Continuous flow drinking water heater, drinking water heating system and method for operating a continuous flow drinking water heater
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Solution Overview
Problem
Flow-through drinking water heaters with two heat exchangers in series face challenges in maintaining hygienic conditions due to temperature fluctuations, which can lead to the multiplication of legionella and other germs, and require complex systems for temperature equalization and germ removal.
Innovation Solution
A control device regulates the pump capacity of the first and second pumps based on measured temperature and volume flow values to maintain the secondary-side return temperature of the first heat exchanger, activating the second heat exchanger only when necessary to prevent stagnation and calcification, thereby keeping the drinking water temperature in a range that inhibits germ multiplication.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If both heat exchangers operate continuously in series, then the overall heat transfer capacity is maximized, but the drinking water temperature in the second heat exchanger falls into the legionella multiplication range (25-45°C)
Solution Approach 1:
The patent implements dynamic operation of the second heat exchanger by controlling the second pump based on hot water consumption patterns. The second heat exchanger operates intermittently rather than continuously, adjusting its operation to match actual demand and avoid creating stagnant water in the legionella temperature range.
Solution Approach 2:
The system uses periodic operation of the second heat exchanger, activating it during periods of hot water consumption and deactivating it during periods of no consumption. This periodic action prevents continuous stagnation of drinking water at harmful temperatures while maintaining heat transfer capacity when needed.
2Loss of energy
If the second heat exchanger operates continuously to preheat cold water, then heat recovery is maximized, but drinking water stagnates at temperatures favorable for germ multiplication
Solution Approach 1:
The system dynamically adjusts the operation of the second heat exchanger based on hot water consumption patterns. The second pump is controlled to operate only when hot water is being consumed, thereby recovering heat during productive periods while avoiding stagnation during idle periods when germ multiplication could occur.
3Reliability
If both pumps operate continuously, then constant hot water supply is ensured, but energy consumption increases and system complexity increases
Solution Approach 1:
The system implements periodic operation of the second pump based on hot water consumption detection. When hot water is consumed and the temperature at the first heat exchanger outlet drops below a threshold, the second pump activates to supplement heating. When no hot water is consumed, the second pump remains off, reducing energy consumption while maintaining supply reliability through the first heat exchanger alone.
4Power
If both heat exchangers are used in series, then the required heat transfer capacity is achieved, but the system complexity increases due to multiple pumps and control mechanisms
Solution Approach 1:
The system uses dynamic control of the second pump based on temperature and flow conditions. A control unit monitors the temperature at the outlet of the first heat exchanger and activates the second pump only when additional heating capacity is required, thereby achieving the necessary total heat transfer capacity while avoiding the complexity of continuously operating both heat exchangers and pumps.
5Object-affected harmful factors
If the second heat exchanger is deactivated, then drinking water temperature remains below 30°C preventing legionella growth, but heat transfer capacity is reduced
Solution Approach 1:
The system periodically activates the second heat exchanger and second pump based on hot water consumption patterns. During periods when hot water is being consumed, the second heat exchanger operates to provide additional heat transfer capacity. During periods of no consumption, it remains deactivated, keeping drinking water temperature below 30°C and preventing legionella growth.
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 maintains drinking water temperature below 30°C, reducing the risk of legionella multiplication and calcification, while ensuring a constant hot water supply with reduced energy consumption and simplified system complexity.
Implementation Method 1
a first heat exchanger (4), with a secondary line arrangement (10) connecting the secondary sides of the heat exchangers (4, 6) in series with a hot water circulation line (16)
Implementation Method 2
the cold water line (18) through the second heat exchanger (6) to the inlet of the first heat exchanger (4)
Implementation Method 3
a controllable first pump (20) for supplying hot water to the primary side of the first heat exchanger (4), with a controllable second pump (22) for supplying hot water to the primary side of the second heat exchanger (6)
Data Source
Figure 1
Figure 2
Figure 3
AI summary
The invention relates to an instantaneous water heater with a first heat exchanger (4), a second heat exchanger (6), a primary line arrangement (8) for connecting the primary sides of the heat exchangers (4, 6) to a heat generator (12), a secondary line arrangement (10) for connecting the secondary sides of the heat exchangers (4, 6) to a hot water circulation line (16) and to a cold water line (18), wherein the primary line arrangement (8) connects the primary sides of the heat exchangers (4, 6) in series, wherein the secondary line arrangement (10) connects the secondary sides of the heat exchangers (4, 6) in series and connects the cold water line (18) through the second heat exchanger (6) to the secondary-side inlet of the first heat exchanger (4), and a controllable first pump (20) for supplying hot water to the primary side of the first heat exchanger (4).with a controllable second pump (22) for supplying hot water to the primary side of the second heat exchanger (6), with a first temperature sensor (24) arranged in the secondary line assembly (10) for detecting the return temperature in the return line of the first heat exchanger (4), and with a control device (26) for detecting the measured values of the temperature sensor (24) and for controlling the first pump (20) and the second pump (22). The technical problem of simplifying and improving the instantaneous water heater, as well as a method for operating an instantaneous water heater and a system for heating drinking water, is solved by the control device (26) being configured to regulate the pumping capacity of the first pump (20) to a predetermined secondary-side return temperature of the first heat exchanger (4), and by the control device (26) being configured to activate the pumping capacity of the second pump (22).if the required total heat transfer power exceeds a predetermined limiting heat transfer power of the first heat exchanger (4), and that the control device (26) is configured to deactivate the pumping power of the second pump (20) when the required total heat transfer power falls below the predetermined limiting heat transfer power of the first heat exchanger (4).