Parallel Compressor Lubricant Management Using Flow Control Device
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Solution Overview
Problem
In HVACR systems with multiple compressors connected in parallel, existing lubricant management systems can disrupt temperature control by modifying compressor operations to maintain lubricant levels, leading to inefficiencies and potential insufficient lubrication.
Innovation Solution
A flow control device is used to separate the heat transfer fluid into lubricant-rich and lubricant-free portions, directing the lubricant-rich portion to a variable speed upstream compressor and the lubricant-free portion to a fixed speed downstream compressor, while maintaining a differential pressure to ensure lubricant transfer between the compressors via a lubricant transfer conduit.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a lubricant level switch is used to monitor lubricant levels and modify compressor operation, then lubricant supply sufficiency is improved, but temperature control performance deteriorates due to compressor operation modifications
Solution Approach 1:
The suction conduit flow is segmented into multiple streams using a flow control device with separate outlets. One outlet provides lubricant-rich flow to the first compressor while another outlet provides lubricant-free flow to the second compressor, allowing independent lubricant management for each compressor without affecting overall system temperature control
Solution Approach 2:
A flow control device acts as an intermediary component between the evaporator and the parallel compressors. This device separates the mixed lubricant and refrigerant flow into distinct streams, enabling precise lubricant distribution to each compressor while maintaining stable system operation and temperature control
2Reliability
If compressor operation is modified to maintain lubricant levels, then lubricant management is improved, but system efficiency deteriorates
Solution Approach 1:
The flow control device performs preliminary separation of lubricant-rich and lubricant-free flows before the refrigerant enters the compressors. This preliminary action ensures each compressor receives the appropriate lubricant concentration from the start, eliminating the need for reactive compressor operation modifications and maintaining continuous efficient operation
Solution Approach 2:
The system uses the inherent lubricant content in the suction refrigerant flow to automatically satisfy the lubricant requirements of each compressor. The flow control device directs lubricant-rich flow to compressors needing lubrication while sending lubricant-free flow to compressors that don't require additional lubricant, allowing the system to self-regulate lubricant distribution without external intervention or operational disruptions
3Device complexity
If lubricant is supplied to multiple parallel compressors from a common suction conduit, then system complexity is reduced, but lubricant distribution control deteriorates
Solution Approach 1:
The common suction conduit is segmented into multiple independent flow paths using a flow control device with separate outlets for each compressor. This segmentation allows independent control of lubricant distribution to each compressor while maintaining a relatively simple overall system architecture without requiring complex external control mechanisms
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 ensures consistent lubricant supply to both compressors, maintaining efficient operation and temperature control by optimizing lubricant distribution and pressure differentials, thereby preventing compressor inefficiencies due to lubricant insufficiency.
Implementation Method 1
The flow control device can separate the gaseous heat transfer fluid of the suction conduit 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 collect in the lubricant sump via gravitational force
Implementation Method 3
the flow control device can be designed to control a differential pressure between the upstream compressor and the downstream compressor. Controlling the differential pressure between the upstream compressor and the downstream compressor can, for example, ensure that excess lubricant flows from the lubricant sump of the upstream compressor to the lubricant sump of the downstream compressor
Data Source
AI summary
A system includes first and second compressors arranged in parallel, a condenser, expansion device, evaporator, and flow control device fluidly connected. The first compressor includes a first lubricant sump and the second compressor including a second lubricant sump. A lubricant transfer conduit fluidly connects the first lubricant sump and the second lubricant sump. The flow control device 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 the first compressor, a second of the two fluid outlets is fluidly connected to the second compressor. The second fluid outlet includes a nozzle disposed within a flow passage of the flow control device such that a space is maintained between an outer surface of the nozzle and an inner surface of the flow passage.