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Thoughts on this earth sheltered greenhouse for an aquaponics system?

 
Sean Kettle
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Ola! Planning to start up an aquaponic tower system in the north of England, figuring out with what kind of shelter to house it in. Seems to fit quite nicely in a Oehler style greenhouse.

Still searching for a site so the angles of the panes aren't set in place, it will probably be erected on a flat site.

Quite a bit of timber to put one of these together! Would like to hear if there's been any adaptations on this form for reducing costs of materials. Oehler recommends 6x6 posts in his constructions, does anyone reckon I'll get away with 4x4 posts on a flat site where there's no hill creep/lateral thrust? I've been reading up on these forums on how best to treat posts for sinking into the ground; I'm now thinking it would be better sinking them onto concrete feet and avoiding contact with the soil.

I'm also toying with the idea of using some passive annual heat storage, sinking a few pipes in, just haven't figured out where yet... pointers would be much appreciated

Our fishes will be in IBCs which are placed in where the cold sink would be. As our towers are raised off the ground and we might incorporate some form of heating in the future I'm not that worried about frost.











Any thoughts on this design would be very much appreciated!

Sean
 
R Scott
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I like the design. I wanted to do something similar, but I hit bedrock at 2 feet so I need to come up with something else.

I do NOT like any wood in an aquaponics greenhouse unless you have a natural rot proof wood to use, like black locust or hedge--no idea of the equivalent for you. Any chemical treatment is either going to leach into the system or not be effective enough for the wood. As "evil" as it sounds, I think a smart use of concrete makes sense in a use like this. I would prefer that embedded energy over poisons any day.

Modern 4x4's won't hold, not at that spacing anyway. They are weak with the fast growth trees, good as a post or a pole but not as a beam. You can make them work, especially as above grade earth-bermed, but you need to run the numbers to see if it is cheaper to use 1 6x6 vs. 2-4 4x4's.

When I looked at it, I think the strength calcs came back as a 4x4 joist on 4.something spacing! So pretty much stack them solid and forego the decking/sheathing.
 
Sean Kettle
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R Scott wrote:I like the design. I wanted to do something similar, but I hit bedrock at 2 feet so I need to come up with something else.

I do NOT like any wood in an aquaponics greenhouse unless you have a natural rot proof wood to use, like black locust or hedge--no idea of the equivalent for you. Any chemical treatment is either going to leach into the system or not be effective enough for the wood. As "evil" as it sounds, I think a smart use of concrete makes sense in a use like this. I would prefer that embedded energy over poisons any day.

Modern 4x4's won't hold, not at that spacing anyway. They are weak with the fast growth trees, good as a post or a pole but not as a beam. You can make them work, especially as above grade earth-bermed, but you need to run the numbers to see if it is cheaper to use 1 6x6 vs. 2-4 4x4's.

When I looked at it, I think the strength calcs came back as a 4x4 joist on 4.something spacing! So pretty much stack them solid and forego the decking/sheathing.


You make a very good point, got so caught up in the dimensions of the thing it hadn't even crossed my mind. I might be able to source some black locust here, otherwise larch might be a good bet. Will investigate making the whole thing out of scaffold too.

6x6's would be the way eh! Cheapest way might be screwing 3 2x6's together. If I find suitable wood thanks!
 
Sean Kettle
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I'm going to whitewash the back wall of this greenhouse to reflect as much of light back as possible. Does anyone have an idea of how best to implement an AGS or PAHS in such a construction as this?
 
R Scott
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The typical key to PAHS is to keep the surrounding dirt DRY to pull up the heat. The original had a layer of foam, 2 layers of 6 mil poly, then another layer of foam to form the "umbrella."
 
Sean Kettle
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R Scott wrote:The typical key to PAHS is to keep the surrounding dirt DRY to pull up the heat. The original had a layer of foam, 2 layers of 6 mil poly, then another layer of foam to form the "umbrella."


Thanks again for the advice R Scott! I have a copy of the the PAHS book somewhere; I need to dig it out. Still pondering where I would put the earth tubes on a design like this - will keep scratching my head
 
Sean Kettle
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Right-o, planning on where to stick some earth tubes on this design, these are my first thought:







Ala the PAHS book, I plan on sticking in an upper and lower earth tube. The pipes here are for illustrative purpose only, not to scale. The angles won't be as tight in reality - struggling to draw tubes in Sketchup!

Anyone with any experience of earth tubes able to give me some pointers? Will looping the tube underneath the structure and then back up cause any problems?

Cheers!
 
R Scott
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Earth tubes need to run at a continuous drain slope or they will collect condensation and mold--VERY bad.
 
Sean Kettle
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R Scott wrote:Earth tubes need to run at a continuous drain slope or they will collect condensation and mold--VERY bad.


R Scott, I should give you a commission if this all works! You're very right, I shall rejig the pipes and figure something out.

Has anyone ever used perforated drainage pipes for earth tubes, ala - http://www.nationalplastics.co.uk/index.php/land-drainage/100mm-x-25m-perforated-land-drainage-coil.html

Or would these crumple under the weight of the earth?
 
Sean Kettle
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Ah, just discovered in the PAHS book that he talks about "drain tile". Very thin and low R value, all the moisture that would collect in it would seep into the surrounding earth which we are wanting to keep dry.
 
Sean Kettle
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Happy new year y'all!

Here are my plans for a more by the book, counterflow earth tube configuration. You'll have to imagine the insulative umbrella for now







The one thing I don't understand about the set up is how excess heat from the greenhouse is pushed down the upper earth tube. I imagine that the heat would simply collect at the highest point, can anyone shed some light on this?

Or is it pushed through as the greenhouse will be sucking in cooler air through the lower tubes, forcing the warmer air through the top tubes as it's nowhere else to go? Maybe I've just answered my own question. Gonna have to be an airtight greenhouse.
 
William Bronson
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If you're using plastic for your earthtubes, consider using 3-4" pvc for the structure itself.

 
andy digwire
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Hiya Sean,
The natural circulation of air through the pipes would seem to depend on the lowest vents being warmer than the low lying air in the greenhouse. When that is the situation the air at the top might be sucked in regardless of its temperature iirc. This part of the system does look ambitious and experimental, its begs to be checked and calibrated by experiment or computer modelling or by someone very experienced in such a system before having any confidence that it is worth the time and expense of installing. The insulated mound itself is a much simpler and more reliable prospect. A less particular way of boosting heat in and out of the earth mound would be to build some significantly sized burrows into it, and manually open and close doors/vents to allow conduction and circulation as weather and conditions require.
 
R Scott
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The warm air rises into the top vent tubes and immediately starts cooling, so it goes downhill just fine. You want it to do that so that way when the earth is warmer than the top of the greenhouse it will pump heat back in.
 
andy digwire
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A crucial factor for those high pipes acting as an effective 'heat ramp' is their diameter, because such ramps work by letting hotter and cooler air slip past each other, in a convection circuit. As far as i understand, relatively warm air rises and cool air sinks as a a matter of convection. This is a very gentle forcing of air up or down depending on its relative temperature, it is relatively gentle but it can move air because there is little resistance involved when a corresponding body can move in the opposite direction. Concerning these ventilation pipes, relatively little convection might occur within them, and where it does occur it may mix and slow through turbulence.
Besides the local dynamics in the top pipes, they are part of a larger circuit with its own tendency for a flow of air through them in one direction or another. It seems intended/hoped that the overall flow will normally exit out bottom vents, and hence, enter through the top vents. I think on the warmest days the low lying air may be warmer than the air in the system - resulting in no overall flow. Without such flow some heat will still be able to move down the top vents by turbulent/mini-convection in the pipes, and by conduction, which might be enough to effective, but the only way i see to be confident of the design is by modelling it, or at least some ball-park heat conduction calculations.
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