Hot Water Heat Exchanger Control for Stable Outlet Temperature
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Solution Overview
Problem
Conventional hot water supply systems face inefficiencies in maintaining a constant temperature due to variations in usage, leading to temporary overshoots and undershoots, and struggle to recover energy in condensing systems and prevent lime extraction, which reduces durability and efficiency.
Innovation Solution
A hot water supply system with a heat exchanger, flow sensors, temperature sensors, and a controller that manages the heating device based on user-set temperature and flow rate variations, incorporating a preheating circulation mode to maintain temperature stability, absorb temperature changes, and control the heat exchanger temperature below lime extraction levels.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If the heating power of the burner is rapidly reduced when flow rate decreases, then the overshoot of hot water temperature is decreased, but an undershoot of temperature occurs for a predetermined time
Solution Approach 1:
The controller pre-heats water in the water tank before it is needed, so that when hot water is requested, pre-heated water is immediately supplied. This eliminates the delay and temperature fluctuations that occur when heating is started after water flow begins, resolving the contradiction between rapid temperature response and temperature stability.
Solution Approach 2:
The system maintains a reserve of pre-heated water in the tank to cushion against sudden changes in hot water demand. When flow rate varies, the buffer of pre-heated water absorbs the thermal inertia effects, preventing both overshoot and undershoot conditions while maintaining stable temperature delivery.
2Temperature
If the outlet temperature of the heat exchanger is controlled to be higher than the user-set temperature, then the temperature of hot water can be maintained despite flow rate variations, but the efficiency of the water heater is decreased
Solution Approach 1:
Water is pre-heated to the exact user-set temperature in advance and stored in the tank. This eliminates the need to overheat water to compensate for flow rate variations, as the pre-heated water is delivered at the precise required temperature, thereby maintaining energy efficiency while ensuring temperature stability.
Solution Approach 2:
The system uses the incoming cold water flow itself as the heating medium through a heat exchanger, recovering heat that would otherwise be wasted. This self-service heating approach maintains energy efficiency while the water tank buffer ensures temperature stability despite flow variations.
3Stability of the object's composition
If the outlet temperature of the heat exchanger is controlled to be higher than the user-set temperature, then temperature stability is improved, but energy recovery in condensing systems is prevented
Solution Approach 1:
Water is pre-heated to the precise user-set temperature in advance using efficient heat exchange methods, eliminating the need for high outlet temperatures. This allows condensing heat exchangers to operate at lower temperatures where condensation and energy recovery can occur, while still delivering stable temperature hot water through the buffer tank system.
Solution Approach 2:
The system converts the incoming cold water, which would normally represent a heat loss, into a useful heating medium. The cold water absorbs heat from the heat exchanger surface, and this pre-heated water is then stored and delivered as hot water. This approach enables energy recovery in condensing systems while maintaining temperature stability.
4Power
If the internal temperature of the heat exchanger is high, then heating efficiency is improved, but lime extraction from water occurs, reducing durability
Solution Approach 1:
Water is pre-heated to the user-set temperature in advance using efficient heat exchange at controlled temperatures. This eliminates the need to maintain high internal heat exchanger temperatures for extended periods, thereby preventing lime extraction and scale formation while maintaining heating efficiency through the pre-heating buffer system.
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 effectively reduces temperature fluctuations, enhances energy recovery in condensing systems, and prevents lime extraction, thereby improving efficiency and durability while maintaining consistent hot water delivery.
Implementation Method 1
a heat exchanger (13) for transferring heat from a heating device to the inflow water
Implementation Method 2
a pump (17) for circulating water, when a user does not use hot water
Implementation Method 3
a check valve (18) for preventing a flow of water from being reversed
Data Source
AI summary
In a hot water supply system, a heat exchanger transfers heat from a heating device to inflow water to supply the inflow water at a user-set temperature. A flow sensor measures a flow rate of inflow water. A water tank stores outflow water discharged from the heat exchanger. A first temperature sensor, installed on an inlet pipe through which the inflow water flows, measures a temperature of the inflow water. A second temperature sensor, installed on an outlet pipe through which the outflow water flows, measures a temperature of the outflow water discharged from the heat exchanger. A controller includes an input unit to receive input from a user, wherein the controller controls an operation of the heating device based on at least one of: (1) comparison between the user-set temperature and the temperature of the outflow water; (2) variation in the flow rate; or (3) any combination thereof.