Refrigeration cycle device

Abstract

This refrigeration cycle device comprises: a refrigerant circuit configured so that a refrigerant circulates, in the stated order, through a compressor, a first flow path, a condenser, a second flow path, an expansion valve, a third flow path, an evaporator, and a fourth flow path; and a control device that controls the compressor. The refrigerant circuit further includes: a liquid injection flow path that communicates the second flow path and the fourth flow path; a bypass flow path that communicates the first flow path and the fourth flow path; and a bypass valve provided in the bypass flow path. The control device: determines whether the differential pressure between the intake side and the discharge side of the compressor is greater than a threshold value if a start condition for the compressor is satisfied; opens the bypass valve, if the differential pressure is greater than the threshold value, and determines whether the differential pressure is less than the threshold value after the bypass valve has been opened; starts the compressor upon determining that the differential pressure is less than the threshold value; and closes the bypass valve after starting the compressor.

Description

Refrigeration Cycle Equipment

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

[0002] Japanese Patent Laid-Open Publication No. 2005-172249 (Patent Document 1) discloses a refrigeration cycle apparatus including a bypass flow path that connects the discharge side and suction side of a compressor and a bypass valve for opening and closing the bypass flow path. In this refrigeration cycle apparatus, the bypass valve is opened before the compressor is started, and the compressor is started after the differential pressure between the discharge side and suction side of the compressor has decreased. This prevents excessive current from flowing through the compressor when the differential pressure between the suction side and discharge side of the compressor is large (high differential pressure start).

[0003] Japanese Patent Laid-Open Publication No. 7-260262 (Patent Document 2) discloses a refrigeration cycle apparatus equipped with a liquid injection flow path for supplying liquid refrigerant condensed in a condenser to the discharge side of a compressor. In this refrigeration cycle apparatus, the compressor is cooled by supplying the liquid refrigerant condensed in the condenser through the liquid injection flow path to the discharge side of the compressor (liquid injection function). This prevents the compressor discharge temperature from rising excessively.

[0004] JP 2005-172249 JP 7-260262

[0005] In a refrigeration cycle device having both a bypass flow path and a liquid injection flow path as described above, if the bypass valve is opened before the compressor is started and all of the liquid refrigerant on the discharge side (high-pressure side) of the compressor moves to the suction side (low-pressure side), it is possible to suppress overcurrent caused by starting the compressor at a high differential pressure. However, after the compressor is started, there is a concern that the liquid injection function will become ineffective due to the absence of liquid refrigerant on the discharge side of the compressor, making it impossible to suppress an excessive rise in the compressor discharge temperature.

[0006] The present disclosure has been made to solve the above-mentioned problems, and its purpose is to appropriately suppress both overcurrent caused by high differential pressure startup of the compressor and excessive rise in compressor discharge temperature caused by inability to perform liquid injection in a refrigeration cycle device equipped with a bypass flow path and a liquid injection flow path.

[0007] A refrigeration cycle apparatus according to the present disclosure includes a refrigerant circuit including a compressor, a first flow path, a condenser, a second flow path, an expansion valve, a third flow path, an evaporator, and a fourth flow path, the refrigerant circulating in this order when the compressor is operated, and a control device for controlling the compressor. The refrigerant circuit further includes a liquid injection flow path connecting the second flow path and the fourth flow path and supplying liquid refrigerant from the second flow path to the fourth flow path, a bypass flow path connecting the first flow path and the third flow path or the fourth flow path and supplying gas refrigerant from the first flow path to the third flow path or the fourth flow path, and a bypass valve provided in the bypass flow path. When a compressor start condition is met, the control device determines whether a differential pressure between the suction side and the discharge side of the compressor is greater than a threshold value, opens the bypass valve if the differential pressure is greater than the threshold value, and after opening the bypass valve, determines whether the differential pressure is smaller than the threshold value, starts the compressor when it is determined that the differential pressure is smaller than the threshold value, and closes the bypass valve after the compressor has started.

[0008] According to the present disclosure, in a refrigeration cycle device having a bypass flow path and a liquid injection flow path, it is possible to appropriately suppress both overcurrent caused by high differential pressure startup of the compressor and excessive rise in the compressor discharge temperature caused by the inability of the liquid injection function.

[0009] 1 is a diagram (part 1) showing a schematic diagram of an example of the overall configuration of a refrigeration cycle device; FIG. 2 is a flowchart (part 2) showing an example of the processing procedure of a control device; and FIG. 3 is a diagram (part 3) showing a schematic diagram of an example of the overall configuration of a refrigeration cycle device; and FIG. 4 is a flowchart (part 4) showing an example of the processing procedure of a control device.

[0010] Hereinafter, embodiments of the present disclosure will be described in detail with reference to the drawings. In the drawings, the same or corresponding parts are designated by the same reference numerals, and description thereof will not be repeated.

[0011] 1 is a diagram schematically illustrating an example of the overall configuration of a refrigeration cycle apparatus 1 according to the present embodiment. The refrigeration cycle apparatus 1 includes a refrigerant circuit 2 through which a refrigerant circulates, and a control device 100. The refrigerant circuit 2 includes a compressor 10, a condenser 20, an expansion valve 30, an evaporator 40, and flow paths P1 to P4. The refrigerant circuit 2 is configured such that, when the compressor 10 is operated, the refrigerant circulates through the compressor 10, flow path P1, condenser 20, flow path P2, expansion valve 30, flow path P3, evaporator 40, and flow path P4 in this order.

[0012] In this embodiment, a refrigerant with a high specific heat ratio, such as R32 alone or a mixed refrigerant containing R32, is used as the refrigerant circulating through the refrigerant circuit 2. A refrigerant with a higher specific heat ratio than R410A may be used as the refrigerant circulating through the refrigerant circuit 2. When a refrigerant with a high specific heat ratio is used, the temperature of the gas refrigerant discharged from the compressor 10 (hereinafter also referred to as the "compressor discharge temperature") tends to be high.

[0013] The compressor 10 draws in low-pressure refrigerant from the flow path P4, compresses it, and discharges it as high-pressure gas refrigerant to the flow path P1. The compressor 10 discharges the refrigerant at a flow rate that corresponds to the frequency (rotation speed). The frequency (rotation speed) of the compressor 10 is controlled by the control device 100.

[0014] The condenser 20 is a heat exchanger having a flow path through which the refrigerant flows. In the condenser 20, heat exchange occurs between the refrigerant flowing inside the flow path and the air outside the flow path. The high-pressure gas refrigerant discharged from the compressor 10 is condensed into liquid refrigerant through heat exchange in the condenser 20.

[0015] The expansion valve 30 is a pressure reducing device that reduces the pressure of the high-pressure refrigerant. As the expansion valve 30, for example, an electronically controlled expansion valve having a valve element whose opening degree can be adjusted can be used.

[0016] The evaporator 40 is a heat exchanger having a flow path through which the refrigerant flows. In the evaporator 40, heat exchange occurs between the refrigerant flowing inside the flow path and the air outside the flow path. The refrigerant decompressed by the expansion valve 30 becomes a gas refrigerant through heat exchange in the evaporator 40. The gas refrigerant discharged from the evaporator 40 is drawn into the compressor 10.

[0017] Furthermore, the refrigerant circuit 2 according to the present embodiment includes a liquid injection flow path 50. As described above, in the present embodiment, a refrigerant with a high specific heat ratio is used as the refrigerant circulating through the refrigerant circuit 2, and the compressor discharge temperature tends to be high. An excessive increase in the compressor discharge temperature can cause damage to the compressor 10. As a configuration for suppressing such an excessive increase in the compressor discharge temperature, the refrigerant circuit 2 is provided with the liquid injection flow path 50.

[0018] The liquid injection flow path 50 connects a connection C1 provided in the flow path P2 between the condenser 20 and the expansion valve 30 with a connection C2 provided in the flow path P4 between the evaporator 40 and the compressor 10. A portion of the liquid refrigerant condensed in the condenser 20 is supplied through the liquid injection flow path 50 to the flow path P4 arranged on the suction side of the compressor 10. The liquid refrigerant condensed in the condenser 20 is supplied through the liquid injection flow path 50 to the discharge side of the compressor 10 (hereinafter also referred to as the "liquid injection function"), thereby cooling the compressor 10 and suppressing an excessive rise in the compressor discharge temperature.

[0019] The liquid injection flow path 50 is provided with a flow rate adjustment valve 51 for adjusting the flow rate of the liquid refrigerant flowing through the liquid injection flow path 50. The opening degree of the flow rate adjustment valve 51 is controlled by the control device 100.

[0020] Furthermore, the refrigerant circuit 2 according to this embodiment includes a bypass flow path 60. If the compressor 10 is started (hereinafter also referred to as "high differential pressure start-up") when the difference between the pressure on the suction side and the pressure on the discharge side of the compressor 10 (hereinafter also referred to as "compressor differential pressure") is large, the load on the compressor 10 will be large, causing an overcurrent, and there is a concern that the compressor 10 may not be able to start up normally. As a configuration for suppressing such an overcurrent due to high differential pressure start-up, the refrigerant circuit 2 is provided with a bypass flow path 60 that connects the discharge side and suction side of the compressor 10.

[0021] The bypass flow path 60 connects a connection C3 provided in the flow path P1 between the compressor 10 and the condenser 20 with a connection C4 provided in the flow path P4 between the evaporator 40 and the compressor 10. The bypass flow path 60 is provided with a bypass valve 61 for opening and closing the bypass flow path 60. By opening the bypass valve 61 when the compressor differential pressure is large, the refrigerant on the high-pressure side (discharge side) of the compressor 10 can be moved to the low-pressure side (suction side) to reduce the compressor differential pressure. By starting the compressor 10 after reducing the compressor differential pressure, high differential pressure startup of the compressor 10 is suppressed, and overcurrent is suppressed, allowing the compressor 10 to start normally. The opening degree of the bypass valve 61 is controlled by the control device 100.

[0022] The refrigerant circuit 2 is further provided with pressure sensors 71, 72 and a temperature sensor 73. The pressure sensor 71 detects the pressure on the discharge side of the compressor 10. The pressure sensor 72 detects the pressure on the suction side of the compressor 10. The temperature sensor 73 detects the compressor discharge temperature. The pressure sensors 71, 72 and the temperature sensor 73 output their detection results to the control device 100.

[0023] The control device 100 includes a CPU (Central Processing Unit) 101, a memory 102, and an input / output port (not shown) for inputting and outputting various signals. The control device 100 controls the various devices (such as the compressor 10, the expansion valve 30, the flow control valve 51, and the bypass valve 61) of the refrigeration cycle device 1 based on signals from various sensors (such as the pressure sensors 71 and 72 and the temperature sensor 73) and devices, as well as programs stored in the memory 102. Note that the control performed by the control device 100 is not limited to software processing, and can also be performed by dedicated hardware (electronic circuits).

[0024] When the compressor discharge temperature detected by the temperature sensor 73 is higher than the threshold temperature, the control device 100 opens the flow control valve 51 to perform liquid injection, supplying liquid refrigerant from the liquid injection flow path 50 to the suction side of the compressor 10. This prevents the compressor discharge temperature from rising excessively.

[0025] Furthermore, when the start-up conditions for the compressor 10 are met and the compressor differential pressure is large, the control device 100 opens the bypass valve 61 before starting the compressor 10 to reduce the compressor differential pressure in order to suppress high differential pressure start-up, and starts the compressor 10 after the compressor differential pressure has dropped below the threshold value.

[0026] However, if the bypass valve 61 is opened before the start of the compressor 10 and all of the liquid refrigerant on the high-pressure side (discharge side) of the compressor 10 moves to the low-pressure side (suction side), there will be no liquid refrigerant on the high-pressure side after the start of the compressor 10, which may disable the liquid injection function and make it impossible to suppress an excessive rise in the compressor discharge temperature. In particular, in this embodiment, as described above, a refrigerant with a high specific heat ratio is used, which tends to increase the compressor discharge temperature, so it is highly desirable to have the liquid injection function function properly.

[0027] Therefore, when the start conditions for the compressor 10 are met, the control device 100 according to this embodiment first determines whether the compressor differential pressure is greater than a threshold value, and if the compressor differential pressure is greater than the threshold value, opens the bypass valve 61 to temporarily reduce the compressor differential pressure, starts the compressor 10 at the moment when the compressor differential pressure is temporarily reduced, and closes the bypass valve 61 after starting the compressor 10. This suppresses overcurrent due to high differential pressure start-up, and also makes it possible to close the bypass valve 61 before all of the liquid refrigerant on the high-pressure side of the compressor 10 moves to the low-pressure side, allowing the liquid injection function to operate normally after starting the compressor 10.

[0028] Fig. 2 is a flowchart showing an example of a processing procedure performed by the control device 100 when starting the compressor 10. The flowchart of Fig. 2 is executed when a start condition for the compressor 10 is met while the compressor 10 is stopped.

[0029] The control device 100 determines whether the compressor differential pressure (the difference between the detected value of the pressure sensor 71 and the detected value of the pressure sensor 72) is greater than a predetermined threshold value (step S10). The threshold value is a value for determining whether an overcurrent occurs when the compressor 10 is started (whether or not a high differential pressure start occurs), and is determined, for example, by experiment or the like and stored in advance in the memory 102.

[0030] If the compressor differential pressure is not greater than the threshold value (NO in step S10), it is assumed that no overcurrent will occur even if the compressor 10 is started as is, so the control device 100 starts the compressor 10 without opening the bypass valve 61 (step S20).

[0031] On the other hand, if the compressor differential pressure is greater than the threshold value (YES in step S10), the control device 100 starts the compressor 10 in high differential pressure start-up mode (steps S31 to S35) because it is expected that an overcurrent will occur if the compressor 10 is started as is.

[0032] Specifically, the control device 100 first opens the bypass valve 61 (step S31). As a result, the gas refrigerant on the discharge side of the compressor 10 quickly moves to the low-pressure side, and the compressor differential pressure temporarily decreases. Then, after opening the bypass valve 61, the control device 100 determines whether the compressor differential pressure is smaller than a threshold value (step S32). If the compressor differential pressure is not smaller than the threshold value (NO in step S32), the control device 100 repeats the process of step S32 and waits until the compressor differential pressure becomes smaller than the threshold value.

[0033] If it is determined that the compressor differential pressure is smaller than the threshold value (YES in step S32), the control device 100 immediately starts the compressor 10 (step S33) and closes the bypass valve 61 (step S35).

[0034] As described above, when the start conditions for the compressor 10 are met and the compressor differential pressure is greater than the threshold value, the control device 100 according to this embodiment opens the bypass valve 61 to temporarily reduce the compressor differential pressure, and when it is determined that the compressor differential pressure is less than the threshold value, instantaneously starts the compressor 10 and closes the bypass valve 61. This makes it possible to appropriately suppress both an overcurrent caused by start-up under high differential pressure and an excessive rise in the compressor discharge temperature caused by the failure of the liquid injection function.

[0035] 3 is a diagram schematically illustrating an example of the overall configuration of a refrigeration cycle apparatus 1A according to Modification 1. In the refrigeration cycle apparatus 1A, the bypass flow path 60 of the above-described refrigeration cycle apparatus 1 is replaced with a bypass flow path 60A.

[0036] The bypass flow path 60A connects a connection C3 provided in the flow path P1 between the compressor 10 and the condenser 20 with a connection C4A provided in the flow path P3 between the expansion valve 30 and the evaporator 40.

[0037] In this way, the bypass flow path 60A may be configured to connect the flow path P1 between the compressor 10 and the condenser 20 with the flow path P3 between the evaporator 40 and the compressor 10. Even in this case, it is possible to achieve substantially the same effects as those of the above-described embodiment.

[0038] [Variation 2] In the above-described embodiment, the timing at which the compressor 10 is started and the timing at which the bypass valve 61 is closed are substantially the same in the high differential pressure start-up mode. However, the timing at which the compressor 10 is started and the timing at which the bypass valve 61 is closed may be shifted.

[0039] Fig. 4 is a flowchart showing an example of a processing procedure performed by the control device 100 according to the present modified example 2 when starting up the compressor 10. The flowchart of Fig. 4 is obtained by adding step S34 to the flowchart of Fig. 2 described above. The other steps of Fig. 4 (steps having the same numbers as the steps shown in Fig. 2 described above) have already been described, and therefore detailed description thereof will not be repeated here.

[0040] In the high differential pressure start-up mode, after starting the compressor 10 in step S33, the control device 100 determines whether the elapsed time since starting the compressor 10 has exceeded a predetermined reference time (step S34). The reference time is preset to a time sufficiently shorter than the time it takes for all of the liquid refrigerant on the discharge side of the compressor 10 to move to the suction side of the compressor 10 as a result of opening the bypass valve 61 in step S31, and is stored in the memory 102. If the elapsed time has not exceeded the reference value (NO in step S34), the control device 100 waits until the elapsed time exceeds the reference value. Then, if the elapsed time exceeds the reference value (YES in step S34), the control device 100 immediately closes the bypass valve 61 (step S35).

[0041] In this way, in the high differential pressure start-up mode, the bypass valve 61 may be closed when the time elapsed since the start-up of the compressor 10 exceeds a reference value. Even in this case, it is possible to achieve substantially the same effects as those of the above-described embodiment.

[0042] [Variation 3] The diameter of the bypass valve 61 when it is opened may be set so that the flow rate of gas refrigerant passing through the bypass valve 61 is equal to or greater than the evaporation speed of liquid refrigerant. By setting the diameter in this manner, when the bypass valve 61 is opened, more gas refrigerant can be moved to the suction side of the compressor 10 than the amount of liquid refrigerant that evaporates on the discharge side of the compressor 10, thereby reliably reducing the compressor differential pressure.

[0043] [Variation 4] The portion of the liquid injection flow path 50 upstream of the flow rate adjustment valve 51 may be arranged vertically below the connection C1 between the liquid injection flow path 50 and the second flow path P2. By arranging it in this manner, when the flow rate adjustment valve 51 is closed, liquid refrigerant can be left in the portion of the liquid injection flow path 50 upstream of the flow rate adjustment valve 51. Therefore, when the flow rate adjustment valve 51 is opened, the liquid injection function can be reliably performed.

[0044] The embodiments disclosed herein should be considered to be illustrative in all respects and not restrictive. The scope of the present disclosure is defined by the claims, not the above description, and is intended to include all modifications within the meaning and scope of the claims.

[0045] 1, 1A refrigeration cycle device, 2 refrigerant circuit, 10 compressor, 20 condenser, 30 expansion valve, 40 evaporator, 50 liquid injection flow path, 51 flow control valve, 60, 60A bypass flow path, 61 bypass valve, 71, 72 pressure sensor, 73 temperature sensor, 100 control device, 101 CPU, 102 memory, C1 to C4, C4A connection portion, P1 to P4 flow path.

Claims

1. A refrigeration cycle apparatus comprising: a refrigerant circuit including a compressor, a first flow path, a condenser, a second flow path, an expansion valve, a third flow path, an evaporator, and a fourth flow path, and configured to circulate a refrigerant in this order by operation of the compressor; and a control device for controlling the compressor, wherein the refrigerant circuit further includes a liquid injection flow path connecting the second flow path and the fourth flow path, a bypass flow path connecting the first flow path and the third flow path or the fourth flow path, and a bypass valve provided in the bypass flow path, wherein the control device, when a start-up condition for the compressor is satisfied, determines whether a differential pressure between the suction side and the discharge side of the compressor is greater than a threshold value, opens the bypass valve if the differential pressure is greater than the threshold value, determines whether the differential pressure is less than the threshold value after the bypass valve is opened, starts the compressor when it is determined that the differential pressure is less than the threshold value, and closes the bypass valve after the compressor is started.

2. A refrigeration cycle device as described in claim 1, wherein the control device starts the compressor without opening the bypass valve when a start condition for the compressor is met and the differential pressure is smaller than the threshold value.

3. A refrigeration cycle device as described in claim 1, wherein the diameter of the bypass valve when opened is set so that the flow rate of gas refrigerant passing through the bypass valve is equal to or greater than the evaporation speed of liquid refrigerant.

4. A refrigeration cycle device as described in claim 1, wherein the refrigerant circuit further includes a flow control valve provided in the liquid injection flow path, and a portion of the liquid injection flow path upstream of the flow control valve is positioned vertically below a connection between the liquid injection flow path and the second flow path.

5. The refrigeration cycle device according to claim 1, wherein the refrigerant is a single refrigerant of R32 or a mixed refrigerant containing R32.

6. The refrigeration cycle device according to claim 1, wherein the refrigerant has a specific heat ratio higher than that of R410A.

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