All that pipe in one trench wil thermally act like one circuit.  If head loss is your issue, why not upsize your diameter of pipe used?  I recently got the climatemaster loop design software and do not care for it.  inho it makes to many rule of thumb general assumptions to be effective, but it was free.

I agree that all the pipes in one trench will act like one circuit but since the software (can't vouch for the accuracy) says I need just one 3/4" circuit my thought was that adding four more pipes won't hurt anything and will decrease pressure drop and give me some redundancy. I'm using 3/4" pipe because it's hard to find larger sizes in 800' lengths.

What software do you use for your loop calculations?

And thanks for the reply!

Can you do several shorter trenches spaced appropriately (per software guidelines) apart? We have 5 total tons, 3 trenches 250' long with a "4 pipe" layout in each trench. Total feet of 3/4" HDPE is 3000' (1000' in each trench.)  There is approximately 12' between trenches (acceptable for our location, so I was told.)

How about 3 trenches @ 300ft each = 900ft trench.

I'm running the trench around a septic field so one long trench is my best option for not getting into that. I also want to use a trencher rather than a backhoe so keep down the mess. My thoughts are to just oversize the ground loop and keep the pressure drop and flow rate where they need to be and I should be OK. The cost for the extra pipe is $800 so that is not prohibitive to install. Is this the wrong approach to take?

How deep can you go with a trencher? My slinkies that were buried last week are 8-10 feet deep. I am in west Tennessee. The trenches were dug with a track hoe using a 42 inch bucket.

The trencher will dig a 6' deep trench. I have considered the slinky method but I'm not really comfortable installing them vertical. It's simple to dig a long ditch with a trencher and put pipes in it. Configuring the slinkies and the cost of a backhoe would be OK if you have limited space. Hope your system works well for you!

I have 3.5 ton total in N. Ark. with 6/400x3/4" loops. They are in three trenches. Two about 10' to 15' apart. The third runs a second system on the other side of the yard. All loops go out at 8' and come back at 6', 3' apart in the trench. I don't remember the head on the systems but I used a single (Taco) pump and it's been working for 15 yrs. I had to turn on the 10Kw strips last week when it was in the single digits but the water temps have recovered since and I hope that I don't have to use it again.

So if I understand correctly, you have a 3.5 ton system on two 400' trenches for a total of 1600' of pipe?

No. It's six, four hundred foot loops, for a total of 2400 feet in the ground. Four loops for a 2.5 ton and two, four hundred foot loops for a one ton console unit that heats and cools the garage.

Other things being equal, 6 (or even 4) pipes in 800' of trench will outperform two pipes in 835' of trench - the pipe surface area more than makes up for the 35' loss. But I'd space the pipes a little bit - say 3 on the bottom and 3 a foot or two up. This is closer to a standard Geolink layout, which is two pipes in a narrow trench spaced 2' apart vertically.

Thanks for the clarification.

Does anyone else have an opinion as to how three 1600' loops (six 800' pipes) in the same ditch will work as a ground loop for a 3.5 ton system?

Unless you abandon your trencher and switch to a track hoe mho is that you are on a very slippery slope.  You can not put a 3.5 ton loop in a 1 ton trench, that has a max depth of 5'.  You stated 6' but I would plan on having to overcome at least 1 foot of trench "sluff" depending on soil type.  Design,design,design, then exicute.

You could conservatively consider three 3/4" tubes as a single 1.25" tube and then, with one "tube" at 6' and one "tube" at 4', use Geolink and its standard options. It came up with 775' of narrow trench, but absolutely do not use this number - you need your climate data, soil type, etc to make it accurate.

Is Geolink available to be downloaded?

Update - I found it.

How close will the trench by to the septic system? I'm not sure how much spacing is needed. I wouldn't reinvent the wheel on trench configuration unless you are prepared to do it over again. I like to do things one time the right way and be done with it.

I'm not sure if this is allowed or not, but what about putting your geothermal loops under your septic drain field?  An advantage I see with this is that the septic field lines would keep the ground moist around your geothermal loops.  Plus, in the winter you would be getting some heat recovery from the warm water that you drain from your showers, tubs, sinks, and washing machine.

arkie, that's an interesting idea that has been discussed on here before. I think the concern was that the cold temps from the loops could interfere with the desirable microbial activity on the septic effluent. Around here the county health department has very strict requirements for septic systems. Best bet would be to discuss it with them.

BTW I've often thought that a coil in the septic tank would be a neat way to run a water to water HP strictly as a water heater. It would be like the air source HP water heaters except that essentially you would recover your heat over and over again from the waste water. It would cool the septic tank a little but probably not enough to affect it. It would be interesting to run the numbers to see how much the temp in the tank would actually be affected.

The "poop loop" has been talked about alot, the stumbling block seems to be that no one in te effluent field wants to go out on a limb and endorse or talk about what the minimum temp in the tank can be, or should be. The other issue is what to do if you inadvertantly freeze the tank. We need a poop thermometor and data monitoring to crack "lol" the mystery.