Abstract:
A heat exchanger system and method for transferring heat from exhaust air from a fireplace to air to be delivered to a living space is described. Heated exhaust air is passed through a heat exchanger before exhaustion from the structure. The heat exchanger couples the exhaust duct and the intake duct and transfers otherwise unused heat from the waste products to the outside air to increase the overall efficiency of the heated product source.

Description:
BACKGROUND 
       [0001]    The present invention generally relates to fireplaces, and more specifically fireplaces equipped with one or more heat exchangers for transferring heat from the fireplace exhaust air to air to be delivered to a living space. 
         [0002]    In combustion fireplaces, such as gas or biomass burning fireplaces, hot exhaust air produced during combustion exits the fireplace at a relatively higher temperature than its surroundings, carrying with it some potentially useful thermal energy. This results in less than optimal fireplace efficiency. 
       SUMMARY 
       [0003]    Some embodiments relate to a heat exchange system including a firebox, a combustion element, a plenum, and at least one heat exchanger. The firebox includes a plurality of panels combining to define a combustion chamber. The combustion chamber includes a combustion air inlet port in fluid communication with a source of combustion air and an exhaust air outlet port. The combustion element is disposed within the combustion chamber. The plenum defines an air intake end and an air output end and includes a plurality of walls defining an air pathway between the air intake and air output ends. The heat exchanger includes a housing having an outer surface disposed within the plenum. The housing includes a first end coupled to the exhaust air outlet port of the combustion chamber and a second end. Additionally, the heat exchanger includes a plurality of baffle plates within the housing. The baffle plates define at least one internal pathway within the housing. The internal pathway extends through a plurality of 180 degree turns from the first end to the second end of the heat exchanger. Additionally, an outer surface of the heat exchanger may include a plurality of heat transfer assist structures such as air foils, pins, ridges, fins, and the like. 
         [0004]    In some embodiment, the heat exchange system includes a second heat exchanger coupled to and in fluid communication with the first heat exchanger. Like the first heat exchanger, the second heat exchanger also includes a housing having an outer surface disposed within the plenum. The housing includes a first end coupled to the exhaust air outlet port of the combustion chamber and a second end. Additionally, the heat exchanger includes a plurality of baffle plates within the housing. The baffle plates define at least one internal pathway within the housing. The internal pathway extends through a plurality of 180 degree turns from the first end to the second end of the second heat exchanger. 
         [0005]    Other embodiments relate to a fireplace heat exchange system located within a building structure defining a living space. The fireplace heat exchange system includes a plenum, a firebox, a combustion element, and at least one heat exchanger. The plenum defines an air intake end and an air output end and includes a plurality of walls defining an air pathway between the air intake and air output ends. The firebox is located within the plenum. The firebox includes a plurality of panels that define a combustion chamber. The combustion chamber includes at least one combustion air inlet port in fluid communication with a combustion air source and an exhaust air outlet port. A combustion element adapted to generate heat and exhaust products via combustion of a fuel source with combustion air received through the combustion air inlet port is disposed within the combustion chamber. Additionally, a heat exchanger is mounted to the firebox located within the plenum. The heat exchanger includes a housing having a first end coupled to the exhaust air outlet port of the combustion chamber and a second end. Additionally, the heat exchanger includes a plurality of baffle plates within the housing. The baffle plates define at least one internal pathway within the housing. The internal pathway extends through a plurality of 180 degree turns from the first end to the second end of the heat exchanger. 
         [0006]    Still other embodiments relate to a method of transferring heat from heated exhaust air to air to be delivered to a living space. The method includes passing relative hot exhaust air from a combustion chamber into a first heat exchanger located within a plenum. The plenum includes a plurality of walls defining an air pathway between an air intake end and an air output end. The heat exchanger includes a housing, an exhaust air inlet and an exhaust air outlet. The housing has an outer surface and a plurality of baffle plates. The plurality of baffle plates defines at least a first internal pathway within the housing. The first internal pathway extends through a plurality of 180 degree turns from the exhaust air inlet to the exhaust air outlet of the heat changer. The method also optionally includes passing air through the plenum along the air pathway defined between the air intake and air output ends and contacting the air with the outer surface of the heat exchanger housing. Additionally, the method includes transferring heat from the relatively hot exhaust air passing through the heat exchanger to the air passing through the plenum. 
         [0007]    While multiple embodiments are disclosed, still other embodiments of the present invention will become apparent to those skilled in the art from the following detailed description, which shows and describes illustrative embodiments of the invention. Accordingly, the drawings and detailed description are to be regarded as illustrative in nature and not restrictive. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0008]      FIG. 1  is a side schematic view of a heat exchange system according to some embodiments. 
           [0009]      FIG. 2  is a side schematic view of a heat exchange system according to some embodiments. 
           [0010]      FIG. 3A  is a side schematic view of a heat exchange system according to some embodiments. 
           [0011]      FIG. 3B  is another side schematic view of a heat exchange system according to some embodiments. 
           [0012]      FIG. 4  is a front schematic view of a heat exchange system according to some embodiments. 
           [0013]      FIG. 5  is a cross-sectional view of a heat exchanger for use in a heat exchange system provided according to some embodiments. 
           [0014]      FIG. 6  is a cross-sectional view of a heat exchanger for use in a heat exchange system provided according to some embodiments. 
           [0015]      FIG. 7  is a cross-sectional view of a heat exchanger for use in a heat exchange system according to some embodiments. 
       
    
    
       [0016]    While the invention is amenable to various modifications and alternative forms, various embodiments have been shown by way of example in the drawings and are described in detail below. The intention, however, is not to limit the invention to the particular embodiments described. On the contrary, the invention is intended to cover all modifications, equivalents, and alternatives falling within the scope of the invention as defined by the appended claims. 
       DETAILED DESCRIPTION 
       [0017]      FIGS. 1-3B  are side schematic views of a fireplace heat exchange system  10  according to various embodiments of the present invention.  FIG. 4  is a front schematic view of a fireplace heat exchange system  10  according to another embodiment of the present invention. The fireplace heat exchange system  10  can be used to extract heat from heated exhaust air produced by the combustion of a variety of fuel sources with air including gas, wood, pellets, corn, biomass, and the like. The heat exchange system  10  is located within a structure, for example within a wall space of a residential, commercial, or industrial building. 
         [0018]    Referring to  FIGS. 1-4 , the heat exchange system  10  includes a firebox  14 , a burner system  26 , and a heat exchanger  40 . The firebox  14  has a plurality of panels  18  combined to define a combustion chamber  22 . In some embodiments, the panels  18  of the firebox  14  include two opposing side panels (not shown), top and bottom panels, and a rear panel. As shown in  FIGS. 1-3B , the firebox  14  also includes at least one panel  20  that allows a user to access the combustion chamber  22 . The front of the firebox  14  optionally includes glass doors or a sealed glass panel. In some embodiments, the firebox  14  is of a type employed with one or more of the following heat generating devices: a wood burning fireplace; a gas fireplace (including fireplaces that include a gas-start mechanism); a wood burning stove; a corn burning stove; a pellet stove; a wood furnace; or other heat generating devices. 
         [0019]    The firebox  14  can be made from a variety of suitable materials capable of withstanding the high temperatures. In some embodiments, the firebox  14  is formed of a compression molded material including an inorganic fiber and a binder, such as the compression molded materials described in U.S. Pat. No. 7,098,269, entitled “Compression Molded Inorganic Fiber Articles, and Methods and Compositions Used in Molding Same,” which is incorporated herein by reference in its entirety, although a variety of firebox materials are contemplated. 
         [0020]    The burner system  26  is located in the combustion chamber  22  and is adapted to generate heat and exhaust products via combustion of a fuel source with combustion air. The burner system  26  is adapted for use with one or more of a variety of fuel sources, such as wood, gas, pellets, corn, and biomass, among others, although in some embodiments the burner system  26  is used to combust natural gas. Depending on the type of fuel, the burner system  26  includes regulator valves, fuel feed lines, igniter mechanisms, nozzles, and/or other elements, for example, generally associated with a burner system. An exemplary gas burner system is shown and described in U.S. Pat. No. 6,048,195, entitled “Hollow Ceramic Fiber Burner-log Element,” which is incorporated herein by reference in its entirety. 
         [0021]    In some embodiments, the combustion chamber  22  includes at least one combustion air inlet port in fluid communication with a source of combustion air and an exhaust air outlet port  36 . Combustion air is optionally drawn from the living space, such air being referred to as room air. Combustion air can also be drawn into the combustion chamber  22  from outside of the structure in which the heat exchange system  10  is located, also described as outside air. In some embodiments, the combustion chamber  22  includes more than one combustion air inlet port with combustion air including a combination of room air and outside air. In some embodiments, faux logs, embers, or other accessories are placed in the combustion chamber  22  to help simulate a wood fire. 
         [0022]    The heat exchanger  40  is coupled to and in fluid communication with the exhaust air outlet port  36  provided in the combustion chamber  22 . The heat exchanger  40  includes a housing  44  defining a first end  48  and a second end  52  and includes a plurality of baffle plates  80  defining at least one internal pathway within the housing  44  (described in further detail below). The heat exchanger  40  defines a substantially closed pathway through which exhaust air travels from the combustion chamber  22  to the outside. 
         [0023]    The heat exchanger  40  is optionally adapted to work with any of a variety of heat generating devices, such as a gas fireplace or pellet stove, for example. According to some embodiments, the heat exchanger  40  maintains a low profile when coupled to the firebox  14 , for example by substantially tracking or otherwise complementing the profile of the firebox  14 , in order to minimize an overall height and/or head space of the heat exchange system  10 . In some embodiments, the heat exchanger  40  is adapted to work with a heat generating device having an energy output ranging from about 15,000 to about 60,000 BTU, from about 30,000 to about 40,000 BTU, for example, as well as other energy outputs. 
         [0024]    The heat exchanger  40  is made from a high heat conductivity, corrosion-resistant material, according to some embodiments. Exemplary materials include: sheet metal, stainless steel, coated stainless steel, aluminum, aluminum alloys, and ceramics, for example, as well as other suitable materials. In some embodiments, the outer surface  50  of the heat exchanger housing  44  may be smooth. In other embodiments, the outer surface  50  of the heat exchanger housing  44  includes a plurality of heat transfer assist structures  46  such as air foils, pins, ridges, fins configured to increase heat transfer, for example by increasing the surface area of the outer surface  50 . For example,  FIG. 3A  schematically shows heat transfer assist structures  46  including a plurality of undulations or ridges whereas  FIG. 3B  shows heat transfer assist structures  46  including a plurality of pins or fins. 
         [0025]    The first end  48  of the heat exchanger housing  44  is coupled to and in fluid communication with the exhaust air outlet port  36  located in the combustion chamber  22 . The second end  52  is in fluid communication with the outside of the structure or other appropriate exhaust location to serve as an exhaust port. Heated exhaust air, including any waste products produced during the combustion process, flows from the combustion chamber  22  via the exhaust air outlet port  36  and into the heat exchanger  40 . The heated exhaust air flows through the heat exchanger  40  along the internal pathway defined by the baffle plates  80 , and is ultimately vented outside via the exhaust port. 
         [0026]    The exhaust air entering the first end  48  of the heat exchanger  40  has a higher temperature than the exhaust air exiting the heat exchanger  40  via the second end  52  which serves as the exhaust port. Typically, the temperature of the heated exhaust air entering the first end  48  of the heat exchanger  40  ranges from about 650° F. to about 850° F. In contrast, the temperature of the exhaust air leaving the heat exchanger  40  via the second end  52  ranges from about 120° F. to about 180° F. According to one embodiment, the heat exchanger  40  is configured such that at least a portion of the exhaust air condenses before being disposed to the outside such that the exhaust air temperature is lowered to a level permitting the use of PVC piping or other ducting material at the exhaust port. For example, the temperature of the air exiting the heat exchanger  40  has a temperature ranging from about 120° F. to about 180° F. The condensate from the exhaust air is optionally collected in a condensate trap located at the lowest point of the heat exchanger  40 . In some embodiments, the condensate trap includes a drain and a seal for draining the condensate from the heat exchanger  40 . Alternately, a pan such as a drip pan, or a reservoir, is used for collecting the condensate. 
         [0027]    As shown in  FIGS. 1-2 , the first end  48  of the heat exchanger housing  44  is optionally coupled to the exhaust air outlet port  36  of the combustion chamber  22  such that the heat exchanger is spaced a distance from the outer surface  53  of the firebox  14 . Air flow is permitted between the outer surface  53  of the firebox  14  and the outer surface  50  of the heat exchanger housing  44 . 
         [0028]    As shown in  FIGS. 3A and 3B , the first end of the heat exchanger  40  is optionally coupled to the exhaust air outlet port  36  of the combustion chamber  22  such that the heat exchanger  40  is mounted flush with the outer surface  53  of the firebox  14  such that no space exists between the outer surface  53  of the firebox  14  and the outer surface  50  of the heat exchanger housing  44 . In some embodiments, the heat exchanger housing  44  shares a common panel with the firebox  14 . 
         [0029]    As shown in  FIGS. 2-3B , the heat exchanger  40  optionally includes a first portion  54  in fluid communication with a second portion  56 . Exhaust air generally flows freely between the first and second portions  54  and  56  of the generally L-shaped heat exchanger  40 . The first portion  54  is angularly offset from the second portion  56  such that the heat exchanger  40  is adapted to fit over the top and rear panels  18  of the firebox  14 . In some embodiments, the first portion  54  is substantially orthogonal to the second portion  56  such that the overall shape of the heat exchanger  40  approaches and L-shape, although a variety of angular offsets are contemplated, including 45 degree angular offsets, for example. In some embodiments, the first portion  54  is angularly offset from the second portion  56  by at least 90 degrees. 
         [0030]    In some embodiments, the heat exchanger system  10  includes a plurality of heat exchangers. For example, as shown in  FIG. 2 , heat exchanger system  10  includes heat exchangers  40   a  and  40   b  which are coupled to one another in a generally stacked configuration. The first end  48   a  of heat exchanger  40   a  is coupled to and in fluid communication with the exhaust air outlet port  36  of the combustion chamber  22 . Exhaust air flows from the combustion chamber  22  and into the first heat exchanger  40   a  via the exhaust air outlet port  36 . The exhaust air flows from the first end  48   a  to the second end  52   a  of the first heat exchanger  40   a . Rather than being exhausted to the outside, the exhaust air from the combustion chamber  22  flows out of the second end  52   a  of the first heat exchanger  40   a  and into the second heat exchanger  40   b  coupled thereto. The exhaust air then flows along the internal pathway defined within the second heat exchanger  40   b  from the first end  48   b  of the second heat exchanger  40   b  to the second end  52   b , where it is then vented to the outside. 
         [0031]    In some embodiments, the first heat exchanger  40   a  is coupled to the second heat exchanger  40   b  in a generally stacked configuration such that space exists between the outer surface  50   a  of the first heat exchanger  40   a  and the outer surface  50   b  of the second heat exchanger  40   b  such that air flow between the outer surfaces  50   a ,  50   b  of the two heat exchangers  40   a ,  40   b  is permitted. The coupled heat exchangers  40   a ,  40   b  are optionally mounted to the firebox  14  such that a space exists between the outer surface  50   a  of the first heat exchanger  40   a  and the outer surface  53  of the firebox  14 , for example to allow airflow therebetween. 
         [0032]    The coupled heat exchangers  40   a ,  40   b  may be mounted flush to the outer surface  53  of the firebox  14 , such that no space exists between the outer surface  50   a  of the first heat exchanger  40   a  and the firebox  14 , for example to enhance heat transfer between the firebox  14  and the heat exchanger(s)  40   a ,  40   b . In still other embodiments, the first heat exchanger  40   a  is mounted to the firebox  14  such that the heat exchanger housing  44  of the first heat exchanger  40   a  and the firebox  14  share a common panel. Similarly, the second heat exchanger  40   b  may be coupled to the first heat exchanger  40   a  such that the outer surface  50   a  of the first heat exchanger  40   a  is flush with the outer surface  50   b  of the second heat exchanger  40   b  and/or the second heat exchanger  40   b  may be coupled to the first heat exchanger  40   a  such that the first and second heat exchanger housings  44  share a common wall. 
         [0033]    According to some embodiments, the first heat exchanger  40   a  is coupled to the second heat exchanger  40   b  in a side by side configuration where exhaust air flows from the first heat exchanger  40   a  to the second heat exchanger  40   b  via an air duct or other fluid communication means extending between them. 
         [0034]    The flow of heated exhaust air out of the combustion chamber  22 , through the heat exchanger  40 , and to the outside may be assisted by an air assist device  58  located within the combustion chamber  22 . The air assist device  58  creates a positive pressure environment within the combustion chamber  22  pushing the heated exhaust air from the chamber  22  into and through the heat exchanger  40  until the exhaust air is vented to the outside. Exemplary air assist devices include, but are not limited to, fans, blowers, and others. 
         [0035]    As shown in  FIGS. 1-3B , the heat exchanger  40  and combustion chamber  22  are optionally disposed within a plenum  62 . The plenum  62  generally includes a plurality of walls defining an air pathway  66  extending between an air intake end  70  and an air output end  74 . In some embodiments, the air intake end  70  is in fluid communication with a source of room air. In some embodiments, the air intake end  70  is in fluid communication with a source of outside air. If desired, the air flowing through the plenum  62  from the air intake end  70  to the air output end  74  is a combination of room air and outside air. 
         [0036]    Air travels through the plenum  62  from the air intake end  70  to the air output end  74  and flows over an outer surface  50  of the heat exchanger housing  44 . As a result, the air traveling along the pathway  66  defined by the plenum  62  becomes heated via a heat exchange process with the heated exhaust air flowing through the heat exchanger  40 . In some embodiments, relatively cool outside air is used as the source of air to be heated, where the outside air becomes superheated and a portion of the exhaust air condenses, increasing the overall efficiency of the heat exchange process. Once the air is heated, it is returned to the living space and the relatively cooler exhaust air is exhausted outside via the second end  52 . 
         [0037]    As shown in  FIG. 4 , in some embodiments heat exchanger  40  is disposed within a plenum  62  provided separately and at a distance from the firebox  14 . This configuration facilitates remote location of the heat exchanger  40  and plenum  62  from the heat generating device that includes the combustion chamber  22 . In some embodiments, the combustion chamber  22  of the heat generating device is fluidly connected to the heat exchanger  40  via one or more air ducts. Additionally, one or more blowers, fans, dampers, deflectors, plenums, and the like may be added to the heat exchange system  10  to assist in the flow of heated exhaust air from the combustion chamber  22  to the heat exchanger  40  located within the plenum  62 . In some embodiments, retrofitting the heat exchanger  40  and plenum  62  to a pre-existing heat generating device to form heat exchange system  10  is simplified by providing heat exchanger  40  in a plenum  62  that is separate and remote from the firebox  14 . The heat exchanger  40  disposed within the plenum  62  can also be adapted to work with an existing heat generating device including an existing heat exchanger. 
         [0038]    According to some embodiments, the flow of air to be heated through the plenum  62  is assisted by one or more air assist devices  64  located within the plenum  62 . The air assist device  64  can be used to push or draw the air from the air intake end to the air output end  74  over the heat exchanger  40  and then to return the heated air to the room or structure. Exemplary air assist devices include, but are not limited to, fans, blowers, and the like. 
         [0039]      FIGS. 5-7  are cross-sectional views of various embodiments of the heat exchanger  40  including one or more internal pathways  84  for exhaust air flow. As briefly described above, the heat exchanger  40  optionally includes a plurality of baffle plates  80  that define one or more internal pathways  84  for exhaust air flow through the heat exchanger  40  to the outside via the second end  52 . In general, the overall effective length of the internal pathway  84  defined by the baffle plates  80  is longer than the length, width, or height of the heat exchanger housing  44 . 
         [0040]    The baffle plates  80  generally slow the flow of heated exhaust air through the heat exchanger  40 , increasing the residence time of the heated exhaust air within the heat exchanger  40 . In general terms, the longer the heated exhaust air resides within the heat exchanger  40 , the more efficient the heat exchange process will be with the air flowing over its outer surface  50 . As described above with reference to  FIGS. 3A and 3B , the outer surface  50  of the heat exchanger  40  may include a plurality of heat transfer assist structures  46  configured to maximize the surface area over which the heat exchange process occurs. 
         [0041]    The various embodiments heat exchangers  40  are each optionally disposed within the plenum  62  such that the air flowing through the heat exchanger  40  is generally parallel or counter to the air flowing from the air intake end  70  to the air output end  74  of the plenum  62 . The 180 degree turns created by the baffle plates  80  result in the addition of a cross flow component between the exhaust air flowing through the internal pathways  90 ,  92  within the heat exchanger  40  and the air to be heated flowing over the outer surface  50  of the heat exchanger housing  44 . 
         [0042]    If more than one heat exchanger  40  is used, the heat exchangers need not have the same internal pathway configuration defined by the baffle plates  80 . Additionally, one heat exchanger  40  may be oriented within the plenum  62  such that the exhaust air flowing through the heat exchanger  40  is generally parallel to the air to be heated flowing through the plenum  62 . An additional heat exchanger  40   b  may be coupled to a first heat exchanger  40   a  such that the exhaust air flow through the second heat exchanger  40   b  is counter to the air flow through the plenum  62  and the first heat exchanger  40   a . In some embodiments, the opposite configuration is used in which the exhaust air flows through the first heat exchanger  40   a  is counter to the air flowing through the plenum  62  and the exhaust air flow through the second heat exchanger  40   b  is generally parallel to or in the same direction as the air flowing through the plenum  62 . 
         [0043]    As shown in  FIG. 5 , in some embodiments the baffle plates  80  define at least one internal pathway  84  extending from the first end  48  to the second end  52  of the heat exchanger  40 . The internal pathway  84  can define a serpentine or tortuous path for the exhaust air such that exhaust air flows in a single general direction from the first end  48  to the second end  52  of the heat exchanger  40  along an internal pathway  84  extending through a plurality of 180 degree turns. As shown in  FIG. 5 , the heat exchanger  40  facilitates the use of cross-flow (perpendicular to F) and parallel flow (in the same direction as F) modes of heat exchange. In other embodiments, the general direction of air flow is opposite to that of the exhaust air flow through the plenum such that the heat exchanger  40  exchanges heat via cross-flow and counter flow (flow in an opposite direction to F) modes of heat exchange. 
         [0044]      FIG. 6  shows another configuration for heat exchanger  40  according to some embodiments where the heat exchanger  40  defines a first side  82   a  and a second side  82   b  and has a first end  83   a  and a second end  83   b . The heat exchanger  40  has an internal pathway  84  defined by the baffle plates  80 . As shown in  FIG. 6 , the internal pathway  84  is divided into a first segment  86   a  corresponding to the first side  82   a  and a second segment  86   b  corresponding to the second side  82   b . The first segment  86   a  carries the air from the first end  83   a  to the second end  83   b  while the second segment  86   b  carries the air back from the second end  83   b  to the first end  83   a . Each segment  86  and  88  extends through a plurality of 180 degree turns. As previously referenced, the first segment  86   a  directs the air flow in a generally first direction. The second segment  86   b  directs the flow of air in a generally second, opposite direction. This configuration allows air flow traveling along a single internal pathway as defined by the baffle plates  80  to have parallel flow, counter flow, and cross-flow components relative to the air flow F through the plenum  62  over the outer surface  50  of the heat exchanger housing  44 . In particular, the first segment  86   a  is adapted for both parallel and cross-flow modes of heat exchange while the second segment  86   b  is adapted for both counter flow and cross-flow modes of heat exchange. 
         [0045]    As shown in  FIG. 7 , some embodiments of the heat exchanger  40  include baffle plates  80  defining two internal pathways  90  and  92 . Exhaust air flows from the combustion chamber  22  (see  FIGS. 1-4 ) into the first end  48  of the heat exchanger  40  where it is split and travels along internal pathways  90  and  92 . Each internal pathway  90  and  92  extends through a plurality of 180 degree turns. In some embodiments, the directions of air flow along a substantial portion of the first and second pathways  90 ,  92  are in generally parallel, though opposite direction. The air flowing through each pathway  90  and  92  converges back together at the second end  52  of the heat exchanger  40  before being exhausted. 
         [0046]    Various embodiments of a heat exchanger according to the present invention increase the overall efficiency otherwise achieved using heat generating devices such as gas fireplaces. For reference, overall energy efficiency or Annual Fuel Utilization Efficiency (AFUE) is calculated according to the Department of Energy Testing procedure (10 CFR Part  430 ). Where the fuel being consumed within the heat generating device, for example natural gas, has a moisture content of about 6% to about 7% energy efficiency of about 93% is an approximate upper limit for the system  10 . Thus, in some embodiments, the system  10  includes a natural gas fireplace heat generating device and is adapted to achieve an energy efficiency of about 93%. According to further embodiments, the system  10  is adapted to have an energy efficient ranging from about 75% to about 93%. According to still further embodiments, the system  10  is adapted to have an energy efficient ranging from about 90% to about 93%, for example. 
         [0047]    Various modifications and additions can be made to the exemplary embodiments discussed without departing from the scope of the present invention. For example, while the embodiments described above refer to particular features, the scope of this invention also includes embodiments having different combinations of features and embodiments that do not include all of the described features. Accordingly, the scope of the present invention is intended to embrace all such alternatives, modifications, and variations as fall within the scope of the claims, together with all equivalents thereof.