EP4030115A1

EP4030115A1 - Outdoor unit and refrigeration cycle device

Info

Publication number: EP4030115A1
Application number: EP19944675.8A
Authority: EP
Inventors: Tomotaka Ishikawa; Yusuke Arii; Motoshi HAYASAKA
Original assignee: Mitsubishi Electric Corp
Current assignee: Mitsubishi Electric Corp
Priority date: 2019-09-09
Filing date: 2019-09-09
Publication date: 2022-07-20
Anticipated expiration: 2039-09-09
Also published as: EP4030115A4; FI4030115T3; JP7154426B2; ES2964740T3; WO2021048899A1; EP4030115B1; CN114341568A; DK4030115T3; CN114341568B; JPWO2021048899A1

Abstract

An injection circuit is configured to return part of refrigerant on an outlet side of a condenser (20) to a compressor (10) without passing through a load unit (3). An expansion valve (70) is provided on a pipe branched from the outlet side of the condenser (20). A receiver (71) is provided on a low-pressure side of the expansion valve (70) and configured to accumulate refrigerant in a gas-liquid two-phase state. A flow control valve (72) is provided downstream of the receiver (71). When a pressure of the refrigerant output from the compressor (10) exceeds a threshold value, a controller (100) increases a degree of opening of the expansion valve (70) and increases a gas-flow ratio of refrigerant returned from the receiver (71) to the compressor (10) by adjusting a degree of opening of the flow control valve (72), more than when the pressure is equal to or less than the threshold value.

Description

TECHNICAL FIELD

The present disclosure relates to an outdoor unit of a refrigeration cycle apparatus, and a refrigeration cycle apparatus including the outdoor unit.

BACKGROUND ART

There is known a refrigeration cycle apparatus including an injection circuit configured to return part of refrigerant on the outlet side of a condenser to a compressor without passing through a decompressing apparatus and an evaporator. For example, Japanese Utility Model Laying-Open No. S59-175961 (PTL 1) discloses an air conditioner (refrigeration cycle apparatus) including a release circuit as the above-described injection circuit. The release circuit includes a release valve, an absorber tank (receiver) provided on the low-pressure side of the release valve, and a plurality of release capillary tubes provided in parallel on the outlet side of the absorber tank.
In the refrigeration cycle apparatus, in a medium load state, a degree of opening of the release valve is small and an amount of liquid refrigerant stored in the absorber tank is also small, and thus, the liquid refrigerant flows to the low-pressure side through the release capillary tube connected to a bottom part of the absorber tank. In a high load state, the degree of opening of the release valve increases as a high-pressure-side pressure of a refrigeration cycle increases, and thus, the amount of liquid refrigerant stored in the absorber tank increases. Then, when a liquid level rises, the liquid refrigerant also flows to the other release capillary tube connected to an upper part of the absorber tank, and thus, an amount of liquid refrigerant flowing to the low-pressure side increases.
As described above, in the refrigeration cycle apparatus, the plurality of release capillary tubes are provided on the outlet side of the absorber tank, and thus, an amount of release of the refrigerant can be set in a stepwise manner in accordance with load fluctuations (refer to PTL 1).

CITATION LIST

PATENT LITERATURE

PTL 1: Japanese Utility Model Laying-Open No. S59-175961

SUMMARY OF INVENTION

TECHNICAL PROBLEM

In the refrigeration cycle apparatus described in Japanese Utility Model Laying-Open No. S59-175961 , the amount of release of the refrigerant can be set in a stepwise manner in accordance with load fluctuations. However, when the high-pressure-side pressure (pressure on the outlet side of the compressor) increases due to load fluctuations, the increase in pressure cannot be suppressed in some cases. That is, in the above-described refrigeration cycle apparatus, in the high load state, an amount of liquid refrigerant that returns from the receiver (absorber tank) to the compressor increases, and thus, the pressure on the outlet side of the compressor increases.
The present disclosure has been made to solve the above-described problem, and an object of the present disclosure is to provide an outdoor unit of a refrigeration cycle apparatus in which an increase in pressure on the outlet side of a compressor can be appropriately suppressed, and a refrigeration cycle apparatus including the outdoor unit.

SOLUTION TO PROBLEM

An outdoor unit according to the present disclosure is an outdoor unit of a refrigeration cycle apparatus. The refrigeration cycle apparatus is configured to circulate refrigerant between the outdoor unit and a load unit connected to the outdoor unit. The outdoor unit includes: a compressor configured to compress refrigerant; a condenser configured to condense the refrigerant output from the compressor; an injection circuit; and a controller. The injection circuit is configured to return part of refrigerant on an outlet side of the condenser to the compressor without passing through the load unit. The injection circuit includes an expansion valve, a receiver and a flow control valve. The expansion valve is provided on a first pipe branched from the outlet side of the condenser. The receiver is provided on a low-pressure side of the expansion valve and configured to accumulate refrigerant in a gas-liquid two-phase state. The flow control valve is provided on a second pipe downstream of the receiver. The controller is configured to control the expansion valve and the flow control valve. When a pressure of the refrigerant output from the compressor exceeds a threshold value, the controller increases a degree of opening of the expansion valve and increases a gas-flow ratio of refrigerant returned from the receiver to the compressor by adjusting a degree of opening of the flow control valve, more than when the pressure is equal to or less than the threshold value.

ADVANTAGEOUS EFFECTS OF INVENTION

In the outdoor unit, when the pressure of the refrigerant output from the compressor exceeds the threshold value, the degree of opening of the expansion valve of the injection circuit is increased, and thus, an amount of refrigerant flowing into the receiver increases. Furthermore, the gas-flow ratio of the refrigerant returned from the receiver to the compressor is increased, and thus, an amount of liquid refrigerant taken out from the receiver decreases. Thus, when the pressure of the refrigerant output from the compressor exceeds the threshold value, an amount of liquid refrigerant stored in the receiver increases effectively, and an amount of refrigerant circulating through the refrigeration cycle apparatus decreases effectively. Therefore, according to the outdoor unit, an increase in pressure on the outlet side of the compressor can be appropriately suppressed.

BRIEF DESCRIPTION OF DRAWINGS

Fig. 1 is an overall configuration diagram of a refrigeration cycle apparatus in which an outdoor unit according to a first embodiment of the present disclosure is used.
Fig. 2 is a block diagram showing an example hardware configuration of a controller.
Fig. 3 is a flowchart illustrating an example of a process procedure of pressure suppression control executed by the controller.
Fig. 4 is a flowchart showing an example of a process procedure of TH control executed in step S30 in Fig. 3.
Fig. 5 is a flowchart showing an example of a process procedure of SC control executed in step S40 in Fig. 3.
Fig. 6 is a flowchart showing an example of a process procedure of control executed by a controller in a modification of the first embodiment.
Fig. 7 is an overall configuration diagram of a refrigeration cycle apparatus in which an outdoor unit according to a second embodiment is used.
Fig. 8 is a flowchart illustrating an example of a process procedure of pressure suppression control executed by a controller in the second embodiment.
Fig. 9 is a flowchart showing an example of a process procedure of control executed by a controller in a modification of the second embodiment.

DESCRIPTION OF EMBODIMENTS

Embodiments of the present disclosure will be described in detail hereinafter with reference to the drawings, in which the same or corresponding portions are denoted by the same reference characters and description thereof will not be repeated.

First Embodiment

Fig. 1 is an overall configuration diagram of a refrigeration cycle apparatus in which an outdoor unit according to a first embodiment of the present disclosure is used. Referring to Fig. 1, a refrigeration cycle apparatus 1 includes an outdoor unit 2 and a load unit 3. Load unit 3 is, for example, provided indoors.
Outdoor unit 2 includes a refrigerant outlet port PO2 and a refrigerant inlet port PI2. Load unit 3 includes a refrigerant outlet port PO3 and a refrigerant inlet port PI3. A pipe 84 connects refrigerant outlet port PO2 and refrigerant inlet port PI3 to each other. A pipe 88 connects refrigerant inlet port PI2 and refrigerant outlet port PO3 to each other. Thus, outdoor unit 2 and load unit 3 are connected to each other by pipes 84 and 88, and refrigerant circulates in outdoor unit 2 and load unit 3.
Outdoor unit 2 includes a compressor 10, a condenser 20, a fan 22, and pipes 80, 81 and 89. Load unit 3 includes an expansion valve 50, an evaporator 60 and pipes 85 to 87.
Pipe 80 connects a discharge port G2 of compressor 10 and condenser 20 to each other. Pipe 81 connects condenser 20 and refrigerant outlet port PO2 to each other. Pipe 85 connects refrigerant inlet port PI3 and expansion valve 50 to each other. Pipe 86 connects expansion valve 50 and evaporator 60 to each other. Pipe 87 connects evaporator 60 and refrigerant outlet port PO3 to each other. Pipe 89 connects refrigerant inlet port PI2 and a suction port G1 of compressor 10 to each other.
Compressor 10 compresses the refrigerant suctioned from suction port G1, and outputs the compressed refrigerant from discharge port G2. Compressor 10 can change a driving frequency through inverter control to adjust a rotation speed. By adjusting the rotation speed of compressor 10, an amount of circulation of the refrigerant can be adjusted and the capability of refrigeration cycle apparatus 1 can be adjusted. Compressor 10 includes an injection port G3 and allows the refrigerant suctioned from injection port G3 to flow into a midway portion of a compression process. Compressors of various types can be used as compressor 10, and a compressor of scroll type, a compressor of rotary type, a compressor of screw type, and the like can, for example, be used.
Condenser 20 condenses the refrigerant discharged from compressor 10 to pipe 80, and outputs the condensed refrigerant to pipe 81. Condenser 20 is configured such that heat exchange (heat dissipation) is performed between the high-temperature and high-pressure gas refrigerant discharged from compressor 10 and the outdoor air. As a result of this heat exchange, the refrigerant is condensed into a liquid phase. Fan 22 supplies, to condenser 20, the outdoor air used for heat exchange with the refrigerant in condenser 20. By adjusting a rotation speed of fan 22, a refrigerant pressure on the outlet side of compressor 10 (high-pressure-side pressure) can be adjusted.
Expansion valve 50 decompresses the refrigerant output from condenser 20 and flowing into pipe 85 through refrigerant inlet port PI3, and outputs the decompressed refrigerant to pipe 86. When a degree of opening of expansion valve 50 is decreased, a refrigerant pressure on the outlet side of expansion valve 50 decreases and a degree of dryness of the refrigerant increases. When the degree of opening of expansion valve 50 is increased, the refrigerant pressure on the outlet side of expansion valve 50 increases and the degree of dryness of the refrigerant decreases. Expansion valve 50 is implemented by, for example, a linear expansion valve (LEV).
Evaporator 60 evaporates the refrigerant output from expansion valve 50 to pipe 86, and outputs the evaporated refrigerant to pipe 87. Evaporator 60 is configured such that heat exchange (heat absorption) between the refrigerant decompressed by expansion valve 50 and the air in load unit 3. When the refrigerant passes through evaporator 60, the refrigerant evaporates into superheated steam. Then, the refrigerant output from evaporator 60 to pipe 87 is suctioned into compressor 10 through refrigerant outlet port PO3, refrigerant inlet port PI2 and pipe 89.
Hereinafter, a circulation flow path of the refrigerant extending from discharge port G2 of compressor 10 through condenser 20, refrigerant outlet port PO2 and refrigerant inlet port PI3, expansion valve 50, evaporator 60, and refrigerant outlet port PO3 and refrigerant inlet port PI2 to suction port G1 of compressor 10 will be referred to as "main refrigerant circuit" of refrigeration cycle apparatus 1.
Outdoor unit 2 according to the first embodiment further includes an expansion valve 70, a receiver 71, a flow control valve 72, a throttle device 73, and pipes 91 to 95. Pipe 91 is branched from pipe 81 and connected to expansion valve 70. Pipe 92 connects expansion valve 70 and receiver 71 to each other. Pipe 93 connects a liquid refrigerant discharge port provided in a lower part (e.g., lower surface) of receiver 71 and flow control valve 72 to each other. Pipe 94 connects flow control valve 72 and injection port G3 of compressor 10 to each other. Pipe 95 connects a gas refrigerant discharge port provided in an upper part (e.g., upper surface) of receiver 71 and throttle device 73 to each other. The other end of throttle device 73 is connected to pipe 94.
Expansion valve 70, receiver 71, flow control valve 72, throttle device 73, and pipes 91 to 95 form "injection circuit" that returns part of the refrigerant output from condenser 20 to compressor 10 without passing through load unit 3.
Expansion valve 70 decompresses the refrigerant flowing from pipe 81 into pipe 91, and outputs the decompressed refrigerant to receiver 71. When a degree of opening of expansion valve 70 is increased, an amount of refrigerant flowing into receiver 71 increases. In contrast, when the degree of opening of expansion valve 70 is decreased, the amount of refrigerant flowing into receiver 71 decreases. Expansion valve 70 is implemented by, for example, an LEV.
Receiver 71 is provided on the low-pressure side of expansion valve 70, and accumulates, in a gas-liquid two-phase state, the refrigerant decompressed by passing through expansion valve 70. That is, in receiver 71, the refrigerant is stored in a state of being separated into liquid refrigerant and gas refrigerant, and the liquid refrigerant is stored in the lower part of receiver 71.
Pipe 93 is connected to the liquid refrigerant discharge port provided in the lower part of receiver 71, and discharges the liquid refrigerant from receiver 71. Flow control valve 72 is provided on pipe 93 and adjusts an amount of liquid refrigerant discharged from receiver 71 to pipe 93. Flow control valve 72 is implemented by, for example, an LEV.
Pipe 95 is connected to the gas refrigerant discharge port provided in the upper part of receiver 71, and discharges the gas refrigerant from receiver 71. Throttle device 73 is provided on pipe 95 and adjusts an amount of gas refrigerant discharged from receiver 71 to pipe 95. Throttle device 73 is implemented by, for example, a capillary tube. The liquid refrigerant that has passed through flow control valve 72, and the gas refrigerant that has passed through throttle device 73 meet at pipe 94 and are returned to injection port G3 of compressor 10. Injection port G3 may be provided in a suction chamber inside a shell of compressor 10, or may be provided in a compression chamber inside the shell.
By providing the above-described injection circuit, the efficiency of refrigeration cycle apparatus 1 can be enhanced. In refrigeration cycle apparatus 1, receiver 71 is provided in the injection circuit.
Although an amount of refrigerant required in the main refrigerant circuit varies depending on load fluctuations in the load unit, the receiver can adjust the amount of refrigerant in the main refrigerant circuit in accordance with load fluctuations. The above-described receiver can also be provided on the high-pressure side of the main refrigerant circuit. However, when the receiver is provided in the main refrigerant circuit, a refrigerant temperature in the receiver is a saturation temperature because gas refrigerant is generally present in the receiver. Therefore, a degree of supercooling of the refrigerant cannot be secured on the outlet side of the receiver, and thus, a subcool heat exchanger or the like must be separately provided on the outlet side of the receiver in order to secure the degree of supercooling.
When supercritical refrigerant such as CO₂ is used, the use in a supercritical state is intended and the supercritical refrigerant is not separated into a gas-liquid state on the high-pressure side. Therefore, the receiver provided on the high-pressure side of the main refrigerant circuit cannot store in a liquid state the refrigerant of a supercritical state and cannot adjust the amount of refrigerant in accordance with load fluctuations.
In outdoor unit 2 according to the first embodiment, receiver 71 is provided in the injection circuit and stores the refrigerant decompressed by expansion valve 70. With such a configuration, the degree of supercooling of the refrigerant can be secured on the outlet side of condenser 20, and even when the supercritical refrigerant such as CO₂ refrigerant is used, the refrigerant can be stored in a liquid state in receiver 71.
In the present disclosure, for ease of explanation, the case of cooling the supercritical refrigerant such as CO₂ will also be referred to as "condenser 20". In addition, an amount of decrease of the refrigerant in a supercritical state from a reference temperature will also be referred to as "degree of supercooling".
In outdoor unit 2, the pressure on the outlet side of compressor 10 (high-pressure-side pressure) may increase suddenly due to load fluctuations in load unit 3. When the high-pressure-side pressure increases excessively, it is required to decrease the pressure quickly while continuing the operation of compressor 10. Particularly when the supercritical refrigerant such as CO₂ is used, quick pressure suppression is required because the refrigerant pressure is higher than that of fluorocarbons.
Thus, in outdoor unit 2 according to the first embodiment, when the high-pressure-side pressure exceeds a threshold value, control for quickly suppressing the high-pressure-side pressure is executed (hereinafter, referred to as "pressure suppression control"). Specifically, the degree of opening of expansion valve 70 is increased and the degree of opening of flow control valve 72 is decreased. By increasing the degree of opening of expansion valve 70, an amount of refrigerant flowing from the main refrigerant circuit into receiver 71 increases. Furthermore, by decreasing the degree of opening of flow control valve 72, a gas-flow ratio of the refrigerant returned from receiver 71 to compressor 10 increases, and thus, an amount of liquid refrigerant taken out from receiver 71 decreases. Thus, when the high-pressure-side pressure exceeds the threshold value, an amount of liquid refrigerant stored in receiver 71 increases and an amount of refrigerant circulating in the main refrigerant circuit decreases. As a result, an increase in high-pressure-side pressure can be effectively suppressed.
Outdoor unit 2 further includes a controller 100 that executes the above-described pressure suppression control. Outdoor unit 2 further includes pressure sensors 110 and 111, and temperature sensors 120 and 121.
Pressure sensor 110 detects a refrigerant pressure on the suction side of compressor 10 (low-pressure-sire pressure) PL, and outputs the detection value to controller 100. Pressure sensor 111 detects a refrigerant pressure on the discharge side of compressor 10 (high-pressure-side pressure) PH, and outputs the detection value to controller 100. Temperature sensor 120 detects a temperature TH of the refrigerant discharged from compressor 10, and outputs the detection value to controller 100. Temperature sensor 121 detects a temperature T1 of the refrigerant on the outlet side of condenser 20, and outputs the detection value to controller 100.
Controller 100 receives the detection values by pressure sensors 110 and 111 and temperature sensors 120 and 121, and executes control of each device in outdoor unit 2 based on these detection values. Specifically, controller 100 controls operations of compressor 10, expansion valve 70 and flow control valve 72 based on the detection values by the sensors. As main control executed by controller 100, when the high-pressure-side pressure exceeds the threshold value, controller 100 executes the pressure suppression control for quickly suppressing the increased high-pressure-side pressure. The pressure suppression control will be described in detail later.
Fig. 2 is a block diagram showing an example hardware configuration of controller 100. Referring to Fig. 2, controller 100 includes a central processing unit (CPU) 132, a random access memory (RAM) 134, a read only memory (ROM) 136, an input unit 138, a display unit 140, and an I/F unit 142. RAM 134, ROM 136, input unit 138, display unit 140, and I/F unit 142 are connected to CPU 132 through a bus 144.
CPU 132 loads programs stored in ROM 136 into RAM 134 and executes the programs. The programs stored in ROM 136 are programs describing a process procedure for controller 100. In outdoor unit 2, control of each device in outdoor unit 2 is executed in accordance with these programs. The control can be implemented by not only software but also dedicated hardware (electronic circuit).
Fig. 3 is a flowchart illustrating an example of a process procedure of the pressure suppression control executed by controller 100. A series of process shown in this flowchart is repeatedly executed during operation of outdoor unit 2.
Referring to Fig. 3, controller 100 obtains refrigerant pressure PH on the discharge side of compressor 10 (high-pressure-side pressure) from pressure sensor 111, and determines whether or not pressure PH is higher than a threshold value (step S10). This threshold value is a value having an appropriate margin with respect to a high pressure protection set value for protecting outdoor unit 2. For example, when outdoor unit 2 is designed such that the use of the CO₂ refrigerant is intended, the threshold value can be set at approximately 9 MPa with respect to the high pressure protection set value of approximately 10 MPa. When outdoor unit 2 is designed such that the use of R410A refrigerant is intended, the threshold value can be set at approximately 3.9 MPa with respect to the high pressure protection set value of 4.15 MPa.
When it is determined in step S10 that pressure PH is higher than the threshold value (YES in step S10), controller 100 changes the degree of opening of expansion valve 70 of the injection circuit to increase, and changes the degree of opening of flow control valve 72 of the injection circuit to decrease (step S20). Thus, the amount of liquid refrigerant stored in receiver 71 increases and the amount of refrigerant circulating in the main refrigerant circuit decreases. As a result, pressure PH can be quickly suppressed to or below the threshold value.
In contrast, when it is determined in step S10 that pressure PH is equal to or lower than the threshold value (NO in step S10), controller 100 executes normal control. That is, controller 100 executes TH control for adjusting temperature TH of the refrigerant discharged from compressor 10 to fall within a target range (step S30), and executes SC control for adjusting a degree of supercooling SC of the refrigerant on the outlet side of condenser 20 to a target value (e.g., approximately 5 K) (step S40). Although the SC control is executed after the TH control is executed in this flowchart, the TH control and the SC control may actually be executed in parallel or concurrently.
Fig. 4 is a flowchart showing an example of a process procedure of the TH control executed in step S30 in Fig. 3. Referring to Fig. 4, controller 100 obtains, from temperature sensor 120, temperature TH of the refrigerant discharged from compressor 10, and determines whether or not temperature TH is higher than a target range upper limit (step S110). This target range upper limit can be set at, for example, 100°C.
When it is determined that temperature TH is higher than the target range upper limit (YES in step S110), controller 100 changes the degree of opening of expansion valve 70 of the injection circuit to increase (step S120). When the degree of opening of expansion valve 70 increases, the amount of low-temperature refrigerant (amount of injection) returned to compressor 10 through the injection circuit increases, and thus, temperature TH of the refrigerant on the outlet side of compressor 10 can be decreased.
In contrast, when it is determined in step S110 that temperature TH is equal to or lower than the target range upper limit (NO in step S110), controller 100 determines whether or not temperature TH is lower than a target range lower limit (step S130). This target range lower limit can be set at, for example, 70°C.
When it is determined that temperature TH is lower than the target range lower limit (YES in step S130), controller 100 changes the degree of opening of expansion valve 70 to decrease (step S140). When the degree of opening of expansion valve 70 decreases, the above-described amount of injection decreases, and thus, temperature TH of the refrigerant on the outlet side of compressor 10 can be increased.
Fig. 5 is a flowchart showing an example of a process procedure of the SC control executed in step S40 in Fig. 3. Referring to Fig. 5, controller 100 obtains degree of supercooling SC of the refrigerant on the outlet side of condenser 20, and determines whether or not degree of supercooling SC is higher than a target range upper limit (step S210). This target range upper limit and a below-described target range lower limit are upper and lower limit values that are appropriately set with respect to a control target value of degree of supercooling SC, and the control target value of degree of supercooling SC is set at, for example, 5 K.
Degree of supercooling SC can be calculated, for example, by converting the refrigerant pressure on the outlet side of condenser 20, which is replaced by pressure PH detected by pressure sensor 111, into a saturation temperature value of the refrigerant, and subtracting temperature T1 of the refrigerant on the outlet side of condenser 20 detected by temperature sensor 121 from the saturation temperature value.
When it is determined that degree of supercooling SC is higher than the target range upper limit (YES in step S210), controller 100 changes the degree of opening of flow control valve 72 of the injection circuit to decrease (step S220). When the degree of opening of flow control valve 72 decreases, the amount of liquid refrigerant taken out from receiver 71 decreases. Therefore, the amount of liquid refrigerant stored in receiver 71 increases and the amount of refrigerant circulating in the main refrigerant circuit decreases. As a result, temperature T1 of the refrigerant on the outlet side of condenser 20 increases and degree of supercooling SC decreases.
In contrast, when it is determined in step S210 that degree of supercooling SC is equal to or lower than the target range upper limit (NO in step S210), controller 100 determines whether or not degree of supercooling SC is lower than the target range lower limit (step S230).
When it is determined that degree of supercooling SC is lower than the target range lower limit (YES in step S230), controller 100 changes the degree of opening of flow control valve 72 to increase (step S240). When the degree of opening of flow control valve 72 increases, the amount of liquid refrigerant taken out from receiver 71 increases. Therefore, the amount of liquid refrigerant stored in receiver 71 decreases and the amount of refrigerant circulating in the main refrigerant circuit increases. As a result, temperature T1 of the refrigerant on the outlet side of condenser 20 decreases and degree of supercooling SC increases.
When it is determined in step S230 that degree of supercooling SC is equal to or higher than the target range lower limit (NO in step S230), controller 100 moves the process to return without performing step S240.
As described above, in the first embodiment, when pressure PH on the high-pressure side exceeds the threshold value, the degree of opening of expansion valve 70 of the injection circuit is increased, and thus, the amount of refrigerant flowing into receiver 71 increases. Furthermore, the gas-flow ratio of the refrigerant returned from receiver 71 to compressor 10 increases, and thus, the amount of liquid refrigerant taken out from receiver 71 decreases. Thus, when pressure PH exceeds the threshold value, the amount of liquid refrigerant stored in receiver 71 increases effectively and the amount of refrigerant in the main refrigerant circuit decreases effectively. Therefore, according to the first embodiment, an increase in pressure on the high-pressure side can be appropriately suppressed.
In addition, according to the first embodiment, when pressure PH on the high-pressure side is equal to or lower than the threshold value, temperature TH on the outlet side of compressor 10 is controlled to fall within the target range, and degree of supercooling SC of the refrigerant on the outlet side of condenser 20 is controlled to the target value. Therefore, according to the first embodiment, when pressure PH is equal to or lower than the threshold value, temperature TH and degree of supercooling SC are controlled to the targets, and thus, efficient operation can be performed.

Modification of First Embodiment

In the above-described first embodiment, when refrigerant pressure PH on the outlet side of compressor 10 (high-pressure-sire pressure) exceeds the threshold value, the degree of opening of expansion valve 70 is increased and the degree of opening of flow control valve 72 is decreased. Thus, the amount of liquid refrigerant stored in receiver 71 can be increased and the amount of refrigerant circulating in the main refrigerant circuit can be decreased. As a result, pressure PH can be suppressed to or below the threshold value.
However, when the amount of refrigerant circulating in the main refrigerant circuit decreases, temperature TH of the refrigerant output from compressor 10 may increase and exceed an upper limit threshold value. Thus, in the present modification, when temperature TH exceeds the threshold value in a case where pressure PH exceeds the threshold value, i.e., during execution of the pressure suppression control, the change (decrease) of the degree of opening of flow control valve 72 is stopped to maintain the degree of opening of flow control valve 72. As a result, an increase in temperature TH can be suppressed, although temperature TH cannot be decreased.
Fig. 6 is a flowchart showing an example of a process procedure of control executed by controller 100 in the modification of the first embodiment. A series of process shown in this flowchart is repeatedly executed during operation of outdoor unit 2.
Referring to Fig. 6, controller 100 obtains pressure PH from pressure sensor 111, and determines whether or not pressure PH is higher than the threshold value (step S310). When it is determined that pressure PH is higher than the threshold value (YES in step S310), controller 100 obtains temperature TH from temperature sensor 120, and determines whether or not temperature TH is higher than the threshold value (step S320).
When temperature TH is equal to or lower than the threshold value (NO in step S320), controller 100 changes the degree of opening of expansion valve 70 of the injection circuit to increase, and changes the degree of opening of flow control valve 72 of the injection circuit to decrease, as described in the first embodiment (step S330). As a result, pressure PH can be quickly suppressed to or below the threshold value.
In contrast, when it is determined in step S320 that temperature TH is higher than the threshold value (YES in step S320), controller 100 changes the degree of opening of expansion valve 70 to increase, and stops the change (decrease) of the degree of opening of flow control valve 72 to maintain the degree of opening of flow control valve 72 (step S340). As a result, a further increase in gas-flow ratio of the refrigerant returned to compressor 10 can be suppressed and an increase in temperature TH can be suppressed.
When temperature TH exceeds the threshold value, it is also conceivable to change the degree of opening of flow control valve 72 to increase. When the degree of opening of flow control valve 72 is increased, a liquid-flow ratio of the refrigerant returned to compressor 10 increases, and thus, the increase in degree of opening of flow control valve 72 has the effect of decreasing temperature TH. However, the amount of refrigerant returned to compressor 10 increases, and thus, pressure PH on the high-pressure side increases. Therefore, in the present modification, when pressure PH is higher than the threshold value (YES in step S310) and temperature TH is also higher than the threshold value (YES in step S320), the degree of opening of flow control valve 72 is maintained.
When it is determined in step S310 that pressure PH is equal to or lower than the threshold value (NO in step S310), controller 100 also determines whether or not temperature TH is higher than a threshold value (step S350). This threshold value may be equivalent to the target range upper limit in the TH control, or may be a set value higher than the target range upper limit.
When it is determined in step S350 that temperature TH is equal to or lower than the threshold value (NO in step S350), controller 100 executes the normal control. That is, controller 100 executes the TH control for adjusting temperature TH to fall within the target range (step S360), and executes the SC control for adjusting degree of supercooling SC to the target value (step S370). The TH control and the SC control are the same as those described in the first embodiment.
When it is determined in step S350 that temperature TH is higher than the threshold value (YES in step S350), controller 100 changes the degree of opening of expansion valve 70 to increase, and also changes the degree of opening of flow control valve 72 to increase (step S380). When the degree of opening of expansion valve 70 increases, the amount of low-temperature refrigerant (amount of injection) returned to compressor 10 through the injection circuit increases, and thus, temperature TH of the refrigerant output from compressor 10 decreases. Furthermore, when the degree of opening of flow control valve 72 increases, the liquid-flow ratio of the refrigerant returned to compressor 10 increases, and thus, temperature TH tends to further decrease.
When the degree of opening of flow control valve 72 increases, pressure PH tends to increase. In this case, however, pressure PH is equal to or lower than the threshold value (NO in step S310). Therefore, as long as pressure PH does not exceed the threshold value, the degree of opening of flow control valve 72 can be increased in order to decrease temperature TH.
As described above, in the present modification, when temperature TH exceeds the threshold value in a case where pressure PH exceeds the threshold value, i.e., during execution of the pressure suppression control, the degree of opening of flow control valve 72 is maintained. As a result, an increase in temperature TH can be suppressed.
In addition, according to the present modification, when temperature TH exceeds the threshold value in a case where pressure PH is equal to or lower than the threshold value, the degree of opening of expansion valve 70 and the degree of opening of flow control valve 72 are both increased, and thus, temperature TH can be effectively decreased.

Second Embodiment

In the above-described first embodiment and the modification thereof, flow control valve 72 is provided on pipe 93 connected to the liquid refrigerant discharge port provided in the lower part of receiver 71, and throttle device 73 is provided on pipe 95 connected to the gas refrigerant discharge port provided in the upper part of receiver 71. In a second embodiment, the flow control valve is provided on pipe 95 and the throttle device is provided on pipe 93.
Fig. 7 is an overall configuration diagram of a refrigeration cycle apparatus in which an outdoor unit according to the second embodiment is used. Referring to Fig. 7, a refrigeration cycle apparatus 1A includes an outdoor unit 2A and load unit 3. Outdoor unit 2A is different from outdoor unit 2 according to the first embodiment shown in Fig. 1 in that outdoor unit 2A includes a flow control valve 75 and a throttle device 76 instead of flow control valve 72 and throttle device 73, respectively, and includes a controller 100A instead of controller 100.
Flow control valve 75 is provided on pipe 95 connected to the gas refrigerant discharge port provided in the upper part (e.g., upper surface) of receiver 71, and adjusts an amount of gas refrigerant discharged from receiver 71 to pipe 95. Throttle device 76 is provided on pipe 93 connected to the liquid refrigerant discharge port provided in the lower part (e.g., lower surface) of receiver 71, and decompresses the liquid refrigerant discharged from receiver 71 to pipe 93 and outputs the decompressed liquid refrigerant to pipe 94.
Similarly to controller 100 in the first embodiment, when refrigerant pressure PH on the discharge side of compressor 10 (high-pressure-side pressure) exceeds a threshold value, controller 100A also executes the pressure suppression control for quickly suppressing increased pressure PH. A hardware configuration of controller 100A is similar to the configuration shown in Fig. 2.
Fig. 8 is a flowchart illustrating an example of a process procedure of the pressure suppression control executed by controller 100A in the second embodiment. This flowchart corresponds to the flowchart shown in Fig. 3. A series of process shown in this flowchart is also repeatedly executed during operation of outdoor unit 2A.
Referring to Fig. 8, controller 100A obtains the detection value of pressure PH from pressure sensor 111, and determines whether or not pressure PH is higher than a threshold value (step S410). The threshold value is the same as the threshold value used in step S10 in Fig. 3.
When it is determined in step S410 that pressure PH is higher than the threshold value (YES in step S410), controller 100A changes the degree of opening of expansion valve 70 of the injection circuit to increase, and changes the degree of opening of flow control valve 75 of the injection circuit to increase (step S420). When the degree of opening of flow control valve 75 increases, the gas-flow ratio of the refrigerant returned from receiver 71 to compressor 10 increases and the amount of liquid refrigerant taken out from receiver 71 decreases. Thus, when pressure PH exceeds the threshold value, the amount of liquid refrigerant stored in receiver 71 increases and the amount of refrigerant circulating in the main refrigerant circuit decreases. As a result, an increase in pressure PH can be effectively suppressed.
In contrast, when it is determined in step S410 that pressure PH is equal to or lower than the threshold value (NO in step S410), controller 100A executes the normal control. That is, controller 100A executes the TH control for adjusting temperature TH to fall within the target range (step S430), and executes the SC control for adjusting degree of supercooling SC to the target value (step S440). The TH control and the SC control are the same as those described in the first embodiment.
As described above, the second embodiment can also provide an effect similar to that of the first embodiment.

Modification of Second Embodiment

Similarly to the modification of the first embodiment, in the second embodiment as well, when temperature TH exceeds the threshold value in a case where pressure PH exceeds the threshold value, i.e., during execution of the pressure suppression control, the change (increase) of the degree of opening of flow control valve 75 is stopped to maintain the degree of opening of flow control valve 75. As a result, an increase in temperature TH can be suppressed, although temperature TH cannot be decreased.
Fig. 9 is a flowchart showing an example of a process procedure of control executed by controller 100A in the modification of the second embodiment. A series of process shown in this flowchart is repeatedly executed during operation of outdoor unit 2A.
Referring to Fig. 9, controller 100A obtains pressure PH from pressure sensor 111, and determines whether or not pressure PH is higher than the threshold value (step S510). When it is determined that pressure PH is higher than the threshold value (YES in step S510), controller 100A obtains temperature TH from temperature sensor 120, and determines whether or not temperature TH is higher than the threshold value (step S520).
When temperature TH is equal to or lower than the threshold value (NO in step S520), controller 100A changes the degree of opening of expansion valve 70 of the injection circuit to increase, and changes the degree of opening of flow control valve 75 of the injection circuit to increase, as described in the second embodiment (step S530). As a result, pressure PH can be quickly suppressed to or below the threshold value.
When it is determined in step S520 that temperature TH is higher than the threshold value (YES in step S520), controller 100A changes the degree of opening of expansion valve 70 to increase, and stops the change (increase) of the degree of opening of flow control valve 75 to maintain the degree of opening of flow control valve 75 (step S540). As a result, a further increase in gas-flow ratio of the refrigerant returned to compressor 10 can be suppressed and an increase in temperature TH can be suppressed.
In contrast, when it is determined in step S510 that pressure PH is equal to or lower than the threshold value (NO in step S510), controller 100A also determines whether or not temperature TH is higher than the threshold value (step S550). When it is determined that temperature TH is equal to or lower than the threshold value (NO in step S550), controller 100A executes the normal control. That is, controller 100A executes the TH control for adjusting temperature TH to fall within the target range (step S560), and executes the SC control for adjusting degree of supercooling SC to the target value (step S570). The TH control and the SC control are the same as those described in the first embodiment.
When it is determined in step S550 that temperature TH is higher than the threshold value (YES in step S550), controller 100A changes the degree of opening of expansion valve 70 to increase, and changes the degree of opening of flow control valve 75 to decrease (step S580). When the degree of opening of expansion valve 70 increases, the amount of low-temperature refrigerant (amount of injection) returned to compressor 10 through the injection circuit increases, and thus, temperature TH of the refrigerant output from compressor 10 decreases. Furthermore, when the degree of opening of flow control valve 75 decreases, the gas-flow ratio of the refrigerant returned to compressor 10 decreases and the liquid-flow ratio increases. Therefore, temperature TH tends to further decrease.
When the degree of opening of flow control valve 75 decreases, pressure PH tends to increase. In this case, however, pressure PH is equal to or lower than the threshold value (NO in step S510). Therefore, as long as pressure PH does not exceed the threshold value, the degree of opening of flow control valve 75 can be decreased in order to decrease temperature TH.
As described above, the modification of the second embodiment can also provide an effect similar to that of the modification of the first embodiment.
In the above-described embodiments and the above-described modifications, the refrigerant flowing through the injection circuit is returned to injection port G3 of compressor 10. However, the refrigerant flowing through the injection circuit may be returned to pipe 89 on the suction side of compressor 10.
In addition, in the above-described embodiments and the above-described modifications, each of throttle devices 73 and 76 is implemented by a capillary tube. However, a flow control valve such as an LEV may be used instead of the capillary tube.
In addition, in the above-described first embodiment and the modification thereof, pipe 95 is connected to the upper part of receiver 71, and throttle device 73 is provided on pipe 95. However, pipe 95 and throttle device 73 do not have to be provided. Alternatively, throttle device 73 do not have to be provided on pipe 95.
In addition, in the above-described embodiments and the above-described modifications, the outdoor unit and the refrigeration cycle apparatus mainly used in a warehouse or a showcase have been representatively described. However, the outdoor unit according to the present disclosure is also applicable to an air conditioner using a refrigeration cycle.
It should be understood that the embodiments disclosed herein are illustrative and non-restrictive in every respect. The scope of the present invention is defined by the terms of the claims, rather than the description of the embodiments above, and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims.

REFERENCE SIGNS LIST

1, 1A refrigeration cycle apparatus; 2, 2A outdoor unit; 3 load unit; 10 compressor; 20 condenser; 22 fan; 50, 70 expansion valve; 60 evaporator; 71 receiver; 72, 75 flow control valve; 73, 76 throttle device; 80 to 95 pipe; 100, 100A controller; 110, 111 pressure sensor; 120, 121 temperature sensor; 132 CPU; 134 RAM; 136 ROM; 138 input unit; 140 display unit; 142 I/F unit; 144 bus; G1 suction port; G2 discharge port; G3 injection port; PI2, PI3 refrigerant inlet port; PO2, PO3 refrigerant outlet port.

Claims

An outdoor unit of a refrigeration cycle apparatus configured to circulate refrigerant between the outdoor unit and a load unit connected to the outdoor unit, the outdoor unit comprising:
a compressor configured to compress refrigerant;

a condenser configured to condense the refrigerant output from the compressor; and

an injection circuit configured to return part of refrigerant on an outlet side of the condenser to the compressor without passing through the load unit,

the injection circuit including
an expansion valve provided on a first pipe branched from the outlet side of the condenser,

a receiver provided on a low-pressure side of the expansion valve and configured to accumulate refrigerant in a gas-liquid two-phase state, and

a flow control valve provided on a second pipe downstream of the receiver,

the outdoor unit further comprising a controller configured to control the expansion valve and the flow control valve,

when a pressure of the refrigerant output from the compressor exceeds a first threshold value, the controller increasing a degree of opening of the expansion valve and increasing a gas-flow ratio of refrigerant returned from the receiver to the compressor by adjusting a degree of opening of the flow control valve, more than when the pressure is equal to or less than the first threshold value.
The outdoor unit of the refrigeration cycle apparatus according to claim 1, wherein
when a temperature of the refrigerant output from the compressor exceeds a second threshold value in a case where the pressure exceeds the first threshold value, the controller maintains the degree of opening of the flow control valve.
The outdoor unit of the refrigeration cycle apparatus according to claim 1 or 2, wherein
the second pipe is a pipe configured to discharge liquid refrigerant from the receiver, and

when the pressure exceeds the first threshold value, the controller decreases the degree of opening of the flow control valve, less than when the pressure is equal to or less than the first threshold value.
The outdoor unit of the refrigeration cycle apparatus according to claim 1 or 2, wherein
the second pipe is a pipe configured to discharge gas refrigerant from the receiver, and

when the pressure exceeds the first threshold value, the controller increases the degree of opening of the flow control valve, more than when the pressure is equal to or less than the first threshold value.
The outdoor unit of the refrigeration cycle apparatus according to any one of claims 1 to 4, wherein
when the pressure is equal to or less than the first threshold value, the controller
adjusts the degree of opening of the expansion valve such that a temperature of the refrigerant output from the compressor falls within a first target range, and

adjusts the degree of opening of the flow control valve such that a degree of supercooling of refrigerant passing through the condenser falls within a second target range.
A refrigeration cycle apparatus comprising:
the outdoor unit as recited in any one of claims 1 to 5; and

a load unit connected to the outdoor unit and configured to receive refrigerant from the outdoor unit and output the refrigerant to the outdoor unit.