What do the Tiruppur manual's variable frequency drive and boiler feed pump reports save, and do their paybacks tie to their own lines?

The Bureau of Energy Efficiency (BEE) Tiruppur manual books a variable frequency drive (VFD) on a 5.6 kilowatt (kW) boiler fan at 4,896 kilowatt hours (kWh) and a feed pump swap at 6,266 kWh a year. The drive pays back in 1.1 years as printed; the pump's own lines give about 10 months, not 8.

The fan drive

• More than 90% of units with boilers or thermic fluid heaters control blower air flow with mechanical dampers, the manual says. Slowing the fan instead saves more because fan power falls with the cube of the speed.
• Case: boiler induced draft fan 5.6 kW, 20% saved, 4,800 hours a year. Printed saving 1.02 kW x 4,800 = 4,896 kWh; at rupees (Rs) 4.7 = Rs 23,011. Drive cost Rs 25,000, so 25,000 / 23,011 = 1.09 years, printed 1.1.
• Check: 20% of 5.6 kW is 1.12 kW, not 1.02. At 1.12 the saving is 5,376 kWh, Rs 25,267, payback 0.99 years. The printed figure is the more cautious one; we could not find why it is 1.02.
• The manual says a 10% flow cut with a 10% speed cut reduces power by 20%. The cube law alone gives 1 minus 0.9 x 0.9 x 0.9 = 27%, so 20% leaves room for drive and motor losses.

The boiler feed pump

• Case: present pump efficiency printed as 7.79%, new 60%. The saving is 1 minus 7.79/60 = 87%, as printed.
• The pump uses 7,200 kWh a year, so the saving is 7,200 x (1 minus 7.79/60) = 7,200 x 0.8702 = 6,265 kWh, printed as 6,266, and Rs 29,449 at Rs 4.7. Investment Rs 25,000.
• Payback: 25,000 / 29,449 = 0.85 years, about 10 months. The manual prints 8 months. If the full cost of Rs 0.31 lakh (1 lakh = 100,000) for a 5 horsepower pump in its cost table is used, the payback is about 12.6 months.
• A 7.79% efficient pump is an extreme case. Measure yours: flow, head and power. A pump already at 45% would save 1 minus 45/60 = 25%.

What the two reports are worth

Both are small: 4,896 and 6,266 kWh a year, which at 0.675 kilograms (kg) of carbon dioxide (CO2) a kWh for financial year (FY) 2025-26 is 3.3 and 4.2 tonnes. They are cheap and fast, and the manual says owners lean to measures that pay back in under two years. For a loan file they add little carbon, so keep them as part of a bundle with the boiler and heat recovery measures.

Both reports re-added from their printed lines

• Fan: 1.02 kW x 4,800 hours = 4,896 kWh x Rs 4.7 = Rs 23,011; 25,000 / 23,011 = 1.09 years
• Fan CO2: 4,896 x 0.675 = 3,305 kg
• Pump: 7,200 x (1 minus 7.79/60) = 6,265 kWh, printed 6,266; Rs 29,449 as printed; 25,000 / 29,449 = 0.85 years = 10.2 months
• Pump CO2: 6,266 x 0.675 = 4,230 kg

Figures are the manual's at study-year prices; CO2 uses the FY 2025-26 grid factor.

What Senseible does here

Senseible reads fuel invoices and electricity bills into monthly records, so monthly kWh before and after a drive or pump change are on file. Fan and pump power need their own meter or a clamp reading.

• Thermic fluid pump drive electricity saving
• Stenter blower speed optimisation
• Tiruppur manual: payback table in months or years
• Green loan readiness check

Sources: BEE, Manual on Energy Conservation Measures in Textile Cluster, Tirupur (prepared by Winrock International India, via SAMEEEKSHA)

Last reviewed 2026-11-05. Figures are from the manual's study year (around 2010 to 2011), with power at Rs 4.7 a kWh. Use your own tariff, a measured pump efficiency and a current quote.