JPH08121882A - Refrigerating machine - Google Patents

Abstract

PURPOSE: To maintain the suction pressure of refrigerant gas at a predetermined target pressure by applying a negative feedback to a cooling capacity control signal with the deviation of the suction pressure of the gas from the target pressure set by a target pressure setter as a reference, and stepwisely correcting the control signal by a real time process. CONSTITUTION: A predetermined target pressure is first set by the operating unit of a target pressure setter 8, and immediately transferred to a control unit 7. The suction pressure of refrigerant gas detected by a pressure sensor 3 is immediately transmitted to the unit 7. A negative feedback is applied to the frequency of a frequency control signal 13 with the deviation of the suction pressure of the gas detected by the sensor 3 from the set target pressure as a reference, and the frequency of the signal 13 is stepwisely corrected by a real time process. Accordingly, a refrigerating machine 1 performs excellent energy conservation effect while maintaining the suction pressure of the gas by this operation, and controls the cooling capacity by following up the variation in a load torque.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention provides a refrigerating apparatus which has an excellent energy saving effect and which can stably maintain a refrigerating or freezing temperature suitable for the kind and property of a preserved object such as a refrigerating or freezing chamber.

[0002]

2. Description of the Related Art Conventionally, a refrigerating apparatus drives a compressor by a drive motor to compress a refrigerant gas sucked from a suction portion of the compressor and liquefy the compressed refrigerant gas in a condenser. Subsequently, this liquefied refrigerant is passed through an expansion valve, evaporated in an evaporator installed in a refrigerating or freezing chamber or the like, gasified into a refrigerant gas, and returned to the suction section of the compressor again. It is for cooling. Conventionally, it has been known that control of cooling capacity is important for stable operation of refrigeration systems, energy saving, and the like.

The control of the cooling capacity in the conventional refrigeration system has been performed by operating two pressure sensitive devices provided between the suction part of the compressor and the evaporator. That is, when the suction pressure of the refrigerant gas reaches the upper limit pressure set in one of the pressure sensitive devices, the drive motor is started, and then the suction pressure of the refrigerant gas reaches the lower limit pressure set in the other pressure sensitive device. The cooling capacity has been controlled by a two-acting method in which the drive motor is stopped when the temperature rises.

The power source received from an electric power company has conventionally been used as it is as a power source for a drive motor of a refrigeration system. In addition, a refrigerating device aiming at energy saving and stable operation has also been used by providing an inverter between a power source that receives power and a drive motor. Furthermore, an operation method has also been adopted in which a plurality of refrigerating devices having different cooling capacities are operated in parallel to save energy. However, even in the case of a refrigerating apparatus equipped with an inverter, or in the case of operating a plurality of refrigerating apparatuses having different cooling capacities in parallel, the two-acting system has been used to control the cooling capacity, as described above.

[0005]

As described above, the control of the cooling capacity of the conventional refrigerating apparatus is based on the two-acting system in which the suction pressure of the refrigerant gas is controlled by the upper limit and the lower limit. Refrigerant gas and liquefied refrigerant are always accumulated in the device, so that the refrigerant is the starting of the drive motor,
It is circulated and circulated in the refrigeration system through liquefaction and gasification with a delay from the cooling and stopping of the drive motor.

For this reason, even if the suction pressure of the refrigerant gas decreases and reaches the lower limit pressure and the drive motor stops, the refrigerant gas further lower than the lower limit pressure temporarily flows from the evaporator and is supercooled. cause. The main cause of this supercooling is that the discharge amount of the refrigerant gas tends to be excessive because the drive motor is rotating at a constant speed, and therefore the cooling is excessive. In order to prevent this, if the lower limit pressure of the suction pressure of the refrigerant gas is set to be high, the above-mentioned two operations are frequently repeated, and there is a problem that the life of the refrigeration system is impaired. Further, there is a problem that it is difficult to control the cooling capacity by following the fluctuation of the cooling load due to the above time delay.

Next, when the suction pressure of the refrigerant gas returns to the upper limit pressure and the drive motor is started, the drive motor rotates at a constant speed, but due to supercooling, the suction pressure of the refrigerant gas is low, so that the refrigerant gas is cooled. The specific gravity of the gas is low, and the compressor temporarily operates at a light load, which is close to idle operation. Therefore, there is a problem that the cooling capacity is reduced, the efficiency of the drive motor is reduced, the power is excessively consumed, and the life of the compressor and the like is shortened.

Further, since the suction pressure of the refrigerant gas repeats pulsation in conjunction with the control of the two-acting system, the cooling capacity periodically fluctuates during the operation of the refrigerating apparatus, and the fluctuation of the temperature in the chamber described above occurs. There was a problem that it became a factor. And,
There was a problem that during operation, the surface of the evaporator was easily frosted, the frequency of defrosting work increased, and man-hours were required for maintenance management.

This supercooling of the refrigerant gas has also been a factor of thermodynamic energy loss. That is, it is the difference between the enthalpy of the liquefied refrigerant and the enthalpy of the gasified refrigerant in the evaporator that effectively acts on the cooling in the cycle of the circulation movement of the refrigerant in the refrigeration system. The compression is a means for performing this cycle, and roughly speaking, the energy required for the compression, that is, the electric power consumed by the drive motor is not directly related to the cooling, and therefore, the suction pressure of the refrigerant gas decreases due to the supercooling. Also contributes to thermodynamic energy loss. Therefore, there is a problem that it is desired to maintain the suction pressure of the refrigerant gas at a required target pressure.

In the refrigerating apparatus having the inverter between the power receiving power source and the drive motor, the number of revolutions of the drive motor is controlled, so that some of the above problems are solved, but the energy saving effect is obtained. Had the problem that it was not worth the investment in the inverter. There is a problem in that even if the operating method is such that multiple refrigeration units with different cooling capacities are operated in parallel and cooling is performed with a low refrigeration unit with a low cooling capacity when the load is low, an energy saving effect commensurate with investment and installation space cannot be obtained. there were.

In order to solve the above-mentioned problems and problems, the present invention maintains the suction pressure of the refrigerant gas at a required target pressure and also has a control mechanism for controlling the cooling capacity by following the cooling load. The purpose is to provide a device.

[0012]

In order to achieve the above-mentioned object, a refrigerating apparatus of the present invention has a compressor for compressing a refrigerant gas, a drive motor for driving the compressor, and a condenser sequentially connected to the compressor. A refrigeration system comprising an expansion valve, an evaporator, and the evaporator connected to a suction part of the compressor via a conduit, wherein a pressure sensor is provided between the compressor and the evaporator. The pressure sensor is configured to transmit the suction pressure of the refrigerant gas detected in real time by the pressure sensor to a control unit equipped with a target pressure setting device, and the control unit is configured to transmit the target pressure. Based on the deviation between the target pressure set by the setter and the suction pressure of the refrigerant gas, a program for correcting the cooling capacity control signal stepwise by real-time processing by adding negative feedback to the cooling capacity control signal is incorporated. And The output current signal of the inverter is connected, while the cooling capacity control signal is input to the inverter, and the output of the inverter is connected to the input of the drive motor. .

The drive motor is an induction motor. The cooling capacity control signal comprises a frequency control signal and a voltage control signal. The program for correcting the cooling capacity control signal, based on the deviation between the target pressure and the suction pressure of the refrigerant gas, adds negative feedback to the frequency of the frequency control signal to gradually adjust the frequency in real time processing. It is characterized by comprising a program for correction and a program for stepwise correcting the voltage of the voltage control signal in synchronization with the real-time processing of the frequency. The program for correcting the voltage of the voltage control signal is synchronized with the real-time processing of the frequency,
It is characterized by comprising a program for calculating the impedance of the equivalent circuit of the drive motor and a program for multiplying the impedance by the current of the output current signal of the inverter.

[0014]

The cooling capacity of the refrigeration system is calculated by adding the specific gravity of the refrigerant gas in the suction part of the compressor and the discharge volume amount per unit time from the compressor to the unit of the refrigerant when liquefied by the condenser. It is proportional to the amount of calories multiplied by the difference between the enthalpy per unit amount and the enthalpy when the liquefied refrigerant is gasified in the evaporator. Here, the specific gravity of the refrigerant gas is proportional to the suction pressure of the refrigerant gas.

From the above, if the number of rotations of the compressor is the same, the higher the suction pressure of the refrigerant gas, the higher the cooling capacity. If the suction pressure of the refrigerant gas is constant, the higher the rotational speed of the compressor, the higher the cooling capacity. However, in order to maintain the number of revolutions of the compressor at the number of revolutions commensurate with the required cooling capacity,
It is necessary to supply electric power to the drive motor according to the load torque applied to the drive motor. Further, if the cooling capacity is controlled by following the disturbance received from the refrigerating or freezing chamber or the like, the temperature of the chamber or the like is basically determined by the suction pressure of the refrigerant gas.

In the refrigerating apparatus of the present invention, first, in order to maintain the suction pressure of the refrigerant gas at a required target pressure, the suction pressure of the refrigerant gas is detected in real time at time intervals, and the target pressure and the detected suction pressure are detected. The negative feedback is added to the cooling capacity control signal on the basis of the deviation of (1) to correct the cooling capacity control signal stepwise in real time processing. Thereby, the cooling capacity is controlled by following the time delay of the circulation movement of the refrigerant in the refrigeration system. At the same time, electric power corresponding to the load torque applied to the drive motor is supplied to the drive motor. In this way, the cooling capacity of the refrigeration system is controlled by following the disturbance received from the refrigeration or freezing chamber. By maintaining the suction pressure of the refrigerant gas at the required target pressure, while increasing the thermodynamic efficiency of the refrigerant cycle in the refrigeration system, the problem of supercooling and reduction of cooling capacity,
Resolve problems and issues such as reduced efficiency of the drive motor.

[0017]

The constitution, operation and effect of the refrigerating apparatus of the present invention will be described below with reference to the embodiments of the present invention. Reference numeral 1 in FIG. 1 is an embodiment of the refrigerating apparatus of the present invention, and the refrigerating apparatus 1 includes a control mechanism 2 which is one of the constituent elements of the present invention.

The control mechanism 2 mainly comprises a pressure sensor 3, a control unit 7 having a target pressure setter 8 and an inverter 9. This target pressure setting device 8
An operating unit for setting a target pressure is provided. The pressure sensor 3 is provided between the compressor 4 and the evaporator 5 by connecting to a short conduit 10 branched from a conduit 6 connected to the suction part of the compressor 4 and the outlet of the evaporator 5. The pressure sensor 3 is connected to the control unit 7.

In this embodiment, a three-phase induction motor is used as the drive motor 11, a three-phase AC power source 12 received from a power company is connected to the inverter 9, and the output of the inverter 9 is the input of the drive motor 11. Connected to. The inverter 9 is a three-phase AC variable voltage variable frequency inverter.

The cooling capacity control signal from the control unit 7 comprises a frequency control signal 13 and a voltage control signal 14, and this cooling capacity control signal is input to the inverter 9. And from the inverter 9, the inverter 9
Of the output current signal 21 is connected to the control unit 7.

The drive motor 11 drives the compressor 4. The conduit 15 from the discharge of the compressor 4 is connected to a condenser 16, which is equipped with a cooling device 17. A conduit 19 from the outlet of the condenser 16 is connected to the inlet of the evaporator 5 via an expansion valve 18, which evaporator 5 is installed in a refrigeration or freezing chamber 20.

The control unit 7 of the control mechanism 2 sends a cooling capacity control signal based on the deviation between the target pressure set by the operation unit of the target pressure setting unit 8 and the suction pressure of the refrigerant gas detected by the pressure sensor 3. It incorporates a program that adds negative feedback and gradually corrects the cooling capacity control signal in real-time processing. The program for correcting the cooling capacity control signal includes a program for correcting the frequency of the frequency control signal 13 and a program for correcting the voltage of the voltage control signal 14.

The program for correcting the frequency of the frequency control signal 13 corrects the frequency of the frequency control signal 13 stepwise in real-time processing by adding negative feedback to the frequency of the frequency control signal 13 on the basis of the above deviation. . The program for correcting the voltage of the voltage control signal 14 is a program for calculating the impedance of the equivalent circuit of the drive motor 11 in synchronization with the real-time processing of the frequency of the frequency control signal 13, and the current of the output current signal 21 from the inverter 9. And a program for multiplying the impedance by the impedance. The voltage of the voltage control signal 14 is corrected stepwise by real-time processing.

In operation of the refrigerating apparatus 1, first, a desired target pressure is set by the operating portion of the target pressure setting device 8. The target pressure is set in consideration of the temperature conditions of the refrigeration or freezing chamber. This target pressure is immediately transmitted to the control unit 7. This target pressure is the only control target that controls the cooling capacity of the refrigeration system 1. And,
The suction pressure of the refrigerant gas detected by the pressure sensor 3 is also immediately transmitted to the control unit 7. By this operation and the action of the above correction program, the cooling capacity control signal from the control unit 7 is corrected stepwise by the real-time processing during operation. The control of the cooling capacity is basically based on the stepwise frequency correction by the real-time processing in which the negative feedback based on the deviation between the set target pressure and the suction pressure of the refrigerant gas detected by the pressure sensor 3 is added as a reference. The correction is a control for following the fluctuation of the load torque applied to the drive motor 11.

The refrigerating apparatus 1 exerts an excellent energy saving effect while maintaining the suction pressure of the refrigerant gas at the target pressure by the above operation, and controls the cooling capacity by following the fluctuation of the load torque. To go. This operation and effect of the refrigerating apparatus of the present invention has been proved by the proof test.

The above-mentioned demonstration test was conducted in secret in the refrigerating or freezing chambers currently in operation at the six stores. This chamber displays, stores, and stores seafood, meat, vegetables, dairy products, and the like. All six stores had conventional refrigeration equipment, and the three-phase AC power received from the power company was directly connected to the three-phase induction motor of the refrigeration equipment, and the refrigeration capacity was controlled by the conventional two-operation system. It depends on.

The test was divided into two times, and each of them was continuously operated for 24 hours. One was a test in which an existing conventional refrigeration system was used as it was as a control. The other is a demonstration test of the present invention. Therefore, the two-acting control device is removed from the existing refrigeration system, and instead, the above-mentioned control mechanism 2 which is a component of the present invention is also included in the inverter 9 as it is. It was installed and reconfigured. With this configuration, this verification test can be regarded as the same as the one actually performed by the refrigeration system of the present invention. Hereinafter, in the description of the demonstration test, this is referred to as the refrigeration apparatus of the present invention.

Table 1 shows a list of comparisons (results of verification tests) between the refrigerating apparatus of the present invention carried out at the six shops A to F and the conventional refrigerating apparatus. Table 1 is a comparison between a demonstration test in which the refrigerating apparatus of the present invention was continuously operated for 24 hours and a control test in which the conventional refrigerating apparatus was continuously operated for another 24 hours on another day.

[Table 1] The results of the proof test of the refrigerating apparatus of the present invention are evaluated by the difference from the power consumption of the conventional refrigerating apparatus which was carried out as a control. The energy saving effect of the amount of electric power consumed in the 24-hour continuous operation is shown in the item of power saving rate in Table 1.
The energy-saving effect of the refrigerating apparatus of the present invention reaches an extremely high value of 18 to 39% as compared with the conventional refrigerating apparatus. Here, the energy saving effect of the refrigerating apparatus of the present invention is demonstrated.

The details will be described below with reference to Tables 2 and 3 by taking the verification test conducted at the store A as an example.

[Table 2] Table 2 shows the results (details) of the verification test at store A.
The graph shows the history of power consumption recorded every 30 minutes during continuous operation for 4 hours. The store A is closed at night and during this time, there is almost no disturbance from the refrigeration or freezing chamber, and operation is performed to balance with steady heat radiation. During the opening hours, operation is performed with disturbance factors added. The change can be easily seen from Table 2. Table 3 graphically illustrates this change. During the hours when there are many visitors from after noon to the evening, disturbance factors increase in the refrigeration system, resulting in a sharp increase in power consumption. Even in this time zone, the refrigerating apparatus of the present invention exhibits a large energy saving effect as compared with the conventional refrigerating apparatus.

[Table 3]

During the above-mentioned demonstration test at store A, the operation data of the refrigerating apparatus of the present invention and the conventional refrigerating apparatus are recorded in a chart. In the operation data of the conventional refrigeration system,
The suction pressure of the refrigerant gas is such that the pulsation is repeated between a minimum of 0.7 kilogram / square centimeter and a maximum of 2.3 kilogram / square centimeter. On the other hand, according to the operation data of the refrigeration system of the present invention, the suction pressure of the refrigerant gas is maintained at a target pressure of 3 kilograms / square centimeter, which is maintained substantially constant. This demonstrates the control effect of the control mechanism which is one of the components of the refrigeration system of the present invention. Moreover, the motivation of the present invention for controlling the operation of the refrigeration system while maintaining the suction pressure of the refrigerant gas at the target pressure has been demonstrated. The details of the verification test at the five stores B to F were the same as those at the store A.

Furthermore, in the six stores A to F,
The refrigerating apparatus of the present invention has been highly evaluated as having a much smaller amount of frost and frequency of frosting during operation as compared with the conventional refrigerating apparatus. Therefore, maintenance is said to be easy.

In the refrigerating apparatus of the present invention, it is easy to cool a chamber, a refrigerating warehouse or the like by operating a plurality of refrigerating apparatuses having different cooling capacities in parallel. By this parallel operation, further energy saving effect can be exhibited. A single-phase induction motor may be used instead of the three-phase induction motor. It is easy to use a DC motor as the drive motor of the refrigerating apparatus of the present invention.

[0033]

Since the present invention is constructed as described above, it has the following effects.

By the control mechanism provided in the refrigerating apparatus of the present invention,
The suction pressure of the refrigerant gas is maintained at the required target pressure.
As a result, the refrigerating apparatus of the present invention exerts an excellent energy saving effect and maintains the temperature suitable for the properties of the refrigerating or refrigerating chamber.

The amount of frost and the amount of frost formed during operation are extremely small, and maintenance management is easy.

The cooling capacity control signal is constituted by real-time processing, and controls the cooling capacity of the refrigeration system by following the fluctuation of the cooling load.

[Brief description of drawings]

FIG. 1 is a block diagram showing the configuration of a refrigerating apparatus of the present invention.

[Explanation of symbols]

 1 Refrigerator of the present invention 2 Control mechanism 3 Pressure sensor 4 Compressor 7 Control unit 8 Target pressure setter 9 Inverter 11 Drive motor 13 Frequency control signal 14 Voltage control signal 21 Output current signal

Claims (5)

[Claims] 1. A compressor comprising a compressor for compressing a refrigerant gas, a drive motor for driving the compressor, a condenser, an expansion valve and an evaporator, which are sequentially connected to the compressor, and the evaporator is provided via a conduit. A refrigeration system connected to the suction part of the compressor, wherein a pressure sensor is provided between the compressor and the evaporator,
The suction pressure of the refrigerant gas detected by the pressure sensor in real time at a time interval is transmitted to a control unit equipped with a target pressure setting device, and the control unit includes the target pressure setting device. Based on the deviation between the target pressure set by and the suction pressure of the refrigerant gas, a program for correcting the cooling capacity control signal stepwise in real time by adding negative feedback to the cooling capacity control signal is incorporated, and an inverter Of the refrigerating machine, wherein the cooling capacity control signal is input to the inverter and the output of the inverter is connected to the input of the drive motor. apparatus. 2. The refrigerating apparatus according to claim 1, wherein the drive motor is an induction motor. 3. The cooling capacity control signal comprises a frequency control signal and a voltage control signal.
Or the refrigerating apparatus according to 2. 4. The program for correcting the cooling capacity control signal is performed in real time by adding a negative feedback to the frequency of the frequency control signal based on the deviation between the target pressure and the suction pressure of the refrigerant gas. 4. A program for dynamically correcting the frequency, and a program for gradually correcting the voltage of the voltage control signal in synchronization with real-time processing of the frequency, according to any one of claims 1 to 3. Refrigeration equipment. 5. A program for correcting the voltage of the voltage control signal is synchronized with real-time processing of the frequency,
5. The refrigerating apparatus according to claim 1, comprising a program for calculating the impedance of the equivalent circuit of the drive motor and a program for multiplying the impedance by the current of the output current signal of the inverter. .