Refrigeration Cycle Equipment

Abstract

The refrigeration cycle apparatus includes a first circuit having a compressor, an indoor heat exchanger, a first throttling device, and an outdoor heat exchanger; a second circuit configured to branch off from the first circuit at a first branching section and merge with the first circuit at a second branching section and having a second throttling device; and a control section that controls the compressor, the first throttling device, and the second throttling device, wherein when the outdoor air temperature is lower than a first temperature, the control section performs a warm-up from when the compressor is started until the temperature of the refrigerant discharged from the compressor reaches a second temperature, and the control section sets the opening degree of the first throttling device and the opening degree of the second throttling device during and after the warm-up is completed so that more refrigerant flows into the second circuit than the first circuit during the warm-up, and after the warm-up is completed, more refrigerant flows into the first circuit than the second circuit.

Description

[Technical field]

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

[0002] Patent Document 1 discloses a control device. This control device is used in a refrigerant circuit including a compressor, a condenser, an expansion valve, an evaporator, a return pipe for returning refrigerant or refrigerating machine oil discharged from the compressor to the compressor, and a flow control valve provided in the return pipe. The control device includes a temperature information acquisition unit and a control unit. The temperature information acquisition unit acquires a first temperature, which is the temperature of the refrigerant or refrigerating machine oil passing through the return pipe, and a second temperature at a lower part of the housing of the compressor. The control unit controls the opening degree of the flow control valve and the expansion valve based on the first temperature and the second temperature. The control unit closes the flow control valve and the expansion valve when the compressor is started, and then opens the flow control valve when the first temperature becomes higher than the second temperature. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2018-200145 A Summary of the Invention [Problem to be solved by the invention]

[0004] However, in the above configuration, the refrigerant remains in the condenser as a condensed liquid, and the oil discharged from the compressor together with the refrigerant at startup remains in the condenser, reducing the amount of oil in the compressor. This makes the compressor more susceptible to breakdowns, reducing the quality of the compressor and the refrigeration cycle device. On the other hand, if the amount of oil sealed in is increased in preparation for the reduction in oil, the energy saving performance of the refrigeration cycle device decreases. Therefore, there was a problem that it was difficult to achieve both quality and energy saving performance.

[0005] The present disclosure has been made to solve the above-mentioned problems, and has an object to provide a refrigeration cycle device that can achieve both quality and energy saving. [Means for solving the problem]

[0006] A refrigeration cycle apparatus according to the present disclosure includes a first circuit provided with a compressor, a first branch section, an indoor heat exchanger, a first throttling device, an outdoor heat exchanger, and a second branch section; a second circuit configured to branch off from the first circuit at the first branch section and merge with the first circuit at the second branch section and provided with a second throttling device; and a control section that controls the compressor, the first throttling device, and the second throttling device, wherein the first branch section is provided downstream of the compressor and upstream of the indoor heat exchanger in the flow of refrigerant during heating operation, and the second branch section is provided downstream of the outdoor heat exchanger and upstream of the outdoor heat exchanger in the flow of refrigerant during heating operation. The first throttling device is provided upstream of the compressor, and the first throttling device is provided downstream of the first branch portion and upstream of the second branch portion in the flow of refrigerant during the heating operation, and when the outdoor air temperature is lower than a first temperature, the control unit executes warm-up from when the compressor is started until a temperature of refrigerant discharged from the compressor reaches a second temperature, and the control unit sets an opening degree of the first throttling device and an opening degree of the second throttling device during and after the warm-up is completed so that more refrigerant flows into the second circuit than into the first circuit during the warm-up, and more refrigerant flows into the first circuit than into the second circuit after the warm-up is completed. When a degree of subcooling of the outlet refrigerant of the indoor heat exchanger becomes equal to or higher than a reference degree of subcooling during the warm-up of the heating operation, the control unit increases the opening degree of the first throttling device to a value greater than an upper limit opening degree of the first throttling device during the warm-up. . Effect of the Invention

[0007] According to the present disclosure, it is possible to achieve both quality and energy saving in a refrigeration cycle device. [Brief description of the drawings]

[0008] [Figure 1] 1 is a circuit diagram showing a schematic configuration of a refrigeration cycle device according to a first embodiment. [Diagram 2]FIG. 5 is a PH diagram showing the state of the refrigerant during warming up of the compressor when the outside air temperature is low. [Diagram 3] 1 is a circuit diagram showing a configuration of a refrigeration cycle device according to a first embodiment during heating operation. [Figure 4] 5 is a flowchart showing a flow of processes executed by a control unit at the time of startup in the refrigeration cycle apparatus according to the first embodiment. [Diagram 5] 3 is a PH diagram showing a state of a refrigerant during warm-up in the refrigeration cycle device according to the first embodiment. FIG. [Figure 6] 4 is a PH diagram showing a state of a refrigerant at the time when a warm-up of a cooling operation is completed in the refrigeration cycle device according to the first embodiment. FIG. [Figure 7] 4 is a PH diagram showing a state of a refrigerant at the time when a warm-up of a heating operation is completed in the refrigeration cycle device according to the first embodiment. FIG. [Figure 8] 4 is a graph showing an example of a change over time in discharge refrigerant temperature in the refrigeration cycle device according to the first embodiment. [Figure 9] 10 is a graph showing an example of a change over time in discharge refrigerant temperature in the refrigeration cycle device according to the second embodiment. [Figure 10] 11 is a graph showing a change over time in the degree of subcooling of the outlet refrigerant of the indoor heat exchanger in the refrigeration cycle apparatus according to the third embodiment. [Figure 11] 11 is a graph showing a change over time in the rotation speed of an outdoor fan in a refrigeration cycle apparatus according to embodiment 4. [Figure 12] FIG. 11 is a circuit diagram showing a configuration of a refrigeration cycle device according to a fifth embodiment during heating operation. [Figure 13] FIG. 13 is a circuit diagram showing a configuration of a refrigeration cycle device according to a sixth embodiment during heating operation. [Figure 14] 13 is a flowchart showing a flow of processes executed by a control unit at the time of startup in a refrigeration cycle apparatus according to a sixth embodiment. [Figure 15] 13 is a graph showing a change over time in the rotation speed of an indoor fan in a refrigeration cycle apparatus according to embodiment 7. [Figure 16]13 is a graph showing a change over time in frequency of a compressor in a refrigeration cycle device according to a seventh embodiment. [Figure 17] 13 is a graph showing another example of a time change in frequency of a compressor in the refrigeration cycle apparatus according to the seventh embodiment. [Figure 18] 4 is a graph showing the relationship between the opening degree of a first throttle device and the amount of liquid outflow at the time of startup in the refrigeration cycle apparatus according to the first embodiment. [Figure 19] 4 is a graph showing the relationship between the frequency of the compressor and the amount of liquid outflow at the time of startup in the refrigeration cycle device according to the first embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0009] Hereinafter, the embodiments of the present disclosure will be described with reference to the drawings. The present disclosure is not limited to the following embodiments, and can be modified in various ways without departing from the spirit of the present disclosure. The present disclosure includes all combinations of the configurations shown in the following embodiments that can be combined. In particular, the combination of components is not limited to the combinations in each embodiment, and the components described in one embodiment can be applied to another embodiment. In the following description, terms indicating directions (e.g., "upper", "lower", "right", "left", "front", "rear", etc.) are used as appropriate to facilitate understanding, but these are for explanation and do not limit the present disclosure. In each drawing, the same reference numerals are assigned to the same or equivalent parts, and this is common throughout the entire specification. In each drawing, the relative dimensional relationship or shape of each component may differ from the actual one.

[0010] Embodiment 1 A refrigeration cycle device according to a first embodiment will be described. The refrigeration cycle device according to the present embodiment is used for refrigeration or air conditioning purposes, such as refrigerators, freezers, vending machines, air conditioners, refrigeration devices, and water heaters. Fig. 1 is a circuit diagram showing a schematic configuration of the refrigeration cycle device according to the present embodiment. As shown in Fig. 1, the refrigeration cycle device has a first circuit 51 and a second circuit 52 as refrigerant circuits through which a refrigerant circulates.

[0011] The first circuit 51 has a configuration in which a compressor 10, a first branching section 11, a flow switching device 12, a flow control valve 13, an indoor heat exchanger 20, a first throttling device 30, an outdoor heat exchanger 40, an accumulator 14, and a second branching section 15 are connected in sequence in a ring shape via refrigerant piping. The second circuit 52 branches off from the first circuit 51 at the first branching section 11 and merges with the first circuit 51 at the second branching section 15. The second circuit 52 is provided with a second throttling device 31.

[0012] The refrigeration cycle device has an outdoor unit 70 and an indoor unit 71. The outdoor unit 70 accommodates a compressor 10, a first branch section 11, a flow path switching device 12, a flow control valve 13, an outdoor heat exchanger 40, an accumulator 14, a second throttling device 31, and an outdoor blower 41 that supplies outdoor air to the outdoor heat exchanger 40. The indoor unit 71 accommodates an indoor heat exchanger 20, a first throttling device 30, and an indoor blower 21 that supplies indoor air to the indoor heat exchanger 20.

[0013] The compressor 10 draws in a refrigerant, compresses the refrigerant, and discharges it in a high-temperature, high-pressure state. The refrigerant compressed by the compressor 10 is discharged and sent to a first branch section 11. The compressor 10 is configured, for example, as a rotary compressor, a scroll compressor, a screw compressor, or a reciprocating compressor. The compressor 10 may be a high-pressure shell type or a low-pressure shell type, but the effect of suppressing oil outflow according to this embodiment is particularly large when the compressor 10 is a high-pressure shell type.

[0014] The first branch section 11 is a portion where the first circuit 51 and the second circuit 52 branch off. The first branch section 11 is provided downstream of the compressor 10 and upstream of the indoor heat exchanger 20 in the flow of the refrigerant during heating operation. The flow rate of the refrigerant flowing from the first branch section 11 to the first circuit 51 and the flow rate of the refrigerant flowing from the first branch section 11 to the second circuit 52 are adjusted by the opening degree of the flow control valve 13 and the second throttling device 31, respectively. The first branch section 11 is constituted by, for example, an oil separator. The oil separator is configured to separate the refrigerating machine oil discharged together with the refrigerant by the compressor 10 from the refrigerant. The refrigerating machine oil separated by the oil separator is returned to the compressor 10 through the second circuit 52.

[0015] The flow path switching device 12 is, for example, a four-way valve, and switches the flow direction of the refrigerant in the first circuit 51. The flow path switching device 12 switches the flow direction of the refrigerant in the refrigeration cycle device between a heating operation and a cooling operation.

[0016] The flow control valve 13 is provided downstream of the first branching portion 11 and upstream of the indoor heat exchanger 20 in the flow of the refrigerant during heating operation. The flow control valve 13 is a valve that adjusts the flow rate of the refrigerant flowing through the first circuit 51. The opening degree of the flow control valve 13 is controlled by the control unit 100 described later. In this embodiment, the indoor unit 71 is provided with a first throttling device 30, and the flow rate of the refrigerant flowing through the first circuit 51 is adjusted by the first throttling device 30. For this reason, as shown in FIG. 12 and the like described later, the flow control valve 13 can be omitted. However, the flow control valve 13 can also be used as the first throttling device, and the flow rate of the refrigerant flowing through the first circuit 51 can be adjusted by the flow control valve 13.

[0017] During heating operation, the indoor heat exchanger 20 functions as a condenser, exchanging heat between the refrigerant that has flowed inside and the indoor air, condensing and liquefying the refrigerant. During cooling operation, the indoor heat exchanger 20 functions as an evaporator, exchanging heat between the refrigerant that has flowed inside and the indoor air, evaporating and vaporizing the refrigerant.

[0018] The indoor blower 21 supplies indoor air to the indoor heat exchanger 20 in order to increase the heat exchange efficiency in the indoor heat exchanger 20. The indoor blower 21 is provided adjacent to the indoor heat exchanger 20.

[0019] The first throttling device 30 has a function as a pressure reducing valve or an expansion valve, and reduces the pressure of the refrigerant by expanding it. The first throttling device 30 is, for example, an electronic expansion valve whose opening degree can be adjusted by the control of the control unit 100.

[0020] The outdoor heat exchanger 40 functions as an evaporator during heating operation, exchanging heat between the refrigerant that has flowed inside and the outdoor air, evaporating and vaporizing the refrigerant. During cooling operation, the outdoor heat exchanger 40 functions as a condenser, exchanging heat between the refrigerant that has flowed inside and the outdoor air, condensing and liquefying the refrigerant.

[0021] The exterior blower 41 supplies outdoor air to the outdoor heat exchanger 40 in order to increase the heat exchange efficiency in the outdoor heat exchanger 40. The exterior blower 41 is provided adjacent to the outdoor heat exchanger 40.

[0022] The accumulator 14 stores excess refrigerant and separates the refrigerant into a liquid refrigerant and a gas refrigerant. The separated gas refrigerant is supplied to the compressor 10.

[0023] The second branch portion 15 is provided on the suction side of the compressor 10. The second branch portion 15 is provided downstream of the outdoor heat exchanger 40 and upstream of the compressor 10 in the flow of the refrigerant during heating operation.

[0024] The second throttling device 31 is a valve that reduces the pressure of the refrigerant and refrigerating machine oil flowing through the second circuit 52. The opening degree of the second throttling device 31 is controlled by the control unit 100.

[0025] The control unit 100 is configured to control the entire refrigeration cycle device including the compressor 10, the flow path switching device 12, the flow control valve 13, the first throttling device 30, the second throttling device 31, the outdoor blower 41, and the indoor blower 21. These controls may be realized by a microcomputer equipped with a CPU (Central Processing Unit), a ROM (Read Only Memory), a RAM (Random Access Memory), etc., or may be realized by dedicated hardware. The control unit 100 may be provided in the outdoor unit 70 or in the indoor unit 71. The control unit 100 may have an outdoor unit control unit provided in the outdoor unit 70 and an indoor unit control unit provided in the indoor unit 71 and capable of communicating with the outdoor unit control unit.

[0026] Next, the overall operation of the refrigeration cycle device will be described. First, the operation in a steady state during heating operation will be described. During heating operation, the flow path of the flow path switching device 12 is switched by the control of the control unit 100, and the first circuit 51 is configured so that the high-pressure refrigerant discharged from the compressor 10 flows into the indoor heat exchanger 20.

[0027] The high-temperature, high-pressure gas refrigerant discharged from the compressor 10 flows into the indoor heat exchanger 20 via the first branch section 11, the flow switching device 12, and the flow control valve 13. When the first branch section 11 is an oil separator, the refrigeration oil discharged from the compressor 10 together with the refrigerant is separated from the refrigerant in the first branch section 11 and returns to the suction side of the compressor 10 through the second circuit 52. During heating operation, the indoor heat exchanger 20 functions as a condenser. That is, in the indoor heat exchanger 20, heat exchange is performed between the refrigerant flowing inside and the indoor air blown by the indoor blower 21, and the condensation heat of the refrigerant is dissipated to the indoor air. As a result, the refrigerant that flows into the indoor heat exchanger 20 is condensed to become a high-pressure liquid refrigerant. In addition, the indoor air blown by the indoor blower 21 is heated by the heat dissipation effect of the refrigerant.

[0028] The high-pressure liquid refrigerant flowing out from the indoor heat exchanger 20 is decompressed by the first throttling device 30 to become a low-pressure two-phase refrigerant. The low-pressure two-phase refrigerant decompressed by the first throttling device 30 flows into the outdoor heat exchanger 40. During heating operation, the outdoor heat exchanger 40 functions as an evaporator. That is, in the outdoor heat exchanger 40, heat exchange is performed between the refrigerant flowing inside and the outdoor air blown by the outdoor blower 41, and the heat of evaporation of the refrigerant is absorbed from the outdoor air. As a result, the refrigerant flowing into the outdoor heat exchanger 40 evaporates to become a low-pressure gas refrigerant or two-phase refrigerant. The low-pressure gas refrigerant or two-phase refrigerant flowing out from the outdoor heat exchanger 40 flows into the accumulator 14 through the flow switching device 12. In the accumulator 14, the gas refrigerant and the liquid refrigerant are separated, and only the gas refrigerant is sucked into the compressor 10. During heating operation, the above cycle is continuously repeated.

[0029] Next, a description will be given of the operation in a steady state during cooling operation. During cooling operation, the flow path of the flow path switching device 12 is switched under the control of the control unit 100, and the first circuit 51 is configured so that the high-pressure refrigerant discharged from the compressor 10 flows into the outdoor heat exchanger 40.

[0030] The high-temperature, high-pressure gas refrigerant discharged from the compressor 10 flows into the outdoor heat exchanger 40 via the first branch section 11 and the flow path switching device 12. If the first branch section 11 is an oil separator, the refrigeration oil discharged from the compressor 10 together with the refrigerant is separated from the refrigerant in the first branch section 11 and returns to the suction side of the compressor 10 through the second circuit 52. During cooling operation, the outdoor heat exchanger 40 functions as a condenser. That is, in the outdoor heat exchanger 40, heat exchange is performed between the refrigerant circulating inside and the outdoor air blown by the outdoor blower 41, and the condensation heat of the refrigerant is dissipated to the outdoor air. As a result, the refrigerant flowing into the outdoor heat exchanger 40 is condensed to become a high-pressure liquid refrigerant.

[0031] The high-pressure liquid refrigerant flowing out from the outdoor heat exchanger 40 is decompressed by the first throttling device 30 to become a low-pressure two-phase refrigerant. The low-pressure two-phase refrigerant decompressed by the first throttling device 30 flows into the indoor heat exchanger 20. During cooling operation, the indoor heat exchanger 20 functions as an evaporator. That is, in the indoor heat exchanger 20, heat exchange is performed between the refrigerant flowing inside and the indoor air blown by the indoor blower 21, and the heat of evaporation of the refrigerant is absorbed from the indoor air. As a result, the refrigerant flowing into the indoor heat exchanger 20 evaporates to become a low-pressure gas refrigerant or two-phase refrigerant. In addition, the indoor air blown by the indoor blower 21 is cooled by the heat absorption effect of the refrigerant. The low-pressure gas refrigerant or two-phase refrigerant flowing out from the indoor heat exchanger 20 flows into the accumulator 14 through the flow control valve 13 and the flow path switching device 12. In the accumulator 14, the gas refrigerant and the liquid refrigerant are separated, and only the gas refrigerant is drawn into the compressor 10. In cooling operation, the above cycle is continuously repeated.

[0032] Incidentally, when the outside air temperature is low, the temperatures of the components of the compressor 10 are also low from when the compressor 10 starts until the warm-up is completed. FIG. 2 is a PH diagram showing the state of the refrigerant while the compressor is warming up when the outside air temperature is low. FIG. 2 only shows the state of the refrigerant in the compression stroke. η in FIG. 2 represents the compressor efficiency. As shown in FIG. 2, the low-pressure gas refrigerant (point A in FIG. 2) is compressed by the compressor 10 and its pressure increases, but it is cooled by the components of the compressor 10 and re-condenses within the compressor 10, becoming a liquid refrigerant (point B in FIG. 2).

[0033] When the refrigerant recondenses in the compressor 10, the refrigeration oil in the compressor 10 is diluted by the liquid refrigerant and carried out to the outside of the compressor 10. This makes it easier for the refrigeration oil in the compressor 10 to run out, which may cause excessive friction, resulting in breakdown of the compressor 10 and a decrease in the performance of the air conditioner.

[0034] In this embodiment, in order to prevent the refrigerant oil in the compressor 10 from running out, the compressor 10 is warmed up at the start of the compressor 10. During the warm-up, a large amount of refrigerant flows through the second circuit 52, thereby suppressing the outflow of the refrigerant oil from the second circuit 52 including the compressor 10 to the outside. The warm-up ends after the refrigerant discharged from the compressor 10 is gasified. When the warm-up ends, the refrigerant flow rate in the second circuit 52 is throttled and the refrigerant flow rate in the first circuit 51 increases. That is, the control unit 100 sets the opening degree of the first throttling device 30 and the opening degree of the second throttling device 31 during and after the warm-up so that more refrigerant flows through the second circuit 52 than through the first circuit 51 during the warm-up, and more refrigerant flows through the first circuit 51 than through the second circuit 52 after the warm-up ends.

[0035] FIG. 3 is a circuit diagram showing a configuration of the refrigeration cycle device according to the present embodiment during heating operation. FIG. 3 shows a circuit similar to that shown in FIG. 1, although the flow path switching device 12 is omitted. As shown in FIG. 3, the refrigeration cycle device has an outdoor temperature sensor 101, a discharge refrigerant temperature sensor 102, and an indoor temperature sensor 103. The outdoor temperature sensor 101 is configured to detect the outdoor air temperature and transmit a detection signal to the control unit 100. The discharge refrigerant temperature sensor 102 is provided in the compressor 10. The discharge refrigerant temperature sensor 102 is configured to detect the temperature of the refrigerant discharged from the compressor 10 and transmit a detection signal to the control unit 100. The indoor temperature sensor 103 is configured to detect the indoor air temperature and transmit a detection signal to the control unit 100.

[0036] The refrigeration cycle apparatus also has a discharge pressure sensor 104 which detects the pressure of the refrigerant discharged from the compressor 10, and a suction pressure sensor 105 which detects the pressure of the refrigerant suctioned from the compressor 10. The discharge pressure sensor 104 is provided between the discharge side of the compressor 10 and the first throttling device 30. The suction pressure sensor 105 is provided between the first throttling device 30 and the suction side of the compressor 10. Each of the discharge pressure sensor 104 and the suction pressure sensor 105 is configured to transmit a detection signal to the control unit 100.

[0037] Fig. 4 is a flowchart showing a flow of a process executed by a control unit at the time of start-up in the refrigeration cycle device according to the present embodiment. The process shown in Fig. 4 is executed in both heating operation and cooling operation.

[0038] When the control unit 100 receives a start signal from the outside, it starts the process shown in Fig. 4. First, in step S1 of Fig. 4, the control unit 100 determines whether or not the outdoor air temperature is lower than a first temperature. The value of the first temperature is stored in advance in the ROM of the control unit 100. If the outdoor air temperature is lower than the first temperature, the process proceeds to step S2, where warming up is performed. If the outdoor air temperature is equal to or higher than the first temperature, the process proceeds to step S6.

[0039] In step S2, the control unit 100 controls the first throttling device 30 so that the opening degree s of the first throttling device 30 is in the range of 0≦s≦the first opening degree. The value of the first opening degree is stored in advance in the ROM of the control unit 100. The first opening degree is smaller than the full opening degree, for example, a slightly open opening degree that is a relatively small opening degree. The first opening degree is the upper limit of the opening degree s of the first throttling device 30 during warm-up. The first opening degree is smaller than the upper limit of the opening degree of the first throttling device 30 that is set during cooling operation or heating operation after warm-up is completed.

[0040] The first opening is desirably 30% or less of the opening of the first throttling device 30 in rated operation. Fig. 18 is a graph showing the relationship between the opening of the first throttling device and the liquid outflow amount at startup in the refrigeration cycle apparatus of this embodiment. The horizontal axis represents the opening of the first throttling device 30 with the opening at rated operation set to 100%. The vertical axis represents the liquid outflow amount to the indoor unit as a liquid flow rate ratio with the liquid outflow amount at rated operation set to 100%. Fig. 18 is a schematic diagram of heating startup operation when the outside air temperature is 3°C with the second throttling device 31 open.

[0041] As shown in Fig. 18, by reducing the opening of the first throttling device 30, the amount of liquid outflow to the indoor unit can be reduced, thereby reducing the amount of oil outflow from the outdoor unit and improving quality. The hatched area in Fig. 18 represents the range of variation in the amount of liquid outflow depending on the specifications of the first throttling device 30. The flow rate through the throttling device depends on the capacity coefficient of the throttle, but the relationship between the opening and the capacity coefficient depends on the specifications of the throttling device. By setting the first opening to 30% or less of the opening of the first throttling device 30 in rated operation, the amount of liquid outflow can be reduced to 50% or less within the specification range of the throttling device used in the refrigeration cycle equipment.

[0042] In step S3, the control unit 100 sets the second throttling device 31 to an open state. The opening degree of the second throttling device 31 is set to an opening degree larger than the upper limit of the opening degree of the second throttling device 31 set during cooling operation or heating operation after warm-up is completed. In step S4, the control unit 100 starts the compressor 10 and controls the compressor 10 so that the frequency of the compressor 10 is in a range larger than 0 and equal to or smaller than the first frequency. The value of the first frequency is stored in the ROM of the control unit 100 in advance. The first frequency is a frequency smaller than the maximum frequency. The first frequency is the upper limit of the frequency of the compressor 10 during warm-up. The first frequency is a frequency smaller than the upper limit of the frequency of the compressor 10 set during cooling operation or heating operation after warm-up is completed.

[0043] The first frequency is desirably 40% or less of the frequency of the compressor 10 in rated operation. Fig. 19 is a graph showing the relationship between the compressor frequency and the liquid outflow amount at startup in the refrigeration cycle apparatus of this embodiment. The horizontal axis represents the frequency of the compressor 10 with the frequency at rated operation set to 100%. The vertical axis represents the liquid outflow amount to the indoor unit as a liquid flow rate ratio with the liquid outflow amount at rated operation set to 100%. Fig. 19 is a schematic diagram of the heating startup operation when the outside air temperature is 3°C with the second throttling device 31 open.

[0044] As shown in Fig. 19, by reducing the frequency of compressor 10, the amount of liquid outflow to the indoor unit can be reduced, and the amount of oil outflow from the outdoor unit can be reduced, improving quality. The hatched area in Fig. 19 indicates the range of dispersion of the amount of liquid outflow depending on the specifications of the heat exchanger. The flow rate through compressor 10 is dominated by the density of suction refrigerant in addition to the frequency, but the relationship between the frequency and the refrigerant density depends on the specifications of the heat exchanger (particularly the evaporator). By setting the first frequency to 40% or less of the frequency of compressor 10 in rated operation, the amount of liquid outflow can be reduced to 50% or less within the specification range of the heat exchanger used in the refrigeration cycle device.

[0045] In step S5, the control unit 100 determines whether the discharge refrigerant temperature is higher than the second temperature. The value of the second temperature is stored in advance in the ROM of the control unit 100. Usually, the second temperature is set to a value higher than the first temperature. If the discharge refrigerant temperature is higher than the second temperature, the warm-up ends and the process proceeds to step S6. If the discharge refrigerant temperature is equal to or lower than the second temperature, the process returns to step S2. As a result, the warm-up continues until the discharge refrigerant temperature becomes higher than the second temperature.

[0046] In step S6, the control unit 100 sets the second throttling device 31 to a closed state or a slightly open state. The opening degree of the second throttling device 31 in the slightly open state is smaller than the opening degree of the second throttling device 31 set in step S3. In other words, the opening degree of the second throttling device 31 after warming up is set to a smaller opening degree than the opening degree of the second throttling device 31 during warming up. The expression "set to a smaller opening degree than the opening degree of the second throttling device 31 during warming up" includes the case where the opening degree is maintained for a certain period of time after warming up is completed and then the opening degree is set to a smaller value. The certain time t1 is a design value for setting the warming up completion judgment in consideration of the detection error of the temperature measurement means. The certain time t1 is set so that 0≦t1<2t0 with respect to the time t0 from the start of activation to the warming up completion judgment. If t1<0, the warming up completion judgment is not made, which is not preferable. If t1≧2t0, the heating start is delayed, which impairs the comfort of the end user, which is not preferable.

[0047] In step S7, the control unit 100 controls the first throttling device 30 so that the opening degree s of the first throttling device 30 is 0≦s≦fully open. In other words, the upper limit of the opening degree s of the first throttling device 30 after warm-up is completed is set to an opening degree larger than the first opening degree, which is the upper limit during warm-up. Note that the expression "set to an opening degree larger than the first opening degree, which is the upper limit during warm-up" also includes a case where the opening degree is not increased for a certain period of time immediately after warm-up is completed, and then the opening degree is set to an opening degree larger than the first opening degree to perform heating operation or cooling operation.

[0048] In step S8, the control unit 100 controls the compressor 10 so that the frequency of the compressor 10 is in a range greater than 0 and less than the maximum frequency. The maximum frequency is the maximum value of the operating frequency range in the specifications of the compressor 10. In other words, the upper limit of the frequency of the compressor 10 after the warm-up is completed is set to a frequency greater than the first frequency, which is the upper limit frequency during the warm-up. For example, the control unit 10 operates the compressor 10 at a frequency greater than the first frequency. Thereafter, normal operation is continued. Note that the expression "operating the compressor 10 at a frequency greater than the first frequency" also includes a case where the compressor 10 is temporarily operated at a frequency less than the first frequency immediately after the warm-up is completed, and then the compressor 10 is operated at a frequency greater than the first frequency to perform heating or cooling operation.

[0049] Fig. 5 is a PH diagram showing the state of the refrigerant during warm-up in the refrigeration cycle device according to the present embodiment. As shown in Fig. 5, as the warm-up progresses, the state of the refrigerant changes in the order of R1, R2, and R3.

[0050] FIG. 6 is a PH diagram showing the state of the refrigerant at the time when the warm-up of the cooling operation is completed in the refrigeration cycle device according to this embodiment. FIG. 7 is a PH diagram showing the state of the refrigerant at the time when the warm-up of the heating operation is completed in the refrigeration cycle device according to this embodiment. In FIG. 6 and FIG. 7, pressure P1 represents the discharge refrigerant pressure of the compressor 10. Temperature Te represents the temperature of the space in which the evaporator is provided. The space in which the evaporator is provided is indoors in the cooling operation and outdoors in the heating operation. Temperature Tc represents the temperature of the space in which the condenser is provided. The space in which the condenser is provided is outdoors in the cooling operation and indoors in the heating operation. Temperature T1 represents the first temperature described above. Temperature T2 represents the second temperature described above. As shown in FIG. 6 and FIG. 7, the state of the refrigerant changes in the same way in the cooling operation and the heating operation, although there is a difference between the first temperature T1 and the second temperature T2 being higher or lower than the temperature Tc.

[0051] Here, the first temperature T1 will be described. Equation (1) shows an example of the first temperature T1 [°C]. The theoretical discharge enthalpy is the enthalpy that indicates the discharge gas entropy Sc = Sesat, where Sesat is the saturated gas entropy at the suction pressure Pe. T1=Tcsat1-120Gr(Hc-Hcsat) / C...(1) Gr: Average refrigerant flow rate at start-up [kg / sec], Tcsat1: Average discharge saturation temperature for 120 seconds at start-up [℃] Hc: Average theoretical discharge enthalpy for 120 seconds at startup [kJ / kg] Hcsat: Average discharge saturation enthalpy for 120 seconds at startup [kJ / kg] C: Heat capacity of compressor [kJ / K]

[0052] When the first temperature T1 satisfying the above formula (1) is taken as a standard, when the first temperature is set to a value higher than T1, oil outflow can be suppressed and the quality of the compressor 10 and the refrigeration cycle device including the same can be improved. When the first temperature is set to a value lower than T1, the heating start-up time can be shortened and the heating capacity per input heat amount can be improved, thereby improving the energy saving performance of the refrigeration cycle device.

[0053] Next, the second temperature T2 will be described. The refrigerant dissolved in the oil in the compressor 10 is in a superheated liquid state, so it is stored as liquid refrigerant up to a certain temperature even if it exceeds the saturation temperature calculated from the oil pressure.

[0054] Equations (2) and (3) show an example of the second temperature T2 [° C.]. T2>Tcsat2 (2) T2-Tcsat2=5 (3) Tcsat2: Discharge saturation temperature [℃]

[0055] That is, the second temperature T2 is set based on the saturation temperature of the discharge pressure of the compressor 10 so as to be a temperature higher than the saturation temperature. The second temperature T2 is set to a temperature at which the degree of superheat relative to the saturation temperature of the discharge pressure of the compressor 10 is 5K or higher. When the second temperature T2 that satisfies the above formulas (2) and (3) is taken as a standard, when the second temperature is set to a value higher than T2, oil outflow can be suppressed and the quality of the compressor 10 and the refrigeration cycle device including the same can be improved. When the second temperature is set to a value lower than T2, the heating start-up time can be shortened and the heating capacity per input heat amount can be improved, thereby improving the energy saving performance of the refrigeration cycle device.

[0056] In particular, when the refrigerant dissolved in oil boils, it may take the oil with it and flow out into the first circuit 51. By suppressing the refrigerant flow rate in the first circuit 51 to a certain degree of superheat as described above, the amount of oil flowing out into the first circuit 51 can be suppressed.

[0057] FIG. 8 is a graph showing an example of the change over time in the discharge refrigerant temperature in the refrigeration cycle device according to the present embodiment. The horizontal axis represents time, and the vertical axis represents temperature. Time ta represents the elapsed time after the compressor 10 is started. As shown in FIG. 8, the second temperature T2 is set to a temperature that is a certain temperature higher than the discharge saturation temperature Tcsat. Therefore, at time ta when the discharge refrigerant temperature reaches the second temperature T2, the refrigerant is reliably in a superheated gas state. Therefore, the amount of oil flowing out to the first circuit 51 can be suppressed.

[0058] As described above, the refrigeration cycle apparatus according to this embodiment includes the first circuit 51, the second circuit 52, and the control unit 100. The first circuit 51 includes the compressor 10, the first branching section 11, the indoor heat exchanger 20, the first throttling device 30, the outdoor heat exchanger 40, and the second branching section 15. The second circuit 52 is configured to branch off from the first circuit 51 at the first branching section 11 and merge with the first circuit 51 at the second branching section 15. The second circuit 52 includes the second throttling device 31. The control unit 100 controls the compressor 10, the first throttling device 30, and the second throttling device 31.

[0059] The first branch section 11 is provided downstream of the compressor 10 and upstream of the indoor heat exchanger 20 in the refrigerant flow during heating operation. The second branch section 15 is provided downstream of the outdoor heat exchanger 40 and upstream of the compressor 10 in the refrigerant flow during heating operation. The first throttling device 30 is provided downstream of the first branch section 11 and upstream of the second branch section 15 in the refrigerant flow during heating operation.

[0060] When the outdoor air temperature is lower than the first temperature T1, the control unit 100 executes warm-up from when the compressor 10 is started until the temperature of the refrigerant discharged from the compressor 10 reaches the second temperature T2. The control unit 100 sets the opening degrees of the first throttling device 30 and the second throttling device 31 during and after the warm-up is completed so that more refrigerant flows into the second circuit 52 than into the first circuit 51 during the warm-up, and more refrigerant flows into the first circuit 51 than into the second circuit 52 after the warm-up is completed.

[0061] According to this configuration, in operation after warming up, i.e., in normal heating operation or cooling operation, most of the refrigerant discharged from the compressor 10 flows into the first circuit 51, whereas during warming up, most of the refrigerant discharged from the compressor 10 flows into the second circuit 52, not the first circuit 51. This makes it possible to suppress the flow rate of the refrigerant flowing through the first circuit 51 during warming up, thereby suppressing the retention of oil in the indoor heat exchanger 20 (e.g., a condenser). In addition, the oil taken out from the compressor 10 during warming up can be returned to the compressor 10 through the second circuit 52. Therefore, it is possible to suppress the decrease in the amount of oil in the compressor 10, and it is possible to prevent the compressor 10 from breaking down, thereby improving the quality of the compressor 10 and the refrigeration cycle device. In addition, since it is not necessary to increase the amount of oil sealed in the compressor 10, it is possible to improve the energy saving performance of the refrigeration cycle device. Therefore, it is possible to achieve both the quality and energy saving performance of the refrigeration cycle device.

[0062] In the refrigeration cycle apparatus according to the present embodiment, the control unit 100 controls the opening degree of the first throttling device 30 after the warm-up is completed so as to be larger than the opening degree of the first throttling device 30 during the warm-up. Large After the warm-up is completed, the control unit 100 changes the opening degree of the second throttling device 31 to a value greater than the opening degree of the second throttling device 31 during the warm-up. Small According to this configuration, the amount of refrigerant flowing through the first circuit 51 during warm-up can be further reduced, so that oil retention in the indoor heat exchanger 20 can be suppressed, and the reduction in the amount of oil in the compressor 10 can be suppressed.

[0063] In the refrigeration cycle device according to the present embodiment, the control unit 100 makes the frequency of the compressor 10 after warm-up is completed higher than the frequency of the compressor 10 during warm-up. With this configuration, the amount of refrigerant flowing through the first circuit 51 during warm-up can be reduced, so that oil retention in the indoor heat exchanger 20 can be suppressed, and the reduction in the amount of oil in the compressor 10 can be suppressed.

[0064] In the refrigeration cycle apparatus according to the present embodiment, the control unit 100 sets the upper limit opening degree of the first throttling device 30 during warm-up to an opening degree smaller than the upper limit opening degree of the first throttling device 30 after the warm-up is completed. The control unit 100 sets the upper limit frequency of the compressor 10 during warm-up to a frequency smaller than the upper limit frequency of the compressor 10 after the warm-up is completed. The control unit 100 sets the opening degree of the second throttling device 31 during warm-up to an opening degree larger than the opening degree of the second throttling device 31 after the warm-up is completed. According to this configuration, the amount of refrigerant flowing through the first circuit 51 during warm-up can be reduced, so that the retention of oil in the indoor heat exchanger 20 can be suppressed, and the reduction in the amount of oil in the compressor 10 can be suppressed.

[0065] In the refrigeration cycle apparatus according to the present embodiment, after warm-up, the control unit 100 operates the compressor 10 at a frequency higher than the upper limit frequency of the compressor 10 during warm-up. This configuration can improve the performance of the refrigeration cycle apparatus after warm-up.

[0066] In the refrigeration cycle apparatus according to the present embodiment, the second temperature T2 is set to a temperature at which the degree of superheat with respect to the saturation temperature of the discharge pressure of the compressor 10 is 5K or more.

[0067] According to this configuration, the refrigerant can be more reliably brought into a superheated gas state when the discharged refrigerant temperature reaches the second temperature T2, so that the amount of oil flowing out into the first circuit 51 can be reduced.

[0068] In the refrigeration cycle apparatus according to the present embodiment, the first throttling device is a flow control valve 13 provided downstream of the first branch portion 11 and upstream of the indoor heat exchanger 20 in the flow of the refrigerant during heating operation.

[0069] According to this configuration, the amount of oil flowing into the indoor heat exchanger 20 during warm-up can be reduced.

[0070] Embodiment 2 A refrigeration cycle apparatus according to a second embodiment will be described. FIG. 9 is a graph showing an example of the change over time in discharge refrigerant temperature in a refrigeration cycle apparatus according to this embodiment. The horizontal axis represents time, and the vertical axis represents temperature. Temperature Tc represents the temperature of the space in which the condenser is provided. Since the operation in this embodiment is a heating operation, the space in which the condenser is provided is indoors. Temperature T1 represents the first temperature. Temperature T2 represents the second temperature. Times ta and tb represent the elapsed time from the start of the compressor 10 (tb <ta)。

[0071] 9, the temperature of the refrigerant discharged from the compressor 10 increases over time after the compressor 10 is started, reaches temperature Tc at time tb, and reaches second temperature T2 at time ta. Time tb is more than half of time ta (tb≧ta / 2). In other words, the saturation temperature of the discharge pressure is controlled to be lower than the temperature of the space in which the condenser is provided for a time period that is more than 50% of the time ta until the temperature of the discharged refrigerant reaches second temperature T2.

[0072] As described above, in this embodiment, the saturation temperature of the discharge pressure of the compressor 10 is lower than the temperature of the space in which the indoor heat exchanger 20 is installed for a time period that is 50% or more of the time ta until the temperature of the refrigerant discharged from the compressor 10 reaches the second temperature T2 when the heating operation is started.

[0073] According to this configuration, during warm-up in heating operation, the saturation temperature of the discharge pressure can be maintained at a temperature lower than the temperature of the space in which the condenser is installed, so that refrigerant retention in the condenser can be suppressed. Therefore, reduction in the amount of oil in the compressor 10 can be suppressed, and the quality of the compressor 10 and the refrigeration cycle device can be improved.

[0074] Embodiment 3 A refrigeration cycle device according to a third embodiment will be described. Fig. 10 is a graph showing the change over time in the degree of subcooling of the outlet refrigerant of the indoor heat exchanger in the refrigeration cycle device according to this embodiment. The horizontal axis represents time, and the vertical axis represents the degree of subcooling. The operation in this embodiment is a heating operation. As described in the first embodiment, during the warm-up period from when the compressor 10 is started until the temperature of the discharged refrigerant reaches the second temperature, the opening degree s of the first throttling device 30 is controlled to be in the range of 0≦s≦the first opening degree.

[0075] As shown in Fig. 10, in this embodiment, when the degree of subcooling of the outlet refrigerant of the indoor heat exchanger 20 becomes equal to or greater than a reference degree of subcooling during warm-up in heating operation, the opening degree s of the first throttling device 30 increases, and the opening degree s becomes greater than the first opening degree. The value of the reference degree of subcooling is stored in advance in the ROM of the control unit 100. From the viewpoint of achieving both quality and energy saving, it is desirable for the reference degree of subcooling to be equal to or greater than 5K and equal to or less than 20K.

[0076] As described above, in this embodiment, when the degree of subcooling of the outlet refrigerant of the indoor heat exchanger 20 becomes equal to or higher than a reference degree of subcooling during warm-up of heating operation, the control unit 100 increases the opening degree of the first throttling device 30 beyond the upper limit opening degree of the first throttling device 30 during warm-up.

[0077] According to this configuration, when liquid refrigerant accumulates in the indoor heat exchanger 20, which serves as a condenser, the liquid refrigerant can be returned to the outdoor unit 70. When liquid refrigerant accumulates in the indoor heat exchanger 20, oil also accumulates in the indoor heat exchanger 20. For this reason, the oil can be returned to the outdoor unit 70 together with the liquid refrigerant. This makes it possible to suppress a decrease in the amount of oil in the compressor 10, improving the quality of the compressor 10 and the refrigeration cycle device. In addition, since an increase in the condensation saturation temperature can be suppressed, energy saving performance can be improved.

[0078] Embodiment 4 A refrigeration cycle apparatus according to a fourth embodiment will be described. Fig. 11 is a graph showing the change over time in the rotation speed of the outdoor blower in the refrigeration cycle apparatus according to this embodiment. The horizontal axis represents time, and the vertical axis represents the rotation speed of the outdoor blower 41. Time ta represents the elapsed time from when the compressor 10 starts to when the temperature of the discharged refrigerant reaches the second temperature T2. The operation in this embodiment is cooling operation.

[0079] 11, when the compressor 10 is started and warm-up is commenced, the outdoor blower 41 is started at a relatively low rotation speed under the control of the control unit 100. The rotation speed at this time is, for example, less than 50% of the maximum rotation speed. The rotation speed of the outdoor blower 41 is not increased from the rotation speed immediately after the start until the temperature of the discharged refrigerant reaches the second temperature T2.

[0080] As described above, the refrigeration cycle apparatus according to the present embodiment further includes the outdoor blower 41 that supplies air to the outdoor heat exchanger 40. During warm-up in cooling operation, the rotation speed of the outdoor blower 41 is not increased from the rotation speed immediately after startup until the temperature of the refrigerant discharged from the compressor 10 reaches the second temperature T2.

[0081] When the rotation speed of the outdoor blower 41 is increased during the warm-up of the cooling operation, the condensation temperature decreases, the apparent degree of supercooling of the refrigerant dissolved in the oil increases, and the amount of refrigerant evaporation increases. As a result, the oil is entrained in the refrigerant and flows out, so the amount of oil that flows out increases.

[0082] According to the above configuration, since the rotation speed of the outdoor blower 41 is not increased, it is possible to suppress a decrease in the amount of oil in the compressor 10, and it is possible to improve the quality of the compressor 10 and the refrigeration cycle device. In addition, the input of the outdoor blower 41 during warm-up, when the operating capacity is small, is reduced, improving energy saving performance.

[0083] Embodiment 5. A refrigeration cycle apparatus according to a fifth embodiment will be described. Fig. 12 is a circuit diagram showing a configuration of the refrigeration cycle apparatus according to this embodiment during heating operation. In this embodiment, the first branch section 11 is an oil separator. The first branch section 11 and the suction side of the compressor 10 are connected by an oil return pipe 32. The second throttling device 31 is provided in parallel with the oil return pipe 32. As the second throttling device 31, an on-off valve capable of one-stage flow control may be used, or a fixed opening valve capable of two-stage flow control including an intermediate opening may be used.

[0084] As described above, in the refrigeration cycle device according to the present embodiment, the first branch section 11 is an oil separator. The second throttling device 31 is provided in parallel with the oil return pipe 32 that connects the oil separator and the suction side of the compressor 10.

[0085] According to this configuration, the second throttling device 31 is provided in a flow path different from the oil return pipe 32, thereby ensuring the oil return flow rate after warm-up and suppressing flow rate variations during warm-up due to malfunction of the second throttling device 31 or individual differences in the second throttling device 31.

[0086] Embodiment 6 A refrigeration cycle device according to a sixth embodiment will be described. FIG. 13 is a circuit diagram showing a configuration of the refrigeration cycle device according to the present embodiment during heating operation. As shown in FIG. 13, the refrigeration cycle device further includes a third circuit 53. The third circuit 53 branches from the first circuit 51 at a third branching portion 16 and merges with the first circuit 51 at a fourth branching portion 17. The third branching portion 16 is provided downstream of the first branching portion 11 and upstream of the indoor heat exchanger 20 in the flow of the refrigerant during heating operation. The fourth branching portion 17 is provided downstream of the outdoor heat exchanger 40 and upstream of the compressor 10 and the accumulator 14 in the flow of the refrigerant during heating operation. The third circuit 53 is provided with a third throttling device 33. The third throttling device 33 is controlled by the control portion 100. When the temperature of the discharged refrigerant is in the range of the third temperature or more and the second temperature or less, the control portion 100 opens the third throttling device 33. At other times, the control unit 100 keeps the third throttling device 33 in a closed state.

[0087] Fig. 14 is a flowchart showing the flow of the process executed by the control unit at the start-up of the refrigeration cycle apparatus according to this embodiment. Steps S11 to S14 and S20 to S22 are similar to the process in Fig. 4. The ROM of the control unit 100 stores a value of a third temperature lower than the second temperature T2. The third temperature is set to be within ±3K of the saturation temperature of the discharged refrigerant.

[0088] In step S15, the control unit 100 closes the third throttling device 33. In step S16, the control unit 100 determines whether the discharge refrigerant temperature is equal to or higher than the third temperature. If the discharge refrigerant temperature is equal to or higher than the third temperature, the process proceeds to step S17. If the discharge refrigerant temperature is lower than the third temperature, the process returns to step S12.

[0089] In step S17, the control unit 100 opens the third throttling device 33. In step S18, the control unit 100 determines whether the discharge refrigerant temperature is higher than the second temperature. If the discharge refrigerant temperature is higher than the second temperature, the warm-up ends and the process proceeds to step S19. If the discharge refrigerant temperature is equal to or lower than the second temperature, the process returns to step S12. In step S19, the third throttling device 33 is closed. As a result, the third throttling device 33 is open while the temperature of the discharge refrigerant is within the range of the third temperature or higher and the second temperature or lower.

[0090] As described above, the refrigeration cycle apparatus according to the present embodiment further includes the third circuit 53, which is configured to branch off from the first circuit 51 at the third branch section 16 and merge with the first circuit 51 at the fourth branch section 17, and is provided with the third throttling device 33. The third branch section 16 is provided downstream of the first branch section 11 and upstream of the indoor heat exchanger 20 in the refrigerant flow during heating operation. The fourth branch section 17 is provided downstream of the outdoor heat exchanger 40 and upstream of the compressor 10 in the refrigerant flow during heating operation. The control section 100 opens the third throttling device 33 when the temperature of the refrigerant discharged from the compressor 10 is equal to or higher than the third temperature and equal to or lower than the second temperature during warm-up. The third temperature is lower than the second temperature.

[0091] During warm-up, the refrigerant dissolved in the oil of the compressor 10 boils when the temperature of the discharged refrigerant reaches the third temperature. When the liquid refrigerant becomes a gas, it expands, causing a flow to the outside of the second circuit 52. As a result, a certain amount of oil may not return to the compressor 10 and may remain outside the compressor 10.

[0092] According to the above configuration, a low-velocity flow mainly composed of oil swept away together with the boiling gas refrigerant returns to the compressor 10 through the second circuit 52, and a high-velocity flow mainly composed of gas refrigerant returns to the compressor 10 through the third circuit 53, which has a longer path length than the second circuit 52. This makes it possible to suppress outflow of oil to the outside of the compressor 10.

[0093] A refrigerant container such as accumulator 14 may be provided between fourth branch portion 17 and second branch portion 15 to suppress the flow of the refrigerant and oil due to the above-mentioned refrigerant expansion.

[0094] Embodiment 7 A refrigeration cycle device according to a seventh embodiment will be described. FIG. 15 is a graph showing the change over time in the rotation speed of the indoor blower in the refrigeration cycle device according to this embodiment. The horizontal axis represents time, and the vertical axis represents the rotation speed of the indoor blower 21 as a ratio to the maximum rotation speed. A rotation speed of 0% represents that the indoor blower 21 is stopped. FIG. 16 is a graph showing the change over time in the frequency of the compressor in the refrigeration cycle device according to this embodiment. The horizontal axis represents time, and the vertical axis represents the frequency of the compressor 10 as a ratio to the maximum frequency. A frequency of 0% represents that the compressor 10 is stopped. Time ta represents the elapsed time from when the compressor 10 is started until the temperature of the discharged refrigerant reaches the second temperature T2.

[0095] 15 and 16, during warm-up, if the indoor blower 21 is stopped at time tc before the temperature of the discharged refrigerant reaches the second temperature T2, the control unit 100 does not stop the compressor 10 until the temperature of the discharged refrigerant becomes equal to or higher than the second temperature T2. During warm-up after the indoor blower 21 is stopped, the opening degree of the first throttling device 30 is controlled to be in the range from fully closed to the first opening degree, and the second throttling device 31 is controlled to be in the open state.

[0096] Fig. 17 is a graph showing another example of the change over time in the frequency of the compressor in the refrigeration cycle apparatus according to the present embodiment. As shown in Fig. 17, the control unit 100 may reduce the frequency of the compressor 10 after the indoor blower 21 is stopped, as long as the compressor 10 is not stopped before the temperature of the discharged refrigerant becomes equal to or higher than the second temperature T2.

[0097] As described above, the refrigeration cycle apparatus according to the present embodiment further includes the indoor blower 21 that supplies air to the indoor heat exchanger 20. During warm-up, if the indoor blower 21 stops before the temperature of the refrigerant discharged from the compressor 10 reaches the second temperature T2, the control unit 100 prevents the compressor 10 from stopping until the temperature of the refrigerant discharged from the compressor 10 reaches the second temperature T2.

[0098] During warm-up, the refrigerant is dissolved in the oil in the compressor 10 until the temperature of the refrigerant discharged from the compressor 10 reaches the second temperature T2. Therefore, if the compressor 10 stops at the same time as the indoor blower 21 stops, the compressor 10 stops with the refrigerant dissolved in the oil inside. Therefore, the next time the compressor 10 is started, the refrigerant dissolved in the oil boils, and the amount of oil flowing out of the compressor 10 increases.

[0099] According to the above configuration, even after the indoor blower 21 stops, the compressor 10 continues to operate until the temperature of the discharged refrigerant reaches the second temperature T2, so that it is possible to reduce the amount of refrigerant dissolved in the oil in the compressor 10. Therefore, the amount of oil flowing out from the compressor 10 can be reduced the next time the compressor 10 is started. [Explanation of symbols]

[0100] 10 compressor, 11 first branch section, 12 flow path switching device, 13 flow control valve, 14 accumulator, 15 second branch section, 16 third branch section, 17 fourth branch section, 20 indoor heat exchanger, 21 indoor blower, 30 first throttling device, 31 second throttling device, 32 oil return pipe, 33 third throttling device, 40 outdoor heat exchanger, 41 outdoor blower, 51 first circuit, 52 second circuit, 53 third circuit, 70 outdoor unit, 71 indoor unit, 100 control section, 101 outdoor temperature sensor, 102 discharge refrigerant temperature sensor, 103 indoor temperature sensor, 104 discharge pressure sensor, 105 suction pressure sensor.

Claims

1. A first circuit is provided with a compressor, a first branching section, an indoor heat exchanger, a first throttling device, an outdoor heat exchanger, and a second branching section. A second circuit is configured to branch off from the first circuit at the first branching point and merge with the first circuit at the second branching point, and is provided with a second throttle device. The compressor, the first throttle device and the second throttle device are controlled by a control unit, Equipped with, The first branch section is located downstream of the compressor and upstream of the indoor heat exchanger in the refrigerant flow during heating operation. The second branch section is located downstream of the outdoor heat exchanger and upstream of the compressor in the refrigerant flow during heating operation. The first throttling device is provided downstream of the first branch and upstream of the second branch in the refrigerant flow during heating operation. If the outdoor air temperature is lower than the first temperature, the control unit starts the compressor and then performs a warm-up until the temperature of the refrigerant discharged from the compressor reaches the second temperature. The control unit, The openings of the first throttle device and the second throttle device are set such that during the warm-up period, more refrigerant flows to the second circuit than to the first circuit, and after the warm-up period, more refrigerant flows to the first circuit than to the second circuit. The control unit, during the warm-up period of the heating operation, increases the opening of the first throttle device to a level greater than the upper limit opening of the first throttle device during the warm-up period if the degree of subcooling of the refrigerant at the outlet of the indoor heat exchanger exceeds a standard degree of subcooling.

2. A first circuit is provided with a compressor, a first branching section, an indoor heat exchanger, a first throttling device, an outdoor heat exchanger, and a second branching section. A second circuit is configured to branch off from the first circuit at the first branching point and merge with the first circuit at the second branching point, and is provided with a second throttle device. The compressor, the first throttle device and the second throttle device are controlled by a control unit, Equipped with, The first branch section is located downstream of the compressor and upstream of the indoor heat exchanger in the refrigerant flow during heating operation. The second branch section is located downstream of the outdoor heat exchanger and upstream of the compressor in the refrigerant flow during heating operation. The first throttling device is provided downstream of the first branch and upstream of the second branch in the refrigerant flow during heating operation. If the outdoor air temperature is lower than the first temperature, the control unit starts the compressor and then performs a warm-up until the temperature of the refrigerant discharged from the compressor reaches the second temperature. The control unit, The openings of the first throttle device and the second throttle device are set such that during the warm-up period, more refrigerant flows to the second circuit than to the first circuit, and after the warm-up period, more refrigerant flows to the first circuit than to the second circuit. The first throttling device is provided in the refrigerant flow during heating operation downstream of the first branch and upstream of the indoor heat exchanger in a refrigeration cycle device.

3. A first circuit is provided with a compressor, a first branching section, an indoor heat exchanger, a first throttling device, an outdoor heat exchanger, and a second branching section. A second circuit is configured to branch off from the first circuit at the first branching point and merge with the first circuit at the second branching point, and is provided with a second throttle device. The compressor, the first throttle device and the second throttle device are controlled by a control unit, Equipped with, The first branch section is located downstream of the compressor and upstream of the indoor heat exchanger in the refrigerant flow during heating operation. The second branch section is located downstream of the outdoor heat exchanger and upstream of the compressor in the refrigerant flow during heating operation. The first throttling device is provided downstream of the first branch and upstream of the second branch in the refrigerant flow during heating operation. If the outdoor air temperature is lower than the first temperature, the control unit starts the compressor and then performs a warm-up until the temperature of the refrigerant discharged from the compressor reaches the second temperature. The control unit, The openings of the first throttle device and the second throttle device are set such that during the warm-up period, more refrigerant flows to the second circuit than to the first circuit, and after the warm-up period, more refrigerant flows to the first circuit than to the second circuit. The third circuit is configured to branch off from the first circuit at a third branching point and merge with the first circuit at a fourth branching point, and further comprises a third throttling device. The third branch is located downstream of the first branch and upstream of the indoor heat exchanger in the refrigerant flow during heating operation. The fourth branch section is located downstream of the outdoor heat exchanger and upstream of the compressor in the refrigerant flow during heating operation. The control unit opens the third throttle device during warm-up if the temperature of the refrigerant discharged from the compressor is between a third temperature and the second temperature, but lower than or equal to the second temperature.

4. The refrigeration cycle apparatus according to claim 3, wherein the third temperature is set to a temperature within ±3 K of the saturation temperature of the discharge pressure of the compressor.

5. A first circuit is provided with a compressor, a first branching section, an indoor heat exchanger, a first throttling device, an outdoor heat exchanger, and a second branching section. A second circuit is configured to branch off from the first circuit at the first branching point and merge with the first circuit at the second branching point, and is provided with a second throttle device. The compressor, the first throttle device and the second throttle device are controlled by a control unit, Equipped with, The first branch section is located downstream of the compressor and upstream of the indoor heat exchanger in the refrigerant flow during heating operation. The second branch section is located downstream of the outdoor heat exchanger and upstream of the compressor in the refrigerant flow during heating operation. The first throttling device is provided downstream of the first branch and upstream of the second branch in the refrigerant flow during heating operation. If the outdoor air temperature is lower than the first temperature, the control unit starts the compressor and then performs a warm-up until the temperature of the refrigerant discharged from the compressor reaches the second temperature. The control unit, The openings of the first throttle device and the second throttle device are set such that during the warm-up period, more refrigerant flows to the second circuit than to the first circuit, and after the warm-up period, more refrigerant flows to the first circuit than to the second circuit. The system further comprises an indoor blower that supplies air to the indoor heat exchanger, A refrigeration cycle device in which, during the warm-up period, the indoor blower and the compressor are operating, and if the operating indoor blower stops before the temperature of the refrigerant discharged from the compressor reaches the second temperature, the control unit prevents the compressor from stopping until the temperature of the refrigerant discharged from the compressor reaches the second temperature.

6. The control unit, A refrigeration cycle apparatus according to any one of claims 1 to 5, wherein, after the warm-up is completed, the opening of the first throttle device is increased to be greater than the opening of the first throttle device during the warm-up, and the opening of the second throttle device is decreased to be less than the opening of the second throttle device during the warm-up.

7. The control unit, The refrigeration cycle apparatus according to any one of claims 1 to 5, wherein the frequency of the compressor is increased after the warm-up is completed compared to the frequency of the compressor during the warm-up.

8. The control unit, The upper limit of the opening of the first throttle device during warm-up is set to a smaller opening than the upper limit of the opening of the first throttle device after the warm-up is complete. The upper limit frequency of the compressor during the warm-up period is set to a frequency lower than the upper limit frequency of the compressor after the warm-up period is completed. The refrigeration cycle apparatus according to any one of claims 1 to 5, wherein the opening of the second throttle device during warm-up is set to a larger opening than the opening of the second throttle device after the warm-up is completed.

9. The refrigeration cycle apparatus according to any one of claims 1 to 5, wherein the control unit operates the compressor at a frequency higher than the upper limit frequency of the compressor during warm-up after the warm-up is completed.

10. The refrigeration cycle apparatus according to any one of claims 1 to 5, wherein, during the warm-up period of the heating operation, for a period of 50% or more of the time from when the compressor is started until the temperature of the refrigerant discharged from the compressor reaches the second temperature, the saturation temperature of the discharge pressure of the compressor is lower than the temperature of the space in which the indoor heat exchanger is provided.

11. The system further includes an outdoor fan that supplies air to the outdoor heat exchanger, The refrigeration cycle apparatus according to any one of claims 1 to 5, wherein during the warm-up period of cooling operation, the rotational speed of the outdoor fan is not increased from the rotational speed immediately after startup until the temperature of the refrigerant discharged from the compressor reaches the second temperature.

12. The refrigeration cycle apparatus according to any one of claims 1 to 5, wherein the second temperature is set to a temperature at which the degree of superheating relative to the saturation temperature of the discharge pressure of the compressor is 5K or more.

13. The first branch section is an oil separator, The refrigeration cycle apparatus according to any one of claims 1 to 5, wherein the second throttle device is provided in parallel with the oil return pipe connecting the oil separator and the suction side of the compressor.

14. The control unit controls the opening degree of the first throttle device during warm-up from fully closed to a first open degree. The refrigeration cycle apparatus according to any one of claims 1 to 5, wherein the first opening is 30% or less of the opening of the first throttle device during rated operation.

15. The control unit controls the frequency of the compressor during warm-up to a first frequency or lower. The refrigeration cycle apparatus according to any one of claims 1 to 5, wherein the first frequency is a frequency that is 40% or less of the frequency of the compressor in rated operation.

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