That brings me to another question, if you don't mind:

The house will be a traditional timber frame with stress-skin panels,
sitting on a basement foundation made of insulating concrete forms and
poured concrete. I am putting radiant floor heat in the basement floor and
using Warmboard panels (or something similar) in the first floor. The
second floor will be plumbed for radiant panels or baseboard but not
installed unless we find that the area gets too cold.

My difficulty lies with cooling. I would like to centrally cool the house,
but am finding it very difficult to find a system that will work in a
timberframe. I have looked at mini-splits (Mitsubishi) and Unico/SpacePak
systems, but I guess I need some more opinions and feedback. You mention
water-cooled condensing units, a cooling tower. Without getting
ridiculously pricey, can this be done effectively in a residence? Also,
what about makeup and excahange air for a tight house? How is this done?

I have no experience with the things, but the dual-use
heating/cooling radiator systems shown he

http://www.burnham.com/

Looked really nifty to me.
Fan driven radiators, which you run, hot/cold
water through according to the season, with
boiler/chiller somewhere else, with both built-in
and free-standing units.