Insulating the ground for SHCS/Climate Battery/Heat storage

I've been considering ways to potentially insulate the bottom of a climate battery to prevent the earth from sucking all the heat down and out of the system.  Laying foam down and covering it with poly is an option but I'm wondering if there are better options.  Two ideas I had were:

1) Using drain pipe laid side by side to create a solid layer of drain pipe.  Water could pass through but the air space should provide some insulation, no?

2) Laying down a thin layer of rocks and then cover with landscape fabric, and do this a few times to create a lasagna of air pockets within the rocks.  

What do you all think?

EDIT:  As soon as I posted this I was shown another thread that discussed this awhile back - https://permies.com/t/74719/air-pocket-beneath-earthen-floor
Reading it I'm learning the drain pipe would allow convection currents to lower it's insulating ability.  But I could stuff it with another material to stop those currents.  

Do the climate batteries normally have insulation under them?  I can't remember.  I know having it around the sides is important.  What's the temperature of your dirt just under your proposed battery?  It might not be that much colder than the desired battery temperature.

Given the choices you laid out, I'd go with gravel vs. the piping.  Maybe with layers of plastic to keep air from circulating in the gravel layer.

I have been thinking about the glass bottles they use in insulating cob ovens.      I considered rows of glass bottles with sand and sheets of plastic to keep it dry.


I don't know but I was just thinking of other methods of insulation, not sure if it would work.

All of the non foam options seem susceptible to moisture in the soil, plastic sheets or not.
Some foams will have the same issue.
If using plastic sheets is OK,  what's the issue with foam board insulation,cost?

BTW, what are you doing vertically along the perimeter?

There is a nearly ideal material, Foam glass:
https://www.buildinggreen.com/blog/foamglas---my-new-favorite-insulation-material

The only drawback is cost.
That could be a deal killer.
Perhaps aircrete is waterproof?
Regular concrete isn't, it will wick moisture, but it can be sealed against moisture.
Papercrete,  same questions.
Hollow micro glassbeads are available, the could be added to a matrix to add insulating qualities.

I think that aircrete would be a good option.  a layer above and below of plastic would limit water infiltration.  It is cheap and this application would be a great use of it.

A layer of sawdust in my lambing pens will bring the temp up by 10 degrees. I would just use that and refresh as needed.

Travis Johnson wrote:A layer of sawdust in my lambing pens will bring the temp up by 10 degrees. I would just use that and refresh as needed.

Sawdust has been used for making ice houses underground for a long time, as long as it does not get wet, should be a good insulator.

William Bronson wrote:There is a nearly ideal material, Foam glass:
( https://www.buildinggreen.com/blog/foamglas---my-new-favorite-insulation-material )

The only drawback is cost.
That could be a deal killer.

I see folks using expanded polystyrene all the time and can't understand that at all.  While it's cheaper than foamed glass, water moves through polystyrene easily and waterlogs it making it useless as an insulation material underground....just turns into toxic ick.  I'd rather use nothing.  The foamed glass doesn't have those problems at all, which is why they use it industrially for ground contact insulation needs.

Between the extensive digging and the insulating details, needed for an in ground climate battery,   I think an above ground heat battery might be preferable.
Insulation could be above grade, opening up possibilities.

You lose out on tapping into the soils ambient temperature, and your mass certainly will be smaller than a "conventionally" dug system,  but as a way to capture daytime heat for nighttime use,  it might be adequate.

Thanks for all the replies!  To give some more information this would be my first time building a greenhouse so I'm doing all the research to make sure I do it right.  I live in Colorado at 7500' on the side of a mountain.  Our well is hundreds of feet deep so I imagine water isn't a major concern (or at least not the water table, and of course we don't get tremendous amounts of rain, correct me if I'm wrong about water not being an issue).  

My concern about insulating the bottom of the battery is my attempt to prolong the growing season as long as possible.  I may be misinformed but I thought a proper battery storing heat all summer could last through fall in possibly into winter.  The greenhouse location only receives 4 hours of daylight in Dec & Jan so I imagine that would be a break in my growing season unless I used LEDs and possibly a heat source.

Are these options like Aircrete and Foam Glass readily available?  No, I don't have a good deal of money for this project unfortunately, I would be borrowing against the house.

Now's the time to go ahead and ask a nagging concern.  Is it agreed here that poly plastic and foam insulation is completely non-toxic?  I don't think there's a way around using those products and was planning on it for the perimeter insulation.  And of course I see experts all the time using poly in their raised beds.  It's just a nagging concern of mine about using plastic, and the foam insulation could possibly be broken up under ground and don't want any contamination.

If you'd all say they are 100% safe products then maybe I would consider them for the bottom insulation.  But then what about water drainage?  I mentioned in my location on a mountain I'd be well away from the water table but wouldn't this impermeable bayer cause a drain issue, or am I completely wrong and it would help retain water which is a good thing?  Sorry for so many questions.  I'm learning all I can!

I remember reading about bricks made by mixing concrete and sawdust. This might be a cheap insulting material. I’ve never tried it, so experimentation is recommended!

Seth, have you seen the greenhouse Gerome Osentowski has in Colorado at 7200 feet?  His site is called CRIMPI.  He uses geothermal air to maintain a tropical greenhouse year-round.

Mike Jay wrote:Seth, have you seen the greenhouse Gerome Osentowski has in Colorado at 7200 feet?  His site is called CRIMPI.  He uses geothermal air to maintain a tropical greenhouse year-round.

Hi, yes, I've visited him and toured CRIMPI.  I have his book "the Forest Garden Greenhouse".  I haven't finished reading it, and I could be wrong, but his design doesn't seem to include insulation beneath his climate battery.  I wish I asked him that question.  He does, however, have other methods of heating during the winter.  My favorite is the sauna he built into his Phoenix greenhouse!  Unfortunately I won't have that luxury and my greenhouse will be significantly smaller.  I don' run a permaculture institute! :)

Yeah, I didn't think it had insulation under it either...

https://www.motherearthnews.com/diy/build-an-ice-house-zmaz72soztak


Plans for icehouse.