By Grainger Editorial Staff 12/10/18
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.
Radial: These are high-pressure fans with medium airflow. Radial-bladed fans are best for industrial applications where there is dust, or in environments where there is gas or moisture in the air.
Forward Curve: These are medium pressure, high airflow fans that can be used in both clean air, ventilating and exhaust applications.
Backward Curve: These are high-pressure, high flow, high efficiency fans. Power reduces as flow increases over the most efficient area of the system.
Airfoil: These are the highest efficiency fans, best in clean air applications.
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.
The environment in which the system operates must also be considered to choose the right blower-motor combination.
Outdoors: Consider a Totally Enclosed Fan Cooled (TEFC) electric motor on direct drive units, or a belt drive unit with an included weather cover.
Dirty or Dusty Environment: A TEFC motor is best for longer life and optimal efficiency.
Corrosive Environment: In wet, humid environments, a stainless steel blower is recommended, preferably with a stainless wash-duty motor.
Hazardous Environment: Consider a non-sparking blower, such as a radial or high-pressure blower, with an explosion-proof motor.
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 Up Blast CW 360
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
Notes:
The drive arrangement names use these abbreviations:
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.
psi | "WG | "Hg |
---|---|---|
1 |
27.736 |
2.036 |
0.03605 |
1 |
0.07341 |
0.49116 |
13.623 |
1 |
0.000145 |
0.00403 |
0.000295 |
0.00142 |
0.03937 |
0.00289 |
0.01934 |
0.53632 |
0.03937 |
14.696 |
407.61 |
29.92 |
N/m2* | mmWG | mmHg | atm |
---|---|---|---|
6894.7 |
704.49 |
51.714 |
0.06805 |
248.36 |
25.4 |
1.8628 |
0.00245 |
3386.4 |
346.02 |
25.4 |
0.03342 |
1 |
0.10219 |
0.0075 |
0.0000098 |
|
1 |
0.07341 |
0.00009661 |
|
|
|
|
|
|
|
|
Symbol | Definition |
---|---|
atm |
Atmospheres |
°C |
Degrees Celsius |
cfm |
Cubic feet per minute |
°F |
Degrees Fahrenheit |
fpm |
Feet per minute |
Hg |
Mercury |
hp |
Horsepower |
hr |
Hours |
kW |
Kilowatts |
m |
Meters |
mm |
Millimeters |
min |
Minutes |
N |
Newtons |
psi |
Pounds per square inch |
sec |
Seconds |
W |
Watts |
WG |
Water gauge |
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.