Multi-Split Air Conditioning Oil Return Under Low Refrigerant Flow
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Solution Overview
Problem
In air conditioning devices with multiple indoor units connected to an outdoor unit, the refrigerant flow rate in gas branch pipes can be lower than the required limit for oil collection, leading to refrigerating machine oil accumulation and increased risk of compressor lubrication-related malfunctions during energy-saving operations.
Innovation Solution
An air conditioning device with an operation controller that calculates the refrigerating machine oil accumulation in the interconnecting pipes and performs oil collection when the flow rate in gas branch pipes falls below a predetermined limit, ensuring the oil is collected back into the compressor, thereby maintaining adequate lubrication.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If the target evaporation temperature rises or target condensing temperature falls to save energy, then energy efficiency is improved, but the refrigerant flow rate in gas branch pipes decreases below the lower limit required for oil collection
Solution Approach 1:
The controller performs preliminary determination of whether the refrigerant flow rate in gas branch pipes is below the lower limit before oil collection is needed. By comparing the refrigerant flow rate with the lower limit threshold in advance, the system proactively identifies conditions that would prevent proper oil collection, and can take preventive actions such as adjusting operating parameters or triggering oil collection routines before oil accumulation becomes problematic.
2Loss of energy
If the refrigerant flow rate in gas branch pipes is low during energy-saving operation, then energy consumption is reduced, but refrigerating machine oil accumulates in the pipes and fails to return to the compressor
Solution Approach 1:
The controller continuously monitors the refrigerant flow rate in gas branch pipes and compares it with the lower limit required for oil collection. This feedback mechanism allows the system to detect when low flow conditions are occurring and automatically respond by initiating oil collection operations or adjusting system parameters to restore proper oil return to the compressor.
Solution Approach 2:
The system changes operating parameters such as the target evaporation temperature or target condensing temperature to alter the refrigerant flow rate. By adjusting these parameters, the controller can increase the refrigerant flow rate above the lower limit threshold when oil collection is needed, while still maintaining energy-efficient operation when conditions permit.
3Productivity
If the refrigerant flow rate in gas branch pipes falls below the lower limit, then the system operates in a low-flow state, but the refrigerating machine oil adheres to heat exchanger tube surfaces and fails to return to the compressor
Solution Approach 1:
The controller performs preliminary determination of whether the refrigerant flow rate in gas branch pipes is below the lower limit before oil collection is needed. By comparing the refrigerant flow rate with the lower limit threshold in advance, the system proactively identifies conditions that would prevent proper oil collection, and can take preventive actions such as adjusting operating parameters or triggering oil collection routines before oil accumulation becomes problematic.
Solution Approach 2:
The controller continuously monitors the refrigerant flow rate in gas branch pipes and compares it with the lower limit required for oil collection. This feedback mechanism allows the system to detect when low flow conditions are occurring and automatically respond by initiating oil collection operations or adjusting system parameters to restore proper oil return to the compressor.
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 solution enhances the precision of oil collection operations, reducing the risk of compressor malfunctions by ensuring the refrigerating machine oil is properly returned to the compressor, even during energy-saving modes where refrigerant flow rates are low.
Implementation Method 1
when a flow rate of the gaseous refrigerant is high, the refrigerating machine oil that adhered to the interior surfaces of the heat exchanger tube and the refrigerant pipe is pushed by the gaseous refrigerant, flows inside the refrigerant circuit, and returns to the compressor
Implementation Method 2
in gaseous portion of the refrigerant, portion of the refrigerating machine oil adheres to interior surfaces of a heat exchanger tube of a heat exchanger and a refrigerant pipe
Data Source
Figure 1
Figure 2
Figure 3~4
AI summary
A multi-type air conditioning device (10) controls an evaporation temperature and a condensing temperature, depending on required capacity of an indoor unit (40). The air conditioning device (10) compares a current evaporation temperature or condensing temperature with a reference value, of an evaporation temperature or an condensing temperature, corresponding to a lower limit flow rate, of a gaseous refrigerant, required for refrigerating machine oil not to accumulate in, but to flow through, the gas branch pipes (72b), and calculates an amount of the refrigerating machine oil accumulated in a gas branch pipe (72b) which does not satisfy the lower limit flow rate. When the calculated amount exceeds a set amount, the air conditioning device (10) performs oil collecting operation, and controls the oil collecting operation in view of a flow rate of a gaseous refrigerant in gas branch pipes (72).