Refrigeration cycle device, control method, and control device

Abstract

Provided is a refrigeration cycle device equipped with a refrigerant circuit using a compressor, the refrigeration cycle device comprising: a temperature acquisition unit that acquires a value indicating the condensation temperature of refrigerant in the refrigerant circuit and a value indicating the evaporation temperature of the refrigerant; and a lower limit determination unit that determines a lower limit for the operating frequency of the compressor on the basis of the condensation temperature and the evaporation temperature. Thus, compressor vibration can be suppressed.

Description

[Technical field]

[0001] The present disclosure relates to a refrigeration cycle device, a control method, and a control device. [Background technology]

[0002] Some conventional refrigeration cycle devices increase the target frequency of the compressor when the compressor discharge pressure exceeds a preset value in order to prevent compressor vibration in the low frequency range during refrigeration cycle operation (see, for example, Patent Document 1). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2010-098871 Summary of the Invention [Problem to be solved by the invention]

[0004] However, in the conventional refrigeration cycle device, when the evaporation temperature is low, the pressure in the refrigeration cycle is relatively low, so that the discharge pressure does not easily exceed the preset pressure. This causes a problem that the temperature difference between the condensation temperature and the evaporation temperature becomes large, which may increase the vibration of the compressor.

[0005] The present disclosure has been made in consideration of the above circumstances, and has an object to provide a refrigeration cycle apparatus, a control method, and a control device that are capable of suppressing vibration of a compressor. [Means for solving the problem]

[0006] This disclosure has been made to solve the above-mentioned problems, and one aspect of the present disclosure is a refrigeration cycle device including a refrigerant circuit using a compressor, the device including a temperature acquisition unit that acquires a value indicating a condensation temperature of a refrigerant in the refrigerant circuit and a value indicating an evaporation temperature of the refrigerant, and a lower limit determination unit that determines a lower limit value of an operating frequency of the compressor based on the condensation temperature and the evaporation temperature.

[0007] Another aspect of the present disclosure is the refrigeration cycle apparatus described above, wherein the lower limit determination unit sets a lower limit of the operating frequency of the compressor when the difference between the condensation temperature and the evaporation temperature is greater than a temperature difference threshold value, higher than when the difference is smaller than the temperature difference threshold value, and the temperature difference threshold value is a constant value.

[0008] Another aspect of the present disclosure is the above-mentioned refrigeration cycle device, wherein the lower limit determination unit sets a lower limit of the operating frequency of the compressor when the difference between the condensation temperature and the evaporation temperature is greater than a temperature difference threshold value, higher than when the difference is less than the temperature difference threshold value, and the temperature difference threshold value is a value corresponding to the evaporation temperature.

[0009] Another aspect of the present disclosure is the refrigeration cycle device described above, wherein the temperature difference threshold value is a larger value as the evaporation temperature is higher.

[0010] Another aspect of the present disclosure is a control method for a refrigeration cycle device including a refrigerant circuit using a compressor, comprising the steps of acquiring a value indicating a condensation temperature of a refrigerant in the refrigerant circuit and a value indicating an evaporation temperature of the refrigerant, and determining a lower limit value of an operating frequency of the compressor based on the condensation temperature and the evaporation temperature.

[0011] Another aspect of the present disclosure is a control device that controls a compressor of a refrigerant circuit, the control device including a temperature acquisition unit that acquires a value indicating a condensation temperature of a refrigerant in the refrigerant circuit and a value indicating an evaporation temperature of the refrigerant, and a lower limit value determination unit that determines a lower limit value of an operating frequency of the compressor based on the condensation temperature and the evaporation temperature. Effect of the Invention

[0012] The refrigeration cycle device of the present disclosure can suppress vibration of the compressor. [Brief description of the drawings]

[0013] [Figure 1] 1 is a refrigerant circuit diagram that illustrates a refrigeration cycle device 100 according to a first embodiment of the present disclosure. [Diagram 2] 4 is a Ph diagram during cooling operation of the refrigeration cycle apparatus 100 in the embodiment. FIG. [Diagram 3] 4 is a graph showing the relationship between the operation frequency of the compressor 1 and the vibration of the compressor 1 in the embodiment. [Figure 4] 4 is a graph showing the relationship between the state of the refrigerant and the vibration of the compressor 1 in this embodiment. [Diagram 5] 4 is a flowchart illustrating the operation of a control unit 15 in the embodiment. [Figure 6] 4 is a time chart illustrating an example of the operation of the control unit 15 in the embodiment. [Figure 7] 13 is a flowchart illustrating an operation of a lower limit value determining section 17 in the second embodiment of the present disclosure. [Figure 8] 4 is a time chart illustrating an example of the operation of the control unit 15 in the embodiment. [Figure 9] 11 is a graph showing the relationship between the state of the refrigerant and the vibration of the compressor 1 in the third embodiment of the present disclosure. [Figure 10] 11 is a graph showing the relationship between the state of the refrigerant and the vibration of the compressor 1 in the fourth embodiment of the present disclosure. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0014] <First embodiment> Hereinafter, a first embodiment of the present disclosure will be described with reference to the drawings. In the first embodiment, an air conditioner is given as the refrigeration cycle device 100, but other devices using a refrigeration cycle, such as a heat pump type water heater, may be used. FIG. 1 is a refrigerant circuit diagram that shows a refrigeration cycle device 100 according to the first embodiment of the present disclosure. The refrigeration cycle device 100 has a compressor 1, a cooling / heating switching device 2 that switches the flow direction of cooling and heating, a heat source side heat exchanger 3, an expansion valve 4, and a circuit in which a utilization side heat exchanger 5 are connected in sequence by pipes 11, 12, 13, and 14, and a control unit 15.

[0015] The cooling / heating switching device 2 is composed of, for example, a four-way valve. The cooling / heating switching device 2 is connected between the pipe 11 on the heat source side of the compressor 1 and the pipe 14 on the utilization side, and switches the flow direction of the refrigerant to the compressor 1. In cooling operation, the cooling / heating switching device 2 is connected in the direction of the solid lines in FIG. 1. This causes the compressor 1 to compress the refrigerant in the pipe 14 on the utilization side and discharge it to the pipe 11 on the heat source side. Conversely, in heating operation, the cooling / heating switching device 2 is connected in the direction of the dotted lines in FIG. 1. This causes the compressor 1 to compress the refrigerant in the pipe 11 on the heat source side and discharge it to the pipe 11 on the utilization side.

[0016] The heat source side heat exchanger 3 functions as a heat source machine or heat source side unit that generates heat to be supplied to the usage side heat exchanger 5. The usage side heat exchanger 5 functions as a load side unit that uses the heat supplied from the heat source side heat exchanger 3. During cooling operation, the heat source side heat exchanger 3 functions as a condenser, and the usage side heat exchanger 5 functions as an evaporator. During heating operation, the heat source side heat exchanger 3 functions as an evaporator, and the usage side heat exchanger 5 functions as a condenser.

[0017] Temperature detectors for detecting the temperature of the refrigerant are provided on the heat transfer tubes and outlet tubes of the heat source side heat exchanger 3 and the user side heat exchanger 5, the downstream discharge piping of the compressor 1, and the surface of the container of the compressor 1. For the detection of the refrigerant temperature, a temperature detector such as a temperature sensor may be used, or a pressure detector may be used instead of a temperature detector to detect the refrigerant pressure and use the saturation temperature to indirectly detect the refrigerant temperature for the heat transfer tube temperature of the heat exchanger functioning as a condenser (hereinafter, condensation temperature) and the heat transfer tube temperature of the heat exchanger functioning as an evaporator (hereinafter, evaporation temperature).

[0018] The control unit 15 controls the operation frequency of the compressor 1. The control unit 15 includes a temperature acquisition unit 16 and a lower limit value determination unit 17. The temperature acquisition unit 16 acquires a value indicating a condensation temperature of the refrigerant in the refrigerant circuit and a value indicating an evaporation temperature of the refrigerant. The lower limit value determination unit 17 determines a lower limit value (lower limit frequency) of the operation frequency of the compressor 1 based on the condensation temperature and the evaporation temperature. For example, when the operation frequency determined based on the difference between the set temperature and the room temperature is smaller than the lower limit value determined by the lower limit value determination unit 17, the control unit 15 may set the lower limit value as the operation frequency. Note that the control unit 15 may be a device (control device) independent of the refrigeration cycle device 100.

[0019] 2 is a Ph diagram during cooling operation of the refrigeration cycle apparatus 100 in this embodiment. Points a to d in Fig. 2 indicate the states of the refrigerant in the portions labeled with the same symbols in Fig. 1.

[0020] When the compressor 1 starts operating, the low-temperature, low-pressure gas refrigerant is compressed by the compressor 1 and discharged as high-temperature, high-pressure gas refrigerant. In this change in the refrigerant caused by the compressor 1, the refrigerant is compressed so as to be heated by the adiabatic efficiency of the compressor 1, compared to the case where the refrigerant is adiabatically compressed on an isentropic line. For this reason, this change in the refrigerant is represented by a line connecting points a and b in Fig. 2, which is inclined to the right of the vertical.

[0021] The high-temperature, high-pressure gas refrigerant discharged from the compressor 1 passes through the cooling / heating switching device 2 and flows into the heat source-side heat exchanger 3. The gas refrigerant that flows into the heat source-side heat exchanger 3 is cooled while heating the outdoor air, and condenses into a medium-temperature, high-pressure liquid refrigerant. Taking into account the pressure loss inside the heat source-side heat exchanger 3, the change in the refrigerant inside the heat source-side heat exchanger 3 is represented by a line that connects points b and c in Figure 2 and is inclined slightly downward to the left from the horizontal.

[0022] The medium-temperature, high-pressure liquid refrigerant flowing out of the heat source-side heat exchanger 3 is expanded and reduced in pressure through the expansion valve 4, becoming a low-temperature, low-pressure, gas-liquid two-phase flow. This change in the refrigerant as it passes through the expansion valve is carried out under a constant enthalpy. The change in the refrigerant at this time is represented by the vertical line connecting points c and d in Figure 2.

[0023] The low-temperature, low-pressure refrigerant in a gas-liquid two-phase flow state that flows out of the expansion valve 4 flows into the user-side heat exchanger 5. The refrigerant that flows into the user-side heat exchanger 5 is heated while cooling the indoor air, and becomes a low-temperature, low-pressure gas refrigerant. Taking into account the pressure loss inside the user-side heat exchanger 5, the change in the refrigerant in the user-side heat exchanger 5 is represented by a line that connects point d to point a in Figure 2 and is inclined slightly to the right from the horizontal.

[0024] The low-temperature, low-pressure gas refrigerant that has flowed out of the utilization-side heat exchanger 5 passes through the cooling / heating switching device 2 and flows into the compressor 1 where it is compressed. Even during heating operation, the refrigerant circuit is switched by the cooling / heating switching device 2, and the evaporator and condenser are simply reversed, but the behavior of the Ph diagram does not change.

[0025] FIG. 3 is a graph showing the relationship between the operating frequency of the compressor 1 and the vibration of the compressor 1 in this embodiment. In FIG. 3, the horizontal axis is the operating frequency [Hz] of the compressor 1, and the vertical axis is the vibration (excitation force) [gf] of the compressor 1. In a compressor such as a single rotary, the excitation force of the compressor due to the torque fluctuation of the compressor increases when the compressor 1 operates at a low frequency. For this reason, as shown in the graph in FIG. 3, the value of the vibration of the compressor 1 tends to increase as the compressor 1 operates at a low frequency. In this embodiment, the lower limit value of the operating frequency is determined based on the condensation temperature and the evaporation temperature, and one of these lower limit values ​​(lower limit frequency Lc of the compressor 1) is set to point L1 in FIG. 3, and the other (lower limit frequency Lf for suppressing the excitation force) is set to point L2, which is a point before the vibration peaks. The lower limit frequency Lc of the compressor 1 is a lower limit value of the frequency at which the compressor 1 can be operated, which is provided for protecting the compressor 1. The lower limit frequency Lf for suppressing the vibration force is a value larger than the lower limit frequency Lc of the compressor 1, and is a lower limit value of the operating frequency of the compressor 1 provided for the purpose of suppressing vibration of the compressor 1. As will be described later, whether to use the lower limit frequency Lc of the compressor 1 or the lower limit frequency Lf for suppressing the vibration force is determined based on the condensation temperature and the evaporation temperature.

[0026] Fig. 4 is a graph showing the relationship between the state of the refrigerant and the vibration of the compressor 1 in this embodiment. In Fig. 4, the horizontal axis is the evaporation temperature [°C], and the vertical axis is the temperature difference [°C] between the condensation temperature and the evaporation temperature. Above graph Th1, the upper side is region A1 where the temperature difference is large, so the load on compressor 1 is large and the compressor vibration is large. Meanwhile, the lower side is region B1 where the temperature difference is not large, so the load on compressor 1 is not large and the compressor vibration is small.

[0027] Therefore, the lower limit value determination unit 17 in this embodiment sets the lower limit frequency Lf for vibration force suppression as the lower limit value of the operation frequency when the state of the refrigerant is in the region A1, that is, when the temperature difference between the condensation temperature and the evaporation temperature is larger than the temperature difference threshold value corresponding to the evaporation temperature. Also, when the state of the refrigerant is in the region B1, that is, when the temperature difference between the condensation temperature and the evaporation temperature is smaller than the temperature difference threshold value corresponding to the evaporation temperature, the lower limit value determination unit 17 sets the lower limit frequency Lc of the compressor as the lower limit value of the operation frequency. As described in FIG. 3, the lower limit frequency Lf for vibration force suppression is larger than the lower limit frequency Lc of the compressor 1. And, since the vibration of the compressor 1 at the lower limit frequency Lf for vibration force suppression is smaller than that at the lower limit frequency Lc of the compressor, even if the state of the refrigerant is in the region A1, it is possible to suppress the vibration of the compressor 1 from becoming large.

[0028] The lower limit value determination unit 17 may store the temperature difference threshold corresponding to the graph Th1 in a table in association with the evaporation temperature. Alternatively, the lower limit value determination unit 17 may store an arithmetic expression for calculating the temperature difference threshold from the evaporation temperature. The arithmetic expression may be provided for each of several intervals into which the evaporation temperature is divided.

[0029] FIG. 5 is a flowchart for explaining the operation of the control unit 15 in this embodiment. First, the lower limit value determination unit 17 of the control unit 15 calculates the temperature difference between the condensation temperature and the evaporation temperature acquired by the temperature acquisition unit 16 (step Sa1). Next, the lower limit value determination unit 17 judges whether the temperature difference calculated in step Sa1 is greater than the temperature difference threshold value (step Sa2). When the lower limit value determination unit 17 judges in step Sa2 that the temperature difference is greater than the temperature difference threshold value (step Sa2-YES), it sets the lower limit frequency Lf for vibration force suppression to the lower limit value of the operation frequency (lower limit frequency L) (step Sa3) and proceeds to step Sa5. When the lower limit value determination unit 17 judges in step Sa2 that the temperature difference is not greater than the temperature difference threshold value (step Sa2-NO), it sets the lower limit frequency Lc of the compressor 1 to the lower limit value of the operation frequency (lower limit frequency L) (step Sa4) and proceeds to step Sa5.

[0030] In step Sa5, the control unit 15 determines whether the operation frequency of the compressor 1 is lower than the lower limit frequency L set in step Sa3 or step Sa4. The operation frequency at this time is, for example, an operation frequency calculated by the control unit 15 based on the difference between the room temperature and the set temperature. When the control unit 15 determines that the operation frequency is lower than the lower limit frequency L (YES in step Sa5), it sets the lower limit frequency L as the operation frequency (step Sa6) and proceeds to step Sa7. When the control unit 15 determines that the operation frequency is not lower than the lower limit frequency L (NO in step Sa5), it proceeds to step Sa7 without changing the operation frequency.

[0031] In step Sa7, the control unit 15 determines whether the compressor 1 is stopped. If the control unit 15 determines that the compressor 1 is stopped (YES in step Sa7), it ends the process. If the control unit 15 determines that the compressor 1 is not stopped (NO in step Sa7), it returns to step Sa1.

[0032] Fig. 6 is a time chart for explaining an example of the operation of the control unit 15 in this embodiment. In the upper and lower parts of Fig. 6, the horizontal axis is time [s], in the upper part, the vertical axis is the temperature difference [°C] between the condensation temperature and the evaporation temperature, and in the lower part, the vertical axis is the compressor frequency (the operation frequency of the compressor 1). In the upper part, the temperature difference threshold Th11 and the temperature difference S1 between the condensation temperature and the evaporation temperature of the refrigerant are plotted. In addition, in the lower part, the operation frequency Fd1 and the lower limit value Fm1 of the operation frequency are plotted.

[0033] Before time T1, the temperature difference S1 is smaller than the temperature difference threshold value Th11. Therefore, the lower limit value Fm1 of the operating frequency is the lower limit frequency Lc of the compressor 1, and the operating frequency Fd1 can be smaller than the lower limit frequency Lf for the excitation force suppression. However, from time T1, the temperature difference S1 exceeds the temperature difference threshold value Th11, so the lower limit value Fm1 of the operating frequency is changed to the lower limit frequency Lf for the excitation force suppression. Accordingly, the operating frequency Fd1 is also changed to the lower limit frequency Lf for the excitation force suppression. As a result, when the temperature difference S1 exceeds the temperature difference threshold value and the load on the compressor 1 is large, the operating frequency is prevented from becoming smaller than the lower limit frequency Lf for the excitation force suppression, thereby making it possible to suppress the increase in vibration.

[0034] <Second embodiment> In the first embodiment, when the temperature difference exceeds the temperature difference threshold, the lower limit frequency Lf for vibration force suppression is used as the lower limit of the operation frequency, but in the second embodiment, when the operation frequency is smaller than the lower limit frequency Lf for vibration force suppression, the lower limit frequency Lf for vibration force suppression is used as the lower limit of the operation frequency. The other points are the same as those in the first embodiment.

[0035] FIG. 7 is a flowchart for explaining the operation of the lower limit value determination unit 17 in the second embodiment. First, the lower limit value determination unit 17 calculates the temperature difference between the condensation temperature and the evaporation temperature acquired by the temperature acquisition unit 16 (step Sb1). Next, the lower limit value determination unit 17 judges whether the temperature difference calculated in step Sb1 is greater than the temperature difference threshold value (step Sb2). When the lower limit value determination unit 17 judges in step Sb2 that the temperature difference is greater than the temperature difference threshold value (step Sb2-YES), it judges that the operating load of the compressor 1 is large (step Sb3) and proceeds to step Sb5. When the lower limit value determination unit 17 judges in step Sb2 that the temperature difference is not greater than the temperature difference threshold value (step Sb2-NO), it judges that the operating load of the compressor 1 is small, sets the lower limit frequency Lc of the compressor 1 to the lower limit value of the operating frequency (lower limit frequency L) (step Sb4), and returns to step Sb1.

[0036] In step Sb5, the lower limit value determination unit 17 judges whether the operating frequency of the compressor 1 is lower than the lower limit frequency Lf for excitation force suppression. When the lower limit value determination unit 17 judges in step Sb5 that the operating frequency is lower than the lower limit frequency Lf for excitation force suppression (YES in step Sb5), the lower limit value determination unit 17 sets the lower limit frequency Lf for excitation force suppression to the lower limit value of the operating frequency (lower limit frequency L) (step Sb6), and proceeds to step Sb8. When the lower limit value determination unit 17 judges in step Sb5 that the operating frequency is not lower than the lower limit frequency Lf for excitation force suppression (NO in step Sb5), the lower limit value determination unit 17 sets the lower limit frequency Lc of the compressor 1 to the lower limit value of the operating frequency (lower limit frequency L) (step Sb7), and proceeds to step Sb8.

[0037] In step Sb8, the lower limit value determination unit 17 judges whether the compressor 1 is stopped or not. If the lower limit value determination unit 17 judges that the compressor 1 is stopped (step Sb8-YES), it ends the process, and if the lower limit value determination unit 17 judges that the compressor 1 is not stopped (step Sb8-NO), it returns to step Sb1.

[0038] In this embodiment, when the temperature difference S1 exceeds the temperature difference threshold Th11, the operating frequency Fd1 that is lower than the lower limit frequency Lf for vibration force suppression becomes the lower limit frequency Lf for vibration force suppression, as in Fig. 6. However, in this embodiment, the operation when the operating frequency is higher than the lower limit frequency Lf for vibration force suppression is different from that in the first embodiment.

[0039] Fig. 8 is a time chart for explaining an example of the operation of the control unit 15 in this embodiment. In the upper and lower parts of Fig. 8, the horizontal axis is time [s], in the upper part, the vertical axis is the temperature difference [°C] between the condensation temperature and the evaporation temperature, and in the lower part, the vertical axis is the compressor frequency (the operation frequency of the compressor 1). In the upper part, the temperature difference threshold Th12 and the temperature difference S2 between the condensation temperature and the evaporation temperature of the refrigerant are plotted. In addition, in the lower part, the operation frequency Fd1 and the lower limit value Fm2 of the operation frequency are plotted.

[0040] Before time T2, the temperature difference S2 is smaller than the temperature difference threshold value Th12. Therefore, the lower limit value Fm2 of the operation frequency is the lower limit frequency Lc of the compressor 1. In addition, the operation frequency Fd2 is a value larger than the lower limit frequency Lf for vibration force suppression. Then, from time T2, the temperature difference S2 exceeds the temperature difference threshold value Th12, but since the operation frequency Fd2 is a value larger than the lower limit frequency Lf for vibration force suppression, the lower limit value Fm2 of the operation frequency remains the lower limit frequency Lc of the compressor 1, and the operation frequency Fd2 is not affected by the lower limit value Fm2 of the operation frequency.

[0041] In this embodiment as well, when the temperature difference S1 exceeds the temperature difference threshold value and the load on the compressor 1 is large, the operating frequency is prevented from becoming smaller than the lower limit frequency Lf for suppressing the vibration force, thereby preventing the vibration from increasing.

[0042] <Third embodiment> In the first and second embodiments, the temperature difference threshold is a value according to the evaporation temperature, but in the third embodiment, the temperature difference threshold is a constant value that does not depend on the evaporation temperature. The rest of the third embodiment may be the same as the first embodiment or the second embodiment.

[0043] FIG. 9 is a graph showing the relationship between the state of the refrigerant and the vibration of the compressor 1 in the third embodiment. In FIG. 9, the horizontal axis is the evaporation temperature [°C], and the vertical axis is the temperature difference [°C] between the condensation temperature and the evaporation temperature. In this embodiment, the graph Th2, which is the boundary between the region A2 where the compressor vibration is large and the region B2 where the compressor vibration is small, i.e., the temperature difference threshold, is a constant value. In other words, in the lower limit value determination unit 17 of this embodiment, the temperature difference threshold used when determining the lower limit value of the operating frequency is a constant value. As a result, the lower limit value determination unit 17 does not need to store the relationship between the evaporation temperature and the temperature difference threshold, and the processing in the lower limit value determination unit 17 can be reduced.

[0044] <Fourth embodiment> In the third embodiment, the temperature difference threshold is a constant value, but in the fourth embodiment, the temperature difference threshold is set to a larger value as the evaporation temperature increases. The rest is the same as in the fourth embodiment.

[0045] Fig. 10 is a graph showing the relationship between the state of the refrigerant and the vibration of the compressor 1 in the fourth embodiment. In Fig. 10, the horizontal axis is the evaporation temperature [°C], and the vertical axis is the temperature difference [°C] between the condensation temperature and the evaporation temperature. In this embodiment, in graph Th3 which is the boundary between region A3 where the compressor vibration is large and region B3 where the compressor vibration is small, the temperature difference threshold value increases as the evaporation temperature increases. That is, in lower limit value determination unit 17 of this embodiment, the temperature difference threshold value used when determining the lower limit value of the operation frequency increases as the evaporation temperature increases.

[0046] When the lower limit frequency Lf for suppressing the vibration force is used, the operating frequency is higher than when the lower limit frequency Lc of the compressor 1 is used, so that the operation is likely to be such that the indoor temperature is maintained close to the set temperature by intermittent operation. Such an operation may be uncomfortable for the user. However, in this embodiment, the higher the evaporation temperature, the larger the temperature difference threshold is. Therefore, when the evaporation temperature is high and the operating load is small, the region in which the lower limit frequency Lc of the compressor 1 is used can be expanded, and the operation described above can be prevented. The temperature difference threshold may be calculated by a linear equation with the evaporation temperature as a variable. This allows the linear equation to be stored, and the processing in the lower limit value determination unit 17 can be reduced.

[0047] In addition, the control unit 15 in Figure 1 may be realized by dedicated hardware, or this control unit 15 may be composed of a memory and a CPU (Central Processing Unit), and the function of the control unit 15 may be realized by loading a program for realizing the function of the control unit 15 into the memory and executing the program.

[0048] In addition, each functional block of the control unit 15 in Fig. 1 may be individually formed into a chip, or may be partially or entirely integrated into a chip. The method of integration is not limited to LSI, and may be realized by a dedicated circuit or a general-purpose processor. Either a hybrid or monolithic method may be used. Some functions may be realized by hardware and some by software. Furthermore, if advances in semiconductor technology result in the emergence of integrated circuit technologies that can replace LSIs, it may also be possible to use integrated circuits using those technologies.

[0049] Although the embodiment of this disclosure has been described in detail above with reference to the drawings, the specific configuration is not limited to this embodiment, and design changes and the like are also included within the scope that does not depart from the gist of this disclosure. [Explanation of symbols]

[0050] 1 Compressor 2. Cooling and heating switching device 3 Heat source side heat exchanger 4 Expansion valve 5 User side heat exchanger 11, 12, 13, 14 Piping 15 Control section 16 Temperature acquisition section 17 Lower limit determination section 100 Refrigeration cycle device

Claims

1. A refrigeration cycle device including a refrigerant circuit using a compressor, a temperature acquisition unit that acquires a value indicating a condensation temperature of the refrigerant in the refrigerant circuit and a value indicating an evaporation temperature of the refrigerant; a lower limit value determination unit that determines a lower limit value of an operation frequency of the compressor based on the condensation temperature and the evaporation temperature; Equipped with the lower limit value determination unit sets a lower limit value of the operating frequency of the compressor when the difference between the condensing temperature and the evaporating temperature is greater than a temperature difference threshold value to be greater than a lower limit value of the operating frequency of the compressor when the difference between the condensing temperature and the evaporating temperature is not greater than the temperature difference threshold value, The temperature difference threshold value is larger as the evaporation temperature is larger. Refrigeration cycle equipment.

2. A method for controlling a refrigeration cycle device including a refrigerant circuit using a compressor, comprising: obtaining a value indicative of a condensation temperature of a refrigerant in the refrigerant circuit and a value indicative of an evaporation temperature of the refrigerant; determining a lower limit value of an operating frequency of the compressor based on the condensing temperature and the evaporating temperature; having In the determining step, a lower limit value of an operation frequency of the compressor when the difference between the condensing temperature and the evaporating temperature is greater than a temperature difference threshold is set to be greater than a lower limit value of an operation frequency of the compressor when the difference between the condensing temperature and the evaporating temperature is not greater than the temperature difference threshold; The temperature difference threshold value is larger as the evaporation temperature is larger. A control method.

3. A control device for controlling a compressor of a refrigerant circuit, a temperature acquisition unit that acquires a value indicating a condensation temperature of the refrigerant in the refrigerant circuit and a value indicating an evaporation temperature of the refrigerant; a lower limit value determination unit that determines a lower limit value of an operation frequency of the compressor based on the condensation temperature and the evaporation temperature; Equipped with the lower limit value determination unit sets a lower limit value of the operating frequency of the compressor when the difference between the condensing temperature and the evaporating temperature is greater than a temperature difference threshold value to be greater than a lower limit value of the operating frequency of the compressor when the difference between the condensing temperature and the evaporating temperature is not greater than the temperature difference threshold value, The temperature difference threshold value is larger as the evaporation temperature is larger. Control device.

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