[AC_Hacker]

Originally Posted by slippy

My plan is to go open-loop. While AC_Hacker is clearly a fan of brazed-plates, I believe I will be going with coaxial heat exchangers, from Edwards or Doucette.

You made the right choice, BP clog easily if there is debris in the working fluid. Open Loop means an inexhaustible supply of debris. Co-ax will let small debris pass through.

Originally Posted by slippy

I have planned to water-flow two shallow supply wells (one on either side of the building, beside the 2 units) and 2 return wells. I believe I will hit fair water at about 20 feet, but hope to make it to 30. I spoke with a drilling contractor today, who seemed to think that this would be a very tough proposition without heavy machinery; apparently the ground can be very rocky here in the foothills of NC. The drilling technique I intend to try will be the one at drillyourownwell.com, which primarily uses pumped water or a bentonite mud drilling fluid through 1-1/4" to 3" PVC, with a modified-to-have-teeth pipe nipple on the end.

Awesome!

Originally Posted by slippy

If I fail to be able to drill with this method, I may try another, but I'm no Vlad!

Vlad was no Vlad either until he did it. He's not superman, but he is resourceful and relentless.

Originally Posted by slippy

First question: Is efficiency realized with lower compressor draw, or by hotter indoor coils (in heating mode)? I did a simple test, pouring 10 gallons of hot water onto the outdoor coils while monitoring current. There was no noticeable change to the current. (Before you say Kill-A-Watt, it is hardwired 208V; I DO have a real power logger I just bought, but haven't installed yet, to better monitor.) I'm not sure if the efficiency will be gained by decreasing run time, or by decreasing current draw.

Not knowing the whole picture, I'd say this, The less 'lift' a heat pump is required to make, the less power it draws, AND the higher the COP (efficiency). The power draw and efficiency aren't exactly the same thing, but they are related. If you made changes to th thermal exchange part of your system, you could have a power increase and also a COP increase, due to better heat transfer.

Originally Posted by slippy

Second question: Assuming a "more than ample" heat exchanger outside, how will I prevent the indoor coil from freezing up? We have had this problem, possibly due to air flow, but more probably resulting from low refrigerant charge. I do not believe there is a TXV inside or out. Outside I can clearly see a distributor and many cap tubes. Inside, I really can't see squat, as the unit is basically inaccessible. The manual for the air handler makes no mention of a TXV, and I suspect it is cap tubes as well. I would like to add a TXV since that is something that should add efficiency, which is something I'm really wanting.

I have seen units with TXV feeding an array of cap tubes. It is being done.

Originally Posted by slippy

Third question: On the subject of TXVs, on the outside unit, do you simply attach the bulb to the return side of the coaxial heat exchanger?

Fourth question: On TXV sizing, I understand this is a "system." But, with a very good heat exchanger outside, how might that change the overall system size? That is, should I stick with a 5T TXV, or step it up (or down)?

I'll leave this for Jeff5may

Originally Posted by slippy

Fifth question: If I am going to be gaining a lot of efficiency (no doubt, going from 30°F air to 63° water will make a huge difference), should I give thought to reducing the size of the compressor?

I'd say yes. You'd be best served with the smallest compressor that meets your needs.

If you were building a GSHP for heating only, I'd advise a compressor that is slightly smaller than what is required to meed your maximum demand. Maximum demand occurs infrequently, and some axillary source could be brought into play at that time.

Sorry, that's all I have time for today, duty calls.

Best of luck in this project.

I know that jeff5may is pressed, too.

-AC_Hacker

P.S.: Photos please!!