Abstract:
A cooling apparatus attaches to a cabinet housing electronics for protecting the electronics from external elements. The cooling apparatus includes an exterior surface for exposure to the external elements and a coupling that attaches the exterior surface to the cabinet. When the cooling apparatus is attached to a surface of the cabinet, the exterior surface is maintained in a spaced-apart relationship from the cabinet, forming an enclosed channel having a pair of openings, one of the openings being located above the other. In such a manner, the cooling apparatus can be added to cool an existing, installed, in-place cabinet without requiring extensive modification to the existing cabinet.

Description:
CROSS-REFERENCES TO RELATED APPLICATIONS 
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     STATEMENT AS TO RIGHTS TO INVENTIONS MADE UNDER FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
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     REFERENCE TO A “SEQUENCE LISTING,” A TABLE, OR A COMPUTER PROGRAM LISTING APPENDIX SUBMITTED ON A COMPACT DISK. 
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     BACKGROUND OF THE INVENTION 
     The present invention relates generally to the field of cabinets for outdoor use for enclosing electronic equipment. More specifically, the invention relates to a passive cooling apparatus for a cabinet that shields the cabinet from solar radiation and extracts heat generated by internal electronic equipment by convection. 
     Outdoor cabinets are often used to house communications equipment such as racks of cards holding electronic or optical components. Such cabinets are provided at outdoor locations where there is no suitable existing building to hold the equipment and protect it from adverse environmental conditions and where the size of the equipment may be too small to justify a dedicated building. Examples of such cabinets include roadside cabinets for housing electronics for controlling traffic signals or cabinets for telecommunications equipment such as digital loop carrier cards and cellular radio base stations. 
     Considerations in the design of such cabinets include: thermal management, level of environmental protection, corrosion resistance, strength-to-cost ratio, public safety, aesthetic considerations, vulnerability to vandalism, ease of installation, ease of access to equipment, and level of electromagnetic shielding. There are two main aspects with respect to thermal management: equipment inside the cabinet generates heat which may need to be extracted, and the cabinet may be subject to external sources of heat such as solar radiation. 
     To avoid deterioration from contaminants and corrosives in the ambient air, cabinets are often designed to prevent ambient air from passing over electronic equipment. Typically, electronic equipment is sealed within the cabinet and fans or a heat exchanger may be used to provide cooling where required. In some cases, the cabinet may be air-conditioned. 
     Several techniques for the cooling of outdoor electronic equipment cabinets are known. For example, it is known from U.S. Pat. No. 6,088,225 to Parry, et al. and U.S. Pat. No. 3,900,700 to Gaudet to provide a double skin or shield for the sides of an enclosure, which assists in cooling the equipment by the “chimney” effect. A chimney effect is produced in the cavity between the skins. An inlet at the bottom of the cavity allows air in, to flow up the cavity, and out of an outlet at the top of the cavity. Heat from the internal skin is thus extracted from the cabinet by convection and thus the equipment inside the cabinet can be kept cool. Furthermore, heat from solar radiation on the external skin can also be extracted and prevented from reaching the equipment inside. 
     One disadvantage of these known techniques is that the passive cooling element is incorporated within the structure of the cabinet itself. Hence, positioning of the cabinet may be constrained if full advantage of the passive cooling element is to be achieved. Furthermore, being incorporated within the structure of these known cabinets, the passive cooling elements cannot be readily applied to cabinets having different structures. Furthermore, since the passive cooling element is incorporated within the structure of the cabinet itself, it is expensive to retrofit existing cabinets. 
     A need therefore exists for an apparatus that will allow for the effective and flexible application of passive cooling techniques to outdoor cabinets of varying structure. Consequently, it is an object of the present invention to obviate or mitigate at least some of the above-mentioned disadvantages. 
     BRIEF SUMMARY OF THE INVENTION 
     In accordance with an aspect of the present invention, there is provided a cooling apparatus for attaching to a cabinet housing electronics for protecting electronics from external elements. The cooling apparatus comprises an exterior surface for exposing to the external elements and a coupling for attaching the exterior surface to the cabinet. When the cooling apparatus is attached to a surface of the cabinet, the exterior surface is maintained in a spaced-apart relationship from the cabinet forming an enclosed channel having a pair of openings, one of the openings being located above the other. 
     It is an advantage of the present invention that this heat removal can be achieved passively without the need for a fan blowing external air across the surface of an air-to-air heat exchanger. The apparatus of the invention uses a heat exchanger surface but rather than utilizing a fan for cooling, it employs natural convection airflow generated by a chimney effect. This chimney effect is achieved by allowing air to enter the bottom and exit from the top of a vertical duct, which is formed by the attachment of a vertical channel to an outer vertical surface of the outdoor cabinet. While this vertical channel provides the advantage of creating additional heat transfer surfaces, its primary purpose is to facilitate the chimney effect in order to enhance the natural convection airflow. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention may best be understood by referring to the following description and accompanying drawings which illustrate an embodiment of the invention. In the drawings: 
     FIG. 1 is a perspective view illustrating a passive cooling apparatus mounted on an outdoor cabinet housing electronic equipment; 
     FIG. 2 is a section view of the passive cooling apparatus illustrated in FIG. 1; and 
     FIG. 3 is a partial top section view of the passive cooling apparatus illustrated in FIG.  1 . 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     In the following description, numerous specific details are set forth to provide a thorough understanding of the invention. However, it is understood that the invention may be practiced without these specific details. In other instances, well-known structures and techniques have not been described or shown in detail in order not to obscure the invention. In the drawings, like numerals refer to like structures. 
     A passive cooling apparatus is applied to outdoor cabinets where the cabinet is sealed to protect internal electronics from wind-driven rain, insects, and/or dirt. Typical examples include digital loop carrier cabinets or cellular equipment cabinets. For example, the passive cooling apparatus may be installed on the doors of Lucent Technologies&#39; 80 Series of Outside Plant Cabinets. According to one embodiment, the passive cooling apparatus is installed on both sides of the cabinet. The main benefit in thermal performance is derived from the solar-loaded side of the cabinet. In addition to upgrading the thermal performance of existing cabinets in the field, the passive cooling apparatus may be added to newly manufactured cabinets prior to field deployment. 
     Referring to FIG. 1, there is shown a perspective view of a mounted passive cooling apparatus, illustrated generally by numeral  100 . A passive cooling apparatus  130  is mounted on doors  120  of an outdoor electronic equipment cabinet  110 . The passive cooling apparatus  130  can be mounted on any essentially vertical surface of the cabinet  110 . Referring to FIG. 2, there is shown a section view of a mounted passive cooling apparatus, illustrated generally by numeral  200 . The cabinet  110  contains heat generating electronic equipment  210  and may include fans  220  for circulating air within the cabinet. Referring to FIG. 3, there is shown a partial top section view of the mounted cooling apparatus, illustrated generally by numeral  300 . 
     Referring to FIGS. 1,  2 , and  3 , the passive cooling apparatus  130  consists of a flat vertical metal shield panel  131  and at least two flat vertical metal spacer panels  132 . The shield panel  131  has an inner surface  133  and an outer surface  134 . Each spacer panel  132  has an apparatus end  135  and a cabinet end  136 . The apparatus end  135  of each spacer panel  132  is attached to the inner surface  133  of the shield panel  131  such that each spacer panel  132  and the inner surface  131  are essentially perpendicular. Thus, the shield panel  131  and spacer panels  132  form at least one vertical essentially C-shaped channel. 
     To mount the passive cooling apparatus  130  on the outdoor electronic equipment cabinet  110 , screws  310 , washers  320 , and thermal pads  330  are used to attach the cabinet ends  136  of at least two spacer panels  132  to a vertical outer surface  111  of the cabinet  110 . The thermal pads  330  function to facilitate conduction of heat from the cabinet  110  to the cabinet ends  136  of the spacer panels  132  of the passive cooling apparatus  130 . These thermal pads  330  are positioned at points of attachment between the cabinet ends  136  of the spacer panels  132  and the vertical outer surface  111  of the cabinet  110 . When mounted, the spacer panels  132 , the inner surface  133  of the shield panel  131 , and the vertical outer surface  111  of the cabinet  110  define at least one vertical duct  340  or “chimney”. Each duct  340  has a bottom opening  230  and a top opening  240 . 
     The shield panel  131  and spacer panels  132  of the passive cooling apparatus  130  are sized and shaped to fit the outer surface  111  of the cabinet  110  to which they are to be attached. The shield panel  131  and spacer panels  132  may be formed or stamped from a single metal plate or sheet. The shield panel  131  and spacer panels  132  may be constructed from a suitable material other than metal. 
     When mounted on a cabinet  110 , the passive cooling apparatus  130  functions to cool the cabinet as follows. Heat generated by the electronics  210  within the cabinet  110  is transferred to the air within the cabinet  110 . The air thus warmed circulates (arrow  250 ) within the cabinet  110 . This circulation (arrow  250 ) may be assisted by fans  220  within the cabinet. Heat from the circulating air is transferred (arrow  350 ) to an inner vertical surface  112  of the cabinet by convection. This heat is transferred to an outer vertical surface  111  of the cabinet by conduction where it warms air in the duct  340  by convection (arrow  360 ). Thus warmed, the air in the duct  340  rises (arrow  260 ) and escapes (arrow  270 ) through the top opening  240  of the duct  340 , drawing (arrow  280 ) fresh cool air through the bottom opening  230 . The outer surface  111  of the cabinet  110  is thus cooled and consequently heat generated by the electronics  210  is extracted from the cabinet  110 . 
     In addition, solar radiation  370  warms the outer surface  134  of the shield panel  131  of the passive cooling apparatus  130 . The shield panel  131  thus prevents the solar radiation  370  from reaching the outer surface  111  of the cabinet  110  and hence provides a cooling effect for the cabinet  110 . Heat from the solar radiation  370  is dissipated by thermal radiation  380  from the outer surface  134  of the shield panel  131 . Similarly, heat generated by the electronics  210  within the cabinet  110 , which is conducted through the thermal pads  330  and the spacer panels  132  to the shield panel  131 , is dissipated by the thermal radiation  380  from the outer surface  134  of the shield panel  131 . Moreover, heat from the solar radiation  370  and from the electronics  210  within the cabinet  110  that has been transferred to the passive cooling apparatus  130  also warms air in the duct  340  by convection (arrow  390 ). As described above, the air in the duct  340  thus warmed rises (arrow  260 ) and escapes (arrow  270 ) through the top opening  240  of the duct  340 , drawing (arrow  280 ) fresh, cool air through the bottom opening  230 . The passive cooling apparatus  130  thus provides passive cooling to the cabinet  110 . 
     While the embodiment above was described with reference to a passive cooling apparatus being applied to a vertical surface of the cabinet, a person skilled in the art will appreciate that the surface does not have to be exactly vertical. While it is preferred that the duct  340  created by mounting the passive cooling apparatus to the cabinet is vertical, as long as the top opening  240  is located at a position higher than the bottom opening  230 , the desired chimney effect will be achieved. Thus, for example, the passive cooling apparatus may be applied to a surface that is 45 degrees from a vertical position. Other positions will become apparent to the person skilled in the art. 
     Furthermore, while the above-embodiment was described with reference to essentially C-shaped channels, a person skilled in the art will appreciate that other shaped channels are applicable. For example, the channels may form the shape of a triangle, with the base of the triangles being attached to the outer surface  111  of the cabinet  110 . Again, other shaped channels will become apparent to a person skilled in the art. 
     Although the invention has been described with reference to certain specific embodiments, various modifications thereof will be apparent to those skilled in the art without departing from the spirit and scope of the invention as outlined in the claims appended hereto.