Experience w/ Geothermal HVAC?

[ExFlyBoy5]

Good Monday Everyone!!!!

DW and I are in the market for a new home and a very strong contender has geothermal heating and AC. We have asked a couple of home inspectors about them but they have very limited experience with them. I have read up on them and they *seem* to be a pretty good system...but was just curious if anyone here has had one for a while and what their opinion was. My biggest concern is ability to cool adequately in a hot/humid area. Thanks for your input!

 

[samclem]

My biggest concern is ability to cool adequately in a hot/humid area.

Why the worry about that? The earth-coupled heat pump should do just fine in that situation.
We do/did have someone here who had a ground-coupled system that caused quite a bit of trouble. The theory behind them is solid, and many people have had good results. The issues tend to be initial cost (depends on how much it costs to establish the thermal link to the ground/body of water) and the small-but-essential details of the system. The person that had trouble here had issues of the second sort.
There are two major architectures for these systems: "Direct" (where the refrigerant used for the rest o the system is also pumped through the ground loop) and "indirect" (where a water/glycol fluid is pumped through the ground loop and a separate heat exchanger is used to interface that fluid with the working fluid in the condenser). The "direct" is simpler, can be cheaper to install, and theoretically more efficient. The "indirect" is probably the way I'd prefer to go if buying one, though. Digging for the ground loop is a major expense, and you never want to do it again. There are already new refrigerants on the horizon, and they may not be compatible with the present ones (just as the lubricants in R-22 systems are incompatible with present refrigerants, including R-410A). If you've got R-410A in the buried loop and it gets badly contaminated (chunks from the compressor, scale from poorly-done brazing of copper lines, etc) or is incompatible with the next gen refrigerant, your investment in that ground loop becomes worthless. If you've got a loop of water/glycol, you can use it with whatever comes next. Plus, I think a low-pressure water/glycol loop is just less likely to leak/cause trouble in the first place.

Unless I was planning to live in the house for a long time, I wouldn't consider a ground-source heat pump. The installation costs are high, and it's unlikely to significantly enhance resale value. In fact, it could put some buyers off. OTOH, if I lived somewhere with high heat/cooling requirements and expensive electricity, and if I planned to stay put a long time, I'd look into it.

 

[CaptTom]

I just want to make a shout-out to Sam for correctly calling it a "ground-source heat pump."

"Geothermal" is actually something very different, but it sounds cool and the marketing folks like to use it.

Personally, I'd consider one. But I have zero experience with actually running one, unless you count marine units which use seawater as the source. They're similar to the indirect units Sam mentions, simple, and pretty efficient.

 

[38Chevy454]

They can be more efficient than air-exchange heat pump systems. As the name "heat pump" implies, it is a lot easier to get heat into or out of the basically 55 degree constant ground temp. When in A/C mode, instead of pushing heat into 90-100F air, you are using 55F coolant to absorb the heat. In heat mode, instead of pulling heat from 20-50F air, you are getting it from 55F coolant.


As said, the main drawback is the higher initial installation cost. There could be possible rebates or other incentives from your utility company, since it is a high efficiency system. Look into that as a possible way to reduce the net cost.

 

[ExFlyBoy5]

I just want to make a shout-out to Sam for correctly calling it a "ground-source heat pump."

"Geothermal" is actually something very different, but it sounds cool and the marketing folks like to use it.

Yep, but since that's the accepted term in the industry, that's what I called it. Similar to folks calling a water heater a "hot water heater"...if it's already hot, then why do you need to heat it?

Thanks for the info...and I would not be installing the system. It's currently installed in a pre-existing home that is about 10 years old. We showed up at the inspection as he was wrapping up and it was 83 degrees in the house with the heat during the ops check (it was about 50 degrees out)...so it worked well. Was more curious if it works as well in the AC mode.

When I was stationed at Little Rock AFB, they installed a similar system (very limited loops that weren't buried very deep) in base housing and it SUCKED. Come mid July, all the houses were given multiple window units until they could be converted back to a traditional Freon system. This back in the early-mid 90s, so perhaps the systems have come a long way.