Abstract:
A generator structure is provided having an improved air flow arrangement. The generator structure includes an enclosure having an interior for receiving an engine and an alternator therein. A roof structure is positioned on the enclosure and includes an eave portion and an attic portion. The eave portion has an inlet which communicates with the ambient air external of the generator structure, an outlet communicating with the interior of the enclosure and input flow path therebetween. The attic portion has an inlet communicating with the interior of the enclosure, an outlet communicating with the ambient air external of the generator structure and an exit flow path therebetween. An air flow generator draws ambient air through the inlet flow path in the eave portion of the roof structure into the interior of the enclosure to cool the engine and the alternator and urges air from the interior of the enclosure through the exit flow path in the attic portion and out of the generator structure.

Description:
FIELD OF THE INVENTION  
         [0001]    This invention relates generally to engine-driven, electrical generators, and in particular, to a generator structure incorporating an improved air flow arrangement for facilitating the cooling of one or more engine-driven, electrical generator sets housed within a single enclosure.  
         BACKGROUND AND SUMMARY OF THE INVENTION  
         [0002]    Engine-driven, electrical generators are used in a wide variety of applications. Typically, such electrical generators utilize a single driving engine directly coupled to a generator or alternator through a common shaft. Upon actuation of the engine, the crankshaft thereof rotates the common shaft so as to drive the alternator which, in turn, generates electricity. It can be appreciated that since the engine and the alternator are housed in a single enclosure, a significant amount of heat is generated within the enclosure during operation of the electrical generator.  
           [0003]    Heretofore, in order to cool the components of a prior electrical generator, louvers were provided in the walls of the enclosure thereof. A fan, coupled to the crankshaft of the engine, rotates during operation of the electrical generator. The rotating fan draws air into the enclosure through the louvers in the walls and blows air over the components of the electrical generator, including the engine, the alternator, and the radiator. In such a manner, it is intended that the air passing over the components of the electrical generator have a cooling effect on the components during their operation such that the temperatures of the components are maintained below safe operating limits.  
           [0004]    While functional under certain conditions, air flow arrangements of prior electrical generators have significant limitations. For example, the air flow arrangements of prior electrical generators merely recirculate the air drawn into the enclosures and fail to provide adequate means for purging the air from the enclosures after a heat exchange is effectuated between the air and the components. As such, the cooling effect on the components of the electrical generator by the ambient air drawn into the enclosure is somewhat limited. As a result, the components of prior electrical generators often operate at higher than desired temperatures. This, in turn, reduces the overall efficiency of prior electrical generators and may cause premature failure of the components thereof. It can be appreciated that by providing additional components, such as a second engine and a second alternator, within a single enclosure, the cooling effect of prior air flow arrangements on these added components would be inadequate. Consequently, it is highly desirable to provide an air flow arrangement for a generator structure which provides adequate cooling of the components thereof during operation.  
           [0005]    Therefore, it is a primary object and feature of the present invention to provide an air flow arrangement for an electrical generator structure which improves the operating efficiency of the same.  
           [0006]    It is a further object and feature of the present invention to provide an air flow arrangement for an electrical generator structure which facilitates greater cooling of the components of the generator within an enclosure than prior air flow arrangements.  
           [0007]    It is a still further object and feature of the present invention to provide an air flow arrangement for an electrical generator structure which is simple and less expensive to implement than prior arrangements.  
           [0008]    It is a still further object and feature of the present invention to provide an air flow arrangement for an electrical generator structure which reduces the noise associated with operation of the same.  
           [0009]    In accordance with the present invention, a generator structure is provided. The generator structure includes an enclosure having first and second spaced sidewalls interconnected by first and second end walls so as to define an interior for receiving an engine and an alternator therein. A roof structure is positioned on the enclosure and includes an eave portion having an inlet communicating with the ambient air external of the generator structure, an outlet communicating with the interior of the enclosure and an input flow path therebetween. The roof structure also includes an attic portion having an inlet communicating with the interior of the enclosure, an outlet communicating with the ambient air external to the generator structure and an exit flow path therebetween. An air flow generator is positioned within the interior of the enclosure for drawing ambient air through the inlet flow path in the eave portion of the roof structure into the interior of the enclosure and for urging air from the interior of the enclosure through the exit flow path in the attic portion of the roof structure and out of the generator structure.  
           [0010]    A muffler may be operatively connected to the engine and positioned within the exit flow path. A radiator is positioned within the interior of the enclosure between the engine and the air flow generator. The air flow generator draws air through the radiator. It is contemplated that the air flow generator be a fan.  
           [0011]    The attic portion of the roof structure may include a second inlet communicating with the interior of the enclosure, a second outlet communicating with the ambient air external of the generator structure and a second exit flow path therebetween. A second air flow generator may be positioned within the interior of the enclosure for drawing ambient air through the inlet flow path in the eave portion of the roof structure into the interior of the enclosure and for urging air from the interior of the enclosure through the second exit flow path in the attic portion of the roof structure and out of the generator structure. A second inlet in the eave portion of the roof structure communicates the ambient air external of the generator structure. A second, inlet flow path in the eave portion of the roof structure extends between the second inlet and the outlet of the eave portion.  
           [0012]    In accordance with a still further aspect of the present invention, a generator structure is provided. The generator structure includes an enclosure having first and second spaced sidewalls interconnected by first and second end walls so as to define an interior for receiving an engine and an alternator therein. A roof structure is supported on the end walls of the enclosure. The roof structure includes an upper panel, first and second side panels, and a separation panel. The upper panel has a first opening therethrough, and first and second sides generally parallel to the sidewalls of the enclosure. The first and second side panels extend from corresponding sides of the upper panel such that each side panel partially overlaps a corresponding sidewall of the enclosure. The first side panel and the first sidewall define a first inlet therebetween and the second side panel and the second sidewall define a second inlet therebetween. The separation panel extends between the side panels such that the separation panel and the upper panel define an attic chamber therebetween. The separation panel and the first end wall define a first attic inlet to allow the interior of the enclosure to communicate with the attic chamber. The separation panel and the second end wall define a second attic inlet to allow for communication between the interior of the enclosure and the attic chamber. An air flow generator is positioned within the interior of the enclosure for drawing ambient air through the first and second inlets in the roof structure and into the interior of the enclosure, and for urging air from the interior of the enclosure through the attic chamber in the roof structure and out of the generator structure through the first opening in the upper panel.  
           [0013]    The generator structure may include a muffler operatively connected to the engine. The muffler is positioned in the attic chamber of the roof structure. A radiator may be positioned within the interior of the enclosure between the engine and the air flow generator. The air flow generator draws air through the radiator. It is contemplated that the air flow generator be a fan.  
           [0014]    The upper panel of the roof structure may include a second opening therethrough. The separation panel divides the attic chamber into a first portion that communicates with the first opening in the upper panel and a second portion that communicates with the second opening in the upper panel. A second air flow generator may be positioned within the interior of the enclosure for drawing ambient air through the first and second inlets of the roof structure and into the interior of the enclosure, and for urging air from the interior of the enclosure through the attic chamber in the roof structure and out of the generator structure through the second opening in the upper panel. A base supports the enclosure above a supporting surface.  
           [0015]    In accordance with a still further aspect of the present invention, a generator structure is provided. The generator structure includes an enclosure having first and second spaced sidewalls interconnected by first and second end walls so as to define an interior. First and second generator sets are positioned within the interior of the enclosure. Each generator set includes an engine, an alternator driven by the engine and a radiator operatively connected to the engine. A roof structure is supported on the end walls of the enclosure. The roof structure includes an upper panel, first and second side panels, and a separation panel. The upper panel has first and second openings therethrough and first and second sides generally parallel to the sidewalls of the enclosure. The first and second side panels extend from corresponding sides of the upper panel such that each side panel partially overlaps a corresponding sidewall of the enclosure. The first side panel and the first sidewall define a first inlet therebetween and the second side panel and the second sidewall define a second inlet therebetween. The separation panel extends between the side panels such that the separation panel and the upper panel define an attic chamber therebetween. The separation panel and the first end wall define a first attic inlet to allow the interior of the enclosure to communicate with the attic chamber. The separation panel and the second end wall define a second attic inlet for allowing communication between the interior of the enclosure and the attic chamber. A first air flow generator is positioned within the interior of the enclosure for drawing ambient air through the first and second inlets in the roof structure, across the engine of the first generator set and through the radiator of the first generator set, and for urging air out of the interior of the enclosure through the attic chamber in the roof structure and out of the generator structure through the first opening in the upper panel. A second air flow generator is also positioned within the interior of the enclosure for drawing ambient air through the first and second inlets in the roof structure, across the engine of the second generator set and through the radiator of the second generator set, and for urging air from the interior of the enclosure through the attic chamber in the roof structure and out of the generator structure through the second opening in the upper panel.  
           [0016]    The generator structure may include a muffler operatively connected to the engine. The muffler is positioned within the attic chamber in the roof structure. A base supports the enclosure above a supporting surface. It is contemplated that each air flow generator be a fan and that the separation panel divide the attic chamber into a first portion that communicates with the first opening in the upper panel and a second portion that communicates with the second opening in the upper panel. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0017]    The drawings furnished herewith illustrate a preferred construction of the present invention in which the above advantages and features are clearly disclosed as well as others which will be readily understood from the following description of the illustrated embodiment.  
         [0018]    In the drawings:  
         [0019]    [0019]FIG. 1 is a side elevational view, with portions broken away, showing a generator structure incorporating the air flow arrangement of the present invention;  
         [0020]    [0020]FIG. 2 is a top plan view, with portions broken away, showing the generator structure of FIG. 1;  
         [0021]    [0021]FIG. 3 is a cross-sectional view taken along line  3 - 3  of FIG. 2;  
         [0022]    [0022]FIG. 4 is a schematic view showing rotation of the drive shafts of each generator set of the generator structure of FIG. 1;  
         [0023]    [0023]FIG. 5 is a cross-sectional view taken along line  5 - 5  of FIG. 2;  
         [0024]    [0024]FIG. 6 is a schematic view showing connection of the generator structure of FIG. 1;  
         [0025]    [0025]FIG. 7 is an enlarged, cross-sectional view taken along line  7 - 7  of FIG. 3; and  
         [0026]    [0026]FIG. 8 is a cross-sectional view taken along line  8 - 8  of FIG. 7. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0027]    Referring to FIGS. 1 and 2, a generator structure in accordance with the present invention is generally designated by the reference numeral  10 . Generator structure  10  includes an enclosure  12  having first and second sidewalls  14  and  16 , respectively, interconnected by first and second end walls  18  and  20 , respectively, and a lower bottom support  22 . Sidewalls  14  and  16  and end walls  18  and  20  define interior  24  of enclosure  12  therebetween. Sidewalls  14  and  16  may include one or more doors  25  therein for allowing a user access to interior  24  of enclosure  12 .  
         [0028]    Referring to FIGS. 1 and 3, base  26  is mounted to the underside  22   a  of support  22  of enclosure  12  for supporting generator structure  10  above a supporting surface  28  such as the ground, a concrete slab or a mounting pad. Base  26  is generally rectangular in shape and defined by vertical sidewalls  30  and  32  interconnected by a bottom wall  34 . Inner surfaces  30   a  and  32   a  of sidewalls  30  and  32 , respectively, and inner surface  34   a  of bottom wall  34  define cavity  36  in base  26 . It is contemplated to provide supports  38  and  40  adjacent outer surfaces  30   b  and  32   b  of sidewalls  30  and  32 , respectively, to stabilize base  26 .  
         [0029]    Generator structure  10  further includes a roof structure, generally designated by the reference numeral  42 . Roof structure  42  includes an upper panel  44  having first and second openings  46  and  48 , respectively, extending therethrough. Upper panel  44  has first and second sides  50  and  52 , respectively, which are generally parallel to sidewalls  14  and  16  of enclosure  12 . First and second side panels  54  and  56 , respectively, extend from corresponding sides  50  and  52 , respectively, of upper panel  44  and diverge from each other. Side panel  54  terminates at a terminal edge  54   a  which is laterally spaced from sidewall  14  of enclosure  12  so as to define a first inlet  57  therebetween. Similarly, side panel  56  terminates at a terminal edge  56   a  which is spaced from sidewall  16  of enclosure  12  so as to define a second inlet  58  therebetween.  
         [0030]    Separation panel  60  extends between inner surface  54   b  of first side panel  54  of roof structure  42  and inner surface  56   b  of second side panel  56  of roof structure  42 . Separation panel  60  includes first and second portions  62  and  64 , respectively, interconnected by a central portion  66 . Central portion  66  intersects upper panel  44  such that first portion  62  of separation panel  60  and upper panel  44  define a first attic chamber  68  therebetween in roof structure  42  and second portion  64  of separation plate  60  and upper panel  44  define a second attic chamber  70  therebetween in roof structure  42 . It can be appreciated that first attic chamber  68  in roof structure  42  may communicate with the ambient air outside of generator structure  10  through opening  46  in upper panel  44 . In addition, second attic chamber  70  in roof structure  42  may communicate with the ambient air outside of generator structure  10  through second opening  48  in upper panel  44 .  
         [0031]    Separation panel  60  includes first end  60   a  spaced from end wall  18  of enclosure  12  so as to define first attic chamber inlet  72  between sidewalls  14  and  16 . First attic chamber inlet  72  allows for first attic chamber portion  68  in roof structure  42  to communicate with interior  24  of enclosure  12  therethrough. Second end  60   b  of separation panel  60  is spaced from end wall  20  of enclosure  12  so as to define second attic chamber inlet  74  between sidewalls  14  and  16 , FIGS.  7 - 8 . Second attic air inlet  74  allows for second attic chamber  70  in roof structure  42  to communicate with interior  24  of enclosure  12  therethrough.  
         [0032]    Lower surface  60   c  of separation panel  60  and the inner surfaces  54   b  and  56   b  of side panels  54  and  56 , respectively, of roof structure  42  define an eave chamber  76  in roof structure  42 . An outlet  78  to eave chamber  76  of roof structure  42  is provided between sidewalls  14  and  16  of enclosure  12 . It can be appreciated that interior  24  of enclosure  12  may communicate with ambient air outside of generator structure  10  through eave chamber  76  in roof structure  42  and through first and second inlets  57  and  58 , respectively.  
         [0033]    As best seen in FIG. 2, generator structure  10  includes first and second generator sets  80  and  82 , respectively, positioned next to one another within interior  24  of enclosure  12 . Generator set  80  includes an alternator end  80   a  adjacent first end wall  18  of enclosure  12  and a fan end  80   b  adjacent second end wall  20  of enclosure  12 . Generator set  82  includes a fan end  82   a  adjacent first end wall  18  of enclosure  12  and an alternator end  82   b  adjacent second end wall  20  of enclosure  12 .  
         [0034]    Generator set  80  includes an engine, generally designated by the reference numeral  84 , which is supported on bottom support  22  of enclosure  12 . As is conventional, engine  84  receives fuel such as diesel, natural gas or liquid propane vapor through an intake. The fuel is compressed and ignited within the cylinders of engine  84  so as to generate reciprocating motion of the pistons of engine  84 . This reciprocating motion of the pistons of the engine  84  is converted to rotary motion such that engine  84  rotates a drive or crankshaft  85 , FIG. 4. Crankshaft  85  of engine  84  is coupled to alternator  86  such that as crankshaft  85  is rotated by the operation of engine  84 , crankshaft  85  drives alternator  86  which, in turn, converts the mechanical energy generated by engine  84  to electrical power for transmission and distribution. Conduit  88  has a first end operatively connected to alternator  86  within connection box  90  and a second, opposite end. Conduit  88  carries the electrical power generated by first generator set  80  to bus  89 .  
         [0035]    First generator set  80  further includes radiator  92  operatively connected to engine  84  such that engine coolant from engine  84  circulates through radiator  92  during operation of engine  84 . As is conventional, radiator  92  includes a plurality of radiator tubes (not shown) through which the engine coolant flows. As hereinafter described, it is intended that air within interior  24  of enclosure  12  pass over the plurality of radiator tubes of radiator  92  so as to effectuate a heat exchange between the engine coolant flowing through the plurality of radiator tubes of radiator  92  and the air within enclosure  12 .  
         [0036]    In order to draw air over the plurality of radiator tubes of radiator  92 , generator set  80  includes a fan, generally designated by the reference numeral  96 . Fan  96  includes a plurality of fan blades  98  extending radially from central hub  100 . Central hub  100  is rotatably supported on a first side  92   a  of radiator  92  by rotatable fan shaft  102 . Fan shaft  102  includes a driven wheel  104  extending radially therefrom. Driven wheel  104  is operatively connected to drive wheel  106  through fan belts  108  and  110  and jack shaft  112 . Drive wheel  106  is operatively connected to crankshaft  85  of engine  84  such that drive wheel  106  is rotated by a crankshaft  85  during operation of engine  84 . Rotation of drive wheel  106  is translated to driven wheel  104  through belts  108  and  110  and jack shaft  112  which, in turn, rotates fan  96 . Rotation of fan  96  draws air through first and second inlets  57  and  58 , respectively, in roof structure  42 ; across engine  84  of first generator set  80 ; and across the plurality of radiator tubes of radiator  92  so as to cool engine  84  and the engine coolant flowing through the plurality of radiator tubes of radiator  92 . In addition, fan  96  urges the air drawn across the plurality of radiator tubes of radiator  92  from the interior  24  of enclosure  12  into second attic chamber  70  in roof structure  42  through second attic chamber inlet  74 ; and out from roof structure  42  through second opening  48  in upper panel  44 .  
         [0037]    The exhaust outlet of engine  84  of first generator set  80  is interconnected to input  114  of muffler  116  through an exhaust pipe  118 . Muffler  116  is positioned within second attic chamber  70  in roof structure  42  such that the air urged by fan  96  from generator structure  10  passes over muffler  116  to cool the same. Output of muffler  116  is operatively connected to the input of exhaust discharge tube  120 . Exhaust discharge tube  120  includes outlet end  122  which extends through opening  48  in upper panel  44  of roof structure  42  and which communicates with the ambient air outside generator structure  10 .  
         [0038]    Second generator set  82  includes an engine, generally designated by the reference numeral  124 , which is supported on bottom support  22  of enclosure  12 . As is conventional, engine  124  receives fuel such as diesel, natural gas or liquid propane vapor through an intake. It is contemplated that engines  84  and  124  receive fuel from a common source. The fuel is compressed and ignited within the cylinders of engine  124  so as to generate reciprocating motion of the pistons of engine  124 . This reciprocating motion of the pistons of engine  124  is converted to rotary motion such that engine  124  rotates a drive or crankshaft  125 . Crankshaft  125  of engine  124  is coupled to an alternator  126  such that as crankshaft  125  is rotated by operation of engine  124 , crankshaft  125  drives alternator  126  which, in turn, converts the mechanical energy generated by engine  124  to electrical power for transmission and distribution. Conduit  128  has a first end operatively connected to alternator  126  within connection box  130  and a second opposite end. Conduit  128  carries the electrical power generated by second generator set  82  to a bus  89 , FIG. 6.  
         [0039]    Second generator set further includes radiator  132  operatively connected to engine  124  such that coolant from engine  124  circulates through radiator  132  during operation of engine  124 . As is conventional, radiator  132  includes a plurality of radiator tubes (not shown) through which the engine coolant flows. As hereinafter described, it is intended that air within interior  24  of enclosure  12  pass over a plurality of radiator tubes of radiator  132  so as to effectuate a heat exchange between the engine coolant flowing through the plurality of radiator tubes of radiator  132  and the air within enclosure  12 .  
         [0040]    In order to draw air over the plurality of radiator tubes of radiator  132 , generator set  82  includes a fan, generally designated by the reference numeral  134 . Fan  134  includes a plurality of fan blades  136  extending radially from central hub  138 . Central hub  138  is rotatably supported on a first side  132   a  of radiator  132  by rotatable fan shaft  140 . Fan shaft  140  includes a driven wheel  142  extending radially therefrom. Driven wheel  142  is operatively connected to drive wheel  144  through fan belts  146  and  148  and jack shaft  150 . Drive wheel  144  is operatively connected to crankshaft  125  of engine  124  such that drive wheel  144  is rotated by a crankshaft  125  during operation of engine  124 . Rotation of drive wheel  144  is translated to driven wheel  142  through belts  146  and  148  and jack shaft  150  which, in turn, rotates fan  134 . Rotation of fan  134  draws air through first and second inlets  57  and  58 , respectively, in roof structure  42 ; across engine  124  of second generator set  82 ; and through radiator  132  across the plurality of radiator tubes thereof so as to cool engine  124  and the engine coolant flowing through the plurality of radiator tubes of radiator  132 . In addition, fan  134  urges the air drawn across the plurality of radiator tubes of radiator  132  from the interior  24  of enclosure  12  into first attic chamber  68  in roof structure  42  through first attic chamber inlet  72 ; and out from roof structure  42  through first opening  46  in upper panel  44 .  
         [0041]    The exhaust outlet of engine  124  of second generator set  82  is interconnected to input  152  of muffler  154  through an exhaust pipe  156 . Muffler  154  is positioned within first attic chamber  68  in roof structure  42  such that the air urged by fan  134  from generator structure  10  passes over muffler  154  to cool the same. Output of muffler  154  is operatively connected to the input of exhaust discharge tube  158 . Exhaust discharge tube  158  includes outlet end  160  which extends through opening  46  in upper panel  44  of roof structure  42  and which communicates with the ambient air outside generator structure  10 .  
         [0042]    Referring to FIG. 6, generator structure  10  includes system controller  170  that is operatively connected to first and second generator sets  80  and  82 , respectively, through communication links  172  and  174 , respectively. In addition, system controller  170  is operatively connected to transfer switch  176 , for reasons hereinafter described, and to switches  178  and  180  in conduits  88  and  128 , respectively.  
         [0043]    Transfer switch  176  includes a first input operatively connected to utility source  182  and a second input electrically connected to generator structure  10  through bus  89 . The output of transfer switch  176  is operatively connected to load  184 . As is conventional, transfer switch  176  incorporates a switch which isolates the electrical power supplied by utility source  182  and the electrical power supplied by generator structure  10  on bus  89 . A monitoring circuit is operatively connected to utility source  182  to monitor the electrical power supplied by utility source  182 . In response to a power outage from utility source  182 , the monitoring circuit of transfer switch  176  advises system controller  170  accordingly.  
         [0044]    System controller  170  starts first and second generator sets  80  and  82 , respectively, in a conventional manner and monitors the magnitude and phase of the electrical power generated thereby on conduits  88  and  128 , respectively. Thereafter, system controller  170  adjusts the engine speed of engines  84  and  124  of first and second generator sets  80  and  82 , respectively, via an electronic governor or the like such that the AC power generated by first and second generators  80  and  82 , respectively, is brought into alignment (synchronized) with each other such that there is no phase difference between the sine waves and that the sine waves are at the same frequency. In addition, system controller  170  regulates the output voltages of generator sets  80  and  82  in a conventional manner such that output voltages of generators sets  80  and  82  are generally equal. System controller  170  closes switches  178  and  180  in conduits  188  and  128 , respectively, such that the combined AC power generated by first and second generator sets  80  and  82 , respectively, is provided on bus  89 . Transfer switch  176  automatically transfers load from utility source  182  to generator structure  10  such that generator structure  10  provides AC power to load  184 . Upon completion of the power outage, the transfer switch automatically reconnects load  184  to the utility source  182 . In addition, the monitoring circuit of transfer switch  176  advises system controller  170  of generator structure  10  accordingly such that system controller  170  terminates operation of first and second generator sets  80  and  82 , respectively.  
         [0045]    As heretofore described, during operation of first and second generator sets  80  and  82 , respectively, engines  84  and  124  drive corresponding fans  96  and  134 , respectively. Rotation of fan  96  draws air through first and second inlets  57  and  58 , respectively, in roof structure  42 ; across engine  84  of first generator set  80 ; and across the plurality of radiator tubes of radiator  92  so as to cool engine  84  and the coolant flowing through the plurality radiator of radiator  92 . Further, rotation of fan  96  urges the air drawn across the plurality of radiator tubes of radiator  92  from the interior of enclosure  12  into second attic chamber  70  in roof structure  42  through second attic chamber inlet  74 . The air in second attic chamber  70  passes over muffler  116  positioned therein so as to cool the same. Thereafter, the air exits roof structure  42  through second opening  48  in upper panel  44 .  
         [0046]    Similarly, rotation of fan  134  draws air through first and second inlets  57  and  58 , respectively, in roof structure  42 ; across engine  124  of second generator set  82 ; and across the plurality of radiator tubes of radiator  132  so as to cool engine  124  and the engine coolant flowing through the plurality of radiator tubes of radiator  132 . In addition, fan  134  urges the air drawn across the plurality of radiator tubes of radiator  132  from the interior  124  of enclosure  12  in first attic chamber  68  in roof structure  42  through first attic chamber inlet  72 . The air in first attic chamber  68  passes over muffler  154  positioned therein so as to cool the same. Thereafter, the air exits roof structure  42  through first opening  46  in upper panel  44 .  
         [0047]    Various modes of carrying out the invention are contemplated as being within the scope of the following claims particularly pointing and distinctly claiming the subject matter which is regarded as the invention.