The gotchas are the energy used to run the circulator for the ground loop, and the fact that over the course of a heating or cooling season the ground temperature lowers or raises, respectively, by enough that the COP isn't even much greater than an air-source system (but this would definitely vary by climate).
Coupled with the much higher installation cost, it's a bit hard to make a system pencil out for a building the size of a single-family house.
I looked into this extensively about 3 years ago, but in the northeast with a well insulated house.
I ended up going with air-source heat pumps rather than geothermal. The geothermal units were less expensive, but the drilling was massively expensive.
Air source heat pumps now work down into pretty cold temperatures. With a high-efficiency air source our average heating/cooling bills are around $250 (down from ~$400 with older models). Even if ground-source got that down to $200, the payback period of the drilling would exceed our expected time in the house.
We still kind of wanted to do it, but the added problem was that no one in the area was really experienced with ground-source installs. So we would be dealing with the hassle of trying to get these HVAC guys to work on projects that they are not that interested in.
In the end we went with air-source, and it worked out very nicely.
Good video. I've been thinking about heat pumps a lot lately, namely, is it possible to make geothermal ground loops cheap and not disruptive? I wrote a bit about it here: https://www.greennewdealio.com/heating/robot-mole/
Air source heat pumps really are great and it seems everyone in mild climates should be moving towards them. In fact, what I'm working on right now is trying to figure out the maximum ground loop "budget", beyond which it would be cheaper to run inefficient heat sources (COP of 1) for the small periods of time where air sourced pumps no longer work.
The author does not mention if their system is air-sourced or ground-sourced (aka geothermal) - ground sourced systems typically use 25-50% less energy and are especially well-suited to places with colder temp extremes where an air-sourced system becomes quite inefficient. Downside is more expensive to install (need to bury a bunch of tubes in your yard)
Geo-thermal is a little misleading because the systems you are talking about use very high temperatures found in volcanic parts of the world, which is obviously pretty easy. A ground source heat pump only requires 10 degrees or more of heat difference, easily found 30 metres below ground in most moderate temperature countries - it then uses the same technology as air-conditioning.
Loads of them are already installed in the UK.
To heat a home with geothermal, you use a heat pump. It works better than an air source heat pump most places because the ground doesn't get as cold as the air does.
More widely deploying ground source heat pumps for home heating seems more promising than pursuing geothermal electricity generation. The problem with ground source heat pumps is that the lifecycle of the equivalent if 30-50 years, well outside the typical homeowner's planning or payback horizon.
"Geothermal is expensive because of labor, not necessarily price gouging."
In my experience, this is true. Comparing the electric heat system from one HVAC contractor to the ground source system I went with, there are a few expenses that are unique to ground source that start to add up. (USA - 2016)
$3,000 for the man and machine to dig the trenches and fill them back in.
Unknown - 2 days with a handful of laborers and 2,400 feet of pipe to lay and fuse together.
1/2 day to fill and purge the air from the pipes.
The equipment is more for sure, but I don't know an exact figure, but multiple thousands.
Overall, the 2 bids were about $15,000 different. Tax credits and even a rebate from the utility co-op made it close enough to a wash that I went with ground source and have been very happy.
When people ask about my monthly bill, the next question is "Why doesn't everyone do that?" I think many people don't care enough to deal with the sticker shock of a more expensive system. Another big reason is the amount of land required for horizontal trenching (there are other options, but this is generally the least expensive).
I also agree that if your climate is mild enough to use an air source pump, go for it. They don't quite cut it where I'm at (USA, just shy of Canada).
I got “away” paying almost exactly €10k for fancier ground-source setup using a 6kW Thermia (i.e. Swedish) heat pump (itself about €6k.) IIRC there were definitely cheaper geothermal options back when I was investigating, but I got sold on the ecology aspects of that particular solution as well.
I can make some comparisons between the two too – ground-source maintains great COP even if its -20°C or less outside (as it was a couple days ago.) The incoming carrier liquid remains comfortably around 5°C, no matter the season. This also enables passive floor-based cooling. With an air-source heat-pump one would need some sort of a reversible cycle setup, I suspect, or perhaps a separate AC, which would likely bring the total cost of an air-source implementation up a little bit further.
It is also no-louder than your modern fridge. My neighbours’ air-source heat pumps’ exterior units were going at it so hard one could have been excused if they mistook there was a busy airport within an earshot. On the other hand if there's already an airport, what does it change if there’re N planes or N+1 planes in it :)
I think that geothermal works better in more extreme climates. If you compare it to an air source heat pump, the main advantage of geothermal is that the sink temperature is the ground temperature, which is roughly the average of the temperature over the course of the year. In say, Austin, TX, the difference between the average high in August and January is 35.5degF. In say, Chicago, it's 52.7degF. In Austin, the average temperature is 69degF. In Chicago, it's 52degF.
The Austin average temperature is essentially room temperature, and the deviation is much less, so the total amount of heating/cooling you have to do is much less, so any efficiency advantage is reduced by the smaller need to heat/cool. This compounds with the fact that the average yearly temperature is closer to the outside air temperature, which makes the advantage of the ground source less.
This compounds with the fact that Texas energy prices are some of the lowest in the country, and it makes it a lot harder to justify a big capital expense to reduce these costs.
Sure, and they could shrug off the cost of installing a ground-source heat pump[1] too, which would be too expensive for more modest homes. But they'd again have to give a damn, which I am only semi-optimistic about...
Exactly, even if you have closed loop geothermal heat pumps (which more efficiently exchanges heat from the thermal mass of the ground and the refrigerant pumped through a heat exchanger) you are still limited in the amount of heat the refrigerant can exhaust into the ground before you've heated up the ground where it's not possible. And vice-versa in winter where you can freeze t he ground solid by doing the opposite. Still a good idea, but has scale issues especially for high-density areas.
It doesn't really compare since ground-source/geothermal systems are designed to work with a smaller temperature difference (since the earth stays about 50F most of the year a few feet down).
Business wise, if this really works at 2COP at 5F, this might take over most of the market served by ground source heat pumps though.
We're building a house in Wisconsin soon. We think that ground-source geothermal is required for efficient electrical HVAC without gas, but if we can save a ton of $$$ and go with air-source heat pump, that would be awesome.
I wish someone would setup neighborhood geothermal heat pumps as a heating utility or coop model. It's so expensive for everyone to bore into the ground for this.
Both require drilling that is a major factor in their cost and inhibit adoption was my point. Ground source heat pumps are called “geothermal” systems even though they don’t generate electricity.
I was comparing air sourced heat pumps to traditional forced air systems. Geothermal heat pumps are much more common outside of the United States, have a much higher upfront cost, but significantly lower operating and energy costs after the install.
My original point is that if you want to combat the climate crisis, you need to utilize the free heat source in the winter and heat sink in the summer that is the earth below us.
Drilling for this type of heat exchange is a specialized skill, requiring specific equipment. In my area, very few people do it, they have a long backlog, and they are using drilling equipment that is not produced domestically.
Geothermal heat pumps (aka ground sourced heat pumps) have a high initial capital cost. Their suitability also depends on the local dirt as much as the local climate. You need good enough ground moisture levels to have a high enough thermal conductivity. Otherwise the cost of the hole becomes prohibitive.
One unfortunate situation is that the word “geothermal” is overloaded for personal use. On one hand you have geothermal power, which is as you describe. On the other hand you have water source heat pumps which are often described as geothermal, but which are completely distinct from the form described in this article.
Water source heat pumps work everywhere, and they seek to use ground-water temperature anti-freeze in a closed loop as the output from a heat pump. So rather than having an AC dump heat outside (or cold for outside for reversible systems), heat is extracted from or dumped into the ground. Expensive to install ($30k seems a common mark), but very efficient and viable everywhere.
Ground source/geothermal would significantly reduce your heating costs but it would be significantly more than 10k. For that large of house something like 40k+ wouldn't be out of the question, with the largest expense being drilling.
I personally think geothermal is great, sadly New England's geography makes getting a ground loop installed more difficult. In the midwest lots of people would do a horizontal loop by trenching like 8 feet underground laying pipe in there. In many parts of new england that isn't really viable with all the rock so vertical drilling is used which is significantly more expensive.
The gotchas are the energy used to run the circulator for the ground loop, and the fact that over the course of a heating or cooling season the ground temperature lowers or raises, respectively, by enough that the COP isn't even much greater than an air-source system (but this would definitely vary by climate).
Coupled with the much higher installation cost, it's a bit hard to make a system pencil out for a building the size of a single-family house.
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