Duty & economics
e.g. 0.7 = 70 % flow
Awaiting Valid Duty Parameters
Adjust the parameters on the left to compute live hydraulic values, ranges, and sizing verdicts.
Justifying a VFD to management?
We fit and commission VFDs on chemical pumps and verify the savings with before-and-after power readings.
VFD payback explained
The cube law does the math
Pump power follows the cube of the speed ratio: at 70 % speed a pump draws about 34 % of full-load power. Against throttled operation — which at 70 % flow typically still draws ~85 % of full power — the saving is dramatic: (0.85 − 0.34) × power × time.
A 4.19 kW pump at 70 % flow for 60 % of 8,000 hours saves about 10,200 kWh a year, worth roughly ₹66,000 at ₹6.5/kWh — a ₹45,000 VFD pays back in under a year.
When VFD savings shrink
The cube law is exact for friction-dominated systems. Where static head dominates, slowing the pump may not reduce flow proportionally and savings fall — run the system-curve tool to check. Also: a pump already running at its duty point saves nothing by slowing further; the saving comes from matching speed to varying demand.
VFDs also add soft starting, which protects the motor and supply, and they remove the need for control-valve throttling — two benefits beyond the energy line.
Full picture
Add the motor and drive losses (VFDs run 95–98 % efficient) and the tariff: the calculator uses your inputs, not averages. For the complete economic case — maintenance, repair and replacement included — take the result into the LCC calculator. Teflow supplies, fits and commissions VFDs on chemical and water pumps across Gujarat — call +91 98251 62709.
Technical & Operational FAQs
Q1.How much does a VFD save on a pump?
Power follows the cube of the speed ratio: 70 % speed ≈ 34 % power, 80 % speed ≈ 51 %. Against throttled operation, a pump running at 70 % flow for most of its duty typically saves 40–60 % of its energy bill. Enter your duty in the calculator for the exact figure.
Q2.How do I calculate VFD payback?
Payback = (VFD + installation cost) ÷ annual savings. Annual savings = (throttled power − VFD power) × running hours × share of time × tariff. A 4.19 kW pump at 70 % flow for 60 % of 8,000 h saves about ₹66,000/yr — under a year payback for a ₹45,000 drive.
Q3.When is a VFD not worth it?
When the pump runs at full speed most of the time, when static head dominates (savings fall below the cube law), or when the duty is fixed. In those cases a trim or a correctly sized pump beats a VFD on cost.
Q4.Does a VFD damage the motor?
A correctly selected VFD with a standard IE2/IE3 motor is safe; long cable runs and some older motors benefit from output filters. VFDs also give soft starting, which reduces motor and coupling stress versus DOL starting.
Q5.What other benefits do VFDs give?
Soft starting, exact flow control without valves, protection against dry-run (with sensors), and energy savings at partial load. They also let the affinity calculator’s speed changes become a real operating mode instead of a pipe dream.
Related Engineering Tools
Pump Energy Cost
Affinity Laws Calculator
Pump LCC Calculator
System Curve Tool
Pump Repair Service
Pump Consultancy
Need a custom hydraulic audit or specific duty curve verification? Call +91 98251 62709 or Request a Detailed Engineering Quote.