Abstract:
An electronics enclosure includes a mounting bracket adapted to mount to a support structure, a heat absorption module adapted to mount to the mounting bracket, and a housing to contain electronic equipment. The housing is adapted to mount alternatively to either the mounting bracket or the heat absorption module dependent upon solar loading conditions.

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates generally to outdoor enclosures for electronic components and, more particularly, to an outdoor enclosure for electronic components that uses passive heating and cooling to control the temperature of the enclosure. 
     When telecommunications equipment is deployed in outdoor locations, a cabinet or enclosure protects the electronics from weather and environmental contaminants. The reliability of electronic components decreases significantly if they are subjected to high temperature extremes, especially if the temperature swings or cycles are frequent. The temperature swings may be due to heat generated by the electronics (i.e., more heat is produced at peak times), natural temperature variations, and solar loading. To protect the electronics equipment, various methods are used to control the internal temperature of the electronics enclosure. 
     Ventilated cabinets are sometimes used to cool electronics equipment inside an enclosure or cabinet. Ventilated cabinets use natural or forced convection to draw ambient air through the cabinet to cool the equipment inside the cabinet. Ventilated cabinets are relatively inexpensive and require little maintenance. However, the electronics inside the ventilated cabinet are exposed to the air flow, which may contain environmental contaminants, such as moisture, nitrates, hydrocarbons, sulfur dioxide, nitrogen oxides, hydrogen sulfides, chlorine, ozone, salt, and the like. 
     Sealed cabinets provide an alternative to ventilated cabinets where environmental contamination is a concern. Sealed cabinets use heating and cooling systems to maintain the electronics in the cabinet within the desired temperature range without exposing the electronics to potentially harmful contaminants. The heating and cooling systems include fans, air conditioners, and heaters, which consume space in the cabinet and add considerably to the cost of the cabinet. Additionally, such components require periodic maintenance to maintain them in proper operating condition. 
     Passive cooling methods for cooling electronics enclosures are also known. Passive cooling relies on conduction and radiation to passively cool the electronics equipment inside an enclosure without fans, air conditioners, or heat exchangers. Passive cooling of electronics enclosures is less expensive than active cooling systems, reduces energy consumption, and minimizes noise. Additionally, because there are fewer components to fail, passive cooling systems are generally more reliable and robust than active cooling systems. 
     Passive cooling systems for electronics enclosures dissipate heat generated by the electronics through natural convection and radiation. However, if the enclosure is placed in direct sunlight, the solar load on the cabinet may be as many more times that of the heating load of the electronics. In order to dissipate heat generated by the solar load using passive methods, a phase change material (PCM) is typically used. Phase change materials are materials that change state (e.g., from solid to liquid and vice versa) as the temperature changes. The temperature at which the PCM changes state is referred to as the phase change temperature. As heat builds up in the enclosure, the PCM begins to change from solid to liquid when the temperature inside the enclosure reaches the phase change temperature. While the phase change is occurring, the PCM continues to absorb heat while the temperature remains the same. The temperature does not begin to increase again until the PCM has changed phase. The amount of heat, or energy, required to change the PCM from one phase to another is called the latent heat of the PCM. Conversely, when the solar load is removed and the temperature inside the enclosure begins to cool, the temperature of the PCM also reduces and it changes back to a solid state. 
     BRIEF SUMMARY OF THE INVENTION 
     The present invention relates generally to a passively-cooled electronics enclosure for use outdoors. The electronics enclosure comprises an electronics cabinet or housing, a mounting bracket for mounting the electronics housing to a support structure, and a heat absorption module. The electronics housing may be directly mounted to the mounting bracket or, alternatively, may be mounted to the heat absorption module which, in turn, mounts to the mounting bracket. Thus, the electronics housing may be used with or without the heat absorption module. When the electronics enclosure is deployed in a location where it is not exposed to direct sunlight, it may be used without a heat absorption module. Conversely, when the electronics enclosure is deployed in a location where it is subjected to solar loading, the heat absorption module may be used to passively cool the electronics housing. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is an exploded perspective view of the modular electronics enclosure of the present invention. 
     FIG. 2 is a perspective view of the modular electronics enclosure assembled without the heat absorption module. 
     FIG. 3 is a perspective view of the modular electronics enclosure assembled with the heat absorption module. 
     FIG. 4 is an exploded perspective view illustrating a second embodiment of the modular electronics enclosure of the present invention. 
     FIG. 5 is a partial perspective view of the heat absorption module with a portion cutaway to illustrate the construction of the heat absorption module. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring now to the drawings, the electronics enclosure of the present invention is shown therein and indicated generally by the numeral  10 . The electronics enclosure  10  comprises three main components: a housing  12 , a heat absorption module  40 , and a mounting bracket  70 . The housing  12  is designed to mount directly to the mounting bracket  70  or, alternatively, to the heat absorption module  40 . The heat absorption module  40 , when used, mounts to the mounting bracket  70 . 
     The housing  12  comprises a main body  14  and an access door  26 . Main body  14  comprises a substantially rectangular box made of a sheet metal or other heat conductive material. The main body  14  includes a top  16 , bottom  18 , sides  20 ,  22 , and back  24 . A hinge  28  pivotally mounts the door  26  to one side  20  or  22  of the housing  12 . Door  26  includes a handle  30  for opening and closing the door  26 . Handle  30  may incorporate a conventional latch or locking mechanism to provide security. A door seal (not shown) may be provided to prevent moisture or other contaminants from entering the housing  12 . The back  24  of the housing  12  includes a series of mounting holes  32  used for mounting the housing  12  to a support structure. The number of mounting holes  32  is not material to the invention. In the exemplary embodiment shown in the drawings, there are four mounting holes  32  disposed adjacent the four corners of the housing  12 . As will be hereinafter described, the mounting holes  32  receive mounting studs  80  on the mounting bracket  70 . 
     The heat absorption module  40  is a sealed enclosure made of metal or other heat conductive material. In the exemplary embodiment shown in FIG. 1, the heat absorption module  40  comprises a front plate  42 , back plate  44 , top  46 , bottom  48 , and sides  50 ,  52 . The front plate  42 , back plate  44 , top  46 , bottom 48 , and sides  50 ,  52  are secured together by welding to form a sealed enclosure. A fill hole  54  and vent hole  56  are formed in the top  46  of the heat absorption module  40 . The fill hole  54  is used to fill the heat absorption module  40  with a phase change material (PCM). The PCM is heated to change it to a liquid state and then poured into the heat absorption module  40 . Vent hole  56  allows air to escape from within the heat absorption module  40  during filling. After filling, the fill hole  54  and vent hole  56  are sealed by plugs  58 . 
     The front plate  42  and back plate  44  of the heat absorption module  40  extend beyond the sides  50 ,  52  in the exemplary embodiment shown in FIG.  1 . Both the front plate  42  and back plate  44  include a series of mounting holes  60 ,  62 . The mounting holes  62  in the back plate  44  receive mounting studs  80  on the mounting bracket  70 , as will be hereinafter described. The mounting holes  60  on the front plate  42  receive a bolt used to fasten the housing  12  to the heat absorption module  40 . 
     Mounting bracket  70  is a formed metal sheet having side portions  72 ,  74  and a recessed central portion  76 . The central portion  76  includes a series of mounting holes  78  to receive bolts, lag screws, or other mounting hardware. Mounting studs  80  project from the side portions  72 ,  74 . When the housing  12  is mounted directly to the mounting bracket  70 , the mounting studs  80  are received in the mounting holes  32  in the back  24  of the housing  12 . When the heat absorption module  40  is used, the mounting studs  80  are received in the mounting holes  62  in the back plate  44  of the heat absorption module  40 . In either case, the housing  12  or heat absorption module  40  is secured in place by nuts  88  that thread onto the mounting studs  80 . When the heat absorption module  40  is required, the housing  12  can be mounted to the heat absorption module  40  by carriage bolts  82  and nuts  84 , or other mounting hardware. In the exemplary embodiment of FIG. 1, the bolts  82  pass through the opening  60  in the front wall  42  of heat absorption module  40  and the opening  32  in the back  24  of housing  12 . The nuts  84  thread onto the end of the carriage bolts  82  to secure housing  12  to the heat absorption module  40 . 
     FIG. 4 illustrates a second embodiment on the modular electronics enclosure  10  of the present invention. The second embodiment of the electronics enclosure  10  uses many of the same components as the first embodiment. Therefore, the reference numerals used to describe the first embodiment will also be used in the description of the second embodiment to indicate the similar components. 
     The second embodiment includes a housing  12 , a heat absorption module  40 , and a mounting bracket  70 . The housing  12  is essentially the same as the first embodiment; whereas the heat absorption module  40  and mounting bracket  70  are slightly modified. In the second embodiment, the sides  50 ,  52  of the heat absorption module  40  are flush with the lateral edges of the front wall  42  and back wall  44 . The opening  60  in the front wall  42  are connected to the openings  62  in the back wall  44  by sleeves  49  (FIG.  5 ). The sleeves  49  define a sealed passage through the interior of the heat absorption module  40  for the mounting hardware (e.g., carriage bolt  82 ) to pass through the heat absorption module  40 . The mounting bracket  70  has openings  86  in place of the mounting studs  80  of the first embodiment. The openings  86  in the mounting bracket  70  align with the openings  60 ,  62  in the heat absorption module  40  and the openings  32  in the housing  12 . A single carriage bolt  82  and nut  84  can therefore be used at each corner of the enclosure to secure the entire assembly together. The carriage bolt  82  is inserted from the rear of the mounting bracket  70  as shown in FIG.  4  and passes through the sleeve  49  in the heat absorption module  40 . The exposed end of the carriage bolt  82 , on which the nut  84  is threaded, is contained inside the housing  12 . 
     The mounting bracket  70  in the second embodiment may include mating elements to align and support the heat absorption module  40  or housing  12 . The mating elements may comprise, for example, locating pins  90  on the mounting bracket  70  that insert into locating holes  92  in either the back wall  44  of the heat absorption module  40  or the back wall  24  of the housing  12 . The heat absorption module  40  likewise may include locating pins  94  that insert into locating holes  92  in the back wall  24  of the housing  12 . The locating pins  90 ,  94  help support the components before the carriage bolts  82  are inserted. Those skilled in the art will recognize that the locating pins  90 ,  94  and locating holes  92  could be reversed or that other forms of mating elements that interlock with one another could be used. 
     When the heat absorption module  40  is used, heat generated by the electronics inside the housing  12  or by the solar load is absorbed by the housing  12  and passed through conduction to the heat absorption module  40 . While below its phase change temperature, the PCM will absorb and remove heat from the housing  12  as the temperature inside the housing  12  increases. After reaching the phase change temperature, the PCM will continue absorbing heat from the housing  12 , but the temperature of the housing  12  and PCM will remain substantially constant until the PCM changes phase. A PCM can be selected which has a phase change temperature that corresponds to the maximum allowable temperature of the electronics enclosure  10 . Therefore, until the PCM completely changes phase, the maximum allowable temperature inside the housing  12  will not be exceeded. 
     In order not to exceed the maximum allowable temperature inside the housing  12 , the heat absorption module  40  must be able to absorb the energy of the solar load on the enclosure  10  without completely changing phase. Therefore, enough PCM must be used to absorb the solar load for as long as it is present. Since the solar load occurs only during the day, the PCM can absorb the energy during the daylight hours and pass the heat back to the housing  12  through conduction to be dissipated at night. Therefore, the amount of PCM used may be computed based on the latent heat of the PCM and the maximum solar load that could be absorbed by the enclosure  10  over one day. 
     Since the enclosure  10  can dissipate the heat generated by the electronics without the heat absorption module  40 , the heat absorption module  40  is not required. The present invention allows the heat absorption module  40  to be deployed when needed and to be omitted when the enclosure  10  is not subjected to solar loading. Using the present invention, the same housing  12  and mounting bracket  70  can be used in applications where solar loading is present, as well as applications when no solar loading is present. Thus, only one housing  12  and one mounting bracket  70  is required. The use of the same parts for both shaded and unshaded applications requires fewer parts to be stocked and simplifies ordering. The additional size, weight, and expense of the heat absorption module  40  is only added when needed. In addition, the present invention allows an enclosure  10  initially deployed without the heat absorption module  40  to be easily upgraded to include a heat absorption module  40  at a later time.