Outdoor Heat Exchanger Defrost Flow Layout for Stable Heating
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Solution Overview
Problem
The existing air-conditioning apparatuses face a decrease in heating capacity due to refreezing drain water at the boundary between the upper and lower heat exchangers during the heating-defrosting operation, which disrupts airflow and hampers heat transfer, leading to inefficient defrosting and reduced comfort.
Innovation Solution
All hairpin pipes at the boundary between the upper and lower heat exchangers are used as refrigerant inlets during defrosting, ensuring that drain water is less likely to refreeze and maintaining a temperature above 0°C to enhance heat transfer and prevent ice growth.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If only one hairpin pipe at the boundary is used as refrigerant inlet during heating-defrosting operation, then the refrigerant flow path is simple, but the temperature does not increase at other hairpin pipes and the refrozen drain water ice cannot be melted
Solution Approach 1:
The patent segments the refrigerant inlet function across multiple hairpin pipes at the boundary between upper and lower heat exchangers. Instead of using a single inlet pipe, the system activates multiple hairpin pipes (specifically the lowermost hairpin pipe of the upper heat exchanger and the uppermost hairpin pipe of the lower heat exchanger) as refrigerant inlets during defrosting operation. This segmentation allows heat to be applied to multiple locations simultaneously, effectively melting refrozen drain water ice that forms at boundary regions.
2Power
If the upper heat exchanger is used as evaporator during defrosting, then heating capacity is maintained, but heat transfer between upper and lower heat exchangers prevents temperature increase at the boundary, causing drain water to refreeze
Solution Approach 1:
The patent applies preliminary heating action by directing high-temperature gas refrigerant through specific hairpin pipes at the boundary before and during the defrosting process. The lowermost hairpin pipe of the upper heat exchanger and the uppermost hairpin pipe of the lower heat exchanger are utilized as refrigerant inlets, pre-heating the boundary region where drain water tends to refreeze. This preliminary thermal action prevents refreezing while maintaining the upper heat exchanger as evaporator for heating capacity.
Solution Approach 2:
The patent applies local quality by creating a temperature gradient differentiated across the heat exchanger boundary. High-temperature gas refrigerant is selectively directed to the boundary hairpin pipes (lowermost of upper exchanger and uppermost of lower exchanger) to create localized high-temperature zones. This local thermal enhancement melts refrozen drain water ice at the boundary without requiring the entire upper heat exchanger to stop functioning as evaporator, thus maintaining overall heating capacity.
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 prevents refreezing of drain water and maintains a higher heating capacity by ensuring effective defrosting and efficient heat transfer between the upper and lower heat exchangers, thereby maintaining room comfort and reducing defrosting time.
Implementation Method 1
heat transfer fin of the outdoor heat exchanger
Implementation Method 2
drain water melts on the upper heat exchanger and flows downward
Implementation Method 3
the temperature at the heat exchanger decreases to 0 degrees C or lower, the drain water refreezes on the lower heat exchanger
Implementation Method 4
when the upper heat exchanger is defrosted during the heating-defrosting operation
Data Source
Figure 1
Figure 2
Figure 3~4
AI summary
An air-conditioning apparatus includes a refrigerant circuit in which a compressor, an indoor heat exchanger, a first expansion device, an outdoor heat exchanger, and a flow switching device are sequentially connected to each other by pipes and through which refrigerant circulates; a hot gas bypass pipe coupling a discharge port of the compressor and the flow switching device to each other; and a controller. The compressor is configured to compress and discharge the refrigerant. The indoor heat exchanger is configured to allow the refrigerant to exchange heat with indoor air. The first expansion device is configured to reduce pressure of the refrigerant. The outdoor heat exchanger includes an upper heat exchanger and a lower heat exchanger having passages in parallel with each other and is configured to allow the refrigerant to exchange heat with outdoor air. The flow switching device is configured to switch flows of the refrigerant toward the upper heat exchanger and the lower heat exchanger. The controller is configured to perform a heating-defrosting operation for alternately defrosting the upper heat exchanger and the lower heat exchanger while performing a normal heating operation. The outdoor heat exchanger includes a plurality of hairpin pipes, which are part of a heat transfer pipe. When the upper heat exchanger is defrosted, all hairpin pipes that are located at a lowermost step of the upper heat exchanger are used as refrigerant inlets. When the lower heat exchanger is defrosted, all hairpin pipes that are located at an uppermost step of the lower heat exchanger are used as refrigerant inlets.