Fruit and vegetables dried in a closed loop
How a dehydration unit handling 1.5 tonnes of fresh produce a day can dry it in a closed-loop heat pump dryer, and what it saves against an LPG-fired tray dryer.
▶Video: Heat pump dryers for food and agri products
V08 · 2–2.5 minClosed-loop drying of spices, fruit, fish, grain and more
Video coming soon01Problem statement
- Browning and colour loss. Hot, open-cycle air above 65 °C browns onion and darkens fruit. Buyers grade dehydrated produce on colour.
- Heat lost with the exhaust. Open-cycle dryers throw out warm, moist air all the time, and with it most of the heat.
- Weather-dependent drying. In the monsoon the intake air is humid, so drying times stretch and batches can spoil.
- 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 unit dries onion flakes most of the year and mango and banana slices in season, about 1.5 tonnes of fresh produce a day. Slicing and blanching run in one shift and drying runs overnight in trolley dryers.
| Product | Drying | Basis | Water removed, kg/day | Conventional heat, kWh/day |
|---|---|---|---|---|
| Onion flakes | Air 55–60 °C | 1,000 kg/day sliced onion, 86% → 6% | 851 | 1,532 |
| Mango and banana slices | Air 55 °C | 500 kg/day slices, 82% → 15% | 394 | 709 |
| Total | 1,245 | 2,241 | ||
Conventional hot-air dryers use about 1.8 kWh of heat per kg of water removed. That figure is the baseline the savings are measured against.
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
- 3 × SE-AA-DR-21 (63 kW total) heat pump drying modules, removing about 1,245 kg of water a day in roughly 17 running hours.
- The LPG-fired hot-air tray dryer stays connected behind a normally closed valve as standby.
- The heat pump dryer recirculates air through the chamber, cools it to condense the moisture and reheats it with the condenser heat.
- Drying air is held at 55–60 °C and low humidity whatever the weather outside.
- Existing trolleys and trays are reused in an insulated chamber.
Selected equipment
| Model | 3 × SE-AA-DR-21 |
|---|---|
| Heating capacity | 21 kW each, 63 kW total |
| Dehumidifying | about 74 L/h total (pro rata to the published 12–120 L/h range) |
| Drying air | rated 70 °C, 75 °C maximum |
| Refrigerant | R134a |
| Ambient | −5 to 43 °C |
| Water removed per kWh | about 2.4 kg |
Ratings from the Sunniva TDS 2026 data sheets.
Control philosophy
TIC-201 holds drying air at the set point for each product. A humidity sensor in the return air sets the dehumidifying duty and moves the dryer to a gentler finishing stage as product moisture falls. The cycle ends on time or on a target return-air humidity.
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 fresh produce | – | – |
| CO₂ per year | – | – |
06Benefits
Better colour and aroma
Lower, steady drying temperature keeps onion white and fruit bright, and retains more volatile aroma.
Same result in the monsoon
The closed loop does not depend on outdoor humidity, so drying times stay the same all year.
Clean product
Air is recirculated inside the chamber, so dust, insects and flue gases do not reach the product.
Heat recovered from the moisture
The evaporator condenses water out of the air and the condenser puts that latent heat back into the drying air, so about 2.4 kg of water leaves per kWh of electricity.
Closed loop, clean product
Air recirculates inside the chamber. No dust, smoke or outside humidity reaches the product, whatever the weather.
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
- Products dried and daily quantities
- Moisture in and target moisture out
- Slice thickness and tray loading
- Present drying time and fuel use
- 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
- Condensate. Water removed from the product drains as condensate. Collect it and do not reuse it in the process.
- Loading. Even tray loading matters more in closed-loop dryers. Keep slice thickness uniform and leave airflow gaps.
- Hygiene. Use stainless trays and food-grade chamber lining that can be washed down.
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
Fruit and vegetables dried in a closed loop
How a dehydration unit handling 1.5 tonnes of fresh produce a day can dry it in a closed-loop heat pump dryer, and what it saves against an LPG-fired tray dryer.
▶Video: Heat pump dryers for food and agri products
V08 · 2–2.5 minClosed-loop drying of spices, fruit, fish, grain and more
Video coming soon01Problem statement
- Browning and colour loss. Hot, open-cycle air above 65 °C browns onion and darkens fruit. Buyers grade dehydrated produce on colour.
- Heat lost with the exhaust. Open-cycle dryers throw out warm, moist air all the time, and with it most of the heat.
- Weather-dependent drying. In the monsoon the intake air is humid, so drying times stretch and batches can spoil.
- 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 unit dries onion flakes most of the year and mango and banana slices in season, about 1.5 tonnes of fresh produce a day. Slicing and blanching run in one shift and drying runs overnight in trolley dryers.
| Product | Drying | Basis | Water removed, kg/day | Conventional heat, kWh/day |
|---|---|---|---|---|
| Onion flakes | Air 55–60 °C | 1,000 kg/day sliced onion, 86% → 6% | 851 | 1,532 |
| Mango and banana slices | Air 55 °C | 500 kg/day slices, 82% → 15% | 394 | 709 |
| Total | 1,245 | 2,241 | ||
Conventional hot-air dryers use about 1.8 kWh of heat per kg of water removed. That figure is the baseline the savings are measured against.
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
- 3 × SE-AA-DR-21 (63 kW total) heat pump drying modules, removing about 1,245 kg of water a day in roughly 17 running hours.
- The LPG-fired hot-air tray dryer stays connected behind a normally closed valve as standby.
- The heat pump dryer recirculates air through the chamber, cools it to condense the moisture and reheats it with the condenser heat.
- Drying air is held at 55–60 °C and low humidity whatever the weather outside.
- Existing trolleys and trays are reused in an insulated chamber.
Selected equipment
| Model | 3 × SE-AA-DR-21 |
|---|---|
| Heating capacity | 21 kW each, 63 kW total |
| Dehumidifying | about 74 L/h total (pro rata to the published 12–120 L/h range) |
| Drying air | rated 70 °C, 75 °C maximum |
| Refrigerant | R134a |
| Ambient | −5 to 43 °C |
| Water removed per kWh | about 2.4 kg |
Ratings from the Sunniva TDS 2026 data sheets.
Control philosophy
TIC-201 holds drying air at the set point for each product. A humidity sensor in the return air sets the dehumidifying duty and moves the dryer to a gentler finishing stage as product moisture falls. The cycle ends on time or on a target return-air humidity.
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 fresh produce | – | – |
| CO₂ per year | – | – |
06Benefits
Better colour and aroma
Lower, steady drying temperature keeps onion white and fruit bright, and retains more volatile aroma.
Same result in the monsoon
The closed loop does not depend on outdoor humidity, so drying times stay the same all year.
Clean product
Air is recirculated inside the chamber, so dust, insects and flue gases do not reach the product.
Heat recovered from the moisture
The evaporator condenses water out of the air and the condenser puts that latent heat back into the drying air, so about 2.4 kg of water leaves per kWh of electricity.
Closed loop, clean product
Air recirculates inside the chamber. No dust, smoke or outside humidity reaches the product, whatever the weather.
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
- Products dried and daily quantities
- Moisture in and target moisture out
- Slice thickness and tray loading
- Present drying time and fuel use
- 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
- Condensate. Water removed from the product drains as condensate. Collect it and do not reuse it in the process.
- Loading. Even tray loading matters more in closed-loop dryers. Keep slice thickness uniform and leave airflow gaps.
- Hygiene. Use stainless trays and food-grade chamber lining that can be washed down.
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.