Low-bake ovens and composite curing with heat pumps
How a plant running a low-bake paint oven and an FRP curing oven can supply most of the oven heat with heat pumps, and what it saves against LPG-fired oven burners.
▶Video: Hot air from heat pump hot water
V05 · 2–2.5 minAir coils for spray dryers, stenters, kilns, paint booths and ovens
Video coming soon01Problem statement
- Low cure temperatures, costly fuel. Ovens at 80–100 °C are fired with LPG burners sized for much higher temperatures, and run mostly at low fire.
- Hot spots harm parts. Plastics and composites can warp or blister if burner air overshoots, so ovens are run cautiously and cycles get longer.
- Exhaust and shell losses. Fresh-air make-up and long oven shells lose heat steadily through the shift.
- Losses between fuel and process. Burning LPG 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 paints plastic and wooden parts in an 80 °C low-bake conveyor oven and cures FRP panels in a 100 °C batch oven. It runs two shifts and cures about 2 tonnes of laminate a day.
| Heat user | Process temp. | Basis | Heat, kWh/day |
|---|---|---|---|
| Low-bake oven fresh air | Air 30 → 80 °C | 2,500 m³/h × 1.2 kg/m³ × 1.005 kJ/kg·K × 50 K × 16 h | 670 |
| Low-bake oven shell and conveyor losses | 80 °C | 120 m² oven shell × 0.15 kW/m² × 16 h | 288 |
| FRP laminate and moulds | 30 → 100 °C | 2 t laminate × 1.2 kJ/kg·K × 70 K + 6 t steel moulds × 0.46 kJ/kg·K × 70 K | 100 |
| FRP oven air and losses | Air 100 °C | 25 kW average × 8 h cure cycle | 200 |
| Storage and pipework standing losses | – | about 5% | 63 |
| Total useful heat | 1,321 | ||
Averaged over 16 running hours, the heat pumps need about 83 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 85 kW, air-source cascade to 120 °C, sized per project.
- A 3,000 L insulated storage tank decouples the heat pumps from the process peaks.
- The LPG-fired oven burners stays connected behind a normally closed valve as standby.
- Finned hot-water coils in the recirculation duct of each oven are fed with pressurised water at up to 120 °C.
- The low-bake oven runs fully on hot water. The FRP oven runs on hot water up to about 100 °C, and the burner trims only for cure stages above that.
- The storage tank lets the heat pumps preheat both ovens before the shift starts.
Selected equipment
| Machine | SE-UHT air-source cascade, R245fa |
|---|---|
| Capacity | about 85 kW, built to duty |
| Concept | air-source cascade to 120 °C, sized per project |
| COP used | 1.6 (estimate) |
| Supply temperature | 120 °C |
| Storage | 3,000 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 112 °C and stops them at 120 °C. TIC-201 holds the low-bake oven at 80 °C by modulating its coil valve. TIC-202 follows the FRP cure profile and enables the LPG burner only when the profile asks for more than the coil can give. The burners remain as full 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 laminate | – | – |
| CO₂ per year | – | – |
06Benefits
Even oven temperature
Water coils give gentle, uniform air heating, which reduces warping and blistering of plastic and FRP parts.
Burner mostly idle
The burner covers only peaks and high cure steps, so LPG use and refills drop sharply.
Cleaner oven air
No combustion products in the oven air, which helps on light colours and clear coats.
Lower energy cost
Each kWh of electricity delivers about 1.6 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
- Oven cure temperatures and cycle profiles
- Oven airflows, fresh-air fraction and shell size
- Daily throughput of painted parts and laminate
- Monthly LPG consumption per oven
- 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 hot water. Water at 120 °C needs a loop rated for at least 4 bar with safety valves, expansion vessel and insulated pipework.
- Cure profile limits. Check resin and paint data sheets. Systems needing more than about 110 °C air will rely on the burner for that step.
- Solvent safety. Keep coil access and controls outside any classified zone and maintain the oven's LEL exhaust as before.
- 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
Low-bake ovens and composite curing with heat pumps
How a plant running a low-bake paint oven and an FRP curing oven can supply most of the oven heat with heat pumps, and what it saves against LPG-fired oven burners.
▶Video: Hot air from heat pump hot water
V05 · 2–2.5 minAir coils for spray dryers, stenters, kilns, paint booths and ovens
Video coming soon01Problem statement
- Low cure temperatures, costly fuel. Ovens at 80–100 °C are fired with LPG burners sized for much higher temperatures, and run mostly at low fire.
- Hot spots harm parts. Plastics and composites can warp or blister if burner air overshoots, so ovens are run cautiously and cycles get longer.
- Exhaust and shell losses. Fresh-air make-up and long oven shells lose heat steadily through the shift.
- Losses between fuel and process. Burning LPG 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 paints plastic and wooden parts in an 80 °C low-bake conveyor oven and cures FRP panels in a 100 °C batch oven. It runs two shifts and cures about 2 tonnes of laminate a day.
| Heat user | Process temp. | Basis | Heat, kWh/day |
|---|---|---|---|
| Low-bake oven fresh air | Air 30 → 80 °C | 2,500 m³/h × 1.2 kg/m³ × 1.005 kJ/kg·K × 50 K × 16 h | 670 |
| Low-bake oven shell and conveyor losses | 80 °C | 120 m² oven shell × 0.15 kW/m² × 16 h | 288 |
| FRP laminate and moulds | 30 → 100 °C | 2 t laminate × 1.2 kJ/kg·K × 70 K + 6 t steel moulds × 0.46 kJ/kg·K × 70 K | 100 |
| FRP oven air and losses | Air 100 °C | 25 kW average × 8 h cure cycle | 200 |
| Storage and pipework standing losses | – | about 5% | 63 |
| Total useful heat | 1,321 | ||
Averaged over 16 running hours, the heat pumps need about 83 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 85 kW, air-source cascade to 120 °C, sized per project.
- A 3,000 L insulated storage tank decouples the heat pumps from the process peaks.
- The LPG-fired oven burners stays connected behind a normally closed valve as standby.
- Finned hot-water coils in the recirculation duct of each oven are fed with pressurised water at up to 120 °C.
- The low-bake oven runs fully on hot water. The FRP oven runs on hot water up to about 100 °C, and the burner trims only for cure stages above that.
- The storage tank lets the heat pumps preheat both ovens before the shift starts.
Selected equipment
| Machine | SE-UHT air-source cascade, R245fa |
|---|---|
| Capacity | about 85 kW, built to duty |
| Concept | air-source cascade to 120 °C, sized per project |
| COP used | 1.6 (estimate) |
| Supply temperature | 120 °C |
| Storage | 3,000 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 112 °C and stops them at 120 °C. TIC-201 holds the low-bake oven at 80 °C by modulating its coil valve. TIC-202 follows the FRP cure profile and enables the LPG burner only when the profile asks for more than the coil can give. The burners remain as full 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 laminate | – | – |
| CO₂ per year | – | – |
06Benefits
Even oven temperature
Water coils give gentle, uniform air heating, which reduces warping and blistering of plastic and FRP parts.
Burner mostly idle
The burner covers only peaks and high cure steps, so LPG use and refills drop sharply.
Cleaner oven air
No combustion products in the oven air, which helps on light colours and clear coats.
Lower energy cost
Each kWh of electricity delivers about 1.6 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
- Oven cure temperatures and cycle profiles
- Oven airflows, fresh-air fraction and shell size
- Daily throughput of painted parts and laminate
- Monthly LPG consumption per oven
- 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 hot water. Water at 120 °C needs a loop rated for at least 4 bar with safety valves, expansion vessel and insulated pipework.
- Cure profile limits. Check resin and paint data sheets. Systems needing more than about 110 °C air will rely on the burner for that step.
- Solvent safety. Keep coil access and controls outside any classified zone and maintain the oven's LEL exhaust as before.
- 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.