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Geothermal heating in an underground house?  RSS feed

 
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Location: Nevada
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Is geothermal heating/cooling useful for an underground house?
 
Posts: 152
Location: Jacksonville, FL
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I'd imagine using geothermal to heat the floor, and only insulating beneath the floor would allow you to reap all of the benefits of being underground while having the ability to add a little heat for extra comfort. I've been looking into a similar design, but using solar hot water. Perhaps having the heat run right in to the middle of the floor and going outward from there. You could also try to minimize thermal conductivity to the walls so more heat dumps inside and less transferred out through the wall. The viability of finding significantly warmer geothermal heat available vs soil temperature of the underground house location would need to be determined.
 
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Well, since you're already doing a lot of excavating / earthmoving machine time, you might prolong the rental or operator time and put in the tubes/loops needed.  I think its not worth it personally,  While the year,round earth temperature usually is colder than people prefer and you have to be fairly deep to avoid winter (12 ft if i recall) with all the insulation of the dry earth around you, you can probably heat your strucuture easily without geothermal.

Investing in a heat exchange ventilation system and some low power resistance ,heaters would probably be easier and lower maintenance.  you might generate enough process heat to warm the structure (cooking, body warmth, hot showers, etc)  

Im above ground but i have 6 inch of rigid foam insulation and 105sqft.  cooking and showering and my 3K calories  are plenty and as long as the temps outside are above 20F inside stays 55 and pushes 75 if im drying laundry,  

Heat exchange ventillation can be diy ( as easy as ,having your air intake run in a 4" duct inside,of your 5"  exhaust duct for about 20'.  make sure you separate your actual intake and,exhaust,vents after this common run so that you arent just inhaling your exhalations back.  smooth wall metal ducting.  )  

thats a lot cheaper than a heat pump and loops.
 
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The underground house is the geothermal part of the equation, so if it is not adequate (and it is not) then supplemental heating will be required. My conventional house with geothermal heat stays at 50 degrees down to about -5 degrees (f), which is pretty good with no occupancy in the house, but is still too cold for human comfort. And my chicken coop, it would run twenty degrees warmer then ambient air, but it still meant water froze on the coldest days of the year. (It was a building, insulated and heated via geothermal)

You could put in a minisplit but really what is the point since a person is still buying 1/3 of their heat via electricity which is most likely coal, nuclear, gas etc...

As others have said, active (not passive) would most likely be the best way to go because it would allow heat to be where you want it. It would also dry out the moisture in the house, give the occupants warm feet, allow for drying clothes, etc. One of my houses has 100% radiant heat and it was the best, but today I live in a Tiny House without it, and we are really seriously considering installing it, that is how much we love radiant heat. In an underground house, it would only be better.

 
Tom Connolly
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My preference....if it it were possible is to have a rocket mass stove and an air exchanger that sends warm air under the floor.  I have been in people's homes that had electric or coolant heaters under the floor and found that the temperature can be 2 or 3 degrees cooler than in a heat from the side or above situation in the winter and still be comfortable.  I would like to have a partial basement in the house - yes, a basement in an underground house - to store things in an even cooler temperature and to have things handy when needed, without having to go outside.  Maybe I can put the rmh there?
 
Travis Johnson
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Tom Connolly wrote:My preference....if it it were possible is to have a rocket mass stove and an air exchanger that sends warm air under the floor.  I have been in people's homes that had electric or coolant heaters under the floor and found that the temperature can be 2 or 3 degrees cooler than in a heat from the side or above situation in the winter and still be comfortable.  I would like to have a partial basement in the house - yes, a basement in an underground house - to store things in an even cooler temperature and to have things handy when needed, without having to go outside.  Maybe I can put the rmh there?



That is true!

It is that way because radiant by its very nature, heats the objects in the room (and occupants) and not the air.

Heat recovery is another factor. When a person opens a door, in a conventionally heated home, the heated air and the home feels cold, but with radiant floor heat, as soon as the door is shut, because the contents of the room are warm, instantly the home is warm again. That does lead to an issue though with radiant floor heat; a drafty house is detrimental to that sort of heating system, BUT an underground house will not suffer from that.

The biggest issue with radiant floor heat is, it cannot take thermal shocks in the ambient temperature. For instance, my house took 12 hours to recover from a sudden drop in temperature should say a cold front blow in. If it drops from 30 to 0 degrees (f), the radiant floor heat could not recover quick enough because the concrete slab takes awhile to heat and cool off. However, a steady temp is what underground houses thrive at, and why they are ideal for radiant floor heat. In my house, because my "radiator"...the concrete slab...was so massive, I only had to pump 76-100 degree water through it to get my house to room temperature. But that was a conventional home. Bringing an underground house that can get no colder than 57 degrees here in Maine, to 70 degrees, is only 13 degrees, so the amount of btus it would take in order to do that would be fairly small...efficient in other words.

But passive solar would mess radiant all up. It does in my house, along with a woodstove!

That is because as the air in the house heated up, it would shut down the thermostats and heat would stop being pumped into the slab. The slab would thus cool off, but at night, when the sun was no longer shining, the house would require heat, and the boiler would run flat out to try to keep up! But this is not a bad thing, if an underground home owner went with active hydronic solar, they would be able to pump hat into the slab, store heat for the days it was cloudy or stormy, and probably not need a backup boiler at all! This would also enable the front of the underground home to be super insulated, or more throughly insulated, and not have to be designed to get the maximum southern sunlight with a glass facade. It could, just far more design options.
 
Travis Johnson
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Tom Connolly wrote:I would like to have a partial basement in the house - yes, a basement in an underground house - to store things in an even cooler temperature and to have things handy when needed, without having to go outside.  Maybe I can put the rmh there?



I designed an underground house, but instead of having a basement, I had the root cellar in the wing walls. I admit that it took up valuable wall space for a door, but it was like having a walk in cooler in your kitchen.
 
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