Flow sensor furnace control

• US 4,708,636 A
• Filed: 10/10/1985
• Issued: 11/24/1987
• Est. Priority Date: 07/08/1983
• Status: Expired due to Fees

• Current Assignee: Honeywell Incorporated (Honeywell International Inc.)
• Original Assignee: Honeywell Incorporated (Honeywell International Inc.)
• Inventors: Johnson, Robert G.
• Primary Examiner(s): Scott, Samuel
• Assistant Examiner(s): Odar, H. A.
• Application Number:
  US06/786,188
• Time in Patent Office: 775 Days
• Field of Search: 431/12, 431/18, 431/19, 431/20, 431/75, 431/84, 431/90, 126/285 B, 126/110 R, 236/15 C, 236/15 B D, 236/25 R, 236/25 A
• US Class Current: 431/20
• CPC Class Codes: F23N 1/02 conjointly with air supply
• CPC Class Codes: F23N 2225/08 temperature
• CPC Class Codes: F23N 2233/04 with variable speed
• CPC Class Codes: F23N 2233/06 at the air intake
• CPC Class Codes: F23N 2233/10 forcing air through heat exchangers
• CPC Class Codes: F23N 5/18 using detectors sensitive to rate of flow of air or fuel

Abstract

Disclosed is a heating system having a combustion air blower, a fuel valve for providing fuel to a burner, and an exhaust stack for exhausting combustion products. Also disclosed is flow sensor apparatus operatively associated with the stack for providing control signals to a furnace control, the control signals being related to flow conditions in the stack.

Claims

1. In a heating system having a combustion chamber with a fuel burner, an induced draft air blower, a control system including an electrically controlled fuel valve for controlling a supply of fuel to the burner, and an exhaust stack for exhausting combustion products, the improvement comprising:

means enabling a dynamic flow between the interior of the exhaust stack and the external ambient atmosphere including a flowmeter housing connected between an opening provided in the wall of the exhaust stack and the external ambient atmosphere, said housing having a single internal chamber having a first opening connected to the opening in the wall of the exhaust stack and having a second opening connected to the external ambient atmosphere;

an electronic flowmeter disposed in said single internal chamber for directly sensing the rate and direction of flow through the chamber and producing electrical output signals indicative thereof;

means connecting said electronic flowmeter output signals with said fuel valve, wherein said signals are used to control said fuel valve when predetermined conditions are indicated.

2. The apparatus of claim 1 further comprising means disposed in said exhaust stack and fixed in spaced relation to said opening in the wall of said exhaust stack to dynamically cause a reduction in the static internal stack pressure at said opening.

3. The apparatus of claim 2 wherein said means for reducing the internal stack pressure is a venturi.

4. The apparatus of claim 2 wherein said means for reducing the internal stack pressure is a deflector member fixed in angular spaced relation to said opening.

5. The apparatus of claim 1 wherein the fuel valve comprises means for permitting fuel flow to the burner under predetermined flow conditions sensed by the flow sensor and for prohibiting fuel flow to the burner under other predetermined flow conditions responsive to said output signals produced by the flow sensor.

6. The apparatus of claim 5 wherein fuel flow to the burner is prohibited when said output signals indicate a condition of abnormally low inward flow or flow outward from said stack.

7. The apparatus of claim 1 wherein the fuel valve comprises means for modulating the flow rate of fuel to the burner is response to said output signals when said output signals are indicatve of a flow rate sensed by the flow sensor within a predetermined range.

14. The apparatus of claim 6 comprising means for preventing intermittent backflow conditions from causing the flow sensor to indicate flow from the stack interior to the stack exterior due to momentary turbulence effects in the stack.

8. In a heating system having a combustion chamber with a fuel burner, an induced air blower, a control system including an electrically controlled fuel valve for controlling a supply of fuel to the burner, and an exhaust stack for exhausting combustion products, the improvement comprising:

means enabling a dynamic flow between the interior of the exhaust stack and the external ambient atmosphere including a flowmeter housing connected between an opening provided in the wall of the exhaust stack and the external ambient atmosphere, said housing having a single internal chamber having a first opening connected to the opening in the wall of the exhaust stack and having a second opening connected to the external ambient atmosphere;

an electronic flowmeter disposed in said single internal chamber for directly sensing the rate and direction of flow through the chamber and producing electrical output signals indicative thereof;

conductor means connecting said electronic flowmeter output signals with said fuel valve, wherein said signals are used to control said fuel valve when predetermined conditions are indicated; and

means disposed in said exhaust stack and fixed in spaced relation to said opening in the wall of said exhaust stack to dynamically reduce the static internal stack pressure at said opening.

9. The apparatus of claim 8 wherein said means for reducing the internal stack pressure is a venturi.

10. The apparatus of claim 8 wherein said means for reducing the internal stack pressure is a flow deflector plate member fixed in angular spaced relation to said opening.

11. The apparatus of claim 8 wherein the fuel valve comprises means for permitting fuel flow to the burner under predetermined flow conditions sensed by the flow sensor and for prohibiting fuel to the burner under other predetermined flow conditions responsive to said output signals produced by the flow sensor.

12. The apparatus of claim 8 wherein the fuel valve comprises means for modulating the flow rate of fuel to the burner responsive to flowmeter output signals indicative of the flow rate sensed by the flow sensor within a predetermined range.

13. The apparatus of claim 11 wherein fuel flow to the burner is prohibited responsive to flowmeter output signals indicating a low flow condition or flow outward from said stack.

15. The apparatus of claim 13 comprising means for preventing intermittent backflow conditions from causing the flow sensor to indicate flow from the stack interior to the stack exterior due to momentary turbulence effects in the stack.

16. In a heating system having a combustion chamber with a fuel burner, an induced draft air blower, a control system including an electrically controlled fuel valve for controlling a supply of fuel to the burner, and an exhaust stack for exhausting combustion products, the improvement comprising:

means enabling a dynamic flow between the interior of the exhaust stack and the external ambient atmosphere including a flowmeter housing connected between an opening provided in the wall of the exhaust stack and the external ambient atmosphere, said housing having a single internal chamber having a first opening connected to the opening in the wall of the exhaust stack and having a second opening connected to the external ambient atmosphere;

an electronic flowmeter disposed in said chamber for directly sensing the rate and direction of flow through said chamber and producing electrical output signals indicative thereof, said flowmeter comprising;

a thin film heater suspended in air; and

a pair of thin film heat sensors suspended in air and disposed on opposite sides of the heater; and

means connecting said electronic flowmeter output signals with said fuel valve, wherein said signals are used to control said fuel valve when predetermined conditions are indicated.

17. The apparatus of claim 16 further comprising means disposed in said exhaust stack and fixed in spaced relation to said opening in the wall of said exhaust stack to dynamically cause a reduction in the static internal stack pressure at said opening.

18. The apparatus of claim 17 wherein said means for reducing the internal stack pressure is a venturi.

19. The apparatus of claim 17 wherein said means for reducing the internal stack pressure is a deflector member fixed in angular spaced relation to said opening.

20. The apparatus of claim 16 wherein the fuel valve comprises means for permitting the fuel flow to the burner under predetermined flow conditions sensed by the flow sensor and for prohibiting fuel flow to the burner under other predetermined flow conditions responsive to said output signals produced by the flow sensor.

21. The apparatus of claim 16 wherein the fuel valve comprises means for modulating the flow rate of fuel to the burner in response to said output signals when said output signals are indicative of a flow rate sensed by the flow sensor within a predetermined range.

22. In a heating system having a combustion chamber with a fuel burner, an induced air blower, a control system including an electrically controlled fuel valve for controlling a supply of fuel to the burner, and an exhaust stack for exhausting combustion products, the improvement comprising:

means enabling a dynamic flow between the interior of the exhaust stack and the external ambient atmosphere including a flowmeter housing connected between an opening provided in the wall of the exhaust stack and the external ambient atmosphere, said housing having a single internal chamber having a first opening connected to the opening in the wall of the exhaust stack and having a second opening connected to the external ambient atmosphere;

an electronic flowmeter disposed in said chamber for directly sensing the rate and direction of flow through said chamber and producing electrical output signals indicative thereof, said flowmeter comprising;

a thin film heater suspended in air; and

a pair of thin film heat sensors suspended in air and disposed on opposite sides of the heater;

conductor means connecting said electronic flowmeter output signals with said fuel valve, wherein said signals are used to control said fuel valve when predetermined conditions are indicated; and

means disposed in said exhaust stack and fixed in spaced relation to said opening in the wall of said exhaust stack to dynamically reduce the static internal stack pressure at said opening.

23. The apparatus of claim 22 wherein said means for reducing the internal stack pressure is a venturi.

24. The apparatus of claim 22 wherein said means for reducing the internal stack pressure is a flow deflector plate member fixed in angular spaced relation to said opening.

25. The apparatus of claim 22 wherein the fuel valve comprises means for permitting fuel flow to the burner under predetermined flow conditions sensed by the flow sensor and for prohibiting fuel flow to the burner under other predetermined flow conditions responsive to said output signals produced by the flow sensor.

26. The apparatus of claim 22 wherein the fuel valve comprises means for modulating the flow rate of fuel to the burner responsive to flowmeter output signals indicative of the flow rate sensed by the flow sensor within a predetermined range.

27. The apparatus of claim 26 wherein fuel flow to the burner is prohibited responsive to flowmeter output signals indicating a low flow condition or flow outward from said stack.