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ian maybury
07-14-2015, 9:16 AM
This is more in hope than expectation, as the company is Swedish and it doesn't seem like the Logosol products are widely sold in the US. This could be changing, there's people named Bailey offering them from Woodland in CA. This is their catalogue (which includes lots of sawmilling equipment which may be of interest), but it doesn't seem to mention the Sauno kiln unit: http://www.logosol.us/cms2/downloads/en_US_productcatalog_baileys_screen.pdf It is mentioned on their page linked below.

As before I'm considering installing one of these to condition wood before use, and probably also to dry it from sawn planks: http://www.logosol.us/all-products/sauno-kiln/ There's seemingly not a whole lot available from the factory by way of kilning process information, and attempts to track down some users in the UK were unsuccessful. (which doesn't necessarily mean there aren't any - maybe just that the sellers i spoke to didn't have contact with them)

Wondering if anybody is familiar with these units, or with the process they use? Is the equipment reliable, does it work well, where would one search for good user experience or drying process related information?

Wondering too if it's possible that there haven't been too many sold except perhaps in Sweden?

Larry Edgerton
07-14-2015, 9:32 AM
They come up for sale here on occasion Ian, so they must have sold some here. If you can get your hands on a copy of the USDA "Drying hardwood lumber" it covers dehumidification drying, and is a good book to have around. I have a copy somewhere but have not seen it since I moved last year. Its in a box somewhere......

ian maybury
07-14-2015, 9:55 AM
Thanks for that Larry. As it happens I have the USDA manual filed away somewhere too, but wasn't sure how applicable it might be to the Sauno.

Sounds like they have sold some kilns then. Some more Googling just now brought up links to several Sauno related topics on this forum since at least 2010, but i'm not yet sure how much is there: http://www.forestryforum.com/board/index.phptopic=47571.0 (http://www.forestryforum.com/board/index.php?topic=47571.0) There's a few topics on this UK forestry forum too: http://arbtalk.co.uk/forum/milling-forum/55636-questions-kiln-drying-process.html

ian maybury
07-14-2015, 7:16 PM
Found this short manual on building and operating a Sauno kiln: http://www.plano.se/pdf/ByggforslagGB.pdf

I'm a little sceptical that a kiln enclosure built of foam panels could be robust enough to tolerate frequent use, but maybe there's a variety of board with some sort of plastic inner liner or whatever that could be used instead?

Larry Edgerton
07-15-2015, 8:00 AM
Found this short manual on building and operating a Sauno kiln: http://www.plano.se/pdf/ByggforslagGB.pdf

I'm a little sceptical that a kiln enclosure built of foam panels could be robust enough to tolerate frequent use, but maybe there's a variety of board with some sort of plastic inner liner or whatever that could be used instead?

Should not be a problem if you are using a cart. I do built up roofs out of 6" foam on log structures and it is pretty tough.

ian maybury
07-15-2015, 10:49 AM
Thanks again Larry - i'll have to take a look at the panels available now as I'm way out of touch and there's lots new.

Brad Morrow
07-18-2015, 8:58 AM
I've had a sauno kiln for about 8yrs now and couldn't be happier with it. I process small batches of hardwood (beech, ash, oak) in planks and rough turned bowl blanks. It does what it says on the tin, it usually takes 45 days to get the timber down to 8% MC. My kiln is 2.4m x 1.0m x 1.2m usable internal space, I boxed out the unit in 12mm ply to protect the rigid insulation and to provide another work surface in the workshop. I've had no issues with it and would highly recommend the sauno.

ian maybury
07-18-2015, 10:53 PM
Thanks Brad, great to get some feedback. The Sauno seems to get consistently good press. I've a client lined up to dry bowl blanks for too - although my main requirement is for well conditioned and stress free small cabinet and box making woods.

The following is to walk through how I think the kiln works - I'd appreciate hearing anything you have to say to confirm/explain/clarify what's actually going on. Don't bother if i'm making it too complicated.

The initial 'steaming' stage sounds like heating with plenty of water about/at around saturation/at about 100% RH since the temperature during that stage is 70 - 75 deg C - well below boiling. Which is fine since it seems to do the required job of making the cells more porous to water vapour while avoiding colour changes, weakening, loss of workability etc.

The bit that i'm struggling with is to properly understand how it dries the wood, in that generally equilibrium moisture content and rate of moisture loss are regarded as directly related to the %RH (relative humidity) of the air surrounding the wood. So that so far as I know most kilns try to control % RH during the drying process.

The Sauno is apparently held at 40 - 50 deg C while controlling its internal humidity/the rate at which moisture is lost from the kiln volume by adjusting ventilating valves. Which presumably results in a progressive (but somewhat indeterminate) reduction in the % RH in the kiln and the EMC of the wood over the 45 or so days required to get down to 8% MC. With the key point probably being the slow drop in %RH - it (with the help of the effect of the steaming) means that case hardening/stress raising is reduced because the outer skin of the board doesn't dry a great deal faster than does the core. The subsequent recommended 1-2 weeks conditioning indoors presumably ensures that any remaining moisture gradient (variation in MC from the outside skin to the core of the wood) gets the chance to equalise - so that it minimises any remaining stresses in the wood. (beyond those present from how it grew)

If I have it right it seems that the %RH inside the kiln is not directly sensed or controlled per se, and that it probably drops slowly at a rate related to the rate of ventilation during the drying period. i.e. that %RH is only indirectly controlled, and that a well sealed kiln must be important. The water content (not the relative humidity) of the air in the kiln will eventually drop to match that of the air outside - maybe 30-35% RH at the kiln temperature of 40 - 45 deg C or threabouts depending on the weather. (presuming say a hot and humid time/poor drying weather at 25 deg C and 90% RH) Which would equate to a minimum of about 6% wood MC. (lower in less humid and colder weather conditions) In practice the use of a wood moisture meter would result in the kiln being switched off and unloaded before that - once the wood got down to say the 8% MC or so needed.

Establishing an optimum drying stage sounds as if (by that explanation) it depends on figuring out a required degree of opening of the ventilating valves. The kiln isn't designed to maximise the speed of drying, but opening the valves too much could dry the wood fast enough to cause case hardening or splitting, while keeping them fairly tight would cause the drying stage to take longer but should deliver even less stressed wood.

Does this description sound correct? If so, do you find that the ventilation valves can just be left at a setting that from experience works? Do you find you need to measure moisture content of the wood every day to adjust the drying rate? What causes air to leave the kiln (taking moisture with it) to be replaced by outside air? Is there a fan that has this effect (the 'motor' shown in the drawing), or is it used purely for internal circulation/equalisation of conditions? The schematic for the larger VT5 version of the kiln shows a condenser - is this a water removal condenser?

Did you skin the foam panels inside the kiln with ply to improve their wear resistance? How has it done in that regard? (8 years is quite a lot of use)

Please pardon all the questions, but neither the local distributor, the factory (the 'expert isn't in house) nor the manual have been a great deal of help on details...

ian maybury
07-26-2015, 2:22 PM
Just by way of a bump, and to add some more information - since presumably there's very few of these kilns about in the US. Pardon another long one.

I've had no luck again in raising support from Logosol, and previous contacts with the factory failed to come up with somebody technically up to speed on the Sauno. It seems it was developed by an outside guy.

Speaking to a couple of users has however added some information. The good news is that both report excellent results - one on a huge variety of tropical woods in warm and wet weather conditions (he's a boutique producer), the other on European hardwoods in Scotland. It seems it's necessary to carefully build, tightly seal and insulate the kiln - that even fairly minor leakage can badly mess with the drying rates and heating. Another positive is that the space can be almost completely filled with stickered wood - it's not necessary to leave large air spaces to facilitate circulation. The optional minimum cost DIY construction from foam panels may be prone to damage unless it's lined with something harder wearing.

It seems that the above understanding of the principle is broadly correct - that as moisture is released from the drying wood the air from inside the kiln is vented outside and replaced by drier outside air. Balancing the temperature and the rate of venting (mostly the latter it seems) makes it possible to achieve the reasonably controlled reduced %RH condition in the kiln required for drying. 43% RH is equivalent to 8% EMC. (wood moisture content)

The actual rate of drying must vary a bit during the cycle, but it's probably in the first instance driven by the % RH in the kiln. (?) After that the ease with which the wood in whatever state it's in gives up its water is presumably also influenced by species, stage in the drying process, thickness, stacking pattern, shape, how effective the prior steaming process was, actual drying temperature, effectiveness of air circulation etc. (which latter seems good - the stock unit is fitted with a fan) All of these variables and no doubt more will combine to determine how long the wood actually takes to reach the target 8% EMC or whatever. The kiln has the potential to dry the wood well below this, especially in Winter conditions - so some means of determining when it's ready may be required.

What's not so easily figured out is how the principle might cope with widely varying outside weather/air conditions, and how much tuning/setting to suit it might require to suit. Freezing weather conditions could see ambient outside air at very low % RH being heated in the kiln. A look at a psychrometric chart suggests that this air could drop to only a few % RH (maybe <3%) when heated to the lower operating temperature of 30 deg C - might it (depending on how stuff balances out) create a risk of drying too fast/splitting etc unless water is added?

In contrast ambient Summer air at say 25 deg C and 90% RH would drop to a useful sounding roughly 40% RH in the kiln at 40 deg C (it contains about 20 times as much water), but might it struggle (depending on water gain from the wood and other stuff too) to get the wood all the way down to 8% at this/in even warmer and more humid conditions without exceeding the normal 50 deg C listed max drying temperature?

Major factors in play include (there's many more) the kiln operating temperature (it seems like lower temperatures could be appropriate in winter), the rate at which moisture is added to the air in the kiln by the drying wood, and the rate at which outside air is admitted to the kiln. (the vent settings)

The Winter situation seems less likely to be a problem since the kiln was developed in Sweden, although the % RH is quite a lot higher in Winter there than in continental US.

It'd help a lot if the factory would specify a range of permitted ambient temperatures and humidities for the kiln to be operated in - plus associated recommended settings and operating kinks for these. Instead of leaving every buyer to run their own R&D programme...

Brad Morrow
11-24-2015, 4:15 PM
My apologies Ian for not answering quicker. Too darn busy.

When I built my kiln I laminated the rigid high density foam externally to a plywood box that measured 2.4m long x 1.2m wide x 1.0m high. I them covered the external insulation with ply to create a sandwich that I figured would protect the insulation. At one end of the box the sauno unit and a openable vent is mounted and on the other end I have another vent mounted. The front face is openable for loading.

I've built in a moisture meter that allows me to attach cables to prongs at the bottom, middle and top of the timber planks in the kiln and I take daily readings throughout the process. Initially the humidity is taken up to 100% (I put a bucket of water in with the timber initially to speed up this end of the process) with the internal temp getting upwards of 50C and then by increasing the fan speed, opening the vents and gently lowering the temperature the MC reduces over time. I usually aim for 8%MC.

Most of the timber that I dry is used for furniture and the rough turned bowls and then turned down to their final sizings.

I dry timber all year round or as I need it. I hope this helps.