Abstract:
A sliding plate air damper allows control over air flow with the sliding plate having a range of positions which do not change the total area of the orifices through the damper. Openings through the fixed plate and the openings through the sliding plate can each make up about 70% of the active area of each plate. The slide plate can be slid to a position where its webbings divide each fixed plate opening into two orifices for air flow. The air flow can be controlled by selecting the slide position of the webbings from a most restrictive position in which the webbings are in the middle of fixed plate openings, through a range of positions where the orifice on one side of the webbing is larger than the orifice on the other side of the webbing, to a maximally opened position where the webbing on the slide plate overlies the webbing on the fixed plate.

Description:
CROSS-REFERENCE TO RELATED APPLICATION(S) 
     The present application claims priority from Provisional Application No. 61/907,011, filed Nov. 21, 2013 and entitled “Constant Total Orifice Area Damper”. The contents of U.S. provisional patent application Ser. No. 61/907,011 are hereby incorporated by reference in entirety. 
    
    
     FIELD/BACKGROUND OF THE INVENTION 
     The present invention relates to air flow dampers used to control or affect the flow of air through a duct, into or out of a duct, or between two volumes. For instance, low wall return dampers are used for any return air system to balance the airflow across spaces. A damper installed in a return system can be adjusted from the room side to distribute airflow across the space for proper air recirculation. Similarly, dampers can be used on a duct output such as in a forced air HVAC system to help control the amount of air flow through a particular location. 
     Such dampers have one or more movable plates which control the characteristic dimensions of one or more orifices through which the air flows. In many dampers, the movable plate(s) rotate about an axis which is transverse to the air flow direction, with the rotation causing the projected amount of surface area of the movable plate restricting air flow (i.e., looking parallel to the air flow direction) to change. In other dampers referred to as slide plate dampers, the plate(s) always extend perpendicular or at least transverse to the air flow direction, and the movement direction of the plate(s) is perpendicular/transverse to the air flow direction. The movement of the slide plate could be linear, or in some instances is rotational about an axis parallel to the air flow direction. The present invention particularly applies to slide plate dampers and similar arrangements, such as disclosed in U.S. Pat. Nos. 5,218,998 and 7,597,617, both incorporated in full by reference, wherein the plates extend generally transverse to the air flow direction through the plate, and wherein the orientation of the plates relative to the air flow direction doesn&#39;t change. 
     For instance, the damper of U.S. Pat. No. 5,218,998 uses two plates with numerous openings in each plate, with flat sides of the plates adjacent or against each other. One plate is generally fixed in place while the other one moves. The relative sliding movement of the plates causes the percentage of the open area in one plate which overlaps with the open area in the other plate to change, i.e, sliding changes the sizes of the orifices through the plate combination. Larger orifices provide less resistance to airflow, smaller orifices provide more resistance to airflow. The combined ribbing of the two plates creates back pressure, which can be used to increase air pressure drop and to direct airflow to other side of the space to create uniform airflow and avoid dead spots. 
     In such prior art air dampers, the opening size is commonly smaller than the web between openings, so two plates can be aligned to create no orifices and thus be used to fully shut off flow. The general thinking is that the flow resistance is a function (not necessarily a linear function, but still a function) of total orifice area. 
     BRIEF SUMMARY OF THE INVENTION 
     The present invention is a sliding plate air damper. The openings through the fixed plate and the openings through the sliding plate are sufficiently large that the active area of the damper provides at least 50% free space. The webbings on the slide plate are smaller in the slide direction that the width of the fixed plate openings, such that with only two plates the air flow cannot be closed off. The slide plate can be slid to a position where its webbings divide each fixed plate opening into two orifices for air flow. The air flow can be controlled by selecting the slide position of the webbings from a most restrictive position in which the webbings are in the middle of fixed plate openings, through a range of positions where the orifice on one side of the webbing is larger than the orifice on the other side of the webbing, to a maximally opened position where the webbing on the slide plate overlies the webbing on the fixed plate. In another aspect, support columns on the fixed plate, which extend across the fixed plate openings in the slide direction and separate the slide plate from the fixed plate, help prevent the webbings on the slide plate from binding into the openings on the fixed plate. The support columns allow use of a thinner slide plate (or narrower webbings on the slide plate) than the fixed plate without flexing of the slide plate becoming a problem. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view of an air damper, schematically showing a preferred embodiment with a sixteen foot long section of air damper. 
         FIG. 2  is a front view of a fixed plate which can be used in the air damper of the present invention. 
         FIG. 3  is a front view of a slide plate which can be used in the air damper of the present invention to mate with the fixed plate of  FIG. 2 . 
         FIG. 4  is a front view showing a damper using the fixed plate of  FIG. 2  and the slide plate of  FIG. 3  in an air damper, with the slide plate positioned fully opened. 
         FIG. 5  is a front view similar to  FIG. 4 , with the slide plate positioned about half way closed. 
         FIG. 6  is a front view similar to  FIGS. 4 and 5 , with the slide plate positioned more than half way closed. 
         FIG. 7  is a front view similar to  FIGS. 4-6 , with the slide plate positioned fully closed. 
     
    
    
     While the above-identified drawing figures set forth preferred embodiments, other embodiments of the present invention are also contemplated, some of which are noted in the discussion. In all cases, this disclosure presents the illustrated embodiments of the present invention by way of representation and not limitation. Numerous other minor modifications and embodiments can be devised by those skilled in the art which fall within the scope and spirit of the principles of this invention. 
     DETAILED DESCRIPTION 
       FIG. 1  is a perspective view showing the general construction of several arrangements of air dampers  10 ,  12 ,  14  in accordance with the present invention, representing a 16′ long section of air damper, with an air flow direction being horizontal through the wall  18  from back to front. On the left hand side, the air damper  10  is arranged vertically in the wall  18 . In the middle section of  FIG. 1 , the air damper  12  is mounted on a 60° supporting wall bracket  20 . The wall bracket  20  is mounted on the downstream (return chase) side, toward the back of the drawing as depicted in  FIG. 1 . A damper to damper connector  22  can be mounted on the upstream (room) side to connect adjacent damper sections  12 . On the right hand side of  FIG. 1 , the air damper  14  is mounted on a 45° supporting wall bracket  24 . Preferably each damper  10 ,  12 ,  14  is attached to the supporting wall brackets  20 ,  24  before attaching to the wall  18 . After mounting the dampers  10 ,  12 ,  14  to the wall  18 , a damper end wall bracket  26  can be mounted to further secure the damper  14 , such as on the upstream (room) side. 
     Each damper  10 ,  12 ,  14  preferably comprises a fixed plate  26  and a slide plate  28 . Because the important concept is that the two plates slide relative to each other, alternatively both of the plates  26 ,  28  can slide relative to the wall  18 . However, a slide plate damper is generally easier to construct with one of the plates being fixed, and for ease of discussion the term “fixed plate” is used to set the frame of reference for the relative movement. Both the fixed plate  26  and the slide plate  28  have an active area with a plurality of openings  30 , which are transverse (i.e., extend across) the air flow. As will be further described below with reference to  FIGS. 4-7 , the locations where the openings  30  on the slide plate  28  overlap the openings  30  on the fixed plate  26  create orifices  32  that the air can flow through. 
     In the left hand section of  FIG. 1 , the slide plate  28  is mounted on the downstream (room) side. In the middle section of  FIG. 1 , the slide plate  28  is mounted on the upstream (return chase) side, with only a few of the openings  30  through the fixed plate  26  illustrated. In the right hand section of  FIG. 1 , the slide plate  28  is mounted on the downstream (room) side, with only a few of the openings  30  through the slide plate  28  shown. The upstream/downstream orientation of the fixed plate  26  relative to the slide plate  28  is not critical to the present invention, and instead can be selected based on the direction for air flow and need for access to the slide plate  28 . 
     A handle  34  may be attached to the slide plate  28  so the motive force for sliding is hand applied. For a slide plate  28  which is moved by hand, preferably the slide plate  28  is on the more accessible side, i.e., usually the room side. Alternatively, a linkage system (not shown), possibly including an actuator or motor for generating the motive force, can be used to move the slide plate  28 . See, for example, the linkage and actuation devices of U.S. Pat. Nos. 4,852,639, 5,014,608, 5,218,998, 5,427,146, 6,786,817 and 7,431,638, each incorporated by reference. The present invention is not particularly concerned with how the slide plate  28  is slid relative to the fixed plate  26 , only that some sliding can be achieved to change the orifice configuration through the two combined plates  26 ,  28 . Similarly, the mounting hardware and arrangement is not critical. The present invention can be used with any mounting arrangement, any motive force, and any linkage. 
     In this configuration shown in  FIG. 1 , for example, one preferred size of a fixed plate  26  is 38″ (vertical)×48″ (horizontal), excluding the attachment frame or brackets for mounting. In a preferred embodiment, this leaves an active area on the fixed plate  26  of 36″×46″. For use in sliding in the 48″ (horizontal) direction on the fixed plate  26 , a preferred slide plate  28  has a size of about 37″×45″. Alternatively, an arrangement could be constructed where the slide direction is vertical (on the left hand side of  FIG. 1 ) or at 60° (middle section of  FIG. 1 ) or 45° (right hand side of  FIG. 1 ), as long as the two plates  26 ,  28  have a relative sliding of one plate to the other and extend transverse to the air flow direction through the two plates  26 ,  28 . As another alternative, the slide direction can be rotary, such as disclosed in U.S. Pat. Nos. 2,470,488 and 6,192,922, each incorporated by reference. 
     The active area on the fixed plate  26  is split into a 19 (in the slide direction)×5 array of openings  30  (not separately shown in  FIG. 1 ), with ribbings  36  (not separately shown in  FIG. 1 ) between the openings  30  to provide sufficient strength to the overall structure. In the preferred embodiment, the ribbings  36  are about ⅔″ wide, leaving openings  30  which are about 6⅔″ long×1.8″ wide in the slide direction. The preferred slide plate  28  includes identically sized, shaped and spaced openings  30  and ribbings  36 , although the matching array is only 18 (in the slide direction)×5, with all  90  slide plate openings  30  drawn in  FIG. 1 . 
     The plates  26 ,  28  are preferably formed of metal, such as 304 stainless steel, 316L stainless steel, aluminum or cold rolled steel. If formed of steel, the fixed plate  26  has a preferred thickness of 18 gauge, and the slide plate  28  has a preferred thickness of 20 gauge. If formed of aluminum, the fixed plate  26  has a preferred thickness of 0.125 inches, and the slide plate  28  has a preferred thickness of 0.060 inches. In such configuration when the slide plate  28  is thinner than the fixed plate  26 , the slide plate  28  is preferably mounted on the upstream side, so any flexing of the slide plate  28  (i.e., more flexing of the slide plate  28  than of the fixed plate  26 ) due to air flow will not increase separation between the two plates  26 ,  28 . Such mounting preference however must be weighed against the need for access to the slide plate  28 . 
       FIG. 2  shows more detail of a smaller version of a fixed plate  38 , having an array of only 7 (in the slide direction)×3 openings  30 . The construction details of this smaller version are fully applicable to the larger versions shown in  FIG. 1 . Four brackets  40  can be welded to the fixed plate  38  or punched/bent into the fixed plate  38  for holding the edges  42  of the slide plate  44  to the fixed plate  38 . Four holes  46  in the middle slide-direction ribbing  36  are provided for fasteners  48 ,  50  (shown in  FIGS. 3-7 ) to further support the slide plate  44 . A marking  52 , this one provided as a short line with a marking “%” to indicate “percent open”, is also provided on the fixed plate  38 . 
     Depending upon the velocity of the air flow, the desired thickness of the slide plate  44  and/or fixed plate  38  may be too thin to prevent flexing of the ribbings  36 . If ribbings  36  flex into the openings  30  of the other plate, the plates  38 ,  44  can bind and prevent sliding back to a position where the ribbings  36  on the two plates  38 ,  44  overlap. To prevent the flexing-ribbing-causing-binding situation, separator columns  54  extending in the slide direction are an optional addition to the preferred embodiment, as shown in  FIGS. 2 and 4-7 . The preferred separator columns  54  are thin strips of wire secured to the fixed plate  38 , separating the fixed plate  38  from the slide plate  44 . 
       FIG. 3  shows more detail of a smaller version of a slide plate  44 , having an array of only 6 (in the slide direction)×3 openings  30 , for use with the fixed plate  38  of  FIG. 2  and shown in  FIGS. 4-7 . The slide plate  44  includes five additional slots  56 ,  58  in the slide-direction ribbing  36 . Four of these slots  56  receive support fasteners  48 ,  50  in conjunction with the four holes  46  in the fixed plate  38 . The fifth slot  58  is a sight window. Markings  60  can be provided adjacent the sight window  58 . A handle  34  is also provided, such as welded to the slide plate  44 . 
       FIGS. 4-7  show operation of the damper using the fixed plate  38  of  FIG. 2  and the slide plate  44  of  FIG. 3 . The slide plate  44  is attached to the fixed plate  38  by the four brackets  40  on the edges  42  as well as with three of the slots  56  used to attach a slide connector  48 . The preferred slide connector  48  has a head which is wider than the slots  56  but which is not tightened down and therefore freely allows sliding. A wing nut  50  and bolt is used in the fourth slot  56 . When the wing nut  50  is hand tightened, it secures the slide plate  44  in position relative to the fixed plate  38 . When the user wants to adjust the position of the slide plate  44  relative to the fixed plate  38 , the user merely loosens the wing nut  50  and hand slides the slide plate  44  using the handle  34 . The bolt for the wing nut  50  can either extend through the fixed plate  38  or can be a stud welded to the fixed plate  38 . As an alternative to the handle  34 , with the locking wing nut  50  absent or loosened, the slide plate  44  can be slid relative to the fixed plate  38  via inserting and pulling with a screw driver (not shown). 
     The progression of  FIGS. 4 through 7  shows various positions of the slide plate  44  relative to the fixed plate  38 . In  FIG. 4 , the slide plate  44  is at a fully opened position. The marking  52  on the fixed plate  38 , visible through the sight window  58 , is at the 100% open mark on the slide plate  44 . The air flow openings  30  in the slide plate  44  overlap exactly with the air flow openings  30  in the fixed plate  38 . For the configuration shown in  FIG. 4 , with a preferred air flow opening size of 6⅔″ long×1.8″ wide and ribbings  36  of about ⅔″ wide (except for the ribbing  36  containing the sight window  58 , which is about 1″ wide), this means a total orifice size of about 252 in 2  in the active area of about 360 in 2 , i.e. the 21 orifices  32  (ignoring the separator columns  54 ) make the active area about 70% open, which is as wide open as this particular configuration of damper can get. In this preferred embodiment, with the air flow openings  30  on both the fixed plate  38  and the slide plate  44  being the same size, shape and layout, both the active area of the fixed plate  38  and the slide plate  44  are about 70% free space. For other embodiments, if the size or number of openings  30  on one plate is larger than on the other plate, then the amount of free space will differ between the two plates. In preferred embodiments, the active areas on both the fixed plate  38  and on the slide plate  44  provide more than 50% free space, with the combined plates  38 ,  44  providing orifices  32  which are more than 50% open. 
     In  FIG. 5 , the slide plate  44  has been slid upward, to a position where the bottom of the horizontal ribbing  36  on the slide plate  44  is exactly at the elevation of the top of the horizontal ribbing  36  on the fixed plate  38 . The marking  52  on the fixed plate  38 , visible through the sight window  58 , is at about the 50% open mark on the slide plate  44 . Each orifice  32  now, instead of being 1.8″ wide, is only about 1.13″ wide. The total orifice size is now about 158 in 2 , i.e., the orifices  32  make the active area about 44% open. 
     In  FIG. 6 , the slide plate  44  has been slid further upward. Now each horizontal ribbing  36  on the slide plate  44  is at a position where it divides the corresponding opening  30  on the fixed plate  38  into two different orifices  32 . The total orifice size is still about 158 in 2 , but the number of orifices  32  has doubled, now to 42. The marking  52  on the fixed plate  38 , visible through the sight window  58 , is just over the 25% open mark on the slide plate  44 . The orifices  32  below the horizontal ribbing  36  on the slide plate  44  make up about 25% of the total orifice area, while the orifices  32  above the horizontal ribbing  36  on the slide plate  44  make up about 75% of the total orifice area. An important realization leading to the present invention is the discovery that the damper in the configuration of  FIG. 6  provides significantly more resistance to air flow than the damper in the configuration of  FIG. 5 , despite having the identical total orifice area. 
     In  FIG. 7 , the slide plate  44  has been slid further upward. Now each horizontal ribbing  36  on the slide plate  44  is at a position where it divides the corresponding opening  30  on the fixed plate  38  into two different orifices  32 , exactly in half. The total orifice size is still about 158 in 2  and the total number of orifices  32  remains  42 . The marking  52  on the fixed plate  38 , visible through the sight window  58 , is at the 0% open mark on the slide plate  44 . The orifices  32  below the horizontal ribbing  36  on the slide plate  44  make up about 50% of the total orifice area, while the orifices  32  above the horizontal ribbing  36  on the slide plate  44  make up 50% of the total orifice area. Another important realization leading to the present invention is the discovery that the damper in the configuration of  FIG. 7  provides significantly more resistance to air flow than the damper in the configuration of  FIG. 6 , despite having the identical total orifice area and the identical number of orifices  32 . In other words, despite have a constant total orifice area in each of the configurations of  FIGS. 5-7 , the damper of the present invention still allows significant airflow control. 
     From the configuration of  FIG. 4  to the configuration of  FIG. 7 , the throw of the slide plate  44  is about 1¼″. The preferred configuration allows the slide plate  44  to be slid even further upward, for a total throw of 1.8″, until the ribbing  36  on the slide plate  44  is at the top of the opening  30  on the fixed plate  38 . This results in retracing the air flow resistance curve back to the resistances provided by the configurations of  FIGS. 6 and 5 , but slightly affects the upward/downward vector of airflow through the damper. Over the entire throw of the slide plate  44 , the air flow orifices  32  cannot be fully closed, because the openings  30  are too large relative to the slide-direction ribbing width. The preferred configuration shown in the 36″×48″ damper shown on the left hand side of  FIG. 1  has been tested to confirm its resistance to air flow. At a given undampened air flowrate, when the damper was fully opened (i.e., in an orifice configuration similar to  FIG. 4 ), it provided a pressure drop of 0.07 psi (pressure drop calculations based on Idelchik pressure drop handbook). When the damper was moved to an orifice configuration similar to  FIG. 5 , it provided a pressure drop of 0.204 psi. When the damper was moved to a fully closed position with an orifice configuration similar to  FIG. 7  (i.e., having the identical total orifice area as the 0.204 psi pressure drop), if provided a pressure drop of 0.375 psi. 
     For the more than half of the slide plate throw, sliding the slide plate  44  horizontally relative to the fixed plate  38  does not change the total amount of orifice surface area through the plate combination, but rather only changes the size of half of the orifices  32  relative to the size of the other half of the orifices  32  through the plate combination. 
     The purpose of the preferred damper is not to create a shut off but change the number of orifices  32  and more importantly change the relative orifice sizes to create back pressure to increase air pressure drop to direct airflow to other side of the space to create uniform airflow and avoid dead spots. 
     Increasing the number of orifices  32  and not having a zero shut off increases the free area similar to perforated plate design. When the preferred damper is fully open, more than 63% free area is achieved (about 68% of the active area, with less than 4% lost on the border around the active area). When the moving plate  44  slides over the fixed plate  38  the orifice areas get smaller because the ribs  36  between orifices  32  are not aligned over one another, and pressure drop is increased. In this case still the same number of orifices  32  are achieved however the free area drops down to 48%, creating more back pressure. When the moving plate  44  continues to move to the middle position, the ribs  36  between the sliding plate openings  30  split the fixed plate openings  30 , doubling the number of orifices  32 . Even though the total area of the orifices  32  is the same (48%) as when the rib  36  is fully exposed and blocking one side of the opening  30 , the pressure drop continues to increase until the rib  36  is in a middle position and the two orifices  32  are half the size of the single (rib  36  blocking one side as shown in  FIG. 5 ) orifice  32 . More back pressure is created by having twice as many, but much smaller orifices  32 . The damper is designed to allow continuous positioning of the slide plate  44  between 100% open (63% free area) to greatest pressure drop (48% free area, orifices  32  in combined plates  38 ,  44  having equal areas). 
     Having more free area allows the designer to use higher air velocities in the return walls. Having low pressure drops between different positions also allows the designer to be able to distribute the airflow across the space and does not penalize a recirculation fan with extra pressure drop, thereby decreasing the energy consumption and noise. 
     In some circumstances the designer may desire to have a fully closed off damper setting, which cannot be achieved with a two plate design in accordance of the present invention. The concepts of the present invention can be used in a full shut-off damper simply by using more than two plates. For example, using the preferred opening width of 1.8″ and a slide-direction ribbing width of ⅔″, three slide plates  44  can be used in conjunction with a single fixed plate  38  to provide a full shut-off. The number of slide plates  44  necessary to fully shut off the air flow depends upon the relative dimensions of the opening width to the slide-direction ribbing width. A relatively narrower slide-direction ribbing width allows for a greater fully open flow, but requires more plates for full shut-off. 
     Although the present invention has been described with reference to preferred embodiments, workers skilled in the art will recognize that changes may be made in form and detail without departing from the spirit and scope of the invention. For example, all the dimensions provided herein are exemplary only, and can be varied for the particular system in which the damper of the present invention is used. While the preferred embodiments use a rectangular array of rectangularly-shaped openings  30 , other arrangements of openings can be used as well as other shapes of opening, such as the opening shapes and arrays of U.S. Pat. Nos. 5,014,608, 5,218,998, and 5,427,146 (but with larger opening widths relative to the slide-direction ribbing width).