Drying Timber - shed

[BobL]

Here is some interesting Temperature (oC) and Relative Humidity (RH %)data about my seatainer based drying shed (see pics below) over a 7 day cycle. I bought some USB portable temperature/humidity sensors and put one inside the container on top of a pile of slabs (blue line), and one I left outside the container but it failed to trigger (still getting the hang of the software) but managed to get local daily min (red rectangles) and max (Black rectangles) temps for the last week from the weather bureau.

http://www.woodworkforums.ubeaut.com.au/attachment.php?attachmentid=62166&stc=1&d=1197291052

It looks like the temperature in the container is consistently about 5 - 10 oC above the outside temp. I was hoping for a bit more but maybe that a good thing. The weather here is quite cool at this time of the year and this weather pattern is more like what we see in spring and autumn. It will be interesting to see what happens when we hit 40oC

It's interesting to see the RH outside varies by around 50% during the day/night cycle but inside it varies by only 30%and doesn't go less than about 40% . I have read on the web that this rise in RH during the night helps the wood recover from the stress of drying out in the day.

[jmaxwell]

hi bob it looks like a standard container with air vents on top . some mod may be required to make more affective . one basic requirement is that you maintain constant temp around 50 deg to start then reduced as the drying cycle continues .
I know you are a handy fella . some ideas from commercial models . solar water panels day time heat source , gas hot water system nite heat source . If you get that baby up to 50 deg then the next step is us your Rh sensor to vent the kiln at not sure what % . thus water and air is expelled and dry air taken in to kiln to repeat process. you can dry MM boards in 2 to 3 weeks with a kiln like this .

[BobL]

hi bob it looks like a standard container with air vents on top .
Yep that's all it is for the moment, and some intakes on the lower sides is all it is as the moment.


some mod may be required to make more affective . one basic requirement is that you maintain constant temp around 50 deg to start then reduced as the drying cycle continues .
I reckon it will easily get it to 50oC when it is 35-40oC outside. At other times I reckon I can get higher temps just by restricting the air flow - currently it's at a maximum. Reducing the venting rate will also reduce heat losses overnight. A decent air recirculating fan inside is as important as anything else.


I know you are a handy fella . some ideas from commercial models . solar water panels day time heat source , gas hot water system nite heat source . If you get that baby up to 50 deg then the next step is us your Rh sensor to vent the kiln at not sure what % Yep - have thought of all of those. The RH% that is required before venting is quite high - like 90%. In the first instance I will reduce the air flow until I get to 90%RH and see what temp I get. I want to keep the system as simple as possible.

According to a CSIRO document on solar drying kilns it doesn't matter if the temp oscillates a bit over 24 hours as it gives the wood a chance to relax and release it's moisture apparently you lose time- instead of 2-3 weeks it will take 6-8 weeks but you also get less warping and splitting.

I'm in no super urgent rush to get the wood. The seatainer is more of a storage than a drying shed. I just thought I would help to process along as much as I could using passive energy control.

[jmaxwell]

one other consideration with keeping it simple would be mass put as much timber in as possible . a solar gas 10 M3 kiln will take two full days to reach 50 deg but once at that temp the doors can be opened for quite awhile with minimum loss of heat

[BobL]

one other consideration with keeping it simple would be mass put as much timber in as possible . a solar gas 10 M3 kiln will take two full days to reach 50 deg but once at that temp the doors can be opened for quite awhile with minimum loss of heat

Good point. I only have the slabs from about 12 shortish logs inside there at the moment

[mobjack68]

I like your idea...my wife runs greenhouses and I slip my timber in there off season to dry and cure. We run cooling fans just to protect the plastic in the summer so I can adjust the temp up or down without a lot of trouble. If you need more temp in your box??? Paint it black....thermo/humidistat controls are not difficult, if you paint, you will need to exhaust...

[Waznme]

G'Day

To do a ° sign just hold Alt down and hit 0176.

Waz

[BobL]

G'Day

To do a ° sign just hold Alt down and hit 0176.

Waz

Unless like me you use a Mac, and just always keep fºrgetting it's ºptiºn º ! :D

[glock40sw]

G'day BobL.
Where did you get the USB sensors from?

I have a research project planned for one of our large Kilns and need remote data logging.

[BobL]

G'day BobL.
Where did you get the USB sensors from?

I have a research project planned for one of our large Kilns and need remote data logging.

Electus. These (http://www.electusdistribution.com.au/productView.asp?ID=9806&CATID=&keywords=logger&SPECIAL=&form=KEYWORD&SUBCATID=) are the ones - I got them for about 35% less than the RRP going through a tradie plus I ordered in bulk - pity you didn't see the post last year where I was collecting up orders.

We use them at work all the time and they generally work great - Over the last two years, 1 of the dozen or so we use has died but it was replaced under warranty.

Cheers

[BobL]

Here some temperature data for January of this year for my drying shed (a vented seatainer) which as about 2/3rd full of timber slabs when these readings were made

Firstly a couple of explanations.
o The red line shows the air temperature in the inside of the shed.
The blue line shows the outside temperature of the shed in the sun - its effectively the skin temperature of the seatainer (I place a temp sensor inside a steel box attached to the outside of the shed).
the Orange line shows the daily Max temp.
The Green line shows the daily min temp.

http://www.woodworkforums.ubeaut.com.au/attachment.php?attachmentid=72482&stc=1&d=1209563303

Some observations:

The highest temperatures are the skin temp of the shed which reaches about 55ºC when it was around 41ºC outside air temp.
The maximum air temp inside the shed is always greater than the daily maximum by ~7ºC but never more than the skin temperature.
The shed air temp never gets outrageously hot - The hottest it got to was just 46ºC when it was 41ºC outside. I could probably boost that by reducing the air extraction (two full sized whirly birds)
The lowest temperatures of the skin are equal to or slightly more than the overnight minima,
The minimum air temp inside the seatainer is ~5ºC greater than outside air temp.

This is an excellent demonstration of how a shed full of timber acts as a buffer against low and high container temperatures.

What I should be showing you is the RH data - it drops to less than 20 during the day but shoots up like a rocket during the night to over 90% when the air temp drops because the timber is still toasty warm and as I said in my first post, this rise in RH during the night helps the wood recover from the stress of drying out in the day and reduces splitting. This would be not good for thin boards but seems to be fine for 2"+ slabs for most wood because there does not appear to be much splitting.

[Tonyz]

Bob just to raise this again, and also my seasonalwork is coming to an end YIPPEE whats your overall impressions of the seatrainer?
A. Has it been worth while? 1. Time saved in drying
2. the overall expense
or are there easier , better ways to dry timber? Iam still trying to get this redgum I was chasing last year.

[BobL]

Bob just to raise this again, and also my seasonalwork is coming to an end YIPPEE whats your overall impressions of the seatrainer?
A. Has it been worth while? 1. Time saved in drying
2. the overall expense
or are there easier , better ways to dry timber? Iam still trying to get this redgum I was chasing last year.

I did not setup the seatainer specifically to dry the wood but for somewhere to store the wood at the yard after I milled the timber. I have no space at my house which is on small suburban inner city block.

When I asked around about storing green timber slabs inside what is essentially a solar oven (a close seatainer) I was advised not to do this but vent it at least a little. When I did a bit of research about solar kilns I realized that once the seatainer was full of timber, if the venting was right it would help speed up drying the timber and that is effectively what it has done.

I have not done any extensive MC testing but in general terms it appears to have almost dried 2" slabs over over one summer (albeit a pretty hot one) with no appreciable difference in splitting than what one would find from covered air drying and a lot less than exposed air drying.

I don't believe the rule of 1" of thickness per year for air drying really applies in Perth eg without even trying I have air dried 2" red gum slabs slab under my house in less than 18 months. By way of comparison, I have read that an intermediate level solar kiln with hot rock storage, will dry 1" thick slabs in ~3 weeks depending on the amount of solar energy available. The will be some cracking loses under the these conditions so there are tradeoffs for speed.

Was it worth it?
Seeing as it only cost about a grand and it dries my timber far faster than I can use it I would say yes. I would still have bought it even if was double that which is what they normally cost. The yard is in a doubtful neighborhood and I also needed some security.

My next main problem is that it is now almost full and I will have to think about getting another. :doh:

There are plenty of other ways of drying timber,
Shaded air drying is the cheapest
- stack with good supportive stickering
- place a shaded rain proof cover over the top
- shaded on the sides so they don't get too much direct sunlight
- make sure they can get plenty of airflow