Abstract:
A modular fan housing configured to hold an array of motors and fans is provided. The modular fan housing is configured for use in an air-handling system that delivers air to a ventilation system for at least a portion of a building. The fan housing comprises a plurality of modular units configured to be stacked adjacent to one another in at least one row or column to form an array. The modular units each include an interior surface and have a front end and a back end that define a chamber. The chambers are configured to receive the motors and fans. Sound attenuation layers extend along at least a portion of the interior surface of the corresponding chambers. The sound attenuation layers are positioned between at least some of the adjacent chambers.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    The present application is a continuation application of U.S. patent application Ser. No. 13/856,174, filed Apr. 3, 2013, which is a continuation application of U.S. patent application Ser. No. 13/546,138 filed Jul. 11, 2012, now U.S. Pat. No. 8,414,251, which is a divisional application of U.S. patent application Ser. No. 13/293,301 filed Nov. 10, 2011, which is a continuation application of U.S. patent application Ser. No. 12/455,914 filed Jun. 8, 2009, now U.S. Pat. No. 8,087,877, which is a continuation application of U.S. patent application Ser. No. 11/097,561, filed Mar. 31, 2005, now U.S. Pat. No. 7,597,534, which is a continuation-in-part of U.S. patent application Ser. No. 10/806,775, filed Mar. 22, 2004, now U.S. Pat. No. 7,137,775, which is a continuation-in-part of PCT Patent Application Serial Number PCT/US2004/008578, filed Mar. 19, 2004, also claims the benefit under 35 USC Section 119(e) of U.S. Provisional Patent Application Ser. No. 60/554,702, filed Mar. 20, 2004, and U.S. Provisional Patent Application Ser. No. 60/456,413 filed Mar. 20, 2003. The present application is based on and claims priority from the above applications, which are incorporated herein by reference in their entirety. 
         [0002]    The U.S. patent application Ser. No. 13/546,138 is also a divisional application of U.S. patent application Ser. No. 13/080,168 filed Apr. 5, 2011 which is a continuation of U.S. patent application Ser. No. 11/982,233 filed Oct. 31, 2007, now U.S. Pat. No. 7,922,442 which is a Continuation of U.S. patent application Ser. No. 11/595,212, filed Nov. 9, 2006, now U.S. Pat. No. 7,527,468 which is a Continuation-in-Part of U.S. patent application Ser. No. 10/806,775, filed Mar. 22, 2004, now U.S. Pat. No. 7,137,775 which is a Continuation-in-Part of PCT Patent Application Serial Number PCT/US04/08578, filed Mar. 19, 2004 and claims benefit of U.S. Patent Application Ser. No. 60/554,702, filed Mar. 20, 2004 and U.S. Patent Application Ser. No. 60/456,413, filed Mar. 20, 2003. The present application is based on and claims priority from the above applications, which are incorporated herein by reference in their entirety. 
     
    
     BACKGROUND OF THE INVENTION 
       [0003]    The present invention is directed to a fan array fan section utilized in an air-handling system. Air-handling systems (also referred to as an air handler) have traditionally been used to condition buildings or rooms (hereinafter referred to as “structures”). An air-handling system is defined as a structure that includes components designed to work together in order to condition air as part of the primary system for ventilation of structures. The air-handling system may contain components such as cooling coils, heating coils, filters, humidifiers, fans, sound attenuators, controls, and other devices functioning to meet the needs of the structures. The air-handling system may be manufactured in a factory and brought to the structure to be installed or it may be built on site using the necessary devices to meet the functioning needs of the structure. The air-handling compartment  102  of the air-handling system includes the inlet plenum  112  prior to the fan inlet cone  104  and the discharge plenum  110 . Within the air-handling compartment  102  is situated the fan unit  100  (shown in  FIGS. 1 and 2  as an inlet cone  104 , a fan  106 , and a motor  108 ), fan frame, and any appurtenance associated with the function of the fan (e.g. dampers, controls, settling means, and associated cabinetry). Within the fan  106  is a fan wheel (not shown) having at least one blade. The fan wheel has a fan wheel diameter that is measured from one side of the outer periphery of the fan wheel to the opposite side of the outer periphery of the fan wheel. The dimensions of the handling compartment  102  such as height, width, and airway length are determined by consulting fan manufacturers data for the type of fan selected. 
         [0004]      FIG. 1  shows an exemplary prior art air-handling system having a single fan unit  100  housed in an air-handling compartment  102 . For exemplary purposes, the fan unit  100  is shown having an inlet cone  104 , a fan  106 , and a motor  108 . Larger structures, structures requiring greater air volume, or structures requiring higher or lower temperatures have generally needed a larger fan unit  100  and a generally correspondingly larger air-handling compartment  102 . 
         [0005]    As shown in  FIG. 1 , an air-handling compartment  102  is substantially divided into a discharge plenum  110  and an inlet plenum  112 . The combined discharge plenum  110  and the inlet plenum  112  can be referred to as the airway path  120 . The fan unit  100  may be situated in the discharge plenum  110  as shown), the inlet plenum  112 , or partially within the inlet plenum  112  and partially within the discharge plenum  110 . The portion of the airway path  120  in which the fan unit  100  is positioned may be generically referred to as the “fan section” (indicated by reference numeral  114 ). The size of the inlet cone  104 , the size of the fan  106 , the size the motor  108 , and the size of the fan frame (not shown) at least partially determine the length of the airway path  120 . Filter banks  122  and/or cooling coils (not shown) may be added to the system either upstream or downstream of the fan units  100 . 
         [0006]    For example, a first exemplary structure requiring 50,000 cubic feet per minute of air flow at six (6) inches water gage pressure would generally require a prior art air-handling compartment  102  large enough to house a 55 inch impeller, a 100 horsepower motor, and supporting framework. The prior art air-handling compartment  102 , in turn would be approximately 92 inches high by 114 to 147 inches wide and 106 to 112 inches long. The minimum length of the air-handling compartment  102  and/or airway path  120  would be dictated by published manufacturers data for a given fan type, motor size, and application. Prior art cabinet sizing guides show exemplary rules for configuring an air-handling compartment  102 . These rules are based on optimization, regulations, and experimentation. For example, a second exemplary structure includes a recirculation air handler used in semiconductor and pharmaceutical clean rooms requiring 26,000 cubic feet per minute at two (2) inches water gage pressure. This structure would generally require a prior art air-handling system with a air-handling compartment  102  large enough to house a 44 inch impeller, a 25 horsepower motor, and supporting framework. The prior art air-handling compartment  102 , in turn would be approximately 78 inches high by 99 inches wide and 94 to 100 inches long. The minimum length of the air-handling compartment  102  and/or airway path  120  would be dictated by published manufacturers data for a given fan type, motor size and application. Prior art cabinet sizing guides show exemplary rules for configuring an air-handling compartment  102 . These rules are based on optimization, regulations, and experimentation. These prior art air-handling systems have many problems including the following exemplary problems: 
         [0007]    Because real estate (e.g. structure space) is extremely expensive, the larger size of the air-handling compartment  102  is extremely undesirable. 
         [0008]    The single fan units  100  are expensive to produce and are generally custom produced for each job. 
         [0009]    Single fan units  100  are expensive to operate. 
         [0010]    Single fan units  100  are inefficient in that they only have optimal or peak efficiency over a small portion of their operating range. 
         [0011]    If a single fan unit  100  breaks down, there is no air conditioning at all. 
         [0012]    The low frequency sound of the large fan unit  100  is hard to attenuate. 
         [0013]    The high mass and turbulence of the large fan unit  100  can cause undesirable vibration. 
         [0014]    Height restrictions have necessitated the use of air-handling systems built with two fan units  100  arranged horizontally adjacent to each other. It should be noted, however, that a good engineering practice is to design air handler cabinets and discharge plenums  110  to be symmetrical to facilitate more uniform air flow across the width and height of the cabinet. Twin fan units  100  have been utilized where there is a height restriction and the unit is designed with a high aspect ratio to accommodate the desired flow rate. As shown in the Greenheck “Installation Operating and Maintenance Manual,” if side-by-side installation was contemplated, there were specific instructions to arrange the fans such that there was at least one fan wheel diameter spacing between the fan wheels and at least one-half a fan wheel diameter between the fan and the walls or ceilings. The Greenheck reference even specifically states that arrangements “with less spacing will experience performance losses.” Normally, the air-handling system and air-handling compartment  102  are designed for a uniform velocity gradient of 500 feet per minute velocity in the direction of air flow. The two fan unit  100  air-handling systems, however, still substantially suffered from the problems of the single unit embodiments. There was no recognition of advantages by increasing the number of fan units  100  from one to two. Further, the two fan unit  100  section exhibits a non-uniform velocity gradient in the region following the fan unit  100  that creates uneven air flow across filters, coils, and sound attenuators. 
         [0015]    It should be noted that electrical devices have taken advantage of multiple fan cooling systems. For example, U.S. Pat. No. 6,414,845 to Bonet uses a multiple-fan modular cooling component for installation in multiple component-bay electronic devices. Although some of the advantages realized in the Bonet system would be realized in the present system, there are significant differences. For example, the Bonet system is designed to facilitate electronic component cooling by directing the output from each fan to a specific device or area. The Bonet system would not work to direct air flow to all devices in the direction of general air flow. Other patents such as U.S. Pat. No. 4,767,262 to Simon and U.S. Pat. No. 6,388,880 to El-Ghobashy et al. teach fan arrays for use with electronics. 
         [0016]    Even in the computer and machine industries, however, operating fans in parallel is taught against as not providing the desired results except in low system resistance situations where fans operate in near free delivery. For example, Sunon Group has a web page in which they show two axial fans operating in parallel, but specifically state that if “the parallel fans are applied to the higher system resistance that [an] enclosure has, . . . less increase in flow results with parallel fan operation.” Similar examples of teaching against using fans in parallel are found in an article accessible from HighBeam Research&#39;s library (http://stati.highbeam.com) and an article by Ian McLeod accessible at (http://www.papstplc.com). 
       BRIEF DESCRIPTION OF THE INVENTION 
       [0017]    The present invention is directed to a fan array fan section in an air-handling system. The fan array fan section includes a plurality of fan units arranged in a fan array. Each fan unit is positioned within a fan unit chamber/cell. Each fan unit chamber/cell has at least one acoustically absorptive insulation surface. The insulation surfaces of the fan unit chambers/cells together form a coplanar silencer. Sound waves from the fan units passing through the insulation surface at least partially dissipate as they pass therethrough. In one preferred embodiments the fan unit chamber/cell is a cell having a frame that supports the insulation surfaces. 
         [0018]    The present invention is also directed to a fan array fan section in an air-handling system that includes a plurality of fan units arranged in a fan array and positioned within an air-handling compartment. One preferred embodiment may include an array controller programmed to operate the plurality of fan units at peak efficiency. The plurality of fan units may be arranged in a true array configuration, a spaced pattern array configuration, a checker board array configuration, rows slightly offset array configuration, columns slightly offset array configuration, or a staggered array configuration. 
         [0019]    The foregoing and other objectives, features, and advantages of the invention will be more readily understood upon consideration of the following detailed description of the invention, taken in conjunction with the accompanying drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0020]      FIG. 1  is a side view of an exemplary prior art air-handling system having a single large fan unit within an air-handling compartment. 
           [0021]      FIG. 2  is a perspective view of an exemplary prior art large fan unit. 
           [0022]      FIG. 3  is a side view of an exemplary fan array fan section in an air-handling system of the present invention having a plurality of small fan units within an air-handling compartment. 
           [0023]      FIG. 4  is a plan or elevation view of a 4×6 exemplary fan array fan section in an air-handling system of the present invention having a plurality of small fan units within an air-handling compartment. 
           [0024]      FIG. 5  is a plan or elevation view of a 5×5 exemplary fan array fan section in an air-handling system of the present invention having a plurality of small fan units within an air-handling compartment. 
           [0025]      FIG. 6  is a plan or elevation view of a 3×4 exemplary fan array fan section in an air-handling system of the present invention having a plurality of small fan units within an air-handling compartment. 
           [0026]      FIG. 7  is a plan or elevation view of a 3×3 exemplary fan array fan section in an air-handling system of the present invention having a plurality of small fan units within an air-handling compartment. 
           [0027]      FIG. 8  is a plan or elevation view of a 3×1 exemplary fan array fan section in an air-handling system of the present invention having a plurality of small fan units within an air-handling compartment. 
           [0028]      FIG. 9  is a plan or elevation view of an alternative exemplary fan array fan section in an air-handling system of the present invention in which a plurality of small fan units are arranged in a spaced pattern array within an air-handling compartment. 
           [0029]      FIG. 10  is a plan or elevation view of an alternative exemplary fan array fan section in an air-handling system of the present invention in which a plurality of small fan units are arranged in a checker board array within an air-handling compartment. 
           [0030]      FIG. 11  is a plan or elevation view of an alternative exemplary fan array fan section in an air-handling system of the present invention in which a plurality of small fan units are arranged in rows slightly offset array within an air-handling compartment. 
           [0031]      FIG. 12  is a plan or elevation view of an alternative exemplary fan array fan section in an air-handling system of the present invention in which a plurality of small fan units are arranged in columns slightly offset array within an air-handling compartment. 
           [0032]      FIG. 13  is a plan or elevation view of a 5×5 exemplary fan array fan section in an air-handling system of the present invention running at 52% capacity by turning a portion of the fans ON and a portion of the fans OFF. 
           [0033]      FIG. 14  is a plan or elevation view of a 5×5 exemplary fan array fan section in an air-handling system of the present invention running at 32% capacity by turning a portion of the fans ON and a portion of the fans OFF. 
           [0034]      FIG. 15  is a side view of an alternative exemplary fan array fan section in an air-handling system of the present invention having a plurality of staggered small fan units within an air-handling compartment. 
           [0035]      FIG. 16  is a perspective view of an exemplary fan array using a grid system into which fan units are mounted. 
           [0036]      FIG. 17  is a perspective view of an exemplary fan array using a grid system or modular units each of which includes a fan units mounted within its own fan unit chamber. 
           [0037]      FIG. 18  is a cross-sectional view of an exemplary insulated grid array system or modular unit system having interior surfaces made from acoustically absorptive material. 
           [0038]      FIGS. 19-23  are cross-sectional view of an exemplary insulated grid array system or modular unit system having interior surfaces made from acoustically absorptive material showing sound wave reaction. 
           [0039]      FIG. 24  is a wave form diagram illustrating the principle of wave cancellation. 
           [0040]      FIG. 25  is a perspective view of an exemplary array of dampeners that may be positioned either in front of or behind the fan units. 
           [0041]      FIG. 26  is a side view of air flowing between insulation boards with an open cell foam facing of the present invention, the insulation boards and open cell foam facing secured by perforated rigid facing. 
           [0042]      FIG. 27  is a side view of an insulation board with open cell foam facings of the present invention such that the fiberglass therein is enclosed in between the facings. 
           [0043]      FIG. 28  is a side view of sound being absorbed within an insulation board with an open cell foam facing of the present invention. 
           [0044]      FIG. 29  is an enlarged side view of protruding open cell foam facing formed between the openings in the perforated rigid facing and sound waves being absorbed by the protruding open cell foam facing. 
           [0045]      FIG. 30  is a front view of an exemplary perforated rigid facing having circular openings defined therein. 
           [0046]      FIG. 31  is a side view of an exemplary air handler having a top section with open cell foam facing secured by perforated rigid facing and a bottom section with layered fiberglass and open cell foam facing secured by perforated rigid facing. 
           [0047]      FIG. 32  is a front view of open cell foam facing secured by an exemplary frame. 
           [0048]      FIG. 33  illustrates a graph with a vertical axis as the absorption coefficient and a horizontal axis showing the frequency. 
           [0049]      FIG. 34  illustrates a table showing an example of a configuration and operating performance level for a fan array implemented in accordance with an embodiment of the present invention. 
           [0050]      FIG. 35  illustrates performance curves for static pressure vs. airflow, and brake horse power (BHP) versus airflow for a fan array implemented in accordance with an embodiment of the present invention. 
           [0051]      FIG. 36  illustrates performance curves for total pressure (TP) vs. airflow, and BHP versus airflow for a conventional air handler. 
           [0052]      FIG. 37  illustrates bar graphs showing an example of sound power levels at octave bands 1-8 produced by a fan array of fan units without with acoustically absorptive material and produced by a fan array of fan units lined with acoustically absorptive material implemented in accordance with an embodiment of the present invention. 
           [0053]      FIG. 38  illustrates control options for a fan array implemented in accordance with an embodiment of the present invention. 
           [0054]      FIG. 39  illustrates a fan array implemented in accordance with an embodiment of the present invention. 
           [0055]      FIG. 40  illustrates a sound power comparison of a fan array implemented in accordance with an embodiment and 55 inch diameter traditional plenum fan. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0056]    The present invention is directed to a fan array fan section in an air-handling system. As shown in  FIGS. 3-12 , the fan array fan section in the air-handling system uses a plurality of individual single fan units  200 . In one preferred embodiment, the fan units  200  are arranged in a true array ( FIGS. 4-8 ), but alternative embodiments may include, for example, alternative arrangements such as in a spaced pattern ( FIG. 9 ), a checker board ( FIG. 10 ), rows slightly offset ( FIG. 11 ), or columns slightly offset ( FIG. 12 ). As the present invention could be implemented with true arrays and/or alternative arrays, the term “array” is meant to be comprehensive. 
         [0057]    The fan units  200  in the fan array of the present invention may be spaced as little as 20% of a fan wheel diameter. Optimum operating conditions for a closely arranged array may be found at distances as low as 30% to 60% of a fan wheel diameter. By closely spacing the fan units  200 , more air may be moved in a smaller space. For example, if the fan wheels of the fan units  200  have a 20 inch fan wheel diameter, only a 4 inch space (20%) is needed between the outer periphery of one fan wheel and the outer periphery of the adjacent fan wheel (or a 2 inch space between the outer periphery of a fan wheel and an the adjacent wall or ceiling). 
         [0058]    By using smaller fan units  200  it is possible to support the fan units  200  with less intrusive structure (fan frame). This can be compared to the large fan frame that supports prior art fan units  100  and functions as a base. This large fan frame must be large and sturdy enough to support the entire weight of the prior art fan units  100 . Because of their size and position, the known fan frames cause interference with air flow. In the preferred embodiment, therefore, the fan units  200  of the fan array may be supported by a frame that supports the motors  108  with a minimum restriction to air flow. 
         [0059]    As mentioned in the Background, others have tried using side-by-side installation of two fan units  100  arranged horizontally adjacent to each other within an air-handling system. As is also mentioned in the Background, fan arrays have been used in electronic and computer assemblies. However, in the air-handling system industry, it has always been held that there must be significant spacing between the horizontally arranged fan wheels and that arrangements with less spacing will experience performance losses. A single large fan moves all the air in a cabinet. Using two of the same or slightly smaller fans caused the air produced by one fan to interfere with the air produced by the other fan. To alleviate the interference problem, the fans had to be spaced within certain guidelines—generally providing a clear space between the fans of a distance of at least one wheel diameter (and a half a wheel diameter to an adjacent wall). Applying this logic, it would not have made sense to add more fans. And even if additional fans had been added, the spacing would have continued to be at least one wheel diameter between fans. Further, in the air-handling system industry, vertically stacking fan units would have been unthinkable because the means for securing the fan units would not have been conducive to such stacking (they are designed to be positioned on the floor only). 
         [0060]    It should be noted that the plenum fan is the preferred fan unit  200  of the present invention. In particular, the APF-121, APF-141, APF-161, and APF-181 plenum fans (particularly the fan wheel and the fan cone) produced by Twin City Fan Companies, Ltd. of Minneapolis, Minn., U.S. has been found to work well. The reason that plenum fans work best is that they do not produce points of high velocity such as those produced by axial fans and housed centrifugal fans and large plenum fans. Alternative embodiments use known fan units or fan units yet to be developed that will not produce high velocity gradients in the direction of air flow. Still other embodiments, albeit less efficient, use fan units such as axial fans and/or centrifugal housed fans that have points of high velocity in the direction of air flow. 
         [0061]    In the preferred embodiment, each of the fan units  200  in the fan array fan section in the air-handling system is controlled by an array controller  300  ( FIGS. 13 and 14 ). In one preferred embodiment, the array controller  300  may be programmed to operate the fan units  200  at peak efficiency. In this peak efficiency embodiment, rather than running all of the fan units  200  at a reduced efficiency, the array controller  300  turns off certain fan units  200  and runs the remaining fan units  200  at peak efficiency. In an alternative embodiment, the fan units  200  could all run at the same power level (e.g. efficiency and/or flow rate) of operation. 
         [0062]    Another advantage of the present invention is that the array controller  300  (which may be a variable frequency drive (VFD)) used for controlling fan speed and thus flow rate and pressure, could be sized for the actual brake horsepower of the fan array fan section in the air-handling system. Since efficiency of the fan wall array can be optimized over a wide range of flow rates and pressures, the actual operating power consumed by the fan array is substantially less than the actual operating power consumed by the comparable prior art air-handling systems and the array controller&#39;s power could be reduced accordingly. The array controller  300  could be sized to the actual power consumption of the fan array where as the controller (which may have been a variable frequency drive) in a traditional design would be sized to the maximum nameplate rating of the motor per Electrical Code requirements. An example of a prior art fan design supplying 50,000 cubic feet per minute of air at 2.5 inches pressure, would require a 50 horsepower motor and 50 horsepower controller. The new invention will preferably use an array of fourteen 2 horsepower motors and a 30 horsepower array controller  300 . 
         [0063]    This invention solves many of the problems of the prior art air-handling systems including, but not limited to real estate, reduced production costs, reduced operating expenses, increased efficiency, improved air flow uniformity, redundancy, sound attenuation advantages, and reduced vibration. 
       Controllability 
       [0064]    As mentioned, preferably each of the fan units  200  in the fan array fan section in the air-handling system is controlled by an array controller  300  ( FIGS. 13 and 14 ) that may be programmed to operate the fan units  200  at peak efficiency. In this peak efficiency embodiment, rather than running all of the fan units  200  at a reduced efficiency, the array controller  300  is able to turn off certain fan units  200  and run the remaining fan units  200  at peak efficiency. Preferably, the array controller  300  is able to control fan units  200  individually, in predetermined groupings, and/or as a group as a whole. 
         [0065]    For example, in the 5×5 fan array such as that shown in  FIGS. 5 ,  13 , and  14 , a person desiring to control the array may select desired air volume, a level of air flow, a pattern of air flow, and/or how many fan units  200  to operate. Turning first to air volume, each fan unit  200  in a 5×5 array contributes 4% of the total air. In variable air volume systems, which is what most structures have, only the number of fan units  200  required to meet the demand would operate. A control system (that may include the array controller  300 ) would be used to take fan units  200  on line (an “ON” fan unit  200 ) and off line (an “OFF” fan unit  200 ) individually. This ability to turn fan units  200  ON and OFF could effectively eliminate the need for a variable frequency drive. Similarly, each fan unit  200  in a 5×5 array uses 4% of the total power and produces 4% of the level of air flow. Using a control system to take fan units  200  on line and off line allows a user to control power usage and/or air flow. The pattern of air flow can also be controlled if that would be desirable. For example, depending on the system it is possible to create a pattern of air flow only around the edges of a cabinet or air only at the top. Finally, individual fan units  200  may be taken on line and off line. This controllability may be advantageous if one or more fan units  200  are not working properly, need to be maintained (e.g. needs general service), and/or need to be replaced. The problematic individual fan units  200  may be taken off line while the remainder of the system remains fully functional. Once the individual fan units  200  are ready for use, they may be brought back on line. 
         [0066]    A further advantage to taking fan units  200  on and off line occurs when building or structure control systems require low volumes of air at relatively high pressures. In this case, the fan units  200  could be modulated to produce a stable operating point and eliminate the surge effects that sometimes plague structure owners and maintenance staff. The surge effect is where the system pressure is too high for the fan speed at a given volume and the fan unit  200  has a tendency to go into stall. 
         [0067]    Examples of controllability are shown in  FIGS. 13 and 14 . In the fan array fan section in the air-handling system shown in  FIG. 13 , the array controller  300  alternates “ON” fan units  200  and “OFF” fan units  200  in a first exemplary pattern as shown so that the entire system is set to operate at 52% of the maximum rated air flow but only consumes 32% of full rated power. These numbers are based on exemplary typical fan operations in a structure.  FIG. 14  shows the fan array fan section in the air-handling system set to operate at 32% of the maximum rated air flow but only consumes 17% of full rated power. These numbers are based on exemplary typical fan operations in a structure. In this embodiment, the array controller  300  creates a second exemplary pattern of “OFF” fan units  200  and “ON” fan units  200  as shown. 
       Real Estate 
       [0068]    The fan array fan section in the air-handling section  220  of the present invention preferably uses (60% to 80%) less real estate than prior art discharge plenums  120  (with the hundred series number being prior art as shown in  FIG. 1  and the two hundred series number being the present invention as shown in  FIG. 3 ) in air-handling systems. Comparing the prior art ( FIG. 1 ) and the present invention ( FIG. 3 ) shows a graphical representation of this shortening of the airway path  120 ,  220 . There are many reasons that using multiple smaller fan units  200  can reduce the length of the airway path  120 ,  220 . For example, reducing the size of the fan unit  100 ,  200  and motor  108 ,  208  reduces the length of the discharge plenum  110 ,  210 . Similarly, reducing the size of the inlet cone  104 ,  204  reduces the length of the inlet plenum  112 ,  212 . The length of the discharge plenum  110 ,  210  can also be reduced because air from the fan array fan section in the air-handling system of the present invention is substantially uniform whereas the prior art air-handling system has points of higher air velocity and needs time and space to mix so that the flow is uniform by the time it exits the air-handling compartment  102 ,  202 . (This can also be described as the higher static efficiency in that the present invention eliminates the need for settling means downstream from the discharge of a prior art fan system because there is little or no need to transition from high velocity to low velocity.) The fan array fan section in the air-handling system takes in air from the inlet plenum  212  more evenly and efficiently than the prior art air-handling system so that the length of the inlet plenum  112 ,  212  may be reduced. 
         [0069]    For purposes of comparison, the first exemplary structure set forth in the Background of the Invention (a structure requiring 50,000 cubic feet per minute of air flow at a pressure of six (6) inches water gage) will be used. Using the first exemplary structure, an exemplary embodiment of the present invention could be served by a nominal discharge plenum  210  of 89 inches high by 160 inches wide and 30 to 36 inches long (as compared to 106 to 112 inches long in the prior art embodiments). The discharge plenum  210  would include a 3×4 fan array fan section in the air-handling system such as the one shown in  FIG. 6 ) having 12 fan units  200 . The space required for each exemplary fan unit  200  would be a rectangular cube of approximately 24 to 30 inches on a side depending on the array configuration. The airway path  220  is 42 to 48 inches (as compared to 88 to 139 inches in the prior art embodiments). 
         [0070]    For purposes of comparison, the second exemplary structure set forth in the Background of the Invention (a structure requiring 26,000 cubic feet per minute of air flow at a pressure of two (2) inches water gage) will be used. Using the second exemplary structure, an exemplary embodiment of the present invention could be served by a nominal discharge plenum  210  of 84 inches high by 84 inches wide, and 30 to 36 inches long (as compared to 94 to 100 inches long in the prior art embodiments). The discharge plenum would include a 3×3 fan array fan section in the air-handling system (such as the one shown in  FIG. 7 ) having 9 fan units  200 . The space required for each exemplary fan unit  200  would be a rectangular cube of approximately 24 to 30 inches on a side depending on the array configuration. The airway path  220  is 42 to 48 inches (as compared to 71 to 95 inches in the prior art embodiments). 
       Reduced Production Costs 
       [0071]    It is generally more cost effective to build the fan array fan section in the air-handling system of the present invention as compared to the single fan unit  100  used in prior art air-handling systems. Part of this cost savings may be due to the fact that individual fan units  200  of the fan array can be mass-produced. Part of this cost savings may be due to the fact that it is less expensive to manufacture smaller fan units  200 . Whereas the prior art single fan units  100  were generally custom built for the particular purpose, the present invention could be implemented on a single type of fan unit  200 . In alternative embodiments, there might be several fan units  200  having different sizes and/or powers (both input and output). The different fan units  200  could be used in a single air-handling system or each air-handling system would have only one type of fan unit  200 . Even when the smaller fan units  200  are custom made, the cost of producing multiple fan units  200  for a particular project is almost always less that the cost of producing a single large prior art fan unit  100  for the same project. This may be because of the difficulties of producing the larger components and/or the cost of obtaining the larger components necessary for the single large prior art fan unit  100 . This cost savings also extends to the cost of producing a smaller air-handling compartment  202 . 
         [0072]    In one preferred embodiment of the invention, the fan units  200  are modular such that the system is “plug and play.” Such modular units may be implemented by including structure for interlocking on the exterior of the fan units  200  themselves. Alternatively, such modular units may be implemented by using separate structure for interlocking the fan units  200 . In still another alternative embodiment, such modular units may be implemented by using a grid system into which the fan units  200  may be placed. 
       Reduced Operating Expenses 
       [0073]    The fan array fan section in the air-handling system of the present invention preferably are less expensive to operate than prior art air-handling systems because of greater flexibility of control and fine tuning to the operating requirements of the structure. Also, by using smaller higher speed fan units  200  that require less low frequency noise control and less static resistance to flow. 
       Increased Efficiency 
       [0074]    The fan array fan section in the air-handling system of the present invention preferably is more efficient than prior art air-handling systems because each small fan unit  200  can run at peak efficiency. The system could turn individual fan units  200  on and off to prevent inefficient use of particular fan units  200 . It should be noted that an array controller  300  could be used to control the fan units  200 . As set forth above, the array controller  300  turns off certain fan units  200  and runs the remaining fan units  200  at peak efficiency. 
       Redundancy 
       [0075]    Multiple fan units  200  add to the redundancy of the system. If a single fan unit  200  breaks down, there will still be cooling. The array controller  300  may take disabled fan units  200  into consideration such that there is no noticeable depreciation in cooling or air flow rate. This feature may also be useful during maintenance as the array controller  300  may turn off fan units  200  that are to be maintained offline with no noticeable depreciation in cooling or air flow rate. A bypass feature, discussed below, uses and enhances the redundancy of the system. 
       Sound Attenuation Advantages 
       [0076]    The high frequency sound of the small fan units  200  is easier to attenuate than the low frequency sound of the large fan unit. Because the fan wall has less low frequency sound energy, shorter less costly sound traps are needed to attenuate the higher frequency sound produced by the plurality of small fan units  200  than the low frequency sound produced by the single large fan unit  100 . The plurality of fan units  200  will each operate in a manner such that acoustic waves from each unit will interact to cancel sound at certain frequencies thus creating a quieter operating unit than prior art systems. 
       Reduced Vibration 
       [0077]    The multiple fan units  200  of the present invention have smaller wheels with lower mass and create less force due to residual unbalance thus causing less vibration than the large fan unit. The overall vibration of multiple fan units  200  will transmit less energy to a structure since individual fans will tend to cancel each other due to slight differences in phase. Each fan unit  200  of the multiple fan units  200  manage a smaller percentage of the total air handling requirement and thus produce less turbulence in the air stream and substantially less vibration. 
       Alternative Embodiments 
       [0078]    As mentioned, in one preferred embodiment of the invention, the fan units  200  are modular such that the system is “plug and play.” Such modular units may be implemented by including structure for interlocking on the exterior of the fan units  200  themselves. Alternatively, such modular units may be implemented by using separate structure for interlocking the fan units  200 . In still another alternative embodiment, such modular units may be implemented by using a grid system into which the fan units  200  may be placed. 
         [0079]      FIG. 16  shows an embodiment using an exemplary grid system  230  into which the fan units  200  may be placed. In this embodiment the grid may be positioned and/or built within the air-handling compartment  202 . The fan units  200  may then be positioned into the grid openings. One advantage of this configuration is that individual fan units  200  may be easily removed, maintained, and/or replaced. This embodiment uses an exemplary unique motor mount  232  that supports the motor  208  without interfering with air flow therearound. As shown, this exemplary motor mount  232  has a plurality of arms that mount around the fan inlet cone  204 . It should be noted that the dimensions of the grid are meant to be exemplary. The grid may be constructed taking into consideration that the fan units  200  in the present invention may be spaced with as little as 20% of a fan wheel diameter between the fan units  200 . 
         [0080]      FIG. 17  shows an embodiment using either a grid system or modular units  240  using separate structure (not shown) for interlocking the fan units  200 . In this exemplary embodiment, each of the fan units  200  are mounted on a more traditional motor mount  242  within its own fan unit chamber  244 . In one preferred embodiment, the fan unit  200  and motor mount  242  are preferably suspended within their own fan unit chamber  244  such that there is an air relief passage  246  therebelow. This air relieve passage  246  tends to improve air flow around the fan units  200 . 
         [0081]    The fan unit chambers  244  shown in  FIG. 17  may include one or more interior surface lined with an acoustically absorptive material or “insulation surface”  248 . Similarly, the fan unit cells  244 ′ shown in  FIGS. 18-23  may include one or more interior surface made from an acoustically absorptive material or “insulation surface”  248 . Going against conventional industry wisdom that surfaces cannot be placed in close proximity with the fan units  200 , the present invention places one or more insulation surfaces  248  at least partially around each fan unit  200  without disrupting air flow. The insulation surfaces  248  may include one or more of the sides, top, bottom, front, or back. Exemplary types of insulation include, but are not limited to traditional insulation board (such as that made from inorganic glass fibers (fiberglass) alone or with a factory-applied foil-scrim-kraft (FSK) facing or a factory-applied all service jacket (ASJ)) or alternative insulation such as open cell foam such as that disclosed in U.S. patent application Ser. No. 10/606,435, which is assigned to the assignee of the present invention, and which the disclosure of which is hereby incorporated by reference herein. Together, the insulation surfaces  248  of the fan unit chambers/cells  244 ,  244 ′ tend to function as a coplanar silencer. Some of the benefits of using the coplanar silencer include (1) no added airway length for splitters, (2) no pressure drop, and/or (3) relatively low cost. The acoustic advantages of this and other embodiments make the present invention ideal for use in concert halls, lecture halls, performing arts centers, libraries, hospitals, and other applications that are acoustically sensitive. 
         [0082]      FIGS. 18-23  show an exemplary insulated grid system or modular unit system interior surfaces are made from acoustically absorptive material or “insulation surface”  248 . In this embodiment, each fan unit cell  244 ′ preferably has a sturdy frame  250  that supports the insulation surfaces  248 . In one preferred embodiment the frame would form only the edges of a cube-shaped fan unit cell  244 ′ and the insulation surfaces  248  would form the sides (e.g. top, bottom, and/or sides) of the cube-shaped fan unit cell  244 ′. In alternative preferred embodiments, the frame may include additional structure or braces for support and/or strength. Together, the insulation surfaces  248  of the fan unit cells  244 ′ tend to function as a coplanar silencer. This is shown graphically in  FIGS. 19-23  where the coplanar silencer (formed by the insulation surfaces  248 ) reduces the sound wave reaction as the sound waves travel through the insulation surfaces  248 . For example, in  FIG. 19 , the central fan unit  200   a  is loudest in its own fan unit cell  244 ′. As the sound of the fan spreads radially, it at least partially dissipates as it passes through the surrounding insulation surfaces  248 . This is shown graphically as the sound wave circles being darkest in the central fan unit cell  244 ′ and lighter in the surrounding fan unit cells  244 ′. The result is that the sound from the central fan unit  200   a  that eventually emanates from the system is softer than sound that would emanate from a system without the coplanar silencer. In  FIG. 20 , the first side fan unit  200   b  is loudest in its own fan unit cell  244 ′. As the sound of the fan spreads radially, it at least partially dissipates as it passes through the surrounding insulation surfaces  248 . This is shown graphically as the sound wave circles being darkest in the central fan unit cell  244 ′, lighter in the surrounding fan unit cells  244 ′, and still lighter in fan unit cells  244 ′ more distant from the originating fan unit  200   b . The result is that the sound from the fan unit  200   b  that eventually emanates from the system is softer than sound that would emanate from a system without the coplanar silencer.  FIG. 21  shows the first side fan unit  200   b , a second side fan unit  200   c , and their respective sound waves. As shown graphically in  FIG. 24 , another principle of the present invention is that as the sound waves interact, there is a degree of wave cancellation such that the waves are self-extinguishing.  FIG. 24  shows wave A and an opposite wave B that are opposites and therefore interact to form a flat wave A+B. If waves are not exactly opposite, then the combined wave will not be flat, but would have some wave cancellation. This is a basic wave principle of which the present invention is able to avail itself. The result of wave cancellation is that the sound from the fan units  200   b  and  200   c  that eventually emanates from the system is softer than sound that would emanate from a system without the coplanar silencer.  FIG. 22  emphasizes a first corner fan unit  200   d  and its wave pattern.  FIG. 23  emphasizes both the first corner fan unit  200   d  and a second corner fan unit  200   b  and their respective wave patterns. The analysis of  FIGS. 22 and 23  would be similar to that of  FIGS. 20 and 21  respectively. It should be noted that in the preferred embodiment, more than two fans might be running simultaneously and all the running fans would have wave patterns. The wave patterns of all the running fans would be able to take advantage of both the dissipation (as they pass though surrounding insulation surfaces  248 ) and wave cancellation of the coplanar silencer. 
         [0083]    Although  FIG. 17  shows the discharge plenum  210  positioned within the fan unit chambers  244 , alternative embodiments of fan unit chambers  244  could enclose the inlet plenum  212 , or at least partially enclose both the inlet plenum  212  and the discharge plenum  210 . Still other alternative embodiments of fan unit chambers  244  may have grid or wire surfaces (that increase the safety of the present invention) or be open (that would reduce costs). 
       Bypass Feature 
       [0084]    Multiple fan units enable the array to operate at a range of flow rates from full flow to partial flow where each fan contributes 1/N air flow (where N equals the number of fans). Most direct drive fan systems operate at speeds other than full synchronous motor speed in order to match the heating or cooling requirements of the structure. Speed control is normally maintained using variable frequency drives. Since variable frequency drives are electronic devices, each drive operating within an air handling structure has a certain probability of failure. In a traditional air handling system, if the VFD fails the air handler will either shut down or be operated at full synchronous speed of the motor in what is known as bypass mode. In traditional systems fan units in the air handler have to be throttled back through some mechanical means in order to limit pressure and flow to meet the building requirements. Mechanical throttling in bypass mode on traditional systems creates excessive noise and reduces fan efficiency. The present invention overcomes this problem by allowing for a change in the fan array output by turning certain fans OFF to meet the design point. The array can be tailored to meet the flow and pressure requirement without the need for mechanical throttling and subsequent added noise and reduction in efficiency. 
       Dampeners 
       [0085]      FIG. 25  shows an array of dampeners  260  that may be positioned either in front of or behind the fan units  200  to at least partially prevent back drafts. In the shown exemplary embodiment, the dampeners  260  include a plurality of plates, each plate positioned on its own pivot. In the shown exemplary embodiment, the plurality of plates slightly overlap each other. The shown embodiment is constructed such that when air is flowing through the fan units  200 , the plates are in the open position and when the air stops, gravity pulls the plates into the closed position. Preferably, each of the dampeners  260  operates independently such that if some of the fan units  200  are ON and some of the fan units  200  are OFF, the dampeners  260  can open or close accordingly. Although shown as a simple mechanical embodiment, alternative embodiments could include structure that is controlled electronically and/or remotely from the dampeners  260 . 
         [0086]    It should be noted that  FIG. 4  shows a 4×6 fan array fan section in the air-handling system having twenty-four fan units  200 ,  FIG. 5  shows a 5×5 fan array fan section in the air-handling system having twenty-five fan units  200 ,  FIG. 6  shows a 3×4 fan array fan section in the air-handling system having twelve fan units  200 ,  FIG. 7  shows a 3×3 fan array fan section in the air-handling system having nine fan units  200 , and  FIG. 8  shows a 3×1 fan array fan section in the air-handling system having three fan units  200 . It should be noted that the array may be of any size or dimension of more than two fan units  200 . It should be noted that although the fan units  200  may be arranged in a single plane (as shown in  FIG. 3 ), an alternative array configuration could contain a plurality of fan units  200  that are arranged in a staggered configuration (as shown in  FIG. 15 ) in multiple planes. It should be noted that cooling coils (not shown) could be added to the system either upstream or downstream of the fan units  200 . It should be noted that, although shown upstream from the fan units  200 , the filter bank  122 ,  222  could be downstream. 
         [0087]    It should be noted that an alternative embodiment would use a horizontally arranged fan array. In other words, the embodiments shown in  FIGS. 3-15  could be used horizontally or vertically or in any direction perpendicular to the direction of air flow. For example, if a vertical portion of air duct is functioning as the air-handling compartment  202 , the fan array may be arranged horizontally. This embodiment would be particularly practical in an air handling compartment for a return air shaft. 
         [0088]    It should be noted that the fan section  214  may be any portion of the airway path  220  in which the fan units  200  are positioned. For example, the fan units  200  may be situated in the discharge plenum  210  (as shown), the inlet plenum  212 , or partially within the inlet plenum  212  and partially within the discharge plenum  210 . It should also be noted that the air-handling compartment  202  may be a section of air duct. 
         [0089]    It should be noted that many of the features and properties associated with the fan unit chambers  244  ( FIG. 17 ) would be identical to or similar to properties of the fan unit cells  244 ′ ( FIGS. 18-23 ). 
         [0090]      FIG. 26  shows airflow between the two panels  20  which represent acoustically insulated surfaces and sound attenuation layers.  FIGS. 26-28  show a first embodiment in which a fiberglass core  22  has an open cell foam  24  layered with at least one side of the fiberglass core  22 . FIGS.  26  and  28 - 31  show a second embodiment combining the use of open cell foam  24  with for use of perforated rigid facing  26 .  FIGS. 31 and 32  show a third embodiment in which the entire insulation board  10  is replaced with an uncoated open cell foam pad  22 . 
         [0091]    Turning first to the first embodiment shown in  FIGS. 26-28 , this layered embodiment includes a fiberglass core  22  (or other type of insulation) that has an open cell foam  24  layered with at least one side of the fiberglass core  22 . One advantage to using both the fiberglass material and the open cell foam material is that it is less expensive than using open cell foam material alone because open cell foam is more expensive than fiberglass. Another advantage to using both the fiberglass material and the open cell foam material is that it weighs less than using fiberglass material alone because fiberglass weighs more than open cell foam. Another advantage to using both the fiberglass material and the open cell foam material is that is that the two materials provide different types of acoustic insulation over a different range of frequencies. Together, the two materials provide sound absorption over greater range of frequencies.  FIG. 33  illustrates a graph with a vertical axis as the absorption coefficient going from 0 to 1 and a horizontal axis showing the frequency going from 0 to 10,000 Htz at approximately the peak point.  FIG. 33  is meant to be exemplary and does not necessarily reflect accurate measurements. 
         [0092]    Alternative embodiments of the first layered embodiment include a fiberglass core  22  with one side layered with open cell foam  24  ( FIG. 26 ), a fiberglass core  22  with both sides layered with open cell foam  24  ( FIG. 27 ), and a fiberglass core  22  and layered with open cell foam  24  secured by perforated rigid facing  26  ( FIG. 28 ). The bottom section of  FIG. 31  shows the embodiment of  FIG. 28  in use in an exemplary air handler. It should also be noted that an alternative embodiment of the present invention could include more than two layers of different types of insulation. For example, a four layer version could be open cell foam, fiberglass, rockwool, and open cell foam. The layered embodiment could actually be “tuned” using different types of insulations, different quantities of insulations, and different thicknesses of insulations to have the desired acoustic properties for the intended use. 
         [0093]    The present invention also includes a method for making an air handler using the panels and layers. The method includes the steps of providing an air handler system with at least one air handler surface, providing a core of first insulation material having at least one layering surface, and providing a facing of open cell foam second insulation material. Then, the facing is at least partially layered to the at least one layering surface to form a layered insulation board. Finally, the at least one air handler surface is at least partially covered with the layered insulation board so that the facing is exposed to airflow through the air handler. 
         [0094]    Turning next to the second embodiment shown in FIGS.  26  and  28 - 31 , this perf-secured embodiment combines the use of open cell foam  24  with use of perforated rigid facing  26 . Combining the use of open cell foam and perforated rigid facing  16  provides significant advantages for use in air handlers. For example, the use of the perforated rigid facing  26  to secure the open cell foam  24  does not significantly reduce the sound absorption qualities of the open cell foam  24 . As shown in  FIG. 29 , the open cell structure of the open cell foam  24  allows portions of the open cell foam  24  to protrude from openings defined in the perforated rigid facing  26  (shown in front view in  FIG. 30 ). The exposed open cell foam  24  is able to absorb sound waves. In one embodiment, protruding open cell foam  24  formed between the openings in the perforated rigid facing  26  absorbs sound waves. This can be compared to prior art embodiments in which sound waves are reflected by the substantially rigid diaphragms formed by the smooth facing  14  being divided by the perforated rigid facing  16 . 
         [0095]    Alternative embodiments of the second perf-secured embodiment include a fiberglass core  22  and layered with open cell foam  24  secured by perforated rigid facing  26  ( FIG. 28 ) and non-layered open cell foam  24  secured by perforated rigid facing  26  (the bottom section of  FIG. 31 ). It should be noted that alternative embodiments may replace perforated rigid facing  26  shown in  FIG. 30  with alternative securing structure such as perforated rigid facing  26  with alternatively shaped openings, straps, netting, wire grids, or other securing structure suitable to prevent the open cell foam  24  from being drawn inward. 
         [0096]    The present invention also includes a method for making an air handler using the perf-secured embodiment. The method includes the steps of providing an air handler system with at least one air handler surface, providing open cell foam insulation material, and providing securing structure through which said facing may be exposed. Then, the at least one air handler surface is at least partially covered with the open cell foam insulation material. Finally, the open cell foam insulation material is secured to the at least one air handler surface so that the protruding open cell foam insulation material is exposed to sound waves and/or airflow through the air handler. 
         [0097]    Turning next to the third preferred embodiment shown in  FIGS. 31 and 32 , in this uncoated embodiment combines the entire insulation board  10  is replaced with uncoated open cell foam  24 . This would be particularly suitable for uses in which the presence of fiberglass would not be satisfactory for the intended use or would be unacceptable to the intended client. For example, pharmaceutical companies involved in ingestible or injectable drugs would find it unacceptable to have any fiberglass in the air handler. Alternative embodiments of the second uncoated embodiment include uncoated open cell foam  24  secured by perforated rigid facing  26  ( FIG. 31 ) uncoated open cell foam  24  secured in a frame  30  ( FIG. 32 ). 
         [0098]    The present invention also includes a method for making an air handler using the uncoated third embodiment. The method includes the steps of providing an air handler system with at least one air handler surface and open cell foam. The method also includes the step of covering at least partially the at least one air handler surface with the open cell foam. 
         [0099]    The present invention is directed to the use of open cell foam in air handlers that has the necessary durability, safety, and cleanliness properties for the particular use. One exemplary open cell foam, melamine foam (Melamine—Formaldehyde-Polycondensate), has been shown to be quite suitable for this purpose. Melamine is a lightweight, high temperature resistant, open cell foam that has excellent thermal properties with superior sound absorption capabilities. Melamine is cleanable in that it is relatively impervious to chemicals (e.g. it is able to withstand relatively caustic cleaning agents such as SPOR-KLENZ® without breaking down). Melamine also meets the flame spread, smoke density, and fuel contribution requirements necessary to comply with Class-I building code regulations. Because it does not shed particles, it can be used in places where fiberglass would be precluded. Still further, as melamine is inert, it would not cause the health problems (such as those associated with fiberglass) for those who are exposed to the product. It also is relatively attractive. It should be noted that melamine foam has been used as acoustic insulation by such companies as illbruk (www.illbruk-sonex.com). It should be noted that alternative open cell foams could be substituted for melamine. For example, silicone or polyethane foam could be used as the open cell foam of the present invention. 
         [0100]    It should be noted that the present invention has been primarily discussed in terms of fiberglass as an alternative type of insulation. It should be noted that other types of insulation may be used in place of fiberglass including, but not limited to rockwool. 
         [0101]    Although the embodiments are discussed in terms of layering fiberglass material and the open cell foam material, alternative embodiments could include, bonding the fiberglass material to the open cell foam material, enclosing the fiberglass material within the open cell foam material, coating the fiberglass material with an open cell foam material, and other means for layering the two materials. The term “layers” or “layering” are meant to encompass all of these embodiments as well as others that would be known to those skilled in the art. 
         [0102]      FIG. 34  illustrates a table showing an example of a configuration and operating performance level for a fan array implemented in accordance with an embodiment of the present invention. 
         [0103]      FIG. 35  illustrates performance curves for static pressure vs. airflow, and brake horse power (BHP) versus airflow for a fan array implemented in accordance with an embodiment of the present invention. 
         [0104]      FIG. 36  illustrates performance curves for total pressure (TP) vs. airflow, and BHP versus airflow for a conventional air handler. 
         [0105]      FIG. 37  illustrates bar graphs showing an example of sound power levels at octave bands 1-8 produced by a fan array of fan units without with acoustically absorptive material and produced by a fan array of fan units lined with acoustically absorptive material implemented in accordance with an embodiment of the present invention. The fan array included AF20 fans (i.e., 20 inch fans), that were operated at 2030 RPMs to product 6000 CFM at 3.7 inches of total static pressure. 
         [0106]      FIG. 38  illustrates control options for a fan array implemented in accordance with an embodiment of the present invention. In  FIG. 38 , one control option includes a controller  3102  that includes a single VFD  3104  with individual motor protection. In  FIG. 38 , another control option includes a controller  3110  that includes variable frequency drives  3112  and a programmable logic controller (PLC)  3114 . 
         [0107]      FIG. 39  illustrates a fan array  3200  implemented in accordance with an embodiment of the present invention. The fan array  3200  includes fan units  3202  arranged in columns. The fan units  3202  include tops  3204 , bottoms  3206  and sides  3208  that are performed. 
         [0108]      FIG. 40  illustrates a sound power comparison of a fan array implemented in accordance with an embodiment and 55 inch diameter traditional plenum fan. 
         [0109]    It should be noted that the term “air handlers” is meant to include, by way of example, recirculation air handlers, central air handlers, silencers, splitters (such as parallel splitters), clean room ceiling systems, and commercial/industrial air handling systems. 
         [0110]    The terms and expressions that have been employed in the foregoing specification are used as terms of description and not of limitation, and are not intended to exclude equivalents of the features shown and described or portions of them. The scope of the invention is defined and limited only by the claims that follow. 
         [0111]    It is to be understood that the above description is intended to be illustrative, and not restrictive. For example, the above-described embodiments (and/or aspects thereof) may be used in combination with each other. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from its scope. Dimensions, types of materials, orientations of the various components, and the number and positions of the various components described herein are intended to define parameters of certain embodiments, and are by no means limiting and are merely exemplary embodiments. Many other embodiments and modifications within the spirit and scope of the claims will be apparent to those of skill in the art upon reviewing the above description. The scope of the invention should, therefore, be determined with reference to the appended claims, along with the full scope of equivalents to which such claims are entitled. In the appended claims, the terms “including” and “in which” are used as the plain-English equivalents of the respective terms “comprising” and “wherein.” Moreover, in the following claims, the terms “first,” “second,” and “third,” etc. are used merely as labels, and are not intended to impose numerical requirements on their objects. Further, the limitations of the following claims are not written in means—plus-function format and are not intended to be interpreted based on 35 U.S.C. §112, sixth paragraph, unless and until such claim limitations expressly use the phrase “means for” followed by a statement of function void of further structure.