The Affinity Laws: Why VFDs Save So Much Energy
Silver State Incentives · Published October 14, 2026
The affinity laws describe how centrifugal fans and pumps behave: flow follows speed, pressure follows speed squared, and power follows speed cubed. That cube relationship is why a VFD that slows a fan by 20% cuts its power to about 51% of full load, roughly halving its energy use.
What are the affinity laws?
For centrifugal fans and pumps: flow ∝ speed; pressure ∝ speed²; power ∝ speed³.
What does that mean in dollars?
At 80% speed, power is 0.8³ = 0.512, or about 51% of full power. If a 25 HP fan runs 6,000 hours a year, the savings are substantial at commercial rates. Our calculator applies load factor, motor efficiency and drive efficiency to estimate them.
Where do VFDs work best?
On variable-torque loads with variable demand: air handlers, cooling-tower fans and chilled or condenser water pumps. Constant-torque loads see smaller savings.
How are VFD savings verified?
We meter the motor before and after installation and follow IPMVP. Vibration sensors confirm smooth operation at new speeds.
Why this matters for your facility
Lower net cost
Incentives reduce the investment.
Verified savings
Measured under IPMVP.
24/7/365
VEM protects results.
Utility capital pays for part of the upgrade
Every project we model shows the incentive, the net cost and the resulting payback, SIR and IRR.
- We identify every eligible NV Energy prescriptive and custom incentive.
- We stack lighting with controls to raise the incentive 20–50%.
- We prepare and submit the application, then verify savings under IPMVP.
Quick savings estimate
Adjust the inputs for a planning estimate. The full calculator adds incentives, payback, CO2 and a 10-year view.
Assumes $0.10/kWh and $12/kW-month. Change rates in the full calculator.
Planning estimate only. Actual savings and incentives are confirmed through an on-site audit and utility program approval.
Related solutions
Frequently asked questions
Is this financial advice?
No. It is general information. Your consultant models your specific project.
Where can I run the numbers?
Use our savings calculator, which reports SIR, IRR, payback and CO2.
Who wrote this?
The Silver State Incentives energy consulting team.
Can SSI review my project?
Yes. Book a consultation.
Turn Your Overhead Into Net Profit.
Book a no-pressure consultation with a veteran energy consultant. We will show you the savings, the incentive and the payback before you commit.
Every month you wait is money lost to inefficiency. Incentive funding is limited per program year.