System and method for OCR control in paralleled compressors
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Solution Overview
Problem
In HVACR systems with compressors arranged in parallel, there is a challenge in reliably maintaining lubricant circulation rates, leading to lubricant loss and reduced compressor reliability due to uneven compressor capacities and operational states, where gas flow can prevent lubricant from returning to the sump.
Innovation Solution
The implementation of a flow restrictor in the lubricant transfer conduit between compressors to control refrigerant flow and reduce lubricant circulation rates, ensuring that lubricant is retained in the sump by increasing gas flow resistance and maintaining a predetermined lubricant circulation rate.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If compressors are arranged in parallel with different capacities, then system flexibility and cooling capacity are improved, but lubricant circulation becomes uneven leading to lubricant loss
Solution Approach 1:
The patent applies local quality by introducing a flow restrictor specifically in the lubricant transfer conduit connected to the lower capacity compressor. This localized modification creates different flow resistance characteristics for different compressors, allowing the system to maintain reliable lubricant circulation in each compressor despite their different capacities. The flow restrictor is positioned at a specific location (lubricant transfer conduit) to address the specific problem of uneven lubricant distribution.
2Productivity
If gas flow rate through lubricant transfer conduit is high, then heat exchange efficiency is improved, but lubricant cannot return to sump causing lubricant loss
Solution Approach 1:
The flow restrictor acts as an intermediary element in the lubricant transfer conduit. It mediates between the gas flow (which needs to move freely for heat exchange efficiency) and the lubricant return (which needs sufficient driving pressure). The flow restrictor selectively increases resistance to gas flow while allowing lubricant to return to the sump, thus resolving the conflict between heat exchange efficiency and lubricant retention.
3Reliability
If flow restrictor is added to control lubricant circulation, then lubricant loss is reduced, but device complexity increases
Solution Approach 1:
The flow restrictor is implemented as a simple, inexpensive component that can be easily installed and maintained. It may be a simple orifice, restriction plate, or small valve rather than a complex active control system. This approach achieves reliable lubricant circulation control without significantly increasing system complexity or cost, making the solution practical for real-world HVACR applications.
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 reduces lubricant loss and improves compressor reliability by maintaining a stable lubricant level in the sump, enhancing heat exchange efficiency and energy savings, particularly under partial load conditions.
Implementation Method 1
controlling a refrigerant flow rate between the first compressor and the second compressor through an increase of a gas flow resistance in the lubricant transfer conduit
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
Implementation Method 3
the lubricant is entrained in a heat transfer fluid of a heat transfer circuit of the HVACR system
Data Source
AI summary
A heating, ventilation, air conditioning, and refrigeration (HVACR) system includes a first compressor having a first capacity, a second compressor having a second capacity, a condenser, an expansion device, and an evaporator fluidly connected. The first compressor and the second compressor are arranged in parallel. The first compressor includes a first lubricant sump. The second compressor includes a second lubricant sump. The first lubricant sump is fluidly connected to the second lubricant sump via a lubricant transfer conduit. A flow restrictor is disposed in the lubricant transfer conduit. The flow restrictor is configured to reduce a refrigerant flow between the first compressor and the second compressor.