Variable Capacity Screw Compressor at Optimum Rotor Speed
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Solution Overview
Problem
Conventional screw compressors for refrigeration systems face challenges in achieving efficient variable capacity operation at rotational speeds above synchronous motor rotational speed, with existing solutions like slide valves, poppets, and variable speed drives leading to efficiency losses, increased complexity, and reduced reliability.
Innovation Solution
A variable capacity screw compressor design featuring a rotor housing with a suction port, working chamber, and discharge port configured for a selected rotational speed that operates at least one screw rotor at an optimum peripheral velocity independent of the rated capacity, utilizing a permanent magnet motor and variable speed drive to achieve high efficiency across different capacities.
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 design is simpler and more reliable, but the peripheral velocity of screw rotors is suboptimal and efficiency is reduced
Solution Approach 1:
The patent changes the operational parameter of rotational speed from synchronous motor speed to a higher selected rotational speed that achieves optimum peripheral velocity of the screw rotors. This parameter change is enabled by configuring the inlet port, discharge port, and screw rotor geometry specifically for this selected speed, allowing the system to operate efficiently above synchronous motor rotational speed for rated capacity
2Adaptability or versatility
If variable capacity operation is implemented using slide valves or poppets, then capacity control is achieved, but mechanical complexity increases and reliability decreases
Solution Approach 1:
The patent extracts and eliminates the slide valve or poppet components from the system. Instead of using these mechanical devices for capacity control, the invention relies on the optimized inlet port configuration and screw rotor geometry that enable efficient variable capacity operation through rotational speed control alone, thereby reducing mechanical complexity and improving reliability
3Adaptability or versatility
If screw compressors are designed for different rated capacities with conventional approaches, then each capacity requires separate optimization, but this increases design complexity and prevents consistent high efficiency across capacities
Solution Approach 1:
The patent creates a universal design approach where the inlet port configuration, discharge port configuration, and screw rotor geometry are optimized for a selected rotational speed that achieves optimum peripheral velocity. This universal optimization enables multiple screw compressors with different rated capacities to all operate at high efficiency when running at their respective selected rotational speeds, eliminating the need for capacity-specific optimizations
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 enables efficient operation at both full-load and part-load conditions with reduced mechanical complexity, increased efficiency, and improved reliability, allowing for a range of capacities to be achieved with consistent high efficiency and reduced size and noise.
Implementation Method 1
a permanent magnet motor and variable speed drive
Data Source
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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. A method for sizing at least two variable capacity screw compressors and a refrigeration chiller incorporating a variable capacity screw compressor are separately presented.