WINDBAND SILENCER WITH MEANS TO REDUCE CROSS-WIND PRESSURE DIFFERENTIAL

Abstract

A windband for an exhaust fan system. The windband comprises an elongate housing receivable about an exit nozzle of the exhaust fan system, an air inducer formed from a perforated material and positioned adjacent the bottom portion of the elongate housing, and a discharge sleeve positioned adjacent and secured to the top portion of the elongate housing. The discharge sleeve is formed from a perforated material and forms a passageway through which gas from the nozzle and induced ambient air passing through the elongate housing are discharged. The perforated air inducer and discharge sleeve together assist in the minimization of a pressure differential between an upwind side of the windband and a downwind side of the windband when the windband is subjected to wind striking the windband at an angle.

Claims

1. A windband for an exhaust fan system, the windband comprising: a vertically orientated elongate housing having an upper end, a lower end and a longitudinal passageway connecting the upper and low ends, the lower end receivable about an exit nozzle of the exhaust fan system, the upper end being open to the atmosphere in a vertical direction such that high velocity exhaust gas exiting the exit nozzle passes through the lower end, through the longitudinal passageway, through the open upper end and is expelled vertically upward at a velocity that permits the exhaust gas to reach a desired altitude before significantly diluting with the surrounding atmosphere, an air inducer secured to the lower end of the elongate housing, the air inducer forming an annulus with the exit nozzle for the induction of ambient air into the longitudinal passageway when high velocity gas exits the exit nozzle and passes through the lower end of the elongate housing, and a discharge sleeve circumferentially mounted about, and exterior to, the elongate housing at the upper end, the discharge sleeve formed from a perforated material with perforations extending from an exterior surface to an interior surface of the discharge sleeve, wherein the perforations of the discharge sleeve assist in the minimization of a pressure differential between an upwind side of the windband and a downwind side of the windband when the windband is subjected to wind having a horizontal component, thereby helping to minimize a reduction in the velocity of and/or the disruption of a laminar flow of exhaust gas expelled through the open upper end caused by turbulent flow conditions that result from pressure differentials formed by the horizontal component of the wind.

2. The windband as claimed in claim 1 wherein the air inducer is formed from a perforated material with perforations extending from an exterior surface to an interior surface of the air inducer, the perforations of the air inducer assisting in the minimization of a pressure differential between an upwind side of the windband and a downwind side of the windband when the windband is subjected to wind having a horizontal component, to thereby help to minimize a reduction in the velocity of and/or the disruption of a laminar flow of exhaust gas expelled through the open upper end caused by turbulent flow conditions that result from pressure differentials formed by the horizontal component of the wind.

3. The windband as claimed in claim 2 wherein exhaust gas passing through the longitudinal passageway is expelled vertically upward through the open upper end without passing through the perforations in the discharge sleeve.

4. The windband as claimed in claim 3 wherein the discharge sleeve has a circumference larger than that of the upper end of the elongate housing, the discharge sleeve set off from the upper end of the elongate housing.

5. The windband as claimed in claim 1 wherein the elongate housing is comprised of an inner wall spaced apart from an outer wall, at least a portion of the inner wall formed from a perforated material.

6. The windband as claimed in claim 5 including acoustic absorbing material between the inner and outer walls of the elongate housing.

7. The windband as claimed in claim 6 wherein the acoustic absorbing material is steel, steel or mineral wool, fiberglass, foam, or plastic.

8. The windband as claimed in claim 4 wherein the elongate housing is substantially conical in configuration, having a generally circular cross section with the cross sectional diameter of the lower end exceeding that of the upper end, the conical configuration assisting in the induction of ambient air through the annulus and into the longitudinal passageway.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0009] For a better understanding of the present invention, and to show more clearly how it may be carried into effect, reference will now be made, by way of example, to the accompanying drawings which show exemplary embodiments of the present invention in which:

[0010] FIG. 1 is a schematic perspective view of a building ventilation system utilizing an upblast fan and incorporating an embodiment of the windband silencer of the present invention.

[0011] FIG. 2 is a side perspective view of the windband silencer in accordance with an embodiment of the invention.

[0012] FIG. 3 is a vertical section view taken along the line A-A of FIG. 2.

[0013] FIG. 4 is an enlarged detail view of portion A of FIG. 3.

[0014] FIG. 5 is an upper side perspective view of the section shown in FIG. 3.

[0015] FIG. 6 is a plan view of the windband silencer shown in FIG. 2.

[0016] FIG. 7 is a vertical section view, similar to FIG. 3, of an alternate embodiment of the windband silencer.

[0017] FIG. 7A is an enlarged detail view of portion A in FIG. 7.

[0018] FIG. 8 is a lower side perspective view of the section shown in FIG. 7.

[0019] FIG. 9 is a plan view of the embodiment of FIGS. 7 and 8.

DESCRIPTION

[0020] The present invention may be embodied in a number of different forms. The specification and drawings that follow describe and disclose some of the specific forms of the invention.

[0021] FIG. 1 is a schematic view of a generic building ventilation system, referenced generally by numeral 1. Ventilation system 1 includes a fan 2 that draws gases through a series of ducts 3 connected to one or more fume hoods 4. It will be appreciated that depending upon the particular application at hand, the fume hoods may be associated with particular pieces of machinery, particular operations within a manufacturing facility, or otherwise associated with sources of noxious gas. Commonly, fan 2 would be mounted on the roof of the associated building and would exhaust gases drawn through ducts 3 vertically upward through an exit nozzle 5. A windband 6, constructed in accordance with an embodiment of the invention, is positioned about nozzle 5. As in the case of traditional upblast fans, gases and air exiting windband 6 are expelled upwardly at a sufficient velocity to permit them to be diluted with ambient air at an elevation, and to minimize their adverse effects closer to the building or ground surface.

[0022] With specific reference to FIGS. 2 through 5, there is shown a preferred embodiment of the structure of windband 6. Windband 6 is generally comprised of an elongate housing 7 that is received about nozzle 5. In the embodiment shown, housing 7 is substantially conical in configuration having a lower or bottom portion 8 and an upper or top portion 9. In application, bottom portion 8 is positioned below the upper end of nozzle 5 with top portion 9 positioned elevationally above the upper end of nozzle 5. In addition, in a preferred embodiment of the invention elongate housing 7 is generally conical with a generally circular cross section, having a cross sectional diameter at bottom portion 8 exceeding that at top portion 9.

[0023] Elongate housing 7 includes a side wall 10 that extends between bottom portion 8 and top portion 9, and that generally defines a hollow inner chamber or passageway through which exhaust gas and induced air flows and is expelled in an upward direction, much like traditional windbands. Sidewall 10 may be comprised of an inner wall portion 11 spaced apart from an outer wall portion 12. To help minimize sound transmission through elongate housing 7, an acoustic absorbing material 13 may be inserted in the space between inner wall 11 and outer wall 12. The particular acoustic material that is utilized could vary from application to application, and the temperature and environmental factors to which windband 6 may be exposed. In most instances it is expected that acoustic material 13 will be comprised of steel, steel or mineral wool, fibreglass, rigid or semi-rigid foam, or plastic. To further help minimize the transmission of sound through the elongate housing, and to enhance its sound dampening effect, inner wall 11 of elongate housing 7 may be entirely or substantially constructed from perforated material. Once again, depending upon the particular environment and conditions under which the windband is intended to be operated, the perforated material comprising inner wall 11 could be formed from a sound dampening material, including plastic, fibreglass and other such materials.

[0024] In accordance with the invention, windband 6 further includes an air inducer 14 positioned at bottom portion 8 of elongate housing 7. As shown in the attached drawings, and as will be appreciated by one of ordinary skill in the art having a thorough understanding of the invention, air inducer 14 could be a separate component physically secured to bottom portion 8 of elongate housing 7, it could be in essence an extension of outer wall 12, or it could be an extension of inner wall 11. In an embodiment, air inducer 14 is of a single wall construction, forming an annulus 15 with nozzle 5 for the induction of ambient air into the hollow interior of elongate housing 7. Air inducer 14 is formed from a perforated material that, as in the case of inner wall 11, could be constructed from a wide variety of different materials.

[0025] Windband 6 is mounted and secured to nozzle 5 through the use of a plurality of elongate fins 16. Fins 16 serve the further purpose of assisting in directing the flow of induced air through elongate housing 7 and helping to minimize turbulent effects. Fins 16 may also be formed from a perforated material to help reduce acoustic resonance and to minimize the production of sound as high velocity air passes over their surfaces.

[0026] Windband 7 further includes a discharge sleeve 17 located and positioned at top portion 9 of elongate housing 7. In the particular embodiment shown in the attached drawings, elongate housing 7 contains at its top or upper portion a right angle cylindrical section 18 that effectively forms a transition between the upper portion of the conical elongate housing and discharge sleeve 17. Cylindrical portion 18 may formed from a solid wall, a perforated wall, or a combination of an exterior solid wall and a perforated inner wall (with or without acoustic insulation there between). Discharge sleeve 17 is formed from a perforated material and is generally circular in cross section, creating a generally cylindrical passageway through which gas from nozzle 5 and induced ambient air drawn through annulus 15 are discharged. In one embodiment, discharge sleeve 17 may be of a diameter greater than that of cylindrical section 18 with the lower portion of discharge sleeve 17 secured to cylindrical section 18 in a manner that prohibits the induction of air between the annulus created between discharge sleeve 17 and cylindrical section 18.

[0027] In some embodiments, windband 6 may, optionally, include one or more bullet style acoustic attenuators 19. FIGS. 3, 5 and 6 illustrate an embodiment utilizing a single bullet style acoustic attenuator. FIGS. 7, 8 and 9 illustrate an embodiment utilizing two bullet style acoustic attenuators. Bullet acoustic attenuators 19 are retained within, and generally parallel to, elongate body 7 through a plurality of fins 20 extending from inner wall 11 to the exterior of the bullet acoustic attenuators. Fins 20 may also extend between adjacent bullet acoustic attenuators where multiple attenuators are utilized. Fins 20 are also preferably aligned with the longitudinal axis of body 7 to minimize drag, turbulent flow, and noise generation. Further, the upper end 21 of each bullet acoustic attenuator 19 may be conical in shape and directed toward discharge sleeve 17. The conical shape of upper end 21 serves to help reduce turbulence, losses, and pressure drop, and to minimize noise generation. The exterior surface of bullet acoustic attenuation member 19 is preferably formed from a perforated material to help “deaden” sound generated by the moving stream of gas as it travels through the windband. The interior of each bullet acoustic attenuator may be filled with a sound absorbing or dampening material 22. Where two or more bullet style acoustic attenuators are used, their cross-sectional shape may be generally obround as shown in FIG. 9. In such an embodiment, the upper ends 21 of the attenuators may be generally triangular in longitudinal section with a blunted or rounded nose, as shown in FIGS. 7 and 8. Where one or more bullet acoustic attenuators are utilized, elongate body 7 may include a stepped expansion 30 to maintain the same velocity through the housing as would be the case if no bullet acoustic attenuators were present. In other embodiments portions or all of top portion 9 of elongate housing 7 may be increased in diameter to maintain velocities.

[0028] It has been discovered that utilization of a windband constructed as above assists in helping to minimize pressure drop from one side of the windband to the opposite side when the windband is subjected to a crosswind. In that regard, it will be appreciated that the portion of a building ventilation system that extends above the roof of a building or a structure is subject to the effects of wind that strikes the exterior surface of the ventilation system components at an angle (which in many cases will be generally horizontal). Wind striking the exterior components of the ventilation system (i.e. the stack) will cause the development of a low pressure system on the opposite side. As noted above, where the wind strikes a windband, there is created a low pressure zone on the opposite side that can affect the draw of ambient air into the windband, can cause turbulent flow conditions, and can cause insufficiently diluted exhaust gases to be drawn downwardly toward the building or ground. Through the use of windband 6, the extent and degree of such pressure drop is reduced. The resulting effect is that windband 6 helps to minimize any swirling or vortex on the opposite side of the windband from that struck by the prevailing wind, thereby helping to also minimize any reduction in induced air flow that can occur and a potential reduction in the diluting effects of noxious gases exhausted by the ventilation system.

[0029] It is to be understood that what has been described are the preferred embodiments of the invention. The scope of the claims should not be limited by the preferred embodiments set forth above, but should be given the broadest interpretation consistent with the description as a whole.