I am pursuing this credit under option 2. My client has bought a 9 story building and the project in question is for 2 partial floors and three full floors. The mechanical scope is the addition of WSHPs on the first floor, computer room cooling on the second floor, and relocating VAV and fan-powered terminals on the other three floors. The rest of teh building is remaining as shell space for now. The existing building is LEED C&S certified. I am modeling the whole building and am looking to pursue the optional base case.

I am modeling the existing central plant and house air system as installed, and will be looking at the new computer room units and water source heat pumps as areas for cost reduction. My question is regarding the base case under step 6A, should I model the base case envelope, lighting and central plant for the whole building using the 90.1 2007 requirements for the whole building, or should I use the existing envelope values for the floors not being renovated? I am modeling the shell floors as typical built out floors based on the areas being renovated to approximate loading of the central plant.