Abstract:
An electrical equipment cabinet is provided that includes an enclosure adapted to contain electrical equipment. A battery compartment, which is located in the enclosure, is adapted to contain at least one battery electrically coupled to the electrical equipment. The battery compartment has first and second opposing side walls, a bottom surface, and a first pair of vents located in the first and second side walls through which external air flows to remove heat. In addition, a second pair of vents, which are also located in the first and second side walls, allow gas emitted by the battery to escape by diffusion. A thermal stabilizing unit is disposed in the battery compartment for regulating the temperature of the battery in contact therewith. The thermal stabilizing unit has a conduit therein for conducting the external air flow between the vents in the first pair of vents.

Description:
FIELD OF THE INVENTION 
     The present invention relates to an outdoor electronics cabinet or the like having a back-up battery power source, and more specifically, to an outdoor electronics cabinet having a ventilated battery compartment that includes a thermal stabilizing unit for maintaining the temperature of the batteries within a specified range. 
     BACKGROUND OF THE INVENTION 
     Outdoor electrical equipment cabinets in the telecommunications industry have traditionally included rectifier units to convert commercially supplied AC power to DC power. Battery back-up systems are employed so that service is maintained in the event of AC power failure. The predominant battery architecture currently used in these cabinets is the sealed  v alve- r egulated  l ead  a cid (VRLA) battery. 
     The temperature extremes experienced annually in certain climatic zones substantially reduce the life of VRLA batteries. For instance, in Florida, the hot temperatures reached in the summer can reduce battery life by a factor of 4 or more. Conversely, freezing temperatures can reduce battery performance. To operate for their maximum lifetime, battery manufacturers generally recommend that the battery temperature be maintained above freezing and below about 80° F. Accordingly, heating and cooling mechanisms are sometimes included with the battery to limit the thermal transients experienced by the VRLA batteries, thus prolonging battery life. 
     A VRLA battery emits hydrogen gas as it ages. An atmosphere with a hydrogen gas concentration above 4% is explosively flammable. Consequently, any chamber or cabinet used to house VRLA batteries must also be ventilated to prevent hydrogen gas build-up. However, this ventilation requirement complicates the task of maintaining the batteries within a desirable temperature range (i.e., through heating and/or refrigeration), since it inherently reduces the efficiency of any system employing active re-circulation of the air within the cabinet. This task is further complicated by the temperature fluctuations that typically accompany ventilation. 
     Accordingly, there is a need in the art for an outdoor electrical equipment cabinet which has a battery compartment that allows adequate ventilation for hydrogen gas to escape, while also maintaining the temperature of the battery within a prescribed range. There is also a need in the art for such a cabinet which is equipped with a mechanism for reducing temperature fluctuations. These and other needs are met by the present invention, as hereinafter described. 
     SUMMARY OF THE INVENTION 
     In accordance with the present invention, an electrical equipment cabinet is provided that includes an enclosure adapted to contain electrical equipment. A battery compartment, which is located in the enclosure, is adapted to contain at least one battery electrically coupled to the electrical equipment. The battery compartment has first and second opposing side walls, a bottom surface, and a first pair of vents located in the first and second side walls through which external air flows to remove heat. In addition, a second pair of vents, which are also located in the first and second side walls, allow gas emitted by the battery to escape by diffusion. A thermal stabilizing unit is disposed in the battery compartment for regulating the temperature of the battery in contact therewith. The thermal stabilizing unit has a conduit therein for conducting the external air flow between the vents in the first pair of vents. 
     In accordance with one aspect of the invention, the thermal stabilizing unit includes a thermally conductive element having first and second opposing surfaces. The first surface is adapted for supporting the battery. A heat sink is thermally coupled to the second surface of the thermally conductive element. 
     In accordance with another aspect of the invention, the conduit extends through the heat sink. 
     In accordance with another aspect of the invention, at least one thermoelectric module is provided for pumping heat from the battery to the heat sink. The thermoelectric unit is disposed between the thermally conductive element and the heat sink. The thermoelectric module may be a Peltier thermoelectric device. 
     In accordance with yet another aspect of the invention, the heat sink includes a substantially planar base and a plurality of parallel fins located on the base. In this case the conduit includes a plurality of channels defined by adjacent ones of the fins. Moreover, the conduit may further include at least one duct connecting the plurality of channels to a vent in the first pair of vents. 
     In accordance with another aspect of the invention, at least one resistive heating element is provided which is in contact with the thermally conductive element. The resistive heating element may be a rubber heating pad affixed to the thermally conductive element. 
     In accordance with another aspect of the invention, an insulating layer is disposed between the resistive heating element and the bottom surface of the battery compartment. 
     In accordance with still another aspect of the invention, a controller is provided for maintaining the temperature of the battery between upper and lower temperature setpoints. The controller may include an adjustment mechanism for selecting the upper and lower temperature setpoints. At least one temperature sensor may be electrically coupled to the controller for determining the temperature of the battery. 
     In accordance with another aspect of the invention, the battery compartment is configured as a slidable cabinet. 
     In accordance with yet another aspect of the invention, at least one support element is provided between the second surface of the thermally conductive element and the bottom surface of the battery compartment for supporting the weight of the battery. The support element may be a steel tube spacer, for example. 
     In accordance with another aspect of the invention, an air blower is provided in the conduit, which forces external air through the channels in the heat sink. 
     In accordance with still another aspect of the invention, an electrical equipment cabinet is provided which comprises a battery compartment segregated into at least first and second interior regions by means of a thermal stabilizing unit adapted to regulate the temperature of a battery in contact with the stabilizing unit. First and second vents are disposed in the first region, said first and second vents being in open communication with each other. Third and fourth vents are disposed in the second region, said third and fourth vents being in open communication with each other. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 illustrates an outdoor electrical equipment cabinet incorporating a ventilated battery compartment constructed in accordance with the present invention; 
     FIG. 2 illustrates a cross-sectional, fragmentary view of the battery compartment of FIG. 1 in which the thermal stabilizing unit is visible; 
     FIG. 3 illustrates a thermoelectric module employed for cooling; and 
     FIG. 4 illustrates a side view of the battery compartment shown in FIG.  2 . 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     FIG. 1 illustrates an outdoor electrical equipment cabinet  100  incorporating a ventilated battery compartment  110  constructed in accordance with the present invention. The cabinet includes a base  112 , side walls  114 ,  114 ′, a roof  116 , and the ventilated battery compartment. The cabinet contains a number of equipment racks or channel banks (not shown) which are located on shelves provided in the cabinet. The interior of the battery compartment contains a thermal stabilizing unit  216  for regulating the temperature of the batteries contained in the battery compartment. The cabinet may be configured as a slide-out drawer to facilitate assess to the batteries. 
     FIG. 2 shows a cross-sectional, fragmentary view of the battery compartment  110 , which depicts left and right sidewalls  212 ,  212 ′ and base  214 . The thermal stabilizing unit  216  is a planar unit that has a footprint largely coextensive with the base of the compartment. The thermal stabilizing unit includes conductive plate  220 , thermoelectric modules  222 , heat sink  230 , resistive heating elements  232 , and insulating pads  236 . The conductive plate of the stabilizing unit serves as the support surface on which the batteries (not shown) rest. The plate is formed from a thermally conductive material such as aluminum or copper to facilitate heat transfer. A series of thermoelectric modules  222  are located below the conductive plate and is in contact with its bottom surface. The thermoelectric modules are Peltier thermoelectric devices of conventional design. 
     As shown in more detail in FIG. 3, individual thermoelectric modules  222  are constructed from two parallel, electrically insulating plates  324  and  326  providing hot and cold thermal transfer faces. A series of alternating n-type and p-type semiconductor elements  328  are located between the insulating plates. Adjacent semiconductor elements are connected by conductive strips  330 . Alternatively, adjacent semiconductor elements may be connected by bonding them with printed circuit bonds to the inner surface of the insulating plates. In operation, the upper plate  324  serves as the cold surface of the thermoelectric module and lower plate  326  serves as the hot surface. That is, heat is pumped from the upper plate to the lower plate. The temperature differential between the upper and lower plates is maintained by providing current to the semiconductor elements. 
     Returning to FIG. 2, a heat sink  230  is in contact with the lower plates of the thermoelectric modules. The heat sink is effectively shrouded by the conductive plate  220  (on the top), support elements  240  (on the sides), and the base  214  of the battery compartment  110  (on the bottom). The heat sink, which may be either an extrusion product or a bonded assembly, comprises a relatively thick base and a series of extended surfaces or “fins”  242 . A series of channels  244  defined by adjacent fins extend through the heat sink. Heat pumped from the upper plates to the lower plates of the thermoelectric modules is transferred to the heat sink. The heat from the heat sink is transferred to external air flowing through the channels of the heat sink in a manner described below in connection with FIG.  4 . 
     One or more thermally insulating pads  236  are located adjacent to the heat sink  230  and between the base  214  of the compartment  110  and the conductive plate  220 . In the embodiment of the invention shown in FIG. 2, in which the heat sink is approximately centrally located on the base of the compartment, two thermally insulating pads are employed. Resistive heating elements  232  are sandwiched between the insulating pads and the conductive plate. In one embodiment of the invention, resistive heating elements are rubber heating pads affixed to the bottom surface of the conductive plate. 
     In operation, when current is supplied to the heating elements heat is generated and transferred to the conductive plate. Because of its high thermal conductivity, the plate conducts the heat so that the plate achieves a relatively uniform elevated temperature. In turn, the plate transfers the heat to the batteries so that their temperature is stabilized. 
     As best seen in FIGS. 1 and 4, the battery compartment  110  has louvers in its front  316  and rear walls  318 . In particular, each wall has an upper set of louvers  310  and a lower set of louvers  312 ,  312 ′. A substantially rectangular duct  332  (indicated by dashed lines) allows ambient air to be communicated between the lower set of louvers on each of the front and rear walls and the channels  244  of the heat sink. The ducts prevent the ambient air from mixing with the air in the remainder of the battery compartment. When the thermal stabilizing unit  216  is situated in the bottom  214  of the battery compartment, the channels in the heat sink align with the duct and the lower set of louvers so that the channels are exposed to the external environment. Accordingly, a flow of external air is established through the bottom of the battery compartment. 
     At least one air blower  314  is located between one of the ducts and the channels. 
     Similar to the heat sink, the air blower is effectively shrouded by the conductive plate  220 , support elements  240 , and the base  214  of the battery compartment  110 . As illustrated in FIG. 4, air is drawn into the rear lower louver array  312 ′ and forced out the front lower louver array  312 . In this way the heat from the heat sink  230  is transferred to the external environment by the flow of air being forced through the channels  244  of the heat sink. 
     The air blower is preferably a low-profile blower. For example, in some embodiments of the invention the blower may be a centrifugal blower with a thickness of 1.5 inches or less, which lies flat on the bottom of the battery compartment and has a circular intake in its top surface. In this way, the blower can be situated between the conductive plate and the bottom of the battery compartment. Alternatively, in some embodiments of the invention, an array of small axial fans could be used to force air through the heat sink. 
     As previously mentioned, the front and rear walls  316  and  318  also include an upper set of louvers  310 ,  310 ′. The upper louvers are situated above the thermal compensating unit so that they are directly exposed to the batteries resting on the conductive plate  220 . In this way, hydrogen emitted by the VRLA batteries can escape the battery compartment  110  by diffusing through the upper louvers. The ambient air flowing through the ducts  332  and the channels  244  of the heat sink  230  does not mix with air in contact with the batteries. By isolating the ambient air flowing through the heat sink from the air in communication with the batteries, the air warmed by heat removed from the batteries is not re-circulated back to the batteries, which would reduce the efficiency of the thermal stabilizing unit  216 . 
     Additional insulating pads may be provided at various locations around the thermal stabilizing unit to reduce the amount of heating and cooling that it requires. For example, in FIG. 2 insulating pads  238  may be provided between the interior surfaces of the battery compartment that contact the thermal stabilizing unit. A gas-permeable blanket may be placed over the batteries to provide additional thermal insulation while still allowing hydrogen gas to escape to an adequate degree. 
     To support the weight of the batteries (which in some cases may weight 800 pounds or more), the thermal stabilizing unit also may include one or more support elements  240 . The support elements ensure that the weight of the batteries is not borne by the thermoelectric modules  222 . In FIG. 2 the support elements are steel tube spacers on which conducting plate  220  rests. Of course, one of ordinary skill in the art will recognize that may other types and arrangements of support elements may be employed. 
     To control the temperature of the batteries, one or more temperature sensors is connected to the conductive plate and/or to the batteries themselves. The temperature sensor is connected to a temperature controller. The controller includes an adjustable means for setting the temperature setpoints. The temperature controller provides current to the thermoelectric modules and the resistive heating elements  232  in response to the temperature measured by the temperature sensor. The controller is set to upper and lower temperature setpoints, which correspond to the desired maximum and minimum battery temperature. When the temperature sensor determines that the battery temperature exceeds the upper setpoint, the controller supplies current to the thermoelectric modules  222  so that the batteries are cooled. Likewise, when the temperature sensor determines that the battery temperature falls below the lower setpoint, the controller supplies current to the resistive heating elements so that the batteries are heated. When current is supplied to the thermoelectric modules, current is also supplied by the controller to the blower  314 . In this way heat pumped to the heat sink is transferred to the flow of air forced through the duct. 
     One advantage of the inventive thermal stabilizing unit is its compactness; in many cases the entire unit may occupy only the bottom 2 or 3 inches of the battery compartment. Accordingly, the overall footprint of the compartment need not be increased, as would be the case is if a bulky compressor-based system were employed rather than thermoelectric modules. 
     Although various embodiments are specifically illustrated and described herein, it will be appreciated that modifications and variations of the present invention are covered by the above teachings and are within the purview of the appended claims without departing from the spirit and intended scope of the invention. For example, while the invention has been depicted as a ventilated battery compartment that is incorporated within an electrical equipment cabinet, the invention is equally applicable to a stand-alone ventilated battery storage cabinet. Such a cabinet may advantageously include two or more of the inventive ventilated battery compartments depicted in the figures, each located on its own shelf. With such a vertically stacked arrangement, the cabinet can store many battery units within a reasonable overall footprint, which is particularly advantageous for higher wattage and/or extended duration back-up power applications.