Anodising seal tanks heated by heat pumps
How an aluminium anodising plant finishing 8 tonnes of profiles a day can heat its hot seal tank with heat pumps, and what it saves against electric immersion heaters.
▶Video: Process heat for engineering and utilities
V06 · 2–2.5 minPlating, phosphating, washers, curing and boiler feedwater
Video coming soon01Problem statement
- Seal tank is the biggest heat user. The seal tank runs near boiling, so it loses far more heat through evaporation than any other tank on the line.
- Large loads cool the bath. Each rack of profiles drops the seal temperature, and seal quality falls if the bath stays below set point.
- Heaters fail in hard water. Immersion elements scale quickly in seal water and burn out, stopping the line while the tank cools.
- Electric heating is expensive heat. Resistance heaters turn one kWh of electricity into one kWh of heat, at the full commercial tariff. A heat pump moves two to four kWh of heat for the same unit.
- Large connected load. Heater banks take a big share of the sanctioned load and push up maximum-demand charges.
02Use case
The reference plant anodises architectural aluminium extrusions. It runs two shifts and finishes about 8 tonnes of profiles a day through a single 5,000 L hot seal tank.
| Heat user | Process temp. | Basis | Heat, kWh/day |
|---|---|---|---|
| Seal tank reheat after night cool-down | 50 → 92 °C | 5,000 L tank with lid, 42 K reheat each morning | 244 |
| Evaporation from seal tank surface | 92 °C | 3 m² surface × 4 kW/m² × 16 h | 192 |
| Aluminium profiles and racks | 30 → 90 °C | 8 t/day × 0.90 kJ/kg·K × 60 K | 120 |
| Make-up for evaporation and drag-out | 30 → 92 °C | 1,500 L/day DI water, 30 → 92 °C | 108 |
| Storage and pipework standing losses | – | about 5% | 33 |
| Total useful heat | 697 | ||
Averaged over 18 running hours, the heat pumps need about 39 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
- A SE-UHT air-source cascade, R245fa machine of about 40 kW, air-source cascade to 120 °C, sized per project.
- A 1,500 L insulated storage tank decouples the heat pumps from the process peaks.
- The electric immersion heaters stays connected behind a normally closed valve as standby.
- A titanium or stainless steel 316 coil in the seal tank is fed with pressurised hot water at 105 °C.
- DI make-up water is preheated in a separate coil tank before it enters the seal tank, so top-ups do not knock the bath temperature down.
- One immersion heater is kept on trim duty to recover temperature after very heavy loads, and the rest stay as standby.
Selected equipment
| Machine | SE-UHT air-source cascade, R245fa |
|---|---|
| Capacity | about 40 kW, built to duty |
| Concept | air-source cascade to 120 °C, sized per project |
| COP used | 1.8 (estimate) |
| Supply temperature | 105 °C |
| Storage | 1,500 L insulated tank |
Capacity is sized from the heat demand above. COP is an estimate until Sunniva engineering confirms the design.
Control philosophy
TT-101 at the tank top starts the heat pumps below 100 °C and stops them at 105 °C. TIC-201 holds the seal tank at 92 °C by modulating its coil valve. TIC-202 holds the make-up preheat tank at 90 °C. If the seal tank stays below 88 °C for 10 minutes the PLC enables the trim immersion heater.
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 aluminium anodised | – | – |
| CO₂ per year | – | – |
06Benefits
Consistent seal quality
Stored heat recovers the bath quickly after each rack, which helps meet seal quality tests.
Fewer heater burn-outs
The heat pump coil runs at a lower surface temperature than electric elements and scales more slowly.
Cheaper evaporation losses
The large, continuous evaporation load is met at a fraction of the cost of resistance heating.
Lower energy cost
Each kWh of electricity delivers about 1.8 kWh of heat at the required temperature, against well under one kWh of useful heat per kWh of fuel burnt.
Smaller electrical load
The heat pump draws roughly 1/1.8 of the power of the heaters it replaces, which frees sanctioned load and cuts demand charges.
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
- Seal tank volume, temperature and seal type
- Tonnes of aluminium anodised per day
- Tank surface area and lid arrangement
- DI make-up volume per day
- 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
- Pressurised loop. Water at 105 °C needs a pressurised loop of at least 3 bar with an expansion vessel and safety valve sized for it.
- Seal water purity. Seal baths are sensitive to silicates and phosphates. Coil and fittings must not leach contaminants, so use titanium or stainless steel 316 only.
- Cover the tank. A lid or floating balls on the seal tank can halve evaporation losses. Fit these before sizing the heat pumps.
- 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.
- Performance figure. The COP on this page is an engineering estimate, not a data sheet value. Sunniva engineering will confirm it for the actual source and supply temperatures.
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
Anodising seal tanks heated by heat pumps
How an aluminium anodising plant finishing 8 tonnes of profiles a day can heat its hot seal tank with heat pumps, and what it saves against electric immersion heaters.
▶Video: Process heat for engineering and utilities
V06 · 2–2.5 minPlating, phosphating, washers, curing and boiler feedwater
Video coming soon01Problem statement
- Seal tank is the biggest heat user. The seal tank runs near boiling, so it loses far more heat through evaporation than any other tank on the line.
- Large loads cool the bath. Each rack of profiles drops the seal temperature, and seal quality falls if the bath stays below set point.
- Heaters fail in hard water. Immersion elements scale quickly in seal water and burn out, stopping the line while the tank cools.
- Electric heating is expensive heat. Resistance heaters turn one kWh of electricity into one kWh of heat, at the full commercial tariff. A heat pump moves two to four kWh of heat for the same unit.
- Large connected load. Heater banks take a big share of the sanctioned load and push up maximum-demand charges.
02Use case
The reference plant anodises architectural aluminium extrusions. It runs two shifts and finishes about 8 tonnes of profiles a day through a single 5,000 L hot seal tank.
| Heat user | Process temp. | Basis | Heat, kWh/day |
|---|---|---|---|
| Seal tank reheat after night cool-down | 50 → 92 °C | 5,000 L tank with lid, 42 K reheat each morning | 244 |
| Evaporation from seal tank surface | 92 °C | 3 m² surface × 4 kW/m² × 16 h | 192 |
| Aluminium profiles and racks | 30 → 90 °C | 8 t/day × 0.90 kJ/kg·K × 60 K | 120 |
| Make-up for evaporation and drag-out | 30 → 92 °C | 1,500 L/day DI water, 30 → 92 °C | 108 |
| Storage and pipework standing losses | – | about 5% | 33 |
| Total useful heat | 697 | ||
Averaged over 18 running hours, the heat pumps need about 39 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
- A SE-UHT air-source cascade, R245fa machine of about 40 kW, air-source cascade to 120 °C, sized per project.
- A 1,500 L insulated storage tank decouples the heat pumps from the process peaks.
- The electric immersion heaters stays connected behind a normally closed valve as standby.
- A titanium or stainless steel 316 coil in the seal tank is fed with pressurised hot water at 105 °C.
- DI make-up water is preheated in a separate coil tank before it enters the seal tank, so top-ups do not knock the bath temperature down.
- One immersion heater is kept on trim duty to recover temperature after very heavy loads, and the rest stay as standby.
Selected equipment
| Machine | SE-UHT air-source cascade, R245fa |
|---|---|
| Capacity | about 40 kW, built to duty |
| Concept | air-source cascade to 120 °C, sized per project |
| COP used | 1.8 (estimate) |
| Supply temperature | 105 °C |
| Storage | 1,500 L insulated tank |
Capacity is sized from the heat demand above. COP is an estimate until Sunniva engineering confirms the design.
Control philosophy
TT-101 at the tank top starts the heat pumps below 100 °C and stops them at 105 °C. TIC-201 holds the seal tank at 92 °C by modulating its coil valve. TIC-202 holds the make-up preheat tank at 90 °C. If the seal tank stays below 88 °C for 10 minutes the PLC enables the trim immersion heater.
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 aluminium anodised | – | – |
| CO₂ per year | – | – |
06Benefits
Consistent seal quality
Stored heat recovers the bath quickly after each rack, which helps meet seal quality tests.
Fewer heater burn-outs
The heat pump coil runs at a lower surface temperature than electric elements and scales more slowly.
Cheaper evaporation losses
The large, continuous evaporation load is met at a fraction of the cost of resistance heating.
Lower energy cost
Each kWh of electricity delivers about 1.8 kWh of heat at the required temperature, against well under one kWh of useful heat per kWh of fuel burnt.
Smaller electrical load
The heat pump draws roughly 1/1.8 of the power of the heaters it replaces, which frees sanctioned load and cuts demand charges.
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
- Seal tank volume, temperature and seal type
- Tonnes of aluminium anodised per day
- Tank surface area and lid arrangement
- DI make-up volume per day
- 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
- Pressurised loop. Water at 105 °C needs a pressurised loop of at least 3 bar with an expansion vessel and safety valve sized for it.
- Seal water purity. Seal baths are sensitive to silicates and phosphates. Coil and fittings must not leach contaminants, so use titanium or stainless steel 316 only.
- Cover the tank. A lid or floating balls on the seal tank can halve evaporation losses. Fit these before sizing the heat pumps.
- 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.
- Performance figure. The COP on this page is an engineering estimate, not a data sheet value. Sunniva engineering will confirm it for the actual source and supply temperatures.
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.