I have several jobs that I am looking into geothermal for. In each case, they are not particularly large loads, often only 3-5 tons total, but they would be easier served by two air handlers. So it would be two rather small units.
I know of several options, I'd be interested in hearing thoughts/experience.
One is multiple self-contained units running off a single geoexchange loop. I wonder if anyone ever plumbs the geoexhange loop as primary/secondary loops, to eliminate the pressure drops through all the exchangers if the units are in series? I'm not sure it's worth it for only two units, and of course there are the additional pumps and controls.
Another option is to put in a single water to water GSHP, then put in air handlers with coils (a chiller approach). Problem is the hot/cold lines that have to snake around the house, and associated heat loss/gain (common enough commercially, not often residentially). Another problem is that the ground source heat pumps don't like cranking out very hot water (about 130F max).
In some cases there's a desire to integrate radiant floor hydronic heating into the equation. A water to water HP would make that easier. It would also make integration of an indirect water heater operating off the heat pump easier (vs. a desuperheater, that can only take care of your hot water loads during system operation, and therefor only reduces DHW energy use by 30% or so). I believe Hydro Delta has something like this integrated into some of their units, though I don't have many details yet.
Thanks for any thoughts and ideas.