Essentially you're correct for HVAC systems. The actual power draw will depend on the final configuration. Understanding that most of your cooling requirement is directly proportionate to your electrical load, having your redundant chillers / HVAC systems active and online will draw additional power in a T4 DC. The software and floor layout designs will help minimize power consumption.
Looking at the big picture, if your IT load is pulling 150 kW of power and you are using two UPS systems powered by two different city power grids, you're not going to suck up 300 kW of power for your IT load. It's the potential for one path or the other(s) to carry the critical load during an incident.
Again, jumping up in tiers, with redundant chillers, you will need higher capacity generators, piping, electrical runs, redundant CUP etc. Additionally, with high density DC's typically found in T4's, you will need hot air return systems in place that you might not see in the lower tiers which also drives the cost up.
Hopefully this helps somewhat.