Combustion Blower Control Using Pressure Switch Calibration
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Solution Overview
Problem
Modulating furnaces require accurate calibration of combustion blower speed to match firing rates, which is a time-consuming and tedious process, affecting fuel efficiency and occupant comfort.
Innovation Solution
Incorporating pressure switches and a controller to dynamically adjust combustion blower speed, using interpolation and extrapolation to derive operating points, and temporarily adjusting speed to ensure safe operation during minor changes in conditions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If manual calibration of combustion blower speed is performed to match firing rates, then accurate control is achieved, but calibration time increases
Solution Approach 1:
The system performs self-calibration by automatically detecting pressure switch state changes at different blower speeds and deriving operating points without requiring installer intervention. The controller autonomously executes the calibration sequence, eliminating the time-consuming manual process while maintaining accuracy.
Solution Approach 2:
The patent replaces manual mechanical calibration procedures with an automated electronic control system. The controller electronically monitors pressure switch states and calculates blower speeds, substituting the manual mechanical adjustment process with an automated electronic measurement and calculation system.
2Measurement precision
If combustion blower speed is manually calibrated during installation and maintenance, then accurate firing rate control is achieved, but the process becomes tedious
Solution Approach 1:
The system performs self-calibration by automatically detecting pressure switch state changes at different blower speeds and deriving operating points without requiring installer intervention. The controller autonomously executes the calibration sequence, eliminating the time-consuming manual process while maintaining accuracy.
Solution Approach 2:
The system changes the calibration approach from manual parameter setting to automatic parameter detection. By monitoring pressure switch state changes and deriving blower speeds from these events, the system automatically determines the operating parameters without requiring manual input or adjustment by the installer.
3Loss of time
If pressure switches are used to derive combustion blower operating points, then calibration time is reduced, but system complexity increases
Solution Approach 1:
The pressure switches serve as intermediaries between the physical blower system and the electronic controller. These switches detect pressure state changes caused by varying blower speeds and provide electrical signals to the controller, which then calculates the corresponding operating points. This intermediary approach enables automated calibration without requiring complex sensors or measurement systems.
Solution Approach 2:
The patent replaces manual mechanical calibration procedures with an automated electronic control system. The controller electronically monitors pressure switch states and calculates blower speeds, substituting the manual mechanical adjustment process with an automated electronic measurement and calculation system.
4Loss of energy
If combustion blower speed is directly proportional to firing rate for efficient operation, then fuel efficiency improves, but calibration precision requirements increase
Solution Approach 1:
The system uses feedback from pressure switch state changes to verify and adjust the relationship between blower speed and firing rate. By monitoring when pressure switches change state at different blower speeds, the controller receives feedback that confirms whether the proportional relationship is accurate, allowing for automatic calibration to maintain fuel efficiency.
Solution Approach 2:
The system changes the calibration approach from manual parameter setting to automatic parameter detection. By monitoring pressure switch state changes and deriving blower speeds from these events, the system automatically determines the operating parameters without requiring manual input or adjustment by the installer.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
Improves combustion gas flow control, reduces calibration time, and ensures efficient and safe furnace operation by accurately matching blower speed with firing rates.
Implementation Method 1
a combustion blower and one or more pressure switches with known pressure switch points
Implementation Method 2
a combustion blower is provided to pull combustion air into the burner, pull the combustion gases through the heat exchanger into the collector box, and to push the combustion gases out the vent
Implementation Method 3
a circulating air blower typically forces return air from the building, and in some cases ventilation air from outside of the building, over or through the heat exchanger, thereby heating the air
Implementation Method 4
a furnace employs a burner that burns a fuel such as natural gas, propane, oil or the like, and provides heated combustion gases to the interior of a heat exchanger
Data Source
AI summary
A furnace includes a combustion blower and one or more pressure switches. In some cases, the one or more pressure switches may be used to calculate one or more operating points for the combustion blower. Additional operating points may be calculated by interpolation and/or extrapolation, as appropriate. The furnace may temporarily alter these operating points as necessary to keep the furnace safely operating in response to minor and/or transient changes in the operating conditions of the furnace.