Heat Pump Water Heater Defrost Control to Prevent Circuit Freezing
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Solution Overview
Problem
Conventional heat pump devices face issues with water freezing in the water circuit during defrosting operations, especially when outdoor air temperatures are low, requiring changes to either the refrigerant or water circuit configurations, and still risk water freezing during reverse cycle defrosting.
Innovation Solution
A heat pump hot water heater that can switch between forward and reverse cycle operations based on the risk of water freezing, using a control unit to deactivate the water supply mechanism and increase the expansion mechanism's opening during forward cycle defrosting to prevent water freezing by inhibiting heat exchange in the second heat exchanger and transferring heat to the first heat exchanger.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If reverse cycle operation is used for defrosting the outdoor heat exchanger, then defrosting efficiency is improved, but water freezing risk in the water circuit increases
Solution Approach 1:
The control unit monitors water temperature and outdoor air temperature parameters, and switches between reverse cycle and forward cycle operations based on these parameter thresholds. When water temperature is above freezing risk threshold or outdoor temperature is above defrosting threshold, reverse cycle is used. When water temperature approaches freezing risk or outdoor temperature is very low, forward cycle is used to prevent water freezing while still achieving defrosting.
Solution Approach 2:
The system dynamically switches between two different operational modes (reverse cycle and forward cycle) based on real-time temperature conditions. This dynamic adaptation allows the system to optimize defrosting efficiency while preventing water freezing under varying environmental conditions, rather than using a fixed operational mode.
2Object-affected harmful factors
If forward cycle operation is used for defrosting, then water freezing risk is reduced, but defrosting efficiency decreases
Solution Approach 1:
The system uses temperature parameter thresholds to determine when to switch between operational modes. By setting appropriate thresholds for water temperature and outdoor air temperature, the system ensures forward cycle operation is only used when necessary to prevent water freezing, thereby minimizing the impact on overall defrosting efficiency while ensuring water safety.
Solution Approach 2:
The control unit periodically monitors temperature parameters and switches between reverse cycle and forward cycle operations in periodic intervals based on accumulated temperature data. This periodic switching strategy allows the system to maintain high defrosting efficiency during safe conditions while periodically using forward cycle to prevent water freezing, balancing both requirements.
3Reliability
If reverse cycle operation is performed for long periods under low outdoor air temperature, then outdoor heat exchanger defrosting is achieved, but water freezing in the water circuit occurs
Solution Approach 1:
The control unit continuously monitors water temperature and outdoor air temperature as feedback parameters. Based on this feedback, the system adjusts its operational mode in real-time. When feedback indicates water temperature is approaching freezing point or outdoor temperature is extremely low, the system switches from reverse cycle to forward cycle operation, preventing water freezing while maintaining outdoor heat exchanger defrosting capability.
Solution Approach 2:
The system proactively switches to forward cycle operation before water freezing can occur by monitoring temperature thresholds in advance. This beforehand cushioning approach prevents water freezing by anticipating dangerous temperature conditions and switching operational modes preemptively, ensuring water circuit operational continuity is maintained.
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
Effectively prevents water freezing in the water circuit during defrosting operations by selecting the appropriate cycle operation, ensuring efficient defrosting without damaging the water circuit, while maintaining heating performance.
Implementation Method 1
the refrigerant, compressed to have high temperature in the compressor, is heat-exchanged with the water and cooled down in the indoor heat exchanger
Implementation Method 2
is reduced in pressure, and then is heat-exchanged with outdoor air and heated in the outdoor heat exchanger
Implementation Method 3
The water, flowing through the water circuit, is heat-exchanged with the refrigerant and heated in the indoor heat exchanger
Implementation Method 4
the refrigerant, compressed to have high temperature in the compressor, flows into the outdoor heat exchanger, and the outdoor heat exchanger is defrosted
Data Source
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AI summary
A heat pump hot water heater (10) includes a refrigerant circuit (20), a water circuit (30) and a control unit (40). The refrigerant circuit includes a first heat exchanger (21) configured to cause heat exchange between air and refrigerant, a second heat exchanger (25) configured to cause heat exchange between the refrigerant and water, and a compressor (22) configured to compress the refrigerant. The water circuit includes the second heat exchanger and a water supply mechanism (31) configured to supply the water to the second heat exchanger. The control unit is configured to control the refrigerant circuit and the water circuit so as to perform a defrosting operation of the first heat exchanger. The refrigerant circuit is capable of switching between a forward cycle operation and a reverse cycle operation. At least either in starting the defrosting operation or during performing the defrosting operation, the control unit is configured to determine a possibility of freezing of the water in the water circuit and select to perform either the forward cycle operation or the reverse cycle operation so as to perform the defrosting operation.