Energy Simulation for CI

You only need to model your portion of the building, not the entire thing. You can model it as a "virtual" building, that is to say, as though your portion of the building is all that exists. Use ASHRAE 90.1 Appendix G as your reference to build up the baseline. I would use the whole building numbers to choose the correct HVAC System (ergo if your space is 50,000 sq ft but the whole building is 250,000 sq ft, use 250,000 to find the correct HVAC System). Once that's complete model your space as it actually exists and use the actual HVAC system from the building. Compare the two in the EAc1.3 form and you should be good.

I apologize Santhosh, I didn't see that you'd responded. The answer is "it depends". You need to be able to isolate your portion of the building from the rest. There are methodologies for doing so, but depending on your software, it can be more or less difficult. In eQUEST, for example, you can manually set up individual electric meters and then indicate which meters you want to report on, but to do so, you must be in detailed edit mode and know the in's and out's of the software. Conversely, if you include in your narrative why you only modeled your portion of the building, a reviewer is much more likely to accept your project. Hope this helps, Paul