VSD Energy Analysis Tool
Enter your local utility rates for an accurate ROI.
How the Calculation Works
The savings calculated above are based on the Affinity Laws, which govern how centrifugal loads (like the fans and pumps in your facility) behave when motor speed changes—formulas given below.
1. Establishing the Baseline ($P_{base}$)
Before calculating savings, we determine the actual power your motor draws from the grid at 100% speed. We don’t just use the nameplate kW; we account for the Motor Efficiency ($\eta_{m}$).
$$P_{base} = \frac{kW_{motor}}{\eta_{m}}$$
2. The Cube Law (The “Magic” of VSDs)
Unlike a lightbulb, where reducing power by 50% saves 50% energy, centrifugal fans and pumps follow a cubic relationship. If you reduce the speed ($N$) of a fan, the power required ($P$) drops by the cube of that change.
$$P_{required} = P_{base} \times \left( \frac{N_{new}}{N_{old}} \right)^3$$
Example: Reducing speed to 80% (0.8) means the power required is $0.8 \times 0.8 \times 0.8$, or only 51.2% of full power.
3. Accounting for VSD & Heat Losses
To ensure our results are “Righteous” and realistic, we do not assume the VSD is 100% efficient. Variable Speed Drives generate heat through internal switching and cooling fans. We apply a Drive Efficiency factor ($\eta_{vsd}$)—typically 97%—to the calculation.
$$P_{total\_vsd} = \frac{P_{required}}{\eta_{vsd}}$$
The final Net Savings is the difference between your Baseline cost and this adjusted VSD operation cost, ensuring the numbers you see are achievable in a real-world industrial environment.