Kiln drying help....fan placement

[Bnewman712]

Hello I have a wood mizer k150 and about to start a first load. Can anyone help me on fan placement? Should I have them at the front blowing the air Thur the stack or on too? Thank you

[WDH]

Auxiliary fans should be in the back on the shelf that sits below the fans built into the dehumidification unit.  They should blow toward the door (front).  Here is a pic of mine.  IOn addition to the two fans in the unit, I have two on each side between the unit and each wall.



 

That is Forum member scleigh standing in front.  On the back wall of the kiln you see the unit, the shelf, and the four auxiliary fans on the shelf pointed up a 45 degrees to blow air over the top of the baffle to the front of the chamber.  There is a 10" diameter hole in the shelf under each auxiliary fan so that they can suck air from through the wood layers and blow it back to the front.

[GeneWengert-WoodDoc]

Many kilns mount the fans about 6 feet from the back wall, and hanging straight down from the ceiling (but as close to the ceiling as possible), facing the front doors. They blow frontward toward the door, although some kilns have reversable motors and reverse direction every two hours. To prevent short-circuiting the air (the air circulates in the kiln without going through the lumber piles), the fans have a vertical baffle with holes for each fan.  This solid baffle, made of plywood often, is in contact with the ceiling and fan housings and runs vertically down from the ceiling from the left wall to the right wall.  The baffle hangs down from the ceiling and extends only a few inches below the fans, so there is a gap between the bottom edge of the baffle and the top of the lumber pile.  This gap is filled with canvas (or other flexible material) to block the gap and force all the air through the pile.  Canvas, if long enough, allows you to have varying pile heights from load to load and still easily block this top gap, if it is small or large.   Plywood or canvas baffles are also used to prevent air loss on the edges of the piles, between the ends of the stack and the walls.  Note that some kilns do not have the extra space between the top of a pile and the ceiling, so the fans are moved to the rear space between the edge of the pile and the rear wall.  WDH discusses this option.

With vertical fans, some people will put a small 45 degree baffle in the joint between the ceiling and front wall; this is to help the air "turn the corner" and blow down the front and into the lumber pile.

In all cases, to be legal and safe, the fans should have a lock-out feature...you have your own padlock that you put on the main switch so that it is impossible to turn the fans on except when you remove the lock and you have the only key.  Kilns should also have two exits with the ability to open the exit door from the inside.  I also suggest having some lights inside...helps when working in the kiln at night.

When the fans are turned on the first time for each load, there can be quite a bit of dust blowing around, some people like to turn on the fans before the big doors are closed for this reason...blow the dust out.

WDH's picture reminds me that you want a good method of securing the big doors when open so that a big gust of wind does not blow them around and damage them or you.

Finally, if the fans are positioned so that they blow directly on to the edge of the pile, we need about 6 feet between the fans and the edge of the pile to allow the air to "spread out" from the fans to cover the entire edge of the pile uniformly and not just blow right in front of the fans.

[WDH]

With the KD150, there are two fans built right into the unit.  Therefore you have to build a shelf around the unit to expose the fans above the shelf.  This separates the fans which pull the air into the condenser from the condenser, forcing the air to flow past the condenser fins.  This air is blown out at a 45 degree angle towards the side walls.  The auxillary fans then blow this air to the front of the chamber where it can be pulled into the wood layers to evaporate the water from the wood.

The KD250 does not require a shelf, so most of the time a fan shroud/bank that hangs from the ceiling is utilized like Dr. Gene describes.

[Bnewman712]

Thank you all for the help. I will most likely need more soon lol

[GeneWengert-WoodDoc]

WDH is correct, but the system I described, with the baffle will actually work well with the KD 150, plus the top of the piles will benefit from using a piece of plywood on top to help the air go through the lumber piles.  Not a big deal for air dried lumber however.

In many kilns, there is a flat, horizontal shelf that begins at the back of the lumber pile and runs to the fans.  It is full width of the kiln. Sometimes it even runs to the edge of the pile near the front door.  This flat shelf is called the fan floor.  In essence, a small room with openings front and back is created in the upper part of the kiln where the fans are located.  A flexible baffle runs from the fan floor to the top of the lumber pile, usually in the rear section of the kiln, as previously described.  I have seen kilns with a second baffle from the fan floor to the lumber pile in the front.  Such an arrangement guarantees 99% of the fan air goes through the lumber piles, but it is more extensive and expensive than the smaller shelf in the rear that WDH mentions.

[Bnewman712]

Is there a thing suck as too many fans and airflow ??

[YellowHammer]

Yes, too much airflow can cause significant problems depending on species and moisture content.  Same with not enough airflow.  
Also, it's just as important to get even airflow, to prevent wet spots in the stacks and also to prevent stagnant dead spots in the kiln chamber itself, which will cause mold.

[GeneWengert-WoodDoc]

When over 25% MC, too much air flow (over 300 fpm) can cause too rapid drying.  This would really be an issue for oak and other check-prone species, and especially over 45% MC.  On the other hand, high air flow (600 fpm) for ash, maple and eastern white pine and some other species is desired.

Appreciate that doubling air flow increases the electric bill by four times or as much as 8 times.  So, excessive air flow can blow your profits away.