Systems and methods for controlling a draft inducer for a furnace

A draft inducer apparatus for use with a furnace that includes a combustion chamber and an exhaust outlet for venting exhaust combustion chamber gases from the furnace and that also includes at least one heat exchanger assembly for extracting heat from the exhaust combustion chamber gases and transferring heat to conditioned air, and for use with a fan for inducing a draft in the combustion chamber which causes a pressure drop across the heat exchanger assembly for moving the exhaust combustion chamber gases through the exhaust outlet, said apparatus comprising:

• a motor including a shaft for driving the fan in response to a motor control signal wherein the draft induced by the fan is a function of motor speed and motor torque;
• a processor for defining a speed vs. torque operating curve having a minimum desired speed and a maximum desired speed between which the speed vs. torque operating curve is coincident with a pressure curve corresponding to a desired pressure drop across the heat exchanger assembly caused by the draft induced by the fan, said speed vs. torque operating curve, for a given speed below the minimum desired speed, defining a torque greater than the torque defined by the pressure curve for the given speed;
• and
• a control circuit for generating the motor control signal in response to the speed vs. torque operating curve for controlling the motor torque as a function of the motor speed whereby operation of the motor is controlled so that the draft induced by the fan causes the desired pressure drop in a desired operating range between the minimum and maximum desired speeds and operation of the motor is inhibited outside the desired operating range.

A furnace system comprising:

• a combustion chamber;
• an exhaust outlet for venting exhaust combustion chamber gases from the combustion chamber;
• at least one heat exchanger assembly for extracting heat from the exhaust combustion chamber gases and for transferring heat to conditioned air;
• a fan for inducing a draft in the combustion chamber which causes a pressure drop across the heat exchanger assembly for moving the exhaust combustion chamber gases through the exhaust outlet;
• a motor including a shaft for driving the fan in response to a motor control signal wherein the draft induced by the fan is a function of motor speed and motor torque;
• a processor for defining a speed vs. torque operating curve having a minimum desired speed and a maximum desired speed between which the speed vs. torque operating curve is coincident with a pressure curve corresponding to a desired pressure drop across the heat exchanger assembly caused by the draft induced by the fan, said speed vs. torque operating curve, for a given speed above the maximum desired speed, defining a torque less than the torque defined by the pressure curve for the given speed;
• and
• a control circuit for generating the motor control signal in response to the speed vs. torque operating curve for controlling the motor torque as a function of the motor speed whereby operation of the motor is controlled so that the draft induced by the fan causes the desired pressure drop in a desired operating range between the minimum and maximum desired speeds and operation of the motor is inhibited outside the desired operating range.

A method of operating a draft inducer apparatus for use with a furnace that includes a combustion chamber and an exhaust outlet for venting exhaust combustion chamber gases from the furnace and that also includes at least one heat exchanger assembly for extracting heat from the exhaust combustion chamber gases and transferring heat to conditioned air, and for use with a fan for inducing a draft in the combustion chamber which causes a pressure drop across the heat exchanger assembly for moving the exhaust combustion chamber gases through the exhaust outlet, said method comprising the steps of:

• driving the fan with a motor in response to a motor control signal wherein the draft induced by the fan is a function of motor speed and motor torque;
• defining a pressure curve corresponding to a desired pressure drop across the heat exchanger assembly caused by the draft induced by the fan;
• defining a speed vs. torque operating curve having a minimum desired speed and a maximum desired speed between which the speed vs. torque operating curve is coincident with the pressure curve, said speed vs. torque operating curve, for a given speed above the maximum desired speed, defining a torque less than the torque defined by the pressure curve for the given speed;
• and
• generating the motor control signal in response to the speed vs. torque operating curve for controlling the motor torque as a function of the motor speed whereby operation of the motor is controlled so that the draft induced by the fan causes the desired pressure drop in a desired operating range between the minimum and maximum desired speeds and operation of the motor is inhibited outside the desired operating range.

A method of operating a draft inducer apparatus for use with a furnace that includes a combustion chamber and an exhaust outlet for venting exhaust combustion chamber gases from the furnace and that also includes at least one heat exchanger assembly for extracting heat from the exhaust combustion chamber gases and transferring heat to conditioned air, and for use with a fan for inducing a draft in the combustion chamber which causes a pressure drop across the heat exchanger assembly for moving the exhaust combustion chamber gases through the exhaust outlet, said method comprising the steps of:

• driving the fan with a motor in response to a motor control signal wherein the draft induced by the fan is a function of motor speed and motor torque;
• defining a pressure curve corresponding to a desired pressure drop across the heat exchanger assembly caused by the draft induced by the fan;
• defining a speed vs. torque operating curve having a minimum desired speed and a maximum desired speed between which the speed vs. torque operating curve is coincident with the pressure curve, said speed vs. torque operating curve, for a given speed below the minimum desired speed, defining a torque greater than the torque defined by the pressure curve for the given speed;
• and
• generating the motor control signal in response to the speed vs. torque operating curve for controlling the motor torque as a function of the motor speed whereby operation of the motor is controlled so that the draft induced by the fan causes the desired pressure drop in a desired operating range between the minimum and maximum desired speeds and operation of the motor is inhibited outside the desired operating range.

A method of operating furnace system that includes a combustion chamber and an exhaust outlet for venting exhaust combustion chamber gases from the furnace system and that also includes at least one heat exchanger assembly for extracting heat from the exhaust combustion chamber gases and for transferring heat to conditioned air, and a fan for inducing a draft in the combustion chamber which causes a pressure drop across the heat exchanger assembly for moving the exhaust combustion chamber gases through the exhaust outlet, said method comprising the steps of:

• driving the fan with a motor in response to a motor control signal wherein the draft induced by the fan is a function of motor speed and motor torque;
• defining a pressure curve corresponding to a desired pressure drop across the heat exchanger assembly caused by the draft induced by the fan;
• defining a speed vs. torque operating curve having a minimum desired speed and a maximum desired speed between which the speed vs. torque operating curve is coincident with the pressure curve, said speed vs. torque operating curve, for a given speed above the maximum desired speed, defining a torque less than the torque defined by the pressure curve for the given speed;
• and
• generating the motor control signal in response to the speed vs. torque operating curve for controlling the motor torque as a function of the motor speed whereby operation of the motor is controlled so that the draft induced by the fan causes the desired pressure drop in a desired operating range between the minimum and maximum desired speeds and operation of the motor is inhibited outside the desired operating range.