Completed VT solar kiln, what’s next?

[BillG102350]

My kiln is complete. Built well, with R-20 in walls and floor and solar glazing. Four circulating fans and vents as VT solar plans require. What should I do regarding measuring humidity, fan control and venting.

I realize that I am asking a lot here, but as a newbie, I just want to get started. I have a band saw mill and have been milling and air drying for several years now. I am going to go slow with this as I'm not willing to ruin wood as I learn.

I guess what I need to know is about initial start-up with a freshly sawn load. I have been reading posts here for a while. It's time to seek advice.

[GeneWengert-WoodDoc]

What species? What thickness?  What part of the country?  Air dried or green?

You might be able to finish a load of air dried in the next month or so with warm weather.  Green might take until April.  So, start with air dried is my suggestion.

Fans come on about 10AM and off at 6 PM this time of year.  Vents cracked open only a very small amount.

Overall, there have been quite a few articles on running a solar kiln in Sawmill & Woodlot magazine.

Questions?

[BillG102350]

Hi Gene,
Thanks for following up on this post. I am actually working with V&F auto on his kiln.  We are at a point where setting up the electrical and electronic components is at hand. We are located in western Massachusetts. We have sawn maple, white and red oak, black walnut, cherry, catalpa, and eastern white pine.

We are trying to automate as much of this as possible as we both work day jobs.

- We want to control the fans to start and stop based on temp. What would you suggest for high and low limits?

We are using four attic vent fans and can move a fair amount of air. They are not variable speed, but we could switch them to control how many run.  Is there a good reason to do this?

Is humidity a factor in controlling the fans as well?

BillG

[YellowHammer]

There is not really that much automation involved in a solar kiln.  Set the vents manually, fans on and off with a timer.

[btulloh]

Read my thread on Using the New Solar Kiln.   https://forestryforum.com/board/index.php/topic,97731.0.html

I had all the same questions.  Most of it was covered just a couple months ago.

The main thing is you have to wing it a little bit at first and then it starts to make sense.  It's nearly impossible to ruin a load of lumber, especially this time of year at your latitude.  About the worst thing you could do is run your fans too long and the only thing that would hurt is your electric bill.

The solar kiln is pretty forgiving.  Don't try to over-think it like I did.

[btulloh]

Others can comment on this, but I think the one fairly critical thing to check and get right is the air flow through the stack. 

I borrowed a quality, hand-held anemometer (Kestrel) to check for uniform air flow when I was running the first couple loads.  I was lucky enough to find that it was about right and pretty uniform.  Sealing up the sides and bottom of the stack is sort of a dark art, because my stacks are different widths and sometimes the board lengths are not uniform.  (There are some good pointers on that in my thread.)

The fans are not so much blowing through the stack but pressurizing the plenum formed on the collector side.  This pressure creates the air flow.  There can/may be some air getting actually blown through the stack, but that's not the main thing.  There is so much turbulence created in the collector that it would be hard to direct an even air flow through the stack.  By pressurizing the plenum, the air flow is created because of the differential pressure.  This also helps the uniformity, and uniform air flow is necessary for uniform drying.  (I'm sure Dr. Gene will jump in and correct my omissions and errors.)

When I was measuring the air flow initially with the anemometer, I took a piece of "calibrated" string (like kite string) and observed how it behaved relative to the speed measured by the anemometer.  Now I just use the string to check air flow when I put a new stack in the kiln.

I also used the Kestrel to check humidity levels, but I have returned the pricey instrument to its owner and just fly by VFR (except for the meat thermometer I use to monitor temperature).  I plan to upgrade my instrumentation, but for now I'm using Kentucky windage and it's all good.

[GeneWengert-WoodDoc]

Air flow does indeed strongly control the rate of drying, but only when the moisture is over 40% MC. 

Under 20% MC, air flow has essentially no effect on the drying rate. 

Note that fans do four things...collect warm air from the black absorber surfaces to heat the air; blow heated air into the lumber pile to provide energy for evaporation; blow air through the pile to collect the evaporated water and remove it from the pile; and cause the vents to work.