JP2024082104A - Refrigeration cycle device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a refrigeration cycle device which has a rotary-type compressor incorporated in a refrigeration cycle, is less likely to reduce volumetric efficiency even when using a low-pressure refrigerant as a refrigerant, and is good in refrigeration efficiency.

SOLUTION: A refrigeration cycle device includes: a compressor having a mechanism pressing a vane brought into contact with a rotary piston by discharge pressure of a refrigerant; and a control part. The control part calculates indoor/outdoor saturation temperature difference from a condenser temperature and an evaporator temperature, performs low-differential pressure-time discharge temperature control of adjusting an expansion valve so as to keep a compressor discharge temperature of the refrigerant at a predetermined second temperature or more when the indoor/outdoor saturation temperature difference is a prescribed first temperature or lower, and performs normal-time discharge temperature control of keeping the compressor discharge temperature when the indoor/outdoor saturation temperature difference is larger than the first temperature.

SELECTED DRAWING: Figure 5

COPYRIGHT: (C)2024,JPO&INPIT

Description

This disclosure relates to a refrigeration cycle device.

Patent Document 1 discloses an air conditioner that can suppress a decrease in compressor durability even when using a refrigerant such as R32, which is prone to a large pressure difference between condensation and evaporation. This air conditioner is equipped with a superheat control mode that adjusts the opening and closing of the expansion valve so as to maintain the superheat temperature of the refrigerant at a predetermined value, and a discharge temperature control mode that adjusts the opening and closing of the expansion valve so as to maintain the discharge temperature of the refrigerant from the compressor at a predetermined value.

International Publication No. 2018/216131

This disclosure provides a refrigeration cycle device that incorporates a rotary compressor into the refrigeration cycle and has good refrigeration efficiency and is less likely to lose volumetric efficiency even when a low-pressure refrigerant is used as the refrigerant.

The refrigeration cycle device disclosed herein is a refrigeration cycle device that includes a compressor having a mechanism for pressing a vane that contacts a rotary piston by the discharge pressure of the refrigerant, a condenser that condenses the refrigerant, an evaporator that evaporates the refrigerant, and an expansion valve that adjusts the amount of the refrigerant supplied to the evaporator, and has a refrigeration cycle configured by the compressor, the condenser, the evaporator, and the expansion valve, and includes a compressor discharge temperature sensor that measures the compressor discharge temperature, which is the temperature of the refrigerant discharged from the compressor, and a condenser temperature sensor that measures the condenser temperature (condensation saturation temperature), which is the temperature of the refrigerant that has become a two-phase state (liquid, gas mixed region) in the condenser. The system is equipped with a sensor, an evaporator temperature sensor that measures the evaporator temperature (evaporation saturation temperature), which is the temperature of the refrigerant that has become in a two-phase state in the evaporator, and a control unit, and the control unit calculates the indoor/outdoor saturation temperature difference, which is the difference between the condenser temperature and the evaporator temperature, and when the indoor/outdoor saturation temperature difference is equal to or lower than a predetermined first temperature, executes low differential pressure discharge temperature control to adjust the expansion valve to keep the compressor discharge temperature of the refrigerant at a value higher than a predetermined second temperature, thereby suppressing the supply amount of the refrigerant, and when the indoor/outdoor saturation temperature difference is higher than the first temperature, executes normal discharge temperature control to maintain the compressor discharge temperature.

The refrigeration cycle device disclosed herein incorporates a rotary compressor into the refrigeration cycle, and is less likely to reduce volumetric efficiency even when using a low-pressure refrigerant, making it possible to improve refrigeration efficiency.

Air conditioner configuration diagram Diagram of a rotary compressor Operational diagram of the compression mechanism FIG. Control unit functional block diagram Flowchart of air conditioner operation control Flowchart of air conditioner operation control Flowchart of air conditioner operation control Experimental result

At the time when the inventors came up with the present disclosure, the refrigeration cycle of an air conditioner was composed of a compressor, a condenser, an expansion valve, an evaporator, etc., and a hydrofluorocarbon called R32 was used as a refrigerant. R32 has been widely used because it does not destroy the ozone layer of the earth's atmosphere and has a relatively small greenhouse effect compared to previous refrigerants. However, in recent years, global warming has become an even bigger problem, and the greenhouse effect of R32 has also become a problem. Therefore, instead of R32, it is being considered to use R290, which has an extremely low greenhouse effect coefficient, that is, a low-pressure refrigerant such as propane, which has a low operating pressure.
However, when the refrigerant used in the refrigeration cycle is propane, the high and low pressure difference is less likely to occur in the refrigeration cycle compared to R32. Therefore, under conditions in which a sufficient high and low pressure difference cannot be secured, such as when the temperature difference between the indoors and outdoors is small, the inventors discovered that there is a problem in that the vanes separating the suction chamber and the compression chamber in the rotary compressor may float, resulting in a decrease in volumetric efficiency. In order to solve this problem, the inventors have come to constitute the subject of the present disclosure.

The present disclosure provides a refrigeration cycle device that incorporates a rotary compressor into the refrigeration cycle and has good refrigeration efficiency and is less likely to lose volumetric efficiency even when a low-pressure refrigerant is used as the refrigerant.

Hereinafter, the embodiments will be described in detail with reference to the drawings. However, more detailed explanation than necessary may be omitted. For example, detailed explanation of already well-known matters or duplicate explanation of substantially the same configuration may be omitted. This is to avoid the following explanation becoming more redundant than necessary and to facilitate understanding by those skilled in the art.
It should be noted that the accompanying drawings and the following description are provided to enable those skilled in the art to fully understand the present disclosure, and are not intended to limit the subject matter described in the claims.

(Embodiment 1)
[1-1. Configuration]
In FIG. 1, the air conditioner 1 (refrigeration cycle device) includes an indoor unit 2 and an outdoor unit 3. The indoor unit 2 includes an evaporator 5 that evaporates a refrigerant to remove heat from the surroundings, and a control unit 50 that controls the entire air conditioner 1. The indoor unit 2 further includes an indoor unit blower (not shown). The refrigerant is R290, i.e., propane. The evaporator 5 includes an evaporator temperature sensor 41 that detects the temperature of the refrigerant inside the evaporator 5. The outdoor unit 3 includes an accumulator 21, a rotary compressor (compressor) 10, a condenser 20, and an expansion valve 30. The outdoor unit 3 includes a compressor intake temperature sensor 43 on the intake side of the rotary compressor 10 that detects the compressor intake temperature, which is the temperature of the refrigerant being sucked in. The outdoor unit 3 includes a compressor discharge temperature sensor 45 on the discharge side of the rotary compressor 10 that detects the compressor discharge temperature, which is the temperature of the refrigerant being discharged. The rotary compressor 10 includes an operation frequency detection sensor 49 that detects the operation frequency. As described below, the rotary compressor 10 includes a rotary piston 13 that is eccentrically disposed inside a cylinder 14. As the rotary piston 13 rotates about the center of the cylinder 14, refrigerant gas is sucked between the rotary piston 13 and the cylinder 14, compressed, and discharged. At the boundary between the suction chamber 11 and the compression chamber 12, there is a vane 15 that functions as a slide valve, and by contacting the rotary piston 13, the compressed refrigerant gas does not leak from the compression chamber 12 to the suction chamber 11.

The rotary compressor 10 constituting the air conditioner 1 according to this embodiment has a structure in which the vanes 15 are pressed against the rotary piston 13 by the discharge pressure, i.e., back pressure, of the rotary compressor 10. Specifically, the chamber housing the vanes is open to the space inside the sealed container 22, which will be described later. Therefore, if there is not a certain difference between the pressure on the suction side and the pressure on the discharge side of the rotary compressor 10, the vanes 15 will not be pressed sufficiently against the rotary piston 13, and the partition between the suction chamber 11 and the compression chamber 12 may become weak, resulting in a vane floating phenomenon.

The condenser 20 is a heat exchanger that cools and liquefies the high-temperature, high-pressure refrigerant gas discharged from the rotary compressor 10. The outdoor unit 3 is equipped with a condenser temperature sensor 47 that detects a condenser temperature (condensation saturation temperature), which is the temperature of the refrigerant in a two-phase state realized in the condenser 20.
The expansion valve 30 reduces the pressure of the high-pressure refrigerant liquefied in the condenser 20 by throttling and expanding it to produce a low-temperature, low-pressure liquid, which is then supplied to the evaporator 5. The expansion valve 30 also adjusts the refrigerant flow rate according to the load on the air conditioner 1. In this embodiment, the expansion valve 30 is an electronic expansion valve that is opened and closed by the control unit 50. At that time, the control unit 50 can operate the air conditioner 1 by controlling the discharge superheat or the compressor discharge temperature to be maintained at a predetermined temperature using PID (Proportional-Integral-Differential) control or the like.

Here, the discharge superheat degree is calculated as the difference between the compressor discharge temperature detected by the compressor discharge temperature sensor 45 and the condensation saturation temperature detected by the condenser temperature sensor 47 .
The components of the air conditioner 1 are connected by piping 35, and a refrigeration cycle operation is achieved by circulating the refrigerant through the piping 35.

2 is an explanatory diagram of the rotary compressor 10. FIG. 2 shows the rotary compressor 10 in a schematic manner. The rotary compressor 10 includes a sealed container 22, which is connected to an accumulator 21. The accumulator 21 separates the liquid refrigerant that has not been completely evaporated in the evaporator 5 from the refrigerant gas. If the liquid refrigerant that has not been completely evaporated is sucked into the rotary compressor 10, the vane 15 and the like will be damaged by liquid compression, so the accumulator 21 is attached upstream of the rotary compressor 10 in the refrigerant flow direction. The accumulator 21 is provided on the discharge port side of the evaporator 5, sucks in the refrigerant from the suction port 29, and discharges the refrigerant gas to the compression mechanism 27. The sealed container 22 includes an electric motor 26 and a compression mechanism 27 driven by the electric motor 26. The compression mechanism 27 is connected to the electric motor 26 by a crankshaft 28, and sucks in and compresses the refrigerant gas. That is, the refrigerant gas is guided from the accumulator 21 to the compression mechanism 27, where it is compressed to a high temperature and pressure, and then discharged from the discharge port 24.

Figure 3A is an explanatory diagram of the refrigerant gas suction operation of the compression mechanism 27 in the rotary compressor 10. In Figure 3A, the compression mechanism 27 is shown in schematic form. The compression mechanism 27 is equipped with a rotary piston 13 that is eccentrically disposed inside the cylinder 14. The rotary piston 13 rotates in the direction of the arrow in Figure 3A around the center of the cylinder 14, and the refrigerant gas is sucked between the rotary piston 13 and the cylinder 14, compressed, and discharged. At the boundary between the suction chamber 11 and the compression chamber 12, there is a vane 15 that functions as a slide valve, and by abutting against the rotary piston 13, the compressed refrigerant gas is prevented from leaking from the compression chamber 12 to the suction chamber 11. In Figure 3A, the refrigerant gas sucked from the suction port 19 is sucked into the suction chamber 11.

Figure 3B is an explanatory diagram of the refrigerant gas compression operation of the compression mechanism 27 in the rotary compressor 10. In Figure 3B, the compression mechanism 27 is shown in schematic form. In the compression mechanism 27, the rotary piston 13 rotates around the center of the cylinder 14 in the direction of the arrow in Figure 3B, and the refrigerant gas from the accumulator 21 is compressed in the compression chamber 12 between the rotary piston 13 and the cylinder 14 to become high-temperature, high-pressure refrigerant gas, which is then discharged from the discharge port 16. The refrigerant gas discharged from the discharge port 16 is discharged from the rotary compressor 10 through the discharge port 24 toward the condenser 20.

4 is a functional block diagram of the control unit 50. The control unit 50 is a computer that controls the operation of the air conditioner 1. Such a computer includes a processor such as a CPU (Central Processing Unit) or MPU (Micro-Processing Unit), and a memory such as a ROM (Read Only Memory) or RAM (Random Access Memory), and realizes various functions by the processor executing programs stored in the memory. The functions realized by the control unit 50 include an expansion valve control function 57 that adjusts the expansion valve 30, and a calculation function 51 that calculates various detected temperature information and the like to obtain necessary information.
The control unit 50 realizes a determination function 53 that makes a determination regarding each condition described in a flowchart described later, a frequency acquisition function 59 that acquires the operating frequency of the rotary compressor 10, and a temperature information acquisition function 61 that acquires various temperature information from refrigerant temperature sensors such as the evaporator temperature sensor 41. The control unit 50 also realizes a storage function 55 that stores various control programs and information on parameters used in each program. The storage function 55 is realized by, for example, electronic devices such as the above-mentioned RAM, ROM, and SSD (Solid State Device).

The control unit 50 performs two types of operation control: low differential pressure discharge temperature control and normal discharge temperature control. In low differential pressure discharge temperature control, the control unit 50 performs control to increase the compressor discharge temperature when the differential pressure is low. Specifically, the control unit 50 adjusts the expansion valve 30 by throttling it down using the expansion valve control function 57, thereby reducing the amount of refrigerant supplied to the evaporator 5. In normal discharge temperature control, the control unit 50 adjusts the expansion valve 30 using the expansion valve control function 57 so that the compressor discharge temperature becomes a predetermined value.

[1-2. motion]
The operation of the air conditioner 1 configured as above will now be described.
FIG. 5 is a flowchart of the operation control of the air conditioner 1 according to this embodiment.
The control unit 50 detects the condenser temperature, which is the temperature of the refrigerant in a two-phase state in the condenser 20, with the condenser temperature sensor 47 and acquires the temperature information with the temperature information acquisition function 61 (step SA1). The control unit 50 detects the evaporator temperature, which is the temperature of the refrigerant inside the evaporator 5, using the evaporator temperature sensor 41 and acquires the temperature information using the temperature information acquisition function 61 (step SA2). The control unit 50 calculates the indoor/outdoor saturation temperature difference, which is the difference between the evaporator temperature and the condenser temperature (step SA3). It is then determined whether the pressure is equal to or lower than the first temperature (step SA4). The first temperature is converted into a pressure of, for example, 0.23 MPa.

If the indoor/outdoor saturation temperature difference is equal to or lower than the first temperature (step SA4: YES), the control unit 50 detects the operation frequency of the rotary compressor 10 by the operation frequency detection sensor 49 and acquires it by the frequency acquisition function 59 (step SA5). The control unit 50 judges by the judgment function 53 whether the operation frequency is equal to or lower than a specific frequency that is predetermined and stored by the storage function 55 (step SA6). The specific frequency is, for example, 20 Hz. If the operation frequency is equal to or lower than the specific frequency (step SA6: YES), the control unit 50 detects the compressor discharge temperature, which is the temperature of the refrigerant discharged from the rotary compressor 10, by the compressor discharge temperature sensor 45 and acquires it by the temperature information acquisition function 61 (step SA7). The control unit 50 uses the acquired compressor discharge temperature and condenser temperature to calculate the discharge superheat degree by the calculation function 51 (step SA8). The control unit 50 determines, by the determination function 53, whether the discharge superheat degree is equal to or lower than a third temperature that is determined in advance and stored by the storage function 55 (step SA9). The third temperature is, for example, 9K.
If the discharge superheat degree is equal to or lower than the third temperature (step SA9: YES), the control unit 50 performs low differential pressure discharge temperature control (step SA10) by adjusting the expansion valve 30 so as to maintain the compressor discharge temperature of the refrigerant at a value higher than a predetermined second temperature, thereby suppressing the amount of refrigerant supplied. Then, the process returns to step SA1. The second temperature is, for example, 66°C.
At this time, the low differential pressure discharge temperature control may be adjusted so as to maintain the discharge superheat temperature at the third temperature.

Returning to the explanation of step SA4, if the indoor/outdoor saturation temperature difference is greater than a predetermined first temperature (step SA4: NO), the expansion valve control function 57 feedback controls the expansion valve 30 to maintain the compressor discharge temperature, i.e., normal discharge temperature control is performed (step SA11).

Returning to the explanation of step 6, if the operating frequency is greater than the specific frequency (step SA6: NO), the expansion valve control function 57 feedback controls the expansion valve 30 to maintain the compressor discharge temperature, i.e., normal discharge temperature control is performed (step SA11).

Returning to the explanation of step 9, if the discharge superheat temperature is greater than the third temperature (step 9: NO), the expansion valve control function 57 feedback controls the expansion valve 30 to maintain the compressor discharge temperature, i.e., normal discharge temperature control is performed (step SA11).
The value of the compressor discharge temperature that is the target to be maintained may be different depending on the indoor/outdoor saturation temperature difference, the operation frequency, and the discharge superheat degree.

[1-3. Effects, etc.]
As described above, in this embodiment, the air conditioner 1 includes the rotary compressor 10 having a mechanism for pressing the vane 15 in contact with the rotary piston 13 by the discharge pressure of the refrigerant, the condenser 20 for condensing the refrigerant, the evaporator 5 for evaporating the refrigerant, and the expansion valve 30 for adjusting the amount of refrigerant supplied to the evaporator 5. The air conditioner 1 is also a refrigeration cycle device having a refrigeration cycle constituted by the rotary compressor 10, the condenser 20, the evaporator 5, and the expansion valve 30, and includes a compressor discharge temperature sensor 45 for measuring a compressor discharge temperature, which is the temperature of the refrigerant discharged from the rotary compressor 10, a condenser temperature sensor 47 for measuring a condenser temperature, which is the temperature of the refrigerant in a two-phase state in the condenser 20, an evaporator temperature sensor 41 for measuring an evaporator temperature, which is the temperature of the refrigerant in the evaporator 5, and a control unit 50. The control unit 50 calculates the discharge superheat, which is the difference between the compressor discharge temperature and the evaporator temperature of the rotary compressor 10, and when the indoor/outdoor saturation temperature difference is equal to or lower than a first temperature, the operating frequency of the rotary compressor 10 is equal to or lower than a specific frequency, and the discharge superheat is equal to or lower than a predetermined third temperature, the control unit 50 executes low differential pressure discharge temperature control, which adjusts the expansion valve 30 to suppress the amount of refrigerant supplied.
In addition, the control unit 50 executes normal discharge temperature control when the indoor/outdoor saturation temperature difference is equal to or lower than a first temperature, the operating frequency of the rotary compressor 10 is equal to or lower than a specific frequency, and the discharge superheat degree is greater than a third temperature.
When the load on the air conditioner 1 is small, the pressure difference becomes low and the force of the vane 15 pressing against the rotary piston 13 in the rotary compressor 10 becomes small, so that there is a possibility that the vane float occurs, which causes leakage between the suction chamber 11 and the compression chamber 12, and the volumetric efficiency decreases. In this embodiment, the control unit 50 performs control to reduce the supply amount of refrigerant by throttling the expansion valve 30 so as to keep the compressor discharge temperature of the refrigerant at a predetermined temperature or higher, so that the discharge superheat degree in the rotary compressor 10 can be kept high. When the discharge superheat degree is high, the viscosity of the oil dissolved in the refrigerant increases and the amount of oil in the sliding part of the vane 15 increases, so that the friction coefficient of the vane 15 decreases and vane float is less likely to occur. As a result, the air conditioner 1 in the present disclosure is less likely to decrease in volumetric efficiency and can improve refrigeration efficiency even when the rotary compressor 10 is incorporated into the refrigeration cycle and a low-pressure refrigerant is used as the refrigerant.

(Embodiment 2)
[2-1. Configuration and operation]
The configuration of the air conditioner 1 according to the second embodiment is similar to that of the first embodiment, and therefore a description thereof will be omitted.
FIG. 6 is a flowchart of the operation control of the air conditioner 1 according to the second embodiment.
The control unit 50 detects the condenser temperature, which is the temperature of the refrigerant in a two-phase state in the condenser 20, with the condenser temperature sensor 47 and acquires it with the temperature information acquisition function 61 (step SB1). The control unit 50 also detects the evaporator temperature, which is the temperature of the refrigerant inside the evaporator 5, with the evaporator temperature sensor 41 and acquires it with the temperature information acquisition function 61 (step SB2). The control unit 50 calculates the indoor/outdoor saturation temperature difference, which is the difference between the evaporator temperature and the condenser temperature, with the calculation function 51 (step SB3). The control unit 50 judges whether the indoor/outdoor saturation temperature difference is equal to or lower than a first temperature that is previously set and stored in the memory function 55 with the judgment function 53 (step SB4). The first temperature is, for example, 0.23 MPa when converted into pressure.

If the indoor/outdoor saturation temperature difference is equal to or lower than the first temperature (step SB4: YES), the control unit 50 uses the expansion valve control function 57 to adjust the expansion valve 30 to throttle so as to maintain the compressor discharge temperature at a predetermined second temperature, thereby reducing the amount of refrigerant supplied to the evaporator 5, i.e., performing low pressure differential discharge temperature control (step SB5). The second temperature is, for example, 66°C. Then, the process returns to step SB1.

Returning to the explanation of step SB4, if the indoor/outdoor saturation temperature difference is greater than a predetermined first temperature (step SB4: NO), the control unit 50 feedback controls the expansion valve 30 using the expansion valve control function 57 to maintain the compressor discharge temperature, i.e., performs normal discharge temperature control (step SB6). Note that the value of the compressor discharge temperature to be maintained as a target may be different depending on the indoor/outdoor saturation temperature difference, the operating frequency, and the discharge superheat degree.

[2-2. Effects, etc.]
As described above, in this embodiment, the air conditioner 1 includes the rotary compressor 10 having a mechanism for pressing the vane 15 in contact with the rotary piston 13 by the discharge pressure of the refrigerant, the condenser 20 for condensing the refrigerant, the evaporator 5 for evaporating the refrigerant, and the expansion valve 30 for adjusting the amount of refrigerant supplied to the evaporator 5. The air conditioner 1 is a refrigeration cycle device having a refrigeration cycle constituted by the rotary compressor 10, the condenser 20, the evaporator 5, and the expansion valve 30, and includes a compressor discharge temperature sensor 45 for measuring a compressor discharge temperature, which is the temperature of the refrigerant discharged from the rotary compressor 10, a condenser temperature sensor 47 for measuring a condenser temperature, which is the temperature of the refrigerant in a two-phase state in the condenser 20, an evaporator temperature sensor 41 for measuring an evaporator temperature, which is the temperature of the refrigerant in the evaporator 5, and a control unit 50.
The control unit 50 calculates the indoor/outdoor saturation temperature difference, which is the difference between the condenser temperature and the evaporator temperature, and when the indoor/outdoor saturation temperature difference is equal to or lower than a predetermined first temperature, executes low pressure differential discharge temperature control to adjust the expansion valve 30 to maintain the compressor discharge temperature of the refrigerant at a value higher than a predetermined second temperature, thereby suppressing the amount of refrigerant supplied, and when the indoor/outdoor saturation temperature difference is higher than the first temperature, executes normal discharge temperature control to maintain the compressor discharge temperature.
When the indoor/outdoor saturation temperature difference is small, the pressure difference becomes low, and the force of the vane 15 pressing against the rotary piston 13 in the rotary compressor 10 becomes small, so that there is a possibility that the vane float occurs, which causes leakage between the suction chamber 11 and the compression chamber 12, and the volumetric efficiency decreases. In this embodiment, the control unit 50 performs control to reduce the supply amount of refrigerant by throttling the expansion valve 30 so as to keep the compressor discharge temperature of the refrigerant at a predetermined temperature or higher, so that the discharge superheat degree in the rotary compressor 10 can be kept high. When the discharge superheat degree is high, the viscosity of the oil dissolved in the refrigerant increases, and the amount of oil in the sliding part of the vane 15 increases, so that the friction coefficient of the vane 15 decreases and vane float is less likely to occur. As a result, the air conditioner 1 in the present disclosure is less likely to decrease in volumetric efficiency and can improve refrigeration efficiency even when the rotary compressor 10 is incorporated into the refrigeration cycle and a low-pressure refrigerant is used as the refrigerant.

(Embodiment 3)
[3-1. Configuration and Operation]
The configuration of the air conditioner 1 according to the third embodiment is similar to that of the first embodiment, and therefore a description thereof will be omitted.
FIG. 7 is a flowchart of the operation control of the air conditioner 1 according to the third embodiment.
The control unit 50 detects the condenser temperature, which is the temperature of the refrigerant in a two-phase state in the condenser 20, with the condenser temperature sensor 47 and acquires it with the temperature information acquisition function 61 (step SC1). The control unit 50 also detects the evaporator temperature, which is the temperature of the refrigerant inside the evaporator 5, with the evaporator temperature sensor 41 and acquires it with the temperature information acquisition function 61 (step SC2). The control unit 50 calculates the indoor/outdoor saturation temperature difference, which is the difference between the evaporator temperature and the condenser temperature, with the calculation function 51 (step SC3). The control unit 50 judges with the judgment function 53 whether the indoor/outdoor saturation temperature difference is equal to or lower than a first temperature that is previously set and stored in the memory function 55 (step SC4). The first temperature is, for example, 0.23 MPa when converted into pressure.

If the indoor/outdoor saturation temperature difference is equal to or lower than a predetermined first temperature (step SC4: YES), the control unit 50 detects the operation frequency of the rotary compressor 10 using the operation frequency detection sensor 49 and acquires it using the frequency acquisition function 59 (step SC5). The control unit 50 determines, using the determination function 53, whether or not the operation frequency is equal to or lower than a specific frequency that is predetermined and stored in the storage function 55 (step SC6). The specific frequency is, for example, 20 Hz.
If the operating frequency is equal to or lower than the specific frequency (step SC6: YES), the control unit 50 adjusts the expansion valve 30 by using the expansion valve control function 57 to keep the compressor discharge temperature at a predetermined second temperature, thereby reducing the amount of refrigerant supplied to the evaporator 5, i.e., performs low differential pressure discharge temperature control (step SC7). The second temperature is, for example, 66°C.
Then, return to step SC1.

Returning to the explanation of step SC4, if the indoor/outdoor saturation temperature difference is greater than a predetermined first temperature (step SC4: NO), the control unit 50 feedback controls the expansion valve 30 using the expansion valve control function 57 to maintain the compressor discharge temperature, i.e., performs normal discharge temperature control (step SC8).

Returning to the explanation of step SC6, if the operating frequency is greater than the specific frequency (step SC6: NO), the control unit 50 feedback controls the expansion valve 30 using the expansion valve control function 57 to maintain the compressor discharge temperature, i.e., performs normal discharge temperature control (step SC8).

[3-2. Effects, etc.]
As described above, in this embodiment, the air conditioner 1 includes the rotary compressor 10 having a mechanism for pressing the vane 15 in contact with the rotary piston 13 by the discharge pressure of the refrigerant, the condenser 20 for condensing the refrigerant, the evaporator 5 for evaporating the refrigerant, and the expansion valve 30 for adjusting the amount of refrigerant supplied to the evaporator 5. The air conditioner 1 is a refrigeration cycle device having a refrigeration cycle constituted by the rotary compressor 10, the condenser 20, the evaporator 5, and the expansion valve 30, and includes a compressor discharge temperature sensor 45 for measuring a compressor discharge temperature, which is the temperature of the refrigerant discharged from the rotary compressor 10, a condenser temperature sensor 47 for measuring a condenser temperature, which is the temperature of the refrigerant in a two-phase state in the condenser 20, an evaporator temperature sensor 41 for measuring an evaporator temperature, which is the temperature of the refrigerant in the evaporator 5, and a control unit 50.
The control unit 50 executes low differential pressure discharge temperature control when the indoor/outdoor saturation temperature difference is equal to or lower than the first temperature and the operating frequency of the rotary compressor 10 is equal to or lower than a predetermined specific frequency, and executes normal discharge temperature control when the indoor/outdoor saturation temperature difference is equal to or lower than the first temperature and the operating frequency of the rotary compressor 10 is greater than the specific frequency.
When the indoor/outdoor saturation temperature difference is equal to or lower than the first temperature and the operating frequency of the rotary compressor 10 is equal to or lower than a predetermined specific frequency, the load on the air conditioner 1 is small, resulting in a low pressure difference. In the rotary compressor 10, the force of the vane 15 pressing against the rotary piston 13 is reduced, which may cause vane floating, which may cause leakage between the suction chamber 11 and the compression chamber 12, resulting in a decrease in volumetric efficiency. In this embodiment, the control unit 50 performs control to reduce the amount of refrigerant supplied by throttling the expansion valve 30 so as to keep the compressor discharge temperature of the refrigerant at or above a predetermined temperature, so that the discharge superheat degree in the rotary compressor 10 can be kept high. When the discharge superheat degree is high, the viscosity of the oil dissolved in the refrigerant increases, increasing the amount of oil in the sliding portion of the vane 15, thereby decreasing the friction coefficient of the vane 15 and making it difficult for vane floating to occur. As a result, the air conditioner 1 of the present disclosure is able to improve refrigeration efficiency without decreasing volumetric efficiency even when the rotary compressor 10 is incorporated into the refrigeration cycle and a low-pressure refrigerant is used as the refrigerant.

(4. Experimental Results)
Experimental results relating to the first, second and third embodiments will be described.
8 shows the results of an experiment conducted to examine the volumetric efficiency of the air conditioner 1 when the refrigerant is R290, i.e., propane, and the indoor/outdoor saturation temperature difference and the discharge superheat are changed. The horizontal axis represents the pressure difference corresponding to the indoor/outdoor saturation temperature difference, i.e., the difference between the pressure of the refrigerant in a two-phase state in the condenser 20 and the pressure of the refrigerant in a two-phase state in the evaporator 5. The vertical axis represents the discharge superheat, i.e., the difference between the temperature of the refrigerant on the discharge side of the rotary compressor 10 detected by the compressor discharge temperature sensor 45 and the condensation saturation temperature of the refrigerant inside the condenser 20 detected by the condenser temperature sensor 47. The numbers attached to each marker indicate the volumetric efficiency.

Here, when the refrigerant in the air conditioner 1 is R32, the volumetric efficiency is 87.5%. Therefore, if the volumetric efficiency is 87.5% or more when the refrigerant is changed from R32 to another refrigerant, it can be said that the air conditioner 1 has achieved sufficient refrigeration efficiency. Now, in FIG. 8, the vertical axis shows that the volumetric efficiency is 87.5% or more when the discharge superheat degree is 9K or more, that is, when the discharge superheat degree is greater than the dashed line in FIG. 8. Also, on the horizontal axis, the volumetric efficiency is 87.5% or more when the differential pressure is 0.23 MPa or more, that is, when the differential pressure is greater than the dashed line in FIG. 8. Therefore, when the expansion valve 30 is adjusted by the expansion valve control function 57 of the control unit 50, by controlling the differential pressure, that is, the indoor/outdoor saturation temperature difference and the discharge superheat degree as the judgment conditions, it can be seen that the air conditioner 1 with volumetric efficiency equal to or greater than that of the conventional refrigerant R32 can be achieved even with R290. By using R290, which has a low global warming potential, as the refrigerant in the refrigeration cycle, an air conditioner 1 that is less likely to have a negative impact on the global environment can be realized.

Other Embodiments
As described above, the above-mentioned embodiments 1 to 3 have been described as examples disclosed in the present application. However, the technology in the present disclosure is not limited to this, and can be applied to embodiments in which modifications, substitutions, additions, omissions, etc. have been made. In addition, it is also possible to combine the components described in the above-mentioned embodiments 1 to 3 to form new embodiments. Therefore, other embodiments will be exemplified below.

In each of the above-described embodiments, an air conditioner 1 is exemplified as the "refrigeration cycle device" of the present disclosure. However, the "refrigeration cycle device" of the present disclosure is not limited to the air conditioner 1. The "refrigeration cycle device" of the present disclosure may be any device that employs a refrigeration cycle, such as a refrigerator.

The functions of the control unit 50 may be configured by a single processor or multiple processors. The processor that realizes the functions of the control unit 50 may be hardware programmed to realize the corresponding functional units. In other words, the processor may be configured, for example, by an ASIC (Application Specific Integrated Circuit) or an FPGA (Field Programmable Gate Array).

The step units of the operations shown in Figures 5, 6, and 7 are divided according to the main processing content in order to make the operations easier to understand, and the operation is not limited by the way in which the processing units are divided or their names. The operations may be divided into more step units depending on 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 purpose of this disclosure.

In addition, in the first embodiment, the expansion valve 30 is adjusted according to the discharge superheat to suppress the amount of refrigerant supplied, but the expansion valve 30 may be adjusted based on the suction superheat, which is the difference between the suction temperature detected by the compressor suction temperature sensor 43 and the evaporator temperature detected by the evaporator temperature sensor 41, to suppress the amount of refrigerant supplied.

The above-described embodiments are intended to illustrate the technology disclosed herein, and various modifications, substitutions, additions, omissions, etc. may be made within the scope of the claims or their equivalents.

(Additional Note)
The above description of the embodiments discloses the following techniques.

(Technology 1) A refrigeration cycle device comprising a compressor having a mechanism for pressing a vane in contact with a rotary piston by the discharge pressure of the refrigerant, a condenser for condensing the refrigerant, an evaporator for evaporating the refrigerant, and an expansion valve for adjusting the amount of the refrigerant supplied to the evaporator, the refrigeration cycle device having a refrigeration cycle constituted by the compressor, the condenser, the evaporator, and the expansion valve, the refrigeration cycle device including a compressor discharge temperature sensor for measuring a compressor discharge temperature, which is the temperature of the refrigerant discharged from the compressor, a condenser temperature sensor for measuring a condenser temperature, which is the temperature of the refrigerant that has become a two-phase state in the condenser, and ...refrigeration cycle device having a refrigeration cycle constituted by the compressor, the condenser, the evaporator, and the expansion valve. The refrigeration cycle device is characterized in that it includes an evaporator temperature sensor that measures the evaporator temperature, which is the temperature of the refrigerant that has become in a two-phase state, and a control unit, and the control unit calculates an indoor/outdoor saturation temperature difference, which is the difference between the condenser temperature and the evaporator temperature, and when the indoor/outdoor saturation temperature difference is equal to or lower than a predetermined first temperature, executes low differential pressure discharge temperature control to adjust the expansion valve so as to maintain the compressor discharge temperature of the refrigerant at a value higher than a predetermined second temperature, thereby suppressing the supply amount of the refrigerant, and when the indoor/outdoor saturation temperature difference is higher than the first temperature, executes normal time discharge temperature control to maintain the compressor discharge temperature.

According to this configuration, the control unit performs control to reduce the amount of refrigerant supplied by throttling the expansion valve so as to maintain the compressor discharge temperature of the refrigerant at or above a predetermined temperature, thereby maintaining a high discharge superheat in the compressor. When the discharge superheat is high, the viscosity of the oil dissolved in the refrigerant increases and the amount of oil in the sliding parts of the vane increases, which reduces the friction coefficient of the vane, making it less likely for the vane to float and preventing a decrease in volumetric efficiency.

(Technology 2) The refrigeration cycle device described in Technology 1, characterized in that the control unit executes the low pressure differential discharge temperature control when the indoor/outdoor saturation temperature difference is equal to or less than the first temperature and the operating frequency of the compressor is equal to or less than a predetermined specific frequency, and executes the normal discharge temperature control when the indoor/outdoor saturation temperature difference is equal to or less than the first temperature and the operating frequency of the compressor is greater than the specific frequency.

According to this configuration, the control unit performs control to reduce the amount of refrigerant supplied by throttling the expansion valve so as to maintain the compressor discharge temperature of the refrigerant at or above a predetermined temperature, thereby maintaining a high discharge superheat in the compressor. When the discharge superheat is high, the viscosity of the oil dissolved in the refrigerant increases and the amount of oil in the sliding parts of the vane increases, which reduces the friction coefficient of the vane, making it less likely for the vane to float and preventing a decrease in volumetric efficiency.

(Technology 3) The control unit calculates a discharge superheat degree, which is the difference between the compressor discharge temperature of the compressor and the evaporator temperature, and executes the low differential pressure discharge temperature control when the indoor/outdoor saturation temperature difference is equal to or lower than the first temperature, the operating frequency of the compressor is equal to or lower than the specific frequency, and the discharge superheat degree is equal to or lower than a predetermined third temperature, and executes the normal discharge temperature control when the indoor/outdoor saturation temperature difference is equal to or lower than the first temperature, the operating frequency of the compressor is equal to or lower than the specific frequency, and the discharge superheat degree is a value greater than the third temperature. The refrigeration cycle device described in Technology 2.

According to this configuration, the control unit performs control to reduce the amount of refrigerant supplied by throttling the expansion valve so as to maintain the compressor discharge temperature of the refrigerant at or above a predetermined temperature, thereby maintaining a high discharge superheat in the compressor. When the discharge superheat is high, the viscosity of the oil dissolved in the refrigerant increases and the amount of oil in the sliding parts of the vane increases, which reduces the friction coefficient of the vane, making it less likely for the vane to float and preventing a decrease in volumetric efficiency.

(Technology 4) A refrigeration cycle device according to any one of Technology 1 to Technology 3, characterized in that the refrigerant is propane.
According to this configuration, by using propane, which has a low global warming potential, as the refrigerant in the refrigeration cycle, a refrigeration cycle device that is less likely to adversely affect the global environment can be realized.

This disclosure is applicable to a refrigeration cycle device that includes an air conditioning device and a refrigerator, etc.

1. Refrigeration cycle equipment (air conditioner)
5 Evaporator 10 Rotary compressor 13 Rotary piston 15 Vane 20 Condenser 30 Expansion valve 41 Evaporator temperature sensor 43 Compressor suction temperature sensor 45 Compressor discharge temperature sensor 47 Condenser temperature sensor 49 Operation frequency detection sensor 50 Control unit

Claims (4)

A refrigeration cycle device including a compressor having a mechanism for pressing a vane in contact with a rotary piston by a discharge pressure of a refrigerant, a condenser for condensing the refrigerant, an evaporator for evaporating the refrigerant, and an expansion valve for adjusting an amount of the refrigerant supplied to the evaporator, the refrigeration cycle device being constituted by the compressor, the condenser, the evaporator, and the expansion valve,
a compressor discharge temperature sensor that measures a compressor discharge temperature, which is the temperature of the refrigerant discharged from the compressor;
a condenser temperature sensor for measuring a condenser temperature, which is the temperature of the refrigerant that has become in a two-phase state in the condenser;
an evaporator temperature sensor for measuring an evaporator temperature, which is the temperature of the refrigerant that has become in a two-phase state in the evaporator;
A control unit,
The control unit is
Calculating an indoor/outdoor saturation temperature difference, which is the difference between the condenser temperature and the evaporator temperature;
When the indoor/outdoor saturation temperature difference is equal to or less than a predetermined first temperature, a discharge temperature control under low differential pressure is executed to adjust the expansion valve so as to maintain the compressor discharge temperature of the refrigerant at a value higher than a predetermined second temperature, thereby suppressing the supply amount of the refrigerant;
When the indoor/outdoor saturation temperature difference is greater than the first temperature, a normal discharge temperature control is executed to maintain the compressor discharge temperature.
A refrigeration cycle device characterized by: The control unit is
When the indoor/outdoor saturation temperature difference is equal to or lower than the first temperature and the operating frequency of the compressor is equal to or lower than a predetermined specific frequency, the low differential pressure discharge temperature control is executed;
When the indoor/outdoor saturation temperature difference is equal to or lower than the first temperature and the operating frequency of the compressor is higher than the specific frequency, the normal discharge temperature control is executed.
2. The refrigeration cycle device according to claim 1. The control unit is
Calculating a discharge superheat degree, which is a difference between the compressor discharge temperature and the condenser temperature of the compressor;
When the indoor/outdoor saturation temperature difference is equal to or lower than the first temperature, the operating frequency of the compressor is equal to or lower than the specific frequency, and the discharge superheat degree is equal to or lower than a predetermined third temperature, the low differential pressure discharge temperature control is executed;
When the indoor/outdoor saturation temperature difference is equal to or lower than the first temperature, the operation frequency of the compressor is equal to or lower than the specific frequency, and the discharge superheat degree is a value greater than the third temperature, the normal discharge temperature control is executed.
3. The refrigeration cycle device according to claim 2. The refrigeration cycle device according to any one of claims 1 to 3, characterized in that the refrigerant is propane.

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