Patent Abstract:
A flow control device has a duct section with a plurality of damper blocking elements, each having a major plane. The damper blocking elements are pivotably connected to the duct section and movable in a range that is limited to ensure that, when the duct section is mounted in a preferred orientation, the damper blocking element major planes always form an angle of at least 45 degrees from the horizontal throughout the range. The range is such that the plurality of damper blocking elements can selectively close and open the duct. The blocking elements can completely close the duct, for example, to block natural convection.

Full Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     The present application claims the benefit of U.S. Provisional Application No. 60/978,606, filed Oct. 9, 2007, which is hereby incorporated by reference in its entirety. 
    
    
     BACKGROUND 
     Exhaust hoods are used in many situations where pollutants are generated. Examples include kitchens, laboratories, factories, and spray paint booths, as well as other examples. In a commercial kitchen environment, multiple exhaust hoods and exhaust ducts may be provided for different appliances at different locations. The load varies with the type of appliance and the way it is being used. Broilers, grills, and fryers, for example, may produce a great deal of smoke and fumes, including grease particles and moisture. Other devices such as ovens and steam tables may produce less. To provide sufficient flow to remove pollutants without removing excessive amounts of air creates a real time flow balancing problem in the commercial kitchen environment. Typical exhaust hoods and ducting systems may be ill-suited to addressing this problem in an optimum way. 
     A typical exhaust hood has an inlet for fumes and air that leads to an exhaust duct. Filters may be provided at the point where air and fumes enter the duct. An exhaust plenum may also connect the hood with the exhaust duct. Hoods are often long and narrow and accommodate multiple cooking units. Variations include exhaust ceilings, wide canopy hoods, and other configurations. 
     Prior art systems have used flow restrictions in the path of the exhaust air to balance the flow of air and fumes. Dampers or other chokes may be used to make adjustments to the flow and real time control systems have been proposed. But fouling is a persistent problem particularly in systems that handle fumes and air with water vapor and grease particles. 
     SUMMARY 
     Generally, the invention is a blocking mechanism that has surfaces, which may or may not be planar, in which the surfaces of the blocking elements remain at angles that form angles greater than 30 degrees from the horizontal and preferably more than 30 degrees such as more than 45 degrees. Balancing dampers suitable for use in ducts carrying grease laden fumes have generally air blocking elements that move between high resistance and low resistance positions to regulate the amount of grease-laden fumes that pass through the duct. 
     A flow control device has a duct section with a plurality of damper blocking elements, each having a major plane. The damper blocking elements are pivotably connected to the duct section and movable in a range that is limited to ensure that, when the duct section is mounted in a preferred orientation, the damper blocking element major planes always form an angle of at least 45 degrees from the horizontal throughout the range. The range is such that the plurality of damper blocking elements can selectively close and open the duct. Preferably the blocking elements are capable of completely closing the duct, for example to block natural convection. In a variation, there are two damper blocking elements. The damper blocking elements may be configured such that they are interconnected to pivot in opposite directions and further such that edges thereof meet in the middle of the duct section when the blocking elements are in a closed position. For example, in a preferred configuration, the major planes are substantially vertical when the blocking elements are in the open position. 
     The blocking elements can be configured each with a flat portion, such as by means of a bend in a plate, that come into parallel abutment with each other when the blocking elements are in the closed position. The damper blocking elements pivot on bearings mounted outside the duct section. Preferably the bearings are durable and low resistance bearings such as roller or ball bearings to allow the damper to be used continuously and adjusted frequently throughout the day over a long lifetime without sticking or breaking down. 
     The blocking elements may be carried on shafts which are mounted to the bearings, and liquid proof seals located at the duct walls may be provided that permit the shafts to rotate while preventing fluid in the duct from escaping to the outside of the duct. The duct may be sealed against fluid within the duct escaping the duct section. The damper blocking elements pivot on bearings mounted inside the duct on one side of the duct and mounted outside the duct on the opposite side of the duct such the one side has no protrusions. A motor drive may be located on the opposite side so that the side with the bearing on the inside can present a flush outer face. 
     A motor drive may be configured to position the damper blocking elements and a controller configured to control the motor drive responsively to a detected fume load. The controller may be configured to control the motor drive responsively to a fume load detected by at least one of a gas sensor, an optical sensor, a temperature sensor, and a flow sensor. 
     Any of the foregoing variations may be applied to another flow control device with a duct section that has a plurality of damper blocking elements, each having a major plane. In this device, the damper blocking elements pivot on bearings connected to the duct section and are movable from an open position in which the blocking elements are in a vertical position in which the major planes are spaced apart and parallel to closed position in which the major planes form an angle of at least 45 degrees with the horizontal. The range is such that the plurality of damper blocking elements can selectively substantially close the duct section completely and open the duct section completely. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  shows a perspective view of a balancing damper. 
         FIGS. 2A-2D  are figurative views of the balancing damper blade positions in various stages of adjustment. 
         FIG. 3  shows the blades of a balancing damper. 
         FIG. 4A  shows a partial section view of a balancing damper assembly. 
         FIG. 4B  shows a perspective view of a balancing damper. 
         FIGS. 5A-5D  show alternative damper blade configurations and mechanisms. 
         FIGS. 6A and 6B  show another alternative blade configuration. 
         FIG. 7  shows a damper unit mounted in a duct of an exhaust hood and various associated features. 
         FIG. 8  shows a configuration of a damper with trough shaped blades. 
     
    
    
     DETAILED DESCRIPTION OF EMBODIMENTS 
     Referring to  FIG. 1 , a balancing damper in a duct segment  100  that carries grease laden fumes has two generally air blocking elements  102  and  112  that rotate on bearings  108 A and  108 B. As illustrated in  FIGS. 2A to 2D , the blocking elements  102  and  112  rotate symmetrically between settings for high resistance  90 , low resistance  93 , and a range of positions in-between including those indicated at  91  and  92  positions. 
     Note that in all of the positions shown, the blocking elements  102  and  112  remain at a minimum angle with respect to the horizontal  80  of more than about 45 degrees, for example, end portions  113  of blocking elements  102  and  112  as well as the major portions  115  all form angles, such as angles φ 1  and φ 2 . For example the minimum angle can be at least about 45 degrees, the closed position being the least vertical. 
     A motor drive  104  may be used to rotate the blocking elements  102  and  112 . The drive  104  may include an indicator  114  that shows the position of the damper. The drive  104  may be replaced by a manual positioning device. A synchronization mechanism, such as a kinematic mechanism (for example, one using linkages including the links  106  and  109 ) may be provided to cause the blocking elements  102  and  112  to pivot back and forth in synchrony. Such a kinematic mechanism could employ gears, hydraulic couplings, electronically synchronized drives or any suitable mechanism. 
     The blocking elements may be planar or any other suitable shape. The embodiment of  FIG. 1  may be modified to fit in a round duct with blocking elements shaped as cylindrical sections to permit the same overall effect as the embodiment of  FIG. 1 . 
     Preferably, bearings are provided, such as bearings  108   a  and  108   b , to support the blocking elements  102  and  112  for pivoting. The bearings may be located inside the duct section  100  or outside. In one configuration, bearings may be located on the inside on a side of the duct opposite the drive motor and on the outside on the side with the drive motor. In the latter configuration, the duct can be located with the side opposite the drive motor lying directly against the wall. Referring to  FIG. 4A , where the bearings are located outside as indicated by  180 , the duct section may have a housing  144  to enclose the external bearing. The bearings may also be provided with a seal  184  to ensure that gas, grease or condensed vapor or any other liquid cannot leak from the duct.  FIG. 4B  illustrates a configuration in which a housing  150  encloses a drive  155  as well as the externally-mounted bearing. Bearings  182  inside the duct may be constructed, as shown in  FIG. 4A , such that no duct wall penetration is required. Preferably, a notch  172  in blocking element  102  provides clearance for any internal bearing. 
     As illustrated, one end of each blocking element  102  and  112  may have a bend at the end. This may enhance rigidity and also help to act as a stop to prevent the blocking elements pivoting too far. Such features may be provided on one or both ends or not at all.  FIG. 3  shows the damper with the duct section  100  removed.  FIGS. 5A to 5D  show alternative mechanisms.  FIGS. 5A and 5B  show blocking elements  202  and  204  that pivot at their ends. In other configurations, the pivot location may be anywhere along the blocking elements. As in the other configurations, the blocking elements are partially vertical, preferably at least  45  degrees to the horizontal, in the closed position ( FIG. 5 a   ) and more vertical in the open position ( FIG. 5 b   ), to help prevent the accumulation of grease by encouraging grease to drip quickly off the blocking elements  202  and  204 . A linkage  206 , which may be located outside the duct  100 , causes the blocking elements  202  and  204  to move in synchrony. An embodiment of  FIGS. 5C and 5D  has blocking elements  208  and  210  configured for a round duct  100 A. 
       FIGS. 6A and 6B  show closed and open positions, respectively, of a mechanism with a single blocking element  220  that pivots at  224 . As in the above embodiments, in the closed position, the blocking element  220  forms a substantial minimum angle with the horizontal. In this and other embodiments the minimum angles are as discussed above with regard to the other embodiments. 
     The above embodiments may be varied in terms of details, such as the shape of the blocking elements and the angle formed by the blocking elements in all positions, even the closed position. For example, although in the above embodiments, the blocking elements form a 45 degree angle, a greater or smaller angle may be used. In preferred embodiments, the angle is at least 30 degrees from the horizontal. In more preferred embodiments, the angle is at least 40 degrees, and more preferably 45 degrees to the horizontal. In alternative embodiments, the angle is greater than 45 degrees to the horizontal. 
     Note in the above embodiments that the blocking elements have bent portions at one or more edges. These also form substantial angles with the horizontal in all positions. Preferably the angles are greater than 45 degrees. 
       FIG. 8  shows a damper configuration  160  with damper blocking elements that are trough shaped with bends  164  providing rigidity and no bends on the upstream  166  and downstream  162  edges. The bends  164  can extend the entire distance between the edges  162  and  166  or they can be interrupted, as shown, at one or more points along that distance. 
     Referring to  FIG. 7 , preferably, grease conveyance  314  is provided below the damper  300  to carry grease that drips from the damper unit  300 .  FIG. 7  shows the damper unit  300  mounted in a duct  316  of an exhaust hood  318  above an exhaust plenum  310 . The exhaust hood  318  is mounted over an appliance  320  that emits fumes. A controller  324  controls the damper unit  300  responsively to an indicator  312  which indicates the conditions of the exhaust stream or the operational state of the appliance  320 . In a preferred configuration, when the appliance  320  is on, the damper  300  is controlled by a controller  324  such that it never fully closes and continues to drain grease generated by the appliance back into the hood grease conveyance or the plenum, depending on the configuration. However, when the appliance is off, the damper fully closes to seal the ductwork to prevent outside air from getting pulled back into the ductwork and into the interior space in which the exhaust hood  318  is located. It is believed that this provides the benefit of reducing the load on any space conditioning system responsible for maintaining enthalpy conditions in the interior space. The indicator  312  may include a cooking sensor (such as an infrared sensor, direct communication with the appliances, etc.), gas sensor, opacity sensor, temperature sensor or any device that can indicate whether exhaust flow is required to eliminate fumes. Loads can be detected in other indirect ways, for example by detecting the fuel or electricity consumed by an appliance, the time of day, or the number of orders placed for cooked food. 
     U.S. Pat. Nos. 6,170,480 and 6,899,095, which are hereby incorporated by reference as if fully set forth in their entireties herein, illustrate various ways to detect the amount of fumes in an exhaust system that may be used to control the damper units of the above embodiments. These documents also discuss applications for a damper, such as balancing of hoods mounted to a common exhaust. The embodiments of the invention can be used with these applications. 
     It is, therefore, apparent that there is provided, in accordance with the present disclosure, a damper suitable for liquid aerosol-laden flow streams and associated methods. Many alternatives, modifications, and variations are enabled by the present disclosure. Features of the disclosed embodiments can be combined, rearranged, omitted, etc. within the scope of the invention to produce additional embodiments. Furthermore, certain features of the disclosed embodiments may sometimes be used to advantage without a corresponding use of other features. Accordingly, Applicants intend to embrace all such alternatives, modifications, equivalents, and variations that are within the spirit and scope of this invention.

Technology Classification (CPC): 5