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kiln construction

Started by jake12, November 24, 2006, 08:30:17 AM

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jake12

i use a hot water boiler to help heat my workshop. i want to build a 2000-2500 bdft kiln . in a room attached .i was thinking of creating another zone from the furnace and putting a few loops inside the kiln. i assume i need some type of vents to get rid of the water? anyone know where i can find some information  on proper construction ?  thanks

Ga_Boy

Hi Jake,

Welcome the forum.

There are several USDA, Forestry Service Publications that you can either down load as PDF files or purchase as hard copies.  The titles you need are:

"Dry Kiln Schedules for Commercial Hardwoods"
"Drying Hardwood Oak Lumber"
"Drying Hardwood Lumber"
"Dry Kiln Operator's Manual"

First a note of caution, ensure you vent is to the outdoors; not in to your building. The moisture has a very high acid content; you do not want this inside your building. My vent is a powered vent with a louvered intake on the opposite side of the kiln. 

As for heating I used 80 feet of finned copper tubing as my heat exchanger, I have four 20' lengths of tubing with three fans washing the air across the tubing to heat it before the air enters the stacks.  Also monitor your temperature and relative humidity before the air enters the stacks.  My preference was to use an RH sensor over the use of dry bulb and wet bulb temps and make the conversion.  After all you are looking to control RH so I went with a good RH sensor. 

If you are close by and want to drop by and check out see my operation you are welcome to visit, I am about 40 miles south of Washington DC, on the Maryland side of the Potomac River.

The best advice I can give you is to spend the $500 and attend the "Kiln Operator's" course.  The $500 should cover the course fee and hotel accommodations.  Not knowing where you live travel could run you another few hundred dollars.  Regardless, if you are serious about drying wood; it is by far you best investment in time and money.  The next best is taking a course on grading logs and lumber. These will be my next training expenses.






Mark



10 Acers in the Blue Ridge Mountains

jake12

thanks Mark...i'm im central pa . i think i will take you up on your offer someday soon and run down and pick your brain a bit . ;D

Den Socling

Jake,

We are in central PA also and my son/partner helped Mark gather up parts and control for his kiln. Also, you can attend a week-long course at Penn State. So you are living in the right neck of the woods to be building your own kiln.  :)

Den

jake12

hi den, whereabouts you from ?   i live near dubois. i could sure use some help building this kiln . i have the basics down as far as constructing the kiln box , but i could use some advice on how to proceed from there .   dale

Den Socling

We are a stretch down I-80 between Lock Haven and Williamsport and can help but Mark is the man with a plan. Do some searching here and you will find a lot of basics and check out the references that Mark mentions.

Ga_Boy

Jake,

When I attended the Kiln Operator's coures I was given hard copies of the publications mentioned.  Prior to the course I down loaded the PDF files and did some reading.

However attending the class brought the concept of drying wood together for me.  There are sevral charts in the books that I use daily when I have a charge in the kiln. Also, the course goes in to depth on the physics of what is happeneing inside the wood and how to dry it properly. 

For me the biggest thing I learned is you get the best product by going from the saw directly in to the kiln.  I do  not have the space or money to build a proper pre-drying shed.  So I go from my mill right in to the kiln.  I also learned that my operation workes best with a conventional kiln over a DH unit.   Your operation may work best with a DH unit, this is something you will have to determine for yourself.  I prefer to have absolute control over each charge, a DH unit is not cost effective in drying green wood.  I use my wood waste to fire my outdoor wood furnance.  If you have a boiler you are a step a head of me as I use a cold water mist to maintain my RH and equalize.  Steam is the preferred way to maintain RH and equalize.

If you choose to use cold water spray let me know and I will share what I have learned thus far on system maintenance.  Do not kid yourself, a cold water spray system is maintenance intensive.




Mark
10 Acers in the Blue Ridge Mountains

jake12

Thanks Mark, I appreciate all the help . I will proceed with this slowly . I dont want to have to do this more than once. The class sounds like a good idea along with the books. I would like to drive down and see your setup as well . seeing things in person helps me to see things a bit more clearly ...thanks again   Dale

SawDust_Studios

Jake,

I was going to do the same thing for my kiln, but after talking to several people, including some guys at Nyle, they talked me out of it.  The radiant heat is good, but not for a kiln. I went with the concrete slab with insulation under it and no heat in the slab.

I guess the logic, as I recall, is that radiant heat isn't kept at the temperatures of the kiln, so after a certain temp, your not heating anymore, your basically stealing heat from the kiln.  And the cost doesn't justify the early help you get in heating the slab.

I'd really look into it before you do it.

Dave
Making Sawdust on a Woodmizer LT40SHD CAT 51 /WM Twin Blade Edger and WM DH Kiln

bseago

I use a outside boiler to heat a 10,000 bf kiln.  The controls were ordered from Nyle the chamber I built my self. There are (5) 24in fans with 250,000 heat exchangers on fan #2&4. If I was to build this kiln again it would have infloor heat. The reason is the floor is a cold and will cause condinsation and will slow the drying of the wood. I would run returning hot water thru the floor before and during the kiln cycle this would solve my cold floor problems. I've run my kiln non stop for 6 years. If I can help please give me a call

Ga_Boy

Hi Bseago,

Welcome to the FF.

When I built my kiln I decided to use four legths of fined copper tubing running the length of the chamber.  My thought was with the heat exhanger running the length I would not have hot or cold spots.

Have you noted hot and/or cold spots in your chamber? 

I am using a 20' insulated shipping container for my chamber. 




Mark
10 Acers in the Blue Ridge Mountains

TexasTimbers

bseago,

where are u located, in a real cold environment? I asked because I have never heard anyone say they would run the heat in the solely in the floor. Or are you saying you would run it as supplemental to the copper tubiing?
The oil is all in Texas, but the dipsticks are in D.C.

firecord

Photo's would really do justice to this thread!  I look at many galleries for ideas, but searching for kiln photo's returns low results.

bseago

I live in northern Wisconsin I would always have the heat exchangers for the fans to blow thru but also run the return line the floor . To not have any cold or hot spots in the kiln the fans change direction every two hours. This would not be necessary if the wood was always the same legnth and stacked the same but in the real world it just doesnot happen.

GregS

Gents,
My kiln and shop are getting concrete poured later this week.  I ran PEX tubing in both.  The kiln is only 200sf but I put close to 600' of tubing in it.  The tubing is 6" on center.  I am hoping to run these 2 kiln loops at a much higher temperatures than the shop.  My plan is to use mixers to lower the temp for the shop.  It is too late to turn back now...I will be the tester.  I realize I will probably need to put in heat exchangers but this is above ground work so it can always be added.  I will take some fresh pictures today and hopefully post them tomorrow.


BBTom

GregS,  I hope that you put some insulation under and around the kiln slab.  I have found that concrete is a very good temperature flywheel.  It is very slow to heat up and very slow to cool down.  And if the kiln slab is attached to the shop floor, it will conduct alot of your heat out of the kiln to the shop while conducting heat into the ground if not insulated well.

I used aluminum sheeting on top of 1" solid wood floor on top of 6" insulation, leaving me with almost no thermal flywheel.  It still takes 2 days for 2000BDFT of lumber to cool from 150 degrees to 100 degrees with the heat off and fans on.  Cannot imagine how long it would take that much hot concrete to cool down.
2001 LT40HDD42RA with lubemizer, debarker, laser, accuset. Retired, but building a new shop and home in Missouri.

Don_Lewis

You might get 100 BTUH per square from the floor. If the kiln is 200 square feet, that is 20,000 BTUH which is a very small amount of heat. If this is a business, it would be impractical. If it is a hobby, then it will eventually get the wood dry.

You can make any system dry wood eventually. Light bulbs, radiant floors, solar collectors, home dehumdifiers, cold water coils,  etc etc etc. If you are doing it to make money, you should probably stick to what works in that kind of operation.  There are thousands of kilns and the engineering is pretty easy to understand. It would be pretty hard to come up with a really new idea. There are no secrets and there is no magic. If you are just playing with it and not in it to make money, then go for any ideas that are interesting.

Jeff

QuoteIf you are just playing with it and not in it to make money, then go for any ideas that are interesting.

I like that advice a lot Don.  :) Ya just gotta love creativity.
Just call me the midget doctor.
Forestry Forum Founder and Chief Cook and Bottle Washer.

Commercial circle sawmill sawyer in a past life for 25yrs.
Ezekiel 22:30

DR_Buck

I went the other route.   I used the Nyle unit from Wood-Mizer.   The link below is to a thread showing pictures of the completed kiln.

DR_Bucks DH Kiln
Been there, done that.   Never got caught [/b]
Retired and not doing much anymore and still not getting caught

SawDust_Studios

Quote from: DR_Buck on November 29, 2006, 09:27:14 PM
I went the other route.   I used the Nyle unit from Wood-Mizer.   The link below is to a thread showing pictures of the completed kiln.

DR_Bucks DH Kiln

Well, that at least makes me feel better. I've only had mine in the box for about 3 months  :-\ :-\

I have the concrete poured and just need to stud 2 walls, build access door and insulate.  Oh, and find the time to do those 3 things.
;)
Making Sawdust on a Woodmizer LT40SHD CAT 51 /WM Twin Blade Edger and WM DH Kiln

old3dogg

Hello Dale.

Im from the DuBois area also and used to do a little drying. Would like to check out your kiln.
Could offer some advice as well.
Mike.

GregS

Quote from: Don_Lewis on November 29, 2006, 07:25:37 AM
You might get 100 BTUH per square from the floor. If the kiln is 200 square feet, that is 20,000 BTUH which is a very small amount of heat.

There are no secrets and there is no magic. If you are just playing with it and not in it to make money, then go for any ideas that are interesting.

Don,  At no point did I say this would be my only heat source.  If a charge of lumber needs X amount of BTUs to dry then my water-to-air heat exchangers only need to produce X-20,000 BTUH.  I hope magic is not needed because I have none of that  ;D.  If heat coming from the bottom of the pile is bad than please explain.  I am no expert and all ears when it comes to learning from others with the experience. 

My new shop has radiant floor heating so I added some to the kiln.  I understand steam heat is the way to go but not so easy for the small guy.

BBTom,  I have insulated under the slab and around the building and hoping it is enough.  I will insulate the ceiling and side walls with as much as I can afford.

If the kiln is operating most of the time, isn't the flywheel effect (thermal mass) of concrete a good thing?  I would think the ability to keep your temperature constant or change very slowly to be a good thing.

GregS

I wanted to bring this thread back for a question....

In a conventional kiln, is the concrete thermal-mass good or bad? 

From the schedules that I have studied the temperature steps are not that large.  The charge may start off at 130 degrees and stay there for many days and then jump 10 degrees.  I would think the ability to hold relative constant temperatures is good.  Of course air heat exchangers are needed to make the jump but at least the delta-T of the concrete to air is not that great.  Just thinking out loud....thanks.





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