COOLING SYSTEM

Description

TECHNICAL FIELD

The present disclosure relates to a cooling system.

BACKGROUND

In order to efficiently utilize the volume of a refrigerator in a building in a large refrigerated/frozen warehouse, a cooling system is known in which the entire cooling system, including an air cooler for generating cold air, is installed on the rooftop of the building (see, for example, Patent Document 1).

CITATION LIST

Patent Literature

Patent Document 1: U.S. Pat. No. 10,520,232B

SUMMARY

Problems to be Solved

However, since the cooling system described in Patent Document 1 is configured such that an NH₃ refrigerant flows through the air cooler, if the NH₃ refrigerant leaks from the air cooler, the leaked NH₃ refrigerant is likely to leak into the refrigerator.

In view of the above, an object of at least one embodiment of the present disclosure is to provide a cooling system that can effectively reduce the possibility that the NH₃ refrigerant leaks into the refrigerator.

Solution to the Problems

A cooling system according to at least one embodiment of the present disclosure is provided with: an NH₃ refrigeration machine installed on a rooftop of a building and including a refrigeration cycle through which an NH₃ refrigerant circulates; a CO₂ liquefaction unit installed on the rooftop and including a heat exchanger for liquefying a CO₂ refrigerant through heat exchange with the NH₃ refrigerant, and a CO₂ receiver for storing the CO₂ refrigerant liquefied by the heat exchanger; a casing installed on the rooftop and housing at least the CO₂ liquefaction unit; and an air cooler installed outside the casing on the rooftop and configured to generate cold air supplied to a refrigerator in the building through heat exchange with the CO₂ refrigerant from the CO₂ liquefaction unit. The casing includes a first barrier wall through which a CO₂ pipe between the CO₂ liquefaction unit and the air cooler passes and which prevents leakage of the NH₃ refrigerant from the inside of the casing to the air cooler.

Advantageous Effects

According to at least one embodiment of the present disclosure, it is possible to effectively reduce the possibility that the NH₃ refrigerant leaks into the refrigerator.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1A is a schematic diagram of a cooling system according to an embodiment.

FIG. 1B is a schematic diagram of a cooling system according to another embodiment.

FIG. 2A is a schematic diagram showing an air cooler and a surrounding configuration of the air cooler according to an embodiment.

FIG. 2B is a schematic diagram showing an air cooler and a surrounding configuration of the air cooler according to another embodiment.

FIG. 2C is a schematic diagram showing an air cooler and a surrounding configuration of the air cooler according to still another embodiment.

FIG. 3 is a schematic diagram of a cooling system according to an embodiment.

FIG. 4 is a schematic diagram of a cooling system according to another embodiment.

DETAILED DESCRIPTION

Embodiments of the present disclosure will be described below with reference to the accompanying drawings. It is intended, however, that unless particularly identified, dimensions, materials, shapes, relative positions, and the like of components described in the embodiments shall be interpreted as illustrative only and not intended to limit the scope of the present disclosure.

For instance, an expression of relative or absolute arrangement such as “in a direction”, “along a direction”, “parallel”, “orthogonal”, “centered”, “concentric” and “coaxial” shall not be construed as indicating only the arrangement in a strict literal sense, but also includes a state where the arrangement is relatively displaced by a tolerance, or by an angle or a distance whereby it is possible to achieve the same function.

For instance, an expression of an equal state such as “same” “equal” and “uniform” shall not be construed as indicating only the state in which the feature is strictly equal, but also includes a state in which there is a tolerance or a difference that can still achieve the same function.

Further, for instance, an expression of a shape such as a rectangular shape or a cylindrical shape shall not be construed as only the geometrically strict shape, but also includes a shape with unevenness or chamfered corners within the range in which the same effect can be achieved.

On the other hand, an expression such as “comprise”, “include”, “have”, “contain” and “constitute”are not intended to be exclusive of other components.

First, with reference to FIGS. 1A and 1B, a cooling system according to some embodiments will be described.

FIG. 1A is a schematic diagram of a cooling system according to an embodiment. FIG. 1B is a schematic diagram of a cooling system according to another embodiment.

In some embodiments, as shown in FIGS. 1A and 1B, a cooling system 1 (1A, 1B) includes an NH₃ refrigeration machine 10, a CO₂ liquefaction unit 20, and an air cooler 50. The CO₂ liquefaction unit 20 liquefies a CO₂ refrigerant through heat exchange with an NH₃ refrigerant of the NH₃ refrigeration machine 10. The air cooler 50 generates cold air through heat exchange with the CO₂ refrigerant from the CO₂ liquefaction unit 20.

The cooling system 1 (1A, 1B) also includes a casing 30. The casing 30 houses the NH₃ refrigeration machine 10 and the CO₂ liquefaction unit 20. On the other hand, the air cooler 50 is disposed outside the casing 30. The air cooler 50 may be housed in an air cooler casing 320 which is separate from the casing 30. The interior space of the air cooler casing 320 may be separated from the interior space of the casing 30 by a first barrier wall 32 of the casing 30, which will be described below.

In some embodiments, as shown in FIGS. 1A and 1B, the NH₃ refrigeration machine 10, the CO₂ liquefaction unit 20, the casing 30, and the air cooler 50 are installed on a rooftop 210 of a building 200.

The building 200 includes a refrigerator 220 and a return air passage 230 (232, 234) connecting the refrigerator 220 to the rooftop 210. One end of the return air passage 230 (232, 234) opens to the refrigerator 220. The other end of the return air passage 230 (232, 234) opens to the floor surface of the rooftop 210 and forms an opening 240 (242, 244).

In some embodiments, as shown in FIGS. 1A and 1B, the return air passage 230 includes a first return air passage 232 for directing cold air produced by the air cooler 50 to the refrigerator 220 and a second return air passage 234 for directing return air from the refrigerator 220 to the air cooler 50. A first opening 242 is formed at the end of the first return air passage 232 adjacent to the rooftop 210. Similarly, a second opening 244 is formed at the end of the second return air passage 234 adjacent to the rooftop 210.

In some embodiments, the NH₃ refrigeration machine 10 includes a refrigeration cycle through which the NH₃ refrigerant circulates. As shown in FIGS. 1A and 1B, the NH₃ refrigeration machine 10 includes an NH₃ refrigerant line 12 as well as a compressor 14, a condenser 16, an expansion valve 18, and an evaporator which are disposed in the NH₃ refrigerant line 12 as refrigeration cycle components. The evaporator of the NH₃ refrigeration machine 10 is shown as a heat exchanger 22 of the CO₂ liquefaction unit 20.

The compressor 14 compresses the NH₃ refrigerant and discharges it to the NH₃ refrigerant line 12. The condenser 16 cools and condenses the NH₃ refrigerant through heat exchange between a cooling medium supplied from a heat dissipation device 80, which will be described below, and the NH₃ refrigerant discharged from the compressor 14. The NH₃ refrigerant that has passed through the condenser 16 is depressurized by the expansion valve 18. The evaporator (heat exchanger 22) exchanges heat between the depressurized NH₃ refrigerant and the CO₂ refrigerant. The NH₃ refrigerant is heated by heat exchange in the evaporator (heat exchanger 22).

In some embodiments, as shown in FIGS. 1A and 1B, the condenser 16 of the NH₃ refrigeration machine 10 is disposed in the casing 30. The condenser 16 is connected to a heat dissipation device 80 described below.

In some embodiments, as shown in FIGS. 1A and 1B, the CO₂ liquefaction unit 20 includes a heat exchanger 22 for cooling and condensing the CO₂ refrigerant, and a CO₂ receiver 24 for storing the CO₂ refrigerant liquefied by the heat exchanger 22. A pipe 26 is connected to the CO₂ receiver 24 to direct the CO₂ refrigerant to the heat exchanger 22. One end of the pipe 26 is connected to the gas phase section of the CO₂ receiver 24, and the other end is connected to the liquid phase section of the CO₂ receiver 24.

In addition to the pipe 26, a CO₂ pipe 40 is also connected to the CO₂ receiver 24. The CO₂ pipe 40 is disposed between the CO₂ receiver 24 and the air cooler 50. The CO₂ pipe 40 includes a supply line 40A connected to the liquid phase section of the CO₂ receiver 24 and a return line 40B connected to the gas phase section of the CO₂ receiver 24. The supply line 40A directs the CO₂ refrigerant in the liquid phase within the CO₂ receiver 24 to the air cooler 50. The return line 40B directs the CO₂ refrigerant that has passed through the air cooler 50 to the gas phase section of the CO₂ receiver 24.

In an embodiment, as shown in FIG. 1A, the cooling system 1A includes a liquid pump 42 for sending the CO₂ refrigerant in the liquid phase within the CO₂ receiver 24 to the air cooler 50. The liquid pump 42 is disposed on the supply line 40A of the CO₂ pipe 40.

In another embodiment, as shown in FIG. 1B, the cooling system 1B includes the CO₂ receiver 24 placed at a position higher than the air cooler 50. The CO₂ receiver 24 is installed at a height H relative to the air cooler 50. The height H is set, for example, in the range of 1.5 m to 2 m.

In the cooling system 1B shown in FIG. 1B, the CO₂ refrigerant in the liquid phase within the CO₂ receiver 24 is supplied to the air cooler 50 by its own weight.

The casing 30 which houses the NH₃ refrigeration machine 10 and the CO₂ liquefaction unit 20 with the above configuration includes, as shown in FIGS. 1A and 1B, a first barrier wall 32 through which the CO₂ pipe 40 passes. The first barrier wall 32 is configured to prevent leakage of the NH₃ refrigerant from the inside of the casing 30 to the air cooler 50. The gap between the through hole (not shown) for the CO₂ pipe 40 in the first barrier wall 32 and the CO₂ pipe 40 should be sealed.

In some embodiments, as shown in FIGS. 1A and 1B, the casing 30 includes a second barrier wall 34 through which a cooling medium pipe 90, which will be described below, passes. The second barrier wall 34 is configured to prevent leakage of the NH₃ refrigerant from the inside of the casing 30 to the outside of the casing 30. The gap between the through hole (not shown) for the cooling medium pipe 90 in the second barrier wall 34 and the cooling medium pipe 90 should be sealed.

In some embodiments, as shown in FIGS. 1A and 1B, the air cooler 50 includes an inlet 52, a cooling tube bundle 54, and an outlet 56. The inlet 52 is provided on the side closer to the second opening 244 of the second return air passage 234. Similarly, the outlet 56 is provided on the side closer to the first opening 242 of the first return air passage 232. The cooling tube bundle 54 is provided inside the air cooler 50 between the inlet 52 and the outlet 56. One end of the cooling tube bundle 54 is connected to the supply line 40A of the CO₂ pipe 40, and the other end is connected to the return line 40B of the CO₂ pipe 40.

In some embodiments, as shown in FIGS. 1A and 1B, the cooling system 1 (1A, 1B) further includes a heat dissipation device 80 installed outside the casing 30. The heat dissipation device 80 is connected to the condenser 16 of the NH₃ refrigeration machine 10 via a cooling medium pipe 90, which is provided with a cooling medium pump 92. The heat dissipation device 80 cools a cooling medium supplied via the cooling medium pipe 90.

In the embodiments shown in FIGS. 1A and 1B, the heat dissipation device 80 is installed on the rooftop 210 of the building 200. In another embodiment, the installation position of the heat dissipation device 80 is not limited, and it may be installed on a ceiling 36 of the casing 30, for example.

Next, with reference to FIGS. 2A to 2C, the air cooler and a surrounding configuration of the air cooler will be described.

FIG. 2A is a schematic diagram showing the air cooler and a surrounding configuration of the air cooler according to an embodiment. FIG. 2B is a schematic diagram showing the air cooler and a surrounding configuration of the air cooler according to another embodiment.

FIG. 2C is a schematic diagram showing the air cooler and a surrounding configuration of the air cooler according to still another embodiment.

In the following, the same reference numerals are used for the parts that are the same as those described above in FIGS. 1A and 1B, and their explanations are omitted as appropriate.

In some embodiments, as shown in FIGS. 2A to 2C, the cooling system 1 is provided with a fan 310 for circulating air between the refrigerator 220 and the air cooler 50. In the example shown in FIGS. 2A to 2C, the fan 310 is disposed between the outlet 56 of the air cooler 50 and the first opening 242 of the first return air passage 232 to allow the cold air generated by the air cooler 50 to be sent to the refrigerator 220 via the first return air passage 232.

In the example shown in FIGS. 2A to 2C, the fan 310 is attached to the outlet 56 of the air cooler 50.

The fan 310 may be disposed between the second opening 244 of the second return air passage 234 and the inlet 52 of the air cooler 50 to allow air in the refrigerator 220 sucked through the second return air passage 234 to be supplied to the air cooler 50.

In some embodiments, as shown by arrow a in FIGS. 2A to 2C, air in the refrigerator 220 flows as the return air from below upward through the second return air passage 234 and is directed from the second opening 244 to the inlet 52 of the air cooler 50. The return air flowing into the air cooler 50 flows horizontally in the air cooler 50 and is cooled by exchanging heat with the CO₂ refrigerant circulating in the cooling tube bundle 54. Thus, the air cooler 50 generates cold air to be supplied to the refrigerator 220 in the building 200. The generated cold air is discharged through the outlet 56 of the air cooler 50 and flows from above downward through the first opening 242 and the first return air passage 232 and is directed to the refrigerator 220.

In some embodiments, for example as shown in FIG. 2C, the system may be provided with an air cooler casing 320 covering the air cooler 50 and the openings 240 (242, 244) of the rooftop 210.

The air cooler casing 320 separates the interior space of the air cooler casing 320 from the space outside the air cooler casing 320. The air cooler casing 320 may be made of a material having heat insulation properties to inhibit the transfer of heat between the interior space of the air cooler casing 320 and the space outside the air cooler casing 320.

For example, when a later-described return air guiding member 60, as shown in FIGS. 2A and 2B, is not provided, a partition wall 322 may be provided to separate the space in the air cooler casing 320 into the space on the inlet 52 side of the air cooler 50 and the space on the outlet 56 side of the air cooler 50.

For example, when the return air guiding member 60 is provided as shown in FIGS. 2A and 2B, it is not essential to provide the air cooler casing 320.

In some embodiments, as shown in FIGS. 2A and 2B, the cooling system 1 further includes a return air guiding member 60 (62, 64) disposed between the opening 240 of the rooftop 210 and the air cooler 50.

In some embodiments, as shown in FIGS. 2A and 2B, the return air guiding member 60 includes a first hood 62 and a second hood 64. The first hood 62 connects the first opening 242 of the rooftop 210 to the outlet 56 of the air cooler 50.

For example, as shown in FIG. 2A, if a damper 70 (72), which will be described below, is attached to the outlet 56 of the air cooler 50 via the fan 310, the first hood 62 may be connected to the outlet 56 of the air cooler 50 via the fan 310 and the damper 70 (72).

For example, as shown in FIG. 2B, if the fan 310 is attached to the outlet 56 of the air cooler 50, the first hood 62 may be connected to the outlet 56 of the air cooler 50 via the fan 310.

In some embodiments, as shown in FIGS. 2A and 2B, the second hood 64 connects the second opening 244 of the rooftop 210 to the inlet 52 of the air cooler 50.

For example, if the fan 310 or a damper 70 (74), which will be described below, is attached to the inlet 52 of the air cooler 50, the second hood 64 may be connected to the inlet 52 of the air cooler 50 via the fan 310 or the damper 70 (74).

In some embodiments, the return air guiding member 60 is not particularly limited and may be, for example, a rectangular duct or flexible duct.

In some embodiments, as shown in FIGS. 2A to 2C, the cooling system 1 further includes a damper 70 (72, 74). The damper 70 (72, 74) is not particularly limited and may be, for example, a louver damper as shown in FIGS. 2A and 2C or a butterfly damper as shown in FIG. 2B.

For example, the damper 70 (72, 74) shown in FIGS. 2A and 2C may be configured to open and close with the return air flow. The damper 70 (72, 74) shown in FIGS. 2A to 2C may be configured to be opened and closed by human or actuator drive force.

In some embodiments, as shown in FIGS. 2A and 2B, the damper 70 (72, 74) is disposed within the return air guiding member 60 (62, 64). The damper 70 (72, 74) is configured to open and close an internal passage 66 of the return air guiding member 60 (62, 64). In the embodiments shown in FIGS. 2A and 2B, the first damper 72 is disposed in the first hood 62, and the second damper 74 is disposed in the second hood 64.

In an embodiment, as shown in FIG. 2A, the dampers 70 (72, 74) are disposed at the outlet 56 and the inlet 52 of the air cooler 50. In the embodiment shown in FIG. 2A, the first damper 72 is installed so that it can block the outlet 56 of the air cooler 50, and the second damper 74 is installed so that it can block the inlet 52 of the air cooler 50. In the example shown in FIG. 2A, if the casing of the damper 70 (72, 74) is regarded as part of the return air guiding member 60 (62, 64), it means that the damper 70 (72, 74) is installed within the return air guiding member 60 (62, 64).

In another embodiment, as shown in FIG. 2B, the damper 70 (72, 74) is disposed on the floor surface of the rooftop 210. In the embodiment shown in FIG. 2B, the first damper 72 is installed so that it can block the first opening 242, and the second damper 74 is installed so that it can block the second opening 244.

Next, the other configuration of the cooling system according to some embodiments will be described with reference to FIGS. 3 and 4.

FIG. 3 is a schematic diagram of the cooling system according to an embodiment.

FIG. 4 is a schematic diagram of the cooling system according to another embodiment.

In FIGS. 3 and 4, for convenience of explanation, the configuration inside the casing 30 is omitted as appropriate, and the configuration outside the casing 30 is mainly shown.

In an embodiment, as shown in FIG. 3, the cooling system 1 (1C) further includes a cooling medium tank 100 installed outside the casing 30. A cooling medium pipe 90 is connected to the cooling medium tank 100. In addition to the cooling medium pipe 90, a heat dissipation circuit 110 and a defrost circuit 140 are also connected to the cooling medium tank 100. The heat dissipation circuit 110 is disposed between the cooling medium tank 100 and the heat dissipation device 80. The defrost circuit 140 is disposed between the cooling medium tank 100 and the air cooler 50.

In an embodiment, as shown in FIG. 3, the cooling medium tank 100 includes a low temperature bath 102 for storing a cooling medium (warm brine) and a high temperature bath 104 for storing a cooling medium with a higher temperature than the cooling medium stored in the low temperature bath 102.

One end of the cooling medium pipe 90 is connected to the low temperature bath 102 of the cooling medium tank 100, and the other end is connected to the high temperature bath 104.

The heat dissipation circuit 110 is provided with a liquid pump 120 and a valve 130. One end of the heat dissipation circuit 110 is connected to the liquid phase section of the high temperature bath 104 of the cooling medium tank 100, and the other end is connected to the gas phase section of the low temperature bath 102.

The defrost circuit 140 is provided with a valve 150 and includes a supply line 142 for the hot cooling medium and a return line 144 for the cold cooling medium. One end of the supply line 142 is connected to the heat dissipation circuit 110 between the liquid pump 120 and the valve 130, and the other end is connected to the air cooler 50. One end of the return line 144 is connected to the air cooler 50, and the other end is connected to the gas phase section of the low temperature bath 102 of the cooling medium tank 100. The defrost circuit 140 passes through the interior of the air cooler 50 and is configured to heat the surface of the cooling tube bundle 54 of the air cooler 50.

In the embodiment shown in FIG. 3, the cooling medium in the high temperature bath 104 can be flowed to either the heat dissipation circuit 110 or the defrost circuit 140 by controlling the open/close state of the valve 130 in the heat dissipation circuit 110 and the valve 150 in the defrost circuit 140.

In an embodiment, as shown in FIG. 3, the heat dissipation device 80 is a closed cooling tower 80A that utilizes vaporization of water (sprayed water) in a separate system from the cooling medium. The closed cooling tower 80A includes a spraying device 82 for bringing sprayed water into contact with the surface of the heat dissipation circuit 110, a water tank 83 for collecting the sprayed water, a pipe 84 connecting the spraying device 82 and the water tank 83, and a pump 85 disposed in the pipe 84. The closed cooling tower 80A also includes an inlet 86 for introducing air from the outside and a fan 87 for discharging the air through an outlet 88.

However, the heat dissipation device 80 may be an open cooling tower or an air-cooled cooling device.

The heat dissipation device 80 shown in FIG. 3 can cool the cooling medium in the high temperature bath 104 which is pumped by the pump 120 and supplied to the heat dissipation circuit 110 via the valve 130. The cooling medium from the high temperature bath 104 cooled by the heat dissipation device 80 is supplied to the low temperature bath 102.

In some embodiments, as shown in FIG. 4, the cooling system 1 (1D) includes a removal device 160 for removing NH₃ gas that has leaked in the casing 30. The removal device 160 includes a sensor 162 for measuring the NH₃ concentration in the casing 30, a discharge device 164 for discharging air in the casing 30 to the outside of the casing 30, and a collection device 166 for collecting NH₃ discharged by the discharge device 164. The collection device 166 is not limited to a particular device and may be configured to neutralize NH₃ or dissolve NH₃ in a solvent.

The removal device 160 may be installed on the side of the casing 30 or on the casing 30 as shown in FIG. 4. The removal device 160 may be disposed outside the casing 30 or may be disposed inside the casing 30.

The present disclosure is not limited to the embodiments described above, but includes modifications to the embodiments described above, and embodiments composed of combinations of those embodiments.

The contents described in the above embodiments would be understood as follows, for instance.

(1) A cooling system 1 according to at least one embodiment of the present disclosure is provided with: an NH₃ refrigeration machine 10 installed on a rooftop 210 of a building 200 and including a refrigeration cycle through which an NH₃ refrigerant circulates; a CO₂ liquefaction unit 20 installed on the rooftop 210 and including a heat exchanger 22 for liquefying a CO₂ refrigerant through heat exchange with the NH₃ refrigerant, and a CO₂ receiver 24 for storing the CO₂ refrigerant liquefied by the heat exchanger 22; a casing 30 installed on the rooftop 210 and housing at least the CO₂ liquefaction unit 20; and an air cooler 50 installed outside the casing 30 on the rooftop 210 and configured to generate cold air supplied to a refrigerator 220 in the building 200 through heat exchange with the CO₂ refrigerant from the CO₂ liquefaction unit 20. The casing includes a first barrier wall 32 through which a CO₂ pipe 40 between the CO₂ liquefaction unit 20 and the air cooler 50 passes and which prevents leakage of the NH₃ refrigerant from the inside of the casing 30 to the air cooler 50.

According to the above configuration (1), the NH₃ refrigerant is not supplied to the air cooler 50, so even if the air cooler 50 has a problem, the NH₃ refrigerant will not leak into the refrigerator 220. Even if the NH₃ refrigerant leaks into the casing 30 due to a defect in the CO₂ liquefaction unit 20, the possibility of the NH₃ refrigerant leaking into the installation area of the air cooler 50 separated by the first barrier wall 32 can be effectively reduced. Thus, it is possible to effectively reduce the possibility that the NH₃ refrigerant leaks into the refrigerator 220.

Additionally, according to the above configuration (1), the volume of the refrigerator 220 can be used efficiently because the air cooler 50 does not need to be placed in the refrigerator 220.

(2) In some embodiments, in the above configuration (1), the casing 30 may house the CO₂ liquefaction unit 20 and the NH₃ refrigeration machine 10. The NH₃ refrigeration machine 10 may include a condenser 16 disposed in the casing 30 and configured to cool and condense the NH₃ refrigerant through heat exchange with a cooling medium (warm brine). The cooling system 1 may be provided with a heat dissipation device 80 installed outside the casing 30, connected to the condenser 16 via a cooling medium pipe 90, and configured to cool the cooling medium (warm brine) supplied via the cooling medium pipe 90. The casing 30 may include a second barrier wall 34 through which the cooling medium pipe 90 passes and which prevents leakage of the NH₃ refrigerant from the inside of the casing 30 to the outside of the casing 30.

According to the above configuration (2), even if the NH₃ refrigerant leaks into the casing 30 due to a defect in the NH₃ refrigeration machine 10, the second barrier wall 34 effectively reduces leakage to the outside of the casing 30.

(3) In some embodiments, in the above configuration (1) or (2), the air cooler 50 may include: an inlet 52 through which return air from the refrigerator 220 enters; a cooling tube bundle 54 for obtaining the cold air by cooling the return air through heat exchange with the CO₂ refrigerant; and an outlet 56 through which the cold air is discharged. The cooling system 1 may be provided with: a first hood 62 connecting a first opening 242 provided on a floor surface of the rooftop 210 so as to communicate with the refrigerator 220 to the outlet 56 of the air cooler 50; and a second hood 64 connecting a second opening 244 provided on the floor surface of the rooftop 210 so as to communicate with the refrigerator 220 to the inlet 52 of the air cooler 50.

According to the above configuration (3), the leakage of cold air from the air cooler 50 and return air from the refrigerator 220 to the outside can be reduced, so that the efficiency of the cooling system 1 can be improved.

(4) In some embodiments, in the above configuration (3), the cooling system may be provided with: an openable first damper 72 disposed in the first hood 62; and an openable second damper 74 disposed in the second hood 64.

According to the above configuration (4), for example, even if hot air or steam is generated during defrosting of the air cooler 50, it is difficult for the hot air or steam to flow into the refrigerator 220. This reduces the possibility that hot air or steam flowing into the refrigerator 220 will raise the temperature in the refrigerator 220, that steam flowing into the refrigerator 220 will freeze unintentionally in the refrigerator 220, or that water droplets generated by thawing after freezing will affect objects to be cooled in the refrigerator 220.

(5) In some embodiments, in the above configuration (1) or (2), the air cooler 50 may include: an inlet 52 through which return air from the refrigerator 220 enters; a cooling tube bundle 54 for obtaining the cold air by cooling the return air through heat exchange with the CO₂ refrigerant; and an outlet 56 through which the cold air is discharged. The cooling system 1 may be provided with: a first damper 72 capable of blocking the outlet 56 of the air cooler 50 or a first opening 242 provided on a floor surface of the rooftop 210 so as to communicate with the refrigerator 220 and allowing the cold air to pass; and a second damper 74 capable of blocking the inlet 52 of the air cooler 50 or a second opening 244 provided on the floor surface of the rooftop 210 so as to communicate with the refrigerator 220 and allowing the return air to pass.

According to the above configuration (5), for example, even if hot air or steam is generated during defrosting of the air cooler 50, it is difficult for the hot air or steam to flow into the refrigerator 220. This reduces the possibility that hot air or steam flowing into the refrigerator 220 will raise the temperature in the refrigerator 220, that steam flowing into the refrigerator 220 will freeze unintentionally in the refrigerator 220, or that water droplets generated by thawing after freezing will affect objects to be cooled in the refrigerator 220.

(6) In some embodiments, in any of the above configurations (1) to (5), the cooling system may be provided with a liquid pump 42 for sending the CO₂ refrigerant in a liquid phase within the CO₂ receiver 24 to the air cooler 50.

According to the above configuration (6), the CO₂ refrigerant in the liquid phase can be stably supplied to the air cooler 50 even if the height difference between the CO₂ receiver 24 and the air cooler 50 is small.

(7) In some embodiments, in any of the above configurations (1) to (6), the CO₂ receiver 24 may be placed at a position higher than the air cooler 50. The CO₂ refrigerant in a liquid phase within the CO₂ receiver 24 can be supplied to the air cooler 50 by its own weight.

According to the above configuration (7), since the liquid pump 42 is not necessary for sending the CO₂ refrigerant in the liquid phase within the CO₂ receiver 24 to the air cooler 50, the configuration of the cooling system 1 can be simplified.

(8) In some embodiments, in any of the above configurations (1) to (7), the cooling system may be provided with a removal device 160 for removing NH₃ gas that has leaked in the casing 30.

According to the above configuration (8), even if the NH₃ refrigerant leaks into the casing 30, the removal device 160 can remove it, effectively reducing the possibility of the NH₃ refrigerant leaking into the installation area of the air cooler 50 separated by the first barrier wall 32. Thus, it is possible to effectively reduce the possibility that the NH₃ refrigerant leaks into the refrigerator 220.

REFERENCE SIGNS LIST

• • 1, 1A, 1B, 1C, 1D Cooling system
  • 10 NH₃ refrigeration machine
  • 16 Condenser
  • 20 CO₂ liquefaction unit
  • 22 Heat exchanger
  • 24 CO₂ receiver
  • 30 Casing
  • 32 First barrier wall
  • 34 Second barrier wall
  • 40 CO₂ pipe
  • 42 Liquid pump
  • 50 Air cooler
  • 52 Inlet
  • 54 Cooling tube bundle
  • 56 Outlet
  • 60 Return air guiding member
  • 62 First hood
  • 64 Second hood
  • 70 Damper
  • 72 First damper
  • 74 Second damper
  • 80 Heat dissipation device
  • 90 Cooling medium pipe
  • 160 Removal device
  • 200 Building
  • 210 Rooftop
  • 220 Refrigerator
  • 230 Return air passage
  • 232 First return air passage
  • 234 Second return air passage
  • 242 First opening
  • 244 Second opening