Abstract:
An equipment-rack power distribution system is described which includes a PDU housing, a power input penetrating the housing, a plurality of power outlets disposed on a surface of the housing, circuitry enclosed in the housing interconnecting the power input and the power outlets, one or more air inlets associated with the housing, one or more air outlets associated with the housing, and an air flow device in fluid communication with one or more of the air inlets and the air outlets. An environmental sensor may activate the air flow device upon detection of predetermined environmental conditions, such as a temperature that is above a defined limit.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     The present Application for Patent claims priority to U.S. Provisional Patent Application No. 61/411,831 entitled “EQUIPMENT-RACK POWER DISTRIBUTION SYSTEM WITH COOLING” filed Nov. 9, 2010, and assigned to the assignee hereof and hereby expressly incorporated by reference herein. 
    
    
     BACKGROUND 
     Power distribution units (PDUs) for electrical equipment racks such as RETMA racks are becoming highly sophisticated. Once little more than a simple plug-strip, today a PDU may include complex circuitry that can perform such functions as switching any of numerous outlets off and on, receiving commands from and transmitting data to remote power managers, and controlling power sources such as uninterruptible power supplies (UPSs). Such a PDU may include a microprocessor and embedded software and may be accessed through a web browser under control of a remotely-located user. Examples of such PDUs may be found in U.S. Pat. Nos. 7,116,550, 7,137,850, 7,171,461, and 7,196,900, all of which are incorporated herein by this reference. 
     Physical space that can accommodate a PDU in an equipment rack is at a premium because most of the space in such a rack is occupied by computers and other electronic appliances. Most or all of these appliances draw power from the PDU. Accordingly, PDUs typically are built in long, narrow, tight enclosures that have barely enough room to accommodate one or more power inlets and up to 24 or more power outlets. Such PDUs are often designed with a vertical form factor to facilitate mounting vertically in a back corner area of an equipment rack, out of the way of the appliances in the rack but accessible from the rear of the rack so that the appliances can readily be plugged into and unplugged from the outlets. 
     In general, PDU housings have not expanded despite the addition of more complex circuitry that gives the PDUs more capabilities. However, this circuitry generates heat, and as more such circuitry is added into the confined space of a PDU housing, dissipating this heat has become a significant problem. 
     Adding to the heat dissipation problem has been the trend to install increasingly-complex computers and other appliances, and more of them, in electrical equipment racks. This has had the effect of generating more heat within the rack, making more demands on the PDU and thereby increasing the amount of heat generated by circuitry within the PDU, and reducing the volume of air in the rack that can dissipate that heat. The combination of more heat generated in a confined space within the PDU, more heat generated by the appliances in the rack, and less air space in the rack, has led to great difficulty in keeping the internal temperatures within PDUs within safe limits. 
     The general problem of thermal management in equipment racks has been recognized, and various methods and devices have been proposed for cooling computers, computer power supplies, and other appliances in an equipment rack. By way of example, in U.S. Pat. No. 7,173,821 issued to Coglitore, it is proposed to install various appliances back-to-back in a rack with an overhead power supply, with cooling air to flow between the appliances, and to locate a central power supply in a rack by itself with a dedicated cooling system. 
     SUMMARY 
     Briefly and in general terms, the problem of heat dissipation in an equipment-rack PDU is solved by circulating cooling air through the PDU. An equipment-rack power distribution system according to an embodiment includes a PDU housing, a power input penetrating the housing, a plurality of power outlets disposed on a surface of the housing, circuitry enclosed in the housing interconnecting the power input and the power outlets, one or more air inlets associated with the housing, one or more air outlets associated with the housing, and an air flow device coupled to at least one of the air inlets and the air outlets. 
     Spaces between the outlets and the housing may be closed with gaskets. The air flow device may include a fan and a conduit defining an air passage between the fan and the housing. In an embodiment having two fans, a baffle may be pivotingly disposed between the fans so that when both fans are activated the flow of air from the fans urges the baffle into a neutral position and when one fan is activated the flow of air urges the baffle against the other fan. An environmental sensor, such as a thermostat, may be used to activate the fan depending on temperature inside the PDU housing. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view of an equipment rack with an installed PDU according to an embodiment, taken from the front of the rack. 
         FIG. 2  is a perspective view of an upper portion of an equipment rack with an installed PDU according to an embodiment, taken from the rear of the rack. 
         FIG. 3  is a perspective view of an upper portion of an equipment rack with an installed PDU according to an embodiment, taken from the front of the rack. 
         FIG. 4  is a perspective of a lower portion of an equipment rack with an installed PDU according to an embodiment, taken from the front of the rack. 
         FIG. 5  is a perspective view of a bracket-and-fan assembly taken from the front. 
         FIG. 6  is a perspective view of a bracket-and-fan assembly taken from the rear and with the conduit removed to show the baffle with both fans operating. 
         FIG. 7  is a perspective view of a bracket-and-fan assembly taken from the rear and with the conduit removed to show the baffle with one fan operating. 
         FIG. 8  is a top view of a plurality of equipment racks with a cooling duct connected to PDUs in the racks. 
     
    
    
     DETAILED DESCRIPTION 
     As shown in  FIGS. 1 through 3 , an equipment-rack power distribution system according to an embodiment includes an elongated power distribution unit (PDU) housing  101 . The housing is shown installed in a rack such as a RETMA equipment rack  103 . The PDU housing may be secured to the rack by any convenient mounting fixture. For example, the PDU housing may be supported by a bracket  105 , by fasteners (not shown) extending through holes in the housing and through a bracket  107  that is part of the rack, or some other mounting arrangement as desired. A plurality of supports such as shelf brackets  109  are included in the rack and are used for supporting computers and other appliances that are installed in the rack. While several of the illustrated embodiments provide PDU housings that are vertically mountable in equipment racks, it will be readily understood that the concepts described herein also apply to PDUs having other form factors, such as horizontally mountable units. 
     A power input  111  penetrates the housing  101  and provides power to the PDU. The power input may be in the form of a single-phase power cord and plug as shown, it may be a 3-phase power cord and plug, or it may be a permanently-wired electrical supply such as Romex cable or the like. The power input may, in some embodiments, include dual or redundant power inputs. Power outlets  113  are disposed in a surface  115  of the housing. Circuitry (not shown) enclosed in the PDU housing interconnects the power input and the power outlets and may perform other functions such as sensing parameters of electrical power flow through the outlets, controlling the outlets, and communicating with an external power manager application (not shown). 
     An air inlet  117  is disposed in a first end  119  of the housing. In the illustrated embodiment, an air flow device  121  is coupled to the air inlet. In another embodiment as shown in  FIG. 4 , an air outlet  123  is disposed in a second end  125  of the housing and an air flow device  127  is coupled to the air outlet. Some embodiments may use air circulation devices for both air inlet and air outlet, other embodiments use an air circulation device only at one of the inlet and the outlet. 
     Returning to  FIG. 2 , in some embodiments a digital readout  129  disposed in the housing, or another indicator in communication with the circuitry, gives a visual display of information such as current flow to one or all of the outlets, voltage, temperature, or other parameter respecting the PDU. 
     A plurality of gaskets such as the gasket  131  may be used to minimize air leakage around the power outlets. Each such gasket forms a seal between one of the outlets and the housing. The gaskets may be rubber, synthetic rubber, or some other substance that conforms to the edges of the outlet and the surface  115  of the housing. 
     The air flow device  121  may include at least one fan  133  and a conduit  135  defining an air passage between the fan and the housing. It will be readily understood that an air flow device may, in other embodiments, may include more or fewer components, such as simply a fan located within, or immediately adjacent to, the PDU housing. With continuing reference to the air flow device  121  of the embodiment of  FIG. 3 , a bracket  137  includes an equipment-rack mounting fixture such as openings  139  that receive a fastener  141  to attach the bracket to the rack. A fan mounting fixture such as a plurality of openings  143  can receive a fastener (not shown) to attach the fan  133  to the bracket  137 . Some embodiments use more than one fan, for example a second fan  145  shown as carried by the bracket  137 . 
     Some embodiments may omit the fan. Air within the housing is warmed by wiring and circuitry in the housing and rises, exiting the housing at the top. This results in fresh, relatively cool air being drawn into the housing at the bottom, setting up a flow pattern of air flowing into the housing at the bottom, drawing heat from the circuitry and wiring in the housing, rising as it draws the heat, and exiting the housing at the top. Conduits may be used to provide air flow paths from the exterior of the rack to the bottom of the housing or from the top of the housing to the exterior of the rack or both. In the illustrated embodiments, an air flow device may be coupled to the air inlet, which may be located at or near either the top or bottom of the housing, so that the device urges cool air through the conduit into the housing. Warmed air is thereupon expelled through the air outlet at or near the opposite end of the housing. An air flow device, in other embodiments, may be coupled to the air outlet to draw warm air out of the housing. In some embodiments air flow devices are used at both the air inlet and the air outlet. The air outlet may, in some embodiments, include a plurality of openings in the PDU housing that allow air that is urged into the housing through the air inlet(s) to exit the PDU housing and draw heat away from components within the housing. The air outlets may be located uniformly along one or more surfaces of the housing, or may be located to provide enhanced air flow around certain components within the housing. 
     In embodiments having a fan, the fan draws cool air, for example, from outside the equipment rack as in the embodiments shown in  FIGS. 1 through 4 , and urges this cool air into the housing. This action of the fan causes air to flow through the housing, drawing away heat, and then out of the housing through the air outlet. In some embodiments a duct may conduct the warmed air away from the air outlet, for example to the exterior of the equipment rack. 
     Two fans may be installed adjacent each other as shown in  FIGS. 5 through 7 . A first fan  147  and a second fan  149  are carried by a bracket  151  and enclosed by a single conduit  153 . A baffle  155  is pivotally disposed between the two fans, according to this embodiment. For example, the baffle may be supported by a pivot shaft  157  on pivot points  159 . The baffle may have first and second air plates  161  and  163 , respectively, the first air plate  161  disposed to receive air flowing from one of the fans  147  and the second air plate  163  disposed to receive air flowing from the other of the fans  149 . When both fans are activated the flow of air from the fans urges the baffle into a neutral position as shown in  FIG. 6 , and when one fan is activated the flow of air urges the baffle against the other fan. For example, as shown in  FIG. 7 , when the first fan  147  is activated and the second fan  149  is not activated, air flow from the fan  147  pushes against the first air plate  161 , urging the baffle to pivot about the pivot shaft  157  and press the second air plate  163  against the second fan  149 , preventing air from escaping through the second fan  149  back out of the rack. 
     An environmental sensor, such as a thermostat, shown generally as  165 , may be used is some embodiments to provide enhanced cooling. The environmental sensor  165  is in electrical communication with the fans and is responsive to temperature in the housing to activate, none, one, or more fans as needed to keep the temperature inside the housing within desired limits. The thermostat may include a temperature sensor (not shown) inside the housing, for example. 
     More than two fans may be provided according to some embodiments. A third fan  167  and a fourth fan  169 , for example, may be installed in the panel  151  and enclosed in a conduit  171 . The conduit  153  may extend to the air inlet  117  of the housing and the conduit  171  may extend to the air outlet  123 . The fans  149  and  147  would draw cool air from outside the rack and urge it into the housing, and the fans  167  and  169  would draw warm air from the housing and urge it out of the rack. Or the conduit  171  may join the conduit  153  to provide a higher rate of air flow or to provide more precise control over the volume of cooling air flow by allowing for selective activation of various ones of the fans. 
       FIG. 8  illustrates a configuration in which a plurality of equipment racks  201 ,  202 ,  203 ,  204 ,  205  and  206  are furnished with cooling air from an external source (not shown). The external source may be a central air conditioner or other device from which a flow of cooling air may be obtained. This cooling air flows from the source through a conduit  207  into a duct  209 . The duct  209  is connected to a PDU housing  211  through a connecting duct  221  in the equipment rack  201 , to a PDU housing  212  through a connecting duct  222  in the equipment rack  202 , to a PDU housing  213  through a connecting duct  223  in the equipment rack  203 , to a PDU housing  214  through a connecting duct  224  in the equipment rack  204 , to a PDU housing  215  through a connecting duct  225  in the equipment rack  205 , and to a PDU housing  216  through a connecting duct  226  in the equipment rack  206 . Or the duct  209  may be configured to connect directly to the various PDU housings, in which case the connecting ducts may be omitted. Other ducting configurations may be used if desired. As with the embodiments already described, the air may flow either up or down through the PDUs. For example, the duct  209  may be located on top of the equipment racks and air may be urged through it, for example by fans (not shown) into the upper extremities of the PDU housings and down through the housings. Or the duct  209  may be located beneath the equipment racks and air urged through it into the lower extremities of the PDU housings. 
     A cooling system constructed according to an embodiment was tested. Sensors were used to detect the actual temperatures of various components within the PDU. First the system was tested with no cooling and with a nominal ambient temperature of 50° C. in the interior of the rack. Next the system was tested with cooling in operation and the same ambient temperature. Finally the system was tested with cooling in operation and a nominal ambient temperature of 70° C. in the interior of the rack. 
     
       
         
               
             
               
               
               
               
               
             
           
               
                 TABLE I 
               
             
             
               
                   
               
               
                 First Test Sequence 
               
             
          
           
               
                   
                   
                 Recorded 
                 Recorded 
                 Recorded 
               
               
                   
                   
                 Temp. 
                 Temp. 
                 Temp. 
               
               
                   
                   
                 Non-Cool 
                 Cool 
                 Cool 
               
               
                   
                   
                 PDU 
                 PDU 
                 PDU 
               
               
                 TC-08-A 
                   
                 @50 C. 
                 @50 C. 
                 @70 C. 
               
               
                 channel# 
                 Thermocouple Location 
                 (deg. C.) 
                 (deg. C.) 
                 (deg. C.) 
               
               
                   
               
               
                 1 
                 Surface of PCB-0275 
                 77.2 
                 55.7 
                 66.1 
               
               
                   
                 (Input Distribution 
               
               
                   
                 Board) Between P1 and 
               
               
                   
                 P9 tabs. 
               
               
                 2 
                 Surface of U1 on 
                 58.9 
                 47.2 
                 58.2 
               
               
                   
                 PCA-0296 
               
               
                   
                 (TRMS Board) 
               
               
                 3 
                 Surface of U1 on 
                 65.2 
                 41.8 
                 49.2 
               
               
                   
                 PCA-0325 
               
               
                   
                 (BCS Board) 
               
               
                 4 
                 Surface of PCB-0349 
                 81.6 
                 39.7 
                 45.2 
               
               
                   
                 (CDU_IPM_C1913) 
               
               
                   
                 on Upper branch (L1.) 
               
               
                 5 
                 Surface of Filtering 
                 66.1 
                 31.8 
                 35.7 
               
               
                   
                 Capacitor of PS 
               
               
                   
                 Board. C2 of Kaga. 
               
               
                 6 
                 Surface of Transformer 
                 74.6 
                 34.9 
                 38.8 
               
               
                   
                 Coil of PS Board. T1 
               
               
                   
                 of Kaga. 
               
               
                 7 
                 Outside Enclosure at 
                 53.9 
                 46.1 
                 59.8 
               
               
                   
                 pre-determined 
               
               
                   
                 product hot spot. 
               
               
                 8 
                 Chamber Ambient 
                 52.0 
                 52.3 
                 72.5 
               
               
                   
                 Temperature. 
               
               
                   
               
             
          
         
       
     
     In the first test sequence, the actual ambient temperatures (line 8) exceeded the nominal ambient temperatures. With no cooling, the temperatures of the various components (lines 1-6) all significantly exceeded the ambient. With cooling, the temperatures of all components were substantially lowered, all but one component being well below the 50° ambient and all of them being substantially below the 70° ambient. 
     While various embodiments of the present invention have been described in detail, it is apparent that modifications and alterations of those embodiments will occur to those skilled in the art. However, it is to be expressly understood that such modifications and alterations are within the scope and spirit of the present invention, as set forth in the following claims. Further, the invention(s) described herein is capable of other embodiments and of being practiced or of being carried out in various ways. In addition, it is to be understood that the phraseology and terminology used herein is for the purpose of description and should not be regarded as limiting. The use of “including,” “comprising,” or “having” and variations thereof herein is meant to encompass the items listed thereafter and equivalents thereof as well as additional items.