Compressed Air Best Practices - January 2008 - (Page 13)

Focus Industry ENERGY MANAGEMENT | 01/08 | Plant Example — Lubricant-Free Rotary Screw One processing plant has a 1,526 cfm, 300 hp compressor and a 1,026 cfm, 200 hp compressor. Both are fixed speed, lubricant free two-stage rotary screw compressors. The 1,526 cfm model runs base load and the 1,026 cfm, 200 hp model is used as the trim machine. A sales presentation on a 1,526 cfm class variable speed drive two-stage lubricant free rotary screw compressor pointed out that at 50% load (750 cfm), the compressor was at only 50% of full-load power. According to the sales presentation, a new variable speed drive 1,526 cfm trim unit in the system could slash electrical energy costs by as much as 40%. The data sheets supplied by the salesperson included BHP (shaft horsepower) ME and full-load amps but not PF or input kW. The manufacturer then supplied input kW data at various loads to allow an accurate comparison. The plant was able to fill out a load profile/ operating cost estimate sheet. For this specific example, the total estimated annual electrical energy cost with the existing 1,526 cfm base load unit and the existing 1,026 cfm trim unit with two-step control is $142,784. The total estimated annual electrical energy cost with the existing 1,526 cfm base load unit and “new” 350 hp class variable speed drive unit is $149,616. In this particular case, the existing 200 hp two-step control unit acting as the trim unit has an estimated $6,832 lower electrical energy cost (at 0.05 kWh) than an alternate variable speed driven lubricant-free rotary screw compressor. However, in another profile with other equipment — or even the same equipment — the variable speed driven unit might offer significant savings. There are other articles and publications describing a complete review of your air system. You can do this yourself, ask the VSD equipment sales personnel or hire an independent consultant. Don’t make unguided decisions because you could miss golden opportunities. The key point is that plants should NOT simply assume the variable speed drive will be the silver bullet that will reduce compressed air energy costs. It is important for plant operators to: p conditions to evaluate true operating cost. The plant example provided here is somewhat simplistic in that the production process does not vary much. However, the example is based on an actual processing plant’s logged data. p Obtain all the important data, particularly input kW, for all units at critical percent-of-load points. Plants can and should evaluate existing equipment. Identify and optimize demand or load profile over all pertinent conditions — production, nonproduction, etc. Assign hours per year to each of these Identify blended electrical power costs in $0.0/kWh, but do not lose sight of the effect on demand charge if a smaller or variable speed drive can trim and shut off a larger unit. Prepare an operating cost comparison. Optimize the system. Is it necessary to have air on during weekends and holidays? How much air is essential? How much air is being lost to leaks? p p p GERMAN ENGINEERING Conclusion It is critical to accurately ascertain the demand profile prior to considering the cost effectiveness of any new compressors. This axiom applies whether considering VSD or any other type of drive and capacity control. Only then can you accurately review the measured or projected input kW and the overall impact on your electric energy cost. DISCOVER W W W.DISCOVERCURTIS.COM ©2007 Curtis-Toledo, Inc. 13 17637 07 CTGNL German Ad.indd 1 www.airbestpractices.com 9/4/07 4:15:30 PM http://WWW.DISCOVERCURTIS.COM http://WWW.DISCOVERCURTIS.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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