Abstract:
Systems and method are provided for recovering heat from waste air being expelled from a livestock poultry barn. A heat recovery unit is specially designed to take advantage of an unused heat source, while avoiding the corrosive effects of waste air from the livestock poultry barn. The novel heat recovery capture heat from the expelled waste air.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    The present application claims priority from, and incorporates by reference in its entirety, Chinese patent application serial number 201320067905.1 filed Feb. 6, 2013. 
       BACKGROUND 
       [0002]    1. Field of the Invention 
         [0003]    The present invention relates to livestock barn heating and cooling systems, and more specifically, to systems and methods of using a waste heat recovery system for a livestock poultry barn. 
         [0004]    2. Description of Related Art 
         [0005]    Commercial meat-bird poultry production in the U.S. includes broilers (chickens), turkeys and ducks. Commercial poultry farms raise thousands, and often many tens of thousands, of poultry birds inside large poultry barns. For example, a chicken being raised for human consumption spends its entire life indoors in a climate controlled atmosphere designed efficiently grow the birds to full, marketable size. Temperature control is a major factor in maintaining the climate controlled atmosphere for maximum efficiency. As such, fuel costs for heating are one of the major expenses in commercial poultry operations, typically the largest cost to poultry farmers aside from feed costs. Poultry barns are located rural areas where there is often no source of cheap fuel available. Propane, which is significantly more expensive than natural gas, is often the only option. Due to the unpredictable price of heating fuel—e.g., propane—a poultry farmer&#39;s ability to make a profit on a flock raised during the winter months is sometimes jeopardized by high fuel costs. Unexpected increases in fuel costs sometimes determines whether a given flock produces a profit or a loss for the farmer. 
         [0006]    Health is another consideration affected by the climate controlled atmosphere of a poultry barn—both the health of the birds and the health of the human consumer who eventually purchases a bird for consumption. In addition, the climate controlled atmosphere of the poultry barn has a great effect on the weight gain efficiency of the flock as the birds grow from hatchlings into marketable sized broilers. 
       SUMMARY 
       [0007]    Embodiments disclosed herein address the above stated needs by providing systems and methods for a poultry barn waste heat recovery system. The present inventor recognized various characteristics specific to the commercial poultry industry. The novel embodiments disclosed herein take advantage of those various characteristics to reduce the fuel consumption for a commercial poultry operation utilizing heated indoor poultry barns. 
         [0008]    Another embodiment provides a system and method of using a waste heat recovery system for a livestock barn with an enclosure containing at least three tube bundle cells. Each of the tube bundle cells has a pair of side panels, one on each side, connected by tubes that are aligned with holes in each of the side panels. The tube bundle cells are arranged in sequence within the enclosure to provide a waste air output path passing transversely through spaces between the tubes of each of the tube bundle cells which forms a waste air output path. A first fan is provided in the fresh air input path to move fresh air through the tubes, and a second fan is provide in the waste air output path to drive waste air through the spaces between the tubes of each tube bundle cell. The system is designed so that the fresh air input path crosses the waste air output path at least three times, helping to heat the fresh air using the heat of the waste air being expelled from the livestock barn. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0009]    The accompanying drawings, which are incorporated in and constitute part of the specification, illustrate various embodiments of the invheat recovery unitention. Together with the general description, the drawings serve to explain the principles of the invention. In the drawings: 
           [0010]      FIG. 1A  depicts a tube bundle cell of a heat recovery unit according to a first embodiment; 
           [0011]      FIG. 1B  depicts different cross-sections of tubes that can be used in various embodiments; 
           [0012]      FIG. 1C  depicts a tube pattern for a tube bundle cell that provides a straight through waste air output path; 
           [0013]      FIG. 2A  depicts a top view of a first configuration of a heat recovery unit and  FIG. 2B  depicts a top view and an oblique view of a single tube bundle cell; 
           [0014]      FIG. 3  depicts a top view of a second configuration of a heat recovery unit; 
           [0015]      FIG. 4  is an oblique view of an embodiment of a heat recovery unit; 
           [0016]      FIG. 5  is an oblique view of a vertical installation embodiment of a heat recovery unit; 
           [0017]      FIG. 6  is a flowchart depicting a method of using the heat recovery unit according to various embodiments disclosed herein; and 
           [0018]      FIG. 7  is a cross-sectional view illustrating the heat forming of tube bundle cells from tubes and pairs of side panels. 
       
    
    
     DETAILED DESCRIPTION 
       [0019]    The climate of a poultry barn can be defined as the sum of environmental factors which influence the health and behavior of the flock. Climatic factors include temperature, humidity, air cleanliness, degree of light, and other such factors. The climate of a poultry barn has a great influence on the health of the birds as well as the efficiency of growing them to market size. Chickens raised in unfavorable climatic conditions are at risk to develop respiratory and digestive disorders and possibly exhibit behavioral issues. In addition to health and behavioral considerations, poor climatic conditions cause inefficiencies in feed utilization, thus reducing the daily rate of gain of the flock. In short, poultry raise in poor climatic conditions cannot be expected to perform optimally. 
         [0020]    The present inventor recognized the interaction between the need for clean air in a poultry barn and the requirement to maintain a given temperature at various stages of poultry production. It typically takes seven to eight weeks to grow a hatchling broiler from several ounces up to a marketable weight of five to seven pounds. During this time the poultry barn is maintained at different heat levels, depending upon the age of the broilers. Young hatchling broilers require a much warmer environment than older, larger birds. When the flock is first introduced into the poultry barn the temperature is kept at around 85 to 90 degrees Fahrenheit for chickens, and around 90 to 95 degrees for turkeys. The temperatures are gradually reduced until reaching a final temperature of around 60 to 70 degrees Fahrenheit. During the winter months farmers spend a great deal of money on fuel costs to keep the barn heated to the initial temperatures which are as high as 90 degrees. 
         [0021]    In order to keep the poultry barn air clean large fans, including side-wall fans and tunnel fans, are used to circulate the air, while constantly venting a portion of the dust ridden air out of the barn and replacing it with clean, fresh air from the outside. A problem with this is that, during the winter months in the Midwestern and northern states the clean, fresh air coming into the barn is too cold for optimal climactic conditions. Therefore, it is necessary to constantly heat the barn to compensate for the incoming clean, fresh air being introduced into the barn&#39;s climate. With conventional climate control systems energy consumption and the associated costs for poultry farms is second only to feed costs. Various embodiments capitalize on the heat being expelled with the dirty air, using heat recovery units to capture part of that heat for the incoming fresh air. 
         [0022]    Heat recovery systems are used in other fields of industry, including implementations to recover at least some of the waste heat being vented from factories and office buildings. Typically, the conventional heat recovery systems use a metal heat exchanger unit since metal interface surfaces tends to conduct heat more efficiently than plastics, vinyls, and other non-metallic synthetic materials. However, the present inventor recognized a characteristics specific to the poultry industry that would pose a drawback in attempting to use a conventional metal heat recovery systems for expelled poultry barn air. The expelled air from poultry barns is quite dirty, containing a high concentration of dust, feathers and other airborne particles as well as ammonia. Ammonia and other gases in a poultry barn are quite corrosive to conventional metallic heat recovery systems. Moreover, the airborne particles include dust from dried poultry feces, a material that is quite corrosive and often includes viruses, bacterial content and parasites. The pollutants in poultry barn air—in particular, the feces dust, feathers and feather parts—result in an airborne pollutant that is very lightweight, somewhat sticky, and prone to causing diseases in poultry and humans. The poor quality of air, including airborne feces dust, feathers and feather parts, renders conventional metal heat recovery systems unsatisfactory for poultry barns. Conventional heat recovery systems with high efficiency metal interfaces quickly build up a layer of dirt and grime from airborne dust, feces dust, feathers and feather parts, and even fly manure. This is especially true of conventional heat recovery units that use closely spaced fins to more efficiently translate the heat from one air stream to another. The buildup of grime and impurities, in turn, corrodes the surface area of conventional heat recovery systems which lowers the heat exchange efficiency, results in reduced air flow, and in some cases, can even cause air flow blockages. 
         [0023]    Meat poultry is raised in flocks consisting of birds of the same age. Hatchlings are introduced into a barn at a young age, generally in sufficient quantities to populate the entire barn. In many operations, the birds remain together for approximately five to eight weeks—the time it takes to reach marketable weight and size. To avoid propagating disease from one flock to the next, farmers thoroughly clean out the poultry barn from top to bottom after a flock is sold out of it. The cleaning typically is done by scrubbing and using high pressure water streams to remove viruses, bacteria, fungi, and parasites. In addition the post-flock cleaning generally involves the use of strong soaps and chemical solvents such as Stalosan F, Net Tex Viratec, Poultry Shield, and other such commercially available poultry barn cleaners known to those of ordinary skill in the art. Commercial poultry barn cleaning agents typically include one or more of the following types of disinfectants in various concentrations: aldehydes (e.g., formalin, formaldehyde, glutaraldehyde); chlorine-releasing agents (e.g., sodium hypochlorite, chlorine dioxide, sodium dichloroisocyanurate, chloramine-T); iodophors (e.g., povidone-iodine, poloxamer-iodine); phenols and bis-phenols (e.g., triclosan and hexachlorophene); quaternary ammonium compounds and peroxygens (e.g., hydrogen peroxide and peracetic acid). 
         [0024]    The thorough post-flock clean is performed to kill any viruses, bacteria, fungi, and parasites present in the poultry barn after the flock is sold. An attempt to use a conventional metallic heat recovery system would prove problematic in view of the rigorous post-flock poultry barn cleaning. Many of the aforementioned chemical solvents and disinfectants used to clean poultry barns are corrosive to metals used in conventional metallic heat recovery systems. Moreover, in addition to corrosion caused by the chemical cleaners and disinfectants, conventional metallic heat recovery systems would tend to corrode over time due to the pollutants that are specific to the meat poultry industry—that is, due to the feces dust, feathers and feather parts from a poultry flock. Once a conventional metallic heat recovery system begins to corrode it becomes nearly impossible to clean it sufficiently for the purposes of a commercial meat poultry barn. The one known commercial alternative would be to use conventional metallic heat recovery systems constructed of stainless steel. This, however, would be cost prohibitive and impractical for a commercial meat poultry operation. Stainless steel is quite expensive and would be difficult to work with in order to tailor fit it to a particular poultry barn. 
         [0025]    To avoid the drawbacks of conventional systems, various embodiments disclosed herein include configurations that minimize the effect of polluted poultry barn air including feathers. Moreover, the various embodiments may be configured from plastics, polymers or other such synthetic materials that are less susceptible to dirt, grime and feather buildup than metal surfaces. For example, some embodiments are constructed partially, or wholly from non-metallic synthetic materials such as high-density polyethylene (HDPE). Other suitable synthetic materials include polyvinyl chloride (PVC), polypropylene, or medium-density polyethylene (MDPE)), polystyrene, or other such non-metallic synthetic materials. The various embodiments of the heat recovery units are constructed from non-metallic synthetic materials that are also resistant to rust and corrosion caused by chemical poultry barn cleaners and disinfectants. Finally, the design of the various embodiments features removable access panels that cover access holes, or doorways, to facilitate cleaning the waste air output paths. 
         [0026]      FIG. 1A  depicts a tube bundle cell  100  of a heat recovery unit according to a first embodiment. The tube bundle cell of this embodiment includes a predetermined number of non-metallic synthetic tubes  101  arranged substantially parallel to each other. By “substantially parallel” it is meant that the largest distance between the two tubes is not more than double the average distance between the two tubes. In this embodiment the tubes  101  are configured in a symmetrical honeycomb pattern. In other embodiments the tubes  101  may be arranged in an elongated honeycomb pattern—that is, vertically elongated with fewer tubes spaced out farther apart in each column or else horizontally elongated with the columns of tubes being spaced farther apart. An elongated honeycomb pattern may allow a brush, pressured flushing jet, or other cleaning tools, to be inserted between the columns of tube (or rows of tubes), thus facilitating the cleaning of the tubes  101 . In other embodiments the tubes  101  may be arranged in various geometric patterns, or randomly, so long as there is space between the tubes  101  sufficient for waste air from the poultry barn to pass in the direction  103  between the tubes  101 . Clean air headed into the barn passes insides the tubes  101  in direction  105  (or in some instances, in the opposite direction of  105 ). 
         [0027]    The tubes  101  may be arrange at varying distances apart, depending upon the particularities of the installation. ( FIG. 2B  depicts the tube spacing  253 .) For example, in some embodiments using relatively small tubes the outer surfaces of the tubes may be spaced as closely together as ⅛ inches, on average. In other embodiments using larger tubes the tube spacing may be as great as 6 inches apart, on average. The tube spacing is often referred to in terms of the average tube spacing being within a given range, for example, any range within the minimum spacing distance of ⅛ inches to the maximum spacing distance of 6 inches, e.g., an average spacing distance of 0.9 inches to 1.1 inches, 0.65 to 0.85 or 1.5 inches to 2.25 inches, or other like ranges within the minimum and maximum specified above. In a typical installation it is more common for the tube spacing to be, on average, within the range of ½ inches to 2 inches, on average. For example, an average tube spacing—that is, the distance between the outer surface of two adjacent tubes—is ¾ inches. 
         [0028]    In some embodiments the tubes  101  are arranged such that there is no straight through path for the outgoing waste air to pass in direction  103  without contacting, or flowing around, at least some of the tubes  101 . For example, in the honeycomb pattern depicted in  FIG. 1A  the air must curve somewhat to flow between any two given tubes and then either above or below the next tube in the outgoing waste air output path. This is because for any two given consecutive tubes  101  in any particular column, there is a tube in the adjacent column aligned horizontally (in direction  103 ) within the gap between the two given consecutive tubes  101 . Providing a path where the air must travel around the various tubes in order to flow in a direction  103  along the outgoing waste air output path ensures that the outgoing air will either contact or flow around the tubes, thus more efficiently passing its heat to the tubes, and in turn, to the incoming cold air within the tubes  101 . In other embodiments the tubes  101  are arranged in straight rows as shown in  FIG. 1C , rather than arranging the tubes in a honeycomb pattern or otherwise being offset from one column of tubes to the next. The straight-row arrangement of  FIG. 1C  provides an unobstructed waste air output path through the heat recovery unit, thus reducing the pressure needed to drive output waste air through the system. As a result, a smaller output fan may be used in these embodiments featuring an unobstructed output waste air output path. 
         [0029]    The tube bundle cell  100  includes two parallel side panels  107  and  109 . Each of the side panels  107  and  109  has an outer face defining the outside of the tube bundle cell  100  and an inner face, with the tubes  101  spanning from the inner face of side panel  107  to the inner face of side panel  109 . The side panels  107  and  109  each have holes from the outer face through to the inner face, each hole corresponding to one of the tubes  101 . In the embodiment of  FIG. 1A  clean air travels in direction  105 , passing through a hole in side panel  107 , through the tube  101  aligned with the hole, and out of a corresponding hole in side panel  109 . In the embodiment depicted in  FIG. 1A  the tubes  101  are straight along the direction that the clean air travels, that is, direction  105 . However, in alternative embodiments the tubes  101  may be curved, angled, or otherwise shaped in a manner that is not straight. 
         [0030]    In the embodiment depicted in  FIG. 1A  the tubes  101  have a circular cross-section.  FIG. 1B  depicts a sampling of some of the different cross-sections of tubes that can be used in various embodiments. In some embodiments the tubes may have an elliptical cross-section  115 , an elongated oval cross-section  117 , a square cross-section or diamond cross-section  119 . In addition, the tubes may be oriented with the elliptical cross-section  115  or elongated oval cross-section  117  positioned in any direction rather than with up/down or side-to-side. Various other embodiments may be implemented using a non-symmetrical cross-section, or other shaped cross-section as would be known to those of ordinary skill in the art. The tubes  101  are typically fastened to each of the side panels  107  and  109  in a manner that is substantially airtight to create a fresh air input path for the fresh incoming air and prevent the outgoing air from leaking back into the barn. By “substantially airtight” it is meant that a stream of air blown at a pressure of 0.2 inch of water column into the holes of side panel  107 , pass through the tubes  101 , and exit the corresponding holes of panel  109  with less than 10% leakage of the air. In some embodiments the tubes  101  are fastened to each of the side panels  107  and  109  by heating the respective pieces and pressing them together to form a substantially airtight seal. That is, for selected non-metallic materials such as polyethylene (PE), a thermal fusion method can be used to connect the tubes  101  to the side panels  107  and  109 . 
         [0031]    Each of the side panels  107  and  109  may be configured with a frame  111  around the outer edge. The frame  111  provides structural support and aids in sealing the side panels  107  and  109  when the tube bundle cell  100  is inserted into a heat recovery unit. In some embodiments the frame  111  is made of the same non-metallic synthetic material as the tubes  101 , while in other embodiments the frame may be made of metal or another material for increased structural support. In some embodiments the frame  111  may have a gasket-like material positioned near its edges to aid in making a substantially airtight seal when the tube bundle cell  100  is inserted into a heat recovery unit. 
         [0032]      FIG. 2A  depicts a top view of a first configuration of a heat recovery unit  200 . Fresh air—for example, air from outside a poultry barn—enters the heat recovery unit  200  at fresh air inlet  215 . This configuration of the heat recovery unit  200  has five tube bundle cells  201 ,  203 ,  205 ,  207  and  209 . Depending upon the requirements of the system, a heat recovery unit  200  may be configured with any number of tube bundle cells, for example, from one tube bundle cell to eleven or more tube bundle cells. The tube bundle cell  100  embodiment depicted in  FIG. 1A  is constructed with alternating columns of 21 tubes and 20 tubes, and has 349 tubes in total. Another embodiment has alternating columns of six tubes and five tubes, for a total of 61 tubes in each tube cell bundle. Depending upon the requirements of the implementation the number of tubes per tube bundle cell may vary from as few as three tubes to as many as ten thousand tubes. The number of tubes depends largely upon the size of the heat recovery unit, and the materials used to construct it. The tubes  101  can be as small as ⅛ inch outside diameter in some embodiments, while other embodiments may be constructed from tubes  101  of up to eight inches in diameter. 
         [0033]      FIG. 2B  depicts a top view of a single tube bundle cell  251 , and an oblique view of a tube bundle cell  261 . The tube bundle cell  261  is shown with only one frame  263 , although a tube bundle cell generally has two frames—one on either end of the tubes to keep the tubes in place. The frame also aids in providing a substantially airtight seal when the tube bundle cell  100  is inserted into a heat recovery unit. The embodiment depicted in  FIG. 2B  has only thirty three tubes per tube bundle cell, three columns of seven tubes each and two columns of six tubes. 
         [0034]    The tube bundle cells  201 - 209  are inserted into the heat recovery unit  200  via the access holes provided to receive the tube bundle cells. In some embodiments the access holes are located on top of the heat recovery unit  200 . The access holes are then covered with access panels to provide a substantially airtight seal. Each of the tube bundle cells  201 - 209  has an air entry compartment. For example, air flowing into the fresh air inlet  215  enters air entry compartment  221  which is associated with tube bundle cell  201 . The air flowing into air entry compartment  221  can enter any of the tubes of tube bundle cell  201 . In this way, if any of the tubes of tube bundle cell  201  becomes obstructed the air can simply flow through the other tubes at a slightly higher rate than if all tubes were completely unobstructed. 
         [0035]    Each air entry compartment has air dividers to contain the air flow and direct it from one tube bundle cell to the next. For example, air entry compartment  225  has air dividers  217  and  219 . These air dividers direct the air coming out of tube bundle cell  203  in the direction of the air and back into tube bundle cell  205 . The air divider  217  is configured with guide groove  213 . The first tube bundle cell  201  is held in place at one corner by guide groove  213 . Each of the tube bundle cells  201 - 209  is inserted through its respective access hole of the enclosure covering the heat recovery unit  200  so that the frames of the tube bundle cells line up with the guide grooves of the heat recovery unit&#39;s enclosure. The frames are dimensioned to fit snugly within the guide grooves so as to provide a substantially airtight seal. The frames slide into the guide groove  213  in a manner akin to a sliding glass window of a house sliding within its window frame. The tube bundle cells are arranged in sequence so as to create a substantially airtight fresh air input path through the tubes of the tube bundle cells. Insertion of the tube bundle cells in the groove guides of the enclosure also creates a waste air output path for the warm waste air to flow transversely through the spaces between the tubes of each tube bundle cell. 
         [0036]    The path of the air flow through the heat recovery unit  200  is as follows: The air flows through the tubes of one tube bundle cell and out into the air entry compartment of the next tube bundle cell, and then the air flows into the tubes of that next tube bundle cell and out into the air entry compartment of the next tube bundle cell. For example, the air flows through the tubes of tube bundle cell  201  and out into the air entry compartment  223  of tube bundle cell  203 . This allows the air to flow from tube bundle cell  201  in the direction of the arrows in air entry compartment  223  and then into tube bundle cell  203 . Routing air along the incoming fresh air path in this manner allows the colder incoming fresh air to cross the path of the heated outgoing waste air once for each tube bundle cells in the heat recovery unit  200 . For example, there are five tube bundle cells  201 - 209  arrange in sequence along the incoming fresh air input path: tube bundle cells  201 ,  203 ,  205 ,  207  and  209 . Since the waste air output path flows transversely through the spaces between the tubes of each tube bundle cell, each time the fresh air flows through the tubes of a tube bundle cell the fresh air input path is said to cross the waste air output path. This can be seen in  FIG. 2A . The waste air output path flows in direction  235  from filter  237  through the spaces between the tubes of each tube bundle cell and out of the heat recovery unit  200  near output fan  233 . The fresh air flows into the heat recovery unit  200  at fresh air inlet  215 , then back and forth through tube bundle cells  201 ,  203 ,  205 ,  207  and  209 , and out of the heat recovery unit  200  near input fan  231 . In this way, the fresh air is said to cross the path of the waste air five times—once for each of tube bundle cells  201 ,  203 ,  205 ,  207  and  209 . 
         [0037]    Once the fresh air has made its way through the sequence of tube bundle cells  201 - 209  it is blown by input fan  231  into the poultry barn fresh air vent system, or in some instances, directly into the poultry barn. Depending upon the specifics of the configuration the input fan  231  may instead be positioned at the beginning of the sequence of tube bundle cells  201 - 209 , just ahead of air entry compartment  221 . In other configurations the input fan  231  may be positioned at a point with the sequence of tube bundle cells  201 - 209 —for example, between tube bundle cell  207  and tube bundle cell  209  (or any other two consecutive tube bundle cells). The input fan  231  may be any of various types of fans such as a propeller blade fan, a squirrel cage fan (sometimes called a centrifugal fan), an axial fan (e.g., a vane_axial fan), or other like type of fan. In one embodiment a variable frequency drive (VFD) fan is used so that the volume of blown air can be adjusted to suit the parameters of the poultry barn. Alternatively, either a variable speed fan or a variable pitch axial (VPA) fan may be used, or any other type of adjustable rate fan as are known by those of ordinary skill in the art. 
         [0038]    The incoming fresh air flow is directed through the tube bundle cells  201 - 209  in order to heat the incoming fresh air. The source of heat is the outgoing, waste air from the poultry barn. Each of the tube bundle cells  201 - 209  serves as a heat exchanger between the cold, incoming air and the heated output waste air. Referring back to  FIG. 1A , the waste air is blown between the tubes of each tube bundle cell (e.g., in direction  103 ) while the incoming fresh air is routed through the tubes themselves (e.g. direction  105 ). Heat is exchanged each time the fresh air passes through one of the tube bundle cells  201 - 209 , acting to heat the incoming fresh air and cool down the outgoing waste air. The outgoing waste air passes through a filter  237  as it exits the poultry barn before passing through the tube bundle cells  201 - 209 . The filter  237  may be embodied as a reusable mesh grid filter that can be cleaned off and reused. Mesh grids, or screens, may be used to cover the fresh air inlet and/or the waste air inlet. For example,  FIG. 2A  depicts filter  237  positioned at the waste air inlet of embodiment  200 . In other embodiments the filter  237  is embodied as a replaceable paper filter akin to the filters used in home and commercial heating/cooling systems. Alternatively, the filter  237  may be a screen or grid that filters out at least some of the particles and features from the waste air, while serving the dual purpose of a safety screen covering the waste air inlet. In yet other embodiments the filter may be a liquid based filter that bubbles air through a layer of water or other liquid in order to capture and remove airborne particles. In some embodiments the filter  237  may be positioned at a different point in the output waste air flow, e.g., near the output by output fan  233 . In other embodiments the filter  237  may be omitted from the system. 
         [0039]    The filter  237  prevents expelling flies, dust, feathers and other airborne particles from the poultry barn. The filter  237  also aids in reducing the buildup of dirt, grime and feathers in the tube bundle cells  201 - 209 . The output waste air is pulled through waste air output path in direction  235  by output fan  233 . Depending upon the specifics of the poultry barn configuration, the output fan  233  may be the same size and/or type of fan as input fan  231 , or a different size and/or type of fan. Some embodiments are configured with a slightly larger input  231  than the output fan  233  so as to keep a slight amount of pressure in the poultry barn (or alternatively, the same sized fans are used with the input fan  231  being set to blow at a greater rate). Keeping a slight positive pressure in the poultry barn aids in preventing cold air from leaking into the barn, e.g., through gaps in the doors and windows of the barn. 
         [0040]    It should be noted that the stream of fresh input air passes through multiple, consecutive tube bundle cells  201 - 209 , with heat being exchanged each time the fresh air passes through one of the tube bundle cells  201 - 209 . Since the same stream of output waste air is blown through the output path, the output waste air cools somewhat as it passes through each consecutive tube bundle cells  201 - 209 . In the embodiment  200  depicted in  FIG. 2A  the output waste air enters the system at the right, near filter  237 , and exits the system at the left, near output fan  233 . On the other hand, the fresh input air enters the system depicted in the figure on the left, at air entry compartment  221 , and then exits the system towards the right, at input fan  231 . The effect of this orientation is that the hottest output waste air—the output waste air entering the system at filter  237 —exchanges heat with the fresh input air at its warmest point, that is, after the fresh input air has already passed through tube bundle cells  201 - 207 . The output waste air exiting the system at tube bundle cell  201  near the output fan  233  is at its coolest, having already passed through the other four tube bundle cells. Thus, the output waste air at its coolest exchanges heat with the fresh input air at its coolest point, that is, as the fresh input air enters the system at air entry compartment  221  which feeds into tube bundle cell  201 . Configuring the system in this manner of counter-current flow maintains a more consistent temperature differential between the input air stream and the output air stream. This provides a more even, efficient transfer of heat from the output air stream to the input air stream. In addition, minimizing the temperature differential between the input air stream flowing through the inside of the tubes and the output air stream flowing out around the tubes tends to reduce the structural strain due to material expansion and contraction caused by flowing hot and cold air. 
         [0041]    The outer walls of heat recovery unit  200  forming an enclosure  239  that may be insulated to prevent heat loss. In some embodiments the fans  231  and  233  are positioned within the insulated walls of heat recovery unit  200 . In other embodiments one or both of the fans  231  and  233  may be positioned outside the insulated walls of heat recovery unit  200 . For example, the output fan  233  may be positioned between the poultry barn and the heat recovery unit  200 , with an air duct connecting the barn, the output fan  233  and the heat recovery unit  200 . In such a configuration with the output fan  233  positioned between the poultry barn and the heat recovery unit  200  it is desirable to provide an insulated container for the fan  233  as well as an insulated duct connecting the components since the output air flowing into the fan  233  at that point contains a considerable amount of heat. However, if the output fan  233  is positioned after tube bundle cell  201  its container and venting does not need to be insulated since any residual heat in the air at that point will simply be released into the atmosphere. Similarly, if the input fan  231  is located between the heat recovery unit  200  and the poultry barn as shown in  FIG. 2A  it is desirable to provide the input fan  231  with an insulated container and insulated duct work. On the other hand, if the input fan  231  is configured outside the fresh air entry point of the heat recovery unit  200  then there is no need to insulate its container or duct work. 
         [0042]      FIG. 3  depicts an alternative configuration of the heat recovery unit. The tube bundles are parallel to each other, but the side panels are not perpendicular to tubes. This allows a different shape of air entry compartment. In  FIG. 2A  the air entry compartments (e.g., air entry compartment  221 ) are rectangular. But in the embodiment depicted in  FIG. 3  the air entry compartments (e.g., air entry compartment  321 ) are triangular in shape. This embodiment allows same amount of air pass through for a given pressure, but reduces the size of the unit by a small amount. 
         [0043]      FIG. 4  is depicts an oblique view of a heat recovery unit  400  according to various embodiments disclosed herein. The figure shows further details of the access holes and access panels covering the access holes. As shown in the figure the heat recovery unit  400  may be embodied with an access hole  411  through which a tube bundle cells may be inserted into the enclosure. The access holes are quite useful for accessing the waste air output path to perform the periodic cleaning that is required between flocks. Typically, each of the tube bundle cells has an access hole accessing it, and an associated access panel to cover the access hole. For example, in the embodiment depicted there is a tube bundle cell beneath each of the access panels  401 ,  403 ,  405 ,  407  and  409 . The fresh air input path is denoted by dotted line  425 , and travels from the fresh air inlet at arrow  419  to the fresh air outlet  417  which is typically connected to ventilation going into the poultry barn. The waste air output path travels from the waste air inlet at arrow  421  to the waste air outlet  423 . 
         [0044]    The air entry compartment  413  receives input air from the tube bundle cell beneath access panel  403  and routes it back into the tube bundle cell beneath access panel  401 . 
         [0045]    In some embodiments the access holes may be configured on the sides of the heat recovery unit  400  rather than the top. The heat recovery unit  400  of  FIG. 4  is configured with guide grooves which line up with the access holes to receive the frames of the tube bundle cells. This allows the tube bundle cells (e.g.,  201 - 209  of  FIG. 2A ) to be installed into the heat recovery unit  400  through the access holes  401 ,  403 ,  405 ,  407  and  409 . 
         [0046]    The enclosure of the heat recovery unit  400 , that is, the framework and outer layer of panels and coverings, may, in some embodiments, be configured as modular units that can be taken apart for transportation and then assembled on site. For example, in some embodiments the various air entry compartments may be removed, revealing portions of the enclosure covering each tube bundle cell that can be taken apart for repair or transportation. The modular configuration also allows the heat recovery unit  400  to be reconfigured in any number of sizes—that is, with any number of tube bundle cell—in order to configure the heat recovery unit  400  to closely match the needs of a given poultry growing operation. 
         [0047]      FIG. 5  is an oblique cut away view of a vertical installation embodiment heat recovery unit. In some instances the space constraints of the poultry farm make it desirable to implement the heat recovery unit with a minimal horizontal footprint. For example, it is sometimes the case where the poultry barn sits next to a road, another building, or other such obstruction and there simply isn&#39;t room to lay the heat recovery unit in a horizontal configuration. In other instances, there is plenty of room to implement either a horizontal configuration or a vertical configuration, but it is desired to pull in fresh air and/or vent the waste air at a point somewhat above ground level. In both of these situations the vertical oriented embodiment  500  of  FIG. 5  provides an apt solution. 
         [0048]    In the vertical installation of  FIG. 5  the fresh input air enters fresh air inlet  501  in direction  503 . The input path is defined by dotted line  505 . As shown in the figure, the fresh input air passes through the top tube bundle cell, into entry compartment  507 , into the middle tube bundle cell, into entry compartment  509 . Upon passing through entry compartment  509  the fresh input air passes through bottom tube bundle cell  511  and out of the vertical installation heat recovery unit  500  into the poultry barn. ( FIG. 5  shows details of the tubes of bottom tube bundle cell  511 , for the sake of illustration.) In the embodiment depicted the output waste air enters the bottom of vertical installation heat recovery unit  500  and travels transversely along the output waste air path  513  through the spaces formed between the tubes of the three tube bundle cells. In some vertical installation embodiments the heat recovery unit  500  is mounted on legs or supporters  515  so as to keep the unit off the ground so waste air can be directed into the unit from beneath. In other configurations the waste air inlet may be configured from the side of heat recovery unit  500  rather than from the bottom. Although the embodiment  500  is shown with three tube bundle cells, in practice this configuration may be constructed with any number of tube bundle cells so as to suit the particular needs of a given poultry barn, e.g., five tube bundle cells, eight tube bundle cells, fifteen tube bundle cell, etc. 
         [0049]      FIG. 6  is a flowchart depicting a method of using the heat recovery unit according to various embodiments disclosed herein. The method begins at block  601  and proceeds to  603  where an enclosure is configured to receive and hold the plurality of tube bundle cells. In block  605  two side panels are provided for each tube bundle cell. Although various embodiments feature a wide range of the number of holes, the embodiment illustrated in  FIG. 6  has at least 61 holes each side panel. In block  607  tubes are fastened between corresponding holes and secured in a substantially airtight manner. In block  609  a frame is provided around the edges of each side panel. 
         [0050]    In block  611  guide grooves are provided in the enclosure in a position which enables the guide grooves to receive the side panels as they are inserted through the various access holes. The frames mate up with guide grooves when the tube bundle cells are inserted into an enclosure, creating a substantially airtight fresh air input path and waste air output path. In block  613  each of the tube bundle cells is inserted into the enclosure, connecting them sequentially to provide a substantially airtight fresh air path. In block  615  an input fan is provide for the fresh air path and an output fan for the waste air path. In block  617  a vent from inside the poultry barn is connected to the waste air path, and an input inlet is opened to the fresh air path. In block  619  the output fan is turn on to vent heated waste air from inside the poultry barn to the waste air path. In block  621  In block  619  the input fan is turned on to route fresh air into the input inlet and through the tubes along the to the fresh air path, thus heating the input air by capturing heat from the waste air being expelled from the poultry barn. 
         [0051]    Various activities may be included or excluded as described above, or performed in a different order, while still remaining within the scope of at least one of the various embodiments. For example, block  603  describes providing an enclosure configured to receive and hold the plurality of tube bundle cells while blocks  605 - 609  describe providing the side panels, fastening the tubes and providing a frame around each of the tube bundle cells. In some instances the activities of blocks  605 - 609  can be performed prior to the activities of block  605 . Other steps or activities of the methods disclosed herein may be omitted or performed in a different manner while remaining within the intended scope of the claimed embodiments and embodiments disclosed herein. 
         [0052]      FIG. 7  illustrates a method of heat forming the tube bundle cells from tubes and pairs of side panels. As shown in the figure the tubes  705  to be formed into bundles are placed in a tube holder template  701  configured to hold the tubes  705  in the proper position and spacing for a tube bundle cell. The tube holder template  701  is maneuvered to hold the tubes  705  over a tray of melted plastic  703  (or other material being used) for the side panels. Typically, the plastic is heated beyond its melting point, either in the pan or in a heating receptacle and then poured in the pan. The tube holder template  701  holding the tubes  705  is then lowered to press the tubes  705  firmly through the melted plastic  703  until the tubes  705  touch the bottom of the tray through the melted plastic  703 . This action typically drives some of the plastic up into the tubes  705 , forming plugs within the tubes. The plugs must then be removed to complete the process of heat forming the tube bundle cell. One way of doing this is to wait until the plugs have hardened, and then dig the plugs out of each tube. Another method is to used compressed air to blow the plugs out of each tube, either while the plastic  709  remains somewhat soft or after it has cooled down and is easier to work with. Yet another method is to insert plugs  707  of wood, metal or another substance into each tube before pressing the tubes  705  into the melted plastic  703 . In this way the wood or metal plugs  707  prevent melted plastic from entering the tubes, and the metal or wood plugs  707  can easily be removed once the tubes  705  have been bonded with the melted plastic  709 . Once the plugs  707  are removed a small amount of waste plastic may need to be trimmed away from the holes to ensure unobstructed passages for the fresh air to be routed through the tubes  705 . 
         [0053]    The various embodiments are discussed throughout this disclosure in terms of a waste heat recovery system for a livestock poultry barn for illustrative purposes. In various embodiments the waste heat recovery system may be implemented in other types of livestock barns, including but not limited to cattle barns, hog barns, sheep barns, horse barns or other types of livestock as are known by those by ordinary skill in the art. 
         [0054]    Air flowing “through” a tube enters one end of the tube, passes through the length of the tube, and exits the other end of the tube. Air passing “transversely” through a space formed between two tubes (which are spaced apart, e.g., parallel) passes over the outer surfaces facing each other of the two tubes, and in between the respective endpoints of the two tubes. 
         [0055]    The term “substantially airtight gaseous path” as this term applies to two or more interconnected parts means that a gas such as air can flow through the parts at an input insertion pressure of 2 PSI without more than 10% of the gas (e.g., air) leaking out before reaching the output of the interconnected parts. For example, given a continuous flow of air into the input of two interconnected parts forming a substantially airtight gaseous path, if 100 cubic meters of air is injected at 2 PSI into the input, then at least 90 cubic meters of air will flow from the output of the two interconnected parts. 
         [0056]    The term “gaseous communication” as this term is applied herein to interconnected parts means that a gas such as air can flow through two interconnected parts. For example, in an embodiment disclosed herein with a fresh air input in gaseous communication with a fresh air output, there is a gaseous pathway through which air may flow. 
         [0057]    The description of the various embodiments provided above is illustrative in nature inasmuch as it is not intended to limit the invention, its application, or uses. Thus, variations that do not depart from the intents or purposes of the invention are intended to be encompassed by the various embodiments of the present invention. Such variations are not to be regarded as a departure from the intended scope of the present invention.