Tool

Blower sizing calculator

Enter the duty you need, the gas you actually have, and the worksheet shows the density correction and the fan-law consequences. It is a sizing aid, not a substitute for a selection - but it will stop the expensive arguments before they start.

Worksheet

Run your duty

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Design air at site conditions
Required duty at the fan inlet

Efficiency is an assumption you control, not a claim about a specific machine. Backward-curved and airfoil wheels sit higher than radial wheels at the same tip speed.

Corrected duty

Air density at site—
Density ratio vs 20 °C sea level—
Mass flow—
Static pressure as supplied at 20 °C air—
Air power at duty gas—
Shaft power at assumed efficiency—
Suggested motor with 15 % margin—
Tip speed if run at RPM—

Ideal-gas density correction only. It sizes the duty point; it does not replace a tested fan curve. Send the output with your enquiry and we confirm against the actual wheel.

Method

What the worksheet is doing

Density
Gas density is absolute pressure divided by the product of the specific gas constant and absolute temperature. For dry air the constant is 287.05 J/kg-K, so at 101,325 Pa and 20 C the answer is about 1.2 kg/m3
Standard air
Fan performance is rated against standard air at 1.2 kg/m3, which is the basis most catalogue curves, including ours, are drawn on
Volume
At a fixed fan and fixed speed, volume flow does not change with density. What changes is what that air weighs
Pressure and power
At constant volume flow, fan pressure and absorbed power both vary directly with gas density
Speed
Fan laws: pressure goes as the square of speed, absorbed power as the cube, flow linearly
Hot duty
To hold a required actual pressure in lighter gas, speed must rise as the square root of the inverse density ratio, and flow rises with it

Honesty clause

What this worksheet will not do

It does not know your system curve, your duct leakage, your filter blinding schedule, your altitude, the dust in your gas or the noise limit at your boundary. It does not select a wheel. It gives you the density-corrected number and the fan-law consequence, which is enough to make the conversation with the works short and specific.

Send the corrected duty

Copy the numbers out of the worksheet into the enquiry form. We will come back with a selection, absorbed power and a GA drawing.

Enquiry form(+91) 990 903 3851

Read next

The notes behind the maths

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