Water Heater Set-Point Control for Tank Stacking Detection
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Solution Overview
Problem
Conventional water heaters with a single temperature sensor at the bottom are susceptible to 'stacking,' where hotter water at the top becomes significantly hotter than the set point, leading to frequent and short heating cycles, which can exacerbate the issue, as the sensor may not accurately detect the temperature at the top due to a small amount of colder water at the bottom during short water draws.
Innovation Solution
A controller that monitors both the temperature and temperature change rate at the bottom of the water heater tank, adjusts the set point temporarily by comparing the rate of change to a threshold, and adjusts the heating element operation to mitigate stacking by reducing the set point when excessive temperature change is detected, and returns to the normal set point when stacking is less of a concern.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a single temperature sensor is located at the bottom of the water heater tank, then the device complexity is reduced, but the measurement precision of water temperature is compromised during stacking conditions
Solution Approach 1:
The patent introduces an intermediary computational layer that processes the temperature sensor signal to infer top water temperature. The controller calculates the temperature difference between top and bottom water based on heating power and thermal characteristics, using this as a mediator to compensate for the single sensor limitation and accurately detect stacking conditions.
Solution Approach 2:
The patent replaces the mechanical/physical approach of using multiple sensors with a computational/algorithmic approach. Instead of physically measuring top water temperature with another sensor, the system uses mathematical modeling and signal processing to estimate the temperature gradient and infer top water temperature from bottom sensor data combined with heating power information.
2Reliability
If the heating element operates frequently to maintain bottom water temperature during short water draws, then the water temperature set point is maintained, but stacking is exacerbated
Solution Approach 1:
The patent implements a feedback control system that monitors bottom water temperature and adjusts heating element operation accordingly. The controller continuously compares the sensed bottom water temperature with the set point and modulates heating cycles to maintain temperature while preventing excessive top water heating that would cause stacking.
Solution Approach 2:
The patent introduces dynamic adjustment of heating parameters based on detected stacking conditions. When stacking is detected through temperature gradient analysis, the system dynamically modifies heating cycle duration and intensity, transitioning from static on/off control to adaptive control that responds to real-time thermal conditions in the water heater.
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 effectively reduces the occurrence of stacking by dynamically adjusting the set point based on temperature change rates, ensuring more stable and efficient heating cycles, thereby maintaining a consistent water temperature and reducing energy consumption.
Implementation Method 1
A sensor is often provided at or near the bottom end of the water heater tank to sense the temperature of the water
Implementation Method 2
a gas-fired burner, an electric heater or some other heater element
Implementation Method 3
a gas-fired burner
Implementation Method 4
the cold or ambient temperature water at or near the bottom of the water heater tank becomes hotter and begins to rise towards the top of the water heater tank. Cooler and denser water, once on top of the water being heated, falls toward the bottom
Implementation Method 5
the cold or ambient temperature water at or near the bottom of the water heater tank becomes hotter and begins to rise
Data Source
AI summary
Methods and systems for operating a water heater to limit the effects of stacking in a water heater tank are disclosed. In some cases, the water heater controller may determine a rate of change of the water temperature in the water heater tank. If the rate of change exceeds a threshold value, the controller may adjust the water heater temperature set point downward to help reduce stacking in the water heater. In some cases, the water heater temperature set point may be returned to the original water heater temperature set point when stacking is no longer likely to be of a concern. In one illustrative embodiment, the controller may track the time that the heater of the water heater is in the “on” state, or the time that the heater is in the “off” state, during subsequent heating cycles. The controller may then compare the “on” time or the “off” time to respective recovery threshold times. If the “on” time or the “off” time exceeds its respective recovery threshold time, then the controller may adjust the set point toward the original water heater temperature set point, sometimes in an incremental manner.