I'm planning a new house with Geo in Eastern Canada (10 000 HDD i believe). Current estimates are for a 2 ton unit.

My questions are in regards to the underground loop.

Manufacturer recommends two loops 250' long at least 10' apart. How much would I gain in separating the loops further apart?

The second question is more theory. What if I were to have 1 single trench 500' long and install the loop such that they flow parrallell in an out and back setup? i.e. think 2 lines running out in a pattern following the outline of the property. Would this not have some gain in efficiency?

10 ft apart should be OK. It could not hurt to have even greater separation but there may not be any advantage depending on loop configuration, depth of trench, soil conductivity, etc.

Regarding your 2nd question, parallel configurations are always more efficient. 2-loops in 1-single linear trench would best be configured by placing headers & runouts at the centre point. Respecting the limits of the property line by placing the trench a minimum of 15 ft from the line would be prudent; 25ft would be even better.

SR

The same amount of pipe is generally going to give you the same "efficiency", unless of course they are too close together.  Seperating them farther apart isn't going to offer any real benifits, but they can't be too close together either. The entire purpose of the pipes in to give you a heat sink you can either draw on or send heat to, more pipe is always better then less. If your heat sink is too small, the ground will freeze and your geothermal system will stop functioning until the ground heats up enough to allow it to operate again.  Having a bigger heat sink (ie more pipe) does offer benefits, since a larger heat sink is going to cool off slower during the heating season, but there is definite point with the cost/benefit ratio comes into pay. That is increase cost of installing more pipe is going to give you progressively smaller and smaller returns on your investment. 

If your not using a installer to design you system, I would recommend going overboard on the amount of pipe your installing.  If they are recommending 250 ft a ton, install at least 300 ft a ton just to be on the safe side.

       

10 feet between vertical loops is percieved as adequate to keep one from interfering with the other.
If the second part of your question is regarding horizontal loops keep in mind that higher and more stable deep earth temps allow vertical loops to be much closer. Horizontals are much more impacted by surface temperatures. Therefore to get enough heat out of the ground in January you may need 2 to 3 times the footprint (loops).
In my area depending on soil we would use 300 foot u tubes in 150' wells/ton in verticals or 6-800' slikies/ton in horizontals.
Good luck,
Joe

Sorry I did not specify but my two questions related to horizontal loops. Maybe I'm misunderstanding the manufacturers recommendations. Here they are Horizontal loop required 500 linear feet per ton, number of horizontal trenches 250' long per ton; 3, minimum spacing between horizontal loop 10'. as far as verticals go they recommend 300' u tube (150' well depth).


So I guess what I'm understanding is that for a 2 ton system I would be better off running two parrallell lines atleast 500'

The amount of pipe needed is determined by the heat load of the house, not the heat pump size.

Depth of trench and soil type also are factors in the loop.

Also are you looking at a two pipe or four pipe trench?

But if the heat load states a 25000 BTU heat load is that not a 2 ton geo unit?

Yes heat load determines heat pumpsize. Heat load, soil conductivity, geographical location (heating or cooling dominated), lot size, depth loops are buried and design parameters (min and max ew temps) all factor in loop design.
What is the diameter of you loop piping? As Dewayne asked, is it possible you are talking about the length of 2, 4 or 6 pipe trenches?
Joe

Yes I agree that soil conditions will affect the size of the horizontal loop but it will still be a 2 ton loop, will it not?

I guess I'm having a hard explaining my concept as in my mind it shouldn't matter what the soil conditions are on this issue.

More explanation.

Standard manufacturer recommendations for horizontal loop sizing for a 2 ton unit

2   250' long  4'-6' deep  4' wide trenches with a single U tube, so 500' of pipe per trench

My thought is that if I have 2  250' long trenches if I join the far end of the trenches I would have 1  500' long trench.

If I then run 2 tubes in parallel in that  500' long trench would that give me better loop efficiency?

The problem with a 1,000' run of pipe (500 out and back) is the excessive head loss resulting from the friction of that much pipe thus requiring too large of pump(s). You need to model the length/diameter with your EWT/antifreeze solution in the loop design software to determine what will work.

-Adam

Loops are not rated by tonnage, though there are rules of thumb in most areas of loop/ton affected by the things mentioned before.
While you restated your design, you still failed to mention pipe diameter, soil etc which all have design impact. I'm not picking on you just unable to help without answers.
j

I guess I don't see how pipe diameter or soil conditions will matter in this case, as my question in my mind is comparative.

If everything is the same which loop field will be more efficient? The one with 2 250' trenches each with a U tube or a 500' u-trench with 2 pipes running in parallel

Do I understand that the choices are two 250' trenches with 500' of pipe in each trench so that the flow is split down each 500' path or one 500' trench with 1000' of pipe and the flow is not split?

The second choice is poor loop design as it will need a bigger circulating pump to force the fluid down a longer path.

The amount of heat exchanged might be the same. I don't think one will be any more efficient than the other.

Splitting flow down multiple paths is part of good loop design. If I were doing this, I would do two 250' trenches.

I guess I'll have to make a drawing, sorry in my mind this was a simple question.

The black boxes are the trenches 250' long, 4' wide. The red lines are the pipes with "arrows" indicating flow direction.

The drawings are helpful. 

I don't see there being much difference in efficiency.  You still have the same amount of pipe exchanging heat with the same amount of ground.  

There is less chance of  interference between the supply and return lines in the second drawing,  it is unclear if this would make any measurable impact.

I agree with Dewayne, however, the biggest possible difference between these 2-configurations might be if one were connected in series and the other in parallel.

SR

Gotcha,
I'm with Dewayne, footprint is footprint. So while you could make it harder or easier to pump, you will have little impact on heat transfer if all else is the same.
j

I guess my concern was with the normal pipe layout and the fact that the out and return pipes were "close" to each other. Being that the pipes were 4' apart I wasn't sure if that was enough distance so as to cause efficiency loss.

If proximity (in your drawing) caused efficiency loss, both systems would be impacted equally.
Putting loops farther apart improves efficiency, but in geo all things are diminishing returns. If you were going to have an operator spend extra time seperating your loops, you may not appreciate a significant ROI for the expense.
J

If you decide to go ahead with your plan to tie the two trenches together at the far end there is one improvement you can make. Reverse the flow in one of the loops. This will give you the greatest temperature differential between the pipe and the earth at all times considering there may be some influence between pipes in a 4-foot wide ditch.

Dick