Shared adventures - Workshop Humidity Control & Kiln Dry

[ondablade]

Hi all. I thought maybe it'd be worth while setting this thread up as an ongoing focus where those interested in the above topics can share experiences - good and bad.

Having whinged of problems getting %RH under control in my shop using a domestic dehumidifier, and discovered that the unit was simply not set up to control to the required 45% RH (and more to the point could not be adjusted) it emerged that Ebac Industrial do purpose made kiln drying and workshop conditioning units.

Here's some sources of information:

Woodweb's page where you can download a copy of the US Dept of Agriculture's Dry Kiln Operator's manual:

http://www.woodweb.com/knowledge_base/D ... anual.html

Contact details for Ebac's industrial division are here: http://www.eipl.co.uk/Websites/UK/

Their model LD 82 here http://www.eipl.co.uk/Websites/UK/ld82.htm is the solution provisionally suggested for small kilns. There's probably some additional control equipment required.

Their WM-80 http://www.eipl.co.uk/Websites/UK/WM-80.htm has provisionally been suggested for workshop humidity control.

It going to take a while it that gaining a basic understanding of drying processes underpins making sense of it all. It's all new to me, so please do not treat anything i may have to say as advice - or for that matter presume that it's technically correct 'cos i'm just another punter groping in the dark!

I've quite a lot of other stuff on as well in getting my workshop set up, and budget limits could slow things too - so don't be surprised if there are some significant delays.

Most of their kiln drying expertise seems to be located in Germany. Please bear in mind that these guys are industrial and not retail suppliers, and proceed accordingly. (they probably will not want to spend all day providing freebie tech support unless there is a decent prospect of business)

As before i have basic data on their smaller end systems. I'll outline the story when i get through extracting what hopefully might be of interest

I wonder if there is anybody else doing small kiln drying and conditioning systems that might be suitable, or that might have evolved other working solutions???

 

[HandyTim]

This is the only home solution for kiln drying I know of.
http://www.classichandtools.com/acatalog/Sauno-Wood-Kiln.html

 

[ondablade]

Thank you very much for that Tim, a great looking lead to investigate. Do you or does anybody you know have experience of those units?

 

[JonnyD]

Thank you very much for that Tim, a great looking lead to investigate. Do you or does anybody you know have experience of those units?

It might be worth giving these people a call to find out information on the kilns as i know they have been selling them for a while

http://www.logosol.co.uk/_industrial/sauno/

cheers

jon

 

[ondablade]

OK. Thanks for that Jon. I've had a word with Logosol. Nice people, they referred me to take a look at the Sauno factory website: http://www.sauno.se/GB/engelska.html They do a 4Kw kiln unit for not much over £800, and a smaller unit for quite a bit less.

There's some nice information there on how to build a small cost effective kiln from rigid insulating foam board, and on the kiln drying process they use which involves steam, and which they suggest makes the risk of splitting and checking much less than typical kiln processes. I've not yet studied these myself.

I had/have some hopes (i've not completely given up on it yet) of maybe being able to fairly effectively finish dry supposedly kiln dried wood that's picked up moisture again/been wetted in an air conditioned 45% RH or so workshop - which would also maintain wood being worked on at around 8% moisture.

It's as you would expect probably possible, but subject to checking out drying times properly i'm being told that even to drop timber from say 16 or 17% moisture to 8% would likely take a month or two this way.

Meaning that if this is not fast enough then maybe it's a case of building a small outside kiln, and with a separate air conditioner keeping the workshop at the right humidity so that wood being worked on or stored there stays at the correct moisture content..

More in due course...

 

[Sgian Dubh]

... which would also maintain wood being worked on at around 8% moisture.

... and with a separate air conditioner keeping the workshop at the right humidity so that wood being worked on or stored there stays at the correct moisture content...

Ian, in the end though it's hard to keep wood at the "correct" moisture content. After all, the correct moisture content of the wood is one that matches the relative humidity. Interior furniture, like any wood, except wood in artificially or unusually stable conditions of RH, moves towards a moisture content level suited to the prevailing RH. A typical inhabited building in the British Isles experiences seasonal daily avaerage RH variations ranging from about ±35% in winter to ±65% in the summer.

It's not really too difficult to build furniture that can cope with the cross grain movement it is likely to experience in the MC range 6.5%- 12.5% over a full year-- these numbers, as I'm sure you know, roughly correlate with the RH numbers given in the previous paragraph.

8-10% MC is a good mid-range MC to build interior furniture, but it can also be done successfully with wood that is either wetter or drier. It's just a case of building enough allowance for the expected range of movement. For instance, for over the last three decades I have successfully built furniture for interior use, as and when needed, out of air dried timber that came into the workshop at 16%MC, or sometimes even more.

Your interest in this subject and your attempts to get to grips with it is interesting and commendable. Coincidentally, I recently sent to an eminent wood scientist in the US a manuscript for academic peer review; it's an illustrated text I've written that discusses some of the subject area you are investigating, and more. One day, perhaps, it may be published and available to read. Slainte.

 

[ondablade]

Hi SD. You're i guess pointing to where i'm headed, and where no doubt many have been already. ;-) It's just that i'm pretty inexperienced, and far too stroppy and stubborn to take too much on a say so - at least not without understanding the dimensions of the problem and the theory that sits behind it.

While it's hugely important (and is in fact be the eventual output of any undertaking like this), I struggle with the custom and practice approach on its own because somehow it seems that there's always such a scope for associated assumptions that didn't get communicated to bite you up the bum.

Another factor that's keeping me digging is that while many don't there are a significant number of people out there using air conditioning and small kilns to get control of their wood.

Taken in isolation the technical dimensions are pretty scary too. It's sobering for example to calculate just how much say an 8in board in something like beech will move across the grain when equilibriated to say a 25% change in RH.

What seems to save our collective asses, and to moderate the situation in reality seems to be the fact that timber takes up moisture pretty slowly, especially when coated and sealed. Meaning that it doesn't produce anything like as much movement especially with short term changes in %RH as the the numbers might suggest.

To tie down quantitatively what this means in practice is however quite another matter. There's then of course the little matter of how this interacts with design too.

What i would say is that if anybody would rather i kept my mutterings to myself please say so - i can understand why this might be the case...