Self-powered automatic secondary air controllers for woodstoves and small furnaces
AssigneeThe United States of America as represented by the United States Department of Energy
InventorDarryl D. Siemer
Life of this patent
Estimating the term…
Abstract
A controller for automatically regulating the supply of secondary combustion air to woodstoves and small furnaces. The controller includes a movable air valve for controlling the amount of secondary air admitted into the chamber. A self powered means monitors the concentration of combustible gases and vapors and actuates the movable air valve to increase the supply of secondary air in response to increasing concentrations of the combustible gases and vapors. The self-powered means can be two fluid filled sensor bulbs, one of which has a coating of a combustion catalyst. Alternatively, the self powered means can be two metallic stripes laminated together, one of which is coated with a combustion catalyst, and when heated, causes the air valve to actuate.
Claims35
A self-powered secondary air controller for a woodstove or the like having a secondary combustion chamber with a secondary air inlet as well as an outlet for the hot combustion products from primary and secondary combustion, said controller comprising:
- sensor means including first and second bulbs filled with a fluid and located in the secondary combustion chamber remotely from the secondary air inlet,
- a movable air valve for increasing and decreasing the amount of secondary air admitted into the chamber through the air inlet,
- a differential pressure responsive actuator connected to said air valve for increasing the supply of secondary air in response to increasing differential fluid pressure,
- first and second fluid-carrying tubes connected from the respective first and second bulbs to said actuator,
- and combustion catalyst means for differentially heating said first bulb by catalytic combustion of combustible gases and vapors around said first bulb, said combustion catalyst means comprising a coating of a combustion catalyst on said first bulb,
- the differential heating of said first bulb being effective to produce differential fluid pressure which is transmitted to said actuator and causes said actuator to increase the supply of secondary air, to produce a negative feedback control, in that the increased secondary air causes increased secondary combustion and thereby reduces the concentration of combustible gases and vapors available for catalytic combustion by said combustion catalyst means.
A self-powered secondary air controller for a woodstove or the like having a secondary combustion chamber with a secondary air inlet as well as an outlet located remotely from the inlet for discharging hot products of primary and secondary combustion, said controller comprising:
- a movable air valve for increasing and decreasing the amount of secondary air admitted into the secondary combustion chamber through the secondary air inlet,
- and self-powered means for monitoring the concentration of combustible gases and vapors at a location in the secondary combustion chamber remote from the air inlet and for actuating the movable air valve to increase the supply of secondary air in response to increasing concentrations of the combustible gases and vapors,
- said self-powered means comprising an elongated laminated strip having one end with a stationary mounting and a remote end with an actuating connection to said movable air valve,
- said laminated strip including first and second elongated strip members fastened together,
- and combustion catalyst means for heating said fist strip member to a greater extent than said second strip member for causing said laminated strip to be curled by differential thermal expansion, said combustion catalyst means including a coating of a combustion catalyst on said first strip member,
- the curling of said laminated strip being effective to actuate the air valve in a direction to increase the supply of secondary air through the inlet,
- whereby a negative feedback control is provided in that the increased supply of secondary air increases the secondary combustion in the chamber and thereby decreases the concentration of available combustible gases and vapors for catalytic combustion.
A self-poWered secondary air controller for a woodstove having a secondary combustion chamber with a secondary air inlet for admitting secondary air into the chamber as well as an outlet located remotely from the inlet for discharging hot products of primary and secondary combustion from the combustion chamber, said secondary air controller comprising
- a mechanically movable air valve for increasing and decreasing the supply of secondary air admitted into the combustion chamber through the air inlet,
- sensor means for monitoring the concentration of combustible gases and vapors in said secondary combustion chamber at a location remote from said air inlet,
- said sensor means including first and second mechanical members,
- said sensor means also including catalytic combustion means for producing greater heating of said first member than of said second member due to catalytic combustion of combustible gases and vapors in the locality being monitored,
- said greater heating of said first member causing differential mechanical action between said first and second members,
- and actuating means for utilizing said differential mechanical action to move said movable air valve for increasing the supply of secondary air admitted to the secondary combustion chamber,
- whereby a negative feedback control is provided, in that the increase of secondary air causes increased secondary combustion in said chamber so that the concentration of combustible gases and vapors available for catalytic combustion is reduced.
A woodstove, comprising:
- a firebox having outside walls with a combustion space therein,
- a plurality of generally horizontal grate tubes extending across said combustion space with spaces between said grate tubes,
- said grate tubes dividing said combustion space into a fuel loading chamber above said grate tubes and a secondary combustion chamber below said grate tubes,
- said grate tubes being adapted to support firewood to be burned,
- primary air inlet means for admitting primary air to said fuel loading chamber,
- said secondary combustion chamber having outlet means located remotely relative to said grate tubes for discharging products of combustion therefrom,
- and secondary air inlet means connecting with the interior of said grate tubes,
- self-powered secondary air controller having an air valve movable toward and away from the secondary air inlet means, and an actuator for operating the air valve,
- said grate tubes having walls with openings therein directed downwardly into said secondary combustion chamber for directing secondary air downwardly to support secondary combustion in said combustion chamber of combustible gases and vapors passing downwardly into said secondary combustion chamber through said spaced between said tubular grates,
- and self-powered secondary air controller producing the desired regulation of the secondary air admitted into the secondary air inlet.
Dependencies are inferred from the claim text.