Estimate the energy, fuel-equivalent operating cost and ROI impact
of adding variable frequency drives to centrifugal marine pumps and
fans. Compare existing throttle, valve, damper or other fixed-speed
control with variable-speed operation while accounting for static
head or fixed-pressure requirements, drive efficiency, operating
hours, installation cost and maintenance.
Currency is display only. No exchange-rate conversion is performed.
Variable-Speed Energy
Flow, dynamic head and static-pressure effects
Existing Control
Compare against measured or estimated fixed-speed power
Investment Case
Annual savings, payback, ROI, NPV and lifetime economics
Pump / Fan Operating Point
For best results, use measured electrical kW at the reference
full-flow operating point and measured power at the current
reduced-flow condition when available.
units
kW / unit
Prefer measured electrical input rather than motor nameplate rating.
% design flow
% full-flow kW
Represents current throttle, valve, damper, bypass or other
fixed-speed control. Use measured power when available.
% design head
Higher static head or fixed-pressure requirements reduce the
savings available from speed reduction.
%
hours/day
days/year
Electricity & Project Cost
$
/kWh
$
$
$
/year
years
%
kg CO2/kWh
Equipment & VFD Assumptions
Advanced mode evaluates multiple annual operating periods.
Baseline fixed-speed power is entered separately for each
flow condition.
units
kW / unit
% design head
%
Annual Operating Profile
Each row represents calendar operating hours at one flow condition.
Active units cannot exceed the number of units being retrofitted.
Operating Mode
Flow %
Hours / Year
Active Units
Existing Power %
Economics
$
/kWh
$
$
$
/year
years
%
kg CO2/kWh
VFD Energy & ROI Results
Average operating-point analysis
Enter operating data
Enter reference electrical power, flow requirement and existing
fixed-speed power to estimate VFD energy savings and retrofit ROI.
Net Annual Savings
N/A
Gross electricity savings minus entered incremental maintenance
Simple Payback
N/A
Total installed project cost ÷ net annual savings
Baseline Energy
N/A
VFD Energy
N/A
Annual Energy Saved
N/A
Energy Saving
N/A
Gross Annual Savings
N/A
Project CAPEX
N/A
First-Year ROI
N/A
Project NPV
N/A
Lifetime Net Benefit
N/A
CO2 Avoided
N/A
Project-Life Break-Even Power Price
N/A
Annual Maintenance Increment
N/A
Operating Power Comparison
Scenario
Flow
Relative Power
Power
Annual Energy
Annual Cost
Operating-Period Savings
Advanced mode
Mode
Flow
Hours
Units
Baseline kW
VFD kW
Saved kWh
Value
Annual Energy-Cost Comparison
Retrofit Economics
Energy Model Summary
Net Annual Savings Sensitivity
Operating hours vs electricity price
Operating Hours \ Price
-20%
Base
+20%
Model approach:
the variable-speed case uses a centrifugal-system relationship.
Flow ratio is treated as proportional to speed. Dynamic head varies
approximately with speed squared while the entered static-head or
fixed-pressure component remains. Relative VFD power is therefore
modeled as flow ratio × [static-head fraction + dynamic-head fraction
× flow ratio²], adjusted for entered VFD efficiency. Existing
fixed-speed power is entered separately so throttling, damper,
bypass and other control losses can be represented directly.
Planning estimate only.
This model is intended for centrifugal pumps, fans and similar
variable-torque loads. Actual VFD savings depend on the equipment
curve, system curve, static head, minimum required pressure,
valve or damper position, flow measurement, motor efficiency,
VFD losses, harmonics, cooling, cable length, motor insulation,
redundancy philosophy, minimum safe speed and operating sequence.
Affinity-law behavior can materially overstate savings where static
head or fixed-pressure requirements dominate. Do not apply this model
to positive-displacement pumps, constant-torque loads or systems that
do not follow centrifugal affinity relationships without appropriate
engineering analysis. VFD selection and installation should follow
vessel-specific electrical, OEM and class requirements.
