Systems and methods for controlling a draft inducer for a furnace

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, said heat exchanger assembly having a plurality of heat exchanger elements which determine furnace capacity;
• 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 wherein the pressure drop across the heat exchanger assembly is affected by the furnace capacity;
• a motor including a shaft for driving the fan in response to a motor control signal;
• a memory for storing information defining a relationship between motor speed, motor torque and parameters defining motor operation;
• a processor for determining the speed and torque of the motor and for retrieving from the memory a retrieved parameter corresponding to the determined motor speed and motor torque, said processor being responsive to the retrieved parameter for defining at least one set of speed/torque curves corresponding to a desired pressure drop across the heat exchanger assembly;
• and
• a control circuit for generating the motor control signal in response to the defined set of speed/torque curves thereby to control the draft induced in the combustion chamber whereby the motor is operated as a function of the determined motor speed and motor torque which are indicative of the furnace capacity.

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 heat exchanger assembly having a plurality of heat exchanger elements which determine furnace capacity wherein the pressure drop across the heat exchanger assembly is affected by the furnace capacity, said method comprising the steps of:

• driving the fan with a motor in response to a motor control signal;
• storing information in a memory defining a relationship between motor speed, motor torque and parameters defining motor operation;
• determining the speed and torque of the motor;
• retrieving from the memory a retrieved parameter corresponding to the determined motor speed and motor torque;
• defining at least one set of speed/torque curves corresponding to a desired pressure drop across the heat exchanger assembly in response to the retrieved parameter;
• and
• generating the motor control signal in response to the defined set of speed/torque curves thereby to control the draft induced in the combustion chamber whereby the motor is operated as a function of the determined motor speed and motor torque which are indicative of the furnace capacity.

A method of operating a furnace system that includes a combustion chamber and an exhaust outlet for venting exhaust combustion chamber gases from the combustion chamber 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 heat exchanger assembly having a plurality of heat exchanger elements which determine furnace capacity wherein the pressure drop across the heat exchanger assembly is affected by the furnace capacity, said method comprising the steps of:

• driving the fan with a motor in response to a motor control signal;
• storing information in a memory defining a relationship between motor speed, motor torque and parameters defining motor operation;
• determining the speed and torque of the motor;
• retrieving from the memory a retrieved parameter corresponding to the determined motor speed and motor torque;
• defining at least one set of speed/torque curves corresponding to a desired pressure drop across the heat exchanger assembly in response to the retrieved parameter;
• and
• generating the motor control signal in response to the defined set of speed/torque curves thereby to control the draft induced in the combustion chamber whereby the motor is operated as a function of the determined motor speed and motor torque which are indicative of the furnace capacity.

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 heat exchanger assembly having a plurality of heat exchanger elements which determine furnace capacity wherein the pressure drop across the heat exchanger assembly is affected by the furnace capacity, said apparatus comprising:

• a motor including a shaft for driving the fan in response to a motor control signal;
• a memory for storing information defining a relationship between motor speed, motor torque and a number of heat exchanger elements;
• a speed circuit providing a speed signal representative of the speed of the motor;
• a control circuit responsive to the speed signal for generating the motor control signal to increase the speed of the motor when the speed signal indicates that the motor speed is less than a reference speed;
• a processor for determining the torque of the motor when the motor speed corresponds to the reference speed and for retrieving from the memory the number of heat exchanger elements corresponding to the determined motor torque and the reference motor speed, said processor being responsive to the retrieved number of heat exchanger elements for defining at least one set of speed/torque curves corresponding to a desired pressure drop across the heat exchanger assembly, said control circuit generating the motor control signal in response to the defined set of speed/torque curves thereby to control the draft induced in the combustion chamber whereby the motor is operated as a function of the determined motor torque and the reference motor speed which are indicative of the furnace capacity.

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 heat exchanger assembly having a plurality of heat exchanger elements which determine furnace capacity wherein the pressure drop across the heat exchanger assembly is affected by the furnace capacity, said apparatus comprising:

• a motor including a shaft for driving the fan in response to a motor control signal;
• a memory for storing information defining a relationship between motor speed, motor torque and a number of heat exchanger elements;
• a control circuit for generating the motor control signal so that the motor operates to produce a reference torque;
• a processor for determining the speed of the motor which results when the motor is operating to produce the reference torque and for retrieving from the memory the number of heat exchanger elements corresponding to the determined motor speed and the reference motor torque, said processor being responsive to the retrieved number of heat exchanger elements for defining at least one set of speed/torque curves corresponding to a desired pressure drop across the heat exchanger assembly, said control circuit generating the motor control signal in response to the defined set of speed/torque curves thereby to control the draft induced in the combustion chamber whereby the motor is operated as a function of the determined motor speed and reference motor torque which are indicative of the furnace capacity.

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 heat exchanger assembly having a plurality of heat exchanger elements which determine furnace capacity wherein the pressure drop across the heat exchanger assembly is affected by the furnace capacity, said apparatus comprising:

• a motor including a shaft for driving the fan in response to a motor control signal;
• a memory for storing information defining a relationship between motor speed, motor torque and a number of heat exchanger elements;
• a pressure switch providing a pressure signal representative of a pressure across the heat exchanger assembly;
• a control circuit responsive to the pressure signal for generating the motor control signal to increase the torque of the motor when the pressure signal indicates that the pressure drop across the heat exchanger assembly is less than the pressure;
• a processor for determining the speed and torque of the motor when the pressure drop corresponds to the pressure and for retrieving from the memory the number of heat exchanger elements corresponding to the determined motor speed and motor torque, said processor being responsive to the retrieved number of heat exchanger elements for defining at least one set of speed/torque curves corresponding to a desired pressure drop across the heat exchanger assembly, said control circuit generating the motor control signal in response to the defined set of speed/torque curves thereby to control the draft induced in the combustion chamber whereby the motor is operated as a function of the determined motor speed and motor torque which are indicative of the furnace capacity.