Variable capacity screw compressor and method
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Solution Overview
Problem
Conventional screw compressors for refrigeration systems face challenges in achieving efficient part-load performance and variable capacity operation, particularly in operating at rotational speeds above synchronous motor speeds, while maintaining high efficiency across different rated capacities, due to increased mechanical complexity and efficiency penalties from slide valves, poppets, and variable speed drives.
Innovation Solution
A variable capacity screw compressor design featuring a rotor housing with a suction port, working chamber, and discharge port, configured with a selected rotational speed to operate at least one screw rotor at an optimum peripheral velocity independent of the rated capacity, utilizing a motor and variable speed drive to achieve efficient operation across different capacities.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If conventional screw compressors use synchronous motor rotational speed for rated capacity, then the design is simpler and more reliable, but the efficiency at part-load conditions deteriorates and variable capacity operation is limited
Solution Approach 1:
The patent applies dynamics by enabling the screw compressor to operate at variable rotational speeds above synchronous motor speed. The system transitions from fixed synchronous speed operation to dynamic variable speed operation, allowing the compressor to adapt its rotational speed to match part-load conditions while maintaining optimal peripheral velocity for efficiency.
Solution Approach 2:
The patent changes the operational parameters by operating the screw compressor at rotational speeds substantially above synchronous motor rotational speed. By adjusting the rotational speed parameter while configuring the inlet port, discharge port, and screw rotors appropriately, the system achieves optimal peripheral velocity at different capacity levels without requiring complex mechanical adjustment mechanisms.
2Loss of energy
If screw compressors operate at rotational speeds above synchronous motor speed, then part-load efficiency improves, but maintaining high efficiency across different rated capacities becomes difficult
Solution Approach 1:
The patent applies parameter changes by configuring the inlet port, discharge port, and screw rotors with specific dimensions and geometries that correspond to the selected rotational speed above synchronous speed. This configuration ensures that the peripheral velocity of the screw rotors operates at an optimum value that maintains high efficiency across different rated capacities when operating at the elevated rotational speed.
Solution Approach 2:
The patent achieves universality by designing a standardized configuration of inlet port, discharge port, and screw rotors that can be applied across multiple screw compressor models with different rated capacities. This universal configuration allows all models to operate at the same optimum peripheral velocity when running at the selected rotational speed, ensuring consistent high efficiency across the product family.
3Adaptability or versatility
If slide valves or poppets are added to improve part-load performance, then capacity control is achieved, but mechanical complexity increases and efficiency is reduced
Solution Approach 1:
The patent applies the taking out principle by removing the need for slide valves, poppets, or other mechanical capacity control devices. Instead of adding these complex components, the system achieves part-load performance through variable speed operation of the screw rotors, extracting the capacity control function from mechanical devices and implementing it through rotational speed variation.
4Loss of energy
If variable speed drives are added to achieve efficient operation above synchronous speed, then part-load efficiency improves, but device complexity and cost increase
Solution Approach 1:
The patent applies dynamics by implementing variable speed operation of the screw compressor. The system dynamically adjusts the rotational speed above synchronous motor speed to match part-load conditions, enabling the compressor to operate at optimal peripheral velocity across different capacity levels and achieve high part-load efficiency through dynamic speed control.
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 the ability to produce screw compressors with different rated capacities that maintain high efficiency at the same optimum peripheral velocity, improving energy savings and scalability.
Implementation Method 1
A motor is operable 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
Implementation Method 2
A variable speed drive receives a command signal from a controller and generates a control signal that drives the motor at the rotational speed
Implementation Method 3
Screw compressors are positive displacement, volume reduction devices. 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. A method for sizing at least two variable capacity screw compressors and a refrigeration chiller incorporating a variable capacity screw compressor are separately presented.