Cooling energy requirements (and costs) can be reduced 30-55% in most data centers. Look for:
- incorrect row directionality
- cascading equipment exhausts
- recirculation within cabinets
- blow-by at the rack bottom
- uneven air flow
- hot spots
- air short-circuiting
- leaky raised floors
- hot and cold air mixing
- humidity instability
- improperly regulated reheat circuits
- limited capacities
- improper set-points
- comfort cooling vs. process cooling

The guy who used to be Google's data center architect started Precision Air and Energy Services. (Disclosure: I'm not affiliated with PA&E, but the founder is a former coworker, friend, and IMO genius at HVAC.) In a typical data center they reduce energy costs 30-55% via precise air flow control and variable water/glycol flow. They also train staff to keep everything in balance after they're gone.