Abstract:
A modular, water-to-air heat exchanger with flexible tubes is adjustable in length to conform to different size cooling coils and thus provides an inexpensive, retro-fittable run-around heat recovery for pre-existing air handling systems. The heat exchanger comprises multiple heat exchange tubes formed of flexible material in a shape that permits them to be lengthened or shortened by simply moving the headers toward or away from each other. Preferably, the tubes are formed of a flexible, non-resilient material such as copper, and are shaped in a serpentine or helical manner. In this way, the tubes can be drawn out to elongate the heat exchanger or compressed to shorten it, depending on the dimension of the cooling coil in the air handler. One convenient way to control the length of the flexible tubes is to support the headers on one or more adjustment bars, each having a threaded adjustment mechanism.

Description:
This application claims the benefit of U.S. Provisional Application No. 60/866,115, filed Nov. 16, 2006, and the contents thereof are incorporated herein by reference. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates to air handling equipment generally and, in particular but without limitation, to heat exchangers for air handlers. 
     BACKGROUND OF INVENTION 
     An “air handler” or “air handling system” is that portion of a central air conditioning system that moves the conditioned (cooled) air throughout a structure&#39;s ductwork or air flow enclosure. Air is forced by a fan through a cooling coil. If the fan is downstream of the cooling coil, the air handler is a “draw-through” type system. If the cooling coil is downstream of the fan, it is referred to as a “blow through” type air handler. 
     In a draw-through type system, some heat is added to the air by the fan after it is cooled. On the other hand, in the blow-through type system, the air is cooled downstream of the fan, so that the air entering the conditioned space is cooler. For this reason, blow-through air handling systems are preferred; because the air entering the space is cooler, less air is required to reach the desired room temperature. This, in turn, reduces the costs of the air handling system including the energy required to operate it efficiently. 
     Blow-through air handlers can be problematic in some applications, such as hospitals, pharmaceutical plants, and other facilities with “clean rooms,” where the conditioned air is passed through a final air filter downstream of the cooling coil and prior to entering the space. Water from the nearly saturated air leaving the cooling coil sometimes condenses on the filter, eventually causing it to become soaked with moisture. Because the air leaving the coil is nearly saturated and because the temperature of this air fluctuates over such a small range, condensate in the filter has no opportunity to evaporate. 
     Thus, there is a need for blow-through air handling system that reduces condensate on air filters downstream of the cooling coil. There is a need for a heat exchanger system that can be retro-fitted to pre-existing air handlers plagued with wet air filters. There is a need for a simple reheat solution that will add as little as one-half to one degree Fahrenheit (0.5-1° F.) to the air leaving the cooling coil and before it enters the filter; this small amount of additional heat would reduce or eliminate condensation in the filter. There is a need for a simple reheat solution that is inexpensive to buy, to install, and to operate. There is a need for a reheat solution that would require no source of heated water or special electrical circuit. There is a need for a reheat solution that would require little or no modification to the air handler cabinet. There is a need for a reheat solution with a relatively low capacity so that its size and cost are minimized. There is a need for an adjustable run-around heat recovery system that can be sized for use with different size cooling coils, eliminating the need for expensive, customized options. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is an elevational view of a first face of a heat exchanger constructed in accordance with the preferred embodiment. 
         FIG. 2  is an elevational view of a first side of the heat exchanger of  FIG. 1 . 
         FIG. 3  is an enlarged elevational view of a first face of the heat exchanger of  FIG. 1  with blind flanges connected to the end flanges on one end of the headers and connector flanges connected to the end flanges on the other end of the headers. 
         FIG. 4  is an elevational view of an array of three heat exchangers interconnected in series by connector flanges between units. 
         FIG. 5  is a schematic illustration of an air handler with a retro-fitted run-around heat recovery system in accordance with the present invention for reheating the air leaving the cooling coil before it blows through the filter. The adjustment bars in the heat exchangers have been omitted from this drawing for clarity of illustration. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Turning now to the drawings in general and to  FIGS. 1 and 2  in particular, there is shown therein a modular heat exchanger made in accordance with the present invention and designated generally by the reference numeral  10 . The heat exchanger  10  comprises first and second headers  14  and  16 , the second header spaced a distance “d” from the first header. 
     Disposed between the first and second headers  14  and  16  are a plurality of heat exchange tubes, designated collectively at  20 . The heat exchange tubes  20  are adapted to transfer heat between a heat exchange fluid, such as water, inside the tubes and air passing through the tubes. Each of the tubes  20  is made of a heat conductive material, such as copper. 
     The tubes  20  are connected to the headers  14  and  16  to provide communication therebetween. Thus, in a conventional manner, heat exchange fluid enters one header  14  or  16 , passes through the heat exchange tubes  20 , and then exits the heat exchanger through the other header. To allow the heat exchanger  10  to be connected to other like units or other fittings, each end of each header  14  and  16  preferably is provided with an end flange. Thus, as best seen in  FIG. 1 , the header  14  has end flanges  24  and  26  on its first and second ends  28  and  30 , and the header  16  has end flanges  32  and  34  on its first and second ends  36  and  38 . 
     With continuing reference to  FIGS. 1 and 2 , each of the plurality of tubes  20  has a resting length. As used herein, “resting length” refers to the length of the tube when no compression or tension is applied to it. In the preferred embodiment shown, the resting length of the tubes  20  is about the same as the distance “d” between the headers  14  and  16 , as seen in  FIG. 1 . 
     Each of the tubes  20  is made of a flexible material and is characterized by a configuration that permits the resting length of the tube to be adjusted. In this way, the distance “d” between the first and second headers  14  and  16  can be adjusted. In the preferred embodiment, use of copper to form the tubes provides good flexibility as well as thermal conductivity. 
     In the embodiment shown in  FIGS. 1 and 2 , each of the tubes  20  is formed into a serpentine or sinusoidal pattern. Where the tubes are serpentine in shape, it may be desirable to arrange the tubes in an alternating fashion, so that adjacent tubes do not have fully overlapping curves. Another suitable configuration is helical. It will be appreciated that copper tubing in the illustrated serpentine shape may be easily stretched out to a length greater than the distance “d” or compressed to a length less than “d.” 
     In the most preferred embodiment the tubes  20  are formed of a material that is non-resilient. As used herein, “non-resilient” denotes a material that is not elastic, that is, a material that, once deformed, retains the deformed shape rather than returning its original configuration. Though flexible, copper is non-resilient. Thus, in the embodiment shown, once the tubes  20  have been compressed, they will tend to retain the shorter, compressed position. Similarly, if pulled or stretched to elongate their length, the tubes  20  will tend to remain in the elongated position. 
     In most applications, it will be desirable that the tubes  20  be configured so that their resting length may be increased or decreased, that is, so that the heat exchanger  10  can be lengthened or shortened. However, in some embodiments, the heat exchanger  10  may comprise tubes that can only be compressed or can only be elongated. Additionally, while non-resilient material is preferred, in some applications a resilient material may be advantageous. 
     A particularly preferred means for controlling the length of the tubes  20  is to simply move the first and second headers  14  and  16  closer together or farther apart. Various ways to accomplish this will be apparent. One preferred way, illustrated in  FIG. 2 , is to use at least one and preferably two adjustment bars, one of which is designated at  42 . The adjustment bar  42  preferably is fixed near the ends  30  and  38  of the headers  14  and  16  at the attachment point  44  and  46  and includes an adjustment mechanism, such as a threaded adjuster  48 . 
     Threaded adjusters of this type are well known and, thus, are not shown or described in detail herein. Typically, such devices have two portions, one threadedly received in the other. The non-threaded ends are fixed axially relative to the outer portions of the adjustment bar; one is fixed against rotation, one is not. Thus, when the rotatable member is turned, the threads cause it to move towards or away from the mating threaded portion, thereby shortening or lengthening the adjustment bar  42 . 
     Now it will be seen that the headers  14  and  16  and the adjustment bar  42  form a framework that supports the specially configured tubes  20  in a manner that preserves their parallel orientation relative to each other but which allows the overall length of the unit, or the distance “d,” to be increased or decreased. Now it will be apparent that the preferred heat exchanger  10  is non-finned. This is acceptable because this particular heat exchanger is designed for flexibility, not efficiency. 
     As shown in  FIG. 3 , the headers  14  and  16  with end flanges  24 ,  26 ,  32  &amp;  34  may be equipped with fittings that permit the heat exchanger  10  to be used in a stand-alone mode, that is, not interconnected with other like units. To that end, the heat exchanger  10  shown in  FIG. 3  may be provided with blind flanges  52  and  54  on the end flanges  26  and  34  and with connecting flanges  58  and  60  on the ends  28  and  36 . The connecting flanges are used to connect the unit to the heat exchange fluid supply and return lines. 
     As shown in  FIG. 4 , the heat exchanger of the present invention is equipped with fittings that permit multiple, similarly formed heat exchangers designated as  10 A,  10 B and  10 C to be connectable in series with other like units to form a bank or array  70  of heat exchangers. To that end, blind flanges  52  and  54  are attached to the end flanges  26  and  34  on the ends  30  and  38  of the headers  14  and  16  in the terminal unit  10 C. The end flanges  26  and  34  of the first and second units  10 A and  10 B are connected directly to the end flanges  24  and  32  on the adjacent units  10 B and  10 C. Connecting flanges  58  and  60  are connected to the end flanges  24  and  32  of the first unit in the series, heat exchanger  10 A. 
     Turning now to  FIG. 5 , there is shown therein the use of the heat exchanger  10  of the present invention to provide a retro-fittable run-around heat recovery system in an existing blow-through air handling system designated generally at  80 . The air handler  80  generally comprises an enclosure  82  and a fan  84  supported inside the enclosure. A cooling coil  86  is supported in the enclosure  82  downstream of the fan, and an air filter  88  is provided downstream of the cooling coil. The air enters at the inlet end  90  and exits into the conditioned space at the outlet end  92 . 
     Also included in the system  80  is a “run-around” heat recovery system  100  in accordance with the present invention and incorporating the previously described heat exchanger. The heat recovery system  100  includes a first or upstream heat exchanger  102  and a second or downstream heat exchanger  104 . The upstream heat exchanger  102  is supported in the enclosure  82  between the fan  84  and the cooling coil  86 . The downstream heat exchanger  104  is supported in the enclosure  82  between the cooling coil  86  and filter  88 . Each of the heat exchangers  102  and  104  is structurally similar to the heat exchanger  10  in  FIGS. 1 and 2  or to the array  70  of heat exchangers in  FIG. 4 . 
     Although the heat exchangers and the run-around heat recovery systems of the present invention are ideally suited for use in blow-through handlers with downstream filters, such as the air handler shown in  FIG. 5 , the present invention is not so limited. Rather, this technology has other applications. For example, the inventive heat recovery system  100  is useful in an air handler with a downstream sound attenuator in which condensation is occurring. 
     During installation of the heat recovery system  100 , the length of the heat exchangers  102  and  104  are adjusted in the manner described previously so that they are about the same length as the cooling coil  86 . If the cooling coil  86  is significantly wider than a single heat exchanger, then two or more heat exchangers can be interconnected in series as previously described. In this way, it is possible to ensure that all air entering the cooling coil  86  will pass through the heat exchanger  102  and likewise that all air leaving the coil will pass through the heat exchanger  104 . This ensures that all of the air is de-saturated. 
     The heat exchangers  102  and  104  are connected in a circulation loop by means of a conduit  112 . A pump  114  is provided for circulating heat exchange fluid through the conduit  112 . Heat exchange fluid (not shown) passes from the pump  114  through the conduit segment  116  into the end  120  of the bottom header (not numbered) of the downstream heat exchanger  104 , flows up through the heat exchange tubes  122  and out the end  124  of the top header (not numbered). Next, the fluid flows through the connecting loop  130  of the conduit  112  and into the end  132  of the upper header (not numbered) on the upstream heat exchanger  102 . After passing down through the heat exchange tubes  134 , the fluids exits the end  136  of the bottom header (not numbered) and returns to the pump  114  through the conduit segment  138 . 
     Through this continuous flow pattern, a small amount of heat is removed from the air passing through the upstream heat exchanger  102 , and this heat—usually one-half to one degree Fahrenheit (0.5-1.0° F.)—is returned to the air by the downstream heat exchanger  104  as it exits the cooling coil  86  and before it enters the filter  88 . Thus, the slightly increased temperature of the cooled air entering the filter  88  causes it to be slightly less saturated resulting in less condensation. 
     Now it will be appreciated that the present invention provides a modular water-to-air heat exchanger that can be used in run-around heat recovery system that is retro-fittable into pre-existing air handlers. Because of the flexibility of the heat exchanger tubes, the heat exchanger can be installed on cooling coils that have a wide range of fin heights. This modular construction, in conjunction with the flexible heat exchange tubes, allows a few models of heat exchangers to fit a very wide variety of cooling coil sizes and to completely cover the downstream face of the cooling coil. Additionally, since the heat exchanger does not have to be very effective, the heat exchanger tubes do not need to be finned. The flexible heat exchanger of the present invention eliminates the need for custom-made units, and thus provides a low cost alternative for run-around heat recovery systems in air handlers with chronic wet filter problems.