Pipe spacing from Vertical loop

Have a 500' vertical loop located about 100' from home. How far apart should the 'supply' and 'return' pipes be? Two foot (typical trench width)? Or dig two trenches further apart (40' is possible in this application).

While it would seem obvious to 'spread' the pipes farther apart to increase ground area involved, at some point there is a practical limit ... after all, the 2 pipes that make the vertical loop are very close together.

Any thoughts?

 

2 feet of seperation is plenty in same trench. 2 feet is a typical commmercial spec.
Eric

 

I've read that vertical loops should be at least 50 feet apart. What do they recommend for the spacing of horizontal loops?

 

Your are referring to a minimum requirement for spacing on a open loop.
Spacing on horizontal loops are generally 10-15 apart, same for vertical loops.

 

Spacing

Spacing of horizontal trenching is different than spacing of the piping. Both are products of design and vary by site and on contractor preferences. Pipe spacing can be 1'. Trench spacing can be 10' - or a giant swimming pool type excavation. Once again - design. Don't just guess.

Spacing of headers is not as above - usually just trench width. That is your original question I believe.

Separation of supply and discharge wells is a matter of the hydroconductivity in the soils, but is usually set at as great a distance and up/down gradient as practical. Greater than 100' is a good rule of thumb.

Spacing of vertical boreholes is site specific as well - but usually in the 10-20' range depending on availability of land.

 

Your are referring to a minimum requirement for spacing on a open loop.

Thinking of closed loops actually.

Spacing of vertical boreholes is site specific as well - but usually in the 10-20' range depending on availability of land.

Have read several places of spacing 50' if land is available - but trying to find accurate information on the internet is kind of like dumpster-diving.

Spacing on horizontal loops are generally 10-15 apart, same for vertical loops

Thanks for the info. There seems to be many configurations available.

Some designs do not make sense to me - for example, some people here have put horizontal loops only 24" deep but frost can reach 4' in winter (Upstate NY). How could such a system have good efficiency? Have heard people say if you go too deep you get permafrost problems ... well, this isn't Alaska where you have it anyway. Six foot seems a better target.

Ultimately the goal would seem to be to get as much warmth as possible (given excavation/boring cost limits). This seems to be the performance 'excitement' about open loops - continuous 50 F water is much better than 30 F.

Spacing of headers is not as above - usually just trench width. That is your original question I believe

Yes. Guess I was thinking there might be advantage to spreading the header out for more ground area. Since I have 100' from borehole to house, wondered if it would help to take advantage of this distance.

Since system EWT dips to 32 F in January, LWT is ~26 F - it seemed it might be advantageous to 'distance' the colder line.

But it is intriguing that vertical loops works so well with the 2 pipes side-by-side --- it isn't the way normal heat-exchangers are designed. I also hear pipe/ton (loop length) figures for horizontal loops 2 to 4 times higher than for vertical loops ... but perhaps this is internet nonsense.

 

Interference

If there was significant interference between header lines, one could think like this.

The cold line goes out and steals heat from the warm line. But then the cold line now goes out warmer and thus the warm line comes back warmer.

 

Being a driller, I can assure you that 50' spacing on vertical loops is not a common practice.

The most I have seen or heard of is 25' spacing.

 

This is not internet nonsense, but the reality of loop design.

 

I would agree with your conclusion here.

 

It is good to know this is accurate.

Why do horizontal loops need to be so much longer than vertical? It is because of ground tempurature?

 

Here is a pic of our 5 trenches, 10' apart, 7-8' deep, 200' long, 1' pipe. Supports 4 ton GSHP in RI.

ChrisJ

 

Pipe temperature

Soil temperature and fluctuation is the main difference.

 

Also being a driller I personally have never read or heard of any loop spacing being anything more than 20' in spacing. I am sure somebody,somewhere has done it though.
That may be Internet non-sense.[/QUOTE]

Never underestimate the ability of those not familiar with geo to add un necassary cost to any given project.
Eric

 

I remember seeing pictures graphically showing the effects of heat absorption to surrounding area ... and with it the 50' figure. It appeared to be a government/scientific report, which might explain the large discrepancy
(Government = measure with micrometer, mark with chalk, cut with axe)

[Note: I hope my negative references to the internet was not offensive - afterall this forum is part of the internet. Ten years ago, getting technical info wasn't so hard. Now there is so much selling, blogging, and exaggerated claims that accurate info is obscured]

Thanks. The trench width looks like 24-30". So each 1" pipe is 400' and loops back within each trench. The soil looks 'clayish'. With this system, you've got 500' pipe per ton.

Thank you -- Yes, that really gets to the heart of my original question.

In order to place the header more than 2' apart would require a 2nd trench (~$300). If done, header length would increase about 50' (200' -> 250'). With increased separation and the addition soil contact, would one ever realistically see their $300 back?

This is a 3 - 3 1/2 ton system with 500' vertical bore in clay and shale. Am told the requirement for vertical loops is 150' / ton (300' pipe). If horizontal loops require twice this length, then 50' added length would only increase capacity 2%. Don't know how to factor the benefit of the additional ground area, but there would be some as well.

I realize this is eggheading a bit, but it seems the most important factor in the success of geothermal 'extraction' is the capacity of the ground loops. Unfortunately this is also the most expensive part of these systems.

 

I would not dig a second trench to separate the supply and return pipes.

 

"Thanks. The trench width looks like 24-30". So each 1" pipe is 400' and loops back within each trench. The soil looks 'clayish'. With this system, you've got 500' pipe per ton."

The trenches were almost 4' wide, pipes like 3' apart, excavator said it was like digging in concrete. Soil is more on the sandy side, gravel like.

One header trench, picture is taken from foundation looking out towards loop field.

PVC pipe is a drip loop. Probably over kill, but in drought could be helpful.

ChrisJ

 

PVC pipe is a drip loop. Probably over kill, but in drought could be helpful

Is this to 'inject' water to keep the field wet and thus more efficient heat transfer?

 

Yes, but I have yet to use it, my EWT's have been fine for 2 1/2 years.

My looper I think had little to no horizontal loop experience. He had me pay for pvc and laid it for nothing extra.

I was told the drip loops are used more often in DX systems.

ChrisJ