Heat Pump Water Heating With Isolated Tank for Legionella Control
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Solution Overview
Problem
Existing electric space heating, space cooling, and water heating systems that rely on heat pumps face challenges such as Legionella proliferation in tanked domestic water heating systems and inefficiencies due to stratification, as well as scaling issues from hard water, which can lead to reduced efficiency and lifespan of heat exchangers.
Innovation Solution
A system comprising a heat pump, a tank with a bath, and a controller that uses a mixing valve and fluid conductors to isolate the tank from the domestic water supply, allowing for efficient heat transfer and storage without direct contact, reducing the risk of Legionella proliferation and minimizing scaling by maintaining high water flow rates through smaller conductors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If a large thermal storage tank is used to accommodate hot water demands, then hot water availability is improved, but Legionella proliferation risk increases due to stagnant water exposure at suitable temperatures
Solution Approach 1:
The patent divides the thermal storage system into two separate tanks: a first tank for storing hot water at temperatures above Legionella growth range (>60°C), and a second tank for storing water at lower temperatures. This segmentation prevents the temperature stratification in a single large tank that creates Legionella-friendly zones, while still providing adequate hot water storage capacity.
Solution Approach 2:
The patent introduces a heat exchanger as an intermediary between the two tanks. The heat exchanger allows thermal energy transfer from the first tank to the second tank without direct water contact, enabling temperature management and preventing stagnant water at dangerous temperatures while maintaining storage capacity.
2Quantity of substance
If a tanked solution is used to meet heating demands, then hot water availability is improved, but scaling issues from hard water reduce heat exchanger efficiency and lifespan
Solution Approach 1:
The patent segments the water storage into two separate tanks with distinct temperature zones. The first tank stores water at high temperatures where scaling is less problematic, while the second tank handles lower temperature water. This reduces the overall scaling impact on heat transfer efficiency compared to a single tank system where scaling occurs across the entire temperature range.
Solution Approach 2:
The heat exchanger acts as an intermediary that minimizes direct contact between hard water and critical heating elements. By separating the storage tanks and using indirect heat transfer, the system reduces scaling accumulation on heat exchanger surfaces, thereby maintaining efficiency and extending component lifespan.
3Loss of energy
If stratification occurs in the thermal storage tank, then heat energy storage is improved, but efficiency is reduced due to uneven temperature distribution
Solution Approach 1:
The patent intentionally creates temperature stratification through segmentation by maintaining separate tanks for different temperature zones. The first tank stores water at high temperatures (>60°C) and the second tank at lower temperatures, with controlled thermal interaction. This segmented approach manages stratification to preserve heat energy while avoiding the inefficiencies of uncontrolled stratification in a single tank.
Solution Approach 2:
The heat exchanger serves as a controlled intermediary that regulates heat transfer between the two tanks. This controlled interaction allows the system to maintain beneficial temperature stratification for heat energy storage while preventing excessive stratification that would reduce efficiency, by managing the rate and direction of thermal energy transfer.
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 the risk of Legionella proliferation and scaling, enhances heat energy storage and retrieval, and maintains system efficiency by isolating the tank from the domestic water supply, ensuring consistent and safe hot water delivery while reducing downtime during power outages.
Implementation Method 1
the outdoor heat exchanger being disposed to transfer heat between the first heat transfer fluid and the outdoor heat exchanger, whereby heat is transferred between the first heat transfer fluid and the stream of fluid over the outdoor heat exchanger
Implementation Method 2
the first heat exchanger being disposed to transfer heat between the first heat transfer fluid and the second heat transfer fluid
Implementation Method 3
the first fluid moving device is a compressor
Data Source
AI summary
A present heating system or heating and cooling system does not include a tank for storing potable hot water in anticipation of a potable hot water demand. Although one or more temperature sensors may be used for providing feedback to heating of the contents of a tank water heater to achieve a setpoint temperature, the effect of stratification can cause layers of fluid having different temperatures in the tank water heater. Therefore, although portions of the contents of a water heater may be disposed at a setpoint temperature that is unfavorable for Legionella proliferation, there potentially exists other portions that may be disposed at temperatures suitable for Legionella proliferation, especially when the contents have been left unused for an extended period of time.