Pros and Cons of a ground loop vs. open loop well injection?

[Geo NR Gee]

If you had a choice of a closed ground loop or a open system with a well and return injection system, what would the pro and cons be?

I see a closed loop as a cleaner system not as subject to contamination, while the open loop would be bringing up the minerals in the water thus shortinging the life of the heat exchangers.

A ground loop system would require a larger area (which I am limited) to be dug up to support the loop field.

I am sure there is a minimum amount of gph needed to support a open loop system?

I was looking at the DIY well drilling and the author used this open loop system by digging a well and then three more injection wells. His diagram is attached.

[ThomSjay]

Originally Posted by braebyrn

I see a closed loop as a cleaner system not as subject to contamination, while the open loop would be bringing up the minerals in the water thus shortinging the life of the heat exchangers.

Reading this I pondered about how to overcome this. How about a 'settling tank' that is fed on one end, and drawn from on the other end? Or is the mineral too small to settle out?

TomS

[Geo NR Gee]

Toms,
I'm not sure myself. I read where at least plate exchangers can clog. But I like your idea.

[Geo NR Gee]

Ok, just received word that we can use the portable well drilling machine. Its small and narrow and able to drill up to 5" holes. I was given a demonstration today and it went down 10' in a matter of 2 minutes.

It didn't hit any hard pan or rocks, so it really wasn't much of a demo, but at least we could see it in action. Its a hydro-drill and here is the link to the model 2001. HD2001 - Deep Rock Manufacturing My friend bought the setup for $1250.

My biggest concern is if we are going to put in a ground loop system, and went down 100' per borehole, and had a 4-5" bore opening, how many loops in each borehole could you have or that would be efficient?

Looks like some of the info is here... http://welldrillingschool.com/course...geothermal.pdf

If my heating requires a 3 ton unit, my idea is to bore one hole. Set it up like AC did and pump water down and up to get an idea of the exchange temperatures. Then thats where I need help in figuring out how to decifer the info. I can't remember how long you need to wait until the temperature is stable? There needs to be an index on AC's heat pump manifesto.

[AC_Hacker]

Originally Posted by braebyrn

My biggest concern is if we are going to put in a ground loop system, and went down 100' per borehole, and had a 4-5" bore opening, how many loops in each borehole could you have or that would be efficient?

One loop per hole. If you put in another loop in the same hole, the extra heat would be almost too small to measure. Better to dig another hole.

Originally Posted by braebyrn

If my heating requires a 3 ton unit, my idea is to bore one hole. Set it up like AC did and pump water down and up to get an idea of the exchange temperatures. Then thats where I need help in figuring out how to decifer the info. I can't remember how long you need to wait until the temperature is stable? There needs to be an index on AC's heat pump manifesto.

You can search for "heat transfer".

You could figure, since we are in just about the same area, and the same type of soil, that one Ton would be about 200 feet.

As I found out, 16 holes that are 12.5 feet deep are not as good as one hole that is 200 feet deep... you'll need more holes, the shallower they are.

This would be a good time for you guys to decide how to do "U-turns".

You saw how I did it with my fusion paddle I made. You can also rent that plastic fusion stuff... I't not too much. I think the preferred way to do it is with socket-welded right angles.

Be sure and take lots of pictures!

-AC_Hacker

[S-F]

You are one lucky duck to know someone with a well drilling rig. The only problem with going down 100' is you may hit some serious rock and need a down the hole hammer.

Man! If I had a friend with a well drilling rig I'd scrap my perfectly good Buderus boiler and hack an ASPH to be geothermal.

[Geo NR Gee]

Originally Posted by S-F

You are one lucky duck to know someone with a well drilling rig. The only problem with going down 100' is you may hit some serious rock and need a down the hole hammer.

Man! If I had a friend with a well drilling rig I'd scrap my perfectly good Buderus boiler and hack an ASPH to be geothermal.

It actually came with a rock drill bit too! Hopefully we won't have to use it, but its there anyway.

[Geo NR Gee]

AC, so if we were able to go 200 feet and put in three bores is that usually enough, or did I read that it is better to have more? Thank you for the assistance too.

[AC_Hacker]

Originally Posted by braebyrn

AC, so if we were able to go 200 feet and put in three bores is that usually enough, or did I read that it is better to have more? Thank you for the assistance too.

If you are going for 3 Tons, then 3 boreholes of 200 feet depth each would be the minimum amount to do the job.

The reason that folks don't usually go well beyond that is because of the expense when you are hiring it done, or the work involved when you do it yourself.

As you use the geothermal heat during the heating season, the ground temperature will decline somewhat as the winter progresses, so your efficiency will also decline somewhat.

The more feet of borehole, the less the decline, so the more efficiency.

I sincerely hope you are able to drill a full 200 feet, that would be really great.

But you should prepare yourself for the possibility that you might not be able to go that far down. You ought to plan a layout for three holes that are 200 feet each, and also for 6+ holes that are 100 feet deep, and for 12++ holes that are 50 feet deep, etc.

Your holes should be about 15 feet apart. I did mine on a staggered plan so I could pack more together, not such a good idea, as it turned out... it made trenching much more difficult. Stay with a grid layout.

And when you get you hole drilled, you should have your HDPE pipe, welded and tested, ready to go, because your borehole will not be so deep, the longer you wait. They start filling themselves in as soon as you stop drilling.

-AC_Hacker

[Geo NR Gee]

Then would there be any reason to use a metal or pvc casing? Direct contact with the soil and filler material seems like it would have a better heat transfer? The mud pump from the drilling equipment has the ability to mix a slurry [ bentonite] and pump it in the bore to fill the gaps.