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The challenge for these is the cost. First, you either have to drill wells that are ~500 feet deep or lay coils of tubing under your yard (if you have one) below the frost line. Doing either is expensive, though the wells are much more so. The downside of the cheaper option (the coils under yard) is that earth shifts, and the coils will too. I've had two separate friends install these (usually 4-6 separate coils) only to have the earth move and rip open a coil or kink it. Usually you have a valve for each one to shut it off so the unit can sill operate on the remaining working coils, however with each lost coil the efficiency goes down.

Also, the ground-source heat-pumps aren't cheap. They are in the $7-10k range - just for the unit - and not many people know how to repair them as they are a bit of a specialty item in the HVAC industry.

Sure, it's cost, but that's solvable.

1. Drilling the wells is not actually that expensive depending where you are.

For me, 3 300 ft wells, bored, piped, and grouted, was about 5k.

2. The units can be gotten for that price with install.

You need to take into account the fact that they are significantly more efficient at both heating, and cooling, and hot water, over their lifetime.

(also, their specs and submittal data usually have real numbers, giving you mappings from incoming water temperature/etc to EER, not BS numbers like most outdoor air A/C units)

They would also be cheaper if they sold more of them :)

3. The units are much easier to keep working, and pretty much never die. They are made much better than the average heat pump. As for your coils, yeah, doing horizontal loops is not a good plan in most cases, though cheaper.

With the 30% federal tax credit that used to exist, a state tax credit, etc, i paid 10k all told.

I made that back in 2 years (the electric bill in the winter went from 600 a month to 100. Yes, the heat pump was functioning properly)

In areas of the country where well drilling is more common, it's a great option. I wouldn't do it in say, the bay area.

But note: none of the wells have to be that expensive to drill, and in fact, when done during new construction, they are often really cheap.

It's just a matter of, in various parts of the country, limited set of people have well drilling rigs because it's not that common. So part of the cost may be "having some guys drive a well drilling rig 5-6 hours to come handle it"

That's cheap for drilling from what I've been quoted. Most systems I looked at when I had a house before were in the $30k range installed.

I have three friends/co-workers that had the systems installed. None were particularly impressed with the average cost savings. They said bills went down, but not dramatically. One person had the whole system redone at the suggestion of another HVAC contractor (saying the first cut many corners) the re-done system wasn't much better.

While they may "pretty much never die" this is basically the "cheap on average, but expensive for the unlucky person" argument. This quickly turns into a prisoner's dilemma. No one buys because of potential repair costs, therefore everyone suffers (from higher bills, and eventually global warming).

Wells are not always an option depending on what your land is sitting on. If you are over a big granite deposit, good luck.

"That's cheap for drilling from what I've been quoted. Most systems I looked at when I had a house before were in the $30k range installed. "

Yeah, i lived near a place where wells were incredibly common, so there were plenty of well drillers. I can believe 30k installed. With the 30% federal tax credit that used to exist, and Maryland's 30% state tax credit, it can be worth it. Now, without the 30% federal tax credit, it's probably only worth it on new home construction.

"I have three friends/co-workers that had the systems installed. None were particularly impressed with the average cost savings. They said bills went down, but not dramatically. One person had the whole system redone at the suggestion of another HVAC contractor (saying the first cut many corners) the re-done system wasn't much better. "

This depends a lot on where you live, the climate, etc. Also how much you are spending on heating/cooling. You know all this. I was in a fairly large house in a climate that seems 90+ summers and ~25-30 winters. This kinda sucks for heat pumps. It's also the case that, as it's become more popular (relatively), there are some crappy untrained contractors looking to make a buck. I definitely did a bunch of research, and talked to a bunch of contractors before doing the system. I think out of 5-6 contractors, 1 was clearly a snake, and 1 didn't really know what they were doing based on the questions i asked. 3 could tell me intricate technical details about the systems (IE one launched into a discussion of the merits of parallel vs series vertical piping and reynolds numbers), etc.

FWIW: I've also meant plenty of happy vertical closed loop people. I haven't met any happy horizontal open or closed loop people.

That said, unlike the air based units[1], all, for example, of the waterfurnace units have detailed submittal that tell you, for a given entering water temperature, what the EER/COP will be, what the pressure drop should be, the leaving air temperature, etc.

http://www.waterfurnace.com/literature/7series/SD2700AN.pdf

Most of these things are easily amenable to sensors. I had an arduino and a bunch of sensors that told me whether the system was performing okay.

After they first flushed the lines, they weren't sure they got everything out of it and told me to try it. So I did, and the measurements told me something was off. System worked, when cooling, water temps were raising too quickly. They ended up digging the manifold back up, and there was a rock in it (terrain is fun!) After redoing the manifold, everything was perfect.

So i can also believe that if you aren't watching the till, you may not know if the system is doing okay. But at least, unlike most random heat pumps, i feel like I could know and track that stuff pretty well. Overall, my system actually overperformed (which means they probably didn't need to go as deep as they did, but such is life).

[1] This data exists, it's just not usually easy to get for air source heat pumps unless you are an installer/technician.

Do you know if there are any effects on groundwater? Like polution, mixing of different layers?

There are two types of systems: closed loop and open loop. Most systems are closed loop. The only place the pipe is open to is the inlet of the system, and the outlet of the system. They stick u shaped pipes in the holes

So they do something like:

The manifolds look like this: https://www.geohydrosupply.com/index.php/fittings/socket-fus...

If it's done in series, each u-bend connects to a set of two outlets on that manifold. If it's done in parallel, each u-bend connects to a single outlet on each of two manifolds, one in, one out.

Here's a drawing: https://blog.heatspring.com/wp-content/uploads/2012/01/paral...

If you can imagine a really huge refrigerant loop, that's what they are, with water+glycol as the refrigerant going through the pipes. But the water only moves in this loop, it's never going into the ground, etc.

Open loop systems exist, and those are the ones where they are sucking something in one pipe, and pushing it out the other.

Sometimes this is done in a pond, sometimes a well, etc. What happens depends a lot of the design (horizontal, vertical, etc).

Open loops are pretty uncommon.

May I ask where you live to get the drilling done in that price range? Just curious. At $10k it's insanely compelling.

This was in Maryland

Thanks for the practical counterpoint. They are definitely pricier and the installation is more complex, but they do pay for themselves over time and should add to the value of the home.

I'm surprised about the earth movement ruining coils. The installations I've seen pictures of show coils with pretty large radii (maybe 18"), I'd think the earth would have to move a lot to do that, and if it's doing that I'd worry about the foundation. Were these small coils? Is the surface really close to the water table?

It's a regional thing; they seem to be common here in Michigan. It seems to be proportional to the degree of temperature swings? They're not great if the ground and air are always warm or always cold.

We have winter lows below 10F/-10C and summer highs above 85F/30C. But the ground temperature is a relatively uniform 50F - useful for both heating (less important, because natural gas is cheap and efficient) and cooling. It's not so useful when the average temp is above your desired room temp.

Would adding layer of concrete around the pipes mitigate the problem?

The reason most people don't use it is that it costs a fortune to install initially and is dependent on local geology. The payback is longer than most people own their houses for and anecdotally the advertised payoffs have been reduced due to efficiencies standard systems. This further reduces the incentives.

There is also a couple of sections on ground loop heat pumps in the book "Sustainable Energy - without the hot air" by David MacKay:

http://www.withouthotair.com/c21/page_152.shtml

> if you run your refrigerant loop through the ground instead of cooling it using the hot ambient air

In the same vein, rejecting heat to the cooler night air is a lot more efficient than using hot day air.

You can operate a chiller at night and generate a bunch of ice efficiently. During the day, you can melt the ice for cooling at day -- without operating any sort of compressor.

Once the melted water gets higher than the desired chilled water temperature, you can turn on the chiller, but you use the water for heat rejection -- which is still colder than the hot outside air.

Interesting, are there any writeups you could point me to on how to size a system like this for the average home and what the energy costs are like?

A Southern California utility is testing out Ice Energy's units, but the focus is more on demand response/energy storage than on efficiency:

http://www.utilitydive.com/news/ice-energy-will-provide-1-mw...

Though the NYTimes article points out that the improvement from AC efficiency is mostly related to peak demand shaving as well, so it serves a similar purpose.

Their commercial page is here:

https://www.ice-energy.com/residential/