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.

Description

BACKGROUND

1. Technical Field

This disclosure relates to controls for modulating gas valves of modulating gas furnace. More specifically, in a modulating gas with an integrated furnace control (IFC), the furnace may enter a lockout mode for any one or more of a variety of safety reasons.

2. Description of the Related Art

Modern gas furnaces are equipped with various safety features which typically include a flame proving sensor, pressure switches and limit switches. A flame sensor or flame sensing electrode detects the presence of a flame at the burner during both on and off cycles. Pressure and limit switches are used to detect abnormal pressures, temperatures or other abnormal operating conditions and prevent the burners from operating if an abnormal condition is detected. A typical gas furnace could have four or more limit switches in various locations throughout the furnace. When these limit switches trip or open, the furnace control board shuts the gas valve and may engage the main blower and the draft induced blower to dissipate as much heat as possible away from the furnace and its heat exchangers if the condition involves temperatures that exceed a predetermined safety limit.

Some of these limit switches reset themselves when the temperature or other sensed condition return to normal. After a reset of a pressure or limit switch, the integrated furnace control (IFC) board may give a small time delay before allowing the gas burners to reignite. Heat will be restored and the gas burners will continue to provide heat until the thermostat satisfies the desired room temperature or until another safety limit is reached.

At the start of a heat cycle, the IFC board may execute a limited number of attempts to light the burners, typically three to four times depending on the manufacturer and the engineering safety limits of IFC. If the IFC detects ignition failure after the limited number of attempts, it may lock the system out for a specific amount of time (e.g., 3 to 4 hours) depending on the engineering safety limits of the IFC board. After the predetermined time period, the IFC will again try for ignition unless a safety circuit is open. The IFC may stay in a permanent lockout mode until the problem is resolved, usually by an HVAC technician.

After ignition when the blower turns on, the IFC board may confirm that the blower motor turned ON by checking the blower RPM. If the blower RPM is not above a minimum RPM limit within a prescribed time period, the IFC will shut down. After a small time delay the IFC will try again and if the blower does not turn ON during a second attempt the IFC may lock the system out for a specific amount of time (e.g., 3 to 4 hours). After the predetermined time period, the IFC will again try to operate unless a safety circuit is open. The IFC may also confirm that the gas valve is not energized at the wrong time due to a short circuit or miswire. If the gas valve is energized at the wrong time due to a short circuit or miswire the IFC may engage the draft induced blower and enter a permanent lockout mode until the problem is resolved, usually by an HVAC technician.

Modern gas furnaces also include single-stage, two-stage or modulating gas valves as a part of the burner control. Single-stage burners operate with very little flexibility. The burner is fully on or operating at full heat or fully off and the ability to modify the gas flow rate delivered to the burner through the gas valve may be limited. Two-stage burners may provide two very different operational modes. During mild winter weather when the demand for heat in the home is low, the burner and gas valve operate at low stage. During colder temperatures, when the heat loss in the home is at its greatest, the burner and gas valve adjust to the high stage. Two-stage systems may cycle the furnace on and off more effectively, offering increased energy savings compared to single-stage furnaces.

Modulating burner systems have the most flexibility in adjusting to heating requirements. A modulating gas valve raises and lowers the flow rate to the burner in response to the heating demand. Modulating burner/gas valve systems may provide improved efficiency and comfort in comparison to single-stage and two-stage burner/gas valve systems.

SUMMARY OF THE DISCLOSURE

A method is disclosed for closing a modulating gas valve of a furnace that includes a regulator with a regulator adjustment screw that is coupled between a stepper motor and a servo diaphragm. Movement of the servo diaphragm controls movement of the main diaphragm and the regulator seat. The disclosed method comprises 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 closure of the regulator seat of the gas valve.

A system for modulating gas flow through a gas valve of a gas furnace is also disclosed that comprises a furnace control linked to a gas valve. The gas valve comprises a regulator seat coupled to a main diaphragm. The gas valve further comprises a seat for receiving the regulator seat when the regulator seat is in a closed position. The regulator seat is coupled to a regulator spring that biases the regulator seat towards the closed position. The gas valve further comprises a regulator for controlling movement of the main diaphragm. The regulator comprises a servo diaphragm that is coupled to an adjustment screw by a regulator spring. The adjustment screw is coupled to a stepper motor. The stepper motor is linked to the furnace control. The furnace control is programmed to send a home command to the stepper motor when an abnormal operating condition is detected. The home signal causes the stepper motor to move to a home position which reduces the force on the servo diaphragm and in turn causes the main diaphragm to move the regulator seat to a closed position.

A furnace incorporating the disclosed system or including a furnace control programmed to carry out the disclosed method is also part of this disclosure.

Other advantages and features will be apparent from the following detailed description when read in conjunction with the attached drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of the disclosed methods and apparatuses, reference should be made to the embodiments illustrated in greater detail in the accompanying drawings, wherein:

FIG. 1 is a perspective view of a disclosed gas furnace that includes an IFC programmed to move a stepper motor coupled to a gas regulator adjustment mechanism to a home or closed position when an abnormal flame is detected or the IFC initiates a safety lockout mode;

FIG. 2 is an electrical schematic diagram of the IFC and other components of the gas furnace illustrated in FIG. 1;

FIG. 3 is a perspective view of a disclosed modulating gas valve equipped with a stepper motor having a stepper motor control for adjusting the regulator adjustment mechanism, the stepper motor control not being shown in this view;

FIG. 4 is a cross sectional view of the modulating gas valve illustrated in FIG. 3; and

FIG. 5 is a schematic illustration of the IFC, the stepper motor, and the stepper motor control module.

It should be understood that the drawings are not necessarily to scale and that the disclosed embodiments are sometimes illustrated diagrammatically and in partial views. In certain instances, details which are not necessary for an understanding of the disclosed methods and apparatuses or which render other details difficult to perceive may have been omitted. It should be understood, of course, that this disclosure is not limited to the particular embodiments illustrated herein.

DETAILED DESCRIPTION OF THE DISCLOSURE

Referring now to FIG. 1, a modulating gas furnace 10 is shown which comprises a burner assembly 11 with a burner box 12 that is in communication with a primary heat exchanger 13. The primary heat exchanger 13 is in fluid communication with a condensing heat exchanger 14 whose discharge end is fluidly connected to a collector box 16 and an exhaust vent 17. In operation, a modulating gas valve (also referred to herein as simply a gas valve) 18 meters the flow of gas to the burner assembly 11 where combustion air from an air inlet 19 is mixed and ignited by an igniter assembly 21. The hot gas is then passed through the primary heat exchanger 13 and the condensing heat exchanger 14, as shown by the arrows 20.

The relatively cool exhaust gases then pass through the collector box 16 and the exhaust vent 17 before being vented to the atmosphere, while the condensate flows from the collector box 16 and through a condensate drain line 22 for disposal. Flow of combustion air into the air inlet 19 and through the heat exchangers 13, 14 and the exhaust vent 17 is enhanced by a draft induced blower 23, which is driven by a variable speed inducer motor 24 in response to control signals from an integrated furnace control (IFC) 29 and pressure switches 31, 32. The household air is drawn into a blower 26 which is driven by a variable speed blower motor 27, in response to signals received from the integrated furnace control (IFC) 29.

The discharge air from the blower 26 passes over the condensing heat exchanger 14 and the primary heat exchanger 13, in a counter-flow relationship with the hot combustion gases to thereby heat indoor air, which then flows from a discharge opening 28 to the duct system within the space being heated.

Referring now to FIGS. 3-5, and referring particularly to FIG. 4, the modulating gas valve 18 will be described in greater detail. The gas valve 18 receives a gas flow 40 at the inlet port 41. The gas flow 40 moves to a redundant valve 47 and subsequently to a main valve 43, both of which may be biased towards a closed position by springs 53 and 55. The redundant valve 47 and the main valve 43 may be opened by energizing a solenoid 25. The redundant valve 47 and main valve 43 may be closed when power is cut off to the solenoid 25, by a power outage, or when the IFC 29 enters a lock-out mode for any one of the safety reasons described below.

After passing through the redundant valve 47 and the main valve 43, the gas flow 40 then moves towards a regulator seat 44, which may be biased towards a closed position by regulator spring 82. Movement of the regulator seat 44 and the gas flow 40 through the regulator seat 44 may be controlled by a main diaphragm 48, which in turn may be controlled by a servo diaphragm 64, as described below. The main diaphragm 48 may divide the space downstream of the regulator seat 44 into a lower chamber 52, disposed below the diaphragm 48, and an upper chamber 50, disposed above the main diaphragm 48. Changes in gas pressure in the upper chamber 50 and/or the lower chamber 52 may control the movement of the main diaphragm 48 and the regulator seat 44, which may be connected to the main diaphragm 48 by a rod 51. The main diaphragm 48 may adjust the degree of opening and closing of the regulator seat 44 in response to pressure differentials between the upper and lower chambers 50, 52, respectively, and may therefore adjust the gas flow 40 through an outlet 45 and to the burner assembly 11 (not shown in FIG. 4; see FIG. 1).

Still referring to FIG. 4, the pressures in the chambers 50 and 52 may be determined by the servo diaphragm 64. The servo diaphragm 64 and the lower chamber 52 both receive gas diverted through a gas control orifice 56 and a gas control chamber 60. More specifically, the gas control chamber 60 may include a first port 62 in communication with a port 59 disposed in the lower chamber 52, below the main diaphragm 48. The gas control chamber 60 may also include a second port 57 that may be in communication with a chamber 58 disposed below the servo diaphragm 64. The gas flow 40 through the second and the first ports 57 and 62, respectively, may be determined by the position of the servo diaphragm 64, which in turn may be determined by the stepper motor 49 and an adjustment screw 61. Preferably, the regulator adjustment screw 61 is connected to the servo diaphragm 64 by a servo spring 72. The servo spring 72, the adjustment screw 61 (or other mechanism) and the stepper motor 49 may adjust the outlet pressure in the upper chamber 50.

For example, referring to FIG. 5 in conjunction with FIG. 4, when the stepper motor 49 receives a signal through the IFC 29 and the stepper motor control 42 to raise the adjustment screw 61, more of the gas flow 40 through the control chamber 60 may be diverted to the upper chamber 50 and less flow may be diverted to the lower chamber 52. As a result, the pressure in the lower chamber 52 may be reduced in comparison to the pressure in the upper chamber 50 and, the main diaphragm 48 may move downward, thereby moving the regulator seat 44 towards a closed position where the regulator seat 44 may engage a seat 39.

In contrast, when the stepper motor 49 receives a signal through the IFC 29 and the stepper motor control 42 to lower the adjustment screw 61, more of the gas flow 40 through the control chamber 60 may be diverted to the lower chamber 52 and less flow may be diverted to the upper chamber 50. As a result, the pressure in the lower chamber 52 may be increased in comparison with the pressure in the upper chamber 50 and, the main diaphragm 48 may move upward, thereby moving the regulator seat 44 towards a more open position.

Referring now to FIGS. 2 and 5, the IFC 29 may communicate with the stepper motor 49 and the gas valve 18 through a multiple pin connector 92. The stepper motor control 42 may also include a communications interface 93, a power supply 94 and a separate microcontroller 95. Another multiple pin connector 96 may be used to couple the stepper motor control 42 to the stepper motor 49, which in turn may be connected to a pressure regulator 46. The use of commands sent from the IFC 29 to the stepper motor control 42 and stepper motor 49 as a redundant safety feature will now be described.

When the furnace 10 is in a lockout mode due to a safety issue or concern, such as: (1) when an abnormal flame indication is sensed at the flame sensor electrode (FSE) 83, (2) a failure to ignite gas after four attempts, (3) when the gas valve is energized at the wrong time due to a short circuit or miswire, (4) a failed blower motor, (5) an open pressure or limit switch, such as, a low gas pressure switch 85, a low pressure switch 86, a draft safeguard switch 89, a flame rollout switch 90 or a limit switch 91 (FIG. 2), the IFC 29 may be programmed to send a command through the multi-pin connector 92 to the interface 93 and power supply 94 of the stepper motor control 42 (FIG. 5). The stepper motor control 42 may include its own microprocessor 95 to translate the command into the appropriate number of steps needed to return the stepper motor 49 and adjustment screw 61 to a home position or a fully raised position in FIG. 4, which may result in a downward movement of the main diaphragm 48 and the regulator seat 44 and closure of the regulator seat 44.

In the event the IFC 29 enters a lockout mode for any one or more of a variety of safety reasons, the IFC 29 may be programmed to send a home signal to the stepper motor 49 to close the regulator seat 44, thereby reducing the outlet pressure of the gas valve 18 to zero or near zero. Even thought the IFC 29 may have several different safety lockout modes, wherein the IFC 29 prevents a heating operation for a set time period (typically 3 hours or until power is reset), an additional home command from the IFC 29 may allow the modulating gas valve 18 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 even mechanically stuck in the on position. By using the disclosed home command, an additional safety redundancy may be provided whenever the furnace 10 enters a lockout mode.

Further, the IFC 29 may monitor the flame proving input at the flame sensor electrode (FSE) 83 even during an off-cycle. In the event that the gas valve 18 fails to open, the IFC 29 may be programmed to sense the flame after the call for heat has ended and may turn inducer motor 24 on and flash a fault code until the flame signal is no longer present. On a modulating furnace 10 that employs a modulating gas valve 18 with a stepper motor 49, the disclosed home command allows the modulating gas valve 18 to position itself to a reference point such that the outlet pressure would approach zero pressure when the valve 18 is on or, in this case, stuck open. By using the disclosed home command, an additional safety redundancy is provided when an abnormal flame is sensed at the FSE 83.

While only certain embodiments have been set forth, alternatives and modifications will be apparent from the above description to those skilled in the art. These and other alternatives are considered equivalents and within the spirit and scope of this disclosure and the appended claims.

Claims

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.