Letterbox ventilation

Why a Letterbox system?
In a letterbox system the pallet openings of the boxes are used as air ducts. In the pressure wall, each pallet opening can be covered with a flap. As a result, you can control per row and per layer whether air flows through the duct. Therefore the letterbox system is highly flexible in use, making it suitable when there is plenty of diversity in your product. The letterbox system is frequently called a “drying wall”, and that is for a reason! The system has excellent drying performance. Keep in mind that the system is mainly suitable for smaller batches, because row lengths are limited to 8 to 10 boxes.

How does it work?
The fans force air down, causing an overpressure in the wall and in the pallet openings of the boxes. This overpressure forces the air through the bottom of the box, and through the product. Any air treatment, such as heating, occurs in the pressure wall. Inlet hatches are positioned in the pressure wall, above the fans. The position of the outlet hatches is flexible.

Closed boxes
In a letterbox system we usually apply closed boxes (even though that is not a must). These boxes have no openings between the boards. Therefore all air that enters the box through the bottom will actually flow through the product. It cannot escape via openings in the sides of the boxes, making the system more efficient. Do you prefer not to use closed boxes? That’s fine, but then we advise to apply more ventilation capacity.

Most commonly used for
We use the letterbox system most commonly for these products:

• Onion (sets)
• Shallots
• Garlic