There's something I'm wondering, If poor soil requires more pipe surface areas in contact with the ground to get the same heat transfer as a loop with less pipe area in better soil. Than if you were to dig your trenches and back fill them with the ideal soil, would this allow you to install smaller loops than you would normally require than just reusing the original soil you removed? Or would the surrounding ground in contact with the better soil have the same heat/cold transfer problems and when the system is in use you could wind up with better soil frozen into a block of ice from extracted heat? 

If so, Im wondering the cost of delievering the better soil would eat up any cost savings you would gain from being able to install shorter ground loops.

   

As the attached table shows,  the moisture content of the soil plays a bigger factor than the type of soil.

Dry sand/gravel has a thermal conductivity of .35 Btu/(h*ft*°F) the lowest rating on the table.  A 5 ton unit would need 6520' of 1" slinky pipe in 815' of trench in this soil.


Saturated sand/gravel has a thermal conductivity of 1.44 Btu/(h*ft*°F) the highest soil rating in the table.   A 5 ton unit would need 2400' of pipe in 300' of trench in this soil.

If you hauled out the dry sand and  brought in dry clay you only move from .35 TC to .50 TC.  Not worth the effort.

The best thing would be to keep some moisture in the ground.  The more the better.

Geodean -

If keeping the ground moist is the best thing you can do then how do you suggest we do this? I assume running the garden hose on it all year would waste more $$ in water than it would save you in electricity.

So should a geo homeowner drain run off water from the house onto the loop field? (i.e. drain the gutters onto the loop field?) Does putting trees in for shading work or do they drain more water from the roots than they keep in by shading it?

Plus if you have vertical loops how do you know if the water is getting 300 feet down?

Thanks in advance - Todd

If you have vertical loops, the water better not be getting 300 ft. down. Most every state requires the hole to be 'sealed' from letting surface water get in contact with ground water.

I'd like to reiterate one point on DX here, too. With EarthLinked DX, the system works based on the temp. of the ground, NOT the thermal conductivity. This is because of the type of heat exchange done in a DX loop vs. a water loop. What I'm getting at is that you won't see a dry ground problem if you go with DX. How do I know? Because we have many of them installed in very dry ground.

as tuffluck mentioned, adding water only works on a horizontal loop. I have heard of putting a drip system in with the pipes. I have not done anything like this, so I really can't say. Shade trees wouldn't do much either.

Sorry to not be of more help.

I would avoid planting trees close to the horizontal ground loops.  In 10 to 20 years the tree roots might damage the loop.

Actually, the temperatures from the ground loop will more likely hurt the trees before the trees would hurt the loop. In the summer, they can get too warm, and kill the tree. In the winter, they can get too cold and kill the tree.