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The importance of flow…

In life, it is all about flow and balance. When you are in flow, you loose track of time and you are feeling at optimum levels of productivity. This is also true for compressed air systems, when using a flow meter.

Recently, we participated in two very cool projects that involved flow-based compressor sequencers. Flow based? Yes, partially. Of course, pressure is still controlled in these systems, but as we all know, too many pressure fluctuations and too many start/stops due to wrong control of a large compressor may lead to stress and eventually to burnout.

Therefore the flow signal should use to solve the following puzzle in real-time: Which compressor combination suits the demand best? If you do this right, it will lead to less pressure fluctuations and the most energy-efficient control of your compressed air system.

[Air Demand at desired pressure ] = [Compressor A]*100% + [Compressor B]*100% + [Compressor C] * X%,

where Compressors A and B are load/unload types (or centrifugal machines) and Compressor C is a variable type.

This way of controlling multiple compressors differs fundamentally from pressure-band / priority-based controllers. Especially in complex large systems with mixed compressor types, this traditional way of pressure-band control can become a recipe for disaster. The system is often fine-tuned by a specialist, during a specific production week which is hopefully representative for the entire year. But as soon as this person leaves the factory and air demand changes, the initial optimum might not be so optimal anymore. Resulting on costly blow-off, or short cycling of machines. Which will result in a stressed-out energy manager, paying 30 to 50% higher energy bills than expected.

With flow-based compressor sequencing, the actual demand will be analyzed continuously and based on this demand, the master controller will decide which compressor combination fits the demand best. The master controller is pre-programmed with essential data:

  • Compressor types and capacity
  • Efficiency curves of the compressors
  • Number of allowed start/ stops (some types cannot be stopped frequently due to motor size or other type-specific restrictions)
  • Running hours, service interval

All this data is fed into an “algorithm”, which seems to be a buzzword nowadays when talking about Industry 4.0, but is basically nothing more than a decision tree. A set of (smart) equations with some variables: Based on air demand, pressure, efficiency, running hours, start/ stops, etc, there will be one or more ideal combinations of compressors that match the equation. And when solved properly – even when demand profiles change over time- this will lead to the best possible efficiency level. On top of this, there is always redundancy, so in case of a problem with the master controller, compressors fall back into their local control, which is less efficient but at least provides a continuous flow of compressed air for production.

VPInstruments delivers high-quality multi-parameter sensors that measure flow, pressure, temperature, and totalized flow. Vital data forms the basis for these algorithms. Using this data to control your compressors can result in large energy savings. If you are interested to learn more, then respond to this article by liking or sharing. We will send you a white paper on this subject or put you into contact with one of our worldwide partners.

Written by Pascal van Putten – Owner, CEO of VPInstruments.