Engineering
VFD Energy Savings Calculator — Variable Frequency Drive
Calculate energy savings from installing a Variable Frequency Drive (VFD) on dairy plant pumps and fans. Calculate payback period and annual savings.
Formula
(motorPower - motorPower * Math.pow(loadFactor / 100, 3)) * hoursPerDay * daysPerYear * tariff
motorPower
Motor Rated Power (kW)
loadFactor
Average Speed / Load (%)
hoursPerDay
Operating Hours per Day (hr/day)
daysPerYear
Operating Days per Year (days)
tariff
Electricity Tariff (₹/kWh)
vfdCost
VFD Installation Cost (₹)
Worked Example
1
Given:
daysPerYear = 330
hoursPerDay = 20
loadFactor = 75
motorPower = 22
tariff = 7.5
vfdCost = 150000
2
Apply the formula:
(motorPower - motorPower * Math.pow(loadFactor / 100, 3)) * hoursPerDay * daysPerYear * tariff
3
Result:63458 ₹63458 kWh63458 months
Why VFDs Save Energy
Without a VFD, a pump runs at full speed and a control valve throttles the flow — wasting energy as heat across the valve. With a VFD, the pump runs at a lower speed to deliver exactly the required flow, consuming dramatically less power.
The Affinity Laws govern this relationship:
- Flow ∝ Speed: Q₂/Q₁ = N₂/N₁
- Head ∝ Speed²: H₂/H₁ = (N₂/N₁)²
- Power ∝ Speed³: P₂/P₁ = (N₂/N₁)³ ← The critical one
If you reduce speed by just 20%, power consumption drops by 49% (0.8³ = 0.512).
How to Use This Calculator
- Enter the motor rated power (kW)
- Enter the average load percentage (what % of full speed does the pump normally run at?)
- Enter the operating hours per day and days per year
- Enter the electricity tariff (₹/kWh)
- Enter the VFD installation cost (₹)
- The calculator gives annual savings, CO₂ reduction, and payback period
Applications in Dairy Plants
| Equipment | Typical Speed Reduction | Typical Power Saving |
|---|---|---|
| Transfer pump (variable flow) | 15–25% | 35–58% |
| Cooling tower fan | 20–30% | 49–66% |
| Refrigeration compressor (VSD) | 10–30% | 27–66% |
| CIP pump (part-time duty) | 20–30% | 49–66% |
| Chiller condenser fan | 15–25% | 35–58% |
Payback Period
Typical VFD payback in Indian dairy plants:
- Small pumps (< 15 kW): 18–36 months
- Medium pumps (15–55 kW): 12–24 months
- Large pumps & fans (> 55 kW): 6–18 months
Many utilities and DISCOM schemes in India offer subsidies on VFD installations — check with your local DISCOM for energy efficiency incentives.