Geothermal heat, why so expensive?

Gmachine

Well-Known Member
Joined
Apr 26, 2005
I have an associates in engineering, but am asking for some simple details I'm confused about. We have an electric heat pump, a well that works, but our house is plumbed to city water (some FHA loan requirement). Why wouldn't a heat exchanger, placed in the duct work using well water to blow through, not work to aid in heating & cooling?

These systems seem very expensive, but simple in theory.
 
I'm having a hard time visualizing what you are proposing.

But from my research on geothermal system many years ago when I wanted one, the big expense was the installation - need to have a whole lot of tubes buried in the ground so you have surface area to drawn from. Maybe current designs are different.
 
If you are proposing using electrical current to heat water via an exchanger and then using the water to heat your house...well...you run into the whole law off efficiency thing. It will always be more efficient to heat the space than to heat enough water to heat the space.

Maybe I am missing what you are proposing but what you seem to be hinting at isnt geothermal...
 
The water will always be cold from the well, so all you would really be doing is cooling down the air going in the house, or cooling down the return air coming back to the unit. Really it would only be helping in the summer time if you put it in the return, and more than likely you will just be introducing more moisture to the system by essentially having two cooling coils.
 
I guess I was considering the HP warming 30 degree air outside to begin with, when its really reheating air inside the home. Now I feel dumb. I should have thought it out more.

I still don't understand why these systems are so expensive.
 
You can use a well but there are a lot of 'issues' that the govt forces you to look at. Probably more hassle than its worth. The other kind uses tubes installed in the ground. Geo systems are very efficient. I've heard a seer rating of about 33. I really like the idea, but not the cost...

Oh, and you aren't moving water through the system. You are using freon in the closed system to extract heat from, or shed heat to, the ground or well. In heating mode you are gathering heat from the 55 deg ground source. In summer you are shedding heat to it.
 
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Broncosbybart is correct in that u do not directly use the water to heat or cool with in a geothermal system. A heat pumps efficency changes as out door temp changes. So ur heat pump is not as effient at 30 as it is at 55. So if u take air temp changes out of equation and can use a constant 55* water to absorb or reject heat to then ur efficiency goes way up. Also where a normal heat pump would need to use aux heat strips when temps drop much below 30* they would no longer be needed with geothermal so futher cost savings there. Works same way in cooling also.

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Few years ago I helped put in 4 geothermal systems in a 5000 square foot house. They had to drill 6 200ft wells for the geothermal loop. System was very expensive but believe he got several tax and energy rebates so that helped alot. This was a new construction so everything in house was "green" but he said his first power bill was less then $100. It cost more to heat my 1200 sqft house then that.

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The best situation is a dual fuel(must be installed correctly). This gives you a furnace instead of electric heat once the balance point is reached according to location and type of outdoor unit you have. The problem with "very high efficient " systems are you could have a dual fuel installed, replace it twice before you spend what a proper geothermal unit will cost to install on a re-model. System's can be very over engineered which basically means guys like me spend 6months doing service calls until I figure out the best way to set up system to run "most efficient". I have a lot of customers that have 21 seer units with all the bells and whistles and every time it goes down it cost them about $1300 and they have to wait a week because nobody keeps $1300 parts in stock. Just what I see from the repair/service side of things.
 
bignick said:
The best situation is a dual fuel(must be installed correctly). This gives you a furnace instead of electric heat once the balance point is reached according to location and type of outdoor unit you have.
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This is what we have. A gas furnace in place of electric heat strips. I see a lot of houses with single-mode AC units sitting inline with gas furnaces. Would be a lot more efficient to use a heat pump teamed with the furnace.

As others have stated, the big problem with geothermal system is the high install cost. Several years ago, when Duke did their "green dorm" project, they started out wanting a geothermal system. Once they looked at TCO, it was cheaper to go with 18 SEER heat pumps.

The payback equation shifts depending on the local climate, too. If you live up north where air-source heat pumps can be used less often and electric, gas, or oil heat has to be used instead, a ground-source heat pump might be cheaper in the long-run. The wells are deep enough that they're not significantly affected by surface temperatures.
 
I agree not worth the money. It would take a long time if ever to break even on the high install cost. I would much rather have a simple unit with generic parts that are cheap and in stock everywhere.

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Dredging this up from the bowels... :flipoff2:

Our current "HVAC" consists of:
  • 1 - 50+ year old fuel oil furnace ducted to each room (all in conditioned space) in dilapidated condition
  • 1 - 30+ year old AC unit (with the exchanger scabbed onto furnace plenum)... that struggles to upper-70s* and triples the electric bill :poop:
  • 1 - 30k BTU (temp selectable, not thermostat controlled) propane wall heater that did pretty dang good considering (kept it warm, sipped the 'pane), but has 2 issues that we're looking to resolve:
    • Condensation... which generally a little isn't bad during the winter-time, made the windows (10-12 year Pella dual-pane) sweat like Niagara
    • Manual manipulation of the control 3-4times/day during the "middle temps" where nighttime is below freezing and daytime into 50's... miss an adjustment and you're cold/sweating
The house is approx. 1800sf (1/2 main level, 1/2 basement that's 2/3rds below grade) with brick exterior/cinderblock lower. While 53 years old, fairly well insulated attic and faces due south.
We have 3 ponds (stair-stepped) that are all fed from multiple natural springs above the house (20' rise). Guesstimating flow in excess of 20GPM and flow year round.

A friend with a surface water/closed loop geothermal system mentioned that his (properly sized/installed) was great... initial install costs (outside of the geo heatpump) were reasonable (a few 1000' of HDPE coils sunk in his large pond) and cut his electric usage year round by 60+% average.

Thinking we could benefit from such a system... higher efficiency/longer life than conventional and while more costly, there is a ROI/savings (7-12 years) vs. never for conventional... & leave the propane heater for outages.
My only concern is whether the current flow is enough and only angst would be filling the lower pond (7' deep) full of slinky coils to the point it couldn't be used to fish/swim...
 
From what I know, the install, if doing wells or loop, are where the Cost are. When I upgraded my heat-pump, one of the contractors that gave an estimate, told me I didn't have enough usable yard, for Geo. I never realized that. Folks that have River or Ocean front property, got it made! Never heard of using a pond, but It's a Great idea. You'd have to have enough Volume & Depth, for the intake to be fairly stable, temperature wise.
 
rodney eppes said:
From what I know, the install, if doing wells or loop, are where the Cost are.
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That's what I'm seeing... figure dropping "slinky" coils of HDPE in the water with weights (to keep them submerged) for a closed loop can't be that hard! The only variable when going that route is the total length of the loop...


paradisePWoffrd said:
How constant is the pond temp? That will effect system efficiency.

Likely the one closest to the source is most constant. Could dip it deeper to help even more.
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The "closest" is the shallowest (2') & smallest... the upper pond (originally dammed to provide water to the house in the 60's) is 7'-8' and likely the most constant temp... the lower is the largest & 7' deep...
Or, if I can draw the supply out of the upper or flow water thru the pond side exchanger, there's 500 of creek to dump it back into between the 3 for an open loop system.

Along with quantifying the flow rate and temp... Will likely drag a designer into the mix if it gets to the "doable without hitting the lotto" stage
 
I would go closed loop to make your water to refrigerant heat exchanger last and to be more usable in the winter. Adding glycol to the circulation will prevent electrolysis, help stop deposits and prevent deposits. I've seen open loop geothermal units installed on well water houses that use less than 75 gallons a day so using a pond with a natural spring would not be an issue. I would start with the top pond but put in some hand holes for future axcess/maintenance. If you needed to you could add a second pond for more thermal mass. If I had access to a body of water this is what I would do for my house.
 
And as for the original question most of the expense is in the ground loops/well. The unit it self is just a regular heat pump without the condenser coil. The liquid to liquid heat exchanger is in the place of the condincing coil. They don't cost any more to make but they still charge a premium for the unit because they can.
 
My friend Steve is an expert on this and was in the industry. It is the installation and grout cost that drives the price.
 
Caver Dave said:
That's what I'm seeing... figure dropping "slinky" coils of HDPE in the water with weights (to keep them submerged) for a closed loop can't be that hard! The only variable when going that route is the total length of the loop...




The "closest" is the shallowest (2') & smallest... the upper pond (originally dammed to provide water to the house in the 60's) is 7'-8' and likely the most constant temp... the lower is the largest & 7' deep...
Or, if I can draw the supply out of the upper or flow water thru the pond side exchanger, there's 500 of creek to dump it back into between the 3 for an open loop system.

Along with quantifying the flow rate and temp... Will likely drag a designer into the mix if it gets to the "doable without hitting the lotto" stage
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you may be able to get away with 7-8 depth if you have enough water flowing in and out of the pond. but from what i can tell most of those systems are put in ponds that are 15-20 ft deep,and fairly large. other wise air temp will effect water temp to much to make it as effective as it should be.
 
tsconver said:
Go measure the water temperature now. It is at or close to its max temp for the summer. If it is above 50 degrees at the bottom then it will not be of much use. Having lived on farms ponds at that depth usually warm up during the summer.
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Stuart2.png

Have no means to measure bottoms, so used my instant read digital 6" below surface.
Ambient air temp at the time was 80*F and it's rained for 3 days

Pond #1 - 64*F (surrounded by trees, so 85% shaded & source of springs)
Pond #2 - 67*F (surprised so cool, given the shallow 2' depth)
Pond #3 - 74*F (surprised so warm, given the 7' depth)
 
Still waters will reach the ambient temps. Running water will stay cooler. You mentioned 1 pond with a Spring. At the point of the Spring, would be the most earth like temp, & that pond would be better if it constantly filled & flowed out.
Where I grew up, we had an acre pond, with a couple springs, & around 6' at the deepest. Get in it & walk around, you'd Know when you got to a Spring!:eek: But they just maintained the closed pond. No water in or out.
 
Caver Dave said:
View attachment 273455
Have no means to measure bottoms, so used my instant read digital 6" below surface.
Ambient air temp at the time was 80*F and it's rained for 3 days

Pond #1 - 64*F (surrounded by trees, so 85% shaded & source of springs)
Pond #2 - 67*F (surprised so cool, given the shallow 2' depth)
Pond #3 - 74*F (surprised so warm, given the 7' depth)
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You need water that is at or close to ground temperature. 50 to 55 degrees year round. You start adding heat to those pounds during the summer from your house cooling system and it will quickly raise the pond temp. Also in the winter I bet those ponds get below 50 and probably freeze over and get down to close to 30 at the bottom. No way to pull heat out of that to warm your house. Good geothermal needs a constant 50 to 55 degrees this is usually done with deep ground loops that ae below the frost line at a depth that has constant temps. That is why it is so expensive.
 
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