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Custom made kiln help

Started by dcrice, November 15, 2019, 02:27:00 PM

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dcrice

Folks, I'm new to this kiln drying process so I appreciate any help or advice you can provide.

I recently built a custom made (insulated) box kiln 4' x 4' x 10' to dry my sawmill lumber in. I'm heating the kiln with 2X 500 watt shop lights. One of which I have plugged into the inkbird controller shown. Even though the actual temp (131deg F) is higher than the target temp (125deg F) this kiln is consistently holding the temp around 125 deg F to within +/-2 deg.  I just added a space heater, as shown in photo to help bring the temp up during the cold nights we've been having lately so that's why the temp was high. I also have 3 fans circulating the air and a dehumidifier to remove moisture.

Anyway, I have the kiln loaded with 8/4 live edge cherry. Most of it is between 15-20% MC. It's been running 3 days and my dehumidifier has yet to pull off any moisture. I was concerned that part of the problem maybe that I do not have any vents. Could this be a problem? Or do I need to add patients?

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K-Guy

@dcrice 
Your household dehumidifier will probably cut out at 104°F. So you won't get anything at that temp.
Nyle Service Dept.
A common mistake people make when trying to design something completely foolproof is to underestimate the ingenuity of complete fools.
- D. Adams

dcrice

That's good to know. Thanks K-Guy!

kelLOGg

I, too, have a room dehumidifier in my kiln. Initially. I let it get as hot as 140°F and that temp would destroy the unit. Now, I don't let it get hotter than 100°F and the replacement unit has survived several years. When the wood is 7-8% MC I remove the dehum unit, crank the heat up to heat the wood core to 133°F for sterilization. That has consistently worked for me.
Cook's MP-32, 20HP, 20' (modified w/ power feed, up/down, loader/turner)
DH kiln, CatClaw setter and sharpener, tandem trailer, log arch, tractor, thumb tacks

GeneWengert-WoodDoc

You do not mention any fans to move the air through the lumber pile.  Do you have fans or just the DH fan?

Do you also have 3/4" stickers? 

 How are you measuring MC...pin meter with insulated needles driven 1/2" deep on a face or ??

About how much lumber is being dried in your box?
Gene - Author of articles in Sawmill & Woodlot and books: Drying Hardwood Lumber; VA Tech Solar Kiln; Sawing Edging & Trimming Hardwood Lumber. And more

dcrice

Quote from: kelLOGg on November 16, 2019, 05:52:34 AM
I, too, have a room dehumidifier in my kiln. Initially. I let it get as hot as 140°F and that temp would destroy the unit. Now, I don't let it get hotter than 100°F and the replacement unit has survived several years. When the wood is 7-8% MC I remove the dehum unit, crank the heat up to heat the wood core to 133°F for sterilization. That has consistently worked for me.
Good to know. I think part of my problem is what K-Guy mentioned. I've been running the kiln at a high temp (125 deg F) and the household DH wouldn't work. I guess I'll need to keep at the lower temperatures for now. It may take longer to dry but it is what it is. How long does it normally take you to dry out Cherry and Walnut to 7-8%? Thanks for the help.....Dr.

dcrice

Quote from: GeneWengert-WoodDoc on November 16, 2019, 06:32:45 AM
You do not mention any fans to move the air through the lumber pile.  Do you have fans or just the DH fan?

Do you also have 3/4" stickers?

How are you measuring MC...pin meter with insulated needles driven 1/2" deep on a face or ??

About how much lumber is being dried in your box?
Yes, I have 3 fans, two in the back and one in front. Yes, I'm using 3/4" stickers.
I'm using a Wagner 220 Moisture Meter.
Currently, I have about 200 to 300 bf of wood in my kiln but it has a capacity of about 400 to 500 bf.
Thanks.....Dr.

doc henderson

the thicker slabs will take longer.  you mentioned that at night it requires aux. heat, but you could follow the solar cycle and let the temp drop below 100 at night and let the DH work at that time.  what is the RH in the kiln?
Timber king 2000, 277c track loader, PJ 32 foot gooseneck, 1976 F700 state dump truck, JD 850 tractor.  2007 Chevy 3500HD dually, home built log splitter 18 horse 28 gpm with 5 inch cylinder and 32 inch split range with conveyor powered by a 12 volt tarp motor

kelLOGg

I have not yet dried cherry or walnut although I have each soon to go into the kiln. I usually dry oak in the kiln after air drying which will take about 2 weeks to get to 7 or 8%. Operating my kiln in the summer is general not a good idea because the ambient temp is close to the max operating kiln temp. So, when the weather is hot drying in the kiln takes longer. Now is a good time to use my kiln and it is busy.  
Cook's MP-32, 20HP, 20' (modified w/ power feed, up/down, loader/turner)
DH kiln, CatClaw setter and sharpener, tandem trailer, log arch, tractor, thumb tacks

dcrice

Quote from: doc henderson on November 16, 2019, 08:31:49 AM
the thicker slabs will take longer.  you mentioned that at night it requires aux. heat, but you could follow the solar cycle and let the temp drop below 100 at night and let the DH work at that time.  what is the RH in the kiln?
I have not checked the RH. I was planning to add a wet bulb to the kiln but haven't got around to it.

doc henderson

not as industrial, but I have had good luck with the 14 dollar accurite temp and humidity monitors with a remote.  I can read from inside a metal container from 200 feet away in my shop.  I also got the sensor push that @YellowHammer  uses and recommends.  they both read about the same.  I have got the accurite monitors from WM or amazon.  if the RH is too low, it will create more stress depending on the MC of the slabs.  if you cycle it like solar it will relieve stress at night when the RH comes up in the air, near the wood surface.
Timber king 2000, 277c track loader, PJ 32 foot gooseneck, 1976 F700 state dump truck, JD 850 tractor.  2007 Chevy 3500HD dually, home built log splitter 18 horse 28 gpm with 5 inch cylinder and 32 inch split range with conveyor powered by a 12 volt tarp motor

scsmith42

Was the cherry air dried before it went into your chamber, or was it green?  IF AD; what was the MC% when it went in?
Peterson 10" WPF with 65' of track
Smith - Gallagher dedicated slabber
Tom's 3638D Baker band mill
and a mix of log handling heavy equipment.

dcrice

Quote from: scsmith42 on November 16, 2019, 10:48:57 PM
Was the cherry air dried before it went into your chamber, or was it green?  IF AD; what was the MC% when it went in?
I was air dried to around 20%.

dcrice

Quote from: doc henderson on November 16, 2019, 08:01:13 PM
not as industrial, but I have had good luck with the 14 dollar accurite temp and humidity monitors with a remote.  I can read from inside a metal container from 200 feet away in my shop.  I also got the sensor push that @YellowHammer  uses and recommends.  they both read about the same.  I have got the accurite monitors from WM or amazon.  if the RH is too low, it will create more stress depending on the MC of the slabs.  if you cycle it like solar it will relieve stress at night when the RH comes up in the air, near the wood surface.
I'll have try one of those. Pardon my ignorance, but how low of a RH is too low and whats a good stable level?

doc henderson

well if the wood is air dried, it is starting low.  the degrade starts early in the drying process.  each thickness and species will have its own schedule of temp and RH or wet bulb depression.  If the relative humidity is low, it is the same as drying in a house or airconditioned shop with heat.  Lets see what @GeneWengert-WoodDoc and others have to say.  @Southside @YellowHammer  @customsawyer   @WDH  and others
Timber king 2000, 277c track loader, PJ 32 foot gooseneck, 1976 F700 state dump truck, JD 850 tractor.  2007 Chevy 3500HD dually, home built log splitter 18 horse 28 gpm with 5 inch cylinder and 32 inch split range with conveyor powered by a 12 volt tarp motor

doc henderson

@dcrice if you have a sealed unit and no leaks, and the DH is not running, then heat is the only thing dropping your RH, so it will go back up when the temp drops.  If it is high, you need to get some out.  if it is low then you have leaks or you are opening it every day, and loosing the water that way.  good luck.  there is lots the has been written, and you first have to see where you are in the schedule.  I am a student of wood drying, but the afore mentioned guys do it every day, and or are experts in the field!  good luck
Timber king 2000, 277c track loader, PJ 32 foot gooseneck, 1976 F700 state dump truck, JD 850 tractor.  2007 Chevy 3500HD dually, home built log splitter 18 horse 28 gpm with 5 inch cylinder and 32 inch split range with conveyor powered by a 12 volt tarp motor

YellowHammer

As @doc henderson has said, it's important to know the wet bulb or relative humidity to know what is really going on in the chamber.    
YellowHammerisms:

Take steps to save steps.

If it won't roll, its not a log; it's still a tree.  Sawmills cut logs, not trees.

Kiln drying wood: When the cookies are burned, they're burned, and you can't fix them.

Sawing is fun for the first couple million boards.

Be smarter than the sawdust

customsawyer

When running the kiln the more information you can get the better off you are.
Two LT70s, Nyle L200 kiln, 4 head Pinheiro planer, 30" double surface Cantek planer, Lucas dedicated slabber, Slabmizer, and enough rolling stock and chainsaws to keep it all running.
www.thecustomsawyer.com

farmfromkansas

Question about room dehumidifiers, if you keep a dehumidifier in your wood dryer during cold weather, and it gets down below freezing, will it ruin your dehumidifier?  Looked in my trailer this afternoon and it was above 80 degrees, but I took out the dehumidifier when it started freezing at night.
Most everything I enjoy doing turns out to be work

Ianab

Quote from: farmfromkansas on November 17, 2019, 04:59:08 PM
Question about room dehumidifiers, if you keep a dehumidifier in your wood dryer during cold weather, and it gets down below freezing, will it ruin your dehumidifier?  Looked in my trailer this afternoon and it was above 80 degrees, but I took out the dehumidifier when it started freezing at night.

I killed one from letting it freeze up in winter. It built up so much ice it got into the electronics in the top and shorted it out.

The dont work very well if the temp is down below about 10C anyway. So may as well turn it off unless you have some heat in there.
Weekend warrior, Peterson JP test pilot, Dolmar 7900 and Stihl MS310 saws and  the usual collection of power tools :)

GeneWengert-WoodDoc

If you have a hot box or kiln that has no air leaks and vents are closed tightly, and if the DH is not running, how will any moisture get out of this kiln?  Unless the floor is cold, which will condense the vapor, the moisture will stay in the chamber and gradually build up to 100% RH.

It is difficult to get really accurate readings in a kiln with the surface meters,  versus the pin meter.  Neither work well above 30% MC.

The best humidity at any specified moisture content of the wood is given in a table called a kiln schedule.  The schedule also has maximum temperatures.  Kiln schedules are species and thickness specific.  The moisture content can vary from piece to piece, heartwood to sapwood, thick to thin, and quarter to flatsawn.  For the wettest, usually look for heartwood, thick, quartersawn.  There is a book DRYING HARDWOOD LUMBER that has some key schedules.  Google it.  In this book, convert the wet-bulb depressions to RH with the tables on p. 16-17.

I agree that humidity sensors that cost $25 to $30 are adequate for small kiln drying operations.  Order at least three and put all three in the same environment (plastic bag) and check that they all read the same.  Return those that are off by more than 5% RH.

You cannot run a household DH at 55F or cooler, as the cold coils will be under 32 F and so will ice up and restrict air flow, which means the unit will likely overheat and destroy seals.  If it is not running, there is nothing magic about 32 F ambient.  However, seals can get brittle when cold, so heat the unit up to 85 F before starting the compressor.
Gene - Author of articles in Sawmill & Woodlot and books: Drying Hardwood Lumber; VA Tech Solar Kiln; Sawing Edging & Trimming Hardwood Lumber. And more

dcrice

Quote from: GeneWengert-WoodDoc on November 17, 2019, 10:44:33 PM
If you have a hot box or kiln that has no air leaks and vents are closed tightly, and if the DH is not running, how will any moisture get out of this kiln?  Unless the floor is cold, which will condense the vapor, the moisture will stay in the chamber and gradually build up to 100% RH.

It is difficult to get really accurate readings in a kiln with the surface meters,  versus the pin meter.  Neither work well above 30% MC.

The best humidity at any specified moisture content of the wood is given in a table called a kiln schedule.  The schedule also has maximum temperatures.  Kiln schedules are species and thickness specific.  The moisture content can vary from piece to piece, heartwood to sapwood, thick to thin, and quarter to flatsawn.  For the wettest, usually look for heartwood, thick, quartersawn.  There is a book DRYING HARDWOOD LUMBER that has some key schedules.  Google it.  In this book, convert the wet-bulb depressions to RH with the tables on p. 16-17.

I agree that humidity sensors that cost $25 to $30 are adequate for small kiln drying operations.  Order at least three and put all three in the same environment (plastic bag) and check that they all read the same.  Return those that are off by more than 5% RH.

You cannot run a household DH at 55F or cooler, as the cold coils will be under 32 F and so will ice up and restrict air flow, which means the unit will likely overheat and destroy seals.  If it is not running, there is nothing magic about 32 F ambient.  However, seals can get brittle when cold, so heat the unit up to 85 F before starting the compressor.
Thanks for the info! I downloaded the book and began reading it last night. Very informative! Thanks for sharing.
The floor of my kiln is well insulated. As far as I know it's sealed pretty tight. I found a cheap digital RH monitor over the weekend and have it plugged into the kiln. If the monitor is correct, the RH was reading 70% this morning. My plan is to ramp up the temp of the kiln today to around 125 deg F with the DH turned off and then let the temp ramp down tonight below 100 deg F, then restart the DH to run over night. Kind of like a solar kiln I guess. Doc Henderson recommended doing this so thought I would try it. I also plan to buy a couple more RH monitors just to make sure I know what's going on with humidity in the kiln.

doc henderson

if you could record some temp vs humidity for a 24 hour period, you will see the relationship.  the sensor push that @YellowHammer recommends show the daily fluctuations, and each temp spike up, corelates with a RH drop.  it costs more so could put that on your Christmas list.  :snowball:.  many of the cheap monitors will maintain a max and min. temp and RH.  early in a schedule, you keep the RH up for a while, but I am guessing you are past that stage due to prev. air drying.  did you mention a MC of the wood? this tells you where you are in the schedule.

tried to take a screen shot and add the graph, but it is an extension and I am too old to figure how to change it to a photo on my phone to include here.
Timber king 2000, 277c track loader, PJ 32 foot gooseneck, 1976 F700 state dump truck, JD 850 tractor.  2007 Chevy 3500HD dually, home built log splitter 18 horse 28 gpm with 5 inch cylinder and 32 inch split range with conveyor powered by a 12 volt tarp motor

doc henderson

clunky but I think I got something.  



 

graph on phone from sensor push
Timber king 2000, 277c track loader, PJ 32 foot gooseneck, 1976 F700 state dump truck, JD 850 tractor.  2007 Chevy 3500HD dually, home built log splitter 18 horse 28 gpm with 5 inch cylinder and 32 inch split range with conveyor powered by a 12 volt tarp motor

dcrice

Quote from: doc henderson on November 19, 2019, 04:43:39 PM
if you could record some temp vs humidity for a 24 hour period, you will see the relationship.  the sensor push that @YellowHammer recommends show the daily fluctuations, and each temp spike up, corelates with a RH drop.  it costs more so could put that on your Christmas list.  :snowball:.  many of the cheap monitors will maintain a max and min. temp and RH.  early in a schedule, you keep the RH up for a while, but I am guessing you are past that stage due to prev. air drying.  did you mention a MC of the wood? this tells you where you are in the schedule.

tried to take a screen shot and add the graph, but it is an extension and I am too old to figure how to change it to a photo on my phone to include here.
I ran the DH through the night last night. Checked this morning and the RH was at 57%. The DH had not removed any moisture. Temp was around 95-100 deg F. I check the MC of the wood a week ago, it was averaging between 12% to 20% MC. I don't know, at this point I'm beginning to doubt my moisture meters readings. I have a new acu-rite RH meter on order. I'm not sure I understand what the sensor push is. Thanks for the graph.

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