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Discussion Starter · #1 · (Edited)
What ideas do folks have to irrigate ~4200' of 3/4 HDPE buried 10' under ground?

PEX? PVC? Perforated pipe, I have found rolls of 3" black perforated drainage tube at Lowes but am curious if there are other, cheaper alternatives.

It will be fed from a new spigot in my basement next to where the loops + irrigation line enters the foundation wall.

I am installing a geothermal ground-source heat pump with 6-7 600' loops. Due to my soil, or lack thereof in lieu of sand and river rock, I need to irrigate the sand around my horizontal loop lines to get the absolute best conductivity possible.

I want to do this as cheaply as possible since it is really just a method for putting water down near the loops to increase their thermal conductivity. I plan on hooking in the gutters and other rainwater capturing mechanisms but I also want a spigot option in case it is the middle of winter and I need to get water to the area around the horizontal loops.
 

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Naildriver
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You are mentioning apples and oranges in your post. PEX and PVC are solid pressure type pipe, while perforated pipe is for drainage. What are you doing with 4200' of pipe? You say "irrigate", but you can't irrigate with PEX or PVC without emitters. A spigot won't fill up a 3" pipe at 4200' in a month, so see if you can more fully explain what you are doing so we can get on the same track. You're talking over 3/4 of a mile.
 

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Discussion Starter · #3 ·
Hi, Yes I understand the differences.

I do not intend to fully "pressurize" a 3" pipe. I just need to run some water to my geothermal ground loops (4200' total of ground loop) to increase thermal conductivity, and to make my system perform more efficiently/better.

I figured I would need to drill holes into PEX or PVC to create the drainage I need. The perforated would just be buried in its "protective sock", The sock ensures the pipe doesn't get clogged.

I was looking for cheaper alternatives in case there was something I was missing.

Thanks!
 

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I would think that rather than trying to irrigate the whole length, run pex the length a foot down, and then about every 10' have a horizontal pex pipe go down 8' to reach near the loop lines. then pressurize the lines and feed the geo loops with water to transfer heat.

You could try the same diverting as much ground water as possible (gutters, slope land etc) over and into the loop field as a passive means instead of running tap water, with verticle drains down to the loops.

Thats the benefit of having verticle bore holes with grout, over horizontal loops, dirt is a poor conductor.
 

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I’m not understanding your concept here. Are you trying to do a pump and dump loop here?
I think his problem is air pockets and dry dirt conductivity to his current loops, he needs water as a heat transfer and wants to keep the loop field wet.

"Soil Types
Heat storage and transfer is best in heavy soils such as clay or rock. Sandy soils cannot store or transfer much heat so larger loop fields are necessary. Decrease in soil moisture below "12.5% has a devastating impact on the performance of heat pumps" states a 2014 study published in Energies (p. 3), while increase in soil moisture above 25% improves heat transfer. So dry soils are not suitable especially in direct heat exchange systems."

 

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Naildriver
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I, too, don't understand what you are doing. The ground temperature is what determines your geothermal return, and I don't think you can improve on what is already there.
 

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Super confusing at first.

Just treat it as irrigating any land area. DIY. All you need is some garden hoses or equivalent tubing and then set up some rotating sprinkler heads. Lots of time and lots of water.

Water wise. I do wonder if it can actually work, because you said your loops are 10 feet deep in the ground. I don't see how you'd get water in the ground 10 ft down without some massive effort to get it to permeate and creating a mote around the area to then try to flood it. And where is all this water going to come from?

I just trenched several hundred feet of line myself. Severe drought area. Looks like zero moisture in the soil. Any normal amount of rain or garden watering just wets the top.

And then about efficiency of the GeoThermal. The soil should be so compacted and so stable temperature wise, 10 feet down, that I doubt anything would change ...

What does the installer advise?
 

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Discussion Starter · #9 ·
I am installing a geothermal ground-source heat pump with 6-7 600' loops. Due to my soil, or lack thereof in lieu of sand and river rock, I need to irrigate the sand around my horizontal loop lines to get the absolute best conductivity possible.

I want to do this as cheaply as possible since it is really just a method for putting water down near the loops to increase their thermal conductivity. I plan on hooking in the gutters and other rain water capturing mechanism but I also want a spigot option in case it is middle of winter and I need to get water to the area around the horizontal loops.
 

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Discussion Starter · #10 ·
Super confusing at first.

Just treat it as irrigating any land area. DIY. All you need is some garden hoses or equivalent tubing and then set up some rotating sprinkler heads. Lots of time and lots of water.

Water wise. I do wonder if it can actually work, because you said your loops are 10 feet deep in the ground. I don't see how you'd get water in the ground 10 ft down without some massive effort to get it to permeate and creating a mote around the area to then try to flood it. And where is all this water going to come from?

I just trenched several hundred feet of line myself. Severe drought area. Looks like zero moisture in the soil. Any normal amount of rain or garden watering just wets the top.

And then about efficiency of the GeoThermal. The soil should be so compacted and so stable temperature wise, 10 feet down, that I doubt anything would change ...

What does the installer advise?
I am the installer :D

Thanks for the information, I already irrigate the ground above it, as it is my horse pasture, but as you stated, ground water takes forever and a day to get down 10'. Thus I wanted to run some sort of lines a few feet above the actual horizontal loop piping to keep the area wet, or even saturated in the winter for optimal heat transfer.
 

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Discussion Starter · #11 ·
I think his problem is air pockets and dry dirt conductivity to his current loops, he needs water as a heat transfer and wants to keep the loop field wet.

"Soil Types
Heat storage and transfer is best in heavy soils such as clay or rock. Sandy soils cannot store or transfer much heat so larger loop fields are necessary. Decrease in soil moisture below "12.5% has a devastating impact on the performance of heat pumps" states a 2014 study published in Energies (p. 3), while increase in soil moisture above 25% improves heat transfer. So dry soils are not suitable especially in direct heat exchange systems."

The referenced content states, "heat storage and transfer is best in heavy soils such as clay or rock". Exactly what "rock" are they referring too? I have tons of river rock in my ground and have been told that is BAD. What type of rock is "good" for heat transfer?
 

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So here's what I would do or try to do in that scenario, unless the loops are already in.

I would dig as needed, put the loops in with the recommended soil around them, filling over them a little bit; probably try to level and compact that a little bit and once you have a safe layer of material over the pipes. Put a few sprinklers on them. Let that settle. Bring in more soil. Repeat?

Unless that could cause trouble for the tractor/... used for the earth moving.

As far as moving water to do bits of irrigation and having long pipes or hoses. I have previously used coils of 1/2 irrigation tubing to get water where I want it remotely for one or two sprinklers at a time, or vegetable drip lines. Just get the right 1/2 barb to 3/4 garden hose thread male & female. Works a treat. Black tubing. UV treated. Decently strong and manageable. Because the pressure rate 1/2 and bigger tubes are rather rigid and stubborn and pricey ... perhaps less stubborn the hot sun.
 

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Has someone else in the area with similar soil done this already? If so, what did they do? Does it work well enough?

I'm guessing you have not trenched and placed loops yet as you'd want to lay the weeping system at the same time. When you backfill are you just pushing the dirt/rocks back into the hole or can you add media (earth) and the "drip" line at that time? Then, where would you get that much water to fill the drip line? I know you say it will be fed from spigot in basement. Is that municipal water, or your own pump? Would all the electricity or water needed to wet the loop maybe supply enough $$ to have an electric backup or make up heater (likely has one already?).

The cost of adding as much pipe as you may need could be prohibitive, or not, based on the cost of water/electricity. Just wondering.
 

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The referenced content states, "heat storage and transfer is best in heavy soils such as clay or rock". Exactly what "rock" are they referring too? I have tons of river rock in my ground and have been told that is BAD. What type of rock is "good" for heat transfer?
I'm not sure, it may be talking about verticle bore holes with the rock, I know mine are two 300' ers through limestone.
 

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Discussion Starter · #15 ·
Has someone else in the area with similar soil done this already? If so, what did they do? Does it work well enough?
Not to my knowledge, the closest I am aware of is ~80 miles away.

I'm guessing you have not trenched and placed loops yet as you'd want to lay the weeping system at the same time. When you backfill are you just pushing the dirt/rocks back into the hole or can you add media (earth) and the "drip" line at that time?
That is the plan, to bring in a few dump truck loads of something if for nothing more than to just protect the loop from damage while back filling. I was thinking of using sand since it compacts somewhat naturally and it would be very conducive thermally if irrigated. Plan is to dump in about 1' of sand and then do my best to level (without getting into trench); laying the pipe; another 1'-1.5' of sand, and then the "irrigation".

With regards to using sand, I am in the process of reaching out to our local quarries to see what else would be available, maybe clay. According to the USDA soil survey, for my precise location, our soil is made up of:
  • 93.6 % sand
  • 5.0 % clay
  • 1.50 % organic matter
  • 1.4 % silt
* Saturated hydraulic conductivity (Ksat) 141.000 (micrometers per second)

Then, where would you get that much water to fill the drip line?

I know you say it will be fed from spigot in basement. Is that municipal water, or your own pump?
Rain gutters, capturing our snow drift melt, etc... well pump if necessary since we are on our on well/septic. We live rurally in southwest Montana, ~20 miles to the nearest town; of 900 people.

Would all the electricity or water needed to wet the loop maybe supply enough $$ to have an electric backup or make up heater (likely has one already?).

The cost of adding as much pipe as you may need could be prohibitive, or not, based on the cost of water/electricity. Just wondering.
Capturing snow drift melt is the primary source of the water; we have massive 10'+ snow drifts that when they melt in the spring create a literal "lake" on our property and I plan on "funneling" that to a storage container for use later. So electricity will be required sometimes to wet the loop but hopefully, it is minimal.
 

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Discussion Starter · #16 ·
I'm not sure, it may be talking about verticle bore holes with the rock, I know mine are two 300' ers through limestone.
Yep, I think you are correct. Limestone, granite, gypsum, etc... are all excellent according to what I just read.

Too bad, I was hoping I could just lay my loop pipe in the large river rock and sand j/k, we definitely have enough of it!!

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Discussion Starter · #18 ·
With regards to using sand, I am in the process of reaching out to our local quarries to see what else would be available, maybe clay. According to the USDA soil survey, for my precise location, our soil is made up of:
  • 93.6 % sand
  • 5.0 % clay
  • 1.50 % organic matter
  • 1.4 % silt
* Saturated hydraulic conductivity (Ksat) 141.000 (micrometers per second)
I wanted to clarify the percentages, those are for a depth of 48" - 120". If I switch to "All Layers", they change to this:

55.4 % sand
28.5 % silt
16.1 % clay
0.42 % organic matter
 

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Have you dug down at all yet?
Depending in the water table you "May" hit very wet soil. That would be better of course.

It sounds like you are in a cold climate, from what I read the top 10 ft will be subject to weather conditions so be aware of that, I had seen recomendations for 20' deep.

For heating in a very cold climate, you have to deal with above ground weather plus all the cold you will be putting down there.

Have you looked into verticle?
 

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Discussion Starter · #20 · (Edited)
Have you dug down at all yet?
Depending in the water table you "May" hit very wet soil. That would be better of course.

It sounds like you are in a cold climate, from what I read the top 10 ft will be subject to weather conditions so be aware of that, I had seen recomendations for 20' deep.

For heating in a very cold climate, you have to deal with above ground weather plus all the cold you will be putting down there.

Have you looked into verticle?
I have not dug this yet. With that said, I have dug a lot in this area before. Had to dig horse graves, 300' water line from house to barn, buried electrical, irrigation supply line for drip system, etc... We do have moisture down around 10' or so (the color changes to a darker color somewhere around 6-7'). I plan on doing a moisture test at 10' when I start digging. I figure I when I hit 10', I will get a gallon zip lock full of soil, weight it, and then put it in the oven for 8 hours at 100 degrees and weight again.

That should help me understand the moisture level at 10'.

Yes, we are in southwest Montana in the middle of a valley between two mountain ranges. We are in the "open space" (very few trees, except the ones I planted) with a lot of wind. When we get winter snow, it stays around until the next breeze kicks up and blows it all away (thus the enormous drifts in our trees I mentioned in a previous thread). The wind kicks ass at ~31MPH average from November through April. We have a Davis Vantage Pro2 w/18 years of historical data :D

I have looked into vertical loops, it is in the 10's of thousands for my area, not to mention that they are scheduling 3-4 years out right now. My neighbor just had his well put in 2 years ago, for that it as $30k @ 280'.

Horizontal is my only real option. I know it works in northern climates, I mean heck the IGSHPA uses Grand Fork, ND in their Ground Source Heat Pump Residential and Light Commercial Design and Installation Guide example. I purchased the PDF version from IGSHPA and it has been invaluable.

My climate is comparable to Grand Forks, ND, or International Falls, MN, IMO.

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