Car body pre-treatment heated by heat pumps
How a paint shop pre-treating 600 car bodies a day can heat its degreasing, phosphating and rinse stages with heat pumps, and what it saves against a PNG-fired hot-water boiler.
▶Video: Process heat for engineering and utilities
V06 · 2–2.5 minPlating, phosphating, washers, curing and boiler feedwater
Video coming soon01Problem statement
- Low-temperature stages, high-temperature boiler. The stages need only 45–60 °C, but the boiler runs at 90 °C or more and loses heat in long distribution pipes and the flue.
- Large, continuous make-up. Cascade overflows bring in tens of thousands of litres of fresh water a day, all of which must be heated.
- Process windows are tight. Phosphate coating weight and ED performance depend on bath temperatures held within ±2 K.
- Losses between fuel and process. Burning PNG 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 passenger car paint shop running about 30 bodies an hour over three shifts, around 600 bodies a day. Its spray-and-dip pre-treatment has heated degreasing, zinc phosphating and hot rinse stages.
| Heat user | Process temp. | Basis | Heat, kWh/day |
|---|---|---|---|
| Heating car bodies through pre-treatment | 30 → 55 °C | 600 bodies × 400 kg × 0.46 kJ/kg·K × 25 K | 767 |
| Tank surface and spray-zone losses | 45–60 °C | 30 m² liquid surface and spray zones × 1.5 kW/m² × 20 h | 900 |
| Cascade overflow make-up | 30 → 55 °C | 30,000 L/day, 30 → 55 °C | 871 |
| Storage and pipework standing losses | – | about 5% | 127 |
| Total useful heat | 2,665 | ||
Averaged over 20 running hours, the heat pumps need about 133 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
- 1 × SE-HT-150V (142 kW) (SE-HT high-temperature heat pump) delivering 70 °C, covering the day's 2,665 kWh in about 18.8 running hours.
- A 4,500 L insulated storage tank decouples the heat pumps from the process peaks.
- The PNG-fired hot-water boiler stays connected behind a normally closed valve as standby.
- The heat pumps supply 70 °C water to the existing external plate heat exchangers on each heated stage.
- Supply at 70 °C is enough for 45–60 °C baths and keeps the heat pumps in an efficient range.
- The boiler remains connected in parallel on the same header and runs only as standby or during Monday start-up.
Selected equipment
| Model | SE-HT-150V × 1 |
|---|---|
| Heating capacity | 142 kW each, 142 kW total |
| COP | 3.4 at A20 °C / W70 °C, interpolated from the data sheet's 60, 70 and 80 °C points |
| Power input | about 41.8 kW total at rated conditions |
| Rating | rated 75 °C, 80 °C maximum, R134a |
| Supply temperature | 70 °C |
| Storage | 4,500 L insulated tank |
Ratings from the Sunniva TDS 2026 data sheets.
Control philosophy
TT-101 at the tank top starts the heat pumps below 65 °C and stops them at 70 °C, staging units so running hours stay even. TIC-201, TIC-202 and TIC-203 hold each stage within ±1 K by modulating the hot-water valve on its PHE. If the tank top falls below 60 °C the PLC enables the boiler on the same header.
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 100 car bodies | – | – |
| CO₂ per year | – | – |
06Benefits
Matches the stage temperatures
Hot water at 70 °C suits 45–60 °C stages directly, with less overshoot and less sludge on exchangers.
Lower carbon per body
Pre-treatment heat is one of the larger gas users in a paint shop, so replacing it cuts CO₂ per vehicle.
Boiler kept for back-up
The existing boiler covers maintenance and long shutdown start-ups.
Lower energy cost
Each kWh of electricity delivers about 3.4 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.
Solar-ready
Running hours can be placed in daylight so rooftop solar supplies much of the electricity, which also cuts CO₂ further.
07Engineering pointers
Site data to collect
- Bodies per hour and operating hours
- Stage volumes and set temperatures
- Existing PHE duties and approach temperatures
- Overflow and make-up flows
- Monthly gas consumption for pre-treatment
- 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
- Look at ED cooling too. The ED bath and phosphating chillers reject heat at 30–35 °C. That stream may later serve as a water source for a ws heat pump.
- PHE fouling. Phosphate sludge fouls plate exchangers. Keep filters on the bath side and plan regular cleaning so supply at 70 °C stays sufficient.
- Electrical. About 42 kW of heat pump input at rated conditions, plus pumps and fans. Check spare sanctioned load before ordering.
- Ambient correction. Ratings are at 20 °C air. Ask Sunniva for the correction at your site's winter design temperature.
- 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
Car body pre-treatment heated by heat pumps
How a paint shop pre-treating 600 car bodies a day can heat its degreasing, phosphating and rinse stages with heat pumps, and what it saves against a PNG-fired hot-water boiler.
▶Video: Process heat for engineering and utilities
V06 · 2–2.5 minPlating, phosphating, washers, curing and boiler feedwater
Video coming soon01Problem statement
- Low-temperature stages, high-temperature boiler. The stages need only 45–60 °C, but the boiler runs at 90 °C or more and loses heat in long distribution pipes and the flue.
- Large, continuous make-up. Cascade overflows bring in tens of thousands of litres of fresh water a day, all of which must be heated.
- Process windows are tight. Phosphate coating weight and ED performance depend on bath temperatures held within ±2 K.
- Losses between fuel and process. Burning PNG 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 passenger car paint shop running about 30 bodies an hour over three shifts, around 600 bodies a day. Its spray-and-dip pre-treatment has heated degreasing, zinc phosphating and hot rinse stages.
| Heat user | Process temp. | Basis | Heat, kWh/day |
|---|---|---|---|
| Heating car bodies through pre-treatment | 30 → 55 °C | 600 bodies × 400 kg × 0.46 kJ/kg·K × 25 K | 767 |
| Tank surface and spray-zone losses | 45–60 °C | 30 m² liquid surface and spray zones × 1.5 kW/m² × 20 h | 900 |
| Cascade overflow make-up | 30 → 55 °C | 30,000 L/day, 30 → 55 °C | 871 |
| Storage and pipework standing losses | – | about 5% | 127 |
| Total useful heat | 2,665 | ||
Averaged over 20 running hours, the heat pumps need about 133 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
- 1 × SE-HT-150V (142 kW) (SE-HT high-temperature heat pump) delivering 70 °C, covering the day's 2,665 kWh in about 18.8 running hours.
- A 4,500 L insulated storage tank decouples the heat pumps from the process peaks.
- The PNG-fired hot-water boiler stays connected behind a normally closed valve as standby.
- The heat pumps supply 70 °C water to the existing external plate heat exchangers on each heated stage.
- Supply at 70 °C is enough for 45–60 °C baths and keeps the heat pumps in an efficient range.
- The boiler remains connected in parallel on the same header and runs only as standby or during Monday start-up.
Selected equipment
| Model | SE-HT-150V × 1 |
|---|---|
| Heating capacity | 142 kW each, 142 kW total |
| COP | 3.4 at A20 °C / W70 °C, interpolated from the data sheet's 60, 70 and 80 °C points |
| Power input | about 41.8 kW total at rated conditions |
| Rating | rated 75 °C, 80 °C maximum, R134a |
| Supply temperature | 70 °C |
| Storage | 4,500 L insulated tank |
Ratings from the Sunniva TDS 2026 data sheets.
Control philosophy
TT-101 at the tank top starts the heat pumps below 65 °C and stops them at 70 °C, staging units so running hours stay even. TIC-201, TIC-202 and TIC-203 hold each stage within ±1 K by modulating the hot-water valve on its PHE. If the tank top falls below 60 °C the PLC enables the boiler on the same header.
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 100 car bodies | – | – |
| CO₂ per year | – | – |
06Benefits
Matches the stage temperatures
Hot water at 70 °C suits 45–60 °C stages directly, with less overshoot and less sludge on exchangers.
Lower carbon per body
Pre-treatment heat is one of the larger gas users in a paint shop, so replacing it cuts CO₂ per vehicle.
Boiler kept for back-up
The existing boiler covers maintenance and long shutdown start-ups.
Lower energy cost
Each kWh of electricity delivers about 3.4 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.
Solar-ready
Running hours can be placed in daylight so rooftop solar supplies much of the electricity, which also cuts CO₂ further.
07Engineering pointers
Site data to collect
- Bodies per hour and operating hours
- Stage volumes and set temperatures
- Existing PHE duties and approach temperatures
- Overflow and make-up flows
- Monthly gas consumption for pre-treatment
- 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
- Look at ED cooling too. The ED bath and phosphating chillers reject heat at 30–35 °C. That stream may later serve as a water source for a ws heat pump.
- PHE fouling. Phosphate sludge fouls plate exchangers. Keep filters on the bath side and plan regular cleaning so supply at 70 °C stays sufficient.
- Electrical. About 42 kW of heat pump input at rated conditions, plus pumps and fans. Check spare sanctioned load before ordering.
- Ambient correction. Ratings are at 20 °C air. Ask Sunniva for the correction at your site's winter design temperature.
- 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.