Abstract:
A plug or plenum fan is located near two walls of the plenum such that they tend to act as the scroll for the fan. Additionally, a partition separates the fan from an adjacent corner further enhancing the formation of a scroll while providing a flow passage and a location for at least a part of the active noise control structure.

Description:
BACKGROUND OF THE INVENTION 
     A plug or plenum fan is the term used to describe the application of backward inclined or airfoil fans housed in large plenums. The fan typically consists of a single-inlet impeller assembly with an inlet bell-mouth. The orifice is mounted flush to one side of the plenum, such that the orifice and shaft of the fan are generally in the direction of the flow. Both draw-through and blow-through applications are used. For draw-through applications, the fan and plenum are located downstream of the heating and cooling coils. For the blow-through applications, the fan and coil sections are reversed. In the draw through case, the fan pressurizes the plenum and one or more discharge ducts are attached at any of the side-walls. For most packaged units however, the discharge is attached directly downstream of the fan/plenum section. This section may include passive mufflers, filter sections and additional coils (blow-through). For cases where passive mufflers are supplied, an additional settling section is required which adds to the overall length of the system. An inlet section is attached at the fan/plenum interface; this may also include the same components as those described for the discharge section. 
     To control the noise from air handling units, duct active noise control (ANC) systems are starting to be employed in air distribution systems. An ANC system basically requires the sensing of the noise associated with the fan for distributing the air, producing a noise canceling signal and determining the results of the canceling signal so as to provide a correction signal to the controller producing the noise canceling signal. There is a time delay associated with sensing the noise and producing a canceling signal. This time delay necessary for the canceling to take place equates to the minimum flow path distance in the system required between the reference, or input, noise sensor and the loudspeaker. Additional space is required between the loudspeaker and the error sensor which adds to the flow path distance in the system. The space limitations in existing buildings severely limits the retrofitting or replacement of existing equipment with equipment using conventional ANC approaches due to the system length requirements. The employing of an active noise control device would eliminate the need for both the downstream settling and passive muffler sections. However, conventional active noise control configurations would also add considerable length to the system, on the order of six to eight feet. 
     SUMMARY OF THE INVENTION 
     The fan is asymmetrically located within the plenum with an offset such that the centerline of the fan is biased towards one of the corners of the plenum. This offset places the fan close to two walls of the plenum such that they effectively act like the scroll of a centrifugal fan, diffusing the flow and providing a more efficient operation. By asymmetrically locating the fan, as described, a corner opposite one in which the fan is located can be the location of the outlet with a partition defining a part of the discharge path as well as a part of the effective scroll for the fan. The partition can serve as a location of at least a portion of the active noise control structure thereby minimizing the system length increase due to the active noise control structure. 
     It is an object of the invention to attenuate noise at the inlet or discharge of a plug fan using active noise control. 
     It is another object of this invention to provide optimized performance in combination with a small package size. 
     It is a further object of this invention to locate the discharge duct relative to the fan so as to increase aerodynamic efficiency. These objects, and others as will become apparent hereinafter, are accomplished by the present invention. 
     Basically, a plug or plenum fan is located near two walls of the plenum such that they tend to act as the scroll for the fan. Additionally, a partition separates the fan from an opposite corner further enhancing the formation of a scroll while providing a flow passage and a location for at least a part of the active noise control structure. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     For a fuller understanding of the present invention, reference should now be made to the following detailed description thereof taken in conjunction with the accompanying drawings wherein: 
     FIG. 1 is a view with the top panels removed of a PRIOR ART air handler unit arrangement employing passive mufflers; 
     FIG. 2 is a view with the side panel removed of an air handler unit arrangement employing the present invention; 
     FIG. 3 is a view with the side panel removed of a modified air handler unit arrangement employing the present invention; and 
     FIG. 4 is a sectional view taken along line  4 — 4  of FIG.  3 . 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     In FIG. 1, the numeral  10  generally designates a conventional air handler unit (AHU) with passive mufflers for sound reduction. The AHU  10  is made up of a plurality of sections and/or subassemblies including settling section  10 - 1  containing passive mufflers  10 - 1   a,  filter section  10 - 2  containing filter  10 - 2   a,  coil section  10 - 3  containing coils  10 - 3   a  and  10 - 3   b,  fan section  10 - 4  containing backward inclined or airfoil fan  12  and, settling section  10 - 5  having a baffle  10 - 5   a  and muffler section  10 - 6  containing passive mufflers  10 - 6   a.  Fan  12  is driven by motor  13  and has an inlet orifice  12 - 1  aligned with the overall flow path through AHU  10 . Fan  12  discharges transversely to the overall flow path. 
     In operation, fan or blower  12  is driven by motor  13  thereby drawing return and makeup air into the AHU  10 , through a heat exchanger defined by coils  10 - 3   a  and  10 - 3   b  to heat or cool the air, thence via inlet orifice  12 - 1  into fan  12  which discharges the air into fan housing  10 - 4 . Baffle  10 - 5   a  provides a circuitous discharge path from fan housing  10 - 4  to settling section  10 - 5 . The flow from settling section  10 - 5  travels through muffler section  10 - 6  which contains passive mufflers  10 - 6   a  and thence into the air distribution system (not illustrated). 
     Referring now to FIG. 2, AHU  110  has a mixing box  110 - 1 , filter  110 - 2 , coil  110 - 3  and fan housing  110 - 4 . A baffle  114  extends from one of the walls of fan housing  110 - 4  and is made up of two legs  114 - 1  and  114 - 2 . Backward inclined or airfoil fan  112  is located in fan housing  110 - 4  transversely to the overall flow path through AHU  110  and is located in proximity to wall  110 - 4   a  and legs  114 - 1  and  114 - 2  of baffle  114  which coact to effectively define a scroll for fan  112 . Additionally, leg  114 - 2  coacts with a portion of walls  110 - 4   b  and  110 - 4   c  and a wall (not illustrated) to define a first portion of the outlet flow path from fan housing  110 - 4 . The outlet flow path is defined by walls  110 - 4   b ,  110 - 4   c ,  110 - 4   d ,  110 - 4   e , and  110 - 4   f , a wall (not illustrated) as well as legs  114 - 1  and  114 - 2  such that it, effectively has three sections at 90° angles. The center of the fan housing  110 - 4  is offset from the center AHU 110  so as to allow the fan  112  to circulate the incoming air downwardly toward the aforementioned outlet flowpath as shown. The outlet flow path containing the ANC system is sized to keep the flow under 2,500 feet per minute to obtain optimum system performance. Guide vanes  116  are located at the 90° bends to guide the flow. Acoustic lining  118  is located on the structure defining the outlet flow path. The circuitous discharge flow path adds flow path length while adding less length than that required by settling section  10 - 5  and muffler section  10 - 6  of AHU  10 . The length reduction achieved through the use of the present invention is roughly the length required by settling section  10 - 5  of AHU  10 . Duct active noise control (ANC) is located relative to the discharge flow path. The locating of ANC structure in the flow path depends upon locating the sensing microphone(s)  120  at or near the blower outlet/inlet to the discharge flow path where noises due to turbulence normally preclude the placement of the sensing microphone(s)  120 . The placement of sensing microphone(s)  120  in the region of the blower outlet is possible through the use of turbulence shields which are the subject of commonly assigned U.S. Pat. No. 5,808,243 and U.S. patent application Ser. No. 08/871,202 filed Jun. 27, 1997. Additionally, commonly assigned U.S. patent application Ser. No. 08/884,231 filed Jun. 27, 1997 discloses the locating of ANC structure in an elbow. The noise canceling speaker(s)  122  and the error sensing microphone(s)  124  are located in the discharge flow path downstream of sensing microphone(s)  120  and, preferably, downstream of guide vanes  116 . 
     In operation, fan  112  is driven by a motor (not illustrated) thereby drawing return air and makeup air into the AHU  110 , through the heat exchanger defined by coil  110 - 3  to heat or cool the air and delivering the resultant conditioned air into fan housing  110 - 4  where it passes into the discharge flow path defined in part by leg  114 - 2  and walls  110 - 4   b  and  110 - 4   c.  The fan noise in the discharge flow path is sensed by microphone(s)  120  and through circuitry (not illustrated) speaker(s)  122  which is located on wall  110 - 4   e  is driven to produce a signal to cancel the fan noise. Microphone(s)  124  which is located on wall  110 - 4   e  senses the result of the noise cancellation by speaker(s)  122  and through circuitry (not illustrated) the output of speaker(s)  122  is corrected. Accordingly, the ANC system is kept wholly within the casing structure of AHU  110 . 
     FIGS. 3 and 4 illustrate a modified embodiment of the invention. AHU  210  differs from AHU  110  in that backward inclined or airfoil fan  212  is rotated 90° such that its axis of rotation is generally aligned with the overall flow path through AHU  210 . The structure and operation would otherwise be the same as that of AHU  110 . Specifically, fan  212  is driven by motor  213  thereby drawing return air and makeup air into AHU  210 , through the heat exchanger defined by coil  210 - 3  to heat or cool the air and delivering the resultant conditioned air into fan housing  210 - 4  where it passes into the discharge flow path defined in part by legs  214 - 1  and  214 - 2  and walls  210 - 4   b  and  210 - 4   c.  The fan noise in the discharge flow path is sensed by microphones  220 - 1  and  220 - 2  and through circuitry (not illustrated) speaker(s)  222  which is located on wall  210 - 4   e  is driven to produce a signal to cancel the fan noise. Microphone(s)  224  which is located on wall  201 - 4   e  senses the result of the noise cancellation by speaker(s)  222  and through circuitry (not illustrated) the output of speaker(s)  222  is corrected. 
     From the foregoing description, it should be clear that the noise canceling structure is incorporated into the fan housing  110 - 4  or  210 - 4  and eliminates the need for the settling section  10 - 5  of AHU  10 . 
     Although preferred embodiments of the present invention have been illustrated and described, other changes will occur to those skilled in the art. For example, the description has been specific to draw-through applications but could be applied to blow-through applications by reversing the fan and coil sections. It is therefore intended that that scope of the present invention is to be limited only by the scope of the appended claims.