Geothermal Closed-Loop System Make Sense in North Georgia?

Greetings,

We are building a 4,000 sq ft home on a 10 acre lot in the north GA mountains that will be totally off-grid. Solar and batteries and a propane-powered generator are pretty much determined (still working on details, including finding an installer/vendor), but we are less decided on geothermal. For one, it's hard to find an installer here. After learning of some folks being disappointed with the efficiency of their geothermal installation, I am concerned that we might not find the experts we need to get the job done right. Assuming we do find the right resource, is it a no-brainer to do geothermal in our case? I guess the other option is to add more solar and use standard heat pump units.

I appreciate any and all feedback!

Don

There have been talk of recent advances in heat pumps with improved performance and efficiency at lower temperatures:


I'd look hard at that before going geothermal. Ground source heat pumps tend to be very expensive.

Given that you already have propane on site, high efficiency low temp heat pump + propane furnace backup sounds like a good combo to me.

Hate to say it, but I agree with eggo here! (just giving you a hard time)

I have a ground source heat pump, and it has worked well for almost 15 years. That said, it requires a perfect install. Issues with the installer or equipment are way harder to fix. Since you live in a fairly temperate area all things considered, I would lean toward an air source heat pump. They are getting ever closer efficiency wise, and when it does break down, you can work above ground.

If something goes wrong with my setup, I would consider air source as well.

Welcome!
Not an expert, but there may be a practical reason why geothermal seems to not be very available in your location. Cost/benefit for your climate simply not worth the expense and chance of failure.

I'm in the same climate zone temperature wise as the op over here at cheaha mountain in alabama and heatpumps that have the backup heating grid on them work great. It's what we use. I have natural gas heat too but we have been weening ourselves off of using it since gas has gotten so expensive of late. I should have enough solar by this winter to not use gas at all.

So basically if you can setup a large enough solar array considering the climate we have I would definitely go that route vs anything complicated.

Not an expert… it seems to me that if you want to hire the project out - then it probably doesn’t make sense - however if you want to DIY - then they seem to make sense. It costs a lot to pay someone to dig all the trenches.

A little different view here. Just so you know where it comes from. I installed and serviced ground source heat pumps for 30+ years the only fossil fuel was oil or a propane backup.

Most dealers don't want to mess with geothermal. If you can find a competent dealer they are very efficient and would likely last 25-30 years before needing replacement. Ground loop 50-100 years.

Payback can be in the 5-10 year range. Longevity for the new mini split low temperature units are still not completely clear but looks promising. Just FYI find the balance point for outdoor air for your build area. No matter what you decide you want your compressor unit to do about 95-98% of the load.

Partimewages said:

…No matter what you decide you want your compressor unit to do about 95-98% of the load.

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Could you explain what this means? Are you saying 98% of the time not having to use using resistance heating in the mini split?

Short answer. Regular speed of the compressor should be able to heat your space about 95-98% of the time. Even though you can over speed the compressor to get into the lower outdoor air temperature it puts undue stress on the compressor unit.
This is why a good heat load calculation is needed for sizing the proper equipment.

You also need to consider the geological environment. Can an installer dig a trench at least six feet deep to lay a horizontal ground loop or will they stop at three feet when they hit limestone (or go to six feet but at a significantly greater cost). A horizontal ground loop needs to be at least six feet deep. The second option is vertical wells drilled to at least 150ft, an additional cost that is probably more expensive depending on what you are drilling into. If installed correctly, a ground loop geothermal HVAC system will be more efficient. You will have to balance installation costs vs return on investment vs how long you plan on living on (or owning) the property. Also take a look at any state or federal tax incentives there might be.

Thanks for the reality check on geothermal. I was beginning to see the writing on the wall when I couldn't find any installers in my area. Thx for pointing out the advances in air to air heat pumps, @sunshine_ego. Thanks everyone for your insights. It looks like I need to put the focus on investing in solar arrays and batteries. I do need to start a separate "Your Ideal Offgrid" thread to see what you would do for new construction today. It seems like things are evolvng so quickly. Too many choices - which is a good thing, right?!

We love our closed loop GSHP but without a ton of incentives we couldn't have done it. This was back when Obama rolled out ARRA and boy howdy was it good for GSHP. 50% up to $10K plus you could still take the 30% tax credit on the full price. We ended up with $3,800 in our 2 ton system.

Two wells x 200' deep each (IIRC). We keep our southern Missouri house shamefully cool in the summer and rarely go over 20 kWH/day and that's only when the highs are hovering around 100f. Pretty much the same 20kWh/day for coldest month of the year as well.

We don't have backup heat strips and have never even come close to needing them in our passive solar house.

However, if I was starting over plus didn't have that extra ARRA bonus money I wouldn't even consider GSHP today. Believe or not, minisplits weren't really even a thing back in 2010 around here. They've come a long ways since then.

I've heard a lot stories about people who aren't happy with thier GSHP, in all of those cases it had to do with the quality of the installer and thier inability to return and resolve the issues.

Thanks again for this excellent feedback! I guess one last question that is relevant to this thread is would you consider air-to-water heat pumps that can also help with heating the water in one's home?

mecdatlanta said:

Thanks again for this excellent feedback! I guess one last question that is relevant to this thread is would you consider air-to-water heat pumps that can also help with heating the water in one's home?

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Yes, but only the passive type. The full time hot water generator does not pay back.

mecdatlanta said:

Thanks again for this excellent feedback! I guess one last question that is relevant to this thread is would you consider air-to-water heat pumps that can also help with heating the water in one's home?

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I'd steer you towards a standalone HP water heater. Keep in mind it will cool off the space it's installed in. No big deal for a small family in a cooling dominated climate but a family of 8 in Minnesota is an entirely different creature.

My geothermal, solar PV, solar hot water journey: 2200sf (heated), well insulated, single story home.

I installed my own geothermal system 13 years ago - a 2 ton ClimateMaster two stage compressor, ECM blower motor, with a hot water generator, heating an 80 SS gal tank, which preheated our 80 gal SS solar hot water tank. The solar hot water tank is heated by two 3 x 10 solar hot water 'panels' on the roof. I live in north Louisisana, so probably close to the OP's heating/cooling needs. For the first 11 1/2 years, I used an open loop system that captured the output of the geo cooling/heating water into an 8,000 gal tank which could be utilized for irrigation, or pumped back into the house for domestic needs.

Two years ago, I changed from open source to closed cooling/heating loop. I installed 1600lf of 3/4" geo pipe, installed in about 550' of trench. Depth of trench was between 3 1/2 and 6' deep. The system has performed as expected with both loop types.

I bought the most efficient, and best (I thought) geo unit that my local preferred distributor had access to, expecting that it would last 15-20 years. Well, about 3 years in, the ECM motor went out. About 7 years in, one of the computer boards went out. Two years ago, I started having cooling issues, and had a leak repaired in the evap coil, replaced the reversing valve, expansion valve and air dryer. Well, that fixed the cooling issue for the next few months until the beginning of the heating system, and we rely mostly on wood heater. So, fast forward to the next summer & cooling was still an issue - brought in a different A/C repairman, and he diagnosed a bad/failing compressor. A new compressor installed was estimated at better than $2k - no thanks! After talking with my HVAC distributor who has 30+ years of experience, he admitted to me that virtually all of these newer hi performance/super efficient systems have 'issues', which is what several techs have also told me. They simply do not last like they used to.

Well, I decided to go barebones on my replacement unit - no 2 stage compressor, variable speed blower motor or hot water generator. My original ClimateMaster 2 ton unit cost me about $3200, and the replacement unit, a more simple Bosch 2 1/2 ton unit, cost about the same. I know the new unit is not as efficient, but shit, I am tired having issues with the top of the line stuff. Kinda like everything these days - cars, fridges, washers, dryers, tv's, or anything with all the bells, whistles and MULTIPLE FRICKIN computer boards.

Anyhow, I had to change my plenum adapter to fit the outlet of the Bosch, and re-route my loop lines, but all works well with the new unit, with no issues so far. Since the blower motor was a regular pcm single speed blower (wide open), I did double insulate the cabinet, and used some external baffling and insulation to reduce the noise. Also installed a compressor soft start.

I have 3 different solar arrays that total 10.4kw, with a Schneider XW6048 inverter. For the household, we use average of 1000kwh per month. We are net metered, and produce approximately the same per month (average). We only pay the minimum grid charge (plus their storm restoration charges), of about $25/month.

To the OP, I am not an expert, but I would think you could probably use 2 two ton geo units on your 4,000 sf home (location, insulation, orientation, etc. would also factor into your requirements). Each 2 ton unit could use basically what I did on my loop piping, or vertical wells, but I am not familiar with those. For your info in planning, my geo unit runs at about 2200 watts. If you would like to talk about some of this, just pm me.

Here are a couple pictures, with the original ClimatMaster first. As the Bosch unit was shorter, I had to build a box for the new unit to sit on.

Oh, once you get your geo system figured out, installing one is not that terribly difficult for a handy DIY'er. The main system is of course in one cabinet and precharged, ready to go. Pretty easy to connect up the loop pump as well, only the special loop piping needs something unusual - manifolds and adapters connected with a pipe fusion tool.

I've got an open loop system in my house, a 2 stage ClimateMaster, 4 tons, in a 2100sq ft single story home. It runs well, the home was built in the late 90's, and I know this is at least the 2nd Geo unit installed on the property. It's about 7 years old now, and it's already had the compressor replaced under warranty, and we've got the high refrigerant pressure sensor by-passed (need to get around to getting it fixed).

It cools great, you can freeze the house out quickly if you drive the temps down. Winter heat, it works, but it's a struggle on the really cold days (if you want to avoid the resistance backup). Honestly, if/when this unit dies (which I suspect will be 1 day past the warranty end date), I'll probably rip it out and replace it with an air to air heat pump system. Just the cost difference is huge, not to mention, it's not cheap to be pumping well water any time the geothermal is running.

kscessnadriver said:

I've got an open loop system in my house, a 2 stage ClimateMaster, 4 tons, in a 2100sq ft single story home. It runs well, the home was built in the late 90's, and I know this is at least the 2nd Geo unit installed on the property. It's about 7 years old now, and it's already had the compressor replaced under warranty, and we've got the high refrigerant pressure sensor by-passed (need to get around to getting it fixed).

It cools great, you can freeze the house out quickly if you drive the temps down. Winter heat, it works, but it's a struggle on the really cold days (if you want to avoid the resistance backup). Honestly, if/when this unit dies (which I suspect will be 1 day past the warranty end date), I'll probably rip it out and replace it with an air to air heat pump system. Just the cost difference is huge, not to mention, it's not cheap to be pumping well water any time the geothermal is running.

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Thanks for that honest assessment. I am seeing a lot of folks that haven't quite been able to come to terms with the fact that their system isn't exactly the cat's meow. I want practical, for sure. Thank you!

Philip53 said:

Oh, once you get your geo system figured out, installing one is not that terribly difficult for a handy DIY'er. The main system is of course in one cabinet and precharged, ready to go. Pretty easy to connect up the loop pump as well, only the special loop piping needs something unusual - manifolds and adapters connected with a pipe fusion tool.

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That's actually a good thing to mention. The GSHP loop portion of ground source is within the reach of pretty much any DIY'er and weekend rental of a Mini-excavator from thier local rental place. Not suggesting that someone tackles it, but it is doable.

kscessnadriver said:

I've got an open loop system in my house, a 2 stage ClimateMaster, 4 tons, in a 2100sq ft single story home. It runs well, the home was built in the late 90's, and I know this is at least the 2nd Geo unit installed on the property. It's about 7 years old now, and it's already had the compressor replaced under warranty, and we've got the high refrigerant pressure sensor by-passed (need to get around to getting it fixed).

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4 tons struggling to keep up with a 2,100 ft2 house is an indicator that there could be a lot of things going on here. I have a 2 ton unit in my 2,500 ft2 house that so rarely needed the 2nd stage I reprogrammed my thermostats to ignore 2nd stage. Longer run times resulted in better humidity control in my case and we NEVER even come close to needing the strips we don't have in the winter.

Open loop systems, AKA "Pump and Dump", seems to give folks a lot of trouble plus they are questionable from an environmental point of view. I'm not even sure that any states will approve one's that use wells today. You might look at converting yours to a closed loop before you abandon it but as I said there's other things going on in your case.

I bought three 5-ton geothermal water to air furnaces. One for my house and one for my workshop and one as a spare (or for spare parts if that’s all that’s needed).

$2,500 each, total $9,500 with shipping.

Still building so not installed yet.

OzSolar said:

4 tons struggling to keep up with a 2,100 ft2 house is an indicator that there could be a lot of things going on here. I have a 2 ton unit in my 2,500 ft2 house that so rarely needed the 2nd stage I reprogrammed my thermostats to ignore 2nd stage. Longer run times resulted in better humidity control in my case and we NEVER even come close to needing the strips we don't have in the winter.

Open loop systems, AKA "Pump and Dump", seems to give folks a lot of trouble plus they are questionable from an environmental point of view. I'm not even sure that any states will approve one's that use wells today. You might look at converting yours to a closed loop before you abandon it but as I said there's other things going on in your case.

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Open loop systems are super common in this part of Indiana, still installed new. House is insulated well, but the crawlspace is much bigger than it needs to be on the house, and isn’t well insulted, so we lose a ton of heat down there. The money it would cost to go closed loop, I could never make it up in efficiency. Just the cost of an air to air system versus what I have, I’d never make up the difference.

I don’t understand how open loop is questionable environmentally at all, but that’s neither here nor there

kscessnadriver said:

House is insulated well, but the crawlspace is much bigger than it needs to be on the house, and isn’t well insulted, so we lose a ton of heat down there.

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If you haven’t already, look into a sealed crawlspace. Lots of benefits.

kscessnadriver said:

Open loop systems are super common in this part of Indiana, still installed new. House is insulated well, but the crawlspace is much bigger than it needs to be on the house, and isn’t well insulted, so we lose a ton of heat down there. The money it would cost to go closed loop, I could never make it up in efficiency. Just the cost of an air to air system versus what I have, I’d never make up the difference.

I don’t understand how open loop is questionable environmentally at all, but that’s neither here nor there

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Seems like insulating your crawl space would a lot easier than a new HVAC system.

The bulk of the systems I've heard of having problems are open loop.

Regarding the environmental issues, Google has plenty of examples. Anytime you're pumping thousands of gallons a day out of one hole and dumping it into another hole there's a potential for screwing up the water aquifer that we all share if something goes awry.

Open loop is dependent on what your aquifer is like. In my area it is relatively popular. Good clean water sources and drainage.

I made a living at fixing other dealers issues. It was nearly always a design issue. A few unit issues. Some equipment was better than others.

OzSolar said:

Seems like insulating your crawl space would a lot easier than a new HVAC system.

The bulk of the systems I've heard of having problems are open loop.

Regarding the environmental issues, Google has plenty of examples. Anytime you're pumping thousands of gallons a day out of one hole and dumping it into another hole there's a potential for screwing up the water aquifer that we all share if something goes awry.

Open-Loop vs. Closed-Loop Ground Source Heat Pumps - GreenBuildingAdvisor

Considerations when comparing open-loop to closed-loop ground source heat pump systems and how to know which--if either--might be right.

www.greenbuildingadvisor.com

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Oh, buying a new HVAC isn’t something I’ll do until this unit dies (which it will, they all do in open loop).

I don’t return water back into the aquifer, it’s a pump and dump, water is discharged onto the surface (into a creek, afaik).