Symmetrical Buffer Tanks for Heat Pump Stratification Control
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Solution Overview
Problem
Conventional heat pump systems with buffer tanks suffer from inefficient temperature control, leading to exergy destruction and reduced system coefficient of performance due to mixing of cold and warm water, and require complex valve systems to maintain stratification.
Innovation Solution
A temperature control system utilizing two symmetrically arranged buffer tanks with alternating pumping to maintain a stable temperature stratification, where colder water is always below warmer water, and the use of check valves and baffles to minimize mixing, allowing efficient heat transfer and reduced thermal losses.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a single buffer tank is used with a heat pump, then the entire tank is cyclically heated to usage temperature, but cold water enters the heat pump during withdrawal and mixing occurs, destroying stratification and reducing system efficiency
Solution Approach 1:
The single buffer tank is segmented into two separate symmetric buffer tanks (first and second buffer tanks). Each tank handles alternating charging and discharging cycles, preventing cold water from entering the heat pump and destroying stratification. This segmentation eliminates the mixing problem while maintaining continuous system operation.
Solution Approach 2:
The system implements periodic action by alternately switching between the first and second buffer tanks. While one tank is being charged by the heat pump, the other discharges to the rest of the system, and vice versa. This periodic switching ensures that the heat pump always operates with thermally favorable boundary conditions and maintains stable stratification in both tanks.
2Loss of energy
If stratified storage is implemented to prevent mixing, then exergy destruction is reduced, but the system requires complex valve arrangements to maintain stratification
Solution Approach 1:
By segmenting the buffer into two separate tanks, the system simplifies the valve requirements. Each tank needs only basic valves for its charging and discharging operations, eliminating the need for complex multi-way valves and control mechanisms that would be required to maintain stratification in a single tank system.
Solution Approach 2:
The periodic switching between two tanks creates a simple cyclic operation that maintains stratification naturally. The alternating use of tanks means that each tank has dedicated charging and discharging phases, requiring only simple valve control rather than complex real-time stratification management.
3Use of energy by moving object
If the heat pump operates with a small temperature spread of 5-10K, then the coefficient of performance is improved, but the buffer tank requires high average temperature leading to increased thermal losses
Solution Approach 1:
The periodic alternation between two buffer tanks allows the heat pump to maintain a small temperature spread (5-10K) during operation, improving its coefficient of performance. Meanwhile, the buffer tanks can be operated at lower average temperatures since they are not continuously heated to high temperatures, reducing thermal losses through insulation while still meeting system demands.
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 maintains stable temperature stratification, increases system efficiency by 20-30%, reduces exergy destruction, and allows for efficient operation with other energy generation systems like condensing boilers or solar systems, while maintaining comfort levels.
Implementation Method 1
The heat pump gives off heat to the hot water tank with the heat transfer medium and in a heat exchanger
Implementation Method 2
heat pump for temperature control of a heat transfer medium and transport of the temperature-controlled heat transfer medium to a residual system
Implementation Method 3
maintain a stable temperature stratification, where colder water is always below warmer water
Implementation Method 4
colder water is always below warmer water for short periods of time, and this condition can lead to unwanted and disadvantageous because exergy-destroying mixing of the cold and warm water
Implementation Method 5
The buffer tank can be run at a low average temperature without any loss of comfort, which leads to low heat losses through the thermal insulation of the buffer tank
Data Source
Figure 1
Figure 2
Figure 3
AI summary
Heat pumps and refrigerating machines operate optimally if the temperature difference (the spread) of the connected heat sources and heat sinks is as small as possible. If this is not the case, two negative effects are the result: 1. At a high spread, increased dissipation occurs in the condensers and evaporators. 2. In order to generate an increased spread, the heat return flow is frequently mixed with the heat pump flow. For this purpose, hydraulic separators and overflow valves are employed. This results in highly dissipative mixing of heat carrier medium with differing temperatures. Using a pair of intermediate storage means according to the invention (also e.g. Fig. 3), the dissipation that occurs can be drastically reduced. The low spread of the heat pump is adjusted to the high spread of the remaining system. The COP of the system is substantially improved by intermediate storage means. With heat pumps, the improvement ranges from about 5% to 20%, depending on the system.