the housing / case of the outdoor unit 30. In addition, as the temperature sensor 101, a thermistor can be used, for example. The low-pressure storage tank 100 and the temperature sensor 101 will be described in detail later.

[0060] The second compressor 51, the second auxiliary accumulator 52, the second outdoor heat exchanger 53, and the second electric valve 54 in the second refrigerant circuit 32 respectively have the same structure as the first compressor 41, the first auxiliary accumulator 42, the first outdoor heat exchanger 44, and the first electric valve 46 in the first refrigerant circuit 31.

[0061] (Flow of refrigerant during refrigeration operation)

[0062] Regarding the flow of refrigerant in the first refrigerant circuit 31 and the second refrigerant circuit 32, an example during refrigeration operation will be described. The four-way switching valve 43 is in a state where the first port (P1) is connected to the second port (P2) and the third port (P3) is connected to the fourth port (P4) during refrigeration operation.

[0063] 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 refrigeration operation. The refrigerant flowing out of the first outdoor heat exchanger 44 enters the cascade heat exchanger 45. During refrigeration operation, the cascade heat exchanger 45 functions as a radiator in the first refrigerant circuit 31. The refrigerant flowing out of the cascade heat exchanger 45 is decompressed when passing through the first electric valve 46 and enters the indoor heat exchanger 21 through the first stop valve 47. The indoor heat exchanger 21 functions as a cooler during refrigeration operation. The refrigerant flowing out of the indoor heat exchanger 21 passes through the second stop valve 48, the four-way switching valve 43, the low-pressure storage tank 100, the first auxiliary accumulator 42, and re-enters the first compressor 41.

[0064] The flow of 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 refrigeration operation. The refrigerant flowing out of the second outdoor heat exchanger 53 is decompressed when passing through the second electric valve 54 and enters the cascade heat exchanger 45. During refrigeration operation, the cascade heat exchanger 45 functions as a cooler in the second refrigerant circuit 32. The refrigerant flowing out of the cascade heat exchanger 45 passes through the second auxiliary accumulator 52 and re-enters the second compressor 51.

[0065] The air conditioning unit 10 of the present embodiment constitutes a binary circuit based on the first refrigerant circuit 31 and the second refrigerant circuit 32. More specifically, in the air conditioning unit 10 during refrigeration operation, the cascade heat exchanger 45 functions as a radiator in the first refrigerant circuit 31 and as a cooler in the second refrigerant circuit 32. In this case, the refrigerant flowing in the first refrigerant circuit 31 is heated and compressed by the first compressor 41, cooled by the first outdoor heat exchanger 44, further cooled by the cascade heat exchanger 45, and decompressed and cooled by the first electric valve 46, and then cools the air in the indoor heat exchanger 21.

[0066] (Flow of refrigerant during heating operation)

[0067] Next, the flow of the refrigerant in the first refrigerant circuit 31 and the second refrigerant circuit 32 during heating operation will be described. The four-way switching valve 43 is in a state where the first port (P1) is connected to the fourth port (P4) and the second port (P2) is connected to the third port (P3) during heating operation.

[0068] In the first refrigerant circuit 31, the refrigerant is first heated and compressed by the first compressor 41. The compressed refrigerant enters the indoor heat exchanger 21 through the four-way switching valve 43 and the second stop valve 48. The indoor heat exchanger 21 functions as a radiator during heating operation. The refrigerant flowing out of the indoor heat exchanger 21 enters the indoor unit 20 through the first stop valve 47 and is decompressed and cooled when passing through the first electric valve 46. The decompressed 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 heating operation. The refrigerant flowing out of the first outdoor heat exchanger 44 passes through the four-way switching valve 43, the low-pressure storage tank 100, and the first sub-liquid storage 42, and then enters the first compressor 41 again.

[0069] Alternatively, it can be configured such that heat exchange based on the cascade heat exchanger 45 is also performed during heating operation. In this case, the cascade heat exchanger 45 functions as a cooler in the first refrigerant circuit 31.

[0070] (Storage of lubricating oil)

[0071] In addition, in the first refrigerant circuit 31, the lubricating oil for ensuring lubrication in the first compressor 41 circulates together with the refrigerant. Therefore, the lubricating oil flowing in together with the liquid refrigerant is stored in the low-pressure storage tank 100.

[0072] If the lubricating oil stored in the low-pressure storage tank 100 is not taken out and the inflow and storage of the lubricating oil continue, the lubricating oil supplied to the first compressor 41 will gradually decrease. Moreover, ultimately, it becomes difficult to supply oil to the first compressor 41, and lubrication failure may occur in the first compressor 41. Therefore, it is necessary to provide an oil supply mechanism in the low-pressure storage tank 100 that can take out the stored lubricating oil and supply it to the first compressor 41. On the other hand, as described above, it is not preferable to suck the liquid refrigerant into the first compressor 41. Therefore, in the oil supply mechanism, it is preferably capable of taking out the lubricating oil and suppressing the taking out of the liquid refrigerant. Figure 2 As described above, it is not preferable to suck the liquid refrigerant into the first compressor 41. Therefore, in the oil supply mechanism, it is preferably capable of taking out the lubricating oil and suppressing the taking out of the liquid refrigerant.

[0073] Here, when the liquid refrigerant and the lubricating oil are immiscible, they are separated into an upper layer and a lower layer in the low-pressure storage tank 100. And, depending on the combination of the liquid refrigerant and the lubricating oil, their densities are reversed at a certain temperature (sometimes called the "inversion temperature"), and the upper layer and the lower layer are swapped.

[0074] Figure 3 is a diagram showing the relationship between the temperature and density of the liquid refrigerant and the lubricating oil. In Figure 3 it, the horizontal axis represents the temperature (°C), and the vertical axis represents the density (kg / m 3 ). In Figure 3 it, an example of the case of using carbon dioxide as the liquid refrigerant and using polyalkylene glycol as the lubricating oil is shown.

[0075] As Figure 3 shown, at temperatures higher than -20°C, the density of the lubricating oil is greater than the density of the liquid refrigerant, the liquid refrigerant is the upper layer, and the lubricating oil is the lower layer. On the other hand, below -20°C, the density of the lubricating oil is smaller than the density of the liquid refrigerant, the lubricating oil is the upper layer, and the liquid refrigerant is the lower layer. In addition, -20°C is an example of the inversion temperature.

[0076] In this specification, "immiscible" does not limit to the liquid refrigerant and the lubricating oil being completely immiscible with each other, but means being mutually hardly soluble to the extent of being separated into layers in at least the low-pressure storage tank 100. In addition, it is not limited to being immiscible in the entire temperature range, as long as it is immiscible at the ambient temperature generally assumed.

[0077] The air-conditioning system 1 applying this embodiment has a structure capable of supplying the lubricating oil stored in the low-pressure storage tank 100 to the first compressor 41 even when the ambient temperature is below -20°C.

[0078] Using Figures 1 to 4, the configuration examples 100-1 and 100-2 of the low-pressure storage tank 100 and the extraction of the lubricating oil stored in the low-pressure storage tank 100 will be described. Hereinafter, the configuration examples 100-1 and 100-2 of the low-pressure storage tank 100 may be referred to as the "low-pressure storage tank 100" without distinction. In addition, unless otherwise specified, the case of the refrigeration operation of the air-conditioning unit 10 will be taken as an example for description.

[0079] Figure 4 FIG. is a diagram for explaining the extraction of the lubricating oil stored in the low-pressure storage tank 100. (a) is a schematic diagram of the low-pressure storage tank 100-1 having an oil return pipe 140, and (b) is a schematic diagram of the low-pressure storage tank 100-2 having an oil return hole 151 in the middle of the compressor-side pipe 150. In addition, in the low-pressure storage tank 100-2, for the same structure as that of the low-pressure storage tank 100-1, the same names and reference numerals may be used and the description may be omitted.

[0080] As Figure 4 shown in FIG. (a), the low-pressure storage tank 100-1 includes: a storage portion 110 capable of storing a 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 portion 110; a compressor-side pipe 130 for discharging the gaseous refrigerant in the storage portion 110 to the first compressor 41 side; and an oil return pipe 140 provided at the bottom surface of the storage portion 110.

[0081] As Figure 4 shown in the "unreversed state" on the left side of the paper surface of FIG. (a), when the ambient temperature is higher than -20°C and the liquid refrigerant and the lubricating oil do not reverse, the low-pressure storage tank 100-1 can suck out the lower-layer lubricating oil through the oil return pipe 140 and supply it to the first compressor 41. However, in the case where the ambient temperature is -20°C or lower and density reversal occurs, if there is no structure capable of supplying the stored lubricating oil to the first compressor 41, since the lubricating oil becomes the upper layer as shown in the "reversed state" on the right side of the paper surface, the suction through the oil return pipe 140 becomes difficult, and thus the supply to the first compressor 41 becomes difficult.

[0082] In addition, as Figure 4 shown in FIG. (b), the low-pressure storage tank 100-2 includes: a storage portion 110; a heat exchanger-side pipe 120; and a compressor-side pipe 150 extending so as to pass near the bottom surface of the storage portion 110. In addition, in the compressor-side pipe 150, an oil return hole 151 is provided at a portion passing near the bottom surface of the storage portion 110.

[0083] As Figure 4As shown by the "non-inverted state" on the left side of the paper surface in (b) of, the low-pressure storage tank 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 when the ambient temperature is higher than -20°C and no inversion of the liquid refrigerant and lubricating oil occurs. However, when the ambient temperature is -20°C or lower and density inversion occurs, if there is no structure capable of supplying the stored lubricating oil to the first compressor 41, since the lubricating oil becomes the upper layer as shown by the "inverted state" on the right side of the paper surface, suction based on the oil return hole 151 becomes difficult, and thus supply to the first compressor 41 becomes difficult.

[0084] Thus, in the case where there is no structure capable of supplying the stored lubricating oil to the first compressor 41 at an ambient temperature of -20°C or lower, if the ambient temperature becomes -20°C or lower, it may become difficult to extract the lubricating oil.

[0085] Therefore, in the air-conditioning system 1 of the present embodiment, as a structure capable of supplying the lubricating oil stored in the low-pressure storage tank 100 to the first compressor 41 even when the ambient temperature becomes -20°C or lower, the control unit 90 can perform control in such a way that the refrigerant flowing into the low-pressure storage tank 100 is superheated when the ambient temperature becomes -20°C or lower.

[0086] The control unit 90 of the present embodiment, for example, makes the opening ratio of the first electric valve 46 smaller than before the ambient temperature is -20°C or lower based on the measured value of the temperature sensor 101 being -20°C or lower, increases the pressure of the refrigerant passing through the indoor heat exchanger 21, and raises the temperature of the refrigerant. Thereby, the refrigerant can be superheated, and the refrigerant flowing into the low-pressure storage tank 100 becomes a gaseous refrigerant.

[0087] In addition, for example, the control unit 90 makes the operating frequency ratio of the first compressor 41 larger than before the ambient temperature is -20°C or lower based on the measured value of the temperature sensor 101 becoming -20°C or lower, increases the pressure of the refrigerant passing through the indoor heat exchanger 21, and raises the temperature of the refrigerant. Through this control, the refrigerant can also be superheated, and the refrigerant flowing into the low-pressure storage tank 100 becomes a gaseous refrigerant.

[0088] (Switching of control mode)

[0089] In this embodiment, the control unit 90 controls various devices included in the air conditioning unit 10, including a normal control mode and a control mode during inversion. When no inversion of the liquid refrigerant and the lubricating oil occurs in the low-pressure storage tank 100, the control unit 90 controls various devices through the normal control mode. On the other hand, when the ambient temperature becomes -20°C or lower, for example, and inversion of the liquid refrigerant and the lubricating oil may occur, the control unit 90 controls various devices through the control mode during inversion. In the control mode during inversion, the control unit 90 performs control in such a way as to superheat the refrigerant flowing into the low-pressure storage tank 100. Hereinafter, using Figure 5 the switching between the normal control mode and the control mode during inversion will be described.

[0090] Figure 5 is a flowchart showing an example of switching between the normal control mode and the control mode during inversion of this embodiment.

[0091] When the air conditioning unit 10 starts operating, the control unit 90 controls various devices included in the air conditioning unit 10 through the normal control mode (step S1001). In the normal control mode, the control unit 90 controls various devices included in the air conditioning unit 10, for example, in such a way that the outlet temperature of the first outdoor heat exchanger 44, which functions as a radiator during refrigeration operation, is constant.

[0092] Next, the control unit 90 determines whether the measured value of the temperature sensor 101 is equal to or lower than the inversion temperature (step S1002). When the measured value of the temperature sensor 101 is higher than the inversion temperature (No in step S1002), the process returns to step S1001, and the control unit 90 controls various devices included in the air conditioning unit 10 through the normal control mode.

[0093] 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 conditioning unit 10 through the control mode during inversion (step S1003). The control unit 90 performs control, for example, in such a way as to superheat the refrigerant flowing into the low-pressure storage tank 100 by reducing the opening degree of the first electric valve 46.

[0094] Next, the control unit 90 determines whether 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 conditioning unit 10 through the control mode during inversion.

[0095] On the other hand, when the measured value of the temperature sensor 101 is equal to or 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 conditioning unit 10 by the normal control mode (step S1005).

[0096] In this way, when the measured value of the temperature sensor 101 becomes equal to or lower than the inversion temperature, the control unit 90 of the present embodiment controls in such a manner as to superheat the refrigerant flowing into the low-pressure storage tank 100. As a result, gaseous refrigerant flows into the low-pressure storage tank 100, so that it is difficult to store liquid refrigerant. Even when the measured value of the temperature sensor 101 is equal to or lower than the inversion temperature, lubricating oil can be sucked out through the oil return pipe 140 or the oil return hole 151.

[0097] In addition, in Figure 5 , the condition for switching the control mode is set according to the measured value of the temperature sensor 101, but it is not limited thereto. For example, the control unit 90 may also switch the control mode based on the low-pressure of the refrigerant or the suction temperature, etc.

[0098] In addition, the above control is an example of the control for superheating the refrigerant flowing into the low-pressure storage tank 100, and other controls may also be performed.

[0099] <Second Embodiment>

[0100] In the second embodiment, as a structure capable of supplying the lubricating oil stored in the low-pressure storage tank 100 to the first compressor 41 even when the ambient temperature is -20°C or lower, there is an oil suction mechanism capable of sucking out the lubricating oil and supplying it to the first compressor 41 even when the liquid refrigerant forms a layer below the lubricating oil in the low-pressure storage tank 100.

[0101] For example, the outdoor unit 30 of the second embodiment has a structure capable of sucking out both the liquid refrigerant and the lubricating oil in the low-pressure storage tank 100. More specifically, for example, in the low-pressure storage tank 100-2 shown in (b) of Figure 4 , on the compressor-side pipe 150, there are a plurality of holes with different heights from the bottom surface of the storage part 110, including the oil return hole 151. By sucking out from the plurality of holes, the liquid refrigerant and the lubricating oil can be sucked out. The sucked liquid refrigerant and lubricating oil are heat-exchanged in the air conditioning system 1 at least with a high-temperature part having a temperature higher than -20°C, and more preferably with a high-temperature part having a temperature higher than the evaporation temperature of the sucked liquid refrigerant, and are supplied to the first compressor 41. Thereby, lubricating oil can be supplied to the first compressor 41, and it is possible to suppress the liquid refrigerant from being sucked into the first compressor 41.

[0102] <Third Embodiment>

[0103] The third embodiment is configured such that even when the ambient temperature is -20°C or lower, the lubricating oil stored in the low-pressure storage tank 100 can be supplied to the first compressor 41, and the liquid refrigerant and lubricating oil stored in the low-pressure storage tank 100 can be heated to eliminate reverse rotation.

[0104] For example, the outdoor unit 30 of the third embodiment has a heater that can heat the liquid stored inside the low-pressure storage tank 100. The heater is provided, for example, close to or in contact with the side or bottom surface of the storage portion 110 of the low-pressure storage tank 100. The heater is turned on according to the control of the control unit 90, and the liquid stored inside the low-pressure storage tank 100 is heated until at least it exceeds the reverse rotation temperature. In this case, the control unit 90 can, for example, turn on the heater when the measured value of the temperature sensor 101 becomes -20°C or lower. Thus, the liquid refrigerant and lubricating oil stored in the low-pressure storage tank 100 can be heated to eliminate reverse rotation.

[0105] In addition, for example, the outdoor unit 30 of the third embodiment can also cause the refrigerant compressed by the first compressor 41 to exchange heat with the low-pressure storage tank 100 or the liquid refrigerant stored in the low-pressure storage tank 100, thereby heating the stored liquid refrigerant. More specifically, the piping from the first compressor 41 to the four-way switching valve 43 can be extended, and the extended piping can be brought into contact with or wound around the periphery of the storage portion 110 of the low-pressure storage tank 100, so as to perform heat exchange between the refrigerant compressed by the first compressor 41 and the low-pressure storage tank 100. In addition, a part of the piping can be inserted into the storage portion 110 in such a way that the extended piping passes through the inside of the storage portion 110 of the low-pressure storage tank 100, and heat exchange can be performed between the refrigerant compressed by the first compressor 41 and the low-pressure storage tank 100.

[0106] Furthermore, for example, the outdoor unit 30 of the third embodiment can also cause the low-pressure storage tank 100 or the liquid refrigerant stored in the low-pressure storage tank 100 to exchange heat with the waste heat of the first compressor 41 or the second compressor 51, thereby heating the stored liquid refrigerant.

[0107] According to these structures, it is also possible to heat the liquid refrigerant and lubricating oil stored in the low-pressure storage tank 100 by using the heat obtained by the liquid refrigerant during heat exchange. In addition, when performing heat exchange between the refrigerant compressed by the first compressor 41 and the low-pressure storage tank 100 or the liquid refrigerant stored in the low-pressure storage tank 100, in order to be able to measure the temperature of the liquid refrigerant stored in the low-pressure storage tank 100, a temperature sensor such as a thermistor can be provided inside the storage portion 110 of the low-pressure storage tank 100.

[0108] <Other>

[0109] In the above-described embodiment, the case where the refrigeration cycle system is applied to the air-conditioning system 1 has been described as an example, but the application scope is not limited. It can also be applied to various devices that use heat absorption in a cooler to cool objects such as a refrigerated warehouse, a refrigerator, an ice maker, etc. In addition, it can also be applied to various devices that use heat dissipation in a radiator to heat objects such as a heating appliance, a water heater, a water heater, etc.

[0110] In addition, 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 obtained by mixing carbon dioxide with other components can be used, or a single refrigerant or a mixed refrigerant that does not contain carbon dioxide can be used. However, the refrigerant circulating in the first refrigerant circuit 31 is immiscible with the lubricating oil of the first compressor 41.

[0111] Incidentally, the inversion temperature depends on the combination of the refrigerant and the lubricating oil, and thus is not limited to the above -20°C.

[0112] Furthermore, in the above-described embodiment, an example where the liquid refrigerant is on the upper layer and the lubricating oil is on 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 where the lubricating oil is on the upper layer and the liquid refrigerant is on the lower layer at a temperature higher than the inversion temperature may also occur. In this case, the above-described embodiment can also be applied, and a structure that can supply the lubricating oil to the first compressor 41 even below the inversion temperature can be designed.

[0113] In addition, the case where the air-conditioning unit 10 constitutes a binary circuit has been described, but for example, it can also be configured as a single circuit without providing the second refrigerant circuit 32 and the cascade heat exchanger 45. In addition, the structure of each refrigerant circuit is not limited to the above structure, and other structures can also be adopted.

[0114] In addition, in the above-described embodiment, an example of using the first electric valve 46 in order to enable the control unit 90 to control the opening degree has been described. In the case where the control unit 90 does not perform control, a capillary tube, an orifice plate, etc. can be used instead of the first electric valve 46.

[0115] The above is the description of the embodiment, but it can be understood that various changes in form or detailed structure can be made without departing from the gist and scope of the claims.

[0116] For example, a part of each structure can also be omitted, or other functions can be added to each structure. In addition, for example, the structures included in one configuration example can be exchanged with the structures included in other configuration examples, or the structures included in one configuration example can be added to other configuration examples.

[0117] Description of reference numerals

[0118] 1…Air conditioning system; 10…Air conditioning section; 21…Indoor heat exchanger; 31…First refrigerant circuit; 32…Second refrigerant circuit; 90…Control section; 100…Low-pressure storage tank; 101…Temperature sensor.

Claims

1. A refrigeration cycle system, characterized in that, the refrigeration cycle system comprises: a compressor lubricated by lubricating oil and compressing a refrigerant; an evaporator through which the refrigerant that has been compressed by the compressor and then dissipated heat and reduced pressure passes, and the passing refrigerant exchanges heat with an object; and a storage container disposed between the evaporator and the compressor, capable of storing the refrigerant and the lubricating oil, even when the ambient temperature at which the storage container is provided becomes the inversion temperature at which the density of the lubricating oil and the density of the refrigerant in the liquid state are inverted, the lubricating oil stored in the storage container can be supplied to the compressor.

2. The refrigeration cycle system according to claim 1, characterized in that, the refrigeration cycle system comprises a control unit for controlling the state of the refrigerant, the control unit can be controlled in such a manner that when the ambient temperature becomes the inversion temperature, the refrigerant flowing into the storage container is superheated.

3. The refrigeration cycle system according to claim 2, characterized in that, the refrigeration cycle system comprises an electric valve for adjusting the pressure of the refrigerant passing through the evaporator, as a control for superheating the refrigerant flowing into the storage container, the control unit can control the opening degree of the electric valve to be smaller than before the control for this superheating.

4. The refrigeration cycle system according to claim 2, characterized in that, as a control for superheating the refrigerant flowing into the storage container, the control unit can control the frequency of the movement for compression in the compressor to be larger than before the control for this superheating.

5. The refrigeration cycle system according to any one of claims 1 to 4, characterized in that, the storage container has an oil suction mechanism, and the oil suction mechanism can suck out and supply the lubricating oil to the compressor even when the ambient temperature becomes the inversion temperature and the refrigerant in the liquid state in the storage container becomes a layer below the lubricating oil.

6. The refrigeration cycle system according to claim 5, characterized in that, the oil suction mechanism has a plurality of holes with different heights from the bottom surface of the storage container on the pipe, wherein the pipe sucks the lubricating oil in the storage container, through the plurality of holes, the refrigerant and the lubricating oil in the liquid state can be sucked out, after the sucked refrigerant and lubricating oil in the liquid state are heat-exchanged with a high-temperature part in the refrigeration cycle system having a temperature higher than the inversion temperature, they are supplied to the compressor.

7. The refrigeration cycle system according to any one of claims 1 to 6, characterized in that, even when the ambient temperature becomes the inversion temperature, the refrigerant and the lubricating oil in the liquid state stored in the storage container can be heated up to eliminate the density inversion.

8. The refrigeration cycle system according to any one of claims 1 to 7, characterized in that, The refrigeration cycle system has a heater, and the heater is installed in the storage container and can raise the temperature of the refrigerant and the lubricating oil in a liquid state stored in the storage container.

9. The refrigeration cycle system according to any one of claims 1 to 8, characterized in that the refrigeration cycle system includes a radiator, and the radiator allows the refrigerant compressed by the compressor to pass through, extracts heat from the passing refrigerant and dissipates the heat, and is capable of performing heat exchange between the storage container or the refrigerant in a liquid state in the storage container and the refrigerant passing through the radiator.

10. The refrigeration cycle system according to any one of claims 1 to 9, characterized in that it is capable of performing heat exchange between the storage container or the refrigerant in a liquid state in the storage container and the waste heat of the compressor.

11. The refrigeration cycle system according to any one of claims 1 to 10, characterized in that the lubricating oil is polyalkylene glycol.

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