And yet, another Solar Kiln thread ...

[jaciausa]

Hi Jim,
 I believe you have the start of a good plan except the slope of the 6/12 pitch roof (rise/ run ) that would make it only 26 + degrees.

[jaciausa]

For your area cutting a 7/pitch roof would give you 35 + degrees. Hope this is helpful.

[50 Acre Jim]

Off topic of your kiln, which I am definitely excited to follow, but had a question.  Ever still find any chestnut logs in the creeks around your parts?  Been 25 years ago, but helped pull a couple of logs out of a creek down towards Franklin.  Made some nice wormy lumber.  Still have a picture frame out of it.

This is the first I've heard of finding/pulling Chestnut out of the creeks.  That would be wonderful to find such a treasure!

The original Virginia Tech design used CD-X plywood.  You might have to replace a sheet or two in a year or two, but the cost is good.

I think CD-X plywood will be fine, especially if it gets a coat of waterproofing somewhere along the line.  :-) 

For your area cutting a 7/pitch roof would give you 35 + degrees. Hope this is helpful.

Although not reflected in any of the previous drawings I have raised the back wall to a height of 5' 6" which I believe will give me a 35* angle.  Let me know if there is a difference in what your saying and my height calculations.   I used the following calculator to get my measurements.     https://myrooff.com/roof-pitch-calculator/

[jaciausa]

Your fine with how you are doing it. i was just stating what the framing square or the speed square shows. That would give a true 7/12 cut for the tails or a birds mouth.  The exact degree is 30.26.

[jaciausa]

Are the top of your walls level? or cut on angle so you do not need a birdsmouth cut top or bottom? Possibly you are blocking them without using a cut.

[50 Acre Jim]

Are the top of your walls level? or cut on angle so you do not need a birdsmouth cut top or bottom? Possibly you are blocking them without using a cut.

At this time I intend to use a birdsmouth cut on each end.  But in retrospect, I can't think of a project I've done that started and ended as planned.  Why should this be any different? 

[jaciausa]

Sixty six inches or 5 ft 6 inch total rise would be an 8.25 inch rise per foot and exactly 35 degree slope as you have planned.

[btulloh]

I think the collector angle deserves a bit more study before you commit to the 35 degree slope.  I went through this with solar panels as well as with my kiln build.  There are a number of solar angle calculators on the web you can play with and the exercise could be useful.

One rule I'd seen for the kiln collector was to use your latitude plus 10 degrees.  There are some other things worth considering.  The ideal angle changes of course with the seasons, so any fixed angle is a compromise.  In the summer, with a high sun angle and high ambient temperatures the kiln gets enough plenty of energy to operate well.  Around the spring and fall equinox, the angle is lower but there seems to be enough energy falling on the collector to produce good results in the kiln.  This angle corresponds roughly to the latitude plus ten degree rule, so that is about optimum for the collector angles we tend to build into these kilns.  As the winter solstice approaches, the sun angle drops and the energy decreases, plus the days are shorter. 

It may be worthwhile to go with a steeper collector angle to help with the winter months where it is harder to get enough energy to run the kiln.  The long days and higher temps in the summer can run the kiln even when the collector is steeper and optimized for a lower sun angle.  From what I've observed with my kiln, I think I would compromise further toward the lower angle (steeper collector) than the 45 degrees I chose.  Of course that complicates the build a bit.

Or you could build a collector that can be adjusted for the season.  Fun.

Another thought on the collector angle thing:  Even though we talk about the pitch of the panels as the collector angle, the real story is not the roof pitch but the black thermal absorptive surfaces inside the the kiln.  The angle of the panels is not the determining factor in energy collection.  The amount of surface area inside the kiln that is struck by the sunlight determines the thermal gain.  The panels just allow the sunlight to get to the black surfaces.  That means that we need to take into account both the panel area admitting the sunlight and the area inside the kiln that is collecting the energy.

I'm starting to ramble a bit, but that's my two cents worth.

[GeneWengert-WoodDoc]

The best overall single unadjustable angle is your latitude. You can add 10 degrees for slightly better performance in late fall and winter, but poorer in the summer, and that means the rear wall is higher and that may be undesirable. As we go further north, then we suggest 45 degrees as it is easy to make that angle.  So, 35 is good for you. A collector that you can tilt from time to time is neat, but it is a lot of work and you might shorten drying time by a day.

As mentioned, the area of the roof measured perpendicular to the sun at noon (or the shadow at noon) controls the amount of energy entering the kiln. Once in the kiln, the light energy must be absorbed and converted to heat energy. We use black surfaces in the kiln- -walls, baffles. Their area is not important.  A few people put the black absorber near the clear roof, but it seems easier to use the walls and baffles rather than make a separate absorber.  Either method will absorb about 100% of the incoming energy, which is the clear area perpendicular to the sun at noon. This is about 1000 BTU per square foot per day, which will evaporate about one pound of water per square foot per day on the average.

Hope this is clear.

[jaciausa]

The latitude here in SE Iowa is around 40 degrees. Being colder the 45 degree will be better choice for me. The best reason for me to use 45 degree is cutting all the rafters using a speed square at 6/12.

The orientation along the other axis to solar noon is just as important if you can still change it. This site can help you with that calculation-https://www.esrl.noaa.gov/gmd/grad/solcalc/-
 I thought my kiln was off a little, but turns out calculating it with solar noon here in Iowa it was correct.
Hope this helped some.
Also Iyou said you were using 8 foot panels for collector and if you are you will need to downsize the width for the total run of rafter.

[jaciausa]

i meant 12/12, just not thinking to clear.

[GeneWengert-WoodDoc]

A solar kiln in SE Iowa is really tough...it has to withstand hail storms, strong thunderstorm winds and nearby tornadoes, heavy snow fall, and maybe a few baseballs if you are close to the Field of Dreams.  The steeper roof will help drain or remove rain and snow.

In general, as you move further north, the summer sun rises in the NE, so with a 45 degree steep roof, it is several hours after sunrise before direct sunlight gets onto a kiln and the interior humidity drops.  Likewise, the south-facing collector at 45 degrees will see the last of direct sunlight several hours before sunset in the NW.  what this means is that until the kiln is about 20 degrees hotter than the morning low temperature, it will not have a very low humidity...it will not dry wood very fast.  So, this is why we suggest turning on the fans several hours after sunrise and off well before sunset.

[50 Acre Jim]

My solar fans arrived a few days ago but the weather wouldn’t permit me testing them.  But I got a chance today and they seem to run just fine.  I plan to use 4-24 volt panels (like the one in the test today) strung together in a parallel configuration.   This may seem like a little overkill but I want the fans to be well supplied even in the earlier hours of the day. 

Also posted a couple of pictures of the location where the solar kiln will sit.   It really is a great location and even in the Winter it’s getting sun from 9:00 until about 4:00.  If the weather holds I hope to get the pier blocks down and the 4X6's laid out this weekend.

[btulloh]

You must be on a first name basis with the Kubota dealer. 

[50 Acre Jim]

You must be on a first name basis with the Kubota dealer. 

And that's just what you see.  I have a barn full of mowers, bush hogs and accessories as well.  But a few years ago Dave retired and the guy that took his place acts like he doesn't even know who I am.  I got tired of being treated like second-hand trash and quit supporting them.  Unfortunately, that seems to be the norm more than the exception these days. 

But hey, what did you think about that fan?  Little rascal really moves the air for a fan that plugs into a solar panel!

[btulloh]

Fans look great.  Four 24 volt panels and 4 fans.  Spare no expense!  That's a great way to do it if you're willing to lay out the dough.

Are you using batteries or just running the fans right off the panels?  Voltage regulation?  Low-voltage conditions?   

It's going to be fun watching all this.  You are jumping right in to the deep end of the pool.  Right on!

Too bad about the dealership.  It does seem to be the way things go these days.  Aggravating.  Customer service seems to be a lost art.  It's almost like to you have to work real hard to spend your money these days.  And nobody ever says "thanks for your business" anymore.

[50 Acre Jim]

No batteries, fans run straight off the panels.  I am using fan thermostats that will turn the fans on when the solar is adequate.  And of course, they will shut down accordingly when the sun starts to depart.   

I’m big on the alternative energy thing which is similar to buying organic vegetables.  Everything looks the same, you just get to spend 5 times more to get the same result.  But hey, if North Korea ever lobs an EMP on us I’ll still be able to produce quality dried lumber for people to make bowls out of….

[slaghunter]

.  But hey, if North Korea ever lobs an EMP on us I’ll still be able to produce quality dried lumber for people to make bowls out of….

 

[50 Acre Jim]

Nasty weather finally went away, and I got some much needed “transition from winter maintenance” out of the way.   And now, back to the solar kiln!

First, what a difference in where the sun is now vs where it was when I cut the pad for this project.  And the trees are not helping me much either.  The good news is, I can cut the offending trees and get the sun back where I need it.   But the position of the sun in the Winter vs were it is now, is simply astounding.

In fairness, it’s late in the afternoon when I took these pictures, so I’ve already gotten about 6+ hours of direct sun so I think I’ll be OK.  And once the trees are gone the shade you see in the pictures will be gone and I will gain another 3 - 3 1/2 hours of sun.

Got the foundation in and the framework for the floor.  Changed from using 4x6 for the floors and went with 2x6 instead.  No strategic reason, just because I had the 2x6 cut already.   Made a trip to Lowe’s for insulation, 30 lb. felt and plywood.  Almost $300.00.    Hope to have that all in by tomorrow afternoon.

 
Yippie!

 

 

 

 

n

[GeneWengert-WoodDoc]

You might consider using metal hardware cloth on the very bottom of the joists to prevent critters from getting in the insulation.  In fact, solid, treated plywood is probably best.  If it is too late, then make a mesh metal skirt around the entire kiln.  We do want good air flow underneath the kiln, so make the skirt with mesh.  Also, consider putting a plastic sheet on the ground to prevent soil moisture from getting into the flooring and joists.

The roof looking south will not “see” much sun in the early morning and late evening as the sun is in the NE or NW and at low angles.  So, you do not need to do too much tree removal, although if you get an ice storm and a tree feel....