L200 capacity questions

[jimbarry]

If it takes 6 days to dry 2 cord from green to 20%MC, how long would it take to dry 3 cord?

For the firewood drying setup we are running with the L200, we dry two cord at a time. The floor space taken up is 17ft x 5ft, stacks are 3ft high in the crates.



 

Tarped on top and baffles to ensure as much as the air is forced through the stack. 



 
(Since that pic was taken we now lay the tarp on the entire top of the crates, this ensures air flow through the stack.)

The 3 overhead fans seem to have little problem pushing air through the stacked wood (air pushing through the 5ft distance of stacked wood).

What I am contemplating is increase from 2 cord to 3 cord. The floor space would remain the same, it's at its limits. So it would have to mean an increase in vertical height from 3ft to 4-1/2ft. I'm thinking the air pressure that is currently being pushed through the 17ftx3ft surface area would decrease as the addition of another 1-1/2 ft of vertical height (50% increase). If my math is right that would result in a 33% decrease in overall air flow. So my question then is, would that mean a 33% increase in drying time? Or longer? 

[KenMac]

It seems reasonable to me that your assumptions are probably close, but the simplest way to determine how much longer it will take to dry an additional cord is to try it once and record the data to make the final decision. 

[K-Guy]

Jim
Add at least one more fan.

[doc henderson]

i think it also depends on if you are at capacity on the DH.  do you measure water output?  any idea the MC of the green wood.  if so, you can calculate the water removed in 6 days and determining if you are at max.  If the water removal is at half capacity, in an ideal world, it may still only take 6 days.  Prob. end up somewhere in the middle. How do you neat the kiln?  can you add additional heat.  you are not worried about drying defects in firewood.  the other issue as you push the cross-sectional area is if you will have some area that is not ideally ventilated, thus the fan suggestion by KGUY.  

[K-Guy]

Doc
Additional heat would speed the warm up but more airflow is important to keep mold from starting.

[jimbarry]

I did measurements early on when we started this process and it worked out to about 180-200L per cord over a 5 day period.

Extra fan makes sense.

Kiln is electric heat.

MC of green wood varies depending on species. Usually its 40-50% for the larger pieces of maple with dark heart. Otherwise 35% is the common numbers we see at the start of a cycle. 

[doc henderson]

I assume he is trying to produce more wood per week as the reason for this question.  I was trying to determine for one thing, if the system is already maxed out.  i.e. it will take 9 days instead of 6.  Or if even in the first days it could do more than it is.  I assume the heat up is part of the 6 days cycle, so faster might reduce time till done.  I agree with more air, nothing to loose until more electric cost, and no further benefit.  what is the engineered max, water out per day or hour?  I am trying to determine if 3 cords will be close to the 6 day cycle, and if not what could help his current setup to do more with less time.  I guess you can see when the RH starts to drop, assuming 100% means more water vapor than the DH can keep up with.  or narrow wet bulb/dry bulb difference.  Jim, how long does it take to get the kiln and contents up to temp? seems you air dry as well, and that should help.

[jimbarry]

This time of year, from a cold start of 34ºF DB



 

26 hours later



 

On average it takes 20 to 24 hours to get up to temp to start the DH. So it's well on its way to drying. 

The previous load I ran last week, I supplemented with a portable salamander heater and a BBQ tank of propane. Instead of waiting the normal 20 or so hours to reach about 85-90 on the DB to start DH process, the bump in heat from the propane started DH in 3 hours. Air was warm but the thermal mass was very cold. The thing I also discovered is once the air temp reached 110ºF the salamander has a safety shut off function. When that first shut off the DB dropped to about 56. I turned the propane heater on again, checked an hour later and air temp had gotten up to 112 but the propane shut off again. I let it run one more time and after it shut off again, I realized what heh safety function was doing so I hauled it out of the kiln. By this time the thermal mass of the contents was up enough to keep air temp about 90 so I let the electric heater do its thing. Overall time frame remained about the same. Actually it took an extra day (6 days total) which I attribute to the really cold start temps.

[Southside]

What do you set the DB and WB values to with firewood?  Guess you don't worry about checking.  :D

[doc henderson]

would radiant heat from halogen work lights heat the wood it is shining on more than the air, and not shut off like the propane.  if you have the electric capacity to run them?

[jimbarry]

What do you set the DB and WB values to with firewood?  Guess you don't worry about checking.  :D

DB set to 125, WB bottoms out at 68 I think. I set it on the first run 4 years ago and haven't looked since. No, not worried about checking. We call that character  But I have thought about case hardening, I don't know if that comes into play for short lengths like firewood. No one's ever complained, so there's that.

would radiant heat from halogen work lights heat the wood it is shining on more than the air, and not shut off like the propane.  if you have the electric capacity to run them?

Capacity is there but I don't know if that's an even trade off with respect to energy created versus energy consumed.

[doc henderson]

casehardening only matter if you want to cut it on a table saw, and make a coffee table.

wondered if the radiant heat would heat the wood rather than the air.

energy is neither created or destroyed.  we can be more or less efficient however in getting a job done.

If you do 2 cords in 6 days then that is 3 days per cord.  If you get 3 cords in 6 days the you gain a day per cord at 2 days per cord.  anything less than 9 days for 3 cords is saving time.  It may take just as much energy per cord, but I would guess you will save a little.  and if time is money, and you have more sales to get out, or get more per kiln dried cord, then there you go.

If it takes 9 days to do 3 cords and just as much energy per cord, or 50% more overall, you have not lost anything.  

[Southside]

Well in this instance I can see case hardening  being a problem in that the moisture difference could negativity impact the wicking effect leaving wood with a wet core. Not sure that it would actually happen, but if it did, dunno. 

[K-Guy]

What do you set the DB and WB values to with firewood?

The settings I would use are 120° DB 75° WB to start and change the WB lower if it isn't dry enough at the end.

[doc henderson]

hopefully the water can exit the ends of short pieces, and if enough stress, may split from the end.  has to be better than waiting for air dry.  nice discussion Jim.

[K-Guy]

For firewood stress and splitting are not concern only getting it dried to 15-20% fast.

[doc henderson]

and the splitting is helpful.  more surface area exposed to the harsh desirable conditions.

[customsawyer]

The biggest gain I get on my kiln is to never let it cool off. I sterilize at 160°F. After I let a load relax a few hours then I take it out and put another in. Keeps the floor and wall temps up and things go a lot faster. I know your climate is different but if it is starting at 34° than that is the first place I would start trimming time. Sounds like you could trim about 24 hours pretty quick. 

[jimbarry]

The biggest gain I get on my kiln is to never let it cool off. I sterilize at 160°F. After I let a load relax a few hours then I take it out and put another in. Keeps the floor and wall temps up and things go a lot faster. I know your climate is different but if it is starting at 34° than that is the first place I would start trimming time. Sounds like you could trim about 24 hours pretty quick.  

We unload and reload within an hour so there is little loss of thermal mass for the bldg interior. The fact that the WB can go from 34 to 104 in 24 hrs is a testament to that. In the past when I was not running one cycle after another there would be time for the bldg to cool down. When that happens the heat up time generally requires an extra 24 hours, as you have noted.

Yesterday we loaded another cycle. This load had a hard frost the night before. The wood and crates had spikes of frost on them as we loaded in.



 

This morning, 22 hours later it looks like this. 



 

169 kWHr were consumed by the kiln during that time.

[jimbarry]

... If it takes 9 days to do 3 cords and just as much energy per cord, or 50% more overall, you have not lost anything.  

Been giving this some thought and its true as you say. Problem is with the setup we have to load, its 4 flat carts rolling on steel. 2 crates (1/2 cord) is just about what the two of us can push into place. You're talking close to 2,000lbs for half cord. To test another full cord, that would be like adding one more crate on per cart. That's like 1,000 lb, making it 3,000 to push into place. I don't think we're capable to move that.
If the kiln floor was at ground level I would consider driving in with the skidsteer. But, that's not how it is at this time.

[barbender]

Jim I would love to have a firewood kiln set up, but I would really want to find a way to burn wood waste, which as you know the firewood operation creates piles of anyways. Probably the easiest way for me would be to plumb it into my OWB with a heat exchanger to heat the kiln. Thankfully I already have the OWB, setting one up for the operation would be a large expense.

[cabindoc]

... If it takes 9 days to do 3 cords and just as much energy per cord, or 50% more overall, you have not lost anything.  

Been giving this some thought and its true as you say. Problem is with the setup we have to load, its 4 flat carts rolling on steel. 2 crates (1/2 cord) is just about what the two of us can push into place. You're talking close to 2,000lbs for half cord. To test another full cord, that would be like adding one more crate on per cart. That's like 1,000 lb, making it 3,000 to push into place. I don't think we're capable to move that.
If the kiln floor was at ground level I would consider driving in with the skidsteer. But, that's not how it is at this time.

If you mount a small quad winch to the back or front of the chamber, you could use it to winch loads in/out with pulleys.

[Crossroads]

Use a 4x4 as a Jill poke to push the carts in with the skiddy