Compressed Air Best Practices - January 2008 - (Page 10)

| 01/08 Focus Industry ENERGY MANAGEMENT | REAL WORLD BEST PRACTICES Selecting a VSD Rotary Compressor 65 Constant Speed Drive versus Variable Speed Drive at Same Load and Pressure 60 When Do You Apply Variable Speed Drive? Of all the capacity controls available on lubricant free and lubricant cooled rotary screw compressors, none are more power efficient in “their effective turn down range” than VSD’s. VSD’s can operate “in part load at or near full load efficiency.” This effective turn down range will vary with different manufactures, different types of VSD drives and the performance profile of the rotary screw air end. For estimating purposes the most effective turn down range will usually run from 40% and up to 80% of full flow. Lubricant cooled rotary screws will usually have a wider effective turn down range than lubricant free models. Review the unit’s specific performance data to establish this. VSD’s also offer the ability to pull down to very low loads (15–25%) with relative efficiency and then shut off and restart more times per hour than a similar constant speed induction motor. Certain types of drives have greater ability for unlimited starts and stops per hour than others. When reviewing various options for a specific load profile do not overlook this very important feature; it can and will save significant energy dollars under certain conditions. Almost all manufacturers offer unlimited starts and stops per hour. Review this performance with careful detail to your application. These statements make it clear that Variable Speed Drives with lubricant free or lubricant cooled rotary screw air ends are a very effective tool, when properly applied can offer great energy dollars savings. They offer: p 55 75 hp modulation compressor 50 K i l o w a t t s 45 40 75 hp VSD 35 30 25 20 15 10 24 hours TYPICAL ELECTRIC MOTOR OPERATING CHARACTERISTICS (.90 ME) ME & PF % 100 100 75 100 80 S AMP EFFIC IENCY % AMPS kW % 75 60 50 P E OW AC RF R TO Rated Load 50 40 TTS WA 25 20 0 0 0 13% 25% 48% 50% 63% 75% 88% 100% Horsepower NOTE: 1. These operating charactersitics will vary with motor type, basic design, motor efficiency, constant or variable speed, etc.. 2. Amperage will vary indirectly with changes in rated voltage. Excellent trim capability when required. Deliver an effective steady pressure 1–2 psig operating band within their turn down range. Ability to effectively start and stop the motor more often when required. BHP / KW p AMPS / VOLTS OLTS O p INPUT HP / KW MOTOR OUTPUT HP / KW 10 www.airbestpractices.com http://www.airbestpractices.com

Table of Contents Feed for the Digital Edition of Compressed Air Best Practices - January 2008

Compressed Air Best Practices - January 2008 Contents Focus Industry Features Compressed Air Industry Articles From the Editor Real World Best Practices: Selecting A VSD Rotary Compressor Audit of the Month: Energy Savings in Peru The Low-Hanging Fruit in Pneumatic Systems Mikropor America, Inc. Wireless Sensor Networks: Improve Efficiency in Compressed Air Systems Special Report: The Chicago Pneumatic Compressor Launch in North America The Importance of Measuring Vacuum The Comp-Air Service Co. Special Report: The 2007 NAACD Wall Street Watch Advertiser Index Job Market

Compressed Air Best Practices - January 2008

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