The Power of the Cube: Understanding Fan Affinity Laws

To understand why duct leakage is so expensive, you must understand the Fan Affinity Laws. These physics principles govern the relationship between a fan’s rotational speed (RPM), the volume of air it moves (CFM), and the energy it consumes (BHP).

While airflow and pressure change significantly with speed, the most critical law for your budget is the Power Law.
The Three Key Relationships:

1. Airflow is Linear: If you increase fan speed by 10%, you get 10% more airflow.
2. Pressure is Squared: A 10% increase in speed generates 21% more static pressure (1.1 x 1.1).
3. Power is Cubed: This is the danger zone. Power consumption increases by the cube of the speed change.

The Real-World Cost

Imagine your duct system has leaks. To maintain the required suction at the machine, you increase the fan speed by just 10% using a Variable Frequency Drive (VFD).

• Math: 1.10 x 1.10 x 1.10 = 1.331
• Result: You are now paying for 33% more electricity to achieve a mere 10% gain in performance.

This geometric progression is why "small" leaks are financial disasters. Conversely, a sealed, low-resistance system like Nordfab Quick-Fit® allows you to reduce fan speed. Thanks to the Power Law, dialing a fan back by just 10% reduces your energy bill by roughly 27%.