Fan Speed control

Computer controlled speed control system B 8400 DS with bypass mode function connecting to direct line power.
The speed control optimizes air flow and speed in reference to the drying progress.

The following are taken into account:

  • Lumber species and thickness
  • Current lumber moisture content  and drying speed
  • Kiln temperature and drying rate
  • Temperature difference between intake and exhaust side
  • Electrical tariffs (special software - option - not included in the basic price)

The speed change is effected by a microprocessor-controlled frequency converter. The bypass operation has following advantages:

  • At full load (for example in the heat up phase), the fans run at 50(60) Hz with their maximum efficiency and without thermal losses.
  • During drying operation, the motors are lowered to a slower speed, therefore saving electrical energy.
  • In case of frequency drive failure, the connected motors continue to run without interruption in the "bypass" mode.


  • Sinus-rated pulse inverter with IGBT power amplifiers
  • square characteristic for fan drives - optimum power savings
  • Ground and short-circuit-proof inverter outputs
  • Max.Load up to 1.1 times the rated current for 30 seconds; Ambient temperatures up to 40 ° C
  • V / f characteristic control
  • Slip compensation
  • Current limiter with U / f   lowering
  • I2t Monitoring as overload protection for the motor
  • Parameterization and diagnosis with keypad and LCD display
  • Parameter can be changed ON-LINE
  • Potential-free digital inputs and outputs

The extensive, elaborate software is always kept up to date by the latest technical standards. Thanks to the easy up/downloading of new programs the speed control will always be up-to-date even after years.


Functional description:

Depending on the lumber species, the thickness and the moisture content of the lumber in the kiln. The control system  supplied by the BRUNNER - HILDEBRAND GROUP automatically controls different fan speeds (air velocities) - between 40% and 100% (20 Hz - 50/60 Hz).

As the wood moisture decreases, the fan speed (air speed) is reduced as the lumber does not require high air speed in the lumber packets for economical and qualitative drying.

Furthermore, further energy savings are possible with the option "tariff program" (taking in account energy power supplier rates for normal, night, peak, weekend end, maximum monitors, critical speeds).


The electrical energy savings (depending on the type of lumber species,  thickness and initial moisture content) is between 30% - 50%.
A reduced air speed applied during drying can lead as well to quality improvement of the lumber, without prolonging the drying times.
Non-binding example for 3 fan motors per 3KW (9KW) With a 30% energy saving:

30% energy savings = approx. 3 KW / h x 0,14 € / KWh (estimated) x 24 hours x 200 days (operation) = € 2.016, saving / year! (See also the enclosed graphic - "red and black characteristic" - as an example).

Download the brochure with an overview of the advantages.