bman...

If your target loop temp is 30°,  the 50° temps found below 30'  can give you a lot more heat per foot of pipe than the 40° temps  found at 5' deep.


Mary,  you are right, the chart is for northern  US climates.  Soil type and moisture content all play a part in loop design,  with moisture having the most effect.

The cost of drilling here on the Delmarva Penninsula is now free!!!!
The average cost of the drilling for any given residential project is 20-30%. That coincides with the stimulus package and I am projecting an extremely busy 2nd quarter. WHOOHOO!!!

Using the Geolink software, I don't see much difference in vertical vs horizontal loop lengths.  The grout on the vertical has a similar effect as additional tubes or slinkys (contact with more soil).  But you could grout a horizontal loop too.

I've seen references to ground water flow being a factor in vertical loops.  This would argue that it is best to maximize the amount of vertical loop that is in sand or gravel (ie, 2x200'  holes might outperform one 400' hole if you have sand from 100' to 200').

Except for these two issues, I would expect no difference between a 30' horizontal loop and a vertical loop.

If soil and weather were constant and predictable, you might be right, but as they are not, a horizontal loop must be built for extremes that a vertical loop will not be affected by. Soil issues close to the surface may not affect vertical wells, so our horizontals may run as much as 600' longer than verts, I don't think you can credit the grout with 3 times the soil contact (remember there are 2 pipes per bore). -18* in MI causes long operating cycles that affect both types of system, but it also affects shallow ground temps with little impact on verticals I don't think you'd find grouting would get it done on a short horizontal.
The difference between paper engineering and contracting is provision for the uncommon. Most formulae don't include that.
I say this because you seem to be trying to "nut-shell" ground loops which can be done to some degree, but you have to remember all of the components of the equation. Loop designers will often have a X'/ton rule that they use. This results in oversized loops in many situations, but why throw away 50' of pipe/ton if you have a 600' roll and only 550' is indicated?

Good Luck,
J

The main function of the grout in a mud rotary borehole is to seal the hole, not enhance conductivity. The main function of the grout in a air rotary hole is to provide a thermal link in a dry hole, plus seal the hole. You are corect that a saturated loop will provide better conductivity than say a shale hole, but to compare the vertical with the horizontal is comparing apples and bannanas.
The two types of exchangers pose very different issues that are addressed in the design phase of a project. If all things are equal a design for a horizontal system and a vertical system, in regard to loop lenght for the same piece of dirt will never yield the same ewt and lwt.

How can you "oversize" a H loop? The cost for moving the extra dirt and piping is nil compared to the insurance you get for more extreme weather condiions... not "overizing" the horizontal is short changing the customer.

Tirade concluded:)
Roomie,
Remember that loop size is just part of the equation.
When I suggest that dropping 50' extra feet in the ground is "over-sizing" that is because it is on top of what was required for my design load. My loop design can be 20, 30 or even 40* depending on what a customer wishes to pay for.
Not short changing, just business. If you want to pay for extra, you can. If you want something for nothing, can't help ya.
Good luck,
Joe