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.