Furnace, a method for operating a furnace and a furnace controller configured for the same

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Solution Overview

Problem

Gas furnaces face downtime and service issues due to safety lock-outs when the low fire pressure switch fails to close under abnormal conditions, preventing adequate airflow and thus preventing operation.

Innovation Solution

A controller is introduced that enables the gas furnace to start at a low fire operation and, if the low fire pressure switch does not close, automatically switches to high fire ignition after a preset time, ensuring safe operation by attempting ignition at high fire and then reverting to low fire if conditions are met.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If the low fire pressure switch is used to prevent unsafe operation, then safety is improved, but the furnace operation reliability deteriorates under abnormal conditions

Engineering Contradiction:

Improvesafe operationVSAvoidfurnace operation availability

Core Design Contradiction:

ReliabilityVSProductivity

Solution Approach 1:

The controller performs preliminary actions by first attempting low fire operation and preparing the high fire pressure switch as a pre-arranged backup. When the low fire pressure switch fails to close, the system has already positioned itself to switch to high fire mode, eliminating downtime without compromising safety.

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

The system cushions against the failure of the low fire pressure switch by having the high fire pressure switch and high fire ignition system ready in advance. This backup arrangement ensures that if the primary safety mechanism fails, an alternative path is already prepared to maintain safe operation.

Inventive Principle:

Principle #11Beforehand cushioning (Prior cushioning)

2Reliability

If the furnace strictly requires the low fire pressure switch to close before ignition, then safety is improved, but the loss of time increases due to lock-out

Engineering Contradiction:

Improvesafe operationVSAvoiddowntime

Core Design Contradiction:

ReliabilityVSLoss of time

Solution Approach 1:

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

Instead of requiring the low fire pressure switch to close as the primary safety mechanism, the system inverts the approach by allowing high fire operation as the primary mode with the low fire mode as the alternative. This inversion maintains safety while eliminating the time loss associated with strict low fire switch requirements.

Inventive Principle:

Principle #13The other way round (Inversion)

3Use of energy by moving object

If the furnace operates only at low fire mode when low fire pressure switch closes, then energy efficiency is improved, but the adaptability deteriorates under abnormal conditions

Engineering Contradiction:

Improveenergy efficiencyVSAvoidoperation under abnormal conditions

Core Design Contradiction:

Use of energy by moving objectVSAdaptability or versatility

Solution Approach 1:

The system dynamically adjusts its operating mode based on the status of pressure switches. It starts with the energy-efficient low fire mode when conditions permit, but automatically transitions to high fire mode when the low fire pressure switch fails to close, maintaining adaptability while prioritizing energy efficiency under normal conditions.

Inventive Principle:

Principle #15Dynamics

Solution Approach 2:

The system changes the operating parameter (fire mode) from low fire to high fire based on the condition of the pressure switches. This parameter change allows the system to maintain energy efficiency under normal conditions while adapting to abnormal conditions when the low fire pressure switch fails.

Inventive Principle:

Principle #35Parameter changes

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

This solution reduces downtime and service calls by allowing safe startup of gas furnaces under abnormal conditions, ensuring reliable operation by safely managing airflow and ignition modes.

Implementation Method 1

The combustion air inducer is used to draw air through the heat exchangers of the gas furnace for combustion

Methodology Applied

Scientific EffectPressure difference: Pressure Gradient

Implementation Method 2

Once combustion air flow has been established, a pressure switch is closed. The pressure switch is a critical safety feature since, if adequate air flow through the heat exchangers is not established

Methodology Applied

Scientific EffectPressure sensing: Pressure Gradient

Implementation Method 3

Once the pressure switch closes to indicate adequate air flow through the heat exchangers, the igniter energizes, the gas valve opens and a flame sensor validates the presence of a flame

Methodology Applied

Scientific EffectCombustion: Combustion

Data Source

PatentUS9765965B2Furnace, a method for operating a furnace and a furnace controller configured for the same

Publication Date: 2017.09.19 LENNOX IND INC

AI summary

A controller for a gas furnace, a computer-usable medium for implementing a method and a gas furnace are disclosed herein. In one embodiment, the controller includes: (1) an interface configured to receive a heating call and (2) a processor configured to enable an inducer of the gas furnace at a low speed based on the heating call and ignite the gas furnace at a high fire operation when determining a low fire pressure switch of the gas furnace is open.