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Drying plant and indirect air drying

Drying garlic in crates with conditioned drying with the drying plant for chests. The air distribution system with the fans is placed in a closed but ventilated cell. Fans suck air and blow it through the product. Moisture from the product must be drained.
This is done by a combination of:

  1. Refresh part of the air by drying outdoor air, draining moist air. The Open Air AV should be lower than the air in the cell.
  2. Condensing moisture at the evaporator due to strong cooling of the sucked air.
  3. Warm up the dried air so that the air can absorb moisture again.

Two methods for the change-up and heating of the air

There are two methods to the change-up and heating of the air

1. Through a hatch in the wall, the evaporator sucks dry outdoor air.

Outdoor air is sucked in and cooled sharply at the evaporator. The cold air plus the air from the product are warmed above the circulation fan by the radiator.

Suck in outdoor air and under…
Sucking outside and indoor air..
Sucking indoor air…
…… and drain moist air
…and partial discharge of air
.. so no air change

The outdoor air is cooled down sharply so that moisture is drained by condensation. The air from the evaporator is reheated (together with the air from the chests) by a radiator above the circulation fan to the desired temperature.


When the outside air is too hot, it is cooled (and dried) at the evaporator; refresh is long possible without the product getting too hot. When cooling quickly to a low temperature, colder outdoor air can be used.

2. Through shutters, the circulation fans suck dry outdoor air.

Through a hatch, the circulation fans suck up to 60 to 70% dry outdoor air. The remaining 30-40% is (dried) within air plus air from the chests.

Outdoor air is sucked into the fan at circulation. This air mixes with highly cooled (and dried) internal air and air from the product The mixed air is warmed up above the circulation fan by the radiator.


The large amount of air change can drain a lot of moisture. In case of too high air, the mixed air can get too hot and the hatch will close proportionally.

Installation with heating batteries above circulation fans. Shutters behind the circulation fans.
Installation with heating batteries after the evaporator. Evaporator with suction hatch for outdoor air.
Schematic representation of a dry cell with an indirect condenser dryer, suction hatch and exhaust hatch plus the air distribution system and chests. The hot cooling medium flows from the evaporator to the plate changer and warm water flows back to the hot water radiators.
Flow schedule of an indirect air dryer by condensation

The drying process using indirect air drying

With the evaporator, the air is cooled down sharply and warmed back to the desired temperature in the heating battery. It is dried at a temperature of 15°-18°C. Drying ends when the AIR HR is stable at 55% at 15°-18°C..

After drying, the product can remain at 15°-18°C, first cleaning and processing or it can be cooled immediately.
After drying (or cleaning and processing), the air will drop to -/-2°C as quickly as possible. The RH shall not be checked during cooling; The air is already drier by condensation during cooling. The rh desired at -/-2°C is held at about 80%.
During drying, continuous measurement is made whether the outside air is suitable (dryer and not too hot) compared to the air in the cell. With a desired difference and more (outside dryer than in the cell) 100% outdoor air is sucked in. In the case of a lower difference, the suction of outdoor air is reduced linearly.

In case of hot (but drier) outdoor air, the suction is reduced so that the desired cooling continues to take place and the temperature in the cell does not rise.
During storage, the temperature of the product is continuously measured.
At rising air temperature in the cell, the evaporator (and cooling system) is automatically switched on and the circulation fan starts.
In addition, during storage, the circulation fans are automatically started after a set time to dispose of any heat around the product.

Per fan/section a T+HR measurement of the blown air and air from the chests.
At the exhaust shutters a T+HR sensor to determine whether the air in the cell is drier than the outdoor air.
A product sensor is placed in the box per fan/section to check and ensure the product temperature.
Tijdens het drogen, wanneer de buitenlucht wordt aangezogen, worden de uitlaatluiken gelijk aan de aan de inlaatluiken geopend en gesloten.
A wake thermostat automatically disables the evaporator when the incoming temperature drops below a defined minimum temperature.