Rotary Screw Compressor Variable Volume Ratio and Speed 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.

Innovation Solution

A system that varies 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 control the volume ratio based on operating conditions.

Engineering Contradictions & Design Principles

VSEngineering 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

Engineering Contradiction:

Improvepart-load performanceVSAvoidcomplex arrangements to avoid interference

Core Design Contradiction:

ProductivityVSDevice complexity

Solution Approach 1:

The invention extracts and eliminates the slide valve component from the compressor system. Instead of using complex slide valve arrangements to control volume ratio, the patent employs a simpler rotor design with varying flute depths that inherently provides variable volume ratio control without requiring additional moving parts or complex mechanisms.

Inventive Principle:

Principle #2Taking out (Extraction)

Solution Approach 2:

Rather than using a slide valve to actively control volume ratio changes, the invention inverts the approach by designing the rotor flutes themselves to have varying depths. This passive geometric design allows volume ratio variation as a natural consequence of rotor geometry rather than requiring active valve control.

Inventive Principle:

Principle #13The other way round (Inversion)

2Use of energy by moving object

If variable speed drives are used to control motor loading, then part-load efficiency is improved, but motor efficiency drops at lower speeds

Engineering Contradiction:

Improvepart-load efficiencyVSAvoidmotor efficiency at lower speeds

Core Design Contradiction:

Use of energy by moving objectVSLoss of energy

Solution Approach 1:

The invention changes the geometric parameters of the rotor flutes (varying depths along the rotor length) to optimize compression throughout the rotation cycle. This allows the compressor to maintain efficient operation across a range of speeds by ensuring proper compression ratios are achieved regardless of rotational velocity.

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The varying flute depths create a dynamic compression profile that adapts to different operating conditions. As the rotor rotates, different sections of the flute engage at different times, providing optimized compression characteristics that maintain efficiency across variable speed ranges.

Inventive Principle:

Principle #15Dynamics

3Stress or pressure

If volume ratio is increased to improve compression, then discharge pressure increases, but gas diversion back to suction port causes suction gas heating and reduced efficiency

Engineering Contradiction:

Improvedischarge pressureVSAvoidsuction gas heating and re-compression

Core Design Contradiction:

Stress or pressureVSLoss of energy

Solution Approach 1:

The rotor is segmented into multiple flute sections with different depths. This segmentation allows different portions of the rotor to handle different compression tasks, enabling smooth compression progression that prevents excessive pressure buildup and gas diversion back to the suction port.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

Different sections of the rotor flute have different depths (local quality variations) optimized for their specific position in the compression cycle. This local optimization ensures that compression occurs efficiently at each stage without creating the pressure differentials that cause gas diversion and suction heating.

Inventive Principle:

Principle #3Local quality

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 enhances efficiency and operational control by matching compressor speed to load conditions, reducing energy consumption and mechanical wear, while maintaining optimal refrigeration performance across varying loads.

Implementation Method 1

a permanent magnet motor connected to a variable speed drive

Methodology Applied

Scientific EffectElectromagnetic induction: Electromagnetic Induction

Implementation Method 2

VSDs typically vary the frequency and/or voltage provided to the motor

Methodology Applied

Scientific EffectFrequency conversion:

Implementation Method 3

Gas compression occurs as the compression pocket volume decreases as the intermeshing screw rotors rotate

Methodology Applied

Scientific EffectVolume reduction compression: Compression

Data Source

PatentUS10533556B2Rotary compressors with variable speed and volume control

Publication Date: 2020.01.14 TRANE INTERNATIONAL INC

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.