Tea withering and dryer air heated by heat pumps
How a bought-leaf tea factory processing 4 tonnes of green leaf a day can heat its withering air and most of its dryer air with heat pumps, and what it saves against a briquette-fired air 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
- Wet-weather withering. In the monsoon the troughs need warm air to wither leaf on time. Uneven warming gives patchy wither and poor liquor.
- Dryer heat is the big load. The fluid-bed dryer uses most of the factory's fuel, heating large volumes of air to 110–115 °C.
- Smoke and fuel handling. Wood and briquette heaters need fuel storage and stoking, and smoke leaks can taint tea.
- Losses between fuel and process. Burning briquettes 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 factory buys green leaf from small growers and makes about 900 kg of CTC tea a day from 4 tonnes of leaf in season. Leaf is withered overnight in troughs, then rolled, fermented and fired in a fluid-bed dryer.
| Heat user | Process temp. | Basis | Heat, kWh/day |
|---|---|---|---|
| Withering trough air | Air 30–35 °C | 4,000 kg leaf, 78% → 68%: 1,250 kg water × 0.7 kWh/kg × 30% from heater | 263 |
| Dryer air preheat to 95 °C | Air 95 °C | 2,750 kg withered leaf, 68% → 3%: 1,843 kg water × 1.2 kWh/kg × 75% share | 1,659 |
| Storage and pipework standing losses | – | about 5% | 96 |
| Total useful heat | 2,018 | ||
Averaged over 18 running hours, the heat pumps need about 112 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 115 kW, air-source cascade to 120 °C, sized per project.
- A 3,500 L insulated storage tank decouples the heat pumps from the process peaks.
- The briquette or wood-fired air heater stays connected behind a normally closed valve as standby.
- Hot water at 105 °C feeds a finned coil on the dryer air inlet, lifting air to about 95 °C before the existing heater.
- The existing heater only tops up the air from 95 °C to the 110–115 °C inlet temperature.
- Withering troughs get hot-water coils on the fan inlets, so warm air is available in wet weather without a separate fire.
Selected equipment
| Machine | SE-UHT air-source cascade, R245fa |
|---|---|
| Capacity | about 115 kW, built to duty |
| Concept | air-source cascade to 120 °C, sized per project |
| COP used | 1.8 (estimate) |
| Supply temperature | 105 °C |
| Storage | 3,500 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 calls the heat pumps on below 100 °C and off at 105 °C. TT-102 at the bottom starts the units before the dryer starts. TIC-201 holds dryer preheat air at 95 °C and the existing heater controls the final inlet temperature. TIC-202 sets trough air temperature to the withering programme.
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 made tea | – | – |
| CO₂ per year | – | – |
06Benefits
Better wither
Controlled warm air gives an even wither in wet weather, which improves liquor and colour.
Most dryer fuel replaced
The heat pumps carry the bulk of the air heating, and the heater only trims the last few degrees.
Cleaner air to the leaf
Indirect hot-water coils add no smoke to the withering or drying air.
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.
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
- Green leaf per day in peak and lean months
- Dryer type, airflow and inlet temperature
- Withering trough count, fan airflow and wet-weather practice
- Present fuel use per kg of made tea
- 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
- Tea fluff. Dryer inlet and withering air carry tea fibre that clogs fins. Use wide fin spacing and filters, and clean daily in season.
- Pressurised loop. Water at 105 °C must be held at about 2 bar. Size the expansion vessel and relief valve for this.
- Two temperature levels. Feed the withering coils from the return side of the dryer coil, so the low-temperature load uses the cooler water.
- 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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Tea withering and dryer air heated by heat pumps
How a bought-leaf tea factory processing 4 tonnes of green leaf a day can heat its withering air and most of its dryer air with heat pumps, and what it saves against a briquette-fired air 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
- Wet-weather withering. In the monsoon the troughs need warm air to wither leaf on time. Uneven warming gives patchy wither and poor liquor.
- Dryer heat is the big load. The fluid-bed dryer uses most of the factory's fuel, heating large volumes of air to 110–115 °C.
- Smoke and fuel handling. Wood and briquette heaters need fuel storage and stoking, and smoke leaks can taint tea.
- Losses between fuel and process. Burning briquettes 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 factory buys green leaf from small growers and makes about 900 kg of CTC tea a day from 4 tonnes of leaf in season. Leaf is withered overnight in troughs, then rolled, fermented and fired in a fluid-bed dryer.
| Heat user | Process temp. | Basis | Heat, kWh/day |
|---|---|---|---|
| Withering trough air | Air 30–35 °C | 4,000 kg leaf, 78% → 68%: 1,250 kg water × 0.7 kWh/kg × 30% from heater | 263 |
| Dryer air preheat to 95 °C | Air 95 °C | 2,750 kg withered leaf, 68% → 3%: 1,843 kg water × 1.2 kWh/kg × 75% share | 1,659 |
| Storage and pipework standing losses | – | about 5% | 96 |
| Total useful heat | 2,018 | ||
Averaged over 18 running hours, the heat pumps need about 112 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 115 kW, air-source cascade to 120 °C, sized per project.
- A 3,500 L insulated storage tank decouples the heat pumps from the process peaks.
- The briquette or wood-fired air heater stays connected behind a normally closed valve as standby.
- Hot water at 105 °C feeds a finned coil on the dryer air inlet, lifting air to about 95 °C before the existing heater.
- The existing heater only tops up the air from 95 °C to the 110–115 °C inlet temperature.
- Withering troughs get hot-water coils on the fan inlets, so warm air is available in wet weather without a separate fire.
Selected equipment
| Machine | SE-UHT air-source cascade, R245fa |
|---|---|
| Capacity | about 115 kW, built to duty |
| Concept | air-source cascade to 120 °C, sized per project |
| COP used | 1.8 (estimate) |
| Supply temperature | 105 °C |
| Storage | 3,500 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 calls the heat pumps on below 100 °C and off at 105 °C. TT-102 at the bottom starts the units before the dryer starts. TIC-201 holds dryer preheat air at 95 °C and the existing heater controls the final inlet temperature. TIC-202 sets trough air temperature to the withering programme.
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 made tea | – | – |
| CO₂ per year | – | – |
06Benefits
Better wither
Controlled warm air gives an even wither in wet weather, which improves liquor and colour.
Most dryer fuel replaced
The heat pumps carry the bulk of the air heating, and the heater only trims the last few degrees.
Cleaner air to the leaf
Indirect hot-water coils add no smoke to the withering or drying air.
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.
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
- Green leaf per day in peak and lean months
- Dryer type, airflow and inlet temperature
- Withering trough count, fan airflow and wet-weather practice
- Present fuel use per kg of made tea
- 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
- Tea fluff. Dryer inlet and withering air carry tea fibre that clogs fins. Use wide fin spacing and filters, and clean daily in season.
- Pressurised loop. Water at 105 °C must be held at about 2 bar. Size the expansion vessel and relief valve for this.
- Two temperature levels. Feed the withering coils from the return side of the dryer coil, so the low-temperature load uses the cooler water.
- 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.