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Old 04-28-15, 11:29 PM   #1
MEMPHIS91
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Default Dxgshpwh (ground source heat pump water heater)

Howdy! I begin by saying thank you, thank you to all who take the time to read my thread, who comment on it, who give advice, who save me money by keeping me from making stupid mistakes, and those of you who just want to see something created. My name is Jake, (I am very bad Dyslexia so I apologize if things get mixed up) my project is a DXGSHPWH that in English is a Direct Expansion (DX) Ground Source (GS) Heat Pump (HP) Water Heater (WH). I will give as many details as I break this all down. My idea is to use an electric hot water heater with the HX coil from a window AC unit coiled inside, with the DX line running 30 feet deep into a 2 inch bore hole. My outline will be broken down into sections of the system as follows: Section 1 Water Heater, the tank, thermostat, HX coil, and back up elements; Section 2 Main AC Systems, heat pump, refrigerant, accumulator, expansion valves, housing, and controls; Section 3 DX System, bore hole drilling, DX coil, bore hole replacement medium, and thermometer.
Section 1 WATER HEATER
I have sourced a used 50 electric hot water heater. I would like to have to already existing thermostat control the compressor I have read on this forum about how to do that and fill like it should work fine. The HX coil is probably the biggest question mark in my head. Iím thinking 25 feet or 3/8 refrigeration copper tubing coiled into either the top or bottom 1 inch element hole. If I can get it the coil correctly would do it in the bottom be best? Also the fitting like on the Air Tap A7 looks perfect but can I just buy that fitting somewhere? Should I consider coating the coil in something to keep it from building up with calcium and other terrible water things? I have seen people electroplate copper with Nickle before, comments? Whatever hole I donít use with have a 120 volt 1,800 watt element for when the heat pump canít keep up (I hope that never happens).
Section 2 MAIN AC SYSTEM
I am hoping to basically just cut existing lines to the heat exchangers and braze with 15% silver rods the coils going to the WH and the DX bore hole on. The only control I should need is the thermostat on the WH because I shouldnít have to deal with defrost. I was thinking about running a temperature probe to the bottom of the bore hole and if it drops below 45F or so to cut off the compressor until the ground can warm back up. I can easily get a 5,000-7,000 BTU window unit, what size would be best? I will be using BBQ propane frozen and then double line dry filtered as my refrigerant.
Section 3 DX SYSTEM
I plan to use 2 inch PVC pipe with a metal cutting head hooked to a 2 inch mud pump from my large pond, and add pipe until I get to 30 feet. I have done this before and gone to 36 feet. Iíll post pictures as I drill and give a run down on the set up. Then I will feed the DX coil down and refill the hole. What are yaílls thoughts on how deep the bore hole is? What diameter DX coil, Iím thinking ľ or 3/8? My biggest concern is the lubricant getting stuck at the bottom of the DX loop, could I just put a bigger compressor and get more flow if the first one is too small? It is much easier to replace a compressor than to bore another hole. Should I paint or electroplate the coil? What should I refill the hole with; I was thinking sand as it would let water in. Should I run a thermometer probe to the bottom? Should I cover the bore hole with concrete? Or should I maybe do 2 bore holes at 20 feet? I can hit water 75% of the year at less than 10 feet. Ground temperature is normally around 55-62F.
I will post some simple drawings and pictures as soon as I get a chance. Thank you again for reading

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Old 04-29-15, 08:48 AM   #2
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First off, welcome to the site!

Very interesting project Memphis91. I look forward to see what you come up with.
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Old 04-29-15, 12:00 PM   #3
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Quote:
Originally Posted by MEMPHIS91 View Post
...My idea is to use an electric hot water heater with the HX coil from a window AC unit coiled inside, with the DX line running 30 feet deep into a 2 inch bore hole...
Jake,

Regarding the vertical bore hole and the lubricant issue, when I cited it as a potential problem, I was acting as a 'devil's advocate', and was (am) trying to visualize possible problems. I was not saying that a 30 ft deep DX hole will not work... it might work just fine.

We have heard from other folks from MS here on EcoRenovator, and from all reports, making vertical boreholes is comparatively easy in MS, compared to some other parts of the country. So in that regard, nature has been very kind to you.

So, I guess what I'm trying to say is that I hope your project doesn't get tied up in knots over my comment about the possibility of lubricant starvation in a 30' vertical hole. Your initial vision is clear and good, and quite likely to work exactly as you originally envisioned it.

& & & & &

Having said all that, only if your vertical idea doesn't pan out, you might want to consider the illustration below:



This is a typical diagram of a DX loop field as it is often implemented commercially. I always thought that this method was used because it resulted in the minimum disturbance to a suburban landscape, which is a very common reason that many people do not want to do a GSHP installation, even knowing the much greater efficiency (my girlfriend being one of them).

But thinking about a potential lubrication issue, and remembering this diagram, I see that a horizontal borehole would give good exposure to the soil, and reduce the vertical vertical lift.

It would also be much harder to dig unless you had specialized diagonal digging equipment, as seen below:




& & & & &

Just in case you didn't see it already, I just came across a Wikipedia entry on DX heat pumps HERE that indicates that vertical DX boreholes have been drilled to depths as great as 100 ft. so do not be discouraged, do not be confused.

Push on!!

Best,

-AC
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Old 04-30-15, 08:26 AM   #4
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Thanks Doax!

AC,
Yeah you just pointed out my biggest concern at the very beginning. The show WILL go on.
Oh the ground here is AMAZING! Plus in about 40-50 feet from a large 2 acre pond. So hitting water will ALWAYS happen. I already have 500 feet for HDPE 3/4 poly pipe in the pond for a geothermal loop idea I was already working on to heat my greenhouse (aquaponics) in the winter.
I have about 10 hours of reading ahead of me. I did find some good sites though.
http://welldrillingschool.com/course...geothermal.pdf "copper has sq.ft-hr-įF per inch of wall thickness, whereas that of HDPE pipe is only 2.7 Btu/sq.ft-hr-įF per inch"
And another forum mentioned using a oil separator, i guess like this one 1 3 8" HVAC Oil Separator 559011 | eBay
Looks from what I can tell the line coming from the HX coil is larger on the way down and smaller on the way up. So I'm thinking 3/8 down, 5/16 up. I will try one 30 foot bore hole and if it doesn't work I'll just drill another hole.
Are there any people with experience with DX installs on this site?
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Old 04-30-15, 08:47 AM   #5
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Quote:
Originally Posted by MEMPHIS91 View Post
...Are there any people with experience with DX installs on this site?
I think that you are the first to do so here, so this is really an interesting project.

I just did some searching on the web, and on THIS page I found an interesting article, which had this picture:


The tubing sizes are different going up and down, and are used for a bigger compressor.

-AC
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Old 04-30-15, 08:55 AM   #6
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AC,
Yes I was just on that page myself. I love diagrams. Those bore holes are at 120 feet. Boy that is deep.
Random thought, if acid is the problem why can I not dump some powdered line into the bore hole as im filling it with sand? Maybe even some sea shells that will release lime over a long period of time?
DX - Direct Exchange Equipment Options This site claims it 25% better than water loops.
NO ONE does DX around my area even though we have awesome ground for it, strange.
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Old 04-30-15, 09:28 AM   #7
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Quote:
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AC,
Yes I was just on that page myself. I love diagrams. Those bore holes are at 120 feet. Boy that is deep.
Random thought, if acid is the problem why can I not dump some powdered line into the bore hole as im filling it with sand? Maybe even some sea shells that will release lime over a long period of time?
DX - Direct Exchange Equipment Options This site claims it 25% better than water loops.
NO ONE does DX around my area even though we have awesome ground for it, strange.
Really great ideas about dealing with PH.

I was also thinking about where your expansion device (cap tube) should go...

Maybe at the top of the hole, before the entire trip... maybe at the bottom of the hole, before the trip back to the top?

If you went for the bottom, the cap tube is pretty fragile, but once you were certain that there were no leaks, you could cast the bottom assembly in plastic or tar... concrete might be too corrosive.

-AC
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Old 04-30-15, 11:27 PM   #8
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AC,
That is something I have yet to ponder on. What would be the advantage of top vs bottom?

I now have an idea to run 2 loops of 1/4 tubing 30 deep feet coming off a common manifold at the top, both sharing the same bore hole. It might be a bit trickier to get all that in 2-2 1/2 inch bore hole, but it will completely solve the lubricant issue.
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Old 05-01-15, 10:05 AM   #9
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Quote:
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...What would be the advantage of top vs bottom?
I don't have any experience with DX, so I'm trying to imagine what the behavior of the vaporized refrigerant would be, based on what I have witnessed so far...

I initially imagined that there might be a condensation problem, but then I realize that condensation will not happen in the low pressure side. Another aspect would be that the temperature of the liquid-flashed-to-gas that is exiting from a high-pressure tube into a low pressure area will be the very lowest in it's trip back to the the compressor, so the delta-T will be greatest and the heat migration into your vaporized refrigerant will be maximum at that point. The delta-T will decline as the vaporized refrigerant gathers more heat. So there could be an advantage to having all that take place at the deepest, most wet, most temperature-stable part of the bore hole.

The opposite scenario would be that if the liquid-to-gas transition happened at the top of the hole, the vapor would have a longer distance, and longer time to gather heat. The construction and maintenance would be much easier. Also, if you went for a TXV, it would need to be at the top of the hole. But I think that a TXV for such a tiny compressor would be just too much techno for what should be a simple, elegant project.


Quote:
Originally Posted by MEMPHIS91 View Post
I now have an idea to run 2 loops of 1/4 tubing 30 deep feet coming off a common manifold at the top, both sharing the same bore hole. It might be a bit trickier to get all that in 2-2 1/2 inch bore hole, but it will completely solve the lubricant issue.


In the IGSHPA manual (CLGS Installation Guide (#21020)), in the section on the loop fields, it looks at various ways of doing loop fields, both trenches and boreholes. There was even a small discussion on putting two loops in the same hole, and I believe that the performance increase was about 3% to 5%.

I'm afraid I don't understand how two loops would remedy the lubrication issue?

-AC

P.S.: This manual is a tad expensive ($45.00), but it is so amazing in the breadth and depth of information regarding Ground Source heating and cooling, that you should seriously consider getting a copy. It can sometimes be found used, sometimes in libraries. But considering the information, it is a miracle. As I recall, the manual does not directly address DX, but most of the principles are the same.
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Old 05-01-15, 10:46 PM   #10
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I will being looking for a cheap used manual. Thanks for the advise.

Yes condensation was a good friend of mines first words when I told him the idea. I now see it as you do, it should not be a issue.

TXV would get complicated for sure. But would be awesome in a future system.

I was thinking a bigger line, being maybe 3/8 or 5/16. But if I went with 2 1/4 I would be getting good enough flow and not loosing as much pressure to get the lubricate up. Plus I think it would help to spread the temperature out a little better.

A random idea I had today, how cool would it be if you could pipe all your hot water users (dishwasher, showers, sink) into a special holding tank that had the DX loop in it. It would be recovering some of the heat from the already heated water. I know that would probably be against code in most places, but here in MS as long as that water makes it back into your septic system its legal. Just an idea.

Back on topic, I like the cap tube being at the average water table, maybe 15 feet down? With the water table being so high I think I will be better off than all the way at the bottom.

Now I need to look into running a DX line into my 2 acre pond (17 feet deep) from my 4 ton central heat pump. I'm going to have to start up a copper factory soon.

I am also trying to get in contact with a DX installer in Memphis, TN. He said he would answer some questions for me.

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