Centrifugal blowers, or fans, are among the most efficient and versatile pieces of air moving equipment. The scroll housing in a centrifugal fan accelerates the air and changes the direction of the airflow twice, a full 90 degree, before leaving the housing. Centrifugal blowers are quiet and reliable and are made to operate in a variety of environments and applications. Here are some basic definitions and guidelines to consider for selecting the right centrifugal blower for your system's needs.
Centrifugal fans come in four basic fan types, each with its own specific purpose.
To choose the appropriate blower, you'll need to know how much pressure is required to reach the desired airflow to move air through the ducting and any filters, dampers or other obstructions in your ventilation system. If you have a lengthy, complicated duct system, you'll of course need a lot more power. Consider the impact of filters on the airflow too as this will also impact the pressure and power needed.
Direct Drive is more typical on smaller blowers and generally offers lower cost, fewer components to assemble, greater efficiency (no drive losses), reduced maintenance (no separate bearings or belts) and greater reliability.
Belt Drive offers greater flexibility in matching airflow requirements when equipped with a variable pitch motor pulley and is typical of larger blowers. When equipped with a variable frequency drive (three-phase blowers), direct drive blowers can offer the flexibility of belt drive blowers.
|PRESSURE (U.S. SYSTEM)|
|U.S. SYSTEM||METRIC||U.S. SYSTEM||METRIC|
|196.85||1||0.00134||1||0.001||°F = (9/5°C +32°)
°C = 5/9 (°F -32°)
|cfm||cubic feet per minute|
|fpm||feet per minute|
|psi||pounds per square inch|
The environment in which the system operates must also be considered to choose the right blower-motor combination.
Clean Air Consider a forward curve, backward incline or airfoil blower for increased efficiency.
Lightly Dusty Air Consider a radial or high-pressure blower. For very light, non-abrasive dusts, a backward inclined blower is acceptable.
Heavier, More Abrasive Dust, Filings and Shavings For this environment, you'll probably want an industrial material handing blower.
Corrosive In wet, humid, corrosive environments, you should opt for a stainless steel blower, preferably with a stainless wash-duty motor.
Combustible If there's combustible dust or particulate in the air, opt for a non-sparking blower, such as a radial or high-pressure blower with an explosion-proof motor.
Air Temperatures Use belt drive units with steel wheels in higher temperatures. If temperatures climb above 250°F, consider an industrial blower with a heat slinger.
The direction of the rotation is determined from the drive side of the fan. On single inlet fans, the drive side is the side opposite the fan inlet. On double inlet fans with drives on both sides, the drive side should be on the same side as the higher-powered drive unit.
|Clockwise Up Blast CW 360||Clockwise Top Angular Up CW 45||Clockwise Top Horizontal CW 90||Clockwise Top Angular Down CW 135|
|Clockwise Down Blast CW 180||Clockwise Bottom Angular Down CW 225||Clockwise Bottom Horizontal CW 270||Clockwise Bottom Angular Up CW 315|
|Counterclockwise Up Blast CCW 360||Counterclockwise Top Angular Up CCW 45||Counterclockwise Top Horizontal CCW 90||Counterclockwise Top Angular Down CCW 135|
|Counterclockwise Down Blast CCW 180||Counterclockwise Bottom Angular Down CCW 225||Counterclockwise Bottom Horizontal CCW 270||Counterclockwise Bottom Angular Up CCW 315|
Drive arrangements for Centrifugal Fans AMCA Standard 99-2404-03
|SW = Single Width||DW = Double Width|
|SI = Single Inlet||DI = Double Inlet|
Please note: Arrangements 1, 3, 7, and 8 are also available with bearings mounted on pedestals or base set independent of the fan housing.
|APR. 1 SWSI - For belt drive or direct connection. Impeller overhung. Two bearings on base.||ARR. 2 SWSI - For belt drive or direct connection. Impeller overhung. Bearings in bracket supported by fan housing.|
|ARR. 3 SWSI - For belt drive or direct connection. One bearing on each side and supported by fan housing.||ARR. 3 DWDI - For belt drive or direct connection. One bearing on each side and supported by fan housing.|
|ARR. 4 SWSI - For direct drive. Impeller overhung on prime mover base mounted or integrally directly connected.||ARR. 7 SWSI - For belt drive or direct connection. Arrangement 3 plus base for prime mover.|
|ARR. 7 DWDI - For belt drive or direct connection. Arrangement 3 plus base for prime mover.||APR. 8 SWSI - For belt drive or direct connection. Arrangement 1 plus extended base for prime mover.|
|APR. 9 SWSI - For belt drive. Impeller overhung, two bearings, with prime mover outside base.||ARR. 10 SWSI - For belt drive. Impeller overhung, two bearings, with prime mover inside base.|
The location of the motor is determined by facing the drive side of the fan and designating the motor positions by the letters W, X, Y or Z as needed.
Facility maintenance pros like you have many jobs to do in the course of the day. So if HVAC isn't your primary field of expertise, we hope these basics provide some of the guidelines you need when it comes time to seek the advice from a trusted HVAC engineer. Choosing the right combination of blowers and motors for the intended workload and environment is critical in making your system the most efficient it can be while helping to keep energy costs down.
The product statements contained herein are intended for informational purposes only. Such product statements do not constitute a product recommendation or representation as to the appropriat ness for a specific application or use. W. W. Grainger, Inc. does not guarantee the result of product operation or assume any liability for personal injury or property damage resulting from the use of such products.
The information contained in this article is intended for general information purposes only and is based on information available as of the initial date of publication. No representation is made that the information or references are complete or remain current. This article is not a substitute for review of current applicable government regulations, industry standards, or other standards specific to your business and/or activities and should not be construed as legal advice or opinion. Readers with specific questions should refer to the applicable standards or consult with an attorney.
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