Abstract: A variable speed motor is regulated responsive to the load torque acting on the blower wheel. The load torque acting on the blower wheel is determined by means of a coast down procedure in which the motor is briefly de-energized and the rate of angular change d.omega./dt is determined. The load torque acting on the blower wheel can be determined knowing the moment of inertia and d.omega./dt. The average motor RPM during the coast down is then related to a torque value where an RPM vs. CFM relationship has been empirically determined for that blower wheel. A microprocessor then computes the final motor RPM necessary to achieve the desired air delivery (CFM) using the fan law equations.

Abstract: A method and apparatus for maintaining the desired level of excess air in a two stage gas furnace system. Low and high pressure switches are placed across the heat exchanger and are successively closed, as the inducer motor accelerates during purging, when the pressure drop reaches the respective theoretically desired low and high firing pressure drop levels. As the switches are closed, the inducer motor speeds are sensed and recorded, with a ratio of the two then being calculated. After firing, the ratio is then directly applied to a desired high firing motor speed to obtain the desired low firing motor speed.

Abstract: An emergency heat bypass arrangement for a furnace in which the normal controller path is supplemented by an alternate path through a relay subject to an emergency heat switch controlling the solenoid of the relay, and the relay includes additional contacts for keeping power on the solenoid even after the furnace high pressure switch changes contacts to provide heating when said controller has malfunctioned.

Abstract: The power output of a variable speed motor is limited to a safe level by determining the maximum allowable speed corresponding to a maximum power output limit over a range of load conditions and then maintaining the speed of the motor below those maximum allowable speeds at the particular load conditions existing at the time.

Abstract: Method and apparatus for maintaining excess air control in a gas furnace. A pressure switch is placed across a heat exchanger to indicate when, while accelerating the inducer motor speed during purging operation, the pressure drop reaches a predetermined level. When that occurs, the motor speed is sensed and recorded. When the furnace is subsequently fired, the desired inducer motor speed is obtained by modifying the recorded motor speed on a correction factor derived from empirical data obtained from a gas furnace operating under selective variable conditions.

Abstract: A furnace is operated such that the air-fuel ratio and the temperature rise are maintained constant so that the efficiency remains constant over the range of operation.

Abstract: An adaptive motor control for a furnace with or without an evaporator coil determines and delivers the desired CFM for each thermostat cycle. Specifically, a circulating air blower driven by an ECM is initially set at a known duty cycle for each thermostat cycle and the delivered CFM is calculated. The RPM necessary to deliver the desired CFM is then determined and the ECM is set accordingly.