Fan assembly for air handling units: the fan, motor and drive module

01

Choose how the motor drives the impeller

The U.S. Department of Energy's Motor Systems Tip Sheet #5 states that about one-third of industrial and commercial electric motors use belt drives. V-belt drives can reach a peak efficiency of 95% or more when installed, but efficiency can deteriorate by as much as 5% over time if the belt slips because it is not retensioned; DOE says tension should be checked every 3 to 6 months after break-in. Notched belts run on the same pulleys and are about 2% more efficient than standard V-belts, and synchronous (toothed) belts run at a consistent 98% over a wide load range. [1]

DOE's worked example is a continuously operating 100 hp supply-air fan at 75% average load using 527,000 kWh a year: replacing a 95% V-belt with a 98% synchronous belt saves 527,000 × (1 − 95/98) = 16,130 kWh a year. DOE adds that synchronous belts are noisier, less suited to shock loads and transmit more vibration, and that on centrifugal fans removing slip raises speed, so sprockets must be sized to the required fan speed or flow and power can rise. [1]

ebm-papst's RadiPac brochure describes the alternative of mounting the impeller directly on the rotor of an external-rotor EC motor, so the whole rotating unit is balanced together and the integrated electronics replace an external frequency converter. [2] Editorial note: for a belt-driven module, ask for the belt type, pulley ratio and retensioning interval; for a direct-drive module, ask whether the quoted efficiency includes the motor electronics.

Give the supplier the airflow and static pressure at each duty point, the space available in the unit (width, height, depth), the drive you want (belt, coupling or EC direct drive), supply voltage and frequency, speed control signal, the air temperature range, and whether the fans will run in parallel as a fan wall.

02

Size the fan module and check whose efficiency is quoted

Aerovent's CPLF plenum fan, an airfoil impeller with nine blades in Arrangement 3 for field-fabricated or factory-built air handling units, pressurises the surrounding plenum so discharge ductwork can leave in any direction and the fan housing, transitions and diffusers are removed. Aerovent lists impeller diameters from 315 mm to 2,265 mm (12.25 to 89 in), airflow to 475,700 m³/h (280,000 CFM) and static pressure to 2,490 Pa (10 in w.g.). [3]

ebm-papst rates its RadiPac EC plug fans in sizes 630 to 1,000 at a static overall efficiency of 68% across a wide optimum range, measured on chamber test rigs for the whole unit of motor, electronics and impeller; it says its GreenTech EC motors exceed 90% efficiency and meet IE4, and that the range improved efficiency by over 13% against its previous models. [2]

Its nominal data list size 630 units at 380–480 V, 50/60 Hz, from 1,275 rpm and 2,670 W up to 1,950 rpm and 9,670 W, and the size 1,000 unit at 750 rpm and 6,340 W, all for ambient temperatures of −25 to +40 °C. [2] Editorial note: a plenum fan's catalogue range is a family envelope; ask for the selection at your duty point, inside your unit's cabinet, with the measured input power.

03

Compare fan assembly types

04

Impeller, EC or belt-drive motor, pulleys, bearings, inlet cone and mounting base

05

Airflow, static pressure, speed and motor input for an air handling unit fan module

Ask whose efficiency is quoted: the airflow and pressure ranges here are catalogue family limits, and the duty point in your own cabinet decides the input power.

06

Send the duty, space and drive data together

Paste it into your enquiry below or into an email to a maker, then replace every bracket.

Duty: [airflow; static pressure; number of fans]
Space: [cabinet width, height, depth]
Drive: [belt type; coupling; EC direct drive]
Electrical: [voltage; frequency; control signal]
Air: [temperature range; humidity]
Data: [measured unit efficiency; sound data]

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