Air Drying Estimator Spreadsheet

[Don P]

This comes from NCSU. Bonus, this is their wood products extension publications tab;
https://sites.cnr.ncsu.edu/wpe/publications/

Scroll down to the software list and hit the air drying estimator, sorry I can't help further, I'm just starting to play with it.

[WDH]

Very useful information.  Thank you. 

[Old Greenhorn]

I DL'd it and messed around a bit. Not a big spreadsheet guy so I can't look under the hood. I don't understand the center chart and what the colors represent. It could use at least a little more documentation and I wish there was a way to choose thicker wood or more species besides the 4 offered.
 Still, it's interesting info. Knowledge is power. Thanks.

[Machinebuilder]

its interesting, i agree with greenhorns comment about thickness and species 

Not being knowledgable on the subject I had heard that wood dries more in the winter due to lower humidity, this shows the opposite

what is correct?

[Ianab]

I had heard that wood dries more in the winter due to lower humidity, this shows the opposite

Temperature also affects drying speed. Wood will still dry in the cold, just slower. In my area Winter humidity is generally higher than summer, so combine the lower temp AND high humidity, air drying is MUCH slower. 

[WDH]

Wood dries much slower in the winter. 

[YellowHammer]

Relative humidity and absolute humidity are two important things to understand to get a "handle" on the effects of temperature on air drying.

Absolute humidity is the actual amount of water mass that air will hold, at a certain temperature.

Relative humidity is the amount of water mass air has absorbed relative to its maximum carrying capacity, or saturation.  

Cold air can hold much less moisture than warm air, so although the relative humidity is higher in winter the amount of water in the air is much lower.

Conversely, warm air can carry more water.

So for example, in a kiln, if the atmosphere is saturated or at 100% Relative Humidity then no more water can be removed.  However, if the temperature is raised, and say the air is not exchanged, although the actual moisture by mass in the air is the same, the carrying capacity of the air has gone up so now the relative has gone down and the air can absorb more water until it again reached its saturation level or maximum carrying capacity.

Since warm air absorbs more water than cold air, then wood will dry better in summer than winter.

[Machinebuilder]

thanks for the answers

[Don P]

However, the reasons I like to saw and begin air drying in the winter is that mold and decay fungi don't work well in the cold and moderate drying rates at the beginning of drying are kinder to the wood. 

[moodnacreek]

Experience has taught me that in my location March is the air drying month although this dry hot summer could be an exception. Green logs sawed when the leaves are falling, put on sticks and roofed over and put so the prevailing winds go cross ways through the stack can be 12 percent by April. I have seen pine sawed in February be at 10 percent first of April. Above freezing, southern exposer and wind do a lot of drying.

[Don P]

In air drying we don't have much control over temperature and relative humidity. In that sense this calc does help show the drying rate based on some localized data. Over the weekend I helped my partner site a new drying shed. The first set of pins, stand back and look at the overall site, was just about the absolute worst place on the site for drying. Although most convenient it is the lower end where water and fog are going to hang around longer than just a few hundred feet away in that old pasture. In other words rate factors can be very localized, as localized as one tree's shade. Just scattering hygrometers in the house this morning I got over a 10% spread in rh.

Tagging on to YH's comment,
At 32°F air can hold about 1/3 of a pound of water per 1,000 cubic feet.
At 100°F it can hold almost 3 pounds of water per 1,000 cu ft.

The same volume of air can hold about 10 times as much water when it is warmed up. That is huge.

From there the graph only gets steeper, the moisture holding capacity of air about doubles again by 150° and it triples again from there to 180°.

You can dry very fast at high heat, then the problem becomes getting something better than toothpicks at the far end of things.

[YellowHammer]

Good point DonP makes on location.  One of the first air drying areas I had was what I thought a perfect spot ---NOPE.   :D  It was by the edge of the woods, in the shade, under the tree limbs, and blocked on 2 sides by trees.  It was too protected, and it ruined several loads of wood before I realized what was going on.  Basically it was a stagnant, high humidity area of wood drying ruin...

So I moved my air drying place maybe 200 feet, at most, to the edge of my gravel driveway.  It was in the open, up on a slight hill to get a breeze and in a spot I noticed the dirt and grass was always growing and mostly dry when other places were still wet.  It was a wonderful spot, and dried perfect wood.  Literally, the two places are only a couple hundred feet apart, but one spot destroys wood the other turn it into gold.

Location, location, location.  

[Stephen1]

Not only is the air drying estimator interesting, so was the rest of the information they looked into.

I have a location I call the wind tunnel, at the end of my parking lot,  NW to SW between 2 buildings, almost full sun, I actually have sun screen cloth on both sides of the air dry sheds to slow down the wind and the drying. It will dry 4/4 pine in a few weeks.  70 feet away next to the trees and the ravine I placed another AD shed which I store WO and RO, it has a less wind more shade and dries the oak at a slower rate.