If you are looking to improve the PUE of a small data center (250kW), Google has shared its best practices they have implemented at 5 locations.
The question I asked Google's Joe Kava was what he thought the PUE could go to with more load in the facility. The current load is 85 kW in a 250kW capacity. PUE is currently at 1.5 and more load in theory bring PUE to 1.35-1.4, but there will be step function when an additional CRAC unit needs to be brought on line.
There are 4 CRAC units in the room and now only 2 are run while the other 2 are back-up. After a week of operation, the operation is flipped evening out the wear on equipment and insuring the back-up cooling is operational.
Here is a PDF that describes the whole project - Google's Green Data Centers: Network POP Case Study.
Here is before and after images of the airflow. Joe said Google samples data once a second to monitor the power and cooling systems in the room.
A 10 minute video goes along with the white paper.
If you want to segment the 10 minute video into specific areas of interest here are 5 video segments you can view.
Data Center Efficiency Best Practices Part 1 - Intro and Measuring PUE
Data Center Efficiency Best Practices Part 2 - Manage Airflow
Data Center Efficiency Best Practices Part 3 - Raise the Thermostat
Data Center Efficiency Best Practices Part 4 - Utilize Free Cooling
Data Center Efficiency Best Practices Part 5 - Optimize Power Distribution
