Compressor Speed Control During Defrost to Protect Suction Pressure
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Solution Overview
Problem
In air conditioners with outdoor and indoor units connected by refrigerant pipes, the suction pressure of the compressor can drop below the performance lower limit during defrosting due to differences in size between the outdoor and indoor heat exchangers, leading to potential compressor damage and delayed heating operation restoration.
Innovation Solution
The air conditioner controls the compressor's rotational speed during defrosting based on a capacity ratio derived from the total rated capacity of the indoor units and the refrigerant pipe length, preventing significant suction pressure reduction and avoiding low-pressure protection control.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the compressor is driven at maximum rotational speed during defrosting operation, then the defrosting efficiency is improved and heating operation restoration is accelerated, but the suction pressure may fall below the performance lower limit value causing compressor damage
Solution Approach 1:
The patent applies dynamics by making the compressor rotational speed variable rather than fixed. The outdoor unit controller dynamically adjusts the compressor's rotational speed based on real-time suction pressure feedback during defrosting operation. When suction pressure approaches the performance lower limit, the controller reduces the rotational speed to maintain safety margins, while allowing higher speeds when pressure is sufficient, thus optimizing both defrosting efficiency and compressor protection.
Solution Approach 2:
The patent implements feedback control by continuously monitoring suction pressure during defrosting operation and using this information to adjust compressor rotational speed. The outdoor unit controller receives suction pressure signals and modifies the compressor speed accordingly, creating a closed-loop control system that automatically balances defrosting performance with compressor safety without requiring manual intervention.
2Reliability
If the compressor rotational speed is reduced to prevent suction pressure drop, then compressor safety is improved, but the defrosting operation time is extended and heating operation restoration is delayed
Solution Approach 1:
The system dynamically adjusts compressor rotational speed based on actual suction pressure conditions rather than using a fixed reduced speed. This allows the compressor to operate at higher speeds when suction pressure is sufficient, minimizing defrosting time, and only reduces speed when necessary to prevent pressure drop below the performance lower limit, thus optimizing the balance between safety and time efficiency.
Solution Approach 2:
Through continuous suction pressure monitoring and feedback control, the system identifies the precise moment when speed reduction is necessary. This feedback mechanism prevents unnecessary speed reductions that would extend defrosting time, while ensuring speed reduction occurs timely enough to prevent compressor damage, achieving optimal timing for the speed adjustment.
3Reliability
If the suction pressure is maintained above the performance lower limit during defrosting, then compressor damage is prevented, but the defrosting operation may take longer due to reduced compressor speed
Solution Approach 1:
The system uses dynamic speed adjustment rather than a fixed reduced speed, allowing the compressor to operate at maximum or near-maximum speeds during most of the defrosting cycle when suction pressure is sufficient. The speed is dynamically reduced only during critical periods when pressure approaches the lower limit, thereby minimizing the impact on overall defrosting time while maintaining compressor protection.
Solution Approach 2:
The feedback control system continuously monitors suction pressure and adjusts compressor speed in real-time, enabling the system to maintain high productivity during periods when pressure is safe while providing protective speed reduction only when necessary. This selective feedback control optimizes the trade-off between compressor protection and heating operation restoration speed.
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 approach prevents compressor damage and ensures timely restoration of the heating operation by maintaining suitable suction pressure during defrosting, even with reduced refrigerant circulation due to installation conditions.
Implementation Method 1
a compressor (21)
Implementation Method 2
an outdoor heat exchanger (23)... heat exchange efficiency in the outdoor heat exchanger... heat exchange conducted between the frost and the refrigerant
Implementation Method 3
a 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
A rotational speed Cr of a compressor 21 during a defrosting operation is controlled within a control range that corresponds to a capacity ratio P, a total sum Pi of rated capacity of an indoor unit, or a refrigerant pipe length Lr. Accordingly, even in the case where a refrigerant circulation amount during the defrosting operation is reduced due to an installation state of an air conditioner 1, it is possible to prevent suction pressure from being significantly reduced and falling below a performance lower limit value of the compressor 21. Thus, damage to the compressor 21 can be prevented. In addition, it is possible to prevent a case where the suction pressure falls below the performance lower limit value of the compressor 21 and thus low-pressure protection control is executed. Therefore, a case where the restoration of the heating operation is delayed does not occur.