System and method for controlling a furnace

• US 8,672,670 B2
• Filed: 11/11/2009
• Issued: 03/18/2014
• Est. Priority Date: 11/11/2009
• Status: Active Grant

• Current Assignee: Trane International Inc. (Trane Technologies plc)
• Original Assignee: Trane International Inc. (Trane Technologies plc)
• Inventors: Hugghins, Gordon Jeffrey
• Primary Examiner(s): McAllister, Steven B
• Assistant Examiner(s): MASHRUWALA, NIKHIL P
• Application Number:
  US12/616,271
• Publication Number:
  US 20110111352A1
• Time in Patent Office: 1,588 Days
• Field of Search: 431/20, 431/2, 431/12, 431/18, 126/116.A, 126/112, 236/15.R, 236/11, 621/81
• US Class Current: 431/2
• CPC Class Codes: F23N 1/002 using electronic means F23N1/04 - F23N1/10 take precedence
• CPC Class Codes: F23N 2005/182 Air flow switch
• CPC Class Codes: F23N 2225/04 pressure
• CPC Class Codes: F23N 2227/02 Starting or ignition cycles
• CPC Class Codes: F23N 2233/08 with variable speed
• CPC Class Codes: F23N 2237/10 High or low fire
• CPC Class Codes: F23N 2241/02 Space-heating
• CPC Class Codes: F23N 3/082 using electronic means
• CPC Class Codes: F23N 5/184 using electronic means
• CPC Class Codes: F23N 5/242 using electronic means
• CPC Class Codes: F24D 19/1084 for air heating systems
• CPC Class Codes: F24H 3/06 the air being kept separate from the heating medium, e.g. using forced circulation of air over radiators

Abstract

Controlling a modulating gas furnace by monitoring a differential pressure associated with the modulating gas furnace using a low pressure limit switch configured to actuate at a first pressure, an intermediate pressure limit switch configured to actuate at a second pressure, and a high pressure limit switch configured to actuate at a third pressure, the second pressure being between the first and third pressure, selectively operating the modulating gas furnace in one of a cycling mode, a modulating mode in a lower range, and a modulating mode in an upper range, the modulating mode in the lower range being associated with an output capacity range between the output capacity ranges of the cycling mode and the modulating mode in the upper range, and selectively operating the furnace in response to at least one of the low pressure limit switch, the intermediate pressure limit switch, and the high pressure limit switch.

Claims

1. A method of controlling a modulating gas furnace, comprising:

monitoring a differential pressure associated with the modulating gas furnace using a low pressure limit switch configured to actuate at a first pressure, an intermediate pressure limit switch configured to actuate at a second pressure, and a high pressure limit switch configured to actuate at a third pressure, wherein the second pressure is between the first pressure and the third pressure;

selectively operating the modulating gas furnace in one of a cycling mode, a modulating mode in a lower range, and a modulating mode in an upper range, the modulating mode in the lower range being associated with an output capacity range between the output capacity ranges of the cycling mode and the modulating mode in the upper range, wherein the modulating gas furnace is configured to selectively maintain steady state operation at a plurality of firing rates within at least one of the modulating mode in the lower range and the modulating mode in the upper range; and

selectively operating the modulating gas furnace in response to at least one of the low pressure limit switch, the intermediate pressure limit switch, and the high pressure limit switch.

2. The method according to claim 1, wherein while the modulating gas furnace is operated in the cycling mode, the modulating gas furnace is operated in response to the low pressure limit switch but not in response to the intermediate pressure limit switch and not in response to the high pressure limit switch.

3. The method according to claim 1, wherein while the modulating gas furnace is operated in the modulating mode in the lower range, the modulating gas furnace is operated in response to the low pressure limit switch and in response to the intermediate pressure limit switch, but not in response to the high pressure limit switch.

4. The method according to claim 1, wherein while the modulating gas furnace is operated in the modulating mode in the upper range, the modulating gas furnace is operated in response to each of the low pressure limit switch, the intermediate pressure limit switch, and the high pressure limit switch.

5. The method according to claim 1, further comprising:

operating the modulating gas furnace in the modulating mode in the lower range to establish an operating curve for the modulating mode in the lower range;

wherein while the modulating gas furnace is operated in the modulating mode in the lower range to establish an operating curve for the modulating mode in the lower range, the modulating gas furnace is operated in response to the low pressure limit switch and the intermediate pressure limit switch but not in response to the high pressure limit switch.

6. The method according to claim 1, further comprising:

operating the modulating gas furnace in the modulating mode in the upper range to establish an operating curve for the modulating mode in the upper range;

wherein while the modulating gas furnace is operated in the modulating mode in the upper range to establish an operating curve for the modulating mode in the upper range, the modulating gas furnace is operated in response to the low pressure limit switch and the high pressure limit switch but not in response to the intermediate pressure limit switch.

7. The method according to claim 1, wherein beginning operation in one or more of the first stage, the modulating mode in the lower range, and the modulating mode in the upper range comprises performing an ignition sequence and wherein the ignition sequence is not performed while any one of the low pressure limit switch, intermediate pressure limit switch, and high pressure limit switch are open.

8. The method according to claim 1, wherein if during operation of the modulating gas furnace in the cycling mode the low pressure limit switch is not closed, a draft blower speed is increased.

9. The method according to claim 8, wherein if the draft blower speed is increased above a maximum draft blower speed for the cycling mode, the furnace cycle is interrupted.

10. The method according to claim 1, wherein if during operation of the modulating gas furnace to establish an operating curve in the modulating mode in the lower range at least one of the low pressure limit switch and the intermediate pressure limit switch is not closed, a draft blower speed is increased.

11. The method according to claim 10, wherein if the draft blower speed is increased above a maximum draft blower speed for the modulating mode in the lower range, the furnace cycle is interrupted.

12. The method according to claim 1, wherein if during operation of the modulating gas furnace to establish an operating curve in the modulating mode in the upper range at least one of the low pressure limit switch, the intermediate pressure limit switch, and the high pressure limit switch is not closed, a draft blower speed is increased.

13. The method according to claim 12, wherein if the draft blower speed is increased above a maximum draft blower speed for the modulating mode in the upper range, the furnace cycle is interrupted.

14. The method according to claim 1, wherein if during operation of the modulating gas furnace in the cycling mode the low pressure limit switch is not closed, a communication is checked.

15. The method according to claim 14, wherein if the communication is lost but later restored with a predetermined time period, the modulating gas furnace continues operation in the cycling mode.

16. The method according to claim 1, wherein if during operation of the modulating gas furnace in the modulating mode in the lower range the intermediate pressure limit switch is not closed, a communication is checked.

17. The method according to claim 16, wherein if the communication is lost but later restored with a predetermined time period, the modulating gas furnace continues operation in the modulating mode in the lower range.

18. The method according to claim 1, wherein if during operation of the modulating gas furnace in the modulating mode in the upper range the high pressure limit switch is not closed, a communication is checked.

19. The method according to claim 18, wherein if the communication is lost but later restored with a predetermined time period, the modulating gas furnace continues operation in the modulating mode in the upper range.