Fan laws

FAN LAWS

Change in frequency (revolutions)

Het is mogelijk om het toerental van een ventilator te regelen met behulp van een (frequentie) regelaar. Door het aanpassen van de frequentie zal ook de bijbehorende capaciteit, druk en opgenomen vermogen veranderen.

The following abbreviations are used in the formulas shown below:

Relevant formula's
Capacity:	Q
Pressure	Pa
Frequency	Hz
Absorbed Power:	Popg.
Speed:	n

Capacity (Q) and speed (n) both have the same formula

(Hz2 / Hz1) x Q1 = Q2

(Hz2 / Hz1) x n1 = n2

Pressure (Pa) (to the 2nd power)

(Hz2 / Hz1) ² x Pa1 = Pa2

Absorbed Power (Popg.) (to the 3rd power)

(Hz2 / Hz1) ³ x Popg.1= Popg.2

Calculation examples:

(Hz2 / Hz1) ³ x Popg.1= Popg.2

Data: 15,000 m³/ hour at 500 Pa at 50Hz (1.400 rpm) with an absorbed power of 2.1 kW. The frequency is reduced from 50 to 30Hz. This has the following implications.

The new values are calculated using the formulas given above:
Speed: (30/50)x1.400	840 rpm.
Capacity: (30/50)x15.000	9.000 m³/ hour
Pressure: (30/50)²x500	180 Pa
Absorbed Power: (30/50)³x2.1	0.45 kW.

The calculation can also be reversed.

To reduce the m³/ hour from 15.000 to 7.500, the frequency can be calculated using the same formula.

(Hz 2/Hz 1) x Q1=Q2

(Hz2 /50) x 15.000=7.500 → Hz2=(7.500/15.000)x50= 25 Hz

Reduce pressure from 500 to 125 pa. The frequency can be calculated using the same formula.

(Hz 2/Hz 1) ² xPa1=Pa2

(Hz2/50)²x500=125 → Hz2=( 125/500)x50 = 25 Hz

To reduce the power from 2.1 to 0.2625 kW, the frequency can be calculated using the same formula.

(Hz 2/Hz 1) ³ x Popg.1=Popg.2

(Hz2/50)³x2.1=0.2625 → Hz2 =( 0.2625/2.1)x50= 25 Hz