Variable frequency drive

Gerber, Daniel L, Richard Liou, and Richard E Brown. "Energy-saving opportunities of direct-DC loads in buildings." Applied Energy 248 (2019) 274–287.

Coles, Henry C, Steve E Greenberg, and Corrine Vita. Demonstration of Intelligent Control and Fan Improvements in Computer Room Air Handlers. Berkeley, CA: Lawrence Berkeley National Laboratory, 2012.