JPH0563703B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a two-stage compression refrigeration system, in particular a control system that utilizes only two sensors, one of which is located in the first stage. Controlling the operation of the compressor device according to the state of the suction side of the compressor device,
Other sensors relate to a two-stage compression refrigeration system that is utilized to control the operation of the second-stage compressor system in response to conditions at an intermediate point between the first-stage compressor system and the second-stage compressor system. It is. An economizer may be utilized in the two-stage compression refrigeration system of the present invention to provide secondary cooling of the condensed refrigerant prior to vaporization in the evaporator.

BACKGROUND OF THE INVENTION Two-stage compression refrigeration systems comprising first and second stage compressors connected in series are well known in the art. The conventional typical two-stage compression refrigeration equipment is shown in Figures 2 and 3 of U.S. Patent No. 2434221 and U.S. Patent No.
As shown in Figure 1 of No.2677844,
They have been constructed with a bypass mechanism that selectively bypasses the first stage compressor (booster) to directly feed the second stage compressor.
Therefore, in this conventional device, the booster is operated only within a range where the evaporation temperature is relatively low.

Although this conventional technique facilitates control of the apparatus, it is disadvantageous in terms of efficiency of the refrigeration apparatus. That is, the capacities of both the first and second stage compressors cannot be controlled in a high evaporation temperature range to achieve maximum system efficiency.

U.S. Patent No. 3759052 describes the following two-stage compression refrigeration system:
The first and second stage compression is performed under control using a controller that operates respectively depending on the combination of the conditions at the intermediate point between the stage and second stage compressors and the conditions at the discharge side of the second stage compressor. A two-stage compression refrigeration system is disclosed in which both parts of the machine are operated at all times. Therefore, in this conventional device, the capacity of the first stage compressor and the capacity of the second stage compressor are
The stage compressor capacity ratio is controlled to maintain maximum efficiency of the refrigeration system.

However, the device disclosed in US Pat. No. 3,759,052 is complex and expensive. That is, this device requires a plurality of sensors placed at three locations in the device and a processor for controlling the second stage compressor. Furthermore, this conventional device is not equipped with an economizer to further improve device efficiency, and an economizer is not installed in the refrigeration device equipped with a closed refrigeration circuit.
There is no teaching as to how the economizer can be provided to operate at all times without causing problems in controlling the capacity of the first and second stage compressors.

Invention Problem Therefore, the main object of the present invention is to provide a two-stage compression refrigeration system having the basic structure disclosed in the above-mentioned US Patent No. 3759052, that is, a first stage compressor system, a second stage compressor system, A condenser, an evaporator, a first-stage compressor device, a second-stage compressor device, a condenser, and an evaporator are connected in series to form a closed circuit in this order to conduct the compressible refrigerant. conduit means,
A two-stage compression refrigeration system comprising a plurality of motors for driving the compressor system described above and a control system for controlling the operation of the compressor system described above, wherein two motors are required to obtain complete system control. To provide a device that is equipped with a control device that utilizes only one sensor, has a simple structure, and is low in cost.

Means for Solving the Problems To this end, the present invention makes it possible to change the capacity of the first stage compressor device, and also makes it possible to change the capacity of the second stage compressor device, while controlling the control device to It was configured like this. That is, the present invention uses the control device to control the operation of the first stage compressor device according to the state of the suction side of the first stage compressor device, and to control the operation of the first stage compressor device and the second stage compressor device. The capacity of the second stage compressor device is controlled according to the state of the intermediate point with respect to the compressor device so as to maintain the state of the intermediate point within a predetermined range.

The two-stage compression refrigeration system according to the present invention is further provided between the above-described condenser and evaporator, and expands a portion of the condensed refrigerant flowing out from the condenser to convert the refrigerant flowing into the evaporator into secondary and supply means for supplying the expanded portion of the refrigerant into the conduit means at the intermediate point.

The second-stage compressor device provided in the apparatus of the present invention includes two or more fixed-capacity compressors connected in parallel, as in the embodiments described later, at least one of which is connected to the second-stage compressor. A compressor system configured to be selectively disconnected from a closed circuit so as to change the capacity of the second stage compressor system in stages without interrupting the operation of the second stage compressor system. be able to. Also, instead of the plurality of fixed displacement compressors mentioned above, the above-mentioned U.S. Patent No.
3759052, the compressor system may be configured with a single compressor of variable capacity type, whereby the capacity of the second stage compressor system can be changed continuously. can. In special cases, the second stage compressor arrangement can also include one or more fixed displacement compressors and one variable displacement compressor.

In the two-stage compression refrigeration apparatus according to this invention, R
Compressible refrigerants such as -502 are always passed through a closed circuit where the refrigerant is first compressed to an intermediate pressure by a first stage or low pressure stage compressor arrangement and then brought to a final pressure by a second stage or high pressure stage compressor. It is circulated so that it is compressed to the maximum. The compressed refrigerant is condensed to a liquid phase in a condenser and then evaporated in an evaporator to provide the required cooling function. The evaporated refrigerant is returned from the evaporator to the suction side of the first stage compressor unit or booster, completing the circulation in the closed circuit. During this operation, the capacity of each of the first and second stage compressor units is controlled to maintain maximum efficiency of the refrigeration unit under the control of a controller that utilizes only two sensors (transducers). be done.

In the structure in which an economizer is provided as described above, the economizer expands a portion of the refrigerant after condensation so as to secondarily cool the remaining portion of the condensed refrigerant that will flow into the evaporator. Therefore, the condensed refrigerant that is then evaporated to provide a cooling function in the evaporator always receives additional cooling in order to provide a high cooling function in the evaporator. 1st stage and 2nd stage
The load on the stage compressor device is reduced. The load on the first stage compressor arrangement is further reduced since a portion of the refrigerant will be supplied to the second stage compressor arrangement without passing through the first stage compressor arrangement. Economizers therefore improve the efficiency of refrigeration equipment.

The portion of the refrigerant expanded in the economizer for secondary cooling of the other or main portion of the condensed refrigerant is in a relatively high pressure vapor state and is therefore compressed in the first stage compressor arrangement. It can be compressed together with the gaseous refrigerant exiting the device. From now on, the present invention provides for returning the above-mentioned portion of the refrigerant to an intermediate point between the first stage compressor system and the second stage compressor system. Since the control device controls the operation of the second stage compressor device according to the state at the intermediate point, it is necessary to return the steam from the economizer to the suction side of the second stage compressor device in a closed circuit. Nevertheless, no interference with the control of multiple compressors occurs.

Any or all of the compressors described above may be a reciprocating compressor, a screw rotary compressor, a vane rotary compressor, or a scroll compressor. The motor for driving the first-stage low-pressure compressor can be configured with an induction motor using an inverter transmission mechanism whose frequency is changed between 20 and 100 hertz (Hz).

Embodiment FIG. 1 shows a multi-stage refrigeration system according to an embodiment of the present invention, with its entire closed circuit indicated by reference numeral 10. This device includes a low-pressure first-stage compressor (booster) 12, a pair of high-pressure second-stage compressors 14, 16,
Air-cooled condenser 18, liquid receiver 20, economizer 2
2 and one or more evaporators 24, which are the basic elements of the closed circuit 10.
The conduit arrangement connects these elements in parallel in a series-connected closed circuit for the two high-pressure stage compressors 14, 16, forming a group, and then in series with each other. A conduit 26 carrying a suitable refrigerant, such as R-502, splits at point 27 into two parallel conduits 28 and 30 to transfer the intermediate pressure discharge stream of the low pressure first stage compressor 12 to the second stage compressor 14. , 16 to the suction side or inlet. The discharge flows of the second stage compressors 14 and 16 pass through conduits 32 and 34 and join at a connection point 33;
From there, high pressure compressed refrigerant gas is supplied by conduit 36 to the inlet of air-cooled condenser 18. From the outlet of the air-cooled condenser 18, condensed refrigerant flows through a conduit 38 to the liquid receiver 20. The refrigerant R in liquid form as shown in the liquid receiver 20 is
It flows via conduit 40 to economizer 22 . At point 41, a portion of the liquid refrigerant R is withdrawn from the main closed circuit by a branch pipe or relief pipe 42, expands through an expansion valve 44, is deposited in the economizer 22, and is passed through a conduit 46 to the evaporator 24. It acts to secondarily cool the main part of the liquid refrigerant to be introduced. The cooled liquid refrigerant expands by passing through the expansion valve 48 and performs the cooling mechanism of the refrigeration system within the evaporator 24. Return refrigerant gas from the evaporator 24 flows via conduit 50 to the suction or low pressure side of the booster or first stage compressor 12, completing the circulation within the closed circuit.

The refrigerant taken out through the conduit 42 which is vaporized into the economizer 22 and performs the above-mentioned secondary cooling effect is transferred through the conduit 52 to the intermediate pressure point 5 of the closed circuit.
4, that is, the outlet of the first stage compressor 12 is
It is directed to a point of communication 54 to said conduit 26 which connects to the inlet of one or both of the stage compressors 14, 16. Only 2 high pressure 2nd stage compressors 1
Although 4 and 16 are shown, it should be noted that three or more high pressure stage compressors may be provided, connected in parallel and conveniently controlled. In the illustrated device, two high-pressure stage compressors are intentionally installed.
is limited to.

The illustrated refrigeration system uses the economizer path constantly, i.e., the low pressure first stage compressor 12 is always running, but the economizer 22 is also always active, so that one or more evaporators can be removed under full load conditions. High efficiency refrigeration is made possible by utilizing the container 24. The use of two high pressure stage compressors 14, 16 is expedient to avoid uncontrollable intermediate pressure fluctuations. Also, the second stage compressor system, including the high pressure stage compressors 14, 16, which may be reciprocating compressors of the low capacity type, is not deactivated and therefore always operates at its maximum efficiency. Low pressure 1st
The stage compressor 12 may be a variable speed screw compressor, a variable speed slide vane type compressor, etc.
In the illustrated case, it is a variable speed reciprocating compressor. It is also possible to use variable speed turbo compressors (centrifugal compressors).

The goal of this system is to obtain as high efficiency as possible, and the system basically combines a low pressure compressor 12 operating under variable speed with two or more fixed capacity high pressure stage compressors. The combination is used to maintain the intermediate pressure at a suitable value.

In the illustrated device, the first motor 56 is driven to the low-pressure first stage compressor 12 while changing the speed of the compressor 12 as shown by a broken line 58, and the refrigerant R passing through the compressor 12 is controlled from 5 to 5. 1 or a wider range. On the other hand, the second stage compressor 16 is operated by the second motor 7
2, and the other second stage compressor 14 is directly driven by a third motor 74.

The control device is essentially simple and stable. The illustrated control device utilizes a control panel 62 connected to a power source S by leads 76. Power is then supplied from the control panel 62 to the motor 56 via the power supply line 60. This device utilizes two transducers. The first transducer 64 is a pressure transducer as shown in the figure, and is designed to sense the suction pressure of the low-pressure first stage compressor 12. It is arranged in said conduit 50 which supplies refrigerant to the side. Instead of sensing the suction pressure of the first-stage compressor 12, the first transducer 64 can also sense the evaporation pressure or evaporation temperature in the evaporator 24. The signal from the first transducer 64 is on line 6
6 to the control panel 62. A second transducer 73 senses the intermediate pressure and is located in said conduit 26 for supplying the discharge flow from the first stage compressor 12 to the inlet side of the second stage compressors 14, 16 in the case shown. has been done. This pressure transducer 7
3 supplies a signal to the control panel 62 through a line 75. In addition to the aforementioned line 60, which is derived from the control panel 62 and serves to vary the speed of the motor 56 which directly drives the low pressure compressor 12, a number of other lines are derived from the control panel 62 and which operate the system. Connected to various components. Among these lines, a control line 70 is provided in the conduit 28 that connects the control panel 62 to the following solenoid valve 68, that is, the inlet of the second stage compressor 14, and is provided under specific conditions described below. It is connected below to a solenoid valve 68 , which functions to isolate the second stage compressor 14 from the closed circuit 10 . A control line 76 is led from the control board 62 and supplies current to the motor 72 which directly drives the second stage compressor 16. A control line 78 is led from the control panel 62 to the motor 7 which directly drives the second stage compressor 14.
Connected to 4.

During operation, as the refrigerant demand for the evaporator 24 decreases, the suction pressure on the inlet side of the low pressure compressor 12 decreases, and the transducer 64 provides a control signal to the control panel 62 via line 66 to increase the suction pressure. signal the decline of In response, the control panel 62 changes the current flowing to the motor 56 to reduce the driving rotation speed of the low pressure compressor 12, thereby reducing the flow rate of refrigerant flowing through the first stage compressor 12. Motor 56 may be an induction motor using a variable speed inverter mechanism, in which case control panel 62 would change the frequency of the current supplied to motor 56 via line 60. For a variable flow range of 5 to 1 for the low pressure compressor 12, the frequency of the control signal applied to the induction motor can be varied in the range of 20-100 Hertz (Hz).

When the intermediate pressure reaches the predetermined minimum value, one of the two second stage compressors 14, 16 is closed and the intermediate pressure is automatically increased to the remaining high pressure stage or Increase the load on the two-stage compressor. In the illustrated system, a second intermediate pressure transducer 73 provides a signal via line 75 to control board 62 indicating the pressure drop in the intermediate stage. Control board 62 then stops driving motor 74 via line 78 to stop compressor 14. At the same time, if necessary, the position of solenoid valve 68 is changed via line 70 so that refrigerant flow directed through conduit 28 to second stage compressor 14 is interrupted.

FIG. 2 illustrates the operation of the system by graphing system load/capacity versus intermediate pressure (psig). The relationship line P shown by two solid lines and
P' represents the variation of the intermediate pressure depending on whether one or both of the high-pressure stage compressors 14, 16 are activated. The relationship line P shows the variation in intermediate pressure when only one high-pressure second stage compressor is operated, and the relationship line P' shows the variation in intermediate pressure in the higher range of equipment load/capacity of 40-100%. It shows. For example, if the device is operating at a low load with only one second stage compressor, that is, the second stage compressor 16, and if the low pressure first stage compressor 12 is running all the time, then Considering that the economizer 22 is always active, when the intermediate pressure reaches a high point on the relationship line P, for example, the preset point B of 60 psig on the relationship line P, another Relationship line when two high pressure second stage compressors 14 are operated, and the intermediate pressure is generated by two high pressure second stage compressors 14 and 16.
It drops to a lower value, point B' on P', about 26 psig. As will be appreciated, the intermediate pressure at which the high-pressure stage compressor 14 will restart due to the increasing load will be at point A on the relationship line P' at which the compressor 14 will be shut off. (re-equilibration intermediate pressure), which in the case shown is approximately 20 psig.

The relationship lines shown are for an efficient and reliable supermarket refrigeration system with one or more evaporators 24, and the refrigerant is R-502 and the system is -20〓( It should be noted that this forms the basis for a comprehensive control logic diagram for the case with an evaporation temperature of -29°C). According to the illustrated device, excessive operation of the high-pressure stage compressors 14 and 16 can be avoided, and the economizer 22 can operate at all times without significantly reducing device efficiency. If the intermediate pressure is along the relation line P′
When the pressure drops to 20 psig and reaches point A, the other high pressure stage compressors 14 are shut off while the high pressure stage compressor 16 continues to operate, and the intermediate pressure immediately rises to about 46 psig under the same load. As the base load continues to decrease, a single high-pressure stage compressor 16 continues operation of the system and a low-pressure stage compressor 12 continues to operate in line 60.
The operating speed is reduced by control of the motor 56 by the control panel 62 via the control panel 62. If the load increases after the system has transitioned to an operating condition in which only a single high pressure stage compressor 16 is operated, the speed of the motor 56 is correspondingly increased as previously described.
The flow rate of the refrigerant flowing through the stage compressor 12 is at a level where the intermediate pressure is 60 psig (point B on the relationship line P)
, at which point one other high-pressure stage compressor 14 is in the closed circuit,
6 is incorporated to flow the refrigerant in parallel with the refrigerant flowing through the refrigerant.

During operation of the illustrated system, the suction pressure transducer 64 reduces the operating speed of the low pressure compressor 12 as the system load decreases. Intermediate pressure point A (on relationship line P')
When this is reached, one second stage compressor 14 is shut off and the intermediate pressure is rebalanced (point A' on the relationship line P). When the load increases, the speed of the low pressure compressor 12 is increased, and then the second stage compressor 14 is also activated (point B on the relationship line P).

As can now be seen, only two basic transducers are required to achieve the desired operational control. That is, one transducer is used to measure the suction pressure or a measured factor equivalent to it, and the other transducer is used to measure the intermediate pressure of the refrigerant circulating in the closed circuit.
each is required. The control logic is straightforward and the control panel can be easily installed to control the operation of the device based on the factors mentioned above. It is believed that the refrigeration system is ideal for both commercial refrigeration purposes as well as air conditioning (heating and cooling) purposes in commercial and other buildings. The device shown has only three compressors, namely one low pressure compressor (booster).
and two high-pressure stage compressors. This equipment has a suitable duplication capacity, that is, as can be understood from the graph in Figure 2, it is possible to handle approximately 50% of the maximum equipment load only with the high-pressure stage compressor without a low-pressure compressor, or with one low-pressure compressor. It has the ability to handle approximately 50% of the maximum equipment load even with one high-pressure stage compressor.
The horsepower consumed by the low pressure compressor (booster) can be made low enough in combination with an inverter or brushless DC motor to provide the necessary speed changes to control the operation of the device.

Effects of the Invention This invention controls the operation of the first and second stage compressor systems by determining the state of the suction side of the first stage compressor system and between the first and second stage compressor systems. Using a control device that controls the operation of each compressor device according to the state of the intermediate point, and controlling to maintain the state of the intermediate point within a predetermined range so as to achieve high efficiency operation of the refrigeration equipment. Since we decided to obtain this by controlling the capacity of the second stage compressor device according to the state of the intermediate point, we decided that two sensors (transducers) would be sufficient and we did not need a complicated arithmetic processor. By eliminating the need to use the two-stage compression refrigeration system, the structure of the two-stage compression refrigeration system is simplified and the cost is reduced.

Further, according to the present invention, since the operation of the second stage compressor device is controlled according to the state at an intermediate point between the first stage and second stage compressor devices, the condensed refrigerant supplied to the evaporator is controlled. The economizer is used for secondary cooling to further improve the efficiency of the refrigeration system, and a portion of the refrigerant expanded in the economizer is returned to the closed refrigeration circuit at the intermediate point without interference with compressor control. In this way, it can be installed in a refrigeration system.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram illustrating a preferred embodiment of the present invention, showing a refrigeration system with a circuit diagram of its closed circuit, and FIG. FIG. 1 is a graph showing the relationship between . 10...Closed circuit, 12...First stage compressor, 1
4, 16...Second stage compressor, 18...Condenser, 2
0...Liquid receiver, 22...Economizer, 24...
Evaporator, 26... Conduit, 28, 30... Conduit, 3
2, 34... conduit, 36... conduit, 38... conduit, 40... conduit, 42... escape pipe, 44...
Expansion valve, 46... Conduit, 48... Expansion valve, 50...
... Conduit, 52 ... Conduit, 54 ... Intermediate (pressure)
Point, 56... Motor, 62... Control panel, 64...
First transducer, 68... Solenoid valve, 72
... motor, 73 ... second transducer,
74...Motor.

Claims (1)

[Claims] 1. A first-stage compressor device, a second-stage compressor device, a condenser, an evaporator, and the above-described first-stage compressor device, second-stage compressor device, and condenser. a conduit means for conducting compressible refrigerant by connecting the evaporator in series to form a closed circuit in this order; a plurality of motors for driving the compressor device described above; and the compressor described above. A two-stage compression refrigeration system comprising: a control device for controlling the operation of the system; and a capacity of the first-stage compressor device is changeable; a capacity of the second-stage compressor device is changeable; The control device controls the operation of the first stage compressor device according to the state of the suction side of the first stage compressor device, and controls the operation of the first stage compressor device and the second stage compressor device.
The second stage compressor device is characterized in that the capacity of the second stage compressor device is controlled according to the state of the intermediate point between the second stage compressor device and the second stage compressor device so as to maintain the state of the intermediate point within a predetermined range. Two-stage compression refrigeration equipment. 2. A two-stage compression refrigeration system according to claim 1, which is inserted between the aforementioned condenser and evaporator, and expands and evaporates a portion of the condensed refrigerant flowing out from the condenser. A two-stage compression refrigeration system, comprising: an economizer for secondary cooling of refrigerant flowing into the container; and supply means for supplying a portion of the expanded refrigerant into the conduit means at the intermediate point. 3. The two-stage compression refrigeration system according to claim 1 or 2, wherein the first sensor detects the state of the suction side of the first stage compressor system and the state of the intermediate point. and a second sensor for sensing. 4. The two-stage compression refrigeration system according to claim 3, wherein the second sensor is configured to sense an intermediate pressure of the refrigerant. 5. The two-stage compression refrigeration system according to claim 4, wherein the control device first changes the capacity of the first-stage compressor device, and then changes the capacity of the second-stage compressor device. , a two-stage compression refrigeration system configured to change the intermediate pressure to maintain it within a predetermined range. 6. The two-stage compression refrigeration system according to claim 3, wherein the control device controls the capacity of the first-stage compressor device according to the state on the suction side of the first-stage compressor device. and the second point depending on the state of the intermediate point.
A two-stage compression refrigeration system configured to control the capacity of a stage compressor system. 7. A two-stage compression refrigeration device according to any one of claims 1 to 6, wherein the second-stage compressor device includes a plurality of compressors. Refrigeration equipment. 8. A two-stage compression refrigeration system according to any one of claims 1 to 6, wherein the second stage compressor system includes at least two fixed capacity compressors. Two-stage compression refrigeration equipment. 9. The two-stage compression refrigeration system according to claim 8, wherein the control device is connected to at least one of the fixed capacity compressors from the first stage compressor device. A two-stage compression refrigeration system configured to selectively shut off refrigerant flow to. 10 The two-stage compression refrigeration system according to claim 8, wherein the control device selects a motor for driving at least one of the fixed capacity compressors described above. A two-stage compression refrigeration system equipped with means for stopping the system automatically. 11. A two-stage compression refrigeration system according to claim 8, in which the constant capacity compressors described above are connected in parallel. 12. A two-stage compression refrigeration apparatus according to any one of claims 1 to 11, comprising:
A two-stage compression refrigeration system, wherein the motor for the first stage compressor system is a variable speed motor.