The purpose of this article is to explain the basis and application of rules used to “estimate” fan performance for a fan installed in a duct system moving air when the speed of the fan is changed.

El propósito de este artículo es explicar los fundamentos y la aplicación de las reglas utilizadas para estimar el rendimiento de un ventilador instalado en un sistema de conductos que mueve aire al variar su velocidad. Con un conocimiento básico de estas reglas, es posible calcular rápidamente el rendimiento de un ventilador para diversas condiciones de velocidad.

Although the earliest practical DC motor was built by Moritz Jacobi in 1834, it was over the next 40 years that men like Thomas Davenport, Emil Stohrer and George Westinghouse brought DC machines into industrial use.  It’s inspiring to realize that work-ing DC motors have been around for over 160 years. For the past century, DC machines over 30 or 40 kW have been cooled in the same manner – by mounting a squirrel cage blower directly over the commutator.

Most service centers balance rotors routinely, with few surprises in the process. Most of us do not balance fans nearly as often as rotors. The fan balancing tips in this article should be helpful.

Most of us involved in the repair of electrical equipment have a good understanding of how an electric motor works — especially the stator and rotor. But the fan can appear deceptively simple. Fans are pretty interesting, once we learn a few "affinity laws" — rules that also apply to blowers and impellers. This article will review some basic facts about fans that explain how small changes to a fan can make a BIG difference.