JP2019128061A - Controller, condensing unit, refrigeration device and control method - Google Patents

Abstract

To provide a controller capable of preventing excessive capacity of a refrigerant circuit in oil return operation.SOLUTION: A controller 30 is configured to, in oil return operation in which the rotational frequencies of compressors 11, 12 which a refrigerant circuit comprises are increased to return to the compressors 11, 12 refrigeration oil discharged together with refrigerant from the compressors 11, 12, perform control of returning part of the discharged refrigerant to the compressors 11, 12 so as not to circulate through the refrigerant circuit, according to change of the capacity of the refrigerant circuit due to increase of the rotational frequencies of the compressors 11, 12. Further, in the oil return operation, the controller is configured to perform control to open valves SVHG1, 2 provided in a hot gas bypass connecting between the discharge side and suction side of the compressors 11, 12 with the rotational frequencies increased.SELECTED DRAWING: Figure 2

Description

  The present invention relates to a control device, a condensing unit, a refrigeration device, and a control method.

  Refrigerating machine oil is enclosed in the compressor of the condensing unit for lubrication. The refrigeration oil is discharged from the compressor together with the refrigerant, and when it is captured by the oil separator, it is separated from the refrigerant and recovered to the compressor. When the amount of refrigerating machine oil recovered to the compressor is insufficient, problems such as seizure of the compressor occur, and it is necessary to perform a refrigerating machine oil return operation so that an appropriate amount of refrigerating machine oil is recovered. The oil return operation is performed, for example, by increasing the rotation speed of the compressor (for example, Patent Document 1).

JP 2008-107060 A

  By the way, if the number of revolutions of the compressor is increased in the oil return operation, more refrigerant will be circulated, and for example, in the condensing unit, the cooling capacity may become excessive. Then, values such as temperature and pressure measured by the refrigerant circuit may exceed the operation allowable threshold value, which may cause inconveniences such as an operation stop.

  Then, this invention aims at providing the control apparatus, condensing unit, freezing apparatus, and control method which can solve the above-mentioned subject.

  According to one aspect of the present invention, in the oil return operation for returning the refrigeration oil discharged together with the refrigerant from the compressor to the compressor by increasing the rotation speed of the compressor included in the refrigerant circuit, the rotation speed of the compressor The control device performs control to return a part of the discharged refrigerant to the compressor without circulating through the refrigerant circuit in accordance with a change in the capacity of the refrigerant circuit due to an increase in the pressure.

  The control device according to one aspect of the present invention controls, in the oil return operation, a valve provided in a hot gas bypass that connects the discharge side and the suction side of the compressor whose rotational speed has been increased to open.

  The control device according to one aspect of the present invention controls, in the oil return operation, the valve provided in the hot gas bypass to be open when the pressure on the suction side of the compressor becomes equal to or less than a predetermined threshold.

  The control device according to one aspect of the present invention controls the opening and closing of a valve provided in the hot gas bypass so that the pressure on the suction side of the compressor becomes a pressure within a predetermined range in the oil return operation.

  One aspect of the present invention includes a hot gas bypass that connects a discharge side and a suction side of a compressor, a valve that controls a flow rate of the refrigerant that flows through the hot gas bypass, and the control device according to any one of the above. , A condensing unit.

  One aspect of the present invention is a refrigeration system including the condensing unit described above and a showcase having a use side heat exchanger.

  According to one aspect of the present invention, in the oil return operation for returning the refrigeration oil discharged together with the refrigerant from the compressor to the compressor by increasing the rotation speed of the compressor included in the refrigerant circuit, the rotation speed of the compressor This is a control method for performing control to return a part of the discharged refrigerant to the compressor without circulating the refrigerant circuit in accordance with a change in the capacity of the heat source device due to the rise in the temperature.

  According to the present invention, it is possible to suppress an excessive increase in the refrigerant circulation amount during the oil return operation, and to control the refrigerant circuit to a stable operating state.

It is a figure which shows an example of the refrigerant circuit in one Embodiment of this invention. It is a block diagram of a control device in one embodiment of the present invention. It is a figure explaining control at the time of oil return operation in one embodiment of the present invention. It is a flowchart which shows an example of the control at the time of the oil return driving | operation in one Embodiment of this invention.

Embodiment
Hereinafter, the oil return operation in an embodiment of the present invention will be described with reference to FIGS. 1 to 4. FIG. 1 is a view showing an example of a refrigerant circuit according to an embodiment of the present invention.
FIG. 1 shows a refrigeration system 100 including a condensing unit 1 and a showcase 2. The condensing unit 1 controls the compressors 11 and 12, the accumulators 3, the oil separators 61 and 62, the gas coolers 51 and 52, the oil pots 71 and 72, the medium pressure receiver 9, and the supercooling coil 10. The apparatus 30 is mainly provided. The showcase 2 includes an expansion valve 81 and a utilization side heat exchanger (evaporator) 80. The refrigerant circuit of the present embodiment includes compressors 11 and 12, gas coolers 51 and 52, an expansion valve 81, a use-side heat exchanger 80, piping that connects them, and the like.

The compressors 11 and 12 compress the refrigerant and supply the compressed high-pressure refrigerant to the refrigerant circuit. The compressor 11 is a two-stage compressor having a first-stage first-stage compression section 11a and a second-stage second-stage compression section 11b. The compressor 12 is a two-stage compressor having a first-stage first-stage compression section 12a and a second-stage second-stage compression section 12b. In the condensing unit 1, the compressor 11 and the compressor 12 are provided in parallel. As will be described later, the compressor 11 and the compressor 12 are connected to each other through the oil pot 71, the oil pot 72, and the oil equalizing pipe 73 so that the refrigeration oil can move. For example, CO ₂ is used as the refrigerant of the present embodiment. The CO ₂ refrigerant has a large pressure difference between the high pressure and the low pressure, and a two-stage compression structure is adopted to improve the compressor efficiency. Further, in order to improve the performance and efficiency, a gas injection mechanism (described later) for supplying a refrigerant at an intermediate pressure (intermediate pressure) is employed in the second stage compression sections 11b and 12b of the compressors 11 and 12. On the discharge side of the compressor 11, a temperature sensor Th-D1 is provided, and on the discharge side of the compressor 12, a temperature sensor Th-D2 is provided.

  A hot gas bypass pipe BP11 is connected to the discharge pipe MP01 on the discharge side of the compressor 11. The hot gas bypass pipe BP11 is provided with a strainer 131, a solenoid valve SVHG1, and a capillary tube 141, and is connected to a return pipe MP13 which is a refrigerant flow path returning from the load side. A flow path including the hot gas bypass pipe BP11, the strainer 131, the solenoid valve SVHG1 and the capillary tube 141 is called a hot gas bypass. The flow of the refrigerant in the hot gas bypass is controlled by opening and closing the solenoid valve SVHG1. That is, when the control device 30 opens the solenoid valve SVHG1, the discharge side and the suction side of the compressor 11 communicate with each other, and the refrigerant flows through the hot gas bypass. Similarly, a hot gas bypass pipe BP12 is connected to the discharge pipe MP02 on the discharge side of the compressor 12. A strainer 132, a solenoid valve SVHG2, and a capillary tube 142 are provided in the hot gas bypass pipe BP12 to form a hot gas bypass, which is connected to the return pipe MP13. The flow of the refrigerant in the hot gas bypass on the side of the compressor 12 is also controlled by the opening and closing of the solenoid valve SVHG 2 as on the side of the compressor 11. The electromagnetic valves SVHG1 and SVHG2 are often opened, for example, before the compressors 11 and 12 are started to equalize their suction side and discharge side, and are often closed after the start. Therefore, during operation of the condensing unit 1, the refrigerant discharged from the compressors 11 and 12 flows through the discharge pipes MP01 and MP02 without flowing through the hot gas bypass.

  The refrigerant flowing through the discharge pipe MP01 is supplied to the oil separator 61. In the oil separator 61, the refrigerant and the refrigerating machine oil dissolved in the refrigerant are separated, and the refrigerant flows to the gas pipe MP10 via the check valve CV1. The bottom of the oil separator 61 and the side surface of the oil pot 71 are communicated with each other via an oil return pipe RP11. The refrigerating machine oil separated by the oil separator 61 is returned to the oil pot 71 through the oil return pipe RP11. The oil return pipe RP11 is provided with a strainer 121, and at the downstream side of the strainer 121, the oil return pipe RP11 is divided into two flow paths. The capillary tube 151 and the solenoid valve SV-OIL 1 are provided in the piping of one flow passage, and the capillary tube 161 is provided in the piping of the other flow passage. The amount of refrigerating machine oil returned to the oil pot 71 is adjusted by opening and closing the solenoid valve SV-OIL1.

  Moreover, the upper part of the oil pot 71 and the discharge side of the first stage compression part 11a of the compressor 11 are connected by piping. Apart from the refrigerating machine oil flowing in from the oil return pipe RP11, during the operation of the compressor 11, the refrigerating machine oil also flows into the oil pot 71 from the discharge side communication pipe of the first stage compression unit 11a. Further, the bottom of the oil pot 71 communicates with the bottom of the compressor 11 through a pipe. The refrigerating machine oil accumulated below the oil pot 71 is returned to the compressor 11 through the piping at the bottom.

  The oil pot 71 is provided with a level switch 71a. The level switch 71a detects the height of the oil level in the oil pot 71. When the oil level is lowered to a predetermined height, the level switch 71a outputs a signal indicating the drop in the oil level to the control device 30.

  The configuration on the compressor 12 side is the same. The refrigerant discharged by the compressor 12 passes through the discharge pipe MP02 to reach the oil separator 62, and the refrigerant separated by the oil separator 62 flows to the gas pipe MP10 via the check valve CV2. The separated refrigeration oil passes through the strainer 122, the capillary tube 152, the capillary tube 162, and the valve SV-OIL2 provided in the oil return pipe RP12, and is returned to the oil pot 72. Further, the refrigerating machine oil flows into the oil pot 72 from the discharge side of the second stage compression unit 12 b of the compressor 12. The refrigerating machine oil supplied to the oil pot 72 is returned to the compressor 12 through the piping at the bottom. In addition, when the level switch 72a provided in the oil pot 72 detects a drop in oil level in the oil pot 72, the level switch 72a notifies the control device 30 of the drop in oil level.

  The oil pot 71 and the oil pot 72 are connected via an oil equalizing pipe 73. The oil equalizing pipe 73 is provided in order to eliminate unevenness in the amount of oil stored in the oil pots 71 and 72. One end of the oil equalizing pipe 73 is higher than the height at which the level switch 71a on the side of the oil pot 71 is provided (the height for detecting a drop in the oil level) and is connected to a position lower than the connection position of the oil return pipe RP11. The other end is connected to a position higher than the height at which the level switch 72a on the side surface of the oil pot 72 is provided and lower than the connection position of the oil return pipe RP21.

The high-temperature and high-pressure refrigerant discharged by the compressors 11 and 12 is supplied to the gas coolers 51 and 52 provided in parallel through the gas pipe MP10. The refrigerant supplied to the gas coolers 51 and 52 is condensed by heat exchange with the air sent by the fans 41 and 42. In the case of CO ₂ refrigerant, it is cooled. On the upstream side of the gas coolers 51 and 52 in the gas pipe MP10, a temperature sensor Th-G1 and a pressure sensor PSH for high pressure measurement are provided.

Cooling or condensed refrigerant in the gas cooler 51 passes through a strainer 111 provided in the gas-liquid two Icahn MP11, by the expansion valve EEVG provided on the inlet side of the intermediate-pressure receiver 9, the CO ₂ refrigerant In this case, the pressure is reduced to, for example, about 6 MPa and supplied to the medium pressure receiver 9. A temperature sensor Tho-G2 is provided downstream of the gas coolers 51 and 52 in the gas-liquid two-phase pipe MP11, and a temperature sensor Tho-M is provided on the inlet side of the intermediate pressure receiver 9.

  Further, on the upstream side of the expansion valve EEVG in the gas-liquid two-phase pipe MP11, liquid bypass pipes BP21 and 22 for returning the cooled or condensed refrigerant to the compressors 11 and 12 are connected. The liquid bypass pipe BP21 is provided with an expansion valve EEV-LB1, and the control device 30 adjusts the amount of refrigerant flowing into the liquid bypass pipe BP21 by controlling the opening degree of the expansion valve EEV-LB1. Similarly, the liquid bypass pipe BP22 is provided with an expansion valve EEV-LB2, and the control device 30 adjusts the amount of refrigerant flowing into the liquid bypass pipe BP22 by controlling the opening degree of the expansion valve EEV-LB2. The liquid bypass pipe BP21 is connected to an injection pipe IP11 described later, and the liquid bypass pipe BP22 is connected to the injection pipe IP12. The expansion valve EEV-LB1 is opened by the control device 30 when the temperature on the discharge side of the compressor 11 becomes equal to or higher than a predetermined temperature. When the expansion valve EEV-LB1 is opened, the refrigerants which perform heat exchange with the gas coolers 51 and 52 and become lower temperature than the discharge side of the compressor 11 are medium pressure of the compressor 11 through the liquid bypass pipe BP21 and the injection pipe IP11. Part (the suction side of the second-stage compression unit 11b) and suppresses an excessive temperature rise on the discharge side of the compressor 11. The same applies to the expansion valve EEV-LB2 and the liquid bypass pipe BP22.

  The intermediate pressure receiver 9 separates the gas-liquid two-phase refrigerant expanded by the expansion valve EEVG into a gas refrigerant that is a gas-phase refrigerant and a liquid refrigerant that is a liquid-phase refrigerant. The medium pressure receiver 9 is provided with a medium pressure receiver level switch 9a that detects whether the liquid level of the liquid refrigerant has reached the upper limit. An injection pipe IP10 is connected to the upper part of the intermediate pressure receiver 9, and gas refrigerant is sent out. The injection pipe IP10 is provided with a pressure sensor PSM1. The gas refrigerant sent out by the injection pipe IP10 is branched into two flow paths (injection pipes IP11 and 12). An expansion valve EEV-INJ1 is provided in the injection pipe IP11, and the control device 30 controls the pressure of the refrigerant flowing into the injection pipe IP11 by controlling the opening degree of the expansion valve EEV-INJ1. A check valve CV3 is provided on the compressor 11 side of the expansion valve EEV-INJ1, and the medium-pressure gas refrigerant flowing into the injection pipe IP11 is supplied to the intermediate pressure portion of the compressor 11. The medium-pressure gas refrigerant supplied from the injection pipe IP11 is recompressed by the second-stage compression unit 11b. Thereby, COP (Coefficient Of Performance) of a refrigerating cycle can be improved (gas injection mechanism). A temperature sensor Tho-INJ1 and a pressure sensor PSM21 are provided on the front side of the connection portion of the injection pipe IP11 with the compressor 11.

  The injection pipe IP12 is provided with an expansion valve EEV-INJ2 and a check valve CV4, and the control device 30 controls the pressure of the refrigerant flowing into the injection pipe IP12 by controlling the opening degree of the expansion valve EEV-INJ2. To do. The medium-pressure gas refrigerant flowing into the injection pipe IP12 is supplied to the intermediate-pressure portion of the compressor 12 and recompressed. A temperature sensor Tho-INJ2 and a pressure sensor PSM22 are provided on the front side of the connection portion of the injection pipe IP12 with the compressor 12.

  On the other hand, the liquid refrigerant separated in the medium pressure receiver 9 flows through the liquid pipe MP 12, passes through the strainer 14, and is cooled by the supercooling coil 10. On the upstream side of the supercooling coil 10, the supercooling pipe MP12A is connected to the liquid pipe MP12, and a part of the liquid refrigerant flowing out from the intermediate pressure receiver 9 branches to the supercooling pipe MP12A. The branched liquid refrigerant is decompressed by the expansion valve EEVSC for the subcooling coil and becomes low temperature, and the subcooling coil 10 cools the liquid refrigerant flowing through the liquid pipe MP12 (the refrigerant supplied to the load side). The refrigerant branched into the supercooling pipe MP12A flows to the accumulator 3 after passing through the supercooling coil 10. The supercooling pipe MP12A is provided with a temperature sensor Th-SC.

  The refrigerant flowing through the liquid pipe MP12 is cooled by the subcooling coil 10, and then flows out from the condensing unit 1 and is supplied to the external load (showcase 2) through the connection pipe 82. The showcase 2 includes an expansion valve 81 and a use side heat exchanger 80. The refrigerant supplied from the condensing unit 1 is decompressed by the expansion valve 81, and heat exchange is performed in the use side heat exchanger 80 to cool the object. The refrigerant after the heat exchange returns to the condensing unit 1 through the connection pipe 83. In the condensing unit 1, the refrigerant returned from the load side flows to the accumulator 3 through the return pipe MP13. A temperature sensor Tho-S and a pressure sensor PSL for low pressure measurement are provided on the front side of the accumulator 3 in the return pipe MP13.

The accumulator 3 performs gas-liquid separation of the refrigerant supplied to the compressors 11 and 12. Part of the gas refrigerant separated by the accumulator 3 passes through the suction pipe MP14 and is supplied to the accumulator 21 attached to the compressor 11. The gas refrigerant from which only the gas phase has been extracted by the accumulator 21 is supplied to the suction side of the first stage compression unit 11 a of the compressor 11. Similarly, the remainder of the gas refrigerant separated by the accumulator 3 passes through the suction pipe MP15, is supplied to the accumulator 22 attached to the compressor 12, and is supplied to the suction side of the first stage compression section 12a of the compressor 12 Is done.
In addition, the condensing unit 1 is provided with a temperature sensor Tho-A that measures an external temperature.

  The control device 30 is connected to each sensor such as the pressure sensor PSL and the temperature sensor Th-R, various valves such as the electromagnetic valve EEVG, and devices such as the compressors 11 and 12, and obtains a measurement value by each sensor. The condensing unit 1 is operated by adjusting the rotation speed of the compressors 11 and 12 and the opening and closing of the expansion valve EEVG and the like. For example, the control device 30 performs an oil return operation in order to collect the refrigeration oil discharged together with the refrigerant from the compressors 11 and 12 while monitoring the pressure measured by the pressure sensor PSL. Next, the function of the oil return operation with which the control apparatus 30 is provided is demonstrated using FIG.

FIG. 2 is a block diagram of a control device in an embodiment of the present invention.
The control device 30 is, for example, a computer device such as a microcomputer. As illustrated, the control device 30 includes a sensor information acquisition unit 31, a timer 32, a storage unit 33, and an oil return operation control unit 34. In addition, although the control apparatus 30 performs various control regarding the condensing unit 1, description of the function regarding control other than an oil return driving | operation is abbreviate | omitted in this specification.

The sensor information acquisition unit 31 acquires measurement values from each sensor. For example, the sensor information acquisition unit 31 acquires the measured value of the refrigerant pressure on the suction side of the compressors 11 and 12 from the pressure sensor PSL for low pressure measurement. The pressure measured by the pressure sensor PSL is the pressure when the refrigerant becomes low pressure in the refrigerant circuit.
The timer 32 measures time.
The storage unit 33 stores various information such as a pressure measurement value acquired by the sensor information acquisition unit 31 and a parameter value necessary for the oil return operation. In addition, the storage unit 33 stores various programs that realize the functions of the control device 30.

  The oil return operation control unit 34 executes the oil return operation. For example, the oil return operation control unit 34 starts the oil return operation when the operation time of the compressors 11, 12 reaches a predetermined time based on the time measured by the timer 32. Alternatively, the oil return operation control unit 34 calculates the amount of refrigeration oil discharged from the compressors 11 and 12, and starts the oil return operation when the calculated oil amount is equal to or more than a predetermined threshold value. Further, the oil return operation control unit 34 starts the oil return operation and ends the oil return operation when a predetermined time passes. The oil return operation control unit 34 includes a compressor control unit 341, a low pressure monitoring unit 342, and a valve control unit 343.

The compressor control unit 341 controls the number of rotations of the compressors 11 and 12 during the oil return operation. Specifically, for example, in the case of performing the oil return operation for the compressor 11, the compressor control unit 341 increases the rotational speed of the compressor 11, and speeds up the flow rate of the refrigerant to become the flooding speed. . When the flow rate of the refrigerant becomes equal to or higher than the flooding speed, the refrigerating machine oil adhering to and staying in each pipe of the refrigerant circuit can be returned to the compressors 11 and 12.
The low pressure monitoring unit 342 monitors how far the pressure measured by the pressure sensor PSL (hereinafter referred to as low pressure) deviates from a predetermined target value or whether the low pressure reaches a predetermined lower limit value. .

  When the low pressure monitored by the low pressure monitoring unit 342 is likely to reach a predetermined lower limit value during the oil return operation, the valve control unit 343 opens at least one of the solenoid valves SVHG1 and SVHG2, and some of the refrigerant is hot gas. It leads to bypass pipes BP11 and 12, and suppresses the amount of refrigerant circulating in the refrigerant circuit. More specifically, the valve control unit 343 controls the electromagnetic valve SVHG1 to be open when the compressor 11 is in the oil return operation (the rotation speed is increasing). Alternatively, if the compressor 12 is in the oil return operation, the valve control unit 343 controls the solenoid valve SVHG2 to be open. The oil return operation control unit 34 is a function realized when a CPU (Central Processing Unit) provided in the control device 30 reads out and executes a program from the storage unit 33.

Next, the oil return operation of the present embodiment will be described by taking the compressor 11 as an example using FIG. 3.
FIG. 3 is a view for explaining control at the time of oil return operation in the embodiment of the present invention.
FIG. 3 (a) shows the change in the rotational speed of the compressor 11, FIG. 3 (b) shows the change in opening / closing of the solenoid valve SVHG1, and FIG. 3 (c) shows the change in low pressure. The vertical axis in FIG. 3 (a) indicates the rotational speed, the vertical axis in FIG. 3 (b) indicates the opening degree, and the vertical axis in FIG. 3 (c) indicates the pressure. Moreover, the horizontal axis of each graph of Fig.3 (a)-FIG.3 (c) shows time, and the same position of each graph has shown the same time.

(Time t0 to t1)
When the oil return operation is not performed, the control device 30 drives the compressor 11 at a rotational speed X1 (for example, 50 rps) corresponding to the load (FIG. 3A). As described above, the solenoid valve SVHG1 is closed during the operation of the condensing unit 1 (FIG. 3B). At this time, the control device 30 controls the rotation speed and the like of the compressor 11 so that the low pressure becomes a predetermined target value corresponding to the load (FIG. 3C). Here, when the cooling target of the showcase 2 is refrigerated (for example, the temperature of the refrigerant is about −10 ° C.), the low pressure target value is relatively high, and the cooling target is frozen (for example, the temperature of the refrigerant is −45 ° C.). In the case of degree), the low pressure target value is set relatively low.

(Time t1 to t3)
Next, when the condition for starting the oil return operation is satisfied at time t1, the oil return operation control unit 34 starts the oil return operation. Specifically, the compressor control unit 341 raises the rotational speed of the compressor 11 to X2. The compressor control unit 341 drives the compressor 11 at the rotation speed X2 until the time L1 elapses from the increase of the rotation speed. When the compressor control unit 341 increases the rotational speed of the compressor 11 to X2, more refrigerant circulates through the refrigerant circuit, and the cooling capacity increases. Then, the low pressure monitored by the low pressure monitoring unit 342 gradually decreases after time t1 when the rotational speed is increased to X2. Then, the low pressure approaches a predetermined lower limit value (abnormality detection value). Here, in the case of a CO ₂ refrigerant, the predetermined lower limit value is a pressure (about −56 ° C., about 0.52 MPa) which is a triple point. In particular, when the object of the showcase 2 is refrigeration, the evaporation temperature is low, and the low pressure target value does not greatly deviate from the abnormality detection value. Therefore, the low pressure easily reaches the abnormality detection value. The control device 30 is designed to stop the operation of the condensing unit 1 when the low pressure reaches the malfunction detection value.

  Therefore, in the present embodiment, a threshold for detecting that the low pressure approaches the abnormality detection value is set, and the low pressure monitoring unit 342 detects that the low pressure is the abnormality detection value when the low pressure reaches this threshold (time t2). Output a warning signal indicating that it is approaching. When the warning signal is output, the valve control unit 343 controls the solenoid valve SVHG1 from close to open (FIG. 3 (b), time t2). When the solenoid valve SVHG1 is opened at time t2, a part of the refrigerant discharged by the compressor 11 is branched to the bypass pipe BP11, and is returned to the compressor 11 through the accumulator 3 and the accumulator 21. A part of the refrigerant is returned to the compressor 11 without circulating through the refrigerant circuit, so that the excessive cooling capacity is adjusted, and accordingly, a decrease in the low pressure measured by the pressure sensor PSL is suppressed. As a result, even when the rotation speed of the compressor 11 is increased for oil return operation and the cooling capacity is increased, the low pressure does not reach the abnormal detection value (without stopping the operation), and the condensate is stabilized. Operating unit 1 can be operated.

(Time t3-)
When the predetermined time L1 has elapsed after starting the oil return operation (time t3), the oil return operation control unit 34 ends the oil return operation. That is, the compressor control unit 341 reduces the rotational speed of the compressor 11 and returns it to the original rotational speed X1 (FIG. 3A). Further, the valve control unit 343 controls the solenoid valve SVHG1 from open to close (FIG. 3 (b)). The control device 30 controls the rotation speed and the like of the compressor 11 so that the low pressure becomes a predetermined target value corresponding to the load.

  Generally, in the oil return operation, the rotation speed of the compressor 11 or the like is increased so that the flow velocity of the refrigerant becomes equal to or higher than a predetermined flow velocity. Then, the cooling capacity is increased, and the pressure (low pressure) on the suction side of the compressor 11 is excessively reduced depending on the low pressure target value (in the case of refrigeration) and various operating conditions, for example, the possibility of the shutdown There is. On the other hand, according to the oil return operation of the present embodiment, when the capacity becomes excessive, the cooling capacity is adjusted using the hot gas bypass, and the operating state of the refrigerant circuit represented by the low pressure is within the allowable range. Can be maintained. Thereby, it is possible to stably operate the condensing unit 1 regardless of whether the load is refrigerated or frozen. Further, since the opening / closing control of the solenoid valve SVHG1 is performed according to the low pressure value, the solenoid valve SVHG1 is not unnecessarily opened to reduce the cooling capacity. In the description of FIG. 3, although the solenoid valve SVHG1 is kept open until the oil return operation is completed, for example, if the low pressure recovers to near the target value by opening the solenoid valve SVHG1, etc. The solenoid valve SVHG1 may be closed before the end of the oil return operation. Alternatively, the opening and closing of the solenoid valve SVHG1 may be controlled so that the low pressure becomes a pressure in a predetermined range with reference to the target value. Alternatively, instead of simply opening and closing, a flow rate adjusting valve may be provided in the hot gas bypass pipe BP11 to adjust the flow rate of the refrigerant branched to the hot gas bypass.

FIG. 4 is a flowchart showing an example of control during oil return operation according to an embodiment of the present invention.
The flow of the oil return operation will be described using FIG. 1 and FIG. 2 as an example with reference to FIG. 4. In FIG. 3, the case where the rotation speed of the compressor 11 is increased has been described as an example. However, in the following description, control for increasing the rotation speed of the compressor 11 and the compressor 12 is performed during the oil return operation. And In addition, the sensor information acquisition unit 31 acquires the measurement value of the pressure sensor PSL at a predetermined time interval and outputs it to the low pressure monitoring unit 342. Further, it is assumed that the solenoid valve SVHG1 and the solenoid valve SVHG2 are closed. In addition, it is assumed that values such as the rotation speed X2 illustrated in FIG. 3, the time L1 for performing the oil return operation, and the threshold value set for the low pressure are recorded in the storage unit 33.

  First, the oil return operation control unit 34 determines that the start condition of the oil return operation is satisfied (step S11). For example, the oil return operation control unit 34 uses the timer 32 to calculate the operation time of the compressors 11 and 12 (accumulation of the operation time from the end of the previous oil return operation to the present). In addition, the oil return operation control unit 34 calculates the discharge amount of the refrigerator oil downstream of the oil separators 61 and 62 in each operation after the previous oil return operation is completed. If the calculated operation time is equal to or greater than the predetermined value and the calculated discharge amount of the refrigerating machine oil is equal to or greater than the predetermined value, the oil return operation control unit 34 determines that the oil return operation start condition is satisfied. When the start condition of the oil return operation is not satisfied (step S11; No), the determination of step S11 is repeated.

  When the start condition of the oil return operation is satisfied (step S11; Yes), the oil return operation control unit 34 starts the oil return operation. First, the compressor control unit 341 raises the rotational speed of the compressor 11 and the compressor 12 from X1 to X2 (step S12). By increasing the rotational speeds of the two compressors 11 and 12 together, the refrigerator oil can be recovered more quickly. Further, the low pressure monitoring unit 342 compares the latest measured value by the pressure sensor PSL with the threshold set for the low pressure, and determines whether the low pressure is equal to or lower than the threshold (step S13). If the low pressure is larger than the threshold (step S13; No), the compressors 11 and 12 are driven at the rotational speed X2, and the determination in step S15 is performed. When the low pressure is less than or equal to the threshold value (step S13; Yes), the valve control unit 343 opens the electromagnetic valve SVHG1 and the electromagnetic valve SVHG2 provided in the hot gas bypass of the compressors 11 and 12 whose rotation speed has been increased (step S14). ).

  Next, the oil return operation control unit 34 determines that the end condition of the oil return operation is satisfied (step S15). For example, the oil return operation control unit 34 uses the timer 32 to determine that the condition for ending the oil return operation is satisfied when a predetermined time (L1 in FIG. 3) has elapsed from the start of the oil return operation. When the end condition for the oil return operation is not satisfied (step S15; No), the oil return operation control unit 34 repeats the processing from step S13 while continuing the oil return operation. When the end condition of the oil return operation is satisfied (step S15; Yes), the valve control unit 343 closes the hot gas bypass solenoid valve SVHG1 and the solenoid valve SVHG2. The compressor control unit 341 returns the number of rotations of the compressor 11 and the compressor 12 to the original number of rotations X1 (step S16). The control device 30 performs the oil return operation in the same procedure after the next time.

  Thus, by opening and closing the hot gas bypass according to the low pressure state during the oil return operation, the amount of refrigerant supplied to the showcase 2 side can be adjusted, and the cooling capacity can be controlled. Thereby, the risk of the operation stop by the fall of the low pressure during the oil return operation can be reduced.

  In addition, the increase in the compressor rotation speed in the oil return operation may be performed simultaneously with the compressors 11 and 12, or may be performed one by one in order, or only one. In any case, when the low pressure is equal to or lower than the threshold value, the valve control unit 343 controls the refrigerant to flow through the hot gas bypass on the compressor side where the rotation speed is increased. Moreover, in FIG. 1, although the refrigerant circuit provided with two compressors was shown, the oil return operation of this embodiment is applied to the refrigerant circuit provided with only one compressor or the refrigerant circuit provided with three or more compressors. May be. Further, in the case of a refrigerant circuit including a plurality of compressors, the compressors may be provided in series (in the case of two units, a high stage, a low stage, etc.). In the refrigerant circuit shown in FIG. 1, the compressors 11 and 12 are two-stage compressors, but are not limited to this and may be one stage.

  In addition, it is possible to appropriately replace the components in the above-described embodiments with known components without departing from the spirit of the present invention. Further, the technical scope of the present invention is not limited to the above embodiment, and various modifications can be made without departing from the scope of the present invention. For example, in the embodiment, the case of cooling by the condensing unit 1 has been described, but the oil return operation of the present embodiment may be applied to a general air conditioner regardless of whether it is cooling or heating. . In the embodiment, the opening and closing of the hot gas bypass is controlled based on the value of the low pressure, but the hot gas bypass is also based on the temperature of the refrigerant at a predetermined position, for example. The opening and closing may be controlled. Alternatively, the hot gas bypass may be opened during the oil return operation regardless of the low pressure value.

DESCRIPTION OF SYMBOLS 100 ... Refrigeration apparatus 1 ... Condensing unit 2 ... Showcase 3 ... Accumulator 9 ... Medium pressure receiver 9a ... Medium pressure receiver level switch 10 ... Subcooling coil 11, 12 ... compressors 11a, 12a ... first stage compression section 11b, 12b ... second stage compression section 21, 22 ... accumulator 30 ... control device 31 ... sensor information acquisition section 32 · · · Timer 33 · · · storage unit 34 · · · oil return operation control unit 341 · · · compressor control unit 342 · · · low pressure monitoring unit 343 · · · valve control unit 41, 42 · · · fan 51, 52 ... Gas cooler 61, 62 ... Oil separator 71, 72 ... Oil pot 71a, 72a ... Level switch 73 ... Oil equalizing pipe 80 ... Use side heat exchanger 81 ... Expansion valve 82, 83 ... Connection piping MP01, MP02 ... Discharge pipe MP10 ... Gas pipe MP11 ... Gas-liquid two-layer pipe MP12 ... Liquid pipe MP12A ... Supercooling pipe MP13 ... Return pipe MP14, MP15 ... Inhalation pipes Tho-D1, Tho-D2, Tho-SC, Tho-S, Tho-G1,
Tho-G2, Tho-M, Tho-INJ1, Tho-INJ2 ... temperature sensor HSL, PSL, PSH, PSM1, PSM21, PSM22 ... pressure sensor CV1, CV2, CV3, CV4 ... check valve BP11 , BP12: hot gas bypass pipe SVHG1, SVHG2: solenoid valve 111, 121, 122, 131, 132, 133, 14: strainer 141, 142, 151, 152, 161, 162: capillary tube RP11, RP12: Oil return pipe BP21, 22: Liquid bypass pipe IP10, IP11, IP12: Injection pipe SV-OIL1, SV-OIL2 ... Solenoid valve EEVG, EEV-LB1, EEV-LB2, EEV-INJ1,
EEV-INJ2, EEVSC ... Expansion valve

Claims (7)

In the oil return operation in which the refrigeration oil discharged together with the refrigerant from the compressor is returned to the compressor by increasing the number of rotations of the compressor included in the refrigerant circuit, the refrigerant circuit of the refrigerant circuit due to the increase in the number of rotations of the compressor In response to a change in capacity, control is performed to return a part of the discharged refrigerant to the compressor without circulating it to the refrigerant circuit.
Control device. In the oil return operation, the valve provided in the hot gas bypass that connects the discharge side and the suction side of the compressor whose rotation speed is increased is controlled to open.
The control device according to claim 1. In the oil return operation, when the pressure on the suction side of the compressor becomes a predetermined threshold value or less, the valve provided in the hot gas bypass is controlled to be opened.
The control device according to claim 2. In the oil return operation, opening and closing of a valve provided in the hot gas bypass is controlled so that the pressure on the suction side of the compressor becomes a pressure within a predetermined range.
The control device according to claim 2 or claim 3. A hot gas bypass connecting the discharge side and the suction side of the compressor;
A valve for controlling the flow rate of the refrigerant flowing through the hot gas bypass;
The control device according to any one of claims 2 to 4;
Condensing unit with A condensing unit according to claim 5;
A showcase having a user-side heat exchanger;
A refrigeration apparatus comprising: In the oil return operation in which the refrigeration oil discharged together with the refrigerant from the compressor is returned to the compressor by increasing the number of rotations of the compressor included in the refrigerant circuit, the refrigerant circuit of the refrigerant circuit due to the increase in the number of rotations of the compressor In response to a change in capacity, control is performed to return a part of the discharged refrigerant to the compressor without circulating it to the refrigerant circuit.
Control method.

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