Drying and storing onions? Do not put a euro in a supporting ventilation system. Henk Tebben, storage specialist at Equans Refrigeration, explains how you can save an investment in forced ventilation with condensation drying and still have an energy-efficient and future-proof drying and storage system.
Drying onions without supporting ventilation sounds like a utopia…
"Drying onions with the outside air is difficult for every arable farmer. That is why we introduced a closed storage system years ago, in which outside air is no longer necessary: condensation drying. That is drying with the energy from the product itself, without using expensive and polluting gas heaters. We also see that box storage is increasingly being chosen for new construction. That offers opportunities to omit forced ventilation."
How do onions dry without a ventilation system?
"By filling in the ventilation differently, it is not necessary to install two ventilation systems behind each other. The drying unit used by our condenser drying technology however, has already been developed to such an extent that the row of boxes can function as a suction wall. We place the boxes under the evaporators, which are already provided with ventilation. In terms of quantity and pressure build-up, we can design these evaporator fans in the same way as the fans in a suction wall. In fact, we omit that suction wall, so that an investment in auxiliary ventilation is no longer necessary."
Critics argue that this means that the air can no longer get through the product. Is that right?
"It doesn't matter whether you get the air quantity with matching pressure from horizontally placed fans from a wall, or whether you supply the drying unit with just as much air with the corresponding external pressure. You can just as well realize the air circulation with the drying unit. in other words: a kilogram of feathers or a kilogram of lead still weighs a kilogram. If the onions come from the land green and moist, then we create enough air that passes through the product and ensures that it dries. In fact, with this system we have we found the optimum air pressure and quantity for an ideal drying process, tailored to what the product requires. With a pressure wall or suction wall, the air pressure and quantity is more often too much or too little, but rarely ideal."
And what are the conditions?
"Using a drying unit as ventilation requires a box plan that is geared to the air distribution and air volume. The maximum depth of the rows of boxes is also important. The rows are often too long, which results in drying differences between products that are stored at the front and at the back. We therefore supply a tailor-made box plan for each application to guarantee air distribution and quantities. Box locations, but also the box height, width and depth are optimal for the product. Creating different zones is also an option , so that growers can drive all kinds of batches into the cell at different times and therefore have a flexible storage system. An optimally functioning condenser dryer without auxiliary ventilation only works with ammonia as a refrigerant."
Why is this only possible with ammonia?
"Ammonia has a great capacity to absorb and release energy. Energy flows can also be better controlled and coordinated with ammonia, both on the hot and on the cold side. You can even control it down to tenths of a degree and thus achieve the optimum drying and storage conditions. Without fluctuations or energy loss."
What are the advantages of this way of storing onions?
"As a grower, if you opt for new construction, then you can invest the money you normally need for a storage and ventilation system in smarter technology: condensation drying. Although that requires almost the same investment at the bottom, with a condensation drying installation you do have a multifunctional storage system that works at all times and with which you can dry homogeneously. You are independent of the outside air and have the option of storing different products. The energy you need to dry the product also comes from the product itself, which saves you a lot of energy costs All heat emitted is used 100%. And because of the ammonia as a refrigerant, you no longer have to phase out synthetic refrigerants and you are ready for the future."