Page 1 of 3 123 LastLast
Results 1 to 15 of 33

Thread: Finished my Solar Lumber Drier Today

  1. #1
    Join Date
    Dec 2010
    Location
    WNY
    Posts
    6,125

    Finished my Solar Lumber Drier Today

    Now that I own a bandsaw lumber mill I need to be able to dry wood a lot more efficiently and hopefully with better control than air drying it in stacks. So I built a solar lumber drier. The design is very similar to one published in Wood Magazine several years ago. It has an 8 x 12' footprint, with 96 ft^2 of glazing and can hold about 1000 BF of lumber up to 10' long.






    The solar panels are wired to two 12V car radiator fans to circulate air though the lumber stack.

    I plan to start with AD lumber to learn how to operate the kiln, following the max. daily drying rates given in the Virginia Tech. kiln documentation. But if anyone has any hands on experience with a solar kiln, your input would be greatly valued. Thanks.

    John

  2. #2
    Join Date
    Jan 2004
    Location
    Lewiston, Idaho
    Posts
    27,038
    John, please keep us updated on the process. That's an interesting idea!
    Ken

  3. #3
    The bonus is unless your putting dead green material in there its pretty hard to foul it up as long as your patient. The main issues become when your putting very green material in and you have to stall the kiln (saturate it). If you are able to air dry for 6mos thats rarely a problem. At that point you can pretty much run wide open.
    Sometimes I just want to look at pretty pictures,... Thats when I go to the Turners Forum

  4. #4
    Join Date
    Dec 2010
    Location
    WNY
    Posts
    6,125
    Yesterday a friend and I loaded about 900 BF of AD ash at 14% MC into the kiln for its first run.



    It will be interesting to see how long it takes to get down to 7%.

    John

  5. #5
    Join Date
    Apr 2017
    Location
    Clarks Summit PA
    Posts
    547
    John, that is an impressive solar lumber drier. Plenty of good sticks in western NY.

  6. #6
    Join Date
    Oct 2007
    Location
    New Hill, NC
    Posts
    2,273
    Looks good John!

    Proper baffling makes a big difference in how well a solar kiln dries. You want to close up all of the opening around, on top, and underneath (leaving a 3/4" - 1" air gap on top and bottom) so that all of the air is forced through the stacked lumber.

    I couldn't tell but it looks like you don't have any baffling below your stacks.

  7. #7
    Join Date
    Dec 2010
    Location
    WNY
    Posts
    6,125
    It just looks that way, Scott. The bottom layer sits on a row of 3/4" stickers directly on the floor. It looks like the bottom layer is a foot off the floor in the photo, but that's because that row is substantially wider than the layers below it.

    I didn't have any side baffles in there until today. Some folks say they aren't needed, but that makes no sense to me and just checking flow by feel showed a lot higher velocity at the open ends than through the stack, so I added some blocking on both sides today.

    After this load is done I need to make some upgrades. I need to add the plastic sheeting on the inside of the rafters behind the glazing I intended to but didn't. I can't seem to drive the internal temp. more than 15 to 20F above ambient even with all the vents closed and I've read it should go at least 30F higher with nearly dry wood. After 5 days in the kiln my sample boards haven't changed weight since day 2. My pin meter shows a MC of 10 - 12%; it started out at 14% EMC. So far I'm a bit underwhelmed.

    John

  8. #8
    Join Date
    Oct 2007
    Location
    New Hill, NC
    Posts
    2,273
    Quote Originally Posted by John TenEyck View Post
    It just looks that way, Scott. The bottom layer sits on a row of 3/4" stickers directly on the floor. It looks like the bottom layer is a foot off the floor in the photo, but that's because that row is substantially wider than the layers below it.

    I didn't have any side baffles in there until today. Some folks say they aren't needed, but that makes no sense to me and just checking flow by feel showed a lot higher velocity at the open ends than through the stack, so I added some blocking on both sides today.

    After this load is done I need to make some upgrades. I need to add the plastic sheeting on the inside of the rafters behind the glazing I intended to but didn't. I can't seem to drive the internal temp. more than 15 to 20F above ambient even with all the vents closed and I've read it should go at least 30F higher with nearly dry wood. After 5 days in the kiln my sample boards haven't changed weight since day 2. My pin meter shows a MC of 10 - 12%; it started out at 14% EMC. So far I'm a bit underwhelmed.

    John
    Generally 30 degree rise is normal for dry wood - less for green lumber as the moisture release has a cooling effect in the kiln.

    I used double pane greenhouse polycarbonate panels in my last 3 solar kilns and they will get hotter than my older kiln with the single pane panels. I've seen 45 degree temp rises in the new ones.

    Are you familiar with the "handkerchief" test for air velocity? Unless you have a hand held anemometer (and most folks dont!), you can check for the proper airflow by holding a clean handkerchief by the corners on the outflow side of the stacks. Hold it by the upper corners, parallel to your stack, about 2-3" away from the stack, so that it drapes down below your hands. 2-3" of deflection at the bottom of the handkerchief indicates around 300 fpm of airflow through the stack - which is your target. Anything more than around 30 degrees deflection at the bottom and your airflow is too high. This is not as big of a problem with dry lumber, but if you have too high an airflow with green boards you will surface check.

    Solar kilns will dry slower than others because they only work for half the day. Be patient my friend.

    Scott

  9. #9
    Join Date
    Dec 2010
    Location
    WNY
    Posts
    6,125
    Quote Originally Posted by Scott T Smith View Post
    Generally 30 degree rise is normal for dry wood - less for green lumber as the moisture release has a cooling effect in the kiln.

    I used double pane greenhouse polycarbonate panels in my last 3 solar kilns and they will get hotter than my older kiln with the single pane panels. I've seen 45 degree temp rises in the new ones.

    Are you familiar with the "handkerchief" test for air velocity? Unless you have a hand held anemometer (and most folks dont!), you can check for the proper airflow by holding a clean handkerchief by the corners on the outflow side of the stacks. Hold it by the upper corners, parallel to your stack, about 2-3" away from the stack, so that it drapes down below your hands. 2-3" of deflection at the bottom of the handkerchief indicates around 300 fpm of airflow through the stack - which is your target. Anything more than around 30 degrees deflection at the bottom and your airflow is too high. This is not as big of a problem with dry lumber, but if you have too high an airflow with green boards you will surface check.

    Solar kilns will dry slower than others because they only work for half the day. Be patient my friend.

    Scott

    Thanks Scott. No, I was unaware of the handkerchief test. I went out and tried it and have no where near that amount of deflection; more like an inch. I thought Dr. W said you need 150 fpm through the stack and to size the fans for 50% extra CFM, which is what I did. If I really need 300 fpm then I need more and/or larger fans, although adding plastic sheeting to the inside of the rafters will help smooth the airflow and should increase the velocity through the stack, so I will do that first.

    After 6 days in the kiln my lumber has gone from 14% to 11.4% mc, measured on samples that were oven dried. Yes, patience; not my strong suit.

    John

  10. #10
    Join Date
    Feb 2015
    Location
    Western, NY
    Posts
    56
    Hi John, as you know, I am building a kiln too, and basing it on Virginia Tech design. I had a few questions and called VT. They actually answered the phone. I spoke with one of their professors in this field, and he helped me understand a few design modifications for my kiln size. He did recommend for me to make sure I can keep 100-150 FPM velocity through the stack. That was his guidance to me. I like the handkerchief method, so thank you Scott for sharing that. My plan is to oversize the CFM ratings on the fans by 50-75% because my stack may be wider than the original VT design. Sounds like you used similar logic. I am going to apply some plastic to the underside of the rafters to reduce speed losses on the air flow like you recommend. Thanks for sharing your process, it has helped me to avoid a few design flaws.

  11. #11
    Join Date
    Oct 2007
    Location
    New Hill, NC
    Posts
    2,273
    Quote Originally Posted by John TenEyck View Post
    Thanks Scott. No, I was unaware of the handkerchief test. I went out and tried it and have no where near that amount of deflection; more like an inch. I thought Dr. W said you need 150 fpm through the stack and to size the fans for 50% extra CFM, which is what I did. If I really need 300 fpm then I need more and/or larger fans, although adding plastic sheeting to the inside of the rafters will help smooth the airflow and should increase the velocity through the stack, so I will do that first.

    After 6 days in the kiln my lumber has gone from 14% to 11.4% mc, measured on samples that were oven dried. Yes, patience; not my strong suit.

    John
    John, 150 FPM is fine; 350 is max. A 1 deflection is about right for 100 - 150 FPM. Air speed can vary depending upon the species; 150 is great for slow drying species such as oak; whereas pine and poplar do just fine with 300.

    You can adjust the FPM simply by varying your sticker thicknesses. Are you using 3/4 or 1 stickers?

  12. #12
    Join Date
    Oct 2007
    Location
    New Hill, NC
    Posts
    2,273
    Quote Originally Posted by Tony Roun View Post
    Hi John, as you know, I am building a kiln too, and basing it on Virginia Tech design. I had a few questions and called VT. They actually answered the phone. I spoke with one of their professors in this field, and he helped me understand a few design modifications for my kiln size. He did recommend for me to make sure I can keep 100-150 FPM velocity through the stack. That was his guidance to me. I like the handkerchief method, so thank you Scott for sharing that. My plan is to oversize the CFM ratings on the fans by 50-75% because my stack may be wider than the original VT design. Sounds like you used similar logic. I am going to apply some plastic to the underside of the rafters to reduce speed losses on the air flow like you recommend. Thanks for sharing your process, it has helped me to avoid a few design flaws.
    Tony, I have one solar kiln that is fairly wide (5 long stickers), and three that are about 1 narrower than the VT design, but 3 taller between the bottom of the collector and the floor of the kiln (4 long stickers).

    I opted for these changes for two reasons. First (and foremost), my Nyle kiln stacks are 40 - 48 deep and 5 - 6 tall. I modified the VT design to allow me to standardize on kiln stacks. Second, the narrower stack will dry more uniformly than a wide stack, and only one of my forklifts has 5 long forks.

  13. #13
    Join Date
    Dec 2010
    Location
    WNY
    Posts
    6,125
    Quote Originally Posted by Scott T Smith View Post
    John, 150 FPM is fine; 350 is max. A 1 deflection is about right for 100 - 150 FPM. Air speed can vary depending upon the species; 150 is great for slow drying species such as oak; whereas pine and poplar do just fine with 300.

    You can adjust the FPM simply by varying your sticker thicknesses. Are you using 3/4 or 1 stickers?
    I'm using 3/4" stickers; 1" would definitely increase the velocity but reduce the BF in the kiln. The combined effect would be faster drying times and might be a good route for species that can tolerate that like ash.

    Are you drying green lumber in your solar driers or AD? The FPL document on drying hardwood lumber says there is no quality advantage for air drying. The drying season up here is coming to an end this year and probably doesn't allow me to do anything more than another batch of AD lumber, but there is next year to plan for, too.

    John

  14. #14
    Join Date
    Dec 2010
    Location
    WNY
    Posts
    6,125
    Just an update to those who might be interested. After sort of being stuck at 8.5% moisture for several days, I put a dehumidifier in the kiln. The RH stays at 45% over night now regardless of the weather outside and goes down to 30% by noon now if the day has much sun. The kiln gets no direct sun at this time of year because of some nearby trees until 10:30 or 11:00 AM. Temps. are now 30F or more above ambient at their peak during the day. Pin moisture meter readings are now consistently 6% and the sample board is below 8%.

    Adding the dehumidifier appears to have made a significant improvement in removing the last couple % moisture now that the days are shorter and the kiln sees fewer hours of direct sun. I'm optimistic it will allow me to dry wood later in the season.

    John

  15. #15
    John, do you run your dehumidifier all the time, or do you have a timer so it runs at night? And did you close all the vents?

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •