JP2009110469A - Rack cooling system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a rack cooling system suitable for cooling a rack, such as a server rack, which stores a heat generation apparatus. <P>SOLUTION: In a machine room 5, an air conditioner 4 always operates as an ambient air conditioner. When a room temperature exceeds an upper limit temperature, a mist cooling apparatus starts its operation. A valve V1 is opened (default opening degree), tap water is supplied into the room through water supply pipe 2e and sprayed from all mist nozzles 2c. During spraying, whether water droplets are generated in indoor air is determined on the basis of the result of measurement in a droplet sensor S1. When droplets are detected, unless the valve opening degree is 0, the opening degree is reduced by one stage to reduce the amount of spraying. When the valve has been completely closed, the operation continues as it is (without spraying). When no droplet is detected, unless the opening degree is maximum, the opening degree is increased by one stage to increase the amount of spraying. When the room temperature falls below a predetermined lower limit temperature, the mist cooling operation is stopped, and the ambient air conditioner system is resumed. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a rack cooling system, and more particularly to a rack cooling system suitable for cooling a rack that stores heat-generating equipment such as a server rack.

  In recent years, with the advancement of IT in society, the speed, capacity, and density of information communication devices are rapidly increasing. These devices are generally stored in a 19-inch server rack conforming to the US IEA standard and housed in an information communication machine room (data center). There are many cases in which a normal air conditioning system (ambient air conditioning system) alone cannot properly handle the entire room.

In order to solve such a problem, a technique of incorporating a heat recovery and cooling device using a refrigerant for each server rack has been proposed (see, for example, Patent Document 1). FIG. 14 shows a server rack 100 according to this method, in which a cooling device 102 that forms a refrigeration cycle is provided in a main body 101, and an evaporator 102a that is a vaporizing section thereof is arranged in the vertical direction of the main body. In the server module 103, the heat generated in the heat generating portion 103a is conveyed to the heat radiating portion 103c via the coolant circulated by the pump 103b, and is brought into close contact with the evaporator 102a and radiated to the refrigerant.
According to this method, local waste heat treatment can be performed, and it can be said that heat treatment is efficient inside the server rack. However, the high temperature exhaust of the rack cooling device 102 may adversely affect adjacent racks, and the high price. There are problems such as the necessity of using a refrigerant, the influence on the global environment (warming), and the need for high-pressure piping design.
JP 2004-363308 A

  The present invention is for solving such problems, and can secure high heat transfer characteristics and high heat transport efficiency, can suppress construction costs, does not require high-pressure piping, and has a global environment (warm climate). The present invention provides a rack cooling system that does not have the problem of

The gist of the present invention is as follows. That is,
(1) A rack cooling system for cooling a server rack on which a heat generating device is mounted, wherein mist generating means for spraying water mist onto a space to be cooled and mist generation amount control for completely evaporating the sprayed mist And a rack cooling system.
(2) In the rack cooling system, the mist generation amount control means includes a water droplet sensor disposed in the cooling target space, and a mist water amount control means for controlling the mist water amount based on a detection result of the water droplet sensor. It is characterized by comprising.
(3) In each of the above inventions, one or more temperature sensors for detecting an abnormally high temperature of the space to be cooled can be further provided.
(4) In each of the above inventions, the mist generation amount control means can further comprise humidity control means for controlling the cooling target space within a predetermined humidity range.
(5) In each of the above inventions, the humidity control means can further comprise linkage control means with the dehumidifier.
(6) In each of the above inventions, the space to be cooled can be an information communication machine room that houses one or more racks.
(7) In each of the above inventions, the cooling target space may be each zone of the information communication machine room divided into a plurality of zones.
(8) In each of the above inventions, a rack cooling system further comprising an ambient air conditioning system that air-conditions the cooling target space, and configured to be capable of mist cooling operation when the ambient air conditioning system malfunctions. be able to.
(9) In each of the above inventions, the water supply path for the mist generating means can be configured to be shared with the fire-extinguishing sprinkler provided in the room.

(10) In the inventions of (1) to (4), the space to be cooled is inside a server rack.
(11) In the invention of the above (10), it is possible to further include pressure reducing means in the rack for promoting complete evaporation of the mist sprayed in the rack.

According to each of the above inventions, since it is a cooling system that uses the latent heat of vaporization of water, it is possible to dramatically increase the efficiency of transporting refrigerant to the controlled object.
In addition, since it is a system that actively controls the amount of evaporation, it is possible to prevent condensation and scattered water from adhering to the part to be controlled, and to avoid problems such as electrical circuit dielectric breakdown.
In addition, in a system that uses a fire extinguishing sprinkler and a water supply facility in common, the construction cost of the cooling system can be reduced.

  Hereinafter, an embodiment of a rack cooling system according to the present invention will be described in more detail with reference to FIGS. In order to avoid duplication, in each figure, the same structure is shown using the same code | symbol. Needless to say, the scope of the present invention is described in the claims and is not limited to the following embodiments.

(First embodiment)
FIG. 1 is a diagram showing a rack cooling system 1 according to an embodiment of the present invention. The rack cooling system 1 is a system for cooling a plurality of server racks 3 housed in a machine room 5 from the outside, and includes a packaged air conditioner 4 as ambient air conditioning and a mist cooling device 2 as auxiliary air conditioning. It is provided as a main component.
The interior of the machine room 5 is divided into three spaces by a floor panel 5d and a ceiling panel 5e. A double floor space 5c is formed in the lower part of the floor panel 5d, and a ceiling space 5b is formed in the upper part of the ceiling panel 5e. ing. The indoor unit 4a of the air conditioner 4 and the double floor space 5c are connected via a forward duct 7a. The ceiling space 5b and the indoor unit 4a are connected via a return duct 7b.

A plurality of server racks 3 are accommodated in the indoor space 5a above the floor panel 5d. The interior of the server rack 3 is divided into a plurality of stages, and a blade server 3a is stored in each stage. An exhaust fan (not shown) is disposed on the rear side of each stage, and is configured to discharge heat generated from the blade server 3a to the outside of the rack.
The air conditioner 4 includes an indoor unit 4a including an evaporator 4e and a blower 4c, an outdoor unit 4b mainly including a compressor, a condenser (all not shown), and a refrigerant pipe 4f connecting the respective components. Yes. With such a configuration, the cold generated by the refrigeration cycle operation is cooled by exchanging heat with the indoor air introduced into the indoor unit 4a, and supplied to the machine room by the blower 4c. The cooling capacity is controlled based on the intake air temperature introduced into the indoor unit 4a.

The mist cooling device 2 includes a water supply system 2a and a control system 2b (in the figure, 2a is corrected to 2b). The water supply system 2a mainly includes a water supply pipe 2e and a plurality of mist nozzles 2c provided in the vicinity of the indoor ceiling portion in the route of the water supply pipe 2e. The control system 2b is a temperature sensor S2 that measures indoor temperature and relative humidity, a relative humidity sensor S3, a water drop sensor S1 for detecting dew condensation during mist spraying, and a flow rate that is an actuator based on the measured values of each sensor. The control unit 6 that controls the opening degree of the control valve V1 is a main component. Each sensor is arranged at the best position for measuring the target physical quantity.
The rack cooling system 1 is configured as described above. Next, air conditioning during normal operation is performed as follows. That is, the indoor air introduced into the air conditioner 4 is cooled by heat exchange in the evaporator 4e, sent to the double floor space 5c via the forward duct 7a by the blower 4c, and further provided in the floor panel 5d. It is supplied into the room from the outlet 5f. The cool air is introduced into each server rack, and after the blade server 3a is cooled, it becomes warm air and is discharged outside the apparatus. The discharged warm air rises in the room, is led to the ceiling space 5b from the suction port 5g of the ceiling panel 5e, and is returned to the air conditioner 4 through the return side duct 7b. The return air is mixed with the outside air introduced through the outside air introduction duct 7c.

Next, referring to FIGS. 2 and 3, a flow of mist cooling control assuming a case where the room has reached an abnormally high temperature due to, for example, a failure of the air conditioner 4 will be described.
In the machine room 5, the air conditioner 4 is always operating as ambient air conditioning (S101). During the control, the room temperature Tr is measured by the sensor S1 (S102), and it is determined whether or not the room temperature Tr has exceeded the upper limit temperature Th defined as the abnormally high temperature level (S103). When the upper limit temperature Th is not exceeded, cooling by only the air conditioner 4 is continued (NO in S103). When the upper limit temperature Th is exceeded, operation by the mist cooling device is started (S104). That is, the valve V1 is opened (default opening), and tap water is supplied indoors through the water supply pipe 2e and sprayed from all the mist nozzles 2c (see FIG. 3). During mist spraying, in order to ensure complete evaporation of the mist, the presence or absence of water droplets in the indoor air is determined based on the measured value of the water droplet sensor S1 (S105).
When a water droplet is detected, in order to promote complete evaporation, unless the valve opening is 0 (NO in S107), the opening is decreased by one step and the mist spray amount is decreased (S110). When the valve opening has already been fully closed (YES in S107), the operation is continued in that state (stop of mist spraying) (S109).

When no water droplet is detected in S105, the mist spray amount is increased by increasing the opening by one step (S108) unless the valve opening is maximum (NO in S106) in order to promote a decrease in room temperature. When the valve opening has already reached the maximum (YES in S106), the operation is continued with the maximum opening (S109).
Thereafter, it is determined whether or not the room temperature Tr has fallen below a predetermined lower limit temperature TL (<Th) (S111). If not below TL, the above steps are repeated (NO in S111). When it falls below TL, the mist cooling operation is terminated and the process returns to the ambient air conditioning system (S112).

(Second embodiment)
Next, another embodiment of the present invention will be described with reference to FIGS.
The configuration of this embodiment is the same as that of the rack cooling system 1. The present embodiment is different from the first embodiment described above in that the mist spray amount is controlled based on the indoor relative humidity by the relative humidity sensor S3.
With reference to FIG. 4, the control principle of mist complete evaporation in this embodiment is demonstrated. This figure is an air diagram (Tx diagram) in which the vertical axis represents absolute humidity x and the horizontal axis represents dry bulb temperature T. φs is a saturation line (relative humidity 100%). By performing the mist cooling operation, the water vapor is self-evaporated, and as a result, the room temperature decreases and the relative humidity increases. Accordingly, assuming that the state before the mist cooling operation is S (0), the temperature and humidity environment in the machine room 5 changes as shown by the curve S as the mist spraying time elapses. When the curve S reaches the saturation line φs, it is a dew condensation condition. Therefore, it is necessary to control so that the relative humidity φ (t) in the state S (t) is always kept below φs. Specifically, equal relative humidity lines φmax and φmin are set as threshold values, and when the relative humidity φ (t) exceeds φmax, mist spraying is immediately stopped. Moreover, when it falls below (phi) min, in order to give priority to cooling, the amount of mist spraying is increased. Thus, complete evaporation can be secured by managing the relative humidity in the room.

Next, a specific control flow of this embodiment will be described with reference to FIG. In the machine room 5, the air conditioner 4 is always operating as ambient air conditioning (S201). During the control, the sensors S2 and S3 measure the room temperature Tr and the relative humidity φ (S202).
Next, it is determined whether or not the room temperature Tr has exceeded a predetermined upper limit temperature Th (S203). When the upper limit temperature Th is not exceeded, cooling by only the air conditioner 4 is continued (NO in S203). When the upper limit temperature Th is exceeded, operation by the mist cooling device is started (S204). That is, the valve V1 is opened (default opening), tap water is supplied through the pipe 2e, and mist is sprayed into the room from each mist nozzle 2c. During the mist spraying, the relative humidity is measured by the humidity sensor S3, and the control unit 6 makes the following determination. In the following description, it is assumed that the operation is continued and the time t is reached.

It is determined whether or not the relative humidity φ (t) at time t exceeds a first threshold φ1 (corresponding to φmax in FIG. 4) (S205). When it exceeds φ1, since there is a risk of condensation, the valve V1 is immediately fully closed and mist spraying is stopped (S213).
If φ1 is not exceeded, it is next determined whether or not φ (t) exceeds the second threshold φ2 (ie, φ1 ≧ φ (t)> φ2) (S206). When φ2 is exceeded, the mist spray amount is decreased by lowering the opening by one step unless the valve opening is minimum (NO in S209) in order to reduce the relative humidity (S212). When the valve opening has already reached the minimum in S209, the current opening is maintained and the operation is continued (S211).

When the relative humidity φ (t) does not exceed the second threshold φ2 in S206, next, φ (t) exceeds the third threshold φ3 (corresponding to φmin in FIG. 4) (that is, φ2 ≧ It is determined whether or not φ (t)> φ3) (S207). When it exceeds φ3, the current opening degree is maintained and the operation is continued (S211). When φ3 or less, in order to lower the room temperature, unless the valve opening is maximum (NO in S208), the opening is increased by one step and the mist spray amount is increased (S210). When the valve opening degree has already reached the maximum in S208, the current opening degree is maintained and the operation is continued (S211).
Thereafter, it is determined whether or not the room temperature Tr has fallen below a predetermined lower limit temperature TL (S214). If not below TL, the above steps are repeated (NO in S214). When it falls below TL, the mist cooling operation is terminated and the process returns to the ambient air conditioning system (S215).

In the present embodiment, the mist spray amount is controlled based on the relative humidity. However, it is also possible to add the information of the water droplet sensor S1 and control according to the first embodiment. is there.
Further, instead of or in addition to the mist spray amount control based on the relative humidity, it is possible to determine and control the possibility of condensation based on the difference between the dry bulb temperature and the dew point temperature.

(Third embodiment)
Furthermore, another embodiment of the present invention will be described with reference to FIGS. In the present embodiment, the machine room is divided into a plurality of zones, and mist spraying is performed on the abnormally high temperature generation zone.
FIG. 6 is a diagram showing the rack cooling system 20 according to the present embodiment. The difference between the rack cooling system 20 and the rack cooling system 1 described above is that the indoor water supply system and the control system are divided into a plurality of control zones Z1 to Z3. For the water supply system 21, mist nozzles 21a to 21c are provided on the terminal side of the branch pipes 25a to 25c branched from the route of the water supply pipe 2e so as to enable mist spraying in units of zones. For the mist amount control system 22, sensor units 22a to 22c are provided in each zone. In each sensor unit, a temperature sensor, a water drop sensor, and a relative humidity sensor are stored as in the first embodiment. Further, flow control valves V2a to V2c are provided upstream of the mist nozzles of the branch pipes 25a to 25c. Since other configurations are the same as those of the above-described embodiment, the description thereof is omitted.
With such a configuration, monitoring is performed for each zone according to the same control flow as in the above-described embodiments, and the zone in which the abnormally high temperature is detected is cooled by mist spraying. For example, referring to FIG. 7, when an abnormally high temperature is detected in the zone Z2, only the flow rate control valve V2b is opened, and mist is sprayed from the mist nozzle 21b. Cooling is possible.

(Fourth embodiment)
Furthermore, another embodiment of the present invention will be described with reference to FIGS. The present embodiment is a system that shares a pre-actuated sprinkler and a water supply pipe.
FIG. 8 is a diagram showing the rack cooling system 30 according to the present embodiment. The difference between the rack cooling system 30 and the rack cooling system 20 described above is that, with respect to the water supply system 31, fire fighting sprinklers 32a to 32d are provided in the water supply pipe 2e in addition to the mist nozzle and the flow rate control valve. Further, V3 is provided on the upstream side of the water supply pipe 2e. Further, on the upstream side, a pre-acting fire extinguishing system, each of which includes a pressurized tank (not shown), a continuous water discharge pump, and the like. Furthermore, fire detectors 33a to 33d are attached to the lower surface side of the ceiling panel 5e. Since other configurations are the same as those of the above-described embodiment, description thereof is omitted.

Next, the control flow of this embodiment will be described with reference to FIG. The temperature in the machine room is always measured for each target zone, and at the same time, the fire detector is operating (S401). First, regarding the fire detection flow, it is determined whether or not an abnormal signal has been received from any of the fire detectors (S402). When an abnormal signal is received, fire water discharge is started only when the sprinkler head melts and operates simultaneously (S404). When the water in the pressurized tank is supplied and the pressure is lowered due to water discharge, the pump is operated, water for fire extinguishing is supplied under pressure, and continuous water discharge is performed.
In parallel with the above flow, it is determined whether or not the temperature sensor has detected an abnormally high temperature (S405). When detected, the regulating valve V5a is opened and mist spraying is started (S406). Thereafter, control similar to that of the rack cooling system 20 described above is executed (S407).

(Fifth embodiment)
Furthermore, another embodiment of the present invention will be described. The present embodiment is a system in which a mist nozzle is provided inside a rack and the server is directly mist cooled by this.
Referring to FIG. 10, the inside of the main body 51 of the server rack 50 according to the present embodiment is divided into three chambers: a spray chamber (cold chamber) 51a, a server storage portion 51b, and an intake chamber (hot chamber) 51c. Yes. The cold chamber 51a and the server storage 51b are partitioned by a rectifying grid 51d, and the server storage 51b and the intake chamber 51c are partitioned by an air filter 51e. The server storage unit 51b is divided into a plurality of stages, and the blade server 52 is stored in each stage. An exhaust fan 53 is disposed on the back side of each stage. Further, the server rack 50 includes a pressure reducing device 56 for sucking air inside the main body and maintaining the inside at a negative pressure. An opening / closing door 51f is provided on the front side of the main body.

Next, the mist water supply system of the server rack 50 includes a condenser 57 that converts the manifold 54 disposed in the cold chamber 51a, the plurality of mist nozzles 54a attached to the manifold 54, and the hot mist collected in the hot chamber 51c into a condenser 57. A mist collecting pipe 58a for sending the liquid to the manifold 54, a circulation pump 58b for sending condensed water to the manifold 54 again via the water supply pipe 58c, and a liquid receiving tank for securing the liquid level between the condenser 57 and the circulation pump 58b. 57e is the main component. The condenser 57 is configured to be supplied with cold heat of a refrigerant from a refrigerator (not shown) via a refrigerant pipe 57a to condense high-temperature mist vapor. A supply water pipe 58d is connected to the water supply pipe 58c.
Next, the control system of the server rack 50 includes a temperature sensor S4 that detects the temperature inside the main body. A water droplet sensor S5 is provided in the vicinity of the rectifying grid 51d in the hot chamber 51c. An on-off valve V4 is provided in the water supply pipe 58c. The valve V4 also has a function as an open / close interlock valve for stopping mist spraying and decompression when the main body door 58 is opened. Further, a makeup water supply valve V5 is provided in the makeup water piping 58d path. Mist cooling control of the server rack 50 is performed by the control unit 59.

Next, the mist cooling control flow of the server rack 50 will be described with reference to FIG. In the server storage unit 51b, the internal temperature Ts is measured by the sensor S4. It is determined whether or not the temperature sensor has detected an abnormally high temperature (Ts> Th) (S502). When detected, the on-off valve V4 is opened, mist spraying is started from the mist nozzle 54a (S503), and the operation of the decompression device 56 is started (S503). The sprayed mist absorbs heat from the blade server 52 in the server storage unit 51b and self-evaporates, and is guided to the hot chamber 51c by the exhaust fan 53. Further, in the condenser 57 via the mist recovery pipe 58a. It is condensed and supplied to the manifold 54 again. When the cold water is insufficient, the cold water is newly supplied from the makeup water supply valve V5. During mist spraying, in order to ensure complete evaporation of the mist, the presence / absence of water droplets in the cabinet is determined based on the measured value of the water droplet sensor S5 (S505). Thereafter, the same control flow as in the first embodiment is performed (S506).
In parallel with the mist control, the open / close state of the main body door is monitored (S507). When the opening of the door is detected, the on-off valve V4 is closed and the mist spray is immediately stopped, and the operation of the decompression device 56 is stopped (S507). Thereafter, this control is interrupted until the door is opened again (S508).

In the present embodiment, the recovered mist is condensed and reused. However, the recovered mist may be discarded to constantly supply cold water.
In the present embodiment, the mist spraying is controlled based on the detection value of the water droplet sensor. However, it is also possible to control the mist using a relative humidity sensor.

(Sixth embodiment)
Furthermore, another embodiment of the present invention will be described with reference to FIGS. FIG. 12 is a diagram showing the rack cooling system 40 according to the present embodiment. The rack cooling system 40 is different from the rack cooling system 1 described above in that the machine room 5 further includes a dehumidifier 41 for performing indoor humidity control. The other configuration is the same as that of the rack cooling system 1, and thus a duplicate description is omitted.

Next, the mist cooling control flow of this embodiment will be described with reference to FIG. In the machine room 5, the air conditioner 4 and the dehumidifier 41 are always operating as ambient air conditioning (S601). Hereinafter, the flow from S602 to S609 is the same as S202 to S209 in FIG.
When φ (t)> φ2 in S606, in order to reduce the relative humidity, unless the valve opening is not minimum (NO in S609), the valve opening is lowered by one step to reduce the mist spray amount. Further, the capacity of the dehumidifier 41 is increased by one level (S612). When the valve opening has already reached the minimum in S209, the current opening is maintained and the operation is continued (S611).

If the relative humidity φ (t) does not exceed the second threshold φ2 in S606, then whether φ (t) exceeds the third threshold φ3 (ie, φ2 ≧ φ (t)> φ3) Is determined (S607). When it exceeds φ3, the current opening degree is maintained and the operation is continued (S611). When φ3 or less, in order to lower the room temperature, unless the valve opening is maximum (NO in S608), the opening is increased by one step and the mist spray amount is increased. Further, the capacity of the dehumidifier 41 is lowered by one level (S610). When the valve opening has already reached the maximum in S608, the current opening is maintained and the operation is continued (S611).
The subsequent flow is the same as the flow of FIG.

  The present invention is widely applicable to rack cooling systems regardless of the types of heat sources, refrigerants, air conditioning systems, building structures, and the like.

It is a figure showing rack cooling system 1 concerning one embodiment of the present invention. It is a figure which shows the mist cooling control flow of the rack cooling system. It is a figure which shows the aspect of the mist spraying of the rack cooling system. It is a figure which shows the control principle of mist complete evaporation in 2nd embodiment. It is a figure which shows the mist complete evaporation control flow in 2nd embodiment. It is a figure which shows the rack cooling system 20 which concerns on 3rd embodiment. FIG. 3 is a diagram showing a mode of mist spraying in a specific zone of the rack cooling system 20. It is a figure which shows the rack cooling system 30 which concerns on 4th embodiment. It is a figure which shows the mist cooling control flow of the rack cooling system. It is a figure which shows the server rack 50 which concerns on 5th embodiment. It is a figure which shows the mist cooling control flow of the server rack. It is a figure which shows the rack cooling system 40 which concerns on 6th embodiment. It is a figure which shows the mist complete evaporation control flow in 6th embodiment. It is a figure which shows the conventional server rack.

Explanation of symbols

1, 20, 30, 40... Rack cooling system 2... Mist cooling device 2c, 21a, 21b, 21c .. Mist nozzle 2e. ... Blade server 4 ... Air conditioner 4a ... Indoor unit 4b ... Outdoor unit 31a ... Fire detector 32a ... Fire extinguishing sprinkler 41 ... Dehumidifier 50 ... Server Rack 51a ... Cold chamber 51b ... Server storage 51c ... Hot chamber 56 ... Pressure reducing device 57 ... Condensers S1, S5 ... Water droplet sensors S2, S4 ... Temperature sensor S3 ..Relative humidity sensor

Claims (11)

A rack cooling system for cooling a server rack equipped with a heat generating device,
Mist generating means for spraying water mist on the cooling target space;
Mist generation amount control means for completely evaporating sprayed mist;
A rack cooling system comprising: The mist generation amount control means includes a water droplet sensor disposed in the space to be cooled, and a mist water amount control means for controlling the mist water amount based on a detection result of the water drop sensor. The cooling system according to claim 1. The rack cooling system according to claim 1 or 2, further comprising one or more temperature sensors for detecting an abnormally high temperature in the space to be cooled. The rack cooling system according to any one of claims 1 to 3, wherein the mist generation amount control means further comprises humidity control means for controlling the space to be cooled within a predetermined humidity range. The rack cooling system according to claim 1, wherein the humidity control unit further includes a link control unit with a dehumidifying device. The cooling system according to claim 1, wherein the space to be cooled is an information communication machine room that houses one or more racks. The cooling system according to any one of claims 1 to 5, wherein the cooling target space is each zone of the information communication machine room divided into a plurality of zones. The rack cooling system according to any one of claims 1 to 7, further comprising an ambient air conditioning system that air-conditions the space to be cooled, and configured to be capable of mist cooling operation when the ambient air conditioning system is malfunctioning. 9. The rack cooling system according to claim 1, wherein a water supply path for the mist generating means is configured to be shared with a fire-extinguishing sprinkler provided in the room. The rack cooling system according to any one of claims 1 to 4, wherein the space to be cooled is inside a server rack. The cooling system according to claim 10, further comprising pressure reducing means in the rack for promoting complete evaporation of the mist sprayed in the rack.

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