Abstract:
A sealed electronic equipment enclosure with a dedicated cooling system is fitted with movable louvers in the enclosure walls. During normal operation, air pressure developed by the dedicated cooling system keeps the louvers closed and maintains the enclosure sealed to the computer room environment. If the dedicated cooling system fails, the internal air pressure developed by the cooling system is reduced and air movers in the electronic equipment force the louvers open, thereby allowing the air movers to draw cooled air from the computer room into the enclosure. This cooled air prevents the equipment from overheating at least for a time period long enough to allow the dedicated cooling system to be replaced or repaired.

Description:
FIELD OF THE INVENTION 
   This invention relates to self-cooled electronic equipment enclosures with internal cooling systems and to mechanisms for avoiding equipment shutdown on cooling system failure. 
   BACKGROUND OF THE INVENTION 
   In many large electronic equipment centers or data centers it is common practice to mount electronic equipment in enclosures called “racks.” In order to cool the equipment, the racks have open fronts and backs and are placed in an air-conditioned computer room. The interior of a typical computer room  100  is illustrated in  FIG. 1 . In such a room, a raised floor  103  is constructed over the actual floor  102 . The raised floor is conventionally constructed of a grid framework  104  that supports modular floor panels  106 . The racks of equipment, of which racks  116 ,  118 ,  120 ,  122  and  124  are shown, are placed on the raised floor  103 . Typically, channels  130  and  132  run across the tops of the racks to allow the electronic equipment to be interconnected by cables. (not shown) that are placed in the channels. 
   At the perimeter of the room  100 , one or more computer room air-conditioning (CRAC) units, of which unit  108  is shown, provide cooling. Unit  108  generates a stream of refrigerated air illustrated schematically by arrow  110  in the space between the raised floor  103  and the actual floor  102 . The cooled air enters the room though perforations  112  in the panels located between the racks  116  and  124  and  120  and  122 . The electronic equipment in the racks typically has air movers comprised of blowers or fans that circulate air over the equipment. Thus, the cooled air is drawn into the equipment as schematically illustrated by arrow  114 . 
   The heated air is exhausted from the back of the racks and rises to the ceiling of the room  100  as schematically illustrated by arrows  140 ,  142  and  144 . Warm  air at the ceiling is then drawn into the intake  160  of the CRAC unit  108  as indicated schematically by arrows  150 ,  152  and  154  in order to begin the cycle again. 
   While this arrangement operates in a satisfactory manner, computer room personnel must take care to physically locate the equipment racks in the room in order to evenly spread the cooling load represented by the electronic equipment. Otherwise localized “hot spots” can develop and cause equipment overheating even though the CRAC units can handle the overall cooling load. In a large data center where equipment is constantly being added, removed and changed, the logistics of maintaining an even cooling load can become difficult. Further, conventional computer room cooling systems have been designed to handle power dissipations of 1–1.5 kilowatts per rack. However, the reduction in electronic component size has resulted in electronic systems currently being built that dissipate 12–20 kilowatts per rack. Even with proper equipment placement, such systems can cause a hot spot and a cooling overload. If an electronic system overheats, it can become damaged. Alternatively, on-board sensors may power down the system, resulting in an unscheduled service interruption. 
   One prior art attempt to solve the hot spot problem is to mount a dedicated cooling system on the top of a rack. This dedicated cooling system can be a self-contained air conditioning unit or it can be a heat exchanger that receives a cooling liquid, such as chilled water, via pipes from a cooling system located at the perimeter of the room. The dedicated cooling system draws in hot air rising from the back of the rack, cools the air and generates a stream of cooled air that is discharged in front of the rack where it can be drawn into the rack by the air movers that are part of the electronic equipment. A problem with this system is that there is little control over the cooled air since the racks are open.1 
   Another alternative is to enclose the electronic equipment in a sealed enclosure that is provided with its own dedicated cooling system. This cooling system can also be a self-contained air conditioning unit or a heat exchanger that receives a cooling liquid from a cooling system located at the perimeter of the room. A sealed enclosure has the advantage that it is completely independent from any of the other  racks in its vicinity. Consequently, such sealed units can be placed anywhere in the computer room without developing hot spot problems. This greatly simplifies the logistics of maintaining the computer room. However, if the cooling system fails, the electronic equipment in the sealed enclosure will rapidly overheat and shut down. One prior art method of solving this latter problem is to include a backup cooling system in the enclosure that can prevent the equipment from overheating at least for a time period long enough to allow the cooling system to be replaced or repaired. Unfortunately, backup cooling systems add significantly to the cost of the enclosure, rendering their use prohibitive in many applications. 
   SUMMARY OF THE INVENTION 
   In accordance with the principles of the invention, a sealed enclosure with a dedicated cooling system is fitted with movable louvers in the enclosure walls. During normal operation, air pressure developed by the dedicated cooling system keeps the louvers closed and maintains the enclosure sealed to the computer room environment. If the dedicated cooling system fails, the internal air pressure developed by the cooling system is reduced and air movers in the electronic equipment force the louvers open, thereby allowing the air movers to draw cooled air from the computer room into the enclosure. This cooled air prevents the equipment from overheating at least for a time period long enough to allow the dedicated cooling system to be replaced or repaired. 
   In accordance with one embodiment, movable louvers are placed in doors at opposite sides of the enclosure. 
   In accordance with another embodiment, the louvers pivot on pins and are closed by gravity. 
   In accordance with yet another embodiment, the louvers are attached to the housing by spring hinges.  

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The above and further advantages of the invention may be better understood by referring to the following description in conjunction with the accompanying drawings in which: 
       FIG. 1  is a perspective view of a conventional computer room schematically illustrating the flow of cooled air produced by a perimeter air conditioning system. 
       FIG. 2  is a perspective view of an electronic equipment enclosure including horizontal air flow controlled louvers in accordance with the principles of the invention. 
       FIG. 3  is a perspective view of an electronic equipment enclosure including vertical air flow controlled louvers in accordance with the principles of the invention. 
       FIG. 4  is a side view of an electronic equipment enclosure wherein the side panel has been cut away to illustrate the air flow within the enclosure when the dedicated cooling unit is in operation. 
       FIG. 5  is a side view of an electronic equipment enclosure wherein the side panel has been cut away to illustrate the air flow within the enclosure when the dedicated air cooling unit is not in operation. 
       FIG. 6  is a detailed end view of a set of louvers that pivot on pins. 
       FIG. 7  is a detailed end view of a set of louvers that are biased by springs. 
       FIG. 8  is a detailed end view of a set of louvers with spring-loaded hinges. 
   

   DETAILED DESCRIPTION 
     FIG. 2  is a perspective view of an electronic equipment enclosure  200  including air flow controlled louvers in accordance with the principles of the invention. As shown in  FIG. 2 , the enclosure  200  may be connected to an external cooling unit that provides a coolant via pipes  202  and  204 . Pipes  202  and  204  connect to a heat  exchanger. 214  located within the enclosure  200 . Alternatively, the heat exchanger (or cooling unit) may be located at either the side of enclosure  200  as shown schematically at  216  or on both sides. The heat exchanger (or cooling unit) may also be located at the bottom of enclosure  200  as shown schematically at  218 . Alternatively, a self-contained dedicated cooling unit may be used within enclosure  200  in which case pipes  202  and  204  are unnecessary. In all cases the inventive air flow controlled louvers work in the same manner. 
   Enclosure  200  is fitted with hinged doors, of which door  206  is shown. Door  206  is attached to enclosure  200  by means of hinges  210  and  212  in order to allow access to the interior of enclosure for equipment repair or replacement. Preferably door  206  is fitted with air tight seals (not shown) to maintain the enclosure sealed when the door is closed. In accordance with the principles of the invention, door  206  contains a set of louvers  208  located within a recess  209  in the door  206 . As will be hereinafter explained, these louvers are controlled by air pressure in order to provide an alternate air path if the cooling system  214  fails. These louvers may be either gravity or spring operated as discussed below. 
   Another door (not shown in  FIG. 2 ) is located on the opposite side of enclosure  200  to allow access to the rear side of the equipment in enclosure  200 . This other door may be similar to door  206  or may be different. For example, it may be a different size or may be fitted with a different hinge arrangement. In any case this other door is also fitted with louvers in the same manner as door  206 . Alternatively, the hinged doors could be replaced with removable panels in which the louvers are mounted without departing from the spirit and scope of the invention. 
   The louvers  208  can also be mounted vertically as shown in  FIG. 3 . In  FIG. 3 , elements that correspond to elements in  FIG. 2  have been given corresponding numeral designations. For example, enclosure  300  in  FIG. 3  corresponds to enclosure  200  in  FIG. 2 . Similarly, louvers  308  in  FIG. 3  correspond to louvers  208  in  FIG. 2 . A door similar to door  306  is also located at the opposite side of enclosure  300  in a manner similar to the enclosure  200  in  FIG. 2 .  
     FIG. 4  is a side view of an enclosure  400  constructed in accordance with the principles of the invention. The side wall of the enclosure has been cut away so that the air flow patterns can be illustrated. Typically, enclosure  400  contains a plurality of equipment trays that are mounted in the center of the enclosure. In  FIG. 4 , trays  420 ,  424 ,  428 ,  432  and  436  are shown. Trays  420 – 436  have sufficient width that they extend across the entire width of enclosure  400 . However, trays  420 – 436  do not extend the full depth of the enclosure and leave air circulation spaces  446  and  448  at the front and back of the enclosure, respectively. 
   The cooling unit  414  is located at the top of the enclosure  400  in this embodiment. Unit  414  typically has a heat exchanger element  415  that cools air passing over the element. Since the heat exchanger element  415  is comprised of fins or other extensions that increase its surface area, it has a high airflow resistance. A powerful fan or blower, schematically illustrated as fan  440 , is used to overcome the airflow resistance of the heat exchanger element and provide air circulation. In particular, heated air is drawn into the heat exchanger element  415  as indicated by arrow  442  and cooled air is discharged as indicated by arrow  444 . 
   In general, the electronic equipment in each tray is also provided with an air mover, in the form of a fan or blower that draws cooled air over the electronics. These air movers are schematically illustrated as fans  422 ,  426 ,  430 ,  434  and  438  for trays  420 ,  424 ,  428 ,  432  and  436 , respectively. The air mover  422  for a tray, such as tray  420 , draws in some of the cooled air discharged by the heat exchanger element  415  as indicated, for example by arrow  450 , passes the air over the electronics as indicated by arrow  452  and discharges heated air into the rear air circulation space  448  as indicated by arrow  454 . A similar airflow occurs in each tray under the action of the associated air mover. The heated air discharged by all air movers into space  448  is then drawn into the heat exchanger element by fan  440 . 
   Because fan  440  has a much larger capacity than the individual air movers  422 – 438 , even with all air movers operating, the pressure P I  in the heat exchanger intake space  448  will be lower than the ambient pressure P A  outside of the  enclosure  400 . Similarly the pressure P D  in the heat exchanger discharge space  446  will be higher than the ambient pressure P A  outside of the enclosure  400 . 
   The pressure differential in the intake space  448  is applied across the back wall  460  of the enclosure  400  in which louvers  409  are located. In  FIG. 4 , louvers  409  are illustrated as pivoting about pins  411 , although other arrangements, discussed below, can also be used. Louvers  409  are biased so that they are normally closed as illustrated in  FIG. 4 . Biasing can be accomplished by gravity or springs. When the louvers are in their closed position as shown in  FIG. 4 , the pressure differential between the air outside the enclosure and the lower pressure of the intake space  448  maintains the louvers in the closed position, thereby sealing the intake space from the ambient air. 
   Similarly, the pressure differential of the higher pressure in the discharge space  448  over the ambient air pressure is applied across the front wall  462  of the enclosure  400  in which louvers  408  are located. As with louvers  409 , louvers  408  are illustrated as pivoting about pins  413 . Louvers  408  are also biased so that they are normally closed as illustrated in  FIG. 4 . When the louvers  408  are in their closed position as shown in  FIG. 4 , the pressure differential between the discharge space  446  and the air outside the enclosure maintains the louvers in the closed position, thereby sealing the discharge space from the ambient air. Consequently, during normal operation, the front and back walls of the enclosure  400  are sealed by the louvers causing the enclosure to act as a totally sealed enclosure independent of the outside environment. 
     FIG. 5  illustrates the operation of the enclosure during a failure of the dedicated cooling system in accordance with the principles of the invention. In  FIG. 5 , elements that correspond to elements in  FIG. 4  have been given corresponding numeral designations. For example, heat exchange element  415  corresponds to heat exchanger element  515 . Elements in  FIG. 5  that correspond to elements in  FIG. 4  will not be described in general. Cooling system failure can occur because the fan  440  fails or because the source of cooling liquid fails or for some other reason. The cooling system is arranged so that fan  440  stops operating regardless of the source of failure.  This can be accomplished, for example, by mounting on the heat exchanger element  515 , a temperature detector  541  that removes power from the fan when the temperature of the heat exchanger element  515  rises above a predetermined threshold. 
   Therefore, upon failure of the cooling system, the fan  540  will stop operating. However, the air movers  522 – 538  in the electronic equipment trays continue to operate. Since the air flow resistance of heat exchange element  515  is considerable, the output air flow of the air movers  522 – 538  quickly reverses the pressure differential between the intake space  448  and the outside air so that the pressure P I  becomes higher than the ambient air pressure P A . This new pressure differential is applied to the louvers  409  causing them to swing out as shown in  FIG. 5 . 
   Similarly, due to the air flow resistance of the heat exchanger element  515 , the intake air flow of the air movers  522 – 538  quickly reverses the pressure differential between the discharge space  446  and the outside air so that the pressure P D  becomes lower than the ambient air pressure P A . This new pressure differential is applied to the louvers  408  causing them to swing in as shown in  FIG. 5 . 
   The opening of louvers  408  and  409  establishes a new air flow path  570  in which the air mover  522  draws cooled air from computer room in through the front of the enclosure  500  and exhausts heated air into the computer room the back of the enclosure  500 . Since the air in the computer room is generally cooled by the conventional CRAC systems, it will provide sufficient cooling for the electronic units until a controlled shut down can be effected or the cooling unit can be repaired by computer room personnel. Similar air paths result from the continued operation of air movers  526 – 538 . 
   The louvers can be of several types as shown in  FIGS. 6 ,  7  and  8 .  FIG. 6  shows the louvers  600  as illustrated in  FIGS. 4 and 5 .  FIG. 6  illustrates one end of each louver, of which louvers  602 ,  604  and  606  are shown. Louvers  602 ,  604  and  606  are pivoted on pin pairs consisting of a pin located at each end of a louver of which pins  608 ,  610  and  612  are illustrated. Another pin (not shown in  FIG. 6 ) would be located in the opposing end of each louver. Louvers  602 ,  604  and  606  are biased in the closed position via gravity.  
     FIG. 7  shows the louvers  700  similar to those illustrated in  FIGS. 4 and 5 .  FIG. 7  also illustrates one end of each louver, of which louvers  702 ,  704  and  706  are shown. Louvers  702 ,  704  and  706  are pivoted on pin pairs consisting of a pin located at each end of a louver of which pins  708 ,  710  and  712  are illustrated. Another pin (not shown in  FIG. 7 ) would be located in the opposing end of the louvers. Louvers  702 ,  704  and  706  are biased in the closed position by means of springs  714 ,  716  and  718 , which could be coil springs as shown or flat springs. Spring-loaded louvers, such as louvers  702 ,  704  and  706 , are suitable for enclosures such as that shown in  FIG. 3 , in which the louvers are vertical. 
     FIG. 8  illustrates louvers  800  that have spring hinges. Three louvers  802 ,  804  and  806  are shown. Each louver, such as louver  802 , comprises a support piece  808  that is attached to the enclosure. The support piece  808  is, in turn, attached, by a spring hinge  812  to the louver  810 . The support piece  808 , the spring hinge  812  and the louver  810  may be formed of the same piece of material that has been molded into the appropriate shape. Advantageously, the louvers  802 ,  804  and  806  could by fabricated from a plastic polymeric material. 
   It is also possible for the louvers to be motor driven. In this case the motor can be controlled by a sensor that causes the motor to open the louvers when the pressure differentials between the intake and discharge spaces reverse due to cooling system failure. 
   Although an exemplary embodiment of the invention has been disclosed, it will be apparent to those skilled in the art that various changes and modifications can be made which will achieve some of the advantages of the invention without departing from the spirit and scope of the invention. For example, it will be obvious to those reasonably skilled in the art that, although the problem stated above was described in terms of a conventional rack enclosure, other enclosures could also be similarly fitted with louvers and realize the advantages and benefits of the inventions. Similarly, other arrangements, such as flaps or doors can be substituted for the louvers in order to achieve the same effect. Other aspects such as the specific size and configuration of the louvers and/or closing mechanisms utilized to achieve a particular function, as well  as other modifications to the inventive concept are intended to be covered by the appended claims.