Geothermal - what if?

[Jim Timber]

There is a reason why people dont just hook their wells up to their pex loop in the concrete.

Because achieving 50F isn't a successful system to them?

I heat my shop to 55F 365 days a year (well, it only needs input about 6 months of that to stay there), so if I could get close to this with a ground loop heated slab for the cost of the electricity to power the pump, it would be a winner of epic proportions for part of my needs.

Maybe a solar HW loop would be more effective/cost and energy inputs wise. The pop can furnace is another possibility, but I wouldn't go with the cans. I'd go with something else that's easier to procure and takes less labor to assemble. I hate to think how long that guy spend slicing the ends to make those fins. :confused2:

 

[Jim Timber]

The new shop will be roughly 6x larger than my current one, so the cost of keeping it comfortable and above the dew point is a concern.

I can run a wood burner or something to bring it up to t-shirt temps on days I'm working out there, but keeping it out of the rusting/freezing zone is my main concern. I have water cooling in several machines.

 

[LD1]

You aren't gonna get close.

If its 0 out and your target is 55, you'd be lucky to maintain 10. Colder just makes it worse. And you have a deal freeze up threat.

1 kw is 3414 btu's. That would be what electric heat is.
Geo heat pumps have the ability to be 4-5 times better. Meaning for every kw you put in you are getting 15000btu +
With what you want for every kw you put into pumping water, you may only get 2000 or 3000 btu. It is a waste of money

 

[SPYDERLK]

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.

I think you are wasting your money for the little gain.

Think about this......a house with no air conditioning but a full basement. Hot 85-90 degree summer days. The basement slab and below grade walls will rarely get above 50 degrees, so you would think there would be a real pronounced cooling effect in the basement. But you would be lucky if the basement stayed 10 degrees cooler right?

Now just think in reverse. 45-50 degree slab (with no below grade concrete walls to help) and outdoor temps of 0F and no other heat source, I doubt you would be able to keep the garage much above 10 degrees. Infact I would be worried about your lines freezing in the concrete with sustained 0F days. For 5000sq ft you would want SHORT runs and flowing pretty fast to a manifold. And SEVERAL to cover that size slab. Which will require a heck of a pump. Just running a single LOOOONG loop or two in 5000sq ft, your water would have done given up its heat and froze by the time it got to the end unless you were pumping it through very fast.

Good thinking. There is a lot to think about here. ... 1st lets qualify a little by recognizing that the temperature control is primarily radiant. You will "feel" heat from a warmer floor much better than you will radiate to a cool floor. It if a confuser to entertain the TRUE thot that the floor is actually always cooler than you. YOU have your own subjective thermostat.

,,,When you walk into your "cold" shop on a calm frigid day your body "heaters" are already full on, having perceived the heat loss from your body radiating to all the frigid stuf in the whole cold horizon. Go inside to a 50* floor and the air temp doesnt change much [because radiation passes right thru air], ... but the floor and every object is warmer. You dont lose your body heat as fast and feel the warmth.

I have floor piping in my 1600 sqft shop that I have just now gotten hooked up. I only have 8kW heat to it so far because the wood stove and related heat exchange is not yet in place. That 8kW will keep the floor about 20* above the average outdoor air temp. You go inside and feel an immediate relative warmth altho the air is only marginally warmer. The whole horizon has changed. You and every object is being shined on by that floor. The walls and objects are warmer than the air and that [and IR reflection] amounts to radiating every which way.

,,,The geoheat situation will have the same effect, but the temperature dynamic has to shift downward. Altho you can move a whole lot of heat out of the earth theres no way you will get your floor above 50* - and probably only 45* as the OP realistically expects. Thats a bit too close to freezing to expect objects in the shop to stay above freezing unless its good and tight and well insulated AND with walls and ceiling that reflect IR well. ... But if the aim is to have a shop you can work in on a 0* day, that 45* floor will give that to you - barely [if youre not an Eskimo].

The technical challenge of moving enuf heat at low delta T is pretty great -- LARGE and deep heat exchanger situated closely, and large piping to and from that plunges immediately to depth to prevent heat loss. Count on about 2kW to move enuf fluid. And a hundred or so gallons of anti freeze in case it ever goes off.

 

[Jim Timber]

Sealed up like a thermos. As some folks would claim - "can heat it with a candle." Right? What I want to know is how close to that being true I can get.

I'm looking at a total system approach where the heavy lifting (keeping the slab above freezing) is handled by a nearly passive system, and can be supplemented with something(s) else to get up to comfortable.

I chose not to insulate the slab in my current shop, mainly because I wasn't familiar enough with the options and benefits at the time. Now I've learned that it's probably my biggest mistake in the whole system, even though it's had no appreciable impact on my energy consumption from an affordability perspective. I'm spending less than $300/yr to keep the shop heated (bumping it up to 68 when I'm out there). Bring that up to the new square footage and it's a bit harder to swallow at $1800. 10 years later (my shop was built 9 years ago) and we're looking at enough to pay for the whole system going conventional geothermal. But what if I could skip the $5K heat pump? That's why we're discussing this.

 

[LD1]

It's hard to figure anything without hard data. Loop size, actual ground temps, just how much insulation, etc.

As I said, my hunch is that you willninput MORE energy into the system pumping water than you will return in BTUs.

If you put x amount of wattage in moving water, and that same x amount of wattage can yield more heat otherways, its not a smart or efficient design. And I think that is going to be the case.

And already with the need for supplement for when you are down there, I think the $5k is well spen for a refrigerant based pump.

I would love to be proved wrong and for this to work out for you, so let us know how it turns out if you proceed

 

[buckeyefarmer]

I think it would work, if you had an open loop system for the summer, feeding constant cold water and a hot spring to feed it in the winter. Other than that, no.

 

[Jim Timber]

If I had a hot spring I'd be set!

I'm not convinced on either side. I know the ground loop would need to be substantial and the transfer efficiency at the slab would need to be exceptional. It's possible you guys are 100% correct that it's not cost effective.

The plus side is that I can install my floor loops and my ground loops and try it without being out anything as long as they're sized correctly to be plugged into a conventional system. I've already planned on doing a heat exchanger for the floor radiant loop so I can use varied input sources.

 

[LD1]

Didn't think of that but think it's an excellent idea.

Install the floor loos and ground loop, with full intention of doing the geo unit, just bypass the compressor and test things out. Run it that way for a few weeks and closely monitor water temps, building timps, and how they compare to ambient.

Then throw an amp clamp on the water pumps and see what they pull. Run an equivalent wattage of electric heaters and NO water circulating (hopefully similar ambient temps) and compare the overall results inside the building. That will give a good baseine.

Then hook up the geo compressor and enjoy the warmth

 

[Jim Timber]

Like I said, I have an ample amount of wood, and will only produce more once I get my sawmill operational, so I want to be able to switch sources to jack the heat up. I just don't want to be tied to feeding a wood burner 4 months out of the year to keep the machines from freezing.