[slippy]

It has taken a little more than a solid week at about 6 hours a day to make it through the entire Manifesto. I swear, some of you I feel like I know already. I look forward to working with some of you, if you are still around after these many years! AC, I promise to remain on-topic, and I hope your arm is better. Without further ado, let's begin.

Plan: either modify existing 5T ASHP and 2T/3T AC/gaspack units to become GSHP, or replace them with home-made, or modified surplus GSHPs. Indoors will be refrigerant-to-air, not radiant floor.

Building: 2-story, 2500sf per floor offices in a 10,000sf metal building located in Matthews NC, zip 28104. Good insulation, with improvements on the way. 40kWac solar array, grid-tied

We have had difficulties in the past keeping the building cool on peak heat days, and keeping it warm (without using tons of propane) in the coldest winter days.

The 5T HP is SEER 10, though I honestly doubt if it is performing that well. We do seem to have some air flow problems, perhaps (that is hard to measure). We have a small leak in the evaporator coil, which is inaccessible without it being a major project. It was installed in 2000. The 2T gas pack was installed in 1993. It seems to run like a top, despite being built in 1988!

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.

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.

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

I have LOTS of questions, despite having read every last post thus far.

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.

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.

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)?

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 have a hard time understanding how a compressor really works; is it like a motor, where it is rated at a CAPACITY, but will only draw the power it needs, up to its rating? For instance, a 5hp motor won't use much energy at all unloaded. But, it'll use 745W of power per HP of load you put on it. So, will a largely unloaded 5T compressor draw the power of a 1T compressor, if the condenser is huge and the evaporator is small?

I have done my best to TRY to figure out our heat load and cooling load, looking at degree-days and the like, which indicate that 7T of cooling and 8T of heating are way more than enough. In reality, though, that hasn't been the case for us, but then again, we use programmable thermostats and set the units back significantly at night.

One last thing to add for now (and there WILL be more questions as things progress) is that we are really trying to limit our power consumption during poor solar hours. I would like to design our GSHPs with this in mind. We buy power for 3 times what we sell it for, so it is advantageous to us to heat/cool in the middle of the day, when there's lots of sun. I try to cheat a little by heating (or cooling) more during the day, to give us a bit more of a buffer through the night. It isn't enough, though, to keep the units from having to come on at, say, 5am to prepare the building for occupancy. I'm interested in heat (or cold) storage for this reason.

Thanks to all of the folks who have contributed to this mountain of info.