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.

The Quantima

The QuantimaThe Quantima is an oil-free centrifugal compressor. The Quantima air compressor has several key technologies that make them the most advanced compressors on the market today.

In this article we are going to focus on the core of the Quantima, the Q-Drive, which is a high-speed electric motor with magnetic bearings. The patented Q-Drive motor incorporates an asynchronous induction design and operates at high speeds to avoid the need for a conventional gearbox. Without a gearbox, you are eliminating costly losses in efficiency and parts that need to be replaced as they wear down. And of course, since there is no gear box, this means the compressor does not require any oil at all. The copper coated, solid steel rotor has the impellers directly coupled to it. This gives the Quantima a single rotating assembly with no mechanical contact. There is a huge gain in efficiency as a result of no gearbox or contact parts. A great example is the Off Load power consumption. The Quantima uses only 2.5% of full load power. No other brand even comes close to that as shown in this chart.

The Active Magnetic Bearings (AMB), are the second part of this unique design. A magnetic bearing is an electro-magnetic bearing which supports a load using magnetic levitation. These bearings levitate the rotor and impellers and permit motion without friction or wear. The bearings maintain the relative position of the rotating assembly (rotor) with respect to the stator. Using position sensors, the AMB controller calculates the appropriate control current to keep the rotor in the desired position and optimize performance. Once again, since there is no mechanical contact in this area, energy savings of up to 25% or more are easily achievable. Another great advantage to this design is that there is no performance degradation over the life of the compressor unlike standard screw technologies with wearing parts.