Green House as Solar Kiln?

[KDubU]

Has anyone entertained or actually used a greenhouse for a solar kiln? I know some are not as permanent as building one but right now time is a tight commodity for me. The one in the pic is smallish, 8x10’ and would need a couple openings at the bottom and a fan or two. Thoughts?

 

[Garbanzo62]

My only concern would be a lack of insulation. Much of the gains during the day could be lost. Not sure how much heat the 'glass' will retain. That is a $600 Greenhouse. I would think you could build a solar kiln that is insulated for about the same $

 

[stoveliker]

Most solar kilns I see are not insulated; just transparent plastic.
I'd say if you can control the air flow, go for it.

 

[peakbagger]

Sure it will work as long as you get the ventilation right. As the various experiments with low budget kilns have revealed, its a fine balance between air flow, humidity and temperature. Moisture will release out of the wood at higher temps faster than low temps, so you want to keep the temps high inside which means less air flow, but crank the air flow too low and the air gets saturated and the moisture is not carried away as fast. If using one, it would need be installed with an air gap between the base and the ground with the wood up on pallets to get air flow up through the stack. Wood should spaced away from the walls as condensate can form on the walls and run down them to the ground. You would need a way to regulate the airflow out of the ridge of the greenhouse while keeping water out. Ideally the wood would need to be restacked so the bottom is at the top as the drying effect would be higher in the stack but expect most folks would just savce the hassle. Note I think most folks would agree that a double row stack will dry faster than a typical triple row stack.

One of the forum members has done a lot of testing with low budget solar kiln drying by wrapping the piles with plastic after forming a roof over the wood to form a vent space from left to right. Unless you need it neat, he seems to get very good results for low bucks.

 

[Garbanzo62]

Based my comments on the VT Kiln design which calls for insulation in the floor and walls

 

[peakbagger]

If someone is heating a kiln 24/7, I agree in fully insulating but with a strictly solar based kiln, the heat source is the sun so I am unsure what the insulation would be doing when the sun is not out. The exception might be if the entry air louvers and exit louvers were automated closed to prevent any air flow through the kiln at night. In theory that would mean the kiln would retain the heat of the volume of wood overnight higher and would warm up faster in the AM.

 

[gthomas785]

As long as you understand the principle of the kiln it will work. Put a plastic vapor barrier over the ground to avoid ground moisture. A few small vents in the bottom and at the top, ideally something you can adjust open and closed to get the right amount of airflow. Buy a couple cheap remote temp/humidity monitors and put them in your stacks so you can see how it's doing.

 

[EbS-P]

I think it be fine for firewood. But…. I don’t see a really cheap green house standing up to snow load or winds. If you have space for 3 seasons of wood I’d just spend that money on a good wood shed and use plastic this year.

 

[Woodsplitter67]

My only concern would be a lack of insulation. Much of the gains during the day could be lost. Not sure how much heat the 'glass' will retain. That is a $600 Greenhouse. I would think you could build a solar kiln that is insulated for about the same $

There is no gain required for night time.. All of the kils that I have made have gotten to 135 degrees daytime temperature. The drying on a daily basis during the daytime is plenty. There is no reason to try an intall Insulation. Retaining the heat is not the key.. The key is to heat the air.. heating the air allows the air to hold more moisture. Lets say its 80 degrees out and the dew point is 60%going in the greenhouse or kiln.. once that moisture laden air heats up in the greenhouse its no longer at 60%.. that dew point dropped in the greenhouse to 20% the combination of heat and low dew point is whats stripping the water out of the wood. The constant flow of dryer air come in and moisture laden air going out..

To the OP.. Of your going with something like in the picture.. dont do the 2mm polly carb.. go with the thicker like 6mm .. the thin pollycarb will blow out during a thunderstorms.. its just not worth it

Get 2 automatic openers.. one for the side vent and one for the top vent. set them to open at a minimum..

 

[KDubU]

There is no gain required for night time.. All of the kils that I have made have gotten to 135 degrees daytime temperature. The drying on a daily basis during the daytime is plenty. There is no reason to try an intall Insulation. Retaining the heat is not the key.. The key is to heat the air.. heating the air allows the air to hold more moisture. Lets say its 80 degrees out and the dew point is 60%going in the greenhouse or kiln.. once that moisture laden air heats up in the greenhouse its no longer at 60%.. that dew point dropped in the greenhouse to 20% the combination of heat and low dew point is whats stripping the water out of the wood. The constant flow of dryer air come in and moisture laden air going out..

To the OP.. Of your going with something like in the picture.. dont do the 2mm polly carb.. go with the thicker like 6mm .. the thin pollycarb will blow out during a thunderstorms.. its just not worth it

Get 2 automatic openers.. one for the side vent and one for the top vent. set them to open at a minimum..

Tks. Yes if I plan to go this route it would be the 6mm. The only reason for considering this is I know I can put his up in a weekend whereas building the VT style one will take longer. I would prefer the latter but time is not on my side right now plus I looked at your method and may go that way.

 

[Woodsplitter67]

Tks. Yes if I plan to go this route it would be the 6mm. The only reason for considering this is I know I can put his up in a weekend whereas building the VT style one will take longer. I would prefer the latter but time is not on my side right now plus I looked at your method and may go that way.

You could do a 3 cord kiln like in my signature for like 50 bucks..

 

[KDubU]

You could do a 3 cord kiln like in my signature for like 50 bucks..

Yeah that is what I am thinking about for a temporary solution although $50 is a bit low these days.

 

[BertP]

Has anyone entertained or actually used a greenhouse for a solar kiln? I know some are not as permanent as building one but right now time is a tight commodity for me. The one in the pic is smallish, 8x10’ and would need a couple openings at the bottom and a fan or two. Thoughts?

View attachment 311340

Pretty cheap to build an insulated solar Kiln to dry firewood. After cyclone Gabrielle damaged a bunch of trees on our property we built an insulated wood shed with a solar panel powered fan to dry the wood faster. Hope I can figure out how to attach a photo.

 

[Jaison]

Silly question, I’m new to this greenhouse for a solar kiln thing. I just purchased a decent pop up one with 4mm poly for a moisture barrier floor and I plan on using a box fan to control the exhaust. My question is, what do I want the humidity and dew point at in the greenhouse, and when do I run the fan?

 

[gthomas785]

Silly question, I’m new to this greenhouse for a solar kiln thing. I just purchased a decent pop up one with 4mm poly for a moisture barrier floor and I plan on using a box fan to control the exhaust. My question is, what do I want the humidity and dew point at in the greenhouse, and when do I run the fan?

You want the temp as high as possible and the humidity as low as possible. If you need to run the fan, only run it enough to just remove the moist air without also sucking out too much heat. Most of the time you can get it to work with passive ventilation.

 

[Jaison]

You want the temp as high as possible and the humidity as low as possible. If you need to run the fan, only run it enough to just remove the moist air without also sucking out too much heat. Most of the time you can get it to work with passive ventilation.

Gotcha. So leave the two exhaust windows open as little as possible. I took a big piece of the wood from the shed where it’s been drying since January, read 18% on a fresh split. So I’m hoping putting it in the green house for the rest of September and October might finish them off and get them to at least 15.

 

[Woodsplitter67]

Gotcha. So leave the two exhaust windows open as little as possible. I took a big piece of the wood from the shed where it’s been drying since January, read 18% on a fresh split. So I’m hoping putting it in the green house for the rest of September and October might finish them off and get them to at least 15.

so you do not want to use an exhaust fan.. at all. you want the temperature to get high. Hot air is able to hold more moisture as as the air moves into the greenhouse and heats it actually gets dryer. for example.. if the temperature outside is 85 degrees and the humidity is 75% when that air enters the greenhouse and gets heated to 135 degrees the humidity in that same air will be 15% My greenhouse has been as low as 5%. Yoor better off just venting the air out the top of the greenhouse and not in large quantities. you can control how much air is removed from the greenhouse by keeping the side vent open at a minimum. if your greenhouse is set up properly your air will feel arid..

 

[Jaison]

so you do not want to use an exhaust fan.. at all. you want the temperature to get high. Hot air is able to hold more moisture as as the air moves into the greenhouse and heats it actually gets dryer. for example.. if the temperature outside is 85 degrees and the humidity is 75% when that air enters the greenhouse and gets heated to 135 degrees the humidity in that same air will be 15% My greenhouse has been as low as 5%. Yoor better off just venting the air out the top of the greenhouse and not in large quantities. you can control how much air is removed from the greenhouse by keeping the side vent open at a minimum. if your greenhouse is set up properly your air will feel arid..

Okay, I’ll try this out. It’s just a pop up green house with two vent windows I’m able to control, and I have 4mil thickness poly for the floor and they wood is about 1.5 cords, and will be stacked inside on pallets. I’ll post a picture when I have it all in. Appreciate the info