GB2602893A

GB2602893A - Outdoor unit and refrigeration cycle device

Info

Publication number: GB2602893A
Application number: GB2201367.6A
Authority: GB
Inventors: Hayasaka Motoshi; Ishikawa Tomotaka; Arii Yusuke
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: JP7155440B2; WO2021048898A1; GB2602893B; JP2022177312A; JP7378561B2; JPWO2021048898A1

Abstract

In the present invention, the flow path from a compressor (10) to a condenser (20), the first passage (H1) of a heat exchanger (30), and a second expansion valve (40), together with a load device (3), forms a circulation flow path through which a refrigerant circulates. An outdoor unit (2) comprises: a first refrigerant flow path (91 to 94) that allows the refrigerant to flow from the portion of the circulation flow path between the outlet of the first passage (H1) and the second expansion valve (40) to the inlet of the second passage (H2); a third expansion valve (71) that is disposed in the first refrigerant flow path (91 to 94); a second refrigerant flow path (96) that allows the refrigerant to flow from the outlet of the second passage (H2) to the suction port (G1) or intermediate pressure port (G3) of the compressor (10); and a flow path switching part (74). The flow path switching part (74) includes: a first on-off valve (75) that is provided between the outlet of the second passage (H2) and the intermediate pressure port (G3); and a pressure reduction device (77) and a second on-off valve (76) that are arranged in series between the outlet of the second passage (H2) and the suction port (G1).

Description

DESCRIPTION

TITLE OF INVENTION

Outdoor Unit and Refrigeration Cycle Apparatus

TECHNICAL FIELD

[000I] The present disclosure relates to an outdoor unit and a refrigeration cycle apparatus.

BACKGROUND ART

[0002] Japanese Patent Laying-Open No. 2014-01917 (PTL 1) discloses a refrigeration apparatus having an intermediate injection flow path and a suction injection flow path.

In this refrigeration apparatus, a portion of refrigerant flowing from a condenser toward an evaporator can be merged with the inteinicdiate pressure refrigerant in a compressor using the intermediate injection flow path, and can also be merged with the low pressure refrigerant to be suctioned into the compressor in a suction flow path using the suction injection flow path. Accordingly, in a case where using the intermediate injection flow path leads to deterioration of operation efficiency, the suction injection flow path can be used to decrease the discharge temperature of the compressor. CITATION LIST

PATENT LITERATURE

[0003] PTL 1: Japanese Patent Laying-Open No. 2014-01917

SUMMARY OF INVENTION

TECHNICAL PROBLEM

[0004] The refrigeration apparatus described in Japanese Patent Laying-Open No. 2014-01917 (PTL 1) switches the intermediate injection flow path to the suction injection flow path when it is necessary to decrease the discharge temperature of the compressor. On this occasion, when the flow path is switched by an on-off valve while the compressor is operated, pressure fluctuation causes the compressor to generate vibration. Therefore, in order to suppress vibration, it is necessary to stop the compressor and then switch the flow path. This requires time to stop and restart the compressor, and contributes to deterioration of operation efficiency. [0005] An object of the present disclosure is to provide an outdoor unit and a refrigeration cycle apparatus with improved operation efficiency. SOLUTION TO PROBLEM [0006] The present disclosure relates to an outdoor unit of a refrigeration cycle apparatus. The outdoor unit is connectable to a load device including a first expansion valve and an evaporator. The outdoor unit includes: a compressor having a suction port, a discharge port, and an intermediate pressure port; a condenser; a heat exchanger having a first passage and a second passage and configured to exchange heat between refrigerant flowing in the first passage and the refrigerant flowing in the second passage; and a second expansion valve. A flow path from the compressor to the second expansion valve via the condenser and the first passage of the heat exchanger forms, together with the load device, a circulation flow path through which the refrigerant circulates. The outdoor unit further includes: a first refrigerant flow path configured to cause the refrigerant to flow from a portion of the circulation flow path between an outlet of the first passage and the second expansion valve to an inlet of the second passage; a third expansion valve disposed on the first refrigerant flow path; a second refrigerant flow path configured to cause the refrigerant to flow from an outlet of the second passage to the suction port or the intennediate pressure port of the compressor; and a flow path switching unit disposed on the second refrigerant flow path and configured to select one of the suction port and the intermediate pressure port as a destination of the refrigerant flowing out from the outlet of the second passage. The flow path switching unit includes a first on-off valve provided between the outlet of the second passage and the intermediate pressure port, and a decompression device and a second on-off valve disposed in series between the outlet of the second passage and the suction port.

ADVANTAGEOUS EFFECTS OF INVENTION

[0007] According to the outdoor unit, and the refrigeration cycle apparatus and a refrigerating machine including the same of the present disclosure, an injection flow path can be switched without stopping the compressor, and thus operation efficiency of a refrigeration cycle can be improved.

BRIEF DESCRIPTION OF DRAWINGS

[0008] Fig. 1 is an overall configuration diagram of a. refrigeration cycle apparatus according to a first embodiment.

Fig. 2 is a diagram showing various sensors and a controller disposed in a refrigeration cycle apparatus 1 shown in Fig. 1.

Fig. 3 is a flowchart for illustrating control of a flow path switching unit 74. Fig. 4 is a flowchart for illustrating control during a pump down operation.

Fig. 5 is a flowchart for illustrating control during an oil recovery operation.

Fig. 6 is a diagram showing a configuration of a refrigeration cycle apparatus of a second embodiment.

Fig. 7 is a flowchart for illustrating control of a flow path switching unit 74A. Fig. 8 is a diagram showing a configuration of a refrigeration cycle apparatus 201 of a first variation.

Fig. 9 is a diagram showing a configuration of a refrigeration cycle apparatus 201A of a second variation.

Fig. 10 is a diagram showing a. configuration of a refrigeration cycle apparatus 201B of a third variation.

DESCRIPTION OF EMBODIMENTS

[0009] Hereinafter, embodiments of the present disclosure will be described in detail with reference to the drawings. Although a plurality of embodiments will be described below, it is originally intended from the time of filing the present application to combine features described in the embodiments as appropriate. It should be noted that identical or corresponding parts in the drawings will be designated by the same reference characters, and the description thereof will not be repeated.

[0010] First Embodiment Fig. I is an overall configuration diagram of a refrigeration cycle apparatus according to a first embodiment. It should be noted that Fig. 1 functionally shows the connection relation and the arrangement configuration of devices in the refrigeration cycle apparatus, and does not necessarily show an arrangement in a physical space. [0011] Referring to Fig. 1, a refrigeration cycle apparatus 1 includes an outdoor unit 2, a. load device 3, and extension pipes 84 and 88.

[0012] Outdoor unit 2 is an outdoor unit of refrigeration cycle apparatus 1, the outdoor unit being connectable to load device 3. Outdoor unit 2 includes a compressor 10 having a suction port Gl, a discharge port 62, and an intermediate pressure port 63, a condenser 20, a fan 22, a heat exchanger 30, a second expansion valve 40, and pipes 80 to 83 and 89. Heat exchanger 30 has a first passage H1 and a second passage H2, and is configured to exchange heat between refrigerant flowing in first passage HI and the refrigerant flowing in second passage H2.

[0013] Load device 3 includes a first expansion valve 50, an evaporator 60, and pipes 85, 86, and 87. Evaporator 60 performs heat exchange between air and the refrigerant. In refrigeration cycle apparatus 1, evaporator 60 evaporates the refrigerant by absorbing heat from the air in a space to be cooled. First expansion valve 50 is an electronic expansion valve which can decompress the refrigerant. It should be noted that first expansion valve 50 may be, thr example, a temperature expansion valve controlled independently of outdoor unit 2.

[0014] Compressor 10 compresses the refrigerant suctioned from pipes 89 and 97, and discharges the compressed refrigerant to pipe 80. Compressor 10 can arbitrarily change a drive frequency by inverter control. Further, compressor 10 is provided with intermediate pressure port 63, and allows the refrigerant from intermediate pressure port G3 to flow into an intermediate portion of a compression process. Compressor 10 is configured to adjust a rotation speed according to a control signal from a controller 100. By adjusting the rotation speed of compressor 10, a circulation amount of the refrigerant is adjusted, and the capability of refrigeration cycle apparatus 1 can be adjusted. As compressor 10, various types of compressors can be adopted, and for example, a compressor of scroll type, rotary type, screw type, or the like can be adopted.

[0015] Condenser 20 is configured such that the high-temperature, high-pressure gas refrigerant discharged from compressor 10 performs heat exchange with outside air (heat dissipation). By this heat exchange, the refrigerant is condensed and transforms into a liquid phase. The refrigerant discharged from compressor 10 to pipe 80 is condensed and liquefied in condenser 20, and flows into pipe 81. Fan 22 for blowing the outside air is attached to condenser 20 in order to increase the efficiency of heat exchange. Fan 22 supplies condenser 20 with the outside air with which the refrigerant performs heat exchange in condenser 20. By adjusting the number of revolutions of fan 22, a refrigerant pressure on a discharge side of compressor 10 (a high pressure-side pressure) can be adjusted. Second expansion valve 40 is an electronic expansion valve which can decompress the refrigerant flowing out from condenser 20.

[0016] Here, it is assumed that the refrigerant used for a refrigerant circuit of refrigeration cycle apparatus I is CO2. However, when there occurs a state where a subcool is less likely to be ensured, another refrigerant may be used.

[0017] It should be noted that, in the present specification, for ease of description, a device which cools the refrigerant such as CO2 in a supercritical state will also be referred to as condenser 20. Further, in the present specification, for ease of description, an amount of decrease from a reference temperature of the refrigerant in the supercritical state will also be referred to as a subcool.

[0018] A flow path from compressor 10 to second expansion valve 40 via condenser 20 and first passage HI of heat exchanger 30 forms, together with a flow path on which first expansion valve 50 and evaporator 60 of load device 3 are disposed, a circulation flow path through which the refrigerant circulates. Hereinafter, this circulation flow path will also be referred to as a "main refrigerant circuit" of a refrigeration cycle.

[0019] Outdoor unit 2 further includes a first refrigerant flow path (91 to 94) configured to cause the refrigerant to flow front a portion of the circulation flow path between an outlet of first passage HI and second expansion valve 40 to an inlet of second passage H2, a second refrigerant flow path (96 to 98) configured to cause the refrigerant to flow from an outlet of second passage H2 to suction port G1 or intermediate pressure port G3 of compressor 10, and a flow path switching unit 74 disposed on the second refrigerant flow path and configured to select one of suction port G1 and intermediate pressure port 03 as a destination of the refrigerant flowing out from the outlet of second passage H2. Hereinafter, this flow path that branches from the main refrigerant circuit and delivers the refrigerant to compressor 10 via second passage H2 will be referred to as an "injection flow path" 101.

[0020] Outdoor unit 2 further includes a receiver 73 disposed on the fir st refrigerant flow path and configured to store the refrigerant. A third expansion valve 71 is disposed between pipes 91 and 92 between an inlet of receiver 73 and the portion of the circulation flow path between the outlet of first passage H1 and second expansion valve 40. Outdoor unit 2 further includes a flow rate control valve 72 disposed between a pipe 93 at an outlet of receiver 73 and a pipe 94 leading to second passage H2, and a degassing passage 95 that connects a gas exhaust outlet of receiver 73 to second passage 112 and is configured to exhaust a refrigerant gas within receiver 73.

[0021] Pipe 91 is a pipe that branches from the main refrigerant circuit and causes the refrigerant to flow into receiver 73. Third expansion valve 71 is an electronic expansion valve which can decrease the pressure of the refrigerant at a. high pressure portion of the main refrigerant circuit to an intermediate pressure. Receiver 73 is a container in which the refrigerant decompressed and having two phases is separated into gas and liquid, and which can store the refrigerant and adjust the amount of the refrigerant in the main refrigerant circuit. Degassing passage 95 connected to an upper portion of receiver 73 and pipe 93 connected to a. lower portion of receiver 73 are pipes for taking out the refrigerant separated into gas refrigerant and liquid refrigerant within receiver 73, in a separated state. Flow rate control valve 72 adjusts a circulation amount of the liquid refrigerant to be exhausted from pipe 93, and thereby can adjust the amount of the refrigerant in receiver 73.

[0022] By providing receiver 73 on the injection flow path as described above, it becomes easy to ensure a subcool in pipes 82 and 83 which are liquid pipes. This is because, since receiver 73 generally includes the gas refrigerant therein and a refrigerant temperature reaches a saturation temperature, it is not possible to ensure a subcool if receiver 73 is disposed on pipe 82.

[0023] Heat exchanger 30 exchanges heat between the refrigerant flowing in first passage HI as a portion of the main refrigerant circuit and the refrigerant flowing in second passage H2 as a portion of injection flow path 101.

[0024] Further, if receiver 73 is provided at an intermediate pressure portion, it becomes possible to store the intermediate pressure liquid refrigerant within receiver 73 even when the pressure at the high pressure portion of the main refrigerant circuit is high and the refrigerant is in the supercritical state. Thus, the design pressure of the container of receiver 73 can be set to be lower than that of the high pressure portion, and cost reduction by thinning the container can also be achieved.

[0025] Fig. 2 is a diagram showing various sensors and the controller disposed in refrigeration cycle apparatus 1 shown in Fig. 1. Referring to Fig. 2, outdoor unit 2 further includes pressure sensors 110 to 113, temperature sensors 120 to 125, and controller 100 configured to control flow path switching unit 74.

[0026] Pressure sensor 110 detects a pressure PL at the suction port portion of compressor 10, and outputs a detection value thereof to controller 100. Pressure sensor 111 detects a discharge pressure PH of compressor 10, and outputs a detection value thereof to controller 100. Pressure sensor 112 detects a pressure PI in pipe 83 at an outlet of second expansion valve 40, and outputs a detection value thereof to controller 100. Further, pressure sensor 113 detects an intermediate pressure PM in pipe 92 behind third expansion valve 71, and outputs a detection value thereof to controller 100.

[0027] By providing second expansion valve 40 to the liquid pipe, outdoor unit 2 can decompress the refrigerant pressure to be lower than or equal to the design pressure o-f load device 3 (for example, 4 MPa), and then deliver the refrigerant to load device 3. Thereby, even if refrigerant utilizing supercritical ity such as CO2 is used, a general-purpose product having the same design pressure as that of a conventional load device can be used as load device 3.

[0028] Temperature sensor 120 detects a discharge temperature TH of compressor 10, and outputs a detection value thereof to controller 100. Temperature sensor 121 detects a refrigerant temperature Ti in pipe 81 at an outlet of condenser 20, and outputs a detection value thereof to controller 100. Temperature sensor 122 detects a refrigerant temperature T2 at the outlet of first passage HI on a cooled side of heat exchanger 30, and outputs a detection value thereof to controller 100.

[0029] Temperature sensor 123 detects an ambient temperature TA of outdoor unit 2, and outputs a detection value thereof to controller 100. Temperature sensor 125 detects a temperature at the outlet of second passage H2 of heat exchanger 30, and outputs a detection value thereof to controller 100. Temperature sensor 124 detects a temperature TL in a suction pipe of compressor 10, and outputs a detection value thereof to controller 100.

[0030] The second refrigerant flow path includes a pipe 96 connecting between the outlet of second passage H2 of heat exchanger 30 and flow path switching unit 74, and flow path switching unit 74. Flow path switching unit 74 includes pipes 97 and 98 branching from pipe 96, a decompression device 77 disposed between pipes 97 and 98, and on-off valves 75 and 76 disposed on pipes 97 and 98, respectively.

[0031] On-off valve 75 is provided between the outlet of second passage 112 and intermediate pressure port G3. Decompression device 77 and on-off valve 76 are disposed in series between the outlet of second passage H2 and suction port Gl. [0032] Pipe 97 is connected between pipe 96 and intermediate pressure port G3. By on-off valves 75 and 76, an injection destination of the refrigerant can be switched between intermediate pressure port 03 and suction port GI of compressor 10.

[0033] In the present embodiment, injection flow path 101 controls discharge temperature TH of compressor 10 by causing the refrigerant decompressed and having two phases to flow into compressor 10. In addition, the amount of the refrigerant in the main refrigerant circuit can be adjusted by receiver 73 placed on injection flow path 101. Further, injection flow path 101 also ensures supercooling of the refrigerant in the main refrigerant circuit by heat exchange by heat exchanger 30. Controller 100 performs switching of injection by on-off valves 75 and 76 such that each purpose can be performed under each operation condition.

[0034] Controller 100 includes a CPU (Central Processing Unit) 102, a memory 104 (a ROM (Read Only Memory) and a RAM (Random Access Memory)), input/output buffers (not shown) for inputting/outputting various signals, and the like. CPU 102 expands programs stored in the ROM onto the RAM or the like and executes the programs. The programs stored in the ROM are programs describing processing procedures of controller 100. According to these programs, controller 100 performs control of the devices in outdoor unit 2. This control can be processed not only by software but also by dedicated hardware (electronic circuitry).

[0035] Controller 100 feedback-controls third expansion valve 71 such that discharge temperature TH of compressor 10 matches a target temperature. Specifically, when discharge temperature TH of compressor 10 is higher than the target temperature, controller 100 increases a degree of opening of third expansion valve 71. Thereby, the refrigerant flowing into intermediate pressure port 03 or suction port 01 via receiver 73 increases, and thus discharge temperature TH decreases.

[0036] On the other hand, when discharge temperature TH of compressor 10 is lower than the target temperature, controller 100 decreases the degree of opening of third expansion valve 71. Thereby, the refrigerant flowing into intermediate pressure port 03 or suction port 01 via receiver 73 decreases, and thus discharge temperature TH increases.

[0037] When discharge temperature TH is equal to the target temperature, controller 100 maintains the degree of opening of third expansion valve 71 in the present state.

[0038] Thus, controller 100 controls the degree of opening of third expansion valve 71 such that discharge temperature TH of compressor 10 approaches the target temperature.

[0039] Further, controller 100 feedback-controls flow rate control valve 72 such that refrigerant kmperature TI at the outlet of condenser 20 matches a target temperature, in order to ensure a subcool SC of the refrigerant at the outlet of condenser 20. Specifically, when subcool SC determined by refrigerant temperature Ti at the outlet of condenser 20 and a pressure in condenser 20 (approximated by PH) is larger than a target value, controller 100 decreases a degree of opening of flow rate control valve 72.

Thereby, the amount of the liquid refrigerant passing through receiver 73 decreases and the amount of the liquid refrigerant within receiver 73 increases, and thus the amount of the refrigerant circulating through the main refrigerant circuit decreases. Accordingly, refrigerant temperature Ti increases, and thus subcool SC decreases.

[0040] On the other hand, when subcool SC determined by refrigerant temperature Ti at the outlet of condenser 20 and the pressure in condenser 20 (approximated by PH) is smaller than the target value, controller 100 increases the degree of opening of flow rate control valve 72. Thereby, the amount of the gas refrigerant increases and the amount of the liquid refrigerant decreases in receiver 73, and thus the amount of the refrigerant circulating through the main refrigerant circuit increases. Accordingly, refrigerant temperature Ti decreases, and thus subcool Sc increases.

[0041] When subcool SC is equal to the target value, controller 100 maintains the degree of opening of flow rate control valve 72 in the present state.

[0042] Thus, controller 100 controls the degree of opening of flow rate control valve 72 such that refrigerant temperature Ti at the outlet of condenser 20 approaches the target temperature.

[0043] Further, when CO2 is used as the refrigerant, controller 100 performs control of compressor 10 and second expansion valve 40 to use a supercritical region of the refrigerant. For example, when an outside air temperature is higher than a supercritical temperature of the refrigerant as in summer, controller 100 increases the rotation speed of compressor 10 to be higher than that for spring or autumn, to increase the pressure at the high pressure portion. In this case, the pressure at the high pressure portion of the main refrigerant circuit increases. In order to allow load device 3 to be used in common with a device used with an ordinary refrigerant, decompression is performed in second expansion valve 40. On this occasion, second expansion valve is controlled as described below-.

[0044] Controller 100 feedback-controls second expansion valve 40 such that pressure Pl matches a target pressure. Specifically, when pressure P1 is higher than the target pressure, controller 100 decreases a degree of opening of second expansion valve 40.

Thereby, the amount of decompression by second expansion valve 40 increases, and thus pressure PI decreases.

[0045] On the other hand, when pressure PI is lower than the target pressure, controller 100 increases the degree of opening of second expansion valve 40. Thereby, the amount of decompression by second expansion valve 40 decreases, and thus pressure P1 increases.

[0046] When pressure PI is equal to the target pressure, controller 100 maintains the degree of opening of second expansion valve 40 in the present state.

[0047] Since pressure PI is controlled as described above, the pressure within load device 3 can be set to be lower than or equal to the design pressure of the device used with an ordinary refrigerant, and load device 3 can be used in common with a load device for a conventional machine which uses refrigerant such as R410A.

[0048] (Control of Switching of Injection Flow Path) When temperature sensor 120 detects an excessive increase in discharge temperature T11 of compressor 10, controller 100 opens on-off valve 75 and closes on-off valve 76 to increase the amount of injection to compressor 10 and prevent a further increase in the discharge temperature.

[0049] On this occasion, if intermediate pressure PM increases with an increase in evaporation temperature or the like with on-off valve 75 being-opened, the saturation temperature of the refrigerant increases, and thus the temperature of the refrigerant passing through second passage H2 of heat exchanger 30 also increases, resulting in an insufficient cooling in heat exchanger 30. Thus, there may be a case where it is impossible to ensure the subcool of the refrigerant in second expansion valve 40. [0050] Accordingly, controller 100 monitors refrigerant temperature T2 at temperature sensor 122 with on-off valve 75 being opened, and when it is detected that the subcool of the refrigerant cannot be ensured, controller 100 closes on-off valve 75 and opens on-off valve 76. Thereby, the refrigerant in injection flow path 101 is merged with the refrigerant on a low pressure side to decrease intermediate pressure PM, and a temperature difference in heat exchanger 30 can be ensured.

[0051] Since decompression is performed on the main refrigerant circuit by third expansion valve 71, the devices such as receiver 73 disposed on injection flow path 101 can have a low design pressure, and thus manufacturing cost can be reduced. Even in a case where the devices have a low desigt pressure, when pressure sensor 113 detects an increase in intermediate pressure PM during operation due to overcharging of the refrigerant, an increase in outside air temperature, or the like, it is possible to take a safety measure that releases pressure to the low pressure side by opening on-off valve 76.

[0052] Fig. 3 is a flowchart for illustrating control of flow path switching unit 74. Referring to Figs. 2 and 3, in step SI, controller 100 determines whether or not on-off valve 75 is opened and on-off valve 76 is closed. When on-off valve 75 is opened and on-off valve 76 is closed (YES in S1), intermediate pressure port G3 is selected as the destination of the refrigerant flowing through injection flow path 101. Conversely, when suction port G1 is selected as the destination of the refrigerant flowing through the injection flow path, on-off valve 75 is closed and on-off valve 76 is opened.

[0053] When on-off valve 75 is opened (YES in Si), in step S2, controller 100 determines whether or not refrigerant temperature T2 at the outlet of first passage HI of heat exchanger 30 is higher than or equal to a first temperature Tthl. Thereby, it is determined whether or not the subcool of the refrigerant passing through pipe 82 can be ensured.

[0054] When refrigerant temperature T2 at the outlet of first passage HI of heat exchanger 30 is higher than first temperature Tthl (YES in S2), in step S3, controller 100 determines whether or not suctioned refrigerant temperature TL is higher than a threshold value TLthl. Also when refrigerant temperature T2 at the outlet of first passage HI of heat exchanger 30 is equal to first temperature Tthl (YES in S2), -I 2 -controller 100 performs the processing in step S3.

[0055] When on-off valve 76 is opened and injection flow path 101 is connected to a low pressure side of extension pipe 88 on a gas side, there may occur a liquid back state where the liquid refrigerant in receiver 73 flows into compressor 10. In step 53, switching of the flow path to on-off valve 76 is stopped in such a case to prevent the liquid refrigerant from flowing into compressor 10.

[0056] When refrigerant temperature TL is low relative to the saturation temperature at pressure PL of the refrigerant to be suctioned by compressor 10, the liquid refrigerant may be suctioned into compressor 10. Since compressor 10 is broken down by liquid compression on this occasion, on-off valve 76 is controlled to remain closed when suction of the liquid refrigerant is detected. Also concerning on-off valve 75, on-off valve 75 may also be closed when suction of the liquid refrigerant occurs. Whether or not compressor 10 may suction the liquid refrigerant can be determined based on that there is no degree of superheat, which is a difference between the saturation temperature at pressure PL detected by pressure sensor 110 and temperature TL detected by temperature sensor 124.

[0057] Further, also when it is detected in injection flow path 101 that the temperature of temperature sensor 125 is low relative to a saturation pressure of pressure sensor 113 and the degree of superheat is not ensured, on-off valve 76 may he closed to prevent the liquid refrigerant from being suctioned into compressor 10.

[0058] Specifically, when suctioned refrigerant temperature TL of compressor 10 is higher than or equal to threshold value TLthl (YES in S3), controller 100 controls flow path switching unit 74 to switch the destination of the refrigerant to suction port GI by sequentially performing the processing in steps S4 to 85. Controller 100 closes on-off valve 75 in step S4, opens on-off valve 76 in step 55, and thereafter returns the processing to a main routine in step 510.

[0059] In the present embodiment, since decompression device 77 is provided between on-off valve 75 and on-off valve 76, pressure fluctuation when flow path switching unit 74 switches the flow path is relieved and transmitted to compressor 10. Accordingly, -13 -vibration during switching of the flow path is reduced, and thus on-off valves 75 and 76 can be opened/closed without stopping the operation of compressor 10. Therefore, the flow path can be switched in a short time, and an energy loss associated with stopping and restarting compressor 10 does not occur.

[0060] It should be noted that, when refrigerant temperature T2 is lower than first temperature Tthl (NO in S2), a subcool can be ensured, and when suctioned refrigerant temperature TL of compressor 10 is lower than threshold value TLth I (NO in 53), the liquid refrigerant may be suctioned into compressor 10. Accordingly, controller 100 returns the processing to the main routine in step 510, without performing switching in flow path switching unit 74 in steps 54 to 55.

[0061] On the other hand, when on-off valve 75 is closed (NO in Si), and suctioned refrigerant temperature TL of compressor 10 is lower than a threshold value TLth2 (NO in 56), controller 100 controls flow path switching unit 74 to switch the destination of the refrigerant to intermediate pressure port (13 by sequentially performing the processing in steps 58 to 59. It should be noted that TLthl is higher than TLth2.

[0062] Further, when suctioned refrigerant temperature TL of compressor 10 is higher than or equal to threshold value TLth2 (YES in 56), controller 100 determines the subcool of the refrigerant in pipe 82, based on whether or not refrigerant temperature T2 at the outlet of first passage HI of heat exchanger 30 is higher than or equal to a second temperature Tth2.

[0063] When refrigerant temperature T2 is higher than or equal to second temperature Tth2 (YES in S7), a subcool cannot be ensured. In this ease, the present state in which on-off valve 75 is closed and on-off valve 76 is opened is maintained, and the processing proceeds to step 510. It should be noted that Tthl is higher than Tth2.

[0064] On the other hand, when refrigerant temperature T2 is lower than second temperature Tth2 (NO in 57), a subcool can be ensured. Thus, in order to return to the normal state of the injection flow path, on-off valve 76 is closed in step 58, on-off valve 75 is opened in step 59, and thereafter the processing proceeds to step Si 0. [0065] As described above, when a pressure difference between pipe 82 and pipe 94 is small, controller 100 controls flow path switching unit 74 to increase the pressure difference, to switch the destination of the refrigerant from intermediate pressure port 03 to suction port GI. Accordingly, the amount of decompression in third expansion valve 71 can be ensured, and thus the amount of temperature decrease M. third expansion valve 71 increases. Thereby, a temperature difference between a refrigerant temperature in first passage HI and a refrigerant temperature in second passage f12 of heat exchanger 30 can be ensured. Therefore, the amount of heat exchange in heat exchanger 30 increases, and thus refrigerant temperature T2 can be decreased.

[0066] Further, since decompression device 77 is disposed between on-off valve 75 and on-off valve 76, the behavior of compressor 10 is stabilized even when the flow path is switched without stopping compressor 10. Therefore, faster switching can be achieved.

[0067] (Control during Pump Down Operation) Next, control during a pump down operation will be described. The pump down operation is an operation to transfer the refrigerant from load device 3 to outdoor unit 2 and store the refrigerant therein, by placing on-off valve 28 or the like on pipe 84 or 85 through which the liquid refrigerant flows in the main refrigerant circuit, and operating compressor 10 with pipe 83 being blocked. The pump down operation is performed, for example, by closing second expansion valve 40 or on-off valve 28 before stopping operation or at relocation, and thereafter operating compressor 10. [0068] When outdoor unit 2 is stopped during the pump down operation, if injection flow path 101 and a. low pressure portion are connected with on-off valve 76 being opened, injection flow path 101 serves as a bypass path between the suction port (low pressure side) and the discharge port (high pressure side) of compressor 10.

Accordingly, the pressure (low pressure) of load device 3 does not decrease even through compressor 10 is operated, and it is not possible to stop outdoor unit 2. [0069] Controller 100 is configured to control compressor 10 and on-off valves 75 and 76. When the pump down operation for recovering the refrigerant to receiver 73 is -15 -performed, controller 100 is configured to close on-off valve 76 while operating compressor 10.

[0070] In the following, control for stopping outdoor unit 2 by closing on-off valve 76 during a pump down will be described.

[0071] Fig. 4 is a flowchart for illustrating control during the pump down operation.

In the pump down operation, when on-off valve 28 is closed and pressure PL at the low pressure portion detected by pressure sensor 110 decreases to a set value, controller 100 is configured to stop compressor 10 and stop the pump down. Since compressor 10 is configured such that the refrigerant may not pass thercthrough when it is stopped, the refrigerant does not flow back to load device 3. Under a certain condition, however, when a subcool is prioritized, the pump down is perfoimed with on-off valve 76 being opened, which may lead to a case where pressure PL does not decrease enough and the outdoor unit is not stopped, or a case where pressure PL increases immediately after the pump down is stopped, and compressor 10 repeats start and stop in a short time.

[0072] Accordingly, when it is detected in step 521 that pressure PL at the low pressure portion rapidly decreases to the set value or lower, controller 100 performs the processing in steps 522 to S25. By closing on-off valve 76 on injection flow path 101 during the pump down, a bypass to the high pressure or intermediate pressure portion is blocked, and the pump down can be stably performed.

[0073] Specifically, in step S22, controller 100 closes on-off valve 76 to block a bypass path between load device 3 and the high pressure portion.

[0074] Then, controller 100 opens on-off valve 75 in step S23, and increases the degree of opening of third expansion valve 71 in step 524. Further, in step S25, controller decreases the degree of opening of flow rate control valve 72 to increase the amount of the refrigerant stored in receiver 73.

[0075] It should be noted that, although the above description describes that on-off valve 75 is opened during the pump down operation, on-off valve 75 may be closed. [0076] Further, although the above description describes that on-off valve 76 is closed during the pump down operation, when pressure sensor I I I or 113 detects an excessive increase in pressure due to overcharging of the refrigerant or the like, on-off valve 76 may be temporarily opened to temporarily release the pressure in liquid reservoir 73 to an air suction side of the compressor. Thereby, compressor 10 can be stopped Mier recovering as much refrigerant as possible to receiver 73 in the pump down operation.

[0077] (Control of Oil Recovery Operation) When receiver 73 is disposed on injection flow path 101 as in the configuration shown in Figs. 1 and 2, if a refrigerating machine oil and the refrigerant are immiscible, the refrigerating machine oil separated from the refrigerant is accumulated in receiver 73, and the refrigerating machine oil is less likely to be recovered to compressor 10.

Accordingly, in the present embodiment, an oil recovery operation is performed.

[0078] Concerning the oil recovery operation, outdoor unit 2 includes degassing passage 95 provided between the gas exhaust outlet of receiver 73 and receiver 73 and configured to exhaust the refrigerant gas within receiver 73, and flow rate control valve 72 disposed at a liquid refrigerant outlet of receiver 73. Further, outdoor unit 2 includes controller 100 configured to control compressor 10 and flow rate control valve 72. When an oil recovery condition that the refrigerating machine oil in compressor 10 decreases is satisfied, controller 100 is configured to increase the degree of opening of third expansion valve 71 and decrease the degree of opening of flow rate control valve 72.

[0079] Fig. 5 is a flowchart for illustrating control during the oil recovery operation.

In step S31, controller 100 determines whether or not the oil recovery condition is satisfied. The oil recovery condition is satisfied, for example, when an operation time has elapsed for a certain period of time, or when low speed operation of compressor 10 continues for a certain period of time or more, or the like.

[0080] When the oil recovery condition is not satisfied (NO in S31), controller 100 temporarily returns the processing to a main routine in step S35, and then monitors again whether or not the oil recovery condition is satisfied in step 531.

[0081] On the other hand, when the oil recovery condition is not satisfied (YES in S31), controller 100 closes on-off valve 76 in step S32, opens on-off valve 75 in step 533, and decreases the degree of opening of flow rate control valve 72 in step 534. Thereby, the amount of the refrigerant flowing out from the liquid refrigerant outlet of receiver 73 decreases, the amount of the liquid refrigerant stored in receiver 73 increases, and the refrigerating machine oil separately stored on the liquid refrigerant flows out from degassing passage 95.

[0082] In this manner, when the refrigerating machine oil and the refrigerant are immiscible and separated in receiver 73, the refrigerating machine oil located on a liquid level side can be recovered from degassing passage 95 to compressor 10 by increasing the amount of the refrigerant within receiver 73 by the pump down operation and causing a liquid level to rise.

[0083] Second Embodiment A second embodiment will describe a refrigeration cycle apparatus that switches a circuit according to a condition, when an accumulator is placed in a main refrigerant circuit.

[0084] Fig. 6 is a diagram showing a configuration of a refrigeration cycle apparatus of the second embodiment. A refrigeration cycle apparatus IA shown in Fig. 6 includes an outdoor unit 2A, instead of outdoor unit 2 in the configuration of refrigeration cycle apparatus I shown in Figs. 1 and 2. Since load device 3 has the same configuration, the description thereof will not be repeated. Further, since the arrangement of the pressure sensors and the temperature sensors is the same as that in Fig. 2, the

description thereof will not be repeated.

[0085] Outdoor unit 2A includes a flow path switching unit 74A, instead of flow path switching unit 74 in the configuration of outdoor unit 2, and further includes an accumulator 89B.

[0086] Accumulator 89B is configured to temporarily accumulate the refrigerant flowing front load device 3 toward suction port GI of compressor 10 in the circulation flow path.

[0087] In addition to the configuration of flow path switching unit 74 in Fig. 1, flow path switching unit 74A further includes an on-off valve 78 that opens/closes a flow -18 -path connecting the outlet of second passage 112 and a refrigerant inlet of accumulator 89B with decompression device 77 being interposed therebetween.

[0088] With such a configuration, injection flow path 101 has three connection destinations: intermediate pressure port G3 and suction port GI of compressor 10, and a pipe 89A upstream of accumulator 89B.

[0089] Fig. 7 is a flowchart for illustrating control of flow path switching unit 74A. Referring to Figs. 6 and 7, in step 531, controller 100 determines whether or not on-off valve 75 is opened and on-off valves 76 and 78 are closed. When on-oft valve is opened and on-off valves 76 and 78 are closed (YES in S31), intermediate pressure port G3 is selected as the destination of the refrigerant flowing through injection flow path 101.

[0090] When on-off valve 75 is opened (YES in 531), in step 532, controller 100 determines whether or not refrigerant temperature T2 at the outlet of first passage HI of heat exchanger 30 is higher than or equal to first temperature Tthl. Thereby, it is determined whether or not the subcool of the refrigerant passing through pipe 82 can be ensured.

[0091] When refrigerant temperature T2 at the outlet of first passage H1 of heat exchanger 30 is higher than first temperature Tthl (YES in S32), in step S33, controller 100 determines whether or not suctioned refrigerant temperature TL is higher than threshold value TLthl. Also when refrigerant temperature T2 at the outlet of first passage H1 of heat exchanger 30 is equal to first temperature Tthl (YES in 532), controller 100 performs the processing in step S33.

[0092] When suctioned refrigerant temperature TL of compressor 10 is higher than or equal to threshold value TLthl (YES in S33), in step S34, controller 100 determines whether or not discharge temperature TH is higher than or equal to a target temperature TIIthi.

[0093] When discharge temperature TH is higher than or equal to target temperature THthl (YES in 534), controller 100 controls flow path switching unit 74A to switch the destination of the refrigerant to suction port G1 by sequentially performing the processing in steps S35 to 836. Controller 100 closes on-off valves 75 and 78 in step 535, opens on-off valve 76 in step 536, and thereafter returns the processing to a main routine in step 548, [0094] When discharge temperature TH is lower than target temperature THthl (NO in S34), controller 100 controls flow path switching unit 74A to switch the destination of the refrigerant to pipe 89A at the inlet of accumulator 89B by sequentially performing the processing in steps S37 to S38. Controller 100 closes on-off valves 75 and 76 in step 537, opens on-off valve 78 in step 538, and thereafter returns the processing to the main routine in step 548.

[0095] In the present embodiment, since decompression device 77 is provided between on-off valve 75 and on-off valve 76, pressure fluctuation when flow path switching unit 74 switches the flow path is relieved and transmitted to compressor 10. Accordingly, vibration during switching of the flow path is reduced, and thus on-off valves 75, 76, and 78 can be opened/closed without stopping the operation of compressor 10.

Therefore, the flow path can be switched in a short time, and an energy loss associated with stopping and restarting compressor I 0 does not occur.

[0096] It should be noted that, when refrigerant temperature T2 is lower than first temperature Tthl (NO in 532), a. subcool can be ensured, and when suctioned refrigerant temperature TL of compressor 10 is lower than threshold value TLthl (NO in S33), the liquid refrigerant may be suctioned into compressor 10. Accordingly, controller 100 returns the processing to the main routine in step S10, without performing switching in flow path switching unit 74 in steps 534 to 538.

[0097] On the other hand, when on-off valve 75 is closed (NO in S31), and suctioned refrigerant temperature TL of compressor 10 is lower than threshold value TLth2 (NO in 539), controller 100 controls flow path switching unit 74 to switch the destination of the refrigerant to intermediate pressure port G3 by sequentially performing the processing in steps S46 to 547. It should be noted that TIAhl is higher than TLth2. [0098] Further, when suctioned refrigerant temperature TL of compressor 10 is higher than or equal to threshold value TLth2 (YES in S39), in step 540, controller 100 -20 -determines the subcool of the refrigerant in pipe 82, based on whether or not refrigerant temperature T2 at the outlet of first passage HI of heat exchanger 30 is higher than or equal to second temperature Tth2. It should be noted that Tth 1 is higher than Tth2. [0099] When refrigerant temperature T2 is higher than or equal to second temperature Tth2 (YES in 540), a subcool cannot be ensured. In this case, in step S41, controller determines whether or not discharge temperature TH is higher than or equal to a target temperature Tlith2, in step S41. It should be noted that THthl is lower than TIIth2.

[0100] When discharge temperature TH is higher than or equal to target temperature THth2 (YES in 541), controller 100 controls flow path switching unit 74A to switch the destination of the refrigerant to suction port G1 by sequentially performing the processing in steps 542 to 543. Controller 100 closes on-off valve 78 in step 542, opens on-off valve 76 in step 543, and thereafter returns the processing to the main routine in step S48.

[0101] When discharge temperature TH is lower than target temperature THth2 (NO in 541), controller 100 controls flow path switching unit 74A to switch the destination of the refrigerant to pipe 89A at the inlet of accumulator 89B by sequentially performing the processing in steps S44 to 545. Controller 100 closes on-off valve 76 in step S44, opens on-off valve 78 in step 545, and thereafter returns the processing to the main routine in step S48.

[0102] On the other hand, when refrigerant temperature T2 is lower than second temperature Tth2 (NO in S40), a subcool can be ensured. Thus, in order to return to the normal state of the injection flow path, on-off valves 76 and 78 are closed in step 546, on-off valve 75 is opened in step S47, and thereafter the processing proceeds to step S48.

[0103] Since a connection destination can be selected as described above, for example when suction of the liquid refrigerant into compressor 10 is detected in a state where a subcool in pipe 82 is not ensured, the connection destination of injection flow path 101 can be switched to a portion in front of accumulator 89B, to ensure the subcool and also -21 -prevent suction of the liquid refrigerant into compressor 10. Further, discharge temperature TH can be suppressed by connecting injection flow path 101 to suction port GI behind accumulator 89B in a state where the subcool cannot be ensured, and directly delivering the cooled refrigerant into suction port Cl.

[0104] Fig. 8 is a diagam showing a configuration of a refrigeration cycle apparatus 201 of a first variation. Refrigeration cycle apparatus 201 has a configuration in which suction port Cl is the only connection destination of the injection flow path. Fig. 9 is a diagam showing a configuration of a refrigeration cycle apparatus 201A of a second variation. Refrigeration cycle apparatus 201A has a configuration in which pipe 89A at the inlet of accumulator 89B is the only connection destination of the injection flow path. Fig. 10 is a diagram showing a configuration of a refrigeration cycle apparatus 201B of a third variation. Refrigeration cycle apparatus 201B has a configuration in which intermediate pressure port 03 is the only connection destination of the injection flow path.

[0105] As shown in Figs. 8 to 10 above, it is also possible that the refrigeration cycle apparatus has a structure having a single connection destination according to its use condition.

[0106] For example, when the refrigeration cycle apparatus is used under a condition that a refrigeration condition or the like is limited, since the intermediate pressure can be sufficiently decreased, the injection flow path can be connected to only intermediate pressure port 03 of compressor 10 as shown in Fig. 10, as long as a subcool can be always ensured. Similarly, when the refrigeration cycle apparatus is limited to be used under such a condition that the discharge temperature does not increase, the injection flow path can be configured to be connected to only pipe 89A as shown in Fig. 9.

[0107] Although the present embodiment has been described by illustrating a refrigerating machine including refrigeration cycle apparatus 1, refrigeration cycle apparatus I may be utilized in an air conditioner or the like.

[0108] It should be understood that the embodiments disclosed herein are illustrative -22 -and non-restrictive in every respect. The scope of the present disclosure is defined by the scope of the claims, rather than the description of the embodiments described above, and is intended to include any modifications within the scope and meaning equivalent to the scope of the claims.

REFERENCE SIGNS LIST

[0109] 1, IA, 201, 20IA, 201B: refrigeration cycle apparatus; 2, 2A: outdoor unit; 3: load device; 10: compressor; 20: condenser; 22: fan; 28, 75, 76, 78: on-off valve; 30: heat exchanger; 40: second expansion valve; 50: first expansion valve; 60: evaporator; 71: third expansion valve; 72: flow rate control valve; 73: receiver; 74, 74A: flow path switching unit; SO to 85, 89, 89A, 91 to 94,96 to 98: pipe; 77: decompression device; 84, 88: extension pipe; 89B: accumulator; 95: degassing passage; 100: controller; 101: injection flow path; 102: CPU; 104: memory; 110 to 113: pressure sensor; 120 to 125: temperature sensor; Gl: suction port; G2: discharge port; G3: intermediate pressure port; HI: first passage; H2: second passage.

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Claims

CLAIMS1. An outdoor unit of a refrigeration cycle apparatus, the outdoor unit being connectable to a load device including a first expansion valve and an evaporator, the outdoor unit comprising: a compressor having a suction port, a discharge port, and an intermediate pressure port; a condenser; a heat exchanger having a first passage and a second passage and configured to exchange heat between refrigerant flowing in the first passage and the refrigerant flowing in the second passage; and a second expansion valve, wherein a flow path from the compressor to the second expansion valve via the condenser and the first passage of the heat exchanger forms, together with the load device, a circulation flow path through which the refrigerant circulates, the outdoor unit further comprising: a first refrigerant flow path configured to cause the refrigerant to flow from a portion of the circulation flow path between an outlet of the first passage and the second expansion valve to an inlet of the second passage; a third expansion valve disposed on the first refrigerant flow path; a second refrigerant flow path configured to cause the refrigerant to flow from an outlet of the second passage to the suction port or the intermediate pressure port of the compressor; and a flow path switching unit disposed on the second refrigerant flow path and configured to select one of the suction port and the intermediate pressure port as a destination of the refrigerant flowing out from the outlet of the second passage, wherein the flow path switching unit includes a first on-off valve provided between the outlet of the second passage and the intermediate pressure port, and -24 -a decompression device and a second on-off valve disposed in series between the outlet of the second passage and the suction port.
2. The outdoor unit according to claim 1, further comprising a receiver disposed on the first refrigerant flow path and configured to store the refrigerant, wherein the third expansion valve is disposed between an inlet of the receiver and the portion of the circulation flow path between the outlet of the first passage and the second expansion valve.
3. The outdoor unit according to claim 2, further comprising a controller configured to control the compressor and the first and second on-off valves, wherein when a pump down operation for recovering the refrigerant to the receiver is performed, the controller is configured to close the second on-off valve while operating the compressor.
4. The outdoor unit according to claim 2, further comprising: a degassing passage provided between an outlet of the receiver and the receiver and configured to exhaust a refrigerant gas within the receiver; and a flow rate control valve disposed at a liquid refrigerant outlet of the receiver.
5. The outdoor unit according to claim 4, further comprising a controller configured to control the compressor and the flow rate control valve, wherein when an oil recovery condition that a refrigerating machine oil in the compressor decreases is satisfied, the controller is configured to increase a degree of opening of the third expansion valve and decrease a degree of opening of the flow rate control valve.
6. The outdoor unit according to claim I, further comprising an accumulator, -25 -wherein the accumulator is configured to temporarily accumulate the refrigerant flowing from the load device toward the suction port of the compressor in the circulation flow path, and the flow path switching unit further includes a third on-off valve that opens/closes a flow path connecting the outlet of the second passage and a refrigerant inlet of the accumulator with the decompression device being interposed therebetween.
7. A refrigeration cycle apparatus comprising: the outdoor unit according to any one of claims 1 to 6; and the load device.-26 -