WO2019212126A1

WO2019212126A1 - Method of controlling water purifier

Info

Publication number: WO2019212126A1
Application number: PCT/KR2019/001405
Authority: WO
Inventors: Sangjoon Lee; Jongho Park; Kwangyong AN
Original assignee: LG Electronics Inc
Current assignee: LG Electronics Inc
Priority date: 2018-05-03
Filing date: 2019-01-31
Publication date: 2019-11-07
Anticipated expiration: 2020-11-03
Also published as: KR102649978B1; KR20190127133A

Abstract

A method of controlling a water purifier includes sensing a temperature of coolant, and operating a compressor and an agitator according to the sensed temperature of the coolant to cool the coolant. A first control process is performed. The first control process includes starting operation of the compressor when the temperature of the coolant increases to a temperature equal to or greater than a first set temperature and less than a second set temperature, starting intermittent operation of the agitator when the temperature of the coolant decreases to a third set temperature, and stopping the operation of the compressor and the agitator when the temperature of the coolant decreases to a fourth set temperature. A temperature value is decreased in order of the fourth set temperature, the third set temperature, the first set temperature and the second set temperature.

Description

METHOD OF CONTROLLING WATER PURIFIER

The present invention relates to a method of controlling a water purifier.

A water purifier is a device for filtering out harmful elements such as foreign materials or heavy metals contained in water using physical and/or chemical methods.

The prior art described below discloses a so-called direct type water purifier.

The direct type water purifier means a water purifier for coolant supplied through a water tap to a set temperature through a cooling unit and directly supplying water to a consumer without using a water tank, when the consumer pressing a water supply button.

Since the direct type water purifier does not require the water tank, there is no problem that foreign materials are accumulated on the bottom of the water tank and that bacteria propagate in the water tank.

The direct type water purifier includes a coolant tank in which coolant is stored, an evaporator disposed inside the coolant tank at the upper side thereof, a cold water pipe disposed inside the coolant tank at the lower side thereof, and an agitator configured to circulate water in the coolant tank and to enable heat exchange between drinking water flowing along the cold water pipe and the coolant, as disclosed in the prior art.

Specifically, coolant at an upper side and cooled by the evaporator flows downwardly toward the cold water pipe by rotation of an agitator and cold water in the space, in which the cold water pipe is received, flows upwardly toward the evaporator.

In addition, when a lump of ice is generated on the surface of the evaporator to accumulate cold air, since heat exchange is performed by latent heat as well as sensible heat, it is possible to cool drinking water passing through the cold water pipe in a short time, which is advantageous for the direct type water purifier.

The direct type water purifier having such a structure and a method of controlling the same are disclosed in the prior art described below.

According to the method of operating the water purifier disclosed in prior art 1, a compressor and an agitator are controlled not to be simultaneously driven in order to rapidly generate ice on the surface of the evaporator. That is, the agitator is not driven when the compressor is driven and only the agitator is driven after the compressor is stopped.

According to such a control method, there may be a phenomenon wherein ice is excessively generated on a specific portion of the evaporator to restrict the agitator.

In addition, under an initial installation condition or when a consumer discharges a large amount of cold water at one time, the operation time of the compressor increases and ice is excessively generated on an inlet portion of the evaporator, thereby ununiformly generating ice. Therefore, cold water discharge performance may be lowered.

In addition, according to the method operating the water purifier disclosed in prior art 2, the operation conditions of the compressor and the agitator are differentiated according to the temperature of the coolant, thereby increasing reliability of the compressor and improving cooling efficiency. However, according to the operation method of prior art 2, supercooling may be caused.

When the compressor is driven and, at the same time, the agitator continuously rotates at a constant speed, the inside of the coolant tank is maintained in a stabilized state, and a supercooling phenomenon wherein coolant is maintained in a liquid state at a temperature lower than a freezing temperature may occur.

Since coolant is phase-changed to ice at a freezing temperature or less to secure latent heat, even if the amount of cold water discharged by a user at one time is large, the temperature of the coolant is maintained at the freezing temperature while the coolant is phase-changed from ice to water. Accordingly, there is an advantage that the driving time point of the compressor can be delayed.

However, if a supercooling phenomenon occurs, the coolant has a temperature less than the freezing temperature but is maintained in the liquid state, thus latent heat is not sufficiently secured. As a result, if the amount of cold water discharged by the user at one time is large, the temperature of the coolant rapidly increases by heat delivered from cold water to coolant. Therefore, the amount of power required to operate a cooling cycle is increased, because the driving time point of the compressor is advanced.

In addition, since the temperature of the coolant rapidly increases, the discharge amount of cold water (or the number of glasses of cold water) relatively decreases.

An object of the present invention is to solve the above-described problems.

To achieve the above objects, there is provided a method of controlling a water purifier including sensing a temperature of coolant, and operating a compressor and an agitator according to the sensed temperature of the coolant to cool the coolant, wherein a first control process is performed, the first control process including starting operation of the compressor when the temperature of the coolant increases to a temperature equal to or greater than a first set temperature and less than a second set temperature, starting intermittent operation of the agitator when the temperature of the coolant decreases to a third set temperature, and stopping the operation of the compressor and the agitator when the temperature of the coolant decreases to a fourth set temperature, and wherein a temperature value is decreased in order of the fourth set temperature, the third set temperature, the first set temperature and the second set temperature.

The method of controlling the water purifier according to the embodiment of the present invention including the above configuration has the following effects.

First, by differently setting the operation conditions of the compressor and the agitator according to the use condition or installation condition of the water purifier, it is possible to improve reliability of the compressor and energy efficiency and to uniformly generate ice in the vicinity of the evaporator.

Second, under the operation condition in which the temperature of the coolant is high due to a large discharge amount of cold water or a long power off time of the water purifier, only the compressor is initially driven and both the compressor and the agitator are driven after the coolant is cooled to a set temperature or less, thereby improving reliability of the compressor and rapidly cooling the coolant.

Third, by simultaneously driving the compressor and the agitator when the coolant is in a specific temperature range, it is possible to uniformly maintain the temperature of the coolant in the coolant tank.

Fourth, when the coolant is in a specific temperature range, only the compressor is initially driven and the agitator is intermittently driven at a predetermined time interval after the coolant is cooled to a set temperature or less, thereby preventing a supercooling phenomenon wherein ice is not generated at a freezing temperature or less.

Fifth, by preventing a supercooling phenomenon, the coolant is rapidly phase-changed to ice upon reaching the freezing temperature. Upon heat exchange with discharged cold water, only phase change occurs without temperature change and, as a result, the driving time point of the compressor can be maximally delayed.

FIG. 1 is an exploded perspective view of a cold water generation unit configuring a water purifier, to which a control method according to an embodiment of the present invention is applied.

FIG. 2 is a perspective view of the cold water generation unit when an insulation case is removed.

FIG. 3 is a vertical sectional view taken along line 3-3 of FIG. 3.

FIG. 4 is a flowchart illustrating a control method for preventing supercooling and reducing power consumption of the water purifier according to an embodiment of the present invention.

Hereinafter, a method of controlling a water purifier according to an embodiment of the present invention will be described in detail with reference to the drawings and flowchart.

FIG. 1 is an exploded perspective view of a cold water generation unit configuring a water purifier, to which a control method according to an embodiment of the present invention is applied, FIG. 2 is a perspective view of the cold water generation unit when an insulation case is removed, and FIG. 3 is a vertical sectional view taken along line 3-3 of FIG. 3.

Referring to FIGS. 1 to 3, the cold water generation unit 30 according to the embodiment of the present invention may include a coolant tank 33 filled with coolant, an insulation case 31 surrounding the coolant tank 33 to prevent heat exchange between the coolant and indoor air, a drain valve 32 passing through the insulation case 31 to communicate with the internal space of the coolant tank 33, a cold water pipe 34 accommodated in the coolant tank 33, a partitioner 36 accommodated in the coolant tank 33 in a state of being placed on the cold water pipe 34, an evaporator 35 placed on the partitioner 36, a tank cover 37 covering the upper end of the coolant tank 33, an agitating motor 38 fixed to the inner side of the tank cover 37 and having a rotation shaft extending downwardly, an agitator 39 accommodated in the coolant tank 33 and connected to the rotation shaft of the agitating motor 38, and a case cover 40 covering the opened upper surface of the insulation case 31.

Specifically, the drain valve 32 is installed to pass through the insulation case 31 and the coolant tank 33, and is inserted through the side surface of the insulation case 31 corresponding to a position adjacent to the bottom of the coolant tank 33. When the drain valve 32 is opened, the coolant stored in the coolant tank 33 is discharged from the water purifier 10.

In addition, the insulation case 31 is made of an insulation member such as Styrofoam and the insulation case 31 may be seated on a tank support part 21.

In addition, the cold water pipe 34 is wound in a spiral shape as shown in the figure to have a cylindrical shape, and pipes vertically adjacent to each other may be in contact with each other or spaced apart from each other. The inlet end 341 and outlet end 342 of the cold water pipe 34 may vertically extend toward the case cover 40. The inlet end 341 of the cold water pipe 34 may be connected to a water pipe connected to a water supply source and the outlet end 342 may be connected to a water pipe connected to the water outlet port of the water purifier.

In addition, the partitioner 35 is placed on the cold water pipe 34 to partition the internal space of the coolant tank 33 into a first space, in which the evaporator 35 is received, and a second space, in which the cold water pipe 34 is received. Accordingly, ice formed in the vicinity of the evaporator 35 cannot move into the second space.

In addition, the evaporator 35 is wound in a spiral shape and is seated on the outer circumferential surface of the partitioner 36. The evaporator 35 is connected to the outlet end of an expansion valve connected to the outlet end of a condenser 19. Refrigerant flowing along a refrigerant pipe forming the evaporator 35 exchanges heat with the coolant stored in the coolant tank 33, thereby cooling the coolant. The coolant exchanges heat with the drinking flowing along the cold water pipe 34, thereby cooling the drinking water to a set temperature.

The coolant may be frozen on the surface of the evaporator 35, thereby generating a lump of ice having a predetermined size. That is, cold refrigerant in the evaporator freezes the coolant through heat absorption, such that the lump of ice accumulates latent heat of melting. That is, even in a state where the compressor 18 is not driven, coolant in an ice state and coolant in a liquid state exchange heat with each other by agitating operation of the agitator 39, such that the coolant in the liquid state is maintained at a reference temperature or less.

The water purifier according to the embodiment of the present invention may be defined as an ice thermal storage type water purifier, because some of coolant is present in an ice state on the surface of the evaporator to store latent heat. Since the ice thermal storage type water purifier may use latent heat as well as sensible heat for heat exchange, cold water discharge performance is significantly better than a non-ice thermal storage type water purifier using only sensible heat.

In addition, the tank cover 37 is provided on the upper end of the coolant tank 33, thereby covering the upper surface of the first space. That is, the first space may be defined between the tank cover 37 and the partitioner 36 and the second space may be defined between the partitioner 36 and the bottom of the coolant tank 33. A coolant inlet port 371 may be formed in one side of the tank cover 37. The coolant inlet port 371 may be connected to a water pipe connected to the water supply source to supply coolant to the coolant tank 33.

In addition, the agitator 39 may be substantially located at an intermediate point of the second space, without being limited thereto. When the agitator 39 rotates, the coolant of the second space flows into the first space to exchange heat with the evaporator 35 or the ice generated on the surface of the evaporator 35, and the coolant of the first space flows into the second space, such that the temperature of the coolant is uniformly maintained at every point of the coolant tank 33. The coolant cooled through heat exchange exchanges heat with drinking water flowing along the cold water pipe 34, thereby cooling the drinking water to a defined cold water temperature or less. Here, the defined cold water temperature may be in a range of 7℃ to 8℃, without being limited thereto.

The agitator 39 may be formed in a blade or impeller shape extending from the rotation shaft in a radial direction as shown in the figure, but is not limited thereto and may be formed in various shapes.

Meanwhile, the case cover 40 is fitted on the outer circumferential surface of the upper end of the insulation case 31 to cover the opened upper surface of the coolant tank 33 and the insulation case 31. A port accommodation hole 401, through which the coolant inlet port 371 passes to be exposed to the outside, may be formed in the case cover 40. A cold water pipe guide groove 402, through which the inlet end 341 and the outlet end 342 of the cold water pipe 34 pass, may be formed in the edge of one side of the case cover 40. An evaporation pipe guide hole 403, through which the pipe of the evaporator 35 passes, may be formed in the edge of the other side of the case cover 40.

In addition, a temperature sensor (not shown) for sensing the temperature of the coolant may be installed on one side of the inside of the coolant tank 33, and the temperature sensor may include a thermistor. The temperature sensor may be placed in the first space close to the evaporator or may be placed in the second space close to the cold water pipe 34.

For example, the temperature sensor may be placed at a position relatively closer to the evaporator 35 to sense not only the temperature of the coolant but also the temperature of ice which is generated on the surface of the evaporator 35 and is in contact with the temperature sensor.

In addition, although not shown, a cooling cycle including an evaporation pipe is provided in the water purifier, in which the cold water generation unit 30 is installed, at the one side thereof. The cooling cycle includes a compressor for compressing refrigerant, a condenser for condensing the refrigerant passing through the compressor, an expansion valve for expanding the refrigerant passing through the condenser, and the evaporation pipe connected to the outlet end of the expansion valve.

Hereinafter, the method of controlling the water purifier according to the embodiment of the present invention will be described in detail with reference to the flowchart.

Referring to FIG. 4, the control method according to the embodiment of the present invention uses the temperature of the coolant sensed by the temperature sensor as a variable.

Specifically, in a state where the water purifier is powered on, the temperature sensor senses the temperature of the coolant (coolant temperature; CT) at a predetermined time interval (S11). The sensed temperature value is transmitted to a controller of the water purifier and is compared with a set temperature.

More specifically, whether the temperature of the coolant is less than a first set temperature T1 is determined. The first set temperature T1 may be an upper limit temperature of the coolant for driving the compressor. Accordingly, when the temperature of the coolant is less than the first set temperature T1, the compressor is not driven. The first set temperature T1 may be set to 1℃, without being limited thereto.

In addition, upon determining that the temperature of the coolant is equal to or greater than the first set temperature T1 and is less than a second set temperature T2 (S14), only the compressor is turned on and the agitator is maintained in the stopped state (S15). In this state, the cooling cycle is driven by driving of the compressor and the temperature of the evaporation pipe is decreased to perform heat exchange between the rcoolant and the two-phase refrigerant which is at a low-temperature and low-pressure two-phase refrigerant in the evaporation pipe, thereby gradually decreasing the temperature of the coolant. The second set temperature T2 may be set to 10℃, without being limited thereto.

Upon determining that the temperature of the coolant decreases to a third temperature (T3) (S16), the agitator intermittently operates (S17). Specifically, the agitator may repeatedly perform operation of rotating during a first set time and then maintaining the stopped state during a second set time. Here, the third temperature may be set to -1.5℃, without being limited thereto. The first set time may be set to 15 seconds and the second set time may be set to 45 seconds, without being limited thereto.

The agitator operates at the third temperature T3 in order to prevent a supercooling phenomenon wherein the coolant is not phase-changed to ice although the temperature of the coolant decreases to a freezing temperature or less.

When the temperature of the coolant reaches the freezing temperature, the coolant is normally phase-changed to ice while constantly maintaining the freezing temperature. However, the coolant may not be phase-changed and may be maintained in a supercooling state. Since such a supercooling phenomenon occurs when the coolant is in a stabilized state, it is necessary to destroy the stabilized state of the coolant.

Even if the agitator rotates at a constant rotation speed in a state where the coolant is in a liquid state, the coolant may be maintained in the stabilized state so as not to generate ice on the evaporation pipe.

Accordingly, when the temperature of the coolant decreases to the freezing temperature or less, intermittent operation of repeating rotation and stoppage of the agitator is performed, thereby rapidly generating ice nucleus in the vicinity of the freezing temperature to be grown into a lump of ice. Since rotation and stoppage of the agitator are periodically repeated in a state where the temperature of the coolant decreases to a temperature equal to or less than the freezing temperature, that is, the third temperature T3, even if the supercooling phenomenon occurs, the stabilized state is destroyed by the intermittent operation of the agitator, thereby generating ice nucleus.

The driving time of the agitator may be set to be less than the stop time, may be set to be equal to the stop time, or may be set to be greater than the stop time.

The agitator rotates to circulate the coolant, such that the temperature of the coolant is uniformly maintained at every point of the coolant case.

Meanwhile, whether the temperature of the coolant increases during the intermittent operation of the agitator is determined (S18). Specifically, when cold water is discharged by a user while the cooling cycle operates, the temperature of the coolant may be increased.

If the cold water is discharged while the coolant is cooled and thus the temperature of the coolant is increased again, the controller stops the compressor and the agitator until the temperature of the coolant increases to the first set temperature T1 (S20), and the operation of sensing the temperature CT of the coolant is repeated in a state where the water purifier is not powered off.

In other words, when cold water is discharged while the coolant is cooled, even if the temperature of the coolant is less than the upper limit temperature for driving the compressor, that is, the first set temperature T1, the compressor is maintained in the stopped state until the temperature of the coolant increases to the first set temperature T1. For example, when the temperature of the coolant decreases to -2℃ and then increases to -1℃ again, the operation of the compressor is stopped and the stopped state of the compressor is maintained until the temperature of the coolant increases to 1℃.

According to such a control method, since the temperature of the coolant is less than the upper limit value for driving the compressor, the temperature of the cold water substantially discharged by the user is equal to or less than a defined cold water temperature. That is, even if the cooling cycle is stopped, the user does not feel inconvenience in use, and the driving time point of the compressor may be delayed, thereby reducing power consumption.

If the temperature of the coolant increases to a temperature between the first set temperature T1 and the second set temperature T2, the compressor is driven and, when the temperature of the coolant decreases to the third set temperature T3, steps S15 to S17 of intermittently operating the agitator is performed again.

The process of controlling the compressor and the agitator when the temperature of the coolant is between the first set temperature T1 and the second set temperature T2 may be defined as a first control process.

In the first control process, the compress is driven and, at the same time, the agitator intermittently operates, thereby generating ice. When the temperature of the coolant does not increase while the agitator intermittently operates, driving of the compressor and intermittent operation of the agitator are continued until the temperature of the coolant decreases to a fourth set temperature T4. Upon determining that the temperature of the coolant reaches the fourth set temperature T4, the compressor and the agitator are stopped and the control process of the compressor and the agitator according to the temperature of the coolant is repeatedly performed until the water purifier is powered off.

The fourth set temperature T4 may be defined as a lower limit temperature of the coolant for stopping the coolant and may be, for example, set to -2.5℃ without being limited thereto. The fourth set temperature does not mean the temperature of the coolant in the liquid state but means the temperature of ice generated on the surface of the evaporator, brought into contact with the temperature sensor, and sensed by the temperature sensor. That is, the ice generated on the surface of the evaporation pipe is grown until being brought into contact with the temperature sensor, and the cooling cycle operates until the temperature of the generated ice decreases to the fourth set temperature T4, thereby accumulating ice storage energy. When the temperature of the ice decreases to the fourth set temperature T4, the cooling cycle is stopped to prevent a phenomenon wherein the ice is excessively grown to restrict operation of the agitator.

Meanwhile, if the initial temperature of the coolant in step S11 of the control method of the present invention or the temperature of the coolant increased when cold water is discharged while the coolant is cooled is in a range equal to or greater than the second set temperature and less than the fifth set temperature, the compressor is driven (S22) and, at the same time, the agitator operates. At this time, the agitator is controlled to continuously operate (S22 and S23). In addition, the compressor and the agitator are controlled to continuously operate until the temperature of the coolant decreases to the lower limit temperature, that is, the fourth set temperature T4. The fifth set temperature T5 may be set to 27℃ without being limited thereto. The control process of the compressor and the agitator when the temperature of the coolant is between the second set temperature and the fifth set temperature may be defined as a second control process.

Upon determining that the temperature of the coolant increases because the cold water is discharged while the coolant is cooled (S24), as described above, the control process corresponding to the sensed temperature of the coolant is performed. For example, if the increased temperature of the coolant is less than the first set temperature, the compressor and the agitator are maintained in the stopped state until the temperature of the coolant increases to the first set temperature. In addition, when the increased temperature of the coolant is in the temperature range for performing the first control process, that is, between the first set temperature T1 and the second set temperature T2, the first control process is performed again.

In addition, upon determining that the increased temperature of the coolant increases to the temperature for performing the second control process again, the compressor and the agitator are controlled to continuously operate without being stopped.

When a large amount of cold water is discharged by the user at one time, the temperature of the coolant may be in the temperature range for the second control process. Accordingly, in this state, since it is necessary to rapidly decrease the temperature of the coolant and to rapidly grow the ice, the compressor and the agitator may be controlled to simultaneously operate.

Meanwhile, upon determining that the temperature of the coolant is greater than the fifth set temperature T5, only the compressor is driven (S26) and, when the temperature of the coolant decreases to a sixth set temperature T6 (S27), the agitator may continuously operate (S23).

Specifically, the control process of the compressor and the agitator when the temperature of the coolant is greater than the fifth set temperature T5 may be defined as a third control process. When the temperature of the space where the water purifier is installed is considerably high and thus a large amount of heat penetrates into the coolant tank like summer or when the water purifier is first installed and thus the temperature of the coolant is a room temperature, the third control process is performed. The sixth set temperature T6 may be set to 5℃ without being limited thereto.

In a fifth control process, since the temperature of the coolant in the vicinity of the evaporation pipe is preferentially required to decrease to a temperature close to the freezing temperature, only the compressor is driven until the temperature of the coolant decreases to the sixth set temperature T6, such that the coolant is not circulated. When the temperature of the coolant decreases to the sixth set temperature T6 or less, the agitator continuously operates (S23), thereby making the temperature of the coolant uniform and generating ice.

In addition, when cold water is discharged while the coolant is cooled to increase the temperature of the coolant, as described above, the control process corresponding to the increased temperature of the coolant is repeatedly performed.

For example, when cold water is discharged during the third control process to increase the temperature of the coolant to the fifth set temperature or more, operation of the agitator is stopped and is maintained in the stopped state until the temperature of the coolant decreases to the sixth set temperature.

However, when the temperature of the coolant increases to a temperature greater than the first set temperature and less than the fifth set temperature, any one of the first control process and the second control process is performed and, when the temperature of the coolant increases to a temperature less than the first set temperature, driving of the compressor and the agitator is stopped.

Here, when the temperature of the coolant increases while the agitator operates, which control process is performed may be determined based on the increased maximum temperature.

Operations of the compressor and the agitator are differently controlled depending on to which temperature range the temperature of the coolant belongs, thereby reducing power consumption.

In addition, if the temperature of the coolant is in a specific temperature range, the compressor is driven and, at the same time, the agitator intermittently operates, thereby preventing a supercooling phenomenon, improving cooling efficiency and reducing power consumption.

Claims

A method of controlling a water purifier, the method comprising:

sensing a temperature of coolant; and

operating a compressor and an agitator according to the sensed temperature of the coolant to cool the coolant,

wherein a first control process is performed, the first control process including:

starting operation of the compressor when the temperature of the coolant increases to a temperature equal to or greater than a first set temperature and less than a second set temperature;

starting intermittent operation of the agitator when the temperature of the coolant decreases to a third set temperature; and

stopping the operation of the compressor and the agitator when the temperature of the coolant decreases to a fourth set temperature, and

wherein a temperature value is decreased in order of the fourth set temperature, the third set temperature, the first set temperature and the second set temperature.
The method of claim 1, wherein, when the temperature of the coolant sensed in a state where the operation of the compressor and the agitator is stopped is less than the first set temperature, the operation of the compressor and the agitator is maintained in a stopped state until the temperature increases to the first set temperature.
The method of claim 2,

wherein the intermittent operation of the agitator is operation of rotating the agitator during a first set time and stopping the agitator during a second set time, and

wherein the first set time is shorter than the second set time.
The method of claim 3, wherein the first set time is 15 seconds and the second set time is 45 seconds.
The method of claim 3,

wherein, when the temperature of the coolant increases to a temperature equal to or greater than the second set temperature and less than the fifth set temperature, the compressor and the agitator simultaneously operate, and the agitator continuously operates, and

wherein, when the temperature of the coolant decreases to the fourth set temperature, a second control process of stopping the operation of the compressor and the agitator is performed.
The method of claim 5,

wherein, when the temperature of the coolant increases to a temperature equal to or greater than the fifth set temperature, the operation of the compressor starts,

wherein, when the temperature of the coolant decreases to a sixth set temperature, the operation of the agitator starts, and the agitator continuously operates, and

wherein, when the temperature of the coolant decreases to the fourth set temperature, a third control process of stopping the operation of the compressor and the agitator is performed.
The method of claim 6, wherein the sixth set temperature is greater than the first set temperature and is less than the second set temperature.
The method of claim 6,

wherein, when the temperature of the coolant increases during the operation of the agitator, a control process corresponding to the increased temperature value is performed again, and

wherein the increased temperature value is a maximally increased temperature value.
The method of claim 8, wherein, when the temperature of the coolant increases to a temperature less than the first set temperature during the operation of the compressor and the agitator, the operation of the compressor and the agitator is stopped.
The method of claim 6,

wherein the first set temperature is 1℃,

wherein the second set temperature is 10℃ ,

wherein the third set temperature is -1.5℃,

wherein the fourth set temperature is -2.5℃,

wherein the fifth set temperature is 27℃, and

wherein the sixth set temperature is 5℃.