JP2003202131A - Coolant natural circulation type cooling system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a coolant natural circulation type cooling system capable of obtaining stable cooling capacity. <P>SOLUTION: In the coolant natural circulation type cooling system, coolant naturally circulates along a channel between a condenser 30 disposed on a high place and evaporators 42 of indoor machines A-N disposed lower than the condenser 30. A control part 12 makes opening of a flow regulating valve 40 approximately full open at the time of starting operation. Then, a detection value of a coolant temperature sensor 10 is inputted to the control part 12. When the temperature of the coolant drops below a prescribed set value, that is, the natural circulation is judged to be stable, the control part 12 makes the flow regulating valve 40 initial opening and performs degree of super heat control. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a refrigerant natural circulation type cooling system, and more particularly to a refrigerant natural circulation type cooling system having improved control of a flow rate control valve for adjusting the amount of refrigerant liquid flowing into an evaporator.

[0002]

2. Description of the Related Art Conventionally, a refrigerant is used as a working medium, and the refrigerant is naturally circulated by a difference in specific gravity between a gas and a liquid due to a gas-liquid phase change accompanying condensation and evaporation of the refrigerant and a pressure difference between constituent devices
A refrigerant natural circulation type cooling system for cooling is used.

FIG. 6 is a schematic diagram showing a conventional refrigerant natural circulation type cooling system.

As shown in FIG. 6, a condenser 30 of a heat exchanger arranged at a high place of a building includes a cold water pipe 32 and a pump 34.
Refrigerant gas is cooled and liquefied by cold water or the like supplied by. The coolant liquid liquefied by the condenser 30 is
The refrigerant liquid pipe 36 descends due to gravity. The liquid reservoir 38
Is provided at a position lower than the condenser 30, and can store the refrigerant liquid that has been cooled and liquefied in the condenser 30.

The refrigerant liquid is supplied to the evaporator 42 through the flow rate control valve 40 in front of the indoor units A, B to N provided in each cooling area. In this way, since the refrigerant liquid is supplied to the evaporator 42 by its own weight, the condenser 30 is installed at a position higher than the evaporator 42. The flow rate control valve 40 supplies the refrigerant liquid to the evaporator 42, and the pressure of the refrigerant liquid is reduced and expanded in the evaporator 42. Further, the flow rate control valve 40 is closed when the cooling system is stopped, and is opened during operation to perform superheat degree control as described later to adjust the amount of refrigerant liquid supplied to the evaporator 42.

In the evaporator 42, heat is exchanged between the air sent from the blower 43 and the refrigerant liquid, the air is cooled and the room is cooled, and the refrigerant liquid is absorbed by heat and evaporated. The refrigerant gas rises through the refrigerant gas pipe 44 and is supplied to the condenser 30. In the condenser 30, the refrigerant gas is cooled and liquefied again.

As described above, in the refrigerant natural circulation type cooling system, the natural circulation of the refrigerant is established by the gravity acting on the refrigerant and the pressure difference between the condenser and the evaporator.

Next, the control of the conventional flow control valve will be described.

A refrigerant gas temperature sensor 46 for detecting the temperature of the refrigerant gas flowing out of the evaporator 42 and a pressure of the refrigerant gas flowing out of the evaporator 42 are provided near the outlet of the evaporator 42 of each indoor unit A-N. A refrigerant gas pressure sensor 48 for detecting is provided. A room temperature sensor 50 for detecting the room temperature is provided near the indoor air inlets to the indoor units A to N. The outputs of the refrigerant gas temperature sensor 46, the refrigerant gas pressure sensor 48, and the room temperature sensor 50 are input to the controller 52. As a result, the control unit 52 causes the sensors 46, 48,
Based on the output of 50, superheat control is performed to control the opening of the flow rate control valve 40 so that the refrigerant gas flowing out from the evaporator 42 maintains a predetermined superheat.

This superheat control method is disclosed, for example, in Japanese Examined Patent Publication No. 7-117254.
As shown in FIG. 2 of the publication, the control unit 52 opens the flow rate control valve 40 to a preset opening (initial opening), and the refrigerant gas temperature detected by the refrigerant gas temperature sensor 46 is higher than the set value. When, or when the refrigerant gas pressure detected by the refrigerant gas pressure sensor 48 becomes lower than the set value, or when the room temperature detected by the room temperature sensor 50 becomes higher than the set value, the flow rate control valve 40 is opened. Direction to control the amount of refrigerant liquid flowing into the evaporator 42. In the opposite situation, the flow rate control valve 40 is controlled in the closing direction, and if the detection values detected by the sensors 46, 48, 50 are substantially the same as the set value, the flow rate control valve 40 is closed. Maintain the opening. In this way, the control unit 52 adjusts the amount of the refrigerant liquid flowing into the evaporator 42 and controls the refrigerant gas evaporated in the evaporator 42 so as to maintain a predetermined degree of superheat.

[0011]

In the refrigerant natural circulation type cooling system, the amount of the refrigerant supplied to the evaporator is adjusted by the superheat control as described above. However, when the amount of the refrigerant liquid is adjusted by superheat control at the start of operation of the cooling system, the following problems occur.

[0012] For example, during operation stop, the temperature and pressure of the refrigerant in the cooling system fluctuate due to the outside air. For example, in the hot season of summer, the temperature and pressure of the refrigerant in the cooling system are higher than during operation of the cooling system, and a part of the refrigerant liquid in the refrigerant liquid pipe 36 and the liquid reservoir 38 is evaporated, The refrigerant liquid pipe 36 and the liquid reservoir 38 are in a gas-liquid two-phase state.

At the start of operation, cold water is supplied to the condenser 30 from the cold water pipe 32, and the flow rate control valve 40
Is opened to the initial opening.

When cold water is supplied to the condenser 30, the refrigerant in the condenser 30 is cooled and condensed, and the pressure of the condenser 30 drops sharply. For this reason, the stable pressure balance is lost, and the refrigerant gas in the refrigerant gas pipe 44 and the refrigerant liquid in the refrigerant liquid pipe 36 tend to move to the condenser 30 side, which hinders the natural circulation of the refrigerant.

Further, since the refrigerant in the refrigerant liquid pipe 36 and the refrigerant in the liquid reservoir 38 are in a gas-liquid two-phase state, the refrigerant liquid passes through the flow rate adjusting valve 40 even if the flow rate adjusting valve 40 is opened to the initial opening. Therefore, the position head is small, and the refrigerant liquid is not rapidly supplied to the evaporator 42. Therefore, there is a problem that it takes time to obtain the cooling effect.

Further, since the amount of the refrigerant liquid supplied to the evaporator 42 is small at the start of the operation as described above, the evaporator 42 is
The degree of superheat of the refrigerant gas that evaporates becomes large. For this reason,
The control unit 52 controls the flow rate control valve 40 in the opening direction.
After that, when the refrigerant gas is cooled and liquefied in the condenser 40 and the refrigerant liquid is started to be supplied to the liquid reservoir 38 and the refrigerant liquid pipe 36, the opening degree of the flow rate control valve 40 becomes excessively large, and an excessive amount is supplied to the evaporator 42. Refrigerant liquid flows in. As a result, a so-called liquid back state occurs in which the refrigerant liquid that cannot be evaporated in the evaporator 42 flows out into the refrigerant gas pipe 44 in a liquid state. When the liquid back state occurs, the refrigerant gas in the refrigerant gas pipe 44 decreases and the pressure loss of the refrigerant gas pipe 44 also increases. For this reason,
A decrease in the refrigerant gas and a decrease in the condensation temperature of the condenser 30 occur, and the cooling capacity of the cooling system decreases.

In particular, at the start of the cooling system operation in the morning after the cooling system is stopped at night, the above-mentioned problems occur remarkably, and it takes time to obtain the cooling effect.

Therefore, the present invention has been made to solve the above problems, and improves the control of a flow rate control valve for controlling the amount of refrigerant liquid flowing into an evaporator to provide a stable cooling capacity. It is an object of the present invention to provide a refrigerant natural circulation type cooling system that can be used.

[0019]

A refrigerant natural circulation type cooling system of the present invention includes a condenser for cooling and liquefying a refrigerant gas,
The evaporator that evaporates the refrigerant liquid, the flow rate control valve that adjusts the amount of the refrigerant liquid that flows into the evaporator, and the opening degree of the flow rate control valve so that the refrigerant gas that flows out of the evaporator maintains a predetermined degree of superheat. A control means for controlling superheat degree to control, in a refrigerant natural circulation type cooling system for cooling by naturally circulating the refrigerant along the flow path between the condenser and the evaporator, the control means is at the start of operation. In, the opening of the flow rate control valve is almost fully opened.

Further, the control means of the refrigerant natural circulation type cooling system of the present invention is characterized in that the superheat control is started after the natural circulation of the refrigerant is stabilized.

Further, the refrigerant natural circulation type cooling system of the present invention further comprises a refrigerant liquid temperature sensor for detecting the temperature of the refrigerant liquid flowing into the evaporator, and the control means is such that the refrigerant liquid temperature sensor has a predetermined temperature. When it is detected, it is determined that the natural circulation of the refrigerant is stable, and superheat control is started.

Further, the refrigerant natural circulation type cooling system of the present invention further comprises a refrigerant liquid pressure sensor for detecting the pressure of the refrigerant liquid flowing into the evaporator, and a refrigerant gas for detecting the pressure of the refrigerant gas flowing out of the evaporator. A pressure sensor, and the control means is
When the pressure detected by the refrigerant liquid pressure sensor and the refrigerant gas pressure sensor has a predetermined pressure difference, it is determined that the natural circulation of the refrigerant is stable, and the superheat control is performed.

[0023]

BEST MODE FOR CARRYING OUT THE INVENTION Preferred embodiments of the present invention (hereinafter referred to as embodiments) will be described below with reference to the drawings.

First Embodiment FIG. 1 is a diagram showing a refrigerant natural circulation type cooling system according to a first embodiment. The same elements as those in the conventional example shown in FIG. 6 are designated by the same reference numerals.

As shown in FIG. 1, a condenser 30 for cooling and liquefying the refrigerant gas, a liquid reservoir 38 for storing the refrigerant liquid chilled and liquefied by the condenser 30, and a position lower than the condenser 30 and the liquid reservoir 38. An evaporator 42 for evaporating the refrigerant liquid is provided in each of the indoor units A to N. The condenser 30 and the evaporator 42 are connected by a refrigerant liquid pipe 36 serving as a refrigerant liquid passage and a refrigerant gas pipe 44 serving as a refrigerant gas passage, and the liquid reservoir 38 is a condenser. It is provided in the refrigerant liquid pipe 36 at a position lower than 30. A flow rate control valve 40 that adjusts the amount of the refrigerant liquid in the evaporator 42 is provided in front of each of the indoor units A to N.

At the outlet of the evaporator 42 of each of the indoor units A to N, a refrigerant gas temperature sensor 46 for detecting the temperature of the refrigerant gas flowing out of the evaporator 42 and indoor air to the indoor units A to N are provided. Near the inlet, a room temperature sensor 50 for detecting room temperature,
Is provided. Further, in the present embodiment, the refrigerant liquid temperature sensor 10 that detects the temperature of the refrigerant liquid flowing into the evaporator 42 is provided. For example, the refrigerant liquid temperature sensor 10 is provided at the inlet of the evaporator 42. The detected values of the refrigerant liquid temperature sensor 10, the refrigerant gas temperature sensor 46, and the room temperature sensor 50 are input to the control unit 12. As a result, the control unit 12 controls the flow rate control valve 40, which is characteristic of the present embodiment, which will be described later, based on the detection values of the sensors 10, 46, 50.

In the refrigerant natural circulation type cooling system of this embodiment, the natural circulation of the refrigerant is performed as described in the conventional example. That is, the condenser 30 cools and liquefies the refrigerant gas with cold water or the like supplied from the cold water pipe 32. The refrigerant liquid descends in the refrigerant liquid pipe 36 via the liquid reservoir 38 due to gravity. It is supplied to the evaporator 42 via the flow rate control valve 40. In the evaporator 42, the pressure of the refrigerant liquid decreases and expands, heat is exchanged between the air sent by the blower 43 and the refrigerant liquid, the air is cooled to cool the room, and the refrigerant liquid absorbs heat. It is evaporated. The refrigerant gas rises through the refrigerant gas pipe 44 and is supplied to the condenser 30. In the condenser 30,
The refrigerant gas is liquefied as a cooling liquid again.

A feature of this embodiment is that the flow control valve is controlled as follows.

FIG. 2 is a flow chart showing the control of the flow rate control valve in the refrigerant natural circulation type cooling system of this embodiment.

As shown in FIG. 2, when the operation of the cooling system is started (S10), the operation of the blower 43 is started (S12). The room temperature (T50) detected by the room temperature sensor 50 and the room temperature set value (Tas) preset by the user or the like are input to the controller 12. The control unit 12 controls the room temperature (T
It is confirmed whether or not 50) is higher than the room temperature set value (Tas) (S14). When the room temperature is higher than the room temperature set value (Yes in S14), the controller 12 causes the flow control valve 40 to be fully opened (S16).

As described above, since the flow rate adjusting valve 40 is almost fully opened at the start of the operation, the resistance of the flow rate adjusting valve 40 can be reduced and the refrigerant liquid can be quickly supplied to the evaporator 42. You can As a result, the pressure balance of the cooling system can be stabilized, and the natural circulation of the refrigerant can be started early.

In the subsequent flow, the superheat control is started after the natural circulation of the refrigerant is stabilized after the flow control valve is fully opened.

In the present embodiment, it is determined that the natural circulation of the refrigerant is stable, based on the value detected by the refrigerant liquid temperature sensor 10. That is, the temperature (T10) of the refrigerant liquid detected by the refrigerant liquid temperature sensor 10 is input to the control unit 12, and the control unit 12 determines that the temperature (T10) of the refrigerant liquid is lower than the preset temperature (Tps) of the refrigerant liquid. It is determined whether or not (S1
6). It is preferable that the predetermined temperature of the coolant liquid is set and set to the temperature of the coolant liquid that normally normally circulates. The temperature (T10) of the refrigerant liquid is the set temperature (Tp) of the refrigerant liquid.
If it becomes lower than (s) (Yes in S18), the flow control valve 4
The initial opening degree is set to 0 (S20), and superheat control is started (S22).

In the present embodiment, the refrigerant liquid temperature sensor 1
0 detects the temperature of the refrigerant liquid at the inlet of the evaporator 42, so that it is possible to detect that the refrigerant liquid cooled and liquefied in the condenser 30 has flowed down. Thereby, it can be determined that the natural circulation of the refrigerant is stable. After the detection, the opening degree of the flow rate control valve 40 is set to the initial opening degree, so that it is possible to prevent an excessive amount of the refrigerant liquid from flowing into the evaporator 42, and to prevent a so-called liquid back state.

The initial opening is the opening of the flow control valve set in consideration of the height difference between the condenser and the evaporator, the pipe lengths of the refrigerant liquid pipe and the refrigerant gas pipe, and the peak cooling load, In the superheat control, the opening is controlled in the opening direction or the closing direction so that the refrigerant gas flowing out of the evaporator from the initial opening maintains a predetermined superheat.

Further, the superheat degree control of this embodiment (S22)
In the above, the difference between the temperature of the refrigerant gas flowing out of the evaporator and the temperature of the refrigerant liquid flowing into the evaporator is taken as the degree of superheat of the refrigerant gas, and the flow control valve is opened so that this degree of superheat maintains a predetermined degree of superheat. Control the degree.

More specifically, for example, the control unit 12 informs the controller 12 of the temperature of the refrigerant gas (T46) detected by the refrigerant gas temperature sensor 46 and the temperature of the refrigerant liquid detected by the refrigerant liquid temperature sensor 10 ( T10) is input and the difference is calculated to calculate the degree of superheat (THS). The control unit 12 controls the degree of superheat (T
If the (HS) is greater than a predetermined superheat degree, the flow rate control valve 4
The opening degree of 0 is controlled in the opening direction to increase the amount of the refrigerant liquid flowing into the evaporator 42 and reduce the degree of superheat of the refrigerant gas. On the contrary, when the degree of superheat (THS) is smaller than the predetermined degree of superheat, the opening degree of the flow rate control valve 40 is controlled in the closing direction to reduce the amount of the refrigerant liquid flowing into the evaporator 42 to reduce the amount of the refrigerant gas. Increase superheat.

Further, in this embodiment, the control unit 12 has
The room temperature (T50) detected by the room temperature sensor 50 is input, and the control unit 12 determines whether the room temperature (T50) is lower than the room temperature set value (Tas) (S24). When the room temperature is lower than the room temperature set value (Yes in S24), the flow rate control valve 40 is closed (fully closed) (S26). When the room temperature becomes higher than the room temperature set value again (S14), the flow rate control valve 4
The opening degree of 0 is almost fully opened (S16), and the above-described flow is repeated. As described above, since the flow rate control valve 40 is closed in step S26, it becomes possible to prevent an excessive amount of the refrigerant liquid from flowing into the evaporator 42. Further, in step S16, when the operation is restarted after the flow rate control valve 40 is closed, the flow rate control valve 40 is almost fully opened, so that the refrigerant liquid can be supplied to the evaporator 42 more quickly. .

As described above, at the start of the operation, the control is performed such that the opening of the flow rate control valve is almost fully opened. Therefore, the natural circulation of the refrigerant can be stabilized earlier, and the stable operation can be achieved. Can provide cooling capacity.

Embodiment 2 FIG. 3 is a view showing a refrigerant natural circulation type cooling system of Embodiment 2. The same elements as those in the conventional example shown in FIGS. 1 and 6 are designated by the same reference numerals.

A characteristic point of this embodiment is that a refrigerant liquid pressure sensor and a refrigerant gas pressure sensor are provided, and the natural circulation of the refrigerant is stabilized when the pressure detected by these sensors reaches a predetermined pressure difference. That is, the superheat control is started.

As shown in FIG. 3, a refrigerant liquid pressure sensor 14 for detecting the pressure of the refrigerant liquid flowing into the evaporator 42, a refrigerant gas pressure sensor 16 for detecting the pressure of the refrigerant gas flowing out of the evaporator 42, An auxiliary control unit 18 that receives the detection values of the sensors 14 and 16 and performs a predetermined calculation is provided. In the present embodiment, the refrigerant liquid pressure sensor 14 is provided near the end of the vertical pipe portion before the refrigerant liquid pipe 36 bends substantially horizontally toward the indoor units A to N, and the refrigerant gas pressure sensor 16 is condensed. It is provided in the refrigerant gas pipe 44 near the container 30.

FIG. 4 is a flow chart showing the control of the flow control valve in the cooling system of this embodiment.

In this embodiment, the determination step of S16 of the flowchart of the first embodiment is different. That is, the pressure (P14) of the refrigerant liquid detected by the refrigerant liquid pressure sensor 14 and the pressure (P16) of the refrigerant gas detected by the refrigerant gas pressure sensor 16 are input to the auxiliary control unit 18. The auxiliary control unit 18
The differential pressure (P14-P16) between the pressure of the refrigerant liquid (P14) and the pressure of the refrigerant gas (P16) is calculated, and the differential pressure is a predetermined set value (ΔP
It is determined whether or not it is larger than (s) (S28). This result is supplied to each control unit 12, and when the differential pressure is large, each control unit 12 sets the flow rate control valve 40 to the initial opening degree (S20).

The determination steps other than S28 are the same as those in the first embodiment.
The detailed description is omitted here.

In this embodiment, in particular, the refrigerant liquid pressure sensor 14 and the refrigerant gas pressure sensor 16 are provided to judge that the natural circulation of the refrigerant is stable.
It is possible to speed up the responsiveness by detecting the temperature.

Third Embodiment FIG. 5 is a diagram showing a refrigerant natural circulation type cooling system according to a third embodiment. The same elements as those shown in FIGS. 1, 3 and 6 are designated by the same reference numerals and the description thereof will be omitted.

The present embodiment differs from the second embodiment in that the refrigerant gas pressure sensor 16 is provided at the outlet of each evaporator 42.

In this embodiment, the refrigerant hydraulic pressure sensor 1 is used.
The pressure (P14) of the refrigerant liquid detected by 4 is input to each control unit 12 via the auxiliary control unit 18. The pressure of the refrigerant gas at the outlet of the evaporator 42 detected by each refrigerant gas pressure sensor 16 (P
16) are input to the control unit 12, respectively. Each control unit 1
2 is the pressure of the refrigerant liquid (P14) and the pressure of the refrigerant gas (P16)
The differential pressure (P14-P16) is calculated, and it is determined whether the differential pressure is larger than a predetermined set value (ΔPs) (S2).
8). When the differential pressure is large, the flow control valve 4
0 is set to the initial opening (S20) (see S28 in the flowchart of FIG. 4).

As described above, since the refrigerant gas pressure sensor 16 is provided at the outlet of each evaporator 42, the flow control valve 40 is controlled corresponding to each indoor unit in consideration of the difference in response of each indoor unit. can do.

Although the superheat control described in the first embodiment is performed in the first to third embodiments, the superheat control applicable to the present invention is not limited to this method.

Further, a refrigerant liquid temperature sensor, a refrigerant liquid pressure sensor,
The installation position of the refrigerant gas pressure sensor is not limited to the position described in the embodiment, but can be installed at a desired position.

[0053]

As described above, according to the present invention, the opening degree of the flow rate control valve is almost fully opened at the start of operation, so that stable cooling capacity can be provided.

Further, since various sensors are provided and it is determined that the natural circulation of the refrigerant is stable at the start of the operation, and the superheat control is started after the flow control valve is set to the initial opening, the evaporator is started. It is possible to control the inflow of the refrigerant liquid more than necessary and suppress the liquid back state.

[Brief description of drawings]

FIG. 1 is a diagram showing a refrigerant natural circulation type cooling system according to a first embodiment.

FIG. 2 is a flowchart showing control of a flow rate control valve in the refrigerant natural circulation type cooling system according to the first embodiment.

FIG. 3 is a diagram showing a refrigerant natural circulation type cooling system according to a second embodiment.

FIG. 4 is a flowchart showing control of a flow rate control valve in the refrigerant natural circulation type cooling system according to the second embodiment.

FIG. 5 is a diagram showing a refrigerant natural circulation type cooling system according to a third embodiment.

FIG. 6 is a configuration diagram schematically showing a conventional refrigerant natural circulation type cooling system.

[Explanation of Codes] 10 Refrigerant Liquid Temperature Sensor, 12 Control Unit, 14 Refrigerant Liquid Pressure Sensor, 16 Refrigerant Gas Pressure Sensor, 18 Auxiliary Control Unit,
30 condenser, 32 cold water piping, 34 pump, 36
Refrigerant liquid pipe, 38 Liquid reservoir, 40 Flow rate control valve, 42 Evaporator, 44 Refrigerant gas pipe, 46 Refrigerant gas temperature sensor, 4
8 Refrigerant gas pressure sensor, 50 Room temperature sensor, A to N Indoor unit.

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Tsuneo Yumikura             2-6-2 Otemachi 2-chome, Chiyoda-ku, Tokyo             Ryoden Building Techno Service Co., Ltd. F-term (reference) 3L060 AA05 CC04 CC16 DD08 EE09

Claims (4)

[Claims] 1. A condenser for cooling and liquefying a refrigerant gas, an evaporator for evaporating the refrigerant liquid, a flow rate control valve for adjusting the amount of the refrigerant liquid flowing into the evaporator, and a refrigerant gas flowing out of the evaporator are predetermined. Control means for controlling the opening degree of the flow rate control valve so as to maintain the superheat degree of, and cooling is performed by naturally circulating the refrigerant along the flow path between the condenser and the evaporator. In the refrigerant natural circulation type cooling system, the control means causes the opening degree of the flow rate control valve to be almost fully opened at the time of starting the operation. 2. The refrigerant natural circulation type cooling system according to claim 1, wherein the control means starts superheat control after the natural circulation of the refrigerant is stabilized. . 3. The refrigerant natural circulation type cooling system according to claim 2, further comprising a refrigerant liquid temperature sensor for detecting a temperature of the refrigerant liquid flowing into the evaporator, wherein the control means has the refrigerant liquid temperature sensor. Is a predetermined temperature, it is determined that the natural circulation of the refrigerant is stable, and superheat control is started. 4. The refrigerant natural circulation type cooling system according to claim 2, further comprising a refrigerant liquid pressure sensor for detecting the pressure of the refrigerant liquid flowing into the evaporator, and the pressure of the refrigerant gas flowing out of the evaporator. And a refrigerant gas pressure sensor, wherein the control means determines that the natural circulation of the refrigerant is stable when the pressure detected by the refrigerant liquid pressure sensor and the refrigerant gas pressure sensor has a predetermined pressure difference, A refrigerant natural circulation type cooling system characterized by performing superheat control.