Furnace Inducer Speed Scaling for Stable Multi-Stage Pressure
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Solution Overview
Problem
Selecting proper inducer blower motor speeds for multistage combustion furnaces is challenging, particularly in maintaining inducer flow pressures above a setpoint at low firing rates to avoid undesirable combustion characteristics, and simplifying the learning of blower motor speeds across different firing rates.
Innovation Solution
A method where a default speed is set for the medium firing rate, and multiples of this speed are used to determine blower motor speeds for low and high firing rates, based on a linear relationship with flow resistance, allowing for proper furnace operation with various venting systems, and potentially using a single pressure switch or sensor.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If default speeds are set for all firing rates, then the learning process is simplified, but the pressure control precision deteriorates
Solution Approach 1:
The patent applies parameter changes by using multiples of the learned medium firing rate speed to determine low and high firing rate speeds. This mathematical transformation allows the system to simplify the learning process (only learning medium rate) while maintaining pressure control precision through the proportional relationship defined by the multiples.
2Use of energy by moving object
If inducer blower speed is reduced at low firing rates, then energy consumption is reduced, but combustion gas pressure drops causing premature valve closure
Solution Approach 1:
The patent uses parameter changes by establishing a proportional relationship between medium and low firing rate speeds through multiples. This allows the system to reduce inducer speed at low firing rates (saving energy) while maintaining sufficient pressure through the optimized multiple factor, preventing premature valve closure.
3Productivity
If inducer blower speed is increased at high firing rates, then combustion efficiency is improved, but system pressure becomes excessively high
Solution Approach 1:
The patent applies parameter changes by using multiples to scale the learned medium firing rate speed to high firing rate speeds. This mathematical relationship enables the system to increase inducer speed for improved combustion efficiency while controlling the pressure increase through the optimized multiple factor, preventing excessively high system pressure.
4Manufacturing precision
If learning algorithms are implemented for all firing rates, then speed optimization is improved, but device complexity increases
Solution Approach 1:
The patent uses parameter changes by transforming the speed determination problem into a mathematical scaling problem. Instead of implementing separate learning algorithms for each firing rate (which would increase complexity), the system learns only the medium rate and uses multiples to derive other rates, maintaining optimization precision while reducing complexity.
Data Source
AI summary
In a multistage combustion furnace having a motor driven inducer blower and a pressure sensing device or set of switches for sensing pressure in the combustion gas flowpath through the furnace, a high firing rate blower speed and low firing rate blower speed are set based on the blower speed setting required for a medium firing rate. Each particular furnace, having its own pressures and combustion gas resistance to flow characteristics, may be provided with a database of inducer blower motor speeds required to achieve predetermined pressures in the combustion gas flowpath for a variety of combustion gas venting systems generating such resistance.