Kiln search ideas

[Firewoodjoe]

I've read many old post on kilns and haven't really found what I'm looking for. I want to dry 5 face cord (4'x8'x16")  once a week. Just for the fall and winter months for selling at that time. I can't stock pile hundreds of cords for a year or more. So I'm thinking like a shed with a wood heat source. And I have my wood boiler going also. Anyone do one with a boiler yet?

[GeneWengert-WoodDoc]

One advantage of building a "special" building that is a kiln is that it becomes a piece of equipment and so that has some tax advantages.  It has to be a kiln all year, although you can park stuff in it in the summer, etc.

Due to the amount of heat used, it is best to use an insulated building and maybe some small fans to stir the air and some vents to exhaust the moisture laden air.  In fact, how about a couple of old reefer trailers.  With the wood on pallets and in bins (pieces randomly within the bins), it should be easy to load and unload.  Probably would not even need a building permit...but it is a  piece of equipment and so treat it like that.

[Firewoodjoe]

Thanks gene! Yeah I'm just thinking small like a 10x12 with a roll up door. And put pallets of split wood in it. Using my wood boiler my register in my house will be 114 before it shuts off. That's using 74 air for a cold air return. (About) So it should grow to be hotter in the kiln. I'm hopping 150 or so. Is that warm enough to dry with a fan?

[GeneWengert-WoodDoc]

Why should it be hotter in the kiln?

[Firewoodjoe]

My boiler runs 180 and if the cold air return just continues to grow in temp then the heat coming off the heat exchanger should grow with it. I'm basically pulling about 40 degree diff heating my house. 74 cold air return and 114 at the register. I would think if the cold air goes up to 100 (inside the building) then when that passes through the heat exchanger and picks up more heat from the 180 water then the air exiting should be 40 or so degrees hotter. Or don't it work like that?

[GeneWengert-WoodDoc]

The return will be quite humid if the wood is drying.  So, you would want to exhaust it.  Now
Five cords of oak weighs about  25,000 pounds and will have about 8000 pounds of water to evaporate which requires about 8 million BTUs at 100% efficiency.  To carry away 8000 pounds of water in a week will require a large amount of air exchange with the outside.  You will need a good size exhaust fan.  Now this exhaust will add about 3 million BTUs plus building heat losses about 2 million.

Ok?

[Firewoodjoe]

Ahh I didn't think about the moister in the return

[Den Socling]

Isn't it good having Gene around.

[beenthere]

Isn't good having Gene around.

??

[thechknhwk]

Couldn't you run some dehumidifiers in there as well as an exhaust.  That way you could exhaust less and lose less heat as well as the DH's creating heat too.

[GeneWengert-WoodDoc]

I have seen DH firewood kilns indeed, but do not know the operating costs.  Usually DH electricity is higher than wood or natural gas fuels, all things considered.  But DH is so easy.

Now, 8000 pounds to evaporate is 8000 pints.  Three "90 pint a day" home DH units will take 30 days and will use about 40 kW per day at $.15 per kW.  The bottom line is $60 of electricity for the DH per cord.  When there is an existing burner (no capital cost) using wood or natural gas, the energy cost would be under $10.

[Firewoodjoe]

I think a half propan tank is looking better. Just feed its lots of scrap and exhaust moister as needed

[5quarter]

Isn't it good having Gene around.

Indeed.
Gene...I've seen firewood processors that claim to take a cord of firewood from green to stove ready dry in 24hrs. I wonder how much energy it would take to dry that fast? It seems that unless you're burning wood to dry wood, that the energy cost would take a huge bite out of any profit made from selling it.

[GeneWengert-WoodDoc]

A cord of beech weighs 5000 pounds green.  It will have about 2000 pounds of water and 3000 of wood.  At 20% MC, the green cord will weigh 3600 pounds.  It will have shrunk, so if it is an air dried cord, then maybe 5% more wood will have to be added, so an air dried cord at 20% MC will weigh 3800 pounds about.

To evaporate 1400 pounds of water will require about 1.5 million BTUs.  Then add building losses and vent losses (and ice melting and heating cold wood to the kiln temperature) will mean about 3 million BTUs total. To dry in 24 hours, the burner would have to supply up to 0.2 million BTUs per hour...easy to do.

If you had air dried wood available for heating, a dry cord of beech supplies about 18 - 20 million BTUs per cord of USEFUL heat, so it would take about 1/10 cord of air dried wood to dry a green cord. So, if you sell firewood at $150 per cord, wood fuel cost would be $15 to dry the wood.

Of course, if the wood is air dried so that kiln drying is 20% of the time for green wood, the energy cost is also reduced proportionally to $3 or $4.  In other words, air drying for a month or two actually saves $12 per cord.  That is, air drying makes money.  And keeping the rain off while air drying also saves.

Again, using electricity (even with part time DH), the electrical energy costs would be four or more times larger.

It is not a question about if it will work, but it is the cost.

[CRThomas]

The return will be quite humid if the wood is drying.  So, you would want to exhaust it.  Now
Five cords of oak weighs about  25,000 pounds and will have about 8000 pounds of water to evaporate which requires about 8 million BTUs at 100% efficiency.  To carry away 8000 pounds of water in a week will require a large amount of air exchange with the outside.  You will need a good size exhaust fan.  Now this exhaust will add about 3 million BTUs plus building heat losses about 2 million.

Ok?

My kiln is about 65 degrees on my NG furnace after I get it up to tempture I go back to pilot light and thats all but I am drying Ash firewood only later

[glassman_48]

Gene,
When I first started going to the logging shows around us the guys selling the "bagging systems" for firewood told me that you can take green wood cut and split into the bag and it would be ready to burn in 40 days.  I have always had a hard time believing that, and I have experimented and asked my friends to take some of my 40 day wood home and they cant seem to tell a difference.  My bagging system is the one from hakmet in canada.  An aluminum frame that sets on a pallet and you hang a mesh bag in it and fill it with wood and tie off the bag and remove the frame.  I know the secret is to having the wood not stacked, just put in randomly so the air can get to it from all 4 sides and bottom.  Still doesnt seem possible, I will get a moisture meter and check it and post my results.  Last winter I would cut and bag wood whenever I had the chance and set it aside and I would sell a pallet of eco bricks with 3 bags of wood in my dump trailer.  Last winter was so tough to get wood that no one complained, I tried to keep the bagged wood at least 40 days and warned the customers what I was doing. 

[beenthere]

that you can take green wood cut and split into the bag and it would be ready to burn in 40 days

Getting the wood to just burn and getting the most heat from the wood while burning it are two different things. IMO

Yes, one can burn green wood, or wood high in moisture content and wood where the ends are dried and cracked. But to get the most heat from the wood, it should be in the 12-15% moisture content range or drier.

[GeneWengert-WoodDoc]

BeenThere has the same two comments that I was going to make...it is about the definition of terms.  The difference in energy between freshly sawn and well kin dried is no more than 15% more useful energy and about 30% to 45% less weight and about 10% shrinkage.  Plus, all insects and their eggs would be dead if you heat the wood to over about 130 F.  Note that creosote is formed as a result of how the burner is run and not how the wood is dried.

[glassman_48]

beenthere,
I have had a "problem" with the 40 day thing also.  I leave mine bagged much longer, like I said when I get a moisture meter I will post my results.  I know a lot of people really dont care what they put into their stoves as long as they can keep the fire going.  Gene, I cleaned my chimney last year and then burned nothing but "eco bricks" compressed firewood bricks that are supposed to be 6 to 8% moisture content if I remember correctly.  This spring I took the stove pipe out and there was less than an 1/8 in of very fine creosote on my stove pipe.  I kept the damper open enough to keep a steady fire the damper was open about 1.5 to 2 notches on my pull knob that operates the draft. The draft notches go to 6 on my stove so it was less than half way open.  Thanks for posting all this good info,,,,,,,,,,,ed

[CRThomas]

beenthere,
I have had a "problem" with the 40 day thing also.  I leave mine bagged much longer, like I said when I get a moisture meter I will post my results.  I know a lot of people really dont care what they put into their stoves as long as they can keep the fire going.  Gene, I cleaned my chimney last year and then burned nothing but "eco bricks" compressed firewood bricks that are supposed to be 6 to 8% moisture content if I remember correctly.  This spring I took the stove pipe out and there was less than an 1/8 in of very fine creosote on my stove pipe.  I kept the damper open enough to keep a steady fire the damper was open about 1.5 to 2 notches on my pull knob that operates the draft. The draft notches go to 6 on my stove so it was less than half way open.  Thanks for posting all this good info,,,,,,,,,,,ed

When I dry my Ash Gene if the ends are 8 percent and I split a piece from the middle it is about 14 to 15 percent Later

[glassman_48]

I am definitely going to have to get a moisture meter, this has really got my interest  up on my bagged wood.  If anyone is going to the pigroast this weekend and has an extra one for sale please bring it and I will give some money to the forum for the sale.   Then I will bag some wood for 40 days and post the results.