Energy Cost Estimator

Estimate annual operating costs for fans, pumps, and cooling equipment. Compare with and without VFDs/variable flow.

⚡ Fan / Pump Energy

% of full load on average (VFD systems run lower)
Average VFD speed — affinity law applies (power ∝ speed³)

🌡️ Cooling System

Centrifugal chiller: 0.45–0.7; DX rooftop: 0.9–1.3

📊 Annual Energy Cost

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Fan/Pump Cost/yr
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With VFD Cost/yr
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VFD Savings/yr
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Cooling Cost/yr
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Total HVAC Cost/yr
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ℹ️ About This Calculator

This estimator puts a dollar figure on the energy a fan, pump, or cooling plant uses over a year. Enter the motor horsepower, efficiency, average load, run hours, and electricity rate for the air or water side, and the chiller capacity, efficiency, and hours for the cooling side. The tool returns annual fan/pump cost, cooling cost, and a combined HVAC total.

It also models a variable frequency drive (VFD) using the affinity law, so you can compare full-speed operating cost against a reduced average speed and see the projected savings and a rough payback. Use it to scope an efficiency project before committing to detailed energy modeling.

🔬 Formula & Method

Input kWkW = HP × 0.7457 ÷ motor efficiency
Annual cost$ = kW × load factor × hours × rate ($/kWh)
VFD powerfraction = (speed)³  →  80% speed ≈ 51% power
Cooling cost$ = tons × (kW/ton) × load factor × hours × rate
Simple paybackyears = install cost ÷ annual savings

The 0.7457 factor is the exact kW-per-horsepower conversion. VFD savings follow the fan/pump affinity laws (power ∝ speed³), which assume a system curve dominated by friction; fixed static pressure reduces the benefit. The payback uses an assumed installed drive cost of about $800/HP — a screening figure, not a quote. This is a simplified operating-cost estimate, not a full hour-by-hour energy model.

❓ Frequently Asked Questions

How does this tool estimate fan and pump energy cost?
It converts motor horsepower to kilowatts (1 HP = 0.7457 kW), divides by the motor efficiency to get input kW, then multiplies by the average load factor, the annual run hours, and the electricity rate. The result is the yearly operating cost at the entered load. Lower the load factor for systems that rarely run at full load.
How are VFD savings calculated?
Variable frequency drive savings come from the fan and pump affinity law: power varies with the cube of speed. At 80 percent speed the motor draws roughly 0.8 cubed, or about 51 percent, of full power. The tool computes cost at the entered VFD speed and reports the difference against full-speed cost. Actual savings depend on the system curve and how much static pressure is fixed versus variable.
How is the VFD simple payback figured?
Simple payback equals installed cost divided by annual savings. This tool assumes an installed drive cost of about 800 dollars per horsepower and divides it by the yearly VFD savings to report payback in years. Treat it as a screening estimate; get a real quote for budgeting because drive pricing varies widely with horsepower and enclosure.
What kW per ton should I use for cooling cost?
Efficient water-cooled centrifugal chillers run about 0.45 to 0.7 kW per ton, while packaged DX rooftop units run roughly 0.9 to 1.3 kW per ton. Cooling energy cost is capacity in tons times kW per ton times the cooling load factor times cooling run hours times the electricity rate. Use the manufacturer full-load and part-load values when you have them.

🔗 Related Tools

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