Patent Publication Number: US-9845969-B2

Title: Gravity shutter

Description:
BACKGROUND OF THE INVENTION 
     Field of the Invention 
     The present invention relates to air handling systems, such as heating and cooling systems and, more particularly, to a gravity exhaust air shutter. 
     Background Information 
     Many commercial buildings are heated and/or cooled by one or more self-contained, packaged air-conditioning units. Many of these units are installed on the roof tops of such buildings. These units typically include cooling equipment, air handling fans, and may further include dehumidifiers and heating equipment. The units receive return air from the building, cool (or heat) the received return air, and supply the cooled (or heated) return air back to the building. Some units also include exhaust fans for discharging some portion of the return air from the building. The exhaust fans are typically mounted next to an exhaust opening of the unit. In a prior design, a series of is louvered slats are disposed at the opening. The louvered slats may extend the width of the opening, and may overlap each other when in the lowered, e.g., closed, position. Pins on the ends of the louvered slats may be mounted in holes formed in the sides of the exhaust opening, thereby allowing the louvered slats to swing open when the exhaust fans are turned on. 
     Outside air often leaks into the unit through these louvered slats. The occurrence of outside air leaking into the unit can degrade its performance. Accordingly, a need exists to improve the performance of packaged units and other air handling systems. 
     SUMMARY OF THE INVENTION 
     Briefly, the invention relates to a gravity exhaust air shutter assembly for use in heating, ventilation and air conditioning (HVAC) systems, such as a packaged air conditioning unit, an air handling unit, and a ventilation unit, among others. A packaged air conditioning unit, which may be mounted on the roof top of a building to be cooled, may include a plurality of components. In particular, the packaged unit may include an economizer designed to mix return air from the building with outside air, and deliver it to one or more air treatment components, such as cooling units, heating units, dehumidifying units, filter units, etc. The air mixture is treated and supplied to the building by one or more supply air blowers. The air conditioning unit may also include a return air unit that includes an inlet for receiving return air from the building, an outlet for delivering at least a portion of the return air to the economizer, and an exhaust unit for discharging at least a portion of the return air to the outside. The exhaust unit may include one or more exhaust fans, and one or more of the gravity exhaust air shutter assemblies of the present invention. The exhaust unit may be configured to reduce or prevent back draft of outside air into the economizer. 
     The exhaust air shutter assembly may include at least one shutter flap mounted adjacent to an open frame with a hinge, such that the shutter flap pivots between a closed position and an open position. When the shutter flap is in the open position, an air flow path exists from the return air inlet, through the one or more exhaust fans, and through the open frame to the outside. When the shutter flap is in the closed position, this air flow path is blocked, preventing return air from being discharged to the outside. The shutter flap and the open frame may each be generally rectangular shaped with the shutter flap sized slightly larger than the frame, although other shapes may be used. The open frame may be positioned at an angle to the horizontal, and the shutter flap, when in the closed position, may sit on top of, and thus close off, the open frame to the outside. Mounted around the perimeter of the frame on the side adjacent to the shutter flap is a gasket. The gasket may be a closed cell material. The shutter flap contacts the gasket when the shutter flap is in the closed position thereby creating a seal between the shutter flap and the open frame. 
     The one or more exhaust fans may be operated by a controller of the packaged unit. When the controller determines that some portion of return air should be discharged to the outside, the controller activates the one or more exhaust fans. Operation of the one or more exhaust fans creates a positive air pressure after the fans that lifts the shutter flap from the closed to the open position. While the shutter flap is in the open position, a portion of the return air is discharged from the packaged unit through the open frame. The remaining return air, i.e., that portion of the return air that is not discharged outside, flows into the economizer and may be mixed with outside air before being cooled and delivered into the building. 
     When the controller determines that no portion of return air needs to be discharged from the packaged unit, it turns the one or more exhaust fans off. With the one or more exhaust fans turned off, gravity forces the hinged shutter flap to the closed position where the shutter flap sits on the open frame. Due to the seal formed between the shutter flap and the gasket, return air is prevented from leaking out of the return air unit, and outside air does not enter the return air unit. In addition, with the one or more exhaust fans turned off, a negative air pressure may be created in the return air unit and the economizer by operation of the supply air blower. The shutter flap is configured so that this negative air pressure draws the shutter flap against the gasket, thereby further reducing any return air leakage, and any outside air entering the return air unit. Furthermore, the higher the negative pressure, the better the seal that is formed, as the shutter flap continues to be drawn against the gasket. The configuration of the exhaust air shutter assembly results in a zero leakage gravity shutter. 
     In an embodiment, the return air unit may include a plurality of exhaust air shutter assemblies. 
     In another embodiment, the exhaust air shutter assembly may be utilized as a pressure relief shutter. In particular, one or more weights may be affixed to the shutter blade. The one or more weights may be configured to hold the shutter blade in the closed position until a determined pressure level is generated on the inside portion of the exhaust air shutter assembly relative to the outside. When the pressure differential between the inside and outside portions reaches the predetermined level, the weighted shutter blade is lifted off of the of the open frame, and air from the inside portion may be released. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The description below refers to the accompanying drawings, of which: 
         FIG. 1  is a schematic side elevation view of a packaged air conditioning unit in accordance with an embodiment of the present invention; 
         FIG. 2  is a schematic, cut-away perspective view of the packaged air conditioning unit of  FIG. 1 ; 
         FIG. 3  is a schematic, cut-away perspective view of a gravity shutter assembly in accordance with an embodiment of the present invention; 
         FIG. 4  is a schematic side elevation view of a gravity shutter assembly in a closed position in accordance with an embodiment of the present invention; 
         FIG. 5  is a schematic side elevation view of a gravity shutter assembly in an open position in accordance with an embodiment of the present invention; 
         FIG. 6  is a schematic, cut-away perspective view of a gravity shutter assembly in accordance with another embodiment of the present invention; and 
         FIG. 7  is a plot of the test results of an embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTIONS OF ILLUSTRATIVE EMBODIMENTS 
       FIG. 1  is a schematic side elevation view of a packaged air conditioning unit  100 , which may be mounted on the roof top of a building being cooled and/or heated.  FIG. 2  is a schematic, cut-away perspective view of the unit  100 . The packaged air conditioning unit  100  may include a plurality of components. In particular, it may include a condenser section  102 , a supply air section  104 , an air treatment section  106 , an economizer  108 , an air discharge section  110 , and a controller  112 . The condenser section  102  may include one or more compressors, such as compressors  114   a - c , and one or more condenser fans, such as condenser fans  116   a - d . The supply air section  104  may include at least one supply air blower, such as blower  118 , adjacent to a supply air duct  120 . The air treatment section  106  may include one or more air treatment elements. For example, the air treatment section  106  may include one or more filters, such as filter assemblies  122   a - b , and one or more cooling coils, such as cooling coil  124 . The air treatment section  106  may include other elements, such as one or more heating units, one or more dehumidifiers, etc. (not shown). 
     The economizer  108  may include one or more air intake vents, such as vent  126 . The air discharge section  110  may include a return air duct  128 , one or more exhaust fans, such as fans  130   a - b , and one or more gravity shutter assemblies  300   a - h . The exhaust fans  130   a - b  and gravity shutter assemblies  300   a - b  may be mounted on opposite sides of exhaust air vents in the air discharge section  110 . In particular, the gravity shutter assemblies  300   a - h  may be disposed on a downstream side of the exhaust air vents relative to the exhaust fans  130   a - b . In the illustrated embodiment, the unit  100  includes four exhaust fans  130 , and two exhaust air shutter assemblies  300  are provided adjacent to each exhaust fan  130 . The exhaust fans  130   a - b  of the air discharge section  110  may be axial fans, and may be mounted and configured to force a portion of return air horizontally from the air discharge section  110  through the exhaust air vents and the exhaust air shutter assemblies  300  to the outside. Each exhaust shutter assembly  300  may include at least one shutter blade as described further herein. 
     One or more hoods and screens (not shown) may be placed over the air intake vent  126  of the economizer  108  to prevent rain, debris, birds or other objects from entering the unit  100 . The economizer  108  also may include a plurality of moveable dampers adjacent to the air intake vent  126  for controlling the amount of outside air that is mixed with the return air received from the air discharge section  110 . A plurality of dampers may also be disposed adjacent to the exhaust air vents of the air discharge section  110  to control the amount of return air that is discharged outside. 
     In operation, the compressors  114   a - c  of the packaged air conditioning unit  100  receive a refrigerant in a vapor state, compress the refrigerant to a liquid state, and provide liquid refrigerant to the cooling coil  124 . Activation of the supply air blower  118  creates a negative air pressure in the air discharge section  110 , the economizer  108  and the air treatment section  106  relative to the outside air and the air in the building. As a result, return air is drawn from the building, through the return air duct  128  into the air discharge section  110 . The received return air is then drawn into the economizer  108  where it may be mixed with outside air entering the economizer  108  through the air intake vent  126 . In addition, a portion of return air may be discharged from the air discharge section  110  through the gravity shutter assemblies  300 , as described further herein 
     From the economizer  108 , the mixed air is drawn through the air treatment section  106 , and into the supply air section  104 . As the air mixture is drawn through the air treatment section  106 , it is filtered and cooled (or heated). It may also be dehumidified. The supply air blower  118  also forces the treated air into the supply air duct  120  from which it may be distributed within the building. Operation of the packaged air conditioning unit  100  is under the control of the controller  112 . Arrow  132  ( FIG. 1 ) shows the general flow of air through the unit  100 . 
     It should be understood that  FIGS. 1 and 2  represent a highly schematized view of a roof top packaged air conditioning unit  100 , and that the unit  100  may include other or different sections, components or elements. Suitable packaged units for use with the present invention include the model PPH 35 from Petra Engineering Industries Co. of Amman Jordan. 
     Nonetheless, the present invention may be used with other packaged units, and with other HVAC systems or components. For example, it may be used with an air handling unit, a ventilation unit, or any other ventilation system that needs to exhaust air from a given space. 
       FIG. 3  is a schematic, cut-away perspective view of a gravity shutter assembly  300 . In an embodiment, the gravity shutter assembly  300  may include a housing  302  having a top panel  304 , a bottom panel  306 , and first and second side panels  308 ,  310 . The panels  304 - 310  define an open interior space of the gravity shutter assembly  300 . At least one dividing wall  312  may be disposed inside the interior space of the gravity shutter assembly  300 . The at least one dividing wall  312  may extend vertically from the bottom panel  306  to the top panel  304 , and horizontally from the first side panel  308  to the second side panel  310 . The at least one dividing wall  312  may thus separate the gravity shutter assembly  300  into an outside portion  314  and an inside portion  316  where the outside portion  314  is open to the outside, and the inside portion  316  is open to the inside of the unit  100 . In particular, the at least one dividing wall  312  seals inside of the unit  100  from the outside. 
     An opening  320  may be formed in the at least one dividing wall  312 . For example, a generally rectangular opening  320  may be formed in the at least one dividing wall  312 . Disposed around a perimeter of the opening  320  may be a frame  322 . The dividing wall  312  may be planar, and the frame  322  may be raised relative to the plane of the dividing wall  312 . The raised frame  322  may extend around the entire perimeter of the opening  320  in the dividing wall  312 . The raised frame  322  may include a support surface that extends around the entire frame  322 . A gasket  324  may be mounted to the support surface of the frame  322 . The gasket  324  may extend around the entire frame  322 . That is, to the extent the frame  322  is rectangular, the gasket  324  may extend around the top edge, the two side edges and the bottom edge of the raised frame  322 . 
     The support surface of the frame  322  may define an elongated flat surface or strip, and the gasket  324  may be in the form of a narrow strip of material sized to cover substantially all of the support surface of the raised frame  322 . 
     A moveable shutter blade  326  may be mounted over the opening  320  in the dividing wall  312 . The shutter blade  326  may be planar, and may be shaped like the opening  320  and the raised frame  322 . That is, to the extent the frame  322  is rectangular, the shutter blade  326  also may be rectangular in shape, and may have a top edge  328 , first and second side edges  330 ,  332  and a bottom edge  334 . The shutter blade  326  may be at least slightly oversized relative to the raised frame  322  to cover the entire frame  322  and thus the opening  320  in the dividing wall  312 . At least one hinge  336  may be mounted to the shutter blade  326  so that the shutter blade  326  is moveable between an open position and a closed position. In particular, the at least one hinge  336  may be mounted to the top edge  328  of the shutter blade  326  and adjacent to the top edge of the raised frame  322 . 
       FIGS. 4 and 5  are partial side elevation views of the gravity shutter assembly  300  of  FIG. 3 .  FIG. 4  shows the shutter blade  326  in the closed position, and  FIG. 5  shows the shutter blade  326  in the open position. Rather than being vertically mounted, the dividing wall  312  may be disposed at an angle within the gravity shutter assembly  300  relative to the vertical (or to the horizontal). An exemplary angle is 45 degrees, although other angles, such as angles between 30 and 70 degrees may be used. Nonetheless, other angles may also be used. As shown, the shutter blade  326  pivots about the hinge  336  between a closed position ( FIG. 4 ) and an open position ( FIG. 5 ). In the closed position, a portion of the planar surface of the shutter blade  326  contacts the gasket  324 . In the closed position, the shutter blade  326  together with the dividing wall  312  seal the inside portion  316  of the gravity shutter assembly  300  from the outside portion  314 . In the open position ( FIG. 5 ) the shutter blade  326  is lifted off of the raised frame  322  and the dividing wall  312 , thereby providing an air flow path from the inside portion  316  to the outside portion  314  through the opening  320  in the dividing wall  312 , as illustrated by arrow  340 . 
     The frame  322  may be formed from sheet metal. Specifically, the frame  322  may be formed as a U-shaped channel having two bends thereby defining a first side, a bottom and a second side. The first side of the frame may be joined to the at least one dividing wall  312 , e.g., by rivets, welding, adhesives, or any combination thereof. The bottom side may define the opening  320 . The second side may define the support surface to which the gasket  324  is mounted. The shutter blade  326  also may be formed from sheet metal. For example, the shutter blade  326  may be substantially planar with downturned edges to provide structural integrity to the shutter blade  326 . Such a shutter blade  326  may generally have an inverted drip pan or cookie sheet shape. 
     The gasket  324  may be a closed cell foam material, such as closed cell polyvinyl chloride foam. Nonetheless, it will be understood that the gasket  324  may be formed from other materials, such as polyethylene foam, or from a combination of materials. 
     The gasket may be made an elastic material, and thus allow a seal to be formed despite irregularities and/or imperfections in the surface of the shutter blade and/or the frame, e.g., due to manufacturing, deformation or wear during operation, etc. 
     While a rectangular opening  320 , frame  322  and shutter blade  326  have been shown, it should be understood that other shapes may be used. For example, circular, oval, triangular or other shapes may be used in the gravity shutter assembly  300 . 
     Other modifications may also be made to the gravity shutter assembly  300 . For example, the hinge  336  may be mounted to the top panel  304  of the housing  302 , rather than to the dividing wall  312 . In addition, rather than a hinge, one or more pivot pins may be used to attach the shutter blade  326  to, e.g., the first and second side panels  308 ,  310  of the housing  302 . Other modifications are also possible. For example, the frame  322  may be omitted, and the gasket  324  may be disposed around the opening  320  in the dividing wall  312 . In another embodiment, multiple frames  322  and shutter blades  326  may be disposed in the housing  302 . In yet another embodiment, the gasket may be omitted and the shutter blade may be configured to close against the frame and/or the dividing wall to create a seal. That is, the surface of the shutter blade may be configured to conform to the surface of the frame and/or dividing wall to create a seal when the shutter blade is in the closed position. 
     During operation of the unit  100 , the controller  112  may determine that some portion of the return air entering the air discharge section  110  should be discharged from the unit  100 . In this case, the controller  112  may active one or more of the exhaust fans  130 . Operation of the exhaust fans  130  generates a positive air pressure on the inside portion  316  of the gravity shutter assembly  300  relative to the outside portion  314 . This positive air pressure overcomes the force of gravity holding the shutter blade  326  down against the gasket  324  and the frame  322 , and lifts the shutter blade  326  off of the gasket  324  and the frame  322  into the open position ( FIG. 5 ). With the shutter blade  326  in the open position, at least a portion of return air entering the air discharge section  110  is discharged to the outside. During operation of the exhaust fans  130 , a negative pressure may still exist in the economizer  108  and in the air discharge section  110 , for example, due to the operation of the supply air blower  118 . 
     When the controller  112  determines that no portion of return air entering the air discharge section  110  needs to be discharged, it deactivates the exhaust fans  130 . With the exhaust fans  130  turned off, the positive pressure in the inside portion  316  is no longer maintained. Gravity, acting on the shutter blade  326 , forces the shutter blade  326  to pivot downwardly about the hinge  336  onto the gasket  324  and the frame  322 . As noted, a portion of the planar surface of the shutter blade  326  contacts the gasket  324  mounted to the frame  322 . With the shutter blade  326  in the closed position, the inside portion  316  is once again sealed from the outside portion  314 , and outside air is blocked from entering the unit  100  through the gravity shutter assemblies  300  and the exhaust air vents in the air discharge section  110 . 
     It should be understood that the hinge  336  may be placed at a location that is spaced from a center of mass of the shutter blade  326 . In this way, gravity, acting on the shutter blade  326  through its center of mass causes the shutter blade  326  to pivot about the hinge  336 . 
     Operation of the supply air blower of the unit  100  may create a negative air pressure in the air discharge section  110  and the economizer  108  relative to the outside air and the air in the building. This negative air pressure draws return air from the building into the air discharge section  110  through the return air vent  128 . The negative air pressure also draws outside air into the economizer  108  where it is mixed with return air. The negative air pressure on the inside  316  of the gravity shutter assembly  300  (relative to the outside  314 ) also causes the shutter blade  326  to be pulled tighter against the gasket  324 , thereby forming a tighter seal between the shutter blade  326  and the gasket  324 . This tighter seal results in the gravity shutter assembly  300  being a zero leakage gravity shutter. Indeed, as the negative air pressure increases, the shutter blade assembly is configured to create an even tighter seal, making the shutter blade assembly especially suited to high negative pressure applications. 
     Testing of an embodiment of the gravity shutter assembly  300 , and an earlier louvered slat design demonstrates the dramatically improved results. More specifically, positive air pressure was induced at the inside  316  of the gravity shutter assembly  300  and the earlier louvered slat design relative to the outside  314 . This positive air pressure was varied, and the volume of air leaking through the gravity shutter assembly  300  and the prior design was measured. Below is a table setting forth the test results.  FIG. 7  is a plot of the test results. 
     
       
         
           
               
               
               
             
               
                   
               
               
                   
                 New 
                 Prior 
               
               
                   
                 design 
                 Design 
               
               
                 Static 
                 Air 
                 Air 
               
               
                 Pressure 
                 Leakage 
                 Leakage 
               
               
                 (in. wg) 
                 (cfm) 
                 (cfm) 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
            
               
                 0.1 
                 8.6 
                 53.4 
               
               
                 0.2 
                 9.9 
                 67.4 
               
               
                 0.3 
                 10.7 
                 77.2 
               
               
                 0.5 
                 11.8 
                 99 
               
               
                 1 
                 12.5 
                 141.4 
               
               
                 1.5 
                 13.1 
                 172.1 
               
               
                 20 
                 14 
                 199.7 
               
               
                 2.5 
                 15.4 
                 212 
               
               
                 3 
                 16.4 
               
               
                 3.5 
                 17.6 
               
               
                 4 
                 20.2 
               
               
                 5 
                 20.8 
               
               
                   
               
            
           
         
       
     
     In  FIG. 7 , the static pressure is given in inches of water gauge (in. wg), which is a pressure differential measured between the inside portion  316  and the outside portion  314  of the gravity shutter assembly  300 . The air leakage is given in cubic feet per minute (cfm). 
       FIG. 6  is a schematic, cut-away perspective view of a shutter assembly  600  in accordance with another embodiment of the present invention. The gravity shutter assembly  600  is similar to the shutter assembly of  FIG. 3 . However, the shutter assembly  600  further includes at least one weight assembly, such as weight assembly  602 , mounted to the shutter blade  326 . The weight assembly  602  may be mounted toward the bottom edge  334  of the shutter blade  326 . That is, the weight assembly  602  may be mounted at a location that is offset from a center of mass of the shutter blade  326 , and opposite to the pivot point defined by the hinge  326  relative to the center of mass. The weight assembly  602  may consist of one or more weight elements, such as weight elements  604   a - b , which may be strips of a selected material, e.g., metal, and size, and thus weight. The weight assembly  602  may be attached to the shutter blade  326  by a plurality of thread studs  606   a - b  and nuts  608   a - b  where the thread studs  606   a - b  are welded to the shutter blade  326 . Nonetheless, other securing techniques may be used, such as welding, nuts and bolts, adhesives, etc. 
     In this embodiment, the gravity shutter assembly  600  may be used as a pressure relief shutter. More specifically, if the pressure on the inside  316  of the shutter assembly  600  builds up and reaches a predetermined value, the pressure causes the shutter blade  326  to move to an open position, thereby releasing air and reducing the pressure on the inside  316  of the shutter assembly  600 . 
     By adjusting the weight of the weight assembly  602 , e.g., by adding or removing one or more weight elements  604 , a user can configure or “tune” the shutter assembly  600  to open at a determined static pressure relative to the outside. For example, by adding one or more weight elements  604 , the shutter assembly  600  may be configured to delay opening until a higher static pressure is reached. By removing one or more weight elements  604 , the shutter assembly  600  may be configured to open earlier when a lower static pressure is reached. 
     It should be understood that those skilled in the art may make modifications or changes without departing from the scope or intent of the invention. For example, the housing may be eliminated, and the shutter blade may be mounted over the exhaust air vents in the air discharge section  110  of the packaged air conditioning unit  100  or other air handling system or device. 
     The foregoing description has been directed to specific embodiments of the present invention. It will be apparent, however, that other variations and modifications may be made to the described embodiments, with the attainment of some or all of their advantages. For example, the gravity shutter assembly may be used in an air handling system, such as an air conditioner, mounted on the roof top of a vehicle, such as a motor home. Therefore, it is the object of the appended claims to cover all such variations and modifications as come within the true spirit and scope of the invention.