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Data centers are an art first, with some basis in science.
If you took the connected nameplate load of all servers, blade servers, routers, processors, etc. you would be over-sized. Typically (and there is no such thing as "typically" with Tel-Data work), the diversity (=actual output versus potential output) can be 0.35 to 0.85. Take your pick! Well, not really.
Data centers thus are like snowflakes. You design to the nth degree and get it right with stated diversities or overall Watts per SF densities and then they expand... 20 percent used to be an acceptable reserve, but that could be void the week after you leave...
So what do you do?
Grab a copy of the ASHRAE Handbook of Fundamentals, latest edition and read the applicable sections. There were recent studies on actual outputs compared to nameplate potentials.
The other approach is redundancy capability. In other words, using more but smaller units allow you some standby capacity and the ability to "tone it down" should the room heat outputs be lower than you think.
Not a lot of help but that is what I can offer by remote..