System and method for lubricant separation and return control
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Solution Overview
Problem
In HVACR systems, lubricant management is challenging when multiple compressors are connected in parallel, as lubricant tends to stay in suction cavities rather than draining to the sump, especially when compressors are staged off, leading to low lubricant levels and reliability issues.
Innovation Solution
A lubricant separator is used to separate the lubricant-rich and lubricant-free portions of the heat transfer fluid, directing the lubricant-rich portion directly to the compressor sumps via a dedicated conduit, while the lubricant-free portion goes to the suction inlets, preventing lubricant from rerunning through the suction line and ensuring it reaches the sump with the highest pressure.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If compressors are connected in parallel with shared suction lines, then system productivity and flexibility are improved, but lubricant management deteriorates as lubricant stays in suction cavities rather than draining to sumps
Solution Approach 1:
The suction line system is segmented into two separate pathways: a lubricant-free suction line for gas flow and a dedicated lubricant return line for lubricant drainage. This segmentation allows independent control of lubricant flow while maintaining parallel compressor operation, resolving the contradiction between system productivity and lubricant management reliability.
Solution Approach 2:
Lubricant is extracted from the shared suction line and routed through a separate dedicated return line directly to the sumps. By taking out the lubricant flow path from the common suction system, the patent prevents lubricant from being rerouted through suction lines while maintaining efficient compressor operation.
2Reliability
If lubricant separator directs lubricant-rich portion to suction inlets, then compressor lubrication is improved, but lubricant accumulates in suction cavities and fails to drain to sumps
Solution Approach 1:
Instead of directing lubricant-rich portion to suction inlets as in conventional systems, the patent inverts the approach by directing lubricant-rich portion through a dedicated return line directly to the sumps. This inversion ensures lubricant reaches the sump for proper drainage while maintaining adequate lubrication through controlled delivery.
Solution Approach 2:
A dedicated lubricant return line acts as an intermediary pathway between the lubricant separator and the sumps. This intermediary structure enables direct, controlled lubricant delivery to the sump without interference from suction line pressure dynamics, resolving the contradiction between lubrication quality and drainage efficiency.
3Loss of energy
If compressors are staged on and off, then energy efficiency is improved, but lubricant levels in operating compressors decrease due to rerunning through suction line
Solution Approach 1:
The system establishes a dedicated lubricant return pathway in advance that remains functional regardless of compressor staging. This preliminary action ensures that when compressors are staged on and off, lubricant from the evaporator and idle compressors is pre-routed directly to the sump through the dedicated line, preventing lubricant level depletion in operating compressors while maintaining energy efficiency.
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 effectively manages lubricant levels across all load steps and conditions, improving compressor reliability by ensuring lubricant is directed into the sump instead of being rerouted through the suction line, thereby maintaining optimal lubrication.
Implementation Method 1
separating a flow of a heat transfer fluid and lubricant mixture into a lubricant rich portion and a lubricant free portion
Implementation Method 2
the lubricant sump is disposed at a relatively vertically lower portion of the compressor such that lubricant can be collected in the lubricant sump via gravitational force
Data Source
Figure 1A
Figure 1B
Figure 1C
AI summary
An HVACR system includes first and second compressors arranged in parallel, a condenser, an expansion device, an evaporator, and a lubricant separator fluidly connected. The first compressor includes a first lubricant sump and a first suction inlet. The second compressor includes a second lubricant sump and a second suction inlet. The lubricant separator is disposed between the evaporator and the first and second compressors, and includes a fluid inlet and two fluid outlets. A first of the two fluid outlets is fluidly connected to at least one of the first and second lubricant sumps. A second of the two fluid outlets is fluidly connected to the first and second suction inlets. The second fluid outlet includes a nozzle disposed within a flow passage of the lubricant separator such that a space is maintained between an outer surface of the nozzle and an inner surface of the flow passage.