Redundant Modulating Furnace Gas Valve Closure System and Method

Abstract

In a modulating furnace with an integrated furnace control (IFC) that may enter a lockout mode for any one or more of a variety of safety reasons, the IFC may be programmed to send a “home” signal to the regulator stepper motor to close the regulator seat thereby reducing the outlet pressure of the gas valve to zero or near zero. Even though the ITC may have several different safety lockout modes, an additional home command from the IFC allows the modulating gas valve to position itself to a reference point such that the outlet pressure would approach zero pressure, even when the gas valve is energized at the wrong time due to a short circuit or miswire, or mechanically stuck open. By using the home command, an additional safety redundancy is provided whenever the furnace enters a lockout mode.

1 . A method for closing a modulating gas valve of a furnace that includes a regulator with a regulator adjustment screw that is coupled to a stepper motor and a servo diaphragm and wherein movement of the servo diaphragm controls movement of a regulator seat, the method comprising:
 detecting an abnormal operating condition that calls for turning the furnace off;   sending a signal to a controller that is linked to the stepper motor to move the stepper motor to a home position which results in moving the regulator seat to a closed position.   
     
     
         2 . The method of  claim 1  wherein the abnormal operating condition is detection of a flame by a sensor during an off cycle. 
     
     
         3 . The method of  claim 2  wherein the sensor is a flame sensing electrode (FSE). 
     
     
         4 . The method of  claim 1  wherein the abnormal operating condition is selected from the group consisting of failure to ignite after a predetermined number of attempts, failed blower motor, an open pressure switch, an open draft safeguard switch, an open flame rollout switch, an open limit switch and combinations thereof. 
     
     
         5 . The method of  claim 1  wherein the abnormal operating condition is the redundant and main valve seats being energized at the wrong time due to a short circuit or miswire or being mechanically stuck in an open position and movement of the stepper motor and regulator adjustment screw to the home position is capable of moving the regulator seat to a closed position or a near-closed position to reduce gas flow at an outlet of the modulating gas valve. 
     
     
         6 . A system for modulating gas flow through a gas valve of a gas furnace, the system comprising:
 a furnace control linked to a gas valve,   the gas valve comprising a regulator seat coupled to a main diaphragm, the gas valve further comprising a seat for receiving the regulator seat when the regulator seat is in a closed position, the regulator seat being coupled to a regulator spring that biases the regulator seat towards the closed position,   the gas valve further comprising a regulator for controlling movement of the main diaphragm, the regulator comprising a servo diaphragm that is coupled to an adjustment screw by a servo spring, the adjustment screw being coupled to a stepper motor, the stepper motor being linked to the furnace control,   the furnace control being programmed to send a home command to the stepper motor when an abnormal operating condition is detected, the home signal causing the stepper motor to move to a home position which moves the main diaphragm and causes the main diaphragm to move the regulator seat to a closed position.   
     
     
         7 . The system of  claim 6  wherein the system further comprises a stepper motor control that is linked to the furnace control and the stepper motor. 
     
     
         8 . The system of  claim 7  wherein the furnace control is an integrated furnace control (IFC) board. 
     
     
         9 . The system of  claim 7  wherein the stepper motor control comprises an interface for receiving signals from the furnace control and a microcontroller for translating the signals from the furnace control into a number of steps and a direction of rotation of the adjustment screw. 
     
     
         10 . The system of  claim 9  wherein the stepper motor control further comprises a power supply. 
     
     
         11 . The system of  claim 6  wherein the abnormal operating condition is detection of a flame by a sensor during an off cycle. 
     
     
         12 . The system of  claim 11  wherein the sensor is a flame sensing electrode (FSE). 
     
     
         13 . The system of  claim 6  wherein the abnormal operating condition is selected from the group consisting of failure to ignite after a predetermined number of attempts, failed blower motor, an open pressure switch, an open draft safeguard switch, an open flame rollout switch, an open limit switch and combinations thereof. 
     
     
         14 . The system of  claim 6  wherein the abnormal operating condition is the redundant and main seats being energized at the wrong time due to a short circuit or miswire, or mechanically stuck in an open position and the home command causes movement of the stepper motor and regulator adjustment screw to a home position that is capable of moving the regulator seat to a closed position or a near-closed position to reduce gas flow at an outlet of the modulating gas valve. 
     
     
         15 . A modulating gas furnace comprising:
 a furnace control linked to a stepper motor of a modulating gas valve,   the modulating gas valve comprising a regulator seat coupled to a main diaphragm, the gas valve further comprising a seat for receiving the regulator seat when the regulator seat is in a closed position, the regulator seat being coupled to a regulator spring that biases the regulator seat towards the closed position,   the modulating gas valve further comprising a regulator for controlling movement of the main diaphragm, the regulator comprising a servo diaphragm that is coupled to an adjustment screw by a servo spring, the adjustment screw being coupled to the stepper motor,   the furnace control being programmed to send a home command to the stepper motor when an abnormal operating condition is detected, the home signal causing the stepper motor to move to a home position which causes the main diaphragm to move the regulator seat to a closed position.   
     
     
         16 . The furnace of  claim 15  wherein the system further comprises a stepper motor control that is linked to the furnace control and the stepper motor. 
     
     
         17 . The furnace of  claim 16  wherein the furnace control is an integrated furnace control (IFC) board. 
     
     
         18 . The furnace of  claim 16  wherein the stepper motor control comprises an interface for receiving signals from the furnace control and a microcontroller for translating the signals from the furnace control into a number of steps and a direction of rotation of the adjustment screw. 
     
     
         19 . The furnace of  claim 16  wherein the stepper motor control further comprises a power supply. 
     
     
         20 . The furnace of  claim 15  wherein the abnormal operating condition is detection of a flame by a sensor during an off cycle, failure to ignite after a predetermined number of attempts, failed blower motor, an open pressure switch, an open draft safeguard switch, an open flame rollout switch, an open limit switch and combinations thereof.