Abstract:
An electronic equipment cabinet configured to support electronic equipment is provided and may include a shelf positioned in the cabinet separating the cabinet into a first zone and a second zone. The first and second zones may be in fluid communication with a cool air source. In some examples, the first zone may receive cool air directly from a cool air source and the second zone may receive cool air from a duct in fluid communication with the cool air source. In another example, both the first and second zones may receive cool air from the cool air source through a duct. In yet other examples, the cabinet may include a baffle between the cool air source and one of the first zones and the second zones to selectively control a quantity of cool air provided to the one of the first and second zones.

Description:
RELATED APPLICATIONS 
     The present application claims the benefit of U.S. Provisional Patent Application No. 60/986,630, filed Nov. 9, 2007, the entire contents of which are hereby incorporated by reference. 
    
    
     FIELD OF INVENTION 
     This invention relates to systems and methods for cooling electronic equipment in equipment cabinets. In particular, the invention relates to ducted cooling systems for directing cooled air through equipment cabinets for cooling electronic equipment. 
     BACKGROUND 
     In a typical data center, equipment cabinets are used to hold various types of electronic equipment, such as servers and other mission-critical data-processing equipment. When in use, the electronic equipment housed in the cabinets generates heat that must be extracted or damage to the equipment can result. As equipment densities in the cabinets increase, so do the heat extraction (cooling) needs. Today, in a typical data center, it is not unusual for electronic equipment to generate 10 kilowatts and beyond of heat per cabinet (typical range 2 to 20 kilowatts per cabinet). 
     Currently, one method for cooling the electronic equipment in a data center is the use of the “hot aisle/cold aisle” concept; that is cool, conditioned air flows underneath a raised floor and enters the room through perforated floor tiles. The perforated tiles are strategically placed in front of the cabinets (thus creating the “cold aisle”) such that the cool air can be pulled into the cabinets, through a perforated door, to cool the equipment. The cool air picks up heat as it is drawn through the equipment by fans and then the warm air exits the back of the cabinet through another perforated door into the “hot aisle.” The exiting warm air is eventually drawn back into the room air conditioners and the cooling cycle repeats. 
     Although it is reasonably effective, the hot aisle/cold aisle method of cooling electronic equipment can be very inefficient and has various drawbacks. For example, warm air that exits the cabinet into the hot aisle can be drawn back to the cold aisle via the action of the equipment fans and normal room air circulation. In addition, the perforated floor tiles must be carefully placed and sized to effectively cool the equipment. If equipment is added or changed, or if a tile is accidentally moved or covered up, inefficient cooling results and cooling must be increased. Finally, since the flow of cool air is not directed to the equipment that needs cooling, any change in the room configuration or even people standing in the aisles can disrupt the cool air flow. These disruptions result in a smaller portion of the cool air actually cooling the equipment, which further decreases efficiency. The inefficiencies of the hot aisle/cold aisle system lead to wasted energy (e.g. electricity to power the air conditioners), due to the need to “overcool” the data center to make up for cooling losses. In addition, data loss and downtime can result due to equipment damage from overheating. 
     Therefore, there is a need for a system and method for cooling electronic equipment in a cabinet that efficiently and effectively delivers cooled air where it is needed, with no warm air mixing. It would also be beneficial to eliminate the dependence on a cold aisle for cool air delivery, for example by sending the cooled air directly into the cabinet. 
     SUMMARY OF THE INVENTION 
     In one example, an electronic equipment cabinet configured to support electronic equipment is provided and may include a shelf positioned in the electronic equipment cabinet separating the electronic equipment cabinet into a first zone and a second zone with the second zone positioned above the first zone. The first zone may be configured to receive cool air directly from a cool air source. The cabinet may also include a duct associated with the electronic equipment cabinet and may include a first opening configured to receive cool air from the cool air source and a second opening configured to deliver cool air to the second zone. 
     In another example, an electronic equipment cabinet configured to support electronic equipment is provided and may include a shelf positioned in the electronic equipment cabinet separating the electronic equipment cabinet into a first zone and a second zone with the second zone positioned above the first zone. The cabinet may also include a duct associated with the electronic equipment cabinet and configured to receive cool air from the cool air source and deliver cool air to the first and second zones. 
     In a further example, an electronic equipment cabinet configured to support electronic equipment is provided and may include a shelf positioned in the electronic equipment cabinet separating the electronic equipment cabinet into a first zone and a second zone with the second zone positioned above the first zone. The first and second zones may be in fluid communication with a cool air source. The cabinet may also include a baffle positioned between the cool air source and one of the first zone and the second zone to selectively control delivery of cool air from the cool air source to the one of the first zone and the second zone. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Certain examples of the present invention are illustrated by the accompanying figures. It should be understood that the figures are not necessarily to scale and that details that are not necessary for an understanding of the invention or that render other details difficult to perceive may be omitted. It should be understood, of course, that the invention is not necessarily limited to the particular examples illustrated herein. 
         FIG. 1  is a front perspective view of one example of a cabinet cooling system installed in an electronic equipment cabinet with the front door and side panels removed and a floor tile exploded; 
         FIG. 1A  is a front perspective view of a duct of the cabinet cooling system of  FIG. 1  with an inside wall of the duct removed; 
         FIG. 1B  is an enlarged view of a portion of the duct designated as  FIG. 1B  in  FIG. 1A ; 
         FIG. 2  is the cabinet cooling system of  FIG. 1  with a portion of the right side duct removed; 
         FIG. 3  is a front perspective view of a second example of a cabinet cooling system installed in an electronic equipment cabinet with the front door and side panels removed and a floor tile exploded; 
         FIG. 4  is an exploded front perspective view of one of the ducts of  FIG. 3 ; 
         FIG. 5  is a rear perspective view of the cabinet cooling system of  FIG. 3  with a portion of the duct removed; 
         FIG. 6  is an enlarged partial view designated as  FIG. 6  in  FIG. 5 ; 
         FIG. 7  is an enlarged partial side perspective view of a third example of a cabinet cooling system installed in an electronic equipment cabinet with the front door and side panels of the cabinet removed and a portion of the duct removed; 
         FIG. 8  is an enlarged partial side perspective view of the cabinet cooling system of  FIG. 7  with an alternative locking mechanism; 
         FIG. 9  is an enlarged partial front view of the cabinet cooling system of  FIG. 8 ; and 
         FIG. 10  is a schematic of at least a portion of the components of the cabinet cooling system in the exemplary embodiment of  FIG. 3 . 
     
    
    
     DETAILED DESCRIPTION 
     Referring to  FIGS. 1-2 , one example of a cabinet cooling system  5  is shown installed in an electronic equipment cabinet  60  (the front door and side panels of cabinet  60  are removed for clarity). As shown and described herein, cabinet  60  is a network cabinet, such as that shown and described in co-pending U.S. patent application Ser. Nos. 11/467,956, 11/538,884, 11/559,708, 11/623,358, 11/623,839, and 11/683,052, which are incorporated herein by reference. However, it will be understood that cooling system  5  can be used with any type of cabinet that is adapted to carry electronic equipment, such as servers. 
     In this example, cooling system  5  is generally made up of ducts  10 , which are minor images of each others and shelf  50 . Each duct  10  is generally rectangular and is formed by front wall  10 A, back wall  10 B, inside wall  10 C, outside wall  10 D, top wall  10 E, and a bottom wall (not shown). As used herein, inside wall  10 C is the wall of duct  10  that faces electronic equipment  62  in the interior of cabinet  60  when duct  10  is installed and front wall  10 A is the wall of duct  10  that faces the front of cabinet  60  when duct  10  is installed. Although the exemplary ducts  10  are described herein as being generally rectangular, ducts  10  could be made of any shape or size required for a particular application or to fit a particular equipment cabinet. In the example shown herein, ducts  10  are approximately 20 inches×4.5 inches×84 inches. 
     With particular reference to  FIG. 1A , an intake opening  68  is formed in the bottom wall of duct  10  and is positioned such that the intake opening  68  will be aligned with a perforated or open cutout  72  in floor tile  70  when duct  10  is installed in cabinet  60 . When installed, the intake opening  68  provides an inlet into duct  10  for cooled air flowing from cutout  72 , which allows a typical perforated front cabinet door to be replaced by a solid cabinet door, if desired, and allows the flow of cool air from under the floor to enter duct  10 . 
     With continued reference to  FIG. 1A , a perforated intake panel  73  may be positioned over the intake opening  68  to deliver more uniform air flow to duct  10 . In the example shown, perforated intake panel  73  includes multiple holes  77  and is positioned over opening  68  to deliver more uniform air flow to duct  10 . Holes  77  are formed in intake panel  73  such that intake panel  73  is approximately 56% open. Alternatively, the intake panel  73  may include more or less holes  77  to respectively increase or decrease the openness of the intake panel. In some instances, it has been found that wide-open inlets may not provide consistent airflow into duct  10  (e.g. the air entering duct  10  will try to take the path of least resistance, so some areas will receive more cool air and be overcooled while others will not receive enough cool air and will be starved). In these instances, the use of a perforated intake panel  73  has been shown to provide more uniform air flow over the entire area of the intake opening  68  by converting high velocity, low pressure air into low velocity, high pressure air. If uniform air flow through the duct  10  is not a problem or concern in a particular application, the perforated intake panel  73  is not needed. 
     Referring to  FIGS. 1 ,  1 A, and  1 B, opening  32  is formed in inside wall  10 C and, in the example shown, extends from top wall  10 E downward approximately 70% of the height of inside wall  10 C and back a predetermined distance from front wall  10 A. Alternatively, the opening  32  can extend along greater or less heights of the inside wall  10 C. Opening  32  provides an exhaust for cool air out of duct  10  and directs the cool air flowing through duct  10  towards the front of electronic equipment  62  mounted in cabinet  60 . 
     In addition, a perforated exhaust panel  75  may be positioned over opening  32  to more uniformly disperse the cool air flowing out of duct  10 . In the example shown, perforated exhaust panel  75  includes multiple holes  78  and is positioned over the opening  32  in inside wall  10 C to more uniformly disperse the cool air flowing out of duct  10 . As can best be seen in  FIGS. 1 ,  1 A, and  1 B, holes  78  are patterned such that each section  75 A-E has an upper portion that is approximately 30% open and a lower portion that is approximately 36% open. Alternatively, each section  75 A-E may include upper and lower sections with more or less openness as desired. In some instances, it has been found that a wide-open exhaust draws too much air in some areas of the exhaust, while causing starvation in other areas. In these instances, the use of the perforated exhaust panel  75  more uniformly disperses the cool air as it leaves duct  10  to enter the area in front of electronic equipment  62 . If uniform air flow out of the duct  10  is not a problem or concern in a particular application, the perforated exhaust panel  75  is not needed. 
     With continued reference to  FIGS. 1 ,  1 A, and  1 B and additional reference to  FIG. 2 , to further assist in providing uniform air flow from duct  10  across the front of electronic equipment  62 , deflector  40  extends from inside wall  10 C along the edge of opening  32 . Deflector  40  is generally L-shaped, extends the entire height of opening  32 , and is used to force all air to the front of equipment  62  and prevent cool air from flowing past the face of equipment  62  by disrupting the cool air flowing from opening  32 , thus providing more uniform air flow across the entire front of equipment  62 . Again, if uniform air flow across the front of equipment  62  is not a problem or concern in a particular application, deflector  40  may not be needed. 
     As can be seen in  FIG. 1A , in this example, baffles  79  are also positioned in the interior of duct  10  and extend horizontally through duct  10  between outside wall  10 D, front wall  10 A, and inside wall  10 C. As shown herein, there are four baffles  79 , each baffle  79  being positioned near the bottom of one of the defined sections  75 A-E of exhaust panel  75 . Each baffle  79  has a different length, with the length of the baffles  79  increasing the higher the position in duct  10  or the further away the baffle  79  is from intake panel  73 . In some instances, it has been found that completely open ducts result in more cool air exiting at the top of the duct (e.g. from the momentum of the air driving it to the top of the duct), thereby starring the lower sections of the duct. Baffles  79  can be used to control the direction, velocity and pressure of the cool air flow by breaking up the vertical air flows and directing the air flow sideways towards the front of the duct  10 . Alternatively, if the flow of cool air through the duct  10  is not a problem or concern in a particular application, baffles  79  can be removed. 
     With particular reference to  FIG. 2 , the illustrated example of each duct  10  also includes an adjustable baffle  20 . Baffle  20  is connected to rod  22 , which extends through duct  10  and protrudes through holes in front wall  10 A and back wall  10 B of duct  10  (also see  FIG. 1 ). The longitudinal axis of rod  22  is parallel to the longitudinal axis of baffle  20  such that rotation of rod  22  also rotates baffle  20  about its longitudinal axis. Knob  24  is also connected to rod  22  and allows a user to adjust baffle  20  from outside of duct  10  (also see  FIG. 1 ). In the example shown in  FIG. 2 , baffle  20  is in a partially closed position such that baffle  20  is limiting the flow of cool air through duct  10 . However, baffle  20  can be positioned in a fully closed position (generally horizontal) such that the flow of cool air will be blocked, in a fully open position (generally vertical) such that the flow of cool air will not be impeded, or in any intermediate position, which will allow control of the amount of cool air provided through duct  10  to equipment  62 . 
     Shelf  50  extends between ducts  10  and is positioned just below openings  32 . In this position, shelf  50  keeps the cool air exhausted from opening  32  within the upper portion of cabinet  60 . Shelf  50  can be mounted to the frame of cabinet  60  or can be connected to inside walls  10 C of ducts  10 . In addition, cutout  74  is formed in floor tile  70  such that it is vertically aligned below shelf  50  to provide cooling air to equipment  62  disposed below shelf  50 . In this instance, shelf  50  will also keep cool air from cutout  74  within the bottom portion of cabinet  60 . To assist in controlling the amount of cool air supplied to the bottom portion of cabinet  60 , moveable baffle  76  is positioned with cutout  74  such that baffle  76  can be positioned to allow full air flow through cutout  74 , prevent all air flow through cutout  74 , or be adjusted to allow any amount of air flow desired. In the illustrated example, the shelf  50  divides the cabinet  60  into two separately controlled zones. The first zone is above the shelf  50  and is provided with air through the ducts  10  and openings  32 , while the second zone is below the shelf  50  and is provided with air through cutout  74 . By separating the bottom portion of cabinet  60  from the upper portion with shelf  50  (i.e., into two zones) and providing a separate cool air source through cutout  74 , electronic equipment  62 , which typically received the smallest amount of cool air, is provided with sufficient cool air without diminishing the cool air supply to equipment  62  located in the upper portion of cabinet  60 . 
     In operation, cool air from cutouts  72  flows through the openings in the bottom walls of ducts  10 , through ducts  10 , and is exhausted through openings  32  into the upper front portion of cabinet  60 . The amount of cool air flowing through ducts  10  can be controlled with baffles  20 . The cool air exiting openings  32  passes over deflectors  40 , which disrupt the cool air flow, thereby preventing the cool air from flowing past the front of electronic equipment  62  and providing uniform distribution exclusively to the front of electronic equipment  62 . Shelf  50  prevents the cool air from flowing into the bottom portion of cabinet  60 , ensuring that all of the cool air is available to equipment  62  located in the upper portion of cabinet  60 . In addition, cool air from cutout  74  flows directly into the bottom portion of cabinet  60  and can be controlled with baffle  76 . Shelf  50  prevents the cool air from cutout  74  from flowing into the upper portion of cabinet  60 , ensuring that all of the cool air is available to equipment  62  located in the lower portion of cabinet  60 . 
     The exemplary cooling system  5  described above provides cool air, in the proper location, with no mixing of warm air from a hot aisle through the locating, sizing, and shaping of ducts  10 , as well as the strategic placement of baffles  20 ,  76  and shelf  50  to control air direction, pressure and velocity. Some additional benefits that may be realized through use of the exemplary cooling system  5  are: it provides all of the cool air required by the cabinet, not just supplemental air to add to hot/cold aisle air; the ability to use a solid front door on the cabinet instead of a perforated door, which prevents unwanted air from entering the cabinet; the delivery of cool air along the full height of the cabinet, not just top or bottom; reduced energy costs; reduction of the number of perforated floor tiles required; and direction of the cool air to the front of the cabinet where it is needed most. 
     Referring to  FIGS. 3-6 , a second example of a cooling system  5 ′ is shown, which in  FIGS. 3 ,  5 , and  6  is shown installed in electronic equipment cabinet  60  (front door, side panels, and one rear door have been removed for clarity). In this example, cooling system  5 ′ is generally made up of ducts  10 ′, which are mirror images of each other, and shelves  50 ′. As can best be seen in  FIG. 4 , in this example each duct  10 ′ is formed by inside section  12  and outside section  14 , which are connected to form duct  10 ′. When inside section  12  and outside section  14  are connected, duct  10 ′ is generally rectangular and has back wall  10 B′ inside wall  10 C, outside wall  10 D′, top wall  10 E′, and bottom wall  10 F. As used herein inside wall  10 C′ is the wall of duct  10 ′ that faces electronic equipment  62  in the interior of cabinet  60  when duct  10 ′ is installed and back wall  10 B is the wall of duct  10 ′ that faces the rear of cabinet  60  when duct  10 ′ is installed. Although the exemplary ducts  10 ′ are described herein as being generally rectangular, ducts  10 ′ could be made of any shape or size required for a particular application or to fit a particular equipment cabinet. 
     Intake opening  26  (see  FIG. 4 ) is formed in bottom wall  10 F and is positioned such that intake opening  26  will be aligned with perforated or open cutout  72  in floor tile  70  when duct  10 ′ is installed in cabinet  60 . Extension member  28  which in this example is formed by vertical walls  28 A-D, extends from bottom wall  10 F and surrounds intake opening  26  to assist in directing cool air from cutouts  72  to intake opening  26 . As shown in  FIG. 3 , wall  28 C can be an extension of outside wall  10 D′. When installed, intake opening  26  and extension member  28  provide an inlet into duct  10 ′ for cooled air flowing from cutout  72 , which allows a typical perforated front cabinet door to be replaced by a solid door, if desired, and allows the flow of cool air from under the floor to enter duct  10 ′. 
     In addition, a perforated intake panel similar to the perforated intake panel  73  shown in  FIG. 1  may be positioned over intake opening  26  to deliver more uniform air flow to duct  10 ′. In some instances, it has been found that wide-open inlets may not provide consistent airflow into duct  10 ′ (e.g. the air entering duct  10 ′ will try to take the path of least resistance, so some areas will receive more cool air and be overcooled while others will not receive enough cool air and will be starved). In these instances, the use of a perforated intake panel has been shown to provide more uniform air flow over the entire area of intake opening  26  by converting high velocity, low pressure air into low velocity, high pressure air. If uniform air flow through the duct is not a problem or concern in a particular application, the perforated intake panel is not needed. 
     As can best be seen in  FIGS. 3 and 4 , in this example, ducts  10 ′ do not contain front walls, which allows cool air flowing through ducts  10 ′ to be exhausted towards the front of cabinet  60 . In addition, the width of outside section  14  is greater than the width of inside section  12 , such that cool air directed toward the front of cabinet  60  can also be directed towards the front of electronic equipment  62  mounted in cabinet  60 . In this particular example, it is intended that cool air flowing through duct  10 ′ will flow towards the front of cabinet  60  and be deflected from the solid front door of cabinet  60  towards the front of equipment  62 . However, rather than relying on a solid front door, duct  10 ′ could also have a front wall similar to the front wall  10 A shown in the example illustrated in  FIGS. 1 ,  1 A,  1 B, and  2  and described above, which will deflect cool air flowing through duct  10 ′ towards the front of equipment  62 . 
     If desired, to further assist in providing uniform air flow from duct  10 ′ across the front of electronic equipment  62 , a deflector could also be used, one that is similar to the deflector  40  illustrated in  FIGS. 1 ,  1 A,  1 B, and  2  and described above, that extends from inside wall  10 C′ along the front edge of inside section  12 . As described above, the deflector could be generally L-shaped, extend the entire height of inside section  12 , and used to force all air to the front of equipment  62  and prevent cool air from flowing past the face of equipment  62  by disrupting the cool air flowing from ducts  10 ′, thus providing more uniform air flow across the entire front of equipment  62 . If uniform air flow across the front of equipment  62  is not a problem or concern in a particular application, the deflector may not be needed. 
     In the illustrated example, shelves  50 ′ extend between ducts  10 ′ and are positioned every 4 rack units to form eleven separate zones and eleven separate intake areas in front of electronic equipment  62 . Alternatively, any number of shelves  50 ′ can be used to separate the cabinet  60  into any number of separate zones with each zone having its own intake area for air. In these positions, shelves  50 ′ keep the cool air supplied to each intake area from migrating to adjacent zones and intake areas. Shelves  50 ′ can be mounted to the frame of cabinet  60  or can be connected to outside walls  10 D′ of ducts  10 ′. 
     As can best be seen in  FIGS. 5 and 6 , baffles or plates  80  are positioned vertically along the inside surface of inside wall  10 C′ such that each plate  80  is aligned between a particular set of shelves  50 ′. Plates  80  are supported by generally U-shaped brackets  85 , which are mounted to the frame of cabinet  60  and prevent the vertical or rotational movement of plates  80 , while allowing plates  80  to move horizontally. When a plate  80  is moved into a fully forward position (extended fully toward the front door of cabinet  60 ), plate  80  will prevent cool air from flowing from duct  10 ′ to the corresponding intake area between shelves  50 ′. When a plate  80  is retracted into a fully rearward position (as seen in the top plate  80  in  FIGS. 5 and 6 ), plate  80  will allow cool air to flow from duct  10 ′ to the corresponding intake area. Depending on the cooling requirements for the particular equipment corresponding to a particular intake area, the corresponding plate  80  could be fully opened to provide maximum cool air flow, fully closed to block all cool air flow, or positioned in any intermediate position to allow a regulated flow of cool air. 
     In this example the movement of plates  80  is controlled by motors  90 , which are mounted to the inside surface of wall  10 C′ at the back edge of wall  10 C′. Motors  90  could be AC powered, DC powered, or any other type of standard drive motor. A rotatable cane arm  92  is mounted to each motor  90  such that motors  90  can rotate cam arms  92  in both clockwise and counterclockwise directions. Connector rods  95  interconnect cam arms  92  and plates  80  such that as cam arms  92  rotate, connector rods  95  will moose plates  80  linearly either forward or backward. Connector rods  95  are connected to cam arms  92  by inserting an L-shaped tip  94  of each connector rod  95  through holes  96  formed in cam arms  92 . Connector rods  95  are also attached to the front portion of plates  80  through a hinge mechanism. 
     Connector rods  95  are also supported by tongues  97  (see  FIG. 6 ) formed on and extending from the surface of brackets  85 . Holes are formed through tongues  97  and receive connector rods  95  to help support and stabilize connector rods  95 . 
     With reference to  FIG. 10 , motors  90  will extend or retract plates  80  based on signals received from a control system  98 . The control system  98  may include a microprocessor  99  and a coded algorithm. Each motor  90  has a corresponding temperature sensor  101  that is positioned near the exhaust of the corresponding equipment  62  to monitor the temperature of the air being exhausted from equipment  62 . If the exhaust air from tile equipment exceeds a predetermined acceptable temperature, motor  90  will rotate cam arm  92  in a counterclockwise direction, which will move the corresponding plate  80  backward and allow more cool air from duct  10 ′ into the intake area corresponding to that equipment. If the exhaust air from the equipment drops below a predetermined acceptable temperature, motor  90  will rotate cam aim  92  in a clockwise direction, which will move the corresponding plate forward and allow less cool air from duct  10 ′ into the intake area corresponding to that equipment. 
     In operation, cool air from cutouts  72  flows through extension members  28  and openings  26  in bottom walls  10 F of ducts  10 ′ and through ducts  10 ′, where the cool air is directed to the front of cabinet  60 . Depending on the positioning of plates  80 , the cool air is then directed in the intake areas in the front portion of cabinet  60  between shelves  50 ′. The amount of cool air provided to each intake area is controlled by the position of plates  80 . Shelves  50 ′ prevent the cool air from migrating between intake areas, ensuring that all of the cool air is available to equipment  62  corresponding to each intake area. 
     The exemplary cooling system  5 ′ described above provides cool air, in the proper location, with no mixing of warm air from a hot aisle through the locating, sizing, and shaping of ducts  10 ′, as well as the strategic placement and control of shelves  50 ′ and plates  80  to control air direction, pressure and velocity. 
     Some additional benefits that may be realized through use of the exemplary cooling system  5 ′ are: it provides all of the cool air required by the cabinet, not just supplemental air to add to hot/cold aisle air; the ability to use a solid front door on the cabinet instead of a perforated door, which prevents unwanted air from entering the cabinet; the delivery of cool air to particular equipment as required; reduced energy costs; reduction of the number of perforated floor tiles required; and direction of the cool air to the front of the cabinet where it is needed most. 
     Referring to  FIG. 7 , a third example of a cooling system  5 ″ is shown installed in electronic equipment cabinet  60  (front door, side panels, and one rear door have been removed for clarity). In this example, cooling system  5 ″ is the same as cooling system  5 ′ of  FIGS. 3-6  in that it is generally made up of ducts  10 ′, which are mirror images of each other, shelves  50 ′, moveable plates  80 , and U-shaped brackets  85 , as described above for cooling system  5 ′. 
     However, in this example, cooling system  5 ″ does not have motors  90 , cam arms  92  or connector rods  95  to automatically adjust the position of plates  80 . Rather, in cooling system  5 ″, the position of plates  80  is adjusted manually by the user. To facilitate the manual adjustment of plates  80 , each plate  80  has a tab  82  at the front end of the plates  80 , which allows a user to grasp each plate  80  to adjust its position forward or back as desired. Once a plate  80  has been positioned, it can be secured by set screw  87 , which is thread through a threaded aperture formed in bracket  85 . As set screw  87  is tightened, it contacts and presses against the side of plate  80 , thereby preventing plate  80  from being moved. 
     Referring to  FIGS. 8 and 9 , cooling system  5 ″ of  FIG. 7  is shown with an alternative locking mechanism in place of set screws  87 . In the example shown in  FIGS. 8 and 9 , each bracket  85  has a cam-type locking mechanism  100  comprising a cylinder  105  that is eccentrically mounted on shaft  110  and can extend through an aperture in bracket  85 . With cylinder  105  positioned such that the point on the surface of cylinder  105  closest to the axis of shaft  110  is adjacent plate  80  (see cylinder  105 B in  FIG. 9 ), cylinder  105  will not contact plate  80  and plate  80  will be free to move within bracket  85 . With cylinder  105  positioned such that the point on the surface of cylinder  105  furthest from the axis of shaft  110  is adjacent plate  80  (see cylinder  105 A in  FIG. 9 ), cylinder  105  will provide through the aperture in bracket  85  and contact and press against the side of plate  80 , thereby preventing plate  80  from being moved. One end of shaft  110 , opposite cylinder  105 , is bent at an angle of approximately 90 degrees relative to the remainder of the shaft  110  to provide a gripping portion  112 , which allows a user to rotate shaft  110  and cylinder  105  to lock or unlock plate  80 . 
     The foregoing description has been presented for purposes of illustration and description, and is not intended to be exhaustive or to limit the invention to the precise form disclosed. The descriptions were selected to explain the principles of the invention and their practical application to enable others skilled in the art to utilize the invention in various embodiments and various modifications as are suited to the particular use contemplated. Although particular constructions of the present invention have been shown and described, other alternative constructions will be apparent to those skilled in the art and are within the intended scope of the present invention.