Refrigeration cycle device and control method of refrigeration cycle device

Abstract

The present application relates to a refrigeration cycle device and a control method for a refrigeration cycle device, the refrigeration cycle device including a refrigerant circuit in which a compressor, a heat exchanger on a heat source side, an expansion valve, and a heat exchanger on a utilization side are connected by refrigerant piping. The refrigeration cycle device includes a detection unit that detects a heat transfer tube temperature and an outlet tube temperature of the heat exchanger functioning as a condenser and a discharge temperature of the compressor, and a control unit that performs a supercooling degree control and a discharge temperature control or a discharge superheat degree control based on a detection result of the detection unit. The control unit controls an opening degree of the expansion valve based on either one of the supercooling degree control and the discharge temperature control or the discharge superheat degree control according to an operating characteristic of the refrigeration cycle device.

Description

Technical Field

[0001] This disclosure relates to a refrigeration cycle device and a control method for the refrigeration cycle device. Background Technology

[0002] In a refrigeration cycle device in which the refrigerant piping connects a compressor, a heat exchanger on the heat source side, an electronic expansion valve, and a heat exchanger on the utilization side, a typical refrigeration cycle device has a subcooling control function that controls the opening of the expansion valve in such a way that the value of the subcooling of the heat exchanger, which functions as a condenser, converges to a specified value range (for example, see Patent Document 1).

[0003] Patent Document 1: Japanese Patent Application Publication No. 2010-96474

[0004] In the existing refrigeration cycle apparatus described in Patent Document 1, the expansion valve opening is controlled by calculating the degree of subcooling based on the temperatures of the heat transfer tubes (which function as a condenser) and the outlet pipe. However, depending on the installation environment or operating conditions of the refrigeration cycle apparatus, it is sometimes impossible to ensure sufficient subcooling while maintaining control. In such cases, because the refrigeration cycle apparatus continuously reduces the expansion valve opening to ensure subcooling, the discharge temperature and discharge superheat increase excessively, which may lead to operation shutdown due to abnormal discharge temperature protection, for example. Summary of the Invention

[0005] This disclosure is made in view of the above circumstances, and one of its purposes is to provide a highly reliable refrigeration cycle device that will not stop operation due to abnormal discharge temperature, even under operating conditions where it is difficult to ensure supercooling.

[0006] The refrigeration cycle apparatus disclosed herein is a refrigeration cycle apparatus comprising a refrigerant circuit formed by connecting a compressor, a heat exchanger on the heat source side, an expansion valve, and a heat exchanger on the utilization side using refrigerant piping. The refrigeration cycle apparatus includes: a detection unit that detects the heat transfer tube temperature and outlet pipe temperature of at least one heat exchanger (which functions as a condenser) of the heat exchanger on the heat source side and the heat exchanger on the utilization side, and the discharge temperature of the compressor; and a control unit capable of performing subcooling control and discharge temperature control or discharge superheat control based on the detection results of the detection unit. When the refrigeration cycle apparatus begins operation, the control unit controls the opening degree of the expansion valve based on the subcooling control. If, based on the operating characteristics of the refrigeration cycle apparatus, it is determined that the subcooling control cannot continue, the control of the expansion valve opening is switched from subcooling control to discharge temperature control or discharge superheat control.

[0007] The control method disclosed herein is a control method for a refrigeration cycle device comprising a refrigerant circuit formed by connecting a compressor, a heat exchanger on the heat source side, an expansion valve, and a heat exchanger on the utilization side using refrigerant piping. The method involves detecting the heat transfer tube temperature and outlet pipe temperature of at least one heat exchanger (which functions as a condenser) of the heat exchanger on the heat source side and the heat exchanger on the utilization side, as well as the discharge temperature of the compressor. Based on the detection results, subcooling control and discharge temperature control or discharge superheat control are performed. At the start of operation of the refrigeration cycle device, the opening degree of the expansion valve is controlled based on the subcooling control. If, based on the operating characteristics of the refrigeration cycle device, it is determined that the subcooling control cannot continue, the control of the expansion valve opening is switched from subcooling control to discharge temperature control or discharge superheat control.

[0008] According to this disclosure, a highly reliable refrigeration cycle device can be provided that will not stop operation due to abnormal discharge temperature, even under operating conditions where it is difficult to ensure supercooling. Attached Figure Description

[0009] Figure 1 This is a block diagram illustrating an example of the configuration of the refrigeration cycle apparatus according to the first embodiment.

[0010] Figure 2 This is a Ph graph of the refrigeration cycle device of the first embodiment during refrigeration operation.

[0011] Figure 3 This is a Ph graph of the refrigeration cycle device of the first embodiment during SC control execution.

[0012] Figure 4 This is a Ph graph of the refrigeration cycle device of the first embodiment when Td control is executed.

[0013] Figure 5 This is a Ph graph of the refrigeration cycle device of the first embodiment during SHd control execution.

[0014] Figure 6 This is a flowchart illustrating an example of the switching process between SC control and Td control or SHd control in the first embodiment.

[0015] Figure 7 This is a flowchart illustrating an example of the switching process between SC control and Td control or SHd control in the second embodiment.

[0016] Figure 8 This is a flowchart illustrating an example of the switching process between SC control and Td control or SHd control in the third embodiment.

[0017] Figure 9 This is a flowchart illustrating an example of the switching process between SC control and Td control or SHd control in the fourth embodiment.

[0018] Figure 10 This is a flowchart illustrating an example of the switching process between SC control and Td control or SHd control in the fifth embodiment. Detailed Implementation

[0019] The implementation method will now be described with reference to the accompanying drawings.

[0020] <First Implementation>

[0021] First, the first embodiment will be described.

[0022] [Composition of the Refrigeration Cycle Unit]

[0023] Figure 1 This is a block diagram illustrating a configuration example of the refrigeration cycle apparatus 100 according to this embodiment. The illustrated refrigeration cycle apparatus 100 includes: a refrigerant circuit 10 and a control unit 20 for controlling the refrigerant circuit 10. The refrigerant circuit 10 is configured to include: a compressor 101, a refrigerant switching device 102 for switching the flow direction of the refrigerant, a heat exchanger 103 on the heat source side, an expansion valve 104 (electronic expansion valve), a heat exchanger 105 on the utilization side, and pipes 11, 12, 13, and 14 connected in sequence as refrigerant piping.

[0024] Pipe 11 is a refrigerant piping connecting the compressor 101 to the heat source-side heat exchanger 103. Pipe 12 is a refrigerant piping connecting the heat source-side heat exchanger 103 to the expansion valve 104. Pipe 13 is a refrigerant piping connecting the expansion valve 104 to the utilization-side heat exchanger 105. Pipe 14 is a refrigerant piping connecting the utilization-side heat exchanger 105 to the compressor 101.

[0025] The refrigerant switching device 102 is configured as a four-way valve that switches the flow direction of the refrigerant and is connected between the downstream piping 11 and the upstream piping 14 of the compressor 101. During refrigeration operation, the refrigerant switching device 102 is connected to... Figure 1 The solid lines shown indicate that during heating operation, the refrigerant switching device 102 is connected in the direction indicated. Figure 1 Connect along the direction of the dashed lines shown.

[0026] The heat source-side heat exchanger 103 functions as a heat source machine or heat source-side unit that generates heat to be supplied to the utilization-side heat exchanger 105. The utilization-side heat exchanger 105 functions as a load-side unit that utilizes the heat supplied from the heat source-side heat exchanger 103.

[0027] Temperature detectors are provided on the heat transfer tubes and outlet pipes (outlet-side piping) of the heat source-side heat exchanger 103 and the utilization-side heat exchanger 105, as well as on the discharge piping downstream of the compressor 101 and the container surface of the compressor 101, as an example of a detection unit for detecting the refrigerant temperature of each.

[0028] exist Figure 1 In this configuration, temperature detector 111 is used to detect the temperature of the heat transfer tubes of the heat source-side heat exchanger 103. Temperature detector 112 is used to detect the outlet pipe temperature (outlet-side piping temperature) of the heat source-side heat exchanger 103. Temperature detector 113 is used to detect the temperature of the heat transfer tubes of the utilization-side heat exchanger 105. Temperature detector 114 is used to detect the outlet pipe temperature of the utilization-side heat exchanger 105. Temperature detector 115 is used to detect the discharge piping temperature downstream of the compressor 101. Temperature detector 116 is used to detect the surface temperature of the compressor 101's container.

[0029] The detection unit for detecting refrigerant temperature can, in addition to using temperature detectors such as temperature sensors, also use a pressure detector to detect the refrigerant pressure (hereinafter referred to as "condensation temperature") instead of a temperature detector, based on the temperature of the heat transfer tubes that function as a heat exchanger (which functions as a condenser). The pressure of the refrigerant is then detected using its saturation temperature, thereby indirectly detecting the refrigerant temperature.

[0030] The control unit 20 controls the flow of refrigerant in the refrigerant circuit 10 and the various parts of the refrigerant circuit 10 according to the operating status, such as cooling operation or heating operation. For example, the control unit 20 controls the opening degree of the expansion valve 104 based on the detection results of the temperature detector and the operating characteristics.

[0031] Figure 2 This is an example of a Ph graph of the refrigeration cycle device 100 during refrigeration operation according to this embodiment. In this graph, the vertical axis represents pressure P (MPa), and the horizontal axis represents specific enthalpy h (kJ / kg). Furthermore, Figure 2 Points (a) to (d) represent points in Figure 1 The state of the refrigerant at the locations marked with the same symbol.

[0032] If compressor 101 starts operating, the low-temperature, low-pressure gaseous refrigerant is compressed by compressor 101 and discharged as a high-temperature, high-pressure gaseous refrigerant. Compared to the case of insulated compression along an isentropic line, the amount of heat insulation efficiency of compressor 101 compressed by heating is used to describe the refrigerant compression process of compressor 101. Figure 2 The line from point (a) to point (b) is used to represent this.

[0033] The high-temperature, high-pressure gaseous refrigerant discharged from compressor 101 passes through refrigerant switching device 102 and flows into heat exchanger 103 on the heat source side. The refrigerant flowing into heat exchanger 103 simultaneously heats the outdoor air and is cooled, becoming a medium-temperature, high-pressure liquid refrigerant. Considering the pressure loss within the heat exchanger, the refrigerant change within heat exchanger 103... Figure 2 The line from point (b) to point (c) is shown as sloping slightly downwards and to the left from the horizontal.

[0034] The medium-temperature, high-pressure liquid refrigerant flowing from the heat exchanger 103 on the heat source side expands and depressurizes as it passes through the expansion valve 104, becoming a low-temperature, low-pressure gas-liquid two-phase flow. The refrigerant change after passing through the expansion valve 104 occurs while maintaining a constant enthalpy. This refrigerant change is described using… Figure 2 The perpendicular line from point (c) to point (d) is shown.

[0035] The low-temperature, low-pressure refrigerant in a gas-liquid two-phase flow state, flowing out of expansion valve 104, flows into the utilization-side heat exchanger 105. The refrigerant flowing into the utilization-side heat exchanger 105 is simultaneously cooled and heated, becoming a low-temperature, low-pressure gaseous refrigerant. Considering the pressure loss within the heat exchanger, the refrigerant change in the utilization-side heat exchanger 105... Figure 2 The line from point (d) to point (a) is shown as sloping slightly downward to the right from the horizontal.

[0036] The low-temperature, low-pressure gaseous refrigerant flowing out of the heat exchanger 105 is compressed by passing through the refrigerant switching device 102 and flowing into the compressor 101. During heating operation, the connection of the refrigerant switching device 102 is switched under the control of the control unit 20, but the evaporator and condenser are reversed, and the direction of the pH curve remains unchanged.

[0037] Conventionally, subcooling control (hereinafter referred to as "SC control") is generally performed. This subcooling control uses the difference between the condensing temperature of the heat exchanger, which functions as a condenser, and the outlet pipe temperature (hereinafter referred to as "condenser outlet temperature"), i.e., the subcooling degree (hereinafter referred to as "SC"), for control. In the refrigeration cycle unit 100, the control unit 20 also uses SC control as a normal control method.

[0038] [Explanation of supercooling control]

[0039] Figure 3This is an example of a Ph graph of the refrigeration cycle device 100 in this embodiment during SC control execution. In SC control, the control unit 20 adjusts the opening of the expansion valve 104 so that the difference between the measured condensing temperature and the measured condenser outlet temperature, i.e., the calculated value of SC (hereinafter referred to as "actual operating SC"), converges to a predetermined SC range (e.g., 2 to 6 degrees). When SC control is executed, if the actual operating SC does not reach the predetermined SC range, the control unit 20 reduces the opening of the expansion valve 104. By reducing the opening of the expansion valve 104, the control unit 20 reduces the refrigerant circulation volume, causing the condensing pressure to rise and the evaporating pressure to fall, thereby increasing the value of SC and controlling the system to converge to the predetermined SC range.

[0040] In addition, with Figure 3 In contrast to the example shown, when SC control is executed, if the actual operating SC exceeds the specified SC range, the control unit 20 opens the expansion valve 104. By opening the expansion valve 104, the control unit 20 increases the refrigerant circulation, reduces the condensing pressure, and increases the evaporating pressure, thereby reducing the SC value and controlling the system to converge within the specified SC range.

[0041] Here, the purpose of SC control is to improve performance. By controlling SC within a specified SC range, the difference between the inlet enthalpy (hereinafter referred to as "condenser inlet enthalpy") and the outlet enthalpy (hereinafter referred to as "condenser outlet enthalpy") of the heat exchanger that functions as a condenser is ensured, i.e., the condenser enthalpy difference, thereby achieving the desired performance of the utilization-side heat exchanger 105.

[0042] [Explanation of discharge temperature control]

[0043] In addition to controlling the refrigeration cycle device 100, the control unit 20 can also use the discharge piping temperature on the downstream side of the compressor 101 or the container surface temperature of the compressor 101 as a representative temperature of the discharge temperature to perform discharge temperature control (hereinafter referred to as "Td control") using the discharge temperature (hereinafter referred to as "Td").

[0044] Figure 4This is an example of a Ph graph of the refrigeration cycle device 100 in this embodiment during Td control execution. In Td control, the control unit 20 adjusts the opening of the expansion valve 104 to bring the measured value of Td (hereinafter referred to as "actual operating Td") within a specified Td range (e.g., 60-100 degrees). During Td control execution, if the actual operating Td exceeds the specified Td range, the control unit 20 opens the expansion valve 104. By opening the expansion valve 104, the control unit 20 increases the refrigerant circulation, lowers the condensing pressure, and raises the evaporating pressure, thereby reducing the Td value and controlling the flow to converge within the specified Td range.

[0045] In addition, with Figure 4 In contrast to the example shown, when the control unit 20 performs Td control, if the actual operating Td does not reach the specified Td range, it reduces the expansion valve 104. By reducing the expansion valve 104, the control unit 20 reduces the refrigerant circulation, causing the condensing pressure to rise and the evaporating pressure to fall, thereby increasing the value of Td and controlling it in a way that converges to the specified Td range.

[0046] [Explanation of superheat control]

[0047] Alternatively, the control unit 20 can replace the Td control by performing discharge superheat control (hereinafter referred to as "SHd control") which uses the difference between Td and the condensing temperature, i.e., discharge superheat (hereinafter referred to as "SHd").

[0048] Figure 5 This is an example of a Ph graph of the refrigeration cycle device 100 in this embodiment during SHd control execution. During SHd control, the control unit 20 adjusts the opening of the expansion valve 104 so that the difference between the actual operating temperature Td and the measured condensing temperature, i.e., the calculated value of SHd (hereinafter referred to as "actual operating SHd"), converges to a predetermined SHd range (e.g., 20-30 degrees Celsius). During SHd control execution, if the actual operating SHd exceeds the predetermined SHd range, the control unit 20 opens the expansion valve 104. By opening the expansion valve 104, the control unit 20 increases the refrigerant circulation, lowers the condensing pressure, and raises the evaporating pressure, thereby reducing the SHd value and controlling it to converge within the predetermined SHd range.

[0049] In addition, with Figure 5 In contrast to the example shown, when SHd control is executed, if the actual operating SHd does not reach the specified SHd range, the control unit 20 reduces the expansion valve 104. By reducing the expansion valve 104, the control unit 20 reduces the refrigerant circulation, causing the condensing pressure to rise and the evaporating pressure to fall, thereby increasing the value of SHd and controlling it in a way that converges to the specified range.

[0050] Here, the purpose of performing Td or SHd control is to ensure operational reliability. During the operation of compressor 101, the compressed refrigerant becomes high-temperature, heating the compressor 101's structural components or the compressor 101's container, including the built-in motor. By controlling Td within a specified range, control unit 20 prevents demagnetization of the compressor 101's motor windings. Furthermore, it is considered that during low-load operation, humid gas is drawn into compressor 101, resulting in liquid recirculation. By controlling Td or SHd within a specified range, control unit 20 controls the compressor 101's intake state, ensuring compressor 101's reliability.

[0051] In the refrigeration cycle apparatus 100 of this embodiment, the control unit 20 can switch between SC control and Td control or SHd control according to the operating characteristics of the refrigeration cycle apparatus 100. For example, the control unit 20 controls the opening degree of the expansion valve 140 based on the detection results of the detection unit and the operating characteristics of the refrigeration cycle apparatus 100, using either SC control, Td control or SHd control.

[0052] [Explanation of control switching actions]

[0053] Next, the operation of the control unit 20 of the refrigeration cycle device 100 in switching between SC control and Td control or SHd control based on the operating characteristics will be explained.

[0054] Figure 6 This is a flowchart illustrating an example of the switching process between SC control and Td control or SHd control in the refrigeration cycle apparatus 100 of this embodiment, based on operating characteristics. Furthermore, at the start of operation of the refrigeration cycle apparatus 100, the control unit 20 performs SC control to ensure the required capacity, similar to conventional control.

[0055] The control unit 20 calculates the SC during operation (step S11). For example, the control unit 20 calculates the SC during operation based on the condensing temperature detected by the temperature detector 111 and the condenser outlet temperature detected by the temperature detector 112. Then, it proceeds to step S12.

[0056] The control unit 20 determines whether SC control can continue based on the operating characteristics of the refrigeration cycle device 100 (step S12). The operating characteristics of the refrigeration cycle device 100 include, for example, the magnitude of the air conditioning load during operation, the value of SC, and the opening degree of the expansion valve 104. The specific method for determining the operating characteristics described above will be explained in the second to fourth embodiments described later. If the control unit 20 determines in step S12 that SC control can continue (yes), it continues SC control (step S13).

[0057] On the other hand, if the control unit 20 determines in step S12 that SC control cannot continue (No), it switches to Td control or SHd control (step S14). For example, the control unit 20 uses temperature detector 115 or temperature detector 116 to detect Td (discharge temperature) and performs Td control based on the detected Td. Alternatively, the control unit 20 may calculate the difference between the detected Td and the condensation temperature, i.e., SHd (discharge superheat), and perform SHd control based on the calculated SHd.

[0058] If the control unit 20 continues SC control in step S13, it determines whether the actual working SC converges within a specified SC range (e.g., 2 to 6 degrees) (step S15). For example, in step S15, the control unit 20 determines whether the actual working SC is above threshold A (e.g., 2 degrees) and below threshold B (e.g., 6 degrees). If the control unit 20 determines that the actual working SC has not converged within the specified SC range (no), it returns to step S12 and re-determines based on the operating characteristics.

[0059] On the other hand, if the control unit 20 determines in step S15 that the actual operating SC converges within the specified SC range (yes), it determines that the refrigeration cycle is in a stable state and ends the control switching process. Alternatively, when the control unit 20 determines that the refrigeration cycle is in a stable state, it may also make the determination after a certain period of time has elapsed and the actual operating SC has converged within the specified SC range.

[0060] In step S14, when switching from SC control to Td control, the control unit 20 determines whether the actual operating Td converges within a specified Td range (e.g., 60–100 degrees) (step S16). For example, the control unit 20 determines whether the actual operating Td is above threshold C (e.g., 60 degrees) and below threshold D (e.g., 100 degrees). If the control unit 20 determines in step S16 that the actual operating Td has not converged within the specified Td range (no), it returns to step S12 and re-determines based on the operating characteristics.

[0061] On the other hand, if the control unit 20 determines in step S16 that the actual operating Td converges within the specified Td range (yes), it determines that the refrigeration cycle is in a stable state and ends the control switching process. For example, when the control unit 20 determines that the refrigeration cycle is in a stable state, it may also make the determination after a certain period of time has elapsed and the actual operating Td has converged within the specified Td range.

[0062] Furthermore, if the control unit 20 switches from SC control to SHd control in step S14, it determines whether the actual operating SHd converges within a specified SHd range (e.g., 20–30 degrees) (step S16). For example, the control unit 20 determines whether the actual operating SHd is above threshold E (e.g., 20 degrees) and below threshold F (e.g., 30 degrees). If the control unit 20 determines in step S16 that the actual operating SHd has not converged within the specified SHd range (no), it returns to step S12 and re-determines based on the operating characteristics.

[0063] On the other hand, if the control unit 20 determines in step S16 that the actual operating SHd converges within the specified SHd range (yes), it determines that the refrigeration cycle is in a stable state and ends the control switching process. For example, when the control unit 20 determines that the refrigeration cycle is in a stable state, it may also make the determination after a certain period of time has elapsed and the actual operating SHd has converged within the specified SHd range.

[0064] Furthermore, the control unit 20 can continue to repeatedly perform the switching process between SC control and Td control or SHd control after the refrigeration cycle has stabilized. As a result, the refrigeration cycle unit 100 can continue to ensure reliable operation even in the face of changes in operating characteristics (such as air conditioning load).

[0065] As explained above, the refrigeration cycle device 100 of this embodiment controls the opening of the expansion valve 104 based on either SC control (subcooling control) or Td control (discharge temperature control) or SHd control (discharge superheat control) according to its operating characteristics, thereby ensuring both the required capacity and protecting operation. Therefore, according to this embodiment, a highly reliable refrigeration cycle device 100 can be provided that will not stop operation due to abnormal discharge temperature even in operating conditions where SC (subcooling) is difficult to ensure.

[0066] For example, given societal trends such as environmental restrictions on the refrigeration cycle device 100, it could also be a refrigeration cycle device 100 using a low GWP (Global Warming Potential) refrigerant. Low GWP refrigerants have the advantage of a lower GWP compared to conventionally used refrigerants, resulting in a lower environmental impact; however, they also have disadvantages such as flammability and slight flammability. In particular, due to recent environmental restrictions, refrigerant-saving measures in refrigeration cycle devices have been continuously developing. Furthermore, in the case of flammable or slightly flammable refrigerants, refrigerant leaks indoors pose safety concerns, thus there is a trend towards minimizing the amount of refrigerant supplied. The refrigeration cycle device 100 of this embodiment is particularly effective when using refrigerants for which reduced refrigerant supply is desired, such as flammable refrigerants.

[0067] <Second Implementation>

[0068] Next, the second embodiment will be described.

[0069] In the first embodiment, an example of switching between SC control and Td control or SHd control based on the operating characteristics of the refrigeration cycle device 100 was described. However, in this embodiment, as a specific example of operating characteristics, an example based on the size of the air conditioning load is described.

[0070] When the air conditioning load is low due to a reduced amount of refrigerant injected into the refrigeration cycle, the required air conditioning capacity decreases, thus reducing the operating frequency of the compressor 101. Consequently, the amount of refrigerant circulating within the refrigeration cycle unit 100 decreases, leading to a situation where the measured value falls below the specified SC range required for SC control. Therefore, when the control unit 20 determines that the air conditioning load on the refrigeration cycle unit 100 is low, it switches from SC control to Td control or SHd control.

[0071] Regarding the air conditioning load, for example, the control unit 20 can determine the load based on the actual operating frequency of the compressor 101 controlled during operation (hereinafter referred to as "actual operating frequency"). For instance, if the actual operating frequency of the compressor 101 is less than a predetermined threshold (e.g., 40Hz), the control unit 20 determines that the air conditioning load is low and switches from SC control to Td control or SHd control. On the other hand, if the actual operating frequency of the compressor 101 is above the predetermined threshold (e.g., 40Hz), the control unit 20 determines that the air conditioning load is not low and continues SC control. Hereinafter, this predetermined threshold will be referred to as "threshold operating frequency".

[0072] Figure 7This is a flowchart illustrating an example of the switching process between SC control and Td control or SHd control in the refrigeration cycle apparatus 100 of this embodiment, based on the operating frequency of the compressor 101. Figure 7 The processes shown in steps S21, S25, and S26 are related to... Figure 6 The processes in steps S11, S15, and S16 shown are the same, and their descriptions are omitted. Here, as in Figure 6 The example shown in steps S12, S13, and S14 is an example of the process of switching control based on operating characteristics. The difference is that in steps S22, S23, and S24, the control is switched based on the air conditioning load (for example, the operating frequency of compressor 101).

[0073] The control unit 20 determines the magnitude of the air conditioning load on the refrigeration cycle unit 100 (step S22). For example, as determining the air conditioning load, the control unit 20 determines whether the actual operating frequency of the compressor 101 is above a threshold operating frequency (e.g., 40Hz). If the control unit 20 determines in step S22 that the actual operating frequency is above the threshold operating frequency (yes), it determines that the air conditioning load is not small and continues SC control (step S23). Then, it proceeds to step S25.

[0074] On the other hand, if the control unit 20 determines in step S22 that the actual operating frequency is less than the threshold operating frequency (no), it determines that the air conditioning load is low and switches the SC control to Td control or SHd control (step S24). Then, it proceeds to step S26.

[0075] In addition, with Figure 6 The same applies to the switching process described in the diagram. Figure 7 In the switching process shown, the control unit 20 can also repeatedly perform the switching process between SC control and Td control or SHd control after the refrigeration cycle has stabilized. Therefore, the refrigeration cycle device 100 can continue to ensure reliable operation even with changes in operating characteristics (such as air conditioning load).

[0076] As explained above, when the operating frequency of the compressor 101 is less than a predetermined threshold, the refrigeration cycle device 100 of this embodiment switches the control of the opening degree of the expansion valve 104 from SC control (subcooling control) to Td control (discharge temperature control) or SHd control (discharge superheat control).

[0077] Therefore, when the refrigeration cycle device 100 is in a state where it is difficult to ensure SC operation, for example, when the air conditioning load is low and the operating frequency of the compressor 101 is reduced, the control of the opening degree of the expansion valve 104 is switched from SC control to Td control or SHd control based on a threshold value of the operating frequency of the compressor 101. Therefore, according to this embodiment, a highly reliable refrigeration cycle device 100 can be provided that prevents excessive reduction of the expansion valve 104 and does not cause the operation to stop due to protective actions such as abnormal discharge temperature.

[0078] <Third Implementation Method>

[0079] Next, the third embodiment will be described.

[0080] In the first embodiment, an example of switching between SC control and Td control or SHd control based on the operating characteristics of the refrigeration cycle device 100 was described. However, in this embodiment, as a specific example of operating characteristics, an example using the value of SC will be described.

[0081] Assuming an operating state where the amount of refrigerant injected into the refrigeration cycle is reduced, resulting in less remaining refrigerant in the refrigeration cycle, and considering the case where the actual operating SC is less than the specified SC range required for SC control, the control unit 20 switches from SC control to Td control or SHd control when the actual operating SC is less than a specified threshold (hereinafter referred to as "threshold SC").

[0082] Figure 8 This is a flowchart illustrating an example of the switching process in the refrigeration cycle apparatus 100 of this embodiment, where SC control is switched to Td control or SHd control based on the value of SC. Figure 8 The processes shown in steps S31, S35, and S36 are related to... Figure 6 The processes in steps S11, S15, and S16 shown are the same, and their descriptions are omitted. Here, as in Figure 6 The example shown in steps S12, S13, and S14 is a case of switching control based on operating characteristics. The difference is that in steps S32, S33, and S34, control is switched based on the value of SC.

[0083] The control unit 20 determines whether the actual operating SC calculated based on the detected condensing temperature and the condenser outlet temperature is above the threshold SC (e.g., 2 degrees Celsius) (step S32). If the control unit 20 determines in step S32 that the actual operating SC is above the threshold SC (yes), it determines that there is refrigerant remaining and continues SC control (step S33). Then, it proceeds to step S35.

[0084] On the other hand, if the control unit 20 determines in step S32 that the actual operating SC is less than the threshold SC (no), it determines that the refrigerant is insufficient and switches the SC control to Td control or SHd control (step S34). Then, it proceeds to step S36.

[0085] In addition, with Figure 6 The same applies to the switching process described in the diagram. Figure 8 In the switching process shown, the control unit 20 can also repeatedly perform the switching process between SC control and Td control or SHd control after the refrigeration cycle has stabilized. As a result, the refrigeration cycle unit 100 can continue to ensure reliable operation even with changes in operating characteristics (such as air conditioning load).

[0086] As explained above, when the SC (subcooling) of the condenser (e.g., the heat source side heat exchanger 103) is less than a predetermined threshold, the refrigeration cycle device 100 of this embodiment switches the control of the opening of the expansion valve 104 from SC control (subcooling control) to Td control (discharge temperature control) or SHd control (discharge superheat control).

[0087] Therefore, even in areas where it is difficult to ensure the operation of the SC (Self-Regulating Function), such as when the proportion of refrigerant in the refrigeration cycle decreases due to differences in the installation environment or the operating mode of cooling or heating, the refrigeration cycle device 100 can switch the control of the opening of the expansion valve 104 from SC control to Td control or SHd control based on the threshold value of the condenser's SC. Thus, according to this embodiment, a highly reliable refrigeration cycle device 100 can be provided that prevents excessive reduction of the expansion valve 104 and does not cause a shutdown due to protective actions such as abnormal discharge temperature.

[0088] <Fourth Implementation>

[0089] Next, the fourth embodiment will be described.

[0090] In the first embodiment, an example of switching between SC control and Td control or SHd control based on the operating characteristics of the refrigeration cycle device 100 was described. However, in this embodiment, as a specific example of operating characteristics, an example of using the opening degree of the expansion valve 104 for determining operating protection is described.

[0091] Assuming an operating state where the amount of refrigerant injected into the refrigeration cycle is reduced, resulting in less residual refrigerant in the refrigeration cycle, and considering the case where the actual operating SC is less than the specified SC range required for SC control, the control unit 20 switches from SC control to Td control or SHd control if the actual opening degree of the expansion valve 104 controlled during operation (hereinafter referred to as "actual operating expansion valve opening degree") is less than a specified threshold (hereinafter referred to as "threshold expansion valve opening degree").

[0092] Figure 9 This is a flowchart illustrating an example of the switching process between SC control and Td control or SHd control in the refrigeration cycle apparatus 100 of this embodiment, based on the opening degree of the expansion valve 104. Figure 9 The processes shown in steps S41, S45, and S46 are related to... Figure 6 The processes in steps S11, S15, and S16 shown are the same, and their descriptions are omitted. Here, as in Figure 6 The example shown in steps S12, S13, and S14 is a case of switching control based on operating characteristics. The difference is that in steps S42, S43, and S44, the control is switched based on the opening degree of the expansion valve 104.

[0093] The control unit 20 determines whether the actual operating expansion valve opening is greater than or equal to the threshold expansion valve opening (e.g., 20%) (step S42). If the control unit 20 determines in step S42 that the actual operating expansion valve opening is greater than or equal to the threshold expansion valve opening (yes), it determines that the expansion valve 104 can be reduced and continues SC control (step S43). Then, it proceeds to step S45.

[0094] On the other hand, if the control unit 20 determines in step S42 that the actual operating expansion valve opening is less than the threshold expansion valve opening (No), it determines that Td or SHd has increased due to the reduction of the expansion valve 104, and operation protection is needed to prevent excessive increase of the condensing pressure in the refrigerant circuit 10. Therefore, the control unit 20 determines that it is necessary to prevent the expansion valve 104 from being reduced, and switches SC control to Td control or SHd control (step S44). Then, it proceeds to step S46.

[0095] In addition, with Figure 6 The same applies to the switching process described in the diagram. Figure 9 In the switching process shown, the control unit 20 can also repeatedly perform the switching process between SC control and Td control or SHd control after the refrigeration cycle has stabilized. As a result, the refrigeration cycle device 100 can continue to ensure reliable operation even in the face of changes in operating characteristics (such as air conditioning load).

[0096] As explained above, in this embodiment, when the opening degree of the expansion valve 104 is less than a predetermined threshold, the refrigeration cycle device 100 switches the control of the opening degree of the expansion valve 104 from SC control (subcooling control) to Td control (discharge temperature control) or SHd control (discharge superheat control).

[0097] Therefore, even in areas where there is an over-adjustment of the expansion valve 104 due to operational protection under conditions where it is difficult to ensure the operation of the expansion valve 104, such as when the expansion valve 104 does not meet the specified control range, the refrigeration cycle device 100 can switch the control of the opening of the expansion valve 104 from SC control to Td control or SHd control based on the threshold value of the opening of the expansion valve 104. Thus, according to this embodiment, a highly reliable refrigeration cycle device can be provided that prevents over-adjustment of the expansion valve 104 and does not cause an operational stoppage due to protective actions such as abnormal discharge temperature.

[0098] <Fifth Implementation>

[0099] Next, the fifth embodiment will be described.

[0100] In this embodiment, an example of switching between SC control and Td control or SHd control based on the air conditioning load (operating frequency of compressor 101), the value of SC, and the opening degree of expansion valve 104 as described in the second, third, and fourth embodiments above will be explained.

[0101] Figure 10 This is a flowchart illustrating an example of the switching process in the refrigeration cycle apparatus 100 of this embodiment, which involves switching between SC control and Td control or SHd control based on the air conditioning load (operating frequency of compressor 101), the value of SC, and the opening degree of expansion valve 104. Figure 10 The processes shown in steps S51, S58, and S59 are related to... Figure 6 The processes shown in steps S11, S15, and S16 are the same, and their descriptions are omitted. Here, with... Figure 6 The difference in the switching process shown is that in steps S52 to S57, the switching control is based on the determination results of the air conditioning load (e.g., the operating frequency of compressor 101), the value of SC, and the opening degree of expansion valve 104.

[0102] The control unit 20 determines the magnitude of the air conditioning load on the refrigeration cycle unit 100 (step S52). For example, as determining the air conditioning load, the control unit 20 determines whether the actual operating frequency of the compressor 101 is above a threshold operating frequency (e.g., 40Hz). If the control unit 20 determines in step S52 that the actual operating frequency is above the threshold operating frequency (yes), it determines that the air conditioning load is not small and continues SC control (step S56). Then, it proceeds to step S58.

[0103] On the other hand, if the control unit 20 determines in step S52 that the actual operating frequency is less than the threshold operating frequency (no), it determines that the air conditioning load is small and proceeds to step S53.

[0104] The control unit 20 determines whether the actual operating SC calculated based on the detected condensing temperature and condenser outlet temperature is above the threshold SC (e.g., 2 degrees) (step S53). If the control unit 20 determines in step S53 that the actual operating SC is above the threshold SC (yes), it determines that there is some refrigerant remaining and continues SC control (step S56). Then, it proceeds to step S58.

[0105] On the other hand, if the control unit 20 determines in step S53 that the actual working SC is less than the threshold SC (no), it determines that the refrigerant is slightly insufficient and proceeds to step S54.

[0106] The control unit 20 determines whether the actual operating expansion valve opening is greater than or equal to the threshold expansion valve opening (e.g., 20%) (step S54). If the control unit 20 determines in step S54 that the actual operating expansion valve opening is greater than or equal to the threshold expansion valve opening (yes), it determines that the expansion valve 104 can be reduced and continues SC control (step S56). Then, it proceeds to step S58.

[0107] On the other hand, if the control unit 20 determines in step S54 that the actual operating expansion valve opening is less than the threshold expansion valve opening (No), it determines that the air conditioning load is low, the refrigerant is slightly insufficient, and it is necessary to prevent the expansion valve 104 from being adjusted too low, and switches the SC control to Td control or SHd control (step S57). Then, it proceeds to step S59.

[0108] As explained above, in this embodiment, when the operating frequency of the compressor 101 is less than a predetermined threshold, the SC (subcooling) of the condenser (e.g., the heat source side heat exchanger 103) is less than a predetermined threshold, and the opening degree of the expansion valve 104 is less than a predetermined threshold, the control of the opening degree of the expansion valve 104 will be switched from SC control (subcooling control) to Td control (discharge temperature control) or SHd control (discharge superheat control).

[0109] Therefore, even in areas where excessive reduction of the expansion valve 104 is required for operation protection due to conditions that make it difficult to ensure the SC (cooling capacity) operation (e.g., low air conditioning load leading to reduced compressor 101 operating frequency), or differences in installation environment or cooling / heating operating modes causing the SC to fall outside the prescribed control range, the refrigeration cycle device 100 can independently determine the compressor 101 operating frequency, the condenser SC, and the opening degree of the expansion valve 104, and switch the control of the expansion valve 104 opening degree from SC control to Td control or SHd control. Thus, according to this embodiment, a highly reliable refrigeration cycle device can be provided that prevents excessive reduction of the expansion valve 104 and avoids operation stoppage due to protection actions such as abnormal discharge temperature.

[0110] The embodiments have been described in detail above with reference to the accompanying drawings, but the specific configuration is not limited to the embodiments described above. The embodiments can be combined, or the embodiments can be appropriately modified or omitted.

[0111] In the above embodiment, an example using the SC of the heat source side heat exchanger 103 was described, but the SC of the utilization side heat exchanger 105 can also be used. Alternatively, both the SC of the heat source side heat exchanger 103 and the SC of the utilization side heat exchanger 105 can be used.

[0112] Furthermore, in the first embodiment described above, for in Figure 6 The process described shows that the control unit 20 can repeatedly perform the switching process between SC control and Td control or SHd control even after the refrigeration cycle has stabilized. However, regarding... Figure 7 , 8 The processes shown in 9 and 10 can also be repeated after the refrigeration cycle has stabilized.

[0113] Alternatively, the program used to implement the functions of the control unit 20 can be recorded on a computer-readable recording medium, and the computer system can read and execute the program recorded on the recording medium, thereby performing the processing of the control unit 20. Furthermore, the "computer system" mentioned here includes hardware such as the operating system and peripheral devices.

[0114] Furthermore, "computer-readable recording media" refers to removable media such as floppy disks, optical disks, ROMs, and CD-ROMs, as well as storage devices such as hard disks built into computer systems. "Computer-readable recording media" also includes recording media that dynamically maintain programs for a short period, such as communication lines used to transmit programs via networks like the Internet or telephone lines, and recording media that maintain programs for a certain period, such as volatile memory within a computer system acting as a server or client in this case. Additionally, the aforementioned program can be a program used to implement the above functions, or it can be a program that can further implement the above functions by combining them with programs already recorded in the computer system. Furthermore, the aforementioned program can be pre-stored on a designated server and distributed (downloaded, etc.) via communication lines upon request from other devices.

[0115] Alternatively, some or all of the functions of the control unit 20 can be implemented as an integrated circuit such as an LSI (Large Scale Integration). Each function can be processed separately, or some or all of them can be integrated and processed. Furthermore, the method of integrated circuit implementation is not limited to LSI; it can also be implemented by dedicated circuits or general-purpose processors. In addition, if an integrated circuit technology that replaces LSI has emerged due to advancements in semiconductor technology, an integrated circuit utilizing this technology can also be used.

[0116] Explanation of reference numerals in the attached figures:

[0117] 10…Refrigerant circuit; 11, 12, 13, 14…Piping; 20…Control unit; 100…Refrigeration cycle unit; 101…Compressor; 102…Refrigerant switching device; 103…Heat source side heat exchanger; 104…Expansion valve; 105…Utilization side heat exchanger; 111, 112, 113, 114, 115, 116…Temperature detectors.

Claims

1. A refrigeration cycle device comprising a refrigerant circuit connecting a compressor, a heat exchanger on the heat source side, an expansion valve, and a heat exchanger on the utilization side via refrigerant piping, characterized in that, have: The detection unit detects the heat transfer tube temperature and outlet pipe temperature of at least one heat exchanger on the heat source side and the heat exchanger on the utilization side, namely the heat exchanger that functions as a condenser, and the discharge temperature of the compressor. as well as The control unit is capable of controlling the degree of supercooling and the discharge temperature or the discharge superheat based on the detection results of the detection unit. When the refrigeration cycle device starts operating, the control unit controls the opening of the expansion valve based on the subcooling control. If the operating characteristics of the refrigeration cycle device determine that the subcooling control cannot continue, the control of the opening of the expansion valve is switched from the subcooling control to the discharge temperature control or the discharge superheat control.

2. The refrigeration cycle device according to claim 1, characterized in that, The operating characteristic is the operating frequency of the compressor. When the operating frequency of the compressor is less than a predetermined threshold, the control unit switches the control of the opening degree of the expansion valve from the subcooling control to the discharge temperature control or the discharge superheat control.

3. The refrigeration cycle device according to claim 1, characterized in that, The operating characteristic is the subcooling degree of the at least one heat exchanger. When the subcooling of at least one heat exchanger is less than a predetermined threshold, the control unit switches the control of the opening of the expansion valve from subcooling control to discharge temperature control or discharge superheat control.

4. The refrigeration cycle device according to claim 1, characterized in that, The operating characteristic is the opening degree of the expansion valve. When the opening degree of the expansion valve is less than a predetermined threshold, the control unit switches the control of the opening degree of the expansion valve from the subcooling degree control to the discharge temperature control or the discharge superheat control.

5. The refrigeration cycle device according to claim 1, characterized in that, The operating characteristics are the operating frequency of the compressor, the subcooling degree of the at least one heat exchanger, and the opening degree of the expansion valve. When the operating frequency of the compressor is less than a predetermined threshold, the subcooling degree of the at least one heat exchanger is less than a predetermined threshold, and the opening degree of the expansion valve is less than a predetermined threshold, the control unit switches the control of the opening degree of the expansion valve from the subcooling degree control to the discharge temperature control or the discharge superheat control.

6. A control method for a refrigeration cycle device comprising a refrigerant circuit formed by connecting a compressor, a heat exchanger on the heat source side, an expansion valve, and a heat exchanger on the utilization side using refrigerant piping, characterized in that... The heat transfer tube temperature and outlet pipe temperature of at least one heat exchanger (which functions as a condenser) on the heat source side and the heat exchanger on the utilization side, as well as the discharge temperature of the compressor, are detected. Based on the results of the detection, supercooling control and discharge temperature control or discharge superheat control are performed. When the refrigeration cycle begins operation, the opening degree of the expansion valve is controlled based on the subcooling degree control. If, based on the operating characteristics of the refrigeration cycle device, it is determined that the subcooling control cannot continue, the control of the opening of the expansion valve will be switched from the subcooling control to the discharge temperature control or the discharge superheat control.

7. The control method according to claim 6, characterized in that, The operating characteristic is the operating frequency of the compressor. When the operating frequency of the compressor is less than a specified threshold, the control of the opening degree of the expansion valve is switched from the subcooling control to the discharge temperature control or the discharge superheat control.

8. The control method according to claim 6, characterized in that, The operating characteristic is the subcooling degree of the at least one heat exchanger. If the subcooling of at least one heat exchanger is less than a predetermined threshold, the control of the opening of the expansion valve will be switched from the subcooling control to the discharge temperature control or the discharge superheat control.

9. The control method according to claim 6, characterized in that, The operating characteristic is the opening degree of the expansion valve. If the opening degree of the expansion valve is less than a predetermined threshold, the control of the opening degree of the expansion valve will be switched from the subcooling control to the discharge temperature control or the discharge superheat control.

10. The control method according to claim 6, characterized in that, The operating characteristics are the operating frequency of the compressor, the subcooling degree of the at least one heat exchanger, and the opening degree of the expansion valve. When the operating frequency of the compressor is less than a predetermined threshold, the subcooling degree of the at least one heat exchanger is less than a predetermined threshold, and the opening degree of the expansion valve is less than a predetermined threshold, the control of the opening degree of the expansion valve will be switched from the subcooling degree control to the discharge temperature control or the discharge superheat control.

Images