JP2007138919A - Two-stage screw compressor and two-stage compression refrigerator using this compressor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To perform efficient operation by reducing a burden of one-stage side and two-stage side compressors in response to a change in the evaporation temperature. <P>SOLUTION: This two-stage screw compressor has a stroke volume ratio adjusting means 28 for adjusting the stroke volume ratio of the one-stage side compressor 1 and the two-stage side compressor 10 by changing at least any stroke volume of the one-stage side compressor 7 and the two-stage side compressor 10 by a capacity variable means 18 in response to a change in suction pressure and a capacity adjusting means 28 for adjusting capacity by changing a rotating speed of a motor 12 by a rotation control means 26. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a two-stage screw compressor and a two-stage compression refrigerator using the same.

  In a two-stage compression refrigerator having a two-stage screw compressor, a condenser, an expansion valve, and an evaporator in the refrigerant circulation channel, the refrigerant evaporating temperature (ET) in the evaporator is a wide temperature range from -30 ° to -60 °. It is required to deal with the range and to deal with this with the same refrigerator.

  Conventionally, in a two-stage screw compressor as described in Patent Document 1, a capacity control mechanism including a slide valve is provided in a first-stage compressor, and partial load operation is performed by unloading the slide valve. Further, in the two-stage screw compressor described in Patent Document 2, partial load operation is performed by controlling the rotation speed of the drive motor that rotates the first-stage compressor and the second-stage compressor. Furthermore, in the refrigeration cycle apparatus of Patent Document 3, the rotation speeds of the low-stage compressor and the high-stage compressor are made variable independently, and each rotation speed is increased or decreased according to the load. However, such partial load operation alone cannot sufficiently cope with a wide temperature range of the refrigerant evaporation temperature (ET) of −30 ° to −60 °.

  In general, the ideal operation of the two-stage compressor is when the compression ratio of the first-stage compressor is equal to the compression ratio of the second-stage compressor. When the suction pressure is Ps, the intermediate pressure is Pm, and the discharge pressure is Pd, the first-stage compression ratio r1 = Pm / Ps, and the second-stage compression ratio r2 = Pd / Pm. When the stage side compression ratios r2 are equal (r1 = r2), Pm = √ (Ps · Pd) from Pm / Ps = Pd / Pm.

  The suction pressure Ps (ata) when the discharge pressure Pd is 15.64 ata and the evaporation temperature ET (° C) is −30, −40, −50, −60, respectively, is 1.67, 1.07,. 658, 0.382, the intermediate pressure Pm (ata) is 5.11, 4.09, 3.21, 2.44 from Pm = √ (Ps · Pd). As shown in FIG. From FIG. 3, when the discharge pressure and the suction pressure of the two-stage screw compressor are determined, an ideal intermediate pressure when the compression ratio of the first-stage compressor and the compression ratio of the two-stage compressor are equal is determined. I understand that.

  However, in practice, the intermediate pressure is determined by the stroke volume ratio R (= V1 / V2), which is the stroke volume ratio between the first-stage compressor and the second-stage compressor. The stroke volume means a volume compressed per unit time in the compressor. If the specific volume of the compression medium corresponding to the suction pressure Ps is v1, and the specific volume of the compression medium corresponding to the intermediate pressure Pm is v2, v1 / v2 = V1 / V2 = R, so v2 = v1 × (1 / From R), v2 is obtained, and the intermediate pressure Pm is obtained from the pressure corresponding to v2. The specific volume refers to the volume per unit weight of the object. Further, the “pressure corresponding to v2” here is obtained by using a Mollier diagram (Ph diagram) well known in the field of refrigerators. For example, when the evaporation temperature ET (° C.) is −30, −40, −50, −60, v1 changes to 0.135, 0.205, 0.323, and 0.536. Using this v1 and the stroke volume ratio R = 3, the intermediate pressure Pm is obtained, plotted in the figure, and shown together with the ideal intermediate pressure, as shown in FIG. From FIG. 4, when the evaporation temperature is −40 ° C., the intermediate pressure is ideally the same as the ideal intermediate pressure. However, when the evaporation temperature is −30 to −40 ° C., the intermediate pressure is higher than the ideal intermediate pressure. It can be seen that the burden on the stage side compressor is large, and when the evaporation temperature reaches −40 to −60 ° C., the intermediate pressure becomes lower than the ideal intermediate pressure and the burden on the two stage side compressor increases.

Thus, the conventional two-stage screw compressor has a constant stroke volume ratio between the first-stage compressor and the second-stage compressor over an evaporation temperature (ET) of −30 ° to −60 °. For this reason, when the design point is determined to be the optimum evaporation temperature, it becomes an ideal intermediate pressure at that point, but at other evaporation temperatures, one of the compressors is overloaded and the efficiency of the compressor deteriorates. It will be.
Japanese Patent Laid-Open No. 11-117879 JP 2003-21089 A JP 2004-278824 A

  The present invention has been made in view of the above-described conventional problems, and adjusts the stroke volume ratio between the first stage and the second stage so that the intermediate pressure is an ideal value, and responds to changes in the evaporation temperature. It is an object of the present invention to provide a two-stage screw compressor capable of reducing the burden on the first-stage and second-stage compressors and performing an efficient operation, and a two-stage compression refrigerator using the same.

  In FIG. 4, in order to bring the intermediate pressure indicated by the two-dot chain line closer to the ideal intermediate pressure indicated by the solid line, in the region where the evaporation temperature is −30 ° C., the specific volume v1 is 0.135. The stroke volume ratio is lowered to R = 0.135 / 0.053 = 2.55 so that v2 becomes a specific volume of 0.053 corresponding to an ideal intermediate pressure of 5.11 ata, that is, one-stage compression The stroke volume ratio of the machine may be 2.55 / 3.0 = 0.85 (15% reduction). The resulting reduction in compression capacity is addressed by increasing the screw compressor speed. On the other hand, in the region where the evaporation temperature is −60 ° C., the reverse operation is performed. Thereby, the intermediate pressure can be brought close to the ideal intermediate pressure. The present invention has been made based on such knowledge.

That is, the present invention includes a first-stage compressor and a second-stage compressor disposed in a compressor body, a single motor that drives the first-stage compressor and the second-stage compressor, and the first-stage compressor. A two-stage screw compressor comprising a capacity variable means for making variable the stroke volume of at least one of the side compressor and the two-stage side compressor, and a rotation control means for controlling the rotational speed of the motor;
The stroke volume ratio of the first-stage compressor and the second-stage compressor is changed by changing the stroke volume of at least one of the first-stage compressor and the second-stage compressor by the capacity varying means according to the change of the suction pressure. Stroke volume ratio adjusting means for adjusting
And a capacity adjusting means for adjusting the capacity by changing the number of rotations of the motor by the rotation control means.

  In the present invention, when the stroke volume ratio of the first-stage compressor and the second-stage compressor is changed by the stroke volume ratio adjusting means, the intermediate pressure changes. Therefore, the intermediate pressure is ideal for a wide range of evaporation temperatures. Can approach the theoretical intermediate pressure.

  The stroke volume ratio adjusting means calculates the theoretical intermediate pressure Pmth by √ (Ps · Pd) based on the measured suction pressure Ps and discharge pressure Pd, and the difference between the measured intermediate pressure Pm and the theoretical intermediate pressure Pmth is zero. It is preferable to change the stroke volume by the capacity varying means.

  When the detected evaporation temperature is higher than the target temperature, the capacity adjusting means increases the rotational speed of the motor by the rotation control means, and when the detected evaporation temperature is lower than the target temperature, the rotation control means It is preferable to reduce the rotational speed of the motor.

  The capacity variable means may be a piston valve or a slide valve. The capacity variable means may be provided in at least one of the first-stage compressor and the second-stage compressor, but is preferably provided in the first-stage compressor. The rotation control means can be an inverter.

  In a two-stage compression refrigerator having a two-stage screw compressor, a condenser, an expansion valve, and an evaporator in the refrigerant circulation channel, the two-stage screw compressor of the present invention can be used as the two-stage screw compressor. .

  According to the present invention, the stroke volume of at least one of the first-stage compressor and the second-stage compressor is changed by the capacity varying means according to the change in the suction pressure, and the first-stage compressor and the second-stage compressor are changed. The stroke volume ratio adjusting means for adjusting the stroke volume ratio and the capacity adjusting means for adjusting the capacity by changing the number of rotations of the motor by the rotation control means are provided. The ideal theoretical intermediate pressure can be approached, and the efficiency of the compressor can be greatly improved. In particular, even when the intermediate pressure has increased in the past from −20 to −30 ° C. and cannot be operated, the operation can be performed by adjusting the stroke volume and lowering the intermediate pressure by the stroke volume ratio adjusting means. be able to.

  Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings.

  FIG. 1 shows a cycle of a two-stage compression refrigerator using a two-stage screw compressor 1 according to the present invention. In this refrigeration cycle, a two-stage screw compressor 1, an oil separator 2, a condenser 3, an expansion valve 4 and an evaporator 5 are connected by a refrigerant circulation channel 6.

  The main body of the two-stage screw compressor 1 includes a first-stage compressor casing 8 that houses a first-stage compressor 7 composed of a pair of male and female screw rotors that mesh with each other, and a male rotor of the first-stage compressor 7. A two-stage compressor casing 11 containing a two-stage compressor 10 having a common drive shaft 9 and a pair of male and female screw rotors engaged with each other, the first-stage compressor 7 and the second-stage side The motor casing 13 accommodates a single motor 12 that drives the drive shaft 9 of the compressor 10.

  The first-stage compressor casing 8 is provided with a suction port 14 communicating with the suction side of the first-stage compressor 7, and a filter 15 is provided on the upstream side of the suction port 14. The discharge side of the first-stage compressor 7 communicates with the suction side of the second-stage compressor 10 through the space in the casing. The two-stage compressor casing 11 is provided with a discharge port 16 communicating with the discharge side of the two-stage compressor 10.

  As shown in FIG. 2, a cylinder 17 is formed in the first-stage compressor casing 8 in parallel with the drive shaft 9 of the first-stage compressor 7, and a piston valve 18 is slidably accommodated in the cylinder 17. ing. The piston valve 18 separates the cylinder 17 into a gas space 19 located on the suction side of the first-stage compressor 7 and a hydraulic space 20 located on the discharge side of the first-stage compressor 7. The piston valve 18 has one end of a coil spring 22 inserted into a hole 21 formed in the axial direction from the gas space 19 side of the cylinder 17, and the other end of the coil spring 22 abuts against the end wall of the cylinder 17. The discharge side of the first stage compressor 7 is urged. The coil spring 22 is guided by a guide bar 23 located inside thereof. The gas space 19 of the cylinder 17 communicates with the suction side of the first-stage compressor 7 and closes the first-stage compressor 7 through a plurality of openings 24 formed in the first-stage compressor casing 8. It is designed to communicate with the space. Hydraulic pressure is supplied to the hydraulic space 20 of the cylinder 17 in order to move the piston valve 18 toward the gas space 19 against the urging force of the coil spring 22.

  Returning to FIG. 1, the motor 12 of the two-stage compressor 10 is supplied with electric power from the power source 25 via the inverter 26, and the rotational speed is controlled. The inverter 26 constitutes rotation control means. Further, the hydraulic pressure is supplied to the hydraulic space 20 of the piston valve 18 by the hydraulic device 27, and the piston valve 18 closes all the openings 24 by adjusting the supply amount of the hydraulic pressure to the hydraulic space 20. Then, an unloaded state in which at least one opening 24 is opened can be achieved. The piston valve 18 constitutes a capacity control means. The inverter 26 and the hydraulic device 27 are controlled by a controller 28. A suction pressure Ps, an intermediate pressure Pm, and a discharge pressure Pd measured with a pressure gauge can be input to the controller 28. The pressure gauge is a flow path communicating with the suction side of the first-stage compressor 7, a space in the casing between the discharge side of the first-stage compressor 7 and the suction side of the second-stage compressor 10, the second stage side Each is attached to a flow path communicating with the discharge side of the compressor 10. Further, the evaporation temperature detected by the temperature sensor 29 provided in the evaporator 5 is input to the controller 28 via the temperature controller 30. The controller 28 constitutes a stroke volume ratio adjusting means and a capacity adjusting means of the present invention.

  Next, the operation of the two-stage compression refrigerator having the above configuration will be described.

  When the suction pressure Ps, discharge pressure Pd, and intermediate pressure Pm measured by the two-stage screw compressor 1 are input to the controller 28 in the operating state, the controller 28 calculates the theoretical intermediate pressure Pmth = √ (Ps · Pd). The piston valve 18 is moved so that the difference between the measured intermediate pressure Pm and the theoretical intermediate pressure Pmth becomes zero.

  For example, it is assumed that the stroke volume ratio R (= V1 / V2) between the stroke volume V1 of the first stage compressor 7 and the stroke volume V2 of the second stage compressor 10 is designed to be R = 3. In this case, if the first-stage compressor 7 is fully loaded and the stroke volume ratio between the first-stage compressor 7 and the second-stage compressor 10 remains R = 3, the intermediate pressure Pm is as shown in FIG. As shown, it is predicted to be 6.3 data that exceeds the theoretical intermediate pressure Pmth. Here, when the piston valve 18 is moved and the first stage compressor 7 is unloaded by 15%, the stroke volume of the first stage compressor 7 becomes 85%, and the stroke volume ratio R is R = 3 × 0. As a result of 85 = 2.55, the intermediate pressure Pm decreases and can approach the theoretical intermediate pressure Pmth. In this way, the intermediate pressure can be brought close to the ideal theoretical intermediate pressure Pmth for a wide range of evaporation temperatures, and the efficiency of the compressor can be greatly improved.

  As described above, when this two-stage compression refrigerator is designed so that the stroke volume ratio R (= V1 / V2) is R = 3 and the discharge pressure Pd is 15.64 ata, as can be understood from FIG. If the evaporation temperature ET (° C.) is −40 ° C. or higher, and the suction pressure Ps is 1.07 at or higher, the piston valve 18 is moved to unload the first stage compressor 7 by a predetermined ratio. The intermediate pressure Pm can be reduced to approach the theoretical intermediate pressure Pmth. Further, a theoretical intermediate pressure Pmth = √ (Ps · Pd) is calculated based on the measured suction pressure Ps and discharge pressure Pd, and the difference is exactly zero based on the theoretical intermediate pressure Pmth and the measured intermediate pressure Pm. As described above, the moving position of the piston valve 18 and thus the unloading ratio of the first stage compressor 7 may be calculated by PID calculation, and the piston valve 18 may be moved. Alternatively, the discharge pressure Pd may be regarded as a predetermined constant value such as 15.64 data and the measurement of the discharge pressure Pd may be omitted.

  On the other hand, the evaporation temperature detected by the temperature sensor 29 in the evaporator 5 is input to the temperature controller 30. The temperature controller 30 compares the detected evaporation temperature with the target temperature. 28 is requested to increase the speed. Thereby, the controller 28 increases the rotation speed of the motor 12 via the inverter 26. As a result, the stroke volumes of the first-stage compressor 7 and the second-stage compressor 10 simultaneously increase, and the capacity and thus the refrigerating capacity can be increased while maintaining the stroke volume ratio R in an ideal state. On the contrary, when the temperature is lower than the target temperature, the number of rotations of the motor 12 is decreased to prevent loss such as excessive cooling.

  In the two-stage compression refrigerator having the above-described configuration, the evaporation temperature ET (° C.) is equal to or higher than a predetermined temperature (specifically −40 ° C.), and the suction pressure Ps is equal to or higher than a predetermined pressure (specifically 1.07 ata). In this case, the intermediate pressure Pm can be brought close to the theoretical intermediate pressure Pmth, but it is desirable to obtain the same effect in other cases. For this purpose, in addition to the above-described configuration, a cylinder is formed in the two-stage compressor casing 11 in parallel with the drive shaft 9 of the second-stage compressor 10 (common to the drive shaft 9 of the first-stage compressor 7). It is desirable that a piston valve other than the piston valve 18 is slidably accommodated. With the two-stage compression refrigerator according to this configuration, not only the stroke volume of the first-stage compressor 7 but also the stroke volume of the two-stage compressor 10 can be changed. In the case of the two-stage compression refrigerator according to this configuration, when the suction pressure Ps is lower than −40 ° C. and thus the suction pressure Ps is lower than 1.07 ata, the piston valve on the second-stage compressor 10 side is moved to 2 By unloading the stage side compressor 10 by a predetermined ratio, the intermediate pressure Pm can be increased and brought close to the theoretical intermediate pressure Pmth.

  In the above embodiment, the piston valve 18 is used as the capacity varying means, but a slide valve may be used. Further, the piston valve 18 and the slide valve may be provided not only in the first stage compressor 7 but also in the second stage compressor 10, or as described above, the first stage compressor 7 and the second stage compressor 10 are provided. You may provide in both.

The figure which shows the two-stage compression refrigerator cycle provided with the two-stage screw compressor concerning this invention. The expanded sectional view of the piston valve of the two-stage screw compressor of FIG. The graph which shows the change of the suction pressure of the two-stage screw compressor with respect to the change of evaporation temperature, intermediate pressure, and discharge pressure. The graph which shows the change of the intermediate pressure when the ideal intermediate pressure and stroke volume ratio of a two-stage screw compressor are constant with respect to the change of evaporation temperature.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 2 stage screw compressor 3 Condenser 4 Expansion valve 5 Evaporator 6 Refrigerant trunk flow path 7 1st stage side compressor 10 2nd stage side compressor 12 Motor 18 Piston valve 26 Inverter 28 Controller

Claims (7)

A first-stage compressor and a second-stage compressor disposed in the compressor body, a single motor for driving the first-stage compressor and the second-stage compressor, the first-stage compressor and the second-stage compressor In a two-stage screw compressor comprising a capacity variable means for changing the stroke volume of at least one of the side compressors, and a rotation control means for controlling the rotation speed of the motor,
The stroke volume ratio of the first-stage compressor and the second-stage compressor is changed by changing the stroke volume of at least one of the first-stage compressor and the second-stage compressor by the capacity varying means according to the change of the suction pressure. Stroke volume ratio adjusting means for adjusting
A two-stage screw compressor comprising: capacity adjusting means for adjusting the capacity by changing the rotation speed of the motor by the rotation control means.   The stroke volume ratio adjusting means calculates the theoretical intermediate pressure Pmth by √ (Ps · Pd) based on the measured suction pressure Ps and discharge pressure Pd, and the difference between the measured intermediate pressure Pm and the theoretical intermediate pressure Pmth is zero. The two-stage screw compressor according to claim 1, wherein a stroke volume is changed by the capacity varying means.   When the detected evaporation temperature is higher than the target temperature, the capacity adjusting means increases the rotational speed of the motor by the rotation control means, and when the detected evaporation temperature is lower than the target temperature, the rotation control means The two-stage screw compressor according to claim 1 or 2, wherein the number of rotations of the motor is reduced.   The two-stage screw compressor according to any one of claims 1 to 3, wherein the capacity changing means is a piston valve.   The two-stage screw compressor according to any one of claims 1 to 3, wherein the capacity varying means is a slide valve.   6. The two-stage screw compressor according to claim 1, wherein the rotation control means is an inverter.   6. A two-stage compression refrigerator having a two-stage screw compressor, a condenser, an expansion valve, and an evaporator in a refrigerant circulation flow path, wherein the two-stage screw compressor has the two-stage according to any one of claims 1 to 5. A two-stage compression refrigerator using a screw compressor.

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