horizontal loop depth question

People and industries have been putting loops in the ground for 50+ years. The time proven consensus is that parallel horizontal with .75" or 1.00 " pipe works the best. Now you want to convince us that you have a better idea??? Sorry, but I have little patience for guys who want me to explain why the sun is going to come up tomorrow.

 

The Climatemaster website, under HVAC Professionals, Residential, Sales & System Sizing Tools, has two programs you can download that are useful for designing a geothermal loop: GeoDesigner Software, and Pressure Drop Calculator. I would suggest you download those programs and run a few different scenarios to see what works best.

I have three 3/4" x 500' vertical loops (~450' of pipe in vertical bore with the remainder in horizontal trench back to the house) for my 3 ton application. I have all loops terminating in my basement so there is no outside header, plus each loop is valved independently so I can flush each loop independently rather than in parallel. You could do the same with a horizontal loop if you have the space.

 

I am not trying to convince anyone of anything, I am just asking questions to try to understand.

Awesome! I will.

What spacing do you have for the 6 basement wall holes?
Do you have any insulation around the horizontal portion of your loops?
Other than just pushing the pipe through the basement wall... did you do anything else?
(I ask, because one site said to use a PVC sleeve to protect the pipe)

 

I have six (6) 2" PVC sleeves spaced ~8" apart (3 supply on bottom, 3 return on top). I installed the PVC sleeves when I poured my ICF basement walls. In the 6" trench from the vertical well bore to the house, I did drop in some leftover 1" thick by 12" high scrap EPS foam (leftover from my basement slab insulation) between the supply and return pipes to serve as a thermal divider between the pipes. I also have sleeve insulation on the the individual pipes in the basement to prevent condensation and dripping. PVC sleeves work well when you are pouring a new wall. If you have an existing block or concrete wall to run the pipes through, you can just core bore the holes a little larger than the pipe you intend to use and fill the gap around the pipes with RTV silicone to seal out water.

 

Milkweed;

I used caleffi geo seals for the basement concrete wall penitrations. So far no leaks.

 

So I am trying to comprehend the Reynolds calculations. I get the concept of needing eddies for turbulence, but the calculations seem to not come out that I recognize as consistent about what I am reading on various sites. I have not considered turbulence in parallel pipes yet which seems to add another variable and will start a new thread to ask that question, so for the sake of this consideration is just a horizontal series loop, yes 2" because that was what I was working on.

Internal diameter of SDR11 2" pipe is 1.917 inches.
The heat pump manufacturer suggested NoBurst at 30% solution. Then proceeds to list that 25 degrees F, 30% NoBurst has 4.7 centipoises (viscosity) and 64.2 lb/ft3 (density).
The calculator I was using online ( http://www.efunda.com/formulae/fluids/calc_reynolds.cfm#calc )
works with lb/in3, so 64.2 lb/ft3 * 0.000578704 ft3/in3 = 0.0371527968 lb/in3.
Using http://irrigation.wsu.edu/Content/Calculators/General/Pipe-Velocity.php
the target is 8 gpm, which is about .89 ft/s velocity.
Reynolds Number = 2890

If I understood correctly, the laminar to transient threshold is ~ 2300, yet all of the geothermal references say the minimum should be 2500, and the turbulent threshold is 4000 which would be the most desirable.

Its my assumption that I am missing something, or using the wrong numbers, relying on bad calculators. Where have I messed up on the calculation?

 

Nevermind, I sent an email to the makers of NoBurst last night, reading their response makes me thing design guide value for the viscosity is incorrect.

 

Again, I don't know any HP manufacturer who is a good system designer.

 

I just wanted to state your not an idiot! The proof is in the pudding and no one will argue with results.

 

Hi Doc/folks. Reading this, and another site that said slinky-style horizontal loop was bad, I am now worried if my installer set my system up properly when it was done 3yrs ago. Does the below sound Ok to you for a 2013 5T Waterfurnace 7 Series with variable speed blower and variable pump? I measured and my trenches ended up being at best about 140ft long each, not 150ft, and I worry they had to cram them a little closer together than expected. Oh, and I live in Maryland, if you want to estimate our weather.

• HORIZONTAL LOOPS: Will consist of 6 trenches, 150 feet in length. Each trench will have 800 feet of ¾ inch diameter coil pipe, buried 5 feet deep. Total pipe 1,600 feet. 2 inch pipe will run from header pit to home. We will flush and fill loop and unit with 80% deionized water and 20% antifreeze.

 

800' of slinky per trench X 6 trenches = 4800' total pipe. 2" header is a good thing.

How has the system been working? 3 yrs is quite a while.

 

Chris, I don't actually know how well it's been working because as fate would have it, the install was completed in April 2013 and we moved away (we now rent the house out) in September 2013. It did seem to work just fine that summer, and I haven't had any complaints. But I was just worried, per articles about the slinky-style piping, that maybe this was putting a strain or something on my unit or pump and would lead to early replacement or something. But again, no problems/complaints yet from tenants.
But, I will move back into it in February, and I'm curious to see for myself how well it works in dead of winter. Anything has to be better than my old oil furnace, especially given all the air sealing and insulation I did as part of the geotherm install.

 

There is no reason a slinky would not work equal to other horizontal designs. The overlapping pipe steals some heat from each other, so you compensate by adding 1/3 more pipe, so the performance is the same. Usually that is the end of the argument.
Whoever states that slinkies do not perform does not monitor them, and does not understand geo.
The loop you describe sounds appropriate in my neck of the woods, but I am not familiar with your region and geology.

 

Slinkies work, I'm just not a fan of them. My coldest EWT comes from one.

I will use them but never as a first resort. Just too ground intensive. Plus they are a pain to put together

On a side note, 800' of 3/4" is not great for headloss.

 

I would argue that if your EWT is too cold, it is not the fault of the slinky per see. We use them as a first resort, and none of our slinkies run below 30F min EWT. And they are super easy to put together onsite, much easier than digging trenches which are 3.5 x as long. Just have to make sure to put them deep, we put them down around 8ft.

Yes, headloss is not the greatest, but at least they used 6 circuits for a 5 ton loop, thus dividing up the flow between 6 and not 5 circuit, thus lowering the low and therefore the pressure drop. An they used 2" header pipe. So they were thinking. We go as far as using 7 circuits for our 5 ton systems, and shortening the length to 600ft each, so we get by with a single pump 32-140 flow center, instead of using a 2 pump flow center.

 

I read the same article a wile back its total hogwash and it's older if i remember right. Besides geo is great even if its undersized remember that a slightly undersized unit will handle your needs efficiency 98% of the year, the other 2% can be suffered through or supplemented with another source. Even if its expencive its only a few days a year. If the system is alread installed i wouldnt lose sleep over it, and definitely wouldnt reinstall the loop field. Not an expert just an enthusiasts .02

 

We have installed slinkies on two schools each with over 20 miles of slinky pipe. Both work just fine. We had to get really good at tying them Those who say slinkies can't work are just flat out wrong.

 

Agreed. The time to put them together is so much less then the additional excavation with a straight horizontal loop field. Once you standardized your approach and you know what you need to do to get the same performance from them, and you confirm that with M & V (monitoring and verification), there is just no better way of putting ground loops in which perform well at a low price for you and your customer.
But I am always open for suggestions if someone can get me a better method, verified by monitoring data.

We tried and monitored every ground loop design we could come up with, and slinkies had the best performance at the lowest cost(labor and material) installed. That does not mean we did not put more pipe in the ground, it was just more effective to add more pipe than to dig longer trenches.

 

I'm not biting

 

Chris, you shall not! You are one of the people here who know what they are doing.
You might have specific reasons in your neck of the woods to not be a fan of slinkies, reasons I yet have to see in my operating area.
It all comes down to verifying our claims with data.