Drinking Water Heating Control for Legionella and Energy Balance
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Solution Overview
Problem
Large-scale drinking water heating systems face challenges in preventing Legionella proliferation while maintaining energy efficiency, as Legionella bacteria multiply rapidly at temperatures between 30-40°C and require water to be heated to 60°C or above to prevent infection, leading to high energy consumption.
Innovation Solution
A system that includes a reservoir, a low-temperature heat pump for heating water to 50-55°C, and a control unit that monitors water throughput and temperature, activating an additional heating device to 60°C when necessary to ensure Legionella protection, while using a solar system for preheating and optimizing energy usage based on water demand.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If water is heated to 60°C or above to prevent Legionella proliferation, then Legionella protection is improved, but energy consumption increases
Solution Approach 1:
The system dynamically adjusts the water temperature based on real-time water usage detection. When water usage is detected, the temperature is maintained at 50-55°C; when no usage is detected for a predetermined period, the temperature is raised to 60°C or above. This dynamic adjustment resolves the contradiction by adapting the temperature level to actual operational conditions rather than maintaining a fixed high temperature.
Solution Approach 2:
The system implements periodic temperature elevation to 60°C or above when water usage ceases for a predetermined period. This periodic high-temperature treatment eliminates Legionella risk while allowing lower energy-consuming temperatures during active usage periods, thus resolving the contradiction between continuous Legionella protection and energy consumption.
2Use of energy by moving object
If water temperature is maintained at 50-55°C to reduce energy consumption, then energy efficiency is improved, but Legionella protection deteriorates
Solution Approach 1:
The system dynamically switches between two temperature regimes based on water usage patterns. During active usage periods, the temperature is maintained at the energy-efficient 50-55°C. When usage stops for a predetermined period, the system automatically raises the temperature to 60°C or above to ensure Legionella protection. This dynamic switching resolves the contradiction by applying the appropriate temperature level at the appropriate time.
Solution Approach 2:
The system performs preliminary temperature elevation to 60°C or above when water usage ceases for a predetermined period before potential reuse. This preliminary high-temperature treatment ensures that when water is next used, Legionella has already been eliminated, allowing the system to return to energy-efficient lower temperatures, thus resolving the contradiction.
3Reliability
If high temperature (60°C+) is continuously applied to ensure Legionella protection, then Legionella protection is improved, but system complexity increases due to additional heating requirements
Solution Approach 1:
The control unit serves multiple functions: it detects water usage, determines usage patterns, decides when temperature elevation is necessary, and controls both the heat pump and auxiliary heating device. This multi-functionality reduces the need for separate dedicated components for each function, thereby managing system complexity while ensuring Legionella protection through coordinated temperature management.
Solution Approach 2:
The system uses its own water usage detection capability to automatically trigger temperature elevation when needed. The control unit monitors water usage patterns and autonomously decides when to activate the auxiliary heating device without requiring external intervention or complex external control systems, thus managing complexity while ensuring protection.
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 approach effectively prevents Legionella proliferation while reducing energy consumption by maintaining lower water temperatures during high usage and switching to higher temperatures only when necessary, thus achieving both Legionella protection and energy efficiency.
Implementation Method 1
a first heating device for heating the drinking water in the reservoir to a first minimum target temperature, in particular of 50°C or up to 55°C
Implementation Method 2
a second additional heating device, in particular an electric flange heater or a boiler
Implementation Method 3
using a solar system for preheating and optimizing energy usage based on water demand
Data Source
Figure 1
Figure 2
AI summary
The drinking water heating plant (2) has a drinking water storage unit (4) with predetermined storage capacity, and a heat pump (6) for heating the drinking water in the storage unit to minimum target temperature. A control unit (10) checks whether desired amount of drinking water is extracted out of the storage unit within predetermined period, and decides whether protection against Legionella is required in response to extraction of the drinking water from the storage unit. An independent claim is included for a method for heating drinking water.