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Pump Energy Cost Calculator - Operating Cost, Efficiency & VFD Savings Analysis

Calculate annual pump operating cost and model VFD retrofit payback

Calculate the actual operating cost for any water or wastewater pump. Enter flow rate, total dynamic head, pump efficiency, runtime, and electric rate to get kW demand, annual energy cost, cost per million gallons, and wire-to-water efficiency rating. Includes a VFD comparison module that uses the affinity laws to estimate savings from variable speed operation with simple payback and 10-year projection.

Pro Tip: Most municipal pumps run at 50-65% wire-to-water efficiency. That means 35-50% of your electric bill for pumping is wasted as heat, vibration, and friction. A pump running at 55% efficiency instead of the nameplate 78% is costing you 42% more in electricity than it should. Worn impellers, oversized motors, and throttled valves are the usual culprits.

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Pump Energy Cost Calculator
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How It Works

  1. Enter Pump Operating Parameters

    Input flow rate (GPM or MGD), total dynamic head (feet), pump efficiency, and motor efficiency. If you don't know pump efficiency, start with 70% for a typical municipal pump.

  2. Set Runtime and Electric Rate

    Enter daily runtime hours and electric rate in $/kWh. Include demand charges if your utility bills them separately (typically $5-15/kW/month for municipal accounts).

  3. Review Energy Cost Results

    See kW demand, daily/monthly/annual energy cost, cost per million gallons pumped, and a wire-to-water efficiency rating with green/yellow/red indicators.

  4. Model VFD Savings (Optional)

    Toggle the VFD comparison section to see projected savings from reducing flow via variable speed. The affinity laws show that reducing flow to 80% reduces power to roughly 51% of full speed.

Built For

  • Public works directors budgeting annual pump station energy costs
  • Operators identifying inefficient pumps that need maintenance or replacement
  • Engineers building business cases for VFD retrofits
  • Utility managers comparing cost per MG across multiple pump stations
  • Energy auditors evaluating municipal pumping efficiency

Frequently Asked Questions

First calculate water horsepower: WHP = (GPM × TDH) / 3960. Then brake horsepower: BHP = WHP / pump efficiency. Convert to kW: kW = (BHP × 0.746) / motor efficiency. Annual cost = kW × runtime hours × 365 × $/kWh. Add demand charges: kW × $/kW/month × 12.
Wire-to-water efficiency is the overall efficiency from electricity input to water output. It combines motor efficiency, pump efficiency, and any drive losses. A pump with 85% motor efficiency and 75% pump efficiency has about 64% wire-to-water efficiency. Municipal pumps typically range from 45-70% overall.
The affinity laws say power varies with the cube of speed. Reducing pump speed to 80% reduces power to about 51% (0.8³ = 0.512). At $0.10/kWh and a 50 HP pump running 24/7, that 49% power reduction saves roughly $16,000 per year. VFD payback is typically 1-3 years for constantly running pumps.
Disclaimer: This calculator provides estimates based on pump affinity laws and standard engineering formulas. Actual energy consumption depends on system curve, pump condition, motor characteristics, and real operating conditions. VFD savings estimates assume the system can operate at reduced flow. Consult with a pump or motor specialist for site-specific analysis.

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