I've done several homes in the country with open loop systems where we drew water from a slightly oversized water well and discharged the heat pump water into a stream.

I was periferally involved in a closed loop system in the city at a doctor's office. The docs contracted with the hvac contractor with no input from me. it turned out the closed loops were not large enough and so as the temps got colder outside they froze up. And in the summer the loops got so hot the effeciancey went way down.

The limit on capacity is on the size of the closed loop. It is affected by the type of soil and the amount of ground water present. Dry soil will not transfer heat as well, wet much better.

In their system the transfer pipe was siamesed like a lamp cord with the end looped together. It was drilled without a case as i remember so the loop had direct contact with the earth.

We found it was a better payback in the country where natural gas was not available. Once the gas lines got out that way they generally ended up converting to that for heat at least.

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[SIGPIC] Diesel loving autocrossing grandpa Architect. 08 Dodge 3/4 ton with Cummins & six speed; I have had about 35 benzes. I have a 39 Studebaker Coupe Express pickup in which I have had installed a 617 turbo and a five speed manual.[SIGPIC]

..I also have a 427 Cobra replica with an aluminum chassis.