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Does wood season quicker in winter, since it’s dry? Weird...

Post in 'The Wood Shed' started by thinkxingu, Jan 1, 2010.

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  1. Rockey

    Rockey Minister of Fire

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    The pictures in this thread dispell it even further: http://www.hearth.com/econtent/index.php/forums/viewthread/49669/

    Helpful Sponsor Ads!





  2. woodgeek

    woodgeek Minister of Fire

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    Didn't mean to beat up on you, Batten, I think we are agreed about the behavior of water/ice. I was just hopped up about all the 'energy' talk in this thread and I painted you with that brush--sorry.

    Your other point is a good one: that water adsorbed in/on wood fibers is not that same as bulk water--agreed. It will have to have a different vapor pressure vs temp. For very hygroscopic compounds, this vapor pressure will be much lower. While wood fiber is certainly somewhat hygroscopic, the fact that its equilibrium MC is pretty low suggests that it does not do such a great job pulling water from the air by adsorption energy--so I think using the bulk water thermodynamics is not likely to be too shabby.

    On your other point that 'transport' is the limiting factor other than partial pressure, well remember that wood is a highly porous structure with a huge specific area. Much of the transport through the wood could be driven by (or limited by) vapor diffusion in the pore spaces. In this limit the diffusive water flux is ALSO proportional to the (temp dependent) vapor pressure.
  3. leaddog

    leaddog Minister of Fire

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    Sorry guys but I just did an experment and just proved that my wood drys faster in the winter. I took a load of wood that was average of 24%. I very carefully placed it in my top compartment of my eko-80 and within 4hrs it was completely dry. This is with a outside air temp of 26* on Jan. 6.
    This has been very interesting though. It's amasing how much a person can learn here on the net.
    leaddog
  4. Battenkiller

    Battenkiller Minister of Fire

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    I may have to throw my hands up on this one. You keep directly quoting me, yet entirely misinterpreting what I am saying. Then you go on to tell me exactly what I have been saying all along. All in good fun, regardless. :)


    72" bow staves are not 16" firewood splits. They are very long relative to their cross sectional area, and if you are drying them properly, you should be sealing the end grain anyway to avoid checking. If sealed, nearly 100% of the water lost will be by diffusion across the thickness and evaporation along the sides, with nothing lost at the ends. Go to any yard that specializes in air-dried lumber. There will be checks in the ends that go down about 4-6" or so (unless they are sealed before stickering) 6" on both ends of a 16" firewood split is most of the whole thing. I have several hundred board feet of air-dried northern white cedar, cherry and basswood 4/4 planks from 6-18' long that all show this end checking. Only way to prevent it is to seal the ends or to start the drying process near the 100% RH mark in a kiln.

    Picture taking slices of a round of oak on a deli slicer (we actually did this with a microtome in my botany course). All drying will occur at the ends, and none will happen along the sides. Regardless of what some guys think, length matters.

    On the sublimation thing, I'm not the one that is claiming that wood is drying while it's frozen. I personally feel that it is likely that very little sublimation occurs once the outside is dry since there is very little ice at the surface to sublime. It's the old timers I used to talk to that called it freeze drying, I'm just looking for a better explanation for the winter drying phenomenon I have experienced with stacked cord wood. I am currently hypothesizing that drying occurs during the thaw cycles, not the freezes. I thought I have made that as obvious as possible in as many ways as I care to say it.

    Anyway, all I am maintaining is that beating up firewood by exposing it to extreme cold may help it dry better later. I never once said anywhere that wood dries faster in the cold, just that deep freezes help loosen up the free water so it can get released easier when the temps rise and RH drops. I have no scientific proof of this, but I have come to this conclusion based on many years of experience. Your experience may be different. LL belives his winter dried wood gets soggier in the summer, and he may be correct if his average RH is higher in the summer than in the winter.


    Anyway, Adios Muchacho. I have to go figure out why I'm getting a smoky burn today even though I'm using the driest, hardest and most thoroughly beat up wood I own. ;-)


    Now... let's turn it back over to the physical chemist. I'm really intrigued by what he is saying. I particularly want to know why (mechanistically) there are lower vapor pressures in hydroscopic materials. And is wood actually hydroscopic to any great degree? Even at 100% RH, it fails to pick up much moisture once it is fully seasoned. Seems entirely driven by RH and cohesive forces rather than the molecular attraction of water molecules to a substrate that I think of when someone uses the term hydroscopic.
  5. iceman

    iceman Minister of Fire

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    what a thread!!!
    this is great!
    there has to be a temp, rh%/ dewpoint/ and breeze that is the ultimate for drying wood......
    we know it dries in the summer...
    we know it dries in the winter....
    which would go back to ooooooooooo
    in which ever season you get the best conditions... that allow the moisture to get out.....thats when your wood will season faster....
    for most it prolly will be summer for some it will be winter.. it all depends on your location AND what weather you experience during the time the wood is "seasoning"
  6. Adios Pantalones

    Adios Pantalones Minister of Fire

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    "72” bow staves are not 16” firewood splits."

    Exactly- but they dry quickly anyway- whether the end is sealed or not (and it's not always necessary- depending on a mess of factors)- which shows that a split will dry without water going through the ends. That's why I quoted you and disagreed- see also the pics etc alluded to earlier.

    "Picture taking slices of a round of oak on a deli slicer" OK- then the bulk of the wood's surface area is end grain- so the analogy is really not appropriate. In a normal split- most of the area is sides.

    "Now… let’s turn it back over to the physical chemist."
    Well, I have a PhD in analytical chemistry- sometimes called applied physical chemistry, but as you wish.

    "I particularly want to know why (mechanistically) there are lower vapor pressures in hydroscopic materials. "

    It's hygroscopic, not hydroscopic (sorry- a pet peeve)- and wood comes to an equilibrium. In fact, bow makers (for shootin' bows) will target 30-40% RH in order to achieve optimum RH in the wood. You can set a hygrometer in a drying box or drying area, and the wood will equilibrate to 6% MC at 30%RH, and something like 9%MC at 50% RH. This is a very reversible process without "firced drying", so the wood is not hygroscopic. I supposeby loose definition- a wood at an MC corresponding to an RH that is lower than ambient is hygroscopic.

    There are several easy treatise on what makes something hygroscopic- but essentially, the material accepts a hydration sphere that's not currently satisfied. Add energy and you drive off water.

    "Even at 100% RH, it fails to pick up much moisture once it is fully seasoned. Seems entirely driven by RH and cohesive forces rather than the molecular attraction of water molecules to a substrate that I think of when someone uses the term hydroscopic. "

    I don't get it- you contradict yourself between the first and second sentence- is it RH or not? Cohesive factors? Huh?
  7. Rockey

    Rockey Minister of Fire

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    The myth(title to this thread) has been busted. Firewood, just like lumber seasons MUCH faster in the summer than the winter in over 50 cities that were tested.


    “In addition to the effect of summer–winter temperature differences,
    estimates of air drying time are affected by the time of year
    when the lumber is stacked. Lumber stacked in the spring
    may dry in a relatively short time because a large portion of
    the drying may be in the warm spring and summer months. In
    contrast, lumber stacked in late summer or early fall may take
    a relatively long time to dry because it will be exposed to
    winter temperatures, when drying may almost stop."
    - US Department of Agriculture Forest Services
  8. Adios Pantalones

    Adios Pantalones Minister of Fire

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    If wood dried through the ends soo much better than the sides, then we would not need to split it to dry it.
  9. JerseyWreckDiver

    JerseyWreckDiver New Member

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    My god. Junk science is one way of putting it... I've been refraining from posting lately on things like this because it seems there are some people who come here just to argue and plenty who think they can keep from being wrong just through shear insistence. Glad to see the likes of; Wood Duck, Woodgeek, Green Energy, Adios, Dave and others posting with good, provable science. (Not to mention punctuation and proper grammar...)

    What the above posters have stated can't be argued, I don't care how much you really really mean it, your wrong. Yes, the air in Winter is much much much much drier. That's because the cold air isn't capable of holding as much moisture as warm air!!!!@#$!@$!@!

    There are some here that just won't be convinced no matter what anybody says. God himself could come down and tell them they are flat out wrong and they would just dance around it. But for those who are interested, do a search for a document from the Department of Agriculture/Forest Service/Forest Products Laboratory General Technical Report FPL-GTR-118 - Drying Hardwood Lumber. It's a lengthy document, 144 pages. I doubt I will be able to attach it to this post but I will try. Page 39 begins the section below, this is only the first paragraph. (Sorry, this also puts the kibosh on you "it dries faster uncovered" people. There are other sections of the document that talk about winter drying and from an extensive, NATIONWIDE study, most areas in December/January etc... have only a few drying days compared to Summer months.



    Climatic Conditions
    The climate of the area or region in which the hardwood air
    drying yard is located greatly influences the air drying rate
    and yard output. The most influential factor is temperature,
    but RH and rainfall also play roles. In the northern United
    States and most of Canada, the drying rate is retarded during
    the winter months by low temperatures
    . In the southern
    United States, where the winter dry-bulb temperatures are
    higher, better drying conditions are expected. However, these
    higher temperatures may be offset in some localities by rain
    that wets the lumber and extends the drying time, unless the
    lumber is well protected. Research on beech, sugar maple,
    and red oak by Peck (1954, 1957, 1959) indicated that hardwoods
    air dry at a moderate rate when the daily mean temperature
    exceeds 45oF (7oC) and at a considerably faster rate
    when the temperature exceeds 60oF (16oC).

    Well, I last put wood in the Vigilant around 9:00 am, about 23f here right now and I hear a bed of coals calling to be fed. Good night all.
  10. Battenkiller

    Battenkiller Minister of Fire

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    Adios, I have no idea what anyone's academic background is on a bulletin board, so don't be offended. And for the record, just because I don't spell a word like hygroscopic correctly doesn't mean you are correct in your analysis just because you point it out. Must I point out that you spoke of the optimum RH in the wood? What exactly is RH in wood, and how exactly does it correlate to MC in wood and the RH of the air the wood is at equilibrium with? :)


    Did you really make an effort to illuminate what hygroscopic means by telling us it's a material that "accepts a hydration sphere that's not currently satisfied"? I never implied that I have any advanced chemistry in my background. My understanding is simply that of a lay person smitten with curiosity, so bear with me, eh? When I am pressed to describe what is going on in a piece of wood, I use terms that I feel are correct, even though they may not be. I know water molecules have a strong attraction to each other because they are highly polar molecules. I thought that on a macro scale, that was called cohesion. The term has been used in the literature to describe why water can stay up way above 32 feet even after transpiration stops. I believe that capillary action is a cohesive force, but feel free to correct me if I am wrong.



    The water in wet wood leaves the end grain primarily through the tubules that run longitudinally within it. The shorter you cut it, the faster it will leave the wood.


    It makes sense to me that water will be drawn along the tubules via capillary action, so when some disappears at the ends, more will be drawn along to replace it. If that has nothing to do with cohesion, then simply correct me, don't accuse me of contradicting myself. When I said, “Even at 100% RH, it fails to pick up much moisture once it is fully seasoned. Seems entirely driven by RH and cohesive forces rather than the molecular attraction of water molecules to a substrate that I think of when someone uses the term hydroscopic.", I was replying to another poster who was speaking of wood being hygroscopic to some degree. I felt that there were other forces that were at play that were responsible for the re-uptake of water into wood, and that even at 100% RH, wood failed to continue to attract water molecules past the point of equilibrium as a truly hygroscopic material would. Therefore, the entire rehydration process had to do with RH alone, and water's strong affinity for itself keeps it from continuing to dry out past equilibrium. Maybe not a solid scientific explanation, but hey, I'm not submitting my posts here for peer review.


    The water in wet wood leaves the faces primarily by the process of diffusion across the grain. The thinner you split it, the faster it leave the wood.


    I cut guitar wood to about 3/16". The pieces are about 24" long and about 9" across. Cut that way like a veneer, they dry so fast through the faces that they never check at the ends. But if I left them in split wedges, they would be useless inside a couple of days because the checks formed at the ends would propagate even after the wood was cut into slices. That's why it is necessary to seal the ends thoroughly if they are left in large splits.



    You don't need to have an analytical physical chemist tell you that wood dries through the faces as well as through the end grain. Anyone who has split green wood for kindling knows it will be dry as a bone in a day or two inside the stove room. I don't think anyone believes that the air sucks it all out of the end grain like a drinking straw.

    All I am saying is that the free water, water that is not bound to the cellular structure of the wood fibers themselves, leaves a lot faster than it does through the faces in most species of wood, but the ratio of drying between the two surfaces depends on how the wood is cut. It's not just about the relative sizes of the surface areas. Wood is not homogenous in structure. That's why checks form at the ends, even in long boards.


    Anyway, aside from all this... I'm interested in the bows you make. You mentioned Tonkin cane on another thread. Are they laminated? Any links so we can see them?
  11. skyline

    skyline Burning Hunk

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    I came here looking for more ideas for improving my wood storage but this has been a fun read and I just can't resist jumping in.

    Some observations:

    We all have trouble being persuaded on anything that is counter to our experiences especially when we think we know why they happen, me included, Rockey too! :coolsmile:

    From my background I will stand firmly in the camp that the Relative Humidity(RH) gradient between the wood and surrounding air PRIMARILY drives the drying process, not temperature, but yes since RH is related to temperature, it is also a factor but less relevant regarding what has been posted and less important as several have explained!!!.
    If my physics, climate and hydrology classes hadn't taught me that, living in Virginia in the summer and Nevada in the winter certainly has.

    But don't take just my word for it, check out http://www.woodweb.com/knowledge_base/Wood_Handbook.html for the most authoritative discussion on wood properties.
    To quote the "Wood Handbook" often considered to be the wood workers bible,
    "The rate at which moisture moves in wood depends on the relative humidity of the surrounding air, the steepness of the moisture gradient, and the temperature of the wood. The lower the relative humidity, the greater the capillary flow. Low relative humidity also stimulates diffusion by lowering the moisture content at the surface, thereby steepening the moisture gradient and increasing the diffusion rate. The greater the temperature of the wood, the faster moisture will move from the wetter interior to the drier surface.

    So everyone deserves some credit but RH is the driving factor.

    Rockey may be correct in that in "most" places of the U.S. for us wood burners, there is an advantage in summer drying over winter, but if you mistakenly think it's primarily temperature driven and not RH it won't necessarily help you with your wood storage design, drying techniques and how best to take advantage of winter's low relative humidity and those things are ultimately why many of us are here. And while others have correctly pointed out, that it depends upon where you are. See Table 12–1."Equilibrium moisture content of wood, exposed to outdoor atmosphere, in several U.S. locations"
    in 1997 in Wood Handbook, often there is negligible difference between summer and winter in natural outdoor conditions and most of us are trying to modify those by covering our wood, sheds etc.

    The original question (I think :-S) about drying faster or slower in summer or winter that morphed into why or how fast our wood dries in winter may not be the right question. The wood will dry the fastest when it is the wettest and the RH is the lowest. RH being the same it will dry faster at higher temps. Just like the temperature of our hot coffee cools the fastest at first (when the gradient is highest), the wood will lose its moisture the fastest when its first cut and split and the gradient is likely to be the highest and gradually slow down from there. This is like every other steep gradient we experience whether it be temperature, humidity, speed etc.

    We probably don't compare this often as I suspect most of us cut and split our wood when the weather is nice, when our wood is the wettest and will therefore dry the fastest. But I recommend everyone buy an extra scale and take it to your wood shed. Weigh a few fresh rounds, split them and tie the pieces back together (bark to bark) and re-weigh them everyday and watch how fast the weight decrease at first and then more slowly after that no matter the temperature. Put one round on the pile, the wind, the garage and see what works best in your location and season and share the data.

    Below freezing temperatures, wood species, cell structure also play a role. I had a shear splitter once and the wood dried faster than when saw cut when tested due to the wood fibers being torn instead of cut.

    For me, I'm hoping for a wood shed that keeps the wood dry, slightly raises the temperature above to ambient to lower the RH,(perhaps solar) and a fan or wind exposure to maximize drying speed. If you have some good ideas pleas pass them on.

    Just my two cents.
  12. woodgeek

    woodgeek Minister of Fire

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    I am giving you a prop on the whole wood adsorbed water is not the same as bulk water issue. I wouldn't use "in" here, so much as "in contact with". The idea is that near the interface between the air and the liquid/solid water the RH is locally 100%, or in equilibrium (by definition), because the two phases are in intimate contact. If a solid material is hygroscopic, there is a binding energy that favors the water to be in/on the solid (moreso than in a bulk liquid) and that will shift the equilibrium partial pressure below the bulk water/vapor equilibrium partial pressure.

    If wood retains finite MC at less that 100% ambient RH in equilibrium (e.g. as Adios points out), then it is by the above definition somewhat hygroscopic. If there were no binding energy it would dry out completely (eventually). So, the vapor pressure of water in the pore spaces of the wood (and presumably the rate of drying) is lower than suggested by the bulk water tables. If there were a temp dependence to this effect, I would expect that it would be more important at lower temp, making winter even less favorable at low temps than the 2-3X slower rate predicted by the bulk water vapor pressure table. That is, hygroscopic things work better at absorbing at low temps (which is why you dry silica gel in an oven to regenerate it).

    On everything stopping below 32F: The pore water will freeze into ice at 32F, but it will still sublime at the previously liquid/vapor interfaces. The vapor/ice partial pressure at 31F and the vapor/liquid pp at 33F are basically the same, so the drying rate of pore water should not change by much on freezing. Moreover, the adsorbed water isn't ice below 32F, its still adsorbed water. The water molecules are touching the wood, not each other, and so can't form an ice crystal. There is no reason why their mobility or vapor pressure should do anything special at 32F either. I get your water crystals breaking the the structure thing, which is intriguing, but do you have any evidence? Can't wood fibers be stretchy enough to accommodate the strain?

    On the end/side drying issue--I think we all know that split wood dries faster, so there must be some drying out the sides. I saw a study once (can't find it) that said the diffusivity of water is 4x higher along the grain than across it, so a drying front would move in from the ends 2x faster than from the sides (its a square root of D). Not a huge difference. The cracking ends are due to the shrinkage being across the grain rather than along it (as lots of folks here will confirm). So, once the wood piece is more than couple times longer than it is wide, that guy will dry as much through the sides as the ends. That square root business also explains why a 'plank' that is much thinner in one cross grain direction dries so much faster than a square cross section--splitting a square into two planks should dry 4x faster, into 3 equal planks should dry 9x faster etc.

    Sorry to those who hate long posts....
  13. iceman

    iceman Minister of Fire

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    the myth isnt busted until "we" do the experiment and make a video!

    so how bout we all split some wood and report back with mc, say over a 4 month period and we can all give - species of the wood our location and we can track it... then we can really see who has the shortest drying time.. as well as see how other fare in other parts of the country.....
    anyone on board?
  14. Adios Pantalones

    Adios Pantalones Minister of Fire

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    "And for the record, just because I don’t spell a word like hygroscopic correctly doesn’t mean you are correct in your analysis just because you point it out."

    Notice that I called it a pet peeve. The spelling is a common misunderstaning :) I didn't state or imply that your use of it proved or disproved anything- just that it crossed my own neurosis.

    Other than that I'll just say that everyone's observation is that wood split thinner dries much quicker- by a huge factor. That tells us that water is leaving the sides at a greater rate than the ends. I have had rounds sit and not dry a lick in a year (have had them gush out free water), but when split they dry lickedy split (pun intended). If end grain was the primary route of drying then wood would dry about as quick in log form. As I pointed out- long pieces (with relatively low end grain area per mass) dry MUCH quicker than an 18" round- therefore It's pretty easy to conclude that through the sides is the primary route of drying for wood that we actually burn (not super thin cross sections).
  15. Wood Duck

    Wood Duck Minister of Fire

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    The diverse and sometimes scientific theoretical points of view posted here indicate to me that drying of firewood is a process that is best quantified empirically. In other words, you have to measure moisture content in real firewood to know how fast it seasons. There are just too many variables and too many assumptions are necessary to apply theory to firewood seasoning. We have all done the experiment, but haven't collected the data. As I sit here, I am thinking it wouldn't be that tough to conduct my own wood seasoning experiment; in fact I am conducting one in the back yard right now, but I know I'll never bother to collect data.
  16. JerseyWreckDiver

    JerseyWreckDiver New Member

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    Skyline, the document you are suggesting as support of your position is contradicting you.
    From pg. 12-6.

    Air Drying
    The main purpose of air drying lumber is to evaporate as
    much of the water as possible before end use or transfer to a
    dry kiln. Air drying usually extends until wood moisture
    content is as low as 20% to 25%, at which time the lumber
    is transferred to a dry kiln if final drying to a lower moisture
    content is required. Sometimes, depending on a mill’s
    scheduling, air drying may be cut short at a higher moisture
    content before the wood is sent to the dry kiln. Air drying
    saves energy costs and reduces required dry kiln capacity.
    Limitations of air drying are generally associated with uncontrolled
    drying. The drying rate is very slow during the cold
    winter months.


    Interestingly this is another Forest Service Document which is mostly a compilation of many others including the more detailed one I referenced above...

    There is no question, RH is a major player in the drying process, but think about it, what drives RH more then anything else???? TEMPERATURE!


    My 0.02 - worth the price charged.
  17. Rockey

    Rockey Minister of Fire

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    Darnit, I was hoping we could open a "busted" section and this could be the first topic

    Attached Files:

  18. iceman

    iceman Minister of Fire

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    well,,.... we could always start a new thread !!!!!!!
  19. Battenkiller

    Battenkiller Minister of Fire

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    After reading how much some of you have invested in your wood burning operations, maybe we can start a "flat busted" thread.

    Anybody got a photo of Keira Knightly?
  20. Rockey

    Rockey Minister of Fire

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    I saw a picture earlier today of Sarah Palin when she was younger wearing a shirt that said "I may be broke but Im not flat busted"
  21. skyline

    skyline Burning Hunk

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    Skyline, the document you are suggesting as support of your position is contradicting you.
    From pg. 12-6.

    Air Drying
    The main purpose of air drying lumber is to evaporate as
    much of the water as possible before end use or transfer to a
    dry kiln. Air drying usually extends until wood moisture
    content is as low as 20% to 25%, at which time the lumber
    is transferred to a dry kiln if final drying to a lower moisture
    content is required. Sometimes, depending on a mill’s
    scheduling, air drying may be cut short at a higher moisture
    content before the wood is sent to the dry kiln. Air drying
    saves energy costs and reduces required dry kiln capacity.
    Limitations of air drying are generally associated with uncontrolled
    drying. The drying rate is very slow during the cold
    winter months.


    Interestingly this is another Forest Service Document which is mostly a compilation of many others including the more detailed one I referenced above...

    There is no question, RH is a major player in the drying process, but think about it, what drives RH more then anything else???? TEMPERATURE!


    My 0.02 - worth the price charged.[/quote]

    Jerseywreckdiver,

    No, the document doesn't contradict me, you do.
    Here's the difference. What I quoted directly addresses RH as the driving force, as well as addressing temperature. To be redundant:

    The rate at which moisture moves in wood depends on the relative humidity of the surrounding air, the steepness of the moisture gradient, and the temperature of the wood. The lower the relative humidity, the greater the capillary flow. Low relative humidity also stimulates diffusion by lowering the moisture content at the surface, thereby steepening the moisture gradient and increasing the diffusion rate. The greater the temperature of the wood, the faster moisture will move from the wetter interior to the drier surface.

    What you've quoted doesn't even mention RH, but you have gone on to ASSUme that temperature is the primary factor since you read "the drying rate is very slow during the cold
    winter months."

    As I stated before, Rockey was correct in that in most areas of the U.S. wood dries faster in summer than winter. No surprise as the Equilibrium Moisture Content is lower in the summer in most places (SE exceptions)

    The science of kiln drying lumber generally boils down to controlling the RH around the wood so that it doesn't dry too fast and check, crack, warp etc. Temperature is often used to speed the process as expected for economic reasons. The goal being to get wood to a state of moisture content close to it's eventual RH environment (regardless of temperature) so that it performs well.

    To quote you "think about it" Why are fans used in kilns regardless of their operating temperatures. To keep the RH at the wood/air interface from becoming saturated so that it continues to dry.
    There's no quicker way to become fired as a kiln operator than to ignore RH. Yes, we all know RH is related to temperature but functionally important for all of us wood burners is how best to dry our wood and know that we can continue to dry our wood in winter especially if we can take advantage of lower RH conditions.

    Few of us have the means to provide summer time temperatures for our wood stacks in winter but we can do lots do reduce RH, such as dry storage, elevated off the ground, increased air movement around pile and even a slight temperature increase over the ambient to reduce RH.

    I match your .02 cents and call!
  22. skyline

    skyline Burning Hunk

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    Oregon
    I hate to post after my post but I think I have found better data to answer some of what we have been discussing, certainly not all.

    So addressing the question, (and only this question!) which is more important, temperature or Relative Humidity in drying our firewood

    Again, according to Wood Handbook http://www.woodweb.com/knowledge_base/Wood_Handbook.html
    See specifically chapter 3 pg 5 & 7

    "The Equilibrium Moisture Content
    The moisture content of wood below the fiber saturation point is a function of both relative humidity and temperature of the surrounding air. Equilibrium moisture content (EMC) is defined as that moisture content at which the wood is neither gaining nor losing moisture; an equilibrium condition has been reached. The relationship between EMC, relative humidity, and temperature is shown in Table 3–4. For most practical purposes, the values in Table 3–4 may be applied to wood of any species."


    So when wood reaches it's EMC conditions it will be happy. Until then it will try to lose (or gain) moisture to match the EMC conditions outside.
    The lower the EMC conditions we provide the steeper the gradient and the faster the wood will try to get there.

    I'll try to reproduce the table here but you may have to check it out for yourselves

    Table 3–4. Moisture content of wood in equilibrium with stated temperature and relative humidity
    Temperature Moisture content (%) at various relative humidity values
    (°C (°F)) 5% 10% 15% 20% 25% 30% 35% 40% 45% 50% 55% 60% 65% 70% 75% 80% 85% 90% 95%
    −1.1 (30) 1.4 2.6 3.7 4.6 5.5 6.3 7.1 7.9 8.7 9.5 10.4 11.3 12.4 13.5 14.9 16.5 18.5 21.0 24.3
    4.4 (40) 1.4 2.6 3.7 4.6 5.5 6.3 7.1 7.9 8.7 9.5 10.4 11.3 12.3 13.5 14.9 16.5 18.5 21.0 24.3
    10.0 (50) 1.4 2.6 3.6 4.6 5.5 6.3 7.1 7.9 8.7 9.5 10.3 11.2 12.3 13.4 14.8 16.4 18.4 20.9 24.3
    15.6 (60) 1.3 2.5 3.6 4.6 5.4 6.2 7.0 7.8 8.6 9.4 10.2 11.1 12.1 13.3 14.6 16.2 18.2 20.7 24.1
    21.1 (70) 1.3 2.5 3.5 4.5 5.4 6.2 6.9 7.7 8.5 9.2 10.1 11.0 12.0 13.1 14.4 16.0 17.9 20.5 23.9
    26.7 (80) 1.3 2.4 3.5 4.4 5.3 6.1 6.8 7.6 8.3 9.1 9.9 10.8 11.7 12.9 14.2 15.7 17.7 20.2 23.6
    32.2 (90) 1.2 2.3 3.4 4.3 5.1 5.9 6.7 7.4 8.1 8.9 9.7 10.5 11.5 12.6 13.9 15.4 17.3 19.8 23.3
    37.8 (100) 1.2 2.3 3.3 4.2 5.0 5.8 6.5 7.2 7.9 8.7 9.5 10.3 11.2 12.3 13.6 15.1 17.0 19.5 22.9
    43.3 (110) 1.1 2.2 3.2 4.0 4.9 5.6 6.3 7.0 7.7 8.4 9.2 10.0 11.0 12.0 13.2 14.7 16.6 19.1 22.4
    48.9 (120) 1.1 2.1 3.0 3.9 4.7 5.4 6.1 6.8 7.5 8.2 8.9 9.7 10.6 11.7 12.9 14.4 16.2 18.6 22.0

    As expected, higher temperatures have lower EMC as do lower RH. If I wanted to know which was more important in drying my wood, RH or Temperature I might ask which is going to drive my EMC lower, raising the temperature 30 °F or lowering RH 30%. Example: from 40 °F to 70 °F or 70% RH to 40% RH. (realistic values for our discussion)
    From the table, wood EMC will decrease between .1 and .5 across RH's between 5% and 80% when raising the temperature by 30 °F.

    If on the other hand one lowers the RH from 70% to 40% the EMC drops between 5.6 (13.5 to 7.9) at 40 °F to 5.4 (13.1 to 7.7) at 70 °F.
    This shows a 30% RH change is about 50X more significant in changing the EMC of wood (the point at which wood doesn't want to release or gain moisture) than changing the temperature by 30 °F
    Incidentally lowering the RH it is more affective at lower temperatures than higher!

    Yes °C are larger degrees than °F but still insignificant compared to RH.

    So how does this translate for us. Effort spent of lowering the RH around our wood piles is more important than raising the temperature unless that also lowers the RH.
    What are the best ways to do that? That's what I came here for in the first place!!!

    I think I want to take back my last hand, match your .02 cent and raise it a quarter. :)
  23. Adios Pantalones

    Adios Pantalones Minister of Fire

    Joined:
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    Skyline- that doesn't really address the question- which is- does it dry faster in the winter. It only addresses - does it dry more.

    The wood will be at a lower EMC, but it could take forever to get there- so it doesn't address the debate I think.

    what was the question again?
  24. skyline

    skyline Burning Hunk

    Joined:
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    No it only address the question I said it addressed.
    "... which is more important, temperature or Relative Humidity in drying our firewood."

    As stated in previous posts, the data http://www.woodweb.com/knowledge_base/Wood_Handbook.html Chapt. 12 pg 4 shows in general, Lower EMC values in "more" places of the U.S. during the summer, thus wood generally dries faster in the summer with no input on our part. This is more pronounced in the arid west than new england.
    But for example Boston's lowest EMC month is February, New York's is April, you throw in local variables of wind and moisture supply and we're back to that old statement for your wood pile, it depends on where you are.
    But the main reason it depends on where you are is because RH is more important in adjusting the EMC conditions than temperature!!!!!!!

    And besides these differences between the EMC across seasons are generally small and we can affect those if we know what to do work on, ie. prioritise RH over temperature.

    My Final Answer, I hope!
  25. Lumber-Jack

    Lumber-Jack Minister of Fire

    Joined:
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    Well this thread probably has some of the most detailed, thought out, researched and convincing information I think I have ever read in this forum, but certainly the most convincing argument was made by Bigg_Redd in his post way back on the first page of the thread. Notice the way he actually took the trouble to spell out the word "period" instead of just hitting the period key. This in itself demonstrations his certainty and conviction in his answer, and as if that wasn't testimony enough, finalizing his post with the statement "The End", surely that alone should have precluded any further discussion or debate on the matter.

    No, Redd had me convinced long ago......... Period, The End


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