Air Conditioner Compressor Speed Control for Defrost Suction Pressure
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Solution Overview
Problem
In air conditioners with outdoor and indoor units connected by refrigerant pipes, the compressor's suction pressure can drop below a 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 the capacity ratio and refrigerant pipe length to maintain adequate suction pressure, preventing it from falling below the performance lower limit.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the compressor rotational speed is increased to maximum 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 compressor rotational speed is dynamically adjusted during defrosting operation based on real-time suction pressure feedback. The control unit monitors suction pressure and modulates the compressor speed between minimum and maximum values, transitioning from static maximum speed operation to dynamic adaptive speed control, resolving the contradiction between defrosting efficiency and compressor safety
Solution Approach 2:
A feedback control mechanism is implemented where the control unit continuously detects suction pressure during defrosting operation and adjusts compressor rotational speed accordingly. When suction pressure approaches the lower limit, the compressor speed is reduced; when suction pressure is adequate, maximum speed is maintained, creating a closed-loop control system that balances defrosting performance with compressor protection
2Reliability
If the compressor rotational speed is reduced to maintain suction pressure, then compressor damage is prevented, but the defrosting operation time is extended and heating operation restoration is delayed
Solution Approach 1:
The compressor operates with dynamically adjusted rotational speed rather than fixed speed, allowing the system to optimize between defrosting speed and suction pressure maintenance in real-time, minimizing unnecessary time loss while ensuring compressor safety
Solution Approach 2:
The control unit changes the operational parameters of the compressor by adjusting rotational speed within a defined range (minimum to maximum values) based on suction pressure conditions, enabling flexible optimization of defrosting time versus compressor protection
3Reliability
If the compressor is stopped due to low-pressure protection control, then compressor damage is prevented, but the defrosting operation is interrupted and heating operation restoration is significantly delayed
Solution Approach 1:
The control unit takes preliminary action by detecting suction pressure trends and reducing compressor speed before the suction pressure falls below the protection threshold. This preventive control avoids triggering the low-pressure protection shutdown, eliminating the harmful effect of defrosting interruption while still protecting the compressor
Solution Approach 2:
Real-time feedback on suction pressure enables the control unit to adjust compressor operation proactively, preventing the condition that would trigger protective shutdown, thereby maintaining continuous defrosting operation and avoiding restoration delays
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.
Implementation Method 1
When the outdoor heat exchanger functions as the condenser, a high-temperature refrigerant discharged from the compressor flows into the outdoor heat exchanger and melts frost formed on the outdoor heat exchanger
Implementation Method 2
the compressor is activated again... the compressor is driven at a predetermined maximum value of the rotational speed
Data Source
Figure 1(A)~1(B)
Figure 2
Figure 3~4
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.