1. Variable Frequency Drive Savings Calculator Tools
Chris Guzdial
March 21, 2017
NP – 00E01561

2. Christopher J. Guzdial, CEA
BSChE – Michigan Tech University
42 years Industrial Water Treatment for Cooling Towers, Boilers and Waste Water Plants
Certified Energy Auditor
14 years RETAP Analyst

3. What is the Tool?
Calculator to determine if installing a Variable Frequency Drive is economical
Identifies data needed to use the calculator

4. What is a Variable Frequency Drive (VFD)?
Type of motor controller that drives AC electric motors
Varies frequency and voltage supplied to the motor
Higher frequency and voltage = higher RPMs
Uses solid state electronics
Reduces energy use to offset increased cost of installing VFD

5. Where can VFDs be Applied?
Centrifugal pumps
Air compressors
Fan motors
Cooling tower fans
Air-cooled condensers
Air Handling Units
Miscellaneous larger motors

6. Conditions Where VFDs May Not Be Applicable
Where a smaller, more efficient motor can replace a larger less efficient motor and may be applied to a system where the duty cycle does not vary with the load.
Where a technically less costly Electrically Commutated Motor (ECM) allows for efficient motors, less than 5 horsepower can be used to operate small fans and recirculating pumps.
Where a plant only occasionally requires above average flow rates used to link two pumps with one used to meet the demands of the lower flow rate and the second pump kicking in to boost pump capacity as required.
The VFD may lose its economic advantage when the static head increases, such as transferring a fluid.

7. What Data is Needed to Use Calculator?
Motor HP
Motor efficiency
Operating hours
Electric rate ($/kWh)
Motor Loading
Hours of operation with flow rates (100%, 75%, 50%)
NP-00E01561

8. Example of Savings Calculator
Reference:
Refer to Handout
NP-00E01561

9. Additional References