Why Alent Dynamic® outperform the competition
The timber is subjected to brief, harmless stress periods and in between longer periods of rest or stress relief. Almost as repeated conditioning sessions. The drying process is enhanced by "pumping" that maintains a high moisture migration inside the timber without building up dangerous tensions. Water evaporates from the wood surface even during fan stop, but then taken heat from the wood rather than from the air. Wood surface is cooler than the interior of the timber, and this helps to increase moisture migration towards the surface. It is the vapor pressure that drives moisture migration. During the stop there is an adding force to the moisture migration due to the temperature gradient in the wood and drying is faster.
Has there been any independent comparison between Alent Dynamic® and reduction of fan speed?
Non-official comparisons have been made and more are to come. Many of our customers have done comparisons before they ordered Alent Dynamic®. Others have taken note of fellow studies and subsequently invested in Alent Dynamic®.
Do you have to add more heat when the fans are shut down?
No, despite that the fans are shut down half of the drying time with the Alent Dynamic® method. The energy saved do not need to be replaced with heat from the boiler. Just like our studies predicted we can now show that our customers are saving heat with Alent Dynamic®.
"I have noticed that during this time, the quality has improved significantly, but especially so has the heat consumption decreased by over 10% and it pleases me. All savings are great."
–Stefan Edström, owner Brännfors Träförädling. Uses Alent Dynamic® in four klins.
This is how it works;
We can not escape that the water from the wood has to vaporize from the wood surface and the evaporation energy. A normal drying rate in a chamber dryer, 120 m3 of pine, 38x110 mm, 75-12% M.C. at -5 ° C outside temperature, draws more than 35 MWh of thermal energy. The evaporation part is almost 22 MWh. Warming pulls over 6 MWh and heating of fresh air just over 5 MWh. The remaining heat requirement is largely dependent on the building. Heat conduction through the door, walls, ceilings and floors may be 1-2 MWh. Large leaks and poor insulation require additional spraying that consume several MWh. The conditioning draws energy for evaporating of spraying water.
Alent Dynamic® has several advantages that reduce heat consumption:
+ Leakage is reduced when the fans are shut down
+ Heat loss through the walls, ceilings and especially port is substantially lower when the air is stationary
+ additional spraying is not needed with Alent Dynamic®
The fan motors adds no heat when they are stopped but you do not need to fully compensate for this. If you are drying to low wood moister content in an old kiln, you are saving heat with Alent Dynamic®.
Do you have to compensate for fan stop with higher timber temp or higher psychrometer?
No, Alent Dynamic® is based on intervals between rapid venting and rest. The timber average temperature is rather lower when drying dynamically. Psy is higher during the short active phase of the pumping but the long rest periods reduces cracking.
Do the fan motors shut down during the process? How does that affect the engines?
Yes, experiences show that the motors life span extends, rather than shortens. All indications are that life expectancy is increasing. The fan motor shut down in intervals of 10-60 minutes. There will be no extra stops for reversal. During these stops the internal motor temperature is decreased and it leads to a longer life. There is no risk of condensation on the engine even during long pump stop. To get condensation the motor temperature has to drop below the dew point temperature in the chamber and it is an impossibility, unless the engine is equipped with active cooling.
Why can you have a higher drying temperature when using Alent Dynamic®?
Since the fan motors are given time to cool down during 10-60 minutes when reversing, you can keep a higher dry temperature during drying without any harm to the motors. The set point in the dry temperature can be slightly higher than the corresponding temperature for conventional and “slow-down” drying methods because the average temperature in the timber during a cycle is a few degrees below the set point when using Alent Dynamic®.
Do you need to prolong the drying time when you stop the fans 50% of the drying time?
No, the theory indicates and practice shows that the drying time is shortened. When drying to low moister content you can save days.
Does drives save as much electrical energy as Alent Dynamic®?
No, far from it. Drives are normally running at 30-50 Hz when drying to lower moisture contents. That compares to Alent Dynamic® which stops the fans 50% of the drying time. In addition, drying time is decreased with Alent Dynamic®. When reducing the fan speed by drives you have to prolong the drying.
Will the moisture content in the middle of the plank get higher with Alent Dynamic®?
No, our follow-up surveys rather suggest a lower gradient.
How much does it cost to install Alent Dynamic®?
Will you save heat with Alent Dynamic®?
During the rest periods the heat valve is closed and the air in the dryer is stationary. Leakage from the dryer decreases. Convection, i.e. heat conduction through walls and ceilings, decreases due to stagnant air layer next to walls and ceilings. Alent Dynamic® does not need spraying and it can save large amounts of heat, especially in older kilns with leakage. Conventional and “slow-down” drying methods schedules spraying can easily consume several MWh of heat.