WO2013073064A1

WO2013073064A1 - Refrigeration unit

Info

Publication number: WO2013073064A1
Application number: PCT/JP2011/078403
Authority: WO
Inventors: 英孝佐々木; 大竹　雅久; 説長谷川; 清小山; 隆寛小林; 西川　弘; 三原　一彦; 賢川久保; 只野　昌也
Original assignee: 三洋電機株式会社
Priority date: 2011-11-18
Filing date: 2011-12-08
Publication date: 2013-05-23
Also published as: CN103946647B; CN103946646B; CN103946652B; CN103946647A; CN103946652A; WO2013073065A1; CN103946646A; WO2013073063A1

Abstract

Provided is a refrigeration unit that is capable of ensuring oil separation efficiency and a quantity of stored oil, and of preventing poor lubrication in compressors, without increasing the volume of an oil separator. The refrigeration unit is configured in such a manner that: an oil tank (61) having a prescribed volume, which stores oil that has been separated by the oil separator (22), is provided, and the oil stored in the oil tank (61) passes through oil return tubes (28, 28A) and returns to the inside of cases (12) of the compressors (11); and motor-operated valves (30) that adjust the openings of the oil return tubes (28A) are provided, and the degree to which the motor-operated valves (30) open is adjusted in response to the operating frequency of the compressors (11).

Description

Refrigeration equipment

The present invention relates to a refrigeration apparatus including an oil return pipe that returns oil captured by an oil separator into a compressor.

In general, a multi-stage (for example, two-stage) compressor that compresses and discharges the sucked refrigerant in multiple stages, an oil separator provided in a high-pressure discharge pipe of the compressor, and oil captured by the oil separator There is known a refrigeration apparatus including an oil return pipe that returns the gas to the compressor (see, for example, Patent Document 1). In this type of refrigeration system, the compressor case is configured to have an intermediate or low pressure, and an electromagnetic return valve is provided in the oil return pipe so that when the amount of oil in the case decreases to the lower limit, this electromagnetic There is a configuration in which oil is returned into the case using a differential pressure between the discharged refrigerant (high pressure) and the inside of the case (intermediate pressure or low pressure) by opening and closing the on-off valve.

JP 2008-144643 A

By the way, in a refrigeration system that uses carbon dioxide (CO2) as a refrigerant, the operating pressure is higher than that of a refrigeration system that uses chlorofluorocarbons (including alternative chlorofluorocarbons, also referred to as a fluorocarbon refrigerant). Therefore, it is difficult to increase the inner diameter of the oil separator, and it is difficult to ensure a large volume of the oil separator.
If the oil separator volume cannot be secured sufficiently, the oil separation efficiency in the oil separator (the efficiency of separating the refrigerant and oil by reducing the flow rate of the refrigerant in the oil separator) will decrease, and the oil that could not be separated will become the low pressure of the refrigeration cycle. It flows to the evaporator on the side and stays in the evaporator, causing deterioration in heat transfer performance and poor lubrication of the compressor.

In addition, if the volume of the oil separator is small, it is difficult to secure a sufficient amount of oil storage, and refrigerant enters the oil that returns to the compressor through the oil return pipe, significantly reducing the efficiency of the refrigeration system or compressing it. The amount of oil returning to the machine may be insufficient, leading to poor lubrication.
Also, in a refrigeration system that uses carbon dioxide as a refrigerant, the pressure difference between the high pressure side and the low pressure side (or intermediate pressure) of the refrigerant circuit is larger than that in a refrigeration system that uses a fluorocarbon refrigerant. The differential pressure between the refrigerant and the compressor case (intermediate pressure or low pressure) increases, making it difficult to properly adjust the oil return with an electromagnetic on-off valve, which also causes poor compressor lubrication. Become.

The present invention has been made in view of the above-described circumstances, and is a refrigeration apparatus that can ensure oil separation efficiency and oil storage amount without increasing the volume of the oil separator and prevent poor lubrication of the compressor. The purpose is to provide.

In order to solve the above-described problems, the present invention includes a refrigerant circuit that performs a refrigeration cycle operation using carbon dioxide as a refrigerant. The refrigerant circuit stores oil in a case and discharges the refrigerant together with the oil to a high-pressure discharge pipe. In the refrigeration apparatus having a compressor that performs, an oil separator provided in the high-pressure discharge pipe, and an oil return pipe that returns the oil separated by the oil separator into the case, the oil separated by the oil separator An oil tank having a predetermined volume to be stored is provided, and oil stored in the oil tank is returned into the case through the oil return pipe, and an electric valve is provided in the oil return pipe, A valve opening adjusting means for adjusting the operating frequency of the compressor is provided.
According to this configuration, the oil tank having a predetermined volume for storing the oil separated by the oil separator is provided, and the oil stored in the oil tank is returned into the case through the oil return pipe, and the oil return pipe An electric valve for adjusting the opening degree of the motor is provided, and the opening degree of the electric valve is adjusted according to the operating frequency of the compressor, so that the oil separation efficiency and the oil storage amount can be increased without increasing the volume of the oil separator. It is possible to ensure and prevent poor lubrication of the compressor.

In the above configuration, the compressor has a plurality of compressors connected in parallel, and the oil separator is provided in a single high-pressure discharge pipe that joins the high-pressure discharge pipes of the plurality of compressors, The oil tank may be formed of a heat resistant container having a lower height than the oil oil separator. According to this configuration, the oil separator can be shared by a plurality of compressors, the number of parts can be reduced, and sufficient oil pressure strength can be easily secured for the oil tank, and the layout in the refrigeration apparatus is facilitated. .

In the above configuration, the oil return pipe may be provided with an oil cooler downstream of the oil tank. According to this configuration, the oil can be efficiently cooled.

In the above configuration, the valve opening adjustment means increases the valve opening of the motor-operated valve when the operating frequency of the compressor increases, and increases the operating frequency of the compressor when the operating frequency of the compressor decreases. You may make it make the valve opening degree of a motor operated valve small. According to this configuration, the amount of oil returned into the case can be controlled in accordance with the amount of oil discharged, so that stable oil return control is possible.

According to the present invention, the oil separation efficiency and the oil storage amount can be secured without increasing the volume of the oil separator, and the lubrication failure of the compressor can be prevented.

It is a circuit block diagram of the freezing apparatus which concerns on this embodiment. It is a flowchart which shows the operation | movement of oil return control. It is a flowchart which shows the operation | movement of operation stop control.

Hereinafter, an embodiment of the present invention will be described with reference to the drawings.
FIG. 1 is a circuit configuration diagram of a refrigeration apparatus according to an embodiment of the present invention.
The refrigeration apparatus 1 includes a refrigeration unit 3 and a plurality of (for example, two)

showcase units

5A and 5B. The refrigeration unit 3 and the

showcase units

5A and 5B include a liquid refrigerant pipe 7 and a gas. A refrigerant circuit 10 that is connected by a refrigerant pipe 9 and performs a refrigeration cycle operation is configured.
The refrigerant circuit 10 uses a carbon dioxide (CO2) refrigerant whose high pressure side has a supercritical pressure. Since the carbon dioxide refrigerant has an ozone depletion coefficient of 0 and a global warming coefficient of 1, the load on the environment is small, and it is safe and inexpensive without toxicity and flammability. In addition to the carbon dioxide refrigerant, oil for lubricating the compressor 11 in the refrigerant circuit 10 is also placed in the refrigerant pipe. In FIG. 1, the flow of the refrigerant is indicated by solid arrows, and the flow of oil is indicated by broken arrows.

The refrigerator unit 3 includes two

compressors

11 and 11 connected by piping in parallel. The

compressors

11 and 11 are internal intermediate pressure type rotary two-stage compressors in which the insides of the

cases

12 and 12 have an intermediate pressure. Each compressor 11 has an electric motor section (not shown) inside the case 12 and a low-stage compression element 11A and a high-stage compression element 11B driven by the electric motor section. The low-stage compression element 11A boosts and discharges low-pressure refrigerant sucked into the compressor 11 through the gas refrigerant pipe 9 to an intermediate pressure, and the high-stage compression element 11B is an intermediate pressure compressed by the low-stage compression element 11A. The refrigerant is further pressurized to a high pressure and discharged. The compressor 11 is a variable frequency compressor, and the rotation speed of the low-stage compression element 11A and the high-stage compression element 11B can be adjusted by changing the operating frequency of the electric motor unit.

The case 12 of the compressor 11 includes a low-stage suction port 12A and a low-stage discharge port 12B communicating with the low-stage compression element 11A, and a high-stage suction port 12C and a high-stage side communicating with the high-stage compression element 11B. A discharge port 12D is formed. Low-

pressure suction pipes

13 and 13 are connected to the low-

stage suction ports

12A and 12A of the

compressors

11 and 11, respectively, and these low-

pressure suction pipes

13 and 13 merge on the upstream side of the low-

stage compression elements

11A and 11A. Are connected to a single gas refrigerant pipe 9 via a single accumulator 14. Further, the low pressure suction pipe 13 is provided with a suction pressure sensor 15 and a suction temperature sensor 16 for detecting the suction pressure and the suction temperature of the refrigerant flowing through the low pressure suction pipe 13, respectively.

Intermediate

pressure discharge pipes

17 and 17 are connected to the low-

stage discharge ports

12B and 12B, respectively, and the intermediate-

pressure discharge pipes

17 and 17 merge at the downstream side of the low-stage compression elements 11A and 11A. 18 is connected to one end. This intermediate cooler 18 cools the intermediate-pressure refrigerant discharged from the low-stage compression element 11A, and an intermediate-pressure suction pipe 19 is connected to the other end of the intermediate cooler 18. The suction pipe 19 is branched into two and then connected to the high-

stage suction ports

12C and 12C. Further, the intermediate pressure suction pipe 19 is provided with an intermediate pressure sensor 20 that detects the intermediate pressure of the refrigerant flowing through the intermediate pressure suction pipe 19. In this configuration, the high stage side suction port 12 </ b> C communicates with the high stage compression element 11 </ b> B through the space in the case 12, and the inside of the case 12 is maintained at an intermediate pressure during the operation of the compressor 11.

High-

pressure discharge pipes

21 and 21 are connected to the high-

stage discharge ports

12D and 12D, respectively, and the high-

pressure discharge pipes

21 and 21 merge on the downstream side of the high-

stage compression elements

11B and 11B to form a single high-pressure discharge. It becomes the tube 21A. The high-pressure discharge pipe 21 </ b> A is connected to the liquid refrigerant pipe 7 via a single oil separator 22, a gas cooler (heat radiator) 23, and a supercooling heat exchanger 24. The high-

stage discharge ports

12D and 12D are respectively provided with a discharge pressure sensor 25 and a discharge temperature sensor 26 for detecting the discharge pressure and the discharge temperature of the refrigerant discharged from the high-

stage compression elements

11B and 11B, respectively. ing.

The oil separator 22 separates and captures the oil contained in the high-pressure discharged refrigerant discharged from the compressor 11 from the refrigerant. The oil separator 22 is an oil that returns the captured oil to the compressor 11. A return pipe 28 is connected. The oil return pipe 28 is provided with an oil cooler 27 that cools the captured oil. On the downstream side of the oil cooler 27, the oil return pipe 28 includes two oil return pipes (an oil return pipe for each compressor 11). ) Branched to 28A and connected to the case 12 of the compressor 11 through the strainer 29 and the motor-operated valve 30 such as a flow rate adjusting valve, respectively. Since the inside of the case 12 of the compressor 11 is maintained at the intermediate pressure as described above, the trapped oil is intermediate between the high pressure in the oil separator 22 (equivalent to the pressure in the high-pressure discharge pipe 21A) and the inside of the case 12. The pressure is returned into the case 12 by the pressure difference.

By the way, since this refrigeration apparatus 1 uses a carbon dioxide refrigerant, the operating pressure is higher than when a fluorocarbon refrigerant is used, and the volume of the oil separator 22 is restricted due to the need to ensure pressure resistance. This means that the oil separation efficiency of the oil separator 22 decreases, and the oil that could not be separated flows to the evaporator (

case heat exchangers

43A and 43B) on the low pressure side of the refrigeration cycle and stays in the evaporator. It may cause deterioration of heat transfer performance and poor lubrication of the compressor. Further, the separated oil cannot be sufficiently stored in the oil separator 22, and refrigerant is mixed into the oil that returns to the compressor 11, so that the efficiency of the refrigeration apparatus 1 is significantly reduced or the amount of oil that returns to the compressor 11 is insufficient. This may cause poor lubrication.
Accordingly, in the present embodiment, a single oil tank 61 having a predetermined volume for storing the oil separated by the oil separator 22 is provided, and the oil stored in the oil tank 61 is supplied to the compressor through the oil return pipes 28A and 28A. 11 and 11 are returned to the case 12.

The oil tank 61 is formed of a small (small volume) heat-resistant container having a height lower than that of the oil separator 22, has sufficient pressure resistance to withstand the high operating pressure of the refrigeration apparatus 1, and the oil separator 22 It is arranged adjacent to.
One end of the oil pipe 28B connecting the oil separator 22 and the oil tank 61 opens near the bottom in the oil separator 22, and the oil near the bottom is drawn into the oil pipe 28B by the above differential pressure. Pull in. One end of a single oil return pipe 28 connected to the

compressors

11, 11 is connected to the oil tank 61, and the oil in the oil tank 61 is sucked into the oil return pipe 28 by the differential pressure, and the

compressor

11, 11 in the case 12.
According to this configuration, the oil separated by the oil separator 22 flows and accumulates in the oil tank 61 due to the negative pressure in the case 12 of the

compressors

11, 11, and accordingly, the oil oil level in the oil separator 22 is lowered. can do. As a result, an oil separation space (a space for separating the oil from the mixed flow of the gas-phase refrigerant and the oil mist) can be secured widely to increase the oil separation efficiency, and a sufficient amount of oil can be secured in the oil tank 61.

The case 12 of the compressor 11 is provided with an oil level sensor (oil level detecting means) 31 for detecting the level of oil stored in the case 12 (oil amount).
The oil level sensor 31 is a two-contact type level sensor that can detect an upper limit level and a lower limit level. Although not shown, the oil level sensor 31 includes a sensor case that communicates with the case 12, and the oil level in the sensor case is the compressor level. 11 according to the oil level in the case 12. Also, a float switch is arranged in the sensor case, which includes a float that floats up and down in response to changes in the oil level, and upper and lower contacts that are opened and closed as the height of the float changes. Yes. In this float switch, a magnet is disposed in the float, and upper and lower contacts disposed at different heights are opened and closed by the magnetic force of the magnet.
Specifically, the upper contact is turned on when the oil level in the case 12 exceeds the upper limit level, and the upper contact is turned off when the oil level falls below the upper limit level. Further, when the oil level in the case 12 exceeds the lower limit level, the lower contact is turned off, and when the oil level falls below the lower limit level, the lower contact is turned on.

The gas cooler 23 cools the high-pressure discharged refrigerant discharged from the compressor 11. In this configuration, the gas cooler 23 is arranged in parallel with the intermediate cooler 18 and the oil cooler 27 described above. The gas cooler 23, the intermediate cooler 18, and the oil cooler 27 are provided adjacent to a cooling fan 32 that blows air toward the gas cooler 23, the intermediate cooler 18, and the oil cooler 27.
The supercooling heat exchanger 24 is cooled by the gas cooler 23, and passes through the high pressure discharge pipe 21A and the liquid refrigerant pipe 7 from the gas cooler 23, and the first expansion valves (first throttle means) 42A included in the

showcase units

5A and 5B. The refrigerant heading for 42B is supercooled using the branched refrigerant branched on the outlet side of the gas cooler 23. A branch pipe 33 branched from the high-pressure discharge pipe 21 on the outlet side of the gas cooler 23 is connected to the branch refrigerant flow path inlet of the supercooling heat exchanger 24 via a second expansion valve 34, and the branch refrigerant flow The passage outlet is connected to an intermediate pressure suction pipe 19 on the outlet side of the intermediate cooler 18. The high-pressure discharge pipe 21 is provided with an inlet temperature sensor 35 and an outlet temperature sensor 36 that detect the temperature of the refrigerant flowing through the high-pressure discharge pipe 21 on the inlet side and the outlet side of the supercooling heat exchanger 24, respectively.

The refrigerator unit 3 includes a main controller 50 that controls the operation of the entire refrigeration apparatus 1. The main controller 50 adjusts the operating frequency of the

compressors

11 and 11 according to the refrigeration loads of the

showcase units

5A and 5B, and adjusts the refrigerant discharge temperature of the high-stage compression element 11B detected by the discharge temperature sensor 26. Based on this, the opening degree of the second expansion valve 34 is adjusted. The opening degree of the second expansion valve 34 may be adjusted based on the outlet temperature of the branch refrigerant, which is an intermediate pressure of the supercooling heat exchanger 24, the refrigerant inlet / outlet temperature difference of the supercooling heat exchanger 24, and the like. good.
Further, the main control device 50 executes oil return control from the oil separator 22 to each of the

compressors

11, 11, and at the time of oil return control, each motor-operated valve 30 is based on the operating frequency of each

compressor

11, 11. , 30 valve opening is adjusted. Further, when performing oil return control, the valve opening is corrected based on the oil level detected by each oil level sensor 31. In this embodiment, the main controller 50 functions as a valve opening adjusting means for adjusting the valve opening of the motor operated

valves

30 and 30 according to the operating frequency of the

compressors

11 and 11, and according to the oil level. It functions as a valve opening correction means for correcting the valve opening.

On the other hand, the

showcase units

5A and 5B are each installed in a store or the like, and are connected in parallel to the liquid refrigerant pipe 7 and the gas refrigerant pipe 9, respectively. Each

showcase unit

5A, 5B includes case

refrigerant pipes

40A, 40B that connect the liquid refrigerant pipe 7 and the gas refrigerant pipe 9, and the case

refrigerant pipes

40A, 40B include

strainers

41A, 41B, respectively, Expansion valves (first throttle means) 42A and 42B and

case heat exchangers

43A and 43B are provided. The

case heat exchangers

43A and 43B are provided with

case fans

44A and 44B adjacent to the

case heat exchangers

43A and 43B.
The

showcase units

5A and 5B include

case control devices

45A and 45B that control the operation of each part of the

showcase units

5A and 5B. The

case control devices

45A and 45B can communicate with the main control device 50. Composed.

Case controller

45A, 45B adjusts the opening degree of

1st expansion valve

42A, 42B based on the inlet-outlet temperature difference (superheat degree) of

case heat exchanger

43A, 43B, respectively.

Next, the operation of the oil return control described above will be described. FIG. 2 is a flowchart showing the operation of oil return control. Since this oil return control is the same for both

compressors

11, 11, only one compressor 11 and the corresponding motor-operated valve 30 will be described below.
When the operation of the refrigeration apparatus 1 is started, main controller 50 acquires the initial opening degree of motor-operated valve 30 (step S1). This initial opening is a valve opening that is set when the refrigeration apparatus 1 (that is, the compressors 11 and 11) is started. In this embodiment, the valve opening (for example, the valve opening that closes the motor-operated valve 30 (for example, 30 pulses).
Subsequently, main controller 50 adjusts the valve opening degree of motor-operated valve 30 according to the operating frequency of compressor 11 (step S2). The valve opening is calculated from the operating frequency of the compressor 11 and the correction coefficient A that is appropriately changed according to the oil level. Specifically, the valve opening is obtained by multiplying the value obtained by the correlation equation f (x) with the operating frequency as the variable x and the correction coefficient A, and when the operating frequency is high, the valve opening is performed. When the degree is large and low, the valve opening is reduced.

When the refrigeration apparatus 1 is started and the operation of the compressor 11 is started, the main controller 50 sets the correction coefficient A to an initial value (A = 2.0) (step S3), and uses this value. Adjust the valve opening. Thereby, after the refrigerating apparatus 1 is started, the valve opening degree of the motor-operated valve 30 is adjusted according to the operating frequency of the compressor 11. For this reason, the valve opening degree of each motor-operated valve 30 can be set to a valve opening degree corresponding to the operating frequency of each compressor 11, and the oil return amount as compared with the configuration in which the oil return amount is adjusted by a conventional electric on-off valve. Can be finely adjusted according to the compressor 11.
Here, the initial value of the correction coefficient A is set to a value that provides a valve opening for obtaining an oil return amount corresponding to the oil amount discharged from the compressor 11, for example, based on the specifications of the compressor 11. Is set. As a result, the balance between the amount of oil discharged from each compressor 11 and the amount of oil returned into the

cases

12 and 12 of each compressor 11 can be improved, and the amount of oil returned to each compressor 11 can be reduced. Can be appropriate.

Subsequently, after resetting the built-in timer (step S4), main controller 50 determines whether or not the lower contacts of the float switches of both

compressors

11 and 11 are off (step S5).
In this determination, when the lower contact of the float switch is not off (step S5; No), that is, when the oil level is below the lower limit level, a predetermined first waiting time (30 seconds in the present embodiment). Is determined (step S6). If this waiting time has not elapsed (step S6; No), the process returns to step S5.
By performing the process of determining whether or not this waiting time has elapsed, it is possible to avoid erroneous detection of the oil level due to oil level fluctuations that occur during compressor operation. Then, when the waiting time has elapsed (step S6; Yes), that is, when the oil level continues below the lower limit level, the amount of oil in the case 12 is determined to be too small, so the main control device 50 Shifts the processing to step S12 to correct the valve opening of the motor-operated valve 30.

When the lower contact of the float switch is off (step S5; Yes), that is, when the oil level exceeds the lower limit level, the main controller 50 resets the built-in timer (step S7). It is determined whether or not the upper contact of the switch is off (step S8).
In step S8, if the upper contact of the float switch is not off (step S8; No), that is, if the oil level exceeds the upper limit level, a predetermined second waiting time (30 in this embodiment) is set. It is determined whether or not (second) has elapsed (step S9). If this waiting time has not elapsed (step S9; No), the process returns to step S8. Thus, similarly to the above, erroneous detection of the oil level can be avoided, and when the waiting time has elapsed, that is, when the oil level continues to exceed the upper limit level, the amount of oil in the case 12 Therefore, main controller 50 shifts the process to step S15 and corrects the valve opening degree of electric valve 30.

On the other hand, when the upper contact of the float switch is off (step S8; Yes), that is, when the oil level is below the upper limit level, the main controller 50 determines whether the

compressors

11 and 11 are stopped. Is determined (step S10). In this determination, if the compressor 11 is not stopped (step S10; No), the process proceeds to step S4, and the oil level determination process shown in steps S4 to S10 is repeatedly executed.
Moreover, when the compressor 11 has stopped (step S10; Yes), the valve opening degree of the motor operated valve 30 is set to an initial opening degree, and a process is complete | finished (step S11).

As described above, when the state where the lower contact of the float switch is not turned off continues (step S6; No), the amount of oil in the case 12 is determined to be too small, so the oil return pipe 28A to the case 12 is provided. It correct | amends so that the valve opening degree of the obtained motor operated valve 30 may be enlarged (diameter expansion). Specifically, the main controller 50 sets the correction coefficient A related to the valve opening degree of the motor-operated valve 30 of the compressor 11 by increasing a predetermined amount (10% in this embodiment) (step S12). Thereby, the valve opening degree of the motor-operated valve 30 adjusted according to the operating frequency of the compressor 11 is corrected based on the oil amount in the case 12. For this reason, the amount of oil returned into the case 12 can be increased, and the state where the amount of oil in the case 12 is too small can be eliminated early.
Further, main controller 50 determines whether or not correction coefficient A is larger than a predetermined upper limit value (6.0 in the present embodiment) (step S13). This upper limit value is an upper limit value when the correction coefficient A is increased. When the correction coefficient A is smaller than the upper limit value (step S13; No), the process returns to step S4.
On the other hand, when the correction coefficient A exceeds the upper limit value (step S13; Yes), the correction coefficient A is set to the upper limit value (step S14), and the process returns to step S4.

When the state in which the upper contact of the float switch is not off continues (step S9; No), it is determined that the amount of oil in the case 12 is excessive, so that the valve opening of the motor-operated valve 30 is decreased (reduced diameter). to correct. Specifically, the main controller 50 sets the correction coefficient A related to the valve opening degree of the motor-operated valve 30 of the compressor 11 by decreasing a predetermined amount (about 5% in the present embodiment) (step S15). Thereby, the valve opening degree of the motor-operated valve 30 adjusted according to the operating frequency of the compressor 11 is corrected based on the oil amount in the case 12. For this reason, the amount of oil returned into the case 12 can be reduced, and the state where the amount of oil in the case 12 is excessive can be eliminated at an early stage.
Subsequently, main controller 50 determines whether or not correction coefficient A is smaller than a predetermined lower limit (0.3 in the present embodiment) (step S16). This lower limit value is a lower limit value when the correction coefficient A is decreased. When the correction coefficient A is equal to or higher than the lower limit value (step S16; No), the process returns to step S4.
On the other hand, if the correction coefficient A is below the lower limit value (step S16; Yes), the correction coefficient A is set to the lower limit value (step S17), and the process returns to step S4.

As described above, in the present embodiment, the two-stage compressor 11 in which the inside of the case 12 has an intermediate pressure, the oil separator 22 provided in the high-pressure discharge pipe 21 of the compressor 11, and the oil separator 22 are captured. An oil return pipe 28 for returning oil into the case 12, a motor operated valve 30 provided in the oil return pipe 28 </ b> A, and a valve opening adjustment for adjusting the valve opening of the motor operated valve 30 according to the operating frequency of the compressor 11. In order to provide the main controller 50 as a means, even in a configuration using carbon dioxide refrigerant, a balance between the amount of oil discharged from the compressor 11 and the amount of oil returned into the case 12 of the compressor 11 is achieved. The amount of oil in the case 12 can be easily controlled.

In the present embodiment, the main controller 50 increases the valve opening degree of the motor-operated valve 30 when the operating frequency of the compressor 11 is increased, and the motor-operated valve when the operating frequency of the compressor 11 is decreased. Since the valve opening of 30 is reduced, the amount of oil returned into the case 12 can be controlled in accordance with the amount of oil discharged from the compressor 11, so that stable oil return control is possible.

Further, in the present embodiment, the oil level sensor 31 that detects the oil level in the case 12 is provided, and the main controller 50 detects that the compressor level when the oil level detected by the oil level sensor 31 exceeds the upper limit level. In order to correct so that the valve opening degree of the motor-operated valve 30 adjusted according to the operation frequency of 11 is made small, and when the oil level falls below the lower limit level, the valve opening degree is made to increase. The state in which the amount of oil in the case 12 is too small or excessive can be quickly eliminated, and control can be performed so that the amount of oil in the case 12 does not become insufficient.

As described above, the refrigeration apparatus 1 performs oil return control for adjusting the valve opening degree of the electric valve 30 provided in the oil return pipe 28A according to the operating frequency of the compressor 11 and the oil level in the case 12. Therefore, it is possible to avoid the situation where the oil amount in the compressor 11 is reduced by optimizing the oil return amount as much as possible.
However, even in the case of this refrigeration apparatus 1, it may take time for the oil to circulate properly in the pipe during a trial run performed immediately after installation, particularly during a trial run when the pipe distance is long. In other words, even if the motor-operated

valves

30 and 30 are opened widely, the oil does not return to the

cases

12 and 12 of the

compressors

11 and 11, and the amount of oil in the

cases

12 and 12 decreases. Furthermore, even when the total amount of oil in the refrigeration apparatus 1 is small, a situation occurs in which the amount of oil in the

cases

12 and 12 of the

compressors

11 and 11 is small regardless of the opening degree of the motor operated

valves

30 and 30.
In the oil return control, since the operation of the compressor 11 is continued even when the amount of oil is small, the operation of the compressor 11 is continued during a trial operation or when the total amount of oil is small, which may lead to poor lubrication. . Therefore, in the present embodiment, in addition to the oil return control described above, operation stop control is performed to avoid the operation of the compressor 11 when the amount of oil in the compressor 11 is small.

FIG. 3 is a flowchart showing the operation of the operation stop control. When the cooling operation of the refrigeration apparatus 1 is started, this flow is repeatedly executed at a predetermined interruption cycle, and is performed in parallel with the oil return control shown in FIG. This operation stop control is similarly performed in both

compressors

11 and 11.
First, main controller 50 resets another built-in timer (step S21), and then determines whether or not the lower contact of the float switch of compressor 11 is off (step S22).
In this determination, when the lower contact of the float switch is not off (step S22; No), that is, when the oil level is below the lower limit level, the oil return control does not increase the oil amount, that is, the oil is insufficient. It is determined whether or not a waiting time (waiting time for operation stop determination) that can be determined as an unavoidable state has elapsed (step S23). This waiting time is set to be longer than the first and second waiting times (30 seconds in the present embodiment) for oil return control and within a time that does not have a significant adverse effect on the compressor 11, In this embodiment, it is set to 10 minutes.

If the waiting time has not elapsed (step S23; No), the main control device 50 returns to the process of step S22. If the waiting time has elapsed (step S23; Yes), the oil level is below the lower limit level. Is stopped (step S24), and the process returns to step S22. Thereby, the driving | operation of the compressor 11 in the state with few oil quantities can be avoided.
On the other hand, when the lower contact of the float switch is off (step S22; Yes), that is, when the oil level is higher than the lower limit level, the main controller 50 is a compressor provided with the float switch. It is determined whether or not 11 is stopped (step S25). If not stopped (step S25; No), the process returns to step S21.

When the compressor 11 is stopped (step S25; Yes), the main controller 50 determines whether or not there is an operation signal for instructing operation, that is, whether or not the operation instruction is continuing or a new operation instruction has been issued. Is determined (step S26). If there is an operation instruction (step S26; Yes), main controller 50 causes compressor 11 to operate again (step S27). That is, after the operation of the compressor 11 is stopped, the operation of the compressor 11 is resumed when the oil level exceeds the lower limit level.
On the other hand, if there is no operation instruction (step S26; No), the main controller 50 ends the processing and keeps the compressor 11 stopped. Thereby, the driving | running of the compressor 11 in a state with few oil quantities is continued and avoided.

Here, when the operation of the compressor 11 is stopped by the process of step S24, the main controller 50 increases the operation capacity of the other compressors 11 to compensate for the decrease in the operation capacity due to the operation stop of the compressor 11. Take control. Specifically, if the other compressor 11 is stopped, the operation of the other compressor 11 is started, and control is performed so that the compressor 11 is operated at the capacity before the stop. Is operating, the operating capacity of the other compressors 11 is increased by the operating capacity of the stopped compressor 11 before stopping. Thereby, the fall of driving capability is suppressed and the freezing operation according to external load (refrigeration load) is continued.

As described above, in the present embodiment, the main controller 50 stops the operation of the compressor 11 when the oil level continues below the lower limit level during the operation of the compressor 11, and the oil level Functions as an operation control means for restarting the operation of the compressor 11 when the value exceeds the lower limit level, so that the operation of the compressor 11 in a state where the amount of oil in the compressor 11 is small is avoided and the lubrication of the compressor 11 is performed. Defects can be prevented.
In addition, in the present embodiment, since the valve opening degree of the motor-operated valve 30 provided in the oil return pipe 28A is controlled according to the operating frequency of the compressor 11, a special operation such as a trial operation or a small total oil amount is performed. As long as it is not in a state, the amount of oil return can be optimized, and a situation in which the state of low oil in the compressor 11 continues can be avoided.
In this way, in the present embodiment, with the configuration using carbon dioxide refrigerant, the compressor 11 can be continuously operated by optimizing the oil return amount, and the compressor 11 is caused due to the special state described above. It becomes possible to prevent the lubrication failure of the compressor 11 when the oil in the inside decreases.

Moreover, in this embodiment, when it has the some

compressors

11 and 11 connected in parallel, and the state where the oil level fell below the minimum level continued, when one of the compressors 11 was stopped, Since the operation capacity of the other compressor 11 is increased so as to compensate for the decrease in the operation capacity due to the operation stop, the decrease in the operation capacity can be suppressed. Therefore, even if one of the compressors 11 is stopped, the operation corresponding to the refrigeration load can be continued. Moreover, since the other compressor 11 is drive | operated, it can make it easy to return oil to the compressor 11 which stopped the operation.

Further, in the present embodiment, an oil tank 61 having a predetermined volume for storing the oil separated by the oil separator 22 is provided, and the oil stored in the oil tank 61 is passed through the oil return pipe 28 in the case 12 of the compressor 11. In addition, the motor-operated valve 30 for adjusting the opening degree of the oil return pipe 28A is provided, and the opening degree of the motor-operated valve 30 is adjusted according to the operating frequency of the compressor 11, so that oil is accumulated in the oil tank 61. Therefore, the oil oil level in the oil separator 22 can be lowered. As a result, a large oil separation space can be secured to increase the oil separation efficiency, and a sufficient oil storage amount can be secured by the oil tank 61.
Therefore, without increasing the volume of the oil separator 22, the oil separation efficiency and the oil storage amount can be ensured, and this also enables stable oil return control in the configuration using the carbon dioxide refrigerant. It is possible to prevent the refrigerant from entering the oil that returns to the compressor 11, and it is possible to more reliably prevent poor lubrication of the compressor 11.

Further, by providing the oil tank 61, the temperature of the oil can be lowered by the oil tank 61, the temperature of the oil returning to the compressor 11 can be efficiently lowered, and the oil level in the oil tank 61 is changed to the oil separator 22. There is also an effect that the oil level is stabilized without being disturbed by the gas-phase refrigerant.
Furthermore, since the oil separator 22 is provided in a single high-pressure discharge pipe 21A that joins the high-

pressure discharge pipes

21 and 21 of the plurality of

compressors

11 and 11, the oil separator 22 can be shared by the plurality of

compressors

11 and 11. The number of parts can be reduced. In addition, since the oil tank 61 is formed of a heat-resistant container having a height lower than that of the oil separator 22, it is easy to ensure sufficient pressure resistance and layout in the refrigeration apparatus 1 is easy.
Further, since the oil cooler 27 is provided in the oil return pipe 21A downstream of the oil tank 61, the oil can be efficiently cooled.

As mentioned above, although one Embodiment of this invention was described, this invention is not limited to this, A various change implementation is possible. For example, in this embodiment, although the case where the two

compressors

11 and 11 were provided was demonstrated, you may make it 1 unit | set or 3 units | sets or more without limiting to this. Moreover, you may apply the well-known compressor which stores oil not only in the two-stage type compressor 11 in which the inside of case 12 becomes intermediate pressure.
Moreover, although this embodiment demonstrated the case where this invention was applied to the refrigeration apparatus 1 which consists of the refrigerator unit 3 used as a heat source side apparatus, and

showcase unit

5A, 5B used as a use side apparatus, well-known freezing You may apply the structure of an apparatus.
In the present embodiment, the case where the oil level sensor 31 is configured by a two-contact type level sensor that can detect the upper limit level and the lower limit level has been described. However, the present invention is not limited to this, for example, between the upper limit level and the lower limit level. It may be constituted by a level sensor that can detect the intermediate level.

Further, in this embodiment, in the operation stop control, the case where the oil level when the operation of the compressor 11 is stopped and the oil level when the operation is restarted is set to the same level (lower limit level) is described, but the present invention is not limited to this. That is, the oil level when the operation of the compressor 11 is stopped may be different from that when the operation is restarted. For example, when the oil level exceeds the intermediate level, the operation of the compressor 11 may be restarted. . In this case, the operation of the compressor 11 can be resumed while more oil is accumulated in the compressor 11, the lubrication failure can be reliably avoided and the operation time of the compressor 11 can be ensured for a long time. It becomes easy to secure time until it circulates appropriately.

1 Refrigeration equipment 3 Refrigerator unit (heat source side equipment)
5A, 5B showcase unit (use side equipment)
DESCRIPTION OF SYMBOLS 10 Refrigerant circuit 11 Compressor 12 Case 21 High pressure discharge pipe 22 Oil separator 23 Gas cooler 27 Oil cooler 28, 28A, 28B Oil return pipe 30 Electric valve 31 Oil level sensor (oil level detection means)
38 Capillary tube (fixed throttle)
50 Main controller (valve opening adjusting means, valve opening correcting means, operation control means)
61 Oil tank A Correction factor

Claims

A refrigerant circuit that performs a refrigeration cycle operation using carbon dioxide as a refrigerant is provided in the high pressure discharge pipe, and a compressor that stores oil in the case and discharges the refrigerant together with the oil to the high pressure discharge pipe. In the refrigeration apparatus having an oil separator and an oil return pipe for returning the oil separated by the oil separator into the case,
An oil tank having a predetermined volume for storing oil separated by the oil separator is provided, and the oil stored in the oil tank is returned into the case through the oil return pipe, and an electric valve is provided in the oil return pipe. A refrigeration apparatus comprising valve opening adjusting means for adjusting the opening of the motor-operated valve according to the operating frequency of the compressor.
The compressor has a plurality of compressors connected in parallel,
The oil separator is provided in a single high-pressure discharge pipe that joins the high-pressure discharge pipes of the plurality of compressors, and the oil tank is formed of a heat-resistant container having a lower height than the oil-oil separator. The refrigeration apparatus according to claim 1, wherein
The refrigeration apparatus according to claim 1 or 2, wherein the oil return pipe is provided with an oil cooler downstream of the oil tank.
The valve opening adjustment means increases the valve opening of the motor-operated valve when the operating frequency of the compressor increases, and opens the valve of the motor-operated valve when the operating frequency of the compressor decreases. The refrigeration apparatus according to claim 1, wherein the refrigeration apparatus is reduced.