Variable Capacity Screw Compressor Operating Above Synchronous Speed
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Solution Overview
Problem
Conventional screw compressors for refrigeration systems face inefficiencies and increased mechanical complexity when attempting to achieve variable capacity operation at part-load conditions, particularly when operating at rotational speeds above synchronous motor speeds, and struggle to maintain high efficiency across different rated capacities.
Innovation Solution
A variable capacity screw compressor design featuring a rotor housing with a suction port, working chamber, and discharge port, driven by a motor and variable speed drive, where the rotational speed is optimized to maintain a constant optimum peripheral velocity independent of the rated capacity, allowing for efficient operation across a range of capacities without the need for slide valves or poppets.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If conventional screw compressors operate at synchronous motor rotational speed for rated capacity, then the motor operates efficiently, but the screw rotor cannot achieve optimum peripheral velocity for high efficiency compression
Solution Approach 1:
The patent applies variable speed drive technology to dynamically adjust the motor's rotational speed above synchronous speed, allowing the screw rotor to operate at its optimum peripheral velocity for high efficiency compression while the motor operates in its efficient range through electronic speed control
Solution Approach 2:
The patent changes the operational parameters by operating the motor at rotational speeds substantially above synchronous motor rotational speed for the rated capacity, and configures the inlet port, discharge port, and screw rotor dimensions to achieve optimum peripheral velocity at these higher speeds
2Adaptability or versatility
If slide valve arrangements are used to achieve variable capacity operation, then part-load performance improves, but mechanical complexity and device reliability deteriorate
Solution Approach 1:
The patent removes the slide valve arrangement from the system entirely, achieving variable capacity operation through variable speed drive control of the motor, thereby eliminating the mechanical complexity, sealing requirements, and reliability issues associated with slide valves
Solution Approach 2:
The patent replaces the mechanical slide valve capacity control system with an electronic variable speed drive system that controls the motor speed, substituting mechanical complexity with electronic control to achieve the same variable capacity function
3Adaptability or versatility
If slide valve arrangements are used for capacity control, then variable capacity operation is achieved, but efficiency at part load deteriorates due to increased leakage area
Solution Approach 1:
The patent removes the slide valve that creates leakage paths, eliminating the source of part-load efficiency deterioration while maintaining capacity control through variable speed operation
Solution Approach 2:
The patent replaces the mechanical slide valve capacity control with electronic speed control, eliminating the leakage area created by the slide valve interface and thereby preventing the efficiency loss that occurs at part-load conditions
4Adaptability or versatility
If different screw compressor configurations are produced for different rated capacities, then capacity requirements are met, but manufacturing complexity and inventory requirements increase
Solution Approach 1:
The patent designs a universal screw rotor with optimized geometry that can operate at high efficiency across a wide range of rotational speeds and capacities, allowing a single rotor design to serve multiple rated capacity applications through variable speed operation
Solution Approach 2:
The patent achieves different rated capacities by changing the operational parameters (rotational speed, inlet port size, discharge port size) rather than changing the fundamental rotor geometry, allowing flexible capacity adjustment without redesigning the core compression element
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 design enhances efficiency and reduces mechanical complexity by enabling operation at higher rotational speeds, achieving approximately constant high efficiency across different capacities, with improved part-load performance and reduced energy losses compared to conventional systems.
Implementation Method 1
a motor and a variable speed drive. The rotor housing comprises a suction port, a working chamber, a discharge port, and at least two screw rotors that comprise a female screw rotor and a male screw rotor being positioned within the working chamber for cooperatively compressing a fluid
Implementation Method 2
Screw compressors are positive displacement, volume reduction devices. The intermeshing screw rotors are mounted for rotation in a working chamber defined by a compressor or rotor housing. As the intermeshing screw rotors rotate, the compression pocket is closed off from the suction port. Gas compression occurs as the compression pocket volume decreases as the intermeshing screw rotors rotate
Data Source
AI summary
A variable capacity screw compressor comprises a suction port, at least two screw rotors and a discharge port being configured in relation to a selected rotational speed that operates at least one screw rotor at an optimum peripheral velocity that is independent of a peripheral velocity of the at least one screw rotor at a synchronous motor rotational speed for a rated screw compressor capacity. A motor is configured to drive the at least one screw rotor at a rotational speed at a full-load capacity that is substantially greater than the synchronous motor rotational speed at the rated screw compressor capacity. A variable speed drive receives a command signal from a controller and generates a control signal that drives the motor at the selected rotational speed.