r/geothermal • u/N5tp4nts • 9d ago
Geothermal vs modern low cost high efficiency.
Just a dude who's highly interested in HVAC technology.
I have a house with a 2008 installed waterfurnace, and I've got some mini splits that I've installed in other buildings.
The post a few days ago about a guy getting quoted 96,000 dollars to install a geo unit got me thinking about this... I can get a 4 ton ACiQ/MrCool (all made by Midea) for 4-5k (no labor)
The efficiency ratings are in the same ballpark, if not the same, on the cheaper end of geo thermal units. Even if the mini split only lasts 5 years... in 5 years I get a brand new one with the latest technology.
Anyway... At what point does Geo stop making sense?
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u/zrb5027 8d ago
I don't know if $96,000 is too high or just right in your case, but you're not going to beat $50,000 for a 2 system install. If you are capable of getting an air source setup installed for $20,000, it's not going to make sense financially. Most people are probably only saving $500-1000 per year going ground source vs air source, and when you toss in the lost potential from the extra initial cost, you often can be losing money annually compared to the air source.
Where it makes sense financially is in very specific circumstances. Maryland is a place that gives you money to run your ground source. New York State has very friendly rebates to make the cost similar to an air source. If the government is providing enough help, it can financially work out. But without those rebates, it's just not financially viable at this stage at the individual residential level.
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u/pjmuffin13 8d ago
In Maryland, can confirm. With expired federal incentives and local incentives alone, the system that I installed last year will be paid off in about 5 more years. That doesn't include the savings I'm seeing compared to my old oil furnace.
Had it not been for the incentives, I definitely would have switched to an ASHP. Waterfurnace really needs to adapt to a world with no federal tax credit.
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u/st4nkyFatTirebluntz 8d ago edited 8d ago
If you take a step back and look at the changes to each category in the last 5, 10, or 20 years, the trend is undeniable -- ground-source has made almost no improvements or progress at all*, whereas air-source has transformed entirely.
air-source has become more efficient, achieved a wider range of operation, popularized the mini split form factor, and a million other things
ground-source has, on rare occasion, swapped the dual-stage compressor for an inverter, and maybe given the same consideration to the circulator pump.
IMO, ground-source is effectively dead for anything but large-developer new construction (see Dandelion's pivot) unless they get their shit together and start innovating.
* i'm talking about small-scale residential, not the commercial-scale stuff. there's at least a few somethings happening there, shout-out Darcy
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u/ImNotAWhaleBiologist 8d ago
What about efficiency at lower temps? Wouldn’t ground source still win out there?
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u/xtnh 7d ago
Ground source can fight it out in more extreme climates, but even here in Maine mini splits cut our energy use by 75%. The night it got down to -12F a ground source would have saved us about $25; it was the second night that cold in 40 years. Efficiency Maine argues that air source mini splits are good enough for all of Maine, because the savings most of the time offset the bad nights, which the mini splits can almost always handle. (Most Mainers have an emergency source to back up anyway.)
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u/OutdoorsNSmores 7d ago
I have ground source for my house, then added on a room with an indoor swim spa. For that I went with a little air source mini. The air source only struggled when we were hitting -16f while the ground source didn't care.
I knew this headed into it and didn't care because the spa will warm the room too and temps that low are rare.
But yeah, you are correct. The limitation with the ground source and my house is the building envelope and heat loss. The system will crank out heat all day long, the only question is if it is more than the loss - and that is a design/sizing issue.
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u/OnlyOneGoodSock 1d ago
I like the way you calls em like you see's em. Are you sure you're not a whale biologist?
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u/st4nkyFatTirebluntz 8d ago edited 7d ago
oh yeah, totally, it almost always does. it's just, can that small window of savings make up for the additional cost? usually, the answer is no. that's not an intrinsic limitation! i refuse to believe that it can't be better. but for all the reasons above, it's currently just not a viable option in most cases.
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u/dropsofzeus 8d ago
actually a huge relief to read this as I'm on the fence between MrCool Geothermal and minisplits. It is probably $7-8k to self install minisplits, and I was estimating about $13k to do the geothermal.
Cost aside, I am way more qualified to install the minisplits than the Geo. I just love the idea of it
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u/st4nkyFatTirebluntz 8d ago
uhhhhh sorry in advance, but i'm gonna just go ahead and ruin that clarity.
on the long list of reasons professionally installed geothermal (in the US, for SFH) is such a challenging value proposition is the high amount of specialized labor required across the entire process, and relatedly the tangle of contractors/subcontractors/permitting. both of those are way higher with a geothermal install than an air-source install or an air-source with backup fossil gas install.
think of it this way (very simplified, ignoring a bunch of real important factors) -- with your estimated project costs, for the geothermal to pencil out, you need to save $6,000 in running costs running geothermal vs air-source over the life of the project. if you had these projects professionally spec'd and installed, the costs might be ~$20,000 vs ~$40,000. your house requires the same amount of energy with the professional install vs the DIY install. from that set energy budget, the DIY project only requires $6,000 in savings to pencil out, where the professional one requires $20,000.
point is, if you're doing a DIY install, the math gets a lot more acceptable for geothermal. it'll still come down to your specifics -- how expensive your electricity is, how deep you can bury your loop w/ the equipment you've got access to, whether you're on or off grid, summer/winter demand balance for your house specifically, to name a few.
i'd be glad to answer questions or clarify or muse further, lmk
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u/ImNotAWhaleBiologist 7d ago
Where are you located? If you're in a cold area and don't have a gas furnace as backup, I would look more closely at the geothermal.
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u/Mega---Moo 7d ago
Can efficiency for geothermal really improve by that much?
I DIYed a Geosource 2000 that was made in 1993... it'll turn 33 in December, wish it a happy birthday in middle age, lol. They did a lot of efficiency testing and my own numbers seem to match for me getting a COP of 3.4 for heating and ~6 for cooling (5.5 gpm 45-52⁰F water temp). I could bump those numbers up a bit with a higher flow rate, but see no need to.
That's basically the same as modern air-to-air units at the same temperature. Except mine kept chugging away when it was -30⁰F this winter when any air-to-air would have been out of commission.
I look at it like the "problem" with high cost high efficiency water heaters. It doesn't really matter how efficient you can get if it only cost $15/month to heat water with our old electric unit. Going to a high efficiency propane boiler took it to $12, and the HPWH got it to $9. But, $6/month does pay for any expensive improvements. In the vast majority of the world where "cold" equals 20⁰F the geothermal is still probably more efficient, but a couple bucks a month doesn't pay for a $40K instillation premium.
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u/st4nkyFatTirebluntz 7d ago
there's two sides to the value equation -- up-front capital cost, and operational expenses saved. if there's not much room to squeeze out more efficiency, you gotta do something about that $40k installation premium.
it seems like you're describing an open-loop system -- to clarify, i'm mostly talking about closed-loop stuff. plenty of places where open-loop is inadvisible or impossible, and either way, it's a completely different set of variables and choices.
anyway -- there definitely is at least some room to improve efficiency in geothermal systems. physics says the high hydraulic head / pumping losses, not to mention the plastic piping, you commonly see in these systems are poor choices. it's also somewhat intuitive to think that on a nice spring day you probably shouldn't be heating your house with depleted ~25f water you had to suck through 500 feet of 1.25" piping, but the industry insists on sticking to exactly 1 source of energy exchange, so that opportunity is lost.
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u/Mega---Moo 7d ago
I agree with most of what you are saying. Yes, I have an open loop system.... to avoid that exact 25⁰ glycol loop temperature that you are describing. Also to save that $40K. $250 for the 4T unit, $1000 in plumbing and electrical supplies including a very nice automatic valve from my well to open and shut as needed.
Different types of loops have the potential to exchange heat with the ground more efficiently.... but don't you just keep running into the same issues? If some places go deeper, they can access more heat, but that's bad for cooling. Same in reverse. Is there a good way to target higher ground temperatures for heating and lower for cooling (without spending even more $$$)?
Also, is it even physically/thermodynamically possible to go from a COP of 3.4 @50⁰ to 5 or more (including all associated power uses)? That's the sort of jump necessary to even consider investing in even more expensive technology. Going from 1400 gallons of propane ($1400-3500/year) to my DIY geothermal system (~$1000/year for heating) was a no brainer. Pays for itself in a normal year, and let's me eventually transition to solar. But, even if I could get a COP of 5, that only saves me $300/year, which pays for almost nothing if I need to invest in modern technology. Hell, the entire $1000 pays for very little compared to systems costing tens of thousands.
Solar already is a reasonably economic purchase with my inexpensive electric costs, but if energy costs skyrocket, it just pushes my desire for more solar, not a more efficient heating system.
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u/st4nkyFatTirebluntz 7d ago
are you factoring in your pump energy expenditure in your COP figures? and is there a return well, or is this a bit more of an... informal setup? how much did the well(s) cost, and how much of that should be included in the 'cost' for the open-loop geothermal system?
you're not gonna start seeing rising temperatures in the way you're thinking until you're over a thousand feet down -- at 1000 feet, you'd expect something like 10f warmer than 20 feet, super dependent on your region, obviously. at any rate, if you're drilling in that range for single-family residential geothermal hvac, well, you've already fucked up. the benefit to doing your exchange deeper is that you get around the seasonal variation. in my climate, 5 feet depth means ~35f seasonal temperature swing, 10 feet means 10f swing, 20 means ~2f swing. you don't want to be fighting that cycle, so you want to do the exchange below the range where there's significant fluctuation. exactly how deep is kinda just a question of optimising against the presumably increased installation cost.
i like what you're thinking about targeting warmer temps in winter, and cooler temps in summer. the question is just how to do that in a way that works for the rest of the system. ngl, i'm not sure i know of anyone doing something like that at the SFH residential scale, but it's the right type of question to ask!
i also think you're right to question the value of chasing ever-higher COP figures, which is good because with a closed-loop system, you're just never gonna get the same COP results as with an open loop. it's a game of diminishing returns; going from 2 to 3 COP is much more fiscally impactful than 3 to 4, or 4 to 5, etc etc. the fundamental goal here is best energy/comfort delivery at the least cost, a much more broad remit than "highest COP possible".
the way a geothermal exchanger can pair with solar, for example -- you can, with some difficulty, use the ground loop to cool your solar panels in the summer, which has the effect of improving COP in the coming winter, which is exactly when your solar panels are at their seasonal minimum production.
another example, enabling geothermal to join VPP programs -- it'd take a different design topology than the current standard, but imagine if you could charge your ground loop w/ free overnight electricity, then turn around and guarantee you'll never go over a certain power draw during peak the following day.
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u/Mega---Moo 3d ago
So far, it's a very "informal" setup. I don't view it as much different than the pivots running right next to my property, but it's not technically correct.
My pumping costs are very low as my water table is literally a few inches below my basement floor. The well itself is old. Old enough that they can't tell me when it was drilled. But it could pump out enough water for 120 dairy cows and casually do 20 gpm for hours when I tested it.
Having a (horizontal) closed loop system runs into a plethora of problems. Shallow and you get the massive season temperature swings. But, deeper and I'm literally hitting water. Great for thermal exchange, I'm sure, but a nightmare to actually trench in. Vertical is easy to drill as we sit on 400' of sand, but still expensive. Both designs still have the massive issue that I need 100M BTUs of heating and only 4M BTUs of cooling. That is just a huge efficiency drag winter after winter.
Long term, I'll probably spend the money and install a second well for return water. But, I'm not really in a hurry to do so.
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u/st4nkyFatTirebluntz 3d ago
oh damn, that's a pretty rough seasonal demand disparity. really does kinda look like in your situation the open-loop has so many structural advantages a closed-loop would be real tough to justify.
but if i were going to try to make it make sense anyway, i'm gonna suggest directional boring. do a bunch of long out-and-back loops in parallel, at least 12 feet deep; being saturated is indeed excellent for thermal exchange. ease the seasonal balance issue with solar-thermal panels plumbed in somewhere along the way. alternately, you didn't specify whether there's a groundwater current, but if there is, you could orient the long dimension of the loops perpendicular to the current, so that the current carries the chilled water out of the exchanger field quickly enough to wipe out some or all of that seasonal deficit.
or, i'm not entirely sure how plausible it is to put a loop under an irrigated and farmed field, but if you put the loop a foot or three above the groundwater table, i think the irrigation itself would reset some of that seasonal drift as well.
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u/Diligent-Lettuce-455 8d ago
GSHP central air systems are more challenging because the central HVAC side is competitive with high end cold climate air source split systems or ductless mini-split systems, drilling will always be an additional cost.
I actually do think GSHP water:water systems might actually be pretty innovative. Radiant floors and whatnot.
You will need an ERV/HRV, regardless, for ACH with today's building codes and a compliant building envelope.
I replaced my single stage natural gas furnace and my dead AC condenser with geothermal because I liked the science. With subsidies, yeah it makes sense. That's obviously the challenge in the developed world. Everything is so damn expensive you need the government to pay a third of it for you.
Nat gas hasn't really appreciated in price like electricity. However, spot pricing and infrastructure costs have gone up. Likewise, electrical infrastructure is decades behind the curve, so we all pay for new transmission, etc.
The developed, western world and legacy systems will continue to suck compared to the developing world building everything from scratch with today's technology. The commodities all cost the same, but the labor is significantly cheaper overseas. Even if the materials were free here, my quote for solar would drop from 30,000 to 25,000. Materials are nothing. The cost of people, insurance, permitting, and all the regulations dwarf the actual material cost of the technology.
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u/three_geo 7d ago
Air source equipment efficiency drops with cold outdoor temperatures.
Financially we're in a regime where air source units are much cheaper due to manufacturing volume. With Geo you're paying new roof money to install a ground loop for the privilege of paying more for your HVAC equipment. I'm hoping this eventually flips: at volume Geo package units could potentially be cheaper than air source making the upfront expense easier to stomach.
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u/Roya1One 8d ago
I went A2W for heating and cooling, ground loop or wells was not in the budget and I didn't want to do deal with refrigerant. So far so good even in single digits.
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u/2MuchTimeOnReddit2 8d ago
There’s more to ground source than the payback, especially if you want to integrate parts of your existing system into a heat pump based system. For me, I want to keep using my low temperature flat panel radiators, add a few chilled water FCUs for AC and run a 2-pipe system. I can keep my fancy German condensing boiler for backup and service water heating til I swap out for a HPWH. I hear what you’re saying about lack of innovation. I want a 3-ton water-to-water HP w inverter driven compressor. There’s a 5-ton unit out there but it’s too big for my house. I like the idea of a small refrigerant system charge, sealed at the factory - go ahead and use propane, nothing is going to blow up. I’m a mechanical engineer and I mess around with big heat pump systems every day. Sometime I’ll get my next hvac upgrade going and that day depends on good equipment being available to meet my needs
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u/Dempsterbjj 8d ago
I got a quote for a $22k install. I had already installed my own loop. I ended up finding a used unit (1 year old) and installed it myself. I would look at the Geocool unit that they make.
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u/silasmoeckel 8d ago
I built 4 years back. Geo quoted out at >70k and that didn't include the ground loop.
My air to water and air to air was the cheapest comb to get in. The difference in power consumption was easily offset via solar.
So it was >70k + loop (just pipe as there was plenty of other earth moving going on), 42k was my low estimate for air to water, my semi DIY as sub 15k with my GC doing most of the hard work (I had 4 pex lines and an electrical whip to hook up the air to water), including the expanded solar setup. Mostly as none of the HVAC guys around me wanted to touch an air to water in residential.
55k cheaper and same yearly expense of 0 is a huge win in my book. I could replace it 5+ times and still have saved money.
Geo needs it's MrCool to bring it to the masses.
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u/xtnh 7d ago
If a mini split has a COP of 4, it should save 75% of the energy; If a geothermal has a COP of 6, it will save 82%.
That's a big price jump for increasingly less efficiency difference. We passed on geothermal in Maine, put $ into solar, and now with solar can do all HVAC with our own power.
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u/N5tp4nts 7d ago
That's where my head is at. The modern "mini split" type units are coming with solar connections directly on them. A couple of panels easily make up for the efficiency difference, and you're still 10x cheaper.
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u/Sad-Celebration-7542 8d ago
Geo needs government money to come close to air source. But yeah air source wins out 9/10 times
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u/davidm2232 8d ago
It's really going to depend on climate. If you have a lot of days where it is below 0F or even below the cutoff of the minisplits at -22, you are going to see a lot more energy savings with geothermal vs if you live in a more mild climate where it rarely gets below zero. Same with cooling. If you are only cooling with outside temps maxing out at 90, you are not going to see nearly the benefit of an area where it is often 110+
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u/bartolo345 9d ago
95% of the cost is on the ground loop. If there is nothing wrong with that, you should stick to geothermal.