Variable speed inducer motor control method

Claim 2

In a fixed-firing rate induced draft furnace, having a heat exchanger and an integrated control inducer motor, an improved method of controlling excess air comprising the steps of: providing at least one pressure switch that is responsive to a preselected pressure drop level in the heat exchanger, said pressure drop level being selected so as to be commensurate with a theoretically desired excess air level under firing operating conditions; accelerating said integrated control inducer motor until said pressure switch closes and thereupon recording a first motor speed and a first current level; calculating a first torque value based on said first motor speed and said first current level using the equation: TORQUE 1=K1 * [AMP * RPM1/RPM (act.)]+K2 where: K1 and K 2 are inducer wheel constants; RPM1 is the inducer motor speed when a low pressure switch makes; AMP1 is a current measurement when the low pressure switch makes; and RPM (act) is a most recently measured RPM; and maintaining a constant CFM by controlling the torque applied to said integrated control inducer motor in accordance with said first torque value.

Claim 3

The method of claim 1 comprising the further steps of: recording most recent motor speed; calculating a current torque value based on said first motor speed, said first current level and said most recent motor speed; maintaining a constant CFM by controlling the torque applied to said integrated control inducer motor in accordance with said current torque value.

Claim 4

The method of claim 1 wherein said calculating is performed by a microprocessor integral to said integrated control inducer motor.

Claim 5

The method of claim 1 wherein said furnace is a single-stage furnace having a single pressure switch.

Claim 6

In a fixed-firing rate induced draft, two-stage furnace, having a heat exchanger and an integrated control inducer motor, an improved method of controlling excess air comprising the steps of: providing a low pressure switch that is responsive to a selected first pressure drop level in the heat exchanger, said first pressure drop level being selected so as to be commensurate with a theoretically desired excess air level under low fire conditions; providing a high pressure switch that is responsive to a selected second pressure drop level in the heat exchanger, said second pressure drop level being selected so as to be commensurate with a theoretically desired excess air level under high fire conditions; upon determination that a call for heat exists: accelerating the integrated control inducer motor at a first rate until said low pressure switch closes and recording a first motor speed and a first current level at that time; determining whether a request for operation under high fire condition exists; if a request for operation under high fire condition does not exist: (1) calculating a first torque value based on said first motor speed and said first current level using the equation: TORQUE 1=K1 * [AMP * RPM1/RPM (act.)]+K2 where: K1 and K 2 are inducer wheel constants; RPM1 is the inducer motor speed when a low pressure switch makes; AMP1 is a current measurement when the low pressure switch makes; and RPM (act) is a most recently measured RPM; and (2) maintaining a constant CFM by controlling the torque applied to said integrated control inducer motor based on said first torque value; and if a request for operation under high fire condition exists: (3) accelerating the integrated control inducer motor at a second rate until said high pressure switch closes and recording second motor speed and second current level at that time; (4) calculating a second torque value based on said second motor speed and said second current level; and (5) regulating torque applied to said integrated control inducer motor based on said second torque value.

Claim 7

In a fixed-firing rate induced draft, two-stage furnace, having a heat exchanger and an integrated control inducer motor, an improved method of controlling excess air comprising the steps of: providing a low pressure switch that is responsive to a selected first pressure drop level in the heat exchanger, said first pressure drop level being selected so as to be commensurate with a theoretically desired excess air level under low fire conditions; providing a high pressure switch that is responsive to a selected second pressure drop level in the heat exchanger, said second pressure drop level being selected so as to be commensurate with a theoretically desired excess air level under high fire conditions; upon determination that a call for heat exists: accelerating the integrated control inducer motor at a first rate until said low pressure switch closes and recording a first motor speed and a first current level at that time; determining whether a request for operation under high fire condition exists; if a request for operation under high fire condition does not exist: (1) calculating a first torque value based on said first motor speed and said first current level using the equation: TORQUE 1=K1 * [AMP * RPM1/RPM (act.)]+K2 where: K1 and K 2 are inducer wheel constants; RPM1 is the inducer motor speed when a low pressure switch makes; AMP1 is a current measurement when the low pressure switch makes; and RPM (act) is a most recently measured RPM; and (2) maintaining a constant CFM by controlling the torque applied to said integrated control inducer motor based on said first torque value; and if a request for operation under high fire condition exists: (3) accelerating the integrated control inducer motor at a second rate until said high pressure switch closes and recording second motor speed and second current level at that time; (4) calculating a second torque value based on said second motor speed and said second current level; and (5) regulating torque applied to said integrated control inducer motor based on said second torque value.

Claim 8

The method of claim 5 comprising the further steps of: recording most recent motor speed; under low fire condition: (1) calculating a first current torque value based on said first motor speed, said first current level and said most recent motor speed; (2) regulating torque applied to said integrated control inducer motor in accordance with said first current torque value and; under high fire condition: (1) calculating a second current torque value based on said second motor speed, said second current level and said most recent motor speed; and (2) maintaining a constant CFM by controlling the torque applied to said integrated control inducer motor in accordance with said second current torque value.