geothermal heating question?

[Handyfarmer]

considering putting up a building.

would like to keep it above freezing in the winter, and preferable without heating it,

I was looking in to old potato cellars designs, that are partly in ground, to take advantage of the earth heat, just like a old root cellar, but lest just say a large root cellar,

now I have a well pit, and a 10 by 20 root/storm cellar, that I built 20 years ago,

looking at OLD usda plans, the narrower (32') potato cellars are about 6 to 8 feet in the soil but the wider ones are progressive less in depth, and the 40 foot wide unit is only a few feet in the soil, and plans that show wider units are on the surface, Plan number 5619 https://www.ag.ndsu.edu/extension-aben/buildingplans/crops,

Question is, at what point in width, does one lose the effectiveness of the geothermal aspect of the building (unless it is completely "under ground")

my cellar is earth covered,

in our area (even basements that are not wall insulated) seldom freeze if the building is left unheated,

but I can see in a logical sense, at some point the wider one goes your not much different than on the surface,

say I have a 50 foot wide building even if it is in the earth 8 foot, and frost line is only 3 feet, and the above frost line is insulated, after a few feet from the wall, the floor is not that much different than if it was a surface building,

the floor will be whatever the air temp is and most likely not giving up much in the way of geothermal energy, I can see a need to insulate below frost line to keep cold from migrating the edge of the building,

so in a wider building (over 40 foot or wider)does it really make any difference if the building is set down in the earth ?


anyone know where one can find the engineering on something like this?,

 

[Copymutt]

At a loss to find engineering specifics, however I’ve built passive a few times. I would not worry too much about the specs and use your own basic concepts. For instance, dig to a depth below frostline for your altitude regardless of footprint. Bury sheet insulation sloped away from the structure for the perimeter
Shoot for southern exposure alignment and berm the north side. Glazing on south and small windows for light on any other walls.

A design I employed for a timberframe above grade was to underlay the slab w/ a full course of 8x16 cmu. Under the block is 60 tons of crusher fines and 3” of polystyrene insulation. Arrange the block holes to line up north to south and tie each termination to a floor chase w/ floor vents. This creates a thermal flow and keeps the mass 60 plus degrees due to the southern glazing. No other heat required. Check solar incident charts for gain in your location. We have the max in the country down here.
Don’t know your use or budget for the structure, but seconds or defect/cracked block will be fine.

 

[stingry]

I live in Western Nebraska. I have a 3600 sq ft shop. It is Very well insulated, r26 walls, r40+ ceiling and insulated overhead doors. Although it is now heated with in floor radiant, it never got below freezing in 4 winters prior to being heated this winter. The temp just under the floor remained a constant 40 to 50 degrees all winter. The slab surface was basically the same temp, radiating heat into the building.

If your goal is to just keep the building above freezing, I would spend your money on insulation. I would also not insulate under the slab but well insulate the perimeter, this would allow the temperature of the earth below the slab to radiate heat into the building.

If you decide to heat the building, I would highly recommend in floor radiant. I heat my shop to 65 degrees for about $100 a month on natural gas.

Just a thought!!

Cheers
Steve

 

[Handyfarmer]

this was what I was wondering
(just insulate very well, and insulate the stem walls good as well ),

and minimize the or skip the in ground part,

 

[theoldwizard1]

say I have a 50 foot wide building even if it is in the earth 8 foot, and frost line is only 3 feet, and the above frost line is insulated, after a few feet from the wall, the floor is not that much different than if it was a surface building,

the floor will be whatever the air temp is and most likely not giving up much in the way of geothermal energy, I can see a need to insulate below frost line to keep cold from migrating the edge of the building,

so in a wider building (over 40 foot or wider)does it really make any difference if the building is set down in the earth ?


anyone know where one can find the engineering on something like this?,

Watch this video !

Nebraska retiree uses earths's heat to grow oranges in snow

The short version, just burying a building in the ground is not sufficient.

Website Greenhouse in the Snow

 

[Handyfarmer]

the "green house in the snow" (i do have his book) is where this idea originated, but his green house only has a trench through the middle of it about 10 foot wide,(I need wider), and down about 4 or 5 feet, the idea of his thermo tubes is being considered,

but the less digging the lower the cost,

using the "green house" plastic, is not a workable idea for the use of the building, but using it for some solar heat panels may be considered, on the south side, to pull in some heat, when the sun is out,

 

[wssix99]

Question is, at what point in width, does one lose the effectiveness of the geothermal aspect of the building (unless it is completely "under ground")

You need to read this: (Page 17 gives a design guide for what you want to do.) https://www.homeinnovation.com/~/me...de-to-Frost-Protected-Shallow-Foundations.pdf

The specific answer to your question will depend on several factors, including your foundation, your insulation, the location of your frost line, etc.

My understanding of this is that you can sink your foundations through the frost line and "tap" into the hot ground to funnel that heat up into the building. This should raise the frost line within your foundation walls. From there, insulate for even better performance.

If you use horizontal insulation radiating out from the foundation (under the soil), you can trade that for foundation depth and save some money.

 

[Handyfarmer]

Thank you, looks like some very good information, and some excellent guidelines,

this is the type of info I was hoping for,

using the insulation, a monolithic slab could easily be used, page 12,

Thank you

 

[theoldwizard1]

the "green house in the snow" (i do have his book) is where this idea originated, but his green house only has a trench through the middle of it about 10 foot wide,(I need wider), and down about 4 or 5 feet, the idea of his thermo tubes is being considered, ...

The floor of the green house is at 4'-5'. The tubes are below that !

IIRC, he has thermo tubes that run OUTSIDE of the building.

You really need to get those thermo tubes a good 2'-3' below your frost line. You are removing heat from the surrounding ground. If the tubes are too close to the frost line they will "encourage" the frost line to go deeper into the ground. If the frost gets down to the level of you tube, it is GAME OVER ! (This happens more often then people care to admit on geothermal horizontal pipe systems.)

Go deep or don't bother !