Annual operating cost for fans, pumps, and cooling equipment, with and without VFDs.
Doing this for a whole building? See this step inside a connected AIM Works project — loads, ventilation, equipment, and Design Review in one place.
Book a Demo →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) on that fan or pump, so you can compare constant-speed operating cost against a reduced average flow and see the projected savings and a rough payback. The VFD model keeps a fixed share of the design pressure and counts drive losses, so it does not promise the full cube-law savings. Use it to scope an efficiency project before committing to detailed energy modeling.
| Input kW | kW = HP × 0.7457 ÷ motor efficiency |
| Annual cost, no VFD | $ = kW × motor load × hours × rate ($/kWh) |
| VFD power fraction | f = q × [f0 + (1 − f0) × q²] ÷ ηVFD (q = flow fraction, f0 = fixed-pressure share) |
| Annual cost, with VFD | $ = kW × motor load × f × hours × rate |
| Cooling cost | $ = tons × (kW/ton) × load factor × hours × rate |
| Simple payback | years = VFD installed cost ÷ annual VFD savings |
0.7457 kW/HP is the mechanical horsepower (745.7 W). The VFD fraction comes from a system curve H = H0 + (Hdesign − H0)·q² with constant fan/pump efficiency: with f0 = 0 it reduces to the ideal cube law (80% flow → 51% power); a duct-static or pump differential-pressure setpoint holds f0 above zero (typically 20–40%) and cuts the savings. Efficiency falling off at low speed, and cubing an average flow instead of an hour-by-hour flow profile, are not modeled — treat the savings as an upper-end screening figure. The baseline assumes the constant-speed motor draws its stated load all year (constant volume, or throttling that saves little). With no quote entered, the drive is priced from the AIM Works app’s installed-cost table ($350/HP to 5 HP, $250/HP to 25 HP, $200/HP to 100 HP, $150/HP above). This is a simplified operating-cost estimate, not a full hour-by-hour energy model.
AIM Works brings peak loads, ASHRAE 62.1 ventilation, equipment and plant sizing, compliance checks, Design Review, and engineering deliverables into one connected mechanical design workspace.
Results are design estimates for preliminary sizing. Verify final designs against applicable codes and standards — engineering judgment and a licensed professional engineer’s review are required.