Rotary compressors with variable speed and volume control
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Solution Overview
Problem
Conventional rotary screw compressors face inefficiencies at part-load conditions due to limitations in controlling the compression ratio and motor efficiency, leading to reduced energy savings and operational control, especially when using slide valve arrangements or variable speed drives independently.
Innovation Solution
A system that controls the radial and axial volume ratios of the discharge port in conjunction with variable speed control of the motor driving the compressor rotors, using a permanent magnet motor connected to a variable speed drive, to optimize rotor tip speed and adjust volume ratios based on operating conditions, thereby enhancing efficiency and operational control.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If slide valve arrangements are used to control volume ratio, then part-load performance is improved, but device complexity and maintenance requirements increase
Solution Approach 1:
The invention removes the slide valve component entirely from the compressor system. Instead of using a slide valve to control volume ratio, the patent employs a fixed displacement compressor paired with a variable speed motor, extracting the problematic moving valve part while retaining the desired part-load performance through electronic speed control.
Solution Approach 2:
The invention replaces the mechanical slide valve arrangement with an electrical control system. A variable speed motor (VSD) electronically controls the compressor speed to match part-load requirements, substituting mechanical volume ratio adjustment with electrical speed variation, thereby eliminating mechanical complexity and maintenance needs.
2Productivity
If variable speed drives are used to control motor loading, then part-load efficiency is improved, but motor efficiency drops at lower speeds
Solution Approach 1:
The invention changes the operating parameters of the motor by using a variable speed drive to optimize the motor's rotational speed and torque output at different load conditions. This allows the motor to operate at efficient points across a range of loads, compensating for the natural efficiency drop at lower speeds through intelligent parameter adjustment.
3Quantity of substance
If conventional compressors operate at part-load conditions, then capacity is reduced, but energy consumption remains high
Solution Approach 1:
The invention makes the compressor system dynamic by implementing variable speed control. Instead of operating at fixed speed with mechanical capacity reduction methods, the compressor motor speed dynamically adjusts to match the actual refrigeration load, ensuring that energy consumption is proportional to the required compression capacity at all operating conditions.
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 approach allows for efficient operation at varying loads by matching compressor speed to system requirements, reducing energy consumption and improving refrigeration system efficiency by minimizing unnecessary work and mechanical wear.
Implementation Method 1
a permanent magnet motor connected to a variable speed drive
Implementation Method 2
VSDs typically vary the frequency and/or voltage provided to the motor
Data Source
AI summary
Systems and methods are used to control operation of a rotary compressor of a refrigeration system to improve efficiency by varying the volume ratio and the speed of the compressor in response to current operating and load conditions. The volume of the axial and/or radial discharge ports of the compressor can be varied to provide a volume ratio corresponding to operating conditions. In addition, permanent magnet motors and/or control of rotor tip speed can be employed for further efficiency gains.