Phosphating line heated by stored hot water
How a pre-treatment line processing 20 tonnes of steel parts a day can heat its degreasing and phosphating tanks with heat pumps, and what it saves against a diesel-fired hot-water generator.
▶Video: Process heat for engineering and utilities
V06 · 2–2.5 minPlating, phosphating, washers, curing and boiler feedwater
Video coming soon01Problem statement
- Tank coils run too hot. Burner-fired hot water at 90 °C or more makes phosphate sludge and scale build up on the coils, which cuts heat transfer and needs frequent descaling.
- Slow start each shift. Degreasing and phosphating tanks take two to three hours to reach temperature, so the line either starts late or the burner runs through the night.
- Bath temperature drifts with load. Cold steel parts pull tank temperature down, and phosphate coating weight changes with even a few degrees of drift.
- Losses between fuel and process. Burning diesel 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 plant is a seven-tank dip pre-treatment line ahead of a powder coating plant. It treats about 20 tonnes of sheet-metal and fabricated steel parts a day over two shifts.
| Heat user | Process temp. | Basis | Heat, kWh/day |
|---|---|---|---|
| Degreasing tank warm-up | 35 → 65 °C | 8,000 L tank, 30 K reheat each day | 279 |
| Phosphating tank warm-up | 35 → 55 °C | 6,000 L tank, 20 K reheat each day | 139 |
| Running load: parts and surface losses | 55–65 °C | 20 t steel × 0.46 kJ/kg·K × 30 K = 77 kWh, plus 10 m² surface × 1.0 kW/m² × 16 h = 160 kWh | 237 |
| Overflow and rinse make-up | 30 → 60 °C | 6,000 L/day make-up, 30 → 60 °C | 209 |
| Storage and pipework standing losses | – | about 5% | 43 |
| Total useful heat | 907 | ||
Averaged over 18 running hours, the heat pumps need about 50 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
- 4 × SE-SHT-16C (64 kW total) (SE-SHT cascade heat pump) delivering 80 °C, covering the day's 907 kWh in about 14.2 running hours.
- A 2,000 L insulated storage tank decouples the heat pumps from the process peaks.
- The diesel-fired hot-water generator stays connected behind a normally closed valve as standby.
- The hot-water loop at 80 °C feeds the existing coils in the degreasing, phosphating and hot rinse tanks.
- Water at 80 °C keeps coil surfaces cooler than burner-fired water, which slows sludge and scale build-up on the phosphating coil.
- The storage tank is charged before the shift so all tanks reach temperature together at start-up.
Selected equipment
| Model | SE-SHT-16C × 4 |
|---|---|
| Heating capacity | 16 kW each, 64 kW total |
| COP | 2.7 at A20 °C / W90 °C (data sheet T1) |
| Power input | about 23.8 kW total at rated conditions |
| Rating | cascade R410A + R515B, rated 90 °C, 95 °C maximum |
| Supply temperature | 80 °C |
| Storage | 2,000 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, TIC-202 and TIC-203 each modulate a coil valve to hold their tank within ±1 K. TT-102 at the tank bottom starts an early charge two hours before the shift. The diesel generator stays connected as standby and starts only if the tank top falls below 68 °C.
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 parts | – | – |
| CO₂ per year | – | – |
06Benefits
Steady coating weight
Tight bath temperature control gives more consistent phosphate coating weight and better paint adhesion.
Less coil descaling
Lower coil surface temperature reduces sludge baking onto the phosphating coil.
Line ready at shift start
Stored hot water brings the tanks to temperature without running a burner overnight.
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
- Tank volumes, chemistry and set temperatures
- Tonnes of parts per day and shift hours
- Tank surface areas and lids
- Overflow and rinse water flows
- 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
- Coil material. Use stainless steel 316 coils in the degreasing tank and check phosphate chemistry compatibility for the phosphating coil.
- Sludge management. Keep coils raised above the sludge layer and plan a regular desludging routine so heat transfer stays stable.
- Electrical. About 24 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
Phosphating line heated by stored hot water
How a pre-treatment line processing 20 tonnes of steel parts a day can heat its degreasing and phosphating tanks with heat pumps, and what it saves against a diesel-fired hot-water generator.
▶Video: Process heat for engineering and utilities
V06 · 2–2.5 minPlating, phosphating, washers, curing and boiler feedwater
Video coming soon01Problem statement
- Tank coils run too hot. Burner-fired hot water at 90 °C or more makes phosphate sludge and scale build up on the coils, which cuts heat transfer and needs frequent descaling.
- Slow start each shift. Degreasing and phosphating tanks take two to three hours to reach temperature, so the line either starts late or the burner runs through the night.
- Bath temperature drifts with load. Cold steel parts pull tank temperature down, and phosphate coating weight changes with even a few degrees of drift.
- Losses between fuel and process. Burning diesel 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 plant is a seven-tank dip pre-treatment line ahead of a powder coating plant. It treats about 20 tonnes of sheet-metal and fabricated steel parts a day over two shifts.
| Heat user | Process temp. | Basis | Heat, kWh/day |
|---|---|---|---|
| Degreasing tank warm-up | 35 → 65 °C | 8,000 L tank, 30 K reheat each day | 279 |
| Phosphating tank warm-up | 35 → 55 °C | 6,000 L tank, 20 K reheat each day | 139 |
| Running load: parts and surface losses | 55–65 °C | 20 t steel × 0.46 kJ/kg·K × 30 K = 77 kWh, plus 10 m² surface × 1.0 kW/m² × 16 h = 160 kWh | 237 |
| Overflow and rinse make-up | 30 → 60 °C | 6,000 L/day make-up, 30 → 60 °C | 209 |
| Storage and pipework standing losses | – | about 5% | 43 |
| Total useful heat | 907 | ||
Averaged over 18 running hours, the heat pumps need about 50 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
- 4 × SE-SHT-16C (64 kW total) (SE-SHT cascade heat pump) delivering 80 °C, covering the day's 907 kWh in about 14.2 running hours.
- A 2,000 L insulated storage tank decouples the heat pumps from the process peaks.
- The diesel-fired hot-water generator stays connected behind a normally closed valve as standby.
- The hot-water loop at 80 °C feeds the existing coils in the degreasing, phosphating and hot rinse tanks.
- Water at 80 °C keeps coil surfaces cooler than burner-fired water, which slows sludge and scale build-up on the phosphating coil.
- The storage tank is charged before the shift so all tanks reach temperature together at start-up.
Selected equipment
| Model | SE-SHT-16C × 4 |
|---|---|
| Heating capacity | 16 kW each, 64 kW total |
| COP | 2.7 at A20 °C / W90 °C (data sheet T1) |
| Power input | about 23.8 kW total at rated conditions |
| Rating | cascade R410A + R515B, rated 90 °C, 95 °C maximum |
| Supply temperature | 80 °C |
| Storage | 2,000 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, TIC-202 and TIC-203 each modulate a coil valve to hold their tank within ±1 K. TT-102 at the tank bottom starts an early charge two hours before the shift. The diesel generator stays connected as standby and starts only if the tank top falls below 68 °C.
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 parts | – | – |
| CO₂ per year | – | – |
06Benefits
Steady coating weight
Tight bath temperature control gives more consistent phosphate coating weight and better paint adhesion.
Less coil descaling
Lower coil surface temperature reduces sludge baking onto the phosphating coil.
Line ready at shift start
Stored hot water brings the tanks to temperature without running a burner overnight.
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
- Tank volumes, chemistry and set temperatures
- Tonnes of parts per day and shift hours
- Tank surface areas and lids
- Overflow and rinse water flows
- 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
- Coil material. Use stainless steel 316 coils in the degreasing tank and check phosphate chemistry compatibility for the phosphating coil.
- Sludge management. Keep coils raised above the sludge layer and plan a regular desludging routine so heat transfer stays stable.
- Electrical. About 24 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.