I am modeling a school that is 156,000 SF under 90.1-2007. The majority of
the school is treated with electric heat pumps but about 26,000 SF of the
building is heated with natural gas furnaces.

So the approach I would take is that the predominant condition is electric
heating, so that should be the main baseline system type. Then per
G3.1.1(a) the natural gas systems are large enough to have their own
baseline system.

My first question is do you think the main baseline should be based on the
whole school area of 156,000 SF, or the 130,000 SF. This is the difference
between system type 6 or 8.

Then, the 26,000 SF is large enough to qualify for the system type 5. But
most of these spaces are large single zone systems (i.e. cafeteria,
gymnasium, ect). And some could qualify for the single zone exceptions.
Which would bring the area under 25,000 SF. How would you account for this
area?

And in general if spaces qualify for exceptions in G.3.1.1(b) or G3.1.1(c)
do you think the single zone systems should match the baseline energy
source or the proposed building energy source. For example if you have a
school that is heated by natural gas, but you have a small server room that
is conditioned with an electric heat pump. Should the baseline system in
that single zone system be electric? Or an electrically heated school with
natural gas in the kitchen. Should the kitchen single zone system be
natural gas like the proposed or electric because that is the baseline fuel
source.

I couldn't find any clarifications to this issue, but if there has been any
official guidance please let me know.

Thanks in advance,
Steve