Best way to model a ceiling and raised floor

edit

3 is the best, but 1 and 2 are used a lot. Yes it is more work to model them as separate zones/spaces, however EnergyPlus thermal zones and OpenStudio spaces have a "Part of Total Floor Area" flag. When set to false the specified zone/space will not be included in what EnergyPlus reports for total floor area and will not impact floor area used for EUI calculations. If you are going to model daylight sensors, then having the relationship correct between the floor, ceiling, and window is particularly important. If you take approach 3 it is important to make sure unexpected internal loads such as lights, people, and ventilation are not included in these additional spaces, however you do still wan to included infiltration.

With approach 3 you also have the option to model the raised floor or dropped ceiling as a plenum to supply air to zones from the air loop and/or return air from zones back into the air loop. You can still use approach 3 when the raised floor and dropped ceiling are not part of the HVAC system, but I wanted to point out that functionality.