Programming Fan Basics Full-Stack Applications

Fans Type


  • Propeller
  • Tube Axial
  • Vane Axial

Mixed Flow

  • Low Pressure
  • High Pressure
  • Extended Pressure


  • Airfoil
  • Backward Inclined
  • Radial
  • Forward Curved

Axial Fans

An axial fan discharges air parallel to the axis of the impeller rotation.

Propeller Fans

  • Cost is generally low
  • Blades attached to a relatively small hub
  • Energy transfer is primarily in the form of velocity pressure

Primarily for low pressure, high volume, non-ducted applications

Tube Axial Fans

  • More useful static pressure range than propeller fans
  • Axial impeller in a tubular housing
  • Blade cross-section either single thickness or airfoil
  • Primarily for low to medium pressure applications such as ducted HVAC applications where downstream air distribution is not critical

Vane Axial Fans

  • Axial impeller in a tubular housing with straightening vanes which improve pressure capabilities & efficiency
  • Cost is generally high
  • Generate medium-to-high pressure at good efficiencies
  • Fixed or adjustable pitch blades
  • Hub diameter is greater than 50% of impeller diameter
  • Used for straight-through flow and compact installations
  • Downstream air distribution is good
  • Noise levels may be high
  • Used for general HVAC in a wide range of pressure applications
  • Industrial applications include: drying ovens, paint spray booths, and fume exhaust systems

Mixed Flow Fans

A mixed flow fan is a hybrid of an axial and a centrifugal fan, with a smaller backplate and angled blades. It discharges air parallel to the axis of the impeller rotation. As a general rule, it is more efficient, smaller and quieter when used in ducted, inline, supply and exhaust.

  • Best selection for most inline airflow applications
  • Higher pressure ability than axial
  • Lower sound levels than equally sized centrifugal inline units
  • Lower rpm than equal sized inline units, for the same flow and pressure
  • Does not require inlet bell or outlet cone

Centrifugal Fans

A centrifugal fan draws in air parallel to the axis of rotation and discharges air perpendicular to the axis of rotation. The air then follows the shape of the fan housing to exit. In general, centrifugal fans are preferred for ducted or higher-pressure systems.

Basic Components

Centrifugal fans are the ‘workhorse’ of the fan industry, operating in a wide variety of configurations, duties and environments. From light commercial, non-ducted applications to high pressure industrial and process ventilation, centrifugal fans can often be configured to meet the application demands. Examples are shown on these two pages.

Airfoil (AF) Fans

  • Highest efficiency of centrifugal impeller designs
  • 10–12 airfoil blades inclined away from the direction of rotation
  • Relatively deep blades provide for efficient expansion
  • Primarily used in general HVAC systems
  • Industrial use in clean air applications

Backward Inclined (BI) Fans

  • Efficiency slightly less than airfoil
  • 10–12 single thickness blades inclined away from the direction of rotation
  • Relatively deep blades provide for efficient expansion within blade passages
  • Primarily used in general HVAC systems
  • Industrial applications where airfoil blade is not acceptable due to a corrosive and/or erosive airstream

Radial Fans

  • Less efficient than airfoil or backward inclined fans.
  • High mechanical strength
  • High speed at given duty relative to other designs
  • 6–10 blades arrayed in a radial configuration
  • Primarily used for material handling applications in industrial environments
  • Often specially coated to resist corrosion or surface erosion
  • Used in high pressure applications not commonly found in HVAC systems.

Forward Curved (FC) Fans

  • Less efficient than airfoil or backward inclined fans
  • Low cost to manufacture
  • Lightweight construction
  • 24–64 shallow blades with blade heel and tip curved in direction of rotation
  • Smallest wheel diameter for given duty of all centrifugal fans types
  • Most efficient at low speeds
  • Primary uses are low pressure
  • HVAC applications such as residential furnaces and packaged air conditioning equipment

Drive arrangements for Centrifugal Fans

SWSI: Single Width, Single Inlet

DWDI: Double Width, Double Inlet

Motor Positions and Rotation for Belt Drive Centrifugal Fans

To determine fan rotation and motor location, face the fan from the drive side and identity the rotation as either clockwise or counterclockwise and the motor position designated by the letters W, X, Y or Z as shown in the drawing below.

Inlet Boxes

Position of inlet box and air entry to inlet box is determined from the drive side as defined below:

On single inlet fans, the drive side is the side opposite of the fan inlet.

On double inlet fans with a single driver, the side with the driver is considered the drive side.

Position of inlet box is determined in accordance with diagrams. Angle of air entry to box is referred to the top vertical axis of fan in degrees as measured in the direction of fan rotation. Angle of air entry to box may be any intermediate angle as required.

Positions 135° to 225° in some cases may interfere with floor structure.

Rotation & Discharge Designations Centrifugal Fans

Spark Resistant Construction

Fan and damper applications may involved the handling of potentially explosive or flammable particles, fumes, or vapors. Such applications require careful consideration to insure the safe handling of such gas streams. AMCA Standard 99–0401–10 deals only with the fan and/or damper until installed in the system. The standard contains guidelines to be used by manufacturer and user to establish general methods of construction. The exact method of construction and choice of alloys is the responsibility of the manufacturer, however, the customer must accept both the type and design with full recognition of the potential hazard and the degree of protection required.

Type A

  • All parts of the fan or damper in contact with the air or gas being handled and subject to impact by particles in the airstream shall be made of non-ferrous material. Ferrous shafts/axles and hardware exposed to the airstream shall be covered by non-ferrous materials.
  • Fans only: Steps must also be taken to assure that the impeller, bearings, and shaft are adequately attached and/or restrained to prevent a lateral or axial shift in these components.
  • Dampers only: Construction shall ensure that linkages, bearings and blades are adequately attached or restrained to prevent independent action. Ferrous containing bearings are acceptable if the bearings are located out of the airstream and shielded from particle impact.

Type B

  • Fans only: Steps must also be taken to assure that the impeller, bearings, and shaft are adequately attached and/or restrained to prevent a lateral or axial shift in these components.
  • Dampers only: Construction shall ensure that linkages, bearings, and blades are adequately attached or restrained to prevent independent action. Damper blades shall be non-ferrous.

Type C

  • Fans only: The fan shall be so constructed that a shift of the impeller or shaft will not permit two ferrous parts of the fan to rub or strike.
  • Dampers only: Construction shall e sure that linkages, bearings, and blades are adequately attached or restrained to prevent independent action. Damper blades shall be non-ferrous.

Notes for AMCA Type A, B & C Construction:

  1. No bearings, drive components or electrical devices shall be placed in the air or gas stream unless they are constructed or enclosed in such a manner that failure of that component cannot ignite the surrounding gas stream.
  2. The user shall electrically ground all fan and/or damper parts.
  3. Non-ferrous material shall be any material with less than 5% iron or any other material with demonstrated ability to be spark resistant.
  4. The use of aluminum or aluminum alloys in the presence of steel which has been allowed to rust requires special consideration. Research by the U.S. Bureau of Mines and others has shown that aluminum impellers rubbing on rusty steel may cause high intensity sparking.
  5. All structural components within the airstream, including non-metallic materials, must be suitable for conducting static charge safely to ground, thus preventing buildup of electrical potential. Dampers with non-metallic bearings must include means by manufacturer of transferring electrical charge from the blades to suitable ground.

This Standard in no way implies a guarantee of safety for any level of spark resistance. “Spark resistant construction also does not protect against ignition of explosive gases caused by catastrophic failure or from any airstream material that may be present in a system.”

Adapted from AMCA Standard 99–401–86

Basic Terms

  • Air Flow (Q): Amount of air moved per rate of time, typically measured in cubic feet of air per minute (CFM).
  • Static Pressure (Ps): Resistance against airflow by the system (ductwork, fittings, dampers, filters, etc.). Typically measured in inches of water gauge (in. wg.) For most applications Static Pressure along with CFM is used for fan selection.
  • Total Pressure (Pt):The amount of pressure exerted by airflow on anything directly in the airstream.
  • Velocity Pressure (Pv): Directly related to the velocity of the airflow at any given point in a system. Used to calculate the airflow at any point in a system. Cannot be measured directly and is calculated as the difference between Total Pressure and Static Pressure.

Pv = Pt — Ps

  • Velocity (V): Speed of air in the direction of flow. Measured in feet per minute (FPM).
  • Power (HP): Rate of doing work, typically measured in Horsepower. For rotating machinery power is the amount of torque applied to a shaft to maintain a given rotating speed (RPM).

HP = RPM × torque (ft-lb) / 5252.

1 HP = 33,000 foot-lbs per minute.

  • Brake Horsepower (BHP): (as listed in a fan performance table) The amount of HP required at the fan shaft to move the specified volume of air against a given system resistance. It does not include drive losses.

Fan Selection Criteria

Before selecting a fan, the following information is needed.

  • Airflow required (CFM)
  • Static pressure or system resistance (in. wg.)
  • Air density or altitude and temperature
  • Type of service ( Environment type, Vapors / materials to be exhausted and Operation temperature)
  • Space requirements (including service access)
  • Fan type (see Fan Basics)
  • Drive type (direct or belt)
  • Allowable noise levels
  • Number of fans
  • System configuration (Supply, Exhaust, Inline, Recirculating and Reversible)
  • Rotation
  • Motor position
  • Expected fan life in years

Fan Testing

Fans are tested and performance certified under ideal laboratory conditions. When fan performance is measured in field conditions, the difference between the ideal laboratory condition and the actual field installation must be considered. Consideration must also be given to fan inlet and discharge connections as they can dramatically affect fan performance in the field. If possible, readings must be taken in straight runs of ductwork in order to ensure validity. If this cannot be accomplished, motor amperage and fan RPM should be used along with performance curves to estimate fan performance. Refer to Fan Installation Guidelines for more information.

Fan Classes of Operation

AMCA has defined classes of operation for various types of centrifugal fans and blowers. The class of operation is defined by a range of pressures and discharge velocities for a given configuration and type of blower. A fan must be physically capable of operating satisfactorily over the entire class range in order to be designated as meeting that fan class. Lower class numbers represent lower discharge velocities and static pressures (See AF and BI SWSI example on next page).

Although AMCA has defined the operating ranges of various classes, it does not prescribe how the fan manufacturer meets that requirement, leaving it up to the ingenuity of each to design the product as they see fit. Higher class operating ranges will often require heavier duty components resulting in a higher cost.

This is an important distinction. When specifying a fan class, the designer is stating that a fan be capable of operating over a specific range, and is not specifying a particular set of features or the physical construction of the fan.

With the advent of modern selection programs, the fan class is determined at the time of selection. For more information, refer to AMCA Standard 99.

Operating Limits —

Centrifugal AF and BI Fans — SWSI

Performance Correction Factors for Altitude & Temperature

Unless otherwise noted, all published fan performance data is at standard operating conditions, 70°F at sea level.

When operating conditions vary significantly from standard, air density should be taken into consideration. When using COOK’s Compute-A-Fan, these calculations will be made automatically based on input conditions.

Air Density Correction Factors for Altitude & Temperature

Example: Fan pressure and horsepower vary directly air density. A cubic foot of air is always a cubic foot of air, it is just more or less dense depending primarily upon the conditions of altitude and temperature.

A fan selected from catalog to operate a 10,000 CFM, 1” wg, and 3.5 BHP (standard air density), but operating at 5000 feet above sea level and 100°F would have a correction factor applied to the static pressure and horsepower of 0.787 as read from the table. The corrected static pressure (SPc) and horsepower (BHPc) would be:

SPc = 0.787 x 1 = 0.787” wg

BHPc = 0.787 x 3.5 = 2.75 BHP.

Fan Laws

CFM varies directly with RPM

CFM1 / CFM2 = RPM1 / RPM2

CFM2 = (RPM2 / RPM1) × CFM1

SP varies with the square of the RPM

SP1 / SP2 = (RPM1 / RPM2 )2

SP2 = (RPM2 / RPM1)2 × SP1

HP varies with the cube of the RPM

HP1 / HP2 = (RPM1 / RPM2 )3

HP2 = (RPM2 / RPM1)3 × HP1


Fan operating at 1000 RPM, 3000 CFM, 0.5” wg, 0.5 BHP. Speed fan up 10% to 1100 RPM; what is the performance of the fan at the new speed?

RPM1 = 1000; CFM1 = 3000; SP1 = 0.5; BHP1 = 0.5; RPM2 = 1100


CFM2 = (1100/1000) x 3000 = 3300 CFM (10% increase in airflow)

SP2 = (1100/1000)2 x 0.5 = 0.605” wg (21% increase in static pressure)

HP2 = (1100/1000)3 x 0.5 = 0.6655 BHP (33% increase in horsepower)

So remember that a 10% increase in fan speed will result in a 33% increase in horsepower!

Fan Balancing

AMCA/ANSI Publication 204–05 has established recommended levels of balance and vibration for fan assemblies. Fans covered by this standard would include those for most commercial HVAC as well as most industrial process applications. The Standard does not address environments involving extreme forces or temperatures.

Balance and Vibration Categories for Fans


These values are for assembled fans balanced at the manufacturing location. Values shown are peak velocity values, filtered (measured at fan RPM).

Balance and vibration levels measured in the field will vary from those taken in the manufacturing plant. This is due primarily to differences in the mass and rigidity of the support system. There will also be situations where fans are shipped without motor or drives installed. In such cases, field or trim balancing will be necessary. For such cases, acceptable vibration levels are provided in the following table for various BV categories for three conditions: startup, alarm and shutdown. All values are unfiltered and are to be taken at the bearing housings.

*Startup values are for newly installed fans (values should be at or below these levels).


Over time, wear and tear will naturally increase vibration levels. Once they increase to “Alarm” values, corrective action should be taken.

If “Shutdown” values are reached, fans should be shut down immediately to prevent severe damage or catastrophic failure, and action should be taken to determine the root cause of the vibration.

Vibration Severity

When evaluating vibration severity, the following factors must be taken into consideration:

  • When using displacement measurements, only filtered displacement readings for a specific frequency should be applied to the chart. Unfiltered or overall velocity readings can be applied since the lines which divide the severity regions are, in fact, constant velocity lines.
  • The chart applies only to measurements taken on the bearings or structure of the machine. The chart does not apply to measurements of shaft vibration.
  • The chart applies primarily to machines which are rigidly mounted or bolted to a fairly rigid foundation. Machines mounted on resilient vibration isolators such as coil springs or rubber pads will generally have higher amplitudes of vibration than those rigidly mounted. A general rule is to allow twice as much vibration for a machine mounted on isolators. However, this rule should not be applied to high frequencies of vibration such as those characteristic of gears and defective rolling-element bearings, as the amplitudes measured at these frequencies are less dependent on the method of machine mounting.

Vibration Severity Chart


System Natural Frequency

The natural frequency of a system is the frequency at which the system prefers to vibrate. It can be calculated by the following equation:

fn = 188 (1/d)1/2 (cycles per minute)

The static deflection corresponding to this natural frequency can be calculated by the following equation:

d = (188/fn)2 (inches)

By adding vibration isolation, the transmission of vibration to the building can be minimized. A common rule of thumb for selection of vibration isolation is as follows


  • Critical installations are upper floor or roof mounted equipment. Non-critical installations are grade level or basement floor.
  • Always use total weight of equipment when selecting isolation.
  • Always consider weight distribution of equipment in selection.

Fan Troubleshooting Guide

Low Capacity or Pressure

  • Incorrect direction of rotation. Make sure the fan impeller rotates in the proper direction.
  • Poor fan inlet conditions. There should be a straight, clear duct at the fan inlet.
  • Wheel to inlet overlap incorrect

Excessive Vibration

  • Excessive belt tension
  • Belts too loose, damaged, worn, or oily
  • Damaged or unbalanced wheel
  • Speed too high
  • Incorrect direction of rotation. Make sure the fan impeller rotates in the proper direction.
  • Bearings need lubrication or replacement
  • Fan surge
  • Loose mechanical components
  • Poor inlet duct connections

Overheated Motor

  • Motor improperly wired
  • Incorrect direction of rotation. Make sure the fan impeller rotates in the proper direction.
  • Cooling air diverted or blocked
  • Incorrect fan RPM
  • Incorrect voltage
  • Overheated bearings
  • Improper bearing lubrication
  • Excessive belt tension

In Conclusion

These framework is not just for Java developers but for any programmer who chooses Java for backend and Javascript for front-end development. They are also very popular and learning them not only improve your chances of getting a better job but also opens new doors of opportunities.

As I have said before, technology is changing rapidly and what works 10 years before may not work now and the biggest challenge for programmers is to keep themselves up-to-date.

Good knowledge of popular libraries, frameworks goes a long way in developing a new application and your day-to-day job. It’s particularly important for experienced programmers or full-stack Java developers as it’s expected from them that they know the latest and greatest tools for application development and can suggest the right tools for the job.

As a full-stack Java developer, you should know about Spring, Spring Boot, and Hibernate but you have to know Big Data frameworks like Spark and Hadoop and that’s what you have to set a goal in 2020.



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