Jim Rodgers

Aubrey Zhang wrote:I have searched for "aircrete" in this section but found none. So I start this topic. Hope t hear from someone who did or who plan to do this as well.

Of course we need to use plastic films or sheets for areas that allow light to come. But since aircrete is light and seals well and has good R value, using it to build a greenhouse should be good. What do you say?

I have thought about aircrete as an option and probably did some calculations regarding it.

What your climate is at its coldest and the volume of the structure you want to insulate/heat seem to be the key elements to get started.
Then you might want to factor in building code permits.

It could very well work in the right climate.
Then again, a straw bale stick structure might work just as well if not better.

Jeff Siewicki wrote:

1.Do you think rigid metal 6" duct will hold up under the weight of the compost?

2. How much duct work would I need to effectively heat the air to reasonable temperature?  

This article should help you understand the heating power of a compost pile.
https://smallfarms.cornell.edu/2012/10/compost-power/

For a brooder house a reasonable size compost pile seems possible.
Using a closed loop water line also seems like it could be used effectively in the different heating zones you set up.

Chris Kott wrote:

That said, I saw recently an article I will attempt to find about a company essentially erecting greenhouses around existing houses, and designing cold-climate villages in northern Europe around this concept, and the idea of growing the community's food in this manner. I know at least one example used a dome.

-CK

That does seem to be the most interesting usecase for domes at this time.
A life size living snow globe with the snow outside the globe.
Very picturesque.

Myrth Montana wrote:
Well, that’s discouraging!

Checkout Northern Homestead Blog.
They genuinely seem to enjoy their dome and wish they had two.

bob day wrote:I had looked into the issue of mold as well when considering my earth tube, and it started to look like the issue would be less problematic in a tube exposed to the earth.  Not so much that there wouldn't be any mold, but more that there would be enough competition to keep truly unhealthy organisms from gaining total control.  I wish I had kept those links that led me to that thought, but it was done some time ago and i figured I would have to do a more complete study later

When asked about using plastic tubing, Bill said something to the effect of preferring sides and floor be earth,whether he was thinking about mold or expense (or both) is difficult to say

Of course the other way to think about it might be that the tubes will create that mold prone environment, and design in some living feature to occupy that niche to prevent any harmful mold growth. (I don't have a clue off hand what that might be)

Most molds should not be an issue if there is no organic matter for it to feed on.

Trace Oswald wrote: This may be completely wrong, but I'm picturing a scenario like a car radiator that had all it's baffles removed, or was simply replaced by a metal box with the same outside dimensions as a radiator.  The surface area would be cut down so much in relation to the amount of water, the water wouldn't be cooled much before it circulated through.

Yes this approach does present many practical problems.  (Forgive me for entertaining possible solutions to those problems as haphazard and half-baked as they might be.)

Rebar comes to mind, it adds to over all costs but it could provide the same function as the radiator baffles...  
Re-purposed Tin Siding could be an effective solution.  
Mini ground trenches was my immediate solution they mostly cost labor.  
If there are enough rocks in the excavated ground rocks in the first few inlet IBC's could create extra surface area to pass air through till it hits the ground floor.  
Or the inlet IBC could spill air out the top that drains down the sides and travels back over a rocky bottom ground surface.  
Subterranean precision engineering seems a little to risky at this point.

Granted, just dropping drainage pipes into the ground seems like the most time cost effective solution.

Mart Hale wrote:

I had and idea of building it over a cave.    Replace the IBC with a cave and you would have huge amount of air to cycle.

That is the gist of the design...  The IBC cages just provide a structural framework for the cave.

Dillon Nichols wrote:
For 4", 5055" length yields a surface area of 127000 Sq in.
This seems pretty significant to me... you could store a lot of cool air, but I can't see that there will be anything like enough time for it to cool back off once it's circulating.

You potentially get the sq inches equal to the trench floor which often is the sq footage of the greenhouse.
This IBC approach could even tap the sidewall surface area.
There are still design problems with this but the potential is there and the cost is competitive.

Dillon Nichols wrote:A 275 gallon IBC is probably about 36×44×40" on the inside.

That gives it a surface area of 9568 square inches.

A 6" nominal ID cylinder of the same volume would be  2246.7 inches long. Surface area 84925 Sq in.

For 4", 5055" length yields a surface area of 127000 Sq in.

This seems pretty significant to me... you could store a lot of cool air, but I can't see that there will be anything like enough time for it to cool back off once it's circulating.

275 gallon IBC is  48×46×40" around the perimeter with the cage.
The bottoms could be cut out.
Hot air rises, cold air sinks.
The trench floor is the surface area in this case and the IBC containers merely cavern baffles.
If used as bulkheads in rows and columns with tubing connections, the insulation of air outside the plastic container and against the trench walls might very well work against the desired effect.

That was the reasoning anyway.  Measure twice cut once.

I acknowledge surface area was only being considered in hindsight as I wrote my response.  

Thanks mike for the calc sheet.

Trace Oswald wrote:
Could you explain the past about the tubes under the growing zone in more detail?  
My understanding is that the tubes can be buried anywhere you like as long as they are 8 to 10 feet deep.
...tubing is determined by the size of the greenhouse

You are correct, the tubes can be anywhere and determined by the volume of the greenhouse.  Conceptually, I was placing them under the growing zone, but they can be anywhere.
Perhaps you all can all help me figure this out with more certainty.

Let me explain my approach and correct me where I am wrong.

I only have anecdotal information on the size of the tubing and logic.  
Russ Finch in one video states this is all high school physics.  LDSPrepper; he mentions that the length of tubing should be the volume of the GH divided by 10 for 6" tubing.  Another misc. source says the air change needs to happen every 5-10 minutes.
I aggregated that information into needing 10% of the greenhouse volume in the air2ground heat exchange tubes.

A 17x80x12 greenhouse = ~12566 cft
The 6" tubing needed would be 1256.6 linear feet if you use LDSPrepper formula

Tubing 6" @100ft for ~$90 so $1170 for (13x100ft) tubing which provides (~19.63cft*13)  255.19 cft of exchange tubing or only 2% of the GH air volume.
To get to 10% of the GH volume I would need closer to 64 100 ft 6" rolls costing $5760.00.

I found 275 gallon IBC containers with cages $25-$30 used in various conditions which is 36.76 cft. which seem to be the more cost effective option if 10% of the GH volume is indeed needed for air exchange.

(The variations of using IBC containers is many.  Packed dirt could be between the containers and plywood placed on top with drainage tubes connecting each container.
The idea of biocement (calcium carbonate microbes) also seemed like an interesting option to create a cavern space if it is cheaper than cement or permitting issues arise.)

The main sticking point here is how much volume is needed to proper heating cooling air exchange.  
The specifics of ibc containers and their interface to the ground heating effect has potential if needed as the air does not strictly need to be in the plastic containers, merely a surface area to allow air to contact ground temperatures.

Thanks mike,
You are giving me hope for a multi-use compost pile of practical size.