Google's "Dandelion" offering $20-25K geothermal

The issue with cost savings is that over time of course they are significant, but in the here and now they are dubious because most on average arent in a home that long, plus having used both oil and propane, I find the almost double cost difference ( 35 vs. 63) suspect.

Those prices seem inline with what I would expect. Our system was about 30k before tax rebates. That included ductwork in the house. Take out the ductwork and it would be in the 20-25k range the range quoted in the article. Thats for a 3000sq/ft house.

If you add the cost of heat and central air together for a new house build you would be surprised its not actually that much more for geothermal.

I dont really agree with their cost analysis. It sounds like they picked the cheapest electric rate and the most expensive fuel cost they could find.

Geothermal pricing is extremely site specific and if its retrofit its even more so. In my area the local well drillers are the one who push geothermal. Not many residential installations, most are either greenwashing by a business http://www.visitwhitemountains.com/...-announces-the-return-of-the-glen-house-hotel or a non profit/government project that is paid for by subsidies or tax money. There have been a few high end vacation homes that got the systems but reportedly the complexity of the systems makes long term maintenance difficult as there are few qualified service techs in the area. The techs inevitably end up driving a couple of hours up and back from more populous (and prosperous) areas, thus every service call is usually $1000 plus.

In most cases the money is far better spent on building a highly efficient building with appropriate thermal mass so heating and cooling loads are minimal to begin with. Most of those homes may have small wood stove and a minisplit for supplemental heating and cooling

Hasufel said:

the details are sketchy but it sounds like drill vs. dig?

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Aren't most geothermal systems already drilled wells? I've had two neighbors install new systems in the last 3 years, and both were drilled well installations. They were talking system costs way below this, although both were replacing ASHP systems. One was talking numbers closer to $5k - $8k for his 6000 sq.ft. The other was heating and cooling 12,500 sq.ft., and I didn't get a cost from him, but a neighbor who discussed with him reported ROI under 5 years.

Ashful said:

Aren't most geothermal systems already drilled wells? I've had two neighbors install new systems in the last 3 years, and both were drilled well installations. They were talking system costs way below this, although both were replacing ASHP systems. One was talking numbers closer to $5k - $8k for his 6000 sq.ft. The other was heating and cooling 12,500 sq.ft., and I didn't get a cost from him, but a neighbor who discussed with him reported ROI under 5 years.

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On large properties its cheaper to put in ground loops assuming its not solid rock. They give the same efficiency. We have 3000ft of pipe on our property took them a day to dig the area put the pipe in and fill it back up with a little clean up the next day.

Our system was well under 20K. We have approximately 2,400 feet of pipe in the ground via two 300 foot long trenches. It can get pricey when you have to drill wells or blast rock.

These houses are on land that was farmed for over 250 years, meaning there are no rocks left, to at least plow depth. But what I'm getting at here is, the costs proposed by the OP's article for a "traditional" GSHP system seem to be grossly over-inflated. Your cases seem to agree with that.

peakbagger said:

....

In most cases the money is far better spent on building a highly efficient building with appropriate thermal mass so heating and cooling loads are minimal to begin with. Most of those homes may have small wood stove and a minisplit for supplemental heating and cooling

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Have not heard much about thermal mass these days, though I agree it plays a role. If you want to minimize heating and cooling loads, insulate the house and cut down on air infiltration .The passive house movement emphasizes both insulation and air sealing ( 0.5 cph @ 50 Pa). I don't think there is much in the current passive house literature about thermal mass ( could be wrong, most of my info comes from green building advisers who recommend not a passive house, but a pretty good house )

With respect to drilling for water for geothermal, all the systems I am aware of in my area are holes drilled in the bedrock. A double pipe with an 180 degree bend on the bottom is slid down the hole and then the hole is grouted in. A non toxic glycol is pumped through the piping whenever there is demand for heat. Since its a loop the pumping horsepower is just the friction loss in the pipe. There is also no need to worry about ground water extraction and disposal. Unfortunately the recommended depth of each borehole is 300 feet per ton (12000 Btu). The buried ground loops don't seem to work as well as the ground temperature is depleted over the course of the winter. Even drilled systems seem to deplete the surrounding ground temps over the course of the winter so most installers add some margin to the system.

That's why the drilling companies are such big supporters. I attached a link to the hotel at the base of Mt Washington. They didn't say the depth fo the boreholes but they sais they were drilling 30 of them. Most local rigs are only equipped with 900 feet of string so at best they have 90 tons of potential cooling or heating.

peakbagger said:

Unfortunately the recommended depth of each borehole is 300 feet per ton (12000 Btu).

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begreen said:

The drilling costs alone for our house needs (3-4 ton) would be astronomical.

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lol... our summer AC is 10 tons, and our heating load is almost 6x our cooling load in this part of the country (5350 HDD's vs. 930 CDD's). Does that mean we'd need 10 or 58 of these 300-foot holes?

Yet I see some of my neighbors heating and cooling similar-sized (but newer) houses on geothermal systems with what appears to be a half dozen holes, and I think each is about half that recommended depth. Is there a popular system that only uses the geothermal sink for a portion of the load, the rest being air-sourced? Around here, we have private wells for our domestic water, and most run 150 feet deep.

My concern, with half a dozen of these installations within a few hundred yards of my house is, what happens to our well water when one of those loops inevitably fails and leaks?

Ashful said:

My concern, with half a dozen of these installations within a few hundred yards of my house is, what happens to our well water when one of those loops inevitably fails and leaks?

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Just use a food safe fluid. You could probably use vegetable oil although I'm sure there are better food safe solutions. There's not a lot of fluid in those things.

They typically use polypropylene glycol which is used as a food additive. The piping is fusion bonded HDPE pipe, I have messed with the stuff and a well done joint is stronger than the pipe. Since the pipe is grouted into the hole it doesn't move around so wear is minimal and the grout acts as secondary containment from the aquifer. Leak detection could be done by monitoring the loop pressure.

Hasufel said:

They claim the loops have a 50-year lifespan (but presumably YMMV). I wonder if there's an easy way to detect leakage and purge the line before there's any significant fluid loss?

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Really? So, when these 5 year old installations start leaking in 45 years, everyone is to abandon this area?

... and move where?

WoodyIsGoody said:

Just use a food safe fluid. You could probably use vegetable oil although I'm sure there are better food safe solutions. There's not a lot of fluid in those things.

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Yes, I could. But I'm more concerned with the three neighbors who don't.

Is it assumed today, that whatever fluid is used is NOT safe to have in our drinking water? Lots of talk of auto pollution from the same folks on this forum discussing the merits of geothermal. Yet, this seems a more guaranteed impact on their immediate situation, should they live in any area containing geothermal loops alongside private wells.

Ashful said:

Really? So, when these 5 year old installations start leaking in 45 years, everyone is to abandon this area?

... and move where?


Yes, I could. But I'm more concerned with the three neighbors who don't.

Is it assumed today, that whatever fluid is used is NOT safe to have in our drinking water? Lots of talk of auto pollution from the same folks on this forum discussing the merits of geothermal. Yet, this seems a more guaranteed impact on their immediate situation, should they live in any area containing geothermal loops alongside private wells.

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You have probably eaten something with polypropylene glycol in it that is what is used in a geothermal well.

Methanol and Ethanol the other antifreeze often used in ground loops ( not wells ) it breaks down very fast. But yes I suppose it could contaminate a well for a short period of time although given the quantity in a ground loop I suspect it would not be detectable. A 600 ft loop is about 15 gallons of water mixture its protected to only about 20F. Thats not much anti freeze.

Sadly the ground loop will be there forever. Short of a natural disaster earthquake Id be surprised when they leak. Theres no joints below ground. I watched them run over a joint with a back hoe when they put in our system to see if they could break it. No luck on breaking the pipe or the joint. This was a piece of scrap pipe we messed around with.

moey said:

You have probably eaten something with polypropylene glycol in it that is what is used in a geothermal well.

Methanol and Ethanol the other antifreeze often used in ground loops ( not wells ) it breaks down very fast. But yes I suppose it could contaminate a well for a short period of time although given the quantity in a ground loop I suspect it would not be detectable. A 600 ft loop is about 15 gallons of water mixture its protected to only about 20F. Thats not much anti freeze.

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I guess I've read too many stories of dead cats from drinking anti-freeze left outside of garages. I'm not sure what the "safe" concentration would be.

Ashful said:

I guess I've read too many stories of dead cats from drinking anti-freeze left outside of garages. I'm not sure what the "safe" concentration would be.

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Its too bad there are safe alternatives to automotive antifreezes the auto industry just wont use them in cars at least not mainstream. Not sure of the reasons why. Car anti-freeze is nasty stuff.