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Author Topic: solar kiln temp  (Read 1256 times)

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Offline ccb

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solar kiln temp
« on: March 21, 2019, 03:48:55 PM »
Can a solar kiln get too hot? Outside temp currently 47 F. Temp in top of building/collector is currently 154 F where the fan isn't running, and is 120 F where the fan is running and blowing air down below to the wood. The solar collector is 36 ft long. This newly operational. Can't imagine what the temp will be in the heat of summer in Wisconsin. Thoughts?

 

Offline henry-sawer

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Re: solar kiln temp
« Reply #1 on: March 22, 2019, 02:40:52 PM »
Hi, mine did that too, all that will change when you put a bunk of wood in there.

Offline GeneWengert-WoodDoc

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Re: solar kiln temp
« Reply #2 on: March 23, 2019, 07:05:28 AM »
The heat at the top can easily reach 200 F and can melt or damage wires, fans, plastic, wood components, roof covering materials, etc. when the air is stagnant.  You need vents near the top that are open when the unit is not in use, or run the fans or put a cover over the roof.
Gene - Author of articles in Sawmill & Woodlot and books: Drying Hardwood Lumber; VA Tech Solar Kiln; Sawing Edging & Trimming Hardwood Lumber. And more

Offline YellowHammer

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Re: solar kiln temp
« Reply #3 on: March 23, 2019, 07:46:07 AM »
I melted the roof on mine, when we had a couple day power outage and I forgot to open the doors.  
HobbyHardwoodAlabama.com

Offline ccb

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solar kiln collector temperature
« Reply #4 on: May 30, 2019, 10:27:18 AM »
I'm in central Wisconsin where air temps have not been too high yet. My new solar kiln collector area is hitting extreme temperatures.  When it's 70-80F, I've noticed the temp in the collector is over 160F degrees.  At one point, I had left a pair of knee pads up there, as well as having a house thermostat setting 2 feet off the floor of the collector.  Later in the day as air temps had decreased, I had glanced in the collector area of the kiln, and noticed my knee pads had partially melted, along with the thermostat.  Fortunately, neither were expensive :-)  

Currently, I have one fan pushing the hot air out of the collector down into one bay drying wood.  I have 3 bays for drying wood.  When one bay is sealed for kiln drying, the other 2 bays are used for air drying. Older photo attached.

My concern is this will be my first full year of utilizing the solar kiln I built.  Is it possible that the collector will get too hot and combust??  The solar kiln was built using twin wall polycarbonate panels.

I'm hoping someone on the Forum can provide advice, or maybe can suggest another resource to contact.  Thanks!

 


Offline btulloh

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Re: solar kiln collector temperature
« Reply #5 on: May 30, 2019, 10:50:48 AM »
It's ok.  Just keep the knee pads somewhere cooler.  :D

When mine is empty, it will get to 180 degrees if the vents are closed.  I leave them open when it's empty, plus everything up top will handle the temps.  

It is unlikely to reach combustion temp.  
HM126

Offline GeneWengert-WoodDoc

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Re: solar kiln temp
« Reply #6 on: May 30, 2019, 04:21:16 PM »
Combustion for solid wood is around 450 F, but dust is lower.

Plastic (some, not all) can melt at 150 F.

Electric fans could be damaged by high heat and then when they fail, create even more heat than solar, especially if not fused correctly.  This would be my concern.

As suggested, vents open when empty and maybe even the fans on during the hottest part of the day to prevent the excessive heat.
Gene - Author of articles in Sawmill & Woodlot and books: Drying Hardwood Lumber; VA Tech Solar Kiln; Sawing Edging & Trimming Hardwood Lumber. And more

Offline Frontier_Paul

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Re: solar kiln temp
« Reply #7 on: June 18, 2019, 02:21:23 PM »
could you mount an attic fan that comes on with a pre-set temperature ?

Offline GeneWengert-WoodDoc

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Re: solar kiln temp
« Reply #8 on: June 18, 2019, 10:46:22 PM »
That would work but you will have to adjust the "on" temperature as the outside heats or cools seasonally.
Gene - Author of articles in Sawmill & Woodlot and books: Drying Hardwood Lumber; VA Tech Solar Kiln; Sawing Edging & Trimming Hardwood Lumber. And more


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