Abstract:
A combined supply and exhaust apparatus for an air using appliance is provided. The combined supply and exhaust apparatus includes air supply and air exhaust passages. The air supply and air exhaust passages extend between inlets and outlets. A common wall separates the air supply passage from the air exhaust passage. The air supply passage supplies air to the appliance and the air exhaust passage exhausts air from the appliance.

Description:
FIELD OF THE INVENTION 
       [0001]    This invention generally relates to clothes dryers and, more particularly, to air supply and air exhaust apparatuses for use with clothes dryers. 
       BACKGROUND OF THE INVENTION 
       [0002]    With increasing energy costs, consumers are becoming more and more energy conscious. As such, consumers are demanding more energy efficiency from their appliances and the homes in which they live. Many appliance manufacturers have responded by attempting to increase their products&#39; energy efficiency. However, no matter how efficient some appliances are made, the use of the appliance may be inefficient by causing other less efficient devices to also activate. 
         [0003]    One such example is the use of a dryer for drying moist articles or goods, commonly referred to as a clothes dryer. Common practice with clothes dryers is to intake air from the room in which the clothes dryer is operating, heat it, pass it through the moist goods housed in a drying chamber, also referred to as a drum, and then exhaust it from the clothes dryer through an exhaust duct to the exterior of the building. During this process, it is common for as much as 150 cubic feet of air to be exhausted from the interior of the building to the exterior of the building per minute of operation. With typical drying cycles lasting approximately 45 minutes in length, the average clothes dryer can consume, on average, 6,750 cubic feet of air during a single cycle. This is the equivalent volume of air in seven rooms having eight foot ceilings and ten foot by twelve foot dimensions. As the air from the interior of the building is exhausted to the exterior of the building, the air that previously occupied the building is replaced by unconditioned air from the exterior of the building. Typically, this replacement air enters the building through doors, windows, cracks and other air passages fluidly communicating the interior of the building with the exterior. 
         [0004]    This replacement of such a substantial volume of conditioned air from within the building with unconditioned air from the exterior of the building typically causes the condition of the air within the building to change. This, in turn, causes the heating, ventilating, and air conditioning system (HVAC system) of the building to activate to return the interior of the building to a pleasing condition. Unfortunately, the HVAC system is the most costly system in most buildings to operate. Thus, even if the individual operation of the clothes dryer can be made more efficient, the use of the clothes dryer causes the HVAC system to activate, reducing the overall efficiency of the clothes drying process. 
         [0005]    Other problems exist with current clothes dryers. For example, the exhaust duct that vents the exhaust air from the clothes dryer to the exterior of the building can become plugged with lint or other particulate and catch fire causing structural damage to the building. Further, the exhaust pipes themselves can become extremely hot as a result of the hot exhaust air flowing through the pipes which can damage walls, wires, and other structure of the building that are positioned proximate the exhaust ducts. In addition, as the clothes dryer expels the humid warmed air from the building, the humid warm air takes with it a large quantity of heat energy that has been produced by the dryer to dry the clothes. This heat energy stored in the exhausted humid warm air is merely dumped into the exterior environment and wasted further reducing the overall operating efficiency. 
         [0006]    Thus, there is a need in the art for an air supply and exhaust system that reduces the amount of conditioned air that is expelled from the interior of the building during operation of the dryer, increases safety, and more efficiently conserves the heat energy that is produced to dry the moist goods. 
       BRIEF SUMMARY OF THE INVENTION 
       [0007]    In view of the above, a new and improved supply and exhaust apparatus for supplying and exhausting air to an air using appliance is provided. An embodiment of the apparatus provides improved safety by insulating an exhaust air passage of the apparatus with an supply air passage by having the exhaust air passage passing through the supply air passage. The air gap between the outer passage and the inner passage reduces the potential for a fire when objects come into contact with the supply and exhaust apparatus. Further, if a fire should occur in the air exhaust passage from lint or other byproducts of the drying process, the concentric configuration reduces the hazard of the fire on walls of the building. 
         [0008]    Further, in an embodiment, the exhaust air passage and supply air passage are separated by thermally conductive material allowing heat transfer between the two passages. As such, incoming air may be preheated by hot exhaust air. To improve the heat transfer capability, heat transfer fins are employed in embodiments to improve extraction and transfer of waste heat energy of the exhausted air stream. This configuration allows heat energy that is normally lost during standard drying cycles to be recaptured, increasing the energy efficiency of the drying system incorporating the supply and exhaust apparatus. 
         [0009]    In a further embodiment, the supply and exhaust system reduces the amount of indoor conditioned air used during the drying process increasing the overall energy efficiency of the drying process. 
         [0010]    In one embodiment, the invention provides a combined supply and exhaust apparatus for an air using appliance including an air flow duct including two air flow passages. The air flow passages extend between two inlets and two outlets, respectively. Preferably, the inlets and outlets are concentrically located to one another so that only a single hole is needed to communicate with the exterior of the building. A common wall separates the first air flow passage from the second air flow passage. One air flow passage is configured as an air supply passage to supply air to the appliance. The other air flow passage is configured as an air exhaust passage to exhaust air from the appliance. 
         [0011]    In another embodiment of a combined supply and exhaust apparatus for an air using appliance, the apparatus includes an air flow duct having two air flow passages being separated by a common wall. A first supply and exhaust manifold is mounted to a first end of the air flow duct. The first supply and exhaust manifold forms a first outlet of the first flow passage and a second inlet of the second flow passage. A second intake and exhaust manifold is mounted to an opposite end of the air flow duct. The second intake and exhaust manifold forms a first inlet of the first flow passage and a second outlet of the second flow passage. The first flow passage is configured as an air supply passage for supplying air to the appliance therethrough and the second flow passage is configured as an air exhaust passage for exhausting air from the appliance therethrough. 
         [0012]    In an embodiment, existing dryer ducts can be retrofit to take advantage of the features of the combined supply and exhaust apparatus. In such an embodiment, a separate smaller air supply means can be installed within the existing duct. Alternatively, the combined supply and exhaust apparatus can be retrofit to work with standard dryers. The combined supply and exhaust apparatus can be used to provide a fresh air induction path directly to the room or environment in which the dryer is located to prevent conditioned air from being drawn from the rest of the building. Such a configuration includes dampers to eliminate free air flow through the apparatus reducing the loss of conditioned air to the exterior of the building when the drying process is inactive. 
         [0013]    Other aspects, objectives and advantages of the invention will become more apparent from the following detailed description when taken in conjunction with the accompanying drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0014]    The accompanying drawings incorporated in and forming a part of the specification illustrate several aspects of the present invention and, together with the description, serve to explain the principles of the invention. In the drawings: 
           [0015]      FIG. 1  is a simplified side view illustration of a dryer positioned within a building and including an supply and exhaust system according to the teachings of the present invention; 
           [0016]      FIG. 2  is a simplified end view of an embodiment of a dual flow duct for a dryer according to the teachings of an embodiment present invention. 
           [0017]      FIG. 3  is a simplified cross-sectional illustration of the dryer of  FIG. 1 ; 
           [0018]      FIGS. 4 and 5  are simplified side views of additional embodiments of dyers and drying systems according to the teachings of the present invention; 
           [0019]      FIGS. 6 and 7  are a simplified end views of additional embodiments of dual flow ducts according to the teachings of the present invention; and 
           [0020]      FIG. 8  is a simplified cross-sectional illustration of the connection between the dual flow duct and a dryer according to the teachings of the present invention. 
       
    
    
       [0021]    While the invention will be described in connection with certain preferred embodiments, there is no intent to limit it to those embodiments. On the contrary, the intent is to cover all alternatives, modifications and equivalents as included within the spirit and scope of the invention as defined by the appended claims. 
       DETAILED DESCRIPTION OF THE INVENTION 
       [0022]    Turning now to the figures,  FIG. 1  illustrates a dryer  10  and a dual flow duct  14  according to the teachings of one embodiment of the present invention. The dryer  10  advantageously draws air from the exterior  16  of the building  17  rather than conditioned air from the interior  18  of the building  17  to dry moist goods  19  within the dryer  10 . This configuration significantly reduces the amount of conditioned air within the building  17  that is needlessly exhausted from the building  17  during a drying cycle and lost to the exterior  16  of the building  17 . Advantageously, by reducing the amount of conditioned air that is exhausted from the building  17 , the same amount of exterior, unconditioned air, is prevented from entering the building  17 . By reducing the amount of unconditioned air that is added to the building  17 , the internal conditions of the building  17  are not significantly altered during the drying process, thereby reducing the work load, and energy use, of the HVAC system of the building (not shown). 
         [0023]    According to the teachings of one embodiment, the dryer  10  functions to dry moist goods  19  such as clothing, towels, rags, and the like placed within the dryer  10  by passing air through and/or across the material of the moist goods  19 . As such, the dryer  10  includes a blower  22 , shown schematically, that forces air through the dryer  10  and in contact with the moist goods  19 . More particularly, in an embodiment, the blower  22  draws air through an air flow passage ducted through the dryer  10  that directs air through the moist goods  19  to be dried. 
         [0024]    One portion of the air flow passage includes a drying chamber  26  in which the moist goods  19  are placed during the drying cycle. In the illustrated embodiment, the drying chamber, indicated generally by reference numeral  26 , is provided by a drum  28  that is rotatably supported within the outer housing  30  of the dryer  10 . The drum  28  rotates during the drying cycle causing the moist goods  19  that are located therein to tumble while drying. The tumbling action beneficially allows individual pieces of the moist goods  19  to separate facilitating the passage of drying air through and across the moist goods  19  to increase the evaporating action of the drying air, thereby increasing the rate of moisture removal from the moist goods  19 . The drum  28  is typically rotatably supported by a plurality of rollers  31  and is rotatably driven by a belt  32  connected to and powered by an electric motor (not shown). In an embodiment, the electric motor that drives the drum  28  also drives the blower  22 . 
         [0025]    In an embodiment, the dryer  10  includes a heater, shown in a simplified manner at reference number  34 . The heater  34  is positioned within the air flow passage passing through the dryer  10  upstream from the drum  28 . The heater  34  heats the air prior to the air passing through the drum  28  and, consequently, prior to the air passing through the moist goods  19 . Warm air can retain and absorb more moisture from the moist goods  19  and thereby reduce the amount of air and the length of time required to dry the moist goods  19 . The heater  34  may be any practicable heater and may include such heaters as electrically resistive heaters, gas fired heaters, and the like. 
         [0026]    In an embodiment, the blower  22  draws the “drying” air, indicated by arrows  40 , into the dryer  10  directly from the exterior  16  of the building  17 . The drying air  40  is then heated and passed through the moist good  19  to dry the moist goods  19 . This configuration of using exterior air as the drying air  40  rather than conditioned air from within the interior  18  of the building  17  reduces the amount of energy used thereby increasing the overall energy efficiency of the process. Particularly, this configuration reduces the amount of conditioned air that is consumed by the dryer and expelled from the building  17 . This, in turn, reduces the amount of non-conditioned air that enters the building from the outside, which, in turn, reduces the load on the HVAC system (not shown) to maintain the desired temperature and humidity levels of the building  17 . As such, a method of drying moist goods  19  using a dryer  10  and dual flow duct  14  disclosed herein by drawing air from the exterior  16  of the building  17  through the dual flow duct  14  rather than drawing air from the interior of the building is highly beneficial. 
         [0027]    Further, this configuration reduces the amount of energy that is wasted during warm periods by exhausting air that previously had been conditioned which required energy to cool the air. As noted previously, the HVAC system of a building is one of the most costly systems in a building to operate. Any reduction in unnecessary operation of the HVAC system will beneficially increase overall efficiency and energy consumption of the building as a whole. 
         [0028]    As the drying air  40  passes through the drying chamber  26  and the moist goods  19 , the previous lower humidity drying air  40  absorbs moisture from the moist goods  19  and becomes humid stale exhaust air, indicated by arrows  44  and proceeds to be exhausted from the dryer  10 . The exhaust air  44  passes through an exhaust air portion of the air passage of the dryer  10  downstream from the drying chamber  26  to the dual flow duct  14 . The dual flow duct  14 , in part, fluidly communicates the exhaust portion of air passage with the exterior  16  of the building  17  and as such allows the exhaust air  44  to be exhausted from the dryer  10  to the exterior  16  of the building  17 . 
         [0029]    More particularly, in an embodiment, a first end  50  of the dual flow duct  14  connects to an air intake and exhaust manifold  52  of the dryer  10 , and the second, opposite, end  54  of the dual flow duct is positioned in and in fluid communication with the exterior  16  of the building  17 . In an embodiment, the second end  54  of the dual flow duct  14  is connected to a second air intake and exhaust manifold  43  positioned outside of the building  17 . As is illustrated, the second air intake and exhaust manifold  43  is configured to prevent rain or other debris from entering the dual flow duct  14 . This can be accomplished by including canted roughs, tops or covers over the openings through which drying air  40  and exhaust air  44  enter and exit, respectively, the second air intake and exhaust manifold  43 . Additionally, the openings in the second air intake and exhaust manifold may include grates, grills, mesh and the like to prevent debris from entering the openings. 
         [0030]    The dual flow duct  14  includes two air flow passages including an air supply passage  60  for drawing in the drying air  40  and an air exhaust passage  62  for exhausting the exhaust air  44 . In an embodiment, the air supply passage  60  and air exhaust passage  62  are positioned proximate one another such that the two air flow passages are separated by a common wall  66 . As such, the air supply passage  60  and the air exhaust passage  62  are formed in a common structure, namely dual flow duct  14 . As such, the air that is drawn in through the air supply passage  60  and the air exhausted through the air exhaust passage  62  flow in the common air flow structure, dual flow duct  14 . 
         [0031]    In an embodiment, as illustrated in  FIGS. 1 and 2 , the air supply passage  60  and air exhaust passage  62  are concentric with one another. In such an embodiment, the dual flow duct  14  is provided by an outer annular wall  68  and the common wall  66  that forms an inner annular wall, with the outer wall  68  and common wall  66  concentrically aligned. In this configuration, the space between an inner surface  69  of the outer annular wall  68  and an outer surface  70  of the common wall  66  provides the air supply passage  60 . The inner surface  71  of the common wall  66  entirely defines the air exhaust passage  62 . When drying moist article  19  using a method of the present invention, drying air  40  and exhaust air  44  are drawn in and exhausted through the dual flow duct  14  in a concentric manner, such that the drying air  40  flows in an opposite direction as the exhaust air  44  and through the radially outer passage. 
         [0032]    In an embodiment, the common wall  66  is made from a thermally conductive material such as metal. Using a common wall  66  of a thermally conductive material beneficially increases the efficiency of the dryer  10 . In such a configuration, some of the heat energy stored by the exhaust air  44  passing through the air exhaust passage  62  is dissipated to the drying air  40  drawn in through the air supply passage  60  through the thermally conductive common wall  66 . The transfer of heat energy from the exhaust air  40  to the drying air  44  reduces the amount of heat energy required to be added to the drying air  44  by the heater  34 . 
         [0033]    As it is beneficial to have as much heat energy transferred from the exhaust air  44  to the drying air  40  as possible, an embodiment of the present invention includes heat transfer structures, such as heat pipes and/or, as illustrated, heat transfer fins  74  that extend from the outer and inner surface  70 ,  71  of the common wall  66  of the dual flow duct  14 . The heat transfer fins  74  increase the amount of surface area for the air flowing through the air intake and air exhaust passages  60 ,  62  to contact and impinge further increasing the amount of heat that will be dissipated from the exhausted air  44  and will be absorbed by the drying air  40 . Further, the heat transfer fins  74  may be used to mount, position and/or support the common wall  66  within the outer annular wall  68 . In such an embodiment, the heat transfer fins  74  extend entirely from the outer surface  70  of the common wall  66  to the inner surface  69  of the outer annular wall  68 . 
         [0034]    Condensation may occur as the warm humid exhaust air  44  reduces in temperature as it dissipates heat energy to the drying air  44 . Therefore, in an embodiment, the outer annular wall  68  and inner common wall  66  are preferably made from a stainless or corrosion resistant material to prevent any condensation that forms thereon from damaging the walls  66 ,  68 , which may include metal or plastic. 
         [0035]    The concentric configuration, having the air exhaust passage  62  passing through the air supply passage  60 , has several beneficial features. First, as noted previously, the dual flow duct  14  functions as a dual flow heat exchanger. With the air exhaust passage  62  positioned within the air supply passage  60 , the entire surface area of the common wall  66  that surrounds the air exhaust passage  62  is in thermal communication with the exhaust air  44  and drying air  40  on opposite sides of the common wall  66 . Thus, any heat energy that is dissipated from the exhaust air  44  will be transferred to the drying air  40 . It should be noted that the illustrated embodiment uses walls  66 ,  68  having round cross-sections, one of skill in the art will recognize that the walls  66 ,  68  are not so limited in shape and can be any shape such as square, rectangular, oval, and the like. Furthermore, as the outer annular wall  68  and common wall  66  are both have the same shape, it is not required that both walls have the same shape. For example and as illustrated in an alternative embodiment of a dual flow duct  414  in  FIG. 7 , the outer wall  451  is rectangular while the inner common wall  466  is round having the air supply passage  460  and air exhaust passage  462  defined between the outer wall  451  and within the common wall  466 , respectively. 
         [0036]    As the wall forming the air exhaust passage can become very hot, it is a benefit of the configuration illustrated in  FIG. 1  that the air supply passage  60  performs the further function of insulating the common wall  66 , which defines the air exhaust passage  62  from its surroundings. This increases safety by preventing the air exhaust passage from damaging any infrastructural components of the building that are proximate to the dual flow duct  14 . Similarly, the dual wall configuration prevents individuals from getting injured upon accidentally contacting the outer surface of the exhaust duct because the individual does not touch the outer surface of the exhaust air passage. Additionally, if a fire should occur in the exhaust air passage  62  because of excess lint or by products of the drying process, the double wall configuration may reduce the hazard of the fire spreading to interior walls or other structure of the building  17 . 
         [0037]    As indicated previously, the dryer  10  includes an air intake and exhaust manifold  52  for connecting the dual flow duct  14  to the dryer  10 . As best illustrated with reference to  FIGS. 1 and 3 , the air intake and exhaust manifold  52  forms the inlet  78  and the outlet  80  for the air passage passing through the dryer  10 . The inlet  78  and outlet  80  are formed in a duct connection end  81  of the air intake and exhaust manifold  52  that is configured to be connected to a dual flow duct  14 , as shown in  FIG. 1 . Additionally, the air intake and exhaust manifold  52  functions to separate the air supply passage  60  from the air exhaust passage  62 . Furthermore, the air intake and exhaust manifold  52  communicates the air supply passage  60  with the portion of the air flow passage within the dryer upstream from the drying chamber  26  and the air exhaust passage  62  to the portion of the air flow passage within the dryer  10  downstream of the drying chamber  26 . As illustrated, in an embodiment, this is accomplished by a first duct  84  interconnecting the air supply passage  60  portion of the air intake and exhaust manifold  52  to the heater  34 . A second duct  86  interconnects the air exhaust passage  62  of the air intake and exhaust manifold  52  to the blower  22  such that the exhaust air  44  exiting the blower  22  is directed to the air intake and exhaust manifold  52  such that the exhaust air  40  is exhausted to the air exhaust passage  62 . The ducts  84 ,  86  may be connected to the air intake and exhaust manifold  52  by standard duct connections. 
         [0038]    In an embodiment, the duct connection end  81  of the air intake and exhaust manifold  52  is configured of easy attachment to the dual flow duct  14 . In an embodiment and as illustrated in  FIG. 3 , the air intake and exhaust manifold  52  has an inner flange  87  that extends outward beyond an end of an outer flange  89 . Alternatively, the dual flow duct  14  could have the ends of the common and outer walls  66 ,  68  offset. 
         [0039]    Preferably, the flanges are configured to minimize resistance on the fresh air  40  flowing through the air supply passage  60  as it passes from the dual flow duct  14  to the air intake and exhaust manifold  52  as well as the exhaust air  44  flowing from the air intake and exhaust manifold  52  to the dual flow duct  14  through the air exhaust passage  62 . To minimize the air resistance and as illustrated in  FIG. 8 , the inner flange  87  can be configured to slide into the common wall  66  of the dual flow duct  14  and the outer flange  89  can be configured to slide around and receive the outer wall  68 . This can be accomplished by having the flanges  87 ,  89  of the air intake and exhaust manifold  52  tapered, or by having the ends of the walls  66 ,  68  of the dual flow duct  14  tapered, or any combination thereof. Tapering can include having a larger continuous diameter sized to receive the corresponding portion of the other component for easy mating between the dual flow duct  14  and the air intake and exhaust manifold  52  as well as continuously varying radii such as in a chamfer. The second air intake and exhaust manifold may be similarly configured to mount to an end of the dual flow duct  14 . 
         [0040]    The dryer  10  may further include sensors  90  for sensing characteristics of the drying air  40  and exhaust air  44  flowing through the dryer  10  as well as the air supply and air exhaust passages  60 ,  62 . These sensors  90  can sense characteristics such as air temperature, flow rate, presence of hazardous gases, humidity and the like. The sensors  90  can operably communicate with a controller  92  or other logic device for operably controlling the dryer  10  in response to the sensed characteristics. Particularly, the sensed condition of the air can be compared with predetermined or user determined values. Air temperature and flow rate sensors can be beneficial in helping determine if any portions of the air flow passages are plugged or if the dryer  10  is functioning properly. In such a case, the dryer  10  and its controller  92  may be configured to activate an alarm (not shown) or cease operation until the dryer  10  or dual flow duct  14  has been inspected and cleared. 
         [0041]    With reference to  FIG. 4 , in another embodiment, the drying air portion of the air intake and exhaust manifold  152  includes a damper  198  that may be opened if a sensor  190  senses the presence of harmful gases proximate the dryer  110 , such as carbon monoxide. Upon sensing the presence of harmful gas, the controller  192  actuates the damper  198  to an open position. The dryer draws the air  135 , which includes the hazardous gasses, from the localized environment of the dryer  110 , i.e. from the interior  18  of the building  17  and exhausts the hazardous gasses out of the building  17  as exhaust air through the air exhaust passage  62 . Additionally, if hazardous gas is sensed, the controller  192  of the dryer  110  may be programmed to lock out operation or activation of the dryer  110  until the controller  192  is reset and/or the presence of hazardous gas is eliminated. 
         [0042]    Although existing ductwork in buildings does not have dual passages for providing an air supply passage and an air exhaust passage, existing structure can be retro fit to form embodiments of dual flow duct work. Rather than removing the existing ductwork and replacing it with new dual flow ducts, existing ducts can be used along with a second duct pipe that is installed in the structure in addition to the existing ductwork. After the new duct pipe is installed in the dwelling, the combination of old and new ducts can function as explained previously, i.e. the old duct will continue to be used to exhaust the dryer, while the new duct will supply outside air to the dryer. 
         [0043]    In a further embodiment of the present invention, illustrated in  FIG. 5 , the embodiment incorporates a standard dryer  210  that draws drying air  240  directly from the room of the building  17  housing the dryer  210 . This embodiment may be used by retrofitting existing ductwork with a second passage as explained previously or with newly installed dual flow duct previously described prior to acquiring a dryer configured to communicate with the dual flow duct  14 . 
         [0044]    As explained previously, standard dryers draw drying air directly from the ambient air within the room housing the dryer and then exhaust it to the exterior of the building. The ambient air directly surrounding the dryer is then replenished with other conditioned air from within the building. Typically, this air enters through the door or gaps around the door leading to the room. The exhaust air exiting the building is replaced by other air from within the building that enters the building through doors or windows. As such, conditioned air is used and exhausted from the building during the drying cycle. However, with the present embodiment, the dryer  210  draws drying air from the room in which it is located, but the air is not replaced by conditioned air from the interior  18  of the building  17 , but the ambient air surrounding the dryer is replaced by unconditioned air from the exterior  16  of the building  17 . 
         [0045]    In this embodiment, the dual flow duct  14  includes both an air supply passage  60  and an air exhaust passage  62  and an air intake and exhaust manifold  252  connected to the dual flow duct  14  external to the dryer  210 . The air intake and exhaust manifold  252  includes an exhaust air inlet  263  that is interconnected to dryer&#39;s exhaust air outlet  164 . As such, exhaust air  244  exhausted from the dryer  210  is exhausted through the air intake and exhaust manifold  252  and then the air exhaust passage  62  of the dual flow duct  14 , similar to the process as explained previously. 
         [0046]    However, the dryer  210  draws the drying air, indicated generally by arrows  240  directly from the ambient air within the interior  18  of the building  17 , and more particularly, the room housing the dryer  210 . However, the ambient air within the room is not primarily replenished by conditioned air from the rest of the building  17 . In this embodiment, the air intake and exhaust manifold  252  includes a drying air outlet  265  that is in fluid communication with the exterior  16  of the building  17  through the air supply passage  60 . As such, when the dryer  210  draws drying air  240  from the room for drying the moist goods  19 , the air is replaced by air, indicated generally by arrows  241 , that is drawn into the building  17  through the duct  14  via a vacuum created by the exhaust air  244  exiting the building  17 . 
         [0047]    This embodiment can be extremely beneficial as the conditioned air from the rest of the building is not used to continue the drying process. Instead, unconditioned air  241  from the exterior  16  of the building  17  is used. To prevent conditioned air from escaping the building  17  when the dryer  210  is inoperative, the air intake and exhaust manifold  252  includes a damper  267  that can close the drying air outlet  265  of the air intake and exhaust manifold  252  and prevent fluid communication between the interior  18  and exterior  16  of the building  17  via the air supply passage  60  of the dual flow duct  14 . The damper  267  may be configured for manual or automatic opening or closing. As such, the damper  267  may be configured to be opened or closed directly by the user or configured to open or close automatically upon activation or deactivation of the dryer  210 . 
         [0048]    In another embodiment, illustrated in  FIG. 6 , the air supply passage  360  and the air exhaust passage  362  are configured such that the two passages  360 ,  362  are side-by-side rather than concentric. In this configuration, a common outer wall  368  provides an outer periphery for the dual flow duct  314  but rather than forming the entire outer periphery of a single passage, like the previously described concentric embodiment, the outer wall  368  forms a portion of both of the air intake and air exhaust passages  360 ,  362 . The dual flow duct  314  further includes a common wall  366  that separates the two passages  360 ,  362  from one another. Preferably, the common wall  366  is formed from a thermally conductive material such that heat energy can be transferred from the air exhausted through the air exhaust passage to the air being brought into the dryer through the air supply passage. This common wall  366  may further include heat transfer fins  374  to increase the heat transfer between the two passages  360 ,  362 . 
         [0049]    It will be recognized by one of ordinary skill in the art that the embodiments of the ducts disclosed previously could be practiced using plastic or other non-thermally conductive material rather than thermally conductive material. However, such configurations will not have the additional benefits of functioning as a heat exchanger. The use of plastic duct could be extremely beneficial when retrofitting existing duct with a second passage by using flexible plastic duct that can be more easily inserted through the existing ductwork.  FIG. 7  illustrates an embodiment where the dual flow duct  414  is formed by an existing duct  451  that is rectangular and the inner duct  466  is formed by circular plastic flexible duct. As discussed previously, the dual flow duct  414  includes an air supply passage  460  and an air exhaust passage  462 . 
         [0050]    All references, including publications, patent applications, and patents cited herein are hereby incorporated by reference to the same extent as if each reference were individually and specifically indicated to be incorporated by reference and were set forth in its entirety herein. 
         [0051]    The use of the terms “a” and “an” and “the” and similar referents in the context of describing the invention (especially in the context of the following claims) is to be construed to cover both the singular and the plural, unless otherwise indicated herein or clearly contradicted by context. The terms “comprising,” “having,” “including,” and “containing” are to be construed as open-ended terms (i.e., meaning “including, but not limited to,”) unless otherwise noted. Recitation of ranges of values herein are merely intended to serve as a shorthand method of referring individually to each separate value falling within the range, unless otherwise indicated herein, and each separate value is incorporated into the specification as if it were individually recited herein. All methods described herein can be performed in any suitable order unless otherwise indicated herein or otherwise clearly contradicted by context. The use of any and all examples, or exemplary language (e.g., “such as”) provided herein, is intended merely to better illuminate the invention and does not pose a limitation on the scope of the invention unless otherwise claimed. No language in the specification should be construed as indicating any non-claimed element as essential to the practice of the invention. 
         [0052]    Preferred embodiments of this invention are described herein, including the best mode known to the inventors for carrying out the invention. Variations of those preferred embodiments may become apparent to those of ordinary skill in the art upon reading the foregoing description. The inventors expect skilled artisans to employ such variations as appropriate, and the inventors intend for the invention to be practiced otherwise than as specifically described herein. Accordingly, this invention includes all modifications and equivalents of the subject matter recited in the claims appended hereto as permitted by applicable law. Moreover, any combination of the above-described elements in all possible variations thereof is encompassed by the invention unless otherwise indicated herein or otherwise clearly contradicted by context.