Variable Speed Rotary Screw Compressors

One of the biggest advances lately in the air compressor industry has undoubtedly been the introduction of the variable speed rotary screw compressor.  With increasing demand for energy-efficient products, this technology has become very popular.  Just about every major compressor manufacturer has a variable speed product.  So let’s take a look at some of the benefits of implementing variable speed compressors and some things you should look for in a variable speed compressor.

Variable Speed Compressors can efficiently and reliably handle the varying air demand found in most plant air systems compared to other compressor types.  These compressors utilize variable speed drives to speed up and slow down the motor, matching air supply to air demand as it fluctuates.  At full load in the upper flow range, most compressor types will perform pretty close to each other.  As air-flow decreases, however, VSD compressors begin to stand out against modulating and even variable displacement compressors.  Once your demand drops down to the middle and lower ranges the VSD savings become even greater.  So what you need to look for is an efficient performance CURVE, not just efficiency at a single point.  By curve we are talking about airflow over the entire speed range of the compressor (x axis) plotted against the power required (y axis) to produce the flow.

Some important things to think about when looking at Variable Speed compressors is how they are put together.  The motor, drive and airend should all be matched so that efficiency is high and constant over a broad speed range.  Be wary of manufacturers who simply “adapt” their current products to a variable speed drive and motor.

If a variable speed compressor has so much potential to deliver such a low electrical cost compared to fixed speed compressor why doesn’t everyone just run out and buy one?  Every compressed air system is unique.  Typically, air demand in a plant varies widely throughout the day.  In addition, fluctuations can occur from one shift to another, by the week and even seasonally.  You need someone to evaluate your unique, often complex requirements and recommend a tailored solution.  If done correctly, a Variable Speed Compressor should save you money and maximize your plant’s productivity.  If you have not had one done recently, a compressed air audit of your plant air system should be your first step.  Not only can it help you decide whether a variable speed compressor is right for you, but an air audit is a great way to uncover many ways to improve energy efficiency and cost savings.