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04 May 2017

TTM-07: Back to the basics – fan laws

An introduction to fan laws and where they can be used.

1. Introduction

Fans are used in a wide variety of applications including air conditioning, refrigeration, medical and transport applications. EC (Electronically Commutated) fans are becoming increasingly popular due to their improved energy efficiency compared to AC (Alternating Current) fans and energy-conserving speed controllability. With increased interest in speed-controllable fans, there is a growing need to understand how speed-control affects the fan behaviour in AC and EC fans differently.

Fan laws are a useful set of tools to develop statistically sufficient estimates on how the performance of an EC product changes when the speed-control feature is used. These fan laws do not apply to AC products due to the different mechanisms used in speed control. This paper will explain the fan laws and show the effects of speed control on EC and AC products based on the example of a 190mm backward curved fan.

2. Speed control of fans

The speed-controlling of fans has been around for a very long time. AC products are typically speed controlled by external devices such as triac controllers or VSDs (Variable Speed Drive). Each of these devices has a different effect on the performance of the AC product and certain precautions have to be taken to prevent possible damages to the fan and motor, such as overheating. These external speed-controlling devices influence the slip and efficiency of the motor and cause power transfer losses. As a result fan laws do not apply for AC speed controlled fans and motors.

With ebm-papst EC products, speed control is a lot simpler as the speed control electronics are integrated into the fan. Speed control can be managed, for example, by applying a 0-10V or PWM (pulse width modulation) signal to the control input, influencing the fan speed and thereby the input power of the fan product. The minimal impact on motor slip or efficiency means that ebm-papst EC products typically follow fan laws.

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Andy Sondalini
Marketing Intern
Phone: (03) 9360 6400
Fax: (03) 9360 6464
E-Mail: sales@au.ebmpapst.com
Internet: www.ebmpapst.com.au