Geothermal heat pumps (GHPs) transfer heat from the ground by circulating water (or an antifreeze solution in places where it is cold) through pipes underground. The technology is not only efficient but doesn’t use fuel of any kind, so it produces zero emissions.
Unfortunately that kind of geothermal requires a quite large upfront cost in the outside part of the system, and no savings at all on the distribution inside the home (still requires a heat exchanger, blowers, thermometer, etc.)
As I have posted before we have geothermal heat-pump HVAC, which is a more reasonable solution for many people. It requires a single water well rather than multiple ground loops, reducing the drilling requirements by 80% or more. In the end it is not quite as efficient as ground loop technology, but getting in the game is so much less costly that it is an attractive alternative for consumers - and should be for environmentalists as well.
The water that my well pumps up is used for the heat-pump thermal conversion, rather than “air cooling” requiring the large, loud, and expensive outdoor cooling fans which age out every 15 years or so. (Ours is 40 and I have had to replace only the inside distribution part.) It is vastly more efficient in winter and summer, using constant 55-60 degree for the process; it has fewer advantages (but still some) in spring and fall, when air temperatures are favorable for heat-pump processes.
While not perfect, it’s like convincing people to give up their full internal combustion engine for a hybrid, rather than insisting they go full-electric, which many people are not prepared to do or are in a situation which simply makes that change untenable.
I appreciate the direction of your post. I have a few quibbles which should be addressed. I will do so.
A single well can be open loop or close loop.
The open loop style dumps the fluid to the reservoir.
Closed loop maintains fluid properties through mechanical separation from the environment (only heat moves from system to reservoir)
There are 3 types of ambient temperature geothermal systems:
This is VERY similar to the ground loops system in that the operating fluid is closed to the environment and only heat transfers. The fluid maintains properties and is never in direct contact with ground water in the reservoir
ATES (aquifer thermal energy storage)
A very nice technical overview of system in operation
This system uses open ended wells with screens that discharge reservoir water directly to the aquifer and USE aquifer water directly as the process fluid for the ground coupled heat exchanger.
Popular misconceptions:
The ground thermal temperature is stable. No, it is not. Even small changes in temperature are enough to provide ENORMOUS heating and cooling potential. All of these systems store heat energy. small changes in the ground aquifer temperature are the result.
All of these systems are in the subset of geothermal called ambient temperature geothermal. To my knowledge, there is no reason for these wells to be more than ~1200’ deep.
There is a concept called “free cooling days”. While the below image is not the whole story, it is an excellent guide for where ambient temperature ATES and BTES can be used:
The red and gold regions are not preferred without VERY specific conditions.
The yellow band is marginal.
There is considerable work being currently completed for systems in New York, Minnesota, Wisconsin and Michigan.
There is a special aquifer condition in Virginia which supports very efficient cooling as a result of high conductivity rock in that area.
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This is entirely different than the deep wells used to harness volcanic activity (over 300F). These wells can be 25,000’ deep and are entirely separate from this discussion.
I’ve always thought it would be great to convert my home to a ground source heat pump.
(Only possible because I own, rather than rent)
But my house is already very efficient and the install costs would be substantial.
But I did see a project that makes a lot more sense. On my daily commute I drive by a large apartment/condo development (maybe 500-1000 units) and one part of it seemed to have some experimental geothermal project. Just before COVID they dug a hole- ~10 ft deep the size of a basketball court, then installed what looked like lots of heat exchangers and lots of piping.
Then it was all buried and lockdowns started.
About 6-12 months later they dug it all up (maybe leaks or they forgot a step).
Then they buried it back and put a dog park on top of it.
Lots of delays but it seems finished now.
So my best guess is that each unit (or groups of them) have their own buried heat exchanger.
It seems like this is a good way to minimize the installation overhead per household…and the common dog park area is a good use for the land above.
Ours is less than 100’ ft deep, if the previous homeowner is to be believed. Anyway, a full ground loop set up will necessarily require much more construction and cost than a simple heat-pump fluid conversion, because you’re using so much less actual water and enhancing it with the electro-mechanical process. Of course that makes it not as “pure” and not as perfectly efficient, but it pulls the costs way down into the range the average homeowner might consider.
On another topic, my brother’s condo in Boston is considering dumping their long-standing oil boiler/steam radiator setup for his 30 unit building and having owners install mini-splits for their heating/AC needs. (Well, the oil system doesn’t do anything for AC, obviously, but more and more windows are spouting window units which are loud and terribly wasteful.) Good news on one front, but of course some owners are grumbling about the up front cost.
