Electric Water Heater Element Cycling for Dry-Fire Detection
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Solution Overview
Problem
Electric water heaters risk overheating and damage due to 'dry firing' when their heating elements are energized before the tank is filled with water, and existing solutions like float switch-based and temperature sensor-based systems are either complex or unreliable, especially with polymer tank materials.
Innovation Solution
A system that uses a temperature sensor and controller to intermittently actuate the heating element, maintaining it below a maximum temperature and ensuring it provides a measurable energy contribution when immersed in water, while preventing overheating by disabling the element if the temperature exceeds a predetermined increment.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If float switch-based protective systems are used to prevent dry firing, then heating element protection is improved, but device complexity and cost increase
Solution Approach 1:
The patent extracts the temperature sensing function from a separate float switch mechanism and integrates it directly into the heating element assembly. The temperature sensor is positioned to sense the temperature of the heating element itself or its immediate surroundings, eliminating the need for float switches and their associated mechanical linkages. This reduces device complexity while maintaining heating element protection.
Solution Approach 2:
The patent introduces a temperature sensor as an intermediary between the heating element and the control system. Rather than using mechanical float switches that directly interrupt circuits, the temperature sensor provides thermal information to an electronic controller that then controls heating element operation. This intermediary approach simplifies the mechanical components while maintaining protection functionality.
2Device complexity
If temperature sensor-based protective systems are used, then device complexity is reduced, but reliability deteriorates with polymer tank materials
Solution Approach 1:
The patent applies local quality by positioning the temperature sensor in direct thermal contact with or in immediate proximity to the heating element, rather than relying on distant tank wall temperature sensing. This localized temperature monitoring ensures accurate detection of dry fire conditions at the heating element itself, independent of the thermal properties of polymer tank materials. The sensor monitors the specific location where dry fire risk exists.
Solution Approach 2:
The patent implements preliminary action by having the temperature sensor continuously monitor heating element temperature before damage can occur. The controller receives temperature data and can preemptively shut down the heating element when temperature approaches dangerous levels, preventing dry fire damage before it happens. This proactive approach compensates for the insulating properties of polymer tanks.
3Productivity
If continuous heating element operation is allowed, then productivity is improved, but risk of dry fire damage increases
Solution Approach 1:
The patent implements feedback control by continuously monitoring heating element temperature via the temperature sensor and using this information to control heating element operation. The controller receives real-time temperature data and adjusts heating element power or shuts it down when temperature thresholds are approached. This feedback mechanism allows continuous operation when safe while preventing overheating, maintaining productivity without increasing dry fire risk.
Solution Approach 2:
The patent employs periodic action through cyclic heating and cooling cycles controlled by temperature monitoring. The heating element operates periodically rather than continuously, with the controller turning it on when temperature is safe and turning it off when temperature approaches dangerous levels. This periodic operation maintains water heating productivity while preventing sustained overheating that could lead to dry fire damage.
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 by ensuring the heating element operates safely and efficiently, reducing the risk of damage to the water heater and its components, even with polymer tanks, through controlled energy delivery and temperature monitoring.
Implementation Method 1
a temperature sensor disposed with respect to the heating element so that the temperature sensor detects temperature of an area ambient to the heating element in the interior volume
Implementation Method 2
upon conclusion of the cumulative actuation period, the heating element contributes at least a predetermined amount of energy to the area that is measurable by the temperature sensor when the heating element is immersed in water
Data Source
AI summary
A water heater has a tank defining an interior volume, a heating element disposed within the interior volume, and a temperature sensor disposed with respect to the heating element so that the temperature sensor detects temperature of an area ambient to the heating element in the interior volume. The heating element is actuated at a predetermined actuation rate and for a cumulative actuation period so that the predetermined actuation rate maintains the heating element below a predetermined maximum temperature in air and so that the actuation period contributes a predetermined amount of energy to the ambient area when the heating element is immersed in water.