Patent Publication Number: US-6988545-B2

Title: Heat exchanger systems

Description:
The present application is related to and claims priority from prior provisional application Ser. No. 60/443,212 filed Jan. 27, 2003, entitled “HEAT EXCHANGE SYSTEM”, the contents of which are incorporated herein by this reference and are not admitted to be prior art with respect to the present invention by the mention in this cross-reference section. The present application is also related to applicant&#39;s U.S. Pat. No. 4,676,007 issued Jun. 30, 1987, entitled “HEAT EXCHANGER FOR GRAIN ELEVATORS OR BINS” and applicant&#39;s U.S. Pat. No. 4,821,428 issued Apr. 18, 1989, entitled “HEAT EXCHANGER FOR GRAIN ELEVATORS OR BINS”, the contents of which are herein incorporated by reference as supporting background and are not admitted to be prior art with respect to the present invention by their mention in this section. 
    
    
     BACKGROUND 
     This invention relates to heat exchanger systems. More particularly, this invention relates to providing heat exchanger systems for improved drying of agricultural products, for example, prunes, and fabrics, for example laundry, using a system of heat recovery. 
     Typically, tremendous amounts of heat energy are wasted in conventional crop drying techniques. Conventional drying processes use large quantities of energy to heat cold ambient air to the temperature required to dry the crop. Much of this heat/energy is wasted by the direct discharge of the hot exhaust air exiting the dryer.  FIG. 1  is a diagrammatic sectional view of a conventional crop dryer  104 . Typically, crop dryer  104  comprises an enclosed tunnel  101  through which heated air  103  passes to dry crop  110 , as shown for, typically, the drying of prunes. In existing systems, energy is wasted by directly discharging moist, heated moist, heated exhaust air  105  from enclosed tunnel  101 , as shown. Users of commercial and household laundry dryers suffer from the same waste heat losses. A need exists for a system that utilizes the large amount of thermal energy typically discarded with the exhaust air as waste. 
     OBJECTS OF THE INVENTION 
     A primary object and feature of the present invention is to provide heat exchanger systems to address the above-mentioned problems and to meet the above-mentioned needs. 
     A further primary object and feature of the present invention is to provide heat exchanger systems adaptable to a variety of crop dryers, laundry dryers, and other devices producing dryer exhaust containing waste heat. 
     A further primary object and feature of the present invention is to provide heat exchanger systems having heat-transfer conduits having large heat-transfer surface areas 
     A further primary object and feature of the present invention is to provide heat exchanger systems having and arrangement of square heat-transfer conduits having effective flow characteristics for drying applications. 
     A further primary object and feature of the present invention is to provide such a system that is efficient, inexpensive, and handy. Other objects and features of this invention will become apparent with reference to the following descriptions. 
     SUMMARY OF THE INVENTION 
     In accordance with a preferred embodiment hereof, this invention provides a heat exchanger system, relating to transferring waste heat from a stream of exhaust air produced in a dryer to a stream of fresh air directed to flow into the dryer, comprising: heat transfer means for substantially convectively transferring the waste heat to the stream of fresh air, comprising array means for arraying substantially vertical, substantially parallel heat-transfer conduit means for internally conducting segregated portions of the stream of exhaust air, wherein such heat-transfer conduit means comprise thermally-conductive conduit wall means for conducting heat from the segregated portions of the stream of exhaust air to the stream of fresh air, wherein such heat-transfer conduit means comprise fluid-dynamic means for influencing dynamics of the fresh air, further wherein such fluid-dynamic means comprises heat-transfer conduit means having substantially square cross-sections; and structure means for structuring a relationship between such heat transfer means and the dryer. 
     Moreover, it provides such a heat exchanger system, wherein such structural means comprises: base support plate means for supporting such heat transfer means; top support plate means for supporting such heat transfer means; and interconnection means for interconnecting at least two of such heat transfer means, such base support plate means, such top support plate means, and the dryer. Additionally, it provides such a heat exchanger system, wherein such fluid-dynamic means further comprises heat-transfer conduit means oriented to have one corner of such square cross-section facing the general direction of flow of the stream of fresh air through such heat transfer means. Also, it provides such a heat exchanger system, wherein such array means comprises staggered alternating rows. 
     In addition, it provides such a heat exchanger system, wherein such array means has dimensional relationship means comprising: external side width of such square cross section of such heat-transfer conduit means; and uniform side-to-side spacing apart of about one-half of such external side width. And, it provides such a heat exchanger system, wherein such thermally-conductive conduit wall means comprise conduit walls about 0.018″ thick. Further, it provides such a heat exchanger system, wherein such thermally-conductive conduit wall means comprise aluminum. Even further, it provides such a heat exchanger system, wherein such heat-transfer means further comprises side constraining means for constraining the flow of the fresh air over such heat-transfer conduit means to move between first and second opposing sides of such heat-transfer means. 
     In accordance with another preferred embodiment hereof, this invention provides a heat exchanger system, related to transferring waste heat from a stream of exhaust air produced in a dryer to a stream of fresh air directed to flow into the dryer, comprising: at least one heat transferor structured and arranged to substantially convectively transfer the waste heat to the stream of fresh air, comprising at least one array structured and arranged to array substantially vertical, substantially mutually parallel plurality of heat-transfer conduits adapted to internally conduct segregated portions of the stream of exhaust air, wherein at least one heat-transfer conduit of such plurality of heat-transfer conduits comprises at least one thermally-conductive conduit wall structured and arranged to conduct heat from the segregated portions of the stream of exhaust air to the stream of fresh air, wherein such at least one heat-transfer conduit comprises at least one fluid-dynamic shape for influencing dynamics of the fresh air, further wherein such fluid-dynamic shape comprises at least one substantially square cross-section; and at least one structure configured to maintain at least one structural relationship between such heat transferor and the dryer. 
     Moreover, it provides such a heat exchanger system, wherein such structure comprises: at least one base support plate structured and arranged to support lower ends of such heat transferor; at least one top support plate structured and arranged to support upper ends of such heat transferor; and at least one interconnector structured and arranged to interconnect at least two of such heat transferor, such at least one base support plate, such at least one top support plate, and the dryer. Additionally, it provides such a heat exchanger system, wherein such at least one fluid-dynamic shape further comprises at least one heat-transfer conduit oriented to have one corner of such square cross-section facing the general direction of flow of the stream of fresh air through such heat transferor. Also, it provides such a heat exchanger system, wherein such at least one array comprises staggered alternating rows. 
     In addition, it provides such a heat exchanger system, wherein such at least one array has at least one dimensional relationship comprising: external side width of such at least one square cross section of such at least one heat-transfer conduit; and uniform side-to-side spacing apart of such plurality of such heat-transfer conduits of about one-half of such external side width of such at least one square cross section of such at least one heat-transfer conduit. And, it provides such a heat exchanger system, wherein such external side width is one-and one-half inches. Further, it provides such a heat exchanger system, wherein such at least one thermally-conductive conduit wall comprises at least one conduit wall about 0.018″ thick. Even further, it provides such a heat exchanger system, wherein such at least one thermally-conductive conduit wall comprises aluminum. Moreover, it provides such a heat exchanger system, wherein such heat-transferor further comprises at least one side constraint structured and arranged to constrain the flow of the fresh air over such heat-transfer conduits to move between first and second opposing sides of such heat-transferor. 
     In accordance with another preferred embodiment hereof, this invention provides a heat exchanger system, relating to transferring waste heat from a stream of exhaust air produced in a dryer to a stream of fresh air directed to flow into the dryer, comprising: a retriever comprising at least one array of at least one plurality of substantially mutually parallel, substantially vertical heat-transfer conduits having square cross-sections arrayed in alternating staggered rows relative to a perpendicular to the general direction of the flow of the stream of fresh air into the dryer, wherein each heat-transfer conduit is oriented to have one corner facing in the general direction of the flow of the stream of fresh air into the dryer; and at least one structure adapted to support such at least one array of such at least one plurality of heat-transfer conduits transverse to the flow of the stream of fresh air into the dryer. 
     Additionally, it provides such a heat exchanger system, further comprising at least one structure for assisting receiving the stream of exhaust air internal to such at least one heat-transfer conduit of such retriever. Also, it provides such a heat exchanger system, further comprising at least one retriever adapted to be integrated with at least one pre-existing particular dryer, wherein such at least one retriever further comprises such at least one structure integrated with such at least one array of heat-transfer conduits. In addition, it provides such a heat exchanger system, comprising such at least one retriever integrated with such at least one particular pre-existing dryer. And, it provides such a heat exchanger system, further comprising such at least one retriever integrated with at least one particular dryer. 
     In accordance with another preferred embodiment hereof, this invention provides a heat exchanger. system, relating to transferring waste heat from a stream of exhaust air produced in a dryer to a stream of fresh air directed to flow into the dryer, comprising the steps of: pre-configuring, responsive to customer requirements, at least one retriever comprising at least one array of at least one plurality of substantially mutually parallel, substantially vertical heat-transfer conduits having square cross-sections arrayed in alternating staggered rows relative to a perpendicular to the general direction of the flow of the stream of fresh air into the dryer, wherein each heat-transfer conduit is oriented to have one corner facing in the general direction of the flow of the stream of fresh air through such retriever. 
     Further, it provides such a heat exchanger system, wherein the step of pre-configuring comprises the step of determining at least one size requirement for such at least one array. Even further, it provides such a heat exchanger system, wherein the step of pre-configuring comprises the step of perforating at least one plate with at least one pattern of a plurality of square perforations in staggered rows, each square perforation oriented cornerwise to the general direction of flow of the fresh air over the plate, responsive to such at least one size requirement. Even further, it provides such a heat exchanger system, further comprising the step of attaching such plurality of heat transfer conduits to such at least one plate, wherein each such heat transfer conduit of such plurality of heat transfer conduits is aligned and oriented to one perforation of such plurality of perforations. 
     Even further, it provides such a heat exchanger system, further comprising the step of attaching structural elements to at least such at least one plate, wherein such structural elements are structured and arranged to at least maintain structural integrity of such retriever. Even further, it provides such a heat exchanger system, further comprising the step of installing such retriever in at least one dryer. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a diagrammatic sectional view of a conventional crop dryer. 
         FIG. 2  is a diagrammatic sectional view of a crop dryer utilizing a heat exchanger system according to a preferred embodiment of the present invention. 
         FIG. 3  is a perspective view in partial section illustrating a crop dryer utilizing the heat exchanger system according to a preferred embodiment of the present invention. 
         FIG. 4  is a perspective view of the heat exchanger system according to the embodiment of  FIG. 3 . 
         FIG. 5A  is a top view of the base plate of the heat-exchanging retriever illustrating a typical layout of holes for receiving heat-exchanging conduits according to the embodiment of  FIG. 3 . 
         FIG. 5B  is a side view of a portion of the base plate of  FIG. 5A , a portion of a top plate, and a heat-transfer conduit connected there between by end-flaring according to a preferred embodiment of the present invention. 
         FIG. 6  is a side elevation diagrammatic view of a heat-exchanging retriever adapted for use with a laundry dryer according to a preferred embodiment of the present invention. 
         FIG. 7  is a flowchart of a heat exchanger system process according to a preferred embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT OF THE INVENTION 
       FIG. 2  is a diagrammatic sectional view of crop dryer  104  utilizing heat exchanger system  100  according to a preferred embodiment of the present invention, as shown. Preferably, retriever  102  of heat exchanger system  100  acts as a pre-heater, returning wasted heat from a stream of moist, heated exhaust air  105  to the input stream of fresh air  116  that then enters the crop dryer  104  as pre-heated intake air  108 , as shown (at least herein embodying heat transfer means for substantially convectively transferring the waste heat to the stream of fresh air; and at least herein embodying at least one heat transferor structured and arranged to substantially convectively transfer the waste heat to the stream of fresh air). Preferably, burner  106  of crop dryer  104  adds thermal energy to the pre-heated intake air  108  to achieve the temperature for the dryer air  103  required to dry crop  110 , as shown (at least one retriever adapted to be integrated with at least one pre-existing particular dryer; and at least herein embodying retriever integrated with said at least one particular pre-existing dryer; and at least herein embodying retriever integrated with at least one particular dryer). 
     Heat exchanger system  100  preferably returns much of the wasted heat to crop dryer  104 , as shown. Upon reading the teachings of this specification, those with ordinary skill in the art will now understand that, under appropriate circumstances, considering such issues as dryer configuration, required flow rates, convenience, economics, user preference, etc., other positions for retriever  102 , such as an external position connected by ductwork, variation of position within crop dryer  104 , etc., may suffice. 
       FIG. 3  is a perspective view in partial section illustrating crop dryer  104  utilizing heat exchanger system  100  according to a preferred embodiment of the present invention. Preferably, before moist, heated exhaust air  105  is allowed to leave dryer system  100 , moist, heated exhaust air  105  enters retriever  102 , preferably containing an array of about 600 heat-exchanging conduits  112  about six feet in length, as shown (at least herein embodying array means for arraying substantially vertical, substantially parallel heat-transfer conduit means for internally conducting segregated portions of the stream of exhaust air; and at least herein embodying at least one array structured and arranged to array substantially vertical, substantially mutually parallel plurality of heat-transfer conduits adapted to internally conduct segregated portions of the stream of exhaust air). Walls of the heat-exchanging conduits  112  are heated as moist, heated exhaust air  105  is exhausted through them into the environment as cooled exhaust air  114 , as shown. Preferably, fresh air  116  entering crop dryer  104  is pulled across the exterior surfaces of the walls of the heated heat-exchanging conduits  112 , thereby producing pre-heated air  108  to reduce the required energy input required at burner  106 , as shown (at least herein embodying thermally-conductive conduit wall means for conducting heat from the segregated portions of the stream of exhaust air to the stream of fresh air; and at least herein embodying at least one thermally-conductive conduit wall structured and arranged to conduct heat from the segregated portions of the stream of exhaust air to the stream of fresh air). Upon reading the teachings of this specification, those with ordinary skill in the art will now understand that, under appropriate circumstances, considering such issues as dryer configuration, type of crop or material to be dried, temperature requirements, required flow rates, convenience, economics, user preference, etc., other numbers of heat-exchanging conduits  112  and other lengths of heat-exchanging conduits  112  for retriever  102 , such as longer or shorter heat-exchanging conduits  112  adapted to a particular dryer configuration or more or fewer heat-exchanging conduits  112  adapted to flow rates and temperature requirements, etc., may suffice. 
       FIG. 4  is a perspective view of the heat exchanger system  100  according to the embodiment of  FIG. 3 . Preferably, a structure  120  and  126 , such as rigid steel framing, supports retriever  102  in the stream of fresh air  116 , as shown (at least herein embodying structure means for structuring a relationship between said heat transfer means and the dryer; and at least herein embodying at least one structure configured to structure a relationship between said heat transferor and the dryer). Preferably, structure  120  includes flow constraints  118  and  119 , such as canvas sidewalls, as shown (at least herein embodying side constraining means for constraining the flow of the fresh air over said heat-transfer conduit means to move between first and second opposing sides of said heat-transfer means; and at least herein embodying at least one side constraint structured and arranged to constrain the flow of the fresh air over said heat-transfer conduits to move between first and second opposing sides of said heat-transferor). Preferably, structure  126  includes a frame for receiving the retriever  102 , as shown (at least herein embodying structure means for structuring a relationship between said heat transfer means and the dryer; and at least herein embodying at least one structure adapted to support said at least one array of said at least one plurality of heat-transfer conduits transverse to the flow of the stream of fresh air into the dryer). In an alternate embodiment, retriever  102  is preferably supported, at least partially, by pre-existing structure of the crop dryer  104 , as shown in  FIGS. 1–2  (at least herein embodying at least one retriever adapted to be integrated with at least one pre-existing particular dryer; and at least herein embodying retriever integrated with said at least one particular pre-existing dryer; at least herein embodying retriever integrated with at least one particular dryer). 
     Preferably, some flow constraints are integral to the crop dryer  104 , such as steel-framed pivoting canvas doors  122  which provides crop  110  access to crop dryer  104  and directs air into retriever  102 , as shown (at least herein embodying structure means for structuring a relationship between said heat transfer means and the dryer; and at least herein embodying at least one structure configured to structure a relationship between said heat transferor and the dryer). In some alternate embodiments, steel-framed pivoting canvas doors  122  may be integral to structure  120 , structure  126  or to retriever  102  (at least herein embodying said at least one structure integrated with said at least one array of heat-transfer conduits). In such an alternate embodiment, the canvas is preferably a PVC coated fabric having a substantially polyester plain weave substrate. Upon reading the teachings of this specification, those with ordinary skill in the art will now understand that, under appropriate circumstances, considering such issues as dryer configuration, available installation sites, type of crop  110  or material to be dried, temperature requirements, required flow rates, convenience, economics, user preference, etc., other adapted structures for supporting the retriever  102  in the stream of fresh air  116 , such as more or less structure  120 , adapted configurations and sizes of flow constraints  118 ,  119 , and  122 , or various adapted materials for the flow constraints  118 ,  119 , and  122  or structure  120 , etc., are included within various embodiments of the present invention adapted to specific dryer-related requirements. 
       FIG. 5A  is a top view of support plate  124  used as the base plate  124   a  and the top plate  124   b  of the heat-exchanging retriever  102  illustrating an exemplary layout and orientation of openings  113  for receiving the array of heat-exchanging conduits  112  according to the preferred embodiment of  FIG. 3 , as shown (at least herein embodying base support plate means for supporting said heat transfer means; and at least herein embodying top support plate means for supporting said heat transfer means; and at least herein embodying at least one base support plate structured and arranged to support lower ends of said heat transferor; and at least herein embodying at least one top support plate structured and arranged to support upper ends of said heat transferor). Preferably, the array of heat-exchanging conduits  112  has staggered alternating rows of square heat-exchanging conduits  112  each oriented to have a corner facing the general direction of the flow of fresh air  116  through the retriever  102 , as shown (at least herein embodying fluid-dynamic means for influencing dynamics of the fresh air, further wherein said fluid-dynamic means comprises heat-transfer conduit means having substantially square cross-sections; and at least herein embodying heat-transfer conduit means oriented to have one corner of said square cross-section facing the general direction of flow of the stream of fresh air through said heat transfer means; and at least herein embodying staggered alternating rows; and at least herein embodying at least one fluid-dynamic shape for influencing dynamics of the fresh air, further wherein said fluid-dynamic shape comprises at least one substantially square cross-section; and at least herein embodying at least one heat-transfer conduit oriented to have one corner of said square cross-section facing the general direction of flow of the stream of fresh air through said heat transferor; and at least herein embodying at least one array of at least one plurality of substantially mutually parallel, substantially vertical heat-transfer conduits having square cross-sections arrayed in alternating staggered rows relative to a perpendicular to the general direction of the flow of the stream of fresh air into the dryer, wherein each heat-transfer conduit is oriented to have one corner facing in the general direction of the flow of the stream of fresh air into the dryer). Preferably, the heat-exchanging conduits  112  are frictionally retained within support plates  124   a  and  124   b  by end-flaring of the aluminum heat-exchanging conduits  112 , as shown in  FIG. 5B  (at least herein embodying the step of attaching said plurality of heat transfer conduits to said at least one plate). Structure  120  further supports plates  124   a  and  124   b  and interconnects plates  124   a  and  124   b  in relation to the array of heat-exchanging conduits  112 , as shown (at least herein embodying interconnection means for interconnecting said heat transfer means, said base support plate means, and said top support plate means; and at least herein embodying at least one interconnector structured and arranged to interconnect said heat transferor, said at least one base support plate, and said at least one top support plate; and at least herein embodying wherein said at least one retriever further comprises said at least one structure integrated with said at least one array of heat-transfer conduits). 
     Preferably, heat-exchanging conduits  112  comprise uncoated, square aluminum tubing having a wall thickness of about 0.018″, as shown (at least herein embodying substantially square cross-sections; and at least herein embodying wherein said thermally-conductive conduit wall means comprise conduit walls about 0.018″ thick; and at least herein embodying wherein said at least one thermally-conductive conduit wall comprises at least one conduit wall about 0.018″ thick; and at least herein embodying wherein said thermally-conductive conduit wall means comprise aluminum; and at least herein embodying wherein said at least one thermally-conductive conduit wall comprises aluminum). Preferably, to improve the heat transfer efficiency of the system, heat-exchanging conduits  112  are 1½″×1½″ square, as shown (at least herein embodying external side width of said square cross section of said heat-transfer conduit means). Preferably, the spacing between heat-exchanging conduits  112  is one-half the width of the sides of heat-exchanging conduits  112 , or three-quarters of an inch, as shown (at least herein embodying wherein said heat-transfer conduits are uniformly spaced-apart three-quarters of an inch side-to-side; and at least herein embodying uniform side-to-side spacing apart of said plurality of said heat-transfer conduits of about one-half of said external side width of said at least one square cross section of said at least one heat-transfer conduit; and at least herein embodying uniform side-to-side spacing apart of about one-half of said external side width). Preferably, the heat-exchanging conduits  112  are oriented such that one corner faces the general direction of flow of fresh air  116  (at least herein embodying heat-transfer conduit means oriented to have one corner of said square cross-section facing the general direction of flow of the stream of fresh air through said heat transfer means; and at least herein embodying at least one heat-transfer conduit oriented to have one corner of said square cross-section facing the general direction of flow of the stream of fresh air through said heat transferor). Applicant has found that, for such aluminum heat-exchanging conduits  112 , the above preferred wall thickness provides an unexpectedly and exceptionally desirable combination of heat exchange efficiency and structural stability. Upon reading the teachings of this specification, those with ordinary skill in the art will now understand that, under appropriate circumstances, considering such issues as dryer configuration, temperature requirements, required flow rates, material costs, material heat-transfer rates, convenience, economics, user preference, etc., other materials, heat-exchanging conduit  112  sizes and relative spacing, etc., may suffice. 
       FIG. 6  is a side elevation diagrammatic view of a heat-exchanging system  600  showing retriever  602  pre-configured for use with a laundry dryer  604 . Laundry dryer  604  produces exhaust air  605 , which enters the heat-exchanging conduits  612  of retriever  602 . Moist, heated exhaust air  605  heats the heat-exchanging conduits  612  which conduct the heat to outer surfaces of the heat-exchanging conduits  612 , where the heat is transferred, mostly by convection, to the input stream of fresh air  616 . The input stream of fresh air  616  is thereby pre-heated to become pre-heated air  608 . Pre-heated air  608  is conducted to the dryer heater  606 , which may include a burner or heater coil or the like, where it is heated to become dryer air  603 . Upon reading the teachings of this specification, those with ordinary skill in the art will now understand that, under appropriate circumstances, considering such issues as dryer type, matter to be dried, convenience, economics, user preference, etc., other retriever  602  configurations and applications, such as a model configured for home laundry use, a model configured for drying died fabrics, a model configured for timber drying, etc., may suffice. 
     Preferably, heat exchanger systems  100  and  600  are easily pre-configured to be integrated to any one or more of a wide range of dryer systems, as shown. Although energy savings potential is dependent on a variety of factors (such as type of product dried, local climate, etc.), The applicant has determined through field testing that a fuel use savings of between 30 and 60 percent is possible for most drying applications. 
       FIG. 7  is a flowchart of a heat exchanger system process  700  according to a preferred embodiment of the present invention. Process  700  preferably begins with determining  710  the requirements of the customer. Such requirements typically include moist, heated exhaust air  105  flow rates, fresh air  116  flow rates, desired temperature of drying air  103 , and information about the crop or material to be dried. For example, prunes must be dried slowly in relatively humid air to prevent premature drying of the exterior surface, which may form a barrier to drying the interior of the fruit. In contrast, raisins may be dried more rapidly because they do not exhibit the dry-surface-barrier effect of prunes. Accordingly, an array size for drying prunes would typically be smaller than an array for drying raisins, given identical dryers  104 . Physical size limits on the retriever  102  may also be imposed by customer requirements related to facility limitations. For example, the retriever  102  may be required to fit within pre-existing spaces or ductwork in the dryer  104 . Upon reading the teachings of this specification, those with ordinary skill in the art will now understand that, under appropriate circumstances, considering such issues as dryer operational parameters, matter to be dried, convenience, economics, user preference, etc., other customer requirements, such as noise abatement, portability, materials compatibility, etc., may influence further steps of process  700 . 
     Array size requirements are preferably determined  720  from the customer requirements, as shown (at least herein embodying determining at least one size requirement for said at least one array). Upon reading the teachings of this specification, those of skill in the art of analyzing heat transfer in fluid flows will understand how to calculate, from the customer&#39;s requirements, the desired array size for the above-disclosed preferred array of square heat-transfer conduits  112 . 
     Preferably, once the array size requirements are determined  720 , top and bottom support plates  124   a  and  124   b , adapted to the determined  720  array size, may be perforated  730  with a pattern of square holes  113  in staggered rows with preferably each square hole  113  oriented to have a corner facing the general direction of fresh air  116  flow through the retriever  102 , as shown (at least herein embodying perforating at least one plate with at least one pattern of a plurality of square perforations in staggered rows, each square perforation oriented cornerwise to the general direction of flow of the fresh air over the plate, responsive to said at least one size requirement). The holes  113  may be made by any conventional means, such as stamping, machine cutting, laser cutting, or other method that may minimize cost at the time of manufacture. The array of holes  113  is preferably centered on the support plates  124   a  and  124   b , and the patterns of holes  113  on each plate  124   a  and  124   b  are preferably substantially identical. Upon reading the teachings of this specification, those with ordinary skill in the art will now understand that, under appropriate circumstances, considering such issues as customer requirements, materials availability, convenience, economics, user preference, etc., minor variations in shape, size, and arrangement of holes  113 , adaptive to customer requirements, may suffice. 
     Preferably, heat-transfer conduits  112  are attached  740  to plates  124   a  and  124   b  to form a retriever  102  by extending each end of each heat-transfer conduit  112  through an aligned pair of holes  113  (one hole  113  on base plate  124   a  and one hole  113  on top plate  124   b ) and end-flaring the heat-transfer conduits  112  to secure them to the base plate  124   a  and the top plate  124   b , as shown in  FIG. 5B  (at least herein embodying attaching said plurality of heat transfer conduits to said at least one plate, wherein each said heat transfer conduit of said plurality of heat transfer conduits is aligned and oriented to one perforation of said plurality of perforations; and at least herein embodying pre-configuring, responsive to customer requirements, at least one retriever comprising at least one array of at least one plurality of substantially mutually parallel, substantially vertical heat-transfer conduits having square cross-sections arrayed in alternating staggered rows relative to a perpendicular to the general direction of the flow of the stream of fresh air into the dryer, wherein each heat-transfer conduit is oriented to have one corner facing in the general direction of the flow of the stream of fresh air through said retreiver). In an alternate embodiment, only base support plate  124   a  is attached  740  to heat-transfer conduits  112  during manufacture, with the function of top support plate  124   b  being provided by some portion of a dryer  104  or  604 . In another alternate embodiment, neither support plate  124   a  nor  124   b  is attached  740  during manufacture, with the functions of both being provided by some portion of a dryer  104  or  604 . Upon reading the teachings of this specification, those with ordinary skill in the art will now understand that, under appropriate circumstances, considering such issues as, materials availability, fastener technology, convenience, economics, user preference, etc., other methods of attaching  740  heat-transfer conduits  112  to plate  124   a  and  124   b , such as welding, gluing, fusing, bolting, screwing, etc., may suffice. 
     Once heat-transfer conduits  112  are attached  740  between perforated support plates  124   a  and  124   b , structures  120  are preferably attached  750  at least between the support plates  124   a  and  124   b  to maintain structural integrity of the retriever  102  (at least herein embodying attaching structural elements to at least said at least one plate, wherein said structural elements are structured and arranged to at least maintain structural integrity of said retriever). Structures  120  are preferably made of steel. Sidewalls  119  preferably serve as additional structural support to the retriever  102  as well as side constraints for the flow of fresh air  116  through the retriever  102 . Sidewalls  119  are preferably made of a rigid material, more preferably a lightweight rigid material, and most preferably fiberglass. In an alternate embodiment, sidewalls  119  are made of a flexible, wind-resistant fabric, preferably canvas, and attach to structures  120 . 
     Additional structure  120  is preferably used to position and support retriever  102  in the flow of fresh air  116 . For example, structure  120  may be used to elevate retriever  102  to engage the flow of fresh air  116  into dryer  104  as shown in  FIG. 4 . Preferably, additional structure  118  assists in directing moist, heated exhaust air  105  into the retriever  102 . Structure  118  is preferably made of a rigid material, more preferably a lightweight rigid material, and most preferably fiberglass. Preferably, structure  126  supports the bottom edge of retriever  102 . Structure  126  is preferably made of steel. The methods of attachment  750  are preferably adapted to the various materials of structures  118 ,  119 ,  120 , and  126 . Preferably the steel is welded, more preferably bolted. Preferably the fiberglass is attached to steel with bolts, less preferably with screws, still less preferably with glue. Upon reading the teachings of this specification, those with ordinary skill in the art will now understand that, under appropriate circumstances, considering such issues as, materials availability, fastener technology, convenience, economics, user preference, etc., other methods of attaching  750  structures  118 ,  119 ,  120 , and  126  to each other, such as riveting, clamping, pressing, etc., may suffice. 
     Once the retriever  102  has the necessary structure  118 ,  119 ,  120 , and  126  attached  750 , the retriever  102  is preferably installed  760  in relation to a dryer  104 , as shown (at least herein embodying installing said retriever in at least one dryer). Installation  760  is preferably near enough to dryer  104  to connect by structure  118 ,  119 , and  120 ,which preferably includes ductwork, more preferably directly adjacent to dryer  104 , and most preferably within dryer  104 . In some alternate embodiments, the retriever  102  is built-in to a dryer  104  during manufacture of the dryer  104 , wherein some or all structure  118 ,  119 ,  120 , and  126  is preferably common to the retriever  102  and the dryer  104 . For example, the retriever  102  shown in  FIG. 2  could have been built in at the time the dryer  104  was constructed. Upon reading the teachings of this specification, those with ordinary skill in the art will now understand that, under appropriate circumstances, considering such issues as, dryer configuration, facility configuration, convenience, economics, user preference, etc., other relationships of the retriever  102  to dryer  104 , such as over, under, beside, integral with the burner  106 , integral with a fresh air  116  inlet vent, vehicle-mounted transportable with at least partially flexible ductwork, integral with an exhaust air  114  fan (not shown), etc., may suffice. 
     Although applicant has described applicant&#39;s preferred embodiments of this invention, it will be understood that the broadest scope of this invention includes such modifications as diverse shapes and sizes and materials. Further, many other advantages of applicant&#39;s invention will be apparent to those skilled in the art from the above-disclosed matters.