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https://www.theguardian.com/environment/2026/jan/2...

45-yr old experiment (in St Paul, MN) proves it works. And it has been replicated in other parts of the metro area. Public school(s), for example (BIG $$$ savings--after cost of building the system and outfitting schools with new heating AND AC systems).

Yes, geothermal works, but is best if you have forced air heating. Installation costs can be handled by a utility, piping water into houses to be used for heating or cooling. The utility covers the injection well costs.

Unfortunately, most of my neighborhood uses forced water heating, and so doesn't have the needed ductwork.

Someone I have known for decades discussed thermal heat and cooling systems with me a few nights ago.

If you do not have a runoff system where the water is released into the nearest body of water, then this is very ineffective. He claimed a 40% efficiency rate with the release of the water. That is not enough for deep-freezing temperatures.

With runoff, you can get very high efficiency rates, but the runoff for better-sized projects is illegal.

Thermal systems are still subsidized by the federal government. Unlike EVs.

if you do not have a runoff system where the water is released into the nearest body of water, then this is very ineffective. He claimed a 40% efficiency rate with the release of the water. That is not enough for deep-freezing temperatures.

I think they must have been talking about a different type of system?

If I am not mistaken, the type of aquifer geothermal being discussed pulls water out of one well, pulls heat from it (or dumps heat into it, depending on the season), and puts all the water back into another nearby well in the same aquifer. No runoff. These open loop systems can be municipal scale, or just your own house if you have a big yard.

The only systems like this that I know of that are not water balanced are ones that are tied to a water supply. So, for example, much of downtown Toronto uses a central air conditioning system that pulls "coolth" from the water from near the bottom of Lake Ontario. After the heat exchangers, the water is then passed on to the municipal drinking water system rather than being pumped back to the lake. (I guess it eventually gets back there as wastewater)

The open loop aquifer approach only works where you have lots of good groundwater in somewhat porous soil. Cities on coasts are better off using the lake or sea as the thermal reservoir, but generally lose out on the efficiency of storing heat in summer and pulling it back out in winter, since large bodies of water are not measurably warmed by the amount of heat dumped into them during the summer.

Jim

If you do not have a runoff system where the water is released into the nearest body of water, then this is very ineffective.

The systems here are all "closed loop"--there is no runoff. It is all returned to the buried reservoir where the earth around it cools/reheats the reservoir. So you are comparing apples and turnips (so to speak).

if you do not have a runoff system where the water is released into the nearest body of water, then this is very ineffective. He claimed a 40% efficiency rate with the release of the water. That is not enough for deep-freezing temperatures.

I think they must have been talking about a different type of system?


Jim,

I have some cognitive problems. I stated that backwards. You are right.

If the system releases the water, the efficiency is very high.

If the system recycles the water into the ground, the efficiency drops to 40%.

Nice catch.

I personally know of this project and worked directly side by side with the Hydro Geologist who designed that system in Minnesota.

https://underground-energy.com/

Get a primer for ATES and BTES at the link above.

ATES (Aquifer Thermal Energy Storage) is an OPEN loop system where ground conditions are highly sensitive to effective efficiency of the system. If karst formations are prevalent in the area AND the hydro gradients are very low (milli darcy or less), efficiencies can be very high.

This is a battery in the form of delta T captured in the summer and released in the winter.

Ground temperature gradients are exceptionally important here, as well as free cooling days.

These systems do not work south of Virginia, for data centers (imbalanced load) or in coastal areas where the imbalance is mitigated by high darcy gradients. (E.g. Florida Keys and a constant flow through the limestone carries away the heat of a data center.)

Fun fact, many of these systems fail to launch because the wells are $100,000's a pair and require relatively adjacent thermal loads (buildings full of HVAC people), with suitable groundwater conditions and free cooling days.

An early system in New Jersey is a poster child for poor early development. Their inlet screens plugged at the well, causing a couple of reworks because the design flow from the pumps was simply too disruptive to the soil conditions locally.

The Dutch and the Danes are EXCEPTIONALLY good at this. Their installation networks show well pairs numbering in the 10,000s.

They have:

Great hydro gradients
Excellent free cooling days
Less demanding HVAC culture
No big oil company influence or governance restricting drilling and ground rights use.

correction to above.

I stated:

(E.g. Florida Keys and a constant flow through the limestone carries away the heat of a data center.)

This was stated just after I said that high water gradients severely reduce efficiency when considering a balanced system.


For a highly imbalanced system (data center, constant heat load, 100% cooling hours, 0% free cooling), the example of a data center cooling itself by exchanging heat with gulf stream waters is a highly efficient one.

(But you have to get a permit first!)

dt downstream of a plant like that would be discharging water 5-10F hotter than ambient. In the gulfstream, at that latitude and location, water temperatures can exceed 99F.

dt +10F would be lethal to many higher aquatic lifeforms.

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