Prepared by:
Bolder Energy Engineers
1320 Pearl St. Suite# 240
Boulder, CO 80302
www.bolderee.com
Motors that drive supply or return air fans in heating, ventilation, and air-conditioning (HVAC)
systems rarely operate at their full-load point and in fact generally operate at under their rated
load1. Instantaneous load measurements conducted as part of the Motor Systems Inventory found
that over 40 percent of motors in use were operating at less than 40 percent part load; in general,
the operating efficiency of a motor decreases significantly at part loads less than 40 percent2.
These findings suggested that the practice of oversizing motors is widespread and therefore, to
better match the motor’s current load within the motor’s efficient operating range, there are
some cases where replacing the oversized motor with a properly sized energy efficient motor is
appropriate and would generate energy savings.
However, eighty-six percent of facility managers
reported they “always or most of the time” use the current size of the motor as the method they
used to size the replacement motor3. To aid facility managers in identifying opportunities for
downsizing motors in their facilities, this report discusses how to assess when motor downsizing is
appropriate, how to select an appropriately sized motor, and the benefits of doing so.
- Jeffrey Jowett and William D. Biesemeyer, Facts and Fiction of HVAC Motor Measuring for Energy Savings. American Council for an Energy Efficient Economy Summer Study on Energy Efficiency in Buildings, Volume 5, Asilomar, California, August 28-September 3, 1994. ↩︎
- The U.S. Department of Energy’s “United States Industrial Electric Motor Systems Market Opportunities Assessment” December, 2002 p70 ↩︎
- The U.S. Department of Energy’s “United States Industrial Electric Motor Systems Market Opportunities Assessment” December, 2002 p86 ↩︎