Paddy soaking water heated by heat pumps
How a rice mill parboiling 30 tonnes of paddy a day can heat its soaking water with heat pumps, freeing the biomass boiler for steaming and drying.
▶Video: Process hot water for food, dairy and beverages
V02 · 2–2.5 minPasteurisers, CIP, cooking and washing on stored hot water instead of boiler steam
Video coming soon01Problem statement
- Soak temperature drifts. Tanks are filled with water heated by open steam, and temperature falls through the 3–4 hour soak. Uneven soaking gives white bellies and broken grains.
- Boiler shared with steaming. Soaking, steaming and drying all draw on one boiler, so soaking water heating competes for steam at peak times.
- Biomass handling. Husk and briquette prices, storage and ash disposal are a daily burden.
- Losses between fuel and process. Burning briquettes in a boiler or heater and distributing the heat loses a quarter or more of the fuel's energy before it reaches the process.
- Compliance, safety and handling. Fired equipment brings boiler inspections, fuel storage and unloading, flue emissions and an attendant on every shift.
02Use case
The reference mill parboils about 30 tonnes of paddy a day by hot soaking in six tanks, followed by steaming and drying. Soak water at 65–70 °C is reused, with fresh make-up for what the paddy absorbs and what is drained. The mill runs round the clock in season.
| Heat user | Process temp. | Basis | Heat, kWh/day |
|---|---|---|---|
| Fresh soak water make-up | 30 → 70 °C | 16,500 L/day (half of soak water replaced) | 766 |
| Paddy warm-up in soak | 30 → 65 °C | 30,000 kg paddy/day, cp 1.9 kJ/kg·K | 554 |
| Soak tank losses | 65 °C | 6 tanks × 1.5 kW × 20 h | 180 |
| Storage and pipework standing losses | – | about 5% | 75 |
| Total useful heat | 1,576 | ||
Averaged over 20 running hours, the heat pumps need about 79 kW.
03P&ID
Tags: HP heat pump, TK tank, SG steam generator, P pump, PHE plate heat exchanger, TCV temperature control valve, TIC temperature indicating controller (panel), TT temperature transmitter, MT moisture transmitter, PT pressure transmitter, LT level transmitter, FS flow switch, NC normally closed. Process fluids are heated through their own exchanger, coil or jacket.
04Solution
System description
- 5 × SE-SHT-16C (80 kW total) (SE-SHT cascade heat pump) delivering 80 °C, covering the day's 1,576 kWh in about 19.7 running hours.
- A 2,500 L insulated storage tank decouples the heat pumps from the process peaks.
- The biomass (husk and briquette) fired boiler stays connected behind a normally closed valve as standby.
- Soak water recirculates from each tank through a plate exchanger heated by the hot-water tank, so temperature holds through the soak.
- Make-up water is heated in a separate exchanger before filling.
- The boiler is left for steaming and drying, which need higher temperatures.
Selected equipment
| Model | SE-SHT-16C × 5 |
|---|---|
| Heating capacity | 16 kW each, 80 kW total |
| COP | 2.7 at A20 °C / W90 °C (data sheet T1) |
| Power input | about 29.8 kW total at rated conditions |
| Rating | cascade R410A + R515B, rated 90 °C, 95 °C maximum |
| Supply temperature | 80 °C |
| Storage | 2,500 L insulated tank |
Ratings from the Sunniva TDS 2026 data sheets.
Control philosophy
TT-101 at the tank top starts the heat pumps below 75 °C and stops them at 80 °C. TIC-201 holds each soaking tank at its set temperature, for example 68 °C, during the soak. TIC-202 holds make-up water at 70 °C. If the tank falls below 70 °C, open steam to the soaking tanks is enabled as standby.
05Energy saving and ROI
Change any input to match a customer's site. Defaults are typical Indian prices for October 2026. The installed cost is a placeholder; replace it with the actual quotation.
| Existing | Heat pump | |
|---|---|---|
| Daily consumption | – | – |
| Annual energy cost | – | – |
| Cost per tonne of paddy | – | – |
| CO₂ per year | – | – |
06Benefits
Better head-rice yield
Holding soak temperature through the soak gives more even gelatinisation and fewer broken grains.
More steam for steaming
The boiler has more capacity for steaming and drying.
Less biomass to handle
Lower fuel use means less storage and ash.
Lower energy cost
Each kWh of electricity delivers about 2.7 kWh of heat at the required temperature, against well under one kWh of useful heat per kWh of fuel burnt.
No flame on site
No burner, flue or fuel tank for this duty, and no fuel deliveries to schedule.
Built-in redundancy
Several machines share the load. If one is serviced, the others and the storage carry most of the day, with the existing heater in reserve.
07Engineering pointers
Site data to collect
- Paddy parboiled per day and tank sizes
- Soak temperature and duration
- Make-up and drain volumes
- Current fuel use and price
- Running hours and season length
- Present fuel or electricity use and monthly bill
- Sanctioned electrical load and spare capacity
- Space for the heat pumps and storage, with service access
- Winter minimum ambient at site
Design notes
- Soak water fouling. Soak water carries starch, husk and colour. Use a strainer and open-able plate exchangers, and clean them weekly.
- Soak water reuse. Reusing soak water saves heat, but it smells if held too long. Follow the mill's existing drain schedule.
- Effluent. Soak water is high in BOD. Heat recovery from the drain stream can be studied with the effluent plant.
- Electrical. About 30 kW of heat pump input at rated conditions, plus pumps and fans. Check spare sanctioned load before ordering.
- Winter output. The SE-SHT cascade gives about 80% of rated output at 7 °C ambient and still runs at −20 °C. Size on the coldest design day for northern sites.
- Water quality. Scale forms quickly above 60 °C. Use softened make-up and keep the heat pump loop closed, with process fluids on the far side of an exchanger or coil.
Service and warranty
Sunniva has supplied 5,000+ heat pumps since 2012, with nine service technicians across India, including remote sites such as Leh. All components carry a one-year warranty.
Talk to us
Paddy soaking water heated by heat pumps
How a rice mill parboiling 30 tonnes of paddy a day can heat its soaking water with heat pumps, freeing the biomass boiler for steaming and drying.
▶Video: Process hot water for food, dairy and beverages
V02 · 2–2.5 minPasteurisers, CIP, cooking and washing on stored hot water instead of boiler steam
Video coming soon01Problem statement
- Soak temperature drifts. Tanks are filled with water heated by open steam, and temperature falls through the 3–4 hour soak. Uneven soaking gives white bellies and broken grains.
- Boiler shared with steaming. Soaking, steaming and drying all draw on one boiler, so soaking water heating competes for steam at peak times.
- Biomass handling. Husk and briquette prices, storage and ash disposal are a daily burden.
- Losses between fuel and process. Burning briquettes in a boiler or heater and distributing the heat loses a quarter or more of the fuel's energy before it reaches the process.
- Compliance, safety and handling. Fired equipment brings boiler inspections, fuel storage and unloading, flue emissions and an attendant on every shift.
02Use case
The reference mill parboils about 30 tonnes of paddy a day by hot soaking in six tanks, followed by steaming and drying. Soak water at 65–70 °C is reused, with fresh make-up for what the paddy absorbs and what is drained. The mill runs round the clock in season.
| Heat user | Process temp. | Basis | Heat, kWh/day |
|---|---|---|---|
| Fresh soak water make-up | 30 → 70 °C | 16,500 L/day (half of soak water replaced) | 766 |
| Paddy warm-up in soak | 30 → 65 °C | 30,000 kg paddy/day, cp 1.9 kJ/kg·K | 554 |
| Soak tank losses | 65 °C | 6 tanks × 1.5 kW × 20 h | 180 |
| Storage and pipework standing losses | – | about 5% | 75 |
| Total useful heat | 1,576 | ||
Averaged over 20 running hours, the heat pumps need about 79 kW.
03P&ID
Tags: HP heat pump, TK tank, SG steam generator, P pump, PHE plate heat exchanger, TCV temperature control valve, TIC temperature indicating controller (panel), TT temperature transmitter, MT moisture transmitter, PT pressure transmitter, LT level transmitter, FS flow switch, NC normally closed. Process fluids are heated through their own exchanger, coil or jacket.
04Solution
System description
- 5 × SE-SHT-16C (80 kW total) (SE-SHT cascade heat pump) delivering 80 °C, covering the day's 1,576 kWh in about 19.7 running hours.
- A 2,500 L insulated storage tank decouples the heat pumps from the process peaks.
- The biomass (husk and briquette) fired boiler stays connected behind a normally closed valve as standby.
- Soak water recirculates from each tank through a plate exchanger heated by the hot-water tank, so temperature holds through the soak.
- Make-up water is heated in a separate exchanger before filling.
- The boiler is left for steaming and drying, which need higher temperatures.
Selected equipment
| Model | SE-SHT-16C × 5 |
|---|---|
| Heating capacity | 16 kW each, 80 kW total |
| COP | 2.7 at A20 °C / W90 °C (data sheet T1) |
| Power input | about 29.8 kW total at rated conditions |
| Rating | cascade R410A + R515B, rated 90 °C, 95 °C maximum |
| Supply temperature | 80 °C |
| Storage | 2,500 L insulated tank |
Ratings from the Sunniva TDS 2026 data sheets.
Control philosophy
TT-101 at the tank top starts the heat pumps below 75 °C and stops them at 80 °C. TIC-201 holds each soaking tank at its set temperature, for example 68 °C, during the soak. TIC-202 holds make-up water at 70 °C. If the tank falls below 70 °C, open steam to the soaking tanks is enabled as standby.
05Energy saving and ROI
Change any input to match a customer's site. Defaults are typical Indian prices for October 2026. The installed cost is a placeholder; replace it with the actual quotation.
| Existing | Heat pump | |
|---|---|---|
| Daily consumption | – | – |
| Annual energy cost | – | – |
| Cost per tonne of paddy | – | – |
| CO₂ per year | – | – |
06Benefits
Better head-rice yield
Holding soak temperature through the soak gives more even gelatinisation and fewer broken grains.
More steam for steaming
The boiler has more capacity for steaming and drying.
Less biomass to handle
Lower fuel use means less storage and ash.
Lower energy cost
Each kWh of electricity delivers about 2.7 kWh of heat at the required temperature, against well under one kWh of useful heat per kWh of fuel burnt.
No flame on site
No burner, flue or fuel tank for this duty, and no fuel deliveries to schedule.
Built-in redundancy
Several machines share the load. If one is serviced, the others and the storage carry most of the day, with the existing heater in reserve.
07Engineering pointers
Site data to collect
- Paddy parboiled per day and tank sizes
- Soak temperature and duration
- Make-up and drain volumes
- Current fuel use and price
- Running hours and season length
- Present fuel or electricity use and monthly bill
- Sanctioned electrical load and spare capacity
- Space for the heat pumps and storage, with service access
- Winter minimum ambient at site
Design notes
- Soak water fouling. Soak water carries starch, husk and colour. Use a strainer and open-able plate exchangers, and clean them weekly.
- Soak water reuse. Reusing soak water saves heat, but it smells if held too long. Follow the mill's existing drain schedule.
- Effluent. Soak water is high in BOD. Heat recovery from the drain stream can be studied with the effluent plant.
- Electrical. About 30 kW of heat pump input at rated conditions, plus pumps and fans. Check spare sanctioned load before ordering.
- Winter output. The SE-SHT cascade gives about 80% of rated output at 7 °C ambient and still runs at −20 °C. Size on the coldest design day for northern sites.
- Water quality. Scale forms quickly above 60 °C. Use softened make-up and keep the heat pump loop closed, with process fluids on the far side of an exchanger or coil.
Service and warranty
Sunniva has supplied 5,000+ heat pumps since 2012, with nine service technicians across India, including remote sites such as Leh. All components carry a one-year warranty.