JP4250320B2 - Operation method of oil-cooled compression refrigerator - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for operating an oil-cooled compression refrigerator in which refrigerant gas is compressed under oil injection.
[0002]
[Prior art]
Conventionally, an oil-cooled compression type refrigerator is disclosed in Japanese Patent Laid-Open No. 1-312361. The refrigerator is branched from a refrigerant circulation passage including an oil-cooled compressor, an oil separator, a condenser, an expansion valve, an evaporator and an accumulator, and a portion of the circulation passage on the primary side of the oil separator. And a bypass flow path that joins the circulation flow path portion on the primary side of the evaporator. The bypass flow path is provided with a first bypass solenoid valve, a high pressure tank, and a second bypass solenoid valve. In this refrigerator, the second bypass solenoid valve is opened, and the flow of gas from the high-pressure tank is guided to the evaporator, so that the oil accumulated in the evaporator is returned to the compressor.
[0003]
[Problems to be solved by the invention]
In the case of the conventional refrigerator described above, the number of rotations can be increased or decreased by controlling the motor that is the drive unit of the oil-cooled compressor, for example, freely changing the number of rotations between 0 rpm and 7000 rpm. It becomes possible. However, if the rotational speed is reduced too much, the above-described oil flow does not become as intended. That is, the bypass channel is branched on the primary side of the oil separator, and the bypass channel contains a large amount of oil.
[0004]
For this reason, when the second bypass solenoid valve is opened as described above, there is a problem that the oil is fed into the evaporator and stays there, and the oil is not necessarily returned to the compressor. When a large amount of oil stays in the evaporator, liquid oil returns to the compressor, which causes a serious problem of damage to the compressor due to so-called liquid compression, and the problem that the operation of the refrigerator becomes impossible occurs. .
An object of the present invention is to eliminate such a conventional problem, and to provide an operation method of an oil-cooled compression type refrigerator capable of appropriately circulating oil and eliminating unnecessary stagnation of oil. It is something to be offered.
[0005]
[Means for Solving the Problems]
The first invention includes a refrigerant circulation passage including an oil-cooled compressor, an oil separator / recovery unit, a condenser, an expansion valve, and an evaporator, and includes detection means for determining the magnitude of the cooling heat load, Based on the signal from the detection means, normal operation control is performed to keep the rotation speed of the compressor drive unit at a value suitable for the cooling heat load in the evaporator between the lower limit rotation speed and the upper limit rotation speed. In the operation method of the oil-cooled compression type refrigerator, the rotation speed of the drive unit is higher than the lower limit rotation speed, and the piping system of the circulation flow path and the compressor so as not to retain oil in the evaporator The oil pressure in the oil separation / recovery unit is lower than a predetermined lower limit level that is considered to reach an allowable limit of oil retention in the evaporator. If the oil level is Until a predetermined upper limit level higher than Le and the rotating speed so as to preferentially perform the oil return control to the operating raised to above the allowable minimum number of revolutions.
[0006]
The second invention is the oil-cooled compressor, the oil separation and recovery, a condenser, provided with a circulation passage of the refrigerant containing an expansion valve and an evaporator, comprising a detecting means for determining the magnitude of the cooling heat load Based on the signal from the detection means, the normal operation control for maintaining the rotational speed of the drive unit of the compressor between the lower limit rotational speed and the upper limit rotational speed to a value suitable for the cooling heat load in the evaporator. In the operation method of the oil-cooled compression refrigerator that is performed, the rotational speed of the drive unit is higher than the lower limit rotational speed, and the piping system of the circulation channel and the above-mentioned so as not to retain oil in the evaporator It falls below the allowable minimum rotational speed determined in advance by the specifications of the compressor, and the differential pressure between the refrigerant pressure between the expansion valve and the evaporator and the suction pressure of the oil-cooled compressor is within the evaporator. Preliminarily considered to reach an acceptable limit of oil retention in Priority is given to oil return control that increases the rotational speed of the drive unit to the allowable minimum rotational speed and operates until the differential pressure becomes lower than the allowable upper limit pressure. I tried to do it.
[0007]
Furthermore, the third invention includes a refrigerant circulation passage including an oil-cooled compressor, an oil separator / recovery unit, a condenser, an expansion valve and an evaporator, and a detection means for determining the magnitude of the cooling heat load. Based on the signal from the detection means, the normal operation control for maintaining the rotational speed of the drive unit of the compressor between the lower limit rotational speed and the upper limit rotational speed to a value suitable for the cooling heat load in the evaporator. In the operation method of the oil-cooled compression refrigerator that is performed, the rotational speed of the drive unit is higher than the lower limit rotational speed, and the piping system of the circulation channel and the above-mentioned so as not to retain oil in the evaporator The pressure falls below the minimum allowable number of rotations determined in advance by the specifications of the compressor, and the difference between the refrigerant pressure at the outlet of the evaporator and the suction pressure of the oil-cooled compressor causes the oil to stay in the evaporator. A predetermined allowance that is deemed to be reached when When the pressure exceeds the upper limit pressure, the oil return control is preferentially performed by increasing the rotational speed of the drive unit to the allowable minimum rotational speed and operating until the differential pressure becomes smaller than the allowable upper limit pressure. I did it.
[0008]
DETAILED DESCRIPTION OF THE INVENTION
Next, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 shows a refrigerator 1A according to a reference example , and an oil-cooled compressor 11, for example, an oil-cooled screw compressor, an oil separator / collector 12, a condenser 13, an expansion valve 14, and an evaporator 15 are circulated in the refrigerant circulation. A flow path I is formed. Further, an oil supply channel II is formed through which oil is guided from the oil separator / collector 12 to the oil supply location such as the rotor chamber and the bearing / shaft seal in the compressor 11 via the oil cooler 16.
[0009]
A motor 21 that is a drive unit of the compressor 11 is connected to a power source 24 via an inverter 23 that receives a control signal corresponding to the number of rotations from a control device 22. Further, a temperature detector 31 for detecting the temperature of the liquid to be cooled is provided at a portion of the liquid flow path 25 that exits the evaporator 15, and a temperature signal indicating the temperature detected by the temperature detector 31 is provided. It is input to the control device 22.
With such a configuration, as will be described in detail below, the control device is operated based on the temperature signal via the inverter 23 so as to operate the compressor 11 appropriately corresponding to the cooling heat load in the evaporator 15. 22, normal operation control for controlling the rotation speed of the motor 21, and oil return control for preferentially removing this oil as needed by monitoring the oil retention state in the evaporator 15 by the control device 22. Done.
[0010]
Next, an operation method according to the present invention applied to the above-described refrigerator 1A will be described.
The motor 21 is controlled by the control device 22 via the inverter 23 between the lower limit rotational speed (example: 1000 rpm) and the upper limit rotational speed (example: 7000 rpm), the compressor 11 is operated, and the oil supply flow path The refrigerant gas compressed while being injected with oil from II is discharged from the compressor 11 to the oil separator / recoverer 12 with oil. In the oil separator / collector 12, the refrigerant gas and the oil are separated, and the refrigerant gas is sent to the condenser 13, while the oil is collected in the lower part of the oil separator / collector 12 and temporarily stored.
[0011]
Further, the refrigerant gas becomes a liquid state through the condenser 13, is expanded through the expansion valve 14, is almost in a gas state and reaches the evaporator 15, where the liquid to be cooled and the heat in the flow path 25 are heated. Exchange. Then, the liquid to be cooled is cooled, and the refrigerant takes heat from the liquid to be cooled, and is completely in a gas state and returns to the compressor 11. On the other hand, the oil accumulated in the lower part of the oil separator / recovery unit 12 is sent out to the oil supply channel II, and is guided to the compressor 11 again through the oil cooler 16.
As described above, the refrigerant gas is compressed while receiving oil injection by the compressor 11, the refrigerant circulates through the refrigerant circulation passage I, and the oil circulates through the oil supply passage II.
[0012]
Further, when the normal operation control is performed during the operation of the above-described refrigerator 1A and the temperature detected by the temperature detector 31 is too high, the cooling heat load in the evaporator 15 in the refrigerator 1A is large, and the capacity of the compressor 11 is increased. However, if the detected temperature is too low, the cooling heat load is small and the capacity of the compressor 11 is excessive. It is necessary to reduce the rotation speed of the motor 21. Therefore, based on the temperature signal indicating the detected temperature from the temperature detector 31, a control signal is output from the control device 22 to the inverter 23 so as to keep the rotation speed of the motor 21 at a value suitable for the cooling heat load.
[0013]
By the way, as described above, the refrigerant gas and the oil are separated by the oil separator / recovery unit 12, but it is difficult to completely perform the separation. In practice, part of the oil is condensed along with the refrigerant gas. It moves to the vessel 13 and further flows from the expansion valve 14 to the evaporator 15. The oil that has entered the evaporator 15 is returned to the compressor 11 and circulates when the rotational speed of the motor 21 is high, but the oil in the evaporator 15 is compressed when the rotational speed of the motor 21 is low. Instead of returning to the machine 11, it stays in the evaporator 15. The allowable minimum number of rotations, which is the minimum value of the number of rotations of the motor 21 that does not cause stagnation, is higher than the lower limit number of rotations described above, and is obtained in advance according to the piping diameter of the refrigerator 1A, the specifications of the compressor 11, and the like.
[0014]
Therefore, under the normal operation control in which the rotation speed of the motor 21 is controlled between the lower limit rotation speed and the upper limit rotation speed, the rotation speed of the motor 21 falls below the allowable minimum rotation speed, and this low-speed rotation state. When the control device 22 determines that the continuous operation time at has reached a predetermined allowable limit time, oil return control is preferentially performed. That is, in this case, the oil staying in the evaporator 15 reaches the allowable limit, and it is necessary to immediately return this oil to the compressor 11, so that the rotation speed of the motor 21 is increased to the allowable minimum rotation speed. The operation is performed for a predetermined period of time during which the accumulated oil can be returned to the compressor 11.
After the operation under the oil return control is performed for a predetermined time, the operation is returned to the normal operation control.
As a result of the oil return control described above, even if the motor 21 is operated in the low-speed rotation state, the operation in this state does not continue abnormally long, and proper circulation of the oil flowing through the oil supply channel II is prevented. It is possible to maintain and limit oil retention in the refrigerant circulation flow path I, and to continue a good operation state of the refrigerator 1A without serious problems such as damage to the compressor 11.
[0015]
In the refrigerator 1A has been described above, the cooling heat load of the magnitude of the decision in the normal operation under the control being performed based on the temperature detected by the temperature detector 31, in place of the temperature detector 31, in FIG. 1 two A refrigerator provided with a pressure detector 32 for detecting the suction gas pressure of the compressor 11 as indicated by a chain line, and determining the magnitude of the cooling heat load based on the pressure detected by the pressure detector 32. Is also included. In this case, when the detected pressure is high, the cooling heat load is large, and when the detected pressure is low, the cooling heat load is small.
As described above, the point that the pressure detector 32 is provided in place of the temperature detector 31 is the same for each invention described below, and redundant description is omitted.
[0016]
FIG. 2 shows the refrigerator 1B according to the first invention, and portions common to the refrigerator 1A shown in FIG.
In this refrigerator 1B, a lower limit level detector 33 and an upper limit level detector 34 for detecting the oil level in the lower oil reservoir 12a are provided in the oil separator / collector 12 for oil return control. A level signal indicating a detection level by each of the signals is input to the control device 22.
The lower limit level detector 33 is provided so as to detect the lower limit level of the oil level that is considered to reach the allowable limit of oil retention in the evaporator 15, and the upper limit level detector 34 performs hunting during oil return control. In order to avoid this, an upper limit level that is slightly higher than the lower limit level is provided separately from the lower limit level detector 33. This upper limit level is sufficient to prevent the above hunting.
[0017]
With this configuration, the same normal operation control as described above is performed. Under this normal operation control, the rotation speed of the motor 21 is lower than the allowable minimum rotation speed, and the oil level is lower than the lower limit level. When it is no longer detected by the level detector 33, oil return control is preferentially performed. This oil return control is continued until the rotational speed of the motor 21 is increased to the allowable minimum rotational speed and the oil level is detected by the upper limit level detector 34, and then the normal operation control is performed.
As a result, as described above, proper circulation of the oil is maintained, oil stagnation in the refrigerant circulation flow path I is limited, and a good operating state of the refrigerator 1B is maintained.
[0018]
FIG. 3 shows a refrigerator 1C according to the second aspect of the invention, and parts common to the refrigerator 1A shown in FIG.
In this refrigerator 1C, a differential pressure gauge 35 that detects a differential pressure between the refrigerant pressure between the expansion valve 14 and the evaporator 15 and the suction pressure of the compressor 11 is provided for oil return control. A pressure signal indicating the detected differential pressure is input to the control device 22.
[0019]
With this configuration, the same normal operation control as described above is performed. Under this normal operation control, the rotation speed of the motor 21 is lower than the allowable minimum rotation speed, and the differential pressure is reduced by the oil in the evaporator 15. When the pressure reaches or exceeds a predetermined upper limit pressure that is considered to be reached when the retention limit is reached, oil return control is preferentially performed. This oil return control is continued until the rotation speed of the motor 21 is increased to the allowable minimum rotation speed until the differential pressure becomes smaller than the upper limit pressure, and then the normal operation control is performed.
As a result, as described above, proper circulation of oil is maintained, oil retention in the refrigerant circulation flow path I is limited, and a good operating state of the refrigerator 1C is maintained.
[0020]
4 shows a refrigerator 1D according to the third aspect of the invention. The difference between the refrigerator 1C shown in FIG. 3 is the difference between the pressure at the outlet of the evaporator 15 and the suction pressure of the compressor 11 instead of the differential pressure gauge 35. Except for the point that a differential pressure gauge 36 for detecting pressure is provided, the others are substantially the same, and portions common to each other are denoted by the same reference numerals and description thereof is omitted.
[0021]
【The invention's effect】
According to the first invention, the rotational speed of the drive unit is higher than the lower limit rotational speed, and it is determined in advance according to the specifications of the piping system of the circulation channel and the compressor so as not to retain oil in the evaporator. When the oil pressure in the oil separation / recovery unit falls below a predetermined lower limit level that is considered to reach the allowable limit of oil retention in the evaporator, when the rotation speed falls below a predetermined allowable minimum rotational speed. Until the oil level reaches a predetermined upper limit level that is higher than the lower limit level, oil return control is performed preferentially so as to increase the rotational speed to the allowable minimum rotational speed.
[0022]
Further , according to the second invention, the rotational speed of the drive unit is higher than the lower limit rotational speed, and the specifications of the piping system of the circulation channel and the compressor so as not to retain oil in the evaporator. The difference between the refrigerant pressure between the expansion valve and the evaporator and the suction pressure of the oil-cooled compressor is reduced by the retention of oil in the evaporator. When the pressure exceeds a predetermined allowable upper limit pressure that is considered to be reached at the allowable limit, the rotational speed of the drive unit is increased to the allowable minimum rotational speed, and the differential pressure is smaller than the allowable upper limit pressure. The oil return control for operating until this is preferentially performed.
[0023]
Further, according to the third aspect of the invention, the rotational speed of the drive unit is higher than the lower limit rotational speed, and the specifications of the piping system of the circulation channel and the compressor so as not to retain oil in the evaporator. And the pressure difference between the refrigerant pressure at the outlet of the evaporator and the suction pressure of the oil-cooled compressor is lower than the allowable limit of oil retention in the evaporator. When the pressure exceeds a predetermined allowable upper limit pressure that is considered to be reached, the rotational speed of the drive unit is increased to the allowable minimum rotational speed, and the operation is performed until the differential pressure becomes smaller than the allowable upper limit pressure. The oil return control is preferentially performed.
[0024]
For this reason, even if the motor, which is the drive unit of the compressor, is operated in a low-speed rotation state, the operation in this state does not continue abnormally long, and proper circulation of the oil flowing through the oil supply flow path is prevented. This maintains the effect of restricting the retention of oil in the refrigerant circulation flow path and allowing the refrigerator to continue to operate in good condition without serious problems such as damage to the compressor.
[Brief description of the drawings]
FIG. 1 is a diagram showing an overall configuration of a refrigerator according to a reference example .
FIG. 2 is a diagram showing an overall configuration of a refrigerator according to the first invention.
FIG. 3 is a diagram showing an overall configuration of a refrigerator according to a second invention.
FIG. 4 is a diagram showing an overall configuration of a refrigerator according to a third invention.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 B, 1C, 1D Refrigerator 11 Oil-cooled compressor 12 Oil separation and recovery device 12a Oil reservoir 13 Condenser 14 Expansion valve 15 Evaporator 16 Oil cooler 21 Motor 22 Control device 23 Inverter 24 Power supply 25 Flow path 31 Temperature Detector 32 Pressure detector 33 Lower limit level detector 34 Upper limit level detector 35 Differential pressure gauge 36 Differential pressure gauge I Refrigerant circulation flow path
II Oil supply flow path

Claims (3)

A refrigerant circulation path including an oil-cooled compressor, an oil separator / collector, a condenser, an expansion valve and an evaporator, and a detection means for judging the magnitude of the cooling heat load, and a signal from the detection means Oil-cooled compression type refrigeration in which normal operation control is performed to keep the rotational speed of the drive unit of the compressor between the lower limit rotational speed and the upper limit rotational speed at a value suitable for the cooling heat load in the evaporator In the operation method of the machine,
The rotational speed of the drive unit is higher than the lower limit rotational speed, and the allowable minimum rotational speed determined in advance by the piping system of the circulation channel and the specifications of the compressor so as not to retain oil in the evaporator. If the oil level in the oil separator / recovery unit becomes lower than a predetermined lower limit level that is considered to reach the allowable limit of oil retention in the evaporator, the oil level becomes lower than the lower limit. A method of operating an oil-cooled compression type refrigerator that preferentially performs oil return control that increases the rotational speed to the allowable minimum rotational speed until a predetermined upper limit level higher than the level is reached. . A refrigerant circulation path including an oil-cooled compressor, an oil separator / collector, a condenser, an expansion valve and an evaporator, and a detection means for judging the magnitude of the cooling heat load, and a signal from the detection means Oil-cooled compression type refrigeration in which normal operation control is performed to keep the rotational speed of the drive unit of the compressor between the lower limit rotational speed and the upper limit rotational speed at a value suitable for the cooling heat load in the evaporator In the operation method of the machine,
The rotational speed of the drive unit is higher than the lower limit rotational speed, and the allowable minimum rotational speed determined in advance by the piping system of the circulation channel and the specifications of the compressor so as not to retain oil in the evaporator. The pressure difference between the refrigerant pressure between the expansion valve and the evaporator and the suction pressure of the oil-cooled compressor is preliminarily assumed to reach the allowable limit of oil retention in the evaporator. Priority is given to oil return control that increases the rotational speed of the drive unit to the allowable minimum rotational speed and operates until the differential pressure becomes smaller than the allowable upper limit pressure when the pressure exceeds a predetermined allowable upper limit pressure. The operation method of the oil-cooled compression type refrigerator characterized by performing in an automatic manner. A refrigerant circulation path including an oil-cooled compressor, an oil separator / collector, a condenser, an expansion valve and an evaporator, and a detection means for judging the magnitude of the cooling heat load, and a signal from the detection means Oil-cooled compression type refrigeration in which normal operation control is performed to keep the rotational speed of the drive unit of the compressor between the lower limit rotational speed and the upper limit rotational speed at a value suitable for the cooling heat load in the evaporator In the operation method of the machine,
The rotational speed of the drive unit is higher than the lower limit rotational speed, and the allowable minimum rotational speed determined in advance by the piping system of the circulation channel and the specifications of the compressor so as not to retain oil in the evaporator. A predetermined allowable upper limit at which the differential pressure between the refrigerant pressure at the outlet of the evaporator and the suction pressure of the oil-cooled compressor is considered to reach the allowable limit of oil retention in the evaporator. When the pressure becomes higher than the pressure, the oil return control is preferentially performed by increasing the rotational speed of the drive unit to the allowable minimum rotational speed and operating until the differential pressure becomes smaller than the allowable upper limit pressure. A method of operating an oil-cooled compression refrigerator.

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