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Kevin Jenness
05-30-2016, 7:59 PM
I have been using my small solar kiln here in VT for a couple of years now. It has a maximum capacity of about 600 bd ft of 8/4 lumber, less for thinner material, and about 70 sq. ft. of single thickness tempered glass. The 2x4 walls are filled with 2 layers of 2" isocyanate foam board (about R22). I use a 10" attic fan on a thermostat and timer to move air through the stack. I mainly use it for conditioning lumber that has been previously air-dried or kiln-dried to equilibrium with the relative humidity found in covered outside storage here (11-14%). Some things I have learned:

Maximum temperature I have observed is 145 F and minimum RH about 10%. The RH rises in the night as the temperature drops, so there is a period of "relaxation" every day as opposed to most kilns where the conditions are more consistent. In the winter the temp may get up as high as 80F on a day when the outside temp is <32F . Wintertime drying is very slow but still happens. I set the thermostat to start the fan at 50F in the winter, more like 70F in the summer and set the timer to match the sun. In the summer it can take several weeks to get lumber down to 6-7% from air-dried depending on species and thickness. I keep the vents closed most of the time. I don't have a problem keeping the RH in the kiln low despite the fact that I built it fairly tight with OSB sheathing caulked at all interior joints and silicone weatherstripping on the doors. It is more of a challenge to keep the RH as high as I want it at times.

When drying green lumber it is important to monitor the drying rate to avoid problems like end and surface checking that occur early in the process . I use sample boards and a postal scale to do that. I have found that I need to cover part of the glass early in the cycle to avoid overdrying. When the MC gets down below 30% it may be time to open the vents, but the drying rate must still be watched. When the load is below 15% MC it becomes harder to squeeze the last bit of moisture from the core, so the vents are closed to keep the temperature high. When it gets down to the end, I open the vents again to try to equalize the load by keeping the RH around 30-35% for a few days if possible.

I am not in a production situation so I try to keep to a moderate schedule. My glass area/bd ft ratio is a bit higher than 1/10, but I am at a fairly high latitude (45 N). I would be interested to know what other folks with a similar setup have experienced and if they have any tips to offer for better operation.

Kim Haubert
05-31-2016, 12:13 AM
TY very much. I am about to erect the walls of my soon solar kiln. Any info is greatly appreciated.

Kim

Bradley Gray
05-31-2016, 7:28 AM
I have an Ebac electric dehumidification kiln. With this type of kiln there is no air exchange. The idea is to keep the interior RH at a similar level to the MC of the wood to prevent degrade. Very different approach. As the wood dries the amount of water drawn out daily decreases from 2 gal/day to a pint or less.

Kim Haubert
05-31-2016, 7:33 AM
How about killing bugs?

Bradley Gray
06-04-2016, 10:39 PM
I use Bora care

Tom Hyde
06-29-2016, 5:19 AM
From everything I've read, it sounds like you are spot on with your operation. I've just put my first load in my new kiln and experience so far is similar. Also at roughly the same latitude on other side of the country. There's a lot of info and solar kiln users over at forestryforum.

Kim Haubert
06-29-2016, 7:10 AM
I've decided not to use the double layer sheets mentioned earlier. Big reason is that they allow about 80% of light through. And the price. Clear single layer sheets allow 90%+. I'll use my storm windows as a second layer underneath. Putting siding on now. Don't have much time to work on it. I have found a nearby kiln to get my wood dried for now.

Thx for the tip. Learning to run is what I need to know.

Scott T Smith
07-03-2016, 10:54 AM
Kevin, thank you for your well written post. I've been running a Nyle DH kiln for 12 years and solar for around 4. We are just about to complete construction on three additional solar kilns (two sized for 2K bd ft and one for 1,400 bd ft), and have cleared and are doing grading work for a new 150K bd ft covered drying barn that will have two Nyle kiln chambers adjoining one end. I opted for closed cell spray foam in the new solar kilns coupled with double pane 8mm greenhouse poly panels; I will be curious to see how the new compares with my existing one with the 3" polyiso foam board and single layer collectors. The new kilns certainly should be tighter than my existing one so I'll most likely need to manage the settings more closely from green to 25% MC.

With any kiln, the operator needs to make adjustments as needed in order to provide the optimum drying environment for the species, thickness and MC%.

Generally speaking, once you get below 25% MC there is not much that an operator can do to damage the lumber, so daily monitoring is not quite as critical (unless you are trying to maximize the drying rate).

I routinely see 150+ in my existing solar during hot summer days, and adjust the 1/10 ratio as needed depending upon species, thickness and MC%. Mine leaks enough that I don't need to adjust the vents

Jim Andrew
07-31-2016, 9:38 AM
A guy on forestryforum uses a room dehumidifier to get the moisture out of his solar kiln, says it benefits from the extra heat normally vented out of a solar kiln. He drilled a hole for the hose, so does not have to dump the dehumidifier daily.