JP2024050494A - Supercritical cooling system and control method thereof - Google Patents

Abstract

A cooling system and a control method thereof are provided that effectively prevent liquid backflow to a compressor.
[Solution] A control method for controlling a cooling system including a compressor 20, a gas cooler 30, a flash tank 40, an expansion valve 60, an evaporator 70, and a gas-liquid separator 80 in this order based on the flow direction of the refrigerant, the control method including the steps of: acquiring a water level of the liquid-phase refrigerant stored in the flash tank 40; and, if the acquired water level of the flash tank 40 is equal to or lower than a predetermined reference tank water level, transferring the refrigerant compressed by the compressor 20 to the gas-liquid separator 80. [Selected Figure] FIG. 3

Description

The present invention relates to a supercritical cooling system and a control method thereof.

A cooling system refers to a system that performs cooling using a cooling cycle. A supercritical cooling system is a cooling system that uses a supercritical fluid such as carbon dioxide as a refrigerant. In a cooling system, a flash tank is installed in the refrigerant flow path between a gas cooler and an evaporator, the refrigerant coming out of the gas cooler is depressurized by an expansion valve, and the gas-liquid mixed refrigerant is sent to the flash tank and separated into a gas phase and a liquid phase. The separated gas refrigerant in the gas phase is supplied to a compressor, particularly a parallel compressor, bypassing the evaporator. This reduces the area required for arranging pressure-resistant piping for high-pressure refrigerant, thereby reducing costs.

It is possible to expand the scope of application of the cooling system while avoiding liquid compression and abnormal overheating due to liquid backflow in the compressor. Figure 1 is a conceptual diagram showing the configuration of an existing cooling system. The existing cooling system disclosed in Japanese Patent Publication No. 2021-105474, which is a prior document shown in FIG. 1, includes a flash tank 101 having a gas phase portion and a liquid phase portion, an evaporator 102 to which a refrigerant from the liquid phase portion of the flash tank 101 is induced, a compressor 108 for compressing the refrigerant gas after passing through the device, a first refrigerant flow path 103 connecting the evaporator 102 and the compressor 108, a second refrigerant flow path 104 for connecting the gas phase portion of the flash tank 101 and the first refrigerant flow path 103, a heat exchanger 105 for exchanging heat with the refrigerant that has passed through the liquid phase portion of the flash tank 101 and the evaporator, and a first expansion valve 106 installed in the second refrigerant flow path 104, a sensor 109 for detecting a pressure or temperature related to the evaporation temperature of the refrigerant in the evaporator 102, and a control unit 107 for controlling the opening degree of the first expansion valve 106 based on the target pressure of the flash tank 101 set based on the detection result of the sensor 109.

By using this method, the pressure in the flash tank 101 can be controlled to a target pressure that does not cause liquid backflow or abnormal overheating in the compressor 108, thereby expanding the range of operational applications of the refrigeration system while avoiding liquid backflow and abnormal overheating in the compressor 108.

However, even if this method is followed, if there is a large amount of liquid phase refrigerant among the refrigerant separated in the flash tank 101, the flow of the gas phase refrigerant may cause the liquid phase refrigerant to be discharged from the flash tank 101 and transferred to the compressor 108. Despite the above configuration, the liquid phase refrigerant may not evaporate sufficiently during the process it passes through after the flash tank 101, and ultimately liquid may return to the compressor 108.

Figure 2 is a conceptual diagram showing the configuration of a cooling system S having multiple evaporators E. As shown in Figure 2, when multiple evaporators E are connected to one cooling system S, an environment in which small loads are often generated can be provided. In this case, when the amount of refrigerant bypassed is adjusted by measuring the degree of superheat from the temperature and pressure of the refrigerant related to the evaporator E, as in the existing cooling system, control to adjust the amount of refrigerant based on the measured value must be performed frequently, which often causes the expansion valve to go out of control range, making stable control of the degree of superheat difficult, and frequent control changes making it easy for each component constituting the cooling cycle to break down.

According to an existing cooling system disclosed in Japanese Patent Publication JP 2021-188881, the compressor of the cooling system may be configured with multiple compressors, including a main compressor and a parallel compressor. By configuring multiple compressors, the cooling system can easily respond to various loads. However, when multiple evaporators are connected as in the example described in FIG. 2, a load smaller than the minimum load at which each compressor can operate may be repeated or sustained, causing frequent start/stop (rapid on/off repetition), which may shorten the life of the entire cooling system.

Due to the above issues, fresh foods can lose quality when stored in refrigerators that use a cooling cycle.

Japanese Patent Publication No. 2021-105474 (published on July 26, 2021) Japanese Patent Publication No. 2021-188881 (published on December 13, 2021)

The present invention has been devised to solve these problems, and has an object to solve at least one of the following problems.
An object of the present invention is to provide a cooling system that effectively prevents liquid from returning to a compressor and a control method thereof.
SUMMARY OF THE PRESENT EMBODIMENT An object of the present invention is to provide a cooling system and a control method thereof that quickly treats the liquid in a gas-liquid separator to ensure normal operation.
An object of the present invention is to provide a cooling system in which the frequency of starting and stopping a compressor is reduced, and a control method thereof.

A cooling system according to an embodiment of the present invention includes a compressor configured to compress a refrigerant, a gas cooler configured to cool the refrigerant compressed by the compressor to liquefy it, a flash tank configured to store the refrigerant cooled by the gas cooler, an expansion valve configured to expand the liquid phase refrigerant transferred from the flash tank, an evaporator configured to evaporate the refrigerant expanded by the expansion valve, a gas-liquid separator configured to separate a portion of the liquid phase and a portion of the gas phase of the refrigerant that has passed through the evaporator and transfer the portion of the gas phase to the compressor, and The system includes a circulation line that transfers the refrigerant compressed by the compressor to the gas-liquid separator, a circulation valve that is disposed in the circulation line to adjust the opening and closing of the circulation line, a tank water level acquisition unit that is installed inside the flash tank to acquire the water level of the liquid refrigerant stored in the flash tank, and a processor that is electrically connected to the tank water level acquisition unit and the circulation valve, and the processor controls the circulation valve to open at a predetermined reference opening when the water level acquired by the tank water level acquisition unit is equal to or lower than a predetermined reference tank water level.

According to an embodiment of the present invention, a control method for controlling a cooling system having a compressor, a gas cooler, a flash tank, an expansion valve, an evaporator, and a gas-liquid separator in that order based on the flow direction of the refrigerant includes the steps of obtaining the water level of the liquid-phase refrigerant stored in the flash tank, and, if the obtained water level of the flash tank is equal to or lower than a predetermined reference tank water level, transferring the refrigerant compressed by the compressor to the gas-liquid separator.

This can achieve at least one of the following effects:
Liquid return to the compressor can be effectively prevented.
The liquid in the gas-liquid separator can be promptly treated to maintain normal operation.
The frequency of starting and stopping the compressor is reduced, and the range of operational applications for stable refrigeration can be expanded.

FIG. 1 is a diagram conceptually illustrating a configuration of an existing cooling system. FIG. 1 is a diagram conceptually illustrating a configuration of a cooling system having multiple evaporators. 1 is a diagram conceptually illustrating a configuration of a cooling system according to an embodiment of the present invention. 4 is a flowchart illustrating a method for controlling a cooling system according to an embodiment of the present invention. 4 is a flowchart illustrating a method for controlling a compressor to continuously operate in a cooling system according to an embodiment of the present invention.

Some embodiments of the present invention will be described in detail below with reference to exemplary figures. When assigning reference numerals to components in each figure, it should be noted that identical components are assigned the same numerals as much as possible even if they are displayed in different figures. In addition, in describing the embodiments of the present invention, if a detailed description of related publicly known configurations or functions is deemed to hinder understanding of the embodiments of the present invention, the detailed description will be omitted.

In addition, in describing components of the embodiments of the present invention, terms such as first, second, A, B, (a), (b), etc. may be used. Such terms are merely used to distinguish the components from other components, and do not limit the nature, order, or sequence of the components. When a component is described as being "coupled," "coupled," or "connected" to another component, it should be understood that the component may be directly coupled or connected to the other component, but that other components may also be "coupled," "coupled," or "connected" between each component.

FIG. 3 is a diagram conceptually showing the configuration of a cooling system according to an embodiment of the present invention.
Referring to the figure, the cooling system according to the embodiment of the present invention includes a compressor 20, a gas cooler 30, a flash tank 40, an expansion valve 60, an evaporator 70, a gas-liquid separator 80, a circulation line 12, a circulation valve 13, a tank water level acquisition unit 41, and a processor P. The compressor 20, the gas cooler 30, the flash tank 40, the expansion valve 60, the evaporator 70, and the gas-liquid separator 80 may be arranged on the main line 11 in the above-mentioned order, and the refrigerant may flow along the main line 11 in the above-mentioned order and be processed by each component. The cooling system according to the embodiment of the present invention may perform a supercritical cycle for performing cooling using a supercritical fluid as a refrigerant, but the cooling cycle that the cooling system can perform is not limited thereto. The line in the embodiment of the present invention means a component that forms a flow path through which the refrigerant can flow. The line may be composed of a pipe, a flexible hose, or the like, but the configuration for forming the flow path is not limited thereto.

The compressor 20 is a device that compresses a gas phase refrigerant. The compressor 20 is connected to a device that generates a rotational force, such as an electric motor or a turbine, and may be a screw type, scroll type, or reciprocating type compressor 20 that compresses the refrigerant using the rotational force, but the type is not limited to these. In one embodiment of the present invention, an electric motor 22 is connected to the compressor 20 to operate the compressor 20, and an inverter 23 is disposed to control the electric motor 22, but the configuration for driving the compressor 20 is not limited to this.

The compressor 20 is connected to the gas-liquid separator 80 and the gas cooler 30, and can compress the gas phase refrigerant discharged from the gas-liquid separator 80 and discharge it to the gas cooler 30.

The gas cooler 30 is a device that cools the refrigerant compressed by the compressor 20 so that the refrigerant can be easily liquefied. The gas cooler 30 can exchange heat between the refrigerant and outside air to cool the refrigerant. Therefore, the gas cooler 30 can include at least one of a plate heat exchanger and a pin-tube heat exchanger, which are heat exchangers that enable heat exchange between different media, but the type of heat exchanger used as the gas cooler 30 is not limited to this.

The cooling system according to one embodiment of the present invention may include a high-pressure expansion valve 14. The high-pressure expansion valve 14 is disposed between the gas cooler 30 and the flash tank 40 to expand the refrigerant discharged from the gas cooler 30 and transferred to the flash tank 40.

The cooling system according to one embodiment of the present invention may include a parallel compressor 21. The parallel compressor 21 is arranged in parallel with the compressor 20 and may compress and discharge the refrigerant. The parallel compressor 21 may receive and compress the gas phase refrigerant from the flash tank 40 and may merge with the compressed refrigerant discharged from the compressor 20. As with the compressor 20, various types of parallel compressors 21 may be used.

The flash tank 40 stores the refrigerant cooled by the gas cooler 30 inside. In the flash tank 40, the refrigerant can be separated into a liquid phase and a gas phase. Therefore, the flash tank 40 may be a flash tank, but the type is not limited to this.

The cooling system according to one embodiment of the present invention may include a supercooling heat exchanger 50. A portion of the liquid refrigerant discharged from the flash tank 40 and another portion that has passed through the supercooling expansion valve 51 may exchange heat in the supercooling heat exchanger 50. Of these, a portion that has not passed through the supercooling expansion valve 51 may be transferred to the expansion valve 60 and the evaporator 70, and may meet with the other portion after passing through the evaporator 70. The supercooling heat exchanger 50 may include at least one of a plate heat exchanger and a pin-tube heat exchanger, which are heat exchangers that enable heat exchange between different media, but the type of heat exchanger used as the supercooling heat exchanger 50 is not limited thereto.

The expansion valve 60 can expand the liquid phase refrigerant separated and transferred from the flash tank 40. The expansion valve 60 may be an electronic expansion valve 60 whose opening and closing is controlled by an electrical signal, but the type is not limited thereto.

The evaporator 70 evaporates the refrigerant expanded by the expansion valve 60. The evaporator 70 can exchange heat between the refrigerant and a non-cooled body such as the outside air or the air inside the refrigerator, thereby heating the refrigerant. Therefore, the evaporator 70 can include at least one of an air cooler, a plate heat exchanger, and a pin-tube heat exchanger, which are heat exchangers that enable heat exchange between different media, but the type of heat exchanger used as the evaporator 70 is not limited thereto.

The gas-liquid separator 80 separates a part of the liquid phase of the refrigerant from a part of the gas phase of the refrigerant when a part of the liquid phase remains in the refrigerant that has passed through the evaporator 70. A part of the gas phase of the refrigerant separated from the gas-liquid separator 80 may be transmitted to the compressor 20. The gas-liquid separator 80 may be an accumulator capable of gas-liquid separation, but the type is not limited thereto.

The cooling system according to one embodiment of the present invention may include a gas-liquid separation water level acquisition unit 81. The gas-liquid separation water level acquisition unit 81 may be installed inside the gas-liquid separator 80 to acquire the water level of the liquid phase refrigerant stored in the gas-liquid separator 80. The gas-liquid separation water level acquisition unit 81 may be a level switch, but the means for measuring the refrigerant water level in the gas-liquid separator 80 is not limited thereto.

The cooling system according to one embodiment of the present invention may include an inlet temperature acquisition unit 24. The inlet temperature acquisition unit 24 may acquire the temperature of the gas phase refrigerant transferred from the gas-liquid separator 80 to the compressor 20. The inlet temperature acquisition unit 24 may include a thermistor, a thermocouple, etc., but the means for measuring the temperature is not limited thereto.

The cooling system according to one embodiment of the present invention may include an inflow pressure acquisition unit 25. The inflow pressure acquisition unit 25 may acquire the pressure of the gas phase refrigerant transferred from the gas-liquid separator 80 to the compressor 20. The inflow pressure acquisition unit 25 may include a capacitance type pressure sensor, a strain gauge, etc., but the means for measuring the pressure is not limited thereto.

The circulation line 12 is a line that connects one point of the main line 11 to another point. The circulation line 12 connects two points of the main line 11 so as to transmit the refrigerant compressed by the compressor 20 to the gas-liquid separator 80. Therefore, the circulation line 12 can connect a point on the main line 11 downstream of the compressor 20 to a point upstream of the gas-liquid separator 80 based on the flow direction of the refrigerant. The circulation line 12 may be directly connected to the gas-liquid separator 80.

The circulation valve 13 is disposed in the circulation line 12 so as to adjust the opening and closing of the circulation line 12. The circulation valve 13 may be an electric valve or a solenoid valve whose opening degree can be adjusted, but the type is not limited thereto.

The tank water level acquisition unit 41 is installed inside the flash tank 40 to acquire the water level of the liquid phase refrigerant stored in the flash tank 40. The tank water level acquisition unit 41 may include a level transmitter, but the means used to acquire the water level are not limited thereto.

The processor P is a component including elements capable of performing logical operations to execute control commands, and may include a central processing unit (CPU). The processor P is connected to various components of the cooling system according to one embodiment of the present invention, and can transmit signals according to control commands to each component, and can receive acquired information in the form of signals by connecting to various sensors or acquisition units. The processor P can be electrically connected to each component, and can communicate with each other by connecting with conductors or having a communication module capable of wireless communication.

The cooling system may further include a memory, and the control instructions executed by the processor P may be stored in the memory and utilized. The memory may be a device such as a hard disk drive (HDD), a solid state drive (SSD), a server, a volatile medium, a non-volatile medium, etc., but is not limited to these types. The memory may further store other data required by the processor P to perform its work.

FIG. 4 is a flow chart illustrating a method for controlling a cooling system according to an embodiment of the present invention.
Hereinafter, a method of controlling the cooling system will be described with a focus on the operation of the processor P. The tank water level acquisition unit 41 can acquire the water level of the liquid phase refrigerant stored in the flash tank 40 (S11). The processor P receives the acquired refrigerant water level of the flash tank 40 from the tank water level acquisition unit 41 and compares it with a predetermined reference tank water level (S12). If the acquired water level is higher than the reference tank water level, it is not a situation in which an excessive amount of liquid phase refrigerant is transferred from the flash tank 40 to the evaporator 70, so the existing operating state may be maintained. The reference tank water level may be 0 m.

If the acquired water level is below the reference tank water level, an excessive amount of liquid-phase refrigerant is transferred from the flash tank 40 to the evaporator 70, so that the refrigerant does not evaporate sufficiently in the evaporator 70 or a large amount of liquid-phase refrigerant is transferred to the gas-liquid separator 80 due to the abnormal opening of the expansion valve 60. Therefore, when the acquired water level is below the reference tank water level, the processor P opens the circulation valve 13 so that the high-temperature gas-phase refrigerant compressed by the compressor 20 is transferred to the gas-liquid separator 80 (S13). The processor P can open the circulation valve 13 at a reference opening, which is a predetermined opening. Therefore, the high-temperature and high-pressure refrigerant compressed and discharged by the compressor 20 along the circulation line 12 can be transferred to the gas-liquid separator 80, and the liquid-phase refrigerant in the gas-liquid separator 80 can be evaporated. The liquid-phase refrigerant is evaporated, and the liquid in the gas-liquid separator 80 can be quickly processed to prevent the liquid return phenomenon, and normal operation can be quickly restored. The reference opening may be 30% when the maximum opening is 100%.

If the water level acquired by the tank water level acquisition unit 41 is equal to or lower than the reference tank water level, the processor P can control the operating speed of the compressor 20 to be lower than the normal speed, which is a predetermined speed (S14). By reducing the load on the compressor 20 and decreasing the amount of refrigerant sucked into the compressor 20, the liquid backflow phenomenon can be prevented. The operating speed may refer to the rotational speed at which the compressor 20 rotates, which may be expressed in units of rpm (revolutions per minute) or Hertz (Hz). The normal speed may be 65 Hz, and the operating speed reduced by the control to 30 Hz.

With the above-mentioned control, even if a temporary problem occurs, the cooling cycle can be operated while maintaining a near-normal operating state. However, if liquid phase refrigerant accumulates in the gas-liquid separator 80 despite the above-mentioned control, it is predicted that a problem such as liquid compression has occurred, and the next step of measures can be taken.

The gas-liquid separation water level acquisition unit 81 can acquire the water level of the liquid refrigerant stored in the gas-liquid separator 80 (S21). The processor P can receive the acquired water level from the gas-liquid separation water level acquisition unit 81 and compare it with the reference gas-liquid separation water level (S22). If the acquired water level is less than the reference gas-liquid separation water level, which is a predetermined water level, the normal operating state is returned to, so no separate measures may be taken. If the water level acquired by the gas-liquid separation water level acquisition unit 81 is equal to or greater than the reference gas-liquid separation water level, the processor P closes the expansion valve 60 (S23). When the expansion valve 60 is closed, the processor P can open the circulation valve 13 at a larger opening than the reference opening so that the compressor 20 is continuously operated above the minimum load (S24). When the expansion valve 60 is closed, the processor P can further reduce the operating speed of the compressor 20 (S25). By closing the expansion valve 60, the transfer of refrigerant from the flash tank 40 to the evaporator 70 is blocked, and the liquid phase refrigerant remaining in the gas-liquid separator 80 is evaporated by the high-temperature, high-pressure refrigerant compressed by the compressor 20, and the compressor 20 is operated at low load to prevent liquid return as much as possible. When the above-mentioned conditions are met, the expansion valve 60 may be closed in step S23, or its opening may simply be reduced.

When the expansion valve 60 is closed, if the refrigerant level in the gas-liquid separator 80 returns to normal and the degree of superheat meets the standard, it is determined to be in a normal state and the operation of the cooling cycle can be returned to its original state.

When the expansion valve 60 is closed, the gas-liquid separation water level acquisition unit 81 can acquire the water level of the liquid phase refrigerant stored in the gas-liquid separator 80 (S31). When the expansion valve 60 is closed, the inlet temperature acquisition unit 24 can acquire the temperature of the refrigerant discharged from the gas-liquid separator 80 (S32). When the expansion valve 60 is closed, the inlet pressure acquisition unit 25 can acquire the pressure of the refrigerant discharged from the gas-liquid separator 80 (S33). The processor P can calculate the degree of superheat from the acquired refrigerant temperature and pressure (S34).

The processor P can compare the acquired water level of the gas-liquid separator 80 and the calculated superheat with the reference gas-liquid separation water level and the reference superheat (S35). The processor P can open the expansion valve 60 when the water level acquired by the gas-liquid separation water level acquisition unit 81 is less than a predetermined reference gas-liquid separation water level and the superheat calculated from the temperature acquired by the inlet temperature acquisition unit 24 and the pressure acquired by the inlet pressure acquisition unit 25 is equal to or greater than the predetermined reference superheat (S36). When opening the expansion valve 60, the processor P can close the circulation valve 13 to block the high-temperature gas phase refrigerant compressed by the compressor 20 from being transferred to the gas-liquid separator 80 (S37). When opening the expansion valve 60, the processor P can set the operating speed of the compressor 20 to a normal speed (S38). Therefore, the cooling system can return to a normal state and continue operating, and can return to the first step of the cycle.

Figure 5 is a flow chart showing a control method for controlling the compressor 20 to operate continuously in a cooling system according to an embodiment of the present invention. The processor P can control the circulation valve 13 to open when the pressure acquired by the inlet pressure acquisition unit 25 is equal to or lower than a predetermined stop pressure, even if the system is operating normally. When the cooling load is small, the load transmitted to the compressor 20 becomes smaller than the minimum load, and the operation may be stopped regardless of other conditions. The compressor 20 does not operate below the minimum load, but when small loads occur frequently, the operation of turning the compressor 20 on and off may be repeated frequently. Therefore, the refrigerant discharged from the compressor 20 is again introduced into the compressor 20 to match the inlet pressure higher than the stop pressure, which is the minimum load, so that the compressor 20 continues to operate without stopping. Therefore, frequent starting and stopping of the compressor 20 can be reduced.

Specifically, in a situation where the compressor is operating (S41), the processor P can compare the inflow pressure, which is the pressure acquired by the inflow pressure acquisition unit 25, with the stop pressure (S42). If the pressure acquired by the inflow pressure acquisition unit 25 is greater than the stop pressure, there is no problem with the operation of the compressor 20, so operation continues as is (S41).

If the pressure acquired by the inlet pressure acquisition unit 25 is equal to or lower than the stop pressure, the processor P can compare the time that the compressor 20 has been operating with a predetermined minimum load operating time (S43). If the operating time of the compressor 20 is less than the minimum load operating time, it is not yet clear whether a clear problem has occurred in the compressor 20 or whether it is a temporary error, so the compressor 20 continues to operate (S41). If the operating time of the compressor 20 is equal to or greater than the minimum load operating time, the processor P can open the circulation valve 13 to prevent an abnormality from occurring in the compressor 20 or to prevent the compressor 20 from stopping (S44).

After the circulation valve 13 is opened, the processor P can determine how long the circulation valve 13 has been open and compare the open time of the circulation valve 13 with a predetermined reference open time (S45). If the open time of the circulation valve 13 is shorter than the reference open time, the circulation valve 13 can remain open (S44). However, if the open time of the circulation valve 13 is equal to or greater than the reference open time, the processor P can close the circulation valve 13 to determine whether the circulation valve 13 has been open long enough and the system has returned to a normal state (S46).

After the circulation valve 13 is closed, the processor P can compare the inlet pressure of the compressor 20 with the stop pressure (S47). If the inlet pressure of the compressor 20 is greater than the stop pressure, the compressor 20 is in a state where it can operate normally, so the processor P can maintain the compressor 20 in an operating state. If the inlet pressure of the compressor 20 is equal to or less than the stop pressure, the compressor 20 cannot operate normally, so the processor P can stop the compressor 20 (S48).

After the compressor 20 is stopped, the processor P can compare the inlet pressure of the compressor 20 with a predetermined operating pressure (S49). The operating pressure may be a pressure value greater than the stop pressure. If the inlet pressure is less than the operating pressure, the stopped state of the compressor 20 can be maintained (S48). If the inlet pressure is equal to or greater than the operating pressure, the compressor 20 is in a state where it can operate normally, and the processor P can cause the compressor 20 to start operating again (S41).

Although it has been described above that all components constituting the embodiments of the present invention are combined or operated in combination, the present invention is not necessarily limited to such an embodiment. In other words, all components may be selectively combined and operated in one or more combinations within the scope of the purpose of the present invention. Furthermore, the terms "comprise", "comprise", "have" and the like described above mean that the component in question may be present, unless otherwise specified to the contrary, and should be interpreted as including other components, not excluding other components. All terms, including technical and scientific terms, have the same meaning as commonly understood by a person having ordinary skill in the art to which the present invention belongs, unless otherwise defined. Commonly used terms, such as dictionary-defined terms, should be interpreted as being consistent with the contextual meaning of the relevant art, and should not be interpreted as being idealized or overly formal, unless expressly defined in the present invention.

The above description is merely an illustrative example of the technical concept of the present invention, and various modifications and variations are possible within the scope of the essential characteristics of the present invention, if one has ordinary knowledge in the technical field to which the present invention pertains. Therefore, the embodiments disclosed in the present invention are intended to illustrate, not limit, the technical concept of the present invention, and such embodiments do not limit the scope of the technical concept of the present invention. The scope of protection of the present invention should be interpreted according to the following claims, and all technical concepts within the scope equivalent thereto should be interpreted as being included in the scope of the present invention.

REFERENCE SIGNS LIST 11 main line 12 circulation line 13 circulation valve 14 high-pressure expansion valve 20 compressor 21 parallel compressor 22 electric motor 23 inverter 24 inlet temperature acquisition unit 25 inlet pressure acquisition unit 30 gas cooler 40 flash tank 41 tank water level acquisition unit 50 supercooling heat exchange unit 51 supercooling expansion valve 60 expansion valve 70 evaporator 80 gas-liquid separator 81 gas-liquid separation water level acquisition unit P processor

Claims (12)

a compressor arranged to compress a refrigerant;
a gas cooler provided to cool the refrigerant compressed by the compressor so as to liquefy the refrigerant;
a flash tank provided to store the refrigerant cooled by the gas cooler;
an expansion valve configured to expand the liquid phase refrigerant transferred from the flash tank;
an evaporator provided to evaporate the refrigerant expanded by the expansion valve;
a gas-liquid separator configured to separate a portion of the liquid phase and a portion of the gas phase of the refrigerant that has passed through the evaporator and to transmit the portion of the gas phase to the compressor;
a circulation line for transferring the refrigerant compressed by the compressor to the gas-liquid separator;
A circulation valve disposed in the circulation line to adjust opening and closing of the circulation line;
a tank water level acquiring unit installed inside the flash tank for acquiring a water level of the liquid phase refrigerant stored in the flash tank;
a processor electrically connected to the tank water level acquisition unit and the circulation valve;
The processor,
A cooling system that controls the circulation valve to be opened at a predetermined reference opening degree when the water level acquired by the tank water level acquisition unit is equal to or lower than a predetermined reference tank water level. the compressor is electrically coupled to the processor;
The processor,
The cooling system according to claim 1 , wherein when the water level acquired by the tank water level acquisition unit is equal to or lower than a predetermined reference tank water level, the operating speed of the compressor is controlled to be slower than a predetermined normal speed. The gas-liquid separator further includes a gas-liquid separation water level acquiring unit installed in the gas-liquid separator to acquire a water level of the liquid phase refrigerant stored in the gas-liquid separator,
The processor is further electrically connected to the gas-liquid separation water level acquisition unit and the expansion valve;
The processor,
The cooling system according to claim 1 , wherein when the water level acquired by the gas-liquid separation water level acquisition unit is equal to or higher than a predetermined reference gas-liquid separation water level, the expansion valve is controlled to be closed. When the expansion valve is closed, the processor
The cooling system according to claim 3 , wherein the circulation valve is controlled to be opened to an opening degree greater than the reference opening degree, and the operating speed of the compressor is controlled to be reduced. an inlet temperature acquiring unit configured to acquire a temperature of the refrigerant discharged from the gas-liquid separator;
and an inlet pressure acquisition unit configured to acquire a pressure of the refrigerant discharged from the gas-liquid separator,
The processor electrically connected to the inlet temperature acquisition unit and the inlet pressure acquisition unit in a state where the expansion valve is closed,
4. The cooling system according to claim 3, wherein when the water level acquired by the gas-liquid separation water level acquisition unit is lower than a predetermined reference gas-liquid separation water level and the degree of superheat calculated from the temperature acquired by the inlet temperature acquisition unit and the pressure acquired by the inlet pressure acquisition unit is equal to or higher than a predetermined reference degree of superheat, the circulation valve is closed, the operating speed of the compressor is set to a predetermined normal speed, and the expansion valve is controlled to be opened. The compressor further includes an inlet pressure acquisition unit electrically connected to the processor and configured to acquire a pressure of the refrigerant flowing into the compressor,
The processor,
The cooling system according to claim 1 , wherein the circulation valve is controlled to be opened when the pressure acquired by the inflow pressure acquisition unit is equal to or lower than a predetermined stop pressure. A control method for controlling a cooling system including a compressor, a gas cooler, a flash tank, an expansion valve, an evaporator, and a gas-liquid separator in this order based on a flow direction of a refrigerant, comprising:
obtaining a level of the liquid refrigerant stored in the flash tank;
and transmitting the refrigerant compressed by the compressor to the gas-liquid separator when the acquired water level of the flash tank is equal to or lower than a predetermined reference tank water level. The cooling system control method of claim 7, further comprising the step of operating the compressor at a speed slower than a predetermined normal speed if the acquired flash tank water level is equal to or lower than a predetermined reference tank water level. obtaining a level of the liquid phase refrigerant stored in the gas-liquid separator;
The cooling system control method according to claim 7 , further comprising: closing the expansion valve when the obtained water level of the gas-liquid separator is equal to or higher than a predetermined reference gas-liquid separation water level. In a state where the expansion valve is closed, further increasing the water level of the liquid phase refrigerant stored in the gas-liquid separator;
obtaining a temperature of the refrigerant exiting the L/G separator with the expansion valve closed;
obtaining a pressure of the refrigerant discharged from the gas-liquid separator with the expansion valve closed;
Calculating the degree of superheat from the acquired temperature and pressure of the refrigerant;
10. The cooling system control method of claim 9, further comprising: opening the expansion valve to block the refrigerant compressed in the compressor from being transferred to the gas-liquid separator when the obtained refrigerant water level is lower than the reference gas-liquid separation water level and the calculated superheat degree is equal to or higher than a predetermined reference superheat degree. The cooling system control method according to claim 10, further comprising a step of returning the operating speed of the compressor to the normal speed when the obtained refrigerant water level is less than the reference gas-liquid separation water level, the calculated superheat degree is equal to or greater than a predetermined reference superheat degree, and the operating speed of the compressor is slower than a predetermined normal speed. obtaining a pressure of a refrigerant entering the compressor;
8. The cooling system control method of claim 7, further comprising: when the obtained pressure of the refrigerant flowing into the compressor is equal to or lower than a predetermined stop pressure, transmitting the refrigerant compressed in the compressor to the gas-liquid separator.

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