Patent ID: 8251671

Claim:
An apparatus for controlling an air distribution system of the type which includes a duct system, a motor drivingly associated with a blower and a target air flow rate signal which represents a target air flow for the air distribution system, the apparatus providing control of the motor speed to maintain a rate of air flow in the system at substantially the target air flow rate, wherein the apparatus comprises: a variable speed motor controller means for controlling the motor speed to a provisional speed or a target speed; a speed detecting device for providing a speed signal relatively representative of the speed of motor; a torque detecting device for providing a torque signal relatively representative of the torque of motor; and a module responsive to inputs from the variable speed controller means to calculate a current air flow rate from a current speed and torque signal from the speed detecting device and torque detecting device, the module using the current air flow rate, the target air flow rate and the current speed to calculate a target air flow speed, the variable speed motor controller means using the target air flow speed to produce a control signal which is supplied to control application of voltage to the motor, the voltage supplied to the motor being sufficient for the motor to produce the target air flow rate; wherein the current air flow rate is calculated in accordance with the following algorithm: Qa=A+B*Ta+C/Ta +( D+E*Ta+F/Ta )* Na +( G+H*Qa+I/Qa )/ Na; wherein the target speed is calculated in accordance with the following algorithm: Nt=Qt/Qa*Na; wherein Qa equals to a current air flow rate, Ta equals to a present value of the torque signal, Na equals to a present value of the motor speed signal, A to I equal to constants, Nt equals to the target speed, and Qt equals to the target air flow rate.