Premix Burner Control System and Method

Abstract

A fan modulated premix burner control system includes a regulating control valve for regulating the pressure of gas fed to a premix chamber. The pressure of the gas is based on the pressure of air also fed into the chamber to produce a constant air/fuel ratio. The system also includes an air restrictor for reducing the pressure of the air to permit operation of the burner at low fan speeds.

1 . A method of maintaining flow of an air/fuel mixture to a burner, the burner fed from a premix chamber enclosing a variable speed fan and defining an air inlet, a fuel inlet, and an outlet in fluidic communication with the burner, said method comprising the steps of:
 sensing a pressure of air at the air inlet;   regulating a pressure and flow of gaseous fuel though the fuel inlet with a regulating control valve;   drawing the gaseous fuel and air into the premix chamber by operation of the fan;   affecting mixture of the gaseous fuel and the air in the premix chamber by operation of the fan to produce an air/fuel mixture;   forcing the air/fuel mixture to the outlet by operation of the fan; and   lowering an inlet air pressure of air drawn through the air inlet by reducing the area of an air duct ahead of the air inlet to decrease the flow rate of the air/fuel mixture.   
   
   
       2 . A method as set forth in  claim 1  further comprising the step of monitoring the speed of the fan. 
   
   
       3 . A method as set forth in  claim 2  wherein said step of lowering an inlet air pressure is done in response to the speed of the fan falling below a certain speed. 
   
   
       4 . A method as set forth in  claim 1  further comprising the step of maintaining a constant ratio of gaseous fuel and air in producing the air/fuel mixture. 
   
   
       5 . A method as set forth in  claim 1  further comprising the step of sensing the pressure of air at the air inlet; 
   
   
       6 . A method as set forth in  claim 5  wherein said step of regulating a pressure and flow of gaseous fuel though the fuel inlet with a regulating control valve is done in accordance with the sensed pressure of the air at the air inlet. 
   
   
       7 . A premix burner control system comprising:
 a housing defining a gas inlet for receiving a gaseous fuel, an air inlet for receiving air, and at least one outlet for connection to a burner;   a fan disposed in said housing for drawing the gaseous fuel and the air into said housing, affecting mixture of the gaseous fuel and the air to produce an air/fuel mixture, and forcing the air/fuel mixture to the outlet;   a motor operatively connected to said fan for turning said fan;   a variable speed drive operatively connected to said motor for turning said fan at a plurality of speeds to control a flow rate of the air/fuel mixture into the outlet;   a regulating control valve in fluid communication with said gas inlet for regulating the flow and pressure of the gaseous fuel; and   a restrictor device in fluid communication with said air inlet for controlling an air inlet pressure of air drawing through said air inlet and into said housing;   said restrictor device operable to lower the air inlet pressure of the air drawn through said air inlet by reducing the area of an air duct ahead of said air inlet to decrease the flow rate of the air/fuel mixture.   
   
   
       8 . A system as set forth in  claim 7  wherein said regulating control valve regulates the pressure of the gaseous fuel based on the pressure of air drawing through said air inlet. 
   
   
       9 . A system as set forth in  claim 8  further comprising a pneumatic sensing tube connected between said air inlet and said regulating control valve such that said regulating control valve can sense the pressure of the air at said air inlet. 
   
   
       10 . A system as set forth in  claim 7  further comprising a gas orifice plate disposed between said gas regulator and said gas inlet and defining a gas orifice through which the gaseous fuel passes. 
   
   
       11 . A system as set forth in  claim 7  further comprising an air orifice plate disposed between said restrictor device and said air inlet and defining an air orifice through which the air passes.