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

• US 6,695,046 B1
• Filed: 08/01/2000
• Issued: 02/24/2004
• Est. Priority Date: 02/18/1997
• Status: Expired due to Fees

• Current Assignee: Hoffman Controls Corp.
• Original Assignee: Hoffman Controls Corp.
• Inventors: Bowman, Walter William, Byrnes, Howard P.
• Primary Examiner(s): Ford, John K.
• Application Number:
  US09/629,328
• Time in Patent Office: 1,302 Days
• Field of Search: 165/293, 165/244, 165/247, 236/78.D, 236/49.3, 236/11, 236/91.F, 236/38, 236/DIG.9, 237/8.R, 126/110.A, 126/110.E, 621/57, 621/80, 621/86, 622/31, 318/439, 318/471, 318/806
• US Class Current: 165/247
• CPC Class Codes: F04D 27/00 Control, e.g. regulation, of pumps, pumping installations or pumping systems specially adapted for elastic fluids
• CPC Class Codes: F24F 11/77 by controlling the speed of ventilators
• CPC Class Codes: Y02B 30/70 Efficient control or regulation technologies, e.g. for control of refrigerant flow, motor or heating
• CPC Class Codes: Y10S 236/09 Fan control

Abstract

A fan motor speed control system for controlling the fan motor speed of an air conditioning system includes a power output circuit including a power triac which is turned on and off by an opto-isolator connected to a pulse generator circuit for varying an AC voltage waveform imposed on the fan motor. The pulse generator circuit is connected to heating and cooling ramp circuits and a minimum speed circuit to provide a variable voltage signal imposed on the pulse generator circuit corresponding to the temperature difference sensed by a return air sensor and a heating or cooling sensor or by separate heating and cooling sensors disposed adjacent respective heating and cooling heat exchangers of the air conditioning system. An adjustable minimum speed circuit and a cutoff circuit are provided to control motor minimum speed or motor shutoff when a predetermined minimum speed is reached to prevent motor bearing failure or overheating. Sensor protection circuits in the control system operate to drive the motor to full speed if any of the temperature sensors experience an open or short circuit condition. The control system circuit maximizes air conditioning system efficiency by capturing additional heating or cooling effect, reduces noise associated with motor startup and shutdown, and reduces rapid change in the sensed temperature in the air conditioned space during motor startup and shutdown.

Claims

1. A control system for controlling the speed of a fan motor for a forced air conditioning system to vary motor speed during operation of the 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 ramp circuit for producing a variable voltage output signal dependent on the difference in temperatures sensed by said first and second sensors;

a pulse generator circuit connected to said ramp output circuit and to a power output circuit for controlling the speed of said motor, said pulse generator circuit being operable to vary a pulse signal to said power output circuit as a function of the output signal of said ramp circuit to vary the speed of said fan 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 an amplifier associated with said power output circuit and an amplifier associated with said ramp circuit.

2. 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 said pulse generator circuit and operable to vary the speed of said fan motor in accordance with a pulse signal generated by said pulse generator circuit.

3. The control system set forth in claim 1 including:

a cutoff circuit operable when a ramp voltage signal decreases to a predetermined value to cause said power output circuit to deenergize said motor.

4. 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.

5. 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.

6. 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.

7. The control system set forth in claim 1 including:

a sensor protection circuit operably connected to said ramp 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 ramp circuit exceeds a predetermined value.

8. The control system set forth in claim 1 including:

a third temperature sensor located downstream of a second heat exchanger of said air conditioning system for measuring the air temperature at the location of said third sensor compared with the air temperature at the location of said first sensor.

9. The control system set forth in claim 8 including:

a circuit operable to receive a signal in response to selection of heat generation by said air conditioning system for causing said motor to run at a minimum speed to provide air circulation at said first sensor and at least one of said second and third sensors.

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 ramp circuit for producing a variable voltage output signal dependent on the difference in temperatures sensed by said first and second sensors;

a circuit connected to said ramp circuit and to a power output circuit for varying the speed of said motor as a function of the output signal of said ramp circuit and in accordance with 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 operably connected to said ramp circuit 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.

11. The control system set forth in claim 10 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.

12. The control system set forth in claim 10 including:

a cutoff circuit operable when a ramp voltage signal decreases to a predetermined value to cause said power output circuit to deenergize said motor.

13. The control system set forth in claim 12 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.

14. The control system set forth in claim 10 including:

a sensor protection circuit operably connected to said ramp 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 ramp circuit exceeds a predetermined value.

15. The control system set forth in claim 10 including:

a third temperature sensor located downstream of a second heat exchanger of said air conditioning system for measuring the air temperature at the location of said third sensor compared with the air temperature at the location of said first sensor.

16. The control system set forth in claim 15 including:

a circuit operable to receive a signal in response to selection of heat generation by said air conditioning system for causing said motor to run at a minimum speed to provide air circulation at said first sensor and at least one of said second and third sensors.