First of all, welcome to the forum. Secondly, let’s talk in terms of “demand factor,” rather than “diversity factor.” It’s a better fit for your question. Third, we don’t assign demand factors for the number of panels, the number of floors, the number of buildings, or anything of that nature. We add up the various types of loads, some of which have demand factors available for our use.

For example, since you are not dealing with a “dwelling unit” installation (or so I surmise from your description), you should be able to take advantage of the lighting demand factors in Table 220.42 and the receptacle demand factors in Table 220.44. Let’s talk about receptacles. The panel that serves an individual student room is unlikely to have more than 10 KVA of receptacle load. So you would have to include that load at 100%, when you calculate the load on that panel. However, depending on how many student rooms are on a floor, the sub main panel (your term) on that floor might serve more than 10 KVA of receptacle load. In that case, when you calculate the load for that panel, you take 100% of the first 10 KVA and 50% of the remainder. Then, when you calculate the main distribution panel for the building, you only count the first 10 KVA of the entire building’s receptacle load, and 50% of the remainder. This allows you a significant reduction. That is because you are saving 5 KVA from the top three floors (i.e., you take each floor above the first floor at 50%, rather than including the first 10 KVA on each floor). You get to do this again when you calculate the load for the 9 buildings.

I don’t know if I made that clear. Essentially, when you calculate the load at each location (main panel, sub panel, branch panel, etc.), you look at all the load served from that location, then take the demand factor on that entire load.