Axial fan (ventilation and cooling)

01

Pick the fan type and duty point

US DOE regulations (10 CFR 431.172) define a fan or blower as a rotary bladed machine converting electrical or mechanical power to air power with energy output up to 25 kJ/kg of air, made of an impeller, shaft and bearings or driver and a structure or housing; they define an axial inline fan as an axial impeller in a cylindrical housing with or without turning vanes, an axial panel fan as an axial fan without cylindrical housing mounted on a panel, orifice plate or ring through a wall, ceiling or other separating structure, and air-circulating fans — including cylindrical and panel types and box fans — as fans that work against zero external static pressure without ducting. [1]

The same definitions treat all blade-pitch variations of an adjustable-pitch axial fan as a single basic model, and list reversible axial fans for tunnel ventilation and fans for explosive atmospheres among safety fans. [1]

Editorial calculation: to remove heat with air, airflow = power ÷ (air density × specific heat × temperature rise); taking 1.2 kg/m³ and 1,005 J/kg·K, 5 kW with a 10 K rise needs 5,000 ÷ (1.2 × 1,005 × 10) ≈ 0.41 m³/s, about 1,490 m³/h or 880 cfm, before allowing for system pressure losses.

Give the supplier the fan type and installation, required airflow and static pressure (duty point) and air density or temperature, available diameter and depth, pusher or puller arrangement, supply voltage and frequency, speed control, noise limit, ingress protection, materials and temperature, efficiency or ErP/DOE requirements and quantity.

02

Size the impeller, blades, material and motor

Multi-Wing's modular axial impellers can be configured by blade geometry (40 shapes), number of blades, material, pitch angle, rotation direction and diameter from 200 to 2,746 mm, for HVAC/R and off-highway engine cooling; pitch is chosen to put the fan at its best efficiency at the required duty point and also sets the fan's width, blade profiles are offered in left- and right-hand versions for pusher or puller use, and three thermoplastics and two aluminium alloys cover applications from low-pressure livestock ventilation to smoke extraction fans across −40 to 400 °C. [2]

At the compact end, Orion lists AC axial fans from 60 to 280 mm frame size at 115 V, 230 V or dual voltage, with standard IP44 and optional higher IP and salt-fog ratings and dual speed; airflow runs from about 8–10 cfm for a 60 × 60 × 30 mm fan to 1,000–1,300 cfm for 254 and 280 mm frames. [3]

Editorial calculation: 1,300 cfm × 1.699 ≈ 2,210 m³/h. [3]

03

Use the fan laws and life definitions behind a data sheet

NMB Technologies' Fan Engineering handbook for its AC and DC axial cooling fans sets out how catalogue figures are produced and how they change with speed. Airflow and static pressure are measured on a double-chamber test rig, with maximum airflow taken at zero static pressure; noise is measured in an anechoic chamber with less than 16 dBA background, in line with JIS C 9603, at 1 m from the inlet for DC fans and 1 m from the side for AC fans. Its fan-law examples start from a fan giving 210 cfm, 0.1 in. of water at the operating point, 22 W and 58 dBA at 3,000 rpm, and ask what each becomes at 3,500 rpm; the laws apply only to fans of the same size, motor and impeller. For life, NMB counts parametric failures, a 15% drop in speed or a 15% rise in current, as well as fans that stop, which it says gives a more conservative L10 and MTTF than counting hard failures only, and it runs accelerated life tests and ongoing reliability tests, for some models beyond 10 years. [4]

Editorial calculation with the usual fan laws (airflow ∝ speed, pressure ∝ speed², power ∝ speed³, noise rising by 50 × log₁₀ of the speed ratio): going from 3,000 to 3,500 rpm gives about 245 cfm, 0.136 in. of water, 34.9 W and 61.3 dBA, so a 17% speed increase costs about 59% more power. When comparing quotations, ask each supplier how its noise was measured and at what distance, and whether its L10 life counts parametric failures. [4]

04

Fan curve, sound and motor data to request from suppliers

Ask each supplier for the fan curve (airflow against static pressure and power) at your speed and air density, sound data, materials and temperature limits, motor data and any efficiency compliance for your market. [1] [2]

05

Blades, hub, housing, motor and material

Blade shape and pitch head the table because Multi-Wing ties pitch to where the fan reaches its best efficiency at the required duty point. [2]

06

Axial fan data sheet lines, filled where a source gives a figure

Speed, power consumption, frequency and weight have no published figure here; take them from the supplier's fan curve at your duty point.

07

Send the duty, envelope and supply data together

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

Type: [inline; panel; circulating; AC compact]
Duty: [m³/h; Pa; air °C]
Envelope: [diameter; depth; pusher/puller]
Supply/control: [V; Hz; speed control]
Material/temp: [plastic; aluminium; °C]
Noise/IP: [dB(A); IP]
Compliance: [DOE; ErP]
Quantity: [units]

See manufacturer records Send an enquiry through CNFX