Refrigeration cycle appartatus and method for controlling same

Abstract

This refrigeration cycle apparatus comprises: a refrigerant circuit in which an expansion valve with a variable opening degree and a heating-medium heat exchanger are connected by a pipe, and through which a refrigerant circulates; a heating medium circuit through which a heating medium that exchanges heat with the refrigerant in the refrigerant circuit by the heating-medium heat exchanger circulates; and a control processing device that controls the opening degree of the expansion valve so as to be the smaller of a refrigerant capacity maintaining opening degree and a freeze-prevention opening degree, the refrigerant capacity maintaining opening degree being the opening degree of the expansion valve for matching a superheat degree of the refrigerant at an outlet of the heating-medium heat exchanger functioning as an evaporator during a cooling operation with a preset superheat degree target value, and the freeze-prevention opening degree being the opening degree of the expansion valve for matching the temperature of the heating medium with the preset lower limit value of the heating medium temperature that is a temperature exceeding the freezing temperature of the heating medium.

Description

Refrigeration cycle device and control method thereof

[0001] The present disclosure relates to a refrigeration cycle apparatus including a heat medium heat exchanger that exchanges heat between a refrigerant and a heat medium, and a control method thereof.

[0002] Conventionally, there has been a refrigeration cycle device that includes an expansion valve, a heat medium heat exchanger, etc., a refrigerant circuit through which a refrigerant circulates, and a heat medium circuit through which a heat medium such as water or brine circulates, and that exchanges heat between the refrigerant and the heat medium in the heat medium heat exchanger and transports the heat medium to an indoor unit to cool a room (see, for example, Patent Document 1).The refrigeration cycle device of Patent Document 1 controls the refrigerant temperature by controlling the expansion valve so that the degree of superheat of the refrigerant is constant at a target value during cooling operation.

[0003] International Publication No. 2017 / 119137

[0004] Although the refrigeration cycle device of Patent Document 1 can maintain stable air conditioning capacity by controlling the refrigerant temperature, it does not mention anything about freezing of the heat medium in the heat medium circuit, which means that the refrigeration cycle device of Patent Document 1 has the problem of possibly breaking down due to freezing of the heat medium.

[0005] The present disclosure has been made in consideration of these points, and aims to provide a refrigeration cycle device and a control method thereof that can maintain stable air conditioning capacity under the constraint of not freezing the heat medium.

[0006] The refrigeration cycle device according to the present disclosure includes a refrigerant circuit in which a refrigerant circulates, and in which an expansion valve whose opening is changeable and a heat medium heat exchanger are connected by piping; a heat medium circuit in which the refrigerant in the refrigerant circuit and a heat medium that exchanges heat in the heat medium heat exchanger circulate; and a control processing device that controls the opening of the expansion valve to the smaller of: a cooling capacity maintenance opening, which is the opening of the expansion valve for making the superheat of the refrigerant at the outlet of the heat medium heat exchanger, which functions as an evaporator during cooling operation, equal to a predetermined superheat target value; and a freeze prevention opening, which is the opening of the expansion valve for making the temperature of the heat medium equal to a predetermined heat medium temperature lower limit value that is above the freezing temperature of the heat medium.

[0007] A control method for a refrigeration cycle device according to the present disclosure is a control method for an expansion valve in a refrigeration cycle device including a refrigerant circuit in which a refrigerant circulates, and a heat medium circuit in which a heat medium that exchanges heat with the refrigerant circulates, in which an expansion valve whose opening is changeable and a heat medium heat exchanger are connected by piping, and in which the refrigerant in the refrigerant circuit and the heat medium in the heat medium circuit exchange heat in the heat medium heat exchanger, and the refrigerant in the refrigerant circuit and the heat medium in the heat medium circuit exchange heat with each other in the heat medium heat exchanger, the control method including the steps of: calculating a cooling capacity maintenance opening, which is the opening of the expansion valve for making the superheat of the refrigerant at an outlet of the heat medium heat exchanger that functions as an evaporator during cooling operation, equal to a predetermined superheat target value; calculating an anti-freeze opening, which is the opening of the expansion valve for making the temperature of the heat medium equal to a predetermined lower limit of the heat medium temperature that is above the freezing temperature of the heat medium; selecting the smaller of the calculated cooling capacity maintenance opening and the anti-freeze opening; and controlling the opening of the expansion valve to achieve the selected opening.

[0008] The refrigeration cycle device and its control method disclosed herein controls the opening of the expansion valve to the smaller of the cooling capacity maintenance opening and the anti-freeze opening, thereby maintaining stable air conditioning capacity under the constraint of not freezing the heat medium.

[0009] 9 is a schematic diagram showing an example of the configuration of a refrigeration cycle apparatus according to Embodiment 1. It is a control block diagram showing the electrical configuration of the heat medium heat exchange unit of FIG. 1. It is a functional block diagram showing an example of a part related to the opening degree control of the expansion valve in the control processing device during cooling operation of the refrigeration cycle apparatus according to Embodiment 1. It is a block diagram showing the configuration of a superheat degree control unit of the refrigeration cycle apparatus according to Embodiment 1. It is a block diagram showing the configuration of an anti-freeze control unit of the refrigeration cycle apparatus according to Embodiment 1. It is a flowchart of an expansion valve opening degree control method in the refrigeration cycle apparatus according to Embodiment 1. It is a time chart showing the relationship between the superheat degree, the heat medium temperature, and the expansion valve opening in the refrigeration cycle apparatus according to Embodiment 1. It is a diagram showing the calculation results of the anti-freeze opening and the cooling capacity maintenance opening of the refrigeration cycle apparatus according to Embodiment 1. It is a schematic diagram showing an example of the configuration of a refrigeration cycle apparatus according to Embodiment 2. It is a control block diagram showing the electrical configuration of the heat medium heat exchange unit of FIG. 9. It is a functional block diagram showing an example of a part related to the opening degree control of the expansion valve in the control processing device during heating operation of the refrigeration cycle apparatus according to Embodiment 2. It is a block diagram showing the configuration of a subcooling degree control unit of the refrigeration cycle apparatus according to Embodiment 2. It is a block diagram showing the configuration of an overheat prevention control unit of the refrigeration cycle apparatus according to Embodiment 2. 1 is a flowchart of an expansion valve opening control method in a refrigeration cycle apparatus according to embodiment 2. FIG. 2 is a time chart showing the relationship between the degree of subcooling, the heat medium temperature, and the expansion valve opening in the refrigeration cycle apparatus according to embodiment 2. FIG. 3 is a diagram showing calculation results of an overheat prevention opening and a heating capacity maintenance opening in the refrigeration cycle apparatus according to embodiment 2.

[0010] Hereinafter, a refrigeration cycle apparatus according to an embodiment of the present disclosure will be described with reference to the drawings. In the following drawings, the same reference numerals denote the same or equivalent parts, and this applies throughout the entire specification.

[0011] Embodiment 1 Fig. 1 is a schematic diagram showing an example of the configuration of a refrigeration cycle apparatus 1 according to Embodiment 1. As shown in Fig. 1, the refrigeration cycle apparatus 1 includes an outdoor unit 2, an indoor unit 3, and a heat medium heat exchange unit 4. The outdoor unit 2 includes a compressor 8, a four-way valve 9, an outdoor heat exchanger 10, and an outdoor blower 10a. The indoor unit 3 includes an indoor heat exchanger 13 and an indoor blower 13a. The heat medium heat exchange unit 4 includes an expansion valve 14, a heat medium heat exchanger 15, and a pump 20.

[0012] The refrigeration cycle apparatus 1 includes a refrigerant circuit A in which a compressor 8, a four-way valve 9, an outdoor heat exchanger 10, an expansion valve 14, and a heat medium heat exchanger 15 are connected by piping, and in which a refrigerant circulates. The refrigeration cycle apparatus 1 also includes a heat medium circuit B in which the heat medium heat exchanger 15, an indoor heat exchanger 13, and a pump 20 are connected by piping, and in which a heat medium circulates.

[0013] The refrigeration cycle apparatus 1 shown in Fig. 1 is the minimum configuration required to realize the refrigeration cycle according to the present disclosure, and may be configured to connect a plurality of indoor unit units 3 and include a flow shunt controller for adjusting the flow shunt, as necessary. Although not shown in Fig. 1, the refrigerant circuit A may include an accumulator, which is a liquid reservoir for storing refrigerant that was not completely gasified and prevents it from being drawn into the compressor 8. The refrigerant circuit A may also include an injection circuit for preventing an excessive rise in the discharge temperature of the compressor 8, and a receiver circuit or power receiver circuit for storing excess refrigerant.

[0014] Each of the devices constituting the refrigeration cycle device 1 will be described below.

[0015] The compressor 8 compresses and discharges the drawn refrigerant. The compressor 8 may have a capacity that can be changed by, for example, arbitrarily changing the drive frequency using an inverter circuit (not shown). The capacity is the amount of refrigerant discharged per unit time.

[0016] The four-way valve 9 is connected to the discharge side of the compressor 8 and switches the flow of the refrigerant discharged from the compressor 8. The four-way valve 9 switches the circulation direction of the refrigerant discharged from the compressor 8 between cooling operation and heating operation. The four-way valve 9 switches the direction of the refrigerant toward the outdoor heat exchanger 10 in cooling operation, and switches the direction of the refrigerant toward the heat medium heat exchanger 15 in heating operation. Note that the refrigeration cycle device 1 only needs to be capable of at least cooling operation, and the four-way valve 9 may be omitted.

[0017] The outdoor heat exchanger 10 is, for example, a fin-tube heat exchanger configured to include pipes through which a refrigerant flows and fins into which the pipes are inserted. The outdoor blower 10a is a fan that blows air into the outdoor heat exchanger 10. The outdoor blower 10a may be a type whose air volume can be changed by arbitrarily changing the drive rotation speed using, for example, an inverter circuit (not shown). The air volume is the amount of air blown out per unit time.

[0018] The indoor heat exchanger 13 is, for example, a fin-tube heat exchanger configured to include piping through which a heat medium flows and fins into which the piping is inserted. The indoor blower 13a is a fan that blows air to the indoor heat exchanger 13. The indoor blower 13a may be a fan whose air volume can be changed by arbitrarily changing the drive rotation speed using, for example, an inverter circuit (not shown). The air volume is the amount of air blown out per unit time.

[0019] The expansion valve 14 is provided in the piping on the refrigerant inlet side of the heat medium heat exchanger 15 in the refrigerant flow during cooling operation. The expansion valve 14 expands the refrigerant. The expansion valve 14 is an electronic expansion valve with an adjustable opening. By adjusting the opening of the expansion valve 14, the evaporation temperature of the refrigerant in the heat medium heat exchanger 15 is adjusted. By adjusting the evaporation temperature of the refrigerant, the degree of superheat of the refrigerant at the outlet of the heat medium heat exchanger 15 and the temperature of the heat medium that exchanges heat with the refrigerant are adjusted. Note that, in the illustrated example, the expansion valve 14 is disposed in the heat medium heat exchange unit 4, but this configuration is not limited thereto and the expansion valve 14 may be disposed in the outdoor unit 2.

[0020] The heat medium heat exchanger 15 functions as an evaporator or a condenser, and exchanges heat between the refrigerant circulating through the refrigerant circuit A and the heat medium circulating through the heat medium circuit B, transferring the cold or hot heat generated in the outdoor unit 2 and stored in the refrigerant to the heat medium. The heat medium heat exchanger 15 functions as an evaporator during cooling operation, transferring the cold heat of the refrigerant to the heat medium. The heat medium heat exchanger 15 functions as a condenser during heating operation, transferring the hot heat of the refrigerant to the heat medium. The heat medium heat exchanger 15 is configured as a double-wall plate heat exchanger or a heat exchanger in which a heat transfer tube through which a refrigerant flows and a heat transfer tube through which a heat medium flows are separately provided and joined together by brazing or the like.

[0021] The pump 20 circulates the heat medium through the heat medium circuit B. The pump 20 is preferably configured as, for example, a pump with controllable capacity so that the flow rate can be adjusted according to the magnitude of the load on the indoor unit 3. When the pump 20 is driven, the heat medium flows through the heat medium circuit B in the order of the pump 20, the indoor heat exchanger 13, and the heat medium heat exchanger 15.

[0022] (Multiple Detectors) The refrigeration cycle apparatus 1 includes multiple detectors, such as an indoor temperature detector 12, a heat medium inlet temperature detector 16, a heat medium outlet temperature detector 17, a liquid-side temperature detector 18, and a gas-side temperature detector 19.

[0023] The indoor temperature detection unit 12 is disposed at an air intake port (not shown) of the indoor unit 3, and detects the temperature of the indoor air drawn into the indoor unit 3. The indoor temperature detection unit 12 is composed of a thermocouple, a thermistor, or the like. The detection results detected by the indoor temperature detection unit 12 are input to the indoor unit control device 6, which will be described later. The detection results are shared between the control devices via wired or wireless communication.

[0024] The heat medium inlet temperature detector 16 is disposed in the heat medium heat exchange unit 4 and detects the temperature of the heat medium flowing into the heat medium heat exchanger 15 in the heat medium circuit B. The heat medium outlet temperature detector 17 is disposed in the heat medium heat exchange unit 4 and detects the temperature of the heat medium flowing out of the heat medium heat exchanger 15 in the heat medium circuit B.

[0025] The liquid side temperature detector 18 is disposed in the heat medium heat exchange unit 4 and detects the temperature of the refrigerant flowing into the heat medium heat exchanger 15 in the refrigerant flow direction during cooling operation in the refrigerant circuit A. The liquid side temperature detector 18 detects the temperature of the refrigerant at the inlet of the heat medium heat exchanger 15 on the refrigerant side in the refrigerant flow direction during cooling operation. The liquid side temperature detector 18 detects the temperature of the refrigerant flowing out of the heat medium heat exchanger 15 in the refrigerant flow direction during heating operation in the refrigerant circuit A. The liquid side temperature detector 18 detects the temperature of the refrigerant at the outlet of the heat medium heat exchanger 15 on the refrigerant side in the refrigerant flow direction during heating operation.

[0026] The gas side temperature detection unit 19 is disposed in the heat medium heat exchange unit 4, and detects the temperature of the refrigerant flowing out of the heat medium heat exchanger 15 in the refrigerant flow direction during cooling operation in the refrigerant circuit A. The gas side temperature detection unit 19 detects the temperature of the refrigerant at the outlet of the heat medium heat exchanger 15 on the refrigerant side in the refrigerant flow direction during cooling operation. The gas side temperature detection unit 19 detects the temperature of the refrigerant flowing into the heat medium heat exchanger 15 in the refrigerant flow direction during heating operation in the refrigerant circuit A. The gas side temperature detection unit 19 detects the temperature of the refrigerant at the inlet of the heat medium heat exchanger 15 on the refrigerant side in the refrigerant flow direction during heating operation.

[0027] The heat medium inlet temperature detection unit 16, the heat medium outlet temperature detection unit 17, the liquid side temperature detection unit 18, and the gas side temperature detection unit 19 are each composed of a thermocouple, a thermistor, etc. The detection results detected by these detection units are input to the heat medium heat exchange unit control device 7, which will be described later.

[0028] (Control Device) The refrigeration cycle apparatus 1 includes an outdoor unit control device 5, an indoor unit control device 6, and a heat medium heat exchange unit control device 7. The outdoor unit control device 5 is disposed in the outdoor unit 2, the indoor unit control device 6 is disposed in the indoor unit 3, and the heat medium heat exchange unit control device 7 is disposed in the heat medium heat exchange unit 4. The processing circuits of the outdoor unit control device 5, the indoor unit control device 6, and the heat medium heat exchange unit control device 7 (hereinafter collectively referred to as control devices) have the following configuration. The processing circuit of the control device is configured by dedicated hardware, or a CPU (also referred to as a central processing unit, processing device, arithmetic device, microprocessor, microcomputer, or processor) that executes a program stored in a memory.

[0029] When the processing circuit of the control device is dedicated hardware, the processing circuit may be, for example, a single circuit, a composite circuit, an ASIC (Application Specific Integrated Circuit), an FPGA (Field Programmable Gate Array), or a combination thereof. In the control device, each functional unit realized by the processing circuit may be realized by a separate piece of hardware, or each functional unit may be realized by a single piece of hardware.

[0030] When the processing circuit of the control device is a CPU, each function executed by the processing circuit is realized by software, firmware, or a combination of software and firmware. The software and firmware are written as programs and stored in a memory unit. The CPU realizes each function of the processing circuit by reading and executing the programs stored in the memory unit. Note that some of the functions of the processing circuit may be realized by dedicated hardware and some by software or firmware.

[0031] As described above, the detection results of each detector provided in the refrigeration cycle apparatus 1 are input to the control device of the unit that includes that detector. Furthermore, each detection result is transmitted and received by wired or wireless communication between the control devices provided in the outdoor unit 2, indoor unit 3, and heat medium heat exchange unit 4, and shared. Although the above description illustrates a configuration in which each unit is provided with its own control device, this is not limiting. For example, the refrigeration cycle apparatus 1 may integrate some or all of the control devices in any combination and install them in any of the outdoor unit 2, indoor unit 3, and heat medium heat exchange unit 4.

[0032] Fig. 2 is a control block diagram showing the electrical configuration of the heat medium heat exchange unit 4 of Fig. 1. As shown in Fig. 2, a heat medium inlet temperature detector 16, a heat medium outlet temperature detector 17, a liquid-side temperature detector 18, and a gas-side temperature detector 19 are connected to the heat medium heat exchange unit control device 7. The heat medium heat exchange unit control device 7 is configured to receive the detection results of these detectors. In addition, user commands and the like are input to the heat medium heat exchange unit control device 7 via an operation unit (not shown). User commands and the like may also be input to the outdoor unit control device 5 or the indoor unit control device 6.

[0033] The heat medium heat exchange unit control device 7 has a control processing device 71, a storage device 73, and a timer device 72. The control processing device 71 performs processes such as calculations and judgments based on the input temperature detection results, and controls the devices of the refrigeration cycle device 1, such as the expansion valve 14. During cooling operation, the control processing device 71 operates to supply a stable air conditioning capacity under the constraint of not freezing the heat medium. Details of this operation will be described later.

[0034] The storage device 73 has data that is a program that describes the processing procedures to be performed by the control processing device 71. The storage device 73 has a volatile storage device (not shown) such as a random access memory (RAM) that can temporarily store data, a hard disk, and a non-volatile auxiliary storage device (not shown) such as a flash memory that can store data for the long term.

[0035] The timing device 72 is configured by, for example, a timer and is used for determining the time by the control processing device 71.

[0036] Each of the control processing device 71, the storage device 73, and the timing device 72 can be configured as dedicated equipment (hardware).

[0037] (Cooling Operation) The cooling operation of the refrigeration cycle device 1 will be described with reference to Fig. 1. In the cooling operation, the four-way valve 9 is switched to the state shown by the solid line in Fig. 1 .

[0038] First, the flow of refrigerant in the refrigerant circuit A will be described. The gaseous refrigerant, compressed by the compressor 8 and having a high temperature and pressure, is discharged from the compressor 8's discharge port and flows into the outdoor heat exchanger 10. The gaseous refrigerant that flows into the outdoor heat exchanger 10 exchanges heat with air from the outdoor blower 10a, dissipates heat to the air, and liquefies under high pressure before flowing out of the outdoor heat exchanger 10. The liquid refrigerant that flows out of the outdoor heat exchanger 10 is decompressed by the expansion valve 14, becomes a low-temperature two-phase refrigerant, and flows into the heat medium heat exchanger 15. The low-temperature two-phase refrigerant that flows into the heat medium heat exchanger 15 exchanges heat with the heat medium circulating in the heat medium circuit B, absorbs heat from the heat medium, and vaporizes under low pressure before flowing out of the heat medium heat exchanger 15. The gaseous refrigerant that flows out of the heat medium heat exchanger 15 is drawn into the compressor 8 and compressed again. By repeating these operations, the refrigeration cycle of the refrigeration cycle apparatus 1 is realized.

[0039] Next, the flow of the heat medium in the heat medium circuit B will be described. The heat medium circulates through the heat medium circuit B by driving the pump 20. The heat medium that flows into the heat medium heat exchanger 15 exchanges heat with the refrigerant circulating through the refrigerant circuit A, dissipates heat, is cooled, and flows out of the heat medium heat exchanger 15. The heat medium that flows out of the heat medium heat exchanger 15 flows into the indoor heat exchanger 13. The heat medium that flows into the indoor heat exchanger 13 exchanges heat with indoor air from the indoor blower 13a, cooling the indoor air. The cooled indoor air is supplied to the indoor space by the indoor blower 13a to cool the room. After exchanging heat with the indoor air, the heat medium flows back into the heat medium heat exchanger 15.

[0040] (Outline of Control) In order to maintain a stable air conditioning capacity during cooling operation under the constraint of not freezing the heat medium, the refrigeration cycle device 1 performs the following control. Here, an outline of the control will be described.

[0041] The refrigeration cycle device 1 sets the degree of superheat SH of the refrigerant in the heat medium heat exchanger 15 functioning as an evaporator to a target value SH of the degree of superheat SH stored in advance in the storage device 73. ｔｇｔ The opening degree of the expansion valve 14 (hereinafter referred to as the cooling capacity maintaining opening degree) U ＳＨ Calculate the target superheat value SH ｔｇｔ The target superheat value SH may be set to any value between 1°C and 30°C, or may be a value calculated from the room temperature and the target room temperature value. ｔｇｔ The range in which the superheat target value SH is set varies depending on the refrigerant. ｔｇｔ Load adjustment is performed by

[0042] The refrigeration cycle device 1 also has a heat medium temperature T ｈｍ is set to the heat medium temperature lower limit value T ｆｒ The opening degree of the expansion valve 14 (hereinafter referred to as the anti-freeze opening degree) U ｆｒ The heat transfer medium temperature T ｈｍ is the temperature detected by the heat medium outlet temperature detection unit 17. ｈｍ The lower limit value T of the heat medium temperature may be the lower of the temperature detected by the heat medium outlet temperature detection unit 17 and the temperature detected by the heat medium inlet temperature detection unit 16. ｆｒ is set to a temperature at which the heat transfer medium does not freeze, and is set to a temperature above the freezing temperature. ｆｒ When the heat medium is water, the temperature is set to, for example, between 0°C and 5°C.

[0043] Here, the degree of superheat SH decreases by increasing the opening degree U of the expansion valve 14 (hereinafter referred to as the expansion valve opening degree), and increases by decreasing the expansion valve opening degree U. ｈｍWhen the expansion valve opening degree U is increased, the flow rate of the refrigerant passing through the heat medium heat exchanger 15 increases, and the cooling capacity increases, so that the opening degree decreases, and when the expansion valve opening degree U is decreased, the opening degree increases. ｆｒ Therefore, the refrigeration cycle device 1 prioritizes preventing the heat medium from freezing, and opens the expansion valve 14 at the cooling capacity maintenance opening degree U ＳＨ and anti-freeze opening U ｆｒ The valve is controlled to the smaller opening.

[0044] By the above control, the refrigeration cycle device 1 is ｆｒ Cooling capacity maintenance opening degree U ＳＨ If the expansion valve opening degree U is smaller than the anti-freeze opening degree U ｆｒ The heat transfer medium temperature T ｈｍ The lower limit of the heat transfer medium temperature T ｆｒ This can be matched to prevent freezing.

[0045] In addition, the refrigeration cycle device 1 has a cooling capacity maintenance opening degree U ＳＨ is the anti-freeze opening U ｆｒ If the expansion valve opening degree U is smaller than the cooling capacity maintenance opening degree U ＳＨ The superheat degree SH is controlled to the superheat degree target value SH ｔｇｔ This allows the temperature to be matched to the desired value, thereby maintaining stable air conditioning capacity.

[0046] The above control is repeatedly performed at each sampling time. As a result, the refrigeration cycle device 1 controls the superheat degree SH to the target superheat degree value SH ｔｇｔ and the heat transfer medium temperature T ｈｍ The lower limit of the heat transfer medium temperature T ｆｒ The control to follow the freezing prevention opening U ｆｒ and cooling capacity maintenance opening degree U ＳＨ This is selectively performed depending on the calculation result.

[0047] Next, a specific control configuration for carrying out the above control will be described.

[0048] Fig. 3 is a functional block diagram showing an example of a portion related to the opening degree control of the expansion valve 14 in the control processing device 71 during cooling operation of the refrigeration cycle apparatus 1 according to Embodiment 1. Fig. 4 is a block diagram showing the configuration of a superheat degree control unit 701 of the refrigeration cycle apparatus 1 according to Embodiment 1. Fig. 5 is a block diagram showing the configuration of an anti-freeze control unit 702 of the refrigeration cycle apparatus 1 according to Embodiment 1. As shown in Fig. 3, the control processing device 71 includes a superheat degree calculation unit 700a, a superheat degree control unit 701, an anti-freeze control unit 702, and a selection unit 703.

[0049] The superheat degree calculation unit 700a calculates the degree of superheat SH in the refrigerant flow direction during cooling operation based on the refrigerant-side heat medium heat exchanger inlet temperature detected by the liquid-side temperature detection unit 18 and the refrigerant-side heat medium heat exchanger outlet temperature detected by the gas-side temperature detection unit 19. The superheat degree calculation unit 700a may calculate the degree of superheat SH based on the saturation temperature (evaporation temperature) converted from the pressure detected by a pressure detection unit (pressure gauge) (not shown) attached near the gas-side temperature detection unit 19 and the refrigerant-side heat medium heat exchanger outlet temperature detected by the gas-side temperature detection unit 19.

[0050] The superheat degree control unit 701 compares the superheat degree SH calculated by the superheat degree calculation unit 700a with the target superheat degree SH ｔｇｔ Based on this, the superheat degree SH is set to the superheat degree target value SH ｔｇｔ Cooling capacity maintenance opening degree U to follow ＳＨ The superheat degree control unit 701 calculates the calculated cooling capacity maintenance opening degree U ＳＨ to the selection unit 703. As shown in Fig. 4, the superheat degree control unit 701 is configured with a controller 711 including at least an integrator 701a. In this example, the superheat degree control unit 701 is configured with a PI controller including a proportional unit 701b and the integrator 701a.

[0051] The superheat degree control unit 701 calculates the superheat degree SH and the target superheat degree value SH as shown in equation (1). ｔｇｔ The superheat degree control unit 701 calculates the superheat degree deviation ΔSH between the target superheat degree value SH and the superheat degree deviation ΔSH using the superheat degree deviation ΔSH as shown in Equation (2). ｔｇｔ The cooling capacity maintaining opening degree U of the expansion valve 14 for following ＳＨ Calculate.

[0052]

[0053]

[0054] Here, K ＰＳＨ is the proportional gain of the PI controller, and K ＩＳＨ is the integral gain of the PI controller.

[0055] The superheat control unit 701 may be configured with a discrete position or speed PI controller. The superheat control unit 701 is not limited to a PI controller, but may be configured with a controller that performs feedback control including an integrator, such as PID control or model predictive control. The integrator 701a may have upper and lower limit values ​​or anti-reset windup that stop integration, as shown in FIG. 4. Note that U in FIG. 4 denotes the final output after selective control or upper and lower limit selection. The anti-reset windup shown in FIG. 4 is an example and is not limited to the one shown.

[0056] The anti-freeze control unit 702 determines the heat medium temperature T ｈｍ and the lower limit of the heat transfer medium temperature T ｆｒ Based on this, the heat transfer medium temperature T ｈｍ The lower limit of the heat transfer medium temperature T ｆｒ The freeze prevention opening degree U of the expansion valve 14 for following ｆｒ Calculate the heat transfer medium temperature T ｈｍ may be the temperature detected by the heat medium outlet temperature detection unit 17 as described above, or may be the lower temperature of the temperature detected by the heat medium outlet temperature detection unit 17 and the temperature detected by the heat medium inlet temperature detection unit 16. ｆｒ to the selection unit 703. As shown in Fig. 5, the anti-freezing control unit 702 is configured with a controller 712 including at least an integrator 702a. In this example, the anti-freezing control unit 702 is configured with a PI controller including a proportional unit 702b and an integrator 702a.

[0057] The anti-freeze control unit 702 calculates the heat medium temperature T ｈｍ and the lower limit of the heat transfer medium temperature T ｆｒ Heat medium temperature deviation ΔT ｆｒThe anti-freezing control unit 702 calculates the heat medium temperature deviation ΔT as shown in equation (4). ｆｒ Using the heat transfer medium temperature T ｈｍ The lower limit of the heat transfer medium temperature T ｆｒ The freeze prevention opening degree U of the expansion valve 14 for following ｆｒ Calculate.

[0058]

[0059]

[0060] Here, K ｐｆｒ is the negative proportional gain of the PI controller, and K Ｉｆｒ is the negative integral gain of the PI controller.

[0061] The anti-freeze control unit 702 may be configured with a discrete position or velocity PI controller. Furthermore, the anti-freeze control unit 702 is not limited to PI control, and may be configured with a controller that performs feedback control including an integrator, such as PID control or model predictive control. The integrator 702a may have upper and lower limit values ​​or anti-reset windup that stop integration, as shown in FIG. 5. Note that U in FIG. 5 denotes the final output after selective control or upper and lower limit selection. The anti-reset windup shown in FIG. 5 is merely an example and is not limited to the one shown.

[0062] The selection unit 703 selects the cooling capacity maintenance opening degree U output from the superheat degree control unit 701. ＳＨ and the freeze prevention opening degree U output from the freeze prevention control unit 702. ｆｒ The control device 7 controls the expansion valve 14 to have the expansion valve opening output from the selection unit 703.

[0063] In the illustrated example, the refrigeration cycle apparatus 1 is configured such that the heat medium heat exchange unit control device 7 has a control processing device 71 and is equipped with a superheat degree control unit 701, an anti-freeze control unit 702, and a selection unit 703. However, the configuration is not limited to this. The refrigeration cycle apparatus 1 may also be configured such that the outdoor unit control device 5 or the indoor unit control device 6 has a control processing device 71 and is equipped with a superheat degree control unit 701, an anti-freeze control unit 702, and a selection unit 703.

[0064] 6 is a flowchart of the expansion valve opening control method in the refrigeration cycle apparatus 1 according to the first embodiment. ＳＨ (Step S1), and the freezing prevention opening degree U ｆｒ (Step S2). ＳＨ and anti-freeze opening U ｆｒ In other words, the control processing device 71 selects the smaller of U ＳＨ ≦U ｆｒ In this case, the cooling capacity maintenance opening degree U ＳＨ (Step S4), ＳＨ >U ｆｒ In this case, the freeze prevention opening U ｆｒ (Step S5). Then, the control processing device 71 controls the expansion valve 14 to have the selected opening degree (Step S6).

[0065] Next, a specific example of control will be described with reference to FIGS.

[0066] FIG. 7 shows the relationship between the degree of superheat SH and the heat medium temperature T ｈｍ 8 is a time chart showing the relationship between the anti-freeze opening U of the refrigeration cycle device 1 according to the first embodiment and the expansion valve opening U. ｆｒ and cooling capacity maintenance opening degree U ＳＨ 7 is a diagram showing the calculation results of the superheat degree SH at time t0. ｔｇｔ is higher than the heat transfer medium temperature T ｈｍ is the lower limit of the heat transfer medium temperature T ｆｒIn this state, the control processing device 71 reduces the superheat degree SH to the target superheat degree SH. ｔｇｔ and the heat transfer medium temperature T ｈｍ Lower the heat transfer medium temperature lower limit T ｆｒ The expansion valve 14 is controlled so that the pressure approaches the pressure.

[0067] As shown in FIG. 8, the cooling capacity maintenance opening degree U ＳＨ and anti-freeze opening U ｆｒ The calculation results are different, and the cooling capacity maintenance opening U ＳＨ is the anti-freeze opening U ｆｒ The degree of superheat SH decreases by increasing the expansion valve opening, and the heat medium temperature T ｈｍ Therefore, as shown in FIG. 8, the calculated opening degree is reduced by increasing the opening degree of the expansion valve. ＳＨ and anti-freeze opening U ｆｒ Here, the cooling capacity maintenance opening degree U ＳＨ is the anti-freeze opening U ｆｒ The anti-freeze opening U ｆｒ is the cooling capacity maintenance opening degree U ＳＨ It is rising more slowly than

[0068] As shown in FIG. 8, the calculated opening degree is the cooling capacity maintenance opening degree U from time t0 to time t1. ＳＨ is the anti-freeze opening U ｆｒ The calculated opening is smaller than the anti-freeze opening U ｆｒ and cooling capacity maintenance opening degree U ＳＨ and thereafter, the anti-freeze opening U ｆｒ Cooling capacity maintenance opening degree U ＳＨ Therefore, as shown in FIG. 7, the control processing device 71 sets the expansion valve opening degree U to the cooling capacity maintenance opening degree U from time t0 to time t1. ＳＨ After time t1, the freeze prevention opening U ｆｒ Select .

[0069] Between time t0 and time t1, the cooling capacity maintenance opening degree U ＳＨSince the superheat degree SH is increasing, as shown in FIG. 7, the superheat degree SH is decreasing, and the target superheat degree SH ｔｇｔ As the temperature approaches the heat transfer medium temperature T ｈｍ decreases, and the lower limit of the heat transfer medium temperature T ｆｒ At time t1, the expansion valve opening degree U approaches the cooling capacity maintenance opening degree U ＳＨ From anti-freeze opening U ｆｒ , the superheat degree SH is changed to the target superheat degree SH as shown in FIG. ｔｇｔ Although it does not match the superheat target value SH ｔｇｔ On the other hand, at time t1, the expansion valve opening degree U is kept close to the cooling capacity maintenance opening degree U ＳＨ From anti-freeze opening U ｆｒ , the heat medium temperature T ｈｍ The lower limit of the heat transfer medium temperature T ｆｒ After matching, the heat transfer medium temperature lower limit T ｆｒ As shown in FIG. 8, the cooling capacity maintenance opening degree U ＳＨ converges to the anti-reset windup convergence value at time t1 or later.

[0070] By the above control, the refrigeration cycle device 1 maintains the heat medium temperature T ｈｍ is the lower limit of the heat transfer medium temperature T ｆｒ The superheat degree SH is prevented from falling below the target superheat degree SH to suppress freezing of the heat medium. ｔｇｔ In other words, the refrigeration cycle device 1 can maintain a stable air conditioning capacity under the constraint that the heat medium is not frozen. ＳＨ and anti-freeze opening U ｆｒ When the heat medium temperature T ｈｍ is the lower limit of the heat transfer medium temperature T ｆｒ The superheat degree SH is prevented from falling below the target superheat degree SH to suppress freezing of the heat medium. ｔｇｔ By maintaining a state that matches the temperature, stable air conditioning control can be performed.

[0071] [Effects of the Refrigeration Cycle Apparatus 1] The refrigeration cycle apparatus 1 of the first embodiment includes a refrigerant circuit A in which the expansion valve 14 whose opening degree can be changed and the heat medium heat exchanger 15 are connected by piping, and in which a refrigerant circulates, and a heat medium circuit B in which the refrigerant in the refrigerant circuit A and the heat medium that exchanges heat in the heat medium heat exchanger 15 circulate. ＳＨ and anti-freeze opening U ｆｒ and a control processing device 71 that controls the opening degree of the expansion valve 14 so that the opening degree becomes the smaller of the cooling capacity maintenance opening degree U. ＳＨ is a value for setting the superheat degree SH of the refrigerant at the outlet of the heat medium heat exchanger 15, which functions as an evaporator during cooling operation, to a preset superheat degree target value SH ｔｇｔ The opening degree of the expansion valve 14 is set to match the freezing prevention opening degree U ｆｒ is a temperature above the freezing point of the heat medium, and is set to a predetermined lower limit value T ｆｒ This is the opening degree of the expansion valve 14 to match the above.

[0072] With the above-described configuration, the refrigeration cycle device 1 can maintain a stable air conditioning capacity under the constraint that the heat medium is not frozen.

[0073] The refrigeration cycle device 1 detects the freezing prevention opening degree U ｆｒ and cooling capacity maintenance opening degree U ＳＨ Here, if the refrigeration cycle device 1 selects the smaller one of the above, the freeze prevention opening degree U ｆｒ and cooling capacity maintenance opening degree U ＳＨ When the control is performed such that the smaller and larger of these values ​​are alternately selected, the following inconvenience occurs: the operation of the expansion valve 14 becomes discontinuous, and the fluctuations in the heat medium temperature become large, resulting in unstable operation. ｆｒ and cooling capacity maintenance opening degree U ＳＨ Since the smaller of these two is continuously selected, the expansion valve 14 operates continuously, which makes it possible to suppress fluctuations in the heat medium temperature and ensure stable operation.

[0074] In addition, in the refrigeration cycle device 1, the controller constituting the superheat degree control unit 701 and the controller constituting the anti-freeze control unit 702 each include at least an integrator, so that the superheat degree SH and the heat medium temperature T ｈｍ and the control values ​​can be made to match the target values. The refrigeration cycle apparatus 1 is not limited to a configuration in which both the controller constituting the superheat degree control unit 701 and the controller constituting the anti-freeze control unit 702 include integrators, and at least one of the controllers may include an integrator.

[0075] Embodiment 2 Embodiment 2 relates to control of the opening degree of the expansion valve 14 during heating operation. The following description will focus on the configuration of Embodiment 2 that is different from Embodiment 1, and the configuration not described in Embodiment 2 is the same as that of Embodiment 1.

[0076] 9 is a schematic diagram showing an example of the configuration of a refrigeration cycle apparatus 1 according to a second embodiment. The refrigeration cycle apparatus 1 according to the second embodiment further includes a refrigerant pressure detection unit 21 in addition to the components of the refrigeration cycle apparatus 1 according to the first embodiment shown in FIG. 1. The refrigerant pressure detection unit 21 is disposed in the heat medium heat exchange unit 4 and detects the pressure of the refrigerant flowing into the heat medium heat exchanger 15 in the refrigerant circuit A during heating operation. The refrigerant pressure detection unit 21 is composed of a pressure sensor. The detection result detected by the refrigerant pressure detection unit 21 is input to the heat medium heat exchange unit control device 7.

[0077] Fig. 10 is a control block diagram showing the electrical configuration of the heat medium heat exchange unit 4 of Fig. 9. As shown in Fig. 10, the heat medium heat exchange unit control device 7 is connected to a heat medium inlet temperature detection unit 16, a heat medium outlet temperature detection unit 17, a liquid side temperature detection unit 18, a gas side temperature detection unit 19, and a refrigerant pressure detection unit 21. The heat medium heat exchange unit control device 7 is configured to receive the detection results of these detection units.

[0078] In the heating operation, the control processing device 71 of the second embodiment maintains stable air conditioning capacity under the constraint that the heat medium does not exceed the guaranteed operating temperature of the pump 20. Details of this operation will be described later.

[0079] (Heating Operation) The heating operation of the refrigeration cycle apparatus 1 will be described with reference to Fig. 9. In the heating operation, the four-way valve 9 is switched to the state shown by the solid line in Fig. 9 .

[0080] First, we will explain the flow of refrigerant in refrigerant circuit A. The gaseous refrigerant, which has been compressed by compressor 8 to a high temperature and pressure, is discharged from the discharge port of compressor 8 and flows into heat medium heat exchanger 15. The gaseous refrigerant that has flowed into heat medium heat exchanger 15 exchanges heat with the heat medium in heat medium circuit B, dissipates heat to the heat medium, and is liquefied under high pressure before flowing out of heat medium heat exchanger 15.

[0081] The liquid refrigerant flowing out of the heat medium heat exchange unit 4 is decompressed by the expansion valve 14, becomes a low-temperature two-phase refrigerant, and flows into the outdoor heat exchanger 10. The low-temperature two-phase refrigerant that has flowed into the outdoor heat exchanger 10 exchanges heat with outdoor air from the outdoor blower 10a, absorbs heat from the outdoor air, and vaporizes under low pressure, before flowing out of the outdoor heat exchanger 10. The gaseous refrigerant that has flowed out of the outdoor heat exchanger 10 is drawn into the compressor 8 and compressed again. By repeating these operations, the refrigeration cycle of the refrigeration cycle apparatus 1 is realized.

[0082] Next, the flow of the heat medium in the heat medium circuit B will be described. The heat medium circulates through the heat medium circuit B by driving the pump 20. The heat medium that flows into the heat medium heat exchanger 15 exchanges heat with the refrigerant circulating through the refrigerant circuit A, absorbs heat, is heated, and flows out of the heat medium heat exchanger 15. The heat medium that flows out of the heat medium heat exchanger 15 flows into the indoor heat exchanger 13. The heat medium that flows into the indoor heat exchanger 13 exchanges heat with indoor air from the indoor blower 13a, heating the indoor air. The heated indoor air is supplied to the indoor space by the indoor blower 13a, heating the room. After exchanging heat with the indoor air, the heat medium flows back into the heat medium heat exchanger 15.

[0083] (Outline of Control) In heating operation, the refrigeration cycle apparatus 1 performs the following control to maintain stable air conditioning capacity under the constraint that the heat medium does not exceed the guaranteed operating temperature of the pump 20. Here, an outline of the control will be described.

[0084] The refrigeration cycle device 1 calculates the degree of subcooling SC of the refrigerant in the heat medium heat exchanger 15 functioning as a condenser by setting the degree of subcooling target value SC ｔｇｔ The opening degree of the expansion valve 14 for matching with the above (hereinafter referred to as the heating capacity maintaining opening degree) U ＳＣ The target subcooling value SC is calculated. ｔｇｔ The target subcooling degree SC may be set to any value between 1°C and 30°C, or may be a value calculated from the room temperature and the target room temperature. ｔｇｔ The range in which the target degree of subcooling value SC is set varies depending on the refrigerant. ｔｇｔ Load adjustment is performed by

[0085] The refrigeration cycle device 1 also has a heat medium temperature T ｈｍ is set to the heat medium temperature upper limit value T ｅｘ The opening degree of the expansion valve 14 (hereinafter referred to as the excessive rise prevention opening degree) U ｅｘ The heat transfer medium temperature T ｈｍ is the temperature detected by the heat medium outlet temperature detection unit 17. ｈｍ The upper limit of the heat medium temperature T may be the lower of the temperature detected by the heat medium outlet temperature detector 17 and the temperature detected by the heat medium inlet temperature detector 16. ｅｘ is set to the guaranteed operating temperature of the pump 20 provided in the heat medium circuit B, that is, the upper limit temperature at which the operation of the pump 20 is guaranteed.

[0086] Here, the degree of subcooling SC decreases when the expansion valve opening degree U of the expansion valve 14 increases, and increases when the expansion valve opening degree U decreases. ｈｍ increases by increasing the expansion valve opening degree U, and decreases by decreasing the expansion valve opening degree U. ｅｘ If the opening degree is larger than the heating capacity maintenance opening degree U, the temperature of the heat medium may become too high above the guaranteed operating temperature of the pump 20, which may cause a breakdown of the pump 20. Therefore, the refrigeration cycle device 1 prioritizes preventing a breakdown of the pump 20, and opens the expansion valve 14 at the heating capacity maintenance opening degree U. ＳＣ and overheat prevention opening U ｅｘ The valve is controlled to the smaller opening.

[0087] By the above control, the refrigeration cycle device 1 is controlled to the excessive temperature rise prevention opening degree U ｅｘ Heating capacity maintenance opening degree U ＳＣ If the expansion valve opening degree U is smaller than the excessive rise prevention opening degree U ｅｘ The heat transfer medium temperature T ｈｍ The upper limit of the heat transfer medium temperature T ｅｘ This allows the refrigeration cycle apparatus 1 to prevent breakdown of the pump 20.

[0088] In addition, the refrigeration cycle device 1 has a heating capacity maintenance opening degree U ＳＣ is the overheat prevention opening U ｅｘ If the expansion valve opening degree U is smaller than the heating capacity maintenance opening degree U ＳＣ The degree of supercooling SC is controlled to the target value SC ｔｇｔ This allows the temperature to be matched to the desired value, thereby maintaining stable air conditioning capacity.

[0089] The above control is repeated at each sampling time, and the refrigeration cycle device 1 sets the degree of supercooling SC to the target value SC ｔｇｔ and the heat transfer medium temperature T ｈｍ The upper limit of the heat transfer medium temperature T ｅｘ The control to follow the excessive rise prevention opening U ｅｘ and heating capacity maintenance opening degree U ＳＣ This is selectively performed depending on the calculation result.

[0090] Next, a specific control configuration for carrying out the above control will be described.

[0091] Fig. 11 is a functional block diagram showing an example of a portion related to the opening degree control of the expansion valve 14 in the control processing device 71 during heating operation of the refrigeration cycle apparatus 1 according to Embodiment 2. Fig. 12 is a block diagram showing the configuration of a subcooling degree control unit 704 of the refrigeration cycle apparatus 1 according to Embodiment 2. Fig. 13 is a block diagram showing the configuration of an overheat prevention control unit 705 of the refrigeration cycle apparatus 1 according to Embodiment 2. As shown in Fig. 11 , the control processing device 71 includes a subcooling degree calculation unit 700b, a subcooling degree control unit 704, an overheat prevention control unit 705, and a selection unit 706.

[0092] The subcooling degree calculation unit 700b calculates the subcooling degree SC based on the refrigerant-side heat medium heat exchanger outlet temperature detected by the liquid-side temperature detection unit 18 in the refrigerant flow direction during heating operation and the condensing temperature obtained by converting the pressure detected by the refrigerant pressure detection unit 21 to a saturation value. The subcooling degree calculation unit 700b may calculate the subcooling degree SC based on the refrigerant outlet temperature detected by the liquid-side temperature detection unit 18 and the two-phase pipe temperature detected by a two-phase temperature detection unit (not shown). The two-phase temperature detection unit detects the temperature of the two-phase region in the heat exchanger (heat medium heat exchanger) functioning as a condenser.

[0093] The supercooling degree control unit 704 compares the supercooling degree SC calculated by the supercooling degree calculation unit 700b with the target supercooling degree SC ｔｇｔ Based on this, the degree of supercooling SC is set to the target value of the degree of supercooling SC ｔｇｔ Heating capacity maintenance opening degree U to follow ＳＣ The subcooling degree control unit 704 calculates the heating capacity maintenance opening degree U ＳＣ to the selection unit 706. As shown in Fig. 12, the subcooling degree control unit 704 is configured with a controller 713 including at least an integrator 704a. In this example, the subcooling degree control unit 704 is configured with a PI controller including a proportional unit 704b and an integrator 704a.

[0094] The subcooling degree control unit 704 calculates the subcooling degree SC and the target subcooling degree SC as shown in equation (5). ｔｇｔ The subcooling degree control unit 704 calculates the subcooling degree deviation ΔSC between the target subcooling degree SC and the subcooling degree deviation ΔSC using the subcooling degree deviation ΔSC as shown in equation (5). ｔｇｔ The heating capacity maintaining opening degree U of the expansion valve 14 for following ＳＣ Calculate.

[0095]

[0096]

[0097] Here, K ＰＳＣ is the proportional gain of the PI controller, and K ＩＳＣ is the integral gain of the PI controller.

[0098] The subcooling degree control unit 704 may be configured with a discrete position or velocity type PI controller. The subcooling degree control unit 704 is not limited to a PI controller, but may be configured with a controller that performs feedback control including an integrator, such as PID control or model predictive control. The integrator 704a may have upper and lower limit values ​​or anti-reset windup that stop integration, as shown in FIG. 12. Note that U in FIG. 12 is written to mean the final output after selective control or upper and lower limit selection. The anti-reset windup shown in FIG. 12 is an example and is not limited to the one shown.

[0099] The overheat prevention control unit 705 controls the heat medium temperature T ｈｍ and the upper limit of the heat transfer medium temperature T ｅｘ Based on this, the heat transfer medium temperature T ｈｍ The upper limit of the heat transfer medium temperature T ｅｘ The expansion valve 14 has an excessive rise prevention opening degree U ｅｘ The excessive rise prevention control unit 705 calculates the calculated excessive rise prevention opening U ｅｘ to the selection unit 706. As shown in Fig. 13, the overheat prevention control unit 705 is configured with a controller 714 including at least an integrator 705a. In this example, the overheat prevention control unit 705 is configured with a PI controller including a proportional unit 705b and an integrator 705a.

[0100] The overheat prevention control unit 705 calculates the heat medium temperature T ｈｍ and the upper limit of the heat transfer medium temperature T ｅｘ Heat medium temperature deviation ΔT ｅｘ The excessive temperature rise prevention control unit 705 calculates the heat medium temperature deviation ΔT as shown in equation (8). ｅｘ Using the heat transfer medium temperature T ｈｍ The upper limit of the heat transfer medium temperature T ｅｘ The expansion valve 14 has an excessive rise prevention opening degree U ｅｘ Calculate.

[0101]

[0102]

[0103] Here, K Ｐｅｘ is the negative proportional gain of the PI controller, and K Ｉｅｘis the negative integral gain of the PI controller.

[0104] The overheat prevention control unit 705 may be configured with a discrete position or speed PI controller. Furthermore, the overheat prevention control unit 705 is not limited to PI control, and may be configured with a controller that performs feedback control including an integrator, such as PID control or model predictive control. The integrator 705a may have upper and lower limit values ​​or anti-reset windup that stop integration, as shown in FIG. 13. Note that U in FIG. 13 denotes the final output after selective control or upper and lower limit selection. The anti-reset windup shown in FIG. 13 is merely an example and is not limited to the one shown.

[0105] The selection unit 706 selects the heating capacity maintenance opening degree U output from the subcooling degree control unit 704. ＳＣ and the excessive rise prevention opening U output from the excessive rise prevention control unit 705 ｅｘ The control device 7 controls the expansion valve 14 to have the expansion valve opening output from the selection unit 706.

[0106] In the illustrated example, the refrigeration cycle apparatus 1 is configured such that the heat medium heat exchange unit control device 7 has the control processing device 71 and is equipped with the subcooling degree control unit 704, the overheat prevention control unit 705, and the selection unit 706, but is not limited to this configuration. The refrigeration cycle apparatus 1 may also be configured such that the outdoor unit control device 5 or the indoor unit control device 6 has the control processing device 71 and is equipped with the subcooling degree control unit 704, the overheat prevention control unit 705, and the selection unit 706.

[0107] 14 is a flowchart of the expansion valve opening control method in the refrigeration cycle apparatus 1 according to the second embodiment. ＳＣ (Step S11), and the excessive rise prevention opening U ｅｘ (Step S12). ＳＣ and overheat prevention opening U ｅｘ In other words, the control processing device 71 selects the smaller of UＳＣ ≦U ｅｘ In this case, the heating capacity maintenance opening degree U ＳＣ (Step S14), ＳＣ >U ｅｘ In this case, the overheat prevention opening U ｅｘ (Step S15). The control processing device 71 controls the expansion valve 14 to have the selected opening degree (Step S16).

[0108] Next, a specific example of control will be described with reference to FIGS.

[0109] FIG. 15 is a graph showing the relationship between the degree of subcooling SC and the heat medium temperature T ｈｍ 16 is a time chart showing the relationship between the expansion valve opening degree U and the excessive temperature rise prevention opening degree U in the refrigeration cycle device 1 according to the second embodiment. ｅｘ and heating capacity maintenance opening degree U ＳＣ 15 is a diagram showing the calculation results of the degree of supercooling SC at time t0. ｔｇｔ is higher than the heat transfer medium temperature T ｈｍ is the upper limit of the heat transfer medium temperature T ｅｘ In this state, the control processing device 71 reduces the degree of supercooling SC to the target value SC ｔｇｔ and the heat transfer medium temperature T ｈｍ Increase the heat transfer medium temperature upper limit T ｅｘ The expansion valve 14 is controlled so that the pressure approaches the pressure.

[0110] As shown in FIG. 15, the heating capacity maintenance opening degree U ＳＣ and overheat prevention opening U ｅｘ The calculation results are different, and the heating capacity maintenance opening U ＳＣ is the overheat prevention opening U ｅｘ The degree of subcooling SC decreases by increasing the expansion valve opening, and the heat medium temperature T ｈｍ 16, the calculated opening degree is increased by increasing the opening degree of the expansion valve. ＳＣ and overheat prevention opening U ｅｘ Here, the heating capacity maintenance opening degree U ＳＣis the overheat prevention opening U ｅｘ The excessive rise prevention opening U ｅｘ is the heating capacity maintenance opening degree U ＳＣ It is rising more slowly than

[0111] As shown in FIG. 16, the calculated opening degree is the heating capacity maintenance opening degree U from time t0 to time t1. ＳＣ is the overheat prevention opening U ｅｘ The calculated opening is smaller than the excessive rise prevention opening U ｅｘ and heating capacity maintenance opening U ＳＣ and thereafter, the overheat prevention opening U ｅｘ Heating capacity maintenance opening degree U ＳＣ Therefore, as shown in FIG. 15, the control processing device 71 sets the expansion valve opening degree U to the heating capacity maintenance opening degree U from time t0 to time t1. ＳＣ After time t1, the excessive rise prevention opening U ｅｘ Select .

[0112] Between time t0 and time t1, the heating capacity maintenance opening degree U ＳＣ Since the target value of the degree of supercooling SC is increasing, the degree of supercooling SC decreases as shown in FIG. ｔｇｔ As the temperature approaches the heat transfer medium temperature T ｈｍ rises, and the upper limit of the heat transfer medium temperature T ｅｘ At time t1, the expansion valve opening degree U approaches the heating capacity maintenance opening degree U ＳＣ to overheat prevention opening U ｅｘ , the degree of supercooling SC is changed to the target value of the degree of supercooling SC as shown in FIG. ｔｇｔ Although it does not match the target subcooling value SC ｔｇｔ On the other hand, at time t1, the expansion valve opening degree U is kept close to the heating capacity maintenance opening degree U ＳＣ to overheat prevention opening U ｅｘ , the heat medium temperature T ｈｍ The upper limit of the heat transfer medium temperature T ｅｘ After matching, the heat transfer medium temperature upper limit T ｅｘ As shown in FIG. 16, the heating capacity maintenance opening degree U ＳＣconverges to the anti-reset windup convergence value at time t1 or later.

[0113] By the above control, the refrigeration cycle device 1 maintains the heat medium temperature T ｈｍ is the upper limit of the heat transfer medium temperature T ｅｘ , and the failure of the pump 20 is suppressed while the degree of supercooling SC is prevented from exceeding the target value of the degree of supercooling SC ｔｇｔ In other words, the refrigeration cycle device 1 can maintain a stable air conditioning capacity under the constraint that the heat medium does not exceed the guaranteed operating temperature of the pump 20. ＳＣ and overheat prevention opening U ｅｘ When the heat medium temperature T ｈｍ is the upper limit of the heat transfer medium temperature T ｅｘ , and the failure of the pump 20 is suppressed while the degree of supercooling SC is prevented from exceeding the target value of the degree of supercooling SC ｔｇｔ By maintaining a state that matches the temperature, stable air conditioning control can be performed.

[0114] [Effects of the Refrigeration Cycle Apparatus 1] The refrigeration cycle apparatus 1 of the second embodiment, like the first embodiment, can maintain a stable air conditioning capacity under the constraint that the heat medium is not frozen during cooling operation, and can also provide the following effects: The refrigeration cycle apparatus 1 of the second embodiment can maintain a stable air conditioning capacity under the constraint that the heat medium does not exceed the guaranteed operating temperature of the pump 20 during heating operation.

[0115] In addition, the refrigeration cycle device 1 adjusts the overheat prevention opening U ｅｘ and heating capacity maintenance opening U ＳＣ Here, if the refrigeration cycle device 1 selects the smaller one of the above, the overheat prevention opening U ｅｘ and heating capacity maintenance opening U ＳＣ When the control is performed such that the smaller and larger of the two is alternately selected, the following inconvenience occurs: the operation of the expansion valve 14 becomes discontinuous, and the fluctuations in the heat medium temperature become large, resulting in unstable operation. ｅｘand heating capacity maintenance opening U ＳＣ Since the smaller of these is selected, the operation of the expansion valve 14 becomes continuous, fluctuations in the heat medium temperature can be suppressed, and stable operation can be achieved.

[0116] In addition, in the refrigeration cycle device 1, the controller constituting the supercooling degree control unit 704 and the controller constituting the overheat prevention control unit 705 include at least an integrator, so that the supercooling degree SC and the heat medium temperature T ｈｍ and the like can be made to coincide with their respective target values. The refrigeration cycle apparatus 1 is not limited to a configuration in which both the controller constituting the supercooling degree control unit 704 and the controller constituting the overheat prevention control unit 705 include integrators, and at least one of them may include an integrator.

[0117] REFRIGERATION CYCLE DEVICE, 2 OUTDOOR UNIT, 3 INDOOR UNIT, 4 HEAT TRANSPORT COMPONENT HEAT EXCHANGE UNIT, 5 OUTDOOR UNIT CONTROL DEVICE, 6 INDOOR UNIT CONTROL DEVICE, 7 HEAT TRANSPORT COMPONENT HEAT EXCHANGE UNIT CONTROL DEVICE, 8 COMPRESSOR, 9 FOUR-WAY VALVE, 10 OUTDOOR HEAT EXCHANGER, 10a OUTDOOR BLOWER, 12 INDOOR TEMPERATURE DETECTION DEVICE, 13 INDOOR HEAT EXCHANGER, 13a INDOOR BLOWER, 14 EXPANSION VALVE, 15 HEAT TRANSPORT COMPONENT HEAT EXCHANGER, 16 HEAT TRANSPORT COMPONENT INlet TEMPERATURE DETECTION DEVICE, 17 HEAT TRANSPORT COMPONENT EXCHANGE SYSTEM, 18 LIQUID SIDE TEMPERATURE DETECTION DEVICE, 19 GAS SIDE TEMPERATURE DETECTION DEVICE, 20 PUMP, 21 REFRIGERANTE ... Anti-freeze control unit, 702a integrator, 702b proportional unit, 703 selection unit, 704 subcooling degree control unit, 704a integrator, 704b proportional unit, 705 overheat prevention control unit, 705a integrator, 705b proportional unit, 706 selection unit, 711 controller, 712 controller, 713 controller, 714 controller, A refrigerant circuit, B heat medium circuit.

Claims

1. A refrigeration cycle device comprising: a refrigerant circuit in which a refrigerant circulates, and an expansion valve and a heat medium heat exchanger whose opening is changeable are connected by piping; a heat medium circuit in which the refrigerant in the refrigerant circuit and a heat medium that exchanges heat in the heat medium heat exchanger circulate; and a control processing device that controls the opening of the expansion valve to the smaller of: a cooling capacity maintenance opening, which is the opening of the expansion valve for making the degree of superheat of the refrigerant at the outlet of the heat medium heat exchanger, which functions as an evaporator during cooling operation, equal to a predetermined target superheat value; and a freeze prevention opening, which is the opening of the expansion valve for making the temperature of the heat medium equal to a predetermined lower limit of the heat medium temperature that is above the freezing temperature of the heat medium.

2. The refrigeration cycle device according to claim 1, wherein the control processing device comprises a superheat control unit that calculates the cooling capacity maintenance opening degree and an anti-freeze control unit that calculates the anti-freeze opening degree, and at least one of the superheat control unit and the anti-freeze control unit is constituted by a controller including at least an integrator.

3. A refrigeration cycle device according to claim 1 or claim 2, wherein the heat medium circuit has a pump that circulates the heat medium through the heat medium circuit, and the control processing device controls the opening of the expansion valve to the smaller of: a heating capacity maintenance opening, which is the opening of the expansion valve for making the degree of subcooling of the refrigerant at the outlet of the heat medium heat exchanger that functions as a condenser during heating operation coincide with a preset subcooling target value; and an overheat prevention opening, which is the opening of the expansion valve for making the temperature of the heat medium coincide with a preset heat medium temperature upper limit value, which is the upper limit temperature at which operation of the pump is guaranteed.

4. The refrigeration cycle device according to claim 3, wherein the control processing device comprises a supercooling degree control unit that calculates the heating capacity maintenance opening degree, and an overheat prevention control unit that calculates the overheat prevention opening degree, and at least one of the supercooling degree control unit and the overheat prevention control unit is constituted by a controller including at least an integrator.

5. A method for controlling an expansion valve in a refrigeration cycle device, in which an expansion valve with a changeable opening and a heat medium heat exchanger are connected by piping, the method comprising: a refrigerant circuit in which a refrigerant circulates; and a heat medium circuit in which a heat medium that exchanges heat with the refrigerant circulates, the refrigerant in the refrigerant circuit and the heat medium in the heat medium circuit exchange heat in the heat medium heat exchanger, the method comprising the steps of: calculating a cooling capacity maintenance opening, which is the opening of the expansion valve for making the superheat of the refrigerant at the outlet of the heat medium heat exchanger, which functions as an evaporator during cooling operation, equal to a predetermined target superheat value; calculating an anti-freeze opening, which is the opening of the expansion valve for making the temperature of the heat medium equal to a predetermined lower limit of the heat medium temperature that is above the freezing temperature of the heat medium; selecting the smaller of the calculated cooling capacity maintenance opening and the anti-freeze opening; and controlling the opening of the expansion valve to achieve the selected opening.

6. A method for controlling a refrigeration cycle device according to claim 5, comprising the steps of: calculating a heating capacity maintenance opening, which is the opening of the expansion valve for making the degree of subcooling of the refrigerant at the outlet of the heat medium heat exchanger, which functions as a condenser during heating operation, equal to a predetermined target value for the degree of subcooling; calculating an overheat prevention opening, which is the opening of the expansion valve for making the temperature of the heat medium equal to a predetermined upper limit value of the heat medium temperature, which is an upper limit temperature at which operation of a pump provided in the heat medium circuit is guaranteed; selecting the smaller of the calculated heating capacity maintenance opening and the overheat prevention opening; and controlling the opening of the expansion valve to achieve the selected opening.

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