Systems of technical wood drying

Fresh-/exhaust air drying technology (conventional drying system): proven technology, easy-to-use, long living time

More than 90% of all timber dryers world-wide work according to the fresh-/exhaust air drying technology because of following advantages:

  • easy-to-use,
  • proven technology since many, many years: thousand of kilns in operation
  • low energy and service costs

In a steam-close and thermal insulated room, warm air is produced by a heating system (electric, hot water or steam) and transported by fans. The climate in the area is accurately set up: the air is heated up and the humidity is raised by spraying of fine water or is lowered by the delivery of exhaust air outside through the air flaps.

The result is an exact climate in the kiln for a controlled drying process to reach a final moisture content as well as the best wood quality. In conventional drying you can choose between different ways of loading, from the front-side, long-side or from the top.


The range of applications for vacuum driers starts wherever conventional drying process takes too long time, for example if thick wood, deciduous species or constructional wood is dried. The speed advantage of a vacuum dryer is particularly good with pre-dried products. Here the drying time is much faster than in conventional timber dryer.

Inside the chamber a vacuum pump creates low pressure. The water in such vacuum sur- rounding boils at lower temperature such as 40°C. The moisture which emerges from the wood is removed during the drying phase. In case the vacuum technology is used without interruption of the vacuum (continuous vacuum), discolouration of the wood can be avoided. The vacuum is complited by a compact condenser on the outside. Air, which is available free of charge, is used as the coolant. Vacuum dryer can be charged from the front-side.

Types of ventilation

Longitudinal ventilation: timber drying along the wood fibre

Longitudinal ventilation: timber drying along the wood fibre
Longitudinal ventilated wood dryer with front side fan

In longitudinal ventilated dryers a radial ventilator is installed at the front side. This fan sucks the air through the wood pile. From all sides of its entire length, each board is ventilated by the air flow. 

The natural water flow in the wood runs parallel to the wood fibre. Due to the natural water flow, this kind of ventilation offers a very efficient drying process. High air speed is possible with a longitudinal ventilation and it guarantees an optimal drying process of the entire pile length. Another advantage is the large pile length with small quantity of wood. Even if the longitudinal dryer is not completely filled, an optimal ventilation is guaranteed: the pile area is adapted automatically by inserting cover plates over the wood that should be dried. 

In order to make the longitudinal air circulation effective, special air-permeable staple ledges (aluminium) are needed.

transversal (cross wise) ventilation: for larger wood quantities

transversal (cross wise) ventilation: for larger wood quantities
LAUBER ventilation tower

Wood dryers with several wood packages in height and width are ventilated transversal (cross wise) to the wood pile. According to the size of the chamber, several fans are installed and therefore chambers can be built in nearly every size. In transversal ventilated drying chambers normal staple ledges of wood are used and pre-stacked pile packages can be directly loaded into the drying chamber.

large wood dryer with fans in a false ceiling,
large wood dryer with fans in a false ceiling,