Paper machine hood air heated from exhaust
How a 40 tonne-per-day writing and printing paper mill can heat its pocket ventilation and hood supply air with a water-source heat pump running on exhaust heat, and what it saves against a furnace-oil fired steam boiler.
▶Video: Waste-heat recovery heat pumps
V10 · 2–2.5 minLifting warm water from condensers, effluent and process cooling to useful heat
Video coming soon01Problem statement
- Steam coils heat the hood air. Pocket ventilation and hood supply air are heated with steam coils after an air-to-air exchanger, using boiler steam.
- Humid exhaust holds the heat. Most of the energy in hood exhaust is latent heat in water vapour, which air-to-air exchangers recover poorly.
- Drying limits machine speed. Hot, dry pocket air is needed to keep drying rates up. If it runs cool, the machine has to slow down.
- Losses between fuel and process. Burning furnace oil 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 makes about 40 tonnes a day of writing and printing paper on one machine with a closed dryer hood. It runs round the clock, and the hood exhaust leaves at about 80 °C with a high moisture content.
| Heat user | Process temp. | Basis | Heat, kWh/day |
|---|---|---|---|
| Pocket ventilation air | Air 65 → 95 °C | 9,000 m³/h × 1.1 kg/m³ × 1.005 kJ/kg·K × 30 K × 24 h | 1,990 |
| Size press section hood supply | Air 65 → 95 °C | 4,000 m³/h × 1.1 kg/m³ × 1.005 kJ/kg·K × 30 K × 24 h | 884 |
| Storage and pipework standing losses | – | about 5% | 144 |
| Total useful heat | 3,018 | ||
Averaged over 20 running hours, the heat pumps need about 151 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
- 6 × SE-WWUHT-27 (162 kW total) (SE-WWUHT water-source, R245fa) delivering 120 °C, covering the day's 3,018 kWh in about 18.6 running hours.
- A 5,000 L insulated storage tank decouples the heat pumps from the process peaks.
- Heat source: hood exhaust heat-recovery water at about 58 °C. Taking more heat out of the hood exhaust lowers the stack temperature and reduces fog at the outlet.
- The furnace-oil fired steam boiler stays connected behind a normally closed valve as standby.
- A water scrubber or coil in the hood exhaust, after the existing air-to-air exchanger, condenses part of the vapour and heats a loop to about 58 °C.
- The heat pump lifts that heat to 120 °C pressurised water feeding coils ahead of the existing steam coils.
- Steam coils stay in series and lift air from about 95 °C to the final 105–110 °C when required.
Selected equipment
| Model | SE-WWUHT-27 × 6 |
|---|---|
| Heating capacity | 27 kW each, 162 kW total |
| COP | 2.93 at the data sheet's rated condition (60/55 °C source water) |
| Power input | about 55.2 kW total at rated conditions |
| Rating | water or steam to 120 °C, R245fa |
| Supply temperature | 120 °C |
| Storage | 5,000 L insulated tank |
Ratings from the Sunniva TDS 2026 data sheets.
Control philosophy
TT-101 at the tank top starts the heat pump below 112 °C and stops it at 120 °C, if the exhaust recovery loop is above 50 °C. TIC-201 and TIC-202 hold air leaving the water coils at 95 °C. The existing steam coil controllers trim each supply to its final set point. A loss of heat pump supply leaves the steam coils to carry the full load.
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 paper | – | – |
| CO₂ per year | – | – |
06Benefits
Latent heat recovered
Condensing part of the exhaust vapour recovers heat an air-to-air exchanger cannot.
Less steam per tonne
Most of the hood air heating moves off boiler steam.
Drying rate kept
The steam coils remain in place, so pocket air temperature is never compromised.
Lower energy cost
Each kWh of electricity delivers about 2.9 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
- Machine output, speed and grade
- Hood supply and exhaust flows, temperatures and humidity
- Existing heat recovery arrangement
- Steam used by hood air coils
- Present fuel or electricity use and monthly bill
- Sanctioned electrical load and spare capacity
- Space for the heat pumps and storage, with service access
Design notes
- Exhaust fouling. Hood exhaust carries fibre dust and size residues. Use cleanable stainless coils or a spray scrubber on the recovery side.
- Pressurised loop. Water at 120 °C needs a loop rated for at least 4 bar with expansion, safety valves and insulation.
- Hood balance. Check hood dew point and exhaust balance before and after. Changing supply air temperature affects hood humidity.
- Electrical. About 55 kW of heat pump input at rated conditions, plus pumps and fans. Check spare sanctioned load before ordering.
- Source stream. The source must give up roughly two-thirds of the heat delivered. Confirm its flow and temperature over a full production day, and filter it before the evaporator.
- 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
Paper machine hood air heated from exhaust
How a 40 tonne-per-day writing and printing paper mill can heat its pocket ventilation and hood supply air with a water-source heat pump running on exhaust heat, and what it saves against a furnace-oil fired steam boiler.
▶Video: Waste-heat recovery heat pumps
V10 · 2–2.5 minLifting warm water from condensers, effluent and process cooling to useful heat
Video coming soon01Problem statement
- Steam coils heat the hood air. Pocket ventilation and hood supply air are heated with steam coils after an air-to-air exchanger, using boiler steam.
- Humid exhaust holds the heat. Most of the energy in hood exhaust is latent heat in water vapour, which air-to-air exchangers recover poorly.
- Drying limits machine speed. Hot, dry pocket air is needed to keep drying rates up. If it runs cool, the machine has to slow down.
- Losses between fuel and process. Burning furnace oil 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 makes about 40 tonnes a day of writing and printing paper on one machine with a closed dryer hood. It runs round the clock, and the hood exhaust leaves at about 80 °C with a high moisture content.
| Heat user | Process temp. | Basis | Heat, kWh/day |
|---|---|---|---|
| Pocket ventilation air | Air 65 → 95 °C | 9,000 m³/h × 1.1 kg/m³ × 1.005 kJ/kg·K × 30 K × 24 h | 1,990 |
| Size press section hood supply | Air 65 → 95 °C | 4,000 m³/h × 1.1 kg/m³ × 1.005 kJ/kg·K × 30 K × 24 h | 884 |
| Storage and pipework standing losses | – | about 5% | 144 |
| Total useful heat | 3,018 | ||
Averaged over 20 running hours, the heat pumps need about 151 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
- 6 × SE-WWUHT-27 (162 kW total) (SE-WWUHT water-source, R245fa) delivering 120 °C, covering the day's 3,018 kWh in about 18.6 running hours.
- A 5,000 L insulated storage tank decouples the heat pumps from the process peaks.
- Heat source: hood exhaust heat-recovery water at about 58 °C. Taking more heat out of the hood exhaust lowers the stack temperature and reduces fog at the outlet.
- The furnace-oil fired steam boiler stays connected behind a normally closed valve as standby.
- A water scrubber or coil in the hood exhaust, after the existing air-to-air exchanger, condenses part of the vapour and heats a loop to about 58 °C.
- The heat pump lifts that heat to 120 °C pressurised water feeding coils ahead of the existing steam coils.
- Steam coils stay in series and lift air from about 95 °C to the final 105–110 °C when required.
Selected equipment
| Model | SE-WWUHT-27 × 6 |
|---|---|
| Heating capacity | 27 kW each, 162 kW total |
| COP | 2.93 at the data sheet's rated condition (60/55 °C source water) |
| Power input | about 55.2 kW total at rated conditions |
| Rating | water or steam to 120 °C, R245fa |
| Supply temperature | 120 °C |
| Storage | 5,000 L insulated tank |
Ratings from the Sunniva TDS 2026 data sheets.
Control philosophy
TT-101 at the tank top starts the heat pump below 112 °C and stops it at 120 °C, if the exhaust recovery loop is above 50 °C. TIC-201 and TIC-202 hold air leaving the water coils at 95 °C. The existing steam coil controllers trim each supply to its final set point. A loss of heat pump supply leaves the steam coils to carry the full load.
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 paper | – | – |
| CO₂ per year | – | – |
06Benefits
Latent heat recovered
Condensing part of the exhaust vapour recovers heat an air-to-air exchanger cannot.
Less steam per tonne
Most of the hood air heating moves off boiler steam.
Drying rate kept
The steam coils remain in place, so pocket air temperature is never compromised.
Lower energy cost
Each kWh of electricity delivers about 2.9 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
- Machine output, speed and grade
- Hood supply and exhaust flows, temperatures and humidity
- Existing heat recovery arrangement
- Steam used by hood air coils
- Present fuel or electricity use and monthly bill
- Sanctioned electrical load and spare capacity
- Space for the heat pumps and storage, with service access
Design notes
- Exhaust fouling. Hood exhaust carries fibre dust and size residues. Use cleanable stainless coils or a spray scrubber on the recovery side.
- Pressurised loop. Water at 120 °C needs a loop rated for at least 4 bar with expansion, safety valves and insulation.
- Hood balance. Check hood dew point and exhaust balance before and after. Changing supply air temperature affects hood humidity.
- Electrical. About 55 kW of heat pump input at rated conditions, plus pumps and fans. Check spare sanctioned load before ordering.
- Source stream. The source must give up roughly two-thirds of the heat delivered. Confirm its flow and temperature over a full production day, and filter it before the evaporator.
- 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.