Fluid heater with perforated flame holder, and method of operation
A water heater includes a water tank having an inlet and an outlet, and a flue extending through the tank. A nozzle is positioned near a first end of the flue, arranged so as to emit a fuel stream into the flue, and a flame holder is located within the flue in a position to receive the fuel stream and to hold a flame entirely within the flue.
1. A method of operating a fluid heater, comprising:
detecting a temperature of a fluid inside a tank;
if the detected temperature of the fluid is below a first temperature threshold, supporting a flame inside a flue that extends through the tank, and repeating the step of detecting a temperature;
transferring heat generated by the flame to fluid inside the tank;
if the detected temperature of the fluid is above a second temperature threshold, greater than the first temperature threshold, and if a flame is present inside the flue, extinguishing the flame, and repeating the step of detecting a temperature; and
if the detected temperature of the fluid is above the second temperature threshold, and if a flame is not present inside the flue, repeating the step of detecting a temperature.
2. The method of claim 1 , wherein the step of supporting a flame inside a flue comprises emitting a stream of fuel toward a flame holder positioned inside the flue.
3. The method of claim 2 , wherein the step of supporting a flame inside a flue comprises holding a flame substantially within a plurality of apertures extending through the flame holder.
4. The method of claim 2 , wherein the step of emitting a stream of fuel toward a flame holder comprises admitting a flow of fuel, to a nozzle positioned to emit the stream of fuel, at a flow rate that produces a stream of fuel whose velocity prevents a flame being supported between the nozzle and the flame holder.
5. The method of claim 2 , wherein the step of emitting a stream of fuel toward a flame holder positioned inside the flue comprises emitting the stream of fuel toward a flame holder positioned between a midpoint and a top end of the flue.
6. The method of claim 1 , wherein, if the detected temperature of the fluid is below the first temperature threshold, and if a flame is not present inside the flue, igniting a flame inside the flue prior to performing the step of supporting a flame inside a flue.
7. The method of claim 6 , wherein the step of igniting a flame inside the flue comprises heating some or all of a flame holder positioned within the flue to at least a selected minimum operating temperature prior to performing the step of supporting a flame inside a flue.
8. The method of claim 6 , wherein the step of heating some or all of a flame holder positioned within the flue comprises:
admitting a flow of fuel to a nozzle positioned to emit a stream of fuel toward the flame holder positioned within the flue; and
energizing an igniter positioned adjacent to the stream of fuel.
9. The method of claim 6 , wherein the step of admitting a flow of fuel to a nozzle comprises admitting a flow of fuel at a flow rate that produces a stream of fuel whose velocity permits a flame to be supported between the nozzle and the flame holder.
10. The method of claim 9 , wherein the step of supporting a flame inside a flue comprises admitting a flow of fuel to the nozzle at a flow rate that produces a stream of fuel whose velocity prevents a flame being supported between the nozzle and the flame holder.