Heat Pump Hot-Water Circuit for Defrosting Without Heat Loss
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Solution Overview
Problem
Conventional heat pump type hot water supply apparatuses struggle to maintain a hot water temperature of 60 degrees C or higher when outside air temperatures drop below 0 degrees C, which is necessary for preventing the outbreak of Legionella bacteria, and they also face inefficiencies in defrosting operations.
Innovation Solution
The apparatus configures a refrigerant circuit that branches off refrigerant from the compressor to flow in parallel with the water heat exchanger during defrosting, maintaining hot water at 65 degrees C by controlling the flow through a flow switching device and using a specific pass pattern in the evaporator to prevent refrigerant accumulation, thereby enhancing defrosting efficiency without reducing heating capacity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If the high limit temperature of hot water is regulated to 58 degrees C when outside air temperature is -5 degrees C or lower, then the load for the compressor is reduced, but the hot water temperature cannot be maintained at 60 degrees C or higher which is required for preventing Legionella bacteria
Solution Approach 1:
The evaporator is divided into multiple passes, with specific passes (e.g., lower portion passes) configured to allow refrigerant flow during defrosting operations while other passes continue heating water. This segmentation enables simultaneous defrosting and hot water generation, resolving the contradiction between reducing compressor load and maintaining hot water temperature.
Solution Approach 2:
The system maintains continuous hot water generation during defrosting operations by directing refrigerant through specific evaporator passes that remain active for heating while other passes perform defrosting. This ensures the hot water temperature is continuously maintained at 60 degrees C or higher without interrupting the heating function, even when outside air temperature is low.
2Reliability
If refrigerant is directed to defrost the evaporator when outside air temperature is low, then defrosting operation is performed, but the heating capacity for removing frost is reduced due to refrigerant shortage
Solution Approach 1:
The evaporator is segmented into multiple passes with different functions: some passes are dedicated to defrosting while others continue heating water. The refrigerant is directed to specific passes (e.g., lower portion passes) during defrosting operations, ensuring sufficient refrigerant flow for effective frost removal without compromising the heating capacity of other passes.
Solution Approach 2:
Different passes of the evaporator are assigned different local qualities or functions: upper passes may be dedicated to defrosting while lower passes continue heating water, or vice versa. This local differentiation allows the system to perform defrosting operations with reduced refrigerant flow to specific areas while maintaining overall heating capacity through other passes.
3Productivity
If refrigerant flows through all passes of the evaporator during hot water supply operation, then heating efficiency is maximized, but refrigerant accumulates in the lower portion passes reducing defrosting efficiency
Solution Approach 1:
The evaporator is divided into multiple passes with different refrigerant flow characteristics. During hot water supply operation, refrigerant flows through all passes for maximum heating efficiency. During defrosting operations, the system selectively directs refrigerant through specific passes (e.g., lower portion passes) to prevent refrigerant accumulation and improve defrosting efficiency, resolving the contradiction between the two operational modes.
Solution Approach 2:
The refrigerant flow path through the evaporator passes is dynamically adjusted based on operational mode. During hot water supply, all passes are active for maximum heating. During defrosting, the flow is dynamically redirected to specific passes to prevent accumulation and enhance defrosting performance, allowing the system to optimize for either heating or defrosting as needed.
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 configuration ensures that hot water is maintained at the required temperature, prevents refrigerant accumulation, and performs defrosting operations efficiently, even at low outside air temperatures, thereby preventing Legionella bacteria growth and maintaining heating capacity.
Implementation Method 1
by conducting a refrigerant (hot gas) discharged from a compressor into a heat source side heat exchanger, frost attached to the heat source side heat exchanger is melted
Implementation Method 2
a heat pump type hot water supply apparatus which uses a heat pump for circulating a refrigerant
Data Source
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Figure 3
AI summary
A heat pump type hot water supply apparatus 100 performs a reverse defrosting operation in which a refrigerant discharged from a compressor 1 is conducted to a pass 31 other than a pass 33 located at a lowermost position of an evaporator 13. After completion of the reverse defrosting operation, when the outside air temperature is a predetermined temperature or less and thereafter a predetermined time has elapsed and a difference between a shell temperature of the compressor 1 and a low pressure saturation temperature becomes a predetermined value or less, the refrigerant discharged from the compressor 1 is branched off between the compressor 1 and the four-way valve 2, and is conducted to the pass 33 located at the lowermost position of the evaporator 13 such that the refrigerant flows in parallel to the water heat exchanger 3 until the predetermined time has elapsed.