Stenter and yarn dryer air preheated with heat pumps
How a textile finishing unit can preheat stenter fresh air and yarn dryer air to about 100 °C with heat pump hot water, against a furnace-oil fired thermic fluid heater.
▶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
- Cold air drawn into a hot machine. Stenters draw in large volumes of ambient air and heat it to drying temperature, which takes most of the thermic fluid heat.
- Fluid heater losses. Oil-fired thermic fluid heaters lose 20 to 25% in flue gas and need pumping and fluid upkeep.
- Yarn dryer bottleneck. Package dryers are slow to come up to temperature and often hold back the dye-house output.
- 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 unit finishes knit and woven fabric on one stenter and dries dyed yarn packages in a hot-air dryer. Both run 16 hours a day on two shifts.
| Heat user | Process temp. | Basis | Heat, kWh/day |
|---|---|---|---|
| Stenter fresh-air preheat | Air 35 → 100 °C | 5,000 kg/h air × 1.005 kJ/kg·K × 65 K = 90.7 kW × 16 h | 1,452 |
| Yarn package dryer air | Air 35 → 100 °C | 1,500 kg/h air × 1.005 kJ/kg·K × 65 K = 27.2 kW × 16 h | 435 |
| Storage and pipework standing losses | – | about 5% | 94 |
| Total useful heat | 1,981 | ||
Averaged over 20 running hours, the heat pumps need about 99 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 100 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 furnace-oil fired thermic fluid heater stays connected behind a normally closed valve as standby.
- A hot-water coil on the stenter fresh-air intake preheats air to about 100 °C before the thermic fluid coils.
- The thermic fluid heater supplies only the remaining lift to the stenter's working temperature.
- The yarn dryer gets its own hot-water coil, which shortens heat-up at the start of each load.
Selected equipment
| Machine | SE-UHT air-source cascade, R245fa |
|---|---|
| Capacity | about 100 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 holds the pressurised tank between 112 and 120 °C. TIC-201 and TIC-202 modulate the coil valves to hold preheat air at about 100 °C, and the existing thermic fluid control trims to the final set-point. If the tank falls below 100 °C, the thermic fluid heater picks up the whole 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 fabric | – | – |
| CO₂ per year | – | – |
06Benefits
Less fuel per metre
Preheating intake air takes a large share of the stenter's heat load off the thermic fluid heater.
Faster yarn drying
Hot air is ready at the start of each load, so package drying keeps pace with dyeing.
Smaller fluid heater duty
The thermic fluid heater runs at lower firing rates, which extends fluid and coil life.
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
- Stenter fresh-air flow and working temperature
- Yarn dryer airflow and load per day
- Thermic fluid heater fuel use
- Existing exhaust heat recovery, if any
- Running hours 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
- Lint and fumes. Stenter air carries lint and finishing oil mist. Put the coil on the clean fresh-air intake, and fit a filter ahead of it.
- Exhaust heat first. Check whether exhaust air recovery is already fitted. Size the heat pump preheat on the air temperature after exhaust recovery.
- Pressurised loop. Hot water at 120 °C needs at least 3 bar loop pressure, with relief valves and an expansion vessel.
- 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
Stenter and yarn dryer air preheated with heat pumps
How a textile finishing unit can preheat stenter fresh air and yarn dryer air to about 100 °C with heat pump hot water, against a furnace-oil fired thermic fluid heater.
▶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
- Cold air drawn into a hot machine. Stenters draw in large volumes of ambient air and heat it to drying temperature, which takes most of the thermic fluid heat.
- Fluid heater losses. Oil-fired thermic fluid heaters lose 20 to 25% in flue gas and need pumping and fluid upkeep.
- Yarn dryer bottleneck. Package dryers are slow to come up to temperature and often hold back the dye-house output.
- 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 unit finishes knit and woven fabric on one stenter and dries dyed yarn packages in a hot-air dryer. Both run 16 hours a day on two shifts.
| Heat user | Process temp. | Basis | Heat, kWh/day |
|---|---|---|---|
| Stenter fresh-air preheat | Air 35 → 100 °C | 5,000 kg/h air × 1.005 kJ/kg·K × 65 K = 90.7 kW × 16 h | 1,452 |
| Yarn package dryer air | Air 35 → 100 °C | 1,500 kg/h air × 1.005 kJ/kg·K × 65 K = 27.2 kW × 16 h | 435 |
| Storage and pipework standing losses | – | about 5% | 94 |
| Total useful heat | 1,981 | ||
Averaged over 20 running hours, the heat pumps need about 99 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 100 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 furnace-oil fired thermic fluid heater stays connected behind a normally closed valve as standby.
- A hot-water coil on the stenter fresh-air intake preheats air to about 100 °C before the thermic fluid coils.
- The thermic fluid heater supplies only the remaining lift to the stenter's working temperature.
- The yarn dryer gets its own hot-water coil, which shortens heat-up at the start of each load.
Selected equipment
| Machine | SE-UHT air-source cascade, R245fa |
|---|---|
| Capacity | about 100 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 holds the pressurised tank between 112 and 120 °C. TIC-201 and TIC-202 modulate the coil valves to hold preheat air at about 100 °C, and the existing thermic fluid control trims to the final set-point. If the tank falls below 100 °C, the thermic fluid heater picks up the whole 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 fabric | – | – |
| CO₂ per year | – | – |
06Benefits
Less fuel per metre
Preheating intake air takes a large share of the stenter's heat load off the thermic fluid heater.
Faster yarn drying
Hot air is ready at the start of each load, so package drying keeps pace with dyeing.
Smaller fluid heater duty
The thermic fluid heater runs at lower firing rates, which extends fluid and coil life.
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
- Stenter fresh-air flow and working temperature
- Yarn dryer airflow and load per day
- Thermic fluid heater fuel use
- Existing exhaust heat recovery, if any
- Running hours 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
- Lint and fumes. Stenter air carries lint and finishing oil mist. Put the coil on the clean fresh-air intake, and fit a filter ahead of it.
- Exhaust heat first. Check whether exhaust air recovery is already fitted. Size the heat pump preheat on the air temperature after exhaust recovery.
- Pressurised loop. Hot water at 120 °C needs at least 3 bar loop pressure, with relief valves and an expansion vessel.
- 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.