Constant air flow control apparatus and method

In an air handling system for delivering air by a blower system utilizing a blower and a blower motor for running the blower, the blower having air flow, pressure, torque and current characteristics, apparatus for providing a constant flow rate of air comprising:

• first sensing means for sensing the operating speed of the motor;
• second sensing means for sensing the current drawn by the motor;
• third sensing for sensing a voltage applied to the motor;
• switch means for controlling application of power to the motor;
• flow control means for establishing a desired air flow rate;
• and,
• processor means responsive to inputs from each of the sensing means and the flow control means to determine a torque required to be produced by the motor for a predetermined air flow rate, the torque being determined as a function of the combined inputs from the first sensing means and the flow control means together with individual inputs from the first sensing means and the flow control means and air flow, pressure, torque, and current characteristics of the blower, the processor means being responsive to a calculated torque value for the motor to supply a signal to the switch means to control application of voltage to the motor, the voltage supplied to the motor being sufficient for the motor to produce the calculated torque, and the processor means being responsive to the inputs from the second and third sensing means to vary the signal supplied to the switch means in accordance with sensed motor operating conditions, the processor means determining the torque required to be produced by the motor in accordance with the formula
• torque=(K1*S*C)+(K2*S)+(K3*C)+K4,
• where S is an input from the first sensing means representing motor speed, C is an input from the control means representing desired air flow, and K1, K2, K3, and K4 are constants for the particular blower being operated by the motor, and respectively represent air flow, torque, pressure, and speed characteristics of the blower, the torque determined by the formula including a constant offset torque which is proportional to the desired air flow rate.

Air handling apparatus for delivering a volume of air at a generally constant flow rate regardless of changes in the operating conditions of an environment with which the apparatus is used comprising:

• a blower for moving air from one point to another;
• a blower motor for running the blower;
• switch means for controlling application of power to the motor;
• sensing means for sensing a voltage supplied to the motor, the current drawn by the motor, and the operating speed of the motor;
• flow control means for establishing a desired air flow rate;
• and,
• processor means responsive to the sensed voltage, current, and motor speed inputs from each of the sensing means, and an input from the flow control means to periodically determine a torque required by the motor to produce a predetermined air flow rate, the torque being determined as a function of the combined motor speed input from the sensing means and an input from the flow control means and current, torque, pressure, and air flow characteristics of the blower, the calculated torque including an offset torque value proportional to the desired constant air flow rate, and the processor means being responsive to a calculated torque value for the motor to supply a control signal to the switch means to control application of voltage to the motor, the voltage supplied to the motor being sufficient for the motor to produce the calculated torque.

A method of controlling the operation of a blower motor in an air handling system to provide a flow rate of air delivered by a blower operated by the blower motor, the air flow rate being substantially constant over a wide range of operating conditions, the method comprising:

• sensing a voltage supplied to the motor, the current drawn by the motor, and an operating speed of the motor and providing output signals representative thereof;
• establishing a predetermined air flow rate and providing a flow rate signal representative thereof;
• periodically processing the motor speed signal in combination with the flow rate signal to determine a torque required to be produced by the motor for a predetermined air flow rate, processing of the motor speed and flow rate signals taking to account, air flow, torque, pressure, and speed characteristics of the blower, the torque value determined including an offset torque value proportional to the desired constant air flow rate;
• generating a control signal and supplying the control signal to a switch means for the switch means to, in turn, supply a voltage to the motor sufficient for the motor to produce the calculated torque;
• and,
• modifying the control signal in response to the sensed voltage and current signals to account for motor operating conditions whereby a constant air flow rate is maintained despite changes in the system.

A method of controlling the operation of a blower motor in an air handling system to provide an air flow rate which is substantially constant over a wide range of operating conditions, the method comprising:

• operating a blower having a predetermined set of operating characteristics to move the air, the blower being operated by a blower motor to which a voltage is supplied;
• sensing a voltage supplied to the motor, a current drawn by the motor, and an operating speed of the motor and providing output signals representative thereof;
• establishing a predetermined air flow rate and providing a flow rate signal representative thereof;
• deriving a set of constant values representing operational characteristics of the blower by performing a double linear approximation from torque/speed curves plotted for the blower;
• processing the motor speed signal in combination with the flow rate signal to determine a torque required to be produced by the motor for a predetermined air flow rate, processing the motor speed signal and flow rate signal including calculating the required torque in accordance with the equation
• torque=(K1*S*C)+(K2*S)+(K3*C)+K4,
• where S is a motor speed input from the sensing means, C is an air flow rate input from the flow control means, and K1-K4 are air flow, torque, pressure, and speed constants respectively derived for the particular blower being operated by the motor;
• generating a control signal which is a function of the calculated torque and supplying the control signal to a switch means for the switch means to supply a voltage to the motor sufficient for the motor to produce the calculated torque, the control signal incorporating an offset torque value which is proportional to the constant air flow rate;
• and,
• modifying the control signal in response to the sensed voltage and current signals to account for motor operating conditions whereby a constant air flow rate is maintained despite changes in the system.

In a method of controlling the operation of a blower motor in an air handling system to provide an air flow rate which is substantially constant over a wide range of operating conditions, the method comprising operating a blower having a predetermined set of operating characteristics to move the air, the blower being operated by a blower motor to which a voltage is supplied, sensing an operating speed of the motor and providing an output signal representative thereof, and establishing a predetermined air flow rate and providing a flow rate signal representative thereof, the improvement comprising:

• deriving a set of constant values representing operational characteristics of the blower by performing a double linear approximation from torque/speed curves for the blower;
• periodically processing the motor speed and flow rate signal to determine a torque required to be produced by the motor for a predetermined air flow rate to be produced by the blower, processing the motor speed signal and flow rate signal including multiplying the flow rate signal together with a constant value representing pressure characteristics of the blower in a first multiplier means, multiplying the speed control signal together with a constant value representing torque characteristics of the blower in a second multiplier means, multiplying the speed control signal together with the flow rate signal and a constant representing air flow characteristics of the blower in a third multiplier means, and additively combining the outputs of the respective multiplier means together with each other and with a constant representing speed characteristics of the blower to produce a motor control signal having an offset torque value proportional to the constant air flow rate;
• generating a control signal which is a function of the calculated torque;
• and,
• supplying the control signal to a switch means for the switch means to supply a voltage to the motor sufficient for the motor to produce the calculated torque.