Excess air control

• US 4,703,747 A
• Filed: 09/17/1986
• Issued: 11/03/1987
• Est. Priority Date: 09/17/1986
• Status: Expired due to Term

• Current Assignee: Carrier Corporation (Carrier Global Corporation)
• Original Assignee: Carrier Corporation (Carrier Global Corporation)
• Inventors: Thompson, Kevin D., Dempsey, Daniel J., Peitz, Robert W. Jr.
• Primary Examiner(s): Jones, Larry
• Application Number:
  US06/908,476
• Time in Patent Office: 412 Days
• Field of Search: 126/112, 431/2, 431/3, 431/6, 236/11, 236/15 C, 236/17, 236/DIG. 9, 236/DIG. 8, 165/16, 165/31
• US Class Current: 126/112
• CPC Class Codes: F23N 1/025 using electrical or electromechanical means
• CPC Class Codes: F23N 2227/04 Prepurge
• CPC Class Codes: F23N 2233/08 with variable speed
• CPC Class Codes: F23N 2233/10 forcing air through heat exchangers

Abstract

Method and apparatus for maintaining excess air control in a gas furnace. A pressure switch is placed across a heat exchanger to indicate when, while accelerating the inducer motor speed during purging operation, the pressure drop reaches a predetermined level. When that occurs, the motor speed is sensed and recorded. When the furnace is subsequently fired, the desired inducer motor speed is obtained by modifying the recorded motor speed on a correction factor derived from empirical data obtained from a gas furnace operating under selective variable conditions.

Claims

1. In a gas furnace of the type having a heat exchanger and a variable speed inducer motor, an improved method establishing a desired level of excess air comprising the steps of:

using empirical data obtained from a gas furnace operating under selective variable conditions, establishing a calibration factor for obtaining a desired excess air level for a furnace of nominal design characteristics;

providing a pressure switch that is responsive to a selected pressure drop level in the heat exchanger, said pressure drop level being selected so as to be commensurate with a theoretically desired excess air level under firing operating conditions;

accelerating the variable speed inducer motor until said pressure switch closes and recording the motor speed at that time; and

applying said calibration factor to said recorded motor speed to obtain a desired induced motor speed.

2. A method as set forth in claim 1 including the further step of maintaining said desired motor speed to obtain the desired level of excess air.

3. In a gas furnace of the type having a heat exchanger and variable speed inducer motor, apparatus for maintaining a desired excess air level during fired operating conditions comprising:

means for sensing when the pressure drop across the heat exchanger reaches a predetermined level while accelerating the inducer motor during purging operating conditions;

means for sensing and recording the actual inducer motor speed when said predetermined level is reached; and

means for calculating, as the function of said actual inducer motor speed and as the function of performance data experimentally obtained, a desired inducer motor speed for operation under fired operating conditions.

4. Apparatus as set forth in claim 3 wherein said predetermined level is that level which is commensurate with a theoretical desired excess air level under fired operating conditions.

5. Apparatus as set forth in claim 3 wherein said means for sensing and recording comprises a microprocessor.

6. In a gas furnace of the type having a heat exchanger and a variable speed inducer motor, a method for maintaining a desired excess air level comprising the steps of:

while accelerating the inducer motor during purging operation, sensing when pressure drop across the heat exchanger reaches a predetermined level;

sensing and recording the actual inducer motor speed when said predetermined level is reached; and

calculating as a function of said actual motor speed and as a function of performance data experimentally obtained, a desired inducer motor speed for operation under fired operating conditions.

7. A method as set forth in claim 6 wherein said predetermined level is determined as being commensurate with a theoretically desired excess air level under fired operating conditions.