Patent Application
20050159102
The present invention relates generally to exhaust fans, and more particularly to exhaust fans of the type that draw contaminated air from one or more fume hoods dispersed throughout a building, mix the contaminated air with ambient air to dilute the contaminants, and vent the diluted air from the building into the ambient environment.
There are many different types of exhaust systems for buildings. In most of these the objective is to simply draw air from inside the building in an efficient manner. In building such as laboratories, fumes are produced by chemical and biological processes, which may have an unpleasant odor, is noxious or toxic. One solution is to exhaust such fumes through a tall exhaust stack which releases the fumes far above ground and roof level. Such exhaust stacks, however, are expensive to build and are unsightly.
Another solution is to mix the fumes with fresh air to dilute the contaminated air, and exhaust the diluted air upwards from the top of the building at a high velocity. The exhaust is thus diluted and blown high above the building. Examples of such systems are described in U.S. Pat. Nos. 4,806,076; 5,439,349 and 6,112,850.
Among these systems, U.S. Pat. No. 4,806,076 discloses a system in which a fan motor has a motor shaft that is directly connected to a fan having rotating fan blades that draw contaminated exhaust air from the building and blow the exhaust air up into the ambient environment. Unfortunately, the bearings that support the motor shaft inside the motor absorb the thrust loads imparted by the fan during operation, thus increasing wear on the motor. Furthermore, because the interface between the motor shaft and the fan is located in an area that receives exhaust air during operation, a person is required to enter an area that is polluted with contaminants when motor maintenance operations involve detachment of the motor shaft from the fan.
What is therefore desired is a building exhaust system including a building exhaust stack coupled to a fan that overcomes the deficiencies associated with conventional systems.
In accordance with one aspect of the present invention, a fan assembly is configured to exhaust contaminated air from a building. The fan assembly includes an outer wall that defines a cavity therein having an air inlet formed at its bottom end. The air inlet receives the contaminated air. An inner wall is fastened to the outer wall and positioned in the cavity to divide it into a central chamber isolated from the contaminated air, and a surrounding annular space that receives the contaminated air. A fan is disposed in the central chamber, and is coupled to a fan shaft to draw exhaust air in through the air inlet and blow it upward through the annular space. A motor is mounted in the central chamber, and has a motor shaft that drives the fan shaft. A coupling is located in the central chamber and connects the fan shaft to the motor shaft.
In accordance with another aspect of the invention, an exhaust assembly is mounted onto a roof of a building for removing contaminated air from one or more building exhaust vents. The exhaust assembly includes an air inlet receiving the contaminated air, at least one ambient air entrainment zone mixing ambient air with the contaminated air to produce diluted air, and an air outlet exhausting the diluted air. A fan chamber retains a fan that is coupled to a fan shaft to draw exhaust air in through the air inlet and blow it in a direction toward the air outlet. A drive chamber is also provided. The drive chamber is isolated from the exhaust air, and retains a motor having a motor shaft operable to drive the fan shaft, and a coupling connecting the fan shaft to the motor shaft.
In accordance with still another aspect of the invention, an exhaust assembly is provided for expelling exhaust air from a building. The exhaust assembly includes a housing defining an inlet end receiving the exhaust air and an outlet end for expelling the exhaust air. The housing defines a fan chamber and a drive chamber that is isolated from the exhaust air. A fan is disposed in the fan chamber and coupled to a fan shaft for rotation to draw the exhaust air through the inlet and direct the exhaust air in a direction toward the outlet. A motor mounted in the drive chamber, the motor including a motor shaft coupled to the fan shaft via a coupling disposed in the drive chamber. At least one passageway extends through the housing, the passageway providing access to the motor and the coupling.
In the following description, reference is made to the accompanying drawings, which form a part hereof, and in which there is shown by way of illustration, and not limitation, a preferred embodiment of the invention. Such embodiment also does not define the scope of the invention and reference must therefore be made to the claims for this purpose.
Reference is hereby made to the following drawings in which like reference numerals correspond to like elements throughout, and in which:
Referring initially to
Referring also to
The control of this system typically includes both mechanical and electronic control elements. A conventional damper 36 is disposed in conduit 32 at a location slightly above each hood 22, and is automatically actuated between a fully open orientation (as illustrated) and a fully closed orientation to control exhaust flow through the chamber 28. Hence, the volume of air that is vented through each hood 22 is controlled.
The building can be equipped with more than one exhaust assembly 42, each such assembly 42 being operably coupled either to a separate group of fume hoods 22 or to manifold 34. Accordingly, each exhaust assembly 42 can be responsible for venting noxious gasses from a particular zone within the building 26, or a plurality of exhaust assemblies 42 can operate in tandem off the same manifold 34. In addition, the manifold 34 may be coupled to a general room exhaust in building 26. An electronic control system (not shown) may be used to automatically control the operation of the system.
As shown best in
The hood 72 extends outwardly from the housing to provide a bypass air inlet 74 to the plenum 44. The hood 72 is formed by a pair of spaced vertical walls 69, a bottom wall 79, and a rain hood 82 which extends horizontally outward from the housing and then slopes downward. An upwardly-turned lip 84 is formed on the drip edge of the rain hood 82 to prevent water from dripping into the bypass air stream.
A damper 86 is mounted beneath the hood 72 to control the amount of ambient air that enters the plenum housing through the bypass air inlet 74. It includes damper blades that are controlled electronically or pneumatically to enable a flow of bypass air into the plenum 44 which maintains a constant total air flow into the fan assembly 46 despite changes in the volume of air exhausted from the building. Exhaust air from the building enters the plenum 44 through an exhaust inlet 88 formed in the bottom of the rectangular housing and mixes with the bypass air to produce once-diluted exhaust air that is drawn upward through an exhaust outlet 90 in the top of the pedestal 68 and into the fan assembly 46.
As shown best in
As shown best in
Referring particularly to
The removable panels 70 also enable access to the interior of the plenum 44 from any direction. This enables routine maintenance and repairs to be made without having to remove the entire exhaust fan assembly 42 from the riser 38 or the fan assembly 46 from the plenum 44. Also, in many installations it is advantageous for the building exhaust air to be brought into the plenum 44 through one of its side walls 64 rather than the bottom. In such installations the appropriate panel 70 is removed to form the exhaust inlet to the plenum 44 and the bottom of the plenum housing is enclosed with a bottom wall (not shown in the drawings).
Referring to
A fan shaft 114 is disposed in drive chamber 108 and is rotatably fastened advantageously by a single bearing 118 to a bottom plate 116 that is welded to the bottom end of inner wall 106. Fan shaft 114 extends down into the fan chamber 112 to support a fan wheel 120 at its lower end, and extends up into drive chamber 108 where it is connected to a motor shaft 152 via a compliant flexible coupling 122 that compensates shaft misalignments in at least one, and more preferably two, orientations (e.g., angular and axial shaft misalignments) as described in more detail below. Motor shaft 152 extends through a rectangular horizontal plate 124 that extends across the interior of the drive chamber 108 and is supported from below by a set of gussets 126 spaced around the interior of the drive chamber 108.
As best illustrated in
Wheelback 130 can also include, if desired, a set of auxiliary fan blades 134 fastened to its upper surface that produce a radially outward directed air flow. Because shaft 114 and bearing 118 should provide a good seal with the bottom plate 116, no source of air should be available and this air flow is not well defined. However, if a leak should occur, an air flow pattern is established in which air is drawn from the drive chamber 108 and directed radially outward through a gap formed between the upper rim of the fan wheel 130 and the bottom plate 116. As a result, exhaust air cannot escape into the drive chamber 108 even if a leak should occur.
As best illustrated in
Referring now to
Referring also to
Coupling 122 includes an upper segment 174 fastened to the motor shaft 152, and a lower segment 176 fastened to the fan shaft 114. Each segment includes an adapter 178 that surrounds the terminal end of the corresponding shaft. Each adapter 178 includes a radial flange 180 at its axially outer end and a sleeve 182 extending axially inwardly from the flange 180. Each sleeve 182 has a cylindrical inner wall that receives the corresponding shaft, and an outer wall that is sloped radially inwardly along direction taken axially inward from flange 180. Each sleeve 182 is fitted inside a corresponding bushing 184 having an inner cylindrical wall that is sloped to mate with sloped outer wall of sleeve 182. Three screws 186 (two shown) are spaced 120° apart from each other, and extend through flange 180 and into bushing 184. As screws 186 are tightened, the sloped inner walls of bushings 184 biases sleeve 182 against the corresponding shaft, thus locking shafts 152 and 114 in the coupling 122.
It should be appreciated that a number of commercially available couplings provide alternative, yet suitable, mechanisms that fasten a shaft to the coupling (e.g., a set screw). All such alternative designs are intended to fall within the scope of the present invention.
A horizontally extending flexible cylindrical plate 188, which can be made from stainless steel or any suitable alternative material, is disposed between bushings 184. The upper bushing 184 is connected to plate 188 via a pair of upright screws 190 and the lower bushing 184 is connected to plate 188 via a pair of inverted screws 192. Each upright screw 190 is radially spaced 180° with respect to each other, and 90° with respect to each adjacent inverted screw 192 (
Each upright screw 190 extends downward through upper and lower bushings bushings 184, and is fastened by a conventional nut 194. A washer 196 is disposed between plate 188 and lower bushing 184. An unthreaded sleeve 198 surrounds the shaft of screw 190 proximal to the screw head, and acts against the upper surface of plate 188. Accordingly, sleeve 198 and nut 194 fasten plate 188 to the lower bushing 184. Sleeve 198 extends through a bore 200 formed in upper bushing 184 that has a diameter greater than the diameter of both the sleeve 198 and the screw head to provide clearance that enables both angular displacement of sleeve 198 within bore 200 and axial displacement of the screw head and sleeve 198 within bore 20. The inverted screws 192 similarly extend upward through lower and upper bushings 184 to fasten the upper bushing 184 to plate 188.
Referring to
Coupling 122 is furthermore axially compliant. Specifically, sleeves 182 and 198 are compressible in the axial direction if, for instance, shafts 114 and 152 are pushed toward each other during operation. If, on the other hand, shafts 114 and 152 are pulled in a direction away from each other, upper and lower bushings 184 separate, thus depressing the screw heads of screws 190 and 192 into the corresponding bores 200. Plate 188 also flexes in this situation to accommodate the axial separation of bushings 184.
When maintenance operations are to be performed on motor 150 or its associated components inside drive chamber 108, screws 186 can be accessed via the passageway through annular space 110 and an access opening that exists between rectangular plate 124 and cylindrical inner wall 106. Once screws 186 have been loosened, shaft 152 can be removed from sleeve 182. Advantageously, coupling 122 is disposed in drive chamber 108 and, accordingly, the user is not exposed to the contaminants of the building exhaust when disengaging shaft 152 from the coupling 122. Furthermore, because only single bearing 118 rotatably supports fan shaft 114, maintenance is reduced compared to conventional systems whose fan/motor shafts require at least two bearings. Moreover, bearing 118 absorbs the thrust loads imparted by fan wheel 120, thus preserving the bearings inside motor 150.
Advantageously, one edge of mounting bracket 154 is connected to plate 124 via a hinge 158 that permits mounting bracket 154 to pivot relative to plate 124 once fastener(s) 156 have been removed. Preferably hinge 158 is oriented perpendicular to an axis extending perpendicular between the passageways. In this regard, hinge 158 extends perpendicular to flanges 168. Hinge 158 permits mounting bracket 154 and motor 150 to pivot between a first position in which shafts 152 and 114 can be engaged by coupling 122 and fasteners 156 can connect bracket 154 to plate 124, and towards one of the passageways in the direction of Arrow A to a second position whereby inspection and maintenance can be performed. Wedge-shaped flanges 168 provide additional structural support for bracket at locations proximal hinge 158 where increased forces result from motor pivoting.
Motor 150 can be manually pivoted about hinge 158 at any angle between 0° and 180° (with respect to bracket 154 and plate 124) to provide the needed access to the components inside chamber 18. In one aspect of the invention, motor 150 pivots at an angle of about 90° such that the vertical surfaces of flanges 168 proximal hinge 158 provide a stop with respect to motor 150 pivoting beyond 90°. Alternatively, the vertical flange surfaces could be positioned to provide additional clearance with respect to plate 124, thereby allowing the motor to pivot beyond 90°. In this instance, a stop in the form of flange 145 could extend from wall 144 (
It should be appreciated that hinge 158 can be disassembled in the usual manner (e.g., by removing the hinge pin) in order to facilitate removal of motor 150 from assembly 42.
Alternatively, referring to
Referring now to also to
Referring particularly to
Referring particularly to
A number of features on this system serve to enhance the entrainment of ambient air and improve fan efficiency. The flared inlet bell 58 at the bottom of the windband 52 has been found to increase ambient air entrainment by several percent. This improvement in air entrainment is relatively insensitive to the angle of the flare and to the size of the inlet bell 58. The same is true of the ring section 60 at the top of the windband 52. In addition to any improvement the ring section 60 may provide by increasing the axial height of the windband 52, it has been found to increase ambient air entrainment by 5% to 8%. Testing has shown that minor changes in its length do not significantly alter this performance enhancement.
It has been discovered that ambient air entrainment is maximized by minimizing the overlap between the rim of the nozzle 162 and the bottom rim of the windband 52. In the preferred embodiment these rims are aligned substantially coplanar with each other such that there is no overlap.
Another feature which significantly improves fan system operation is the shape of the nozzle 162. It is common practice in this art to shape the nozzle such that the exhaust is directed radially inward to “focus” along the central axis 56. This can be achieved by tapering the outer wall radially inward or by tapering both the inner and outer walls radially inward to direct the exhaust towards the central axis 56. It is a discovery of the present invention that ambient air entrainment can be increased and pressure losses decreased by shaping the nozzle 162 such that exhaust air is directed radially outward rather than radially inward towards the central axis 56. In the preferred embodiment this is achieved by flaring the top end 166 of the inner wall 106. Air entrainment is increased by several percent and pressure loss can be reduced up to 30% with this structure. It is believed the increase in air entrainment is due to the larger nozzle perimeter that results from not tapering the outer wall 100 radially inward. It is believed that the reduced pressure loss is due to the fact that most of the upward exhaust flow through the annular space 110 is near the outer wall 100 and that by keeping this outer wall 100 straight, less exhaust air is diverted, or changed in direction by the nozzle 162.
Referring particularly to
As shown in
In addition to the performance enhancements discussed above, the structure of the exhaust assembly lends itself to customization to meet the specific needs of users. Such user specifications include volume of exhaust air, plume height, amount of dilution with ambient air, and assembly height above roof top. User objectives include minimizing cost. Such customization is achieved by selecting the size, or horsepower, of the fan motor 150, and by changing the four system parameters illustrated in
Nozzle Exit Area:
Windband Exit Area:
Windband Length:
Windband Entry Area (minor effect)
For example, for a specified system, Table 1 illustrates how windband length changes the amount of entrained ambient air in the exhaust and Table 2 illustrates how windband exit diameter changes the amount of ambient air entrainment.
Table 3 illustrates how the amount of entrained ambient and changes as a function of nozzle exit area and Table 4 illustrates the relationship between the amount of entrained ambient air and windband entry area.
In Tables 1-4 the dilution is calculated by dividing the windband exit flow by the flow through the fan assembly.
Referring particularly to
Referring particularly to
The above description has been that of the preferred embodiment of the present invention, and it will occur to those having ordinary skill in the art that many modifications may be made without departing from the spirit and scope of the invention. In order to apprise the public of the various embodiments that may fall in the scope of the present invention, the following claims are made.
This is a continuation-in-part of U.S. patent application Ser. No. 10/924,532 filed Aug. 24, 2004, and further claims the benefit of U.S. Provisional Patent Application No. 60/537,609 filed Jan. 20, 2004, and further claims the benefit of U.S. Provisional Patent Application No. 60/558,074 filed Jul. 15, 2004, the disclosure of each of which is hereby incorporated by reference as if set forth in their entirety herein.
| Number | Date | Country | |
|---|---|---|---|
| 60537609 | Jan 2004 | US | |
| 60558074 | Mar 2004 | US |
| Number | Date | Country | |
|---|---|---|---|
| Parent | 10924532 | Aug 2004 | US |
| Child | 11003257 | Dec 2004 | US |
