Outdoor Unit Defrost Interval Control for Multi-Split Heating
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Solution Overview
Problem
In air conditioners with multiple indoor units coupled to a single outdoor unit, the defrosting operation is prolonged when the compressor's rotational speed is reduced to prevent suction pressure from falling below the performance limit, leading to delayed restoration of heating operation, especially when the number of indoor units is small or their capacity is low.
Innovation Solution
The air conditioner employs a controller that adjusts the defrosting operation interval time and compressor rotational speed based on the capacity ratio of indoor to outdoor units and refrigerant pipe lengths, allowing for efficient defrosting by maintaining suitable suction pressure and reducing defrosting time.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the compressor rotational speed is increased during defrosting operation, then the defrosting efficiency is improved and defrosting time is shortened, but the suction pressure falls below the performance limit causing compressor damage or operation stop
Solution Approach 1:
The patent applies dynamics by making the compressor rotational speed adjustable and variable during defrosting operation. The controller dynamically changes the rotational speed based on detected suction pressure values, allowing the system to adapt between high-speed defrosting and low-pressure protection modes, thus resolving the contradiction between defrosting efficiency and operational reliability
Solution Approach 2:
The patent changes the operational parameters of the compressor by adjusting its rotational speed according to suction pressure conditions. When suction pressure is above the lower limit, high rotational speed is maintained for efficient defrosting; when pressure approaches the limit, speed is reduced to prevent damage, thereby balancing productivity and reliability
2Reliability
If the compressor rotational speed is reduced to maintain suction pressure, then the compressor operation stability is improved, but the defrosting operation time is extended and heating operation restoration is delayed
Solution Approach 1:
The patent implements periodic monitoring and adjustment of compressor rotational speed based on suction pressure detection. The controller continuously detects pressure values and periodically adjusts speed accordingly, creating a rhythm of high-speed defrosting interspersed with low-speed pressure maintenance, thus minimizing total defrosting time while ensuring reliability
Solution Approach 2:
The system uses feedback control where the controller detects suction pressure values and adjusts compressor rotational speed based on this feedback. This closed-loop control ensures that the compressor operates reliably by preventing pressure from falling below the performance limit while minimizing defrosting time through appropriate speed adjustments
3Productivity
If the defrosting operation is performed frequently, then the frost accumulation is prevented and heat exchange efficiency is maintained, but the heating operation is interrupted more often
Solution Approach 1:
The patent applies preliminary action by performing defrosting operations proactively when suction pressure indicates approaching frost conditions, rather than waiting for severe frosting. This prevents major frost accumulation while minimizing interruptions to heating operation through timely, controlled defrosting cycles
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 shortens the defrosting operation interval, preventing extended defrosting times and ensuring timely restoration of heating operations by optimizing compressor speed and refrigerant flow according 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 may be degraded... 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 3
a four-way valve (22)... the outdoor heat exchanger is shifted from a state of functioning as an evaporator to a state of functioning as a condenser
Data Source
Figure 1(A)~1(B)
Figure 2
Figure 3
AI summary
An outdoor unit control unit 200 has a defrosting operation condition table 300a that defines a defrosting operation interval time Tm in accordance with a total sum of rated capacity of indoor units 5a to 5c and a refrigerant pipe length as lengths of a liquid pipe 8 and a gas pipe 9. The outdoor unit control unit 200 uses the total sum of the rated capacity of indoor units 5a to 5c input by using an installation information input unit 250 and refers to the defrosting operation condition table 300a, so as to determine the defrosting operation interval time Tm. Then, the outdoor unit control unit 200 forcibly performs a defrosting operation when the defrosting operation interval time Tm elapses without establishment of a defrosting operation start condition since the last defrosting operation is terminated.