passive solar wood shed and seasoning

[pyper]

I have a passive solar design book, and my location has a ton of solar heat falling on vertical west-facing surfaces in the summer, which is handy because it's the only side of my shed that isn't shaded. I also plan on using the north west corner for storing wood, because it's the space that works best. It's an 8 foot cube, which is plenty for storing all the wood I'll need for a few year's supply.

I've been thinking about how seasoning works in relation to my climate.

In the summers it's hot and humidity. On a typical summer day the humidity ranges from about 50% to about 98%. Given the way humidity works, the highs are at night when it cools off. We get a lot of dew as it cools off. Water will condense on anything.

So I'm thinking of making a solar chimney on the west exposure of my shed to draw the relatively dryer afternoon air into the wood area. It would automatically stop at dusk (when the RH starts to climb). Having the wood in the shed with relatively dryer air would prevent dew from collecting on the wood, which would happen outdoors.

My shed has openings at the bottom, and open soffets, so air moves through it easily.

Thoughts?

 

[skyline]

I'm thinking it would work well. From my testing see https://www.hearth.com/talk/threads/52010/
I was able to lose over 21% (fir) & >41% (alder) moisture in 10 days on splits with just a fan and no heat at an average RH of 84% and average temp of 47 F.

So at your temperatures and reduced RH over ambient from solar gain, you should be able to "bake" it pretty quickly as long as you get enough air flow to remove the moisture you pull out of the wood.
I recommend the scale method to evaluate your progress. Just make sure you weigh your splits at the very beginning because they may lose half their moisture in the first few days.

The information below is from this website (broken link removed) which may help.

How Wood Dries

Wood will seek an equilibrium moisture content (EMC) in relation to the relative humidity (RH) and temperature of its surroundings. That is, as wood is dried below its FSP, the amount of moisture leaving the wood will be determined by the relative humidity of the atmosphere surrounding the wood. Table 1 shows the EMC over a range of humidities. For wood to air dry, the moisture content of the air must be less than that of the wood.

Table 1. EMCs at Different Humidities for 30 to 90°F
RH 10 20 30 40 50 60 70 80 90
EMC 2-3 4 6 7-8 9-10 10-11 12-13 15-16 10-21

 

[Adios Pantalones]

There have been a number of studies to see if certain passive solar methods will speed drying. These include several variations of vented sheds and plastic covered stacks with airspace below and vents above. It seems that in many cases ( I haven't seen them for all arrangements) there's a tradeoff between total airflow and heat that about breaks even- so when there's a nice stiff breeze, it doesn't help your wood dry if it's enclosed. Tell us more about your shed design (or provide pics- I love shed pics!)

Solar lumber dryers often rely on windows to allow in sunlight, and electric fans to supplement the airflow (even the somewhat famous Mother earth News design).

I think that if one constructed a good sized sheet metal box painted flat black, and attached it to the inlet- maybe it would give a nice boost to heat and convective airflow. If I had lots of time on my hands I'd love to experiment with it.

 

[pyper]

Thanks. I actually got the idea from the other thread!

That's a neat link. I think he must have a typo in the last column though -- I bet it's supposed to be 18-21.

It sounds like my biggest challenge will be in finding a way to get air to circulate to the interior portion.

 

[WoodPorn]

How about a seperate fan to move a column of air up from the center?

You could also (fairly inexpensively) use solar panels to power some 12v fans.

 

[skyline]

I think that if one constructed a good sized sheet metal box painted flat black, and attached it to the inlet- maybe it would give a nice boost to heat and convective airflow. If I had lots of time on my hands I'd love to experiment with it.

I have been thinking of using this same box idea. Just a few extra degrees heat lowers the RH quite a bit and both help to drive the EMC down.
I'm guessing the ultimate setup would have your vents controlled by the RH and wind speed. I'll let you know and send pics when I have that all figured out ;-)

I'm guessing pyper is right that would be a typo on the website (should probably be 20-21) I'm not sure I totally follow the table with so little variation in EMC across 60°F at the same RH. If it were a typo I'm assuming that at 90 °F and 90% RH the wood EMC could go to 20 but at 30 °F it would only go to 21?

 

[Adios Pantalones]

When I made lots of bows the rule was 30% RH gets you about 6% MC- that's borderline too dry. 50% RH gets you about 9% MC- that's getting too wet to make a nice bow. Idependent of temperature (which drives the time part)

 

[savageactor7]

My shed has openings at the bottom, and open soffets, so air moves through it easily.

Thoughts?

While I wouldn't swear under oath to this, I still be willing to bet that other deep south members here have commented how fast fire wood will rot down there.

With that in mind I wound NOT store my wood in any kind of hot box. Instead I want it stored in an open shed like you would shelter horses in.

 

[midwestcoast]

I've kicked around the idea of a solar shed too, but don't have a good location (unless I burn a shade-tree or 2...)

"It sounds like my biggest challenge will be in finding a way to get air to circulate to the interior portion." Assuming your shed has a floor, how about moving some or all of your inlets to the floor near the center of the shed instead of at the perimeter? Or just duct inlet(s) to the center within the shed.

""Adios Pantalones - 04 February 2010 02:15 PM
I think that if one constructed a good sized sheet metal box painted flat black, and attached it to the inlet- maybe it would give a nice boost to heat and convective airflow.""

"I have been thinking of using this same box idea. Just a few extra degrees heat lowers the RH quite a bit and both help to drive the EMC down." Cool idea! Guess you'd just have to keep the box below the inlet to keep it flowing & voila, pre-heated, turbo-charged inlet!

How are you planning to make the chimney? Just a black pipe or are you glazing one side?

 

[Wood Duck]

Instead of focusing on solar energy heating the wood, think about how to use solar to circulate air through the stacks. It seems like a chimney could be rigged to use solar energy to create a strong updraft, and that could move air through the stacks. Of course the wood will heat up, but air movement will be key to removing the water.