JPH0526524A - Two-stage compression type freezing device - Google Patents

Abstract

PURPOSE:To enable the use of a general purpose compressor, to reduce a device cost, and to save energy through realization of a high-precise temperature control by a method wherein compressors being different from each other and individually operable are used, the one forms a compressor on the low stage side and the other forms a compressor on the high stage side, and a frequency varying device is provided. CONSTITUTION:In a two-stage compression type freezing device 1 formed such that a compressor 4 on the low stage side, a compressor 7 on the high stage side, a condenser 9, an expansion valve 13, and a vaporizer 14 are interconnected, a frequency varying device 27 is provided. Capacity of the compressor 4 on the low stage side and that of the compressor 7 on the high stage side are controlled by the frequency varying device 27 according to a freezing load and the two compressors 4 and 7 are driven by means of the same frequency.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a two-stage compression type refrigerating apparatus used for showcases, refrigerators and the like.

[0002]

2. Description of the Related Art Generally, many two-stage compression type refrigerating apparatuses are provided with a low-stage compression mechanism and a high-stage compression mechanism in one casing as disclosed in Japanese Patent Publication No. 60-51617. That is, a two-stage compression refrigeration system is constructed by connecting a compressor having a low-stage compression mechanism and a high-stage compression mechanism in one casing, an oil separator, a condenser, a decompression device, and an evaporator. Are configured. For this reason, the compressor did not run out of oil by returning the oil separated by the oil separator to the compressor.

Further, in such a two-stage compression refrigeration system, in order to obtain a lower evaporation temperature, the outlet pipe of the condenser is branched and one of them is connected to the evaporator through a supercooler, The other side was connected to the supercooler via the solenoid valve and the expansion valve for the supercooler, and was further connected to the connecting pipe between the low-stage compressor and the high-stage compressor.

[0004]

However, according to the above configuration, since the two-stage compressor has the low-stage side compression mechanism and the high-stage side compression mechanism in one casing, the compressor has a two-stage compression mechanism. Since it is exclusively for the refrigeration system, it has poor applicability to other devices, resulting in high cost.

Further, in this type of two-stage compression type refrigerating apparatus, there is a demand for development of an apparatus capable of varying the capacity according to the refrigerating load.

The present invention has been made in view of the above problems, and separate compressors that can be operated independently are used, one of which is a low-stage compressor and the other is a high-stage compressor. This makes it possible to configure a two-stage compression refrigeration system with a general-purpose compressor and to reduce the cost of the system.

It is another object of the present invention to make it possible to change the capacity of a two-stage compression refrigerating apparatus composed of a plurality of compressors according to the refrigerating load.

[0008]

DISCLOSURE OF THE INVENTION The present invention relates to a two-stage compression refrigerating apparatus in which a low-stage compressor, a high-stage compressor, a condenser, a pressure reducing device, and an evaporator are connected to each other, and a variable frequency device is provided. Is provided, the capacity of the low-stage compressor and the high-stage compressor are controlled by the frequency variable device according to the refrigeration load, and both compressors are driven at the same frequency.

Further, in a two-stage compression type refrigerating apparatus in which a low-stage side compressor, a high-stage side compressor, a condenser, a pressure reducing device, and an evaporator are connected, a frequency varying device is provided, and the low-stage side compressor is provided. It is configured such that only one of the compressor and the high-stage compressor is capacity-controlled by the frequency variable device according to the refrigeration load.

Further, in a two-stage compression type refrigerating apparatus in which a low-stage side compressor, a high-stage side compressor, a condenser, a pressure reducing device, and an evaporator are connected, a frequency varying device is provided, and the low-stage side compressor is provided. Configured so that only one of the compressor and the high-stage compressor is capacity-controlled by the frequency varying device according to the refrigerating load, and the frequency of this frequency varying device is controlled according to the intermediate pressure. Is.

[0011]

According to the two-stage compression refrigerating apparatus of the present invention, by using the above-mentioned constitution, separate compressors that can be operated independently are used, one of which is a low-stage compressor and the other is a high-stage compressor. By doing so, it becomes possible to configure a two-stage compression refrigeration system with a general-purpose compressor, the compressor can be used for other devices, the cost of the device can be reduced, and the frequency variable device can be used. The capacity can be changed according to the refrigeration load, which enables accurate temperature control and contributes to energy saving. Moreover, since both compressors are drive-controlled at the same frequency, the compression ratio of the low-stage side compressor and the high-stage side compressor can always be kept at an appropriate value, and the refrigerating capacity can be exhibited well.

Further, by driving only one of the low-stage side compressor and the high-stage side compressor by the frequency variable device, the capacity can be controlled by the frequency variable device having a small capacity. This can reduce power consumption and further contribute to energy saving.

Here, when only the low-stage compressor is driven by the frequency variable device, the intermediate pressure rises, so that the efficiency of the low-stage compressor is somewhat deteriorated, but the efficiency of the high-stage compressor is low. On the contrary, there is no concern that it will be improved and the efficiency of the entire device will be reduced.

Further, by driving only one of the low-stage side compressor and the high-stage side compressor by the frequency variable device, and controlling the frequency of the frequency variable device according to the intermediate pressure, The capacity can be controlled while maintaining the compression ratio between the low-stage compressor and the high-stage compressor at an optimum value, and the refrigerating capacity can be exhibited satisfactorily.

[0015]

Embodiments of the present invention will be described below with reference to the drawings.

Reference numeral 1 is a two-stage compression type refrigerating apparatus. This refrigeration system has a compression mechanism and an electric motor for driving the compression mechanism, which are housed in a crank chamber 2 and a motor chamber 3 in one casing. A mechanism and an electric motor for driving the mechanism are housed in a crank chamber 5 and a motor chamber 6 in one casing, and a high-pressure side compressor 7 of 10 hp serving as a high-stage side, an oil separator 8, and a condenser 9, a double-pipe subcooler 12 connected to both pipes 10 and 11 branched from the outlet pipe of the condenser 9, an expansion valve 13, an evaporator 14, and an accumulator 15 It is configured by connecting the pipes as in 1.

Reference numeral 27 is a frequency variable device connected to both the low-stage compressor 4 and the high-stage compressor 7. This frequency changing device 27 has a frequency of 25 Hz to 75 H in steps of 5 Hz.
It can be changed within the range of z, and the low pressure detector 2 described later
6 and both compressors 4 and 7 according to signals from the controller 25.
Are controlled to be driven at the same frequency.

Reference numeral 16 is a pipe for sending the gas discharged from the low-stage compressor 4 to the high-stage compressor 7, and a muffler 17 for preventing discharge pressure pulsation is provided in the middle of the pipe 16. The mixer 18 is connected.

An electromagnetic valve 19 and a subcooler expansion valve 20 are connected to one pipe 10 branched from the condenser 9, and this pipe 10 passes through the inner pipe of the subcooler 12 and then the muffler 17 described above. , And is connected to the pipe 16 between the mixers 18.

The other pipe 11 branched from the condenser 9 passes through the outer pipe of the subcooler 12 and is connected to the evaporator 14 via a solenoid valve 21 and an expansion valve 13.

Reference numeral 22 is an oil pipe for connecting the low-stage compressor 4 and the high-stage compressor 7, and an electromagnetic valve 23 and a capillary tube 24 are connected to the pipe 22.

Reference numeral 25 is a signal from a low-pressure detector 26 provided in the suction pipe of the low-stage compressor 4, and the low-stage compressor 4 is supplied with the signal.
And stop of operation of high-stage compressor 7 and frequency changing device 27
Capacity change via solenoid and solenoid valves 19, 21, 2
3 is a control device for controlling opening and closing of No. 3.

In the two-stage compression refrigerating apparatus having the above-mentioned structure, the gas vaporized by exchanging heat with the fluid to be cooled in the evaporator 14 is sucked into the low-stage compressor 4 through the suction pipe. The low pressure side compressor 4 pressurizes it to an intermediate pressure and then pipes 1
The refrigerant gas discharged to 6 is mixed with the low-temperature liquid refrigerant sent from the subcooler 12 at the place where it exits the muffler 17, cooled to a predetermined temperature, and then sucked into the high-stage compressor 7. To be done.

The high-temperature, high-pressure refrigerant gas pressurized to the discharge pressure by the high-stage compressor 7 separates the oil in the gas by the oil separator 8 and then enters the condenser 9 to be condensed.

The condensed liquid refrigerant is branched into the pipes 10 and 11, and the liquid refrigerant flowing into one of the pipes 10 is reduced to an intermediate pressure by the expansion valve 20 for the subcooler through the solenoid valve 19. Then, the liquid refrigerant supplied to the outer pipe for the heat source refrigerant of the subcooler 12 and flowing into the other pipe 11 passes through the inner pipe of the subcooler 12 for the cooled refrigerant as it is, as described above. It flows into the pipe 16.

That is, both liquid refrigerants branched by the pipes 10 and 11 exchange heat with the supercooler 12, and the subcooler 1
The liquid refrigerant passing through the inner pipe of No. 2 is sufficiently cooled and the expansion valve 13
Flow into.

The liquid refrigerant flowing into the expansion valve 13 is decompressed here and then enters the evaporator 14 to be evaporated.

Thus, the low-stage compressor 4 and the high-stage compressor 7
Both of them have a frequency of 5H by the frequency variable device 27 which receives the signals from the low pressure detector 26 and the control device 25.
Since the drive is controlled in z steps and at the same frequency,
Even if the refrigeration load fluctuates and the low-pressure changes, the rotational speeds of both compressors 4 and 7 can be changed while maintaining the compression ratio of the low-stage compressor 4 and the high-stage compressor 7 at appropriate values. It can be changed according to the state, and accurate temperature control can be realized.

As a result, by using separate compressors 4 and 7 that can be operated independently, one of them is configured as the low-stage compressor 4 and the other is configured as the high-stage compressor 7, so that general-purpose compression can be performed. It is possible to configure the two-stage compression refrigeration system 1 with a machine, and the cost of the system can be reduced.

During operation of the two-stage compression type refrigeration system 1,
The solenoid valve 23 is opened by the control device 25, and the oil separated by the oil separator 8 is first returned to the crank chamber 5 of the high-stage compressor 7. When the amount of oil returned to the crank chamber of the high-stage compressor 7 exceeds a predetermined amount, the oil overflowing from this crank chamber flows into the oil pipe 22.

Since the oil flowing into the oil pipe 22 is throttled by the capillary tube 24, the oil is gradually supplied little by little to the crank chamber of the low-stage compressor 4.

Therefore, the low-stage compressor 4 and the high-stage compressor 7
Is a separate compressor, and even if there is a pressure difference between the compressors, it is possible to secure a predetermined amount of oil in each compressor 4, 7, and lock the compressor due to lack of oil. Can be prevented.

Further, the control device 25 controls the low-stage side compressor 4 and the high-stage side compressor 7 synchronously so that when one of them stops, the other also stops. The solenoid valves 19 and 23 are controlled so as to be closed when the compressors 4 and 7 are stopped. Therefore, the normal operation as the two-stage compression type refrigeration system can be maintained at all times, and for example, when the compressors 4 and 7 are stopped, the liquid refrigerant remaining in the condenser 9 flows into the high-stage side compressor 7 and restarts. It is possible to prevent the simultaneous liquid compression from being caused, and further, it is possible to prevent the pressure rise of the low-stage side compressor 4 and prevent the short cycle at the same time as the restart.

It is also possible to stop the compressors 4, 7 by a so-called pump-down method by the control device 25. In this case, a temperature sensor or the like for detecting a decrease in the ambient temperature of the evaporator 14 is used. Solenoid valve 1 by the signal of
9, 21 are closed.

Therefore, the refrigerant supply from the condenser 9 to the subcooler 12 and the evaporator 14 is stopped, but the compressor 4,
Since the operation of 7 continues, the suction side pressure decreases, and the compressors 4 and 7 are stopped by the signal of the low pressure detector 26 to bring the refrigerant into the condenser 9.

As a result, the stagnation of the refrigerant in the compressors 4 and 7 can be prevented, the liquid backing can be prevented at the same time when the two-stage compression refrigerating apparatus 1 is restarted, and the startability can be improved.

Further, when the two-stage compression type refrigerating apparatus 1 is started up, since the low-stage side compressor 4 is turned on after a fixed time when the high-stage side compressor 7 is turned on, the controller 25 controls the intermediate pressure. To prevent abnormal rise of the high-stage compressor 7
Can be started in a state close to no load, and operating efficiency can be improved.

FIG. 2 shows another embodiment in which the frequency varying device 28 is provided only in the low stage side compressor 4 and the high stage side compressor 7 is driven by a commercial power source.

In this case, the capacity can be controlled by the frequency variable device 28 having a small capacity, and the power consumption can be reduced to further contribute to energy saving.

When only the low-pressure stage compressor 4 is driven by the frequency variable device 28, the intermediate pressure rises, so that the efficiency of the low-pressure stage compressor 4 deteriorates somewhat, but the high-pressure stage compressor 7 does not operate. On the contrary, the efficiency is improved, and there is no concern that the efficiency of the entire device will decrease.

Further, FIG. 3 also shows another embodiment, in which the frequency varying device 29 is provided only in the high-stage side compressor 7, the low-stage side compressor 4 is driven by the commercial power source, and the low-stage side compressor 4 is used. The intermediate pressure detector 30 for detecting the pressure in the connecting pipe 16 between the high pressure side compressor 7 and the high pressure side compressor 7 is provided, and the frequency of the frequency varying device 29 is controlled according to the intermediate pressure.

In this case, not only the energy saving can be promoted by reducing the power consumption but also the capacity control can be performed while keeping the compression ratio between the low stage side compressor 4 and the high stage side compressor 7 at an optimum value. It can be performed, and the refrigerating capacity can be exhibited well.

[0043]

As described above, according to the present invention, separate compressors that can be operated independently are used, and one of them is a low-stage compressor and the other is a high-stage compressor. , It is possible to configure a two-stage compression refrigeration system with a general-purpose compressor, the compressor can be used for other devices, the cost of the device can be reduced, and its capacity can be reduced by the frequency variable device. Can be changed according to the refrigeration load,
Accurate temperature control can be performed and it can contribute to energy saving. Moreover, since both compressors are drive-controlled at the same frequency, the compression ratio of the low-stage compressor and the high-stage compressor can always be kept at an appropriate value, and the refrigerating capacity can be exhibited well.

Further, by driving only one of the low-stage side compressor and the high-stage side compressor by the frequency variable device, the capacity can be controlled by the small frequency variable device. This can reduce power consumption and further contribute to energy saving.

Further, when only one of the compressors is driven and controlled by the frequency variable device, the frequency of the frequency variable device is controlled according to the intermediate pressure, so that the low-stage compressor and the high-stage compressor can be operated. The capacity can be controlled while the compression ratio between the two is kept at an optimum value, and the refrigerating capacity can be satisfactorily exhibited.

[Brief description of drawings]

FIG. 1 is a refrigerant circuit diagram of a two-stage compression refrigeration system.

FIG. 2 is a refrigerant circuit diagram of a two-stage compression type refrigeration system showing another embodiment.

FIG. 3 is a refrigerant circuit diagram of a two-stage compression type refrigeration system showing another embodiment.

[Explanation of symbols]

4 Low-stage compressor 7 High-stage compressor 9 condenser 12 Supercooler 13 Expansion valve 14 Evaporator 27, 28, 29 Frequency variable device 30 Intermediate pressure detector

Claims (3)

[Claims] 1. A low-stage compressor, a high-stage compressor, a condenser,
In a two-stage compression refrigeration system in which a decompression device and an evaporator are connected, a frequency variable device for controlling the capacity of the low-stage compressor and the high-stage compressor at the same operating frequency is provided. Two-stage compression type refrigeration equipment. 2. A low-stage compressor, a high-stage compressor, a condenser,
In a two-stage compression type refrigeration system in which a pressure reducing device and an evaporator are connected, a frequency for controlling the capacity of only one of the low-stage side compressor and the high-stage side compressor according to the refrigeration load. A two-stage compression type refrigeration system comprising a variable device. 3. A low-stage compressor, a high-stage compressor, a condenser,
In a two-stage compression refrigeration system in which a pressure reducing device and an evaporator are connected, only one of the low-stage side compressor and the high-stage side compressor is used depending on the intermediate refrigerant pressure of both compressors. A two-stage compression type refrigerating apparatus, which is equipped with a frequency variable device for controlling capacity.