Multi-Unit Refrigerant Equalization During Defrost and Load Changes
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Solution Overview
Problem
Air-conditioning apparatuses face challenges in managing refrigerant flow during non-normal operations, such as switching from heating to defrosting or rapid changes in load, leading to backflow of liquid refrigerant into the compressor and uneven distribution among heat source units.
Innovation Solution
An air-conditioning apparatus with a controller that determines non-normal operations and adjusts the flow control valves to equalize liquid refrigerant among heat source units, using a determination unit to identify such operations and a liquid equalization unit to manage the flow, thereby preventing backflow and ensuring balanced refrigerant distribution.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If a common gas pipe and common liquid pipe connect multiple heat source units to increase system capacity, then the system can serve larger loads, but liquid refrigerant backflow to compressors occurs during non-normal operations such as defrosting or rapid load changes
Solution Approach 1:
An accumulator is introduced as an intermediary device between the common liquid pipe and each heat source unit. The accumulator acts as a buffer that temporarily stores liquid refrigerant, preventing it from flowing back to the compressor during non-normal operations such as defrosting or rapid load changes, while still allowing the system to operate at high capacity
2Manufacturing precision
If flow control valves are adjusted to equalize liquid refrigerant distribution among heat source units during normal operation, then refrigerant distribution is balanced, but the system cannot respond quickly enough during rapid load changes or start-stop operations
Solution Approach 1:
The accumulator is positioned upstream in the refrigerant flow path, performing preliminary action by equalizing liquid refrigerant distribution before it reaches the heat source units. This preliminary equalization ensures that even during rapid load changes or start-stop operations, the refrigerant reaching each unit is already balanced, eliminating the need for slow reactive adjustments
3Adaptability or versatility
If the heat source unit is stopped before liquid equalization control is completed during load changes, then the system can adapt to load variations, but excess liquid refrigerant accumulates and may backflow to the compressor
Solution Approach 1:
The accumulator serves as a cushioning device that anticipates potential liquid refrigerant accumulation problems. By providing a storage buffer beforehand, it cushions against the harmful effects of excess liquid refrigerant that would otherwise backflow to the compressor when units are stopped during load changes, allowing the system to adapt to load variations without compromising reliability
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
The solution effectively prevents backflow of liquid refrigerant into the compressor and ensures even distribution during non-normal operations, maintaining system efficiency and reliability by reducing the need for larger accumulator volumes.
Implementation Method 1
a heat-source-side heat exchanger (4) that causes heat exchange to be performed between refrigerant and outdoor air
Implementation Method 2
a compressor (2) that compresses refrigerant gas
Implementation Method 3
a flow control valve (6) that controls a flow rate of refrigerant
Data Source
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AI summary
An air-conditioning apparatus includes: a plurality of heat source units each including a compressor, a heat-source-side heat exchanger, a flow control valve, and an accumulator; a use-side load connected to the heat source units by pipes, and including a use-side heat exchanger that causes heat exchange to be performed between refrigerant supplied from each of the heat source units and a use-side heat medium; and a controller that controls an operation of each of the heat source units. The controller includes a determination unit and a liquid equalization unit. The determination unit determines whether or not a current operation is a non-normal operation in which the heat source units and the use-side load operate in a different manner from that in a heating operation or a cooling operation. The liquid equalization unit equalizes the amounts of liquid refrigerant that flows in the heat source units, when the determination unit determines that the current operation is the non-normal operation.