Hot-air dryer preheat without burning oil
How a chemical plant running tray and fluid bed dryers at 90–120 °C can preheat its drying air with heat pump hot water, against a furnace-oil fired hot-air generator.
▶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
- Open-flame air heating. Direct or indirect oil-fired air heaters run at high flame temperatures to make air at 100 °C, with flue losses of 20 to 25%.
- Contamination risk. Indirect heater tubes can crack and leak flue gas into the drying air, which discolours white products.
- Poor turndown. Burners cycle at part load, so the inlet air temperature swings and the outlet moisture varies.
- 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 speciality salts, micronutrient fertilisers and processed minerals. It runs a fluid bed dryer and a flash dryer for 16 hours a day, drying about 15 tonnes of product.
| Heat user | Process temp. | Basis | Heat, kWh/day |
|---|---|---|---|
| Fluid bed dryer inlet air | Air 35 → 110 °C | 3,000 kg/h air × 1.005 kJ/kg·K × 75 K = 62.8 kW × 16 h | 1,005 |
| Flash dryer air preheat | Air 35 → 100 °C | 2,000 kg/h air × 1.005 kJ/kg·K × 65 K = 36.3 kW × 16 h | 581 |
| Storage and pipework standing losses | – | about 5% | 79 |
| Total useful heat | 1,665 | ||
Averaged over 20 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 furnace-oil fired hot-air generator stays connected behind a normally closed valve as standby.
- A finned hot-water coil is added upstream of the existing air heater on each dryer. Pressurised hot water at up to 120 °C heats the air to 100–110 °C.
- Where the product needs a hotter inlet, the existing heater adds only the last few degrees.
- The storage tank lets the heat pumps run 20 hours a day while the dryers run 16.
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 and TIC-202 trim the hot-water valve on each coil to hold the dryer inlet temperature. If the coil cannot reach set-point, the existing oil-fired heater fires to top up, and it remains the 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 product | – | – |
| CO₂ per year | – | – |
06Benefits
Cleaner drying air
Hot-water coils carry no flue gas, so white and food-grade products are not discoloured.
Steadier inlet temperature
Coil control holds the inlet air within a narrow band, so outlet moisture is more consistent.
Less oil handling
Oil firing drops to a top-up role, cutting storage, heating and burner upkeep.
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
- Dryer type, airflow and inlet temperature set-point
- Product throughput and moisture in and out
- Fuel use per day on the air heaters
- Dryer running hours
- Space for coils in the air intake duct
- 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 120 °C must be kept at 3 bar or more to stay liquid. Fit an expansion vessel, pressure relief and low-pressure alarm.
- Dust on coils. Fit an intake filter ahead of each coil. Fine mineral dust on the fins quickly cuts heat transfer.
- Corrosive products. Where the air carries chloride or acid dust, specify coated or stainless steel fins for the coils.
- 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.
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Hot-air dryer preheat without burning oil
How a chemical plant running tray and fluid bed dryers at 90–120 °C can preheat its drying air with heat pump hot water, against a furnace-oil fired hot-air generator.
▶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
- Open-flame air heating. Direct or indirect oil-fired air heaters run at high flame temperatures to make air at 100 °C, with flue losses of 20 to 25%.
- Contamination risk. Indirect heater tubes can crack and leak flue gas into the drying air, which discolours white products.
- Poor turndown. Burners cycle at part load, so the inlet air temperature swings and the outlet moisture varies.
- 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 speciality salts, micronutrient fertilisers and processed minerals. It runs a fluid bed dryer and a flash dryer for 16 hours a day, drying about 15 tonnes of product.
| Heat user | Process temp. | Basis | Heat, kWh/day |
|---|---|---|---|
| Fluid bed dryer inlet air | Air 35 → 110 °C | 3,000 kg/h air × 1.005 kJ/kg·K × 75 K = 62.8 kW × 16 h | 1,005 |
| Flash dryer air preheat | Air 35 → 100 °C | 2,000 kg/h air × 1.005 kJ/kg·K × 65 K = 36.3 kW × 16 h | 581 |
| Storage and pipework standing losses | – | about 5% | 79 |
| Total useful heat | 1,665 | ||
Averaged over 20 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 furnace-oil fired hot-air generator stays connected behind a normally closed valve as standby.
- A finned hot-water coil is added upstream of the existing air heater on each dryer. Pressurised hot water at up to 120 °C heats the air to 100–110 °C.
- Where the product needs a hotter inlet, the existing heater adds only the last few degrees.
- The storage tank lets the heat pumps run 20 hours a day while the dryers run 16.
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 and TIC-202 trim the hot-water valve on each coil to hold the dryer inlet temperature. If the coil cannot reach set-point, the existing oil-fired heater fires to top up, and it remains the 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 product | – | – |
| CO₂ per year | – | – |
06Benefits
Cleaner drying air
Hot-water coils carry no flue gas, so white and food-grade products are not discoloured.
Steadier inlet temperature
Coil control holds the inlet air within a narrow band, so outlet moisture is more consistent.
Less oil handling
Oil firing drops to a top-up role, cutting storage, heating and burner upkeep.
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
- Dryer type, airflow and inlet temperature set-point
- Product throughput and moisture in and out
- Fuel use per day on the air heaters
- Dryer running hours
- Space for coils in the air intake duct
- 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 120 °C must be kept at 3 bar or more to stay liquid. Fit an expansion vessel, pressure relief and low-pressure alarm.
- Dust on coils. Fit an intake filter ahead of each coil. Fine mineral dust on the fins quickly cuts heat transfer.
- Corrosive products. Where the air carries chloride or acid dust, specify coated or stainless steel fins for the coils.
- 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.