Where is the best placement for extra kiln fans?

[Glenn1]

My Nyle L53 is coming along as I now have the walls and trusses in place.  My next step is adding  additional fans as suggested by WDH and Yellowhammer.  I ordered 2 fans that have been previously suggested by WDH.  Just an afterthought but are 2 enough?  I think I read that Yellowhammer added 6 fans.  Thank you for the suggestions.

Below is a diagram that comes from the L200.  I may be mistaken but I think the configuration should work with my L53. 

Should I put the fans in the same location as those shown below or should I have them closer to the end walls?

Your thoughts would be appreciated.

[scsmith42]

I would use the same location as in the drawing follow Danny's advice!

[WDH]

The set-up for the L53 and the L200 are very different.  The L53 has two fans that are a part of the dehumidification unit itself, and they blow out at a 45 degree angle on the top.  The L200 has separate fans that are not part of the unit itself.  Here is a pic of my L53 set up.  The dehumidification unit is in the center, and you can see the two 45 degree angled sections of the top where the fans are housed.  You build a table over the the top of the unit, leaving the fans exposed above the table.  The table serves as a platform on which you lay the baffles to force the air through the layers of wood. 

Based on what Yellowhammer had done and perfected, I added two additional fans in corners, set at 45 degrees blowing toward the front of the chamber.  You can see the corner fans in the pic.  Here is the pic with the unit in the middle with two fans, and the two extra fans in the corner, all above the baffle table.



 

Here is a view with the baffles laid over the table, forcing the air to the front of the chamber, and then through the layers of wood.



 

Since then, I have added two more fans, again based on the fine research by Yellowhammer.  They are located halfway between the corner fans and the dehumidification unit.  So there are now 6 fans, two in the unit, one in each corner, and one halfway from the corner to the unit on each side. 

[GeneWengert-WoodDoc]

A couple of points to keep in mind:
First, fans and the electricity to run them are expensive.  For the desired air flow, two fans that deliver the correct cfm will use less electricity than four fans giving the same cfm.  The reason is efficient of a fan, friction, etc.

The shroud around the fan is really important.  To maximize air flow the shroud should be very close to the tips of the blades.  further, the inflow and the outflow sides should be curved (like the carb in an old car, if you are old enough to recall that, or like the bellow of a trumpet)

Plug all leaks.

The higher the air flow, the faster wood will dry, so spending money for more fans will increase drying speed, BUT ONLY if the MC is above around 40% MC.  At lower MCs, the fan speed is not very important, as we are waiting for the water to wiggle its way to the surface and not for the air to scrub the moisture off the surface.  (So, a DH unit used for air-dried lumber would not benefit from having more fans.) 

Note that going from 200 fpm to 500 fpm will approximately double the drying rate for very wet lumber, but the electric costs are at least four times more.  Of course, some woods like oak may not like being dried faster.  But, is drying faster worth the large extra cost for electricity?

Air flow tends to move fairly straight off the fan and does not spread out unless there is something that blocks the air flow.  So, with the DH unit in the center, you need to have something that will push the air toward the sides (a baffle) and then have two fans for every 16' of lumber length.

To determine the CFM that you need for wet lumber (two fans without enough cfm are not that useful), use the following formula and then add about 25% more for air leaks. 

CFM = (sticker thickness in inches /12) x air velocity desired x number of sticker openings x length of lumber in feet.
Example:  for 3/4" stickers, 300 fpm desired, 25 layers giving 26 openings and 16' lumber,
cfm = (3/4)/12 x 300 x 26 x 16' = 7800 cfm and then add 25% to get 10,000 cfm.  With two fans, that would be 5000 cfm each.

Of course, if the air flow dries the wood faster but the DH compressor cannot remove that much moisture, the actual RH will be quite a bit higher than what you want and drying will not be as fast.  So compressor size is also important.  Basically, for wet wood, a compressor that is running 100% will not benefit from higher air flow as the compressor is already removing the maximum amount of water.

[WDH]

I have 600 BF of cherry in the kiln now.  4/4 (1 1/8") and 9.5' long with 1" stickers.  Using the formula:

1/12 x 300 x 9.5 x 18 x 1.25 = 5344 CFM desired. 

With the 6 fans at 800 CFM each in my kiln, that is 4800 CFM. 

[GeneWengert-WoodDoc]

Excellent

[Glenn1]

I have 600 BF of cherry in the kiln now.  4/4 (1 1/8") and 9.5' long with 1" stickers.  Using the formula:

1/12 x 300 x 9.5 x 18 x 1.25 = 5344 CFM desired. 

With the 6 fans at 800 CFM each in my kiln, that is 4800 CFM.

Hi WDH,

What does the last number (1.25) represent?
Also, what was the moisture content of the cherry when you put it into the kiln?

[WDH]

The 1.25 is to add the 25% for air leaks.  The cherry was sawn on Saturday afternoon a week ago and it went into the kiln on Sunday morning, so it was green right off the saw. 

[YellowHammer]

I think I read that Yellowhammer added 6 fans.  Thank you for the suggestions.

I have a total of 6 fans, 2 in the unit, 4 in the horizontal baffle.

I have also added 4 halogen work lamps, 500 watts each, weatherproof, to augment the 1kw heat strips.  These cut my sterilization temperature ramp time very significantly.  These work much better that a heater as they will not rust or corrode, and have easy to replace heater elements (light bulbs).

Also, since the air inlet is on the front side of the unit, and the unit is fairly high off the ground, there is an airflow dead spot at the bottom of the kiln chamber under the pedestal, which will cause problems when drying wet white wood.  So after discussions with Nyle, I ended up cutting an additional air inlet on the bottom of the kiln unit, added an additional air filter, and have cleared out the stagnant spot.  This issue can also be solved by adding more fans to blow out the stagnant area.
YH

[Glenn1]

I think I read that Yellowhammer added 6 fans.  Thank you for the suggestions.

I have a total of 6 fans, 2 in the unit, 4 in the horizontal baffle.

I have also added 4 halogen work lamps, 500 watts each, weatherproof, to augment the 1kw heat strips.  These cut my sterilization temperature ramp time very significantly.  These work much better that a heater as they will not rust or corrode, and have easy to replace heater elements (light bulbs).

Also, since the air inlet is on the front side of the unit, and the unit is fairly high off the ground, there is an airflow dead spot at the bottom of the kiln chamber under the pedestal, which will cause problems when drying wet white wood.  So after discussions with Nyle, I ended up cutting an additional air inlet on the bottom of the kiln unit, added an additional air filter, and have cleared out the stagnant spot.  This issue can also be solved by adding more fans to blow out the stagnant area.
YH

Since you have done all the hard work, it would be foolish of me to try to re-invent the wheel.   :D  So, let me ask where you mounted the 4 halogen lamps?  Was the 2nd inlet made to the same dimensions as the original?

Besides the additional fans, lamps, and new inlet, did you make any other significant changes?  From what I remember, you leave the wood in the kiln for 24 hours after the sterilization cycle to "condition the lumber"? 

Thanks for all your help!!

[YellowHammer]

I placed the 4 halogens on the shelf, each directly adjacent to a fan so that the air would blow over the lights to heat the air and keep the lights relatively cool.  I turn them on to accelerate the pre heat cycle, as well as for sterilization.  Otherwise, they are off, as the kiln itself creates enough heat, and in many cases, excess heat that allows me to open the vents a little and dump excess moisture so increasing the amount of moisture removed, above the kiln capacity.

The rectangular opening I cut on the bottom off the kiln is approximately half the size as the one in front, and I used a replacement cook top hood filter, made of an aluminum weave, from Lowes.  Its very important to keep the filters clean, and make sure you have no possibility of debris from the kiln getting to the heat strips.

Use a 5 gallon bucket, preferably marked with gallon increments, outside, under the condensate discharge, and inspect and empty this daily.  This will give you a direct measurement of the amount of water coming out of the kiln and after awhile you will be able to quickly judge how the load is doing, how much water is removed, and general kiln performance simply by looking at the condensate drip rate and how much is in the bucket.  This will keep you from having to open the kiln doors every day to inspect the load.  You will know exactly how much water is coming out because it is in the bucket. 

Its very important to have effective door seals, absolutely airtight, so spend the extra effort to get them right.  If not, your will be paying for a lot of wasted electricity.  In order to close the doors, the very best I have come up with is to use trailer cam lock door hardware, like used on cargo and semi trailers.  They have enough locking force to compress and hold the seals tight, and you can get them online for about $30.  Here's a picture of one of the kits without the  steel bar, which is a piece of pipe welded to the cams. 


 

I also used aluminum tape on the inside of the doors where the seals fit to give a smooth surface for the rubber to contact.  You can see it in this in the picture on the right side door.


All the wood is placed on 4x8 foot pallets, 10 layers of wood per pallet or 320 bdft per pallet, and a maximum of three pallets per load or 960 bdft feet.

Using pallets really cuts down on the labor, simplifies and allows direct loading and unloading with a forklift, and makes it convenient to use partial loads.  The pallets are set so the runners are directly under the stickers.  Lots of other tricks, but these'll get you some good mileage.
YH

[WDH]

7 Stickers on 8' lumber is s sticker spacing of 16".  Really helps keep the lumber flat.

[Glenn1]

Thank you WDH and YH for allowing us to share in your experiences and your expertise.  I hope there are others just getting started with their kiln and will benefit from your help.  I have the metal siding and roofing on order and should be able to dry in the kiln soon.  Then I go to the Syracuse University kiln school in two weeks to learn even more.

Thanks again for both of your help!