Condensation drying or mechanical cooling?

Condensation drying and mechanical cooling are now widely used technologies. This allows crops to be stored for longer at quality, with less or even without sprout inhibitors. With their durability, minimal energy consumption and natural refrigerants, both storage systems have many similarities. But where are the differences?

Henk Tebben, storage specialist at EQUANS (formerly ENGIE Refrigeration), explains: "First the definitions. Mechanical cooling takes place in a completely closed storage environment. The computer continuously measures the temperature, the humidity and the CO₂ in storage and adjusts the cooling capacity and the storage program to the cooling demand of the product. As a result, the different phases of the storage process are fully under control. 7°C remains 7°C. Does the CO . come₂content above a certain value, the system extracts this to the outside air. Due to the stable conditions, products remain as good as fresh until summer."

"You basically do nothing else with condensation drying. By bringing the air in the room below the condensation point, moisture is removed and the products dry. The big difference with mechanical cooling is that the heat released during the cooling process can be used again. Cooled air can hardly absorb moisture. That is why we heat the air with the released heat so that it can absorb moisture again. If the moisture has disappeared from the product, you can also heat the products with condensation drying to combat diseases. In that case, a heat pump uses the heat released during the cooling process (drying process) to heat up or maintain the temperature of the crops."

Drying surface
Whether you as a grower choose one or the other storage method depends on whether you want to heat or not. And that depends on your product type. Products in which moisture can evaporate via a large surface, such as carrots and potatoes, require mechanical cooling. For a product where moisture evaporates via a small surface, the energy flow must be started. In that case, condensation drying is a wiser choice.

Tebben: "Take an onion. The skin does not release any moisture. The onion only dries through the neck. That is also an ideal place for fungus to develop, the head rot. By bringing the temperature in the room to 30°C, the energy flow comes in the product and the onion dries. This makes it more difficult for the fungus. The energy released during drying is therefore also used for heating. That energy is 100% free, because it comes from the product. not." Condensation drying is therefore better for products such as onion, cabbage, ginger and garlic. But also sweet potato. "Sweet potatoes need 28°C to ferment, so to become sweet. Storage afterwards requires 14°C to keep the sugars intact," says Tebben.

With and without exterior shutters
Another decisive factor is whether or not to use outside air. Although both systems can work completely without outside air, condensation drying can also be used with outside hatches. Tebben: "We have refined the hatch control so that it is possible to use favorable outside conditions and to combine it with the drying capacity of the condenser dryer. The smart control can control the hatches and thrust fans extremely accurately. If you do not want to use the outside air for a while, then the the system automatically switches to a closed environment, so you have the best of both worlds."

Germ inhibitors
Do germ inhibitors and specifically the ban on chemical germ inhibitors play a role in the choice? "Germs are caused by temperature fluctuations. With both condensation drying and mechanical cooling, you can reduce the CO₂, humidity and temperature. This is important for the tranquility of the product and acts as a natural brake. As a result, much less germination occurs and you can greatly reduce or even eliminate germ inhibitors. This makes the systems very interesting, especially for organic growers. If you still want to use germ inhibitors, you can keep them indoors with closed storage and they won't evaporate."

Budget
Budget is often decisive when choosing between different storage systems. But that kite doesn't seem to hold up in this comparison. "Condensation drying can be more expensive, but not always. The bigger the installation, the smaller the investment per tonne of product. It's all about what you want to do with your product. It's about energy savings.

And on combating quality losses. The capacity of your design also plays a role. In the ideal situation, you have capacity available when it is needed and you work energy-efficiently when possible. EQUANS recalculate for each situation. We offer a solution for every budget."

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