Solar Kiln, Sterilizing ?

[Road Runner]

I'm in the planning stage of building a Va Tech style solar kiln. I have an old elec. range that the oven works in.
Is it possible/practical to build the oven into the end of the kiln to use at the end of drying to sterilize the wood to kill any insects or eggs?  I will build the kiln next to my barn to run power for the fans and running 220 will not be a problem.  I'm also assuming that I'll need to have an additional fan to help distribute the heat from the oven.

[GeneWengert-WoodDoc]

Probably not enough heat energy to achieve the high temperatures needed.  The interior of the lumber must be at 133 degrees F, so the air around the lumber needs to be around 150 degrees or hotter. 

The oven is insulated and maybe can heat inside the chamber this hot in 10 minutes, but heat losses in the kiln are quite a bit larger, plus there is the heat required to heat the lumber itself.

[Road Runner]

Thanks Gene,  I guess I'll scrap the old oven.

[Tree Dan]

Probably not enough heat energy to achieve the high temperatures needed.  The interior of the lumber must be at 133 degrees F, so the air around the lumber needs to be around 150 degrees or hotter. 

The oven is insulated and maybe can heat inside the chamber this hot in 10 minutes, but heat losses in the kiln are quite a bit larger, plus there is the heat required to heat the lumber itself.

Hey Gene, if this oven wont get up to the required temp...What other types of heat could we add to get up the the  150 degree mark?

Cheers

[YellowHammer]

If I was going to do it, I would look at sources of heat that naturally lend themselves or cheap BTU's, and lots of them.  I would stay away from electric heat as too expensive, but would lean toward Wood Boiler style heaters and radiators, assuming I could get the wood for free or very low cost. Maybe even consider propane or fuel oil heat. The idea would be to overwhelm the heat losses of the kiln with inexpensive heat for a relatively short period of time, a couple days or so, during the sterilization cycle.  I would also probably spend some time making sure the space between the two solar collectors is a dead air space, with little convective heat loss.

[69bronco]

Been considering something similar using a woodstove. Was thinking a small lean to addition to hold the stove with the door exposed to the outside. Would be simple enough and surely cheap enough to run. Thoughts?

[Tree Dan]

Been considering something similar using a woodstove. Was thinking a small lean to addition to hold the stove with the door exposed to the outside. Would be simple enough and surely cheap enough to run. Thoughts?

Good Idea :P...I will be back :P

[bkaimwood]

I've had similar thoughts, but figured on using 2 oven elements... I thought of and liked the woodstove option too... One thing to remember is that, if u have an airtight kiln, anything that requires oxygen to burn (everything but electric), and uses air intake from the kiln, will burn itself out due to running out of oxygen...good test if u want to know if your kiln is tight enough.... This is a fact...don't ask me how I know...
Electricity is most expensive, but due to the time and complications involved with other methods, may be the best, as its a short term useage...
Gene .w...could you remind us how long a load should stay at, say 160, once that air temp is reached?

[GeneWengert-WoodDoc]

1.  Will the high temperatures hurt or damage the insulation?  Will the heat damage the fan motors?

2.  This he time required at 160 F to achieve a core temperature of 133 F depends on MC and wood density, but I would guess around 6 hours.

3.  The energy needed to heat the kiln and lumber and then maintain the temperature of 150 or 160 F with the kiln solar collector covered and insulated is probably around 300,000 BTU, but I did not do a detailed calculation to get this, so it is based on experience.    Kiln insulation is a big factor.

4.  The solar kiln is about 50 times larger than a home oven.

[sandsawmill14]

gene would blowing the hot air in from outside source matter as far as  not have proper air flow through the lumber after it has reached the 6-8% as the fan i was thinking of would likely over power the kiln fans or at least have a crossflow that would disrupt normal air flow ??? the fans would circulate the air in the room but i doubt that the flow through the stack as it normally would while drying 

[bkaimwood]

I would think recirculating outside air into a kiln full of lumber kiln dried to 6% for a sterilization cycle would be not a great idea...the heating source will dry it out some, but the important question would be how much?...

[sandsawmill14]

the air im talking about would off of wood fire i dont think moisture would be a problem at 250+ degrees i but i bet gene will know for sure

[GeneWengert-WoodDoc]

Sands,
If you take outside air, heat it to 160 F, you will likely have about 2% EMC (less if the air is hotter), so you run the risk of drying the load further...you may not want that.  Cool the air back to 80 F and you will have the original 65% RH conditions and 12% EMC.  So, when sterilizing lumber, as it is called, you may want to add moisture to the air to get more reasonable drying conditions...about 30% RH or 6% EMC.

[sandsawmill14]

thanks gene i knew you would know

[bkaimwood]

Gene knows everything...thankfully for the rest of us!!! :)

[sandsawmill14]

now if we could only remember all he tells us :-\ :D :D :D

[Tree Dan]

Agree with the guys above...Thanks Gene 8)

Cheers

TreeDan ;D

[GeneWengert-WoodDoc]

Wow.  Thanks indeed.

[plowboyswr]

Now I'm just throwing out an idea here if you want an external heat source how bout this

http://www.outsidewoodheater.com/index.html

Just curious if it could work. Burn chamber is a 55 gallon drum sealed off from a forced air vent system fan doesn't turn on until the heat above the vent reaches a certain temp. Return air pulled from the structure reheated then forced back through main vent. Been looking at a kiln in my future and this idea has been running through my head. :P

[69bronco]

That looks like a great idea to me! Build it big enough to handle good sized slabwood.