What does a desuperheater on a 210 tonne of refrigeration dairy plant save compared with a 100 tonne one, and why does the payback improve?

A desuperheater, a heat exchanger that turns the hot gas leaving a dairy's ammonia compressors into hot water, saves 38,410 kilograms of furnace oil a year on a 210 tonne of refrigeration (TR) plant and 19,047 on a 100 TR plant in the Bureau of Energy Efficiency (BEE) Gujarat reports. The saving doubles; the cost does not.

What a desuperheater does, in plain words

A dairy's refrigeration does not make cold from nothing. It pumps heat out of the milk, and the compressors push that heat out as very hot gas, which is normally thrown away. Think of the warm back of a household fridge. A desuperheater is a heat exchanger on the compressor's outlet pipe that catches part of that heat in water, so the oil-fired boiler has less water to heat for cleaning in place (CIP) and boiler feed.

The two reports side by side

• 100 TR plant, in a chilling centre taking 200,000 litres of milk a day: 72.9 TR on load (the report notes the average load may be lower), 20 hours a day, 360 days. Waste heat caught 30,863 kilocalories an hour, which is 18,518 litres a day of water at 60 degrees. Oil saved 19,047 kilograms a year. Pump power added 2,686 kilowatt hours (kWh). Net benefit 5.36 lakh rupees (Rs) a year, where a lakh is 100,000. Cost Rs 20.81 lakh, payback 3.88 years.
• 210 TR plant, in a dairy taking 400,000 litres of milk a day: 147 TR on load (again the report notes the average load may be lower), the same hours. Heat caught 62,238 kilocalories an hour, 37,343 litres a day at 60 degrees. Oil saved 38,410 kilograms. Pump power added 5,371 kWh. Net benefit Rs 10.85 lakh. Cost Rs 32.37 lakh, payback 2.98 years.
• Oil is valued at Rs 29 a kilogram in both. Power is Rs 5.98 a kWh in the 100 TR report and Rs 5.33 in the 210 TR report.

Why the payback improves

In plain words, both plants catch the same share of their heat, so the saving grows with the load. Our reading: the saving works out to 14% of the heat absorbed from the milk (72.9 TR x 3,024 kilocalories x 14% and 147 TR x 3,024 x 14%). That is 10% of the heat rejected at the condenser, which the report also prints (30,863 of 308,630 kilocalories an hour). The reports themselves call it 10 to 14%. So the saving is in step with the load: 19,047 / 72.9 = 261 kilograms of oil for each TR on load, and 38,410 / 147 = 261 as well.

The cost is not in step. It is Rs 0.285 lakh for each TR on load in the small plant and Rs 0.220 lakh in the large one, because piping, tank and controls are partly fixed. Our own arithmetic, from the printed figures.

The share of the plant's oil is different. The 100 TR chilling centre burns 105,972 kilograms a year, so 19,047 is 18%. The 210 TR dairy burns 442,020 kilograms, so 38,410 is 8.7%. A big saving in tonnes can still be a small cut in the oil bill.

Two things to check in the 210 TR report

• Its specification paragraph talks of two 45 TR refrigeration systems with a 50 TR desuperheater on each. Its baseline table shows two 210 TR screw compressors, one working and one on standby, with 147 TR on load. Ask the supplier which one the price covers.
• It shows 130.6 tonnes of carbon dioxide (CO2) saved, which is 3.4 kilograms per kilogram of oil. The 100 TR report works to the same 3.4. At the IPCC default of 3.13 kilograms of CO2 per kilogram of furnace oil, 38,410 kg is 120.2 tonnes, less 3.6 tonnes for the pump power at 0.675 per kWh: about 116.6 tonnes net.

Before you fit one

1. Check you can use about 37,000 litres of 60 degree water a day. Heat with nowhere to go saves nothing.
2. Read the compressor's discharge temperature and on-load TR from the plant log, not the nameplate. The saving moves with the load.
3. Check what fuel makes your hot water now. If it is gas or wood, redo the money and the CO2 with that fuel.

Both plants, line by line

• 100 TR: 72.9 TR x 3,024 = 220,450 kilocalories an hour absorbed; 14% = 30,863. Oil saved 19,047 kg x Rs 29 = Rs 5.52 lakh. Pump 2,686 x Rs 5.98 = Rs 0.16 lakh. Net Rs 5.36 lakh. 20.81 / 5.36 = 3.88 years
• 210 TR: 147 TR x 3,024 = 444,528 kilocalories an hour absorbed; 14% = 62,238. Oil saved 38,410 kg x Rs 29 = Rs 11.14 lakh. Pump 5,371 x Rs 5.33 = Rs 0.29 lakh. Net Rs 10.85 lakh. 32.37 / 10.85 = 2.98 years
• Cost check, 210 TR: 28.66 + 0.75 + 1.95 + 0.53 + 0.48 = Rs 32.37 lakh
• CO2, 210 TR at 3.13 per kg of oil: 38,410 x 3.13 = 120,223 kg, or 120.2 tonnes. Pump: 5,371 x 0.675 = 3.6 tonnes. Net 116.6 tonnes

These are the reports' printed figures with simple arithmetic on top. The CO2 line is our reading at a different oil factor from the report's, not a figure the report prints. Prices are the reports' 2010 prices.

What Senseible does here

Senseible reads fuel invoices and electricity bills into monthly records, so the fall in furnace oil after fitting shows up against the small rise in power. Water metering can be added as a custom service, on request. Meanwhile keep a water meter reading or tank log beside the bills.

• Desuperheater on a 100 TR dairy plant: oil saved
• Dairy plant energy per kg of milk
• Vapour absorption chiller from waste heat: emissions
• Green loan readiness check

Sources: BEE and SAMEEEKSHA detailed project report: waste heat recovery by desuperheater, 210 TR, Gujarat dairy cluster, BEE and SAMEEEKSHA detailed project report: waste heat recovery by desuperheater, 100 TR, Gujarat dairy cluster, IPCC 2006 Guidelines, Volume 2 Energy, Table 1.2 (net calorific values) and Chapter 2 tables, CEA CO2 Baseline Database for the Indian Power Sector, version 22.0 (FY 2025-26 grid factor)

Last reviewed 2026-11-07. Costs and paybacks are at the reports' 2010 prices. The per-TR figures and the CO2 reading at 3.13 are our own arithmetic on the printed numbers; recheck with today's oil price and a current quote.