I'm wondering if you guys think I did the right thing. I'm in the process of getting a 4-ton WF geo installed and the "diggers" came by today to trench the loops. Their plan was to dig 4-250 foot trenches, one for each ton. When they showed up, they had a 5' trencher. I asked them how they run the loops and they said they run a 5' foot trench, lay the 500' pipe in the trench and run the last 250' back at 3' foot deep. This didn't sit well with me. I expected them bury the lines 6' below grade. I told them that I want wells instead of trenches, so they're coming back next week to dig wells instead. They said they'll run 4 wells at 150 feet deep each. It'll cost me at least 1000 buck more for the wells, but their trench method didn't sound right to me. This is all they do, and they do it for many of the HVAC companies around here. Is this the norm? I'm in Southern Illinois, btw.

Others may contradict me but IMO, about 250' per ton drilled is pretty standard.

Generally 5' is the depth we would shoot for in mid MI, so trench guys would go 6' and 4' for an average of 5.
In Southern Illinois, 4' average depth may be fine. there is very little info (i.e. load, length of loop etc.) for me to determine if it works for your job.
Why not ask for references of other people they have trenched for and see how it has performed for them.
Vertical loops are shorter so performance is generally the same as horizontal.
Volunteering to spend $1000/ton more without research seems like a bad idea to me.
j

Posted By MikeSolar on 19 Jun 2012 07:16 AM
Others may contradict me but IMO, about 250' per ton drilled is pretty standard.

If there is a drilling standard,  it is closer to 150' of drilling than 250.

Drilling is our business,  we calculate the drilling needed on every job based on the Manual J, the soil conductivity,the job location, the bin hours.

I agree with Joe, you need more info before making a decision.

Spending more money might not give you better loop performance.

Posted By MikeSolar on 19 Jun 2012 07:16 AM
Others may contradict me but IMO, about 250' per ton drilled is pretty standard.

Yeah, as Dewayne said 150'/ton would be closer to "standard" but there are lots of variables.

I dont beleive they calculate anything. He simply stated they do 250 foot trenches horizontal and 150 foot deep wells. The problem is that the hvac company contracts the service out. They seem ignorant of the whole process. A week ago I asked them how the trenches will be dug and the installer said he really didnt know, that the pipes were always sitting there waiting for him to hook everything up. Oh, the total cost is about 1000 more total, not per ton. 4 trenches would have cost me around 3000, and 4 wells will cost me around 3800. I appreciate all of your responses. Unfortunately I really dont know how I can research this further.

Posted By jeepster on 19 Jun 2012 09:54 AM
Unfortunately I really dont know how I can research this further.

Because of all the variables it will be hard to research. On the other hand I think Joe offered a solid research strategy. Ask for some references and give them a call.

Loops should be sized for the annual load on them, heat pumps for the peak load (or the 97% percentile of that). Loop performance drops quickly and seasonal swing increases quickly when you get down to only 4 ft or less.

Thus 500' horizontal pipe/ton at 4ft average sounds short, unless they are laying in a pond, no matter what your location is. With 150ft vertical you are likely more on target. The problem is that most of the guys do not have any feedback on how the loops perform over the season. We are down to 130ft/ton vertical with 1.25" pipe.

System pressure drop and flow requirements determine circulation pump size, not the number of circuits. We have a 6 ton heatpump with a 10 circuit loopfield on a single 26-99.
http://welserver.com/WEL0267/

We are doing an average of vertical 180'x1" per ton in silts,sands. We have done 150' x1" per ton spec'd out by a Diy'er, and that was in sandy wet silts the whole bore. We have never had an issue with Any of our loop fields. I know local horizontal loopers in our area are doing 600-800 ft/ton depending on the ground soils they encounter while digging the field.

I have an old igshpa report somewhere that basically suggest 600'/ton slinkies work about everywhere (don't recall 5 or 6' depth). I think our collective sophistication is a little higher now, but I also believe the safe zone is a little wider than many installers realize.
Some doggedly oversize ignorance or percieved performance enhancement vs docs strategy to avoid lengthy compaction man hours.

In the Dallas area:

Down deep undisturbed soil temperature is approximately 68 - 70°F.

Soil is generally a sandy loam clay.

General practice for vertical loops, without paying much attention to soil geology, is 300 ft borehole depth per ton, spaced 20 feet apart, with 1" pipe, with standard grout.  At 10 feet per drilling rod extension, it takes a while to drill multiple boreholes.

Key challenges are two fold: (1) getting enough short term (during the season) loop capacity to handle intense ambient heat conditions during any part of the Summer season; and (2) getting further enough loop capacity to avoid long term (multi-year) borehole field heating.

Designing the vertical loop for adequate heating is a 'no brainer' here.  Don't even need to include aux heat strips.

Designing the vertical loop for adequate cooling, if departing from the above general practice comments, is tricky and takes a good amount of loop design expertise.

Best regards,

Bill

I'm going to guess that horizontal loops suffer far less from multi-year heating - there is somewhere for the heat to go.

In theory, yes.

In practice, multi-year heating is far less of concern down here in the deep south than immediate, this-season, right-effing-now problems if a drought and a heat wave combine to heavily load a horizontal loop that dries out from lack of rain.

Wet sand is an excellent conductor of heat...dry sand is an abysmal conductor of heat. Unfortunately, we don't get to choose which of those two soil conditions obtain during any given summer.

Translation - no horizontal loops for me here in sunny Florida, thank you very much.

Burying a soaker hose with the loop is impractical? Given that the loop area is reasonably sealed, it should take little water to keep it damp.

Of course the presence of ground water effects loops - even in sunny Florida there are places where it's consistently a few feet down.

How is sandy soil "reasonably sealed?

The surficial aquifer is often within a few feet of the surface, and as long as that is true, all will be well. Every so often the surficail aquifer falls...in fact we are in the midst of a multi-year drought so severe that many lakes in the southern pert of my county are completely dried up, leaving former waterfront homeowners with huge dry backyards. Anyone with a horizontal loop in those conditions would be outta luck.

Posted By jonr on 23 Jun 2012 12:36 PM
Burying a soaker hose with the loop is impractical? Given that the loop area is reasonably sealed, it should take little water to keep it damp.

Of course the presence of ground water effects loops - even in sunny Florida there are places where it's consistently a few feet down.

Soaker hoses are a product of the DX design that is less effective without perfect compaction. They were never intended as a btu booster.

Employing them as such is to design a hybrid open loop as the benefit they offer is in the btu's of the water poured on your loops. Once you stop dumping water on your loops, the benefit is soon gone.

Damp soil speeds delivery of btus from distances past what you will moisten with a few gallons of water poured on the loops. If someone has a notion that a soaker hose can cure dry conditions that weren't designed for, they are sorely mistaken. 

Pumping costs or worse yet municipal water bills for tens of thousands of gallons required to combat a drought would quickly offset any savings for purchasing a less expensive horizontal field.

"Burying a soker hose with the loops impractical?" How bout we just design the loops correctly for the region and the conditions and not spend money on a hose that (I presume most haven't seen them) may or may not deliver water reliably down the road.

j

Supporting data? How long does it take for a cubic yard of wet sand buried at 5 feet take to turn into dry sand?

I don't think it matters how long it will take. 

How is the homeowner going to  know when to add water?

I use soaker hoses in my garden and I have to replace them every couple of years since they get plugged up.

The idea sounds good...I just don't see it working out very well in the long run.

I generally don't suggest something unless I already know that it will work.

Do you know anyone that has successfully employed soaker hoses.

There are numerous references to using them to address dry soil but I haven't seen results data.

Go Vertical!
That should be my new slogan!