Humidification (ultrasonic humidifier)
Also known as: cold room humidification, ultrasonic humidifier, fogging
Short definitionRaising relative humidity by adding a water mist to the room air that is fine enough not to wet anything. Vegetables, fruit and flowers lose less water. The most widely used device is the ultrasonic humidifier, which vibrates water into mist.
When a customer says the vegetables are wilting in the room, a humidifier is the first thing that comes to mind, but the evaporator is checked first. As it cools, the evaporator also takes water out of the air; a system with a temperature difference of 8–10 K does this without pause. Adding water to such a room increases the ice on the fins and the number of defrosts. Where high humidity is wanted, the evaporator is chosen with a 4–6 K difference and the humidifier only makes up the shortfall. For most fruit and vegetables the target is 90–95% relative humidity.
An ultrasonic unit breaks water into droplets of a few microns; the mist evaporates without wetting surfaces, and a humidity sensor switches the unit on and off. In a large store, high-pressure fogging through nozzles is more economical. Steam types are not used because they bring heat into the room. Water treatment also goes into the quote: hard mains water leaves white dust on the product, so demineralised or reverse osmosis water is needed. The mist is fed into the discharge air, and water must not drip onto the product. Rooms below zero are not humidified.