Abstract:
An air chamber for the housing of air handling components including an interior shell surrounded by an exterior shell, the shells being separated by materials of relatively low thermal conductivity. The interior shell is peripherally mounted on an interior base. The interior base is disposed within an exterior base that supports the exterior shell. A structural thermal insulation material is disposed interstitially between the interior and exterior bases and the interior base and interior shell are thermally isolated from the exterior base and exterior shell.

Description:
TECHNICAL FIELD 
     This invention relates to air handling equipment. Specifically, it relates to thermal isolation of chambers that house heating, ventilation and air conditioning components. 
     BACKGROUND ART 
     The delivery of a cool, dry air stream is necessary for a variety of applications ranging from industrial processes (e.g. plastics, food processing), to comfort control of large indoor spaces, to clean room environment control. Air handling chambers are designed to house the appurtenances necessary for the treatment of such air flow streams. The chambers are designed to accommodate a variety of components, depending on the application (e.g. cooling coils, desiccant wheels, and filtration systems). 
     The temperature within an operating air handling chamber is often substantially below the temperature surrounding the chamber. Such chambers are often deployed in high humidity environments. For example, outdoor or roof mounted chambers are routinely exposed to high temperature, high humidity ambient conditions associated with summer time operation. Indoor units are often installed within a high humidity environment associated with the process that requires air handling. 
     Conventional air handling chambers utilize a modular panel design. The walls of the chamber are constructed from pre-formed panels that mate with each other along jointed seams. The panels typically have a hard (often metallic) shell that is filled with a thermal insulation material. Some modular panel designs feature edges that are enclosed with the shell material, so that the mating edges of abutting panels have a stiff interface suitable for the insertion of a sealing material. The shell, typically constructed from a higher thermal conductivity material than the insulation material within, thermally bridges the thickness of the panel, creating a zone of lower temperature on the shell exterior along the seam of the joint. Condensation can form and accumulate when the temperature of these zones fall below the dew point temperature of the surrounding air. 
     Other designs leave the insulation exposed on the panel edges, the insulating material of one panel being formed to mate directly with the insulation of an adjoining panel. Such designs are more difficult to seal with interstitial materials at the joints and are prone to leakage of the cooler interior air because insulation materials tend to be of lower density and are less resistant to wear. Leakage through the joints effectively cools the outer surfaces of the panels near the seams, which also leads to the formation and accumulation of condensation on the exterior shell. 
     Conventional air handling chambers also utilize a base design that is prone to the formation of external condensation. Some chambers house heavy components, such as high capacity compressors or large banks of air-to-fluid heat exchangers. For the sake of rigidity, standard base structures form a thermal bridge between the chamber interior and the exterior of the base. 
     The food processing industry is particularly sensitive to condensation or “sweating” on the exterior of air handling equipment. Accumulation of condensation leads to the formation of droplets that can fall into food products or otherwise contaminate sanitized areas. Even outdoor units can cause contamination of food processing areas. For example, a roof-mounted unit typically has ductwork that extends from the bottom of the chamber and into the building through the roof. Condensation that forms on the exterior of the walls and base of the chamber can flow downward, attach to exterior of the ducting and make its way into the food processing area, thereby posing a contamination risk. The Food and Drug Administration has recognized the health risks associated with condensation in food processing facilities, and has promulgated rules and guidelines regarding condensation on air handling enclosures. See, e.g., 9 CFR Part 416, “Sanitation Requirements for Official Meat and Poultry Establishments, Final Rule,” 2000. 
     Heat flux through a solid medium, expressed in Watts per square meter, is directly proportional to the thermal conductivity of the medium (hereinafter referred to as k) and inversely proportional to the thermal path length (hereinafter referred to as L). That is, heat flux is proportional to the ratio k/L. In the case of a planar wall such as utilized in a thermal isolation chamber, the thermal path length L is dominated by the thickness of the insulation between the inner and outer wall assembly. A thicker wall enables the use of a higher conductivity material, whereas a thin wall requires the use of a lower conductivity material to maintain the exterior temperatures above the dew point temperature. 
     Generally, the thermal conductivity of so-called “thermal insulation” or “thermal insulative” materials can be of any magnitude, provided the available thermal path length L is long enough (i.e. the wall is thick enough) to maintain the exterior temperatures above the dew point temperature. 
     There exists a need for an air handling chamber design that minimizes or avoids the formation of condensation on exterior surfaces, yet is readily adapted to the construction of chambers of various sizes. 
     SUMMARY OF THE INVENTION 
     The air handling chamber in accordance with the present invention in large measure solves the problems outlined above. The wall, ceiling and base structures of the air chamber hereof thermally isolate the external surfaces and the base from the chamber interior, thus preventing the formation of exterior condensation. Inherent advantages of the design also include improved wall strength, enhanced thermal efficiency, less leakage into or out of the controlled gas stream, and improved suppression of the noise generated by the components within the chamber. Moreover, the method of construction allows the designer to specify a chamber of any size and walls of any thickness without compromising the thermal and flow containment integrity of the unit. 
     The side walls of certain embodiments of the invention have a continuous outer wall and a continuous inner wall with no structural element bridging the two walls. That is, if the inner wall and outer wall are each made of metal, there is no need for a metallic bridge to exist between the two structures. A gap separates the two walls and is filled with an insulation material to thermally isolate the interior of the chamber from the exterior wall. Likewise, the top of the chamber has a continuous internal ceiling and a continuous external roof, with no direct contact therebetween. The roof and ceiling are separated by a gap that may be filled with a rigid insulation board that is self supporting and provides additional strength to the structure. 
     For larger embodiments, each interior or exterior surface may be constructed by joining segments of sheet material together to form a continuous surface. In certain embodiments of the invention, flanges are formed on the abutting edges of the segments. The segments are then joined at the flanges by crimping, welding, fusing, riveting, capping or by other joining techniques available to the artisan. The joined flanges create a rib that protrudes from one surface of the joined segments. The rib may be oriented to extend into, but not all the way across, the gap, to provide essentially continuous surfaces on the interior and exterior of the chamber. The ribs also serve to stiffen the structure. 
     With many joining techniques, seams will be formed at each junction between adjacent sheets. The seams on the outer wall may be offset or “staggered” with respect to the seams on the inner wall. A staggered arrangement lengthens the leak path between seams through the insulation, providing a better seal than with standard modular constructions. Also, for embodiments implementing flanged abutments that reside between the interior and exterior walls, the staggered arrangement provides a longer thermal path between the flange and the opposing wall than an arrangement where the flanges are directly opposite each other. 
     Accordingly, the various configurations of the present invention implement a structural scheme that combines the advantages of both increased thermal resistance and increased leak resistance through the sidewall assembly. 
     In another embodiment of the invention, the base assembly features an internal base structure and an external base structure. The internal base structure is mounted within the external base structure, with a thermally resistant interstitial material disposed between the two structures. The interior shell (interior wall and ceiling) is supported on the internal base structure, and the exterior shell (exterior wall and roof) is supported on the external base structure. The base structures are characterized by large interfaces in contact with the interstitial material to distribute the weight of the chamber and appurtenances within over a large area. The distributed load allows the use of non-metallic or non-structural material as the interstitial material, thereby increasing the thermal resistance between the internal and external base frames. Also, any appendages or penetrations that pass through the base assembly, side walls or roof (e.g. drain pan fixtures, electrical conduits, etc.) are also thermally broken between the interior surface and the exterior surface by bifurcating the appendage or penetration into an interior and an exterior segment, and interposing a low conductivity coupling therebetween. 
     The spatial and structural constraints of the subject thermal isolation chambers provide for the use of insulation materials having a thermal conductivity of  1  Watt per meter per Kelvin or less. Such insulators have a thermal conductivity that is substantially lower (an order of magnitude or more) than the metals commonly used in construction of the chamber walls. The thermal isolation provided by the structure of the air chamber is greatly improved over conventional chambers. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view of an air chamber in accordance with the present invention. 
         FIG. 2  is a partially exploded view of the air chamber base assembly. 
         FIG. 3  is a perspective view of the base assembly depicted in  FIG. 2 . 
         FIG. 4  is a sectional end view of the base assembly. 
         FIG. 5  is a sectional view taken along line  5 - 5  of  FIG. 3 . 
         FIG. 6  is a fragmentary sectional side view of the base assembly. 
         FIG. 7  is a fragmentary plan view of the sidewall assembly of the air chamber. 
         FIG. 7A  is an enlarged view taken at  7 A of  FIG. 7 . 
         FIG. 7B  is an enlarged view taken at  7 B of  FIG. 7 . 
         FIG. 8  is a sectional, elevation view of the air chamber. 
         FIG. 8A  is an enlarged view taken at  8 A of  FIG. 8 . 
         FIG. 8B  is an enlarged view taken at  8 B of  FIG. 8 . 
         FIG. 9  is a fragmentary, perspective view of a portion of a sidewall assembly, without insulation, but depicting the installation of insulation. 
         FIG. 10  is similar to  FIG. 9 , but depicting insulation partially installed in the sidewall. 
         FIG. 11  is similar to  FIG. 10 , but with insulation installation completed. 
         FIG. 12  is a perspective view of an air chamber in accordance with the invention, having an extended chamber. 
         FIG. 13  is a sectional, elevation view of the air chamber of  FIG. 12 . 
         FIG. 14  is a plan view of a sidewall assembly of the air chamber depicted in  FIG. 12 . 
         FIG. 15  is a sectional view of an electrical feed through assembly taken at  15  of  FIG. 8 . 
         FIG. 16  is a sectional view of plumbing feed through assembly. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring to the drawings, a thermally broken chamber  10  includes a base assembly  15  and an upper assembly  20 . Referring to  FIGS. 2 through 4 , the base assembly  15  includes an exterior base  25  and an interior base  30 . The exterior base  25  is generally rectangular and has an exterior frame  35  having side members  40 ,  45  and end members  50 ,  55 . The exterior frame  35  defines an interior perimeter  60 , and outer perimeter  62  and a lower or grounding plane  65 . The exterior base  25  also includes a number of cross members  70  that extend between the side members  40  and  45  of the base frame  35 . The cross members  70  each have an upper surface  75  and a lower surface  80 . The lower surfaces  80  of the cross members  70  may be arranged flush with the lower plane  65 , as illustrated in  FIGS. 2 and 6 . 
     The interior perimeter  60  of the exterior frame  35  has an upper portion  85  extending above the upper surfaces  75  of the cross members  70 , best portrayed in  FIG. 4 . The upper portion  85  of the interior perimeter  60  and the upper surfaces  75  of the cross members  70  are lined with structural thermal insulation materials  90  and  92 , respectively. 
     Referring again to  FIG. 2 , the lined surfaces of the exterior base  25  define a caging  95  that houses interior base  30 . The interior base  30  includes an interior frame  100  having side members  105 ,  110  and end members  115 ,  120 . The interior frame  100  has a top face  102  and defines an exterior perimeter  125  and an upper plane  130 . The interior base  30  has a number of cross members  135  that extend between the side members  105  and  110  of the interior frame  100 . Referring to  FIG. 5 , the cross members  135  are positioned within the interior frame  100  to align with the cross members  70  of the exterior base  25  longitudinally when the interior base  30  is placed within the caging  95  of the exterior base  25 . Each of the cross members  135  of the interior base  30  are dimensioned so that an upper surface  140  is flush with the upper plane  130  and a lower surface  145  contacts the structural thermal insulation material  92  that lines the upper surfaces  75  of the cross members  70  of the exterior base  25  when the interior base  30  is placed within the caging  95  of the exterior base  25 . The interior base also includes a floor plate  150  that generally covers the cross members  135  and interior frame  100 . An air passage  155  or other access port may be provided through the floor plate  150 , as required by the particular application. 
     By the arrangement described above, there is no direct contact between the exterior base  25  and the interior base  30 . Rather, the structural thermal insulation materials  90  and  92  are interstitial between the structural interfaces of the exterior base  25  and the interior base  30 . Where the interior base  30  and exterior base  25  are metallic, there is no metal that bridges the two structures, resulting in enhanced thermal isolation between the interior and exterior of the chamber  10 . 
     Referring to  FIG. 6 , the base assembly  15  also includes a thermal insulation material  160  deposited between and within the cross members  70  and  135  of the exterior base  25  and interior base  30 , respectively. The base assembly  15  may be inverted for this operation, so that the grounding plane  65  of the base assembly  15  is on top, as depicted in  FIG. 6 . Inverting the base assembly  15  entails capturing the interior base  30  within the exterior base  25  so that the base assembly  15  remains assembled during the inverting operation. Excess thermal insulation  160  that extends above the grounding plane is then removed flush with grounding plane  65 . A cladding sheet (not depicted) may be affixed to the base assembly  15  at the grounding plane  65  to protect the underside of the base assembly  15 . 
     Preferably, the thermal insulation material  160  is a multi-component polyurethane foam, such as HANDI-FOAM® Quick-Cure manufactured by Fomo Products, Inc. of Norton, Ohio. Foam insulation of this type can be injected into voids and comers in the base assembly  15 , thereby providing uniform thermal insulation between the cross members  70  and  135 . 
     For most applications, the structural thermal insulation material  90  that lines the upper portion  85  of the interior perimeter  60  of the exterior frame  35  is subject to less contact pressure than the structural thermal insulation material  92  that lines the upper surfaces  75  of the cross members  70 . Accordingly, a material of lower density (and therefore typically lower thermal conductivity) may be used for the structural thermal insulation material  90  than for the structural load-bearing thermal insulation material  92 . 
     Functionally, the use of numerous cross members  70  and  135 , or the use of cross-members  70  and  135  having larger contact surfaces  75  and  145 , respectively, allows the weight of the interior base  30  and any structure or appurtenances mounted thereon to be spread over a large contact area  165 . For a given weight load, a larger contact area  165  will distribute the weight, reducing the contact pressure exerted on the interstitial structural thermal insulation material  92 . A lower contact pressure typically allows the use of a lower density structural thermal insulation material  92 , which in turn will generally decreases the thermal conduction between the exterior base  25  and the interior base  30 . Accordingly, depending on the contact pressures of a particular application, a variety of materials may be used for the structural thermal insulation material  92 , ranging from higher density structural plastics to moderate density rubber or silicone matting to lower density thermal insulation boards. 
     Furthermore, the use of a lower density structural thermal insulation material  90  will result in less heat conduction through the interior perimeter  60 . Likewise, the thermal insulation material  160  reduces the thermal conduction between the floor plate  150  of the interior base  30  and the lower plane  65  of the base assembly  15 . The reduced thermal conduction provided by the thermal break scheme of the base assembly  15  results in higher operating temperatures on the exterior surfaces of exterior base  25 . As a result, there is less chance of forming or accumulating condensation on the exterior surfaces of the base assembly  15 . 
     An alternative configuration for the thermal isolation between the interior base  30  and the exterior base  25  is also presented in  FIG. 2 . The upper surfaces  75  of the exterior cross members  70  may be only partially lined with a number of structural thermal insulation segments  93 . Intermediate areas  94  between the structural thermal insulation segments  93  may be left exposed (as depicted) or fitted with a low density thermal insulation (not depicted). If the intermediate areas  94  are left exposed, air may serve as an insulator between the aligned cross members  70  and  135 , or the void may be filled with thermal insulation  160  during the buildup of the base assembly  15  (see  FIG. 6  and accompanying text). 
     Functionally, the structural thermal insulation segments  93  suspend the cross members  135  of the interior base  30  above the upper surfaces  75  of the exterior cross members  70 , thereby preventing direct contact between the interior base  25  and the exterior base  30 . The thermal conductivity through intermediate areas  94  are inhibited either by air, the thermal insulation  160 , or a low density thermal insulation, and the functional utility of the unit may be enhanced over the configuration of  FIG. 2 . Again, where the interior base  30  and the exterior base  25  are of metallic construction, there is no metal-to-metal contact between the structures, resulting in greater thermal isolation between the interior and exterior of the chamber  10 . 
     Returning to  FIG. 1 , the upper assembly  20  of the thermally broken chamber  10  includes a sidewall assembly  170  and a cap assembly  175 . Referring to  FIGS. 7 ,  7 A and  7 B, an embodiment of the sidewall assembly  170  is depicted having an interior wall  180 , an exterior wall  190 , and an opening  201 . The interior and exterior walls  180  and  190  are separated by a gap  202  that may be of constant dimension. The gap  202  defines a center line  203  equidistant between the interior wall  180  and the exterior wall  190 . The interior wall  180  is a continuous structure that does not bridge to the exterior wall  190 . The interior wall  180  may be constructed of a series of interior wall panels, as illustrated in  FIG. 7  by numerical references  181  through  188 . Each of the interior wall panels  181 - 188  have an inward surface  204  that faces toward the interior of the sidewall assembly  170  and an outward surface  205  that faces the gap  202 . 
     The embodiment depicted in  FIGS. 7 ,  7 A and  7 B has interior wall panels  181 - 188  with flanged edges  210 , each flanged edge  210  having a rib portion  215  projecting perpendicular to the outward surface  205 , and a free end portion  220  that depends from the rib portion  215  in a direction parallel to the outward surface  205 . Adjacent interior wall panels  181 - 188  are joined by connecting the abutting rib portions  215  to each other, forming a seam  217  between the adjoined wall panels. A filler material  218  may be interstitially placed between the abutting rib portions  215 . The version of the invention illustrated in  FIG. 7  depicts the free end portions  220  extending over the outward surface  205 , so that the abutting flanged edges  210  form a T-shaped cross-section  222 . The configuration depicted in  FIG. 7  represents the flanged edges  210  oriented within the gap  202 , thereby providing a relatively smooth interior surface for interior wall  180 . 
     While the invention is not limited to locating the flanges  210  within the gap  202 , there are certain applications where such an arrangement provides advantages. 
     For example, orienting the flanges  210  within the gap  202  provides a smooth flow boundary for air flowing through the chamber, thus reducing frictional and turbulent head losses. Also, a smooth interior wall inhibits the growth of bacterial and is more readily cleaned—an important consideration for units servicing the food industry. 
     The opening  201  is defined by a split frame  223  having an inner portion  224  and an outer portion  226 . The two portions  224  and  226  are separated by a thermal break  228 , such as an o-ring or bellows made of a compliant material such as neoprene or silicone. The opening may be used as a doorway for chamber access, or as an airway for connecting ductwork. When the opening  201  is used as a doorway, a split door  229  may be mounted to form a closure. The door is of a construction similar to the split frame  223 ; specifically, it has an inner portion  230  and an outer portion  231  separated by a thermal break  232 . 
     The function of the split frame  223  and split door  229  configurations is to reduce the thermal conduction between the interior of the thermally broken chamber  10  and the ambient surroundings. The thermal isolation provided by the thermal breaks  228  and  232  enable the exterior surfaces near the opening  201  to operate at a higher temperature, thereby inhibiting the formation and accumulation of condensation on the exterior of the thermally broken chamber  10 . 
     Referring to  FIG. 8 , the interior wall  180  is dimensioned and positioned so that it is entirely supported by the interior frame  100 . A bottom flange  207  is formed on the bottom of each interior wall panel  181 - 188 . The bottom flange  207  is fastened or otherwise connected to the top face  102  of the interior frame  100 . 
     Once the interior wall  180  is constructed and mounted onto the interior frame  100 , the exterior wall  190  is built around the interior wall  180 . The exterior wall  190  is also continuous, and may be constructed from a series of exterior wall panels  191 - 196  and corner panels  197 - 200 . Each of the exterior wall and corner panels  191 - 200  have an inward surface  233  that faces toward the gap  202  and an outward surface  234 . In the embodiment depicted in  FIG. 7 , the exterior wall and corner panels  191 - 200  have at least one flanged edge  235 , each having a rib portion  240  that projects perpendicular to the inward surface  233  and a free end portion  245  that depends from the rib portion  240  in a direction parallel to the inward surface  233 . 
     Adjacent flanged edges (e.g. between wall panels  193  and  194 ) are joined by connecting the abutting rib portions  240  to each other, forming a seam  242  between the adjoined panels. A filler material  244  such as caulk or gasket material may be interstitially located between the abutting rib portions  240 . The version of the invention depicted in  FIG. 7A  illustrates the free end portions  245  of abutting flanged edges  235  extending in the same direction, thereby forming an L-shaped cross-section. The  FIG. 7  depiction portrays the joining of a flangeless edge portion  250  on exterior wall panel  193  to exterior corner panel  198 . The flangeless edge portion  250  is connected to a portion of the outward surface  234  of the corner panel  198 . Flangeless panel edges may be joined to flanged panel edges at any junction on the exterior or interior panels. The seam formed by the union of the flangeless edge portion  250  and the corner panel  198  may be filled with an appropriate sealer (not depicted). 
     The exterior wall  190  is dimensioned and positioned so that it is entirely supported by the exterior frame  35 . In the configuration depicted in  FIG. 8 , the exterior wall  190  is mounted to the exterior frame  35  through the outer perimeter  62 . By this construction, a bottom surface  255  terminating the gap  202  is formed by the top faces  58  and  102  of the exterior frame  35  and interior frame  100 , respectively. 
     The method of joining abutted flanged edges  210  or  235 , or for joining the flangeless edges  250  to adjacent panels, as well as the method for mounting the sidewall assembly  170  to the base assembly  15 , may be by fusing, welding, crimping, fasteners, or by any other means available to an artisan. In addition to providing a workable means for connecting adjacent panels, the flanged edges  210  and  235  provide strength and buckling resistance to the sidewall assembly  170 . 
     The configuration of the invention illustrated in  FIG. 7  limns the flanged edges  210  and  235  of the interior wall panels  181 - 188  and exterior wall panels  191 - 200  protruding into the gap  202 . While this arrangement may be preferred in many applications, the flanges may also be oriented to protrude away from the gap  202 . 
     Referring to  FIGS. 9 through 11 , the gap  202  is filled with an insulation material  260 . Neoprene spacers  265  may be used to maintain proper spacing between the interior wall  180  and the exterior wall  190 . While any appropriate insulation may be used, a preferred insulation material is a multi-component “slow rise” polyurethane foam  261 , such as HANDI-FOAM® SR, manufactured by Fomo Products, Inc. of Norton, Ohio. The slow rise polyurethane  261  is gunned into the gap  202 , as portrayed in  FIG. 9 , and onto the bottom surface  255  of the gap  202 . The slow rise polyurethane  261  slowly expands to fill the gap  202  and overflow the top edges of the sidewall assembly  170 , as depicted in  FIG. 10 . After the slow rise polyurethane  261  is cured, the excess overflow is shaved flush with the top edges of the sidewall assembly  170 . 
     The embodiment of  FIG. 7  also illustrates some flanged edges  210  of the interior wall  180  in a “staggered” arrangement with respect to the flanged edges  235  of the exterior wall  190 . That is, the flanged edges  235  of the exterior wall  190  are sometimes located approximately mid-way between the flanged edges  210  of the interior wall  180 . 
     The filler materials  218  and  244  help prevent leakage through the sidewall assembly  170  and the attendant transpiration cooling of the exterior seams  242 . The “staggered” relationship between interior flanged edges  210  and exterior flanged edges  235  serves at least two functions. First, if the interior and exterior flanged edges  210  and  235  are aligned directly opposite each other, there is a relatively short conduction path through the thermal insulation material  260  between the respective free ends  220  and  245 . By staggering the interior and exterior flanged edges  210  and  235 , the thickness of the insulation material  260  between a given free end  220  or  245  and the opposing exterior or interior wall  190  or  180  is increased, resulting a higher operating temperatures for the exterior wall  190 , thereby reducing the chance of condensation formation and accumulation. 
     Second, the staggered arrangement functions to increase the path length between any leaks that may occur between the corresponding interior seams  217  and exterior seams  242 . The increased path length through the insulation material  260  reduces leakage through the sidewall assembly  170 . Also, it is preferred, but not necessary, that the insulation material  160  be of a closed-cell form to further inhibit leakage through the side wall assembly  170 . 
     The T-shaped and L-shaped cross-sections  222  and  237  also cooperate to enhance leakage resistance through the sidewall assembly  170 . Air leaking through a T-shaped cross-section  222  will initially enter the insulation material  260  in the gap  202  at an angle that is perpendicular to the center line  203  of the gap  202 . On the other hand, air leaking through an L-shaped cross-section  237  will initially enter the gap  202  in a direction that is parallel to the center line  203 . The orthogonal relationship between the entry vectors forces the air to travel a tortuous path, further increasing the leak path resistance. The various means of increasing the leak path resistance combine to reduce the leakage of air through the sidewall assembly  170  and to decrease the attendant transpiration cooling of the exterior wall  190  near the exterior seams  242 . This allows the exterior wall to operate at a higher temperature, thereby reducing the chance of forming and accumulating condensation. 
     A cross-sectional view of the cap assembly  175  is also illustrated in  FIG. 8 . The cap assembly  175  includes a ceiling  270  and a roof assembly  275  that define a cap interior  285 . The cap interior is filled with thermal insulation material  290 . The ceiling  270  may be formed by joining individual ceiling panels  295  and  296 , or as one continuous sheet (not depicted). As in the formation of the interior and exterior walls  180  and  190 , the ceiling panels  295  and  296  may be formed with flanged edges  300  appropriate for the formation of T-shaped cross-sections  305  or L-shaped cross-sections (not depicted), as previously discussed. The flanged edges may protrude into the cap interior  285  as limned in  FIG. 8 , or protrude downward from the ceiling  270  (not illustrated). 
     While the thermal insulation material  290  may be of any appropriate type, a preferred form is rigid insulation board  291 . Rigid insulation board  291  is structurally self-supporting (meaning that it can span a significant distance without external support) and lends structural support to the roof assembly  275 . Also, the insulation scheme for the cap assembly  175  may involve a combination of different insulation materials, such as a loose fill insulation between flanged edges  300  of the ceiling panels  295  and  296 , capped with rigid insulation board  291  that rests on the flanged edges  300 . 
     The ceiling  270  has an edge portion  310  that extends over the interior wall  180 . The weight of the ceiling  270  and the portion of the weight of the insulation material  290  that is supported by the ceiling  270  is thereby transferred to the interior base  30  through the interior sidewall  180 . In some instances, the self-supporting nature of rigid insulation board  291  allows its weight to be shifted to the roof assembly  275  or directly to the exterior wall  190 . 
     The roof assembly  275  includes a top portion  276 , an outer portion  280  and a channel frame  355 . The top portion  276  may be formed by joining individual roof panels  315 - 318 , or may be constructed from one continuous sheet (not portrayed). As in the formation of the interior and exterior walls  180  and  190 , the roof panels  315 - 318  may be formed with flanged edges  320 . The flanged edges  320  may protrude into the cap interior  285  (not depicted), or protrude upward from the top portion  276  of the roof assembly  275 , as detailed in  FIG. 8 . 
     While T-shaped and L-shaped cross-sections may be formed between the roof panels  315 - 318 , an alternative is a J-shaped cross-section  325  as detailed in  FIG. 8 . Like the L-shaped cross section, the J-shaped cross-section includes rib portions  330  and  331  and free end portions  335  and  336  that depend from the rib portions  330  and  331  in the same direction, and a filler material  338  disposed between rib portions  330  and  331 . However, the uppermost free end portion  336  of the J-shaped cross section  325  also has a cap edge portion  340  that extends downward from the uppermost free end portion  336 . The cap edge portion  340  provides an effective shield against inclement elements such as rain, industrial sprays and the like from entering the seam formed by the junction of the flanged edges  320 . 
     The outer perimeter portion  280  of the roof assembly  275  depends from an edge portion  345  of the top portion  276 . The outer perimeter may have a skirt portion  350  at the lower extremity. A channel frame  355  is attached to the top portion  276  inside the outer perimeter portion  280  in the  FIG. 8  embodiment of the invention. A spacer  360  is placed between the channel frame  355  and the outer perimeter portion  280 , creating a gap  365  therebetween. The spacer  360  may be formed from a gasket or caulk material. The spacer  360  is seated on a protruding upper edge  270  of the exterior wall  190 , the upper edge  370  extending into the gap  365 . 
     The skirt portion  350  serves to guide placement of the roof assembly  275  onto the exterior wall  190 , and also serves as a drip lip that directs water shedding from the roof assembly  275  away from the unit. The weight of the roof assembly  275 , as well as any thermal insulation material  290 ,  291  supported by these elements, is transferred to the exterior base  25  through the exterior wall  190 . When the spacer  360  is formed from a gasket or caulk material, it provides a seal between the exterior wall  190  and the roof assembly  275 . 
     The cap assembly  175  is assembled on the sidewall assembly  170  in the  FIG. 8  configuration. The ceiling  270  is placed over the interior wall  180  so that the edge portion  310  of the ceiling  270  extends over the top edge of the interior wall and is attached thereto. The thermal insulation material  290  is then placed over the ceiling  270 , followed by the placement of a layer of the rigid insulation board  291  over the thermal insulation material  290 . The roof assembly  275  is guided over the protruding upper edge  370  of the exterior wall  190  to encapsulate the thermal insulation  290 ,  291 . 
     Effectively, the construction of  FIG. 8  provides an interior shell  372  mounted on the interior base  15  and an exterior shell  374  mounted on the exterior base  25 , with thermal insulation  260  isolating the two structures. The interior shell  372  includes the interior wall  180  and the ceiling  270 . The exterior shell  374  includes the exterior wall  190  and the roof assembly  275 . There is no direct contact between the interior shell  372  and the exterior shell  374 . Accordingly, where metals are used in the fabrication of the interior shell  372  and exterior shell  374 , there is no metal-to-metal contact between the two shells. 
     Referring to  FIGS. 12 through 14 , another version of the invention is presented. Sometimes, it is necessary to divide or split a thermally broken chamber  375  into one or more sections (e.g. to ship the unit or move it into a confined space). Accordingly, the thermally broken chamber  375  is divided into a first section  380  and a second section  385 . The first section  380  and the second section  385  each have open ends  382  and  386  that define planes  390  and  395 , respectively. A pair of shipping split channels  396  are located at the open end of each section  380  and  385 . The base assembly  15 , sidewall assembly  170  and cap assembly  175  of each section  380  and  385  are configured to have continuous flanged faces  400  and  405  that are flush with planes  390  and  395 , respectively. A sealing material  420  such as a gasket, caulk line or o-ring is placed between the flanged faces  400  and  405  before joining the two sections  380  and  385 . An upward extending flange  410  is formed on the top portion  276  of the roof assembly  275  at the interface of the continuous flanged faces  400  and  405 . A flange cap  425  is mounted over upward extending flange  410 . Sidewall seams (not depicted) that are formed at the interface of the two sections  380  and  385  are covered with strips  415  that may be fastened or bonded to the adjoining exterior walls  190 . A sealant such as a gasket or calking (not depicted) may be sandwiched between the strips  415  and the sidewall seams. 
     In operation, the sealing material  420  seals the interface upon joining the two sections. The shipping split channels  396  provide support for the open ends during shipment and movement, and are used to draw the two sections  380  and  385  together once the chamber  375  is in place. The flange cap  425  and strips  415  prevent incendiary elements such as rain or industrial sprays from seeping into the unit. 
     Referring to  FIG. 15 , an electrical feed through  430  abiding with the concept of the invention is depicted. The electrical feed through  430  includes an electrical conduit  434  joined to a thermal insulative coupling  436  having electrical or signal cabling  438  passing therethrough. The thermal insulative coupling  436  and the electrical conduit  343  may be threadably engaged using thread sizes that are standard in the electrical industry. The thermal insulative coupling  434  is fabricated from a material having a thermal conductivity that is lower than standard electrical conduit, such as PVC pipe or some other polymer or fluoropolymer. The electrical conduit  434  penetrates and is connected to the exterior wall  190  of the sidewall assembly  170 , but does not bridge all the way across the gap  202 . Rather, the thermal insulative coupling  436  bridges between interior wall  180  and the electrical conduit  434 . The region within and/or near the thermal insulative coupling  436  is filled with a thermally insulating sealant  440  such as silicone or epoxy. 
     Functionally, the electrical feed through  430  thermally isolates the interior wall  180  from the exterior wall  190  by interposition of the thermal insulative coupling  436 , which inhibits axial heat conduction through the electrical feed through  430 . The thermally insulating sealant  440 , in addition to maintaining the pressure integrity of the chamber, prevents cool air from inside the chamber from reaching the electrical conduit  434 , thereby cooling it from the inside. The thermally insulating sealant also inhibits radial conduction from the interior wall  180  to the electrical or signal cabling  438 , which tend to be high thermal conductors. All of these factors combine to inhibit the cooling of the external wall  190  and the electrical conduit  434 , and the attendant formation of condensation thereon. The use of standard threaded couplings on the thermal insulative coupling  436  enables the use of standard electrical conduit during field installation. 
     Referring to  FIG. 16 , a plumbing feed through  432  is illustrated. The particular embodiment of the plumbing feed through  432  is tailored to service a drain pan  442 , and is conceptually similar to the electrical feed through  430 . Specifically, the plumbing feed through  432  includes a drain pipe  444  that passes through the exterior frame  35  and is in fluid communication with the drain pan  442  through a thermal insulative coupling  446 , the coupling  446  penetrating the interior frame  100 . Alternatively, the drain pipe  444  may be replaced with a plug (not depicted) that blocks the thermal insulative coupling  446 , the plug being preferably of a low thermal conductivity. 
     The effect of the plumbing feed through  432  is the same as for the electrical feed through  430 —namely, the interposition of the thermal insulative coupling  446  reduces conduction between interior frame  100  and the exterior frame  35 , thus allowing the base assembly  15  to operate at a higher temperature and reduce the chance of condensation formation. Of course, the thermal insulative coupling  446  cannot be filled with a permanent sealant, lest the plumbing feed through not serve its intended purpose of draining the chamber. However, the effect of chamber air cooling the drain pipe  444  may be mitigated by the presence of water that fills the drain pipe  444  and thermal insulative coupling  446 . The drain pipe  444  may be sealed off downstream (e.g. with a valve) and drained only periodically, so that over most of the operational life of the chamber there is no air circulating into the drain pipe  444 . The water within the drain pipe  444  and thermal insulative coupling  446  will be stagnant, and tend to equilibrate with the local temperature of the surroundings. Hence the mitigation of the cooling effect of an open drain pipe  444 . The aforementioned plug in the thermal insulative coupling  446  would produce the same effect. 
     The preceding discussions assume that the air streams being handled by the various embodiments of the invention are at a temperature less than the temperature of the ambient surroundings. Also, some reference is made to certain structural components being metallic. Such examples are not to be considered limiting, as the invention may have utility in a wide range of air and fluid handling situations, and thermally conductive structural components are not limited to metals. Furthermore, the invention may be embodied in other specific and unmentioned forms without departing from the spirit or essential attributes thereof, and it is therefore asserted that the foregoing embodiments are in all respects illustrative and not restrictive.