US 5,331,944 AGranted

Variable speed inducer motor control method

AssigneeCarrier Corporation

InventorsMatthew Kujawa, Kevin D. Thompson

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Abstract

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, the pressure drop level being selected so as to be commensurate with a theoretically desired excess air level under firing operating conditions; accelerating the integrated control inducer motor until the pressure switch closes and thereupon recording a first motor speed and a first current level; calculating a first torque value based on the first motor speed and the first current level; and regulating torque applied to the integrated control inducer motor in accordance with the first torque value.

Claims6

Dependent claims

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.sub.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.

7 more elements

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.sub.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.

16 more elements

Dependencies are inferred from the claim text.