Damper for direct vent fireplace insert

Abstract

A damper mechanism restricting combustion and exhaust air flow in response to temperature changes in a direct vent sealed combustion gas fireplace is provided. The mechanism allows the fireplace to have unrestricted air flow when the fireplace is not on and to restrict the air flow when the fireplace is on. A bi-metallic temperature responsive element is used to move a restrictor element to restrict air flow allowing maximum air displacement during cold ignition and enhancing operating efficiency when the fireplace is on.

Claims

1. A direct vent gas fireplace having a combustion air supply and exhaust system that is substantially sealed in relation to a room in which said gas fireplace is disposed, said combustion air supply being drawn from a substantially vertical inlet duct and said fireplace being connected to a substantially vertical exhaust duct, said fireplace comprising a single combustion air inlet for drawing combustion air from outside the building in which said fireplace is located into a firebox, further comprising a restrictor element located in and spanning said inlet and a temperature-sensitive element located near said inlet to react to an increase in temperature of a combustion chamber of said fireplace, said restrictor element and said temperature-sensitive element being operative to cause said restrictor element to allow a maximum throughput through said inlet when the fireplace has not been ignited and being operative to partially restrict said inlet in response to an increase in temperature of a temperature-sensitive element.

2. A direct vent gas fireplace having a firebox and a combustion air supply and exhaust system that is substantially sealed in relation to a room in which said gas fireplace is disposed, said combustion air supply being drawn from a substantially vertical inlet duct comprising a single substantially vertical combustion products exhaust duct for venting combustion products from the fireplace to the outside of a building in which said fireplace is located, further comprising a restrictor element located in and spanning said exhaust duct and a temperature-sensitive element located in proximity to said combustion chamber to react to an increase in the temperature of a combustion chamber of said fireplace, said restrictor element and said temperature-sensitive element being operative to cause said restrictor element to allow a maximum throughput through said duct when the fireplace has not been ignited and being operative to partially restrict said duct in response to an increase in temperature of a temperature-sensitive element.

3. A direct vent gas fireplace having a combustion air supply and exhaust system that is substantially sealed in relation to a room in which said gas fireplace is disposed, said combustion air supply being drawn from a substantially vertical inlet duct and said fireplace being connected to a substantially vertical exhaust duct, said fireplace comprising a single combustion air inlet for drawing combustion air from outside the building in which said fireplace is located into a firebox, further comprising a restrictor element located in and spanning said inlet and a temperature-sensitive element located near said inlet to react to an increase in temperature of a combustion chamber of said fireplace, said restrictor element and said temperature-sensitive element being operative to cause said restrictor element to allow a maximum throughput through said inlet when the fireplace has not been ignited and being operative to partially restrict said inlet in response to an increase in temperature of said temperature-sensitive element, said temperature sensitive element comprises a bi-metallic element, wherein said restrictor element is mounted on a shaft, said shaft being displaced axially along the central axis of the air inlet by said deformation of said bi-metallic element, and further comprising a coil spring positioned concentrically around said shaft for biasing said restrictor toward said bimetallic element and wherein said bi-metallic element is mounted in an enclosure on a wall of said firebox by a retainer, said retainer constraining the direction of deformation of said bi-metallic element as it is heated, said coil spring being delimited by the restrictor element and by a bracket spanning the air inlet.

4. The gas fireplace of claim 3 wherein said spring biases said restrictor element toward a position wherein said restrictor element does not restrict said air flow when said firebox is cold.

5. The gas fireplace of claim 3 wherein said restrictor element comprises a plurality of apertures.

6. The gas fireplace of claim 3 further comprising an elongated shaft between said bi-metallic element and said restrictor element, said shaft actuating movement of said restrictor element by abutment against an end of said shaft when said bi-metallic element deforms under the influence of a change in temperature.

7. A method of controlling combustion air flow and facilitating ignition in a direct vent, sealed combustion gas fireplace, said fireplace having a combustion chamber and a single combustion air inlet from the outside of a building in which the fireplace is located into said fireplace said combustion air supply being drawn from a substantially vertical inlet duct and said fireplace being connected to a substantially vertical exhaust duct, comprising the steps of: operating a bi-metallic element to physically react to an increase in temperature in a combustion chamber of said fireplace; operating a restrictor element that spans said air inlet to move so as to decrease the throughput of combustion air through said inlet upon deformation of said bi-metallic element in response to an increase in temperature, to thereby automatically restrict the entire throughput of combustion air to said fireplace as the temperature in the combustion chamber increases.

8. The method of claim 7 wherein said bi-metallic element is spring-biased away from said air passageway.

9. The method of claim 7 further comprising the step of igniting a combustion gas source within a firebox in said fireplace to increase the temperature of said fireplace.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The invention will be described by reference to the detailed description of the preferred embodiment and to the drawings thereof in which:

(2) FIG. 1 is a perspective view of an insert for a sealed combustion gas fireplace including the damper mechanism of the invention in accordance with the preferred embodiment;

(3) FIG. 2 is a top view of the insert of FIG. 1;

(4) FIG. 3 is a front view of the insert of FIG. 1;

(5) FIG. 4 is a front view of the shroud of the insert of FIG. 1, with the walls defining the firebox having been removed;

(6) FIG. 5 is a sectional view of the insert of FIG. 3, taken along line A-A of FIG. 3;

(7) FIG. 6 is an exploded perspective view of the elements of the damper mechanism;

(8) FIG. 7 is an enlarged sectional view of the damper mechanism of the invention, in which the damper is open;

(9) FIG. 8 is an enlarged sectional view of the damper mechanism of the invention, in which the damper is closed; and

(10) FIG. 9 is a schematic view of the insert and ducting in place within a fireplace;

(11) FIG. 10 is a sectional view of an insert for a sealed combustion gas fireplace in accordance with an alternate embodiment of the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

(12) Referring to FIGS. 1-3, a sealed direct vent gas fireplace 10 includes an outer shroud 12 surrounding a firebox 14. A glass panel 16 seals the firebox 14 from the air inside the room in which the fireplace is located. Fireplace 10 also includes burner 23 and logset 25 within the firebox. It will be understood that certain elements such as false walls, baffles and various cosmetic elements are omitted from the drawings for clarity, but may or may not be included in a fireplace 10 comprising the invention described herein.

(13) Combustion air is supplied to the fireplace by means of an air inlet 18 and gas combustion products are vented through exhaust outlet 20. As best seen in FIG. 9, during installation of the fireplace in a building, air inlet 18 is connected to an intake duct 52 to allow combustion air from outside the building to be drawn into the fireplace and the firebox 14. Similarly, exhaust outlet 20 is connected to an exhaust duct 54 for exhausting gas combustion products out of the building. The combination of the air inlet 18 and intake duct 52 define a combustion air intake system 56 while the combination of the exhaust outlet 20 and the exhaust duct 54 define a combustion products exhaust system 58. The combustion air intake system 56 and combustion products exhaust system 58 form an air supply and venting system denoted by arrows 60, through which combustion air is drawn from outside the building into the firebox 14 through the combustion air intake 56, and gas combustion products are vented to the outside through the combustion products exhaust 58.

(14) The air supply and venting system 60 is substantially sealed relative to the room in which the fireplace is located such that air flows only in from outside the building, through the firebox 14 and back outside though a vent terminal 62. When the fireplace is off, the air pressure inside the firebox 14 should equal the outside atmospheric pressure in the vicinity of the vent terminal 62.

(15) Referring again to FIGS. 1-3, a damper mechanism 22 is provided in the air supply and venting system 60 to restrict the system 60 when the temperature increases as a result of operation of the burner 23. As a result, prior to ignition when the fireplace is cold and the air in the air supply and venting system 60 is stagnant, the system 60 is as unrestricted as possible, allowing a substantial volume of air to quickly be displaced to support ignition and minimize burner flame lift-off. Once the fireplace is in normal operation, the damper will operate to restrict the system 60 and promote more efficient burning by reducing heat losses to the outside. It will be appreciated that restriction along any portion of the system 60 will be effective to reduce the flow of air and combustion gases therethrough. As a result, the restriction may be applied with equal results along the combustion air intake system 56 or the combustion products exhaust system 58. According to the preferred embodiment, the restriction provided by the damper is applied to the combustion air intake system 56 and in particular to the air inlet 18. This is preferred over providing the damper 22 in the combustion products exhaust system 58 due to the relatively lower temperatures in the vicinity of the incoming combustion air, allowing the use of less temperature tolerant materials for the damper 22 while still being responsive to changes in temperature.

(16) In FIG. 4, the firebox walls 9, 11, 13 and 15 that are visible in FIGS. 1 and 3 have been removed to more clearly reveal the structure of shroud 12. A collar 24 is mounted to exhaust outlet 20 to direct exhaust gases from the firebox 14 through the shroud 24. Baffle 26 and rear false wall 28 direct incoming combustion air from air inlet 18 to openings 30 in the vicinity of the burner 23 (not shown). The combustion air then passes through corresponding openings 31 (seen in FIG. 3) at the rear of the firebox 14. Heated air, now comprising combustion products from combustion of the gas in the fireplace, will eventually pass through exhaust outlet 20 into the exhaust duct 54 (not shown) and to the outdoors.

(17) The flow of air and gasses is also shown in FIG. 5, including the flow from the air inlet 18, past damper mechanism 22, along rear wall 28 of shroud 12, and into the firebox 14 through rear intake vents 30. FIG. 5 also shows the convection passageway 32 through which room air may enter the insert 10, pass around firebox 14, and re-enter the room heated by contact with the outside of firebox 14, as is typical of sealed fireplace inserts. Convection passageway 32 is entirely separate and not in communication with the passageway that comprises the combustion air and combustion products venting system 60 (not shown).

(18) The components of the damper mechanism 22 of the preferred embodiment are shown in FIGS. 5 and 6. Retainer 34 is attached to an inside wall segment 27 of the firebox 14 in the general vicinity of the air inlet 18. Retainer 34 is preferably in the form of an enclosure suitable for housing a bi-metallic element 36, and to constrain the direction of deformation of the bi-metallic element as it reacts to the the influence of changes of temperature in the firebox 14. The bi-metallic element 36 is shown in FIG. 6 as a pair of elongated bi-metallic strips 36a, 36b arranged to deform in opposite directions. Any appropriate size and shape of bi-metallic material may be used, but according to the preferred embodiment the bi-metallic strips 36a, 36b are configured and constrained to displace a shaft 38 that is secured through wall segment 27.

(19) The top surface of the uppermost bi-metallic strip 36a is in contact with shaft 38. A spring 40 is provided on shaft 38 and rests against a disk-shaped restrictor plate 42 through which shaft 38 extends. Bracket 46 is mounted across the air inlet 18 to retain the free end of shaft 38.

(20) Restrictor plate 42 corresponds in diameter to the air inlet 18. Spring 40 biases restrictor plate 42 towards the bi-metallic strips 36, such that movement of bi-metallic strips 36 must overcome the spring force of spring 40 to move restrictor plate 42 which is therefore in a normally open state in relation to air inlet 18.

(21) Restrictor plate 42 may be provided with one or more apertures 44, in order to allow some air flow into the fireplace insert, even when the damper mechanism 22 is in a closed position. The number and size of apertures 44 may be selected based on the minimum amount of air flow necessary for efficient operation of the fireplace.

(22) The operation of damper mechanism 22 is shown in FIGS. 7 and 8. In the open vent position, as shown in FIG. 7, the bi-metallic strips 36 are flat, allowing spring 40 to extend along shaft 38, biasing the restrictor plate 42 as far as possible away from bracket 46. Bracket 46 is preferably attached to the inside surface of a shroud 12 at an air vent 18, and is preferably of a configuration, such as the narrow elongated shape shown in FIG. 6, that impedes air flow through the vent as little as possible. In the embodiment shown in FIGS. 5, 7, and 8, the damper mechanism 22 is attached to the intake air vent 18, but it will be understood that the damper mechanism 22 may also be positioned in the exhaust vent as shown in FIG. 10.

(23) FIG. 7 shows the damper mechanism 22 in an inactive or open vent position, which is the position of the damper mechanism 22 when the fireplace is cold or not in use. In this situation, it is preferable to have essentially unrestricted air flow, such that sufficient air is available to the fireplace to maintain initial ignition. The restrictor plate 42 is therefore biased by spring 40 away from retainer 34, such that air vent 18 is clear, allowing essentially unobstructed, maximum air flow.

(24) Once the ignition has taken place and the burner is operating normally, a lower level of air flow is required for optimal operation of the fireplace. Bi-metallic strips 36, exposed to the heat generated within the firebox will flex under the heat, eventually reaching an active or closed vent position, best shown in FIG. 8. In this position, strips 36 flex away from each other within retainer 34, and mechanically push shaft 38 up towards air vent 18, compressing spring 40 and moving restrictor plate 42 towards bracket 46. In this position, restrictor plate 42 partially closes air vent 18, impeding the air flow through the vent 18 and allowing for more efficient burning and better heat retention during operation of the fireplace.

(25) As it is not desirable to completely cut off the air flow to the fireplace, apertures 44 may be provided to allow some minimum constant air flow. Alternatively or in addition, the damper mechanism 22 may be adjusted, such as by lengthening the spring 40 or adjusting the position of the restrictor plate 42 on shaft 38, such that the restrictor plate does not contact the bracket 46. This embodiment would also restrict the air flow through the air vent 18 without closing off the vent completely.

(26) The pair of bi-metallic strips 36 may be replaced with a single bi-metallic strip. It may be necessary to make appropriate adjustments, such as changing the length of the shaft 38 or the length of the spring 40 to ensure that the amount of flexion of the strip under typical heating conditions is sufficient to move the restrictor plate as far towards the air vent as necessary. The length of shaft 38 and the position of the restrictor plate 42 on shaft 38 may also be adjusted such that shaft 38 and bi-metallic element 36a are not in physical contact until after the bi-metallic element 36a has flexed a certain amount. After contact is made, the damper mechanism 22 will operate as described above, until the restrictor element 42 reaches its final position near air vent 18.

(27) In an alternative embodiment, the restrictor element itself be a bi-metallic element, such that it flexes to directly restrict the passageway in which it is installed. Such an arrangement would reduce the need for multiple components in the damper mechanism but may require a lateral positioning of the restrictor along a portion of the passageway.

(28) In the preferred embodiment, the damper mechanism is mounted on a firebox wall such that the bimetallic elements react to the changes in temperature in the firebox. Nonetheless, it is contemplated that the damper mechanism may be arranged in the combustion products exhaust system 58 (either in the exhaust duct 54 or in the vicinity of the exhaust outlet 20) to react to the increase in temperature of the combustion gases in that system as the fireplace enters full burning operation. Accordingly, the damper may be configured to react to changes of temperature in the combustion products exhaust system 58 rather than directly sensing temperature changes in the firebox 14. Alternatively, the damper mechanism 22 may be placed within convection passageway 32, from where it can respond to changes in temperature of the air flowing through convection passageway 32 to and from the room where the fireplace is located, in the same manner as described above.

(29) It will be appreciated by those skilled in the art that the preferred and alternative embodiments have been described in some detail but that certain modifications may be practiced without departing from the principles of the invention.