Control system for burner

Abstract

A method of controlling operation of a furnace having a pre-mixed burner, a heat exchanger, and an inducer blower downstream of the heat exchanger includes monitoring a pressure drop across the heat exchanger. The speed of the inducer blower is controlled in response to the monitored pressure drop to thereby control mass flow through the furnace.

What is claimed is: 
     
         1 . A method of controlling operation of a furnace having a pre-mixed burner, a heat exchanger, and an inducer blower downstream of the heat exchanger, comprising:
 monitoring a pressure drop across the heat exchanger;   controlling the speed of the inducer blower in response to the monitored pressure drop to thereby control mass flow through the furnace.   
     
     
         2 . The method of  claim 1 , wherein the burner is an ultra low NO x  burner. 
     
     
         3 . The method of  claim 1 , wherein the pressure drop is monitored with a pressure sensor extending into a control volume within the heat exchanger. 
     
     
         4 . The method of  claim 1 , wherein the step of controlling the speed of the inducer blower comprises controlling the speed of an electronically commutated motor connected to the inducer blower. 
     
     
         5 . The method of  claim 4  further comprising wave chopping a control signal to the motor. 
     
     
         6 . The method of  claim 5 , wherein the wave chopping comprises zero-cross wave chopping. 
     
     
         7 . The method of  claim 1 , wherein the step of controlling the speed of the inducer blower comprises controlling the speed of the inducer blower prior to ignition of the pre-mixed burner. 
     
     
         8 . The method of  claim 1 , wherein the step of controlling the speed of the inducer blower comprises controlling the speed of the inducer blower while the pre-mixed burner produces a flame. 
     
     
         9 . The method of  claim 1 , wherein the step of controlling the speed of the inducer blower comprises controlling the speed of the inducer blower during a purge cycle of the pre-mixed burner. 
     
     
         10 . The method of  claim 1 , wherein the inducer blower speed is controlled such that the mass flow through the heat exchanger has a different frequency than the resonant frequency of the heat exchanger. 
     
     
         11 . A control system for a furnace having a pre-mixed burner, a heat exchanger, and an inducer blower downstream of the heat exchanger, comprising:
 a sensor for measuring one of pressure and mass flow through the heat exchanger; and   a controller connected to the sensor and the inducer blower and controlling the speed of the inducer blower in response to receiving a signal from the sensor indicative of the pressure or mass flow to control mass flow through the furnace.   
     
     
         12 . The control system of  claim 11 , wherein the burner is an ultra low NO x  burner. 
     
     
         13 . The control system of  claim 11 , wherein the sensor extends into a control volume within the heat exchanger. 
     
     
         14 . The control system of  claim 10 , wherein the controller controls the speed of an electronically commutated motor connected to the inducer blower. 
     
     
         15 . The control system of  claim 14 , wherein the controller sends wave chopped control signals to the motor. 
     
     
         16 . The control system of  claim 15 , wherein the wave chopping comprises zero-cross wave chopping. 
     
     
         17 . The control system of  claim 11 , wherein the controller controls the speed of the inducer blower prior to ignition of the pre-mixed burner. 
     
     
         18 . The control system of  claim 11 , wherein the controller controls the speed of the inducer blower while the pre-mixed burner produces a flame. 
     
     
         19 . The control system of  claim 11 , wherein the controller controls the speed of the inducer blower during a purge cycle of the pre-mixed burner. 
     
     
         20 . The control system of  claim 11 , wherein the inducer blower speed is controlled such that the mass flow through the heat exchanger has a different frequency than the resonant frequency of the heat exchanger. 
     
     
         21 . A method of reducing noise in a furnace, comprising:
 determining a resonant frequency of heat exchanger tubes in the furnace; and   controlling the mass flow of combustion products into the heat exchanger such that the combustion products have a different resonant frequency than the heat exchanger tubes.   
     
     
         22 . The method of  claim 21 , wherein the step of controlling the mass flow of combustion products comprises controlling the speed of an inducer blower upstream of the heat exchanger tubes with a wave-chopped control signal.