Number of systems required by 90.1?

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I'm working on a model of a 5-story building - my Proposed system is
floor-by-floor chilled water AHUs connected to a water-cooled chiller
central plan. Airside is shutoff VAV boxes with hot water reheat.

For the size of the building, the baseline model is almost identical.
It is System 7 - Packaged rooftop VAV system with reheat boxes, chilled
water, hot water boilers.

My question is whether or not the Baseline model has to have a single
system for the building, or should it have 5 separate RTUs (doesn't
really make any sense) since my proposed building has 5 systems?

I'm pretty sure the answer is that the Baseline should just have one
packaged RTU for the building, but it actually makes a big difference on
energy use. By breaking the systems down into one-per-floor, as is the
case with the proposed model, I end up saving a LOT of energy, possibly
because the 1st floor is slab-on-grade, and the 5th floor has a roof.

Just wanted to make sure I have the correct number of "systems" for the
Baseline model.


James Hansen, PE, LEED AP

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Joined: 2011-09-30
Reputation: 200