Hi Everyone, I have two different geothermal companies telling me two different things. I need 8 tons of cooling power and am looking at waterfurance NDW100. Both geothermal companies acknowledge that I need 200 foot holes per ton. The drilling company wants to do 267 foot holes and do just 6 of them. I have geothermal company A telling me thats fine and you will still get 8-tons. I have another geothermal company B telling me that anything over 200 feet you get a diminishing return and you won't get 8-tons. You may be able to get 7 tons of out of it and upgrade one ton, but you really need 8-200 foot holes. The spacing would be 10 feet for both, 6 holes, or 8 holes. The type of soil is silt / clay saturated, from pretty much 100 feet all the way down to 300 feet. My question, which geothermal company, is right? Would the loop length really get demising returns the farther you go down. Or does tonage only depend on the length of the pipe. If we were to do one 1600 foot hole and have silt clay saturated all the way down, would that give 8 tons, or just a few tons? Thanks for your help

I see no reason why it should not work either way. You worry about pressure drop a bit, but not at 400 vs 530 ft of pipe per bore hole.

We have done 150 ft of bore hole per ton wit 3/4" pipe, now we do 400 ft of bore hole with 1.25" pipe for every 3 ton capacity. Our driller has good equipment and does not like to move the rig as much. We measure the performance of the systems with the WEL, and cannot find a performance difference. Nor does loop design software show any difference in performance.

1600 ft would be difficult because of pressure. You would have 1600ft of water column bursting the SDR pipe down there, unless you fill the pipe together with the grouting, applying outside pressure on the pipe. You could use some higher SDR number to help with the pressure, and you would need to deal with the department of mining, becoming a mining operation below 500 ft. But in terms of heat exchange, it would work as good as 8 x 200ft, given that you use the same SDR number pipe. Probably even a bit better, since you would pick up some real geothermal energy down there.

The company that told you that you will get diminishing return on deeper loops does not have a true and full understanding of the construction of the heat exchanger.

Any loop software will bear out what has been said above, it is about feet of pipe total, not how and where.

That being said, I would not penalise the company/salesman that does not truly understand the partner trades scope of work. Obsessing about the loop field is time spent unwisely. Your time would be better spent verifying the manual J loads and the balance points for each system, and the design temps that were used to generate your design.

The loops only perform as well or as poorly as the design will allow.

I think I have "nice equipment" but do not mind moving it. We typically do 3/4x200 for each ton of load, or 1x300 for each 1.5 ton of load, or 1.25x400 for 2 tons of load, vertically. or 1x600 for each ton of load if we do a trench system at 4 feet deep.

Hope this helps
Eric

Posted By brandonm on 18 Dec 2011 01:41 AM
Would the loop length really get demising returns the farther you go down?

No.    As the others have said,  it is all about feet of pipe in the ground.  

You get increased cross talk and higher pumping losses with deeper holes (edit: holding other things constant of course). On the other hand, you get more pipe below the water level, which is much more important.

Try to get the 10' spacing bumped up to 15-20' and make sure they don't put all the holes in a line, each one downstream (as the groundwater flows) of others.

Posted By jonr on 18 Dec 2011 09:15 AM
  higher pumping losses with deeper holes. 

Usually deeper holes use larger diameter pipe.

Eight tons? What are you cooling? I also agree with Jonr about increasing the spacing to 15'.


Bergy

Posted By jonr on 18 Dec 2011 09:15 AM

Try to get the 10' spacing bumped up to 15-20' and make sure they don't put all the holes in a line, each one downstream (as the groundwater flows) of others.

Are you seriously proposing that a groundwater flow test is to be done and that the loops be drilled perpendicular to flow????

Talk about a diminishing return.

Have you been reading the Grundfos propaganda or brushing up on the Franklin vfd?  The industry term "cross talk" is commonly applied to electric as it relates to vfd's not to thermal dynamics in a residential application.

Eric
P.S. I have missed you jonr

Are you seriously proposing that a groundwater flow test is to be done and that the loops be drilled perpendicular to flow????

Duh, of course not. Just .. no, you figure it out, I think you need some practice reading, especially on this subject. And yes, putting holes downstream of each other has a large and measurable effect. And I'm not surprised that you don't understand the generic term "crosstalk" or the negative effects of heat transfer between the supply and return pipes.

Larger or multiple pipes are beneficial in that they decrease pumping losses and increase surface area/conduction. And despite what some people think, the grout used makes a significant difference.

Posted By jonr on 18 Dec 2011 11:33 AM

Are you seriously proposing that a groundwater flow test is to be done and that the loops be drilled perpendicular to flow????

Duh, of course not. Just .. no, you figure it out, I think you need some practice reading, especially on this subject. And yes, putting holes downstream of each other has a large and measurable effect. And I'm not surprised that you don't understand the generic term "crosstalk" or the negative effects of heat transfer between the supply and return pipes.

Larger or multiple pipes are beneficial in that they decrease pumping losses and increase surface area/conduction. And despite what some people think, the grout used makes a significant difference.

Thank you.
Eric