System and method for combustion-air modulation of a gas-fired heating system

• US 20070238057A1
• Filed: 04/07/2006
• Published: 10/11/2007
• Est. Priority Date: 04/07/2006
• Status: Active Grant

• Current Assignee: Reznor LLC (Melrose Industries Plc)
• Original Assignee: Thomas & Betts International Incorporated (ABB Limited)
• Inventors: Specht, Werner
• Granted Patent: US 7,802,984 B2
• Time in Patent Office: Days
• US Class Current: 431/89
• CPC Class Codes: F23N 1/025 using electrical or electromechanical means
• CPC Class Codes: F23N 2005/185 using detectors sensitive to rate of flow of fuel
• CPC Class Codes: F23N 2221/10 Analysing fuel properties, e.g. density, calorific
• CPC Class Codes: F23N 2225/06 for determining flow
• CPC Class Codes: F23N 2225/08 temperature
• CPC Class Codes: F23N 3/082 using electronic means

Abstract

A system and method for providing a gas-fired heating system with improved thermal efficiency includes modulating a quantity of combustion air flow to a combustion mixture in response to a measured change in fuel-gas pressure using a DC (e.g., brushless) motor to drive a combustion air blower. A pressure transducer in a manifold transporting fuel-gas into the combustion mixture outputs a signal proportional to the measured pressure to the motor. The motor speed and thus the resultant quantity of combustion air flow are modulated in proportion to the quantity of fuel-gas to the mixture. Accordingly, a constant fuel-gas to combustion air ratio is maintained. The system and method may further provide for adjusting the output signal to accommodate measured intake air temperature, and/or measured atmospheric pressure in order to maintain a constant, good thermal efficiency (preferably ≦80%) regardless of air temperature and altitude at the system'"'"'s installation location.

Claims

1. A method for improving the thermal efficiency of a gas-fired heating system, the method comprising the step of:

modulating a quantity of combustion air flow into a combustion mixture in a gas-fired heating system in response to a measured change in fuel-gas pressure in an input manifold by an amount required to maintain a constant fuel-gas to combustion air ratio in said combustion mixture.

2. The method of claim 1, wherein said modulating comprises:

continuously measuring said fuel-gas pressure in said input manifold;

generating an electrical signal that is proportional to the measured fuel-gas pressure, wherein said electrical signal increases in response to an increase in the measured fuel-gas pressure; and

increasing the speed of a combustion air blower in response to an increase in said electrical signal thereby proportionately increasing the combustion air and fuel-gas in said combustion mixture.

3. The method of claim 2, wherein said modulating further comprises:

inputting said electrical signal to a motor for controlling said speed of said combustion air blower, wherein said speed varies linearly with said electrical signal.

4. The method of claim 3, wherein said motor is a brushless direct current motor.

5. The method of claim 1, further comprising:

varying a quantity of fuel-gas flow in response to a measured temperature differing from a temperature set point on a temperature regulator, said varying including at least partially closing a valve in said input manifold in response to said measured temperature increasing above said temperature set point, and at least partially opening said valve in response to said measured temperature decreasing below said temperature set point.

6. The method of claim 5, further comprising manually adjusting said temperature set point above or below said measured temperature.

7. The method of claim 1, further comprising:

generating said combustion air flow by pulling in outside air;

measuring the intake air temperature; and

readjusting the modulated quantity of combustion air flow to compensate for effects of the intake air temperature on maintaining said constant fuel-gas to combustion air ratio in said modulating step.

8. The method of claim 1, further comprising:

measuring the atmospheric pressure at an installation location of a gas-fired heating system; and

readjusting the modulated quantity of combustion air flow to compensate for effects of the atmospheric pressure on maintaining said constant fuel-gas to combustion air ratio in said modulating step.

9. The method of claim 1, further comprising providing a thermal efficiency of at least 80%.

10. A system for improving the thermal efficiency of a gas-fired heating system, the system comprising:

a burner for receiving a combustion mixture;

an input manifold for transporting a fuel-gas to said combustion mixture;

a pressure transducer for measuring the fuel-gas pressure in said input manifold;

a combustion blower for providing combustion air flow to said combustion mixture; and

a direct current motor operatively connected to said combustion blower and said pressure transducer for driving said combustion blower at a speed proportional to the measured fuel-gas pressure in said input manifold thereby maintaining a constant fuel-gas to combustion air ratio in said combustion mixture.

11. The system of claim 10, further comprising a motor control module, wherein said motor control module is operatively connected between said pressure transducer and said direct current motor, and wherein said motor control module outputs an electrical signal to said direct current motor in response to an input signal from said pressure transducer which is proportional to the measured fuel-gas pressure.

12. The system of claim 10, wherein the direct current motor is a brushless direct current motor.

13. The system of claim 10, further comprising:

a fuel-gas valve upstream of the pressure transducer; and

a temperature regulator comprising an adjustable temperature set point, wherein said fuel-gas valve is configured to vary a quantity of said fuel-gas transported to said combustion mixture such that a difference between a sensed temperature and said temperature set point is minimized.

14. The system of claim 11, wherein said motor control module comprises a temperature control module, the system further comprising a temperature sensing device for sensing the temperature of intake air into said combustion air blower, and wherein said output electrical signal is adjusted by said temperature control module in accordance with the sensed intake air temperature to maintain said constant fuel-gas to combustion air ratio in said combustion mixture.

15. The system of claim 10, wherein said constant fuel-gas to combustion air ratio provides a thermal efficiency of at least 80%.

16. The system of claim 11, wherein said motor control module comprises an atmospheric compensation module, the system further comprising a barometer for sensing atmospheric pressure, and wherein said output electrical signal is adjusted by said atmospheric compensation module in accordance with the sensed atmospheric pressure to maintain said constant fuel-gas to combustion air ratio in said combustion mixture.

17. The system of claim 10, wherein said pressure transducer comprises one or any combination of a solid-state sensor, a silicon-based sensor, a piezoelectric sensor, a Hall effect sensor, a micro electro mechanical systems sensor.

18. The system of claim 17, wherein said pressure transducer comprises a micro electro mechanical systems silicon-based sensor.

19. The system of claim 10, wherein said gas-fired heating system is one of a fuel-gas space heater or a make-up air heating system.

20. The system of claim 10, wherein said fuel-gas comprises one of a natural gas and a propane gas.