With an estimated 80% of electric motor applications being fixed speed processes perhaps it isn’t surprising that variable speed drives are consistently being misapplied. Many motor driven systems are being designed with VSDs to add flexibility that isn’t needed, compromising efficiency while adding to capital and operating costs.
US-based JDA consulting engineers (now part of global consulting firm Exp Global.) offer an interesting discussion of this phenomenon in a blog on the Staticworx website. “As JDA's team commissions large, complex mechanical plants, we find more systems where the VSD is practically abandoned in place. Rather than providing the precise control of flow and pressure or reducing energy consumption and demand, the VSDs appear to be "stuck" at a single speed.”
In the case study discussed in the blog JDA Consultants encountered such a situation when commissioning the cooling system for a large data centre project. In addition to poor pump selections, JDA concluded that the specified VSDs were superfluous; the design required the pump to run at full speed to maintain the required head pressure.
Ultimately JDA recommended a new system, specifying more appropriately sized motors and removing VSDs from the design. These changes reduced the capital costs of the system by over $US150,000 and saved more than $US130,000 per year in electricity costs.
You can read the full case study here: http://www.staticworx.com/articles/Inappropriate-Use-of-VSDs.php