How to model vertical shafts in open studio ?

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This is a good question. There are a number of possible solutions.

1. You can model the fully height of the shaft as a single space which is assigned to a single zone
2. You can model each story of the shaft as its own space but then assign all of those spaces to one thermal zone
3. Or you can model each story of the shaft as its own space and assign each space to its own zone.

If you take option 2 be sure to look at this post about Stacked Spaces in OpenStudio.

Some factors that change with the different options.

• If "Part of Total Floor Area" is checked then the floor area reported by EnergyPlus for Options 1 and 2 would only include the area of the shaft for one floor. For Option 3 it would include the area for every floor. If this is an un-occupied shaft you might exclude it from the Total Floor Area.
• If you have internal loads in the shaft you want to carefully consider where they are and make sure they are not duplicated. For example if you have a load in an "Elevator Shaft" space type equal to the load in watts of the elevator, and then make 5 spaces like that, you may have 5 times the loads you expected. Often we just add the elevator load directly to one space; top or bottom depending on if the elevator is hydraulic or traction.
• Thermally Options 1 and 2 are almost the same, one large volume of well mixed air. Option 2 does have an additional amount of thermal mass but the zone heat transfer surfaces are the same. Option 3 will have separate temperatures for each story of the shaft. There would be some thermal conductance between them, but no direct air flow unless you add in zone mixing objects or other objects that moves air between zones.

Whichever option you take now, you can always go back and change it later. I would choose one method and get the model up and running. Then you can go back to this later if you feel the way you initially modeled it isn't accurate enough. How to best model vertical spaces in EnergyPlus is a good question. Here is a post on just that subject that you may want to look at when choosing which option to take.