Refrigeration cycle equipment

Abstract

This suppresses the decrease in COP of a refrigeration cycle system equipped with a refrigerant circuit that uses carbon dioxide as a refrigerant. [Solution] A refrigeration cycle device comprising a refrigerant circuit (10) connected to a compression unit (11), a heat sink (25), a pressure reducing mechanism (13, 14), and an evaporator (12), and filled with carbon dioxide refrigerant, has a control unit (100) that performs a refrigeration cycle operation in which the refrigerant circuit (10) increases the pressure of the suction refrigerant at low pressure to high pressure using the compression unit (11), defines a first isentropy line including a first point on the saturated vapor curve at low pressure, and controls the refrigerant circuit (10) so that the difference between a first refrigerant temperature Ta, which indicates the refrigerant temperature at a second point on the first isentropy line at high pressure, and a second refrigerant temperature Tb, which indicates the temperature of the discharged refrigerant discharged from the compression unit (11), is within ±2℃.

Description

Technical Field

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

Background Art

[0002] In a refrigeration cycle device having a refrigerant circuit using carbon dioxide as a refrigerant, the high-pressure side may be in a so-called supercritical state. Therefore, suppression of a decrease in the COP of such a refrigeration cycle device is required. In the refrigeration cycle device disclosed in Patent Document 1, by adjusting the opening degree of a pressure reducer based on the discharge temperature of the refrigerant discharged from a compressor, a decrease in the COP of the refrigeration cycle device is suppressed, and an increase in the discharge temperature of the refrigerant is also suppressed.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] However, in the control method of the pressure reducing mechanism based on the discharge temperature disclosed in Patent Document 1, the suction superheat degree may become negative. In such a case, since the refrigerant in a two-phase state is sucked into the compressor, it may cause damage to the compressor. On the other hand, in the control method of the pressure reducing mechanism based on the suction superheat degree, it is impossible to determine whether the refrigerant sucked into the compressor is in a two-phase state or a saturated state. Therefore, it is necessary to ensure a certain degree of suction superheat degree, but if the suction superheat degree is too sufficient, there is a risk of deteriorating the COP of the refrigeration cycle device.

[0005] An object of the present disclosure is to suppress a decrease in the COP of a refrigeration cycle device provided with a refrigerant circuit using carbon dioxide as a refrigerant.

Means for Solving the Problems

[0006] The first aspect is, A refrigeration cycle device comprising a refrigerant circuit (10) filled with carbon dioxide refrigerant, to which a compression section (11), a heat sink (25), a pressure reducing mechanism (13, 14), and an evaporator (12) are connected, The refrigerant circuit (10) performs a refrigeration cycle operation in which the low-pressure intake refrigerant is increased to a high-pressure level by the compression unit (11). This refrigeration cycle device has a first isentropy line defined that includes a first point on the saturated vapor curve at low pressure, and a control unit (100) that performs a first control to control the refrigerant circuit such that the difference between a first refrigerant temperature Ta, which indicates the refrigerant temperature at a second point on the first isentropy line at high pressure, and a second refrigerant temperature Tb, which indicates the temperature of the discharged refrigerant discharged from the compression unit (11), is within ±2°C.

[0007] In the first embodiment, the control unit (100) controls the temperature of the discharged refrigerant using isentropy lines. This enables refrigeration cycle operation with reduced suction superheating, thereby suppressing the decrease in the COP of the refrigeration cycle system.

[0008] A second aspect is, in the first aspect, The system further includes a first detection unit (89) that detects an indicator of the low pressure of the refrigerant circuit (10).

[0009] In the second embodiment, the first detection unit (89) can easily determine the low pressure of the refrigerant circuit (10), making it easy to perform the first control.

[0010] A third aspect is, in the first aspect, The system further includes a second detection unit (88) that detects an indicator of the high pressure of the refrigerant circuit (10).

[0011] In the third embodiment, the second detection unit (88) can easily determine the high pressure of the refrigerant circuit (10), making it easy to perform the first control.

[0012] A fourth aspect is, in the first aspect, The system further includes a third detection unit (80) that detects an index indicating the temperature of the high-pressure discharged refrigerant discharged from the compression unit (11).

[0013] In the fourth embodiment, the temperature of the discharged refrigerant can be easily determined by the third detection unit (80), so the first control can be easily performed.

[0014] The fifth aspect is one of the first to fourth aspects, The first refrigerant temperature Ta is a value obtained by correcting the refrigerant temperature at the second point.

[0015] In the fifth embodiment, the first refrigerant temperature Ta can be determined with high accuracy by using a correction value. This improves the effect of suppressing the decrease in COP.

[0016] The sixth aspect is as described in the fifth aspect. The first refrigerant temperature Ta is a value obtained by correcting the refrigerant temperature at the second point based on the rotational speed of the compression unit (11), the power consumption of the compression unit (11), the high pressure value, the low pressure value, the temperature of the refrigerant discharged from the compression unit (11), or the ambient temperature.

[0017] In the sixth embodiment, the accuracy of the first control can be improved by using a correction value based on the amount of heat dissipated or input to such a compression section (11).

[0018] The seventh aspect is one of the first to sixth aspects, The control unit (100) stops the execution of the first control if the discharge superheat of the refrigerant falls below a predetermined first temperature during the execution of the first control.

[0019] In the seventh embodiment, the first control can be stopped if the discharge superheat of the refrigerant falls below the first temperature.

[0020] The eighth aspect is as described in the seventh aspect. After the execution of the first control is stopped, the control unit (100) controls the opening degree of the decompression mechanism (13, 14) so that the discharge superheat degree does not fall below the first temperature.

[0021] In the eighth aspect, it is possible to suppress the discharge superheat degree from falling below the first temperature. Thereby, for example, when the first temperature is a temperature at which the use of the compression part (11) is restricted, if the operation of the compression part (11) is continued at a discharge superheat degree lower than the first temperature, the compression part (11) may malfunction, but in the eighth aspect, such a malfunction of the compression part (11) can be suppressed.

[0022] The ninth aspect is any one of the first to eighth aspects, During the execution of the first control, when the temperature of the discharged refrigerant from the compression part (11) exceeds a predetermined second temperature, the control unit (100) stops the execution of the first control.

[0023] In the ninth aspect, when the temperature of the discharged refrigerant exceeds the second temperature, the first control can be stopped.

[0024] The tenth aspect is in the ninth aspect, After the execution of the first control is stopped, the control unit (100) controls the opening degree of the decompression mechanism (13, 14) so that the temperature of the discharged refrigerant does not exceed the second temperature.

[0025] In the tenth aspect, it is possible to suppress the temperature of the discharged refrigerant from exceeding the second temperature. If the temperature of the discharged refrigerant becomes too high, the operating load on the compression part (11) increases. If such a state continues, the compression part (11) may be damaged. In the tenth aspect, such damage to the compression part (11) can be suppressed.

[0026] The eleventh aspect is any one of the first to tenth aspects, During the execution of the first control, when the high-pressure pressure in the refrigerant circuit (10) exceeds the first pressure, the control unit (100) stops the execution of the first control.

[0027] In the eleventh embodiment, the first control can be stopped when the high pressure of the refrigerant circuit (10) exceeds the first pressure.

[0028] The twelfth aspect is as follows, in the eleventh aspect: After the execution of the first control is stopped, the control unit (100) controls the opening degree of the pressure reducing mechanism (13, 14) so ​​that the high pressure of the refrigerant circuit (10) does not exceed the first pressure.

[0029] In the twelfth embodiment, it is possible to suppress the high pressure of the refrigerant circuit (10) from exceeding the first pressure. If the high pressure becomes too high, the operating load on the compression section (11) increases. If this condition continues, the compression section (11) may be damaged. In the tenth embodiment, such damage to the compression section (11) can be suppressed.

[0030] The 13th aspect is, A refrigeration cycle device comprising a refrigerant circuit (10) having a main refrigerant circuit (10) through which the refrigerant flows in the order of a compression section (11), a heat sink (25), a first pressure reducing mechanism (13, 14), and an evaporator (12), and an economizer circuit (30) in the main refrigerant circuit (10) that connects the space between the heat sink (25) and the first pressure reducing mechanism (13, 14) to the compression section (11), The aforementioned economizer circuit (30) A second pressure reduction mechanism (33) for reducing the pressure of a high-pressure refrigerant to an intermediate-pressure refrigerant, The system includes an economizer heat exchanger (31) in which the intermediate-pressure refrigerant and the high-pressure refrigerant between the radiator (25) and the first pressure reducing mechanism (13, 14) in the main refrigerant circuit (10) exchange heat. A second isentropy line containing the third point on the saturated vapor curve at low pressure, A third isentropy line containing the fourth point on the saturated vapor curve at intermediate pressure, and A seventh point is defined between the fifth point on the second isentropy line at high pressure and the sixth point on the third isentropy line at high pressure. The system includes a control unit (100) that performs a second control to control the refrigerant circuit so that the difference between the third refrigerant temperature Tc, which indicates the refrigerant temperature at the seventh point, and the second refrigerant temperature Tb, which indicates the temperature of the discharged refrigerant discharged from the compression unit (11), is within the range of ±2°C.

[0031] In the 13th embodiment, even in a refrigeration cycle device equipped with a refrigerant circuit (10) having an economizer circuit (30), the decrease in the COP of the refrigeration cycle device (1) can be suppressed by performing the second control.

[0032] The 14th aspect is, A refrigeration cycle device comprising a refrigerant circuit (10) having a main refrigerant circuit (10) through which the refrigerant flows in the order of a compression section (11), a heat sink (25), a first pressure reducing mechanism (13, 14), and an evaporator (12), and an economizer circuit (30) in the main refrigerant circuit (10) that connects the space between the heat sink (25) and the first pressure reducing mechanism (13, 14) to the compression section (11), The aforementioned economizer circuit (30) A second pressure reduction mechanism (33) for reducing the pressure of a high-pressure refrigerant to an intermediate-pressure refrigerant, The system includes an economizer heat exchanger (31) in which the intermediate pressure refrigerant and the high-pressure refrigerant between the radiator (25) and the first pressure reducing mechanism (13, 14) in the main refrigerant circuit (10) exchange heat. The fourth isentropy line containing the eighth point on the saturated vapor curve at low pressure, The ninth point on the fourth isentropy line at intermediate pressure, The fifth isentropy line including the tenth point obtained by subtracting Δh from the enthalpy at the ninth point, and The 11th point on the fifth isentropy line at high pressure is defined, The system includes a control unit (100) that performs a sixth control to control the refrigerant circuit so that the difference between the fourth refrigerant temperature Td, which indicates the refrigerant temperature at the 11th point, and the second refrigerant temperature Tb, which indicates the temperature of the discharged refrigerant discharged from the compression unit (11), is within ±2°C. The aforementioned Δh is, The enthalpy of the refrigerant at the aforementioned 9th point, This is an amount corresponding to the enthalpy of the refrigerant downstream of the economizer heat exchanger (31) in the economizer circuit (30).

[0033] In the 14th embodiment, even in a refrigeration cycle device equipped with a refrigerant circuit (10) having an economizer circuit (30), the decrease in the COP of the refrigeration cycle device (1) can be suppressed by performing the third control. [Brief explanation of the drawing]

[0034] [Figure 1] Figure 1 is a piping diagram of the refrigerant circuit in the embodiment. [Figure 2] Figure 2 is a block diagram of the main components of the hot water supply system. [Figure 3] Figure 3 is a piping diagram of the hot water supply system, showing the flow of refrigerant during heating operation. [Figure 4] Figure 4 is a flowchart showing the operation of the control unit during the first control execution. [Figure 5] Figure 5 shows a saturated steam curve illustrating how the discharge temperature is determined by the first control method. [Figure 6A] Figure 6A is a graph showing the relationship between the discharge superheat of the refrigerant discharged from the compressor and the COP when the refrigerant circuit is operated under predetermined operating conditions. [Figure 6B] Figure 6B is a graph obtained by transforming Figure 6A into a relationship between ΔT1 and COP. [Figure 7A] Figure 7A shows the relationship between the discharge superheat of the refrigerant discharged from the compressor and the COP when the refrigerant circuit is operated under different operating conditions than those in Figure 6A. [Figure 7B] Figure 7B is a graph obtained by transforming Figure 7A into a relationship between ΔT1 and COP. [Figure 8] Figure 8 is a piping diagram of the refrigerant circuit in a modified example. [Figure 9] Figure 9 is a flowchart showing the operation of the control unit during the execution of the second control. [Figure 10] Figure 10 shows a saturated steam curve illustrating how the discharge temperature is determined by the second control method. [Figure 11] Figure 11 is a flowchart showing the operation of the control unit during the execution of the third control. [Figure 12] Figure 12 shows a saturated steam curve illustrating how the discharge temperature is determined by the third control method. [Figure 13] Figure 13 is a graph showing the relationship between ΔT and COP to explain the temperature range of ΔT under given operating conditions. [Figure 14] Figure 14 is a graph showing the relationship between ΔT and COP to explain the temperature range of ΔT under different operating conditions than those shown in Figure 13. [Modes for carrying out the invention]

[0035] Embodiments of this disclosure will be described in detail below with reference to the drawings. This disclosure is not limited to the embodiments shown below, and various modifications are possible without departing from the technical idea of ​​this disclosure. Since the drawings are for conceptual illustration of this disclosure, dimensions, ratios, or numbers may be exaggerated or simplified as necessary for ease of understanding.

[0036] (1) Overall structure The refrigeration cycle device is applied to the hot water supply device (1). The hot water supply device (1) generates hot water. The generated hot water is stored in a hot water storage tank and supplied to a predetermined target. The hot water supply device (1) of this embodiment has an outdoor unit (OU) installed outside and an indoor unit (IU) installed inside.

[0037] As shown in Figure 1, the hot water supply system (1) has a refrigerant circuit (10) and a water circuit (60). The refrigerant circuit (10) is filled with a first refrigerant. The first refrigerant is carbon dioxide.

[0038] (1-1) Refrigerant circuit The refrigerant circuit (10) performs a refrigeration cycle using a first refrigerant. The refrigerant circuit (10) mainly comprises a compressor (11), an outdoor heat exchanger (12), a first expansion valve (13), and a second expansion valve (14). The refrigerant circuit (10) in this embodiment further comprises a four-way switching valve (15), a receiver (16), and a bridge circuit (20). These devices are installed in the outdoor unit (OU). The refrigerant circuit (10) performs a refrigeration cycle operation in which the compressor (11) increases the pressure of the low-pressure intake refrigerant to high pressure.

[0039] The compressor (11) compresses the inhaled refrigerant and discharges the compressed refrigerant. The compressor (11) is a so-called high-pressure dome-type compressor. Specifically, the compressor (11) has a casing, a motor located inside it, and a compression mechanism driven by the motor. The inside of the casing is filled with high-pressure refrigerant discharged from the compression mechanism. An oil reservoir of refrigerant oil is formed at the bottom of the casing. This refrigerant oil is supplied to the sliding parts of the compression mechanism and bearings by an oil supply pump. The compressor (11) is an example of a compression unit of this disclosure.

[0040] The outdoor heat exchanger (12) is an air heat exchanger that exchanges heat between the outdoor air transported by the outdoor fan (17) and the first refrigerant. The outdoor heat exchanger (12) is an example of an evaporator in this disclosure. The first expansion valve (13) and the second expansion valve (14) are an example of a pressure reducing mechanism. The first expansion valve (13) and the second expansion valve (14) are, for example, electronic expansion valves that reduce the pressure of the refrigerant.

[0041] The four-way directional control valve (15) has a first port (P1), a second port (P2), a third port (P3), and a fourth port (P4). The four-way directional control valve (15) switches between a first state, shown by the solid line in Figure 1, and a second state, shown by the dashed line in Figure 1. In the first state, the four-way directional control valve (15) connects the first port (P1) and the second port (P2) and simultaneously connects the third port (P3) and the fourth port (P4). In the second state, the four-way directional control valve (15) connects the first port (P1) and the third port (P3) and simultaneously connects the second port (P2) and the fourth port (P4).

[0042] The bridge circuit (20) is composed of first to fourth pipes (21, 22, 23, 24), each having a check valve (CV). Each check valve (CV) allows the flow of refrigerant in the direction indicated by the arrow in Figure 1 and prohibits the flow of refrigerant in the opposite direction. The outlet end of the first pipe (21) and the outlet end of the second pipe (22) are connected to the inlet side of the receiver (16). The inlet end of the third pipe (23) and the inlet end of the fourth pipe (24) are connected to the outlet side of the receiver (16). The inlet end of the first pipe (21) and the outlet end of the third pipe (23) are connected to the liquid side end of the outdoor heat exchanger (12). The inlet end of the second pipe (22) and the outlet end of the fourth pipe (24) are connected to the third flow path (25a) of the water heat exchanger (25).

[0043] The water heat exchanger (25) is composed of, for example, a plate heat exchanger. The water heat exchanger (25) has a third flow path (25a) through which the first refrigerant of the refrigerant circuit (10) flows, and a fourth flow path (25b) through which the water of the water circuit (60) flows. The water heat exchanger (25) exchanges heat between the first refrigerant in the third flow path (25a) and the water in the fourth flow path (25b). The water heat exchanger (25) is a counterflow type in which the flow of the first refrigerant in the third flow path (25a) and the flow of water in the fourth flow path (25b) are in opposite directions. The water heat exchanger (25) is an example of a heat radiator.

[0044] (1-2) Water circuit In the water circuit (60), water supplied to the target circulates. The water circuit (60) is provided with a hot water storage tank (not shown) in which water heated by the water heat exchanger (25) (hot water) is stored. The water circuit (60) is provided with a pump (61) for circulating the water. The hot water storage tank and the pump (61) are installed in the indoor unit (IU).

[0045] (2) Sensor The hot water supply device (1) has multiple sensors. As shown in Figure 1, the multiple sensors include an intake pressure sensor (89), a discharge pressure sensor (88), and a discharge temperature sensor (80). The intake pressure sensor (89) detects the low pressure of the refrigerant circuit (10) as a first detection unit. The discharge pressure sensor (88) detects the high pressure of the refrigerant circuit (10) as a second detection unit. The discharge temperature sensor (80) detects the temperature of the high-pressure discharge refrigerant discharged from the compressor (11) as a third detection unit.

[0046] Multiple sensors include an outside air temperature sensor (86). The outside air temperature sensor (86) is positioned around the compressor (11) and detects the temperature of the outdoor air.

[0047] Multiple sensors may include sensors (not shown) that detect information necessary to determine the rotational speed of the compressor (11) and the power consumption of the compressor (11). For example, there may be a current sensor that detects the current value input to the compressor (11) and a voltage sensor that detects the voltage. Based on the current value and the voltage value, the rotational speed of the motor provided in the compressor (11) and the power consumption of the compressor (11) can be determined.

[0048] The hot water supply system has a pressure switch. The pressure switch includes a high-pressure switch (87). The high-pressure switch (87) is located on the discharge side of the compressor (11) and activates when the high pressure exceeds the first pressure. This stops the operation of the compressor (11).

[0049] (3) Control Unit The control unit (100) shown in Figure 2 includes an MCU (Micro Control Unit), electrical circuits, and electronic circuits. The MCU includes a CPU (Central Processing Unit), memory, and a communication interface. The memory stores various programs for the CPU to execute. The control unit (100) may consist of one physically independent element, or it may consist of two or more physically separated elements.

[0050] The control unit (100) controls the refrigerant circuit (10). Specifically, the control unit (100) controls the starting and stopping of the compressor (11), the rotational speed of the compressor (11), the opening degree of the first expansion valve (13), the opening degree of the second expansion valve (14), the starting and stopping of the outdoor fan (17), and the rotational speed of the outdoor fan (17). The control unit (100) receives detection signals from the various sensors mentioned above.

[0051] (4) Heating operation The hot water supply system (1) performs a heating operation to generate hot water in the water circuit (60). During the heating operation, a refrigeration cycle is performed in which the outdoor heat exchanger (12) of the refrigerant circuit (10) functions as an evaporator and the water heat exchanger (25) functions as a heat radiator.

[0052] In the heating operation shown in Figure 3, the control unit (100) operates the compressor (11), the outdoor fan (17), and the pump (61), sets the four-way switching valve (15) to the first state, and adjusts the opening degrees of the first expansion valve (13) and the second expansion valve (14) as appropriate.

[0053] In the refrigerant circuit (10), the first refrigerant, compressed by the compressor (11), releases heat to the water in the water circuit (60) in the water heat exchanger (25). The first refrigerant, after releasing heat, is depressurized in the first expansion valve (13), passes through the receiver (16), and is further depressurized in the second expansion valve (14). Subsequently, the first refrigerant absorbs heat from the outdoor air in the outdoor heat exchanger (12), evaporates, and is drawn into the compressor (11).

[0054] In the water circuit (60), water transported by the pump (61) is heated in the water heat exchanger (25) and used to generate hot water in the hot water storage tank.

[0055] (5) Refrigeration cycle of a refrigerant circuit using carbon dioxide as a refrigerant In refrigeration systems with a refrigerant circuit using carbon dioxide as the refrigerant, the high-pressure side of the refrigerant cycle may reach a so-called supercritical state. In this case, the discharge pressure of the refrigerant discharged from the compressor increases, resulting in increased power consumption of the compressor and a decrease in COP. For refrigeration systems using refrigerants that result in relatively high pressures like this, it is desirable to suppress the decrease in COP. One method to suppress the decrease in COP is to control the refrigerant circuit to minimize the intake superheat or discharge superheat as much as possible.

[0056] However, when controlling the refrigerant circuit based on the intake superheat, it is not possible to determine whether the intake refrigerant is in a two-phase state or a saturated state, so it is necessary to ensure a certain amount of extra intake superheat. Also, when controlling the refrigerant circuit based on the discharge superheat, the compressor is required to operate at or above a specified discharge superheat, so it is necessary to ensure a discharge superheat with an additional margin beyond that specified discharge superheat. Thus, ensuring extra intake and discharge superheat may reduce the COP of the refrigeration cycle system.

[0057] (6) First control To address these challenges, the hot water supply system (1) of this disclosure performs a first control that controls the refrigerant circuit (10) so that the refrigerant discharge temperature is at a predetermined temperature or within a predetermined temperature range. The first control suppresses the suction superheating and prevents a decrease in the COP of the hot water supply system (1). The operation of the control unit (100) when the first control is performed will be described below with reference to Figures 4 and 5. The control unit (100) may also have the saturated vapor curve shown in Figure 5 as data.

[0058] In step ST01, the control unit (100) acquires the pressure value Pd of the discharged refrigerant, the pressure value Ps of the suctioned refrigerant, and the second refrigerant temperature Tb, which is the discharge temperature of the refrigerant.

[0059] In step ST02, the control unit (100) determines whether the discharge superheat SH can be calculated. The discharge superheat SH is calculated based on the Pd, Ps, Tb and saturated steam curve obtained in step ST01. If the discharge superheat SH can be calculated (YES in step ST02), the discharge superheat SH is obtained. If it is determined that the discharge superheat SH cannot be calculated (NO in step ST02), it is determined that the high pressure of the refrigeration cycle is supercritical, and step ST04 is executed.

[0060] In step ST03, the control unit (100) determines whether the discharge superheat SH obtained in step ST02 is equal to or greater than the first temperature T1. The first temperature T1 is the minimum discharge superheat that is pre-designed and required for the operation of the compressor (11). The first temperature T1 is a value related to the limitation of the use of the compressor (11), and if the operation of the compressor (11) continues when the discharge superheat SH is below the first temperature T1, there is a risk of damage to the compressor (11). The first temperature is set to, for example, 10°C. If it is determined that the discharge superheat SH is equal to or greater than the first temperature T1 (YES in step ST03), step ST04 is executed. If it is determined that the discharge superheat SH is below the first temperature T1 (NO in step ST03), step ST05 is executed.

[0061] In step ST04, the control unit (100) determines whether the discharge temperature Tb is less than or equal to the second temperature T2. The second temperature T2 is a temperature that is higher than the refrigerant discharge temperature during normal operation of the compressor (11). When the refrigerant discharge temperature is high, the operating load on the compressor (11) is relatively high. If this condition continues, the compressor (11) may be damaged. The second temperature is, for example, 120°C. If it is determined that the discharge temperature Tb is less than or equal to the second temperature T2 (YES in step ST04), step ST07 is executed. If it is determined that the discharge temperature Tb is higher than the second temperature T2 (NO in step ST04), step ST06 is executed.

[0062] In step ST05, the control unit (100) reduces the opening of at least one of the first expansion valve (13) and the second expansion valve (14) by a predetermined value. This reduces the flow rate of the refrigerant and increases the discharge superheat SH. After step ST05, step ST01 is executed again.

[0063] In step ST06, the control unit (100) increases the opening of at least one of the first expansion valve (13) and the second expansion valve (14) by a predetermined value. This increases the flow rate of the refrigerant and lowers the discharge temperature Tb. After step ST06, step ST01 is executed again.

[0064] In step ST07, the control unit (100) defines a first isentropy line that includes the first point on the saturated vapor curve at Ps obtained in step ST01, and obtains the refrigerant temperature at the second point on the first isentropy line at Pd obtained in step ST01 (see Figure 5).

[0065] In step ST08, the control unit (100) determines whether to correct the refrigerant temperature at the second point. If it is determined that correction should be made, step ST09 is executed. If it is determined that no correction should be made, step ST10 is executed with the refrigerant temperature at the second point set as the first refrigerant temperature Ta.

[0066] In step ST09, the control unit (100) corrects the refrigerant temperature at the second point. An example of the correction at the second point is shown below. The correction of the refrigerant temperature at the second point is performed based on, for example, the rotational speed of the compressor (11), the power consumption of the compressor (11), the high-pressure value Pd, the low-pressure value Ps, the discharge refrigerant temperature Tb, or the ambient temperature. Specifically, the correction of the refrigerant temperature at the second point is performed based on at least one of the following correction parameters: the rotational speed of the compressor (11), the power consumption of the compressor (11), the current value of the compressor (11), the differential pressure ΔP which is the difference between Pd and Ps, and the temperature difference ΔT which is the difference between the discharge temperature Tb and the ambient temperature.

[0067] More specifically, let α be the correction value based on the above correction parameter, and let Ta be the first refrigerant temperature, which is the refrigerant temperature at the second point plus the correction value α. In other words, the first refrigerant temperature Ta is the corrected value of the refrigerant temperature at the second point. The correction value α increases or decreases depending on the change in the above correction parameter. The relationship between the correction value α and the correction parameter is shown in the table below.

[0068] [Table 1]

[0069] In step ST10, the control unit (100) determines whether ΔT1, which represents the difference (Tb-Ta) between the discharge temperature Tb and the first refrigerant temperature Ta, is equal to a first value. The first value is, for example, 1°C. If ΔT1 = the first value (YES in step ST10), this control is terminated. If ΔT1 ≠ the first value (NO in step ST10), step ST11 is executed.

[0070] In step ST11, the control unit (100) determines whether ΔT1 is higher than the first value. If ΔT1 is higher than the first value (YES in step S11), step S12 is executed. If ΔT1 is lower than the first value (NO in step S11), step S13 is executed.

[0071] In step ST12, the control unit (100) reduces the opening of at least one of the first expansion valve (13) and the second expansion valve (14) by a predetermined value. Then, step ST10 is performed again.

[0072] In step ST13, the control unit (100) increases the opening of at least one of the first expansion valve (13) and the second expansion valve (14) by a predetermined value. Then, step ST10 is performed again.

[0073] (7) Characteristics (7-1) Feature 1 The hot water supply device (1) of this embodiment has a control unit (100) that performs a first control, which defines a first isentropy line that includes a first point on the saturated vapor curve at low pressure, and controls the refrigerant circuit (10) so that the difference between a first refrigerant temperature Ta, which indicates the refrigerant temperature at a second point on the first isentropy line at high pressure, and a second refrigerant temperature Tb, which indicates the temperature of the discharged refrigerant discharged from the compressor (11), is 1°C.

[0074] As described above, the control unit (100) of this embodiment controls the discharge temperature using isentropy lines. This allows for refrigeration cycle operation with the degree of superheating kept to a minimum, thereby suppressing a decrease in the COP of the refrigeration system. In particular, with carbon dioxide refrigerant, there is no saturation state in the supercritical region, so the degree of discharge superheating cannot be calculated. Therefore, when switching the control method of the expansion valves (13,14) between the subcritical and supercritical regions, there is a possibility of control hunting occurring when moving between the subcritical and supercritical regions. However, in the control unit (100) of this embodiment, it is unnecessary to switch the control method between the subcritical and supercritical regions, so such control hunting can be suppressed.

[0075] Here, we will explain why the COP of the refrigeration cycle (1) is highest when ΔT1 is 1°C, using Figures 6A to 7B. Figures 6A and 7A are graphs showing the relationship between the discharge superheat SH and COP under different operating conditions. Under the operating conditions in Figure 6A, the difference between high and low pressure is smaller than under the operating conditions in Figure 7A.

[0076] Under the operating conditions in Figure 6A, the COP is highest when the discharge superheat SH is around 13°C, and under the conditions in Figure 7A, the COP is highest when the discharge superheat SH is around 30°C. Thus, since the discharge superheat SH at which the COP is highest differs depending on the operating conditions, it is not desirable to control only the discharge superheat SH. Therefore, in the first control of this embodiment, the value of ΔT1 at which the COP is highest was determined. As shown in Figures 6B and 7B, it was shown that the COP is highest when the refrigerant circuit (10) is controlled so that ΔT1 is 1°C, which is the first value.

[0077] (7-2) Feature 2 The hot water supply device (1) of this embodiment has an suction pressure sensor (89) that detects the low pressure of the refrigerant circuit (10). By using the suction pressure sensor (89), the first control can be easily performed.

[0078] (7-3) Feature 3 The hot water supply device (1) of this embodiment has a discharge pressure sensor (88) that detects the high pressure of the refrigerant circuit (10). By using the discharge pressure sensor (88), the first control can be easily performed.

[0079] (7-4) Feature 4 The hot water supply device (1) of this embodiment has a discharge temperature sensor (80) that detects the temperature of the high-pressure discharged refrigerant discharged from the compressor (11). By using the discharge temperature sensor (80) that detects the discharge temperature of the refrigerant, the first control can be easily performed.

[0080] (7-5) Feature 5 In the first control of this embodiment, when the control unit (100) corrects the refrigerant temperature at the second point, it sets the corrected value of the refrigerant temperature at the second point as the first refrigerant temperature Ta. By using this corrected value, it is possible to determine the first refrigerant temperature Ta with high accuracy. This improves the effect of suppressing the decrease in COP.

[0081] (7-6) Feature 6 In the first control of this embodiment, when the control unit (100) corrects the refrigerant temperature at the second point, it corrects the first refrigerant temperature Ta at the second point based on the rotational speed of the compressor (11), the power consumption of the compressor (11), the high pressure value, the low pressure value, the temperature of the refrigerant discharged from the compression unit (11), or the ambient temperature. By using such a correction value based on the amount of heat dissipated or input to the compressor (11), the accuracy of the first control can be improved.

[0082] (8) Variations As shown in Figure 8, the refrigerant circuit of the modified hot water supply device (1) has an economizer circuit (30). The economizer circuit (30) is provided in the refrigerant circuit (10) of the above embodiment, which serves as the main refrigerant circuit (10). Only the configurations of this modified hot water supply device (1) that differ from the hot water supply device (1) of the above embodiment will be described. In this modified example, the first expansion valve (13) and the second expansion valve (14) are examples of the first pressure reducing mechanism (13,14).

[0083] (8-1) Economizer Circuit The economizer circuit (30) introduces intermediate-pressure refrigerant into the compressor (11). Specifically, the economizer circuit (30) reduces the pressure of the refrigerant flowing through the main refrigerant circuit (10) to an intermediate pressure and merges the intermediate-pressure refrigerant with the refrigerant that is being compressed.

[0084] The economizer circuit (30) is positioned between the bridge circuit (20) and the receiver (16). Specifically, the economizer circuit (30) is provided to connect the water heat exchanger (25), which is a heat radiator in the main refrigerant circuit (10), and the first expansion valve (13) to the compressor (11).

[0085] The economizer circuit (30) includes an economizer heat exchanger (31), a branch pipe (32), a third expansion valve (33), and an inlet pipe (34).

[0086] The economizer heat exchanger (31) is composed of, for example, a plate heat exchanger. The economizer heat exchanger (31) exchanges heat between the high-pressure refrigerant and the intermediate-pressure refrigerant between the water heat exchanger (25) and the first expansion valve (13) in the main refrigerant circuit (10). Specifically, the economizer heat exchanger (31) has a first flow path (31a) and a second flow path (31b). The economizer heat exchanger (31) exchanges heat between the high-pressure refrigerant flowing through the first flow path (31a) and the intermediate-pressure refrigerant flowing through the second flow path (31b). The economizer heat exchanger (31) is a counter-flow type in which the flow of refrigerant in the first flow path (31a) and the flow of refrigerant in the second flow path (31b) are in opposite directions. The first flow path (31a) constitutes part of the main refrigerant circuit (10). The second flow path (31b) constitutes part of the economizer circuit (30). In other words, the main refrigerant circuit (10) has a first flow path (31a), and the economizer circuit (30) has a second flow path (31b).

[0087] The branch pipe (32) branches off from the refrigerant piping located downstream of the bridge circuit (20) in the main refrigerant circuit (10) and connects to the upstream end of the second flow path (31b) of the economizer heat exchanger (31). The third expansion valve (33) is connected to the branch pipe (32). The third expansion valve (33) is an example of the second pressure reducing mechanism (33). The third expansion valve (33) is an electrically operated valve with adjustable opening. The third expansion valve (33) reduces the high-pressure refrigerant to an intermediate pressure. The inlet pipe (34) connects the downstream end of the second flow path (31b) to the compressor (11).

[0088] (8-2) Sensor The modified hot water supply device (1) includes, in addition to the suction pressure sensor (89), discharge pressure sensor (88), and discharge temperature sensor (80) of the above embodiment, a high-pressure sensor (85), an intermediate-pressure sensor (90), a first temperature sensor (91), a second temperature sensor (92), and a third temperature sensor (93). The detection signals from the high-pressure sensor (85), intermediate-pressure sensor (90), first temperature sensor (91), second temperature sensor (92), and third temperature sensor (93) are transmitted to the control unit (100).

[0089] The high-pressure sensor (85) is installed in the refrigerant piping downstream of the bridge circuit (20) and upstream of the first flow path (31a). The high-pressure sensor (85) detects the pressure of the refrigerant in the main refrigerant circuit (10) just before it flows into the economizer heat exchanger (31). Alternatively, the pressure of the refrigerant in the main refrigerant circuit (10) just before it flows into the economizer heat exchanger (31) may be measured using the value detected by the discharge pressure sensor (88) instead of the high-pressure sensor (85).

[0090] The intermediate pressure sensor (90) is installed in the inlet pipe (34). The intermediate pressure sensor (90) detects the pressure of the refrigerant downstream of the second flow path (31b). The intermediate pressure sensor (90) detects the pressure of the intermediate-pressure refrigerant, which has been reduced by the third expansion valve (33).

[0091] The first temperature sensor (91) is installed in the refrigerant piping downstream of the bridge circuit (20) and upstream of the first flow path (31a). The first temperature sensor (91) detects the temperature of the refrigerant immediately before it enters the first flow path (31a).

[0092] The second temperature sensor (92) is installed in the refrigerant piping downstream of the first flow path (31a). The second temperature sensor (92) detects the temperature of the refrigerant that has undergone heat exchange in the first flow path (31a).

[0093] The third temperature sensor (93) is installed in the inlet pipe (34). The third temperature sensor (93) detects the temperature of the refrigerant downstream of the second flow path (31b). The third temperature sensor (93) detects the temperature of the refrigerant that has undergone heat exchange in the second flow path (31b).

[0094] (8-3) Operation of the control unit In the modified hot water supply system (1), a second or third control is performed to control the refrigerant circuit (10) so that the refrigerant discharge temperature reaches a predetermined temperature or a predetermined temperature range. The second and third controls will be described below.

[0095] (8-3-1) Second control An example of the second control performed by the control unit (100) will be explained using Figures 9 and 10.

[0096] In step ST21, the control unit (100) obtains the pressure value Pd of the discharged refrigerant, the pressure value Ps of the suctioned refrigerant, the discharge temperature Tb of the refrigerant, and the pressure value Pm of the intermediate-pressure refrigerant.

[0097] In step ST22, the control unit (100) determines the third refrigerant temperature Tc (see Figure 10). Specifically, the control unit (100) defines a second isentropy line including the third point on the saturated vapor curve at Ps, and a third isentropy line including the fourth point on the saturated vapor curve at Pm. The control unit (100) determines the fifth point on the second isentropy line at Pd and the sixth point on the third isentropy line at Pd, and determines the seventh point between the fifth and sixth points at Pd as the third refrigerant temperature Tc. The seventh point can be arbitrarily determined and only needs to be between the fifth and sixth points at high pressure (Pd).

[0098] In step ST23, the control unit (100) determines whether ΔT2, which represents the difference (Tb-Tc) between the discharge temperature Tb and the third refrigerant temperature Tc, is equal to the second value. The second value is, for example, 1°C. If ΔT2 = the second value (YES in step ST23), this control is terminated. If ΔT2 ≠ the second value (NO in step ST23), step ST24 is executed.

[0099] In step ST24, the control unit (100) appropriately controls the opening degrees of the first to third expansion valves (13, 14, 33). For example, when it is determined that ΔT2 is higher than the second value, the control unit (100) increases the opening degree of at least one of the first expansion valve (13) and the second expansion valve (14) by a predetermined value while maintaining the opening degree of the third expansion valve (33). Also, when it is determined that ΔT2 is lower than the second value, the control unit (100) decreases the opening degree of at least one of the first expansion valve (13) and the second expansion valve (14) by a predetermined value while maintaining the opening degree of the third expansion valve (33). After that, step ST23 is executed again.

[0100] (8-3-2) Third control The operation of the control unit (100) when executing the third control will be explained using Figures 11 and 12.

[0101] In step ST31, the control unit (100) obtains the pressure value Pd of the discharged refrigerant, the pressure value Ps of the suctioned refrigerant and the discharge temperature Tb of the refrigerant, the pressure value Pm of the intermediate-pressure refrigerant, the pressure value Pf of the refrigerant upstream of the first flow path (31a), the temperature Tg of the refrigerant downstream of the first flow path (31a), and the temperature Th of the refrigerant downstream of the second flow path (31b).

[0102] In step ST32, the control unit (100) obtains the fourth refrigerant temperature Td (see Figure 12). Specifically, the control unit (100) defines a fourth isentropy line that includes the eighth point on the saturated vapor curve at Ps. The control unit (100) defines the ninth point on the fourth isentropy line at Pm and defines a fifth isentropy line that includes the tenth point obtained by subtracting Δh from the enthalpy at the ninth point. Furthermore, the control unit (100) defines the eleventh point on the fifth isentropy line at Pd. The refrigerant temperature at the eleventh point is defined as the fourth refrigerant temperature Td.

[0103] Δh is determined based on the enthalpy of the refrigerant at point 9 and the enthalpy of the refrigerant downstream of the second flow path (31b) of the economizer heat exchanger (31) (the intermediate-pressure refrigerant before it flows into the compressor (11)). An example of how to determine Δh is explained below. Point 11 is the state of the refrigerant downstream of the second flow path (31b), which is the outlet of the economizer heat exchanger (31). Let Δh1 be the enthalpy difference between point 9 and point 11. Point 9 represents the refrigerant state considered to be the state of the refrigerant in the compressor (11) immediately before the introduction of the intermediate-pressure refrigerant that has passed through the economizer circuit (30). Here, the circulation rate of the refrigerant that does not flow into the economizer circuit (30) but flows through the main refrigerant circuit (10) is Gm, and the circulation rate of the refrigerant that flows into the economizer circuit (30) is Gi. In other words, the circulation rate of the low-pressure refrigerant is Gm, and the circulation rate of the intermediate-pressure refrigerant is Gi. The amount of refrigerant circulating in the compressor (11) after the introduction of the intermediate-pressure refrigerant is Gm + Gi. Therefore, the 10th point is determined based on the ratio of Gm to Gi. Specifically, Δh can be calculated from equation (1), Δh = Δh1 × Gi / (Gm + Gi). The 10th point is obtained by subtracting Δh from the enthalpy at the 9th point.

[0104] Here, from the heat balance relationship in the economizer heat exchanger (31), the amount of heat dissipated by the refrigerant in the first channel (31a) and the amount of heat absorbed by the refrigerant in the second channel (31b) can be considered equivalent. Therefore, when the enthalpy difference before and after inflow of the first channel (31a) of the refrigerant is Δh2, and the enthalpy difference before and after inflow of the second channel (31b) of the refrigerant is Δh3, the relationship Δh2 × Gm = Δh3 × Gi holds as equation (2). From equations (1) and (2), we can derive Gi / (Gm + Gi) = 1 / (Δh3 / Δh2 + 1). Substituting this into equation (1), we can derive equation (3) Δh = Δh1 × 1 / (Δh3 / Δh2 + 1). Since Δh1, Δh2, and Δh3 can be determined based on the refrigerant pressure and temperature detected by each sensor, Δh can be calculated based on equation (4).

[0105] In step ST33, the control unit (100) determines whether ΔT3, which represents the difference (Tb-Td) between the discharge temperature Tb and the fourth refrigerant temperature Td, is equal to the third value. The third value is, for example, 1°C. If ΔT3 = the third value (YES in step ST50), this control is terminated. If ΔT3 ≠ the third value (NO in step ST50), step ST51 is executed.

[0106] In step ST34, the control unit (100) appropriately controls the opening degrees of the first to third expansion valves (13, 14, 33). For example, when it is determined that ΔT3 is higher than the third value, the control unit (100) increases the opening degree of at least one of the first expansion valve (13) and the second expansion valve (14) by a predetermined value while maintaining the opening degree of the third expansion valve (33). Also, when it is determined that ΔT3 is lower than the third value, the control unit (100) decreases the opening degree of at least one of the first expansion valve (13) and the second expansion valve (14) by a predetermined value while maintaining the opening degree of the third expansion valve (33). After that, step ST33 is executed again.

[0107] (9) Other embodiments In the above embodiment, ΔT1 may not be a specific value but a temperature range. In this case, ΔT1 may be determined as a range of ΔT that includes the value corresponding to when the COP is highest. For example, ΔT1 may be set as a range that includes each ΔT value corresponding to when the COP is highest for several different operating conditions. The same applies to ΔT2 and ΔT3 in the above modified example.

[0108] In the above embodiment, when ΔT1 represents the range of ΔT, ΔT1 may be in the range of ±2°C. For example, ΔT1 may be in the range of 0°C to 1°C, 0°C to 2°C, -1°C to 1°C, or -2°C to 0°C. The range of ΔT1 will be explained using Figures 13 and 14. Under the operating conditions in Figure 13, it can be seen that when ΔT1 is in the range of ±2°C, ΔT1 is approximately 2% lower than the COP at zero°C. Also, under the operating conditions in Figure 14, it can be seen that when ΔT1 is in the range of ±2°C, ΔT1 is approximately 0.2% lower than the COP at zero°C. Thus, even if the operating conditions of the refrigeration cycle device (1) differ, ΔT1 is determined to be in the range of ±2 or ±1 as a value that can secure a certain level of COP. On the other hand, focusing on the value of COP, ΔT1 may be defined as the range of ΔT that is 2% lower than the maximum value of COP. ΔT1 may be defined as a range of ΔT values ​​that are 0.5%, 1.0%, or 1.5% lower than the maximum value of COP.

[0109] In the above modified example, the refrigerant circuit (10) may be a two-stage compression type refrigerant circuit. In this case, the compression unit (11) has a compressor and a second compressor connected in series. The compressor and the second compressor are connected in series, and the suction refrigerant drawn into the compressor is compressed to an intermediate pressure, and the intermediate-pressure refrigerant discharged from the compressor is drawn into the second compressor and compressed to a high pressure. The introduction pipe of the economizer circuit (30) is connected to the refrigerant piping connecting the compressor and the second compressor.

[0110] In the above embodiment, the control unit (100) may execute step ST01 again after step ST10 while the first control is being executed. In this case, if it is determined in step ST03 that the discharge superheat SH is below the first temperature T1, the execution of the first control may be stopped. After stopping the execution of the first control, the control unit (100) may control the opening of the first and second expansion valves (13, 14) in step ST05 so that the discharge superheat does not fall below the first temperature. For example, the opening of at least one of the first expansion valve (13) and the second expansion valve (14) may be controlled to decrease. This operation may also be applied to the second or third control of the above modified example.

[0111] In the above embodiment, the control unit (100) may execute step ST01 again after step ST10 while the first control is being executed. In this case, if it is determined in step ST04 that the refrigerant discharge temperature Tb exceeds the second temperature T2, the execution of the first control may be stopped. After stopping the execution of the first control, the control unit (100) may control the opening degree of the first and second expansion valves (13, 14) in step ST11 so that the discharge temperature Tb does not exceed the second temperature T2. For example, the opening degree of at least one of the first expansion valve (13) and the second expansion valve (14) may be increased. This operation may be applied to the second or third control of the above modified example.

[0112] In the above embodiment, the control unit (100) does not need to perform the correction determination in step ST08. In other words, the first control does not need to include the correction determination. In this case, the refrigerant temperature at the second point obtained in step ST07 is determined as the first refrigerant temperature Ta.

[0113] In the above embodiment, the control unit (100) may stop the execution of the first control if the high pressure of the refrigerant circuit (10) exceeds the first pressure during the execution of the first control. In this case, after stopping the execution of the first control, the control unit (100) may control the opening degree of the first and second expansion valves (13, 14) so ​​that the high pressure of the refrigerant circuit (10) does not exceed the first pressure. For example, the control unit (100) may appropriately increase the opening degree of the first and second expansion valves (13, 14). This operation may also be applied to the second or third control of the above modified example.

[0114] In the above modified example, the second and third controls may perform operations corresponding to the corrections in steps ST08 and ST09 of the first control.

[0115] Regarding the third control of the above modified example, in step ST32, the control unit (100) may define a fourth isentropy line including the eighth point on the saturated vapor curve at Ps, then define a point on the fourth isentropy line at Pd, and define the point obtained by subtracting Δh from the enthalpy at that point as the eleventh point.

[0116] The first detection unit only needs to detect an indicator showing the low pressure of the refrigerant circuit (10), and is not limited to a pressure-detecting sensor.

[0117] The second detection unit only needs to detect an indicator showing the high pressure of the refrigerant circuit (10), and is not limited to a pressure-detecting sensor.

[0118] The third detection unit only needs to detect an indicator of the temperature of the high-pressure discharged refrigerant discharged from the compression unit (11), and is not limited to a temperature sensor. For example, if the indicator is pressure, it may be a pressure sensor that detects the discharge pressure.

[0119] The first, second, or third control may control the rotational speed of the compressor in addition to controlling the expansion valve.

[0120] While embodiments and modifications have been described above, it will be understood that a variety of changes in form and details are possible without departing from the spirit and scope of the claims. Furthermore, these embodiments and modifications may be combined or substituted as appropriate, as long as they do not impair the functions of the subject matter of this disclosure. The terms “First,” “Second,” etc., used above are used to distinguish the phrases to which these terms are attached, and do not limit the number or order of such phrases. [Industrial applicability]

[0121] As explained above, this disclosure is useful for refrigeration cycle systems. [Explanation of Symbols]

[0122] 1. Hot water supply system (refrigeration cycle system) 10 Refrigerant circuit, main refrigerant circuit 11 Compression section 12. Outdoor heat exchanger (evaporator) 13. First expansion valve (pressure reducing mechanism, first pressure reducing mechanism) 14. Second expansion valve (pressure reduction mechanism, first pressure reduction mechanism) 25 Water heat exchanger (radiator) 30 Economizer Circuit 31 Economizer Heat Exchanger 33. Third expansion valve (second pressure reducing mechanism) 80 Discharge temperature sensor (third detection unit) 88 Discharge pressure sensor (second detection unit) 89. Intake pressure sensor (first detection unit) 100 Control Unit

Claims

1. A refrigeration cycle device comprising a refrigerant circuit (10) to which a compression section (11), a heat sink (25), a pressure reducing mechanism (13, 14), and an evaporator (12) are connected and which is filled with carbon dioxide refrigerant, The refrigerant circuit (10) performs a refrigeration cycle operation in which the low-pressure intake refrigerant is increased to a high-pressure level by the compression unit (11). A first isentropy line is defined that includes a first point on the saturated vapor curve at low pressure, and a control unit (100) performs a first control that controls the refrigerant circuit such that the difference between a first refrigerant temperature Ta, which indicates the refrigerant temperature at a second point on the first isentropy line at high pressure, and a second refrigerant temperature Tb, which indicates the temperature of the discharged refrigerant discharged from the compression unit (11), is within ±2°C. Refrigeration cycle device.

2. The system further includes a first detection unit (89) that detects an indicator of the low pressure of the refrigerant circuit (10). The refrigeration cycle apparatus according to claim 1.

3. The system further includes a second detection unit (88) that detects an indicator of the high pressure of the refrigerant circuit (10). The refrigeration cycle apparatus according to claim 1.

4. The system further includes a third detection unit (80) that detects an index indicating the temperature of the high-pressure discharged refrigerant discharged from the compression unit (11). The refrigeration cycle apparatus according to claim 1.

5. The first refrigerant temperature Ta is a value obtained by correcting the refrigerant temperature at the second point. A refrigeration cycle apparatus according to any one of claims 1 to 4.

6. The first refrigerant temperature Ta is a value obtained by correcting the refrigerant temperature at the second point based on the rotational speed of the compression unit (11), the power consumption of the compression unit (11), the high pressure value, the low pressure value, the temperature of the refrigerant discharged from the compression unit (11), or the ambient temperature. The refrigeration cycle apparatus according to claim 5.

7. The control unit (100) stops executing the first control when the discharge superheat of the refrigerant falls below a predetermined first temperature during the execution of the first control. A refrigeration cycle apparatus according to any one of claims 1 to 4.

8. After the execution of the first control is stopped, the control unit (100) controls the opening of the pressure reducing mechanism (13, 14) so ​​that the discharge superheating level does not fall below the first temperature. The refrigeration cycle apparatus according to claim 7.

9. The control unit (100) stops executing the first control if the temperature of the refrigerant discharged from the compression unit (11) exceeds a predetermined second temperature during the execution of the first control. A refrigeration cycle apparatus according to any one of claims 1 to 4.

10. After the execution of the first control is stopped, the control unit (100) controls the opening degree of the pressure reducing mechanism (13, 14) so ​​that the temperature of the discharged refrigerant does not exceed the second temperature. The refrigeration cycle apparatus according to claim 9.

11. The control unit (100) stops executing the first control if the high pressure of the refrigerant circuit (10) exceeds the first pressure during the execution of the first control. A refrigeration cycle apparatus according to any one of claims 1 to 4.

12. After the execution of the first control is stopped, the control unit (100) controls the opening of the pressure reducing mechanism (13, 14) so ​​that the high pressure in the refrigerant circuit (10) does not exceed the first pressure. The refrigeration cycle apparatus according to claim 11.

13. A refrigeration cycle device comprising a refrigerant circuit (10) having a main refrigerant circuit (10) through which the refrigerant flows in the order of a compression section (11), a heat sink (25), first pressure reducing mechanisms (13, 14), and an evaporator (12), and an economizer circuit (30) in the main refrigerant circuit (10) that connects the space between the heat sink (25) and the first pressure reducing mechanisms (13, 14) to the compression section (11), The aforementioned economizer circuit (30) A second pressure reduction mechanism (33) for reducing the pressure of a high-pressure refrigerant to an intermediate-pressure refrigerant, The system includes an economizer heat exchanger (31) in which the intermediate-pressure refrigerant and the high-pressure refrigerant between the radiator (25) and the first pressure reducing mechanism (13, 14) in the main refrigerant circuit (10) exchange heat. A second isentropy line containing the third point on the saturated vapor curve at low pressure, A third isentropy line containing the fourth point on the saturated vapor curve at intermediate pressure, and A seventh point is defined between the fifth point on the second isentropy line at high pressure and the sixth point on the third isentropy line at high pressure. The system includes a control unit (100) that performs a second control to control the refrigerant circuit so that the difference between the third refrigerant temperature Tc, which indicates the refrigerant temperature at the seventh point, and the second refrigerant temperature Tb, which indicates the temperature of the discharged refrigerant discharged from the compression unit (11), is within ±2°C. Refrigeration cycle device.

14. A refrigeration cycle device comprising a refrigerant circuit (10) having a main refrigerant circuit (10) through which the refrigerant flows in the order of a compression section (11), a heat sink (25), first pressure reducing mechanisms (13, 14), and an evaporator (12), and an economizer circuit (30) in the main refrigerant circuit (10) that connects the space between the heat sink (25) and the first pressure reducing mechanisms (13, 14) to the compression section (11), The aforementioned economizer circuit (30) A second pressure reduction mechanism (33) that reduces the pressure of the high-pressure refrigerant to an intermediate-pressure refrigerant, The system includes an economizer heat exchanger (31) in which the intermediate pressure refrigerant and the high-pressure refrigerant between the radiator (25) and the first pressure reducing mechanism (13, 14) in the main refrigerant circuit (10) exchange heat. The fourth isentropy line containing the eighth point on the saturated vapor curve at low pressure, The ninth point on the fourth isentropy line at intermediate pressure, The fifth isentropy line including the tenth point obtained by subtracting Δh from the enthalpy at the ninth point, and The 11th point on the fifth isentropy line at high pressure is defined, The system includes a control unit (100) that performs a third control to control the refrigerant circuit so that the difference between the fourth refrigerant temperature Td, which indicates the refrigerant temperature at the 11th point, and the second refrigerant temperature Tb, which indicates the temperature of the discharged refrigerant discharged from the compression unit (11), is within the range of ±2°C. The aforementioned Δh is, The enthalpy of the refrigerant at the aforementioned ninth point, This is an amount corresponding to the enthalpy of the refrigerant downstream of the economizer heat exchanger (31) in the economizer circuit (30). Refrigeration cycle device.

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