It consumes much time to evaluate a motor for a fan in designing the air handling equipment. There are some factors involved in selecting right electrical characteristics and construction features that not everyone knows. This article aims to help select proper type of motor for a specific application and fan in terms of the electrical and mechanical design.
As a motor is to be selected, the fan and application shall be checked to be in consistence with each other. For instance, for a fan to be used in normal ventilation applications, the use of a high cost, special duty motor would result in the waste of huge amount of money. The requirement is not to have to cope with special design requests which may lead to more extra costs and longer lead times.
Regarding the selection of the right motor for a specific application, some factors can be neglected. The following represents the most common two:
Motor selections can be limited by the space that can be allotted for mounting. For fans not designed to be used for explosion proof applications, two speed and explosion resistant motors may not be the choice.
In selecting the drive types of fans, fan noise levels, motor cost, and maintenance shall be considered. For fans of the belt drive type, belts, shafts, pulleys and bearings add up the costs. But motors that have lower costs and high speed are normally chosen. Because of the belt and bearing losses, fans of the belt drive type have lower efficiency. There will be lower sound levels if fans of larger belt driven fans that move more slowly.
The wheel of smaller fans of the direct drive type will rotate faster under the condition of same air delivery, delivering higher efficiency, yet producing more sound. Fans of the belt drive type and very large or fans of the direct drive type require split-phase, capacitor-start, or three-phase motors to have high starting torque. If it is difficult to access bearings and belts, direct driven motors are a great choice. For fans of the belt drive type, motors run typically at a speed of 1725 rpm. Fans of the direct drive type have motors with specific speeds available for accommodation. Motors below the speeds of 1725 rpm cost more, have bigger size, require longer lead times, and present fewer motor options.