I recently participated in a discussion on LinkedIn about the best, most energy-efficient way to control temperature: either the classic sensor in the return of each individual CRAC/CRAH or supply air either by under-floor sensors or sensors in the cold aisles. Of course, that just led to the inevitable discussion of where and how many sensors would be required, and how would the control system decide what to do if there were some areas that were too warm and some that were too cold.
I wrote that I believed that the IT equipment is already aware of the intake temperature and, that ideally, sensors placed everywhere would ultimately become unnecessary, once DCIM systems become truly intelligent gateways between facilities and IT.