Patent Publication Number: US-2007101987-A1

Title: Apparatuses and methods for balancing combustion air and exhaust gas for use with a direct-vent heater appliance

Description:
TECHNICAL FIELD  
      This invention is directed to direct-vent heater appliances, and more particularly, to apparatuses and methods for balancing combustion air and exhaust gas in direct-vent heater appliances.  
     BACKGROUND OF THE INVENTION  
      Vented heater appliances are well known and commonly used in residential dwellings and other structures for heating and esthetic purposes. Examples include gas-burning furnaces and gas-burning and wood-burning fireplaces. Traditional wood-burning fireplaces are not particularly efficient heaters, they tend to be dirty and require frequent cleaning due to the nature of the fuel used, and they require a constant supply of wood or other fuel. In view of the disadvantages of traditional wood-burning fireplaces, there has been a move to cleaner and more efficient gas-burning fireplaces.  
      Top-vent and direct-vent fireplaces make up the majority of gas-burning fireplaces sold in the United States. A top-vent fireplace vents exhaust to the outside and draws combustion air from the surrounding room. Direct-vent fireplaces draw combustion air from outside of the structure and vent exhaust gas to the outside using either a duct-within-a-duct arrangement or two separate ducts. Direct-vent fireplaces are either a free-standing style or a fireplace insert style positionable into a fireplace cavity built into the wall of a house, apartment, condominium, or other residential dwelling or structure. These direct-vent fireplaces are connected to suitable combustion air and exhaust gas ducts that communicate with the exterior of the dwelling.  
       FIG. 1  is a schematic side-elevational view of a conventional direct-vent fireplace insert installation in accordance with the prior art. The direct-vent fireplace insert  100  is situated within a preformed fireplace cavity  112 . Windows  122  may be provided on the insert  100  for viewing a fire  123  within a firebox  110 . The insert  100  is connected to an exhaust duct  114 , which is routed through a chimney  118  that communicates with the fireplace cavity  112 . The illustrated fireplace insert  100  is also connected to a combustion air intake duct  116  concentrically disposed around the exhaust duct  114 . In an alternate embodiment, the exhaust duct  114  can be spaced apart from the intake duct  116  so that the exhaust duct is not inside the intake duct.  
      Direct-vent fireplaces require a balanced flow of combustion air and exhaust gas moving through the intake and exhaust ducts  116  and  114 , respectively, to provide an aesthetically desirable flame in the firebox  110 . Desirable flame characteristics can include, for example, appearing similar to a natural wood-fire flame. The size, color and action of the flames in the firebox  110  can be adjusted by selectively balancing the flow of combustion air and exhaust gas. A balanced flow also allows direct-vent fireplaces to function in a thermally efficient manner. Accordingly, an important part of the fireplace insert&#39;s installation is to properly balance the combustion air intake flow and the exhaust gas flow.  
      The conventional insert-style fireplace insert  100  is typically installed and balanced by first sliding the insert into a close-fit fireplace cavity  112  so a limited access space  126  is provided between the fireplace insert and the cavity&#39;s walls. The installer reaches through the limited access space  126  to connect the fireplace insert to the exhaust duct  114  and the intake duct  116 . The installer then balances the flow of combustion air and the exhaust gas while the fire  123  is bunting in the firebox  110  in order to visually analyze the flame characteristics. Limited access to the adjustment mechanisms for the intake duct  116  or the exhaust duct  114  can make this balancing a time-consuming and labor intensive process requiring multiple adjustments of the adjustment mechanisms during installation.  
     SUMMARY OF THE INVENTION  
      The present invention is directed toward apparatuses and methods for balancing combustion air and exhaust gas for use in direct-vent heater appliances. In one embodiment, the apparatus is a combustion air and exhaust gas balancing system that is in fluid communication with a firebox of a direct-vent heater appliance. The balancing system includes a first valve that is movably adjustable to affect a flow of combustion air into the firebox and a second valve that is movably adjustable to affect a flow of exhaust gas out of the firebox. The second valve is operatively coupled to the first valve so that movement of the first valve is accompanied by a movement of the second valve. In one aspect of this embodiment, the second valve is mechanically and synchronously coupled to the first valve by an elongate actuator shaft so that the flow of combustion air into the firebox and the flow of exhaust gas out of the firebox can be simultaneously adjusted by a single operation of the elongate actuator shaft.  
      One method for balancing combustion air and exhaust gas in a direct-vent heater appliance in accordance with an embodiment of the invention includes igniting a fire in the firebox, providing a flow of combustion air to the firebox and a flow of exhaust gas from the firebox, visually analyzing the flame to determine if the flows of combustion air and exhaust gas should be adjusted to modify the flame, and manipulating an actuator shaft that synchronously moves a combustion air valve and an exhaust gas valve to simultaneously adjust the flow of combustion air and exhaust gas to provide a selected flame characteristic. Manipulating the actuator shaft can include translating the actuator shaft in a first direction to simultaneously increase the flows of combustion air and exhaust gas, or translating the actuator shaft in a second direction to simultaneously restrict the flows of combustion air and exhaust gas.  
      In another embodiment of the invention, a direct-vent heater appliance includes a firebox, a combustion air duct in communication with the firebox, and an exhaust gas duct in communication with the firebox. The exhaust gas duct having at least one dilution air inlet aperture exterior of the firebox. The dilution air inlet aperture is in fluid communication with the combustion air duct and is configured to permit a portion of the combustion air to pass from the combustion air duct to the exhaust gas duct without first passing through the firebox. A separator flue can be positioned in the interior portion of the exhaust gas duct adjacent to the dilution air inlet aperture to form a dilution air passage that receives combustion air from the combustion air duct and disperses the combustion air into the exhaust gas duct at a higher elevation than where the combustion air was received. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       FIG. 1  is a side-elevational view of a prior art direct-vent fireplace insert.  
       FIG. 2  is a partial cut-away isometric view of a direct-vent fireplace insert showing an insert manifold and a combustion air and exhaust gas balancing system in accordance with an embodiment of the invention.  
       FIG. 3  is an enlarged cross-sectional isometric view taken substantially along line  3 - 3  of  FIG. 2  showing an insert manifold with the combustion air and exhaust gas balancing system.  
       FIG. 4  is a reduced cross-sectional side-elevational view taken substantially along line  4 - 4  of  FIG. 2  showing a flow path of combustion air and exhaust gas in relation to the combustion air and exhaust gas balancing system.  
       FIG. 5  is an enlarged cross-sectional isometric view of an alternate embodiment of the present invention showing an insert manifold with the combustion air duct spaced apart from the exhaust gas duct. 
    
    
     DETAILED DESCRIPTION OF THE ILLUSTRATED EMBODIMENTS  
      In the following description, certain specific details are set forth in order to provide a thorough understanding of various embodiments of the invention. The present disclosure describes apparatuses and methods for controlling the flow of combustion air and exhaust gas in a direct-vent heater appliance. Many specific details of certain embodiments of the invention are set forth in the following description and in  FIGS. 2 through 5  to provide a thorough understanding of these embodiments. One skilled in the art will understand, however, that the present invention may have additional embodiments, or that the invention may be practiced without several of the details described below. In other instances, well known structures associated with direct-vent heater appliances, such as gas lines and burner assemblies in a firebox, have not been shown or described in detail to avoid unnecessarily obscuring the description of the embodiments of the invention.  
       FIG. 2  is a partial cut-away isometric view of a direct-vent fireplace insert  200  in accordance with one embodiment of the invention. The direct-vent fireplace insert  200  has a firebox  210 , a face panel  224  that attaches to the front of the firebox, and an insert manifold  250  that mounts to the top and rear of the firebox. Combustion air  242  is introduced into the firebox  210  through a combustion air intake duct  216 , and exhaust gases  244  are expelled from the firebox  210  via an exhaust gas duct  214 . The exhaust gas duct  214  is concentrically disposed within the combustion air intake duct  216 . The insert manifold  250  has an annular inlet flange  217  connected to the intake duct  216 . An annular exhaust flange  215  is concentrically disposed within the annular inlet flange  217  and is connected to the exhaust gas duct  214 . The inlet flange  217  and the exhaust flange  215  are spaced apart to form a combustion air passage  219  therebetween through which the combustion air from the combustion air duct  216  passes before flowing to the firebox  210 . The exhaust flange  215  defines an interior exhaust passage  221  thorough which the exhaust gases from the firebox  210  pass before entering the exhaust duct  214 .  
      The insert manifold  250  includes a flow balancing system  230  having an actuator handle  234  located near the front of the insert manifold  250 . As will be discussed in greater detail below, the balancing system  230  is configured to allow easy adjustment of the flow of combustion air  242  in the intake duct  216  and exhaust gas  244  in the exhaust duct  214  by adjusting the position of the actuator handle  234 .  
       FIG. 3  is a cross-sectional isometric view of the insert manifold  250  illustrating the combustion air and exhaust gas balancing system  230  in accordance with an embodiment of the invention. The balancing system  230  has a combustion air valve  362  positioned in fluid communication with the annular inlet flange  217 . The combustion air valve  362  is adjustable between open and restricted positions to affect the flow of combustion air  242  entering the firebox  210  ( FIG. 2 ).  
      The balancing system  230  also has an exhaust gas valve  360  positioned in fluid communication with the annular exhaust flange  215 . The exhaust gas valve  360  is adjustable between open and restricted positions to affect the flow of exhaust gas  244  exiting the firebox  210 . The exhaust gas valve  360  is coupled by an elongate actuator shaft  332  to the combustion air valve  362  so that an installer can simultaneously move the valves between their respective open and restricted positions. Accordingly, the installer can simultaneously adjust the flow of intake air  242  into the firebox  210  and the flow of exhaust gas  244  out of the firebox  210  by moving the actuator shaft  332 .  
      The actuator shaft  232  of the illustrated embodiment is positioned perpendicular to, and at least approximately intersecting, the central axes of the inlet flange  217  and the exhaust flange  215 . The actuator shaft  232  is translationally moveable in a closing direction  370  along its longitudinal axis toward a closed or restricted position, and in an opening direction  371  toward an open position opposite to the restricted position.  
      The combustion air valve  362  is moveably coupled to a distal end  363  of the actuator shaft  332  in a location generally below the inlet flange  217 . The combustion air valve  362  is a generally flat plate pivotally attached to a housing  310  of the insert manifold  250  with a hinge  366 . The combustion air valve  362  is moveably coupled to the distal end  363  of the actuator shaft  332  with a sliding bracket  364  SO that the combustion air valve extends downwardly and away from the actuator shaft  332  and is angularly positionable with respect to the flow of combustion air  242  flowing through the combustion air passage  217 . Accordingly, as the actuator shaft  332  moves in the opening direction  371 , the combustion air valve  362  pivots about the hinge  366  toward its open position and increases the flow of combustion air  242  entering the firebox  210 .  
      As the actuator shaft  332  moves in the closing direction  370 , the combustion air valve  362  pivots about the hinge  366  toward its closed position and restricts the flow of combustion air  242  entering the firebox  210 . The combustion air valve  362  in the illustrated embodiment is sized and shaped so that the flow of combustion air  242  through the combustion air passage  219  will not be completely stopped when the actuator shaft  332  is moved to the fully restricted position. The combustion air valve  362  is also sized and shaped to minimize tile restriction of the flow of combustion air  242  through the combustion air passage  219  when the actuator shaft  332  is in the fully open position. The sliding bracket  364  is sized and shaped so that the combustion air intake valve  362  will rest flush against the insert manifold housing  310  when the actuator shaft  332  is retracted in the opening direction  371  to the fully opened position.  
      The exhaust gas valve  360  is attached to the midsection  365  of the actuator shaft  232  by a connector bracket  361  in a location adjacent to the exhaust flange  215  that communicates with the firebox  210 . The exhaust gas valve  360  is a generally flat plate mounted to the actuator shaft  332  with the connector bracket  361  SO that the exhaust gas valve  360  is substantially parallel to tile actuator shaft  332  and perpendicular to the flow of exhaust gas  244  through the exhaust passage  221 . Accordingly, as the actuator shaft  332  moves in the opening direction  371 , the exhaust gas valve  360  retracts across the opening of the exhaust passage  221  and increases the flow of exhaust gas  244  entering the exhaust gas duct  214 . Conversely, as the actuator shaft  332  moves in the closing direction  370 , the exhaust gas valve  360  slides across the opening of the exhaust passage  221  and restricts the flow of exhaust gas  244  entering the exhaust gas duct  214 .  
      The exhaust gas valve  360  ill the illustrated embodiment is sized and shaped so that the flow of exhaust gas  244  through the exhaust passage  221  will not be completely stopped when the actuator shaft  232  is moved into the fully restricted position. The connector bracket  361  for the exhaust gas valve  360  is positioned to stop the actuator shaft  332  at a predetermined fully restricted position in closing direction  370 . The connector bracket  361  is shaped to provide a cantilever support for the exhaust gas valve  360  so that when the actuator shaft  332  is retracted in direction  371  toward the open position, the exhaust gas valve  360  will slide neatly under the lower end of the annular exhaust flange  215  to minimize the restriction of exhaust gas  244  through the annular exhaust flange  215 .  
      The balancing system  230  includes a retention bracket  338  mounted to the insert manifold  250  for securing the actuator shaft  332 , and, thus, the exhaust gas valve  360  and combustion air valve  362  in the selected position needed to tune the balancing system  230 . The retention bracket  338  has a fastener hole  339  which can be aligned with any one of a plurality of index holes  335  in the actuator shaft  332 . A lock bolt  340  or other suitable fastener (pin, screw, etc.) removably extends through the holes  339  and  335  to secure the actuator shaft  332  in the selected position after the balancing system  230  has been tuned. The availability of the index holes  335  in the actuator shaft  332  permits graduated adjustments of the intake and exhaust flows, and also permits selection of pre-determined valve positions to achieve a particular flame characteristic or to adjust the valves for a seasonal change in atmospheric conditions.  
       FIG. 4  is a cross-sectional schematic view of the direct-vent fireplace insert  200  illustrating a flow path of the combustion air  242  and the exhaust gas  244  through the balancing system  230  in accordance with one embodiment of the invention. The combustion air  242  flows in through the intake duct  216 , through the combustion air passage  219 , and around the intake valve  362  before arriving at the firebox  210 . The exhaust gas  244  exits the firebox  210  and moves past the exhaust gas valve  360  before flowing through the exhaust passage  221  and into the exhaust gas duct  214 . When the actuator shaft  332  is moved in the closing direction  370  toward the closed position, both the combustion air valve  362  and the exhaust gas valve  360  simultaneously move toward their respective closed positions by a selected amount to increase the restriction of their respective ducts  216  and  214 . Conversely, when the actuator shaft  232  is moved in the opening direction  371  toward the open position, the combustion air valve  362  and the exhaust gas valve  360  simultaneously move toward their respective open positions by a selected amount to decrease the restriction of their respective ducts  216  and  214 .  
      Referring back to  FIGS. 2 and 3  one advantage of the balancing system  230  is that the flow of exhaust gas  244  and combustion air  242  can be simultaneously balanced in a single operation of moving the actuator shaft  332  to a selected position between the open and closed positions. Accordingly, the simultaneous movement simplifies and expedites the installation and tuning of the direct-vent fireplace insert  200 . For example, it is often desirable to tune a flame  223  to look like a flame from a wood or other natural fuel fire, even though simulated logs are actually placed in the firebox  210  over a gas-burner assembly. To tune the direct-vent fireplace insert  200  to produce a thermally efficient flame with these characteristics, the installer ignites the fire  223  in the firebox  210 , and then slides the actuator handle  234  in the closing direction  370  or the opening direction  371  to simultaneously adjust the flow of combustion air  242  and exhaust gas  244  as required to produce the desired flame characteristics in the firebox  210 . Once the actuator shaft  332  has been properly positioned to balance the combustion air  242  with the exhaust gas  244  to achieve the desired flame characteristic, the handle  234  is secured to the retention bracket  338  with the lockbolt  340  to maintain the setting. The face plate  224  is then mounted to the front of the direct-vent fireplace insert  200  to complete the installation.  
      As best seen in  FIG. 3 , in one embodiment of the invention, the insert manifold  250  includes an annular separator flue  350  that is concentrically disposed within the exhaust flange  215 . In the illustrated embodiment, the exhaust flange  215  includes at least one dilution air aperture  351  positioned toward the lower end of the exhaust flange exterior of the firebox  210 . Thus, an annular dilution air passage  352  is formed between the annular separator flue  350  and the exhaust flange  215  that communicates with the combustion air passage  219  through the dilution air aperture  351 . The dilution air passage  352  permits combustion/dilution air  346  to be siphoned off of the intake air  242  and dispersed into the exhaust passage  221  without first passing through the firebox  210 . Accordingly, the diverted portion of combustion air  242  acts to partially dilute and cool the exhaust gas  244  flowing through the exhaust passage  221  and the exhaust gas duct  214 .  
      The combustion/dilution air enters the dilution air passage  352  through the dilution air aperture  351  at an elevation lower than where the combustion/dilution air  346  is dispersed into the exhaust gas  244 . Because of this elevation change, the exhaust gas  244  is unlikely to recirculate into the combustion air inlet  217  and mix with the combustion air  242  and adversely affect performance of the fireplace insert  200 .  
      The combustion/dilution air  346  entering the exhaust gas duct  214  can slow the flow of exhaust gas, which will effect the flame&#39;s characteristics in the firebox  210  ( FIG. 2 ). The combustion/dilution air  346  is much cooler than the exhaust gas  244  flowing through the exhaust passage  221 . This cooler combustion/dilution air  346  lowers the temperature of the hot exhaust gas  244 , thereby reducing the temperature differential between the exhaust gas  244  in the exhaust gas duct  214  and the outside air into which the exhaust gas duct opens. Reducing this temperature differential reduces the draw or velocity of exhaust gas  244 , which in turn will reduce the velocity of combustion air  242  in the combustion air intake duct  216  or other gas being drawn into the firebox  210 , thereby reducing the pull on the flames. Accordingly, the extent of cooling of the exhaust gas  244  affects the characteristics of the flame in the firebox  210 .  
       FIG. 5  is a partial cross-sectional isometric view of an insert manifold  550  having a combustion air and exhaust gas balancing system  530  in accordance with an alternate embodiment of the present invention. In this embodiment, the balancing system  530  is in fluid communication with a combustion air intake duct  516  and an exhaust gas duct  514  that are spaced apart from each other and not concentrically disposed. The combustion air intake duct  516  is connected to the insert manifold  550  at an annular inlet flange  517 , and the exhaust gas duct  514  is connected to the insert manifold  550  at an annular exhaust flange  515  spaced apart from the inlet flange  517 .  
      The balancing system  530  has a combustion air valve  562  positioned in fluid communication with the inlet flange  517 . The combustion air valve  562  is adjustable between open and restricted positions to affect the flow of combustion air  242  passing through the inlet flange  517 . The balancing system  530  also has an exhaust gas valve  560  positioned in fluid communication with the exhaust flange  515 . The exhaust gas valve  560  is adjustable between open and restricted positions to affect the flow of exhaust gas  244  passing through the exhaust flange  515 . The exhaust gas valve  560  is coupled by an elongate actuator shaft  532  to the combustion air valve  562  so that an installer can simultaneously adjust the flow of intake air  242  into a firebox and the flow of exhaust gas  244  out of the firebox by a single operation of the actuator shaft  532 .  
      The actuator shaft  532  is positioned perpendicular to and at least approximately intersecting the central axes of the inlet flange  517  and the exhaust flange  515 . Importantly, the actuator shaft  532  is translationally moveable in a closing direction  570  along its longitudinal axis toward a restricted position, and in an opening direction  571  toward an open position.  
      The combustion air valve  562  is attached to a distal end portion  565  of the actuator shaft  532  in a location adjacent to the inlet flange  517  that communicates with the firebox. The combustion air valve  562  is a generally flat plate mounted to the actuator shaft  532  with a connector bracket  563  so that the combustion air valve  562  is substantially parallel to the actuator shaft  532  and perpendicular to the flow of combustion air  242  through the inlet flange  517 . Accordingly, as the actuator shaft  532  moves in the closing direction  570  toward the closed position, the combustion air valve  562  slides across the opening of the intake flange  517  and restricts the flow of combustion air  242  entering the firebox. Conversely, as the actuator shaft  532  moves in the opening direction  571  toward the open position, the combustion air valve  562  retracts across the opening of the inlet flange  517  and increases the flow of combustion air  242  entering the firebox. The combustion air valve  562  in the illustrated embodiment is sized and shaped so that the flow of combustion air  242  through the inlet flange  517  will not be completely stopped when the actuator shaft  532  is moved into the fully restricted position.  
      The exhaust gas valve  560  is attached to the midsection of the actuator shaft  532  in a location adjacent to the exhaust flange  515  that communicates with the firebox. The exhaust gas valve  560  is a generally flat plate mounted to the actuator shaft  532  with a connector bracket  561  so that the exhaust gas valve  560  is substantially parallel to the actuator shaft  532  and perpendicular to the flow of exhaust gas  244  passing through the exhaust flange  515 . Accordingly, as the actuator shaft  532  moves in the closing direction  570  toward the closed position, the exhaust gas valve  560  slides across the opening of the exhaust flange  515  and restricts the flow of exhaust gas  244  exiting the firebox. Conversely, as the actuator shaft  532  moves in the opening direction  571  toward the open position, the exhaust gas valve  560  retracts across the opening of the exhaust flange  515  and increases the flow of exhaust gas  244  exiting the firebox. The exhaust gas valve  560  in the illustrated embodiment is sized and shaped so that the flow of exhaust gas  244  through the exhaust flange  515  is not completely stopped when the actuator shaft  532  is moved into the fully restricted position.  
      The connector brackets  561  and  563  are shaped to provide a cantilever support for their respective valves so that when the actuator shaft  532  is retracted in opening direction  571  toward the open position, the exhaust gas valve  560  and combustion air valve  562  will slide neatly under the lower ends of the exhaust flange  515  and intake flange  517  respectively, in order to minimize restriction of the respective ducts.  
      Although the exhaust flange  515  and inlet flange  517  are not concentrically disposed like their counterparts are in tile balancing system  230  ( FIGS. 2-4 ) discussed above, it will be apparent to those of ordinary skill in the relevant art that the exhaust gas valve  560  and combustion air valve  562  of the balancing system  530  function to achieve a substantially similar balancing of the exhaust gas and combustion air flow to obtain a desired flame characteristic. Accordingly, it will also be apparent to those of ordinary skill in the relevant art that various alternative configurations of the balancing system  230  are possible without departing from the spirit or scope of the present invention.  
      Referring again to  FIG. 5 , the balancing system  530  can also include an alternate embodiment of a dilution air passage  552  for passing combustion/dilution air  546  between the inlet flange  517  and the exhaust flange  515  without first passing it through the firebox  210 . The dilution air passage  552  call be provided in the form of an inclined conduit. It will be apparent to those of ordinary skill in the relevant art, that various alternate configurations of the dilution air passage  352  are possible in accordance with other embodiments of the present invention.  
      Although specific embodiments of, and examples for, the invention are described herein for illustrative purposes, various modifications can be made without departing from the spirit and scope of the invention, as will be recognized by those of ordinary skill in the relevant all. The teachings provided herein of the present invention can be applied not only to direct-vent gas-burning and wood-burning fireplace assemblies, but to all direct-vent heater appliances as well, whether they are incorporated into cavities in the dwelling or structure in which they are used, or if they are free-standing. The teachings provided herein apply to these other embodiments, and not necessarily the exemplary direct-vent fireplace insert assembly generally described above. These and other changes can be made to the invention in light of the above detailed description. In the following claims, the terms used should not be construed to limit the invention to the specific embodiments disclosed in the specification and the claims, but should be construed to include all direct-vent heater appliances that operate in accordance with the claims. Accordingly, the invention is not limited by the disclosure, but instead its scope is to be determined entirely by the following claims.