Deeper is generally better since the temperature is more stable and rises with depth.

"Deeper is generally better since the temperature is more stable and rises with depth."

Hogwash. My understanding is that the temperature difference in most locations between a bore with an average depth of 150 feet versus one of 300 feet is irrelevant to the operation of a ground source heat pump.

OP, you've got 1200 linear feet of bore either way, should be the same.

Thanks, all. So, linear feet, in any combination is the only thing that matters? I just want to be sure the contractor isn't cutting a corner because of how steep the driveway is.

I'm just a fellow homeowner, I don't know enough to tell you what form of excavation is best for your (unknown) circumstances.

I know enough to understand that the ground temperature variations with depth neither enable nor preclude the use of this technology. There's a lot of info available on various websites. Heat pumps transfer heat, so it's out of the house into the ground to cool the hosue, and out of the ground and into the house to heat it.

If you want an indication of how heat can be extracted from cold ground, feel the warm air blowing from your fridge - same general technology as a heat pump, that heat was taken from the 40 degree F compartment. It's cooled by having the heat removed.

If the question is, âÂÂwill it workâÂÂ?â The answer is, if properly installed, then yes. What does the installer mean by, âÂÂbased on the topography of the lotâÂÂ? Are no other configurations possible?

Often the contractors want to do whatâÂÂs easiest for them. That may mean abandoning âÂÂbest practicesâ and optimal efficiency for contractor expediency. Have a detailed and frank conversation with your installer about all the options and the implications of each choice - good and bad as it relates to âÂÂbest practicesâ and its impact on cost, both installation and operating.

Things are not so simple. Deeper is not necessarily better. While it is true that the ground gets warmer the deeper we drill, that may not be an advantage. If youâÂÂre in an air-conditioning dominated climate warmer average ground temperature will not be an advantage, strictly speaking, as we would want the ground to be a cool as possible for better transfer of heat.

Linear feet is NOT the only thing that matters. 6-boleholes of 200-feet each, configured in parallel is still the same 1200-linear feet as 2-boreholes of 600-feet each, configured in series but they are not the same. Both configurations can work but the 6-boleholes of 200-feet each configured in parallel better conforms to âÂÂbest practicesâ as less pumping energy will be required. This is in part because for high efficiency pumping the 600-foot deep borehole will require 1-1/2in diameter HDPE pipe. A 200-ft borehole will require only 3/4in HDPE pipe. The larger diameter pipe is more expensive, generally harder to work with, will require more fluid and more antifreeze.

âÂÂOP, you've got 1200 linear feet of bore either way, should be the same.âÂÂ

The reality is that itâÂÂs rarely the same, every situation is at least somewhat unique and there are many ramifications with every choice of configuration.

SR

"My understanding is that the temperature difference in most locations between a bore with an average depth of 150 feet versus one of 300 feet is irrelevant to the operation of a ground source heat pump. "

Deeper is more stable, even if the small temp difference (and it is not always that small) is not used.

So I guess your saying that tubing in shallow horizontal trenches and coils in shallow ponds don't work?

No, of course, you're not saying that, because those two both work very well. It's all about heat transfer on the earth side of the system, and a lot of different approaches work fine without your suggestion of stability being an issue.

I'll clarify the circumstance. We have a large, steep lot, which is narrower at the street level, and widens out as it goes up. Because of retaining walls and a VERY steep drive, the installer thinks he will have a hard time getting his equipment higher up the lot to the wider space. For that reason, he wants to use two well-spaced deep bores closer to the street, rather than 4 shallower bores higher on the lot. We live in Atlanta, so are definitely AC dominated. I'll bring these issues up with him. Anything specific to bring up?

In your case what the contractor is proposing seems reasonable. Other drillers may have smaller tracked drill rigs that might be able to drill where this contractorâÂÂs equipment cannot.

You might want to discuss how he plans to connect these boreholes and whether he plans to use pressurized flow centers or not and why.

SR

Here is a link that might be useful: QT Flow Center

Adamdoc, I'd get your HVAC contractor to pass judgement on what the driller is proposing. After all, he's the one that needs to live with the consequences (because he's on the hook to have the system work as intended).

Good luck to you.

Hi all - so drilling starts this week, and our driller (who is also our geothermal installer - he owns a large company that does quite a bit of work, so he owns his own stuff) is saying that we'll have 2x600 foot bores, with 1.25" HDPE pipe.

His rationale is that with 1.5" we'll need a larger pump to get good turbulent (non-laminar) flow, and that will use more energy, while we can get sufficient flow volume (3gal/min/ton), and speed (2ft/second) with the 1.25". Does that sound suspect?

Thanks again to all!

Adam

Yes 1-1/4in pipe will work - but you are at the maximum length limit for just âÂÂAdequateâ flow!

Your installer is NOT using âÂÂBest Practicesâ in this regard. 1-1/2in pipe is recommended for âÂÂHighâ efficiency pumping at this borehole depth.

Is your installer IGSHPA trained and accredited?

IMPO

SR