PS: How much savings could be achieved from a centrifugal compressor compared to a screw compressor with VFD?
SB: It depends on the size of the demand and the percentage of time that you spend base loaded. Centrifugal compressors are excellent base load machines. If there are multiple machines, there's a lot of controls work where you can do load sharing. You can even combine a centrifugal with a variable speed with the proper controls. You also need to consider the age of your equipment, how well it has been maintained, etc. There's a lot of factors that go into it.
PS: Why do you need a tough VSD when there are multiple other options available today?
SB: Customers by the thousands continuously and regularly purchase standard variable speed units and put them into tough applications, with full knowledge that there are other options. Customers want VSDs because of large load variations, whether it's breaks or weekends or evenings.
And some of these other options don't fit every installation and aren't necessarily as cost effective. People want variable speed for various reasons to improve efficiency, but if the technology is misapplied, the user will pay in reliability and downtime because it wasn't designed for that environment.
PS: What is the most common misapplication for VSD air compressors today?
SB: The most common misapplication is dirty environments. Contaminants, dust, and dirt get into the air, clogging the filters. The typical VSD within the industry is an indoor NEMA 1 variable speed, and it does require some level of a clean environment. To put a standard VSD in an extreme environment is just asking for trouble.
