Variable speed fan motor control for forced air heating/cooling system

Claim 2

A control system for controlling the speed of a fan motor for a forced air conditioning system operable in an air heating mode and an air cooling mode, respectively, to vary motor speed during operation of said air conditioning system to minimize temperature stratification and heating or cooling exchange losses in said air conditioning system, said control system comprising: a first temperature sensor disposed in a return air flowpath of air returning from an enclosed space to said air conditioning system; a second temperature sensor located downstream of at least one heat exchanger of said air conditioning system for measuring the air temperature at the location of said second sensor compared with the air temperature at the location of said first sensor; a first control circuit including first and second amplifiers connected to each other and to at least one of said sensors and third and fourth amplifiers connected to each other and to at least one of said sensors for producing a variable output signal dependent on the difference in temperatures sensed by said first and second sensors and dependent on whether said air conditioning system is operating in an air heating mode or an air cooling mode; a power output circuit for controlling the speed of said motor as a function of said output signal to vary the speed of said motor in accordance with the difference in temperatures sensed by said first and second sensors; and a heating operation and cooling operation selection circuit operably connected to said power output circuit and said first control circuit.

Claim 3

The control system set forth in claim 1 wherein: said power output circuit includes an opto-isolator and a triac operably connected to said motor and to a pulse generator circuit and operable to vary the speed of said motor in accordance with a pulse signal generated by said pulse generator circuit.

Claim 4

The control system set forth in claim 1 including: a cutoff circuit operable when a voltage signal generated by said first control circuit decreases to a predetermined value to cause said power output circuit to de-energize said motor.

Claim 5

The control system set forth in claim 3 including: a minimum speed circuit operably connected to said cutoff circuit to cause said power output circuit to operate said motor at a predetermined minimum speed.

Claim 6

The control system set forth in claim 4 including: an adjustable resistor operably disposed in said minimum speed circuit for adjusting the minimum speed of said motor.

Claim 7

The control system set forth in claim 5 wherein: said resistor is operable to adjust the minimum speed of said motor to operate in a range from approximately 180 rpm to 620 rpm.

Claim 8

The control system set forth in claim 1 including: a sensor protection circuit operably connected to said first control circuit and said power output circuit for causing said power output circuit to operate said motor at full speed when an output signal from said first control circuit exceeds a predetermined value.

Claim 9

A control system for controlling the speed of a fan motor for a forced air flow air conditioning system operable in a heating mode and a cooling mode and including means forming an air flowpath therein, said control system being operable to vary motor speed during operation of said air conditioning system to minimize temperature stratification in said air flowpath and to minimize heat exchange losses from at least one heat exchanger disposed in said air flowpath, said control system comprising: a first temperature sensor disposed in a return air part of said air flowpath for measuring the temperature of air returning from an enclosed space to said air conditioning system; a second temperature sensor located in said air flowpath downstream of said at least one heat exchanger for measuring the air temperature at the location of said second sensor compared with the air temperature at the location of said first sensor; a first control circuit including first and second amplifiers connected to each other and to at least one of said sensors and third and fourth amplifiers connected to each other and to at least one of said sensors for producing a variable output signal dependent on the difference in temperatures sensed by said first and second sensors and dependent on whether said air conditioning system is operating in an air heating mode or an air cooling mode; a second control circuit connected to said first control circuit and to a power output circuit for varying the speed of said motor as a function of the difference in temperatures sensed by said first and second sensors to minimize temperature stratification in said air flowpath and to minimize heat exchange losses by continuing a progressively changing flow of air across said at least one heat exchanger and through said air flowpath during at least one of startup and shutoff of heat transfer to or from said at least one heat exchanger; and a heating operation and cooling operation selection circuit operable for controlling the speed of said motor in accordance with operation of said air conditioning system in said heating mode and said cooling mode, respectively.

Claim 10

A control system for controlling the speed of a fan motor for a forced air flow air conditioning system operable in a heating mode and a cooling mode and including means forming an air flowpath therein, said control system being operable to vary motor speed during operation of said air conditioning system to minimize temperature stratification in said air flowpath and to minimize heat exchange losses from at least one heat exchanger disposed in said air flowpath, said control system comprising: a first temperature sensor disposed in a return air part of said air flowpath for measuring the temperature of air returning from an enclosed space to said air conditioning system; a second temperature sensor located in said air flowpath downstream of said at least one heat exchanger for measuring the air temperature at the location of said second sensor compared with the air temperature at the location of said first sensor; a first control circuit including first and second amplifiers connected to each other and to at least one of said sensors and third and fourth amplifiers connected to each other and to at least one of said sensors for producing a variable output signal dependent on the difference in temperatures sensed by said first and second sensors and dependent on whether said air conditioning system is operating in an air heating mode or an air cooling mode; a second control circuit connected to said first control circuit and to a power output circuit for varying the speed of said motor as a function of the difference in temperatures sensed by said first and second sensors to minimize temperature stratification in said air flowpath and to minimize heat exchange losses by continuing a progressively changing flow of air across said at least one heat exchanger and through said air flowpath during at least one of startup and shutoff of heat transfer to or from said at least one heat exchanger; and a heating operation and cooling operation selection circuit operable for controlling the speed of said motor in accordance with operation of said air conditioning system in said heating mode and said cooling mode, respectively.

Claim 11

The control system set forth in claim 8 wherein: said power output circuit includes an opto-isolator and a triac operably connected to said motor and operable to vary the speed of said motor in accordance with a pulse signal.

Claim 12

The control system set forth in claim 8 including: a cutoff circuit operable when a ramp voltage signal decreases to a predetermined value to cause said power output circuit to de-energize said motor.

Claim 13

The control system set forth in claim 10 including: a minimum speed circuit operably connected to said cutoff circuit to cause said power output circuit to operate said motor at a predetermined minimum speed.

Claim 14

The control system set forth in claim 8 including: a sensor protection circuit operably connected to said first control circuit and said power output circuit for causing said power output circuit to operate said motor at full speed when an output signal from said first control circuit exceeds a predetermined value.