JP7507402B2 - Air Conditioning Equipment - Google Patents

Description

The present invention relates to an air conditioning device.

Conventionally, there is known an air conditioner equipped with an accumulator that separates the refrigerant returned to the compressor into gas and liquid and stores the liquid refrigerant (see, for example, Patent Document 1). In this type of air conditioner, when the discharged refrigeration oil circulates through the refrigerant circuit and returns to the compressor, the refrigeration oil may accumulate in the accumulator together with the liquid refrigerant. In this case, if the liquid refrigerant and the refrigeration oil are separated into two layers in the accumulator, it becomes difficult for the refrigeration oil accumulated in the accumulator to return to the compressor, which may cause a shortage of refrigeration oil in the compressor and cause poor lubrication of the compressor.
Therefore, in Patent Document 1, when a two-layer separation state is detected, the rotation speed of the compressor is increased to agitate the liquid refrigerant and the refrigeration oil that have separated into two layers in the accumulator, thereby attempting to eliminate the two-layer separation state.

JP 2016-211774 A

However, since whether or not the refrigerant is in a two-phase state depends on the refrigerant temperature in the accumulator, there is a problem in that the two-phase state is difficult to resolve even if the rotation speed of the compressor is increased to stir the refrigerant.
The present invention has been made in consideration of the above-mentioned circumstances, and has an object to provide an air conditioner that makes it easy to eliminate the two-layer separation state and to easily maintain the lubrication of the compressor.

In order to solve the above problems, the present invention provides an air conditioning apparatus comprising a compressor, a condenser, an evaporator, and an accumulator that separates refrigerant flowing in from the evaporator into gas and liquid and stores the liquid refrigerant, comprising detection means arranged on the suction side of the compressor and including at least one of a suction temperature sensor that detects a refrigerant temperature, an outside air temperature sensor that detects an outside air temperature, a concentration sensor that detects a refrigerant oil concentration in the accumulator, and a low pressure sensor arranged on the suction side of the compressor that detects a refrigerant pressure, and a control unit that determines whether or not the refrigerant oil is separated from the liquid refrigerant in the accumulator based on a detection value of the detection means , and the detection means is The control unit is provided with a suction temperature sensor arranged on the suction side of the compressor to detect the refrigerant temperature, and the control unit determines whether or not the refrigerant temperature corresponding to the detection value of the suction temperature sensor is below a preset threshold temperature based on the temperature at which the two-layer separation state occurs, thereby determining whether or not the refrigerant is in the two-layer separation state, and when the control unit determines that the refrigerant is in the two-layer separation state, executes two-layer separation elimination control to raise the suction temperature of the compressor, and the control unit executes the two-layer separation elimination control so that the refrigerant temperature detected by the suction temperature sensor is higher than the threshold temperature and lower than a second threshold temperature that is preset so that air conditioning performance can be maintained .
According to this, the refrigerant temperature of the refrigerant flowing out from the evaporator can be increased, and the refrigerant temperature flowing into the accumulator can be increased.

According to the present invention, the refrigerant temperature in the accumulator can be increased to easily eliminate the two-phase separation state in the accumulator, which makes it easier for the refrigeration oil to return to the compressor and makes it easier to maintain the lubrication of the compressor.

FIG. 1 is a diagram showing a configuration of an air conditioning device according to an embodiment. FIG. 1 is a block diagram showing a control configuration according to an embodiment. A diagram showing the relationship between the oil content and the two-layer separation temperature FIG. 13 is a diagram showing the relationship between the compressor discharge condensation temperature, the compressor container surface temperature, and the operation time at the beginning of operation start-up. A flowchart showing the determination and execution operation of the two-layer separation elimination control of the air conditioner according to the embodiment. A diagram showing the relationship between the differential temperature, operation frequency, and operation time when recondensation occurs. FIG. 1 shows the relationship between the differential temperature, the operating frequency, and the operating time when recondensation is eliminated before the two-layer separation state is eliminated.

A first invention is an air conditioning apparatus comprising a compressor, a condenser, an evaporator, and an accumulator that separates the refrigerant flowing in from the evaporator into gas and liquid and stores the liquid refrigerant, and further comprising detection means comprising at least one of an intake temperature sensor arranged on the suction side of the compressor to detect the refrigerant temperature, an outside air temperature sensor to detect the temperature of the outside air, a concentration sensor to detect the concentration of refrigeration oil in the accumulator, and a low pressure sensor arranged on the suction side of the compressor to detect the refrigerant pressure, and a control unit that determines whether the accumulator is in a two-layer separation state in which the refrigeration oil has been separated from the liquid refrigerant based on the detection value of the detection means, and when the control unit determines that the accumulator is in the two-layer separation state, it executes two-layer separation elimination control to increase the suction temperature of the compressor.
This increases the temperature of the refrigerant flowing out of the evaporator, thereby increasing the temperature of the refrigerant flowing into the accumulator. By increasing the refrigerant temperature in the accumulator, the two-phase separation state in the accumulator can be easily eliminated, making it easier for refrigeration oil to return to the compressor and making it easier to maintain the lubrication of the compressor.

In a second invention, the detection means includes an inlet temperature sensor arranged on the suction side of the compressor to detect the refrigerant temperature, and the control unit determines whether or not the refrigerant temperature corresponding to the detection value of the suction temperature sensor is below a preset threshold temperature based on the temperature at which the two-phase separation state occurs, thereby determining whether or not the refrigerant is in the two-phase separation state.
This makes it possible to determine whether the refrigerant is in a two-layer separation state based on the refrigerant temperature and to execute two-layer separation elimination control.

In a third invention, the control unit executes the two-layer separation elimination control so that the refrigerant temperature detected by the suction temperature sensor is higher than the threshold temperature and lower than a second threshold temperature that is preset so as to maintain air conditioning performance.
This makes it possible to avoid damaging the air conditioning performance by excessively increasing the suction temperature of the compressor, and makes it possible to maintain the air conditioning performance while ensuring the ability to eliminate the two-layer separation state.

In a fourth aspect of the present invention, the control unit executes the two-phase separation elimination control by operating the compressor at a frequency that is suppressed below a frequency during normal operation.
This allows the suction temperature of the compressor to be increased by controlling the compressor.

The fifth invention includes a discharge temperature sensor arranged on the discharge side of the compressor to detect the refrigerant temperature, and the control unit determines whether the refrigerant is re-condensing based on the detection value of the discharge temperature sensor at the beginning of air conditioning operation startup, and executes the two-layer separation elimination control if the refrigerant is re-condensing.
As a result, when recondensation of the refrigerant is detected at the beginning of the air conditioning operation, the two-layer separation elimination control is executed to suppress the operating frequency of the compressor, thereby suppressing the amount of refrigeration oil discharged from the compressor, making it easier for refrigeration oil to remain in the compressor and suppressing damage to the compressor.

In a sixth aspect of the present invention, the control unit executes the two-layer separation elimination control in a cooling operation and does not execute the two-layer separation elimination control in a heating operation.
As a result, since the air conditioning load is large during heating operation, by not executing the two-layer separation elimination control, it is possible to avoid a significant drop in air conditioning performance.

Hereinafter, an embodiment of the present invention will be described with reference to the drawings.
[1. First embodiment]
FIG. 1 is a diagram showing the configuration of an air conditioning device 1 according to an embodiment.
As shown in Fig. 1, the air conditioning device 1 of this embodiment includes an outdoor unit 10, an indoor unit 20 connected to the outdoor unit 10 via a refrigerant pipe 11, and a control unit 100. However, although this embodiment shows an example in which one indoor unit 20 is installed, the present invention is not limited to this, and for example, two indoor units 20 may be installed, or three or more indoor units 20 may be installed.

The outdoor unit 10 has variable capacity by changing the operating frequency using an inverter. In other words, it is equipped with a variable capacity compressor 12 whose capacity changes depending on the operating frequency. An oil separator 13 is connected to the discharge side of the compressor 12 via a refrigerant pipe 11.

An outdoor heat exchanger 16 is connected to the oil separator 13 through a check valve 14 and a four-way valve 15 via a refrigerant pipe 11. Outside air is blown to the outdoor heat exchanger 16 by an outdoor fan 16a. An indoor unit 20 is connected to the outdoor heat exchanger 16 through the refrigerant pipe 11. An expansion valve 17 is provided in the refrigerant pipe 11 between the outdoor heat exchanger 16 and the indoor unit 20.

The indoor unit 20 is equipped with an indoor heat exchanger 21 and an indoor expansion valve 22. An indoor fan 21a blows indoor air into the indoor heat exchanger 21. The four-way valve 15 of the outdoor unit 10 is connected to the indoor unit 20 via the refrigerant piping 11. The four-way valve 15 is connected to the suction side of the compressor 12 via the accumulator 18.

The accumulator 18 has a function of separating the refrigerant into gas and liquid and storing surplus refrigerant. The accumulator 18 separates the refrigerant returned from the indoor heat exchanger 21 functioning as an evaporator or the outdoor heat exchanger 16 into gas and liquid, making it easier for the gas refrigerant to be sent to the compressor 12.
An oil return hole 18b is provided at the bottom of the U-shaped refrigerant pipe 18a of the accumulator 18. Refrigeration oil is returned to the compressor 12 side through the oil return hole 18b.
In the accumulator 18 of the present embodiment, the oil return hole 18b is provided in the refrigerant pipe 18a, but the refrigerant oil may be returned to the compressor 12 without using the oil return hole 18b in the refrigerant pipe 18a (i.e., without the oil return hole 18b). For example, an oil drain pipe extending from the refrigerant pipe 18a outside the accumulator 18 may be provided at the bottom of the accumulator 18, and a solenoid valve or an electric valve may be provided on the oil drain pipe. In the accumulator 18 of this configuration, when returning the refrigerant oil to the compressor 12, the solenoid valve or the electric valve is operated to open the oil drain pipe, so that the refrigerant oil can be returned to the compressor 12.

An oil pipe 25 is also connected to the oil separator 13. One end of the oil pipe 25 is connected to the oil separator 13, and the other end is connected to the refrigerant pipe 11 on the suction side of the compressor 12. The oil pipe 25 is provided with a capillary tube 26 for returning oil. The refrigeration oil separated from the refrigerant by the oil separator 13 is returned to the compressor 12 via the oil pipe 25.

A plurality of filters 27 are disposed in the refrigerant pipes 11 and the oil pipes 25. Specifically, the filter 27 is disposed between the expansion valve 17 and the on-off valve 19a. The filter 27 is also disposed between the on-off valve 19b and the four-way valve 15. The filter 27 is also disposed on the suction side of the compressor 12.
The outdoor unit 10 is equipped with on-off valves 19 a, 19 b connected to a refrigerant pipe 11 extending from the indoor unit 20 .

A discharge temperature sensor 30 is provided on the discharge side of the compressor 12 to detect the temperature of the refrigerant discharged from the compressor 12. A high-pressure sensor 31 and a high-pressure switch 32 are provided between the oil separator 13 and the check valve 14. The high-pressure sensor 31 detects the pressure of the refrigerant discharged from the compressor 12. The high-pressure switch 32 is a switch for stopping the operation of the air conditioning device 1 when the pressure of the discharged refrigerant reaches a predetermined maximum pressure.

An outdoor gas temperature sensor 33 is provided on one side of the outdoor heat exchanger 16 (the refrigerant inflow side during cooling operation) to detect the temperature of the gas refrigerant in the outdoor heat exchanger 16. An outdoor liquid temperature sensor 34 is provided on the other side of the outdoor heat exchanger 16 (the refrigerant outflow side during cooling operation) to detect the temperature of the liquid refrigerant in the outdoor heat exchanger 16. Furthermore, the outdoor heat exchanger 16 is provided with an outdoor air temperature sensor 35 that detects the outdoor air temperature.

The refrigerant piping 11 on the suction side of the compressor 12 is provided with a suction temperature sensor 36 for detecting the temperature of the refrigerant sucked into the compressor 12 and a low pressure sensor 37 for detecting the pressure of the refrigerant sucked into the compressor 12. In this embodiment, the suction temperature sensor 36 is disposed between the four-way valve 15 and the accumulator 18. The low pressure sensor 37 is disposed between the accumulator 18 and the compressor 12. The suction temperature sensor 36 may be disposed between the accumulator 18 and the compressor 12, and closer to the accumulator 18 than the connection between the oil piping 25 and the refrigerant piping 11, instead of between the four-way valve 15 and the accumulator 18. The suction temperature sensor 36 and the low pressure sensor 37 constitute a superheat detection means.

An indoor liquid temperature sensor 38 is provided on one side of the indoor heat exchanger 21 (the refrigerant inflow side during cooling operation) to detect the temperature of the liquid refrigerant in the indoor heat exchanger 21, and an indoor gas temperature sensor 39 is provided on the other side of the indoor heat exchanger 21 (the refrigerant outflow side during cooling operation) to detect the temperature of the gas refrigerant in the indoor heat exchanger 21. The indoor heat exchanger 21 is provided with an indoor air temperature sensor 40 that detects the indoor air temperature (room air temperature).

An oil concentration sensor 41 is provided at the bottom of the accumulator 18. The oil concentration sensor 41 detects the concentration of refrigeration oil in the accumulator 18.

The outdoor unit 10 of the air conditioning apparatus 1 includes a control unit 100. The control unit 100 is electrically connected to the components and devices to be controlled. The control unit 100 controls the air conditioning apparatus 1. However, the control unit 100 does not necessarily have to be provided in the outdoor unit 10, and the location of the control unit 100 may be changed as appropriate. Furthermore, the control unit 100 does not necessarily have to be provided in only one place, and may be configured to be divided and provided in, for example, the outdoor unit 10 and the indoor unit 20.
1 does not show wiring for the control unit 100. The control unit 100 is electrically connected to electronic components such as sensors as described below, and transmits necessary commands and communicates information between them as required.
However, the electrical connection may be a connection using wireless communication or the like other than a connection using electric wires or cables.

Figure 2 is a block diagram showing the control configuration according to the embodiment. The control unit 100 comprehensively controls each part of the air conditioning device 1, and as shown in Figure 2, includes a CPU as an arithmetic execution unit, a ROM that stores basic control programs executable by the CPU and predetermined data in a non-volatile manner, a memory such as a RAM that stores data in a volatile manner, and other peripheral circuits.

The control unit 100 also receives detection values from the discharge temperature sensor 30, high pressure sensor 31, high pressure switch 32, outdoor gas temperature sensor 33, outdoor liquid temperature sensor 34, outdoor air temperature sensor 35, suction temperature sensor 36, low pressure sensor 37, indoor liquid temperature sensor 38, indoor gas temperature sensor 39, indoor air temperature sensor 40, and oil concentration sensor 41. Based on these detection values, the control unit 100 is configured to control the operating frequency of the compressor 12, the drive of the outdoor fan 16a of the outdoor heat exchanger 16, and the indoor fan 21a of the indoor heat exchanger 21, and to control the opening of the expansion valve 17 and the indoor expansion valve 22.

In addition, in this embodiment, the control unit 100 executes two-layer separation elimination control when a predetermined condition is reached during cooling operation. Note that cooling operation in this embodiment refers to operation of the air conditioner 1 in which the outdoor heat exchanger 16 functions as a condenser and the indoor heat exchanger 21 functions as an evaporator, and so-called dehumidification operation is also included in cooling operation.

FIG. 3 is a diagram showing the relationship between the oil content and the two-phase separation temperature.
As shown in Fig. 3, when the R32 refrigerant has an oil content of about 10 wt% to 30 wt%, the two-layer separation temperature (refrigerant temperature) when the liquid refrigerant and the refrigeration oil are separated into two layers is plotted, and the two-layer separation temperature appears near the minus a specified temperature and near the plus a specified temperature. In other words, whether the liquid refrigerant and the refrigeration oil are in a two-layer state in the accumulator 18 depends on the refrigerant temperature.

Line L1, which connects the plotted points near the minus specified temperature, divides the temperature into a separation region R1 where the liquid refrigerant and the refrigeration oil separate, and a dissolution region R2 where the refrigeration oil dissolves in the liquid refrigerant. Line L2, which connects the plotted points near the plus specified temperature, divides the temperature into a dissolution region R2 where the refrigeration oil dissolves in the liquid refrigerant, and a separation region R3 where the liquid refrigerant and the refrigeration oil separate.

Generally, during air conditioning operation, the refrigerant temperature may reach a temperature belonging to separation region R1, so when the refrigerant temperature is at a temperature belonging to separation region R1, the refrigerant temperature is increased to transition to a temperature belonging to dissolution region R2.
Here, the R410A refrigerant, which has been used in many air-conditioning operations, has a low minus-predetermined temperature corresponding to the line L1. In contrast, the R32 refrigerant used in this embodiment has a significantly higher minus-predetermined temperature than the R410A refrigerant, so the refrigerant temperature is more likely to reach the separator R1 temperature and the two-layer separation state occurs more easily when the R32 refrigerant is used than when the R410A refrigerant is used. Therefore, in the air-conditioning device 1 of this embodiment, which uses the R32 refrigerant, it is highly necessary to eliminate the two-layer separation state.

Therefore, in the present embodiment, the control unit 100 executes two-layer separation elimination control to raise the suction temperature of the compressor 12 when the two-layer separation state occurs. Specifically, the control unit 100 raises the evaporation temperature of the indoor heat exchanger 21 functioning as an evaporator in order to raise the suction temperature of the compressor 12. This makes it easier to bring the refrigerant temperature in the accumulator 18 to the temperature of the dissolution range R2, and makes it easier for the refrigerant oil to dissolve in the liquid refrigerant and eliminate the two-layer separation state. Therefore, the refrigerant oil dissolved in the liquid refrigerant is easier to return to the compressor 12 through the oil return hole 18b, making it easier to maintain the lubrication of the compressor 12.
Generally, the evaporation temperature for ensuring the air conditioning capacity required during air conditioning operation is 5° C. or higher and 15° C. or lower. Therefore, in practice, two-layer separation elimination control may be executed based on the two-layer separation temperature of 15° C. or lower.

FIG. 4 is a diagram showing the relationship between the discharge condensation temperature (discharge saturation temperature) of the compressor 12 at the beginning of operation, the surface temperature of the container of the compressor 12, and the operation time.
4, the discharge condensation temperatures of the compressor 12 are indicated by symbols A1 and A2. Of these, the high-temperature side discharge condensation temperature A1 indicates a case where the operating frequency of the compressor 12 is higher than the low-temperature side discharge condensation temperature A2. Also, the surface temperature of the container of the compressor 12 is indicated by symbol B.
4, in the early stage of starting up the air conditioning operation, the surface temperature B of the compressor 12 increases with the lapse of the operation time of the compressor 12. The discharge condensation temperatures A1 and A2 also tend to increase with the lapse of the operation time of the compressor 12, but the higher the operation frequency of the compressor 12, the more likely the discharge condensation temperatures A1 and A2 become high temperatures.

Therefore, at the beginning of operation, the higher the operating frequency of the compressor 12, the larger the temperature difference C of the saturation temperature (condensation temperature) A1 relative to the surface temperature B of the compressor 12 becomes. When the temperature difference C becomes large, when the gas refrigerant is cooled on the surface of the container of the compressor 12, it is easy for the temperature to fall below the saturation temperature (condensation temperature). Therefore, in the compressor 12, the phenomenon in which the gas refrigerant is cooled and liquefied by the surface temperature of the compressor 12, that is, recondensation, occurs easily. When recondensation occurs, liquid refrigerant is easily discharged from the compressor 12, so that the refrigerant oil dissolves in the liquid refrigerant and is discharged, and the refrigerant oil in the compressor 12 is easily reduced. On the other hand, when recondensation does not occur, it is difficult to discharge the liquid refrigerant, so the amount of refrigerant oil in the compressor 12 is less likely to decrease than when recondensation occurs.

Therefore, when it is determined that re-condensation will occur in the early stage of air conditioning operation, the control unit 100 of this embodiment executes two-layer separation elimination control to set the operating frequency of the compressor 12 to a frequency that is suppressed below the frequency during normal operation. Normal operation is an operation in which two-layer separation elimination control is not executed.
This reduces the temperature difference C between the saturation temperature (condensation temperature) A2 and the surface temperature B of the compressor 12, thereby reducing the amount of refrigeration oil discharged from the compressor 12. In addition, the two-phase separation elimination control makes it easier for refrigeration oil to return to the accumulator 18.

Next, the determination and execution operation of the two-layer separation elimination control in this embodiment will be described.
5 is a flowchart showing the determination and execution operation of the two-layer separation elimination control of the air conditioning apparatus 1 according to the embodiment. The operation in FIG.

As shown in FIG. 5, when the control unit 100 starts the process of the determination and execution operation of the two-layer separation elimination control, it determines whether or not the operation is cooling (step ST1).
In the case of cooling operation (step ST1; YES), the control unit 100 determines whether or not the refrigerant is in a two-layer separation state (step ST2). In this embodiment, whether or not the refrigerant is in a two-layer separation state is determined based on the suction refrigerant temperature corresponding to the detection value of the suction temperature sensor 36. The control unit 100 determines whether or not the suction refrigerant temperature is equal to or lower than a preset threshold temperature. The threshold temperature is set based on the two-layer separation temperature. In this embodiment in which the refrigerant is R32, the threshold temperature is set based on the temperature indicated by the line L1 in FIG. 3. As an example, the threshold temperature is set to a first temperature T1 at which the refrigerant temperature is maximum indicated by the line L1 in FIG. 3. When the control unit 100 determines that the refrigerant temperature is equal to or lower than the threshold temperature (first temperature T1), the control unit 100 determines that the refrigerant is in a two-layer separation state. When the control unit 100 determines that the refrigerant temperature is not equal to or lower than the threshold temperature (first temperature T1), that is, that the refrigerant temperature is higher than the threshold temperature (first temperature T1), the control unit 100 determines that the refrigerant is not in a two-layer separation state.

In this embodiment, the two-layer separation state is determined based on the refrigerant temperature, but it may be determined based on the outside air temperature acquired by the outside air temperature sensor 35. That is, it may be determined that the two-layer separation state has occurred in the accumulator 18 when the outside air temperature is equal to or lower than a predetermined temperature. In addition, instead of determining whether the two-layer separation state has occurred based on the refrigerant temperature or the outside air temperature, it may be determined whether the two-layer separation state has occurred in the accumulator 18 based on the concentration of the refrigerant oil detected by the oil concentration sensor 41. That is, it may be determined that the two-layer separation state has occurred when the concentration of the refrigerant oil is equal to or lower than a predetermined threshold concentration. Furthermore, it may be determined that the two-layer separation state has occurred based on the saturation temperature of the refrigerant (low-pressure refrigerant saturation temperature) corresponding to the suction refrigerant pressure detected by the low-pressure sensor 37. It may also be determined that the two-layer separation state has occurred based on the detection values of multiple sensors, including the suction temperature sensor 36, the outside air temperature sensor 35, the oil concentration sensor 41, and the low-pressure sensor 37, rather than the detection value of only one sensor.

When the control unit 100 determines that the two-layer separation state exists (step ST2; YES), it determines whether or not recondensation of the refrigerant has occurred in the compressor 12 (step ST3). In this embodiment, the control unit 100 determines whether or not recondensation has occurred based on the discharge refrigerant temperature corresponding to the detection value of the discharge temperature sensor 30 and the discharge refrigerant pressure corresponding to the detection value of the high pressure sensor 31.

In detail, the control unit 100 acquires the saturation temperature of the refrigerant corresponding to the discharge refrigerant pressure based on the lookup table information stored in advance. When the control unit 100 acquires the saturation temperature of the refrigerant, it calculates the temperature difference ΔT (see FIG. 6, FIG. 7) by subtracting the saturation temperature from the discharge refrigerant temperature. The control unit 100 determines whether this temperature difference ΔT is equal to or greater than a predetermined difference threshold Δa (see FIG. 6, FIG. 7). When the control unit 100 determines that the temperature difference ΔT is equal to or less than the difference threshold Δa, it determines that re-condensation has occurred. When the control unit 100 determines that the temperature difference ΔT is not equal to or less than the difference threshold Δa, that is, that the temperature difference ΔT is greater than the difference threshold Δa, it determines that re-condensation has not occurred. Note that the difference threshold Δa can be set to 0 [°C], but a value between 0 [°C] and 10 [°C] is set in consideration of a margin. In this embodiment, as an example, the difference threshold Δa is set to 5 [°C].

In this embodiment, whether or not recondensation has occurred is determined based on the discharge refrigerant temperature corresponding to the detection value of the discharge temperature sensor 30 and the discharge refrigerant pressure corresponding to the detection value of the high pressure sensor 31. However, whether or not recondensation has occurred may be determined based on the discharge refrigerant temperature rather than the discharge refrigerant pressure.

When the control unit 100 determines that re-condensation has occurred (step ST3; YES), it determines whether the intake refrigerant temperature is equal to or lower than a preset first temperature T1 (see FIG. 3) (step ST3). The first temperature T1 is a temperature for determining whether the refrigerant oil is in a two-layer separation state in which it has been separated from the liquid refrigerant in the accumulator 18, and is set based on the two-layer separation temperature. In this embodiment, the first temperature T1 is set to the same temperature as the threshold temperature described above.

When the control unit 100 determines that the suction refrigerant temperature is equal to or lower than the first temperature T1 (step ST4; YES), it sets the operating frequency of the compressor 12 to the first suppression frequency (step ST5). The first suppression frequency is a frequency obtained by subtracting a predetermined frequency from the operating frequency during normal operation when the two-layer separation elimination control is not executed. However, since the first suppression frequency is set to a frequency at which the refrigerant can circulate in the refrigeration circuit of the air conditioner 1, the first suppression frequency has a lower limit. As an example, the lower limit is 25 [Hz]. In step ST5, the control unit 100 operates the compressor 12 at the first suppression frequency. As a result, the suction temperature of the compressor 12 is higher than that during normal operation, and the refrigerant temperature in the accumulator 18 is more likely to rise.
When the control unit 100 sets the first suppression frequency (step ST5), the process returns to step ST3.

When the control unit 100 determines that the intake refrigerant temperature is not equal to or lower than the first temperature T1 (step ST4; NO), it determines whether the intake refrigerant temperature is equal to or lower than a preset second temperature T2 (see FIG. 3) (step ST6). The second temperature T2 is set to a temperature that is higher than the first temperature T1 and does not impair air conditioning performance.

When the control unit 100 determines that the suction refrigerant temperature is equal to or lower than the second temperature T2 (step ST6; YES), it sets the operating frequency of the compressor 12 to the second suppression frequency (step ST7). The second suppression frequency is higher than the first suppression frequency and lower than the operating frequency during normal operation. The second suppression frequency is a frequency obtained by subtracting a predetermined frequency from the operating frequency during normal operation. In step ST7, the control unit 100 operates the compressor 12 at the second suppression frequency. This makes it easier for the suction temperature of the compressor 12 to rise than during normal operation, and makes it easier for the refrigerant temperature in the accumulator 18 to rise.
When the control unit 100 sets the second suppression frequency (step ST7), the process returns to step ST3.

When the control unit 100 determines that the suction refrigerant temperature is not equal to or lower than the second temperature T2 (step ST6; NO), it determines whether the suction refrigerant temperature is equal to or lower than the third temperature (second threshold temperature) T3 (see FIG. 3) (step ST8). The third temperature T3 is set to a temperature that is higher than the second temperature T2 and does not impair air conditioning. The suction refrigerant temperature required for general air conditioning is 5°C or higher and 15°C or lower. The third temperature T3 is set so that the suction refrigerant temperature does not become higher than the upper limit of 15°C by the two-phase separation elimination control. In other words, the third temperature T3 is set to a temperature lower than 15°C.

When the control unit 100 determines that the suction refrigerant temperature is equal to or lower than the third temperature T3 (step ST8; YES), it sets the operating frequency of the compressor 12 to the third suppression frequency (step ST9). The third suppression frequency is higher than the second suppression frequency and lower than the operating frequency during normal operation. The third suppression frequency is a frequency obtained by subtracting a predetermined frequency from the operating frequency during normal operation. In step ST9, the control unit 100 operates the compressor 12 at the third suppression frequency. This makes it easier for the suction temperature of the compressor 12 to rise than during normal operation, and makes it easier for the refrigerant temperature in the accumulator 18 to rise.
When the control unit 100 sets the third suppression frequency (step ST9), the process returns to step ST3.

When the control unit 100 determines that the operation is not cooling (step ST1; NO), it sets the operating frequency of the compressor 12 to the normal frequency (the frequency during normal operation) when two-layer separation elimination control is not executed (step ST10). In step ST10, the control unit 100 operates the compressor 12 at the normal frequency. This allows the operation to be performed with good air conditioning performance.

When the control unit 100 determines that the two-layer separation state is not occurring (step ST2; NO), the control unit 100 sets the operating frequency of the compressor 12 to the normal frequency (step ST10).
When the control unit 100 determines that re-condensation is not occurring (step ST3; NO), it sets the operating frequency of the compressor 12 to the normal frequency (step ST10). There is a trade-off between suppressing damage to the compressor 12 by eliminating two-layer separation and maintaining operating performance. By setting the two-layer separation elimination control as the control, and executing the two-layer separation elimination control only when re-condensation is occurring, it is possible to suppress damage to the compressor 12 while suppressing deterioration of operating performance.

When the control unit 100 determines that the intake refrigerant temperature is not equal to or lower than the third temperature T3 (step ST8; NO), that is, when the control unit 100 determines that the intake refrigerant temperature is higher than the third temperature T3, the control unit 100 sets the frequency to the normal frequency (step ST10). This makes it possible to suppress deterioration of the performance of the air conditioning operation.
When the control unit 100 sets the operation frequency to the normal frequency (step ST10), the process returns to step ST1.

In the air conditioning device 1 of this embodiment, when it is determined that the accumulator 18 is in a two-layer separated state and recondensation is occurring during cooling operation, steps ST1 to ST3 of the determination and execution operation of the two-layer separation elimination control are executed to execute steps ST3 to ST9 of the determination and execution operation of the two-layer separation elimination control. That is, the two-layer separation elimination control is executed to operate the compressor 12 at a frequency that is suppressed compared to the frequency during normal cooling operation. This increases the evaporation temperature in the indoor heat exchanger 21, which functions as an evaporator, and makes it easier for the temperature of the refrigerant flowing into the accumulator 18 to increase. In addition, the temperature of the refrigerant flowing out of the accumulator 18 is easier to increase, making it easier for the suction temperature of the compressor 12 to increase.

At this time, when the operation starts, the position showing the relationship between the oil content ratio and the temperature in the accumulator 18 shifts from the separation region R1 to the dissolution region R2, as shown by the arrow L in FIG. 3. That is, in the accumulator 18, the refrigeration oil becomes more easily dissolved in the liquid refrigerant, and the two-layer separation state becomes easier to resolve. Therefore, the refrigeration oil becomes easier to return to the compressor 12 from the oil return hole 18b of the accumulator 18, and the lubrication of the compressor 12 becomes easier to maintain.

Fig. 6 is a diagram showing the relationship between the temperature difference ΔT, the operation frequency F, and the operation time when recondensation occurs. Fig. 7 is a diagram showing the relationship between the temperature difference ΔT, the operation frequency F, and the operation time when recondensation is eliminated before the elimination of the two-layer separation state. In Figs. 6 and 7, the horizontal axis indicates the operation time, and the vertical axis indicates the temperature [°C] or the frequency [Hz]. In Figs. 6 and 7, the symbol TL indicates the period during which the two-layer separation state can be considered to exist. Also, ta indicates the timing of switching from the two-layer separation elimination control to the control during normal operation.
6 and 7, when two-layer separation elimination control is executed, the compressor 12 is operated at a suppression frequency that is suppressed more than the normal frequency, thereby increasing the suction temperature of the compressor 12. As the suction refrigerant temperature increases, the suppression frequency is gradually increased to approach the frequency during normal operation, thereby increasing the suction temperature of the compressor 12 while maintaining air conditioning performance.

At this time, when the intake refrigerant temperature becomes equal to or higher than the third temperature T3 as a result of the processing of steps ST3 to ST9, the two-layer separation elimination control ends at timing ta as shown in FIG. 6, and the compressor 12 is switched to operation at normal frequency. Therefore, the two-layer separation elimination control is executed until the temperature reaches the third temperature T3, which is higher than the first temperature T1 based on the two-layer separation temperature, and with the two-layer separation state sufficiently eliminated, the refrigeration oil is more likely to return to the compressor 12 from the oil return hole 18b of the accumulator 18, making it easier to maintain the lubricity of the compressor 12.

Furthermore, as shown in FIG. 7 , even if the refrigerant temperature does not become equal to or higher than the third temperature T3, if the temperature difference ΔT becomes greater than the difference threshold value Δa and it is determined by the processing of step ST3 that re-condensation has been eliminated, the two-layer separation elimination control is terminated at timing ta, and the compressor 12 is switched to operation at the normal frequency.
When re-condensation is not occurring, it becomes difficult for refrigeration oil to be discharged from the compressor 12, and therefore the lubrication of the compressor 12 is likely to be maintained even if refrigeration oil is not replenished from the accumulator 18. Therefore, in this embodiment, when re-condensation is not occurring, the control of the compressor 12 is switched to the normal frequency, and air conditioning performance can be prioritized.

In the air conditioning device 1 of this embodiment, in the case of heating operation, the two-layer separation elimination control is not executed, and the compressor 12 is operated at the operating frequency during normal operation for heating operation. Since heating operation requires a large air conditioning operating load, executing the two-layer separation elimination operation has a large effect on the air conditioning performance. Therefore, by not executing the two-layer separation elimination control in heating operation, it is possible to prevent a significant loss of air conditioning performance.

Here, in this embodiment, as an example of two-layer separation elimination control, the control unit 100 executes the process of steps ST4 to ST9 to set the operating frequency of the compressor 12 to a suppressed frequency that is suppressed below the normal frequency during normal operation. However, instead of setting the operating frequency of the compressor 12 to a suppressed frequency, the two-layer separation elimination control may be configured to control the air conditioner 1 so that the suction superheat degree is lower than during normal operation. In addition, the two-layer separation elimination control may be configured to control the indoor fan 21a to increase the airflow rate. Furthermore, the two-layer separation elimination control may be a combination of control to suppress the operating frequency of the compressor 12 below the normal frequency, control to operate the air conditioner 1 so as to lower the suction superheat degree, and control to drive the indoor fan 21a so as to increase the airflow rate of the indoor fan 21a.

In addition, in the determination and execution operation of the two-layer separation elimination control shown in FIG. 5, step ST1 is executed to determine whether or not the operation is cooling. However, step ST1 of the determination and execution operation of the two-layer separation elimination control shown in FIG. 5 may be omitted, and the determination and execution operation of the two-layer separation elimination control may be executed only during cooling operation.

As described above, the air conditioning device 1 of this embodiment is an air conditioning device 1 equipped with a compressor 12, an outdoor heat exchanger 16 corresponding to a condenser, an expansion valve 17 corresponding to a pressure reducing device, an indoor expansion valve 22, an indoor heat exchanger 21 corresponding to an evaporator, and an accumulator 18 that separates the refrigerant flowing in from the indoor heat exchanger 21 into gas and liquid and stores the liquid refrigerant. The air conditioning device 1 is equipped with a suction temperature sensor 36 arranged on the suction side of the compressor 12 to detect the suction refrigerant temperature, an outdoor air temperature sensor 35 that detects the temperature of the outdoor air of the outdoor heat exchanger 16 corresponding to the outdoor air, and an accumulator 18 that detects the temperature of the outdoor air of the outdoor heat exchanger 16 corresponding to the outdoor air. The system includes a detection means consisting of at least one of an oil concentration sensor 41 that detects the concentration of the refrigerant oil in the accumulator 18 and a low pressure sensor 37 that is arranged on the suction side of the compressor 12 and detects the refrigerant pressure, and a control unit 100 that corresponds to a control unit that determines whether or not the refrigerant oil is in a two-layer separation state in which it is separated from the liquid refrigerant in the accumulator 18 based on the detection value of the detection means. If the control unit 100 determines that the refrigerant oil is in a two-layer separation state, it executes two-layer separation elimination control to increase the suction temperature of the compressor 12.

This increases the refrigerant temperature of the refrigerant flowing out of the indoor heat exchanger 21, and increases the refrigerant temperature flowing into the accumulator 18, thereby increasing the refrigerant temperature in the accumulator 18. By increasing the refrigerant temperature in the accumulator 18, it becomes easier to eliminate the two-layer separation state in the accumulator 18, which makes it easier for refrigeration oil to return to the compressor 12 and makes it easier to maintain the lubrication of the compressor 12.

In this embodiment, the detection means includes an inlet temperature sensor 36 arranged on the suction side of the compressor 12 to detect the inlet refrigerant temperature, and the control unit 100 determines whether or not the suction refrigerant temperature corresponding to the detection value of the suction temperature sensor 36 is below a threshold temperature preset based on the two-layer separation temperature at which the two-layer separation state occurs, thereby determining whether or not the refrigerant is in a two-layer separation state.
This makes it possible to determine whether the refrigerant is in a two-layer separation state based on the refrigerant temperature and to execute two-layer separation elimination control.

In addition, in this embodiment, the control unit 100 executes two-layer separation elimination control so that the suction refrigerant temperature detected by the suction temperature sensor 36 is higher than the threshold temperature and lower than a third temperature T3 corresponding to a second threshold temperature that is preset so as to maintain air conditioning performance.
This makes it possible to avoid excessively increasing the suction temperature of the compressor 12, which would impair the air conditioning performance, and makes it possible to maintain the air conditioning performance while ensuring the ability to eliminate the two-layer separation state.

In addition, in this embodiment, the control unit 100 executes two-phase separation elimination control by operating the compressor 12 at a suppression frequency corresponding to a frequency that is suppressed more than a normal frequency corresponding to a frequency during normal operation.
This allows the suction temperature of the compressor 12 to be increased by controlling the compressor 12 .

In addition, in this embodiment, a discharge temperature sensor 30 is provided that is arranged on the discharge side of the compressor 12 and detects the discharge refrigerant temperature, and the control unit 100 determines whether the refrigerant is re-condensed based on the detection value of the discharge temperature sensor 30 at the beginning of air conditioning operation startup, and executes two-layer separation elimination control if the refrigerant is re-condensed.
As a result, when recondensation of the refrigerant is detected at the beginning of air-conditioning operation, two-layer separation elimination control is executed to suppress the operating frequency of the compressor 12. This suppresses the amount of refrigeration oil discharged from the compressor 12, making it easier for refrigeration oil to remain in the compressor 12 and suppressing damage to the compressor 12.

In addition, in this embodiment, the control unit 100 executes two-layer separation elimination control in cooling operation, but does not execute two-layer separation elimination control in heating operation.
As a result, since the air conditioning load is large during heating operation, by not executing the two-layer separation elimination control, it is possible to avoid a significant drop in air conditioning performance.

2. Other embodiments
Although the present invention has been described based on the embodiment, the present invention is not limited to this embodiment. Since this is merely an example of one embodiment of the present invention, any modification and application is possible without departing from the spirit of the present invention.

In the above embodiment, as an example, a configuration in which two-layer separation elimination control is executed during cooling operation is described, but two-layer separation elimination control may also be executed during heating operation.

In the above embodiment, as an example, the control unit 100 has been described as being configured to set the first temperature as the maximum value of the temperature indicated by line L1 as the threshold temperature for determining whether or not the two-layer separation state is in place. Alternatively, the minimum value of the temperature indicated by line L1 may be set. The oil concentration during actual operation may be used as a reference, and the temperature on line L1 corresponding to that oil concentration may be set as the threshold temperature. Furthermore, instead of a configuration in which the threshold temperature is a single fixed value, the relationship between the oil content ratio indicated by line L1 in FIG. 3 and the two-layer separation temperature may be stored in advance, and the corresponding temperature on line L1 may be found from the oil content ratio corresponding to the detection value of the oil concentration sensor 41, and this temperature may be set as the threshold temperature.

In the above embodiment, as an example, a configuration has been described in which the determination of whether recondensation has occurred is based on the discharged refrigerant temperature and the saturation temperature of the discharged refrigerant, but other configurations are also possible. For example, the compressor 12 may be provided with a temperature sensor that detects the surface temperature of the compressor 12, and the determination may be based on the surface temperature of the compressor 12 and the saturation temperature of the discharged refrigerant.

As described in the above embodiment, when two-layer separation elimination control is executed, it is desirable to operate at the suppression frequency until the suction refrigerant temperature reaches a third temperature T3 that is higher than the first temperature T1 based on the two-layer separation temperature in order to fully eliminate the two-layer separation state, but when the suction refrigerant temperature becomes higher than the first temperature T1, the two-layer separation elimination control that operates at the suppression frequency may be terminated and normal operation may be resumed.

In the above embodiment, as an example, when two-layer separation elimination control is executed, a configuration based on three temperatures, the first temperature T1, the second temperature T2, and the third temperature T3, is described. However, a configuration based on only two temperatures, the first temperature T1 and the second temperature T2, or a configuration based on four or more temperatures in which the suppression frequency is gradually increased to approach the frequency during normal operation may also be used.

In the above embodiment, as an example, the air conditioning device 1 is described as having the configuration of a room air conditioner with one outdoor unit 10 and one indoor unit 20, but the present invention is not limited to this. For example, the present invention can also be applied to a packaged air conditioner with one outdoor unit 10 and multiple indoor units 20, a packaged air conditioner in which multiple outdoor units 10 are connected to multiple indoor units 20, and a multi-air conditioner for buildings.

For example, the step units of the operation shown in FIG. 5 are divided according to the main processing content in order to facilitate understanding of the operation of each part of the control unit 100, and the present invention is not limited by the manner in which the processing units are divided or the names of the processing units. The processing units may be divided into more step units according to the processing content. Furthermore, one step unit may be divided so as to include more processing. Furthermore, the order of the steps may be changed as appropriate within the scope of the present invention.

As described above, the air conditioner according to the present invention can be suitably used as an air conditioner that can eliminate the two-layer separation state in the accumulator.

1 Air conditioner 12 Compressor 16 Outdoor heat exchanger (condenser, evaporator)
18 Accumulator 20 Indoor unit 21 Indoor heat exchanger (evaporator, condenser)
21a Indoor fan 30 Discharge temperature sensor 35 Outside air temperature sensor 36 Suction temperature sensor 37 Low pressure sensor 41 Oil concentration sensor (concentration sensor)
100 Control unit (control section)
T1 First temperature (threshold temperature)
T3: Third temperature (second threshold temperature)

Claims (4)

An air conditioning apparatus comprising a compressor, a condenser, an evaporator, and an accumulator that separates a refrigerant flowing from the evaporator into gas and liquid and stores the liquid refrigerant,
a detection means including at least one of a suction temperature sensor disposed on the suction side of the compressor and detecting a refrigerant temperature, an outside air temperature sensor disposed on the suction side of the compressor and detecting an outside air temperature, a concentration sensor disposed on the suction side of the compressor and detecting a refrigerant pressure, and a low pressure sensor disposed on the suction side of the compressor and detecting a refrigerant pressure;
and a control unit that determines whether or not the refrigeration oil is in a two-layer separated state from the liquid refrigerant in the accumulator based on a detection value of the detection means,
The detection means includes a suction temperature sensor disposed on the suction side of the compressor to detect a refrigerant temperature,
the control unit determines whether the refrigerant temperature corresponding to the detection value of the suction temperature sensor is equal to or lower than a threshold temperature that is preset based on a temperature at which the two-phase separation state occurs, thereby determining whether the two-phase separation state occurs;
When it is determined that the two-layer separation state exists, the control unit executes a two-layer separation elimination control for increasing a suction temperature of the compressor ,
The control unit executes the two-layer separation elimination control so that the refrigerant temperature detected by the suction temperature sensor is higher than the threshold temperature and lower than a second threshold temperature that is preset so as to maintain air conditioning performance. The air-conditioning apparatus according to claim 1 , wherein the control unit executes the two-layer separation elimination control by operating the compressor at a frequency that is suppressed compared to a frequency during normal operation. a discharge temperature sensor disposed on a discharge side of the compressor to detect a refrigerant temperature,
The air-conditioning apparatus according to claim 2, characterized in that the control unit determines whether or not the refrigerant is re-condensing based on the detection value of the discharge temperature sensor at the beginning of air-conditioning operation startup, and executes the two -layer separation elimination control if the refrigerant is re-condensing. The air-conditioning apparatus according to any one of claims 1 to 3 , wherein the control unit executes the two-layer separation elimination control in a cooling operation and does not execute the two-layer separation elimination control in a heating operation.

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