Subcooling Bypass Circuit for Stable AC Discharge Temperature
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Solution Overview
Problem
Existing air-conditioning apparatuses face challenges in stabilizing discharge temperature and subcooling control, particularly when switching between cooling and heating modes or with long extension pipes, leading to potential compressor damage and operational instability.
Innovation Solution
The air-conditioning apparatus includes a refrigerant circuit with a subcooling heat exchanger, bypass pipes, and expansion devices to manage refrigerant flow rates, ensuring stable subcooling and discharge temperature control across operation modes, even with long extension pipes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If liquid injection is performed only to the portion between the high-pressure liquid pipe and the compressor, then the discharge temperature can be controlled, but the system cannot cope with mode switching between cooling and heating operations
Solution Approach 1:
The injection device is designed to function in both cooling and heating operations by injecting refrigerant into the high-pressure liquid pipe regardless of operation mode. The device universally applies liquid refrigerant injection to control discharge temperature in both cooling and heating modes, eliminating the need for mode-specific injection mechanisms.
2Adaptability or versatility
If check valves are arranged in parallel to expansion devices to enable suction injection in both cooling and heating modes, then discharge temperature control is improved, but a special indoor unit is required reducing general-purpose usability
Solution Approach 1:
The injection function is extracted from the indoor unit and relocated to the outdoor unit. The injection device is installed in the high-pressure liquid pipe within the outdoor unit, eliminating the need for special indoor unit configurations. This extraction allows standard indoor units to be used while still achieving discharge temperature control through refrigerant injection.
3Temperature
If an expansion device controls refrigerant flow rate to the subcooling heat exchanger to control discharge temperature, then discharge temperature can be regulated, but the degree of subcooling cannot be independently controlled to target values
Solution Approach 1:
The single expansion device is segmented into two separate expansion devices: one dedicated to controlling refrigerant flow to the subcooling heat exchanger (controlling subcooling degree) and another for discharge temperature control via injection. This segmentation allows independent control of subcooling degree and discharge temperature, resolving the conflict between these two control objectives.
4Reliability
If discharge temperature is controlled to target value with long extension pipes, then compressor safety is improved, but the refrigerant may become two-phase state at indoor unit due to pressure loss
Solution Approach 1:
Refrigerant injection is performed in advance in the high-pressure liquid pipe before the refrigerant reaches the indoor unit. This preliminary injection lowers the discharge temperature proactively, preventing excessive temperature rise that would cause two-phase state formation in the indoor unit, especially over long extension pipes where pressure loss occurs.
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 excessive discharge temperature increases, maintains compressor longevity, and ensures stable operation by reliably subcooling refrigerant to a liquid state, reducing noise and control instability.
Implementation Method 1
a subcooling heat exchanger that includes a first flow passage and a second flow passage and exchanges heat between a portion of the refrigerant flowing in the first flow passage and another portion of the refrigerant flowing in the second flow passage to subcool the portion of refrigerant flowing in the first flow passage
Implementation Method 2
a compressor to compress refrigerant and discharge the compressed refrigerant
Implementation Method 3
a third expansion device to adjust a flow rate of the refrigerant flowing in the second bypass pipe
Implementation Method 4
a second heat exchanger that exchanges heat with the refrigerant
Data Source
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AI summary
Provided is an air-conditioning apparatus100 including a refrigerant circuit formed by connecting, with pipes, a compressor10 to compress refrigerant and discharge the compressed refrigerant, a first heat exchanger12 that exchanges heat with the refrigerant, a subcooling heat exchanger13 that includes a first flow passage and a second flow passage and exchanges heat between a portion of the refrigerant flowing in the first flow passage and another portion of the refrigerant flowing in the second flow passage to subcool the portion of refrigerant flowing in the first flow passage, a first expansion device16 to decompress the refrigerant, a second heat exchanger17 that exchanges heat with the refrigerant, and an accumulator15 connected to a suction side of the compressor10 and configured to store excess refrigerant, so that the refrigerant is circulated through the refrigerant circuit, the air-conditioning apparatus100 comprising: a first bypass pipe4a that connects the second flow passage of the subcooling heat exchanger13 with a segment of the pipes, the segment being positioned on a refrigerant inflow side of the accumulator15; a second expansion device14a to adjust a flow rate of the refrigerant flowing in the first bypass pipe4a; a second bypass pipe4b that connects a segment of the pipes, the segment being positioned between the first heat exchanger12 and the second heat exchanger17 with another segment of the pipes, the another segment being positioned between a refrigerant outflow side of the accumulator15 and the suction side of the compressor10; and a third expansion device14b to adjust a flow rate of the refrigerant flowing in the second bypass pipe4b.