Abstract:
Apparatus and methods for thermal conditioning equipment. In a preferred embodiment, an equipment enclosure comprises a body, a wall, a fluid port, and a fixture. The body defines an outer plenum and an inner chamber in the latter of which the fixture retains the equipment. The wall, which is between the outer plenum and the inner chamber, isolates the thermally conditioned first fluid from a second fluid in the inner chamber. Since the wall is thermally conductive it allows heat to be transferred between the outer plenum and the inner chamber. The fluid port is in communication with the outer plenum to allow the thermally conditioned first fluid to flow into the outer plenum. Baffle plates are also provided to distribute flow of the second fluid to the equipment.

Description:
FIELD OF THE INVENTION 
   This invention relates generally to environmental control system and, more particularly, to environmental control systems for commercial-off-the-shelf (COTS) electronic equipment for use onboard mobile platforms such as aircraft. 
   BACKGROUND 
   Commercial-Off-the-Shelf (COTS) equipment is increasingly being used in military environments to take advantage of advancements in commercially available technology. By definition, COTS equipment has no or comparatively relaxed design environmental requirements. As a result, integration of the COTS equipment with systems designed to meet military specifications has proven to be difficult, especially for aircraft applications. A comprehensive solution to this integration challenge that accommodates all of the military operational requirements and FAA flight requirements has yet to be developed. 
   Such a solution would preferably allow for unforeseen variability in the COTS equipment and allow for quick, low cost integration of new equipment as it becomes available. Previously available attempts to solve these difficulties use unique equipment and are therefore expensive to modify even slightly. Without the unique equipment, however, it is difficult to efficiently provide the proper environment for the COTS equipment. Therefore the COTS equipment must be maintained in a mild environment while operating on military or even commercial aircraft. In addition to meeting the functional requirements for the equipment, the COTS equipment must also meet various requirements imposed by the relevant specifications for military applications and by the relevant Federal Aviation Administration (FAA) regulations for commercial applications. The various design requirements that the COTS equipment must meet include touch temperature, redundancy, smoke detection and clearing, fire suppression, thermal shock, vibration, electromagnetic interference, access, maintenance, redundancy. All of these requirements are preferably integrated into a comprehensive design approach that accommodates each potential piece of COTS equipment that might one day reside on the aircraft. However, the main parameters that are typically controlled are temperature and humidity. 
   Temperature control is typically accomplished by the aircraft environmental control system (ECS) which provides a source of air that has been conditioned to a pre-selected temperature. The cooling air is ducted to the various pieces of equipment or to the equipment cabinets or racks in which they are frequently located. From the equipment, or cabinets, the warmed exhaust air is then returned to the ECS system for re-cooling and recirculation. Because COTS equipment typically has very low limits on its air exhaust temperature COTS equipment is inefficient to cool. The low cooling efficiency in turn leads to very high cooling air flow demands (and therefore fan power consumption). The low temperature differential also makes transferring the heat off the plane very difficult. Additionally, changing the ducting configuration within a cabinet is costly and may involve changes to the configuration of the overall ECS system to accommodate even a single new piece of COTS equipment. 
   In addition to temperature control, humidity control can also be a challenge because many aircraft ground operations are conducted in humid environments with the cabin doors open. In such situations, elevated external ambient temperatures can limit cooling capacity while excessive humidity can cause moisture and condensation to be present in the aircraft. By way of contrast, in flight, the air is sometimes too dry for optimal performance of the COTS equipment. Unfortunately, a humidification system with the capacity to control the humidity for all of the equipment onboard a typical aircraft is prohibitively heavy. 
   SUMMARY OF THE INVENTION 
   It is in view of the above problems that the present invention was developed. In a first preferred embodiment, the present invention provides an equipment enclosure for use on an aircraft or other vehicle that has an Environmental Control System (ECS). The enclosure includes a body, a thermally conductive wall, a fluid port, and a fixture. The body defines an outer plenum and an inner chamber in which the equipment is mounted to the fixture. The fluid port is in communication with the outer plenum to allow a thermally conditioned first fluid to flow into the outer plenum. The thermally conductive wall, which is between the outer plenum and the inner chamber, prevents the thermally conditioned first fluid in the outer plenum from communicating with a second fluid in the inner chamber. Since the wall is thermally conductive, however, the wall allows heat to be readily transferred between the two fluids. The outer plenum may have a second port to collect the warmed first fluid for subsequent re-cooling and recirculation particularly by the aircraft ECS system. In the alternative, the outer plenum may allow the first fluid to flow out of the enclosure and into the aircraft cabin for eventual recirculation with the ambient air via aircraft cabin air returns. 
   A baffle that includes multiple baffle plates may also be provided with the current embodiment to distribute flow of the second fluid to the equipment in the enclosure. More specifically, the baffle plates are re-configurable so that they can fit around the front side of any piece of COTS equipment that is likely to be placed in the enclosure. Preferably, the baffle plates include segments of fabric, metal, or plastic with hook and loop fasteners (e.g., Velcro®) along the edges of each segment. To form a baffle plate for a particular piece of equipment, one or more fabric segments are attached to one another using the hook and loop fasteners to form a plate tailored for the particular piece of equipment. In particular, the baffle plate may be configured to include an aperture that will align with a cooling air intake of the piece of equipment when the baffle plate is attached to the shelf that holds the piece of equipment. The baffle plate may then be removably attached to that shelf. The baffle plate should preferably extend beyond the width of the piece of equipment such that the baffle plate will seal the gap between the equipment and the wall of the inner chamber. Additionally, the baffle plate should preferably extend slightly below the equipment to seal against the shelf. Likewise, the baffle plate should extend beyond the top of the equipment so as to seal against the shelf that is adjacent to the equipment&#39;s position in the enclosure. If the equipment is to be placed on the top shelf, then the baffle plate may seal against the top inside surface of the inner chamber. Additionally, the baffle plate may extend in any direction enough to create a lip that can be placed adjacent to the sealing surface for improved sealing performance. For shelves having no equipment, a baffle plate without an aperture can be fabricated to obstruct the flow of air through the resulting aperture at that particular location. Thus, the baffle plates create a seal between the equipment and the inner surfaces of the chamber such that a flow path exists through the equipment itself from the front of the inner chamber to the back of the inner chamber. Moreover, the baffle plates can be placed relative to the body of the enclosure and the equipment to form a plenum in the front of the inner chamber for mixing the re-circulated air before it enters the equipment. To recirculate the re-cooled air back to the equipment, the walls of the inner chamber may be hollow to form a return flow path or plenum there through. A fan may also be provided to aid the recirculation of the second fluid through the equipment. 
   In another preferred embodiment, the enclosure includes an inner chamber with an overall height. In this case the fixture(s) for mounting the equipment includes a plurality of shelves which are removably attachable to the body at pre-determined heights within the inner chamber. Further, a collection of baffle segments is provided that allow the creation of baffles of many different sizes. Thus, particular baffles can be created so that for any shelf spacing within the inner chamber, a baffle can be created that extends from the shelf to which it is attached to the next shelf or to the top, inner surface of the inner chamber. 
   Further variations of the present invention are also possible. For instance, the thermally conditioned first fluid can be air that is ducted to the enclosure from the thermal conditioning system and the second fluid can be air also. Additionally, a pair of valves can be included in the enclosure in a position to cause air from the ECS system to circulate through the inner chamber and then return to the aircraft ECS system. It is also preferred that the equipment enclosure of the current embodiment include an access door on the front side of the body and another door on the back side. Additionally, a seal between the door(s) and the body may form a hermetic and pressure tight seal between the inner chamber and the door when the door(s) are closed. 
   Other alternative embodiments of the enclosures provided herein include active temperature control loops. For instance, a temperature controller may sense the temperature of the second fluid in the inner chamber and adjust the flow of the first fluid in response thereto. In the alternative, a thermoelectric cold plate may be placed at the upstream side of die outer plenum with the temperature controller operating the cold plate in response to the temperature of the second fluid. The humidity in the inner chamber may also be controlled by, for instance, placing a water vapor source in communication with the inner chamber or by operating the pair of valves that allow ECS fluid to circulate in the inner chamber. 
   In another preferred form, the present invention provides a method of thermally conditioning equipment in an environment where a thermal conditioning system supplies a thermally conditioned first fluid. Generally, the method of the current form includes isolating the equipment from the thermally conditioned first fluid and then using the thermally conditioned first fluid to indirectly exchange heat with the equipment. More particularly, the method includes exchanging heat between the equipment and a second fluid in the inner chamber of the equipment enclosure. The heat is also exchanged between the first fluid and the thermally conditioned second fluid (which is flowing in an outer plenum of the equipment enclosure). The isolation of the equipment from the thermally conditioned second fluid may include using a thermally conductive wall between the inner chamber and the outer plenum. 
   Both fluids can be air and, more particularly, air from the ECS system of an aircraft. In cases where the fluid in the inner chamber is air, the method may also include humidifying that air. Further, depending on operating conditions (e.g., the temperature of the fluid exiting the inner chamber), the method may include allowing the thermally conditioned first fluid to flow through the inner chamber. In the alternative, or in addition, the method may include adjusting the flow of the thermally conditioned first fluid through the outer plenum. 
   A baffle may also be constructed in the inner chamber to form an inlet plenum for mixing the second fluid before it flows through the equipment. The baffle of the current embodiment includes several baffle plates that are preferably assembled from a collection of segments of fabric, plastic, or metal. The baffles may be removably attached to the shelves, the equipment or even the inner surfaces of the inner enclosure. Additionally, the baffles can be located in such a manner that the second fluid is forced to flow through the equipment. 
   Another preferred embodiment of the present invention provides an equipment enclosure that allows complete humidity and temperature control of COTS equipment. The enclosures of the current embodiment use existing aircraft (or other vehicle) ECS systems to remove heat from the enclosure. Moreover, the enclosures of the current embodiment distribute cooling air to the individual pieces of equipment rather than relying on the ECS systems for this function. Additionally, the enclosures of the current embodiment isolate the equipment mounted therein from harsh conditions that are likely to be encountered on the vehicle. The enclosures also isolate the equipment from direct contact with the cooling air in the ECS systems. Moreover, the current embodiment also provides redundant cooling capacity that is independent of the vehicle ECS system. These enclosures are easy to reconfigure for, inter alia, changing the mixture of equipment within the enclosure. 
   The present invention provides several other advantages over previous approaches. First, because the equipment is in a contained space, only minimal amounts of water can be used to maintain humidity levels in the cooling air for the equipment. Second, the equipment that controls the flow of cooling air to the COTS equipment is isolated from the ECS flow path. Thus the flow of coolant is independent of the ECS system flow rate. More particularly, the cooling air can be isolated from the ECS flow by a wall of the enclosure. This wall can also serve as a heat exchanger between the cooling air and the air in the ECS system. Because the wall isolates the COTS equipment from the ECS system, individual pieces of COTS equipment may have as much cooling air flow as the draw of the equipment&#39;s built-in fan can provide. As a result of the unique configuration of the enclosures provided herein, the ECS system is only used to remove heat from the COTS equipment. This practice is in contrast to the previous approaches of using the ECS system to both remove heat from the equipment and to provide flow control of the cooling air to the specific pieces of equipment. 
   In another preferred embodiment, a baffle is created near the front of the enclosure and just upstream of the equipment in the enclosure. The baffles are positioned to direct the cooling air into the equipment from which the warmed air is discharged toward the rear of the enclosure. Thus, the enclosure contains a mixing plenum upstream from the equipment and a discharge plenum downstream from the equipment and that is formed between the equipment and the rear wall of the enclosure. Return plenums in the hollow side walls of the inner chamber complete a circuit for the cooling air to circulate between the mixing plenum and the exhaust plenum of the inner chamber. Fans, which may be provided with the enclosure, draw air from the exhaust plenum and cause it to flow to the mixing plenum thereby creating a one-way flow path within the enclosure. The circulating air flows through the equipment from the mixing plenum to the exhaust plenum and thence through the return plenums to return to the mixing plenum. These plenums, particularly the exhaust plenum, reduce the pressure drop associated with the cooling air flowing along the circulation path. The resulting minimal pressure drop in turn allows the low power fans that may be provided with the pieces of equipment to supply the motive force to move the cooling air instead of relying on the fans or other equipment of the aircraft ECS. By creating the baffle in the manner described herein, the enclosure is easy to reconfigure for changing the mix of equipment therein by way of modifying the baffle. This is a much simpler solution than reconfiguring the typical ducted plenums found in previously available avionics cabinets or racks. The configuration of the current embodiment also makes it possible to have a single temperature control point, preferably in the mixing plenum, for the cooling air circulating within the enclosure. Accordingly, the current embodiment provides accurate temperature control of the cabinet and parallel flow of cooling air to each piece of equipment within the enclosure. 
   Further features and advantages of the present invention, as well as the structure and operation of various embodiments of the present invention, are described in detail below with reference to the accompanying drawings. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The accompanying drawings, which are incorporated in and form a part of the specification, illustrate exemplary embodiments of the present invention and together with the description, serve to explain the principles of the invention. In the drawings: 
       FIG. 1  illustrates a vehicle that is constructed in accordance with the principles of the present invention; 
       FIG. 2  illustrates an avionics bay of the vehicle of  FIG. 1 ; 
       FIGS. 3A-3D  illustrate embodiments of the equipment enclosure of  FIG. 2  constructed in accordance with the principles of the present invention; 
       FIG. 4  illustrates various embodiments of equipment enclosures; 
       FIG. 5  schematically illustrates an environmental control system in accordance with one embodiment of the invention; 
       FIG. 6A  illustrates an inner chamber in accordance with one embodiment of the invention; and 
       FIG. 6B  illustrates baffle plates and baffles of the inner chamber shown in  FIG. 6A . 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   Referring to the accompanying drawings in which like reference numbers indicate like elements,  FIG. 1  illustrates an exemplary aircraft that is constructed in accordance with the principles of the present invention. 
   More particularly,  FIG. 1  shows a model  747  commercial aircraft  10  that is available from The Boeing Company of Chicago, Ill. The aircraft  10  is exemplary and could be any aircraft either civilian, military, or otherwise.  FIG. 1  also shows a lower lobe  12  of the aircraft  10 , an avionics bay  14 , several electronic equipment racks  16 , numerous pieces of electrical equipment  18 , and an equipment enclosure  20  of the present invention. The lower lobe  12  includes the avionics bay  14  in a convenient location near the crew cabin so that the crew can access the electrical equipment  18  that resides in the avionics bay. The avionics bay  14  is maintained at a pre-selected temperature by an environmental control system (ECS) of the aircraft  10 . The ECS system supplies fresh air at a pre-selected temperature and a flow rate deemed suitable for ventilating and cooling (i.e. thermal conditioning) the avionics bay  14  and the objects present therein. 
   More specifically, and referring to the aviation bay  14  shown in  FIG. 2 , the ECS system typically includes ducting installed behind and throughout the equipment racks  16 . The ducting is usually unique for any given avionics bay  14 , equipment rack  16 , and even for any given equipment shelf  19  and piece of equipment  18 . Since the avionics bay  14 , the ECS system, and the equipment  18  are desired in view of each other, orifices are installed in the ducting to ensure that the proper amount of air flow is distributed to each piece of equipment  18 . This design approach allows the ECS system to be optimized for efficient operation. However, because the orifices and ducting are behind and within the equipment racks  16 , they are difficult to access and costly to alter. Moreover, because some of the flow paths through the ducts are not parallel, heat from one piece of equipment  18  may impact the cooling of another piece of equipment  18 . 
   Once the ECS system distributes the air to the pieces of equipment  18 , internal fan(s) of the pieces of equipment  18  (when provided by the equipment vendor) draw the air into the equipment  18  to cool its component parts. These internal fans cause the warmed air to exhaust to the avionics bay  14  where return ducts gather the warmed air for cooling, filtration, and recirculation. Accordingly, die pieces of equipment  18  are typically designed to operate at, and about, the pre-selected temperature of the avionics bay  14 . Additionally, the pieces of equipment  18  are designed to operate with the range of humidity that typically occurs in the avionics bay  14 . Humidity is typically not controlled by the ECS system, although most ECS systems do remove moisture via condensation when the air is cooled. Just removing the moisture however is not sufficient because many types of equipment  18  can be affected by excessively dry air. 
   Nonetheless, because of weight limitations onboard the typical aircraft  10 , humidification is usually only provided for the air that will be distributed to the crew cabin. That being said, the avionics bay  14  that is illustrated in  FIGS. 1 and 2  is a rather benign environment because it is a bay on a commercial  747  aircraft  10 . However, the avionics bays on other aircraft and vehicles may present a wider range of temperatures and humidity (as well as other environmental conditions) than the avionics bay  14  of  FIGS. 1 and 2 . 
   In flight, the ambient environment of die avionics bay  14  provides a large heat sink in which the equipment  18  dumps heat via the cooling air. Often the ECS system and equipment  18  are scaled to allow full operation of all of the equipment  18  in flight and some limited operation of the equipment when ambient, external temperatures limit the available cooling capacity. Ground operations on hot days are a typical example of a situation in which ambient, external temperatures might limit the available cooling capacity, unless ground cooling carts are available. For “bare base” operations, ground cooling carts may not be available at all and equipment  18  operations are sometimes limited accordingly. 
   The aviation industry has begun placing commercial-off-the-shelf (COTS) equipment onboard vehicles such as the aircraft  10 . These pieces of COTS equipment, however, were not necessarily designed for the environment of the avionics bay  14 . Thus, to accommodate the COTS equipment it sometimes becomes necessary to reconfigure the avionics bay or the ECS system of the aircraft. However, given the unique equipment involved (e.g., the ducting) such reconfigurations are typically costly. Furthermore, COTS equipment is typically not designed to operate in the relatively arid environment that might be present in the avionics bay from time to time. Additionally, when the aircraft is on the ground the operation of the COTS equipment may also be constrained due to excessive humidity (depending on the geographic location of the aircraft) or by the limited cooling capacity sometimes available on the ground. Thus, the COTS equipment, and for that matter many other pieces of avionics equipment, are dependent on the mechanical systems of the aircraft. Also, the COTS equipment in the avionics bay is exposed directly to ECS system pressure and the dust or other particulate matter that might be entrained therein. Since the ECS system pressure (i.e., cabin pressure) can change, it may not be desirable to expose the COTS equipment to such change if the COTS equipment has not been designed for changing ambient pressure. 
   Turning now to  FIG. 3A , an enclosure  20  of a preferred embodiment of the present invention is shown. The enclosure  20  contains various pieces of COTS equipment  24 . Preferably, a body  26  is constructed of a sheet metal such as aluminum and includes a number of channels, ducts, vessels, or other structures. These structures define an inner chamber  28 , an outer plenum  30 , and a pair of return plenums  32  among other things. Also shown are a mixing plenum  34  and an exhaust plenum  36 . As illustrated in  FIG. 3A , the structures of the enclosure  20  include an inner vessel  40 , a pair of return ducts  42 , a wall  43  of the return ducts  42  with optional heat exchange surfaces  44  (e.g., fins), a front door  46 , a door frame or door way  48 , a pair of elbows or turning vanes  50 , a baffle  51 , a pair of (Preferentially tangential) recirculation fans  52 , a pair of return guide vanes  54 , and a pair of ECS air channels  56 . Further,  FIG. 3B  shows the ports and ducting for the ECS supply and return. The ECS subassembly includes an ECS supply duct  60 , an ECS supply port  62 , an ECS return duct  64 , and an ECS return port  66 . Also,  FIG. 3B  shows a thermo-electric cold plate  70  of a preferred embodiment of the present invention. 
   Together these components define two flow paths in particular. The first flow path is for the ECS cooling air and the second flow path is an internal recirculation path for the cooling air that is in direct contact with the COTS (or other) equipment  24 . The thermally conductive wall  43  and heat fins  44  allow the two fluids to exchange heat so that the enclosure  20  thermally conditions the COTS equipment  24  in the inner chamber  28 . More particularly and starting with the internal recirculation path,  FIG. 3A  shows that the air in the exhaust plenum  36  of the inner chamber  28  (or “internal air”) flows into the fans  52  and then through the return ducts  42  that are along either side of the inner chamber  28 . Within the return ducts  42 , the internal air transfers heat to the heat exchange surfaces  43  and  44 . From the return ducts  42 , the internal air then flows through the low pressure drop turning vanes  50  and thence into the door way  48  wherein the streams of air exiting the two vanes  50  mix. The doorway  48 , or large mixing plenum  34 , is defined by the door  46  and the baffle  51  which is placed just upstream of the equipment  24 . As the internal air enters the mixing plenum  34  it slows down and recovers pressure from this change in speed. The internal air also mixes in the mixing plenum  34  so that it assumes a generally isothermal condition before exiting the mixing plenum  34  to the inner chamber  28 . 
   Continuing along the recirculation path, the baffle  51  has one or more apertures that are aligned with the cooling air intakes of the various pieces of equipment  24 . Otherwise, the baffle  51  seals against the walls  43  and the topmost inner surface and the bottommost surface of the inner chamber  28 . Meanwhile, the shelves  19  generally support the baffle  51  and assist it in resisting the pressure differential that develops across the baffle  51  as a result of the air flowing through it. Further, the baffle  51  directs the mixed internal air to the cooling air intakes of the equipment  24 . If the pieces of equipment  24  include internal fans, these fans draw the internal air into the pieces of equipment  24 . Thus, depending on how these fans are controlled by the pieces of equipment  24  or otherwise, the internal fan of any particular piece of equipment  24  largely determines the flow rate of the cooling air through that piece of equipment  24 . Otherwise, the motive force supplied by the fans  52  drives the recirculation of the internal air through the equipment  24 . As the internal air flows through the equipment  24  it absorbs heat from the internal components of the equipment  24  and is discharged from the equipment  24  into the exhaust plenum  36 . As shown in  FIG. 3A , the exhaust plenum  36  is formed by the downstream (or rear face) of the equipment  24  and the entrance to the guide vanes  54  which preferably forms an oblique angle with the rear surface of the equipment  24 . Again, because of the decrease in velocity of the internal air as it enters the exhaust plenum  36 , the internal air recovers pressure. As in the mixing plenum  34 , mixing of the internal air again occurs in the exhaust plenum  36 . From the exhaust plenum  36 , the air flows into the guide vanes  54  which are configured to guide the air into the fans  52  in a direction and at a speed that is optimal for the fans  52 . In this manner, the pressure loss (and energy required to compensate for it) associated with the recirculation of the internal air is minimized. Thus, in general, the internal air flows from the fans  52  through a heat exchanger in the return plenums  32  where it is cooled (or warmed if desired). The cool internal air then flows into the mixing plenum  34  and thence to the equipment  24 . Once in the equipment  24 , the internal air cools the equipment  24  and returns to the fans  52  via the exhaust plenum  36 . 
   On the other side of the heat exchangers formed by the return plenums  32 , the thermally conductive wall  43 , and preferably the heat transfer fins  44 , the ECS air absorbs heat, which originated in the equipment  24 , from the heat exchange surfaces  43  and  44 . The ECS air enters the outer plenum  30  (which forms the other side of the heat exchanger) from the ECS supply port  62  via the ECS supply duct  60 . Once through the heat exchanger, the warmed ECS air then exits the enclosure  20  via the ECS return duct  64  and ECS return port  66 . As best seen in  FIG. 3B , a preferred embodiment of the enclosure  20  is constructed such that the outer plenum  30  is formed in two portions  30 A and  30 B. Cool ECS air flows in an upwardly direction past the thermoelectric cold plate  70  (or optionally a heater if warming of the equipment  24  is preferred) and into the riser section  30 A of the outer plenum  30  and flows up alongside the side of the enclosure  20 . The thermo-electric cold plate  70  can be used if it is desired to supply the outer plenum  30  with cooler air than otherwise provided by the ECS system. The cool ECS air reaches the topmost portion of the riser  30 A and turns back to flow through the downcomer portions  30 B of the outer plenum  30 . In the downcomers  30 B the ECS air encounters the heat exchange surface or wall  43  and absorbs the heat that originated with the equipment  24 . From the downcomers  30 B, the now warm ECS air exits the enclosure  20  via the return port  66  for reconditioning in the ECS system of the aircraft  10  (see  FIG. 1 ). Of course, such terms as “up” “down,” are used herein for convenience and do not imply that the enclosure  20  must be placed in the avionics bay  14  in any given orientation although the vertical orientation implied herein is preferred. 
     FIG. 3A  also shows a rear door  47  connected to the body of the enclosure  20  by a hinge  57 . The door  47  includes the fans  52  (and the structure support the fans) and the guide vanes  54  rigidly connected to each other to form a sturdy structure. Thus the hinge allows the door  47 , including the fans  52  and the guide vanes  54 , to pivot away from the enclosure. This pivoting action allows access to the interior chamber  28  and the rear of the equipment  24  therein. A latch or handle can secure the door  47  to the body of the enclosure at any suitable location such as on the outer shell or plenum  30  on the side of the enclosure opposite the hinge  57 . 
     FIG. 4  shows several pairs of plan and elevation views of yet other preferred embodiments of the present invention. More particularly,  FIG. 4  illustrates six of the many possible variations of how air from the ECS system may be used to cool an enclosure. From left to right, the first pair of views of  FIG. 4  shows ECS air being supplied to a heat exchanger of an active cooling device  370  with the ECS air being exhausted out of the bottom of the enclosure  320  and back to the ECS system. The active device  370  thus cools the internal air (that is circulating through the enclosure  320 ) while keeping the two air streams separated. From the active cooling device  370 , the cooled internal air flows to the air plenum  336  in front of the COTS electronics (not shown). The COTS fans draw the internal air into the COTS equipment and exhaust the air to the plenum  334  in the back side of the enclosure  320 . The enclosures tangential fans  352  pull this air back to the front plenum  336  via the active cooling device  370 . 
   Regarding the second pair of views of  FIG. 4 , the embodiment shown therein is similar to the embodiment of the first pair of views except that in the first column (or pair of views) the tangential fans  352  are located on both sides of the enclosure  320 . In the second column there is only one tangential fan  352  on one side of the enclosure  320  and the rear plenum  334 ′ is modified to collect the warmed internal air from across the width of the enclosure  320 . The fan  352  is used to distribute the internal air from the cooling device  370  evenly over the face of the COTS equipment. From the front plenum  336  the COTS internal fans then pull the internal air into the COTS equipment thereby cooling the electronics and other devices in these packages. The third column of views is also similar to the first column except that the plenum  336 ′ that is used to collect the cooled internal air from the active cooling device  370  is located in the door  346  and not built into the main body of the enclosure  320 . Columns  4  through  6  illustrate ECS air being brought in and blown across the heat exchangers located in the side plenum(s)  330  of the enclosure  320 . Heat is then exchanged with the internal air that is inside the enclosure  320  via these heat exchangers. Again the two air sources are kept separated. In all of the embodiments of  FIG. 4  the bottom active heat exchange components  370  also provide humidity control in addition to thermally conditioning the internal air. 
   Referring now to  FIG. 5 , a cooling system that is constructed in accordance with another preferred embodiment of the present invention is shown schematically. The system  100  includes a heat exchanger  102 , a branch of the ECS system  104  of an aircraft  10  (see  FIG. 1 ) and a cooling air recirculation loop  106 . The two systems  104  and  106  interact in the heat exchanger  102  to remove (or add) heat to the recirculation loop  106  so that the system  100  thermally conditions the equipment in the enclosure  120 . In addition to the components that correspond to the structures and plenums of the enclosure  20  of  FIG. 3 , the system of the current embodiment also includes a pair of mixing valves  180  and  182 , a humidity sensor  184 , a temperature sensor  186  (e.g., a thermocouple), a water vapor supply valve  187 , a fan  188  that is internal to a piece of COTS equipment  124  and internal components  190  of a piece of COTS equipment  124  in the inner chamber  128 .  FIG. 5  also shows a controller  192  for coordinating various operations of the system  100 . 
   Preferably, the system  120  allows for closed loop humidity control of the internal air that circulates within the loop  106 . More particularly, the humidity sensor  184  is located in the mixing plenum  134  and the pair of mixing valves  180  and  182  are plumbed between the outer plenum  130  and (indirectly) the inner chamber  128 . Moreover, the mixing valves  180  and  182  are located such that when the valves  180  and  182  open, ECS air from the outer plenum  130  flows through the ECS supply mixing valve  180  and into the recirculation loop  106  where it joins the internal air in recirculating through the recirculation loop  106 . Some air from the recirculation loop  106  then exits through the ECS return mixing valve  182 . The valves  180  and  182  are opened by the controller  192  when the controller determines from the humidity sensor  184  that it is desirable to adjust the humidity in the inner chamber  128 . Thus, by introducing ECS air into the inner chamber  128 , opening the valves  180  and  182  allows the inner chamber  128  humidity to be regulated. In addition, the valves  180  and  182  may be opened in response to the temperature sensed by the temperature sensor  186  to provide closed loop temperature control of the inner chamber  128  and the equipment  124  therein. The cold plate  170  may also be turned on by the controller  192  in response to the temperature of the air in the mixing plenum  134 . While the cold plate  170  is shown as being in the ECS branch  104 , it could instead be located in the return plenums  132  of the internal air loop  106 . With the cold plate  170  in the recirculation loop  106 , the enclosure  120  provides additional cooling capacity above that offered by the ECS system and independently thereof. Accordingly, the enclosure  120  provides redundant cooling capacity for the equipment  124 . 
   In another preferred embodiment that is also shown in  FIG. 5 , the humidity sensor  184  is located in the mixing plenum  134  with the water vapor supply valve  187  being plumbed between a source of water vapor and the front mixing plenum  134 . 
   In the current embodiment, the controller  192  communicates with the humidity sensor  184  to sense whether the air in the mixing plenum  134  is at a desirable humidity level. The controller  192  also communicates with the water vapor supply valve  187  to open and close it in response to the humidity of the cooling air. Thus, the controller  192  or “cabinet control system” controls the humidity of the air in the inner chamber  128 . 
   With reference now to  FIG. 6 , the inner chamber  228  of a preferred embodiment of the present invention is shown with equipment  224  installed in it in  FIG. 6A  and with a baffle  251  in place in  FIG. 63 .  FIGS. 6A and 63  are elevation views of the inner chamber  228  (with the door and other structures of the enclosure not shown). More particularly,  FIG. 6A  shows that each of the pieces of equipment  224  in the inner chamber  228  preferably rests on and is mounted to one of the shelves  219 . While the inner chamber  228  has an overall height “h,” each of the shelves  219 A and  2193  (and the bottom of die chamber also) has a predetermined height “ha” and “h b ” (and “h c ”) at which it has been attached to the enclosure. The inner chamber  228  also has an overall width “w.” The baffle  251  fills the overall height “h” and width “w” of the inner chamber  228 . Further, the baffle  251  includes several baffle plates  202  that are associated with and removably attach to each of the shelves  219 . Where the particular pieces of equipment  224 A and  224 B have cooling air inlets  204 A and  204 B the baffle plates  202 A and  2023 , respectively, have apertures  206 A and  2063  to allow the interior air of the enclosure to pass through. Also shown are the bottom, top, and side walls  208 ,  210 , and  212  and  214  of the inner chamber  228 . 
   While some of the pieces of equipment  224  will largely fill the overall width “w” of the inner chamber  228  many other pieces of equipment  224  will allow a substantial gap to exist between themselves and the side walls  212  and  214  of the inner chamber. Similarly, gaps may exist between the individual pieces of equipment  224 A and  224 B and the shelf (or top wall  210 ) that is above it. It is also conceivable that gaps may exist between the equipment  224 A and  224 B and the shelves  219 A and  2193  (or bottom wall  208 ) of the inner chamber  228 . One or mote positions (e.g., a shelf  219 ) in the enclosure may be empty as illustrated in the bottommost position of the inner chamber  228  shown in  FIG. 6A . Referring to  FIG. 3A  and recalling that the baffle  51  forms one wall of the mixing plenum  34 , each of these gaps, if not blocked, will allow the internal cooling air of the inner chamber  228  to bypass the equipment  224 . Thus, the baffle plates  202  are shown filling the gaps around each of the pieces of equipment  224  to prevent the cooling air from bypassing the equipment  224 . 
   Preferably, the baffle plates  202  are made from one or more regularly sized rectangular segments. These segments can be made of any convenient material with metals, plastics and fabrics being preferred.  FIG. 6B  shows several exemplary baffle plates  202 A,  202 B, and  202 C having been assembled from a collection of baffle segments  220 ,  222 ,  224 ,  226 ,  228 ,  230 , and  232  as shown. Each of the segments  220 ,  222 ,  224 ,  226 ,  228 ,  230 , and  232  includes one half of a hook and loop fastener on one side and the other half of the hook and loop fastener on the other side. Thus, the segments  220 ,  222 ,  224 ,  226 ,  228 ,  230 , and  232  can be quickly assembled into one or more baffle plates  202  for any of the pieces of equipment  224  that might be mounted on a particular shelf  219 . In particular, the resulting baffle plates  202  may extend from the sides of the shelves  219  a distance sufficient to reach and seal against the inner surfaces of the inner chamber side walls  212  and  214 . The hook and loop fasteners on the segments  220 ,  222 ,  224 ,  226 ,  228 ,  230 , and  232  provide a convenient attachment mechanism for attaching the baffle plates  202  to the shelves  219  (with hook and loop fasteners also on the edges of the shelves  219 ). Likewise, each of the baffle plates  202  may extend from the shelf  219  that it is attached to at least an adjacent shelf. If the baffle plate  202  is attached to the top shelf  219 B, then the baffle plate  202  can be constructed in such a manner to extend to the top inside surface of the inner chamber  228 . In this manner, the baffle plates  202  on the shelves  219  block the flow of air from a mixing plenum toward an exhaust plenum. The segments  220 ,  222 ,  224 ,  226 ,  228 ,  230 , and  232  can be assembled into a baffle plate  202  with an aperture  206  sized, shaped, and positioned to align with the cooling air inlet  204  on a particular piece of equipment  224 . Thus, with the baffle plates  202  fastened to the shelves  219 , the overall baffle  251  directs the internal air from the mixing plenum into the cooling air inlets  204  of the pieces of equipment  224 . In turn, the internal fans in the equipment  224  draw the internal air through the equipment  224  and expel the warmed exhaust air toward the exhaust plenum  236 . Thus, if any of the pieces of equipment  224  use its internal fan as part of a temperature control loop (by, for instance, adjusting the speed of the internal fan in response to an internal temperature measurement) then the piece of equipment  224  can regulate its own supply of cooling air independently of the ECS system flow rate. Likewise, the piece of equipment  224  can regulate its internal temperature independently of the ECS flow rate. 
   In another preferred embodiment and with reference again to  FIG. 3 , the present invention provides a metal cabinet or enclosure  20  that provides environmental control for COTS equipment  24  (as well as other pieces of equipment  18 ) while alleviating the limitations of the previously available approaches. The enclosure  20  includes an outer shell that acts as a plenum  30  through which cooling air from the ECS system of an aircraft  10  circulates. A pair of ducts  60  and  64  from the ECS system attaches to the plenum  30  preferably on the top or the bottom of the enclosure  20 . The enclosure  20  also includes an inner chamber  28  that is generally surrounded by the outer plenum  30 . The inner chamber  28  holds COTS and other types of equipment  18  and  24 . A wall  43  between the outer plenum  30  and the inner chamber  28  isolates the ECS air from the air in the inner chamber  28  and serves as a heat exchanger to cool the inner chamber  28  air. Otherwise the walls of the inner chamber  28  are hollow and form a pair of return plenums  32 . Cool air enters the inner chamber  28  near the front side of the inner chamber  28  and flows through the equipment  24  thereby thermally conditioning the equipment  24 . The warmed exhaust air exits the equipment  24  near the rear of the inner chamber  28  and then flows through the return plenums  32  back toward the front side of the inner chamber  28 . Because one side of the hollow inner chamber wall is highly thermal conductive, the exhaust air exchanges heat with the ECS air via this thermally conductive wall and cools sufficiently to be recirculated through the equipment  24  once more. 
   Within the inner chamber  28  a series of shelves  19  support and restrain the equipment  24 . The inside surfaces of the inner chamber  28  walls have numerous mounting holes, brackets, or other attachment means for the shelves  19 . Thus, the shelves  19  are reconfigurable and can be placed in many different positions within the inner chamber  28  by selection of the mounting holes used to attach the shelves to the inner chamber  28 . 
   Doors  46  and  47  are also provided on the front and back sides of the enclosure  20  for accessing the COTS equipment  24  in the inner chamber  28 . Since the COTS equipment may be considered as LRUs (line replaceable units) the resulting front and back accessibility speeds maintenance on the aircraft. The doors  46  have seals associated with them so that when the doors  46  are closed the inner chamber  28  is hermetically sealed and isolated from the ECS air in the avionics bay  18  and from the ECS air in the outer plenum  30 . Moreover, the enclosure  20  is made of preferably light weight material (e.g., aluminum) and is of sturdy rugged construction such that it can withstand a pressure difference of several psi between the internal and external pressures. Thus, if cabin pressure is “lost” the COTS equipment  24  in the inner chamber  28  is not affected. 
   In view of the foregoing, it will be seen that the several advantages of the invention are achieved and attained. The present invention provides a standardized, modular solution that allows COTS equipment to be easily integrated into aircraft or other vehicle environments, while allowing for typical military operations. Among other things, the present invention provides embodiments with an isolated, controlled environment for COTS equipment even on vehicles with the harshest service conditions. Since the COTS equipment is isolated in accordance with the principles of the present invention the need for air filters for the COTS equipment is eliminated. 
   The present invention also provides complete dial-in moisture and temperature control for COTS equipment. Additionally, because the ECS system is not relied on for distributing cooling air to the various pieces of equipment, no balancing of the ECS system is needed for individual pieces of equipment (or individual cabinets). Also, the present invention allows for simple reconfiguration of the cooling system (i.e., the baffle of the enclosure) to accommodate equipment changes. Moreover, the enclosures of the present invention can include native cooling capacity (i.e., a thermo-electric cold plate) that is independent of the ECS system. Since the thermo-electric cold plate uses electric power that can be supplied from the ground while the aircraft is stationary instead of relying on power from an auxiliary power unit the present invention also provides “green” air conditioning for the COTS equipment. For embodiments with more than one recirculation fan in the enclosures of the present invention, redundant cooling air flow is also provided to the COTS equipment. Moreover, the present invention allows significant COTS equipment operation even with the doors of the aircraft open (thereby limiting cooling capacity and exposing the avionics bay to potentially undesirable humidity levels. 
   The embodiments were chosen and described in order to best explain the principles of the invention and its practical application to thereby enable others skilled in the art to best utilize the invention in various embodiments and with various modifications as are suited to the particular use contemplated. 
   As various modifications could be made in the constructions and methods herein described and illustrated without departing from the scope of the invention, it is intended that all matter contained in the foregoing description or shown in the accompanying drawings shall be interpreted as illustrative rather than limiting. Thus, the breadth and scope of the present invention should not be limited by any of the exemplary embodiments, but should be defined in accordance with the claims and their equivalents.