No Drying for 1 week in July……Ugh! An update, 87 days of drying

[skyline]

The last few weeks have been interesting. We finally had some real drying conditions(for NW Oregon) and all but the smallest split outside have now lost more moisture than my control in the garage. They should have, as all but 1 were heavier to start with.

It is clear from my data that the drying rate is driven by how wet the wood is and the Equilibrium Moisture Conditions (EMC) outside. The farther apart these two are, that is, the steeper the gradient, the more grams of water my splits lose. Period. If nothing else, understand this and you will know how your wood dries. Clear from the graphs are that in the first half (~45 days) about 3x the water is lost than in the last half even though the drying conditions have been much better in the latter half. I like to use the EMC calculator here: http://www.dpcalc.org/ to see how a few degrees changes the RH and EMC. It helps explain why so little moisture is lost at night and while the control split in the garage can lose more than splits outside especially at night.

Two weeks ago we had a nice 83 degree day between a 70 and 71 degree day. Even though the average temp was only 3-4 degrees warmer, the splits lost between 3 & 4 times as much moisture as the day before and after. See data table. Meanwhile, I started drying 4 fresh c/s maple that same day. While the 2 month seasoned fir lost an average 46 grams that 80 degree day, my wet maple lost an average of 246 grams. It's moisture content was higher = steeper gradient, so they lost more moisture.

With 2 rain events this last week, my Doug Fir splits have lost almost nothing, even the 4 splits under cover gained moisture during the week! But the 4 fresh maple splits I started just a few weeks ago still managed to lose an average of 133 grams. Almost 3 months down and my fir splits have lost between 31.5 - 45.4% of their starting weight. That means that if they all started at 95% MC the driest would be at 7% and the heaviest would be at 34%. They clearly didn't start at the same MC, but it points out that after equal drying time, the size and shape of my splits has a huge effect on their current MC.

It's clear that if you have the room and time, stacking splits in a single row for a couple of years will usually get the job done. But drying inside can be equally effective and considerably faster during some parts of the year especially when temperatures inside are slightly above outside temps. (Nov-May in NW Oregon) Some have said that wood doesn't soak up the rain like a sponge and that is "kind of true". It will get heavier after rainy or wet periods, even if under cover, but that moisture is more quickly lost than the first time it was lost so in the long haul it is not a big deal when we are just trying to get MC's under 20%. But if you're trying to dry quickly, it slows the process. And of course the dryer the wood the more likely it will gain weight in wet conditions.

For the curious, my control split now measures 15% on the moisture meter after 87 days of drying and since it is loosing just a few grams per day, I think it is pretty close to equilibrium. If the meter is accurate, it means it started at 87% MC which I think is about right. Also, being in the garage, it has never gained wt throughout this drying process.

To see how bad our "seasoning weather" has been, check out the monthly weather summaries here: http://www.wunderground.com/history/airport/KPDX/2011/6/23/MonthlyHistory.html#calendar

If you really want to know how your wood is drying, get a scale and see when your wood is really drying and when it's not! What I found is that there is a lot of wasted time in the typical seasoning process.

To recap: I started seasoning some splits from a 120' fir felled, c/s/s the same day and started weighing back on April 18th.
Previous post:
https://www.hearth.com/talk/threads/75789/

 

[jimbom]

Very interesting. Please keep the updates coming. Thanks for your effort.

 

[NordicSplitter]

More helpful than you'll ever know. Thanks so much

 

[Battenkiller]

Nice work, Sky! Been waiting for this for awhile now. Glad to see you followed up on it.

Nice to see the same basic curve shapes I was getting in the Battenkiln, even if the drying times themselves are longer here. It's totally what I expected to see, of course, just good to see more confirmation. As is apparent to me, tracking the weight of your wood as it dries is the best possible way to predict when it will be ready to burn. That was, after all, the real reason for me doing my drying experiment in the first place, not to try to convince folks that a heated basement is the best place to season your fuel. ;-)

 

[skyline]

Nice work, Sky! Been waiting for this for awhile now. Glad to see you followed up on it.

Nice to see the same basic curve shapes I was getting in the Battenkiln, even if the drying times themselves are longer here. It's totally what I expected to see, of course, just good to see more confirmation. As is apparent to me, tracking the weight of your wood as it dries is the best possible way to predict when it will be ready to burn. That was, after all, the real reason for me doing my drying experiment in the first place, not to try to convince folks that a heated basement is the best place to season your fuel. ;-)

Thanks Batten,
After a second week of wet weather here and a high of 63 yesterday when our normal is 80, I really wish I had a nice heated basement to dry my wood supply. But what I do think it shows is that a solar dryer will be the solution here in the wet NW. I'm thinking it also might take care of a few pests hanging around. I'll send pics when I get er' dun!

 

[Jutt77]

Good stuff, thanks.

 

[woodchip]

What I found is that there is a lot of wasted time in the typical seasoning process.

Surely the "wasted" time is just a period when the wood is apparently seasoning a bit slower.
Although a split will lose weight slower, the moisture deep inside will still come towards the surface during this "wasted" time, and when the weight loss speeds up again it is because the moisture is nearer the surface and is released into the atmosphere during the next dry breezy spell.

So is that really wasted time, or have I read it wrong?

BTW, Thanks for the update so far

 

[DexterDay]

Nice work, Sky! Been waiting for this for awhile now. Glad to see you followed up on it.

Nice to see the same basic curve shapes I was getting in the Battenkiln, even if the drying times themselves are longer here. It's totally what I expected to see, of course, just good to see more confirmation. As is apparent to me, tracking the weight of your wood as it dries is the best possible way to predict when it will be ready to burn. That was, after all, the real reason for me doing my drying experiment in the first place, not to try to convince folks that a heated basement is the best place to season your fuel. ;-)

Thanks Batten,
After a second week of wet weather here and a high of 63 yesterday when our normal is 80, I really wish I had a nice heated basement to dry my wood supply. But what I do think it shows is that a solar dryer will be the solution here in the wet NW. I'm thinking it also might take care of a few pests hanging around. I'll send pics when I get er' dun!

I still have yet to start my experiment. With my Sons baseball, The Newborn baby girl and all the work around the house. It may be later in the year before I start mine. But as far as the science of things. You are way more in depth than I know I will be. I know to weigh the wood instead of the Moisture meter (still going to use it though). Just letting you know, I/We appreciate the work. Good job. Cant wait till I can do my Barn/Shed/Outdoor Testing...

 

[karl]

What shape split leads to a quicker drying time?

 

[skyline]

What I found is that there is a lot of wasted time in the typical seasoning process.

Surely the "wasted" time is just a period when the wood is apparently seasoning a bit slower.
Although a split will lose weight slower, the moisture deep inside will still come towards the surface during this "wasted" time, and when the weight loss speeds up again it is because the moisture is nearer the surface and is released into the atmosphere during the next dry breezy spell.

So is that really wasted time, or have I read it wrong?

BTW, Thanks for the update so far

Woodchip,

Unfortunately we've had more wet weather and now some of the splits weigh the same today(July 18) as they did back on the July 3rd. Even the splits under cover are back to their weights on the 10th. No doubt much of this is surface moisture that will be more quickly lost as soon as we get some warm dry weather.

I'm not sure totally agree with your assessment even though I understand the logic. I think you are kind of assuming that if the interior is at 30% gradually going towards the surfaces at 20% that moisture would still be moving along towards the exterior. If the exterior is suddenly at 100%, I suspect the interior moisture would have essentially no driving force towards the exterior (in fact the opposite) until the surface dries below 20% again. Even though conditions will always try to equalize, with no moisture leaving the surface, the gradient in the interior would be almost flat and I think the wet surface would provide the steepest gradient towards the center and like a traffic jam, with no moisture leaving, it won't be moving from the interior towards the edges either.

There is a lot of guessing going here but what I see in my data is that when conditions are right, moisture leaves very quickly at rates that would completely dry the wood in a few weeks if continuous. Since it often takes a year to season, I think we tend to over estimate the time it takes moisture to travel through the wood but that is because our gradients are usually not very steep for very long. Even if you didn't know about kiln's, Battenkiller's dry basement experience is more than enough data to show that seasoning doesn't need the year often quoted around here.

 

[woodchip]

Thanks for your thoughts.
I have half a cord spread out in a couple of glasshouses to speed up drying.
Plenty of warm dry wind, and they are drying really quickly, but watching your more natural seasoning with much interest.

Mine is birch, which dries quite easily anyway though.

 

[joefrompa]

You've obviously got the info nailed down, but I'll just add that the amount temperature drives wood-drying has blown me away. For me, in PA, wood seasons fairly slowly between 30-50 degrees. And by slowly I mean no notable weight change in ~1 month.

But when I'm at 90-100 degrees outside, the wood is getting seasoned in a matter of weeks (including no rain during this time, or a bare sprinkling)

In my neck of the woods, what I'm seeing is that I can season maple in 3 months, pine in 6 weeks, and oak is probably still a year but just a year - as long as I get it split by ~June. Elm is good in 3-4 months as well under the same guidelines.

So for me, it's not about getting it all C/S/S for 1 year. It's about getting it C/S/S in time for the ~3 really hot months (June 15-Sep 15) and I'll be good to go for all but the most stubborn woods.

 

[skyline]

You've obviously got the info nailed down, but I'll just add that the amount temperature drives wood-drying has blown me away. For me, in PA, wood seasons fairly slowly between 30-50 degrees. And by slowly I mean no notable weight change in ~1 month.

But when I'm at 90-100 degrees outside, the wood is getting seasoned in a matter of weeks (including no rain during this time, or a bare sprinkling)

In my neck of the woods, what I'm seeing is that I can season maple in 3 months, pine in 6 weeks, and oak is probably still a year but just a year - as long as I get it split by ~June. Elm is good in 3-4 months as well under the same guidelines.

So for me, it's not about getting it all C/S/S for 1 year. It's about getting it C/S/S in time for the ~3 really hot months (June 15-Sep 15) and I'll be good to go for all but the most stubborn woods.

Joe and Woodchips,

Thanks for your input. Glad to see that both greenhouse seasoning and the hot weather is really working for you. For us in the Pacific NW it is the same. Wintertime seasoning barely happens, heck event the last 2 weeks have not dried my wood any except the recently split maple. You might pay attention to the calculated EMC, (http://www.dpcalc.org/ ) you'll find that with a 30 °F increase in temp. you may have a corresponding 30 % drop in RH and cut your EMC by 60%.

For example if you have conditions of 70 °F, 60% RH and 56 °F Dew point, this calcs an EMC of 11. A green house that increases the temp 30°F will lower the RH to 22% and the EMC to 4.5. This will make the moisture gradient a lot steeper and moisture will really want to leave your wood. I hope to have a solar test soon.

Skyline

 

[joefrompa]

The thing that really impresses me about your research is that indoor seasoning is not only possible, but actually preferable if the differential between what would be actualized outside is great enough.

For example: putting your wood in a closed shed during winter, or in the garage where the ambient temp might be 20 degrees higher than outside, is probably preferable than keeping it covered outside.

 

[Battenkiller]

You might pay attention to the calculated EMC, (http://www.dpcalc.org/ ) you'll find that with a 30 °F increase in temp. you may have a corresponding 30 % drop in RH and cut your EMC by 60%.

For example if you have conditions of 70 °F, 60% RH and 56 °F Dew point, this calcs an EMC of 11. A green house that increases the temp 30°F will lower the RH to 22% and the EMC to 4.5. This will make the moisture gradient a lot steeper and moisture will really want to leave your wood. I hope to have a solar test soon.

Sky, I have read this several times and I still don't understand what you are trying to say. Are you saying that the instantaneous drying rate is entirely dependent on what the EMC is at a given time? If so, you are neglecting the effect of internal wood temperature on the diffusion rate of the water inside the splits. Raising the temperature of the wood itself will create a high diffusion rate independent of the RH of the surrounding air. This is done in kilns to accelerate drying times.

Also, from your other thread (which I originally missed because I was very ill) I get the idea that you are downplaying the effect of air movement on drying time. I have to disagree with that notion. It is well known that air movement is very critical to fast drying. When air is just barely moving through the wood, the flow is primarily laminar. As air velocity increases, air flow become much more turbulent. Just as turbulent air flow inside your stove drastically improves the mixing of fuel gases with air and increases combustion efficiency, so does it improve the mixing of water vapor leaving the wood with the drier air passing by, thereby increasing the drying rate.

 

[Woody Stover]

In my neck of the woods, what I'm seeing is that I can season maple in 3 months, pine in 6 weeks, and oak is probably still a year but just a year - as long as I get it split by ~June. Elm is good in 3-4 months as well under the same guidelines.

So for me, it's not about getting it all C/S/S for 1 year. It's about getting it C/S/S in time for the ~3 really hot months (June 15-Sep 15) and I'll be good to go for all but the most stubborn woods.

I'm behind, so I'm hoping this holds true for me, even though the humidity is probably higher here. The way things are going, I get the feeling that August will be a scorcher as well. A warm September with lower humidity would sure be welcome. At any rate, I'm in better shape this year than ever before. Ash and Cherry for this Fall, instead of Oak, and I've got more split earlier. I think we'll be in good shape but the suspense is killing me. :lol:

 

[maplewood]

Wow. Very interesting and detailed.
One of the most in depth studies I've read on this site.
I just wait at least a year, and put the wood in after at least 7 days of dry weather.
I put in about 3 cord over the last week. We had rain last today, so I'll have to wait to put in the next 9 cord.
Yes - that's 12 full cord. At about 20% moisture content. And it dries out more in the house: in floor heating is a wonder!
Happy burning.

 

[fire_man]

Skyline:
Posts this good are gonna make Craig start to charge us to access the site! Can you dumb it down some? :bug:

 

[skyline]

What shape split leads to a quicker drying time?

What I see clearly in my data is skinny is best. My 21'' skinny split has lost considerably more than the fatter 17" long split even though the fatter split had more to lose.
Specifically, sample A (17.5" long) started at 7394 g and has lost 2368 g after 2284 hrs. Sample F (20.5" long) started at 6496 g and has 2611 g after 2284 hrs. What's important is that if you assumed their starting MC at 90%, and do the math, sample A is at 29% and sample F is at 14%. Splits from the same tree C/S/S the same time!

The thing that really impresses me about your research is that indoor seasoning is not only possible, but actually preferable if the differential between what would be actualized outside is great enough.

For example: putting your wood in a closed shed during winter, or in the garage where the ambient temp might be 20 degrees higher than outside, is probably preferable than keeping it covered outside.

Yes, exactly but I think a fan or other air movement is important. It doesn't have to be a gail, just enough to keep the surface unsaturated.

You might pay attention to the calculated EMC, (http://www.dpcalc.org/ ) you'll find that with a 30 °F increase in temp. you may have a corresponding 30 % drop in RH and cut your EMC by 60%.

For example if you have conditions of 70 °F, 60% RH and 56 °F Dew point, this calcs an EMC of 11. A green house that increases the temp 30°F will lower the RH to 22% and the EMC to 4.5. This will make the moisture gradient a lot steeper and moisture will really want to leave your wood. I hope to have a solar test soon.

Sky, I have read this several times and I still don't understand what you are trying to say. Are you saying that the instantaneous drying rate is entirely dependent on what the EMC is at a given time? If so, you are neglecting the effect of internal wood temperature on the diffusion rate of the water inside the splits. Raising the temperature of the wood itself will create a high diffusion rate independent of the RH of the surrounding air. This is done in kilns to accelerate drying times.

Also, from your other thread (which I originally missed because I was very ill) I get the idea that you are downplaying the effect of air movement on drying time. I have to disagree with that notion. It is well known that air movement is very critical to fast drying. When air is just barely moving through the wood, the flow is primarily laminar. As air velocity increases, air flow become much more turbulent. Just as turbulent air flow inside your stove drastically improves the mixing of fuel gases with air and increases combustion efficiency, so does it improve the mixing of water vapor leaving the wood with the drier air passing by, thereby increasing the drying rate.

BK, Sorry I was out and missed your post and hope you are feeling better. What I was trying to emphasize is that the bigger the difference between your woods MC and external EMC conditions, the faster the drying. And yes the higher the temperature of the wood, the higher the diffusion rate, but from a practical point of firewood drying, we're not choosing between raising our wood temp vs. lowering EMC conditions, we usually are doing both at the same time. If we use a solar shed or dry our wood in the garage over winter, we are raising the temperature of the air around our wood and the wood as well and lowering RH and lowering the EMC. Also, I'm guessing the kiln's have to raise the temp. to dry the wood quickly at the high RH's they try to dry wood at. And with the high RH's the dry at, they definitely need to be sure to mix the air thoroughly as you mention air moving slowly over long flat boards will have laminar flow even with the stickers. But I'm quite sure my wood stacks have never created laminar flow, maybe Zaps ;-) I think we all recognize the importance of air flow, but I think sometimes it is over emphasized on this forum at the expense of increasing temp and lowering RH. From my experiments, just a small amount constantly from a fan or convection in a solar shed was way better than fully exposed to wind outside during marginal conditions.

Interestingly, my wood splits drying in the shade versus in the sun don't seem to show any trend in difference in drying even though I can clearly feel their temperature differences when weighing them.
The good news is we finally have a drying weekend and we should get back on track for the summer. And with this good weather moving in, maybe you folks in the midwest will get a break from the heat!

In case you haven't seen it, but from Wiki's article on "Wood Drying"

A simple model for wood drying
The rate at which wood dries depends upon a number of factors, the most important of which are the temperature, the dimensions of the wood, and the relative humidity. Simpson and Tschernitz[1] have developed a simple model of wood drying as a function of these three variables. Although the analysis was done for red oak, the procedure may be applied to any species of wood by adjusting the constant parameters of the model.
Simply put, the model assumes that the rate of change of the moisture content M with respect to time t is proportional to how far the wood sample is from its equilibrium moisture content Me, which is a function of the temperature T and relative humidity h: