Outdoor Unit Defrost Interval Control for Faster Heating Recovery
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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 in configurations with small indoor units or large refrigerant pipe lengths.
Innovation Solution
The air conditioner employs a controller that adjusts the defrosting operation interval time based on the capacity ratio of indoor to outdoor units and refrigerant pipe lengths, allowing for a higher compressor rotational speed during defrosting when possible, thereby shortening the defrosting time and preventing delays in heating operation restoration.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the compressor's rotational speed is reduced during defrosting operation, then suction pressure is maintained above the performance limit, but defrosting operation time is extended
Solution Approach 1:
The system performs preliminary assessment of frost accumulation conditions (detecting outdoor heat exchanger temperature and operation time) before initiating defrosting operation. This allows the controller to determine whether defrosting is actually necessary, avoiding unnecessary defrosting operations that would extend operational interruptions.
Solution Approach 2:
The system dynamically adjusts the compressor rotational speed during defrosting operation based on real-time monitoring of suction pressure. The controller increases rotational speed only when suction pressure exceeds the predetermined threshold, and reduces it when suction pressure approaches the performance limit. This dynamic adjustment optimizes the balance between maintaining reliable operation and minimizing defrosting time.
2Loss of time
If the compressor's rotational speed is increased during defrosting operation, then defrosting operation time is shortened, but suction pressure falls below the performance limit
Solution Approach 1:
The system implements a feedback control mechanism where the controller continuously monitors suction pressure during defrosting operation and adjusts compressor rotational speed in real-time. When suction pressure exceeds the predetermined threshold, the controller increases rotational speed to accelerate defrosting. When suction pressure approaches the performance limit, the controller reduces rotational speed to maintain reliable operation. This closed-loop feedback system resolves the contradiction by making rotational speed a dynamic variable rather than a fixed value.
3Productivity
If the defrosting operation interval time is extended, then heating operation restoration is delayed, but frost accumulation is allowed to grow larger
Solution Approach 1:
The system performs preliminary detection of frost accumulation conditions by monitoring outdoor heat exchanger temperature and heating operation duration before frost becomes problematic. When the heat exchanger temperature is below the predetermined threshold and operation time exceeds the predetermined duration, the system proactively initiates defrosting operation. This preliminary action prevents excessive frost accumulation while minimizing interruptions to heating operation.
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 ensures that the defrosting operation is completed efficiently, even when the compressor's rotational speed cannot be increased, thereby preventing extended defrosting times and ensuring timely restoration of heating operations.
Implementation Method 1
a compressor (21), an outdoor unit control means (200)
Implementation Method 2
an outdoor heat exchanger (23)
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
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.