Variable speed inducer motor control method
First Claim
1. In an induced draft furnace having a heat exchanger, an ignition circuit, and an integrated control inducer motor having a fluctuating motor speed, an improved method of controlling the air combustion level in said furnace, said method comprising the steps of:
- establishing a lookup table including (a) a combustion operating lookup plot wherein motor speed is correlated with torque values required to achieve desired combustion operation motor speeds at various flow restrictions and (b) a threshold combustion operating plot correlating current motor speed with minimum torque required for ignition;
determining whether a call for heat has been made; and
upon determining that a call for heat has been made,controlling said motor by increasing the speed of said inducer motor until said motor exceeds a speed suitable for a combustion operating state and activating said ignition circuit when the current motor tongue exceeds said minimum torque from said lookup table,reading motor speed values from said motor, andmaintaining a constant flow of air through said furnace by controlling the torque applied to said integrated control inducer motor in accordance with torque values from said lookup table correlated with said motor speed.
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Accused Products
Abstract
The present invention is a method and apparatus for controlling the flow of combustion air and/or combustion products through a furnace which may experience changing flow restrictions. The method provides constant flow through an induced-draft furnace by determining torque values applied to an inducer motor of the furnace from a lookup table, which is established by operating a test furnace under changing flow restrictions, typically by measuring furnace flue gas carbon monoxide concentration. A lookup table according to the invention may include motor operating performance plots for controlling inducer speed under operating conditions, and threshold plots, which may be employed for determining activation of furnace events such as ignition, gas valve energizing, and shutdown. In an adaptive method of the invention, an adaptive lookup table is provided by averaging torque values from each of several lookup tables. A pressure switch is provided having an opening pressure commensurate with a minimum excess air level. The pressure switch has a closing pressure which determines a torque biasing level for the furnace based on motor RPM and torque values determined from the adaptive lookup table.
132 Citations
21 Claims
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1. In an induced draft furnace having a heat exchanger, an ignition circuit, and an integrated control inducer motor having a fluctuating motor speed, an improved method of controlling the air combustion level in said furnace, said method comprising the steps of:
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establishing a lookup table including (a) a combustion operating lookup plot wherein motor speed is correlated with torque values required to achieve desired combustion operation motor speeds at various flow restrictions and (b) a threshold combustion operating plot correlating current motor speed with minimum torque required for ignition; determining whether a call for heat has been made; and upon determining that a call for heat has been made, controlling said motor by increasing the speed of said inducer motor until said motor exceeds a speed suitable for a combustion operating state and activating said ignition circuit when the current motor tongue exceeds said minimum torque from said lookup table, reading motor speed values from said motor, and maintaining a constant flow of air through said furnace by controlling the torque applied to said integrated control inducer motor in accordance with torque values from said lookup table correlated with said motor speed. - View Dependent Claims (2, 3, 4, 5, 6)
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7. In an induced draft furnace having a heat exchanger, an ignition circuit, and an integrated control inducer motor having a fluctuating motor speed, an improved method of controlling the air level in said furnace, said method comprising the steps of:
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establishing a lookup table wherein motor speed is correlated with torque values required to achieve desired combustion operation motor speeds at various flow restrictions;
wherein said step of establishing a lookup table includes the steps of;a) providing several test furnaces, each corresponding to a different furnace size; b) operating each of said test furnaces under changing flow restrictions; c) recording motor speed and corresponding torques commensurate with desired excess air levels for each of said furnaces while each of said furnaces is operated, said desired excess air levels being determined on the basis of flue gas carbon monoxide concentration; and d) averaging the recorded torque values recorded at the various motor speeds to establish an adaptive lookup table; determining whether a call for heat has been made; and upon determining that a call for heat has been made, controlling said motor by increasing the speed of said inducer motor until said motor exceeds a speed suitable for a combustion operating state, reading motor speed values from said motor, and maintaining a constant flow of air through said furnace by controlling the torque applied to said integrated control inducer motor in accordance with torque values from said lookup table correlated with said motor speed. - View Dependent Claims (8, 9, 10)
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11. In an induced draft, two-stage furnace having a heat exchanger, an ignition circuit, a high stage gas valve, and an integrated control inducer motor having fluctuating motor speed, an improved method of controlling the combustion excess air level in said furnace, said method comprising the steps of:
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establishing a lookup table including (a) a first combustion operating lookup plot correlating motor speed with first torque values required for achieving a desired low stage excess air level, (b) a second combustion operating lookup plot correlating motor speed with second torque values required for achieving desired high stage excess air level and (c) at least one threshold operating plot correlating current motor speed with minimum torque required for ignition; determining whether a call for low stage has been made; upon determining that a call for low stage has been made, controlling said motor by (a) increasing the speed of said inducer motor and activating said ignition circuit when the current motor torque exceeds said minimum torque from said lookup table and (b) maintaining a constant flow of air through said furnace in a low stage operating state by controlling the torque applied to said motor in accordance with said first torque values from said lookup table, and determining whether a call for high stage has been made; and upon determining that a call for high stage has been made, maintaining a constant flow of air through said furnace in a high stage operating state by controlling the torque applied to said motor in accordance with said second torque values. - View Dependent Claims (12, 13, 14, 15, 16)
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17. In an induced draft furnace having a heat exchanger, an ignition circuit, and an integrated control inducer motor having a fluctuating motor speed, an improved method of controlling the combustion air level in said furnace, said method comprising the steps of:
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establishing a lookup table wherein motor speed is correlated with torque values required to achieve desired combustion operation motor speeds at various flow restrictions;
wherein said establishing step includes the steps of;(a) providing a plurality of test furnaces, each corresponding to a different furnace size; (b) operating each of said test furnaces under changing flow restrictions; (c) recording motor speed and corresponding torques commensurate with desired excess air levels for each of said furnaces while each of said furnaces is operated, said desired excess air levels determined on the basis of flue gas carbon monoxide concentration; and (d) averaging the recorded torque values recorded at the various motor speeds seen during operation of said plurality of furnaces to establish an adaptive lookup table; determining whether a call for heat has been made; and upon determining that a call for heat has been made, controlling said motor by increasing the speed of said inducer motor until said motor exceeds a speed suitable for a combustion operating state, reading motor speed values from said motor, and maintaining a constant flow of air through said furnace by controlling the torque applied to said integrated control inducer motor in accordance with torque values from said lookup table correlated with said motor speed. - View Dependent Claims (18, 19, 20, 21)
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Specification