Gas-fired appliance and control algorithm for same
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Solution Overview
Problem
Gas-fired appliances operating in environments with contaminants like lint, dirt, and oil can experience incomplete combustion due to oxygen starvation, leading to carbon monoxide production, necessitating a system to monitor combustion chamber conditions and automatically shut down the appliance.
Innovation Solution
A controller with a temperature sensor and electronic processor in a gas-fired water heater that monitors temperature changes and compares them to predetermined thresholds to control the gas valve, shutting it down if the rate of change is below set thresholds to prevent incomplete combustion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the appliance operates in contaminated environments, then heating function is maintained, but incomplete combustion and carbon monoxide production occur due to oxygen starvation
Solution Approach 1:
The system performs preliminary monitoring of combustion chamber temperature at multiple predetermined times during the heating cycle. By detecting temperature changes before incomplete combustion occurs, the system can preemptively shut down the gas valve to prevent carbon monoxide production, rather than reacting after contamination has already caused harmful effects.
Solution Approach 2:
The system continuously monitors combustion chamber temperature and uses this feedback to determine whether the temperature change between predetermined times meets the required threshold. This feedback mechanism allows the system to adjust gas valve operation in real-time, shutting down when temperature changes indicate improper combustion conditions, thus preventing carbon monoxide generation while maintaining heating efficiency during normal operation.
2Reliability
If contaminants starve the combustion chamber of oxygen, then combustion efficiency decreases, but the system lacks automatic shutdown capability
Solution Approach 1:
The system uses its own temperature sensor and controller to automatically monitor combustion conditions and make shutdown decisions without external intervention. The controller compares temperature changes against predetermined thresholds and autonomously actuates the gas valve when incomplete combustion is detected, enabling the system to self-regulate and maintain reliability without requiring manual monitoring or external control systems.
3Reliability
If temperature monitoring is performed continuously, then combustion safety is improved, but system complexity and energy consumption increase
Solution Approach 1:
Instead of continuous monitoring, the system performs temperature measurements at multiple predetermined times during the heating cycle (such as at startup, mid-cycle, and near completion). This periodic sampling approach provides sufficient safety monitoring to detect incomplete combustion conditions while minimizing the complexity of the control system and reducing energy consumption compared to continuous real-time monitoring.
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
Effectively prevents incomplete combustion and carbon monoxide production by automatically shutting down the gas supply based on monitored temperature changes, ensuring safe operation in contaminated environments.
Implementation Method 1
a temperature sensor coupled to the combustion chamber, wherein the temperature sensor generating a signal related to the temperature of the combustion chamber
Implementation Method 2
a burner assembly disposed within the combustion chamber, wherein the burner assembly for providing a heat to the water tank
Data Source
AI summary
A gas-fired water heater including a water tank, a combustion chamber, a burner assembly disposed within the combustion chamber, a gas valve for controllably supplying gas to the burner assembly, a temperature sensor coupled to the combustion chamber, wherein the temperature sensor generating a signal related to the temperature of the combustion chamber, and a controller having an electronic processor and memory. The controller is configured to receive the signal at a first predetermined time and at a second predetermined time, calculate a change in temperature based on the signal received at the first predetermined time and the signal received at the second predetermined time, compare the change in temperature to a rate of change threshold to produce a first comparison, and shut the gas valve in response to the change in temperature being less than the rate of change threshold.