For my own edification I duplicated the FSU calculation Nhi provided in the attached spreadsheet. Hopefully I got it right.

Then for fun I "swapped" savings and FSU values between the two buildings in two different scenarios to see the impact on Portfolio FSU. Again, I hope someone will check these thought experiments to see if they make sense.

If they are, it shows that the individual project saving rates, absolute saving amounts, and FSU percentage have big impacts on the portfolio FSU.

  -Steve