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.

 

[quicksandfarmer]

A passive system is going to have to be far larger than a heat pump to get the same result.

Let's say you want to keep your space at 40F and your groundwater is at 45F. The heat released by a radiator (which is what your slab will be) is determined by two things: the different between the surface temperature and the air, and the are of the radiator. Let's say a typical heat pump puts out water at 110F. The most efficient case for a radiator is when the water leaves at the air temperature, that means all of the heat in the radiator is lost to the air. So in both cases the water is leaving at 40F. In the passive system it's entering at 45F and leaving at 40F, the average temperature is 42.5F. The difference between the radiator temperature and the air is 2.5F. In the heat pump case the water enters at 110F and leaves at 40F, the average temperature is 70F, the difference is 30F -- twelve times what it would be for the passive case. To get the same result, the area of the passive radiator has to be twelve times as big!

Let's look at circulator pump and piping sizing. That's determined by the drop in temperature of the water as it circulates. Passive case, it comes in at 45F and leaves at 40F, a five degree drop. Heat pump, it comes in at 110F and leaves at 40F, a seventy degree drop. The passive case needs to move 14 times as much water to get the same result, which means much bigger pumps, bigger pipes, and electricity used pumping water.

It's the same on the underground side. With the passive system you're taking water out of the ground at 45F and returning it at 40F. With the heat pump, it depends whether you have an open or closed loop. With an open loop your fluid is water and you can't chill it below freezing, so you'd be returning it around 33F. With a closed loop you can use antifreeze and return it at perhaps 15F. So your temperature delta with a heat pump is 2.5 to six times as big as with a passive system. The bigger your delta the smaller your pumps and pipes.

 

[SPYDERLK]

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

Its going to depend on how many degrees below ground water Temp is acceptable to him.

,,, With 2KW pumping he can move a lot of water at low pressure. ... Say pipe friction limits it to 40gpm and the design of the system brings 50* water based fluid to the slab and exits the slab at 45*. -- Thats 320lb/min x 5* = 1600BTU/m. ... A BTU/m is 17.6 Watts. -- So 17.6 x 1600 = 28,160W. > So in that case he gets 28kW for 2kW invested.

As the slab warmed the efficiency would go down of course. At 50* slab the efficiency would be pretty low.
,,,larry

 

[buckeyefarmer]

Read up on what that freon loop is doing for you. One of the most amazing inventions.

 

[Jim Timber]

I'm well aware of the physics involved in the conventional heat pump process. There's still an energy input needed to compress the Freon/ammonia/what have you.

I also happen to have a 3 cylinder ammonia pump. I should see if I still have the photos of it and maybe some of you guys could ID the maker for me. I bought it years ago off a guy who'd been using it as an air compressor (talk about inefficient) for 50 bucks.

 

[Jim Timber]

As the slab warmed the efficiency would go down of course. At 50* slab the efficiency would be pretty low.
,,,larry

My shop floor right now is at 45F and the inner face of the block sill around it is 39F (it's filled with pea gravel and capped with cement - thermal mass and poor conduction), the sheetrock above it is 48F. It was 12F outside when the measurements were taken, and the I-beam of my bridge crane measures 52F with the thermostat set to 55F. Granted, this is from being heated via a hanging forced air furnace.

If the slab was able to radiate enough heat into the air, it's possible it could keep it above freezing with fluid movement alone. I'm thinking you guys are right about it not being enough to keep the air above warm enough though. Kinda like how lumens dissipate the farther they are from the source. The not-hot slab wouldn't have the energy to raise the air to the desired temps. At least not at our subsurface temperatures.

 

[Redneck in training]

I'm well aware of the physics involved in the conventional heat pump process. There's still an energy input needed to compress the Freon/ammonia/what have you.

I also happen to have a 3 cylinder ammonia pump. I should see if I still have the photos of it and maybe some of you guys could ID the maker for me. I bought it years ago off a guy who'd been using it as an air compressor (talk about inefficient) for 50 bucks.

Ammonia refrigeration is more efficient than R22 or R410. It is not used in residential applications because of danger it presents if released. You can build a HP out of the pump but I would place it outside of the house, equip it with ammonia sensor that would trigger water shower if leak is detected. So it won't be easy to do in MN due to freezing temp.

 

[Jim Timber]

I'll have no less than 4 buildings on this property, and I'm aware of the dangers of ammonia. It'd probably live in it's own structure if I end up using it. I'm not sure how big it is, other than it's three cylinders.

 

[Redneck in training]

I'll have no less than 4 buildings on this property, and I'm aware of the dangers of ammonia. It'd probably live in it's own structure if I end up using it. I'm not sure how big it is, other than it's three cylinders.

Are the cylinders the same volume (stroke and diameter)? If they are different displacement it will makes significant difference in power consumption. Three stage with stages in series with three heat expanders will use about half of the power for the same performance. The problem is complexity.

 

[Jim Timber]

Honestly, I don't know. I haven't looked at it in around 10 years other than passing it in my parents garage. It was still there last week. :laughing:

 

[pat32rf]

When you pour the slab, make sure that you put foam frost walls around the perimeter to keep the ground below the slab warmer. This can make a large difference in your slab temp no matter how you heat it. A few simple things that often are forgotten in the shuffle...
Ground temp below the frost line stays fairly constant year round.
Heat rises, BUT it conducts and radiates in ALL directions.

We have two adjacent houses. One is geothermal with a lake loop, the other just got an old outdoor wood boiler. It will have a cool water feed run from the lake next summer (its about 55 degrees year round) for AC and we will be running a heating loop from the OWB to the geo house as well to save hydro...