Modeling District Cooling / Heating

Dear All, I've been reading through the details of modeling a district heating / cooling plant, and it seems rather complicated! Two options, many methods.. The project is a new build school on a campus. The campus plant initially had 1 building with chillers & boilers installed (1 year ago only), and now with the proposed new building, additional chillers & boilers will be installed, and so the campus plant will then serve both buildings (and probably more buildings in the future). It seems that I will have to model district cooling & heating as per LEED requirements. 1) Which option is better to use in my case: Option 1 (streamlined) or Option 2 (full accounting)? 2) Under option 1, I read in the additional guidance that the energy source is modeled as purchased energy. What is meant by "purchased energy"? Will I be able to at least input the upstream district plant equipment efficiencies (we are proposing high efficiency heating boiler and high COP chillers)? 3) What would actually differ if I didn't model the whole district plant and assumed we have normal dedicated chiller / boiler to the building? Since the purpose of a district plant is to reduce initial & operating costs, will the USGBC accept the "more conservative approach" (higher energy consumption for the Proposed) of a dedicated plant to the proposed building? Thanks!