Mix Tank Time Delay for Feedforward Water Heater Temperature Control
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Solution Overview
Problem
In distributed hot water heating systems, regulating the temperature of hot water supplied to buildings is challenging due to varying loads, especially in commercial settings, where direct measurement of mix water temperature is inoperative for feedforward control, and there is a need for a causal relationship between measured temperature and valve action to prevent scald hazards and ensure stable temperature control.
Innovation Solution
A water heater system incorporating a mixing tank with a constant flow pump and a controllable three-way proportional valve, where the temperature of time-delayed mixed water is measured to adjust the flow of boiler water into the heat exchanger using a feedforward control process, and additional delay tanks or pipes can be used to establish a causal feedforward control system for stable temperature regulation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If direct measurement of mix water temperature is used for control, then temperature regulation responsiveness is improved, but it is inoperative in distributed heating systems where the measurement location is inaccessible
Solution Approach 1:
The patent introduces a mixing tank as an intermediary device that receives hot water from the heat exchanger and cold water from the building supply, allowing temperature measurement at an accessible location (the mixing tank) rather than at the inaccessible heat exchanger outlet. This mediator enables indirect measurement that achieves the same control objective.
2Speed
If feedforward control is implemented without time delay compensation, then control responsiveness is improved, but temperature instability and scald hazards occur due to causal relationship breakdown
Solution Approach 1:
The patent incorporates a fluid time delay chamber that introduces a predetermined time delay to the mixed water before it reaches the temperature sensor. This preliminary action of delaying the water flow ensures that the temperature measurement corresponds to the actual mix conditions at the heat exchanger outlet, maintaining the causal relationship necessary for stable feedforward control.
3Adaptability or versatility
If varying hot water loads are accommodated, then system adaptability is improved, but temperature regulation stability deteriorates
Solution Approach 1:
The patent implements a feedback control loop where the temperature sensor continuously monitors the mixed water temperature and the controller adjusts the proportional valve position based on the measured temperature and desired setpoint. This feedback mechanism maintains temperature stability despite varying hot water loads by dynamically compensating for load changes.
4Manufacturing precision
If proportional valve flow adjustment is made for temperature control, then temperature precision is improved, but system complexity increases
Solution Approach 1:
The patent replaces complex mechanical temperature control mechanisms with an electronic control system that uses a temperature sensor, processor, and electronically controlled proportional valve. This substitution of mechanical systems with electronic/control systems achieves precise temperature regulation while managing system complexity through integrated control logic.
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
The system provides a stable and accurate regulation of hot water temperature, preventing scald hazards and maintaining desired temperatures even with varying loads, with improved accuracy and efficiency by using a feedforward control process based on mixed water temperature measurements.
Implementation Method 1
Heat exchanger type hot water heaters transfer heat energy from a flow of heated gas or heated water, to heat a domestic cold water
Implementation Method 2
The mixing tank mixes the cold water and a hot water from the mt hot water inlet
Implementation Method 3
A constant flow pump is fluidly coupled to and disposed between the hx domestic hot water outlet and the mt hot water inlet
Implementation Method 4
A temperature sensor is disposed in or on the mixing tank to measure a temperature of the time delayed mixed water
Data Source
Figure 1A
Figure 1B
Figure 1C
AI summary
A water heater includes a heat exchanger. A controllable three-way proportional valve provides a proportionally controllable flow to the hot water inlet of the heat exchanger and a boiler return water outlet. A mixing tank mixes a cold water and a hot water. The mixing tank provides a time delayed mixed water. A temperature sensor is disposed in or on the mixing tank to measure a temperature of the time delayed mixed water to provide a time delayed mixed water temperature. A feedforward control process running on a processor adjusts a proportional operating position of the controllable three-way proportional valve to regulate a temperature of hot water at the hx domestic hot water outlet based on the temperature of the time delayed mixed water temperature. A method for controlling a hot water temperature of a water heater a water heater using a flowmeter based feedforward control are also described.