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Author Topic: Custom made kiln help  (Read 1606 times)

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Offline GeneWengert-WoodDoc

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Re: Custom made kiln help
« Reply #20 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.
Gene - Author of articles in Sawmill & Woodlot and books: Drying Hardwood Lumber; VA Tech Solar Kiln; Sawing Edging & Trimming Hardwood Lumber. And more

Offline dcrice

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Re: Custom made kiln help
« Reply #21 on: November 19, 2019, 10:44:28 AM »
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.

Offline doc henderson

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Re: Custom made kiln help
« Reply #22 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.
timberking B 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 12 volt tarp motor

Offline doc henderson

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Re: Custom made kiln help
« Reply #23 on: November 19, 2019, 05:18:07 PM »
clunky but I think I got something.  



 

graph on phone from sensor push
timberking B 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 12 volt tarp motor

Offline dcrice

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Re: Custom made kiln help
« Reply #24 on: November 20, 2019, 09:25:40 AM »
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.

Offline YellowHammer

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Re: Custom made kiln help
« Reply #25 on: November 20, 2019, 02:14:24 PM »
I calculated your Equilibrium Moisture Content value at 57% RH and 100F.  It is 9.8%.  Thats where you wood will try to dry to under these conditions.

The sensor push is a small device that interfaces with a cell phone to provide remote and historical trends of both Temp and RH.  Basically, when I walk by my kilns and get into Bluetooth range, it automatically uploads all the data to my phone, where not only can the instantaneous reading be seen, but also the historical trends.

Robot Check



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Offline dcrice

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Re: Custom made kiln help
« Reply #26 on: November 20, 2019, 05:11:51 PM »
I calculated your Equilibrium Moisture Content value at 57% RH and 100F.  It is 9.8%.  Thats where you wood will try to dry to under these conditions.

The sensor push is a small device that interfaces with a cell phone to provide remote and historical trends of both Temp and RH.  Basically, when I walk by my kilns and get into Bluetooth range, it automatically uploads all the data to my phone, where not only can the instantaneous reading be seen, but also the historical trends.

Robot Check
Thanks for link YellowHammer.
Being new to all this I decided to start with a small kiln (4'x4'x10') just to try and understand a kiln environment. This info you guys are providing me with has really opened my eyes to the wood drying world. It's interesting and I'm staying positive. Maybe I need to start with some pine as a baseline instead of air dried cherry. Do you recommend running freshly cut "green" wood through the kiln or air dried?

Offline btulloh

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Re: Custom made kiln help
« Reply #27 on: November 20, 2019, 05:23:59 PM »
Enjoy the learning process. Before I started drying lumber I had no idea what was involved. I quickly learned that its a deep and wide subject. And then some. 

Thankfully there are a lot of knowledgeable folks on here willing to share what they know. Digging around and reading threads on here can provide a lot of practical info. There also many references to books and articles that really help. 

The more I learn about drying, the more I realize I dont know. But at least now Im getting good results and learning more all the time. It has been a rewarding and enjoyable process, and theres still a lot of learning ahead. 

Youre in a good place here on the FF to move forward. Have a good trip!
HM126

Offline doc henderson

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Re: Custom made kiln help
« Reply #28 on: November 20, 2019, 09:55:59 PM »
@YellowHammer do you have more practical info on the sensor push.  I got a good pleth at first.  I have to open the app to get info on my phone near the container.  now it seems to have a strait line over several days instead of the minute to minute. I have done several uploads, is there a reset or something.  not getting the same graph as before.
timberking B 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 12 volt tarp motor

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Re: Custom made kiln help
« Reply #29 on: November 20, 2019, 10:54:25 PM »
I dont know, that hasnt happened to me.  What happens if you move it into a known environment, such as in your house to see if it responds?  I'm wondering if the sensor hole is covered with sawdust or otherwise obstructed? 
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Offline doc henderson

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Re: Custom made kiln help
« Reply #30 on: November 21, 2019, 11:28:23 AM »
thanks I will check.  the instructions are rather technical.  the lines are so straight it seems like maybe it is broke.  I thought maybe it needed reset.
timberking B 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 12 volt tarp motor

Offline kelLOGg

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Re: Custom made kiln help
« Reply #31 on: November 24, 2019, 06:37:04 AM »
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.
Why heat the unit as high as 85 F? In a domestic room the temp will probably never be that high.
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Offline dcrice

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Re: Custom made kiln help
« Reply #32 on: November 27, 2019, 08:39:12 PM »
Folks, I'm sort of at a dead end with drying my cherry slabs. I bought a $35 General pin moisture meter at Lowes just to get a second opinion and the
slabs are reading 5-6% MC. I check them with my pricey Wagner 220 pinless meter and the MC is everywhere (11-24%). I removed the cherry from the kiln for now. I plan to load it with some maple next. I'm hoping for some improvements so we shall see.

Offline farmfromkansas

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Re: Custom made kiln help
« Reply #33 on: November 29, 2019, 06:08:11 AM »
I bought my first moisture tester from MLCS, and it would read about 6 percent on air dried lumber.  Bought a mini Ligno, and it reads from 11 to about 13 on air dried lumber.  A cheap meter is about worthless.

Offline GeneWengert-WoodDoc

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Re: Custom made kiln help
« Reply #34 on: November 29, 2019, 06:35:21 AM »
All moisture meters measure an electrical property and relate that to MC.  So, the accuracy of any meter depends on the calibration (electrical property to MC) used by the manufacturer.  Typically, foreign-made meters have a different calibration than US made meters, so foreign made meters are not as accurate, so by 5% or more.  You get what you pay for. 

No electric meter, pin or pinless, can measure accurately above 30% MC.  Pin meters cannot do well under 6.5% MC.  Pinless can go down to 4% accurately.

PINLESS
The pinless meter requires care in its use.  If you measure two 1 thick boards and get a readings on each separately, with an air space underneath each one when you take the reading, and then put the two together, face to face so they act like one 2 piece, you will get a higher MC than the individual.

You can read the MC on one face and then turn the lumber over and measure again, you will sometimes get two different MC readings by several %MC

The pinless meter also responds to density differences...a heavy piece of oak, fast grown, will pave a higher MC than a slow grown lower density piece of the same species and same oven-dry MC.  


PIN
To be fair, the pin meter also has issues that must be accommodated, including wood temperature, depth of pins, internal MC gradient, species and pin insulation, to name a few.
Gene - Author of articles in Sawmill & Woodlot and books: Drying Hardwood Lumber; VA Tech Solar Kiln; Sawing Edging & Trimming Hardwood Lumber. And more

Offline Old Greenhorn

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Re: Custom made kiln help
« Reply #35 on: November 29, 2019, 06:49:25 AM »
My requirements on a meter are lower than most. I just want to know if it is fully air dried or not and maybe how much more it needs to go. With that in mind and no experience in my pocket I bought a really cheap 2 pin one on fleabay for $16.00 or so. It would max out if the wood was over 30% which is fine, that's just 'green' and all I need to know. But for firewood and air drying boards, my sense is it was fairly close. It also seemed to be 'off' on KD lumber. Then I had some slabs I needed to plane and a fellow FF member offered to do that for me on his brand new Grizzly IF the MC was below 15%. Well I checked them and my meter said 12%. I brought the slabs to his place and he pulled out his fancy expensive meter to double check. I figured it was the moment of truth where I would come up looking stupid and and his meter said .......... 12%   8)
 At that point I thought I had a pretty good 'first glance' meter. It worked good until my wife ran it through the washer and dryer last week. It is destroyed now. A new one, slightly different brand, should arrive today. We will see if that is close enough.
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Offline rweiss1110

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Re: Custom made kiln help
« Reply #36 on: March 13, 2020, 10:39:24 AM »
Here is a thought, if using a Dehumdifer during the summer when the outside humidity and temp is high and that dosn't work. How about replacing that with a portable LG 12,000 BTU AIR CONDITIONER. Just thinking outside the box.


Offline doc henderson

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Re: Custom made kiln help
« Reply #37 on: March 13, 2020, 10:58:32 AM »
it would help.  the idea of a kiln is to speed the drying process, so increased temp over the normal household temp is better, and a way to remove the moisture.  the ac unit would pump the heat outside.  you could put the unit inside entirely so the heat and cold mix.  that is kind of what a dehumidifier is.  my 70 pint dehumidifier was about 300 bucks.  comes with a water bucket and an adapter to a garden hose to discharge the condensate water outside.  if your plan is to mimic indoor conditions, then you can just put the wood in an air-conditioned space.
timberking B 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 12 volt tarp motor

Offline GeneWengert-WoodDoc

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Re: Custom made kiln help
« Reply #38 on: March 14, 2020, 10:57:51 PM »
Consider a dehumidifier kiln...it is a box with lumber and air.  It may have a vent that operates when the unit gets to hot, but basically it is a closed system, so the humidity outside has no effect on the humidity inside the kiln.

A dehumidifier in the kiln is a heat pump and is essentially identical to an air conditioner, except both hot and cold coils are inside the kiln, compared to operating as an air conditioner where the hot coils are outside.  By putting the hot coils in the kiln, we have the energy needed to evaporate water.

If the kiln overheats, that means that energy is not being used for evaporation.  At the same time, if you exhaust heated air, the incoming air will be cooler and fairly dry.
Gene - Author of articles in Sawmill & Woodlot and books: Drying Hardwood Lumber; VA Tech Solar Kiln; Sawing Edging & Trimming Hardwood Lumber. And more

Offline Southview1

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Re: Custom made kiln help
« Reply #39 on: March 19, 2020, 01:53:15 PM »
i have started running a dehumidification kiln this winter and I initially had the same issue dcrice is having with the dehumidifier not taking any moisture out.  So, I took mine apart and confirmed the pump was working but the coils barely got cold.  I then went and bought the cheapest dehumidifier the local home store had and  that one started taking out a gallon a day.  Maybe your dehumidifier is weak.
My kiln is 4x4x11, insulated and the inside is sealed with plastic sheeting so its sealed pretty well.  My dehumidifier will easily keep my kiln about 110 degrees if I let it but I keep turning it off so as not to burn it out.  I have been running my last batch for about 10 days with approximately 300-350 bf in the kiln and have removed about 15 gallons of water.  I use a Lignomat Mini pin type meter.  I have been measuring both external and internal MC daily.  Surface MC this morning was 6 % lowest on meter but internal was 12%.  I have fans running 24/7 to keep air moving but only run the dehumidifier about 12 hrs a day.  It has started to remove much less water so I am planning on running the temp up to about 145 degrees for about 2 days or until the internal temp of the thickest board 8/4 is 140 for at least 6 hours but probably 12 hrs. I will then run the dehumidifier again when the temp drops to 100 because the high heat brings out more internal moisture.  I then plan another couple more days with the dehumifier and slowly let the kiln cool with the fans running.  which will take about 3 more days.  Last run 17 days total.
I really appriciated reading all the MC comments since I'm new to kiln drying.


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