How do the 65, 300 and 420 tonne-hour low loss cold stores for milk chilling compare on power saved and payback, and what drives the saving?

A low loss cold store for milk chilling saves 18,720 kilowatt hours a year at 65 tonne-hours of storage, 71,640 at 300 and 110,880 at 420 in the Bureau of Energy Efficiency (BEE) Gujarat reports. Cost per tonne-hour is about the same, so payback sits at 3.1 to 3.5 years. Running hours decide the saving.

What the cold store is, in plain words

Many milk chilling centres cool water in a concrete tank with a plank cover and keep it cold overnight, ready for the morning rush of milk. The tank leaks cold, much as an open cooler box does. A low loss cold store is a sealed, insulated tank filled with a liquid that freezes and thaws to hold the cold much better. A tonne of refrigeration (TR) is a measure of cooling power. A tonne-hour (TRH) is that cooling power for one hour, so it measures how much cold the store holds.

The three reports side by side

• 65 TRH: refrigeration of 35 TR rated, 28.7 TR actual, drawing 21.7 kilowatts (kW), run 24 hours a day. Saves 52 kilowatt hours (kWh) a day, 18,720 a year. Cost 3.24 lakh rupees (Rs), where a lakh is 100,000, saving Rs 1.03 lakh a year at Rs 5.50 a kWh, payback 3.14 years. Carbon dioxide (CO2) shown: 15.91 tonnes.
• 300 TRH: 90 TR rated, 72.9 TR actual, 96.3 kW, 20 hours a day. Saves 199 kWh a day, 71,640 a year. Cost Rs 14.87 lakh, saving Rs 4.28 lakh at Rs 5.98, payback 3.48 years. CO2 shown: 60.89 tonnes.
• 420 TRH: 210 TR rated, 147 TR actual, 176 kW, 16 hours a day. Saves 308 kWh a day, 110,880 a year. Cost Rs 20.89 lakh, saving Rs 5.91 lakh at Rs 5.33, payback 3.53 years. CO2 shown: 94.25 tonnes.
• All three use 360 days a year and leave out any time-of-day tariff benefit.

How the daily saving is built

Each report makes two savings. One is lost cold. The table takes the old tank's loss as 8% and the new store's as 0.063%, a net 7.94% of the power drawn, for each hour the refrigeration runs. The report describes the new store's loss as 1.5% in one day. The other saving is charging colder water less hard: charging at minus 7 instead of minus 9 degrees saves 6% over 8 night hours.

So the saving a day is kW x 7.94% x running hours, plus kW x 8 hours x 6%. For 65 TRH that is 21.7 x 0.0794 x 24 + 21.7 x 8 x 0.06 = 41.4 + 10.4 = 51.8, printed as 52. For 300 TRH, 96.3 x 0.0794 x 20 + 46.2 = 152.9 + 46.2 = 199. For 420 TRH, 176 x 0.0794 x 16 + 84.5 = 223.6 + 84.5 = 308.

The hours are what differ: 24, 20 and 16, taken from each report's annexure. A cold store on a plant that runs fewer hours saves less for each kW. That is why the 65 TRH case saves 2.4 kWh a day for every kW drawn, the 300 TRH case 2.07 and the 420 TRH case 1.75.

Cost per tonne-hour is flat, saving per tonne-hour is not

• Cost for each TRH: Rs 3.24 lakh / 65 = Rs 4,985; Rs 14.87 lakh / 300 = Rs 4,957; Rs 20.89 lakh / 420 = Rs 4,974. Close to Rs 5,000 for each TRH, whatever the size.
• Saving for each TRH a year: 18,720 / 65 = 288 kWh; 71,640 / 300 = 239 kWh; 110,880 / 420 = 264 kWh. So payback depends on how hard your own plant works, not on how big the store is.
• Check the storage hours in the table against the tank. The reports say the store should cover 3, 4 and 4 hours of peak load. But TRH divided by the actual TR gives 65 / 28.7 = 2.3 hours, 300 / 72.9 = 4.1 hours and 420 / 147 = 2.9 hours. That is our own arithmetic. Ask the supplier how many hours of your actual load the store really covers.

What it does and does not do for carbon

None of the three reports prints a factor, but their carbon dioxide figures (15.91 / 18,720, 60.89 / 71,640 and 94.25 / 110,880) each work out to 0.85 kilograms for each kWh. On the grid factor Senseible uses for financial year (FY) 2025-26, 0.675, the same savings are 12.6, 48.4 and 74.8 tonnes. Charging at night can lower your bill under a time-of-day tariff, but it does not lower the yearly kWh, and only the kWh actually not used count for emissions.

Before you buy

1. Log your compressor kWh on a day with no milk intake to see what your tank loses overnight.
2. Ask for the daily loss of the new store in writing, as a share of stored cold.
3. Meter the refrigeration on its own, so the saving can be shown and not assumed.

The 420 TRH case, line by line

• Plant: 176 kW x 7.94% = 13.97 kW saved in lost cold. x 16 hours = 223.6 kWh a day
• Colder charging: 176 kW x 8 hours x 6% = 84.5 kWh a day
• Total 308 kWh a day x 360 days = 110,880 kWh. x Rs 5.33 = Rs 5.91 lakh. 20.89 / 5.91 = 3.53 years
• CO2: 110,880 x 0.675 = 74,844 kg, or 74.8 tonnes (the report shows 94.25 at 0.85)

These are the reports' printed figures with simple arithmetic on top. The 'saving for each kW' and storage hours lines are our own reading. Prices are the reports' 2010 prices.

What Senseible does here

Senseible reads fuel invoices and electricity bills into monthly records, so the kWh actually saved shows once the bills are uploaded. Tank temperature and compressor hour logging can be added as a custom service, on request. Meanwhile keep your plant log with the bills.

• 300 tonne-hour thermal storage in milk chilling: power saved
• Dairy plant energy per kg of milk
• Compressor soft starters in a dairy
• Green loan readiness check

Sources: BEE and SAMEEEKSHA detailed project report: low loss compact thermal storage, 420 TRH, Gujarat dairy cluster, BEE and SAMEEEKSHA detailed project report: low loss compact thermal storage, 300 TRH, Gujarat dairy cluster, BEE and SAMEEEKSHA detailed project report: low loss compact thermal storage, 65 TRH, Gujarat dairy cluster, 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 saving-per-kW and storage-hours lines are our own arithmetic on the printed tables; recheck with your own plant log and a current quote.