solar kiln,fans,ect

[twobears]

I,AM getting ready to build a solar kiln.years ago,my dad build one from the virginia tech plans.it had three wallly world box fans and they where controled by a attic thermstat.
i,ve been looking at the new plans and i don,t see where they control the fans anymore other then turning them off by hand at dark.
am i just missing something or what?? they talk alot about moving the air,ect but,don,t seem to include controls in the plans.
i,am thinking about using a set of attic fans i found at the local lumber yard sturaday.they move 3000 cfm each and come with a thermstat for $47.00 each.
there a single speed fan.i was thinking about adding a timer so they go off at dark and let them come on at a high tempture(sp) i even thought about controling the fan speed.i just wish i had more info on the control of the fans and temp in a kiln.
if you read the plans and info it all seems kinda important yet the plans don,t seem to give what you need to set it all up.
if  i remember right dads kiln kicked the fan on at like 120 degress and off at say 90. i might be wrong but it was something like that.
they did say something about using a humidstat to control the fans but,didn,t give on more info on that.i wish i had more info.

delbert

[Larry]

I set my thermostat to turn on the fans when the kiln temperature rises to 30 degrees over the expected morning low.  When the sun is shining that normally happens around 10AM.  My thermostat operates on line voltage so I installed a timer in series, which supplys juice at sunup and cuts it off at sundown.

[twobears]

LARRY:thanks for the info.thats what i was thinking about. a timer then the fan thermstat and maybe a fan speed control after that.
in the va tech plans/info they talk about tempture,controling the fans,ect but really don,t give any info on doing it.they just say how important everything is..unless,i missed something in all that info..i don,t think i did tho.
i,am thinking about when,it,s stays hot for days the kiln might not cool down at night like it should and the fans could be running 24/7 and drying the lumber way to fast.

delbert

[Larry]

Your right about the fans running 24/7 in the summer...but after dark the humidty goes up to maybe 80-90%.  So if your vents are open the wood doesn't dry at all...and I suppose could go in the opposite direction.  Not good.

[timcosby]

its my understanding that you want it humid at nite to equilize the wood and prevent case hardening and thats why no fans at nite.

[solidwoods]

A solar kiln can ruin wood if you don't know how to run a kiln and if it can't control the Humidity and Temp and its effects on drying.

Read and understand:  Wood and how to dry it,, and Kiln operators handbook.

Dry woods that are below fiber saturation point  for your first few loads.  It's real easy  (compared to wet wood) and will let you get experience with the kiln.

Fans are needed most when wood is  in the wet stages.

Softwoods and bright hardwoods and easy dry woods get a little taller stickers than woods you need to dry a little slower (this is advanced,, you need to know your kiln first)

The rate that the moisture is being removed from the wood is what kiln drying is all about ... not if the box can get hot in the day from the sun.
To control the moisture removal you need to know the difference in the wet and dry bulb readings (wet bulb depression wbd).  The difference is listed on the kiln chart for that wood species, along with temp.

now you can't control temp by adding heat,, just subtracting heat (and moisture with it). 
you must have a way to vent heat and moisture in a way that you know how much is venting and what the effect will be on the wbd.

Most critical times are fresh wet woods until they are below fsp.

The wood on the top of the stack will dry first so know and sample.
Yes you have to take samples according to the kiln operators handbook or use a mechanical sampling device like Kilmotroll or other.