We will be building in the Central Texas area so we are more concerned about the cooling capacity of a Geo Thermal system.  I would appreciate any comments you would have on  special design considerations.   I am guessing that the well system would work better for cooling than the ground loop because the ground temperature would not be as cool?

Alot of systems in TX have a hard time cooling with horizontal loops. Solicit bids from local contractors and we can help you digest them.
good luck,
joe

Horizontal loops are especially prone to periods of hot dry weather. Very dry soil conducts heat poorly. We do not install horizontal loop systems in Florida owing to a combination of often dry, often sandy and often warm near-surface soil temperatures.