Compressor Speed Control During Air Conditioner Defrosting
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Solution Overview
Problem
During defrosting operations in air conditioners, the increased rotational speed of the compressor can lead to a significant reduction in suction pressure, potentially below the compressor's performance lower limit, causing damage or requiring low-pressure protection control, which extends the defrosting time and delays heating operation restoration due to differences in size between the outdoor and indoor heat exchangers and refrigerant pipe lengths.
Innovation Solution
The air conditioner is configured to drive the compressor at a predetermined activation rotational speed based on the capacity ratio of the indoor to outdoor units and refrigerant pipe lengths for a specific time during defrosting, preventing suction pressure from falling below the compressor's performance limits by optimizing the defrosting operation control according to installation conditions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of time
If the compressor activation rotational speed is increased to high speed (e.g., 90 rps) at the start of defrosting operation, then the amount of high-temperature refrigerant discharged is increased and defrosting operation time is shortened, but the suction pressure is significantly reduced and may fall below the performance lower limit value of the compressor
Solution Approach 1:
The patent applies dynamics by making the compressor activation rotational speed variable rather than fixed. The outdoor unit controller sets the activation rotational speed based on the capacity ratio between indoor and outdoor units, allowing the system to adapt the rotational speed dynamically to different installation conditions. This resolves the contradiction by enabling high rotational speed when capacity ratio is high (shortening defrosting time) while maintaining adequate rotational speed when capacity ratio is low (preventing suction pressure from falling below limits).
Solution Approach 2:
The patent changes the parameter of compressor activation rotational speed based on the capacity ratio parameter. By establishing a relationship between these parameters, the system optimizes defrosting performance while ensuring reliable operation. When the capacity ratio indicates a large outdoor unit relative to indoor units, a higher activation rotational speed is set to reduce defrosting time, whereas when the capacity ratio indicates a small outdoor unit, a lower activation rotational speed is set to maintain sufficient suction pressure.
2Productivity
If the compressor activation rotational speed is increased to high speed, then the defrosting operation is accelerated, but the pull-down effect is intensified and suction pressure reduction is exacerbated
Solution Approach 1:
The patent changes the activation rotational speed parameter according to the capacity ratio to balance defrosting efficiency and suction pressure maintenance. By adjusting this parameter based on system configuration, the patent prevents excessive pull-down effects while maintaining adequate defrosting performance.
3Loss of time
If the compressor activation rotational speed is set to high speed, then the heating operation can be restored faster, but the risk of compressor damage increases due to suction pressure falling below performance limits
Solution Approach 1:
The patent adjusts the activation rotational speed parameter based on capacity ratio to minimize both time loss and compressor damage risk. The optimized parameter selection ensures rapid heating operation restoration when system conditions permit while preventing compressor damage when conditions are unfavorable.
Solution Approach 2:
The patent implements feedback control by using the capacity ratio (derived from rated capacities of indoor and outdoor units) to determine the appropriate activation rotational speed. This feedback mechanism ensures that the compressor operates at an optimal speed that balances rapid defrosting completion with compressor protection.
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 compressor damage and ensures uninterrupted defrosting and heating operations by maintaining adequate suction pressure, reducing the risk of low-pressure protection control and extending the defrosting time.
Implementation Method 1
a compressor (21), a four-way valve (22), an outdoor heat exchanger (23), and an outdoor fan (27)
Implementation Method 2
an outdoor heat exchanger (23)... heat exchange efficiency in the outdoor heat exchanger may be degraded
Implementation Method 3
the high-temperature refrigerant discharged from the compressor flows into the outdoor heat exchanger and melts frost formed on the outdoor heat exchanger
Data Source
AI summary
An outdoor unit control unit has a defrosting operation condition table that defines an activation rotational speed based on the total sum of the rated capacity of indoor units and a refrigerant pipe length that is the length of a liquid pipe or of a gas pipe. The outdoor unit control unit uses the total sum of the rated capacity of the indoor units and refers to the defrosting operation condition table, so as to determine the activation rotational speed, and then the outdoor unit control unit activates a compressor at the determined activation rotational speed when starting a defrosting operation, maintains this activation rotational speed for a predetermined time (one minute) from the start of the defrosting operation, and drives the compressor.