U.S. patent application number 12/462172 was filed with the patent office on 2011-02-03 for back draft damper.
This patent application is currently assigned to Huntair, Inc.. Invention is credited to David Benson, Lawrence Hopkins, Emily Jones, Albert Passadore.
Application Number | 20110028080 12/462172 |
Document ID | / |
Family ID | 43527475 |
Filed Date | 2011-02-03 |
United States Patent
Application |
20110028080 |
Kind Code |
A1 |
Hopkins; Lawrence ; et
al. |
February 3, 2011 |
Back draft damper
Abstract
A back draft damper includes a rectangular shell having a
central opening which air can pass through. A plurality of vanes
rotatably mounted in the shell are rotatable between open positions
where air can pass through the shell and closed positions where air
cannot pass through the shell. The axes the vanes rotate about are
slightly offset from vertical.
Inventors: |
Hopkins; Lawrence; (Happy
Valley, OR) ; Jones; Emily; (Tualatin, OR) ;
Passadore; Albert; (Beaverton, OR) ; Benson;
David; (West Linn, OR) |
Correspondence
Address: |
DEAN D. SMALL;THE SMALL PATENT LAW GROUP LLP
225 S. MERAMEC, STE. 725T
SAINT LOUIS
MO
63105
US
|
Assignee: |
Huntair, Inc.
|
Family ID: |
43527475 |
Appl. No.: |
12/462172 |
Filed: |
July 29, 2009 |
Current U.S.
Class: |
454/259 |
Current CPC
Class: |
F24F 13/1426 20130101;
F24F 13/1413 20130101 |
Class at
Publication: |
454/259 |
International
Class: |
F24F 13/14 20060101
F24F013/14 |
Claims
1. A damper comprising: a. a shell having a central opening through
which air passes; b. a plurality of vanes mounted rotatably in said
shell; c. said vanes are rotatable, about axes which are slightly
off set from vertical at a predetermined angle, between open
positions where air can flow through said central opening and
closed positions where air substantially cannot flow through said
central opening.
2. The damper of claim one wherein at least some of said vanes
rotates independently of at least some of the other vanes so that
when in its open position each said blade is aligned with the
localized direction of the air flowing over it.
3. The damper of claim 1 wherein said shell is rectilinear in cross
section.
4. The damper of claim 1 wherein said shell is elliptical in cross
section.
5. The damper of claim 1 wherein said shell is circular in cross
section.
6. The damper of claim 1 wherein said vanes have leading edges and
trailing edges, and said axes are proximate said leading edges.
7. The damper of claim 1 wherein said vanes have top ends and
bottom ends and said axes are closer to said inlet at said top ends
than at said bottom ends.
8. The damper of claim 1 wherein said shell has a vertical center
line and said axes are closer to said vertical center line at said
top ends than at said bottom ends.
9. The damper of claim 6 wherein said shell has a depth and said
vanes have a width which is not greater than said depth.
10. The damper of claim 9 wherein said vanes are substantially
located within said shell.
11. The damper of claim 1 wherein said shell has a vertical center
line and a portion of said vanes located on one side of said
vertical center line rotate clockwise when rotating toward their
closed positions and a portion of said vanes located on the other
side of said vertical center line rotate counterclockwise when
rotating toward their closed positions.
12. The damper of claim 11 wherein there are an even number of
vanes with one half of said vanes on one side of said vertical
center line and the other half of said vanes on the other side of
said vertical center line.
13. The damper of claim 1 wherein said vanes are symmetrical in
cross section and have a shape which minimizes drag.
14. The damper of claim 1 wherein said predetermined angle is
between 0.5 degrees and 45 degrees.
15. The damper of claim 1 wherein said predetermined angle is 1.6
degrees.
16. The damper of claim 1 wherein said predetermined angle is such
that said vanes are free to start rotating towards said open
positions when there is any airflow through said shell from said
inlet to said outlet.
17. The damper of claim 1 where said predetermined angle is such
that said vanes move to their closed positions when there is no
airflow through said shell from said inlet toward said outlet.
18. The damper of claim 1 wherein said vanes have tops and bottoms
and there is a bearing between the top of each vane and said shell
and the bottom of each vane and said shell.
19. The damper of claim 18 wherein said bearing is a ball
bearing.
20. The damper of claim 1 wherein said vanes have a thickness of
between 0.250 inches and 0.400 inches at a leading edge thereof and
of between 0.050 inches and 0.100 inches at a trailing edge of said
vane.
21. The damper of claim 20 wherein said vanes have a thickness of
0.32 at said leading edge and a thickness of 0.086 at said trailing
edge.
22. The damper of claim 1 wherein said vanes weight approximately 2
pounds.
23. The damper of claim 1 wherein said shell has a horizontal
center line and a vertical center line and said axes are offset
from vertical by positioning said shell such that said vertical
center line is offset from vertical.
24. The damper of claim 1 wherein said shell has a horizontal
center line and a vertical center line and said axes are offset
from vertical by positioning said shell such that said horizontal
center line is offset from horizontal.
Description
BACKGROUND OF THE INVENTION
[0001] Large air handling systems often require back draft dampers
to be placed at critical locations to prevent air from flowing in
the direction opposite normal air flow when the fan that is
creating the airflow is not operating. This is particularly true
with multi-fan systems such as shown in Hopkins, U.S. Pat. Nos.
7,137,775 and 7,727,468. With multi-fan systems it is common to
shut off one or more of the fans to allow the remaining fans to run
at peak efficiency. When this occurs some air from the operating
fans will flow back through the non-operating fans if the
non-operating fans do not have back draft dampers.
[0002] There basically are three types of back draft dampers:
manual systems where a blank off plate or damper is deployed to
prevent reverse airflow; remotely actuated dampers where actuators
are used to close a damper; and gravity actuated dampers where the
damper is opened by the pressure of air passing through it and is
closed by the force of gravity acting on its vanes. The prior art
gravity actuated dampers typically comprise several stacked
side-by-side vanes which are mounted in a shell and rotate about
horizontal axes. The rotational axes are typically near the leading
edge of the vanes to maximize the effect of gravity on the vanes so
that gravity causes the vanes to be fully closed when there is no
positive airflow past them. However, the down side of this is that
it takes a considerable amount of airflow to fully open the vanes
and if the airflow is to low to fully open the vanes they will
create excess drag and overall efficiency of the system is reduced.
While the gravity effect on damper vanes that rotate about
horizontal axes can be reduced by counter weighting the vanes in
some manner, this adds to the cost and in many situations the
counter weighting has to be customized.
SUMMARY OF THE INVENTION
[0003] The subject invention typically mounts the vanes of a back
draft damper generally vertically in the shell but with their
rotational axes being slightly offset from vertical so that a small
amount of gravitational force acts on the vanes to make them rotate
to their closed positions. As a result, a small amount of force is
required to overcome this gravitational force and rotate the vanes
to their fully opened positions. This means that the vanes will
open more quickly and with less force than vanes that rotate about
horizontal axes and be more fully open at lower airflow levels.
[0004] 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
[0005] FIG. 1 is a perspective view of a back draft damper
embodying the subject invention.
[0006] FIG. 2 is a cross sectional view taken on the line 2-2 of
FIG. 1.
[0007] FIG. 3 is a cross sectional view taken on the line 3-3 of
FIG. 1.
[0008] FIG. 4 is a cross sectional view of one of the vanes of the
subject invention.
[0009] FIG. 5 is a front elevation view of an alternative
embodiment the damper.
[0010] FIG. 6 is a detailed view of how the damper is rotatably
mounted in the shell.
[0011] FIG. 7 is a side elevation view of an alternate embodiment
of the invention.
[0012] FIG. 8 is a front elevation view of the embodiment shown in
FIG. 7.
[0013] FIG. 9 is a front elevation view of another embodiment of
the invention.
[0014] FIG. 10 is a perspective view of yet another embodiment.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
[0015] Referring to FIG. 1 of the drawings, a back draft damper
comprises a shell 10 which defines a central opening 12 having an
inlet 11 and an outlet 13 through which air passes. The shell is
constructed to fit into a duct or passageway (not shown) through
which air flows, or be placed immediately upstream or downstream of
a fan unit (not shown). The size of the shell depends upon the size
of the duct, passageway or fan unit. In the preferred embodiment
illustrated, which is sized for fans in a multiple fan array, the
shell is 27''.times.27'' and has a depth of 8''. The shell is
constructed of 16 gauge sheet metal and has a lip 14 located at its
outlet which engages an optional egg crate flow straightener 16.
The shell 10 has a top 18, bottom 19 and sides 20. The shell can be
rectangular, as shown in FIGS. 1 and 2 or elliptical as shown in
FIG. 9. The shell can be fabricated from many types of materials
and have different dimensions based on the particular
application.
[0016] A plurality of vanes 22 extend between the top and bottom
surfaces, 18, 20 of the shell 10. The vanes move between open
positions, FIG. 1 and solid line in FIG. 2, where air can flow
substantially unimpeded through the central opening 12, and closed
positions, dashed line in FIG. 2 and FIG. 5, where air cannot flow
through the central opening. Referring now also to FIG. 4, the
vanes 22 have top ends and bottom ends, rounded leading edges 24
and sides 26 which converge to thinner trailing edges 28 resulting
in a neutral aerodynamic shape which creates little drag due to air
flowing over the vanes. In the preferred embodiment referred to
above, the vanes have a width which is less than or equal to the
depth of the shell and a length which is slightly less than the
height of the shell. With the 27.times.27.times.8 inch shell
described above the vanes have a length of approximately 261/2
inches and a width of between 6 and 8 inches, and have a thickness
of between 0.250 and 0.400 inches at their leading edge 24 and
between 0.050 and 0.100 inches at their trailing edge 28. In a
preferred embodiment the blades have a thickness of 0.320 inches at
their leading edge and 0.086 inches at their trailing edge. The
vanes preferably are formed from an aluminum extrusion and are
hollow to reduce their weight. In the preferred embodiment
described above the vanes weigh approximately 2 pounds each.
Cylindrical openings 24 extend through the vanes at their leading
edge, the center line of which acts as the axes 36 the vanes rotate
about. The axes 36 are located close to the inlet 11. The top and
bottom portions of the openings 34 are threaded. In the embodiment
illustration in FIGS. 1 and 2 the vanes 22 are rotatably mounted in
the shell 10 such that their axes of rotation 36 are slightly
offset front to back from the vertical at an angle A, with the tops
of the vanes being closer to the inlet 11 than the bottoms of the
vanes. The amount of offset depends on the size and weight of the
vanes and the amount of airflow that will pass through the damper.
The purpose of the offset is to cause gravity to rotate the vanes
to their fully closed position when there is no positive airflow
through the damper, much in the same manner that a refrigerator
door closes. However, the offset should be as little as possible to
obtain this result so that the vanes can rotate to their open
positions quickly when there is any positive airflow through the
shell. Moreover, it is desired to have the vanes become fully
opened with as little airflow as possible. Thus the angle of the
offset should be quite small and in the embodiment described above
is 1.6 degrees. In general the angle could be as low as 0.5 and
probably would never exceed 46 degrees.
[0017] If desired the axes 36 of the vanes 22 can also be offset at
an angle B from side-to-side with the tops of the vanes being
closer to the vertical center line L of the shell than the bottoms
of the vanes, FIG. 5. This may help cause the vanes to rotate to
their closed positions, particularly if one of the vanes rotates
past being aligned with the airflow. The angle B of the
side-by-side offset is similar to that of the angle A of front to
back offset.
[0018] In the embodiment illustrated in FIGS. 7 and 8, the shell
has a vertical center line L and a horizontal center line D and
rather than offsetting the axes 36 of the vanes 22 relative to the
shell 10, the vertical center line L of the shell is offset from
the vertical by angle A to create the offset of the axes 36 front
to back. The horizontal center line D of the shell also may be
offset from the horizontal by angle B to create the offset of the
axes 36 from side to side.
[0019] Referring now to FIG. 6, the vanes rotate in the shell 10 on
bearings 38. The outer race 40 of each bearing is press fit into an
opening 42 in the shell and the inner race 44 is positioned on the
shoulder 46 of a bolt 48 which fits into the circular opening in
the vane. A bearing 38 is located at the top and bottom of each
vane 22. The bearing may be a ball bearing but other types of
bearing and rotating techniques can be utilized.
[0020] Preferable the vanes rotate independently of one another so
that each vane is aligned with the localized direction of the air
flowing over it. In most cases this means that most of the blades
will be oriented at an oblique angle with their trailing edges
being closer to the center of the shell than their leading edges.
This, along with the axes 36 of the vanes being offset from
vertical causes the vanes on one side of the shell to rotate
clockwise as they rotate to toward their closed positions and the
vanes on the other side of the shell to rotate counterclockwise as
they rotate toward their closed positions. Preferable there are an
even number of vanes 22, one half of which are located on each side
of the vertical center line of the shell. In the embodiment
illustrated there are six vanes and they slightly overlap when they
are in their closed position to provide a seal between them.
[0021] Referring now to FIG. 10 a plurality of the dampers 10 of
the subject invention could be incorporated into a single shell 50
which is placed next to a fan array of the type disclosed in U.S.
Pat. Nos. 7,137,775 and 7,727,468. While the embodiment illustrated
is a 5.times.5 rectilinear array it can be made to mate with any
type of fan array.
[0022] The terms and expressions which have been employed in the
foregoing specification are used therein as terms of description
and not of limitation, and there is no intention in the use of such
terms and expressions of excluding equivalents of the features
shown and described or portions thereof, it being recognized that
the scope of the invention is defined and limited only by the
claims which follow.
* * * * *