Solar kiln w/ aux. heat not drying, any ideas?

[Kelvin]

I posted this problem on that other sawmilling site, and haven't figured out what is happening.  It doesn't make any sense.  Here is the known facts
4/4 quarter sawn oak went into kilns 3 months ago here in central michigan where there is no sun in the winter to warm the lumber. (solar kiln, gene wengert design)  1 month ago i built and added a woodburning furnace to heat kilns with.  I have two solar kilns side by side.  This is important.  I have two meters in each kiln, so i don't doubt my readings.  The outside temps are 10-20 degrees.  I can raise the temps inside the kilns to about 90 degrees peak temp, at which point the RH is 22%.  My fans in each kiln come on at 55 degrees.  The temps are back to outside temps by morning when i start the fire again.
The furnace draws air from kilns and pumps it back in.  No outside air in loop.
The lumber in the kilns has stayed at 20-25%MC measured with a wagner L606 pinless meter after planing outside to account for possible condensation.  Lumber sawn at the same time, that is still air drying outside is 15-18% MC.  
I know i should not have put green lumber in kilns in NOV in michigan, but i thought they would at least do better than outside.  WRONG!
The only thing i can think of is that the lumber core is frozen, and not thawing b/c the heat cycle is too short.  Any other ideas?  MC meter has been tested and works fine.  

[DanG]

Kelvin, I've been following your project with interest. It seems like a solid idea.
I'm thinking you may need to be exhausting some of that air and bringing in fresh air via the furnace enclosure. I'm sure you would fair better if the kiln were insulated, too. I think that is the main reason the "Perfesser" doesn't advise using auxiliary heat in a solar kiln. But, you don't have a solar kiln, right now, you just have a conventional kiln that isn't very efficient. Maybe you could install some sort of insulated baffle over your stack, so you don't have to heat the whole building. You also gotta ask yourself if that furnace is big enough to run both kilns at once. Could you  shut one of them down to see if it improves the performance of the remaining one?
Keep up the good work! You are doing valuable research, and we are all going to school on your efforts. I think you are close to a workable solution, but you just gotta keep making adjustments till you hit the right combination.

[OneWithWood]

Kelvin,
I agree with Dan.  You need to exchange some of that moisture laden air with drier air.  That is why the air dried wood is fairing better.  

[J_T]

I too agare with Dan I like your reasearch and been folloeing you an the Proffser rebuttels . Been wanting to cheer you on but only post at home 8)

[cut2size]

I, too have been following this thread on the other forum.  I don't know why there is no outside air.  If you don't vent to the outside the water is staying in the system.  You have to vent the moisture laden air to the outside and replace with drier air from outside or from your furnace to acheive any drying results.  Otherwise the system is closed and can't get rid of moisture.
HTH,
David

[VA-Sawyer]

I was reading this on the other site as well. Just curious, are you exhausting the combustion air into the kiln ?  The burning process creates a lot of moisture.  Had the problem of a space heater in my shop causing all my tools to rust when I ran it in the winter.  Switched to a gas furnace and ducted the exhaust outside. Rust problem went away. Shop smelled better too.  ;)

VA-Sawyer

[Ianab]

Hi Kelvin
Like the others I've been following your experiments with interest.

Just a thought, are you sure the meter is reading the wood mc correctly? (I know you have tested the meter, but maybe something about the wood is thowing the reading off)

I would cut off a sample piece of wood, weigh it on digital scale and then dry it in microwave oven. You can then calculate the exact mc and see if it agress with what the meter is telling you. Dr Gene has a note on using microwave oven to work out mc , make sure you dont set fire to the sample
Ian

[EZ]

Being the temp is around 80 to 90 degrees, you probably have to much air flow also. BTW, nice job on the kilns and furnace.
EZ

[Wes]

I think That I would break the loop, The outside air is very dry this time of year,but you may have to preheat the intake air another way,possibly with some extra ductwork around your furnice.

[Kelvin]

Michigan is very humid outside in the winter.  outside is 50% RH or better.  Inside my kiln is 22%RH already.  I believe if i vented i would loose all my heat, and RH would go up?  i know that warm air holds more moisture, so that cold air at 50% rh warmed in the kilns will drop, but to what?  Inside the kilns are dry as can be i would say.  I think the lumber is staying frozen in the core.  What do you think?  I will test w/ micro right now, and repost the results.  The wood feels dry when i pick up a 4/4 oak board and it feels light.  It doesn't make any sense to me.  I'll test this morning.  Thanks for the support guys.
Kelvin

[Frank_Pender]

Kelvin, I

[Frank_Pender]

Woops, sorry Jeff.  Anyway, Kelvin I use a heat exchanger in heating my kiln.  I have a Taylor hotwater furnace I use all year round for drying.  I also us an Ebac 800 to remove the moisture.  Now, I know that the Ebac cannot remove the initial moisture that is created from the heat exchange but I have some very nice hot steam in the kiln while drying is occuring.   I got into it with the same fella a year or two ago over the system I am using and I just gave of on trying to discuss the issue.  I have found that the way in operate this unit, I have great success.  
 
I an now drying my first load of Fir, be it Grand fir, 1" x 6" x 12'.  It will come out this weekend.  I just kicked up the temp to 165*, yesterday, to run for the next 4 days or so.  I run the same for hardwoods but for 4 weeks and not two, due to density of the species.  
So, I guess what I am sayingis, you might have to have a system in place that causes the temp to rise higher, like an exchanger of some sort.  
I have probably just juddied the waters.  Hope not.

[Minnesota_boy]

That load of wood has a lot of moisture in it.  When you heat the wood chamber, some of the moisture will evaporate from the wood and begin the drying process, but you need some way to get rid of that moisture.  That mean replacing some of the moisture laden air with drier outside air.  If you don't bring some outside air into the system, the water is trapped in your closed loop and will simply condense on the coldest surface it finds when the kiln temperaturedrops at night, most likely on the wood that has a frozen core.

The outside air has a high relative humidity.  That humidity is relative to the temperature, so when you heat it as you bring it into the kiln, the relative humidity of that air will go down, and it will be able to pick up the moisture from the wood and help it out of the kiln as warmer, moisture laden air.  When you remove the moisture like this, it will not return at night (not much anyway) so the wood will continue to become dryer with each warm up/cool down cycle.  You have to control how fast the air is exchanged to limit how fast the moisture is removed to avoid degrade on the surface of the wood.

[HORSELOGGER]

Kelvin, I'm wondering about your readings. Was the lumber that is air drying outside also oak? I would be very surprised to see fresh sawn oak got to a 15-18% reading in late fall /winter. Is anybody around with a pin type meter that you could use?