Multi-Split Air Conditioning Oil Collection Under Low Refrigerant Flow

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 minimum for oil collection, leading to refrigerating machine oil accumulation and increased risk of compressor lubrication 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 threshold, ensuring the oil is returned to the compressor, thereby maintaining adequate lubrication.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Loss of energy

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

Engineering Contradiction:

Improveenergy efficiencyVSAvoidoil collection reliability

Core Design Contradiction:

Loss of energyVSReliability

Solution Approach 1:

The system performs oil collection operations in advance before the refrigerant flow rate becomes too low to carry oil back to the compressor. The controller predicts when oil collection will be needed based on the scheduled temperature changes and executes oil collection proactively during energy-saving operations, preventing oil accumulation in branch pipes before it becomes a problem.

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

The controller monitors the refrigerant flow rate in gas branch pipes and compares it against the lower limit required for oil collection. When the flow rate approaches the threshold, the system automatically executes oil collection operations and adjusts future temperature scheduling to maintain adequate flow rates, creating a closed-loop control system that balances energy efficiency with oil collection reliability.

Inventive Principle:

Principle #23Feedback

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

Engineering Contradiction:

Improveenergy consumptionVSAvoidoil accumulation in pipes

Core Design Contradiction:

Loss of energyVSObject-generated harmful factors

Solution Approach 1:

The system implements periodic oil collection operations during energy-saving modes when refrigerant flow rates are low. The controller schedules these oil collection cycles at appropriate intervals to prevent oil accumulation while maintaining the energy-efficient low flow rate conditions, creating a rhythm of operation that alternates between energy-saving mode and oil collection mode.

Inventive Principle:

Principle #19Periodic action

3Reliability

If the flow rate of gaseous refrigerant in gas branch pipes is increased to ensure oil collection, then oil collection reliability is improved, but energy efficiency decreases

Engineering Contradiction:

Improveoil collection reliabilityVSAvoidenergy efficiency

Core Design Contradiction:

ReliabilityVSLoss of energy

Solution Approach 1:

The system performs oil collection operations in advance before the refrigerant flow rate becomes too low to carry oil back to the compressor. The controller predicts when oil collection will be needed based on the scheduled temperature changes and executes oil collection proactively during energy-saving operations, preventing oil accumulation in branch pipes before it becomes a problem.

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

The controller monitors the refrigerant flow rate in gas branch pipes and compares it against the lower limit required for oil collection. When the flow rate approaches the threshold, the system automatically executes oil collection operations and adjusts future temperature scheduling to maintain adequate flow rates, creating a closed-loop control system that balances energy efficiency with oil collection reliability.

Inventive Principle:

Principle #23Feedback

Data Source

PatentUS10184683B2Air conditioning device

Publication Date: 2019.01.22 DAIKIN INDUSTRIES LTD

AI summary

A multi-type air conditioning device controls an evaporation temperature and a condensing temperature, depending on required capacity of an indoor unit. The air conditioning device 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, and calculates an amount of the refrigerating machine oil accumulated in a gas branch pipe which does not satisfy the lower limit flow rate. When the calculated amount exceeds a set amount, the air conditioning device performs oil collecting operation, and controls the oil collecting operation in view of a flow rate of a gaseous refrigerant in gas branch pipes.