Electric Water Heater Pulse Testing for Dry Fire Detection

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Solution Overview

Problem

Electric water heaters often suffer from 'dry firing' where the heating elements are energized before the tank is filled with water, leading to premature failure and substantial repair costs, necessitating a solution to prevent this damage.

Innovation Solution

A pulsed electrical power-based dry fire protection system that measures current flow through the heating element using a signal conditioning circuit and microcontroller to detect and prevent dry firing by comparing average current values against a threshold, activating an alarm and preventing energization if a dry fire condition is detected.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If traditional continuous test firing is used to detect dry fire conditions, then detection reliability is improved, but energy consumption and heating element exposure time to potential damage increase

Engineering Contradiction:

Improvedry fire detection reliabilityVSAvoidenergy consumption during testing

Core Design Contradiction:

ReliabilityVSUse of energy by moving object

Solution Approach 1:

The patent implements periodic pulsed testing instead of continuous test firing. The microcontroller applies test voltage in short pulses at predetermined intervals, measuring current flow during each pulse. This periodic approach maintains detection reliability while significantly reducing energy consumption and exposure time compared to continuous testing methods.

Inventive Principle:

Principle #19Periodic action

Solution Approach 2:

The system performs preliminary pulsed testing before allowing continuous operation. By conducting brief test pulses first and evaluating the current flow characteristics, the system determines whether the heating element is properly immersed in water before committing to sustained operation, preventing energy waste on dry-fired elements.

Inventive Principle:

Principle #10Preliminary action

2Use of energy by moving object

If pulsed testing with short duration is used, then energy consumption is reduced, but measurement precision may deteriorate

Engineering Contradiction:

Improveenergy consumption during testingVSAvoidcurrent flow measurement accuracy

Core Design Contradiction:

Use of energy by moving objectVSMeasurement precision

Solution Approach 1:

The microcontroller measures current flow during each test pulse and uses this feedback to determine whether the heating element is properly immersed. The system continuously monitors current characteristics and compares them against threshold values, adjusting operation based on the measured feedback to maintain measurement precision despite short pulse durations.

Inventive Principle:

Principle #23Feedback

Solution Approach 2:

The patent replaces traditional mechanical continuous testing with an electronic pulsed measurement system. By using a microcontroller to generate precise test pulses and measure resulting current flow electronically, the system achieves accurate measurements with minimal energy input, substituting mechanical continuity with electronic precision.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

3Reliability

If multiple test pulses are applied to ensure accurate detection, then detection reliability is improved, but device complexity increases

Engineering Contradiction:

Improvedry fire detection reliabilityVSAvoidcontrol circuit complexity

Core Design Contradiction:

ReliabilityVSDevice complexity

Solution Approach 1:

The microcontroller serves multiple functions: generating test pulses, measuring current flow, determining immersion status, controlling relay operation, and managing alarm signals. By consolidating these diverse functions into a single microcontroller unit, the system achieves high detection reliability through multiple test pulses without proportionally increasing overall device complexity.

Inventive Principle:

Principle #6Universality (Multi-functionality)

Solution Approach 2:

The patent combines the test pulse generation, current measurement, decision logic, and control functions into an integrated microcontroller-based system. This merging of functions allows the system to perform multiple test pulses and complex evaluations while maintaining relatively simple overall device architecture compared to using separate dedicated circuits for each function.

Inventive Principle:

Principle #5Merging (Combining)

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 dry firing of electric water heater heating elements, reducing warranty costs and repair frequencies by accurately distinguishing between wet and dry fire conditions without requiring sustained test firing, ensuring reliable operation.

Implementation Method 1

electric resistance type heating element(s)

Methodology Applied

Scientific EffectJoule heating: Joule Heating

Data Source

PatentUS9377342B2Pulsed power-based dry fire protection for electric water heaters

Publication Date: 2016.06.28 RHEEM MFG CO

AI summary

A water heater having an electric heating element therein is provided with apparatus for preventing dry firing of the heating element. The apparatus is operative to (1) power the heating element with electrical test pulses having first predetermined durations and being separated by rest periods of second predetermined durations during which the heating element is depowered, (2) determine the average electrical current flow through the element during each of the test pulses, and (3) preclude energization of the heating element if the average current flow therethrough during an electrical test pulse subsequent to the first test pulse is less by a predetermined magnitude than the average electrical current flow through the heating element during the first electrical test pulse.