Dear All, 

I am working on a project which has two parts, A & B. Part A is an existing building with a new fenestration system and piping system, but all other systems are existing. Part B connects with part A by a conditioned lobby. The HVAC system is separated for part A and part B.  
My question is:
1) Can I simulate part A and part B together for LEED review?
2) Should I use the baseline system in ASHRAE 90.1-2010 for part A or should I use the existing HVAC system for part A's baseline?
3) Since they connect through a conditioned lobby, are part A and part B two separated buildings?

Thank you.