How much does a VFD on a tea dryer's hot air blower save?

About a third of the blower's power. BEE's Jorhat report measured 25 HP dryer blowers at 12.69 kW on average and expects 8.41 kW with a VFD in place of the damper: 15,408 kWh a year. Cost Rs 1.98 lakh, saving Rs 1.15 lakh, payback 1.72 years at 2010 prices.

The damper problem

The hot air blower pushes air from the coal or gas heater through the dryer at constant speed. Airflow is trimmed by a manual damper kept 20 to 40% closed, so the motor works against its own restriction. Factories run 10 to 12 hours a day, about 300 days a year.

Seven factories, seven different loads

• Measured blower power: 14.00, 15.20, 12.00, 12.00, 18.24, 9.90 and 7.50 kW.
• Average 12.69 kW, or 45,684 kWh a year at 3,600 hours.
• The report expects 8.41 kW after the VFD, a 33.7% cut, but does not show how it got there. Log your own blower's kW before you buy.

The money at 2010 prices

• 4.28 kW x 3,600 hours = 15,408 kWh.
• At Rs 7.45 a kWh (70% grid at Rs 5.50, 30% generator at Rs 12): Rs 1.15 lakh.
• Cost: Rs 1.71 lakh VFD and panel with tax, Rs 0.10 lakh commissioning, Rs 0.17 lakh contingency: Rs 1.98 lakh. One day of downtime.

The CO2 figure

15,408 kWh x 0.675 = 10.4 t of CO2 a year on today's grid, not the 15.86 t in the report, which used 1.03 kg a kWh. Hours on the generator save more: 2.645 kg for each litre of diesel not burned.

Smallest and largest blower in the survey

• 7.50 kW x 33.7% = 2.53 kW saved x 3,600 h = 9,106 kWh
• Rs 0.68 lakh a year: payback about 2.9 years
• 18.24 kW x 33.7% = 6.15 kW saved = 22,147 kWh
• Rs 1.65 lakh a year: payback about 1.2 years

Scales the report's 33.7% cut to each measured blower at its Rs 7.45 a kWh. An estimate; your damper position decides the real figure.

What Senseible does here

Senseible reads electricity bills and diesel invoices into monthly kWh, litres and CO2, so the saving shows against last season's bills. For one blower, the free electricity bill calculator turns kWh saved into CO2.

• Free carbon calculators
• Tea withering: automatic airflow
• VFD savings on pumps and fans
• Tea factory footprint per kg
• Jorhat tea factories: coal, gas and CO2

Sources: BEE, Detailed project report: VFD fitment in hot air blowing system of drier with 25 HP motor, Jorhat tea cluster (2010, SAMEEEKSHA), CEA, CO2 Baseline Database for the Indian Power Sector, version 22.0 (FY 2025-26 grid factor)

Last reviewed 2026-11-01. Report figures are from a BEE SME programme project report; costs and paybacks are at the report year's prices. Check today's fuel and power prices and a current quote before you rely on the payback.