Karen,

I agree with your interpretation -- the system would be 4-PSZ-HP -
assuming you are using the 2004 edition of ASHARE 90.1. The User's
Manual states that if the heating energy source for the proposed
building is electricity, then the heating energy source for the baseline
building has to be electricity too. This system would not actually be
used in Wisconsin either. Fortunately for me, the utility programs that
I model for allow me to use "engineering judgment" (common sense), so I
can use a realistic system for the baseline. But if you have to go by
the book, then 4-PSZ-HP it is! I can see how this could overstate the
savings for a ground-source heat pump system in a cold climate like
ours.

Sincerely,

Keith Swartz, PE, LEED(r) AP