“Why Can’t I Just Install a Dust Collection VFD?”

It’s a question we get fairly regularly.

All you need to slow down the the fan on your dust collection system is a VFD, right? So simply installing the VFD will slow down the fan and therefore save electricity, right?

Yup, that’s right – installing the VFD will slow down the fan, which will reduce its energy use. However, this will also reduce the air volume moving through the system, and thus decrease the amount of suction at all drops. Unless your existing system is dramatically oversized – more air volume than necessary, and higher air velocities than needed – this will create a health and safety hazard.

So what can you do to save money on dust collection without compromising health and safety?

High Level View of a Dust Collection System

Let’s take a quick step back to so that we can build up a more complete picture. Here’s an idealized version of a dust collection system:

Simple Dust Collection System Overview Diagram

Let’s assume that this system is designed well, and that if the fan is running at full speed all workstations have adequate suction. Of course, this is not always the case in practice – even in systems that are well-designed the day they are installed, machines are moved and additions over time will generally degrade performance. But for the rest of this article, let us assume that we are dealing with a well-designed, well-performing system.

The relationship between the fan power and air volume is governed by the Affinity Laws (also known as the “Fan Laws”):

The Fan Law describes the relationship between the fan power and the air volume moved by the fan.

When running the system at full speed, we are all the way in the top right corner of the graph: 100% fan power, and 100% air volume.

Slowing the fan down using a VFD will move our operating point down down and to the left along the curve. This is intuitive – there is no way to reduce the fan power without also reducing the air volume.

So Why Can’t I Just Add a VFD?

Now it’s obvious why just adding a VFD alone won’t be able to save any energy – it would reduce the system air volume, and thus decrease the air volume and suction at all drops. Unless your system is dramatically oversized for your machines’ requirements, this will compromise the function of the dust collection system.

OK, so in order to reduce electricity use we must also reduce the total air volume. Can we somehow reduce the total air volume without compromising system performance?

The good news is that in the vast majority of factories, not all machines actually need suction at the same time. Here’s a representative example (showing real data from a US-based furniture manufacturer) of how much different workstations are used:

Workstation utilization at a US furniture manufacturer.

This means that the vast majority of the time, the air volume that is actually required by the entire system is significantly less than the design air volume – the air volume needed when all workstations need suction at the same time.

So, to answer our previous question: YES, we can reduce the total system air volume without compromising system performance – if we can somehow direct air flow exactly to the machines that need it.

How could we do that?

Let’s Direct Air Flow

The obvious answer is to install blast gates in the ducting leading to each machine, and always open blast gates to machines that require suction while closing blast gates to machines that do not require suction.

Blast gates can be either manual or automated. Manual gates are much cheaper, but have a number of significant drawbacks that make them a bad option for most applications:

  1. They require an operator to always open/close them. This takes away the operator’s time and focus from his job. Also, they are hardly ever opened and closed as intended; we have yet to see a factory equipped with manual gates that are consistently being used as designed.

  2. Manual blast gates are not tied in with the rest of the system – the VFD has no idea which gates are open or closed, and therefore cannot adjust its operation accordingly. This could lead to ducting collapse or material settling in the ducting.

For these reasons, automatic blast gates lead to better results. These can be tied in with machine activity sensors that automatically detect when each machine needs suction. The end result is that blast gates to active machines are always open, while blast gates to inactive machines are closed – and the machine operators do not need to think about this at all.

Automatic dust collection blast gate

OK, so now we have sensors and automatic blast gates that close to inactive machines. This generally reduces the system air volume on-demand, which finally lets us slow down the fan using a VFD in order to save electricity. Are we done?

Almost, but not quite. The above system doesn’t handle some situations adequately:

  1. What if only one machine is on at a time? Opening only the gate to that one machine wouldn’t provide sufficient air volume and would lead to dust settling in the main duct and potentially in branch ducts as well. That’s a safety hazard.

  2. What if no machines need dust collection? If all of the gates close and the fan runs, this will collapse the ducting!

  3. What if a machine is being used frequently, but in short intervals? Surely we shouldn’t cycle the gate and change fan speed over and over again!

How can you make sure the system always does what it should – even when it’s nontrivial to figure that out?

You Need a Brain!

Ultimately, you need intelligence in the loop. In order to reduce electricity consumption without compromising health and safety, a control system that is aware of exactly what is going on in your dust collection system – and exactly how to respond to it in every scenario – is needed.

For the two tricky situations described above:

  1. If only one workstations needs suction, the system should automatically open blast gates to additional machines so that the air volume is sufficient to maintain minimum transport velocities

  2. If no machines need dust collection, the system should automatically stop then fan and dust collector. This is an additional source of electricity savings.

  3. Your controller should know how machines are used. If a workstation is likely to be used within a minute of its last use, it probably makes sense to keep the gate to that workstation open during that minute.

You also need to automatically maintain minimum transport velocities through the ducting system to ensure no dust settles in the ducts.

In other words, you need a truly intelligent system – one that takes care of all of your dust collection needs automatically and that does not interfere with the machine operators’ work.

…and that’s what we’ve built!

That’s exactly what we’ve built – a completely automated control system that will make your dust collection system work better while reducing the electricity use by more than 50%.

Here’s what the complete picture looks like with Ecogate controls:

Ecogate Dust Collection System Overview

The system knows exactly what is going on in the dust collection system, and always responds appropriately. The fan starts, stops, speeds up, and slows down automatically. Gates open automatically to machines that are producing dust and close automatically to machines that do not need suction at that time. The controller directs everything such that minimum transport velocities are maintained in the system.

It’s easy to make changes through our intuitive graphical user interface – want to keep a specific gate open longer after its machine stops working? That’s a single number change. Want to know what the air velocity is at a particular machine? Just look on the screen!

These are the pieces that make it all work:

Components of an Ecogate system, including a dust collection variable frequency drive (VFD).

If you’re looking to make your dust collection system work better – whether it’s because you need to increase suction at certain machines or whether you’d just like to make the system more energy efficient – you can get in touch with us here.

We’d love to have one of our experts take a look at your situation and to see if and how we can help you meet your goals.

Contact us today and make your dust collection system work for you!

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