Apparatus and methods for variable furnace control

• US 20070003891A1
• Filed: 06/14/2006
• Published: 01/04/2007
• Est. Priority Date: 08/30/2002
• Status: Active Grant

• Current Assignee: Copeland Comfort Control LP (Emerson Electric Company)
• Original Assignee: Emerson Electric Company
• Inventors: Jaeschke, Horst
• Granted Patent: US 7,735,743 B2
• Time in Patent Office: Days
• US Class Current: 431/19
• CPC Class Codes: F23N 2225/04 pressure
• CPC Class Codes: F23N 2233/08 with variable speed
• CPC Class Codes: F23N 2235/14 electromagnetically operated
• CPC Class Codes: F23N 2235/18 Groups of two or more valves
• CPC Class Codes: F23N 3/08 by power-assisted systems
• CPC Class Codes: F23N 5/18 using detectors sensitive to rate of flow of air or fuel

Abstract

A furnace control system for controlling a gas-fired induced-draft furnace having a variable speed inducer blower. A control apparatus, responsive to a signal corresponding to the magnitude of a pressure difference between an inlet and outlet of the combustion chamber, controls blower motor speed to maintain the pressure difference at a predetermined magnitude corresponding to a selected gas flow rate. Inducer blower motor speed is varied directly and precisely to maintain an optimal pressure drop across the combustion chamber. The control system can be used in multi-stage and modulating furnace systems and in furnace systems utilizing pressure-assist modulating gas valves.

Claims

1. A furnace control system for controlling a gas-fired induced-draft furnace having a variable speed motor-driven inducer blower that draws combustion air through a combustion chamber and a variable-speed motor-driven circulator blower that draws heated air from a heat exchanger, the system comprising a control apparatus configured to select a flow rate of gas through a gas valve to the combustion chamber;

the control apparatus further configured to, responsive to a signal corresponding to temperature of air leaving the circulator blower and a signal corresponding to the magnitude of a pressure difference between an inlet and an outlet of the combustion chamber, control speeds of the blower motors to maintain the pressure difference at a predetermined magnitude corresponding to the selected gas flow rate.

2. The system of claim 1, wherein the control apparatus is further configured to keen the circulator blower motor at a stage-related default speed based on a status of a sensor providing the temperature signal.

3. The system of claim 1, wherein the control apparatus is further configured to interrupt gas flow when the pressure difference magnitude varies from the predetermined magnitude by more than a predetermined amount.

7. The system of claim 1, wherein the control apparatus is further configured to determine whether a gas valve of the furnace is electronically modulated or pressure-modulated.

8. The system of claim 1, wherein the predetermined pressure magnitude and the selected gas flow rate correspond to a heating stage of the furnace.

4-6. -6. (canceled)

9. (canceled)

10. A furnace control system for controlling a gas-fired induced-draft furnace having a variable speed motor-driven inducer blower that draws combustion air through a combustion chamber past a heat exchanger and a variable speed motor-driven circulation blower that circulates air heated via the heat exchanger, the system comprising:

a control apparatus configured to select a flow rate of gas through a gas valve to the combustion chamber;

a pressure sensing apparatus configured to sense a pressure difference between an inlet and an outlet of the combustion chamber and generate a signal indicating a magnitude of the pressure difference; and

a temperature sensing apparatus configured to sense temperature of heated air leaving the circulation blower and generate a signal indicating the sensed temperature;

wherein the control apparatus, responsive to the pressure difference magnitude signal and temperature signal, adjusts at least one of (a) the speed of the inducer blower motor to maintain the pressure difference at a predetermined magnitude corresponding to the selected gas flow rate and (b) the speed of the circulation blower motor to maintain the sensed temperature within a predetermined temperature range.

11. The system of claim 10, wherein the control apparatus is further configured to save the at least one adjusted speed for reuse upon a subsequent call for heat.

12. The system of claim 10, wherein the control apparatus is further configured to interrupt gas flow when the pressure difference magnitude varies from the predetermined magnitude by more than a predetermined amount.

16. The system of claim 10, wherein the control apparatus is further configured to determine whether a gas valve of the furnace is electronically modulated or pressure-modulated.

17. The system of claim 10, wherein the predetermined pressure magnitude and the selected gas flow rate correspond to a heating stage of the furnace.

18. The system of claim 17, wherein the adjusted speed of the circulation blower motor corresponds to the heating stage.

13-15. -15. (canceled)

19. A furnace control system for controlling a gas-fired induced-draft furnace having a variable speed motor-driven inducer blower that draws combustion air through a combustion chamber, and a variable speed motor-driven circulator blower that circulates air heated by a heat exchanger, the system comprising:

a control apparatus configured to select a flow rate of gas through a gas valve to the combustion chamber;

a pressure sensing apparatus configured to sense a pressure difference between an inlet and an outlet of the combustion chamber and generate a signal corresponding to a magnitude of the pressure difference; and

a temperature sensing apparatus configured to sense temperature of the air leaving the circulator blower;

the control apparatus further configured to, in response to a call for heat;

based on whether the call for heat was upon a power-up of the system, tart at least one of the blower motors using one of a default speed and a speed last utilized by the at least one of the motors; and

select a flow rate of gas associated with a stage with which the starting speed is associated.

20. The system of claim 19, wherein the control apparatus is further configured to, responsive to the pressure difference magnitude signal, control speed of the blower motor to maintain the pressure difference at a predetermined magnitude corresponding to the selected gas flow rate.

21. The system of claim 19, wherein the signal generated by the pressure sensing apparatus comprises an analog signal.

25. The system of claim 19, wherein the control apparatus is further configured to determine whether a gas valve of the furnace is electronically modulated or pressure-modulated.

26. The system of claim 19, wherein the stage is further associated with a predetermined pressure magnitude associated with the selected gas flow rate.

22-24. -24. (canceled)

27. (canceled)

28. A method for controlling a gas furnace having a burner box, a gas valve through which the flow of gas to the burner box is controlled, a motor-driven inducer blower for pulling combustion air through the burner box, and a heat exchanger through which return air is heated and drawn by a motor-driven circulator blower, said method comprising the steps of:

sensing the magnitude of a differential pressure between an inlet and outlet of the burner box, said step performed using a pressure sensing apparatus;

sensing a temperature change in the heated return air leaving the circulator blower; and

adjusting the inducer blower motor speed and adjusting the circulator blower motor speed based on the sensed temperature chance to maintain the differential pressure at a predetermined magnitude.

29. The method of claim 28 wherein the adjusting step comprises the steps of:

comparing the sensed differential pressure magnitude to the predetermined magnitude; and

varying a signal to the blower motor until the sensed differential pressure magnitude equals the predetermined magnitude.

30. The method of claim 28 wherein the predetermined magnitude corresponds to a selected flow rate of gas to the burner box.

31. The method of claim 28 further comprising the step of varying a gas flow rate responsive to a rate of change of return air temperature.

32. (canceled)