Patent Application
20160265806
This invention relates to airflow dampers. In particular the invention relates to backdraft dampers.
Backdraft dampers are used to prevent the backdraft of air in various industrial and commercial heating, ventilating and air conditioning (HVAC) systems.
Such dampers typically comprise an outer frame sized to either fit into a specified opening or to cover a specific opening, in various environments. The damper blades are movable from an open position in which air is permitted to flow through the damper frame in one direction, and a closed position blocking the flow of air through the damper frame in the other direction, in order to prevent the contamination of air within a premises and/or the ingress of thermally unfavourable air (warm or cold) into a thermally controlled premises.
A backdraft damper must work automatically under the force of air, flowing either in the intended (outflow) direction, in which the airflow maintains the backdraft blades in an open condition, or in the reverse (backdraft) direction in which the loss of outflow air causes the backdraft blades to move to the closed position under the influence of gravity, and the backdraft maintains the blades in the closed position for the duration of the backdraft current. In order to ensure this, the blades must be biased to the closed position by gravity. However, this means that some of the force of the air flowing in the outflow direction is always sacrificed in order to maintain the damper blades in the open position, which reduces the airflow of the outflow current. HVAC systems are typically carefully designed to distribute air evenly about a premises, and this reduction in airflow can have the effect of skewing the pressure distribution to some flow-paths over others, reducing the intended airflow rates to some parts of the premises.
One solution to this is to try and balance the blades about their respective pivot rods so that little force is required to open them. However, this can cause inadvertent leakage in the backdraft direction, resulting in lower efficiency where the backdraft damper is providing thermal protection, and in situations where the backdraft damper is preventing the potential ingress of toxic or noxious gasses can result in a serious risk to occupants of the premises.
It would accordingly be advantageous to provide a backdraft damper having blades which are biased to the closed position with sufficient force to prevent the blades from remaining open when the outflow current is disrupted, but which can be opened with a relatively low force without impeding the airflow through the damper and thus without losing pressure to maintaining the damper in the open position.
In drawings which illustrate by way of example only a preferred embodiment of the invention,
The invention provides a heavy duty backdraft blade 30. The blade 30 may for example be extruded from aluminium, having a thickness which imparts strength and rigidity. The blade 30 is counterweighted, balancing the blade 30 so that it readily pivots to the open position under the influence of an airflow in the output direction, and pivots to the closed position under the influence of gravity when the airflow ceases.
In the preferred embodiment the leading edge of the blade 30 has a bull nosed profile, which helps to un-restrict air flow across the blade profile, described in detail below. Also, in the preferred embodiment the downstream portion of the blade 30 has a trough-like feature designed to capture the air flow by creating a static head in the trough, which enables the blade 30 to smooth out the air flow while maintaining a 90 degree opening position in order to maximize the transverse opening through the damper frame.
The invention thus provides a backdraft damper 10 for permitting a flow of air in an outflow direction, shown by the arrows in
The damper 10 illustrated comprises a generally rectangular frame 12. The frame 12 comprises opposed sides 14, 16 respectively providing opposed mounting flanges 14a, 16a projecting outwardly, generally in a plane containing the respective front and rear faces 22, 24 of the damper 10. The frame sides 14, 16 are affixed to opposed ends 18, 20, each similarly comprising mounting flanges 18a, 20a, and having blade stops 26, 28 and extending laterally across the respective end 18, 20 of the frame for the purposes described below. The sides 14, 16 may be extruded from any suitable material so as to produce a rigid frame 12 that is not subject to substantial deformation when the damper 20 is in use, for example 0.05″ to 0.25″ (1.27 mm to 6.25 mm) aluminium or steel, and joined to the ends 18, 20 of the damper 10 by welding, fasteners (such as metal screws or rivets) or by any other suitable securing means.
The interior of the frame 12 thus defines a transverse opening allowing the passage of air through the frame 12, creating an airflow region extending between the inflow and outflow faces 22, 24. The airflow region is bounded by the side panels 14, 16 and the end panels 18, 20, and thus has a cross-section defined by the open area of the faces 22, 24. The blades 30 extend across and are mounted to the frame 12 in the manner described below.
Each blade 30 comprises a blade body 31 having central portion 32 for connection to a linkage rod 50 via crank arm linkage assembly 70, illustrated in
In the preferred embodiment the pivot pin 72 is mounted via a dual bearing system, comprising a durable polymer proximal bearing 76, for example formed from a polyacetyl polymer such as Celcon (trademark), disposed over the portion of the pivot pin 72 projecting from the pin channel 52 and having a circular external profile. The proximal bearing 76 is capped by a polycarbonate medial bearing 78 having a circular internal profile for slip-fit engagement over the proximal bearing 76, which permits free rotation between the proximal and medial bearings 76, 78. The proximal and medial bearings 76, 78 are disposed between the ends of the blade 30 and the sides 14, 16 of the frame and the pivot pin 72 extends beyond the proximal and medial bearings 76, 78 into a first opening 74a in the crank arm 74, as best seen in
A durable polymer distal bearing 80, which may also be formed from a polyacetyl polymer such as Celcon (trademark), has a circular exterior profile for engagement in a second opening 74b in the crank arm 74, spaced from the first opening. The second opening has a circular profile for slip-fit engagement by the distal bearing 80. The internal profile of the distal bearing 80 is also circular, for receiving a trunnion bearing 82 through which the linkage rod 50 extends and is axially fixed by cup point fastener 82a. The medial bearing 78 is preferably fixed in the damper frame 16 via a hexagonal shaped hole. The pivot pin 72 is placed through the bearings 76 and 78 and then located into the first crank arm opening 74 a by a fastener 75.
Thus, when mounted to the frame 12 each blade 30 can rotate between an open position in which the blade 30 allows air to flow through the frame 12, as illustrated in
The blade body 31 further comprises a leading portion 34 upstream of the central portion 32 (relative to the outflow direction of the damper 10). The leading portion 34 of the blade body 31 comprises a planar section 35 merging into the wall of a channel 62 for receiving a counterweight 60. The counterweight 60 may for example be formed from steel or another suitably heavy material.
In the preferred embodiment the leading edge 36 of the leading portion 34 is rounded, forming a bullnose profile that reduces the formation of eddies and currents as the air flows past the blade 30. Thus, the part of the leading portion 34 forming the leading face of the channel 62 for the counterweight 60 can be formed as a bullnose. This diminishes friction and thus resistance to the airflow, in turn reducing the pressure and velocity required for operation and pressure losses downstream of the damper 10. The other side of the channel 62 may be formed by a generally “L”-shaped flange 38 depending from the planar section 35 of the leading portion 34. These features are readily formed by extrusion, and allow the counterweight 60 to be inserted into the blade body 31 from the side.
In preferred embodiments the planar section 35 of the leading portion 34 is transversely offset from the axis of the pivot pin 72. This results in an arcuate occlusion at the central portion 32 which allows for the formation of a static head upstream of the central portion 32 both above and below the planar section 35 of the leading portion 34 of the blade 30, as shown in
The blade body 31 further comprises a trailing portion 40 downstream of the central portion 32. The trailing portion 40 of the blade body 31 provides a seal 41, for example a silicone bubble gasket having a spline lodged (for example crimped) in a slot 41a extending across the distal edge of the trailing portion 40. The seal 41 seals against either the planar section 35 of the leading portion 34 of an adjacent blade 30 or, in the case of the lowest blade 30′, against the blade stop 28 projecting from the bottom end 20 of the frame 12, to prevent backflow in the closed position shown in
The heavier the counterweight 60, the closer the counterweight 60 may be disposed to the pivot pin 52 in order to properly balance the blade 30 to be slightly gravitationally biased to the closed position shown in
The trailing portion 40 is similarly preferably transversely offset from the axis of the pivot pin 72, on the opposite side of the pivot pin 72 from the leading portion, which allows for the formation of a static head immediately downstream of the central portion 32 of the blade 30. The trailing portion 40 is preferably provided with a generally planar portion 42 extending from the central portion 32, and a lateral depression 44 open opposite to the direction of the offset of the trailing portion 40 from the central portion 32, adjacent to the distal edge of the trailing portion 40. The lateral depression 44 may be formed essentially as a return flange, for example by upward bend 46, downstream bend 47 and downward bend 48.
The lateral depression 44 allows for the creation of a static head below the trailing portion 40, as shown in
In operation, the damper 10 is mounted vertically into a structure with the leading portions 34 of the blades 30 at the top in the closed position shown in
As each blade 30 pivots the rotational interlock between the pin channel 54 and the pivot pin 72 rotates the crank arm 74, which moves the linkage rod 50, causing all blades 30 to pivot in synchronization to open the damper 10 uniformly across its full cross-section.
When the airflow stops, the blades return to the closed position illustrated in
Thus, absent any airflow and solely under the influence of gravity the trailing portion 40 has greater torque than the leading portion 34, but a slight airflow in the desired (downstream) direction is sufficient to overcome this differential. In the event of a backdraft airflow, the force of the backdraft against the trailing portion 40 due to its larger surface area is greater than the force against the leading portion 34, but in the case of a backdraft this force is additive to the gravitational biasing force and thus increases the bias to the closed position, and increases the efficacy of the seals 41.
The static heads formed at the central portion 32 and beneath the lateral depression 44 reduce friction and allow for a smoother flow of air past the blade bodies 31. The double bends forming the lateral depression 44 and the bullnose formation about the counterweight both also serve to impart additional strength and rigidity to the blade body 31.
Various embodiments of the present invention having been thus described in detail by way of example, it will be apparent to those skilled in the art that variations and modifications may be made without departing from the invention. The invention includes all such variations and modifications as fall within the scope of the appended claims.
