Industrial Airflow Guide: Centrifugal Fans, Axial Fans, Duct Fans and Cooling Fans
Air Movement and Ventilation Systems: Cross Flow, Centrifugal and Axial Fan TechnologiesFans and blowers are essential components in ventilation, HVAC, electronics cooling, machinery and industrial air-movement systems.
Cross Flow Fans, Centrifugal Blowers, Inline Duct Fans, Compact Cooling Fans, Axial Flow Fans, Centrifugal Fans and Backward Centrifugal Fans represent several important approaches to moving air.
A fan's actual airflow in an installed system can differ from an unrestricted or nominal airflow figure.
Understanding Fan and Blower Technology
A fan uses a rotating impeller or wheel to transfer energy to air and create airflow.
The selected fan must operate effectively against the resistance created by these components.
Two similarly sized fans can have substantially different performance characteristics.
Cross Flow Fans
They differ substantially from conventional axial and centrifugal arrangements.
Air generally passes through the rotating wheel rather than simply moving straight along its rotational axis.
Cross Flow Fans can be useful where compact depth and broad airflow distribution are important design considerations.
Applications of Cross Flow Fans
The exact application depends on the fan's specifications.
Their broad discharge can help distribute airflow across components or surfaces rather than concentrating it at a small circular outlet.
Obstructions around the inlet and outlet can alter performance.
Centrifugal Blowers
This change in airflow direction distinguishes centrifugal designs from many axial arrangements.
Depending on the specific wheel and housing, they can provide pressure characteristics suited to ducts, filters or equipment passages.
A product should therefore be evaluated according to its documented pressure and airflow characteristics rather than terminology alone.
How Centrifugal Fans Work
A surrounding housing or system configuration then manages the discharge airflow.
Centrifugal Fans are available in multiple configurations suited to different airflow systems.
These fans can be considered for HVAC, ventilation, equipment cooling and industrial air-handling applications where their pressure-flow characteristics are appropriate.
Comparing Centrifugal Fans and Blowers
Both can use rotating wheels to accelerate air outward and produce a pressure difference.
A product described as a fan can outperform a product marketed as a blower under certain operating conditions.
Selection should therefore focus on required airflow, system resistance, operating point, efficiency and installation conditions.
Understanding Backward Curved Centrifugal Fans
Backward Centrifugal Fans use blades oriented backward relative to the direction of wheel rotation when viewed according to the applicable impeller geometry.
The blade direction alone does not establish a specific efficiency level.
Product documentation should determine installation requirements.
Backward Centrifugal Fans vs Other Centrifugal Fans
Backward, forward and radial arrangements can behave differently as airflow and system resistance change.
Backward Centrifugal Fans can be attractive where efficiency across an appropriate operating range is important.
The expected system operating point should be plotted or evaluated against manufacturer performance information.
Understanding Axial Fan Technology
Their propeller-like blades create airflow through the fan opening.
An axial fan should therefore not automatically be selected simply because high airflow is required.
Inlet and outlet obstructions can significantly affect installed performance.
Comparing Axial and Centrifugal Airflow
The primary distinction between Axial Flow Fans and Centrifugal Fans is the way air moves through the rotating assembly.
Axial fans can be well suited to applications requiring relatively direct airflow through an opening or short airflow path.
Space, airflow, pressure, efficiency, noise and maintenance requirements all influence selection.
Inline Duct Fans
Inline Duct Fans are designed to operate as part of a ducted airflow path.
Nominal duct diameter alone is therefore insufficient for fan selection.
Some models employ axial or mixed-flow concepts, while others can incorporate centrifugal characteristics.
Applications of Inline Duct Inline Duct Fans Fans
The fan must be appropriate for the air being handled and the installation environment.
Excessive bends, restrictive grilles or poorly sized ducts can increase system resistance.
Service access should also be considered during installation.
Compact Cooling Fans
Their purpose is generally to help move heat away from components or through an enclosure.
A compact fan must still move sufficient air through the actual enclosure resistance.
A poorly arranged enclosure can develop hot spots even when a fan is operating.
Designing Airflow Through Equipment Enclosures
Electronic components can generate heat that must be transferred away to maintain appropriate operating conditions.
Inlet and exhaust openings should therefore be considered together.
Fan selection should account for the pressure drop created by filtration.
Choosing a Fan for Equipment Cooling
The enclosure layout should guide selection.
A long heat-generating surface may benefit from a different airflow pattern than a small concentrated electronic assembly.
Thermal testing can help reveal hot spots and airflow deficiencies.
Why Airflow Alone Is Not Enough
A high free-air airflow value does not guarantee the same airflow after ducts, filters or heat exchangers are added.
Different fan designs respond differently to this resistance.
The selected fan can then be evaluated against the expected operating point.
Selecting Fans by Operating Point
It can help designers estimate how a fan will behave when connected to a particular system.
The airflow system itself can also be represented by a system resistance curve.
The useful operating range is generally more important than a single maximum number.
Fan Efficiency and Energy Use
Efficiency should therefore be evaluated where the fan will actually operate.
Axial and other fan types can also perform efficiently when correctly matched to their systems.
Reducing avoidable pressure losses can improve overall system performance.
Fan Speed Control
Some fan systems allow speed to be adjusted according to airflow or cooling demand.
Not every motor can be controlled using the same technique.
Control strategies should therefore be coordinated with the complete system.
Reducing Fan and Blower Noise
Noise from a fan system can originate from aerodynamic airflow, the motor, bearings, structural vibration or interactions with nearby components.
Restrictive or turbulent airflow paths can increase aerodynamic noise.
However, mounts and connectors must remain suitable for the equipment and operating conditions.
Installing Fans and Blowers
Correct installation helps a fan achieve its intended performance.
Inline Duct Fans should be integrated carefully with ductwork.
Qualified personnel should perform installation where required.
Maintaining Cooling and Ventilation Fans
Dust or debris on an impeller can affect airflow and potentially contribute to imbalance.
Bearings, motors, mounting hardware and electrical connections may also require attention according to equipment instructions.
Maintenance procedures should follow relevant safety requirements.
Fan and Blower Selection Guide
The first step in fan selection is defining the required function.
Inline Duct Fans are specifically arranged for integration into ducted systems.
Cross Flow Fans can provide broad airflow distribution, while Compact Cooling Fans can fit confined equipment spaces.
Which Fan Technology Fits the Application?
Axial Flow Fans generally move air along their axis and are commonly suited to direct ventilation or cooling paths.
Compact Cooling Fans focus on fitting airflow capability into restricted equipment spaces.
These categories can overlap.
Frequently Asked Questions About Fans and Blowers
Cross Flow Fans move air through an elongated rotating wheel and can provide airflow across a relatively broad outlet.
Centrifugal Blowers use a rotating wheel to draw in and redirect air through a housing.
Inline Duct Fans are designed for installation within or along a duct airflow path.
Compact Cooling Fans provide forced airflow in applications where installation space is limited.
Axial Flow Fans generally move air in a direction broadly parallel to their rotational axis.
Different centrifugal blade and housing designs provide different performance.
They can offer useful aerodynamic characteristics for suitable operating conditions.
No.
Does a larger fan always move more air?
Can maximum airflow be used to select a fan?
Building an Effective Airflow System
Understanding these differences helps narrow the selection process.
Centrifugal Fans and Centrifugal Blowers offer different pressure-flow characteristics for more resistive airflow systems.
However, no fan category automatically guarantees a particular airflow, pressure, efficiency or noise level.
Effective fan selection ultimately requires the fan and airflow system to be considered together.