how many fans for white oak in Nyle l200

[forrestM]

Hello,

I am about to dry about 1800 bdft of white oak 1x6 from green to 12%. I have a Nyle l200M and I have 3 fans in my kiln chamber. Should I use less than 3 fans for green oak? I have the option to turn off the center one, or turn off both of the outer ones. 

thanks,
forrest

[YellowHammer]

Generally, with hardwood, it's a good idea to stay in the 100 to 150 feet per minute range,  but in reality, the fan speed isn't as important as not exceeding the max allowable drying rate for 4/4 white oak, which is about couple percent per day.  So it's important to keep the moisture in the kiln and slow the drying process, so no leaking vents, door or anything.  Also, keep the temperatures very low, 90F until you get down into a semi dry level.  

High fan speeds will remove moisture very fast, but it's still important to get good air circulation.  

[scsmith42]

Generally, with hardwood, it's a good idea to stay in the 100 to 150 feet per minute range,  but in reality, the fan speed isn't as important as not exceeding the max allowable drying rate for 4/4 white oak, which is about couple percent per day.  So it's important to keep the moisture in the kiln and slow the drying process, so no leaking vents, door or anything.  Also, keep the temperatures very low, 90F until you get down into a semi dry level.  

High fan speeds will remove moisture very fast, but it's still important to get good air circulation.  

What Robert said above.
I've found that number of fans required varies with sticker thickness and how well the kiln is baffled. For 1800 bd ft, I'd probably run two, but would check the airflow to verify.
Years ago either Joe Denig, Don Lewis or Dr Wengert ( I think that it was Gene) taught me the "handkerchief method" for checking air flow. With doors closed and the kiln fully baffled, hold a clean handkerchief between your fingers close to the discharge side of the stack. A 3" deflection at the bottom is equal to around 200 - 300 FPM air flow, which is what you usually target inside a kiln. A 1" deflection should indicate around 100-150 FPM as recommended by Robert above.

[forrestM]

Is there a time during the drying process where it is safe to increase the fan speed? Like once you've hit 30 percent or 20 percent mc?

[scsmith42]

Once you are below 25% Mc it's hard to damage the lumber. 

[Mhaaland]

Can fan speed be varied by using some sort of a potentiometer switch?

[YellowHammer]

Air velocity effect on drying decreases as the wood surface dries. So you could increase the fan speed if you like.  The easiest way is to simply switch some of them on or off.

Or equally easy is to increase or decrease your baffling and let the flow blow around the stacks and not through them. 

[GeneWengert-WoodDoc]

Today you are drying oak, but next year maybe yellow poplar or basswood or ??  For some species you need more air flow than for oak.

A variable speed fan system is well over $10K.  So, consider having a fan motor and fan shaft with two sets of two different sizes of pulleys (sometimes called a sheave instead of a pulley) so you can imagine adjust the fan speed.  Small pulley on motor and larger on fan shaft means slow speed; larger pulley on motor shaft and smaller on fan shaft means faster fan.  Every fan has a maximum rpm rating that must be adhered to.

[scsmith42]

Today you are drying oak, but next year maybe yellow poplar or basswood or ??  For some species you need more air flow than for oak.

A variable speed fan system is well over $10K.  So, consider having a fan motor and fan shaft with two sets of two different sizes of pulleys (sometimes called a sheave instead of a pulley) so you can imagine adjust the fan speed.  Small pulley on motor and larger on fan shaft means slow speed; larger pulley on motor shaft and smaller on fan shaft means faster fan.  Every fan has a maximum rpm rating that must be adhered to.

Gene, what about using 3 phase fan motors with VFD's?  My L200 uses 1/3 hp fan motors, and a VFD that size is less than $300.00