[double0jimb0]

Ground source heat pump owner here in the US. The original system was installed in 2007, and the loop field was designed to "best knowledge at the time". Well in the 20 years since then, NREL changed guidance on how far apart and how deep loops need to be installed. Rightly so, because our circa-2007 is "short looped", it's not sufficient for the house loads, but there is nothing we do about it other than putting on more expensive pumps, more expensive antifreeze and live with heat pump compressors dying pre-maturely because they are working at their design limits. All this makes it as expensive as traditional system (and if we tried to go net-zero with solar, the amount of solar required (because it runs so inefficiently) is larger than our roof area.

So I'm looking at a backup gas boiler to take load of the heatpump/ground loop (house has radiant heat).

And they are not quiet. 5-Ton water to water compressors are not quiet.

And the control system (HDX) and amount of expertise required to keep the thing running is a major barrier to getting low cost maintenance.

Maybe a 2026-designed system will work better and actually live up to the hype you talk about, but there are decades of poorly designed and discarded ground loop heat pumps that have "poisoned the well" if you will.

[adonovan]

Does the ground source heat up (or cool down) over time, making it less effective? The deep ground is very well insulated, which is why after a century of operation the London Underground is 10 degrees warmer. I wonder whether GSHP users need to balance their load by (say) consuming more heating than they actually need in winter so that summer cooling remains effective.

[double0jimb0]

I think there are two types of this, only have experience with 1 so far. Within a single season, absolutely. In deep winter entering water temp (EWT) is around 30degF (this is a pretty accurate measure of bulk ground temp). Typical for where I live is 50degF.

Other type is permanent change that persists year over year. Haven't lived here long enough to measure this. But if you pull more heat from the ground in the winter than you put back into it into summer (we use a water to air compressor for AC in summer), then yes, it can happen and does happen. Don't know if we are in this bucket yet.

[maxerickson]

I wonder if you could cost effectively store heat during the summer, running a system strictly to do that vs doing it as a side effect of conditioning.

[hvb2]

Out of curiosity, has the demand stayed the same? I'm asking because you see the same with electricity grids, designed in a different time with much lower demand.

Sorry to hear this, it seems like a great system to me but you have to have the capacity right. I'm planning on getting one in the next year but the drilling will be more than we need and we opt for no glycol (yet) as that also gives us headroom

[double0jimb0]

I don't think system ever met demand when commissioned (we are 3rd owners). 1st owner largely neglected the system (which I interpret as reaction to it not working well), 2nd owner had local company known for "fixing geothermal" do a lot of retrofits (new higher flow pumps, increasing diameter on plumbing within the utility room to decrease "lift/work" required of the compressors, more feedback sensors / logic boards, added backup electric water tank heating for the radiant system, switch to methanol). These fixes have seamed to limit failure modes to a smaller set of things: mainly compressors dying early.

Currently system is running 20% methanol to combat the 29degF EWT (entering water temp) in deep winter. House is in Zone 6a.

One thing I learned in researching all of this is that use of ground source over many years can move the bulk ground temp permanently. (House also has water-to-air water furnace for AC). If heat pulled from ground in winter is not sufficiently replaced by heat added during summer, can move bulk ground temp over time. (If densely packed residential ground loops ever became a thing, I think this is a real risk.). But I am not sure if we have this issue at our place, still in first year, not enough data points.

[bluGill]

It seems like you need to add new pipes. That isn't impossible, but it isn't cheap even compared to compressors.