Artificial intelligence (AI) policy: ASHRAE prohibits the entry of content from any ASHRAE publication or related ASHRAE intellectual property (IP) into any AI tool, including but not limited to ChatGPT. Additionally, creating derivative works of ASHRAE IP using AI is also prohibited without express written permission from ASHRAE.

logoShaping Tomorrow's Built Environment Today

To Affinity… and Beyond! Estimating VFD Power Draw From Motor Speed

Share This

©2024 This excerpt taken from the article of the same name which appeared in ASHRAE Journal, vol. 66, no. 5, May 2024.

About the Author
Dave Moser, P.E., is a principal engineer at Cascade Energy, Inc.

Variable frequency drives (VFDs) are an energy-efficient method of matching system output to the load. Energy engineers often estimate the power draw of a VFD-driven system using the full load (100% speed) power draw and the estimated or actual operating speed. This article offers guidance on the equations to use when developing those calculations and aims to clarify the differences between the speed-to-power and flow-to-power exponent values.

Let’s say you’re an energy engineer that has found a VFD-driven fan operating at 100% speed during an energy audit due to a faulty duct static pressure sensor. Control system trend data is available for VFD speed, but not VFD power (a common scenario). The maintenance staff replaces the sensor, and fan speeds drop to ~60% speed on average. How do you calculate the fan energy savings associated with that change, with only fan nameplate horsepower (HP) and VFD speed trend data? This article addresses how to answer this question.

Read the Full Article

ASHRAE Members have free access to the full-text PDF of this article as well as the complete ASHRAE Journal archives back to 1997 in the Free Member Access Area.

Non-members can purchase features from the ASHRAE Bookstore. Or, Join ASHRAE!

Return to Featured Article Excerpts

Return to ASHRAE Journal Featured Article Excerpts