Consulting-Specifying Engineer, Jan./Feb. 2014, by John Yoon, PE, LEED AP.
http://www.csemag.com/single-article/vfd-motor-strategies-for-energy-efficiency/5d507c13fed1f2680da1f419b85cefa6.html

"A variable frequency drive (VFD) often is specified to save money by reducing energy consumption in pumps, fans, compressors, or any other motor loads that may be found in a typical building. These best practices will provide the engineer with information on how to specify a VFD to meet load conditions while achieving efficiency."