Abstract:
A casing assembly suitable for use in a heat exchange assembly comprises a first panel including a first bottom portion, a second panel including a second bottom portion, and a third panel including a third bottom portion. The second bottom portion is interlocked with the first and third bottom portions.

Description:
CROSS-REFERENCE TO RELATED APPLICATION(S)  
       [0001]     The following application is filed on the same day as the following co-pending applications: “METHOD AND SYSTEM FOR HORIZONTAL COIL CONDENSATE DISPOSAL” by inventors Arturo Rios, Floyd J. Frenia, Jason Michael Thomas, Michael V. Hubbard, and Thomas K. Rembold (attorney docket number U75.12-003); “CONDENSATE PAN INSERT” by inventors Jason Michael Thomas, Floyd J. Frenia, Thomas K. Rembold, Arturo Rios, Michael V. Hubbard, and Dale R. Bennett (attorney docket number U75.12-005); “METHOD AND SYSTEM FOR VERTICAL COIL CONDENSATE DISPOSAL” by inventors Thomas K. Rembold, Arturo Rios, Jason Michael Thomas, and Michael V. Hubbard (attorney docket number U75.12-006); “CASING ASSEMBLY SUITABLE FOR USE IN A HEAT EXCHANGE ASSEMBLY” by inventors Arturo Rios, Thomas K. Rembold, Jason Michael Thomas, Stephen R. Carlisle, and Floyd J. Frenia (attorney docket number U75.12-007); “LOW-SWEAT CONDENSATE PAN” by inventors Arturo Rios, Floyd J. Frenia, Thomas K. Rembold, Michael V. Hubbard, and Jason Michael Thomas (attorney docket number U75.12-008); “CONDENSATE PAN INTERNAL CORNER DESIGN” by inventor Arturo Rios (attorney docket number U75.12-009); “VERTICAL CONDENSATE PAN WITH NON-MODIFYING SLOPE ATTACHMENT TO HORIZONTAL PAN FOR MULTI-POISE FURNACE COILS” by inventor Arturo Rios (attorney docket number U75.12-010); “CONDENSATE SHIELD WITH FASTENER-FREE ATTACHMENT FOR MULTI-POISE FURNACE COILS” by inventor Arturo Rios (attorney docket number U75.12-011); and “SPLASH GUARD WITH FASTENER-FREE ATTACHMENT FOR MULTI-POISE FURNACE COILS” by inventor Arturo Rios (attorney docket number U75.12-012), which are incorporated herein by reference.  
       BACKGROUND  
       [0002]     The present invention relates to a casing assembly. More particularly, the present invention relates to a casing assembly suitable for use in a heat exchange assembly.  
         [0003]     In a conventional refrigerant cycle, a compressor compresses a refrigerant and delivers the compressed refrigerant to a downstream condenser. From the condenser, the refrigerant passes through an expansion device, and subsequently, to an evaporator. The refrigerant from the evaporator is returned to the compressor. In a split system heating and/or cooling system, the condenser may be known as an outdoor heat exchanger and the evaporator as an indoor heat exchanger, when the system operates in a cooling mode. In a heating mode, their functions are reversed.  
         [0004]     In the split system, the evaporator is typically a part of an evaporator assembly coupled with a furnace. However, some cooling systems are capable of operating independent of a furnace. A typical evaporator assembly includes an evaporator coil (e.g., a coil shaped like an “A”, which is referred to as an “A-frame coil”) and a condensate pan disposed within a casing. An A-frame coil is typically referred to as a “multi-poise” coil because it may be oriented either horizontally or vertically in the evaporator assembly.  
         [0005]     During a cooling mode operation, a furnace blower circulates air into the casing of the evaporator coil assembly, where the air cools as it passes over the evaporator coil. The blower then circulates the air to a space to be cooled. Depending on the particular application, an evaporator assembly including a vertically oriented A-frame coil may be an up flow or a down flow arrangement. In an up flow arrangement, air is circulated upwards, from beneath the evaporator coil assembly, whereas in a down flow arrangement, air is circulated downward, from above the evaporator coil assembly.  
         [0006]     Refrigerant is enclosed in piping that is used to form the evaporator coil. If the temperature of the evaporator coil surface is lower than the dew point of air passing over it, the evaporator coil removes moisture from the air. Specifically, as air passes over the evaporator coil, water vapor condenses on the evaporator coil. The condensate pan of the evaporator assembly collects the condensed water as it drips off of the evaporator coil. The collected condensation then typically drains out of the condensate pan through a drain hole in the condensate pan.  
       BRIEF SUMMARY  
       [0007]     The present invention is a casing assembly suitable for use in a heat exchange assembly. The casing assembly includes a casing, which includes at least one interlocking interior corner. The interlocking corner strengthens the casing and helps maintain the integrity of the casing. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0008]      FIG. 1A  is a perspective view of an evaporator assembly, which includes an evaporator coil and condensate pan disposed within a casing.  
         [0009]      FIG. 1B  is an exploded perspective view of the evaporator assembly of  FIG. 1A .  
         [0010]      FIG. 2A  is a perspective view of a casing assembly, which includes a casing and a front deck.  
         [0011]      FIG. 2B  is a cross-sectional view of a left bottom portion of the casing of  FIG. 2A .  
         [0012]      FIG. 2C  is a cross-sectional view of a rear bottom portion of the casing of  FIG. 2A .  
         [0013]      FIG. 2D  is a cross-sectional view of a right bottom portion of the casing of  FIG. 2A .  
         [0014]      FIG. 3  is a bottom view of the casing of  FIG. 2A , illustrating a flange configured to receive a vertical condensate pan.  
         [0015]      FIG. 4  is a partial perspective view of an interlocking design between a left inner surface of the left bottom portion and a rear inner surface of the rear bottom portion of the casing of  FIG. 2A .  
         [0016]      FIG. 5  is a partial perspective view of an interlocking design between a right end of the front deck and a left flange of the left bottom portion of the casing assembly of  FIG. 2A .  
         [0017]      FIG. 6  is a plan view of a sheet of material that is used to form the casing of  FIG. 2A . 
     
    
     DETAILED DESCRIPTION  
       [0018]      FIG. 1A  is a perspective view of evaporator assembly  2 , which includes casing  4  in accordance with the present invention, A-frame evaporator coil (“coil”)  6 , coil brace  8 , first delta plate  10 , second delta plate  12 , horizontal condensate pan  14 , drain holes  15 , vertical condensate pan  16 , drain holes  17 , first cover  18 , input refrigerant line  20 , and output refrigerant line  22 . When evaporator assembly  2  is integrated into a heating and/or cooling system, evaporator assembly  2  is typically mounted above an air handler. The air handler includes a blower that cycles air through evaporator assembly  2 . In a down flow application, the blower circulates air in a downward direction (indicated by arrow  24 ) through casing  4  and over coil  6 . In an up flow application, the blower circulates air in an upward direction (indicated by arrow  26 ) through casing  4 .  
         [0019]     Coil  6 , condensate pan  14 , and condensate pan  16  are disposed within casing  4 , which is preferably a substantially airtight space for receiving and cooling air. That is, casing  4  is preferably substantially airtight except for openings  4 A and  4 B (shown in  FIG. 1B ). In a down flow application, air is introduced into evaporator assembly  2  through opening  4 A and exits through opening  4 B. In an up flow application, air is introduced into evaporator assembly  2  through opening  4 B and exits through opening  4 A. In the embodiment shown in  FIGS. 1A and 1B , casing  4  is constructed of a single piece of sheet metal that is folded into a three-sided configuration, and may also be referred to as a “wrapper”. In alternate embodiments, casing  4  may be any suitable shape and configuration and/or formed of multiple panels of material.  
         [0020]     Coil  6  is a multi-poise A-frame coil, and may be oriented either horizontally or vertically. The vertical orientation is shown in  FIGS. 1A and 1B . In a horizontal orientation, casing  4  is rotated 90° in a counterclockwise direction. Coil brace  8  is connected to air seal  28  and helps supports coil  6  when coil  6  is in its horizontal orientation.  
         [0021]     Coil  6  includes first slab  6 A and second slab  6 B connected by air seal  28 . A gasket may be positioned between air seal  28  and first and second slabs  6 A and  6 B, respectively, to provide an interface between air seal and slabs  6 A and  6 B that is substantially impermeable to water. First and second delta plates  10  and  12 , respectively, are positioned between first and second slabs  6 A and  6 B, respectively. First slab  6 A includes multiple turns of piping  30 A with a series of thin, parallel plate fins  32 A mounted on piping  30 A. Similarly, second slab  6 B includes multiple turns of piping  30 B with a similar series of thin, parallel fins mounted on piping  30 B. Tube sheet  29 A is positioned at an edge of slab  6 A, and tube sheet  29 B is positioned at an edge of slab  6 B. Delta plates  10  and  12 , and air seal  28  may be attached to tube sheets  29 A and  29 B.  
         [0022]     In the embodiment shown in  FIG. 1A , coil  6  is a two-row coil. However, in alternate embodiments, coil  6  may include any suitable number of rows, such as three, as known in the art. Refrigerant is cycled through piping  30 A and  30 B, which are in fluidic communication with one another (through piping system  62 , shown in  FIG. 1B ). As  FIG. 1A  illustrates, coil  6  includes input and output lines  20  and  22 , respectively, which are used to recycle refrigerant to and from a compressor (which is typically located in a separate unit from evaporator assembly  2 ). Refrigerant input and output lines  20  and  22  extend through first cover  18 . Evaporator assembly  2  also includes access cover  38  (shown in  FIG. 1B ) adjacent to first cover  18 , and together, first cover  18  and access cover  38  fully cover the front face of evaporator assembly  2  (i.e., the face which includes first cover  18 ). Access cover  38  will be described in further detail in reference to  FIG. 1B .  
         [0023]     As discussed in the Background section, if the temperature of coil  6  surface is lower than the dew point of the air moving across coil  6 , water vapor condenses on coil  6 . If coil  6  is horizontally oriented, condensation from coil  6  drips into condensate pan  14 , and drains out of condensate pan  14  through drain holes  15 , which are typically located at the bottom of condensate pan  14 . If coil  6  is vertically oriented, condensate pan  16  collects the condensed water from coil  6 , and drains the condensation through drain holes  17 , which are typically located at the bottom of condensate pan  16 .  
         [0024]     Because evaporator assembly  2  includes horizontal condensate pan  14  and vertical condensate pan  16 , evaporator assembly  2  is configured for applications involving both a horizontal and vertical orientation of coil  6 . In an alternate embodiment, evaporator assembly  2  is modified to be applicable to only a vertical orientation of coil  6 , in which case horizontal condensate pan  14  and brace  8  are absent from evaporator assembly  2 . In another alternate embodiment, evaporator assembly  2  excludes vertical condensate pan  16  such that evaporator assembly  2  is only applicable to horizontal orientations of coil  6 .  
         [0025]      FIG. 1B  is an exploded perspective view of evaporator assembly  2  of  FIG. 1A . Front deck  39  and upper angle  40  are each connected to casing  4  with screws  41 . Another suitable method of connecting front deck  39  and upper angle  40  to casing  4  may also be used, such as welding, an adhesive or rivets. Front deck  39  and upper angle  40  provide structural integrity for casing  4  and provide a means for connecting front cover  18  and access cover  38  to casing  4 . Screw  43  attaches brace  8  (and thereby, air seal  28 ) to horizontal condensate pan  14 . Of course, other suitable means of attachment may be used in alternate embodiments. In addition to air seal  28 , air splitter  44  is positioned between first slab  6 A and second slab  6 B of coil  6  and is attached by tabs on tube sheets  29 A and  29 B of coil  6 .  
         [0026]     Horizontal and vertical condensate pans  14  and  16  are typically formed of a plastic, such as polyester, but may also be formed of any material that may be casted, such as metal (e.g., aluminum). Horizontal condensate pan  14  slides into casing  4  and is secured in position by pan supports  46 . Tabs  46 A of pan supports  46  define a space for condensate pan  14  to slide into. When coil  6  is in a horizontal orientation (and casing  4  is rotated about 90° in a counterclockwise direction), coil  6  is positioned above horizontal condensate pan  14  so that condensation flows from coil  6  into horizontal condensate pan  14 . Air splitter  44  and splash guards  45 A and  45 B also help guide condensation from coil  6  into horizontal condensate pan  14 .  
         [0027]     Condensation that accumulates in horizontal condensate pan  14  eventually drains out of horizontal condensate pan  14  through drain holes  15 . Gasket  52 A is positioned around drain holes  15  prior to positioning first cover  18  over drain holes  15  in order to help provide a substantially airtight seal between drain holes  15  and first cover  18 . First cover  18  includes opening  53 A, which corresponds to and is configured to fit over drain holes  15  and gasket  52 A. The substantially airtight seal helps prevent air from escaping from casing  4 , and thereby increases the efficiency of evaporator assembly  2 . Caps  56 A may be positioned over one or more drain holes  15 , such as when evaporator assembly  2  is used in an application in which coil  6  is vertically oriented.  
         [0028]     Vertical condensate pan  16  slides into casing  4  and is supported, at least in part, by flange  48 , which is formed by protruding sheet metal on three-sides of casing  4  and top surface  39 A of front deck  39 . Specifically, bottom surface  16 A of condensate pan  16  rests on flange  48  and top surface  39 A of front deck  39 . Condensate pan  16  includes outer perimeter  49 , insert  50 , drain holes  17  (which are sealed by gasket  52 B) and plurality of ribs  54 .  
         [0029]     One or more channels are positioned about outer perimeter  49  of vertical condensate pan  16  for receiving condensation from coil  6 . In the vertical orientation of coil  6  illustrated in  FIGS. 1A and 1B , coil  6  is positioned above vertical condensate pan  16  to allow condensation to flow along one slab  6 A or  6 B and eventually into one or more of the channels along outer perimeter  49  of vertical condensate pan  16 . In this way, condensation collects in condensate pan  16 . In some applications, such as when coil  6  is a three row coil, insert  50  is positioned in condensate pan  16  to help shield coil  6  from condensate blow off from condensate pan  16 .  
         [0030]     Evaporator assembly  2  includes features, such as ribs  54  and shield  58 , that are configured to help direct condensation into the one or more channels along outer perimeter  49  of vertical condensate pan  16  (when coil  6  is vertically oriented). Shield  58  is attached to tube sheet  29 A and is configured to both guide condensation into a channel along outer perimeter  49  of condensate pan  16  and help protect coil  6  from condensation blow-off, which occurs when condensation that is collected in condensate pan  16  is blown into the air stream moving through evaporator assembly  2 . A similar shield is attached to tube sheet  29 B.  
         [0031]     Condensation that accumulates in vertical condensate pan  16  eventually drains out of vertical condensate pan  16  through drain holes  17 . Gasket  52 B is positioned around drain holes  17  prior to positioning first cover  18  over drain holes  17  in order to help provide a substantially airtight seal between drain holes  17  and first cover  18 . First cover  18  includes opening  53 B, which corresponds to and is configured to fit over drain holes  17  and gasket  52 B. The airtight seal helps prevent air from escaping from casing  4 , and thereby increases the efficiency of evaporator assembly  2 . Cap  56 B may be positioned over one or more drain holes  17 .  
         [0032]     Piping system  62  fluidically connects piping  30 A of first slab  6 A and piping  30 B of second slab  6 B. Refrigerant flows through piping  30 A and  30 B, and is recirculated from and to a compressor through inlet and outlet tubes  20  and  22 , respectively. Specifically, refrigerant is introduced into piping  30 A and  30 B through inlet  20  and exits piping  30 A and  30 B through outlet  22 . As known in the art, refrigerant inlet  20  includes rubber plug  64 , and refrigerant outlet  22  includes strainer  66  and rubber plug  68 . Inlet  20  protrudes through opening  70  in first cover  18  and outlet  22  protrudes through opening  72  in first cover  18 . By protruding through first cover  18  and out of casing  4 , inlet  20  and outlet  22  may be connected to refrigerant lines that are fed from and to the compressor, respectively. Gasket  74  is positioned around inlet  20  in order to provide a substantially airtight seal around opening  70 . Similarly, gasket  76  is positioned around outlet  22 .  
         [0033]     First cover  18  is attached to casing  4  with screws  78 . However, in alternate embodiments, other means of attachment are used, such as welding, an adhesive, or rivets. Further covering a front face of evaporator assembly  2  is access cover  38 , which is abutted with first cover  18 . Again, in order to help increase the efficiency of evaporator assembly  2 , it is preferred that joint  81  between first cover  18  and access cover  38  is substantially airtight. A substantially airtight connection may be formed by, for example, placing a gasket at joint  81 .  
         [0034]     Access cover  38  is attached to casing  4  with screws  82 . However, in alternate embodiments, any means of removably attaching access cover  38  to casing  4  are used. Access cover  38  is preferably removably attached in order to provide access to coil  6 , condensate pan  16 , and other components inside casing  4  for maintenance purposes. One or more labels  84 , such as warning labels, may be placed on first cover  18  and/or access cover  38 .  
         [0035]      FIG. 2A  is a perspective view of casing assembly  86  in accordance with the present invention, which includes casing  4  and front deck  39 . Casing assembly  86  includes left internal rear corner  87 , right internal rear corner  88 , left internal front corner  89 , and right internal front corner  90 . Each corner  87 ,  88 ,  89 , and  90  includes an interlocking structure that increases the strength of casing assembly  86 , and increases the integrity of casing assembly  86 , such that casing assembly  86  is able to substantially withhold its shape during shipping and handling (e.g., installation). In each internal rear corner  87  and  88 , two surfaces intersect, and thereby interlock. In each internal front corner  89  and  90 , two surfaces mate together to interlock. The interlocking structure and design of each internal corner  87 ,  88 ,  89 , and  90  will be described in further detail in reference to  FIGS. 4 and 5 .  
         [0036]     Casing  4  includes left panel  92 , rear panel  94 , and right panel  96 . Left panel  92  of casing  4  includes left top portion  98  and left bottom portion  100 , while rear panel  94  of casing  4  includes rear top portion  102  and rear bottom portion  104 , and right panel  96  of casing  4  includes right top portion  106  and right bottom portion  108 . Left top portion  98  includes left lip  110 , which is folded inward (toward opening  4 B of casing  4 ) in order to tuck away edge  110 A of left lip  110 , which may be sharp. As previously discussed, in one embodiment, casing  4  is formed of sheet metal, which may form a sharp edge when cut. If edge  110 A of left lip  110  is sharp, certain problems may be presented. For example, if coil  6  (shown in  FIGS. 1A and 1B ) comes into contact with left lip  110 , such as during manufacture of evaporator assembly  2 , a sharp edge  110 A may damage coil  6 .  
         [0037]     Rear top portion  102  includes rear lip  112 , and right top portion  106  includes right lip  114 . Just as with left lip  110 , rear lip  112  and right lip  114  are folded inward in order to help minimize potentially sharp edges  112 A and  114 A (shown in phantom), respectively. In an alternate embodiment, each lip  110 ,  112 , and  114  folds outward, such that edges  110 A,  112 A, and  114 A, respectively, point away from opening  4 B of casing  4 . In yet another alternate embodiment, each lip  110 ,  112 , and  114  includes multiple folds.  
         [0038]      FIG. 2B  is a cross-section of left bottom portion  100  of left panel  92  of casing  4  taken along line  2 B- 2 B in  FIG. 2A . Left bottom portion  100  is comprised of four generally planar surfaces: left outer surface  120 , left bottom surface  122 , left inner surface  124 , and left flange  126 . Left outer surface  120  and left inner surface  124  extend in a z-axis direction and left bottom surface  122  and left flange  126  extend in an x-axis direction. Outer, bottom, and inner surfaces  120 ,  122 , and  124 , respectively, define a channel  128 . Casing  4  is often insulated in order to help maintain a temperature inside casing  4  within a preferred range. Insulation for left panel  92  of casing  4  may be introduced into channel  128 , which supports the insulation and helps to hold the insulation flush with left outer surface  120 . In an alternate embodiment, left bottom portion  100  includes at least one nonplanar surface.  
         [0039]     As  FIG. 2C  illustrates, a cross-section of rear bottom portion  104  of casing  4  take along line  2 C- 2 C in  FIG. 2A  is similar to  FIG. 2B . Rear bottom portion  104  is comprised of four generally planar surfaces: rear outer surface  130 , rear bottom surface  132 , rear inner surface  134 , and rear flange  136 . Rear outer surface  130  and rear inner surface  134  extend in a z-axis direction and rear bottom surface  132  and rear flange  136  extend in a y-axis direction. Rear outer, bottom, and inner surfaces  130 ,  132 , and  134 , respectively, define a channel  138 . Insulation for rear panel  94  of casing  4  may be introduced into channel  138 , which supports the insulation and helps to hold the insulation flush with rear outer surface  130 . In an alternate embodiment, rear bottom portion  104  includes at least one nonplanar surface.  
         [0040]      FIG. 2D  is a cross-sectional view of right bottom portion  108  of casing  4  taken along line  2 D- 2 D in  FIG. 2A . Again,  FIG. 2D  is similar to  FIGS. 2B and 2C . Right bottom portion  108  is comprised of four generally planar surfaces: right outer surface  140 , right bottom surface  142 , right inner surface  144 , and right flange  146 . Right outer surface  140  and right inner surface  144  extend in a z-axis direction and right bottom surface  142  and right flange  146  extend in an x-axis direction. Right outer, bottom, and inner surfaces  140 ,  142 , and  144 , respectively, define a channel  148 . Insulation for right panel  96  of casing  4  may be introduced into channel  148 , which supports the insulation and helps to hold the insulation flush with right outer surface  140 . In an alternate embodiment, right bottom portion  108  includes at least one nonplanar surface.  
         [0041]      FIG. 3  is a bottom view of casing  4  of  FIG. 2A . Left panel  92  is generally perpendicular to rear panel  94 , which is generally perpendicular to right panel  96 . Left, rear, and right flanges  126 ,  136 , and  146 , respectively, extend around an inner perimeter of casing  4  and define opening  4 B in casing  4 , through which air is either introduced into or moved out of evaporator assembly  2 . Together with front deck  39  (shown in  FIG. 2A ), left, rear, and right flanges  126 ,  136 , and  146 , respectively, also define flange  48  ( FIG. 1B ), which is essentially a shelf that is configured to receive and support vertical condensate pan  16 .  
         [0042]     In order to strengthen casing  4  and help maintain the integrity of casing  4  during shipping and handling of casing  4  and/or evaporator assembly  2 , casing  4  includes an interlocking design at left internal rear corner  87  and right internal rear corner  88 . At left internal rear corner  87 , left inner surface  124  of left bottom portion  100  and rear inner surface  134  of rear bottom portion  104  are designed to interlock. An embodiment of an interlocking design is shown in  FIG. 4 , which is a partial perspective view of casing  4 , illustrating left internal rear corner  87  in which left panel  92  of casing  4  meets rear panel  94  of casing  4 .  FIG. 4  also shows left flange  126 , which is adjacent to rear flange  136 . At left internal rear corner  87  shown in  FIG. 4 , left inner surface  124  (shown in phantom) intersects with rear inner surface  134  (shown in phantom) at interface  151  to interlock left and rear bottom portions  100  and  104 , respectively. Specifically, left inner surface  124  interfaces with rear inner surface  134 , thereby distributing force between left and rear panels  92  and  94 , respectively, which may help prevent casing  4  from warping (i.e., substantially changing shape). Rear inner surface  134  (shown in  FIG. 3 ) similarly interlocks with right inner surface  144  (shown in  FIG. 3 ) at right internal rear corner  88  (shown in  FIG. 3 ).  
         [0043]     In the embodiment shown in  FIG. 4 , left and rear inner surfaces  124  and  134 , respectively, interlock by interfacing. In alternate embodiments, any suitable means of interlocking left and rear inner surfaces  124  and  134 , respectively, to reinforce internal corners  87  and  88  ( FIG. 3 ) may be incorporated into casing  4 . For example, a mating design may be used. An example of a mating design includes, but is not limited to, a groove cut into rear inner surface  134 , into which left inner surface  124  closely fits.  
         [0044]     Returning to  FIG. 2A , front deck  39  includes top surface  39 A, bottom surface  39 B, left end  39 C, right end  39 D, and rear surface  39 E (shown in  FIG. 5 ). Left end  39 C of front deck  39  interlocks with left flange  126  of left bottom portion  100 , while right end  39 D of front deck  39  interlocks with right flange  146  of right bottom portion  108 .  
         [0045]      FIG. 5  is a partial perspective view showing an underside of casing assembly  86  of  FIG. 2A .  FIG. 5  illustrates an embodiment of an interlocking design between right end  39 D of front deck  39  and left flange  126  of left bottom portion  100 . In this embodiment, the interlocking design between left end  39 C of front deck  39  and right flange  146  of right bottom portion  108  is similar.  
         [0046]     Front deck  39  includes flange  154 , which is integral with front deck surface  156 . Flange  154  and front deck surface  156  are cut at right end  39 D of front deck  39 , such that groove  158  is formed between flange  154  and front deck surface  156 . Left flange  126  of left bottom portion  100  of casing  4  is introduced into and engages with groove  158  to interlock left bottom portion  100  and front deck  39 . As  FIG. 5  illustrates in phantom, front deck surface  156  extends underneath left flange  126 . Interlocking front deck  39  with left bottom portion  100  helps maintain the integrity of casing assembly  86  by reinforcing left front internal corner  89  of casing  4 . In alternate embodiments, other means of interlocking front deck  39  with left bottom portion  100  may be used.  
         [0047]     As known in the art, casing  4  is typically connected to an air handler (e.g., a furnace), and in typical residential configurations, casing  4  is mounted on top of the air handler. Left, rear, and right inner surfaces  124 ,  134 , and  144 , together with rear surface  39 E of front deck  39  define a space that is configured to receive or be introduced into a corresponding part of an air handler. Bottom surface  152  of casing  4  and bottom surface  39 B of front deck  39  typically engage with the air handler. Bottom surface  152  (shown in  FIG. 2A ) of casing  4  remains substantially flat due to the increased strength of casing  4 , which is attributable to interlocking rear corners  87  and  88 . Similarly, bottom surface  39 B of front deck  39  remains substantially flat and in the same plane as bottom surface  152  of casing  4  because of interlocking internal front corners  89  and  90 . Together, substantially flat bottom surface  152  of casing  4  and bottom surface  39 B of front deck  39  help minimize any potential gaps that may be created at an interface between bottom surface  152  and the air handler. By minimizing gaps between bottom surface  152  and the air handler, the efficiency of evaporator unit  2  increases because the amount of air that is lost between evaporator unit  2  and the air handler is minimized.  
         [0048]     As previously described, casing  4  may be formed from a single sheet of material, as shown in  FIG. 6 . However, casing  4  may also be formed of multiple pieces that are attached together.  FIG. 6  is a plan view of a single sheet  160  of material that is cut to form casing  4  of casing assembly  86  of  FIG. 2A . The material may be, for example, sheet metal. Sheet  160  is folded to form the configuration of casing  4  shown in  FIG. 2A . Fold lines are illustrated in phantom. Sheet  160  is folded about 90° along fold line  162  to define left panel  92 . Rear and right panels  94  and  96 , respectively, are defined by folding sheet  160  about 90° along fold line  164 . Lip  110  along left top portion  98  of left panel  92  is defined by folding sheet  160  about 90° along fold line  166 . Sheet  160  is then folded about 90° along fold line  168 . Finally, lip  110  is folded along line  169  as close to about 180° as possible in order to tuck edge  110 A inward. Lip  112  along rear top portion  102  of rear panel  94  is defined by folding sheet  160  about 90° along fold line  170 , and along fold line  172  about 90°. Lip  112  is then folded along fold line  173  as close to about 180° in order to tuck edge  112 A inward. Lip  114  along right top portion  106  of right panel  96  is defined by folding sheet  160  about 90° along fold line  174 , and folding along line  176  about 90°. Lip  114  is then folded along fold line  177  as close to about 180° in order to tuck edge  114 A inward.  
         [0049]     Left outer surface  120  of left bottom portion  100  of left panel  92  of casing  4  is defined by folding along fold line  178  about 90°. As  FIG. 6  illustrates, left outer surface  120  of left bottom portion  100  is integral with a majority of left panel  92  of casing  4 . In an alternate embodiment, left outer surface  120  is distinct from a majority of left panel  92  of casing  4 . Similarly, in an alternate embodiment, rear outer surface  130  and right outer surface  140  are distinct from rear panel  94  and right panel  96 , respectively. Left bottom surface  122  of left bottom portion  100  of left panel  92  of casing  4  is defined by folding about 90° along fold line  180 . Left inner surface and left flange  124  and  126 , respectively, of left bottom portion  100  of left panel  92  of casing  4  are defined by folding about 90° along fold line  182 . Similarly, rear outer, bottom, and inner surfaces  130 ,  132 , and  134 , respectively, and flange  136  of rear bottom portion  104  of rear panel  94  of casing  4  are defined by folding about 90° along lines  184 ,  186 , and  188 . Right outer, bottom, and inner surfaces  140 ,  142 , and  144 , respectively, and right flange  146  of right bottom portion  108  of right panel  96  of casing  4  are defined by folding about 90° along lines  190 ,  192 , and  194 .  
         [0050]     Terminology, such as references to “left”, “right”, “front”, “rear”, “bottom”, and “top” throughout the description of the present invention is used for purposes of description, and not limitation. Specific structural and functional details disclosed herein are not to be interpreted as limiting, but merely as bases for teaching one skilled in the art to variously employ the present invention. While the present invention has been described with reference to evaporator unit  2 , a casing in accordance with the present invention is suitable for use with any heat exchanger.  
         [0051]     Although the present invention has been described with reference to preferred embodiments, workers skilled in the art will recognize that changes may be made in form and detail without departing from the spirit and scope of the invention.