Modulating Furnace Inducer RPM Control Without Pressure Transducers

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Solution Overview

Problem

Existing modulating furnaces face challenges in smoothly controlling the inducer speed over a range of heating capacities without requiring additional components like pressure transducers.

Innovation Solution

A method and system that control the RPM of the inducer motor based on a modulation percentage, using a microprocessor-based controller to adjust the inducer motor speed in response to varying heat demands across different operating capacities.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Ease of operation

If traditional inducer control methods are used in modulating furnaces, then the furnace can operate at different heating capacities, but the inducer speed transition is not smooth and requires additional components like pressure transducers

Engineering Contradiction:

Improvesmooth transition of inducer speedVSAvoidadditional components such as pressure transducers

Core Design Contradiction:

Ease of operationVSDevice complexity

Solution Approach 1:

The patent removes the pressure transducer component from the system by extracting the pressure measurement function and replacing it with a modulation percentage-based control algorithm that calculates the required inducer speed directly from the desired heating capacity percentage

Inventive Principle:

Principle #2Taking out (Extraction)

Solution Approach 2:

The control system achieves multiple functions using a single parameter (modulation percentage): it simultaneously determines the inducer speed, gas valve position, and blower speed, eliminating the need for separate pressure sensing and multiple control mechanisms

Inventive Principle:

Principle #6Universality (Multi-functionality)

2Adaptability or versatility

If the inducer speed is controlled over a range of operating capacities, then the furnace can meet varying heat demand efficiently, but the control of inducer becomes challenging without additional sensors

Engineering Contradiction:

Improveoperation across different heating capacitiesVSAvoidcontrol system complexity

Core Design Contradiction:

Adaptability or versatilityVSDevice complexity

Solution Approach 1:

The patent changes the control parameter from physical pressure measurement to modulation percentage, allowing the system to adapt to different heating capacities through a simple percentage-based parameter that directly correlates with required inducer speed

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The control system uses feedback from the modulation percentage (determined by heat demand) to continuously adjust the inducer motor RPM, creating a closed-loop control system that adapts to varying operating conditions without additional sensors

Inventive Principle:

Principle #23Feedback

Data Source

PatentUS8925541B2Method and system for controlling an inducer in a modulating furnace

Publication Date: 2015.01.06 CARRIER CORP

AI summary

A furnace includes an induced draft blower; an inducer motor driving the induced draft blower; and a furnace control determining a modulation percentage, the furnace control controlling RPM of the inducer motor in response to the modulation percentage.