I have wondered whether a geothermal circulation system could keep all or part of a pond in the 50 degree range. Since here in Oklahoma deep ground temperature is 55 it seems feasible. Since there is no lifting of the water but just a circular circulation it looks like energy costs could be pretty low. I know that it requires much more heat to raise the temperature of water than it does for air so that the amount of unerground run for heat exchange would have to be longer than for the home heat exchange systems. Maybe someone with some engineering savvy in this area will weigh in on this subject.

Layton Runkle