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Old 05-16-14, 02:39 PM   #1
EcoInPA
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Default Standing Column Well with Horizontal Loop Return

Hi,

I'm brand new to the forum and am very interested in a DIY Geothermal install in central PA. I've read many of the threads here and am currently working my way through the Homemade Manifesto thread (which looks like a great thread), but am in a little bit of a crunch to determine what I'm going to do for my outside loop.

What prompted this project was being forced onto the public water supply and basically abandoning my current standing column well for anything but outdoor use/irrigation/etc. I just can't stomach leaving that much available heat/cooling energy just sitting in the ground. I was thinking of a simple open loop system using the same well for both pump and dump.

However, the current well is only about 150' deep with roughly 100' of standing water which from all the estimates I can find should support a 1 ton SCW install. I'd like to try to extend that to 2 to 2.5 ton by adding some horizontal loop on the water return line by utilizing the trenching I'm going to have to do to install the new water line for the public water system, plus possibly an addtional trench or two. I am able to dig my own trenches using a backhoe I have, but I am however limited in overall space to put in the trenches, hence the reuse of the trench I'm going to have to dig anyway. Overall I can probably manage 200' or so of trench. And in the spring/summer/fall there will be some added bleed off of the water for outside use, that will help regulate the temperature with fresh water as the well replenishes.

Is this feasible to use a horizontal return loop to bring the water temperature somewhat back to ground temperature before return to the well? What would the best pipe for the return be (other than the obvious of copper)?

From a pumping standpoint, I get roughly 8-10 gpm from the existing pump and bladder tank, but am concerned about the added length of pushing the exit water through the new loop. I was thinking I could have the outside loop continuously slop down slightly so once the water was out of the house again, gravity would take over. Should I use a slinky configuration for this or just a straight pipe to be able to keep the downward pitch consistent?

If I can come up with a good inexpensive field design in the next couple weeks I think I can incorporate the two efforts at once for the outside work. Any thoughts/feedback/help would be greatly appreciated.

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Old 05-16-14, 06:31 PM   #2
stevehull
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Is the primary issue heating or cooling? It makes a difference as you can use the existing well (pump and dump), with a water temp of about 45F, as GREAT summer heat pump cooling. Plenty of "cold" BTUs there (for your area).

Winter heating is tougher . . .

Think of about 3 GPM per ton of heating or cooling.


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Old 05-17-14, 02:47 AM   #3
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Thanks for the reply and yes, the 3GPM per ton is roughly what I'm using in my estimates. I figure 8-10 GPM current water production would easily support the 2 to 2.5 ton system I'm thinking about for water flow.

Ideally, I'd like the system to support both heating and cooling. Heating and Cooling seasons here are split almost equally, which is why I'm concerned about the thermal capacity of the well primarily in the winter getting too cold.

In the summer, I'll probably bleed enough water for outdoor use to keep it fairly cold and I may go the route of a standard unit (rather than homemade as I see in the manifesto), so I can incorporate a desuperheater for hot water production. However, in the winter, I'm not ideally situated to be able to dump the water anywhere but directly back into the source well, which I'm afraid would get too cold. I can probably bleed off some allowing warmer aquifier water to replenish, but not what I'd really need to in order to support a 2 or 2.5 ton system. This is where I'm hoping a horizontal return loop would work to help bring the water back up toward ground temp before being re-injected.
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Old 05-17-14, 04:07 PM   #4
stevehull
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Let's see . . . Calculate the number of BTUs you would be dumping into the well in the winter. Figure out the standing volume of water, the temp and assume that the returning water is about 10F higher than the input.

Your well will move the winter "cold" laterally through the adjacent rock/strata. I know that in northern Canada they use geo from wells that are about 38F and get a lot of water. But the output water is dumped elsewhere (not back into the well).

But first, tell us about your house. The key is to tighten it up first, THEN put in a ghp.
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Old 05-18-14, 04:58 AM   #5
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Yeah, that's the crux of my problem. Sized by itself, the well used as both source and return will only support about a 1 ton installation in the winter as I cannot dump the water anywhere but back in the well. And it's currently cost prohibitive for me to get a second return well dug or have my current well dug deeper.

As for the house, it's about 30 years old and I've done all the tightening up on it I can over the last couple years as I've been chained to an oil furnace system. It's already a zoned system, so I've closed off any areas not regularly used. I've had the house checked for air leaks, sealed them all, doubled up on insulation in the attics, etc. etc.

For the gph system I can size it however I can and just zone it appropriately, which is why I'm trying to cost effectively get the max system I can put in place.

I guess to boil my immediate need down to the most important question, it would be. Is it feasible to create a hybrid standing column well system with a horizontal ground loop return to take advantage of both type of systems? Does using water only in the return horizontal loop have an impact on it's thermal conductivity vs. the normal anti-freeze mix in a closed loop system?

Should I just punt and go with what I can get out of a 1 ton system for one area and look into mini-splits for some of the other zones in the future to keep costs spread out?
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Old 05-18-14, 10:02 AM   #6
stevehull
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What about drilling one vertical bore hole well and using it for your return to the water well?

Alternatively, your idea of doing a horizontal loop could work, but do you have sufficient space (and soil free of rock)?

So long as you keep the horizontal loop below frost depth (4 feet in your area?), I don't think a glycol mix is needed. But be aware of where those pipes come out of the ground!

I know of a guy in NH that uses water in his horizontal closed loop field and he has a fractional TACO pump (1/20th HP) that is always on in the winter to prevent freezing. Then a larger pump kicks on when he needs the loop field.


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