Geothermal - what if?

[Jim Timber]

What if you skipped the compressor part of the system and just circulated ground temp fluid through a cement slab when the temps were above or below where you wanted them to be?

Would having that much thermal mass at least temper the temperature in the building? So in the winter, it would potentially keep the building above freezing, and in the summer it would keep it from being overly hot. Would that work?

 

[davesl708]

You would need a LOT of ground loop or wells to dissipate the heat. The main reason for the compressors.
If you could loop the pipe through a lake that is over 40ft deep you may get where you want to be but would probably need 500ft of pipe per ton of heat/cool load.:2cents:

 

[Jim Timber]

So if I tap the water table I'm good to go? :laughing:

I'm seeing 400-600' per ton advised on a regular system, so you're saying it wouldn't change anything.

I'm not sure how much system I'll need yet, but keeping the shop over 45F with a circulator pump would pay dividends over propane given our recent gas prices.

 

[s219]

You will get some effect out of it, but nowhere near the efficiency or punch of a system with a compressor and working refrigerant, where the ground loop is just used to reject heat from the refrigerant cycle (which is the primary heating/cooling mechanism).

I suspect it would be usable for small areas, but it really depends on how well the area is insulated, etc. Just think about how deep you have to go to get below frost line in winter -- obviously the ground temp gets overwhelmed to that depth.

No doubt the electricity needed to run the pumps could be used more efficiently in a system with a compressor. They are just so much more efficient.

 

[k0ua]

Jim, what if your pump was solar powered? What if you built one of these soda can solar air heaters? many more on you tube, but here is one guys. below

https://www.youtube.com/watch?v=Jzxw1j-dzY4

https://www.youtube.com/watch?v=AXL707XI-4s

https://www.youtube.com/watch?v=R9bBnRQWRro

 

[Jim Timber]

I'll need to go rather deep regardless of what I do, if I end up doing this at all. I was just thinking if the ground remains 54F, then having the slab at 45F wouldn't be too much of a stretch (yes?), and that much mass at that temp would keep the air at least above freezing for the cost of a circulator pump. Closed loop, gear pump - wouldn't hardly draw a load in a horizontal system.

Our frost line hit 7' last winter. I need to clear a bunch of ground for the building, house, yard (truck turn around area), and lumber storage for drying and storing whole logs. So I've got the room to dig up if it'll be worth it.

I'm investigating all the options right now. Not even close to building anything yet.

 

[JCByrd24]

By the seat of my pants if your goal is just above freezing your best bet is to just build a very well insulated building with properly spec'd south facing windows and forget any of the half baked geothermal systems. If you do all the work of tubes and pumps and no refrigeration/compressor you are missing out on a lot of potential for the money spent. Better off putting all that money into insulation and windows.

 

[Jim Timber]

We have weeks where the daytime temps don't get above 0F more winters than not.

Insulation is a given. Windows alone aren't practical for the layout of the building (monitor barn). The middle bay would be dark and thus cold.

Solar is a strong possibility. I've measured 132F at 4" beneath the sheathing in our roof with "weathered wood" asphalt shingles when the temp was in the mid 60's outside, so there's certainly some potential there to be captured. The vacuum tube solar collectors are also interesting (as was the pop can heater). We did parabolic mylar hotdog cookers in 8th grade and I knew even then that such a technique had more useful applications than bursting the edges on Oscars wieners. :laughing:

I'm looking at roughly 5000sf with a nominal 12' ceiling for the main floor for the shop, and something around 2-3K for the house. So roughly 10Ksf of heated floors between the two buildings. So by using the slab to take the bottom edge off the heating needs, and then also using it to help chill the area when the outside temps are high, I think there's possibly some merit in exploring that. Ground loops are only one technique. You could have buried heat exchangers with barrels of water acting like a water body. It's entirely possible I'll hit the water table too, as I have a spring fed seep maybe 400' from the house site and it's only about 20' lower in elevation.

What'd be sweet, but completely impractical would be to drill down deep enough to get 100F core temps and place an exchanger there.

Honestly, reading about the costs of short lived geothermal pumps makes buying propane and simply having 2000 gallons of it on hand while buying in the summer when prices drop a better solution than doing GT heating at all. I'll be encasing the whole exterior in 2" of high density foam and sealing it again. My current shop has 1.5" pink foam and R19 in the cavities and it's pretty darn efficient even given the fact I made it drafty intentionally so I could get air moving when I'm welding. The new shop won't be drafty, I'll have some make up air ducting in place instead.

 

[chim]

Around here if you circulated cold water in the slab I'm sure there would be times that the floor would be wet from condensation in hotter humid weather.

 

[JimRB]

What is this talk of short lived geothermal pumps? Granted I have only been living in my house for 18 years, but my system keeps working. OK, I was victim of the crummy quality coil common 18 years ago in practically all systems and it started leaking. Coil was replaced and all is good again. The brand I have reportedly has had systems in service 30-40 years. My neighbor has a tech at her house 3-4 times a year for her not geothermal system. The rest of the neighbors have heat pumps and traditional systems without all the service calls. I question her install as at most, a visit every few years to check the system should be enough.

I have a tack room in the barn. Concrete slab. 1" foam caulked to the outside walls and r19 fiberglass in the ceiling and walls. An incandescent light bulb keeps the room above freezing when we get our 0-10F spells.