Adaptive microprocessor control system and method for providing high and low heating modes in a furnace

• US 5,340,028 A
• Filed: 07/12/1993
• Issued: 08/23/1994
• Est. Priority Date: 07/12/1993
• Status: Expired due to Term

• Current Assignee: Carrier Corporation (Carrier Global Corporation)
• Original Assignee: Carrier Corporation (Carrier Global Corporation)
• Inventors: Thompson, Kevin D.
• Primary Examiner(s): Tanner, Harry B.
• Application Number:
  US08/090,340
• Time in Patent Office: 407 Days
• Field of Search: 236/10, 236/11, 236/1 E, 236/1 EA, 236/1 EB, 236/46 R, 236/46 E, 236/46 F, 236/15 BG, 236/9 R
• US Class Current: 236/10
• CPC Class Codes: F23N 1/002 using electronic means F23N1/04 - F23N1/10 take precedence
• CPC Class Codes: F23N 2223/08 Microprocessor; Microcomputer
• CPC Class Codes: F23N 2225/04 pressure
• CPC Class Codes: F23N 2233/04 with variable speed
• CPC Class Codes: F23N 2233/08 with variable speed
• CPC Class Codes: F23N 2235/14 electromagnetically operated
• CPC Class Codes: F23N 2237/10 High or low fire
• CPC Class Codes: F23N 5/20 with a time programme acting through electrical means, e.g. using time-delay relays
• CPC Class Codes: G05D 23/1917 using digital means

Abstract

A method for providing a low fire mode and a high fire mode of a heating cycle in a current cycle of a furnace as a function of the previous heating cycle wherein the current heating cycle is a function exclusively of time run in low fire mode and time run in high fire mode of the previous heating cycle, comprising the steps of: (1) determining the existence of a heating load to be satisfied; (2) running burners in low fire mode for a first time interval that does not exceed a predetermined limit, L_des ; (3) running the burners in high fire mode for a second time interval until the heating load is satisfied; (4) calculating a BtU load requirement, as a function of the first time interval and the second time interval; and (5) determining the desired low fire mode time limit, L_des, for the next cycle from the calculated BtU load requirement.

Claims

1. A method for providing a low fire mode and a high fire mode of a heating cycle in a current cycle of a furnace as a function of the previous heating cycle wherein the current heating cycle is a function exclusively of time run in the low fire mode and time run in the high fire mode of said previous heating cycle, comprising the steps of:

determining an existence of a heating load to be satisfied;

running burners in said low fire mode for a first time interval that does not exceed a predetermined limit, L_des ;

running the burners in said high fire mode for a second time interval until the heating load is satisfied;

calculating a Btu load requirement, as a function of said first time interval and said second time interval; and

predetermining the low fire mode time limit, L_des, for a next cycle from the calculated Btu load requirement.

2. The method of claim 1, further comprising the steps of:

determining if the heating load is satisfied while the burners are operating in low fire mode;

if the heating load is satisfied, terminating the low fire mode; and

if the heating load is satisfied in low fire mode, aborting initiation of operation in high fire mode.

3. The method of claim 1 where determining the existence of a heating load to be satisfied is performed by a single-stage thermostat.

4. The method of claim 1 where the Btu load requirement (DH) to satisfy a call for heat is calculated as:

space="preserve" listing-type="equation">DH=(228×

LFT)+(350×

HFT)

where;

228 represents low fire output per cell in Btu/min, 333 represents high fire output per cell in Btu/min, LFT is the first time interval, in minutes, and HFT is the second interval, in minutes, and

space="preserve" listing-type="equation">L.sub.des =(5600-DH)/122.

5. A method for providing a low fire mode and a high fire mode of a heating cycle in a furnace as a function of previous heating cycles comprising the steps of:

determining the existence of a heating load to be satisfied;

running burners in the high fire mode only for at least two cycles;

determining from the heating load of at least two previous cycles, whether the burners should be run in low fire mode for each subsequent cycle; and

running the burners in low fire mode if it is determined that said burners should run in low fire mode.

6. The method of claim 5 further comprising, after determining the existence of a heating load to be satisfied, the steps of:

initiating the burners in high fire mode;

providing the high fire mode for a predetermined period of time;

terminating the high fire mode if the heating load is satisfied during the predetermined period of time.

7. The method of claim 6 wherein the predetermined period of time is one minute.

8. The method of claim 5 wherein, if running the burners in low fire mode does not satisfy the heating load prior to having a first Btu load requirement reach a predetermined figure, the furnace is subjected to a shutdown and restart procedure.

9. The method of claim 8 wherein said predetermined figure for said first Btu load requirement is 6,945 Btu.

10. The method of claim 5 wherein the burners are run in low fire mode upon meeting a second Btu load requirement wherein:

an actual Btu load requirement has been below a lower predetermined Btu load requirement for at least a first and a second cycle; and

the actual Btu load requirement has remained below an upper predetermined Btu load requirement for all cycles between said first cycle and said second cycle; and

the actual Btu load requirement has remained below said upper predetermined Btu load requirement for all cycles subsequent to said second cycle.

11. The method of claim 10 wherein said lower predetermined Btu load requirement is 3,525 Btu and said upper predetermined Btu load requirement is 4,665 Btu.

12. The method of claim 5 wherein the actual Btu load requirement for a current cycle (Q_i+1), is calculated as:

Q.sub.(i+1) =Q_i +dQ;

where;

space="preserve" listing-type="equation">Q.sub.i =(350×

HFT)+(228×

LFT);

where;

228 represents low fire output per cell in BtU/min,

350 represents high fire output per cell in BtU/min, LFT is a time interval in minutes, spent in low fire mode during a most recent cycle, HFT is a time interval in minutes, spent in high fire mode during the most recent cycle; and

space="preserve" listing-type="equation">dQ=Q.sub.i -Q.sub.(i-1)

where dQ is a change in BtU load requirement from a next most recent cycle to the most recent cycle.

13. The method of claim 5 wherein, if running the burners does not satisfy the heating load prior to a predetermined elapsed time, the furnace is subjected to a shutdown and restart procedure.

14. The method of claim 13 wherein said predetermined elapsed time is 30 minutes.